Deterioration of silk fabrics and their crystallinity

We report an investigation of the deterioration mechanism of aged silk fabrics treated in various ways. When we examine the deteriorated silk with thermal and amino acid analyses, we find that the decomposition temperature (above 300 degrees C) of aged silk is higher than that of newer silk fabrics, and the amino acids in the amorphous region of aged silk are much reduced compared to those in the crystalline region. This suggests that the degree of silk's crystallinity increases relative to the aging period. Moreover, the decomposition temperature of gamma-ray irradiated silk is reduced according to the increased amount of irradiation, and all amino acids in the crystalline and amorphous regions are reduced without exception. Amino acid analysis of coagulated silk in the silk gland with heat treatment shows that the amino acids are remarkably reduced in air above 250 degrees C, and the reduction of tyrosine and phenyl alanine in the amorphous region is less in nitrogen gas.