SELF-REINFORCEMENT OF POLYPROPYLENE BY OSCILLATING PACKING INJECTION-MOLDING UNDER LOW-PRESSURE

The influences of processing variables on the mechanical properties of general grade polypropylene prepared by oscillating packing injection molding under low pressure were reported. The density as a function o f oscillating holding pressure was measured using density gradient col umns. The existence of spherulites and shear-induced shish-kebab cryst als was confirmed from DSC measurements. The texture of self-reinforce d polypropylene was investigated using an X-ray diffractometer and an X-ray flat film camera. Investigations indicate that the mechanical pr operties of polypropylene can be greatly enhanced using oscillating pa cking injection molding. The Young's modulus and tensile strength have been enhanced from original 1.4 GPa, 31.0 MPa to 3.0 GPa, 57.8 MPa, r espectively. The improvement in mechanical properties is mainly ascrib ed to perfect spherulites, the existence of shear-induced shish-kebab crystals, and the orientation of molecular chains. (C) 1996 John Wiley & Sons, Inc.