Macroscopic heterogeneity in stabilized polypropylene thermal oxidation

The thermal oxidation of stabilized polypropylene films of 100 mum thickness has been studied at 130 degreesC in air. After an induction period corresponding to stabilizer consumption, films exhibit randomly nucleated macroscopic highly oxidized zones. Their growth is associated with radial cracks. SEC, optical microscopy and FTIR mapping have been used to determine the nature and the extent of these zones. SEM observations showed the crack propagation mechanisms and confirmed that propagation is governed by the free volume variation and shrinkage induced by differential oxidation conversion. Finally, initiation and propagation mechanisms of these highly oxidized zones are discussed in terms of reaction and diffusion kinetics. (C) 2002 Elsevier Science Ltd. All rights reserved.