High resolution solid state NMR study on the radiation damage of polyethylene

Radiation damages of linear and high pressure-method polyethylenes were studied by high resolution solid state NMR. Changes on the solid state properties by irradiation were well analyzed with spin lattice relaxation of carbon nucleus. Crystalline, amorphous, and the border area between the two regions were clearly separated from each other in the relaxation curve of 13C magnetization by a non-linear least square method, through which the ratio between those regions and the molecular mobilities were obtained. The amorphous region of high pressure-method polyethylene increased prominently with the dose of 5 MGy. On the other hand, in the case of linear polyethylene, no increase in amorphous region was detected but it became a little solidified with the irradiation up to 4 MGy. Since there is an induction period for the increase of amorphous region, it is suggested that multi-shot in a small region is necessary for the formation of amorphous region by irradiation. (author)