Calcium salts of suberic (Ca-Sub) and pimelic (Ca-Pim) acids were synthesized and implemented as in different grades of isotactic polypropylene (iPP). Propylene homopolymer, as well as random and block copolymers containing these additives, crystallized iPP into pure or nearly pure  modification in the isothermal and nonisothermal crystallization experiments. Recently, Ca-Sub proved to be the most effective -nucleating agent of iPP. The Ca-Sub nucleating agent widens the upper crystallization temperature range of pure -iPP formation up to 140°C. In this study the effect of the these additives on the crystallization, melting characteristics, and structure of the PP were studied. The degree of crystallinity of -iPP was markedly higher than that of ␣-iPP. A widening in the melting peak of the samples crystallized in a high temperature range was first observed and discussed in regard to literature results of the same phenomenon for ␣-iPP. The morphology of the -iPP samples was revealed by scanning electron microscopy. Independent of the type of polymer or nucleating agent, hedritic structures were found in the early stages of growth of the -spherulites.
ABSTRACT:The fracture and failure mode of a-and b-isotactic polypropylene ( a-iPP and b-iPP, respectively) were studied in high speed (1 m/s) three-point bending tests on notched bars cut from injection-molded dumbbell specimens and compared. The fracture response of the notched Charpy-type specimens at room temperature (RT) and 040ЊC, respectively, was described by terms of the linear elastic fracture mechanics (LEFM), namely fracture toughness (K c ) and fracture energy (G c ). K c values of both iPP modifications were similar, while G c values of the b-iPP were approximately twofold of the reference a-iPP irrespective of the test temperature. It was demonstrated that b-iPP failed in a ductile and brittle-microductile manner at RT and 040ЊC, respectively. By contrast, brittle fracture dominated in a-iPP at both testing temperatures. Based on the fracture surface appearance, it was supposed that b-to-a (ba) transformation occurred in b-iPP. The superior fracture energy of b-iPP to a-iPP was attributed to a combined effect of the following terms: morphology, mechanical damping, and phase transformation. Results indicate that their relative contribution is a function of the test temperature.
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