Noncovalent functionalization of multi-walled carbon nanotubes with hydroxyl group-containing pyrene derivatives for their composites with polycarbonate

Pyrene derivative-containing hydroxyl groups such as 1-hydroxypyrene (PO), 1-pyrenemethanol (PMO) and 1-pyrenebutanol (PBO) were examined as new interfacial agents for bisphenol-A polycarbonate (PC)/multi-walled carbon nanotube (MWCNT) composites. The pyrene units adsorbed onto the MWCNT surface by physisorption and the hydroxyl groups in the pyrene derivatives reacted with the carbonate groups in the PC during melt extrusion. The reactivity of the hydroxyl groups in the pyrene derivatives with the carbonate groups in the PC increased as the nucleophilicity of the hydroxyl groups in the pyrene derivatives increased. As a result, the amount of PC grafted onto the MWCNT surface by the reaction between the PC and the pyrene derivative increased in the order of PBO > PMO > PO. The PC/MWCNT composite used PBO as an interfacial agent exhibited the best interfacial adhesion between the MWCNT and PC and the highest level of MWCNT dispersion in the PC matrix among the composites examined. When the MWCNT content in the composite was fixed, the PC/MWCNT composite with the highest interfacial adhesion energy between the PC and the MWCNT exhibited the best tensile strength and modulus.     

Noncovalent functionalization of multi-walled carbon nanotubes with pyrene-linked nylon66 for high performance nylon66/multi-walled carbon nanotube composites

A new interfacial agent, 1-pyrenebutyric chloride (PBC), was synthesized for use in nylon 66 (PA66)/multi-walled carbon nanotube (MWCNT) composites. It has been shown that the pyrene units in PBC adsorb onto the MWCNT surface by physisorption, and the acyl chloride units in PBC react with amine end groups in PA66 during melt extrusion. As a result, PBC that was covalently bonded with PA66 formed at the interface between the MWCNT and PA66 matrix. The PA66/MWCNT composite containing PBC exhibited the best interfacial adhesion between MWCNT and PA66 and the highest level of MWCNT dispersion in the PA66 matrix among the composites examined. It was also found that the PA66/MWCNT composite with the higher interfacial adhesion energy between PA66 and MWCNT exhibited a higher level of reinforcement.     

Surface functionalization of carbon nanotubes by biological adhesive polymers carbopol for developing high‐permittivity polymer composites

Surface functionalization of carbon nanotubes (CNTs) by biological adhesive polymers carbopol (CP) was developed by simply mixing CNT suspension and an aqueous solution of CP without any toxic solvents. CP can be easily coated onto CNTs through hydrogen bonds O?C? OH?NH₂? C?O and electrostatic interaction between ? COO? on CP and ? NH₃⁺ on CNTs. After modification, the surface of the CNT is endowed with a large number of carboxyl groups, which can effectively prevent the reaggregation of CNT by electrostatic repulsion between the ionized carboxyl groups. Hence, highly dispersed functionally modifying CNT by CP (CP‐CNT) filler in polydimethylsiloxane (PDMS) matrix can be obtained. More important, with the help of adhesive properties of CP, the interfacial compatibility between fillers and matrix can also be improved. Thus, the CP‐CNT/PDMS composites exhibited higher dielectric permittivity comparing with CNT/PDMS composites at the same filler content. We present a potential and green approach of surface functionalization of CNT for preparing high‐permittivity polymer composites. J. VINYL ADDIT. TECHNOL., 26:165–172, 2020. © 2019 Society of Plastics Engineers     

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.     

Covalent functionalization of carbon nanotubes and their use in dielectric epoxy composites to improve heat dissipation

A method to enhance the thermal dissipation of epoxies is described. The method exploits the transport of heat by phonons so that the composite material designed remains dielectric. The improvement in thermal transport is guaranteed by the addition of functionalized carbon nanotube fillers which are covalently bonded to the epoxy matrix. We demonstrate that even if the covalent grafting of functional molecules affects the thermal transport within the nanotubes because of the disruption in periodicity of the structure, it improves the interfacial thermal conductance between the matrix and fillers. The trade-off has a net positive impact on the effective thermal conductivity of the composite material.     

Non-destructive functionalization of multi-walled carbon nanotubes with naphthalene-containing polymer for high performance Nylon66/multi-walled carbon nanotube composites

A new compatibilizer, poly(vinyl benzyloxy methyl naphthalene)-g-poly(t-butyl methacrylate-co-methacrylic acid), was synthesized for Nylon 66 (N66)/multi-walled carbon nanotube (MWCNT) composites. It has been shown that the naphthalene unit in the main chain of the compatibilizer interacts with MWCNTs by π–π interaction and that the carboxylic acid unit in the graft chain of the compatibilizer interacts with the amide group of N66. The use of the compatibilizer produces well-dispersed MWCNTs in N66 matrix, which results in improved mechanical and electrical properties of the composites, while the simple mixture of N66/MWNCTs without the compatibilizer exhibits poor mechanical and electrical properties due to severe aggregation of MWCNTs. It is also found that the compatibilizer with a small amount of carboxylic acids is more effective for improving the mechanical and electrical properties of N66/MWCNT composites.     

The effect of surface functionalization of carbon nanotubes on properties of natural rubber/carbon nanotube composites

The objective of this study was to prepare natural rubber composites filled with carbon nanotubes (CNTs) that show an electrical percolation threshold at very low CNT concentrations. Therefore, two methods of surface functionalization of CNTs were investigated to enable an improved dispersion of CNTs and chemical interaction between CNTs and rubber matrix. On one hand, the CNTs have been functionalized ex situ by acid treatment and silanization reaction with bis(triethoxysilylpropyl) tetrasulfide before mixing with the rubber and otherwise in situ functionalization was directly carried out during the processing of the composites in the internal mixer. The grafting of silane molecules onto CNT surface was established by Fourier transform infrared spectroscopy and scanning electron microscopy. Tensile tests revealed the outstanding properties of composites prepared by in situ silanization method. The in situ silanization led to a better dispersion of the CNTs and the formation of chemical linkages between CNT surface and rubber and this became manifest in higher reinforcement of the rubber, higher crosslink densities, and a lower electrical percolation threshold. It was also shown that the in situ silanization is retarding the vulcanization reaction. POLYM. COMPOS., 36:2113–2122, 2015. © 2014 Society of Plastics Engineer     

Amino functionalization of multiwalled carbon nanotubes by gamma ray irradiation and its epoxy composites

In this paper, γ‐ray radiation technique was utilized to simply functionalize multi‐walled carbon nanotube (MWCNT) with amino groups. The successful amino functionalization of MWCNTs (MWCNTs‐Am) was proven and the physicochemical properties of MWCNTs before and after radiation grafting modifications were characterized using FT‐IR, X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results indicated that the γ‐ray radiation had the visible effects on the surface properties of MWCNTs. The effects of various functionalized MWCNTs on morphological, thermal, and mechanical properties of an epoxy‐based nanocomposite system were investigated. Utilizing in situ polymerization, 1 wt% loading of MWCNT was used to prepare epoxy‐based nanocomposites. Compared to the neat epoxy system, nanocomposites prepared with MWCNT‐Am showed 13.0% increase in tensile strength, 20.0% increase in tensile modulus, and 24.1% increase in thermal decomposition temperature. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Noncovalent functionalization of carbon nanotubes using branched random copolymer for improvement of thermal conductivity and mechanical properties of epoxy thermosets

A branched random copolymer, poly[(hydroxyethyl acrylate)‐r‐(N‐vinylcarbazole)] (BPHNV), was synthesized through a facile one‐pot free radical polymerization with hydroxyethyl acrylate and N‐vinylcarbazole monomers, using 4‐vinylmethylmercaptan as the chain transfer agent. BPHNV was employed to noncovalently modify multiwall carbon nanotubes (MWCNTs) by π–π interaction. The as‐modified MWCNTs were then incorporated into epoxy resin to improve the thermal conductivity and mechanical properties of epoxy thermosets. The results suggest that, due to both the conjugation structure and the epoxy‐philic component, BPHNV could form a polymer layer on the wall of MWCNTs and inhibit entanglement, helping the uniform dispersion of MWCNTs in epoxy matrix. Owing to the unprecedented thermal conductivity of MWCNTs and the enhancement in the interfacial interaction between fillers and matrix, the thermal conductivity of epoxy/MWCNTs/BPHNV composites increases by 78% at extremely low filler loadings, while the electrical resistivity is still maintained on account of the insulating polymer layer. Meanwhile, the mechanical properties and glass transition temperature (T_g) of the thermosets are elevated effectively, with no significant decrease occurring to the modulus. The addition of as little as 0.1 wt% of MWCNTs decorated with 1.0 wt% of BPHNV to an epoxy matrix affords a great increase of 130% in impact strength for the epoxy thermosets, as well as an increase of over 13 °C in T_g. © 2018 Society of Chemical Industry     

Water-soluble carbon nanotubes through sugar azide functionalization

In this work we report a covalent functionalization of pristine single-walled carbon nanotubes (SWCNTs) directly with three sugar azides, 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl, 2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl or 2,3,4,6-tetra-O-acetyl-β-d-mannopyranosyl azide. Microwave-assisted functionalization was carried out for SWCNTs prepared with the HiPCO method. The as-prepared, new type of sugar-functionalized SWCNTs were analyzed by Raman and IR spectroscopy. Deacetylation of the functionalized tubes by sodium methoxide yielded nitrogen-linked, sugar-functionalized carbon nanotubes (CNTs) that formed stable dispersions in water. Reactivity of the sugar azides towards SWCNTs was estimated from the solubility experiments. The water solubility was found to be highest for galactopyranosyl and lowest for gluco- and mannopyranosyl derivatives.     

Improving dispersion of multiwalled carbon nanotubes in polyamide 6 composites through amino‐functionalization

The focus of this study is to investigate the state of dispersion of different treated multiwalled carbon nanotubes (MWNTs) in polyamide 6 (PA6). The MWNTs used in composites were grafted by 1,6‐hexamethylenediamine (HMD) via acid‐thionyl chloride to improve their compatibility with PA6 matrix. A microstructure transformation of MWNTs is found during the treatment process. Acidification makes the MWNTs compact and grafting HMD promotes the compact structure loose again. The MWNTs after different treatment were used to fabricate MWNTs/PA6 composites through melt blending. The dispersion of different MWNTs in PA6 was observed by a combination of scanning electron microscopy, optical microscopy, and transmission electron microscopy. The results show that the amino‐functionalized MWNTs are dispersed more homogeneously in PA6 than the purified MWNTs, and the poorest dispersion is achieved for acid treated MWNTs. It is indicated that the loose structure and functionalized surface of MWNTs benefit the dispersion of MWNTs in PA6. In addition, the amino‐functionalization of MWNTs improves the compatibility between the MWNTs and PA6, resulting in stronger interfacial adhesion. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

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.     

Efficient microwave-assisted radical functionalization of single-wall carbon nanotubes

The efficiencies of two methods of functionalizing single wall carbon nanotubes (SWCNTs) are compared, either through a radical addition of 4-methoxyphenylhydrazine hydrochloride by a classical thermally activated procedure, or via a microwave-assisted method. X-ray photoelectron spectroscopy and thermal gravimetric analysis clearly indicate the efficiency of both methods. Raman and absorption spectroscopy further confirm the functionalization and reveal the covalent nature of the bonds created at the carbon nanotube surface. For the microwave-assisted reaction, 5-15 min is enough to functionalize the SWCNTs. Longer microwave exposure times reduce the functionalization yield and lead to a removal of groups which were bonded in a previous stage. An optimal choice of microwave irradiation time allows reducing the reaction time from days to minutes.     

Effects of the composition and molecular weight of maleimide polymers on the dispersibility of carbon nanotubes in chloroform

We synthesized maleimide polymers (MIPs) as effective carbon nanotube (CNT) dispersants for stable CNT-dispersed solutions. The MIPs were random copolymers which consist of N-phenyl maleimide (PhMI) units that imparted strong physical adsorption to the CNT surfaces and methyl methacrylate units; we evaluated the effects of the PhMI content and molecular weight in the MIPs on the dispersibility of the CNTs in chloroform. Increasing the PhMI content in the MIPs increased the grafting amount (GA) (g m⁻²) of MIPs on the CNT surfaces and led to a large increase of CNT dispersion. In particular, when single-walled carbon nanotubes (SWCNTs) were used, MIPs having 100 mol% PhMI units (MIP100s) were imperative for a drastic increase in the GA value. Increasing the weight average molecular weight (M_w) of the MIPs resulted in no significant effect on CNT dispersibility; however, the particularly low M_w (?10,000) of the MIPs dramatically improved CNT dispersion. Therefore, MIP100s with particularly low M_w’s were extremely effective for dispersing various CNTs with different diameters. In the case of SWCNTs, much more effective exfoliation of SWCNT bundles was achieved by MIP100s with particularly low M_w’s than MIP100s with higher M_w’s.     

Microwave-induced rapid chemical functionalization of single-walled carbon nanotubes

The microwave-induced chemical functionalization of single-walled carbon nanotubes (SWNTs) is reported. The major advantage of this high-energy procedure is that it reduced the reaction time to the order of minutes and the number of steps in the reaction procedure compared to that of conventional functionalization processes. Two successful model reactions, namely amidation and 1,3-dipolar cycloaddition of SWNTs were carried out. The amidation was completed in two steps as compared to three in the conventional approach. The step involving acid chloride formation was eliminated here, and the yield remained the same. The 1,3-dipolar cycloaddition of SWNTs was carried out in 15 min under microwave conditions, and the results were similar to what was achieved in 5 days using conventional methods. This finding opens the door to fast and inexpensive processing to produce functional SWNTs, which is extremely important for their use in real-world applications.     

Rapid surface functionalization of iron-filled multi-walled carbon nanotubes

Iron-filled multi-walled carbon nanotubes (Fe@MWCNTs) were surface functionalized with various functionalities via a rapid, single-step process involving ultrasonication assisted and microwave-induced radical polymerization reactions. Both hydrophobic (e.g., polystyrenes and polymethyl methacrylate) and hydrophilic (e.g., polyacrylamide, polyacrylic acids, and polyallyl alcohols) polymer chains can be chemically grafted onto the surface of MWCNTs by the same process within 10 min. The surface grafted polymers were identified by FTIR, TGA, TEM, EELS and Raman spectra. The solubilities of the surface derivatized MWCNTs are in the range of 1200–2800 mg/l in solutions. The polyacrylic acids modified iron filled MWCNTs have a saturated magnetic dipole moment of 40 emu/g at room temperature with a coerceive field of nearly zero gauss.     

Functionalization of multi-walled carbon nanotubes with furan and maleimide compounds through Diels-Alder cycloaddition

Functionalization of multi-walled carbon nanotubes (MWCNTs) is performed through Diels-Alder (DA) reaction, using either furfuryl alcohol (a diene) or N-(4-hydroxyphenyl)maleimide (NHMI, a dienophile) as a functionalization agent. The structures of the functionalized MWCNTs are characterized with Fourier-transform infrared spectroscopy and Raman spectroscopy. Thermogravimetric analysis results also demonstrate the presence of organic portions of the functionalized MWCNTs. The DA reaction is further applied to incorporate polymer chains onto MWCNT surfaces, using a polyamide with maleimide pendent groups. Transmission electron microscopy images show the presence of a polymer layer of about 2-5 nm around the polymer modified MWCNTs.