Carbon Nanotube Reinforced Alumina-Based Ceramics with Novel Mechanical, Electrical, and Thermal Properties

The extraordinary mechanical, thermal, and electrical properties of single-wall carbon nanotubes (SWCNT) have prompted the development of advanced engineering materials with improved properties through the incorporation of carbon nanotubes in selected matrices. Dense SWCNT reinforced alumina nanocomposites have been fabricated by novel spark-plasma-sintering (SPS) technique. SWCNT were also successfully used to convert insulating nanoceramics to metallically conductive composites. Additionally, novel anisotropic thermal properties have been observed in the carbon nanotube composites. Such multifunctional carbon nanotube/ceramic composites with improved mechanical and electrical properties along with anisotropic thermal properties are envisaged for a wide range of applications.     

Exploitation of Carbon Nanotubes in High Performance Polyvinylidene Fluoride Matrix Composite: A Review

Among nanocarbon fillers, carbon nanotubes are considered to be an ideal reinforcement due to their miniscule size, and excellent electrical, thermal, and mechanical properties. However, carbon nanotubes can be utilized in polymer nanocomposites only if they are homogenously dispersed into polymer matrices. The multiwalled carbon nanotube has been concentrated as a reinforcement for an important type of thermoplastic polyvinylidene fluoride. This review initially focuses on carbon nanotubes modification both by mechanical methods and chemical functionalization to improve their dispersion. Moreover, the processing methods for polyvinylidene fluoride/carbon nanotubes nanocomposite have been discussed. Multiwalled carbon nanotubes facilitate the electrical conductivity, thermal, rheological, and mechanical properties of polyvinylidene fluoride.     

Modified and unmodified multiwalled carbon nanotubes in high performance solution-styrene-butadiene and butadiene rubber blends

The outstanding properties of carbon nanotubes have generated scientific and technical interests in the development of nanotube-reinforced polymer composites. Therefore, we investigated a novel mixing approach for achieving a good dispersion of multiwalled carbon nanotubes (CNTs) in a rubber blend. In this approach the CNTs were incorporated into a 50:50 blend of solution-styrene-butadiene rubber and butadiene rubber. First, the CNTs were predispersed in ethanol and then this CNT-alcohol suspension was mixed with the rubber blend at elevated temperature. The rubber nanocomposites prepared by such method exhibit significantly enhanced physical properties already at very low nanotube concentrations. Additionally, we have analysed the dielectric and thermal properties of the compound. The high aspect ratio of the carbon nanotubes enabled the formation of a conductive percolating network in these composites at concentrations below 2 wt.%. In contrast to the electrical conduction behaviour, the thermal conductivity of the composites has not been influenced significantly by the presence of carbon nanotubes. Dynamic mechanical analysis indicates that the incorporation of CNTs affects the glass transition behaviour by reducing the height of the tan δ peak considerably. Above the glass transition temperature the storage modulus has been increased after incorporation of a small amount of CNTs. Finally, the ‘Payne effect’, an indication of filler-filler interactions, was observed at very low concentrations of CNT in the rubber matrix.     

Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review

Thermally conductive polymer composites offer new possibilities for replacing metal parts in several applications, including power electronics, electric motors and generators, heat exchangers, etc., thanks to the polymer advantages such as light weight, corrosion resistance and ease of processing. Current interest to improve the thermal conductivity of polymers is focused on the selective addition of nanofillers with high thermal conductivity. Unusually high thermal conductivity makes carbon nanotube (CNT) the best promising candidate material for thermally conductive composites. However, the thermal conductivities of polymer/CNT nanocomposites are relatively low compared with expectations from the intrinsic thermal conductivity of CNTs. The challenge primarily comes from the large interfacial thermal resistance between the CNT and the surrounding polymer matrix, which hinders the transfer of phonon dominating heat conduction in polymer and CNT.This article reviews the status of worldwide research in the thermal conductivity of CNTs and their polymer nanocomposites. The dependence of thermal conductivity of nanotubes on the atomic structure, the tube size, the morphology, the defect and the purification is reviewed. The roles of particle/polymer and particle/particle interfaces on the thermal conductivity of polymer/CNT nanocomposites are discussed in detail, as well as the relationship between the thermal conductivity and the micro- and nano-structure of the composites.     

Comparison among Different Processing Conditions in Synthesis of Polypropylene/Carbon Nanotubes Composites Using Raman Spectroscopy

This work presents a simple and rapid method for determining which of three combined processing conditions, rotation speed, mixing temperature and duration of mixing that is the most efficient for the preparation of polypropylene/carbon nanotube composites. For this purpose, polypropylene nanocomposites with a constant amount of carbon nanotubes (5.0 wt.%) and different processing conditions are examined through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Raman Spectroscopy. The latter, Raman Spectroscopy, specializes in and reveals which processing condition among them is the most significant, in order to construct nanocomposites with good dispersion of nanotubes in the polymer matrix.     

Mechanical properties and electrical conductivity in a carbon nanotube reinforced silicon nitride composite

The influence of carbon nanotubes (CNTs) addition on basic mechanical, thermal and electrical properties of the multiwall carbon nanotube (MWCNT) reinforced silicon nitride composites has been investigated. Silicon nitride based composites with different amounts (1 or 3 wt%) of carbon nanotubes have been prepared by hot isostatic pressing. The fracture toughness was measured by indentation fracture and indentation strength methods and the thermal shock resistance by indentation method. The hardness values decreased from 16.2 to 10.1 GPa and the fracture toughness slightly decreased by CNTs addition from 6.3 to 5.9 MPa m^1/2. The addition of 1 wt% CNTs enhanced the thermal shock resistance of the composite, however by the increased CNTs addition to 3 wt% the thermal shock resistance decreased. The electrical conductivity was significantly improved by CNTs addition (2 S/m in 3% Si₃N₄/CNT nanocomposite).     

Investigation on flame retardancy and rheological and thermomechanical characterisation of multiwall carbon nanotube reinforced nanocomposites

Abstract

In the present work, the influence of multiwalled carbon nanotubes (MWCNTs) on the flame retardancy and rheological, thermal and mechanical properties of polybutilen terephthalate (PBT) and polypropylene (PP) matrixes has been investigated. The carbon nanotube content in the thermoplastic materials was 2 and 5?wt‐%. The nanocomposites were obtained by diluting a masterbatch containing 20?wt‐% nanotubes using a twin‐screw extruder and the thermal properties were analysed by differential scanning calorimetry and thermogravimetric analysis; thermomechanical properties were determined by dynamic mechanical thermal analysis and the rheological behaviour was studied by a Thermo Haake Microcompounder. The results concerning the flame retardancy show that the MWCNTs are not equally effective as flame retardants in PP and PBT. The ignition time is increased only for PBT whereas the extinguishing time is decreased for PP and PBT. The reinforcement of the thermoplastics with multiwall carbon nanotubes is improved regarding the mechanical and thermal properties of the nanocomposites compared to pristine materials and the behaviour of thermoplastic nanocomposites regarding fire retardancy depends on the nature of the polymeric matrix.     

Microstructural,mechanical, and thermal characteristics of recycled cellulose fiber‐halloysite‐epoxy hybrid nanocomposites

Epoxy hybrid‐nanocomposites reinforced with recycled cellulose fibers (RCF) and halloysite nanotubes (HNTs) have been fabricated and investigated. The dispersion of HNTs was studied by synchrotron radiation diffraction (SRD) and transmission electron microscopy (TEM). The influences of RCF/HNTs dispersion on the mechanical properties and thermal properties of these composites have been characterized in terms of flexural strength, flexural modulus, fracture toughness, impact toughness, impact strength, and thermogravimetric analysis. The fracture surface morphology and toughness mechanisms were investigated by SEM. Results indicated that mechanical properties increased because of the addition of HNTs into the epoxy matrix. Flexural strength, flexural modulus, fracture toughness, and impact toughness increased by 20.8, 72.8, 56.5, and 25.0%, respectively, at 1 wt% HNTs load. The presence of RCF dramatically enhanced flexural strength, fracture toughness, impact strength, and impact toughness of the composites by 160%, 350%, 444%, and 263%, respectively. However, adding HNTs to RCF/epoxy showed only slight enhancements in flexural strength and fracture toughness. The inclusion of 5 wt% HNTs into RCF/epoxy ecocomposites increased the impact toughness by 27.6%. The presence of either HNTs or RCF accelerated the thermal degradation of neat epoxy. However, at high temperature, samples reinforced with RCF and HNTs displayed better thermal stability with increased char residue than neat resin. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

碳纳米管改性氟橡胶的性能研究

开展了碳纳米管材料对氟橡胶复合材料的改性研究,探究碳纳米管含量对氟橡胶复合体系物理性能、热性能、微观结构形貌、透气性以及宏观力学性能的影响。在此基础上模拟高温高压条件进行老化试验,对老化试验前后材料的硬度变化、体积变化、拉伸性能、撕裂性能和压缩永久变形量进行了测量与分析。结果表明,拉伸强度和撕裂强度随碳管含量增加表现增加的规律,基于脆断表面和热失重断面证实了本文实现了高含量碳纳米管的均匀分散,并且一维纳米材料构筑的碳纳米管网络结构有助于氟橡胶复合材料气体阻隔性能提升;基于老化前后的性能对比数据,表明碳纳米管的存在有助于老化后氟橡胶宏观性能的保持。     

The Effect of WS2 Nanotubes on the Properties of Epoxy-Based Nanocomposites

In this paper we evaluated the effect of embedding inorganic nanotubes (INT) of tungsten disulfide (WS₂) in an epoxy matrix, on the mechanical, thermal and adhesion properties of the resulting nanocomposites. The nanotube content spanned a range of values (0, 0.1, 0.3, 0.5 and 1.0 wt%), and the nanotube incorporation process consisted of a combination of both distributive (magnetic stirring) and dispersive (ultrasonic mixing) methods. The adhesion of the nanocomposites to an aluminum substrate was characterized by both a single lap shear and a T-peel test. The fracture toughness (K _IC) of the nanocomposites was characterized by a standard compact tension (CT) plane-strain fracture test. The thermal properties of the nanocomposites were determined by dynamic mechanical thermal analysis (DMTA). Overall, the addition of INT-WS₂ was found to improve the shear strength and peel properties of the nanocomposite, and to significantly improve its fracture toughness and glass transition temperature. The extent and character of the nanotube–epoxy interaction were examined by electron microscopy, as was the energy dissipation mechanisms during fracture.     

Thermal,mechanical, and rheological properties of biodegradable polybutylene succinate/carbon nanotubes nanocomposites

Biodegradable poly(butylene succinate)/carbon nanotubes nanocomposites were prepared by melt mixing process, and the influence of carbon nanotubes on the properties of the nanocomposites was investigated. Differential scanning calorimetry showed that crystallization temperature (T_c) increase with increasing carbon nanotube content. Improvement of tensile modulus was observed by the addition of carbon nanotubes compared with pure poly(butylene succinate). Electrical conductivity showed that conductivity of polybutylene succinate/carbon nanotube composites increased with addition of carbon nanotube content. The storage moduli of polybutylene succinate/carbon nanotube composites are higher than the neat polybutylene succinate. The processability of polybutylene succinate/carbon nanotubes composites was improved and more pronounced in higher content of carbon nanotubes. POLYM. COMPOS., 31:1309–1314, 2010. © 2009 Society of Plastics Engineers     

Effect of carbon nanotubes on the curing and thermomechanical behavior of epoxy/carbon nanotubes composites

The processing of carbon nanotube based nanocomposites is one of the fastest growing areas in materials research due to the potential of significantly changing material properties even at low carbon nanotube concentrations. The aim of our work is to study the curing and thermomechanical behavior of carbon nanotube/epoxy nanocomposites that are critical from an application standpoint. Multiwall carbon nanotubes–epoxy composites are prepared by solvent evaporation based on a commercially available epoxy system and functionalized multiwalled carbon nanotubes. Three weight ratio configurations are considered (0.1, 0.5, and 1.0 wt%) and compared to both the neat epoxy to investigate the nano‐enrichment effect. We focus here on the modification of the curing behavior of the epoxy polymer in the presence of carbon nanotubes. It has been observed that introducing the multiwall carbon nanotubes delays the polymerization process as revealed by the modification of the activation energy obtained by differential scanning calorimetry. The viscoelastic response of the nanocomposites was studied from the measurements of storage modulus and the loss factor using dynamic mechanical analysis to evaluate the effect of the interface in each matrix/carbon nanotube system with changing matrix mobility. These measurements provide indications about the increase in the storage modulus of the composites, shift in the glass transition temperature due to the restriction of polymer chain movement by carbon nanotubes. POLYM. COMPOS., 35:441–449, 2014. © 2013 Society of Plastics Engineers     

A comparison of reinforcement efficiency of various types of carbon nanotubes in polyacrylonitrile fiber

Polyacrylonitrile (PAN)/carbon nanotubes (CNTs) composite fibers were spun from solutions in dimethyl acetamide (DMAc), using single wall (SWNTs), double wall (DWNTs), multi wall (MWNTs) carbon nanotubes, and vapor grown carbon nanofibers (VGCNFs). In each case, CNT content was 5 wt% with respect to the polymer. Structure, morphology, and properties of the composite fibers have been characterized using X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, tensile tests, dynamic mechanical tests, as well as thermal shrinkage. While all nanotubes contributed to property improvements, maximum increase in modulus (75%) and reduction in thermal shrinkage (up to 50%) was observed in the SWNT containing composites, and the maximum improvement in tensile strength (70%), strain to failure (110%), and work of rupture (230%) was observed in the MWNTs containing composites. PAN orientation is higher in the composite fiber (orientation factor up to 0.62) than in the control PAN fiber (orientation factor 0.52), and the PAN crystallite size in the composite fiber is up to 35% larger than in the control PAN (3.7 nm), while the overall PAN crystallinity diminished slightly. Nanotube orientation in the composite fibers is significantly higher (0.98 for SWNTs, 0.88 for DWNTs, and 0.91 for MWNTs and VGCNFs) than the PAN orientation (0.52-0.62). Improvement in low strain properties (modulus and shrinkage) was attributed to PAN interaction with the nanotube, while the improvement in high strain properties (tensile strength, elongation to break, and work of rupture) at least in part is attributed to the nanotube length. Property improvements have been analyzed in terms of nanotube surface area and orientation.     

Mechanically robust,electrically and thermally conductive graphene-based epoxy adhesives

This study develops a facile approach to fabricate adhesives consists of epoxy and cost-effective graphene platelets (GnPs). Morphology, mechanical properties, electrical and thermal conductivity, and adhesive toughness of epoxy/GnP nanocomposite were investigated. Significant improvements in mechanical properties of epoxy/GnP nanocomposites were achieved at low GnP loading of merely 0.5?vol%; for example, Young’s modulus, fracture toughness (K_1C) and energy release rate (G_1C) increased by 71%, 133% and 190%, respectively compared to neat epoxy. Percolation threshold of electrical conductivity is recorded at 0.58?vol% and thermal conductivity of 2.13?W m^?1 K^?1 at 6?vol% showing 4 folds enhancements. The lap shear strength of epoxy/GnP nanocomposite adhesive improved from 10.7?MPa for neat epoxy to 13.57?MPa at 0.375?vol% GnPs. The concluded results are superior to other composites or adhesives at similar fractions of fillers such as single-walled carbon nanotubes, multi-walled carbon nanotubes or graphene oxide. The study promises that GnPs are ideal candidate to achieve multifunctional epoxy adhesives.     

Preparation and properties of polyurethane/multiwalled carbon nanotube nanocomposites by a spray drying process

A spray drying approach has been used to prepare polyurethane/multiwalled carbon nanotube (PU/MWCNT) composites. By using this method, the MWCNTs can be dispersed homogeneously in the PU matrix in an attempt to improve the mechanical properties of the nanocomposites. The morphology of the resulting PU/MWCNT composites was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observations illustrate that the MWCNTs are dispersed finely and uniformly in the PU matrix. X‐ray diffraction results indicate that the microphase separation structure of the PU is slightly affected by the presence of the MWCNTs. The mechanical properties such as tensile strength, tensile modulus, elongation at break, and hardness of the nanocomposites were studied. The electrical and the thermal conductivity of the nanocomposites were also evaluated. The results show that both the electrical and the thermal conductivity increase with the increase of MWCNT loading. In addition, the percolation threshold value of the PU composites is significantly reduced to about 5 wt % because of the high aspect ratio of carbon nanotubes and exclusive effect of latex particles of PU emulsion in dispersion. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of alkylated carbon nanotube/polyimide nanocomposites

BACKGROUND: The development of carbon nanotube‐reinforced composites has been impeded by the difficult dispersion of the nanotubes in polymers and the weak interaction between the nanofiller and matrices. Efficient dispersion of carbon nanotubes is essential for the formation of a functional nanotube network in a composite matrix. RESULTS: Multiwalled carbon nanotubes (MWNTs) were incorporated into a polyimide matrix to produce MWNT/polyimide nanocomposites. To disperse well the MWNTs in the matrix and thus improve the interfacial adhesion between the nanotubes and the polymer, ‘branches’ were grafted onto the surface of the nanotubes by reacting octadecyl isocyanate with carboxylated MWNTs. The functionalized MWNTs were suspended in a precursor solution, and the dispersion was cast, followed by drying and imidization to obtain MWNT/polyimide nanocomposites. CONCLUSION: The functionalized MWNTs appear as a homogeneous dispersion in the polymer matrix. The thermal stability and the mechanical properties are greatly improved, which is attributed to the strong interactions between the functionalized MWNTs and the polyimide matrix. Copyright © 2009 Society of Chemical Industry     

Microstructure and mechanical properties of hot-pressed carbon nanotubes compacted by spark plasma sintering

Bulk carbon nanotube samples were prepared by spark plasma sintering. The as-prepared bulk carbon nanotube material exhibited brittle fracture similar to that of common ceramics. Its fracture toughness was around 4.2 MPa m^1/2 while flexural strength was 50 MPa due to the weak bonding between carbon nanotubes. Obvious carbon nanotube bridging was found during the development of the crack induced by an indenter, which provides a possibility of carbon nanotube tough material.     

Effect of high SWNT content on the room temperature mechanical properties of fully dense 3YTZP/SWNT composites

This paper is devoted to correlate the microstructure and room temperature mechanical properties of single-wall carbon nanotube (SWNT) reinforced 3 mol% yttria stabilized tetragonal zirconia with high SWNT content (2.5, 5 and 10 vol%). Fully dense composites were prepared by using a combination of aqueous colloidal powder processing and Spark Plasma Sintering. SWNTs were located at the ceramic grain boundaries and they were not damaged during the sintering process. The weak interfacial bonding between SWNTs and ceramic grains together with the detachment of SWNTs within thick bundles have been pointed out as responsible for the decrease of hardness and fracture toughness of the composites in comparison with the monolithic 3YTZP ceramic.     

Fabrication of composites with excellent mechanical properties based on cubic boron nitride reinforced with carbon nanotubes

Composites consisting of cubic boron nitride (cBN) as a matrix and carbon nanotubes (CNTs) as reinforcing additives were fabricated by high-temperature and high-pressure sintering (HTHP). Microstructures, mechanical properties, fracture modes and toughening mechanisms of these composites were investigated. Composites exhibited excellent bending strength, wear resistance, and fracture toughness. Fracture toughness of composites reached 7.02 MPa·m^1/2. Comparing to pure cBN matrix, bending strength improved from 475.27 to 600.15 MPa, and wear resistance increased by 43.23%. Such improvements of mechanical properties were mainly attributed to pullout and bridging reinforcements by CNTs. CNTs incorporation also changed fracture mode from inter-to trans-granular.     

Carbon nanotube reinforced pyrocarbon matrix composites with high coefficient of thermal expansion for self-adapting ultra-high-temperature ceramic coatings

The mismatch in the coefficients of thermal expansion (CTE) of the carbon fiber reinforced pyrocarbon (Cf/C) composites and their thermal barrier coatings (TBCs) has significantly restricted the service life of Cf/C composites in high-temperature environments. Owing to the high CTE of TBCs, it is vital to find a material with similar mechanical properties and higher CTE than Cf/C composites. In this work, carbon nanotube reinforced pyrocarbon (Ct/C) nanocomposites with high CTEs were prepared to self-adapt to the TBCs. Different CTEs (～4.0–6.5 × 10^?6/°C) were obtained by varying the carbon nanotube (CNT) content of the Ct/C composites. Owing to the decreased mismatch in the CTEs, no cracks were formed in the TBCs (SiC and HfB₂-SiC-HfC coatings) deposited on the Ct/C composites. After heat treatment at 2100 °C, several wide cracks were found in the TBCs on the Cf/C composite, whereas the TBCs on the Ct/C composites were intact without cracks. We found that the CTE-tunable Ct/C composites can self-adapt to different TBCs, protecting the composites from oxidation at high temperatures.