Studies on the Oxidation of High Polymers

V. Effect of Thickness of Samples on the Oxidation Rate of Polyethylene

Abstract

The rates of oxidation of high polymers are influenced by the thickness of samples. Their reaction rates depend upon principally their oxidizability and oxygen diffusibility into samples. The author measured the oxidation rates of polyethylene at 120°C and above, varing the thickness between 0.05 mm and 3.0 mm. On oxidation existed short induction periods, and after that periods, reaction rates increased rapidly, via maximum, decreased also rapidly. Activation energy calculated from maximum rates was 33 kcal/mol, if the samples were enough slight. When the samples were sufficiently thick, activation energy was 17 kcal/mol. And the diffusion equation on supposing that oxidation rates are proportional to the oxygen content, was solved and compared with experimental results.