Rheological properties and UV photo-oxidation of montmorillonite-filled random propylene-ethylene copolymers

Random propylene-ethylene copolymers (RPC) are a type of polyolefin in increasing demand, mainly for packaging, due to its high impact resistance, large durability as well as high transparency and flexibility. The present study aims to investigate the morphological and rheological properties, as well as the photo-oxidation by UV irradiation, of five different RPCs and their nanocomposites. Organophilic montmorillonite is used as filler and maleic anhydride grafted RPCs as compatibilizers. Aging was performed by exposing strips of materials to UVA radiation for a maximum period of 96 h, and material degradation was analyzed following the evolution of carbonyl and hydroperoxide groups by FTIR and crystallinity by DSC. All nanocomposites display intercalated-exfoliated structure being the largest particle disaggregation presented by the polymer with the largest molecular weight. Rheological results support these observations. Neither the chemical composition of the polymers nor the presence of nanoclay/compatibilizer affects the photo-degradation mechanism of copolymers although the composite structure promotes the matrix photo-degradation. A parabolic relation was found between carbonyl and hydroxyl indexes of all stabilized and extracted materials, with or without clay. An increase in crystallinity with UV radiation dose was observed in all systems with a maximum determined in the case of the extracted systems.