Course of the changes in thick and thin isotactic polypropylene samples subjected to natural aging

The course of degradation in natural environment of polypropylene items was studied with DSC and thermogravimetric techniques. The enthalpic patterns of the materials vary with time of exposure. Measurements of the melting enthalpies in comparison with the heats of crystallization enabled to assess the evolution of crystallinity during exposure of plates and films of iPP. The induction time before the photochemical attack is of 800 h regardless of the thickness.The plates lose all practical mechanical properties after 4800 h of exposure, the film only after 2000 h. At the end of exposure, the plate provides a brittle and cracked material that includes a volatile phase and a heat resistant share due to crosslinking reactions. Some hypotheses on the degradation mechanism are presented.