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Abstract

A process for treating an impure thermoplastic polymer, including raw and recycled polymers, during extrusion to separate low molecular weight compounds therefrom, including: introducing a separating agent into plasticized impure thermoplastic polymer passing through a first high pressure zone, the low molecular weight compounds of the plasticized polymer being at least partially soluble in the separating agent; extracting at least a part of the low molecular weight compounds from the plasticized polymer into the separation agent during passage of the plasticized polymer through an extraction zone; removing the separating agent charged with low molecular weight compounds from the extruder as the plasticized polymer passes through a low pressure zone having a residual pressure, P, which is lower the introductory pressure, P.sub.e, and for which 1 bar.gtoreq.P.gtoreq.P.sub.c ; collecting the charged separating agent as it is removed from the extruder; thermal vacuum treating the plasticized polymer as it passes through a last low pressure zone to vacuum degas the plasticized polymer at a pressure, P.sub.v, for which P.sub.v <0.5 bar and thereby further remove separating agent and low molecular weight compounds from the plasticized polymer; and passing the plasticized polymer through a last high pressure zone to an extruder head. The combination of solvent extraction in the extruder with subsequent vacuum degassing results in removal of large amounts of low molecular weight compounds with a relatively small expenditure of energy since energy-intensive vacuum degassing is needed only for removal of residuals.

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First Claim