RAFT-mediated radiation grafting on natural fibers in aqueous emulsion

Using aqueous emulsion as the medium in radiation-induced graft polymerization (RIGP) offers an environment-friendly shift from organic solvents while increasing polymerization efficiency through known water radiolysis-based graft initiation. It has been successfully applied to a variety of hydrophobic vinyl monomers conventionally grafted in bulk or solution. Here, we further extend the applicability of RIGP in emulsion under the influence of reversible addition-fragmentation chain transfer (RAFT) polymerization mechanisms. Emulsions consisting of glycidyl methacrylate, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid, and Tween-20 showed good colloidal stability for several hours. These emulsions were then used to graft abaca fibers through simultaneous gamma irradiation up to 6 kGy. Emulsions with smaller monomer micelles seemed to enhance the degree of grafting as a function of diffusion coefficient and surface area coverage. The degree of grafting also increased linearly with irradiation time before plateauing, at which point conversion indicated complete consumption of monomers. Indirect molecular weight analysis – using the free polymers generated during RIGP – showed good agreement with theoretical calculations and displayed relatively low polydispersity. Successful grafting was further supported by IR, SEM, and TG analysis. RAFT-mediated RIGP in aqueous emulsion shows good potential as a versatile and green surface modification technique for natural fibers for various functional and industrial applications.