Influence of initial mixing methods on melt‐extruded single‐walled carbon nanotube–polypropylene nanocomposites

We report the first direct comparison of melt‐extruded polypropylene–single‐walled carbon nanotube (PP/SWNT) nanocomposites prepared by three different initial mixing methods. The standard deviation of the G‐band intensity obtained using Raman mapping was found to be the best measure of dispersion uniformity in the extruded composites, and dispersion uniformity was found to generally correlate with rheological and thermal properties. For all three initial mixing methods, both unmodified and sidewall‐functionalized purified SWNTs were evaluated. Surprisingly, in all cases, dodecylated SWNTs prepared using the reductive alkylation method were less uniformly dispersed in the final composite than the unmodified SWNTs. The simplest process, dry blending, resulted in poor nanotube dispersion and only polymer crystallization was significantly affected by the presence of the nanotubes. A slightly more complex rotary evaporation process resulted in significantly more uniform dispersion and significant changes in rheological properties, polymer crystallization, and thermal stability. The most elaborate process tested, hot coagulation, enabled the most uniform dispersion and the greatest change in properties but also resulted in some polymer degradation. POLYM. ENG. SCI., 50:1831–1842, 2010. © 2010 Society of Plastics Engineers     

Fabrication of pH‐ or temperature‐responsive single wall carbon nanotubes via a graft from photopolymerization

An ultraviolet light initiated “graft from” polymerization method to fabricate polymer‐functionalized single wall carbon nanotubes (SWNTs) with pendant pH‐ and temperature‐responsive polymer chains is utilized. The attached polymer chains, formed from methacrylic acid and poly(ethylene glycol) methyl ether methacrylate monomers, are well established for its pH‐responsive swelling/deswelling behavior. This special property was utilized here to control the aqueous dispersibility of the carbon nanotubes. Furthermore, poly(N‐isopropylacrylamide), a temperature‐responsive polymer, was utilized in the fabrication of SWNTs whose dispersibility was dependent on solution temperature. The morphology of the polymer‐functionalized carbon nanotubes was characterized by scanning electron microscopy (SEM) before and after functionalization. Environmental SEM was used to further characterize the morphology of the functionalized SWNTs. In addition, covalent bonding of the polymer to the carbon nanotube surface was established using Raman and Fourier transform infrared spectroscopic techniques. The physical and chemical properties of the functionalized nanotubes were further characterized by energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2980–2986, 2012     

Rapid, low temperature microwave synthesis of novel carbon nanotube-silicon carbide composite

Single wall carbon nanotubes (SWNTs) incorporated into ceramic matrices are known to impart enhanced mechanical, thermal and electrical properties to the composites formed. Current procedures for their synthesis face challenges, such as, the non-uniform dispersion of the SWNTs and their damage during high temperature processing in a reactive environment. These have led to poor interfacial matrix to SWNT adhesion and the ineffective utilization of the unique properties of the nanotubes. Here we report a rapid, low temperature microwave-induced reaction to create a novel nanoscale silicon carbide (SiC)-SWNT composite. The reaction, which was completed in 10 min, involves the decomposition of chloro-trimethylsilane and the simultaneous nucleation of nanoscale SiC spheres on the SWNT bundles. The bulk composite is a branched tree-like structure comprised of three-dimensionally arrayed SiC-SWNTs. The uniqueness of this approach lies in the formation of a ceramic directly on the SWNTs, rather than physical mixing, or the growth of nanotubes in a ceramic matrix.     

Synthesis and properties of poly(methyl methacrylate)/carbon nanotube composites covalently integrated through in situ radical polymerization

Poly(methyl methacrylate) (PMMA)/single‐walled carbon nanotube (SWNT) composites were synthesized by the grafting of PMMA onto the sidewalls of SWNTs via in situ radical polymerization. The free‐radical initiators were covalently attached to the SWNTs by a well‐known esterification method and confirmed by means of thermogravimetric analysis and Fourier transform infrared spectroscopy. Scanning electron microscopy and transmission electron microscopy were used to image the PMMA–SWNT composites; these images showed the presence of polymer layers on the surfaces of debundled, individual nanotubes. The PMMA–SWNT composites exhibited better solubility in chloroform than the solution‐blended composite materials. On the other hand, compared to the neat PMMA, the PMMA–SWNT nanocomposites displayed a glass‐transition temperature up to 6.0°C higher and a maximum thermal decomposition temperature up to 56.6°C higher. The unique properties of the nanocomposites resulted from the strong interactions between the SWNTs and the PMMA chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of temperature on the selection of semiconducting single walled carbon nanotubes using Poly(3-dodecylthiophene-2,5-diyl)

We report on the investigation of the temperature effect on the selective dispersion of single-walled carbon nanotubes (SWNTs) by Poly(3-dodecylthiophene-2,5-diyl) wrapping. The interaction mechanism between polymer chains and SWNTs is studied by controlling the polymer aggregation via variation of the processing temperature. Optical absorption and photoluminescence measurements including time resolved photoluminescence spectroscopy are employed to study the degree of interaction between the polymer in different aggregation states and the carbon nanotubes. At low processing temperatures, results are consistent with the planarization of the polymer chains and with SWNTs working as seeds for polymer aggregation. The formation of small clusters due to the inter-digitation of alkyl tails between neighboring polymer-wrapped SWNTs allows the formation of the SWNT bundles, as experimentally evidenced and investigated by molecular dynamics simulations. The interaction between the tubes within the bundles, which is reflected in the variation of the photoluminescence dynamics of the polymer, can be suppressed by warming up the sample.     

New hybrid system: Poly(ethylene glycol) hydrogel with covalently bonded pegylated nanotubes

Hydrogels containing carbon nanotubes (CNTs) are expected to be promising conjugates because they might show a synergic combination of properties from both materials. Most of the hybrid materials containing CNTs only entrap them physically, and the covalent attachment has not been properly addressed yet. In this study, single‐walled carbon nanotubes (SWNTs) were successfully incorporated into a poly(ethylene glycol) (PEG) hydrogel by covalent bonds to form a hybrid material. For this purpose, SWNTs were functionalized with poly(ethylene glycol) methacrylate (PEGMA) to obtain water‐soluble pegylated SWNTs (SWNT–PEGMA). These functionalized SWNTs were covalently bonded through their PEG moieties to a PEG hydrogel. The hybrid network was obtained from the crosslinking reaction of poly(ethylene glycol) diacrylate prepolymer and the SWNT–PEGMA by dual photo‐UV and thermal initiations. The mechanical and swelling properties of the new hybrid material were studied. In addition, the material and lixiviates were analyzed to elucidate any kind of SWNT release and to evaluate a possible in vitro cytotoxic effect. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization of processing effects in HIPS‐CNF composites using thermogravimetric analysis

To completely establish the processing–structure–property relationships of polymer composites such as Carbon Nanofibers (CNFs) in high‐impact polystyrene, it is necessary to understand the effects of different processes and processing conditions on the properties of the composites. In this work, using thermogravimetric analysis, the effects of solvent processing and twin‐screw extrusion on the weight loss rates and the corresponding temperatures were studied. While there were only marginal effects of the CNF concentration, the type of processing significantly affected the thermo‐oxidative behavior. Extrusion resulted in composites that had better thermal stability compared to the solvent processed ones. Furthermore, higher shear rates in extrusion also led to composites with higher thermal stability. This has important implications in choosing the appropriate process and processing conditions for producing polymer‐CNF composites. It was also demonstrated that thermogravimetric analysis can provide a means of characterizing the degree of dispersion resulting from the processing of the composites that complements conventional microscopy techniques. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Polypropylene fibers reinforced with carbon nanotubes

The strength properties of polypropylene fibers were enhanced with single‐wall carbon nanotubes (SWNTs). Solvent processing was used to disperse SWNTs in a commodity polypropylene. After the solvent was removed, the solid polymer was melt‐spun and postdrawn into fibers of unusual strength. For a 1‐wt % loading of nanotubes, the fiber tensile strength increased 40% (from 9.0 to 13.1 g/denier). At the same time, the modulus increased 55% (from 60 to 93 g/denier). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2079–2084, 2002     

Nanofiber‐reinforced thermoplastic composites. I. Thermoanalytical and mechanical analyses

This article is a portion of a comprehensive study on carbon nanofiber–reinforced thermoplastic composites. The thermal behavior and dynamic and tensile mechanical properties of polypropylene–carbon nanofibers composites are discussed. Carbon nanofibers are those produced by the vapor‐grown carbon method and have an average diameter of 100 nm. These hollow‐core nanofibers are an ideal precursor system to working with multiwall and single‐wall nanotubes for composite development. Composites were prepared by conventional Banbury‐type plastic‐processing methods ideal for low‐cost composite development. Nanofiber agglomerates were eliminated because of shear working conditions, resulting in isotropic compression‐molded composites. Incorporation of carbon nanofibers raised the working temperature range of the thermoplastic by 100°C. The nanofiber additions led to an increase in the rate of polymer crystallization with no change in the nucleation mechanism, as analyzed by the Avrami method. Although the tensile strength of the composite was unaltered with increasing nanofiber composition, the dynamic modulus increased by 350%. The thermal behavior of the composites was not significantly altered by the functionalization of the nanofibers since chemical alteration is associated with the defect structure of the chemical vapor deposition (CVD) layer on the nanofibers. Composite strength was limited by the enhanced crystallization of the polymer brought on by nanofiber interaction as additional nucleation sites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 125–133, 2001     

Investigation of molecular interaction between single‐walled carbon nanotubes and conjugated polymers

Single‐walled carbon nanotubes (SWNTs) have unique properties such as high electrical conductivity and high tensile strength. Their composites with polymers have a great role in new sciences such as organic solar cells and ultrastrong lightweight materials. In this article, molecular dynamic simulations with polymer consistent force field are performed to study the interaction between SWNTs and conjugated polymers including poly(2‐methoxy‐5‐(3‐7‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (MDMO‐PPV), poly(3‐hexythiophene) (P3HT), and poly[(9,9′‐dioctylfluorenyl‐2,7‐diyl)‐co‐bis(N,N′‐(4,butylphenyl))bis(N,N′‐phenyl‐1,4‐phenylene)diamine] (PFB). We computed the interaction energy and morphology of polymers adsorbed to the surface of SWNTs was studied by the radius of gyration (Rg). The influence of important factors such as SWNT radius, chirality, and the temperature on the interfacial adhesion of SWNT–polymer and Rg of polymers were studied. We found that the strongest interaction between the SWNTs and these polymers was, first observed for P3HT, then MDMO‐PPV, and finally PFB. Our results showed that the interaction energy is influenced by SWNT radius and the specific monomer structure of the polymers, but the effects of chirality and temperature are very weak. In addition, we found that the temperature, chirality, and radius have not any important effect on the radius of gyration. POLYM. COMPOS.,, 2012. © 2012 Society of Plastics Engineers     

Synthesis of novel single-walled carbon nanotubes/poly (<Emphasis Type="Italic">p</Emphasis>-phenylene benzobisoxazole) nanocomposite

Poly (p-phenylene benzobisoxazole) (PBO) fibers are some of the strongest organic polymer fibers. However, the introduction of single-walled carbon nanotubes (SWNT) into the PBO backbone might lead to improvements in their alignment and physical properties. Therefore, SWNT was cut and functionalized by three oxidative cutting methods. After cutting, three different types of SWNT were obtained. Furthermore, copolymerization of SWNTs with PBO polymer was successfully carried out in a mixed solvent of polyphosphoric acid and methanesulfonic acid. The SWNTs were homogeneously distributed throughout the films of copolymerized products, as determined by Raman spectroscopy. The benzoxazole moieties could be formed between the carboxyl of SWNTs and o-aminophenol derivatives of PBO polymer. The length of SWNTs affected the dispersion and reaction activity. Short SWNTs could react with the PBO polymer more easily and form more covalent bonds.     

Processing and properties of carbon nanotube/poly(methyl methacrylate) composite films

A systematic study of the reinforcement of single‐walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes, and vapor‐grown carbon nanofibers (VGCNFs) in poly(methyl methacrylate) (PMMA) is reported. SWNT/PMMA composite films with various SWNT concentrations (from 0.5 to 50 wt % with respect to the weight of PMMA) were processed from nitromethane. Two types of SWNTs were used: SWNT‐A, which contained 35 wt % metal catalyst, and SWNT‐B, which contained about 2.4 wt % metal catalyst. Properties of different nanotubes containing composites were compared with 15 wt % carbon nanotubes (CNTs). Property enhancement included electrical conductivity, mechanical properties, and solvent resistance. The thermal degradation of PMMA in the presence of CNTs in air and nitrogen environments was studied. No variation in the thermal degradation behavior of PMMA/CNT was observed in nitrogen. The peak degradation temperature increased for the composites in air at low CNT loadings. Dynamic and thermomechanical properties were also studied. At a 35 wt % SWNT loading, a composite film exhibited good mechanical and electrical properties, good chemical resistance, and a very low coefficient of thermal expansion. Property improvements were rationalized in terms of the nanotube surface area. Composite films were also characterized with Raman spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reactive extrusion of recycled bottle waste material

The objective of this study is to investigate the effect of reactive processing of commingled bottle waste polymer in an extruder. A variety of peroxides and monomers were tested to assess their influence on the final mechanical properties of the product. The reactive extruded polymer blends were prepared in two types of extruders: a co‐rotating twin‐screw extruder and a Buss co‐Kneader single‐screw extruder. Blends were analyzed for mechanical and thermal properties. The effectiveness of the different monomers and peroxides was evaluated in terms of improvement in impact properties. It has been found that the toughness of the polymer blend is improved by reactive processing. Depending on the amount and type of reactants, the impact strength can be improved by 220%, with a slight reduction in the modulus compared to an unmodified physical blend. The most suitable monomers were n‐butylmethacrylate (BMA), t‐butylamino ethylmethacrylate (TBAEMA) and a combination of styrene/maleic anhydride (ST/MAH). The peroxide should have a short half‐lifetime compared to the average residence time in the extruder. The most effective monomers have a high initial reactivity and low rate of evaporation at the processing conditions used. Changes in processing conditions in the extruder influence the reaction conditions and therefore the final properties of the blend. Results were interpreted in terms of residence time, melting profile and peroxide concentration.     

Preparation and properties of the single‐walled carbon nanotube/cellulose nanocomposites using N‐methylmorpholine‐N‐oxide monohydrate

Single‐walled carbon nanotube (SWNT)/cellulose nanocomposite films were prepared using N‐methylmorpholine‐N‐oxide (NMMO) monohydrate as a dispersing agent for the acid‐treated SWNTs (A‐SWNTs) as well as a cellulose solvent. The A‐SWNTs were dispersed in both NMMO monohydrate and the nanocomposite film (as confirmed by scanning electron microscopy) because of the strong hydrogen bonds of the A‐SWNTs with NMMO and cellulose. The mechanical properties, thermal properties, and electric conductivity of the nanocomposite films were improved by adding a small amount of the A‐SWNTs to the cellulose. For example, by adding 1 wt % of the A‐SWNTs to the cellulose, tensile strain at break point, Young's modulus, and toughness increased ～ 5.4, ～ 2.2, and ～ 6 times, respectively, the degradation temperature increased to 9°C as compared with those of the pure cellulose film, and the electric conductivities at ? (the wt % of A‐SWNTs in the composite) = 1 and 9 were 4.97 × 10^?4 and 3.74 × 10^?2 S/cm, respectively. Thus, the A‐SWNT/cellulose nanocomposites are a promising material and can be used for many applications, such as toughened Lyocell fibers, transparent electrodes, and soforth. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Surface grafting of carbon fibers with artificial silver‐nanoparticle‐decorated graphene oxide for high‐speed electrical actuation of shape‐memory polymers

Poor heat conduction in the interface between the carbon fiber and polymer matrix is a problem in the actuation of shape‐memory polymer (SMP) composites by Joule heating. In this study, we investigated the effectiveness of grafting silver‐nanoparticle‐decorated graphene oxide (GO) onto carbon fibers to improve the electrothermal properties and Joule‐heating‐activated shape recovery of SMP composites. Self‐assembled GO was grafted onto carbon fibers to enhance the bonding of the carbon fibers with the polymeric matrix via van der Waal's forces and covalent crosslinking, respectively. Silver nanoparticles were further self‐assembled and deposited to decorate the GO assembly, which was used to decrease the thermal dissimilarity and facilitate heat transfer from the carbon fiber to the polymer matrix. The carbon fiber was incorporated with SMP to achieve the shape recovery induced by Joule heating. We found that the silver‐nanoparticle‐decorated GO helped us achieve a more uniform temperature distribution in the SMP composites compared to those without decoration. Furthermore, the shape‐recovery behavior and temperature profile during the Joule heating of the SMP composites were characterized and compared. A unique synergistic effect of the carbon fibers and silver‐nanoparticle‐decorated GO was achieved to enhance the heat transfer and a higher speed of actuation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41673.     

PEDOT‐PSS/singlewall carbon nanotubes composites

Poly(3,4‐ethylenedioxythiophene)‐single wall carbon nanotube (SWNT) composites were prepared via coating methods for improving electrical conductivity and flexibility, minimizing loss of transparency. Three types of surface modified SWNTs were prepared through different modification methods: carboxylated SWNT treated with nitric acid to form carboxylic acid group on their surfaces, 1‐pyrenebutyric acid wrapped SWNT, and 1‐pyrenebutyric acid, lithium salt wrapped SWNT. The surface modifiers had influence on the dispersion states of the SWNTs in 2‐propanol. The dispersion states had influence of aggregate concentrations of surface modified SWNTs in polymer matrix, showing lower aggregate concentration for the carboxylated SWNT than those of the other surface modified SWNTs. The dispersion behaviors of SWNTs were also related with transparency and electrical resistance, and flexibility of composite films. Based on the layer‐by‐layer coating method, SWNT composite film properties such as thickness, transparency, and electrical conductivity could be controlled and would be a good example for improving contradictory properties. POLYM. ENG. SCI., 48:1–10, 2008. © 2007 Society of Plastics Engineers     

化学气相沉积法制备单壁碳纳米管研究进展

单壁碳纳米管的独特性能使其成为一种有着极大应用前景的新兴纳米材料,本文主要介绍了催化剂、裂解温度、载气等因素对化学气相沉积法（CVD）制备单壁碳纳米管的影响和采用化学气相沉积制备定向单壁碳纳米管方面的研究进展情况。     

Effect of nanofillers on the properties of flexible protective polymer coatings

Nanofillers with different size, shape, chemical structure, aspect ratio, and purity, including pristine montmorillonite (MMT‐Na) and hydrotalcite (HT) lamellar clays, and nonpurified single‐walled carbon nanotubes (SWNT) and fullerenes (FUL) were dispersed in a waterborne flexible acrylic coating. SEM and WAXD analysis of drawn‐down composite films containing 5 and 10 wt% fillers confirmed the random orientation of the MMT‐Na and HT platelets having intercalated or partially exfoliated structures. SEM analysis of composites containing SWNTs revealed the presence of clusters rather than single fibers and irregularly shaped carbonaceous impurities. Low aspect ratio, but well‐dispersed particles were observed in the FUL composites. Only the SWNT filler improved the thermal stability of the unfilled polymer; the presence of SWNT and MMT‐Na had a negligible effect on the glass transition temperature (T_g) of the coating. The presence of all nanofillers increased the tensile secant modulus of the polymer and decreased somewhat tensile strength and elongation at break to different degrees depending on type of filler and concentration. Some nanofillers significantly reduced the water vapor transmission rate of the unfilled matrix. Experimental data are discussed in terms of parameters known to affect mechanical and barrier properties including volume fraction, orientation, aspect ratio, dispersion, interfacial adhesion, and filler hydrophilicity. The results of this work indicate that it is possible to improve certain properties of acrylic protective coatings through the addition of low cost, unmodified nanoclays or by using nonpurified carbon allotropes, without a significant compromise of the strength and ductility of the polymeric matrix. POLYM COMPOS., 27:368–380, 2006. © 2006 Society of Plastics Engineers     

Low percolation threshold in single-walled carbon nanotube/high density polyethylene composites prepared by melt processing technique

A new method was developed to disperse carbon nanotubes (CNTs) in a matrix polymer and then to prepare composites by melt processing technique. Due to high surface energy and strong adsorptive states of nano-materials, single-walled carbon nanotubes (SWNTs) were adsorbed onto the surface of polymer powders by spraying SWNT aqueous suspected solution onto fine high density polyethylene (HDPE) powders. The dried SWNTs/powders were blended in a twin-screw mixture, and the resulting composites exhibited a uniformly dispersion of SWNTs in the matrix polymer. The electrical conductivity and the rheological behavior of these composites were investigated. At low frequencies, complex viscosities become almost independent of the frequency as nanotubes loading being more than 1.5 wt%, suggesting an onset of solid-like behavior and hence a rheological percolation threshold at the loading level. However, the electrical percolation threshold is ∼4 wt% of nanotube loading. This difference in the percolation thresholds is understood in terms of the smaller nanotube-nanotube distance required for electrical conductivity as compared to that required to impede polymer mobility. The measurements of mechanical properties indicate that this processing method can obviously improve the tensile strength and the modulus of the composites.     

Effects of carbon nanotubes on the crystallization behavior of polypropylene

The effect of the incorporation of single‐walled carbon nanotubes (SWNTs) on the PP crystallization kinetics is investigated by thermal analysis, microscopy and Raman spectroscopy. The results of the investigation show that SWNT acts as a strong nucleation agent. A marked decrease of the half‐time of PP crystallization as well as a sensible increase of the overall crystallization rate is observed in the presence of SWNTs. Moreover, these effects are already noticeable at the lowest SWNT content in the composite with slow further effects at higher concentrations, suggesting a saturation of the nucleating action at the higher concentrations studied. The Avrami model can represent the crystallization kinetics of PP in the composite. The kinetic curves obtained under non‐isothermal conditions confirm the results obtained in isothermal tests and demonstrate the nucleation ability of SWNTs on the PP crystallization. Raman spectroscopy and scanning electron microscopy (SEM) are successfully applied to demonstrate that in the composite films, the changes in the crystallization kinetics can be explained in terms of the changes of the distance between nanotubes in bundles following a different intercalation of the polymer matrix.