Characterization of Higher-order Structures in Injection-molded Polypropylene with Thermal Diffusivity Measurements

Abstract

The higher-order structures of skin and core layers in an injection-molded polypropylene were studied by means of thermal diffusivity measurements. Test pieces of 50-150μm thick were cut from the injection-molded plates in three different directions by use of a diamond cutter and microtome; flow direction (MD), transverse direction (TD), and thickness direction (ND). The thermal diffusivities of the test pieces were measured by a simple non-steady method using AC Joule heating, which had been developed in our laboratory. The measured thermal diffusivity and its anisotropy were correlated with the higher-order structure revealed by means of polarizing microscopy, differential scanning calorimetry and wide angle X-ray diffraction. The results clearly show that the thermal diffusivity is isotropic in the core layer while that in the skin layer is anisotropic.