Self-Healable Epoxy Vitrimer Composites for Enhancing Wind Turbine Blade Sustainability

Thermosetting polymers are widely recognized for their outstanding thermal stability, mechanical strength, and chemical resistance. One notable application is in wind energy, where wind turbine blades are made from petroleum-derived thermosetting fiber-reinforced polymers. While wind power, as a renewable energy source, is favored for its low environmental impact, ecosystem preservation, and role in mitigating global warming, it also faces challenges due to the difficulty in recycling or repairing the thermosetting turbine blades.
The difficulty of recycling waste thermosets stems from their inherent irreversible crosslinks. An alternative and promising strategy is to incorporate dynamic exchangeable covalent bonds into the thermoset systems, allowing for reversible breaking and bonding in response to external stimuli. These thermosets, known as covalent adaptive networks (CANs), are categorized into two types based on their exchange mechanisms: dissociative and associative CANs. In dissociative CANs, old bonds break first and new bonds form afterward, leading to a loss of crosslink density and structural integrity. In contrast, associative CANs involve the simultaneous breaking of old bonds and formation of new ones, maintaining a constant crosslink density and ensuring structural stability. In 2011, Leibler and colleagues developed epoxy networks with associative CANs, coining the term "vitrimer."
In this work, we conducted a series of molecular dynamics simulations to investigate the self-healing properties of epoxy vitrimers. In our simulations, DGEBA (Diglycidyl ether of bisphenol A) was chosen as the epoxy resin, and AFD (aminophenyl disulfide) was used as the hardener/crosslinker. The crosslinking mechanism and resulting network structure were verified against experimental data, which demonstrated significant volume shrinkage and density variations at different conversion rates. Designing vitrimer composites with a high glass transition temperature (Tg) and strong mechanical properties is a key objective. Initially, we conducted molecular dynamics (MD) simulations to determine the Tg, and our results closely matched the experimentally measured values. The influence of crosslink density on Tg was examined and validated through relevant experiments.
Subsequently, the mechanical properties such as stiffness, strength, and fracture toughness were examined at various temperatures and strain rates. These findings further highlight the exceptional recovery ability of epoxy vitrimer, as it returns to its original shape after unloading, demonstrating its potential as a self-healing material. Self-repair MD simulations were then carried out, showing that cracks and holes in epoxy vitrimer can be healed through heat treatment due to the dynamic exchangeable covalent bonds in its network structure. The mechanical properties of the repaired epoxy vitrimer were assessed and compared to those of the initial pristine model. The results showed only slight or negligible decreases in strength and stiffness, demonstrating effective structural repair.
This work emphasizes the role of CANs in enhancing the recyclability and sustainability of thermosetting polymers, providing a foundation for future low-environmental-impact advanced materials. Potential applications of this research include the development of recyclable and self-healing materials for the automotive, aerospace, and construction industries, thereby improving material lifespan, safety, and eco-efficiency. These findings lay the groundwork for further exploration of the potential of CANs in various industrial applications.