The determination of the reaction rates, water vapor permeability, and activation energy for thermal oxidation of LDPE films

To understand the mechanism of degradation of plastics under environmental conditions, thermal oxidation of LDPE thin film from a single manufacturer was studied. Oxidation was carried out in a pressure vessel with control at four temperatures(22,50,70 and 80℃ and at 30 and 50psi oxygen pressures. Cup tests were done to determine the permeability of water vapor across the LDPE film at 60, 70, and 90^0C. The extent of oxidation was monitored using ATR-FTIR and the carbonyl content calculated from the spectra. Bands centered at 1711 and 1735 cm^-1 was determined resulted from the carbonyl stretches. A broad band at 3100-3600cm^-1 is attributed to O-H stretching and the fingerprint region (<1400 cm^-1) shows evidence of C-O stretches. The carbonyl content and permeability to water vapor increased with temperature, oxidation time, and oxygen pressure. Water permeation is a result of the disruption of the semi-crystalline structure of the film to produce amorphous regions within which the water vapor is more permeable. This study was a step in the direction for determining a reliable model for the degradation and eventual failure of medium voltage power cables in nuclear power plants (NPPs).