CHEMICAL-STRUCTURE AND DYNAMIC-MECHANICAL BEHAVIOR OF SILK FIBERS MODIFIED WITH DIFFERENT KINDS OF EPOXIDES

The chemical reactivity of epoxide molecules toward silk fibroin was i nvestigated by determining the rate of conversion of reactive amino ac id residues. Significant differences were found between two different bifunctional epoxides, diglycidyl ethers of ethylene glycol (E) and re sorcinol (R), the former reacting at a higher extent with arginine and tyrosine. The moisture regain decreased by reaction with epoxides, at a variable rate and extent, according to the hydrophobic / hydrophili c properties of epoxides. A two-step behavior was observed when moistu re regain values relating to the silk content in modified silk fibers were plotted as a function of the weight gain. Dynamic mechanical data showed that the major loss peak became broader and its temperature sh ifted to lower values following the increase of weight gain. The loss peak temperatures showed a linear relationship with the amount of weig ht gain. The fine structural changes induced by reaction with epoxides will be discussed in terms of chemical and steric factors of the epox ides, as well as of epoxide location within the different structural d omains of silk fibers. (C) 1994 John Wiley & Sons, Inc.