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Zinc oxide nanorod (ZnO NR)-grown woven carbon fiber/polyamide 6 composites were fabricated using hydrothermal synthesis and thermoplastic resin transfer molding. The in-situ polymerization of e-caprolactam, which exhibits extremely low viscosity and high reaction speed, enabled excellent penetration of the resin into the densely grown ZnO forest on the carbon fibers. This further increased the mechanical interlocking and chemical interaction between the fiber and resin, leading to enhanced interfacial bonding. By increasing the number of oxygen functional groups and the surface roughness of the fiber surfaces through an atmospheric plasma treatment, the ZnO NRs were observed to grow even with very low growth-solution concentrations (20 mM), fewer seed cycles (4), and a short hydrothermal treatment time (4 h). By using the plasma-treated carbon fibers for ZnO NR growth, the impact resistance and in-plane shear strength were enhanced by up to 72 and 50%, respectively, as compared to carbon fiber composites without ZnO NRs, while the use of ZnO precursors and growth time was minimized.

We report an experimental study on improvement of mechanical properties of a multiscale hybrid composite consisting of in-situ polymerized polyamide-6 and zinc oxide nanorod(ZnO NR)-grown woven carbon fiber (WCF) coated with carbon nanotube(CNT)-modified silane. The ZnO growth process and silane coating process were performed on the fiber surface, and then the composite was fabricated by ultra-fast (

High-speed molding of continuous carbon fiber-reinforced composites was carried out by thermoplastic resin transfer molding using a very-low-viscosity thermoplastic monomer. After dispersing 0.1 wt.% of various nanomaterials in e-caprolactam, a monomer of anionic polymerized polyamide 6 (A-PA6), the processing temperature and catalyst-activator contents were optimized based on the polymerization induction time required for resin injection in the mold. Additionally, the dispersion stability, solidification time, monomer conversion, crystallinity and mechanical properties of the composites were evaluated. Higher dispersion stability of the nanomaterials in A-PA6 resulted in a significantly shortened process cycle time – on the order of seconds –and higher crystallinity in the composite. In addition, carbon fibers treated with atmospheric plasma were used to increase the rate of resin impregnation into fibers. These factors not only increased composite fabrication productivity but also enhanced its mechanical properties.

A novel sandwich-structured composite comprising a three-dimensionally (3D) printed core and a woven carbon fiber/polyamide-6 facesheet was fabricated and characterized. By using selective laser sintering, which is a 3D printing technology, a structurally reinforced honeycomb-truss hybrid core was produced, which had superior compressive stiffness in various directions compared with conventional honeycomb cores. The interface between the core and the facesheet was enhanced by laser power control during the sintering as well as plasma surface treatment. The sandwich composite was produced by the reactive thermoplastic resin transfer molding (T-RTM) technique using anionic polymerization of e-caprolactam, which has an ultra-low viscosity in the molten state. This in-situ polymerization not only enabled manufacturing process simplification by combining fabrication and bonding processes of the facesheet, but also provided excellent resin impregnation into the fiber fabrics and core surface. Therefore, the 3D printing technology, interfacial strengthening techniques, and T-RTM process induced synergistic effects on mechanical properties of the sandwich composite by forming structural reinforcement and strong mechanical and chemical interactions. The edgewise compressive properties of the hybrid core were significantly better than those of a normal honeycomb core. In addition, the interlaminar fracture toughness, impact energy absorption, and penetration limit of the sandwich composite consisting of the structurally and interfacially strengthened hybrid core increased by 76, 77, and 125%, respectively, compared to those of a nonreinforced sandwich composite.