MECHANICAL-BEHAVIOR OF INJECTION-MOLDED BETA-CRYSTALLINE PHASE POLYPROPYLENE

High purity and a large amount of beta-modification can be produced in polypropylene (PP) by adding a bicomponent beta-nucleator consisting of equal amounts of pimelic acid and calcium stearate. Wide angle X-ra y diffraction (WAXD), scanning electron microscopy(SEM), static tensil e tests, Izod impact tests, and instrumented drop weight impact testin g were used to characterize the structure, morphology, and mechanical behavior of the beta-phase PP. The WAXD patterns show that the relativ e content of the beta-phase (K value) in the skin layer of the injecti on molded specimen is 0.54, whereas the K value in the core section is 0.92, SEM observations reveal that the beta-spherulite exhibits a she af-like structure and there are no clear boundaries between the spheru lites. Static tensile tests indicate that the elongation at break of p ure PP is enhanced by the addition of a beta-nucleator. The impact and drop weight tests also indicate that the impact resistance of PP is i mproved by adding the beta-nucleating agent. The improvement in impact toughness is associated with the formation of microcrazes within the PP.