The document details various properties of fibers crucial for their applications, including tenacity, flexibility, uniformity, and moisture regain. It emphasizes the importance of fiber morphology, strength, and chemical resistance, highlighting how these attributes influence the quality and functionality of textile products. Additionally, specific properties of cotton and wool fibers are explored, including their structural characteristics, durability, and performance under different conditions.

1. Fiber properties

2. Fiber properties are essential thing to know for
various end uses and the products made from it
qualify on the basis of certain parameters.
The various properties are
 High fiber length to width ratio
 Tenacity (adequate strength)
 Flexibility or pliability
 Cohesiveness or spinning pliability
 Uniformity

3.  Fiber morphology
 Specific gravity
 Elongation and elastic recovery
 Resiliency
 Moisture regain
 Flammability and other thermal reactions
 Electrical conductivity
 Abrasion resistance
 Chemical reactivity and resistance
 Sensitivity to environmental conditions.

4.  High length to width ratio-
 A pre-requisite for processing of fibers into yarns
and fabrics is that their lengths must be more than
widths. The minimum length to breadth ratio is
100:1.
 Length of fibers is also a basis for classifying them
into two groups staple and filament. Staple fibers
are of relatively short length fibers; and filament
fibers are continuous length fibers.
 The fineness of a natural fiber is a major factor in
ascertaining quality and is measured in microns(1
microns= 1/1000millimeter). In general, finer fibers
are softer, more pliable and have better drapability.
They are, thus, considered superior and form
better yarns and fabrics. Fineness of man-made

5.  Tenacity-
 Strength of textile fibers is referred to as their
tenacity. It is determined by measuring the
force required to rupture or break the fiber.
Sufficient tenacity is required to withstand the
mechanical and chemical processing as well as
make textile products which are durable.
 Tenacity is, directly related to the length of the
polymers, degree of polymerization, strength in
dry and wet conditions, and types of inter-
polymer forces of attraction formed between the
polymers.

6.  Flexibility-
 Fibers should be flexible or pliable in order to
be made into yarns and thereafter into fabrics
that permit freedom of movement. Certain end
uses require greater flexibility, e.g., automobile
seat belts.
 Uniformity-
 Uniformity of fibers towards its length, ensure
production of even yarns which can then form
fabrics of uniform appearance and consistent
performance.

7.  Cohesiveness or spinning quality-
 It is the ability of the fiber to stick together
properly during yarn manufacturing processes.
 Natural fibers have inherent irregularities in
their longitudinal or cross sections which permit
them to adhere to each other during fiber
arranging.
 In case of synthetics, filament lengths aid in
yarn formation. Texturing introduces coils,
crimps, curls or loops in the structure of an
otherwise smooth filament. It is used to impart

8.  Morphology-
 It is the study of physical shape and form of a
fiber. It includes microscopic structure like
longitudinal and cross sections. These also
include fiber length, fineness, crimp, color and
luster.
 Physical shape-
 shape of a fiber include, its longitudinal
sections, cross section, surface contour,
irregularities and average length.

9.  Luster-
 It refers to the sheen or gloss that a fiber
possesses. It is directly proportional to the
amount of light reflected by a fiber.
 This in turn is affected by their cross section
shape.
 Among the natural fibers, silk or the queen of
Cross sectional shape Degree of luster
Round High
Irregular Low
Kidney shaped Low
Oval High
Trilobal High
octagonal Low

10.  Specific gravity-
 The specific gravity of a fiber is the density
related to that of water(at 4°c).
 The density of water at that temperature is 1.
fiber density will affect their performance and
laundering.
 If the specific gravity of a fiber is less than 1, it
will float in water, making its washing and
dyeing very difficult. E.g. Olefins fiber.
 A related property is density which is defined as
the mass per unit volume and measured in

11.  Elongation and elastic recovery-
 The amount of extension or stretch that a fiber
accepts is referred to as elongation. Elongation
at break is the amount of stretch a fiber can
take before it breaks.
 Elastic recovery indicates the ability of fibers to
return to their original length after being
stretched. A fiber with 100% elastic recovery
will come back to its original length after being
stretched to a specific degree for specified
period of time. After removing and re-
measured.

12.  Resiliency
 Resiliency refers to the ability of a fiber to come
back to its original position after being creased
or folded. Resilient fibers recover quickly from
wrinkling or creasing. Good elastic recovery
usually indicates good resiliency. This property
is described qualitatively and ranges from
excellent to poor. Excellent resiliency is
exhibited by polyester, wool and nylon fibers.
Flax, rayon and cotton, on the other hand, have
a low resiliency.

13.  Moisture regain-
 The ability of a bone dry fiber to absorb
moisture is called moisture regain.
Measurements are done under standard testing
conditions (70°± 2F and 65% ±2% relative
humidity). Saturation regain is the moisture
regain of a material at 95-100% relative
humidity. Both regain and content are
expressed as a percentage.
 Moisture regain= wt. of water in a material × 100
oven dry wt.
 Moisture content= wt. of water in a material × 100
total wt.

14.  Flammability and other thermal reactions-
 Burning characteristics of fiber groups vary
from each other and can, thus be used as an
authentic identification method. Reaction to
flame can be further broken down into; behavior
when approaching flame, when in flame, after
being removed from flame.
 Thermal characteristics of fibers are important
in their use and care like washing, drying and
ironing are selected on the basis of a fiber’s
ability to withstand heat.

15.  Electrical conductivity-
 It is the ability of a fiber to transfer or carry
electrical charges. Poor or low conductivity
results in building up of static charges. This
leads to the clinging of clothing and in extreme
cases can produce electrical shocks, which
produce crackling sound or even a tiny spark.
Acrylic is a poor conductor of electricity.
 water is an excellent conductor of electricity
and fibers with high moisture regains will never
face the problem of static build-up.

16.  Abrasion -
 The wearing away of a material by rubbing
against another surface is called abrasion.
Different kinds of abrasion are identified, these
are-
 Flex abrasion- when a fabric bends/folds and
rubs against another surface e.g. on elbow or
knee areas.
 Flat or plane abrasion: when a flat surface rubs
against another surface e.g. on thigh area of a
pair of jeans.

17.  Chemical reactivity and resistance-
 Chemical reactivity plays a key role in
manufacture, application of finishes and care of
fabrics.
 Resistance to acids, alkalis and organic
solvents in similar for fibers of one chemical
composition. Thus, cellulosic's are fairly
resistant to alkalis but get harmed by acids and
the reverse is true for protein fiber.

18. Morphology of cotton fiber
 Cellulosic fiber
 70 % crystalline and 30 % amorphous region
 Under a microscope, a cotton fiber appears as a very fine,
regular fiber.
 length: 10 mm to 65 mm
 Diameter: 11 micron meters to 22 micron meters.
 Length to breadth ratio: 6000:1 (longest) to 350:1 (shortest)
 Look like a twisted ribbon or a
collapsed and twisted tube.
 Twists are called convolutions.

19. Chemical Composition of
Cotton Fiber
 Cellulose 94
%
 Protein 1.3
%
 Ash 1.2
%
 Pectin 1.2
%
 Oil, Fat and
Wax 0.6%
 Trash 0.3

20.  Cuticle is the outer waxy layer, exists very outside
of the cotton fiber. Cuticle consists of pectin and
proteinaceous materials. It serves as a smooth,
water-resistant coating, which protects the fiber
from chemical and other degrading agents. The
waxy nature of the cuticle enables it to adhere
tenaciously to the primary wall of the fiber. This
layer is removed from the fiber by scouring.
 primary wall is the original thin cell wall, which is
immediately present underneath the cuticle . It is
200nm thick. It mainly consists of cellulose or
network of small strands of cellulose, called fibrils.
The fibrils spiral at about 70° to the fiber axis. This
spiraling imparts strength to the primary cell, and
hence, to the fiber. This makes for a well-organized
system of continuous, very fine capillaries. The fine
surface capillaries of each cotton fiber contribute
greatly to cotton’s wipe-dry performance
Macro-structure of cotton

21. Macro structure of cotton fiber

22.  The “secondary wall” layers of cellulose consist of
concentric layers present beneath the primary cell wall ,
which constitutes the main portion of the cotton fiber. After
the fiber has attained its maximum diameter, new layers of
cellulose fibrils are added to form the secondary wall. Its
fibrils are about 10 nm thick, but of undefined length. Near
the primary cell wall, the fibrils of the secondary wall spiral
at about 20° to 30° to the fiber axis. The fibrils are packed
close together, again, forming small capillaries. As the
fibrils change the direction of their spirals, a weak area
exists in the secondary wall structure which results in weak
areas are responsible for alternation of the direction of the
twists of the convolutions.
 The “lumen” is the hollow canal that runs the length of the
fiber. It is filled with cell sap during the growth period. The
lumen was once the central vacuole of the growing cotton
fiber . After the fiber matures and the boll opens, the
protoplast dries up, and the lumen naturally collapses,
leaving a central void in each fiber. When the sap
evaporates , its constituents remain behind to contribute to
the color of the cotton fiber . As the sap evaporates, the
pressure inside the fiber become less than the
atmospheric pressure on the outside. This caused the fiber
to collapse inward resulting in the bean or kidney-shaped
cross-section of the cotton fiber.

23. The microscopic appearance of
cotton
 Cross-sectional view of cotton fiber is kidney-
shaped
 swelling almost round when moisture absorption
takes place.
 This shape occurs from the inward collapse of
the cotton fiber when it dries out. The cross-
section tends to provide an indication of the
relative dimensions of the lumen and fiber walls.

24. Under the microscope, each cotton fiber is
a single elongated cell that is flat twisted
and ribbon like with a wide inner hollow
canal as lumen. These twists are also
referred as convolutions Formation of
convolutions occurs after the cotton boll
bursts open. Then the limp, sap-filled
cotton seed hairs begin to dry out and
their cell walls collapse inward which
decreases the size of the lumen.
Shrinkage, twisting of the cotton seed
hair results in the removal of sap from
the lumen and at last in the formation of
convoluted fiber.

25.  The seed end of the fiber is quite irregular. The main
part of the fiber, about three-quarters to fifteen-
sixteenths of its length, is quite regular, with a thick fiber
wall, canal along the centre of the fiber called the
lumen, and about sixty convolutions per centimeter. The
fiber tip is less than one-quarter of the fiber length, and
tapers to a cylindrical, pointed tip with no convolutions.
The convolutions give cotton an uneven fiber surface,
which increases inter-fiber friction and enables fine
cotton yarns of adequate strength to be spun.
 The convolutions and kidney-shaped cross-section of
the cotton fiber enable it to make only random contact
with the skin, which is more comfortable and compatible
to human skin. Moisture absorbance of cotton fiber is
due to the countless minute air spaces which exist
because of the convolutions and kidney-shaped cross-
section of cotton fibers, thus making them more
comfortable to wear.

26.  Structure: The cotton fibre is short (1/2 inch -2 long inch) and
cylindrical or tubular as it grows. The cotton fibre is essentially
cellulose consisting of carbon, hydrogen and oxygen. Bleached
cotton is almost pure cellulose raw cotton contains about 5% of
impurities.
 Strength: Cotton fibre is relatively strong which is due to the
intricate structure and 70% crystalline.
 Elasticity: Cotton is relatively inelastic because of its crystalline
polymer system and for this reason cotton textile wrinkle and
crease readily.
 Hygroscopic moisture: Cotton does not hold moisture so well as
wool or silk but absorbs it and so feels damp much more
quickly. It also rapidly spreads throughout the material.
 Electrical property: The hygroscopic nature ordinarily prevents
cotton textile materials from developing static electricity.
 Absorbency: As cotton has cellulose it is a good absorbent of
fibre.
Physical properties

27.  Thermal properties Cotton fibres have the ability to conduct
heat energy, minimizing any destructive heat accumulation
thus they can withstand hot ironing temperature.
 Drape ability: Cotton does not have good body to drape well
in shape. The type of construction of the fabric may improve
this property.
 Resilience: Cotton wrinkles easily some wrinkle resistant
finishes may reduce this property.
 Cleanliness and wash ability: Though cotton absorbs dust
due to its rough nature. It can be washed easily in the hot
water and strong soaps without damaging the fibre.
 Luster: The natural cotton has no pronounced lustre. This can
be improved by the mercerization finish of the cotton(that is
sodium hydroxide treatment).
 Shrinkage: The fibre itself does not shrink but cotton fibre
which has been stretched in the finishing process tends to
relax back creating shrinkage.
 Heat conductivity: Cotton is the better conductor of heat than
wool or silk but not as good as rayon

28.  Action of acids and alkalis Strong acids will destroy the fibres
immediately. Dilute inorganic acids will weaken the fibre and if left dry
will rot it. Therefore after treatment with acidic solutions cotton articles
should be thoroughly rinsed in water. They are affected very little by
organic acids. They are also quite resistant to alkalis even to strong
caustic alkalies at high temperature and pressure. In 8% NaOH
cotton fibres swells, spirals, twisted uncoil and shrinks and become
thicker. The resultant fibre is smoother, lustrous, and stronger and
has increased water and dye absorption.
 Effect of bleaching: These have no effects until used in uncontrolled
conditions and with heat.
 Effect of sunlight and weather: Ultraviolet rays of sunlight affect the
strength of fibre and change the colour to yellow when exposed to
prolonged period. Pollution also effect fibre.Concentrated and diluted
mineral acids like sulphuric acids will discolor fibre .
 Affinity to dyes: Cotton takes in dyes better than linen but not as
readily as silk and wool. If a mordant is used cotton is easy enough to
dye mordant colours, direct or substantive dyes should be applied to
Chemical properties

29. Properties of cotton fibers
Property Evaluation
Shape
Fairly uniform in width, 12-20 microns; length varies from ½ to 2½ inches;
typical length is ⅞ to 1¼ inches.
Luster low
Tenacity (strength)
Dry
Wet
3.0-5.0 g/d
3.3-6.0 g/d
Resiliency low
Density 1.54/1.56 g/ccm
Moisture absorption
raw:conditioned
saturation
mercerized: conditioned
saturation
8.5%
15-25%
8.5-10.3%
15-27%+
Dimensional stability good
Resistance to
acids
alkali
organic solvents
sunlight
microorganisms
insects
damage, weaken fibers
resistant; no harmful effects
high resistance to most
Prolonged exposure weakens fibers.
Mildew and rot-producing bacteria damage fibers.
Silverfish damage fibers.
Thermal reactions
to heat
to flame
Decomposes after prolonged exposure to temperatures of 150˚C or over.
Burns readily.

30. Test
Fiber
Soda
ash
40%
sol.
Causti
c soda
25%
sol.
Sodi
um
hypo
chlo
ride
Hyd
ro
chlo
ric
acid
40%
Nitr
ic
acid
15%
Nitric
acid
70%
Sulp
huric
acid
15%
Sulp
huric
acid
70%
Burning
in Flame
Microsc
opic
View
Remarks
Cotto
n
swells Swells
&
Shines
Whit
ened
Turn
s
yello
wish
Ope
ns
up
looses
strengt
h
Dissol
ves
slowly
Disso
lves
on
heat
ing
Disso
lves
quick
ly
Burns
continuo
usly
leaving
grey ash
of
burning
paper
smell
Longitud
inal
twists.
Resistanc
e to
alkalis.
IDENTIFICATION OF COTTON FIBRE

31. Wool fiber
 Wool is the natural protein fiber from the fleece of
sheep
 Length of the fiber ranges from 5cm for finest to
35cm for the coarsest wools.
 Diameter for finer 14μm, coarse 45μm,
 Length width ratio ranges from 2500:1 for the fine
and shorter, 7500:1 for coarse and longer
 Colors vary from off white to light cream.
 The wool fiber is a crimped, fine to thick, regular
fiber.
 Fine wools have 10 crimps per centimeter, while
coarse wool has less than 4 crimps per 10
centimeters. As the diameter of wool fibre
increases, the number of crimps per unit length

32.  The number of crimps per unit length may
be taken as an indication of wool fiber
diameter or wool fiber fineness. As the
diameter of the wool fiber increases the
crimp per unit length decreases
 The crimped configuration prevents wool
fibers from aligning themselves too
closely when being spun into yarn. As a
result it is possible to have wool textile
materials with air spaces occupying about
two-thirds of the volume. The warmth of
wool fabrics is due more to the air spaces
in material than to the fiber

33. Microscopic appearance of
wool
 Longitudinal microscopic appearance of wool is
the overlapping surface cell structure. These
surface cells, known as epithelial cells and
commonly known as scales, which point towards
the tip of the fiber
 The cross section of wool fibre is usually oval in
shape

34. Macro-structure of wool
The micro structure of wool fiber consists of three main
components
 Cuticle : The cuticle is the layer of overlapping epithelial cell's
surrounding the wool fiber. There are three cuticle.
Epi Cuticle: The epicuticle is the outermost layer covers of the wool fiber.
Exocuticle : The overlapping epithelial cell forms the exocuticle.
Endocuticle: The endocuticle is the intermediate connecting layer bonding the
epithelial cell of the cortex of the wool fiber.
 Cortex: The cortex or core, of the fiber forms about 90% of the
fiber volume. It consists of countless, long, spindle shaped cells
or cortical cells. It is composed of two regions known as ortho
and para cortex. The ortho cortex absorbing more dye than para
cortex. The ortho and para cortex spiral around one another.
Fine wool fibers have about 20 such cells, whereas coarse wool
fibers have about 50 cortical cells across diameter of their cross-
section.
 Medulla: Coarser fibers have a hollow space running
lengthwise through the center

37. Wool polymer
 Wool polymer is a linear, alpha-keratin polymer which has a
helical configuration. Steps in the formation of wool polymer
are not known. So the repeating unit of wool polymer is amino
acid which is linked to each other by the peptide bond (-CO-
NH-). As a result, it is not possible to determine the extent or
degree of polymerization for wool. It consists of a long
polypeptide chain constructed from 18 amino acids.
 wool polymer is about 140 nm and about 1nm thick in its
normal relaxed state , the wool polymer has alpha keratin
structure stretching of the wool fiber tend to stretch, straighten
with unfolded configuration called called beta-keratin. A beta-
keratin wool polymer always tends to return to its relaxed
alpha keratin structure.
 Amorphous : Wool polymer system is extremely amorphous,
as it is about 25 to 30% crystalline. The spiraling of the proto-
fibrils, micro-fibrils and macro-fibrils does not imply a well
aligned polymer system.

38. The complexity of the wool polymer is due to
important chemical groupings it contains and the
inter-polymer forces of attraction.
 Polar peptide groups: The oxygen of the carbonyl
groups (-CO-) is slightly negatively charged and as
a result will form hydrogen bonds with the slightly
positively charged hydrogen of the amino groups (-
NH-) of another peptide group.
 Salt linkages or ionic bonds: carboxyl radicals (-
COOH) and (-NH2) as side groups of amino acids
which are basically the acidic and basic groups,
salt linkages or ionic bond will forms.
 Covalent bonds: cystine, the sulphur containing
amino acid which is present in wool, makes the
wool polymer system the only one with cystine
linkages, also known as di-sulphide bonds. Cystine
bonds are covalent bonds, they occur within and
between wool polymers.
 Van der Waals forces

40. Physical properties
Tenacity:
 When wool absorbs moisture, the water
molecules gradually force sufficient polymers
apart to cause a significant number of hydrogen
bonds to break. Water molecules hydrolyze salt
linkages in the amorphous regions of the wool
fiber. Breakage of these inters –polymer forces of
attraction are apparent as swelling of the fiber
and results in a loss in tenacity of the wet wool
textile material.
 Wool is comparatively weak fiber
 Wool is composed principally of proteins which
are polycondensation products in which the
different amino acids are linked together to form
a polypeptide chain:

41. They possess a large number of highly polar peptide linkages which
can give rise to inter- and intra-molecular hydrogen bonding.
While these bonds contribute much toward increasing the
strength of the fiber, such close spacing of these groups along the
molecular chain would be detrimental to other desirable fiber
properties. They contain relatively large side chains (R groups in
the scheme of the polypeptide chain) which prevent close packing
of the protein molecules and thus decrease the extent to which
hydrogen bonding can occur. The low tensile strength of wool is
due to the relatively few hydrogen bonds that are formed.
Elasticity: wool has very good elastic recovery and excellent
resiliency. The ability of wool fibres to recover from being
compressed is due to
 a) crimped configuration of wool fiber
 b) alpha–keratin configuration of the wool polymer
 Covalent bonds can stretch, but they are strong. The disulphide
bonds in the amorphous parts of the strand or fibre are able to
stretch when the strand is extended. When the strand is released
the disulphide bonds pull the protein molecules back into their
original positions
3) Hygroscopic nature: absorbent nature of wool is due to the
polarity of the peptide groups, salt linkages and amorphous
nature of its polymer system. The peptide groups and salt
linkages attract water molecules which readily enter the

42. Conductivity of heat:
 It has a low conductivity of heat and therefore
makes it ideal for cold weather. The resiliency of the
fibre is significant in the warmth properties of the
fabric. Wool fibres do not pack well in yarns
because of the crimp and scales, and this makes
wool fabric process and capable of inserting much
air. Air is one of the best insulators since it keeps
body heat close to the body. The medulla of the
wool fibre comprises air spaces that increase the
insulating power of the fibre.
 This strand can take up moisture in vapor form.
Absorbency is a factor also in the warmth of
clothing. In winter, when people go from a dry
indoor atmosphere into the damp outdoor air, the
heat developed by the fibre in absorbing moisture
keeps to protect their bodies from the impact of the
cold atmosphere

43. Chemical properties
Effect of acids
Wool is more resistant to acids than to alkalis. Acid
hydrolyze the peptide group but leaves the disulphide
group. The polymer weakens but does not dissolve
though it become very vulnerable to further
degradation. it is essential to neutralize wool after
acid treatment.
Effect of bleaches
No method is known for bleaching wool permanently.
The effective method of bleaching wool is to use a
reducing bleach followed by an oxidizing bleach.
Reducing bleach such as sodium bisulphite, sodium
sulphite converts discoloration on the fibre surface to
colourless compounds. Due to the application of
oxidizing bleach the colourless compounds are
converted into water soluble compounds and then
can be rinsed off

44. Effect of alkalis
Wool dissolve readily in alkaline solution. Alkali
dissolve the hydrogen bonds, disulphide bonds
and salt linkages. Prolong exposure to alkies
cause fragmentation and complete destruction
of wool fibres
Effect of sunlight and weather
Sunlight cause yellowing or dullness of wool
fabric. The ultraviolet rays of sunlight degrade
the peptide and disulphide linkages;
degradation products cause wool fibre to
absorb more light and to scatter the incident
light even more to give yellowing or dulling
effect on fabric.

45. Dye ability of wool fiber
Ortho-cortex absorb more dye than the para-cortex
 Different staining is due to the different composition of the
para-cortex and the ortho-cortex. The chemical
composition of the para-cortical cells shows a higher
cystine content than ortho-cortical cells. Cystine is a
sulphur containing amino acid, capable of forming di-
sulphide cross-links. This increased cross-linking tends
towards greater chemical stability resulting in less dye
absorption of para-cortical cells.
 The cortical cells of the wool fibre consist of a number of
macro-fibrils. These macro-fibrils held together by a
protein matrix. Each macro-fibril consists of micro-fibrils of
indeterminate length. And each micro-fibril composed of
eleven proto-fibrils these protofibrils spiral about each
other. Finally, each proto-fibril consist of three wool
polymers (alpha keratin polymers), which also spiral
around each other. It is the fibrillar and spiralling structure,
within the cortical cells, which contributes towards the
flexibility, elasticity and durability of the wool fibre.

46. Silk fiber
 Silk is a natural protein fiber
 Cultivation of cocoons for the filament
 Silk filaments are 600-1700 m long and
 Diameter ranges from 12-30 µm depending
upon the health, diet and state under which
the silk larvae extruded the silk filaments.
 Fiber length to breadth ratio is 2000:1
 It is off-white to yellow in color

47. Micro structure
 Silk polymer is linear, fibroin polymer. It is
composed of 16 different amino acids.
 Silk polymer occurs only in the beta-
configuration. Length of the silk polymer is about
140nm which is slightly longer than wool
polymer, and about 0.9 nm thick. The important
chemical groupings of the silk polymer are the
peptide groups which give rise to hydrogen
bonds, and the carboxyl and amine groups
which give rise to the salt linkages.
 Polymer system of silk is composed of layers of
folded linear polymers. This results in 65-70%
crystalline polymer system. The major forces of
attraction between silk polymers are hydrogen
bonds, which are effective across a distance of
less than 0.5nm. This ensures that fibroin

48. Alanine and Glycine contribute 65-70%
of silk protein

49. Cross section of silk fiber

50. Physical properties
 Physical characteristics of fiber are
determined by the structure of the
macromolecule composing the fibroin. Partly
the macromolecule comprises of amino acids
with a low molecular weight, result in a series
of crystalline regions which gives a high
degree of tenacity. The rest of the
macromolecule is characterized by the
presence of amorphous areas enclosing
amino acids of a higher molecular weight.
Crystalline and amorphous zones give
combination of strength, flexibility and
elasticity

51. Tenacity - The silk filament is strong. This
strength is due to its linear, beta configuration
polymers and very crystalline polymer
system. These two factors permit many more
hydrogen bonds to be formed in a much more
regular manner. Silk loses strength on
wetting. This is due to water molecules
hydrolyzing a significant number of hydrogen
bonds and in the process weakening the silk
polymer.
Specific gravity - silk is less dense than
cotton. It has a specific gravity of 1.3. Silk
fibre are often weighted by allowing filaments
to absorb heavy metallic salts; this increases
the density of the material and increases
its draping property.

52.  Elasticity Very crystalline polymer system does not
permit the amount of polymer movement which
results in plastic nature of silk than elastic. Hence, if
silk textile material is stretched, the silk polymers
which have beta-configuration will slide past each
other. This stretching results in rupturing of
hydrogen bonds. After stretching, the polymers do
not return to their original position, which leads to
distortion and wrinkling or creasing of the silk textile
material.
 Effect of heat Heating of silk fiber remains
unaffected for a long period at 1400C. It is more
sensitive to heat compared to wool, which is due to
the lack of any covalent cross links in the polymer
system of silk, compared with the di-sulphide bonds
which are present in wool’s polymer system.
Peptide bonds, salt-linkages and hydrogen bonds of
silk fiber decompose quickly at 1750C.

53. Hygroscopic nature: Moisture regain of silk is about
11% compared to cotton which has 8.5% this is due
to the very crystalline polymer system. The amount
of moisture absorbed by silk depends on whether it
is raw or degummed silk or on the species of silk and
in the humidity
Electrical properties - Silk is a poor conductor of
electricity and tends to form static charge when it is
handled. This causes difficulties during processing,
particularly in dry atmosphere.
Hand feel - The handle of the silk is described as a
medium and its very crystalline polymer system
imparts a certain amount of stiffness to the filaments.
This is often misinterpreted, in that the handle is
regarded as a soft, because of the smooth, even
and regular surface of silk filaments.

54. Drapes Property - Silk fibre is flexible enough
and if silk fibre is used to make garments, then
the fabric drapes well and this is why it can be
tailored well too.
Abrasion resistance - Silk fabric possess
good abrasion resistance as well as resistance
to pilling.
Effect of sunlight - Silk is more sensitive light
than any other natural fibre. Prolonged
exposure to sunlight can cause partially spotted
color change. Yellowing of silk fibre is generally
occurred due to photo degradation by the action
of UV radiation of sunlight. The mechanism of
degradation is due to the breaking of hydrogen
bonds followed by the oxidation and the
eventual hydrolytic fission of the polypeptide
chains.

55. Investigation of fiber structure
 Fiber structure helps to acquire
knowledge about fiber an its
composition for improving use of fiber
in textile.
 Measuring of fiber structure manly
introduce the fiber composition, length,
weight, thickness, fineness, flexibility,
stability etc
 So fiber investigation methods and
study of fiber structure is very
important to knowing about the fiber
properties

56. Methods for investigation of fiber
structure
◦ The absorption of infrared radiation and
Raman scattering of light;
◦ Optical and X-ray diffraction
◦ Optical microscopy
◦ Electron microscopy and electron diffraction
◦ Optical properties
◦ Thermal analysis
◦ Density method

57. Absorption of infrared radiation
and Raman scattering
 When electromagnetic waves interact with
matter, they are scattered and absorbed.
 In infrared spectroscopy, radiation with
wavelengths between 1 and 15 μm is absorbed
at certain characteristic frequencies, which
yield structural information.
 Elastic scattering does not give molecular
information, though light scattering does give
larger-scale information
 the variation in absorption can be found and
plotted against wavelength

58. Absorption spectrum of nylon

59.  The wavenumber at which absorption takes
place depends primarily on the nature of the
two atoms and of the bond between them.
Thus there will be absorption frequencies
characteristic of such groupings as C--H, C-
-O, ,O--H, N--H, C--C and so on. To a
smaller extent, the absorption frequency is
influenced by the other groups in the
neighborhood
 For example, the absorption frequency for a
carbon–hydrogen bond in a terminal group,
—CH3, is different from that for the same
bond in a chain, —CH2—.

60. Application
 Identification of the presence of certain
groups in the molecule, leading to the
determination of its chemical formula.
 The method can also be used in routine
analysis to identify and estimate
quantitatively the presence of given
substances, even in small quantities in a
mixture, by observation of their
characteristic spectrum.
 It can be used to determine the amount of
water in fibre

61.  Other structural information can also be
obtained. If the infrared radiation is polarised,
then the oscillation of the atoms will vary from a
maximum for one orientation to a minimum for
an orientation at right angles. The variation in
the absorption spectrum with the direction of
polarisation can therefore be used to investigate
the degree of orientation of the molecules in a
fibre.
 For example, in nylon, the >N—H, >CH2 and
>C=O absorption bands all show weak
absorption. It is due to the vibration direction of
the electric vector is along the molecular chain
and strong absorption when it is vibrating
perpendicular to the chain axis.

62. Raman spectroscopy
 It is the incidence of the photons shifts electrons from one
state to another. The energy of the change comes from the
photon. Consequently the scattered photon has a different
energy and hence a different frequency. The effects are
manifested in the visible region.
 Raman spectra are influenced by material structure in a
way similar to that described for infrared absorption
spectra, but the greater complication of the interaction
yields more directional information.
 Raman spectroscopy has become a powerful tool for
investigating fibre structure as a result of the development
of Raman microscopes. With a spot size less than a fibre
diameter, spectra can be obtained from single fibres.
 If the fibre is mounted on an extension stage in the
microscope, it is possible to observe the shift in the spectral
lines with fibre extension. In this way it is possible to show
which parts of the structure are changing.
 An account of the use of Raman spectroscopy in various
ways in the study of aramid, polyester and carbon fibres is
given by Young

63. Optical diffraction
 When a beam of light is
passed through a
photographic slide, the light
is scattered in many
directions.
 By using a lens in the right
place, we can recombine this
scattered information about
the picture into an image on
a screen.
 Example: There is a
characteristic diffraction
pattern from a single slit. The
difference between the image
that must be focused at a
particular place and the
angular diffraction pattern
that can be intercepted
anywhere is shown in Fig.

64.  The use of polarized light in
either of the above two
techniques changes the
pattern and thus, in principle,
increases the available
information about structure if
it can be interpreted.
 A diffraction grating of
regularly spaced lines,
illuminated normally by
parallel light, will give a set of
fringes, with the maxima of
the bright bands at angles φ
defined by the relation:
◦ nλ = a sinφ
◦ Where n is an integer, λ the
wavelength of light and a the
spacing of the lines in the
grating.

65. X-ray diffraction
 X-radiation (composed of X-rays) is a
form of electromagnetic radiation.
 X-rays have a wavelength in the range of
0.01 to 10 nanometers, corresponding to
frequencies in the range 30 petahertz to
30 exahertz (3×1016 Hz to 3×1019 Hz)
and energies in the range 100 eV to 100
keV.
 The wavelengths are shorter than those
of UV rays and longer than those of
gamma rays.

67.  X-radiation (composed of
X-rays) is a form of
electromagnetic
radiation.
 X-rays have a
wavelength in the range
of 0.01 to 10
nanometers,
corresponding to
frequencies in the range
30 petahertz to 30
exahertz (3×1016 Hz to
3×1019 Hz) and
energies in the range
100 eV to 100 keV.
 The wavelengths are
shorter than those of UV
rays and longer than

68. X-ray diffraction
 The condition that a
particular reflection
should occur is that
the layer of atoms
should make the
required angle with the
X-ray beam. This will
happen for a series of
orientations of the
crystals distributed
around a cone. The X-
rays will be reflected
around a cone of twice
this angle, as shown in
Fig.

69. Electron microscopy and Electron diffraction
 Electron diffraction refers to the wave nature of
electrons. However, from a technical or practical point
of view, it may be regarded as a technique used to
study matter by firing electrons at a sample and
observing the resulting interference pattern. This
phenomenon is commonly known as the wave-particle
duality, which states that the behavior of a particle of
matter can be described by a wave.
 Normal optical microscope we can find out up to 0.5 Å
only.
 By using of electron microscope we can able to find out
up to 5 Å.
 The rays from electron source are condensed on the
specimen.
 Here only dry sample can be examined.
 Contrast in the image depends on the variation in
scattering of the electrons by parts of the specimen of
differing density.

70. Electron microscopy and Electron diffraction
 Electron microscope
method is better to
examining the
surface of the fiber
 The main use of EM
in fiber science has
been in the range of
medium to high
magnification, which
is near or beyond
the limit of the
microscope .