Relating microhardness to injection molding induced morphology: A study of microbeam synchrotron WAXD

Abstract

AbstractThe relationship between microhardness and morphology of polypropylene near the surface of injection molded plaques was investigated. Crystal structures and molecular orientation from the surface to shear oriented layer were characterized by microbeam synchrotron wide angle X‐ray diffraction, polarizing optical microscope and Fourier transformed infrared spectroscopy. From precise measurements, using an X‐ray beam with width of 0.35 μm, the frozen layer was divided into two layers. Molecular and crystal orientations changed greatly in the surface layer but remained constant in the inner layer. These oriented morphology did not affect microhardness along the depth direction on the cross‐cut surface. Microhardness was proportional to crystallinity and showed a local maximum at shear oriented layer and a minimum at the surface. Then, positional dependence of microhardness was compared at the gate and the center of the plaque. Although crystallinity near the gate was lower than that at the center position, microhardness was higher. Therefore, crystallinity mainly affects microhardness but superstructure like cross‐hatching lamellae which is induced in biaxially extended melt flow is also not neglected in injection molded polypropylene parts. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010