Physical characteristics and structure of Indian silk fibres

The physical characteristics and structures of the four commercial varieties of Indian silk fibres, namely Mulberry, Tasar, Eri and Muga, have been studied. It is observed that the silk filaments from the same cocoon show considerable variation in linear density. As one moves from the outer layers to the inner layers of the cocoon, the fibres show a slight initial increase in linear density before showing steady decrease. Mulberry silk is the finest, followed by Eri, Tasar and Muga. Mulberry silk also has the highest density, indicating a relatively more compact structure compared to the non-Mulberry silk fibres. The cross-section of Mulberry silk is near triangular whereas the cross-sections of all the non-Mulberry silk fibres are near rectangular. Birefringence data reveals, on an average, a more oriented molecular arrangement in Mulberry silk whereas the three non-Mulberry silk fibres have lower orientation and their birefringence values are not significantly different. The principal differences in the physical characteristics and structures of the Mulberry and non-Mulberry silk fibres have been attributed to the differences in the chemical compositions of these fibres.