Thermal stability of nanocomposites based on polypropylene and bentonite

A polycationic bentonite clay (PB) was organically modified with a quaternary organic salt and added to isotactic polypropylene (PP). The compounds were prepared by melt intercalation using a twin extruder then characterized by X-ray diffraction (XRD), thermogravimetry (TG) and scanning electron microscopy (SEM) for clarifying the composite nanostructure. Compression moulded films were exposed to a thermal oxidative environment at 110 °C in an attempt to evaluate the thermal stability of PP matrix after chemical modification of bentonite. The carbonyl index results, as obtained by infrared spectroscopy, showed that the modified clay had higher thermal stability in the solid state than the natural clay. This may be connected to a higher dispersion of clay particles, reducing oxygen diffusion through the sample. On the other hand, the degradation of the composites was more intense than the unfilled polymer and this may be due to the presence of acidic sites on the clay surface that act as a catalyst to the polymer oxidation, and/or due to salt decomposition, initiating the free radical degradation of PP.