Degumming of silk with lipase and protease

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 25, March 2000, pp Degumming of silk with lipase and protease M L Gulrajani & Ritu Agarwal Department of Textile Technology, Indian Institute of Technology, New Delhi , India and Amrit Grover & Mona Suri Lady Irwin College, New Delhi I, Indi a Received J 8 Jam'([lI), J 999; accepted J 3 April J 999 A lipase enzyme in combinati on with a protease enzyme has been used for dewaxing and degumming of silk and the combined effect of dewaxing and degumming on weight loss, wettability, dye uptake, yellowing, microscopic structure, handle and lustre has been studied. It is observed that the combined enzyme treated samples show the same weight lo ss, cleaner longitudinal su rface and better wettability when compared with the Marseilles' soap treated samples. Keywords: Dewaxing, Degumming, Lipase, Protease, Silk 1 Introduction The raw si lk does not merely consist of an inner filament fibroin, sheathed in natural size sericin, but is also contaminated with small amounts of nonproteinaceous impurities like dust, minerals, pigments and waxy matter'. Along with sericin, these waxes playa role in obscuring the brilliance and softness of the silk. Only a few studies have been conducted on waxes and oils present in si lk, their nature, composition, properties, exact quantities and methods of removal. Apart from naturally occurring waxes and oils, some additional waxes are applied to the yarns while weaving them into fabric which do not get removed even after degumming. These waxes hamper the processi ng of si lk due to poor wetting properties. Hence, complete elimination of these waxy substances is very essential. Due to the ambiguity about the true nature and composition of these waxes, no method has been successfully devised to remove them completely. It is believed that a fraction of these waxes is saponifiable and therefore can be removed with alkali or soap treatment, but these methods are believed to be harmful to fibroin. The use of enzymes in the silk industry is relatively unexplored and has generated a lot of interest and much research is being carried out internationally. For this purpose, a special class of enzymes called lipases, which are specialised in hydrolysing waxes into fatty acids and alcohols, seem to be ar appropriate answer. The present work was therefore undertaken to study the effect of lipase treatment on silk wax and the combined effect of dewaxing and degumming on weight loss, wettability, dye uptake, microscopic structure, handle and lustre. 2 Materials and Methods 2.1 Materials Two varieties of raw si lk fabric with plain weave (Silk A) and crepe weave (S ilk B) were used in this study. Lipase enzyme Amano AK 20, from Pseudomonas sp., with activity of 9.98 AU/g was obtained from the Department of Biochemical Engineering and Biotechnology, lit-delhi. Protease enzyme Alcalase 2,4 LFG with activity of 2.4 AU/g was procured from Novonordisk, Denmark. 2.2 Methods Preparation of Samples Samples from each silk were cut weighing 3 g each. They were conditioned at 30% RH and 25 C for 48 h and weighed again Fabric Treatment The recipes used for treatment of the fabric with lipase, protease and soap are given below:

2 70 INDIAN 1. FIBRE TEXT. RES., MARCH 2000 Dewaxing (with lipase) Buffer solution Lipase Temperature ph MLR Degumming (with protease) Alcalase Sandopan DTC NaHCO J Temperature ph MLR O.IM NaHC0 3 40%C h 1: gpl 7.5% owf 60 C 8.5 2h 1:50 Degumming (with Marseilles' soap) Marseilles' soap 25% owf Temperature 93 C ph 10 MLR 1.5 h 1: Optimization of Lipase Concentration The samples were treated with 0%, 5% and 10% lipase enzyme. The effectiveness of lipase was estimated by measuring the weight loss Optimization of Conditions for Alcalase Treatment Degumming of dewaxed and raw silk samples was carried out with two concentrations of Alcalase, viz. 10% and 15 % (owf), for 45 min and 3 h Combined Treatment of Lipase and Alcalase To see the effect of combined treatment of lipase and protease in the same bath the samples were treated under the following conditions: Alcalase Lipase Sandopan DTC 1.5 gpl Buffer solution 0.1 M NaHC0 3 Temperature 60 C ph 8.5 2h MLR 1: Determination of Weight Loss Samples were weighed accurately before and after the enzyme treatment using Sartorius moisture analyzer and the weight loss was calculated as follows: Weight loss (%) = (WI - W 2 ) x 100 WI where WI and W 2 are the weights of fabric before and after the enzyme treatment Determination of Wettability Five samples (I in.x3 in.) were cut from both warp and weft directions. On each sample, two lines were drawn I inch apart with an ink marker. With the help of a clamp stand the samples were immersed in distilled water till the lower line. The spreading of colour showed the rise of water. The time taken by water to travel from lower mark to upper mark was recorded Determination of Increase in Dye Uptake To see the extent of wax removal from silk, the ease by which the sample will get dyed was measured. Samples were dyed with reactive dye (Remazol Red BS ill, 3% owf) for 5, IS and 45 min at 80 C with 60 gpl Glauber's salt, maintaining the materialto-liquor ratio at I :50. Dye uptake was measured by taking the K/S values of the samples on the spectrophotometer Determination of Yellowing Samples were cut in 2 in.x4 in. size and their initial whiteness was determined by taking Hunter's whiteness index using spectrophotometer. The samples were than exposed to light equivalent to sunlight for 24 h. Their whiteness was again measured SEM Studies The extent of degumming can be qualitatively assessed by viewing the degummed fibres under Cambridge scanning electron microscope. Residual sericin appears as lumps on the surface of the fibre. The extent of fibre damaged can also be assessed by this method. The splitting of fibres into minute fibrillae is frequently observed in silk. This has been attributed to the mechanical injury of the fibre caused by chaffing and abrasion during degummingl Determination of Handle and Lustre The samples of equal size (2 in.x2 in.) were mounted on black sheet and ten people were asked to evaluate these samples on the basis of handle and lustre. Mean ranking was taken. 3 Results and Discussion 3.1 Optimization of Lipase Concentration Treatment of Silk A with 5% owf enzyme concentration gave a weight loss of 1.37% and the control

3 GULRAJANI et af.: DEGUMMING OF SILK WITH LIPASE AND PROTEASE 71 sample gave a weight loss of 1.33%. Whereas the treatment with 10% enzyme concentration gave a weight loss of 4.62%. As the weight loss with 5% enzyme concentration was very close to that of the control sample, enzyme concentration was chosen. Further, the results were not reproducible. Therefore, lipase treatmf'nt was tried as pretreatment for degumming process. 3.2 Optimization of AJcalase Concentration Due to the erratic weight loss, the conditions for dewaxing treatment could [lot be standardized. There: fore, the conditions for the degumming treatment which could be applied to the lipase pretreated samples were optimized. Table I shows the weight loss obtained after the treatment of silk with AIcalase. As the weight loss obtained after 45 min and 180 min was comparable, time period of 45 min was taken. Weight loss obtained after dewaxing was compared with the weight loss obtained without dewaxing treatment. Table 2 shows that the lipase pretreated samples show only marginal increase in weight loss after degumming. Therefore, lipase was not used as pretreatment. combined treatment with aicalase and lipase. This shows that there is improved degumming by the combined treatment and hence improvement in absorbency. Both the silk samples show better wicking property in warp direction due to formation of capillaries Dye Uptake Table 5 shows that the KlS values of the combined enzyme treated samples are comparable to that of the samples treated with Marseilles' soap Microscopic Structure The scanning electron micrographs of control sample, aicalase-treated sample, lipase-treated sample, combined enzyme treated sample and soap-treated sample of Silk A and Silk B are shown in Figs 1 and 2 respectively. It is observed that aicalase-treated samples are equally clean as the samples obtained on combined enzyme treatment. But in case of only alcalase enzyme treatment, certain small remnants of sericin are noticed. Marseilles' soap treated samples show fibrillation of fibre. There is not much difference in Silk A and Silk B samples. In case of plain 3.3 Effect of Combined Dewaxing and Degumming Weight Loss Table 3 shows that the maximum weight loss is obtained by Marseilles' soap treatment and the weight loss on combined treatment of lipase and protease is comparable with that of soap treatment. Though the Marseilles' soap treatment results in complete removal of serecin, the quantity of soap required is high (25% owf) which is not economical. Al so, the high temperature(at boil) and alkaline ph (10.5) used might cause degradation of fibroin. The enzymatic treatment, on the other hand, is milder (temp e and ph 9) and gives fairly good weight loss Wettability It is observed from Table 4 that for both Silk A and Silk B, the minimum wicking time is in case of Table I-Weight loss obtained after treatment with A1calase Alcalase Weight loss, % (owf), % min Plain silk Crepe si lk Table 2-Weight loss obtained after sequential treatment of li pase and alcalase Lipase conc. A1calase conc. Weight loss (owf) % (owf) % % Treatment Table 3-Effect of enzyme treatment on weight loss Only buffer Only lipase Only A1calase Lipase and A1calase Marseilles' soap Weight loss, % Plain silk Crepe silk Table 4-Effect of enzyme treatment on wicking time Treatment Wicking time, min Plain sil k Crepe silk Warp- Weft- Warp- Weftwise wise wise wise Only buffer Only lipase Only A1calase Lipase and Alcalase Marseilles' soap

4 72 INDIAN 1. FIBRE TEXT. RES., MARCH 2000 Table 5-Effect of enzyme treatment on K/S value Treatment K/S value Plain silk Crepe silk 5 min 15 min 45 mi n 5 min 15 min 45 min Only Alcalase Lipase and Alcalase Marseilles' soap Fig. I-Scanning electron micrographs of Silk A samples : (a) untreated, (b) treated with buffer or control, (c) treated with lipase, Cd) treated with Alcalase, (e) treated with Alcalase and lipase, and (f) treated with Marseilles' soap

5 GULRAJANI e/ al.: DEGUMMING OF SILK WITH LIPASE AND PROTEASE 73 Fig. 2-Seallning c1eetrol, mi crogrnphs of Silk B samples: (n) untreated, (b) treated with buffer or control, (c) treated with li p 3 ~e, (d) treated with Alcalase, (e) tn:ated with Alcalase 3nd lipase, and (f) ueated with Marsei ll es' soap Table 6-Effect of enzyme treatment on handle and lu stre Treatment Pl ain silk Crepe silk Handle Lu stre Handie Lustre Only buffer Only lipase Only Alcalase 3 I 2-3 Lipase and Alealase Marseilles' soap 3 3 woven silk samples (Silk A), more crimp is observed than in case of crepe silk or satin weave samples (Silk B) Haudle and Lustre The data in Table 6 shows that Marseilles' soap treated sample has been ranked first in case of handle and third in case of lustre. Good handle could be due to uniform dissolution of sericin by the action of alkali, resulting in a

6 74 INDIAN J. FIBRE TEXT. RES., MARCH 2000 smooth surface. Excess of alkali of the hydrolyzed soap diminishes the lustre 2. Best results in terms of lustre is observed for the samples treated with only alcaiase. The combined treatment gives better results in terms of lustre but the samples are ranked lower in terms of handle as compared to the soap-treated samples. 4 Conclusion Lipase enzyme can be used along with protease to improve the degumming of silk. The combined enzyme treatment gives the same weight loss, better wettability and cleaner longitudinal surface as compared to Marseilles' soap treatment. This combined enzyme treatment can be a useful replacement to the traditional method of treatment with Marseilles' soap. Acknowledgement The authors acknowledge the financial support received from the Department of Biotechnology, Ministry of Science and technology, Govt. of India, for conducting this study. References I Gulrajani M L, Degumming of silk in Chemical processing of silk, edited by M L Gulrajani (Indian Institute of Technology, New Delhi), 1993,63. 2 Tsunkaye V D, J Soc Dyers Colour, 48 (1932) 280.