Kinetic Study Of Graft Copolymerization Of Acrylate/MAAm, Methacrylate/MAAm Monomer Mixture With Silk Fibroin And The Properties Of The Resultant Silk Product

Silk fabrics have a lot of advantages, such as soft handling, high hygroscopicity andcomfortable wearability. Meanwhile, silk macromolecules are easy to slip in the water, so theirfabrics are poorly in the aspect of shape retaining. Extensive studies show that, after graftingcopolymerization with water-soluble monomer, silk fiber not only retains its original admirablefeatures, but also improves its crease-resistant properties. Nevertheless, the unexpected homo-polymerization occurring in the aqueous medium is accompanied with grafting copolymerization,which causes the decrease of grafting efficiency (Ge) and hard handling. In the latest reports,radicals with high hydrophobicity and low reactivity are proved to be favored by graftcopolymerization. Being inspired by these results, monomer mixtures of MAAm with acrylate ormethacrylate are engaged during silk graft copolymerization. The grafting yield (Gy) andgrafting efficiency (Ge) are investigated.It is found that, in the case of methyl acrylate, ethyl acrylate and butyl acrylate, Gysincrease with dosage and hydrphobicity of acrylate monomer, but Ges are inevitably less than thevalue found for MAAm. When the acrylate is replaced by methacrylate, similar rules areobserved for Gys as the monomer dosage is increased. Moreover, Ges are even higher than thatof MAAm. Further investigation indicates that, other than the increased hydrophobicity effects,the reason for the increased Ges is ascribed to the relatively low reactivity of methacrylatereadical than that of acrylate radical. The detailed mechanism is described as follows: as theradicals become more hydrophobic, they tend to leave the water phase and migrate to the surfaceof silk fibers. Furthermore, the dormant radicals are more readily to migrate to the fibers beforethe occurrence of propagation. Both the two factors enhance the formation of silk radicals, andthus the graft copolymerization.SEM, FT-IR, moisture regaining, and strength measurement are preformed on the silk fibersand grafted silk fibers. Polymer granules and strips are found on the outer surface of fibers. The fiber cross-section become irregular and its surface area grow even higher. In the FT-IR spectra,new peaks centered at1732cm-1and1150cm-1are found for the grafted fibers, which areascribed to the–C(=O)-O-stretching mode and demonstrate the successful graftcopolymerization. Strength loss and low dye uptake properties are also observed for the graftedfibers, but they still meet the wearability requirement for the silk fibers.