Photodegradation characterization and heterogeneity evaluation of the exposed and unexposed faces of stabilized and unstabilized LDPE films

The impact of climatic ageing on the characteristics of both unexposed and exposed faces of unstabilized and stabilized LDPE films was investigated. The effects on chemical and mechanical properties and on the heterogeneity in the films properties were discussed. The exposure periods were 8 and 21 months for the unstabilized and stabilized films, respectively. The ATR-FTIR spectra detected initial presence of vinylidene groups that disappeared after 4 months of weathering for both faces of the unstabilized films and disappeared earlier for stabilized films. It identifies also a progressive evolution of other photooxidation products, i.e. vinyl and carbonyl groups. The stabilized film demonstrated much better mechanical stability. Considerable reduction in the tensile toughness of unstabilized film was observed. The unstabilized film became quite fragile after 6 months of exposure to sunlight to the extent it cannot be tested, while the stabilized film was exposed up to 21 months exhibiting much higher durability. The microhardness MH measurements show increasing trend with weathering time and the impact on the exposed face of the unstabilized film was more severe. The ageing resulted in heterogeneity in the films properties and the MH and ATR-FTIR techniques could be used to evaluate its level.