Reinforcing mechanisms of single-walled carbon nanotube-reinforced polymer composites

The reinforcing mechanisms of single-walled carbon nanotube-reinforced epoxy composites were studied by micromechanics models. The modeling results obtained from both Halpin-Tsai and Mori-Tanaka models are in good agreement with the experimental results. It has been found that these two models are also applicable to other single-walled carbon nanotube-reinforced, amorphous-polymer composites, given the existence of efficient load transfer. The reinforcing mechanisms that work in polymer-carbon nanotube composites were studied. The reasons responsible for the low mechanical property enhancement of single-walled carbon nanotube in polymer composites were discussed in conjunction with the effective fiber length concept, interface between nanotube bundles and the matrix, properties of the reinforcements and matrix, bundle effects, bundle curvature, and alignment.     

Silver-plated carbon nanotubes for silver/conducting polymer composites

Carbon nanotubes (CNTs) have advantages as conductive fillers due to their large aspect ratio and excellent conductivity. In this study, a novel silver/conducting polymer composite was developed by the incorporation of silver-plated CNTs. It is important to achieve a homogeneous dispersion of nanotubes and to improve the interfacial bonding to utilize the excellent properties of reinforcements in the matrix material. The homogeneous dispersion of nanotubes was achieved by an acid treatment process, and the interfacial contact was improved by electroless silver plating around nanotubes. The resistivity of the silver/conducting polymer composite was decreased by 83% by the addition of silver-plated single-walled carbon nanotubes. Conductive bumps were also screen-printed to demonstrate the capability of the composite as electrical interconnects for multi-layer printed circuit boards.     

Electrical and mechanical properties of aluminosilicate inorganic polymer composites with carbon nanotubes

The DC electrical conductance of potassium aluminosilicate inorganic polymers (geopolymers) containing up to 6 wt% single-wall carbon nanotubes has been determined as a function of temperature up to 340 °C. After removal of the processing water during the first heating cycle, the conductance in subsequent heating cycles increases as a function of carbon nanotube content and temperature from 9.75 × 10⁻⁴ to 1.87 × 10⁻³ S m⁻¹ in the composites containing 0 and 0.2 wt% carbon nanotubes, respectively, at 290 °C. By comparison, the electrical conductance of potassium inorganic polymer composites containing graphite was generally lower. The conductance activation energies of the carbon nanotube and graphite composites were similar, and decreased from about 55 to 5 kJ mole⁻¹ with increasing carbon content. The tensile strengths of carbon nanotube and graphite-containing potassium geopolymer composites, determined by the Brazil method on 10–12 replicates, were about 2 MPa, and showed little change with increasing carbon nanotube content up to 0.3 wt%. By contrast, the tensile strengths of an analogous set of sodium composites were up to four times greater, possibly reflecting the necessity for less processing water in the synthesis of the sodium samples.     

碳纳米管/高分子阻燃复合材料研究进展

综述了近年来各种类型的碳纳米管(CNTs)/高分子阻燃复合材料的研究进展,重点对其制备方法、阻燃性能进行了分析总结,并阐释了CNTs与传统阻燃剂复配时对复合物的协同阻燃作用,最后探讨了以CNTs作为阻燃添加剂的阻燃机理,展望了CNTs作为阻燃添加剂的应用前景。     

Aligning carbon nanotubes using bulk acoustic waves to reinforce polymer composites

Bulk acoustic waves (BAWs) are used to align multi-walled carbon nanotubes (MWCNTs) in polymer composite materials. MWCNTs are first dispersed in the liquid state of a thermoset resin and aligned using standing BAWs. Cross-linking of the resin fixates the aligned MWCNTs in the polymer matrix material. We have quantified the alignment obtained with this method on the macro, micro, and nanoscale, and it is found to be similar to other alignment techniques such as stretching, slicing, and wet spinning. The elastic modulus and ultimate tensile strength of composite material specimens with aligned MWCNTs, fabricated using this technique, are evaluated and compared with specimens consisting of randomly oriented MWCNTs and resin material without MWCNTs. Different MWCNT loading rates are considered. The elastic modulus of composite material specimens with only 0.15 weight percent aligned MWCNTs is observed to be 44% higher than specimens with randomly oriented MWCNTs, and 51% higher than specimens without MWCNTs. However, further increasing the MWCNT loading rate does not significantly increase the elastic modulus and ultimate tensile strength, likely because of insufficient dispersion of MWCNTs in the thermoset matrix material.     

Multiscale carbon fibre–reinforced polymer (CFRP) composites containing carbon nanotubes with tailored interfaces

Pristine and functionalized multiwalled carbon nanotubes (MWCNTs) with tailored interfaces were efficiently dispersed in an epoxy matrix using a three‐roll mill and further reinforced with carbon fibres. 1.3‐Dipolar cycloaddition of azomethine ylides was used for the chemical modification of MWCNTs by a solvent‐free approach. The influence of different loadings and types of MWCNTs on the final properties of the epoxy matrix was studied. Moreover, the most promising formulations were selected for manufacturing of prepreg sheets. The transversal tensile properties and the interlaminar fracture toughness under mode I loading (G_IC) of multiscale carbon fibre–reinforced polymer (CFRP) composites were characterized. The results point out that it is not straightforward to transfer the remarkable intrinsic properties of MWCNTs to the composite level, although an overall positive trend was found. Double cantilever beam experiments showed that G_IC of CFRP composites was improved 44% at ultralow content of functionalized MWCNTs (0.043 wt%).     

Reinforcing effect of carbon nanotubes on PEEK composite filled with carbon fibre

Abstract

The main objective of the present paper is to develop high wear resistance carbon fibre reinforced polyether ether ketone composite with addition of multiwall carbon nanotubes. These compounds were well mixed in a batch mixer, and compounded polymers were fabricated into sheets of known thickness by compression moulding. Samples were tested for wear resistance with respect to different concentration of fillers. The wear resistance properties of these samples depend on filler aspect ratio. Wear resistance of composite with 20 wt-% of carbon fibre increases when multiwall carbon nanotubewas introduced. The worn surface features have been examined using scanning electron microscope. Photomicrographs of the worn surfaces revealed higher wear resistance with the addition of carbon nanotube. Also better interfacial adhesion between carbon and vinyl ester in carbon reinforced vinyl ester composite was observed.     

Magnetic orientation of single-walled carbon nanotubes or their composites using polymer wrapping

Abstract

The magnetic orientation of single-walled carbon nanotubes (SWNTs) or the SWNT composites wrapped with polymer using poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV) as the conducting polymer were examined. The formation of SWNT/MEHPPV composites was confirmed by examining absorption and fluorescence spectra. The N,N-dimethylformamide solution of SWNT/MEHPPV composites or the aqueous solution of the shortened SWNTs was introduced dropwise onto a mica or glass plate. The magnetic processing of the composites or the SWNTs was carried out using a superconducting magnet with a horizontal direction (8 T). The AFM images indicated that the SWNT/MEHPPV composites or the SWNTs were oriented randomly without magnetic processing, while with magnetic processing (8 T), they were oriented with the tube axis of the composites or the SWNTs parallel to the magnetic field. In polarized absorption spectra of SWNT/MEHPPV composites on glass plates without magnetic processing, the absorbance due to semiconducting SWNT in the near-IR region in horizontal polarized light was almost the same as that in vertical polarized light. In contrast, with magnetic processing (8 T), the absorbance due to semiconducting SWNT in the horizontal polarization direction against the direction of magnetic field was stronger than that in the vertical polarization direction. Similar results were obtained from the polarized absorption spectra for the shortened SWNTs. These results of polarized absorption spectra also support the magnetic orientation of the SWNT/MEHPPV composites or the SWNTs. On the basis of a comparison of the composites and the SWNTs alone, the magnetic orientation of SWNT/MEHPPV composites is most likely ascribable to the anisotropy in susceptibilities of SWNTs.     

Radar absorbing properties of carbon nanotubes/polymer composites in the V-band

This research is devoted to the study of radar absorbing properties of the composites, based on the epoxy binder and carbon nanotubes (CNT) in the frequency range of 52–73 GHz. Three species of unmodified multi-walled CNT differing in length and diameter were investigated as fillers. The reflection coefficients (K _refl) at the radar absorbing material (RAM)–air interface and the electro-magnetic radiation (EMR) absorption coefficients (K _abs) in the materials with the different content of nanotubes were measured (K _refl and K _abs were calculated using the highest (the worst) value of the voltage standing-wave ratio (VSWR) in the frequency range of 52–73 GHz). It was established that the increase in nanotubes aspect ratio (a ratio of CNT length to its diameter) leads to K _abs rising for polymer composites. Also, CNT diameter decrease leads to K _refl reduction. CNT of 8–15 nm in diameter and more than 2 μm in length are the most effective from all investigated fillers. The reflection loss values were calculated and CNT optimal concentrations were obtained at different thickness of RAMs.     

Enhancing thermal conductivity of glass fiber/polymer composites through carbon nanotubes incorporation

Carbon nanotubes were effectively incorporated into low-viscosity polyester/vinyl ester resins and then used for infusion of glass fiber textiles by high-pressure injection, resulting in carbon nanotubes/glass fiber/polymer multiscale composites. The nanotubes distribution in the composites was examined by measuring the local density of as-produced composites. The uniformity of local density and scanning electron microscope characterization verified the homogeneous morphology of as-produced composites. Both theoretical calculation and experimental characterization indicated thermal conductivity was significantly improved. Incorporation of 3 wt% carbon nanotubes has resulted in 1.5-folds enhancement of thermal conductivity. These results will further increase industrial application of the fiber composites.     

Thermal conductivity of polymer composites based on the length of multi-walled carbon nanotubes

The anisotropic development of thermal conductivity in polymer composites was evaluated by measuring the isotropic, in-plane and through-plane thermal conductivities of composites containing length-adjusted short and long multi-walled CNTs (MWCNTs). The thermal conductivities of the composites were relatively low irrespective of the MWCNT length due to their high contact resistance and high interfacial resistance to polymer resins, considering the high thermal conductivity of MWCNTs. The isotropic and in-plane thermal conductivities of long-MWCNT-based composites were higher than those of short-MWCNT-based ones and the trend can accurately be calculated using the modified Mori-Tanaka theory. The in-plane thermal conductivity of composites with 2 wt% long MWCNTs was increased to 1.27 W/m·K. The length of MWCNTs in polymer composites is an important physical factor in determining the anisotropic thermal conductivity and must be considered for theoretical simulations. The thermal conductivity of MWCNT polymer composites can be effectively controlled in the processing direction by adjusting the length of the MWCNT filler.     

Reduction of thermal residual stresses of laminated polymer composites by addition of carbon nanotubes

This paper studies the effects of multi-walled carbon nanotubes (MWCNTs) on the thermal residual stresses in polymeric fibrous composites. Reinforced ML-506 epoxy nanocomposites with different amounts of homogeneously dispersed MWCNTs (0.1 wt.%, 0.5 wt.% and 1 wt.%) were fabricated using the sonication technique. Thermo-mechanical analysis and tensile tests of the specimens were carried out to characterize the thermal and mechanical properties of MWCNTs/epoxy composites. Due to the negative thermal expansion and high modulus of MWCNTs, addition of MWCNTs resulted in a great reduction of the coefficient of thermal expansion (CTE) of epoxy. The MWCNTs also moderately increased the Young’s modulus of the epoxy. Then, the effects of adding MWCNTs on micro and macro-residual stresses in carbon fiber (CF)/epoxy laminated composites were investigated using the energy method and the classical lamination theory (CLT), respectively. The results indicated that the addition of low amounts of MWCNTs leads to a considerable reduction in thermal residual stress components in both micro and macro levels.     

Soluble carbon nanotubes and nanotube-polymer composites

For these two decade, tremendous amount of researches and developments dealing with carbon nanotubes (CNTs) have been carried out. Most of them are focusing on finding the unique and outstanding properties of CNTs and trying to utilizing them as the advanced materials. Whenever we start the research and the development of CNTs, the first difficulty is the dispersion of CNTs into the solvents since the CNTs form strong aggregation. Up to date, large efforts have been carried out for the preparation of CNT dispersion and the typical strategies are summarized. Such a dispersion technique allows us to use CNT as a material. Several applications of the CNT dispersion is also introduced.     

Ceramic matrix composites containing carbon nanotubes

Due to the remarkable physical and mechanical properties of individual, perfect carbon nanotubes (CNTs), they are considered to be one of the most promising new reinforcements for structural composites. Their impressive electrical and thermal properties also suggest opportunities for multifunctional applications. In the context of inorganic matrix composites, researchers have particularly focussed on CNTs as toughening elements to overcome the intrinsic brittleness of the ceramic or glass material. Although there are now a number of studies published in the literature, these inorganic systems have received much less attention than CNT/polymer matrix composites. This paper reviews the current status of the research and development of CNT-loaded ceramic matrix composite (CMC) materials. It includes a summary of the key issues related to the optimisation of CNT-based composites, with particular reference to brittle matrices and provides an overview of the processing techniques developed to optimise dispersion quality, interfaces, and density. The properties of the various composite systems are discussed, with an emphasis on toughness; a comprehensive comparative summary is provided, together with a discussion of the possible toughening mechanism that may operate. Last, a range of potential applications are discussed, concluding with a discussion of the scope for future developments in the field.     

超支化聚合物/碳纳米管复合物的制备及流变性能研究进展

简述了聚合物/碳纳米管复合物的制备方法,超支化聚合物改性碳纳米管及其制备纳米复合材料的方法,进一步就超支化聚合物/碳纳米管复合材料在流变性能方面的研究进行了综述,并对超支化聚合物/碳纳米管复合材料未来的发展方向提出了几点建议。     

The friction and wear properties of carbon nanotubes/graphite/carbon fabric reinforced phenolic polymer composites

In this paper, either graphite (Gr) or carbon nanotubes (CNTs), or both of them were incorporated into carbon fabric reinforced phenolic (CFRP) composites, preparing by a dip-coating and heat molding process, the tribological properties of the resulting composites were investigated using a block-on-ring arrangement. The worn surfaces were observed by scanning electron microscope to understand the mechanism. Experimental results showed that the optimal Gr was more beneficial than CNTs in improving the tribological properties of the CFRP composites when they were singly incorporated. It is well worth noting that the friction and wear behavior of the CNTs-filled CFRP composites were improved further when Gr was added, indicating that there is a synergistic effect between them. Tribological tests under different sliding conditions revealed that the Gr and CNTs-filled CFRP composites seemed to be the most suitable for tribological applications under higher sliding speed and load, and oil lubrication.     

碳纳米管聚合物复合材料弹性模量预测模型研究进展

碳纳米管具有优异的力学、电学、光学和磁学等性能,是聚合物复合材料理想的增强体。弹性模量是材料重要的力学性能参数之一,本文介绍了近年来碳纳米管聚合物复合材料弹性模量的研究状况,综述了混合法则、Hashin-Shtrikman模型、Cox模型、Halpin-Tsai模型和数值模拟法预测碳纳米管聚合物复合材料弹性模量的方法,并提出了研究中面临的一些问题以及发展方向。     

Photoelectrochemical reactions of electrodes modified with composites between conjugated polymer or ruthenium complex and single-walled carbon nanotubes

Composite materials between conjugated polymer; poly[2-methoxy-5-(2'-ethylhexyloxy)-1.4-phenylene vinylene] (MEHPPV), or ruthenium(II)-tris(2,2'-bipyridine) (Ru(bpy)₃²⁺)-poly(sodium 4-styrenesulfonate) (PSS) complex and single-walled carbon nanotubes (SWNTs) were fabricated using polymer wrapping method. Formation of SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite was confirmed by absorption and fluorescence spectra, and AFM images. Electrode modified with SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite was prepared by casting from DMF solution of SWNT/MEHPPV or aqueous solution of SWNT/PSS/Ru(bpy)₃²⁺. The electrode modified with SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite showed photocurrent response due to photoexcitation of MEHPPV or Ru(bpy)₃²⁺. The photocurrents are ascribed to photoinduced electron-transfer reaction from excited state of MEHPPV or Ru(bpy)₃²⁺ to SWNT.     

Electron field emitters based on multi-walled carbon nanotubes coated with conducting polymer/metal/metal-oxide composites

The present work describes the field emission properties of multi-walled nanotubes (MWNTs)-based conducting polymer/metal-oxide/metal/MWNTs composites (polyaniline (PANI)/SnO₂/Sn/MWNTs). MWNTs were synthesised by chemical vapour deposition technique. SnO₂/Sn/MWNTs were prepared by using chemical reduction followed by calcination. By in situ polymerisation method, surface of SnO₂/Sn/MWNTs were coated with PANI. PANI/SnO₂/Sn/MWNTs field emitters were fabricated over flexible graphitised carbon fabric substrate by spin coating technique. High-resolution transmission electron microscopy and scanning electron microscopy were used to characterise the field emitters. Field emission properties have been studied using an indigenously made facility. The fabricated PANI/SnO₂/Sn/MWNTs field emitters exhibited excellent field emission properties with a turn on field of 1.83 V µm^?1 and a field enhancement factor of 4800.