Thermal curing behavior of MWCNT modified vinyl ester‐polyester resin suspensions prepared with 3‐roll milling technique

This study aims to investigate the curing behavior of a vinyl ester‐polyester resin suspensions containing 0.3 wt % of multiwalled carbon nanotubes with and without amine functional groups (MWCNTs and MWCNT‐NH₂). For this purpose, various analytical techniques, including Differential Scanning Calorimetry (DSC), Fourier infrared spectroscopy (FTIR), Raman Spectroscopy, and Thermo Gravimetric Analyzer (TGA) were conducted. The resin suspensions with carbon nanotubes (CNTs) were prepared via 3‐roll milling technique. DSC measurements showed that resin suspensions containing CNTs exhibited higher heat of cure (Q), besides lower activation energy (E_a) when compared with neat resin. For the sake of simplicity of interpretation, FTIR investigations were performed on neat vinyl ester resin suspensions containing the same amount of CNTs as resin. As a result, the individual fractional conversion rates of styrene and vinyl ester were interestingly found to be altered dependent on MWCNTs and MWCNT‐NH₂. The findings obtained from RS measurements of the cured samples are highly proportional to those obtained from FTIR measurements. TGA measurements revealed that CNT modified nanocomposites have higher activation energy of degradation (E_d) compared with the cured polymer. The findings obtained revealed that CNTs with and without amine functional groups alter overall thermal curing response of the surrounding matrix resin, which may probably impart distinctive characteristics to mechanical behavior of the corresponding nanocomposites achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1511–1522, 2009     

Carbon nanotube assisted synthesis of CeO2 nanotubes

CeO₂ nanotubes have been synthesized facilely using carbon nanotubes (CNTs) as templates by a liquid phase deposition method. The properties of the CeO₂ nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) as well as thermogravimetry and differential thermal analysis (TG-DTA). The obtained CeO₂ nanotubes with a polycrystalline face-centered cubic phase have a uniform diameter ranging from 40 to 50 nm. The CeO₂ nanotubes are composed of many tiny interconnected nanocrystallites of about 10 nm in size. The pretreatment of CNTs and calcination temperature were confirmed to be the crucial factors determining the formation of CeO₂ nanotubes. A possible formation mechanism has been suggested to explain the formation of CeO₂ nanotubes.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.     

Floating catalyst CVD synthesis of carbon nanotubes from CpFe(CO)2X (X = Me, I): Poisoning effects of I

Multiwalled carbon nanotubes (MWCNTs), carbon fibers (CFs) and carbon spheres (CSs) were synthesized by an injection chemical vapour deposition (CVD) method using toluene solutions of CpFe(CO)₂Me as catalyst. The effect of pyrolysis temperature (800-1000 °C), catalyst concentration (5 and 10 wt% in toluene) and solution injection rate (0.2 and 0.8 ml/min) on the type and yield of carbonaceous product synthesized was investigated. The carbonaceous materials were characterized by transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and Raman spectroscopy. The use of CpFe(CO)₂I as catalyst generated only carbon fibres and balls (wide range of conditions). Studies involving the addition of I₂ to catalyst solutions confirmed the poisoning effect of I on CNT production.     

Electropolymerized film of functionalized thiadiazole on glassy carbon electrode for the simultaneous determination of ascorbic acid, dopamine and uric acid

The present study reports the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) in 0.20 M phosphate buffer solution (pH 5.0) using electropolymerized ultrathin film of 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) on glassy carbon (GC) electrode. The bare GC electrode does not separate the voltammetric signals of AA, DA and UA. However, electropolymerized AMT (p-AMT) modified GC electrode not only resolved the voltammetric signals of AA, DA and UA but also dramatically enhanced their oxidation peak currents when compared to bare GC electrode. The enhanced oxidation currents for AA, DA and UA at p-AMT modified electrode are due to the electrostatic interactions between them and the polymer film. Using amperometric method, we achieved the lowest detection of 75 nM AA, 40 nM DA and 60 nM UA at p-AMT modified electrode. The amperometric current was linearly increased from 200 nM to 0.80 mM for each AA, DA and UA and the lowest detection limit was found to be 0.92, 0.07 and 0.57 nM, respectively (S/N = 3). The practical application of the modified electrode was demonstrated by the determination of DA in dopamine hydrochloride injection.     

A comparison of the role of boehmite (AlOOH) and alumina (Al2O3) in the thermal stability and flammability of poly(methyl methacrylate)

In this paper, a comparison of the role of boehmite (AlOOH) and alumina (Al₂O₃) in the thermal stability and flame retardant behaviour of poly(methyl methacrylate) (PMMA) is presented. PMMA–AlOOH and PMMA–Al₂O₃ nanocomposites were prepared by melt blending with different filler contents. These nanocomposites were studied by thermogravimetric analysis (TGA) and cone calorimetry. In the presence of the filler (alumina or boehmite), the thermal stability of the polymer appeared to be significantly improved. An increase of the decomposition temperature of between about 19 and 35 °C was demonstrated by TGA. Cone calorimeter measurements showed that the peak of heat release rate is lowered in the presence of AlOOH or Al₂O₃ in comparison to pure PMMA and that this decrease is higher when the filler content increases. When loading rate is higher (15 wt%), a significant improvement in fire resistance of PMMA was observed in both systems but with two different modes of action.     

Thermal Degradation Behavior and Kinetic Analysis of Ultra High Molecular Weight Polyethylene Based Multi-Walled Carbon Nanotube Nanocomposites Prepared Via in-situ Polymerization

Thermal degradation behavior of multi-wall carbon nanotubes (MWCNTs)/ultra high molecular weight polyethylene (UHMWPE) nanocomposites, with different nanotubes contents (0.5, 1.5 and 3.5 wt%) prepared via in-situ polymerization technique have been investigated using thermal gravimetric analysis (TGA). TGA spectra revealed that these nanocomposites had enhanced thermal stability and no significant mass loss (<0.4 wt%) occurred up to 350°C. Thermal degradation of these UHMWPE/MWCNT nanocomposites was investigated in terms of parameters such as the onset temperature of degradation (T₁₀), the decomposition temperature at 50% wt loss (T₅₀), the degradation temperature of maximum rate of the weight loss (T_m), and the residual yields (W_R) from TGA. The degradation activation energies (E) of virgin UHMWPE and its nanocomposites were estimated using the Friedman, the Ozawa, Flynn, and Wall (OFW), and the Kissinger's methods. Results indicated that the degradation activation energy for the virgin UHMWPE was 281.3 kJ/mol. The activation energy increased with increasing nanotube loading up to 1.5 wt% indicating that MWCNTs had a stabilizing effect on the degradation of the matrix. However, loadings of 3.5 wt% of nanotube or more could slightly decrease the activation energy. The decrease in the activation energy for degradation of nanocomposites with higher MWCNT concentrations might be attributed to the catalytic effects of nanotubes and polymerization catalyst residues. The “model fitting” method indicated a mechanism of n ^th-order auto-catalysis from the form of the conversion curves for UHMWPE/MWCNTs nanocomposites prepared via in-situ polymerization.     

Effect of thermal dehydration and rehydration on Na-magadiite structure

The effect caused by dehydration and rehydration of the synthetic Na-magadiite was investigated by TGA, XRD, SEM, and ²⁹Si NMR. Thermal analysis of Na-magadiite presented two well-defined loss mass stages between 20 and 150 °C and another between 270 and 310 °C, both related to the removal of interlayer water. The swelling behavior of Na-magadiite was studied by thermal dehydration data obtained at 150 and 300 °C, and respective rehydration by water addition. X-ray patterns showed that the dehydration of Na-magadiite at 150 and 300 °C provoked the basal spacing decrease. The XRD also showed that only the material treated at 150 °C returned to the original structure with the rehydration. ²⁹Si NMR spectra showed that after rehydration, the Q₃/Q₄ relationship presented the same value for Na-magadiite treated at 150 °C. However, this Q₃/Q₄ value decreased when the treatment was done at 300 °C. Kinetic studies of thermal decomposition showed that the dehydration of magadiite is based on a phase boundary-controlled reaction, caused by contracting areas. The exfoliation of lamellas with thermal treatment can explain this behavior, as observed in SEM images.     

In situ PEI and formic acid directed formation of Pt NPs/MWNTs hybrid material with excellent electrocatalytic activity

A hybrid material based on Pt nanoparticles (Pt NPs) and multi-walled carbon nanotubes (MWNTs) was fabricated with the assistance of PEI and formic acid. The cationic polyelectrolyte PEI not only favored the homogenous dispersion of carbon nanotubes (CNTs) in water, but also provided sites for the adsorption of anionic ions PtCl₄²⁻ on the MWNTs’ sidewalls. Deposition of Pt NPs on the MWNTs’ sidewalls was realized by in situ chemical reduction of anionic ions PtCl₄²⁻ with formic acid. The hybrid material was characterized with TEM, XRD and XPS. Its excellent electrocatalytic activity towards both oxygen reduction in acid media and dopamine redox was also discussed.     

Synthesis, curing kinetics and thermal properties of bisphenol-AP-based benzoxazine

A novel bisphenol-AP-aniline-based benzoxazine monomer (B-AP-a) was synthesized from the reaction of 4,4′-(1-phenylethylidene) bisphenol (bisphenol-AP) with formaldehyde and aniline. The chemical structures were identified by FT-IR, ¹H and ¹³C NMR analyses. The polymerization behavior of the monomer and the types of hydrogen bonding species were monitored by differential scanning calorimetry (DSC) and FT-IR. The curing kinetics was studied by isothermal DSC and the isothermal kinetic parameters were determined. The thermal properties of cured benzoxazine were measured by DSC and thermogravimetric analysis (TGA). The bisphenol-AP-aniline-based polybenzoxazine (poly(B-AP-a)) exhibited higher glass transition temperature (T_g) and better thermal stability than corresponding bisphenol A-aniline-based polybenzoxazines (poly(BA-a)). The T_g value of poly(B-AP-a) is 171 °C. The temperatures corresponding to 5% and 10% weight loss is 317 and 347 °C, respectively, and the char yield is 42.2% at 800 °C. The isothermal curing behavior of B-AP-a displayed autocatalysis and diffusion control characteristics. The modified autocatalytic model showed good agreement with experimental results.     

Polymerized ionic liquid-wrapped carbon nanotubes: The promising composites for direct electrochemistry and biosensing of redox protein

Polymerized ionic liquid-wrapped carbon nanotubes (PIL-CNTs) were firstly designed for direct electrochemistry and biosensing of redox proteins. The CNTs were coated successfully with polymerized ionic liquid (PIL) layer, as verified by transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The PIL-CNTs were dispersed better in water and showed superior electrocatalysis toward O₂ and H₂O₂ comparing to pristine CNTs and the mixture of IL monomer and CNTs. With glucose oxidase (GOD) as a protein model, the direct electrochemistry of the redox protein was investigated on the PIL-CNTs modified glassy carbon (GC) electrode and excellent direct electrochemical performance of GOD molecules was observed. The proposed biosensor (GOD/PIL-CNTs/GC electrode) displayed good analytical performance for glucose with linear response up to 6 mM, response sensitivity of 0.853 μA mM⁻¹, good stability and selectivity.     

Polymerization kinetic pathways of epoxidized linseed oil with aliphatic bio-based dicarboxylic acids

The curing of epoxidized linseed oil (ELO) with three different bio-based dicarboxylic acids (sebacic acid, suberic acid, and succinic acid) has been investigated. No accelerators or catalysts were used and the resulting thermosets are 100% bio-based. Structural investigations of the three crosslinked ELO resins were made using FTIR spectroscopy and TMA, that is, tensile tests, TGA, and DMA. As evidenced by FTIR measurements ELO and dicarboxylic acids reacts but no major differences can be distinguished between the dicarboxylic acids. Non-isothermal curing has been conducted by rheological and DSC measurements. Advanced isoconversional analysis applied to DSC data in association with the complex viscosity variations gives new insights into the polymerization mechanism. The length of dicarboxylic acid carbon chain modifies the reaction rate. Then, a correlation between reaction rate, activation energy, pre-exponential factors, polymerization mechanism, and change in rate-limiting step was shown. DMA and tensile tests highlight the relationship between the carbon chain length, reactivity, and thermomechanical properties. The use of succinic acid allows reaching a higher T_g and thermal stability.     

Facile synthesis of multifunctional multiwalled carbon nanotubes/Fe3O4 nanoparticles/polyaniline composite nanotubes

With an average diameter of 100-150 nm, composite nanotubes of polyaniline (PANI)/multiwalled carbon nanotubes (MWNTs) containing Fe₃O₄ nanoparticles (NPs) were synthesized by a two-step method. First, we synthesized monodispersed Fe₃O₄ NPs (d=17.6 nm, σ=1.92 nm) on the surface of MWNTs and then decorated the nanocomposites with a PANI layer via a self-assembly method. SEM and TEM images indicated that the obtained samples had the morphologies of nanotubes. The molecular structure and composition of MWNTs/Fe₃O₄ NPs/PANI nanotubes were characterized by Fourier transform infrared spectra (FTIR), energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and Raman spectra. UV-vis spectra confirmed the existence of PANI and its response to acid and alkali. As a multifunctional material, the conductivity and magnetic properties of MWNTs/Fe₃O₄ NPs/PANI composites nanotubes were also investigated.     

Covalent Grafting of BPin functions on Carbon Nanotubes and Chan–Lam–Evans Post-Functionalization

The chemical functionalization of carbon nanotubes is often a prerequisite prior to their use in various applications. The covalent grafting of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (BPin) functional groups directly on the surface of multi- and single-walled carbon nanotubes, activated by nucleophilic addition of nBuLi, was carried out. Thermogravimetric analysis (TGA) coupled with mass spectrometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ions mass spectrometry (ToF-SIMS) confirmed the efficiency of this methodology and proved the integrity and covalent grafting of the BPin functional groups. These groups were further reacted with various nucleophiles in the presence of a copper(II) source in the conditions of the aerobic Chan–Lam–Evans coupling. The resulting materials were characterized by TGA, XPS and ToF-SIMS. This route is efficient, reliable and among the scarce reactions that enable the direct grafting of heteroatoms at carbonaceous material surfaces.     

Synthesis and characterization of a novel arylacetylene oligomer containing POSS units in main chains

A novel arylacetylene oligomer containing octamethyl POSS units in main chains was prepared from difluoride octamethyl POSS (diexo-(CH₃)₈Si₈O₁₁F₂) and diethynylbenzene (DEB) by Grignard reaction and characterized by FT-IR, NMR, WAXD, GPC, DSC, and TGA. The curing reaction kinetic of the oligomer was studied by Kissinger and Ozawa methods and the kinetic parameters were obtained. The cured polymer had good thermal and thermal-oxidative properties. TGA analyses demonstrated that the thermal decomposition temperature (T_d5) of the cured polymer in nitrogen and air were 503 and 479 °C, respectively.     

Effect of P/Si polymeric silsesquioxane and the monomer compound on thermal properties of epoxy nanocomposite

The unique polymeric silsesquioxane/4,4′-diglycidyether bisphenol A (DGEBA) epoxy nanocomposites have been prepared by sol-gel method. The structure of nanocomposites was characterized by attenuated total reflectance (ATR) and solid state ²⁹Si NMR. The characteristic intensity of trisubstituted (T) structure was higher than that of tetrasubstituted (Q) structure from solid state ²⁹Si NMR spectra of 3-isocyanatopropyltriethoxysilane (IPTS) modified epoxy. The activation energies of curing reaction of epoxy system and IPTS modified epoxy system are 28-66 kJ/mol and 57-75 kJ/mol, respectively, by Ozawa’s and Kissinger’s methods. The triethyoxysilane side chain of IPTS modified epoxy might interfere the curing reaction of epoxy/amine and increase the activation energy of curing. The thermal degradation of nanocomposites was investigated by Thermogravimetric analysis (TGA). The char yield of nanocomposites was proportional to the 2-(diphenylphosphino)ethyltriethoxysilane (DPPETES) moiety content at high temperature. A higher char content could inhibit thermal decomposition dramatically and enhance the thermal stability. Moreover, the nanocomposites possess high optical transparency.     

The effect of carbon nanotubes on epoxy matrix nanocomposites

The paper concerns thermal properties of epoxy/nanotubes composites for aircraft application. In this work, influence of carbon nanotubes on thermal stability, thermal conductivity, and crosslinking density of epoxy matrix was determined. Three kinds of nanotubes were used: non-modified with 1- and 1.5-μm length, and 1-μm length modified with amino groups. Scanning electron microscopy observations were done for examining dispersion of nanotubes in the epoxy matrix. Glass transition temperature (T _g) was readout from differential scanning calorimetry. From dynamic mechanical analysis, crosslinking density was calculated for epoxy and its composites. Also, thermogravimetric analysis was done to determine influence of nanotubes addition on thermal stability and decomposition process of composites. Activation energy was calculated from TGA curves by Flynn–Wall–Ozawa method. Thermal diffusivity was also measured. SEM images proved the uniform dispersion of carbon nanotubes without any agglomerates. It was found that nanotubes modified with amino groups lead to the increase of epoxy matrix crosslinking density. The significant increase in T _g was also observed. On the other hand, addition of carbon nanotubes leads to the decrease of thermal stability of polymer due to the increase of thermal diffusivity.     

Polypyrrole/γ-Fe2O3 magnetic nanocomposites synthesized in supercritical fluid

Polypyrrole/iron oxide (PPy/γ-Fe₂O₃) nanocomposites were synthesized by in situ oxidative polymerization of pyrrole in the presence of surface modified γ-Fe₂O₃ in supercritical carbon dioxide (scCO₂). The structural properties of nanocomposite particles thus obtained were characterized by FT-IR, thermal analysis (TGA), X-ray diffraction (XRD), and transmission electron microscopy (TEM). It was found that ca. 50 nm γ-Fe₂O₃ nanoparticles were well dispersed in PPy powder in TEM pictures. X-ray photoelectron spectroscopy (XPS) analysis also support that all γ-Fe₂O₃ nanoparticles are encapsulated by PPy. Magnetic property of the nanocomposites was measured by SQUID, which indicated that the nanocomposites are superparamagnetic. The effects of different loadings of γ-Fe2O3 on the polymerization were also investigated.     

Thermal stability and viscoelastic properties of MF/PVAc hybrid resins on the adhesion for engineered flooring in under heating system; ONDOL

The thermal properties of blends of melamine-formaldehyde (MF) resin and poly(vinyl acetate) (PVAc) for engineered flooring used on the Korean traditional ONDOL house floor heating system were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The viscoelastic properties of the blends were also studied. Because MF resin is a thermosetting adhesive, the effect of MF rein was shown across all thermal behaviors. The addition of PVAc reduced the curing temperature. The TGA results showed that the DTG_max temperature and thermal stability of the blends increased with increasing PVAc content. The blends were examined in non-isothermal DSC experiments at a heating rate of 10 °C/min. There was an exothermic peak in all the heating scanning curves, with each blend displaying a single curing peak temperature (T_p), intermediate between those of the two pure components and varying with the blend composition. The DMTA thermogram of MF resin showed that the storage modulus (E′) increased as the temperature was further increased as a result of the cross-linking induced by the curing reaction of the resin. E′ of MF resin increased both as a function of increasing temperature and with increasing heating rate.     

Influence of amine-grafted multi-walled carbon nanotubes on physical and rheological properties of PMMA-based nanocomposites

In this work, poly(methyl methacrylate) (PMMA) was grafted onto amine treated multi-walled carbon nanotubes (NH-MWNTs) and the physical and rheological properties of the NH-MWNTs–g-PMMA nanocomposites were investigated. The graft reaction of NH-MWNTs and the PMMA matrix was confirmed from the change of the N_1S peaks, including those of amine oxygen and amide oxygen, by X-ray photoelectron spectroscopy (XPS). The thermal and mechanical properties of the NH-MWNT–g-PMMA nanocomposites were enhanced by the graft reaction between NH-MWNTs and PMMA matrix. In addition, the viscosity of the nanocomposites was increased with the addition of NH-MWNTs. Storage (G′) and loss modulus (G″) were significantly increased by increase in the NH-MWNT content compared to acid-treated MWNTs/PMMA nanocomposites. This increase was attributed to the strong interaction by the grafting reaction between NH-MWNTs and the PMMA matrix.