Micromechanical approach of the dynamic behavior of a high impact PP and a PP compound: Recycling and pollution effects

Abstract
In this work, pollution and recycling effects are studied on two polypropylene-based materials. These materials are used in car bumpers and are submitted to impact and crash. In order to re-use them as structural part of cars, the pollution, the recycling and combined effects have been studied [Directive 2003/53/CE, du Parlement Européen et du Conseil, Journal official de l'Union Européenne, 2003; Dasari A. and Misra R. D. K., Mat. Sci. and Engin. 358 (2003), 356-371.]. Model pollutants chosen in this study were ethylene glycol and engine oil. They were added during the extrusion process to simulate the degradation due to the pollutants. The recycling process was simulated by performing several extrusion runs with the same material in order to have a better comprehension of the multi recycling effects. The pollutants, the recycling and the effects of both were identified not only on the elastic properties but also on viscoelastic and viscoplastic properties at various strain rates. Dynamic mechanical analysis, quasistatic tensile tests, and dynamic compression tests on Split Hopkinson pressure bars have been performed. The analysis of the different obtained results led to a better understanding of the impact of pollution and reprocessing. Pollutants slightly affect the rheological properties while mechanical properties are more influenced. Concerning the recycling, six reprocessing have been necessary to observe a significant modification of the rheological and mechanical properties. But surprisingly, the presence of both pollutants not only decreases the recycling effects but also doesn't affect the micromechanical morphology leading to an improvement of the behavior of recycled materials.