Infrared Spectroscopic Study of the Thermo-Oxidative Aging of Polyethylene Containing Pro-Oxidant

Abstract

Synthetic polymers are not normally biodegradable until they are degraded into low molecular mass species that can be assimilated by microorganisms. This means that biodegradation must be preceded by an abiotic degradation that produces monomeric and oligomeric products. It has been shown that carboxylic acids, alcohols, ketones, etc... can be utilized by microorganisms as nutrients to produce cell biomass. Polyethylene is resistant to oxidation and biodegradation because of the presence of antioxidants and stabilizers. However, it can be made oxo-biodegradable by the use of prooxidant additives. The most active prooxidants are those based on transition metal particulary Fe, Co and Mn. This study is an attempt to investigate the effect of prooxidant additives on the thermo-oxidation of polyethylene. Three differentes mulch films of polyethylene, two films with prooxidant additives consisting of salt based on cobalt and iron and the third film whitout prooxidant, were subjected to thermo-oxidative degradation which was conducted in an air oven at 70°C that normally occur during composting conditions, for extended time periods. Based on Fourier transform infrared spectroscopy the chemical and structural changes induced by this exposure were followed by monitoring the changes in carbonyl index and cristallinity. The results reveal an increase in the carbonyl groups with aging time more important for the polyehylene films containing a combination of Fe and Co additives than these obtained by the films with only one transition metal additive (Co) while the LDPE without additives represents no increase in carbonyl groups. The results show also a small variation of cristallinity for the two differents polyethylene films with pro-oxidant. This indicates that the transition metal prooxidant plays an important role in the degradation of PE films and accelerates the degradation of PE.