Characterization of recent and historical silks : effects of silk processing on chemical composition and amino acid racemization

Abstract

In this work, the influence of dyeing, mordanting and degumming techniques on the amino acid (AA) composition and the AA racemization (AAR) of (non-)mulberry silks is studied by a chiral GC-MS method. The tested dyeing and mordanting procedures as well as a pre-treatment of the silk filaments with EDTA-DMF, which enables a parallel dyestuff analysis by HPLC-DAD, do not cause any significant change in the AA composition. However, an increased proportion of e.g. (D)-Asx can be observed for some of the mordanted BM silks. Increased D/L Asx ratios can also be observed in indigo dyed silks and after an alkaline treatment at 110°C (pH > 9). Furthermore, the GC-MS method was used for the characterization of historical silk samples from finding sites in the Tarim Basin (China). The analysis of these silk fabrics reveals the presence of degraded Bombyx silk with significantly increased D/L Val, D/L Glx and D/L Asx ratios. Including microscopic and spectroscopic investigations, the results of this multi-analytical approach offer insights into the silk processing techniques and raw materials used.