Elastic Properties of Spandex Plated Cotton Knitted Fabric

Elastic Properties of Spandex Plated Cotton Knitted Fabric M Senthilkumar, Associate Member N Anbumani, Non-member Mario de Araujo, Non-member The elastic ex and recovery of a fabric is an important property for functional wear, such as, sportswear. It gives a better performance by providing freedom of body movement. It is very important to study the elastic behaviour of knitted fabrics in order to produce body fitted comfortable garments. The objective of this paper is to study the effect of spandex yarn in-put, yarn loop length and spandex yarn linear density on the elastic properties of spandex knitted fabrics. The number of courses and wales/cm, stitches /cm 2, fabric mass /m 2 and fabric thickness of spandex fabrics were higher than those for normal fabrics (knitted without spandex yarn) in all the cases. Selection of spandex yarn in-put, yarn loop length and spandex yarn linear density have significant effects on the elastic properties of spandex fabrics. Spandex fabric growth was lower than that of normal fabrics for all spandex yarn in-put s and loop lengths. The fabric direction of loading plays a significant role on the elastic properties of knitted fabrics. The amount of spandex yarn in-put, the cotton loop length and the spandex yarn linear density are to be optimized for each yarn count, in order to control the cost of manufacture and to obtain the required degree and direction of fabric stretch. Keywords : Spandex/cotton fabric; Plating; Loop length; Spandex in-put ; Knitted fabric NOTATION C : courses/cm W : wales/cm S : stitch density A : g/m 2 T : fabric thickness, mm ESW : fabric elastic stretch in the walewise direction (lengthwise or machine take down ESC : fabric elastic stretch in the coursewise direction (widththwise/ machine width EGW : fabric elastic growth in the walewise direction (lengthwise or machine take down), % EGC : fabric elastic growth in the coursewise direction (widththwise/ machine width T 1 : 5 cn cotton / 2 cn spandex yarn in-put M Senthilkumar and N Anbumani are with the Department of Textile Technology; PSG Polytechnic College, Coimbatore; while Mario de Araujo is with School of Engineering, University of Minho, Campus de Azurem, Guimarães, Portugal. This paper (modified) was received on May 11, 2011. Written discussion on this paper will be entertained till October 31, 2011. T 2 : 7 cn cotton / 4 cn spandex yarn in-put T 3 : 9 cn cotton / 6 cn spandex yarn in-put L 1 : 2.30 mm loop length, cotton L 2 : 3.05 mm loop length, cotton L 3 : 3.70 mm loop length, cotton D 1 : 20 dtex linear density, spandex D 2 : 30 dtex linear density, spandex D 3 : 40 dtex linear density, spandex NF : normal fabric, without spandex INTRODUCTION Stretch fabrics are an important route to achieve comfort by freedom of movement for body fitted sports and outdoor wear. Stretch garments used in athletics and sports may improve the athlete s performance in cycling, swimming and so on. They are also important for inner wear. This type of fabric enables freedom of body movement by reducing the fabric resistance to body stretch. A simple body movement may extend the body skin by about 50% and the fabric must easily accompany the stretch and recover on relaxation. Strenuous movements involved in active sports may require even greater garment stretch. Drastic differences between skin and fabric movement result in restrictions of movement to the wearer. Stretch fiber, yarn and fabric, provide the necessary elasticity for a garment to respond to every movement of the body and return to its original size and shape 9. Volume 92, August 2011 1

The most outstanding properties for stretch sports garments are body fit, moisture management and durability. Furthermore, fabric elastic recovery is as important as fabric stretch. A fabric with good elasticity will enable good sportswear. The degree and direction of the elastic properties determines the end use of stretch garments. Previous research work provides information about the production of stretch yarns with different materials. Modified yarns with elastic stretch use spandex as core and cotton roving as wrapped material in ring 2, rotor and vortex spinning 1. Another method of manufacturing stretch yarns produces highly elastic and complex yarns by using a self -designed, multi-section drawing frame and a rotor twister 4. Normally, stretch yarns are produced by using a core yarn spinning system. Spandex (generic name of Lycra) is used as core and cotton as sheath. Stretch yarn production using core spinning is loosing importance because of the lower production rates achieved in spinning and quality inconsistency (sheath covering effect and dynamic elastic recovery 3 ). In order to overcome the limitations of core stretch yarn production, plating techniques have been adopted in knitting 6. Bare spandex yarns are fed together with normal non-stretch yarns during knitting through a plaiting feeder to form a plaited loop and to produce a stretch fabric. Many knitting machines are also provided with special spandex yarn feeding systems to control yarn in-put. Few studies are available in the literature on the dimensional properties of spandex plated knitted fabrics 5. The current work is a contribution to the study of the elastic properties of spandex plated knitted fabrics to be used in functional sportswear. More specifically, the object of this work is to study the effect of spandex yarn in-put, yarn loop length and spandex yarn count on the elastic properties of spandex plaited knitted fabrics. EXPERIMENTATION Materials A Mayer and Cie knitting machine was used to manufacture the fabrics (Figure 1). The machine characteristics were as follows, diameter = 23 gauge = 24 (needles/circumferential inch), feeders = 74 speed = 30 rpm to 40 rpm. The cotton yarns were fed through a positive feeding system and the spandex yarns were fed by using a special feeding system to assure the control of yarn in-put. Plating feeders assured that the two yarns were plated with the cotton yarn at the technical front and the spandex yarn at the technical back of the fabric. In order to study the effect of the spandex yarn in-put on the elastic properties of spandex/cotton fabrics, a 30 dtex spandex filament yarn was back plated with a 19.68 tex cotton yarn with a 3.05 mm stitch length. The spandex yarn was fed to all feeders in the knitting machine. The cotton and spandex yarn in-put s were varied by setting them at 5 cn and 2 cn (T 1 ), 7 cn and 4 cn (T 2 ), and 9 cn and 6 cn (T 3 ), respectively. In order to study the effect of stitch length on the elastic properties of spandex/ cotton knitted fabrics, the cotton yarn stitch length was varied and set at 2.3 mm (L 1 ), 3.05 mm (L 2 ) and 3.7 mm (L 3 ). The cotton and spandex yarn in-put s were set at 7 cn and 4 cn, respectively. Spandex yarn with three different linear densities, ie, 20 dtex (D 1 ), 30 dtex (D 2 ) and 40 dtex (D 3 ) was fed along with cotton yarn to all feeders in the knitting machine, in order to study the effect of spandex yarn linear density on the elastic properties of spandex/cotton knitted fabric. These three different spandex yarns were back plated with cotton to produce knitted fabrics with a 3.05 mm stitch length and a yarn in-put of the cotton yarn relatively to the spandex yarn set at 7 cn to 4 cn. All three sets of fabrics produced were subjected to heat setting at 205 C. This was followed by H 2 O 2 bleaching and hot brand reactive dyeing in an open winch. After dyeing, the fabrics were once again heat set at 93 C. Finally the fabrics were relaxed for 24 h. The relaxed fabrics were tested for its dimensional and elastic properties. TESTING METHODS Ground yarn Spandex Figure 1 Plain knit spandex /cotton plated fabric structure 5 The spandex/cotton knitted fabrics were tested for their dimensional and elastic properties. The average course and wale density were measure with the aid of a counting glass. The average loop length was measured with the aid of the HATRA course length tester. The fabric areal density was measured using an electronic scale according to method ISO 3801:1977. It was expressed in g/m 2. The fabric thickness was measured with the aid of 2 IE(I) Journal TX

thickness gauge according to method ISO 5084:1996. Fabric areal density and thickness were measured at ten different places in the fabric in each case. Fabric stretch and growth properties were determined in accordance with the ASTM - 2594 procedure. A typical way to undertake the fabric stretch analysis consists of making a loop of the fabric with a certain initial loop length (L 1 ) and then hanging it freely with a dead load of 2.268 kg (five lb) for one min. The change in loop length ( L 1 ) is evaluated and the fabric stretch is calculated. Then the load is removed and the fabric is left free for five min, so that dimensional recovery can take place. Thereafter, the final change ( L 2 ) in loop length is again evaluated with which fabric growth is calculated. Fabric stretch and growth are calculated by using the following equations. Fabric stretch, % = ( L 1 ) / L 1 100 (1) Fabric growth, % = ( L 2 ) / L 1 100 (2) Effect of spandex yarn input, cotton loop length and spandex linear density on elastic properties of spandex/ cotton knitted fabrics were analysed with one way (ANOVA) analysis of variance at 95% confidence level. And normal cotton fabric was compared with spandex/ cotton fabric using t-test statistical tool. RESULTS AND DISCUSSION Effect of Spandex Yarn input Tension The effect of spandex yarn input on the elastic properties of spandex/cotton fabrics, are tabulated in Table 1. The number of wales/cm (W) of the spandex/cotton fabrics is almost equal to that of the normal fabric (100% cotton). However, the spandex/cotton fabrics contract more in the coursewise direction than in the walewise direction when compared with the normal fabric (NF ). Stitch density (S), areal density (A) and thickness (T ) of the spandex/ cotton fabrics are higher than NF. Wales/cm (W ) and courses/cm (C) of the spandex fabrics increased with increasing yarn input. Stitch density of spandex fabrics increases linearly with yarn input. When the spandex yarn input increases, the retractive force of the yarn in the fabric also increases which leads to increased fabric stitch density. There is no significant change in loop length by changing the spandex yarn input Table 1 Effect of the spandex and cotton yarn in-put on the dimensional and elastic properties of the fabric T 1 25.2 14.57 367.04 237 0.36 54.4 56 4 4.8 T 2 28.35 14.96 424.08 270 0.43 63.2 59.2 4 3.2 T 3 28.35 15.75 446.4 267 0.37 60.8 57.6 4 4 NF 17.32 13.39 231.88 125 0.24 27.2 80 5.6 21.6. Changes in dimensional properties without affecting loop length are possible by altering the spandex yarn input in the knitting plating technique. Fabric areal density first increases and then slightly decreases with increasing the yarn input. This is possibly due to a significantly smaller mass of spandex fibre being available per loop with a more stretched spandex yarn. The spandex yarn seems to change the loop shape by contracting the loop dimensions as projected on the plane of the fabric and by increasing the third dimension of the plated fabric. The spandex / cotton fabric thickness was considerably higher than that of normal fabric and it was positively correlated to areal density. The spandex/ cotton fabric stretch or ex was higher in the wales direction and lower in courses direction than normal fabric irrespective of spandex yarn input. Further, the spandex fabric growth was lower than for normal fabric in both directions. The spandex/cotton fabric elastic stretch in the coursewise direction (ESC) and in the walewise direction (ESW) first increases and then decreases with increasing the spandex yarn in-put. Elastic growth or time dependent (elastic) deformation in the course wise direction (EGC) first diminishes and then increases with increasing the spandex yarn input. There is no change in elastic growth in the walewise direction (EGW) with spandex yarn input. It is interesting to note that the spandex/ cotton fabric elastic stretch was higher and the growth lower for medium spandex yarn input in both directions. Mechanical set due to the whole finishing process affects the elastic properties of the fabrics 8. Elastic ex and recovery of knitted fabrics are not influenced by the amount of spandex yarn fed which in turn depends on the spandex yarn input at 95% confidence level. It was found out that normal fabric has 30% higher ex in the coursewise direction than any of the three spandex / cotton fabrics. That is, wales and courses/cm of normal fabric are lower than that of all the selected fabrics. This inter yarn space in the fabric will give freedom of movement. But, the normal fabric has lower recovery than spandex fabric. Higher recovery of the spandex fabrics is mainly due to the presence spandex yarn and its residual energy even after heat set. Table 2 Effect of yarn stitch length on the dimensional and elastic properties of the fabrics L 1 28.35 15.75 446.4 237 0.48 41.6 36 4 3.2 L 2 28.35 14.96 424.08 270 0.43 63.2 59.2 4 3.2 L 3 25.2 14.17 357.12 252.8 0.39 72 75.2 6.4 6.4 NF 17.32 13.39 231.88 125 0.24 27.2 80 5.6 21.6 Volume 92, August 2011 3

Effect of Cotton Loop Length Fabric loop length is a key variable in weft knitting. Loop length is directly proportional to course spacing, wale spacing and inversely proportional to square root of stitch density and tightness factor for fabrics knitted with standard dimensionally stable yarns 7, 8. The effect of cotton loop length on spandex/ cotton knitted fabrics is tabulated in the Table 2. The values of wales / cm, courses/cm, stitch density, areal density and fabric thickness of spandex/ cotton fabrics are higher than for normal fabrics. When the loop length of spandex fabric increases with decreasing the wales/cm, courses/cm, stitch density and areal density. The stitch density of fabric from L 1 to L 2 was not much affected by the increase in cotton yarn loop length. That is why medium loop length has higher areal density. Loop length of fabric increases with increasing the amount of spandex for each single loop. So, the retractive force on the spandex fabric also increases. But, this force does not change the stitch density of the fabric. There is good correlation between calculated and actual areal density. Stitch density negatively correlated with thickness of the spandex fabric. For the normal fabric in the coursewise direction, both the ESC and the EGC are higher than for the spandex/ cotton knitted fabrics. However, in the walewise direction, for normal fabric the ESW was always lower than that of all other spandex/ cotton fabrics and the EGW was higher than that of the spandex/ cotton knitted fabric knitted with the same loop length (L 2 ). As the loop length of the spandex/cotton knitted fabrics increases, the fabric ex or stretch both in the walewise and the coursewise directions also increases. For the spandex/cotton fabrics produced with L 1 and L 2 loop lengths the growth/recovery behaviour is similar in both directions. For the L 3 loop length spandex/ cotton fabric, the growth is higher and therefore the recovery is lower in both the directions, when compared with L 1 and L 2. Effect of Spandex Yarn Linear Density Table 3 shows that the effect of spandex linear density on elastic properties of spandex knitted fabric. The C/cm, W/cm, stitch density, areal density and thickness of spandex fabric was higher than normal fabric in case of all three denier spandex fabric. Table 3 Effect of spandex yarn linear density on the dimensional and elastic properties of the fabrics D 1 25.2 14.96 376.96 211.8 0.366 54.4 76 4 6.4 D 2 28.35 14.96 424.08 270 0.434 63.2 59.2 4 3.2 D 3 29.92 16.54 494.76 282.6 0.36 60.8 51.2 4 2.4 NF 17.32 13.39 231.88 125 0.236 27.2 80 5.6 21.6 The Wales/cm, courses/cm and stitch density of spandex fabric linearly increases with spandex linear density. Higher spandex linear density gives higher retractive force. Stitch density of spandex fabric is positively correlated with areal density. Thickness is first increases and then decreases when increasing the spandex fineness. There is no correlation between areal density and thickness of spandex fabric. Normal fabric ESC and EGC were higher than that of spandex knitted fabrics. But, normal fabric ESW was lower and EGW was higher than that of spandex fabrics from all three spandex linear density. Spandex fabric ESW was first increases and then decreases when the spandex linear density increases in the fabric. But ESC of spandex fabric decreases with increasing spandex linear density in the spandex fabric. EGW of spandex fabric is same for all three spandex fabrics. EGC value of spandex fabric decreases with increasing spandex linear density. High linear density spandex fabric improves the elastic recovery after stress relaxation. It may be due to higher residual energy. Geometrical property of different linear density spandex fabrics does not correlate with its elastic properties. CONCLUSION The direction of loading plays an important role in the elastic properties of knitted fabrics. The wales density, courses density, stitch density, areal density and thickness values of spandex/ cotton fabrics are higher than those for normal fabric in all the cases studied. Spandex/ cotton fabrics have a better recovery from deformation than normal fabric. The spandex yarn input, the cotton yarn loop length and the spandex yarn linear density produce significant effects (at 95% confidence level) on the elastic properties of spandex/ cotton plaited plain knitted fabrics. For the spandex/ cotton fabrics no real trend is found between the spandex yarn input and the elastic properties of the fabrics and this parameter those not seem to produce significant differences amongst the fabrics studied. An increase in fabric loop length increases the stretch or ex of the fabrics in both directions. As concerned growth or unrecovered deformation, loop length only makes a difference, when it is large and in this case it does not help recovery as much in both directions. In the walewise direction, an increase in spandex yarn linear density does not seem to affect growth and there is no real trend for stretch. However, in the coursewise direction, an increase in spandex yarn linear density decreases stretch and increases elastic recovery. The amount of spandex yarn input, the fabric loop length and the spandex yarn linear density have to be optimized for each cotton yarn count, in order to control the cost of manufacture and to obtain the required degree and directional stretch and recovery. 4 IE(I) Journal TX

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