Abstract
Fracture mechanics analysis at high speed and low temperature has been carried out on polypropylene samples of various molecular weights, obtained under different crystallization conditions. In addition differential scanning calorimetry measurements and morphological observations by scanning electron microscopy have been also performed. It has been found that the fracture mechanics parametersG c andK c increase markedly with enhancing the molecular weight, whereas an opposite trend is observed with increasing the crystallization temperature. Furthermore it has been seen that an annealing procedure, on the already solidified samples, strongly enhances the fracture toughness parameters. The above findings have been confirmed by fracture surface observations showing that crazing is the dominant feature of deformation in such materials. Possible underlying molecular mechanisms, which can explain the overall properties and the morphological characteristics, are discussed as well.
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