Hydrogel‐MWCNT nanocomposites: Synthesis,characterization, and heating with radiofrequency fields

Hydrogel nanocomposites are attractive biomaterials for numerous applications including tissue engineering, drug delivery, cancer treatment, sensors, and actuators. Here we present a nanocomposite of multiwalled carbon nanotubes (MWCNT) and temperature responsive N‐isopropylacrylamide hydrogels. The lower critical solution temperature (LCST) of the nanocomposites was tailored for physiological applications by the addition of varying amounts of acrylamide (AAm). The addition of nanotubes contributed to interesting properties, including tailorability of temperature responsive swelling and mechanical strength of the resultant nanocomposites. The mechanical properties of the nanocomposites were studied over a range of temperatures (25–55°C) to characterize the effect of nanotube addition. A radiofrequency (RF) field of 13.56 MHz was applied to the nanocomposite discs, and the resultant heating was characterized using infrared thermography. This is the first report on the use of RF to remotely heat MWCNT‐hydrogel nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Experimental characterization and modeling stiffness of polymer/clay nanocomposites within a hierarchical multiscale framework

To provide a better understanding of the relationship between nanostructure and overall material stiffness in the case of polymer/clay nanocomposites, both analytical and finite element modeling were considered. A micromechanical analytical approach based on a multiscale framework is presented in which special attention is devoted to the constrained region around reinforcements. The thickness of the constrained region is seen as a characteristic length scale and the effect of particle size is explicitly introduced in the model. Moreover, the constrained region presents graded properties. The hierarchical morphology of intercalated silicate stacks is also explicitly introduced in the micromechanical model from an equivalent stiffness method in which the silicate stacks are replaced by homogeneous particles with constructed equivalent anisotropic stiffness. The orientational averaging process is used to derive the overall stiffness tensor of nanocomposite materials containing randomly oriented reinforcements. The respective influence of volume fraction, aspect ratio, size and orientation of the reinforcements, matrix properties, number of silicate layers per stack, and interlayer spacing on the overall nanocomposite stiffness is analyzed. The overall stiffness of polymer/clay nanocomposite systems is also evaluated by means of finite element simulations and the results compare favorably with model predictions. From an experimental point of view, relevant morphological and mechanical data were obtained on polyamide‐6 nanocomposites prepared using a modified montmorillonite Cloisite 30B and an unmodified sodium montmorillonite Cloisite Na⁺. The amount of constrained region around reinforcements was estimated using results issued from dynamic mechanical analyses and differential scanning calorimetry. Comparison to the model clearly underlines the contribution of the constrained region to the stiffness improvement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Electrical conductivity modeling of carbon black/polycarbonate,carbon nanotube/polycarbonate,and exfoliated graphite nanoplatelet/polycarbonate composites

Adding conductive carbon fillers to electrically insulating thermoplastic polymers increases the resulting composite's electrical conductivity, which would enable them to be used in electrostatic dissipative and semiconductive applications. In this study, varying amounts of carbon black (CB: 2 to 10 wt %), multiwalled carbon nanotubes (CNT: 0.5 to 8 wt %), or exfoliated graphite nanoplatelets (GNP: 2 to 15 wt %) were added to polycarbonate (PC) and the resulting composites were tested for electrical conductivity (EC = 1/electrical resistivity). The percolation threshold was ～ 1.2 vol % CNT, ～ 2.4 vol % CB, and ～ 4.6 vol % GNP. In addition, three EC models (Mamunya, additive, and general effective media) were developed for the CB/PC, CNT/PC, and GNP/PC composites. The general effective media (GEM) model showed the best agreement with the experimental results over the entire range of filler concentrations (above and below the percolation threshold) for all three composite systems. In addition, the GEM model can be easily adapted for composites containing combinations of different conductive fillers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characterization and preparation of new multiwall carbon nanotube/conducting polymer composites by in situ polymerization

Composites based on poly(diphenyl amine) (PDPA) and multiwall carbon nanotubes (MWNTs) were prepared by chemical oxidative polymerization through two different approaches: in situ polymerization and intimate mixing. In in situ polymerization, DPA was polymerized in the presence of dispersed MWNTs in sulfuric acid medium for different molar composition ratios of MWNT and DPA. Intimate mixing of synthesized PDPA with MWNT was also used for the preparation of PDPA/MWNT composites. Transmission electron microscopy revealed that the diameter of the tubular structure for the composite was 10–20 nm higher than the diameter of pure MWNT. Scanning electron microscopy provided evidence for the differences in the morphology between the MWNTs and the composites. Raman and Fourier transform IR (FTIR) spectroscopy, thermogravimetric analysis, X‐ray diffraction, and UV–visible spectroscopy were used to characterize the composites and reveal the differences in the molecular level interactions between the components in the composites. The Raman and FTIR spectral results revealed doping‐type molecular interactions and coordinate covalent‐type interactions between MWNT and PDPA in the composite prepared by in situ polymerization and intimate mixing, respectively. The backbone structure of PDPA in the composite decomposed at a higher temperature (>340°C) than the pristine PDPA (～300°C). This behavior also favored the molecular level interactions between MWNT and PDPA in the composite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3721–3729, 2006     

Multiscale numerical investigation on failure behaviour of three-dimensional orthogonal woven carbon/carbon composites subjected to pin-loading

On the basis of the experimental results in previous work, a multiscale numerical modeling strategy on the failure behaviour of three-dimensional orthogonal woven carbon/carbon composites under pin-loading was presented. In consideration of the complexity of internal woven architecture, the finite element analysis at micro-/meso-/macro-scale levels was performed to exhibit the effective material properties and mechanical behaviour. The geometric models were reconstructed via X-ray tomography technology to obtain feasible configurations based on actual microstructure, meanwhile the models considered the fibers random arrangement in the yarn and voids stochastic distribution in the matrix. The anisotropic composites damage evolution was characterized by Murakami-Ohno damage theory. Additionally, for a further exploration on the practical bearing failure mode, the macro-scale open-hole plate model was established using mesh superposition method to expose the damage mechanism of each component in composites at hole edge, and the numerical predictions agreed reasonably well with the experimental results.     

Influences of polymer matrix melt viscosity and molecular weight on MWCNT agglomerate dispersion

In order to study the influence of melt viscosity and molecular weight on nanotube dispersion and electrical volume resistivity, three different polycarbonates (PCs) varying in molecular weight were melt compounded with 1 wt% multiwalled carbon nanotubes (MWCNTs, Baytubes^® 150 HP) using a small-scale compounder. The experiments were performed at constant melt temperature but at varying mixing speeds, thereby applying different magnitudes of shear stress. Light transmission microscopy was used to access the state of agglomerate dispersion, and electrical resistivities of the composites were measured on pressed plates. The results indicate that with increasing matrix viscosity the agglomerate dispersion gets better when using constant mixing conditions but worse considering comparable shear stress values. To study the effect of molecular weight, in a second set of experiments melt temperatures were adjusted so that all PCs had similar viscosity and mixing was performed at constant mixing speed. As investigated on two viscosity levels, the composites based on the low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices, highlighting the role of matrix infiltration into primary nanotube agglomerates as the first step of dispersion. The resistivity values of composites prepared using low viscosity matrices were lower than those of composites from high viscosity matrix.     

Parametric numerical simulation of impact response of carbon nanotube/polymer nanocomposites

A numerical model has been developed using the explicit FE code LS-DYNA in order to study the effect of geometrical and material parameters on the low-velocity impact response of carbon nanotube (CNT)/polymer nanocomposites. The model is based on a Representative Volume Element (RVE). The RVE is prismatic with a rectangular cross-section while the impactor is spherical. The simulations show that the presence of CNT significantly enhances the impact stiffness and the energy absorption capacity of the material. The enhancement increases with the CNT's volume fraction and it is larger at larger impact velocities. The effect of CNT's aspect ratio is found to be minor. The orthotropic behaviour of CNT assigns the RVE a higher energy absorption capacity than the isotropic behaviour at small impact velocities. The prediction of impact damage at large impact velocities indicates that the CNT makes the polymer more susceptible to fracture.     

Tensile modulus of polymer/CNT nanocomposites containing networked and dispersed nanoparticles

The properties of three‐dimensional networks of nanoparticles in polymer/carbon nanotubes (CNT) nanocomposites (PCNT) are particularly interesting from fundamental and application views. In this article, a new model is suggested for predicting the tensile modulus of PCNT using the Ouali and Paul models. The Ouali model considers the network of CNT in a polymer matrix, while the Paul model predicts the tensile modulus of samples containing dispersed nanoparticles. The predictions of the suggested approach are compared with experimental data from several samples. Also, the roles of the main parameters in the tensile modulus of PCNT are evaluated. The predictions agree with the experimental results at different filler concentrations. The roles of these parameters on the tensile modulus of PCNT are discussed based on the properties of CNT networks. © 2017 American Institute of Chemical Engineers AIChE J, 63: 220–225, 2018     

Effects of mixing on electrical properties of carbon nanofiber and polymer composites

We examined electrical properties of composites of carbon nanofibers (CNFs)/linear low‐density polyethylene (LLDPE) in the range of mixing time. An addition of CNFs into LLDPE led to a decrease of electrical resistivity, and the large amounts of CNFs were required to reach the electrical percolation threshold for the longer mixing time. For the research of these phenomena, we examined the effects of mixing time on the size (length) and spatial distributions of CNFs in the composites. SEM micrographs revealed the size reduction of CNFs in a series of mixing times, although the spatial dispersion of CNFs became more uniform at longer mixing time. To describe the reduction of CNFs theoretically, we hypothesize the size distribution of CNFs obeys a governing population balance kinetics based on an irreversible dissolution process. For the process, we proposed a size dependent breakage rate coefficient proportional to the size of CNFs. The model prediction for the time evolution of size distribution of CNFs has been validated with the experimental measurement showing good agreement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal conductivity and dynamic mechanical property of glycidyl methacrylate‐grafted multiwalled carbon nanotube/epoxy composites

The well dispersed multiwalled carbon nanotube (MWCNT)/epoxy composites were prepared by functionalization of the MWCNT surfaces with glycidyl methacrylate (GMA). The morphology and thermal properties of the epoxy nanocomposites were investigated and compared with the surface characteristics of MWCNTs. GMA‐grafted MWCNTs improved the dispersion and interfacial adhesion in epoxy resin, and enhanced the network structure. The storage modulus of 3 phr GMA‐MWCNTs/epoxy composites at 50°C increased from 0.32 GPa to 2.87 GPa (enhanced by 799%) and the increased tanδ from 50.5°C to 61.7°C (increased by 11.2°C) comparing with neat epoxy resin, respectively. Furthermore, the thermal conductivity of 3 phr GMA‐MWCNTs/epoxy composite is increased by 183%, from 0.2042 W/mK (neat epoxy) to 0.5781 W/mK. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fabrication of surfactant‐removed polymer composites with single‐walled carbon nanotube networks

Polystyrene (PS) composites with a network of single‐walled carbon nanotubes (SWNTs) were fabricated by using monodispersed PS micospheres. First, PS spheres and surfactant‐dispersed SWNTs were mixed in water, then a hybrid cake was obtained by filtration via a microporous membrane and the SWNTs were filled within the spaces of packed polymer spheres. At this stage, the surfactants for dispersing SWNTs were totally removed from the composites by a thorough washing. Then the composite films with SWNT networks were obtained by compression molding at 160°C. Structure of the composites had been characterized by transmission electron microscopy and scanning electron microscopy. The present SWNT composites showed a low percolation threshold of electrical conductivities. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of a cyclic butylene terephthalate oligomer on the processability and thermoelectric properties of polycarbonate/MWCNT nanocomposites

The thermoelectric properties of melt-processed nanocomposites consisting of a polycarbonate (PC) thermoplastic matrix filled with commercially available carboxyl (–COOH) functionalized multi-walled carbon nanotubes (MWCNTs) were evaluated. MWCNTs carrying carboxylic acid moieties (MWCNT-COOH) were used due the p-doping that the carboxyl groups facilitate, via electron withdrawing from the electron-rich π-conjugated system. Preliminary thermogravimetric analysis (TGA) of MWCNT-COOH revealed that the melt-mixing was limited at low temperatures due to thermal decomposition of the MWCNT functional groups. Therefore, PC was mixed with 2.5 wt% MWCNT-COOH (PC/MWCNT-COOH) at 240 °C and 270 °C. In order to reduce the polymer melt viscosity, a cyclic butylene terephthalate (CBT) oligomer was utilized as an additive, improving additionally the electrical conductivity of the nanocomposites. The melt rheological characterization of neat PC and PC/CBT blends demonstrated a significant decrease of the complex viscosity by the addition of CBT (10 wt%). Optical and transmission electron microscopy (OM, TEM) depicted an improved MWCNT dispersion in the PC/CBT polymer blend. The electrical conductivity was remarkably higher for the PC/MWCNT-COOH/CBT composites compared to the PC/MWCNT-COOH ones. Namely, the PC/MWCNT-COOH/CBT processed at 270 °C exhibited the best values with electrical conductivity; σ = 0.05 S/m, Seebeck coefficient; S = 13.55 μV/K, power factor; PF = 7.60 × 10⁻⁶μW/m K⁻², and thermoelectric figure of merit; ZT = 7.94 × 10⁻⁹. The PC/MWCNT-COOH/CBT nanocomposites could be ideal candidates for large-scale thermal energy harvesting, even though the presently obtained ZT values are still too low for commercial applications.     

Multiwalled carbon nanotube polymer composites: Synthesis and characterization of thin films

The aim of this article was to elucidate the basic relationships between processing conditions and the mechanical and electrical properties of multiwalled carbon nanotube reinforced polymer composites. In conventional chopped fiber reinforced polymer composites, uniform distributions of fibers throughout the matrix are critical to producing materials with superior physical properties. Previous methods have dispersed carbon nanotubes by aggressive chemical modification of the nanotubes or by the use of a surfactant prior to dispersion. 1 , 2 Here, ultrasonic energy was used to uniformly disperse multiwalled nanotubes (MWNTs) in solutions and to incorporate them into composites without chemical pretreatment. Polystyrene (PS) solutions containing MWNTs were cast and spun to yield thin film MWNT composites. The rheology of PS/MWNT suspensions was modeled using the Carreau equation. MWNTs were found to align at the shear rates generated by the spin casting process. The tensile modulus and strain to failure of samples compared well to classical micromechanical models, increasing with MWNT loading. The composite films showed lower strains at the yield stress than neat PS films. The presence of MWNTs at 2.5 vol % fraction approximately doubles the tensile modulus, and transforms the film from insulating to conductive (surface resistivity, ρ, approaching 10³ Ω/□). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2660–2669, 2002     

Experimental and numerical analysis of single lap bonded joints: Epoxy and castor oil PU-glass fibre composites

ABSTRACT

Currently, there is a growing concern for the environment. Several studies of new materials to reduce environmental impact have been carried out by different research groups, and many companies have replaced parts made of fossil sources by renewable materials. The use of polyurethane (PU) derived from castor oil as a matrix for composite materials and adhesives is one example. Hence, the present work aims to compare the numerical and experimental analyses of castor oil PU and epoxy resin not only as a matrix of composite materials, but also as an adhesive of bonded joints. The joint coupons were manufactured by using castor oil PU-glass fibre and epoxy-glass fibre as adherents, which were bonded by epoxy or castor oil PU. Thus, four combinations of adherents and adhesives were investigated. Specimens with identical geometry were used in all tests, which were based on guidelines for single lap bonded joints. Computational simulations via Finite Element Method were performed for predictions of the adhesive layer stresses and strength. In addition, a material model is proposed to predict the failure of the adhesive layer. The experimental and numerical results showed that PU derived from castor oil has good mechanical performance, making this material a feasible alternative for bonded joints, mostly nowadays when environment is a major concern.     

Polypyrrole/carbon nanotube composites: Molecular modeling and experimental investigation as anti-corrosive coating

In this work we present a computational method based on molecular mechanics (MM) and dynamics (MD), to predict mechanical properties of polypyrrole (PPy)/polyaminobenzene sulfonic acid-functionalized single-walled carbon nanotubes (CNT-PABS) and PPy/carboxylic acid-functionalized single-walled carbon nanotubes (CNT-CA) composites. Furthermore, experiments were carried out to assess the anticorrosive features of the PPy film and CNT-PABS and CNT-CA PPy reinforced composite coatings. Computational bulk models of PPy/CNT-PABS and PPy/CNT-CA were implemented at atomistic scale and composite coatings were grown in situ onto carbon steel (OL 48-50) electrodes. PPy, PPy/CNT-PABS and PPy/CNT-CA computational models and films were investigated concerning mechanical properties by using computational tools. The obtained films were assessed experimentally as anticorrosive materials using potentiodynamic measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results clearly confirmed that the CNT-PABS and CNT-CA are properly dispersed in the composite coatings and have beneficial effect on mechanical integrity. Moreover, the anticorrosion protecting ability of the composite coatings is significantly higher than the one characteristic to pure PPy. The Young's moduli generally increased with increasing of CNT content and values ranged from 2.67 GPa in the case of pure PPy to 4.15–4.61 GPa in the case of PPy/CNT-PABS composite system.In agreement with earlier results from the literature for conducting polymer organic coatings, the higher conductivity of material leads to a more efficient anticorrosion protection capability, our results exhibited an enhance of conducting features even for very low mass of CNT-PABS or CNT-CA loaded in composites coatings therefore, an improvement of anticorrosion protecting ability.     

Morphology,crystallization, and mechanical properties of poly(ethylene terephthalate)/multiwalled carbon nanotubes composites

Poly(ethylene terephthalate)/multiwalled carbon nanotubes (PET/MWCNTs) with different MWCNTs loadings have been prepared by in situ polymerization of ethylene glycol (EG) containing dispersed MWCNTs and terephthalic acid (TPA). From scanning electronic microscopy images of nanocomposites, it can be clearly seen that the PET/MWCNTs composites with low‐MWCNTs contents (0.2 and 0.4 wt %) get better MWCNTs dispersion than analogous with high‐tube loadings (0.6 and 0.8 wt %). The nonisothermal crystallization kinetics was analyzed by differential scanning calorimetry using Mo kinetics equation, and the results showed that the incorporation of MWCNTs accelerates the crystallization process obviously. Mechanical testing shows that, in comparison with neat PET, the Young's modulus and the yield strength of the PET nanocomposites with incorporating 0.4 wt % MWCNTs are effectively improved by about 25% and 15%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

An experimental and numerical investigation of adhesive bonding strengths of polymer materials

We employed the Iosipescu shear specimens and butt-joint specimens to measure the shear and tensile strengths of five types of adhesive bonds for brittle poly(methyl methacrylate) and Homalite polymers. In order to examine the possible stress singularities due to property mismatch between the adhesives and polymers, and ensure uniform stress distributions along the bonded interfaces, two optical techniques, photoelasticity and coherent gradient sensing, were employed to record full field, in situ fringe patterns until specimens failed. Direct comparison of finite element analysis and experimental stress analysis of Iosipescu shear specimens showed that along the polymer/adhesive/polymer interface, only a very weak stress singularity existed. Consequently, the stress distributions were quite uniform. Butt-joint tensile experiments verified negligible stress singularities and uniform stress distributions along the interface. However, for some shear specimens with strong bonds, the final failure occurred in a tensile mode at the upper edge, rather than a shear failure mode in the gauge section. Hence, only the lower limits of the shear strength rather than the actual magnitude could be measured.     

Functionalization of MWCNT with P(MMA-co-S) copolymers via ATRP: Influence on localization of MWCNT in SAN/PPE 40/60 blends and on rheological and dielectric properties of the composites

In this work, the localization of functionalized multi-walled carbon nanotubes (MWCNT) with random copolymers of methyl methacrylate and styrene (P(MMA-co-S)) in poly(styrene-co-acrylonitrile)/poly(2, 6-dimethyl-1,4-phenylene ether) blends (SAN/PPE) and its influence on morphological, rheological and dielectric properties of the composites were investigated. P(MMA-co-S) copolymers were grafted onto MWCNT via atom transfer radical polymerization (ATRP). The molecular weight of the copolymers was adjusted by controlling the time of reaction. In SAN/PPE blends, MWCNT grafted with low molecular weight copolymers were predominantly located at the interface of the blend and a few individual tubes were dispersed in the PPE phase. Aggregation of MWCNT was observed nearby the interfacial region because of micellization of grafted copolymers. Aggregation was more pronounced with increasing molecular weight of the grafted P(MMA-co-S) copolymer. In the melt, the composite containing MWCNT with low molecular weight copolymers had higher dynamic moduli than the one with pristine MWCNT. An increasing molecular weight of grafted copolymer led to a softening effect which resulted in a reduction of the moduli of the composite. Although a pronounced enhancement was observed for the composites with pristine MWCNT, only a small increase in electrical conductivity was achieved by adding functionalized MWCNT owing to the poor network formed by functionalized MWCNT in the blends.     

碳纳米管的制备及其聚合物基复合材料的研究进展

本文综述了单壁碳纳米管的制备方法,重点阐述了化学气相沉积法的合成运用,并对目前碳纳米管在聚合物基纳米复合材料方面的研究做了综合阐述。