Interaction Of Supercritical Carbon Dioxide Research Articles

Dewatering Green Sapwood Using Carbon Dioxide Undergoing Cyclical Phase Change between Supercritical Fluid and Gas.

Conventional kiln drying of wood operates by the evaporation of water at elevated temperature. In the initial stage of drying, mobile water in the wood cell lumen evaporates. More slowly, water bound in the wood cell walls evaporates, requiring the breaking of hydrogen bonds between water molecules and cellulose and hemicellulose polymers in the cell wall. An alternative for wood kiln drying is a patented process for green wood dewatering through the molecular interaction of supercritical carbon dioxide with water of wood cell sap. When the system pressure is reduced to below the critical point, phase change from supercritical fluid to gas occurs with a consequent large change in CO2 volume. This results in the efficient, rapid, mechanical expulsion of liquid sap from wood. The end-point of this cyclical phase-change process is wood dewatered to the cell wall fibre saturation point. This paper describes dewatering over a range of green wood specimen sizes, from laboratory physical chemistry studies to pilot-plant trials. Magnetic resonance imaging and nuclear magnetic resonance spectroscopy were applied to study the fundamental mechanisms of the process, which were contrasted with similar studies of conventional thermal wood drying. In conclusion, opportunities and impediments towards the commercialisation of the green wood dewatering process are discussed.

Comparisons of the sorption and diffusion of supercritical carbon dioxide into polycarbonate and polysulfone

Diffusion and interaction of supercritical carbon dioxide (SCCO 2) with polycarbonate (PC) and polysulfone (PSF) is investigated in this study. Experiments on the sorption of SCCO 2 at 40 °C and 20 MPa into these polymers were carried out. Both the sorption amount of SCCO 2 ( M s) and the desorption diffusivity ( D d) were determined by employing Fick's diffusion model. The M s and D d values for SCCO 2 in PC were greater than those in PSF, owing to different interactions of SCCO 2 with the polymers in the sorption process. The FTIR spectroscopy results for both polymers showed that CO 2 desorbed faster from PSF than from PC. This indicated that the carbonyl group in PC had a stronger interaction with SCCO 2. The plasticization effect of SCCO 2 on these polymers was also investigated by comparing the DMA measurement results on pure and SCCO 2 treated polymers. It is shown that PC had a larger shift in glass transition temperature than that of PSF after the SCCO 2 treatment. This implied that there is a greater extent of plasticization on PC.

An investigation of the interaction of supercritical carbon dioxide with poly(ethylene terephthalate) and the effects of some additive modifiers on the interaction

In order to investigate the interaction between supercritical carbon dioxide (scCO 2) and poly(ethylene terephthalate) (PET) and the effect on this interaction of some additive modifiers such as alcohols, the swelling behaviors of PET in scCO 2/modifier systems were examined. A special apparatus equipped with two observation windows was constructed. The change in the dimension of the PET yarn in the scCO 2/modifier was monitored using a CCD camera pointing through one of the windows. It was confirmed that the swelling of PET due to scCO 2 is accompanied by the crystallization of PET, but the crystallization induced by scCO 2 can be prevented by adding specific modifiers to the fluid. The equilibrium swelling of PET in scCO 2/modifier increased as the solubility parameter of the fluid approached to the solubility parameter of PET.

Investigation of sorption and diffusion of supercritical carbon dioxide into poly(vinyl chloride)

The interaction of supercritical carbon dioxide (scCO 2) with poly(vinyl chloride) (PVC) was systematically investigated. PVC films of 0.5 mm thickness were treated with CO 2 at pressures between 5 and 40 MPa, at temperatures between 40 and 70°C and soaking times between 0.5 and 7 h. The gravimetric desorption data were kinetically and thermodynamically evaluated assuming Fickian diffusion and the morphology changes due to the CO 2 treatment investigated by microscopic methods. The sorbed amount of CO 2, q ( q= g CO2/ g polymer) ranged between 0.03 (5 MPa, 70°C) and 0.13 (15 MPa, 40°C). The desorption diffusivities, D d, were in the order of 0.1×10 −11 m 2/s and decreased with decreasing amounts of CO 2. In contrast, the sorption diffusivities, D s, were markedly higher and varied between 0.7×10 −11 and 2.5×10 −11 m 2/s (20 MPa, 40–70°C). The CO 2 treatment changed the polymer chain structure, macroscopically visualized by the film opaqueness and by the density decrease to 1.05 g/cm 3. Microcellular structures were not detected.

Interaction of supercritical carbon dioxide with polymers. I. Crystalline polymers

Supercritical fluid (SCF) technology involving carbon dioxide is recently receiving wide attention due to its vast potential application in various fields such as cleaning, extraction, synthesis, etc., in addition to its environmental benefits. To fully exploit the use of SCFs in new technologies, it is important to understand how SCFs interact with materials. To this end, we have undertaken a systematic study involving a wide pressure and temperature range to investigate the interaction of supercritical carbon dioxide (SC CO2) with nine different crystalline polymers, namely, substituted and unsubstituted polyethylene (four varieties), polypropylene, nylon 66, poly(ethylene terephthalate), poly(oxymethylene), and poly(vinylidine fluoride). Critical factors such as changes in appearance and weight, temperature, pressure and time of the supercritical fluid treatment, and dimension of samples have been observed. The influence of SC CO2 on the thermal properties of treated polymers has been investigated through TGA analysis. Further, changes in the mechanical properties such as yield strength, ultimate elongation, and modulus of elasticity of the investigated crystalline polymers were also observed. A discussion has been included to show the possible implications of the observed changes in realizing various applications. © 1996 John Wiley & Sons, Inc.

Interaction of supercritical carbon dioxide with polymers. I. Crystalline polymers

Supercritical fluid (SCF) technology involving carbon dioxide is recently receiving wide attention due to its vast potential application in various fields such as cleaning, extraction, synthesis, etc., in addition to its environmental benefits. To fully exploit the use of SCFs in new technologies, it is important to understand how SCFs interact with materials. To this end, we have undertaken a systematic study involving a wide pressure and temperature range to investigate the interaction of supercritical carbon dioxide (SC CO2) with nine different crystalline polymers, namely, substituted and unsubstituted polyethylene (four varieties), polypropylene, nylon 66, poly(ethylene terephthalate), poly(oxymethylene), and poly(vinylidine fluoride). Critical factors such as changes in appearance and weight, temperature, pressure and time of the supercritical fluid treatment, and dimension of samples have been observed. The influence of SC CO2 on the thermal properties of treated polymers has been investigated through TGA analysis. Further, changes in the mechanical properties such as yield strength, ultimate elongation, and modulus of elasticity of the investigated crystalline polymers were also observed. A discussion has been included to show the possible implications of the observed changes in realizing various applications. © 1996 John Wiley & Sons, Inc.

Interaction of supercritical carbon dioxide with polymers. II. Amorphous polymers

In continuation of our goal to implement supercritical fluid (SCF) technology for various applications such as precision cleaning, foaming, and impregnation of materials, a systematic study has been performed involving amorphous polymers. Eleven different polymers of amorphous nature have been subjected to supercritical carbon dioxide (SC CO2) treatment under a wide pressure and temperature range (1000–3000 psi and 25–70°C, respectively). The influence and impact of such treatment on the appearance, weight change, and thermal and mechanical properties were followed systematically. In addition, the effect of treatment conditions and dimension of the samples on weight changes were also monitored. It has been found that amorphous polymers can absorb carbon dioxide to a greater extent than crystalline polymers and, in turn, the phenomenon of plasticization was also very high. In addition to morphology, the polarity of the polymer is also crucial in determining the solubility in carbon dioxide. Comparison was also made with the behavior of crystalline polymers. © 1996 John Wiley & Sons, Inc.

Interaction of supercritical carbon dioxide with polymers. II. Amorphous polymers

Interaction of supercritical carbon dioxide with polymers. II. Amorphous polymers