Migration of MWCNTs during melt preparation of ABS/PC/MWCNT conductive composites via PC/MWCNT masterbatch approach

The migration of multi-walled carbon nanotubes (MWCNTs) from the thermodynamically favored polycarbonate (PC) phase to the acrylonitrile-butadiene-styrene (ABS) phase is observed when PC/MWCNT masterbatch is diluted with PC and ABS by melt mixing for 5 min with 70% of ABS having relatively high rubber content. The migration is explained by a combination of the morphology evolution, high rubber content and higher affinity of MWCNTs to polybutadiene (PB) than to PC. The high rubber content increases the probability of the contact between MWCNTs and elongated rubber particles during the morphology evolution, most MWCNTs are dragged out of the PC phase to the ABS phase by the surrounding rubber particles because of the better affinity of MWCNTs to PB than to PC. As a result of the selective localization of most MWCNTs in the continuous ABS phase, the resulting ABS/PC/MWCNT composites are conductive. However, with a long mixing time of 60 min, most MWCNTs come back to the PC phase due to the change in the structure of PB chains which decreases the interaction between MWCNTs and rubber particles, resulting in non-conductive materials.     

Photodegradation of EPDM/MWCNT nanocomposites: Effect of singlet oxygen

The photo-oxidation of ethylene propylene diene monomer (EPDM)/multiwall carbon nanotubes (MWCNT) nanocomposites has been studied under accelerated UV-irradiation (λ ≥ 290 nm) in the presence of singlet oxygen. The rate of photodegradation of EPDM/MWCNT is found to be higher when compared to the pristine polymer in presence of singlet oxygen. The enhancement of the rate of degradation of composite has been described through [2 + 2] photocycloaddition reaction between singlet oxygen and double bonds on composite which is followed by cleavage. The rate of degradation and the formation of new functional groups on the composite has been monitored by FTIR spectroscopy and found to be increased with irradiation time. The changes in surface morphology have been studied by scanning electron microscope. Differential scanning calorimetry measurements revealed an increase in the glass transition temperature of photodegraded EPDM and EPDM/MWCNT nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effect of processing techniques on the performance of Epoxy/MWCNT nanocomposites

The aim of this study is to investigate the optimum technique to disperse Multi‐Walled Carbon Nanotubes (MWCNTs) in SC‐1 epoxy uniformly and to evaluate the effect of processing technique on the performance of SC‐1 epoxy. To achieve better dispersion, MWCNT was mixed with SC‐1 resin directly or premixed with a solvent and then mixed with SC‐1 resin after evaporating the solvent using sonication, thinky mixing and three‐roll mill methods either in isolation or combination. Flexural tests were performed to evaluate mechanical performances and results exhibit up to 27.13, 13.51, and 21.99% improvement on flexural strength, flexural modulus, and maximum strain, respectively, over neat epoxy with only 0.2 wt % loading. Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) indicated improvement in storage modulus, T_g, inflection temperature, and residue content, respectively over neat SC‐1 epoxy. Thermal and mechanical properties at higher loading conditions were seen to either reduce or not significantly improve. This was attributed to high viscosity of nanocomposites as determined by rheological analysis which prevents good dispersion of MWNCTs into epoxy system at 0.4 wt % loading. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of ABS Rubber Content on the Localization of MWCNTs in PC/ABS Blends and Electrical Resistivity of the Composites

Three types of acrylonitrile‐butadiene‐styrene rubbers with different rubber contents were used in the preparation of PC/ABS/MWCNT composites. It was found that localization of MWCNTs changes from PC to ABS phase when rubber content of ABS varies from 5 to 60%. This is discussed by a combination of thermodynamics and kinetics. Melting sequence and high viscosity of ABS are used to explain the localization of MWCNTs in the high viscosity ABS phase. The relationship between the localization of MWCNTs and the electrical resistivity of the composite is also investigated.

     

Graphene/polyethylene nanocomposites: Effect of polyethylene functionalization and blending methods

Since its recent successful isolation, graphene has attracted an enormous amount of scientific interest due to its exceptional physical properties. Graphene incorporation can improve electrical and mechanical properties of polymers including polyethylene (PE). However, the hydrophobic nature and low polarity of PE have made effective dispersion of nano-fillers difficult without compatibilization. Graphene was derived from graphite oxide (GO) via rapid thermal exfoliation and reduction. This thermally reduced graphene oxide (TRG) was blended via melt and solvent blending with linear low density PE (LLDPE) and its functionalized analogs (amine, nitrile and isocyanate) produced using a ring-opening metathesis polymerization (ROMP) strategy. TRG was well exfoliated in functionalized LLDPE while phase separated morphology was observed in the un-modified LLDPE. Transmission electron micrographs showed that solvent based blending more effectively dispersed these exfoliated carbon sheets than did melt compounding. Tensile modulus was higher for composites with functionalized polyethylenes when solvent blending was used. However, at less than 3 wt.% of TRG, electrical conductivity of the un-modified LLDPE was higher than that of the functionalized ones. This may be due to phase segregation between graphene and PE, and electrical percolation within the continuous filler-rich phase.     

Electrospun PVDF/MWCNT/OMMT hybrid nanocomposites: preparation and characterization

Electrospinning technique was employed to prepare neat PVDF, nanoclay-PVDF and carbon nanotube (MWCNT)-PVDF nanocomposites, and nanoclay-carbon nanotube-PVDF hybrid nanocomposites. A mixture of dimethyl formamide/acetone (60/40) was used to fluidize the polymer and nanofillers. Electrospinning process was conducted under optimized conditions. Maximum modification was achieved at 0.15 wt% nanofiller. Rheological measurements on the prepared solutions revealed decreased material functions in the presence of nanoclay, whereas the rheological properties of MWCNT-PVDF solution did not show any significant reduction compared with those of neat PVDF solution. The behaviors of the hybrid nanocomposite solutions, though dependent on their composition and their material functions, increased with MWCNT concentration. These differences, together with variations in electrical properties of nanoclay and MWCNT, led to changes in morphology of the fiber during electrospinning process. Under electrospinning conditions designed for neat PVDF solution, mats with beads and with the highest fiber diameter were produced. Meanwhile, incorporation of both nanoclay and MWCNT into the solutions resulted in bead-free fibers with thinner diameter. Fourier transformed infrared spectrophotometry (FTIR) and X-ray diffractometry (XRD) were used to measure the β-phase crystalline content in electrospun mats. Complete agreement was found between the FTIR and XRD results. The lowest and highest β-phase contents were obtained for neat PVDF mat and hybrid nanocomposite mat containing 0.1 wt% clay, respectively. The mixing procedure of nanofillers and the PVDF solution was also found to be important. In case of hybrid nanocomposites, more β-crystals were formed when the nanoclay was first mixed in the absence of MWCNT.     

Electrical and rheological properties of MWCNT/polycarbonate nanocomposites

The electrical and rheological percolation behaviors of polycarbonate/multiwall carbon nanotube nanocomposites were investigated. To determine the effects of surface functionalization on a carbon nanotube surface, poly(styrene-co-acrylonitrile) (SAN)-grafted multiwall carbon nanotubes were prepared using surface-initiated atom transfer radical polymerization. The amount of grafted SAN was controlled by changing the polymerization time and was characterized using TGA. FT-IR and TEM were used to characterize the surface of the functionalized carbon nanotubes. The rheological and electrical percolation behaviors of the SAN-grafted multiwall carbon nanotube/polycarbonate nanocomposites were compared to those of pristine multiwall carbon nanotubes, where the effects were shown to increase with increasing SAN content. The results are attributed to the compatibility of SAN with polycarbonates, which induced uniform dispersion of the functionalized carbon nanotubes. Uniform dispersion was also confirmed by evaluating a tensile-fractured nanocomposite specimen.     

Nonisothermal crystallization kinetics study of LDPE/MWCNT nanocomposites: Effect of aspect ratio and surface modification

In this article, the effect of aspect ratio and chemical modification of multiwall carbon nanotubes (MWCNT) on the nonisothermal crystallization kinetics of LDPE/MWCNT nanocomposites was studied. Nine different samples were prepared using different MWCNT to study both effects. The cooling rate (R) was varied in the range 2–10°C/min. In this article, the effect of CNT loading, surface modification, and aspect ratio were studied. For the same MWCNT concentration, aspect ratio and  COOH modification had weak influence on both the peak crystallization temperature and the crystallization onset temperature. However, the crystallization onset temperature was significantly affected by the amount of MWCNT. The rate parameters in the modified Avrami method and Mo method [F(T)] of analyses show a very good fit of data. The Vyazovkin and Sbirrazzuoli method of analysis, which is based on Hoffman–Lauritzen theory for secondary crystallization, was also used. Temperature dependency of activation energy was obtained for 30–75% relative crystallinity of the produced nanocomposites. Activation energy based on calculations of Hoffman‐Lauritzen theory showed a decrease with the increase in the concentration of MWCNT and crystallization temperature. A proposed model of the form E = a exp (‐bXT) which relates the activation energy, E, to relative crystallinity, X, and crystallization temperature, T, was able to fit the whole set of data. Incorporation of MWCNT in nanocomposites lowers the activation energy; hence enhances the initial crystallization process as suggested by the different methods of data analyses. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Surface modification of MWCNT and its influence on properties of paraffin/MWCNT nanocomposites as phase change material

Multiwalled carbon nanotubes (MWCNTs) were modified by an organo-silane in order to improve their dispersion state and stability in paraffin wax. A family of paraffin-based phase change material (PCM) composites filled with MWCNTs was prepared with different loadings (0, 0.1, 0.5, and 1 wt%) of pristine MWCNTs and organo-silane modified MWCNTs (Si-MWCNT). Structural analyses were performed by means of Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and rheological studies using temperature sweeps. Moreover, phase change transition temperatures and heat of fusion as well as thermal and electrical conductivities of the developed PCM nanocomposites were determined. The SEM micrographs and FTIR absorption bands appearing at approximately 1038 and 1112 cm⁻¹ confirmed the silane modification. Differential scanning calorimetery (DSC) results indicate that the presence of Si-MWCNTs leads to slightly favorable enhancement in the energy storage capacity at the maximum loading. It was also shown that the thermal conductivity of the PCM nanocomposites, in both solid and liquid phases, increased with increasing the MWCNT content independent of the kind of MWCNTs by up to about 30% at the maximum loading of MWCNTs. In addition, the modification of MWCNTs made the samples completely electrically nonconductive, and the electrical surface resistivity of the PCMs containing pristine MWCNTs decreased with increasing MWCNTs loading. Furthermore, the rheological assessment under consecutive cyclic phase change demonstrated that the samples containing modified MWCNTs are more stable compared to the PCM containing pristine MWCNTs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48428.     

Effect of convergent–divergent flow on thermal and crystallization properties of PP/MWCNTs nanocomposites

A melt‐mixing process based on convergent–divergent flow has been used to prepare PP/MWCNT composites with a self‐built convergent–divergent die (C‐D die) composed of different numbers of convergent plates. Dynamic extensional deformation was generated in the C‐D die, which improved the mixing effect and mixing efficiency of the composites during extrusion. The C‐D die acted as a mixer for composites when mounted onto a capillary rheometer. The residence time of PP/MWCNTs melt in the extensional flow field is adjusted by changing the numbers of convergent plates and the velocity of the ram. The intensity of extensional flow field is controlled by the structure of the convergent plate and the ram velocity. Influences of convergent–divergent flow on PP/MWCNTs composites were characterized in terms of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). TEM results showed that MWCNTs disperse more homogeneously with the increase of convergent plates. DSC showed that the crystallinity of PP/MWCNTs composites increased and the crystallization temperature shifted to higher temperature with the increase of the numbers of the convergent plates. TGA showed that the thermal stability of composites improved remarkably. The decomposition temperature increases from 381 to 408.2°C when the numbers of convergent plates increased from 2 to 8. In addition, the increase of ram velocity also has the same influences on the dispersion of MWCNTs in the resin and the properties of PP/MWCNTs nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42330.     

Dynamic cure kinetics of epoxy/TiO2/MWCNT hybrid nanocomposites

The effect of multi-walled carbon nanotubes (MWCNTs) on cure kinetic parameters of the epoxy/amine/TiO₂ (1 wt%) resin system was studied dynamically at four heating rates using DTA. The presence of MWCNT in various amounts (0.1, 0.2, 0.4 and 0.6 wt%) neither retarded nor accelerated the cure reaction of the epoxy/amine/TiO₂ system in a considerable extent. Addition of MWCNTs increased the extent of cure of the corresponding nanocomposites, especially at higher contents up to 0.4 wt% MWCNT filled composite. However, increasing the MWCNT content to 0.6 wt% adversely affected the extent of cure due to nanoparticle agglomeration. The fracture surface morphology of the nanocomposites revealed that the cracks deviated on reaching the MWCNTs, while propagating in the polymer matrix. Fractional extent of conversion (α) was calculated using genetic algorithm. Flynn–Wall–Ozawa and Kissinger methods were used to analyze the kinetic parameters. The presence of MWCNTs did not affect the autocatalytic cure mechanism of epoxy/amine/TiO₂ resin system and also did not cause any considerable barrier effect on the curing process. Activation energy data fitted well in the cubic polynomial regression equations and the changes of E _a with respect to α proved the autocatalytic cure mechanism, being followed by all the MWCNT-containing epoxy-based hybrid nanocomposites.     

Cure kinetics of epoxy/MWCNTs nanocomposites: Nonisothermal calorimetric and rheokinetic techniques

Nonisothermal calorimetric and isothermal rheokinetic analyses were used to study cure kinetics of epoxy/anhydride systems containing very low concentration of pristine and amine‐functionalized multiwalled carbon nanotubes (MWCNTs). Isoconversional methods were applied in calorimetric modeling of cure kinetics. E _α vs. α dependency and autocatalytic nature of curing were identified for both types of nanocomposites by isoconversional models. Fall in E _α value from 90 to 82.5 kJ mol^?1 thanks to amine functionalization (with E _α of blank epoxy/anhydride of 80.3 kJ mol^?1) was indicative of high potential of nanocomposites to cure at low concentration of functionalized MWCNTs (0.1 g with respect to 100 g of resin). Times of gelation and vitrification of epoxy were measured using storage and loss modulus data provided by isothermal rheokinetic analysis, showing a drop upon attachment of amine groups to MWCNTs. In complete agreement with nonisothermal calorimetric studies, variation of storage and loss modulus of nanocomposites confirmed hindered/accelerated cure devoted to pristine/amine‐functionalized MWCNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45221.     

Effect of the clay size on the dispersion morphology and emulsion stability of ABS/layered silicate nanocomposites

ABS/layered silicate nanocomposites were synthesized through an emulsion polymerization with different sizes of silicates. The particle sizes of Laponite, Cloisite‐Na and Kunipia‐F are about 20–30, 70–150, and 300–500 nm, respectively. When ABS was synthesized by the emulsion polymerization in the presence of Laponite and Cloisite‐Na, ABS/layered silicate nanocomposite emulsion showed a stable suspension without the precipitation of solid particle. On the other hand, ABS/layered silicate nanocomposite synthesized with Kunipia‐F showed the precipitation of large aggregated particles and the phase separation. Smaller sizes of silicates like Laponite and Cloisite‐Na than polymerized particle worked as resided barrier preventing the emulsion particle from coagulation. Larger size of silicate like Kunipia‐F than emulsion particle was not able to enclose the emulsion particle delicately because of its stiffness and large aspect ratio. The monomers inserted into the intercalated Kunipia‐F connected the ABS particles and clay particles. The Kunipia‐F particles anchored ABS particles around them inducing the aggregation and precipitation of ABS particles. ABS copolymer emulsion and aqueous silicate dispersion were mixed to compare with synthesized ABS/layered silicate nanocomposites and showed a stable suspension. With small amount of Laponite or Cloisite‐Na, nanocomposite emulsion of Kunipia‐F was also stabilized. Laponite and Cloisite‐Na worked as a steric stabilizer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tuning the functionalization chemistry of polypropylene for polypropylene/clay nanocomposites

New polypropylene (PP)-graft-maleic anhydride (PP-g-MA) samples have been successfully synthesized by adding N-bromosuccinimide (NBS) during the reactive extrusion process. These NBS-mediated PP-g-MAs possess higher graft content than classic PP-g-MAs (i.e. without NBS) while they keep acceptable molar masses. NBS-mediated PP-g-MAs were used as matrices in model PP-g-MA/organoclay nanocomposites and compared with commercial and home-made classic PP-g-MAs in order to evaluate their ability to disperse the clay. Significantly better degrees of clay delamination and dispersion were reached using NBS-mediated PP-g-MAs than with classic PP-g-MAs. As expected, PP-g-MAs having high graft content showed the best clay dispersion. Within the examined range of molar masses, the PP-g-MA molar mass had no influence on the clay dispersion. However PP-g-MAs exhibiting important reduction of crystallinity lead to poor clay dispersion whatever the graft content. The PP-g-MA/organoclay nanocomposite prepared using the selected “optimized” NBS-mediated PP-g-MA exhibited the best improvement of thermal properties and one of the best clay dispersions. PP/PP-g-MA blends were prepared to evaluate the miscibility between PP and selected PP-g-MAs. No problem of miscibility between the selected NBS-mediated PP-g-MA and PP was noticed. Finally the PP/organoclay prepared using the selected NBS-mediated PP-g-MA as compatibilizer showed much better clay dispersion and thermal stability than the one prepared with the corresponding classic PP-g-MA, thus establishing the interest to use such new NBS-mediated PP-g-MAs as compatibilizers.     

Effects of microcompounding process parameters on the properties of ABS/polyamide‐6 blends based nanocomposites

Melt intercalation method was applied to produce acrylonitrile‐butadiene‐styrene/polyamide‐6 (ABS/PA6) blends based organoclay nanocomposites using a conical twin‐screw microcompounder. The blend was compatibilized using a maleated olefinic copolymer. The effects of microcompounding conditions such as screw speed, screw rotation‐mode (co‐ or counter‐), and material parameters such as blend composition and clay loading level on the morphology of the blends, dispersibility of nanoparticles, and mechanical properties were investigated. Furthermore, corotating screws were modified to achieve elongational flow which is efficient for obtaining dispersive mixing. The morphology was examined by SEM analysis after preferential extraction of the minor phase. Subsequently, the SEM micrographs were quantitatively analyzed using image analyzer software. The morphology of the blends indicated that processing with counter‐rotation at a given screw speed yielded coarser morphology than that of processed with corotation. X‐ray diffraction analysis showed that highest level of exfoliation is observed with increasing PA6 content, at 200 rpm of screw speed and in corotation mode. Also, the effects of screw speed, screw rotation mode, and screw modification were discussed in terms of XRD responses of the nanocomposites. The aspect ratio of the clay particles which were measured by performing image analysis on TEM micrographs exhibited a variation with processing conditions and they are in accordance with the modulus of the nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Microcompounding of organoclay–ABS/PA6 blend‐based nanocomposites

In this study, acrylonitrile–butadiene–styrene (ABS) and polyamide‐6 (PA6) were blended in the presence of an olefin‐based compatibilizer and organoclays. The effects of ABS to PA6 ratio, clay content, and screw speed of the microcompounder were examined by performing morphological (i.e., XRD, SEM, and TEM) and tensile tests. The average aspect ratio of the clay platelets after processing was obtained by applying semiautomatic image analysis method. SEM analysis showed that addition of the compatibilizers to the ABS/PA6 blend system resulted in a decrease in diameter of dispersed phase when one of the phases was continuous. The addition of 5 wt% compatibilizer altered the dispersed morphology to cocontinuous morphology when the weight percentage of ABS was equal to that of PA6. The results of XRD analysis implied that clays were exfoliated in the presence of PA6. It was observed in TEM micrographs that clays were selectively dispersed in PA6 phase. Aspect ratio of the platelets increased as the PA6 content increased. Moduli of the nanocomposites were improved by enriching blend with PA6 and increasing screw speed. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Effect of functionalization on dispersion of POSS‐silicone rubber nanocomposites

The nanocomposite of PDMS using functionalized fumed silica and nonreactive POSS as fillers were prepared by blend method in a planetary mixer. Fumed silica was functionalized by aliphatic and aromatic groups to study the filler–filler interactions with the aliphatic and aromatic POSS fillers and consequently their influence on the properties in the PDMS matrix. Transmission electron microscope (TEM) showed a good dispersion in the systems having the silica and POSS fillers with similar modifications. However, aliphatic and aromatic filler combinations showed more aggregated structures. Moreover, aliphatic POSS despite of good dispersion at higher loadings, act as lubricant, which is attributed to the disturbance in the PDMS‐ silica filler interaction and also the filler–filler interaction within fumed silica. There is a decrease in complex viscosity with the functionalization of fumed silica and with the aromatic/aliphatic POSS fillers. The thermal stability of aromatic functionalized fillers improves owing to the thermally stable phenyl groups. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Cure behavior of epoxy/MWCNT nanocomposites: The effect of nanotube surface modification

The effect of carboxyl and fluorine modified multi-wall carbon nanotubes (MWCNTs) on the curing behavior of diglycidyl ether of bisphenol A (DGEBA) epoxy resin was studied using differential scanning calorimetry (DSC), rheology and infrared spectroscopy (IR). Activation energy (E_a) and rate constants (k) obtained from isothermal DSC were the same for the neat resin and fluorinated MWCNT system (47.7 and 47.5 kJ/mol, respectively) whereas samples containing carboxylated MWCNTs exhibited a higher activation energy (61.7 kJ/mol) and lower rate constant. Comparison of the activation energies, rate constants, gelation behavior and vitrification times for all of the samples suggests that the cure mechanisms of the neat resin and fluorinated sample are similar but different from the carboxylated sample. This can be explained by the difference in how the fluorinated nanotubes react with the epoxy resin compared to the carboxylated nanotubes. Although the two systems have different reaction mechanisms, both systems have similar degrees of conversion as calculated from the infrared spectroscopic data, glass transition temperature (T_g), and predictions based on DSC data. This difference in reaction mechanism may be attributed to differences in nanotube dispersion; the fluorinated MWCNT system is more uniformly dispersed in the matrix whereas the more heterogeneously dispersed carboxylated MWCNTs can hinder mobility of the reactive species and disrupt the reaction stoichiometry on the local scale.     

Thermal conductivity of MWCNT/epoxy composites: The effects of length,alignment and functionalization

Carbon nanotubes (CNTs) show great promise to improve composite electrical and thermal conductivity due to their exceptional high intrinsic conductance performance. In this research, long multi-walled carbon nanotubes (long-MWCNTs) and its thin sheet of entangled nanotubes were used to make composites to achieve higher electrical and thermal conductivity. Compared to short-MWCNT sheet/epoxy composites, at room temperature, long-MWCNT samples showed improved thermal conductivity up to 55 W/mK. The temperature dependence of thermal conductivity was in agreement with κ ∝ Tⁿ (n = 1.9–2.3) below 150 K and saturated around room temperature due to Umklapp scattering. Samples with the improved CNT degree of alignment by mechanically stretching can enhance the room temperature thermal conductivity to over 100 W/mK. However, functionalization of CNTs to improve the interfacial bonding resulted in damaging the CNT walls and decreasing the electrical and thermal conductivity of the composites.