Increasing CNT Content Research Articles

Cationic UV-curing of bio-based epoxidized castor oil vitrimers with electrically conductive properties

The growing appeal of carbon nanotube composites in the contemporary market derives from their exceptional thermal and chemical stability, coupled with electrical conductivity. In this study, we combined these salient features with a biobased epoxy matrix having vitrimeric properties, hence being reprocessable and resheapable, to obtain a biobased conductive coating. Epoxidised castor oil (ECO) was chosen as a monomer precursor for the straightforward synthesis. The synthesis relied on a cationic UV-curing process, embedding the conductive carbon nanotubes in the matrix. Photo DSC and transmission FTIR analysis were conducted to determine the final conversion of the epoxy rings in the cationic photocuring process. Thermo-mechanical properties were evaluated by tensile tests, and DMTA. Thermal stability was assessed by TGA. Dielectric spectroscopy confirmed increased electrical conductivity in the presence of increasing CNT content, reaching a percolation threshold at 0.5 phr of CNTs. Vitrimeric properties were proved by stress relaxation experiments, and the UV-cured composite underwent a thermo-activated transesterification reaction starting from 70 °C, catalysed by dibutyl phosphate. Overall, the ECO-CNT composite showed high thermal resistance (up to 400 °C) electrical conductivity with 0.5 phr CNT concentration, and vitrimeric properties. The study can be, therefore, considered a promising starting point to obtain sustainable biobased and electrically conductive vitrimers.

Multifunctional nanocomposites based on a polyamide 6/polyamide 12 blend and multi‐walled carbon nanotubes

AbstractNanocomposites based on an immiscible blend of polyamide 6 (PA6) and polyamide 12 (PA12) 50/50 wt.% with different contents of multi‐walled carbon nanotubes (MWCNTs) were prepared by extrusion followed by compression molding. These materials have been proved to be electrically conductive in previous investigations for the range of filler content assayed. The morphology of the nanocomposites was analyzed using scanning electron microscopy, both on cryo‐fractured and postmortem uniaxial tensile samples. Rheological measurements were performed along with differential scanning calorimetry, to assess the materials microstructure and thermal transitions. Furthermore, uniaxial tensile tests were carried out to determine mechanical properties such as stiffness, strength, and strain at break and to investigate the effect of MWCNTs on these properties. Finally, fracture tests were also conducted to evaluate how incorporating MWCNTs affected nanocomposites toughening capabilities. The obtained results suggest a notable improvement in the mechanical properties in the nanocomposites with low amounts of nanofiller. This expands their potential applications as conductive polymer composites (CPCs) and positions them as promising multifunctional materials.Highlights CPCs based on a PA blend and MWCNTs were successfully obtained. CNTs strongly affected the blend morphology and rheological properties. CNTs significantly modified the crystallization behavior of PA6. Ductility greatly improved at low CNT contents but decreased at high loadings. Stiffness increased steadily with increasing CNT content.

Study on the cutting force responses in machining multiscale carbon nanotube/carbon fiber reinforced polymer composites

Orthogonal cutting experiments were performed on the multiscale carbon nanotube/carbon fiber (CNT/CF) reinforced polymer composites with various wt. fractions of multiwalled CNTs (MWCNTs) filled in the epoxy to investigate the machinability of the material. In particular, the characteristics of the cutting force were studied as a response to the CNT content, the fiber orientation and the depth of cut. Results show that the effect of the CNT content on the principle cutting force in 135° orientation shows a different pattern than that in the other orientations. The mechanism was studied with an analytical mode proposed for the chip formation process. The depth of cut has a more significant effect on the principle cutting force for the tested condition, with the effect further enhanced by the inclusion of CNTs. Furthermore, with increasing CNT content or depth of cut, the resultant cutting force tends to shift along the cutting direction with a decreased coefficient of friction along the tool/chip interface.

Fracture analysis of CNT reinforced FG structures under thermo-mechanical loading using XIGA framework

This paper discusses the fracture analysis of FG structures reinforced by CNT exposed to thermo-mechanical load by means of the XIGA framework. The equivalent properties of functionally graded structures reinforced by CNT (SWCNT & MWCNT) are computed using micro-mechanics models. The volume fraction of CNT has an impact on the mechanical and thermal properties. Then, a preexisting crack is considered in the CNT reinforced FG square structure to perform the fracture analysis. The SIFs are calculated by the interaction integral method. It is noted that delaying of the fracture is possible with the increase of CNT content in FG structure.

A novel carbon nanotubes doped natural rubber nanocomposite with balanced dynamic shear properties and energy dissipation for wave energy applications

Mechanical characterizations of natural rubber filled with carbon-based nanomaterials were extensively studied in tensile and tear modes whereas fewer attempts have been conducted on a dynamic shear condition using a double-bonded shear test piece. This is of importance since natural rubbers are widely used as flexible membranes for wave energy harvesting devices. Therefore, this study was aimed to explore the microstructural, rheological, and dynamic viscoelastic characteristics of natural rubbers filled with different Multi-Walled Carbon Nanotubes (MWCNTs) contents. A combined compounding approach was employed to ensure a homogenous CNT dispersion was achieved. Transmission electron microscopy (TEM) was performed for the materials characterization while the processability and curing parameters of the compounds were investigated using the Mooney viscosity and rheometry test. Dynamic shear properties were compared using a cyclic test performed on a double-bonded shear test piece. TEM images showed that an optimum CNTs dispersion was reached at 3 phr MWCNTs loading whereas increasing CNT content resulted in further inhomogeneity. The addition of CNTs into the natural rubber not only improved the curing properties of the compound, i.e., low scorch and curing times, but it also increased the Mooney viscosity, the rheological properties, and the dynamic shear properties of the nanocomposite compared to the pristine rubber. The Payne and Mullins effects were also observed for all compounds manifesting dependency on the CNTs content and applied strain amplitude. Finally, MWCNT enhanced the dissipated energy of the nanocomposites with respect to the neat rubber in which an increase of 1040 % in energy dissipation for 10 phr MWCNTs compared to the control at a strain amplitude of 200 % was achieved.

3D printing of ABS Nanocomposites. Comparison of processing and effects of multi-wall and single-wall carbon nanotubes on thermal, mechanical and electrical properties

• Multi-Wall and Single-Wall carbon nanotubes affect thermoelectrical behavior. • Fuse Filament Fabrication of conductive nanocomposites at selected low resistivity. • 3D manufactured nanocomposites with applications for thermoelectric devices/sensors. • Anisotropy in electro-mechanical behaviour of multilayer nanocomposites. • Conductivity of CNT composites depends on filler content, process and geometry. The following paper reports on a comparative study of the effects of two types of carbon nanotubes, namely multiwall (MWCNT) and single-wall (SWCNT) carbon nanotube, on the properties of 3D-printed parts produced with acrylonitrile-butadiene-styrene (ABS) nanocomposites with various CNT loadings of 5-10 wt.%. Quasi-static tensile properties and Vicat softening temperature of 3D-printed parts were enhanced with the increasing CNT content. The highest enhancement in tensile properties was observed for the ABS/CNT nanocomposites at 10 wt.% filler loading. 3D-printed ABS/SWCNT composites showed higher tensile modulus, better creep stability and higher Vicat temperature. However, the strength of ABS/SWCNT 3D samples is relatively lower than that of ABS/MWCNT. In addition, 3D-printed parts exhibited anisotropic electrical conductive behaviour, which has a conductivity of through-layer of about 2-3 orders of magnitude higher than cross-layer. The highest conductivity of 3D-printed samples reached 25.2 S/m, and 9.3 S/m for ABS/MWCNT and ABS/SWCNT composites at 10 wt.%, respectively. The results obtained, i.e. the successful fuse filament fabrication and the consequent electromechanical properties, confirm that these 3D printable nanocomposite could be properly utilized for the production, and application up to about 90 °C, of thermoelectric devices and/or resistors for flexible circuits.

Influence of Soft Phase and Carbon Nanotube Content on the Properties of Hierarchical AZ61 Matrix Composite with Isolated Soft Phase.

Carbon nanotube-reinforced magnesium matrix (CNTs/Mg) composite has great application potential in the transportation industry, but the trade-off between strength and ductility inhibits its widespread application. In order to balance the strength and plasticity of the composite, in this work, on the basis of the AZ61 matrix composite homogeneously reinforced by Ni-coated CNTs (hard phase), 30 vol.% large-size AZ61 particles are introduced as an isolated soft phase to fabricate hierarchical CNTs/AZ61 composites. The compression tests show the fracture strain and compressive strength of this composite increases by 54% and 8%, respectively, compared with homogeneous CNTs/AZ61 composite. During deformation, the hard phase is mainly responsible for bearing the load and bringing high strength, due to the precipitation of the Mg17Al12 phase, uniformly dispersed CNT and strong interfacial bonding of the CNTs/Mg interface through nickel plating and interfacial chemical reaction. Furthermore, the toughening of the soft phase results in high ductility. With the increase in CNT content, the compressive strength of composites is nearly unchanged but the fracture strain gradually decreases due to the stress concentration of CNT and its agglomeration.

CNT loaded PVDF-KNN nanocomposite films with enhanced piezoelectric properties

The emerging smart PVDF-based composites can compensate for the intrinsic property deficiencies in either of their components. The properties of the composite are determined by the properties of the constituents and its fabrication method. In this research, a lead-free piezoelectric ceramic, potassium sodium niobate (KNN), was used as the primary reinforcement, and MWCNTs were added to improve the electrical properties. Solution casting was used to prepare PVDF-KNN-CNT composite films. After phase and structure identification of composites using SEM, XRD, FTIR, and TGA methods, the dielectric, piezoelectric and ferroelectric properties of the products were investigated. The obtained results indicated a strong dependency of dielectric, piezoelectric, and ferroelectric properties of composites on KNN content. Samples with the highest KNN content rendered εr, d33 and g33 values of 156, 28 pC/N, and 20.32 mV m/N, respectively. Introducing a small amount of conductive CNT to primary PVDF-KNN composites can drastically affect the electrical properties by severely interfering in the charge distribution within the sample. While the dielectric constant was enhanced by increasing CNT content, both piezoelectric and ferroelectric properties showed their best behavior at a critical CNT loading. Beyond this limit, a percolation path formed, which is responsible for power consumption. At the optimum CNT amount, d33 and g33 reached 50 pC/N and 31.93 mV m/N, respectively. The presence of conducting CNTs gave rise to the formation of more round polarization curves with higher remnant polarization. The present findings give a prospective understanding of smart piezoelectric polymer-based composites that can be used as sensors and energy harvesters.

Complex Geometry Strain Sensors Based on 3D Printed Nanocomposites: Spring, Three-Column Device and Footstep-Sensing Platform.

Electromechanical sensing devices, based on resins doped with carbon nanotubes, were developed by digital light processing (DLP) 3D printing technology in order to increase design freedom and identify new future and innovative applications. The analysis of electromechanical properties was carried out on specific sensors manufactured by DLP 3D printing technology with complex geometries: a spring, a three-column device and a footstep-sensing platform based on the three-column device. All of them show a great sensitivity of the measured electrical resistance to the applied load and high cyclic reproducibility, demonstrating their versatility and applicability to be implemented in numerous items in our daily lives or in industrial devices. Different types of carbon nanotubes—single-walled, double-walled and multi-walled CNTs (SWCNTs, DWCNTs, MWCNTs)—were used to evaluate the effect of their morphology on electrical and electromechanical performance. SWCNT- and DWCNT-doped nanocomposites presented a higher Tg compared with MWCNT-doped nanocomposites due to a lower UV light shielding effect. This phenomenon also justifies the decrease of nanocomposite Tg with the increase of CNT content in every case. The electromechanical analysis reveals that SWCNT- and DWCNT-doped nanocomposites show a higher electromechanical performance than nanocomposites doped with MWCNTs, with a slight increment of strain sensitivity in tensile conditions, but also a significant strain sensitivity gain at bending conditions.

Microwave properties of epoxy composites with mixed filler carbon nanotubes/BaTiO3

The microwave properties of composite materials (CMs) based on epoxy resin and mixed filler carbon nanotubes/barium titanate (CNT/BT) at CNT concentrations up to 5 wt% and 34 wt% of BT were investigated. The complex permittivity of epoxy composites was measured in the frequency range 1–67 GHz via vector network analyzer. The CNT/BT/epoxy composite showed the increase of permittivity with the increase of CNT content in CM. The electromagnetic shielding properties of developed CMs were measured using waveguide spectroscopy in the frequency range from 26 to 37.5 GHz. Increasing of CNT content enhances the conductivity, resulting in an increase of the EMR reflection at the interface air–composite as well as EMR absorption inside of the composite. The increase of the shields’ thickness (up to 2.5 mm) leads to the increase of shielding effectiveness for transmission up to 30 dB for sample with 5% CNT content due to higher EMR absorption inside, while the changes of the reflection index versus frequency depend on CNT content and composite thickness. The reflection loss (RL) of composites was calculated for various thicknesses using the complex permittivity and the obtained results show that composite 2 wt% CNT/BT/epoxy exhibits superior absorptive properties in the frequency range 10–67 GHz. The BT primary role in such CMs (with conductive fillers) is to move the percolation threshold further for conductive filler, increasing its real part of permittivity.

Novel carbon nanotube and fly-ash reinforced Al composites for automobile and aerospace applications

The present study is focused on the fabrication of novel material carbon nanotube-fly-ash (CNT-FA) reinforced aluminium (Al) composite for automobile and aerospace applications using powder metallurgy technique. CNTs (0.25, 0.5, 0.75 wt%) and FA (4, 8, 16 wt%) were blended with aluminium matrix at 250 rpm for 4 h using ball milling technique. Blended composite powders were then compacted at 285 MPa and sintered at 500 °C for 1 h. Mechanical properties were analysed by density, Vickers hardness and wear tests. The microstructure was analysed by scanning electron microscope. The role of reinforcements was such that relative density decreased with increasing the content of FA and CNT while hardness increased with increase in FA up to 8 wt% but decreased with increase in CNT content. The wear rate was also found to be low compared to monolithic materials. The microstructure of the composite revealed excellent bonding between the reinforcements and matrix which resulted in improved properties over unreinforced matrix material. From the experimental results it can be concluded that CNT-FA reinforced composites can become a novel material to substitute for the lightweight materials.

Application of carbon nanotubes prepared from CH4/CO2 over Ni/MgO catalysts in CO2 capture using a BEA–AMP bi-solvent blend

Abstract Carbon nanotubes (CNTs) were synthesized by the chemical vapour deposition of methane and carbon dioxide over a Ni/MgO catalyst. The synthesized CNTs were then mixed with K/MgO catalyst at different ratios and used as the catalyst for CO2 absorption in butylethanolamine-2-amino-2-methyl-l-propanol bi-solvent blend. The catalysts were characterized using X-ray diffraction, scanning electron microscopy, butylethanolamine, thermal gravimetric analysis and temperature-programmed desorption of carbon dioxide in order to determine the characteristics responsible for good CO2-absorption performance. The results showed that, with the addition of a catalyst into the amine solution, the amine reached equilibrium CO2 loading faster than without a catalyst. Also, the increase in the CNT content of the KMgO/CNTs catalyst made the CO2 absorption reach equilibrium much more quickly compared with just KMgO alone and without a catalyst. The KMgO/CNTs at a ratio of 1:4 yielded the fastest time to reach CO2-loading equilibrium at 240 min, which was mainly due to the increase in strong basic sites as well as the highest total basic sites with an increase in CNT content. In addition, because of the extremely large specific surface area and pore volume generated due to the CNT, the number of exposed active centres per unit mass increased tremendously, leading to a corresponding tremendous increase in CO2 absorption.

Effects of CNTs content on microstructure and mechanical properties of Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3 composites

Abstract In this work, CNTs and short carbon fiber reinforced α-Al2O3 matrix composites (i.e., Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3) were prepared by sol-gel dispersing method followed by hot pressing process. Effects of CNTs content on the mechanical properties of Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3 composites were investigated and the inter- and transgranular fracture mechanisms in Cnt-Csf/α-Al2O3 composites were analyzed. The hardness and relative density of Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3 composites slightly decrease as CNTs content increases. The flexural strength and fracture toughness monotonically increase with the increase in Cnt content for both Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3 composites. Addition of Csf and CNTs into α-Al2O3 matrix results in a bimodal grain size microstructure of Cnt-Csf/α-Al2O3 composites, which accounts for the unique fractograph and the enhanced toughness of Cnt-Cf/α-Al2O3 composites. The flexural strength and fracture toughness of Csf5-nt06 composite are 465 MPa and 7.08 MPa/m2, 37% and 13% higher than that of Cnt06, and 42% and 34% higher than that of Csf5, respectively.

Friction and Wear Characteristics of Polymeric Composites Reinforced by Nano Particles and Impregnated with Paraffin Oil

A pin on disk machine is designed and constructed to experimentally measure and investigate the friction coefficient and wear rate of two groups of compounds of (PET) – CNT, and PET – CNT and paraffin oil under variable applied loads. Polymeric Composites Reinforced by Nano Particles and Impregnated with Paraffin Oil have low friction coefficients and highly resistant to wear so it is widely used in aerospace, automobiles, packing materials and in bearing applications. The effect of both percentages of PET with CNT and PET, CNT and paraffin oil under variable loads on coefficient of friction and wear values are carefully recorded and studied. A historical review of the available published work has shown a need for this work. This research used test specimens were prepared by casting method. The Addition of carbon Nanotubes to the polyethylene terephthalate with specified contents of Group I showed decrease in friction coefficient and wear values with increasing CNT content and applied loads. The tested specimens of Group II were filled by 3, 5, 10 wt. % paraffin oil introduced with the composites of PET and CNT. Applied loads of 8, 13, 18, 23, 28, 33 N were used during the test. The coefficient of friction was calculated by dividing the frictional forces by the applied normal load. Specimens were weighed before and after the test and the difference between the two weights represented the wear loss. Results of conducted tests on the compound of PET and CNT and paraffin oil under the previous loads were plotted for friction coefficient as of CNT content showed decreasing trend of friction coefficient with increasing the content of paraffin oil. According to increase of the applied loads of wear rate decreased. Finally, this research proposes a good assessment of testing polymer matrix for various applications such as bearing materials and guide ways.

Change in Pull-off force by increasing CNT content in silicone/ CNT composite sheet

Change in Pull-off force by increasing CNT content in silicone/ CNT composite sheet

Mechanical property evaluation of carbon nanotubes reinforced plasma sprayed YSZ-alumina composite coating

Yttria (8%) stabilized zirconia (8YSZ)-alumina-carbon nanotube (CNT) composite coatings were deposited using air plasma spray (APS) technique. Three zirconia alumina (ZA) composite coatings, without CNT reinforcement, and with 1%CNT, 3%CNT reinforcement were deposited using identical process parameters (500A and 66V). Indentation method was used to characterize mechanical behavior of coatings. The CNT reinforced composite coating showed superior mechanical properties as compared to the conventional 8YSZ coating. The addition of alumina and 1%CNTs increased the Young's modulus by around 25% and 40%, respectively. However, the increase in CNT content decreased the Young's modulus as a result of CNT agglomeration. The hardness, fracture toughness increased with addition of alumina and CNT. The fracture toughness increased from 0.55 ± 0.26MPam1/2 for 8YSZ to 1.76 ± 0.65MPam1/2 for 17%alumina-3%CNT reinforcement due to various toughening mechanisms like crack deflection, bridging etc. The maximum displacement of indenter was found to decrease from ~ 176nm for conventional YSZ coating to ~ 120nm for 3% CNT reinforced coating. The surface roughness (Ra) was found to be decrease with alumina addition and CNT reinforced coating. The CNT reinforced coating showed surface roughness of around 6µm. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used to characterize the coating microstructure and elemental composition respectively.

Effect of multi-walled carbon nanotubes on the physical properties and crystallisation of recycled PET/TPU composites.

Thermoplastic polyurethane (TPU) was blended with recycled polyethylene terephthalate (rPET) to prepare rPET/thermoplastic polyurethane (TPU) composites. Meanwhile, multiple-walled carbon nanotubes (MWCNTs) were employed as a reinforcing filler to study the synergistic effect between CNTs and rPET/TPU composites. The effect of CNT content on the morphology and micro-structure of the composites was investigated using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The thermal properties were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The mechanical properties were investigated using tensile tests and hardness measurements. The results showed that TPU was compatible with rPET. The existence of rPET changed the crystalline phase and affected the glass transition and crystallisation temperature of the TPU matrix. The rPET/TPU composites displayed poor thermal stability and tensile properties when compared to pure TPU. The addition of CNTs had no effect on the crystalline phase of the rPET/TPU composites. Due to the occurrence of interfacial adhesion between the CNTs and rPET, the CNTs displayed an offset effect on the reaction of rPET and decreased the rigidity of the molecular chain in the rPET/TPU composites. The thermal stability and tensile strength of the CNTs/rPET/TPU composites improved with an increase in CNT content.

Ecotoxicity evaluation of Cu- and Fe-CNT complexes based on the activity of bacterial bioluminescence and seed germination

The toxic effects of the composites of Fe0 and Cu0 with different percentages of CNTs were examined based on the activity of bacterial bioluminescence and seed germination. In terms of the EC50 values, the toxic effects of Cu0 on bacterial bioluminescence and seed germination were approximately 2 and 180 times greater than that of Fe0, respectively. The toxicity increased with increasing CNT content in the Cu-CNT mixtures for both organisms, whereas opposite results were observed with Fe-CNT mixtures. The mean toxic effects of Cu-CNT (6%) were approximately 1.3–1.4 times greater than that of Cu-CNT (0%), whereas the toxic effects of Fe-CNT (6%) were approximately 2.1–2.5 times lower than that of Fe-CNT (0%) for both the bioluminescence activity and seed germination. The causes of this phenomenon are unclear at this point. More research will be needed to elucidate the mechanism of the toxicity of nano-mixture materials and the causes of the different patterns of toxicity with Cu- and Fe-CNT mixtures.

Effect of carbon nanotube addition on the thermite reaction in the Al/CuO energetic nanocomposite

In this work, the Al/CNT/CuO nano-thermite samples are prepared by ultrasonic mixing with variable CNT content. The morphology of nano-thermites analysed by electron microscopy revealed that the CNTs are dispersed and there are intimate contacts between fuels (Al and CNT) and oxidiser (CuO) constituents of the nano-thermite. Raman spectroscopy technique is used to analyse the structural integrity of the CNTs in the nano-thermite. The thermite reaction characteristics are evaluated by simultaneous thermogravimetric analysis/differential scanning calorimetry technique. The exothermic enthalpy of the Al/CNT/CuO nano-thermite samples increased with increasing CNT content. The effect of Al particle size and Al/Cu molar ratio variation on the thermite reaction enthalpy is also analysed. The ignition temperature of the thermite reaction is also lowered by 71 °C than that of Al/CuO nano-thermite. The activation energy for thermite reaction of Al/CNT/CuO nano-thermite is also lowered by 23% to that of pure Al/CuO. The residues of the nano-thermites after the thermite reaction at 1010 °C are collected and analysed by the X-ray diffraction.

Tribological Behaviour of Multi-Walled Carbon Nanotubes (MWCNT) Filled Polybutylene Terephthalate (PBT) Nanocomposites

This paper focuses on evaluating the tribological properties of PBT/MWCNT nanocomposites at low CNT concentrations of 0.1, 0.2, 0.3, 0.4 and 0.5 wt%. The composites were prepared by melt-compounding and samples were tested in a pin-on-disc sliding configuration under different load conditions. It was found that the friction coefficient of the composites reduced with increasing CNT content, irrespective of the test load. Meanwhile, the specific wear rate of the composites first decreased and later increased with increasing CNT content. SEM of the worn out surfaces indicated that ploughing and peeling phenomenon of PBT was suppressed at lower CNT addition, but with increasing CNT content the surface seemed to be more damaged. The transfer film formed on the counter-face was also investigated by SEM. It was revealed that the PBT/MWCNT composites formed a thin and more uniform film as compared to the thick and grainy films deposited by virgin polymers. But at higher CNT concentrations, the transfer film once again became lumpy. These findings could be attributed to the presence of CNT agglomerates within PBT matrix at higher CNT concentrations due to non-uniform dispersion.