Abstract

MIREYA, Matos et al. Propiedades Mecánicas y Comportamiento a Fractura de un Polipropileno Homopolímero comparado con un Copolímero de impacto grado comercial. Rev. LatinAm. Met. Mat. [online]. 2005, vol.25, n.1-2, pp.31-45. ISSN 0255-6952.

A detailed mechanical characterization of two injection molding grade Venezuelan Polypropylenes (PP), an isotactic Polypropylene homopolymer (PPh) and a material which is marketed as "impact copolymer" (PPc), was carried out. Among the properties that were evaluated, the following can be found: density measurements, conventional and volumetric melt flow index, Scanning Electron Microscopy (SEM) for morphological evaluation, thermal characterization through Differential Scanning Calorimetry (DSC), HDT and Vicat softening points. The mechanical properties were determined by evaluating tensile, three point bending and falling dart impact testing methods at 25 and -30°C. The fracture behavior was analyzed by employing the Linear Elastic Fracture Mechanics (LEFM) theory and by fractography. According to the results obtained by thermal and morphological characterization of the materials employed, it can be concluded that PPc is a biphasic material with a PP matrix and an elastomeric dispersed phase of polyethylenic nature. Nevertheless, an exhaustive mechanical characterization demonstrated that, even though PPc possesses a limited strain at break (possibly caused by the decohesion between the matrix and the dispersed phase), it is capable of undergoing a large plastic deformation and mechanical energy absorbance upon the application of an impact load. The fractography study showed that the dispersed phase in the PPc is capable of modifying the micromechanisms of plastic deformation of the PP matrix in order to enhance its toughness under impact load.