PHYSICAL-PROPERTIES OF 2-HYDROXYETHYL METHACRYLATE-GRAFTED SILK FIBERS

This paper deals with the physical properties of silk fibers grafted w ith 2-hydroxyethyl methacrylate (HEMA). Both tensile strength and elon gation measured in the dry and wet states gradually decreased with inc reasing weight gain. The initial modulus of the grafted silk fibers in the dry state sharply increased in the weight gain range of 0-16%, th en decreased to a lower value than the reference untreated sample. The refractive indices parallel and perpendicular to the fiber axis decre ased, though the former showed a steeper slope. Accordingly, birefring ence and isotropic refractive index also decreased, suggesting a lower degree of crystallinity and molecular orientation of grafted silk fib ers. DSC, TMA, and TGA curves of the HEMA-grafted silk fibers indicate d an increased higher thermal stability of silk fibers due to the HEMA grafting. The dynamic mechanical measurements showed that the thermal ly induced molecular movement of both amorphous and crystalline domain s of silk fibers was enhanced by HEMA grafting. X-ray diffraction curv es, however, implied that the crystalline structure of the silk fibroi n remained unchanged regardless of HEMA polymerization. The introducti on of HEMA polymer in silk fibers was evidenced by the infrared spectr a, exhibiting the absorption bands characteristic of either the grafte d HEMA polymer and the fibroin molecules with ordered beta structure. (C) 1993 John Wiley & Sons, Inc.