Method for measuring the permeability of superabsorbers
A method of measuring indices in superabsorbents, by initially charging excess aqueous solution or dispersion, swelling the superabsorbent in the initially charged aqueous solution or dispersion while stirring, dissolving or dispersing a component A in the aqueous solution or dispersion, measuring the enrichment of component A in the aqueous solution or dispersion during the swelling of the superabsorbent, using the enrichment of component A in the aqueous solution or dispersion to measure the time-dependent swelling characteristics and using these to determine the swelling constant k or the characteristic swell time τ, the index being dependent on the permeability of the superabsorbent, and ascertaining the index by means of a correlation measured beforehand between swelling constant k and index or characteristic swell time τ and index.
1. A method of measuring an index in a superabsorbent comprising initially charging excess aqueous solution or dispersion, swelling the superabsorbent in the initially charged aqueous solution or dispersion while stirring, dissolving or dispersing at least one component A in the aqueous solution or dispersion and measuring an enrichment of the at least one component A in the aqueous solution or dispersion during the swelling of the superabsorbent, wherein the enrichment of component A in the aqueous solution or dispersion is used to measure the time-dependent swelling characteristics and these are used to determine the swelling constant k or the characteristic swell time τ, the index is dependent on the permeability of the superabsorbent, and the index is ascertained by a correlation measured beforehand between swelling constant k and index or characteristic swell time τ and index.
2. The method according to claim 1 , wherein component A is a soluble salt and the enrichment of component A is measured via a rise in electrical conductivity of the solution.
3. The method according to claim 1 , wherein component A is a soluble dye and the enrichment of component A is measured via a rise in light absorption of the solution.
4. The method according to claim 1 , wherein the amount of aqueous solution or dispersion used is from 10 to 200 ml.
5. The method according to claim 1 , wherein the amount of superabsorbent used is from 0.5 to 5 g.
6. The method according to claim 1 , wherein a quotient of amount of aqueous solution or dispersion used and total swelling capacity of the superabsorbent used in the aqueous solution or dispersion is in a range from 2.5 to 5.
7. The method according to claim 1 , wherein the index is a time taken for a layer of superabsorbent particles to swell by a particular value.
8. The method according to claim 7 , wherein the layer of superabsorbents consists of 0.5 to 5 g of the superabsorbent and covers a circular area having a diameter of 5 to 7 cm.
9. The method according to claim 1 , wherein the correlation is measured by calculating the swelling constant k or the characteristic swell time τ and measuring the index of at least three superabsorbents having different permeability.
10. The method according to claim 9 , wherein the superabsorbents of different permeability are produced by changing an amount of crosslinker in a polymerization and/or by changing an amount of surface postcrosslinker in a surface postcrosslinking operation.
11. The method according to claim 1 , wherein the superabsorbent has an average particle size of 200 to 600 μm.
12. The method according to claim 1 , wherein the superabsorbent has a saline flow conductivity of at least 10×10 −7 cm 3 s/g.
13. The method according to claim 1 , wherein the superabsorbent has a centrifuge retention capacity of at least 10 g/g.
14. The method according to claim 1 for quality control in the continuous production of superabsorbents.