Ultrastrong and high-elongation degradable bio-based hyperbranched epoxy resins and carbon fiber composites

Abstract

Thermosetting epoxy resins typically struggle to achieve high strength and high toughness simultaneously. Furthermore, the difficulty of recycling of epoxy resin/carbon fiber (EP/CF) composites after use poses severe environmental pollution issues. The preparation of EP/CF composites that simultaneously exhibit high strength, toughness, elongation at break, and recyclability remains a significant challenge. We synthesized bio-based hyperbranched epoxy resins (BAFI-n, n = 6, 12, 24) by combining hyperbranched topological networks with rigid–flexible units. BAFI-n demonstrates exceptional performance in simultaneously enhancing the strength, toughness, and degradability of diglycidyl ether of bisphenol A (DGEBA). Specifically, the tensile strength, elongation at break, and tensile toughness of the cured 12 wt% BAFI-12/DGEBA copolymer increased significantly by 58.46%, 166.67%, and 361.15%, respectively. Optimal mechanical properties were achieved at maximum crosslinking density and minimum free volume fraction, attributed to the synergistic interaction between rigid and flexible structures within the crosslinked network. The prepared TCF-BAFI-12/DGEBA composites exhibit superior mechanical properties compared to the original PCF/DGEBA composites, with tensile strength, flexural strength, and interlaminar shear strength increasing by 65.66%, 58.62%, and 84.21%, respectively. The enhanced properties stem from an interfacial reinforcement mechanism: the hyperbranched topology enables efficient load transfer, while the crosslinked network forms mechanical interlocking. Furthermore, the TCF-BAFI-12/DGEBA composites completely degrade under acidic conditions, allowing for damage-free recovery of the carbon fiber fabric. The resins achieve a 96% recovery rate, enabling high-value recycling. The strategy of combining rigid–flexible structures with hyperbranched topological crosslinking networks provides a pathway for designing high-strength, high-toughness, and recyclable EP/CF composites.