In situ FTIR micro-spectroscopy to investigate polymeric fibers under supercritical carbon dioxide: CO2 sorption and swelling measurements

An original experimental set-up combining a FTIR (Fourier Transformed InfraRed) microscope with a high pressure cell has been built in order to analyze in situ and simultaneously the CO₂ sorption and the polymer swelling of microscopic polymer samples, such as fibers, subjected to supercritical carbon dioxide. Thanks to this experimental set-up, we have determined as a function of the CO₂ pressure (from 2 to 15 MPa) the CO₂ sorption and the polymer swelling at T = 40 °C of four polymer samples, namely PEO (polyethylene oxide), PLLA (poly-l-lactide acid), PET (polyethylene terephtalate) and PP (polypropylene). The quantity of CO₂ sorbed in all the studied polymers increases with pressure. PEO and PLLA display a significant level of CO₂ sorption (20 and 25% respectively, at P = 15 MPa). However, we observe that a lower quantity of CO₂ can be sorbed into PP and PET (7 and 8% respectively, at P = 15 MPa). Comparing their thermodynamic behaviors and their intrinsic properties, we emphasize that a high CO₂ sorption can be reach if on one hand, the polymer is able to form specific interaction with CO₂ in order to thermodynamically favor the presence of CO₂ molecules inside the polymer and on the other, displays high chains mobility in the amorphous region. PLLA and PEO fulfilled these two requirements whereas only one property is fulfilled by PET (specific interaction with CO₂) and PP (high chains mobility). Finally, we have found that for a given CO₂ sorption, the resulting swelling of the polymer depends mainly on its crystallinity.     

The swelling behavior of interpenetrating polymer networks composed of polyurethane and unsaturated polyester

The kinetics of swelling and the sorption performance were observed for the polymer compositions with interpenetrating polymer networks made up of polyurethane and unsaturated polyester during their exposure to chlorobenzene at 25°C. It was found that the rates for solvent transport and solvent absorption processes were controlled by the chemical composition of the formulation studied. On the basis of the observed swelling process, parameters could be assessed which were specific for the mass transfer process, i.e., diffusion coefficient, sorption coefficient, and permeability coefficient. Moreover, an attempt was made to evaluate structural parameters that describe topology of the obtained networks. It was found that the increasing share of polyurethane in the composition reduced crosslinking density in the polyester network that resulted in faster diffusion of the solvent and higher sorption capacity for the solvent. The higher the styrene content in the composition, the higher the crosslinking density in the system, and hence the diffusion of solvent and its sorption inside the polymer network was much more difficult. In the scanning electron microscope analysis of samples, which had been subjected to swelling, no leaching was observed for any phase present in the system, despite phase separation for both the components. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3511–3519, 2006     

Swelling kinetics of linseed oil‐based polymers

Kinetics of swelling and sorption behavior of copolymers (based on linseed oil, styrene, divinylbenzene, and acrylic acid via cationic and thermal polymerization) is studied in tetrahydrofuran (THF) at different temperatures. The values of n in the transport equation are found to be below 0.4, showing non‐Fickian or pseudo‐Fickian transport in the polymers. The dependence of diffusion coefficient on the composition and temperature has also been studied for the linseed oil‐based polymers. The diffusion coefficient in cationic samples decreases with an increase in the oil contents in the samples. In case of thermal samples, the diffusion coefficient first increases up to 30% oil contents and then decreases. The diffusion coefficient decreases with an increase in temperature for all of the linseed oil polymer samples. The sorption coefficient increases with an increase in the oil contents for all samples. The crosslink density (calculated from the THF swelling) ranges from 20.16 to 92.34 × 10⁶ mol/cm³ for cationic samples and 20.62 to 86.01 × 10⁶ mol/cm³ for thermal samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

Experimental evaluation of the influence of saturation media on the mineralogical and physicochemical stability of bentonites

Three bentonite buffer materials (Rokle bentonite, FEBEX bentonite, and Mock-Up-CZ mixture composed of 85% Rokle bentonite, 10% silica sand and 5% graphite) interacted with natural water collected from Josef Underground Educational Facility (UEF) Czech Republic, and four different types of artificial groundwater enriched in K⁺ and/or Mg^2 +. The experimental material was prepared in the form of (1) highly compacted samples, (2) dispersion of bentonites (both at temperature of 95 °C), (3) drill hole filling during in situ tests at the Josef UEF (at ordinary temperature), and (4) common batch laboratory experiments (at 20 °C and at 80–90 °C). Partial samples were extracted after 3, 6, 12, and/or 18 months of interaction in the first three set-ups, and after 1 week, 2 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 7 months, 10 months, and 12 months in the batch experiment.Phase composition and its potential changes were evaluated by X-ray diffraction. In the first three experimental set-ups, no changes were identified. For the batch experiment, formation of illite was detected in FEBEX bentonite saturated with artificial groundwater with K⁺ concentration of 1083 mg/L. By using the same saturation medium, gypsum and/or bassanite formed in the Rokle and FEBEX bentonite. Other media did not affect mineralogical composition.The stability of studied materials was also evaluated by using adsorption and through-diffusion experiments on the basis of migration behaviour of ¹³⁴Cs. Dispersion of bentonites at laboratory temperature and bentonite samples from in situ test were used as solid phase, and four types of saturation media (artificial groundwater) were used as liquid phase. The distribution coefficient (Kd) is influenced by high concentration of K⁺ and Mg^2 + in saturation media on retention of Cs⁺. In Rokle bentonite, the increase concentration of K⁺ and Mg^2 + led to a decrease of Kd. In the case of FEBEX bentonite influence of composition of saturation media was not observed.The diffusion experiments showed good retardation ability of Rokle and FEBEX bentonites. The values of apparent diffusion coefficient (D_a) of cesium were influenced by composition of saturation media only for Rokle bentonite.     

Study of electrical transport properties of Eu+3substituted MnZn-ferrites synthesized by co-precipitation technique

Eu substituted MnZn-ferrites with nominal composition Mn_0.78Zn_0.22Eu_x Fe_(2?x)O₄ (x=0.0, 0.02, 0.04, 0.06, 0.08 and 0.10) were prepared by co-precipitation technique. The effect of Europium substitution on electrical transport properties of Mn–Zn ferrites is reported. XRD analysis reveals fcc phase in all the samples along with few traces of second phase. The lattice constant shows decreasing trend with the substitution of Eu due to partial solubility of Eu-ions in the lattice. Room temperature resistivity both at 10 and 20 V shows on average an increasing trend. This increase in resistivity is attributed to the unavailability of Fe⁺³ ions in the lattice due to Eu-substitution. The dc resistivity decreases with temperature for all the samples at 10 V and 20 V indicating the semiconducting behavior of these samples. Room temperature dc resistivity and activation energies show similar trend both at 10 V and 20 V indicating that the samples with high resistivity have high activation energies and vice versa. The dielectric constant (ε′), complex dielectric constant (ε″) and loss tangent of these samples decreased with the increase of Eu-concentration, following the Maxwell–Weigner model.     

The influence of mineral variability of Callovo-Oxfordian clay rocks on radionuclide transfer properties

The upper part of the Callovo-Oxfordian clay-rich rock formation (C2c unit) (Meuse/Haute-Marne, France) displays large variations in mineralogical composition of quartz, carbonate and clay minerals. This study deals with the effects of this composition variability on the diffusion-dominated transport properties of HTO (tritiated water)³, ³⁶Cl⁻ and ¹³⁷Cs⁺ for these rocks. Effective diffusion coefficients D_e and accessible porosities ε were determined using the through-diffusion method for a set of C2c unit samples characterized by a contrasted mineralogy especially in terms of clay mineral content (4–29%).The relative variations of the effective diffusion coefficients measured for HTO, ³⁶Cl⁻ and ¹³⁷Cs⁺ remain limited within a range of a factor 5 down to a clay mineral content of ~ 10%. In the range of clay mineral content higher than 15%, the effective diffusion coefficient tends to increase for ¹³⁷Cs⁺ and decreases for ³⁶Cl⁻ whereas D_e(HTO) stays relatively stable. Anion exclusion and surface enhanced diffusion for caesium were quantified and can explain this behaviour. Below 10% of clay minerals, these effective coefficients and the accessible porosities decreased drastically. For 4% of clay minerals, D_e were equal to 1.3 · 10^− 12 m² s^− 1 for HTO, 3.5 · 10^− 13 m² s^− 1 for ³⁶Cl⁻ and 7 · 10^− 12 m² s^− 1 for ¹³⁷Cs⁺. One of the main findings is that the anion exclusion and the enhanced diffusion for caesium still occur for the samples characterized by the lowest clay mineral contents. Finally, the set of diffusion data has been analysed against the well-known Archie's relation linking the accessible porosity to the effective diffusion coefficient.     

Integral sorption with induced crystallization

We studied the integral sorption of saturated, organic vapors in amorphous films of poly (ethylene terephthalate) (PET) using a spring balance apparatus. The penetrants employed (methylene chloride [MeCl₂] and N. N. dimethyl formamide [DMF]) induce substantial crystallization of the polymer during sorption. The experimental data (mass of vapor absorbed versus exposure time) do not obey Fick's law for diffusion but reflect the influence of time dependent polymer swelling and crystallization. The data show that polymer swelling controls the penetrant transport in thin films, while molecular diffusion in the highly swollen semi-crystalline polymer controls in thick films. Small activation energies were found for transport in thin films suggesting that ductile deformation controls the swelling in PET. A mathematical model developed previously explains the important features of the experiments.     

Effects of carbon nanofiber on the dissolution and diffusion of CO2 in polypropylene nanocomposites

The effects of nanofiller with elongated structure on the dissolution and diffusion behaviors of CO₂ in polypropylene (PP)/carbon nanofiber (CNF) composites were investigated in this work. The solubility of CO₂ in PP and PP composites containing 5 wt% and 10 wt% CNF was measured by using magnetic suspension balance (MSB) combined with the experimental swelling correction by using a self-designed high-temperature and -pressure view cell at the temperatures of 200 and 220 °C and pressures up to 20 MPa. The diffusion coefficient of CO₂ in PP and PP composites was also determined from the sorption line at CO₂ pressures ranging from 5 to 10 MPa. It was found that the solubility and diffusivity of CO₂ in PP/CNF composites increased with increasing the filler content, which should be mainly attributed to the change of the distribution of free volume in the polymer matrix besides the small amount of adsorption capacity of CO₂ in CNF. A modified Henry model incorporated with Langmuir adsorption factor was proposed to correlate the solubility of CO₂ in the PP/CNF composites with an average relative deviation less than 3%. A new model based on free volume theory incorporated with the diffusion driving force factor was established to correlate the experimental diffusion coefficient of CO₂ in the PP/CNF composites within an average relative deviation of 2%.     

Moisture diffusion coefficients of mortars in absorption and desorption

Water vapor diffusion coefficients have been determined with a new set-up of the cup method for mortars with three binders (OPC, OPC + 70% slag, OPC + 10% silica fume) and two water/binder-ratios (0.4, 0.5). The measurements were made as a function of relative humidity with samples on both the absorption and desorption limbs of the sorption isotherm. For OPC samples the results show a clear difference between absorption and desorption. For the samples with supplementary cementitious materials the dependence on RH is small.     

Carbon molecular sieve membranes derived from Matrimid® polyimide for nitrogen/methane separation

A commercial polyimide, Matrimid® 5218, was pyrolyzed under an inert argon atmosphere to produce carbon molecular sieve (CMS) dense film membranes for nitrogen/methane separation. The resulting CMS dense film separation performance was evaluated using both pure and mixed N₂/CH₄ permeation tests. The effects of final pyrolysis temperature on N₂/CH₄ separation are reported. The separation performance of all CMS dense films significantly exceeds the polymer precursor dense film. The CMS dense film pyrolyzed at 800 °C shows very attractive separation performance that surpasses the polymer membrane upper bound line, with N₂ permeability of 6.8 Barrers and N₂/CH₄ permselectivity of 7.7 from pure gas permeation, and N₂ permeability of 5.2 Barrers and N₂/CH₄ permselectivity of 6.0 from mixed gas permeation. The temperature dependences of permeabilities, sorption coefficients, and diffusion coefficients of the membrane were studied, and the activation energy for permeation and diffusion, as well as the apparent heats of sorption are reported. The high permselectivity of this dense film is shown to arise from a significant entropic contribution in the diffusion selectivity. The study shows that the rigid ‘slit-shaped’ CMS pore structure can enable a strong molecular sieving effect to effectively distinguish the size and shape difference between N₂ and CH₄.     

Effects of supercritical CO2 extraction parameters on soybean oil yield

A series of operational parameters of supercritical fluid extraction of soybean oil (pressure: 300–500 bar, temperature: 40–60 °C, CO₂ mass flow rate: 0.194–0.436 kg/h and characteristic particle size: 0.238–1.059 mm) were investigated in a laboratory scale apparatus. The results show that the extraction yields were significantly affected by applied operational extraction parameters. The increase in pressure, temperature and solvent flow rate improved the extraction yield. The extraction yield increased as the particle size decreased depending on decreasing intra-particle diffusion resistance. To describe the extraction process Sovova's model was used and very good agreement with the experimental results was obtained. Based on the experimental data the internal and external mass transfer coefficients were estimated. To explore the influence of the extractor size on this process, soybean samples were extracted using different extraction basket volumes (0.2 L and 5 L) and related model parameters were examined. The mass transfer coefficient in the fluid phase increased with the increase in extractor size, while the mass transfer coefficient in the solid phase was independent of the extractor size.     

Low temperature firing of BiSbO4 microwave dielectric ceramic with B2O3–CuO addition

The influence of B₂O₃–CuO addition on the sintering behavior, phase composition, microstructure and microwave dielectric properties of BiSbO₄ ceramic have been investigated. The BiSbO₄ ceramics can be well densified to approach above 95% theoretical density in the sintering temperature range from 840 to 960 °C as the addition amount of B₂O₃–CuO increases from 0.6 to 1.2 wt.%. Sintered ceramic samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microwave permittivity ?_r saturated at 19–20 and Qf values varied between 33,000 and 46,000 GHz while temperature coefficient of resonant frequency shifting between ?70 and ?60 ppm/°C at sintering temperature around 930 °C. Lowering sintering temperature of BiSbO₄ ceramics makes it possible for application in low temperature co-fired ceramic technology.     

Microstructure and electrical transport properties of Ca3Co4−xMnxO9+δ ceramics fabricated under two-step external magnetic field

A series of Ca₃Co_4−xMn_xO_9+δ (x=0, 0.25 and 0.5) samples were prepared under two-step external magnetic field during both processes of sol–gel and pre-pressing. The effects of Mn doping and external magnetic field on the microstructure and electrical transport properties of the samples have been studied systematically. The investigated results show that Mn-doping can improve the electrical transport properties slightly. After using external magnetic field, the textured structures of all the samples are enhanced dramatically, which results in the obvious decrease of the electrical resistivity and increase of Seebeck coefficient. The difference of ρ between the x=0.5 samples without and with external magnetic field is about 24.73 mΩ cm at room temperature. All the samples with magnetic field show higher power factors (PF), for example, the PF at x=0.5 with magnetic field can reach the maximum value of 0.29 mW/m K² at 1073 K.     

Diffusion of niobium in yttria-stabilized zirconia and in titania-doped yttria-stabilized zirconia polycrystalline materials

Bulk and grain boundary diffusion of Nb⁵⁺ cations in yttria-stabilized zirconia (YSZ, 8 mol% Y₂O₃–92 mol% ZrO₂) and in titania-doped yttria-stabilized zirconia (Ti–YSZ, 5 mol% TiO₂–8 mol% Y₂O₃–87 mol% ZrO₂) was studied in air in the temperature range from 900 to 1300 °C. Experiments were performed in the B-type kinetic region. Diffusion profiles were determined using the secondary ion mass spectrometry (SIMS). The temperature dependencies of the bulk diffusion coefficient D and the grain boundary diffusion parameter D′δs for both the materials were calculated. The activation energies of these transport processes in YSZ amounts to 258 and 226 kJ mol⁻¹, respectively, and 232 and 114 kJ mol⁻¹ in Ti–YSZ. The results were compared to the diffusion data of other cations previously obtained for the same material.     

Evidence for anomalous water vapor sorption kinetics in cement based materials

We used dynamic sorption balance measurements to evaluate the diffusivity for cement pastes with three different binders (OPC, OPC + 70% slag, OPC + 10% silica fume). The diffusion of water vapor in cement based materials is normally assumed to follow Fick's law of diffusion, but our results clearly show that Fick's law cannot completely describe the sorption process in our materials. In this paper we report the evidence for this anomalous sorption behavior and discuss a possible method to evaluate diffusivities from such measurements.     

Effect of polymer concentration on porosity and pore size characteristics of alumina membrane substrates prepared by gelcasting

The effect of urea–formaldehyde (UF) polymer concentration on porosity and average pore size of alumina membrane substrates prepared by gelcasting has been studied. The soluble UF oligomers formed in the initial stages of polymerization act as steric stabilizer for alumina particles in the suspension. The porosity and average pore size of the substrate samples decreased with both the decrease of amount of polymer in the gelcast body and the increase of sintering temperature. Membrane substrates obtained by sintering of gelcast bodies containing UF polymer concentrations from 24.3 to 15.6 wt% at temperatures from 1250 to 1450 °C showed porosity and average pore size of 62.5–27 vol% and 0.43–0.20 μm, respectively. The membrane substrates prepared by the gelcasting method had narrow pore size distribution.     

Removal of paraquat from water by an Algerian bentonite

The sorption–desorption of the cationic pesticide 1,1′-dimethyl-4,4′-bipyridinium dichloride (paraquat) on a bentonite from Maghnia (Algeria) desiccated at 110 °C (M), and calcined at 400 °C (M400) and 600 °C (M600) from aqueous solution at 25 °C has been studied using batch experiments. A complete characterization of the natural and heat activated bentonite samples has been carried out through the following techniques: X-ray fluorescence spectroscopy, FTIR, X-ray diffraction, thermogravimetric and differential thermogravimetric analysis and surface analysis. In order to have a better understanding of the variables affecting the sorption of this herbicide, factors such as the working temperature or the ionic strength of the solution have been investigated. The sorption experimental data have been fitted to the Langmuir equation in order to calculate the maximum sorption capacities (X_m) of the samples. The results show that the sorption capacity of the calcined samples greatly decreased with heat treatment. On the other hand, the sorption process is hardly affected by the working temperature, whereas the higher electrolyte concentration, the lower sorption of this pesticide. In addition to batch experiments, a decontamination continuous process (DCP) was designed by the authors using the natural clay to evaluate the potential application of this adsorbent for removing paraquat from water.     

A kinetic study of organic compounds (acetone,toluene, n-hexane and n-decane) adsorption behavior on activated carbon under supercritical carbon dioxide conditions at temperature from 313 to 353 K and at pressure from 4.2 to 15.0 MPa

Adsorption kinetics of four volatile organic compounds (VOCs) (acetone, toluene, n-hexane and n-decane) on activated carbon under supercritical carbon dioxide (scCO₂) conditions was studied. Breakthrough curve measurements of VOCs in scCO₂ were performed with a fixed bed method for activated carbon (ca. mean particles diameter: 100 μm, specific surface area: 1300 m²/g and mean pore diameter: 0.687 nm, respectively). The measured breakthrough curves could be correlated with a kinetic model by using only one fitting parameter (effective diffusion coefficient in pore) within 10% of average relative deviation. The determined effective diffusion coefficient decreased with decreasing temperatures and increasing pressures at all conditions. Additionally, a generalized model of the determined effective diffusion coefficients was developed, and the proposed model could satisfactorily describe temperature and pressure dependence at all VOCs conditions.     

Preparation and characterization of waterborne polyurethane/silica hybrid dispersions from castor oil polyols obtained by glycolysis poly(ethylene terephthalate) waste

Castor oil polyols (COLs) have been synthesized from glycolyzed oligoester polyol in order to produce waterborne polyurethane (WPU)/silica hybrid dispersions. Soft drinks poly(ethylene terephthalate) (PET) bottles were depolymerized by glycolysis with different molar ratio of poly(ethylene glycol) ( PEG 400), in the presence of zinc acetate as catalyst. The obtained glycolyzed products were reacted with castor oil (CO) to attain castor oil polyols by the process of transesterification. Five castor oil polyols were used with hydroxyl values of 255, 275, 326, 366 and 426 mg KOH g⁻¹. Several castor oil-based, polyurethane/silica hybrid dispersions having soft segment content of 39.6% to 28.2% and two concentrations of SiO₂ nanoparticles (0.5 and 1.0) have been prepared.The incorporation effect of SiO₂ nanoparticles into the PU matrix and the hydroxyl functionality of the COLs on the thermal and mechanical properties of resulting polyurethane films has been examined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TG) and measurement of the mechanical properties. The degree of phase separation (DPS) between oxide nanoparticles and hard segment, and particle size in the polyurethane, depends to some extent on nanosilica content and the hydroxyl functionality of the polyols employed in the polyurethane preparation process.Thermal stability of obtained hybrid materials depends on the hydroxyl functionality of the COLs and nanosilica content. The T_10% and T_50% (the temperature where 10 and 50% weight loss occurred) of WPU films decreased with the rise of OH functionality of castor oil polyols, caused by the increase of hard segment content. Glass transition temperature increased with increasing OH functionality and SiO₂ content. The hardness, adhesion and gloss quality of the polyurethane films were also determined with a view to assessing the effect of mole ratios of PET to glycol in glycolyzed products, the hydroxyl functionality and the SiO₂ content.