Novel polyimide-based aqueous nano-dispersions as sizing agents for carbon fiber-reinforced thermoplastic composites

Abstract

With the increasing demand for the high strength and high fracture toughness composites in aerospace, automobile and other structural applications, great efforts have been devoted to the development of carbon fiber reinforced thermoplastic composites. However, the majority of commercial carbon fibers are sized for reactive thermosetting epoxy matrix, and therefore cannot be used directly for thermoplastic resin impregnation due to the high processing temperatures and poor interfacial interactions with polymer matrix. In this work, novel surfactant-free aqueous dispersions were derived from commercial polyimide resins through emulsion/solvent evaporation technique. The obtained nano-dispersions with uniform particle size around 100 nm and a high Zeta potential of -48.1 mV were deposited on carbon fibers via electrochemical deposition and dip coating method, respectively. The sized carbon fibers were characterized by scanning electron microscopy (SEM) and thermogravimetric (TGA) analysis, and the sizing performance was assessed by single fiber pull-out testing using polyetherimide (PEI) as the polymer matrix. The results show that the prepared polyimide sizing presents a positive effect on the interfacial adhesion of carbon fiber/PEI composites. Moreover, the carbon fibers sized by electrochemical deposition method exhibit higher interfacial shear strength (IFSS) compared to the dip-coated ones due to the increased van der Waals forces between the PEI matrix and sizing layer as well as the chemical bonding between the sizing layer and carbon fiber surface. The developed aqueous polyimide nano-dispersions exhibit great potential for application in the manufacturing of continuous carbon fiber reinforced thermoplastic prepregs.