Improving Mechanical Properties and Self-Healing by Dynamic Bonds at Interface in Carbon Fiber Reinforced Epoxy Laminate and its Recycling

Abstract

Carbon fiber-reinforced epoxy (CFRE) laminates have revolutionized aerospace engineering due to their exceptional strength-to-weight ratio, corrosion resistance, and design flexibility. However, challenges such as weak interfacial bonding, low electrical conductivity, limited damage tolerance, and poor recyclability hinder their broader adoption. This thesis investigates advanced material engineering strategies to address these limitations by enhancing interfacial adhesion, functional performance, and sustainability. The research focuses on improving the mechanical and functional properties of CFRE laminates through the incorporation of modified sizing agents and conductive nanomaterials. Polyetherimide (PEI)-based sizing agents, including a self-healing (SH) disulfide metathesis variant (BA), significantly improve interfacial bonding, resulting in up to 22% enhancement in flexural strength (FS) and 35% in interlaminar shear strength (ILSS). Further improvements are achieved through the integration of graphene oxide (GO) and its functionalized derivatives. The BA-GO conjugate (BAGO) and dynamic covalent adaptive network-functionalized GO (hGO) show enhanced interfacial compatibility and conductivity, enabling up to 44% and 41% improvements in FS and ILSS, respectively, while maintaining or increasing SH efficiency up to 61%. Additionally, the thesis introduces a novel composite design using both hGO and BA-hGO (BAhGO), supported by density functional theory (DFT) simulations confirming strong interfacial interactions. These multifunctional enhancements also preserve or improve key functional properties such as electromagnetic interference (EMI) shielding, Joule heating, and deicing capabilities. To address the critical issue of recyclability, a simple, patented, environmentally friendly method using seawater and citric acid is developed to fully depolymerize epoxy matrices. The reclaimed epoxy is successfully reused as a hardener in new laminates, demonstrating a sustainable closed-loop recycling pathway. Overall, this work presents a comprehensive approach to advancing CFRE laminate technology by integrating interfacial engineering, functional nanomaterials, self-healing mechanisms, and sustainable recycling methods. These findings contribute significantly to the development of next-generation, high-performance, and eco-friendly composites for aerospace applications.