Colour-stable superabsorbent

Abstract

Superabsorbents comprising at least one compound of formula (I)

##STR00001##

or salt thereof, where R1 and R2 independently are H, organic or functional substituents, exhibit improved stability against discolouration.

Claims

1. A superabsorbent comprising at least one compound of the formula (I): ##STR00004## or salt thereof, where R1 and R2 independently are H, organic, or functional substituents.

2. The superabsorbent of claim 1, wherein the compound of formula (I) is selected from the group consisting of (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl, 4-Hydroxi-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 4-Acetamido-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 4-Acetyl-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 4-Oxo-(2,2,6,6-Tetramethylpiperidin-1-yl)oxyL and 1,4-dihydroxy-2,2,6,6-tetramethylpiperidinium 2-hydroxy-1,2,3-propanetricarboxylate.

3. The superabsorbent of claim 1, comprising at least 0.0001 wt. % and at most 5 wt. % of the compound of formula (I), based on the total weight of the dry superabsorbent comprising the compound of formula (I).

4. The superabsorbent of claim 3, comprising at least 0.001 wt. % and at most 1 wt. % of the compound of formula (I), based on the total weight of the dry superabsorbent comprising the compound of formula (I).

5. The superabsorbent of claim 1, wherein the superabsorbent is surface postcrosslinked.

6. The superabsorbent of claim 1, wherein the superabsorbent is surface complexed with polyvalent metal ions.

7. The superabsorbent of claim 6, wherein the superabsorbent is surface complexed with aluminium ions.

8. A process for producing a superabsorbent comprising at least one compound of the formula (I): ##STR00005## or salt thereof, where R1 and R2 independently are H, organic, or functional substituents, by polymerising an aqueous monomer solution comprising a) at least one ethylenically unsaturated monomer which bears an acid group and is optionally present at least partly in salt form, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerisable with the monomer mentioned under a), e) optionally one or more water-soluble polymer, the process further comprising: drying of the resulting polymer, optionally grinding of the dried polymer and sieving of the ground polymer, optionally surface postcrosslinking of the dried and optionally ground and sieved polymer, and mixing the polymer with at least one compound of formula (I).

9. The process according to claim 8, wherein at least one compound of formula (I) is mixed with the polymer after surface postcros slinking.

10. The process according to claim 9, wherein at least one compound of formula (I) is mixed with the polymer in a cooler.

11. An article for absorption of fluids, comprising a superabsorbent defined in claim 1.

12. A process for producing articles for absorption of fluid, wherein the production of the articles comprises addition of a superabsorbent defined in claim 1.

Description

EXAMPLES

[0164] Lignostab® 1198 is a mark of BASF for 1-Oxyl-4-hydroxy-2,2,6,6-tetramethylpiperidine, CAS no.2226-96-2, “4 Hydroxy TEMPO”. The compound is available e.g. from BASF Canada Inc. 100 Milverton Drive, 5th Floor, Mississauga, ON L5R 4H1, Canada, or BTC Europe GmbH, Rheinpromenade 1, 40789 Monheim am Rhein, Germany.

[0165] Tinogard® Q is a mark of BASF for 1,4-dihydroxy-2,2,6,6-tetramethylpiperidinium 2-hydroxy-1,2,3-propanetricarboxylate, CAS no 220410-74-2. The compound is available e.g. from BASF SE, Carl-Bosch-Straβe 38, 67056 Ludwigshafen, Germany, or BTC Europe GmbH, Rheinpromenade 1, 40789 Monheim am Rhein, Germany.

[0166] HySorb® T9900 and Hysorb® T9400, respectively, are marks of BASF for two of its commercial superabsorbents. The products are available e.g. from BASF SE, Carl-Bosch-Straβe 38, 67056 Ludwigshafen, Germany, or BASF Corporation, 11501 Steele Creek Road, Charlotte, N.C. 28273, U.S.A.

Example 1

[0167] 200 g of HySorb® T9900 superabsorbent were set in the plastic bowl of a Bosch MUM 4770 ProfiMixx 47 mixer (Robert Bosch Hausgeräte GmbH, Carl-Wery-Straβe 34, 81739 Munich, Germany) equipped with a metal beater. 0.667 g of a 30 wt. % aqueous solution of Lignostab® 1198 were added (0.1 wt. % of Lignostab® 1198 based on polymer (“bop”, referring to the superabsorbent prior to adding)). The sample was coated with the solution at room temperature by spraying using a syringe during mixing at 180 rpm (speed setting 3). Spraying was followed by further stirring the polymer at speed of 105 rpm for another 5 minutes.

Example 2

[0168] Example 1 was repeated, however, 3.34 g of the 30 wt. % aqueous solution of Lignostab® 1198 were added (0.5 wt. % bop Lignostab® 1198).

Example 3

[0169] Example 1 was repeated, however, 2.0 g of a 10 wt. % aqueous solution of Tinogard Q were added (0.1 wt. % bop Tinogard Q).

Example 4

[0170] Example 3 was repeated, however, 10 g of the 10 wt. % aqueous solution of Tinogard Q were added (0.5 wt. % bop Tinogard Q).

Example 5

[0171] Example 1 was repeated, however, 0.334 g of a 30 wt. % aqueous solution of 4-Hydroxy-TEMPO (Sigma-Aldrich, Germany) were added (0.05 wt. % bop 4-Hydroxy-TEMPO).

Example 6

[0172] Example 5 was repeated, however, 0.667 of the 30 wt. % aqueous solution of 4-Hydroxy-TEMPO were added (0.1 wt. % bop 4-Hydroxy-TEMPO).

[0173] The water-absorbing polymer particles coated in examples 1 to 6 and an untreated HySorb® T 9900 sample were subjected to the ageing test. The results are compiled in Table 1.

TABLE-US-00001 TABLE 1 Effect of post coating of HySorb ® T9900 on its colour stability in the Ageing Test Initial colour After ageing Example Coating L a b H60 L a b H60 HySorb ®T9900*.sup.) no coating 94.3 −0.9 5.1 78.9 48.0 11.8 18.2 −6.6 Ex. 1 0.1% Lignostab 1198 90.7 0.0 7.8 67.4 77.7 2.1 9.8 48.2 Ex. 2 0.5% Lignostab 1198 90.0 0.7 15.2 44.3 84.9 0.6 9.9 55.3 Ex. 3 0.1% Tinogard Q 93.8 −0.6 6.2 75.2 82.3 2.6 10.2 51.7 Ex. 4 0.5% Tinogard Q 93.3 −0.3 7.6 70.5 82.3 2.0 11.5 47.8 Ex. 5 0.05% Hydroxy-TEMPO 92.6 −0.1 6.9 71.9 81.9 2.8 10.2 51.2 Ex. 6 0.1% Hydroxy-TEMPO 91.8 0.2 8.4 66.7 84.8 1.5 9.0 58.0 *.sup.)comparative

Example 7

[0174] 100 g of HySorb® T9400 were coated in a Waring variable speed laboratory blender, Model #38BL54 (Waring Commercial, 314 Ella T. Grasso Ave., Torrington, Conn. 06790, U.S.A.), using a syringe. The coating solution contained no, 0.005 or 0.01 wt. % of Lignostab® 1198 and 40 wt. % of water with respect to dry polymer. The sample was coated with the solution by applying it with a syringe at room temperature over 15 seconds to the polymer while mixing at 2000 rpm. The mixing was continued for an additional 45 seconds after completing the solution addition.

Example 8

[0175] Example 7 was repeated, however, using HySorb® T9900 instead of HySorb® T 9400.

[0176] The water-absorbing polymer particles coated in examples 7 and 8 were subjected to the accelerated ageing test. The results are compiled in Table 2.

TABLE-US-00002 TABLE 2 Effect of post coating of superabsorbents on their colour stability in the accelerated ageing test Example Coating Days to L = 75 Ex. 7 a)*.sup.) no coating 0.8 Ex. 7 b) 0.005 wt. % Lignostab ® 1198 0.8 Ex. 7 c) 0.01 wt. % Lignostab ® 1198 2.0 Ex. 8 a)*.sup.) no coating 0.8 Ex. 8 b) 0.005 wt. % Lignostab ® 1198 1.1 Ex. 8 c) 0.01 wt. % Lignostab ® 1198 3.2 *.sup.)comparative

[0177] The examples demonstrate that the addition of small amounts of TEMPO derivatives improve superabsorbent resistance to colour degradation in hot and humid environments.