Comfort properties of mulberry and tassar silk fabrics

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1 Indian Journal of Fibre & Textile Research Vol., March 000, pp. -8 Comfort properties of mulberry and tassar silk fabrics I C Sharma, A Mukhopadhyay, P K Sinha & R K Boruah The Technological Institute of Textile & Sciences, Bhiwani 17 01, Indi a Received June J'998; revised received and accepted 18 December 1998 The tensile, bending, shearing, compressional and surface properties of mulberry and tassar si lk fabrics have been studied to investigate their hand values. Using the data obtained, the quality characteristics of mulberry and tassar silk fabrics have been objectively evaluated and then compared. It is observed that mulberry silk fabric is better in terms of shear stiffness, bending ri gidity, geometrical roughness, hand values and draping behaviour but possesses lower compressional resilience as compared to tassar si lk fabric. Keywords : China tassar, Comfort properties, Korea tassar, Mulberry, Silk fabric 1 Introduction The preference for natural silk over silk-like synthetic fibre can be explained by its superior handle. The chemical nature of silk fibre has been studied by several researchers. However, silk fabric hand cannot be explained by the fabric's chemical nature alone. The primary factors affecting the fabric hand are its mechanical characteristics l. The hand characteristics of silk fabric can be described by its ultra-soft touch, high flexibility, very high volumetric feeling, deep colour and scrooping. Except the deep colour, other hand characteristics may be attributed to the geometrical characteristics of silk filament cross-section and natural layout in a fabric repeat unit and weave structure,. In contrast to the chemical characteristics, there are not many comparative studies on mechanical properties of mulberry and tassar silk fabrics. Objective evaluation of the hand of apparel fabrics was first attempted by Peirce in 190 but the credit for providing a feasible instrumental technique to evaluate hand qualities goes to Kawabata.. His objective hand evaluation method in vo lves five groups of mechanical properties, a measurement system and multi-correlation constants which relate expert judgement and mechanical properties. Matsudiara and Kawabata 7 observed that silk fabrics exhibit very low stiffness and hysteresis and are very deformable in their compressional and tensile properties at a very low strain level. In the second part of their work, they postulated a gap between the warp and weft to explain the very low values of shear stiffness and hysteresis of shear force in silk fabrics. In the third part, they showed that two different tensile deformation mechanisms are active for the very small load region of extension due to the existence of the gap. The utility of moisture transfer properties on fabrics has also been reported earlier In the present work, the tensile, bending, shearing, compressional and surface properties of mulberry and tassar silk fabrics have been studied to investigate hand values. Using the data obtained, the quality characteristics of mulberry and tasser silk fabrics have been objectively evaluated and then compared. Materials and Methods.1 Materials Six fabric samples, three each of mulberry and tassar, were prepared. The constructions details of the fabrics are given in Table I.. Methods All the fabrics were conditioned fo r h and then tested for their mass per unit area and thickness, tensile, shear, bending, compression and surface properties using the KES-FB set of instruments to the normally accepted test procedures 1o. 11 Fabric tensile, bending and surface properties were tested in both warp and weft direction of the fabric. All the tests were carried out in an atmosphere of 7± C and S±% RH...1 Drape Coefficient Drape coefficient (D j ) can be calculated by KES FB system l. Drape coefficient, which is a criterion of static drapping behaviour of clothes, was calculated from the mechanical characteristics of bending and shear properties and fabric weight using the following equation:

2 SHARMA et al. : COMFORT PROPERTIES OF MULBERRY AND TASSAR SILK FABRICS Table I--{:onstruction details of mulberry and tassar silk fabric Sample Warp Weft Warp Weft Endslin. Pickslin. Weight Cover No. denier denier mg/cm factor Korea tassar China tassar (Filament yam) (Filament yam) Korea tassar Korea tassar (Filament yam) (filament yam) Korea tassar Tassar waste (Filament yam) (Mill spun) ' Mulberry (single) Mulberry (Fil ament yam) (Spun yam) Mulberry (single) Mulberry (single) (Filament yam) (Filament yam) Mulberry (Piled) Mulberry (single) 0-/ (Filament yam) (Filament yam) Table -Shear properties Sample Shear stiffness(g) Hysteresis of shear force Hysteresis of shear force No gfcrn/deg at 0." shear angle (HG), gf/cm at shear angle (HG ), gf/cm Warp Weft Mean Warp Weft Mean Warp Weft Mean D j = (B/W)I"+.(HB/W)11 +.(G/W) 1" +7. I 9(HG/W) where B is the bending rigidity (gf cm /cm); W, the fabric weight (mg/cm ); HB, the hysteresis of bending moment (gf cm/cm); G, the shear stiffness (gf cm/deg); and HG, the mean value of hysteresis of shear force at 0. 0 and 0 shear angles (gf/cm). The parameters Band HB were evaluated by the instrument KES-FB and the parameters HG and G by the instrument KES-FB I... Thermal Insulation Thermal insulation of the fabric was determined by KES-FBS (Thermolab II). The dry contact method 8 with an air velocity of 0 cmls was used for the measurement of thermal insulation. Other parameters were kept as per the standard... Moisture Transfer Properties The modified evaporation cup method 8 was used to measure the resi stance of fabric to water vapour transfer. 0.% soap solution was used to measure the drop absorption time and total absorbency. Results and Discussion.1 Shear Stiffness and Hysteresis Table shows that the fabric prepared from Korea tassar yams in warp and tassar spun yams in weft has the highest shear stiffness and hysteresis followed by the fabric prepared from Korea tassar yams in both warp and weft. Mulberry silk fabrics show substantially lower values of shear stiffness (G) and hysteresis (HG, HG) as compared to tassar silk fabrics. The above results conform to the findings that mulberry silk is soft and elastic in shear deformation? Shear properties are dominated by inter-yam normal force and frictional coefficients. With the increase in warp resilience, the shear stiffness and shear hysteresis increases I.".. Compressional Energy, Linearity of Compression and Compressional Resilience Table shows that the compressional energy (WC) and linearity of compression (LC) of all the silk samples are approximately the same. But among the tassar fabrics, the linearity of compression is higher for the fabrics prepared from Korea tassar and China tassar in warp and weft respectively. This may be due to the difference in the stiffness of yams constituting these

3 INDIAN 1. FIBRE TEXT. RES., MARCH 000 Table }----Compressional properties Sample Linearity of compression (LC) energy (WC) resilience (RC) mm mg/cm Compressional Compressional Fabric thickness (7) Fabric weight (W) No. 0.9 gfcm/cm % Table --Bending properties Sample Bending rigidity (B) Hysteresis of bending moment (HB) No. gfcm/cm gf/cm Warp Weft Mean Warp Weft Mean Table --Surface properties Sample No. Coefficient of friction (M/ V) Mean deviation of MIU (MMD ) Geometrical roughness (SMD), 11m Warp Weft Mean Warp Weft Mean Warp Weft Mean S fabrics 7 The values of compressional resilience (RC) are lower for mulberry fabrics as compared to those for tassar fabrics. Among the mulberry silk fabrics, the higher value of RC is observed r r fabric prepared from mulberry filament warp and mulberry spun weft. It may be due to the difference in structure of China and Korea tassar yam in the weft. The linearity of compression depends upon the compressional behaviour of yam and fabric thickness. Compressional energy per unit area depends upon the linearity and extent of compression.. Bending Rigidity and Hysteresis of Bending Moment Table shows that the bending rigidity (B) is lower for mulberry silk fabrics and that among the mulberry silk fabrics, it is lowest for spun weft fabric. However, among the tassar silk fabrics, the bending rigidity is higher for spun weft fabric. This is due to the fact that spun yarn fabric thickness is maximum in case of tassar silk fabrics and minimum in case of mulberry silk fabrics. The hysteresis of bending mr l1ent (HB) also shows the same trend as shown by bending rigidity and it is a measure of recovery from bending deformation, J.. Surface Properties Table shows that the coefficient of friction (M/ U) is higher for mulberry si lk fabrics and that among the mulberry silk fabrics, MIU is hi ghest for spun weft fabric. However, among the tassar silk fabrics, MIU is lower for spun weft fabrics. Further, it is also observed that geometrical roughness (SMD) is higher for spun weft fabri(; among the mulberry fabrics and for filament fabrics among the tassar silk fabrics. This may be due to the rough texture of tassar filament fabrics than that of mulberry filament fabrics. The mean deviation of MIU (MMD) is higher for tassar

4 SHARMA et al. : COMFORT PROPERTIES OF MULBERRY AND TASSAR SILK FABRICS Sample No. I Strain at 00gf/cm of tensile load (EM) Table --Tensile properties Linearity of Tensile energy (WI) Tensile resilience (R7) load/extension curve (L7) gfcmlcm % Warp Weft Mean Warp Weft Mean Warp Weft Mean Warp Weft Mean 0. O.W Table 7-Hand values for lady's summer suit (KN LOY) Sample Koshi Numeri Fukurami Total No. (Stiffness) (S moothness) (Fullness and hand softness) value silk fabrics and substantially lower for mulberry silk fabrics. This may be due to the higher variation on tassar silk yam structure. Coefficient of friction (MIU) depends upon the contact area of the fabric with that of the body. MMD is a measure of the variation of MIU whereas SMD is a measure of geometrical roughness.. Tensile Linearity, Tensile Energy, Tensile Resilience and Extensi bili ty Table shows that the tensile linearity (LI) is greater for mulberry filament fabrics and that it is lowest for spun weft tassar fabrics followed by a slightly higher value for spun weft mulberry fabrics. This may be due to the greater tenacity of mulberry yams. Tensile energy (WI) does not show any trend but tensile resilience (RI) is lower for mulberry silk fabrics. This may be due to the higher extensibility and lower tenacity of tassar silk yams. Tensile linearity depends upon the ease of crimp removal and the elasticitiy of yam. Tensile energy represents the tensile energy per unit area.. Fabric Hand..1 Lady's Summer Suit Table 7 and Fig. I show that the value of Koshi (stiffness) is higher for tassar silk fabrics. Substantiall y higher value of stiffness is observed for KOSBlIstiflhetS Total hood value (THVJ t-"*---'1:f-i-+-*-l (a) SampIcNo.. l : Sample No. : Sample No. S : FUKtJIfulIAea A: JOftDew Sample No. ; KOSBlfItifrQcsa Total hand value (lhv) r--:---i----j>-+----l (b) NUMERIIsmoothncss Sample No. : Simple No. " : HKU/fUllne...olooft... Fig. I-Fabric hand values for lady's slimmer suit [ (a) filament warp and weft fabrics, and (b) filament warp and spun weft fabrics] tassar silk fabrics having spun weft yam. Koshi depends on the bending properties of the fabrics. It is a stiff feeling promoted by springiness in the fabric. High value of Numeri (smoothness) is observed for mulberry si lk fabrics. Smoothness of spun weft mulberry fabrics resembles very much to that of mulberry filament fabrics. However, the smoothness is pretty lower for spun weft tassar fabrics. Fukurami (fullness ad softness) of spun weft mulberry silk fabric is higher than that of any other silk fabric. Fukurami is bulky, rich and well-formed feeling and is mainly governed by the fabric bulk and compressional behaviour. It depends l1pon the bending and shear properties as well? Total hand value shows greater importance of mulberry silk fabrics for lady's summer garments. Even the spun weft mulberry silk fabric is more

5 INDIAN J. FIBRE TEXT. RES., MARCH 000 suitable for women dresses during summer than tassar filament fabrics... Men's Summer Shirting ssstable 8 shows the higher value of Koshi (stiffness) for tassar silk fabrics and substantiall y higher value of Koshi for spun weft tassar fabrics. Koshi of the fabric is contributed by the bending property and springiness. Lower value of Shari (crispness) is observed in mulberry fabrics. Among all the samples studied, the crispness is lowest for spun weft mulberry fabric and highest for spun weft tassar fabric. Shari is a feeling of crispness coming from the rigid and highly twisted yarns. Fukurami (ful lness and softness) required for men's summer shirting is very good for spun weft mu lberry fabrics, moderate for the other two mulberry fi lament yarn fabrics and very poor for tassar yarn fabrics. Fukurami is mainly affected by fabric bulk and compressional behaviour. It is the bulky, rich and well-formed feeling of the fabrics. Hari (antidrape stiffness) is higher for tassar silk fabrics, very poor for mulberry spun weft fabrics (good drapability) and very hi gh for tassar spun weft fabrics. The lowest value of Hari for mulberry silk fabrics may be due to their high bending and shear properties. Table 8 and Fig show greater preference of mulberry silk fabrics for men's summer shirting. Tassar si lk fabrics prepared by Korea tassar as warp and China tassar as weft resemble very much to mulberry fabrics. But all these samples are suitable fer men's summer shirting purposes..7 Drape Coefficient Table 9 shows lower value of drape coefficient for all the mulberry si lk fabrics. Among the tassar silk fabrics, the spun weft fabric has the highest value of drape coefficient. Fabrics having the smaller values of drape coefficient are considered to hang down well and cling to a curved surface easilyl. Tassar fabrics have higher drape coefficient because of rough texture and harsh feel of tassar yarns..8 Thermal Insulation Lower value of thermal insulation is observed for mulberry silk fabric (Table 10) as against that of tassar si lk fabric. This property depends upon the air permeability and the thickness of the fabric as well. However, insulation of silk fabric is very low as compared to that of other fabrics 1..9 Moisture Transfer Properties It is observed that water vapour resistance of the fabric increases with the increase in layers. But from second to third layers, 0.% increase in water vapour resistance is marked in mulberry fabrics and 11 % in tassar fabrics. Total absorbency is greater in mulberry fabrics with spun weft (Table I I). Among both mulberry and tassar silk fabrics, the spun weft fabrics Total hand value ( lily) UARII antj..drapc.tiffneu Trcxal baoo value (THV KOSUlllliftnen KOSB1lnifthess (a) SIlA(Ulcrispness Sample No. 1: S&mple No. : Sample No. : Sample No. : FUKUltUllneu &: iottnw S lar.iicrispncu Fig. -Fabric hand val ues for men's summer shirting [(a) filament warp and weft fabrics, and (b) filament warp and spun weft ~ri~. Table 8-Hand val ues for men's summer shirting (KN DS) Sample Koshi Shari Fukurami Hari Total hand No. (Stiffness) (Crispness) (Fu llness and (Anti-drape value softness) stiffness) I

6 SHARMA et at. : COMFORT PROPERTIES OF MULBERRY AND TASSAR SILK FABRICS 7 Sample No. Without Sample Mean Bending rigidity(b) gfcm/cm Table 9--Drape coefficient (Kawabata method) Hysteresis of bending moment(hb) gfcrn/cm Shear stiffness(c) gfcrn/deg Hysteresis of shear force at 0. 0 shear angle (HC), gf/cm Fabric weight(w) mgicm Table IO-Thermal insulation (Dry Contact Method) Body temperature Room temperature Difference in tem- Ground tempera- Heat loss "c (B7) "c (R7) perature, "c (7) ture, "c (C7) (Wo) Drape coefficient % Heat loss (WI/IO"C) With sample No Mean Insulation, %. With sample No Mean Insulation, %. Table II-Fabric moisture transfer properties Sample Dry weight Wet weight Total ab- Drop absorb- No. g g sorbency, % ence time, min take more time for water drop absorption. Drop absorption time seems to be related to fabric cover or the number of air pores available on the fabric surface. Fabric moisture transfer properties depend upon the air permeability of the fabric also 8,1, Conclusions Mulberry silk fabrics have substantially lower values of shear stiffness, hysteresis of shear force at OS shear angle, compressional resilience, bending

7 8 INDIAN J. FIBRE TEXT. RES., MARCH 000 rigidity, hysteresis of bending moment and tensile resilience but excellent drape behaviour, hand values, coefficient of friction and tensile linearity as compared to tassar silk fabrics. On the other hand, tassar silk fabrics show higher mean deviation of MIU, geometrical roughness and Koshi but lower value of Numeri (smoothness). References I Hwo Seo Mon & Jang Cho Hang, Text Asia,S (199) 1. Krishnaswami S, Narsimhanna M N, Suryanaryan S K & Kumararaj S, FAO Agric Serv Bull, (197) 9. Krishnaswami S, Madhavarao N R, Suryanarayan S K & Sundaramurthy T S, FAO Agric Serv Bull, (197) I. Kawabata S, Postle R & Niwa M, Objective specification of fabric quality, mechanical properties & peliortnance (The Textile Machinery Society of Japan, Osaka), Kawabata S, The standardization and analysis of hand evaluation, (The Textile mach inery Society of Japan, Osaka), 197. Kawabata S, The stalldardization alld analysis of hand evaluation, nd edn, (The Textile Machinery Society of Japan, Osaka), Matsudaira M & Kawabata S, J Text blst, (1988) 7. 8 Behera B K, Ishtiaque S M & Chand S, J Text /n st, 88 (1997). 9 Sharma I C, Chhabra S, Agarwal B R & Arya S,/ndian J Text Res, 7( 198). 10 Mohar T J, Dhingra R C & Postle R, Text Res J, 7 (1987) 7. II Kawabata S & Niwa M, J Text Res, 80 (1989) 0. 1 Matsudaira M, J Text Mach Soc Japan, 8 (199). 1 Postle R & Ping G, /ndian J Text Res, 19 (1 99) 1. 1 Emori T, The handle offabrics (Textile Machinery Society of Japan, Osaka), Jolly M S, Sen S K, Sonwalkar T N & Prasad G K, FAO Agric Serv Bull, (1979) 1. 1 Gulrajani M L, /ndiall Text J, 101 (1991) 110.