Effect of crease behaviour, drape and formability on appearance of light weight worsted suiting fabrics

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1 Indian Journal of Fibre & Textile Research Vol. 32, September 2007, pp Effect of crease behaviour, drape and formability on appearance of light weight worsted suiting fabrics B K Behera a & Rajesh Mishra Department of Textile Technology, Indian Institute of Technology, New Delhi , India Received 24 March 2006; revised received and accepted 17 October 2006 The total appearance value has been correlated with the crease retention property, drape and formability measured using the simple testing procedures. Fabrics with a low crease recovery angle can tolerate a lower level of formability and have acceptable appearance. However, the fabrics with a larger crease recovery angle require a higher level of formability to achieve the same acceptable appearance. Keywords: Crease recovery angle, Drape coefficient, Fabric appearance, Formability, Light weight fabrics IPC Code: Int. Cl. 8 D03D 1 Introduction Fabric appearance is a major criterion for its consumer acceptance. Fabric tailorability depends largely on its formability. Thus, the formability is a major determiner of the final garment appearance. Pressing performance is yet another important aspect for good aesthetic appeal of a suit. Crease recovery angle can be treated as an index to predict the pressing performance of fabrics. Apart from crease retention property, drapability of a cloth significantly contributes to graceful appearance of a suiting cloth. This is strongly related to the low-stress mechanical properties of the fabric, like bending rigidity. Thus, the measurement of drape and its correlation to the total appearance value of the fabric would make the understanding of the inter-dependence of these parameters more relevant and object oriented. 1 A shift towards the use of light weight suiting fabrics has been observed globally for almost a decade. When fabric areal density decreases substantially, the major appearance attributes which are normally secondary determinants of fabric mechanical properties are significantly affected. Because these attributes, such as drape, crease recovery angle and wrinkle, have direct influence on human vision perception, it is very crucial to study the inter-dependence of creasing, drape and formability to develop fabrics of acceptable appearance level. Creasing behaviour of conventional worsted fabrics has already been established by a To whom all the correspondence should be addressed. behera@textile.iitd.ernet.in several researchers. 2 However, the present trend of light weight suiting fabrics with introduction of various natural fibres has made it necessary to investigate the formability as well as aesthetic properties of these new fabrics. The present study is aimed at examining the use of simple measurement of fabric crease recovery angle and drapability to predict the aesthetic performance of worsted fabrics or the suit made there of. As pressing performance has a greater influence on garment appearance for light weight fabrics as compared to heavy weight fabrics, other fabric properties which may influence tailorability have also been examined. 3 2 Materials and Methods 2.1 Materials Worsted suiting fabrics of non-conventional blends were developed in a wide range of areal densities and compositions, like 100% wool, 100% silk, wool-tassar blends, wool-silk blends, wool/silk blends with natural cellulosic fibres like cotton & linen and wool blends with synthetic fibres. The fabric constructional specifications are given in Table Methods Evaluation of Fibre Properties The fibre tensile properties were evaluated on the Instron tensile tester as per ASTM D Kawabata Evaluation System KES FB2, bending tester was used to measure the bending rigidity of fibres. Paper windows of 10 cm length and 1 cm width were prepared for this purpose (no. of fibres per window, 10 and maximum curvature, 2.5 cm -1 ). Fibre

2 320 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2007 Fabric code Blend Blend % Warp count Nm Table 1 Constructional parameters of worsted fabric samples Weft count Nm EPI PPI Weave Fabric weight gsm A Wool 100 1/40 1/ Plain 120 B Wool 100 2/78 1/ Plain 122 C Wool 100 2/50 2/ /1Twill 160 D Mulberry silk 100 1/20 1/ /1Twill 181 E Mulberry silk 100 1/12 1/ /1Twill 282 F Wool: tassar silk 80:20 1/48 1/ Plain 122 G Wool: tassar silk 80:20 2/100 1/ Plain 124 H Wool: tassar silk 70:30 1/48 1/ Plain 120 I Wool: tassar silk 70:30 2/100 1/ Plain 121 J Wool: tassar silk 60:40 1/48 1/ Plain 128 K Wool: tassar silk 60:40 2/100 1/ Plain 130 L Wool: mul. silk 70:30 1/48 1/ Plain 126 M Wool: mul. silk 70:30 2/100 1/ Plain 125 N Wool: mul. silk 70:30 1/48 1/ /1Twill 130 O Wool: mul. silk 70:30 2/100 1/ /1Twill 132 P Wool: mul. silk 50:50 2/56 2/ /1Twill 160 Q Wool: linen 70:30 2/48 1/ /1Twill 221 R Wool: cotton 65:35 1/20 1/ /1Twill 191 S Mul. silk:linen 80:20 2/60 2/ /1Twill 162 T Wool: PET 50:50 2/38 2/ /1Twill 177 U Wool: nylon 80:20 2/22 2/ /1Twill 311 V Wool: acrylic 32:68 2/52 2/ /1Twill 155 diameter was measured using projectina microscope. Denier value for all types of fibre samples was calculated by taking weight of a known length of fibres using a digital balance Evaluation of Crease Recovery Angle Fabric crease recovery angles were measured in order to examine the pressing performance. Small samples of each fabric were folded and crease pressed using a standard cycle on a crease recovery tester. The samples were trimmed back leaving one centimeter of fabric on one side of the fold. The creases were then allowed to recover for about 30 min and the angle of the crease measured. The angle was measured after recovery under standard conditions (65% RH, 25 C) Evaluation of Drape Coefficient The drape coefficient for the fabric samples is evaluated by using the digital image processing based drapemeter. 4 In this image analysis system, the shadow projected from the fabric is quantified into a binary image after being digitized. The threshold value that sets the criteria for converting a grey scale image into a black and white image can be controlled at the user interface of the system. For this reason, this image analysis method is not influenced by the fabric colour. The digitized binary image is processed with a closing operation which removes noise and segmentizes the shadow image of the draped fabric from the background image. The closing operation is a dilation operation followed by an erosion operation. This operation fills in single pixel object abnormalities. After digitizing the image of the draped fabric, the image analysis system searches the boundary between fabric shadow and central disk on the drapemeter and the boundary between fabric shadow and outer region of the fabric shadow. By using this boundary description, the software calculates the projected area of the central ring on the drapemeter and the projected shadow area of draped fabric. From these calculated values, the drape coefficient is calculated using the following relationship: Drape coefficient =[(A d - A 1 )/ (A 2 A 1 )] 100 where A d is the area of draped fabric image; A 1, the area of the fabric supporting disc; and A 2, the area of the undraped fabric sample Evaluation of Formability The formability is defined as the product of bending rigidity and low stress extensibility. In fact, formability is a measure of the degree of longitudinal compression sustainable by a fabric in a certain direction before fabric buckles. This parameter was

3 BEHERA & MISHRA: LIGHT WEIGHT WORSTED SUITING FABRICS 321 first introduced by Lindberg 1 and since then has been used by various other workers to assess fabric tailorability. 5, Evaluation of Total Appearance Value The total appearance value (TAV) was calculated from the fabric low-stress mechanical properties tested on the KES (Kawabata Evaluation System) instrument. The Kawabata equation for calculating total appearance value is given below 7-9 : 8 TAV = C 0 + [C 1i (P i m 1i )/σ 1i + C 2i (P i m 2i ) 2 / σ 2I ] i=1 where C 0, C 1i and C 2i are the coefficients/constants for the i th parameter; P i, the mechanical property of the i th variable term; m 1i & σ 1i, the population mean and standard deviation; and m 2i & σ 2i, the square mean and standard deviation. 3 Results and Discussion 3.1 Effect of Crease Recovery Angle on Appearance The crease recovery angle in warp and weft directions for various fabric samples along with the TAV obtained from KES results are given in Table 2. Formation of creases in the fabric and recovery there from is largely dependent on the properties of the constituent fibres. Therefore, a study was carried out to analyze the effect of fibre properties on the creasing behaviour. The fabrics being studied are of a variety of blend compositions, e.g. 100% wool, 100% silk, wool:tassar, wool:silk, wool/silk: natural cellulosic fibre and wool:synthetic fibre blends. The fibre dimensional and mechanical properties are depicted in Table 3. It is observed that irrespective of the composition of the fabrics the warp crease recovery angle is negatively related to the total appearance value. That means lower crease recovery angle or high crease retention is related to better appearance. The most noticeable feature is the cut-off in warp crease recovery angle value above which all the fabrics have a poor appearance. This indicates that for the fabric weight range used ( g/m 2 ), an optimum crease recovery angle of about is permissible before the appearance is judged unacceptable. This cut-off is observed for all the fabric compositions. The relationship between warp crease recovery angle and TAV is plotted in Fig. 1. It shows very good negative correlation between warp crease recovery angle and TAV. This clearly reveals that for a very high crease recovery angle of about 170 the fabric becomes unacceptable with Table 2 Effect of crease recovery angle, drape and formability on appearance of worsted fabrics Fabric code Crease recovery angle, deg Drape coefficient Formability, mm 2 TAV Warp Weft Mean % Warp Weft Mean A B C D E F G H I J K L M N O P Q R S T U V

4 322 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2007 Fibre type Average diameter µm Average fibre denier Table 3 Fibre properties Average bending rigidity, cn.cm 2 /tex 2 Average initial modulus cn/den Average extensibility, % Average tenacity cn/den Wool Mulberry silk Tassar silk Linen Cotton Silk comber noil appearance. Crease retention along weft direction is better as compared to warp. This can be attributed to lower bending rigidity of fabric along weft direction due to less thread density and inherent lower bending rigidity of the weft yarns which are almost invariably low twisted, single yarns. On critical examination of the results given in Table 2, it may be observed that the fabrics of similar weight have a limiting creasing angle above which the fabrics exhibit poor appearance. Analysis of the influence of fabric weight on fabric appearance suggests that for a fabric/suit to appear good, light-weight fabrics require a lower crease recovery angle (or good pressing performance) while medium or heavy-weight fabrics can tolerate a higher crease recovery angle (or borderline pressing performance). However, a low crease recovery angle does not guarantee good appearance. Fig. 1 Correlation of warp and weft crease recovery angles with appearance respect to appearance. Most of the fabrics show a warp crease recovery angle between 140 and 160, i.e. the acceptable range for good appearance for light weight suiting fabrics. Similarly, the weft crease recovery angle also is correlated to the appearance of the fabrics under investigation. It shows a similar trend of appearance value in relation to weft crease recovery angle. A lower crease recovery angle in most of the cases is associated with a better appearance value. This is basically dependent on the bending behaviour of the fabrics and the retention of the crease deformation with respect to time. The correlation of weft crease recovery angle and TAV is plotted in Fig. 1. The results show a negative correlation. Majority of the fabrics lie within the range of weft crease recovery angle to have acceptable Crease Recovery as a Function of Fibre Properties The fibre properties play a major role in determining crease behaviour and appearance of fabrics. Basically, creasing and recovery are the functions of fibre bending rigidity. This is also reflected in the results obtained. However, the deviation is observed in linen blended fabrics. This is because of very high degree of orientation of polymeric chains inside the fibre structure, leading to a notoriously bad creasing property. As the crease formation is a complex phenomenon of combination of several forces coming into picture, other properties of the fibre are also taken into consideration. Fibre initial modulus has a significant role in deciding the creasing behaviour as it involves an elastic extension component. The higher the initial modulus the higher is the crease resistance and also higher is the crease recovery. But the exception again is the linen blends because of the dominance of orientation of polymer chains in fibre. During creasing, there is extension on the outer surface and compression on the inner surface along the creasing line. Thus, the fibre extensibility again plays a role in determining crease resistance and recovery.

5 BEHERA & MISHRA: LIGHT WEIGHT WORSTED SUITING FABRICS 323 Higher elastic extensibility is preferable for good crease recovery. Higher fibre tenacity results in better crease recovery. Higher low-stress mechanical properties enhance appearance but crease recovery angle is negatively correlated with appearance value. This opens up a scope to investigate other mechanical and aesthetic parameters to explain fabric appearance. 3.2 Effect of Drape on Appearance Drape or the falling behaviour of the fabrics is strongly related to the appearance of the garments. Hence, a study was carried out to correlate these two parameters for newly developed worsted fabric samples. These results are shown in Table 2. It is observed that for worsted fabrics a lower drape coefficient is favorable with respect to appearance. Drape coefficients of 30-40% are most common in these kinds of fabrics. However, too low value of DC sometimes may prove detrimental to fabric appearance. Lower drape coefficient means limpiness of fabric due to low bending rigidity. Tailoring this kind of fabrics into garments needs utmost care. Thus, an optimum drape coefficient of 35-40% is most acceptable for better appearance of fabric. Figure 2 shows a negative correlation between drape coefficient and TAV and this correlation is apparently poor as compared to crease. However, the fabric appearance depends on other aesthetic attributes and hence drape alone cannot be considered as an index for determining fabric appearance. For many years, textile researchers studied this attribute in order to evaluate the drape quality and improve the drape appearance of garments. Fabric appearance can be more realistically investigated by considering other low-stress mechanical properties. the appearance depends on several other parameters, a more intensive study of fibre properties is essential. Higher initial modulus, tenacity and extensibility improve the low-stress mechanical properties and hence the improved appearance value. These are responsible for a higher drape coefficient as well. Thus, drape alone cannot be considered as a deciding factor for fabric appearance. 3.3 Effect of Formability on Appearance To study the relationship between fabric formability and total appearance value, these two parameters of FAST and KES systems respectively are correlated and analyzed. The study was carried out with respect to warp and weft formability. The formability values measured by FAST instruments are shown in Table 2 and are correlated with TAV. The results show that a higher warp formability is required for better appearance value. This may be attributed to the fact that in case of suiting fabrics a graceful appearance resulting from slightly higher bending rigidity is preferable. However, too high bending rigidity is harmful with respect to other low-stress properties and some times may hamper appearance of fabric as well. Thus, an optimum warp formability of is most favourable with respect to worsted suiting fabrics. The correlation is plotted in Fig. 3. The fact that warp Drape as a Function of Fibre Properties Again the fibre properties can be very well correlated to the drape behaviour. Coarser fibres have higher bending rigidity and lead to higher drape coefficient of fabric but poor appearance value. But, as Fig. 2 Correlation of drape coefficient with TAV for worsted fabrics Fig. 3 Correlation of warp and weft formability with appearance of worsted fabrics

6 324 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2007 Fig. 4 Multiple correlations [the regression equation: TAV = CRA DC(%) formability fabric gsm] formability shows good correlation with total appearance value of the fabric is revealed from Fig. 3. However, as the appearance of a fabric is dependent on so many other attributes, solely formability cannot explain the phenomenon. Studies were also carried out to understand the dependence of TAV with weft formability (Fig. 3). From the results again it is observed that higher weft formability gives better appearance value for the worsted fabrics. However, in general the formability in weft direction is lower as compared to warp way formability. Weft formability also shows a good correlation with the appearance value for most of the worsted fabrics of all compositions. It is observed that for all fabric samples, appearance is dominated by the formability. This may be attributed to the fibre characteristics which are responsible for the bending rigidity and low-stress extensibility of the fabrics Formability as a Function of Fibre Properties Finer fibres for the same linear density of yarn facilitate for more number of fibres in the crosssection, thus a higher specific surface area is available for fibre interaction and this generates more cohesivity between fibres, leading to higher bending rigidity. This increases fabric formability and at the same time a better appearance is achieved due to better low-stress mechanical properties and more uniform structure of yarn developed from finer fibres. Higher initial modulus, tenacity and extensibility are also favourable both for fabric formability and appearance. 3.4 Multiple Correlation between Creasing, Drape, Formability, Fabric Areal Density and Appearance To establish a multiple correlation among all the parameters studied, a regression analysis was undertaken and an equation was derived to study the combined effect of above parameters on total appearance value. The relationship curves and regression equation are shown in Fig. 4. A constant of 6.58 signifies that fabric appearance is determined by many other parameters and a detailed investigation into other low-stress parameters can be further extended. Among the four parameters under investigation, it is found that the formability has got maximum influence on appearance followed by creasing and drape behaviour respectively. However, the fabric areal density is found to have negligible effect on its appearance. 4 Conclusions 4.1 It is observed that irrespective of the composition of the fabrics the crease recovery angle is negatively related to the total appearance value. This indicates that the lower crease recovery angle or high crease retention is related to better appearance. 4.2 The fibre properties play a major role in determining crease behaviour and appearance of fabrics. Basically, creasing and recovery are the functions of fibre bending rigidity. However, the deviation is observed in the linen blended fabrics. This is because of very high degree of orientation of polymeric chains in the fibre structure, leading to a notoriously bad creasing property.

7 BEHERA & MISHRA: LIGHT WEIGHT WORSTED SUITING FABRICS For worsted fabrics a lower drape coefficient is favorable with respect to appearance. Drape coefficients of 30-40% are most common in these kinds of fabrics. However, too low value of drape coefficient sometimes may prove detrimental to fabric appearance. 4.4 Again the fibre properties can be very well correlated to the drape behaviour. Coarser fibres have higher bending rigidity and lead to higher drape coefficient of fabric but poor appearance value. As the appearance of fabric depends on several other parameters, a more intensive study of fibre properties is essential. Thus, drape alone cannot be considered as a deciding factor for fabric appearance. 4.5 A higher formability is required for better appearance value. This may be attributed to the fact that in case of suiting fabrics a graceful appearance resulting from slightly higher bending rigidity is preferable. 4.6 Finer fibres for the same linear density of yarn facilitate for more number of fibres in the crosssection. Thus, a higher specific surface area is available for fibre interaction and this generates more cohesivity between fibres, leading to higher bending rigidity. This increases fabric formability and at the same time a better appearance is achieved. 4.7 An optimum warp formability of is most favorable with respect to worsted suiting fabrics appearance. In case of very light constructions, sometimes a formability lower than 0.25 is obtained which may prove detrimental to appearance. References 1 Lindberg J, Waesterberg L & Svenson R, J Text Inst, 51 (1960) T Biglia U, Roczniok A F, Fassina C & Ly N G, Textile Objective Measurement and Automation in Garment Manufacture (Ellis Horwood Publishers, Chichester, England), 1991, Ly N G, Tester D H, Buckenham P, Rocznniok A F, Brothers M, Iscaysbrook F & Jong S de, Report, IWTO Technical Committee Meeting, Paris, 11 (1988) Behera B K & Pangadiya A, Text Asia, 34 (2003) Mahar T J, Dhingra R C & Postle R, J Text Mach Soc Jpn, 35, (1982) Postle R & Dhingra R C, Proceedings, 6th International Wool Textile Research Conference (The Textile Machinery Society of Japan), 1980, Roczniok A F, Biglia U & Ly N G, Proceedings, 8th International Wool Textile Research Conference (The Textile Machinery Society of Japan), 1991, Niwa M, Kawabata S & Ishizuka K, J Text Mach Soc Jpn, 36 (1983) Inoue T, Niwa M, Yamashita Y, Minamide Y, Inoue D, Ishikawa A & Kawabata S, Int J Clothing Sci Technol, 12 (2000) 205.