Functionalized aramid nanofibers prepared by polymerization induced self-assembly for simultaneously reinforcing and toughening of epoxy and carbon fiber/epoxy multiscale composite

Abstract Aramid nanofibers (ANFs) are polymeric nanofibers that have been drawing tremendous attention as new nanoscale building blocks of advanced composites. Herein, we report a new strategy to rapidly synthesize functionalized ANFs (fANFs) through polymerization-induced self-assembly of poly(phenylene terephthalamide) (PPTA) using soluble sulfonated PPTA to tailor the size of fANTs, and the extraordinary reinforcing and toughening effect of fANFs on epoxy (EP) resin and multiscale carbon fiber (CF)/EP composites. With a diameter of ∼30 nm, and reactive sulfonic acid groups on the surfaces, the branched fANFs can be easily dispersed in EP and are reactive with the matrix, therefore, remarkably improve the interfacial interaction and mechanical properties (including both strength and toughness) of EP at low fANF contents. The tensile strength, Young's modulus, toughness and elongation at break of fANFs/EP nanocomposites are increased by ∼59%, ∼19%, ∼112% and ∼36%, respectively. The flexural strength, interlaminar shear strength, total energy dissipation and flexural strain at break of fANFs/CF/EP multi-scale composite are increased by ∼57%, ∼38%, ∼65% and ∼71%, respectively. To the best of our knowledge, the enhancement in the strengths is comparative with those provided by graphene oxide, and the total fracture energy and flexural strain at break are more significantly increased by fANFs than almost all of the nanofillers ever reported.