Mechanisms and kinetics of hydrogen yield from polymers by irradiation

Abstract

Hydrogen yield from polyethylene by gamma-rays radiolysis was studied to understand the saturation phenomena of products with increase of dose in radiation resistance and also radiation processing of polymers. The hydrogen yield as a primary product was proportional with dose in the lower dose range and decreases gradually with dose above 10 kGy. The mechanism and kinetics were analyzed with a model of radiation protection effect by double bonds formed in polyethylene matrix during irradiation, that is, the double bond formed by primal irradiation reduces the hydrogen detachment from polyethylene molecules surrounding double bond by the following irradiation. By this analysis, one double bond covers about 800 methylene (–CH 2–) groups for the reduction of hydrogen detachment from polyethylene chains. When the 800 (–CH 2–) were concentrated in a sphere with a double bond at center, the radius was calculated to be 1.6 nm, where the radiation energy might be stabilized. G(H 2) was 4.0 for virgin polyethylene chains and was estimated to be 0.6–1 for the chains within the sphere.