Design and evaluation of the interface between carbon nanotubes and natural rubber

To design the interface between carbon nanotubes and natural rubber (NR), a silane coupling agent, bis(3‐triethoxysilylpropyl) tetrasulfide (TESPT), was used to modify the surface of multiwalled carbon nanotubes (MWCNTs) in a two‐step method, and the silane‐modified multiwalled carbon nanotubes (s‐MWCNTs) were combined with NR by solvent casting. The s‐MWCNTs with an amorphous layer were visualized by transmission electron microscopy, the functional groups of which were confirmed by Raman and Fourier transform infrared analyses, and the functionalization degree was characterized by thermogravimetric analysis. The interface between s‐MWCNTs and NR was investigated by Raman analysis and field emission scanning electron microscopy (FESEM). Raman analysis showed a shift from 1,340 to 1,353 cm⁻¹ of D band of s‐MWCNTs in the NR/s‐MWCNT composite, and FESEM observation indicated that s‐MWCNTs were embedded deeply in NR. All of these results proved that s‐MWCNTs were grafted with TESPT and they reacted with the active double bonds of NR to form a strong interface. The improved interface resulted in an extreme nonlinear viscoelastic behavior and enhanced dynamic mechanical property of NR/s‐MWCNT composite as compared to NR/MWCNT composite. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Functionalization of multi-wall carbon nanotubes to reduce the coefficient of the friction and improve the wear resistance of multi-wall carbon nanotube/epoxy composites

Functionalization of multi-wall carbon nanotubes (MWCNTs) was achieved by grafting carboxyl groups and amino groups. Fourier transform infrared spectroscopy was used to detect the changes produced by functional groups on the surface of the MWCNTs. Three different MWCNTs were incorporated into epoxy resin and the friction and wear behavior of MWCNT/epoxy composites was investigated using a M-2000 wear testing machine at different sliding speeds under different applied loads. Scanning electron microscopy was used to observe the worn surfaces of the samples. The results indicated that the functional groups had been grafted on the surface of MWCNTs. Compared with neat epoxy, the composites with MWCNTs showed a lower friction coefficient and wear rate, and the wear rate decreased with the increase of MWCNT loading. Combining epoxy resin with MWCNTs is an efficient method to improve the wear resistance and decrease the coefficient of friction.     

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     

Effects of glucose‐functionalized multiwalled carbon nanotubes on the structural,mechanical, and thermal properties of chitosan nanocomposite films

A series of multiwalled carbon nanotubes (MWCNTs) grafted by chitosan nanocomposite (NC) films were prepared by a direct blending process and solution casting method. In this study, we modified multiwalled carbon nanotubes with glucose (MWCNT–Gl) for this purpose, and the effects of MWCNT–Gl on the structural, mechanical, and thermal properties of chitosan films with different contents of MWCNT–Gl were investigated. The structure, thermal stability, and mechanical properties of the composite were examined by X‐ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and mechanical testing. The results indicate that the MWCNTs treated by glucose were dispersed well in the chitosan matrix, and the tensile properties of the NC films were improved greatly compared with neat chitosan. Also, with increasing MWCNT–Gl content, the crystalline nature of chitosan decreased. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42022.     

High performance polyurethane composites with isocyanate‐functionalized carbon nanotubes: Improvements in tear strength and scratch hardness

A microwave‐assisted functionalization of carbon nanotubes (CNTs) with isocyanate groups allowed a reduction of functionalization time from 24 h to 30 min with no change in the degree of functionalization or in the nanotube characteristics. Polymer nanocomposites with enhanced mechanical properties were obtained because of the tailored interface by the covalent linkage between the surface‐modified multiwalled‐carbon nanotubes (MWCNTs) and an elastomeric polyurethane (PUE) matrix. The mechanical data revealed that the composite containing 0.25 wt % of MWCNT‐NCO showed an increase of 31% in tear strength and 28% in static toughness. A good adhesion between the matrix and individually dispersed nanotubes was observed in the scanning electron microscopy and transmission electron microscopy images. Nanoindentation and nanoscratch experiments were conducted to investigate the properties on the sub‐surface. An increase by a factor of 3 in the scratch hardness was observed for the composite with 0.50 wt % of MWCNT‐NCO with respect to the neat PUE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44394.     

High dispersion ability of fluorene‐based polyester as a polymer matrix for carbon nanotubes

The high compatibility of fluorene‐based polyester (FBP‐HX) as a polymer matrix for multiwalled carbon nanotubes (MWCNTs) is discussed. A low surface resistivity due to the fine dispersion of MWCNTs in FBP‐HX and polycarbonate (PC) is reported. With a solution‐casting method, a percolation threshold with the addition of between 0.5 and 1.0 wt % MWCNTs was observed in the MWCNT/PC and MWCNT/FBP‐HX composites. Because of the coverage of FBP‐HX on the MWCNTs, a higher surface resistivity and a higher percolation ratio of the MWCNT/FBP‐HX composites were achieved compared with the values for the MWCNT/PC composites. In the MWCNT/FBP‐HX composites, MWCNTs covered with FBP‐HX were observed by scanning electronic microscopy. Because of the coverage of FBP‐HX on the MWCNTs, FBP‐HX interfered with the electrical pathway between the MWCNTs. The MWCNTs in FBP‐HX were covered with a 5‐nm layer of FBP‐HX, but the MWCNTs in the MWCNT/PC composites were in their naked state. MWCNT/PC sheets demonstrated the specific Raman absorption of the MWCNTs only with the addition of MWCNTs of 1 wt % or above because of the coverage of the surface of the composite sheet by naked MWCNTs. In contrast, MWCNT/FBP‐HX retained the behavior of the matrix resin until a 3 wt % addition of MWCNTs was reached because of the coverage of MWCNTs by the FBP‐HX resin, induced by its high wettability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of poly(trimethylene terephthalate)‐poly(ethylene oxide terephthalate) segmented copolymer/multiwalled carbon nanotubes composites by in situ polymerization

Poly(trimethylene terephthalate)‐poly(ethylene oxide terephthalate) block copolymer (PTG)/multiwalled carbon nanotubes (MWCNTs) composites were prepared via in situ polymerization. To improve the dispersion of MWCNTs in the PTG matrix, the poly(ethylene glycol)‐grafted multiwalled carbon nanotubes (MWCNT‐PEG) were produced by the “graft to” method. The transmission electron microscopy observation demonstrated that a homogeneous dispersion of MWCNT‐PEG was obtained. As a consequence, the percolation threshold for the rheology was around 0.5 wt% and the conductivity was ～1 wt%, respectively. Differential scanning calorimetry and polarized optical microscopy results confirmed that MWCNT‐PEG can act as an effective heterogeneous nucleating agent. Interestingly, the effects of MWCNT‐PEG on crystallization and melting of the poly(ethylene oxide terephthalate) blocks were more pronounced than on those of the PTT blocks. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Dispersion of multiwalled carbon nanotubes in polyacrylonitrile‐co‐starch copolymer matrix for enhancement of electrical,thermal, and gas barrier properties

Nanomaterials gained great importance on account of their wide range of applications in many areas. Carbon nanotubes (CNTs) exhibit exceptional electrical, thermal, gas barrier, and tensile properties and can therefore be used for the development of a new generation of composite materials. Functionalized multiwalled carbon nanotubes (MWCNTs) reinforced Polyacrylonitrile‐co‐starch nanocomposites were prepared by in situ polymerization technique. The structural property of PAN‐co‐starch/MWCNT nanocomposites was studied by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The conductivity, tensile strength, and thermal properties of nanocomposites were measured as a function of MWCNT concentrations. The thermal stability, conductivity, and tensile strength of PAN‐co‐starch/MWCNT nanocomposites were improved with increasing concentration of MWCNTs. Oxygen barrier property of PAN‐co‐starch/MWCNT nanocomposites was calculated and it was found that, the property was reduced substantially with increase of MWCNTs proportion. The synthesized PAN‐co‐starch/MWCNT nanocomposites may used for electrostatically dissipative materials, aerospace or sporting goods, and electronic materials. © 2013 Society of Plastics Engineers     

Preparation and properties of multiwalled carbon nanotube/epoxy‐amine composites

Different amounts of multiwalled carbon tubes (MWCNTs) were incorporated into an epoxy resin based on diglycidyl ether of bisphenol A and both epoxy precursor and composite were cured with 4,4′‐diamino diphenyl sulfone. Transmission and scanning electron microscopy demonstrated that the carbon nanotubes are dispersed well in the epoxy matrix. Differential scanning calorimetry measurements confirmed the decrease in overall cure by the addition of MWCNTs. A decrease in volume shrinkage of the epoxy matrix caused by the addition of MWCNTs was observed by pressure–volume–temperature measurements. Thermomechanical and dynamic mechanical analysis were performed for the MWCNT/epoxy composites, showing that the T_g was slightly affected, whereas the dimensional stability and stiffness are improved by the addition of MWCNTs. Electrical conductivity measurements of the composite samples showed that an insulator to conductor transition takes place between 0.019 and 0.037 wt % MWCNTs. The addition of MWCNTs induces an increase in both impact strength (18%) and fracture toughness (38%) of the epoxy matrix with very low filler content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication of polystyrene/multiwalled carbon nanotube composite films synthesized by in situ microemulsion polymerization

A microemulsion polymerization method was used to achieve better compatibility between polystyrene (PS)/multiwalled carbon nanotubes (MWCNTs) nanocomposites and the host PS matrix to form films with excellent electrical and thermal properties. The films were prepared by embedding the PS/MWCNTs nanocomposite into the PS matrix. The MWCNTs were functionalized with PS nanoparticles to avoid the phase separation problem between the filler and host matrix and to enhance the good dispersibility of MWCNTs in the PS host matrix. The confirmation of the synthesis was analyzed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and Raman spectroscopy. The variation effect of the PS‐linking density on the MWCNT was revealed by scanning electron microscopy and transmission electron microscopy. An enhancement of the thermal and mechanical properties was revealed by thermal gravimetric analysis, differential scanning colorimetric analysis, and dynamic mechanical analysis. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Effects of carbon nanotube content on adhesion strength and wear and corrosion resistance of epoxy composite coatings on AA2024-T3

The effects of multiwalled carbon nanotube (MWCNT) content on the adhesion strength and wear and corrosion resistance of the epoxy composite coatings prepared on aluminum alloy (AA) 2024-T3 substrates were evaluated using atomic force microscopy (AFM), blister test, ball-on-disk micro-tribological test and electrochemical impedance spectroscopy (EIS). The adhesion strength of the epoxy composite coatings improved with increasing MWCNT content. Increased MWCNT content also decreased the friction coefficient and increased the wear resistance of the epoxy composite coatings due to improved solid lubricating and rolling effects of the MWCNTs and the improved load bearing capacity of the composite coatings. Finally, EIS indicated that increased MWCNT content increased the coating pore resistance due to a decreased porosity density, which resulted in an increase in the total impedance of the coated samples.     

Controlled dispersion of multiwalled carbon nanotubes modified by hyperbranched polylysine

Hyperbranched polymers have been found effective in controlling the dispersibility of carbon nanotubes in aqueous solutions. In this study, hyperbranched polylysine (HBPL) was synthesized using lysine and N,N′‐methylenebisacrylamide as precursors via Michael addition. The HBPL then was used to noncovalently modify multiwalled carbon nanotubes (MWCNTs) to prepare MWCNTs‐HBPL. The obtained MWCNTs‐HBPL composites were characterized using FTIR spectroscopy, Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The results showed that the HBPL was successfully attached to the surface of MWCNTs via noncovalent interactions. The dispersibility of the MWCNTs‐HBPL composites in aqueous solutions was investigated using digital photographs, ultraviolet–visible absorption spectroscopy, and zeta potential measurements. The results demonstrated that both the mass ratio of MWCNT to HBPL and the pH of the solution had a significant impact on the dispersibility of the MWCNTs/HBPL solution, suggesting that HBPL treatment is an effective method of controlling the dispersibility of MWCNTs in aqueous solutions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46249.     

Microwave assisted functionalization of carboxylated‐multiwalled carbon nanotubes with 5‐aminoisophthalic acid and its application for the preparation of chiral poly(ester‐imide)/CNT nanocomposites

This article presents the results of investigation into surface modification of carboxylated‐multiwalled carbon nanotubes (MWCNT)s by 5‐aminoisophthalic acid under microwave irradiation as a fast, safe, and simple method. The different contents of functionalized MWCNTs (5, 10, 15 wt%) were effectively dispersed in an aromatic polymer through ultrasonic irradiation to prepare MWCNT reinforced polymer nanocomposites (NC)s. The chiral poly(ester‐imide) (PEI) was prepared by a direct polycondensation of chiral diacid with 4,4′‐thiobis(2‐tert‐butyl‐5‐methylphenol). The effect of the presence of MWCNTs on morphological and thermal properties of the NCs was investigated by X‐ray diffraction, FT‐IR spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy, and field emission scanning electron microscopy. According to TGA data, the PEI/MWCNT NCs showed a much better thermal stability than pristine polymer. The microstructure study of the NCs indicated the compatibility of functionalized MWCNTs with PEI and uniform distribution of them in the polymer matrices. POLYM. COMPOS., 37:835–843, 2016. © 2014 Society of Plastics Engineers     

Natural rubber/multiwalled carbon nanotube composites developed with a combined self-assembly and latex compounding technique

Carbon nanotubes (CNTs), with their high aspect ratio and exceptionally high mechanical properties, are excellent fillers for composite reinforcement if they are uniformly dispersed without aggregation. Combining the latex compounding and self-assembly techniques, we prepared a novel natural rubber (NR)/multiwalled carbon nanotube (MWCNT) composite. Before self-assembly, the MWCNTs were treated with mixed acid to ensure that the MWCNTs were negatively charged under an alkaline environment. The structure of the MWCNTs was tested with Fourier transform infrared spectroscopy. The properties of composites with different MWCNT loadings were characterized with transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, and tensile testing. The results indicate that the MWCNTs were homogeneously distributed throughout the NR matrix as single tubes and had good interfacial adhesion with the NR phase when the MWCNT loading was less than 3 wt %. In particular, the addition of the MWCNT led to a remarkable reinforcement in the tensile strength, with a peak value of 31.4 MPa for an MWCNT content of 2 wt %, compared to the pure prevulcanized NR (tensile strength = 21.9 MPa). The nanocomposites reinforced with MWCNTs should have wide applications because of the notable improvement in these important properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Field emission properties of Cu/multiwalled carbon nanotube composite films fabricated by an electrodeposition technique

Composite films of Cu and multiwalled carbon nanotubes (MWCNTs) were fabricated by an electrodeposition technique, and their field emission properties were examined. Commercially available MWCNTs with various diameters (60–150 nm) were used. The microstructure of the composite films was analyzed by scanning electron microscopy and the field emission properties were measured using a diode-type system. Cu/MWCNT composite films with homogeneous dispersion of MWCNTs were fabricated using each type of MWCNT. Bare MWCNTs were present on the surface of the composite films and the ends of the protruding tips were fixed by the deposited copper matrix. The composite films produced clear emission currents and the corresponding Fowler–Nordheim (F–N) plots showed that these were field emission currents. The turn-on electric field tended to decrease with decreasing MWCNT diameter. A light-emitting device incorporating the Cu/MWCNT composite film as a field emitter was fabricated, and its light-emitting properties were investigated. Light emission with a brightness of around 100 cd m^?2 was observed for approximately 100 h.     

A comparative study on the properties of the different amino‐functionalized multiwall carbon nanotubes reinforced epoxy resin composites

Multiwall carbon nanotubes (MWCNTs) were amino‐functionalized by 1,2‐ethylenediamine (EDA)' triethylenetetramine (TETA), and dodecylamine (DDA), and investigated by fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA). The dispersion of the DDA functionalized MWCNT in DMF is better than that of the MWCNT functionalized by the EDA and the TETA. Carbon nanotubes reinforced epoxy resin composites were prepared, and the effect of the amino‐functionalization on the properties of the composites was investigated by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and TGA. The composites reinforced by the MWCNTs demonstrate improvement in various mechanical properties. The increase of T_g of the composites with the addition of amino‐functionalized MWCNT compared to the T_g of the composites with the addition of unfunctionalized MWCNT was due to the chemical combination and the physical entanglements between amino group from modified MWNTs and epoxy group from the epoxy resin. The interfacial bonding between the epoxy and the amino group of the EDA and the TETA‐modified MWCNT is more important than the well dispersion of DDA‐modified MWCNT in the composites for the improvement of the mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improving thermal conductivity and shear strength of carbon nanotubes/epoxy composites via thiol‐ene click reaction

This study investigates the effect of the thiol‐ene click reaction on thermal conductivity and shear strength of the epoxy composites reinforced by various silane‐functionalized hybrids of sulfhydryl‐grafted multi‐walled carbon nanotubes (SH‐MWCNTs) and vinyl‐grafted MWCNTs (CC‐MWCNTs). The results of Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM) show that the sulfhydryl groups and vinyl groups are successfully grafted onto the surface of MWCNTs, after treatment of MWCNT with triethoxyvinylsilane and 3‐mercaptopropyltrimethoxysilane, respectively. Scanning electron microscopy (SEM), HotDisk thermal constant analyzer (HotDisk), optical microscope, and differential scanning calorimetry (DSC) are used to characterize the resultant composites. It is demonstrated that the hybrid of 75 wt % SH‐MWCNTs and 25 wt % CC‐MWCNTs has better dispersion and stability in epoxy matrix, and shows a stronger synergistic effect in improving the thermal conductivity of epoxy composite via the thiol‐ene click reaction with 2,2′‐azobis(2‐methylpropionitrile) as thermal initiator. Furthermore, the tensile shear strength results of MWCNT/epoxy composites and the optical microscopy photographs of shear failure section indicate that the composite with the hybrid MWCNTs has higher shear strength than that with raw MWCNTs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44579.     

Characteristics of nylon 6,6/nylon 6,6 grafted multi-walled carbon nanotube composites fabricated by reactive extrusion

Nylon 6,6 composites containing nylon 6,6 grafted multi-walled carbon nanotubes (nylon 6,6-g-MWCNT) were fabricated from nylon 6,6 and acyl chloride grafted MWCNT (MWCNT–COCl) by reactive extrusion. MWCNT–COCl was produced by reacting acid-treated MWCNTs with thionyl chloride. Formation of nylon 6,6-g-MWCNT by reactive extrusion was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and scanning electron microscopy. To quantify the interfacial adhesion energies of nylon 6,6 and pristine and functionalized MWCNTs, the contact angles of cylindrical drop-on-fiber systems were determined using the generalized droplet shape analysis. The interfacial adhesion energy of the nylon 6,6/nylon 6,6-g-MWCNT composite was twice that of the nylon 6,6/pristine MWCNT composite. Nylon 6,6-g-MWCNTs exhibited excellent dispersion in the composite, whereas pristine MWCNTs exhibited poor dispersion when composite films were prepared by solvent casting. The reinforcement level of the composite increased with increasing MWCNT content. Among the composites examined, the nylon 6,6/nylon-g-MWCNT composite with a fixed MWCNT content exhibited the highest level of reinforcement.     

Covalent functionalization of carbon nanotubes with polyhedral oligomeric silsequioxane for superhydrophobicity and flame retardancy

Multiwalled carbon nanotubes (MWCNTs) were covalently functionalized with polyhedral oligomeric silsequioxane (POSS). The results of Fourier Transform Infrared Spectroscopy, Raman spectroscopy and Transmission Electron Microscopy indicated that POSS particles were grafted onto MWCNTs. The POSS content determined by thermo‐gravimetric analysis (TGA) was estimated to be ～25 wt%. A stable and superhydrophobic surface characteristic was observed for the film made of MWCNTs grafted with POSS (MWCNT‐g‐POSS) even after an exposure to a high‐humidity environment for three weeks. The water contact angle of the sample was measured to be 160.5 ± 1.1°. Buckypapers were made from both pristine MWCNTs and chemically converted to MWCNT‐g‐POSS. The pore structures of the buckypapers were characterized by mercury intrusion porosimetry and scanning electron microscopy. The flame‐retardant performance of the buckypaper‐based composites was evaluated by TGA and microscale combustion calorimetry (MCC) test. The TGA test results indicated that the MWCNT‐g‐POSS dramatically increased the char residues of the composite. Approximately 72% reduction in peak heat release rate was achieved for the MWCNT‐g‐POSS /resin composite from the MCC testing. The fire‐retardant mechanism was discussed. POLYM. ENG. SCI., 2013. © Society of Plastics Engineers     

Fabrication of robust multiwalled carbon nanotube buckypapers through crosslinking reaction of epoxy chains with its curing agent

Vacuum filtration method was used to fabricate robust multiwalled carbon nanotube buckypapers (MWCNT‐BPs). MWCNTs were functionalized by epoxy resin (diglycidyl ether of bisphenol A) to enhance their dispersibility. Fabricated BPs were immersed in epoxy hardner to covalently attach functional groups of MWCNTs to each other. Functionalization of MWCNTs was characterized qualitatively by Fourier transform infrared spectroscopy and quantitatively using thermogravimetric analysis. The morphology study of BPs was studied using scanning electron microscopy. Functionalization of MWCNTs resulted in more uniform and homogeneous BPs. Moreover, considerable improvements were achieved in the mechanical and electrical properties of BPs. POLYM. COMPOS., 38:2727–2733, 2017. © 2015 Society of Plastics Engineers