| Supercritical fluids (SCFs) possess much potential as solvents in a variety of polymer processes including extraction, fractionation, particle formation and reactions. This attention stems from the fact that the solvating power of a SCF can be adjusted with small variations in temperature and pressure. The phase behavior of polymers in supercritical solvents can be determined experimentally and by using equations of state.; In Chapter 3 the phase behavior of polypropylene (PP) in n-pentane and in n-pentane/carbon dioxide solvent mixtures is presented. The cloud point pressure (the pressure required to solubilize the polymer) is measured using a high-pressure variable volume view cell. The phase behavior of PP in n-pentane exhibits lower critical solution temperature (LCST) type behavior. The cloud point pressure is relatively insensitive to the polymer concentration and molecular weight. At a given temperature, the cloud point pressure of the PP/n-pentane/carbon dioxide system increases almost linearly with increasing carbon dioxide solvent concentration (for carbon dioxide concentrations less than 30 mass%). The Sanchez-Lacombe (SL) equation of state is used to model the experimental data. The model correctly predicts the effects of temperature, composition, and polymer molecular weight.; In Chapter 4, the phase behavior of poly(propylene glycol) (PPG) in ethane and ethane+cosolvent mixtures is presented. The cosolvents studied are chloroform and carbon tetrachloride. The phase behavior of the PPG+ethane system transitions from LCST to merged upper-lower critical solution temperature (U-LCST) behavior as the polymer concentration or the polymer molecular weight increases. The addition of chloroform cosolvent reduces the cloud point pressure more than carbon tetrachloride due to hydrogen bonding between PPG and chloroform. The Lattice Fluid Hydrogen Bonding (LFHB) equation of state is used to model the experimental data. The LFHB model is able to predict the effect of polymer concentration, polymer molecular weight, temperature, and cosolvent concentration on the cloud point pressure.; In Chapters 5 and 6, the phase behavior of an anionic surfactant, sodium bis (2-ethylhexyl) sulfosuccinate (AOT) in ethane and in ethane+cosolvent mixtures is presented. The cosolvents studied included benzene and several alcohols (methanol, propanol, octanol, and benzyl alcohol). The demixing pressure was found to decrease with increasing benzene, methanol, or propanol concentration at constant temperature. Propanol was found to be a better cosolvent/surfactant than methanol. The addition of benzyl alcohol had an antisolvent effect. The effect of the various cosolvents was correlated in terms of the solvent density.; In Chapter 7, precipitation with a compressed antisolvent (PCA) is presented as an application to SCF processing. Micron-sized budesonide particles are produced in a semi-continuous spray apparatus. The effect of various operating conditions (i.e. concentrations, flow rates, temperature, and pressure) is presented. In addition, budesonide is coprocessed with poly(lactic acid) in an attempt to provide a controlled release of budesonide. |
