Effect of sodium carbonate concentrations on the degumming and regeneration process of silk fibroin

Abstract

Silk degumming process is regarded as the first key point in the preparation of silk-based materials. Emphasis of this paper is placed on the effect of sodium carbonate (Na2CO3) concentrations on degummed silk fibers, the derived aqueous silk solutions, and the final regenerated silk films. Obvious damage with exposure of silk fibrils was caused at 5% Na2CO3 concentration but no microstructure destruction was observed at 0.005% Na2CO3 concentration. Weight loss increased dramatically with increasing Na2CO3 concentration, further leading to a reduction in the degummed silk diameter and poorer thermal stability. Although little change has been found on β-sheet content of degummed silks, differences in molecular weight and rheological behavior of aqueous silk solutions from different Na2CO3 concentrations are clearly found which are associated with the subsequent structure and physical properties of the regenerated silk films. The results indicate that there is an inverse relationship between Na2CO3 concentrations and the thermal degradation, wettability, and mechanical properties of regenerated silk films. Hence, a suitable choice of Na2CO3 concentrations should be seriously considered to promote the development of different performances and applications of silk-based materials.