Characteristics of Rotor Spun Cotton/Spandex Composite Yarns

RJTA Vol. 9 No. 3 2005
Characteristics of Rotor Spun Cotton/Spandex Composite Yarns
Haixia Zhang1, Yuan Xue2 and Shanyuan Wang3
1
College of Textiles, Donghua University, Shanghai 200051, China
2
College of Clothing and Art Design, Jiaxing University, Jiaxing 314001, China
College of Textiles, Donghua University, Shanghai 200051, China
ABSTRACT
Spandex fibers have superior stretch and elastic recovery ability, which is why clothes
containing spandex fibers fit well and are comfortable. The most common methods of
producing elastic yarns are core-spun on a modified ring frame and hollow spindle technique.
Rotor spinning has many advantages over ring spinning and has been adopted worldwide. In
this paper, a method of producing the cotton/spandex composite yarns on a modified
open-end rotor spinning is introduced. By changing the draft ratio and linear density of
spandex filaments, different kinds of cotton/spandex composite yarns are produced on a
modified rotor spinning frame, and their appearance and properties are tested and analyzed at
the same time. The results show that the spandex draft ratio has great influence on the
appearance and properties of rotor spun cotton/spandex composite yarns. The linear density of
spandex filaments also has influence on the properties of composite yarns.
Keywords: characteristics, composite yarns, rotor spun, spandex
1.
Introduction
Spandex fibers have superior stretch and elastic
recovery ability, which is why clothes containing
spandex fibers, such as underwear, swimwear,
pantyhose, fashionable clothing, etc., fit well and
are comfortable. The most common methods of
producing elastic yarns are core-spun on a
modified ring frame, hollow spindle technique, air
entangling, friction spinning, and Siro spinning
(Babaarslan, 2001; Lin & Chang, 2004; Sawhney
et al., 1992; Sawhney et al., 1992). These
processes are characterized by different yarn
properties, structures, and yarn count range.
Open-end rotor spinning is well-established, not
only for the production of a wide variety of
regular yarn types from common fibers, but also
for a range of fancy yarns.
Rotor spinning has been adopted worldwide at
present. Its main advantages over ring spinning
are high yarn output rates, reduced production
costs, increased bulkiness and improved evenness
of the yarns. However, the relatively low breaking
strength and wrapper fibers of yarn surface are
still matters of concern (Basu, 2000; Huth et al.,
2002). These disadvantages may be improved by
combining staple fibers with a continuous
filament yarn in rotor spinning process. Some
researchers have studied the spinning conditions
and characteristics of rotor spun composite yarns.
Nield (1977) described a mechanism for
producing open-end-spun core-spun yarns. Cheng
(2000) reported a method of making cover spun
yarns on an open-end rotor spinning frame.
Matsumoto and Pouresfandiari (2002) reported
their progress in producing different kinds of
novel hybrid yarns on an experimental open-end
spinning frame.
In this paper, we introduce a method of producing
a cotton/spandex composite yarn on a modified
open-end rotor spinning frame. Different kinds of
rotor spun cotton/spandex composite yarns are
produced under varying spandex draft ratio and
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RJTA Vol. 9 No. 3 2005
the effects of spandex draft ratio on the structure
and properties of the composite yarns are studied.
Draft ratio of the spandex filament was given by
(composite yarn take-up speed) / (spandex feed
speed).
2.
Experimental
2.1
Spinning Method
Fig. 1. Schematic diagram of rotor spun cotton/
spandex composite yarns spinning
process.
The schematic diagram in Figure 1 showed an
open-end rotor spinning process modified to
allow spandex filaments to be fed into the rotor.
The spandex filament was fed from a supply
bobbin by the filament feed roller, then passed
straight through the filament guide tube and was
drawn into the rotor freely by suction, in which
the spandex filament was combined with the
staple fiber strand to form the composite yarn,
then the composite yarn was drawn through the
doffing tube and finally on to the take-up roller.
The filament guide tube was positioned along the
axis of rotation of the hollow rotor shaft, which
rotated freely about it. The filament feed roller
was able to feed the spandex filament positively
with a wide range of constant feeding speeds.
2.2
Materials and Spinning Parameters
We used two kinds of spandex filaments
(44.4dtex and 77.8dtex) produced by Dupont as
the filament yarns and a cotton sliver (3.7g/m
sliver size) as the staple fiber. The breaking load
and elongation of spandex (44.4dex) was 46.2cN
and 410%, and the breaking load and elongation
of spandex (77.8dex) was 72.4cN and 470%.
Spinning parameters for composite yarns were as
follows: 58tex normal linear density, 617 tpm
designed twist, 7000 rpm opening roller speed,
45000 rpm rotor speed, 72.9 m/min take-up speed,
68.9 staple fibers draft ratio. For a comparison,
we made a normal rotor spun yarn under the same
spinning conditions and it was called C. The draft
ratio and feed speed of spandex filaments were
listed in Table 1.
Table 1. Draft ratio and feed speed of the spandex filaments.
Samples a
Draft ratio
Feed speed, m/min
a
2.3
D1
(D1’)
3
24.3
D2
(D2’)
3.3
22.1
D3
(D3’)
3.5
20.8
D4
(D4’)
3.7
19.7
D5
(D5’)
4
18.2
D6
(D6’)
4.5
16.2
The linear density of spandex filaments in sample D1 to D6 is 44.4dtex, and that in sample D1’to D6’is 77.8dtex.
Testing of Yarn Properties
of 29cN, initial extension of 5%, retention period of
30s, stretched cycle of 10. Irregularity was
measured by YG135G irregularity tester with the
yarn speed of 400m/min and the testing time of 1
minute. Hairiness was tested by Y731 hair tester
with the testing speed of 30m/min and test length of
100m, and the hairs above 2mm per meter was
measured. All the tests were performed under a
standard atmosphere of 20±2℃ and 65±2% RH.
The longitudinal view of composite yarns was
observed by Questar Hi-scope video microscope
system. Breaking strength and extension were
determined by XL-1 tensile tester with a test length
of 500mm, extension rate of 500mm/min and
pretension of 58cN. Elastic recovery ratio was
obtained by AG-10 material tester with a test length
of 100mm, extension rate of 50mm/min, pretension
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RJTA Vol. 9 No. 3 2005
3.
Results and Discussion
3.1
Yarn Morphology
The spandex filament in the rotor spun composite
yarns follows a helical path as shown in figure 2
(b). The spandex filament in the major sections of
composite yarns is covered by the staple fibers,
but in some sections, the spandex filament lies
near the surface of composite yarn and the
morphology is different. When the staple fibers
join the spandex filament in the rotor, the tension
in the staple fibers strand (resulting from the
centrifugal force) is pulling on the spandex and
causing it to deviate from the core. We are
investigating the yarn formation and twisting
mechanism in the rotor during yarn production in
order to improve the appearance and structure of
rotor spun cotton/spandex composite yarns.
Figure 2 shows the magnified longitudinal
photographs of the cotton/spandex composite
yarns and the normal rotor spun yarn. Compared
with the normal rotor spun yarn, the appearance
of the composite yarns is more regular and clearer.
Rotor spun yarn is known to have a skin-core
structure, consisting of a central core that
resembles ring spun yarn, and an outer sheath
containing a random disarray of fibers and
wrappers (Morton & Yen, 1952). The morphology
of wrapper fibers lying near the surface of rotor
spun yarns is relatively loose. Because of the
insertion and wrapping of the spandex filament,
the morphology of wrapper fibers on the cotton
strand surface becomes tighter and clearer than
that of the normal rotor spun yarn.
The spandex filament in the composite yarn is
twisted with the cotton strand and follows a
helical path. According to idealized helical yarn
geometry (Hearle et al., 1965), when a composite
yarn is made from two components, it is
necessary to have different component lengths in
the yarn. If one component is a filament yarn, the
length can be easily controlled by the tension.
During the spinning process of rotor spun
composite yarns, the take-up speed of composite
yarns is higher than the spandex feed speed, so
the spandex tension is greater than the staple fiber
strand tension, and the spandex filament tends to
lie in the inner layer of composite yarns as a core
and can be covered by the staple fiber strand.
(a) Normal rotor spun yarns
(b) Cotton/spandex composite yarns
Fig. 2. Yarn appearance.
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RJTA Vol. 9 No. 3 2005
3.2
Yarn Properties
Table 2. Yarn properties.
Samples
Load,
Elongation,
Irregularity
Thin places
Thick places
Neps
cN
%
Cycle of 1
Cycle of 10
CV, ％
-50%
+50%
+280%
C
831.6
7.3
97.27
96.63
11.86
0
10
2
D1
882.4
7.4
97.26
96.55
10.97
5
5
5
0.50
D2
882.2
7.3
97.30
96.76
11.80
0
5
22
0.44
D3
912.5
7.6
97.34
96.84
10.69
0
2
0
0.00
D4
903.7
7.4
97.56
96.90
11.84
5
15
8
0.28
D5
929.9
7.4
97.29
96.44
11.35
0
8
10
0.54
D6
930.8
7.5
97.26
96.74
11.62
0
10
8
0.70
D1’
889.0
8.0
97.20
96.54
10.18
0
2
5
0.86
D2’
899.6
8.4
97.24
96.64
10.46
0
2
0
0.92
D3’
905.2
8.5
97.36
96.66
10.35
0
2
5
0.38
D4’
920.4
8.2
97.24
96.72
10.30
0
2
0
0.78
D5’
916.4
7.9
97.23
96.63
10.15
0
2
2
1.42
D6’
929.8
8.1
97.18
96.60
10.13
2
2
5
1.04
Elastic recovery ratio, %
Hairiness
19.50
Table 2 lists the properties of cotton/spandex composite yarns and normal rotor spun yarn, which include
tensile properties, elasticity, irregularities and hairiness.
on yarn breaking load.
3.2.1 Tensile Properties
Figure 3 and figure 4 show the effects of spandex
draft ratio on the breaking load and elongation of
cotton/spandex composite yarns. While the
spandex draft ratio increases, both the breaking
loads of composite yarns have a tendency to
increase and the trend of breaking elongation is
not significant. Both the breaking elongations of
cotton/spandex composite yarns are high around
the spandex draft ratio of 3.5. Compared with
Fig. 4. Effects of spandex draft ratio on
yarn breaking elongation.
composite yarn containing fine-denier spandex,
the composite yarn containing coarse-denier
spandex has higher breaking elongation. That is
because the coarse-denier spandex has superior
stretch and elasticity.
The composite yarns show a marked increase in
the breaking load and elongation compared with
the normal rotor spun yarn. The morphology of
wrapper fibers on the surface of the rotor spun
the
Fig. 3. Effects of spandex draft ratio
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RJTA Vol. 9 No. 3 2005
shows the effects of spandex draft ratio on the
elastic recovery of composite yarns at different
stretched cycles. The elastic recovery ratio of
composite yarns with spandex is high around the
draft ratio of 3.5 to 3.7. The spandex has greater
stretch elasticity when its draft ratio increases;
nevertheless, the elasticity declines when the draft
ratio is high. When the spandex draft ratio is low
or high relatively, the elastic recovery ratio of
rotor spun cotton/spandex composite yarns is
slightly less than that of the normal rotor spun
yarn. Maybe this is because that the structure of
composite yarns is not very perfectly. So the
spandex draft ratio is very important to the elastic
recovery of rotor spun cotton/spandex composite
yarns. The elastic recovery decreases when the
stretched cycle increases. This is because
increased extension cycling will cause the
permanent extension to accumulate, thus reducing
the tendency toward elastic recovery.
yarn is relatively loose and they have little
contribution to the yarn strength. During the
formation of composite yarns, owing to the
insertion and wrapping of the spandex filament,
the morphology of wrapper fibers becomes much
tighter and the transverse pressure as well as
cohesive forces among fibers will be increased,
then the breaking load of the composite yarn will
be increased.
3.2.2 Irregularity and Hairiness
(a) Stretched cycle of 1
Figure 6 and figure 7 show the effects of spandex
draft ratio on the irregularities and hairiness of
composite yarns respectively. Both the CV% and
hairiness of cotton/spandex composite yarns are
less than that of the normal rotor spun yarn. The
evenness of the composite yarn is better and its
surface is clearer, that is consistent with the
results obtained from the yarn longitudinal
photographs (as shown in Figure 2). The
improvement of hairiness on the surface of the
composite yarn is great. This phenomenon can be
explained by the wrapping of the spandex
filament on the cotton fiber strand. The evenness
and hairiness of composite yarns with spandex are
better around a spandex draft ratio of 3.5.
Elastic Recovery (%)
98. 0
97. 6
97. 2
Composite Yarn (44.4dtex)
Composite Yarn (77.8dtex)
Normal OE Yarn
96. 8
96. 4
96. 0
2. 8
3. 2
3. 6
4. 0
4. 4
Draft Ratio
(b) Stretched cycle of 10
Fig. 5. Effects of spandex draft ratio
on yarn elastic recovery.
Compared with the composite yarn containing
fine-denier spandex, the composite yarn
containing coarse-denier spandex have less CV%
and slightly more hairiness. As table 2 shows,
when the spandex is coarse, the numbers of yarn
imperfections (thin places, thick places and neps)
are smaller than that of the composite yarn
containing fine-denier spandex.
There is a gradual increase in permanent
extension (decrease in elastic recovery) in
successive cycles of simple extension cycling.
These effects correspond to the same secondary
creep (unrecoverable time-dependent extension)
as the test procedure (Su et al., 2004). Figure 5
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fine-denier spandex, the composite yarns
containing coarse-denier spandex have higher
breaking elongation, less irregularity CV% and a
smaller number of imperfections.
In comparison with normal rotor spun yarn, the
cotton/spandex composite yarns have higher
breaking strength, breaking elongation and elastic
recovery, less irregularity CV% and a lower
degree of hairiness.
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Fig. 6. Effects of spandex draft ratio
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Fig. 7. Effects of spandex draft ratio
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4.
[4]
Conclusions
We have developed a composite yarn spinning
system that produces different cotton/spandex
composite yarns on a modified open-end rotor
spinning frame. The spandex filament in the
composite yarn is twisted with the cotton strand,
and the appearance of the composite yarn is more
regular and clearer than that of the normal rotor
spun yarn.
[5]
[6]
The spandex draft ratio has a great influence on
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hairiness of rotor spun cotton/spandex composite
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around the draft ratio of 3.5.
[7]
The linear density of spandex filament also has
influence on the properties of composite yarns.
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