Effects of multi-walled carbon nanotubes on thehydration heat properties of cement composites

In recent years, there has been an increasing demand for electromagnetic interference (EMI) shielding with the development of advanced electronic devices and communication instruments because high-frequency microwaves generate undesired noise, which can affect the proper operation of commercial, military, and scientific electronic devices as well as the health of our human body. In this study, we investigated the effect of multiwalled carbon nanotube (MWCNT) addition to the Fe-Si-Al alloy (Sendust)/polymer blend on the electromagnetic wave absorption and electromagnetic interference (EMI) shielding. Ternary composites (flaky Fe-Si-Al alloy (Sendust)/MWCNTs/polymer) were fabricated using a twin-screw internal mixer and a roll-milling machine. The flaky Sendust alloy particles were well oriented in the roll-milling direction at a thickness of 1 mm, and MWCNTs were also well dispersed. The addition of MWCNTs increases the dielectric loss of the composite by increasing the interfacial polarizations and dipolar polarizations and generating conductive paths. The reflection loss reached -17 dB at 4.5 GHz with 5 wt % MWCNT addition, but the power loss in the near field rises more rapidly with MWCNT addition. The absorption efficiency of the ternary composite (Sendust/MWCNTs/polymer) was significantly increased compared to the binary composite (Sendust/polymer) due to dielectric property enhancement by MWCNT addition. The total shielding effectiveness (SE) value increased with the amount of MWCNT. The ternary hybrid composites are light but exhibit a high SE in a wide frequency range. Thus, they are appropriate for the production of light and thin-film materials that are suitable for electromagnetic wave absorption and EMI shielding.

This paper studies the effects of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and durability of polymer latex-modified cement mortar. Latex-modified cementitious materials possess many advantages. However, reduction of mechanical properties due to the introduction of an amorphous structure within the cement composite has limited its application. In this study, multi-walled carbon nanotubes functionalised with carboxyl group (MWCNTs-COOH), ranging from 0% to 0.15% by weight, are added into mortar modified with 0.6 wt.% polyvinyl alcohol (PVA) latex. Mechanical properties including compressive strength and flexural strength are measured. Water absorption test and rapid chloride diffusion test are performed to assess durability performance. Results indicate considerable increase of compressive strength and flexural strength, as well as improvement in durability, by the addition of MWCNTs-COOH. With Scanning Electron Microscopy conducted on both the latex solution and cement composite, the microstructural changes resulted from MWCNT addition are revealed.

Hydrate formation is an important technology for gas storage and transportation. In this work, the effect of multiwalled carbon nanotubes (MWCNTs) on CH4 hydrate formation was examined by determining the phase equilibrium conditions and kinetics characteristics of a mixed system of CH4, tetra-n-butyl ammonium bromide (TBAB), and MWCNTs. The phase equilibrium was examined in the temperature range of 286.13–293.04 K and the pressure range of 0.55–6.56 MPa for various mass fractions of MWCNTs (0.004, 0.1, 0.5, and 1.0 wt%). In the CH4 + TBAB system, the presence of MWCNTs was found to shift the phase equilibrium conditions to a lower temperature by about 1 K compared with those in the absence of MWCNTs. However, the concentration of MWCNTs had little effect on the phase equilibrium conditions. When the concentration of MWCNTs was 1.0 wt%, the addition of MWCNTs reduced the induction time of hydrate formation by 79.5%. When the concentration of MWCNTs was 0.1 wt%, the addition of MWCNTs enhanced the hydrate growth rate by 61.5%. Powder X-ray diffraction patterns revealed that hydrates with orthorhombic structures (corresponding to TBAB·38H2O with 3D cages) were formed in the systems with and without MWCNTs. Moreover, peaks corresponding to MWCNTs were not observed in the patterns of the hydrates and the addition of MWCNTs had no influence on the structure and type of hydrate. Thus, MWCNTs were not incorporated into the hydrate cages.

The effect of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and microstructure of sulfur aluminate cement (SAC) composites was investigated. The dispersed MWCNTs were added into SAC in various weight contents.The results of mechanical properties of the MWCNTs/SAC composites indicated that the addition of 0.08 wt% MWCNTs can improve the SAC compressive strength, flexural strength, and bend-press ratio by 15.54%, 52.38%, and 31.30% at maximum, respectively. The degree of SAC hydration and porosity and pore size distribution of the matrix were measured by X-ray diffraction (XRD), thermal analysis (TG/DTG), and mercury intrusion porosimetry (MIP). Results show that the addition of MWCNTs in SAC composites can promote the hydration of SAC and the formation of C-S-H gel, reduce the porosity and refine the pore size distribution of the matrix. The microstructure was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the MWCNTs have been dispersed homogeneously between the hydration products of SAC paste and act as bridges and networks between cracks and voids, which prevents the development of the cracks and transfers the load.

Introduction: Concrete's filler material gets strengthened over time by specific chemical reactions that harden it. Multi-walled carbon nanotubes (MWCNTs) are more frequently used as fillers than SWCNTs, owing to their lower cost of production and their superior reinforcement properties in cement composites. Methods: Mechanical properties like compressive strength, splitting tensile strength, and modulus of elasticity are proportional to the water/cement ratio (w/c) and are considered critical criteria in the design of structural elements. Results: The aim of the present work was to prepare, characterize, and determine the effects that multi-walled carbon nanotubes (MWCNTs) can have on the mechanical strength of various matrix cementitious composites. Conclusion: The results showed that the addition of multi-walled carbon nanotubes to the concrete greatly improved both its compressive strength and its splitting tensile strength.

Effects of multi-walled carbon nanotubes (MWNTs) on flame retardation as well as thermal stabilization efficiency of two phosphorus-containing flame retardant systems i.e., ammonium polyphosphate/pentaerythritol (APP/PER) and red phosphorus (RP) in polypropylene (PP) have been investigated. Limiting oxygen index, thermo-gravimetric analysis, melt flow index, and tensile tests have been performed in this study. Moreover, the structure of the nanocomposites was characterized by scanning electron microscopy (SEM). SEM images revealed good dispersion of fillers in the polymer matrix. Furthermore, it was shown that the addition of MWNTs alone at a minimum loading level of 4 wt% improves thermal stability of PP considerably without any undesirable effect on its flow-ability and mechanical properties. Moreover, addition of MWNTs alone resulted in a slight improvement of flammability of the polymer. However, comparison between thermal stability and flame retardancy of PP samples containing a combination of MWNTs and APP/PER or RP and those of the samples containing APP/PER or RP alone proved that MWNTs interfere with thermal stabilization and flame retardation efficiency of both APP/PER and RP in the polymer.

When nanoparticle and microbes meet: The effect of multi-walled carbon nanotubes on microbial community and nutrient cycling in hyperaccumulator system

Effect of multi-walled carbon nanotubes on linear viscoelastic behavior and microstructure of zwitterionic wormlike micelle at high temperature

ABSTRACTThe present experimental investigation focuses on the combined effects of multiwalled carbon nanotubes (MWCNTs) and exhaust gas recirculation (EGR) of a diesel engine fuelled with Calophyllum inophyllum biodiesel blends. The C. inophyllum biodiesel-diesel blend was prepared in a proportion of 20% biodiesel and 80% diesel (B20) by a volumetric basis with a magnetic stirrer. The MWCNTs (in the mass fraction of 40 ppm) were dispersed into the B20 fuel with the help of an ultrasonicator. The results show that brake thermal efficiency increases by 7.6% with the addition of MWCNTs to the B20 fuel, decreases by 2.42% with the EGR to the B20 fuel, and increases by 2.26% with the addition of MWCNTs and EGR to the B20 fuel compared to the B20 fuel. The maximum cylinder pressure and heat release rate was occurred as 67.35 bar and 74.80 kJ/m3 deg for the B20MWCNT40 fuel at full load condition. The CO and HC emissions for the B20MWCNT40+20%EGR fuel sample were lower compared to the B20 fuel. The Smoke emissions were reduced for B20MWCNT40 fuel compared to the B20 fuel. The NOx emissions were reduced by 25.6%, 29.7% for B20+20%EGR, B20MWCNT40+20%EGR fuel samples compared to the B20 fuel.

A series of chitosan (CS)/multi-walled carbon nanotubes (MWCNTs) composite hydrogel beads with different MWCNTs contents are prepared via a solution blending method. The effects of MWCNTs on the morphology, structure and properties of chitosan beads have been investigated. Digital pictures show that the composite beads obtained are of good morphological characteristics, and the SEM micrographs indicate that the addition of MWCNTs into CS beads made the surface of the CS/MWCNTs hydrogel beads contain much larger wrinkles. Fourier transform infrared spectra (FTIR) show that the main chain of CS bead is not changed, but there are some electrostatic interactions between CS and MWCNTs, which lead to very significant changes in the crystallization behavior of CS and MWCNTs. The thermal stability of CS/MWCNTs composites at high temperatures is increased with the existence of MWCNTs, indicating a possible electrostatic interaction between MWCNTs and CS lattices to limit the motivation of CS. The adsorption capacity of CS beads doped with a lower percentage of MWCNTs (0.02 wt%) for acid fuchsin is 112.76 mg/g, higher than that of pure CS beads (35.62 mg/g).

Effect of multi-walled carbon nanotubes (MWCNTs) on the strength development of cementitious materials

Incorporating multi wall carbon nanotube (MWCNT) into the polymer can improve the electrical properties of the nanocomposites. The effects of MWCNT on the electrical and rheological properties of polypropylene/MWCNT (PP/MWCNT) nanocomposites are investigated. The nanocomposites were prepared using melt mixing technique at chamber temperature of 180°C and rotor rotation of 100 rpm for 10 minutes. Addition of MWCNT increases the electrical surface conductivity up to 10 −7 S. The electrical percolation threshold of the nanocomposites is found to occur at 1.3 wt% MWCNT content. Viscosity of the nanocomposites increased with the addition of MWCNT. The rheological percolation threshold of the PP/MWCNT is found occur at 1.4 wt% MWCNT content. Well dispersion is observed by mean Scanning Electron Microscope (SEM) analysis.

In this paper, nanocomposites based on polypropylene (PP) filled with up to 5 wt.% of multi-walled carbon nanotubes (MWCNTs) were investigated for determining the material property data used in numerical simulation of manufacturing processes such as the injection molding and extrusion. PP/MWCNT nanocomposite pellets were characterized for rheological behavior, crystallinity, specific volume and thermal conductivity, while injection-molded samples were characterized for mechanical and electrical properties. The addition of MWCNTs does not significantly change the melting and crystallization behavior of the PP/MWCNT nanocomposites. The effect of MWCNTs on melt shear viscosity is more pronounced at low shear rates and MWCNT loadings of 1–5 wt.%. However, with the addition of up to 5 wt.% of MWCNTs, the PP/MWCNT nanocomposite still behaves like a non-Newtonian fluid. The specific volume of the PP/MWCNT nanocomposites decreases with increasing MWCNT loading, especially in the MWCNT range of 1–5 wt.%, indicating better dimensional stability. The thermal conductivity, depending on the pressure, MWCNT wt.% and temperature, did not exceed 0.35 W/m·K. The PP/MWCNT nanocomposite is electrical non-conductive up to 3 wt.%, whereas after the percolating path is created, the nanocomposite with 5 wt.% becomes semi-conductive with an electrical conductivity of 10−1 S/m. The tensile modulus, tensile strength and stress at break increase with increasing MWCNT loading, whereas the elongation at break significantly decreases with increasing MWCNT loading. The Cross and modified 2-domain Tait models are suitable for predicting the melt shear viscosity and specific volume as a function of MWCNTs, respectively. These results enable users to integrate the PP/MWCNT nanocomposites into computer aided engineering analysis.

This work reports the effect of multiwalled carbon nanotubes on mixed-mode I/II interlaminar fracture toughness ([Formula: see text]) of unidirectional carbon fiber/epoxy composite laminates made by prepregs. The carbon fiber/epoxy laminates were fabricated in an autoclave with a previous deposition of different multiwalled carbon nanotube contents at their middle plane interface by spraying technique. Mixed-mode bending tests were conducted on carbon fiber/epoxy laminate specimens under different mixed-mode ratios. The results of mixed-mode bending tests showed that the addition of multiwalled carbon nanotubes can effectively improve the [Formula: see text] of carbon fiber/epoxy laminates. With a 0.2 wt.% multiwalled carbon nanotubes content in carbon fiber/epoxy laminates, the [Formula: see text] under mixed-mode ratios of 0.2, 0.5 and 0.8 increased by 25%, 12% and 19%, respectively. These results were explained in terms of the damage mechanisms observed at the fracture surfaces of tested specimens by scanning electron microscopy.

The effect of simultaneous addition of multiwall carbon nanotubes (MWNTs) and a reactive compatibilizer (styrene maleic anhydride copolymer, SMA) during melt‐mixing on the phase morphology of 80/20 (wt/wt) PA6/ABS blend has been investigated. Morphological analysis through scanning and transmission electron microscopic analysis revealed finer morphology of the blends in presence of SMA + MWNTs. Fourier transform infrared spectroscopic analysis indicated the formation of imide bonds during melt‐mixing. Non‐isothermal crystallization studies exhibited the presence of a majority faction of MWNTs in the PA6 phase of 80/20 (wt/wt) PA6/ABS blend in presence of SMA + MWNTs. Rheological analysis, dynamic mechanical thermal analysis, and thermogravimetric analysis have demonstrated the compatibilization action of simultaneous addition of a reactive compatibilizer (SMA copolymer) and MWNTs in PA6/ABS blends. An attempt has been made to investigate the role of simultaneous addition of SMA copolymer and MWNTs on the morphology of 80/20 (wt/wt) PA6/ABS blend through various characterization techniques. POLYM. ENG. SCI., 55:457–465, 2015. © 2014 Society of Plastics Engineers