Isotactic polypropylene/EPDM blends: Effect of testing temperature and rubber content on fracture |
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Authors: | F Coppola R Greco G Ragosta |
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Affiliation: | 1. Institute of Research on Polymer Technology and Rheology, Arco Felice, Naples, Italy
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Abstract: | Charpy impact tests in the temperature range ?100 to +20° C have been carried out on two isotactic polypropylenes (PP) having different molecular weight and their blends containing as rubbery phase an ethylene-propylene-diene terpolymer (EPDM). For fractures of brittle nature the impact data were analysed in terms of the linear elastic fracture mechanics andK c andG c were determined. This behaviour was observed for the homopolymers over the temperature range investigated, and for the blends only up to ?20° C. At higher temperatures such materials showed fracture of a semiductile type with visible evidence of craze whitening around the crack tip, followed by brittle type fracture. In this case the results were analysed in terms of a ductile contribution (energy required to form the crazed area) and of a brittle one (relative to the crack propagation area) from whichG c could be derived according to a procedure proposed in the literature. Tentative interpretations of the results also on a molecular and structural basis have been given. A critical discussion of the elaboration of the semiductile fracture data proposed in the literature has also been provided. |
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