Effect of multiple extrusions on the impact properties of polypropylene/clay nanocomposites

Polypropylene (PP)-based polymer nanocomposites containing organically modified montmorillonite (OMMT) with and without maleic anhydride grafted PP, were compounded by twin-screw extrusion. The extrusion process was repeated various numbers of times to increase the extruder residence time (TR) and, through that, the particle dispersion. Rheological measurements fitted to a modified CarreauYasuda model defining a melt yield stress were used to indicate changes in the particle dispersion with regard to TR. This analysis showed a monotonically increased dispersion of clay particles in the PP matrix with increasing extruder TR. The small-strain tensile properties were tested at both ambient (20 degrees C) and elevated (90 degrees C) temperatures, and no significant changes were observed in the tensile strength or modulus as a function of TR. Instrumented Izod impact tests showed that the nanocomposite impact strength (si) increased monotonically with increased TR by 70% from least dispersed to best dispersed, which was still 20% below the level for neat PP. Both the fracture initiation energy and propagation energy increased with TR, but the primary effect on si came from the fracture propagation energy, which delivered 80% of the improvement. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012