Tensile stress-strain and recovery behavior of Indian silk fibers and their structural dependence

The tensile stress-strain and recovery behavior of all the four commercial varieties of Indian silk fibers, namely Mulberry, Tasar, Eri, and Muga, hav e been studied along with their structures. Compared to the non-Mulberry si lk fibers, Mulberry silk fiber is much finer and has crystallites of smalle r size, higher molecular orientation, and a more compact overall packing of molecules. These structural differences have been shown to result in (1) t he presence of a distinct yield and a yield plateau in non-Mulberry silk an d their absence in Mulberry silk, and (2) relatively higher initial modulus and tenacity along with lower elongation-to-break and toughness and superi or elstic recovery behavior of mulberry silk compared to non-Mulberry silk. It is also observed that fine silk fibers have a relatively more ordered a nd compact structure with higher orientation compared to their coarse count erparts, and this gives rise to higher initial modulus and higher strength in the finer fibers. (C) 2000 John Wiley & Sons, Inc.