Presence Of Supercritical Carbon Dioxide Research Articles

Properties of supercritical fluid extrusion‐based crosslinked starch extrudates

AbstractStarch microcellular foam was produced by supercritical fluid extrusion (SCFX) using native and pregelatinized starch mixtures. The starch solution was reacted with epichlorohydrin (EPI) under alkaline conditions in a continuous twin‐screw extruder in the presence of supercritical carbon dioxide. The relationship between crosslinking density and cell size and their distribution in the foamed extrudates was studied. An increase in the EPI concentration from 0 to 0.5% was accompanied by an increase in the degree of crosslinking as measured by differential scanning calorimetry and confirmed by diffusion coefficient measured by nuclear magnetic resonance. The diffusion coefficient of crosslinked sample was observed to be 12.5 times lower than that of non crosslinked control. The average cell size of the microporous structure, observed by scanning electron microscopy, showed a decrease from 147 to 61 μm as the concentration of EPI was increased. The cell size distribution of the crosslinked samples was significantly improved but the total expansion was lowered. The results obtained to date indicate, for the first time, that reactive extrusion of starch with EPI with supercritical carbon dioxide as a blowing agent offers a promising new technique to generate microporous foams for use in various applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis of biodiesel from edible and non-edible oils in supercritical alcohols and enzymatic synthesis in supercritical carbon dioxide

Biodiesel is an attractive alternative fuel because it is environmentally friendly and can be synthesized from edible and non-edible oils. The synthesis of biodiesel from edible oils like palm oil and groundnut oil and from crude non-edible oils like Pongamia pinnata and Jatropha curcas was investigated in supercritical methanol and ethanol without using any catalyst from 200 to 400 °C at 200 bar. The variables affecting the conversion during transesterification, such as molar ratio of alcohol to oil, temperature and time were investigated in supercritical methanol and ethanol. Biodiesel was also synthesized enzymatically with Novozym-435 lipase in presence of supercritical carbon dioxide. The effect of reaction variables such as temperature, molar ratio, enzyme loading and kinetics of the reaction was investigated for enzymatic synthesis in supercritical carbon dioxide. Very high conversions (>80%) were obtained within 10 min and nearly complete conversions were obtained at within 40 min for the synthesis of biodiesel in supercritical alcohols. However, conversions of only 60–70% were obtained in the enzymatic synthesis even after 8 h.

Solid-state Processing of Polymer in the Presence of Supercritical Carbon Dioxide

Open cell microporous bisphenol-A polycarbonate (PC) films are made by a novel, solvent-free processing: drawing PC in supercritical carbon dioxide (scCO2). The pore size is less than 1.0 m, and the porosity is in the range of 20-70% and is highly tunable. The porous film has mechanical properties nearly as high as the original film. The influence of temperature and pressure on drawability, porosity, and mechanical integrity are systematically studied.

Dye uptake and partition ratio of disperse dyes between a PET yarn and supercritical carbon dioxide

The equilibrium uptake of three disperse azoic dyes in a commercial PET yarn in presence of supercritical carbon dioxide was measured. The dye uptake was found to be much more sensitive to temperature than to pressure in the tested operative conditions. The equilibrium partition coefficient between the fibre and the supercritical fluid was evaluated from previously measured solubility data [A. Ferri, M. Banchero, L. Manna, S. Sicardi, An experimental technique for measuring high solubilities of dyes in supercritical carbon dioxide, J. Supercrit. Fluids 30 (2004) 41; A. Ferri, M. Banchero, L. Manna, S. Sicardi, A new correlation of solubilities of azoic compounds and anthraquinone derivatives in supercritical carbon dioxide, J. Supercrit. Fluids 32 (2004) 27]. The high values of the partition coefficients demonstrated that the partition of the dye between the fluid and the polymer is an important parameter to evaluate the feasibility of the dyeing process in supercritical carbon dioxide. The partition coefficients were correlated with three equations: an equation proposed by Funazukuri et al. with four fitting parameters [Ind. Eng. Chem. Res. 41 (2002) 2812]; a semi-empirical equation, with five fitting parameters, that was developed assuming a Langmuir-type absorption of the dyes into the yarn; and an empirical equation, with three fitting parameters, developed from simple experimental data observation. The best agreement was obtained with the second, semi-empirical equation. Good results were also obtained with the third, empirical equation and the agreement with experimental data was better than that obtained with the equation proposed by Funazukuri et al. even though it makes use of one fitting parameter less.

Surface-Constrained Foaming of Polymer Thin Films with Supercritical Carbon Dioxide

Microcellular polymer foams afford a wide variety of attributes relative to their dense analogues, and efforts remain underway to establish viable routes to generate foams with substantially reduced pore cell size and increased pore cell density. Barrier constraints are applied in the present work to achieve diffusion-controlled isothermal foaming of thin polymer films in the presence of supercritical carbon dioxide (scCO2). Poly(methyl methacrylate) (PMMA) films measuring ca. 95−100 μm in thickness are physically constrained between two impenetrable plates so that scCO2 exit diffusion is restricted to the film edges. Results obtained here demonstrate that the pore size can be systematically reduced to less than 100 nm in such systems by applying high saturation scCO2 pressures, relatively low foaming temperatures (near the glass transition temperature of the scCO2-plasticized polymer), and a rapid pressure quench. Classical nucleation theory (CNT) modified to account for the compressible nature of scCO2 ...

Determination of Domain Sizes in Blends of Poly(ethylene) and Poly(styrene) Formed in the Presence of Supercritical Carbon Dioxide

Well-mixed blends of poly(ethylene) and poly(styrene) have been synthesized using supercritical carbon dioxide as a solvent. The morphology of the blends has been conclusively characterized using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), Raman microprobe microscopy, and 13C solid-state cross-polarization magic angle spinning NMR (13C CPMAS NMR). DSC measurements demonstrate that poly(styrene) in the blends resides solely in the amorphous regions of the poly(ethylene) matrix; however, corroborative evidence from the SAXS experiments shows that poly(styrene) resides within the interlamellar spaces. The existence of nanometer-sized domains of poly(styrene) was shown within a blend of poly(styrene) and poly(ethylene) when formed in supercritical carbon dioxide using Raman microprobe microscopy and 13C CPMAS NMR spectroscopy coupled with a spin diffusion model. This contrasts with blends formed at ambient pressure in the absence of solvent, in which domains of poly(styrene) in the micrometer size range are formed. This apparent improved miscibility of the two components was attributed to better penetration of the monomer prior to polymerization and increased swelling of the polymer substrate by the supercritical carbon dioxide solvent.

Influence of interchain forces and supermolecular structure on the drawing behavior of nylon 66 fibers in the presence of supercritical carbon dioxide

AbstractThe drawing behavior and mechanical properties of as‐spun and highly oriented nylon 66 fibers drawn in supercritical carbon dioxide (SCCO2) were investigated. Conditions including different temperatures, CO2 pressures, and plasticizers with different polarity were systematically studied. Results indicate that CO2 is an efficient plasticizer for as‐spun nylon 66 fibers as shown by decreases in the draw stress. In contrast, CO2 shows only a slight influence on the drawability of highly oriented nylon 66 fiber. The effect of other plasticizers such as water, methanol, and ethanol on the drawability of nylon 66 fibers is very similar to that of CO2. Tenacity and modulus of one‐stage drawn fibers were less than 0.8 and 5.0 GPa, respectively. Fibers with the highest tenacity and modulus, 0.96/5.04 and 1.06/5.04 GPa, were obtained by two‐stage drawing in SCCO2 from as‐spun and drawn nylon 66 fibers, respectively. The main reason for the extremely low draw ratios (<6.0) of nylon 66 fibers was the presence of hydrogen bonds in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2282–2288, 2004

Grafting of Maleic Anhydride onto Isotactic Polypropylene in the Presence of Supercritical Carbon Dioxide as a Solvent and Swelling Fluid

Grafting of maleic anhydride (MA) onto isotactic polypropylene (iPP) was carried out by thermal decomposition of dicumylperoxide (DCP) using supercritical carbon dioxide (scCO2) as a solvent and swelling fluid. Provided that the initial concentration of anhydride dissolved in scCO2 is higher than 1% w/w, the grafting occurs without significant molecular weight modification of the polymer, and with a proper selection of the operative conditions, a grafting level higher than 0.5% w/w with respect to the polymer mass was obtained. The amount of grafted MA was determined by FT-IR spectroscopy and polymer degradation was monitored by dynamic mechanical tests in the melt state. The effect of MA and DCP concentration, of the scCO2 density, and of the reaction time on the grafting yield and on the melt flow behavior was studied. Maleic anhydride homopolymerization during the grafting is suggested by FTIR spectra. The home-synthesized maleated iPP was used as effective compatibilizing agent in the preparation of iPP/Nylon-6 blends.

Enhanced crystallization of bisphenol-A polycarbonate by nano-scale clays in the presence of supercritical carbon dioxide

Enhanced crystallization of bisphenol-A polycarbonate by nano-scale clays in the presence of supercritical carbon dioxide

Phase behavior of the monoolein–water system: The effects of addition of the hydrocarbon 1,8-cineole and supercritical carbon dioxide

The results of a study on the phase behavior of the monoolein/water system with the addition of the hydrocarbon 1,8-cineole (C 10H 18O) and supercritical carbon dioxide at 15 MPa is presented. To two mixtures consisting of 9 and 18 wt.% water in monoolein, 5, 10, and 20 wt.% cineole were added and heated to between 35 and 80 °C at atmospheric pressure and in the presence of supercritical carbon dioxide. The phase changes were followed by deuterium nuclear magnetic resonance ( 2 H NMR), light microscopy, and ocular inspection. The mesomorphic structures developed in the 9 wt.% water sample suffered little change due to the presence of the supercritical carbon dioxide. However, in the mixture with 18 wt.% water, the native phase structures were dramatically affected and an isotropic fluid phase developed. The addition of cineole has lowered the LC-L α→LC-H II phase transition in the samples with 9 and 18 wt.% water in monoolein. The surplus of supercritical carbon dioxide in the samples has resulted in similar developments. Regardless of the amount of cineole present in the system, only the isotropic fluid phase was observed in the samples with 18 wt.% water in monoolein.

Enhanced crystallization of bisphenol-A polycarbonate by nano-scale clays in the presence of supercritical carbon dioxide

The crystallization behavior of bisphenol-A polycarbonate (PC) and PC/clay nanocomposites were studied in the presence of supercritical carbon dioxide (SCCO 2) using DSC, WAXD and AFM. In the absence of SCCO 2, nano-scale clay itself does not change the crystallization behavior of PC under our experimental conditions. In the presence of SCCO 2, clay appears to be an efficient nucleating agent and enhances the crystallization of PC. The addition of clay reduces the induction time of crystallization and increases the crystallization rate. The increase in crystallinity with clay depends on the crystallization time. When the crystallization time is sufficient, PC and PC/clay composites tend to have similar crystallinity in the range of 26%. Two melting temperatures are observed during the DSC heating scan, and are mainly associated with the melting of both secondary and primary crystals. Results show that the clay influences the primary crystallization process more than the secondary crystallization process.

Iodine doping of poly(3‐undecylbithiophene) and its composites with polystyrene using supercritical carbon dioxide

AbstractPartially doped conductive poly(3‐undecylbithiophene) and its composites with porous, crosslinked polystyrene were chemically doped with iodine using supercritical carbon dioxide to transport iodine to the conductive regions of the composite. The amount of iodine incorporated into the composite increased from 9.3 wt % at ambient conditions without carbon dioxide to 21.4 wt % in the presence of supercritical carbon dioxide. The conductivity of the composite increased by up to two orders of magnitude with iodine doping using supercritical carbon dioxide. The highest conductivity was obtained in samples treated at moderate temperatures and pressures (313 K and 20.7 MPa). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3876–3881, 2003

Drawing of ultrahigh molecular weight polyethylene fibers in the presence of supercritical carbon dioxide

AbstractThe drawing behavior of ultrahigh molecular weight polyethylene fibers in supercritical carbon dioxide (scCO2) is compared to that in air at different temperatures. The temperature substantially influences the drawing properties in air, whereas in scCO2, a constant draw stress and tensile strength are observed. Differential scanning calorimetry shows an apparent development of a hexagonal phase along with a significant increase in the crystallinity of air‐drawn samples with increasing temperature. The existence of this phase is not confirmed by wide‐angle X‐ray scattering, which instead shows that air‐drawn samples crystallize in an internally constrained manner. In contrast, scCO2 allows crystals to grow without constraints through a possible crystal–crystal transformation, increasing the processing temperature to 110 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1375–1383, 2003

Reactive extrusion of polypropylene with supercritical carbon dioxide: Free radical grafting of maleic anhydride

AbstractA reactive extrusion process for the functionalization of polypropylene with maleic anhydride in the presence of supercritical carbon dioxide was studied. Supercritical carbon dioxide was used in this reactive extrusion system to reduce the viscosity of the polypropylene melt phase by forming a polymer–gas solution in order to promote better mixing of the reactants. Subsequently, the effect of supercritical carbon dioxide on the level of grafting, product homogeneity, and molecular weight was evaluated. Analysis of the products revealed that the use of supercritical carbon dioxide led to improved grafting when high levels of maleic anhydride were used. The experimental results showed no evidence of an improvement in the homogeneity of the product, while melt flow rate measurements showed a reduction in the degradation of polypropylene during the grafting reaction when low levels of maleic anhydride were employed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1116–1122, 2003

Effect of the supercritical CO 2 on surface structure of PMMA/PS blend thin films

The phase structure development in the surface of poly(methyl methacrylate)/polystyrene (PMMA/PS) blend thin film in the presence of supercritical carbon dioxide (SCCO 2) was studied by means of phase contrast microscopy and atomic force microscopy. The surface structures obtained after spin-coating are far from thermodynamic equilibrium. A stable surface structure, which the PS-rich phase is elevated by PMMA-rich phase, is formed after annealed in supercritical CO 2. The structure can be explained by the different aggregation of the PMMA and PS in the two interfaces: air-polymer and substrate-polymer. The different surface structures are investigated as a function of treatment pressure and temperature of supercritical CO 2. A critical phase structure transition temperature/pressure was found at an explicit pressure/temperature by adjusting the condition of the supercritical CO 2. The phase structure transition point indicates a glass transition point could be found by tuning the working condition of SCCO 2. Due to the experimental difficulties in the measurement of T g of the thin films in supercritical CO 2, this study, by observing the resulting surface structure formed in supercritical CO 2, provides us a new angle to look at the problem.

Liquid crystalline properties and extractability of monoolein–water systems by supercritical carbon dioxide

The influence of phase structure on the extraction recovery of monoolein from monoolein–water systems by supercritical carbon dioxide was investigated. Two monoolein–water mixtures at concentrations of 9 wt% water and 18 wt% water, respectively, were studied. 2 H-NMR was used to monitor changes of the phase structures in supercritical conditions. The results showed that the phase structure and the water–monoolein interactions play a role on the extraction yield. The monoolein recovery was higher in the 9 wt% water sample in which L α phase was present compared to the 18 wt% water sample in which the L α melted to yield a L 2 phase. When the phase structures were the same in both samples, the extraction recovery was determined by the solubility properties of the components of the system. The changes due to the presence of supercritical carbon dioxide were shown also to depend on the water concentration of the monoolein–water mixture besides the temperature. The 18 wt% mixture showed a L 2 phase structure in all the range of the temperature investigated while the 9 wt% water mixture showed phase changes from L α phase to L 2 phase in the same temperature range.

Microcellular Polymeric Foams (MPFs) Generated Continuously in Supercritical Carbon Dioxide

ABSTRACTMicrocellular polymeric foams (MPFs) hold tremendous promise for engineering applications as substitutes to their solid analogs in light of reduced manufacturing/materials costs and improved properties. We present a two-part study addressing the generation of such materials in the presence of supercritical carbon dioxide (scCO2). The first part describes the production of polystyrene MPFs in a continuous extrusion process, as well as the effect of operating conditions such as temperature and CO2 concentration on foam morphology. The second part discusses microcellular foaming of poly (vinylidene fluoride) (PVDF), a semicrystalline polymer, via blending with the amorphous polymer poly (methyl methacrylate) PMMA. Foams of pure PVDF possess ill-defined morphologies, whereas those of PVDF-PMMA blends show an improvement with cell sizes on the order of 10 mm or less and cell densities in excess of 109 cells/cm3.

Enhanced Miscibility of Low-Molecular-Weight Polystyrene/Polyisoprene Blends in Supercritical CO2

While ongoing efforts continue to explore the high-pressure phase equilibria of polymer blends, few studies have attempted to address the impact of a supercritical (sc) fluid on such equilibria. In this work, we report on the phase behavior of an upper critical solution temperature (UCST) polymer blend in the presence of supercritical carbon dioxide (scCO2), a nonselective plasticizing agent. Blends composed of low-molecular-weight polystyrene and polyisoprene have been examined as a function of temperature in scCO2 by visual inspection, small-angle neutron scattering, and spectrophotometry. In the presence of scCO2, the cloud point temperature is depressed by as much as 28 °C, depending on both blend composition and CO2 pressure. Complementary studies performed with nitrogen decouple the plasticization efficacy of CO2 from free-volume compression due to hydrostatic pressure. Existence of a pressure yielding a maximum in CO2-induced cloud point depression is established. These results provide evidence for enhanced polymer miscibility as a result of the plasticizing effectiveness and tunable solubility of scCO2.

Adsorption of ethyl benzene on activated carbon from supercritical CO2

AbstractOur work involves experimental and simulation studies of the adsorption breakthrough and equilibria of ethyl benzene (a pollutant commonly encountered in industrial waste streams) on activated carbon in the presence of supercritical carbon dioxide. Frontal and single breakthrough saturations were analyzed for a range of operating conditions of pressure (100–130 bar) and temperature (313–338 K). The equilibrium data correlated well with the Langmuir isotherm. The adsorption process was successfully modeled by a three‐parameter model with comparable fitting parameters for the two types of breakthrough curves.

Total fatty acid analysis of vegetable oil soapstocks by supercritical fluid extraction/reaction

AbstractSoapstock from vegetable oil refining operations is a value‐added by‐product that finds further industrial use based on its fatty acid content. Since the fatty acid content of soapstock can vary according to its vegetable oil source or method of refining, determination of its total fatty acid (TFA) by an accurate analytical method is of key importance to purchasers of this refinery by‐product. Traditionally, the TFA content of soapstock has been determined by the AOCS Official Method G3‐53 based on a gravimetric assay. Unfortunately, this gravimetric‐based assay requires considerable time and incorporates a considerable quantity of organic solvent per assay. In this study, the authors have applied supercritical fluid extraction (SFE) with an enzymatic‐based reaction (SFR), in the presence of supercritical carbon dioxide (SC‐CO2), to determine the TFA content of soapstocks. The SFE/SFR sequence was conducted using two commercially available extractors using an in situ supported lipase in the extraction cell to form fatty acid methyl esters (FAME). Gas chromatographic (GC) determination of the individual FAME, followed by quantitation based on the calculated sum of all the fatty acids from the GC analysis, allowed a precise determination to be made of the soapstock’s TFA content. The TFA contents of three different soapstocks determined by this method were slightly higher than the values derived from Official Method G3‐53. The reported method takes less than one‐half of the time of Official Method G3‐53 and reduces organic solvent use from 575 mL to under 2 mL of solvent by using SC‐CO2.