Sepiolite-based epoxy nanocomposites: relation between processing, rheology, and morphology

Rheology of sepiolite-based epoxy suspensions as well as morphology and dynamic mechanical properties of the corresponding nanocomposites are discussed in this paper. The influence of the type of sepiolite used, i.e. non-modified, aminosilane and glycidylsilane surface modified, and of the process developed to prepare the epoxy suspensions were investigated. Except for low amount of filler, a shear thinning behavior was observed in the others sepiolite-based epoxy suspensions. The interactions developed between the sepiolite and the epoxy matrix are responsible for the magnitude of the shear thinning effect and are related to the morphology of the nanocomposites. The best dispersion of sepiolite was achieved using either an emulsion process or a glycidyl functionalized sepiolite.     

Miscibility and compatibilization of poly(trimethylene terephthalate)/acrylonitrile-butadiene-styrene blends

Poly(trimethylene terephthalate)/acrylonitrile-butadiene-styrene (PTT/ABS) blends were prepared by melt processing with and without epoxy or styrene-butadiene-maleic anhydride copolymer (SBM) as a reactive compatibilizer. The miscibility and compatibilization of the PTT/ABS blends were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), capillary rheometer and scanning electron microscopy (SEM). The existence of two separate composition-dependent glass transition temperatures (T_gs) indicates that PTT is partially miscible with ABS over the entire composition range. In the presence of the compatibilizer, both the cold crystallization and glass transition temperatures of the PTT phase shifted to higher temperatures, indicating their compatibilization effects on the blends.The PTT/ABS blends exhibited typical pseudoplastic flow behavior. The rheological behavior of the epoxy compatibilized PTT/ABS blends showed an epoxy content-dependence. In contrast, when the SBM content was increased from 1 wt% to 5 wt%, the shear viscosities of the PTT/ABS blends increased and exhibited much clearer shear thinning behavior at higher shear rates. The SEM micrographs of the epoxy or SBM compatibilized PTT/ABS blends showed a finer morphology and better adhesion between the phases.     

The improvement in interfacial shear strength of wood fiber/epoxy composite by sizing with epoxy sizing agent containing MWCNTs

This paper discloses a feasible and high efficient strategy for wood fiber treatment to introducing multi‐wall carbon nanotubes (MWCNTs) to the surface of wood fibers for the aim of improving the interfacial shear strength of wood fiber/epoxy composite. Briefly, a layer of MWCNT was deposited on wood fibers through sizing wood fibers with epoxy sizing agent containing amine‐treated MWCNTs (MWCNT‐PEI). The surface functional groups, morphology, wettability, and interphase properties of MWCNTs on the surface of wood fiber were studied. The remarkable enhancements were achieved in interfacial shear strength of reinforced composites by dipping wood fiber in MWCNTCOOH suspension and wood fiber sizing containing MWCNT‐PEI.     

Experimental fracture study of MWCNT/epoxy nanocomposites under the combined out-of-plane shear and tensile loading

In order to explore the role of multi-walled carbon nanotubes (MWCNTs) on the fracture behavior of epoxy-based nanocomposites, fracture tests were conducted under the combined out-of-plane shear and tensile loading. Epoxy resin LY-5052 together with MWCNT contents of 0.1, 0.5 and 1.0 wt% were used to produce nanocomposite specimens. The results showed that increasing the contribution of out-of-plane shear from pure mode I towards pure mode III enhanced fracture toughness for both pure epoxy and nanocomposites. Additionally, it was found that in both loading conditions of pure mode III and mixed mode I/III, increasing MWCNT content up to 1.0 wt% enhanced fracture toughness with an ascending trend. The mechanisms involved in the fracture behavior of polymer-based nanocomposites were also studied in detail using the photographs taken from the fracture surfaces by scanning electron microscopy.     

Preparation and Properties of Pyrene-Modified Multi- Walled Carbon Nanotube/Epoxy Resin Nanocomposites

Nanocomposites of multi-walled carbon nanotube (MWCNT)/bis-phenol A type epoxy resin were prepared and physical properties of the nanocomposites were investigated. For the fine dispersion of MWCNT in the epoxy resin, MWCNT was modified with pyrene butyric acid (PBA) in the supercritical carbon dioxide (CO₂). The physical adsorption of PBA on the surface of MWCNTs was studied with a thermogravimetric analyzer and a transmission electron microscopy. The electrical surface resistivities of the nanocomposites showed threshold decreases due to percolations above the critical concentration of the MWCNT. The resistivities showed maximum depending on the concentration and the modification of the surface of the MWCNT with PBA. It is postulated that the dispersion of the MWCNT in epoxy resins resulted in dispersion systems which exhibit rheological properties similar to lyotropic liquid crystalline polymers. The surface resistivities of the MWCNT/epoxy systems reflected the morphological characteristics of the systems which also determined rheological properties of the systems.     

Improved flame retardant properties of epoxy resin by fluorinated MMT/MWCNT additives

Flame retardant additives of montmorillonite (MMT) and multi-walled carbon nanotube (MWCNT) were embedded in epoxy resin to improve the resin's flame retardant properties. MMT was fluorinated to exfoliate its layers and enhance its dispersion into the epoxy resin. The MWCNT was also fluorinated to create hydrophobic functional groups for improved dispersion into the epoxy resin. The MWCNT reduced the degradation rate of the epoxy resin and increased the char yield. Limiting oxygen index also increased showing first order against char yield. The exfoliated MMT acted as an energy storage medium to hinder thermal transfer within the epoxy resin. The activation energy increased almost two times by fluorinated MMT/MWCNT additives. The fluorination of the additives, MMT and MWCNT significantly improved the flame retardant properties of the epoxy resin.     

Rheological and dynamic-mechanical behavior of carbon nanotube/vinyl ester-polyester suspensions and their nanocomposites

Rheological properties of vinyl ester-polyester resin suspensions containing various amounts (0.05, 0.1 and 0.3 wt.%) of multi walled carbon nanotubes (MWCNT) with and without amine functional groups (-NH₂) were investigated by utilization of oscillatory rheometer with parallel plate geometry. Dispersion of corresponding carbon nanotubes within the resin blend was accomplished employing high shear mixing technique (3-roll milling). Based on the dynamic viscoelastic measurements, it was observed that at 0.3 wt.% of CNT loadings, storage modulus (G′) values of suspensions containing MWCNTs and MWCNT-NH₂ exhibited frequency-independent pseudo solid like behavior especially at lower frequencies. Moreover, the loss modulus (G″) values of the resin suspensions with respect to frequency were observed to increase with an increase in contents of CNTs within the resin blend. In addition, steady shear viscosity measurements implied that at each given loading rate, the resin suspensions demonstrated shear thinning behavior regardless of amine functional groups, while the neat resin blend was almost the Newtonian fluid. Furthermore, dynamic mechanical behavior of the nanocomposites achieved by polymerizing the resin blend suspensions with MWCNTs and MWCNT-NH₂ was investigated through dynamic mechanical thermal analyzer (DMTA). It was revealed that storage modulus (E′) and the loss modulus (E″) values of the resulting nanocomposites increased with regard to carbon nanotubes incorporated into the resin blend. In addition, at each given loading rate, nanocomposites containing MWCNT-NH₂ possessed larger loss and storage modulus values as well as higher glass transition temperatures (T_g) as compared to those with MWCNTs. These findings were attributed to evidences for contribution of amine functional groups to chemical interactions at the interface between CNTs and the resin blend matrix. Transmission electron microscopy (TEM) studies performed on the cured resin samples approved that the dispersion state of carbon nanotubes with and without amine functional groups within the matrix resin blend was adequate. This implies that 3-roll milling process described herein is very appropriate technique for blending of carbon nanotubes with a liquid thermoset resin to manufacture nanocomposites with enhanced final properties.     

Preparation and rheological characterization of poly(n-butyl methacrylate)/montmorillonite composites

Intercalated nanocomposites constituted of poly(butyl methacrylate) (PBMA) as the matrix and an organically modified montmorillonite as the nanosize filler were prepared and rheologically characterized in detail. The rheological behavior of the composites showed dependence on both temperature and clay content. For composites of low clay contents, the steady shear viscosity showed a Newtonian plateau in the low shear rate region at low temperatures and the plateau was replaced by a shear-thinning curve when the temperature was raised. For composites of higher clay contents, strong shear-thinning behavior were observed at all shear rates and all temperatures. The viscoelastic data of the composites showed unusual terminal behavior of a decreasing terminal slope at low frequencies with increasing temperature and clay loading. X-ray diffraction spectra showed that annealing process at higher temperatures shifted the Bragg reflection peaks to a lower angle and broadened the peaks, which provided the evidence for the existence of a temperature-induced solid-like structure that was responsible for the shear thinning and the unusual terminal viscoelastic behavior.     

Use of surfactants in cellulose nanowhisker/epoxy nanocomposites: effect on filler dispersion and system properties

Cellulose nanowhiskers (CNWs) prepared via TEMPO mediated oxidation are used as biodegradable filler in an epoxy matrix. Since CNWs are hydrophilic and epoxy is hydrophobic, amphiphilic block copolymer surfactants are employed to improve the interactions between the filler and the matrix. The surfactants used are Pluronics, a family of triblock copolymers containing two poly(ethylene oxide) blocks and one poly(propylene oxide) block. In this study, Pluronic L61 and L121 with molecular weight of 2000 and 4400 g/mol and hydrophilic to lipophilic balance of 3 and 1 respectively, are used and their effect on the dispersion of CNWs in epoxy is discussed. The hydrophilic tails of Pluronics interact with the hydroxyl and carboxylic groups on the CNW surface and then these surfactant-treated CNWs are directly incorporated into epoxy by high speed mixing. The dispersion state of the surfactant-treated CNWs in epoxy is assessed by rheological measurements and the mechanical properties of the resulting composites are characterized by tensile test and dynamic mechanical thermal analysis. The Pluronic L61 treated CNW/epoxy composites show the highest storage modulus at high temperatures (about 77 % increases) indicative of improved interfacial interactions between the CNWs and the epoxy matrix. Also, an increase of around 10 °C in the glass–rubbery transition temperature of the L61 treated CNW/epoxy composite leads to potential application at higher service temperatures.     

Effects of graphene and carbon nanotube fillers on the shear properties of epoxy

The effects of quantity of graphene and carbon nanotube‐based fillers and their pendant functional groups on the shear properties of a thermoset epoxy were investigated. Two novel functionalized graphenes, one with epoxy functionality and the other with an amine, are synthesized for this purpose. Nanocomposites are prepared at concentrations of 0.5, 1, 2, 3, 5, and 10 wt % and the effects of functionalization on the homogeneity of dispersion and the shear mechanical properties are investigated. The properties of the epoxy nanocomposites containing epoxy‐ and amine‐functionalized graphene are compared with those containing graphene oxide, Claisen‐functionalized graphene, neat multiwalled carbon nanotubes (MWNTs), three types of epoxy‐functionalized MWNT (EpCNT), and the unfilled epoxy. One of the EpCNT ( EpCNT3 ) was found to increase the plateau shear storage modulus by 136% (1.67–3.94 MPa) and the corresponding loss modulus by almost 400% at a concentration of 10 wt %. Several other fillers were also found to increase shear properties at certain concentrations. A hybrid system of EpCNT3 and graphite was also studied, which improved the storage modulus by up to 51%. SEM images reveal a correlation between thorough dispersion of the additive and enhancement of shear modulus. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 997–1006     

Responses and thermal conductivity measurements of multi-wall carbon nanotube (MWNT)/epoxy composites

In the present study, the MWNT/epoxy composites are prepared with three weight percentages (0.0, 0.3, and 0.5%) of multiwall carbon nanotube (MWNT). The temporal response of multi-wall carbon nanotube (MWNT)/epoxy composite with different wt% of multi-wall carbon nanotube (MWNT) is measured by experiment. Also, a cavity-type measuring system is designed to experimentally measure the surface temperatures and obtain the thermal conductivity of these composites at different heating rates. It is found that the responses of the 0.3 and 0.5% weight percentage of multi-wall carbon nanotube (MWNT)/epoxy composites are found to be about 25 and 47.8%, respectively, faster than that of the pure epoxy resin. Both the responding characteristics and the variation trends of the measured surface temperatures of these composites can be well predicted by the lumped-heat capacity model. Besides, the higher the weight percentage (wt%) of multi-wall carbon nanotube (MWNT) in the composite, the larger is the thermal conductivity. Relative to the pure epoxy, the thermal conductivities for the composites with 0.3 and 0.5% of multi-wall carbon nanotube (MWNT) increase by 15.9 and 44.9%, respectively. For the weight percentages studied, the thermal conductivity of these composites is found to increase mildly at low heating rates; however, it remains nearly constant at high heating rates.     

Electrorheology and creep-recovery behavior of conducting polythiophene/poly(oxymethylene)-blend suspensions

Electrorheological properties and creep-recovery behavior of polythiophene/polyoxymethylene-blend having PT（50%）/POM（50%） composition were investigated.Particle size,conductivity and dielectric values were measured to be 24.77μm,3.85×10^-5 S·m^-1 and 26.75,respectively.Sedimentation ratio was measured to be 64%at the end of 16 days.The effects of dispersed particle volume fraction,external electric field strength,shear rate,frequency and temperature on ER properties and storage modulus of PT/POM-blend/silicone oil（SO） suspensions were examined.Enhancement were observed in the electric field viscosities of the suspensions and thus they were classified as a smart material.Shear thinning non-Newtonian viscoelastic behavior was determined for PT/POM-blend/SO system.Further,time-dependent deformation was examined by creep-recovery tests and recoverable viscoelastic deformation established.     

Enhanced corrosion protection performance with MWCNT dispersed epoxy coating prepared under supercritical CO2 assistance

The corrosion protection performance of epoxy coatings could be enhanced by incorporation of nanofillers such as MWCNT. However, a homogeneous dispersion of MWCNT in epoxy polymer is still a teasing challenge. Herein, we report an environmentally benign single‐step supercritical CO₂ processing method to improve the dispersion of MWCNT in epoxy matrix in order to achieve an effective anticorrosive coating. The executed approach provides a cluster‐free uniform distribution of MWCNT in epoxy matrix as characterized with UV‐visible spectroscopy, Fourier transforms infrared spectroscopy, X‐ray diffraction, and surface analysis. The anticorrosive characteristics of MWCNT/epoxy coating were studied in NaCl as well as in photodegraded dye medium through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. We observed the remarkable corrosion of model metal substrate in photodegraded dye medium besides NaCl medium. In both mediums, the protection efficacy of MWCNT/epoxy coating was deduced from the stable impedance arcs in Nyquist plot and increased impedance modulus. The electrochemical impedance spectra were best fitted with equivalent circuits showing the higher values of pore resistance. Also, the MWCNT/epoxy coating exhibited a positive shift of corrosion potential and possessed a lower corrosion rate as compared with neat epoxy coating. More direct evidence of the excellent barrier properties for MWCNT/epoxy coating was visualized in SEM images. The obtained results implied that the superior dispersion of MWCNT into epoxy matrix significantly reduces the porosity of coating and inhibits the permeability of corrosive ions. We expect supercritical CO₂ assisted dispersion method can offer an efficient, cost‐effective, and industrially viable route to develop high performance protective coatings for varied commercialized applications.     

A novel procedure able to predict the rheological behavior of trifunctional epoxy resin/hyperbranched aliphatic polyester mixtures

A hyperbranched polymer (HBP), based on a highly branched polyester, was added to a trifunctional triglycidyl-p-aminophenol (TGAP) epoxy resin as a possible route to increase the toughness of the resin. Different amounts of the HBP, up to 26.5% wt. of resin, were dispersed in the TGAP resin. The rheological behavior of the formulations produced was studied as function of the shear rate and the filler content using a cone and plate rheometer. The rheological behavior of the TGAP resin, initially Newtonian, was modified displaying a pseudo-plastic trend when the hyperbranched polymer was added. An increase in the viscosity of the resin was observed with increasing volume fraction of the filler. The Cross equation was used to predict the viscosity of each formulation as a function of the shear rate. A novel procedure was developed to predict the viscosity of each mixture as a function of the filler volume fraction. This could be employed to provide quantitative information on the filler volume fraction in epoxy/HBP systems, necessary to achieve the characteristic viscosity values corresponding to the typical shear rates for a specific processing technology.     

Combined electrical and rheological properties of shear induced multiwall carbon nanotube agglomerates in epoxy suspensions

In this work the rheological and electrical properties of semi-dilute carbon nanotube (CNT)–epoxy suspensions have been discussed. The suspensions are produced using two types of industrially available CNTs (Nanocyl 3150 and 7000) and using two different dispersion techniques, namely 3-roll milling and sonication. In-situ optical microscopic analysis and electrical conductivity measurements have been conducted. It is shown that despite using CNTs with similar aspect ratios, the dispersability of the raw material and the time stability of the suspensions are quite different. Additionally, viscosity measurements are used to evaluate the initial dispersion quality and time stability.     

Characterization of MWCNT/TPU systems by large amplitude oscillation shear

Interest in polymeric materials with dispersed nanotubes has increased in recent years. There are several methods to characterize this kind of dispersions that may be based on evaluating the percolation concentration, the “goodness” of the dispersion, or the matrix-nanotube interphase. Among other techniques, rheology and conductivity are used to this aim. Commonly, the oscillatory rheology measurements are performed within the linear viscoelastic range, which is achieved by operating at small amplitude oscillation shear. Nevertheless, these measurements do not fully describe the behavior of the dispersion structure. In this work, we propose the use of medium amplitude oscillation shear and large amplitude oscillation shear to characterize the dispersion/structure of a thermoplastic polyurethane matrix filled with multiwalled carbon nanotubes. The Ewoldt framework mathematical approach is used to analyze the non-linear stress response. That approach allows obtaining physically grounded magnitudes from the experimental data. These magnitudes allow for a better understanding of the effects of the filler content.     

Surfactant assisted dispersion of MWCNT's in epoxy nanocomposites and adhesion with aluminum

This article presents an experimental investigation into the adhesion between aluminum and epoxy nanocomposites reinforced with multi-walled carbon nanotubes (MWCNT's). The nanotubes are dispersed in epoxy chemically with the aid of a surfactant, rather than mechanically via high shear mixing or ultrasonication. Four MWCNT weight fractions are considered viz. 0%, 0.1%, 0.5% and 1%. The adhesion with aluminum is tested via end-notched flexure tests conducted on specimens consisting of Aluminum strips adhered together with various epoxy nanocomposite glues. The best results are obtained for 1% MWCNT, where the tests show a notable increase in adhesion, evidenced by an intact bond despite considerable plastic deformation of Aluminum. However, the peak load capacity is seen to be not enhanced. The higher adhesion with 1% MWCNT addition is seen to successfully suppress the brittle debonding failures even at very high levels of adherend plasticity. For this weight fraction the overall response is highly ductile involving shearing of the glue and is desirable for engineering applications. Despite promising results, the surfactant itself is seen to be not very effective as a dispersing agent for the epoxy resin considered here.     

Rheological behavior and particle suspension capability of guar gum: sodium tetraborate decahydrate gels containing cellulose nanofibrils

Guar gum (GG) fracturing fluids were studied by incorporating cellulose nanofibrils (CNFs) in anhydrous borax crosslinked guar gum gels. To fully understand the impact of CNF on the proppant suspension capability of developed fracturing fluids, their shear rate-dependent viscosity and viscoelasticity were investigated. The shear rate dependencies of fluids was fitted to the Carreau model. The zero shear rate viscosity and elasticity of fracturing fluids increased significantly by incorporating CNF in guar gum gels. On the other hand, the viscosity at high shear rates (>100 s^?1) decreased as desired. The proppant settling velocities through fracturing fluids were evaluated by modeling the terminal falling velocity of proppants moving through a Carreau model fluid. The experimental results of the rheological behavior and the modeling results of the proppant settling rate indicated that the fracturing fluids containing CNF had better suspension capabilities. In addition, the lower viscosities of CNF formulated GG gels at higher shear rates will make them more pumpable.     

Effect of carbon nanofibers on mechanical and electrical behaviors of acrylonitrile‐butadiene rubber composites

Recently, carbon nanofibers have become an innovative reinforcing filler that has drawn increased attention from researchers. In this work, the reinforcement of acrylonitrile butadiene rubber (NBR) with carbon nanofibers (CNFs) was studied to determine the potential of carbon nanofibers as reinforcing filler in rubber technology. Furthermore, the performance of NBR compounds filled with carbon nanofibers was compared with the composites containing carbon black characterized by spherical particle type. Filler dispersion in elastomer matrix plays an essential role in polymer reinforcement, so we also analyzed the influence of dispersing agents on the performance of NBR composites. We applied several types of dispersing agents: anionic, cationic, nonionic, and ionic liquids. The fillers were characterized by dibutylphtalate absorption analysis, aggregate size, and rheological properties of filler suspensions. The vulcanization kinetics of rubber compounds, crosslink density, mechanical properties, hysteresis, and conductive properties of vulcanizates were also investigated. Moreover, scanning electron microscopy images were used to determine the filler dispersion in the elastomer matrix. The incorporation of the carbon nanofibers has a superior influence on the tensile strength of NBR compared with the samples containing carbon black. It was observed that addition of studied dispersing agents affected the performance of NBR/CNF and NBR/carbon black materials. Especially, the application of nonylphenyl poly(ethylene glycol) ether and 1‐butyl‐3‐methylimidazolium tetrafluoroborate contributed to enhanced mechanical properties and electrical conductivity of NBR/CNF composites.