High water reduction powder preparation for dry mortar

Abstract

PCE-type copolymers in powder form can be obtained by spry-drying and are easily re-dispersed in water. The fineness and the anti-caking properties of said PCE-type copolymers in powder form, as well as their water reduction potential and influence on slump life are improved. A production process of said PCE-type copolymers in powder form is by a spray-drying method, and PCE-type copolymers can be used for the improvement of mineral binder compositions and especially dry mortars.

Claims

1. A process for the production of a powdered copolymer P, said process comprising the steps of i) preparing an aqueous copolymer solution comprising 30-99 w %, based on the total weight of said aqueous solution, of a PCE-type copolymer comprising a) a molar parts of a structural unit S1 of formula I ##STR00009## b) b molar parts of a structural unit S2 of formula II ##STR00010## c) c molar parts of a structural unit S3 of formula III ##STR00011## and d) d molar parts of a structural unit S4 of formula IV ##STR00012## wherein each M independently from each other represents H+, an alkali metal ion, an alkaline earth metal ion, a di- or trivalent metal ion, an ammonium ion or an organic ammonium group, each R.sup.u independently from each other represents hydrogen or a methyl group, each R.sup.v independently from each other represents hydrogen or COOM, m is 0, 1, 2 or 3, p is 0 or 1, each R.sup.1 and each R.sup.2 independently from each other represents C.sub.1- to C.sub.20-alkyl, -cycloalkyl, -alkylaryl or for -[AO].sub.nR.sup.4, where A represents a C.sub.2- to C.sub.4-alkylene, R.sup.4 represents H, C.sub.1- to C.sub.20-alkyl, -cyclohexyl or -alkylaryl, and n is an integer in the range of from 2-350, each R.sup.3 independently of the others represents NH.sub.2, NR.sup.5R.sup.6, OR.sup.7NR.sup.8R.sup.9, wherein R.sup.5 and R.sup.6 independently from each other stand for C.sub.1- to C.sub.20-alkyl, -cycloalkyl alkylaryl or -aryl, or for a hydroxyalkyl- or acetoxyethyl-(CH.sub.3COOCH.sub.2CH.sub.2) or hydroxyisopropyl-(HOCH(CH.sub.3)CH.sub.2) or acetoxyisopropyl group (CH.sub.3COOCH(CH.sub.3)CH.sub.2); or R.sup.5 and R.sup.6 together form a ring of which the nitrogen is part, to form a morpholine or imidazoline ring, R.sup.7 is a C.sub.2-C.sub.4-alkylene group, each R.sup.8 and R.sup.9 independently from each other represent C.sub.1- to C.sub.20-alkyl, -cycloalkyl, -alkylaryl, -aryl or a hydroxyalkyl group, and a, b, c and d stand for the molar parts of the structural units S1, S2, S3 and S4, with a/b/c/d having values in the following ranges: (0.1-0.9)/(0.1-0.9)/(0-0.8)/(0-0.8), with the provision that a+b+c+d is equal to 1, ii) adding a base to adjust the pH of the aqueous copolymer solution to at least 10, iii) adding 0.01 to 5 w %, based on the weight of the aqueous copolymer solution, of at least one additive selected from anti-caking agents and/or anti-oxidants, iv) spray-drying the aqueous copolymer solution to obtain a powder, and v) optionally sieving.

2. A process according to claim 1 wherein the powdered copolymer P that is obtained after spray-drying the aqueous copolymer solution has a particle size distribution with a D90 of <250 m, a D10 of <60 m, and a D50 of between 70-130 m.

3. A process according to claim 1 wherein each R.sup.1 and R.sup.2 in the powdered copolymer P independently from each other represents -[AO].sub.nR.sup.4, each R.sup.4 independently from each other is selected from H or CH.sub.3, and n is an integer in the range of from 50-115.

4. A process according to claim 1 wherein the ratio of a/b in the powdered copolymer P is in the range of from 0.5/1 and 15/1.

5. A process according to claim 1, wherein the PCE-type copolymer in step i) is prepared by a radical polymerization process.

6. A process according to claim 1, wherein the base added in step ii) is chosen from LiOH, NaOH, KOH, Mg(OH).sub.2, Ca(OH).sub.2 or mixtures thereof.

7. A process according to claim 6, wherein the base added in step ii) is Ca(OH).sub.2 and the pH of the aqueous copolymer solution is between 10 and 14.

8. A process according to claim 1, wherein step iv) is performed at a spray-dry inlet temperature of not more than 150 C.

9. The process according to claim 1, wherein the base added in step ii) is added in an amount effective to adjust the pH of the aqueous copolymer solution to at least 11.

Description

BRIEF DESCRIPTION OF FIGURES

(1) FIG. 1 shows a particle size distribution of polymer powders P1 and P2 as prepared according to the following working examples.

(2) The following working examples illustrate the invention. The examples are not intended to limit the scope of the invention in any way.

Working Examples

(3) Preparation of Polymer Solution SP1

(4) 330 g of water, 330 g of methallyl polyethylene glycol (OH-terminated, M.sub.w=4000 g/mol), 42 g of acrylic acid, 102 g of a 16% aqueous solution of NaOH, 1.5 g of a 10% aqueous solution of Fe(II)SO.sub.4.Math.7 H.sub.2O, and 2 g sodium hypophosphite were added into a reaction vessel with a stirrer.

(5) Then 10 g of a 30% aqueous hydrogen peroxide solution and 4 g of a 5% aqueous rongalite solution were added dropwise at a temperature of 20 C.-35 C. over a period of 70 min with stirring.

(6) 120 minutes after the start of the dropwise addition, a clear viscous polymer solution was obtained.

(7) Preparation of Polymer Solution SP2

(8) Polymer SP2 was prepared as polymer SP1 above but with 366 g of methallyl polyethylene glycol (OH-terminated, M.sub.w=2400 g/mol).

(9) Preparation of Polymer Solution SP3

(10) 145 g of a 50 w % aqueous solution of partly neutralized polyacrylic acid (M.sub.w=4000 g/mol), and 7.5 g 50 w % sulfuric acid were placed in a glass reactor fitted with a thermometer, stirrer, a gas inlet tube, and a distillation assembly. The solution was heated to 70 C. and a mixture of 52 g of methoxy-terminated polyethylene glycol with M.sub.w=1000 g/mol and 300 g of methoxy-terminated polyethylene glycol with M.sub.w=3000 g/mol was added. The mixture was heated up under a steady stream of nitrogen and kept at 165 C. After stirring at this temperature for 6 h, the mixture was allowed to cool to room temperature. The pH of the resulting mixture was appr. 3.

(11) Preparation of Polymer Solution SP4

(12) Polymer SP4 was prepared as polymer SP3 above but with 347.5 g of methoxy-terminated polyethylene glycol with M.sub.w=5000 g/mol instead of the mixture of two different methoxy-terminated polyethylene glycols. The pH of the resulting mixture was appr. 3.

(13) Preparation of Polymer Powder P1

(14) 3g of Ca(OH).sub.2, 68 g of water, and 3 g of fumed silica (Aerosil 150 from Evonik) were added to 200 g of SP1. The resulting suspension had a pH of appr. 13. The resulting suspension was dried in a lab spray dryer of the type Mini Spray Dryer B-290 (Bchi AG, Switzerland). Spray drying was conducted by inserting the suspension with a nozzle at the head of the spray dryer. Compressed air flowing in the same direction as the sprayed material was used at a flow rate of 600 L/h and with a pressure of 0.5 MPa. The inlet temperature was 120 C. The dosage speed was adjusted so that the outlet temperature reached 65-70 C. The discharged powder was separated from the air stream by means of a cyclotrone.

(15) Preparation of Polymer Powder P2

(16) The polymer powder P2 was prepared as polymer powder P1 above but the amount of Ca(OH).sub.2 was adjusted to 60 mg. The pH of the resulting suspension was appr. 9.

(17) Preparation of Polymer Powder P3

(18) The polymer powder P3 was prepared as polymer powder P1 above but without the addition of Ca(OH).sub.2. The pH of the resulting suspension was appr. 5.

(19) Preparation of Polymer Powder P4

(20) The polymer powder P4 was prepared as polymer powder P1 above but SP2 was used instead of SP1.

(21) Preparation of Polymer Powder P5

(22) Polymer solution SP3 was poured into an open aluminum dish of appr. 100 mm diameter and 7 mm height and dried under ambient temperature and pressure. The resulting solid material was grinded to form a fine powder with a standard mortar and pestle.

(23) Preparation of Polymer Powder P6

(24) Polymer powder P6 was prepared as polymer powder P5 above but using polymer solution SP4 instead of SP3.

(25) The following table 1 shows an overview of the powders obtained. Polymer powders P1 and P4 are according to the present invention.

(26) TABLE-US-00001 TABLE 1 Polymer Solu- Particle size Performance tion [m] Spray Powder (SP) pH of SP D10 D50 D90 drying Powder P1 SP1 13 35 87 187 excellent no caking P2 SP1 9 44 105 202 excellent caking P3 (Ref) SP1 5 n.m. n.m. n.m. not possible P4 SP2 13 32 86 206 excellent no caking P5 (Ref) SP3 3 n.m. n.m. n.m. n.m. no caking P6 (Ref) SP4 3 n.m. n.m. n.m. n.m. no caking n.m.: not measured

(27) It can be seen from the above table 1 that spray-drying is possible from polymer solution SP1 only if the pH is 9 or higher. If the polymer solution has a pH of only 5, no powder could be obtained. It can further be seen that if the pH of the polymer solution is increased to 13, a finer powder P with non-caking properties can be obtained.

(28) Performance Testing in Cementitious Compositions (Examples M1-M6)

(29) The slump flow test, as a measure for fluidity of the cementitious mixture, was performed according to JC/T 985-2005 for examples M1-M3 and according to GB/T 50448-2008 for examples M4-M6. The slump flow test was performed on individual samples at defined points of time after mixing with mixing water.

(30) Compressive strength was determined according to standard GB/T17671-1999 using 4416 cm prisms after the time of curing at 23 C./50% r.h as indicated in tables 2-4 below.

(31) Linear shrinkage was measured according to JC/T 985-2005 after 28 d of curing at 23 C./50% r.h.

(32) For the preparation of examples M1-M3, 200 g of cement (CEM I 52.5), 340 g of calcium aluminate cement, 160 g of -hemihydrate, 400 g of limestone, 860 g of quartz sand (0.1-0.3 mm grain), and 4 g of the powder P1, P4, and P6 respectively were dry mixed in a Hobart mixer for 1 minute at 23 C. to give a dry mortar.

(33) Within 10 seconds mixing water was added to the dry mix to give a water/binder ratio of 0.22. Mixing was continued for 170 seconds.

(34) The following table 2 shows an overview of the results.

(35) TABLE-US-00002 TABLE 2 Compressive Powder Slump flow [mm] strength [MPa] Shrinkage Example used 0 min 20 min [%] after 1 d [%] M1 P1 143 120 16 9.0 0.068 M2 P4 129 112 13 7.4 0.079 M3 (Ref) P6 155 123 21 7.1 0.090

(36) These results show that powders P1 and P4, which are according to the present invention, have good liquefying properties and especially low loss of slump flow over time. Powders according to the present invention also lead to increased compressive strength after 1 d as well as to low shrinkage.

(37) For the preparation of examples M4-M6, 750 g of cement (CEM I 52.5), 120 g of blast furnace slag, 40 g of silica fume, 340 g of fine quartz sand, 120 g of fine river sand (grain size 0.3-0.6 mm), 560 g of coarse river sand (grain size 0.6-2.3 mm), and 2.8 g of the powder P1, P4, and P5 respectively were dry mixed in a Hobart mixer for 1 minute at 23 C. to give a dry mortar.

(38) Within 10 seconds mixing water was added to the dry mix to give a water/binder ratio of 0.15. Mixing was continued for 170 seconds.

(39) The following table 3 shows an overview of the results.

(40) TABLE-US-00003 TABLE 3 Slump flow [mm] Compressive Powder Delta strength [MPa] Examples used 0 min 20 min [%] after 3 d M4 P1 360 350 3 65.5 M5 P4 335 338 +1 60.3 M6 (Ref) P5 350 323 8 58.3

(41) These results show that powders P1 and P4, which are according to the present invention, have good liquefying properties and especially low loss of slump flow over time. Powders according to the present invention also lead to increased compressive strength after 3 d.