Thermal stability of end‐capped and linear sulfonated polyimides,sulfonated polystyrene,and Nafion 117

The thermal stability of end‐caped and linear sulfonated polyimides (SPIs), sulfonated polystyrene (SPS), and a sulfonated perfluorinated hydrocarbon, Nafion 117, and the corresponding triethylammonium sulfonate salts was investigated by dynamic and isothermal thermogravimetric analysis (TGA). Gas chromatographic‐mass spectrographic analysis (GC/MS) of the sulfonated polymers and the salts to determine the volatiles released from acid and salt groups over a temperature range 200–275 °C was also investigated. GC/MS analysis reveals that water and sulfur dioxide volatiles are released from the sulfonic acids and water, sulfur dioxide and triethyl amine are released from the sulfonate salts. Dynamic and isothermal TGA studies based on weight loss revealed that the SPIs exhibited superior thermal stability than SPS and Nafion 117 sulfonic acids. However, dynamic TGA curves to determine the onset decomposition temperature of the sulfonic acid group reveal that Nafion 117 and SPS sulfonic acids exhibited greater thermal stabilities than the SPIs. The mechanisms of sulfonic acid and triethylammonium sulfonate salt decompositions based on GC/MS, ¹³C‐NMR, and dynamic TGA curves are proposed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45694.     

Sorption phenomena in nafion membranes

Sorption phenomena of water and aqueous salt solutions by a perfluorinated polymer containing sulfonic acid groups (Nafion) were investigated. The temperature and concentration dependencies of the sorption by the membranes in the acid and salt forms were studied. The apparent activation energies for the diffusion of water in the H-form membrane and in the K-salt form were obtained as 4.9 and ca. 13.0 kcal/mole, respectively. The sorption kinetics during the neutralization of the membranes were observed in several aqueous solutions. A maximum in the sorption curve during the neutralization process was found and explained as resulting from the differences in the diffusion coefficients of water and of the cations and from the different number of water molecules absorbed by a SOH⁺ (acid) site and a neutralized site. The diffusion coefficients D of several cations (K⁺, Cs⁺, Ba²⁺, and Ca²⁺) were determined and found to be considerably smaller than that of water. For the various cations, log D was related linearly to q/a, where q is the cation charge and a is the separation between centers of charge of the cation and anion. The dependence of water sorption upon the degree of neutralization of the membrane was also studied at room temperature. It was observed that for membranes of a low degree of neutralization a secondary sorption process existed, while no such secondary sorption could be found for the pure acid or the highly neutralized membranes. This secondary sorption was attributed to a structural rearrangement in the polymer. The apparent diffusion coefficient of water and the number of water molecules absorbed at equilibrium by an ionic site, n_s, were obtained as a function of the degree of neutralization. The diffusion coefficient of water was dependent strongly on both the degree of neutralization and type of the salt, but no quantitative relation could be established. For all the salts studied in this paper, n_s was linearly related to the degree of neutralization, x, supporting the assumption that the value of n_s could be divided into those water molecules absorbed by an SOH⁺ (acid) site, n_h, and those absorbed by a neutralized site, n_m. It was found that the value of q × n_m had a strong correlation with a characteristic constant of the cations since a plot of q × n_s versus log (q/r) yielded a straight line (r being the radius of the cation).     

Preparation and testing of Nafion/titanium dioxide nanocomposite membrane electrode assembly by ultrasonic coating technique

Membrane electrode assemblies with Nafion/nanosize titanium dioxide (TiO₂) composite membranes were manufactured with a novel ultrasonic‐spray technique (UST) and tested in proton exchange membrane fuel cell (PEMFC). The structures of the membranes were investigated by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and thermogravimetric analysis. The composite membranes gained good thermal resistance with insertion of TiO₂. The SEM and XRD techniques have proved the uniform and homogeneous distribution of TiO₂ and the consequent enhancement of crystalline character of these membranes. The existence of nanometer size TiO₂ has improved the thermal resistance, water uptake, and proton conductivity of composite membranes. Gas diffusion electrodes were fabricated by UST. Catalyst loading was 0.4 (mg Pt) cm^?2 for both anode and cathode sides. The membranes were tested in a single cell with a 5 cm² active area operating at the temperature range of 70°C to 110°C and in humidified under 50% relative humidity (RH) conditions. Single PEMFC tests performed at different operating temperatures indicated that Nafion/TiO₂ composite membrane is more stable and also performed better than Nafion membranes. The results show that Nafion/TiO₂ is a promising membrane material for possible use in PEMFC at higher temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40541.     

Green Chemicals from d-glucose: Systematic Studies on Catalytic Effects of Inorganic Salts on the Chemo-Selectivity and Yield in Aqueous Solutions

The use of inorganic salts as catalysts for the reactions of d-glucose in aqueous solutions in a batch reactor is reported. The type of salt and effect of reaction time were examined in detail at a fixed salt (5 mM) and d-glucose concentration (0.1 M) and at a temperature of 140 °C. Al(III) and Cr(II) salts gave the highest conversion of d-glucose. Typical reaction products were organic acids like lactic acid, levulinic acid, furanics like hydroxymethylfurfural and insoluble products (humins). The chemo-selectivity is a clear function of the type of inorganic salt. For Al(III), the major water soluble product was lactic acid, for Zn(II) HMF was formed in the highest yields. A reaction scheme is proposed to explain the observed product compositions.     

Temperature dependence of diffusion of a disperse dye in the multiple layers of nylon fabric

The apparent diffusion coefficients of a disperse dye in the multiple layers of nylon fabric at 45-75°C are determined as the dyeing model of the textile assembly. The modified pore model is introduced to explain the diffusion behavior in the multiple fabric. The Arrhenius plot of the diffusion coefficient of dye in the spaces or pores of nylon fabric gave a straight line and the activation energy of diffusion was about 9.4 kcal/mol. The temperature dependence of the dye diffusivity in polymer matrix was quantitatively described by a WLF-type relation, where a_T is a shift factor of diffusion and T_s is the reference temperature.     

The effect of temperature on limiting current density and mass transfer in electrodialysis

This study focuses on a high-temperature operation in electrodialysis of salt solutions and studies the effect of temperature on limiting current density and mass transfer. Experiments were conducted under various conditions of temperature (T), varying from 15 to 90°C; of dialysate concentration (C_d), varying from 5 × 10^?3 to 3 × 10^?2M ; and of dialysate velocity (u_d), varying from 0.206 to 2.44 cm s^?1. A least squares fitting of the experimental data on limiting current density (I_lim) yields an Arrhenius equation as follows: The molar flux N? (mol cm^?2 s^?1), initial concentration (C₀; M ) and temperature (T; °C) were found to have the following relationship: N?/C₀ is slightly increased with increasing temperature ranging from 25 to 70°C.     

Silicate and zirconium phosphate modified Nafion/PTFE composite membranes for high temperature PEMFC

The PEMFC performance of MEAs prepared from Nafion-212 (thickness 50 μm, Du Pont Co), porous poly(tetrafluoro ethylene) (PTFE, thickness 15 ~ 18 μm) film reinforced Nafion (NF, thickness 20 ± 2 μm), silicate hybridized NF (NF-Si, thickness 21 ± 2 μm), and zirconium phosphate hybridized NF (NF-Zr, thickness 21 ± 2 μm) membranes were investigated at 110 °C/ 51.7% RH, 120 °C/ 38.2% RH, and 130 °C/ 28.6% RH. We show PEMFC performances of these MEAs decrease in the sequence of: NF-Zr> NF-Si> NF> Nafion-212. The NF, NF-Si, and NF-Zr membranes have lower membrane thickness and lower Nafion content and require less water for proton transport than Nafion-212 at temperatures above 110 °C, and thus have higher conductivity and better PEMFC performance than Nafion-212. Incorporating silicate and zirconium phosphate into NF membranes enhances water retention of membranes at temperatures above 110 °C and improves PEMFC performances. Besides enhancing water retention, incorporating zirconium phosphate into membranes also provides more routes for proton transport via H⁺ exchange between H₃ ⁺O and HPO₄-Zr- and between H₂ ⁺PO₄-Zr- and HPO₄-Zr-. Thus NF-Zr has a higher conductivity and better PEMFC performance than NF and NF-Si.     

The state of water in swollen ionomers containing sulfonic acid salts

The proton magnetic resonance relaxation times and heat capacity of water in perfluoroethylene sulfonic acid (Nafion), chlorosulfonated polyethylene (SPE), and sulfonated polysulfone (SPS) were measured as a function of temperature. Only the relaxation data for water present in Nafion conformed to the BPP model. The data indicate that the presence of fine pores, ～12 Å in diameter, causes water–surface interactions to play a significant role. For materials with the same pore size, a difference in spin-lattice relaxation time T₁ may be correlated to the Flory–Huggins parameter χ calculated for the interaction of water with the neutral portion of the polymer backbone. Only a part of the water present in Nafion and SPE undergoes freezing, while no transition was observed for water in SPS for temperatures down to ?60°C. For Nafion and SPE, the heat of fusion ΔH_f calculated from combined FID data and the DSC study was ?20 cal/g.     

Continuous Hydrolysis of Cuphea Seed Oil in Subcritical Water

Cuphea seed oil (CSO) is a source of decanoic acid which is useful in the preparation of estolide lubricants among other applications. Decanoic acid and other free fatty acids (FFA) can be hydrolyzed from CSO using a catalyst like KOH, followed by neutralization with HCl and extraction with hexane. This procedure, however, uses caustic materials, hazardous solvents and generates waste salt streams. This study investigated the use of water without catalysts to hydrolyze CSO in a continuous flow tubular reactor. Parameters such as the interaction of pressure and temperature, temperature, water to cuphea oil fatty acid residue (H₂O:COFAR) molar ratio, and flow rate were examined. The lowest conversions of CSO to FFA were at the lowest temperature (i.e., 300 °C) and the hydrolysis was ca. 90% at 350 °C and 13.8 MPa and ca. 80% at 365 °C and 13.8 MPa. Hydrolysis increased with pressure and leveled off at 13.8 MPa. Hydrolysis increased with temperature and leveled off at ca. 330 °C. The optimal H₂O:COFAR molar ratio was found to be 6:1. Conversion rates were inversely proportional to flow rate with 95% conversion at the lowest flow rate (i.e., 0.25 mL/min) corresponding to the longest residence time (i.e., ca. 45.2 min). These results demonstrate a continuous subcritical water process for hydrolyzing CSO to FFA that is effective, requires no catalysts and does not generate a waste salt stream.     

Dynamic mechanical properties of polystyrene-polydimethylsiloxane blends

It was found that commercial silicone grease incorporated accidentally into polystyrene bars yields a major dynamic mechanical loss peak at ca. ?128°C. This finding was followed up with a study of various polydimethylsiloxanes and silicone rubber, in which up to three peaks were found. In order of increasing temperature (at 1 Hz) these are the glass transition (T_g; ca. ?128°C), crystallization (T_c; ca. ?110°C) and melting peaks (T_m; ca. ?50°C). Hydrocarbon-based greases were also investigated. The results indicate that the methods employed may be of use for the investigation of the dynamic mechanical properties of small amounts of material of varying particle sizes, such as powders of cross-linked polymers, that need not be compatible with, or soluble in, the host matrix. The sensitivity of the method is such at a 1 percent by weight contamination of silicone grease in polystyrene gives a loss tangent peak of at least 0.002 above background, and emphasizes the necessary care to be taken during sample preparation to exclude unwanted substances.     

Experimental Study of the Salt Effect in Vapor/Liquid Equilibria Using Headspace Gas Chromatography

The salt effect on vapor/liquid equilibrium for an ethanol/water system was studied at 70 °C using the Headspace Gas Chromatography technique. The azeotropic point of the system was eliminated in the presence of the salts studied. All the salts investigated in this work exhibited a salting out effect which followed the order of NH₄Cl > NaCl > CaCl₂ and which increased with increasing salt concentration. Good agreement with Furter's equation was observed for the experimental data with unsaturated NaCl salt. The salt effect parameter, determined from Furter's equation, was found to be a function of the liquid concentration.     

Sillimanite‐mullite transformation observed in synchrotron X‐ray diffraction experiments

High‐resolution synchrotron powder X‐ray diffraction (XRD) experiments were conducted to clarify the transformation of sillimanite to mullite (mullitization) and determine the mullitization temperature (T_c). We were able to distinguish sillimanite and mullite in the XRD patterns, despite their very similar crystallographic parameters, and to detect the appearance of small mullite peaks among sillimanite peaks. Analysis of the Johnson‐Mehl‐Avrami (JMA) equation for mullitization ratio (ζ) revealed that at temperatures T≥1240°C the mullitization had the same kinetics. The activation energy E at T≥1240°C obtained from the Arrhenius plot was 679.8 kJ mol^?1. In analysis using a time‐temperature‐transformation diagram for mullitization, a mullitization curve of ζ=1% can be described as where t is time, n is a reaction‐mechanism‐dependent parameter determined as 0.324 by JMA‐analysis, k₀ is the frequency factor, E_A is the activation energy for atomic diffusion, and represents the activation energy for nucleation. The results of fitting the data to this equation were T_c=1199°C, A=3.9×10⁶ kJ mol^?1 K^?2, E_A=605 kJ mol^?1, and k₀=3.65×10¹⁵. We conclude that the boundary between sillimanite and mullite+SiO₂ in the phase diagram is ~1200°C.     

Hot-Air Drying and Rehydration Characteristics of Red Kidney Bean Seeds

The effects of pretreatments such as citric acid and hot water blanching and air temperature on drying and rehydration characteristics of red kidney bean seeds were investigated. Drying experiments were carried out at four different drying air temperatures of 50°C, 60°C, 70°C, and 80°C. It was observed that drying and rehydration characteristics of bean seeds were greatly influenced by air temperatures and pretreatments. Four commonly used mathematical models were evaluated to predict the drying kinetics of bean seeds. The Weibull model described the drying behaviour of bean seeds at all temperatures better than the other models. The effective moisture diffusivities (D_eff) of bean seeds were determined using Fick's law of diffusion. The values of D_eff were between 1.25 × 10^?9 and 3.58 × 10^?9 m²/s. Activation energy was estimated by an Arrhenius-type equation and was determined as 24.62, 21.06, and 20.36 kJ/mol for citric acid, blanch, and control samples, respectively.     

Humid aging of polyetherimide. I. Water sorption characteristics

The sorption and desorption kinetics of water into polyetherimide (ULTEM 1000) were studied at various temperatures ranging from 20 to 100°C. The water equilibrium concentration increases slightly with temperature from 1.39% (by weight) at 20°C to 1.50% at 100°C. The solubility coefficient, S, calculated from these data, and the water vapor pressure decrease with temperature. The calculated heat of dissolution H_s is close to −43 kJ mol⁻¹, which explains the low effect of temperature on the equilibrium concentration. The diffusion coefficient, D, varies from about 1.10⁻¹² m² · s⁻¹ at 20°C to about 16.10⁻¹² m² · s⁻¹ at 100°C. The apparent activation energy of diffusion, E_D, and the heat of dissolution, H_s, of water in the polymer have opposite values (respectively, +43 and −42 kJ · mol⁻¹). From this observation and a comparison of these data with water diffusion characteristics in other glassy polar polymers, it is hypothesized that the transport rate of water is kinetically controlled by the dissociation of water–polymer complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1439–1444, 2000     

The limiting pressure-velocity (PV) of plastics under unlubricated sliding

The limiting pressure-velocity (PV) of plastics materials under normal contacting pressure P and sliding velocity V when the sliding goes on continuously unlubricated has been discussed theoretically in this study. The sliding friction tests between the rotating edge of a hollow cylinder against a stationary metal surface were carried out in room air and when the metals were cooled with circulating water. The results obtained were as follows:

• The relation between PV_max and the critical temperature τ_bmax of the surface above which ordinary frictional conditions are not maintained may be represented by the following formula, Where C = Hn/μk, and H is the mean total heat conductivity between materials and environment in cal/cm². °C · s, n the area ratio of heat radiation surface to frictional surface, μ the kinetic frictional coefficient, k the thermal equivalent of frictional work in cal/kg · cm · s, and τ_a the cooling or environment temperature.
• The value of C ranges from 1 to 10 in cal/kg · cm s · °C, and the value of PV_max from 45 to 750 in kg/cm² · cm/s under prevailing room temperature air cooling in this experiment, however, the value of C has been increased about 2.3 times as much as those values by circulating water of 2°C around the lower side of the test piece.

     

Influence of cure treatment on extent of reaction and glassy modulus for BADGE‐DDM epoxy resin

The extent of conversion of epoxy groups cured with diaminodiphenyl methane, a diamine, at 100°C was approximately 100%, and the glass‐transition temperature (T) was found to be an increasing function of cure time with very large increases with extended postcure treatments at 180°C. However, this considerable increase in the T_g with postcure at 180°C was not due to the reactions of epoxy and amine groups. The specific volume reduced with the T_g to a minimum at 103° for the cured samples but showed a very slight increase with the T_g for the postcured samples. It was also found that the glassy modulus (E_g) was a linear decreasing function of the T_g. There were two separate relationships between the E_g and the rubbery modulus that depended on the cure conditions and suggested that the “structure” formed due to cure at a temperature of 100°C was different than that at postcure, which was 180°C. The most sensitive structural parameter for these cured epoxy resins was their T. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1265–1276, 2001     

Nafion®—titania nanocomposite proton exchange membranes

Proton exchange membranes consisting of Nafion^® and crystallized titania nanoparticles have been developed to improve water‐retention and proton conductivity at elevated temperature and low relative humidity. The anatase‐type titania nanoparticles were synthesized in situ in Nafion solution through sol–gel process and the size of the formed titiania nanoparticles is in the range of 3–6 nm. The formed nanoparticles are well‐dispersed in Nafion solution at the titania concentration of 5 wt %. The glass transition temperature of the formed Nafion‐titania composite membrane is about 20^oC higher than that of plain Nafion membrane. At elevated temperature (above 100°C), the Nafion‐titania nanocomposite membrane shows higher water uptake ability and improved proton conductivity compared to pure Nafion membrane. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Predicting the compressive properties of rigid urethane foam

The classic equation¹ in use throughout the urethane industry to predict the compressive properties of rigid foams is ((1)) The value of K and a need to be determined experimentally for each foam system at a given temperature. By evaluating the compressive properties of 14 different rigid urethane foams, a was defined as 1.75 for all materials at all test temperatures. General equations for predicting the foam's compressive properties over a temperature range of ?65° to 325°F (?54° to 204°C) were then developed. These general equations appear to be reasonably accurate in predicting the compressive properties of any rigid urethane at any temperature up to the foam's softening point. The equations are of the form shown above with K being a function of temperature only. Finally, the K term was defined as a function of temperature. The equations developed for predicting the compressive strength and modulus of the rigid urethane foams are: ((2)) for T equal to or greater than 77°F (25°C), and ((3)) for T equal to or greater than ?65°F (?54°C), where the compressive strength and modulus are in pounds per square inch and density is pounds per cubic foot. These equations are valid up to the softening point of the foam.     

Dissolution of ferritic stainless steel scrap in hydrochloric acid

The dissolution of a ferritic stainless steel (15.44% Cr, 0.39% Mn, 0.12% C) in hydrochloric acid has been investigated from the point of view of large scale processing. Over the range of experimental conditions employed, the rate of dissolution at 80.5°C can be represented by the equation: where [MCl₂] is the total molar concentration of divalent metal chlorides in the acid solution. The rate of dissolution is not influenced by the degree of agitation. The apparent activation energy is 21.6 K. cal. mole^?1.     

Yield stress and flow measurements in ABA block copolymer melts

A parallel-plate constant-stress rheometer is used to measure the yield stress τ_y, and the post-yield flow curve T(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}), where τ is shear stress and \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} is shear rate, for microphase-separated triblock copolymer melts. Five polymer samples, all styrene-butadiene-styrene but with differing composition ratios and molecular weights, are tested at 125°C. Specimens are prepared by casting sheets from solutions made with different solvents. The τ(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}) is found usually to be sigmoidal, for the range 10^?5 < \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} < 10^?3 s^?1, representing different stages of microstructural degradation in flow. Measurements indicate that a true τ_y exists, with values in the range 100 < τ_y < 500 Pa for these melts. A general trend is detected for τ_y to decrease as the casting solvent solubility parameter increases. A scheme for correlating the dependence of τ_y, on composition and molecular weight is proposed for the various polymers. For selected samples, the effect of mechanical history (sequence of stress application) and a temperature variation that crosses T_s (110 to 150°C) are also explored.