Keywords: Eri silk fibre, Wool fibre, Intimate blending, Box-Behnken designing method, Fabric comfort, Fabric handle.

1 STUDIES ON COMFORT PROPERTIES OF ERI SILK AND WOOL BLENDED FABRICS FOR WINTER WEAR APPLICATIONS Brojeswari Das, Naveen V Padaki, Jaganathan K and S. V. Naik Central Silk Technological Research Institute, Central Silk Board, Bangalore Abstract: Eri fibre possesses unique dual nature with excellent strength and softness properties of silk fibre coupled with warmth properties similar to wool fibres. Wool is known for excellent thermal insulation properties. In the present article work has been done to evaluate the impact of blending on thermophysiological and aesthetic comfort of wool/ eri silk blended yarn fabric and also determine the effect of GSM and weave design on the same. Along with the 100 % eri and wool fabric three different eri-wool blended yarns were prepared. The blending was conducted at draw frame. In order to study the effect of simultaneous effect of blend proportion, fabric GSM and weave design, 3 level 3 factorial Box and Behnken designing method was used. Fabric samples were evaluated for mechanical, thermal and aesthetic comfort properties. Low stress mechanical properties of the eri silk and wool blended fabrics have been evaluated using Kawabata Evaluation System (KES). Tensile strength, bending rigidity, wetting and wicking ability of the eri silk / wool blended fabrics are found to improve with the increase in eri silk fibre proportion; whereas thermal insulation values increases with the increase in wool proportion, in case of plain woven fabrics. Present study reveals that by blending eri silk and wool, better fabric properties with respect to tenacity, aesthetic and wear comfort can be achieved while retaining the excellent thermal insulation properties. Keywords: Eri silk fibre, Wool fibre, Intimate blending, Box-Behnken designing method, Fabric comfort, Fabric handle. 1. Introduction Wool has been used from ages in winter wear application, due to its excellent thermal insulation properties. But the discomfort causes due to the

2 scaly surface of wool has always been an issue to the consumer, especially when it is worn next to the skin. Also pure woollen fabrics display poor dimensional stability due to directional frictional effect of the surface scaly structure (Gohl, & Vilensky, 1999). In order to address these issues many work has been done to blend wool with cotton, polyester etc. Present work deals with the blending of eri silk fibre with wool for winter wear applications. Eri silk and wool fibres are both natural protein fibres. Also the fineness, density, strength, cross-sectional shape surface properties and dyeing characteristics of eri silk promises its excellent blending capability with wool fibre (Kulkarni, 2007, Kariyappa et al., 2009; Kariyappa et al., 2014). Eri silk is known for its excellent strength, soft-smooth feel, comfort and luster besides having good thermal behavior (Kulkarni, & Bahuguni, 2011). The blending of eri silk with wool fibre is expected to improve the strength, softness and elegance of the product, providing better comfort feeling. Thermophysiological comfort, aesthetic comfort, pilling behaviour, surface and strength properties are very important properties, in deciding the performance behaviour of a winter wear clothing. Along with the blend proportion fabric weight (gsm) and weave design (interlacement index) is expected to have important influence on these properties. Present work focus to evaluate the impact of blend proportion of eri silk and wool fibre, along with fabric GSM and weave design on the thermophysiological and aesthetic comfort properties of wool/ eri silk blended fabric and optimization of those parameters to achieve the required properties, as per the end use requirement. 2. Materials and methods 2.1 Materials Eri silk and wool fibre was procured from Ms. Karim Silks, Karnataka and Ms. Jayashree Textiles, West Bengal respectively. Eri silk and wool fibre of similar length and micron has been used for preparation of the blended

3 yarns. Details of the procured eri silk and wool fibre have been given in Table 1. Table 1 Properties of eri silk and wool fibres Eri silk Fibre Parameters Wool fibre fibre Average fibre length, cm 11.4 (10.2) 12.1 (11) Fibre diameter, micron 20.6 (9.7) 19.4 (11.5) (CV%) Spinning has been carried-out in worsted spinning system (long staple fibre spinning). Fibre blending was done in draw frame stage. Along with the 100 % eri and wool, three different eri-wool blended yarn have prepared. Details of the developed blended yarn have been given in Table 2. Table 2 - Details of developed eri silk and wool fibre blended yarn Yarn Sample Code Yarn count (Nm) Tenacity (cn/tex) Elongation % Blend Proportio n (Eri:Wool ) Actual blend proportion (Eri:Wool) W100 0:100 2/81.4 (3.5) 8.1 (10.2) 16 (8.5) 0:100 WE1 33:67 2/97.6 (2.2 11 (8.8) 12 (23.4) 32:68 WE2 50:50 2/91.2 (2.1) 12.3 (7.9) 13 (15.3) 52:48 (2.1) WE3 67:33 15.4 2/93.0 (3.7) (11.7) 13 (10.7) 64:36 (1.5) E100 100:0 2/81.6 (1.6) 22.2 (6.9) 17 (17.4) 100:0 (CV%) As per the objectives of the research work, 2 sets of fabric samples were prepared using the developed yarns. In order to determine the effect of blend proportion only on fabric properties, 5 plain woven fabric samples were prepared using the above mentioned 5 yarns, as given in Table 2. Details of the first set of fabrics have been given in Table 3. In order to evaluate the simultaneous effect of blend proportion along with fabric GSM

4 and weave design (interlacement factor), another set of fabric samples (15 Nos.) were prepared using 3 level 3 factorial Box-Behnken designing method. WE1, WE2 and WE3 have been used for this purpose. Details of the second set of fabrics have been given in Table 3. Developed fabric samples were washed with 1 gpl neutral soap solution at 60-70 0 C for 30 mins, rinsed twice and then dried in relaxed state at atmospheric temperature to remove any traces of finish. Prior to testing, all the fabric samples were conditioned in standard atmospheric condition (65±5 % R.H. and 20±2 0 C temperature) for 48 hr. Sample No. Table 3 Constructional details of developed eri silk and wool blended fabric (1 st set of fabric) Blend Planne Weave Reed EPI PPI Thickne proportion d GSM Design ss (mm) (ERI:WOOL) Actual GSM 1 0:100 170 Plain 76 77 55 0.47 182 2 33:67 170 Plain 76 76 58 0.43 165 3 50:50 170 Plain 76 78 57 0.43 172 4 67:33 170 Plain 76 76 58 0.42 160 5 100:0 170 Plain 76 77 55 0.43 175 Table 4 - Constructional details of developed eri silk and wool blended fabric as per Box-Behnken designing method Sample No. Blend proportion (Eri:Wool) Planned GSM Weave Design Reed EPI PPI Thickness (mm) Actual GSM 1 33:67 130 Twill 48 48.80 49.20 0.47 136.36 2 67:33 130 Twill 56 58.80 65.60 0.46 148.60 3 33:67 170 Twill 76 75.33 58.00 0.50 170.60 4 67:33 170 Twill 76 77.20 58.00 0.50 168.20 5 33:67 150 Plain 56 58.33 59.33 0.43 143.80 6 67:33 150 Plain 56 59.20 59.20 0.38 131.40 7 33:67 150 Satin 56 58.33 57.67 0.56 154.62 8 67:33 150 Satin 56 59.60 84.00 0.53 158.80 9 50:50 130 Plain 48 48.67 48.40 0.41 124.08 10 50:50 170 Plain 76 78.00 56.80 0.43 171.67

5 11 50:50 130 Satin 48 49.00 48.33 0.58 136.79 12 50:50 170 Satin 76 77.20 60.80 0.59 189.94 13 50:50 150 Twill 56 58.67 58.67 0.45 146.93 14 50:50 150 Twill 56 58.67 58.67 0.45 146.93 15 50:50 150 Twill 56 58.67 58.67 0.45 146.93 Interlacement index of the developed fabrics, Plain 2, 2/2*1/1*1/1 Twill 1.5, 4 end satin 1. 2.2 Testing Methods 2.2.1 Fabric constructional parameters The fabric constructional parameters evaluated were: thread density (ends per inch EPI) and picks per inch PPI), fabric weight per unit area and fabric thickness. Warp and weft densities were measured according to the ASTM D3775-03 standard, using the counting glass. Yarn linear density and fabric weight per unit area were determined according to ASTM D1059 standard using electronic weighing balance. The thickness of the fabrics was measured according to ASTM D1777-96 standard using gauge type thickness tester (Maker Techno Instrument) at a pressure of 100 Pa. Standard atmospheric conditions have been maintained for all experiments. 2.2.2 Dimensional stability test (Shrinkage) Fabric dimensional stability with respect to shrinkage test was conducted as per IS 3561: 1989 standard test method. For each variety of fabric, 5 replications were taken. Dimensional changes of specimens are calculated separately in each direction. Degree of shrinkage (expressed in %) was calculated using the following formula: Dimensional change, % =100(b-a)/a Where, a = mean original dimension before treatment for each test specimen. b = mean final dimension after treatment for each test specimen. 2.2.3 Tensile properties Tensile strength (breaking load-kg) and elongation (%) of the fabric samples were tested using Instron Tensile Tester as per IS 1969:1985: Ravelled strip test method.

6 2.2.4 Fabric stiffness Fabric stiffness was tested using Prolific Stiffness Tester as per IS 6490:1971 test method. Flexural rigidity of the fabric was then calculated, as per the formula given below. Flexural rigidity (dyne.cm) = Where, W is weight g/m2 of the fabric and L is bending length in cm. Over all Flexural rigidity of the fabric (G 0 ) = Where, G1 is Flexural rigidity of the fabric in warp direction and G2 is Flexural rigidity of the fabric in weft direction. 2.2.5 Low stress mechanical properties Low stress mechanical properties, including tensile, shear, bending, compression, roughness and friction of the fabric samples were measured on a Kawabata fabric evaluation system (KESF) under the following testing (tensile, bending, compression and surface property) modules. In addition to these properties, fabric weight per unit area (W); mg/cm 2 and fabric thickness (T), in mm are also reported in KESF system. Using the values of those 16 low stress mechanical properties, fabric Total Hand Value (THV) as slacks and as winter dress were estimated, using the Kawabata system of equations [4]. 2.2.6 Drape coefficient % Drape testing is carried out as per as IS 8357:1977 test method. The drape coefficient is calculated as the ratio of the projected area of the drape specimen to its theoretical maximum, as per formula given below - Drape co-efficient % = Where, A - Area of circle of 25 cm diameter, a - Area of circle of 12.5 cm diameter, w mass of drape pattern and W Mass / area of ammonia paper, used for drape testing.

7 2.2.7 Crease recovery Crease recovery properties of the fabric samples were determined by measuring the Crease recovery angle following IS 4681: 1981 standard using Crease Recovery Tester (Maker Toyoseiki, Tokyo). 2.2.8 Pilling resistance Resistance to pilling plays a very important role to determine the wear ability of clothing. Pilling resistance of the eri silk / wool blended fabrics were tested using Paramount digital pilling tester following BS 5811:1986 standard. 2.2.9 Thermal insulation Thermal property of the samples was tested on Alambeta instrument by following ASTM standard D1518. Thermal resistance of the fabrics measured by this instrument has been given in the consecutive section. The testing was conducted at Indian Institute of Technology, Delhi. 2.2.10 Air permeability Prolific inclined tube manometer was used for testing air permeability of the fabrics as per ASTM D737:1981 test standard. 2.2.11 Water vapour permeability Water vapour permeability through fabric samples was determined in PERME W3/330 Water Vapor Transmission Rate Test System, as per ASTM D1653 standard. This tester measures the water vapour transmission rate based on gravimetric method (cup method). Test results were received in terms of transmission rate in g/(m 2.day) and transmission coefficient in g.cm/cm 2.s.Pa. 3. Results and discussion Results obtained from shrinkage testing are plotted in Figure 1. It can be observed that blending of these fibres has marginally increased the shrinkage in the fabric in warp direction with highest shrinkage noticed in case of 50:50 wool and eri silk blended fabrics. Difference in shrinkage values is not significant in the weft direction for all the samples.

Shrinkage % 8 Effect of blend proportion on tensile properties of the fabric has been given in Figure 2. From the results, it is observed that with the increase in eri silk proportion maximum load bearing capacity of the fabric increases, where as for elongation it has been observed that 100 % wool fibre fabric is having higher elongation, comparative to the other blends, but no significant difference has been observed among other samples. Warp way Weft way Figure 1. Shrinkage in Eri silk and Wool blended fabrics (a) Tensile strength (b) Elongation Figure 2 Tensile properties of Eri silk and wool blended fabrics Effect of blend proportion on air and water vapour permeability of the fabric has been given in Figure 3. From the results, it is observed that even with the similar constructional parameters, fabric sample with 100 % eri silk has shown very less air permeability compared to 100 % wool and other blended fabric samples, this may be due to the flat fibre structure

9 (rectangular and elongated fibre cross section) of eri silk fibre, which has caused more compactness in the fabric structure. Whereas, water vapour permeability index, as determined by dish method, has been observed to increase with the increase in eri silk proportion, which signifies that at higher percentage of eri silk proportion fabric will be more breathable. (a) Air Permeability (b) Water vapour permeability Figure 3 Transmission properties of Eri silk and wool blended fabrics Effect of blend proportion on wetting and wicking properties of the fabric has been given in Figure 4. From the results, it is observed that, 100 % wool has not shown any wetting to liquid water. Incorporation of eri fibre through blending has improved the wettability and wickability of fabric sample. With the increase in eri proportion time requires for spreading of the water drop reduces. Same trend has been observed in the wicking test as well, wicking height at 10 min has been observed highest in case of 100 % eri silk fabric, followed by the fabrics with 67% eri, 50 % eri and 33 % eri silk.

10 (a) Wettability (b) Wickability Figure 4 Wetting and wicking properties of Eri silk and wool blended fabrics Effect of blend proportion on moisture regain and thermal insulation of the fabric has been given in Figure 5. From the results, it is observed that moisture regain and thermal insulation both has been observed highest in case of 100 % wool fabric and gradually reduces with the increase in eri silk proportion. (a) Moisture regain (b) Thermal insulation Figure 5 Moisture regain and thermal insulation properties of Eri silk and wool blended fabrics

11 From the results it has been observed highest crease recovery has been observed in case of 67:33 eri : wool fabric sample, as has been shown in Figure 6 (a). From Figure 6 (b), we can see that bending rigidity has been observed to increase with the increase in eri silk proportion. (a) Crease recovery (b) Bending length Figure 6 Crease recovery and bending properties of Eri silk and wool blended fabrics Effect of blend proportion on surface roughness and total hand value of the fabric has been given in Figure 7. 100 % wool fabric has been observed to have highest co-efficient of friction, which points up the rough surface of the fabric, which will cause displeasure feeling to the wearer. Surface property of the fabric has been observed to change to a significant extent after the blending with eri fibre. Low stress mechanical properties of the eri/wool blended fabrics have been tested in Kawabata Evaluation System (KES). Total hand value (THV) of the fabrics has been calculated using those test results in the system of equations given by Kawabata. THV value has been observed to be good in case of 100 % eri and 67:33 eri: wool fabric sample and it has been observed to increase linearly with eri silk %.

12 (a) Co-efficient of friction (b) Total hand value Figure 7 Surface property and Total hand value of Eri silk and wool blended fabrics The simultaneous effect of fabric weigth (gsm) and weave design (interlacement index) along with the fibre blend proportion on different properties of eri silk wool blended fabrics have been analyzed using statistical software and the plots have been given the figures below (Figure 8-11). Effect of the above mentioned three parameters on fabric shrinkage at washing has been shown in Figure 8. Shrinkage % has been observed to reduce with the increase in eri silk % and with the increase in interlacement index. In case of lower gsm fabric, higher shrinkage has been observed.

13 Contour Plots of Shrinkage % (Warp) 168 160 152 144 136 2.00 GSM*Eri Silk % 40 50 60 Interlacement factor*gsm 2.00 1.75 1.50 1.25 1.00 Interlacement factor*eri Silk % 40 50 60 Shrinkage % (Warp) < 8 8 9 9 10 10 11 11 > 12 12 Hold Values Eri Silk % 50 GSM 150 Interlacement factor 1.5 1.75 1.50 1.25 1.00 136 144 152 160 168 Figure 8 Effect of blend proportion, gsm and interlacemen index on shrinkage % of Eri silk and wool blended fabrics

14 Contour Plots of Max load Kgf (Warp) 168 160 152 144 136 2.00 GSM*Eri Silk % 40 50 60 Interlacement factor*gsm 2.00 1.75 1.50 1.25 1.00 Interlacement factor*eri Silk % 40 50 60 Max load Kgf (Warp) < 35 35 40 40 45 45 50 50 55 > 55 Hold Values Eri Silk % 50 GSM 150 Interlacement factor 1.5 1.75 1.50 1.25 1.00 136 144 152 160 168 Figure 9 Effect of blend proportion, gsm and interlacemen index on tensile strength of Eri silk and wool blended fabrics Breaking load has been observed to increase with the increase in eri silk proportion and GSM of the fabric (Figure 9). Interlace factor has not found to influence much on the load bearing capacity of the fabric samples. Effect of blend proportion, fabric gsm and interlacement index on thermal resistance of the fabric has been shown in Figure 10. It has been observed that, thermal insulation reduces with the increase in eri silk proportion and interlacement index. With same fibre blend proportion low gsm satin fabric has shown higher thermal insulation, higher shrinkage has occurred in case of low gsm fabric, which causes to entrap more air pockets.

15 Contour Plots of Ther. Resis. (x10-3 K.m2/W) 168 160 152 144 136 GSM*Eri Silk % 40 50 60 2.00 1.75 1.50 1.25 1.00 Interlacement factor*eri Silk % 40 50 60 Ther. Resis. (x10-3 K.m2/W) < 22 22 24 24 26 26 28 28 30 30 32 > 32 2.00 1.75 Interlacement factor*gsm Hold Values Eri Silk % 50 GSM 150 Interlacement factor 1.5 1.50 1.25 1.00 136 144 152 160 168 Figure 10 Effect of blend proportion, gsm and interlacemen index on thermal resistance of Eri silk and wool blended fabrics Effect of blend proportion, gsm and interlacemen index on wettability of eri silk and wool blended fabrics has been shown in Figure 11. It has been observed that blend proportion plays most important role in it. At higher eri fibre proportion more spreading has been observed. Contour Plots of Wetting time (s) 168 160 152 144 136 2.00 GSM*Eri Silk % 40 50 60 Interlacement factor*gsm 2.00 1.75 1.50 1.25 1.00 Interlacement factor*eri Silk % 40 50 60 Wetting time (s) < 50 50 75 75 100 100 125 125 150 150 175 > 175 Hold Values Eri Silk % 50 GSM 150 Interlacement factor 1.5 1.75 1.50 1.25 1.00 136 144 152 160 168 Figure 11 Effect of blend proportion, gsm and interlacemen index on wettability of Eri silk and wool blended fabrics

16 Conclusions From the statistical analysis it has been that blend proportion, gsm and interlacement index play very important role in eri wool blended fabric, to decide its performance as winter wear. The optimized values from this research have shown many interesting findings. Tensile strength of the fabric sample has been observed to increase with the increase in eri silk fibre proportion in a significant way. Thermal insulation and moisture regain values increase with the increase in wool proportion. THV value as slack has been observed good for eri : wool 67:33 and 100 % eri silk. Eri silk and wool blended fabrics show excellent THV values (winter suit) of 4 and above. Shrinkage % has been observed to be reduced with the increase in eri silk % and with the increase in interlacement index. In case of low weight satin weave fabric very high shrinkage has been observed, which has resulted in increased thickness, i.e. more air entrapment and high thermal insulation. Wrinkle recovery has been observed to be poor in case of wool rich fabric. In terms of aesthetic comfort eri wool blended fabric with eri : wool 67:33 has been observed to be the best one. 50:50 eri wool fabric sample with satin weave and 130 gsm, has been observed to have very good thermal properties, good pilling resistance, low drape and reasonable wetting property. This material can be very well used as winter scarf. Along with improved strength, smoothness (surface) characteristics and thermal insulation property, it is confirmed that the eri silk and wool blended fabric will provide much better comfort to the wearer than the pure wool or pure eri could have. So it is beyond doubt that the eri silk blending with wool is a grand success for winter wear applications. References 1. Kulkarni, A.A. (2007). Quality characteristics of viscose rayon and eri silk union fabrics. MSc. Thesis, July, University of Agricultural Sciences, Dharwad. 2. Kulkarni, P.R., & Bahuguni, R.S. (2011). Optimum machinery, process and products for eri silk /wool blends. Wool Tech, 01 (02). 3. Gohl, E.P.G., & Vilensky, L.D. (1999). Textile Science, 2nd edition, CBS publishers.

17 4. Behera, B.K. (2007). Comfort and handle behaviour of linen-blended fabrics. AUTEX Research Journal, 7(1), 33-47. 5. Kariyappa, Radhalakshmi, Y.C., & Shivkumar, K.P. (2014). Evaluation of low stress mechanical properties of eri/wool blended fabrics, Sericologia, 54 (1), 59-65. 6. Kariyappa, Shivkumar, K.P., Rao, P.M. D. & Roy, S. (2009). Evaluation of physical and comfort poperties of eri and wool spun yarn woven fabrics, Man Made Textile in India, Nov., 393-396.