Cyano-Functionalized p -Aramid Copolymer Fibers Enabling Intrinsic Rubber Adhesion for Electric-Vehicle Hose Reinforcement

The transition to electric vehicles (EVs) has intensified durability demands on rubber hoses used for battery thermal management and coolant circulation, where para-aramid (p-aramid) fibers serve as the reinforcement of choice owing to their high strength, thermal stability, and chemical resistance. However, the chemically inert surface of p-aramid fibers necessitates a hazardous resorcinol-formaldehyde-latex treatment to achieve adequate rubber adhesion, raising environmental and processing concerns. Here, we report cyano-functionalized p-aramid copolymer (CN-pAC) fibers, synthesized by copolymerizing a cyano-functionalized monomer (3,4'-ODA-CN) into the aramid backbone via in situ polymerization. The cyano groups enhanced spinning-dope homogeneity and improved fiber drawability, yielding fibers with a tensile strength of 3.63 GPa and a modulus of 90.9 GPa. The surface-accessible cyano groups increased both the polar and dispersive components of surface energy, raising the total surface energy from 23.2 to 27.7 mJ m-2. Without any surface treatment, the interfacial shear strength increased from 2.96 to 4.66 MPa with polar ethylene acrylic elastomer (AEM) rubber and from 2.39 to 3.65 MPa with nonpolar silicone rubber. This enhanced adhesion shifted the failure mode of AEM rubber-impregnated strands from fiber pull-out to fiber fracture, boosting strand tensile strength from 0.92 to 1.38 GPa. These results establish a surface-treatment-free strategy for durable aramid-rubber composites in next-generation EV components.