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. 1. Introduction Thermoplastic olefin elastomers (TPO) constitute the largest single market of the automotive field: excellent weatherability, low density, and relatively low cost make TPO as current material of choice for automotive bumpers and fascias. At the beginning of the years 2000, the automotive segments were using 7 million ton/yr of polymers and polypropylene based materials accounted for 41% [1]. In Italian cars in the years 2000, polymers contribute on average to 12% of the total weight and bumper contributes to 7%–10% of the plastic fraction [2]. TPO are blends of isotactic polypropylene (PP) with ethylene-propylene rubber (ethylene-propylene monomer, EPM, or ethylene propylene-diene monomer, EPDM). The production by in situ synthesis of specialty ethylene-propylene copolymers extended their uses in a wide range of applications: in the first section of the process PP or PP-rich copolymers are usually produced with a high molecular weight and medium crystallinity, and in the following sections, copolymers richer in ethylene, an amorphous elastomeric material, are formed [3]. Front bumpers are made from neat TPO to take advantage from its elasticity whereas rear ones are often