Extrinsic toughening of recycled carbon fibers in polypropylene composites in the absence of plasticity penalty

Advanced composite materials used in high-tech fields are widely reinforced with carbon fibers. One of the growing application areas for carbon fibers is their reinforced composites which are used to replace metallic automotive parts. This reduces carbon footprint through weight reduction, which is a strategy pursued globally to reduce the environmental impacts of passenger vehicles. In this study, we assess the reinforcement potential of recycled carbon fibers in a polypropylene (PP) homopolymer with high strength and flowability. The highly crystalline PP homopolymer with low impact properties was used to minimize intrinsic plasticity penalty associated with fiber reinforcement and ascribe the impact strength enhancement solely to extrinsic toughening mechanisms. The reinforced composites are manufactured through extrusion compounding followed by injection molding. Modification of the transition phase connecting the bulk matrix with the bulk carbon fibers led to 78% enhancement in the strength of the composites, compared to the unmodified composites, without any loss in other properties. Compared to a commercial steel bonnet, the compatibilized composites reinforced with recycled carbon fibers exhibited superior specific strength accompanied by ∼87% weight reduction. Morphological analysis showed that all the extrinsic toughening mechanisms are effectively used by the recycled fibers in the reinforced composites.