46 CHAPTER 5 COMPARISON OF DYNAMIC ELASTIC BEHAVIOUR OF SPANDEX BACK PLATED COTTON FABRIC AND SPANDEX CORE COTTON SPUN YARN FABRIC 5.1 INTRODUCTION Spandex core cotton spun yarn fabric and spandex plated cotton fabric production techniques are the most commercial elastic knitted fabric production methods. A spandex core spun yarn is a structure composed of a separable spandex core surrounded by cotton fibre and suitable for use as a yarn (Mahendra Gowda 2006). Normal core spun yarn manufacturing system is used to produce elastic yarn by feeding spandex separately by feed roller arrangement in ring spinning. It is to be feed in the main drafting zone. Input spandex yarn tension and the draft applied to the core fibres decide the quality of the yarn. Yarn resultant count and elasticity is difficult to maintain uniformly throughout the production. Ring spinning machine speed should be reduced for core spun yarn production than the normal yarn production (Ching and Hsiao 2004). Plating technique in knitting is an alternate technique to produce elastic fabric. Elastic fabric can be produced by spandex back plated with cotton yarn in the knitting machine. Bare spandex is directly fed along with normal yarn during knitting. Normal yarn and spandex is passed through the same needle to form a loop and to produce a fabric. Normal knitting machine has special spandex feed attachment at the top of the machine for this plated
47 fabric production (Bayazit 2003 and Ching and Hsiao 2004). The details of the fabric production methods are discussed in the section 3.3.2. Selection of the elastic fabric is important for constructing specific tight fit sportswear, since, the fabric could have the ability to improve or to maintain the stamina of the sports person by offering free body movement and quick recovery. One kind of garment doesn t serve the purpose of all type of sports events; hence, it is necessary to know the dynamic elastic behaviour of the spandex plated fabric and spandex core spun yarn fabric, in order to select the right fabric for right sports event; thus the comparative study was made. The aim of the study is to compare the dynamic elastic behaviour of Spandex Core Cotton Spun yarn knitted fabric (SCCS fabric) and Spandex Back Plated Cotton knitted fabric (SBPC fabric), in order to select a right fabric for tight fit sportswear which improves stamina and power of the sports person. 5.2 MATERIALS AND METHODS Spandex core cotton spun yarn was produced with ring spinning machine and the specifications of the machine are given in Table 5.1. Table 5.1 Ring spinning machine specifications Make Lakshmi Reiter D J/5 (1993) Draft 25 Twists per centimeter 11 Spindle speed (rpm) 18,000 Roving feed hank (tex) 369.06 Spandex count (Denier) 40 Spandex feed (%) 9.5
48 The SCCS yarn was fabricated in 24 gauge, 21 inch diameter, Mayer and Cie circular knitting machine with a speed of 25 rpm. In order to produce SBPC fabric, the 40 denier spandex was back plated with 14.76 tex cotton yarn in the same knitting machine. The spandex feed was kept the same as SCCS fabric and feed tension was observed as 4 cn / tex. The fabrics were subjected to heat setting, dyeing and compacting treatments as mentioned in sections 3.3.2.1, 3.3.2.2 and 3.3.2.3 respectively. 5.3 RESULTS AND DISCUSSION In order to study the suitability of the fabric for tight fit sportswear, a comparative study was made between Spandex Core Cotton Spun yarn (SCCS) and Spandex Back Plated Cotton (SBPC) knitted fabrics with respect to dynamic work recovery and stress at specific extension. 5.3.1 Geometrical Characteristics The finished fabrics were tested (as per section 3.3.3.3) for their geometrical characteristics and are given in Table 5.2. Table 5.2 Geometrical characteristics of SCCS and SBPC fabrics Fabric specifications Wales per centimeter Courses per centimeter Loop density (Loops/ cm 2 ) Loop length (mm) Thickness (mm) Areal density (g /m 2 ) SCCS Fabric 18.50 30.71 568.14 2.63 0.35 285.58 SBPC Fabric 18.11 31.50 570.47 2.58 0.36 292.05 Even though the production method of SCCS fabric and SBPC fabric were different, the geometrical characteristics such as wales per centimeter, courses per centimeter, loop density, loop length, thickness and
49 areal density of both the fabrics have no significant change at 95 % confidence level. 5.3.2 Dynamic Work Recovery These fabrics were tested for their dynamic work recovery at different extension levels such as 20%, 30%, 40% and 50% extension. The effect of fabric method of production and extension levels on dynamic work recovery of the fabrics were analysed by Two way ANOVA statistical tool at 95 % confidence level. From the elastic hysteresis shown in Figures 5.1 and 5.2, the dynamic work recovery was measured for various levels of extension (Table 5.3). The dynamic work recovery of the fabrics increases at 20 to 30% extension level and then decreases from 30 to 50 % extension level for both the fabrics in walewise and coursewise directions. Fabric extension from 20 % to 30% may cause only loop deformation which may not affect the residual energy of the elastane. This is similar to the trend observed as mentioned in the section 4.3.3. So, the fabrics have higher DWR for both walewise and coursewise directions. The fabrics at extensions from 30 % to 50% cause yarn stretch from its loop structure and at this extension level, the elastane in the fabrics reduce its residual energy. SBPC fabric has higher DWR than that of SCCS fabric at both walewise and coursewise directions for all four levels of extension. That is, SBPC fabric has nearly 23% higher DWR in walewise direction and nearly 2% higher DWR in coursewise direction, than that of SCCS fabric. So, SBPC fabric has the benefit of higher DWR values and this reduces the fabric resistance during fabric stretch thereby enhancing the power during recovery.
50 Table 5.3 DWR of SCCS and SBPC fabrics Fabric specifications 20 % 30 % 40 % 50 % SCCS Fabric - Wale 58.68 69.41 57.15 51.01 SBPC Fabric - Wale 78.8 82.10 75.76 71.60 SCCS Fabric - Course 67.72 70.09 65.48 60.06 SBPC Fabric - Course 68.10 70.55 66.67 64.68 The fabric production method and extension level on DWR of the fabrics has significant effect on walewise direction. F observed > F critical at F (1, 3) = 97.78 (for fabric type) and F (3, 3) = 10.85 (for extension level) P <0.05. Effect of fabric type on DWR of the fabric has no significant effect and different level of extension has significant effect on coursewise direction. F observed < F critical at F (1, 3) = 2.75 (for fabric type) and F observed > F critical at F (3, 3) = 11.18 (for extension level) P <0.05. Fabric production method has significant effect on DWR of the fabric in walewise direction. But, there is no effect on coursewise direction. In general, analysis of DWR test results for the knitted fabric is difficult due to the directional effect. If the walewise and coursewise direction have the same effect, then it is easy to interpret the findings. If not, the combination of wale and coursewise directions effect has to be studied, to bring common conclusion. Hence, the ratio of DWR in course wise direction and DWR in wale wise direction has been taken for the study. The fabric production method on ratio of DWR of the fabrics has significant effect. F observed > F critical at F (1, 3) = 58.95, P <0.05.
(a) 20 % (b) 30 % (c) 40 % (d) 50 % Figure 5.1 Elastic hysteresis of SCCS and SBPC fabrics walewise direction 51
(a) 20 % (b) 30 % (c) 40 % (d) 50 % Figure 5.2 Elastic hysteresis of SCCS and SBPC fabrics coursewise direction 52
53 5.3.3 Stress at Specific Stress value of fabric has to be kept as low as possible to minimise the skin strain. So, the assessment of stress value of the fabrics at specific extension levels is an additional measure; therefore, it is important to simulate and evaluate the skin strain during sports performance. The stress value of the fabrics at specific extension levels were observed for the fabrics at both the directions (Table 5.4). Table 5.4 Stress values of SCCS and SBPC fabrics Fabric specifications SCCS Fabric Walewise direction SBPC Fabric Walewise direction SCCS Fabric Coursewise direction SBPC Fabric Coursewise direction 20 % 30 % 40 % 50 % 0.05 0.055 0.072 0.08 0.055 0.07 0.089 0.13 0.05 0.07 0.09 0.113 0.065 0.095 0.12 0.145 SBPC fabric has higher stress value than that of SCCS fabric for both directions at all the four extension levels. That is, SBPC fabric has nearly 25 % higher stress value in walewise direction and nearly 24 % higher stress value in coursewise direction, than that of SCCS fabric. Fabric stress value increases with increasing extension level for both the fabrics in both directions. This may be due to the change in the position of spandex in the yarn structures (In the case of SCCS fabric, spandex is in the core of the yarn structure; in the case of SBPC fabric, spandex is plated with the cotton yarn
54 back side) and frictional resistance of the yarns. The SBPC fabric leads to higher skin strain due to higher stress value than that of the SCCS fabric. The fabric production methods and extension levels on stress value of the fabrics have no significant effect on walewise direction. F observed < F critical at F (1, 3) = 4.95 (for fabric type) and F (3, 3) = 5.56 (for extension level) P <0.05. The fabric type and extension level on stress value of the fabrics has a significant effect on coursewise direction. F observed > F critical at F (1, 3) = 45.10 (for fabric type) and F (3, 3) = 64.96 (for extension level) P <0.05. In order to study the combined effect, the ratio of stress (Coursewise direction) and stress (Walewise direction) have been taken for the study. The fabric type on ratio of stress of the fabrics has no significant effect. F observed < F critical at F (1, 3) = 0.02, P <0.05. 5.3.4 DWR of Spandex Yarn In order to find out the reason for the difference in the DWR and stress value of both the fabrics, spandex yarn was unraveled from both SBPC and SCCS fabrics and analysed their residual energy by calculating their DWR. The spandex yarn was tested for its DWR value using Instron with 5 N load at a speed of 500 m / min, 50 mm gauge length for 10 cycles. Both the spandex yarns were subjected to the extension of 150 %. Spandex yarn was gently unraveled from SBPC fabric. The spandex was bonded with cotton yarn at many places due to annealing effect during heat setting. Similarly, spandex (SCCS) yarn was unraveled from SCCS fabric. It is very difficult to unravel spandex from the core portion of the SCCS yarn. So, the cotton sheath was opened only at top and bottom of the test specimen (at clamped portions). Spandex present in core was only gripped in between clamps during each test. Even though cyclic load was applied to the SCCS yarn, the spandex only got stressed. In order to compare
55 both the spandex yarns unraveled from SCCS and SBPC fabrics, the stress applied on cotton sheath in SCCS yarn was ignored. at 150 % Figure 5.3 DWR of the spandex yarns removed from SCCS and SBPC fabrics From Figure 5.3, spandex unraveled from SBPC fabric has shown higher DWR (92.55 %) than that of spandex of SCCS fabric (79.47 %). Stress value of the SBPC spandex has shown higher value than that of spandex of SCCS yarn at 150 % extension. It was observed that the DWR of the fabric is influenced by the spandex residual energy in the fabric. When residual energy of the spandex is higher, the DWR of the fabric is also higher. This trend reflects in the DWR and stress value of the fabrics.
56 5.4 CONCLUSION The comparative analysis on dynamic elastic behaviour of SBPC and SCCS fabrics was made to assess dynamic garment response during sports activity. It is found that the SBPC fabric has higher DWR than that of SCCS fabric for both walewise and coursewise directions. The stress values of these fabrics have no significant effect. So, the SBPC fabric is preferable than SCCS fabric with respect to DWR, though it gives slightly higher fabric stress due to its insignificance. This objective analysis will help to select a right garment for right sports activity like Javelin, shot-put and athletic sprint.