Effect of reprocessing and clay concentration on the degradation of polypropylene/montmorillonite nanocomposites during twin screw extrusion

An evaluation was made of the degradation of polypropylene (PP) and montmorillonite (MMT) nanocomposites. The nanocomposites were compatibilized with polypropylene grafted with maleic anhydride (PP-g-MA) and with acrylic acid (PP-g-AA). The concentration of MMT varied from 1 to 5% (w/w). Nanocomposites were processed in a twin screw extruder up to five times. X-ray diffraction showed a decrease in the refraction angle with reprocessing steps and for PP-g-MA based nanocomposites, indicating an increase in the interplanar distance due to clay intercalation and exfoliation. Infrared analysis showed an increase in the concentration of carbonyl and unsaturated groups with the increase in the number of reprocessing cycles, and reduction as the MMT concentration increased. Colorimetry assays indicated a decrease in the luminosity and degree of redness due to the oxidation of the iron ions present in MMT to Fe2O3. The intensity of the yellow color of the b* coordinate was augmented with the number of reprocessing cycles but decreased with MMT concentration, confirming the FTIR analysis. Rheological measurements showed no crossing point between storage (G′) and loss (G″) moduli versus frequency, which is characteristic of a percolated nanocomposite networks. Within a range of frequencies, complex viscosity decreased with the number of reprocessing cycles, but the presence of montmorillonite was found to be responsible for lower differences between viscosity of nanocomposites reprocessed one and five times.