Thermo-Oxidative Aging of LDPE/Stearoyl Chloride-Grafted Cellulose Nanocrystals Blown Films

The effect of the incorporation of pristine and stearoyl chloride grafted CNCs on the chemical, mechanical, thermal and microstructural properties, during the thermo-oxidative aging, of LDPE blown films at 60 °C was studied. The success of the pristine CNCs grafting was assessed by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Thermal-gravimetric analysis (TGA), Atomic Force Spectroscopy (AFM) and contact angle measurements. The results show that chemical modification decreases both, the CNCs thermal stability and the polar component of surface energy, i.e. increases the nanocrystals hydrophobicity. Also, it was found that neither CNCs crystalline structure nor its dimensions changed with grafting. The changes on the blown film properties during thermo-oxidative aging were monitored using FT-IR, DSC, DRX and tensile testing. It was found that the CNCs catalyzed the production of carboxylic acids as a final degradation by-product, whereas the CNC-g-C₁₈ inhibits its formation, i.e. in presence of CNCs grafted with stearoyl chloride the catalytic effect attributed to the pristine CNCs was partially inhibited. The DSC, DRX and tensile testing results show the microstructural arrangements due to the annealing and the chains oxidation predominated during the first 30 days of aging and then chain scissions prevail. These findings suggest an analogous reduction in molecular weight at the end thermo-oxidative aging. In addition, the presence of a high concentration of carboxylic acid and the drop in molecular weight after LDPE aging will facilitate the biodegradation of these oxo-degradable films.