A two-step recycling method for upgraded glass fiber from wind turbine blades and its failure mechanisms

To address the growing accumulation of waste wind turbine blades (predominantly glass fiber-reinforced epoxy composites), pyrolysis has emerged a promising recycling strategy. However, recycled glass fibers-the most valuable component- are inevitably contaminated by pyrolytic char, severely restricting high-value reutilization. Consequently, a two-step approach (pyrolysis and post-oxidation) is considered critical. This article optimized synergistic oxidation conditions for different pyrolysis temperatures (350-500 °C), with paying a special attention on the strength evolution of fibers from low-temperature pyrolysis residues during oxidation. The mechanism of fiber strength loss during post-oxidation was also detailed investigated. Results showed recycled fibers could reach 1.2 GPa, meeting partial resin reinforcement requirements. The overall fiber strength loss remained at 60-70% despite different pyrolysis temperatures. Reduced low-temperature pyrolysis damage was offset by severe oxidative damage. Oxidation and resulting fiber failure mechanisms differed between high/low-temperature chars. Fibers from low-temperature chars suffered from severe thermal shock, which was alleviated by 10% O₂. While fibers from high-temperature chars required low oxidation temperatures to limit etching, with 20% O₂ promoting a passivation layer formation. Grey relationship analysis prioritized factors during thermal conditioning: pyrolysis temperature, O₂ concentration, oxidation temperature. This work provides a guidance for for high-value recycling of waste wind turbine blades.