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Design and fabrication of multi-walled hollow nanofibers by triaxial electrospinning as reinforcing agents in nanocomposites

Multi-walled triaxial hollow fibers with two different outer wall materials are fabricated by core-sheath electrospinning process and integrated into epoxy matrix with or without primary glass fiber reinforcement to produce composites with enhanced mechanical properties. The morphologies of multi-walled hollow fibers are tailored by controlling the materials and processing parameters such as polymer and solvent types. The triaxial hollow fiber fabrication is achieved through using a nozzle containing concentric tubes, which allows for the transport of different fluids to the tip of the nozzle under the applied high voltage. In comparison to uniaxial electrospun fibers, the hollowness of electrospun fibers enables one to manufacture new reinforcing agents that can improve the specific strength of composites. It is shown that the mechanical properties of epoxy matrix composite incorporated with electrospun fibers as primary fiber reinforcement can be significantly tailored by properly selecting the wall materials, diameters, and the amount of electrospun fibers. We have also presented that triaxial electrospun hollow fibers as co-reinforcement in the glass fiber-laminated epoxy matrix composites enhance the flexural modulus by 6.5%, flexural strength by 14%, the onset of first layer of glass fabric failure strain by 12.5%, and final failure strain by 20%.