Polyesters from bisacid A2. Electrical properties of glass fiber laminates

The preparation and purification of bisacid A2, the preparation of crosslinkable polyesters from bisacid A2, and some of the properties of the resulting resins and laminates have been reported in earlier communications.^1–7 This paper reports the surface and volume resistivities of laminates according to B.S. 2782 as well as their dielectric loss and permittivity at 23°C over a frequency range of about 9 decades and discusses the significance of the results.     

The stability of solutions in reactive monomers of crosslinkable polyesters containing bisacid A2

Earlier papers^1–6 have dealt with the synthesis and purification of bisacid A2; the preparation of unsaturated polyesters by cocondensing bisacid A2 with maleic anhydride in varying proportions in the presence or absence of phthalic anhydride as a further modifying acid, using propylene glycol as the polyesterification diol; the hardness and the thermal and mechanical properties of cast, cured resins and glass fiber-reinforced laminates; and the water and chemical resistance of the cured resins. This paper deals with the solution stability of the liquid resins prior to cure and, in particular, with the observed fact that solutions containing esters of bisacid A2 in sufficient quantity do not require the addition of stabilizers commonly needed for commercial polyesters in order to impart an acceptable shelf life to the liquid resins.     

Superabsorbent polymeric materials. I. Swelling behaviors of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) in aqueous salt solution

A series of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) based on sodium acrylate (SA), 2-hydroxyethyl methacrylate (HEMA), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The resultant crosslinking polymers are xerogellants. This work investigates not only the absorbency or swelling behavior for these xerogellants composed of different ratios of HEMA/SA in water, but also the effects of various salts and pH values on the swelling properties. Experimental results indicate that the absorbency in deionized water decreases with an increase in the HEMA in copolymeric gel, which is related to the degree of expansion of the network and the strength of the hydrophilic group. The absorbency in the chloride salt solutions decreases with an increase in the salt concentration (swelling is 50 times for the IA group chloride salt solutions, but is less than 5 times for the IIA group salt solution), owing to the osmosis of water and ions between the polymeric gel and the external solution. A decrease in the extent of swelling occurs for divalent and trivalent chloride salt solutions. For the salt solutions of the same ionic strength, the swelling amount has the following tendency: LiCl(aq) = NaCl(aq) = KCl(aq), CaCl₂(aq) < SrCl₂(aq) < BaCl₂(aq), and Fe³⁺ > Ca²⁺ > Zn²⁺ > Cu²⁺. These orders are related to the complexing ability between metallic cations and the carboxylate group in the polymeric chains. Finally, the adsorption of ferric ion by these gels is also investigated. © 1996 John Wiley & Sons, Inc.     

Thermal properties of unfilled cast cured sheets of polyesters based on bisacid A2

The synthesis of bisacid A2 in a high state of purity, the preparation of unsaturated copolyesters therefrom, the preparation of solutions of the latter in suitable monomers, followed by casting of those solutions after addition of catalysts and curing of the material to obtain crosslinked polyester sheet, has been described in earlier communications.^1–3 This paper deals with the heat distortion temperatures⁴ and the (modified) Vicat softening points⁵ of the cast sheets of various copolyesters at various monomer contents.     

Separation and characterization of the vinyl side chains from grafted polyacrylonitrile–cotton copolymers

A method of separation of polyvinyl side chains from grafted polyacrylonitrile–cotton copolymers was developed in order to study the effect of length of side chain on copolymer properties. The method consists of dispersion of the copolymer (1 g.) containing 20% polyacrylonitrile in 75% aq. ZnCl₂ (100 ml.), addition of 6N HCl (100 ml.), heating for 1 hr. at 100°C., and precipitation and purification of the resulting vinyl polymer. The effect of hydrolysis on the intrinsic viscosity, the nitrogen content, and the infrared absorption spectra of the polyacrylonitrile polymers was investigated. It was concluded that this method of separation of the grafted polymers permitted a comparison of samples grafted by various techniques. A series of grafted copolymers was hydrolyzed, and the molecular weights of the isolated products were determined by measurements of intrinsic viscosity. Copolymer samples prepared by a post-irradiation grafting technique had the longest polyacrylonitrile side chains (molecular weight, 1 × 10⁶). Samples grafted by a simultaneous irradiation technique varied in side-chain length, depending upon the monomer-solvent system used in the preparation of the copolymer (molecular weight, 3 × 10⁴?5 × 10⁵). Chemically initiated grafting to cotton resulted in a copolymer containing relatively short side chains (molecular weight, 9 × 10⁴).     

Effect of the third acrylated vinyl comonomer on absorption and desorption properties of styrene–divinylbenzene–alkyl acrylate terpolymers,imbibing solvent on a water surface

A series of imbiber terpolymer beads was prepared by radical suspension copolymerization of styrene–divinylbenzene with varied contents of acrylated vinyl monomers, n‐butyl acrylate and 2‐ethyl hexyl acrylate, as the third comonomer. A DVB content of 6 wt % and a mixture of 60/40 wt % toluene/n‐heptane as the diluent were used throughout this study. The influence of acrylated vinyl comonomers on bead properties and swelling properties was investigated. The imbiber beads are capable of absorption and desorption of organic solvents having solubility parameters in the range of 14.9–20.9 (MPa)^1/2. Styrenic imbiber beads were swelled in a toluene/n‐heptane mixture of 50% by volume and the kinetics of absorption was studied. The imbiber beads could absorb the toluene/n‐heptane mixture completely within 20 min and yielded a maximum swelling ratio of 6.8. The diffusion coefficient values of these beads were in the range of 6.40 × 10⁻⁶ to 1.52 × 10⁻⁵ cm² s⁻¹. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 504–516, 2001     

Synthesis and Spectral Properties of Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-Doped Sodium Silicophosphate Glass

Combined UV-visible and FTIR spectral studies of undoped and Nd₂O₃ –doped sodium silicophosphate glasses were carried out to characterize the optical and structural properties of such glasses. The base undoped silicophosphate glass exhibits strong UV absorption which is due to the presence of unavoidable trace iron impurities (mainly Fe³⁺ ions) present contaminated within the raw materials used for the preparation of such glasses. Nd₂O₃ –doped glasses show characteristic absorption bands extending in the entire visible region which are attributed to the contribution of Nd³⁺ ions with distinct peaks which are almost constant with the increase of dopant. This comes from the combined compact glass structure containing two glass forming units and the shielding of the rare-earth ions. Infrared absorption spectra of the studied glasses reveal characteristic IR bands due to the combination of both silicate and phosphate groups. The introduction of Nd₂O₃ within the dopant level (2 %) produces no variations in the IR vibrational bands due to the presence of the two structural silicate and phosphate groups giving compactness of the network structure. The deconvoluted spectra reveal the presence of phosphate groups in a slightly high ratio due to the high content of P₂O₅ in the composition.     

“Bishydrazid A2”: A new semiaromatic film and fiber-forming polymer based on bisacid A2

We report the preparation of the dihydrazide of bisacid A2 (“bisdihidrazide A2”). Its composition and structure have been verified by elemental analysis and by means of infrared and NMR spectra. This material was then converted into a polyhydrazide (“bishydrazid A2”) in an HCl-accepting solvent. The polymer was converted to fiber by wet spinning the dope obtained during the polycondensation reaction without prior neutralization or dilution. Film was cast from a solution of the precipitated and washed polymer which had an inherent viscosity of about 0.8; mechanical tests on the film—both before and after treatment with formic acid—were carried out. Differential scanning calorimetry showed an α/β transition comparable to that shown by bisacid A2 polyaramides and described in preceding papers^1,2. Wide-angle x-ray scattering showed that the polymer is amorphous. Scanning electron micrographs revealed the physical structure of wet-spun fiber and the probable mechanism of fiber formation by dope extrusion into a water bath.     

Influence of potassium humate on the swelling properties of a poly(acrylic acid‐co‐acrylamide)/ potassium humate superabsorbent composite

A novel superabsorbent composite, poly(acrylic acid‐co‐acrylamide)/potassium humate (PAA‐AM/KHA), was prepared by aqueous solution polymerization from acrylic acid, acrylamide, and potassium humate (KHA) with N,N′‐methylenebisacrylamide as a crosslinker and potassium peroxydisulfate as an initiator. The effects of incorporated KHA on the water absorbency, swelling rate, and reswelling capability were investigated. The swelling property of PAA‐AM/KHA in various saline solutions was studied systematically. The results show that the comprehensive properties and especially salt‐resistant ability of PAA‐AM/KHA were enhanced. There was a linear relationship between the saturated water absorbency and the minus square root of the ionic strength of the external medium, and the water absorbency of PAA‐AM/KHA in various salt solutions had the following order: NH₄Cl_(aq) = KCl_(aq) = NaCl_(aq) > MgCl_2(aq) > CaCl_2(aq) > AlCl_3(aq) > FeCl_3(aq). Moreover, the polymeric net structure of PAA‐AM/KHA was examined with respect to that of poly(acrylic acid‐co‐acrylamide). The results indicate that the polymeric net of PAA‐AM/KHA was improved by the introduction of a moderate amount of KHA into the superabsorbent composite and made more suitable for agriculture and horticulture applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Antimony Solubility and Speciation in Aqueous Sulphuric Acid Solutions at 298 K

This work is an experimental and theoretical study of antimony speciation and the solubility of Sb₂O₅, Sb₂O₃ and Sb₂(SO₄)₃ at 298 K in aqueous sulphuric acid solutions (0 to 6 kmol/m³). A thermodynamic model was developed to quantify the solubility products and aqueous metal speciation. Main dissolved species were H₃SbO_3(aq) and H₃SbO_4(aq). The solubility of antimony increases with increasing solution acidity and with the presence of hydrogen peroxide in the solution. The following standard equilibrium constants at 298 K were obtained: Log K⁰_(Sb2O5) = 11.7±0.5, Log K⁰_(Sb2O3) = 32±1, and Log K⁰_(Sb2(SO4)3) = 55±2.     

Characterization of metal (Ba, Al, Si, V, and W)-incorporated TiO2 and toluene photodecomposition in the presence of H2O

This study focused on toluene photodecomposition in the presence of H₂O over metal (Ba, Al, Si, V, and W)-incorporated TiO₂. The nanometer-sized, metal-TiO₂ photocatalyst samples, including Ba²⁺, Al³⁺, Si⁴⁺, V⁵⁺, and W⁶⁺ ions, were prepared by using the solvothermal method. The X-ray photoelectron spectroscopy (XPS) results showed that the Ti-OH peak, which indicates hydrophilicity, increased with increasing Al and Si ion components but decreased with increasing Ba, V, and W ion components. The contact angles were distributed over the range of 0–10° on almost all films (200-nm thick) after irradiation for 2 h, and in particular approached 0° on the Al-TiO₂ and Si-TiO₂ nanometer-sized films after just 30 min. The toluene (100 ppm) photodecomposition in the continuous system increased in the order of Al-TiO₂>Si-TiO₂>pure TiO₂>W-TiO₂>Ba-TiO₂>V-TiO₂, and the maximum toluene conversion rate achieved was 45% over Al-TiO₂ film after 120 min. The toluene conversion remarkably increased; however, over all photocatalysts, with H₂O addition during the toluene photo-decomposed reaction, and in particular, the conversion reached up to 90% after 120 min over Al-TiO₂ and Si-TiO₂ with increased hydrophilicity. After photoreaction for 24 h, minimal carbon was deposited on the photocatalyst under both reaction conditions, with and without H₂O addition, although the deposited carbon amounts were smaller for the former. These results confirmed that the hydrophilicity of the photocatalyst had a greater effect on toluene decomposition, while the photocatalytic deactivation could be retarded by H₂O supplementation during toluene decomposition.     

Comprehensive impedance model of cobalt deposition in sulfate solutions accounting for homogeneous reactions and adsorptive effects

A comprehensive physicochemical model for cobalt deposition onto a cobalt rotating disk electrode in sulfate-borate (pH 3) solutions is derived and statistically fit to experimental EIS spectra obtained over a range of CoSO₄ concentrations, overpotentials and rotation speeds. The model accounts for H⁺ and water reduction, homogeneous reactions and mass transport within the boundary layer. Based on a thermodynamic analysis, the species CoSO_4(aq), B(OH)_3(aq), B₃O₃(OH)₄⁻, H⁺ and OH⁻ and two homogeneous reactions (B(OH)_3(aq) hydrolysis and water dissociation) are included in the model. Kinetic and transport parameters are estimated by minimizing the sum-of-squares error between the model and experimental measurements using a simplex method. The electrode response is affected most strongly by parameters associated with the first step of Co(II) reduction, reflecting its control of the rate of Co deposition, and is moderately sensitive to the parameters for H⁺ reduction and the Co(II) diffusion coefficient. Water reduction is found not to occur to any significant extent under the conditions studied. These trends are consistent with that obtained by fitting equivalent electrical circuits to the experimental spectra. The simplest circuit that best fits the data consists of two RQ elements (resistor-constant phase element) in parallel or series with the solution resistance.     

Preparation,characterization and catalytic application of Barium molybdate (BaMoO4) and Barium tungstate (BaWO4) in the gas-phase oxidation of toluene

Barium molybdate and Barium tungstate are important materials due their photoluminescent properties and they also have catalysis and photocatalysis applications. In this work, powders of these compounds were prepared by microwave-assisted hydrothermal (MAH) method and polymeric precursor method (PPM) and their structural and optical properties were studied. Furthermore, these materials were employed as solid catalysts towards gas phase toluene oxidation reactions. X-ray diffraction confirms the purity of materials at both preparation methods and reveals a preferential growth when the powders are prepared by MAH due polymeric agents and processing using microwave, which was confirmed by Field emission scanning electron microscopy. Photoluminesce emission was attributed to the charge-transfer transitions within the [WO₄]^2- and [MoO₄]^2- complexes. The H₂ Temperature-Programmed Reduction (H₂-TPR), O₂-chemisorption and extended X-ray absorption fine structure (EXAFS) results indicated that BaWO₄ samples, compared with BaMoO₄ samples, have higher oxygen mobility and oxygen vacancies that appear as key factors for the achievement of better catalytic performances.     

Preparation and thermal shock resistance of corundum-mullite composite ceramics from andalusite

Corundum-mullite composite ceramics have high hardness, small plastic deformation and other excellent performances at high temperature. Corundum-mullite composite ceramics were fabricated from andalusite and α-Al₂O₃ by in-situ synthesis technology. Effects of mullite/corundum ratio and sintering temperatures on the water absorption, apparent porosity, bulk density, bending strength, thermal shock resistance, phase composition and microstructure of the sample were investigated. Results indicated that the in-situ synthesized mullite from andalusite combined with corundum satisfactorily, which significantly improved the thermal shock resistance as no crack formed after 30 cycles of thermal shock (1100 °C-room temperature, air cooling). Formula A4 (andalusite: 37.31 wt%, α-Al₂O₃: 62.69 wt%, TiO₂ in addition: 1 wt%, mullite: corundum=6:4 in wt%) achieved the optimum properties when sintering at 1650 °C, which were listed as follows: water absorption of 0.15%, apparent porosity of 0.42%, and bulk density of 3.21 g⋅cm⁻³, bending strength of 117.32 MPa. The phase composition of the sintered samples before and after thermal shock tests were mullite and corundum constantly. The fracture modes of the crystals were transgranular and intergranular fractures, which could endow the samples with high thermal shock resistance.     

Secondary Isotope Effects Part IV Complex Formation Between Aromatic Hydrocarbons and HCl,

The isotope effects on complex formation between HCl and variously deuterated benzenes and toluenes have been measured at ?80°C, using a differential solubility technique. Both methyl and nuclear deuteration increase the basicity of the hydrocarbon, the two effects being additive in toluene. All the results can be fit with values of: δ F_M^° = ?3.1₅^? cal / g. atom D for methyl deuteration of toluene, and δ F_N^° = ?3.5₆^? cal/g. atom D for nuclear deuteration of either benzene or toluene. The implications of these results for the theory of secondary isotope effects are discussed.     

Structure,morphology, thermal,and sorption characteristics of epoxidized natural rubber conjugated spent coffee via one-pot synthesis

The present work highlights the preparation of the epoxidized natural rubber conjugated spent coffee biocomposites (ENR-g-SC) via one-pot synthesis to control petroleum oil spills. The structural determination of the spent coffee grafted epoxidized natural rubber (ENR-g-SC) was confirmed through FTIR and ¹H-NMR spectroscopic analyses. The thermal performance, tensile tests, and morphological properties of the synthesized (ENR-g-SC) biocomposites were performed. The data revealed that ENR-g-SC biocomposite with 20 phr of spent coffee (SC) exhibited the highest tensile properties due to maximal chemical linkages of spent coffee and epoxide groups in ENR. The epoxidized natural rubber conjugated spent coffee copolymers were evaluated as oil sorbers for oil absorbency applications in chloroform, toluene, and 10% crude petroleum diluted with toluene. The data revealed that the oil absorbency increased slightly with chloroform or toluene instead of 10% crude oil diluted with toluene. Furthermore, swelling and network parameters including the maximum oil absorbency (Q_max), swelling rate constant (k), polymer-solvent interaction (χ), effective crosslink density (ύe), equilibrium modulus of elasticity (G_T), and average molecular weight between crosslinks (M_c) and theoretical crosslink density (ύ_t) were determined, and correlated to the efficiency of the synthesized epoxidized natural rubber conjugated spent coffee.     

THE EFFECTS OF A MULTIFUNCTIONAL ADDITIVE ON CURING CHARACTERISTICS,MECHANICAL PROPERTIES,AND SWELLING BEHAVIOR OF NATURAL RUBBER/POLYCHLOROPRENE RUBBER BLENDS

The effects of a diamine salt of fatty acid of general structure [RNH₂ ⁺[CH₂)₃NH⁺] [R′COO^?]₂ referred to as a multifunctional additive (MFA) on curing characteristics and mechanical properties and swelling behavior of natural rubber (SMR L) and polychloroprene (CR) rubber blends were studied. Compared to SMR L/CR blends without MFA, the incorporation of 2 phr (parts per hundred parts of rubber) of MFA in the blends increased mechanical properties, i.e., tensile strength, tensile modulus and hardness, and improved swelling resistance toward toluene and ASTM oil No. 1. However the scorch time, t ₅ and cure index, Δt _L decrease with incorporation of MFA into the blends.     

Antioxidants from a heated histidine-glucose model system. I: Investigation of the antioxidant role of histidine and isolation of antioxidants by high-performance liquid chromatography

The radical-combining activity of Maillard reaction products [MRP_(aq)], produced by heating d-glucose and l-histidine (3:1) in a 0.1 M phosphate buffer for 10 h at 105°C (final pH 6.53), was estimated directly by means of a diphenylpicrylhydrazyl radical (DPPH^·) method. Additionally, the indirect methods of peroxide values changes (oven test), hexanal formation, and protection factors (Rancimat method) were determined on a lipid model system that consisted of sunflower seed oil/water (1:2), emulsified with 3% (w/w) Tween 40. Results from the DPPH^· method showed a potential antioxidant activity of MRP_(aq), which was confirmed by the indirect methods. Surprisingly, histidine in solution alone (heated or not) exhibited an antioxidant activity greater than or similar to the MRP_(aq) activity in the indirect methods with the lipid model system, in contrast to the results from the DPPH^· method. The suitability of various solvents for extraction of potential antioxidant compounds from freeze-dried MRP_(aq) was examined, and ethanol extracts showed the greatest activity by the DPPH^· method. Consequently, the ethanol extract of freeze-dried MRP_(aq) was separated by means of preparative reverse-phase high-performance liquid chromatography (HPLC) with a 0.05 M phosphate buffer (pH 4.4)/water/acetonitrile gradient system. The antioxidant activity of the eluate was measured through the DPPH^· method, and a fraction (Fraction A) with antiradical activity was further purified by preparative HPLC. Fraction B was collected, and its freeze-dried residue exhibited potent antiradical activity, significantly greater than that of the same level of n-propyl gallate.     

Sintering behaviour and characterisation of low-cost ceramic foams from coal gangue and waste quartz sand

New ceramic foams have been successfully synthesised with coal gangue and waste quartz sand, which supply a feasible way to recycle these hazardous solid wastes. An objective of this research was to investigate the sintering behaviour and effects of sintering conditions on the crystalline phase change, microstructure and main properties of final ceramic foams. Good correlations among porosity, thermal conductivity, water absorption, bulk density, mechanical properties were studied. Results indicated that increasing sintering temperature or time had similar effects on the physical–mechanical properties. Samples sintering at 1140°C for 1 hour exhibited the highest porosity (87.5%), lowest bulk density (0.39?×?10^?3?kg?m^?3), lowest thermal conductivity (0.085?W·(m?K)^?1), moderate water absorption (9.38%) and adequate flexible strength (2.4?MPa). Combined with excellent properties and low-cost characteristics, the new development for ceramic foams preparation will be widely used in building insulation materials for no-load bearing walls.     

Acrylonitrile graft copolymerization of casein proteins for enhanced solubility and thermal properties

Casein proteins are soluble in 5% aq. ethanolamine, triehtylamine, and triethanolamine, but insoluble in organic solvents. Graft copolymerization of casein (40 g/L) with acrylonitrile (AN) was carried out in 5% w/v aq. triethanolamine at 60°C using potassium persulfate K₂S₂O₈ as an initiator. Percent grafting and grafting efficiency increased with increasing initiator concentrations (up to 1.7 × 10⁻² mole L⁻¹) and reaction times, but decreasing [M]/[I] ratios. Fourier transform IR spectra confirmed the formation of the acrylonitrile‐grafted‐casein (AN‐g‐casein) copolymers. Under the reaction conditions studied, the grafted PAN side chains were characterized by gel permeation chromatography to have M_n between 1.58 and 5.88 × 10⁴ dalton and polydispersities between 2.6 and 4.5. The AN‐g‐casein copolymers behaved more like a PAN homopolymer in terms of their thermal properties and solubilities. The decomposition temperatures of AN‐g‐casein copolymers were between 255 and 273°C, closer to the T_d of the PAN homopolymer (275°C) and significantly higher than that of casein (180°C). The AN‐g‐casein copolymers are soluble in 50% aq. NaSCN and ZnCl₂, but are insoluble in 32:28:40 wt % CaCl₂/CH₃CH₂OH/H₂O like PAN and dimethylformamide‐like casein. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2543–2551, 2000