ELECTRON-BEAM IRRADIATION-INDUCED GRAFTING OF ACRYLONITRILE ONTO POLYETHYLENE

Low- and high-density polyethylene (PE) films were grafted with acrylonitrile (AN) by electron beam prior to irradiation. The distribution of graft chains over the cross section of the sample film was analyzed in terms of the distribution of nitrogen atoms contained in the AN by means of an electron probe microanalyzer (EPMA), and graft sites were studied in relation to the effect of grafting temperature on the percent graft and the oxygen permeability of the sample films. It was found that diffusion of AN into the film was the rate-limiting step in the grafting process, thus restricting the grafting to the surface of the film in the initial grafting stages. However, the grafting shifted to the center of film as the graft process proceeded, until a uniform distribution of graft chains was observed across the entire film thickness. High-density polyethylene (HDPE) was found to display a higher percent graft than did low-density polyethylene (LDPE), and percent graft tended to increase with increasing grafting temperature. On the other hand, film oxygen permeability decreased with increasing percent graft, but this decreasing trend decreased with increasing percent graft. These findings suggest that the grafting is initiated by radicals trapped in the amorphous phase near the crystalline regions and at the surface of crystallites and that graft chains grow toward the amorphous regions. As for the radicals contributing to graft polymerization, it appears that AN permeates deeper near the crystalline surface and that graft chains grow from these sites.