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.