Todd P. Dinoia

Solubility of vinylidene fluoride polymers in supercritical CO2 and halogenated solvents

The cloud-point behaviors of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-22 mol % hexafluoropropylene) (VDF–HFP22) are reported at temperatures up to 250 °C and pressures up to 3000 bar in supercritical CO2, CHF3, CH2F2, CHClF2, CClF3, CH3CHF2, CH2FCF3, CHF2CF3, and CH3CClF2. The molecular weight of PVDF has a smaller effect on the cloud point than the solvent quality. Cloud-point pressures for both fluoropolymers decrease as the solvent polarizability, polar moment per molar volume, and density increases. However, it is extremely difficult to dissolve either fluoropolymer in CClF3, which has a large polarizability and a small dipole moment. CO2 is an effective solvent because it complexes with the CF dipole at low temperatures where energetic interactions fix the phase behavior. In addition, polymer architecture has a strong impact on the cloud-point pressure. VDF–HFP22 has lower cloud-point pressures than PVDF in all solvents because it has a larger free volume that promotes facile interactions between the solvent and the polymer segments. Cloud-point data are also reported for amorphous poly(tetrafluoroethylene-co-x mol % 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole) (TFE–PDDx ; x = 65 and 85) in CO2. These data provide an interesting comparison to the PVDF–CO2 and VDF–HFP22–CO2 systems because TFE–PDD65 and TFE–PDD87 have very high glass-transition temperatures of 160 and 240 °C, respectively.

Solubility and phase behavior of PEP binders in supercritical carbon dioxide

Abstract Solubility and phase behavior data to temperatures of 300°C and pressures to 3000 bar are presented for various propellant, explosive, and pyrotechnic (PEP) binder polymers in supercritical (SC) carbon dioxide (CO 2 ) with and without modifiers. The binder polymers investigated in this study are polyethylene (PE), oxidized PE, poly(urethane), cellulose acetate butyrate (CAB), poly(vinylidene fluoride-co-hexafluoropropylene) with ∼20mol% hexafluoropropylene (Fluorel™ and Viton™), and poly(chlorotrifluoroethylene-co-vinylidene fluoride) with 24 mol% (Kel-F™ 800) and 69 mol% (Kel-F™ 3700) vinlyidene fluoride. CO 2 has the characteristics of a weak polar solvent which does not dissolve polyethylene although it is can dissolve low molecular weight nonpolar waxes. However, CO 2 is not polar enough to dissolve very polar polymers, such as oxidized PE, polyurethane, Kel-F™ 3700, and CAB. Moderately polar poly(vinylidene fluoride-co-hexafluoropropylene), which is a partially fluorinated polyolefin, and Kel-F™ 800 are soluble in CO 2 due to the polar contributions of the vinylidene fluoride repeat units. The solubility of these two copolymers can be further enhanced using acetone as a modifier with CO 2 . Additionally, oxidized PE is soluble in CO 2 with acetone and ethanol as modifiers, but temperatures greater than ∼200°C are needed. The fact that many of these polymers are soluble in neat CO 2 suggests the potential for a substantial impact upon environmentally sound processing technologies for polymer-based PEP materials.