The project outlines a study of the rapid precipitation of homogeneous polymer blends from ternary solutions having a supercritical fluid (SCF) as the solvent. Although polymers can have substantial solubility in SCF's, they are insoluble in the same fluids in the gaseous state. Hence, density reduction, which can be accomplished at the speed of sound, results in precipitation of the polymer dissolved in the SCF. Because the time scale for precipitation can be significantly shorter than the time scale for phase segregation to occur by polymer diffusion, expanding a single phase ternary SCF solution will result in a single-phase blend of solid polymers. Thus, the supercritical fluid precipitation technique suggests the possibility of producing a homogeneous, compatible blend of polymers that otherwise have been found to be incompatible by melt blending or conventional solution blending techniques. The objectives of this project are: (1) to develop the capability of producing compatible polymer blends via a supercritical fluid blending process, and (2) to assess the stability of these prepared blends. These objectives will be achieved through studies of polymer/polymer/SCF phase equilibria, through experimental and theoretical investigations of the dynamics of the SCF expansion process, and through examination of the kinetics of phase separation in the precipitated blends. If new, fine-state polymer mixtures can be developed using this novel technique, they may have high strength or other unique properties that will be useful in the manufacture of high- performance components.
