Distribution Of Multi-walled Carbon Nanotubes Research Articles

Multi-Walled Carbon Nanotubes Improve the Development of Chrysanthemum × morifolium (Ramat.) Hemsl. ‘Jinba’ Inflorescences

The application of cut flower preservation technology can significantly enhance both the ornamental and economic value of fresh-cut flowers. Research on vase solutions has become a concentrated area in current studies on cut flower preservation. Multi-walled carbon nanotubes (MWCNTs), as a type of carbon nanomaterial with bactericidal and membrane-penetrating properties, can be used as a component in vase solutions. This supplementation of energy substances aims to improve antioxidant enzyme activity, thereby enhancing the postharvest quality of cut chrysanthemums. In this study, deionized water and a standard preservative solution were employed as control groups to compare the effects of MWCNTs applied at different concentrations, combined with common preservatives such as sugar and 8-hydroxyquinoline, on the postharvest flowering and preservation of Chrysanthemum × morifolium ‘Jinba’. By observing the distribution of MWCNTs in the tissues surrounding the cut and changes in water content, carbon sources, osmoregulatory substance levels, and the expression of relevant key genes, a formulation with excellent postharvest treatment effects was identified. Preliminary investigations into its action and mechanism were also conducted. The results indicated that the combined treatment with 5 mg L−1 MWCNTs, 30 g L−1 sucrose, and 0.2 g L−1 8-hydroxyquinoline effectively promoted water and sugar uptake in chrysanthemum flowers, accelerating bud opening, maintaining larger inflorescence diameter, and extending the vase life. Ultimately, this enhanced the ornamental value of cut chrysanthemums. These research findings provide theoretical and experimental foundations for the application of multi-walled carbon nanotubes as auxiliary additives to improve the ornamental quality of cut flowers.

Effects of PVA fibers and multi-walled carbon nanotubes reinforcement on uniaxial compression fatigue properties of Engineered geopolymer composites

As a new type of green and environmentally friendly cementing material, engineered geopolymer composites (EGC) have broad application prospects. In this study, uniaxial compression fatigue tests were conducted to investigate the fatigue properties of geopolymer material. A total of 137 samples were tested to investigate the effects of carbon nanotubes content, polyvinyl alcohol (PVA) fibers volume content, and maximum stress level on the fatigue life and deformation of geopolymers. The results showed that the fatigue life of geopolymers obeys Weibull distribution, and PVA fibers and multi-walled carbon nanotubes (MWCNTs) achieved multiscale enhancement of the fatigue life by up to 16.34 times. The total strain accumulation, residual strain, and fatigue stiffness of the geopolymers under fatigue loading exhibited a three-stage evolution rule, with stability within the secondary creep branch. In the process of EGC production, the innovative adoption of optimized MWCNTs surface modification and dispersion strategies improved the uniformity of MWCNTs distribution in the matrix. Scanning electron microscopy (SEM) confirmed the hybridization of MWCNTs and PVA fibers at the microscopic level, which can achieve multi-scale enhancement of geopolymers. This study successfully optimized the content of MWCNTs and PVA fibers, further expanding the application range of composite materials.

BIOCOMPATIBLE ELASTIC POLYMER NANOCOMPOSITES BASED ON MULTIWALLED CARBON NANOTUBES FOR APPLICATION IN CARDIOVASCULAR SURGERY

HighlightsThe incorporation of multi-walled carbon nanotubes into the structure of the poly(styrene-block-isobutylene-block-styrene) polymer matrix leads to an increase in the tensile strength and Young's modulus of the nanocomposites. The resulting nanocomposites retain high biocompatibility and can be used as elements of implanted cardiovascular products. AbstractAim. To synthesize and modify poly(styrene-block-isobutylene-block-styrene) (SIBS) with two types of multi-walled carbon nanotubes (MWCNTs) in different concentrations to improve its mechanical properties.Methods. SIBS was synthesized by controlled cationic polymerization. Polymer nanocomposites were prepared using ultrasonic dispersion followed by casting films from a polymer solution. The resulting nanocomposite films were subjected to mechanical tests under uniaxial tensile conditions. Tensile strength, elastic-strain properties, and plastic deformation under cyclic loading were assessed. The structure of the nanocomposites was analyzed by scanning electron microscopy. The hydrophilicity of the surface of the materials was studied by measuring the contact angle with water. The cytotoxicity of the resulting polymer films was assessed by the viability and metabolic activity of endothelial cells cultured on the surface of the nanocomposites.Results. Polymer nanocomposites with a uniform distribution of MWCNTs in the polymer matrix were obtained. SIBS films modified with 1% MWCNTs with a diameter of 50–90 nm showed an increase in tensile strength by 16.4% compared to SIBS polymer. Increasing the concentration of MWCNTs to 8% led to a decrease in the strength of polymer materials by 19,6%. The inclusion of nanoparticles into the polymer matrix significantly increased the Young's modulus of the studied polymers with a MWCNT content above 4%. With an increase in the content of MWCNTs in the nanocomposites, an increase in hydrophilicity was also observed, while the cytotoxicity of the samples towards endothelial cells was not noted.Conclusion. Nanocomposites based on SIBS and MWCNTs, due to their high strength and biocompatibility, can become a promising material for the development of various medical products, in particular prosthetic heart valves.

Improved Heat Dissipation of NR/SBR-Based Tire Tread Compounds via Hybrid Fillers of Multi-Walled Carbon Nanotube and Carbon Black.

The development of thermally conductive rubber nanocomposites for heat management poses a formidable challenge in numerous applications, notably within the realm of tire technology. Notably, rubber materials are characterized by their inherently low thermal conductivity. Consequently, it becomes imperative to incorporate diverse conductive fillers to mitigate the propensity for heat build-up. Multi-walled carbon nanotubes (MWCNTs), as reinforcement agents within the tire tread compounds, have gained considerable attention owing to their extraordinary attributes. The attainment of high-performance rubber nanocomposites hinges significantly on the uniform distribution of MWCNT. This study presents the influence of MWCNTs on the performance of carbon black (CB)-reinforced natural rubber (NR)/styrene butadiene rubber (SBR) tire compounds prepared via high shear melt mixing. Morphological analysis showed a good distribution of MWCNTs in the NR/SBR/CB compound. The vulcanization parameters, such as the maximum and minimum torque, cross-linking density, hardness, abrasion resistance, tensile strength, and Young modulus, exhibited a progressive improvement with the addition of MWCNT. Remarkably, adding MWCNT into CB improved the heat conductivity of the NR/SBR/CB compounds, hence decreasing the heat build-up. A percolation mode was also proposed for the hybrid carbon fillers based on the data obtained.

Influence of multi-walled carbon nanotubes on the solidification process of an Al-12 %Si alloy

This paper investigates the influence of multi-walled carbon nanotubes (MWCNT) on the solidification process of an Al-12 %Si alloy. Amulti-phase Eulerian model of solidification is deployed to numerically handle the problem. The simulation determines the cooling curve and addresses the recalescence phenomena along with the estimation of the columnar and globular solid phases;precipitating silicon (PSP) phase and MWCNT phase distributions. The findings reveal that MWCNT significantly affects the cooling rate, leading to multiple recalescence phenomena, and influences the formation and evolution of the columnar and globular grains. MWCNT also impacts silicon segregation, causing fluctuations in silicon phases and redistribution. Furthermore, the study explores the distribution of MWCNT throughout the material and identifies a critical time period for their influence. Overall, the study enhances our understanding of the complex dynamics within the solidification process and provides insights into the role of MWCNT in shaping the microstructure through a mathematical model.

Electromagnetic interference shielding composites and the foams with gradient structure obtained by selective distribution of MWCNTs into hard domains of thermoplastic polyurethane

In this paper, multilayer thermoplastic polyurethane (TPU)/multiwalled carbon nanotubes (MWCNTs) electromagnetic interference shielding composite foams with gradient structure was prepared. The gradient distribution of effective concentration of filler and cell size were realized by selective distribution of MWCNTs into hard domains of TPU, which improved interlayer interface polarization of electromagnetic waves and impedance matching between the material and the air. The average electromagnetic interference shielding efficiency (EMI SE) of TPU/MWCNTs composites with gradient structure is 1.2 times larger than that of homogeneous composites. After foaming, the average EMI SE of the gradient foams was higher than that of the homogeneous foams, with maximum average EMI SE of 35.4 dB. This work is the first time to correlate the interaction of fillers with the soft domains and hard domains of TPU and EMI shielding performance, providing a feasible method for designing lightweight composites with low filler and better EMI shielding performance.

Origin of non-universal percolation/scaling and universal non-Debye relaxation in PVDF/MWCNT polymer nanocomposites

Polymer Nanocomposites (PNC) comprising polyvinylidene fluoride (PVDF)/Multi-walled Carbon Nanotubes (MWCNT) were studied. The structural composition and thermal stability were confirmed from XRD and DSC/TGA data, respectively. The extent of distribution of MWCNT in the PNC increases and the clustering of MWCNT also increases with an increase in the volume fraction of MWCNT ([Formula: see text], as confirmed by FESEM. The PNC shows an insulator-to-metal transition (IMT), with both non-universal percolation threshold [Formula: see text] of [Formula: see text] and scaling exponents [Formula: see text], respectively, attributed to adhesiveness/cold pressing and the higher aspect ratio/conductivity of MWCNT. Modulus spectroscopy confirms a non-Debye type universal relaxation behavior [Formula: see text] only for the percolative sample due to Maxwell–Wagner–Sillars/interfacial polarization, while only dipolar relaxation was probed or the samples below [Formula: see text]. The [Formula: see text] with static effective dielectric constant [Formula: see text] and low tan [Formula: see text] may be suitable for charge storage applications.

Free-standing polymer/multiwalled carbon nanotubes composite thin films for high thermal conductivity and prominent EMI shielding

Lightweight composite materials with efficient thermal conductivity (TC) and high electromagnetic interference (EMI) shielding effectiveness (SE) are of paramount importance for a wide range of applications such as electronics, aerospace, and stealth technology. In this work, lightweight, flexible, and free-standing poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/multiwalled carbon nanotube (MWCNT) composite thin films are fabricated by a single-step, solution casting method. Fabricated PVDF-HFP/MWCNT composite thin films are characterized by many physicochemical techniques such as Raman spectra, Fourier transform infrared spectra, X-ray diffractometer, and high-resolution transmission electron microscope. The resulting composite thin film exhibits a TC of 1.1 Wm−1K−1 at room temperature. Further analysis shows that the TC of the composite film is increased up to 1.8 Wm−1K−1 at 100 °C. As fabricated flexible and free-standing composite thin film (thickness ∼ 150 µm) exhibit an excellent EMI SE of ∼ 36 dB in the X-band region (8.2–12.4 GHz) at just 15 wt. % loading of MWCNT. The outstanding EMI shielding and high TC of PVDF-HFP/MWCNT composite films are attributed to the homogenous distribution and well-connected network of MWCNT within the polymer matrix, forming a conductive network throughout the composite film.

Influence of MWCNTs additives on the thermal conductivity of HA–MWCNTs composite

Possible changes in the temperature dependence of the coefficient of thermal conductivity of the hydroxyapatite (HA) composite with multi-walled carbon nanotubes (MWCNTs) with small amounts of MWCNTs additives (0.5 wt%) were analyzed in comparison with the dependence of HA matrix without additives. It was found that MWCNTs can contribute to the increase of the thermal conductivity coefficient. The magnitude of the effect of increasing thermal conductivity varies from relatively small values (about 1%) to a significant increase up to ∼ 20 times that depending on the interaction at the HA–MWCNTs interface and the degree of homogeneity of the MWCNTs distribution in the HA matrix. It was found that long-term high-temperature annealing can lead to changes in the anisotropy, structure, and properties of MWCNTs due to oxidation effects, which can influence the resulting composite properties.

Multi-objective optimization of mechanical and microstructural characteristics in a stir casting process of MWCNTs/Al6082 composites using neutrosophic TOPSIS and GRA

ABSTRACT The objective of this paper is to find optimum process parameters of stir casting process for multi-walled carbon nanotubes (MWCNTs) reinforced Al6082 composites in a multi-objective optimization context. In this work, output parameters include ultimate tensile strength (UTS), hardness, compressive strength (CS), and uniform distribution of MWCNTs. Among these, first three parameters can be measured, and data can be obtained in quantitative terms. However, uniformity of distribution of MWCNT is a qualitative variable, and hence neutrosophic sets are used in this work. Each of the four input process parameters, such as fraction weight of MWCNTs, stirring speed, furnace temperature, and stirring time, are taken at three levels each, and experiments are designed using Taguchi L27 array. Information entropy method is used to compute the weights of output parameters. TOPSIS method is used to normalize the quantitative data, and neutrosophic TOPSIS is applied for normalizing the data related to uniformity. It is found that MWCNT’s percentage of 0.9, speed of 450 rpm, temperature of 800°C, and time of 10 minutes, yield best output parameters. Neutrosophic gray relational analysis is also used to find optimum solution for above case, and the optimum values obtained from both methods are compared.

Highly Conductive Flexible Conductor Based on PEDOT:PSS/MWCNTs Nano Composite

Flexible textiles with strong electrical conductivities have enormous potential as active components in wearable electronics. In this study, we fabricated highly flexible electrical conductors based on cotton fabrics using multiwalled carbon nanotubes (MWCNTs) and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) nanocomposites. We propose that mixing and drop-casting with different amounts of MWCNTs and a fixed amount of doped PEDOT:PSS using a cotton fabric provides a wide range of conductivities depending on the amount of MWCNTs in the mixture. Scanning electron microscopy (SEM) confirmed that the distribution of MWCNTs in the PEDOT:PSS films coated the surface of the cotton fabric, thereby increasing its electrical conductivity. We found that the amount of MWCNTs significantly affected the electrical properties of the nanocomposite cotton in two ways. First, the sheet resistance of the nanocomposite cotton decreased from 78.35 Ω/□ to 2.86 Ω/□ when the concentration of the nanocomposite was increased from 9.21 wt% to 60.27 wt%. This implies that the electrical properties of the nanocomposite cotton can be adjusted by controlling the amount of MWCNTs in the blend. Moreover, we found that the relationship between the sheet resistance and nanocomposite concentration obeys the power law with an exponent α ~ 1.676. Second, the study of the effect of temperature on the resistance indicates that the conductive nanocomposite exhibits semiconductor behavior in the temperature range 24–120 °C and obeys the variable range hopping model. The characteristic temperatures, resistance prefactor, and density of localized states and activation energies depend on the concentration of MWCNTs and can be described by power laws with exponents of 0.470, −1.292, −0.470 and 0.118, respectively. The novel nanocomposite cotton fabric developed in this study exhibits suitable electrical and thermal properties and good long-term electrical stability, which make the nanocomposite cotton fabric a potential flexible conductor with a wide range of electrical conductivities, making it suitable for various applications.

An experimental study of spectral radiative properties of multi-walled carbon nanotube coating for heat dissipation

Thermal management serves a crucial role in the stable operation of electronic equipment due to its miniaturization and functionality. Enhancing radiation heat transfer through heat dissipation coating is an effective method to improve the heat dissipation performance of electronic devices in thermal management of narrow space. In this paper, we employed the high emissivity property of multi-walled carbon nanotubes to improve the radiative heat dissipation performance of the coating. The effect of the distribution of multi-walled carbon nanotubes on the emissivity of the coating was studied with the finite-difference time-domain method. The emissivity of the coating with random distribution of multi-walled carbon nanotubes was found to be greater than that of the coating with vertical distribution of multi-walled carbon nanotubes. In order to further investigate the radiative properties of randomly distributed multi-walled carbon nanotube coatings, we experimentally investigated the effect of coating thickness and multi-walled carbon nanotube mass fraction on the spectral radiative properties of the coatings. We obtained the relationships between coating thickness, carbon nanotube mass fraction and coating radiation power. The data can provide some guidance for the regulation of radiation power of heat dissipation coatings and the selection of common coating processes. The maximum average emissivity and radiation power of the multi-walled carbon nanotube coating is 0.97, and 491.6 W m−2, respectively.

Combination of enhanced strength-ductility trade-off and stress relaxation resistance of MWCNTs reinforced Sn–5Sb-0.3Cu matrix composite

In this study, the strength-ductility trade-off and stress relaxation (SR) behavior of Sn–5Sb-0.3Cu (SSC503) alloy reinforced with (0, 0.05and 0.1 wt%) multi-walled carbon nanotubes (MWCNT) have been investigated under different pre-strains and initial stress levels. The results show that the pre-deformation can extend the duration of initial SR stage and significantly promote the stress reduction rate. The SSC503–0.05MWCNT composite alloy exhibits the optimum increase in SR resistance, yield strength (σy), ductility, and creep threshold stresses with the values of 75.8%, 17.3%, 77.9% and 10.6%, respectively. The scanning transmission electron microscopy (STEM) images and electron probe microanalyzer (EPMA) revealed that the distribution of MWCNT in SSC503 alloy was concentration dependent. 0.05MWCNT concentration induced a dendritic/cellular transition of β-Sn grains and restrained the growth of β-Sn, Cu6Sn5, SnSb, Sn3Sb2 and Cu2Sb IMC compositions, whereas 0.1MWCNT led to the partial agglomeration of MWCNT into β-Sn grain surfaces. MWCNTs are adsorbed at the surface-active atoms of Sb metalloid to form Sb-coated MWCNTs (Sb/C) in situ, which act as a bridge between MWCNT and Cu6Sn5 particles. The modified composites represent a vital technological progress for utilization in high temperature solder applications.

Spatial distribution characteristics and microscopic mechanisms for enhancing mechanical properties of MWCNTs in recycled coarse aggregate shotcrete

This study aimed to investigate the spatial distribution characteristics of multi-walled carbon nanotubes (MWCNTs) in recycled coarse aggregate shotcrete (RCAS) and the influence of the dosage of MWCNTs on flow characteristic, mechanical properties and its microscopic mechanism. In this paper, 100% of natural coarse aggregate (NCA) was replaced by recycled coarse aggregate (RCA). Multiple nano-characterization techniques were adopted, and the wet-mix shotcrete technology and a combined device for variable addition of MWCNTs suspension were used. The experimental results showed that with the increase of the dosage of MWCNTs, the flow characteristic of RCAS in fresh state decreased. In terms of mechanical properties, the compressive strength, splitting tensile strength and flexural strength of RCAS all showed a trend of increasing first and then decreasing, when MWCNTs was 0.09 wt%, the flexural strength and splitting strength of RCAS reached the peak value. When the dosage of MWCNTs was 0.03 wt%, 0.06 wt% and 0.09 wt%, the quantity distribution of MWCNTs in the RCAS was average and centered. Appropriate dosage of MWCNTs (0.06 wt% or 0.09 wt%) had a positive effect on improving the compactness of interface transition zone (ITZ) of the RCA, optimizing the internal pore size distribution of RCAS, accelerating the hydration reaction rate and increasing the yield of hydration products.

Flexible and High-Performance Electromagnetic Shielding Materials from Waste Polyurethane Foams

In the modern society, polymer composites utilizing various wastes for electromagnetic interference (EMI) shielding are of great economic and social significance. Herein, we report that waste polyurethane foams (WPUF) can be facilely converted into high-performance EMI shielding materials via surface coating of carbon nanotubes followed by hot pressing. The merit of this work lies in the novel skin-core segregated structure from the complete three-dimensional skeleton of WPUF, which is well retained after compression molding. The uniform distribution of multiwalled carbon nanotubes (MWCNTs) on the polyurethane skeleton surface assisted by cellulose nanofibers (CNFs) provides the material with remarkable electrical conductivity, leading to excellent EMI shielding properties. The resultant composite (WPUF-MC) achieves a high EMI shielding effectiveness (SE) of 63.2 dB at a low loading of MWCNTs (6.6 wt %), far surpassing the values for many early reported shielding materials of this kind. Moreover, the WPUF-MC also exhibits sufficient flexibility and reliable EMI shielding performance. Even if bent or twisted 1000 times, it can still maintain EMI SE at a fairly high level. This work not only offers an effective strategy for high-value utilization of WPUF but also may expand the application potential of flexible shielding materials.

Harnessing the thermo-mechanical properties and toughness of MWCNT/TiO2 hybrid epoxy nanocomposites

One of the significant challenges of developing high-performance polymer nanocomposites is the best exploitation of the potential of nanofillers. In this study, the multi-walled carbon nanotubes (MWCNTs) are exfoliated by TiO2 nanoparticles using ultrasonic waves. The obtained MWCNT/TiO2 hybrid nanofiller, in different wt.%, is infused into an epoxy (EP) matrix using an ultrasonic dual mixing (UDM) technique to obtain multifunctional nanocomposites with enhanced thermo-mechanical properties and toughness. XRD crystallography, Raman spectroscopy, TEM analysis, TGA, DMA, tensile, and 3-P single edge notch bending tests are used to investigate the properties of the MWCNT/TiO2 hybrid nanofiller and resulting composites. Results reveal that the optimum loading of MWCNT/TiO2 hybrid nanofiller (1.0 wt.%) in EP matrix provides 23.5%, 39.8%, and 46.8% improvement in storage modulus, tensile strength, and fracture toughness, respectively, compared to those of neat EP. The FESEM images of the fractured surface of nanocomposite specimens confirm the cluster-free distribution of MWCNTs in the EP matrix ensuring enhanced thermo-mechanical properties and toughness.

Mechanical Properties of AA2024 Aluminum/MWCNTs Nanocomposites Produced Using Different Powder Metallurgy Methods

Metal matrix composites are a class of materials with high potential for industrial application due to the multifaceted properties that they possess. In the present research, mechanical alloying via ball milling was used to produce AA2024 powder that was subsequently reinforced with multiwalled carbon nanotubes (MWCNTs). Dispersion of the MWCNTs in the AA2024 matrix was achieved also by ball milling. Two different powder metallurgy sequencies, (i) double pressing double sintering and (ii) hot pressing were used for compaction and consolidation of the AA2024 reinforced by MWCNTs. The produced nanocomposites outperform the pristine AA2024 in terms of compressive strength, elongation to failure, and microhardness. The strengthening mechanism was associated with the homogeneous distribution of MWCNTs in the AA2024 matrix and their efficient interfacial bonding, which was attested also by microstructural characterization. Hot pressing resulted in higher mechanical properties of the nanocomposite material. However, when reinforcement content was above 2 wt.% a dramatic decrease of mechanical properties was observed, attributed to clustering and inhomogeneous dispersion of the MWCNTs. The homogeneous dispersion of MWCNTs in the AA2024 matrix and the retaining of their structural integrity are pivotal in increasing the mechanical properties, which can be directly associated with the efficient interfacial load transfer between MWCNTs and AA2024 matrix.

Microstructural evolution and mechanical properties of multiwalled carbon nanotubes/Al6082 nanocomposites through optimized T6 heat treatment process

A modified stir casting method was used to fabricate novel Al6082 composites reinforced with 0, 0.3, 0.6, 0.9, and 1.2 wt% of multiwalled carbon nanotubes (MWCNTs). A field emission scanning electron microscope was used to examine the microstructure, while elemental evaluation was performed with an energy dispersive X-ray spectrometer. MWCNTs/Al6082 composites were subjected to a heat treatment cycle (T6) to enhance their mechanical strength. Mechanical alloying and ultrasonication enhanced the wettability during fabrication resulting in the uniform distribution of MWCNTs up to 0.9 wt%. Ultimate tensile strength, yield strength, and hardness of 0.9 wt% MWCNTs/Al6082 nanocomposites were enhanced over Al6082 alloy by 41.94%, 40.73%, and 42.97% at the as-cast condition and 76.96%, 81.61%, and 64.62% at peak-aged condition, respectively. Furthermore, nanocomposite fractography represented a mixture of ductile and brittle fracture for 0.3 wt% MWCNTs and brittle fracture for further addition of MWCNTs.

Effects of MWCNTs on Char Layer Structure and Physicochemical Reaction in Ethylene Propylene Diene Monomer Insulators.

As one of the most promising ablative fillers, multi-walled carbon nanotubes (MWCNTs) have been used to improve the ablative resistance of Ethylene–Propylene–Diene Monomer (EPDM) insulators by facilitating the carbothermal reduction reaction of silica. However, the contribution of MWCNTs to char layer structure of the insulators was unclear. In this work, the effects of MWCNTs on char layer structure and ablative resistance were investigated in different EPDM-based insulators with and without silica. The results showed that adding only 3 phr MWCNTs can reduce the linear ablation rate of EPDM-based insulators without silica by 31.7%, while 6 phr MWCNTs are required to obtain similar results in EPDM-based insulators with silica. The char layer morphology of the two insulators gradually evolved into a dense porous structure as MWCNTs content increased, but their formation mechanisms were different. The XRD and Raman spectrum showed that different physicochemical reactions occurred around MWCNTs under different charring components. The proposed ablation mechanism was further verified by designing alternating multilayer distribution of MWCNTs and silica. This work can guide the construction of desirable char layer structure for increasing the ablative resistance of EPDM-based insulators.

Synthesis of MWCNTs from xylenes for fabrication of highly electrically conductive and gas-sensitive polymer composites

For Multi-Walled Carbon Nanotubes (MWCNTs), high quality, purity, and low cost are very desirable. Therefore, in this reported research work, qualitative and pure MWCNTs were synthesized using a cheap and affordable carbon source-xylenes (a mixture of isomers) by the Aerosol Chemical Vapor Deposition Method (A-CVD). The high quality, purity, and homogeneity of the synthesized material have been verified by Raman spectroscopy, EDX, XRD, and SEM results. In the present study, Polystyrene/xMWCNT, Polyvinyl acetate/xMWCNT, and Polyvinyl alcohol/xMWCNT composites with different MWCNT contents of (x = 1, 2, 4, 8, and 16) wt% were prepared by an optimized technique for irreversible dispersion of MWCNTs inside polymers, which was developed by our research group. SEM analysis results revealed that the MWCNTs are well incorporated inside all three polymer matrices, and a highly dispersed distribution of MWCNTs has been obtained inside all three matrices due to this technique. Also, the electrical conductivity of the prepared composites was measured, and the prepared nanocomposites show high electrical conductivity for all concentrations of MWCNTs. Based on the maximum dispersion of MWCNTs inside the PS polymer matrix, the highest electrical conductivity is observed for this composite, which once more proves that the dispersion technique as well as the nature of the polymer play an important role in the preparation of highly electroconductive nanocomposites (1%-0.136 S/m; 2%-1.053 S/m; 4%-5.376 S/m; 8%-71.48 S/m; 16%-933.71 S/m). Comparison of electrical conductivity results of these composites with literature results demonstrates the advantages of this technique in substitution of the another dispersion methods. The nanocomposites prepared by our research group also show a sensor effect (change of resistivity) under different gases (methane, propane, carbon monoxide). It is interesting that, for analyzed gases, the resistivity of some nanocomposites increased, whereas for others it decreased. This effect can be explained by the different nature of the adsorption interaction between the analyzed gas and the polymer composite, and this depends on the chemical composition and properties of both gases and polymer matrices.