Rheological, morphological and thermal properties of pickering-like EVA/organoclay nanocomposites

Abstract

Pickering-like ethylene vinyl acetate copolymer (EVA)/organoclay nanocomposites were prepared by melt mixing with two different compatibilizers: polyethylene-grafted maleic anhydride and ethylene propylene diene monomer-grafted maleic anhydride. The linear dynamic viscoelasticity, transient and intermittent shear flows, thermal stability, and dispersion state of organoclays were investigated in detail. Before taking rheological measurements, transmission electron microscopy (TEM) and X-ray diffraction were employed to evaluate organoclay intercalation and exfoliation in the nanocomposites. Interestingly, TEM micrographs showed that organoclay platelets were trapped at the interface and bent around the compatibilizer droplets, such as in Pickering emulsions. The intermittent shear flow experiments indicate that structural reorganization during the rest period upon cessation of the initial transient occurred in the EVA/Cloisite 20A nanocomposites, while there was very little evidence of such a state for the EVA/Cloisite 30B nanocomposites. Addition of the compatibilizers to the nanocomposites leads to an increase in overshoot peak both in the initial transient flow and during intermittent shear flow after a rest time. Thermogravimetric analysis and real time Fourier transform infrared spectroscopy indicated that organoclays retard thermal degradation depending on organoclay concentration. The results of micro-scale cone calorimetry showed that the peak of the heat release rate and total heat release of the EVA/organoclay nanocomposites decreased dramatically compared with those of pure EVA, and both compatibilizers could considerably improve the thermal stability and remarkably delayed thermal oxidative degradation of nanocomposites.