Use of processing aids and coupling agents in mica-reinforced polypropylene

Low molecular weight waxes prepared by the maleation of thermally degraded polypropylene are effective substitutes for silane coupling agents in filled polypropylene resins. The addition of 1 to 5 percent maleated polypropylene wax increased the tensile and flexural strength of mica-filled polypropylenes without significant changes in the modulus or fracture toughness. The waxes also aided dispersion, reduced melt viscosity, and permitted direct injection molding of powder blends without precompounding. The influence of maleated polypropylene wax coupling agents on the mechanical properties is similar to the published behavior of chlorinated paraffin waxes, but without the undesirable corrosiveness. The efficient utilization of untreated micas as reinforcing fillers for general purpose polypropylene homopolymers can have important cost savings in the fabrication of mica-reinforced automotive components.