Hydrolytically stable postcrosslinked superabsorbents
View Patent ↗The present invention relates to a process for producing postcrosslinked water-absorbing polymeric formations, comprising the steps of contacting water-absorbing polymeric formations P 1 obtained by polymerization of ethylenically unsaturated acid-functional monomers or salts thereof in the presence of a crosslinker with a fluid F 1 comprising a postcrosslinker, heating the water-absorbing polymeric formations in contact with the fluid F 1 to a temperature in a range from 40 to 300° C. to obtain postcrosslinked water-absorbing polymeric formations P 2 , the water-absorbing polymeric formations P 1 having a thermal stability, as determined in accordance with the test method described herein, of less than 3.0%. The invention also relates to water-absorbing polymeric formations, to the water-absorbing polymeric formations obtainable by this process, to water-absorbing polymeric formations based on crosslinked carboxyl-bearing monomers, to a composite comprising water-absorbing polymeric formations and a substrate, to a process for producing a composite, to a composite obtainable by this process, to chemical products comprising water-absorbing polymeric formations or a composite, to the use of water-absorbing polymeric formations or of a composite in chemical products and also to the use of triallyl isocyanurate as an internal crosslinker in the production of water-absorbing polymeric formations based on crosslinked carboxyl-bearing monomers.
1. A process for producing postcrosslinked water-absorbing polymeric formations, comprising the steps of:
a) contacting water-absorbing polymeric formations P 1 , obtained by polymerization of ethylenically unsaturated acid-functional monomers or salts thereof in the presence of a triallyl isocyanurate crosslinker, with a fluid F 1 comprising a postcrosslinker;
b) heating the water-absorbing polymeric formations P 1 in contact with the fluid F 1 to a temperature in a range from 40 to 300° C. to obtain postcrosslinked water-absorbing polymeric formations P 2 ;
wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 3.0%.
2. The process of claim 1 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 2.0%.
3. The process of claim 1 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 1.0%.
4. The process of claim 1 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 0.5%.
5. The process of claim 1 , wherein said water-absorbing polymeric formations P 1 are obtained in the absence of surface-active agents.
6. The process of claim 1 , wherein the surface of said water-absorbing polymeric formations P 1 is contacted with a tervalent cation before, during or after postcrosslinking.
7. The process of claim 1 , wherein said ethylenically unsaturated acid-functional monomer, are acrylic acid.
8. A process for producing postcrosslinked water-absorbing polymeric formations, comprising the steps of:
a) producing water-absorbing polymeric formations P 1 by polymerizing ethylenically unsaturated acid-functional monomers or salts thereof in the presence of a triallyl isocyanurate crosslinker,
b) drying the water-absorbing polymeric formations of step a) at a temperature in the range of 80 to 200° C.;
c) contacting the dried water-absorbing polymeric formations produced in step b) with a fluid F 1 comprising a postcrosslinker at a temperature in a range from 40 to 300° C. to obtain postcrosslinked water-absorbing polymeric formations P 2 ;
wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 3.0%.
9. The process of claim 8 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 2.0%.
10. The process of claim 8 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 1.0%.
11. The process of claim 8 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 0.5%.
12. The process of claim 8 , wherein said water-absorbing polymeric formations P 1 are obtained in the absence of surface-active agents.
13. The process of claim 8 , wherein the surface of said water-absorbing polymeric formations P 1 is contacted with a tervalent cation before, during or after postcrosslinking.
14. A process for producing postcrosslinked water-absorbing polymeric formations, comprising the steps of:
a) producing water-absorbing polymeric formations P 1 , by polymerizing compounds of structure I:
wherein R 1 , R 2 and R 3 may be the same or different and represent an ethylenically unsaturated hydrocarbon having 2 to 20 carbon atoms;
b) contacting the dried water-absorbing polymeric formations produced in step a) with a fluid F 1 comprising a postcrosslinker at a temperature in a range from 40 to 300° C. to obtain postcrosslinked water-absorbing polymeric formations P 2 ;
wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 3.0%.
15. The process of claim 14 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 2.0%.
16. The process of claim 14 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 1.0%.
17. The process of claim 14 , wherein the water-absorbing polymeric formations P 1 have a thermal stability of less than 0.5%.
18. The process of claim 14 , wherein said water-absorbing polymeric formations P 1 are obtained in the absence of surface-active agents.
19. The process of claim 14 , wherein the surface of said water-absorbing polymeric formations P 1 is contacted with a tervalent cation before, during or after postcrosslinking.