Enhanced mechanical and thermal performance of polypropylene composites reinforced with recycled carbon fibre via multiscale surface modification

Recycled carbon fibre (rCF) is a low-carbon reinforcement for polypropylene (PP), but performance is often limited by weak interfacial adhesion. Here, rCF was modified with a multiscale SiO2/polydopamine (SiO2/PDA) coating to engineer the interphase in rCF/PP composites. SEM shows reduced interfacial gaps and resin adhered fibres with a more tortuous fracture path after modification. As a result, tensile and flexural strengths increase by 30% without loss of impact strength. rCF also markedly improves thermo-mechanical performance, raising HDT from 109.7 °C (PP) to 155.8 °C (rCF/PP), and surface modification further upgrades HDT. DSC indicates largely preserved crystallinity (50%) with a slight reduction after coating, while DMA shows higher storage modulus and lower damping, confirming improved modulus retention and restricted segmental mobility. This scalable interphase route enables effective upcycling of rCF into PP composites with enhanced mechanical properties and thermo-mechanical stability.