Investigation of thermal and thermooxidizing degradation of irradiated polyethylene

Abstract The peculiarities of thermal and thermooxidizing degradation of low‐ and high‐density polyethylene (PELD, PEHD) and the ethylene‐propylene copolymer (CEP‐7) irradiated over the range of 1 to 300 Mrad have been studied. It was established that the change of structure of polymer by irradiation resulted in an increase of thermostability and a decrease of thermooxidation stability. The change of content of double bonds as a result of pyrolysis was studied. It was suggested that trans ‐vinylene double bonds promoted the development of thermal degradation of irradiated polymer and vinylidene double bonds were slowing down this process. It was found that in nonirradiated branched PELD and CEP‐7 side groups and tertiary carbon atoms oxidized. In nonirradiated linear PEHD the oxidation occurred mainly with the partipation of secondary carbon atoms. The initial polymer structure had an influence on the process of oxidation of irradiated polymers. Cross‐linking bonds and tertiary carbon atoms were the most vulnerable to the oxidation of irradiated polymers. Simultaneously with the degradation, during oxidation of irradiated polymers a structuralization with the formation of ether bonds R‐O‐R takes place.