Multifunctional properties of high volume fraction aligned carbon nanotube polymer composites with controlled morphology
Introduction
Bulk nanostructured composites combining existing advanced fibers, structural polymers, and carbon nanotubes (CNTs) with tailorable and enhanced macroscopic engineering properties are being developed by many groups for aerospace and other applications [1]. Development of such materials requires scaling and establishing long-range order of the nanostructures, and also an understanding of the properties of the constituents and how they interact [2], [3], [4], [5], [6], [7]. Here, an aligned-CNT polymer nanocomposite (A-PNC) is fabricated using a high-performance (aerospace-grade structural epoxy) thermoset, and anisotropic multifunctional properties quantified and discussed relative to morphology of the samples. High volume fraction (Vf) continuous-CNT A-PNCs are fabricated via a novel mechanical densification [8] technique (see Fig. 1). This avoids the issue of dispersion, random orientation, and discontinuity (non-continuous CNTs) of the CNTs inherent in the extant work on PNCs which has focused almost solely on filler-like concepts [9], [10], [11]. Controlling morphology of the PNCs is critical for interpreting the multifunctional property results, and both SEM and X-ray scattering provide detailed quantification of PNC morphology herein. Randomly-oriented PNCs (R-PNCs) are also fabricated for comparison of unaligned vs. aligned reinforcement. Modulus and electrical conductivity are maximal along the CNT axis in A-PNCs, and are the highest reported to date due to the aligned CNT morphology and use of an unmodified aerospace-grade structural polymer [12], [13], e.g., the modulus is 1000× greater than recently reported for an elastomeric A-PNC [14], and the highest bulk conductivity (23 S/m) is reported for an epoxy PNC along the axis of the continuous CNTs. The measured modulus is in agreement with micromechanics predictions that consider waviness of the CNTs, and both modulus and electrical conductivity trends are consistent with standard physical models. Control of nanostructure morphology is essential for understanding and predicting properties of a broad array of new materials, including CNT-based fibers, 3D nano-engineered composites, and metamaterials [15], [16], [17], [18], [19].
Theoretical calculations and experimental measurements on individual CNTs show that these one dimensional materials have elastic moduli between 0.5 and 1 TPa and tensile strengths of perhaps 50–200 GPa [20], [21], [22] making them ideal reinforcement candidates for composites, and even more attractive given their low densities. From the existing literature, extensive efforts have focused on dispersing single or multiwalled CNTs in low modulus polymers for reinforcing thermoplastics [13], [23] for applications such as electrically conducting composites [24].
However, the poor properties of these polymers and the necessary processing conditions make these nanocomposites unsuitable for advanced structural composites. Dispersion and distribution challenges limit the reinforcement volume fraction typically to below 5% of randomly-oriented CNTs. Alternatively, some researchers have focused on synthesizing aligned CNTs [25], [26], [27], [28] and the combination of aligned and continuous CNTs with structural resins like epoxy could achieve maximal mechanical reinforcement and transport properties. In this work, both aligned and random PNCs are compared up to CNT volume fractions of 20% (A-PNCs only), close to practical and theoretical packing limits for 8–10 nm diameter CNTs.
Section snippets
Experimental
Fabrication of aligned-CNT and randomly-oriented CNTs polymer nanocomposites (A-PNCs and R-PNCs, respectively) are described before morphology characterization, mechanical, and electrical testing are discussed.
Results and discussion
Polymer nanocomposites were fabricated from vertically-aligned multi-walled CNT forests (sometimes called VANTA, vertically-aligned nanotube arrays) grown via a modified chemical vapor deposition (CVD) process [25]. The resulting forests have been characterized previously for alignment, distribution and spacing [32]. A-PNCs were fabricated for various volume fractions via mechanical densification of the VANTA followed by capillary-induced wetting with an aerospace-grade thermoset epoxy (see
Conclusions and recommendations
The inclusion of aligned CNTs in bulk materials such as existing advanced composites is an important step forward in engineering materials, and can provide several advantages including tailoring and manufacturability of complex architectures. Control of nanoscale morphology in polymer nanocomposite as demonstrated herein allows measured properties to be appropriately interpreted. The results and trends in this study demonstrate anisotropic behavior via morphology control makes clear the classic
Acknowledgements
This study was supported by Airbus S.A.S., Boeing, Embraer, Lockheed Martin, Saab AB, Spirit AeroSystems, Textron Inc., Composite Systems Technology, and TohoTenax Inc. through MIT’s Nano-Engineered Composite aerospace STructures (NECST) Consortium. Hülya Cebeci acknowledges support from Scientific and Technical Research Council of Turkey (TUBITAK) for a 2214-International Research Fellowship Programme. Roberto Guzman de Villoria is grateful for the support of the Ministry of Science and
References (55)
- et al.
Reinforcement of polymers with carbon nanotubes. The role of an ordered polymer interfacial region. Experiment and modeling
Polymer
(2006) - et al.
Carbon nanotube (CNT) – polymer composites
Compos Sci Technol
(2007) - et al.
Nanocomposites in context
Compos Sci Technol
(2005) - et al.
Advances in the science and technology of carbon nanotubes and their composites: a review
Compos Sci Technol
(2001) - et al.
A review and analysis of electrical percolation in carbon nanotube polymer composites
Compos Sci Technol
(2009) - et al.
Small but strong: a review of the mechanical properties of carbon nanotube–polymer composites
Carbon
(2006) - et al.
Determination of mechanical properties of carbon nanotubes and vertically aligned carbon nanotube forests using nanoindentation
J Mech Phys Solids
(2003) - et al.
Fabrication and multifunctional properties of a hybrid laminate with aligned carbon nanotubes grown in situ
Compos Sci Technol
(2008) - et al.
Fiber waviness in nanotube-reinforced polymer composites-II: modeling via numerical approximation of the dilute strain concentration tensor
Compos Sci Technol
(2003) - et al.
Fiber waviness in nanotube-reinforced polymer composites-1: modulus predictions using effective nanotube properties
Compos Sci Technol
(2003)
Effect of nanotube waviness on the electrical conductivity of carbon nanotube-based composites
Compos Sci Technol
Science of fullerenes and carbon nanotubes
Nanocomposites – paving the way to stronger materials
Nat Nanotechnol
Polymer nanocomposites for aerospace applications: properties
Adv Eng Mater
Polymer nanocomposites for aerospace applications: characterization
Adv Eng Mater
Polymer nanocomposites
MRS Bull
Viscoelasticity in carbon nanotube composites
Nat Mater
Fabrication, characterization of ultrahigh-volume-fraction aligned carbon nanotube–polymer composites
Adv Mater
Continuous carbon nanotube reinforced composites
Nano Lett
Direct spinning of carbon nanotube fibers from chemical vapor deposition synthesis
Science
Multifunctional composites using reinforced laminae with carbon-nanotube forests
Nat Mater
Large-scale fabrication of aligned single-walled carbon nanotube array and hierarchical single-walled carbon nanotube assembly
J Am Chem Soc
Strong, transparent, multifunctional, carbon nanotube sheets
Science
The structure of materials
Exceptionally high Young’s modulus observed for individual carbon nanotubes
Nature
Nanobeam mechanics: elasticity, strength, and toughness of nanorods and nanotubes
Science
Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load
Science
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