A conductive thermoplastic material was developed to increase the interlaminar fracture toughness and through-the-thickness conductivity of carbon-fiber-reinforced plastics materials. A polyamide 12 nonwoven fabric was coated with graphene/graphite particles in a solution of hexane, water, and graphite particles. The graphite powders were exfoliated in the sonication bath and the resulting layers of graphene resided at the interface of the immiscible solvents, where the graphene layers/graphite simultaneously infused into the polyamide 12. The sonication time and graphite content were optimized to maximize the surface conductivity of conductive polyamide 12 fabric. The presence of pristine graphene flakes and graphite on the polyamide 12 fabric was confirmed by X-ray diffraction and scanning electron microscopy. The dry fabric preform was interleaved with the conductive polyamide 12 and the composite laminates were manufactured by a vacuum-assisted resin transfer molding process. The resulting composite laminate resulted in a significant increase in Mode I and Mode II fracture toughness up to 42% and 141%, respectively, and a decrease in the volume resistivity from 100 MΩm to 402 Ωm.

The process and high-temperature performance of bisphenol-A based benzoxazine were tailored by copolymerizing with bi-functional cycloaliphatic epoxy resin in order to be used as a matrix for the advanced composite fabrication. The melt viscosity, cure kinetics, thermo-mechanical, and tensile properties of the systems with various cycloaliphatic epoxy resin and benzoxazine concentrations were studied using rheometer, differential scanning calorimetry, dynamic mechanical analyzer, and micro-tensile tester, respectively. Mixtures with cycloaliphatic epoxy resin concentration greater than 25 wt.% provided a suitable viscosity for composite processing by resin infusion. The isothermal and nonisothermal cure kinetics of the benzoxazine and cycloaliphatic epoxy resin reaction was studied. The predicted kinetic curves based on Kamal and Sourour phenomenological reaction model expanded with a diffusion factor resulted in an agreement with the experimental kinetic curves. The investigation of copolymers with various mixture compositions showed an increase of 56% in glass-transition temperature ([Formula: see text] and 79% in cross-linking density by increasing epoxy concentration up to 40 wt.% in comparison with homopolymerized benzoxazine.

Conductive fabrics have received significant attention because of their widespread applications from smart textiles to energy storage devices. Conductive colloidal materials are preferred as a coating on the fabric to achieve desirable electronic conductivity; however, obtaining a uniform coverage with a simple and effective route is a challenge. Herein, we report exfoliated graphene nanoplatelets (GNPs) in low boiling point solvents and their subsequent coating onto a polyamide fabric surface. Few-layered (average <7 layers) GNPs were obtained by optimizing solubility parameters of solvent mixtures and sonication time. Raman spectroscopy showed that the I D/I G ratio changed from 0.33 to 0.38 in the GNP solution before and after the sonication, confirming an insignificant increase in defects on the basal plane of graphene after sonication treatment. Uniform coating of GNPs was obtained by optimizing concentration and sonication times. Scanning electron microscopy showed a uniform coverage of GNPs, and the surface resistivity of the polyamide fabric decreased from infinity to ∼40 kΩ after 4 h of coating. X-ray diffraction analysis confirmed the minimal effect on the fabric crystallinity during processing. This interface engineering approach is simple and scalable, and it is applicable for the coating of different polymeric fabrics with a great promise in electronic textiles.

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