Process and apparatus for manufacture of processable polyvinyl alcohol

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

introducing into a mixing reactor a polyvinyl alcohol polymer comprising homopolymeric polyvinyl alcohol or a blend thereof having a degree of hydrolysis in the range of 93% to less than 98%;

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 the primary outlet, the at least two inter-engaging components being arranged to apply a shearing force to the polyvinyl alcohol polymer while the polyvinyl alcohol polymer is conveyed by the at least two inter-engaging components from the primary inlet through a reaction zone to the primary outlet;

one or more secondary inlets located downstream from the primary inlet for introducing reactants comprising water as a processing aid and a plasticizer to the blending chamber to form a reaction mixture;

wherein the plasticizer comprises triacetin, and dipentaerythritol;

wherein the blending chamber comprises a plurality of heated regions arranged so that the reaction mixture is subjected to a temperature profile whereby the temperature increases from the primary inlet to the primary outlet;

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

reacting the water, the plasticizer and the polyvinyl alcohol polymer in the reaction zone to form the plasticized polyvinyl alcohol polymer mixture; and

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

2. The method as claimed in claim 1 wherein the polyvinyl alcohol polymer has a degree of hydrolysis of 93 wt % to 97 wt %.

3. The method as claimed in claim 2 wherein the polyvinyl alcohol polymer has a degree of hydrolysis of 93 wt % to 95 wt %.

4. The method as claimed in claim 1 , wherein the polyvinyl alcohol polymer comprises a lower viscosity polymer and a higher viscosity polymer, wherein both polymers have the same degree of hydrolysis.

5. The method as claimed in claim 1 wherein the reactants further comprise a reactive stabilizer selected from the group consisting of:

sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethyl propionic acid and mixtures thereof.

6. The method as claimed in claim 5 , wherein the amount of the reactive stabilizer is from 0.2 wt % to 5 wt %.

7. The method as claimed in claim 6 , wherein the amount of the reactive stabilizer is from 0.5 wt % to 3 wt %.

8. The method as claimed in claim 7 , wherein the amount of the reactive stabilizer is from 0.5 wt % to 2 wt %.

9. The method as claimed in claim 8 , wherein the amount of the reactive stabilizer is from 0.5 wt % to 1.5 wt %.

10. The method as claimed in claim 9 , wherein the amount of the reactive stabilizer is 1 wt %.

11. The method as claimed in claim 1 wherein the plasticizer further comprises a compound selected from: diglycerol, triglycerol, xylose, triacetin, D-mannitol, 1,4-butanediol, 3,3-dimethyl-1,2-butanediol and caprolactam.

12. The method as claimed in claim 1 , wherein the amount of each plasticizer compound is from 2 wt % to 15 wt %.

13. The method as claimed in claim 1 , wherein the total amount of the plasticizers is from 15 wt % to 30 wt %.

14. The method as claimed in claim 1 , wherein the water content of the plasticized polyvinyl alcohol polymer mixture is in the range 0.1 wt % to 5 wt %.