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, have been studied along with their structures. Compared to the non-Mulberry silk fibers, Mulberry silk fiber is much finer and has crystallites of smaller size, higher molecular orientation, and a more compact overall packing of molecules. These structural differences have been shown to result in (1) the presence of a distinct yield and a yield plateau in non-Mulberry silk and their absence in Mulberry silk, and (2) relatively higher initial modulus and tenacity along with lower elongation-to-break and toughness and superior elastic recovery behavior of mulberry silk compared to non-Mulberry silk. It is also observed that fine silk fibers have a relatively more ordered and compact structure with higher orientation compared to their coarse counterparts, and this gives rise to higher initial modulus and higher strength in the finer fibers.