Determination of essential work of fracture in EPBC sheets obtained by different transformation processes

1 mmsheets of polypropylene and ethylene-propylene block copolymers (EPBC) have been obtained using different processing methods in order to study the influence of processing induced morphology in the fracture properties of these materials. The processing methods employed were compression moulding (CM), extrusion-calendering (EC) and injection moulding (IM). Additionally, the sheets obtained by extrusion and injection were submitted to an annealing process with the aim to obtain more homogeneous morphologies that would ease their characterization. The morphology has been characterized by different techniques: Polarizing light microscopy (MLP), differential scanning calorimetry (DSC), wide-angle X-ray diffraction scattering (WAXS) and scanning electron microscopy (SEM). The fracture properties were determined by the essential work of fracture (EWF) method for deeply double edge notched specimens (DDENT), since these materials show ductile and post-yielding fracture behaviour. The EWF technique was applied in both the melt flow (MD) and the transversal (TD) directions in the sheets obtained by extrusion and injection moulding. Results show that the sensitivity of the technique allows examining the effect of morphological variations of thin sheets, as well as a better characterization of the orientation level (versus other parameters like yielding stress or elastic modulus obtained by tensile test). C 2005 Springer Science + Business Media, Inc. 1. Introduction The use of Ethylene-Propylene Block Copolymers (EPBC) is nowadays being increased in plastic industries. Melting and glass-transition temperatures are higher for polypropylene than for polyethylene. For this reason, EPBC can be used in a wider range of temperatures than polypropylene and polyethylene homopolymers. EPBC have a good mechanical resistance above the glass-transition temperature of polyethylene and a good behaviour under stress below the melting temperature of polypropylene. This combination allows the EPBC to be used in a wide range of common items, from packaging to automobile industries. Polyolefins are in general semi crystalline polymers, whose structure and final morphology are not only depending on chain distribution and chemical disposition, but also on the thermal history and moulding conditions, which strongly affect the structure of the final specimens. In order to show an example, Young’s modulus of about 100 GPa has been found for an oriented ∗Author