ESR STUDIES ON OXIDATION PROCESSES IN IRRADIATED POLYETHYLENE .2. DIFFUSION OF OXYGEN INTO CRYSTALLINE REGIONS

The oxidation process in irradiated polyethylene was investigated by means of the e.s.r. method, and diffusion of oxygen molecules into the crystalline region of polyethylene was studied in detail. Computer simulation was carried out in order to determine various parameters of the process including diffusion constant. In the course of the simulation, the crystallite was assumed to have a plate-shaped form and the diffusion constant was considered to be larger at the region near the surface of the crystallite, Df, and to be smaller at the inner region of the crystallite, Ds. Making these assumptions in the simulation gave a much better result than the assumption based on a sphere-shaped crystallite. Df Ds was found to be about 2 for thicker crystallite and it was 4 ∼ 5 for thinner crystallite. Diffusion constants at various temperatures were determined, and the order of magnitude of diffusion constants in the crystalline region was found to be 10-16 cm2/sec at about 320K both for thicker and thinner crystallites. The activation energy of diffusion of oxygen in the crystallites was found to be 32 kcal/mol. © 1979.