Addition Of Multi-walled Carbon Nanotubes Research Articles

Heat Transfer Enhancement of MHD Natural Convection in a Star-Shaped Enclosure, Using Heated Baffle and MWCNT–Water Nanofluid

Fluids have played and still play a vital role in attaining an optimized output from industrial processes. However, due to technological advancement, fluids with high hydrothermal characteristics are required. In order to overcome these challenges, researchers have developed fluids with dispersed nanoparticles, which are recognized as nanofluids. Various types of nanoparticles can be added to base fluids to produce thermally enhanced liquids. Among these, the addition of multi-walled carbon nanotubes (MWCNTs) is considered the best due to the considerable enhancement of thermophysical properties and the stability of the solution. Thus, in the present investigation, an analysis of the heat transfer characteristics of an MWCNT–water nanofluid included in a star-shaped cavity equipped with a hot rectangular baffle is conducted. In addition, a uniform magnetic field is applied along the x-direction to oppose the convective flow generated by variations in density. Mathematical formulations under assumed boundary conditions and physical assumptions are established in the form of dimensionless PDEs. The finite-element-method-based software “COMSOL” is used to execute the numerical simulations. PARADISO is employed to resolve the developed non-linear system of equations. The effects of the governing parameters on the velocity and temperature fields are presented through streamlines and isotherms. The Nusselt number is evaluated to depict the impact of the addition of nanoparticles (MWCNTs) on the heat transfer enhancement. Changes in the horizontal and vertical components of velocity are also evaluated against the Rayleigh number and nanoparticle volume fraction via cutline representation.

MWCNTs-GNPs Reinforced TPU Composites with Thermal and Electrical Conductivity: Low-Temperature Controlled DIW Forming.

As an effective technique for fabricating conductive and thermally conductive polymer composites, a multi-filler system incorporates different types and sizes of multiple fillers to form interconnected networks with improved electrical, thermal, and processing properties. In this study, DIW forming of bifunctional composites was achieved by controlling the temperature of the printing platform. The study was based on enhancing the thermal and electrical transport properties of hybrid ternary polymer nanocomposites with multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates (GNPs). With thermoplastic polyurethane (TPU) used as the matrix, the addition of MWCNTs, GNPs and both mixtures further improved the thermal conductivity of the elastomers. By adjusting the weight fraction of the functional fillers (MWCNTs and GNPs), the thermal and electrical properties were gradually explored. Here, the thermal conductivity of the polymer composites increased nearly sevenfold (from 0.36 W·m-1·k-1 to 2.87 W·m-1·k-1) and the electrical conductivity increased up to 5.49 × 10-2 S·m-1. It is expected to be used in the field of electronic packaging and environmental thermal dissipation, especially for modern electronic industrial equipment.

Microwave-assisted synthesis of iron sulfide motifs for electrochemical applications

The syntheses of FeS2 and Fe3S4 nanomaterials were optimized using a novel facile, surfactant-free, and microwave-assisted, one-pot synthesis method, run under ambient and reasonably mild reaction conditions. Synthetic parameters, such as metal precursor salt identity, reaction time, reaction temperature, metal:sulfur molar ratios, and solvent combinations, were all systematically investigated and optimized. A series of FeS2 (pyrite) samples was initially fabricated using thioacetamide (TAA) as the sulfur precursor to generate a distinctive, uniform octahedra-based morphology. Switching the sulfur precursor from TAA to L-cysteine resulted in a corresponding transformation in not only chemical composition from FeS2 to an iron thiospinel structure, Fe3S4 (otherwise known as greigite), but also an associated morphological evolution from octahedra to nanosheet aggregates. The study of these materials has enabled crucial insights into the formation mechanisms of these materials under a relatively non-conventional microwave-assisted setting. Furthermore, in separate experiments, multi-walled carbon nanotubes (MWNTs) and graphene were added in with underlying metal sulfide species to create conductive Fe–S/MWNT composites and Fe–S/graphene composites, respectively. The method of addition of either MWNTs or graphene was also explored, wherein an ‘ex-situ’ synthetic procedure was found to be the least disruptive means of attachment and immobilization onto iron sulfide co-reagents as a means of preserving the latter’s inherent composition and morphology. The redox acidity for the parent material and associated composites demonstrates the utility of our as-developed synthetic methods for creating motifs relevant for electrochemical applications, such as energy storage.

ENHANCING THE MECHANICAL, THERMAL AND ELECTRICAL PROPERTIES OF ALUMINA-MWCNT HYBRID NANOFILLER REINFORCED EPOXY COMPOSITES

In this work, alumina and multi-wall carbon nanotube (MWCNT) hybrid nanofiller reinforcing pure epoxy at varying weight fractions of (0.1, 0.2, 0.3, 0.4 and 0.5) w/% is investigated to enhance the mechanical, electrical and thermal properties. The porosity, tensile strength, electrical and thermal conductivity of epoxy hybrid nanocomposites are studied after the effects of the alumina-MWCNT hybrid nanofillers. The interfacial adhesion and mechanical interlocking between the hybrid nanofillers and epoxy are greatly increased with the addition of alumina and MWCNTs, thus leading to an improvement in the mechanical properties. Additionally, a uniform distribution of hybrid nanofillers results in a larger increase in the thermal and electrical conductivity. The presence of voids in specimens is gradually decreased when the nanofiller content is increased up to 0.3 w/%. The alumina-MWCNT reinforcement significantly improves the tensile strength, by 88 %, compared with pure epoxy. Similarly, the electrical and thermal conductivity increase by 85 % and 64 %, respectively, when compared with low weight fractions of the hybrid nanofiller. Agglomeration during the fabrication of nanocomposites is manageable but it is inevitable. During the formation of chains and networks, the alumina-MWCNT reinforcement of pure epoxy greatly influences the thermal conductivity. This strategy provides a prospective new concept for the use of epoxy and its composites in structural and thermal engineering applications.

Microstructure, mechanical properties and tribological behavior of Cu-nano TiO2-MWCNTs composite sintered materials

The paper presents the results of microstructure, mechanical and tribological tests of copper matrix sinters with the addition of nano-TiO2 and copper-decorated multi-walled carbon nanotubes. A powder metallurgy was used for the production of composite materials. The aim of the work was to determine the properties and wear mechanism of the produced sinters with single additives and to investigate the synergistic interaction of titanium dioxide and carbon nanotubes. Wear tests were carried out using the pin-on-disc method at room temperature and 600 °C. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Raman Microscopy, Thermogravimetric Analysis (TGA), Dilatometry (DIL), X-Ray Diffraction (XRD), and profilometer were used for the research. Moreover, the stiffness and hardness of the sinters were examined. The main wear mechanisms of the friction pairs tested at room temperature and 600 °C were adhesive, abrasive, and oxidation wear. Furthermore, at the test temperature of 600 °C, the formation of a tribofilm was observed on the surface of the friction pairs, which reduced friction wear. The introduced additions to the copper matrix increased its hardness, stiffness, work of axial deformation, and wear resistance. Moreover, additions decreased the relative value of the thermal expansion coefficient of the sintered copper. The friction pair no. 2 (Cu + 1 wt % MWCNTs – Inconel®625) was characterized by the lowest coefficient of friction at room temperature and 600 °C, of approximately 0.62 and 0.56, respectively. The sintered composite material of Cu – 10 wt% nano TiO2 – 1 wt%. MWCNTs was characterized by the highest mechanical properties and the lowest wear.

Osteogenesis, hemocompatibility, and foreign body response of polyvinylidene difluoride-based composite reinforced with carbonaceous filler and higher volume of piezoelectric ceramic phase

Hybrid polymer-ceramic composites have been widely investigated for bone tissue engineering applications. The incorporation of a large amount of inorganic phase, like barium titanate (BaTiO3) with good dispersion, in a polymeric matrix using a conventional processing approach has always been challenging. Also, the comprehensive study encompassing the interactions of key components of living organisms (cell, blood, tissue) with such hybrid composites is not well explored in many published studies. Built on our earlier studies and recognizing the importance of poly(vinylidene fluoride) (PVDF) as a widely used polymer for a wide spectrum of biomedical applications, the present study reports the qualitative and quantitative analysis of the biocompatibility of PVDF composite (PVDF/30BT/3MWCNT) reinforced with large amounts of BaTiO3 (30 wt %) and tailored addition of multiwalled carbon nanotubes (MWCNT; 3 wt %). The melt mixing-extrusion-compression moulding-based processing approach resulted in an enhancement of β-phase content, thermal stability, and wettability in the semi-crystalline PVDF composite. The enhanced hemocompatibility of PVDF/30BT/3MWCNT has been established conclusively by a series of in vitro blood-material interaction assays, including haemolysi, analysis of platelets attachment and activation, dynamic blood coagulation, and plasma recalcification time. The cytocompatibility study confirms an improved adhesion, proliferation, and migration of osteoprogenitor cells (preosteoblasts; MC3T3-E1) on PVDF/30BT/3MWCNT, in a manner better than neat PVDF, in vitro. When these cells were cultured in osteogenic differentiating media, the modulated osteogenesis, in terms of alkaline phosphatase activity, intracellular Ca2+ concentration, and calcium deposition on the PVDF/30BT/3MWCNT, was recorded. Following subcutaneous implantation of PVDF/30BT/3MWCNT in rat model, no apparent variation was recorded in the complete hemogram (blood hematology analysis) or serum biochemistry, post 30-, 60-, and 90-days surgery. Importantly, 90-days post-implantation, the fibrous capsule thickness was significantly reduced in the composites w.r.t PVDF alone, together with better blood vessel formation, indicating improved neovascularization around the composite. This study establishes the efficacy of inorganic fillers in enhancing the biocompatibility of PVDF, which could open up a wide range of biomedical applications.

Morphological analysis and high-temperature phase stability of spark plasma sintered TiN-MWCNTs ceramic composite

The microstructure, mechanical properties, and phase stability of TiN+MWCNTs ceramic-based composite were studied. Ball milling and spark plasma sintering (SPS) techniques were adopted for synthesizing titanium nitride (TiN) composites containing 1, 3, and 5 wt. percent (wt. %) multiwalled carbon nanotubes (MWCNT). At a temperature of 1000 °C where the phase stability was investigated, the effects of MWCNT addition on thermal treatment and mechanical characteristics of the fabricated composites were explored. According to the results, the resultant effect of ball milling on the ad-milled powders and sintering at a temperature of 1800 °C played a critical role in the homogenous diffusion of MWCNTs into the TiN ceramic matrix. It was further noted that the addition of different wt. % of multiwalled carbon nanotube helped in stabilizing the FCC-crystal phases at this elevated temperature. A slight transformation was observed in the microstructures, as the core and the outer rim phases remained stable in their crystallographic orientation. The varying addition of MWCNTs retained the α-FCC phase both at the core and the outer rim phase during and after thermal exposure of 1000 °C for 3 h. The composite with 1wt. % MWCNT content exhibited the highest hardness of 40 GPa with a fracture toughness of 12.22 MPa m1/2, while the least hardness value of 12.5 GPa was recorded by the unreinforced TiN sample. The effect of mechanical alloying and thermal exposure of the ceramic composites significantly enhanced the strengthening and toughening of the composites.

Effect of Diameter of Carbon Nanotubes in Nanocomposite Membrane for Methyl Orange Dye Removal

It is worth noticing that structure of nanomaterials affects the membrane performance, however, the effect of diameter of multiwalled carbon nanotubes (MWCNTs) has not been discussed in the past. This research aims to investigate the effect of diameter of MWCNTs on the performance of graphene oxide (GO)/ MWCNTs nanocomposite membrane for methyl orange dye removal. MWCNTs with different diameters (12-15 nm, 30-50 nm) with the same length (< 10 µm) are used to synthesize the nanocomposite membrane. The characteristics of the synthesized nanocomposite membrane were determined by surface hydrophilicity, pore size and porosity, zeta potential, and Fourier-transfer infrared (FTIR) spectroscopy. Besides, the membrane performance was evaluated by the water permeability test, dye rejection test, and antifouling test. The result showed that pure MWCNTs (30-50 nm) nanocomposite membrane (M2b) has the best performance among the synthesized membrane. The dye rejection of M2b membrane reached 86.77% and the normalized flux was approximately 0.82. Lower dye rejection (83.37%) and normalized flux (0.76) were attained by M2a membrane with smaller diameter MWCNTs (12-15 nm). This was due to M2b membrane having a smaller pore size (0.032 nm), which helped reduce the tendency of dye to pass through the membrane. Besides, M2b membrane has a more negative surface charge (-10.93 mV) that produces larger repulsion force, resulting in more dye being rejected. In conclusion, the performance of the synthesized nanocomposite membrane particularly antifouling properties can be enhanced with the addition of MWCNTs with larger diameter.

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.

Mechanical Properties and Damage Behaviours of Polyurethane Composites Reinforced With BNNP and MWCNT Hybrid Nanoparticles

In recent years, with increasing engineering applications, structural adhesives have played an increasingly important role in joining both metallic and non-metallic components. Polyurethane is frequently used in the adhesive industry due to its morphological structure, versatile material, and excellent matrix material. In addition, by doping polyurethane with single/multi-walled carbon nanotubes and boron nitride nanoplates materials, the mechanical properties of the polyurethane adhesive can be further increased. This study aimed to increase the mechanical properties of PU (thermoset polyurethane), which is frequently used in adhesively bonded joints by addition of MWCNT (multi-walled carbon nanotubes), BNNP (boron nitride nanoplates). For this purpose, nanoparticles synergistic interaction was investigated by adding a mass of 0.25%, 0.35%, and 0.45% MWCNT into PU, which was reinforced by 0.5% BNNP before. Samples mechanical properties were determined by tensile test according to ASTM D638-10 standard, flexure test according to ASTM D790-02 standard, and Shore D test according to ASTM D2240 standard. All sample test results were graphed, and each graph was compared. Also, broken surfaces were analyzed by scanning electron microscopy (SEM) to examine the damage mechanism of nanoparticles.

Ultra-high thermal conductivity of Mg-4Sm-2Al alloy by MWCNTs addition

The thermal conductivity of pure metals will be deteriorated by alloying and the composite is the inevitable choice to optimize the thermal conductivity of alloys surpassing pure metals. The Mg-based composites with ultra-high thermal conductivity surpassing pure Mg, optimized mechanical properties, and superior lightweight were achieved synergistically by the Multiwalled carbon nanotubes (MWCNTs). The thermal conductivity of the Mg-4Sm-2Al (SA42) matrix composites dramatically surpassed pure Mg with 2 vol% MWCNTs. The yield strength, ultimate tensile strength, and elongation of the composites were ameliorated by introducing MWCNTs. The behaviors of the thermal conductivity and mechanical properties were investigated from thermal conductivity models and microstructures. The present findings shed lights on designing composites which thermal conductivity surpasses pure matrix and exhibits integrative structure–function.

Application of Thermally Fluorinated Multi-Wall Carbon Nanotubes as an Additive to an Li4Ti5O12 Lithium Ion Battery.

In this study, multi-walled carbon nanotubes (MWCNTs) were modified by thermal fluorination to improve dispersibility between MWCNTs and Li4Ti5O12 (LTO) and were used as additives to compensate for the disadvantages of LTO anode materials with low electronic conductivity. The degree of fluorination of the MWCNTs was controlled by modifying the reaction time at constant fluorination temperature; the clear structure and surface functional group changes in the MWCNTs due to the degree of fluorination were determined. In addition, the homogeneous dispersion in the LTO was improved due to the strong electronegativity of fluorine. The F-MWCNT conductive additive was shown to exhibit an excellent electrochemical performance as an anode for lithium ion batteries (LIBs). In particular, the optimized LTO with added fluorinated MWCNTs not only exhibited a high specific capacity of 104.8 mAh g-1 at 15.0 C but also maintained a capacity of ~116.8 mAh g-1 at a high rate of 10.0 C, showing a capacity almost 1.4 times higher than that of LTO with the addition of pristine MWCNTs and an improvement in the electrical conductivity. These results can be ascribed to the fact that the semi-ionic C-F bond of the fluorinated MWCNTs reacts with the Li metal during the charge/discharge process to form LiF, and the fluorinated MWCNTs are converted into MWCNTs to increase the conductivity due to the bridge effect of the conductive additive, carbon black, with LTO.

Tribocorrosion Performance of WC-12Co HVOF-Sprayed Coatings Reinforced with Carbon Nanotubes

WC-12Co HVOF-sprayed coatings (~400 µm in thickness) reinforced with multiwalled carbon nanotubes (MWCNTs), were deposited on a steel substrate. The aim of this work is to provide and analyze data from HVOF WC-12Co sprayed coatings, concerning the influence of the addition of MWCNTs on their tribocorrosion performance, in a 3.5% NaCl electrolyte. Electrochemical data (current density and corrosion potential from potentiodynamic polarization curves) and wear data (coefficients of friction, coating volume losses and wear constants) are reported for the coatings, with and without the addition of MWCNTs (labeled WCCNT and WCAS-RECEIVED, respectively), considering the synergistic effects of wear and corrosion coupling. Scanning electron microscopy (SEM) and profilometry are used to explain both the wear and corrosion mechanisms that account for each coating’s performance in this environment. During the tribocorrosion tests, similar wear constants, of the order of approximately 10−12 m3/Nm, were found for all samples, with an increase of ~20% due to the MWCNTs presence. However, for the coatings reinforced with MWCNTs, a remarkable increase in icorr, representing almost 3 times the icorr of the WCAS-RECEIVED coating, was determined. The above results illustrate the complex mechanisms that occur when these coatings are tested under tribocorrosion conditions, which give rise to concurrent interacting phenomena, involving both electrochemical and mechanical responses.

Effect of Multi-Walled Carbon Nanotube on the Microstructure, Physical and Mechanical Properties of ZrO2–CaO/Poly(methyl methacrylate) Biocomposite for Bone Reconstruction Application

After bone implant, short-term complications can lead to a complicated approach to recovery, requiring surgical correction associated with additive risks, such as deep infection and double fracture. The development of synthesized biomaterials for bone replacement or repair, as well as the prevalence of osteoporosis, bone fracture, and bone cancer, is therefore of significant importance. This work aims to demonstrate the effect of adding multi-walled carbon nanotube (MWCNTs) to the (PMMA/ZrO2–CaO) bio-composites to fabricate a new hybrid biocomposite system for bone recovery and replacement applications. Four groups of composite samples were produced PMMA/(0, 5, 10, 15, 20)% weights of ZrO2–CaO and adding (0, .1, 0.25, 0.5, 1)% weights of (MWCNTs) to each group. X-ray powder diffraction (XRD), surface topography by field emission scanning electron microscopy (FE-SEM), and fracture strength tests were performed to evaluate the samples’ properties. A number of the most significant characteristics obtained through XRD exhibited a high degree of homogeneous mixing of the composites. In the examination, smooth peaks were obtained and the homogeneous distribution resulted in phase stability. A FE-SEM analysis demonstrated the presence of fibrous structures following the addition of MWCNTs, indicating that this approach would promote adhesion and healing of the tissue, as well as a fibrous arrangement that mimics that of natural bone. The results also showed improvements in mechanical properties by approximately 57%, 38%, 45%, and 6.5% due to the addition of MWCNTs compared to the version sample. Based on the experimental results, the study highlights the potential of these composites in bone reconstruction applications.

Multilayered Composites with Carbon Nanotubes for Electromagnetic Shielding Application.

Bulk polylactic acid (PLA)/multiwall carbon nanotube (MWCNT) composites were prepared and investigated in wide frequency ranges (20 Hz-1 MHz and 24-40 GHz). It was determined that the percolation threshold in bulk PLA/MWCNT composites is close to 0.2 vol.% MWCNT. However, the best microwave dielectric properties and absorption were observed in composites with 3.0-5.0 vol.% MWCNT. Therefore, for future investigations, we selected layered (laminate) polymeric structures with gradual changes in MWCNT concentration from 0.2 to 8.0 vol.% MWCNT. Two approaches to laminate structure designs were examined and compared: a five-layer composite and a nine-layer composite that included four pure PLA middle layers. The addition of MWCNT enhanced the elastic modulus by up to 1.4-fold and tensile strength by up to 1.2-fold, with the best performance achieved at 5.0 vol.% loading. High microwave shielding was observed for these layered PLA/MWCNT structures with a gradient change in MWCNT concentration (up to 26 dB in both transmission and absorption coefficients) in the broad frequency range (from 24 to 40 GHz). Obtained structures are highly anisotropic, and the absorption coefficient is 2-5 dB higher in the direction of MWCNT concentration increase; however, the transmission coefficient is the same in both directions. The properties of microwave absorption are mainly unaffected by the additional polymeric layers. The absorption of the layered structure is greater than the absorption of single-layer composites with an optimal MWCNT concentration of the same thickness. The proposed laminate structure design is promising in the field of efficient electromagnetic shielding.

Ultrasound assisted lignin-decorated MWCNT doped flexible PVA–Chitosan composite hydrogel

This study reports a facile ultrasound-assisted synthesis and characterization of physically-crosslinked polyvinyl alcohol (PVA)-chitosan conductive hydrogels with lignin-decorated multi-walled carbon nanotube (MWCNT) as nanofiller. Homogeneous dispersion of MWCNT in the hydrogel matrix was achieved through the addition of lignin nanoparticles (optimum LP:MWCNT ratio of 2:1) in presence of acetone, followed by sonication of the mixture. FETEM images reveal lignin particles adhere onto the surface of the MWCNT, which assists de-agglomeration and dispersion of MWCNT in the aqueous medium. The hydrogels produced were mechanically stable and flexible in nature. The elastic moduli (G′) of hydrogels with 0.5 and 1 wt% MWCNT were 11170 and 11757 Pa, respectively, whereas the tensile strengths were 2.22 and 2.56 MPa. Further, addition of lignin (1 and 2 wt%) and MWCNT (0.5 and 1 wt%) imparted thermal stability to PVACS hydrogels. FESEM images confirmed the porous internal structure of the hydrogel with mesh size ∼7 nm for 1 wt% MWCNT content. The hydrogel with 1 wt% MWCNT possessed the highest conductivity (8.22 mS cm−1) among all the other hydrogels. These hydrogels have potential applications as electrodes or electrolytes for energy storage devices, ECG electrodes, and flexible sensors.

Improving a solar collector's efficiency by selecting the composition of the working fluid used

Abstract The study's purpose was to determine the efficiency, as well as the energy and exergy analysis of the vacuum tube solar collector when using a mixture of water with Fe3O4 nanoparticles and multiwall carbon nanotubes in the selected percentage ratio as the working fluid. By varying the concentration of Fe3O4 nanoparticles in the working fluid from 0.05 to 0.15 wt.%, it was found that the maximum efficiency is achieved at a Fe3O4 content equal to 0.1 wt.%. At this concentration, the ratio of Fe3O4 and multiwall carbon nanotubes in the mixture varied from 4:1 to 1:4. It was found that the Fe3O4/multiwall carbon nanotubes ratio (1:4) can increase the efficiency of the solar collector up to 84%. Exergy analysis performed showed that water without the addition of nanoparticles Fe3O4 and multiwall carbon nanotubes was characterized by the maximum values of exergy destruction and entropy generation at any level of solar radiation, and water with the addition of nanoparticles Fe3O4/multiwall carbon nanotubes in a ratio of 1:4 was characterized by the minimum values of exergy destruction and entropy generation.

MWCNTs polymer nanocomposite with enhanced thermomechanical properties and electrical insulation for effective encapsulation

This study presents the effect of the variation in weight fraction of multiwall carbon nanotubes (MWCNTs) in polymer with the objective of enhancing the thermo-mechanical properties along with the electrical insulating properties. Polymer multi-walled nanocomposites (PMWCNC) and MWCNTs/Al2O3 bi-layer nanocomposites were prepared by solution mixing method with ultrasonication and magnetic stirring, then molded in vertical sandwich molds, made of acrylic and aluminum sheet as per ASTM standards. The tensile strength of PMWCNC was enhanced by 32%, 23%, 15%, and 5% compared to unmodified epoxy with the incorporation of 1 wt%, 0.75 wt%, 0.5 wt%, and 0.25 wt% of MWCNTs. The dispersion morphology of MWCNTs in epoxy was observed with field emission-scanning electron microscope (FE-SEM). The thermogravimetric analyzer (TGA) investigation found that increasing the weight percentage of MWCNTs resulted in improved thermal stability. The enhanced electrical conductivity of PMWCNC caused by the addition of MWCNTs was countered through the deposition of a thin film layer of alumina-filled polymer nanocomposite on the top surface of PMWCNC to retain the electrical insulation properties. The representative volume element (RVE) technique was employed to predict the effective modulus of nanocomposite based on the various constituent properties, weight fractions and interfacial behavior between MWCNTs and epoxy with the help of finite element analysis. Additionally, Modified Mori-Tanaka (MMT) micromechanics scheme was used to find the effective elastic modulus of the nanocomposite with the help of the MATLAB code. The elastoplastic behavior of polymer nanocomposites was also simulated in ANSYS APDL through the Voce model. The enhanced thermomechanical properties while retaining the electrical insulation properties suggest that the MWCNTs-based polymer would make the electronic chip more reliable.

Can additive carbon nanotubes reduce the PMMA fire risk?

The flammability and melt dripping illustrate polymer's fire risk. The high-efficiency thermal shielding effect of carbon nanotubes has been widely concerned to improve polymer's flame retardancy. However, the high thermal conductivity and wick effect of carbon nanotubes may enhance heat and mass transfer to promote fire development. A series of experiments about ignition, heat release, horizontal flame spread and dripping behaviors were carried out to comprehensively analyze the fire risk of polymer composite including polymethyl methacrylate (PMMA) and multi-walled carbon nanotubes (MWCNTs). The results showed after the addition of MWCNTs, the limiting oxygen index (LOI) increased from 18% to 20%, the peak of heat release rate (PHRR) decreased from 548 kW/m2 to 372 kW/m2, and the flame spread rate (FSR) increased from 0.28 mm/s to 1.1 mm/s, respectively. These results indicate that MWCNTs decreased the ignition risk of PMMA and its heat generation, however, the fire growth rate increased sharply. That was due to the thermal shielding effect and the heat and mass transfer effect of the char layer, respectively. Therefore, the effects of MWCNTs addition on the fire risk of polymer composites need a comprehensive assessment of multiple factors including the fire growth risk.

Development and Characterization of a Sustainable Bio-Polymer Concrete with a Low Carbon Footprint.

Polymer concrete (PC) has been used to replace cement concrete when harsh service conditions exist. Polymers have a high carbon footprint when considering their life cycle analysis, and with increased climate change concerns and the need to reduce greenhouse gas emission, bio-based polymers could be used as a sustainable alternative binder to produce PC. This paper examines the development and characterization of a novel bio-polymer concrete (BPC) using bio-based polyurethane used as the binder in lieu of cement, modified with benzoic acid and carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs). The mechanical performance, durability, microstructure, and chemical properties of BPC are investigated. Moreover, the effect of the addition of benzoic acid and MWCNTs on the properties of BPC is studied. The new BPC shows relatively low density, appreciable compressive strength between 20-30 MPa, good tensile strength of 4 MPa, and excellent durability resistance against aggressive environments. The new BPC has a low carbon footprint, 50% lower than ordinary Portland cement concrete, and can provide a sustainable concrete alternative in infrastructural applications.