In India, terry fabrics are manufactured mainly in decentralised
handloom and power looms sectors. Till last decade only 10-15% of total
terry fabric production was produced in organised sector. Most of the
organised sector units are engaged in catering to export market and high
priced domestic market segment. In order to cater to export market, it
is essential that terry fabrics must meet the stringent quality
requirements especially in terms of functional characteristics.
Softness and water absorbency are the most important functional
characteristics. Role of yarn in achieving improved functional
properties of terry fabrics is considered to be primary. It is
well-established fact that yarn TPI plays a vital role in deciding the
softness of the terry fabrics; further lower the TPI higher will be the
fabric softness. Hence in this study, an attempt has been made to
produce terry towels with twistless yarn to have maximum softness. This
study also highlights the methods of producing twistless yarn using
water-soluble PVA filament.
Materials & methods Twistless yarn
For producing twistless yarn, cotton ring spun yarn was wound with a
water-soluble PVA filament yarn in a parallel winding machine. The wound
yarn was twisted in doubler twisting machine. The direction of double
yarn twist was opposite to that of the single spun yarn twist, and the
amount of twist was equal to the twist in the spun yarn. By this
process, the PVA filament wrapped around the cotton yarn and the yarn
was sufficiently strong due to the cohesion given by the filament. The
sequence of process is shown in Figure 1.
Preparation of terry towels
For the preparation of terry towels, three different yarns for ground,
pile and weft were used. For ground warp and weft, commercial ring spun
cotton yarn of 2/20s Ne and 10s Ne were used. For pile, the twistless
yarn was used. The twistless yarns were produced using 10s Ne cotton
yarn and 42 dtex water-soluble PVA filament yarn manufactured by I C
Ltd, Japan. Terry fabrics were produced on plain loom using three-pick
terry weave. Combined scouring and bleaching of all terry fabric samples
was carried out under identical conditions.
During the process, PVA filament yarn was dissolved and as a result the terry fabrics having twistless pile yarn were produced.
Design of experiment
In the present study two independent variables and three levels of each
variable were chosen to conduct the experiments. The parameters selected
as independent variables were: (i) Picks Per Inch (X1), and (ii)
Ground-Pile Ratio (X2). The details of experimental plan are given in
Table 1.
Table 1: Experimental plan
The dependent variables studied were abrasion resistance, fabric
thickness, pile withdrawal force, water absorption in terms of sinking
time, wicking height, water retention and surface water absorption.
Results & discussions
Terry towels developed in the present study were classified into two
groups, namely normal towels and twistless towels. In the case of normal
towel, 10s Ne normal cotton ring spun yarn was used as pile warp and in
the twistless towels, 10s Ne twistless cotton yarn wrapped with PVA
filament was used as pile warp.
Effect on abrasion
The results given in Table 2 show that for the fabrics made out of
twistless yarn, the weight loss is much higher than that of fabrics made
out of ring spun yarn. Even though the pile yarns are held in between
the weft yarns, if the twist level in the yarn is lower as in the
present case, during abrasion yarns can lose fibres easily. Even though,
the twistless fabrics was found to lose about 1.3% weight, the piles
were almost intact and the fabric was found to be usable.
From the Figure 2, it can be clearly seen that as the PPI of the fabric
increases, the weight loss decreases. With the increase in PPI, the
number of pile per unit area increases, and due to this the amount of
abrasion for each pile decreases, thus resulting in lower weight loss.
This probably could be due to the fact that the twists less yarn once
starts abrasion was not able to move away the abrader and present a new
pile yarn.
Table 2: Abrasion (Weight loss %)
Effect on fabric thickness
Results, given in the Table 3, how that the fabric thickness at 2 kpa
load as well as at 5 kpa load is higher for the twistless towels than
that of the normal towels. The reason for higher thickness of twistless
towels may be attributed to the fact that the twistless pile warp yarn,
due to lower packing density, has occupied more volume than that of
normal pile yarn.
Contour graphs given in Figure 3 show that the pile ratio has greater
influence on fabric thickness in case of both kinds of towels. The
reason for increase of fabric thickness is that a longer pile length is
offered to the towels at higher pile ratio. Mansaur et al (1997) also
observed that the thickness of terry towel increases with the increase
of pile ratio.
Effect on pile withdrawal force
The
results given in Table 4 clearly show that the pile withdrawal force is
lower for the towels produced from twistless yarn than the towels
wherein normal yarn was used in pile warp. During the course of testing,
it was observed that the fibres of twistless towel's pile yarn were
opened before the pile was completely with-drawn. The opening of fibres
during testing had shown that twistless pile yarn was not able to
withstand tensile forces exerted on it at the time of testing.
It is clear from Figure 4 that the pile withdrawal force for normal
towel increases with the increase of PPI. The reason for increase in
pile withdrawal force with the increase of PPI is based on the fact that
the gripping forces applied to hold the pile yarn also increases with
the compactness of construction of ground fabric. As the compactness of
fabrics increase with the increase of PPI, the pile withdrawal force is
observed increasing with the increase of pick density.
Effect of washing on fabric stability in terms of pile withdrawal force
Due to open/loose arrangement of fibres in twistless yarn, and the
behaviour of yarn as observed at the time of assessment of pile pulling
force, it was felt essential to study the effect of repeated washing
treatments on fabric stability in terms of pile withdrawal force of
terry towels.
It can be clearly seen from the results given in Table 5 that the pile
withdrawal force of twistless towels yarn is increased after washings.
The increase in pile withdrawal force probably due to the fact that the
loose fibres of twistless pile yarn are interlaced with the other fibres
of yarn.
The interlacement of loose/open fibres of twistless pile yarn prevented
the breakage, to some extent, of pile yarn during testing.
Effect on water absorption Effect on sinking time
It can be observed from the results given in Table 6 that the sinking
time for the twistless towels is lesser than the sinking time for the
normal towels.
The reason for earlier sinking of twistless towels is attributed to the
fact that twistless towels offer more surface area than that of normal
towels to absorb water. Higher surface area in twistless towels was due
to the reason that fibres in twistless pile yarns occupied more volume
than that of the volume of normal yarn.
From the contour graphs (Refer to Figure 5) of normal towels as well as
of twistless towels, it can be observed that sinking time for both kinds
of towels decreases with the increase of PPI and pile ratio. The
contours also show that PPI and pile ratio have almost equal influence
on the sinking time of the normal as well as the twistless towels. The
decrease in sinking time with the increase of PPI and pile ratio is due
to the fact that the surface area of yarn available to absorb water has a
direct relation with pile density and pile length. With the increase of
PPI and pile ratio, to absorb water, available surface area was
increased, and thus sinking time was decreased.
Effect on water retention
The results given in Table 7 show that average water retention capacity
of twistless towels is higher than that of normal towels. The higher
water retention capacity for twistless towels is attributed to the fact
that higher space is available in twist-less yarn piles to retain water.
From the contour graph shown in Figure 6, it can be observed that the
water retention capacity increases with the increase absorption
established that pile density has direct influence over the maximum
water absorption.
Effect on wicking height
Table 8 gives the results of wicking height after 1, 2 and 5 minutes for
the terry towels produced from the normal yarn and from the twistless
yarn.
It can be observed from the results that the wicking height for
twistless towels is lower in comparison to normal towels in almost all
the cases. The reason for lesser wicking height in twistless towels can
be explained with the help of factors involved in the process of
wicking. Wicking is governed with two separate kinds of processes of
which first is physical transportation of water and second is interface
between the fibre and liquid.
Vertical transportation of water depends on size of capillary and
availability of surface area to absorb water. It is a well-known fact
that wicking height increases with the decrease of capillary diameter.
Twistless yarn is more bulky, therefore, capillaries formed in twistless
yarn are of greater diameter than that of normal yarn. Thus lesser
wicking height is observed in twistless towels. This agrees with the
finding of Swani et al (1984) and Lord (1974) that wicking height varies
directly with packing density of fibres in yarn.
From the Figure 7, it can be clearly seen that pile ratio has a greater
influence on wicking height in case of normal yarn towels while incase
of twistless yarn towels PPI and pile ratio have almost equal influence
on wicking height. The reason for more wicking height of towels with
greater pile ratio may be attributed to the fact that area of contact of
towels increases with the increase of pile ratio. This is in line with
the findings of Tarafdar et al (2000) that greater the contact area for
water better is the wicking height.
Effect on surface water absorption
The results of surface water absorption for normal towels and for twistless towels are given in Table 9.
The results given in Table 9 show that the surface water absorption for
twistless towels is better than that of the normal towels. Higher
surface water absorption for twistless towels may be attributed to the
fact that higher surface area (due to bigger diameter of twistless pile
yarn) was available in twistless towels than that of the normal towels.
It is clear from graphs that surface water absorption increases with the
increase of pile ratio for both types of towels. Increase in surface
water absorption with the increase of pile ratio is attributed to the
fact that the surface area available to absorb water is directly
proportional to the free length of pile. Tarafdar et al (2000) and
Srivastava et al (1997, 1998) also observed that surface water
absorption increases with increase of pile ratio
Conclusion
1) Abrasion resistance of twistless towels was lower in comparison to that of normal towels.
2) Thickness of twistless towels was found higher at 2 kPa and at 5 kPa.
This has shown that twistless towels were more bulky and softer than
that of normal towels.
3) Pile pulling force of twist-less towels was found lower than that of normal twist towels.
4) Towel's stability, after 5, 10 and 15 washing cycles in terms of pile-withdrawal force, was found to have increased.
5) Properties relating to water absorbency in terms of rate of water
absorption, ie, sinking time, capacity to absorb water in terms of water
retention and surface water absorption were found better in twistless
towels than that of normal towels.
6) Rate of wick up was lower in twistless towels. This may be attributed
to the fact that the formation of air pockets in zero twist yarn
resisted the wicking process in the fabrics being developed by using
twistless yarn.
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