METHOD FOR MEASURING THE PERMEABILITY OF SUPERABSORBERS

Abstract

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 T, 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 T and index.

Claims

1. A method of measuring indica 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 T, the index is dependent on the permeability of the superabsorbent, and the index is ascertained by means of a correlation measured beforehand between swelling constant k and index or characteristic swell time T 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 component A is a soluble dye and the enrichment of component A is measured via a rise in light absorption of the solution.

5. The method according to claim 1, wherein the amount of aqueous solution or dispersion used is from 10 to 200 ml.

6. The method according to claim 1, wherein the amount of superabsorbent used is from 0.5 to 5 g.

7. 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.

8. 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.

9. The method according to claim 8, 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.

10. The method according to claim 1 to 9, wherein the correlation is measured by calculating the swelling constant k or the characteristic swell time T and measuring the index of at least three superabsorbents having different permeability.

11. The method according to claim 10, 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.

12. The method according to claim 1, wherein the superabsorbent has an average particle size of 200 to 600 m.

13. The method according to claim 1, wherein the superabsorbent has a saline flow conductivity of at least 1010.sup.7 cm.sup.3s/g.

14. The method according to claim 1, wherein the superabsorbent has a centrifuge retention capacity of at least 10 g/g.

15. The method according to claim 1 for quality control in the continuous production of superabsorbents.

16. A measurement apparatus for performing measurements according to claim 1.

Description

EXAMPLES

[0054] Four superabsorbents of different permeability were produced for the examples. Centrifuge retention capacity (CRC) and liquid absorption of 20 g/g (T20) of the superabsorbents were measured. The results are collated in table 1.

TABLE-US-00001 TABLE 1 Properties of the superabsorbents CRC [g] T20 [s] SAP1 25.5 110 SAP2 26.6 134 SAP3 26.2 170 SAP4 26.1 200

[0055] The time-dependent swelling characteristics of the superabsorbents were measured. For this purpose, 100 ml of a 0.9% by weight aqueous sodium chloride solution was initially charged. The initially charged solution additionally comprised 20 mg of dextran blue as component A. The concentration of dextran blue in the solution was measured by photometry. At time t=0, 0.75 g of superabsorbent was added and the measurement was started. The data obtained were used to calculate the characteristic swell time T. The results are collated in table 2.

TABLE-US-00002 TABLE 2 characteristic swell time T T [s] SAP1 248 SAP2 253 SAP3 274 SAP4 287

[0056] This results in the correlation (calibration curve) shown in FIG. 1 for the liquid absorption of 20 g/g (T20).

[0057] Table 3 below shows a comparison of the measured liquid absorption of 20 g/g (T20).sub.meas with the liquid absorption of 20 g/g (T20).sub.calc obtained via the correlation.

TABLE-US-00003 TABLE 3 Comparison of the measured liquid absorption of 20 g/g (T20).sub.meas with the liquid absorption of 20 g/g (T20).sub.calc obtained via the correlation (T20).sub.meas [s] (T20).sub.calc [s] SAP1 110 116 SAP2 134 127 SAP3 170 172 SAP4 200 199

[0058] The table shows that the variance is less than 6% and hence is within the range of error of the actual measurement.

[0059] In addition, the liquid absorption at 0.5 hours is used to calculate centrifuge retention capacity (CRC).sub.calc and this is compared with the measured centrifuge retention capacity (CRC).sub.meas:

TABLE-US-00004 TABLE 4 Comparison of measured centrifuge retention capacity (CRC).sub.meas with centrifuge retention capacity obtained via time-dependent swelling characteristics (CRC).sub.calc (CRC).sub.meas [g/g] (CRC).sub.calc [g/g] SAP1 25.5 25.5 SAP2 26.6 25.9 SAP3 26.2 26.3 SAP4 26.1 25.8

[0060] The table shows that the variance is less than 3% and hence is within the range of error of the actual measurement.