A comparative analysis of lightweight, high-performance flax fiber and upcycled graphene reinforced polypropylene sustainable composites for automotive industry

The automotive industry's pursuit of lightweight, high-performance, and sustainable materials has driven interest in natural fiber-reinforced thermoplastics. However, challenges such as moisture sensitivity, lower strength, and fiber-matrix compatibility hinder their widespread adoption. To address these constraints, this study developed sustainable compound formulations incorporating recycled waste components and natural fibers as alternatives to injection-molded composites reinforced with long glass fibers (LGF) for structural applications in the automotive industry. The newly developed compound comprised PP reinforced by 40 wt% alkaline treated flax fiber (FF), 1 wt% waste tire-derived graphene nanoplatelets (GNP), and 3 wt% compatibilizer, resulting in significant improvements in flexural modulus and strength, surpassing both neat homopolymer PP (homoPP) and recycled PP (rePP) by 202% and 92.5%, and 161.5% and 54.7%, respectively. To assess their viability, mechanical, thermal, and rheological properties were compared with commercial counterparts used in serial production. Furthermore, a comparative life cycle assessment evaluated the carbon footprint of different matrix types, revealing that the rePP-based formulation reduced CO2 emissions by 50% compared to LGF/homoPP while achieving a 7.2% weight reduction. This study successfully demonstrates the potential of integrating natural fibers and waste-derived reinforcements into PP composites, offering a lightweight, high-performance, and environmentally friendly alternative for automotive applications. Highlights Sustainable PP composites developed as alternatives to glass fiber materials Flax fibers and upcycled GNP utilized for lightweight composite fabrication Flexural modulus and strength significantly improved in PP composites. Life Cycle Assessment performed for developed and commercial composites 50% CO2 emission reduction achieved using recycled PP as a matrix in composites.