Session: Rising Stars of Mechanical Engineering Celebration & Showcase

Paper Number: 150011

150011 - Advancing Wind Turbine Sustainability: Designing Self-Healable and Re-Processable Vitrimer Composites Through Covalent Adaptable Networks 

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. For 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.

Presenting Author: Ning Zhang Baylor University

Presenting Author Biography: Dr. Ning Zhang joined the Department of Mechanical Engineering as a tenure-track Assistant Professor at Baylor University in 2022. She received her B.S. in Engineering Mechanics from Dalian University of Technology, China, her M.S. in Solid Mechanics from Huazhong University of Science & Technology, China, and her Ph.D. in Mechanical Engineering from the University of Florida. Before Baylor, Dr. Zhang worked as an Assistant Professor at the University of Alabama from 2019 to 2022. She was also affiliated with the Colorado School of Mines as a Research Assistant Professor and with Missouri S&T and Rice University as a Postdoc. Now her research group focuses on combining experimental and numerical techniques to predict, quantify, and optimize the relationship between the structure-property-processing of various materials including biomaterials, sustainable polymer composites, and high/medium entropy alloys. Dr. Zhang received NSF CAREER Award (2022), ORAU Ralph E. Powe Junior Faculty Enhancement Award (2021), TMS FMD Young Leaders Professional Development Award (2019). Dr. Zhang was also the winner of TMS SMD Young Professional Poster Contest (2019). During her PhD study, she was awarded the University of Florida Outstanding Academy Achievement (2013).

Authors:

Amin Kuhzadmohammadi Baylor University
Ning Zhang Baylor University