Functionalizing carbon nanotubes by grafting cyclotriphosphazene derivative to improve both mechanical strength and flame retardancy

An intumescent flame‐retardant, hex(4‐carboxylphenoxy) cyclotriphosphazene (HCPCP) was synthesized and covalently grafted on to the surface of multiwalled carbon nanotubes (MWNTs) to obtain MWNT‐HCPCP. MWNT/epoxy resin (EP) and MWNT‐HCPCP/ EP nanocomposites were prepared via thermal curing. Transmission electron microscopy results showed that a core–shell structure with MWNTs as the hard core and HCPCP as the soft shell were formed after HCPCP (10 wt%) were attached to the MWNTs. The results of flammability tests showed an increased limited oxygen index value for MWNT‐HCPCP/EP nanocomposites. The mechanical properties including tensile strength and elongation were both dramatically improved due to the better dispersion of MWNT‐HCPCP in the EP matrix. The grafting of HCPCP can improve both the dispersion of nanotubes in polymer matrix and flame retardancy of the nanocomposites. POLYM. COMPOS., 35:2187–2193, 2014. © 2014 Society of Plastics Engineers     

Grafting polyamide 6 onto multi‐walled carbon nanotubes using microwave irradiation

Chemical reactions under microwave irradiation can be very efficient, with a significant shortening of reaction time. Few studies have reported the use of microwaves to functionalize carbon nanotubes. In the work reported, a new method of formulating functionalized multi‐walled carbon nanotubes (MWNTs) was developed by covalent grafting of polyamide 6 (PA6) chains onto the carbon nanotubes assisted by microwave irradiation. PA6 chains were grafted onto acidified MWNTs through condensation reaction between the carboxylic groups of the MWNTs and the terminal amine groups of PA6 using microwave radiation heating. The functionalized carbon nanotubes (MWNT‐g‐PA6) were characterized systematically using infrared and Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). TEM showed that the surface of the MWNTs was covered with a layer of PA6. TGA results indicated that the MWNT‐g‐PA6 contained about 47 wt% of polymer. A novel, convenient and efficient functionalization approach is reported, involving covalently grafting PA6 chains onto MWNTs assisted by microwave irradiation. Copyright © 2010 Society of Chemical Industry     

Doped polyaniline/multiwalled carbon nanotube composites: Preparation and characterization

Polyaniline (PANI)/multiwalled carbon nanotube (MWNT) composites with a uniform tubular structure were prepared from in situ polymerization by dissolving amino‐functionalized MWNT (a‐MWNT) in aniline monomer. For this the oxidized multiwalled nanotube was functionalized with ethylenediamine, which provided ethylenediamine functional group on the MWNT surface confirmed by Fourier‐transform infrared spectra (FT‐IR). The a‐MWNT was dissolved in aniline monomer, and the in situ polymerization of aniline in the presence of these well dispersed nanotubes yielded a novel tubular composite of carbon nanotube having an ordered uniform encapsulation of doped polyaniline. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that the nanotubes were coated with a PANI layer. The thermal stability and electrical conductivity of the PANI /MWNTs composites were characterized by thermogravimetric analysis (TGA) and conventional four‐probe method respectively. Compared with pure PANI, the electrical conductivity and the decomposition temperature of the MWNTs/PANI composites increased with the enhancement of MWNT content in PANI matrix. POLYM. COMPOS., 34:1119–1125, 2013. © 2013 Society of Plastics Engineers     

Synthesis and characterization of novel hybrid polyoxazoline‐grafted multiwalled carbon nanotubes

The novel hybrid polyoxazoline‐grafted multiwalled carbon nanotubes (POZO‐grafted MWNTs) were synthesized by the reaction of partially hydrolyzed polyoxazolines (Hydrolyzed‐POZO) and MWNTs having carboxylic acid groups (MWNT‐COOH) in the presence of DCC as a condensing agent. Hydrolyzed‐POZO (degree of hydrolysis, 20.2 mol % by ¹H‐NMR) were produced from the hydrolysis of polyoxazolines in an aqueous NaOH solution at reflux for 72 h. MWNT‐COOH were prepared by acid treatment of pristine MWNTs. The composition, structure, thermal property, and surface morphology of the novel hybrid POZO‐grafted MWNTs were fully characterized by FT‐IR, Raman, ¹H‐NMR, DSC, TGA, SEM, and TEM. The obtained POZO‐grafted MWNTs are well soluble in various organic solvents and water. It was observed that the glass transition temperature (T_g) of POZO‐grafted MWNTs was lower than that of Hydrolyzed‐POZO due to the absence of hydrogen bonding interactions between Hydrolyzed‐POZO itself caused by the incorporation with MWNTs. It was also found that Hydrolyzed‐POZO was homogeneously attached to the surfaces of MWNTs through the “grafting‐to” method. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of poly(butylene terephthalate)/multiwalled carbon nanotube nanocomposites prepared by in situ polymerization and in situ compatibilization

A novel cyclic initiator was synthesized from dibutyl tin(IV) oxide and hydroxyl‐functionalized multiwalled carbon nanotubes (MWNTs) and was used to initiate the ring‐opening polymerization of cyclic butylene terephthalate oligomers to prepare poly(butylene terephthalate) (PBT)/MWNT nanocomposites. The results of Fourier transform infrared and NMR spectroscopy confirmed that a graft structure of PBT on the MWNTs was formed during the in situ polymerization; this structure acted as an in situ compatibilizer in the nanocomposites. The PBT covalently attached to the MWNT surface enhanced the interface adhesion between the MWNTs and PBT matrix and, thus, improved the compatibility. The morphologies of the nanocomposites were observed by field emission scanning electron microscopy and transmission electron microscopy, which showed that the nanotubes were homogeneously dispersed in the PBT matrix when the MWNT content was lower than 0.75 wt %. Differential scanning calorimetry and thermogravimetric analysis were used to investigate the thermal properties of the nanocomposites. The results indicate that the MWNTs acted as nucleation sites in the matrix, and the efficiency of nucleation was closely related to the dispersion of the MWNTs in the matrix. Additionally, the thermal stability of PBT was improved by the addition of the MWNTs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High electrical conductivity of nylon 6 composites obtained with hybrid multiwalled carbon nanotube/carbon fiber fillers

The synergetic effect of multiwalled carbon nanotubes (MWNTs) and carbon fibers (CFs) in enhancing the electrical conductivity of nylon 6 (PA6) composites was investigated. To improve the compatibility between the fillers and the PA6 resin, we grafted γ‐aminopropyltriethoxy silane (KH‐550) onto the MWNTs and CFs after carboxyl groups were generated on their surface by chemical oxidation with nitric acid. Fourier transform infrared spectroscopy and thermogravimetric analysis proved that the KH‐550 molecules were successfully grafted onto the surface of the MWNTs and CFs. Scanning electron microscopy and optical microscopy showed that the obtained modified fillers reduced the aggregation of fillers and resulted in better dispersion and interfacial compatibility. We found that the electrical percolation threshold of the MWNT/PA6 and CF/PA6 composites occurred when the volume fraction of the fillers were 4 and 5%, respectively. The MWNT/CF hybrid‐filler system exhibited a remarkable synergetic effect on the electrically conductive networks. The MWNT/7% CF hybrid‐filler system appeared to show a second percolation when the MWNT volume fraction was above 4% and a volume resistivity reduction of two orders of magnitude compared with the MWNT/PA6 system. The mechanical properties of different types of PA6 composites with variation in the filler volume content were also studied. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40923.     

Effects of surface modification with 3‐aminopropyltriethoxysilane on structure and mechanical property of multiwalled carbon nanotube/polycarbonate composites

Hydroxyl functionalized multiwalled carbon nanotubes (H‐MWNTs) were silanized using 3‐aminopropyltriethoxysilane (APTES) in order to improve the dispersion and interfacial interaction in composites. MWNT/polycarbonate (PC) composites filled with H‐MWNTs and silanized MWNTs (S‐MWNTs) were fabricated by melt mixing and injection molding. Fourier transform infrared spectrometry (FTIR) and energy dispersion X‐ray spectroscopy (EDS) were employed to prove the presence of APTES on the surface of S‐MWNTs. In addition, thermogravimetric analysis (TGA) was used to evaluate the relative amount of introduced APTES. The microstructure and mechanical property of both composites were investigated by scanning electron microscopy (SEM), transmission electron microscope (TEM), tensile test and dynamic mechanical analysis (DMA). The SEM and TEM images showed that S‐MWNT/PC composites had better dispersion and interfacial adhesion than H‐MWNT/PC composites. A reinforcing and toughening effect on tensile behavior of composites was obtained after silane functionalization. The storage modulus of composites increased markedly as a function of MWNTs content, especially for the composites with S‐MWNTs. In summary, the silanization can improve the dispersion of MWNTs and the interfacial adhesion between MWNTs and PC so as to enhance the mechanical properties of composites. POLYM. COMPOS., 37:1914–1923, 2016. © 2015 Society of Plastics Engineers     

Characterizing composite of multiwalled carbon nanotubes and POE‐g‐AA prepared via melting method

Multiwalled carbon nanotubes (MWNTs) with acyl chloride functional groups and a metallocene polyethylene–octene elastomer (POE) or an acrylic acid‐grafted metallocene polyethylene–octene elastomer (POE‐g‐AA) were used to prepare hybrids (POE/MWNTs or POE‐g‐AA/MWNTs) using a melting method, with a view to identify a hybrid with improved thermal properties. Hybrids were characterized using Fourier transform infrared spectroscopy, ¹³C solid‐state nuclear magnetic resonance, X‐ray diffraction, thermogravimetry analysis, and scanning electron microscopy. MWNTs were purified using acid treatment, and results showed that ? COOH of MWNTs increased with acid treatment time and leveled off after 24‐h treatment. Much better dispersion and homogeneity of MWNTs was obtained with POE‐g‐AA in place of POE as the matrix. As a result, tensile strength at break of POE‐g‐AA/MWNTs was significantly improved even at 5 wt % MWNT content. Moreover, temperature of thermal decomposition for POE‐g‐AA/MWNTs was about 40–50°C higher than that for POE‐g‐AA, indicating higher thermal stability. This was because the carboxylic acid groups in POE‐g‐AA and the acyl chloride functional sites in MWNTs allow the formation of stronger chemical bonds. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1328–1337, 2007     

Styrene‐butadiene‐styrene copolymer compatibilized interfacial modified multiwalled carbon nanotubes with mechanical and piezoresistive properties

In this study, styrene‐butadiene‐styrene tri‐block copolymer/multiwalled carbon nanotubes (SBS/MWNTs) were prepared by means of a solution blending method. To enhance the compatibility between SBS and MWNTs, the SBS grafted MWNTs (SBS‐g‐MWNTs) were used to replace MWNTs. The MWNTs were chemically hydroxylated by the dissolved KOH solution with ethanol as solvent and then reacted with 3‐Aminopropyltriethoxysilane (APTES) to functionalize them with amino groups (MWNT‐NH₂). The SBS‐g‐MWNTs were finally obtained by the reaction of MWNT‐NH₂ and maleic anhydride grafted SBS (MAH‐g‐SBS). The SBS‐g‐MWNTs were characterized by X‐ray photoelectron spectroscopy (XPS), Fourier transform‐infrared spectroscopy (FT‐IR), transmission electron microscopy (TEM), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). The results showed that the SBS molecules were homogeneously bonded onto the surface of the MWNTs, leading to an improvement of the mechanical and electrical properties of SBS/SBS‐g‐MWNTs composites due to the excellent interfacial adhesion and dispersion of SBS‐g‐MWNTs in SBS. A series of continuous tests were carried out to explore the electrical‐mechanical properties of the SBS/SBS‐g‐MWNTs composites. We found out that, near the percolation threshold, the well‐dispersed SBS/SBS‐g‐MWNTs composites showed good piezoresistive characteristics and small mechanical destructions for the development of little deformation under vertical pressure. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42945.     

Fabrication of conducting polyaniline–multiwalled carbon nanotube nanocomposites and their use as templates for loading gold nanoparticles

A new and effective route to synthesize conducting polyaniline‐multiwalled carbon nanotube (PANI ‐f‐MWNT) nanocomposites (where ‘f’ denotes that the MWNTs have been functionalized) starting with amine‐protected 4‐aminophenol is reported. Aminophenol‐functionalized MWNTs were initially synthesized by functionalizing acyl chloride‐terminated nanotubes with N‐(tert‐butoxycarbonyl)‐4‐aminophenol followed by the in situ chemical oxidative grafting of aniline in the presence of ammonium persulfate as an oxidizing agent. Control of the morphology and thickness of the polymer–MWNT nanocomposites was achieved by varying the weight ratios of aniline monomers and MWNTs in the polymerization process. Fourier transform infrared spectroscopy was employed to characterize the initial changes in surface functionalities which also confirmed that PANI was covalently grafted to the MWNTs. Electron microscopy and UV‐visible absorption spectroscopy were employed to characterize the morphology and chemical structure of the resulting hybrids. The results obtained indicate that the structure of the MWNTs was not perturbed by the incorporation of PANI. The content of the polymer in the nanocomposites was determined thermogravimetrically, while the electrical conductivity was obtained using four‐probe measurements. The PANI ‐f‐MWNT nanocomposites were adopted as templates for further decoration with gold nanoparticles in solution, thus opening new possibilities for their prospective technological applications. Copyright © 2010 Society of Chemical Industry     

A comparative study on dispersion of carbon nanotubes in (styrene‐butadiene rubber)‐based nanocomposites

The efficient dispersion of carbon nanotubes (CNTs) is a challenging task in reaching the usable nanocomposites. In this study, a comparative analysis on dispersion of multiwalled CNTs multiwalled carbon nanotubes (MWNTs) in styrene‐butadiene rubber (SBR) latex was carried out by using two anionic surfactants, sodium dodecyl benzene sulfonate and sodium lauryl sulfate. The MWNTs were first predispersed in distilled water using two surfactants individually followed by gentle mixing the MWNT predispersion into SBR latex. By using the technique of ultraviolet‐visible spectroscopy, the study on MWNT dispersion in aqueous media was focused on surfactant concentration, MWNT functionality, and ultrasonication time. The ultraviolet‐visible absorptions showed the positive effect of MWNT functionality in addition to surfactant concentration with no great effect of ultrasonication time over 15 min. In comparison with sodium lauryl sulfate, the existing benzene ring in the sodium dodecyl benzene sulfonate structure seems to result in higher adsorption of surfactant onto the MWNTs surface and, hence, better MWNT dispersion. The MWNT dispersion was further improved by using hydroxyl functionalized MWNTs mainly because of the formation of hydrogen bonding between the hydrophilic head of surfactant and the existing hydroxyl group of the functionalized MWNTs. After mixing the MWNT predispersion into SBR latex, the dispersion of MWNTs was further characterized by using electrical volume conductivity, microscopy technique, and rheological measurements. In rheometry tests of the lattices, the storage modulus at terminal zone was utilized for tracking the degree of MWNT dispersion in the nanocomposite. The pictures of scanning electron microscopy showed the efficiency of MWNT functionality in enhancing the degree of dispersion. In conductivity tests, the percolation threshold was obtained at about 1 part by weight per hundred parts of resin of the functionalized MWNT in dried film. J. VINYL ADDIT. TECHNOL., 23:28–34, 2017. © 2015 Society of Plastics Engineers     

Mechanical reinforcement of poly(1‐butene) using polypropylene‐grafted multiwalled carbon nanotubes

The mechanical properties of poly(1‐butene) reinforced by pristine multiwalled carbon nanotubes (MWNTs) and polypropylene‐grafted MWNTs (PP‐g‐MWNTs) were evaluated. The incorporation of pristine MWNTs to PB led to an improvement in stiffness, but not in strength, ductility, and toughness. In comparison, PP‐g‐MWNTs were able to improve the stiffness, strength, and toughness of PB significantly, without compromising the ductility. The mechanical properties of PB improved with increasing amount of PP‐g‐MWNTs up to an effective MWNT content of 1.5 wt%. Further increase in the effective MWNT content led to a downturn in mechanical properties due to the existence of MWNTs bundles as observed by microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on the photoinduced electron‐transfer activity of poly(p‐phenylene benzobisoxazole)/carboxylic multiwalled carbon nanotubes composites prepared by in situ polymerization

This article focused on the synthesis of poly(p‐phenylene benzobisoxazole)/carboxylic multiwalled carbon nanotubes (PBO/MWNT‐COOH) composites through in situ polymerization. The effect of MWNT‐COOH on thermal stability and photophysical properties was investigated thoroughly. Especially an in‐depth study was carried out on the detailed process of energy transfer. Ultraviolet‐visible‐near infrared and fluorescence spectroscopy of composites revealed that MWNT interacted with PBO through strong covalent bonds, which was a significant photoinduced charge‐transfer interaction between the two components. Therefore, compared with PBO, both the thermal stability and PL quantum efficiency of PBO/MWNT‐COOH composites were improved. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Synthesis of hyperbranched aromatic polyamide–imide and its grafting onto multiwalled carbon nanotubes

A flexible hyperbranched aromatic polyamide–imide (PAI) having an amine group in the center and carboxyl groups in the ends was synthesized from a AB₂ type of monomer of 2‐(6‐aminohexylcarbomoyl) terephthalic acid that was prepared from trimellitic anhydride and 1,6‐diaminohexane. Fourier transformed infrared spectra (FTIR), NMR, and ES‐MS were used to characterize the structure of the monomer and the synthesized hyperbranched polymer. Then the hyperbranched PAI was grafted onto the multiwalled carbon nanotubes (MWNTs) that was first treated by acid and changed into MWNT‐COCl by SOCl₂ in a tetrahydrofuran solution. By observation with transmission electron microscopy and characterization with FTIR and thermal gravity of analysis, the functionalized MWNTs were terminally enclosed with polymer; it was believed that the MWNTs were linked with a big carboxylic claw at the end and the adsorption ability of the MWNTs to NH₂‐substrate was enhanced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of antibacterial PDMAEMA‐functionalized multiwalled carbon nanotube via atom transfer radical polymerization

Poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) was grafted onto the bromine‐functionalized multiwalled carbon nanotubes (MWNTs) by applying an atom transfer radical polymerization (ATRP). The PDMAEMA‐functionalized MWNT was characterized by Fourier transform infrared, transmission electron microscopy, Raman spectroscopy, thermal gravimetric analysis, and four‐probe resistivity meter. The wt % of PDMAEMA present in the PDMAEMA‐functionalized MWNT was estimated by applying the thermogram results for thermal gravimetric analysis. Variations of PDMAEMA content in the PDMAEMA‐functionalized MWNT were tried by changing the ATRP process conditions such as the type of ligand and copper complex, the amount of DMAEMA based on the weight of bromine‐functionalized MWNT, and the polymerization temperature. The phase behavior of PDMAEMA‐functionalized MWNT in water depending on temperature and pH value was analyzed, and the PDMAEMA‐functionalized MWNT showed the amphipathic nature. The PDMAEMA‐functionalized MWNT clearly showed an antibacterial effect against E. coli as well as S. aureus. The highest viability loss of E. coli achieved in this study was ～ 42% with the PDMAEMA‐functionalized MWNT containing 53.9 wt % of PDMAEMA. The PDMAEMA‐functionalized MWNT showed sheet resistance less than ～ 9.68 × 10³ Ω/sq. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci., 2013     

Poly(2‐(methacryloyloxy) ethyl phosphorylcholine)‐functionalized multi‐walled carbon nanotubes: Preparation,characterization, solubility,and effects on blood coagulation

Water‐soluble multi‐walled carbon nanotubes (MWNTs) were prepared via surface‐initiated atom transfer radical polymerization (ATRP) of 2‐(methacryloyloxy) ethyl phosphorylcholine (MPC) from carbon nanotubes (CNTs). The success of the surface functionalization of MWNTs with poly(2‐(methacryloyloxy) ethyl phosphorylcholine) (pMPC) was ascertained using fourier transform infrared spectrophotometry (FTIR), thermogravimetric analysis (TGA), hydrogen nuclear magnetic resonance (¹H‐NMR), and transmission electron microscopy (TEM). Different from the results of the previous work, in our work, we demonstrate that the amount of pMPC on CNTs can be easily regulated by ATRP approach. In addition, from TGA results, a linear relationship between the weight loss fraction of MWNT‐pMPC and the weight of MPC fed and as high as 48.1% weight loss of MWNT‐pMPC (MWNTs grafted by pMPC) are observed. Through TEM, the core‐shell structure of MWNT‐pMPC is clearly observed, which is also different from the previous report. The pMPC‐modified MWNTs are highly soluble, which can also resist pH and saline concentration changes and remain stable in physiological environment. PMPC‐modified MWNT does not significantly affect the blood coagulation as demonstrated in plasma recalcification time (PRT) test. These highly soluble MWNTs are expected to enable their wide use in biomedical areas. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of crosslink density on thermal conductivity of epoxy/carbon nanotube nanocomposites

The effect of the polymeric crosslink density on the thermal conductivity of an epoxy nanocomposite was investigated by adding two different diamine‐functionalized multiwalled carbon nanotubes (diamine‐MWNTs) to the epoxy resin as co‐curing agents and conducting fillers. Tetramethylenediamine (TMDA)‐MWNTs resulted in an epoxy nanocomposite with a higher crosslink density than octamethylenediamine (OMDA)‐MWNTs. Interestingly, epoxy/TMDA‐MWNT nanocomposites under 1.5 wt % nanotube concentration, showed a higher thermal conductivity than an epoxy/OMDA‐MWNT nanocomposite with the same concentration of nanotubes. In contrast, for higher diamine‐MWNT concentrations (over 2.0 wt %), the thermal conductivity of the epoxy/OMDA‐MWNT nanocomposite was higher than that with TMDA‐MWNTs. We observed that for low MWNT concentrations, where a percolating network was not formed, a high crosslink density enhanced the thermal conductivity via phonon transport. However, for high MWNT concentrations, a high crosslink density hinders the formation of a percolating network and lowers the thermal conductivity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44253.     

Poly (N‐methylaniline)/multi‐walled carbon nanotube composites—Synthesis,characterization, and electrical properties

This study described the synthesis of hydrochloric acid (HCl)‐doped poly (N‐methylaniline) (PNMA) with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) via in situ polymerization. Based on the π–π electron interaction between c‐MWNTs and the N‐methylaniline monomer and the hydrogen bond interaction between the carboxyl groups of c‐MWNTs and imine groups of N‐methylaniline monomers, N‐methylaniline molecules were adsorbed on the surface of c‐MWNTs and polymerized to form PNMA/c‐MWNT composites. Scanning electron microscopy images showed that both the thinner fibrous phase and the larger block phase could be observed. The individual fibrous phases had diameters from several tens to hundreds of nanometers, depending on the PNMA content. Transmission electron microscopy proved that PNMA/c‐MWNTs composite fibrous phases were core (c‐MWNT)‐shell (PNMA) tubular structures. The structure of PNMA/c‐MWNT composites was characterized by FTIR, UV–vis spectra, and X‐ray diffraction patterns. The electrical conductivities of PNMA/c‐MWNT composites were much higher than that of PNMA without c‐MWNTs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2356–2361, 2006     

Functionalization of multiwalled carbon nanotubes by reversible addition fragmentation chain-transfer polymerization

In this study, a new way was used to chemically synthesize polymer-connected MWNT nanocomposites. Reversible addition fragmentation chain-transfer (RAFT) agent was successfully grafted onto the surface of multiwalled carbon nanotubes (MWNTs). Polystyrene (PS) chains were successfully grafted from the surface of MWNTs via RAFT process by using RAFT agent immobilized on MWNTs. FTIR, XPS and TGA were used to determine chemical structure and the grafted PS quantities of the resulting products. TEM images of the samples provide direct evidence for the formation of a core-shell nanostructure, i.e. the MWNT coated with polymer layer and the solubility be improved.     

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