ELSEVIEP 0142-9418(94)00033-6 Polymer Testing 14 (1995) 369-380 c 1995 Elsevier Science Limited Printed in Malta. All rights reserved 0142-9418/95/$9.50 MATERIAL BEHAVIOUR A Study of Polypropylene Peroxide Promoted Degradation Marisa C. G. Rocha,” Fernanda M. B. Coutinho: & Stephen T. Balke” ‘lnstituto de Macromoltculas, UFRJ, P. 0. Box 68525, 21945-970, Rio de Janeiro, RJ, Brazil “Chemical Engineering Department, University of Toronto, Toronto, Canada (Received 23 October 1994; accepted 14 November 1994) zyxwvutsrqponmlkjih ABSTRACT A stepwise peroxide initiated degradation of a PRO-FAX reactor grade polypropy- lene hy reactive extrusion was compared with a single step degradation process. Measured properties of the polypropylene and the degraded products included shear and intrinsic viscosity, melt flow index, melting and crystallization temperatures, Jlexural modulus, tensile modulus and yield stress. It was found that there is a trend to achieve higher MFI values if a stepwise degradation is carried out. It was also verified that a stepwise process results in a stronger reduction in the overall viscosity ofthe polypropylene and in the slope of the viscosity curves. The change in the slope of the viscosity-shear rate relationship is especially evident at lower shear rates. This eflect appears to be more pronounced as the peroxide concentration increases. INTRODUCTION The intentional degradation of polypropylene by the addition of peroxide during extrusion is now a well recognized manufacturing process.’ The product, controlled rheology polypropylene (CRP), has 10-100 times higher melt flow than conventional polypropylene resins and superior processing properties.2 These better properties are the result of a polymer chain scission reaction which statistically favors the rupture of the highest molecular weight chains first and consequently leads to the narrowing of the molecular weight distribution.3