Polymerization In Carbon Dioxide Research Articles

Evolving an Accurate Decision Tree‐Based Model for Predicting Carbon Dioxide Solubility in Polymers

AbstractSolubility is one of the most indispensable physicochemical properties determining the compatibility of components of a blending system. Research has been focused on the solubility of carbon dioxide in polymers as a significant application of green chemistry. To replace costly and time‐consuming experiments, a novel solubility prediction model based on a decision tree, called the stochastic gradient boosting algorithm, was proposed to predict CO2 solubility in 13 different polymers, based on 515 published experimental data lines. The results indicate that the proposed ensemble model is an effective method for predicting the CO2 solubility in various polymers, with highly satisfactory performance and high efficiency. It produces more accurate outputs than other methods such as machine learning schemes and an equation of state approach.

A new experimental system for combinatorial exploration of foaming of polymers in carbon dioxide: The gradient foaming of PMMA

A unique foaming system has been developed to explore the consequences of different pressures and temperatures employed in foaming of polymers in supercritical carbon dioxide. The cell employs a temperature gradient field extending over 25cm. It thereby generates a continuum of temperatures to which a long strip of polymer is exposed at a given CO2 pressure in a single experiment. It allows a powerful combinatorial approach to explore foaming. This manuscript describes the experimental system and demonstrates its utility in gradient foaming of polymers using long strips (25cm) of poly(methyl methacrylate) in thick sheet (2.1mm) and thin film (100μm) forms at nominal pressures of 14, 21, 28, 35MPa under an imposed temperature gradient extending over 25cm with a temperature difference from 40°C to 125°C. By generating a rich array of sections foamed at different temperatures at a given pressure, the experimental approach provides new insights not only on the pore formation and growth as a function of pressure and temperature, but also on the importance of other factors such as the time allowed or needed for CO2 sorption and escape, and the changes in the softening and vitrification state of the polymer that are important in cell nucleation, growth, or collapse. Progress of the diffusion front, which is readily identified as the boundary between the plasticized and glassy domains, is documented which provides an assessment of the diffusion coefficient as a function of temperature at a given pressure, and as a function of pressure at a given temperature.

POxylated Polyurea Dendrimers: Smart Core-Shell Vectors with IC50 Lowering Capacity.

The design and preparation of highly efficient drug delivery platforms using green methodologies is at the forefront of nanotherapeutics research. POxylated polyurea dendrimers are efficiently synthesized using a supercritical-assisted polymerization in carbon dioxide. These fluorescent, pH-responsive and water-soluble core-shell smart nanocarriers show low toxicity in terms of cell viability and absence of glutathione depletion, two of the major side effect limitations of current vectors. The materials are also found to act as good transfection agents, through a mechanism involving an endosomal pathway, being able to reduce 100-fold the IC50 of paclitaxel.

Revolutionary, Evolutionary Ideas for Lowering the Cost of Gas Separation

CO2 removal Demand for a better way to remove carbon dioxide (CO2) from natural gas led to the creation of a new material at Rice University in Houston that does something unprecedented on the molecular scale, and might even change gas processing. For professor James Tour, the fundamental science behind this porous carbon material created in his laboratory “is really profound.” The black powdery material developed by a Rice graduate student, Chih-Chau Hwang, absorbs nearly its weight of carbon dioxide by creating long polymer chains of carbon dioxide at a pressure level that is elevated, but easily attained, in a gas processing facility. For Tour, it is an exciting development because the carbon dioxide polymer structure, which was observed using spectroscopy, is something that he said has never been seen in nature, and only rarely in labs at extreme pressures. But the pioneering chemist recognizes that for those developing new oilfield technologies, what matters is what it can do, not how it might do so. Rice’s patents have been licensed by Apache Corp., which supported research seeking a new material for gas separation for the past 2½ years. On the plus side, it appears to be energy-efficient, can hold a large volume relative to its weight, and is highly selective at grabbing carbon dioxide without also removing some natural gas as well. The investment by the independent oil company reflects the exploration and production industry’s appetite for improved methods that are more compact, cost less to run, and occupy less space. One indication of that is the increased demand for improved membrane-based separation methods, which are far more compact and adaptable to offshore environments than liquid chemical separation methods using amines. Cameron recently began selling a new, more efficient membrane material, called PN-1 multifiber membrane element, which was developed in partnership with Petronas, the Malaysian national oil company. Better carbon dioxide removal is a pressing concern in southeast Asia, where many large gas deposits have not been developed because of carbon dioxide levels that can equal the gas in the ground. Production growth there, and in far-flung regions from Russia to Brazil, will require dealing with higher levels of carbon dioxide and hydrogen sulfide, which often are found together and removed using similar processes.

Absorption and foaming of plastics using carbon dioxide

In this study, carbon dioxide was used as a foaming agent for common plastics, such as acrylonitrile–butadiene–styrene (ABS) polymer, polystyrene (PS), polypropylene (PP), high-density polyethylene (HDPE), and high impact polystyrene (HIPS). Carbon dioxide was first absorbed by the sample plastics placed within a pressure vessel at various pressure levels and absorption time intervals. The Henry’s constant of the absorbed carbon dioxide in the plastics was determined. The diffusion coefficient of carbon dioxide in polymer was also identified by curve-fitting with the relationship between the absorbed amount and time. The results showed that ABS, PS, and HIPS absorbed more gas than did PP and HDPE, because PP and HDPE exhibit higher crystallinity. Generally, a polymer can take up saturation absorption of gas under higher pressure. After absorption, the foaming process occurred at various temperatures and time intervals. The cell structure, density, and size of the plastic foams were then investigated using scanning electron microscopy. A longer foaming period and higher temperature increase the size of the cell and decrease the cell density (the number of bubbles per unit volume). A dense skin layer without bubbles appeared directly adjacent to the surface of the foamed plastics. Its thickness decreased if the foaming process took place at higher temperatures.

Crystallinity effects in polylactic acid-based foams

The use of carbon dioxide for the production of polylactic acid foams has been increasingly studied recently. Much of the reported work has used supercritical carbon dioxide as a processing or foaming medium. However, a new foaming process which uses sub-critical liquid carbon dioxide conditions has been developed by the Biopolymer Network Limited. It is generally recognised that processing crystalline thermoplastics, including crystalline polylactic acid polymers, into foam products using carbon dioxide is difficult due to lower solubility of liquid carbon dioxide in polymers and the increased polymer rigidity hindering the expansion of the polymer matrix. However, fundamental studies, and the associated knowledge of the foaming mechanisms at play, have allowed some new approaches to be developed within sub-critical carbon dioxide conditions which overcome many of these difficulties in polylactic acid foams. In this study, several commercially available grades of polylactic acid, ranging from crystalline to amorphous, were processed using carbon dioxide via the Biopolymer Network Limited process (sub-critical carbon dioxide). By adequately adjusting the process parameters, different crystalline grades were successfully foamed to low density. The resulting foams exhibited low to high levels of crystallinity, and consequently displayed varying thermal or physical properties. Cellular structures were observed by scanning electron microscopy. Crystallinity and thermal behaviour of the foamed samples were characterised using differential scanning calorimetry. Mechanical properties and dimensional stability were also investigated. It was shown that the selection of polylactic acid feedstock, and its associated processing conditions, had a significant impact on the final quality and properties of the foams.

A theoretical study of structure–solubility correlations of carbon dioxide in polymers containing ether and carbonyl groups

This work involves a theoretical study to investigate the effects of the structure on CO(2) sorption in polymers, where poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), poly(vinyl acetate) (PVAc), poly(ethylene carbonate) (PEC) and poly(propylene carbonate) (PPC) were examined. In the theoretical approach, the multi-site semiflexible chain model and the renormalized technique of electrostatic potentials were incorporated into the polymer reference interaction site model (PRISM). To test the theory, molecular dynamic simulations were performed using the TraPPE-UA force field. The theoretically calculated reduced X-ray scattering intensities and intermolecular correlation functions of these five polymers are found to be in qualitative agreement with the corresponding molecular simulation data. The theory was then employed to investigate the distribution functions between CO(2) and different sites of the polymers with consideration of the Lennard-Jones, potential of mean force, and columbic contributions. Based on the detailed structure characteristics of CO(2) in contact with different groups, the CO(2) coordination molecular numbers were obtained and their sorption intensities analyzed. Finally, the sorption isotherms of CO(2) in these five polymers were calculated. The results for PEO, PPO and PVAc are close to the available experimental curves, and the trend of CO(2) solubility is PPC > PEC > PVAc ~ PPO > PEO.

Refrigeration plants using carbon dioxide as refrigerant: measuring and modelling the solubility and diffusion of carbon dioxide in polymers used as sealing materials

Because of increased environmental pressure, there is currently a movement away from more traditional refrigerants such as HCFC's toward refrigerants with lower global warming potential such as carbon dioxide (CO 2). However, the use of CO 2 as a refrigerant requires a refrigeration cycle with greater extremes of pressure, placing greater demands on the polymer materials used for seals and packing. In this work we have measured the solubility and diffusivity of gaseous CO 2 in two polymers used as sealing materials in CO 2 refrigeration plants. These are Hydrogenated Nitrile Butadiene Rubber (HNBR) and Ethylene Propylene Diene Monomer (EPDM) which are used in seals such as O-rings. The experiments were performed on a high-pressure microbalance. Solubility results were modelled using an equation of state for polymers (simplified PC-SAFT). The necessary polymer parameters were obtained using a previously published method. The measured results can be successfully correlated using simplified PC-SAFT.

Application of adaptive neuro-fuzzy inference system for solubility prediction of carbon dioxide in polymers

Solubility of carbon dioxide in poly(vinyl acetate) (PVAc), poly(2,6-dimethyl-1,4-phenylene ether) (PPO), polypropylene (PP), and high-density polyethylene (HDPE), poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA) and polystyrene (PS) are modeled by adaptive neuro-fuzzy inference system (ANFIS) in wide range of pressure and temperature. The results obtained in this work indicate that ANFIS is effective method for prediction of solubility of carbon dioxide in polymers and have better accuracy and simplicity compared with the classical methods.

超臨界流体を用いたポリマーの混練，成形，加工，リサイクル技術 超臨界ＣＯ２を用いた高分子加工技術

Supercritical carbon dioxide is an environmentally friendly material and has great potential for the modification and processing of polymers. Addition of supercritical carbon dioxide to various polymers may lower the glass transition temperature, melt viscosity, and interfacial tensions. The aim of this study is to contribute to the development of the new processes and new products of high value and conserving the global environment. We have studied processes of foaming, reactive processing, and impregnation using supercritical carbon dioxide. The results from our work indicate that the solubility and diffusivity of carbon dioxide in polymers are key parameters for control of these processes.

Prediction of carbon dioxide solubility in polymers based on a group-contribution equation of state

The group-contribution, lattice-fluid equation of state (GCLF-EoS), has been previously shown to predict accurately vapor solubilities in polymers. The method has been extended to the predictions of carbon dioxide–polymer binary systems. Applying the GCLF-EoS to binary systems requires the characterization of all the groups in the system and estimating the molecular binary interaction parameter from the group interaction parameters. The group parameters for pure carbon dioxide and the group interaction parameters of carbon dioxide with other organic groups commonly found in polymers were estimated. A new mixing rule for the calculation of the molecular interaction parameter is proposed and compared with the one developed originally by Lee and Danner. Results show that the new mixing rule as applied to the sorption of carbon dioxide in polymers and copolymers gives good predictions in large ranges of pressure and temperature.

Pressure and Temperature Dependence of the Propagation Rate Coefficient of Free-Radical Styrene Polymerization in Supercritical Carbon Dioxide

Free-radical polymerization of styrene in homogeneous phase of supercritical carbon dioxide (scCO2) has been studied at temperatures between 40 and 80 °C and pressures between 300 and 1500 bar. Applying pulsed-laser polymerization in conjunction with size-exclusion chromatography yields propagation rate coefficients, kp. Within the extended pressure range under investigation, kp for solution polymerization in carbon dioxide, at CO2 contents up to 46 wt %, is identical to kp of styrene bulk polymerizations. The studies with CO2 suggest that solvent effects on kp occur in systems where the solvent quality for the polymer is not very high and where intrasegmental interactions are important.

High-energy mechanical alloying of thermoplastic polymers in carbon dioxide

High-energy ball milling was performed on low density polyethylene (LDPE) and isotactic polypropylene (iPP) as well as on 20/80 binary mixture of both polymers. Mechanical alloying was carried out at high pressure with carbon dioxide for a short period. The presence of CO2 avoids oxidative mechano-chemical degradation of polymers and enhances the effectiveness of the milling. The effects of the mechano-chemical treatment on the molecular and physical properties of both single polymers and blends of intrinsically incompatible polymers were explored by FTIR spectroscopy, thermal analysis, intrinsic viscosity determination and solvent fractionation. Structural changes on PP and PP/LDPE blend were observed and have a strong dependence on the milling time. Mechanical tests confirm an overall improvement in blend properties by mechanical alloying. Experimental evidences are presented to suggest that CO2 high-energy ball milling causes a self-compatibilization of the blend LDPE–iPP by breaking iPP polymer chains and allowing them to recombine with the neighboring LDPE chains.

Alternative solvents for cellulose derivatives:: Miscibility and density of cellulosic polymers in carbon dioxide+acetone and carbon dioxide+ethanol binary fluid mixtures

Identification of alternative solvents for processing of cellulosic polymers is of interest in a number of industrial applications, ranging from fibers to films. In this study, miscibility of cellulose acetate, cellulose triacetate, cellulose acetate butyrate, cellulose propionate and ethyl cellulose in `carbon dioxide+acetone' and `carbon dioxide+ethanol' binary fluid mixtures have been investigated. Data are reported at 3% by mass polymer concentration in two binary solvent fluid mixtures containing 30% and 70% by mass carbon dioxide. Demixing pressures are reported in the temperature range from 60 to 175°C. Complete miscibility of the polymers was achieved at all pressures in carbon dioxide+ethanol mixtures containing 30% carbon dioxide, while in mixture containing 70% carbon dioxide, miscibility required pressures greater than 20 MPa. Higher pressures were required for miscibility in carbon dioxide+acetone mixtures with pressures being greater than 5 MPa and greater than 35 MPa for mixtures containing 30 and 70% carbon dioxide, respectively. The solutions all displayed LCST (lower critical solution temperature) behavior, with demixing pressures increasing with temperature. The relative ease of miscibility of the polymers followed essentially the same order in either the ethanol or acetone fluid mixtures, with demixing pressures increasing as ethyl cellulose<cellulose propionate<cellulose acetate butyrate<cellulose triacetate<cellulose acetate, except that in acetone mixture, cellulose acetate butyrate displayed higher demixing pressures than cellulose triacetate. For solutions of cellulose acetate butyrate and cellulose propionate in 70/30 carbon dioxide/ethanol fluid mixture, pressure–density isotherms were determined both in the one-phase and in the two-phase regions and the demixing densities were noted. The solution density at the demixing pressure gives a measure of the volume expansion needed to bring about phase separation at a given temperature.

Solubility of carbon dioxide in polymers by the quartz crystal microbalance technique

The use of a quartz crystal microbalance (QCM) has been demonstrated to be an accurate and relatively easy technique to measure gas solubility in polymers at high pressures. The technique is reversible and could be used for real-time monitoring of a process. We have compared solubility measurements of CO 2 into numerous polymers with literature data, obtained from measurements using a gravimentric approach, with good agreement. With improved electronic sensitivity, this technique could be extended to measure the partitioning of a component present at low levels of CO 2 into polymers. This would provide a direct measurement technique that would provide value to investigations into the use of CO 2 as an agent to infuse chemicals into polymers.

Generation of microcellular polyurethane foams via polymerization in carbon dioxide. I: Phase behavior of polyurethane precursors

AbstractOn investigating the generation of microcellular polyurethane foam via reaction in carbon dioxide, we have observed that common polyurethane precursors are CO2 miscible, whereas typically fluorinated compounds or specially designed surfactants are needed to solubilize polymers in CO2. Both isocyanates and polyols are CO2‐miscible at workable pressures and temperatures and in useful concentrations to allow generation of polyurethane foams in CO2. By characterizing the phase behavior of several series of propylene oxide and ethylene oxide polyols, we have observed that the combined effects of molecular weight and hydroxyl number fix the location of the phase separation pressures. In general, lower molecular weights and lower hydroxyl mole fractions produce phase boundaries at relatively lower pressures in carbon dioxide. It also has been shown that CO2‐soluble compounds may have a com̀patibilizing effect on less CO2‐soluble materials.

Generation of microcellular polyurethane foams via polymerization in carbon dioxide. II: Foam formation and characterization

AbstractMicrocellular polyurethane foams are generated through phase separation, which is induced by reaction‐induced crosslinking or by a pressure quench. The phase separation conditions are shown to impact the microstructure of the foams. Pore growth will occur through two mechanisms: diffusion of CO2 from polymerrich regions into the pores and also through CO2 gas expansion (boiling of liquid CO2 at reduced pressure). Higher CO2 pressures for polymerization (hence, higher fluid density) provide more CO2 molecules for foaming, generate lower interfacial tension and viscosity in the polymer matrix, and thus produce higher cell densities. Increasing the functionality of the polyurethane precursors increases the Tg of the polymer network and leads to smaller cell diameters by raising the vitrification pressure and allowing less time for CO2 gas expansion to play a role in cell growth. Higher reaction temperatures result in an increase in bulk density as the cell density remains invariant and the cell size drops. The use of the more polar fluoroform as a foaming agent results in larger cells, as it is able to plasticize the polymer network and allow for gas expansion during depressurization. A constant composition method of pressure quench results in smaller cell diameters.

Ring-Opening Metathesis Polymerizations in Carbon Dioxide

Abstract The polymerization of norbornene was successfully initiated with Ru(H2O)6(tos)2 in a carbon dioxide medium. The resultant poly(norbornene) was prepared with yields and molecular weights comparable to those obtained in other solvent systems. It was also found that the cis/trans ratio of the polymer microstructure could be controlled by the addition of various amounts of methanol to the reaction mixture. A detailed account of the polymerizations is described and believed to be the first example of a ring-opening metathesis polymerization in carbon dioxide.

5506317 Heterogeneous polymerization in carbon dioxide

5506317 Heterogeneous polymerization in carbon dioxide

Sorptive dilation of poly(vinyl benzoate) and poly(vinyl butyral) by carbon dioxide

AbstractDilation of poly(vinyl benzoate) and poly(vinyl butyral) accompanying sorption of carbon dioxide is measured with a cathetometer under pressures up to 50 atm at 25°C. Sorption isotherms for carbon dioxide in these polymers were also determined gravimetrically. Each dilation isotherm plotted versus pressure, as well as the sorption isotherm, showed an inflection point corresponding to the glass transition of the polymer‐gas system. The dilation isotherms changed their form at that point from concave to convex to the pressure axis or to a straight line. Dilation and sorption isotherms exhibited time‐dependent hysteresis below the inflection point but not above the point. Partial molar volumes of carbon dioxide in polymers, which were determined from dilation and sorption data above the point, were found to be independent of concentration and larger than those below the point. The latter volumes depended on concentration. Based upon the extended dual‐mode sorption concept, which takes account of plasticization of polymer by sorbed gas, a dilation model was developed. Dilation data were described well by the model.