Influence of the morphology of ZnO nanomaterials on photooxidation of polypropylene/ZnO composites

In this study, the effect of zinc oxide (ZnO) morphology on photooxidation of polypropylene (PP)/ZnO nanocomposite films was analyzed by characterizations of their structure, morphology and properties. PP/ZnO nanocomposite films containing 0.25, 0.5, 0.75 and 1.0 weight percentage (wt%) of quasi-spherical (0D-ZnO) and rods (1D-ZnO) ZnO particles were prepared by melt processing followed by compression molding and they were exposed under xenon-arc light irradiation for different durations. Photooxidation process of these nanocomposites was monitored by the presence of oxidative products as well as the weight loss observed using infrared spectroscopy (FTIR) and gravimetric analysis respectively. Surface morphology of PP/ZnO nanocomposite films was analyzed by scanning electron microscopy (SEM). Molecular weight of the polymer was used to observe the extent of cleavage promoted by ZnO morphology in the polymer chains. The morphology of ZnO particles showed an important influence on photooxidation of PP/ZnO nanocomposites. A catalytic effect was observed in the photooxidation of PP nanocomposites with 0D-ZnO by an increase in the carbonyl index, weight loss and erosion of the film surface compared to the pristine PP. The 1D-ZnO nanostructures had a UV-screening effect inhibiting the photooxidation of PP and consequently the rupture of polymer chains during longer periods of time with fewer imperfections on the surface. The results obtained show the effects of the semiconductor nanomaterial concentration and morphology on photo-oxidation of polymer-semiconductor nanocomposites, in this case ZnO particles on PP/ZnO nanocomposites.