SynopsisBy use of a mod with a film gate, two straight polypropylenes (PP) with different melt flow index (MFZ) and a glass fiber-reinforced polypropylene (FRPP) were injection molded at various temperatures into square plates with orientational anisotropy. The anisotropies of tensile property, tensile impact strength, and flexural property were studied on the molded sample cut mainly in the machine direction (MD), 45"-direction (45"), and transverse direction (TD). Both the orders of the yield strength and tensile impact strength of the FRPP, and those of the necking stress and tensile impact strength of the straight PP, were MD >45" >TD, which are reasonable tendencies. The orders of the yield strength and flexural modulus of the straight PP were MD > TD > 45O, which suggests the presence of shear deformation between the lamellae in the skin layer. The variation of the flexural modulus with the angle to the MD fitted well to Hearmon's equation. Generally, for straight PP, the anisotropy of various properties increased as the MFI and cylinder temperature became lower, or as the skin layer became thicker. For the FRPP, the anisotropy increased as the cylinder temperature became higher, or as the degree of the orientation of glass fibers became higher.

SynopsisThe effect of some molecular parameters on the mold shrinkage, annealing shrinkage, and melting shrinkage of injection-molded polypropylene was studied. The mold shrinkage in the machine direction (MD) became higher as the melt flow index (MFI) became lower and the molecular weight distribution became broader. On the other hand, the mold shrinkage in the transverse direction (TD) showed a similar value (about 1.6%), regardless of the kind of resin, except for a glass fiberreinforced polypropylene which showed a very low value. The annealing shrinkage and melting shrinkage showed similar tendencies as the mold shrinkage. The mold shrinkage and annealing shrinkage in the MD were in linear relationships with the thickness of the skin layer having positive slopes; the melting shrinkage in the MD was in a downward-curved relationship with the thickness of the skin layer having a positive slope, respectively, regardless of the cylinder temperature and the kind of resin.

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