Distribution of higher‐order structures in injection moldings of particulate‐filled polypropylenes

Abstract

AbstractFlexural test specimens were injection‐molded from polypropylenes filled with flaky talc or spherical calcium carbonate at levels of 0‐40 wt % under cylinder temperatures of 200‐320°C. Distributions in the flow direction of higher‐order structures such as thickness of skin layer, a*‐axis‐oriented component fraction [A*], and crystalline orientation functions and distributions in the thickness direction of higher‐order structures such as crystallinity, β‐crystal content, [A*], and crystalline orientation functions were studied. These higher‐order structures are inhomogeneous in the flow and thickness directions also for injection moldings of particulate‐filled polypropylenes, which strongly influences the product properties such as mechanical and thermal properties. Molecular orientation process in injection molding was theoretically analyzed from a viewpoint of growth of recoverable shear strain at the gate and its relaxation in the cavity, which could considerably well explain the influences of particulate filling and cylinder temperature on not only the mean values but also the changes in the flow and thickness directions, of the quantities such as thickness of the skin layer and crystalline orientation functions, which express the degree of molecular orientation.