Composite materials with nanofibrous reinforcements are capable of high mechanical performance and enhanced properties despite their low volume fraction of reinforcement. In this study, tensile properties of epoxy-matrix nanocomposites were investigated after reinforcing by hand layup method implementation of randomly oriented electrospun nanofiber layers. The reinforcements were produced from polyacrylonitrile (PAN), Polyamide-6,6 (PA-6,6), and their 50/50 hybrid. The results indicated that PAN enhanced the tensile toughness of the matrix by almost 4 times, increasing both the ductility (an expected 23% due to fiber being more elastic than the matrix) and the ultimate tensile strength (a surprising 35% even though the fibers were less stiff than the matrix). These results indicate significant improvements in the impact properties for advanced applications. The results revealed that PA-6,6 did not show the characteristics of a promising reinforcement whether used solely or added to PAN.

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%.

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This article reports the production, morphological analyzes, and application of electrospun self‐same nanocomposites with milled carbon fibers (MCFs). The new hybridized structure was also incorporated into conventional fiber reinforced epoxy composites with improved properties. The MCF‐hybridized polymeric nonwoven mats were formed with the simultaneous dual electrospinning of a soften‐able (m‐phase) and a crosslink‐able (x‐phase) variants of poly(styrene‐co‐glycidyl methacrylate). The morphology of the hybrid material was investigated using scanning electron microscopy (SEM). The results showed that electrospinning can successfully deposit reinforcing particles of giant size (MCFs are 7 μm in diameter, 50 μm to 3 mm in length) compared to the diameter of the carrier nanofibers (nanometers). The new hybrid structure preserved the fibrous morphology of the polymer phases up to 250°C. The overall morphology of the hybrid composite was tunable by changing the fractions of the two polymeric phases. The particle‐polymer hybrid structures created morphologies that might find applications in various areas such as the interlayer toughening of laminated composites. It was shown that m‐phase/MCF@x‐phase nonwoven integrated into epoxy matrix composite laminates as interlayer, increased the strain at failure and ultimate strength under tensile loading by 11% and 9%, respectively.

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