Water in different poly(styrene sulfonic acid)‐grafted fluoropolymers

We investigated the water present in a series of radiation‐grafted fluoropolymers with similar poly(styrene sulfonic acid) (PSSA) contents with the aim of determining the influence of the initial fluoropolymer. Radiation‐grafted membranes were compared with Nafion 117 and 105. Sorption curves and differential scanning calorimetry thermograms showed that all the membranes contained the same number of water molecules tightly bound to the sulfonic acid groups; this water did not freeze. In radiation‐grafted membranes, the content of freezing water absorbed from the liquid‐phase water varied according to the swelling abilities of the membrane, which were dependent on the initial fluoropolymer. Larger pores accompanied high water uptakes and high conductivity. The amount of water absorbed from the vapor phase was similar for all radiation‐grafted membranes with similar PSSA contents, irrespective of matrix material. Nafion membranes had higher conductivities at intermediate hydration levels, and the relaxation times measured by NMR were longer than for the radiation‐grafted materials. This suggests that the channels for water and proton conduction are different in the two types of materials. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 33–42, 2002     

Use of the unique properties of fluoropolymers in the design of new,highly effective,ecologically friendly technologies for the fine purification of hydrogen halides and their aqueous solutions

A number of properties of fluoropolymers in aqueous solutions of hydrogen halides were investigated. The results enable fluoropolymers to be used in the purification of hydrogen halides and their aqueous solutions. The hydrophobicity of fluoropolymers and their diffusion permeability enable production of hydrogen halides of low moisture content. A second unit for hydroionic convection is based on hydroionic repulsion (determined by the hydrophobic properties of the fluoropolymer) and ionic elimination. The two units enable the highly effective, ecologically safe manufacture of highly pure hydrogen halides and their aqueous solutions to be carried out with minimum feedstock, cooling water, and power consumption. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1383–1387, 2001     

FLUOROPOLYMERS IN TECHNOLOGIES OF HYDROGEN HALIDES

A number of properties of fluoropolymers in aqueous solutions of hydrogen halides have been investigated. The results enable fluoropolymers to be used in the purification of hydrogen halides and their aqueous solutions. The hydrophobicity of fluoropolymers and their diffusion permeability enable a production of hydrogen halides of low moisture content. A second unit for hydroionic convection is based on hydroionic repulsion (determined by the hydrophobic properties of the fluoropolymer) and ionic elimination. The two units enable the highly effective, ecologically safe manufacture of highly pure hydrogen halides and their aqueous solutions to be carried out with minimum feedstock, cooling water, and power consumption.     

Hydrodynamics and mass transfer in bubble column: Influence of liquid phase surface tension

According to literature, few experiments are performed in organic solvents which are mostly used in commercial gas-liquid reactors. However, it is commonly accepted that data obtained in aqueous solution allow to predict the surface tension effects, and to model the behaviour of organic solvents. In this work, we examine the validity of this approximation.In this objective, the flows observed in two pure media having similar viscosity but different surface tension—respectively, water (reference) and cyclohexane (solvent)—are successively compared at two scales: in a bubble column and in bubble plumes.In bubble plumes, as expected, the mean bubble size is smaller in the medium having the smallest surface tension (cyclohexane), but for this medium the destabilisation of flow is observed to occur at smaller gas velocity, due to break-up and coalescence phenomena. In bubble column, these phenomena induce the bubbling transition regime at lower gas velocity, whatever the operating conditions for liquid phase: batch or continuous. Consequently, when the two media are used at similar gas superficial velocity, but in different hydrodynamic regimes, greater gas hold-up and smaller bubble diameter can be observed in water; the interfacial area is then not always higher in cyclohexane.This result differs from the behaviour observed in the literature for aqueous solutions. The analysis of bubble plumes in aqueous solutions of butanol shows that this difference is due to a fundamental difference in coalescent behaviour between pure solvents and aqueous mixtures: the surface tension effect is less important in pure liquid than in aqueous solutions, because of the specific behaviour of surfactants.It is then still difficult to predict a priori the bubbling regime or the flow characteristics for a given medium, and all the more to choose an appropriate liquid as a model for industrial solvents.     

Analysis of carbon dioxide gas/liquid mass transfer in aerated stirred vessels using non–Newtonian media

Gas/liquid mass transfer has been investigated in an aerated stirred tank using non‐Newtonian media and carbon dioxide as absorbent and gas phase respectively. The volumetric mass transfer coefficients at different operational variables have been measured. The non‐Newtonian media (liquid phases) used were aqueous solutions of two polymers, carboxymethyl cellulose and alginate sodium salts. The influence upon the mass transfer of the rheological properties, polymer concentration, stirring rate and gas flow rate was studied. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymers employed. Reasonable agreement was found between the predictions of proposed models and the experimental data. The results shown in the present paper allow us to understand carbon dioxide transfer to a non‐Newtonian liquid phase and to evaluate the effect of the liquid phase characteristics. The equations used in this paper allow accurate simulation of the transfer of a pure gas to a rheologically complex solution. Copyright © 2004 Society of Chemical Industry     

Radiation assisted compatibilisation of blends of vinylidenefluoride polymers with fluorosilicone elastomers by means of crosslinking coagents

An experimental study was carried out to demonstrate the possibility of compatibilising blends of polyvinylidenefluride with minor amounts of fluorosilicone elastomer, thereby achieving better low temperature ductility without excessively reducing the melting point and degree of crystallinity of the fluoropolymer. The principle that has been explored is the use of multifunctional crosslinking agents acting as a common solvent for the two polymers during mixing, and providing interpenetrating networks through the two polymer phases by means of peroxide-induced crosslinking reactions. It has been found that mixtures of triallyl isocyanurate with diallyl phthalate are particularly effective in compatibilising the combination of polymers in question, giving the best overall balance of properties. Compatibilisation was enhanced by grafting part of the coagent on to the chains of the fluoropolymer prior to being blended with the fluorosilicone gum. Further evidence for enhanced compatibilisation by such a procedure was obtained from dynamic mechanical tests, which revealed an increase in glass transition temperature for the fluorosilicone phase and a suppression of α-relaxations in the fluoropolymer component.     

FP-based formulations as protective coatings in oil/gas pipelines

Corrosion in the interior of pipelines is a major and costly problem encountered in the oil and gas industry. In this context, a fluoropolymer and a hybrid epoxy/fluoropolymer resin were studied for their potential use to prevent corrosion. The fluoropolymer coating required the use of a primer layer. The coatings were formulated to maintain the excellent abrasion and chemical resistance properties of fluoropolymers, while enhancing adhesion to the substrates. Standard corrosion experiments, including chemical immersion, adhesion, and salt fog tests, were used for preliminary evaluation. Coatings were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy before and after exposure to corrosive environments. Electrochemical properties were studied with electrochemical impedance spectroscopy, by monitoring the resistance and capacitance of the coatings over time. The results obtained in this work will fill a knowledge gap and will aid in the selection of the proper composition and thickness of anticorrosion coatings for use in a highly corrosive media.     

Fluoropolymer Fibres: Physicochemical Nature and Structural Dependence of their Unique Properties, Fabrication, and Use. A Review

Fluorine-containing fibre-forming polymers, fibres, and fibre materials have unique properties due to the presence of fluorine atoms. Totally fluorinated polymer materials are distinguished by the highest resistance to all kinds of chemical reagents and physically active media, low wettability by polar liquids, and other specific functional properties. In examining the physicochemical nature of the unique properties of fluoropolymer fibres and fibre materials with respect to the theory of chemical structure and D. I. Mendeleev's Periodic Table of the Elements, we found that they are due to the features of the fluorine atoms, which have the highest electronegativity of all elements, high ionization energy, high energies of bonds with carbon atoms, and simultaneously shield the molecular chain from external effects. Fibre-forming fluoropolymers, fibres, and fibre materials made from them have high resistance to external effects, biostability and bioinertness, and highly effective protective and other functional characteristics. This relates to the totally fluorinated materials PTFE, HFP, and CP-TFE-HFP to the greatest degree. Fibres and fibre materials based on totally fluorinated polymers (PTFE, HFP, CP-TFE-HFP) are placed in a special group for use in articles utilized in extreme conditions in exposure to especially aggressive media and other external active effects where the use of other kinds of fibres and fibre materials is difficult or impossible because of their low stability and rapid destruction.     

Corrosion control methods in supercritical water oxidation and gasification processes

Use of supercritical water (SCW) as a medium for oxidation reactions, conversion of organic materials to gaseous or liquid products, and for organic and inorganic synthesis processes, has been the subject of extensive research, development, and some commercial activity for over 25 years. A key aspect of the technology concerns the identification of materials, component designs, and operating techniques suitable for handling the moderately high temperatures and pressures and aggressive environments present in many SCW processes. Depending upon the particular application, or upon the particular location within a single process, the SCW process environment may be oxidizing, reducing, acidic, basic, nonionic, or highly ionic. Thus, it is difficult to find any one material or design that can withstand the effects of all feed types under all conditions. Nevertheless, several approaches have been developed to allow successful continuous processing with sufficient corrosion resistance for an acceptable period of time. The present paper reviews the experience to date for methods of corrosion control in the two most prevalent SCW processing applications: supercritical water oxidation (SCWO) and supercritical water gasification (SCWG).     

Characterisation of hydrophobic carbon nanofiber-silica composite film electrodes for redox liquid immobilisation

Carbon (50-150 nm diameter) nanofibers were embedded into easy to prepare thin films of a hydrophobic sol-gel material and cast onto tin-doped indium oxide substrate electrodes. They promote electron transport and allow efficient electrochemical reactions at solid|liquid and at liquid|liquid interfaces. In order to prevent aggregation of carbon nanofibers silica nanoparticles of 7 nm diameter were added into the sol-gel mixture as a “surfactant” and homogeneous high surface area films were obtained. Scanning electron microscopy reveals the presence of carbon nanofibers at the electrode surface. The results of voltammetric experiments performed in redox probe—ferrocenedimethanol solution in aqueous electrolyte solution indicate that in the absence of organic phase, incomplete wetting within the hydrophobic film of carbon nanofibers can cause hemispherical diffusion regime typical for ultramicroelectrode like behaviour.The hydrophobic film electrode was modified with two types of redox liquids: pure tert-butylferrocene or dissolved in 2-nitrophenyloctylether as a water-insoluble solvent and immersed in aqueous electrolyte solution. With a nanomole deposit of pure redox liquid, stable voltammetric responses are obtained. The presence of carbon nanofibers embedded in the mesoporous matrix substantially increases the efficiency of the electrode process and stability under voltammetric conditions. Also well-defined response for diluted redox liquids is obtained. From measurements in a range of different aqueous electrolyte media a gradual transition from anion transfer dominated to cation transfer dominated processes is inferred depending on the hydrophilicity of the transferring anion or cation.     

Effect of fluoropolymer antidripping agent on the microstructure and properties of polyesters

Poly(ethylene terephthalate) (PET) is of excellent mechanical properties and melt processability and is widely used as raw material for textile fibers. However, the flame retardant properties of PET were rather poor, and both reactive and additive phosphorus- and halogen-containing compounds have been employed to enhance the reaction-to-fire properties while the meltdripping behaviour during burning hasn’t been handled properly with the flame retardants. In this work, fluoropolymer was blended with both pure PET (pPET) and reactive phosphorus-containing flame retarded copolyester (fPET), and the flame retardance and char formation and mechanical properties of the resulted pPET and fPET blends were investigated. The tensile strengths of modified pPET samples were worsen whereas those of modified fPET samples were improved at low concentrations. The initial thermal degradation in nitrogen was accelerated remarkably for the two polyesters with fluoropolymer. The oxygen indices of the all modified samples were reduced while char formation and meltdripping suppression were encouraged. The apparent melt viscosity and elasticity for the two polyesters were gained much with antidripping agent. Therefore, fluoropolymer improved char formation of the two polyesters based on the gaseous phase mechanism while the partial suppression of meltdripping behavior and the decrease of mechanical properties mainly originated from the increase of melt viscosity via fibrillation for pPET.     

New soluble teflon for coating onto plastics

Teflon PTFE, FEP, and low melting HFP/TFE copolymers can be made to have excellent adhesion to substrates if residual stresses from large changes in temperature can be eliminated. PTFE and FEP can be adhered using a high boiling saturated perfluorinated oligomer to plasticize the fluoropolymer at the interface. Low melting HFP/TFE copolymers can be deposited as very thin films from solution in common perfluorinated solvents. Highly durable coatings can be prepared owing to the intimate degree of contact obtained between the substrate and the fluoropolymer chains. The use of low boiling solvents allow coatings on temperature sensitive substrates, such as plastics, rubber, and paper. Possible commercial applications range from mold release coatings, clear protective coatings on photographs, paintings, and documents and optical coatings on plastic and glass.     

Polymer miscibility in mixed organic liquids. An extension of the two-dimensional approach

Previous work on the two-dimensional approach to polymer miscibility in organic liquids is extended to polymer–mixed liquid system. From thermodynamic considerations methods for calculating δ_h of the mixed liquid and χ_H of the polymer–mixed liquid system from properties of pure components are proposed, where δ_h is the hydrogen-bonding solubility parameter of the liquid, and χ_H is a term which takes account of the dispersion and polar interactions between the liquid and the polymer and of effects due to temperature and molecular size of the liquid. Using these two calculated parameters, the solvent power of the mixed liquid can be determined from its location on the χ plane.     

Liquid crystalline polymer/fluoropolymer blends: Preparation and properties of unidirectional “prepregs” and composite laminates

Extruded films of liquid crystalline polymer (LCP)/fluoropolymer blends were melt drawn to develop uniaxial orientation of a microfibrillar dispersed LCP phase. The anisotropy of the films increased with increasing draw and LCP content in the blend. Laminated composite plates were prepared using the extruded sheets as prepreg. The mechanical properties and coefficient of thermal expansion (CTE) of the prepreg and laminates agreed well with predictions from composite lamination theories. The potential for replacing glass fiber reinforced fluoropolymers with LCP/fluoropolymer blends in applications such as microwave circuit boards is discussed.     

Connection of surface tension with multiple tribological properties in epoxy + fluoropolymer systems

Contact angles of free liquids on solid samples were measured and the van Oss–Good method was applied for evaluating surface tensions of the solids. A parachor method was used for comparison: in this case the respective values were calculated for the polymer solids from molecular and group contributions. Surface tensions were computed from the parachors and the two methods compared. Effects of varying the fluoropolymer added to the epoxy before curing are discussed. For a given fluoropolymer, effects of changing its concentration on surface tension have also been evaluated and compared to the changes in scratch resistance (scratch penetration depth, recovery depth) and in static and dynamic friction. Morphological and phase structure changes are reflected in all these properties, showing a strong connection between the surface tension and tribological properties. Copyright © 2003 Society of Chemical Industry     

Comparison of distillation arrangement for the recovery process of dimethyl sulfoxide

In this study, computer modeling and comparative works have been performed to obtain highly pure dimethyl sulfoxide (DMSO) which is used for fiber spinning solvent for two different distillation sequences. These two distillation sequences remove methanol and water and recover DMSO solvent from the mixture of methanol and water using two distillation columns. Non random two liquid mixture (NRTL) liquid activity coefficient model was used for the modeling of each binary vapor-liquid equilibria for DMSO, methanol and water systems and we used PRO/II with PROVISION release 7.1 as a commercial chemical process simulator. As a result of computational simulation, we obtained a highly pure DMSO with its purity over 99.9 wt% and water contents which is main impurity was very low weight percent under 500 ppm.     

Study of the crystal structure of P(HBA/HNA)/PET blend fibers

The crystal structure of p‐hydroxybenzoate/2‐hydroxy‐6‐naphthoic acid copolyester [P(HBA/HNA)]/poly(ethylene terephthalate) (PET) blend (ACPET) fiber was studied with wide‐angle X‐ray diffraction and differential scanning calorimetry. The results showed that crystallites of P(HBA/HNA) and PET were formed in ACPET fibers; that is, some crystallites of ACPET fiber were composed of PET chains, and others were composed of P(HBA/HNA) chains. The thermal behaviors of the crystals of each component in the blend fiber were different from those of each corresponding pure component. For the fibers heat‐treated at 300 and 350°C, the degree of supercooling of P(HBA/HNA) segments in the blend fibers was the same as that of P(HBA/HNA) fiber, but the degree of supercooling of PET in the blend fibers was distinctly higher than that of pure PET fibers. Evidently, the aforementioned changes were attributable to the blending of PET with P(HBA/HNA). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 394–400, 2002     

Swelling and dissolution behavior of poly(methyl methacrylate) films in methyl ethyl ketone/methyl alcohol mixtures studied by optical techniques

Swelling and dissolution behavior of poly(methyl methacrylate) (PMMA) films during unidimensional penetration of methyl ethyl ketone/methyl alcohol (MEK/MA) liquid mixtures at 22°C is presented. Optical microscopy and two‐beam interferometry were applied to clamped PMMA films to obtain information on penetration kinetics and penetrant concentration profiles. Dissolution by pure MEK was initially controlled by Case II penetration kinetics and at later stages of the process, by stress cracking in the absence of a surface layer. Introduction of increasing amounts of MA in the liquid solvent resulted in moderation of the fragmentation process, enhanced penetration rates at the early stages of the process, deviations from Case II kinetics at the later stages, and the existence of a surface layer. These results indicate that penetration of MEK/MA mixtures and dissolution of PMMA are characterized by lower diffusion Deborah, and higher dissolution, numbers compared to those of pure MEK. Swelling by pure MA, as well as by nonsolvent MEK/MA mixtures, was characterized by Case II penetration kinetics. A pronounced minimum in the penetration rate versus liquid mixture composition plot was observed at 30 : 70 v/v MEK/MA composition. Laser interferometry was applied to very thin PMMA films, supported on a silicon substrate, to study selected cases. The results obtained were very similar to those obtained by optical microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2823–2834, 2002; DOI 10.1002/app.10258     

Pore-network modelling of combined molecular diffusion and gravity drainage mechanisms in a porous matrix block: The competitive role of driving forces

A large part of the world's hydrocarbon resources are located in fractured reservoirs, and mass transfer phenomena play a crucial role in enhanced hydrocarbon recovery from these reservoirs. Pore-network models have been widely used to study kinetic and pore-scale micro-mechanisms. Molecular diffusion involves mass transfer and liquid–vapour phase change and can be simulated by a modified invasion percolation model. Despite the existence of separate pore-scale studies on molecular diffusion and gravity drainage, no articles have been published that evaluate the combined effect of both mechanisms. This study investigates the competitive roles of the two phenomena and the effective factors controlling each mechanism with the aid of pore-network models. According to the results obtained, gravity drainage and molecular diffusion would have a synergic effect when they are simultaneously active. Although for a single-component liquid system, there would be a capillary holdup residual saturation in the pure gravity drainage process (between 11% and 14% for the evaluated cases) and a slow and lengthy evaporation in pure molecular diffusion (between 47% and 57% longer for the cases under study), our investigation revealed that when the two mechanisms coexist, a faster process with no residual liquid is expected. Our findings clarify that when the system is strongly gravity dominated, the liquid body remains integrated, gas–liquid contact recedes in a piston-like manner, and three-stage liquid desaturation is observed. Furthermore, highly clustered liquid saturation is observed in strongly capillary-dominated systems, and the liquid desaturation curve in a capillary-dominated model has two distinguishable stages. The competitive contribution of gravity drainage and molecular diffusion as the main driving forces of liquid extraction from a single-block model is quantified for the entire period of desaturation. Depending on the dominance of the production mechanisms, the process is either gravity-assisted molecular diffusion or diffusion-assisted gravity drainage.     

Degradation of thin films of a fluoropolymer

1H-1H-Pentadecafluorooctyl methacrylate, a fluoropolymer, is used as a barrier coating to control spreading of thin liquid films, notably silicone oil. Using infrared spectroscopy and thermogravimetric analysis, this work describes the thermal degradation of thin films of this fluoropolymer. The conclusions are that the degradation is a two-stage, thermal bond-breaking phenomenon which does not required an additional reactant such as oxygen or water vapor. Rate constant data are presented for both stages of the degradation.