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
|X1 = Picks per inch
|X2 = Ground pile ratio
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 %)
||Weight loss (%)
|Towel with |
normal yarn pile
|Towel with '0'
twist yarn pile
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
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.
The authors express a deep sense of gratitude to Dr J V Rao, Director, NITRA, Ghaziabad for his constant inspiration, valuable suggestion and permission to publish this research work. Thanks are also due to pilot plant staff and testing laboratory technicians of NITRA for their help in sample preparation.
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Note: For the detailed version of this article please refer the print version of The Indian Textile Journal - Feb 2007.
Mr U C Sharma is Principal Scientific Officer, NITRA, Sector-23, Raj Nagar, Ghaziabad, 201 002. Dr M Madhusoothanan is Professor at the Dept of Textile Technology, Anna University, Chennai.