Interfacial Bonding and Mechanical Properties of Aramid Fiber/Unsaturated Polyester Resin Composites Reinforced by Physically Anchoring-Chemically Bonding Gradient Interfaces

Aramid fiber/unsaturated polyester resin (AF/UP) composites suffer from weak interfacial adhesion which limits their applications in demanding environment. This study proposes a synergistic modification strategy utilizing polydopamine (PDA) and \(\gamma\)-methacryloxypropyltrimethoxysilane (KH570) which constructs a dual-mechanism interface combining mechanical interlocking and covalent bonding. PDA layer was first formed on AF surface via dopamine (DA) oxidative self-polymerization. KH570 formed covalent bonds with PDA layer to yield KH570–PDA–AF. Multi-scale characterization revealed that PDA and KH570 were successfully grafted on AF surface. KH570–PDA–AF/UP composite achieved an interfacial strength of 35.03 MPa (a 57.4% enhancement) due to copolymerization between KH570 and UP. The tensile strength of KH570–PDA–AF/UP reached 1054.86 MPa (a 47.62% increase) and Young's modulus was 23.64 GPa (a 135.93% enhancement) compared to AF/UP. Dynamic mechanical analysis showed reduced loss modulus above 76 °C which signified optimized interfacial energy dissipation mechanisms. These results manifest that PDA–KH570 synergistic modification strategy effectively optimizes interfacial bonding of AF/UP which offers a novel approach for designing high-performance fiber-reinforced composites with both theoretical innovation and engineering applicability.