Multifunctional Short Carbon Fiber Composites Interfacially Engineered by Imidazolium Ionic Liquid

ABSTRACT The interfacial incompatibility between short carbon fibers (sCF) and epoxy matrices is a significant obstacle in achieving high thermomechanical performance, particularly for unsized fibers. To overcome this limitation, this study investigates the incorporation of different ionic liquids (ILs), 1‐butyl‐3‐methylimidazolium chloride, 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1‐(2‐hydroxyethyl)‐3‐methylimidazolium chloride as multifunctional modifiers to enhance the interaction between fibers and matrix in sCF/epoxy composites. Composites were prepared with optimized 1% (w/v) modified sCF and incorporated into the epoxy matrix, keeping 20 wt% of fiber weight. Epoxy was spread on the fibers with a brush followed by compression molding at room temperature. 1‐(2‐hydroxyethyl)‐3‐methylimidazolium chloride treated sCF/epoxy composites revealed improved thermomechanical properties, with storage modulus increasing by 33% and loss modulus by 39%. Differential scanning calorimetry revealed minimal changes in glass transition temperature, confirming little impact on the epoxy network. Meanwhile, a pronounced increase in curing enthalpy (from 12.0 to 21.4 Jg ⁻¹ ) was obtained. Furthermore, electrical resistance decreased by up to 36%, showing improved charge transport pathways across the fiber‐matrix interface. Fracture surface analysis confirmed improved fiber‐epoxy adhesion and localized interfacial plasticization. Overall, this study shows that low‐concentration imidazolium‐based ILs provide a sustainable, scalable, and tunable approach for interfacial engineering of sCF/epoxy composites, particularly for a high‐value use of unsized and recycled carbon fibers.