Thermal degradation of polyethylene

Abstract

Abstract : The thermal degradation of high and low pressure polyethylene (HPPE and LPPE) at temperatures from 325 to 415C was investigated under vacuum in a closed system and under conditions of removal of the volatiles from the reaction space. An IR spectrum analysis of the degradation products demonstrated that when the reaction is carried out in the closed system at 360C and higher, secondary reactions between the pyrolysis products leading to increase in trans-vinylene and decrease of vinyl unsaturation become of importance. The increase in the relative number of trans-vinylene double bonds in the PE pyrolysis products is not in accord with the scheme of formation of such bonds in degradation of the polymeric chain at the free radical center close to the branching node of the chain. It is suggested that trans-vinylene double bonds are formed as the result of migration of the end double bonds to the middle of the chain, and also of intramolecular encounter of two free radical centers. It was found that inorganic impurities in PE effect the distribution of the unsaturation in its thermal degradation products. The reason for the higher thermal resistance of LPPE than HPPE is discussed. (Author)