Abstract: A process for the removal of impurities from a thermoplastic polymer, comprising mixing with the polymer in a molten state a stripping agent comprising a solution of carbon dioxide in water, passing the mixture to a vessel held at a pressure and which is less than atmospheric pressure, allowing impurities to defuse out of the polymer into the volatilised stripping agent, and removing the volatilised stripping agent with the impurities from the mixture. The invention also relates to the stripping agent itself, which is a solution of carbon dioxide in water.

Abstract: Devolatilization of molten polymer is carried out using a vertical static mixer which opens directly into a flash tank. Expansion of a stripping agent injected at an inlet of the static mixer occurs in the static mixer and the continued shearing causes disengagement of the vapor from the polymer, so that expansion is complete before the polymer enters the flash tank and stripper and volatiles are removed by a pump and condenser arrangement which holds the flash tank at a reduced pressure. Polymer outlets are in the floor of the flash tank and have metering pumps at their bottom end.