Process and apparatus for manufacture of processable polyvinyl alcohol

1. A method for manufacture of plasticized homopolymeric polyvinyl alcohol, the method comprising the steps of:

introducing into a mixing reactor a polyvinyl alcohol polymer consisting of polyvinyl alcohol or a blend thereof having a degree of hydrolysis greater than 93 wt %;

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 polymer while the 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 ingredients consisting of water, a plasticizer and a reactive stabilizer to the chamber;

wherein the plasticizer is selected from the group consisting of: diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methyl pentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol, caprolactam, tricyclic trimethylolpropane formal, erucamide and mixtures thereof;

wherein the reactive stabilizer is selected from the group consisting of:

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

wherein the blending chamber comprises a plurality of heated regions arranged so that the ingredients are subjected to a temperature profile whereby the temperature increases from the inlet to the outlet;

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

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

allowing the plasticized polymer to pass from the primary outlet.

2. A method as claimed in claim 1 , wherein the reactive stabilizer is sodium benzoate.

3. A method as claimed in claim 1 , wherein the amount of the reactive stabilizer relative to the amount of the composition is from 0.2 wt % to 5 wt %.

4. A method as claimed in claim 3 , wherein the amount of the reactive stabilizer relative to the amount of the composition is from 0.5 wt % to 3 wt %.

5. A method as claimed in claim 4 , wherein the amount of the reactive stabilizer relative to the amount of the composition is from 0.5 wt % to 2 wt %.

6. A method as claimed in claim 5 , wherein the amount of reactive stabilizer relative to the amount of the composition is from 0.5 wt % to 1.5 wt %.

7. A method as claimed in claim 1 , wherein the polyvinyl alcohol polymer comprises polyvinyl alcohol or a blend thereof wherein the polyvinyl alcohol has a degree of hydrolysis of 93 wt % to 98 wt %.

8. A method as claimed in claim 7 , wherein the degree of hydrolysis is 93 wt % to 97 wt %.

9. A method as claimed in claim 8 , wherein the degree of hydrolysis is 93 wt % to 95 wt %.

10. A method as claimed in claim 1 , wherein the polyvinyl alcohol polymer is a blend of two or more polyvinyl alcohol polymers.

11. A method as claimed in claim 10 , wherein the blend comprises a polymer having a molecular weight in the range 13,000 to 27,000 and a degree of polymerization of 300-600 and a medium/high viscosity grade having a molecular weight in the range 107,000 to 120,000 and a degree of polymerization of 2,400 to 2,600.

12. A method as claimed in claim 1 , wherein at least two or more plasticizers are selected from the group consisting of dipentaerythritol, methyl pentanediol, triacetin, 2-hydroxy-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, tricyclic trimethylolpropane formal, D-mannitol, triglycerol, and xylose.

13. A method as claimed in claim 1 , wherein the amount of reactive stabilizer relative to the amount of the composition is 1 wt %.