Polymeric carbon nanocomposites from multiwalled carbon nanotubes functionalized with segmented polyurethane

Multiwalled carbon nanotubes (MWNT) were functionalized with segmented polyurethanes (PU) by the “grafting to” approach. Raman and X‐ray photoelectron spectroscopy (XPS) spectra show that the sidewalls of MWNTs have been functionalized with acid treatment, and the amount of COOH increases with increasing acid treatment time. FTIR and X‐ray diffraction (XRD) spectra confirm that PU is covalently attached to the sidewalls of MWNTs by esterification reaction. Similar to the parent PU, the functionalized carbon nanotube samples are soluble in highly polar solvents, such as dimethyl sulfoxide (DMSO) and N,N‐dimethylformamide (DMF). The functionalized acid amount and the grafted PU amount were determined by thermogravimetric analyses (TGA). Comparative studies, based on SEM images between the PU‐functionalized and chemically defunctionalized MWNT samples, also reveal the covalent coating character. Dynamic mechanical analysis (DMA) of nanocomposite films prepared from PU and PU‐functionalized MWNTs show enhanced mechanical properties and increased soft segment T_g. Tensile properties indicate that PU‐functionalized MWNTs are effective reinforcing fillers for the polyurethane matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Toughening of cycloaliphatic epoxy resin by multiwalled carbon nanotubes

The toughness of cycloaliphatic epoxy resin 3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate (ERL‐4221) has been improved by using multiwalled carbon nanotubes (MWCNTs) treated by mixed acids. The MWCNT/ERL‐4221 composites were characterized by Raman spectroscopy and their mechanical properties were investigated. A significant increase in the tensile strength of the composite from 31.9 to 55.9 MPa was obtained by adding only 0.05 wt % of MWCNTs. And a loading of 0.5 wt % MWCNTs resulted in an optimum tensile strength and cracking energy, 62.0 MPa and 490 N cm, respectively. Investigation on the morphology of fracture surface of the composites by field emission scanning electron microscopy demonstrated the crack pinning‐front bowing and bridging mechanisms of toughening. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical and thermal properties of functionalized multiwalled carbon nanotubes and multiwalled carbon nanotube–polyurethane composites

Multiwalled carbon nanotube (MWNT)–polyurethane (PU) composites were obtained by an in situ polycondensation approach. The effects of the number of functional groups on the dispersion and mechanical properties were investigated. The results showed that the functionalized MWNTs had more advantages for improving the dispersion and stability in water and N,N′‐dimethylformamide. The tensile strength and elongation at break of the composites exhibited obvious increases with the addition of MWNT contents below 1 wt % and then decreases with additions above 1 wt %. The maximum values of the tensile strength and elongation at break increased by 900 and 741%, respectively, at a 1 wt % loading of MWNTs. Differential scanning calorimetry measurements indicated that the addition of MWNTs resulted in an alteration of the glass‐transition temperature of the soft‐segment phase of MWNT–PU. Additionally, new peaks near 54°C were observed with differential scanning calorimetry because of the microphase‐separation structures and alteration of the segment molecular weights of the hard segment and soft segment of PU with the addition of MWNTs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of nylon610/functionalized multiwalled carbon nanotubes composites

Nylon610 nanocomposites containing functionalized multiwalled carbon nanotubes (MWCNTs) were prepared using wet melt blending method, which is a novel preparation technique. In comparison with the pure nylon610, the elastic modulus, tensile strength, bending modulus, and bending strength of the composites increase significantly with the increase of MWCNTs content, and the mechanical properties of the composites are also improved significantly by adding a small amount of MWCNTs (0.1 wt %). The crystallization peak of the composites shifts to higher temperature with the addition of MWCNTs, and among the two melting peaks, the intensity of melting peak at low temperature decreases with increasing MWCNTs content. The composites are more stable than pure PA610 and decompose at higher temperature, suggesting that the accession of MWCNTs can improve the composites' thermal stability. The storage modulus of the composites decreases with the temperature increasing, but under lower temperature it increases significantly with the addition of MWCNTs–COOH except for PANT‐0.1 sample. Transmission electron microscope (TEM) images of composites exhibit that the wet melt blending technique can avoid the excess agglomeration of MWCNTs under vacuum dryness, which benefits MWCNTs to disperse uniformly in matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Protein adsorption on functionalized multiwalled carbon nanotubes with amino‐cyclodextrin

A novel amino‐cyclodextrin was synthesized, and it was covalently attached to multiwalled carbon nanotubes (MWNTs). The functionalized MWNTs (f‐MWNTs) have very good aqueous dispersibility. Bovine serum albumin (BSA) was adsorbed onto f‐MWNTs through noncovalent interactions, including the hydrophobic interaction of the residues of BSA with the wall of MWNT and the guest–host interaction of the residues with the cyclodextrin (CD) moieties of f‐MWNTs. The ultraviolet–visible (UV–vis) absorption of the f‐MWNT‐BSA hybrid was measured with UV–vis spectrometer, and the absorbance can be described well with the Beer–Lambert law. The X‐ray diffraction patterns have indicated that the crystalline form of BSA has been changed after the adsorption of BSA on f‐MWNTs. The circular dichroism spectra have shown that a high percentage of α‐helical content can be retained for BSA adsorbed on f‐MWNTs. The results also indicate that the change of secondary structure of BSA is mainly due to the hydrophobic interaction of the residues of BSA with the wall of f‐MWNT, whereas the secondary structure is much less affected by the interaction of the CD moieties with BSA. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

High-density attachment of gold nanoparticles on functionalized multiwalled carbon nanotubes using ion exchange

The attachment of gold nanoparticles (NPs) onto chemically functionalized multiwalled carbon nanotubes (MWCNTs) by ion pairing interaction is reported. The structure and composition of the resulting gold NP/MWCNT hybrids were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. A high-density of gold NPs was homogeneously dispersed on the modified MWCNTs. The hybrids show characteristic plasmon absorption of gold NPs in the UV-visible spectrum and good electrochemical properties.     

Properties of ultrahigh‐molecular‐weight polyethylene nanocomposite films containing different functionalized multiwalled carbon nanotubes

We compared the thermomechanical properties, morphologies, gas permeabilities, and electrical conductivities of ultrahigh‐molecular‐weight polyethylene (UHMWPE) nanocomposite films containing two types of functionalized multiwalled carbon nanotubes (functionalized MWNTs). Both 2‐hydroxyethyl triphenyl phosphonium‐MWNT (Ph3P‐MWNT) and 1,1,1,3,3,3‐hexafluoro‐2‐phenyl‐2‐propanol‐MWNT (CF3‐MWNT) were used as reinforcing fillers in the fabrication of UHMWPE hybrid films. UHMWPE nanocomposites with various functionalized MWNT contents were solution‐cast to produce the films. The thermomechanical properties and morphologies of the UHMWPE hybrid films were then characterized using differential scanning calorimetry, thermogravimetric analysis, electron microscopy, and mechanical tensile analysis. Transmission electron microscopy studies showed that some of the MWNT particles were dispersed homogeneously within the polymer matrix (on the nanoscale), whereas others were agglomerated. We also found that the addition of only a small amount of functionalized MWNTs was sufficient to improve the thermomechanical properties and the gas barrier of the UHMWPE hybrid films. Even, those hybrid films with low functionalized MWNT contents (i.e., <1 wt%) were found to exhibit much better thermomechanical properties than the pure UHMWPE films. On the other hand, the values of the electrical conductivity remained constant, regardless of the amount of functionalized MWNTs. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

In situ polymerization of ethylene with functionalized multiwalled carbon nanotubes using a zirconocene aluminohydride system in solution

This study reports nanocomposite synthesis based on high-density polyethylene with carbon nanotubes through in situ polymerization by coordination, and the use of an aluminohydride zirconocene/MAO system as a catalyst. Nanocomposites of linear polyethylene exhibit higher molar masses than pure high-density polyethylene synthesized under similar conditions; where multiwalled carbon nanotubes (MWCNTs) acted as nucleating agents, shifting the crystallization temperature to higher values than neat high-density polyethylene. Well-dispersed MWCNTs in the HDPE matrices of the obtained nanocomposites are observed by SEM, where most of the nanocomposites showed an improvement in their thermal stability and electric conductivity, besides it is possible to obtain nanocomposites containing up to 41 wt% of nanofiller in the polymeric matrix. The aluminohydride complex n-BuCp₂ZrH₃AlH₂, activated with MAO at Al/Zr ratios of 2000, produced homogeneous HDPE/MWCNT composites under in situ polymerization conditions, at 70°C and 2.9 bar of ethylene pressure, with minimal residual alumina in the HDPE matrix.     

Synthesis and characterization of multiwalled carbon nanotubes-protoporphyrin IX composites using acid functionalized or nitrogen doped carbon nanotubes

In this research we describe the synthesis and characterization of composite materials based on multiwalled carbon nanotubes and protoporphyrin IX. We compare the results of using three types of carbon nanotubes: pristine (diameter < 10 nm), acid functionalized (diameter < 10 nm), and nitrogen doped carbon nanotubes (diameter ≈ 20 nm). Carbon nanotubes were mixed with protoporphyrin IX via two simple and straightforward methods using sonication, or heating-stirring. The characterization of the composites was done by Raman spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, ultraviolet-visible and fluorescence spectroscopy and infrared spectroscopy. A diversity of coatings of the nanotubes by protoporphyrin were obtained depending on the type of nanotube used or the method of synthesis. Some carbon nanotubes increased their diameter up to 40% after the reaction with protoporphyrin. Percentages by weight up to 20% of protoporphyrin were measured by thermogravimetric analysis. We obtained experimental evidences by different techniques of the electronic interaction and the formation of covalent bonds between both constituents, above all for the composites using nanotubes < 10 nm in diameter. Some of these evidences were ~ 98% of fluorescence quenching, reduction in the intensity of the absorption bands in ultraviolet visible spectroscopy, strong reduction in the intensity of some bands in Raman spectroscopy, red and blue shifts, as well as the presence of new absorption bands in infrared spectroscopy. Nitrogen doped carbon nanotubes showed low chemical reactivity to protoporphyrin IX, perhaps due to their lower acceptor character as they could have charge transfer from nitrogen dopants to the nanotube network, or because of their metallic character.     

Chemical oxidation of multiwalled carbon nanotubes

The effect of oxidation on the structural integrity of multiwalled carbon nanotubes through acidic (nitric acid and a mixture of sulfuric acid and hydrogen peroxide) and basic (ammonium hydroxide/hydrogen peroxide) agents has been studied. In order to purify the as-received material, a non-oxidative treatment (with hydrochloric acid) was also applied. Electron microscopy and thermogravimetric analysis clearly revealed that the nitric acid-treated material under reflux conditions suffered the highest degree of degradation, such as, nanotube shortening and additional defect generation in the graphitic network. Basic oxidative treatment led to the complete removal of amorphous carbon and metal oxide impurities but the structural integrity was found to be intact. X-ray photoelectron spectroscopy was employed to confirm the different functionalities produced for each oxidation agent, whereas titration measurements determined the relative concentration of carboxylic functions onto the graphitic surface. Moreover, a general relationship between the chemical treatment and the amount of non-graphitic carbon was established by means of Raman spectroscopy measurements. The possibility of controlling the required amount of functionality, carboxylic and hydroxyl, via these oxidation procedures is discussed.     

Effect of functionalized multiwalled carbon nanotubes on weather degradation and corrosion of waterborne polyurethane coatings

A series of waterborne polyurethane/functionalized multiwalled carbon nanotube (WBPU/f-MWCNT) nanocomposite dispersions was prepared using three defined concentrations of 0.5, 1.0 and 2.0 wt% carboxyl functionalized multiwalled carbon nanotubes (f-MWCNTs). All dispersions were coated on mild steel and exposed under natural weather condition for a maximum of 365 days. Both exposed and unexposed coatings were characterized by potentiodynamic polarization (PDP) and X-ray photoelectron spectroscopy (XPS) analyses. The pristine WBPU coating showed slight degradation and corrosion protection. Inclusion of a higher content of f-MWCNTs significantly improved both the degradation and corrosion protection efficiencies of the coatings. Maximal degradation and corrosion protection was observed when 2.0 wt% f-MWCNT was mixed with WBPU for all of the coatings.     

Tailoring in thermomechanical properties of ethylene propylene diene monomer elastomer with silane functionalized multiwalled carbon nanotubes

The incorporation of silane treated multiwalled carbon nanotubes (S‐MWCNTs) is used as an effective path for tailoring thermomechanical properties of ethylene propylene diene monomer (EPDM). In this study, S‐MWCNTs were introduced into EPDM using internal dispersion kneader and two roller mixing mill. By altering the mass ratio of S‐MWCNTs from 0 to 1, thermal conductivity, thermal stability and phase transition temperatures and their respective enthalpies are discussed of the fabricated nanocomposites. It is observed that silane modification improves their dispersion and increases the interfacial bonding between MWCNTs and polymer matrix. Scanning electron microscopy along energy dispersive spectroscopy analysis is performed to confirm the silane functionalized MWCNTs are selectively distributed in the host polymer. More importantly, an important increase in mechanical properties like ultimate tensile strength and hardness is achieved through introducing silane functionalized MWCNTs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43221.     

Synthesis and characterization of poly(acrylonitrile-co-methylmethacrylate) nanocomposites reinforced by functionalized multiwalled carbon nanotubes

Polyacrylonitrile-co-poly(methylmethacrylate)/multiwalled carbon nanotubes (PAN-co-PMMA/MWCNTs) nanocomposites were synthesized by an in situ emulsifier-free polymerization method with variable percentages of functionalized carbon nanotube (f-MWCNT). MWCNTs were functionalized with concentrated H₂SO₄ and HNO₃ with a continuous sonication process. Chemical interaction of f-MWCNT with the copolymer was studied by UV-visible spectroscopy. Fourier transform infrared spectroscopy proved the interaction of f-MWCNT with the PAN-co-PMMA copolymer matrix. The structural interaction of f-MWCNT with copolymer matrix was investigated by X-ray diffraction study. The dispersion and morphology of the f-MWCNT in the copolymer matrix were studied by scanning electron microscopy and high-resolution transmission electron microscopy. It was noticed that the f-MWCNTs were uniformly dispersed within the copolymer matrix. The thermal property of the PAN-co-PMMA/f-MWCNT nanocomposite was analyzed by thermogravimetric analysis. It was noticed that the thermal stability of the PAN-co-PMMA/f-MWCNT nanocomposite was more than that of the virgin copolymer matrix. When the electrical conductivity property of the synthesized nanocomposite was measured, it was noticed that the better dispersion of f-MWCNT in the non-conductive PAN-co-PMMA copolymer matrix made the PAN-co-PMMA/f-MWCNT nanocomposites conductive. From the measurement of gas barrier properties of synthesized nanocomposites, it was assumed that the well-dispersed f-MWCNT in the copolymer matrix creates the huddles for penetration of oxygen gas. It was noticed that the oxygen permeability of the PAN-co-PMMA/f-MWCNT nanocomposite was reduced by five times as compared to that of the neat PAN-co-PMMA copolymer matrix. The PAN-co-PMMA/f-MWCNT nanocomposites with higher thermal stability and reduced oxygen permeability properties may be suitable for application as conducting packaging materials.     

Interfacial improvement of carbon fiber-reinforced methylphenylsilicone resin composites with sizing agent containing functionalized carbon nanotubes

A liquid sizing agent containing multiwall carbon nanotubes (MWCNTs) was prepared for carbon fiber (CF) reinforced methylphenylsilicone resin (MPSR) composite applications. In order to improve the dispersion of MWCNTs in the sizing agent and interfacial adhesion between CF and MPSR, MWCNTs and CF were functioned by the chemical modification with tetraethylenepentamine (TEPA) used as a MPSR curing agents. The CF before and after the sizing treatment-reinforced MPSR composites were prepared by a compression molding method. The microstructures, interfacial properties, and impact toughness of CF were systematically investigated. Experimental results revealed that a thin layer of MPSR coating containing functionalized MWCNTs (MWCNT-TEPA) was uniformly grafted onto the surface of CF. The sized CF-reinforced MPSR composite showed simultaneously remarkable enhancement in the interlaminar shear strength and impact toughness. Meanwhile, the tensile strength of CF had no obvious decrease after sizing treatment. In addition, the interfacial reinforcing and toughening mechanisms were also discussed. We believe that the facile and effective method in preparing multifunctional fibers provides a novel interface design strategy of carbon fiber composites for different applications.     

Thermal and mechanical properties of carbon nanotube/epoxy nanocomposites reinforced with pristine and functionalized multiwalled carbon nanotubes

In this study, the effects of functionalization and weight fraction of mutliwalled carbon nanotubes (CNTs) were investigated on mechanical and thermomechanical properties of CNT/Epoxy composite. Epoxy resin was used as matrix material with pristine‐, COOH‐, and NH₂‐functionalized CNTs as reinforcements in weight fractions of 0.1, 0.5, and 1.0%. Varying (increasing) the weight fraction and changing type (pristine or functionalized) of CNTs caused increment in Young's modulus and tensile strength as observed during mechanical tests. CNT reinforcement improved thermal stability of the nanocomposites as observed by thermogravimetric analysis. Thermomechanical analysis showed a slight reduction in free volume of the polymer, that is a drop in coefficient of thermal expansion, prior to glass transition temperature (T_g) beside a slight increase in T_g value. Dynamic mechanical analysis indicated an increase in storage modulus and T_g owing to the strength addition of CNT to the matrix alongside the hardener. Scanning electron microscopy analysis of the fractured surface(s) revealed that CNTs were well dispersed with no agglomeration and resulted in reinforcing the matrix. POLYM. COMPOS., 36:1891–1898, 2015. © 2014 Society of Plastics Engineers     

Poly(ethylene terephthalate) nanocomposite fibers with functionalized multiwalled carbon nanotubes via in-situ polymerization

Poly(ethylene terephthalate) (PET) hybrids with newly synthesized functionalized multiwalled carbon nanotubes (MWNTs) were obtained by carrying out the in situ polycondensation of ethylene glycol with dimethyl terephthalic acid. The PET hybrids were melt-spun to produce monofilaments with various functionalized MWNT contents and draw ratios (DRs). The thermomechanical properties and morphologies of the PET hybrid fibers were determined using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide angle X-ray diffraction (XRD), electron microscopy (SEM and TEM), and a universal tensile machine (UTM). The XRD analysis and TEM micrographs show that the levels of nanosize dispersion can be controlled by varying the MWNT content. It was found that the addition of only a small amount of functionalized MWNTs was sufficient to improve the properties of the PET hybrid fibers. The maximum enhancement in the ultimate tensile strength was found to arise at a functionalized MWNT content of 0.5 wt %. However, the initial modulus was found to increase linearly with increases in the functionalized MWNT loading from 0 to 1.5 wt %. The thermal properties and conductivities of the PET hybrid fibers were found to be better than those of pure PET fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dispersability of multiwalled carbon nanotubes in polycarbonate-chloroform solutions

The dispersion of commercial multiwalled carbon nanotubes (MWCNTs, Nanocyl™ NC7000) in chloroform and in polycarbonate (PC)-chloroform solutions was investigated by variation of the polymer concentration, MWCNT amount and sonication time and compared with PC/MWCNT composites, which were processed by melt mixing, subsequently dissolved in chloroform and dispersed via sonication under the same conditions. The sedimentation behaviour was characterised under centrifugal forces using a LUMiSizer^® separation analyser. The space and time resolved extinction profiles as a measure of the stability of the dispersion and the particle size distribution were evaluated. Sonication up to 5 min gradually increases the amount of dispersed particles in the solutions. A significant improvement of the MWCNT dispersion in chloroform was achieved by the addition of PC indicating the mechanism of polymer chain wrapping around the MWCNTs. In dispersions of melt mixed PC/MWCNT composites the dispersion of MWCNTs is significantly enhanced already at a low sonication time of only 0.5 min due to very efficient polymer wrapping during the melt mixing process. However, the best dispersion quality does not lead to the highest electrical conductivity of thin composite films made of these PC/MWCNT dispersions.     

Improved impact strength of epoxy by the addition of functionalized multiwalled carbon nanotubes and reactive diluent

Multiwalled carbon nanotubes (MWCNTs), both oxidized and amine functionalized (triethylenetetramine—TETA), have been used to improve the mechanical properties of nanocomposites based on epoxy resin. The TGA and XPS analysis allowed the evaluation of the degree of chemical modification on MWCNTs. Nanocomposites were manufactured by a three‐roll milling process with 0.1, 0.5, and 1.0 wt % of MWCNT–COOH and MWCNT–COTETA. A series of nanocomposites with 5.0 wt % of reactive diluent was also prepared. Tensile and impact tests were conducted to evaluate the effects of the nanofillers and diluent on the mechanical properties of the nanocomposites. The results showed higher gains (258% increase) in the impact strength for nanocomposites manufactured with aminated MWCNTs. Optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to investigate the overall filler distribution, the dispersion of individual nanotubes, and the interface adhesion on the nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42587.     

Effect of multiwalled carbon nanotubes and phenethyl-bridged DOPO derivative on flame retardancy of epoxy resin

In this study, a phenethyl-bridged DOPO derivative (DiDOPO) was combined with multi-walled carbon nanotubes (MWNT) in epoxy resin (EP) to improve its flame retardancy. The introduction of only 10 wt% DiDOPO/0.8 wt% MWNT into EP increased the limited oxygen index (LOI) from 21.8% to 38.6%, achieving the UL 94 V-0 rating. The thermogravimetric analyses demonstrated that the presence of MWNT raised the char yield and formed thermally stable carbonaceous char. The decomposition and pyrolysis products in the gas phase were characterized by thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), and found large amounts of phosphorus released into the gas phase. The flame-retardant effect evaluation by cone calorimetry testified that the MWNT improved the protective-barrier effect of the fire residue of EP/DiDOPO/MWNT, as shown by digital photo and scanning electron microscopy (SEM). Raman showed that MWNT could enhance the graphitization degree of the resin during combustion. Overall, these findings indicated that combination of DiDOPO with MWNT is an effective way in developing high-performance resins with attractive flame retardancy.