Enhanced strength and excellent transport properties of a superaligned carbon nanotubes reinforced copper matrix laminar composite

Superaligned carbon nanotube (SACNT) reinforced copper matrix laminar composites have been fabricated by means of the traditional copper sulfate electroplating process. The mechanical properties and transport properties of the Cu/SACNT composites with different SACNT content have been studied systematically, and the experimental results show that the as-prepared composites possess a better comprehensive performance than pure copper. The simple rule of mixtures (ROM) has been used to estimate the potential maximum properties of the Cu/SACNT composites. The Cu/SACNT composite is considered to be a promising material for electronics and communications applications.     

Effects of hybrid carbon fillers of polymer composite bipolar plates on the performance of direct methanol fuel cells

The effects of carbon filler type on the properties and performance of composite bipolar plates fabricated by compression molding of carbon fillers such as graphite, carbon black (CB), multi-walled carbon nanotube (MWNT), carbon fiber (CF) and powder type epoxy have been investigated. The electrical conductivity and flexural properties of the composites are increased by increasing the content of fibrous conducting fillers, e.g. MWNT and CF. On the contrary, incorporation of particulate fillers such as CB and graphite plays a significant role in enhancing the electrical conductivity but has a negative effect on the flexural properties of the composites. The current–voltage curve of the fuel cell indicates that the performance of the fuel cell is improved upon selection of an optimum amount of carbon filler in the composite bipolar plates.     

High temperature thermal stability of pure copper and copper–carbon nanotube composites consolidated by High Pressure Torsion

The thermal stability of ultrafine-grained (UFG) microstructures in pure copper samples and copper–carbon nanotube (CNT) composites processed by High Pressure Torsion (HPT) was compared. The UFG microstructure in the sample consolidated from pure Cu powder exhibited better stability than that developed in a casted Cu specimen. The addition of CNTs to the Cu powder further increased the stability of the UFG microstructure in the consolidated Cu matrix by hindering recrystallization, however it also yielded a growing porosity and cracking during annealing. It was shown that the former effect was stronger than the latter one, therefore the addition of CNTs to Cu has an overall benefit to the hardness in the temperature range between 300 and 1000 K. A good agreement between the released heat measured during annealing and the calculated stored energy was found for all samples.     

Poly(vinyl alcohol) reinforced with large-diameter carbon nanotubes via spray winding

For practical application of carbon nanotube (CNT)/polymer composites, it is critical to produce the composites at high speed and large scale. In this study, multi-walled carbon nanotubes (MWNTs) with large diameter (∼45 nm) and polyvinyl alcohol (PVA) were used to increase the processing speed of a recently developed spraying winding technique. The effect of the different winding speed and sprayed solution concentration to the performance of the composite films were investigated. The CNT/PVA composites exhibit tensile strength of up to 1 GPa, and modulus of up to 70 GPa, with a CNT weight fraction of 53%. In addition, an electrical conductivity of 747 S/cm was obtained for the CNT/PVA composites. The good mechanical and electrical properties are attributed to the uniform CNTs and PVA matrix integration and the high degree of tube alignment.     

Influence of carbon nanotubes and dispersions of SiC on the physical and mechanical properties of pure copper and copper‐nickel alloy

This paper investigates the physical and mechanical properties of copper‐nickel alloy (at 50 wt.%–50 wt.%) and pure copper, mixed with various types of reinforcement materials such as carbon nanotubes (0.5 wt.%–2 wt.%) as nanoparticles, silicon carbide (1 wt.%–4 wt.%) as microparticles. The acquired composite specimens characteristics were estimated such as microstructure, density, electrical and thermal conductivity, hardness, and compression stress properties to determine the suitable reinforcement percentage that has the best physical and mechanical properties with different main matrix material whether copper‐nickel mechanical alloying or pure copper powder. The micron‐sized silicon carbide and nanosized carbon nanotubes were added to improve the mechanical and physical properties of the composite. The electrical and thermal conductivity of pure copper alloy enhanced compared with the copper‐nickel alloy matrix material. The hardness and compression yield stress of both pure copper and copper‐nickel composites have enhancement values and for copper‐nickel base composites hardness and compression yield stress have enhanced with the most positive enhancement values to examined an optimum percentage of reinforcing material.     

超顺排碳纳米管/硅橡胶复合材料各向异性的电学性能和力学性能

采用直接浸润法制备了具有不同层数的超顺排碳纳米管(SACNT)薄膜与硅橡胶的复合材料,使碳纳米管薄膜能够在硅橡胶基体表面均匀分散。测量了SACNT薄膜/硅橡胶复合材料在各个方向的导电性能和力学性能,研究了影响复合材料导电性和力学性能的因素。实验结果表明:SACNT薄膜/硅橡胶复合材料的导电性和杨氏模量都随着碳纳米管薄膜厚度的增加而增加,且具有显著的各向异性。垂直于碳纳米管排列方向的电阻率平均比平行方向的大一个数量级。当碳纳米管层数为240层时,平行于碳纳米管排列方向的杨氏模量为116.9 MPa(比纯硅橡胶基体增加了142倍),而垂直方向的杨氏模量仅为1.23 MPa(比纯硅橡胶基体增加50%),两者之间相差近100倍。结果表明,可以通过选择不同的参数,获得具有特定导电性和杨氏模量的SACNT薄膜/硅橡胶复合材料,并在实际中加以应用。     

Effects of carbon nanotubes and carbon fiber reinforcements on thermal conductivity and ablation properties of carbon/phenolic composites

The ablation properties and thermal conductivity of carbon nanotube (CNT) and carbon fiber (CF)/phenolic composites were evaluated for different filler types and structures. It was found that the mechanical and thermal properties of phenolic-polymer matrix composites were improved significantly by the addition of carbon materials as reinforcement. The concentrations of CF and CNT reinforcing materials used in this study were 30 vol% and 0.5 wt%, respectively. The thermal conductivity and thermal diffusion of the different composites were observed during ablation testing, using an oxygen–kerosene (1:1) flame torch. The thermal conductivity of CF mat/phenolic composites was higher than that of random CF/phenolic composites. Both CF mat and CNT/phenolic composites exhibited much better thermal conductivity and ablation properties than did neat phenolic resin. The more conductive carbon materials significantly enhanced the heat conduction and dissipation from the flame location, thereby minimizing local thermal damage.     

Mechanical,electrical and thermal properties of aligned carbon nanotube/polyimide composites

Carbon nanotubes (CNTs) have high strength and modulus, large aspect ratio, and good electrical and thermal conductivities, which make them attractive for fabricating composite. The poly(biphenyl dianhydride-p-phenylenediamine) (BPDA/PDA) polyimide has good mechanical and thermal performances and is herein used as matrix in unidirectional carbon nanotube composites for the first time. The strength and modulus of the composite increase by 2.73 and 12 times over pure BPDA–PDA polyimide, while its electrical conductivity reaches to 183 S/cm, which is 10¹⁸ times over pure polyimide. The composite has excellent high temperature resistance, and its thermal conductivity is beyond what has been achieved in previous studies. The improved properties of the composites are due to the long CNT length, high level of CNT alignment, high CNT volume fraction and good CNT dispersion in polyimide matrix. The composite is promising for applications that require high strength, lightweight, or high electrical and thermal conductivities.     

Fabrication and effective thermal conductivity of multi-walled carbon nanotubes reinforced Cu matrix composites for heat sink applications

A novel particles-compositing method was used for the first time to disperse different contents of multi-walled carbon nanotubes (CNTs) in micron sized copper powders, which were subsequently consolidated into CNT/Cu composites by spark plasma sintering (SPS). Microstructural observations showed that the homogeneous distribution of CNTs and dense composites could be obtained for 0–10 vol.% CNT contents. The CNT clusters were appeared in the powder mixture with 15 vol.% CNTs, which resulted in an insufficient densification of the composites. The effective thermal conductivity of the composites was analyzed both theoretically and experimentally. The addition of CNTs showed no enhancement in overall thermal conductivity of the composites due to the interface thermal resistance associated with the low phase contrast of CNT to copper and the random tube orientation. Besides, the composite containing 15 vol.% CNTs led to a rather low thermal conductivity due possiblely to the combined effect of unfavorable factors induced by the presence of CNT clusters, i.e. large porosity, lower effective conductivity of CNT clusters themselves and reduction of SPS cleaning effect. The CNT/Cu composites may be a promising thermal management material for heat sink applications.     

Fabrication and characterization of recyclable carbon nanotube/polyvinyl butyral composite fiber

A surface-draw method to fabricate recyclable carbon nanotube/polyvinyl butyral (CNT/PVB) composite fibers is reported. This method is effective for both single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube. The CNT mass content of CNT/PVB composite fibers can vary from 0 to 80 wt.%, which is higher than most CNT/polymer composites reported to date. The diameter of the composite fibers can be controlled in the range of 10-100 μm, with essentially unlimited draw length. The composite fibers with 7.4 wt.% SWCNTs showed optimal tensile properties. Compared with pure PVB fibers, the tensile strength, failure strain, and elastic modulus of the composite fiber have improved about 127%, 27%, and 73%, respectively. In addition, SWCNT/PVB composites with 66.7 wt.% SWCNTs have the highest conductivity of 42.9 S m⁻¹. More importantly, the major benefit is the “greenness” of the method, which involves environment friendly ethanol-water solvent with no functionalization of the nanotube required, and only simple apparatus are needed. The CNT/PVB composite fibers obtained can be dissolved in ethanol solution and reformed with the surface draw method without any additional treatment; and the material properties after recycle is comparable to those fabricated in the first round.     

Mechanical and electrical property improvement in CNT/Nylon composites through drawing and stretching

The excellent mechanical properties of carbon nanotubes (CNTs) make them the ideal reinforcements for high performance composites. The misalignment and waviness of CNTs within composites are two major issues that limit the reinforcing efficiency. We report an effective method to increase the strength and stiffness of high volume fraction, aligned CNT composites by reducing CNT waviness using a drawing and stretching approach. Stretching the composites after fabrication improved the ultimate strength by 50%, 150%, and 190% corresponding to stretch ratios of 2%, 4% and 7%, respectively. Improvement of the electrical conductivities exhibited a similar trend. These results demonstrate the importance of straightening and aligning CNTs in improving the composite strength and electrical conductivity.     

Formicary-like carbon nanotube/copper hybrid nanostructures for carbon fiber-reinforced composites by electrophoretic deposition

An electrophoretic deposition process has been applied to produce unique carbon nanotube (CNT)/copper nanostructures on the carbon fiber surfaces. During the deposition process, ionized copper and positively charged CNTs are accelerated towards the carbon fiber under applied electric fields. An interconnected formicary-like network of nanotubes and nanoparticles is formed where copper nucleation and growth occurs predominantly at nanotube crossing and edge-contact locations. When embedded in a structural composite the CNT/copper structures create a highly conductive and strongly bonded network shown by significant enhancements in both electrical conductivity and interlaminar shear strength as compared to composites without the CNT/copper nanostructures.     

Microstructure and properties of polyurethane nanocomposites reinforced with methylene-bis-ortho-chloroanilline-grafted multi-walled carbon nanotubes

Methylene-bis-ortho-chloroanilline (MOCA), an excellent cross-linker widely used to prepare cured polyurethane (PU) elastomers with high performance, was used to modify a multi-walled carbon nanotube. PU/carbon nanotube (CNT) nanocomposites were prepared by incorporation of the MOCA-grafted CNT into PU matrix. Fourier transform infrared spectra have shown that the modified CNTs have been linked with PU matrix. The microstructure of composites was investigated by Field-Emission Scanning Electron Microscopy. The results of Dynamic Mechanical Thermal Analysis and Differential Scanning Calorimetry have investigated the grafted CNTs as cross-linker in the cured composites. The studies on the thermal and mechanical properties of the composites have indicated that the storage modulus and tensile strength, as well as glass transition temperature and thermal stability are significantly increased with increasing CNT content.     

Synthesis of uniformly dispersed carbon nanotube reinforcement in Al powder for preparing reinforced Al composites

In order to obtain homogeneously dispersed carbon nanotube (CNT) reinforcement with well structure in Al powder, a novel and simple approach was developed as a means of overcoming the limits of traditional mixing methods. This process involves the even deposition of Ni catalyst onto the surface of Al powder by impregnation route with a low Ni content (0.5 wt.%) and in situ synthesis of CNTs in Al powder by chemical vapor deposition. The in situ synthesized CNTs with well-crystallized bamboo-like structure in the composite powders can obviate the reaction with Al below 1000 °C. The feasibility of fabricating CNT/Al composites with high mechanical properties using the as-prepared composite powders was proved by our primary test, which indicated that the compressive yield stress and elastic modulus of 1.5 wt.%-CNT/Al composites synthesized by hot extrusion are 2.2 and 3.0 times as large as that of the pure Al matrix.     

Investigation of carbon nanotube reinforced aluminum matrix composite materials

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.     

Effect of multi-walled carbon nanotubes on mechanical,thermal and electrical properties of phenolic foam via in-situ polymerization

In this study, phenolic foam (PF)/multi-walled carbon nanotubes (MWCNTs) composites were fabricated by in-situ polymerization, and carbonized foams based on these PF foams were prepared and the electrical property was investigated. TEM results indicated excellent dispersion of MWCNTs in the phenolic resin matrix. Scanning electron microscope results indicated that PF composites exhibited smaller cell size, thicker cell wall thickness, and higher cell density, compared with pure PF. The incorporating of MWCNTs significantly improved the mechanical properties of PF. All PF composites showed a lower thermal conductivity versus pure PF. Moreover, the carbonized pure and composites PF exhibited open-cell three-dimensional skeleton carbon structure and the MWCNTs were well-dispersed on the surface of the skeletons. It is noteworthy that the introduction of MWCNTs significantly improved the electrical performances of foams and carbonized foams by construction of conductive MWCNTs network.     

Damage mode characterization of mechanically fastened composite joints using carbon nanotube networks

The practice of upgrading metal parts with composites in large structures has led to an increased use of composite joints, particularly mechanical fastenings, due to ease of assembly and replacement. A drawback of mechanical joints is that damage is difficult to detect visually. In this research, an embedded carbon nanotube network has been used to modify the conductivity of bolted composite joints. In situ electrical resistance measurements in conductive composites have potential to provide quantitative evidence of damage as well as insight into the type of damage which occurs during tensile loading. We demonstrate that the electrical resistance of a bolted composite joint is more sensitive to certain modes of damage (e.g., matrix cracking and delamination) than others (bearing and shear-out), due mostly to the varying amount of void space created, thus proving the potential of an embedded carbon nanotube network in the health monitoring of mechanically fastened cross-ply composites.     

A facile method for preparing CNT-grafted carbon fibers and improved tensile strength of their composites

Carbon nanotube (CNT)-grafted carbon fibers (CFs) have emerged as new reinforcements for improving the mechanical properties of CF-reinforced composites but such enhancement in macroscale composites has not been realized. This paper reports a facile method for preparing CNT-grafted CFs and improving the tensile strength of their composites. A CNT/polyacrylonitrile solution was sprayed onto the surface of the CF woven fabrics, and the CNTs were grafted by a thermal treatment at 300 °C. CNT-grafted CF composites were fabricated using the CNT-grafted CF woven fabrics using a vacuum-assisted resin transfer molding process with epoxy resin. The CNT-grafted CF composite exhibited 22% enhancement in the tensile strength compared to that of the pristine CF composite. Fracture surfaces of the CNT-grafted CF composites showed that the grafted CNTs obstructed the propagation of micro-cracks and micro-delamination around the CFs and also yarn boundaries, resulting in improved tensile strength of CNT-grafted CF composites.     

Multifunctional properties of high volume fraction aligned carbon nanotube polymer composites with controlled morphology

Advanced composites, such as those used in aerospace applications, employ a high volume fraction of aligned stiff fibers embedded in high-performance polymers. Unlike advanced composites, polymer nanocomposites (PNCs) employ low volume fraction filler-like concepts with randomly-oriented and poorly controlled morphologies due to difficult issues such as dispersion and alignment of the nanostructures. Here, novel fabrication techniques yield controlled-morphology aligned carbon nanotube (CNT) composites with measured non-isotropic properties and trends consistent with standard composites theories. Modulus and electrical conductivity are maximal along the CNT axis, and are the highest reported in the literature due to the continuous aligned-CNTs and use of an unmodified aerospace-grade structural epoxy. Rule-of-mixtures predictions are brought into agreement with the measured moduli when CNT waviness is incorporated. Waviness yields a large (10×) reduction in modulus, and therefore control of CNT collimation is seen as the primary limiting factor in CNT reinforcement of composites for stiffness. Anisotropic electron transport (conductivity and current-carrying capacity) follows expected trends, with enhanced conductivity and Joule heating observed at high current densities.     

Preparation and thermal properties of soluble poly(phthalazinone ether sulfone ketone) composites reinforced with multi-walled carbon nanotube buckypaper

A nanocomposite with soluble high-performance poly(phthalazinone ether sulfone ketone) (PPESK) as matrix and multi-walled carbon nanotube buckypaper (MWCNT-BP) as reinforcement was fabricated by hot-press processing. The morphologies, dynamic and static mechanical behavior, thermal stability of the MWCNT-BP/PPESK composites were studied using scanning electron microscope (SEM), dynamic mechanical analyzer (DMA) and thermogravimetric analyzer (TGA). SEM microphotographs revealed a high impregnation degree of the MWCNT-BP/PPESK composites. Dynamic and static mechanical analysis revealed that the nanocomposites possessed high storage modulus, and good retention rate of mechanical strength even at 250 °C, which is mainly attributed to satisfied impregnation and strong interactions between MWCNT-BP and PPESK. Thermogravimetric analysis exhibited that the nanocomposites had excellent thermal stability. These investigations confirm that MWCNT-BP can be effectively used to manufacture high-loading CNT/PPESK composites with improved properties.