International Journal of Fiber and Textile Research

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1 Available online at International Journal of Fiber and Textile Research Universal Research Publications. All rights reserved ISSN Original Article Comparative assessment & empirical modeling for aesthetic behavior of vortex & ring yarn knitted fabrics on laundering Dinesh Bhatia 1 and S. K. Sinha 2 Department of Textile Technology 1,2 Dr. B.R. Ambedkar National Institute of Technology, Jalandhar (India) Cell: , E mail: dineshbhatia55@rediffmail.com Received 10 September 2014; accepted 01 October 2014 Abstract Visual presence of a garment or clothing provides physical qualities in relationship with the body. Both functional and aesthetic attributes contribute to the overall performance of the apparel system for a consumer. Development of new technology, materials and newer research is adding to the expectation of the consumer. Aesthetic of any fabric attracts a customer first. The aesthetic of a fabric prior to use can be altered either by changing the raw material or by the type of yarn or by the method of manufacturing the fabric. The spinning system, loop length, yarn linear density, washing cycle were found to have significant effect in influencing the aesthetic properties of knitted fabric. Contribution of loop length and spinning system on spirality was found to be more dominating as compared to linear density and number of washing cycles. Pilling of fabric and dimensional stability, which influence the visual appearance of a fabric, was mainly influenced by the spinning system used as compared to other factors under consideration. Reflectance, which is generally influenced more by the washing cycle, has also been found to be influenced by the spinning system and loop length used in producing the fabric Universal Research Publications. All rights reserved Keywords: Dimensional Stability, Pilling, Ring Yarn, Spirality, Vortex yarn. 1. Introduction As a result of changing lifestyle, the number of features expected from textile products has increased. The clothing industry is under a continuous and unplanned obligation to meet the diverse array of customer demands. Accordingly yarn industry needs to produce diverse, novel and creative yarns. Murata Vortex Spinner (MVS), the latest development in air jet spinning technology targets the apparel sector. High productivity (up to 500m/min), alongwith shortened preparatory stage, possibility of automation, less hairy yarn even from 100% cotton and capability to widen the existing count range from wider fiber length gives premium over the existing air jet spinning system [1]. The properties of fabric are interrelated with the properties of its constituent fibres and yarns. Different spinning systems produce different types of structure leading to a significant difference in the properties. Fibre packing density, arrangement and number of fibres in the yarn structure have significant role in deciding fabric properties [2]. Every garment has a visual presence and provides physical qualities in relationship with the body. Both functional and aesthetic attributes contribute to the overall performance of the apparel system for the consumer. When we go to buy any fabric, the first thing that strikes us is its aesthetic properties. Fabric appearance is always considered to be one of the most important aspects of fabric quality. Testing for fabric appearance is the process of inspecting, measuring and evaluating characteristics and properties of a fabric surface; the purpose of testing and evaluation is to assess the performance of a fabric or predicate its performance in conjunction with its end use. Aesthetic appeal of a fabric can be affected by different parameters viz; spirality (for knitted fabric), pilling propensity, dimensional stability, reflectance etc. Such parameters are also influenced by the constituent fibre properties, yarn structure and fabric structure [3].Ring spinning being the most widely accepted spinning system, it is important to compare the aesthetic behavior of the fabrics made out of vortex yarn to the product made from conventional ring spun yarn. Spirality, a defect in knitted fabrics generally caused due to non-perpendicular disposition of wales with respect to the courses. This can be influenced by various factors related to knitting process [4, 5, 6, 7, 8]. It may appear in grey, washed or finished state and cause serious problem when 62

2 fabric is made up into garments due to shifting of seams, mismatched pattern or even sewing difficulty. Yarn twist liveliness and linear density are also contributed factors. Number of feeder in a machine influence indirectly tightness factor is also a factor apart from contribution from loop length [4]. Spirality, causing due to non-perpendicular disposition of wales with respect to the courses is a dimensional distortion in circular plain knitted fabrics influencing both aesthetic and functional performance of knitted fabrics during use. Pilling is a fault in which entangled fibres cling to the cloth surface during wearing or laundering, giving a poor appearance to the garment. The entanglements of loose fibres forming balls on the fabric surface not only results in an poor appearance, but also initiates the attrition of the garment and causes premature wear [9]. The dimensional instability of a fabric, which is a measure of the extent to which it keeps its original dimensions in the post manufacture processes. The performance and appearance of a fabric changes made from a fabric which is not dimensionally stable and creates serious problem from the point of view of fabric quality control [10]. Light reflectance of a fabric mainly refers to the colour and luster properties.colour is one of the most important factors in consumer acceptance of fabricmaterials. The color appearance of an object depends on the source of illumination,the object s interaction with light and the response of sensors inthe observer s eye to the light reflected from the object [3]. In order to maintain uniform aesthetic appeal of a fabric during use and subsequent laundering, the constituent yarn must offer sufficient resistance to any physical and structural change. The fabric and hence the constituent yarns are subjected to various kind of forces during use and during laundering which may lead to a change in the Table 3.1 Properties of yarns surface structure and hence appearance of the fabric [11, 12]. In the present study, an attempt has been made to study the variation in aesthetic properties of single jersey fabrics from vortex and ring yarn after repeated laundering. An attempt has also been made to develop an empirical model to predict the role of yarn and fabric parameters influencing the aesthetic properties of fabric. 2. Materials and Methods Polyester (38mm and 1.2 denier) and Indian cotton (J-34 variety 29 mm and 4.1mic) were used to produce 40/60 polyester/cotton blended yarns of three different linear densities (24tex, 20tex and 16tex). These yarns were produced on vortex spinning and on conventional ring spinning systems. A total of eighteen single jersey fabrics were prepared from ring (RY) and vortex yarns (VY) using three different loop lengths on a circular knitting machine. The scouring recipe was prepared with soda ash (1%) and non-ionic detergent (0.5%) and the samples were treated in the solution at C for 2.5 hrs maintaining the material to liquor ratio of 1:30. The scoured samples were washed with commercial detergent following AATCC standard. The water level was set at 18± 1 gal and the samples were agitated at the speed of 119 ± 2 rpm for 12 min ±10 s. The spin speed was maintained at 430 ± 15 rpm with the final spin time of 6 min ± 10s. The fabrics were tested for spirality, pilling propensity, dimensional stability and reflectance using standard procedure [13, 14, 15, 16]. 3. Results and Discussion 3.1 Yarn Properties The properties of the yarns are given in Table 3.1. It is observed from the table that the unevenness, imperfections and hairiness of vortex yarn are less as compared to ring yarn. Tenacity elongation and twist liveliness has been found to be more for ring spun yarn. Yarn Structure Linear Density (Tex) Unevenness (U %) Tenacity (cn/tex) Elongation (%) Liveliness (cm) Hairiness Index VY RY VY RY VY RY Aesthetic properties In order to evaluate the effect of individual factors and their interaction on the different aesthetic properties ANOVA technique was employed. From the analysis, contribution of different factors was evaluated using the following expression [17]: Contribution (%) = (SS f df f.v e) / SS T Where, SS f= Sum of square of the factor, df f = Degree of freedom, V e = Mean square of pooled error, and SS T = Total sum of squares Spirality The contribution of loop length, linear density, spinning systems and washing cycles on angle of spirality of fabric was found to be approximately 30%, 24%, 28% and 15% respectively. The effect of loop length on spirality is represented in Fig

3 Figure 3.1 Effect of Loop Length on Spirality Generally, the yarns are stabilized before they are used for knitting. But the process of fabric formation involves imposition of bending and torsional stresses on each loop making it unstable. Relaxation treatment helps such stresses of the yarns to get relieved through readjustment of its position in the structure and shifting from its own position. A structure with higher loop length provides more freedom for readjustment of constituent loops resulting in more spirality [6]. The dependence of yarn spirality with linear density at a particular twist multiplier is represented in Fig The spirality has been found to be inversely related to linear density (tex). Variation in the number fibres in the cross section changes the radial position of fiber in the structure and hence the level of yarn torque. More will be thenumber of fibers less will be the residual torque in the yarn. In a coarser yarn with more number of fibres in the cross section possibility of mutual sharing of torque through readjustment leads to less residual torque. Finer yarn spun Figure 3.3 Effect of Spinning System on Spirality Fibers in ring yarn are arranged in different radial distance. The fibres when travel from one layer to the other due to migration, the helix angle changes. Such arrangement of fibers at different radial distance causes different degree of stress in fibers. The stress alongwith the imparted torsion in the fibers remains stored in fibre making the yarn twist lively. But in vortex spinning, the fibres are arranged in the structure more or less in a parallel fashion wrapped by wrapper fibres [18, 19]. Vortex yarns are less twist lively. Poor migration and low spinning tension internal leads to less stress development in the fibres resulting less twist lively yarn. Spirality is thus, low in vortex spun yarn fabrics. Effect of washing cycles on angle of spirality is represented in Fig It is observed from the figure that the degree of spirality increases with increase in number of cycles. Up to five cycles there is steep increase in spirality beyond which the increase in spirality is relatively less prominent. The asymmetrical stresses imposed on the loops during knitting Figure 3.2 Effect of Linear Density on Spirality at the same twist multiplier is more twist lively and leads to higher degree of spirality [5]. The effect of spinning system on spirality is represented in Fig It has been found that the fabric made out of vortex yarn shows less spirality as compared to that made of ring spun yarn. The arrangement of fibres in the yarn structure also decides the level of stress on individual constituent fibre. In order to relieve the stress the yarn readjusts its position in the fabric and such readjustment causes the wale line to shift with respect to the normal position results spirality. Figure 3.4 Effect of Washing Cycles on Spirality are expected to be released fully during wet processing. During initial cycle release in stress is more which reduces with increase in washing cycle Pilling propensity From ANOVA analysis, it is observed that only spinning system (y) and number of washing cycles (w) affect the pilling resistance/propensity of fabric and contribution of spinning system and washing cycles on pilling of fabric has been found to be approximately 69% and 8% respectively. The effect of spinning system on pilling grade is represented in Fig It has been found that fabric made 64

4 from vortex yarn shows higher pilling grade as compared to fabric made from ring spun yarn. Higher pilling grade refers to good pilling resistance / less pilling propensity. Wrapper fibres in vortex yarn ensure less protruded fibre and hence the fabric generates very less pills as compared to ring spun yarn fabric [20]. Ring spun yarns due to their structure are more hairy as compared to vortex yarn. Pilling is the result of entanglement of surface fibres in presence of abrasive force. Hence presence of less number of protruding fibres in vortex yarn reduces the pilling propensity of the fabric as compared to ring yarn fabric. Figure 3.6 Effect of Washing Cycles on Pilling Grade Dimensional stability It has been observed that all factors viz. spinning system (y), linear density (t), loop length (l) and number of washing cycles (w) affect the shrinkage of fabric.the contribution of loop length, linear density, spinning system and washing cycles on lengthwise shrinkage and widthwise shrinkage are 7% and 35% respectively, 18% and 7%respectively, 11% and 31% respectively and 45% and 20% respectively.the effect of loop length on lengthwise shrinkage and widthwise shrinkage is represented in Fig. 3.7 and 3.8 respectively. Figure 3.5 Effect of Spinning System on Pilling Grade Ring spun yarn is generally more irregular than vortex yarn in terms of mass and twist variation. The mass variation can also influence the twist variation. Presence of a thick place produces a soft twisted part while a thin place produces a hard twisted portion thereby giving a differential fibre integration character. A soft twisted portion of a yarn will have less holding power for its constituent fibres which will easily come out of the surface on abrading. Rubbing the fabric surface by an applied load will produce a frictional force on the fibers. If the frictional forces are greater than the cohesive forces between the fibers, then the fiber will migrate to the surface to form fuzz. In vortex yarn due to the presence of wrapper fibers the cohesive force is greater than frictional force, so there is less chance of formation of pills on fabric surface as compared to ring spun yarn [18, 19, 20]. The effect of washing cycles on pilling grade is represented in Fig 3.6. It has been observed that with increase in number of cycles there is decrease in number of pills. Up to ten cycles its effect is less but after that its effect looks more pronounced. Laundering is done to remove the external particles which are present on the surface of fabric. During laundering abrasion, complex thermal, mechanical and physical actions act on the surface of fabric. Loose fibers get entangled by the applied abrasion to form pills. As the abrasion continues the entangled fibers are eventually broken and the pills break off. When the abrasion continues the source of loose fiber become exhausted so total number of pills decreases. During washing strength of fiber on the surface of fabric get reduced. So there is decrease in number of pills with increase in number of cycles. Figure 3.7 Effect of Loop Length on Lengthwise Shrinkage Figure 3.8 Effect of Loop Length on Widthwise Shrinkage It has been found that with increase in loop length there is increase in shrinkage in both lengthwise as well as widthwise direction. During fabric formation bending and torsional stresses are imposed on each loop which makes the loop unstable. Such stresses needs to be relieved to get a stable structure. But a structure with higher loop length provides more freedom for readjustment of constituent loops resulting in more shrinkage. So there is increase in shrinkage with increase in loop length [10]. The effect of linear density on lengthwise shrinkage and widthwise shrinkage is represented in Fig. 3.9 and 3.10 respectively. It has been found that with increase in linear 65

5 density there is decrease in shrinkage in both lengthwise as well as widthwise direction. When the yarn is coarse, the number of fibres in the cross section is high which facilitates internal redistribution of induced stress among the fibres. When the yarn is fine having less number of fibres in the cross section the possibility of redistribution of stress reduces and accordingly the process of fabric shrinkage helps the dissipation and redistribution of stress to make a stable structure. Figure 3.9 Effect of Linear Density on Lengthwise Shrinkage Figure 3.10 Effect of Linear Density on Widthwise Shrinkage It is clear from Fig there is more lengthwise shrinkage in vortex yarn as compared to ring yarn but widthwise shrinkage is less for vortex yarn as seen from Fig Shrinkage in a knitted fabric can either be due to shrinkage in yarn or due to shrinkage of the structure itself. Shrinkage due to yarn occurs when the yarn having high twist or twist liveliness in yarn is more. A twist lively yarn always shows a tendency to get relieved of the stress induced during torque application. Figure 3.12 Effect of Spinning System on Widthwise Shrinkage If twist liveliness in yarn is more then there is more possibility for yarn to relax. Vortex yarn is less twist lively as compared to ring yarn so chance of shrinkage of yarn in fabric is less for vortex yarn as compared to ring yarn. In single jersey fabric loops are formed in course direction i.e. in width wise direction. So, when yarn shrinkage is more, it leads to increase in width wise shrinkage [20]. The effect of washing cycles on lengthwise shrinkage and widthwise shrinkage is represented in Fig and 3.14 respectively. It has been found that with increase in number of washing cycles there is increase in shrinkage in both longitudinal and transverse directions. Washing is a process of relaxation; the fabric tries to relieve its stress which develops in fabric during knitting. The process of washing allows the fabric to release its stress and by the process it tries to attain a shape of minimum energy which encourages shrinkage [11, 12]. This process continues until the structure comes to fully stable state. So the shrinkage of fabric continues with Figure 3.11 Effect of Spinning System on Lengthwise Shrinkage Figure 3.13 Effect of Washing Cycles on Lengthwise Shrinkage washing cycles, the degree of shrinkage however, reduces as the fabric approaches fully relaxed state. 66

6 Figure 3.14 Effect of Washing Cycles on Widthwise Shrinkage Reflectance percentage The experimental results and subsequent analysis show that washing cycle (50%) and loop length (20%) have more influence on the reflectance of the fabric while linear density (10%) and spinning system (8%) show relatively less influence on reflectance. The effect of loop length and linear density on reflectance is represented in Fig and 3.16 respectively. Both loop length & linear density have been found to maintain an inverse relation with reflectance. With increase in loop length the number of wales/unit length reduces making the fabric structure more open leading to a reduction in the available reflecting surface and lowering fabric reflectance. A finer yarn having more specific surface and accordingly fabric made out of a finer yarn will have more available space for light reflection. Higher back scattering effect in case of finer yarn also results in higher reflectance percentage of fabric [21, 22]. The effect of spinning system on reflectance percentage is represented in Fig It has been observed that fabric made of ring spun yarn shows higher percentage reflectance as compared to fabric made of vortex spun yarn. The packing density of vortex yarn is less as compared to ring yarn. It means inter fibre space available in vortex yarn is more as compared to ring yarn. So back scattering effect in a fabric made from vortex yarn is less as compared to Figure 3.16 Effect of Linear Density on Reflectance (%) Figure 3.17 Effect of Spinning System on Reflectance (%) fabric made from ring yarn. The effect of washing cycles on reflectance percentage is represented in Fig Figure 3.15 Effect of Loop Length on Reflectance (%) Figure 3.18 Effect of Washing Cycles on Reflectance (%) It has been observed that there is decreased in percentage reflectance with increase in number of cycles. As the number of washing cycles increased, the reflectance decreased. The reason was attributed to the deterioration of fabric structure due to opening of surface fibers on washing. Laundering cycles increased the surface roughness of the fabric that lead to the irregular reflection of light and hence the reflectance decreased. 67

7 Table 4.1 Factors with their levels and coded values. Parameters Factor codes Levels Coded Value Spinning system y 2 (VY and RY) -1, 1 Tex t 3 (24, 20 and 16) -1, 0, 1 Loop length l 3 (2.7, 3.2 and 3.7) -1, 0, 1 Washing cycles w 4 (0, 5, 10 and 15) -1, -1/3, 1/3, 1 4. Empirical modeling In the present work, an investigation was made on spirality, dimensional stability and reflectance percentage from ring and vortex yarn fabric. A response surface methodology based on step regression with backward elimination was adopted using MINITAB 16 statistical software for developing a regression equation for aesthetic parameter. Backward elimination is considered to be a very effective tool for selection of variables and the final expression can also be developed in case of multi-colinearity among factors. Here significant terms were retained in the response surface equation by eliminating insignificant terms step-wise at 95% significance level. Through backward elimination, the least important factors are pooled as error and thereby retaining the important factors in the developed model. Factors with their levels and coded values are given in Table 4.1. The regression equations for spirality of fabrics are given below. Spirality angle (vortex) = l t w 0.70w 2 (4.1) Spirality angle (ring) = l t w 0.48w l t (4.2) The regression equation for lengthwise and widthwise shrinkage of vortex yarn fabrics are given below: Shrinkage (Lengthwise) = l t w (4.3) Shrinkage (Widthwise) = l t w l w 2 (4.4) The regression equation for lengthwise and widthwise shrinkage of ring yarn fabrics are given below Shrinkage (Lengthwise) = l t w l^2 0.26w^( 2) 0.23l t (4.5) Shrinkage (Widthwise) = l t w l 2 (4.6) The regression equations for reflectance percentage of fabrics are given below. Reflectance Percentage (vortex) = l t 1.62w t w l t (4.7) Reflectance Percentage (ring) = l t 1.53w 0.32l w 2 (4.8) 5. Conclusions In the present study, an attempt has been made to study the effect of different parameters viz; loop length, yarn linear densities and number of washing cycles to analyze the effect on aesthetic properties in terms of fabric spirality, pilling propensity, dimensional stability and reflectance. The investigation of spirality of fabric revealed that all factors have significant influence on the fabric spirality. The effect of loop length and spinning system was more dominating followed by linear density and washing cycles. The results showed that fabric made from vortex yarn had less spirality as compared to fabric made from ring spun yarn. The pilling propensity of single jersey knitted fabric was observed to be dependent on spinning system. Fabric made of vortex spun yarn showed less pilling as compared to ring spun yarn fabric. Washing cycles, on the other hand, also contributed to pilling of fabric. However, a fall in the number of pills was observed with increase in the number of cycle. It was also found that relaxation shrinkage for single jersey knitted fabric was associated with all factors. Unlike lengthwise shrinkage, the widthwise shrinkage was mostly affected by loop length and spinning system and widthwise shrinkage is more for fabric made of ring spun yarn. Reflectance percentage, which mainly influences the visual appearance, has been found to be affected by loop length and washing cycles while contribution of spinning system and washing cycles was very less. Reflectance percentage for fabric made of ring spun yarn was higher as compared to vortex spun yarn fabric. References 1. Murata Vortex Spinner No.810, Instruction Manual, Muratec, Murata Machinery Ltd, J.W.S. Hearle, P. Grosberg, S. Backer, Structural mechanics of fibers, yarns, and fabrics, John Wiley & Son, Inc, H.U. Jinlian, Fabric Testing, Woodhead Publishing in Textiles Number Y.M. Lau, X.M. Tao, R.C. Dhingra, Spirality in Single-Jersey Fabrics, Textile Asia. 8 (1995) M.D. Araujo, M.D. Smith, Spirality of knitted fabrics: Part 1. The nature of spirality, Text. Res. J. 59(5) (1989) M.D. Araujo, M.D. Smith, Spirality of knitted fabrics: 68

8 Part 2. The nature of spirality, Text. Res. J.59 (6) (1989) P.K. Banerjee, T.S. Alaiban, Geometry and Dimensional properties of plain loops made of rotor spun cotton yarns, Text. Res. J.58(3) (1988) A. Primentas, Spirality of weft-knitted fabrics: Part I- Descriptive approach to the effect, Indian Journal of Fiber and Textile Research. 28 (2003) R.B. Ramgulam, J. Amirbayat, I. Porat, The Objective Assessment of Fabric Pilling, Part I: Methodology, Journal of Textile Institute. 84 (1993) Gadah Ali AbouNassif, Dimensional Stability and Sewing Performance of Single Jersey Knitted Fabrics, Life Science Journal. 10(1) (2013) S.C. Anand, K.S.M. Brown, L.G Higgins, D.A. Holmes, et al, Effect of Laundering on the Dimensional Stability and Distortion of Knitted Fabrics, AUTEX Research Journal. 2(2) (2002) N.A. Kotb, Changes in Knitted Cotton/ Polyester Fabric Characteristics Due to Domestic Laundering Journal of American Science. 8(5)(2012) J. Tao, R.C. Dhingra, C.K. Chan, M. S. Abass, Text. Res. J.67 (1) (1957) IS 10971, Textiles - Determination of fabric propensity to surface fuzzing and pilling Part 1 Pilling Box Method. 15. AATCC Dimensional Changes of Fabrics after Home Laundering. 16. AATCC - Evaluation Procedure 6Instrumental Color Measurement. 17. D.C. Montgomery, Design and Analysis of Experiments, Fifth ed, John Wiley and Sons, New York, A.K. Soe, M. Takahashi, M. Nakajima, Structure and Properties of MVS Yarns in Comparison with Ring Yarns and Open-End Rotor Spun Yarns, Textile Res. J. 74(9) (2004) Y. Beceren, B.U. Nergis, Comparison of the Effects of Cotton Yarns Produced by New, Modified and Conventional Spinning Systems on Yarn and Knitted Fabric Performance, Textile Res. J. 78(4) (2008) H.G. Ortlek, L. Onal, Comparative Study on the Characteristics of Knitted Fabrics Made of Vortex- Spun Viscose Yarns, Fibers and Polymers. 9(2) (2008) B. Rubin, H. Kobsa, S.M. Shearer, Modeling the dependence of fabric reflectance on denier per filament, Textile Res J. 64 (1994) M. Akgun, B. Becerir, H.R. Alpay, (2012) The effect of fabric constructional parameters on percentage reflectance and surface roughness of polyester fabrics,textile Res J. 82 (2012) APPENDIX Table 1 Analysis of variance for spirality (degree) Loop length Linear density Spinning system Washing cycles Loop length* Linear density Loop length*spinning system Loop length*washing cycles Linear density*spinning system Linear density*washing cycles Spinning system*washing cycles Error Pooled error Total S = R-Sq = 98.77% R-Sq (adj) = 97.82% Table 2 Analysis of variance for pilling grade Loop length Linear density Spinning system Washing cycles Loop length* Linear density Loop length*spinning system Loop length*washing cycles Linear density*spinning system Linear density*washing cycles Spinning system*washing cycles Error Pooled error Total S = R-Sq = 92.36% R-Sq(adj) = 86.44% 69

9 Table 3 Analysis of variance for lengthwise shrinkage (%) Loop length Linear density Spinning system Washing cycles Loop length* Linear density Loop length*spinning system Loop length*washing cycles Linear density*spinning system Linear density*washing cycles Spinning system*washing cycles Error Pooled error Total S = R-Sq = 94.72% R-Sq(adj) = 90.00% Table 4 Analysis of variance for widthwise shrinkage (%) Loop length Linear density Spinning system Washing cycles Loop length* Linear density Loop length*spinning system Loop length*washing cycles Linear density*spinning system Linear density*washing cycles Spinning system*washing cycles Error Pooled error Total S = R-Sq = 97.51% R-Sq(adj) = 95.28% Table 5 Analysis of variance for reflectance percentage Loop length Linear density Spinning system Washing cycles Loop length* Linear density Loop length*spinning system Loop length*washing cycles Linear density*spinning system Linear density*washing cycles Spinning system*washing cycles Error Pooled error Total S = R-Sq = 94.39% R-Sq(adj) = 90.03% Source of support: Nil; Conflict of interest: None declared 70