Simultaneous study of cure kinetics and rheology of montmorillonite/vinyl ester resin nanocomposites

In this work, the effect of quaternary ammonium salt containing nanoclay content (1–5 wt%) on phase morphology, rheology, cure kinetics, and mechanical properties of the vinyl ester resin (VER)‐based nanocomposites was studied. The morphological characterization including d‐spacing measurement, microscopy observation and phase‐height image processing were performed on the prepared nanocomposites using small angel X‐ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). According to the results obtained from these techniques, it was concluded that an intercalated morphology existed for all the nanocomposites. The kinetic analyses of the isothermal curing followed by storage modulus obtained from the rheometry experiments are shown to be an affective rheological characteristic to investigate the cure behavior of VER/clay nanocomposites. In addition, the most important finding regarding the effect of nanoclay on the cross‐linking behavior of VER systems lays on the chemisorption and physisorption of the reacting monomers and initiator molecules on the nanoclay platelets surface which is found to be responsible for the retardation of the cure reaction caused by organoclay. Eventually, the mechanical characterizations were performed through the tensile, flexural and impact analysis tests. In this case, a considerable improvement of the bulk mechanical responses such as tensile and flexural strengths and also the corresponding moduli were observed for the nanocomposites. Copyright © 2011 John Wiley & Sons, Ltd.     

Description of complementary actions of mineral and organic additives in thermoplastic polymer composites by Flame Retardancy Index

This work visualizes the complementary actions of organic and mineral additives in model thermoplastic polymer composites in terms of Flame Retardancy Index (FRI). Thermal and flame retardancy behaviors of ethylene‐vinyl acetate copolymer (EVA) composites containing calcium carbonate (CC) mineral and ammonium polyphosphate (APP) organic additives were studied varying composition of additives in the 80/20 EVA/(xCC + (20 ? x)APP) composites with x denoting 0, 5, 10, 15, and 20 wt%. Thermogravimetric analysis (TGA) revealed that the onset temperature of composites and the remaining residue were increased by combination of APP and CC, while cone calorimetry results were indicative of a promising flame retardancy performance at a given composition of APP and CC. Based on FRI values, we made distinguished samples from flame retardancy performance viewpoint, where the best flame retardancy was obtained by combination of 15 wt% APP and 5 wt% CC, as reflected in FRI value of 3.08. By contrast, samples containing only APP or CC revealed low resistance against flame, as signaled by FRI values of 0.99 and 0.89, respectively. X‐ray diffraction (XRD) analysis was made on remaining residue collected at the end of cone calorimetry measurements. Moreover, Raman analysis confirmed barrier effect of flame retardancy for EVA/(5APP + 15CC) sample, featured by a higher graphitization level as well as a thicker yet more homogenous char layer. Mechanical behavior analysis of composites revealed an acceptable level of properties, particularly high elongation at break, which was almost independent of formulation. However, a minor loss in yield stress was observed, especially for EVA(10CC + 10APP) sample.     

P-doped g-C3N4 as an efficient photocatalyst for CO2 conversion into value-added materials: a joint experimental and theoretical study

The photocatalytic yield of g-C₃N₄ for CO₂ reduction was modified by phosphorus doping. Possible reaction pathways for CO₂ reduction on the P-doped g-C₃N₄ (PCN) surface were investigated by density function theory calculations for the first time. The experimental results showed that P doping increases the carriers' lifetime, which improves the production of CH₄ through the increase in the driving force of the electrons. The partial density of states of the PCN showed that the valence band maximum and conduction band minimum are composed of p_x, p_y, and, s orbitals of the N atoms and p_z states of carbon, nitrogen, and phosphorus, respectively. Mechanism studies confirm that formic acid, formaldehyde, methanol, and methane are the most probable products. Methane, having positive adsorption energy, can be easily desorbed from the PCN surface, and the Gibbs activation energy of the final step is 1.98 eV. The formation of H₂COOH is the rate-determining step.     

Determination of cobalt in water samples by atomic absorption spectrometry after pre-concentration with a simple ionic liquid-based dispersive liquid-liquid micro-extraction methodology

A rapid dispersive liquid-liquid micro-extraction (DLLME) methodology based on the application of 1-hexylpyridinium hexafluorophosphate [C₆py][PF₆] ionic liquid (IL) as an extractant solvent was applied for the pre-concentration of trace levels of cobalt prior to determination by flame atomic absorption spectrometry (FAAS). 1-Phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) was employed as a chelator forming a Co-PMBP complex to extract cobalt ions from aqueous solution into the fine droplets of [C₆py][PF₆]. Some effective factors that influence the micro-extraction efficiency include the pH, the PMBP concentration, the amount of ionic liquid, the ionic strength, the temperature and the centrifugation time which were investigated and optimized. In the optimum experimental conditions, the limit of detection (3s) and the enrichment factor were 0.70 μg L⁻¹ and 60, respectively. The relative standard deviation (RSD) for six replicate determinations of 50 μg L⁻¹ Co was 2.36%. The calibration graph using the pre-concentration system was linear at levels 2–166 μg L⁻¹ with a correlation coefficient of 0.9982. The applicability of the proposed method was evaluated by the determination of trace amounts of cobalt in several water samples.      

Analytical solution in transient thermo‐elasticity of functionally graded thick hollow cylinders (Pseudo‐dynamic analysis)

This work studies transient thermal stresses in a thick hollow cylinder made of a functionally graded material (FGM). Material properties are considered to be nonlinear with a power law distribution through the thickness. The cylinder is assumed to be of infinite length, and the plane strain condition is supposed. The displacement and the distribution of stresses are obtained by analytical solution of governing differential equations of the Navier type. The transient dynamic behavior of thermal stresses is determined and discussed for various power law exponents appearing in functions determining mechanical properties of FGMs. Copyright © 2009 John Wiley & Sons, Ltd.     

Ready Access to Anhydrous Anionic Lanthanide Acetates by Using Imidazolium Acetate Ionic Liquids as the Reaction Medium

Access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. A straightforward, reproducible synthetic procedure by treating lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) has been developed. This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C₂mim]_n[{Ln₂(OAc)₇}_n] and the dimeric [C₂mim]₂[Ln₂(OAc)₈], based on the ion size and the ratio of IL used. A reaction with an IL : Ln-salt ratio of 5 : 1, where Ln=Nd, Sm, and Gd, led exclusively to the polymer, whilst for the heaviest lanthanides (Dy−Lu) the dimer was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. When the amount of IL and/or the size of the cation was increased, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where η²μκ² is the most represented in both structure types.     

Pre-concentration and quantification of aluminum in fish samples using a dispersive liquid–liquid micro-extraction–spectrofluorimetric method based on Al(III)–8-hydroxyquinoline complex’s fluorescence properties

A simple and fast dispersive liquid–liquid micro-extraction (DLLME)–spectrofluorimetric technique was developed and validated for the extraction and quantification of trace amounts of Al in fish samples, where 8-hydroxyquinoline was utilized as a spectrofluorimetric probe. In order to optimize the efficacy of the DLLME technique, the impact of experimental parameters on the extraction of Al(III) from fish samples was evaluated. Under the optimal conditions, the method was linear in the concentration range of 0.1–7.0 μg/g (r = 0.9996) with a LOD of 0.092 μg/g; additionally, the method was accurate (RE% of ? 3.0 to + 10.0%), precise (RSD% of 1.2–14.3%) and robust (RSD% of 3.8 and p value of 0.21) and its recovery was in the range of 97.0 ± 3.89–110.0 ± 12.5%; moreover, samples were stable before and during the analyses. Therefore, it can be claimed that the developed method could be successfully applied for the quantification of Al in fish samples.     

Synthesis of TiO2 and ZnO Nanoparticles and CTAB-Stabilized Fe3O4 nanocomposite: kinetics and thermodynamics of adsorption

Research on Chemical Intermediates - In the present study, TiO2, ZnO, and CTAB-stabilized Fe3O4 nanocomposite were successfully synthesized and employed for the removal of yellow 145 dye from...