Processing of all-polypropylene composites for ultimate recyclability

This paper describes the development of so-called all-polypropylene composites, namely polypropylenes (PPs) reinforced with oriented polypropylene fibres rather than glass or natural fibres. These all-polypropylene composites have specific economic and ecological advantages since, upon recycling, a polypropylene blend is obtained that can be reused to make all-PP composites again or, alternatively, be used for other PP-based applications. One of the main challenges in the development of all-PP composites is to create a processing window that is large enough to keep the oriented PP reinforcement intact while this is combined or impregnated with PP resin. The technological breakthrough in the processing of all-PP composite that has been established is based on the hot compaction (welding) of coextruded tapes. These coextruded tapes consist of an oriented polymer core, providing strength and stiffiness, and a polymer skin with a lower melting temperature than the core material forming the matrix and bonding the tapes together. Consolidation is achieved by simply 'welding' the tapes together, thus avoiding typical impregnation problems encountered in traditional thermoplastic composite manufacturing. Pilot studies have already shown the potential of a wide range of manufacturing technologies including thermoforming and filament winding.