Carbon Nanotube Epoxy Research Articles

Improvement in mechanical and thermal properties of epoxy hybrid composites by functionalized graphene and carbon-nanotubes

Thermo-mechanical properties of amine functionalized multi-layered graphene (Af-MLG) and amine functionalized multi walled carbon nanotube (Af-MWCNT) epoxy hybrid composites is investigated. Ratio of hybrid fillers is being kept as 1:1 with a variation in wt% from 0.25 to 2.0. An optimum dispersion of hybrid nanofillers in epoxy matrix environment by using a probe sonicator has confirmed through TEM images. The presence of amine group in their corresponding composites (Af-M(Gr:CNT)/Ep-C) is confirmed through Fourier transform Infrared spectroscopy (FTIR), while amorphous nature of composite has been substantiate by using X-ray diffraction (XRD). Scanning electron microscope and transmission electron microscopy (SEM) images of Af-M (Gr: CNT)/Ep-C shows interaction between graphene sheet and MWCNT. Thermal decomposition temperatures of composites are investigated by using thermo-gravimetric analysis (TGA). A maximum increase of 52.8% in tensile strength for composites with 0.5 wt% loading of hybrid fillers shows collegial effects of both fillers when used in combination. Composites with 1.0 wt% loading of hybrid fillers demonstrate the highest flexural strength and thermal properties (degree of degradation of composites) as compared to the neat epoxy samples.

Determination of electrical percolation threshold of carbon nanotube‐based epoxy nanocomposites and its experimental validation

The electrical conductivity of polymer nanocomposites plays a critical role in applications like aerospace and electromagnetic shielding. Electrical conductivity and other electromagnetic parameters of carbon nanotube (CNT)-based epoxy nanocomposites are being analysed in this work for their suitability in electromagnetic shielding. Unfilled epoxy and CNT epoxy nanocomposite samples with various filler loadings are prepared. Impedance measurements are conducted over the frequency range of 20 Hz–10 MHz. Micromechanics model is used for the theoretical estimation of electrical conductivity of CNT-based epoxy nanocomposites. Interface thickness in the conventional model is modified to avoid the overestimation of electrical conductivity. DC conductivity of nanocomposites determined experimentally is found to obey classical law of percolation theory and percolation threshold is determined to be 0.17 wt% which agrees well with theoretical value of 0.18 wt% obtained using modified micromechanics model. AC conductivity is found to obey universal dynamic response. Dipolar polarisation mechanism is prominent in the tested frequency range whose frequency of occurrence increases with CNT content due to a greater number of interfaces formed between CNT and epoxy. CNT epoxy nanocomposites are found to have negative permeability thus acting as absorbers in electromagnetic shielding.

Study on the performance of syntactic foam reinforced by hybrid functionalized carbon nanotubes

ABSTRACTHollow glass microspheres (HGMs)/epoxy syntactic foam were reinforced by hybrid functionalized carbon nanotubes that were synthesized by simultaneous covalent and noncovalent functionalization of carbon nanotubes. The effect of hybrid functionalized carbon nanotubes on density, mechanical properties, and water absorption of HGMs/epoxy syntactic foam was studied. The study indicated that the dispersion of carbon nanotubes in epoxy resin can be improved by hybrid functionalization. The compression strength of syntactic foam reinforced by hybrid functionalized carbon nanotubes was significantly enhanced. The maximum compressive strength of syntactic foam corresponding to chitosan modified carbon nanotubes approached 60 MPa. Hybrid functionalized carbon nanotubes had little effect on the water absorption ability of syntactic foam, and was less than 1%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48586.

Different Methods of Dispersing Carbon Nanotubes in Epoxy Resin and Initial Evaluation of the Obtained Nanocomposite as a Matrix of Carbon Fiber Reinforced Laminate in Terms of Vibroacoustic Performance and Flammability.

Different industrial mixing methods and some of their combinations ((1) ultrasound; (2) mechanical stirring; (3) by roller machine; (4) by gears machine; and (5) ultrasound radiation + high stirring) were investigated for incorporating multi-walled carbon nanotubes (MWCNT) into a resin based on an aeronautical epoxy precursor cured with diaminodiphenylsulfone (DDS). The effect of different parameters, ultrasound intensity, number of cycles, type of blade, and gear speed on the nanofiller dispersion were analyzed. The inclusion of the nanofiller in the resin causes a drastic increase in the viscosity, preventing the homogenization of the resin and a drastic increase in temperature in the zones closest to the ultrasound probe. To face these challenges, the application of high-speed agitation simultaneously with the application of ultrasonic radiation was applied. This allowed, on the one hand, a homogeneous dispersion, and on the other hand, an improvement of the dissipation of heat generated by ultrasonic radiation. The most efficient method was a combination of ultrasound radiation assisted by a high stirring method with the calendar, which was used for the preparation of a carbon fiber reinforced panel (CFRP). The manufactured panel was subjected to dynamic and vibroacoustic tests in order to characterize structural damping and sound transmission loss properties. Under both points of view, the new formulation demonstrated an improved efficiency with reference to a standard CFRP equivalent panel. In fact, for this panel, the estimated damping value was well above the average of the typical values representative of the carbon fiber laminates (generally less than 1%), and also a good vibroacoustic performance was detected as the nanotube based panel exhibited a higher sound transmission loss (STL) at low frequencies, in correspondence with the normal mode participation region. The manufactured panel was also characterized in terms of fire performance using a cone calorimeter and the results were compared to those obtained using a commercially available monocomponent RTM6 (Hexcel composites) epoxy aeronautic resin with the same process and the same fabric and lamination. Compared to the traditional RTM6 resin, the panel with the epoxy nanofilled resin exhibits a significant improvement in fire resistance properties both in terms of a delay in the ignition time and in terms of an increase in the thermal resistance of the material. Compared to the traditional panel, made in the same conditions as the RTM6 resin, the time of ignition of the nanotube-based panel increased by 31 seconds while for the same panel, the heat release rate at peak, the average heat release rate, and the total heat release decreased by 21.4%, 48.5%, and 15%, respectively. The improvement of the fire performance was attributed to the formation of a non-intumescent char due to the simultaneous presence of GPOSS and carbon nanotubes.

Graphene and carbon nanotube reinforced epoxy nanocomposites: A review

The continuous demand for low weight, economical and high strength materials have been the driving force for the search of new materials. The discovery of carbon nanofillers, viz. graphene (Ga) and carbon nanotubes (CNTs), has brought tremendous revolution in the field of epoxy-based nanocomposites. The extraordinary thermo-mechanical, electrical and flame-retardant properties offered by Ga and CNTs have led to the development of Ga/CNT-epoxy nanocomposites. The paper reviews the research conducted in the last ten years pertaining to the fabrication, characterization and applications of Ga/CNTs-epoxy composites. The major challenges faced by the researchers in developing epoxy nanocomposites for high performance applications are also highlighted. It is revealed by simultaneously reinforcing Ga and CNTs in epoxy, one could resolve major issues like poor dispersion and agglomeration of nanofillers in epoxy, which can help in developing ultra-high-performance nanocomposites. But further research is needed to explore the full potential of Ga/CNTs/epoxy hybrid nanocomposites.

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. ...

Multifunctional primer film made from percolation enhanced CNT/Epoxy nanocomposite and ultrathin CNT network

Here we demonstrate a high performance multifunctional thin primer film made from sandwich structured ultrathin carbon nanotube (CNT) networks and carbon nanotube-epoxy nanocomposite. For this, percolation enhanced CNT-epoxy nanocomposites were fabricated by mixing CNTs with two extremely different length/diameter aspect ratios followed by a unique convective coating process assembling SWNTs into ultrathin, uniform and large-scale film on hydrophobic CNT-epoxy substrates without any pretreatment of the surface. This multifunctional-sandwiched film exhibits relatively low surface roughness, high conductivities, excellent adherence to both polymers and metals, and tunable high EMI-shielding effectiveness of 32.54 dB in the range of 8.2–12.4 GHz (X-band). These results open the pathway to design multifunctional primer thin films that can be used for fabricating hybrid thermal management systems, EMI shielding film and structurally integrated sensors.

The mechanical and electrical properties of direct-spun carbon nanotube mat-epoxy composites

Composites of direct-spun carbon nanotube (CNT) mats and epoxy are manufactured and tested in order to determine their mechanical and electrical properties. The mats are spun directly from a floating catalyst, chemical vapour deposition reactor. The volume fraction of epoxy is varied widely by suitable dilution of the epoxy resin with acetone. Subsequent evaporation of the acetone, followed by a cure cycle, leads to composites of varying volume fraction of CNT, epoxy and air. The modulus, strength, electrical conductivity and piezoresistivity of the composites are measured. The CNT mats and their composites exhibit an elastic-plastic stress-strain response under uniaxial tensile loading, and the degree of anisotropy is assessed by testing specimens in 0°, 45° and 90° directions with respect to the draw direction of mat manufacture. The electrical conductivity scales linearly with CNT volume fraction, irrespective of epoxy volume fraction. In contrast, the modulus and strength depend upon both CNT and epoxy volume fractions in a non-linear manner. The macroscopic moduli of the CNT mat-epoxy composites are far below the Voigt bound based on the modulus of CNT walls and epoxy. A micromechanical model is proposed to relate the macroscopic modulus and yield strength of a CNT mat-epoxy composite to the microstructure.

Mechanical Improvements of Multi-Walled Carbon Nanotube-Epoxy Composite: Covalent Functionalization of Multi-Walled Carbon Nanotube by Epoxy Chains

In this study, multi-walled carbon nanotubes (MWCNTs) were functionalized with epoxy chains via a microwave-assisted method. The effect of MWCNT functionalization with epoxy chains was studied on mechanical properties of MWCNT-reinforced epoxy composites. It was found that functionalization of MWCNT with epoxy chains can significantly enhance the compatibility of MWCNTs with the epoxy matrix. Consequently, remarkable improvements were achieved in mechanical properties, tensile strength and elastic modulus, of the MWCNT-reinforced epoxy composites. Fractography observation of reinforced composites was carried out to study the reinforcing effect of functionalized MWCNTs on the epoxy composites. It was found that the reinforcing effect of MWCNTs changed the fracture mood of the composite from ductile mood to a brittle fracture.

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 Diluent on the Rheological and Mechanical Properties of Epoxy-Carbon Nanotubes Composite

The incorporation of carbon nanotubes (CNTs) with polymer material has been the focus of research for many years, due to relatively simple processing procedure and high potential application. However, it is found to be difficult to get very good CNT dispersion, due to the viscosity built-up during the CNTs dispersions. This project investigated the effect of viscosity of the polymer resin through rheological and mechanical characterization. The key ingredient applied for the modification of the epoxy-CNTs viscosity properties is the ethanol diluent. The effect of ethanol diluent on epoxy-CNTs composites was studied through addition of 5% and 10% weight ratio of ethanol to the epoxy-CNTs suspension with increasing CNTs content up to 0.5% weight proportion. The produced specimens were studied and compared with non-diluent specimens through viscometer, optical microscope and tensile strength testing. The addition of ethanol was found to reduce the viscosity of epoxy-CNTs composite through shear-thinning behaviour, in which results due to a high shear rate condition and was found to be beneficial in reducing the CNTs agglomerations and clusters formation within the composite structure. Moreover, improvement in tensile strength of epoxy-CNTs suspension with diluent was observed over non-diluent epoxy-CNTs specimens. The highest gain in tensile strength among the epoxy-CNTs sample was the one containing 0.5% CNTs and 5% ethanol weight ratio, the highest CNTs content tested in this experiment. The experimental results proved that ethanol diluent is beneficial to epoxy-CNTs composites in reducing agglomeration, improving flow-ability and tensile strength.

Study of Carbon Nanotube Epoxy Resin Coated Carbon Unidirectional Fiber Fabric in Radiation Shielding

Study of Carbon Nanotube Epoxy Resin Coated Carbon Unidirectional Fiber Fabric in Radiation Shielding

Spall Characterization of EPON 828 Epoxy with Embedded Carbon Nanotubes

The increasing use of polymer nanocomposites in armor applications requires an understanding of how these materials behave at strain-rates relevant to ballistic impacts. Of particular interest is the role of the microstructure on the failure of these materials under dynamic tensile loading. In the present study, plate impact experiments were conducted in order to measure the spall strength of a neat epoxy (EPON 828) and an epoxy–carbon nanotube composite. The addition of pristine carbon nanotubes (CNTs) to the epoxy resulted in a composite material with a lower spall strength than the neat epoxy matrix material. Recovered composite fragments were imaged with a scanning electron microscope. Instances of nanotube pull-out were identified on internal fracture surfaces. The lower spall threshold of the epoxy–CNT composite was attributed to the comparatively weak epoxy–CNT interface, which provides potential sites from which spall failure can favorably nucleate.

Injection and Interface-Dominated Nonlinear Resistors from Tin-Carbon Nanotube Junctions

Abstract:This manuscript describes low-voltage epoxy-carbon nanotube composites with highly nonlinear resistances. Carbon nanotube paste was deposited on interdigitated electrodes and I-V characteristics were obtained over different voltage ranges and at different sweep speeds. In most cases, the injection process into the electrode-composite interface region was dominant, with exponential voltage dependence of the current.

The electrical behavior of functionalized multiwall carbon nanotubes decorated with polymer nanocomposites

Simple and facile technique of Chemical Vapor Deposition technique were employed to synthesize the multiwall carbon nanotubes, their morphology and characteristics were proven ability to deliver excellent mechanical, electrical properties and multi-functional properties for diverse applications. In order to delivering the benefits of technology, acidified and functionalized multiwall carbon nanotubes as an efficient reinforcement in terms of polymer nanocomposite. New comprehensive strategy of appropriate dispersion and good interfacial adhesion between the functionalized multiwall carbon nanotubes and Polymer matrix are desire able and addressed. Functionalized multiwall carbon nanotubes have been confirmed by using “Scanning Electron Microscopy (SEM)”, “Transmission Electron Microscopy (TEM)”, “Fourier Transform Infrared Spectroscopy (FTIR)”, and “Energy Dispersive X-Ray Spectroscopy (EDS)”. For effective and uniform dispersion of functionalized multiwall carbon nanotubes in Epoxy resin, various form of experimental strategies have been employed to achieve their maximum stability/strength and enhanced electrical properties. The engineering and adaptation of functionalized multiwall carbon nanotubes by epoxy provides not only excellent dispersion but also provide eminence interfacial adhesion. The mobility of the nanocomposite has been carried out by Hall analysis. The detailed investigation of electrical behavior of such nanocomposite also confirmed the insulative behavior of the matrix. It is expected that following product will contribute significantly in field of electronics sue to countless attractive features.

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.

Quasi-static and dynamic interfacial evaluations of plasma functionalized carbon nanotube fiber

Carbon nanotube (CNT) fibers composed of well-oriented and twisted CNT bundles are desirable as a strong and lightweight reinforcement for the high-performance composites. Herein, CNT fibers were functionalized by atmospheric pressure helium/oxygen plasma to build up the sufficient fiber/matrix interfacial bonding. The micro-bond test (quasi-static test) and electrical resistance measurement under cyclic loading (dynamic test) were carried out to evaluate the interfacial properties between CNT fiber and epoxy resin. The results illustrated 84.6% improvement in the interfacial shear strength (IFSS) of the functionalized CNT fiber and epoxy from 17.37 MPa to 32.08 MPa, since the generated oxygenic groups and roughed morphology on CNT fiber surface. Moreover, the linear and repeatable gauge factors (between 1.1 and 1.4) of the functionalized CNT fiber embedded in epoxy under dynamic cyclic loading demonstrated their good interfacial bonding as well. In addition, the tensile strength of the functionalized CNT fiber showed 49.5% increment. Our study for the first time reveals the interface interaction in a fiber-matrix system to provide the direct evidence for the interfacial enhancement of the plasma functionalized CNT fiber. The interface-enhanced CNT fiber can be generally applied in composites with much improved mechanical and electrical performance.

Multiscale modeling of thermal conductivity of carbon nanotube epoxy nanocomposites

Epoxy is among the most important polymers, which is extensively employed in various technologies and applications. Nevertheless, epoxy polymers present low thermal conductivities and thus the enhancement of their thermal conductivity is an important research topic. Carbon nanotubes (CNTs) owing to their excellent thermal conductivities have been widely considered for the enhancement of the thermal conduction of epoxy polymers. In this work, we developed a combined molecular dynamics finite element multiscale modelling to investigate the heat transfer along CNT/epoxy nanocomposites. To this aim, the heat transfer between the CNT and epoxy atoms at the nanoscale was explored using the atomistic classical molecular dynamics simulations. In this case, we particularly evaluated the interfacial thermal conductance between the polymer and fillers. We finally constructed the continuum models of polymer nanocomposites representative volume elements using the finite element method in order to evaluate the effective thermal conductivity. The developed multiscale modelling enabled us to systematically analyze the effects of CNT fillers geometry (aspect ratio), diameter and volume fraction on the effective thermal conductivity of nanocomposites. Our results suggest that the interfacial thermal conductance between the CNT additives and epoxy polymer dominate the heat transfer mechanism at the nanoscale. The obtained findings in this study provide good vision regarding the enhancement of thermal conductivity of polymeric materials using highly conductive nanofillers.

Covalent Functionalization of Single-Walled Carbon Nanotubes Through the Fluorination Stage for Integration into an Epoxy Composite

The upper limit of the elastic modulus has been estimated for a polymer–carbon nanotube–epoxy matrix nanocomposite. This limit can be achieved if the nanotubes are integrated into the matrix, i.e., they form a continuous reinforcing network inside the matrix, and if the nanotubes are single-walled or double-walled carbon nanotubes. A technique for carbon nanotube functionalization via fluorination and fluorine substitution and a technique for calculating the degree of nanotube functionalization based on reaction yield measurements are proposed. For fluorine substitution by epoxy-diane resin and diaminodiphenylmethane, the degree of functionalization is С–(FG)x, x ~ 0.011–0.013 and the FG-molecular fragment containing the epoxy (amino) group corresponding to functionalization of ~5% of the surface С atoms of nanotubes. The control reaction showed that the epoxy groups preserve the chemical activity, while part of the amino groups are deactivated. The grafted epoxy(amino) groups ensure nanotube surface lyophilicity in epoxy composites and integrate the nanotubes into the epoxy matrix owing to the chemical bonds.

Smart dispersion: Validation of OCT and impedance spectroscopy as solutions for in-situ dispersion analysis of CNP/EP-composites

In this study, we demonstrate the applicability of three-roll milling (TRM) process for carbon nanotube-epoxy dispersion in industrial scale and two methods to characterize the dispersion quality based on optical coherence tomography (OCT) and impedance spectroscopy were utilized. These methods are easily applicable for industrial continuous TRM dispersion process monitoring. Modeling impedance spectra with equivalent circuit enhances the possibility to quantify the grade of dispersion. We monitored the dispersion development over a complete seven step three-roll mill process for several batches. The gained results are in good accordance to the particle size measurements by grindometry. Results show, on the one hand, that the real part of impedance undergoes a minimum during processing. The most homogeneous dispersion state is not the favorable for gaining electrical conductive materials. On the other hand, imaginary part of impedance undergoes a maximum. High reactance correlates with small particle sizes as well as homogeneous distribution. A developed model from impedance spectra leads to an improved understanding of network formation. OCT results allow a qualitative analysis of the dispersion and detection of in-homogeneous agglomerate sizes.