Characterisation of Used PP-Based Car Bumpers and Their Recycling Properties

Three used PP-based car bumpers are characterized by many techniques (fractionation, IR, TGA, DSC, DMTA, and SEM). They show different impact and static and dynamic mechanical properties depending on their composition and morphology. It appears that block copolymer compatibilizers constituted by polyethylene-polypropylene sequences allow a better compatibility between the rubber domains and the PP matrix leading to relatively high impact resistance. Indeed if the ethylene sequences of the copolymer are large enough to crystallize, the decreased mobility of the whole system impairs the impact resistance. In addition, a higher amount of rubber in domains regular in shape and of greater dimension (1–3 μm) promotes a more homogeneous dispersion of external force inside the material, decreasing the risk of fracture. The amount of mineral fillers regulates the elastic modulus (the higher the load, the higher the modulus); however, a fairly good interfacial adhesion is required for satisfactory impact strength. All PP-based bumpers have been mechanically recycled in an internal mixer to redistribute oxidized species and to reestablish phase compatibilization. Recycling improves mechanical properties in slow speed test but fails to increase impact strength particularly in filled bumper, in which the quality of the matrix/filler interphase is hard to improve by simple remixing.