Method for preparing polyanhydroglucuronic acid and/or salts thereof

1. A method for preparing polyanhydroglucuronic acid salts comprising the steps of:

hydrolysis of a polyanhydroglucuronic acid-containing material in the presence of an inorganic and/or organic salt or base to form a homogenous solution comprising a fully hydrolysed salt of polyanhydroglucuronic acid; and

subsequently subjecting the homogenous solution formed by the hydrolysis step to ion exchange in the presence of one or more water soluble and/or partially soluble inorganic and/or organic salt or base with a different cation from the inorganic and/or organic salt or base used in the hydrolysis step to form a binary or higher salt of polyanhydroglucuronic acid, the method being carried out at a temperature of from 15° C. to 30° C.;

wherein the hydrolysis is carried out in an aqueous solution;

wherein the inorganic and/or organic salt and/or base used in the hydrolysis step is selected from the group consisting of any one or more of chlorides, sulphates, carbonates, formates, acetates or alkali and/or alkaline earth metals, hydroxides of alkali and/or alkaline earth metals, alkylamines and alkanolamines, in concentrations ranging from 0.001 to 5 mol/1;

wherein the water soluable and/or partially soluble inorganic and/or organic salt and/or base used in the ion exchange step is selected from the group consisting of any one or more of hydroxides, chlorides, nitrates, borates, sulphides, sulphates and acetates;

wherein hydrolysis is carried out for a period of from 15 to 30 minutes; and

wherein ion exchange is carried out for a period of from 15 to 30 minutes.

2. The method as claimed in claim 1 wherein the polyanhydroglucuronic acid-containing material is obtained by oxidation of a polysaccharide.

3. The method as claimed in claim 2 wherein the polyanhydroglucuronic acid-containing material is obtained by oxidation with nitrogen oxides or using sodium hypochorite in the presence of a 2,2,6,6-tetramethylpiperidine-1-oxyl radical catalyst.

4. The method as claimed in claim 1 comprising supplemental oxidation of the product of the ion exchange step in the presence of one or more of organic and inorganic peroxides.

5. The method as claimed in claim 1 wherein the aqueous solution comprises an admixture of an organic solvent.

6. The method as claimed in claim 5 wherein the organic solvent is selected from the group consisting of any one or more of ethanol, isopropanol and other water-miscible alcohol or organic solvents.

7. The method as claimed in claim 4 wherein supplemental oxidation is carried out for a period of from 15 to 30 minutes.

8. The method as claimed in claim 1 further comprising the step of precipitating, washing and drying the product.

9. The method as claimed in claim 1 further comprising the step of dehydrating the product.

10. The method as claimed in claim 8 wherein the pH is adjusted to between 2.0 and 8.5 prior to concentration.

11. The method as claimed in claim 8 wherein the product is washed and/or dehydrated, using water miscible or partially miscible organic solvents and/or converted, in an appropriate manner, for intended subsequent use.

12. The method as claimed in claim 7 wherein the product is dried at a temperature of between 20 and 105° C.

13. The method as claimed in claim 12 wherein after drying, the product is milled and/or sieved.

14. The method as claimed in claim 4 wherein an oxidative environment during supplemental oxidation is established by the presence of oxidising agents selected from the group consisting of one or more of hydrogen, sodium or magnesium peroxide, peroxoacids and their salts, hypochlorites and chlorites.

15. The method as claimed in claim 2 wherein the polysaccharide is selected from the group consisting of native or regenerated cellulose and starch.