Process for producing high-swellability polymer composites

Abstract

The invention relates to a process for producing polymer composites suitable for absorbing and storing aqueous liquids, to the polymer composites obtainable by this process, and to the use of the polymer composites. The process comprises free-radical polymerization of a monomer composition M comprising 50 to 100% by weight, based on the total amount of monomers A and B, of at least one monomer A having one ethylenic double bond and at least one neutralizable acid group, 0 to 50% by weight of optionally one or more comonomers B which are different than the monomers A and have one ethylenic double bond, and 1 to 10% by weight, based on the total amount of monomers A and B, of at least one crosslinker C.

Claims

1. A process for producing polymer composites suitable for absorbing and storing aqueous liquids, comprising: a free-radical polymerization of a monomer composition M which comprises a) 50 to 100% by weight, based on the total amount of monomers A and B, of at least one monomer A having one ethylenic double bond and at least one neutralizable acid group, b) 0 to 50% by weight of optionally one or more comonomers B which are different than the monomers A and have one ethylenic double bond, and c) 0 to 10% by weight, based on the total amount of monomers A and B, of at least one crosslinker C, in an aqueous suspension of a water-insoluble particulate substance S comprising cellulose or lignocellulose, the weight ratio of the monomer composition M to the substance S being in the range from 9:1 to 1:9; wherein the monomers A used for polymerization are present in the aqueous suspension in anionic form to an extent of at least 10 mol %; and wherein the aqueous suspension contains urea during the polymerization.

2. The process of claim 1, wherein the monomer A used for polymerization is present in the aqueous suspension in anionic form to an extent of 30 to 80 mol %.

3. The process of claim 1 wherein the amount of urea is from 5 to 50% by weight, based on the total amount of monomers A and B.

4. The process of claim 1, wherein the particulate substance S comprises a lignocellulose material.

5. The process of claim 4, wherein the substance S is selected to an extent of at least 50% by weight, based on the total amount of substance S, from hemp dust, flax dust, sawdust, bran, ground straw, ground olive stones, ground tree bark, reject material from pulp production, sugar beet peel, sugar cane waste, rice husks, cereal husks, ground hemp fibers, ground flax fibers, ground Chinese silvergrass fibers, ground coconut fibers, ground kenaf fibers or ground wood fibers, and wastes from biogas production.

6. The process of claim 1, wherein the weight ratio of particulate substance S and of the total amount of monomers in the monomer composition M is from 1:9 to 9:1.

7. The process of claim 1, wherein at least 90% by weight of the substance S has maximum particle dimensions below 1000 μm, determined by sieve analysis.

8. The process of claim 1, wherein the monomers A are selected from monoethylenically unsaturated C.sub.3-C.sub.8-monocarboxylic acids, mixtures thereof and mixtures of at least one monoethylenically unsaturated C.sub.3-C.sub.8-monocarboxylic acid with one or more monoethylenically unsaturated C.sub.4-C.sub.8-dicarboxylic acids.

9. The process of claim 1, wherein the monomers A account for at least 90% by weight, based on the total amount of monomers A and B.

10. The process of claim 1, wherein the monomer composition comprises at least one crosslinker C having at least two ethylenically unsaturated groups.

11. The process of claim 1, wherein the aqueous suspension comprises at least two different polymerization initiators.

12. The process of claim 11, wherein the aqueous suspension comprises a first polymerization initiator which is selected from the group consisting of azo-initiators and redox-initiators and a second initiator, which is selected from the salts of peroxodisulfuric acid.

13. The process of claim 1, wherein the polymer after the polymerization is subjected to a drying step.

14. The process of claim 13, wherein the drying step comprises (i) a first step, where the polymer obtained after the polymerization is subjected to drying at reduced pressure of less than 100 mbar and temperatures below 100° C. and (ii) a subsequent second step where the polymer is dried at temperatures above 100° C.

Description

II. PREPARATION EXAMPLES

(1) Elucidation of Trade Names

(2) Lutensol® AT 80: ethoxylated C.sub.16-C.sub.18 fatty alcohol with about 80 ethylene oxide units (BASF SE),

(3) Laromer® PO 9044: Triacrylate of ethoxylated glycerol having with about 3 ethylene oxide units (BASF SE)

(4) ARBOCEL® BC 1000: ground cellulose having a maximum fiber length of 0.7 cm (Rettenmeier Holding AG),

(5) Further feedstocks used:

(6) Flax dust: conventional flax dust having the following grain distribution: 2% by weight >600 μm; 73% by weight 50-600 μm; 25% by weight <50 μm.

(7) Solution A: aqueous solution of the following composition 1000 μM Ca, 2000 μM NO.sub.3, 200 μM NH.sub.4, 651 μM SO.sub.4, 850 μM K, 325 μM Mg, 300 μM Cl, 100 μM PO.sub.4, 8 μM B, 1 μM Mn, 0.2 μM Cu, 0.2 μM Zn and 0.2 μM Mo. Solution A was used to determine the free swellability or absorption capacity of the polymers produced by means of the above-specified method.

Example 1

(8) The reaction which follows was performed under protective gas atmosphere and all the starting materials mentioned were purged in a nitrogen stream before addition:

(9) 28.4 g of acrylic acid, 0.43 g of methylenebisacrylamide, 104.42 g of 37.5% sodium acrylate solution and 213.83 g of water were blended in a 1 L reaction vessel. This was followed by the addition of 2.0 g of a 20% solution of Lutensol® AT 80 in 1.6 g of acrylic acid, and also 30 g of flax dust and 10 g of ARBOCEL® BC 1000. All constituents were mixed vigorously to give a homogeneous mass. After the addition of 2×2 g of a 10% aqueous ammonium peroxodisulfate solution in portions and repeated stirring, the reaction mixture was heated at external temperature of 95° C. while stirring. After 25 min, the reaction mixture had attained the maximum temperature of 72° C. The soft elastic gel obtained was dried at 155° C. for 90 min and then mechanically comminuted. The pale brown, free-flowing solid thus obtained showed, together with deionized water or solution A at room temperature, the following free swellability or absorption capacity per g of solids as a function of time:

(10) TABLE-US-00001 2 h 24 h 72 h 168 h Solution A 76.4 76.8 73.5 74.2 Water 132.8 151.2 163.7 155.0

(11) The solid produced comprised 39987 ppm of residual acrylic acid and 15.2% soluble components containing carboxyl groups.

Example 2

(12) The process according to example 2 was repeated, except that the addition of the 10% aqueous ammonium peroxodisulfate solution was followed by additional addition of 1.0 g of a 0.245% aqueous hydrogen peroxide solution and 1.0 g of a 5.67% aqueous ascorbic acid solution while stirring. Without external heat supply, the reaction mixture attained the maximum temperature of 30.4° C. after 38 min.

(13) The pale brown, free-flowing solid thus obtained showed, together with deionized water or solution A at room temperature, the following free swellability or absorption capacity per g of solids as a function of time:

(14) TABLE-US-00002 2 h 24 h 72 h 168 h Solution A 73.6 71.7 62.9 55.5 Water 92.6 99.2 96.4 102.7

(15) The solid produced comprised 1755 ppm of residual acrylic acid and 1.15% soluble components containing carboxyl groups.

Example 3

(16) The process according to example 2 was repeated, but the material obtained after the drying was thermally aftertreated at 155° C. for 1 h.

(17) The solid thus produced comprised 2328 ppm of residual acrylic acid.

Example 4

(18) The process according to example 1 was repeated, except that 23.4 g of acrylic acid, 0.36 g of methylenebisacrylamide, 87.5 g of 37.5% sodium acrylate solution, 222 g of water, 37.5 g of flax dust, 12.5 g of ARBOCEL® BC 1000 and 1.0 g of the 10% aqueous ammonium peroxodisulfate solution were used. After 30 min, the reaction mixture attained a temperature of 30.0° C. This was followed by heating at external temperature of 95° C. with stirring for 1 h, in the course of which the reaction mixture attained the maximum temperature of 73.6° C. after 53 min.

(19) The pale brown, free-flowing solid thus obtained showed, together with deionized water or solution A at room temperature, the following free swellability or absorption capacity per g of solids as a function of time:

(20) TABLE-US-00003 2 h 24 h 72 h 168 h Solution A 37.5 40.9 31.2 27.7 Water 66.2 80.1 81.1 83.6

(21) The solid produced comprised 60 016 ppm of residual acrylic acid and 15.8% soluble components containing carboxyl groups.

Example 5

(22) The process according to example 4 was repeated, except that the soft elastic gel obtained was dried at 40° C. under reduced pressure for 48 h.

(23) The pale brown, free-flowing solid thus obtained showed, together with deionized water or solution A at room temperature, the following free swellability or absorption capacity per g of solids as a function of time:

(24) TABLE-US-00004 2 h 24 h 72 h 168 h Solution A 67.3 63.2 41.5 35.7 Water 127.6 213.3 227.6 243.8

(25) The solid produced comprised 96 821 ppm of residual acrylic acid and 23.2% soluble components containing carboxyl groups.

Example 6

(26) The reaction which follows was performed under protective gas atmosphere and all the starting materials mentioned were purged in a nitrogen stream before addition:

(27) A kneader was charged with 897 g of flax dust and 299 g of ARBOCEL® BC 1000. Subsequently, the kneader was put into operation, and a solution of 897 g of acrylic acid and 12.86 g of methylenebisacrylamide, 3147.46 g of 37.2% sodium acrylate solution and 930.15 g of deionized water were added and blended together stepwise. Thereafter, 119.6 g of a 10% aqueous solution of Lutensol® AT 80 were added and kneaded in. After a solution of 3.15 g of sodium peroxodisulfate, 0.985 g of 30% hydrogen peroxide solution, 10 g of water and 0.3594 g of ascorbic acid in 10 g of water had been added and the temperature of the reaction mixture began to rise, it was heated to 80° C. and this temperature was maintained for 1 h.

(28) The soft elastic gel obtained was dried at 85° C. for 1 h and at 150° C. for 1 h and then comminuted.

(29) The pale brown, free-flowing solid thus obtained showed, together with deionized water or solution A at room temperature, the following free swellability or absorption capacity per g of solids as a function of time:

(30) TABLE-US-00005 2 h 24 h 168 h Solution A 51.1 26.4 15.7 Water 70.0 72.4 78.4

(31) The solid produced comprised 52 519 ppm of residual acrylic acid and 9.7% soluble components containing carboxyl groups.

Example 7

(32) The process according to example 4 was repeated, except that a solution of 64.29 g of urea in 1000 g of deionized water per kg of solids was then added and the mixture was then kneaded for 1 h. The soft elastic gel obtained was dried at 150° C. for 1 h and then comminuted.

(33) The solid thus produced comprised 15 149 ppm of residual acrylic acid and 11.3% soluble components containing carboxyl groups. The water absorption capacity after 7 days was 59.5 g per g of solids and the absorption capacity of solution A was 29.6 g per g of solids.

Example 8

(34) The process according to example 4 was repeated, except that 37.5 g of deionized water and a solution of 2.4 g of urea in 1000 g of deionized water per 35.9 g of solids were then added and the mixture was then kneaded for 30 min. The soft elastic gel obtained was dried at 60° C. under reduced pressure for 24 h and then comminuted. The solid thus produced comprised 36 530 ppm of residual acrylic acid.

Example 9

(35) The process according to example 6 was repeated, except that the soft elastic gel obtained was dried at 150° C. for 1 h and then comminuted. The solid thus produced comprised 11 411 ppm of residual acrylic acid. The water absorption capacity after 7 days was 60.3 g per g of solids and the absorption capacity of solution A was 35.4 g per g of solids.

(36) The following example 10 was performed in a Drais 1200 ploughshare mixer with 8 ploughshares having a cylindrical geometry and an internal volume of 1000 l.

Example 10

(37) 32.6 kg of urea, 0.77 kg Lutensol® AT 80 and 97.8 kg of distilled water were mixed together. The mixture is called solution 1.

(38) 0.836 kg of N,N′-methylenebis(acrylamide) and 58.23 kg of acrylic acid were mixed together and this mixture is then called solution 2.

(39) The mixer was first filled 116.4 kg of flax dust, solution 1, 255.0 kg of a potassium acrylate solution (35 weight % in water) and finally with the solution 2. The mixer was set to maximum speed (90 rpm) and the mixture stirred for 30 minutes. Afterwards a mixture of 1.17 kg sodium persulfate with 10.5 kg of distilled water and 0.35 kg 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride with 23.76 kg distilled water was filled into the mixer. The oil temperature of the mixer was set to 120° C. and the reaction mixture was heated to 60° C. At 60° C. the mixer was stopped and held for three hours. After three hours the mixer was set again to maximum speed and the obtained polymer gel was dried under vacuum (<100 mbar) until reaching 20% residual moisture.

(40) Drying was then continued under normal pressure conditions at a temperature of 110 to 120° C. using a stream of dry nitrogen of 2 m.sup.3/h. After reaching 6% residual moisture the drying was continued for one hour at vacuum (<100 mbar) at a temperature of about 100 to 110° C.

(41) 258 kg final material was obtained as a pale brown powder with a residual acrylic acid content of 610 ppm and 15.3% extractable content. The obtained material showed the following free swellability or absorption capacity per g of solids as a function of time and the following CRC.

(42) TABLE-US-00006 Free Swellability [g/g] CRC 2 h 24 h 48 h 168 h [g/g] Solution A 59.4 39.3 25.2 16.5 5.9 Water 79.0 87.9 90.9 97.5 43.6

Example 11

(43) An IKA laboratory kneader was heated to 80° C. and 38.8 g of flax dust were filled inside during maximum mixing speed. During this time the reactor was flushed for 30 minutes with 200 l/h CO.sub.2.

(44) A monomer solution containing 16.9 g of acrylic acid, 2.79 g of 10% solution of N,N′-methylenebis(acrylamide) in acrylic acid, 85.1 g of a 35% aqueous potassium acrylate solution, 2.56 g of a 10% aqueous solution of Lutensol AT 80, 43.3 g of a 25% aqueous solution of urea and 7.5 g distilled water was prepared by mixing and the solution was flushed for 30 minutes with 200 l/h nitrogen.

(45) The monomer solution was put into the kneader with the flax dust and mixed at 80° C. to obtain a homogenous mixture. Then, 1.94 g of a 20% aqueous sodium persulfate solution and 1.17 g of a 10% aqueous solution of 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride were added to the reactor. After 60 minutes of polymerization at 80° C., the reactor was cooled down to 40° C. The obtained polymer gel was cut into small pieces and dried for 60 minutes at 150° C.

(46) 80 g final material was obtained as a pale brown powder with a residual acrylic acid content of 8100 ppm and 14.1% extractable content.

Example 12

(47) An IKA laboratory kneader was heated to 80° C. and 38.8 g of flax dust were filled inside during maximum mixing speed. During this time the reactor was flushed for 30 minutes with 200 l/h CO.sub.2.

(48) A monomer solution containing: 16.9 g of acrylic acid, 2.79 g of 10% solution of N,N′-methylenebis(acrylamide) in acrylic acid, 85.1 g of a 35% aqueous solution of potassium acrylate, 2.56 g of a 10% aqueous solution of Lutensol AT 80, 43.3 g of a 25% aqueous solution of urea, 5.8 g distilled water was prepared by mixing and the solution was flushed for 30 minutes with 200 l/h nitrogen.

(49) The monomer solution was put into the kneader with the flax dust and mixed at 80° C. to obtain a homogenous mixture. Then, 1.94 g of a 20% aqueous solution of sodium persulfate, 1.17 g of a 2% aqueous solution of hydrogen peroxide, 1.56 g of a 2% aqueous solution ascorbic acid were added to the reactor. After 90 minutes of polymerization at 80° C., the reactor was cooled down to 40° C. The obtained polymer gel was cut into small pieces and dried for 60 minutes at 150° C.

(50) 82 g final material was obtained as a pale brown powder with a residual acrylic acid content of 12000 ppm and 17.5% extractable content. The obtained material showed the following free swellability or absorption capacity per g of solids as a function of time and the following CRC.

(51) TABLE-US-00007 Free Swellability [g/g] CRC 2 h 24 h 48 h 168 h [g/g] Solution A 53.1 19.1 9.6 7.3 2.3 Water 77.3 81.4 80.7 84.6 37.1

Example 13

(52) An IKA laboratory kneader was heated to 80° C. and 38.8 g of flax dust were filled inside during maximum mixing speed. During this time the reactor was flushed for 30 minutes with 200 l/h CO.sub.2.

(53) A monomer solution containing: 16.6 g of acrylic acid, 3.11 g of 10% solution of Laromer® PO 9044 in acrylic acid, 85.0 g of a 35% aqueous solution of potassium acrylate, 2.56 g of a 10% aqueous solution of Lutensol AT 80, 43.3 g of a 25% aqueous solution of urea, 5.9 g distilled water was prepared by mixing and the solution was flushed for 30 minutes with 200 l/h nitrogen.

(54) The monomer solution was put into the kneader with the flax dust and mixed at 80° C. to obtain a homogenous mixture. Then, 1.94 g of a 20% aqueous solution of sodium persulfate, 1.17 g of a 2% aqueous solution of hydrogen peroxide, 1.56 g of a 2% aqueous solution of ascorbic acid was added to the reactor. After 90 minutes of polymerization at 80° C., the reactor was cooled down to 40° C. The obtained polymer gel was cut into small pieces and dried for 60 minutes at 150° C.

(55) 78 g final material was obtained as a pale brown powder with a residual acrylic acid content of 7100 ppm and 20.2% extractable content. The obtained material showed the following free swellability or absorption capacity per g of solids as a function of time and the following CRC.

(56) TABLE-US-00008 Free Swellability [g/g] CRC 2 h 24 h 48 h 168 h [g/g] Solution A 67.0 24.0 20.1 14.8 4.4 Water 116.5 121.8 121.1 127.6 67.1

Example 14

(57) An IKA laboratory kneader was heated to 80° C. and 38.9 g of flax dust were filled inside during maximum mixing speed. During this time the reactor was flushed for 30 minutes with 200 l/h CO.sub.2.

(58) A monomer solution containing: 16.7 g of acrylic acid, 3.11 g of 10% solution of Laromer® PO 9044 in acrylic acid, 85.3 g of a 35% aqueous potassium acrylate solution, 43.4 g of a 25% aqueous solution of Urea, 7.9 g distilled water was prepared by mixing and the solution was flushed for 30 minutes with 200 l/h nitrogen.

(59) The monomer solution was put into the kneader with the flax dust and mixed at 80° C. to obtain a homogenous mixture. Then, 1.95 g of a 20% aqueous solution of sodium persulfate, 1.17 g of a 2% aqueous solution of hydrogen peroxide, 1.56 g of a 2% aqueous solution of ascorbic acid was added to the reactor. After 90 minutes of polymerization at 80° C., the reactor was cooled down to 40° C. The obtained polymer gel was cut into small pieces and dried for 60 minutes at 150° C.

(60) 75 g final material was obtained as a pale brown powder with a residual acrylic acid content of 7300 ppm and 19.5% extractable content. The obtained material showed the following free swellability or absorption capacity per g of solids as a function of time and the following CRC.

(61) TABLE-US-00009 Free Swellability [g/g] CRC 2 h 24 h 48 h 168 h [g/g] Solution A 61.4 19.2 14.8 12.4 3.9 Water 104.5 112.4 111.2 113.7 55.4

III. STUDY OF GROWTH-PROMOTING ACTION

(62) With the aid of the test described hereinafter, the effects of the inventive polymers on the shoot and root growth of corn plants were studied.

(63) The polymer to be studied (0.01-10 g/kg) was added to a water-moistened plant substrate and mixed in until homogeneously distributed. To determine the blank value, correspondingly moistened quartz sand was used. Then five precultivated corn seedlings were planted into each pretreated substrate and cultivated at ambient temperature for about 3 weeks, in the course of which the plants were watered with a compound fertilizer solution once per week. The plants were removed from the pots along with the roots, the roots were cleaned by washing and the plants were assessed for appearance and size. Then the shoot and root were separated from each other in each case and both parts were weighed to determine their fresh weight. The shoots and roots were subsequently dried to constant weight and their dry weights were determined. The final weights for the shoots and roots of 5 identically treated plants in each case were used to calculate the mean values for fresh and dry weights. In this test, for the polymer composites of examples 1, 3, 5, 6, 7, 10 and to 11, an improvement in the shoot and root growth was found.

(64) TABLE-US-00010 Mass increase of fresh weight [%] compared to Mass increase of dry weight [%] untreated sample compared to untreated sample Example Shoot Root Shoot Root 1 32.7 51.6 32.1 53.8 2 24.4 65.4 31.2 48.4 3 14.3 46.9 14.7 32.6 4 36.6 53.9 67.0 21.5 5 11.6 31.8 — 72.0 8 42.8 35.4 45.7 39.7 9 69.3 45.9 67.7 65.9