Extrusion process for recovery of polymers from their dispersions in liquids

• US 4,136,251 A
• Filed: 09/12/1977
• Issued: 01/23/1979
• Est. Priority Date: 09/12/1977
• Status: Expired due to Term

• Current Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Burchett, Donald K., Bice, Archie R.
• Primary Examiner(s): Levin, Stanford M.
• Application Number:
  US05/832,354
• Time in Patent Office: 498 Days
• Field of Search: 528/502, 528/486, 528/494, 260/821, 260/816
• US Class Current: 528/486
• CPC Class Codes: B29C 48/03 characterised by the shape of the extruded material at extrusion
• CPC Class Codes: B29C 48/76 Venting , drying means; Degassing means
• CPC Class Codes: C08C 1/14 Coagulation
• CPC Class Codes: C08F 6/22 Coagulation
• CPC Class Codes: Y10S 528/931 Physical treatment of natural rubber or natural rubber containing material or chemical treatment of non-rubber portion thereof, e.g. extraction of rubber from milk weed

Abstract

Polymers are isolated from their dispersions in liquid media in a twin-screw extruder, wherein the screws in the feed area are intermeshing and fully wiping each other and the extruder bore, the polymer dispersion or latex (which is coagulated in the first zone) being conveyed to a high pressure seal zone, liquid being forced upstream and out of the extruder, and the polymer being conveyed through the seal, into a reduced pressure zone, where most remaining liquid is removed, and finally into a pumping zone from which it is extruded. The invention avoids high pressure pumping of polymer dispersions and also is applicable to dispersions of sticky thermoplastic or elastomeric materials, which have caused considerable difficulties in the past.

Claims

1. 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.

2. The process of claim 1 wherein the dispersion is a slurry.

3. The process of claim 1 wherein the dispersion is a latex.

4. The process of claim 3 wherein the polymer is a chloroprene polymer.

5. The process of claim 4 wherein the coagulating agent is added through a port in the extruder housing upstream of the point of introduction of the chloroprene polymer.

6. The process of claim 5 wherein a basic agent is added through a port located in the extruder area from the downstream end of zone 2 to the upstream end of zone 4 to bring the alkaline reserve of the polymer to the desired level.

7. The process of claim 6 wherein the coagulant is at least one of aqueous acetic acid and aqueous solution of sodium acetate.

8. The process of claim 1 wherein a thickener dispersible in the liquid dispersing medium is introduced into the extruder.

9. The process of claim 8 wherein the liquid dispersing medium is water and the thickener is hydroxyethylcellulose.

10. The process of claim 1 wherein the temperature in zone 4 is at least about 110°

C. and the pressure is below about 200 mm Hg.