Keratinaceous Waste Valorization in Polymer Technology: A Comprehensive Review

Waste hair represents an underutilized keratin-rich residue with potential value in sustainable polymer technology. This review examines the composition, mechanical behavior, thermal characteristics, processing requirements, and polymer applications of waste human hair, with emphasis on its use as a filler, reinforcement, modifier, and keratin source. The reviewed literature shows that hair-derived keratin and hair fibers can improve selected mechanical, thermal, sorption, and biocompatibility properties of polymer composites, including polyurethane, epoxy, polyester, polypropylene, polyethylene, and bio-based matrices. Particular attention is given to extraction and pretreatment strategies, interfacial adhesion, biodegradation, biomedical materials, water remediation membranes, and hybrid composites incorporating other natural wastes. Despite promising laboratory-scale results, wider implementation is limited by inconsistent waste collection, contamination concerns, keratin extraction efficiency, matrix compatibility, and scalability. Future progress will depend on greener processing methods, standardized characterization, improved surface functionalization, and pilot-scale validation. Overall, waste hair from sewage and related streams offers a viable route for circular material development, reducing environmental burdens while supporting the design of cost-effective and sustainable polymer composites.