Fracture mechanism under dynamic loading of elastomer-modified polypropylene

摘要

In last decades, rubber-toughened polymer blends have been the object of considerable interest by many investigators, owing to their attractive mechanical as well as physical properties. Polypropylene (PP) is a type of polyolefin which can be toughened using rubber particles. In another paper [J. Appl. Polym. Sci., submitted for publication], the role of ethylene―propylene (EPR) particles on the deformation mechanism during tensile tests and the fracture mechanism under quasi-static loading tests has been investigated. This paper is instead focused on the role of EPR particles on the fracture mechanism under dynamic loading (impact properties) of EPR/PP blends. Blends with different weight percent of elastomer phase were produced. Impact tests at different temperatures, and microscopy techniques were used in this study. The results show that impact strength rises with both EPR content and test temperature, showing a brittle-to-ductile transition temperature (BDTT). In particular, increasing rubber content shifts BDTT to lower temperatures. For clarifying the fracture behaviour, impact tests were also simulated by slow bending tests. The results illustrate that the dominant fracture mechanism is due to the formation of craze-like structures that appear to be highly localised dilatational bands. This type of deformation pattern is discussed in relation to the interparticle distance effect observed previously in some rubber toughened polymers, and supports a model previously proposed by Lazzeri [A. Lazzeri, The Kinetics of Dilatational Bands and the Interparticle Distance Effect in Rubber Toughened Polymers, 10th International Conference on Deformation, Yield and Fracture of Polymers, April 7―10, 1997, Cambridge, UK, p. 75] to explain the interparticle distance effect on the basis of the stability of dilatational band propagation.