Multi-walled Carbon Nanotubes In Epoxy Research Articles

Nano filler incorporated epoxy based natural hybrid fiber confinement of concrete systems: Effect of fiber layers and nano filler addition

The utilization of environment friendly materials in the construction industry is essential for sustainable development. For the purpose of strengthening and retrofitting concrete structures, fiber reinforced polymer (FRP) composites have been predominantly used. In the area of structural strengthening, as an alternative to synthetic fiber reinforced composites, the application of natural fiber reinforced composites is of immense interest. This study discusses the mechanical properties of externally strengthened concrete cylinders using a natural hybrid fiber system with two layers of sisal fiber sheets followed by 1 to 3 layers of basalt fiber sheets. In addition, the effect of multi walled carbon nanotubes (MWCNT) incorporation in the epoxy matrix from 0.5 to 1.5 wt%, on the various properties are analyzed. The inclusion of MWCNT in the epoxy matrix improved the overall performance of the FRP significantly. The results show that there is substantial improvement in mechanical properties up to 1 wt% MWCNT content in composites, beyond which it is reduced due to agglomeration of nanofiller. The MWCNT incorporated epoxy based five layered hybrid sisal basalt FRP confined specimens showed an improvement of 114% and 427% in peak strength and strain values under axial compressive strength tests. Moreover, the axial compressive behavior, stress–strain response, energy absorption and ductility characteristics of the confined column specimens were evaluated. The major focus of the study is to assess the influence of basalt FRP layers on the ultimate load carrying capacity and performance of hybrid sisal basalt FRP (HSBFRP) confined specimens. Statistical analysis of variance (ANOVA) was carried out and revealed that the number of FRP layers and addition of MWCNT in epoxy significantly affect the overall performance. The addition of basalt fiber layers in hybrid sisal basalt FRP systems is found to improve the load carrying capacity and energy absorption characteristics of confined specimens. Therefore, HSBFRP confinement can be used in areas where moderate strength and greater ductility is commanded.

Preparation and Properties of Epoxy/Multiwalled Carbon Nanotube Nanocomposite Foams with an Alternating Layer Structure.

Multilayered epoxy/multiwalled carbon nanotube (EP/MWCNT) composite foams with a density of 0.713 g/cm3 were prepared through the chemical foaming of laminated epoxy sheets in a mold with a fixed cavity. The difference in cell morphology and properties between adjacent layers in the multilayer foams (two- and four-layer) was tuned by MWCNT or chemical foaming agent (CFA) concentration. It was found that the storage modulus and microwave-absorbing ability of the multilayered EP/MWCNT foams were strongly associated with the loading direction, the thermal diffusivity was slightly direction-dependent, and the electromagnetic interference (EMI) shielding effectiveness (SE) was direction-independent. In addition, as the layer number increased, the mechanical, thermal, and electrical conductivity properties and EMI shielding performances of the multilayered composite foams showed different change tendencies. These results indicated that the effect of the multilayer structure on the properties of composite foams was different when they underwent force, heat, or electromagnetic microwave, and the underlying reasons were investigated in detail.

Morphologies and properties of epoxy/multi-walled carbon nanotube nanocomposite foams prepared through the free-foaming and limited-foaming process

Microcellular epoxy/multi-walled carbon nanotube (EP/MWCNT) composite foams loaded with 2 wt% (mass fraction) of MWCNT were prepared through the free-foaming process (Fre-foam) and limited-foaming process (Lim-foam) using chemical foaming agent (CFA), respectively. The morphologies of EP/MWCNT composite foams with different densities were analyzed by scanning electron microscopy (SEM). It was found that the cell size of both Fre-foam and Lim-foam decreased with increasing the density, while Lim-foam exhibited a smaller cell size and a higher cell density in contrast to those of Fre-foam at similar density. In addition, the dynamic mechanical properties, thermal stability, and electrically and thermal conductive properties of the EP/MWCNT foams in the density range of 0.278 g/cm3–1.108 g/cm3 were investigated and the difference in performances between Fre-foam and Lim-foam was analyzed. Lim-foam had an obviously lower crosslink density than that of Fre-foam due to the effect of compressed gas, which was clearly reflected in the results of gel fraction, glass transition temperature (Tg), molecular weight between crosslinks (Mc), and initial thermal decomposition temperature. Compared with Fre-foam, Lim-foam had superior thermal conductive property and exhibited weak electrically conductive property, indicating the conductive pathway was affected by the foaming process.

Mechanical and viscoelastic study of functionalized MWCNTs/epoxy/Kevlar composites

Nanomaterials‐strengthened diglycidyl ether of bisphenol A (DGEBA) epoxy resin and aramid fiber composites were investigated for 0.16 wt% and 0.32 wt% of industrial and COOH‐functionalized multiwalled carbon nanotubes (MWCNTs). Epoxy/Kevlar fiber/MWCNT hybrid composites were prepared using a vacuum resin‐infusion molding method (VRIM) based on 0.68 aramid fiber mass fractions. The effects of MWCNTs on the viscoelastic, mechanical, and thermal properties of composites were investigated. The chemical structure of composites was studied using Fourier‐transform infrared spectroscopy. Samples with COOH‐functionalized nanotubes showed a strong impact on thermogravimetric analysis, in contrast to composites having the equivalent amount of industrial grade MWCNTs. The outcomes show that addition of MWCNTs to epoxy has a substantial influence on viscoelastic properties. The viscoelastic and thermal analyses show that storage modulus escalates with the addition of functionalized MWCNTs. Micrographs of MWCNTs‐enriched epoxy and Kevlar/epoxy samples revealed the uniform distribution of COOH‐functionalized MWCNTs in epoxy (as compared to industrial grade MWCNTs), resulting in increased interfacial strength between fiber/matrix. POLYM. COMPOS., 39:E2064–E2073, 2018. © 2017 Society of Plastics Engineers

CNT-reinforced adhesive joint between grit-blasted steel substrates fabricated by simple resin pre-coating method

ABSTRACT A simple method of applying and distributing multi-walled carbon nanotubes (MWCNTs) onto grit-blasted steel substrates has been investigated in this study to overcome the difficulty of mixing MWCNTs in epoxy adhesives forming the MWCNT-reinforced adhesive joints. MWCNTs were dispersed in an acetone and resin (no hardener) solution with the weight ratio of 1:3:100 for MWCNT/resin/acetone, which was then applied onto the grit-blasted steel substrates. After evaporation of acetone, an ultra-thin layer of resin pre-coating kept well-distributed MWCNTs within the micro-cavities created by grit blasting. Epoxy adhesives (with hardener) were then applied to bond the steel substrates to create MWCNTs-reinforced adhesive joints. The results show that the MWCNT pre-coating (PC) method is beneficial to strong adhesive bonding. Most importantly, the MWCNT-PC method can be easily applied for structural applications on site. In the current study, MWCNTs were simply dispersed in the acetone and resin (no hardener) solution by simple rod stirring for around 1 minute, which can be adopted for large-scale applications. Scanning electron microscopy (SEM) observations on fracture surfaces and cross sections of the MWCNT-reinforced adhesive joints showed MWCNT micro-bundles were well dispersed within the epoxy adhesive joints taking the contour of microscopically uneven substrate surfaces.

Thermo-mechanical and anti-corrosive properties of MWCNT/epoxy nanocomposite fabricated by innovative dispersion technique

Abstract To obtain cluster free homogeneous dispersion of carbon nanotubes in polymer matrix, variety of strategies were applied. In the present work, we report a systematic approach to obtain a superior level of dispersion of multi-walled carbon nanotubes (MWCNTs) in epoxy by applying simultaneously ultrasonic waves and shear force generated by axial flow impeller. The influence of dispersion of MWCNTs on anti-corrosion, mechanical and thermal properties of MWCNT/epoxy nanocomposite was investigated. Field Emission Scanning Electron Microscopy (FESEM) studies confirmed cluster free uniform dispersion of MWCNTs in epoxy matrix, which lead to enhanced tensile strength by 35%, toughness by 53% and storage modulus by 35% on loading of 0.75 wt% of MWCNTs in epoxy. It was found that when mild steel was coated with MWCNT/epoxy nanocomposite (0.75 wt%), the corrosion rate decreased upto 2.5 × 10 −3 MPY and protection efficiency increased upto 99.99%.

Rheology of electrostatically tethered nanoplatelets and multi-walled carbon nanotubes in epoxy

Multi-walled carbon nanotubes (MWCNTs) dispersed using α-zirconium phosphate (ZrP) nanoplatelets in a glassy epoxy have previously been reported to tremendously improve modulus, strength and ductility in a manner that could not be explained based on continuum-level descriptions of particle-level reinforcement. Several other recent studies have shown similar synergistic improvements in bulk properties for low concentrations of co-dispersed plate-like and rod-like nanoparticles. In this work, we have used rheology as a tool to probe the microstructure and interactions for the ZrP/MWCNT hybrid system in an uncured epoxy pre-polymer fluid. The results are compared to the behavior of model suspensions containing the individually dispersed nanoparticles to more clearly differentiate between particle-level and mesostructural interactions. The linear viscoelastic results show that the ZrP-assisted dispersion approach fully disentangles and stabilizes the MWCNTs in the epoxy fluid. When subjected to large amplitude oscillatory shear or steady shear, the hybrid suspensions show pronounced strain-hardening and shear thickening behaviors, respectively, that were not observed with suspensions containing either individual component. The non-linear behavior is attributed to the direct tethering of the exfoliated ZrP nanoplatelets to the disentangled MWCNTs, which are proposed to serve as mechanically robust junctions. In the solid state, this hybrid network retains sufficient mechanical integrity to delocalize stress concentrations near flaws and cracks in the epoxy matrix, and is responsible for the enormous strengthening behavior observed in this system. The present study provides several potential design considerations for preparation of high-performance nanocomposite systems containing a co-dispersion of interacting nanoparticles.

Using supercritical CO2-assisted mixing to prepare graphene/carbon nanotube/epoxy nanocomposites

In this study supercritical carbon dioxide (scCO2) was employed to incorporate graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) into an epoxy matrix to enhance the electrical and thermal properties of the epoxy. The percolation threshold for electrical conductivity for the nanocomposite prepared through scCO2 mixing was 2 wt%, one-third that obtained after acetone mixing. When the weight ratio of GNPs to MWCNTs was 1:3, the electrical conductivity (2.6 × 10−7 S/cm) of the GNP/MWCNT/epoxy nanocomposite prepared through scCO2 mixing at 35 °C and 1200 psi was twice that obtained when using subcritical CO2 mixing at 30 °C and 1000 psi. On the other hand, when the weight ratio of GNPs to MWCNTs was 3:1, the thermal conductivity (0.89 W/mK) of the nanocomposite prepared using scCO2 was 287% higher than that of the neat epoxy. A synergistic effect of the GNPs and MWCNTs was observed, with 68 and 190% increases in the thermal conductivity of the GNP/MWCNT/epoxy nanocomposite over the individual GNP/epoxy and MWCNT/epoxy nanocomposites, respectively, after applying scCO2 mixing. The proposed scCO2 mixing process not only aids the dispersion of GNPs and MWCNTs in epoxy but also eliminates the presence of solvent after decreasing the pressure.

Effect of Amino Multi Walled Carbon Nanotubes Reinforcement on the Flexural Properties of Neat Epoxy

The effect of amino multi-walled carbon nanotubes (MWCNTs) on the flexural properties of epoxy/ nanocomposites was studied. Sonication technique was employed for dispersion of amino MWCNTs in epoxy. The properties of both neat epoxy and nanocomposites extensively studied by using three point bend test and scanning electron microscopy. From the experimental results, it was found that reinforcement with carbon nanotubes improved the flexural properties, namely (a) flexural modulus, (b) flexural strength, (c) nonlinear deformation and (d) total flexural toughness.

Rheology of Disentangled Multiwalled Carbon Nanotubes Dispersed in Uncured Epoxy Fluid

The rheological behaviors of clustered and disentangled multiwalled carbon nanotubes (MWCNTs) dispersed in a stable, non-reactive Newtonian epoxy fluid have been investigated. Suspensions of untreated and chemically oxidized MWCNTs in epoxy show strong rate-dependent behavior and long-time elastic response that is characteristic of a flocculated microstructure. Suspensions of disentangled MWCNTs in epoxy were prepared by a functionalization reaction with nitrobenzene, and show distinct rheological behavior that is attributed to the motion and rotation of the individual nanoparticles. Characteristic features of the disentangled MWCNTs in epoxy are a lack of low-frequency plateau in storage modulus and shear thickening behavior at high shear rate. The rheological behavior is discussed on the basis of continuum-level predictions for the motion of individual, semiflexible fibers under shearing flows. Implications of MWCNT disentanglement on fundamental study and applications of MWCNT-filled systems are discussed.

Transparent, electrically conductive, and flexible films made from multiwalled carbon nanotube/epoxy composites

Optically transparent, conductive, and mechanically flexible epoxy thin films are produced in the present study. Two types of multiwalled carbon nanotubes (MWCNTs) with different aspect ratios are dispersed in epoxy resin through an ultrasonication process. The MWCNT content is varied during the preparation of the thin films. The light transmittance and electrical conductivity of the thin films are characterized. Results show that composites containing MWCNTs with a lower aspect ratio exhibit enhanced electrical conductivity compared to those with a higher aspect ratio. A sheet resistance as low as 100Ω/sq with nearly 60% optical transparency in 550nm is achieved with the addition of MWCNTs in epoxy. In summary, transparent, conductive, and flexible MWCNT/epoxy thin films are successfully produced, and the properties of such films are governed by the aspect ratio and content of MWCNTs.

Covalent and non-covalent functionalized MWCNTs for improved thermo-mechanical properties of epoxy composites

Two simplified methods for non-covalent and covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with surfactants were developed, the functionalization degree and properties of their epoxy nanocomposites were studied. Physical absorption and covalent attachment of nonionic surfactants was proved by an increase of the mass loss in TGA and the appearance of characteristic peaks in XPS. The DSC analysis of the epoxy nanocomposites proved a low catalytic influence of 1% modified MWCNTs on the epoxy curing process, while DMA showed a higher flexibility compared with the neat epoxy. Dispersion state of modified MWCNTs in epoxy was related to their functionalization degree.

Plasma Treated Multi-Walled Carbon Nanotubes (MWCNTs) for Epoxy Nanocomposites

Plasma nanocoating of allylamine were deposited on the surfaces of multi-walled carbon nanotubes (MWCNTs) to provide desirable functionalities and thus to tailor the surface characteristics of MWCNTs for improved dispersion and interfacial adhesion in epoxy matrices. Plasma nanocoated MWCNTs were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), surface contact angle, and pH change measurements. Mechanical testing results showed that epoxy reinforced with 1.0 wt % plasma coated MWCNTs increased the tensile strength by 54% as compared with the pure epoxy control, while epoxy reinforced with untreated MWCNTs have lower tensile strength than the pure epoxy control. Optical and electron microscopic images show enhanced dispersion of plasma coated MWCNTs in epoxy compared to untreated MWCNTs. Plasma nanocoatings from allylamine on MWCNTs could significantly enhance their dispersion and interfacial adhesion in epoxy matrices. Simulation results based on the shear-lag model derived from micromechanics also confirmed that plasma nanocoating on MWCNTs significantly improved the epoxy/fillers interface bonding and as a result the increased composite strength.

Effect of block-copolymer dispersants on properties of carbon nanotube/epoxy systems

The effects of the addition of eight different block copolymers on the dispersion stability of multi-walled carbon nanotubes (MWCNTs) are reported. Suspensions of CNTs in different components of an epoxy system have been prepared using a tip sonicator and different amounts of block copolymers. The resistance to sedimentation of MWCNTs in various media was systematically investigated by using a centrifugation technique. Block copolymers that result in dispersions of MWCNTs in epoxy and hardener stable for more than 1week have been obtained. Dispersions using a single or a combination of two different dispersing agents have been used for the fabrication of MWCNT nanocomposites. The effect of different preparation routes and use of block copolymers on the tensile properties and surface resistivity of the composites have been evaluated. The results obtained have been related with the dispersion stability of the MWCNTs in the epoxy components.