Yarn pacxking density

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Packing Density of Compact Yarns
Article in Textile Research Journal · September 2007
DOI: 10.1177/0040517507078796
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1
PACKING DENSITY OF COMPACT YARNS
Demet Yilmaz, Fatma Göktepe, Dana Kremenakova*
and Özer Göktepe
Suleyman Demirel University, Textile Engineering Department, Isparta-Turkey
*
Technical University of Liberec, Textile Faculty, Dept. of Textile Technology, 46117
Liberec, Czech Republic
E-mail: fgoktepe@mmf.sdu.edu.tr
Fax: +90 246 211 1180
Abstract
In this work, fibre distribution through the cross-sections of compact yarns and their packing
density values were investigated to provide a better understanding of the internal structures of
compact yarns produced by different compact spinning systems since there is no information
available so far regarding their internal structure. The results of packing density analysis
indicate that compact yarns have nearly 15-30% higher packing density values compare to
that of the conventional ring spun yarns. Also, the packing density values of compact yarns
produced by three different compact yarn spinning systems, namely Rieter K44, Suessen Elite
and Zinser Air-Com-Tex700, reveal that there are no significant differences among these
systems, in terms of yarn packing density values.
Keywords: Yarn Packing Density, Compact Yarn, Fibre Distribution.
1. INTRODUCTION
The mechanical properties of staple yarns depend not only on the physical properties of the
constituent fibres, but also the yarn structure characterized by the arrangement of the
individual fibres in yarn cross-section. Therefore, the arrangement of the individual fibres has
attracted much attention to understand yarn structure and explain resulting yarn properties in a
better way. Many properties, such as yarn strength, extensibility, appearance, compactness as

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well as uniformity of the structure are related to fibre distribution along yarn cross-section,
and packing density analysis reveals quite valuable information regarding these properties.
In this work, we investigated internal structure of compact yarns obtained from three different
systems, namely Rieter K44, Suessen Elite and Zinser Air-Com-Tex700 as these are the
dominant systems in compact spinning field today and a better understanding of internal
structure is still needed for compact yarns.
In most of the researches related to the compact yarns, mainly the properties of compact and
conventional ring spun yarns are compared. These studies reveal that compact yarns have
better properties in many ways as the fibres in compact yarns are almost completely
integrated into yarn body [1, 3, 19]. On the other hand, Başal [2] indicated that migration
occurs at higher levels for a compact yarn in contrary of the expectations and this leads to
better yarn structure and quality. The main advantages of compact yarns are lower yarn
hairiness, higher strength and elongation values depending on their compactness as well
known today, but we have no information about a value indicating their compactness in
comparison to the conventional ring spun yarns. The packing density values would give us
such information and therefore that is the main focus of this work.
In packing density evaluation, there are various approaches used by different researchers. One
of the early approaches was proposed by Schwarz [18] based on mainly open and hexagonal
close packing while an improved approach is based on dividing the yarn cross-section into
zones of equal radius by which fibre distribution is defined by yarn packing fraction [8]. On
the other hand, Doğu [4] indicated fibre packing density is a function of the radial distance
and defined it as the number of fibres per unit area perpendicular to fibre axis. However, it is

3
suggested that fibre packing density measurements should be based on the ratio of the cross-
sectional area of fibres in a given zone to the area of that zone since fibre-number density per
unit cross-sectional area is inapplicable [9]. Driscoll and Postle [5], later on, defined fibre
distribution as the ratio of fibre volume to yarn volume at radius (r) generalizing the definition
of yarn packing fraction suggested by Hearle and also taking into account of the obliquity of
the fibres to improve the earlier approaches further. Neckar also followed the similar
approaches above dividing yarn cross-section into several annular zones having equal widths
or equal areas [13] as similarly Punj et. al. [17] divided the yarn cross-section into five
concentric zones having equal widths to determine packing density of MJS yarns. On the
other hand, more recently Grishanov et al. proposed a different approach called as virtual
locations as fibres are virtually distributed neither in the form of a ring nor a hexagonal
configuration but a combination of these two [7]. This approach enables the simulation of air
gaps between fibres and gives a good representation of fibre location. Morris et. al. [12],
developed a geometric model to predict the possible arrangements of fibres within a
continuous filament yam as the model includes some of the randomness found in real yarns.
Different from above, Petrulis and Petrulyte [16] proposed new approaches for calculating the
packing indices of close-packed yarn. In spite of all these various approaches and different
methods, the one based on dividing yarn cross-section into zones of equal radius or areas is
still used commonly since it can be applied easily and more precise results can be obtained.
2. MATERIAL AND METHOD
2.1. Yarn Production
We produced 100% cotton, combed compact yarns of 29.5 tex, 20 tex and 14.4 tex by using
three different compact yarn spinning systems.

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The yarns of 29.5 tex and 20 tex were produced from Agean cotton of 695 tex rovings while
the yarns of 14.4 tex were produced from Greek cotton of 590.6 tex roving. The fibre
properties are given in Table 1.
Table 1. The fibre properties
Mean values
Properties
Agean Cotton Greek Cotton
Staple Length (mm) 30.1 28.2
Micronaire 4.6 4.2
U.I. 85.6 82.6
Strength (g/tex) 30.6 27.9
Breaking Elongation (%) 7.3 6.9
SFI 6.7 11.6
+b 8.0 7.6
Rd 76.5 74.85
CG 31-2 41-1
SCI 153 128.6
During yarn spinning, the same rovings were fed in the same order to the spindles of each
different compact yarn spinning machine to eliminate the any variation between roving
bobbins. In addition, all yarn samples were produced with the same spinning parameters, e.g.
the same twist multiplier, draft and spindle speed etc.
2.2. Compact Yarn Spinning Systems Used
We used three different systems: Rieter K44, Suessen Elite and Zinser Air-Com-Tex700 as
these systems are the most commonly used compact spinning systems today in short staple
spinning mills. The basic principles of these systems are mainly the same that fibres are first
drafted by 3 over 3 classical drafting systems and then condensed at the end of the drafting
region pneumatically while the design details differ significantly.
2.3. The Evaluation of Yarn Packing Density and Yarn Diameter Values

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The yarn packing density analysis method which we used here is based on the Internal
Standard No. 22-103-01/01 mainly characterised by Neckar’s theory [11]. The packing
density is calculated by the ratio between total areas of the fibres in a given zone to the area of
this zone in a yarn cross section which is shown as:
µ =V/Vc ~ S/Sc (1)
Where µ is yarn packing density, V is fibre volume, Vc is whole volume, S is fibre area and Sc
is whole yarn cross sectional area, respectively.
For packing density analysis, the main requirement is to acquire yarn cross sectional images
to provide input data for calculations. As a result, sample preparation is required. Samples are
prepared according to the IS 46-108-01/01 standard. This standard includes two different
methods to prepare the samples: we used soft section method. By this method, a sample block
is formed and placed in a freezer under 18 °C temperature for 24 hours for hardening and then
clamped onto a microtome. The thickness of a section or a slice is set about 15 µm. A xylene
drop is put on the slices for a better illumination. The cross-sectional images were observed
under a microscope and captured by a camera. During the examinations of the cross sections
under microscope, it is essential to find precise and proper images. Therefore we prepared and
analysed 40 sample blocks for each type. LUCIA software is used for the packing density
analysis.
During the analysis, the gravity centre of the each fibre cross-section is determined and this
step is called as ‘yarn axis definition’. Gravity centres of the fibres are defined by co-
ordinates (Xj,Yj). The centre of yarn (X0,Y0) is estimated by the median of the fibre co-

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ordinates in the yarn cross section. Also each gravity centre co-ordinates (Xj,Yj) define the
number of the fibres in yarn cross section.
In the following step, the area of fibre cross sections is reconstructed around the gravity centre
of the section. At first we consider that fibres are ideal fibres, so they have circular cross
section (de) and cross section is parallel to yarn axis. The fibre diameter de is calculated from
fibre fineness and mass density as following and then one fibre area is calculated using the
fibre diameter value which is presented by Equations 2 and 3:
πρ/4Tde = (2)
S=
4
2
edπ
(3)
Where de is fibre diameter (mm), T is fibre fineness (tex) and ρ is fibre mass density (kg/m3
),
S is fibre area (mm2
).
In the next step, the radial rings are placed with constant width h from the yarn axis centre
(X0,Y0) towards the yarn radius (rk).
According to the helical yarn model, as well known fibres follow a helical path because of the
yarn twist; therefore, fibre cross-sections perpendicular to the yarn axis would have elliptical
shapes. At the beginning, we considered that fibres are ideal fibres and so they have circular
cross section. Therefore, the ideal circular area should be corrected according to yarn twist as
well as the distance between fibre gravity centre and yarn axis. As it is shown in Equation 4,
the radial packing density (µk) in k-th radial ring and i-th yarn cross section is calculated by
the ratio of the total fibre area in related radial rings (Sk) to the area of individual radial rings
(Sck).

7
µk=Sk/Sck k=1,2,3…. (4)
Where k is the number of a radial ring, each k number includes the fibre areas of related radial
ring as well as that of the previous one. Therefore, the radial packing density (µk) changes
from yarn centre to yarn radius surface and this change is represented by a histogram (Figure
1). Histogram gives information about the variation in yarn packing density along the yarn
radius and identifies the distribution of fibres in yarn cross-section.
On the last radial ring, a few fibre areas can be located at a considerably higher distance than
that of the most fibres. To get real yarn diameter as much as possible, the term of effective
yarn diameter (Def) is therefore identified as it is obtained from the radial packing density
curves (Figure 1). In those curves, Def values are obtained according to radial packing density
value of 0.15. Yarn diameter found this way was confirmed as the best value representing the
real yarn diameter and found empirically [11].
The effective packing density is calculated by the ratio between the total fibre areas in a circle
of diameter Def and the area of the circle of the effective diameter Def, this calculation is
shown in Equation 5. Therefore, effective packing density represents the overall packing
density of the yarn.
µef = Sef /Scef (5)
Where Sef is the total fibre areas in a circle of diameter Def, Scef is the area of the circle of the
effective diameter Def and µef is the effective packing density.

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3. RESULTS and DISCUSSIONS
3.1. Yarn Appearance
The yarn appearances were analysed by Scanning Electron Microscopy and typical views
were shown in Figure 2 as indicating that more compact yarn structure would be obtained as
the yarns get finer.
3.2. Yarn Packing Density Values
The evaluation of yarn packing density gives information about the radial distribution of the
fibres. Typical views for compact yarn cross-sections are shown in Figures 3-5. As can be
seen by these figures, compact yarns have more compact yarn structure and fibres are not
scattered as much as conventional ring spun yarns leading to more circular cross-sections as
might be well expected.
On the other hand, the packing density values of compact yarns are depicted in Figure 1. It
shows that packing density of all compact yarns is not uniform along the yarn cross section as
the packing density decreases from yarn centre towards the yarn surface for all compact yarns
which we analysed, therefore it changes parabolicaly. This trend is very similar to the
conventional ring and rotor yarns studied earlier [9-10].
The packing densities are very high near yarn centre and reach to its maximum level which is
located around one fifth of the yarn radius. After such a peak value, packing densities start to
decrease towards the yarn surface as such a trend shows that fibre arrangement is very dense
in the yarn centre. The Figure 1 shows that packing density values at the centre is between
0.55 and 0.7. Moreover, the yarn produced by Zinser Air-Com-Tex700 system has even a
value higher than 0.7. As well known, the packing density value is about 0.5-0.6 for

9
conventional ring spun (combed) yarn while it is around 0.38-0.55 for carded ring spun yarns
[14]. Similarly, OE-rotor spun yarns have much lower packing density compared to the
conventional ring spun yarns [6, 15]. These packing density values indicate that compact
yarns have higher packing density values as might be well expected and this is almost 15-30%
higher compare to the conventional ring spun yarns. On the other hand, yarns produced on
Zinser Air-Com-Tex700 have the highest packing value of all at the centre. For all packing
density values however, there is no statistically significant differences between the yarns
produced on three different systems.
From Figure 1, also we can see the effect of twist and yarn count on packing density and this
is similar to that of conventional yarns: i.e. as the twist increases, higher packing density
values are obtained.
On the other hand, when we analysed the effective packing density values, we can easily see
that yarns produced by Zinser Air-Com-Tex700 and Suessen Elite have the same trends
(Figure 6): As the yarns get coarser, effective packing density values decrease. This can be
easily explained by increasing fibre numbers in yarn cross section as it is shown by Figure 7.
The differences between the effective packing density values are considerably high for 29.5
and 20 tex yarn counts.
For Rieter K44, on the other hand, the effective packing density shows different trend for 29.5
tex yarn count. This may result from the high variation in yarn properties observed with the
yarns produced by this system. Finally, Zinser Air-Com-Tex700 has the highest effective
packing density values for all yarn counts we examined.

10
The change in yarn diameter was shown by Figure 8 indicating that all yarns which we
analysed have similar yarn diameter values for the three different yarn counts produced.
4. CONCLUSIONS
In this work, we aimed to provide a better understanding of compact yarn internal structure.
For this purpose, we investigated fibre distribution in yarn cross-section as well as yarn
packing density values of compact yarns produced on three different compact spinning
systems, namely Rieter K44, Suessen Elite and Zinser Air-Com-Tex700, which are
commonly used systems in spinning industry today.
Packing density analysis results show that packing densities of all compact yarns are not
uniform in yarn cross section, but decrease from yarn centre towards the yarn surface as it was
the case for conventional ring spun yarns, too.
The packing density values of compact yarns we investigated are between 0.55 and 0.7 while
this value is known to be between 0.5-0.6 and 0.38-0.55 for combed and carded cotton ring
spun yarns, respectively. This result confirms that compact yarns have much higher packing
density values, therefore they have more compact yarn structure compared to the conventional
ring spun yarns as expected.
On the other hand, there is no significant difference between the packing density values of the
yarns produced on three different systems mentioned above.
We were also able to determine the number of fibres in yarn cross-section. As in the
conventional ring spun yarns, the number of fibres in yarn cross-section and yarn diameter

11
increase as the yarns get coarser. However, significant differences were not observed
regarding fibre numbers in yarn cross-sections of the yarns produced by three compact yarn
spinning systems.
In conclusion, compact yarns have almost 30% higher packing density compare to that of
conventional ring spun yarns as such a compact structure would of course affect yarn
properties significantly.
LITERATURE CITED
1. Artzt, P., The Special Structure of Compact Yarns-Advantages In Downstream
Processing, ITB Yarn And Fabric Forming, No 2, 41-48, (1997).
2. Başal, G.D., The Structure And Properties Of Vortex And Compact Spun Yarns, North
Caroline State University, PhD Thesis, Raleigh, U.S.A. (2003).
3. Cheng, K.P.S., Yu, C., A Study Of Compact Spun Yarns, Textile Research Journal, 73
(4), 345-349 (2003).
4. Doğu, I., The Distribution Of Transverse Pressure In A Twisted Yarn Allowing For The
Fiber Migration And Variation Of Fiber Packing Density, Textile Research Journal, 42
(12), 726-733 (1972).
5. Driscoll, R.H., Postle, R., Modelling The Distribution Of Fibres In A Yarn, Journal of The
Textile Institute, 79 (1), 141-143 (1986).
6. Göktepe, F., The Effect of Yarn Structure of the Deformation of the Yarn Cross-Section,
University of Leeds, PhD Thesis, Leeds, England (1997).
7. Grishanov, S.A., Lomov, S.V., Harwood, R.J., et al., The Mechanical Simulation of the
Geometry of a Two-Component Yarn, Part II: Fibre Distribution in the Yarn Cross-
Section, Journal Of The Textile Institute, Vol. 88, 352-372 (1997).

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8. Hearle, J.W.S., Grosberg, P., Backer, S., Structural Mechanics of Fibers, Yarns and
Fabrics, Volume I, Wiley Interscience, United States of America, 113, (1969).
9. Hickie, T.S., Chaikin, M., Some Aspects of Worsted-Yarn Structure, Part III: The Fibre-
Packing Density in the Cross-Section of Some Worsted Yarns, 432-437 (1973).
10. Jiang, X.Y., Hu, J.L., Cheng, K.P.S., Postle, R., Determining the Cross-Sectional Packing
Density of Rotor Spun Yarns, Textile Research Journal, Vol. 75, No. 3, 233-239 (2004).
11. Kremenakova, D., Internal Standards: Textile Materials and Design of Textile Products,
Technical University of Liberec, Liberec, Czech Republic, 2004.
12. Morris, P.J., Merkin, J.H., Rennell, R.W., Modelling of Yarn Geometry: Continuous
Filament Yarns, Mathematical Engineering In Industry, 6 (1): 63-78 (1997).
13. Neckar, B., Ishtiaque, S.M. and Svehlova, L., Rotor Yarn Structure by Cross-Sectional
Microtomy, Textile Research Journal, Vol. 79, 625-632 (1988).
14. Neckar, B., Sayed, I., Structural Theory of Fibrous Assemblies and Yarns: Structure of
Fibrous Assemblies, Technical University of Liberec, Liberec, Czech Republic (2003).
15. Novackova, J., Kremenakova, D., Structural Analysis Of Fine Cotton Yarns, Technical
University of Liberec, Liberec, Czech Republic (2003).
16. Petrulis, D., Petrulyte, S., Properties Of Close Packing Of Filaments In Yarn, Fibres &
Textiles In Eastern Europe, 11 (1): 16-20 (2003).
17. Punj, S.K., Debnath, S., Ishtiaque, S.M., Radial Packing Density Of MJS Yarns, Indian
Journal Of Fibre & Textile Research, 23 (4): 229-232 (1998).
18. Schwarz, E., Certain Aspects of Yarn Structure, Textile Research Journal, Volume 21,
No. 3, 125-136 (1951).
19. Stalder, H., Ring Spinning Advance, Textile Asia, 43-46, March (2000).
FIGURES LIST

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0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
0 0,05 0,1 0,15 0,2 0,25
Yarn Radius [mm]
YarnPackingDensityµk[-]
Air-Com-Tex700-29.5 tex
K44-29.5 tex
Elite-29.5 tex
Air-Com-Tex700-20 tex
K44-20 tex
Elite-20 tex
Air-Com-Tex700-14.4 tex
K44-14.4 tex
Elite-14.4 tex
Figure 1. The change in packing density values along yarn radius
14.4 tex 20 tex 29.5 tex
Figure 2. Typical views of compact yarns (40x)
(A, B, C denote the yarns produced on Suessen Elite, Rieter K44 and
Zinser Air-Com-Tex700, respectively)

14
Suessen Elite Rieter K44 Zinser Air-Com-Tex700
Figure 3. Typical cross-sectional views of compact yarns (29.5 tex) (100x)
Figure 4. Typical cross-sectional views of compact yarns (20 tex) (100x)
Figure 5. Typical cross-sectional views of compact yarns (14.4 tex) (100x)

15
0,45
0,47
0,49
0,51
0,53
0,55
0,57
0,59
0,61
14.4 tex 20 tex 29.5 tex
EffectivePackingDensityµef[-]
Air-Com-Tex700
K44
Elite
Figure 6. The effective packing density values of compact yarns
100
120
140
160
180
200
220
240
14.4 tex 20 tex 29.5 tex
NumberofFibers
Air-Com-Tex700
K44
Elite
Figure 7. The variation of fibre numbers in compact yarn cross sections

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0,12
0,14
0,16
0,18
0,2
0,22
0,24
14.4 tex 20 tex 29.5 tex
EffectiveYarnDiameterDef[mm]
Air-Com-Tex700
K44
Elite
Figure 8. The variation in effective yarn diameter
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