Process and apparatus for manufacture of processable polyvinyl alcohol

1. A method for the manufacture of a plasticized polyvinyl alcohol polymer mixture, the method comprising the steps of:

introducing a blend comprising two or more polyvinyl alcohol polymers, each polymer having a degree of hydrolysis of at least 98%, and wherein the blend comprises one high molecular weight polyvinyl alcohol polymer having a molecular weight in the range of about 60,000 to about 120,000 and at least one low molecular weight polyvinyl alcohol polymer having a molecular weight in the range of from about 5,000 to about 30,000 into a mixing reactor;

wherein the mixing reactor comprises a blending chamber having a primary inlet, a primary outlet and at least two inter-engaging components extending between the primary inlet and primary outlet, the components being arranged to apply a shearing force to the polyvinyl alcohol polymer while the polyvinyl alcohol polymer is conveyed by the components from the inlet through a reaction zone to the outlet;

one or more secondary inlets located downstream from the primary inlet for introducing reactants comprising a processing agent and a plasticizer, which is pentaerythritol, to the chamber to form a reaction mixture;

wherein the blending chamber comprises a plurality of heated regions arranged so that the mixture is subjected to a controlled temperature profile;

a secondary outlet located between the reaction zone and primary outlet arranged to allow removal of processing agent from the chamber;

reacting a reaction mixture comprising the processing agent, plasticizer and polyvinyl alcohol polymer in the reaction zone to form plasticized polyvinyl alcohol polymer;

wherein the processing agent is water, or a mixture of water and one or more C 1 -C 4 alcohols or other hydroxyl compounds wherein the boiling point of the processing agent is less than the boiling point of the plasticizer;

wherein the processing agent is from 3 wt % to 18 wt % in the reaction mixture; and

allowing the plasticized polyvinyl alcohol polymer mixture to pass from the primary outlet.

2. The method according to claim 1 , wherein the ratio of high to low molecular weight polyvinyl alcohol polymer in the polyvinyl alcohol polymer blend is in the range from 2:1 to 10:1, in the range from 3:1 to 7:1, in the range from 4:1 to 6:1, or about 5:1.

3. The method of claim 1 , wherein the processing agent is water.

4. The method of claim 1 , wherein the amount of processing agent is 3 wt % to 15 wt %, 3 wt % to 12 wt %, or 5 wt % to 10 wt %.

5. The method of claim 4 , wherein the processing agent is water.

6. The method according to claim 1 , wherein the temperature profile increases from ambient temperature at a first region to 200° C. adjacent the secondary outlets, and wherein the reaction zone has a temperature of at least 200° C.

7. The method according to claim 1 , wherein the location of the reaction zone is controlled by changing one or more of: the temperature profile, rotational speed of the one or more screws, and the rate of feed of the reaction mixture into the mixing reactor.

8. The method according to claim 1 , comprising an intensive mixing region located downstream of the reaction zone, wherein the intensive mixing region comprises a paddle mixer located between the reaction zone and the secondary outlet.

9. The method according to claim 8 , wherein the intensive mixing region comprises a kneading region comprising one or more pairs of inter-engaging rotor blades or paddles.

10. The method according to claim 1 , wherein a pump is located downstream of the primary outlet, and wherein the pump comprises a single screw extruder unit.

11. The method according to claim 1 , wherein the secondary outlet is a vent configured to permit removal of processing agent from the mixing reactor.

12. The method according to claim 1 , wherein the plasticized polyvinyl alcohol polymer has a water content of less than 5 wt %, less than 2 wt %, or less than 0.5 wt %.