Impact of fiber fragmentation on mechanical performance and environmental footprint of recycled glass fiber-reinforced polyamide composites

Due to their mechanical strength and durability, the automotive industry increasingly incorporates glass fiber–reinforced composites. However, evolving environmental regulations necessitate the integration of recycled materials, presenting challenges, particularly with fiber fragmentation, which compromises composite strength. This study investigates the effects of recycling on the mechanical properties and carbon footprint of polyamide composites reinforced with varying glass fiber contents (15%, 30%, 45%, and 60%). Injection-molded specimens were subjected to tensile testing to evaluate the effects of varying fiber length distribution on mechanical performance across multiple recycling cycles. Findings revealed that fiber fragmentation increased with successive recycling cycles, decreasing tensile strength and modulus due to shortened fiber lengths. The long fiber ratio of the composites decreased to half after the first recycling. If all fibers were assumed to break below the critical length, strength would drop by 18%, 28%, 68%, and 74% for PA6-GF15, PA6-GF30, PA6-GF45, and PA6-GF60, respectively, compared to when all fibers stay above the critical threshold. Despite these challenges, the recycled composites retained acceptable structural integrity for specific automotive applications, highlighting their potential market value. Using recycled materials in injection-molded parts can reduce the carbon footprint by up to 30%, depending on fiber content. Despite increased emissions with higher fiber content, PA6-GF45 offers the optimal balance of strength, modulus, and sustainability. This research provides insight into optimizing fiber content and recycling cycles to balance environmental impact and performance, thereby supporting cleaner production in the automotive sector.