Thermo-oxidative aging of low density polyethylene blown films in presence of cellulose nanocrystals and a pro-oxidant additive

Abstract

The effect of the presence of cellulose nanocrystals (CNC) and a commercial pro-oxidant additive on the production of oxidized species, crystallinity, thermal and tensile mechanical properties of low-density polyethylene (LDPE) blown films, thermally aged for 75 days at 60 °C, was studied. The oxidation products were monitored by Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Changes in the crystallinity were determined by X-ray diffraction (XRD), whereas the thermal properties with differential scanning calorimetry (DSC). The change in the strain at break and maximum strength of films were determined by tensile testing according to the ASTM D882 Standard Test Method. The results indicate that the thermal degradation of the LDPE films consisted of two stages: the oxidation of the polymer chains (determined by XPS, FT-IR and XRD) in the first aging stage; and the scission of the polymer chains in the advanced stage of oxidation (suggested by the drop in the strain at break of blown films). It was found that the addition of the pro-oxidant additive catalyzes the formation and decomposition of hydroperoxides and carbonyl groups during the thermal aging process; whereas the addition of CNC induces a slight thermo-oxidation during the blowing process and promotes the formation of carboxylic acid groups. Even more, the production of oxidized species induced by the CNC is comparable to that from the commercial pro-oxidant additive throughout the thermal aging. These findings suggest that CNC would be an attractive green alternative to metallic pro-oxidants to produce oxo-biodegradable polyethylene blown films.