Enhancing Interfacial Properties in Aramid Fiber/Epoxy Composites via Hyperbranched Polyimide for Superior Performance

Aramid fiber (AF) reinforced epoxy resin (EP) composites are widely regarded as promising candidates for fabricating advanced composites. However, the inherently weak interfacial adhesion between AF and EP considerably restricts the overall performance of AF/EP composites. Therefore, the effective interfacial optimization of is crucial for realizing high-performance AF/EP composites. In this work, an amino-terminated hyperbranched polyimide (HBPI) was synthesized via low-temperature solution polycondensation and utilized as a novel AF sizing agent. Thereafter, the AF/EP interfacial interactions were enhanced through the combined effects of chemical bonding between the HBPI sizing agent and EP and physical interactions (hydrogen bonding and π–π interactions) between HBPI sizing agent and AF, thereby benefiting stress transfer at the interfacial region. As a result, the 90° tensile strength and NOL-ring interlaminar shear strength (ILSS) of AF0.04/EP composites (with a 0.04 wt% HBPI sizing concentration) were improved by 38.45% and 14.31%, respectively, compared with the AFunsized/EP specimen. Furthermore, the tensile strength and elongation at break of the impregnated filament increased by 17.86% and 14.73%, respectively. These findings demonstrate that the HBPI sizing agent offers significant potential for enhancing the interfacial performance of AF/EP composites, providing valuable theoretical insights for the development of high-performance composite materials.