Design and Application of Rigid Flexible Structure for High Strength Recyclable Bio-Based Epoxy Composite Materials

Abstract To address the health hazards posed by the BPA epoxy resins traditionally used in carbon fiber reinforced polymers (CFRP), a high-performance and recyclable epoxy resin (EP) was developed by integrating two bio-based components—phenolic compounds from straw tar (ST) and lignin (LI)—with a flexible long-chain curing agent, decenyl succinic anhydride (DA): i) rigid conjugated benzene rings and ii) flexible long-chain fatty acids. Thanks to the combination of rigid structures and flexible chains, the EP achieved a record tensile strength of 104.1 MPa, which far exceeds most reported in the literature. After thermal aging at 100 °C and UV irradiation for 7 days, the tensile strength retention rate reached 95.8%. Furthermore, a new strategy combining mechanical interlocking and interpenetrating network at the interface was proposed. By synergistically modifying carbon fibers (CF) with ultrasonic cavitation treatment (UCT) and aqueous sizing agents (SA), the composite materials saw a 55.8% increase in tensile strength and a 131.5% increase in shear strength. This material can be applied in drone wings and lightweight automotive structural components. Additionally, the material can be recycled, and the regenerated resin can bond with various substrates. Therefore, this study developed environmentally friendly thermosetting resins and carbon fiber reinforced composites by constructing a bio-based covalent network that balances rigidity and flexibility.