Self-reinforcement of polypropylene by oscillating packing injection molding under low pressure

The influences of processing variables on the mechanical properties of general grade poly‐propylene prepared by oscillating packing injection molding under low pressure were reported. The density as a function of oscillating holding pressure was measured using density gradient columns. The existence of spherulites and shear‐induced shish‐kebab crystals was confirmed from DSC measurements. The texture of self‐reinforced polypropylene was investigated using an X‐ray diffractometer and an X‐ray flat film camera. Investigations indicate that the mechanical properties of polypropylene can be greatly enhanced using oscillating packing 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, respectively. The improvement in mechanical properties is mainly ascribed to perfect spherulites, the existence of shear‐induced shish‐kebab crystals, and the orientation of molecular chains. © 1996 John Wiley & Sons, Inc.