Water-absorbing polymer

1. A particulate, water-absorbent polycarboxypolysaccharide, wherein said polycarboxypolysaccharide is chemically modified with an average degree of carboxyl substitution within a range from 0.4 to about 1.5 and has (α1) an absorption under load value at a pressure of 0.9 psi within a range from 10 to 22 g/g and with a centrifuge retention capacity value within a range from 15 to 20 g/g; or (α2) an absorption under load value at a pressure of 0.9 psi within a range from 6 to 20 g/g and with a centrifuge retention capacity value within a range from 20 to 25 g/g, obtainable by a process comprising: a) providing an uncrosslinked polycarboxypolysaccharide; b) adding from about 0.001 to 20 wt. % based upon a weight of the polysaccharide of a crosslinking agent including polyphosphoric acid; c) adding an alkali hydroxide to neutralize the polycarboxypolysaccharide from step b) to at least about 50 mol %; and d) drying the polycarboxypolysaccharide to produce the water-absorbent polycarboxypolysaccharide.

2. The particulate, water-absorbent polycarboxypolysaccharide according to claim 1 , further comprising a blowing agent selected from the group consisting of azo and diazo compounds, carbonate salts, ammonium salts and urea.

3. The particulate, water-absorbent polycarboxypolysaccharide according to claim 1 , wherein the particulate polycarboxypolysaccharide has a particle size distribution of from 150 to 850 μm.

4. The particulate, water-absorbent polycarboxypolysaccharide according to claim 1 , wherein the particulate, water-absorbent polycarboxypolysaccharide has a Gel Bed Permeability of from about 20×10 −9 cm 2 to about 500×10 −9 cm 2 .

5. The particulate, water-absorbent polycarboxypolysaccharide according to claim 1 , further comprising from about 0.001 to about 20 wt %, based upon the weight of the polycarboxypolysaccharide, of a post-crosslinking agent.

6. A composite comprising a water-absorbent, at least partially neutralized polycarboxypolysaccharide according to claim 1 and a substrate.

7. The particulate, water-absorbent polycarboxypolysaccharide according to claim 1 , wherein the polyphosphate comprises as crosslinking agent the formula M I n+2 [P n O 3n+1 ] or M I n [H 2 P n O 3n+1 ], wherein M I is a monovalent metal and n has a value of at least 2.

8. The particulate, water-absorbent polycarboxypolysaccharide according to claim 1 , wherein the polyphosphoric acid as crosslinking agent has the formula H n+2 P n O 3n+1 or (HPO 3 ) n , in which n has a value of at least 2.

9. A process for producing a particulate water-absorbent polycarboxypolysaccharide wherein said water-absorbent polycarboxypolysaccharide is chemically modified with an average degree of carboxyl substitution within a range from 0.4 to about 1.5 and has (α1) an absorption under load value at a pressure of 0.9 psi within a range from 10 to 22 g/g and with a centrifuge retention capacity value within a range from 15 to 20 g/g; or (α2) an absorption under load value at a pressure of 0.9 psi within a range from 6 to 20 g/g and with a centrifuge retention capacity value within a range from 20 to 25 g/g, the process comprising the steps of: a) preparing an aqueous solution having a pH of from about 8 to about 12 by mixing an uncrosslinked polycarboxypolysaccharide with a crosslinking agent consisting essentially of polyphosphoric acid in an amount within a range from 0.001 to 20 wt. %, based upon a weight of the uncrosslinked polycarboxypolysaccharide, in the presence of water to form a polycarboxypolysaccharide gel; and b) drying the polycarboxypolysaccharide gel.

10. The process according to claim 9 , wherein carboxyl group of the uncrosslinked polycarboxypolysaccharide are neutralized to at least about 50 mol %.

11. The process according to claim 9 , wherein the crosslinking or the drying occurs at a temperature above about 70° C.

12. The process according to claim 9 , wherein the mixing step of the uncrosslinked polycarboxypolysaccharide with the crosslinking agent occurs in the absence of an organic solvent.

13. The process according to claim 9 , wherein the water-absorbent polycarboxypolysaccharide comprises a salt content of less than about 20 wt. %, based upon a total weight of the polycarboxypolysaccharide.

14. The process according to claim 9 , wherein the polyphosphate comprises as crosslinking agent the formula M I n+2 [P n O 3n+1 ] or M I n [H 2 P n O 3n+1 ], wherein MI is a monovalent metal and n has a value of at least 2.

15. The process according to claim 9 , wherein the polyphosphoric acid as crosslinking agent has the formula H n+2 P n O 3n+1 or (HPO 3 ) n , in which n has a value of at least 2.

16. The process according to claim 9 , wherein the dried polycarboxypolysaccharide gel is milled, so that the particulate, crosslinked polycarboxypolysaccharide is obtained.

17. The process according to claim 16 , wherein the particulate, crosslinked polycarboxypolysaccharide is post-crosslinked in the outer part with a post-crosslinking agent.

18. The process according to claim 17 , wherein the post-crosslinking agent is used in a form of about 0.01 to about 80 wt. % aqueous solution.

19. The process according to claim 17 , wherein the post-crosslinking agent is a polyphosphate or polyphosphoric acid.

20. The process according to claim 17 , wherein the post-crosslinking of the crosslinked polycarboxypolysaccharides with the post-crosslinking agent occurs in the presence of inorganic particles.

21. The process according to claim 9 comprising the step of drying the polycarboxypolysaccharide gel on a belt drier at a temperature of from about 120° C. to about 130° C. for a time period of from about 50 minutes to about 150 minutes.