Low stress mechanical behaviour of fabrics obtained from different types of cotton/nylon sheath/core yarn

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1 Indian Journal of Fibre & Textile Research Vol. 34, June 2009, pp Low stress mechanical behaviour of fabrics obtained from different types of cotton/ sheath/core yarn P Pramanik Shri Guru Govind Singhji Institute of Engineering and Technology, Nanded , India and Vilas M Patil a College of Engineering and Technology, Akola , India Received 14 July 2008; revised received and accepted 22 October 2008 Low stress mechanical properties of apparel fabrics prepared from different types of cotton/ (sheath/core) yarns on ring frame and air-jet spinning have been compared and their influence on fabric properties studied. Three different types of crimped filament, namely 30, 44 and 70 denier, are used to prepare different cotton/ (sheath/core) yarns of the proportions 85/15, 75/25, 60/40 respectively on both ring and air-jet spinning systems separately. Total six different sheath/core yarns have been prepared under identical conditions and then converted into plain woven fabrics. These fabrics have been tested on Kawabata instrument and the results are compared with those of the fabrics made from 100% cotton ring-spun yarns. It is observed that the fabric stiffness increases with the increase in synthetic filament part in the sheath/core yarn, irrespective of the spinning process. Total hand value is increased when the filament percentage in the core material is increased. The fabrics obtained from air-jet spinning have more stiffness than that of the fabrics obtained from ring spinning system. Keywords : Air-jet spinning properties, Core yarn, Cotton, Nylon, Ring frame, Low stress mechanical properties 1 Introduction Woven fabrics provide outstanding comfort and hence are preferred as valuable fabrics than many other kinds of clothing. This fact combined with new technological advancements has opened many avenues and approximately 50% of the apparel fabrics used in the world is made from weaving till today. According to Curiskis 1, the quality/handle of fabrics, their tailorbility, appearance and performance in garments are closely related to six basic fabric properties. Low stress mechanical properties such as extension, bending, shear, compression, surface friction and surface roughness, are the basic engineering properties of apparel fabrics which determine the handle of the fabric. The fabrics are generally tested on KES-F Kawabata instruments. The primary hand values are depicted by Koshi (firmness/stiffness), Numeri (smoothness/sleekness), and Fukumari (fullness/loftiness). The predicted primary hand values are then put into translation a To whom all the correspondence should be addressed. patil.vilas@rediffmail.com equation to predict an overall total hand value (THV) for the fabric. Fabric properties, especially bending and compression, significantly influence their handle and draping behaviour. Thierron 2 followed by Subramanian et al. 3 have found that the yarn structure which relates to fibre arrangement within the yarn has an important influence on the bending behaviour of yarns and fabrics. Radhakrishnaiah et al. 4, Pau-lin et al. 5 and Ghosh et al. 6 conducted theoretical and experimental analysis of the bending behaviour of plain weave fabrics and found that when the fabric approaches to jamming condition, rapid increase in bending rigidity is developed. Karolia et al. 7, Soe et al. 8, Grosberg et al. 9 and Grosberg 10 have observed that many conventional yarns and fabric properties can be significantly improved by preferentially positioning component fibres within the yarn. Radhakrishnaiah and Sawhney 4 observed that the woven fabrics made from cotton sheath and polyester staple core yarns exhibit superior handle and comfort properties of fabric as compared to random blended yarn. They found that the yarns produced by homogenous blending (cotton and polyester were

2 156 INDIAN J. FIBRE TEXT. RES., JUNE 2009 processed together through blow room, carding, drawing, roving and ring frame) and staple core spinning system (USDA patent) have significant difference (95 % confidence limit) in major Kawabata values (EMT, LT, WT, RT, G, 2HG, 2HG5, B, 2HB, LC, RC, MIU, MMD, SMD, T 0, 2T 0 ). The cotton/polyester sheath/core yarn is characterised by lower values for bending rigidity (B), compressive resilience (RC), linearity of compression curve (LC), and tensile elongation (EMT). The same yarn also gives higher percentage thickness reduction under compression (EMC) and for tensile modulus (M). The higher EMC value as well as the lower LC and RC values suggest that this sheath/core yarn is softer than random blended yarn. The yarn also shows lower bending rigidity and that is why it is more flexible than random blended yarn. From the work of Thierron 2 on the bending behaviour of ring-spun, rotor-spun and friction-spun cotton/polyester yarns, it is observed that the DREF-3 yarns have much higher flexural rigidity as compared to ring-spun and rotor-spun yarns. He found that the DREF-3 yarn exhibits very little relative fibre movement, owing to the binding action of the highly twisted sheath fibres. This logic is believed to make the core bend more as a beam rather than as individual fibres, thus giving higher flexural rigidity to DREF-3 yarn. The bending rigidity of friction core yarn fabric is more than the 100% cotton ring-spun yarn fabric. In the present study, low stress mechanical properties of plain woven fabrics, prepared by cotton sheath and three different core yarns on two different spinning systems (ring-spun and air-jet) have been compared. The study will help designers of woven fabrics in selecting a particular construction to achieve the best handle and other physical properties of the fabric. 2 Materials and Methods Cotton/ yarn fabrics of three blend ratios 85/15, 75/25 and 60/40 were prepared using cotton sheath and core (crimped filament) of 30, 44 and 70 denier respectively on both ring and air-jet systems. All the six samples (three for ring and three for air-jet) were prepared and compared with 100% cotton fabrics. Using conventional ring spinning process cotton/ sheath/core yarns (hereafter referred as sheath/core) were prepared on ring frame by passing filament through the front roller nip of ring frame 10,11 and one cotton roving through the drafting zone of the ring frame. Three different types of ring core yarns were prepared on ring frame under identical conditions by varying sheath/core ratio as mentioned above. Using same sheath/core ratios and core yarn deniers, another three sheath/core yarns were also prepared on Murata air-jet spinner MJS802 machine 12. Total six different types of sheath/core yarns were prepared on ring and air-jet systems under identical conditions and these were converted into plain weave fabrics. The parameters such as draft and denier of core yarn were changed. The twist multiplier and other spinning process parameters were kept constant. By using same mixing and same machine, 100% cotton yarn was also produced for comparative study. After preparing all single core yarns, 2/20 tex double yarns were made on TFO (Vijay Laxmi) machine under identical conditions. After preparing the double yarns, warping beam was prepared on single end warping machine. Fabrics were woven (plain weave) on Sulzer loom, keeping ends/cm, 27; picks/cm, 23; warp and weft count, 2/20 tex; and nominal fabric weight, 128 gsm unchanged through out the process. Fabrics were finally tested on Kawabata KES-FB tester for different fabric mechanical properties such as tensile, shear (stiffness or ease with which yarns of the fabric slide against each other, resulting in soft/pliable to stiff/rigid structures) and bending (the force required to bend the fabric at 0.1-1cm curvature). Coefficient of friction (MIU) and surface roughness (SMD) were obtained through the different probes. Again compression tests were also measured through another probe. Tests were designed to provide values of linearity (LC), compression work (WC) and resilience (RC). These tests also provide the data for degree of compression, deformation and recovery of the test fabric at 0-50 gf/cm 2. The load registered by the fabrics at 1% elongation (m) is thus taken as a measure of tensile modulus. Tests were conducted under different machine settings as mentioned in Table 1. All the fabrics were conditioned at 65±2% RH and 22±1 C before the measurement. Various low stress mechanical properties tested on Kawabata KES-FB tester are given in Table 2.

3 PRAMANIK & PATIL: LOW STRESS MECHANICAL PROPERTIES OF COTTON/NYLON FABRICS Results and Discussion 3.1 Tensile Strain under Biaxial Extension The tensile properties of sheath/core yarns made from ring and air-jet systems are shown in Table 3. It is observed that all ring-spun and air-jet spun yarns possess significantly higher EMT (tensile strain under biaxial extension) values than 100% cotton yarn. Air- Table 1 Setting of different parameters on Kawabata KES-FB testing machine Parameter Value Compression Rate of compression 0.02 mm/s Area compressed 2.0 cm 2 Bending Rate of bending 0.5cm -1 /s Maximum curvature ±2.5cm -1 Sample size (L W) 20cm 1 cm Tensile Rate of extension Maximum tensile force Sample size (L W) 0.1 mm/s 5 N/cm 5cm 10 cm jet sheath/core yarns show lesser EMT values than the ring-spun sheath/core yarns. As more wrapper fibres are there over the surface and straight filaments in the core of air-jet yarn, the chances of elongation are less as compared to that in ring-spun core yarns. According to Behera and Sardana 18, larger the EMT value, the greater will be the wearing comfort. The value of EMT indicates that 100% cotton is the least extensible yarn than all sheath/core yarns made from either ring frame or air-jet spinning system. All sheath/core yarn fabrics hinder the least to the movement of body part due to their high extensibility and hence all the sheath/core yarns, irrespective of ring-spun or air-jet systems, may provide better tactile comfort than the 100% cotton ring-spun fabric. Airjet fabrics show lesser values of EMT than the ringspun fabrics and hence the air-jet sheath/core fabrics provide lesser comfort than the ring- spun sheath/core fabrics. 3.2 Linearity of Stress-strain Curve Linearity of the stress-strain (LT) curve shows some correlation with the handle of the fabric. Higher value of LT means more elastic recovery of a fabric at a particular load. The higher LT values are always Table 2 Description of test parameters on Kawabata KES-FB testing machine Test Parameter Definition of parameter Unit Compression LC Linearity of compression curve none WC Compression energy at 5kPa pressure J/m 2 RC Resilience or ratio of the energy recovered to energy spent % EMC Thickness compression as a % of original fabric thickness % T o Thickness at 0.5 gf/cm 2 mm 2T o Thickness at 5 gf/cm 2 mm Tensile EMT Tensile strain under biaxial extension % EM Elongation at 5 N/cm tension % LT Linearity of stress strain curve none WT Energy to extend fabric to 5 N/cm tension J/m 2 RT Resilience or ratio of energy recovered to energy spent % M Observed load at 1% extension g Bending B Fabric bending stiffness at 1.0 cm -1 curvature unm 2 2HB Hysteresis at ±0.5 cm -1 curvature mn MIU Coefficient of friction none SMD Surface roughness none

4 158 INDIAN J. FIBRE TEXT. RES., JUNE 2009 Table 3 Low stress mechanical properties of ring and air-jet cotton covered core yarn fabrics Parameter 100% cotton 70den R/F 70den A/J 44den R/F 44den A/J 30den R/F 30den A/J LT RT, % WT, g.cm/cm B, g.cm 2 /cm HB, g.cm /cm G, gf.cm.deg HG, g/cm HG5, g/cm LC WC, gf.cm/cm RC, % MIU MMD SMD, um T o (at 0. 5gf/cm 2 ), mm T o (at 5.0 gf/cm 2 ), mm W, mg/cm EMT, % R/F Ring frame, and A/J Air-jet. better in terms of dimensional stability of the fabric. The fabric sample with 100% cotton presents the highest LT values. As the amount of cotton is reduced the LT value is also decreased. Air-jet sheath/core yarn fabrics show higher value of LT as compared to ring-spun sheath/core yarn fabric. Hence, there is positive indication of higher handle value of air-jet sheath/core yarn fabric. 3.3 Tensile Energy Tensile energy (WT) is measured by the area under the load-elongation curve. It is strongly related with the movement of the body parts in a particular garment and fabric handle. Lower value of WT means that the lower energy is required for deformation, indicating that the fabric will bend easily and its drape is better. The higher the WT value the stiffer is the fabric. Hence, lower WT value of fabric is always better. In this respect, it may be observed from Table 3 that 100% cotton fabric is the best. No trend is observed in WT values when the amount of synthetic filament is increased in the core. 3.4 Tensile Resilience A higher value of RT (tensile resilience) makes the fabric more elastic. In this respect, sheath/core fabric with 70 denier in the core yarn is found to be the best. With the increase in proportion of synthetic component in the core, the recovery value increases, showing a clear trend in ring-spun sheath/core yarn fabric. In the case of air-jet sheath/core yarn fabric, RT values do not change with the increase in in the core but as compared to 100% cotton fabric the air-jet sheath/core yarn fabrics show higher RT value and hence they are more elastic. 3.5 Shear Rigidity Shear rigidity (G) of a fabric depends mainly on the mobility of warp/weft thread within the fabric while the mobility depends on the type of weave, yarn diameter and surface properties of yarn. The lower value of G is preferred for better handle of the fabric as reported by Behera and Sardana 18. A high value of G indicates a paper-like property and causes difficulty in tailoring and discomfort in wearing. It is observed from the study that amongst the ring-spun sheath/core yarn fabrics, the fabric with 70den at the core shows least G values, and as the per cent of increases in the core the value of G decreases. Amongst the air-jet sheath/core yarn fabrics, similarly the fabric with 70den at the core shows lowest value of G which is comparable to ring-spun sheath/core yarn fabrics. It indicates that the

5 PRAMANIK & PATIL: LOW STRESS MECHANICAL PROPERTIES OF COTTON/NYLON FABRICS 159 movement of yarn within its structure is increased with the increasing amount of synthetic component in the core. Therefore, 70 den air-jet and ring-spun sheath/core yarn fabrics show better hand values. But air-jet yarn fabrics show higher values of G as compared to ring-spun yarn fabric. This is because of the more wrapper fibres in the sheath which make the yarn little harsh. But when per cent of synthetic component in the core increases the wrapper fibres are decreased over the sheath and the yarn shows least rigidity. 3.6 Hysteresis of Shear Both 2HG and 2HG5 are the hysteresis of shear force at 0.5 and 5 respectively. The higher the values of 2HG and 2HG5 the lesser will be the recovery from shear deformation and this will create more trouble in tailoring and formation of wrinkle at the wear of the fabric. It is observed from Table 3 that 100% cotton and the sheath/core yarn having more amount of cotton in the sheath show poor recovery from deformation. It is observed that as the synthetic filament percentage in the core is increased the hysteresis losses are gradually reduced. The least hysteresis value is observed for the sheath/core fabric with 70 den in the core due to the presence of more amount of synthetic component in the core. This is observed in the case of sheath/core yarns made through both ring spinning and air-jet spinning systems. The air-jet yarns are more prone to hysteresis losses than the ring-spun cotton yarns, may be due to more bulkiness of yarn. 3.7 Bending Rigidity and Hysteresis of Bending Moment Bending rigidity (B) is a measure of how easily a fabric can be bent. It depends upon the bending rigidity of the yarns and the mobility of threads within the fabric. It is observed that 100% cotton ring-spun yarn shows maximum rigidity and as the cotton percentage is decreased in the sheath/core yarn the rigidity value is decreased. Out of ring and air-jet sheath/core yarn fabrics, air-jet fabric shows more rigidity than ring-spun fabric. Out of all the yarns, 70den filament at the core shows the least bending rigidity and hence expected to be more pliable. Hysteresis of bending moment (2HB) indicates a measure of recovery from bending deformation. A lower value of 2HB is better. In this respect the trend is same as for B value. 3.8 Linearity of Compression and Resilience Linearity of compression (LC), compression energy (WC), thickness at 0.5gf/cm 2 (T o ) and thickness at 5gf/cm 2 (2T o ) are related to the softness of yarn. Lower values of LC and WC and higher values of difference in T o and 2T o indicate softness. Results show that 100% cotton has the least LC and WC values and highest differences in T o and 2T o values. Hence, cotton yarn fabric is supposed to be softer. It indicates that the cotton yarns are subjected to be compressed easily. The behaviour of the fabric with 70 den filament at the core yarn is found to be similar to 100% cotton yarn fabric as far as LC and WC values are concerned, but the same yarn shows the lower difference in T o and 2T o values. The other sheath/core yarn fabrics show no trend considering the LC and WC values. If the difference in T o and 2T o values is considered it is observed that the increase in amount of cotton increases the above values. Because of more crimped fibres in the core yarn, the sheath/core fabric with 70den filament at the core may have the above improved properties. Increase of denier in the core does not show any trend, considering the LC and WC value. Air-jet sheath/core yarns are softer than ring- spun sheath/core yarns as the difference in T o and 2T o values is more. From the above, it is observed that the influence of the difference in T o and 2T o shows a clear trend in every sheath/core yarn. 3.9 Coefficient of Friction Coefficient of friction (MIU) is found to be highest for 100% cotton fabric. Sheath/core yarns having more percentage of cotton in the sheath show higher values of MIU and hence are less smooth.this is observed in both ring-spun yarn and air-jet spun core yarn fabrics Fabric Hand Value and Appearance Value The primary hand values (Koshi, Numeri and Fukurami) and total hand value (THV) of the fabric samples were also estimated. During prediction of primary hand values, all the foregoing parameters are jointly combined and a single hand value is obtained. Air-jet sheath/core yarn fabric shows higher LT value as compared to ring-spun yarn fabrics. Higher LT value is preferable because it gives more elastic recovery and dimensional stability. The difference in T o and 2T o is more for air-jet sheath/core yarn fabrics which indicates more bulkiness and softness as

6 160 INDIAN J. FIBRE TEXT. RES., JUNE 2009 compared to ring-spun yarn fabrics. Considering the other properties, air-jet sheath/core yarn fabrics show the values which are comparable to ring-spun sheath/core yarn fabrics. Considering the above properties, it can be concluded that total hand value of air-jet sheath/core yarn fabrics is higher than that of ring-spun counterparts. Primary hand values jointly give the total hand value of the fabric. It is therefore necessary to discuss the results obtained for both primary hand values and total hand values. Table 4 shows that using crimped filaments, sheath/core ring yarn firmness or stiffness (Koshi) of the fabrics reduces as compared to 100% cotton. No general trend is observed with respect to increase in cotton in the sheath. As such no trend is observed in case of Fukurami values. Fukurami relates to fullness property of the fabric. Here, it is observed that with the introduction of crimped filaments in the core, fullness values are comparable with 100% cotton ring- spun fabric. Fabrics manufactured from air- jet sheath/core yarn are stiffer (Koshi) than their ring counterparts and 100% cotton fabric. This is because of the inherent characteristics of air-jet yarn which itself is stiffer than ring-spun yarn because of more wrapper fibres over the beam of parallel fibres in the core. When the Numeri values are analysed it shows that maximum filaments in the core and fewer cotton fibres in the sheath provide smoother surface than the yarns having more cotton in the sheath. It is observed that 100% cotton yarn and the yarn having only 30den in the core show least Numeri values (rough). It is observed from Table 4 that as the amount of filament in the core increases the total hand value also increases for both ring-spun as well as air-jet sheath/core yarns. In the case of air-jet sheath/core Table 4 Fabric total hand value and primary hand value Fabric THV Koshi Numeri Fukurami 30den R/F den R/F den R/F den A/J den A/J den A/J % cotton yarns, total hand values are higher as compared to ring-spun sheath/core yarns. This is because of the higher Fukurami value (fullness) along with the higher Koshi value (firmness) with comparable Numeri value of the air-jet sheath/core yarn fabrics over the ring-spun sheath/core fabrics. Denier ranging from 44 to 70 in the core of sheath/core yarn fabrics shows comparable total hand value with 100% cotton fabric. The yarns with 70 den filament at the core of sheath/core yarn fabric show the best total hand value for both the ring-spun and air-jet systems. It is also observed that the fabrics made with cotton/ sheath/core yarn on air-jet system show higher total hand value as compared to that made on ring spinning system. 4 Conclusions 4.1 All the sheath/core yarn fabrics provide tactile comfort value which is comparable with 100% cotton ring-spun yarn fabric. The increase in percentage of filament in the core increases the recovery from tensile deformation. Ring- spun sheath/core yarn shows clear trend but air-jet yarn does not show any trend in this respect. 4.2 The increase in percentage of crimped in the core reduces the bending rigidity value; air-jet sheath/core yarn fabrics show higher rigidity than their ring counterparts, and 100% cotton ring-spun yarn fabrics show maximum rigidity values. 4.3 The more the cotton in the sheath the less smooth is the fabric in case of ring-spun sheath/core yarn fabrics, but no clear trend is observed for air-jet sheath/core yarn fabrics. 4.4 When all the properties are considered, it is observed that the increase in percentage of crimped filament in the core increases the fabric total hand value which is comparable with 100% cotton fabric. 4.5 Air-jet sheath/core yarn fabrics also show comparably good hand values like ring sheath/core fabrics, the 70den filament in the core shows highest hand value, even better than 100 % cotton fabric. Industrial Importance: Designing a new fabric having cotton feel and more strong yarn than 100% cotton yarn is possible. Application of new permanent finish on cotton covered surface of filament core yarn will be easily possible rather than difficult task of applying permanent finishes to blended or virgin synthetic yarn surface. Also, there is possibility to prepare cotton covered filament core yarn on air-jet

7 PRAMANIK & PATIL: LOW STRESS MECHANICAL PROPERTIES OF COTTON/NYLON FABRICS 161 spinning system which is very difficult to manufacture. Acknowledgement Authors are thankful to Dr R P Nachane, Sr. Scientist, and Dr Shila Raj, Jr. Scientist, both of CIRCOT, Mumbai, and to Mr. A K Barik, General Manager, RSR Mohata Mill, Higanghat, for their timely help and co-operation during the research work. The authors are also thankful to the All India Council for Technical Education, New Delhi for funding the project. References 1 Curiskis J I, Text Asia, May (1990) Thierron W, J Text Inst, 76, (1985) Subramaniam V, Nalankilli G & Mathivanan V, J Text Inst, 79 (1988) Radhakrishnaiah P & Sawhney A P S, Text Res J, 66 (2) (1996) Pau-lin Chenand Roger L, Baker Gary smith & Barbara, Text Res J, 68 (2) (1998) Ghosh T K, Batra S K & Barker R L, J Text Inst, 81 (1990) Karolia Anjali & Shetti Varsha, J Text Assoc, 6-7 (1999) Aung Kyaw Soe, Takahashi Masaoki & Masaru Nakajma, Text Res J, 69 (2) (1999) Grosberg P & Kedia S, Text Res J, 36 (1966) Grosberg P, Text Res J, 36 (1966) 205, Harper R J & Ruppeenicker G F, Text Res J, 57 (1987) Livsey R G & Owen J D, J Text Inst, 55 (1964) T Oloffson J A, J Text Inst, 55 (1964) T Bhortakke M K, Nishimuraand T & Matsuo T, Text Res J, 69 (2) (1999) Onions W J E & Townend P P, J Text Inst, 58 (1967) Ruppenicker G F, Harper R J (Jr.), Sawhney A P S & Robert K Q, Am Dyest Rep, Jan (1991) The instruction Manual for the Kawabata Evaluation System (KES) Bending Tester Model KES FB 2, DC Kato Tech Co. Japan. 18 Behera B K & Sardana Ajay, Indian J Fibre Text Res, 26 (2001)