Degradation products formed during UV exposure of polyethylene-ZnO nano-composites

Photodegradation of low density polyethylene (LDPE) containing nano-particulate ZnO has been studied using FTIR to follow the development of oxidation products in the polymer film and to monitor carbon dioxide evolved as a principal product of oxidation. The degradation behaviour of ZnO-free LDPE has been compared with that of compounds containing 0.25% and 0.75% ZnO and these results are compared with those obtained using similar films containing nano-particulate TiO₂. Under UV exposure, the presence of ZnO accelerated the development of carbonyl groups and CO₂ production. The carbonyl group development was more rapid when TiO₂ was used whereas ZnO caused greater CO₂ generation. Carbonyl group development seemed to correlate better with the reduction in mechanical properties whereas CO₂ generation correlated better with weight change measurements. The influence of ZnO on the oxidation pathways in LDPE is discussed; it is proposed that photo-oxidation is relatively much more likely to occur at terminal sites (rather than at pendent sites) when ZnO is present.