Oxidation induced embrittlement in polypropylene - a tensile testing study

The thermal oxidation of polypropylene films (100 pm) in air at 90 degreesC was studied by IR spectroscopy, rheometry at 210 degreesC and tensile testing. Tensile testing reveals a sudden embrittlement before the end of the induction period determined from carbonyl build-up curves. Embrittlement occurs at a very low conversion of the chain scission process (only 1 chain scission per 3 initial chains) and it can be demonstrated that it results from a decrease in polymer toughness rather than from the build-up of defects linked to a presumed heterogeneity of the oxidation process. Tensile testing is not necessarily a good tool to characterize embrittlement given that phenomena such as necking and crack initiation at geometric defects are not taken into account with the usual measuring methods. The sudden drop of ultimate elongation could be, at least partly, an artifact. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.