Structures and Properties of Injection Moldings of β-Crystal Nucleator-Added Polypropylenes

An isotactic polypropylene homopolymer (PP) was added with 0 to 10000 ppm of γ-quinacridone, a β-crystal nucleator of PP. Flexural test specimens were injection-molded from the PP at cylinder temperatures of 200 to 320 °C and the structures and properties have been studied. The results can be summarized as follows: The crystallization temperature increases with γ-quinacridone content. The β-crystal content decreases with increasing cylinder temperature and shows a maximum at a γ-quinacridone content of about 100 ppm. The thickness of the skin layer scarcely depends on γ-quinacridone content. The orientation of β-crystals decreases with increasing cylinder temperature. It is high at the surface regions and decreases toward the interior. The Izod impact strength increases with γ-quinacridone content. The degree of the increase is higher as the β-crystal content is higher and reaches more than threefold in the highest case. The flexural modulus and strength decrease by about 10 % in the highest case. The heat distortion temperature increases with γ-quinacridone content. The mold shrinkage increases with γ-quinacridone content. From these results, it is concluded that the injection moldings of PPs containing γ-quinacridone are superior in impact strength and heat resistance.