Measurement and Modeling of Polystyrene Viscosity in Supercritical CO2 Expanded Decahydronaphthalene

Heterogeneous catalytic
hydrogenation can improve the chemical, thermal, and oxidative resistance of
polystyrene.  The hydrogenation reaction
requires the polystyrene molecules to diffuse into microscopic catalyst pores.
When diffusing into the catalyst, the polymer coils experience mass transfer
limitations associated with the high viscosity of the polystyrene
solution.  Supercritical fluids have
been shown to increase mass transfer rates by enhancing diffusivity and
lowering viscosity.  Supercritical CO₂
was investigated as a co-solvent with 76/24 wt% trans/cis -decahydronaphthalene (decalin) to determine the effect
CO₂ would have on the polystyrene solution viscosity.  Phase behavior and viscosity measurements
were obtained for decalin, supercritical CO₂ expanded decalin,
polystyrene in decalin, and polystyrene in supercritical CO₂
expanded decalin.  The effects of the
decalin isomers on viscosity and phase behavior were investigated to obtain
binary interaction parameters and pure component parameters for the solvent
system.  The viscosity data of the
solutions compares well to the Free Volume Model (FVM) for viscosity.  Both the model and the experimental data
show a significant decrease in viscosity for the polystyrene in supercritical
CO₂ expanded decahydronaphthalene. 
Future work will investigate the effect of hydrogen on the solution
properties and determine the kinetic properties of the hydrogenation
reaction.