Simple dilatometer for polymer density and thermal expansivity measurements

A dilatometer is described to study the temperature dependence of density (ρ) of solid and semiliquid polymers and the following linear relations have been established. Atactic poly(vinylisobutyl ether) (25–90°C): ρ = 0.9166 ? 7.15 × 10^?4 × T. Isotactic poly(vinylisobutyl ether) (25–70°C): ρ = 0.9184 ? 7.13 × 10^?4 × T. Poly(n-butyl methacrylate) (90–150°C): ρ = 1.0622 ? 8.41 × 10^?4 × T. Poly(dimethyl siloxane) (30–51°C, using Lipkins pycnometer): ρ = 0.9846 ? 8.81 × 10^?4 × T; where ρ is in g.cm^?3, temperature T is in Celsius, and the linearity correlation coefficient r is better than 0.9998. Their volume–temperature plots are also linear. As the plots of polyn-butyl methacrylate curved slightly near its glass transition (20°C), the quadratic equation ρ = 1.0402 ? 4.79 × 10^?4 × T ? 1.46 × 10^?6 × T² (standard deviation = 1.57 × 10^?3) has been suggested for the entire range of 30–150°C scrutinized in this study. The data have been utilized to derive thermal expansivity and some equation-of-state parameters of the polymers at the reference temperature (ca. 20°C).     

The rate of selenium removal from tellurium by hydrogen purging

The reaction between hydrogen gas and selenium dissolved in liquid tellurium is described as follows H₂(g) + Se ? H₂Se(g) The kinetics of this reaction have been investigated at temperatures ranging between 525 and 625°C and at concentrations of selenium varying between 250 and 3,300 ppm. Under all conditions investigated the reaction was controlled by transport processes in one or other of the two phases depending on the relative values of the mass transfer coefficients. Subject to the assumption that the solution of selenium in tellurium is an ideal one the molecular diffusion coefficient of mixtures of hydrogen selenide in hydrogen, Dg, is approximately 1.6 cm.² sec.^?1 at 525°C, and 2.1 cm.² sec.^?1 at 625°C. In view of complicating factors accurate values of the diffusivity of selenium in liquid tellurium cannot be deducted from the experimental results. However, the value obtained from experimental measurements of 7.59 × 10^?4 cm.² sec.^?1 at 525° is in reasonable agreement with the value of 9.85 × 10^?5 cm.² sec.^?1 reported in the literature.     

Kinetics of leaching of tunisian phosphate ore particles in dilute phosphoric acid solutions

Van der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P₂O₅). When the temperature rises from 25 to 90°C, for a given particle size, the mass-transfer coefficients, k_L°, vary from 3 × 10^?3 to 8 × 10^?3 m ·s^?1. The corresponding diffusion coefficients, D, lies between 6 × 10^?7 and 27 × 10^?7 m²·s^?1. Activation energy is equal to 14 kJ·mol^?1 and values of k_L°, at 25°C, are in the range of 0.28 × 10^?3 and 4 × 10^?3 m·s^?1 when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.     

Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150?µm and 500?µm) and at different heating rates (10, 15, 20, and 25?°C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150?µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500?µm, whereas 500?µm particle sizes exhibited higher peak temperatures compared to 150?µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27?kJ mol^?1 and 3.84?×?10⁵?min^?1 for 150?µm particle size, whereas for 500?µm particle size were 97.12?kJ mol^?1 and 3.74?×?10⁷?min^?1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35?kJ mol^?1, 1.29?×?10⁷?min^?1, and 88.50?kJ mol^?1, 1.32?×?10⁷?min^?1 for 150?µm particle sizes. While for 500?µm particle sizes, the E and A were 108.46?kJ mol^?1, 3.14?×?10⁹?min^?1, and 113.05?kJ mol^?1, 7.56?×?10⁹?min^?1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.     

Ultra‐Low Fire Glass‐Free Li3FeMo3O12 Microwave Dielectric Ceramics

A new ultra‐low fire glass‐free microwave dielectric material Li₃FeMo₃O₁₂ was investigated for the first time. Single phase ceramics were obtained by the conventional solid‐state route after sintering at 540°C–600°C. The atomic packing fraction, FWHM of the A_g oxygen‐octahedron stretching Raman mode and Qf values of samples sintered at different temperatures correlated well with each other. The sample with a Lower Raman shift showed a higher dielectric constant. Interestingly, the system also showed a distinct adjustable temperature coefficient of resonant frequency (from ?84× 10^?6/°C to 25 × 10^?6/°C).     

Effect of temperature on viscosity of amylose

Viscosity parameters were obtained for maize maylose (molecular weight of 107,000) in 1N KOH at 25, 30, 35, and 40°C. Intrinsic viscosity continuously decreased and Huggins' constant k' continuously increased with increasing temperature. The temperature dependence of intrinsic viscosity, d[η]/dT, was ?2.12 × 10^?2/°C.     

Transitions of polytetrafluoroethylene at about 90 and 130°C. studied by x-ray diffraction and infrared spectra

By means of x-ray diffraction, the lattice spacing of the (100) plane for molded polytetrafluoroethylene was measured at different temperatures from 25 to 190°C. In the crystalline region, the linear expansion coefficient, in the direction perpendicular to the molecular chain axis, was obtained as 1.1 × 10^?4°C.^?1 below 60°C., as 1.2 × 10^?4°C.^?1 above 90°C., and as a minimum value of some 0.2 × 10^?4°C.^?1 at about 80°C. As the linear expansion coefficient of the crystalline region in bulk was observed as some 0.6 × 10^?4°C.^?1, the expansion coefficient in the direction of molecular chain axis must be negative except in the transition region near 80°C. The variation of molecular chain axis separation with temperature showed an irregularity at about 80°C. but none near 130°C. in the crystalline region. Infrared absorbance of film samples of PTFE was measured at different temperatures of 25 to 150°C. range for 518, 627, and 639 cm.^?1 bands. On absorbance–temperature curves for those b?ands, irregularities were observed near 30, 50, 90, and 130°C. Particularly with 518 cm.^?1 band, a more crystalline sample gave more distinct irregularities near 50 and 90°C. than a less crystalline sample. The change at about 90°C. in infrared spectra may correspond to that obtained by x-ray measurements near 80°C., which was thought to occur in the crystalline region. The results obtained by x-ray and infrared measurements support the previous results by thermal, rheological, and dielectric methods: there exist first-order transitions in the crystalline region at about 90°C. and second-order transitions in the amorphous region at about 130°C.     

Synthesis,characterization, and thermo‐optical properties of azobenzene polyurethane containing chiral units

An optically active levoazobenzene polyurethane (PU) was synthesized and was based on the chromophore 4‐(4′‐nitrophenylazo) phenylamine, the chiral reagent L (?)‐tartaric acid, and toluene diisocyanate. The chemical structure and thermal properties were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, and differential scanning calorimetry. The PU had high number‐ and weight‐average molecular weights up to 52 300, a large glass‐transition temperature of 235.7°C, and an optical rotation of ?18.06°, The optical parameters, including the refractive index (n) and thermo‐optic coefficient (dn/dT); the dielectric constant (?) and its variation with temperature; and the thermal volume expansion coefficient and its variation with temperature of PU were obtained. The dn/dT and ? values for the polymer were in the range ?4.1200 to 3.6257 × 10^?4 °C^?1 and 2.00 ± 0.11, respectively. The dn/dT values were one order of magnitude larger than those of inorganic glasses, such as zinc silicate glass (5.5 × 10^?6 °C^?1) and borosilicate glass (4.1 × 10^?6 °C^?1), and were larger than organic materials, such as polystyrene (?1.23 × 10^?4 °C^?1) and poly(methyl methacrylate) (?1.20 × 10^?4 °C^?1). The ? values were lower than that of alicyclic polyimide and semiaromatic polyimide. The obtained PU is expected to be useful for optical switching and optical waveguide areas. The conclusion has a little significance for the development of a new digital optical switch. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of high pressure on mass transfer kinetics of granny smith apple

The mass transfer kinetics during osmotic dehydration of granny smith apple slices in 60 Brix fructose and sucrose solution was studied at atmospheric pressure and at elevated pressure of 200–600?MPa at 40°C. The moisture and solute fractions in apple slices during osmotic dehydration under high pressure were predicted by Weibull frequency distribution model. The calculated effective moisture diffusivity values of apple slices suspended in fructose and sucrose solution during high-pressure treatment (0.1–600?MPa) were in the range of 6.35?×?10^?10 to 3.60?×?10^?9?m²/s and 7.96?×?10^?10 to 4.32?×?10^?9?m²/s, respectively.     

Kinetics of ultrasound pretreated apple cubes dried in fluidized bed dryer

Abstract

This work evaluated the effect of ultrasonic pretreatment on the production of dehydrated apples (Malus domestica L. var Granny Smith) in a fluidized bed dryer. Cube-shaped apple samples were subjected to ultrasound in an ultrasonic bath and dried in a fluidized bed drier. The experimental design evaluated the effect of ultrasound pretreatment time (0 to 30?min) on the soluble solids loss during pretreatment and on the drying time. The ultrasonic pretreatment was carried out in a bath ultrasound operating at 25?kHz and outputting 55?W/m³ of power density. Distilled water was applied in the pretreatment to produce low-calorie apple cubes. Fluidized bed drying was carried out at 30, 40, and 50?°C. Fick’s law was used to model the drying process and to determine the apparent water diffusivity. The soluble solid loss ranged between 8.7 and 21.2% during the pretreatment, and the apparent water diffusivity during air drying ranged from 1.09?×?10^?6 to 2.81?×?10^?6 m²/min. Ultrasound pretreatment increased the apparent water diffusivity up to 58%. Apple cubes subjected to 20?min of ultrasound pretreatment and dried at 50?°C presented the highest apparent water diffusivity and dried to achieve a water activity of 0.4 in 100?min.     

Synthesis and characterization of novel aromatic polyamides derived from 2,2′‐bis(p‐phenoxyphenyl)‐4, 4′‐diaminodiphenyl ether

BACKGROUND: Wholly aromatic polyamides (aramids) are high‐performance polymeric materials with outstanding heat resistance and excellent chemical stabilities due to chain stiffness and intermolecular hydrogen bonding of amide groups. Synthesis of structurally well‐designed monomers is an effective strategy to prepare modified forms of these aramids to overcome lack of organo‐solubility and processability limitations. RESULTS: A novel class of wholly aromatic polyamides was prepared from a new diamine, namely 2,2′‐bis(p‐phenoxyphenyl)‐4,4′‐diaminodiphenyl ether (PPAPE), and two simple aromatic dicarboxylic acids. Two reference polyamides were also prepared by reacting 4,4′‐diaminodiphenyl ether with the same comonomers under similar conditions. M?_w and M?_n of the resultant polymers were 8.0 × 10⁴ and 5.5 × 10⁴ g mol^?1, respectively. Polymers resulting from PPAPE exhibited a nearly amorphous nature. These polyamides exhibited excellent organo‐solubility in a variety of polar solvents and possessed glass transition temperatures up to 200 °C. The 10% weight loss temperatures of these polymers were found to be up to 500 °C under a nitrogen atmosphere. The polymers obtained from PPAPE could be cast into transparent and flexible films from N,N‐dimethylacetamide solution. CONCLUSION: The results obtained show that the new PPAPE diamine can be considered as a good monomer to enhance the processability of its resultant aromatic polyamides while maintaining their high thermal stability. The observed characteristics of the polyamides obtained make them promising high‐performance polymeric materials. Copyright © 2009 Society of Chemical Industry     

Nitrophenoxy groups containing polybenzimidazoles as polymer electrolytes for fuel cells: Synthesis and characterization

Polybenzimidazoles containing different contents of pendant nitrophenoxy groups were prepared by condensation of 3,3′‐diamino‐benzidine with a mixture of 3,5‐dicarboxyl‐4′‐nitro diphenyl ether and isophthalic acid (IPA) in different ratios in polyphosphoric acid. The polymers are soluble in polar aprotic solvents, they have inherent viscosities in the range of 0.75–1.10 dL g^?1 and they form tough and transparent films on solution casting. They have good thermal stability with initial decomposition temperature ranging from 380 to 416°C in nitrogen, good tensile strength ranging from 56 to 65 MPa and reasonably good oxidative stability. Phosphoric acid uptake of these polymers is low compared with PBI and membranes doped with phosphoric acid exhibit good proton conductivity in the range of 6.6× 10^?3 to 1.9× 10^?2 S/cm at 25°C and 1.2× 10^?2 to 4.9× 10^?2 S/cm at 175°C, compared with 3.9× 10^?3 S/cm at 25°C and 3.2× 10^?2 S/cm at 175°C for PBI. These membranes are suitable for applications as polymer electrolyte for fuel cell and presumably for gas separation at high temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The interaction of hydrogen sulfide with lead- and barium–cadmium–zinc-stabilized poly(vinyl chloride)

Poly(vinyl chloride) polymers stabilized with tribasic lead sulfate discolor upon exposure to hydrogen sulfide gas as a result of lead sulfide formation. The discoloration occurs for samples in both cord and sheet forms and is shown to be a function of total H₂S exposure, reaching a limiting value that is determined by the amount of lead stabilizer used in the polymer formulation. The permeation and diffusion constants for H₂S through PVC stabilized with tribasic lead sulfate and with a liquid Ba–Cd–Zn formulation are found to be P_Pb = (6.0 ± 0.2) × 10^?9, P_BaCdZn = (5.2 ± 0.2) × 10^?9 (both in cm³ gas?cm film/cm² area?sec?cm Hg), D_Pb = (1.3 ± 0.2) × 10^?7 cm²/sec, and D_BaCdZn = (6.4 ± 0.6) × 10^?8 cm²/sec, all measured at 21°C. The stabilizing efficiencies of the formulations were assessed by HCl evolution measurements, which show that exposure to H₂S decreases the initial polymer stability for both Pb-stabilized and Ba–Ca–Zn-stabilized formulations. Protection of stabilized PVC formulations from diffusing hydrogen sulfide is thus advisable for long-term stability as well as for color integrity.     

Experimental and fundamental critical analysis of diffusion model of airflow drying

Scientific literature of agromaterial drying present contradictory conclusions in terms of the kinetic effect of airflow velocity. Some authors confirmed that it does not trigger any modification of drying, while some articles tried to establish empirical models of the effective diffusivity D_eff versus the airflow velocity, what is fundamentally erroneous. By analyzing internal and external transfer phenomena, this research aimed at recognizing that once air velocity is higher than a critical airflow velocity (CAV), the internal transfers become the limiting phenomenon. CAV depends on the effective diffusivity and the product size. It was calculated in the cases of two studied raw materials (apple and carrot), differently textured by instant controlled pressure drop (DIC). Values of CAV greatly depend on diffusivity of water within the matrix. At temperature T?=?40°C, they were 1?m/s for untreated carrot and 2.1?m/s for DIC-textured carrot, whose D_eff values were 1.31 and about 3?×?10^?10?m²/s, respectively. Also, at temperature T?=?40°C, they were 2.1?m/s for untreated apple and 3?m/s for DIC-textured apple, whose D_eff were 1.4 and about 10.4?×?10^?10?m²/s, respectively.     

Kinetics of Estrone Ozone/Hydrogen Peroxide Advanced Oxidation Treatment

Ozone/hydrogen peroxide batch treatment was utilized to study the degradation of the steroidal hormone estrone (E1). The competition kinetics method was used to determine the rate constants of reaction for direct ozone and E1, and for hydroxyl radicals and E1 at three pH levels (4, 7, and 8.5), three different molar O₃/H₂O₂ ratios (1:2, 2:1, and 4:1) and a temperature about 20°C. The average second-order rate constants for direct ozone-E1 reaction were determined as 6.2?×?10³?±?3.2?×?10³ M^?1s^?1, 9.4?×?10⁵?±?2.7?×?10⁵ M^?1s^?1, and 2.1?×?10⁷?±?3.1?×?10⁶ M^?1s^?1 at pH 4, 7, and 8.5, respectively. It was found that pH had the greatest influence on the reaction rate, whereas O₃/H₂O₂ ratio was found to be slightly statistically significant. For the hydroxyl radical-E1 reaction, apparent rate constants ranged from 1.1?×?10¹⁰ M^?1s^?1 to 7.0?×?10¹⁰ M^?1s^?1 with an average value of 2.6?×?10¹⁰ M^?1s^?1. Overall, O₃/H₂O₂ is shown to be an effective treatment for E1.     

Effect of sintering temperature on the thermal expansion behavior of ZrMgMo3O12p/2024Al composite

A 2024Al metal matrix composite with 10?vol% negative expansion ceramic ZrMgMo₃O₁₂ was fabricated by vacuum hot pressing, and the influence of sintering temperature on the microstructure and thermal expansion coefficient (CTE) of alloys was investigated. Experimental results showed that all ZrMgMo₃O_12p/2024Al composites sintered at 500–530?°C had a similar reticular structure and exhibited different linear expansion coefficients at 40–150?°C and 150–300?°C. The addition of 10?vol% ZrMgMo₃O₁₂ decreased the CTEs of 2024Al by ~ 16% at 40–150?°C and by ~ 7% at 150–300?°C. This addition also increased the hardness of 2024Al by ~ 23%. The density of the composites and the content of Al₂Cu in ZrMgMo₃O_12p/2024Al increased as the sintering temperature increased. The CTEs of the composites decreased, whereas hardness increased. Thermal cycling from 40?°C to 300?°C caused the CTEs of the composites to decrease gradually and reach a stable value after seven cycles. The lowest CTEs of 15.4?×?10^?6 °C^?1 at 40–150?°C and 20.1?×?10^?6 °C^?1 at 150–300?°C were obtained after 10 thermal cycles and were reduced by ~ 32% and ~ 17%, respectively, compared with the CTE of the 2024Al. Among the current reinforcements, ZrMgMo₃O₁₂ negative expansion ceramics showed the highest efficiency to decrease the CTE of Al matrix composites.     

Sonocrystallization of Interesterified Soybean Oil With and Without Agitation

Interesterified soybean oil was crystallized at 29, 34, and 35 °C with and without the use of high‐intensity ultrasound. Samples were crystallized using either (1) continued agitation for the entire crystallization process (CA) or (2) agitation for 10 min (A10) followed by static crystallization. Sonication and agitation decreased the induction period of nucleation at higher temperatures and changed the crystal morphology, crystallization kinetics, and viscoelasticity of the sample. Sonication reduced the crystal sizes and significantly (P <0.05) increased the viscosity (5.2 ± 1.2 to 2369.6 ± 712.1 Pa s) and elastic modulus (83.2 ± 4.1 to 69,236.7 ± 26,765 Pa) of the crystalline networks obtained at 29 °C under A10 condition. An increase in viscosity and elasticity was also observed for sonicated samples crystallized at 34 and 35 °C under A10 and all CA conditions but these differences were not statistically significant (P >0.05). Sonication increased crystallization rates for all conditions tested. Kinetic constants obtained from an Avrami fit increased from1.3 × 10^?5 to 6.8 × 10^?5 min^?n for samples crystallized at 29 °C A10 without and with sonication, respectively, and from 2.6 × 10^?9 to 2.4 × 10^?7 min^?n for samples crystallized at 34 °C A10 without and with sonication, respectively. This increase in the crystallization rate was also observed for samples crystallized under the CA condition at 29 °C.     

MASS TRANSFER AND DIFFUSION COEFFICIENT DETERMINATION IN THE WET AND DRY SALTING OF MEAT

ABSTRACT

Dehydrated salted meat is widely used in Brazil as a very important source of animal protein. The main objective of this kind of processing is water removal. initially by osmotic pressure changes and then by drying, resulting in a product with intermediate moisture levels.

In this work, mass transfer and salt diffusion in pieces of meat submitted to wet and dry salting were studied. Slabs of beef m. trapezius with an infinite plate geometry were salted in a NaCl saturated solution or in a dry salt bed, at two temperatures (10 and 20°C) and different time exposures (120 min and 96 hours). Equilibration studies were extended up to six days.

It was observed that water loss increased with salt uptake, for increasing periods of times. At 20°C the moisture loss was higher than it was at 10°C in both salting processes. On the other hand, the kinetics of salt uptake and moisture loss were of greater importance in the process of dry salting than in that of wet salting.

The salt diffusion coefficient for wet salting was 0.26 × 10^?10m²/s at20°C and 0.25 × 10^?10 m²/s at 10°C and for the dry salting the values were 19.37 × 10^?10 m²/s at 20°C and 17.21 × 10^?10 m²/s at 10°C.     

Preparation and characterization of sulfonated block‐graft copolyimide/sulfonated polybenzimidazole blend membranes for fuel cell application

Polymer electrolyte blend membranes composed of sulfonated block‐graft polyimide (S‐bg‐PI) and sulfonated polybenzimidazole (sPBI) were prepared and characterized. The proton conductivity and oxygen permeability coefficient of the novel blend membrane S‐bg‐PI/sPBI (7 wt%) were 0.38 S cm^?1 at 90 °C and 98% relative humidity and 7.2 × 10^?13 cm³(STP) cm (cm² s cmHg)^?1 at 35 °C and 76 cmHg, respectively, while those of Nafion^® were 0.15 S cm^?1 and 1.1 × 10^?10 cm³(STP) cm (cm² s cmHg)^?1 under the same conditions. The apparent (proton/oxygen transport) selectivity calculated from the proton conductivity and the oxygen permeability coefficient in the S‐bg‐PI/sPBI (7 wt%) membrane was 300 times larger than that determined in the Nafion membrane. Besides, the excellent gas barrier properties based on an acid ? base interaction in the blend membranes are expected to suppress the generation of hydrogen peroxide and reactive oxygen species, which will degrade fuel cells during operation. The excellent proton conductivity and gas barrier properties of the novel membranes promise their application for future fuel cell membranes. © 2015 Society of Chemical Industry     

Physical solubility of hydrogen sulfide in several aqueous solvents

The solubility of hydrogen sulfide in several aqueous solutions was measured over the temperature range 25°C to 60°C. The solvents investigated in this work include 0 to 50% aqueous solutions of polyethylene glycol, ethylene glycol, methyldiethanolamine and diethanolamine. The amine solutions used in this work were neutralized by the addition of hydrochloric acid in order to suppress the hydrogen sulfide reaction (H₂S → H⁺ + HS^?) so that only the physical solubility of hydrogen sulfide would be measured. The solubility data determined in this work are expressed in terms of Henry's law. The Henry's law constants found in this work were correlated well by a particularly simple empirical formula based on the molecular weight of the solvent.