Enhancement of mechanical and electrical properties of continuous-fiber-reinforced epoxy composites with stacked graphene.

Naum Naveh,Olga Shepelev,Samuel Kenig

doi:10.3762/bjnano.8.191

Abstract

Impregnation of expandable graphite (EG) after thermal treatment with an epoxy resin containing surface-active agents (SAAs) enhanced the intercalation of epoxy monomer between EG layers and led to further exfoliation of the graphite, resulting in stacks of few graphene layers, so-called “stacked” graphene (SG). This process enabled electrical conductivity of cured epoxy/SG composites at lower percolation thresholds, and improved thermo-mechanical properties were measured with either Kevlar, carbon or glass-fiber-reinforced composites. Several compositions with SAA-modified SG led to higher dynamic moduli especially at high temperatures, reflecting the better wetting ability of the modified nanoparticles. The hydrophilic/hydrophobic nature of the SAA dictates the surface energy balance. More hydrophilic SAAs promoted localization of the SG at the Kevlar/epoxy interface, and morphology seems to be driven by thermodynamics, rather than the kinetic effect of viscosity. This effect was less obvious with carbon or glass fibers, due to the lower surface energy of the carbon fibers or some incompatibility with the glass-fiber sizing. Proper choice of the surfactant and fine-tuning of the crosslink density at the interphase may provide further enhancements in thermo-mechanical behavior.

Highlights

Carbon nanotubes (CNTs) have been suggested as an efficient conductive filler because of the outstanding electrical properties and the high aspect ratio
Enhanced rigidity in three-point bending and increased DMA storage moduli were achieved for compositions where expanded graphite (EG) was impregnated with epoxy resin modified with the surfactants Triton X-100, Triton X-15 or MEMO
These results are in good correlation with the changes in morphology of the composite materials determined by SEM

Summary

Introduction

Carbon nanotubes (CNTs) have been suggested as an efficient conductive filler because of the outstanding electrical properties and the high aspect ratio. Other treatments have been attempted, among these, oxidation of the carbon fibers, plasma treatment, radiation, modification with rubber, silica, carbon or other nanoparticles, showing interesting enhancements in interlaminar shear strength. Graphite nanoplatelets (GNPs) or stacked graphene (SG) have been developed as a low-cost conductive alternative [7]. GNPs can be produced by intercalation of the graphitic layers with an appropriate agent followed by exfoliation of the graphite flakes. Exfoliation is obtained by rapid heating resulting in conversion of the intercalant to a gas phase forcing the adjacent graphene layers to separate. Formation of worm-like accordion structured materials takes place with partially separated graphite sheets, i.e., expanded graphite (EG), characterized by a high expansion ratio of 100–400 cm3/g. Sonication in an acetone bath allowed for further exfoliation and separation of the loosely connected graphite nanosheets

Methods

Results

Conclusion