Characterization study of gamma-irradiated, high melt-strength polypropylene

Polypropylene undergoes simultaneous crosslinking and degradation when irradiated. However, there is some speculation regarding the occurrence of branching under special conditions. It is also well known that the melt-strength property of a polymer increases with molar mass and with long chain branching. The aim of this study was to examine the amount of branching, as well as the formation and molar mass of branched molecules. The hypothesis that PP fragments are grafted with high molar mass PP molecules to form the branched molecules was also investigated. Temperature rising elution fractionation (TREF) was performed to fractionate the sample and allow the study of molecular configuration and molar mass. To verify crystal parameters, TREF fractions were analyzed with DSC. Molar mass distribution was determined by SEC. The results showed that the primary reaction in the initial step of irradiation was degradation. The highly modified molecules were present in both the high and the low molecular weight fraction, but the high molecular weight fraction appeared to have higher concentrations. The results also confirm the presence of branching. (C) 2003 Elsevier B.V. All rights reserved.