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TRAINING MANUAL
FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY
CHAPTER – 1
1.0 QUALITY EVALUATION OF TEXTILES :
1.1 INTRODUCTION
Testing of textiles provides valuable aid to those engaged in the production,
distribution & consumption of textiles provided instruments & techniques are
used effectively but testing instrument can not make decisions & at the end
some person has to interpret & analyze the data available. The type of textile
testing instruments available is large. Many of them are simple in principle and
have been used by the textile industry for a long time. Some important
instruments are relatively new, as also are commercial models of equipment
developed in research laboratories. The choice of instruments and the testing
techniques employed will be governed largely by the information required as well
as how accurate and detailed that information has to be.
The subject of textile testing can be covered by answering few ‘W’ questions.
Why do we test? What do we test? When do we test? Who should do the test?
1.2 WHY DO WE TEST?
1.2.1 Selection of Raw Materials :
Raw material cost is the highest amongst all component of cost. This
accounts for 60-70% in cotton & synthetics. Therefore selection of raw
material becomes extremely important & any lapse in this part may lead
the organization to run into trouble. Ensuring optimum quality of raw
material not only reduces the product cost at desired level but also ensure
good working conditions inside the mills.
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Raw material differs from manufacturer to manufacture. For some, it may
be fibre, for some it may be yarn & for processor it may be grey fabric.
1.2.2 Process Control :
Testing of intermediate products i.e. lap, sliver, roving & some of wastes
like comber noil extends lot of help in process control. In the spinning
mill, most common testing for process control is testing count (Hank) at
various stages. For reliable corrective action, one can use ‘Quality
Control Charts’ for control of the count.
1.3 RESEARCH
Testing helps in determining direction in research work. Often research worker
finds himself at cross roads & the result of testing will help the scientist to decide
which path to follow next.
1.4 PROCESS DEVELOPMENT
Process development can be taken as applied form of research. The objective
of process development is to investigate simpler, cheaper, quicker or energy
efficient methods of doing the same work, improving the quality of product
without changing inputs i.e. blending of different fibres at different stages. Here
one should be clear about which properties are to be listed in order to avoid
unnecessary wastage of time.
1.5 TESTING OF FINISHED PRODUCT
Even if we have selected raw material of right quality & it seems that our process
is fairly controlled, we cannot assure product of specified quality because of lack
of knowledge about lot of variables in the process. Therefore it is a standard
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practice to test finished product against specifications and the products which
are falling beyond tolerances are being rejected. Some times a forecast of the
probable performance in a subsequent process is required. Now from fibre
properties we can predict that what is going to be C.S.P. of cotton or from yarn
properties we can have some idea about performance of yarn in Winding as well
as in weaving.
1.6 CHECKING SPECIFICATIONS
To ensure the goods purchased are as per given specification or purchased
machines are capable of producing goods of the quality as desired by
manufacturers, testing is a must.
Sometimes samples are being sent with a tag to produce identical product, here
again suitable analysis techniques and testing are required to produce sample of
same specification.
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2.0 SELECTION OF SAMPLE
In textile most of the tests are destructive in nature therefore testing is conducted
on a very very small part of the population i.e. referred as “sample”
2.1 RANDOM SAMPLE
In case of random sampling every individual in the population has got an equal
chance of being included in the sample without any bias. Normally it is desired
that a sample should be random & representative of the lot.
2.2 BIASED SAMPLE
Some time unknowingly bias occurs during sample collection due to location or
any other reason . Some specimen have more chance of being included in the
sample.
For different tests , different type of sampling techniques are adopted ( in case
of fibre , yarn and fabric ) to get correct test results .
2.3 PLANNED SAMPLE
Some time it might be useful to draw test sample in a planned manner,
particularly when we want to cover entire process or deliveries of machines in a
given time frame i.e. checking of uster & imperfections in case of ring frame.
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3.0 FIBRE TESTING
Testing of fibres is required for determining their quality. Unless quality of raw
material is not controlled it will not be possible to get a quality finished product.
We can broadly divide fibre testing in two categories –
1) Testing of Cotton Fibre
2) Testing of Man-made Fibres
3.1 Testing of Cotton Fibre
Following are the main properties of cotton fibre –
i) Fibre length
ii) Fibre fineness
iii) Fibre strength
iv) Maturity of cotton
v) Colour
vi) Trash%
vii) Neps
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CHAPTER – 2
SAMPLING PROCEDURE FOR FIBRE TESTING
The quality of a cotton sample is mainly dependent on the various physical
properties of the fibres in the sample. The most important physical
characteristics are length, fineness, maturity and strength of the fibres. There are
large variations in these characteristics not only between fibres of different
samples but also between the fibres constituting the same sample.
Investigations have shown that the variations in length observed between fibres
in a bulk sample are of the same order as those observed between fibres on a
single seed of that variety. The characters of any random sample picked out
from a bulk cannot be expected to be representative of the bulk in view of this
large variation. Hence, before carrying out any tests for fibre characteristics, it is
preferable to prepare a test sample which is, as far as possible, truly
representative of the constituents of the bulk. The details of the procedures
employed for proper sampling and the methods adopted for determining the
various physical quality factors of cotton fibres are described in the following
sections.
Sampling Techniques For The Determination of Fiber Properties
The sampling method used to select a fiber for testing depends upon the form in
which the fiber is available. Therefore fibers in bales, in sliver, card web, yarn etc
will require different techniques The test result of sample may not be the same
as obtained by testing bulk sample. Two source of error may be present.
Random error & error due to bias.
Sampling from Bales
In order to obtain a representative sample from a lot of bales it is necessary to
distribute the sample to be selected over the bales in the lot and different layers
in the bale. The number of bales to be selected at random from a lot shall be in
accordance with Table-1.
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Table-1 : Number of Bales to be selected from a lot
No. of Bales
In the Lot
No. of Bales to be
Selected
Up to 50
51 to 100
101 to 150
151 to 300
301 to 500
501 to 1000
1001 & Above
2
4
7
13
20
32
40
In view of the variation observed in most of the fibre properties, both within and
between the layers of cotton in a bale, it is desirable to open the bale and draw
tufts from different positions in at least 10 equally-spaced layers. In practice the
selection of the layers from a bale may be done as given below:
The bale is kept lengthwise on the ground and the hoops are broken. A thin
layer of cotton is removed from the top and the tufts are drawn from various
positions on the exposed surface. Then a thick slab (about one-tenth the height
of the bale) is removed and the tufts are drawn from the newly exposed surface.
The procedure is repeated till the tufts are drawn from at least 10 layers. While
drawing the tufts from various layers, care shall be taken to avoid any bias in
selecting the positions for drawing the tufts. The material so drawn from the bale
shall not be less than 2 kg.
In case it is not economical to open the bale completely, the gross sample may
be obtained by breaking one or more of the hoops round the bale and then
taking out a lump of at least 1 kg of material from each of the two exposed sides
of the bale. The material so taken shall include portions from the hard, soft and
middle parts of the bale.
The material so obtained from all the bales selected from the lot shall be
thoroughly mixed to get a gross sample.
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Reduction of Gross Sample
The gross sample shall be spread out evenly on a level ground in the form of
either a square with each side slightly greater than 1 m, or in the case of a larger
sample, a rectangle with the shorter side slightly greater than 1 m, and the larger
side slightly greater than 2 m. A suitable framework of size 1 x 1 m with 25 sub-
squares or 1 x 2 m with 50 sub-squares, one or more tufts of fibres shall be
pulled out at random, taking care not to exercise and bias in favour of or against
any particular place within a sub-square, and that tufts drawn from each sub-
square weigh about 4 g in the former case and about 2 g in the latter case. The
quantity of cotton thus drawn shall constitute the reduced sample.
The reduced sample shall be well mixed and divided into 25 or 50 approximately
equal parts. From each of these parts, one or more tufts of fibres shall be
extracted at random, taking care that the fibres drawn are nearly equal in weight,
and the total weight of fibres thus drawn is not less than the quantity required for
relevant tests. The material so taken out shall constitute the test sample.
CTRL Method of Sampling and Preparation of Drawbox Sliver
The reduced sample is divided into 32 approximately equal parts by successive
dichotomy. From each portion a small tuft of fibres is extracted in a
random manner. Approximately the same quantity of fibres is taken from
each group so that the total weight of the final test sample is between 200
mg and 500 mg.
For most fibre tests like length by Balls and Baer sorters, maturity by Caustic
soda method, and bundle strength by Pressley Strength Tester and Stelometer,
it is convenient to prepare a representative sliver out of the test sample, by
cleaning it free of leaf bits and other extraneous matter, mixing various portions
thoroughly and then parallelising the fibres. For this purpose, the test sample,
after cleaning by hand and mixing is passed through a drawbox repeatedly 5 to
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10 times. The sliver so prepared can be taken to be completely representative of
the bulk sample.
B.S. Zoning Method
This method gives a numerical sample, obtained by repeatedly halving the
representative samples. The total number of fibres required(n) in the sample is
estimated and tuft of fibres from various parts (m) of the bulk is taken. The
portion so taken is divided into two taking care to avoid fibre breakage, and
rejecting one-half, the choice of which half to be rejected being half is rejected at
random. This process for each tuft is continued until a number of fibres equal to
about n/m of the total required in each group is obtained. The required sample
consists of all the fibres remaining in each group. If two samples are required the
m halves remaining after the last division may be used for the second sample,
provided any further reduction of sample size which is required is carried out in a
manner similar to that just given.
Sampling for Other Tests
For tests on the Fibrograph, the test specimen is directly prepared from the
reduced sample. For tests on the Nickerson-Hunter Cotton Colorimeter, a larger
reduced sample, of about ½ kg is prepared, which is divided into three or four
tests on the Micronaire instrument sufficient quantity from the laboratory sample
is well-opened, cleaned and thoroughly mixed to get about 8 gms, of sample.
Textiles and moisture
Introduction
The properties of textile fibres are in many cases strongly affected by the atmospheric
moisture content. Many fibres, particularly the natural ones, are hygroscopic in that they
are able to absorb water vapour from a moist atmosphere and to give up water to a dry
atmosphere. If sufficient time is allowed, equilibrium will be reached. The amount of
moisture that such fibres contain strongly affects many of their most important physical
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properties. The consequence of this is that the moisture content of all textile products has
to be taken into account when these properties are being measured. Furthermore because
the percentage of moisture that can be retained by fibres is quite high (up to 40% with
some fibres), the moisture content can have a significant effect on the mass of the
material. This factor has a commercial importance in cases where material such as yarns
and fibres is bought and sold by weight.
Effect of moisture on physical properties
The physical properties of fibres can be affected by their moisture content. In general the
fibres that absorb the greatest amount of moisture are the ones whose properties change
the most. Three main types of properties are affected.
i) Dimensional
The mass of the fibres is simply the sum of the mass of the dry fibre plus the mass of the
water. The absorption of moisture by fibres causes them to swell, because of the
insertion of water molecules between the previously tightly packed fibre molecules.
Because the fibre molecules are long and narrow most of the available intermolecular
spaces are along the length of the molecules rather than at the ends, so that the swelling
takes place mainly in the fibre width. Nylon is a notable exception to this,
The change in volume of a fibre is linked to the changes in its length and cross-
sectional area by simple geometry. The change in volume is also linked to the
amount of water that has been absorbed. The swelling of fibres is a continuous
process which takes place in step with their increasing moisture content.
Fabrics made from fibres that absorb large amounts of water are affected by the
swelling. When such a fabric is soaked in water the increase in width of the
fibres leads to an increase in diameter of the constituent yarns. Depending on
the closeness of spacing of the yarns this can lead to a change in dimensions of
the fabric. However, on subsequent drying out the structure does not necessarily
revert to its original state. This behaviour is responsible for the dimensional
stability problems of certain fabrics. Advantage is taken of fibre swelling in the
construction of some types of water proof fabrics whose structures are designed
to close up when wetted, so making them more impermeable to water.
2. Mechanical
Some fibres, such as wool and viscose, lose strength when they absorb water and some,
such as cotton, flax, hemp and jute, increase in strength Furthermore the extensibility,
that is the extension at a given load, can increase for some fibres when they are wet.
These changes in strength and extension have consequences for many other textile
properties besides tensile strength. Some properties such as fabric tearing strength are
ones that are obviously likely to be affected by fibre strength, but for other ones such as
crease resistance or abrasion resistance the connection between them and changes in
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fibre tensile properties is less apparent. It is because of these changes in properties that
textile tests should be carried out in a controlled atmosphere.
3) Electrical
The moisture content of fibres also has an important effect on their electrical properties.
The main change is to their electrical resistance. The resistance decreases with increasing
moisture content. For fibres that absorb water the following approximate relation
between the electrical resistance and the moisture content holds for relative humidities
between 30% and 90%.
RMn
= k
Where R = resistance,
M = moisture content (%)
and n and k are constants
The changes in resistance are large : there is approximately a tenfold decrease
in resistance for every 13% increase in the relative humidity. This fall in
resistance with increasing moisture content means that static electrical charges
are more readily dissipated when the atmospheric relative humidity is high.
Atmospheric moisture
The moisture content of textile materials when they are in equilibrium with their
surroundings is determined by the amount of moisture in the air. Therefore the
moisture content of those materials that absorb water can vary from day to day
or from room to room. The atmospheric moisture level is normally expressed in
terms of relative humidity and not absolute water content.
Relative humidity
The amount of moisture that the atmosphere can hold increases with its temperature so
that warmer air can hold more water than cold air.
When considering the effects of atmospheric moisture on textile materials the
important quantity is not how much moisture the air already holds, but how much
more it is capable of holding. This factor governs whether fibres will lose
moisture to or gain moisture from the atmosphere. The capacity of the
atmosphere to hold further moisture is calculated by taking the maximum
possible atmospheric moisture content at a particular temperature and working
out what percentage of it has already been taken up. This quantity is known as
the relative humidity (RH) of the atmosphere and it can be defined in two ways .
In terms of the mass of water vapour in the atmosphere:
Mass of water vapour in given volume of air
RH = ----------------------------------------------------------- x 100 %
Mass of water vapour required to saturate
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this volume at the same temperature
Alternatively it can also be defined as the ratio of the actual vapour pressure to
the saturated vapour pressure at the same temperature expressed as a
percentage.
Actual vapour pressure x 100%
RH = -------------------------------------------
Saturated vapour pressure
The absolute humidity is defined as the weight of water present in unit volume of
moist air measured in grams per cubic metre.
It is important to note that the relative humidity of the atmosphere changes with
temperature even when the total quantity of water vapour contained in the air
remains the same.
The amount of moisture contained by fibres that are in equilibrium with the
atmosphere is dependent on the relative rather than the absolute humidity.
Standard atmosphere
Because of the important changes that occur in textile properties as the moisture
content changes, it is necessary to specify the atmospheric conditions in which
any testing is carried out. Therefore a standard atmosphere has been agreed for
testing purposes and is defined as a relative humidity of 65% and a temperature
of 20o
C. For practical purposes certain tolerances in these values are allowed
so that the testing atmosphere is RH 65% + 2%.; In tropical regions a
temperature of 27 + 2o C may be used.
Regain and moisture content
The amount of moisture in a fibre sample can be expressed as either regain or moisture
content. Regain is the weight of water in a material expressed as a percentage of the oven
dry weight.
100 x W
Regain = ------------- %
D
where D is the dry weight and W is the weight of absorbed water.
Moisture content is the weight of water expressed as a percentage of the total
weight
100 x W
Moisture content = -------------- %
D + W
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Regain is the quantity usually used in the textile industry
Factors affecting the regain
Different fibre types absorb different amounts of moisture depending on their affinity for
water.
For a given fibre type the moisture content is governed by a number of factors:
1. Relative humidity. The higher the relative humidity of the atmosphere,
the higher is the regain of textile material which is exposed to it.
2. Time. Material that is in equilibrium at a particular relative humidity which
is then moved to an atmosphere with a different relative humidity takes a
certain amount of time to reach a new equilibrium. The time taken
depends on the physical form of the material and how easily the moisture
can reach or escape from the individual fibres.
3. Temperature. Temperature will affect the regain of material. In testing
laboratory as temp. variation are small, for practical purposes the
temperature does not affect the regain of a sample.
4. Previous history. The moisture content of textile materials in equilibrium
with a particular relative humidity depends on the previous history of the
material.
The material will have a different moisture content depending on whether it was
previously wet or dry. Processing of the material can also change its regain value by
altering its ability to absorb moisture. The removal of oils, waxes and other impurities
can also change the regain by removing a barrier on the fibre surface to the flow of
moisture vapour. For example the standard regain value for scoured wool is 16% and that
for oil combed tops is 19%.
Method of measuring regain
To measure the regain of a sample of textile material it is necessary to weigh the
material, dry it and then weigh it again. The difference between the masses is then the
mass of water in the sample.
Mass of water x 100%
Regain = ------------------------------
Oven dry mass
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Regain is based on the oven dry mass, which for most fibres is the constant
mass obtained by drying at a temperature of 105 + 2o
C. Constant mass is
achieved by drying and weighing repeatedly until successive weighing differ by
less than 0.5%.
This is also called oven dry weight.
Standard Regain Values
Fibre type Regain (%)
Man-made fibres
Acetate 6.5
Acrylic 1.5
Nylon 6, 6 and 6 4.5
Polyester 0.4
Polypropylene 0
Triacetate 3.5
Viscose 11-12
Natural fibres
Cotton – natural yarn 8.5
Linen fibre 12
Linen yarn 8.75
Silk 11
Wool 16-18.0
Shirley Moisture Meter
Electrical resistance of different textile materials varies considerably at different
regains. This principal is used in Shirley Moisture Meter. Initially instrument was
designed to measure moisture of Raw cotton & yarn however later its use was
extended to other textile materials & tables were prepared to give corrected
values.
The electrode consist of a central conductor insulated from an outer circular
sheath. When pressed into the cotton the fiber bridges the insulation &
resistance is measured. Two electrode one for raw cotton & one for yarn is used.
The difference being that for yarns spacing between conducting element is
increased.
This counteracts the increased conductivity of yarns due to more or less parallel
arrangement of the fibers compared with random arrangement of the fibers in
loose cotton. The indicating unit translate resistance value into regain values
On one of two dials.. One dial covers normal range from 7-11 percent & other
For Damp 9-15 & Dry from 5-9 percent range.
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CHAPTER – 4
FIBRE LENGTH
Among the various properties which determine the quality of cotton, fibre length
occupies a dominant position as it influences, to a large extent, the spinnability of
a cotton. Moreover fibre length can be easily estimated. Hence, this
characteristic of cotton has assumed great importance in commercial
transactions and the price of a cotton sample is largely based on this
characteristic.
Any sample of cotton will contain fibres varying in length from 2mm onwards, the
upper limit being decided by the variety of cotton under consideration and the
conditions under which it has been grown. This variation is found markedly even
when fibres removed from an individual cotton seed are considered. In view of
the above, what we generally aim at is to obtain a measure of fibre length which
can be considered as average for the whole sample or which is likely to influence
the spinning performance most.
DEFINITIONS OF FIBRE LENGTH PARAMETRES
Mean length:
The arithmetic mean of the length of all the fibres present in a small but
representative sample of cotton, based on weight-length distribution or relative
number-length distribution.
Upper Quartile Length:
The length for which 75 per cent of all the observed values are lower and 25 per
cent higher, by weight or by number
Modal Length:
The most frequently occurring length of fibres in the weight distribution of the
sample.
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Median:
The particular value of length above and below which exactly 50% of the fibres
lie. For moderately skewed distributions the median is related to the mean and
modal lengths in the following way:
Mode – mean = 3 (median – mean)
Effective Length:
It is difficult to give a clear scientific definition for effective length. It may be
defined as the upper quartile of the numerical length distribution from which
some of the shortest fibres are eliminated by an arbitrary construction. The fibres
eliminated are those shorter than half the effective length.
Percentage of Short Fibres:
The percentages of fibres less than half the effective length or less than any
specified length.
Coefficient of Variation:
The standard deviation of weight-length or relative number-length frequencies
expressed as a percentage of the mean length.
Span Length:
The distance spanned by a specified percentage of the fibres in the test beard.
2.5% span length is the distance from the clamp on a fibre beard to a point upto
which only 2.5% of the fibres extend. 50% span length is the distance of the
point to which 50% span length is the distance of the point to which 50% of the
fibres extend and 66.7% span length is the distance upto which 66.7% of the
fibres extend.
Uniformity Ratio:
The ratio of 50% span length to the 2.5% span length expressed as a
percentage.
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Dispersion:
It represents the variation in the length of fibres. It is the interquartile range
expressed as a percentage of effective length.
MEASUREMENT OF FIBRE LENGTH
Single Fibre Measurement
It is possible, with patience, good lighting, a microscope slide over a scale, and
medicinal paraffin to control the fibres, to measure the length of individual cotton
fibre. Each fibre is taken and gently straightened over the slide with the tips of
the little fingers; the length is then recorded. This method is obviously tedious
and time consuming and not used in the mill laboratory. At least 400-500 fibers
are measured in case of cotton to arrive at mean length due to large variation in
the sample.
PRINCIPLE OF BAER SORTER
A numerical sample of fibres is arranged in the form of an array in the
descending order of length and form a tracing of this array of length, mean
length, percentage of short fibres and dispersion are calculated.
DESCRIPTION
The Baer Sorter consists of a abed of combs which control and enable the
sample of fibres to be fractionalized into length groups. The Baer Sorter has 12
bottom combs are hinged at one end and are supported by a rod, extending the
width of the frame at the other end. The rod can be moved from its position and
when it is drawn, the rod can be dropped one by one. The needle of the bottom
combs are pointing upwards and in between the bottom combs, three top combs
are placed. The space between the two bottom combs is ¼ inch except the first
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two bottom combs which will be 3/16 inch apart. The top combs, when placed
between the two bottom combs, the distance between them will be 1/8 inch.
Manipulation of the fibres is done by a grip called tweezer, depressor and a blunt
needle.
PROCEDURE
The position of fibre unit in the instrument is shown in fig. A representative
sample of cotton is made into sliver by drawing and doubling several times with
the fibres strengthened and parallelised. The bundle of fibres must be as narrow
as possible through out the whole process. The method of sorting is a s follows:
1. The sorter is placed with the back facing the operator. The prepared sample
is slightly twisted and placed on the bottom combs at the right hand side
of the sorter, with a small tuft protruding.
2. From the protruding end, all the loose fibres are removed by means of the
tweezer until, the ends are aligned. The removed loose fibres are kept
separately and introduced in the original sample later.
3. A tuft of fibres all pulled out, combed and transferred to the left hand side of
the sorter so that the comb nearest to the operator forms the starting line
for the tuft, while at the other end the longest fibres protrude out. The tuft
is pressed into the combs by means of depressor.
4. The process is repeated till all fibres on the right side, all combings are
transferred to the let hand side.
5. The top combs are inserted in their position to grip and to control the slippage
of the fibres.
6. The sorter, is then turned round so that the front faces the operator.
7. The bottom combs are dropped one by one successively till the tips of the
longest fibres are seen.
8. The fibres are pulled by the tweezer, combed, straightened and laid
perpendicular to a base line on a black velvet pad. When these fibres are
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exhausted. One comb is dropped and the fibres next in order of length
are similarly pulled out and laid on the pad all fibres being carefully
spread out to uniform density. The process is continued until the tuft is
exhausted and the fibre array is obtained.
After the pattern is built up, a transparent scale, with 1/8 inch lines is placed over
the pattern. Reading on the transparent scale, the values of the co-ordinates are
marked on a graph sheet and the pattern is drawn. The diagram is called
“SORTER DIAGRAM”. The diagram is analysed for the following fibre
particulars.
1. Effective Length
2. Mean length
3. Percentage of short fibres
4. Dispersion
Fibre Sorter Methods
As single fibre measurement takes time and hand stapling requires experience
(although even then this is a subjective test), alternative methods have been
developed. One of the most popular is the use of the fibre sorter, examples of
which are the Baer, the Shirley, and the Suter Webb. The fibre sorter is an
instrument which enables the sample to be fractionalised into length groups.
Basically, the operation involves four main steps:
1. The preparation of a fringe or tuft with all the fibres aligned at one end.
2. The separation or withdrawal of fibres in order of decreasing length.
3. The preparation of a sorter diagram by laying the fibres on a black velvet
pad in decreasing order of length, the fibre parallel and their lower ends
aligned along a horizontal base line.
4. The analysis of the diagram.
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Analysis of Sorter Diagram
By placing the tracing over graph paper ruled in sixteenths of an inch, the
diagram can be readily divided into 1/8 in. classes. Alternatively it can be read in
mm also by using paper of 1 mm square.
Average or Mean Length
The sum of the base line readings divided by the base line length gives the
mean length in units of 1/8 in. or mm, the class interval. Multiplying by 4
expresses the mean length in 1/32 in. units. This is the mean height of the curve
and is obtained by dividing the total area under the curve by the base length.
Maximum Length
This is read directly from the diagram.
Modal Length
The mode of a frequency distribution is the class value of the class with the
highest frequency; in other words, the most ‘fashionable’ value. Since distances
along the base line are assumed to be proportional to frequency, the modal
length will be given by the class which has the greatest base length.
Effective Length
This value has been defined as the length of the main bulk of the longer fibres. It
is obtained by a geometrical construction on the sorter diagram, a construction
which also produces several other useful quantities. Figure illustrates this
operation.
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1. Q is the mid-point of OA, i.e. OQ = OA.
2. From Q draw QP’ parallel to OB to cut the curve at P’.
3. Drop the perpendicular P’P.
4. Mark off OK equal to ¼ OP and erect the perpendicular K’K. This is a firs
approximation to the effective length.
5. S is the mid point of K’K.
6. From S draw SR’ parallel to OB to cut the curve at R’.
7. Drop the perpendicular R’R.
8. Mark off OL equal to ¼ OR.
9. Erect the perpendicular L’L. This is the effective length.
There are one or two points to note about this construction. The short fibres are,
in the main, ignored; this action is justified since the classers deliberately reject
the short fibre when hand stapling. Further, the effect of the initial rapid change
in length from the maximum is reduced; therefore the effective length is a
characteristic of the bulk of the longer fibres. The term ‘effective’ is used
because it is to this length value that many machinery settings are related, in
particular the distance between the nips of successive pairs of drafting rollers.
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The Relation Between Effective Length and Staple and Staple Length
We have seen earlier that basis of judgement of staple differs between markets
and types of cotton. These differences can be accommodated by making certain
corrections to the effective length. Lord and Underwood report that, ‘For
American Upland cottons, from about ¾ in. to 11/4 in, staple and classed on the
basis of American Staple Length Standards, a simple conversion formula is;
American Staple = 0.91 x effective length
For Egyptian-type cottons no staple length standards are in universal use, but on
the average it is found that the staple length is equal to the effective length.
Percentage Short Fibre
This is the percentage of fibres less than half the effective length. In figure the
percentage short fibre is therefore given by (RB x100/OB) (per cent)
Dispersion
The uniformity, or perhaps more aptly the variability of the cotton, can be
expressed as the ‘inter-quartile range’. In Figure L’L is the upper quartile and
M’M is the lower quartile, the inter-quartile range. This measure of the dispersion
may now be expressed as a range. This measure of the dispersion may now be
expressed as a percentage of the effective length:
NL’
Dispersion = ------ x 100 (per cent)
LL’
The Fibrograph
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A fringe of cotton is prepared by taking about ½ OZ of cotton and combing it by
means of two hand combs. The prepared sample is in a straightened condition
with the fibres divided between the tow combs; those longer than ¼ in. are
caught in the teeth in a random position along their length. The fibre fringes are
places on the measuring unit in such a way that they lie over a long narrow slot
behind which are mounted the photo-electric cells. A light source illuminates the
fringes and the amount of light penetrating through the fringes is measured
electronically. At the start of the measurement the fringes are scanned across
the densest region, i.e. near the comb teeth, and the light which penetrates will
be a minimum. As the sample is traversed towards the fibre ends, more and
more light will fall on to the photo-electric cells.
The new ‘Servo-Fibrograph’ automatically records the change in the amount of
light reaching the cells, not in terms of intensity of illumination but as a special
form of frequency distribution. This curve is traced out on a card which is then
removed from the instrument and analysed.
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Construct the tangent to the curve to cut the horizontal at N and the vertical axis
at A. OA is then the average length of fibres longer than ¼ in. Distance along ON
represent the frequency percentage of fibres longer than ¼ in.
From S, the 50 percent mark, construct the tangent ST to cut the vertical axis at
T. OT is then the upper half mean length of fibres longer than ¼ in., based on a
weight distribution. The ratio OA/OT x 100 percent gives the length uniformity
ratio of the fibres. The upper half mean length approximates to the staple length
obtained by the cotton classers.
The Digital Fibrograph
Principal
As its name implies, the Digital Fibrograph presents the test results in digital or
numeric form. Preferably, a special fibre sampler, a ‘Fibrosampler’, is used to
prepare the beards by a light source is similar to that used in the earlier
fibrograph but the signals from the measuring console are fed into a separate
transistorised unit. The signals are electronically processed and the results fed
back to the measuring unit which has two four-digit counters facing the operator.
One counter is for selecting % S.L. and the other counter gives ‘Length’. A
Servo-follower system connected to the photoelectric cells indicates on the
‘Amount’ counter the relative number of fibres in the sample beards at the point
where the light beam passes through them. A Servo-computer ‘remember’ the
total number of fibres in the sample at 0.15 in. distance from the center of the
comb teeth and computes the number of fibres corresponding to the different
Span Lengths. When a span length is selected, the comb carrier moves until the
number of fibres under the lighthouse is equal to the number of fibres
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corresponding to that span length. The span length is then indicated by the
‘Length’ counter, which indicates, in mm, the movement of the comb carrier. Now
there are two counters t set the amount and these two corresponding Length
counter to give two length i.e., 2.5% & 50% simultaneously.
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Relationship Between Fibre Length (mm)
Measured by Different Instruments
BAER SORTER EFFECTIVE LENGTH (Y)
Digital Fibrograph Y = 1.013x + 4.39
2.5% Span Length (x)
Uster Apparatus Y = 0.933x + 9.04
Effective Length (x)
Uster Apparatus Y = 0.996x + 9.12
Upper half mean length (x)
BAER SORTER MEAN LENGTH (Y)
Digital Fibrograph Y = 1.242x + 9.78
50% Span Length (x)
Uster Apparatus Y = 0.941x + 9.45
Mean Length (x)
DIGITAL FIBROGRAPH 2.5% SPAN LENGTH (Y)
Uster apparatus – Upper half Y = 0.946x + 5.64
Mean length (x)
Uster Apparatus – Effective length (x) Y = 0.878x + 5.77
DIGITAL FIBROGRAPH 50% SPAN LENGTH (Y)
Uster Apparatus – Mean length (x) Y = 0.672x – 1.60
Note: If the 2.5% span length of a cotton as tested on Digital fibrograph is
30mm, then the Baer sorter effective length is estimated to be 34.8mm
(1.013 x 30 + 4.39).
The conversions for fibre length and strength are subject to appreciable error
and should be used only as approximate estimates.
Mean Length
Uniformity Ratio = x 100
Upper half mean length
Based on uniformity ratio, the cotton samples can be graded as per United
States Department of Agriculture (USDA). The rating is given as:
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Uniformity Ratio Rating
Above 80% Uniform
75 – 80% Average uniform
71 – 75% Slightly irregular
70 and below Irregular
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CHAPTER – 5
FIBRE FINENESS
Fibre fineness is another very important parameter which plays significant role in
yarn spinning. Fibre fineness denotes the size of cross section of the fibre or in
other terms it can be expressed as linear density of the fibres in micrograms per
inch (10-6
g/inch). The fineness is also expressed in millitex which is weight inn
milligrams of one kilometre length of fibre. This is identical to the unit of
10-6
gm/cm. The fineness plays a prominent part in determining the spinning
performance. When irregularity is considered, the best yarn that con be
produced is one in which the fibres are distributed along the strand in a random
order. The irregularity in the strand is dependent upon the average number of
fibres in cross-section. With a greater number of fibres in the cross-section, the
basic irregularity is reduced. If the fibres are fine, the number of fibres in cross-
section is more and irregularity is less. The finer the fibre the greater the total
surface area available in inter-fibre contact and less twist is needed to provide
necessary cohesion. The resistance of fibre to twisting and bending are also
affected by the fineness.
SIGNIFICANCE
1. To spin finer yarn we require finer fibres as certain minimum number of
fibres is must to spin in yarn (70-80).
2. From finer fibres, apart from better spinnability, better evenness can also
be achieved for the same count.
3. Yarn strength is also affected by fibre fineness to some extent.
4. A finer fibre can be spun to finer counts than a coarse fibre.
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MEASUREMENT OF FIBRE FINENESS
Fineness can be measured by measuring fibre cross section but as cross section
of fibres are not regular, direct determination of area is not possible. Some
dimensional features i.e. swollen hair diameter, ribbon width etc., can be used to
specify fibre fineness to some extent.
The fineness of cotton fibres can be determined by either direct method such as
gravimetric dimensional measurement or by indirect method i.e. Air flow method.
DIRECT METHOD
Gravimetric Method:
In this method two types of practices are prevalent:
(a) In ASTM procedure about 100 fibres are taken from each comb sorter
groups and weighted, from which weight per unit length is calculated. In
this case meanlength is used to calculate the weight per unit length.
(b) In another method known number of fibres are first cut into in 1cm length
and then they are weighed on a torsion balance or quartz micro-balance.
There are two objections in this method.
(i) Fibre of different length grade may have different fineness value.
(ii) In a single fibre, fineness may vary over the whole length.
INDIRECT METHOD
The direct methods are generally tedious and more time consuming therefore
indirect method of the measurement of fineness are more popular. These are
mainly based on measurement of resistance to the flow of air by fibre plugs, or
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on the principle of vibrating strings in the case of single fibres, as described
below:
Air-flow Method
In this method a fibre of constant weight are filled-in a fixed area and air is
allowed to pass through. The flow of air is affected by the surface area of the
fibres. The variation in air-flow is directly translated into the values of linear
density.
Specific surface is defined as the ratio of surface area to volume,
Eg specific surface of a cylinder
Let the volume= ^ ( d/2) square X l where d is the diameter of cylinder
The surface area ignoring the end = ^ d l
Specific surface area S= ^ dl / ^ ( d/2) square X l = 4/d
This ratio also equals the ratio Perimeter of cross-section/ Area of cross-section
= ^ d / ^ ( d/2) square = 4/d
Thus S Is proportional to 1/ d
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VARIOUS INSTRUMENTS TO MEASURE FIBRE FINENESS
(Air-flow Method)
1) Sheffield Micronaire:
The Micronaire instrument works in conjunction with an air-compressor. The
latter, through the pressure regulation system supplies air to the Micronaire
instrument at the constant pressure of 0.33 kg/cm2
(4.7 psi for the Sheffield
Micronaire). Initially, the instrument is calibrated with the master-plug. A test
specimen of 3.24g is weighed and well opened by hand. It is then placed into
the cylindrical chamber of the Micronaire instrument. The fibre compression
plunger is inserted into the cylinder and locked by turning. The air at definite
pressure is forced through the sample and the volume rate of airflow is
measured on the scale to the nearest 0.1 scale unit at the point level with the top
of rotometer type float. Usually two specimens are taken from each cotton and
duplicate tests are carried out on each specimen. The second test on each
specimen is carried out by removing the specimen from the chamber and
repacking it in the reverse direction. The sample for the Micronaire test should
be well opened, cleaned and thoroughly mixed.
The fineness scale in the Sheffield Micronaire is suitable only for very fine and
medium fine cottons. The coarse desi varieties of cotton give a high reading
beyond the range of the scale, necessitating the determination of fibre fineness
by direct gravimetric method which is time-consuming. Recently two techniques
(a) by using a plug of 60 grains (3.89g) sample weight and normal air pressure of
6 psi; and (b) by suing a plug of 50 grains (3.24 g) sample weight and reduced
air pressure of 4 psi, were tried at the Laboratory whereby the flowmeter reading
could be kept within the range of the Micronaire scale. Both the testing methods
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were found to be accurate for predicting fineness. The first method is
recommended for testing very coarse desi varieties of Indian cottons.
2) WIRA Cotton Fineness Meter:
A new version of WIRA Cotton Fineness Meter has been marketed by the
Shirley Developments Ltd. The scale of this instrument is graduated in
Micronaire units. It takes a 5g sample. The standard samples for the calibration
of instrument are provided by the Shirley Institute.
3) Arealometer:
The instrument is portable and it measures the parameters such as specific
surface area, fibre weight and immaturity ratio. A small sample of 152 mg is
used. The instrument is similar to the Wheatstone bridge in which the three of
the resistances consist of copper capillaries and the fourth is the fibre plug under
test.
4) Port-Ar:
The resistance a plug of cotton fibres offers to the flow of air is measured as an
approximate indication of the fineness of fibre. A predetermined mass of loose
cotton fibres is placed in the specimen holder and compressed to a fixed volume,
the resistance to air flow is measured and expressed as Micronaire reading.
Instruments available to measure resistance to air flow use compressed air or
vacuum and are constructed to measure air flow under constant pressure drop
across the plug, to measure pressure drop when a constant flow of air is
maintained.
The Micronaire reading of cotton fibres is a function of both fineness and
maturity and is related to mill processing performance and to the quality of the
end products. Factors correlated with Micronaire reading include cleaning
efficiency, neppiness, and the strength & uniformity of the yarn.
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This portable instrument does not require compressed air or electric power for
operation. It determines the Micronaire value and equivalent fibre thickness (in
terms of specific surface area). The instrument is provided with Micronaire scale
ranging from 2.5 to 7. Port-Ar does not need a separate balance for weighing. It
tests a specimen of 8 g.
5) Speedar:
It measures specific surface area. This instrument does not require any fixed
weight of sample. Any weight between 5g to 10g can be used. Therefore, it is
speedier in testing the sample.
6) ATIRA Fineness Tester:
In this instrument, air pressure is built up by pumping air by hand into a small
tank containing a loosely fitting float. This arrangement maintains fairly constant
air pressure when the float descends in the tank. The escaping air flows through
an adjustable needle valve connected in series with the sample chamber. An
accurately weighted 5g quantity of the fluffed sample is taken in the sample
chamber and compressed into a plug of fixed dimensions by the perforated
piston. The junction of the needle valve and the sample chamber is connected to
a reservoir manometer, the calibrated portion of which is in an incli8ned position
to spread out the scale increase the sensitivity. When the air from the air tank
flows out under constant pressure through the regulated needle valve and the
cotton sample, the manometer indicates directly the fibre fineness in micrograms
per inch. This instrument is also provided with an MH scale, as this scale is
believed to agree better with the air-flow than the fibre weight sale.
Note: Nowadays most of fineness tester used are either Portar or Speedar type
as testing is quicker in such instruments. Instruments can give data
directly in the form of computer printout for vide variety of cotton.
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CHAPTER – 6
FIBRE STRENGTH
Fibre strength is generally considered to be next to fibre length and fineness in
the order of importance amongst fibre properties and for cottons beyond a
certain staple length this property assumes greater significance.
The different measures available for reporting fibre strength are ‘breaking
strength’, ‘tensile strength’ and ‘tenacity or intrinsic strength’. Breaking strength
denotes the maximum tension the fibre is able to sustain before it breaks. In the
case of cotton fibre, it depends upon various factors such as the inherent
strength of the material constituting it, the number and intensity of weak places
and the area of cross-section of the fibre. It is mainly due to the last factor that
coarse cottons generally record higher values for fibre breaking strength than
finer ones. Therefore, in order to compare strength of two cottons differing in
fineness, it is necessary to eliminate the effect of the difference in cross-
sectional area by calculating from the values the fibre strength per unit cross-
sectional area. However, the determination of the area of cross-section is
difficult in the case of cotton fibres due to irregular shape of the cross-sections.
Hence it is a common practice to divide the breaking load by the fibre weight per
unit length which can be taken as proportional to cross-sectional area, assuming
the density to be the same for all varieties of cotton. The value so obtained is
known as ‘intrinsic strength’ or ‘tenacity’. Intrinsic strength is found to be better
related to spinning quality than the breaking strength. The strength
characteristics can be determined either on individual fibres or on bundles of
fibres.
DIFFERENT TYPES OF INSTRUMENTS
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The instruments generally used for determining the tensile strength or the ‘load-
extension’ diagram of textile materials can be classified into three groups, based
on the principle used for the application of load, namely, those of: (i) the rate of
traverse (CRT); (ii) the constant rate of specimen elongation (CRE); and (iii) the
constant rate of loading (CRL) types.
i) Constant Rate of Traverse:
In the instruments of the CRT type, the specimen is held between two
clamps, one of which (the lower clamp in a vertical arrangement) is
traversed at a constant speed to exert a load on the specimen. The other
clamp works against a spring or a pendulum suitable weighted. The load
on the specimen is measured by the extension of the spring or the swing
of the pendulum, as the case may be. In these instruments, the rate of
loading depends on the extensibility of the specimen and hence will vary
with the type of specimen under test. In the case of instruments using a
pendulum principle, the errors due to inertia are appreciable. As there is
a time lag before the pendulum is accelerated to the required speed, there
will be a lag in the rate of loading in the initial stages, while at the later
stages there is a likelihood of the pendulum overshooting beyond the
breaking load of the specimen.
ii) Constant Rate of Specimen Elongation:
In the instruments of the CRE type, the application of load is made in such
a way that the rate of elongation of the specimen is kept constant. This
can be accomplished by modifying the CRT instruments suitably so as to
render negligible movement of the upper clamp. For this purpose, the
upper clamp is fixed to a stiff support and the load on this support is
measured by suitable means such as a strain gauge as in the case of the
Instron Tester.
iii) Constant Rate of Loading:
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In the instruments of the CRL type, the mode of application of load is such
that the rate of loading is constant throughout the duration of the test.
This can be effected by the sliding of a weight down an inclined plane or
by the extension of a spring or flow of water at a constant rate etc. The
CRL type of instruments are usually preferred for accurate scientific work
in view of the case of interpretation of the results obtained with these
instruments.
In the CRE and the CRL types of instruments, it is easy to adjust the
‘time-to-break’ while this adjustment is not easy in the CRT type of
instruments. The test results with the CRE and the CRL instruments
show less variation than those obtained with the CRT type of instruments
as in the latter the rate of loading is dependent on the extensibility of the
specimen. Hence, where accurate interpretation of results is required the
CRT instruments are not recommended although these are widely used in
view of the ease of operation and rapidity of testing. Some instruments
like the Instron can be made to function both on the CRE and the CRL
principles.
FACTORS INFLUENCING STRENGTH TEST RESULTS
Tensile strength of cotton fibres is influenced by various factors such as the time
taken to rupture the specimen, the test length of the specimen and relative
humidity of the atmosphere in which the sample is conditioned and tested. For
comparing the results on different samples and to obtain reproducible results on
a given sample, it is necessary that tensile tests are carried out under specified
conditions.
The tensile strength recorded by a fibre depends on the time taken for the
progressive deformation and its eventual rupture. A lower ‘time to break’
invariably results in a higher breaking load. In most instruments used for tensile
strength test on fibres, the time to break can be varied by controlling the ‘rate of
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loading’, ‘rate of traverse’ or ‘rate of extension’ depending on the nature of the
instrument.
Another factor influencing fibre strength values is the ‘gauge length’ used, the
strength obtained at a longer gauge length being generally lower. The
dependence of fibre strength on gauge length is due to the presence of weak
places in the fibre. Lord pointed out that the strength of a fibre is the strength of
the weakest place, no matter how much stronger the specimen is at other
places. Thus, if structural imperfections are distributed along the length of a
fibre, some short elements may contain one or more weak places and others
may be free of them such that the chance of a weak place appearing in a
specimen increases with the test length. The extent of change of strength with
gauge length when fibres are broken individually or in the form of a bundle was
studied by Morlier et.al. Strength tests on fibre bundles are generally carried out
at nominal zero gauge length. However, tests at zero gauge length do not give
all the information required about the strength of the fibres in a sample, as the
influence of weak spots would not come into play at this test length and,
therefore, it would be desirable to carryout the tests at finite gauge lengths.
Moreover, it has been well established that the bundle strength measured at 1/8
in. (3mm) gauge length has better correlation with yarn strength than the
strength values measured at other gauge lengths. Hence the use of 1/8 in.
(3mm) gauge length for bundle strength tests has now become very common.
The strength of cotton fibres is affected by the humidity of the atmosphere in
which it is conditioned and tested, the strength increasing with the rise in relative
humidity. On the basis of extensive studies on the variation of single fibre
strength with increase in relative humidity, it has been possible to arrive at
correction factors (Table) with the help of which one can calculate the single fibre
strength at the standard atmosphere of 65% RH from the strength obtained at
any ambient humidity.
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Table: Humidity Correction Factors for Single Fibre Strength
Relative
Humidity
(%)
30 40 50 60 70
0
1
2
3
4
5
6
7
8
9
1.218
1.211
1.294
1.196
1.189
1.181
1.174
1.168
1.160
1.153
1.146
1.140
1.134
1.127
1.120
1.114
1.107
1.101
1.096
1.089
1.083
1.077
1.071
1.065
1.059
1.054
1.048
1.043
1.037
1.031
1.026
1.020
1.016
1.010
1.005
1.000
0.994
0.989
0.984
0.980
0.975
0.970
0.965
0.960
0.955
0.951
0.951
0.951
0.951
0.951
Bundle strength measurements are also affected by factors such as the
condition of the leather in the jaws holding the fibres under test on the
instrument, jaw pressure, bundle alignment, fibre selection in the combing
process prior to clamping etc., some of which could give a ‘personal bias’ to the
results. In order to have a check on the results of bundle strength
measurements, it is necessary to test suitable control samples and keep the
instruments properly calibrated. The results on various samples tested could
then be corrected by a factor depending upon the test results on the control
sample.
SINGLE FIBRE STRENGTH
The tenacity of a fibre is dependent upon many factors related to its structure
and the conditions under which the test is carried out. The structural features
contributing to strength are the chain length of the molecules, their orientation
and the size and distribution of the crystallites. Testing conditions which affect
the strength values are as mentioned earlier, the gauge length used, the rate of
loading, the type of instrument employed and the relative humidity prevailing in
the testing room.
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INSTRUMENTS FOR MEASURING SINGLE FIBRE STRENGTH
There are various types of instruments available for carrying out single fibre
strength tests. They can be classified in mainly two types of instruments.
Universal Tensile Tester:
This is a robust and versatile instrument used for measurement of a variety of
mechanical properties. Its versatility rests in the fact that it is capable of
recording the tensile load-elongation curves of a range of samples from single
fibres to thick fabric strips, which cover a wide spectrum of mechanical
characteristics.
The specimen under test is clamped between two jaws. The upper jaw is
suspended from the ‘load cell’ which is the load sensing device, while the lower
jaw is mounted on the ‘cross-head’ which can be moved up and down at
controlled speeds. The crosshead speed, which decides the rate of extension of
the specimen, can be varied from 0.05 cm/min to 50 cm/min in 12 steps. The
choice of the suitable load cell from among the four cells which cover a range
from 2 g to 500 kg. is made in accordance with the load requirements of the
specimen under test. The load cell contains a bonded wire type of strain gauge
which consists essentially of a cantilever beam with a resistance wire bonded to
the surface. The upper jaw carrying the specimen is suspended from the free
end of the cantilever beam such that the tension developed in the specimen
leads to an infinitesimally small bending of the beam. As a result, the wire
bonded to the beam increases in length and hence in electrical resistance in
proportion to the tension in the specimen. Since this resistance wire forms one
arm of a wheatstone bridge circuit, which is excited by an oscillator and which
remains normally balanced, any tension in the specimen would cause disbalance
in the circuit. The resulting signal is amplified to operate a recorder pen. Thus
when the test specimen is extended, the recorder pen moves across the chart
through a distance proportional to the tension in the specimen. Since the
deflection of the end of the beam is infinitesimally small, the Instron works as a
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‘constant-rate-of-extension’ instrument when the crosshead is moved at a steady
rate. The crosshead and chart are driven synchronously through magnetic
clutches and convenient gears to provide a choice of constant and reversible
extension speeds. The chart movement can be varied to achieve a range of
extension magnifications. As a result of the simultaneous movement of the pen
and the chart, the former responding to the tension in the specimen and the
latter synchronized to the specimen extension; the trace on the chart represents
the load-elongation curve. The Instron is also equipped with an Integrator which
is a convenient device for obtaining the area under the load-elongation curve
which measure the work of rupture.
Bundle Strength:
The determination of strength on individual fibres, as discussed above, involved
considerable amount of time as tests have to be made on a large number of
fibres in view of the high variability in fibre strength. Moreover in actual practice,
fibres are not used individually but in groups, such as in yarns or fabrics. Thus,
bundles or groups of fibres come into play during the tensile break of yarns or
fabrics. Further, the correlation between spinning performance and bundle
strength is at least as high as that between spinning performance and intrinsic
strength determined by testing individual fibres. The testing of bundles of fibres
takes less time and involves less strain than testing individual fibres. In view of
these considerations, determination of breaking strength of fibre bundles has
assumed greater importance than single fibre strength tests.
INSTRUMENTS FOR BUNDLE STRENGTH DETERMINATION
In the past, various methods were tried for the determination of bundle strength.
In one of the methods (which was being used at this laboratory), a small tuft
containing about 80 to 120 fibres was taken and the ends fixed between two
pairs of paper strips by means of some good adhesive, taking care to see that
the test length was 1 cm; the paper strips were gripped between the jaws of a
schopper testing machine and the bundle broken in the usual manner. The
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bundle strength that was recorded on the machine was divided by the number of
fibres in the bundle to get an idea of the strength realized per fibre.
In this category mainly two instruments are in use.
1. Pressley Strength Tester
2. Stelometer
Pressley Strength Tester:
It works on the principle of inclined plane apparatus. Now this instrument is not
much in use because of service limiting factors.
Error is likely to occur on account of the fact that the tension applied to straighten
the fibres while keeping them in the clamps and the torque applied for tightening
the jaw screws would vary from operator to operator. This error can be reduced
by using a torque vice, in which tension is adjusted to about 8 lb-in. (1.5 kg/cm).
Further, as this instrument works on the principle of constant but increases with
the traverse of the moving load carriage further away from the initial position;
hence, for bundles having higher breaking strength, the rate of loading at
breaking point would be higher than that for bundles of lower strength. Also,
there is an increased likelihood of the rolling weight overshooting the breaking
point before coming to rest in the former case due to inertia.
Stelometer:
The Stelometer is a pendulum type of instrument in which, contrary to usual
practice, the pendulum weight remains stationary while the pendulum axis
moves through an arc. By means of a special dashpot device, the rotation of the
pendulum axis (beam) is controlled in such a manner that the rate of loading is
approximately constant. An arrangement has been provided to check the
calibration of the instrument and adjust the rate of loading. Normally, the rate of
loading used is 1 kg/sec. A pointer, freely mounted on the axis and driven by a
sensing pin mounted on the pendulum, moves over a scale graduated from 2 to
7 kg. indicating the breaking load. In addition, a smaller pointer suspended from
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the above indicates the percentage elongation on an auxiliary scale. The
indicators can be read to nearest 0.01 kg and 0.1 percent for breaking load and
elongation respectively. The clamps, after removal of the protruding fibres, are
loaded in the slots on the top of the Stelometer and the beam is released. One
part of the Pressley clamps is held in the adjustable holder carried by the beam
while the other is held in a slot on the top end of the pendulum. The movement
of the beam applies tension to the bundle by pulling apart the two parts of the
clamps. As soon as the bundle breaks, the sensing pin falls away and the
pointer stops immediately. The breaking load can be read on the scale. The
broken fibres are collected from the clamps and the weight in milligrams
determined accurately. Six bundles are tested by two operators, on every
sample. The bundle tenacity is obtained by dividing breaking load by the weight
of the sample.
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CORRECTION OF OBSERVED TEST RESULTS
Standard value for calibration cotton
Correction Factor =
Observed value for calibration cotton
After finding out the correction factor, the test values obtained on the instrument
are adjusted by this factor. Therefore, for any sample under test,
Adjusted value = Observed value x Correction factor
Breaking strength of bundle in kg x 11.81
Stelometer value at zero =
gauge length (g/tex) Weight of bundle in mg.
Breaking strength of bundle in kg x 15.0
Stelometer value at 1/8 in. =
gauge length (g/tex) Weight of bundle in mg.
FIBRE QUALITY INDEX
In order to decide the quality characteristics of the cotton required for spinning
different counts with desired CSP values, a single measure for the overall quality
of cotton has been established by SITRA. This measure known as Fibre Quality
Index (FQI), is derived from the following formula:
lu s m
FQI =
f
where,
lu = product of 2.5% span length (l) in mm and uniformity ratio % (u)
measured on Digital Fibrograph divided by 100
s = Bundle strength in g/tex at 3mm gauge length (Stelometer)
m = Maturity coefficient
f = Fibre fineness as determined on Micronaire and expressed as
Micronaire value (micrograms/in.)
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AT OPTIMUM TWIST MULTIPLIER
Achievable Lea CSP = 320 (√FQI + l) – 13C for carded counts
= [320 (√FQI + l) – 13C] (l+W/100)
for combed counts
where,
C = Count spun
W = % Waste extracted during combing
In the case of combed counts, the lea CSP would be more by 1% for every 1%
waste extracted at the combers.
FIBRE-YARN RELATIONSHIPS USING HVI TEST SYSTEM
(a) Prediction Expressions for Yarn lea CSP using HVI/FMT measured
fibre properties (ICC Mode):
SITRA has developed the following prediction expressions connecting
fibre properties measured by High Volume Instrument (HVI) and Shirley
Maturity Tester with yarn lea CSP.
Lea CSP = 280 √FQI + 700 – 13C (For carded counts)
Lea CSP = {280 √FQI + 700 – 13C} {l+W/100} (For combed counts)
Where,
C = Yarn count, Ne
W = % Comber Noil
Lsm
FQI =
f
Values of L, s, m are measured using HVI test system and that of m using
Shirley FMT.
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L = 50% span length, mm
s = Bundle strength, gm/tex
f = Fineness (Micronaire value in micrograms/inch)
m = Maturity ratio
If maturity ratio values are not readily available then, as an approximation,
the lea CSP values may be arrived at from following expression:
Lea CSP = 250 (√Ls/f) + 590 – 13C
(b) Prediction Expressions for Yarn lea CSP using Fibre properties
measured by HVI test system (HVI Mode):
Lea CSP = 165 (√FQI) + 590 – (13C) (For carded counts)
Lea CSP = {165 (√FQI) + 590 – (13C)} {l+W/100} (For combed counts)
Where,
C = Yarn count, Ne
W = % Comber Noil
Ls
FQI =
f
Values of L, s, m are measured using HVI test system and that of m using
Shirley FMT.
L = Mean length, mm
s = Bundle strength, gm/tex
f = Fineness (Micronaire value in micrograms/inch)
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MISCELLANEOUS PROPERTIES
1. Fibre Friction or Clinging Power:
Fibre friction is considered as an important factor that contributes to yarn
strength especially of the low twist yarns in which breakage often occurs
as a result of fibre slippage rather than fibre fracture. Prediction of
spinning value of cotton could therefore be rendered more accurate by
quantitative information on fibre friction. Three methods are employed for
determining fibre friction. In one method, which is a modification of
Adderley’s method, a 3/8 in. length of a group of 10 cotton fibres is pulled
between two pads made of parallelised fibres of the same cotton and
subjected to a known pressure. The force required to pull out the group of
10 fibres is measured by a mechanism similar to the one employed on the
0’ Neill single fibre strength tester. In another method frictional force is
determined at two angles of slippage (0o
and 30o
) by means of an
elaborate apparatus designed for this purpose. In the third method the
technique used for the application of pressure between fibre pads is
simplified and the force required to withdraw 20 parallel fibres is
determined.
2. Torsional Rigidity:
The resistance of a fibre to twisting is determined by its torsional rigidity.
This property is important in spinning where the difficulty of binding rigid
fibres together could result in the production of bulky yarns. The torsional
rigidity of a fibre is defined as the torque required to twist one centimeter
length of it through 360o
. The torsional rigidity can be shown to be
proportional to the product of the rigidity modulus and the square of the
area of cross-section of the fibre, the constant of proportionality being
dependent on the cross-sectional shape.
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As the determination of single fibre rigidity involves considerable testing
time, a quicker method has been developed. In this method, the rigidity is
determined on a bundle of fibres weighing about 1 mg and the single fibre
rigidity is estimated from the bundle rigidity by dividing the latter by the
number of fibres in the bundle. Although the values obtained by this
method are not identical with those obtained by measurement on single
fibres, there is a high correlation between the two and hence the bundle
method can be adopted to save time.
3. Lustre:
Luster and colour of cotton are two characteristics that appeal to the
aesthetic sense of the observer. Luster denotes the ability of the fibre to
reflect light preferentially in some directions whereas colour refers to the
hue and to the strength of the hue. While a white cotton does not
necessarily have to show lustre, a creamy or yellowish variety can be
highly lustrous. Lustre is measured by means of a lustre meter fabricated
for this purpose. In this instrument, the sample is illuminated at an angle
of 45o
by a collight reflected from the sample is received by a photocell
and the intensity is obtained in terms of photo-current measured on an
ammeter. The intensity of specular reflection (45o
) and the intensity of
diffuse reflection in the direction normal to the sample are noted. The
ratio of the two intensities are known as the contrast ratio is used to
express the lustre of the sample. The instrument can be used for tests on
fibre, yarn or fabric.
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CHAPTER – 6
TRASH
Trash cannot be termed as fibre property but it has its own importance as the
amount of trash present in cotton directly affects the cost of cleaned cotton. Even
if we keep commercial aspect aside trash affects the yarn quality considerably.
Even after removing the trash in Blowroom and Cards small amount of trash
remains in the sliver.
Infact removal of trash in Blowroom and Cards depends upon nature of trash.
Seed coats amongst all impurities are most difficult to remove.
Recent studies have confirmed tha6 remnant trash in sliver mostly consists of
seed coats and it is directly related with the uster neps and classimate faults.
MEASUREMENT OF TRASH
100g. of cotton sample ‘S’ to be analysed is weighed accurately and is passed
through the Trash Analyser giving L1g. of lint and T1g. of trash. The trash T1 is
collected and again processed giving L2g. of lint and T2g. of trash. The lint portions
L1 and L2 are weighed together and give the total lint content in the sample.
S (100 g)
Lint L1 Trash T1
Lint L2 Trash T2
L = Lint content % = L1 + L2
T = Trash content % = T2
Invisible Loss % = 100 – (L + T)
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If the Trash T2 is still found to contain a sizable amount of lint, it is passed once
again through the Analyser giving L3g. of lint and T3g. of trash. Then lint content L
= L1 + L2 + L3 and Trash T = T3.
In general, two such 100 g. samples are analysed and the average calculated. It
is essential that the sample processed must be fairly representative of the bulk
sample.
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PRECAUTIONS
(1) While feeding the cotton, it is necessary to open it by hand and fed it
uniformly in a fairly thin fleece. For example, when feeding 100g. of
sample, half of it should be spread evenly on the feed table and as the
test proceeds the remaining sample should be added gradually.
(2) Hard lumps of trash or full seeds in the test sample must be collected by
hand and weighed along with the trash. If allowed to pass along with the
cotton, these are likely to damage the feed plate and licker-in wire points.
(3) A lever is provided for opening and closing the valve controlling the air
flow from the cage into the filter. This valve should be opened at the
beginning of a test. At the end of each test, the valve is closed so that all
the lint falls down into the lint box.
ANALYSIS OF TRASH
The visible trash so collected is passed through a set of wire meshy of mesh size
of BS 10 & BS 36 and is analysed as:
Trash over mesh 10 = Seed coats
Trash over mesh 36 = Leafy matter, kitties etc.
Trash below mesh 36 = Dust etc.
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The Cleaning Efficiency of a Machine:
The cleaning efficiency helps to evaluate the performance of a machine. If it falls
below a certain level the machine needs to be checked. The removal of trash
particles such as seed & leaf particles, stalks, sand and dust from cotton is
quantitatively expressed as cleaning efficiency which can be estimated as follow:
About 200gm of sample is taken from the feed & delivery of a machine like Blow
room, Card or Beaters. These samples are analysed for trash content. This is
done by processing a 100gm of sample through a Trash Analyser and collecting
the trash obtained & weighing it accurately. Two samples must be analysed and
average trash content is calculated.
T1 – T2
Cleaning Efficiency % = x 100
T1
Where, T1 = % trash in the material fed
T2 = % trash in the material delivered
Speeds and Settings of Shirley Trash Analyser:
Speeds:
1. Taker-in … 900 rpm
2. Feed roller … 0.9 rpm
3. Cage … 800 rpm
4. Fan … 1500 rpm
5. Motor … 1400 rpm
Setting:
1. Feed plate to taker-in … 4/1000 inch (4 thou)
2. Streamer plate to taker-in … 5/1000 inch (5 thou)
(lead-in edge)
3. Streamer plate to taker-in … 7/1000 inch (7 thou)
(lead-off edge)
4. Stripping knife to taker-in … 4/1000 inch (4 thou)
(Bottom edge)
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5. Stripping knife to cage … 5/16 inch
(lead in edge)
6. Taker-in to cage … 13/64 to 15/64 inch
7. Separation sheet to cage … 1/4 inch
(Top edge)
8. Delivery plate to cage … 1/16 inch
Note: These settings will vary depending on the model of the machine.
CHAPTER – 7
THE MATURITY OF COTTON
Fibre maturity is another important characteristic of cotton and is an index of the
extent of development of the fibres. The maturity of cotton fibre varies not only
between fibers of different samples but also between fibres on the same seed.
Thus a ripened, full mature cotton boll contains fibers both mature and immature.
A cotton fibre consists of a cuticle, a primary layer and secondary layers of
cellulose surrounding the lumen or central canal. In the case of mature fibres,
the secondary wall thickening is very high and in some cases, the lumen is not
visible. In the case of immature fibres, due to some physiological causes, the
secondary wall thickening is practically absent, leaving a wide lumen throughout
the fibre. Hence to a cotton breeder, the presence of excessive immature fibres
in a sample would in dictate some defect in plant growth, either varietal or
environmental. To a technologist, the presence of excessive percentage of
immature fibres in a sample is undesirable as this causes waste, losses in
processing, lowering of the yarn appearance grade due to formation of neps
uneven dyeing etc.
The determination of fineness of a cotton is affected by maturity of the sample.
An immature fibre will show a lower weight per unit length than a mature fibre of
he same cotton, as the immature fibre will have less deposition of cellulose
inside the fibre. Hence it is essential to measure the maturity of a cotton whether
the observed fineness is an inherent varietal characteristic or is a result of
immaturity.
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Importance of Maturity:
The maturity of the fibre is concerned with development of the cell wall. The cell
wall thickening is highly sensitive to growing conditions. Adverse weather, poor
soil, plant diseases and pests etc., will increase the proportion of immature fibre
and lead to trouble in processing.
One of the main troubles causes by the presence of these thin walled immature
fibres is nepping. Apart from maturity, causes like small bits or fragments of seed
particles attached to the fibre also forms neps. Neps are created during
processing starting at the ginning stage. Further when rubbing of surfaces takes
place, as in carding, minute knots of tangled fibres are caused and the immature
fibres are more prone of this nepping effect. When fine cottons are being
process4d, the danger of nepping is even more acute, since even the mature
fibres are likely to cause neps by faulty processing. In addition, the neps so
formed are usually more prominent because of their size relative to the diameter
of the fine yarn.
Immaturity also affects the shade after dyeing. As the response of the primary
wall t certain classes of dyestuffs is less intense, the thinner the secondary wall
lighter will be the shade. Hence fine cotton tends to be lighter in shade than
coarse cotton. Apart from this the reflecting surfaces of the fibres of the
immaturity is with respect to the patches being shown or the weft bars seen in
the fabric when yarn made of immature fibres or yarn spun from cotton of
different maturity is used as warp and weft. The presence of neps in a yarn will
also form weak places and therefore the average strength of the yarn will be
reduced. Neps will show up as specks in the dyed cloth. So summarizing the
maturity, the following points are noted.
1. Maturity affects the quality of the yarn and also the processing. The
effects of immature fibres are seen especially in the spinning process.
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2. The large number of ends down in a ring frame is due to the immature
fibres.
3. The loss in yarn strength, the dyeing troubles are all due to the presence
of immature fibres.
In order to assess the quality of cotton with respect to maturity and its effect on
ends down, yarn strength, dyeing troubles and so on, some method of
measurement is required. The most important one amongst them being the
degree of thickening θ. It may be expressed as the ratio of the actual cross
sectional area of the wall to the area of the circle with the same perimeter. The
reciprocal of this measures, 1/10 is called Immaturity ratio.
A
From the above figure, the degree of thickening θ =
A1
Where, A = Area of cross section of the cell wall
A1
= Area of the circle of equal perimeter
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A1
= πr2
4π 4π2
r2
= x πr2
=
4π 4π
Perimeter P = 2πr
∴ P2
= (2πr)2
= 4π2
r2
P2
∴ A1
=
4π
A 4πA
∴ θ = =
A1
P2
Direct measurement of this ratio is not a practicable routine test and is not
normally done. An indirect method known as Cotton fibre immaturity count is
used to determined the degree of cell wall thickening.
MEASUREMENT OF MATURITY
1. DIRECT METHOD
In these methods, the fibres after being swollen with 18 percent caustic
soda are examined under the microscope with suitable magnification. The
fibres are classified into different maturity groups depending upon the
relative dimensions of the cell wall and the lumen. However, the
procedures followed in different countries for sampling and classification
differ in certain respects.
i) Maturity Coefficient:
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A thin tuft of fibres in drawn by means of tweezers from a sliver
held in a comb sorter. Its thickness is so regulated that about 100
fibres are spread in a parallel array over a width of an inch in order
to facilitate the examination of each fibre separately under the
microscope. The tweezer end of the tuft is clamped first on the
narrower strip of the fibre mounting device called the ‘Maturity
slide’. The fibres are spread across the glass slide and the
overlapping fibres are again separated with the help of teasing
needle. The free ends of the fibres are then held in the clamp on
the second strip of the maturity slide, which is adjustable to keep
the fibres stretched to the desired extent.
The fibres are then irrigated with 18 percent caustic soda solution
and covered with a suitable cover slip.
The slide is then placed on the mechanical stage of a microscope
and examined. Beginning at one edge of the tuft, all fibres are
classed into three categories namely mature, half-mature and
immature, based on the ratio of lumen width (L) to wall thickness
(W) as indicated below:
Lumen width (L)
Category
Wall thickness (W)
L
Mature < 1
W
L
Half-mature 1 < < 2
W
L
Immature > 2
W
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About four to eight slides are prepared from each sample and
examined. The results are presented as percentages of mature,
half-mature and immature fibres in a sample. The results are also
expressed in terms of ‘maturity coefficient’ which is a unitary
expression signifying the multiple character of fibre maturity usually
represented by the percentage of mature, half-mature and
immature fibres, calculated from the formula:
(M + 0.6H + 0.4I)
Mc =
100
where Mc is the maturity coefficient, and M, H and I are the
percentage of mature, half-mature and immature fibres,
respectively, in the sample. Based on the maturity coefficient the
cottons are classed into different groups as shown in Table below.
Table: Classification of Cottons on the basis of Maturity
Coefficient
Category Range of maturity coefficient
Very immature
Immature
Average maturity
Good maturity
Very high maturity
Below 0.60
0.60 to 0.70
0.71 to 0.80
0.81 to 0.90
Above 0.90
ii) Percentage of Mature Fibres:
This is the US Standard (ASTM) method, in which the percentage
of mature fibres, Pm alone is determined.
Test specimen is prepared by any one of three following methods:
a) Array Method:
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From each length group, a bundle of about 100 fibres is taken
and spread uniformly on microscope slides. The series of
slides constitutes a test sample. A second set of slides is
prepared by another operator using fibres drawn from a
different array.
b) Laboratory Blended Sample:
Three slides of about 200 fibres each are prepared by each of
the two operators from a laboratory blended sliver of 50mm
length.
c) Fibrograph Beard:
Beards from two combs are removed and each one is divided
into two halves forming four sub-samples. From these sub-
samples, test specimens are prepared by the same procedure
as the one described in the case of the laboratory blended
sample.
The fibres laid parallel on the microscope slide are irrigated
with 18% caustic soda and are examined through a microscope
at 400 x magnification. They are classified into two categories,
mature and immature as shown below:
Lumen width (L)
Category
Wall thickness (W)
L
Mature < 2
W
L
Immature > 2
W
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From the total number of fibres and number of mature fibres,
the percentage of the mature (Pm) is calculated.
Pm = Mature Fiber/ Total Fibers x100
iii) Maturity Ratio:
In this method, which is also the British Standard method, the test
specimen is prepared either by the random sampling technique
(Zoning method) or the selective sampling technique (i.e. by
drawing fibres from various groups of the sorter pattern), and it is
recommended that test be made on five tufts of fibres from each
sample. Each tuft is taken separately on a slide and irrigated with
19% caustic soda. The swollen fibres are then examined under a
microscope magnification (100x) and classed into three groups,
viz. normal, thin-walled and dead. Rod-like fibres with no
convolution and no continuous lumen are classed as ‘normal’,
convoluted fibres with wall thickness one-fifth or less of the
maximum ribbon width are classed as ‘dead’, and the intermediate
ones are classed as ‘thin-walled’. A combined index known as
‘maturity ratio’ is used to express the results. Maturity ratio is
calculated by using the following equation:
N – D
Mr = + 0.70
200
where, Mr = Maturity ratio, N = Percentage of normal fibres and
D = Percentage of dead fibres.
Relationship between different Indices of Maturity:
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Some workers have established the formulae connecting the three
commonly used measures of maturity such as maturity ratio (Mr),
percentage of mature fibre (Pm) and maturity coefficient (Mc). These
formulae are useful for predicting one measure from another.
Pm = (Mc – 0.394) (3.434 – 1.783 Mc)
Pm = (Mr – 0.2) (1.5652 – 0.471 Mr)
Mr = (Mc – 0.301) (2.252 – 0.526 Mc)
2. INDIRECT METHOD
i) Polarised Light Methods:
These methods have been developed taking advantage of the
birefringence property of cotton fibres. In the simplest method,
about 200 fibres are mounted parallel to each other on a slide and
observed under a polarizing microscope. A selenite plate is placed
between the crossed polariser and analyser with the slow vibration
direction set at 45o
to the polarized and parallel to the fibres. The
classification for maturity is made depending upon the interference
colours produced, the immature fibres appear blue or purple and
the mature fibres appear yellow or green. The number of immature
and mature fibres thus differentiated are counted and expressed as
percentages. Fairly good agreement is found between maturity
obtained by this method and caustic soda method.
ii) Air-flow Methods:
In this method, the Micronaire reading on a 40 grain sample is
noted, and then by adding to it a 10 grain sample, a composite
sample of 50 grains is prepared and tested. The authors have
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derived separate regression equations for the different species of
cottons connecting the maturity coefficient by the caustic soda
method and the difference in Micronaire readings between 40 grain
and 50 grain samples.
There are other techniques for measuring maturity using the
Micronaire instrument. As the fineness value determined by the
Micronaire is dependent both on the intrinsic fineness (perimeter of
fibre) and the maturity, it may be assumed that if the intrinsic
fineness is constant then the Micronaire value is a measure of the
maturity. For example, if samples of the same variety are tested, it
can be assumed that the intrinsic fineness would be the same and
hence a higher Micronaire value would indicate a higher maturity
value. This is especially so with regard to American Upland
cottons as there is little variation in intrinsic fineness between
different varieties. Hence, certain arbitrary Micronaire values have
been suggested to denote the maturity of a cotton; thus cottons
having a Micronaire value less than 3.5 are considered immature,
while those having over 4.0 are considered as mature.
iii) Dyeing Methods:
Mature and immature fibre differ in their behaviour towards various
dyes. Certain dyes are preferentially taken up by the mature fibres
while some dyes are preferentially absorbed by the immature
fibres. In this technique, the sample is dyed in a bath containing a
mixture of two dyes, namely, Diphenyl Fast Red 5 BL and
Chlorantine Fast Green BLL. The mature fibres take up the red
dye preferentially, while the thin-walled immature fibres take up the
green dye. An estimate of the average maturity of the sample can
be visually made from the amount of red and green dyed fibres.
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Fig. : Immature Fibre
Fig. : Immature Fibre
Fig. : Mature Fibre
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FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY
CHAPTER – 8
SOME PRECAUTIONS DURING COTTON FIBRE TESTING
1. FIBRE LENGTH
(a) Baer sorter:
Take a representative test specimen as per ISI method.
Prepare a uniform hand made sliver without applying much tension to
avoid fibre rupture.
Slightly twist the fibres before putting it over combs.
Straighten the edge of protruding sliver before transferring the fibre from
one side to another or over velvet board.
Straighten the edge of protruding sliver before transferring the fibre from
one side to another or over velvet board.
Comb the fibres 2-3 times before transferring.
Transfer all the fibres over velvet board.
Draw a line over transparent sheet just over the end of fibres.
Use a pointed pencil.
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(b) Fibrograph:
Warm up & calibrate the instrument according to the instruction manual
before testing.
Clean the Doffer of Fibro-sampler before and after sampling.
For best precision in testing, sample size should be between 600 to 900
fibres.
Brush the fibre beard to remove trash & loose fibres carefully because
light brushing will remove fewer loose fibre and heavy brushing will pull
out long fibres and disturb the random arrangement.
Press the sample uniformly with the heel of left hand side to protrude the
fibres through the hole of fibro sampler plate.
Use standard cotton for the correction.
2. MATURITY:
Prepare a uniform hand made sliver from random test specimen.
Spread the cotton fibres over glass slide separately or without over-
lapping.
Avoid the contact of NaOH solution with skin and use a glass rod.
Remove the air bubble by rubbing the glass slide to each other.
Focus the projectina over glass slide properly for better identification.
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3. FINENESS:
Pass the test specimen through trash analyser before testing.
Level and calibrate the instrument according to the instruction manual.
Allow to stabilize the indicator before observation.
Take more observation if large variation is observed.
Use standard cotton foe the correction.
4. BUNDLE STRENGTH:
Level and calibrate the instrument according to instruction manual.
Use standard cotton for correction. Correction Factor should be within the
limit i.e., 1 ± 0.1.
Check the leather of fibre clamps.
Apply equal force and tension for each and every test.
Breaking strength of bundle should be between 3.0 kg. to 6.0kg.
Condition the standard cotton and test specimen before testing.
5. TRASH ANALYSIS:
Clean thoroughly the trash analyser before and after test.
Separate the seed from cotton sample manually.
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FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY
Condition the sample before and after trash analysis for weighing.
Manually open the big tufts of cotton before passing it through the trash
analyser.
Keep your fingers away from the feed rollers.
Page 67 of 85
TRAINING MANUAL
FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY
CHAPTER – 9
HIGH VOLUME INSTRUMENT
Zellweger Uster HVI test system measures seven important characteristics of
cotton and they are:
• Length
• Length uniformity
• Micronaire
• Bundle Strength
• Elongation
• Colour and reflectance
• Trash content (optical determination)
As per manufacturers claim, about 180 samples (each sample – 1test) can be
tested for all the above seven properties/hour with two operatives manning the
instrument.
However, as per practical experience in Indian Laboratories, about 100
samples/shift of 8 hours (each sample – 4 tests) could be conveniently tested
using HVI. Because of the high speed of testing, now technicians are in a
position to determine the raw material characteristics with reference to a large
enough sample.
High volume instruments are of two type.
Semi Automatic
Fully Automatic
In addition, automatic testing systems offer the following advantages:
• The results are practically independent of the operator error.
• The results are based on large volume samples and therefore more
significant.
Page 68 of 85
TRAINING MANUAL
FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY
• The respective fibre data are immediately available.
• The data are clearly arranged in summarized reports (HVI test system has
microprocessors to format the test data for analysis, storage and retrieval)
• They make possible the best utilization of the raw material data.
• Problems as a result of the fibre material can be predicted & corrective
measures can be instituted before such problems can occur.
HVI test system enables testing of large volume of samples and arrive at a
correct estimate of the fibre properties within a short time so that appropriate
mixing can be prepared. Besides, quality of all individual bales and within bale
and between bale variations can be assessed. The bales can be categorized into
different lots depending on the actual fibre properties. The mills can
subsequently evolve a bale management system which would enable them to
maintain the quality at a consistent level at minimum cost.
The length, strength, length uniformity, elongation, Micronaire, colour, trash &
the NIR value of cotton fibres are all important in fibre research, in development
of improved fibre blends and in verifying that purchased fibre meet
specifications.
This test system offers precise and reliable automated operation with computer
controlled calibration and diagnostics. All functions are controlled by dedicated
microprocessors to simplify operation and to provide flexibility in testing
parameters.
Separate version of the software is available to measure properties of man-made
fibres. Included with the system are keyboard, monitor & balance. The monitor
display the menu selection, operating instructions and test results. As tests are
completed for each sample, the results can be transmitted to the printer of the
host computer system.
Page 69 of 85
TRAINING MANUAL
FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY
There are two ways of testing a sample. First one is the system testing which is
designed to allow linear measuring procedure that includes the length/strength,
Micronaire, colour/trash & NIR Modules. This procedure allows one operator to
perform all task. In this procedure only one test is performed for Micronaire &
NIR.
The second way is the module testing. There are different module for
length/strength, Micronaire, colour/trash & NIR. Testing is done in steps, but the
number of test for Micronaire & NIR can be increased.
The instrument is calibrated by using calibration cottons and standard colour tiles
provided with the instrument. The standard cottons are stored in an environment
of 270
C and 65% Relative Humidity because the moisture content of he cotton
affects its length, strength & Micronaire.
There are two kinds of cotton that can be used to calibrate HVI systems.
1. International Calibration Cotton (I.C.C).
2. High Volume Instrument calibration cottons (HVI). The HVI can be calibrated
on Stelometer level or pressley level.
ICC cotton are well blended card web. Two samples of these cotton are required
for Micronaire calibration, one with low Micronaire value & another with high
Micronaire value.
The word “Calibration” refers to adjustment of values. The HVI is calibrated
following engineering principle using hardware devices. After proper calibration,
adjustment to raw test values are made by means of automatic software
manipulation to cause test values to agree with designated values of standard
samples.
Page 70 of 85
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING
TEXTILE TESTING

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TEXTILE TESTING

  • 1. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 1 1.0 QUALITY EVALUATION OF TEXTILES : 1.1 INTRODUCTION Testing of textiles provides valuable aid to those engaged in the production, distribution & consumption of textiles provided instruments & techniques are used effectively but testing instrument can not make decisions & at the end some person has to interpret & analyze the data available. The type of textile testing instruments available is large. Many of them are simple in principle and have been used by the textile industry for a long time. Some important instruments are relatively new, as also are commercial models of equipment developed in research laboratories. The choice of instruments and the testing techniques employed will be governed largely by the information required as well as how accurate and detailed that information has to be. The subject of textile testing can be covered by answering few ‘W’ questions. Why do we test? What do we test? When do we test? Who should do the test? 1.2 WHY DO WE TEST? 1.2.1 Selection of Raw Materials : Raw material cost is the highest amongst all component of cost. This accounts for 60-70% in cotton & synthetics. Therefore selection of raw material becomes extremely important & any lapse in this part may lead the organization to run into trouble. Ensuring optimum quality of raw material not only reduces the product cost at desired level but also ensure good working conditions inside the mills. Page 1 of 85
  • 2. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Raw material differs from manufacturer to manufacture. For some, it may be fibre, for some it may be yarn & for processor it may be grey fabric. 1.2.2 Process Control : Testing of intermediate products i.e. lap, sliver, roving & some of wastes like comber noil extends lot of help in process control. In the spinning mill, most common testing for process control is testing count (Hank) at various stages. For reliable corrective action, one can use ‘Quality Control Charts’ for control of the count. 1.3 RESEARCH Testing helps in determining direction in research work. Often research worker finds himself at cross roads & the result of testing will help the scientist to decide which path to follow next. 1.4 PROCESS DEVELOPMENT Process development can be taken as applied form of research. The objective of process development is to investigate simpler, cheaper, quicker or energy efficient methods of doing the same work, improving the quality of product without changing inputs i.e. blending of different fibres at different stages. Here one should be clear about which properties are to be listed in order to avoid unnecessary wastage of time. 1.5 TESTING OF FINISHED PRODUCT Even if we have selected raw material of right quality & it seems that our process is fairly controlled, we cannot assure product of specified quality because of lack of knowledge about lot of variables in the process. Therefore it is a standard Page 2 of 85
  • 3. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY practice to test finished product against specifications and the products which are falling beyond tolerances are being rejected. Some times a forecast of the probable performance in a subsequent process is required. Now from fibre properties we can predict that what is going to be C.S.P. of cotton or from yarn properties we can have some idea about performance of yarn in Winding as well as in weaving. 1.6 CHECKING SPECIFICATIONS To ensure the goods purchased are as per given specification or purchased machines are capable of producing goods of the quality as desired by manufacturers, testing is a must. Sometimes samples are being sent with a tag to produce identical product, here again suitable analysis techniques and testing are required to produce sample of same specification. Page 3 of 85
  • 4. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY 2.0 SELECTION OF SAMPLE In textile most of the tests are destructive in nature therefore testing is conducted on a very very small part of the population i.e. referred as “sample” 2.1 RANDOM SAMPLE In case of random sampling every individual in the population has got an equal chance of being included in the sample without any bias. Normally it is desired that a sample should be random & representative of the lot. 2.2 BIASED SAMPLE Some time unknowingly bias occurs during sample collection due to location or any other reason . Some specimen have more chance of being included in the sample. For different tests , different type of sampling techniques are adopted ( in case of fibre , yarn and fabric ) to get correct test results . 2.3 PLANNED SAMPLE Some time it might be useful to draw test sample in a planned manner, particularly when we want to cover entire process or deliveries of machines in a given time frame i.e. checking of uster & imperfections in case of ring frame. Page 4 of 85
  • 5. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY 3.0 FIBRE TESTING Testing of fibres is required for determining their quality. Unless quality of raw material is not controlled it will not be possible to get a quality finished product. We can broadly divide fibre testing in two categories – 1) Testing of Cotton Fibre 2) Testing of Man-made Fibres 3.1 Testing of Cotton Fibre Following are the main properties of cotton fibre – i) Fibre length ii) Fibre fineness iii) Fibre strength iv) Maturity of cotton v) Colour vi) Trash% vii) Neps Page 5 of 85
  • 6. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 2 SAMPLING PROCEDURE FOR FIBRE TESTING The quality of a cotton sample is mainly dependent on the various physical properties of the fibres in the sample. The most important physical characteristics are length, fineness, maturity and strength of the fibres. There are large variations in these characteristics not only between fibres of different samples but also between the fibres constituting the same sample. Investigations have shown that the variations in length observed between fibres in a bulk sample are of the same order as those observed between fibres on a single seed of that variety. The characters of any random sample picked out from a bulk cannot be expected to be representative of the bulk in view of this large variation. Hence, before carrying out any tests for fibre characteristics, it is preferable to prepare a test sample which is, as far as possible, truly representative of the constituents of the bulk. The details of the procedures employed for proper sampling and the methods adopted for determining the various physical quality factors of cotton fibres are described in the following sections. Sampling Techniques For The Determination of Fiber Properties The sampling method used to select a fiber for testing depends upon the form in which the fiber is available. Therefore fibers in bales, in sliver, card web, yarn etc will require different techniques The test result of sample may not be the same as obtained by testing bulk sample. Two source of error may be present. Random error & error due to bias. Sampling from Bales In order to obtain a representative sample from a lot of bales it is necessary to distribute the sample to be selected over the bales in the lot and different layers in the bale. The number of bales to be selected at random from a lot shall be in accordance with Table-1. Page 6 of 85
  • 7. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Table-1 : Number of Bales to be selected from a lot No. of Bales In the Lot No. of Bales to be Selected Up to 50 51 to 100 101 to 150 151 to 300 301 to 500 501 to 1000 1001 & Above 2 4 7 13 20 32 40 In view of the variation observed in most of the fibre properties, both within and between the layers of cotton in a bale, it is desirable to open the bale and draw tufts from different positions in at least 10 equally-spaced layers. In practice the selection of the layers from a bale may be done as given below: The bale is kept lengthwise on the ground and the hoops are broken. A thin layer of cotton is removed from the top and the tufts are drawn from various positions on the exposed surface. Then a thick slab (about one-tenth the height of the bale) is removed and the tufts are drawn from the newly exposed surface. The procedure is repeated till the tufts are drawn from at least 10 layers. While drawing the tufts from various layers, care shall be taken to avoid any bias in selecting the positions for drawing the tufts. The material so drawn from the bale shall not be less than 2 kg. In case it is not economical to open the bale completely, the gross sample may be obtained by breaking one or more of the hoops round the bale and then taking out a lump of at least 1 kg of material from each of the two exposed sides of the bale. The material so taken shall include portions from the hard, soft and middle parts of the bale. The material so obtained from all the bales selected from the lot shall be thoroughly mixed to get a gross sample. Page 7 of 85
  • 8. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Reduction of Gross Sample The gross sample shall be spread out evenly on a level ground in the form of either a square with each side slightly greater than 1 m, or in the case of a larger sample, a rectangle with the shorter side slightly greater than 1 m, and the larger side slightly greater than 2 m. A suitable framework of size 1 x 1 m with 25 sub- squares or 1 x 2 m with 50 sub-squares, one or more tufts of fibres shall be pulled out at random, taking care not to exercise and bias in favour of or against any particular place within a sub-square, and that tufts drawn from each sub- square weigh about 4 g in the former case and about 2 g in the latter case. The quantity of cotton thus drawn shall constitute the reduced sample. The reduced sample shall be well mixed and divided into 25 or 50 approximately equal parts. From each of these parts, one or more tufts of fibres shall be extracted at random, taking care that the fibres drawn are nearly equal in weight, and the total weight of fibres thus drawn is not less than the quantity required for relevant tests. The material so taken out shall constitute the test sample. CTRL Method of Sampling and Preparation of Drawbox Sliver The reduced sample is divided into 32 approximately equal parts by successive dichotomy. From each portion a small tuft of fibres is extracted in a random manner. Approximately the same quantity of fibres is taken from each group so that the total weight of the final test sample is between 200 mg and 500 mg. For most fibre tests like length by Balls and Baer sorters, maturity by Caustic soda method, and bundle strength by Pressley Strength Tester and Stelometer, it is convenient to prepare a representative sliver out of the test sample, by cleaning it free of leaf bits and other extraneous matter, mixing various portions thoroughly and then parallelising the fibres. For this purpose, the test sample, after cleaning by hand and mixing is passed through a drawbox repeatedly 5 to Page 8 of 85
  • 9. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY 10 times. The sliver so prepared can be taken to be completely representative of the bulk sample. B.S. Zoning Method This method gives a numerical sample, obtained by repeatedly halving the representative samples. The total number of fibres required(n) in the sample is estimated and tuft of fibres from various parts (m) of the bulk is taken. The portion so taken is divided into two taking care to avoid fibre breakage, and rejecting one-half, the choice of which half to be rejected being half is rejected at random. This process for each tuft is continued until a number of fibres equal to about n/m of the total required in each group is obtained. The required sample consists of all the fibres remaining in each group. If two samples are required the m halves remaining after the last division may be used for the second sample, provided any further reduction of sample size which is required is carried out in a manner similar to that just given. Sampling for Other Tests For tests on the Fibrograph, the test specimen is directly prepared from the reduced sample. For tests on the Nickerson-Hunter Cotton Colorimeter, a larger reduced sample, of about ½ kg is prepared, which is divided into three or four tests on the Micronaire instrument sufficient quantity from the laboratory sample is well-opened, cleaned and thoroughly mixed to get about 8 gms, of sample. Textiles and moisture Introduction The properties of textile fibres are in many cases strongly affected by the atmospheric moisture content. Many fibres, particularly the natural ones, are hygroscopic in that they are able to absorb water vapour from a moist atmosphere and to give up water to a dry atmosphere. If sufficient time is allowed, equilibrium will be reached. The amount of moisture that such fibres contain strongly affects many of their most important physical Page 9 of 85
  • 10. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY properties. The consequence of this is that the moisture content of all textile products has to be taken into account when these properties are being measured. Furthermore because the percentage of moisture that can be retained by fibres is quite high (up to 40% with some fibres), the moisture content can have a significant effect on the mass of the material. This factor has a commercial importance in cases where material such as yarns and fibres is bought and sold by weight. Effect of moisture on physical properties The physical properties of fibres can be affected by their moisture content. In general the fibres that absorb the greatest amount of moisture are the ones whose properties change the most. Three main types of properties are affected. i) Dimensional The mass of the fibres is simply the sum of the mass of the dry fibre plus the mass of the water. The absorption of moisture by fibres causes them to swell, because of the insertion of water molecules between the previously tightly packed fibre molecules. Because the fibre molecules are long and narrow most of the available intermolecular spaces are along the length of the molecules rather than at the ends, so that the swelling takes place mainly in the fibre width. Nylon is a notable exception to this, The change in volume of a fibre is linked to the changes in its length and cross- sectional area by simple geometry. The change in volume is also linked to the amount of water that has been absorbed. The swelling of fibres is a continuous process which takes place in step with their increasing moisture content. Fabrics made from fibres that absorb large amounts of water are affected by the swelling. When such a fabric is soaked in water the increase in width of the fibres leads to an increase in diameter of the constituent yarns. Depending on the closeness of spacing of the yarns this can lead to a change in dimensions of the fabric. However, on subsequent drying out the structure does not necessarily revert to its original state. This behaviour is responsible for the dimensional stability problems of certain fabrics. Advantage is taken of fibre swelling in the construction of some types of water proof fabrics whose structures are designed to close up when wetted, so making them more impermeable to water. 2. Mechanical Some fibres, such as wool and viscose, lose strength when they absorb water and some, such as cotton, flax, hemp and jute, increase in strength Furthermore the extensibility, that is the extension at a given load, can increase for some fibres when they are wet. These changes in strength and extension have consequences for many other textile properties besides tensile strength. Some properties such as fabric tearing strength are ones that are obviously likely to be affected by fibre strength, but for other ones such as crease resistance or abrasion resistance the connection between them and changes in Page 10 of 85
  • 11. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY fibre tensile properties is less apparent. It is because of these changes in properties that textile tests should be carried out in a controlled atmosphere. 3) Electrical The moisture content of fibres also has an important effect on their electrical properties. The main change is to their electrical resistance. The resistance decreases with increasing moisture content. For fibres that absorb water the following approximate relation between the electrical resistance and the moisture content holds for relative humidities between 30% and 90%. RMn = k Where R = resistance, M = moisture content (%) and n and k are constants The changes in resistance are large : there is approximately a tenfold decrease in resistance for every 13% increase in the relative humidity. This fall in resistance with increasing moisture content means that static electrical charges are more readily dissipated when the atmospheric relative humidity is high. Atmospheric moisture The moisture content of textile materials when they are in equilibrium with their surroundings is determined by the amount of moisture in the air. Therefore the moisture content of those materials that absorb water can vary from day to day or from room to room. The atmospheric moisture level is normally expressed in terms of relative humidity and not absolute water content. Relative humidity The amount of moisture that the atmosphere can hold increases with its temperature so that warmer air can hold more water than cold air. When considering the effects of atmospheric moisture on textile materials the important quantity is not how much moisture the air already holds, but how much more it is capable of holding. This factor governs whether fibres will lose moisture to or gain moisture from the atmosphere. The capacity of the atmosphere to hold further moisture is calculated by taking the maximum possible atmospheric moisture content at a particular temperature and working out what percentage of it has already been taken up. This quantity is known as the relative humidity (RH) of the atmosphere and it can be defined in two ways . In terms of the mass of water vapour in the atmosphere: Mass of water vapour in given volume of air RH = ----------------------------------------------------------- x 100 % Mass of water vapour required to saturate Page 11 of 85
  • 12. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY this volume at the same temperature Alternatively it can also be defined as the ratio of the actual vapour pressure to the saturated vapour pressure at the same temperature expressed as a percentage. Actual vapour pressure x 100% RH = ------------------------------------------- Saturated vapour pressure The absolute humidity is defined as the weight of water present in unit volume of moist air measured in grams per cubic metre. It is important to note that the relative humidity of the atmosphere changes with temperature even when the total quantity of water vapour contained in the air remains the same. The amount of moisture contained by fibres that are in equilibrium with the atmosphere is dependent on the relative rather than the absolute humidity. Standard atmosphere Because of the important changes that occur in textile properties as the moisture content changes, it is necessary to specify the atmospheric conditions in which any testing is carried out. Therefore a standard atmosphere has been agreed for testing purposes and is defined as a relative humidity of 65% and a temperature of 20o C. For practical purposes certain tolerances in these values are allowed so that the testing atmosphere is RH 65% + 2%.; In tropical regions a temperature of 27 + 2o C may be used. Regain and moisture content The amount of moisture in a fibre sample can be expressed as either regain or moisture content. Regain is the weight of water in a material expressed as a percentage of the oven dry weight. 100 x W Regain = ------------- % D where D is the dry weight and W is the weight of absorbed water. Moisture content is the weight of water expressed as a percentage of the total weight 100 x W Moisture content = -------------- % D + W Page 12 of 85
  • 13. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Regain is the quantity usually used in the textile industry Factors affecting the regain Different fibre types absorb different amounts of moisture depending on their affinity for water. For a given fibre type the moisture content is governed by a number of factors: 1. Relative humidity. The higher the relative humidity of the atmosphere, the higher is the regain of textile material which is exposed to it. 2. Time. Material that is in equilibrium at a particular relative humidity which is then moved to an atmosphere with a different relative humidity takes a certain amount of time to reach a new equilibrium. The time taken depends on the physical form of the material and how easily the moisture can reach or escape from the individual fibres. 3. Temperature. Temperature will affect the regain of material. In testing laboratory as temp. variation are small, for practical purposes the temperature does not affect the regain of a sample. 4. Previous history. The moisture content of textile materials in equilibrium with a particular relative humidity depends on the previous history of the material. The material will have a different moisture content depending on whether it was previously wet or dry. Processing of the material can also change its regain value by altering its ability to absorb moisture. The removal of oils, waxes and other impurities can also change the regain by removing a barrier on the fibre surface to the flow of moisture vapour. For example the standard regain value for scoured wool is 16% and that for oil combed tops is 19%. Method of measuring regain To measure the regain of a sample of textile material it is necessary to weigh the material, dry it and then weigh it again. The difference between the masses is then the mass of water in the sample. Mass of water x 100% Regain = ------------------------------ Oven dry mass Page 13 of 85
  • 14. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Regain is based on the oven dry mass, which for most fibres is the constant mass obtained by drying at a temperature of 105 + 2o C. Constant mass is achieved by drying and weighing repeatedly until successive weighing differ by less than 0.5%. This is also called oven dry weight. Standard Regain Values Fibre type Regain (%) Man-made fibres Acetate 6.5 Acrylic 1.5 Nylon 6, 6 and 6 4.5 Polyester 0.4 Polypropylene 0 Triacetate 3.5 Viscose 11-12 Natural fibres Cotton – natural yarn 8.5 Linen fibre 12 Linen yarn 8.75 Silk 11 Wool 16-18.0 Shirley Moisture Meter Electrical resistance of different textile materials varies considerably at different regains. This principal is used in Shirley Moisture Meter. Initially instrument was designed to measure moisture of Raw cotton & yarn however later its use was extended to other textile materials & tables were prepared to give corrected values. The electrode consist of a central conductor insulated from an outer circular sheath. When pressed into the cotton the fiber bridges the insulation & resistance is measured. Two electrode one for raw cotton & one for yarn is used. The difference being that for yarns spacing between conducting element is increased. This counteracts the increased conductivity of yarns due to more or less parallel arrangement of the fibers compared with random arrangement of the fibers in loose cotton. The indicating unit translate resistance value into regain values On one of two dials.. One dial covers normal range from 7-11 percent & other For Damp 9-15 & Dry from 5-9 percent range. Page 14 of 85
  • 15. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 4 FIBRE LENGTH Among the various properties which determine the quality of cotton, fibre length occupies a dominant position as it influences, to a large extent, the spinnability of a cotton. Moreover fibre length can be easily estimated. Hence, this characteristic of cotton has assumed great importance in commercial transactions and the price of a cotton sample is largely based on this characteristic. Any sample of cotton will contain fibres varying in length from 2mm onwards, the upper limit being decided by the variety of cotton under consideration and the conditions under which it has been grown. This variation is found markedly even when fibres removed from an individual cotton seed are considered. In view of the above, what we generally aim at is to obtain a measure of fibre length which can be considered as average for the whole sample or which is likely to influence the spinning performance most. DEFINITIONS OF FIBRE LENGTH PARAMETRES Mean length: The arithmetic mean of the length of all the fibres present in a small but representative sample of cotton, based on weight-length distribution or relative number-length distribution. Upper Quartile Length: The length for which 75 per cent of all the observed values are lower and 25 per cent higher, by weight or by number Modal Length: The most frequently occurring length of fibres in the weight distribution of the sample. Page 15 of 85
  • 16. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Median: The particular value of length above and below which exactly 50% of the fibres lie. For moderately skewed distributions the median is related to the mean and modal lengths in the following way: Mode – mean = 3 (median – mean) Effective Length: It is difficult to give a clear scientific definition for effective length. It may be defined as the upper quartile of the numerical length distribution from which some of the shortest fibres are eliminated by an arbitrary construction. The fibres eliminated are those shorter than half the effective length. Percentage of Short Fibres: The percentages of fibres less than half the effective length or less than any specified length. Coefficient of Variation: The standard deviation of weight-length or relative number-length frequencies expressed as a percentage of the mean length. Span Length: The distance spanned by a specified percentage of the fibres in the test beard. 2.5% span length is the distance from the clamp on a fibre beard to a point upto which only 2.5% of the fibres extend. 50% span length is the distance of the point to which 50% span length is the distance of the point to which 50% of the fibres extend and 66.7% span length is the distance upto which 66.7% of the fibres extend. Uniformity Ratio: The ratio of 50% span length to the 2.5% span length expressed as a percentage. Page 16 of 85
  • 17. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Dispersion: It represents the variation in the length of fibres. It is the interquartile range expressed as a percentage of effective length. MEASUREMENT OF FIBRE LENGTH Single Fibre Measurement It is possible, with patience, good lighting, a microscope slide over a scale, and medicinal paraffin to control the fibres, to measure the length of individual cotton fibre. Each fibre is taken and gently straightened over the slide with the tips of the little fingers; the length is then recorded. This method is obviously tedious and time consuming and not used in the mill laboratory. At least 400-500 fibers are measured in case of cotton to arrive at mean length due to large variation in the sample. PRINCIPLE OF BAER SORTER A numerical sample of fibres is arranged in the form of an array in the descending order of length and form a tracing of this array of length, mean length, percentage of short fibres and dispersion are calculated. DESCRIPTION The Baer Sorter consists of a abed of combs which control and enable the sample of fibres to be fractionalized into length groups. The Baer Sorter has 12 bottom combs are hinged at one end and are supported by a rod, extending the width of the frame at the other end. The rod can be moved from its position and when it is drawn, the rod can be dropped one by one. The needle of the bottom combs are pointing upwards and in between the bottom combs, three top combs are placed. The space between the two bottom combs is ¼ inch except the first Page 17 of 85
  • 18. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY two bottom combs which will be 3/16 inch apart. The top combs, when placed between the two bottom combs, the distance between them will be 1/8 inch. Manipulation of the fibres is done by a grip called tweezer, depressor and a blunt needle. PROCEDURE The position of fibre unit in the instrument is shown in fig. A representative sample of cotton is made into sliver by drawing and doubling several times with the fibres strengthened and parallelised. The bundle of fibres must be as narrow as possible through out the whole process. The method of sorting is a s follows: 1. The sorter is placed with the back facing the operator. The prepared sample is slightly twisted and placed on the bottom combs at the right hand side of the sorter, with a small tuft protruding. 2. From the protruding end, all the loose fibres are removed by means of the tweezer until, the ends are aligned. The removed loose fibres are kept separately and introduced in the original sample later. 3. A tuft of fibres all pulled out, combed and transferred to the left hand side of the sorter so that the comb nearest to the operator forms the starting line for the tuft, while at the other end the longest fibres protrude out. The tuft is pressed into the combs by means of depressor. 4. The process is repeated till all fibres on the right side, all combings are transferred to the let hand side. 5. The top combs are inserted in their position to grip and to control the slippage of the fibres. 6. The sorter, is then turned round so that the front faces the operator. 7. The bottom combs are dropped one by one successively till the tips of the longest fibres are seen. 8. The fibres are pulled by the tweezer, combed, straightened and laid perpendicular to a base line on a black velvet pad. When these fibres are Page 18 of 85
  • 19. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY exhausted. One comb is dropped and the fibres next in order of length are similarly pulled out and laid on the pad all fibres being carefully spread out to uniform density. The process is continued until the tuft is exhausted and the fibre array is obtained. After the pattern is built up, a transparent scale, with 1/8 inch lines is placed over the pattern. Reading on the transparent scale, the values of the co-ordinates are marked on a graph sheet and the pattern is drawn. The diagram is called “SORTER DIAGRAM”. The diagram is analysed for the following fibre particulars. 1. Effective Length 2. Mean length 3. Percentage of short fibres 4. Dispersion Fibre Sorter Methods As single fibre measurement takes time and hand stapling requires experience (although even then this is a subjective test), alternative methods have been developed. One of the most popular is the use of the fibre sorter, examples of which are the Baer, the Shirley, and the Suter Webb. The fibre sorter is an instrument which enables the sample to be fractionalised into length groups. Basically, the operation involves four main steps: 1. The preparation of a fringe or tuft with all the fibres aligned at one end. 2. The separation or withdrawal of fibres in order of decreasing length. 3. The preparation of a sorter diagram by laying the fibres on a black velvet pad in decreasing order of length, the fibre parallel and their lower ends aligned along a horizontal base line. 4. The analysis of the diagram. Page 19 of 85
  • 20. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Analysis of Sorter Diagram By placing the tracing over graph paper ruled in sixteenths of an inch, the diagram can be readily divided into 1/8 in. classes. Alternatively it can be read in mm also by using paper of 1 mm square. Average or Mean Length The sum of the base line readings divided by the base line length gives the mean length in units of 1/8 in. or mm, the class interval. Multiplying by 4 expresses the mean length in 1/32 in. units. This is the mean height of the curve and is obtained by dividing the total area under the curve by the base length. Maximum Length This is read directly from the diagram. Modal Length The mode of a frequency distribution is the class value of the class with the highest frequency; in other words, the most ‘fashionable’ value. Since distances along the base line are assumed to be proportional to frequency, the modal length will be given by the class which has the greatest base length. Effective Length This value has been defined as the length of the main bulk of the longer fibres. It is obtained by a geometrical construction on the sorter diagram, a construction which also produces several other useful quantities. Figure illustrates this operation. Page 20 of 85
  • 21. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY 1. Q is the mid-point of OA, i.e. OQ = OA. 2. From Q draw QP’ parallel to OB to cut the curve at P’. 3. Drop the perpendicular P’P. 4. Mark off OK equal to ¼ OP and erect the perpendicular K’K. This is a firs approximation to the effective length. 5. S is the mid point of K’K. 6. From S draw SR’ parallel to OB to cut the curve at R’. 7. Drop the perpendicular R’R. 8. Mark off OL equal to ¼ OR. 9. Erect the perpendicular L’L. This is the effective length. There are one or two points to note about this construction. The short fibres are, in the main, ignored; this action is justified since the classers deliberately reject the short fibre when hand stapling. Further, the effect of the initial rapid change in length from the maximum is reduced; therefore the effective length is a characteristic of the bulk of the longer fibres. The term ‘effective’ is used because it is to this length value that many machinery settings are related, in particular the distance between the nips of successive pairs of drafting rollers. Page 21 of 85
  • 22. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY The Relation Between Effective Length and Staple and Staple Length We have seen earlier that basis of judgement of staple differs between markets and types of cotton. These differences can be accommodated by making certain corrections to the effective length. Lord and Underwood report that, ‘For American Upland cottons, from about ¾ in. to 11/4 in, staple and classed on the basis of American Staple Length Standards, a simple conversion formula is; American Staple = 0.91 x effective length For Egyptian-type cottons no staple length standards are in universal use, but on the average it is found that the staple length is equal to the effective length. Percentage Short Fibre This is the percentage of fibres less than half the effective length. In figure the percentage short fibre is therefore given by (RB x100/OB) (per cent) Dispersion The uniformity, or perhaps more aptly the variability of the cotton, can be expressed as the ‘inter-quartile range’. In Figure L’L is the upper quartile and M’M is the lower quartile, the inter-quartile range. This measure of the dispersion may now be expressed as a range. This measure of the dispersion may now be expressed as a percentage of the effective length: NL’ Dispersion = ------ x 100 (per cent) LL’ The Fibrograph Page 22 of 85
  • 23. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY A fringe of cotton is prepared by taking about ½ OZ of cotton and combing it by means of two hand combs. The prepared sample is in a straightened condition with the fibres divided between the tow combs; those longer than ¼ in. are caught in the teeth in a random position along their length. The fibre fringes are places on the measuring unit in such a way that they lie over a long narrow slot behind which are mounted the photo-electric cells. A light source illuminates the fringes and the amount of light penetrating through the fringes is measured electronically. At the start of the measurement the fringes are scanned across the densest region, i.e. near the comb teeth, and the light which penetrates will be a minimum. As the sample is traversed towards the fibre ends, more and more light will fall on to the photo-electric cells. The new ‘Servo-Fibrograph’ automatically records the change in the amount of light reaching the cells, not in terms of intensity of illumination but as a special form of frequency distribution. This curve is traced out on a card which is then removed from the instrument and analysed. Page 23 of 85
  • 24. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Construct the tangent to the curve to cut the horizontal at N and the vertical axis at A. OA is then the average length of fibres longer than ¼ in. Distance along ON represent the frequency percentage of fibres longer than ¼ in. From S, the 50 percent mark, construct the tangent ST to cut the vertical axis at T. OT is then the upper half mean length of fibres longer than ¼ in., based on a weight distribution. The ratio OA/OT x 100 percent gives the length uniformity ratio of the fibres. The upper half mean length approximates to the staple length obtained by the cotton classers. The Digital Fibrograph Principal As its name implies, the Digital Fibrograph presents the test results in digital or numeric form. Preferably, a special fibre sampler, a ‘Fibrosampler’, is used to prepare the beards by a light source is similar to that used in the earlier fibrograph but the signals from the measuring console are fed into a separate transistorised unit. The signals are electronically processed and the results fed back to the measuring unit which has two four-digit counters facing the operator. One counter is for selecting % S.L. and the other counter gives ‘Length’. A Servo-follower system connected to the photoelectric cells indicates on the ‘Amount’ counter the relative number of fibres in the sample beards at the point where the light beam passes through them. A Servo-computer ‘remember’ the total number of fibres in the sample at 0.15 in. distance from the center of the comb teeth and computes the number of fibres corresponding to the different Span Lengths. When a span length is selected, the comb carrier moves until the number of fibres under the lighthouse is equal to the number of fibres Page 24 of 85
  • 25. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY corresponding to that span length. The span length is then indicated by the ‘Length’ counter, which indicates, in mm, the movement of the comb carrier. Now there are two counters t set the amount and these two corresponding Length counter to give two length i.e., 2.5% & 50% simultaneously. Page 25 of 85
  • 26. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Relationship Between Fibre Length (mm) Measured by Different Instruments BAER SORTER EFFECTIVE LENGTH (Y) Digital Fibrograph Y = 1.013x + 4.39 2.5% Span Length (x) Uster Apparatus Y = 0.933x + 9.04 Effective Length (x) Uster Apparatus Y = 0.996x + 9.12 Upper half mean length (x) BAER SORTER MEAN LENGTH (Y) Digital Fibrograph Y = 1.242x + 9.78 50% Span Length (x) Uster Apparatus Y = 0.941x + 9.45 Mean Length (x) DIGITAL FIBROGRAPH 2.5% SPAN LENGTH (Y) Uster apparatus – Upper half Y = 0.946x + 5.64 Mean length (x) Uster Apparatus – Effective length (x) Y = 0.878x + 5.77 DIGITAL FIBROGRAPH 50% SPAN LENGTH (Y) Uster Apparatus – Mean length (x) Y = 0.672x – 1.60 Note: If the 2.5% span length of a cotton as tested on Digital fibrograph is 30mm, then the Baer sorter effective length is estimated to be 34.8mm (1.013 x 30 + 4.39). The conversions for fibre length and strength are subject to appreciable error and should be used only as approximate estimates. Mean Length Uniformity Ratio = x 100 Upper half mean length Based on uniformity ratio, the cotton samples can be graded as per United States Department of Agriculture (USDA). The rating is given as: Page 26 of 85
  • 27. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Uniformity Ratio Rating Above 80% Uniform 75 – 80% Average uniform 71 – 75% Slightly irregular 70 and below Irregular Page 27 of 85
  • 28. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Page 28 of 85
  • 29. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 5 FIBRE FINENESS Fibre fineness is another very important parameter which plays significant role in yarn spinning. Fibre fineness denotes the size of cross section of the fibre or in other terms it can be expressed as linear density of the fibres in micrograms per inch (10-6 g/inch). The fineness is also expressed in millitex which is weight inn milligrams of one kilometre length of fibre. This is identical to the unit of 10-6 gm/cm. The fineness plays a prominent part in determining the spinning performance. When irregularity is considered, the best yarn that con be produced is one in which the fibres are distributed along the strand in a random order. The irregularity in the strand is dependent upon the average number of fibres in cross-section. With a greater number of fibres in the cross-section, the basic irregularity is reduced. If the fibres are fine, the number of fibres in cross- section is more and irregularity is less. The finer the fibre the greater the total surface area available in inter-fibre contact and less twist is needed to provide necessary cohesion. The resistance of fibre to twisting and bending are also affected by the fineness. SIGNIFICANCE 1. To spin finer yarn we require finer fibres as certain minimum number of fibres is must to spin in yarn (70-80). 2. From finer fibres, apart from better spinnability, better evenness can also be achieved for the same count. 3. Yarn strength is also affected by fibre fineness to some extent. 4. A finer fibre can be spun to finer counts than a coarse fibre. Page 29 of 85
  • 30. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY MEASUREMENT OF FIBRE FINENESS Fineness can be measured by measuring fibre cross section but as cross section of fibres are not regular, direct determination of area is not possible. Some dimensional features i.e. swollen hair diameter, ribbon width etc., can be used to specify fibre fineness to some extent. The fineness of cotton fibres can be determined by either direct method such as gravimetric dimensional measurement or by indirect method i.e. Air flow method. DIRECT METHOD Gravimetric Method: In this method two types of practices are prevalent: (a) In ASTM procedure about 100 fibres are taken from each comb sorter groups and weighted, from which weight per unit length is calculated. In this case meanlength is used to calculate the weight per unit length. (b) In another method known number of fibres are first cut into in 1cm length and then they are weighed on a torsion balance or quartz micro-balance. There are two objections in this method. (i) Fibre of different length grade may have different fineness value. (ii) In a single fibre, fineness may vary over the whole length. INDIRECT METHOD The direct methods are generally tedious and more time consuming therefore indirect method of the measurement of fineness are more popular. These are mainly based on measurement of resistance to the flow of air by fibre plugs, or Page 30 of 85
  • 31. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY on the principle of vibrating strings in the case of single fibres, as described below: Air-flow Method In this method a fibre of constant weight are filled-in a fixed area and air is allowed to pass through. The flow of air is affected by the surface area of the fibres. The variation in air-flow is directly translated into the values of linear density. Specific surface is defined as the ratio of surface area to volume, Eg specific surface of a cylinder Let the volume= ^ ( d/2) square X l where d is the diameter of cylinder The surface area ignoring the end = ^ d l Specific surface area S= ^ dl / ^ ( d/2) square X l = 4/d This ratio also equals the ratio Perimeter of cross-section/ Area of cross-section = ^ d / ^ ( d/2) square = 4/d Thus S Is proportional to 1/ d Page 31 of 85
  • 32. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY VARIOUS INSTRUMENTS TO MEASURE FIBRE FINENESS (Air-flow Method) 1) Sheffield Micronaire: The Micronaire instrument works in conjunction with an air-compressor. The latter, through the pressure regulation system supplies air to the Micronaire instrument at the constant pressure of 0.33 kg/cm2 (4.7 psi for the Sheffield Micronaire). Initially, the instrument is calibrated with the master-plug. A test specimen of 3.24g is weighed and well opened by hand. It is then placed into the cylindrical chamber of the Micronaire instrument. The fibre compression plunger is inserted into the cylinder and locked by turning. The air at definite pressure is forced through the sample and the volume rate of airflow is measured on the scale to the nearest 0.1 scale unit at the point level with the top of rotometer type float. Usually two specimens are taken from each cotton and duplicate tests are carried out on each specimen. The second test on each specimen is carried out by removing the specimen from the chamber and repacking it in the reverse direction. The sample for the Micronaire test should be well opened, cleaned and thoroughly mixed. The fineness scale in the Sheffield Micronaire is suitable only for very fine and medium fine cottons. The coarse desi varieties of cotton give a high reading beyond the range of the scale, necessitating the determination of fibre fineness by direct gravimetric method which is time-consuming. Recently two techniques (a) by using a plug of 60 grains (3.89g) sample weight and normal air pressure of 6 psi; and (b) by suing a plug of 50 grains (3.24 g) sample weight and reduced air pressure of 4 psi, were tried at the Laboratory whereby the flowmeter reading could be kept within the range of the Micronaire scale. Both the testing methods Page 32 of 85
  • 33. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY were found to be accurate for predicting fineness. The first method is recommended for testing very coarse desi varieties of Indian cottons. 2) WIRA Cotton Fineness Meter: A new version of WIRA Cotton Fineness Meter has been marketed by the Shirley Developments Ltd. The scale of this instrument is graduated in Micronaire units. It takes a 5g sample. The standard samples for the calibration of instrument are provided by the Shirley Institute. 3) Arealometer: The instrument is portable and it measures the parameters such as specific surface area, fibre weight and immaturity ratio. A small sample of 152 mg is used. The instrument is similar to the Wheatstone bridge in which the three of the resistances consist of copper capillaries and the fourth is the fibre plug under test. 4) Port-Ar: The resistance a plug of cotton fibres offers to the flow of air is measured as an approximate indication of the fineness of fibre. A predetermined mass of loose cotton fibres is placed in the specimen holder and compressed to a fixed volume, the resistance to air flow is measured and expressed as Micronaire reading. Instruments available to measure resistance to air flow use compressed air or vacuum and are constructed to measure air flow under constant pressure drop across the plug, to measure pressure drop when a constant flow of air is maintained. The Micronaire reading of cotton fibres is a function of both fineness and maturity and is related to mill processing performance and to the quality of the end products. Factors correlated with Micronaire reading include cleaning efficiency, neppiness, and the strength & uniformity of the yarn. Page 33 of 85
  • 34. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY This portable instrument does not require compressed air or electric power for operation. It determines the Micronaire value and equivalent fibre thickness (in terms of specific surface area). The instrument is provided with Micronaire scale ranging from 2.5 to 7. Port-Ar does not need a separate balance for weighing. It tests a specimen of 8 g. 5) Speedar: It measures specific surface area. This instrument does not require any fixed weight of sample. Any weight between 5g to 10g can be used. Therefore, it is speedier in testing the sample. 6) ATIRA Fineness Tester: In this instrument, air pressure is built up by pumping air by hand into a small tank containing a loosely fitting float. This arrangement maintains fairly constant air pressure when the float descends in the tank. The escaping air flows through an adjustable needle valve connected in series with the sample chamber. An accurately weighted 5g quantity of the fluffed sample is taken in the sample chamber and compressed into a plug of fixed dimensions by the perforated piston. The junction of the needle valve and the sample chamber is connected to a reservoir manometer, the calibrated portion of which is in an incli8ned position to spread out the scale increase the sensitivity. When the air from the air tank flows out under constant pressure through the regulated needle valve and the cotton sample, the manometer indicates directly the fibre fineness in micrograms per inch. This instrument is also provided with an MH scale, as this scale is believed to agree better with the air-flow than the fibre weight sale. Note: Nowadays most of fineness tester used are either Portar or Speedar type as testing is quicker in such instruments. Instruments can give data directly in the form of computer printout for vide variety of cotton. Page 34 of 85
  • 35. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 6 FIBRE STRENGTH Fibre strength is generally considered to be next to fibre length and fineness in the order of importance amongst fibre properties and for cottons beyond a certain staple length this property assumes greater significance. The different measures available for reporting fibre strength are ‘breaking strength’, ‘tensile strength’ and ‘tenacity or intrinsic strength’. Breaking strength denotes the maximum tension the fibre is able to sustain before it breaks. In the case of cotton fibre, it depends upon various factors such as the inherent strength of the material constituting it, the number and intensity of weak places and the area of cross-section of the fibre. It is mainly due to the last factor that coarse cottons generally record higher values for fibre breaking strength than finer ones. Therefore, in order to compare strength of two cottons differing in fineness, it is necessary to eliminate the effect of the difference in cross- sectional area by calculating from the values the fibre strength per unit cross- sectional area. However, the determination of the area of cross-section is difficult in the case of cotton fibres due to irregular shape of the cross-sections. Hence it is a common practice to divide the breaking load by the fibre weight per unit length which can be taken as proportional to cross-sectional area, assuming the density to be the same for all varieties of cotton. The value so obtained is known as ‘intrinsic strength’ or ‘tenacity’. Intrinsic strength is found to be better related to spinning quality than the breaking strength. The strength characteristics can be determined either on individual fibres or on bundles of fibres. DIFFERENT TYPES OF INSTRUMENTS Page 35 of 85
  • 36. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY The instruments generally used for determining the tensile strength or the ‘load- extension’ diagram of textile materials can be classified into three groups, based on the principle used for the application of load, namely, those of: (i) the rate of traverse (CRT); (ii) the constant rate of specimen elongation (CRE); and (iii) the constant rate of loading (CRL) types. i) Constant Rate of Traverse: In the instruments of the CRT type, the specimen is held between two clamps, one of which (the lower clamp in a vertical arrangement) is traversed at a constant speed to exert a load on the specimen. The other clamp works against a spring or a pendulum suitable weighted. The load on the specimen is measured by the extension of the spring or the swing of the pendulum, as the case may be. In these instruments, the rate of loading depends on the extensibility of the specimen and hence will vary with the type of specimen under test. In the case of instruments using a pendulum principle, the errors due to inertia are appreciable. As there is a time lag before the pendulum is accelerated to the required speed, there will be a lag in the rate of loading in the initial stages, while at the later stages there is a likelihood of the pendulum overshooting beyond the breaking load of the specimen. ii) Constant Rate of Specimen Elongation: In the instruments of the CRE type, the application of load is made in such a way that the rate of elongation of the specimen is kept constant. This can be accomplished by modifying the CRT instruments suitably so as to render negligible movement of the upper clamp. For this purpose, the upper clamp is fixed to a stiff support and the load on this support is measured by suitable means such as a strain gauge as in the case of the Instron Tester. iii) Constant Rate of Loading: Page 36 of 85
  • 37. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY In the instruments of the CRL type, the mode of application of load is such that the rate of loading is constant throughout the duration of the test. This can be effected by the sliding of a weight down an inclined plane or by the extension of a spring or flow of water at a constant rate etc. The CRL type of instruments are usually preferred for accurate scientific work in view of the case of interpretation of the results obtained with these instruments. In the CRE and the CRL types of instruments, it is easy to adjust the ‘time-to-break’ while this adjustment is not easy in the CRT type of instruments. The test results with the CRE and the CRL instruments show less variation than those obtained with the CRT type of instruments as in the latter the rate of loading is dependent on the extensibility of the specimen. Hence, where accurate interpretation of results is required the CRT instruments are not recommended although these are widely used in view of the ease of operation and rapidity of testing. Some instruments like the Instron can be made to function both on the CRE and the CRL principles. FACTORS INFLUENCING STRENGTH TEST RESULTS Tensile strength of cotton fibres is influenced by various factors such as the time taken to rupture the specimen, the test length of the specimen and relative humidity of the atmosphere in which the sample is conditioned and tested. For comparing the results on different samples and to obtain reproducible results on a given sample, it is necessary that tensile tests are carried out under specified conditions. The tensile strength recorded by a fibre depends on the time taken for the progressive deformation and its eventual rupture. A lower ‘time to break’ invariably results in a higher breaking load. In most instruments used for tensile strength test on fibres, the time to break can be varied by controlling the ‘rate of Page 37 of 85
  • 38. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY loading’, ‘rate of traverse’ or ‘rate of extension’ depending on the nature of the instrument. Another factor influencing fibre strength values is the ‘gauge length’ used, the strength obtained at a longer gauge length being generally lower. The dependence of fibre strength on gauge length is due to the presence of weak places in the fibre. Lord pointed out that the strength of a fibre is the strength of the weakest place, no matter how much stronger the specimen is at other places. Thus, if structural imperfections are distributed along the length of a fibre, some short elements may contain one or more weak places and others may be free of them such that the chance of a weak place appearing in a specimen increases with the test length. The extent of change of strength with gauge length when fibres are broken individually or in the form of a bundle was studied by Morlier et.al. Strength tests on fibre bundles are generally carried out at nominal zero gauge length. However, tests at zero gauge length do not give all the information required about the strength of the fibres in a sample, as the influence of weak spots would not come into play at this test length and, therefore, it would be desirable to carryout the tests at finite gauge lengths. Moreover, it has been well established that the bundle strength measured at 1/8 in. (3mm) gauge length has better correlation with yarn strength than the strength values measured at other gauge lengths. Hence the use of 1/8 in. (3mm) gauge length for bundle strength tests has now become very common. The strength of cotton fibres is affected by the humidity of the atmosphere in which it is conditioned and tested, the strength increasing with the rise in relative humidity. On the basis of extensive studies on the variation of single fibre strength with increase in relative humidity, it has been possible to arrive at correction factors (Table) with the help of which one can calculate the single fibre strength at the standard atmosphere of 65% RH from the strength obtained at any ambient humidity. Page 38 of 85
  • 39. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Table: Humidity Correction Factors for Single Fibre Strength Relative Humidity (%) 30 40 50 60 70 0 1 2 3 4 5 6 7 8 9 1.218 1.211 1.294 1.196 1.189 1.181 1.174 1.168 1.160 1.153 1.146 1.140 1.134 1.127 1.120 1.114 1.107 1.101 1.096 1.089 1.083 1.077 1.071 1.065 1.059 1.054 1.048 1.043 1.037 1.031 1.026 1.020 1.016 1.010 1.005 1.000 0.994 0.989 0.984 0.980 0.975 0.970 0.965 0.960 0.955 0.951 0.951 0.951 0.951 0.951 Bundle strength measurements are also affected by factors such as the condition of the leather in the jaws holding the fibres under test on the instrument, jaw pressure, bundle alignment, fibre selection in the combing process prior to clamping etc., some of which could give a ‘personal bias’ to the results. In order to have a check on the results of bundle strength measurements, it is necessary to test suitable control samples and keep the instruments properly calibrated. The results on various samples tested could then be corrected by a factor depending upon the test results on the control sample. SINGLE FIBRE STRENGTH The tenacity of a fibre is dependent upon many factors related to its structure and the conditions under which the test is carried out. The structural features contributing to strength are the chain length of the molecules, their orientation and the size and distribution of the crystallites. Testing conditions which affect the strength values are as mentioned earlier, the gauge length used, the rate of loading, the type of instrument employed and the relative humidity prevailing in the testing room. Page 39 of 85
  • 40. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY INSTRUMENTS FOR MEASURING SINGLE FIBRE STRENGTH There are various types of instruments available for carrying out single fibre strength tests. They can be classified in mainly two types of instruments. Universal Tensile Tester: This is a robust and versatile instrument used for measurement of a variety of mechanical properties. Its versatility rests in the fact that it is capable of recording the tensile load-elongation curves of a range of samples from single fibres to thick fabric strips, which cover a wide spectrum of mechanical characteristics. The specimen under test is clamped between two jaws. The upper jaw is suspended from the ‘load cell’ which is the load sensing device, while the lower jaw is mounted on the ‘cross-head’ which can be moved up and down at controlled speeds. The crosshead speed, which decides the rate of extension of the specimen, can be varied from 0.05 cm/min to 50 cm/min in 12 steps. The choice of the suitable load cell from among the four cells which cover a range from 2 g to 500 kg. is made in accordance with the load requirements of the specimen under test. The load cell contains a bonded wire type of strain gauge which consists essentially of a cantilever beam with a resistance wire bonded to the surface. The upper jaw carrying the specimen is suspended from the free end of the cantilever beam such that the tension developed in the specimen leads to an infinitesimally small bending of the beam. As a result, the wire bonded to the beam increases in length and hence in electrical resistance in proportion to the tension in the specimen. Since this resistance wire forms one arm of a wheatstone bridge circuit, which is excited by an oscillator and which remains normally balanced, any tension in the specimen would cause disbalance in the circuit. The resulting signal is amplified to operate a recorder pen. Thus when the test specimen is extended, the recorder pen moves across the chart through a distance proportional to the tension in the specimen. Since the deflection of the end of the beam is infinitesimally small, the Instron works as a Page 40 of 85
  • 41. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY ‘constant-rate-of-extension’ instrument when the crosshead is moved at a steady rate. The crosshead and chart are driven synchronously through magnetic clutches and convenient gears to provide a choice of constant and reversible extension speeds. The chart movement can be varied to achieve a range of extension magnifications. As a result of the simultaneous movement of the pen and the chart, the former responding to the tension in the specimen and the latter synchronized to the specimen extension; the trace on the chart represents the load-elongation curve. The Instron is also equipped with an Integrator which is a convenient device for obtaining the area under the load-elongation curve which measure the work of rupture. Bundle Strength: The determination of strength on individual fibres, as discussed above, involved considerable amount of time as tests have to be made on a large number of fibres in view of the high variability in fibre strength. Moreover in actual practice, fibres are not used individually but in groups, such as in yarns or fabrics. Thus, bundles or groups of fibres come into play during the tensile break of yarns or fabrics. Further, the correlation between spinning performance and bundle strength is at least as high as that between spinning performance and intrinsic strength determined by testing individual fibres. The testing of bundles of fibres takes less time and involves less strain than testing individual fibres. In view of these considerations, determination of breaking strength of fibre bundles has assumed greater importance than single fibre strength tests. INSTRUMENTS FOR BUNDLE STRENGTH DETERMINATION In the past, various methods were tried for the determination of bundle strength. In one of the methods (which was being used at this laboratory), a small tuft containing about 80 to 120 fibres was taken and the ends fixed between two pairs of paper strips by means of some good adhesive, taking care to see that the test length was 1 cm; the paper strips were gripped between the jaws of a schopper testing machine and the bundle broken in the usual manner. The Page 41 of 85
  • 42. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY bundle strength that was recorded on the machine was divided by the number of fibres in the bundle to get an idea of the strength realized per fibre. In this category mainly two instruments are in use. 1. Pressley Strength Tester 2. Stelometer Pressley Strength Tester: It works on the principle of inclined plane apparatus. Now this instrument is not much in use because of service limiting factors. Error is likely to occur on account of the fact that the tension applied to straighten the fibres while keeping them in the clamps and the torque applied for tightening the jaw screws would vary from operator to operator. This error can be reduced by using a torque vice, in which tension is adjusted to about 8 lb-in. (1.5 kg/cm). Further, as this instrument works on the principle of constant but increases with the traverse of the moving load carriage further away from the initial position; hence, for bundles having higher breaking strength, the rate of loading at breaking point would be higher than that for bundles of lower strength. Also, there is an increased likelihood of the rolling weight overshooting the breaking point before coming to rest in the former case due to inertia. Stelometer: The Stelometer is a pendulum type of instrument in which, contrary to usual practice, the pendulum weight remains stationary while the pendulum axis moves through an arc. By means of a special dashpot device, the rotation of the pendulum axis (beam) is controlled in such a manner that the rate of loading is approximately constant. An arrangement has been provided to check the calibration of the instrument and adjust the rate of loading. Normally, the rate of loading used is 1 kg/sec. A pointer, freely mounted on the axis and driven by a sensing pin mounted on the pendulum, moves over a scale graduated from 2 to 7 kg. indicating the breaking load. In addition, a smaller pointer suspended from Page 42 of 85
  • 43. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY the above indicates the percentage elongation on an auxiliary scale. The indicators can be read to nearest 0.01 kg and 0.1 percent for breaking load and elongation respectively. The clamps, after removal of the protruding fibres, are loaded in the slots on the top of the Stelometer and the beam is released. One part of the Pressley clamps is held in the adjustable holder carried by the beam while the other is held in a slot on the top end of the pendulum. The movement of the beam applies tension to the bundle by pulling apart the two parts of the clamps. As soon as the bundle breaks, the sensing pin falls away and the pointer stops immediately. The breaking load can be read on the scale. The broken fibres are collected from the clamps and the weight in milligrams determined accurately. Six bundles are tested by two operators, on every sample. The bundle tenacity is obtained by dividing breaking load by the weight of the sample. Page 43 of 85
  • 44. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CORRECTION OF OBSERVED TEST RESULTS Standard value for calibration cotton Correction Factor = Observed value for calibration cotton After finding out the correction factor, the test values obtained on the instrument are adjusted by this factor. Therefore, for any sample under test, Adjusted value = Observed value x Correction factor Breaking strength of bundle in kg x 11.81 Stelometer value at zero = gauge length (g/tex) Weight of bundle in mg. Breaking strength of bundle in kg x 15.0 Stelometer value at 1/8 in. = gauge length (g/tex) Weight of bundle in mg. FIBRE QUALITY INDEX In order to decide the quality characteristics of the cotton required for spinning different counts with desired CSP values, a single measure for the overall quality of cotton has been established by SITRA. This measure known as Fibre Quality Index (FQI), is derived from the following formula: lu s m FQI = f where, lu = product of 2.5% span length (l) in mm and uniformity ratio % (u) measured on Digital Fibrograph divided by 100 s = Bundle strength in g/tex at 3mm gauge length (Stelometer) m = Maturity coefficient f = Fibre fineness as determined on Micronaire and expressed as Micronaire value (micrograms/in.) Page 44 of 85
  • 45. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY AT OPTIMUM TWIST MULTIPLIER Achievable Lea CSP = 320 (√FQI + l) – 13C for carded counts = [320 (√FQI + l) – 13C] (l+W/100) for combed counts where, C = Count spun W = % Waste extracted during combing In the case of combed counts, the lea CSP would be more by 1% for every 1% waste extracted at the combers. FIBRE-YARN RELATIONSHIPS USING HVI TEST SYSTEM (a) Prediction Expressions for Yarn lea CSP using HVI/FMT measured fibre properties (ICC Mode): SITRA has developed the following prediction expressions connecting fibre properties measured by High Volume Instrument (HVI) and Shirley Maturity Tester with yarn lea CSP. Lea CSP = 280 √FQI + 700 – 13C (For carded counts) Lea CSP = {280 √FQI + 700 – 13C} {l+W/100} (For combed counts) Where, C = Yarn count, Ne W = % Comber Noil Lsm FQI = f Values of L, s, m are measured using HVI test system and that of m using Shirley FMT. Page 45 of 85
  • 46. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY L = 50% span length, mm s = Bundle strength, gm/tex f = Fineness (Micronaire value in micrograms/inch) m = Maturity ratio If maturity ratio values are not readily available then, as an approximation, the lea CSP values may be arrived at from following expression: Lea CSP = 250 (√Ls/f) + 590 – 13C (b) Prediction Expressions for Yarn lea CSP using Fibre properties measured by HVI test system (HVI Mode): Lea CSP = 165 (√FQI) + 590 – (13C) (For carded counts) Lea CSP = {165 (√FQI) + 590 – (13C)} {l+W/100} (For combed counts) Where, C = Yarn count, Ne W = % Comber Noil Ls FQI = f Values of L, s, m are measured using HVI test system and that of m using Shirley FMT. L = Mean length, mm s = Bundle strength, gm/tex f = Fineness (Micronaire value in micrograms/inch) Page 46 of 85
  • 47. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY MISCELLANEOUS PROPERTIES 1. Fibre Friction or Clinging Power: Fibre friction is considered as an important factor that contributes to yarn strength especially of the low twist yarns in which breakage often occurs as a result of fibre slippage rather than fibre fracture. Prediction of spinning value of cotton could therefore be rendered more accurate by quantitative information on fibre friction. Three methods are employed for determining fibre friction. In one method, which is a modification of Adderley’s method, a 3/8 in. length of a group of 10 cotton fibres is pulled between two pads made of parallelised fibres of the same cotton and subjected to a known pressure. The force required to pull out the group of 10 fibres is measured by a mechanism similar to the one employed on the 0’ Neill single fibre strength tester. In another method frictional force is determined at two angles of slippage (0o and 30o ) by means of an elaborate apparatus designed for this purpose. In the third method the technique used for the application of pressure between fibre pads is simplified and the force required to withdraw 20 parallel fibres is determined. 2. Torsional Rigidity: The resistance of a fibre to twisting is determined by its torsional rigidity. This property is important in spinning where the difficulty of binding rigid fibres together could result in the production of bulky yarns. The torsional rigidity of a fibre is defined as the torque required to twist one centimeter length of it through 360o . The torsional rigidity can be shown to be proportional to the product of the rigidity modulus and the square of the area of cross-section of the fibre, the constant of proportionality being dependent on the cross-sectional shape. Page 47 of 85
  • 48. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY As the determination of single fibre rigidity involves considerable testing time, a quicker method has been developed. In this method, the rigidity is determined on a bundle of fibres weighing about 1 mg and the single fibre rigidity is estimated from the bundle rigidity by dividing the latter by the number of fibres in the bundle. Although the values obtained by this method are not identical with those obtained by measurement on single fibres, there is a high correlation between the two and hence the bundle method can be adopted to save time. 3. Lustre: Luster and colour of cotton are two characteristics that appeal to the aesthetic sense of the observer. Luster denotes the ability of the fibre to reflect light preferentially in some directions whereas colour refers to the hue and to the strength of the hue. While a white cotton does not necessarily have to show lustre, a creamy or yellowish variety can be highly lustrous. Lustre is measured by means of a lustre meter fabricated for this purpose. In this instrument, the sample is illuminated at an angle of 45o by a collight reflected from the sample is received by a photocell and the intensity is obtained in terms of photo-current measured on an ammeter. The intensity of specular reflection (45o ) and the intensity of diffuse reflection in the direction normal to the sample are noted. The ratio of the two intensities are known as the contrast ratio is used to express the lustre of the sample. The instrument can be used for tests on fibre, yarn or fabric. Page 48 of 85
  • 49. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 6 TRASH Trash cannot be termed as fibre property but it has its own importance as the amount of trash present in cotton directly affects the cost of cleaned cotton. Even if we keep commercial aspect aside trash affects the yarn quality considerably. Even after removing the trash in Blowroom and Cards small amount of trash remains in the sliver. Infact removal of trash in Blowroom and Cards depends upon nature of trash. Seed coats amongst all impurities are most difficult to remove. Recent studies have confirmed tha6 remnant trash in sliver mostly consists of seed coats and it is directly related with the uster neps and classimate faults. MEASUREMENT OF TRASH 100g. of cotton sample ‘S’ to be analysed is weighed accurately and is passed through the Trash Analyser giving L1g. of lint and T1g. of trash. The trash T1 is collected and again processed giving L2g. of lint and T2g. of trash. The lint portions L1 and L2 are weighed together and give the total lint content in the sample. S (100 g) Lint L1 Trash T1 Lint L2 Trash T2 L = Lint content % = L1 + L2 T = Trash content % = T2 Invisible Loss % = 100 – (L + T) Page 49 of 85
  • 50. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY If the Trash T2 is still found to contain a sizable amount of lint, it is passed once again through the Analyser giving L3g. of lint and T3g. of trash. Then lint content L = L1 + L2 + L3 and Trash T = T3. In general, two such 100 g. samples are analysed and the average calculated. It is essential that the sample processed must be fairly representative of the bulk sample. Page 50 of 85
  • 51. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY PRECAUTIONS (1) While feeding the cotton, it is necessary to open it by hand and fed it uniformly in a fairly thin fleece. For example, when feeding 100g. of sample, half of it should be spread evenly on the feed table and as the test proceeds the remaining sample should be added gradually. (2) Hard lumps of trash or full seeds in the test sample must be collected by hand and weighed along with the trash. If allowed to pass along with the cotton, these are likely to damage the feed plate and licker-in wire points. (3) A lever is provided for opening and closing the valve controlling the air flow from the cage into the filter. This valve should be opened at the beginning of a test. At the end of each test, the valve is closed so that all the lint falls down into the lint box. ANALYSIS OF TRASH The visible trash so collected is passed through a set of wire meshy of mesh size of BS 10 & BS 36 and is analysed as: Trash over mesh 10 = Seed coats Trash over mesh 36 = Leafy matter, kitties etc. Trash below mesh 36 = Dust etc. Page 51 of 85
  • 52. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY The Cleaning Efficiency of a Machine: The cleaning efficiency helps to evaluate the performance of a machine. If it falls below a certain level the machine needs to be checked. The removal of trash particles such as seed & leaf particles, stalks, sand and dust from cotton is quantitatively expressed as cleaning efficiency which can be estimated as follow: About 200gm of sample is taken from the feed & delivery of a machine like Blow room, Card or Beaters. These samples are analysed for trash content. This is done by processing a 100gm of sample through a Trash Analyser and collecting the trash obtained & weighing it accurately. Two samples must be analysed and average trash content is calculated. T1 – T2 Cleaning Efficiency % = x 100 T1 Where, T1 = % trash in the material fed T2 = % trash in the material delivered Speeds and Settings of Shirley Trash Analyser: Speeds: 1. Taker-in … 900 rpm 2. Feed roller … 0.9 rpm 3. Cage … 800 rpm 4. Fan … 1500 rpm 5. Motor … 1400 rpm Setting: 1. Feed plate to taker-in … 4/1000 inch (4 thou) 2. Streamer plate to taker-in … 5/1000 inch (5 thou) (lead-in edge) 3. Streamer plate to taker-in … 7/1000 inch (7 thou) (lead-off edge) 4. Stripping knife to taker-in … 4/1000 inch (4 thou) (Bottom edge) Page 52 of 85
  • 53. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY 5. Stripping knife to cage … 5/16 inch (lead in edge) 6. Taker-in to cage … 13/64 to 15/64 inch 7. Separation sheet to cage … 1/4 inch (Top edge) 8. Delivery plate to cage … 1/16 inch Note: These settings will vary depending on the model of the machine. CHAPTER – 7 THE MATURITY OF COTTON Fibre maturity is another important characteristic of cotton and is an index of the extent of development of the fibres. The maturity of cotton fibre varies not only between fibers of different samples but also between fibres on the same seed. Thus a ripened, full mature cotton boll contains fibers both mature and immature. A cotton fibre consists of a cuticle, a primary layer and secondary layers of cellulose surrounding the lumen or central canal. In the case of mature fibres, the secondary wall thickening is very high and in some cases, the lumen is not visible. In the case of immature fibres, due to some physiological causes, the secondary wall thickening is practically absent, leaving a wide lumen throughout the fibre. Hence to a cotton breeder, the presence of excessive immature fibres in a sample would in dictate some defect in plant growth, either varietal or environmental. To a technologist, the presence of excessive percentage of immature fibres in a sample is undesirable as this causes waste, losses in processing, lowering of the yarn appearance grade due to formation of neps uneven dyeing etc. The determination of fineness of a cotton is affected by maturity of the sample. An immature fibre will show a lower weight per unit length than a mature fibre of he same cotton, as the immature fibre will have less deposition of cellulose inside the fibre. Hence it is essential to measure the maturity of a cotton whether the observed fineness is an inherent varietal characteristic or is a result of immaturity. Page 53 of 85
  • 54. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Importance of Maturity: The maturity of the fibre is concerned with development of the cell wall. The cell wall thickening is highly sensitive to growing conditions. Adverse weather, poor soil, plant diseases and pests etc., will increase the proportion of immature fibre and lead to trouble in processing. One of the main troubles causes by the presence of these thin walled immature fibres is nepping. Apart from maturity, causes like small bits or fragments of seed particles attached to the fibre also forms neps. Neps are created during processing starting at the ginning stage. Further when rubbing of surfaces takes place, as in carding, minute knots of tangled fibres are caused and the immature fibres are more prone of this nepping effect. When fine cottons are being process4d, the danger of nepping is even more acute, since even the mature fibres are likely to cause neps by faulty processing. In addition, the neps so formed are usually more prominent because of their size relative to the diameter of the fine yarn. Immaturity also affects the shade after dyeing. As the response of the primary wall t certain classes of dyestuffs is less intense, the thinner the secondary wall lighter will be the shade. Hence fine cotton tends to be lighter in shade than coarse cotton. Apart from this the reflecting surfaces of the fibres of the immaturity is with respect to the patches being shown or the weft bars seen in the fabric when yarn made of immature fibres or yarn spun from cotton of different maturity is used as warp and weft. The presence of neps in a yarn will also form weak places and therefore the average strength of the yarn will be reduced. Neps will show up as specks in the dyed cloth. So summarizing the maturity, the following points are noted. 1. Maturity affects the quality of the yarn and also the processing. The effects of immature fibres are seen especially in the spinning process. Page 54 of 85
  • 55. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY 2. The large number of ends down in a ring frame is due to the immature fibres. 3. The loss in yarn strength, the dyeing troubles are all due to the presence of immature fibres. In order to assess the quality of cotton with respect to maturity and its effect on ends down, yarn strength, dyeing troubles and so on, some method of measurement is required. The most important one amongst them being the degree of thickening θ. It may be expressed as the ratio of the actual cross sectional area of the wall to the area of the circle with the same perimeter. The reciprocal of this measures, 1/10 is called Immaturity ratio. A From the above figure, the degree of thickening θ = A1 Where, A = Area of cross section of the cell wall A1 = Area of the circle of equal perimeter Page 55 of 85
  • 56. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY A1 = πr2 4π 4π2 r2 = x πr2 = 4π 4π Perimeter P = 2πr ∴ P2 = (2πr)2 = 4π2 r2 P2 ∴ A1 = 4π A 4πA ∴ θ = = A1 P2 Direct measurement of this ratio is not a practicable routine test and is not normally done. An indirect method known as Cotton fibre immaturity count is used to determined the degree of cell wall thickening. MEASUREMENT OF MATURITY 1. DIRECT METHOD In these methods, the fibres after being swollen with 18 percent caustic soda are examined under the microscope with suitable magnification. The fibres are classified into different maturity groups depending upon the relative dimensions of the cell wall and the lumen. However, the procedures followed in different countries for sampling and classification differ in certain respects. i) Maturity Coefficient: Page 56 of 85
  • 57. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY A thin tuft of fibres in drawn by means of tweezers from a sliver held in a comb sorter. Its thickness is so regulated that about 100 fibres are spread in a parallel array over a width of an inch in order to facilitate the examination of each fibre separately under the microscope. The tweezer end of the tuft is clamped first on the narrower strip of the fibre mounting device called the ‘Maturity slide’. The fibres are spread across the glass slide and the overlapping fibres are again separated with the help of teasing needle. The free ends of the fibres are then held in the clamp on the second strip of the maturity slide, which is adjustable to keep the fibres stretched to the desired extent. The fibres are then irrigated with 18 percent caustic soda solution and covered with a suitable cover slip. The slide is then placed on the mechanical stage of a microscope and examined. Beginning at one edge of the tuft, all fibres are classed into three categories namely mature, half-mature and immature, based on the ratio of lumen width (L) to wall thickness (W) as indicated below: Lumen width (L) Category Wall thickness (W) L Mature < 1 W L Half-mature 1 < < 2 W L Immature > 2 W Page 57 of 85
  • 58. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY About four to eight slides are prepared from each sample and examined. The results are presented as percentages of mature, half-mature and immature fibres in a sample. The results are also expressed in terms of ‘maturity coefficient’ which is a unitary expression signifying the multiple character of fibre maturity usually represented by the percentage of mature, half-mature and immature fibres, calculated from the formula: (M + 0.6H + 0.4I) Mc = 100 where Mc is the maturity coefficient, and M, H and I are the percentage of mature, half-mature and immature fibres, respectively, in the sample. Based on the maturity coefficient the cottons are classed into different groups as shown in Table below. Table: Classification of Cottons on the basis of Maturity Coefficient Category Range of maturity coefficient Very immature Immature Average maturity Good maturity Very high maturity Below 0.60 0.60 to 0.70 0.71 to 0.80 0.81 to 0.90 Above 0.90 ii) Percentage of Mature Fibres: This is the US Standard (ASTM) method, in which the percentage of mature fibres, Pm alone is determined. Test specimen is prepared by any one of three following methods: a) Array Method: Page 58 of 85
  • 59. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY From each length group, a bundle of about 100 fibres is taken and spread uniformly on microscope slides. The series of slides constitutes a test sample. A second set of slides is prepared by another operator using fibres drawn from a different array. b) Laboratory Blended Sample: Three slides of about 200 fibres each are prepared by each of the two operators from a laboratory blended sliver of 50mm length. c) Fibrograph Beard: Beards from two combs are removed and each one is divided into two halves forming four sub-samples. From these sub- samples, test specimens are prepared by the same procedure as the one described in the case of the laboratory blended sample. The fibres laid parallel on the microscope slide are irrigated with 18% caustic soda and are examined through a microscope at 400 x magnification. They are classified into two categories, mature and immature as shown below: Lumen width (L) Category Wall thickness (W) L Mature < 2 W L Immature > 2 W Page 59 of 85
  • 60. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY From the total number of fibres and number of mature fibres, the percentage of the mature (Pm) is calculated. Pm = Mature Fiber/ Total Fibers x100 iii) Maturity Ratio: In this method, which is also the British Standard method, the test specimen is prepared either by the random sampling technique (Zoning method) or the selective sampling technique (i.e. by drawing fibres from various groups of the sorter pattern), and it is recommended that test be made on five tufts of fibres from each sample. Each tuft is taken separately on a slide and irrigated with 19% caustic soda. The swollen fibres are then examined under a microscope magnification (100x) and classed into three groups, viz. normal, thin-walled and dead. Rod-like fibres with no convolution and no continuous lumen are classed as ‘normal’, convoluted fibres with wall thickness one-fifth or less of the maximum ribbon width are classed as ‘dead’, and the intermediate ones are classed as ‘thin-walled’. A combined index known as ‘maturity ratio’ is used to express the results. Maturity ratio is calculated by using the following equation: N – D Mr = + 0.70 200 where, Mr = Maturity ratio, N = Percentage of normal fibres and D = Percentage of dead fibres. Relationship between different Indices of Maturity: Page 60 of 85
  • 61. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Some workers have established the formulae connecting the three commonly used measures of maturity such as maturity ratio (Mr), percentage of mature fibre (Pm) and maturity coefficient (Mc). These formulae are useful for predicting one measure from another. Pm = (Mc – 0.394) (3.434 – 1.783 Mc) Pm = (Mr – 0.2) (1.5652 – 0.471 Mr) Mr = (Mc – 0.301) (2.252 – 0.526 Mc) 2. INDIRECT METHOD i) Polarised Light Methods: These methods have been developed taking advantage of the birefringence property of cotton fibres. In the simplest method, about 200 fibres are mounted parallel to each other on a slide and observed under a polarizing microscope. A selenite plate is placed between the crossed polariser and analyser with the slow vibration direction set at 45o to the polarized and parallel to the fibres. The classification for maturity is made depending upon the interference colours produced, the immature fibres appear blue or purple and the mature fibres appear yellow or green. The number of immature and mature fibres thus differentiated are counted and expressed as percentages. Fairly good agreement is found between maturity obtained by this method and caustic soda method. ii) Air-flow Methods: In this method, the Micronaire reading on a 40 grain sample is noted, and then by adding to it a 10 grain sample, a composite sample of 50 grains is prepared and tested. The authors have Page 61 of 85
  • 62. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY derived separate regression equations for the different species of cottons connecting the maturity coefficient by the caustic soda method and the difference in Micronaire readings between 40 grain and 50 grain samples. There are other techniques for measuring maturity using the Micronaire instrument. As the fineness value determined by the Micronaire is dependent both on the intrinsic fineness (perimeter of fibre) and the maturity, it may be assumed that if the intrinsic fineness is constant then the Micronaire value is a measure of the maturity. For example, if samples of the same variety are tested, it can be assumed that the intrinsic fineness would be the same and hence a higher Micronaire value would indicate a higher maturity value. This is especially so with regard to American Upland cottons as there is little variation in intrinsic fineness between different varieties. Hence, certain arbitrary Micronaire values have been suggested to denote the maturity of a cotton; thus cottons having a Micronaire value less than 3.5 are considered immature, while those having over 4.0 are considered as mature. iii) Dyeing Methods: Mature and immature fibre differ in their behaviour towards various dyes. Certain dyes are preferentially taken up by the mature fibres while some dyes are preferentially absorbed by the immature fibres. In this technique, the sample is dyed in a bath containing a mixture of two dyes, namely, Diphenyl Fast Red 5 BL and Chlorantine Fast Green BLL. The mature fibres take up the red dye preferentially, while the thin-walled immature fibres take up the green dye. An estimate of the average maturity of the sample can be visually made from the amount of red and green dyed fibres. Page 62 of 85
  • 63. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Page 63 of 85 Fig. : Immature Fibre Fig. : Immature Fibre Fig. : Mature Fibre
  • 64. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 8 SOME PRECAUTIONS DURING COTTON FIBRE TESTING 1. FIBRE LENGTH (a) Baer sorter: Take a representative test specimen as per ISI method. Prepare a uniform hand made sliver without applying much tension to avoid fibre rupture. Slightly twist the fibres before putting it over combs. Straighten the edge of protruding sliver before transferring the fibre from one side to another or over velvet board. Straighten the edge of protruding sliver before transferring the fibre from one side to another or over velvet board. Comb the fibres 2-3 times before transferring. Transfer all the fibres over velvet board. Draw a line over transparent sheet just over the end of fibres. Use a pointed pencil. Page 64 of 85
  • 65. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY (b) Fibrograph: Warm up & calibrate the instrument according to the instruction manual before testing. Clean the Doffer of Fibro-sampler before and after sampling. For best precision in testing, sample size should be between 600 to 900 fibres. Brush the fibre beard to remove trash & loose fibres carefully because light brushing will remove fewer loose fibre and heavy brushing will pull out long fibres and disturb the random arrangement. Press the sample uniformly with the heel of left hand side to protrude the fibres through the hole of fibro sampler plate. Use standard cotton for the correction. 2. MATURITY: Prepare a uniform hand made sliver from random test specimen. Spread the cotton fibres over glass slide separately or without over- lapping. Avoid the contact of NaOH solution with skin and use a glass rod. Remove the air bubble by rubbing the glass slide to each other. Focus the projectina over glass slide properly for better identification. Page 65 of 85
  • 66. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY 3. FINENESS: Pass the test specimen through trash analyser before testing. Level and calibrate the instrument according to the instruction manual. Allow to stabilize the indicator before observation. Take more observation if large variation is observed. Use standard cotton foe the correction. 4. BUNDLE STRENGTH: Level and calibrate the instrument according to instruction manual. Use standard cotton for correction. Correction Factor should be within the limit i.e., 1 ± 0.1. Check the leather of fibre clamps. Apply equal force and tension for each and every test. Breaking strength of bundle should be between 3.0 kg. to 6.0kg. Condition the standard cotton and test specimen before testing. 5. TRASH ANALYSIS: Clean thoroughly the trash analyser before and after test. Separate the seed from cotton sample manually. Page 66 of 85
  • 67. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY Condition the sample before and after trash analysis for weighing. Manually open the big tufts of cotton before passing it through the trash analyser. Keep your fingers away from the feed rollers. Page 67 of 85
  • 68. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY CHAPTER – 9 HIGH VOLUME INSTRUMENT Zellweger Uster HVI test system measures seven important characteristics of cotton and they are: • Length • Length uniformity • Micronaire • Bundle Strength • Elongation • Colour and reflectance • Trash content (optical determination) As per manufacturers claim, about 180 samples (each sample – 1test) can be tested for all the above seven properties/hour with two operatives manning the instrument. However, as per practical experience in Indian Laboratories, about 100 samples/shift of 8 hours (each sample – 4 tests) could be conveniently tested using HVI. Because of the high speed of testing, now technicians are in a position to determine the raw material characteristics with reference to a large enough sample. High volume instruments are of two type. Semi Automatic Fully Automatic In addition, automatic testing systems offer the following advantages: • The results are practically independent of the operator error. • The results are based on large volume samples and therefore more significant. Page 68 of 85
  • 69. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY • The respective fibre data are immediately available. • The data are clearly arranged in summarized reports (HVI test system has microprocessors to format the test data for analysis, storage and retrieval) • They make possible the best utilization of the raw material data. • Problems as a result of the fibre material can be predicted & corrective measures can be instituted before such problems can occur. HVI test system enables testing of large volume of samples and arrive at a correct estimate of the fibre properties within a short time so that appropriate mixing can be prepared. Besides, quality of all individual bales and within bale and between bale variations can be assessed. The bales can be categorized into different lots depending on the actual fibre properties. The mills can subsequently evolve a bale management system which would enable them to maintain the quality at a consistent level at minimum cost. The length, strength, length uniformity, elongation, Micronaire, colour, trash & the NIR value of cotton fibres are all important in fibre research, in development of improved fibre blends and in verifying that purchased fibre meet specifications. This test system offers precise and reliable automated operation with computer controlled calibration and diagnostics. All functions are controlled by dedicated microprocessors to simplify operation and to provide flexibility in testing parameters. Separate version of the software is available to measure properties of man-made fibres. Included with the system are keyboard, monitor & balance. The monitor display the menu selection, operating instructions and test results. As tests are completed for each sample, the results can be transmitted to the printer of the host computer system. Page 69 of 85
  • 70. TRAINING MANUAL FIBRE TESTING AND CONTROL OF RAW MATERIAL QUALITY There are two ways of testing a sample. First one is the system testing which is designed to allow linear measuring procedure that includes the length/strength, Micronaire, colour/trash & NIR Modules. This procedure allows one operator to perform all task. In this procedure only one test is performed for Micronaire & NIR. The second way is the module testing. There are different module for length/strength, Micronaire, colour/trash & NIR. Testing is done in steps, but the number of test for Micronaire & NIR can be increased. The instrument is calibrated by using calibration cottons and standard colour tiles provided with the instrument. The standard cottons are stored in an environment of 270 C and 65% Relative Humidity because the moisture content of he cotton affects its length, strength & Micronaire. There are two kinds of cotton that can be used to calibrate HVI systems. 1. International Calibration Cotton (I.C.C). 2. High Volume Instrument calibration cottons (HVI). The HVI can be calibrated on Stelometer level or pressley level. ICC cotton are well blended card web. Two samples of these cotton are required for Micronaire calibration, one with low Micronaire value & another with high Micronaire value. The word “Calibration” refers to adjustment of values. The HVI is calibrated following engineering principle using hardware devices. After proper calibration, adjustment to raw test values are made by means of automatic software manipulation to cause test values to agree with designated values of standard samples. Page 70 of 85