Structural analysis of methyl methacrylate‐grafted silk fibers

Abstract

AbstractThe structural changes of silk fibers grafted with methyl methacrylate (MMA) were investigated in relation to the weight gain. Both the refractive indices, parallel and perpendicular to the fiber axis, decreased with increasing weight gain, although the former showed a step drop in the weight gain range of 0–30%. Accordingly, birefringence and the isotropic refractive index also decreased, suggesting a lower degree of molecular orientation and crystallinity of MMA‐grafted silk fibers. However, X‐ray diffraction curves demonstrated that the crystalline structure remained unchanged, regardless of MMA grafting, implying that the MMA polymer attached preferentially within the amorphous regions of the fiber. Tensile strength and elongation at break of the grafted silk fibers, measured in dry and wet states, gradually decreased over the weight gain range examined. MMA‐grafted silk fibers in wet state exhibited comparatively lower values of strength and elongation, though the hydrophobicity, induced by the grafted polymer, resulted in an attenuation of the differences, especially at high weight gains. TMA analysis demonstrated that the onset temperature of the final extension shifted to a higher value, in the weight gain range 30–50% Dynamic mechanical measurements showed that the thermally induced molecular movement of MMA‐grafted silk increased, as illustrated by the trend of both dynamic storage and loss modulus curves. © 1993 John Wiley & Sons, Inc.