Increasing Carbon Nanotubes Content Research Articles

Effect of carbon nanotubes addition on properties of 0–3 pyroelectric ceramic/polymer composites

0–3 pyroelectric ceramic/polymer composites were fabricated using (Pb[(Mn1/3 Nb2/3)1/2(Mn1/3Sb2/3)1/2]0.04(Zr0.05Ti0.95)0.96O3)(PZT) and Poly(vinylidene fluoride) (PVDF) by hot-pressing technology. The influences of carbon nanotubes (CNTs) on the volume conductivity, specific heat capacity, dielectric, piezoelectric, and pyroelectric properties were discussed. The results indicated that the CNTs acted as a conductive phase which is helpful to improve the conductivity of the composites and thereby enhance the pyroelectric properties. With the increasing CNTs content, the specific heat capacity of the composites decreased, while the dielectric constant, dielectric loss and volume conductivity all exhibit an increasing trend. As a result, the piezoelectric strain factor (d 33 ), pyroelectric coefficient (p) and figure of merit (F D ) are all significantly improved. And 0.9 wt% CNTs corresponds to the maximum d 33 , p and F D . It was concluded that CNTs-addition was an effective method to enhance the piezoelectric and pyroelectric performance of the composites.

Low temperature synthesis of carbon nanotube-reinforced aluminum metal composite powders using cryogenic milling

Abstract

Effect of Carbon Nanotube on the Mechanical Properties of Compatibilized Polylactic Acid/Natural Rubber Blend

Polylactic acid (PLA)/ Natural rubber (NR) in the presence of PLA grafted Maleic Anhydride (PLAGMA) as compatibilizer was prepared by the melting blend method. In attempt to achieve high performance of the blend, nanocomposites were formed by incorporating different ratio of carbon nanotube (CNT) in PLA/NR/PLAGMA blend. The effect of CNT content on mechanical properties was investigated. With increasing CNT content, Young’s modulus and flexural modulus were increased firstly and then decreased as CNT was further added. In other hand, impact strength was dropped as expected as the CNT loading was increased.

Preparation and properties of carbon-nanotube composites with natural rubber and epoxidized natural rubber

Composites of carbon-nanotubes (CNTs) and natural rubber (NR), as well as epoxidized natu- ral rubber (ENR), were prepared by melt compounding in an internal mixer. The state of CNT dispersion was determined by examination of the electrical percolation threshold of the composites. The composites with the more polar ENR exhibit a lower percolation threshold than those with NR matrices. It was also shown that two-step processing using an internal mixer and two roll mill resulted in a better CNT disper- sion and lower percolation threshold. The effect of CNTs on vulcanization and crosslinking were investi- gated by oscillating rheometer and DSC measurements. The crosslink densities of the composites were determined by equilibrium swelling measurements as well as hysteresis tensile tests. A significant increase in crosslink densities of the composites with increasing CNT content was detected. Increasing CNT content also resulted in accelerated crosslinking reaction. The thermal conductivity of the compo- sites was tested by DSC measurements. A very large increase of thermal conductivity could be obtained with a low CNT content. However, it turned out that the increase of thermal conductivity is restricted by the thermal resistance at the interface between CNTs and the matrix.

Hybrid multi-scale basalt fiber-epoxy composite laminate reinforced with Electrospun polyurethane nanofibers containing carbon nanotubes

In this study, we report the fabrication and evaluation of a hybrid multi-scale basalt fiber/epoxy composite laminate reinforced with layers of electrospun carbon nanotube/polyurethane (CNT/PU) nanofibers. Electrospun polyurethane mats containing 1, 3 and 5 wt% carbon nanotubes (CNTs) were interleaved between layers of basalt fibers laminated with epoxy through vacuum-assisted resin transfer molding (VARTM) process. The strength and stiffness of composites for each configuration were tested by tensile and flexural tests, and SEM analysis was conducted to observe the morphology of the composites. The results showed increase in tensile strength (4–13 %) and tensile modulus (6–20 %), and also increase in flexural strength (6.5–17.3 %) and stiffness of the hybrid composites with the increase of CNT content in PU nanofibers. The use of surfactant to disperse CNTs in the electrospun PU reinforcement resulted to the highest increase in both tensile and flexural properties, which is attributed to the homogeneous dispersion of CNTs in the PU nanofibers and the high surface area of the nanofibers themselves. Here, the use of multi-scale reinforcement fillers with good and homogeneous dispersion for epoxy-based laminates showed increased mechanical performance of the hybrid composite laminates.

Low Temperature Oxidation Behaviors of CNTs/MoSi<sub>2</sub> Composites

Molybdenum disilicide (MoSi2) matrix composites with various contents of carbon nanotubes (CNTs) were fabricated by sintering in vacuum at 1550 °C for 1 h. The oxidation behaviors of CNTs/MoSi2composites at 400 °C and 500 °C for 200 h in air were studied. Results showed that the weight loss of CNTs/MoSi2composites increased with the increase of CNTs content. “Pest” phenomenon happened at 400 °C but not at 500 °C. Phase identification and microstructure of the samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that many MoO3whiskers and microcracks only occurred on the surface of CNTs/MoSi2composites when oxidized at 400 °C in air, which leaded to the catastrophic disintegration of CNTs/MoSi2composites.

Cold spray deposition characteristics of mechanically alloyed Cu-CNT composite powders

• Cu-CNT composite coatings were fabricated by mechanical alloying and cold spraying. • Cu-CNT composite coatings with up to 15 vol.% CNT were fabricated. • Cold spray deposition efficiency of powders decreased as CNT content increased. • Surfaces of the composite coatings contained about 1.0–2.5 vol.% micropores. • Uniform dispersion of CNT within the composite coatings was observed. Copper (Cu)-carbon nanotube (CNT) composite surface coatings with CNT contents of up to 15 vol.% were fabricated by mechanical alloying (MA) and cold gas dynamic spray (CGDS) process. The MA powder and CGDS coating samples were characterized by weight and size measurements, optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The coatings were also examined by profilometry and porosimetry. The results showed that the particle sizes of MA composite powders and their deposition efficiencies (DEs) in CGDS decreased with the increase of CNT content. The DE also decreased with the increase of coating layers. The XRD results indicated that the composite powders and coatings had microstrains and undergone grain size reduction due to the deformation caused by MA and CGDS. The coating surface and internal microstructures had flattened lamellar features, which indicated severe deformation that resulted from impact during the deposition of particles as well as from the impact of the rebounded particles. Some internal pores were present along the interfaces of the deposited particles. The surface roughness values of the coatings were observed to be related to the sizes of the powder particles. The roughness tended to decrease with the reduction of particle sizes. Also, the coatings contained about 1.0–2.5 vol.% surface micropores. However, the comparison between the trend of the surface roughness and the quantity of surface pores did not show direct correlation. Composition analysis of the coatings revealed the uniform dispersion of CNTs within the coatings.

Mechanical Properties and Durability of CNT Cement Composites.

In the present paper, changes in mechanical properties of Portland cement-based mortars due to the addition of carbon nanotubes (CNT) and corrosion of embedded steel rebars in CNT cement pastes are reported. Bending strength, compression strength, porosity and density of mortars were determined and related to the CNT dosages. CNT cement paste specimens were exposed to carbonation and chloride attacks, and results on steel corrosion rate tests were related to CNT dosages. The increase in CNT content implies no significant variations of mechanical properties but higher steel corrosion intensities were observed.

Basalt Fabric-Electrospun Nanofiber-Based Composite Laminates

This study investigated the influence of electrospun polyurethane mats containing different contents of carbon nanotubes (CNTs) stacked in between basalt fabric layers to form a composite laminate. The composite laminate was fabricated using a vacuum-assisted resin transfer molding (VARTM) process. Flexural test were carried out to investigate the strength and stiffness of composites for each configuration, while the failure characteristics were observed using a field emission scanning electron microscopy (FESEM) analysis. The results showed that flexural strength and stiffness of the hybrid composites with increasing CNT content in polyurethane (PU) nanofiber were increased by 6.5% and 17.3%, respectively. Furthermore, the addition of surfactants for the dispersion of CNTs in nanofibers significantly improved the flexural property of the composite interply basalt fabric-CNT/PU laminates. This study proved that the use of multi-scale reinforcement fillers with good and homogeneous dispersion increased the mechanical performance of the composite.

Pebax‐1657 nanocomposite membranes incorporated with nanoparticles/colloids/carbon nanotubes for CO2/N2 and CO2/H2 separation

ABSTRACTPebax‐1657 is known as a promising polymeric membrane material for CO2/N2 and CO2/H2 separation. In order to further improve its gas separation performance and reinforce the membrane, different fillers including silica nanoparticles, polystyrene (PS) colloids, and carbon nanotubes (CNTs) were incorporated into the polymer matrix to form nanocomposite membranes. The nanocomposite membranes of Pebax‐1657/silica and Pebax‐1657/PS colloid had a decreased CO2 permeability and selectivity over N2 or H2 compared to the pure Pebax‐1657 membrane, while the Pebax‐1657/CNT nanocomposite membranes had an increased CO2 permeability, retaining similar CO2/N2 or CO2/H2 selectivity compared to the pure polymer membrane. The CO2 permeability increased with increasing CNT content and reached a maximum at 5 wt % CNTs. The CNT‐enhanced gas permeability was attributed to the increase in gas diffusivity. The tensile modulus of Pebax‐1657 increased 43% after adding 5 wt % single‐wall CNTs (SWNTs), and increased 24% after adding 5 wt % multi‐wall CNTs (MWNTs). Thus, it is feasible to add CNTs to Pebax‐1657 membranes for improved mechanical strength and gas separation performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2867–2876, 2013

Microwave sintering carbon nanotube/Ni0.5Zn0.5Fe2O4 composites and their electromagnetic performance

Carbon nanotube (CNT)–Ni0.5Zn0.5Fe2O4 powders were prepared by in situ chemical precipitation and hydrothermal processing, and further sintered by microwave sintering technology. The results show that CNTs acted as ‘heating source’ and promoted the consolidation of composites during the microwave sintering process. However, too much CNTs (such as 5 wt%) led to phase decomposition and reduction of ferrite materials because of the ultra-high localized temperature building up in the interface of CNTs and ferrite grains. The electrical conductivity of composites increased by more than seven orders of magnitude when compared to that of pure Ni0.5Zn0.5Fe2O4, and remained a high value at the temperature of 70 K (for example, 1 wt% CNT/Ni0.5Zn0.5Fe2O4 sample kept conductivity of 0.1 S/m). The saturation magnetization was strongly dependent on the mass percentage of CNTs. With the increase in CNT content, both the real and the imaginary permittivity were increased in the frequency region 0.6–5 GHz (L and S bands). According to the measured results of ϵr and μr, the frequency-dependent reflectance loss (RL) of CNT/Ni0.5Zn0.5Fe2O4 composite ceramics with different CNT content was evaluated. The CNT-doped ferrite ceramics discussed herein is very promising to be used in an on-beam-line high-order mode (HOM) load in particle accelerators based on superconducting RF due to their excellent low-temperature characteristics.

On the thermal expansion of CNT/Cu composites for electronic packaging applications

Carbon nanotubes (CNTs) exhibit both excellent high thermal conductivity and low coefficient of thermal expansion (CTE), which are an ideal reinforcement in composite materials for high performance electronic packaging applications. In the present study, CNT/Cu composites containing CNTs varying from 0 vol.% to 15 vol.% are prepared, and their CTE behavior is studied in detail. The results indicate that the CTE of 0–10 vol.% CNT/Cu composites is significantly decreased with increasing CNT content. However, as the CNT content increases to 15 vol.%, the decrease in CTE of the composites is pronouncedly reduced. Possible mechanisms are discussed in combination with CTE model predictions.

Processing of copper–carbon nanotube composites by vacuum hot pressing technique

Copper (Cu) matrix composites reinforced with 0.2, 5 and 10vol% single wall carbon nanotubes (SWCNT) and 5 and 10vol% multi-wall carbon nanotubes (MWCNT) were processed by high energy milling of pure copper powder with carbon nanotubes (CNTs) and subsequent consolidation by vacuum hot pressing. Microstructural observations of the sintered composites revealed equiaxed twinned microstructure for 0.2vol% SWCNT composite and elongated grain structure, with CNT layers in between, in composites having higher CNTs content. The porosity in the composites was associated with CNT layers. The distribution of CNTs was found to be different in axial and transverse directions. Significant improvement in hardness of Cu–SWCNT composite was observed with increase in CNTs content. Whereas, in case of MWCNT composite, hardness reduced for 10vol% CNT composites. Compression strength of the SWCNT samples was found to be higher than the MWCNT reinforced samples.

Preparation and properties of carbon nanotube composites with nitrile‐ and styrene‐butadiene rubbers

AbstractThe work deals with the preparation and characterization of elastomer/multiwalled carbon nanotube (CNT) composites. Nitrile‐butadiene‐rubber (NBR), emulsion styrene‐butadiene‐rubber (E‐SBR) with random segment distribution, and solution styrene‐butadiene‐rubber (S‐SBR) having a blocked styrene content were used as elastomer matrix. The preparation of composites by a masterbatch process was compared to the direct melt‐mixing process using two different types of multiwalled CNT. It turned out that extremely low‐percolation thresholds of ∼0.2 and 1 wt% CNT can be reached by direct melt mixing of Nanocyl 7000 CNT with S‐SBR and NBR, respectively. The effect of CNT on the vulcanization reaction was studied by application of a first‐order kinetic model. It can be shown that the rate constants are decreasing with increasing CNT content especially at higher reaction temperatures and that CNT cause a decrease in activation energies. Temperature scanning stress‐relaxation measurements were used to prove the reinforcing effect of the CNT, to verify the phase structure of the S‐SBR, and to estimate the effect of CNT on crosslink density. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

A Cu-based bulk amorphous alloy composite reinforced by carbon nanotube

Bulk Cu50Zr40Ti10 amorphous alloy composites reinforced with carbon nanotube (CNT) were successfully fabricated by hot pressing technique. Their density, thermal conductivity, and mechanical properties were systemically investigated. The density and the compression strength of the compacts both decrease with increasing CNT content. The thermal conductivity of the compacts decreases when the CNT content is less than 0.10% or exceeds 0.60% (mass fraction), while increases when the CNT content is in the range of 0.1%–0.6%. The strain limit and the modulus of the compacts are obviously improved when the CNT content is less than 1.0% and then decrease significantly when the CNT content exceeds 1.00%. The optimum CNT addition is less than 0.20% at the comprehensive properties point of view.

Research on the electrochemical performance of nanocomposites of vanadium oxide and carbon nanotubes as cathode materials

The vanadium oxide (VOx)/carbon nanotubes (CNTs) nanocomposites were synthesized by a hydrothermal method. The morphologies and structures of composites were characterized by XRD, SEM and TEM. The results indicated that the VOx/CNTs nanocomposites have a crossing network structure. The electrochemical cycling stability of the nanocomposites as cathodes could be improved with the increase of CNTs content. Specially, when the CNTs content was 20wt%, the initial discharge capacity of the nanocomposites was about 190mAh/g in 2.0–4.0V vs. Li+/Li, and the capacity could remain 93.1% after fiftieth cycle.

STRAIN-INDUCED CRYSTALLIZATION AND MECHANICAL PROPERTIES OF NBR COMPOSITES WITH CARBON NANOTUBE AND CARBON BLACK

Abstract The mechanical properties and strain-induced crystallization (SIC) of elastomeric composites were investigated as functions of the extension ratio (λ), multiwalled carbon nanotube (CNT) content, and carbon black (CB) content. The tensile strength and modulus gradually increase with increasing CNT content when compared with the matrix and the filled rubbers with same amount of CB. Both properties of rubber with CB and CNT show the magnitude of each CNT and CB component following the Pythagorean Theorem. The ratio of tensile modulus is much higher than that of tensile strength because of the CNT shape/orientation and an imperfect adhesion between CNT and rubber. The tensile strength and modulus of the composite with a CNT content of 9 phr increases up to 31% and 91%, respectively, compared with the matrix. Differential scanning calorimetry (DSC) analysis reveals that the degree of SIC increases with an increase in CNT content. Mechanical properties have a linear relation with the latent heat of crystallization (LHc), depending on the CNT content. As the extension ratio increases, the glass-transition temperature (Tg) of the composite increases for CB- and CNT-reinforced cases. However, the LHc has a maximum of λ = 1.5 for the CNT-reinforced case, which relates to a CNT shape and an imperfect adhesion with rubber. Based on these results, the reinforcing mechanisms of CNT and CB are discussed.

EFFECT OF CARBON NANOTUBES ON THE KINETICS OF IN SITU POLYMERIZATION OF METHYL METHACRYLATE

The effect of carbon nanotubes on the kinetics of free radical polymerization of methyl methacrylate (MMA) was investigated. To do this, pristine, acid treated, alcoholic and methacrylate-modified carbon nanotubes with different loadings were used and Conversion, molecular weight and polydispersity index (PDI) of all samples were monitored during polymerization. The results show that carbon nanotubes induce an induction time to polymerization system which is independent of modification system while decrease in monomer conversion can be improved by developing organic moieties on surface. Molecular weight and polydispersity index for free and attached-on-surface chains were studied separately and different kinetics behaviors were observed for them. Molecular weight of free chains was increased by adding carbon nanotubes while more modified nanotubes resulted in much increased molecular weight. On the other hand, more system stability of more modified nanotubes, which was tested using UV-Visible spectra, resulted in higher molecular weights. Adding more nanotubes in the case of MMA-modified nanotubes caused to determine an optimum loading value to reach maximum molecular weight of free chains which was ascribed to system stability according to UV-Visible results. In this optimum loading value, free chains had minimum PDI value. However, increasing carbon nanotubes content led to decreased molecular weight of attached chains while PDI values increased because of shielding effect as physical phenomenon.

Electrical Conductivity of Anisotropic iPP Carbon Nanotube Thin Films

ABSTRACTPolymer and carbon nanotubes (CNTs) nanocomposites exhibit many properties that are not present in either the pure polymer or CNTs. The polymer crystallization kinetics and crystal forms are greatly changed by dispersion of CNTs nanotubes. In addition to various thermophysical properties, CNTs are metallic or semiconductive and highly anisotropic while the polymer hosts are typically excellent insulators and isotropic. In this work, measurements of the electrical conductivity, σ, of thin-film nanocomposites of isotactic polypropylene (iPP) and CNTs as a function of CNT concentration (0, 1, 2, and 5% by weight of CNT) and melt-shearing induced anisotropy in σ between parallel and perpendicular to the shearing axis is presented and compared them with analogous data for their thermal transport properties. The iPP host is itself one of the most widely used polymers, has liquid crystalline phases, and it is expected that iPP/CNT nanocomposites will be widely used in many polymer applications, some of which are for flexible electrodes, medical and electronics packaging and chemical sensors. The effect of melt-shearing is expected to induce anisotropy in the various properties of the iPP/CNT thin film that should be particularly apparent in the electrical conductivity of the polymer films, higher in the direction of the alignment and lower in the direction perpendicular to it. With increasing CNT content, the average conductivity 〈σ〉 increases slightly from 0 to 2% CNT then dramatically increases by eight orders of magnitude for 5%. The shear induced property of anisotropy, δσs = (σ‖ − σ┴) / 〈σ〉, overall increases with CNT content, revealing a large spike for the 1% sample, indicating the possibility of enhanced δσs due to optimized orienting procedures.

Preparation, characterization and properties of acid functionalized multi-walled carbon nanotube reinforced thermoplastic polyurethane nanocomposites

The multi-walled carbon nanotube (MWNT) reinforced thermoplastic polyurethane (TPU) nanocomposites were prepared through melt compounding method followed by compression molding. The spectroscopic study indicated that a strong interfacial interaction was developed between carbon nanotube (CNT) and the TPU matrix in the nanocomposites. The microscopic observation showed that the CNTs were homogeneously dispersed throughout the TPU matrix well apart from a few clusters. The results from thermal analysis indicated that the glass transition temperature (Tg) and storage modulus (E′) of the nanocomposites were increased with increase in CNTs content and their thermal stability were also improved in comparison with pure TPU matrix. The rheological analysis showed the low frequency plateau of shear modulus and the shear thinning behavior of the nanocomposites. The electrical behaviors of the nanocomposites are increased with increase in weight percent (wt%) of CNT loading. The mechanical properties of nanocomposites were substantially improved by the incorporation of CNTs into the TPU matrix.