Impact of Combined Thermo- and Photo-Oxidation on the Physicochemical Properties of Oxo-Biodegradable Low-Density Polyethylene Films

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This research addresses the study of the combined effect of two abiotic treatments, a thermo-oxidative treatment followed by a photo-oxidative treatment with ultraviolet light, on the physicochemical properties of commercially available low-density polyethylene films with an oxo-degradant additive (OXOLDPE) and without (LDPE). The change in the oxidized film properties was characterized using FTIR, XRD, TGA, GPC, and SEM analytical techniques. The results indicated that the increment in carbonyl index (CI) and crystallinity percentage (XXRD) was higher for those films that received the combined oxidative treatments compared with those that received only one of them, thermo- or photo-oxidative treatment. Moreover, the combined oxidative treatments produced more ester and carboxylic groups on the degradation products than the other single treatments. An analysis of variance (ANOVA) was carried out, and a synergistic effect was observed between the thermo- and photo-oxidative treatments for both ester and carboxylic degradation products. TGA results revealed that the loss of thermal stability in the films was more significant after their exposure to the combined thermo- and photo-oxidative treatments compared with those which received only one. The GPC results showed that the combined oxidative treatment is necessary to decrease the Mz and Mz+1 average molecular weight of degraded films containing an oxo-degradant additive to the same extent as MW and Mn. The SEM surface appearance of the films changed more drastically after their exposure to the combined thermo- and photo-oxidative treatments, and they seemed to erode with the presence of inorganic fillers (CaCO3). These results suggest that the combined oxidative treatments produced degradation products with lower molecular weight and greater content of ester and carboxylic groups that should enhance its environmental biodegradability.