Thermal properties of polyethylene/montmorillonite nanocomposites prepared by intercalative polymerization

A comparative study of thermal and thermal-oxidative degradation processes for polyethylene/organically modified montmorillonite (PE-MMT) nanocomposites, prepared by the ethylene intercalative polymerization in situ with or without subsequent addition of an antioxidant is reported. The results of TGA and time/temperature-dependent FTIR spectroscopy experiments have provided evidence for an accelerated formation and decomposition of hydroperoxides during the thermal oxidative degradation tests of PE-MMT nanocomposites in the range of 170-200 degrees C as compared to the unfilled PE, thus indicating to a catalytic action of MMT. It has been shown that effective formation of intermolecular chemical cross-links in the PE-MMT nanocomposite has ensued above 200 degrees C as the result of recombination reactions involving the radical products of hydroperoxides decomposition. Apparently, this process is induced by the oxygen deficiency in PE-MMT nanocomposite due to its lowered oxygen permeability. It is shown that the intermolecular cross-linking and dehydrogenation reactions followed by the shear carbonization lead to appreciable increase of thermal-oxidative stability of PE nanocomposite, as compared to that of pristine PE. Notably, the TGA traces for the antioxidant-stabilized PE-MMT nanocomposites recorded in air were quite similar to those obtainable for the non-stabilized PE-MMT nanocomposites in argon. The results of treatment of the experimentally acquired TGA data in frames of an advanced model kinetic analysis are reported and discussed.