Recycling of polymer composite materials: A review of the state of the art

Research into recycling of composite materials has accelerated in recent years, driven by rising sustainability expectations, circular-economy policy pressures, and the expanding use of composites in transport and renewable-energy systems. Composites have significant potential to address sustainability goals through the use phase of many transport applications particularly within the automotive and aerospace sector through lightweighting and resulting energy savings. Yet the very features that make composites attractive such as highly tailorable properties and multi-phase architectures, also create substantial barriers to high-value reuse. Covering both glass and carbon fibres, this review provides a timely, system-level assessment that extends beyond traditional fibre-recovery-focused surveys. It examines the full recycling chain, from disassembly through fibre liberation, intermediate materials, and second-life product integration. Mechanical, thermal, and chemical recycling technologies are critically compared with attention to fibre quality, scalability, energy demand, resin-chemistry compatibility, and the potential to generate materials suitable for structurally meaningful reuse. Emerging insights into fibre degradation mechanisms, surface and interfacial behaviour are synthesised to clarify their influence on recycled composite performance. A notable trend in recent literature is the shift from proof-of-concept fibre recovery towards optimisation of downstream processing and manufacturable intermediate formats. Advances in non-wovens, aligned discontinuous fibre architectures, moulding compounds, and additive-manufacturing feedstocks demonstrate that recycled fibres can begin to approach the performance of virgin materials, though variability remains a limiting factor. The review also evaluates the environmental implications of recycling routes, highlighting the substantial energy-savings potential while underscoring the sensitivity of reported benefits to process scale, data quality, and assumptions around material displacement. Gaps, including scale-up of chemical processes, management of contaminated waste streams, and the absence of robust quality standards, are identified as priorities for future work. Progress will depend on tighter integration between materials development, manufacturing technologies, and design-for-recycling strategies, alongside continued innovation in recyclable resin systems.