Multiscale reinforcing interlayers of self-same P(St-co-GMA) nanofibers loaded with MCF for polymer composites and nanocomposites

Official URL: http://dx.doi.org/10.2514/6.2019-1762

Electrospinning has become a proven technique to introduce polymeric sub-phases into composites. The sub-phases such as nanofibers can also be used as a carrier platform for reinforcing particles at different scales, enabling a multiscale reinforcement approach. However, the polymeric nanofibers may lose their intended fibrous morphology during the composite curing at elevated temperature. As such, polymeric sub-phase can not contribute effectively as fibers to the mechanical properties of the composite. This paper exemplifies introduction of milled carbon fibers (MCF) carried by electrospun polymeric nanofibers and the use of the resultant multi-scale reinforcement as interlayer within conventional structural composites. The issue of polymeric nanofibers exposed to elevated temperature curing is circumvented by implementing a novel self-same nanofibrous strategy. While a base polymer for the nanofibers is chosen as epoxy compatible P(St-co-GMA), its derivative by a cross-linker Phthalic Anhydrate, P(St-co-GMA)/PA is also incorporated by dual-electrospining, i.e. simultaneous electrospinning of the two polymers. It was shown that the nanofibers of the base polymer melt and fuse over the cross-linkable nanofibers forming the self-same nanofibrous morphology during the heat treatment in accordance with the cure cycle of the epoxy resin in this study. MCFs were mixed into the cross-linkable polymer solution and electrospun with the P(St-co-GMA)/PA nanofibers. The dual polymer and MCF loaded nanofibrous structures were analyzed morphologically before and after heat treatment. Homogenous distribution of particles in the fibrous structures, melting of the neat copolymer, crosslinking of the polymer mix, and selfsame fibrous structure were characterized. The nanofiber mats were used as the reinforcement to epoxy resin films and as interlayers for carbon fiber-reinforced composites. In the case of nanocomposites, MCF enhanced the elastic modulus by about 9%. In the use of multiscale nanofibrous mats as interlayers of continuous carbon fiber composites, they improved the ultimate tensile strength of a cross-ply laminate by 9%.