Correlation between the fracture toughness and -crystal fraction in a -nucleated propylene-based propylene-ethylene random copolymer

Propylene-based propylene-ethylene random copolymer (PPR) has been widely used in the production of hot-water pipes. To further improve its toughness and thermal resistance, -nucleating agents (-NAs) are frequently incorporated. In this study, PPR containing 5.6 mol % ethylene units was modified by two kinds of -NAs, that is, calcium pimelate and N,N-dicyclohexylterephthalamide. The notched Izod impact strength of PPR increased with the addition of the -NAs. Drastically different toughening effects were found between the two -NAs. The structure of PPR with and without a -NA was investigated by calorimetry, X-ray diffraction, and thermomechanical analysis. The results indicated that the relative fraction of crystals (k) in the injection-molded specimens was determined by the type and content of -NA. The relationship between k and the impact toughness was summarized. A critical value for k (0.68) was identified for the brittle-ductile transition of PPR. PPR with -NA having a k greater than 0.68 displayed a higher impact strength than the other mixtures. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42930.