Recycling of wind turbine blades into polypropylene composites: influence of reprocessing on mechanical and thermal performance

Recent studies have investigated shredded wind turbine blade (SWTB) waste as reinforcement in polypropylene (PP) composites; however, the recyclability and performance retention of these secondary composites remains largely unexplored. This study evaluates the effect of multiple reprocessing on the mechanical and thermal performance of SWTB-reinforced PP composites. Virgin PP/glass fiber composites (10 and 15 wt%) were compared with recycled SWTB composites (with and without compatibilization). Composites were produced via twin-screw extrusion and injection molding, followed by two additional reprocessing cycles. FTIR analysis showed no significant chemical degradation, while SEM revealed improved fibre–matrix adhesion in compatibilized composites. After three cycles, the 50 wt% compatibilized SWTB composite recovered its tensile strength and exhibited 5 % higher flexural strength than 15 wt% virgin PP/glass fiber composites. Thermal analysis indicated 5–12 °C higher degradation temperatures and increased crystallinity due to enhanced nucleation effects. Melt flow rate (MFR) increased after reprocessing, indicating improved processability. Additionally, these findings demonstrate that mechanically recycled SWTB has the potential to effectively substitute 10–15 wt% virgin glass fibers and 25–50 wt% PP while retaining equivalent mechanical performance after repeated reprocessing, highlighting its potential as a sustainable reinforcement for circular thermoplastic composite applications.