Injection molding of polypropylene reinforced with thermotropic liquid crystalline polymer microfibrils. Part II: Effect of impact toughening

This paper represents a continuation of our effort to develop a robust composite system based on polypropylene (PP) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) microfibrils. The focus of this paper is the effect on mechanical properties of replacing a conventional PP with a toughened PP (Hivalloy from Basell). It was observed that using the Hivalloy matrix in place of a conventional PP lead to a 50% increase of impact toughness (unnotched Izod test), and the values were only about 20% less than those observed for a glass reinforced Hivalloy (G7155). Furthermore, the tensile modulus, strength, and elongation-at-break of the injection molded Hivalloy/TLCP composites are statistically identical to those values for conventional PP/TLCP composites. The modulus of PP/TLCP composites could be made to exceed those of Hivalloy/glass composites by increasing the level of TLCP beyond what is possible with glass. Furthermore, the surface roughness of the PP/TLCP composites as measured by an atomic force microscope was significantly less than that of glass reinforced PP.