Rapid and scalable synthesis of novel carboxylated aramid nanofibers for simultaneously improving the strength and toughness of carbon fiber/ epoxy laminates

Carbon fiber reinforced composites (CFRCs) are widely used in the aviation, aerospace and automotive industries. The modification of CFRCs with nanomaterials has attracted extensive research interests in recent years. Herein, we report the preparation of novel carboxylated aramid nanofibers (cANFs) by polymerization induced self-assembly, i.e. polycondensation of para-phenylenediamine with terephthaloyl chloride in the presence of a polyamide acid as both a dispersant and surface modifier, for the modification of epoxy resin and CFRCs. cANFs effectively improve the mechanical properties of epoxy resin, and after being sprayed onto CF fabrics, greatly improve the mechanical properties of CFRCs. With the addition of only 0.42 mg/cm2 of cANFs on each CF sheets, storage modulus, flexural strength, flexural modulus and total energy dissipation are enhanced by 27 %, 51 %, 29 % and 67 %, respectively; interlaminar shear strength (ILSS) and Mode II interlayer fracture toughness (GIIC) are improved by 24 % and 74 %, respectively. cANFs can be comparable or even superior to most previously reported carbon nanomaterials in improving flexural strength and ILSS; and exceed most previously reported electrospun nanofibrous mats in increasing GIIC. This study provides a new method for the rapid synthesis of functionalized ANFs to simultaneously increase the flexural properties and interlayer properties of CFRCs.