CHANGES IN PHYSICAL-PROPERTIES OF METHACRYLONITRILE (MAN) - GRAFTED SILK FIBERS

Changes in physical properties of silk fibers, grafted with methacrylo nitrile (MAN), were investigated as a function of the weight gain. The weight gain increased steadily during the first 60 min of reaction an d gradually attained an equilibrium value (60%) after about 4 h. The i nitial tensile resistance of silk fibers decreased by MAN grafting. Th e crystalline structure of silk fibers remained unchanged, regardless of MAN grafting, however, a minor and broad peak appeared in the X-ray diffraction curves of MAN-grafted silk fibers with a weight gain of 6 0%, corresponding to the unoriented MAN polymer attached inside the fi bers. Molecular orientation of silk fibroin chains in the crystalline regions, evaluated from X-ray diffraction curves, did not change signi ficantly, while both birefringence and isotropic refractive index decr eased as the weight gain increased, implying that MAN polymer attached preferentially to the amorphous and not to the crystalline regions. D ynamic viscoelastic measurements showed that the position at which the E' value began to decrease shifted to a lower temperature as the weig ht gain increased. These findings suggest that the thermal movement of silk fibroin molecules was accelerated by the presence of the poly-MA N chains attached to the amorphous regions of silk fibroin fibers.