Action of water in the degradation of low-density polyethylene studied by X-ray photoelectron spectroscopy

Industrial low-density polyethylene (LDPE) was aged in stagnant distilled water during one year. Two types of this material were studied. The first one was without additives and the second type was doped with 4% of hindered-amine light stabilizers (HALS). Using X-ray photoelectron spectroscopy (XPS), the evidence that an oxidation occurs was demonstrated for the two types of LDPE (with and without HALS). One objective was to observe the chemical groups resulting of the ageing and to propose a mechanism of hydrolytic degradation for LDPE. The analysis of C1s spectra shows that the main oxidation products are C-O and C=O groups. Unlike the hydrolytic degradation of polypropylene, there is no presence of O=C-O groups, which suggests that there is no oxidative chain scission during hydrolytic ageing of the LDPE. The other objective of the study was to observe if the HALS can have an influence in the hydrolytic ageing of the LDPE. The values of the atomic concentration of the oxygen for the two types of samples show that the HALS could slightly slow down the oxidation of the LDPE.