Extrusion process for recovery of polymers from their dispersions in liquids

A process for recovering a polymer from a dispersion in a liquid medium comprising introducing the dispersion, and, if the dispersion is a latex which requires a chemical means of coagulation, separately introducing a latex coagulating agent, into a first zone of screw flights of a twin screw extruder having counter-rotating screws and comprising five zones;

• the flights of both screws in the first zone intermeshing and fully wiping each other as well as the extruder bore;
• the screw flights in zones 2, 4, and 5 being disposed tangentially to each other, a pressure seal between the second zone and the fourth zone constituting the third zone, and a liquid evacuation port being provided in the second zone;
• if the dispersion is a latex, the latex being coagulated in said first zone of the extruder;
• the polymer together with the liquid being conveyed by the positive displacement of the screws from said first zone into said second zone, the pressure in said second zone being sufficiently high to allow the polymer to pass through the pressure seal, while the liquid flows back and out through the evacuation port;
• the polymer in said fourth zone of the extruder being subjected to subatmospheric pressure in order to remove a major portion of liquid still held by the polymer;
• and the substantially dry polymer being conveyed out of the extruder by the pumping action of the screws.