Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content : I. Changes in molecular weight distribution

Abstract

Unstabilisedsamples of low-density polyethylene were heated in nitrogen containing small amounts of oxygen. The changes in molecular weight distribution were followed by gel permeation chromatography and intrinsic viscosity. A threshold temperature was found at 315° and a threshold oxygen concentration in the range 410–1000 p.p.m. In accordance with the theory of random scission, degradation caused a shift of the peak position towards lower molecular weights and an increasing skewness of the molecular weight distributions within the original molecular weight limits. No drastic drop of M w/ M n observed. A simplified method for the construction of gel permeation chromatography calibrations for low- and high-density polyethylene, from measurements on polystyrene standards, is demonstrated. The method is based on the concept of “universal calibration”.