In a recent article published in the journal Communications Engineering, researchers explored alternative techniques that can efficiently separate composite components during the disposal and recycling of fiber-reinforced polymer (FRP) composites, while maintaining material integrity and minimizing environmental impacts.
Image Credit: Anton Foltin/Shutterstock.com
Background
Fiber-reinforced composites, especially glass fiber-reinforced epoxy (GRE), are prized for their high strength-to-weight ratios, durability, and versatility across wind energy, automotive manufacturing, aerospace, and construction sectors. However, the end-of-life management of these materials remains problematic due to their chemical cross-linking and thermoset nature, which makes recycling difficult.
Conventional methods such as high-temperature pyrolysis, chemical solvolysis, and thermal degradation can compromise fiber quality, introduce toxic residues, and demand significant energy inputs. These limitations hinder the widespread adoption of recycling practices suitable for large-scale industrial applications. Consequently, there is an urgent push for innovative, environmentally benign approaches that can recover fibers and resins with high fidelity, enabling their reuse in future products and reducing waste.
Recent advancements have focused on mechanical, chemical, and physical methods to balance efficiency, environmental safety, and material preservation.
The Current Study
The study introduces a novel freeze-thaw (FT) cycling technique to exploit physical phenomena at the fiber-matrix interface for composite separation.
Wind turbine blades containing GRE composites were sourced from decommissioned sites and processed into standardized specimens.
The core idea involves subjecting these specimens to controlled freeze-thaw cycles in water, where ice expansion within the resin matrix induces micro-cracks at the interface.
Multiple cycles of freezing and thawing were conducted with precise temperature control parameters. Analytical tools, including scanning electron microscopy (SEM), micro-computed tomography (micro-CT), and nanoindentation, were employed to evaluate the morphological and mechanical changes before and after treatment.
Environmental assessments involved analyzing the treated water for pH, total organic carbon (TOC), and chemical residues to ensure compliance with safety standards.
The process relies solely on physical principles without chemical reactants or high temperatures, offering an eco-friendly alternative to conventional methods.
Results and Discussion
The results demonstrated that freeze-thaw cycling effectively induces debonding at the fiber-resin interface, leading to the liberation of glass fibers.
SEM and micro-CT scans revealed a significant increase in microcracking and porosity within the composite post-treatment, with crack volumes increasing by approximately 65%. Notably, the critical mechanical properties of the fibers, including elastic modulus, showed minimal degradation, preserving up to 96% of their original strength.
Nanoindentation measurements confirmed that the fibers maintained their structural integrity, while chemical analyses via energy-dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR) indicated no substantial chemical deterioration.
The environmental assessment showed that the water used in the process remained within safety thresholds for pH and TOC, containing only trace amounts of epoxy fragments that could be filtered through standard methods.
These findings underscore that the freeze-thaw method can dissociate fibers cleanly and efficiently while maintaining their properties, which is critical for reuse in manufacturing.
The discussion emphasizes the advantages of this physical approach, notably its environmental compatibility, low energy requirements, and ability to preserve fiber quality.
Unlike thermal or chemical techniques that involve harsh conditions and potential degradation, the freeze-thaw cycle operates at ambient temperatures, relying on water’s physical expansion. However, the method's scalability poses challenges, including longer processing times and the need for industrial-scale freezing infrastructure.
Regulatory validation and economic viability assessments remain future steps. Nonetheless, the technique shows promise as a pre-processing step within broader multi-phase recycling frameworks, where recovered fibers and resins can be repurposed for use in construction materials, automotive components, or other structural applications. The approach aligns well with sustainability goals, proposing a low-impact, scalable solution for managing composite waste.
Conclusion
The study concludes that freeze-thaw cycling offers a groundbreaking, environmentally friendly strategy for recycling GRE composites, particularly those sourced from decommissioned wind turbine blades.
By harnessing the physical expansion of ice within the resin matrix, the method enables effective separation without chemicals or high temperatures, thereby preserving the integrity of the fibers.
The comprehensive analyses confirmed substantial interface debonding, increased porosity, and minimal fiber damage. Environmental assessments indicated safe effluent water and low chemical residues.
This establishes the freeze-thaw process as a scalable, low-carbon alternative to traditional techniques. It has the potential to be integrated into multi-phase recycling schemes that facilitate the full recovery of composite components.
The method's adaptability to other composite materials also suggests its broader applicability across industries, advancing waste valorization, resource efficiency, and sustainability in composite manufacturing and end-of-life management. Further research is needed to optimize process parameters, evaluate industrial feasibility, and conduct detailed lifecycle assessments, but the findings point toward a promising avenue for sustainable composite recycling.
Source:
Ahmed K., Jiang X., et al. (2025). Freeze–thaw recycling for fiber–resin separation in retired wind blades. Communications Engineering 4, 153. DOI: 10.1038/s44172-025-00490-7, https://www.nature.com/articles/s44172-025-00490-7