Pyrolysis and In Situ Oxidation Process for Recycling Glass Fibers from Retired Wind Turbine Blades

The impending wave of retired wind turbines has brought the issue of blade recycling to the forefront, presenting a major test for global sustainable resource management. Among the recycling methods, pyrolysis can be regarded as the most effective treatment approach, which can recycle the glass fibers that account for about 80% of the total weight of the blade. However, the pyrolytic char remaining on the fiber surface and the damage to the fiber structure caused by the excessively high pyrolysis temperature can both have a negative impact on fiber recycling. In this paper, a pyrolysis and in situ oxidation process with low treatment temperature is proposed for the recycling of glass fibers from the thermosetting epoxy resin–glass fiber composite material in the blades. Pyrolysis is performed at 450 °C, yielding a residual char content of 3.56%. Subsequently, in situ oxidation is conducted at the same temperature by switching the atmosphere to air, while the char content is reduced to below 0.01%, meeting the industrial recycling standard and achieving a glass fiber yield of 74%. Characterization reveals that the fiber structure and properties are well maintained. Additionally, through a series of characterization and density functional theory (DFT) calculations, the pyrolysis pathway from the resin repeating unit to various liquid phase products is supposed, and the corresponding pyrolysis mechanism is concluded. This paper provided a practical and feasible process scheme and theoretical basis for the efficient and clean resource recovery of retired wind turbine blades.