Carbon Nanotube Epoxy Composites Research Articles

Bending Analysis of Multiwall Carbon Nanotube Reinforced Functionally Graded Composite Cylindrical Shell

The curved structural components of aircraft, automobiles, and marine vessels, such as cylindrical panels, are primarily exposed to loading, which can result in bending failure, particularly in lightweight structures. The bending analysis of cylindrical panels made of functionally graded multiwall carbon nanotube (FG-MWCNT) epoxy composites is subjective in this study. In the first section, FG-MWCNT composite cylindrical panels are simulated in the ANSYS software. There are three methods for distributing uniaxially aligned reinforcements. The material properties of the carbon nanotubes uniformly distributed and functionally graded over the thickness of the shell structure are estimated using an extended rule of mixture micromechanical model that incorporates certain useful characteristics. To demonstrate the effectiveness and applicability of the proposed finite element approach, deflection data are presented. The analysis of the shell structure's bending includes an investigation of the impact of CNT volume fraction, boundary condition, lengthto-thickness ratio, and other geometrical factors

Interphase elastic properties of carbon nanotube-epoxy composites and their application in multiscale analysis

A multiscale framework was developed to predict the elastic properties of carbon nanotube (CNT)–epoxy composites. The interfacial vacuum layer between the CNTs and epoxy was equivalent to transversely isotropic elastomer. The elastic constants were calibrated based on the interaction energy density in the molecular dynamics simulations; the results exhibited significant differences between these constants. The out-of-plane shear modulus (46.64 MPa) is four orders of magnitude smaller than the in-plane Young’s modulus (362.68 GPa). Subsequently, representative volume elements containing transversely isotropic interphases were developed using the finite element method and analysed comparatively to models without interphases. The results indicated that their difference in the Young’s modulus enhancement ratio was sensitive to the CNT aspect ratio. The enhancement ratio of the model containing the interphase was lower when the CNT aspect ratio exceeded a certain value. This difference increased with increasing CNT aspect ratio and was significant at high CNT aspect ratios (7.35 % when the aspect ratio reached 30). In addition, shear-lag analysis indicated that the interphase increased the interfacial load transfer length. This framework provides efficient interfacial simulations, giving a more accurate prediction of bulk elastic properties and can be extended to a wider range of nanocomposites.

Multiscale analysis method and experiments for the fracture toughness optimization analysis of carbon nanotube-epoxy composites

To better understand the facture mechanics and optimize the fracture toughness of carbon nanotube (CNT)-epoxy composites, a multiscale analysis method was established in this paper. The multiscale analysis method includes three scales: (1) at the microscale, an interfacial model was established based on the Cauchy-Born rule to deduce the relationship between the interfacial stress tensor and CC bond vector; (2) at the mesoscale, the transition condition of the failure mode from the CNT pullout to CNT fracture was established based on the shear-lag theory. And the relationships between the pulling force and CNT pullout displacement were given corresponding to these two failure modes; (3) at the macroscale, the analytical solution of fracture toughness increment was given to conduct the fracture toughness optimization analysis. By validating this method by the experiment, we found that the optimal CC bonds volume density and interfacial length are reached under the transition condition of the failure mode from the CNT pullout to CNT fracture. At last, we proposed a method to approximately estimate the optimal CC bonds volume density and CNT length.

Carbon Nanotube Reinforced Poly(ε-caprolactone)/Epoxy Blends for Superior Mechanical and Self-Sensing Performance in Multiscale Glass Fiber Composites.

In this paper, a novel carbon nanotube (CNT) polycaprolactone (PCL), epoxy, and glass fiber (GF) composite is reported. Here, the nanoreinforced composites show a flexural strength increase of around 30%, whereas the interlaminar shear strength increases by 10–15% in comparison to unenhanced samples. This occurs because the addition of the CNTs induces a better PCL/epoxy/GF interaction. Furthermore, the nanoparticles also give novel functionalities to the multiscale composite, such as strain and damage monitoring. Here, the electrical response of the tensile- and compressive-subjected faces was simultaneously measured during flexural tests as well as the transverse conductivity in interlaminar tests, showing an exceptional capability for damage detection. Moreover, it was observed that the electrical sensitivity increases with PCL content due to a higher efficiency of the dispersion process that promotes the creation of a more uniform electrical network.

Impact of Current and Temperature on Extremely Low Loading Epoxy-CNT Conductive Composites.

Carbon nanotube (CNT) conductive composites have attracted significant attention for their potential use in applications such as electrostatic dissipation and/or electromagnetic interference shielding. The focus of this work is to evaluate resistivity trends of extremely low loading (<0.1 wt%) epoxy-CNT composites that lack a connected CNT network, but still present electrical conductivity values appropriate for those uses. The impact of current, temperature, and cycle life on electrical properties are here identified and tied to possible performance limits. At extremely low loadings, the CNT content is not sufficient to form a completely interconnected grid, thus, electrons must travel through insulating media. While still in the semi-conductor range, resistivity values are observed to decrease with increasing direct current and demonstrate a non-ohmic behavior. CNT epoxy composites were subjected to elevated currents and/or temperatures over diverse periods of time to examine impacts on resistivity. Microstructural analyses of composite samples were conducted to observe signs of damage for specimens taken to extreme temperatures/currents. An understanding of the electrical conductivity characteristics of extremely low loading epoxy-CNT composites and their failure mechanisms will aid in understanding risks associated with their use in challenging environments that may include high temperatures, high currents, and/or high frequencies.

Electrophoretic Fabrication of Robust Carbon Nanotube “Buckyfilms” for Flexible Electronics

This report demonstrates the facile fabrication of conductive, high-strength, all-carbon “buckyfilms”, which spontaneously delaminate from their depositing substrates. Electrophoretic deposition (EPD) is a scalable technique that has been underutilized in the fabrication of freestanding, bulk carbon nanotube (CNT) materials. Here, Derjaguin–Landau–Verwey–Overbeek (DLVO) theory is applied to understand and optimize the deposition process of oxidized multiwall carbon nanotubes. As a result, unprecedented deposition rates of 0.3 mg/(cm2 min) and film thicknesses of >40 μm were achieved. The deposited films are electrochemically reduced to achieve enhanced electrical conductivities (55 S/cm), demonstrating a freestanding carbon nanotube analogue to reduced graphene oxide. Examination of the films using electron microscopy revealed a densely packed structure (1.61 g/cm3) and cross-linking effects, which produce tensile strengths (>60 MPa) comparable to CNT–epoxy composites and many common structural polymers. ...

On the effect of electric field application during the curing process on the electrical conductivity of single-walled carbon nanotubes–epoxy composites

Single-walled carbon nanotube (SWCNT)/epoxy composites were cured under external electric fields and the influence of the processing parameters (electric field magnitude and frequency, SWCNT concentration and curing temperature) on the electrical response of the system was evaluated. A mold for the electric field application was designed and manufactured, allowing in situ measurements of the electrical resistivity of the composite, during and after the curing process. The resulting electrical properties revealed a strong dependence on the processing parameters. By rising the curing temperature, the solid bulk resistivity was decreased by one order of magnitude. Further reduction was observed with electric fields, up to an additional order of magnitude. Such improvements can be related with the decrease in viscosity and improvement of interconnected-nanotube paths within the polymer matrix. The effect of the electric field on the rotation and interconnection of the SWCNTs was investigated using a classical mechanics model based on the dielectrophoretic theory for the liquid state. The influence of inter-nanotube distances on the bulk electrical properties was calculated at different particle concentrations, using finite element models of the microstructure. This processing technique presents promising results for enhancing the electrical conductivity of polymer composites with carbon-based nanoparticles.

Effect of Carbon Nanotube Aspect Ratio on the Thermal and Electrical Properties of Epoxy Nanocomposites

The novel properties of carbon nanotubes have generated much interest in polymer nanocomposites. The thermal and electrical properties of multi-walled carbon nanotube-epoxy composites were investigated both experimentally and theoretically. Experiments were performed to evaluate the effect of the aspect ratio of carbon nanotubes. Comparisons were made between the results obtained for the nanocomposite materials containing carbon nanotubes with a high (800) and a low (80) aspect ratios. Design recommendations were made, and potential applications were also discussed. It was shown that the aspect ratio plays an important in determining the physical properties of the epoxy nanocomposite. The electrical conductivity of the nanocomposite is highly dependent on the aspect ratio of carbon nanotubes. In contrast, the aspect ratio plays a considerable role in the thermal conductivity of the nanocomposite. Carbon nanotubes have clearly demonstrated their capability as thermally and electrically conductive fillers in epoxy nanocomposites. In contrast to the orders of magnitude enhancement in electrical conductivity with a very low loading of carbon nanotubes, the thermal conductivity of the nanocomposite has shown only moderate improvement. The improvement in physical properties of the nanocomposite can be interpreted in terms of carbon nanotube networks.

Role of the particle size polydispersity in the electrical conductivity of carbon nanotube-epoxy composites

Carbon nanotubes (CTNs) with large aspect-ratios are extensively used to establish electrical connectedness in polymer melts at very low CNT loadings. However, the CNT size polydispersity and the quality of the dispersion are still not fully understood factors that can substantially alter the desired characteristics of CNT nanocomposites. Here we demonstrate that the electrical conductivity of polydisperse CNT-epoxy composites with purposely-tailored distributions of the nanotube length L is a quasiuniversal function of the first moment of L. This finding challenges the current understanding that the conductivity depends upon higher moments of the CNT length. We explain the observed quasiuniversality by a combined effect between the particle size polydispersity and clustering. This mechanism can be exploited to achieve controlled tuning of the electrical transport in general CNT nanocomposites.

Effective electrical conductivity of carbon nanotube–epoxy nanocomposites

The electrical conductivity of carbon nanotube–epoxy composites is investigated analytically and experimentally. The theoretical predictions of the effective electrical conductivity of carbon nanotube–epoxy composites were performed by the analytical approach based on a micromechanical model of composites. The parametric analysis carried out revealed an influence of geometrical and electrical parameters of the micromechanical model on the effective electrical conductivity of carbon nanotube–epoxy nanocomposite. The nanocomposites made from the DGEBA-based and RTM6 epoxy resins filled with different weight content of Baytubes C150P and N7000 multi-walled carbon nanotubes were prepared. The experimental values of the electrical conductivity of the nanocomposites were compared with those calculated by means of the analytical model.

Molecular simulations of the influence of defects and functionalization on the shear strength of carbon nanotube-epoxy polymer interfaces

Unlike earlier studies, which focused on thermoplastics, in this work attention is devoted to carbon nanotube (CNT) reinforced thermoset polymer composites. Specifically, extensive molecular dynamics (MD) simulations were conducted to study the effect of defects and functionalization on the interfacial shear strength (ISS) of carbon nanotube-epoxy composites before and after cross-linking. Three main types of defects (vacancies, adatom, and Stone-Wales (SW)) as well as phenyl functional group were considered in a representative volume element (RVE). The RVE comprised a single-walled CNT embedded in an epoxy matrix, and consistent valence force field (CVFF) was used in all MD simulations. Our results reveal that (i) vacancy defects degrade the ISS, and that the degradation effects depend predominantly on the number of missing atoms and not on the type of vacancy defects, (ii) adatom defects have a marginal effect on the ISS, (iii) SW defects promote greater ISS of cured systems, (iv) phenyl groups dramatically increase the ISS of cured systems, and (v) uncured systems experience lower ISS which is not affected by the number and type of defects and functionalization. The findings of this study will assist in improving our understanding of the operating toughening/weakening mechanisms and the load transfer capability in epoxy-based nanocomposites.

Aligned carbon nanotube–epoxy composites: the effect of nanotube organization on strength, stiffness, and toughness

A protocol has been developed for the production of epoxy-based composites containing high-volume fractions of aligned carbon nanotubes. The nanotubes were fabricated as continuous fibres or aligned mats directly from the CVD reactor, in which they were synthesized. The block composites with highly aligned and tightly packed nanotube assemblies were prepared via epoxy resin infiltration, and their volume fraction, distribution, and internal porosity being analysed prior to mechanical testing. The samples were tested in both axial tension and three-point bending. The results show that the strength and stiffness enhancements were close to pro rata with the volume fraction of the carbon nanotubes added. The failure modes were distinctly different from those characteristic of the conventional aligned carbon fibre composites. The fracture surface showed considerable evidence of pull-out of bundles of (~50) nanotubes, but the pull-out appeared to involve the resin matrix which drew out along with the bundles. Subsidiary cracks were bridged by nanotube bundles giving structures reminiscent of crazes in glassy polymers, what constitutes the distinct toughness mechanism and higher resistance to the transverse cracks propagation.

Processing of Functionalized and Pristine Carbon Nanotube Epoxy Composites with Silane-Treated Glass Fiber

In this work, an attempt has been made to study the bonding between the silane coupling agents and the glass fiber (GF) surface. The mechanical properties of the composites so obtained have been specifically analyzed. It has been experimentally found that epoxy silane (ES)-treated GF mat in a neat epoxy matrix showed considerable improvement compared to amino silane (AS)-treated GF. The effect of heat treatment on GF has also been looked into. Moreover, a new processing technique has been explored, which involves the use of amino functionalized nanotube (ACNT) and pristine nanotube (PCNT), homogeneously and uniformly dispersed in an epoxy matrix. Additionally, the effect of ES- and AS-treated GF in the presence of PCNTs and ACNTs has been studied and it has been found that AS shows strong interfacial adhesion in the ACNT matrix, whereas ES shows improved mechanical behavior in the PCNT matrix. The findings from this study have certainly helped us design improved fiber reinforced nanocomposites with enhanced mechanical properties suitable for marine structures.

Carbon nanotube-epoxy composites: The role of acid treatment in thermal and electrical conductivity

Wet acid oxidation treatment methods have been widely reported as an effective method to purify and oxidize the surface of industrial multi-walled carbon nanotubes. This work examines the use of a concentrated HNO3/H2SO4 mixture in an attempt to optimize the purification procedure of industrial multi-walled carbon nanotubes with diameter distribution statistics. It is shown that acid treatments of several hours are enough to purify the nanotubes. The electrical and thermal conductivities of epoxy composites containing 0.05–0.25 wt% of an acid-treated multi-walled carbon nanotube have been studied. The electrical conductivity of the composites decreases by more than three orders, whereas the thermal conductivity of the same specimen increases very modestly as a function of the filler content.

The effect of choline-based ionic liquid on CNTs' arrangement in epoxy resin matrix

This work focuses on the effect of ionic liquids (ILs) on the arrangement of carbon nanotubes (CNTs) in CNTs–epoxy composites. Electrical conductivity experiments on epoxy–CNTs–ILs suggested that, compared to Ethaline, Oxaline and Reline, Glyceline had a more distinguishable effect on the CNTs' arrangement in the epoxy–CNTs–Glyceline (CG) composites based on scanning electron microscope results. The electrical conductivity of CG composites was improved by increasing the weight content of Glyceline up to 50 times that of CNTs (Gly/CNTs=50), and for weight ratios higher than 50, a downward trend was observed. According to the proposed model, the increase in electrical conductivity seems to be a result of the formation of liquid vesicles which push the CNTs closer outside the Glyceline vesicles. Conversely, the drop in the electrical conductivity can be due to the enlargement of the vesicles, which dissolve CNTs and reduce their content in the epoxy. In addition, the tensile strength of CG composites increased by ratio of Gly/CNTs=10 followed by a significant drop thereafter.Thermal stability of the CG composites was seen to decrease as Glyceline content is increased in the composite. This reduction was attributed to the early decomposition of Glyceline vesicles present inside the epoxy matrix.

The sonication effect on CNT-epoxy composites finally clarified

Carbon nanotube-epoxy composites were prepared using amino-functionalized CNTs and sonication as a mixing process. Different times and sonication powers were used for preparing composites in order to study how the sonication process may influence the curing reaction of both systems: neat epoxy resin and amino-CNT/epoxy composite.The curing reaction was investigated with differential scanning calorimetry and the results were associated with analysis of gel permeation chromatography. The results showed that the effect of CNTs on the cure behavior of the epoxy resin depends on the sonication power. The sonication of neat resin with a 150 W powered device led to a molar mass reduction of the resin and an increase in the cure enthalpy. The CNT addition to this system reduced the cure enthalpy. However, when neat epoxy resin was sonicated with a 200 W powered device, the molar mass did not decrease (i.e. it was increased or was not changed) and the cure enthalpy did not increase (essentially it decreased or did not change). The CNT addition to such solutions did not reduce (i.e. it was increased or did not change) the cure enthalpy, which is a contrary result from that obtained with a 150 W powered device. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Toward improved mechanical performance of multiscale carbon fiber and carbon nanotube epoxy composites

A novel class of multiscale epoxy composites was developed containing carbon fibers (CFs) and multiwalled carbon nanotubes (MWCNTs) to explore their mutual effect on the mechanical performance of composites. The loading of CFs in composites was kept constant at ∼60 wt%, while the contents of MWCNTs were increased from 0.5 wt% to 2.0 wt%. MWCNTs were functionalized through acid treatment before incorporating into epoxy matrix to promote dispersion quality. The developed composites were characterized microstructurally by scanning electron microscopy and mechanically by tensile, flexural, edgewise compression, and hardness tests. Homogeneous dispersion of MWCNTs was observed until their loading of 1.5 wt%, which enhanced the mechanical performance of composites. Hardness increased up to 47% while tensile, flexural, and edgewise compressive moduli increased to 40%, 16.3%, and 164%, respectively. Moreover, tensile, flexural, and edgewise compressive strengths showed rises of 45%, 15.2%, and 43%, respectively. The fracture strain increased in both the tensile and flexural tests while it decreased in edgewise compressive tests. Increasing the MWCNTs in composites to 2.0 wt% produced their agglomerates and reversed the rising trend in mechanical properties. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Temperature-compensated force/pressure sensor based on multi-walled carbon nanotube epoxy composites.

In this study, we propose a multi-walled carbon nanotube epoxy composite sensor for force and pressure sensing in the range of 50 N–2 kN. A manufacturing procedure, including material preparation and deposition techniques, is proposed. The electrode dimensions and the layer thickness were optimized by the finite element method. Temperature compensation is realized by four nanocomposites elements, where only two elements are exposed to the measurand. In order to investigate the influence of the filler contents, samples with different compositions were prepared and investigated. Additionally, the specimens are characterized by cyclical and stepped force/pressure loads or at defined temperatures. The results show that the choice of the filler content should meet a compromise between sensitivity, temperature influence and noise behavior. At constant temperature, a force of at least 50 N can be resolved. The measurement error due to the temperature influence is 150 N in a temperature range of −20°C−50°C.

Hygro-Thermo-Electric Properties of Carbon Nanotube Epoxy Nanocomposites with Agglomeration Effects

In the present study, the effective electric, thermal, and moisture properties of carbon nanotube (CNT) epoxy composites are derived by considering the agglomeration effect of CNT concentrations in the epoxy matrix. In this direction, the Voigt and Reuss homogenization method is adopted in the derivations. It is well known from experiments that the CNT thermal and electrical conductivities and the epoxy hygro-thermal expansion coefficients have significant effects on the behavior of CNT nanocomposites. Moreover, it has been experimentally proved that the agglomeration of CNTs in the matrix with high and low concentrations of the CNTs certainly affects the resistivity and, hence, the thermal expansion properties. Therefore, the effective elastic, thermal, electrical, and moisture properties for the randomly distributed CNTs in the matrix has been derived in terms of the agglomeration volume fractions of CNTs. In the effective relations, a single agglomeration parameter is considered to be active for a given potential. The results of variation in the hygro-electro-thermal properties due to change in CNT volume fraction as well as agglomeration parameters have been presented. The results and observation show that CNT agglomeration has a strong influence on the effective hygro-thermo-electric properties of the nanocomposites.

Pull-out simulations of interfacial properties of amine functionalized multi-walled carbon nanotube epoxy composites

In this work the effect of amine functionalization of carbon nanotubes (CNTs) on the interfacial bonding characteristics between amine functionalized CNTs and LY556 resin has been investigated using molecular dynamics (MD) simulations. By analyzing the interfacial shear stress of nano composites (reinforced with single, double and triple walled CNTs), the effect of functionalization with Ethylene-di-amine (E-NH2) functional group has been examined. This study investigates the effect of functionalization with up to ten E-NH2 groups on the potential energy, pull-out energy and interfacial shear strength of different functionalized CNTs structures with reference to pristine CNTs. MD simulation proves that the interfacial bonding and shear stress between the CNTs and LY556 resin matrix depends on the degree of functionalization of CNTs. Thus optimum functionalization of CNT surface can be an effective way to improve the load transfer between the CNTs and resin. An artificial neural network based non-linear regression model is also developed for energy required to pullout different walled CNTs from the epoxy matrix. It has been observed that ANN modeling produced best results for MWCNT pullout as compared to SWCNT and DWCNT. This study will assist in the modeling, simulation and design of advanced nanotube reinforced polymer composites for potential real life applications, particularly in military structural applications.