Dose rate effect on radiation‐induced oxidation of polyethylene and ethylene‐propylene copolymer

Abstract

In the presence of oxygen the oxidation reaction is fundamentally important among the effects of radiation on polymer degradation. When a thick polymer film is irradiated in air the oxidation reaction is controlled by the diffusion of oxygen and the cause of the effect of dose rate on radiation degradation of polymer. This dose rate effect may be eliminated if oxygen is supplied to the sample during irradiation at a rate higher than its consumption. Even under this condition, however, the dose rate effect may still be observed.' To estimate the degradation of polymer under a low dose rate for a long period this dose rate effect should be investigated. Accordingly, the yield of oxidative product in the polymer matrix and the changes in gel fraction are being studied. The first results are reported here for polyethylene (PE) and ethylene-propylene copolymer (EPR).Polyethylene (Sumitomo Chemical Co. Ltd., Sumikathene G804) was used in powder form and film 0.5 mm thick after recrystallization from xylene solution for purification; EPR (Japan Synthetic Rubber Co. Ltd., EP07P) was used in film 0.5 mm thick by compression molding without further purification. The samples were evacuated in a glass tube equipped with a break-off-seal and filled with pure oxygen at various pressures. They were then irradiated by co-60 y-ray up to 2.0 X lo7 rad with a dose rate of 1.4 X lOf2 X lo6 rad/h. To eliminate the oxygen-diffusion-controlled reaction

Mechanism of Post-Radiation-Chemical Graft Polymerization of Styrene in Polyethylene

“…Thus, it can be stated that, as a result of irradiation, the surface of PE samples is enriched with oxygen-containing compounds, including peroxides [ 24 ], to a greater extent as compared to their volume. We found that the radiation yield of oxygen-containing compounds slightly decreases with increasing sample thickness over 100 μm, which should be taken into account when analyzing the products of graft polymerization [ 25 , 26 ].…”

The effect of oxygen on the irradiation process of ethylene–butene copolymer

“…Irradiation-induced oxidation has been reported to depend on the crystallinity of the polymer [4,5,11e13], oxygen diffusion [1,2,4], the presence of antioxidant or antirad agents [3,14], and total dose. Several authors have concluded that irradiation rate is also an important variable, although at least in some cases this could be assimilated to the effect of oxygen diffusion, since lower irradiation rates allow time for oxygen to diffuse into the samples [15].…”

Effects of radiation types and dose rates on selected cable-insulating materials

“…Of course, this simple relation could hold only at low enough dose rates, where the degradation is dominated by the reactions considered in its derivation [8,9]. For instance, for oxygen to be available throughout a sample of our type and thickness, dose rates should be lower than 30-60 mGy/s.…”

“…This result has been expected under the assumption that a peroxy chain-reaction degradation mechanism is fully operative. In the discussion of a previous long-term irradiation experiment [3] a relation between the end-point dose De and dose rate D has been used in the limit of small dose rates [8,9]:…”