Assessing the Critical Multifunctionality Threshold for Optimal Electrical, Thermal, and Nanomechanical Properties of Carbon Nanotubes/Epoxy Nanocomposites for Aerospace Applications

Georgios Psarras,Elias Koumoulos,Aikaterini-Flora Trompeta,Costas Charitidis,Theodoros Velmachos,Sotirios Stavropoulos

doi:10.3390/aerospace6010007

Georgios Psarras, Elias Koumoulos + Show 4 more

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https://doi.org/10.3390/aerospace6010007

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Abstract

Epoxy composites are widely used in primary aerospace structures, where high impact damage properties are necessary. However, challenges appear when multiple functionalities, including electrical and thermal conductivity, are needed in parallel with increased mechanical properties. The current study aims at the assessment of a critical concentration of multiwalled carbon nanotubes (MWCNTs), incorporated in epoxy resin, which will indicate a threshold for optimal electrical, thermal and mechanical properties. For the evaluation of this optimal concentration, electrical conductivity, thermal stability and nanomechanical properties (Young modulus and nanohardness) have been assessed, for epoxy nanocomposites with 0 to 15 parts per hundred resin per weight (phr) MWCNTs. Percolation theory was applied to study the electrical conductivity for different contents of MWCNTs in the epoxy nanocomposite system. Thermogravimetric analysis was employed for the assessment of the epoxy composites’ thermal properties. Nanohardness and elastic modulus were measured, and the hardness versus modulus index was calculated. Emphasis was given to the dispersion of MWCNTs in the epoxy matrix, which was assessed by both microscopy techniques and X-ray micro–computed tomography. A correlation between the optimum dispersion and MWCNTs content in terms of electrical conductivity, thermal stability, and nanomechanical properties revealed a threshold concentration at 3 phr, allowing the manufacturing of aerospace structures with multifunctional properties.

Highlights

Nanocomposite materials combining a polymer with nanofillers have attracted research interest the last decades, due to the combined advantages they offer [1]
The chosen method for the synthesis of multiwalled carbon nanotubes (MWCNTs) used in the preparation of the composites was thermal chemical vapor deposition (T-CVD)
In order to fully exploit the properties of Carbon nanotubes (CNTs) and to transfer the mechanical, electrical, and thermal stability enhancements to the polymer matrix, an effective dispersion should be achieved [37]

Summary

Introduction

Nanocomposite materials combining a polymer with nanofillers have attracted research interest the last decades, due to the combined advantages they offer [1]. The extraordinary properties of CNTs offer the ability to manufacture conducting polymers at low concentrations of the nanofiller, without altering the Aerospace 2019, 6, 7; doi:10.3390/aerospace6010007 www.mdpi.com/journal/aerospace. Aerospace 2019, 6, 7 performance of the polymer, in comparison with the use of other additives such as carbon black, which requires higher concentrations for an effective functionality [3]. If the desired performance can be achieved at low concentrations, novel lightweight materials can be fabricated, to be used in a range of advanced applications. The benefits of composite materials are clearly depicted on aerospace applications which require lightweight, high-strength, high-stiffness, and highly fatigue-resistant materials [4].

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