Enhanced formation of free radicals in irradiated LDPE containing ZnO

Abstract

The concentration of free radicals formed under γ-irradiation in low-density polyethylene (PE) containing zero, 0.01, 0.02; 0.05; 0.1; 0.2 and 0.4 vol% ZnO was measured by using the technique of ESR spectroscopy. When samples are irradiated in air an increase of the total amount of free radicals compared to that of pure polymer without ZnO was observed. This increase appeared over the whole range of ZnO content, with a maximum at about 0.02 vol% ZnO. The results obtained by ESR are consistent with the data on gel formation reported in a previous paper.(1) A comparison of ESR data obtained on samples in air and in vacuo suggests that the phenomenon is due to the presence of oxygen during irradiation and that it is probably the result of two dominant processes taking part at the interface of ZnO and PE chains: the first one is the preferential formation of free radicals on the chains distorted in the neighbourhood of ZnO particles, whereas the second process is relevant to the interaction between formed radicals and oxygen diffused into the system. Other possible causes of the increased generation of free radicals are also considered. © 1987.