Non-covalent/non-specific functionalization of multi-walled carbon nanotubes with a hyperbranched polyethylene and characterization of their dispersion in a polyolefin matrix

This communication reports the non-covalent, non-specific surface functionalization of multi-walled carbon nanotubes (MWCNTs) with a hyperbranched polyethylene (HBPE). The adsorption characteristics of the HBPE macromolecule on the MWCNTs were studied through an adsorption isotherm. Partial coverage of the nanotubes, estimated to be up to 25%, can be accomplished using this functionalization approach. The treated MWCNTs exhibited significantly improved dispersion within an ethylene–octene copolymer matrix, compared to the untreated fillers.     

Molecular stability of chitosan in acid solutions stored at various conditions

The stability of chitosan with a degree of deacetylation (DD) of 88 and 81% was investigated in solution during storage for 60 days at various temperatures (60, 28, and 5°C) and acid concentrations (0.8M, 0.2M, and 0.1M). The first‐order rate constant of chain hydrolysis of 88%DD chitosan at 60°C was about 1.4 times higher than that of the 81%DD sample. At 28°C, the rates of hydrolysis for both chitosan samples were four to five times lower than those at 60°C and are similar. At 5°C, chain degradation was not significant. Although acetic acid caused significantly higher (P ≤ 0.05) chain scission than formic acid, no significant difference of rate change was observed among three different acid concentrations. Reprecipitation of dissolved chitosan was applied for its purification and to transfer dissolved chitosan to the solvent used to measure its molecular weight. Reprecipitation resulted in slightly lower molecular weight (P ≤ 0.05) for both 88%DD and 81%DD samples. The molecular weight of chitosan before and after reprecipitation had good linear relationship (r² > 0.9). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improving rheological properties of covalently MWCNT/epoxy nanocomposites via surface re-modification

This article describes the application of the chemical surface re-modification of carboxylated multi-walled carbon nanotubes (MWCNTs) through in-situ esterification of oligomeric unsaturated aliphatic hydroxyl terminated polyesters. The Fourier transform infrared spectroscopy and the thermogravimetric analysis proved covalent treatment of MWCNTs. Consequently, the acid–base titration method was employed to determine the population of the re-modified sites within the polyester chains. The dispersion state of the re-modified MWCNTs was investigated by the transmission electron microscopy relevant to the cured nanocomposite sample along with the Ultraviolet–Visible spectroscopy while using various solvents. The degree of dispersion was correlated to the Hansen solubility parameters. In summary, our study shows an appropriate dispersion of the re-modified MWCNTs into the solvents with a high dispersive fashion. In addition, the rheological properties of the re-modified MWCNTs/epoxy resin having various nanoinclusions were considerably studied and discussed. Also, an improved rheological response was observed in the case of the re-modified MWCNT nanocomposite samples.     

Influence of silane concentration on the silanization of multiwall carbon nanotubes

The relationship between the concentration of silane, the degree of surface coverage and the functionalization of multiwall carbon nanotubes (MWCNTs) upon silanization is experimentally investigated. MWCNT silanization is conducted using a γ-methacryloxypropyltrimethoxy silane varying its concentration with respect to the weight of the MWCNTs from 3.5% to 1000% (10×). Physicochemical characterization of the MWCNTs points out that the optimum range of silane concentration required to generate adequate surface coverage on the MWCNTs is between one and two times the weight of the MWCNTs. This optimum range of silane concentration is further confirmed by mechanical testing of silanized MWCNT/vinyl ester polymer composites.     

Surface modification of multiwalled carbon nanotubes via gliding arc plasma for the reinforcement of polypropylene

To increase the applicability of multiwalled carbon nanotubes (MWCNTs), functional groups were generated on the generally inert surface of MWCNTs using gliding arc (GA) plasma. MWCNTs were modified using plasma polymerization with styrene (St) as monomer. The surface compositional and structural changes that occur on MWCNTs were investigated using FT‐IR, Raman spectroscopy, BET surface area, and elemental analysis. Dispersion of the treated MWCNTs in different solvents was evaluated. Transmission electron microscopy images showed that the plasma‐treated MWCNTs had a better dispersion than the untreated ones in nonpolar solvents. Subsequently, MWCNTs‐reinforced polypropylene (PP) composites were prepared by internal batch mixing with the addition of 1.0 wt % MWCNTs. The morphology of MWCNTs/PP nanocomposites was studied through scanning electron microscopy. Observations of SEM images showed that the plasma‐treated MWCNTs had a better dispersion than the untreated MWCNTs either on the composite fracture surfaces or inside the PP matrix. Moreover, the mechanical tests showed that the tensile strength and elongation at break were improved with the addition of polystyrene‐grafted MWCNTs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

改性碳纳米管/壳聚糖复合材料的制备及防污性能

通过控制溶液的pH,在酸性条件下制备了单层多巴胺改性的多壁碳纳米管,然后以戊二醛作为反应中间桥梁,共价接枝制备得到碳纳米管/壳聚糖复合材料。通过透射电子显微镜(TEM)、红外光谱(FTIR)和热重分析法(TGA)对复合材料的结构和性能进行表征,结果表明碳纳米管的管壁外面和管端都被均匀包覆起来,包覆层厚度在6 nm左右;采用多巴胺单层膜包覆碳纳米管,达到了减小对碳纳米管结构造成破坏同时增加表面活性基团数量的目的,使得复合材料中壳聚糖的接枝量增加到71.78%。复合材料兼具了壳聚糖和碳纳米管在抑菌性、缓释、硅藻生长抑制方面优异的性能,在对大肠杆菌、金黄色葡萄球菌、鳗弧菌及小舟形藻、成排舟形藻的防污性能实验中,复合材料在抑菌及抑制硅藻生长方面均表现出广谱、长效的抑制性能。     

High dispersion and electrochemical capacitive performance of NiO on benzenesulfonic functionalized carbon nanotubes

This work describes an effective method to synthesize structurally uniform composite of nickel oxide/benzenesulfonic functionalized multiwalled carbon nanotubes composite (NiO/f-MWCNTs) using benzenesulfonic MWCNTs as the substrate. Benzenesulfonic group here is bifunctional both for solubilizing MWCNTs into aqueous solution and for tethering Ni²⁺ precursor onto MWCNTs surfaces to facilitate the follow-up chemical deposition of NiO by supplying surface binding and anchoring groups. The composite has a uniform surface dispersion and large coverage of NiO onto f-MWCNTs, which is characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscope, cyclic voltammetry and galvanostatic charge/discharge measurements. The NiO/f-MWCNTs composite improved the utilization of electrochemical capacitive materials and delivered capacity of 384 F/g at the constant current of 0.20 A/g due to f-MWCNTs as substrate.     

Effect of processing methods and functional groups on the properties of multi-walled carbon nanotube filled poly(dimethyl siloxane) composites

Pristine and functionalized multi-walled carbon nanotubes (MWCNTs) filled poly(dimethyl siloxane) (PDMS) composites were produced by two different methods, namely the solution mixing method and the mini-extruder method. The composites produced using the mini-extruder exhibit relatively higher tensile strength and higher thermal conductivity due to better nanotubes dispersion. On the other hand, the composites prepared via solution mixing have higher electrical conductivity and better thermal stability due to the high aspect ratio of nanotubes. Scanning electron micrographs of composites fracture surface revealed that composites produced by mini-extruder resulted shorter nanotube length, thus lowering the aspect ratio of MWCNTs. In general, functionalization of nanotubes increases the tensile strength, thermal conductivity, and thermal stability of the PDMS composites due to the improved interfacial adhesion and nanotubes dispersion.     

Synthesis and processing of PMMA carbon nanotube nanocomposite foams

Poly(methyl methacrylate) (PMMA) multi-walled carbon nanotubes (MWCNTs) nanocomposites were synthesized by several methods using both pristine and surface functionalized carbon nanotubes (CNTs). Fourier transform infrared (FTIR) spectroscopy was used to characterize the presence and types of functional groups in functionalized MWCNTs, while the dispersion of MWCNTs in PMMA was characterized using scanning electron microscopy (SEM). The prepared nanocomposites were foamed using carbon dioxide (CO₂) as the foaming agent. The cell morphology was observed by SEM, and the cell size and cell density were calculated via image analysis. It was found that both the synthesis methods and CNTs surface functionalization affect the MWCNTs dispersion in the polymer matrix, which in turn profoundly influences the cell nucleation mechanism and cell morphology. The MWCNTs are efficient heterogeneous nucleation agents leading to increased cell density at low particle concentrations. A mixed mode of nucleation mechanism was observed in nanocomposite foams in which polymer rich and particle rich region co-exist due to insufficient particle dispersion. This leads to a bimodal cell size distribution. Uniform dispersion of MWCNTs can be achieved via synergistic combination of improving synthesis methodology and CNTs surface functionalization. Foams from these nanocomposites exhibit single modal cell size distribution and remarkably increased cell density and reduced cell size. An increase in cell density of ∼70 times and reduction of cell size of ∼80% was observed in nanocomposite foam with 1% MWCNTs.     

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     

壁碳纳米管的表面改性与分散工艺研究

通过浓硝酸对多壁碳纳米管(MWCNTs)进行纯化,以钛酸四丁酯为原料,采用溶胶-凝胶法对纯化后的MWCNTs进行表面改性,采用XRD、TEM分析手段对表面改性的多壁碳纳米管的物相组成和形貌进行表征,并研究了MWCNTs在乙醇中的分散性,结果表明:采用浓硝酸浸泡可以有效地纯化MWCNTs;采用溶胶-凝胶法在MWCNTs表面负载了纳米TiO2;纯化、负载纳米TiO2和超声波震荡提高了MWCNTs在乙醇中的分散性.     

Morphology evolution induced by carbon nanotubes on thermal and mechanical characters of semi-crystalline aromatic polyimide

A series of nanocomposites based on a new semi-crystalline polyimide (PI) and multi-walled carbon nanotubes (MWCNTs) were prepared by in situ polymerization. The TEM measurement reveals the improved dispersion of carboxylic acid-functionalized MWCNTs (COOH-MWCNTs) in semi-crystalline PI compared with pristine MWCNTs. The TGA analysis show that the concentration of carboxylic acid groups on the surface of nanotubes is about 4.34 wt%. The FT-IR spectroscopy analysis indicate that the imide rings of the PI interact non-covalently with nanotubes. The Polarized optical microscopy observation reveals significant morphology evolution in semi-crystalline PI induced by MWCNTs. The SEM micrographs suggest the strong interfacial interaction between COOH-MWCNTs and PI main chains, and significant changes in the fracture surfaces morphology. The WAXRD measurements reveal that COOH-MWCNTs promote the semi-crystalline PI crystallinity and structure change. COOH-MWCNTs can more efficiently improve the mechanical and thermal properties of resulting nanocomposites than pristine MWCNTs. COOH-MWCNT/PI nanocomposites show increases of Young’s modulus and yield strength, as high as 20–30 %, without sacrificing the elongation at break at loadings of 0.5 wt% nanotubes. Furthermore, with increasing the loadings of COOH-MWCNTs to 1.0 wt%, Young’s modulus and yield strength decrease due to nanotube aggregation, but elongation at break increase about 46 %. An abrupt increase of elongation at break in pristine MWCNT/PI nanocomposites was also registered at nanotubes loadings increasing from 0.5 to 1 wt%. These results indicate that the properties of semi-crystalline PI nanocomposites reinforced with carbon nanotubes are not only determined by the dispersion of nanotubes in the PI matrix and their interfacial interactions, but also by the crystalline phase morphology evolution in the PI matrix.     

Morphology of polystyrene/poly(methyl methacrylate) blends: Effects of carbon nanotubes aspect ratio and surface modification

Multiwalled carbon nanotubes (MWCNTs) with aspect ratios (ARs) ranging from 94 to 474 were incorporated into polystyrene (PS)/poly(methyl methacrylate) blends using solution mixing and melt mixing. Also, two functionalized MWCNTs were prepared from the nanotubes having AR 94: one was oxidized by nitric acid while the other was further modified with amine‐terminated PS attached to carboxyl groups to form amides. The two functionalized MWCNTs (1 wt %) were used to show that which phase the carbon nanotubes (CNTs) were located in could be controlled with nanotube surface chemistry. When nanotubes were confined to the minor phase, the size of the minor domain first decreased with adding low AR CNT as expected due to the increased viscosity of the minor phase. However, at higher ARs, the size increased beyond the size for the minor domain with no nanotubes, and at high enough AR, the shape of the minor domain changed from spherical to an elongated irregular shape. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3500–3510, 2015     

Electrochemical investigation of Pd nanoparticles and MWCNTs supported Pd nanoparticles-coated electrodes for alcohols (C1–C3) oxidation in fuel cells

Incorporation of palladium nanoparticles (PdNPs) and multi-walled carbon nanotubes (MWCNTs) into chitosan-coated glassy carbon (GC) electrode for alcohols (methanol, ethanol, and isopropanol) electrooxidation has been studied. PdNPs–chitosan and MWCNTs–PdNPs–chitosan nanocomposites are successfully prepared and characterized by transmission electron microscopy images and UV–Vis spectroscopy. Based on the results, PdNPs–chitosan nanocomposite indicates high electrochemical activity and excellent catalytic characteristic for alcohol (C₁–C₃) electrooxidation on a GC electrode in an alkaline medium. The current density of the alcohols oxidation at GC–PdNPs–chitosan electrode is investigated in optimized conditions and compared with that obtained at the GC-modified electrode by Pd with different polymers. Also, our results show that the dispersion of Pd nanoparticles on the MWCNTs significantly improved the performance of the PdNPs/chitosan composite for electrooxidation of the C₁–C₃ alcohols.     

Evaluation of molar weight and deacetylation degree of chitosan during chitin deacetylation reaction: Used to produce biofilm

Chitosan is a polysaccharide derived from chitin, mainly of crustacean shells and shrimp wastes. The utilization of chitosan is related to the molar weight and deacetylation degree of the biopolymer. The aim of this work is to study the chitin deacetylation reaction, by the viscosity average molar weight and deacetylation degree of chitosan as a function of reaction time. Deacetylation was carried out in concentrated alkaline solution, 421 g L⁻¹, at 130 °C and the reaction occurred during 4 h. Chitosan paste obtained after 20, 90 and 240 min was used to produce biofilms, which were characterized according water vapor permeability and mechanical properties (tensile strength and percentage tensile elongation at break). During the reaction time deacetylation degree reached 93%, and a 50% reduction in the viscosity average molar weight value in relation to the value of the first 20 min of reaction was found Both reactions presented a kinetic behavior of the pseudo-first order. Biofilm produced from the paste of chitosan with high deacetylation degree showed higher water vapor permeability (WVP), tensile strength (TS) and elongation (E) when compared to films with a low deacetylation.     

Functionalization of carbon nanotubes using a silane coupling agent

A new method is developed to chemically functionalize multi-walled carbon nanotubes (MWCNTs) based on silanization reaction for use as the reinforcement for polymer matrix composites. To oxidize and create active moieties on the MWCNTs, the samples were exposed to UV light within the ozone chamber, followed by silanization using 3-glycidoxypropyltrimethoxy silane after the oxidized MWCNTs were reduced by lithium aluminum hydride. FT-IR, TEM and XPS were employed to characterize the changes in carbon nanotubes surface morphology, chemistry and physical conditions at different processing stages. The results indicate improved dispersion and attachment of silane molecules on the surface of the MWCNTs.     

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.     

不脱蛋白质壳聚糖制备工艺

采用D -近似最优设计法系统地研究了NaOH质量分数、碱处理时间及碱处理温度这三个主要因素对制备壳聚糖的影响 :当碱液质量分数增加时 ,壳聚糖的脱乙酰度增加 ,但其速度却在减小 ,当碱液质量分数达到 40 %时 ,脱乙酰度出现峰值 ,约为 90 % ,而后增加碱液质量分数时 ,脱乙酰度反而下降 ;随着反应温度的升高 ,其脱乙酰度几乎线性递增 ,当温度达到 2 0 0℃附近时 ,曲线趋于平直并且脱乙酰度达到最大 ;随着反应时间的增加 ,脱乙酰度开始呈线性增加 ,当反应时间超过 5 0min后 ,脱乙酰度有下降趋势 ;在一定碱液质量分数 (4 0 % )条件下 ,脱乙酰度随着温度的增加而增加 ,因此 ,若需获得较高质量的壳聚糖 ,必须提高反应温度     

Effects of three surfactant types of anionic, cationic and non-ionic on tensile properties and fracture surface morphology of epoxy/MWCNT nanocomposites

Three types of surfactants were used to enhance the dispersion of multi-wall carbon nanotubes (MWCNTs) in the epoxy matrix. MWCNTs were separately treated with non-ionic (polyoxyethylene octyl phenyl ether, Triton X-100), cationic (hexadecyl-trimethyl-ammonium bromide, CTAB) and anionic (sodium dodecyl sulfate, SDS) surfactants and their effects were evaluated on the dispersion state and surface chemistry, as well as on the tensile properties and tensile fracture surface morphology of MWCNTs/epoxy nanocomposites. The active surfaces of the carbon nanotubes were characterized by FTIR. The non-ionic surfactant, Triton X-100, had the best effect on dispersion of the MWCNT in the epoxy matrix, thus, positively affecting the tensile parameters of the corresponding nanocomposites which were attributed to the ??bridging?? effects between the MWCNT and epoxy, introduced by the hydrophobic and hydrophilic heads of the corresponding surfactant. Presence of MWCNTs as reinforcing agent increased the elastic modulus of nanocomposites, indicating the improved interfacial adhesion between CNTs and polymer matrix. The regions of nucleation and propagation of cracks were clearly seen in the SEM micrographs of the tensile fracture surface of the nanocomposites. The cracks deviated on reaching the carbon nanotubes. The dispersing aiding capabilities of the three surfactants used in the present study were as follows: cationic?<?anionic?<?non-ionic.     

Effect of the addition of multi‐walled carbon nanotubes on the thermomechanical properties of epoxy resin

The influence of multi‐walled carbon nanotubes (MWCNTs) on thermosetting epoxy is examined using dynamic mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry (DSC). Specimens are prepared with loadings of 0.1 and 1 wt% MWCNTs which are dispersed in the resin using two different dispersion methods. While the storage modulus of the specimens is improved, both the glass transition temperature and the thermal stability are reduced by the addition of MWCNTs with both effects being greater for the higher MWCNT loading, for both dispersion systems. The DSC results additionally indicate that the level of residual unreacted epoxy increases progressively with the addition of the nanotubes. This finding is considered as confirmation that the MWCNTs obstruct crosslinking of the epoxy resin. POLYM. COMPOS., 38:1873–1880, 2017. © 2015 Society of Plastics Engineers