Mechanical enhancement of natural-fiber-reinforced composites modified with recycled thermoset composite fillers

Synthetic-fiber-reinforced thermoset composites pose a significant threat of environmental pollution owing to their nonbiodegradable nature. To address this issue, it is essential to establish an adequate recycling strategy to reduce composite waste. In this study, we prepared flax-fiber-reinforced thermoplastic composites and modified a liquid thermoplastic resin (Elium 188 O) with recycled thermoset composite fillers. The introduction of 15% silane-treated fillers into the polymer matrix resulted in a substantial increase in the energy release rate and fracture toughness at the fracture initiation stage in modes I and II. Specifically, compared with the unmodified matrix, the energy release rate and fracture toughness were enhanced by 44.8% and 42.8% (for mode I) and 40.5% and 85.4% (for mode II), respectively. Similarly, the flexural strength and modulus increased by 25.1% and 34.8%, respectively. Furthermore, the mechanical properties of thermoplastic composites will deteriorate significantly because of the low bonding strength between virgin and recycled materials. However, the flax-fiber-reinforced composites with a 15% silane-treated filler-modified polymer matrix maintained Young’s modulus and tensile strength of 89.9% and 91.2%, respectively, after 20 cycles of recycling. Overall, the strategy of inducing chemical-treated powdered composite wastes is a sufficient and low-labor-cost method to mitigate environmental pollution and improve the sustainability of recycled composite structures.