Radiation Effects on Polyethylene

Polyethylene is known as one of the typical polymers which crosslink under the influence of ionizing radiation. The radiation-induced crosslinking (the formation of C-C covalent bonds between polymer chains) of polyethylene has long attracted the interest of a large number of research workers, because this polymer has the most simple chemical structure for the fundamental study of radiation effects on polymers, and also because the irradiation with ionizing radiation is a practically important means of modifying the mechanical and thermal properties of polyethylene. 

The recombination between two alkyl radicals is believed to be the main source of radiation-induced crosslinks in polyethylene [21], so that it is important to study the mechanism for formation and reaction of the alkyl radical. We have applied the ESE method to elucidate the paramagnetic relaxation mechanism and the spatial distribution of the alkyl radical, in order to get further insight into the radiation-chemical reactions of polyethylene resulting in the formation of crosslinks. 

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The primary event caused by radiation is ionization or direct excitation of polyethylene chains, RH, which leads to the alkyl radical formation. Toriyama et al. [4] proposed a reaction mechanism for the radiation effect on polyethylene based on the ESR study. They presumed that an alkyl radical and an H atom were generated either directly from the dissociation of the excited state polymer or from the recombination between the cation radical and the electron primarily generated by ionization. There are three possible reaction paths involving the charge recombination ... 

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