Changes in Structure of Silk Fibers by Tannin-weighting

Abstract

The changes in the structure of domestic (Bombyx mori) and wild (Antheraea pernyi) silk fibers when the fibers were tannin weighted have been investigated by means of the wide and small angle X-ray scattering. The crystallinity index decreased and the average crystallite size was increased by tannin-weighting. It was suggested that crystallites with smaller sizes were destroyed by tannin-weighting. With increasing tannic acid content under wet conditions, the intensity of small angle X-ray scattering decreased in domestic silk fibers, whereas it showed a maximum before decreasing monotonously in wild silk fibers. The volume fraction of microvoids and number of microvoids per unit area for dry wild silk fibers had a maximum value at a certain tannin-weighting percentage, and the average cross-section area of microvoids monotonously decreased with increasing tannin-weighting percentage. The increase in number of microvoids caused the increase in volume fraction of microvoids. Furthermore, the dyeing rate and amount of dye adsorbed at equilibrium were measured for tannin-weighted silk fibers. The diffusion coefficient of the dye was decreased by tannin-weighting. From these experimental results, the fiber structures of domestic and wild silk fibers were proposed.