Local aggregation effect of CNT on the vibrational behavior of four‐parameter continuous grading nanotube‐reinforced cylindrical panels

Free vibrations analysis of four‐parameter continuously graded nanocomposite cylindrical panels reinforced by randomly oriented straight and local aggregation single‐walled carbon nanotubes (CNTs) are presented based on three‐dimensional theory of elasticity. The material properties of continuously graded carbon nanotube‐reinforced composites (CG‐CNTRCs) are estimated through the Eshelby–Mori–Tanaka approach based on an equivalent fiber. The generalized differential quadrature method as an efficient and accurate numerical tool is used to discretize the governing equations and impediment the boundary conditions. One of the contributions of this work is to illustrate the influence of the four parameters of power‐law distributions on the vibration behavior of functionally graded orthotropic cylindrical panels reinforced by nanotube. The properties of CG‐CNTRC are affected by its microstructure, especially the degree of CNT aggregation that is described by an aggregation coefficient. It is shown the degree of aggregation canseriously reduce the effective stiffness and frequency parameter. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Characterizing elastic properties of carbon nanotube‐based composites by using an equivalent fiber

Effective elastic properties for carbon nanotube (CNT)‐reinforced composites are obtained through a variety of micromechanics techniques. An embedded CNT in a polymer matrix and its surrounding interphase is replaced with an equivalent fiber for predicting the mechanical properties of the CNT/polymer composite. Formulas to extract the effective material constants from solutions for the representative volume element under three loading cases are derived based on the elasticity theory. The effects of an interphase layer between the nanotubes and the polymer matrix as result of effective interphase layer are also investigated. Furthermore, this research is aimed at characterizing the elastic properties of CNTs‐reinforced composites using Eshelby–Mori–Tanaka approach based on an equivalent fiber. The variations of mechanical properties with tube radius, interphase thickness, and degree of aggregation are investigated. It is shown that the presence of aggregates has stronger impact than the interphase thickness on the effective modulus of the composite. This is because aggregates have significantly lower modulus than individual CNTs. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

Preparation and properties of T300 carbon fiber‐reinforced thermoplastic polyimide composites

In this study, a series of T300 carbon fiber‐reinforced polyimide (CFRPI) composites were prepared by laminating premolding polyimide (PI) films with unidirectional carbon fiber (CF) layers. On the basis of PI systems design, the effect of CF volume fraction, processing conditions, and PI molecular structure on the properties of CFRPI composites was studied in detail. In addition, two kinds of nano‐particles, including carbon nano‐tube (CNT) and SiO₂ were filled into the premolding PI films with different concentrations. And the effect of nano‐particles on the properties of CFRPI composites was also investigated. The surface characteristic of T300 CF was measured by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The properties of premolding PI film and CFRPI composites were measured by dynamic mechanical analysis (DMTA), SANS testing machine, scanning electron microscopy (SEM), and so forth. These experimental results showed that the properties of CFRPI composites were mainly affected by the premolding PI film and molding condition. The change of CF volume fraction from 55% to 65% took little effect on the mechanical properties of CFRPI composites. In addition, the incorporation of nano‐particle SiO₂ could further improve the properties of CFRPI composites, but CNT hardly improved the properties of CFRPI composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 646–654, 2006     

Electrical and mechanical properties of carbon nanotube‐epoxy nanocomposites

In this work, electrical conductivity and thermo‐mechanical properties have been measured for carbon nanotube reinforced epoxy matrix composites. These nanocomposites consisted of two types of nanofillers, single walled carbon nanotubes (SW‐CNT) and electrical grade carbon nanotubes (XD‐CNT). The influence of the type of nanotubes and their corresponding loading weight fraction on the microstructure and the resulting electrical and mechanical properties of the nanocomposites have been investigated. The electrical conductivity of the nanocomposites showed a significantly high, about seven orders of magnitude, improvement at very low loading weight fractions of nanotubes in both types of nanocomposites. The percolation threshold in nanocomposites with SW‐CNT fillers was found to be around 0.015 wt % and that with XD‐CNT fillers around 0.0225 wt %. Transmission optical microscopy of the nanocomposites revealed some differences in the microstructure of the two types of nanocomposites which can be related to the variation in the percolation thresholds of these nanocomposites. The mechanical properties (storage modulus and loss modulus) and the glass transition temperature have not been compromised with the addition of fillers compared with significant enhancement of electrical properties. The main significance of these results is that XD‐CNTs can be used as a cost effective nanofiller for electrical applications of epoxy based nanocomposites at a fraction of SW‐CNT cost. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Three‐dimensional solution for the vibration analysis of functionally graded multiwalled carbon nanotubes/phenolic nanocomposite cylindrical panels on elastic foundation

In this study, based on the three‐dimensional theory of elasticity, free vibration characteristics of nanocomposite cylindrical panels reinforced by multiwalled carbon nanotubes (MWCNT) are considered. The response of the elastic medium is formulated by the Winkler/Pasternak model. Modified Halpin–Tasi equation was used to evaluate the Young's modulus of the MWCNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin–Tsai equation from expressing a straight line to a nonlinear one in the MWNTs wt% range considered. Symmetric and asymmetric volume fraction profiles are provided in this article for comparison. It is shown that using only few grid points, accurate results are obtained which demonstrate the efficiency and convenience of the generalized differential quadrature method for the problem under consideration. The validity of the Young's modulus and frequency response were assessed by a comparison with available literature data, providing a good agreement. POLYM. COMPOS., 34:2040–2048, 2013. © 2013 Society of Plastics Engineers     

Mechanical and thermo-mechanical properties of carbon nanotube reinforced composites

A study on the mechanical and thermo-mechanical properties of carbon nanotube (CNT) reinforced nanocomposites is presented in this article. Mori–Tanaka method is used for modeling the effective stiffness and coefficient of thermal expansion. Regression formulas were developed to describe the effects of CNT orientation, aspect ratio, and CNT volume fraction. Given the statistical distributions of CNT orientations and aspect ratios, the effective properties can be conveniently derived by numerical integration using these formulas.     

The characteristics of carbon nanotube‐reinforced poly(phenylene sulfide) nanocomposites

Multiwall carbon nanotube reinforced poly (phenylene sulfide) (PPS) nanocomposites were successfully fabricated through melt compounding. Structural, electrical, thermal, rheological, and mechanical properties of the nanocomposites were systematically studied as a function of carbon nanotube (CNT) fraction. Electrical conductivity of the polymer was dramatically enhanced at low loading level of the nanotubes; the electrical percolation threshold lay between 1 and 2 wt % of the CNTs. Rheological properties of the PPS nanocomposites also showed a sudden change with the CNT fraction; the percolation threshold was in the range of 0–0.5 wt % of CNTs. The difference in electrical and rheological percolation threshold was mainly due to the different requirements needed in the carbon nanotube network in different stages. The crystallization and melting behavior of CNT‐filled PPS nanocomposites were studied with differential scanning calorimetry; no new crystalline form of PPS was observed in the nanocomposites, but the crystallization rate was reduced. The thermal and mechanical properties of the nanocomposites were also investigated, and both of them showed significant increase with CNT fraction. For 5 wt % of CNT‐filled PPS composite, the onset of degradation temperature increased by about 13.5°C, the modulus increased by about 33%, and tensile strength increased by about 172%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical properties of defective carbon nanotube/polyethylene nanocomposites: A molecular dynamics simulation study

Because of their remarkable performance properties and technological promise, polymer nanocomposites reinforced with single‐walled carbon nanotubes (SWCNTs) have attracted considerable attention in the engineering, applied physics, and materials science communities. Recent experimental and computational investigations have shown that the presence of nanoscale defects in CNTs can significantly impact their electrical, mechanical, and thermal properties. In this article, for the first time, we examine the effect of defective CNTs on the interfacial characteristics and mechanical properties of CNT/polyethylene (PE) nanocomposites. Our molecular dynamics simulations show that as few as five vacancy defects in each CNT in a high‐volume‐fraction CNT/PE nanocomposite can decrease the longitudinal Young's modulus of the nanocomposite by as much as 18%, and the shear stress at the CNT/polymer interface by as much as 38%. By accounting for nanoscale defects and their effect on the CNT/polymer interfacial mechanics, our findings provide a practical guide for designing nanocomposites that are capable of attaining a desired set of elastic performance properties. POLYM. COMPOS., 305–314, 2016. © 2014 Society of Plastics Engineers     

Synergistic strengthening effect of graphene-carbon nanotube hybrid structure in aluminum matrix composites

High-performance reinforcement and tailored architecture are currently explored to develop advanced metal matrix composites. In this work, aluminum (Al) matrix composite reinforced by hybrid carbon nanofillers was fabricated by a composite flake assembly process. It was found that for various carbon nanofiller volume fractions, a striking synergistic strengthening effect was achieved by employing graphene (reduced graphene oxide, RGO) and carbon nanotube (CNT) hybrid structure as reinforcement in the Al matrix. Particularly, a tensile strength of 415 MPa was achieved with the addition of 1.5 vol.% of RGO-CNT hybrid, which is significantly higher than those reinforced by individual CNT or RGO (326 and 331 MPa, respectively). The synergistic strengthening effect was attributed to the formation of a planar network of RGO and CNT, which improves the load transfer efficiency between the matrix and the reinforcement in composites. Our study highlights the importance of reinforcement architecture for enhancing the strengthening ability in composites, and provides an effective route to fully take the advantage of the superior properties of various reinforcements.     

Effect of annealing treatment on the structure and properties of polyurethane/multiwalled carbon nanotube nanocomposites

The thermoplastic polyurethane/multiwalled carbon nanotube (TPU/CNT) nanocomposites with high conductivity and low percolation threshold value were prepared by melting blending and annealing treatment. The effect of annealing process on the microphase structure and the properties of TPU/CNT nanocomposites was studied. It has been shown that CNT flocculation can occur in TPU/CNT nanocomposites during the annealing process. At a critical CNT content, which defined the percolation threshold, CNTs could form conductivity network. The conductive percolation threshold value of TPU/CNT nanocomposites was decreased from 10 to 4% after annealing process, and the conductivity of TPU/CNT nanocomposites with 10 vol % of CNT could reach 1.1 S/m after an annealing time of 1 h. The significant enhancement of electrical conductivity was influenced by the annealing time and the content of CNTs. The formation of CNT networks was also verified by dynamic viscoelastic characterization. The results of X‐ray diffraction and differential scanning calorimetry indicated that annealing process reinforced the microphase separation of the nanocomposites. Mechanical properties test showed that the annealing treatment was in favor of improving the mechanical properties; however, further increase in the annealing time has negative effect on the mechanical properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Assessment of intertube interactions in different functionalized multiwalled carbon nanotubes incorporated in a phenoxy resin

In this work, about 1 wt% of different functionalized carbon nanotubes (CNTs), namely CNT? COOH (CNT with carboxylic groups), CNT? NH₂ (CNT with amine groups) and CNT? OH (CNT with hydroxyl groups), as well as nonfunctionalized CNTs were incorporated into a phenoxy resin via a melt mixing process. The extent of intertubes and polymer–tubes interactions and their influence on state of CNTs dispersion were assessed through determination of electrical, rheological, and morphological characteristics. CNT? NH₂ showed the lowest intertubes interactions followed by CNT? OH and CNT? COOH. Nanocomposite made from CNT? COOH showed the poorest state of CNTs dispersion and the biggest CNTs agglomerates and it remained nonconductive. The acid‐functionalized CNTs were not able to form strong polymer–tube interactions because of their high cohesive energy and therefore in the melt rheological investigations they exhibited the lowest storage modulus and complex viscosity as well as the highest loss factor among all the studied CNTs. A good balance between intertubes and polymer–tube interactions is necessary through proper selection of CNTs functional groups for achieving a good state of CNTs dispersion and consequently obtaining enhanced electrical and viscoelastic properties. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Size‐dependent vibration of double‐bonded carbon nanotube‐reinforced composite microtubes conveying fluid under longitudinal magnetic field

In the present research, vibration and instability of visco‐elastically coupled carbon nanotube reinforced composite (CNTRC) microtubes conveying fluid is investigated. Single‐walled carbon nanotubes are arranged in a longitudinal direction inside poly methyl methacrylate matrix. The longitudinal magnetic field is applied on coupled system. The surrounding medium is simulated by visco‐Pasternak model due to considerable damping and shearing effects. Based on Mori–Tanaka theory, the properties of composite microtubes are obtained. In order to achieve more accurate results, strain gradient theory is developed in Timoshenko beam model. The motion equations are derived utilizing Hamilton's principle and solved by means of differential quadrature method. Considering slip flow regime, the influences of various parameters such as magnetic intensity, elastic medium, Knudsen number, and volume fraction of CNTs on the vibration characteristics of coupled system are studied in details. Results demonstrated that the stability of coupled system can be significantly improved by applying magnetic field. The result of this study can be useful to control and improve the performance of micro‐mechanical systems conveying fluid. POLYM. COMPOS., 37:1375–1383, 2016. © 2014 Society of Plastics Engineers     

Effect of processing technique on the dispersion of carbon nanotubes within polypropylene carbon nanotube‐composites and its effect on their mechanical properties

Carbon nanotube‐reinforced polymer composites are being investigated as promising new materials having enhanced physical and mechanical properties. With regards to mechanical behavior, the enhancements reported thus far by researchers are lower than the theoretical predictions. One of the key requirements to attaining enhanced behavior is a uniform dispersion of the nanotubes within the polymer matrix. Although solvent mixing has been used extensively, there are concerns that any remaining solvent within the composite may degrade its mechanical properties. In this work, a comparison is carried out between solvent and “solvent‐free” dry mixing for dispersing multiwall carbon nanotubes in polypropylene before further melt mixing by extrusion. Various weight fractions of carbon nanotubes (CNTs) are added to the polymer and their effect on the mechanical properties of the resulting composites is investigated. Enhancements in yield strength, hardness, and Young's modulus when compared with the neat polymer, processed under similar conditions, are observed. Differences in mechanical properties and strain as a function of the processing technique (solvent or dry) are also clearly noted. In addition, different trends of enhancement of mechanical properties for the solvent and dry‐mixed extrudates are observed. Dry mixing produces composites with the highest yield strength, hardness, and modulus at 0.5 wt% CNT, whereas solvent mixing produces the highest mechanical properties at CNT contents of 1 wt%. It is believed that this difference is primarily dependent on the dispersion of CNTs within the polymer matrix which is influenced by the processing technique. Field emission scanning electron microscopy analysis shows the presence of clusters in large wt% CNT samples produced by dry mixing. Samples produced by solvent mixing are found to contain homogeneously distributed CNTs at all CNT wt fractions. CNT pull‐out is observed and may explain the limited enhancement in mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effects of the dispersion state and aspect ratio of carbon nanotubes on their electrical percolation threshold in a polymer

The electrical percolation threshold of carbon nanotubes (CNTs) is correlated with their dispersion state and aspect ratio through modeling. An analytical percolation model based on excluded volume theory and developed for systems containing two types of fillers is used. CNTs are modeled as two types of fillers: single CNT and m‐CNT bundle, and a variable P representing the dispersion state of CNTs is introduced. An equation showing the effects of the dispersion state and aspect ratio on the electrical percolation threshold of CNTs is established and verified with some of the published experimental data. It is useful for predicting the conductive behavior of polymer/CNT composites and for the design of their processing conditions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reinforcement of rigid PVC/wood‐flour composites with multi‐walled carbon nanotubes

Multi‐walled carbon nanotubes (CNT) were compounded with PVC by a melt blending process based on fusion behaviors of PVC. The effects of CNT content on the flexural and tensile properies of the PVC/CNT composites were evaluated in order to optimize the CNT content. The optimized CNT‐reinforced PVC was used as a matrix in the manufacture of wood‐plastic composites. Flexural, electrical, and thermal properties of the PVC/wood‐flour composites were evaluated as a function of matrix type (nonreinforced vs. CNT‐reinforced). The experimental results indicated that rigid PVC/wood‐flour composites with properties similar to those of solid wood can be made by using CNT‐reinforced PVC as a matrix. The CNT‐reinforced PVC did not influence the electrical and thermal conductivity of the PVC/wood‐flour composites. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Synthesis of hybrid polyaniline/carbon nanotubes nanocomposites in toluene by dynamic interfacial inverse emulsion polymerization under sonication

This work describes an empirical study of in situ interfacial dynamic inverse emulsion polymerization process under sonication of aniline in the presence of nine different types of carbon nanotubes (CNT) in toluene. The polymerization method described in this work is simple and very fast (5 min) compared to the other literature reports (3–12 h). During polymerization, CNT are coated with polyaniline (PANI) forming a core‐shell structure of nanowires as evidenced by transmission electron microscopy (TEM) and high‐resolution scanning microscopy (HRSEM). HRSEM images and surface resistivity imply that PANI coating of CNT leads to a remarkable improvement in separation and dispersion of CNT in toluene, which otherwise would have rapidly coagulate and settle. Two of the nine different CNT studied have shown the lowest surface resistivities. Films of uniform thickness were successfully produced (HRSEM of cross‐sections). The effect of film thickness on conductivity and optical properties is reported in the work. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Compression behaviour of a fibre bundle with grafted carbon nanotubes

When carbon nanotubes (CNTs) are grown on carbon fibres, with the goal to increase toughness of a carbon fibre reinforced composite, the compressibility of the carbon fibre bundle or a fabric decreases significantly. The pressure, necessary to achieve the desired fibre volume fraction in a composite, should be increased by several bars. The paper proposes modelling approaches for calculation of the change of compression resistance of the CNT-grafted fibre bundle and fabric. The models use a previously developed algorithm for calculation of the compression resistance of a random assembly of CNTs. Two possible scenarios for the CNT-growth positioning are considered: a CNT assembly that homogeneously fills the free space between the fibres and a CNT assembly that is localised on the surface of the fibres. The model is validated against measurements of the compression resistance of carbon fibre bundles and fabrics with CNTs grown using the CVD method.     

Free vibration analysis and design optimization of nanocomposite‐laminated beams using various higher order beam theories and imperialist competitive algorithm

In this article, two goals are followed. First, free vibrations of laminated beams reinforced by Single‐Walled Carbon Nanotubes (SWCNTs) are studied based on various Higher order Shear Deformation Beam Theories (HSDBTs) and using an analytical method. The SWCNTs are assumed to be aligned and straight with a uniform layout. The extended rule of mixture is applied to describe the effective material properties of the structure. The natural frequencies of the nanocomposite beam are compared with the existing solutions to verify the validity of the theories. Results show the simplicity and accuracy of the method for free vibration analysis of nanocomposite beams. The effects of Carbon Nanotube (CNT) volume fractions in the layers and span‐to‐depth ratio on the fundamental frequency of the structure are also studied. As for the second goal of this study, optimization of nanocomposite‐laminated beams is presented. The main objective of the optimization problem is maximizing the fundamental frequency of the structure. The total amount of CNT in the structure is considered as a constraint on the optimization problem. The primary optimization variables are the values of CNT volume fraction in layers of a 10‐layer laminated nanocomposite beam. Since the search space of the optimization problem is large, the optimization processes becomes so complicated and time consuming. Thus, a novel meta–heuristic approach called Imperialist Competitive Algorithm (ICA), which is a socio‐politically motivated global search strategy, is applied to find the optimal solution. Results show the success of ICA for the design of nanocomposite structures. POLYM. COMPOS., 37:2442–2451, 2016. © 2015 Society of Plastics Engineers     

Improved tensile properties of carbon nanotube modified epoxy and its continuous carbon fiber reinforced composites

Carbon nanotubes (CNTs) were used to improve the tensile properties of an epoxy resin and its continuous carbon fiber (CF) reinforced composites. Micrography picture showed that CNTs has been well incorporated into the composites, and made the fracture cross section more rougher through sharing the stress. For the CNT/epoxy composite, the tensile strength and modulus both increased upon the CNT addition, and at a CNT volume concentration of 2.0%, the maximum enhancements in the tensile strength and modulus were achieved as 26.7% and 21.5%, respectively. For the CNT‐CF/epoxy composite, the maximum enhancement in tensile strength was achieved as 11.6% at a CNT volume concentration of 1.0% and then decreased with the further increase of the CNT addition, but the tensile modulus increased monotonically upon the CNT addition. POLYM. COMPOS., 36:1664–1668, 2015. © 2014 Society of Plastics Engineers     

Bending properties of the multilayer‐connected biaxial weft knitted fabrics‐reinforced composites made with carbon fibers

This article presents an experimental study of bending properties of multilayer‐connected biaxial weft knitted (MBWK) fabrics‐reinforced composites made with carbon fibers. Three types of composites are used in bending test, which are three‐layer‐connected biaxial weft knitted fabric‐reinforced composite, four‐layer‐connected biaxial weft knitted fabric‐reinforced composite and five‐layer‐connected biaxial weft knitted fabric‐reinforced composite. Two‐way ANOVA analyzing method was used to deal with whether the carbon fiber volume fraction and the cutting direction have significant effect on the bending strength of the MBWK fabrics‐reinforced composites. Failure analysis is also available by means of samples debris examination to identify the failure mode. POLYM. COMPOS., 36:2291–2302, 2015. © 2014 Society of Plastics Engineers