Effect of a multiscale reinforcement by carbon fiber surface treatment with graphene oxide/carbon nanotubes on the mechanical properties of reinforced carbon/carbon composites

Abstract

An effective carbon fiber/graphene oxide/carbon nanotubes (CF-GO-CNTs) multiscale reinforcement was prepared by co-grafting carbon nanotubes (CNTs) and graphene oxide (GO) onto the carbon fiber surface. The effects of surface modification on the properties of carbon fiber (CF) and the resulting composites was investigated systematically. The GO and CNTs were chemically grafted on the carbon fiber surface as a uniform coating, which could significantly increase the polar functional groups and surface energy of carbon fiber. In addition, the GO and CNTs co-grafted on the carbon fiber surface could improve interlaminar shear strength of the resulting composites by 48.12% and the interfacial shear strength of the resulting composites by 83.39%. The presence of GO and CNTs could significantly enhance both the area and wettability of fiber surface, leading to great increase in the mechanical properties of GO/CNTs/carbon fiber reinforced composites.

Introduction

Carbon fiber (CF), as an ideal reinforcement, has been widely used in advanced structural materials due to its exceptional mechanical properties and excellent thermal properties. There has been an increasing demand of carbon fiber composites in sports, automotive and aerospace industries [1], [2], [3]. However, the smooth and chemically inert surface of inorganic carbon fiber may lead to poor matrix compatibility and weak adhesion of fiber-matrix, which in turn negatively affects the mechanical properties of carbon fiber reinforced composites. To overcome the limitations imposed by impediments of the smooth and inert fiber surface, many researches concerning surface modification of carbon fiber have been reported [4], [5]. Recently, the introduction of carbon nanotubes (CNTs) in the composites has been developed as an effective reinforcement for enhancement of composite properties [6], [7]. Therefore, hybridizing carbon fiber with carbon nanotubes arises as a novel method to produce high mechanical performance of composites, because CNTs could increase carbon fiber surface area and mechanical interlocking between fiber and epoxy [8], [9], [10]. Although directly grafting CNTs onto fiber surface is an effective method to improve the properties of fiber-matrix interface, the lack of chemical bonding limits the further increase of the interfacial properties of the resulting composites [11], [12].

Graphene oxide (GO) with excellent mechanical properties could uniformly disperse and firmly adsorb on the carbon fiber surface to develop a new hierarchical reinforcement [13], [14]. As a novel carbon materials, graphene oxide (GO) possesses a two-dimension structure and exhibits extraordinary mechanical, thermal [15], [16] properties. Specially, GO with various oxygen functional groups [17] can be prepared in large quantities at a relatively low cost [18]. GO grafted on the fiber surface, which can offer both intralaminar and interlaminar reinforcement, could greatly improve the mechanical properties of carbon fiber reinforced composites [19]. In a previous study, our group has reported that GO directly grafted on the carbon fiber surface could effectively increase the interfacial adhesion of the resulting composites [14].

In the work reported here, we further modified GO/carbon fiber with CNTs by amidation reaction between amine groups of CNTs and acyl chloride groups of GO on the carbon fiber surface. This new reinforcement was aimed to investigate the effects of the newly introduced component on the interfacial properties of carbon fiber-epoxy matrix. The surface chemical composition, wettability and morphologies of carbon fiber were characterized by X-ray photoelectron spectroscopy (XPS), dynamic contact angle analysis (DCA), scanning electron microscopy (SEM), respectively. Mechanical properties of the composites were investigated by interlaminar shear strength (ILSS) and interfacial shear strength (IFSS).