Effect of joint action of high pressure and shear deformation on mechanical degradation of isotactic polypropylene

The degradation of isotactic polypropylene (iPP) subjected to the joint action of high pressure of 1, 2, and 5 GPa and shear deformation on the Bridgman anvils was evaluated by following the changes in the molecular weight distribution curves obtained by gel-permeation chromatography. It was shown that M-w and M-n values decrease with shear deformation. The melting behavior of isotactic polypropylene samples treated under high pressure and shear deformation was studied by differential scanning calorimetry. The melting temperature was found to decrease linearly with number-average molecular weight. decreasing. The changes in thermodynamic parameters for various iPP samples were accounted for differences in molecular weight. The tensile mechanical behavior of iPP samples subjected to the joint action of high pressure and shear deformation followed by repressing at 190 and 220 degreesC was investigated. It was found that the drawability of such samples is controlled by molecular weight and polymer morphology. It was shown that the lower is the repressing temperature, the lower the plastic deformability. (C) 2004 Published by Elsevier Ltd.