Pulverulent polymers crosslinked on the surface
The present invention relates to a pulverulent polymer post-crosslinked on the surface and absorbing water or aqueous liquids, synthesised from polymerised, optionally pre-crosslinked monomers containing partially neutralised carboxyl groups. The present invention also relates to a process for the post-treatment of the aforementioned polymers and the use of a solution of at least one salt of an at least trivalent cation for restoring the gel permeability of the aforementioned polymers that have been damaged by mechanical action.
1. A pulverulent polymer suitable for absorbing water or aqueous liquids and post-crosslinked on the surface, the pulverulent polymer is synthesized from polymerized, optionally pre-crosslinked, partially neutralized monomers containing carboxyl groups, wherein the pulverulent polymer further comprises a surface post-crosslinking agent wherein the pulverulent polymer has been reacted, after the surface post-crosslinking, with a solution of at least one salt of an at least trivalent cation.
2. The pulverulent polymer according to claim 1 , characterized in that the trivalent cation is at least one aluminium cation, iron cation, and/or manganese cation.
3. The pulverulent polymer according to claim 1 , characterized in that the trivalent cation is used in an amount of about 0.001 wt. % to about 1 wt. % based on the weight of the polymer.
4. The pulverulent polymer according to claim 1 , characterized in that before the reaction with the solution of at least one salt of a at least trivalent cation.
5. The pulverulent polymer according to claim 1 , characterized in that the water content of the polymer during the reaction increases by about 0.05 wt. % to about 10 wt. %.
6. The pulverulent polymer according to claim 1 , characterized in that the grain fraction less than about 150 μm before the reaction is less than about 15 wt. %.
7. The pulverulent polymer according to claim 1 , wherein the pulverulent polymer comprises carboxyl groups that are neutralized in an amount of about 25 mol % to about 85 mol %.
8. The pulverulent polymer according to claim 1 , comprising further comonomers and/or graft polymers.
9. A process for the production of pulverulent polymer according to claim 1 , post-crosslinked on the surface and absorbing water or aqueous liquids, comprising the steps of (1) solution of at least one salt of an at least trivalent cation is added to the pulverulent polymer after the post-crosslinking and heat treatment; and (2) the heat-treated post-crosslinked pulverulent polymer, and the solution are preferably thoroughly homogeneously mixed.
10. The process according to claim 9 , wherein the temperature of the polymer powder during the post-treatment is about 60° C. to about 100° C.
11. The process according to claim 9 , wherein the thorough mixing pulverulent polymer and solution is effected with a stirrer operating at a rotational speed of about 700 r.p.m. to about 1000 r.p.m.
12. A pulverulent polymer obtained by the process according to claim 9 .
13. An absorption agent for liquids, in particular water and aqueous liquids comprising the pulverulent polymer according to claim 1 .
14. An absorption agent for aqueous liquids, in structures for absorbing body fluids, in foamed and non-foamed two-dimensional structures, in packaging materials, in plant growing, and as a soil amelioration agent, the absorption agent comprising the polymer according to claim 1 .
15. A hygiene article comprising the polymer of claim 1 such as diapers or tampons.
16. A carrier substance for active constituents, in particular for fertilizers or other active constituents that are optionally released in delayed form, wherein the carrier substance comprises the polymer of claim 1 .