Graft copolymerization onto silk (Bombyx niori) was carried out with vinyl monomers (methyl methacrylate and acrylamide) and initiated by a semiconductorbased photocatalyst (cadmium sulfide). The utility of a semiconductor as an initiator in free-radical photografting and the effects of ethylene glycol and triethylamine with cadmium sulfide on graft copolymerization were explored. Depending on the reaction conditions, 10-48% grafting with methyl methacrylate and,4-26% grafting with acrylamide were achieved. The reaction conditions were optimized, and the grafted fibers were characterized with scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetry analysis, and tensile strength measurements. The chemical resistance and water absorption of the grafted fibers were compared with those ungrafted fibers. (c) 2007 Wiley Periodicals, Inc.