SOLUBILITY AND PHASE-BEHAVIOR OF PEP BINDERS IN SUPERCRITICAL CARBON-DIOXIDE

Solubility and phase behavior data to temperatures of 300 degrees C an d pressures to 3000 bar are presented for various propellant, explosiv e, and pyrotechnic (PEP) binder polymers in supercritical (SC) carbon dioxide (CO2) with and without modifiers. The binder polymers investig ated in this study are polyethylene (PE), oxidized PE, poly(urethane), cellulose acetate butyrate (CAB), poly(vinylidene fluoride-co-hexaflu oropropylene) with similar to 20mol% hexafluoropropylene (Fluorel(TM) and Viton(TM)), and poly(chlorotrifluoroethylene-co-vinylidene fluorid e) with 24 mol% (Kel-F(TM) 800) and 69 mol% (Kel-F(TM) 3700) vinlyiden e fluoride. CO2 has the characteristics of a weak polar solvent which does not dissolve polyethylene although it is can dissolve low molecul ar weight nonpolar waxes. However, CO2 is not polar enough to dissolve very polar polymers, such as oxidized PE, polyurethane, Kel-F(TM) 370 0, and CAB. Moderately polar poly(vinylidene fluoride-co-hexafluoropro pylene), which is a partially fluorinated polyolefin, and Kel-F(TM) 80 0 are soluble in CO2 due to the polar contributions of the vinylidene fluoride repeat units. The solubility of these two copolymers can be f urther enhanced using acetone as a modifier with CO2. Additionally, ox idized PE is soluble in CO2 with acetone and ethanol as modifiers, but temperatures greater than similar to 200 degrees C are needed. The fa ct that many of these polymers are soluble in neat CO2 suggests the po tential for a substantial impact upon environmentally sound processing technologies for polymer-based PEP materials. (C) 1997 Elsevier Scien ce Ltd. All rights reserved.