Background
Over the past two decades, wind turbines have been widely deployed as a cornerstone of global sustainability efforts. Wind blades, primarily made from glass fiber-reinforced epoxy (GRE) composites, are engineered with strong fiber–resin interfaces to ensure long-term durability. However, after 20–25 years of service, environmental aging and fatigue-induced interfacial micro-cracking necessitate their decommissioning. These tightly bonded glass fiber-epoxy (GF-epoxy) composites are difficult to separate, and as a result, retired blades are often classified as non-recyclable material and are therefore landfilled despite the huge economic benefits of the reusable high performance material GRE composites. Wind blades installed 20 years ago have begun reaching end-of-life, leading to a growing wave of decommissioned blades by 2025. Estimates suggest that 43 million tonnes of retired blade material will accumulate by 2050, creating an alarming challenge for managing such a vast volume of retired composites.
Challenge
Among various end-of-life (EoL) strategies for decommissioned blades, recycling is widely regarded as the most circular and sustainable option, due to its ability to reclaim glass fibers and resin for potential reuse. Current thermal and chemical methods achieve GF-epoxy separation by breaking the epoxy’s C–O bonds at elevated temperatures or through aggressive chemical treatments. While effective in separating the glass fibers and epoxy, these methods are associated with significant drawbacks, including glass fiber degradation, epoxy dissolution, high energy demand, toxic emissions, and complex wastewater management. These environmental burdens and post-treatment steps reduce the feasibility of large-scale deployment of wind blades.
Fig.1 Challenge and breakthrough
Breakthrough
Our study proposes a novel, environmentally friendly, cost-effective, and technically feasible freeze–thaw method that relies solely on ice and water at human-tolerable temperatures to efficiently separate GF–epoxy in decommissioned wind blades. The present work, for the very first time, strategically repurposes the pre-existing micro-cracks in decommissioned blades for targeted fiber–resin separation in GRE composites. The method’s performance is evaluated through multi-modal characterization, including interfacial separation efficiency (SEM, weight change, micro-CT), material integrity (FTIR, EDS, TGA), retention of basic nano-mechanical properties of glass fibers, and environmental safety of this approach via pH, TOC, and microplastic content of effluent water, which are critical factors in the real-world adoption of any recycling approach. This work focuses solely on GF–epoxy interface separation, with full fiber reclamation planned in the future through multi-phased recycling frameworks of pre-weakened GRE composites. This work aligns with the hot research aspect on advancing sustainable technologies and waste management solutions that address global environmental challenges.
Genesis
Herein, we propose a novel freeze-thaw cycling method to separate fiber and resin in glass fiber-reinforced epoxy (GRE) composites by harnessing the unimaginable power of water at temperatures comfortably bearable to humans. Our method is inspired by the natural process of rock-splitting through freeze-thaw weathering. In nature, water enters pre-existing micro-cracks in rocks, expands as it freezes during cold cycles, and exerts pressure at the boundary area that propagates the cracks, ultimately leading to material fracture. This same principle can be utilized to de-bond fiber-resin interfaces in GRE composites.
Wind turbine blades, which must be retired after their service life due to fatigue, typically exhibit micro-cracks at or near the interface between the glass fibers and epoxy resin. Although these micro-cracks are not large enough for complete failure of the structure, they are sufficient enough to provide a channel for water ingress into them. Moreover, these blades are designed to be lightweight, with some voids intentionally created during the composite manufacturing process using foaming agents or other techniques, while others may form unintentionally due to poor manufacturing practices. These micro-cracks, along with voids and other structural defects formed during operation, can be effectively harnessed for fiber-resin separation through freeze-thaw cycling.
Schematic demonstration
We schematically demonstrate how this unique freeze-thaw approach works as shown in Fig. 2. The freeze-thaw method works by infiltrating water into the pre-existing cracks and voids within the epoxy matrix during the thawing phase. Once the water has penetrated these defects, it expands during the freezing phase, exerting mechanical stress at the fiber-resin interface. With each freeze-thaw cycle, the cracks progressively propagate and expand, connecting with nearby voids. This chain reaction causes further stress concentrations, leading to more extensive cracking and eventual debonding of the glass fibers from the resin.
Fig. 2 Mechanism of eco-friendly fiber–resin separation via freeze–thaw cycling. (a) Schematic showing pre-existing micro-cracks (black lines) and voids or air pockets (circles) in the composite structure. (b) Water ingress (blue arrows) into micro-cracks during thawing, followed by ice expansion (red arrows) during freezing, which exerts pressure on the boundary walls, leading to the formation of new cracks (orange regions). (c) Crack propagation and permanent fiber–resin debonding after repeated freeze–thaw cycles.
Conclusion
Our study proposes an innovative and sustainable freeze-thaw method for interface separation in glass fiber reinforced epoxy (GRE) composites, addressing a critical challenge in composite waste recycling, particularly for decommissioned wind turbine blades. Our research demonstrates a novel, eco-friendly process that uses drinkable water at ambient temperatures to propagate interfacial cracks, and capable of facilitating glass fiber-epoxy separation without the use of toxic chemicals or high temperatures while requiring least equipment. Environmental assessment further validated the proposed recycling process’s safety, as the effluent water exhibited near-neutral pH, low TOC, and contained filterable epoxy fragments, all within WHO/EPA limits. The findings show no chemical leaching or degradation of the recovered materials, ensuring their reuse in secondary applications and promoting a closed-loop recycling system. Moreover, our proposed fiber-resin separation concept is particularly relevant for retired composites and offers strong potential for integration into multi-phase recycling frameworks aimed at full-component recovery and circular economy implementation in wind blade end-of-life management. Owning to its universally adaptable interface-driven fiber-resin separation mechanism, the proposed method may also be extended to other fiber-reinforced composites used in the automotive, aerospace, and marine sectors, supporting global efforts toward environmental sustainability and economic inclusivity.