Glass fibres coated with flame synthesised carbon nanotubes to enhance interface properties

https://doi.org/10.1016/j.coco.2020.100623Get rights and content

Highlights

  • Carbon nanotubes were rapidly and successfully synthesised in an ethanol flame and coated onto glass fibres.

  • Significant interfacial bonding strength increases of ~33% was observed for CNTs coated glass fibres.

  • After coating CNTs onto glass fibres, glass fibres-epoxy surface wettability was enhanced.

Abstract

Carbon nanotubes (CNTs) were coated onto glass fibres (GFs) using a one-step flame synthesis method. The GF/epoxy resin matrix interfacial bonding strength was investigated by fibre bundle pull-out tests. Results showed that, compared to the as-received GF/epoxy, significant interfacial bonding strength enhancement of ~33% was obtained for CNT-coated GFs/epoxy. Moreover, the wettability of CNT-coated GF by epoxy was increased significantly evidenced by the reduction of CNT-coated GF/epoxy contact angles. The flame synthesis method possesses the potential of efficient high-performance composites fabrication.

Introduction

Fibre-reinforced composites have been widely used in both industrial applications and household appliances owing to their remarkable characteristics and properties. The overall mechanical performance of these composites is highly sensitive to the fibre/matrix interface properties. The fibre/matrix interfacial property measurement approaches can be summarised into matrix loading and fibre loading methods [1]. The matrix loading methods mainly include the single fibre fragmentation test [2] and Broutman test [3]. However, interface failures are difficult to determine using this kind of methods. Fibre loading methods mainly include single fibre pull-out/push-in tests [4,5], microbond tests [6] and fibre bundle pull-out tests [1]. The stress distribution and failure modes of single fibre pull-out/push-in and microbond tests are simple. However, as a single fibre is very fragile, the test specimens may cause frequent fibre breaks, limiting the types of fibres that can be tested [3]. The fibre bundle pull-out method gives a more realistic interfacial failure mode since detailed composite fracture surface study displays that fibre bundles rather than single fibres are often pulled out from the matrix [7]. Additionally, this test method is applicable for a wide range of fibres [8].

CNTs are considered as the next-generation reinforcing phase in high performance composites owing to their small size, low density and high elastic stiffness. CNTs can be either dispersed into the composite matrix [9] or as fibre surface sizing [10] to enhance the preform of composite materials. Comparing to dispersing CNTs into the matrix, the use of CNTs as fibre sizing was more effective in improving the fibre/matrix interfacial property. A good reason is that while one ends of the CNTs are attached on the fibre surface, the other ends diffuse into the nearby matrix, yielding a tougher and stiffer interfacial region and increasing the fibre/matrix bonding [4]. Conventional CNT synthesis methods often require high energy input which is usually achieved by high temperature generated by a laser or a furnace. Nevertheless, a low-cost and time-effective flame synthesis of CNTs method has been developed [11,12] based on Singer and Grumer [13]. Our previous work showed that after flame synthesis of a CNT coating onto glass fibre (GF) fabrics, the electrical and thermal conductivities of the fabricated multi-scale CNT-GF/epoxy composite laminates were significantly improved [11]. However, the interfacial bonding of CNT-coated GF/epoxy matrix has not been investigated to date.

In this work, we present an energy efficient approach to improve the interfacial bonding of GF/epoxy matrix by the flame synthesis method to directly coat CNTs onto GFs. The GF/epoxy interfacial bonding strength was characterised by fibre bundle pull-out tests. To show the function of the CNT coating, the interfacial bonding strength of CNT-coated GF was compared to those of as-received and unsized GFs. Furthermore, the wettability of these three types of GFs by epoxy was investigated.

Section snippets

Sample preparation

E-glass fibre bundles with ~0.2 mm thickness and ~1.5 mm width were directly extracted from a twill weave style fibreglass fabric (Play with Carbon Pty). Carbon nanotubes were in situ coated onto GF bundles with the flame synthesis method [13]. Nickel chloride (NiCl2) dissolved in ethanol (0.4 mol/L) was used as a catalyst precursor. Before synthesising CNTs on GFs, the initial sizing (3-glycidyloxypropyltrimethoxysilane) on the fibres was removed by immersion in acetone for 24 h. The purpose

Flame synthesis of CNTs on GFs

The surface of as-received GF is shown in Fig. 1b. After 1 min of flame synthesis, as shown in Fig. 1c, the GF surface was covered with a bush of CNTs with diameters of ~70 nm and lengths of ~1.2–2.0 μm. The XPS spectrum of flame synthesised GFs is displayed in the inset of Fig. 1d. Three elements of silicon, carbon and oxygen are detected in the samples. Deconvolution of the C(1S) peak shows the highest sp2 C–C bond (~70 at.%) which represents the graphitic structures in the flame. The peak at

Summary

The GF/epoxy matrix interface was modified with CNT-coating by utilising the flame synthesised method, and fibre bundle pull-out tests were conducted to evaluate the change in interfacial bonding strength. After the initial GF surface size was removed, the average interfacial bonding strength of unsized GFs reduced by ~19%. However, for CNT-coated GFs, the interfacial bonding strength was increased by ~33%. The bonding strength enhancement was mainly caused by the improved GF/epoxy mechanical

CRediT authorship contribution statement

Guixiang Zhao: Conceptualization, Methodology, Investigation, Formal analysis, Writing. Hong-Yuan Liu: Conceptualization, Methodology, Supervision. Xusheng Du: Conceptualization, Methodology, Supervision. Helezi Zhou: Investigation. Yiu-Wing Mai: Supervision, Writing - review & editing. Yuan-Yuan Jia: Investigation. Wenyi Yan: Conceptualization, Methodology, Supervision, Writing - review & editing, Project administration.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was funded by an Australian Research Council Linkage Project grant (LP160100213). We acknowledge the use of facilities at the Monash Centre for Electron Microscopy and the Sydney Analytical.

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