Abstract
The 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 modl 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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