1993 Volume 2 Pages 60-67
Molded silk was prepared from the powder of silk yarn. It was found that the properties of this molded silk were influenced by the properties of fibroin powder.
Two methods for the preparation of silk powder had been studied. In calcium chloride method, very little breakage in the molecules of fibroin were observed and the molecules took random coil structure. It was found that the relatively high crystalline powder could be produced due to destruction of non-crystalline part of fibroin by sulfuric acid treatment.
But the longer treatments with sulfuric acid damaged the crystalline part and the strength of the molded products decreased. Treatment with sulfuric acid for 2 hours was most suitable for silk molding. It was found that the strength of molded product was high when the fibroin powder contained 8% water molecules. Treatment for 30 minutes at 120°C under a pressure of 1 ton/cm2 were the best conditions.
The silk molding has a strength of only about one-third that of polyamide resin, which was not sufficient for practical use. Moreover cracking appears in the molding when immersed in water, and this may become a problem to be solved when used in practice. Therefore, silk powder was chemically modified with methacrylic acid ester (MMA : Methylmethacrylate, GMA : Glycidylmethacrylate). As a result, the water resistance of the molding was improved.
Furthermore, the GMA-silk mold acquired a strength comparable to ordinary plastics. It was found that the functional epoxy gorup was bonded with the C-terminal of the silk fibroin.