Preparation of superabsorbent polymers
View Patent ↗The invention describes superabsorbent polymers composed of surface-post crosslinked polycarboxypolysaccharides having excellent age-stable absorption properties, even under load, high attrition resistance and biodegradability and their use for absorbing water, aqueous or serous fluids and also blood. Also disclosed is a method of making which is impervious to changes in raw material quality and which provides consistent product quality.
1. A process for preparing superabsorbent polymers comprising the steps of:
a) forming a hydrogel by mixing an uncrosslinked polycarboxypolysaccharide with water; b) the hydrogel is mechanically comminuted and dried; c) the dried hydrogel is comminuted and classified to form a polymer particles; and d) the polymer particles are coated with a solution of a crosslinker and subjected to a surface post crosslinking wherein said post crosslinked superabsorbent polymer has an absorbency against pressure (AAP 0.7 ) value of 12.5 g/g or more.
2. The process of claim 1 wherein the mixing of polycarboxypolysaccharide and water is carried out in a continuous mixer.
3. The process of claim 1 wherein the mixing of polycarboxypolysaccharide and water is carried out in a batch mixer.
4. The process of claim 1 wherein the mixture of polycarboxypolysaccharide and water has a pH of about 6 or more.
5. The process of claim 1 wherein the mixture of polycarboxypolysaccharide and water has a pH of about 10 or more.
6. The process of claim 1 wherein the mixture of polycarboxypolysaceharide and water includes from about 5 to about 65% by weight of polycarboxypolysaccharide.
7. The process of claim 1 wherein the mixture of polycarboxypolysaccharide and water includes about 0.01 to about 20% by weight, based on the solids content, of one or more water-soluble additives from the group consisting of bases, salts and blowing agents.
8. The process of claim 1 wherein the carboxyl groups of the polycarboxypolysaccharide are 80% neutralized or more.
9. The process of claim 1 wherein up to about 30% by weight of the water in the mixture of polycarboxypolysaccharide and water is replaced by one or more water-miscible organic solvents which do not dissolve the polycarboxypolysaccharide.
10. The process of claim 1 wherein the mixture of polycarboxypolysaccharide and water includes about 0.01 to about 20% by weight, based on the solids content, of one or more antiblocking additives.
11. The process of claim 1 wherein the drying of the hydrogel is effected at temperatures above about 70° C.
12. The process of claim 1 wherein the hydrogel is dried to a moisture content of about 30% by weight or less.
13. The process of claim 1 wherein about 0.01 to about 25% by weight of covalent or ionic surface post crosslinkers or a combination of at least two thereof, based on the polymer powder, is added in the form of about 0.01 to about 80% by weight aqueous solution.
14. The process of claim 13 wherein the aqueous solution of the covalent surface post crosslinker further includes a crosslinking catalyst.
15. The process of claim 14 wherein the weight ration of surface crosslinker to crosslinking catalyst is about 1:0.001 to about 1:1.
16. The process of claim 1 characterized in that the surface post crosslinking is carried out at temperatures of about 40° C. to about 250° C.