Double stage oxidation of polyethylene as measured by chemiluminescence

The double stage oxidation of LDPE has been investigated by chemiluminescence (CL) with the aim of determining the processes corresponding to each oxidation stage. The nonisothermal chemiluminescence exhibiting two peaks used for monitoring evolution of hydroperoxides in thermo-oxidatively aged samples confirms two stages of oxidation and reveals a gradual reduction in stability of formed peroxides and in crystalline content of recrystallised sample after ageing. The effect of oxygen concentration on CL of PE oxidation has been examined indicating that the double stage oxidation is related to the transfer of the system to a strictly oxygen diffusion controlled process. The results are supported by FTIR measurements and determination of gel content which reveal that crosslinking takes place only in the second oxidation step.