Temperature dependence of gas evolution from polyolefins on irradiation under vacuum

The yields of gases evolved from three types of polyethylene and ethylene-propylene copolymer during radiation were precisely measured after gamma ray irradiation under vacuum over a wide range of temperatures (−196 to 200 °C). For all polymers the major gas evolved was H2 and the minor products were C1, C2, C3 hydrocarbons and the oxidation compounds CO2 and CO. The total gas yield increased with an increase in the irradiation temperature, but the ratio of the yields among the gas components was not greatly changed. The H2 would originate from H-bond scission and the concomitant formation of crosslinks and double bonds in the polymer chains. The minor products of C1, C2, C3 hydrocarbons were products of chain scission at the chain ends, including branched chains, and the oxidation compounds of CO and CO2 were the products formed by reactions of oxygen remaining trapped in the polymer matrix. The yield of H2 increased with increasing irradiation temperature, which is closely related to the molecular motions of the polymer chains during irradiation.

► The study concerns the effect of irradiation temperature on gas evolution of polymers.
► Major gas is H2 and the minor gases are C1, C2, C3 hydrocarbons.
► CO and CO2 are the oxidation products formed by reaction of a polymer radical.
► H2 is related to the molecular motions of the polymers during irradiation.