Multi-walled Carbon Nanotube Epoxy Research Articles

Design of a high-efficient metamaterial X-band absorber composed of a dielectric cylinder combined with a thin magnetic cylinder unit

High-efficient microwave absorbers (MAs) with excellent absorption performance and lightweight characteristics have important applications in the military and civil. Here, we propose a dielectric-magnetic hybrid microwave absorber composed of a lattice of dielectric cylinders combined with thin magnetic cylinders backed by a perfect electrical conductor ground plane. The dielectric material that is designed as the dielectric cylinder is based on multi-walled carbon nanotubes-epoxy (MWCNT-EP). The MWCNT-EP is prepared and the S-parameters are measured by the standard transmission/reflection (T/R) method. The thin magnetic cylinder is based on a commercial magnetic material with a height of only 1 mm. With the coaction of magnetic loss and dielectric loss, the proposed microwave absorber’s reflection loss is less than −20 dB under normal incident with a total height of 5 mm in the X-band. Besides, the dielectric-magnetic microwave absorber can maintain good absorption performance with different incident angles and polarizations. In this work, we provide a method to combine the properties of magnetic and dielectric material to construct the MA with high-efficient absorption performance.

Design of a lattice dielectric cylinder based on multiwalled carbon nanotube-epoxy composite for microwave absorption in the X-band

To meet the urgent electromagnetic compatibility (EMC) requirements for the electronic products, microwave absorbers with a lattice of the dielectric cylinder were investigated. The elements of the lattice have a cylindrical shape and are composites of epoxy resin filled with multi-walled carbon nanotubes (MWCNTs-EP). The relative complex permittivity of the MWCNT-EP was obtained from the S-parameters measured by the transmission-reflection method with X-band waveguide. The numerical simulation results show that the reflection coefficient of the uniform lattice of the dielectric cylinder is less than −10 dB in the entire X-band (8 GHz–12 GHz) and the reflection coefficient of the hybrid lattice of the dielectric cylinder (HLDC) is less than −15 dB in the same band. Moreover, the reflection coefficient of HLDC is less than −20 dB at normal incidence in the frequency range of 8.4 GHz–11.3 GHz. Further investigation demonstrates that the proposed HLDC could maintain good absorption performance under different incident angles and polarizations. This study suggests that HLDC with the characteristics of lightweight, excellent absorption performance, good angle, and polarization stability provide a promising prospect in the EMC field.

Evaluation of the effect of MWCNT amount and dispersion on bending fatigue properties of non-crimp CFRP composites

Multi-walled carbon nanotubes (MWCNTs) have many unique features that improve composite material properties, including a large surface area, thermal and chemical stability, and thermal and electrical conductivity. Our study aimed to examine the influence of MWCNT weight percentage on the fatigue characteristics of a polymer matrix composite strengthened with carbon fiber in fabric form. This study aimed to explore the additional properties and functions of these MWCNTs. For the experiments, MWCNTs were prepared by mixing them in solution with epoxy in three different weight percentages (0.5 %, 1.0%, and 1.5%) using a surfactant, and at 0.5 wt% without a surfactant. The prepared solutions were injected into four-axis non-crimp carbon fiber fabric plates via the vacuity mixture method and then cured for 48 h to produce nanocomposite plates. Using five types of composites, fatigue tests were carried out at six different amplitudes and a fixed frequency. Fatigue test specimens were subjected to detailed SEM analysis of their fatigue fracture surfaces. The investigational results revealed that the 0.5 wt% MWCNT epoxy solution had been homogeneously dispersed and exhibited the highest absorbance spectrum. The 0.5 wt% MWCNT specimen achieved the highest value in the fatigue life experiments. In addition, electron microscopy studies of the fracture surfaces of the test specimens determined that individual COOH-MWCNTs interrelated with the fibers and formed a bridge between fiber and matrix, whereas agglomerations caused weak bonding between the reinforcement fibers and matrix, making the material more brittle.

Improved mechanical performance of three-dimensional woven glass/epoxy spacer composites with carbon nanotubes

Three-dimensional polymer composites offer various features and design options due to their hollow structure and lightweight. However, to exploit their advantages, it is a must to improve their structural features and mechanical performances including out-plane direction. Although introducing thermoplastic fillers between the plies or multilayered design addresses on this critical issue, the benefits offered by the nanoparticles with superior mechanical properties come a step forward as an another engineering solution. Based on this motivation, the goal of this study is to investigate the impact of multiwalled carbon nanotubes on the mechanical and thermomechanical performances of three-dimensional woven glass/epoxy spacer composites. Therefore, multiwalled carbon nanotubes at various content were introduced into epoxy matrix, and the multiwalled carbon nanotubes–epoxy mixture was infused to three-dimensional woven fabric with the vacuum-assisted resin transfer method. The obtained results indicated that the three-point bending strength and modulus were enhanced up to 25 and 80% for warp direction and enhanced up to 44 and 85% for weft direction with carbon nanotube addition, respectively. Tensile strength developed in the warp direction by 7%, while the strength value in the weft direction did not change. The tensile strain values for warp and weft directions enhanced up to 19 and 12% with carbon nanotube addition, respectively. In addition, thermomechanical analysis has revealed that the glass transition temperature and storage modulus were also improved. Particle dispersion detection with color measurement and scanning electron microscopy analyses revealed the effectiveness of the ultrasonic mixing on the dispersion of carbon nanotubes in the epoxy matrix. The consequences of carbon nanotube addition on microscale morphology were discussed based on the fracture morphologies to nanoscale and microscale toughening mechanisms in the existence of carbon nanotube reinforcement.

Reinforcing Microwave Absorption Multiwalled Carbon Nanotube–Epoxy Composites Using Glass Fibers for Multifunctional Applications

Herein, the enhancement of the mechanical properties of microwave absorption composites, multiwalled carbon nanotubes (MWCNTs)–epoxy with various MWCNT loadings, using glass fiber (GF) reinforcement is focused upon. The tensile strength, morphologies, dielectric permittivity, and electromagnetic (EM) wave absorption properties (in a frequency range from 1 to 26 GHz) of the composites are investigated. The tensile strength of the composites is enhanced to about 400 MPa, which is comparable with that of commercial aluminum alloy 6061 (about 300 MPa), whereas the tensile strength of the pristine MWCNT–epoxy composite is around 15 MPa. The mass density of the MWCNT–epoxy–GF composites herein is found to be around 1.6 g cm−3, whereas aluminum alloy 6061 has a mass density of ≈2.7 g cm−3. In addition, the MWCNT (9 wt%)–epoxy–GF composite presents a strong EM wave absorption in a wide frequency band from 14 to 26 GHz, whereas aluminum alloys do not have much EM wave absorption. The high microwave absorption together with the enhanced mechanical strength of the composites provides a multifunctional potential for some applications.

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.

Release of radiolabeled multi-walled carbon nanotubes (14C-MWCNT) from epoxy nanocomposites into quartz sand-water systems and their uptake by Lumbriculus variegatus

Once plastic products containing multi-walled carbon nanotubes (MWCNT) are disposed, UV-light exposure may destabilize their structural integrity, leading to a release of MWCNT into the environment that can possibly be taken up by organisms and cause adverse effects. The aim of this study was to quantify the released amount of embedded 14C–MWCNT epoxy (E) nanocomposites. Furthermore, bioaccumulation of the released material was investigated in Lumbriculus variegatus.The release of radioactivity (RA) from irradiated (+SSR) E/14C-MWCNT composites was quantified after a series of mechanical treatments and in a quartz sand-water system. Non-irradiated composites served as control group (-SSR). Unlabeled ±SSR-nanocomposites were analyzed by means of electron microscopy. The exposure of blackworms to the released material and the amount of RA in the water phase, the quartz sand, and the faeces was quantified.About 0.1% of the embedded RA was released from +SSR-nanocomposites by mechanical treatment and exposure in the quartz sand-water system, which was about 23 times higher compared to -SSR composites. This corresponds to around 3 mg 14C-MWCNT m−2 for both approaches. Based on the released mass per composite area, +SSR plates set free a 50-fold higher amount of RA. A detectable amount of 7.3 ± 1.8 ng of 14C-MWCNT was also found in the water phase of the quartz sand-water systems. Electron microscopy revealed an enhanced surface degradation of the composites after SSR and mechanical treatments. Released polymer particles also contained protruding MWCNT. An amount of 2.4 ± 1.8% of released RA was taken up by blackworms after 2 d and about 66% of ingested material was eliminated again after 24 h.The results of this study show that SSR leads to an enhanced release of mostly E-polymer associated MWCNT from nanocomposites that are bioavailable for sediment-dwelling organisms, although the absolute amount of released material is low. Follow-up studies examining toxicological effects after uptake are essential for the environmental risk assessment of MWCNT and E/MWCNT-composites.

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.

MWCNT–Epoxy Nanocomposite Sensors for Structural Health Monitoring

We address multi-walled carbon nanotubes (MWCNTs) for structural health monitoring in adhesive bonds, such as in building structures. MWCNT-loaded composites are employed to sense strain changes under tension load using an AC impedance measurement setup. Different weight percentages of 1, 1.5, 2 and 3 wt % MWCNTs are added to the base epoxy resin using different dispersion times, i.e., 5, 10, and 15 min. The equivalent parallel resistance of the specimens is first measured by applying an alternating voltage at different frequencies. To determine the mechanical as well as sensory properties, the specimens are then subjected to a tensile test with concurrent impedance measurement at a fixed pre-chosen frequency. Using alternating voltage, a higher sensitivity of the impedance reading can be achieved. Employing these sensors in buildings and combining the readings of a network of such devices can significantly improve the buildings’ safety. Additionally, networks of such sensors can be used to identify necessary maintenance actions and locations.

Unified equivalent circuit model for carbon nanotube-based nanocomposites

Carbon nanotubes form a complex network in nanocomposites. In the network, the configuration of the nanotubes is various. A carbon nanotube may be curled or straight, and it may be parallel or crossed to another. As a result, carbon nanotube-based composites exhibit integrated characteristics of inductor, capacitor and resistor. In this work, it is hypothesised that carbon nanotube-based composites all adhere to a RLC interior circuit. To verify the hypothesis, three different composites, viz multi-walled carbon nanotube/polyvinylidene fluoride (MWCNT/PVDF), multi-walled carbon nanotube/epoxy (MWCNT/EP), multi-walled carbon nanotube/polydimethylsiloxane (MWCNT/PDMS) were fabricated and tested. The resistances and the dielectric loss tangent (tanδ) of the materials were measured in direct and alternating currents. The measurement shows that the value of tanδ is highly affected by the volume fraction of MWCNT in the composites. The experimental results prove that the proposed RLC equivalent circuit model can fully describe the electrical properties of the MWCNT network in nanocomposites. The RLC model provides a new route to detect the inductance and capacitance of carbon nanotubes. Moreover, the model also indicates that the carbon nanotube-based composite films may be used to develop wireless strain sensors.

Excellent mechanical properties of long multiwalled carbon nanotube bridged Kevlar fabric

The major causes of failure of Kevlar reinforced composites are inter-yarn slippage and poor adhesion with polymer. Herein, long length multiwalled carbon nanotubes (MWCNTs) are used as a secondary reinforcement to enhance the interfacial interaction between Kevlar and epoxy through bridging action. Different wt. % of MWCNT based Kevlar reinforced hybrid composite tape and their laminar composites have been prepared and their quasi-static unidirectional and dynamic mechanical properties are studied. It is found that the maximum tensile strength, Young's modulus and storage modulus of optimized i.e. 0.3 wt % of MWCNTs in epoxy resin (0.3KE) composite showed an overall improvement of ∼81%, ∼56% and ∼139%, respectively over base line composite tape (KE). The flexural modulus, Young's modulus and storage modulus of 0.3 wt % multi-scaled laminar composite (KEC) showed an overall improvement of ∼33%, ∼50%, and ∼233%, respectively over KE. The effects of MWCNTs on interfacial properties of multi-scaled composite tapes are correlated by Raman spectral shift, FTIR and XRD analysis. Further the bridging actions of long length MWCNTs are visualized by using high resolution transmission electron microscopy.

Linear strain sensor made of multi-walled carbon nanotube/epoxy composite

In this study, a fabrication process was developed to make the multi-walled carbon nanotubes/epoxy (MWCNT/EP) composite films. The electrical-strain behaviour of the films in direct and alternating current circuits were both tested. It is found that the direct current resistance and the dielectric loss tangent of the MWCNT/EP composite films are dependent on the strain and the weight fraction of the carbon nanotubes. In an alternating current circuit, the test frequency affects the impedance and the phase angle of the composite film, but it has nothing to do with the change ratio of the dielectric loss tangent of the film in tension. This phenomenon can be interpreted by a proposed equivalent circuit model. Experiment results show that the change rate of the dielectric loss tangent of the MWCNT/EP sensor is linearly proportional to the strain. The findings obtained in the present study provide a promising method to develop ultrasensitive linear strain gauges.

Industrial-Graded Epoxy Nanocomposites with Mechanically Dispersed Multi-Walled Carbon Nanotubes: Static and Damping Properties.

The majority of currently published dispersion protocols of carbon nanotubes rely on techniques that are not scalable to an industrial level. This work shows how to obtain polymer nanocomposites with good mechanical characteristics using multi-walled carbon nanotubes epoxy resins obtained by mechanical mixing only. The mechanical dispersion method illustrated in this work is easily scalable to industrial level. The high shearing force due to the complex field of motion produces a good and reproducible carbon nanotube dispersion. We have tested an industrial epoxy matrix with good baseline mechanical characteristics at different carbon nanotube weight loads. ASTM-derived tensile and compressive tests show an increment in both Young’s modulus and compressive strength compared with the pristine resin from a starting low wt %. Comparative vibration tests show improvement in the damping capacity. The new carbon nanotube enhanced epoxy resin has superior mechanical proprieties compared to the market average competitor, and is among the top products in the bi-components epoxy resins market. The new dispersion method shows significant potential for the industrial use of CNTs in epoxy matrices.

Enhanced thermomechanical and electrical properties of multiwalled carbon nanotube paper reinforced epoxy laminar composites

Thermomechanical and electrical properties of multiwalled carbon nanotubes (MWCNTs) bucky paper reinforced epoxy laminar composites have been studied. Incorporation of bucky paper in epoxy matrix led to improvement in thermomechanical properties but it reduced through-plane electrical conductivity. Therefore, 0.05 wt.% of MWCNTs is incorporated as secondary network in epoxy matrix to improve the electrical conductivity. The storage modulus for a 0.05 wt.% dispersed MWCNTs in epoxy resin impregnated 20 plies of bucky paper based composites (20Ply.05) was 4.84 GPa as compared to 2.24 GPa of pure epoxy. The glass transition temperature of 20Ply.05 laminar composite reaches to 191.6 °C as compared to pure epoxy (168.5 °C). The increment in electrical conductivity (792%) is reflected in improved electromagnetic shielding effectiveness (SE) over a wide frequency range of X & Ku band. The SE of more than 50 dB for 20Ply.05 laminar composite in both the bands was obtained.

Improving shear strength of bolted joints in pultruded glass fiber reinforced polymer composites using carbon nanotubes

The structural design of the bolted fiber reinforced polymer elements is typically governed by the capacity of the joint rather than the fiber reinforced polymer member, while the joint capacity is typically governed by the shear strength of the fiber reinforced polymer. Here, the possibility of improving the shear strength of bolted joints is investigated in the unidirectional glass fiber reinforced polymer plates by incorporating the multiwalled carbon nanotubes during glass fiber reinforced polymer fabrication. Glass fiber reinforced polymer double-shear bolted lap joints were fabricated using up to 1.0 wt% multiwalled carbon nanotubes–-epoxy nanocomposites. Finite element modeling using multicontinuum theory and element deletion techniques was performed to explain the joint behavior. The experimental investigations show that incorporating multiwalled carbon nanotubes improved the shear strength, ductility, and energy absorption significantly. Microstructural analysis proves that a chemical reaction between multiwalled carbon nanotubes and epoxy improves the shear strength of the matrix.

Piezoresistive performance characterization of strain sensitive multi-walled carbon nanotube-epoxy nanocomposites

Carbon nanotubes polymer nanocomposites have attracted a significant research, which provide interesting aspects for the realization of cost effective, highly sensitive piezoresistive strain sensors. Here, we report on an extensive piezoresistive performance investigation of multi-walled carbon nanotubes (MWCNTs)/epoxy nanocomposite under uniaxial cyclic tensile and compressive loading in low strain range. Dispersion quality of MWCNTs in the epoxy polymer matrix was monitored by scanning electron microscopy. MWCNTs/epoxy nanocomposite was deposited directly on a glass-reinforced epoxy cantilever beam on the same axis with a commercial metallic strain gauge. The strain sensitive nanocomposite presents high-performance properties, including gauge factor up to 78, good stability of ±0.26% for 10h and durability of −0.08% after cyclic loading and unloading. Furthermore, MWCNTs/epoxy nanocomposites show quite small creep up to ±0.26%, fast response and recovery times, low hysteresis under cyclic tensile and compressive loadings and temperature response make the proposed nanocomposites suitable in various potential strain sensor applications including structural health monitoring.

Piezoresistive characterization of multi-walled carbon nanotube-epoxy based flexible strain sensitive films by impedance spectroscopy

In this study, we investigate the piezoresistive properties of flexible, strain sensitive multi-walled carbon nanotubes (MWCNTs)/epoxy composites. The deformation over the sensor area was tested by digital image correlation (DIC) under quasi-static uniaxial tension. The piezoresistive characteristics of the films were investigated quantitatively by electrochemical impedance spectroscopy (EIS) over a wide range of frequencies from 40 Hz to 110 MHz. Scanning electron microscopy (SEM) images confirmed that MWCNTs/epoxy composites with different CNT concentrations have a good homogeneity and dispersion. Additionally, in order to tailor the piezoresistivity of the strain sensor, an RC equivalent circuit was derived based on the impedance responses and the corresponding parameters were extracted under tensile strain. Compared with traditional strain gauges, higher sensitivity is obtained in particular at the concentrations close to the percolation threshold (13.6 for 0.3 wt.%). Due to the tunneling effect, a non-linear piezoresistivity is observed at low concentrations. It was found that sensors with 1 wt.% shows the highest linearity with a correlation coefficient of 0.999. The standard deviation of the cyclic readings was found to be 0.05%, indicating a high repeatability.

Synergistic effect of carbon nanotubes and copper particles in an epoxy-based nanocomposite using electroless copper deposited carbon nanotubes: Part I – Mechanical properties

In this study, the mechanical properties of epoxy nanocomposites reinforced by different contents of copper (Cu)-coated multiwalled carbon nanotubes (MWCNTs) are evaluated and discussed. Electroless deposition process is employed for Cu metallization of the MWCNTs. The functionalization step (as one of the prerequisite steps for deposition process) is carried out using hybrid approach with Triton and HNO3. The functionalized and Cu deposited MWCNTs are characterized by Fourier transform infrared, Raman spectroscopy, thermogravimetric analysis, atomic absorption spectroscopy, and scanning electron microscopy. For comparison, functionalized MWCNT–epoxy nanocomposites are also fabricated through the same fabrication process. Our results indicate that applying functionalized MWCNTs are more effective for enhancing tensile properties. On the contrary, Cu-coated MWCNT–epoxy nanocomposites show more improvement in flexural and impact behaviors. Accordingly, compared to neat epoxy, enhancement of up to ∼51% and ∼95% respectively in flexural strength and impact resistance are achieved by the addition of 0.1 wt% Cu-coated MWCNT.

Correlation of electrical conductivity, dielectric properties, microwave absorption, and matrix properties of composites filled with graphene nanoplatelets and carbon nanotubes

The DC electrical conductivity, percolation threshold, and dielectric properties of Graphene Nanoplatelets (GNPs) filled epoxy composites are studied and correlated with microwave absorption. The properties of GNPs filled composites are also compared with multiwalled carbon nanotubes (MWCNTs) composites, and GNPs are observed to have superior conductivity than MWCNTs. In all batches, the nanofillers have 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 wt. %. All composites irrespective of the type of nanofiller and viscosity of the matrix have shown electrical percolation threshold at 3.0 wt. %. The dielectric properties, i.e., complex permittivity, tan loss, and AC conductivity, are studied in 100 Hz–5.5 MHz. The DC and AC electrical conductivities (at and below the percolation) measured in 100 Hz–5.5 MHz are correlated to the GNPs and MWCNTs epoxy composites in the microwave frequency range (11–17 GHz). The maximum return loss of −12 dB and −6 dB was determined for MWCNTs and GNPs, respectively. The effects of nanofiller shape and the viscosity of the matrix on the dispersion and interparticle spacing of the conductive fillers within the polymer matrix have been discussed based on the results of conductivity, dielectric, and absorption properties.

High strength toughened epoxy nanocomposite based on poly(ether sulfone)‐grafted multi‐walled carbon nanotube

Hydroxyl terminated poly(ether sulfone) (PES) has been grafted on multi‐walled carbon nanotube (MWCNT). The grafting reaction was confirmed by different characterization techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The extent of the grafting was found to be around 58 wt%. Hybrid nanocomposite of epoxy with the modified MWCNT was also prepared. Effect of grafting on the mechanical, thermal, and viscoelastic properties was studied. Dynamic mechanical studies show an increase in the storage modulus for the nanocomposite prepared using PES‐grafted MWCNT compared with neat epoxy system. PES‐grafted MWCNT–epoxy nanocomposite induces a significant increase in both tensile strength (26%) and fracture toughness (125%) of the epoxy matrix. Field emission scanning electron micrographs of fractured surfaces were examined to understand the toughening mechanism. Copyright © 2015 John Wiley & Sons, Ltd.