Thermal Behaviour of Silk

Silk is a natural protein fibre. It is the only natural fibre available in continuous filament form. Earlier research studies on physical structure and mechanical properties of silk have indicated that the physical and chemical architecture varies between different varieties of silk and a substantial variation of these properties was observed within the cocoon. The amino acid composition and even the dyeing behaviour are different in different silk. Silk is considered as a non-thermoplastic fibre and is generally not expected to undergo significant morphological changes as a result of thermal shrinkage like synthetic fibres, viz., polyester and nylon. Needless to mention, silk fibres do undergo several kinds of heat treatments either in dry or wet state in the course of textile processing. Hence, an attempt has been made in this paper to deal with the response of different silk varieties (mulberry and non-mulberry) to thermal inputs. Five varieties of silk, two mulberry (bivoltine and crossbreed) and three non-mulberry (tasar, muga and eri) were subject to thermal treatments using TGA and DTA techniques. It was found that both mulberry and non-mulberry varieties behave differently to thermal inputs. Non-mulberry varieties show lower weight loss of 35-37% at 400oC as compared to about 41- 44% for mulberry varieties. They also exhibit a higher decomposition temperature. Interestingly, an additional transition at around 290°C is clearly observed with all the nonmulberry silks. The DTA results indicate higher stability of non-mulberry silks towards thermal treatments.