STUDIES ON THE CHEMICAL MODIFICATION OF SILK

Abstract

Instead of using free formaldehyde solution, hexamethylenetetramine (CH2)6N4 was used as acidic solution for the formalization of silk fibroin. Experimental results obtained may be summarized as follows.(1) The best reaction conditions were found to treat silk fibroin in 0.5-1.0% solution of (CH2)6N4, to which 8 equivalents of acetic acid were added (bath ratio 1:50), warmed to 90°C and kept for 40-60 minutes, then rinsed well, centrifuged and dried.(2) CH2O combined with silk fibroin was found to be 0.7% and its alkali solubility was 0.40% which corresponds to 1/6 of that of untreated silk.(3) The tensile strength of the treated silk fibroin, especially its wet strength increased remarkably and the ratio of wet and dry strength reached 92.5%, which is the same value for synthetic fiber, Nylon.(4) Silk fibroin formalized by (CH2)6N4 showed absolute insolubility by Schweitzer's reagent.(5) Affinities of dyestuff and absorption of bromine decreased more than that formalized by free CH2O solution This formalization seems to take place not only in the formation of cross-linkages between serine residues but also between tyrosine residues.(6) The X-ray pattern of (CH2)6N4 treated silk fibroin coincides with that of untreated silk, so that it is true that in this case also formalization took place only in the amorphous region, crystalline region being left intact.(7) The basal costs of chemicals used in both cases of (CH2)6N4 and free CH2O solution were the same, so that the more effective process of hexamethylenetetramine may be applied advantageously in industrial scales.