Oxygen permeability of novel organic-inorganic coatings: I. Effects of organic-inorganic ratio and molecular weight of the organic component

The oxygen barrier properties of composite materials, consisting of a 45 μm thick LDPE substrate coated by a thin layer (0.7-1 μm) of new hybrid organic-inorganic materials based on SiO₂ and PE-PEG block copolymers, have been characterized at 35 and 50 °C. A significant decrease (25-40%) of the oxygen transfer rate has been observed for coated samples with respect to bare substrate both at 35 and 50 °C. The effects on the coating permeability of organic-inorganic ratio, molecular weight of the PE-PEG block copolymers and temperature are discussed.     

Habit modification of calcium carbonate in the presence of malic acid

The ability of malic acid to control calcium carbonate morphology has been investigated by aging calcium chloride solution in the presence of urea in a 90 °C bath. Malic acid favors the formation of calcite. A transition from single block to aggregate with special morphology occurs upon increasing malic acid concentration. The morphological development of CaCO₃ crystal obviously depends on the starting pH. CaCO₃ crystal grows from spindle seed to dumbbell in the pH regime from 7 to 11; while it evolves from spindle seed, through peanut, to sphere at pH=11.5. Both dumbbell and sphere consist of rods that are elongated along c-axis and capped with three smooth, well-defined rhombic {1 0 4} faces. A tentative growth mechanism is proposed based on the fractal model suggested by R. Kniep and S. Busch [Angew. Chem. Int. Ed. Engl. 35 (1996) 2624].     

Preparation and properties of polybenzoxazole-silica nanocomposites via sol-gel process

A novel organic/inorganic hybrid material has been prepared through the sol-gel process. A high temperature polymer, polybenzoxazole (PBO), was chosen as the organic phase due to its inherent low dielectric constant and low water absorption. The inorganic phase was generated via sol-gel reaction from a silica precursor, phenyltriethoxysilane (PTEOS). Due to the hydroxyl groups in the PBO precursor backbone and the water release during the cyclization of the precursor, the sol-gel reaction proceeded without the addition of water and any catalyst. After curing at 350 °C, we obtained the PBO/silica nanocomposites. From TEM and SEM photographs, the silica particles dispersed in the PBO matrix were nano-sized. With an addition of 100 wt% of PTEOS, the T_g of PBO was increased 35 °C. The dielectric constant of the hybrid materials increased with the increasing amount of PTEOS.     

A novel zinc chelate complex containing both phosphorus and nitrogen for improving the flame retardancy of low density polyethylene

A novel metal chelate complex containing phosphorus, nitrogen and zinc (II) ion was synthesized and used as the flame retardant of low density polyethylene (LDPE). The zinc chelate complex was synthesized by reacting zinc acetate with the ligand of tetraethyl (1,2-phenylenebis(azanediyl)) bis (2-hydroxylphenylmethylene) diphosphonate (TEPAPM). The chemical structure of the target Zn-TEPAPM was confirmed by FTIR, ¹H NMR, ¹³C NMR and ³¹P NMR spectra. The flame retardancy and thermal behavior of LDPE containing various amount of Zn-TEPAPM were investigated by limiting oxygen index test, thermogravimetric (TG) analysis and cone calorimetry. The results show that Zn-TEPAPM can greatly increase the thermal stability, the char formation and smoke suppression ability of LDPE. The TG curves show that even when the filler content of Zn-TEPAPM is as low as 1 wt% in LDPE, the onset degradation temperature of LDPE is increased from 429 °C to 442 °C, and the maximum degradation temperature is increased from 469 °C to 488 °C. Also, a reduction of 32% for the peak heat release rate (PHRR) is obtained in the cone test. Moreover, Zn-TEPAPM is demonstrated to be a very effective synergist of ammonium polyphosphate (APP). When 1 wt% of Zn-TEPAPM was introduced into the LDPE/APP (mass ratio 80/19) blend, the PHRR value is reduced by 32%, compared with that of LDPE/APP blend without Zn-TEPAPM, and the char layer becomes more compact and intact.     

Microwave-assisted digestion of organoarsenic compounds for the determination of total arsenic in aqueous, biological, and sediment samples using flow injection hydride generation electrothermal atomic absorption spectrometry

A microwave assisted wet digestion method for organoarsenic compounds and subsequent determination of total arsenic in aqueous, biological and sediment samples by means of flow injection hydride generation electrothermal atomic absorption spectrometry (FI-HG-ETAAS) is described. Sodium persulfate, sodium fluoride and nitric acid serve as digestion reagents, which allow a quantitative transformation of organoarsenic compounds to hydride forming species in a commercial microwave sample preparation system. The maximum operating pressures of the applied tetrafluorometoxil (TFM) liners are 75 bar (high pressure vessels) and 30 bar (medium pressure vessels), corresponding to maximum solution temperatures of 300 and 260 °C. For the investigated samples, digestion temperatures of 210-230 °C (medium pressure vessels) and 240-280 °C (high pressure vessels) were obtained.In medium pressure vessels, arsenic recovery from aqueous testing solutions of dimethylarsinic acid (DMA), phenylarsonic acid (PAA) and tetraphenylarsonium chloride (TPA) at initial concentrations of 100 and 10 μg l⁻¹ is complete, even in the presence of an excess of organic carbon (potassium hydrogen phthalate, 2000 mg l⁻¹) or fatty acids (linolenic acid 70%; linoleic acid ≈20-25%; Oleic acid ≈3%, 900-4500 mg l⁻¹).Arsenic recovery from aqueous arsenobetaine (ASB) solutions with the same initial concentrations is also complete if high pressure vessels and a higher concentration of fluoride ions are used, whereas the addition of organic carbon (potassium hydrogen phthalate, 2000 mg l⁻¹, fatty acids, 900-4500 mg l⁻¹) leads to a decrease in arsenic recovery of about 2-5%. In all cases, residual carbon contents are close to the limit of detection for the applied analytical method (15 mg l⁻¹).Results of arsenic analysis in reference standard materials revealed a significant dependence on the material’s nature (sediment samples, plant materials and seafood samples). Sediment samples and plant materials show recoveries for arsenic around 100% after a single-step digestion in medium pressure TFM liners. Seafood (fish/lobster/mussel samples) usually require either the use of high pressure vessels or a second digestion step, if medium pressure vessels are used.     

Electron-beam irradiation on poly(propylene carbonate) in the presence of polyfunctional monomers

Poly(propylene carbonate) (PPC) showed predominantly degradation under electron-beam irradiation, accompanied by deterioration of its mechanical performance due to sharp decrease of the molecular weight. Crosslinked PPC was prepared by addition of polyfunctional monomer (PFM) to enhance the mechanical performance of PPC. When 8 wt% of PFM like triallyl isocyanurate (TAIC) was added, crosslinked PPC with a gel fraction of 60.7% was prepared at 50 kGy irradiation dose, which showed a tensile strength at 20 °C of 45.5 MPa, whereas it was only 38.5 MPa for pure PPC. The onset degradation temperature (T_i) and glass transition temperature (T_g) of this crosslinked PPC was 246 °C and 45 °C, respectively, a significant increase related to pure PPC of 211 °C and 36 °C. Therefore, thermal and mechanical performances of PPC could be improved via electron-beam irradiation in the presence of suitable PFM.     

Effect of clay on the corrosion protection efficiency of PMMA/Na-MMT clay nanocomposite coatings evaluated by electrochemical measurements

The preparation of PMMA-clay nanocomposites was investigated by using sodium dodecylbenzenesulfonate (SDS) and potassium peroxodisulfate (KPS) as a surfactant and chain initiator for an in situ emulsion polymerization reaction, respectively. The as-prepared nanocomposites were then characterized by Fourier transformation infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXRD) patterns and transmission electron microscopy (TEM).It should be noted that the nanocomposite coating containing 1 wt% of clay loading was found to exhibit an observable enhanced corrosion protection on cold-rolled steel (CRS) electrode at higher operational temperature of 50 °C, which was even better than that of uncoated and electrode-coated with PMMA alone at room temperature of 30 °C based on the electrochemical parameter evaluations (e.g., E_corr, R_p, I_corr, R_corr and impedance). In this work, all electrochemical measurements were performed at a double-wall jacketed cell, covered with a glass plate, through which water was circulated from a thermostat to maintain a constant operational temperature of 30, 40 and 50 ± 0.5 °C. Moreover, a series of electrochemical parameters shown in Tafel, Nyquist and Bode plots were all used to evaluate PCN coatings at three different operational temperatures in 5 wt% aqueous NaCl electrolyte. The molecular barrier properties at three different operational temperatures of PMMA and PCN membranes were investigated by gas permeability analyzer (GPA) and vapor permeability analyzer (VPA). Effect of material composition on the molecular weight and optical properties of neat PMMA and PCN materials, in the form of solution and membrane, were also studied by gel permeation chromatography (GPC) and UV-vis transmission spectra.     

Interaction between low molecular weight organic acids and hydroxyapatite with different degrees of crystallinity

In this study, two types of hydroxyapatite (HAP) with different degrees of crystallinity were prepared by a sol-gel method and a chemical precipitation method. Influences of crystallinity on the adsorption and dissolution properties of HAP, and the release of phosphorus (total phosphorus) during the adsorption of organic acid were investigated. Results showed that crystallinity had a great effect on the adsorption capacity and dissolution properties of HAP, as well as the adsorption mechanisms of organic acids on HAP surfaces. The poorly crystallized (the degree of crystallinity X_c = 0.23) HAP adsorbed greater amounts of oxalic, citric, or malic acid than the well crystallized (X_c = 0.86) HAP, and the former could release more phosphorus in the presence of organic acids. The adsorption capacity of oxalic acid was much higher than citric and malic acids on both the well and the poorly crystallized HAP, which was due to the strong coordination of oxalic acid with calcium on HAP surface, and that physical adsorption was more inclined to dominate the adsorption of malic or citric acid on the well crystallized HAP. These findings might be of importance in understanding the effects of crystallinity and organic acid binding on the dissolution of calcium phosphates and the adsorption characteristics of HAP.     

The interaction of water vapors with H3PO4 imbibed electrolyte based on PBI/polysulfone copolymer blends

The interaction of steam with phosphoric acid imbibed electrolyte composed of PBI/PPy(50)coPSF 50/50 polymer blend and its effect on fuel cell performance was studied regarding its permeability through and its chemical interaction with the membrane. It was found that steam is the only gas that permeates the membrane with a permeability coefficient 1.1 × 10⁻¹⁴ mol cm cm⁻² s⁻¹ Pa⁻¹ at 150 °C. This is attributed either to the high solubility of water in phosphoric acid or to the chemical interaction with pyrophosphoric acid_. The latter was demonstrated by carrying out TGA experiments under various water vapor partial pressures. Water reacts with pyrophosphoric acid in order to maintain the equilibrium concentration of phosphoric acid at high level, thus improving proton conductivity and fuel cell performance. In addition it is shown that excess water dissolves in the membrane thus maintaining the “membrane/acid” system at high hydration level. This depends both on temperature and steam partial pressure. Although in the present study it is shown that steam plays a significant role in the performance of the high temperature Polymer electrolyte membrane (PEM) fuel cell, nevertheless its feed with humidified gases is not necessary, due to the back transport of the water produced at the cathode.     

Nanocrystalline F-doped tin dioxide materials: texture, morphology and photosensitization with a perylene-substituted organotin

The controlled hydrolysis of fluoro(2-methylbutan-2-oxy)di(pentan-2,4-dionato)tin followed by annealing at 400-550 °C gave conductive mesoporous F-doped SnO₂ materials. The materials consist of a porous network of aggregated nanoparticles, the mesoporosity observed corresponding to the interparticle space. Tuning of the annealing temperature enabled us to prepare materials with surface areas ranging from 70 to 150 m² g⁻¹, with an average pore size comprised between 50 and 100 Å and with a mean particle diameter ranging from 50 to 120 Å. Resistivities as low as 1-2 Ω cm were measured for the sample treated at 550 °C which contained 2-3 at.% of fluorine. This powder reacted with 3-(6-trihex-1-ynylstannylhexyl)perylene to furnish a dye-sensitized F-doped SnO₂ mesoporous materials. An intensity-dependent photocurrent was produced under blue light illumination using the cavity microelectrode (CME) technique. With an aqueous NaBr solution, the photopotential reaches 700 mV, a value slightly higher than that found for an undoped sensitized SnO₂ powder (∼600 mV).     

Synthesis and characterization of some novel aromatic polyimides

Three new diamines 1,2-di(p-aminophenyloxy)ethylene, 2-(4-aminophenoxy)methyl-5-aminobenzimidazole and 4,4-(aminopheyloxy) phenyl-4-aminobenzamide were synthesized and polymerized with 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BP), 4,4′-(hexafluoroisopropyledene)diphthalic anhydride (HF) and 3,4,9,10-perylene tetracarboxylic acid dianhydride (PD) either by one step solution polymerization reaction or by two step procedure. The later includes ring opening poly-addition to give poly(amic acid), followed by cyclodehydration to polyimides with the inherent viscosities 0.62-0.97 dl/g. Majority of polymers are found to be soluble in most of the organic solvents such as DMSO, DMF, DMAc, m-cresol even at room temperature and few becomes soluble on heating. The degradation temperature of the resultant polymers falls in the ranges from 240 °C to 550 °C in nitrogen (with only 10% weight loss). Specific heat capacity at 300 °C ranges from 1.1899 to 5.2541 J g⁻¹ k⁻¹. The maximum degradation temperature ranges from 250 to 620 °C. T_g values of the polyimides ranged from 168 to 254 °C.     

The effects of annealing in inert atmospheres and of oxygen concentration on chemiluminescence from polypropylene

It has been shown that heating polypropylene powder under a nitrogen atmosphere leads to the significant prolongation of the oxidation induction time measured by chemiluminescence in oxygen at 130 and 140 °C. While heating in nitrogen from 0 to 4 h at 140 °C leads to the linear increase of oxidation induction time, the maximum chemiluminescence intensity I_stat increases with the time of sample annealing until 2 h; then it starts to decay. The different and sometime unknown thermal history of the sample may thus explain the scatter of induction times of oxidation observed with different PPs whether they be pure or stabilised. Maximum chemiluminescence intensity plotted vs. concentration of oxygen in the surrounding atmosphere at 130 and 140 °C also increases linearly; however, this does not correspond with very small reduction of oxidation induction time. The four-parametric “master equations” used in our earlier papers were applied to fit the chemiluminescence runs both in oxygen and in nitrogen. The equation operates with the rate constants of hydroperoxide decomposition and oxidation spreading but at the same time, it takes into account the possible effect of oxidation products on decomposition of hydroperoxides.     

Correlation of optical properties and temperature-induced irreversible phase transitions in europium-doped yttrium carbonate nanoparticles

Nanophase europium-doped yttrium carbonate precursors are subjected to heat treatments, ranging from 300 °C to 1100 °C for dwell times of 5 min, 30 min, and 180 min. XRD, TEM, FT-IR, fluorescence, fluorescence excitation, and fluorescence lifetime measurements are used to characterize the materials. Upon heating, the material transitions through several amorphous stages until it reaches the crystalline cubic Y₂O₃ phase. DSC measurements show an exothermic transition at 665.7 °C, indicating the formation of crystalline Y₂O₃. The grain size development is fitted by the relaxation equation and yields an activation energy of 50.3 kJ/mol. The amorphous phases are characterized by inhomogenously broadened optical spectra. Heating up to 700 °C leads to an increased fluorescence lifetime (from about 1 ms to 2.4 ms). As the material is heated to higher temperatures and completes the formation of the crystalline cubic Y₂O₃ phase, the optical spectra become narrower and the fluorescence lifetime decreases to about 1.2 ms.     

Fabrication of dissolved O2 metric uric acid biosensor using uricase epoxy resin biocomposite membrane

Uricase purified from 20-day-old leaves of cowpea was immobilized on to epoxy resin membrane with 80% retention of initial activity of free enzyme and a conjugation yield of 0.056 mg/cm². The uricase epoxy resin bioconjugate membrane was mounted over the sensing part of the combined electrode of ‘Aqualytic’ dissolved O₂ (DO) meter to construct a uric acid biosensor. The biosensor measures the depletion of dissolved O₂ during the oxidation of uric acid by immobilized uricase, which is directly proportional to uric acid concentration. The biosensor showed optimum response within 10-12 s at a pH 8.5 and 35 °C. A linear relationship was found between uric acid concentration from 0.025 to 0.1 mM and O₂ (mg/l) consumed. The biosensor was employed for measurement of uric acid in serum. The mean value of uric acid in serum was 4.92 mg/dl in apparently healthy males and 3.11 mg/dl in apparently healthy females. The mean analytic recoveries of added uric acid in reaction mixture (8.9 and 9.8 mg/dl) were 93.6 ± 2.34 and 87.18 ± 3.17% respectively. The within and between batch CVs were <6.5 and <5.0%, respectively. The serum uric acid values obtained by present method and standard enzymic colorimetric method, showed a good correlation (r = 0.996) and regression equation being y = 0.984x + 0.0674. Among the various metabolites tested only, glucose (11%), urea (38%), NaCl (25%) and cholesterol (13%) and ascorbic acid (56%) caused decrease, while, MgSO₄ and CaCl₂ had no effect on immobilized enzyme. The enzyme electrode showed only 32% decrease during its use for 100 times over a period of 60 days at 4 °C.     

Effect of temperature variation on the visible and near infrared spectra of wine and the consequences on the partial least square calibrations developed to measure chemical composition

Many studies have reported the use of near infrared (NIR) spectroscopy to characterize wines or to predict wine chemical composition. However, little is known about the effect of variation in temperature on the NIR spectrum of wine and the subsequent effect on the performance of calibrations used to measure chemical composition. Several parameters influence the spectra of organic molecules in the NIR region, with temperature being one of the most important factors affecting the vibration intensity and frequency of molecular bonds. Wine is a complex mixture of chemical components (e.g. water, sugars, organic acids, and ethanol), and a simple ethanol and water model solution cannot be used to study the possible effects of temperature variations in the NIR spectrum of wine. Ten red and 10 white wines were scanned in triplicate at six different temperatures (25 °C, 30 °C, 35 °C, 40 °C, 45 °C and 50 °C) in the visible (vis) and NIR regions (400-2500 nm) in a monochromator instrument in transmission mode (1 mm path length). Principal component analysis (PCA) and partial least squares (PLS) regression models were developed using full cross validation (leave-one-out). These models were used to interpret the spectra and to develop calibrations for alcohol, sugars (glucose + fructose) and pH at different temperatures. The results showed that differences in the spectra around 970 nm and 1400 nm, related to OH bonding were observed for both varieties. Additionally an effect of temperature on the vis region of red wine spectra was observed. The standard error of cross validation (SECV) achieved for the PLS calibration models tended to inverse as the temperature increased. The practical implication of this study it is recommended that the temperature of scanning for wine analysis using a 1 mm path length cuvette should be between 30 °C and 35 °C.     

Thermal stability of solid and aqueous solutions of humic acid

The effects of temperature on the stability of a soil humic acid were studied in the present work. Solid samples of Gohy-573 humic acid (HA) and dissolved ones in aqueous solution (pH 6.0, 0.1 mol L⁻¹ NaClO₄) were investigated in order to understand the impact of temperature on the chemical properties of the material. The methods applied to solid samples in the present investigation were thermogravimetric analysis (TGA), temperature-programmed desorption coupled with mass spectrometry (TPD-MS), and in situ diffuse reflectance infrared Fourier transformed spectroscopy (in situ DRIFTS). Humic acid samples were studied in the 25-800 °C range, with focus on thermal/chemical processes up to 250 °C. The reversibility of the changes observed was investigated by cyclic changes to specified temperature ranges (40-110 °C). All measurements were conducted under inert-gas atmosphere in order to avoid samples combustion at increased temperatures. Aqueous solutions were analyzed by UV-vis absorption spectroscopy after storage at temperatures up to 95 °C, and storage times up to 1 week. For temperatures below 100 °C experiments on solid and aqueous samples have shown results which were consistent to each other. The amount of water desorbed is temperature dependent and up to 70 °C this process was totally reversible. Above 70 °C an irreversible loss of water was also observed, which according to UV-vis spectroscopy corresponds to water produced by condensation leading to more condensed polyaromatic structures. The water released up to 110 °C was about 7 wt% of the total mass of the dried humic acid, where less than 50% corresponded to reversibly adsorbed water. At higher temperatures (>110 °C), gradual decomposition resulting in the formation of carbon dioxide (110-240 °C), and carbon monoxide (140-240 °C) takes place. Hence, thermal treatment of Gohy-573 humic acid above 70 °C results in irreversible structural changes, that could affect chemical properties (e.g., complex formation) of the material.     

Fluorine-doped nanocrystalline SnO2 powders prepared via a single molecular precursor method as anode materials for Li-ion batteries

Fluorine-doped nanocrystalline tin dioxide materials (F:SnO₂) have been successfully prepared by the sol-gel process from a single molecular precursor followed by a thermal treatment at 450-650 °C. The resulting materials were characterized by FTIR spectroscopy, powder X-ray diffraction, nitrogen adsorption porosimetry (BET) and transmission electron microscopy (TEM). The mean particle size increased from 5 to 20 nm and the specific surface area decreased from 123 to 37 m²/g as the temperature of heat treatment was risen from 450 to 650 °C. Fluorine-doped nanocrystalline SnO₂ exhibited capacity of 560, 502, and 702 mA h/g with 48%, 50%, and 40% capacity retention after 25 cycles between 1.2 V and 50 mV at the rate of 25 mA/g, respectively. In comparison, commercial SnO₂ showed an initial capacity of 388 mA h/g, with only 23% capacity retention after 25 cycles.     

Electrochemical behaviour of isatin at a glassy carbon electrode

A rapid, reliable and simple capillary zone electrophoresis method for the determination of organic acids in beverages was developed. The complete separation of oxalic, formic, tartaric, malic, succinic, maleic, glutaric, pyruvic, acetic, lactic, citric, butyric, benzoic, sorbic, ascorbic and gluconic acids can be achieved in less than 3.5 min with a simple electrolyte composed by phosphate as the carrier buffer (7.5 mM NaH₂PO₄ and 2.5 mM Na₂HPO₄), 2.5 mM TTAOH as electroosmotic flow modifier and 0.24 mM CaCl₂ as selectivity modifier, adjusting the pH at 6.40 constant value. Injection was performed in hydrodynamic mode (30 s) and the detection mode was UV direct at 185 nm. The running voltage was −25 kV at thermostated temperature of 25 °C. The method developed has been applied to several beverage samples with only a simple dilution and filtration treatment of the sample. The proposed method is fast because the separation time decrease two, four or, even, six times the separation times of the previous reported CZE methods. It is also simple and cheap due to a low consumption of chemicals and samples. These reasons permit it to be considered adequate for routine analysis of organic acids in beverage samples.     

Screen-printed enzyme electrodes for the detection of marker analytes during winemaking

Biosensors for malic acid and glucose have been developed, using screen-printed electrodes and two different classes of enzymes: NAD(P)⁺-dependent dehydrogenases and oxidases. The active surface of the electrodes was modified using Meldola Blue (malic acid) and Prussian Blue (glucose) and in this way sensitive, low cost and reliable NAD(P)H and H₂O₂ probes were obtained. Fixed potential amperometry was used for the detection of substrates in small volumes of sample (50 μl). Immobilization of the enzymes in a polyethylenimine-glutaraldehyde cross-linking membrane allowed sensors to be obtained with sufficient operational stability. The detection limits were of 10⁻⁵ M for malic acid and 10⁻⁶ M for glucose. The sensors were applied in the analysis of different samples of wine.     

Systematic investigation on new SrCo1−yNbyO3−δ ceramic membranes with high oxygen semi-permeability

SrCo_1−yNb_yO_3−δ (y = 0.025–0.4) were synthesized for oxygen separation application. The crystal structure, phase stability, oxygen nonstoichiometry, electrical conductivity, and oxygen permeability of the oxides were systematically investigated. Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y = 0.025–0.2. However, the further increase in niobium concentration led to the formation of impurity phase. The niobium doping concentration also had a significant effect on electrical conductivity and oxygen permeability of the membranes. SrCo_0.9Nb_0.1O_3−δ exhibited the highest electrical conductivity and oxygen permeability among the others. It reached a permeation flux of ∼2.80 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C for a 1.0-mm membrane under an air/helium oxygen gradient. The further investigation demonstrated the oxygen permeation process was mainly rate-limited by the oxygen bulk diffusion process.