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.     

Preparation and characterization of barium titanate nanofibers by electrospinning

PVP–BaTiO₃ composite nanofibers were successfully prepared by electrospinning and pure BaTiO₃ fibers were produced after calcination at 1000 °C. A homogeneous viscous solution of barium acetate + titanium acetate/titanium isopropoxide in poly vinyl pyrrolidone (PVP) was prepared by varying PVP concentration in the range of 8–12%. The above sols were electrospun at 9 kV DC by maintaining tip to collector distance (TCD) of 7 cm. The electrospun fibers were calcined at 1000 °C for 2 h. Thermo gravimetric analysis (TGA) of the fibers indicates the complete decomposition of organics below 700 °C with 45% weight loss. Scanning electron microscopy (SEM) study shows the fibers cylindrical, smooth with diameters in the range of 50–400 nm and the aspect ratio >1000. The average diameter of the fibers increases with the increase in PVP concentration. The calcined BaTiO₃ nanofibers were found to be coarse, brittle and diameter reduced by 12%. FT-IR study confirms the formation of metal oxide bond at higher temperature.     

Synthesis and properties of 1D Sm-doped CeO2 composite nanofibers fabricated using a coupled electrospinning and sol–gel methodology

Ce_1−xSm_xO₂(x=0, 0.2, 0.5 and 0.8) nanofibers (NFs) were synthesized by coupling sol–gel with electrospinning and using poly-vinyl pyrrolidone (PVP) as the polymer medium, in an ethanol/water mixture. Control over the fabrication conditions was achieved through analysis of the most key synthetic factors, which include: (i) the applied field strength; (ii) the solution feed rate and (iii) the PVP content in the electrospinning solution. The optimum microstructural fiber morphology (high quality beeds-free fibers) was achieved using the following electrospinning parameters: an applied voltage of 18.5 kV, a 7 ml/h of solution feed rate and a 12% (w/w) of PVP composition. Morphological features of the resulting fibers were examined by scanning electron microscopy (SEM). The average fiber diameter was typically found to be in the range of 200–1100 nm and 50–300 nm, before and after calcination at 500 °C, respectively. X-ray diffraction (XRD) results showed that the fluorite cubic structure was preserved for the entire Ce_1−xSm_xO₂ compositional range studied, while elemental analysis using EELS and X-ray photoelectron spectroscopy (XPS) confirmed the purity of the bulk and surface composition of the fibers. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) proved that the NFs are highly crystalline. The thermal stability of the composite (polymer/inorganic nitrate salts) NFs was further investigated in an inert atmosphere (N₂) using thermogravimetric analysis (TGA), which allowed the transformation process of the NFs from composite to oxide to be monitored. The reducibility of the metal oxide NFs (mobility of oxygen species in the fluorite cubic lattice) as well as their thermal stability in successive oxidation–reduction cycles was evaluated using temperature-programmed reduction in a H₂ atmosphere (H₂-TPR). Acidic–basic features of the NFs and powder surfaces were studied through temperature programmed desorption (TPD) using NH₃ and CO₂ as probe molecules, where weak, medium and strong acid sites were successfully traced with profound differences depending on the morphology. The NFs' potential performance towards NH₃ oxidation was also evaluated. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the NFs, as probed by CO₂ adsorption. Pyridine adsorption followed by infrared spectroscopy (Py-FT-IR) studies unveiled the more profound Lewis acid presence in Ce_0.5Sm_0.5O₂ NFs compared to bulk powder Ce_0.5Sm_0.5O₂.     

Synthesis of a biocompatible polymer using siloxane-based surfactants in supercritical carbon dioxide

Poly(N-vinyl-2-pyrrolidone) (PVP) particles were prepared by dispersion polymerization in the presence of 2,2′-azobisisobutyronitrile as the initiator and siloxane-based surfactant in supercritical carbon dioxide (scCO₂). The dispersants used in this study were non-ionic, non-reactive and commercially produced siloxane-based surfactants (Monasil PCA and KF-6017). We investigated the effect of kinds and concentrations of the surfactants, in addition to the reaction temperature and the concentration of the monomer on the particle size and morphology. PVP microspheres were prepared in 0.23–0.74 μm size range with Monasil PCA and 0.71–1.98 μm size range with KF-6017, respectively. The resulting polymer particle of >90% yield was obtained. Particle size slightly increased with the amount of monomer in polymerization with Monasil PCA. In the case of KF-6017 as the surfactant, there was not an obvious variation in particle size with increasing monomer. Particle size of PVP decreased as surfactant concentration increased from 5.0 to 15.0 wt.% basis on concentration of monomer. The narrow particle size distribution (D_n = 0.23 μm and PSD = 1.06) was presented at the high concentration of Monasil PCA (15 wt.% on monomer concentration). As indicated by the reaction temperature and the addition of organic solvent, which affected solubility of monomer, polymer and surfactant in scCO₂, particle size and particle size distribution of PVP varied. PVP particles with Monasil PCA strongly aggregated at 75 °C in contrast to KF-6017 which showed discrete particles at 65 and 70 °C, but particle size distribution was broad. Particle size was slightly reduced with a little amount of hexane, with an inverse relationship of adding hexane reduced the particle size. The amount of the relative residual surfactants on surface of the polymer after extracting with supercritical fluid process (SFE) was measured by using SEM/EDS and EPMA analysis to map out the distribution of silicon element qualitatively. The original polymer particle before the extraction using CO₂ had the high level of silicon element, but the average level of silicon element became low after CO₂ extraction.     

Supercritical antisolvent micronization of PVP and ibuprofen sodium towards tailored solid dispersions

The supercritical antisolvent technology is used to precipitate polyvinylpyrrolidone (PVP) particles and crystallise ibuprofen sodium (IS) crystals separately and in the form of solid dispersion together. Supercritical carbon dioxide (scCO₂) is used as antisolvent. For PVP particle generation, ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of PVP in the solution was varied between 0.5 wt% and 1.5 wt%, the operation pressure between 10 MPa and 30 MPa and the composition of ethanol/acetone solvent mixtures between 100 wt% and 0 wt% of ethanol at a constant temperature of 313 K. Furthermore, the mean molecular weight of the polymer was varied between 40 kg mol⁻¹, 360 kg mol⁻¹ and 1300 kg mol⁻¹. An increase of the content of the poor solvent acetone in the initial solvent mixture as well as the usage of PVP with a higher molecular weight, leads to a significant decrease in mean particle size. At all the investigated parameters always fully amorphous PVP powder precipitates. For IS, only ethanol was used as the solvent, the initial IS concentration in the solution was varied between 1 wt% and 3 wt% and the operation pressure between 10 MPa and 16 MPa. A variation of these parameters leads to a manipulation of the size and the morphology of the crystallised IS crystals. Irrespective of the parameters used, always the same polymorphic form of ibuprofen sodium is produced. The solid dispersions were generated at different compositions of PVP to IS and with two different molecular weights of PVP at otherwise constant conditions. Fully amorphous solid dispersions consisting of IS and PVP together were generated at different ratios of PVP to IS.The mechanisms that control the final particle properties are discussed taking into account two different models for “ideal” and “non-ideal” solutes. Furthermore, the study of the “unconventional” SAS parameters, molecular weight and solvation power of the solvent shows that these parameters qualify to tailor polymer particle properties via SAS processing. Next to the investigation into the behaviour of both solutes separately, fully amorphous solid dispersions consisting of IS and PVP together were generated. While X-ray diffraction was used to analyze the crystalline structure of the particles, respectively, solid dispersions, their morphology was analysed using scanning electron microscopy (SEM).     

Density and viscosity of the binary polyethylene glycol/CO2 systems

Density of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight was measured in pressure range from 8.0 MPa up to 47.7 MPa at a temperature of 343 K by a volumetric method. To validate the method density of pure CO₂ was measured at different pressures and a temperature of 293 K. The results were compared to the literature data and the accuracy was better than 2%. The density was between 1.17 g/mL for PEG 1000/CO₂ at 14.5 MPa and 1.78 g/mL for the system PEG 4000/CO₂ at 35 MPa. Further, the data were compared to results, obtained by a gravimetric method using magnetic suspension balance (MSB).Viscosity of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight at different pressures and at a temperature of 343 K was measured using a high pressure view cell. Also a temperature impact on the viscosity of pure PEGs was observed at ambient pressure. After saturating PEG 1500 with 10 MPa of CO₂ pressure its viscosity decreases from 76.6 mPa s to 2.24 mPa s at 333 K. Further addition of CO₂ and increasing the pressure results in even lower viscosity and the highest viscosity reduction was reached at the highest pressure; at 35 MPa viscosity of the system PEG 1500/CO₂ is only 0.665 mPa s.     

Ovicidal activities of supercritical CO2 and N2O on Ascaris suum eggs

This study examined whether supercritical CO₂ and N₂O fluids are effective in inactivating Ascaris suum eggs, which were chosen as a model for parasite eggs. The treatments were carried out in a multibatch apparatus, in which, the eggs could be placed atop a solid surface (non-immersed condition) or in aqueous solution (immersed condition). Various CO₂ and N₂O phases—including gas (6 MPa, 30 °C), liquid (8 MPa, 30 °C), subcritical (10 MPa, 30 °C), and supercritical (10 MPa, 37 °C)—were tested with exposure times ranging from 1 to 20 min. Supercritical CO₂ and N₂O both showed a similar, strong ovicidal effect, requiring only 1 min in non-immersed conditions and 5 min in water-immersed conditions to achieve a 2.4-log inactivation. Subcritical CO₂ and N₂O showed a weaker ovicidal effect. The effect was significantly reduced for the gas and liquid phases, compared with the supercritical phases. This study reports that supercritical CO₂ and N₂O can be effectively employed as a non-thermal treatment technique to control parasite egg contamination in fecal matter and food.     

Microstructure and properties of 2D-Cf/SiC composite fabricated by combination of CVI and PIP process with SiC particle as inert fillers

2D-C_f/SiC composite was manufactured by chemical vapor inflation (CVI) combined with polymer impregnation and pyrolysis (PIP) with SiC particle as inert fillers. The effects of CVI processes on SiC morphologies and the properties of composite were investigated. The composites were characterized by XRD, flexural strength test and SEM. The results revealed that uniform SiC coatings and nanowires were prepared when MTS/H₂ ratio of 1:8 was employed, while gradient thick coatings were fabricated as MTS/H₂ ratio of 1:1 was employed. The flexural strength of composites varied from 156 MPa at MTS/H₂ ratio of 1:1 to 233 MPa at MTS/H₂ ratio of 1:8. All of composites exhibited toughness due to significant debonding and pullout of fibers. The laminated structure of coatings on the fibers and nanowires were manufactured by combination of above different CVI process, and the obtained composites showed flexural strength of as high as 248 MPa and impressive toughness.     

Anti-solvent effect in the production of lysozyme nanoparticles by supercritical fluid-assisted atomization processes

Particles of lysozyme in the range of 0.1–5 μm were generated by high pressure CO₂ or N₂ (at pressures between 8 MPa and 25 MPa) from aqueous ethanol solutions using an atomization process similar to the supercritical assisted atomization technology. Perfect nanosized spheres of lysozyme were produced using both supercritical fluids. However, while N₂ assisted atomization-produced spheres at all experimental conditions reported here, supercritical CO₂ assisted atomization produced particles of two distinct morphologies depending on the pre-mixing conditions. This work shows that CO₂ assisted atomization produces particles by two different mechanisms depending on the mixture pre-expansion phase equilibria conditions: anti-solvent crystallization and spray drying crystallization. Depending on the governing precipitation mechanism (anti-solvent or spray drying), fibers or spherical particles were obtained with CO₂. Lysozyme activity was severely affected by pure anti-solvent processing, while N₂ processed lysozyme conserved mostly its activity.     

Hierarchically structured polymer-derived ceramic fibers by electrospinning and catalyst-assisted pyrolysis

Hierarchically structured polymer-derived ceramic fibers were successfully produced by electrospinning a commercially available preceramic polymer to which a cobalt-based catalyst precursor was added, followed by pyrolysis in nitrogen at temperatures ranging from 1250 to 1400 °C. The nanowires formed via the vapor–liquid–solid (VLS) mechanism, involving the reaction of SiO and CO gases, generated from the decomposition of the polymer-derived-ceramic at high temperature, with the heating atmosphere assisted by the presence of nano-sized CoSi droplets. The main crystalline phase for the nanowires was Si₃N₄ below 1350 °C, and Si₂N₂O at 1400 °C, and the amount of nanowires increased with increasing heating temperature. Hierarchically structured fiber mats possessed a higher specific surface area (14.45 m²/g) than that of a sample produced without the cobalt catalyst (4.37 m²/g).     

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%.     

Extraction of bioactive enriched fractions from Eruca sativa leaves by supercritical CO2 technology using different co-solvents

Supercritical fluid extraction from freeze-dried Eruca sativa leaves is assessed with the aim of studying the feasibility to obtain bioactive enriched fractions containing different classes of valuable compounds. Total extraction yields and compositions using pure CO₂ and CO₂ + selected co-solvents are compared. Overall extraction curves, fitted by the model of broken and intact cells developed by Sovová, are reported and the influence of the main parameters that affect the extraction process is analysed. The extract with the highest content in glucosinolates and phenols was collected at 30 MPa and 75 °C using 8% (w/w) of water with respect to the CO₂ flow rate, whereas the fraction richest in lipids was obtained using 8% (w/w) of ethanol as co-solvent at 45 °C and 30 MPa. A process including a first step with supercritical CO₂ extraction using water as co-solvent followed by a second step, where a fraction rich in lipids is extracted using ethanol as co-solvent, is proposed. SCCO₂ results are compared with Soxhlet and other methods that combine organic solvents with ultrasounds.     

Phase equilibrium of two CO2+ biodegradable oil systems up to 72 MPa

A setup based on a static visual synthetic method for determining phase equilibria up to 100 MPa is presented. Solubilities of carbon dioxide (CO₂) in a high-oleic sunflower oil (HOSO) and in an additivated vegetable lubricant (BIO-2T-05) were determined from 298 K to 363 K up to CO₂ mass compositions of 0.42. The experimental device was verified comparing the solubilities of CO₂ in HOSO with values from other laboratory. For both systems, the values of CO₂ solubility show cross-over pressures among the different isotherms. A new equation was used to correlate the solubility data, with deviations in CO₂ mole fraction in the oil-rich phase lower than 1.6%. The prediction ability of Carvalho and Coutinho equation was tested with experimental data. Vapor–liquid–liquid equilibria were also investigated for CO₂ + BIO-2T-05 in the range 288–305 K. Furthermore, densities and viscosities at 0.1 MPa for BIO-2T-05 were measured from 278 K to 373 K.     

Extraction of jojoba seed oil using supercritical CO2+ethanol mixture in green and high-tech separation process

In this study, the extraction of jojoba seed oil obtained from jojoba seed using both supercritical CO₂ and supercritical CO₂+ethanol mixtures was investigated. The recovery of jojoba seed oil was performed in a green and high-tech separation process. The extraction operating was carried out at operating pressures of 25, 35 and 45 MPa, operating temperatures of 343 and 363 K, supercritical fluid flow rates of 3.33 × 10⁻⁸, 6.67 × 10⁻⁸ and 13.33 × 10⁻⁸ m³ s⁻¹, entrainer concentrations of 2, 4 and 8 vol.%, and average particle diameters of 4.1 × 10⁻⁴, 6.1 × 10⁻⁴, 8.6 × 10⁻⁴ and 1.2 × 10⁻³ m. It was found that a green chemical modifier such as ethanol could enhance the solubilities, initial extraction rate and extraction yield of jojoba seed oil from the seed matrix as compared to supercritical CO₂. In addition, it was found that the solubility, the initial extraction rate and the extraction yield depended on operating pressure and operating temperature, entrainer concentration, average particle size and supercritical solvent flow rate. The solubility of jojoba seed oil and initial extraction rate increased with temperature at the operating pressures of 35 and 45 MPa and decreased with increasing temperature at the operating pressure of 25 MPa. Furthermore, supercritical fluid extraction involved short extraction time and minimal usage of small amounts entrainer to the CO₂. About 80% of the total jojoba seed oil was extracted during the constant rate period at the pressure of 35 and 45 MPa.     

Electrospinning nanoribbons of a bioengineered silk-elastin-like protein (SELP) from water

Electrospinning of a silk-elastin-like protein (SELP), a repeat sequence protein polymer (RSPP) from aqueous solution, is reported here. The electrospinning of SELP47K resulted in fibers with a uniform, ribbon-like morphology. The solution properties of SELP47K provide ideal conditions for electrospinning and resultant nanoribbons are demonstrated to form self-standing, non-woven fiber meshes. The mechanical properties of these meshes have also been evaluated, and the ultimate tensile strength was found to be 30.8 MPa with an average initial modulus of 0.88 GPa. Furthermore, the effect of electrospinning parameters, such as solution concentration, applied voltage, collecting distance, and rate of spinning, on the fiber dimensions and morphology are studied. Within the experimental matrix, the width of these nanoribbons is found to be between 25 nm and 1800 nm. The secondary structure of SELP47K nanoribbons is analyzed by FTIR and WAXD and the methanol treatment resulted in improvements in the crystalline β-sheet structure when compared to as spun electrospun nanoribbons.     

Effect of the porous structure in carbon materials for CO2 capture at atmospheric and high-pressure

Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO₂ capture both at atmospheric (∼168 mg CO₂/g at 298 K) and high pressure (∼1500 mg CO₂/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure, in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores (pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO₂/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.     

Electrospinning preparation and characterization of alumina nanofibers with high aspect ratio

Alumina nanofibers were successfully prepared via an electrospinning technique combined with a sol–gel method. The electrospinning solution was prepared by dissolving aluminum isopropoxide (AIP) in distilled water and then mixing with a polyvinyl alcohol (PVA) aqueous solution. The as-spun fibers were calcined at different temperatures and characterized by TG–DTA, XRD, SEM–EDS, TEM–SAED, and BET analysis. Results showed that the average fiber diameter decreases with increasing calcination temperature. The as-spun nanofibers were amorphous. After calcination at 1000 °C, the nanofibers formed were composed of α-Al₂O₃ and γ-Al₂O₃, showing an average diameter of 30–90 nm and an aspect ratio of greater than 1000. The pore size of the obtained fibers was approximately 5 nm, which implies that these fibers are mesoporous materials.     

Supercritical CO2 oilseed extraction in multi-vessel plants. 2. Effect of number and geometry of extractors on production cost

The objective of this work was to study production costs for the supercritical CO₂ extraction of a pre-pressed oilseed (packed bed with 2-mm particles) in a 2-m³ industrial multi-vessel plant operating at 40 °C and 30 MPa, using a fully predictive mass transfer model to simulate the process. We modified the inner diameter (47.3 ≤ D ≤ 65.6 cm) and number (n = 2, 3, or 4) of extraction vessels, and the mass flow rate of CO₂ (Q = 3000 or 6000 kg/h), thus changing the aspect ratio of the extraction vessels (3 ≤ L/D ≤ 8), and superficial velocity (2.71 ≤ U ≤ 10.8 mm/s) and specific mass flow rate (6 ≤ q ≤ 24 kg/h per kg substrate) of CO₂. Production cost decreased when increasing the mass flow rate of CO₂ or the number of extraction vessels (or when increasing q). Production cost did not depend on the geometry of extraction vessel for a constant specific mass flow rate of CO₂, but it decreased with a decreasing of the L/D ratio of the vessel for a constant superficial velocity of CO₂. For any given plant, the contribution of fixed cost items (capital, labor) to the production cost increased with extraction time, unlike that of variable cost items (substrate, CO₂, energy), which decreased. Thus, there was an optimal extraction time that minimized production cost for each plant. This work proposes an expression for capital cost of an industrial multi-vessel plant as a function of the mass flow rate of CO₂ (which defines the cost of the solvent cycle of the plant), and the volume of the extraction vessels (which together with number of extraction vessels define the cost of extraction section of the plant), with a scaling factor of 0.48 for both items. Under optimal conditions, capital cost represented 30–40% of the production cost, but uncertainties in capital cost estimates (about ±50% using the proposed expression) may largely affect these estimates. The lowest production cost estimated in this work was USD 7.8/kg oil for the extraction of prepressed oilseed in a four-vessel plant using 6000 kg/h of CO₂. The mass flow rate of CO₂ and number of extraction vessels also affected annual productivity that was about 360 ton oil for the same plant operating 7200 h per year. Oil yields were above 90% for both three- and four-vessel plants.     

Effects of humidity on titania-based polyvinylpyrolidone (PVP) electrospun fibers

Humidity effects on titania-based nanofibers were studied by electrospinning solutions of different weight percentages of titanium (IV) n-butoxide (TNBT) and polyvinylpyrolidone (PVP) in N,N-dimethylformamide (DMF). Ambient humidities during electrospinning were typically varied between 25 and 75% RH. XRD and SEM were used to examine crystallization and determine optimal conditions for fiber formation. A specific combination of solute concentration (45–55 wt%) and ambient humidity (25–60% RH) allowed fiber formation. Lower solute concentrations resulted in electrospraying while higher humidities induced excessive plasticization of the PVP. Using a heated target allowed fiber formation at higher humidities (>60%). Following electrospinning, slight degradation of the 60 wt% (but not the 50 wt%) TNBT microstructure was observed when stored for longer periods possibly due to higher moisture uptake in case of higher solids loading. Examination of the fibers following pyrolysis at 500 °C for 6 h in air revealed the presence of individual nanoscale crystallites that could potentially boost ionic and electronic diffusion in batteries and solar applications.     

A shrinking core model and empirical kinetic approaches in supercritical CO2 extraction of safflower seed oil

Utilization of supercritical CO₂ in safflower seed extraction was performed using a semi-batch extractor. Different extraction parameters, such as 40–60 MPa pressure, 323–347 K temperature, 20–76 min time, and 1–3 mL/min CO₂ flow rate were applied. A two-stage experimental design application was performed in order to maximize the oil yield. First of all, a 3² factorial design was applied to estimate the effect of the main factors and their interactions. The second part of the experimental design was improved and accelerated using the steepest ascent method. Optimum extraction parameters were determined to be 50 MPa pressure, 347 K temperature and 76 min time at a constant CO₂ flow rate (3 mL/min) according to the 2² design. Under these conditions, the oil yield obtained was 39.42%, comparable with Soxhlet extraction (40%) for 8 h. Shrinking core and empirical kinetic models were applied in order to generalize the extraction process. The predicted data was compatible with the experimental data.