Method for treating gypsum

Abstract

The present invention relates to a method for producing a gypsum-containing foamed prefabricated building material and to a gypsum-containing foamed prefabricated building material.

Claims

1. A method for producing a gypsum-containing foamed prefabricated building material core, comprising: (a) preparing a mixture of gypsum hemihydrate or anhydrite with at least one of a ketene dimer of formula (I) ##STR00009## or of formula (II) ##STR00010## wherein R.sup.1 and R.sup.2 are identical or different hydrocarbon radicals comprising 10 to 24 carbon atoms, (b) homogenizing the aqueous ketene gypsum hemihydrate or anhydrite mixture to obtain a uniform distribution of the ketene in the gypsum hemihydrate or anhydrite, (c) adding an aqueous foam having a density of from 50 to 300 g/l to the homogenized aqueous mixture of the ketene and gypsum hemihydrate or anhydrite to obtain a gypsum composition; and (d) forming, optionally curing and drying the gypsum composition to obtain the foamed prefabricated building material gypsum core comprising the ketene dimer of formula (I) or Formula (II), wherein a content of surfactant in the aqueous foam is from 0.01 to 2 g per kg of gypsum hemihydrate or anhydrite in the homogenized aqueous mixture of the ketene and gypsum hemihydrate or anhydrite, and a density of the foamed prefabricated building material gypsum core obtained is from 0.4 to 1.1 kg/dm.sup.3.

2. The method according to claim 1, wherein the ketene dimer is employed in the form of an aqueous dispersion.

3. The method according to claim 2, wherein the gypsum hemihydrate or anhydrite is used in solid form or in the form of an aqueous suspension.

4. The method according to claim 2, wherein the aqueous ketene dispersion is stabilized by a protective colloid.

5. The method according to claim 4, wherein the protective colloid is a starch, a cellulose or a cellulose modified by ammonium structural units.

6. The method according to claim 2, wherein the aqueous ketene dispersion comprises 1 to 60 wt % of ketene dimer, based on the total weight of the dispersion.

7. The method according to claim 2, wherein the disperse phase of the aqueous ketene dispersion has an average diameter of less than 10 m.

8. The method according to claim 1, wherein 0.02 to 8.0 wt % of the ketene dimer, based on the mass of the gypsum hemihydrate or anhydrite, is used.

9. The method according to claim 1, wherein the gypsum hemihydrate or anhydrite is selected from the group consisting of -hemihydrate, /-hemihydrate, -hemihydrate, natural anhydrite, synthetic anhydrite and anhydrite obtained from flue gas desulfurization, and mixtures thereof.

10. The method according to claim 1, wherein the aqueous foam comprises a fatty alkylsulfate or fatty alkylethersulfate.

Description

EXAMPLE 1

(1) A fatty alkyl sulfate-based foam was produced as follows:

(2) A 0.3% strength surfactant solution (based on lauryl sulfate) was converted into foam in a foam generator by rotation of a stator-rotor system and with addition of compressed air. The foam density achieved was 75 g/L.

(3) Test specimens were prepared using the following dispersions of the hydrophobizing agents:

(4) Sasol Hydrowax 170 (comparative dispersion):

(5) Hydrowax 170 from Sasol is a special dispersion available commercially (solids content approximately 37%) for hydrophobization of gypsum plasterboard panels, and comprises mutually aligned waxes (including paraffin wax) and emulsifiers, and is silicone-free.

(6) AKD Dispersion I (According to the Invention):

(7) Aqueous dispersion of a C.sub.16/C.sub.18 (50:50) alkylketene dimer dispersed with 3 wt % of a cationically modified starch (in formula I and II: R.sup.1 and R.sup.2 are C.sub.14 and C.sub.16 alkyl, respectively). The average particle diameter is about 1000 nm. The total solids content is about 24%.

(8) AKD dispersion II (according to the invention):

(9) Aqueous dispersion of a C.sub.16/C.sub.18 (20:80) alkylketene dimer dispersed with 3 wt % of a cationically modified starch (in formula I and II: R.sup.1 and R.sup.2 are C.sub.14 and C.sub.16 alkyl, respectively). The average particle diameter is about 1000 nm. The total solids content is about 18%.

(10) The dispersion of the hydrophobizing agent was diluted with water in a vessel and homogenized to form a liquid component, to give the amounts of hydrophobizing agent indicated in table 1 below in 480 g of waterin other words, the water present in the hydrophobizing agent dispersion was included in the calculation. -Hemihydrate (600 g) obtained in flue gas desulfurization was subjected to preliminary homogenization with 0.13 g of finely ground calcium sulfate dihydrate (accelerator for setting a solidification time of about 2.5 minutes) in a mixer to give a dry component. The dry component was sprinkled into the liquid component. After standing for 15 seconds, the resulting gypsum slurry was stirred using a Hobart mixer at setting II (285 revolutions per minute) for 30 seconds, and during this stirring time the fatty alkyl sulfate-based foam (20.4 g with a density of 75 g/L) was admixed. The density of the resulting gypsum slurry was 1050+/10 kg/m.sup.3. Filling of a cylindrical plastic beaker with a height of 10 cm and a diameter of 8 cm with a portion of the gypsum slurry was followed by curing and drying to form a specimen having a height of about 2 cm. After the specimen has hardened (storage at 20 C. for 15 minutes) it is removed from the plastic mold and dried at 100 C. for 60 minutes and then at around 40 C. to constant mass. The mass of the specimen (M.sub.D) was ascertained by weighing. For the measurement of the water adsorption, the specimen was stored in a water bath at a set temperature of 20 C. The fill level of the water bath was set such that the highest point on the specimen was covered by 3 cm of water. After water bath storage for two hours, the specimen was removed from the water bath, and excess water was removed using a cloth. The mass of the specimen (M.sub.W) was ascertained again by weighing, and the water uptake W in % was determined in accordance with the following formula:
W=100%((M.sub.WM.sub.D)/M.sub.D)

(11) TABLE-US-00001 TABLE 1 Water uptake of specimens following addition of different hydrophobizing agents and different amounts of hydrophobizing agent according to example 1. Hydrophobizing agent: (Metering in mass % Sasol AKD AKD based on -hemihydrate) Hydrowax 170 dispersion I dispersion II 0 54.2% 54.2% 54.2% 1.0 19.1% 8.4% 5.0% 1.2 10.1% 3.8% 2.9% 1.5 4.9% 0.5% 0.4% 2.0 0.5% 0.3% 0.3%

(12) From table 1 it is evident that for a water uptake of less than 5 wt % it is necessary to add about 1.5 wt % of the wax emulsion (Sasol Hydrowax 170), whereas for the two inventive examples (AD dispersion I and II) this figure is already achieved with an addition of less than 1.2 wt %.

EXAMPLE 2

(13) Comparative Experiment 2.1:

(14) 3.0 g of the plasticizer Melflux PCE 1493 L from BASF (40% strength polycarboxylate ether solution for reducing the water/gypsum ratio), 600 g of gypsum (-hemihydrate obtained from flue gas desulfurization), and 1.3 g of accelerator (finely ground calcium sulfate dihydrate for setting a solidification time of about 2.5 minutes) were introduced into 367.5 g of water and the mixture was left at rest for 15 seconds. The Hobart mixer was then used on setting II (285 revolutions per minute) for 30 seconds, and during this stirring time the fatty alkyl sulfate-based foam (38.6 g with a density of 75 g/L) was admixed, until the density of the resulting gypsum slurry was 955+/10 kg/m.sup.3.

(15) Comparative Experiment 2.2:

(16) A diluted wax emulsion was prepared by weighing out 32.4 g of the 37% wax emulsion (Sasol Hydrowax 170) into 347 g of water. This corresponds to 2 mass % of wax solid, based on gypsum. Then 3.0 g of Melflux PCE 1493 L (from BASF), 600 g of gypsum (-hemihydrate obtained from flue gas desulfurization), and 1.3 g of accelerator (finely ground calcium sulfate dihydrate for setting a solidification time of about 2.5 minutes) were introduced into the diluted wax emulsion, and the mixture was left at rest for 15 seconds. The Hobart mixer was then used on setting II (285 revolutions per minute) for 30 seconds, and during this stirring time the fatty alkyl sulfate-based foam (38.6 g with a density of 75 g/L) was admixed, until the resulting gypsum slurry had a density of 955+/10 kg/m.sup.3.

(17) Experiment 2.3:

(18) A diluted AKD dispersion was prepared by weighing out 33.3 g of the 18% AKD dispersion I into 340.1 g of water. This corresponds to 1 mass % of AKD solid, based on gypsum. Then 3.0 g of Melflux PCE 1493 L (from BASF), 600 g of gypsum (-hemihydrate obtained from flue gas desulfurization), and 1.3 g of accelerator (finely ground calcium sulfate dihydrate for setting a solidification time of about 2.5 minutes) were introduced into the aqueous AKD dipersion, and the mixture was left at rest for 15 seconds. The Hobart mixer was then used on setting II (285 revolutions per minute) for 30 seconds, and during this stirring time the fatty alkyl sulfate-based foam (38.6 g with a density of 75 g/L) was admixed, until the resulting gypsum slurry had a density of 955+/10 kg/m.sup.3. The production of specimens from the plaster slurry, the investigation of the water absorption, and the calculation of the water uptake took place, in the experiments and comparative experiments of example 2, in the manner described in example 1.

(19) The water uptake of specimens of comparative experiment 2.1 was 34.2%. The water uptake of specimens of comparative experiment 2.2 was 27.8%. The water uptake of specimens of inventive experiment 2.3 was 9.6%.

EXAMPLE 3

(20) A fatty alkyl ether sulfate-based foam was prepared as described in example 1.

(21) Comparative Experiment 3.1:

(22) 3.0 g of Melflux PCE 1493 L (from BASF), 600 g of gypsum (-hemihydrate obtained from flue gas desulfurization), and 1.0 g of accelerator (finely ground calcium sulfate dihydrate for setting a solidification time of about 2.5 minutes) were introduced into 354.7 g of water and the mixture was left at rest for 15 seconds. The Hobart mixer was then used on setting II (285 revolutions per minute) for 30 seconds, and during this stirring time the fatty alkyl ether sulfate-based foam (36.5 g with a density of 75 g/L) was admixed, until the density of the resulting gypsum slurry was 970+/20 kg/m.sup.3.

(23) Experiment 3.2:

(24) A diluted AKD dispersion II was prepared by weighing out 24.0 g of the 25% AKD dispersion II into 336.7 g of water. Then 3.0 g of Melflux PCE 1493 L (from BASF), 600 g of gypsum (-hemihydrate obtained from flue gas desulfurization), and 0.9 g of accelerator (finely ground calcium sulfate dihydrate for setting a solidification time of about 2.5 minutes) were introduced into the diluted AKD dispersion II, and the mixture was left at rest for 15 seconds. The Hobart mixer was then used on setting II (285 revolutions per minute) for 30 seconds, and during this stirring time the fatty alkyl ether sulfate-based foam (36.5 g with a density of 75 g/L) was admixed, until the resulting gypsum slurry had a density of 970+/20 kg/m.sup.3.

(25) In comparative experiment 3.1 and in experiment 3.2, one minute after the beginning of stirring in the Hobart mixer, determinations were made of the slump flow (table 2), and 4416 cm.sup.3 prisms were produced for strength investigation (in accordance with DIN 196-1). The prisms were first stored in open steel molds for 24 hours at 20 C./65% relative humidity. After 24 hours they were demolded, dried to constant mass as indicated in example 1, and then subjected to the flexural tensile and pressure tests. The solidification time was measured using the knife cut method (in accordance with DIN EN 13279-2).

(26) TABLE-US-00002 TABLE 2 Slump flows, solidification times and strength values of foamed prisms of example 3. Comparative experiment Experiment Parameter 3.1 3.2 Slump flow [cm] 18.2 18.5 Solidification time [min:s] 2:35 2:40 Flexural tensile strength [N/mm.sup.2] 1.75 2.03 Compressive strength [N/mm.sup.2] 3.74 4.23

(27) Example 3 shows that with densities, slump flows, and solidification times that are set the same, the strength values can also be increased by addition of AKD dispersion. At a level of addition of one percent AKD dispersion, not only the flexural tensile strength but also the compressive strength rose by more than 10% in comparison to the reference mixture.