The stress relaxation of thermoplastic elastomer–the influence of oxygen on the network structure of SBS during γ‐radiation

Abstract

Abstract Thermoplastic elastomer (TPR) of the SBS type was irradiated in a vacuum and in air with various gamma dosages of Co‐60 at room temperature, and the stress relaxation behavior of the irradiated TPR was studied in air and in a nitrogen atmosphere. It was found that TPR was crosslinking during irradiation both in air and in a vacuum, and the crosslinking density of TPR irradiated in air was found to be higher than that irradiated in a vacuum. This result may be attributed to the presence of oxygen which could participate in the radiation‐induced reaction. A TPR sample irradiated in a vacuum showed very extensive physical stress relaxation and minor chemical stress relaxation, measured both in air and in nitrogen. The latter could be caused by oxidative chain scission along the main chain. However, the chemical stress relaxation of TPR irradiated in air was found to be different from that irradiated in vacuum. In addition to the oxidative chemical stress relaxation, the former was further caused by the scission of crosslinking site which was formed during Co‐60 irradiation.