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     

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.     

Physical and mechanical behavior of single‐walled carbon nanotube/polypropylene/ethylene–propylene–diene rubber nanocomposites

The effects of the incorporation of single‐walled carbon nanotubes (SWNTs) on the physical and mechanical properties of thermoplastic elastomers based on blends of isotactic polypropylene (iPP) and ethylene–propylene–diene rubber (EPDM) are described. A marked decrease of the half‐time of PP–EPDM crystallization and a sensible increase of the overall crystallization rate were observed in the presence of SWNTs. These results confirmed the expected nucleant effect of nanotubes on the crystallization of polypropylene. This effect was not linearly dependent on the SWNTs' content, showing a saturation of the nucleant effect at high nanotube concentrations. Dynamic mechanical analysis results showed a significant and controversial change of the mechanical behavior of the PP–EPDM/SWNT composites depending on the nanotube content. In particular, the storage modulus increased at the lowest incorporation of SWNTs, whereas a further increase of nanotubes led to a reduction of the storage modulus with respect to the pristine polymer matrix. Raman spectroscopy and scanning electron microscopy were successfully applied to demonstrate that in the composite films, the changes in the crystallization kinetics and mechanical properties could be explained in terms of the changes of the distance between nanotubes in bundles after a different intercalation of the polymer matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2657–2663, 2003     

Effects of single‐walled carbon nanotubes on the crystallization behavior of polypropylene

Polypropylene matrix composites reinforced with single‐walled carbon nanotubes (SWNTs) were produced with different nanotube concentrations. The characterization of these new materials was performed by differential scanning calorimetry and Raman and Fourier transform infrared spectroscopy to obtain information on the matrix–nanotube interaction, on the crystallization kinetics of polypropylene, and especially on the macrostructure and organization of the nanotubes in the composite. On the one hand, the results confirmed the expected nucleant effect of nanotubes on the crystallization of polypropylene, but on the other hand, this effect was not linearly dependent on the SWNT content: there was a saturation of the nucleant effect at low nanotube concentrations. Raman spectroscopy was successfully applied to demonstrating that in the composite films, the crystallization kinetics were strongly affected by the distance between the nanotube bundles as a result of a different intercalation of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 708–713, 2003     

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     

Morphology control in polysulfone‐modified epoxy resins by demixing behavior

Polysulfone (PSu) was used as a modifier of epoxy/aromatic diamine formulations. Two epoxy monomers, based on diglycidyl ether of bisphenol A (DGEBA), were used. The cure agent was 4,4′‐diaminodiphenylsulfone. PSu was miscible with DGEBA, as shown by the existence of a single glass‐transition temperature within the whole composition range. The effect of PSu addition on the cure kinetics was investigated. The reaction rate of the epoxy–amine species was slightly lower in the presence of PSu. The morphology was analyzed by optical and scanning electron microscopy. A range of microstructures were obtained by control over the cure temperature, the amount of PSu incorporated, and the molecular weights of the epoxy resins. The variations in the morphology resulted from the different stages of demixing, which were arrested because of the different developments of the viscosity of the system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 405–412, 2003     

Crosslinking reaction of epoxy resin (diglycidyl ether of bisphenol A) by anionically polymerized polycaprolactam: I. Mechanism and optimization

Different ratios of epoxy resin, diglycidyl ether of bisphenol A (DGEBA) and ?‐caprolactam (starting from 10:90 DGEBA and vice versa), were used to synthesize reactive DGEBA and polycaprolactam blends by the anionic polymerization of ?‐caprolactam at 140°C. Anionic polymerization was conducted with a strong base such as sodium hydride as a catalyst along with a cocatalyst such as N‐acetyl caprolactam. The reaction mechanism, possible cure reactions, and reaction conditions of the reactive blends were studied with Fourier transform infrared spectroscopy and differential scanning calorimetry. The experiments were carried to study the optimization ratio and the effect of the composition on properties such as hardness and tensile strength of the reactive blends. The DGEBA was crosslinked by polycaprolactam through the reaction of the oxirane group with the amide nitrogen, and the reaction was very fast. A ratio of 80:20 (DGEBA:?‐caprolactam) was optimum, and the resulting blend showed the highest tensile strength and hardness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3237–3247, 2003     

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     

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     

Synthesis,thermal behavior,and cone calorimetry of organophosphorus epoxy materials

An organophosphorus epoxy resin with diglycidyl ether of bisphenol A (DGEBA), which has improved fire performance, was synthesized from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and DGEBA. The epoxy resin was then cured with an isomeric mixture of 3,5‐diethyltoluene‐2,4‐diamine and 3,5‐diethyltoluene‐2,6‐diamine. The reaction kinetics were measured by Fourier transform IR, ¹H‐NMR, and differential scanning calorimetry. The effect of the incorporation of a phosphorus species into the epoxy network structures was also measured using thermogravimetric, thermal conductivity, and dynamic mechanical thermal analyses. The fire performance was measured using cone calorimetry, which showed that a significant improvement was achieved by the addition of only 1–4% phosphorus into the epoxy backbone. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3696–3707, 2003     

Modeling the chemorheological behavior of epoxy/liquid aromatic diamine for resin transfer molding applications

The analysis of the chemorheological behavior of an epoxy prepolymer based on a diglycidylether of bisphenol‐A (DGEBA) with a liquid aromatic diamine (DETDA 80) as a hardener was performed by combining the data obtained from Differential Scanning Calorimetry (DSC) with rheological measurements. The kinetics of the crosslinking reaction was analyzed at conventional injection temperatures varying from 100 to 150°C as experienced during a Resin Transfer Molding (RTM) process. A phenomenological kinetic model able to describe the cure behavior of the DGEBA/DETDA 80 system during processing is proposed. Rheological properties of this low reactive epoxy system were also measured to follow the cure evolution at the same temperatures as the mold‐filling process. An empirical model correlating the resin viscosity with temperature and the extent of reaction was obtained to carry out later a simulation of the RTM process and to prepare advanced composites. Predictions of the viscosity changes were found to be in good agreement with the experimental data at low extents of cure, i.e., in the period of time required for the mold‐filling stage in RTM process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4228–4237, 2006     

Synthesis and characterization of composites of polyaniline and polyurethane‐modified epoxy

A toughened, semiconductive polyaniline/polyurethane (PANI/PU)‐epoxy nanocomposite was prepared using a conductive polymer, PANI, and a PU prepolymer‐modified diglycidyl ether of bisphenol A (DGEBA) epoxy. The formation of a nanostructure was confirmed by Fourier transform infrared spectroscopy and SEM. The mechanical properties of the composites were evaluated and compared with those of the corresponding matrix. The improvement in impact strength of the composites (especially in the PANI/PU(PPG2000)‐epoxy system) was explained after fracture surface analysis using SEM. DSC and TGA studies indicated that the thermal properties of these composites were comparable to those of DGEBA epoxy. A conductivity in the range 10^?9–10^?3 S cm^?1 was obtained, depending on the testing frequency (10³–10⁷ Hz) and the PANI content incorporated. Copyright © 2006 Society of Chemical Industry     

Cure study of epoxy resin reinforced with multiwalled carbon nanotubes by Raman and luminescence spectroscopy

Carbon nanotubes (CNTs) were annealed at high temperature under vacuum, followed by a chemical treatment using acids and ethylenediamine. The presence of acid and amine chemical groups on CNT surface was confirmed by infrared spectra. The amount of iron remaining in the CNTs after the treatments was evaluated by thermogravimetry and by energy dispersion spectroscopy. The crystalline property of CNTs was evaluated by Raman spectroscopy, showing that the acid treatment performed after the thermal treatment did not damage the nanotubes walls. Micrographs showed that the most dispersed CNTs were obtained after the amine functionalization step. The curing process of the neat resin and composites was studied by Raman and Luminescence spectroscopies and both techniques showed similar results. The presence of CNTs, functionalized or not, increased the cure degree of the epoxy resin when the same cure time was used in the comparison. Nanocomposites synthesized with annealed CNT and acid‐treated CNT had cure rates considerably higher at the beginning of the reaction. The difference in the cure rate was explained by means of the sample's homogeneity and the presence of chemical groups. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

New carbon nanotube–conducting polymer composite electrodes for drug delivery applications

A novel drug delivery system (DDS) based on a carbon nanotube (CNT)–poly(3,4‐ethylenedioxythiophene) (PEDOT) composite was constructed via a layering method. Single‐walled CNTs (SWNTs) were immobilized on a gold electrode using a layer‐by‐layer technique. In particular, cysteamine (Cys) was firstly bonded to the gold surface through the strong S? Au association and SWNTs were subsequently linked onto the Cys layer through condensation reaction of ? NH₂ and carboxyl groups by 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide/N‐hydroxysuccinimide coupling. X‐ray photoelectron spectroscopy and Raman spectroscopy demonstrate that this is a facile route for immobilizing CNTs on gold electrodes. Finally PEDOT was electropolymerized on the SWNT‐functionalized electrode to make a SWNT–PEDOT composite, and the modified electrode was applied as a DDS. Dexamethasone, as a model drug, was incorporated into PEDOT in the electropolymerization. Investigations of the electrochemical properties of SWNT–PEDOT demonstrate that SWNTs greatly improve the conductivity and increase the charge capacity of PEDOT. The composite exhibits a petal‐like surface structure, 20–30 nm thick and 100–200 nm wide. Compared to a DDS based on pure PEDOT synthesized under the same conditions, SWNT–PEDOT has the merits of higher drug release rate and larger release amount. The average mass release for every five voltammetry cycles increases from 1.4126 to 1.8864 mg cm^?2. Copyright © 2011 Society of Chemical Industry     

Microstructure and thermal properties of silyl-terminated polycaprolactone–polysiloxane modified epoxy resin composites

With a direct nucleophilic addition between  OH groups of polydiol and  NCO of a silane, a blend of silyl-terminated polycaprolactone PCL-Si and silyl-terminated polydimethylsiloxane PDMS-Si oligomer, PCS-2Si, were firstly prepared, and then blended with a commercial epoxy resin (diglycidyl ether of bisphenol-A, DGEBA) to form a ternary composite. The formed ternary composites of different content of DGEBA were cured using a polyamidoamine as a curing agent and a sol–gel process at ambient temperature. The microstructures and properties of the cured composites were investigated by SEM, TGA, and energy dispersive spectroscopy. The results showed the compatibility between DGEBA and PDMS increased with increasing content of PCS-2Si, but higher content of PCS-2Si resulted in a slight enrichment of silicon in the surface of the cured film. TGA showed that incorporating PCS-2Si into epoxy resin altered the composites' thermal stability and degradation characteristics. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Covalent addition of diethyltoluenediamines onto carbon nanotubes for composite application

Diethyltoluenediamines (DETDA) was grafted to single‐walled carbon nanotubes (SWNTs) through diazonium‐based addition for improving dispersion and interfacial bonding in SWNT/epoxy nanocomposites. Characterization results of Fourier Transformed Infrared spectroscopy and Raman spectroscopy validated covalent bonding between DETDA and carbon nanotubes. The degree of functionalization was about 4% based on thermo‐gravimetric analysis. Interfacial bonding strength was computed in the presence of chemical bonding and the computation results indicated that the interfacial shear strength in the presence of functionalized carbon nanotubes was significantly enhanced. The experimental test revealed that the tensile strength of nanocomposites was enhanced about 23% and Young's modulus about 25%, with 0.5 wt% loading of functionalized‐nanotubes. These considerable improvements further verified the load‐transfer enhancement in the functionalized‐SWNTs/epoxy nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Thermal degradation mechanisms of epoxy composites filled with tin particles

This article reports an evaluation study of the thermal degradation mechanisms of electrically insulating and conducting epoxy/Sn composites by using solid‐state kinetic approaches and structural characterizations. Comparison of the thermoanalytical data of epoxy/Sn composites with pure epoxy shows that the addition of tin in epoxy catalyzes the thermal degradation of epoxy and the catalytic ability of tin depends upon its contents in epoxy. Kinetic modeling of the phenomena elaborates the thermal behaviors of epoxy/Sn composites in terms of the comparison of their activation parameters and reaction models. Friedman's differential and Arshad–Maaroufi's generalized linear integral isoconversional methods are used to obtain the variation in activation energies with the advancement of reaction. Advanced reaction model determination methodology is effectively employed to evaluate the reaction mechanisms of epoxy/Sn composites. Kinetic analysis suggests that tin increases the thermal degradation rate of epoxy by lowering the activation energy barrier of reaction. It is worth noticing that the parameters of the probable reaction model, i.e., Šesták Berggren have been found nearly the same for pure epoxy and epoxy/Sn composites, revealing weak epoxy–tin interactions in the composites. The mechanistic information obtained by kinetic analysis fairly agrees with the scanning electron microscopy and X‐ray diffraction results. POLYM. COMPOS., 38:1529–1540, 2017. © 2015 Society of Plastics Engineers     

Nonisothermal cure kinetics of diglycidylether of bisphenol‐A/amine system reinforced with nanosilica particles

Epoxy‐silica nanocomposites were obtained from directly blending diglycidylether of bisphenol‐A (DGEBA)‐based epoxy and nanoscale silica (NS) and then curing with 4,4′‐diaminodiphenylamine (DDA). The effect of amount of nanosilica (NS) particles as catalyst on the mechanism and kinetic parameters of cure reaction of DGEBA/DDA system was studied. The kinetics parameters were obtained from nonisothermal differential scanning calorimeter (DSC) data using the Kissinger and Ozawa equations. The exothermic peak was shifted toward lower temperatures in DGEBA/DDA/NS system with increasing the amount of nanoslica particles. However, the existence of NS particles with hydroxyl groups in the structure in the mixture of DGEBA/DDA catalyzes the cure reaction and increases the rate constant. The activation energy of cure reaction of DGEBA/DDA system obtained from two methods were in good agreement, and showed a decrease when NS particles were present in the mixture. The mechanism of reaction of DGEBA with DDA was carried out by isothermal curing in the oven at 130°C and measuring the disappearance peak of epoxide group at 916 cm^?1 using FTIR. The diffusive behavior of two systems was investigated during water sorption at 25°C and the experimental results fitted well to Fick's law. Diffusion coefficient of cured sample from DGEBA/DDA/10% NS blend decreased in comparison with the sample without NS particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3855–3863, 2007     

Epoxy matrices for filament-wound carbon fiber composites

Epoxies suitable for filament-winding fibrous composites must be processible at ambient temperatures, nontoxic, chemically simple, undergo full cure at ≤ 100°C and, also, be tough and exhibit a T_g > 120°C. In this paper, we report the cure characteristics, processibility, toxicity, and mechnical and physical properties of a number of amine-cured diglycidyl ether of bisphenol-A (DGEBA) epoxide candidate systems suitable for filament-wound carbon fiber composites. 2,5-Dimethyl-2,5-hexane diamine (DMHDA)-cured DGEBA epoxy was found to be the most promising candidate. The good processibility and thermal properties, together with the low cure characteristics of the DGEBA–DMHDA epoxy system, are discussed in terms of molecular structure of the amine molecule. The network structural parameters that control epoxy toughness and subsequent embrittlement upon plastic flow are discussed. Evidence is presented for plastic flow-induced thermal and mechanical property deterioration of epoxies as a result of network chain scission.     

Preparation and nonisothermal cure kinetics of DGEBA‐nanosilica particles composites

Nanocomposites from nanoscale silica particles (NS), diglycidylether of bisphenol‐A based epoxy (DGEBA), and 4,4′‐diaminobiphenyl benzidine (DAPB) as curing agent were obtained from direct blending of these materials. This homogenous mixture was cured in the oven at a particular temperature for a certain time or scanned from room temperature up to 300°C in differential scanning calorimeter (DSC). Mechanism and kinetic of the cure reaction of nanocomposite and thermal stability of the cured sample were studied with FTIR, DSC, and thermogravimetric analysis, respectively. The effect of amount of nanosilica (NS) particles as catalyst on the cure reaction of DGEBA/DAPB system was studied by the Kissinger and Ozawa equations. The existence of NS particles with hydroxyl groups in the structure catalyzes the cure reaction of DGEBA/DAPB system, increased the rate constant, and shifted the exothermic peak toward lower temperatures with increasing amount of NS particles. The activation energies of cure reaction of pure DGEBA/DAPB system obtained from two methods were in good agreement and decreased when NS particles were present in the mixture. The isothermal cure reaction at 145°C in an oven was followed by measuring the disappearance peak of epoxide group at 916 cm⁻¹ using FTIR. The diffusive behavior of cured samples was investigated during water sorption at 25°C and the experimental results fitted well according to Fick's law. Diffusion coefficient of cured sample containing 10% NS decreased in comparison to the sample without NS particles. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers