Methods for producing water-absorbent foamed polymer particles

Abstract

A process for preparing water-absorbing polymer particles, comprising polymerization of a foamed monomer solution or suspension, drying, grinding and classification.

Claims

1. A process for producing water-absorbing polymer particles by polymerizing a foamed aqueous monomer solution or suspension comprising a) at least one ethylenically unsaturated monomer which bears an acid group and has been neutralized to an extent of 25 to 95 mol %, b) at least one crosslinker, c) at least one initiator, and d) at least one surfactant, the monomer solution or suspension being polymerized to a polymeric foam and predried to a water content of 5 to 30%, by weight, which comprises subsequently grinding the predried polymeric foam, drying the resulting water-absorbing polymer particles, and classifying the resulting water-absorbing polymer particles.

2. The process according to claim 1, wherein at least 50 mol % of the neutralized monomer a) are neutralized by means of an inorganic base.

3. The process according to claim 2, wherein the inorganic base is potassium carbonate, sodium carbonate, or sodium hydroxide.

4. The process according to claim 1, wherein the ground polymeric foam is classified to a particle size in the range from 100 to 1 000 m.

5. The process according to claim 1, wherein the monomer solution or suspension comprises at least 1% by weight of the crosslinker b), based on the unneutralized monomer a).

6. The process according to claim 1, wherein the monomer a) is acrylic acid to an extent of at least 50 mol %.

7. The method of claim 1 wherein the polymeric foam is predried to a water content of 8 to 25%, by weight.

8. The method of claim 1 wherein the polymeric foam is predried to a water content of 10 to 20%, by weight.

Description

EXAMPLES

Example 1

(1) 149.0 g of acrylic acid, 782.1 g of a 37.3% by weight aqueous sodium acrylate solution, 15.4 g of Sartomer SR-344 (diacrylate of a polyethylene glycol having a molar mass of approx. 400 g/mol), 23.5 g of a 15% by weight aqueous solution of Lutensol AT80 (addition product of 80 mol of ethylene oxide onto 1 mol of a linear saturated 016-018 fatty alcohol; BASF SE; Ludwigshafen; Germany) and 30.0 g of water were mixed in a beaker.

(2) The resulting homogeneous solution was transferred to a pressure vessel and saturated there with carbon dioxide at a pressure of 10 bar for 25 minutes. Under pressure, 14.7 g of a 3% by weight aqueous solution of 2,2-azobis(2-amidinopropane) dihydrochloride were added and admixed with a strong carbon dioxide stream. Subsequently, carbon dioxide was passed through the reaction mixture for a further 5 minutes. The carbon dioxide-saturated reaction mixture was then extruded at a pressure of 12 bar through a die with a diameter of 1.0 mm, which formed a fine-cell, free-flowing foam.

(3) The resulting monomer foam was applied to a glass plate of DIN A3 size with edges of height 3 mm, and covered with a second glass plate. The foam sample was irradiated with UV light synchronously from both sides over 4 minutes, from above with a UVASPOT 1000/T UV/VIS radiator (Dr. Hnle AG; Grfelfing; Germany), and from below with 2 UVASPOT 400/T UV/VIS radiators (Dr. Hnle AG; Grfelfing; Germany).

(4) The resulting foam layer was completely dried in a forced air drying cabinet at 100 C., then ground in a Retsch mill and screened off to a particle size of 150 to 600 m.

(5) Solids content of the reaction mixture: 45.3% by weight

(6) Degree of neutralizing: 60 mol %

(7) Monomer foam density: 0.16 g/cm.sup.3

(8) The properties of the resulting water-absorbing polymer particles are reported in Table 1 and Table 2.

Example 2

(9) The procedure was as in Example 1. Instead of 15.4 g of Sartomer SR-344, only 10.3 g of Sartomer SR-344 were used. The properties of the resulting water-absorbing polymer particles are reported in Table 1.

Example 3

(10) The procedure was as in Example 1. Instead of 15.4 g of Sartomer SR-344, only 7.7 g of Sartomer SR-344 were used. The properties of the resulting water-absorbing polymer particles are reported in Table 1.

Example 4

(11) The procedure was as in Example 1. Instead of 15.4 g of Sartomer SR-344, only 4.4 g of Sartomer SR-344 were used. The properties of the resulting water-absorbing polymer particles are reported in Table 1.

Example 5

(12) The procedure was as in Example 1. Instead of 15.4 g of Sartomer SR-344, only 2.2 g of Sartomer SR-344 were used. The properties of the resulting water-absorbing polymer particles are reported in Table 1.

(13) TABLE-US-00001 TABLE 1 Variation of the amount of crosslinker AUL0.7 Crosslinker FSC CRC Vortex SFC psi Ex. [g] [g/g] [g/g] [s] [10.sup.7 cm.sup.3s/g] [g/g] 1 15.4 33.8 13.1 8 85 20.4 2 10.3 36.9 16.1 7 13 19.1 3 7.7 38.5 16.9 6 8 17.9 4 4.4 40.1 18.2 6 5 14.5 5 2.2 43.3 21.1 6 0 10.2

Example 6 (Noninventive)

(14) By continuously mixing deionized water, 50% by weight sodium hydroxide solution and acrylic acid, an acrylic acid/sodium acrylate solution is prepared, such that the degree of neutralization was 69 mol %. The solids content of the monomer solution was 35.5% by weight.

(15) The polyethylenically unsaturated crosslinker used was triply ethoxylated glyceryl triacrylate (approx. 85% strength by weight). The amount used was 1.33 g per kg of monomer solution.

(16) To initiate the free-radical polymerization, per kg of monomer solution, 2.84 g of a 15% by weight aqueous sodium peroxodisulfate solution and 28.4 g of a 0.5% by weight aqueous solution of Bruggolite FF7 (Bruggemann Chemicals; Heilbronn; Germany) were used.

(17) The throughput of the monomer solution was 1200 kg/h. The reaction solution had a temperature of 23.5 C. at the feed.

(18) The individual components were metered in the following amounts continuously into a List ORP 250 Contikneter reactor, (LIST AG, Arisdorf, Switzerland): 1200 kg/h of monomer solution 1.600 kg/h of triply ethoxylated glyceryl triacrylate 3.410 kg/h of sodium peroxodisulfate solution 34.10 kg/h of Bruggolite FF7 solution

(19) Between the addition point for crosslinker and the addition sites for the initiators, the monomer solution was inertized with nitrogen.

(20) The residence time of the reaction mixture in the reactor was 15 minutes.

(21) The resulting product gel was applied to a belt drier. On the belt drier, an air/gas mixture flowed continuously around the polymer gel which was dried at 175 C. The residence time in the belt drier was 43 minutes.

(22) The dried polymer gel was ground and screened off to a particle size fraction of 150 to 710 m. The base polymer thus obtained had the following properties:

(23) CRC: 35.7 g/g

(24) AUL 0.3 psi 19.1 g/g

(25) 1200 g of the base polymer were transferred to a Gebr. Ldige laboratory mixer (M5R). At approx. 23 C., a mixture of 0.6 g of 2-hydroxyethyloxazolidin-2-one, 0.6 g of 1,3-propanediol, 6.0 g of 1,2-propanediol, 22.8 g of water, 11.0 g of 2-propanol, 0.096 g of sorbitan monococoate and 5.4 g of aluminum lactate were sprayed on by means of a nozzle. The sprayed polymer particles were transferred to another Gebr. Ldige laboratory mixer, which was heated rapidly to 175 C. and held at this temperature for 50 minutes. After cooling, the surface postcrosslinked polymer particles were screened off to a screen cut between 150 and 710 m. The properties of the resulting water-absorbing polymer particles are reported in Table 2.

Example 7

(26) In a 500 ml glass bottle, 50 g of water-absorbing polymer particles according to Example 1 and 50 g of water-absorbing polymer particles according to Example 6 were mixed by means of a Turbula T2F mixer (Willy A. Bachofen AG Maschinenfabrik; Muttenz; Switzerland) at 45 rpm for 15 minutes. The properties of the resulting mixture are reported in Table 2.

Example 8

(27) In a 500 ml glass bottle, 10 g of water-absorbing polymer particles according to Example 1 and 90 g of water-absorbing polymer particles according to Example 6 were mixed by means of a Turbula T2F mixer (Willy A. Bachofen AG Maschinenfabrik; Muttenz; Switzerland) at 45 rpm for 15 minutes. The properties of the resulting mixture are reported in Table 2.

(28) TABLE-US-00002 TABLE 2 Blends with conventional water-absorbing polymer particles Proportion of inventive polymer particles FSR CRC AUL 0.7 psi SFC Ex. [% by wt.] [g/gs] [g/g] [g/g] [10.sup.7 cm.sup.3 s/g] 1 100 1.70 13.1 20.4 85 6 0 0.18 29.1 25.2 129 7 50 0.71 20.5 117 8 10 0.17 28.8 25.1 158

Example 9 (Noninventive)

(29) 17.9 g of acrylic acid and 139.6 g of a 37.3% by weight aqueous sodium acrylate solution were weighed into a 1 000 ml plastic beaker (internal diameter 105 mm and height 145 mm). While stirring by means of a magnetic crossbeam stirrer, 0.24 g of triply ethoxylated glyceryl triacrylate (approx. 85% strength by weight) and 41.0 g of water were added. Subsequently, the plastic beaker was closed with a polymer film, a PTFE-coated temperature sensor was positioned in the middle of the solution and nitrogen was passed through the solution via a glass frit.

(30) After 30 minutes, 0.46 g of a 15% by weight aqueous solution of sodium peroxodisulfate, 0.69 g of a 0.4% by weight aqueous solution of ascorbic acid and 0.08 g of a 10% by weight aqueous solution of hydrogen peroxide were injected by means of disposable syringes, and the temperature recording was started. The maximum temperature during the polymerization was 102.5 C.

(31) The resulting polymer gel was dried, ground and screened off to a particle size of 150 to 850 m. The properties of the resulting water-absorbing polymer particles are reported in Table 3.

Example 10

(32) The procedure was as in Example 9. Directly after the addition of the last initiator, 7.0 g of water-absorbing polymer particles according to Example 1 with a particle size of less than 150 m were added. The properties of the resulting water-absorbing polymer particles are reported in Table 3.

(33) TABLE-US-00003 TABLE 3 Addition of inventive polymer particles to the monomer solution Addition of inventive polymer particles FSR CRC AUL 0.3 psi Ex. [g] [g/gs] [g/g] [g/g] 9 0 0.24 42.8 8.1 10 7 0.29 31.2 17.3

Example 11

(34) 145.0 g of acrylic acid, 761.4 g of a 37.3% by weight aqueous sodium acrylate solution, 15.0 g of Sartomer SR-344 (diacrylate of a polyethylene glycol having a molar mass of approx. 400 g/mol) and 34.3 g of a 10% by weight aqueous solution of Lutensol AT80 (addition product of 80 mol of ethylene oxide onto 1 mol of a linear saturated 016-018 fatty alcohol; BASF SE; Ludwigshafen; Germany) were mixed in a beaker.

(35) The resulting homogeneous solution was transferred to a pressure vessel and saturated there with carbon dioxide at a pressure of 10 bar for 25 minutes. Under pressure, 43.5 g of a 3% by weight aqueous solution of 2,2-azobis(2-amidinopropane) dihydrochloride were added and admixed with a strong carbon dioxide stream. Subsequently, carbon dioxide was passed through the reaction mixture for a further 5 minutes. The carbon dioxide-saturated reaction mixture was then extruded at a pressure of 12 bar through a die with a diameter of 1.0 mm, which formed a fine-cell, free-flowing foam.

(36) The resulting monomer foam was applied to a glass plate of DIN A3 size with edges of height 3 mm, and covered with a second glass plate. The foam sample was irradiated with UV light synchronously from both sides over 4 minutes, from above with a UVASPOT 1000/T UV/VIS radiator (Dr. Hnle AG; Grfelfing; Germany), and from below with 2 UVASPOT 400/T UV/VIS radiators (Dr. Hnle AG; Grfelfing; Germany). The distance of the upper lamp from the monomer foam was 39 cm and the distance of the lower lamps from the monomer foam was 13 cm.

(37) The resulting foam layer was completely dried in a forced air drying cabinet at 100 C., then ground in a Retsch mill and screened off to different particle sizes, and the free swell rate (FSR) thereof was determined.

(38) Solids content of the reaction mixture: 44.9% by weight

(39) Degree of neutralizing: 60 mol %

(40) Monomer foam density: 0.16 g/cm.sup.3

(41) The properties of the resulting screen cuts are reported in Table 4.

(42) TABLE-US-00004 TABLE 4 Free swell rate (FSR) of individual screen cuts FSR Screen cut [g/s] <150 m 0.33 150 to 250 m 1.75 250 to 300 m 2.22 300 to 400 m 2.36 400 to 500 m 2.36 500 to 600 m 2.22 600 to 710 m 2.22 710 to 800 m 2.49 800 to 900 m 2.36 900 to 1000 m 2.45 1000 to 2000 m 2.35 2000 to 4000 m 2.10