Effect Of Supercritical Carbon Dioxide Research Articles

Synthesis of cellulose/titanium dioxide hybrids in supercritical carbon dioxide

The modifications and applications of natural cellulose have attracted more and more interest in recent years, sparked by the progressive shortage of the fossil energy resources and increase in the technological interests in sustainable and renewable raw materials. In this paper, a novel approach for preparation of cellulose/titanium dioxide hybrids was achieved by utilizing supercritical carbon dioxide-assisted impregnation. The hybrids, with a very small scale in length, suggest that the titania particles were not only coating on the external surface but also penetrating into the micro-cavity structure of the cellulose fibers. The penetrating and swelling effect of supercritical carbon dioxide, with a colsovent of ethanol, on the cellulose was also investigated. It was found that such actions of carbon dioxide in the supercritical state influenced the interactions between the molecular chains of cellulose. The titania particles were facilitated by the effect of supercritical carbon dioxide to access and impregnate into the crystalline structure of cellulose fibers by formation and stabilization of hydrogen bonds with abundant hydroxyl groups of cellulose, resulting in a change of its thermal stability in pyrolysis. This preparative procedure is facile and environmentally friendly, and provides a simple approach for the synthesis of useful materials in various applications.

Effects of supercritical carbon dioxide on volatile formation from Maillard reaction between ribose and cysteine

AbstractBACKGROUND: Supercritical carbon dioxide (SC‐CO2) technology is being used in an increasing number of food‐manufacturing applications; however, its effect on the Maillard reaction is not well studied. The objective of this study was to investigate the effect of SC‐CO2 treatment (140 °C, 40 MPa) on the Maillard reaction of an aqueous ribose–cysteine model system under varying pH conditions (5.6, 7.0 and 8.0), with emphasis on the formation of volatile compounds.RESULTS: SC‐CO2 had a suppressing effect on the browning stages of the reaction under acidic and neutral pH conditions, while it appeared to have an accelerating effect at pH 8.0. Over 70 volatile compounds were positively identified from the headspace of the model system by gas chromatography–mass spectrometry. The volatiles were dominated by sulfur‐containing compounds including thiophenes and fused bicyclic sulfur‐containing compounds under all experimental conditions. Several compounds, including 2‐methyl‐3‐furanthiol, 2‐furanmethanethiol, 3‐thiophenethiol, and 2‐methyl‐3‐thiophenethiol, and one of the intermediates, furfural, were generated in much higher amounts in the SC‐CO2‐treated samples, especially at alkaline and neutral pH values.CONCLUSION: SC‐CO2 treatment was inhibitory to the formation of most volatiles in the Maillard reaction, but enhanced the formation of some intermediates and well‐known meaty flavoured compounds. Copyright © 2007 Society of Chemical Industry

Novel route to nanoparticle dispersion using supercritical carbon dioxide

An experimental study was carried out to determine the effects of supercritical carbon dioxide (scCO 2) on the break up of untreated and treated alumina agglomerates in polystyrene. Alumina nanoparticles were treated with fluoroalkanes to achieve a better affinity with scCO 2. All agglomerates were found inside pores (cells) that were created by scCO 2 expansion during depressurization, and the observed cell size increased with increasing alumina agglomerate size. When untreated alumina was used, the agglomerates were not affected by scCO 2 expansion. On the other hand, large agglomerates ( L ≥ 15 μm) of the treated alumina showed signs of catastrophic fragmentation, whereas small agglomerates of the treated alumina were intact upon scCO 2 expansion. This was attributed to the amount of scCO 2 saturation around and within small agglomerates, which does not provide enough energy to break up the agglomerate. This conclusion was also supported by the fact that cell sizes were proportional to agglomerate size. Large agglomerates can absorb more scCO 2 than smaller ones, and therefore, have an adequately larger bursting pressure to overcome interactions between individual alumina nanoparticles that make up the agglomerate.

New insights on the use of supercritical carbon dioxide for the accelerated carbonation of cement pastes

This study aims to analyze the effects of supercritical carbon dioxide (SCCO 2) on the carbonation of Portland cement pastes, with and without mineral addition. The process is based on the advantages of the low viscosity and surface tension of SCCO 2 that allow the complete wetting of complex substrates with intricate geometries, including internal surfaces of agglomerates such of these found in cement pastes. The supercritical treatment alters the bulk chemical and structural properties of cement pastes by accelerating natural carbonation reactions, while at the same time it reduces both free and bound water. The observed overall effects of supercritical carbonation on Portland cement pastes were the neutralization of pore water alkalinity, the formation of calcium carbonate and the reduction in the Ca/Si ratio of the calcium silicate hydrate (CSH) gel. Moreover, the massive precipitation of calcium carbonate inside microcracks after supercritical treatment caused the refinement of the microstructure, thus, reducing water permeability to a large extent. Supercritical carbonation method can be completed in few hours, rendering it technically interesting. This work also contributes to the idea of increasing the durability of concrete by means of a preventive hydrophobic supercritical treatment against water ingress. A generic SCCO 2 method for concrete silanization is proposed here.

Effect of supercritical carbon dioxide on polystyrene extrusion

A study on the extrusion of polystyrene was carried out using supercritical carbon dioxide (scCO 2) as foaming agent. scCO 2 modifies the rheological properties of the material in the barrel of the extruder and acts as a blowing agent during the relaxation at the passage through the die. For experiments, a single-screw extruder was modified to be able to inject scCO 2 within the extruded material. The effect of operating parameters on material porosity was studied. Samples were characterized by using water-pycnometry, mercury-porosimetry and scanning electron microscopy. Polystyrene with expansion rate about 15–25% was manufactured. A rapid cooling just downstream the die is important to solidify the structure. The die temperature allows the control of the porosity structure. CO 2 concentration shows no significant influence.

Effects of supercritical carbon dioxide treatment for sterilization purpose on meat quality of porcine longissimus dorsi muscle

The objective of this study was to investigate the effect of supercritical carbon dioxide (SC-CO 2) treatment for the sterilization purpose on meat quality and protein denaturation of the porcine longissimus dorsi muscle. The conditions of SC-CO 2 treatment were 7.4 and 15.2 MPa at 31.1 °C for 10 min. SC-CO 2 treatment had no effect on muscle pH, tenderness, and water-holding capacity (WHC). However, the samples treated at 7.4 MPa had a higher lightness value (52.97 vs. 46.94, P<0.001) and a more pronounced extent of sarcoplasmic protein denaturation (73.80 vs. 80.73, P<0.01) than the control samples. These results suggest that the paler color of samples treated with SC-CO 2 was associated with the sarcoplasmic protein denaturation, and the major denaturated proteins were determined to be phosphorylase b (PH), creatine kinase (CK), triosephophate isomerase (TPI), and one unknown protein. On the other hand, other quality traits were generally unaffected by the SC-CO 2 treatments at 7.4 or 15.2 MPa.

Glucose oxidase immobilization on conducting polymers in supercritical CO 2 environment: An exploratory study

Glucose oxidase (GOX) is immobilized on two conducting polymers: polypyrrole (PPY) film and polyurethane/polypyrrole (PU/PPY) composite foam, via supercritical fluid immobilization (SFI) for use in the preparation of biosensors. The effects of supercritical carbon dioxide (scCO 2) (80–150 bar, 40 °C) and temperature (30–60 °C) on free-enzyme buffer-solution activity are investigated for 24 h scCO 2 exposure time. Results show that enzymatic activity of GOX after exposure to scCO 2 is retained. The enzymatic activity of GOX-buffer solution does not show a noticeable decrease between 30 and 50 °C, whereas 30 and 94% activity losses are noticed at 55 and 60 °C temperatures. The GOX immobilized PPY films and PU/PPY composite foams are analyzed via environmental scanning electron microscopy (ESEM) and enzymatic activity methods. Four different immobilization mediums are used for PPY films: dry GOX and dry PPY (Dry); dry GOX and dry PPY with water vapor (Semi-Dry); GOX and PPY in water (Wet); GOX and PPY in buffer (Wet-b). In “Dry” and “Semi-Dry” procedures (up to 150 bar, 40 °C and 72 h), the PPY films showed no noticeable activity, whereas films processed in “Wet” and “Wet-b” methods showed enzymatic activity. In “Wet” method (150 bar and 40 °C), as the immobilization time increased (5–72 h) the activity was enhanced. The maximum activity is observed for GOX immobilized PPY in the “Wet-b” medium. Thus, during GOX immobilization of PU/PPY, buffer solution is used as the immobilization medium. Experiments are conducted at 40 °C and for 24 h. The immobilization pressure effect (75–150 bar) on the activities of GOX-immobilized PU/PPY composites are investigated. Activity of the immobilized enzyme increases significantly from 75 to 105 bar. Further pressure increase to 150 bar causes a decrease in the activity of the GOX-immobilized PU/PPY composite sample. Immobilization of GOX onto PU/PPY composite at 1 bar is not found feasible.

Physicochemical characterization of drug-cyclodextrin complexes prepared by supercritical carbon dioxide and by conventional techniques

The objective of this study was to investigate the effectiveness of supercritical carbon dioxide (SC CO2) technique for preparing solid complexes between β-cyclodextrin and three local anesthetic agents (benzocaine, bupivacaine, and mepivacaine) by comparing it to more traditional methods such as kneading, co-evaporation, co-grinding, and sealed-heating. Effects of variation of experimental conditions, i.e. temperature, pressure and exposure time, on the products prepared by SC CO2 method were also examined. The products obtained were characterized by powder X-ray diffractometry and Fourier transform infrared spectroscopy, and tested for dissolution properties. Results suggested the possibility of complex formation between β-cyclodextrin and the three anesthetic agents, and indicated that it was influenced by the preparation technique. The co-grinding method was the only one resulting in completely amorphous products for all three drugs. Almost amorphous products, with only limited residual crystallinity, were obtained by co-evaporation and kneading techniques, while SC CO2 and sealed-heating methods gave rise to more crystalline systems. As for the SC CO2 method, temperature (for benzocaine and bupivacaine) or exposure time (for mepivacaine) had significant effects on the solid-state properties of the final products. Dissolution studies indicated that all the examined methods were more effective than the simple physical mixing in improving drug dissolution properties, but the different rank orders observed for the different drugs suggested that there is no general rule for the selection of the most effective preparation method, which depends on the type of drug-Cyd system considered. Nevertheless, in all cases, products obtained by the SC CO2 method showed satisfactory dissolution properties.

Effects of Supercritical Carbon Dioxide on Adhesive Strength between Micro-sized Photoresist Patterns and Silicon Substrates

AbstractAdhesive bend testing for micro-sized photoresist components has been performed to clarify the effects of supercritical CO2 (ScCO2) treatment. Multiple microsized cylindrical specimens were fabricated on a silicon substrate using epoxy-type photoresist. The specimens were ScCO2 treated at a temperature of 323K at a pressure of 15MPa for 30 min, and then, decompressed to atmospheric pressure at two different rates. Double refraction appeared in the SU-8 specimens near by the interface between the SU-8 specimens and a substrate after ScCO2 treatment. Adhesive bend strength of ScCO2 treated specimen with slow decompression process is approximately 60% higher than that of non- ScCO2 treated specimens, however, the strength of the microsized photoresist was slightly degraded by ScCO2 treatment with quick decompression process. All the results suggest that ScCO2 treatment improves the adhesive strength between microsized photoresist components and a silicon substrate by control of the decompression process.

A comparative study on the transalkylation of diisopropylbenzene with benzene over several zeolitic materials in supercritical CO 2 and liquid phase

This work describes the catalysts screening and the analysis of the effect of supercritical carbon dioxide on the transalkylation of diisopropylbenzene with benzene. The catalysts included three acidic commercial zeolites: beta, Y and mordenite with different aluminum contents (e.g. Si/Al molar ratio). Their performance was compared in terms of cumene yield and selectivity, taking into account the competitive isomerization, and the by-products formation. The influence of the Si/Al molar ratio on the catalytic activity was discussed in terms of total acidity and strength of acid sites. Liquid, subcritical and supercritical conditions were comparatively investigated. The results proved that transalkylation rates were not accelerated by the increase in pressure from subcritical to supercritical conditions. Comparing to conventional liquid phase conditions, the use of supercritical CO 2 did not result in superior catalytic transalkylation activity for the Y-zeolite. On the contrary, an important improvement in product yield was obtained with the beta and mordenite zeolites. Results were related to reactant mixture mass transport properties and catalysts structure.

Supercritical carbon dioxide assisted grafting of polyacrylamide to polypropylene

AbstractThe grafting of polyacrylamide to polypropylene was realized with supercritical carbon dioxide as a substrate‐swelling agent and monomer/initiator carrier. The effects of supercritical carbon dioxide assisted impregnation and graft polymerization conditions on the grafting ratio were studied. The original polypropylene and grafting products were characterized with infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2614–2618, 2006

Change of polyphenol oxidase activity, color, and browning degree during storage of cloudy apple juice treated by supercritical carbon dioxide

The effects of supercritical carbon dioxide (SCCO2) treatment of 8, 15, 22, and 30 MPa for 60 min at 55 °C on polyphenol oxidase (PPO) activity, color, and browning degree in cloudy apple juice during storage at 4 °C for 4-weeks were investigated. The SCCO2 treatment had significant effects on inactivation of PPO and the least residual activity of PPO was 38.50% at 30 MPa. The restoration of PPO residual activity after SCCO2 treatment was also observed, which was dependent on the pressure level. A greater reduction of lightness L and a minor increase of redness a of cloudy apple juices after SCCO2 treatment occurred. Moreover, the total color difference (ΔE), which was significantly less than that of untreated sample, was decreased by enhancing the pressure level. The changes of lightness L and browning degree A during storage were well fitted to a first-order kinetic model. The rate constants of k L and k A of samples subjected to SCCO2 treatment reduced from 4.75×10−2 to 0.42×10−2 and 37.19×10−2 to 8.02×10−2, respectively, when pressure increased from 0 MPa (untreated sample) to 30 MPa.

Inactivation and reactivation of horseradish peroxidase treated with supercritical carbon dioxide

Effects of supercritical carbon dioxide (SCCO2) on the activity of horseradish peroxidase (HRP) in pH 5.6 acetate buffer solution were investigated. SCCO2 treatment could effectively inactivate HRP. Higher pressure, higher temperature, and longer treatment time caused more inactivation. The maximum reduction of HRP activity reached nearly 90% at 30 MPa and 55 °C for 60 min. Analysis of first-order reaction kinetic data (characterized by a rate constant k and by a decimal reduction time D) showed that D value was closely related to the pressure and temperature of SCCO2 treatment. Higher pressures or higher temperatures resulted in lower D values (higher k), the D value of HRP was minimized to 64.52 min treated by the combination of 30 MPa and 55 °C. The Zp, representing the range of applied pressure between which the D values change by a factor of 10, was 114.81 MPa. The activity of HRP treated by SCCO2 was reactivated significantly after initial 7-day storage at 4 °C apart from the samples at 30 MPa for 60 min, indicating the HRP inactivation may be reversible and the reactivation of HRP is dependent on the pressure level and treatment time.

Improved water permeability of sugi heartwood by pretreatment with supercritical carbon dioxide

Treating wood with aqueous solutions, such as preservatives, fire retardants, and dimensional stabilization agents, generally requires uniform distribution of the agents within the wood. Penetration and diffusion of such solutions into wood, however, are often obstructed in part by extractives and polyphenolic substances, especially in the heartwood. These substances adhering to or accumulating in pit and porous structures of wood may block the pathways for liquid transport. This study investigated the effect of supercritical carbon dioxide (CO2) (critical point; 31°C/ 7.4MPa) pretreatment on the water permeability of sugi heartwood. Supercritical CO2 diffuses and penetrates like gas but has solvating properties that approach those of liquid. It has low surface tension, easily seeps into micro pores and voids, and extracts nonpolar and weakly polar substances effectively. Thus, its uses for washing precision machines and semiconductors as well as dry cleaning have been investigated. Ohira reported that supercritical CO2 extraction was effective in extracting some useful chemical components in wood. Takeshita et al. studied the effects of supercritical CO2 in removing heavy metals from chromated copper arsenate (CCA)-treated wood. Acda et al. and Muin et al. used supercritical CO2 as a carrier solvent for preservative treatment of wood-based composites. In this study, we aimed to improve the water permeability of wood by pretreating the wood with supercritical CO2 that would remove substances that inhibit the permeation. We examined the effects of some treatment conditions on the water permeability of sugi heartwood, and observed bordered pits before and after supercritical CO2 treatment under a scanning electron microscope (SEM).

Conformational changes of poly(ethylene oxide) in poly(ethylene oxide)/poly(methyl methacrylate) blends by supercritical carbon dioxide

AbstractThe effects of supercritical carbon dioxide (SC CO2) fluids on the morphology and/or conformation of poly(ethylene oxide) (PEO) in PEO/poly(methyl methacrylate) (PMMA) blends were investigated by means of differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and Fourier transform infrared (FTIR). According to DSC data for a given blend, the melting enthalpy and, therefore, degree of crystallinity of PEO were increased, whereas the melting temperature of PEO was decreased, with SC CO2 treatment. The enhancement of PEO crystallization with SC CO2 treatment, as demonstrated by DSC data, was supported by WAXD data. According to FTIR quantitative analyses, before SC CO2 treatments, the conformation of PEO was transformed from helix to trans planar zigzag via blending with PMMA. This helix‐to‐trans transformation of PEO increased proportionally with increasing PMMA content, with around 0.7% helix‐to‐trans transformation per 1% PMMA incorporation into the blend. For a given blend upon SC CO2 treatments, the conformation of PEO was transformed from trans to helix. This trans‐to‐helix transformation of PEO decreased with increasing PMMA contents in the blends because of the presence of interactions between the two polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2479–2489, 2004

Measurement of interfacial tension in PS/LDPE melts saturated with supercritical CO2

AbstractThe effect of supercritical carbon dioxide (scCO2) on the interfacial tension between a polymer melt pair—polystyrene (PS) and low density polyethylene (LDPE)—was studied using the pendant drop method at temperatures varying from 200 to 240°C and CO2 pressures up to 18 MPa. The LDPE melt was prepared in a high pressure optical cell and the PS pendant drop was injected into the LDPE melt with a special high pressure syringe. For measurements with scCO2, the optical cell was first pressurized with scCO2 and measurements were taken after the saturation of scCO2 into both polymer melts. Excellent agreement was found with literature data for the same system without using scCO2. For the polymer pair saturated with scCO2, it was found that the interfacial tension decreases significantly with increasing CO2 pressure and appears to level off at higher CO2 pressures.

Effect of supercritical carbon dioxide on the crystallization and melting behavior of linear bisphenol A polycarbonate

AbstractThe crystallization and melting behavior of bisphenol A polycarbonate treated with supercritical carbon dioxide (CO2) has been investigated with differential scanning calorimetry. Supercritical CO2 depresses the crystallization temperature (Tc) of polycarbonate (PC). The lower melting point of PC crystals increase nonlinearly with increasing treatment temperature. This indicates that the depression of Tc is not a constant at the same pressure. Tc decreases faster at a higher treatment temperature than at a lower temperature. The leveling off of the depression in Tc at higher pressures is due to the antiplasticization effect of the hydrostatic pressure of CO2. The melting curves of PC show two melting endotherms. The lower melting peak moves to a higher temperature with increasing treatment temperature, pressure, and time. The higher temperature peak moves toward a higher temperature as the treatment temperature is increased, whereas this peak is independent of the treatment pressure, time, and heating rate. The double melting peaks observed for PC can be attributed to the melting of crystals with different stability mechanisms. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 280–285, 2004

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

Polymers and supercritical fluids: opportunities for vibrational spectroscopy

Supercritical fluids are used for enhanced processing of polymeric materials. Therefore, there is a need to understand how supercritical fluids interact with polymeric materials and how they may modify many facets of process operations. In situ spectroscopy provides a route for understanding and optimising polymer processing with supercritical fluids. In situ spectroscopy probes interactions between supercritical CO2 and polymers at a molecular level and provides a fundamental understanding of the origin of the plasticising effect of supercritical carbon dioxide on glassy polymers. The changes in polymers subjected to supercritical fluids have been elucidated via in situ ATR(Attenuated Total Reflectance)-IR spectroscopy. The key feature of our new approach is the use of a modified diamond ATR accessory to measure spectra of polymers subjected to high-pressure gas, supercritical fluids or near-critical water. A variety of novel applications for the use of in situ ATR-IR spectroscopy to polymers are described.

Effect of supercritical carbon dioxide on PMMA/rubber and polystyrene/rubber blending: Visosity ratio and phase inversion

AbstractSupercritical carbon dioxide (scCO2) was added during blending of polystyrene or poly(methyl‐methacrylate) (PMMA) and a rubber impact modifier (SP 2207). The resulting blend morphologies were compared. The compounding took place in a Leistritz ZSE‐27 twin‐screw extruder at 100 RPM, at a temperature of 200°C, and with 2.0 wt% CO2 Injection. The viscosity reduction of PMMA, polystyrene, and SP 2207 was measured using a slit die rheometer attached to the twin‐screw extruder. A viscosity reduction of up to 84% was seen with PMMA, 70% with polystyrene and 30% with SP 2207. The solubility of CO2 in these polymers was measured in a high‐pressure vessel at 200°C and 13.78 MPa (2000 psi). A solubility of 5.79 wt% CO2 was seen with PMMA, 3.65 wt% with polystyrene, and 2.60 wt% with SP 2207. The injection of CO2 reduced the size of the dispersed rubber phase in both polystyrene and PMMA. For both blends (polystyrene/SP 2207 and PMMA/SP 2207) with and without the injection of CO2, the extruder length for phase inversion was shortened by about L/D = 4, or 10% of the total extruder length. The impact strength for a 70/30 polystyrene/SP 2207 blend was increased by 26% by the addition of CO2. The improvement in impact strength was not as large for blends of PMMA and SP 2207.