Thermo-physiological comfort of compression athletic wear

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 39, June 2014, pp Thermo-physiological comfort of compression athletic wear M Manshahia & A Das a Department of Textile Technology, Indian Institute of Technology, New Delhi , India Received 16 January 2013; accepted 8 March 2013 Thermo-physiological comfort aspects of compression athletic wear have been studied. Core-spun elastane-cotton blended yarns with different elastane proportion, elastane stretch and twist multiplier have been spun and single jersey knitted fabrics are prepared. A three-level three-variable factorial design technique proposed by Box and Behnken has been used to study the interaction effects of the variables on the characteristics of fabrics. The influence of these variables on physical and comfort properties of fabric is studied, the response surface equations for all the properties are derived and the design variables are optimized for various fabric properties. The fabrics become heavier and thicker, and show improved thermal resistance, lower air and water permeability and poor moisture management properties, with the increase in proportion of elastane and level of elastane stretch. Higher twist results in better air and water vapour permeability but lower thermal resistance and wicking. Keywords: Air permeability, Core-spun elastane yarn, Moisture vapour permeability, Overall moisture management capacity, Thermo-physiological comfort, Thermal resistance 1 Introduction Elastane is manmade synthetic fibre which is a linear polymer chain composed of 85% of polyurethane and alternating hard and soft segments linked by urethane bonds. Soft segments provide recoverable stretch ability, whereas hard segments provide sufficient strength and long term stability 1. Knits plated with elastane are tighter and heavier with higher course and wale density as compared to pure spun yarns. Loop length reduces and density increases due to yarn relaxation and elastic recovery of elastane yarn 2,3. Single jersey fabric knitted with core-spun elastane yarn have decreased structural spacing and increased stitch density with fabric tightness which further shows positive correlation with loop length 4. Tightness factor prominently affects the dimensional parameters and linearly correlated to stitch density growth of cotton/ spandex rib and interlock knitted fabric 5. Spandex plated cotton single jersey fabric shows higher level of stretch and better recovery as compared to 100% cotton 6. The amount of elastane has a significant influence on dimensional and elastic properties of plaited fabric. Cotton/elastane plaited plain knitted fabric shows better recovery when a Corresponding author. apurba65@gmail.com elastane is fed at a lower tension with less feeder speed which gives high elastane consumption inside fabric 7. Spandex brand and spandex tightness factor significantly affect the dimensional and physical properties of cotton/spandex knitted structures. Spandex yarn with higher tension values knitted at the same draw ratio gives heavier and thicker fabric with high stitch density but lower permeability to air; however spandex yarns with same elongation values are reported to have same stitch density. Spandex yarn with shorter loop length decreases the fabric width but increases the fabric thickness 8. Dynamic elastic recovery (DER) can assess the instantaneous garment response due to body movement and spandex bare plaited fabrics found to have higher DER than the fabrics knitted from spandex core spun 9. Knits with elastane yarns are less permeable to air than knits with pure yarn and knits with polyamide yarns 10. Elastic yarns cannot absorb water and are non-wettable by liquid sweat, thus reducing the thermo-physiological wear comfort 11. Woven fabric with core-spun elastic yarn with PC blend in sheath has shown better sensorial comfort with improved hand feel and similar thermal comfort which remains persistent with washing cycles 12. Woven light thin fabric with high degree of weft stretch shows better sensorial comfort and same or improved thermophysiological comfort than non stretchable fabric 13.

2 140 INDIAN J. FIBRE TEXT. RES, JUNE 2014 Superior stretch and recovery characteristics of elastic fibre and fabric enhance the freedom of movement, ergonomic comfort, and shape retentions which provide the necessary compression and anatomic fit for compression athletic wear (CAW). Critical physical properties of CAW are air permeability, moisture absorption, wicking ability and thermal insulation 14. Compression garments as a base layer of sportswear increase heat storage which leads to higher sweat rate and higher skin temperature 15. Elastane changes the dimensional characteristics of fabric which can affect its thermo-physiological response. In earlier studies, substantial work has been done to assess the stretch properties and dimensional properties but little work has been done on the study of its effect on thermo-physiological comfort which is equally important for player s performance. Hence, the basic objective of the present work is to study the thermo-physiological comfort aspects of compression athletic wear made from elastane-cotton core-spun yarns. To fulfil this objective, effect of elastane proportion, elastane stretch and twist multiplier on thermal properties, moisture management properties and moisture vapour transmission through fabric has been studied. 2 Materials and Methods 2.1 Materials Fifteen single jersey plain knitted fabrics were prepared using core-spun cotton/elastane yarns. The three level variable factorial design proposed by Box and Behnken was used to study the interactive influence of elastane%, elastane stretch and twist multiplier of core-spun cotton/elastane yarn on thermo-physiological comfort properties of single jersey knitted fabric. The factorial design is given in Table 1 and the corresponding coded values of variables are given in Table 2. Fifteen core-spun yarn samples were spun on ring frame by taking cotton in sheath and 44 dtex elastane in core as per experimental plan as given in Table 1. Single jersey knitted fabric samples were made from these yarns on 14 gauge circular knitting machine at same level of tightness factor. Knitted fabrics were immersed in water containing 0.05g/L standard wetting agent and allowed to relax with minimum agitation for 24 h. Wet relaxed fabrics were washed thoroughly, briefly hydro extracted for 1 min and tumble dried for 60 min at around 70ºC. Samples were then laid on flat surface in a conditioning cabinet of 21ºC±1ºC at relative humidity 65%±2 for 48 h, free of tension. The single jersey knitted fabric details measured were wale density, coarse density, fabric weight per unit area and fabric Thickness. The wales per inch (wpi) and courses per inch (cpi) of knitted fabrics were measured according to the ASTM D-3887 standard. The fabric mass per unit area and thickness were measured according to ASTMD 3776/D 3776M - 09a and ASTM D respectively. The fabric parameters used are given in Table Test Methods Air Permeability Air permeability of the fabric has been measured on TEXTEST FX 3300 air permeability tester at a pressure of 100Pa according to ASTM D737 test method Relative Water Vapour Permeability The relative water vapour permeability (RWVP) determines the water vapour transmission through the fabrics. It has been measured according to ISO11092 standard using Permatest instrument developed by Hes 16. The principle of instrument is heat flux sensing. In this method, test is performed in isothermal condition by maintaining same temperature of the measuring head and atmosphere. Variable Table 1 Box and Behnken design sample plan Standard order X 1 X 2 X Table 2 Range of the variable Level Elastane stretch (X 1 ) Twist multiplier (X 2 ) Lycra, % (X 3 )

3 MANSHAHIA & DAS: THERMO-PHYSIOLOGICAL COMFORT OF COMPRESSION ATHLETIC WEAR 141 Water flows onto measuring head beneath the skin layer and heat is lost due to evaporation of water on to the measuring head. When fabric is placed over measuring head, heat loss is reduced due to resistance offered by fabric to water vapour transmission. The ratio of heat loss from the measuring head with fabric (u 1 ) and without fabric (u 0 ) determines this resistance in terms of relative water vapour transmission. The transfer of water vapour from the measuring head to the atmosphere reaches steady state very quickly (2-3 min) due to the isothermal conditions. RWVP is measured using the following formula: RWVP % = 100 u 1 / u Thermal Resistance The thermal resistance of the samples has been measured using the Alambeta tester 17 developed by Sensora, Czech. This instrument simulates the heat flow from human skin to a fabric during short initial contact in the absence of body movement and external wind flow. The fabric of size mm 2 is placed between hot plate and cold plate at a pressure of 200 Pa. The amount of heat flow from the hot surface to the cold surface through the fabric is detected by heat flux sensors as the hot plate touches the surface of the fabric. The heat flow values are used to calculate the thermal resistance of the fabric. One measurement takes 3-5 min based on the thickness of the material. Ten tests of each sample were performed at different places and average is taken Vertical Wicking Test The vertical wicking performance of fabrics was analyzed using vertical wicking tester according to Table 3 Fabric constructional parameters of samples Sample no. Experimental variables Wales per inch Courses per inch Fabric mass g/m 2 Fabric thickness mm Stretch, % Twist multiplier Lycra, % DIN method. A fabric strip of size 20cm 2.5cm was hanged vertically with its lower end (2.5 cm) immersed in reservoir of distilled water. Water movement through fabric was tracked by adding 1% reactive dye in the reservoir and wicking height was measured after 5 min. Four strips of each sample were tested and average of readings was taken Absorption The absorption capacity of fabric samples was measured by using M/K GATS instrument in accordance with standard test method ISO :2002. The instrument delivers the liquid to a circular porous plate from water reservoir whose weight is continuously monitored. Fabric sample was cut in same size and placed on the porous plate and mass absorbed against time was recorded automatically by the software. Four tests were performed per sample and average of their maximum absorption capacity was taken Moisture Management Properties The moisture management tester (MMT) was used to measure the liquid moisture transport capability of textiles. This instrument consists of upper and lowers concentric moisture sensors and fabric is placed between them. A special solution containing NaCl (0.15 g) was introduced on the fabric top surface to simulate the sweating. When water is transported in a fabric, the contact electric resistance of the fabric will change and this change is related to water content in fabric.

4 142 INDIAN J. FIBRE TEXT. RES, JUNE 2014 A series of indexes were calculated to characterize liquid moisture management performance of fabric such as wetting time, absorption, spreading speed, accumulative one way transport capacity and overall moisture management capacity. Overall moisture management capacity (OMMC) indicates the overall ability of fabric to manage liquid moisture transport which is calculated using the following formulae 18 : OMMC = 0.25BAR + 0.5OWTC +O.25SS b where BAR is the moisture absorption rate of bottom side; OWTC, one way liquid transport capacity; and SS b, the spreading speed of bottom side. 3 Results and Discussion Thermo-physiological comfort characteristics of fabrics are given in Table 4. MINITAB software was used to obtain contour plots. Response surface equations and optimized values of design variables were also evaluated and tabulated in Table Physical Properties of Fabric Physical properties of fabrics are given in Table 3. From surface response equations (Table 5), it is observed that fabric becomes heavier and thicker with increase in elastane% and elastane stretch %, however fabric mass per unit area and fabric thickness are found to be less at higher twist. At higher elastane stretch, elastane core component is at higher stress Sample no. vertical wicking cm Table4 Comfort properties of fabric samples Air permeability cm 3 /cm 2 s RWVP % Thermal resistance km 2 /W Absorption g OMMC Table 5 Response surface equations of fabric samples (using coded values) Property Response surface equation R 2 Optimized values Fabric wieght, g/m X X X X X X X 1 X X 1 X X 2 X 3 Thickness, mm X X X X X X X 1 X X 1 X X 2 X 3 Air permeability cm 3 cm 2 /s Thermal resistance km 2 /W Relative water vapour permeability, % X X X X X X X 1 X X 1 X X 2 X X X X X X X X 1 X X 1 X X 2 X X X X X X X X 1 X X 1 X X 2 X 3 Vertical wicking,cm X X X X X X X 1 X X 1 X X 2 X 3 Absorption, g X X X X X X X 1 X X 1 X X 2 X 3 Overall moisture management capacity X X X X X X X 1 X X 1 X X 2 X X 1 =1.5, X 2 =4.5, X 3 = X 1 =1.5, X 2 =4.5, X 3 = X 1 =1.5, X 2 =4.5, X 3 = X 1 =2.36, X 2 =4.5, X 3 = X 1 =1.5, X 2 =3.62, X 3 = X 1 =1.5, X 2 =3.5, X 3 = X 1 =2.5, X 2 =3.5, X 3 = X 1 =1.5, X 2 =4.5, X 3 =10

5 MANSHAHIA & DAS: THERMO-PHYSIOLOGICAL COMFORT OF COMPRESSION ATHLETIC WEAR 143 level during spinning. After washing, yarns relieve these stresses to great extent as compared to their counterpart, thus result in compact and thicker fabric structure. With higher elastane %, cotton component is less at sheath which is not able to lock the elastane and cause higher shrinkage during relaxation, thus results in higher weight and thickness. Less values of thickness at higher twist may be due to increase in yarn compactness. At higher values of twist, cotton sheath component will be able to hold the elastane core component at its positions which may results in lower shrinkage and low values of fabric mass per unit area. 3.2 Air Permeability Air permeability values of the fabric samples are given in Table 4. From response surface equations (Table 5) and contour plots (Fig. 1), air permeability is found to be less for higher values of elastane stretch and elastane content. This can be explained by fabric shrinkage after knitting due to relaxation of yarn. More shrinkage of yarn at higher elastane and elastane stretch gives compact and thick structure, which results in less open space available for air movement. Higher value of twist shows maximum air permeability, as with the increase in twist, yarn becomes more compact and thus gives large inter yarn pores within fabric, resulting in higher air permeability to air. 3.3 Relative Water Vapour Permeability contour plots (Fig. 2), RWVP is found to increase with the increase in twist multiplier, however it reduces with increase in elastane % and elastane stretch. Moisture vapour can transfer through voids of fabric by diffusion process or through fibre surface by sorption desorption. With increase in elastane %, cotton content in fabric reduces. Cotton is hydrophilic in nature and thus helps in moisture vapour transfer due to sorption desorption process, hence lower cotton content may result in lower permeability to water vapour. Fabric becomes compact with increase in elastane stretch and elastane%, and reduces the void space available for moisture vapour transmission. Due to yarn compactness at higher twist, inter yarn gaps become large within fabric which may help in moisture vapour transmission through diffusion, resulting in higher RWVP. Fig. 1 Effect of variables on air permeability (cm 3 /cm 2 s) Fig. 2 Effect of design variables on relative water vapour permeability (%)

6 144 INDIAN J. FIBRE TEXT. RES, JUNE Thermal Resistance contour plots (Fig. 3), it is observed that the elastane stretch and elastane % significantly affect the thermal resistance. In the present set of experiment, Heat transfer through fabric mainly depends on the thermal conductions, whereas heat loss by convection and radiations are negligible. At higher elastane stretch and elastane %, fabric thickness increases which results in high thermal resistance, as both properties are directly related, as shown below: R=h/ λ, where R is the thermal resistance; λ, the thermal conductivity; and h, the fabric thickness. 3.5 Vertical Wicking contour plots (Fig. 4), liquid moisture transportation in vertical direction is found to be higher for lower twist multiplier and medium range of elastane%. The effect of elastane stretch is found insignificant. At higher level of twist, yarn becomes very compact and some of capillaries get blocked and become unable to transport the liquid moisture. Cotton is hydrophilic in nature and has strong affinity towards water, which helps in easy wetting of structure but it binds the water molecules within the structure, leading to slow transport of liquid in vertical direction. At low level of elastane%, cotton content is high in the fabric, leading to poor wicking. Compact and thick fabric structure at higher elastane% reduces no. of capillary, resulting in slow liquid transport. 3.6 Absorption contour plots (Fig. 5), it has been analyzed that elastane% and twist multiplier significantly affect the absorption of fabric. Absorption capacity of the material depends on the no. of hydrophilic sites present in the material and bulk porosity of the material where water molecules can be trapped. Less absorption capacity of fabric may be due to reduction in cotton content and increase in fabric compactness with increase in elastane %. This reduces the hydrophilic sites and free space available in the material where the water can be entrapped. At higher twist values, fabric becomes thin and reduces the bulk Fig. 3 Effect of design variables on thermal resistance (Km 2 /W) Fig. 4 Effect of design variables on vertical wicking (cm)

7 MANSHAHIA & DAS: THERMO-PHYSIOLOGICAL COMFORT OF COMPRESSION ATHLETIC WEAR 145 Fig. 5 Effect of design variables on absorption (g) Fig. 6 Effect of design variables on overall moisture management capacity space available for the water entrapment, resulting in less water absorption. 3.7 Overall Moisture Management Capacity (OMMC) contour plots (Fig. 6), a significant effect of all variables is observed on OMMC. OMMC is found to be higher for lower values of elastane% and elastane stretch, and higher range of twist multiplier. OMMC predicts the overall capability of fabric to manage the liquid moisture and moisture transfer from one face to another. With increase in elastane% and elastane stretch, fabric becomes compact so less amount of water is transferred from back side to face side. Less absorption and wicking ability reduce the moisture absorption rate and spreading speed of bottom side, resulting in lower value of OMMC at higher range of elastane% and elastane stretch. Inter yarn gap increases due to yarn compactness at higher twist which may increase one way transport capacity, resulting in higher value of OMMC. 4 Conclusion It is observed that with increase in elastane % and elastane stretch, fabric becomes compact and thick with higher thermal resistance and reduced permeability to air and moisture vapour. The wicking height, absorption and overall moisture management capacity are found to be higher for lower range of elastane stretch and elastane%. Yarn twist plays a significant role in determining heat and moisture transfer through fabric. Air permeability, water vapour permeability and overall moisture management capacity increase, whereas wicking height and absorption reduce with increase in twist. References 1 Merdith R, Elastomeric Fibres (Wood head Publication, Cambridge, UK), 1971,21. 2 Abramaviciute J, Mikucioniene D & Ciukas R, Material Sci, 17 (2011) Uçar N, Karaka H & Sen S, Fibers Polym, 8 (2007) Herath C N & Kang B C, Text Res J, 78 (2008) Herath C N & Kang B C, Int J Clothing Sci Technol, 19 (2007) Bayazit M A, Text Res J, 73 (2003) Abdessalem S B, Abdelkader Y, Mokhtar S & Elmarzougui S, J Eng Fibers Fabrics, 4 (2009) Tezel S & Kavusturan Y, Text Res J, 78 (2008) Senthilkumar M & Anbumani N, J Industrial Text, 41 (2011) Čiukas R & Abramavičiūtė J, Fibres Textil East Eur, 18 (2010) 84.

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