Increasing Multi-walled Carbon Nanotubes Content Research Articles

Thermal behavior and mechanical properties of nanocomposites of polycarbonate reinforced with multiwalled carbon nanotubes

Nanocomposites of polycarbonate (PC) reinforced with different contents (0–10 wt%) of multi‐walled carbon nanotubes (MWCNTs), PC/MWCNT, were prepared in a two‐step dispersion process: extrusion followed by injection molding. The effects of the MWCNT content and injection conditions on thermal, mechanical, and dynamic mechanical properties of the prepared nanocomposites were investigated and compared. Thermogravimetric analysis showed that a small MWCNT content (i.e., 1 wt%) was more propitious for improving thermal stability of the nanocomposites. Analysis of the mechanical properties demonstrated that the tensile properties of the nanocomposites with low MWCNT content could be comparable to that of PC; but as the content was increased to 10 wt%, the tensile strength and bending strength decreased by 35% and 47%, respectively, from the values for PC. The impact strength and microhardness was improved; however, with the increase in MWCNT content. Results of dynamic mechanical analysis showed that the storage modulus of PC was increased by the incorporation of MWCNTs, particularly at high temperatures. Scanning electron microscopy was also carried out to investigate the microstructures of the nanocomposites. It is concluded that the incorporation of MWCNTs by injection molding was more effective in enhancing the thermal, mechanical, and dynamic mechanical properties of PC. POLYM. COMPOS., 38:E303–E313, 2017. © 2015 Society of Plastics Engineers

Thermo‐mechanical and tribological properties of multi‐walled carbon nanotubes filled friction composite materials

Multi‐walled carbon nanotubes (MWCNTs) filled graphite lubricated phenolic‐based friction composites reinforced with combination of lapinus/Kevlar fibers have been fabricated and subsequently evaluated for their dynamic‐mechanical and tribological properties. The experimental results indicated that the higher MWCNT content enhances the thermal stability, whereas, lower MWCNT content enhances the thermo‐mechanical properties of the friction composites. The tribo‐performance evaluation has revealed that with the increase in MWCNT content, the friction‐fade and friction‐recovery performances are enhanced. The friction‐stability and friction‐variability coefficients are influenced by the combination of MWCNT, graphite, lapinus, and Kevlar constituents. The wear performance decreases with the increase in lapinus and MWCNT, whereas, it increases when the amount of Kevlar or graphite is increased in the composites. Wear surface morphological studies have led to the qualitative characterization of the topographical attributes and the nature of the frictional contact patches which is crucial in understanding the role of MWCNT on friction and wear mechanisms of the investigated automotive brake friction materials. POLYM. COMPOS., 38:1183–1193, 2017. © 2015 Society of Plastics Engineers

Mechanical and biological properties of silk fibroin/carbon nanotube nanocomposite films

Multi-walled carbon nanotubes (MWCNTs) were homogeneously dispersed in silk fibroin (SF) solutions at different compositions, and a simple solvent-casting method was used to fabricate SF/MWCNT films. Structure, viscosity, and mechanical properties of the SF/MWCNT nanocomposites were characterized by FTIR (Fourier Transform Infrared Spectroscopy), viscometry, and tensile testing. Fibroblast cells were used to examine cell viability and attachment to nanocomposite films. Compared to a pure SF film, adding just 0.5 % (w/w) of MWCNT to the SF matrix could enhance the Young’s modulus and ultimate tensile strength by approximately 24 % and 39 %, respectively. In addition, with increasing MWCNTs content, the percentage of β-sheet structure increased significantly. When the content of MWCNTs increased from 0 to 1 % (w/w), the β-sheet content improved from 17.8 % to 53.6 %. Furthermore, adding up to 1 % (w/w) MWCNT increased the viscosity of the SF solution ten fold. From a biological point of view, no toxic effect was observed on fibroblast cells in the presence of MWCNTs after 3 and 7 days. This investigation suggests that SF/MWCNT nanocomposite films with improved mechanical properties and biocompatibility are well-suited as novel biomaterials.

Influence of multi-walled carbon nanotube (MWNT) concentration on the interconnection properties of solderable anisotropic conductive adhesives (SACAs)

In this work, a novel CNT-filled solderable anisotropic conductive adhesive (SACA) containing a low melting-point alloy (LMPA) and multi-walled carbon nanotubes (MWNTs) was proposed. To evaluate the influence of MWNT concentration on the interconnection properties of SACA joints, six types of CNT-filled SACAs with different chemically functionalized MWNT content (from 0 to 2 wt%) were formulated. At a low MWNT concentration, a stable conduction path was formed due to the excellent coalescence and wetting behavior of the molten LMPA filler, and the electrical and mechanical properties of the CNT-filled SACA joints were also enhanced due to the reinforcing effect of MWNTs. However, the conduction path area decreased with increasing MWNT content due to increased polymer viscosity and diminished molten LMPA mobility, which attenuated the bonding properties.

γ Irradiation effects on optical, thermal, and mechanical properties of polysulfone/MWCNT nanocomposites in argon atmosphere

ABSTRACTPolymer‐based composites find use in many nuclear and space application for their ease of fabrication, tailor made properties and light weight. Certain polymers like PTFE, unfilled polyesters and polyamides are prone to degradation in presence of high energy radiation while polymers like epoxies, polyimides, and poly‐ether ether ketone have good stability to ionizing radiation. Incorporation of fillers like carbon nanotubes (CNTs) is likely to improve the radiation resistance of the polymers. In this work, polysulfone (PSU)‐based nanocomposites were fabricated using multiwalled carbon nanotube (MWCNT) by solution mixing process. The morphology of the PSU/ MWCNT nanocomposites films were studied using Field Emission Scanning Electron Microscopy (FESEM). The prepared films were subjected to γ radiation in an argon environment (to avoid the effect of air/oxygen). Different techniques were used to understand the radiation‐induced changes. Gel Permeation Chromatography (GPC) traces of neat PSU before and after exposure to radiation shows a decrease in molecular weight. Infrared spectroscopy shows changes in chemical structure. Differential Scanning Calorimetry (DSC) thermograms reveal dose‐related changes. For neat PSU, a decrease in Tg was observed with increase in dose. For PSU/ MWCNT nanocomposites, the increase in MWCNT content and dose (up to 1.5 MGy) increased the Tg. Thermo Gravimetric Analysis (TGA) showed a marginal decrease in thermal stability for pristine PSU as well as PSU/MWCNT nanocomposites with irradiation. Tensile strength increased with increasing MWCNT content but decreased with dose. Elongation at break decreased with MWCNT content as well as radiation dose. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42017.

Magnetic‐field‐assisted electrospinning highly aligned composite nanofibers containing well‐aligned multiwalled carbon nanotubes

ABSTRACTComposite nanofiber meshes of well‐aligned polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP) nanofibers containing multiwalled carbon nanotubes (MWCNTs) were successfully fabricated by a magnetic‐field‐assisted electrospinning (MFAES) technology, which was confirmed to be a favorable method for preparation of aligned composite nanofibers in this article. The MFAES experiments showed that the diameters of composite nanofibers decreased first and then increased with the increase of voltage and MWCNTs content. With the increase of voltage, the degree of alignment of the composite nanofibers decreased, whereas it increased with increasing MWCNTs concentration. Transmission electron microscopy observation showed that MWCNTs were parallel and oriented along the axes of the nanofibers under the low concentration. A maximum enhancement of 178% in tensile strength was manifested by adding 2 wt % MWCNTs in well‐aligned composite nanofibers. In addition, the storage modulus of PAN/PVP/MWCNTs composite nanofibers was significantly higher than that of the PAN/PVP nanofibers. Besides, due to the highly ordered alignment structure, the composite nanofiber meshes showed large anisotropic surface resistance, that is, the surface resistance of the composite nanofiber films along the fiber axis was about 10 times smaller than that perpendicular to the axis direction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41995.

Thermal and mechanical properties of phenolic-based composites reinforced by carbon fibres and multiwall carbon nanotubes

The thermal, mechanical and ablation properties of carbon fibre/phenolic composites filled with multiwall carbon nanotubes (MWCNTs) were investigated. Carbon fibre/phenolic/MWCNTs were prepared using different weight percentage of MWCNTs by compression moulding. The samples were characterized by scanning electron microscopy (SEM), flexural tests, thermal gravimetric analysis and oxyacetylene torch tests. The thermal stability and flexural properties of the nanocomposites increased by increasing MWCNTs content (wt% ⩽1), but they decreased when the content of MWCNTs was 2wt%. The linear and mass ablation rates of the nanocomposites after modified with 1wt% MWCNTs decreased by about 80% and 52%, respectively. To investigate the material post-test microstructure, a morphological characterization was carried out using SEM. It was shown that the presence of MWCNTs in the composite led to the formation of a strong network char layer without any cracks or opening.

Electrical and mechanical properties of multiwalled carbon nanotubes-reinforced solderable polymer nanocomposites

In recent years, carbon nanotubes have attracted attention as potential reinforcement materials for composites. Because there is a current lack of research investigating the electrical and mechanical properties of multiwalled carbon nanotube (MWCNT)-reinforced solderable polymer nanocomposites (SPNs), this study focuses on the influence of MWCNT concentration on the interconnection properties of SPN joints. Six types of MWCNT-reinforced SPNs with 40 vol.% of a low-melting point alloy (LMPA) and chemically functionalized MWCNTs (ranging from 0 to 2 wt%) were formulated. Our results indicate that a wide and stable conduction path was formed for all MWCNT concentrations due to the excellent coalescence and wetting behavior of the molten LMPA. However, the interconnection properties degraded with increasing MWCNT content due to an increase in the number of internal defects that were caused by the polymer matrix becoming trapped in the LMPA joints.

Effects of carbon nanotube content on the mechanical and electrical properties of epoxy-based composites

The effects of multi-wall carbon nanotube (MWCNT) content on the mechanical and electrical properties of MWCNT/epoxy composites were investigated. Results indicate that both tensile strength and flexural modulus exhibit maxima at MWCNT contents of 0.1% and 0.25% (mass fraction), respectively. The tensile modulus increases and the strain to failuredecreases with MWCNT content, indicating a transition from plastic to brittle failure with increasing MWCNT content. The flexural strength of a sample with a MWCNT content of 0.05% is the highest. The electrical percolation threshold of the composite is found to occur at a 0.5% MWCNT addition. A good dispersion of MWCNTs in epoxy is important to improve the mechanical properties of the composites. A non-uniform dispersion leads to agglomeration of MWCNTs, which causes an early-stage failure under loading. The electrical properties of the composites are less affected by the presence of agglomerates.

Cut growth and abrasion behaviour, and morphology of natural rubber filled with MWCNT and MWCNT/carbon black

Various amounts of predispersed multi-wall carbon nanotubes (MWCNT) were mixed with natural rubber (NR), with and without carbon black (CB), for preparing MWCNT-filled NR (NC) and MWCNT/CB-filled NR (NH) vulcanizates. All NH vulcanizates contained 30 phr CB and the amount of MWCNT for both NC and NH was varied from 0 to 8 phr. Helium ion microscopy (HIM) and FE-SEM images showed that MWCNT in the NH was dispersed much better than in the NC. Additionally, the well dispersed CB and MWCNT in the NH functioned synergistically in promoting an increase in longitudinal crack growth, leading to enhancement of edge-cut tensile strength (CTS) with increasing MWCNT loading. In contrast, all NC specimens ruptured in a simple lateral direction relating to their lower CTS. Results also revealed that abrasion resistance of the NH was not significantly changed with increasing MWCNT, whereas that of the NC increased. Nevertheless, abrasion resistance of both vulcanizates showed good correlation with the average value of ridge spacing on their abraded surfaces. It was also found that tensile strength of the NH was almost unchanged when the MWCNT loading was increased because the reinforcement by CB predominates over the MWCNT. However, 100% modulus and hardness of both NC and NH increased with increasing MWCNT content.

Low Resistance, Carbon Black-free Magnetite Anode for Li-ion Batteries Obtained by One-step Attachment of Carbon Nanotubes

The paper describes a simple, one-step synthetic route for the fabrication of nanometric iron (III) oxide attached to multiwalled carbon nanotubes (MWCNT). TEM images show that magnetite nanoparticles with primary particle sizes of ca. 10 nm are preferentially located on the outer walls of carbon nanotubes. The obtained nanocomposites have been examined on reversible electrochemical insertion of lithium cations in a Li-ion cell. The presence of MWCNT brings about a substantial increase of the magnetite reversible capacities in the absence of any additional carbonaceous conductivity enhancing agent. With increasing MWCNT content in the material, reversible capacity consistently rises from 207 mAhg-1 for pure iron (III) oxide up to 763 mAhg-1 for the composite with 40 % of MWCNT. Cyclic voltammetry measurements reveal the expected large hysteresis between the reduction and oxidation peaks associated with Li+ insertion/deinsertion into magnetite crystal lattice. The reductive current peak maxima steadily rise with increasing MWCNT content from 0.15 A g-1 for pure iron (III) oxide up to 0.4 A g-1 for the composite with 40 % of MWCNT which confirms faster kinetics of electrochemical processes. EIS measurements directly proved the internal resistance decrease connected with the incorporation of MWCNT.

Pre-localized MWCNT network for a low percolation threshold in MWCNT/ABS nanocomposites: experiment and theory

Nanocomposites of well-dispersed multi walled carbon nanotubes (MWCNTs) in an acrylonitrile–butadiene–styrene (ABS) matrix were prepared by dry tumble mixing and a subsequent hot compression technique. The preparation method is analysed here to assist in the explanation and understanding of the experimental observations. The vision of the processing method has been confirmed using scanning electron microscopy. As a result of decent dispersion and pre-localization of MWCNTs in the ABS matrix, the electrical conductivity of the nanocomposite as a function of filler content exhibits a distinctive percolation behavior with a percolation threshold of only 0.0005 volume fraction. The high aspect ratio of MWCNTs enables the creation of interconnected networks within the ABS matrix at a very low nanofiller loading, while their high inherent electrical conductivity yields nanocomposites with a high bulk electrical conductivity. To explain the conductivity behaviour, statistical percolation theory and GEM theory are employed. The model parameters elaborated show that both models can adequately describe the behaviour. A comparative analysis of the applicability of percolation theory and GEM theory for expressing the conductivity behavior of the MWCNT/ABS composites with other research works has been performed. Finally, the electrical conductivity of MWCNTs based on the data in this work and elsewhere is evaluated. The universal exponent t is found to be 1.93 for a best-fit value of percolation threshold of 0.000485 vol. fraction of MWCNTs in this work. The D shore hardness results have revealed a random increase in hardness and density with an increasing MWCNT content.

Nanoindentation and fracture toughness of nanostructured zirconia/multi-walled carbon nanotube composites

Multi-walled carbon nanotubes (MWCNTs)/3mol% yttria-doped tetragonal zirconia (3Y-TZP) composites were produced using spark plasma sintering (SPS) with MWCNT content ranging within 0–2wt%. In the present paper, it was shown that the addition of MWCNTs results in a refinement of the composites microstructure. Moreover, nanoindentation tests were performed in order to monitor the change in elastic modulus and hardness with MWCNT content and it was found that both properties decrease with the addition of MWCNT content. A novel method was used to measure the true fracture toughness of the composites by producing a shallow surface sharp notch machined by ultra-short pulsed laser ablation on the surface of beam specimens. The true fracture toughness obtained on this laser machined single edge V-notch beam (SEVNB) specimens tested in four point bending was compared to the indentation fracture toughness measured using a Vickers indenter. It was found that the indentation fracture toughness increases with increasing MWCNT content, while the true fracture toughness determined with SEVNB was practically independent of the composition. Finally, it was concluded that the increase in the resistance to indentation cracking of the composites with respect to 3Y-TZP matrix cannot be associated to higher true fracture toughness. The results were discussed in terms of transformation toughening, damage induced in front of the notch tip, microstructure of the composites, and fracture toughness of 3Y-TZP.

Coefficient of friction and wear resistance of zirconia–MWCNTs composites

Composites of 3mol% yttria-doped tetragonal zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (MWCNT) up to 2wt% content have been produced using spark plasma sintering (SPS). The theoretical densities of the studied composites were found to be between 99.4% and 97.4%. The addition of MWCNT content resulted in reduction of 3Y-TZP grain size from 174 to 148nm. The effect of MWCNT on the friction coefficient (COF) was studied by performing nano- and macro-scratches using diamond Berkovich and Rockwell indenters, respectively. Moreover, the COF and the wear rate were also investigated in reciprocating sliding against a zirconia ball under a load of 5N. The results showed that the COF decreased upon the increase in MWCNT content. However, in macro-scratch testing, there was a critical load over which brittle fracture sets in and its value decreases as the MWCNT content increases. The wear resistance was found to be decreasing very slightly for less than 1wt% MWCNT, while it increases strongly for the addition of 2wt% MWCNT under the conditions studied. The results were discussed in terms of material properties, scanning electron microscopy observations of the wear track and nanoindentation tests.

Thermal conductivity and heat capacity of poly(3-octylthiophene-2,5 diyl) and its multi-wall carbon nanotube composites

Poly (3-octylthiophene-2,5-diyl) (P3OT) is one of the most important semiconducting polymer materials used for organic solar cells. Thermal properties data, especially the thermal conductivity of the active material of solar cells, is of fundamental importance. Such data for P3OT are barely available in the literature. The photoacoustic technique is employed to measure thermophysical properties of P3OT including thermal diffusivity, thermal effusivity, specific heat capacity and thermal conductivity. The obtained results are confirmed by many measurements as well as by using more than one method. A remarkable method for thermal effusivity measurements of surface coating as well as bulk samples is introduced. The development of P3OT thermophysical properties with multi-wall carbon nanotube (MWCNT) loading as high as 6% volume fraction is investigated. Continuous enhancement of thermal diffusivity as well as thermal effusivity of P3OT is obtained with increasing MWCNT content. By using the mixed model for the thermal conductivity of a two phase system, we are able to estimate the thermal diffusivity and the thermal effusivity of MWCNTs. A considerable enhancement in thermal conductivity of larger than twice that of neat P3OT at nanotube loading ≈6% volume fraction is obtained. Theoretical analysis of the experimental results generating an interfacial thermal resistance of MWCNTs as Rk = 5.8 × 10−8 m2K W−1.

MWCNTs decorated Mn0.8Zn0.2Fe2O4: Synthesis, characterization and compositional effect on the structural and magnetic properties

Abstract In the present study, Mn0.8Zn0.2Fe2O4 nanoparticles, synthesized from spent Zn–C batteries extract, were successfully used for decoration of multi-walled carbon nanotubes (MWCNTs). This MWCNTs/Mn0.8Zn0.2Fe2O4 magnetic nano-composites were prepared by the addition of MWCNTs during the preparation of the entire ferrite using sucrose combustion method. The effect of MWCNTs content (0–70%) on the structural, morphological and magnetic properties of entire ferrite was investigated and discussed. The results showed that high purity Mn0.8Zn0.2Fe2O4 nano-crystallites were completely decorated on the sidewalls of the MWCNTs up to 30% content and the decoration behavior, shape and density are dependent on the composition. The saturation magnetization was observed to decrease with increasing MWCNTs content while coercivity showed a particle size dependent behavior. The composition with 70% MWCNTs was examined as adsorbent for methylene blue dye (MB) from aqueous media based on its relatively high surface area and the capability of removing the nano-composite after adsorption process using normal magnet. The nano-composite showed a very high adsorption capacity and the kinetic as well as the thermodynamics of adsorption/removal process were investigated and discussed. Repeated testing showed the applicability of the nano-composite for the removal of MB from aqueous solution frequently with acceptable efficiencies.

Developing nanocomposite PI membranes: Morphology and performance to glycerol removal at the downstream processing of biodiesel production

Nanocomposite solvent resistant (NCSR) membranes were developed and utilized for separation of organic biodiesel rich phase. The modified membranes were fabricated via nonsolvent induced phase separation by addition of different concentrations of functionalized multiwall carbon nanotubes (MWCNTs) in the polyimide (PI) casting solution. The morphological studies, molecular weight cut-off (MWCO), mean pore size, pore size distribution and porosity were evaluated and discussed. The physicochemical properties of the membrane were improved significantly after bulk modification with functionalized MWCNTs. Surface hydrophilicity and roughness were improved with an increase in MWCNTs up to 1wt%. This was confirmed by fouling analysis where flux recovery (FR) was strongly increased by more than 47% for M2 at the maximum value. To evaluate the performance of modified PI membranes, the crude biodiesel prepared by transesterification reaction of canola oil with an alkaline catalyst was filtered with a dead-end filtration system at 5bar and 25°C. The glycerol removal increased with increasing MWCNTs content in the modified PI membranes until it reached to 100% for M3 membrane without any significant changes in methyl ester flux. It may be due to the smaller surface pore size and higher membrane porosity after bulk modification.

Effect of low‐content carbon nanotubes on the dielectric and microwave absorption properties of graphite/polymer nanocomposites

ABSTRACTHoneycomb cores (HCs) coated with graphite and multiwalled carbon nanotubes (MWCNTs) filled in a thermoplastic resin are proposed as microwave absorbers. The MWCNT contents varied from 0.2 to 0.6 wt % in a graphite‐filled (15 wt %) thermoplastic resin. The HCs were coated with three different types of coating materials for the sake of comparison: graphite, MWCNTs, and graphite plus MWCNTs. The dielectric properties [the real and imaginary parts of complex permittivity (ε′ and ε″, respectively)] and reflection loss (RL) of all of the coated HCs were measured and compared. We observed that the permittivities and RL increased significantly with increased weight percentage of the MWCNTs in the graphite‐filled thermoplastic resin. The RL measurements showed a maximum loss of −20 dB around 7 GHz and a bandwidth of 2.7 GHz at −10 dB in the HCs coated with the 0.4 wt % MWCNT plus graphite. There was also a shift in the RL peak position from the x band to the c band after the increase of MWCNT content. We also observed from the measurements that a combination of graphite and MWCNTs resulted in a broadband microwave absorber; a bandwidth of 13 GHz was observed for 80% RL when the MWCNT content increased to 0.6 wt % in the graphite‐incorporated resin. The possible mechanism that increased RL with the incorporation of MWCNTs in the graphite‐mixed thermoplastic resin is discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40891.

Atmosphere Plasma-Sprayed Carbon Nanotubes/Cordierite Nanocomposite Coatings for Microwave Absorption Applications

Multi-walled carbon nanotubes (MWCNTs)/cordierite (MAS) nanocomposite coatings with different MWCNT contents were prepared via atmosphere plasma spraying method. The characteristics of the MWCNTs/MAS powders and as-sprayed coatings, such as microstructure and phase constitution, were observed and measured. The dielectric properties and microwave absorption properties of MWCNTs/MAS powders and nanocomposite coatings have been investigated at the frequency of 8.2-12.4 GHz with different MWCNT contents and sample thicknesses. When the MWCNT content increased to 7%, the nanocomposite coating revealed the highest dielectric constant and optimal microwave absorption property. Further increase in MWCNT content led to severe oxidation of MWCNTs during the plasma spray process, which resulted in lower dielectric constants and poor microwave absorption property. Moreover, the sample thickness has a noticeable influence on the reflection loss (RL) of the MWCNTs/MAS coatings, and the coating of 2.4-mm thickness shows optical microwave absorption with a minimum RL of −15.61 dB and bandwidth of 2.35 GHz.

Nanoindentation and thermal characterization of poly (vinylidenefluoride)/MWCNT nanocomposites

We report the preparation, thermal and micro/nanomechanical behavior of poly (vinylidine diflouride) (PVDF)/multiwalled carbon nanotube (MWCNT) nanocomposites. It has been found that the addition of MWCNT considerably enhances the β-phase formation, thermal and mechanical properties of PVDF. Atomic force microscope (AFM) studies have been performed on the composites under stress conditions to measure the mechanical properties. The nanoscale mechanical properties of the composites like Young's modulus and hardness of the nanocomposites were investigated by nanoindentation technique. Morphological studies of the nanocomposites were also studied, observations show a uniform distribution of MWCNT in the matrix and interfacial adhesion between PVDF and MWCNT was achieved, which was responsible for enhancement in the hardness and Young's modulus. Differential scanning calorimetry (DSC) studies indicate that the melting temperature of the composites have been slightly increased while the heat of fusion markedly decreased with increasing MWCNT content.