A Wet Accelerator, A Method of Preparing A Wet Accelerator and A Method of Producing A Gypsum Product

Abstract

According to the present invention, there is provided a wet accelerator for use in the manufacture of a gypsum product, said wet accelerator comprising water, particles of calcium sulphate dihydrate and a stabiliser. Additionally, a method of preparing a wet accelerator and a method of producing a gypsum product are described.

Claims

1. A wet accelerator for use in the manufacture of a gypsum product, said wet accelerator comprising water, particles of calcium sulphate dihydrate (CaSO.sub.4.2H.sub.2O), and a stabiliser, wherein said stabiliser comprises a soluble polymer of the formula; ##STR00003## wherein R.sub.1 is selected from the group consisting of H and a cation; and wherein m is any positive integer.

2. The wet accelerator of claim 1, wherein R.sub.1 is H.

3. The wet accelerator of claim 2, wherein the first pK.sub.a of said stabiliser is larger than or equal to 4.

4. The wet accelerator of claim 1, wherein said stabiliser has an average molecular weight of between 500 and 10,000 g/mol inclusive.

5. The wet accelerator of claim 1, wherein the stabiliser is present in an amount of at least 0.01 wt. % relative to the dry weight of the particles of calcium sulphate dihydrate.

6. The wet accelerator of claim 1, wherein particles of calcium sulphate dihydrate form at least 10 wt. % and at most 50 wt. % of the wet accelerator.

7. The wet accelerator of claim 1, wherein at least 50% of the particles of calcium sulphate dihydrate have a diameter of less than 5 μm.

8. The wet accelerator of claim 1, wherein said particles of calcium sulphate dihydrate have a surface area of between 5 and 30 m.sup.2/g.

9. A method of producing a gypsum product comprising: providing a slurry comprising water and inorganic material, said inorganic material comprising at least one of calcium sulphate hemihydrate and calcium sulphate anhydrite, providing the wet accelerator of claim 1, introducing said wet accelerator into said slurry in an amount of between 0.1 and 4 wt. % of said inorganic material relative to the total dry weight of the constituents of the slurry and of the accelerator, and allowing said slurry to set.

10. A method of preparing a wet accelerator comprising: providing particles of inorganic material with the composition CaSO.sub.4(X)H.sub.2O, where X is in the range 0≤X≤2, adding water, and adding a stabiliser, wet milling said particles of inorganic material, wherein said stabiliser comprises a soluble polymer of the formula: ##STR00004## wherein R.sub.1 is selected from the group consisting of H and a cation; and wherein m is any positive integer.

11. The method of claim 10, wherein the step of adding said stabiliser occurs after the step of adding said water, and said wet milling step begins after the addition of said water and before the addition of said stabiliser.

12. The method of claim 10, wherein X is equal to 0.5

13. The method of claim 10, wherein the stabiliser is present in an amount of at least 0.01 wt. % relative to the dry weight of the inorganic material.

Description

DETAILED DESCRIPTION

[0030] To investigate the properties of new wet accelerator formulations, a variety of wet accelerators were prepared using a wet grinding process. In each of the experiments discussed herein, calcium sulphate containing inorganic material, calcium sulphate dihydrate, was ground in the presence of water and stabiliser in a Labstar LS1 laboratory mill with a Zeta rotor. This process served to reduce the particle size of the inorganic material to increase the efficacy of the wet accelerator at the end of the production process.

[0031] During the wet grinding process, the Labstar LS1 was 85% filled with 0.8 mm Yttria-Zirconia beads and water, inorganic material and stabiliser added as required, with the mixture then ground for various periods to form wet accelerators. An agitator speed of 3700 rpm was used for all experiments.

[0032] The following wet accelerator formulations were tested.

TABLE-US-00001 Particles of Calcium Sulphate Dihydrate Stabiliser Composition 20 wt. % Polyacrylic acid (PAA) at 1.0 wt. % of the 1 of wet inorganic material (PAA molecular weight: accelerator 2000 g/mol). Composition 20 wt. % Polyamino Polyether Methylene 2 of wet Phosphonic Acid (PAPEMP) at 1.0 wt. % of accelerator the inorganic material (PAPEMP molecular weight: 600 g/mol). Composition 20 wt. % STMP at 1.0 wt. % of the inorganic material 3 of wet accelerator Composition 20 wt. % STMP at 10.0 wt. % of the inorganic 4 of wet material accelerator Composition 20 wt. % PAA at 0.5 wt. % of the inorganic material 5 of wet (PAA molecular weight: 2000 g/mol) and accelerator PAPEMP at 0.5 wt. % of the inorganic material (PAPEMP molecular weight: 600 g/mol).

[0033] For each of the above compositions, water made up the remainder of the wet accelerator. The amount of water added was sufficient to ensure that the particles of calcium sulphate dihydrate was 20 wt. % of the overall wet accelerator. Each of the above compositions was ground for four hours to produce the final wet accelerator.

[0034] To investigate the effect of each composition on the setting time of a stucco slurry, samples of each composition were used to obtain experimental data. Here, each of the selected compositions was added to a stucco slurry and the variation in setting time measured. The stucco slurry comprises demineralised water and stucco with a water to stucco ratio of 0.8. Additionally, fluidiser (Naphthalene sulphonic acid condensation product (PNS)) and retarder (Plastretard™) were added to the stucco slurry to adjust the setting working range in accordance with the blender used for the mixing. In these experiments, each wet accelerator was added to the stucco slurry in four different amounts such that the solid content of the wet accelerator was between 0.2 and 1.2 wt. % of the stucco content of the slurry.

[0035] To characterise the effect of each wet accelerator on the setting time of the stucco slurry, the temperature of the slurry was monitored during the setting process. As the conversion of calcium sulphate hemihydrate to calcium sulphate dihydrate is an exothermic process, the temperature change of the slurry during the setting process can be used to deduce the speed at which the slurry is setting.

[0036] Control measurements were taken using a prior art dry accelerator with a surface area of 7 to 8 m.sup.2/g measured by BET. The method of BET measurement used was as described in the Journal of American Chemical Society 60 (1938), pages 309 to 316. The equipment used for the experiments was aa Tristar II from Micromeritics. The degassing conditions used before analysis were 1080 minutes at 45° C.

[0037] For all experiments, the slurry formulation was mixed in a blender and then placed into a semi-adiabatic cell. The total increase in temperature during setting was measured via a thermocouple, and the time taken to reach half the total temperature increase was calculated (t50.sub.ref). Slurry setting experiments were then performed with each of the wet accelerator compounds, with the time taken for the slurry to reach half the total measured temperature increase measured in the same manner (t50.sub.wet accelerator). The difference between the two was then taken as follows.

Δt50=t50.sub.wet accelerator−t50.sub.ref

[0038] Δt50 was then plotted for each of the compositions and accelerator weight percentages in FIG. 1.

[0039] As can be seen from FIG. 1, Δt50 is negative for all compositions where the wet accelerator is added to the slurry at 0.4 wt. % or above. Therefore, in these cases the wet accelerator compositions were more effective in accelerating the setting of the slurry than the prior art dry accelerator. Additionally, it is notable above 0.4 wt. % accelerator, the use of PAA achieved the greatest increase in slurry setting speed, indicating that PAA is an effective stabiliser for wet accelerators.