Aminofunctionalization effect on the microtribological behavior of carbon nanotube/bismaleimide nanocomposites

Original multiwalled carbon nanotubes (O‐MWCNTs) and aminofunctionalized ethylenediamine‐treated multiwalled carbon nanotubes (MWCNTs‐EDA) were mixed with bismaleimide (BMI) resin to prepare O‐MWCNT/BMI and MWCNT‐EDA/BMI composites, respectively. Raman spectroscopy, thermogravimetric analysis, and infrared spectroscopy were used to investigate the influence of aminofunctionalization on the multiwalled carbon nanotube (MWCNT) framework. Dynamic mechanical analysis, scanning electron microscopy images of the fractured surface, and field emission scanning electron microscopy of the worn surface were used to determine the possible friction and wear mechanisms of the system. The MWCNT‐EDA/BMI composite exhibited a higher friction coefficient value and a lower wear loss rate value than the O‐MWCNT/BMI composite, which was attributed to the larger number of defects caused by the aminofunctionalization of the MWCNTs, the stronger interfacial adhesion formed between the MWCNTs‐EDA and the BMI resin, and the better dispersive state of the MWCNTs‐EDA in the BMI matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of a doubly modified carbon nanotube derivative on the microstructure of epoxy resin

The surface of multi wall carbon nanotubes (MWCNTs) was first covalently functionalized with oleyl amine and then non-covalently wrapped with polycarbosilane (PCS). The hybrid functional groups were chosen to introduce different features in the MWCNTs properties. For covalent functionalization a long chain unsaturated aliphatic amine was used to simultaneously achieve the dissociation of MWCNT bundles along with the dispersion and interaction with the host matrix using the amide functionality and double bond. On the other hand, a thermally stable polymer was selected which can interact with both resin and glass fabric to promote interfacial adhesion. This hybrid doubly modified MWCNT is thus possesses duel advantages in glass fiber based epoxy composite. The pristine, covalent, noncovalent and covalent-noncovalent doubly modified MWCNT systems were used to study the viscoelastic behavior and interactions of functionalized MWCNTs in the matrix above and below the glass transition temperature of the matrix. The PCS coating on the MWCNTs is amorphous and thermally insulating whereas the nanotube is highly graphitized and thermally conducting. This contrasting behavior provides us to insight into the temperature dependant resin microstructure and curing thermodynamics of epoxy resin in the presence of MWCNTs.     

Synthesis and properties of macromer-grafted polymers for noncovalent functionalization of multiwalled carbon nanotubes

We prepared macromer-grafted polymers (MGPs) containing suitable polymer side chains for improving solubility and pyrene units for improving adsorption on multiwalled carbon nanotube (MWCNT) surfaces, and demonstrated that these MGPs act as MWCNT solubilizers that improve solubility of MWCNTs in typically poor solvents such as alkanes and that improve flowability of polymer/MWCNT composites. The polydimethylsiloxane (PDMS)-MGPs, synthesized using PDMS macromers and pyrene-containing monomers, improved solubility of MWCNTs not only in chloroform but also in hexane, which is a poor solvent for MWCNTs. Moreover, the addition of PDMS-MGP-adsorbed MWCNTs (MWCNT/PDMS-MGPs) to epoxy resin monomers or polybutylene terephthalate (PBT) drastically reduced the viscosity of the obtained epoxy resin monomer/MWCNT/PDMS-MGP mixtures and PBT/MWCNT/PDMS-MGP composites in comparison to the epoxy resin monomer/MWCNT mixtures and PBT/MWCNT composites, respectively. The viscosity of PBT/MWCNT/PDMS-MGP composites including ?1 vol% of MWCNTs, in particular, was almost equal to that of pristine PBT.     

Effect of functionalized carbon nanotubes on the thermal conductivity of epoxy composites

Direct functionalized carbon nanotubes (CNTs) were utilized to form the heat flow network for epoxy composites through covalent integration. A method of preparing a fully heat flow network between benzenetricarboxylic acid grafted multi-walled carbon nanotubes (BTC-MWCNTs) and epoxy matrix is described. A Friedel-Crafts modification was used to functionalize MWCNTs effectively and without damaging the MWCNT surface. Raman spectra, X-ray photoelectron spectra and thermogravimetric analysis reveal the characteristics of functionalized MWCNTs. The scanning electron microscope images of the fracture surfaces of the epoxy matrix showed BTC-MWCNTs exhibited higher solubility and compatibility than pristine-MWCNTs. The MWCNTs/epoxy composites were prepared by mixing BTC-MWCNTs and epoxy resin in tetrahydrofuran, followed by a cross-linking reaction with a curing agent. The BTC was grafted onto the MWCNTs, creating a rigid covalent bond between MWCNTs and epoxy resin and forming an effective network for heat flow. The effect of functionalized MWCNTs on the formation of the heat flow network and thermal conductivity was also investigated. The thermal conductivity of composites exhibits a significant improvement from 0.13 to 0.96 W/m K (an increase of 684%) with the addition of a small quantity (1-5 vol%) of BTC-MWCNTs.     

Preparation and wear behavior of carbon/epoxy resin composites with an interpenetrating network structure derived from natural sponge

Natural sponge was used as the template to produce carbon/epoxy resin composites with interpenetrating network structure. Carbon with a network structure was first obtained by the pyrolysis of natural sponge. The composites were then obtained by injecting epoxy resin into the carbon. Their microstructures and wear properties were analyzed. The results show that the natural structure of sponge controlled the interpenetrating network structures of the carbon/epoxy resin composites. The carbon-network in the composites was shown to stabilize the coefficient of friction of epoxy resin. The carbon also reduces the wear rate of the epoxy resin remarkably.     

Rheological properties and fracture toughness of epoxy resin/multi‐walled carbon nanotube composites

Multi‐walled carbon nanotubes (MWCNTs), surface‐treated via chemical functionalization, i.e., oxidation and amidation, were used to reinforce diglycidylether of bisphenol F (DGEBF) epoxy resin. The effects of the functionalization on the dispersion stability, rheological properties, and fracture toughness of DGEBF/MWCNT composites were investigated. The dispersion homogeneity of the MWCNTs in the epoxy matrix improved after functionalization. In addition, isothermal rheology measurements revealed that the DGEBF/dodecyl amine‐functionalized MWCNT (D‐MWCNT) composite had a longer gel time and higher activation energy of cross‐linking than the DGEBF/acid‐treated MWCNT (A‐MWCNT) composite. The fracture toughness of the former was also significantly higher than that of the latter; this resulted from the relatively high dispersion stability of the D‐MWCNTs in the epoxy matrix, owing to the presence of alkyl groups on the D‐MWCNT surface. POLYM. ENG. SCI., 55:2676–2682, 2015. © 2015 Society of Plastics Engineers     

Synergetic effect of fly ash cenospheres and multi-walled carbon nanotubes on mechanical and tribological properties of epoxy resin coatings

The multiform wear of friction pair components is the main cause of marine equipment failure and epoxy resin (EP) coatings have been widely used in this field. Fly ash cenospheres (FACs) and multi-walled carbon nanotubes (MWCNTs) were used to reinforce the tribological properties of EP coatings. The synergetic effects of FACs and MWCNTs on the mechanical and tribological properties of EP coatings were studied. Experimental results show that the tensile and flexural properties of FACs-MWCNTs/EP composites are significantly reinforced. The tribological performance of EP composite coatings under seawater conditions is improved by the synergetic effect of FACs and MWCNTs, especially, the 10 wt.% FACs-1 wt.% MWCNTs/EP coatings behave the most excellent tribological properties. It indicates that FACs can increase the hardness of EP coatings and provide a smoother surface for the water film formation, which decreases the friction coefficient and wear volume. MWCNTs can increase the elasticity modulus of EP, and act as a rope to prevent EP matrix and FACs from being desquamated.     

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

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

Effect of amino‐functionalization of multi‐walled carbon nanotubes on the dispersion with epoxy resin matrix

Amino‐functionalization of multiwalled carbon nanotubes (MWCNTs) was carried out by grafting triethylenetetramine (TETA) on the surfaces of MWCNTs through the acid–thionyl chloride way. The amino‐functionalized MWCNTs show improved compatibility with epoxy resin and, as a result, more homogenous dispersion in the matrix. The mechanical, optical, and thermal properties of the amino‐functionalized MWCNT/epoxy composites were also investigated. It was found that introducing the amino‐functionalized MWCNTs into epoxy resin greatly increased the charpy impact strength, glass transition temperature, and initial decomposing temperature of cured epoxy resin. In addition, introducing unfunctionalized MWCNTs into epoxy resin was found greatly depressing the light transmission properties, which would affirmatively confine the application of the MWCNTs/epoxy composites in the future, while much higher light transmittance than that of unfunctionalized MWCNTs/epoxy composites was found for amino‐functionalized MWCNTs/epoxy composites. SEM of the impact cross section and TEM of ultrathin film of the amino‐functionalized MWCNTs/epoxy composites showed that the amino‐functionalized MWCNTs were wetted well by epoxy matrix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 97–104, 2006     

Mild functionalization of carbon nanotubes filled epoxy composites: Effect on electromagnetic interferences shielding effectiveness

The effect of nitric acid mild functionalized multiwalled carbon nanotubes (MWCNTs) on electromagnetic interference (EMI) shielding effectiveness (SE) of epoxy composites was examined. MWCNTs were oxidized by concentrated nitric acid under reflux conditions, with different reaction times. The dispersion of MWCNTs after functionalization was improved due to the presence of oxygen functional groups on the nanotubes surface. Functionalization at 2 h exhibits the highest EMI SE and electrical conductivity of MWCNTs filled epoxy composites. However, EMI shielding performance of MWCNTs filled epoxy composite declined when the functionalization reaction time was prolonged. This was due to extensive damage on the MWCNT structure, as verified by a Raman spectroscope. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42557.     

Direct functionalization with 3,5‐substituted benzoic acids of multiwalled carbon nanotube/epoxy composites

Directly functionalized multiwalled carbon nanotubes (MWCNTs) with benzene‐1,3,5‐tricarboxylic acid (BTC) and 3,5‐diaminobenzoic acid (DAB) were successfully accomplished with less structural damage as confirmed by XPS and FT‐Raman results. Their dispersibility and thermal stability were achieved after the functionalization. The functional groups on MWCNT surfaces can accelerate the curing reaction of epoxy composites remarkable inducing rather low exothermic peak temperature (T_p) and exothermic heat of reaction (ΔH). The values of activation energy (E_a) obtained from Kissinger and Ozawa methods obviously decreased with the introduction of MWCNTs, especially DAB‐MWCNTs. The dynamic mechanical properties notably enhanced with the incorporation of unmodified and functionalized MWCNTs. The crosslink density (ρ) increased and free volume fraction (f_g) decreased, resulting in dramatic increase of glass transition temperatures (T_g) and decrease of coefficient of thermal expansion. Additionally, epoxy composites exhibited low dielectric constant close to that of neat epoxy resin. From these remarkable properties, MWCNT/epoxy composites can be considered as a good candidate for high performance insulation materials. POLYM. ENG. SCI., 53:2194–2204, 2013. © 2013 Society of Plastics Engineers     

Multi-functional multi-walled carbon nanotube-jute fibres and composites

Jute fibres and corresponding epoxy based composites with sensing abilities could be realized by depositing multi-walled carbon nanotubes (MWCNTs) on the surfaces of jute fibres or fabrics using simple and scalable dip coating. The formation of electrically semiconducting MWCNT networks on jute fibre surfaces was confirmed, which in turn caused the formation of jute/epoxy interphases with highly concentrated MWCNTs. The sensing behaviour of the MWCNT coated jute fibres and jute/epoxy composites for temperature, relative humidity and stress/strain was further established in detail, which were strongly influenced by the intrinsic physical and chemical features of the fibres. In addition, a significant improvement in dielectric properties of the MWCNT-jute/epoxy composites was observed compared to neat jute/epoxy composites. Based on this approach, the electrically insulating natural fibres along with semiconducting MWCNTs on surface will stimulate and realize a broad range of multi-functional applications.     

Prediction of the mechanical characteristics of multi-walled carbon nanotube/epoxy composites using a new form of the rule of mixtures

Multi-walled carbon nanotubes (MWCNTs) were used in the low-viscosity, thermosetting polyester epoxy/amine resin LY-5052 with high temperature resistance to fabricate MWCNT/epoxy composites. Tensile tests of the specimens were carried out to obtain mechanical properties of MWCNT/epoxy composites for various weight-percents (wt.%) of MWCNTs. Experimental results show that the Young’s modulus and the tensile strength of the composites can be significantly improved by adding a small percentage of MWCNT. A new form of the rule of mixtures, including an exponential shape function, length efficiency parameter, orientation efficiency factor and a waviness parameter, is proposed for a more accurate prediction of the mechanical properties of MWCNT-reinforced epoxy composites, for both low and high wt.% ranges. In order to verify the suitability of the model, the ensuing predictions are compared to the available experimental data in the literature. Results demonstrate a good predictability of the modified form over a wide range of tests.     

Increasing the interfacial strength in carbon fiber/epoxy composites by controlling the orientation and length of carbon nanotubes grown on the fibers

Multi-walled carbon nanotubes (MWCNTs) were grafted onto carbon fibers (CFs) using an injection chemical vapor deposition method. The orientation and length (16.6–108.6 μm) of the MWCNTs were controlled by the surface treatment of the CFs and the growth time, respectively. The interface between the MWCNTs and the CFs indicated the grafted CNTs were immobilized by embedding catalyst on CFs. Two orders of magnitude increase in the specific surface areas of CFs was obtained by grafting the MWCNT. MWCNT–CF hybrids exhibited good wettability with the epoxy resin due to the surface roughness and capillary action. Single-fiber composite fragmentation tests revealed an remarkable improvement of interfacial shear strength (IFSS) controlled by the orientation and length of MWCNTs. MWCNTs with an perpendicular alignment and long length showed a high IFSS in epoxy composites due to better wettability and a large contact interface between the hybrids and the resin. Hybrids with an optimum length (47.2 μm) of aligned MWCNTs showed a dramatic improvement of IFSS up to 175% compared to that of pristine CFs.     

Functionalization of multi‐walled carbon nanotubes and their effect on the tribological properties of poly(ether ether ketone) composites

A series of copolymers containing conjugated fluorene groups as a compatibilizer to improve the dispersion of multi‐walled carbon nanotubes (MWCNTs) were prepared and used to improve the wear resistance of poly(ether ether ketone)/graphite (PEEK/GP) composites. The solubility of MWCNTs had a maximum at a concentration ratio of 2:1 polymer:MWCNTs. Transmission electron microscopy indicated that polymer ? MWCNT interactions were capable of partially debundling the nanotubes in chloroform, with individual nanotubes or small bundles clearly observed. The tribological properties of PEEK composites incorporating the modified MWCNTs were investigated using a pin‐on‐disc apparatus and a block‐on‐ring apparatus. The PEEK composites had a lower frictional coefficient under the block‐on‐ring testing condition, but a lower wear rate was achieved in the pin‐on‐disc test. © 2017 Society of Chemical Industry     

Preparation and thermal,electrical, and morphological properties of multiwalled carbon nanotubeand epoxy composites

Multiwalled carbon nanotube (MWCNT)/epoxy composites are prepared, and the characteristics and morphological properties are studied. Scanning electron microscopy microphotographs show that MWCNTs are dispersed on the nanoscale in the epoxy resin. The glass‐transition temperature (T_g) of MWCNT/epoxy composites is dramatically increased with the addition of 0.5 wt % MWCNT. The T_g increases from 167°C for neat epoxy to 189°C for 0.5 wt % CNT/epoxy. The surface resistivity and bulk resistivity are decreased when MWCNT is added to the epoxy resins. The surface resistivity of CNT/epoxy composites decreases from 4.92 × 10¹² Ω for neat epoxy to 3.03 × 10⁹ Ω for 1 wt % MWCNT/epoxy. The bulk resistivity decreases from 8.21 × 10¹⁶ Ω cm for neat epoxy to 6.72 × 10⁸ Ω cm for 1 wt % MWCNT/epoxy. The dielectric constant increases from 3.5 for neat epoxy to 5.5 for 1 wt % MWCNT/epoxy. However, the coefficient of thermal expansion is not affected when the MWCNT content is less than 0.5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1272–1278, 2007     

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     

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.     

Effect of functionalization on the thermo-mechanical and electrical behavior of multi-wall carbon nanotube/epoxy composites

The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, the mechanical and electrical properties of composites was investigated. Samples based on epoxy resin with different weight percentage of MWCNTs or COOH-functionalized carbon nanotubes (MWCNT–COOH) were prepared and characterized. Dynamic-mechanical thermal analysis shows that the storage modulus increases with the addition of MWCNTs, whereas a constant value or even a weak reduction was observed for functionalized nanotubes. Two phases were suggested in the composites with MWCNT–COOH, both by dynamic-mechanical properties and by water transport. Chemical functionalization of MWCNTs increases the compatibility with the epoxy matrix due to the formation of an interface with stronger interconnections. This, in turn, causes a significant decrease in the electrical conductivity of this type of composite with respect to the untreated MWCNTs which can be explained in terms of tunnelling resistance between interacting nanotubes.     

Thermo‐mechanical and tribological properties of multi‐walled carbon nanotubes filled friction composite materials

Multi‐walled carbon nanotubes (MWCNTs) filled graphite lubricated phenolic‐based friction composites reinforced with combination of lapinus/Kevlar fibers have been fabricated and subsequently evaluated for their dynamic‐mechanical and tribological properties. The experimental results indicated that the higher MWCNT content enhances the thermal stability, whereas, lower MWCNT content enhances the thermo‐mechanical properties of the friction composites. The tribo‐performance evaluation has revealed that with the increase in MWCNT content, the friction‐fade and friction‐recovery performances are enhanced. The friction‐stability and friction‐variability coefficients are influenced by the combination of MWCNT, graphite, lapinus, and Kevlar constituents. The wear performance decreases with the increase in lapinus and MWCNT, whereas, it increases when the amount of Kevlar or graphite is increased in the composites. Wear surface morphological studies have led to the qualitative characterization of the topographical attributes and the nature of the frictional contact patches which is crucial in understanding the role of MWCNT on friction and wear mechanisms of the investigated automotive brake friction materials. POLYM. COMPOS., 38:1183–1193, 2017. © 2015 Society of Plastics Engineers