Structure and properties of injection moldings of β-crystal nucleator-added PP -: Part 5, Co-addition of β- and α-crystal nucleators

In this paper we aim at a synergism of improvements of impact strength of polypropylene by the addition of beta-crystal nucleator and of its rigidity by the addition of alpha-crystal nucleator. Co-addition of both the nucleators has been studied. 30 ppm of gamma-quinacridone which is a beta-crystal nucleator and 0 to 10000 ppm of talc (TC), aluminum salt of benzoic acid (BA), or dibenzylidene sorbitol (GA) which are alpha-crystal nucleators were added to a homo isotactic polypropylene (PP). Flexural and Izod impact test specimens were injection-molded from the PPs under constant molding conditions and the structure and properties have been investigated. Although the alpha-crystal nucleators scarcely affect the beta-crystal content (K value) at nucleator contents below 100 ppm, the K value decreases with increasing nucleator content at contents above 100 ppm. The decrease is in the order of BA > GA > TC. Although the Izod impact strength scarcely changes at alpha-crystal nucleator for contents below 100 ppm, if decreases with increasing nucleator content at contents above 100 ppm. The decrease is the larger as the decrease of K value is the larger. The flexural modulus shows a reverse tendency of the Izod impact strength. Front above, it may be said that the properties of injection molding of beta- and alpha-crystal nucleator-added PP are unitarily determined by the beta-crystal content and thus the expected synergism could not be obtained.