Gypsum-based building products and method for the manufacture thereof

Abstract

A building product comprises calcium sulphate dihydrate particles bound by an organic binder. The calcium sulphate dihydrate particles each have a longest dimension and a lateral dimension, wherein the lateral dimension corresponds to the maximum breadth of the particle about the axis defined by the longest dimension. The calcium sulphate dihydrate particles have a low aspect ratio such that for at least 75% of the calcium sulphate dihydrate particles, the value of the lateral dimension is at least 20% of the value of the longest dimension.

Claims

1. A building product comprising calcium sulphate dihydrate particles bound by an organic binder: the building product being a self-supporting body; the calcium sulphate dihydrate particles each have a longest dimension and a lateral dimension, the lateral dimension corresponding to the maximum breadth of the particle about the axis defined by the longest dimension, and; the calcium sulphate dihydrate particles have a low aspect ratio such that for at least 75% of the calcium sulphate dihydrate particles, the value of the lateral dimension is at least 20% of the value of the longest dimension; characterised in that the calcium sulphate dihydrate particles are present in an amount of 50-90 wt % of the product.

2. A building product according to claim 1, wherein the calcium sulphate dihydrate particles each have a longest dimension and a lateral dimension, the lateral dimension corresponding to the maximum breadth of the particle about the axis defined by the longest dimension, and; the calcium sulphate dihydrate particles have a low aspect ratio such that for at least 75% of the calcium sulphate dihydrate particles, the value of the lateral dimension is at least 40% of the value of the longest dimension.

3. A building product according to claim 1, wherein the binder is a vegetable-derived organic binder that is optionally modified through cross-linking.

4. A building product according to claim 3, wherein the binder comprises one or more of the following: soy and/or a derivative of soy; starch and/or a starch derivative.

5. A building product according to claim 1, wherein the binder is present in an amount of 0.5-30 wt % of the product.

6. A building product according to claim 1, having a density in the range 250-1600 kg/m.sup.3.

7. A building product according to claim 1, further comprising an inorganic binder, the inorganic binder optionally comprising a cementitious material.

8. A building product according to claim 7, wherein the inorganic binder is present in an amount of up to 20 wt %.

Description

(1) Certain advantageous features of the invention and the way it can be put into operation are now illustrated in the following worked illustrative Examples, with reference to the following Figures:

(2) FIG. 1 is a scanning electron micrograph of a building product according to a first embodiment of the first aspect of the invention.

(3) FIG. 2 is a scanning electron micrograph of a building product according to a second embodiment of the first aspect of the invention.

(4) FIG. 3 is a scanning electron micrograph of a comparative example of a gypsum-based building product.

(5) FIG. 4 shows the building product of FIG. 3 at a higher magnification.

(6) FIG. 5 shows the building product of FIG. 3 at a lower magnification.

(7) FIG. 6 shows a typical particle size distribution for gypsum particles in a composite specimen according to an embodiment of the present invention.

Example 1

(8) Test specimens in the shape of prisms were prepared from gypsum, a starch binder, and optionally, a filler material. The starch was either a non pre-gelatinised starch (in this case, a native corn starch), or one of two pre-gelatinised starches (pre-gelatinised starch 1=staramic 747 from Tate & Lyle; pre-gelatinised starch 2=ICB 1300 from Tate & Lyle). The density and flexural strength were measured and are set out in Table 1.

(9) TABLE-US-00002 TABLE 1 flexural strength composition density (kg/m.sup.3) (N/mm.sup.2) 100 parts of gypsum- 30 m 646 1.1 5 parts of pregelatinised starch 1 1.5 part of EPS 100 parts of gypsum- 30 m 1395 1.32 0.13 parts of pregelatinised starch 1 100 parts of gypsum- 30 m 1488 5.6 2 parts of pregelatinised starch 1 100 parts of gypsum- 30 m 1430 9.8 5 parts of pregelatinised starch 1 100 parts of gypsum- 100 m 1330 5.6 5 parts of pregelatinised starch 1 100 parts of gypsum- 1 mm 1243 1.3 5 parts of pregelatinised starch 1 100 parts of gypsum- 30 m 1397 5.4 2.5 parts of non pregelatinised starch 100 parts of gypsum- 30 m 1372 9.5 5 parts of non pregelatinised starch 100 parts of gypsum- 30 m 798 3.1 5 parts of non pregelatinised starch 35 parts of Expended Clay (2-4 mm) 100 parts of gypsum- 30 m 1082 5.1 5 parts of non pregelatinised starch parts of rubber 100 parts of gypsum- 30 m 1085 4.5 5 parts of non pregelatinised starch 12.5 parts of Expended clay 100 parts of gypsum- 30 m 1103 3.5 5 parts of non pregelatinised starch 25 parts of Expended clay 100 parts of gypsum- 30 m 769 1.2 5 parts of pregelatinised starch 2 Lightened with foam 100 parts of gypsum- 30 m 734 1.2 5 parts of pregelatinised starch 2 Lightened with foam 100 parts of gypsum- 30 m 652 0.8 5 parts of pregelatinised starch 2 Lightened with foam 100 parts of gypsum- 30 m 592 0.5 5 parts of pregelatinised starch 2 Lightened with foam

Example 2

(10) Test specimens in the shape of prisms were prepared from gypsum, an alkyd resin binder, a filler material, and optionally, a siccative agent. The alkyd resin is a commercial product from Cray Valley. A siccative agent from OMG Borcher was used for several examples. The density and flexural strength were measured and are set out in Table 2.

(11) TABLE-US-00003 TABLE 2 flexural strength composition density (kg/m3) (N/mm.sup.2) 100 parts of gypsum- 30 m 1013 5.15 5 parts of Synaqua 4804 0.3 parts of siccative 0.5 part of EPS 100 parts of gypsum- 30 m 825 3.81 5 parts of Synaqua 4804 0.3 parts of siccative 1. parts of EPS 100 parts of gypsum- 30 m 645 2.3 5 parts of Synaqua 4804 0.3 parts of siccative 1.5 parts of EPS 100 parts of gypsum- 30 m 578 1.04 5 parts of Synaqua 4804 0.3 parts of siccative 2 parts of EPS 100 parts of gypsum- 30 m 988 4.99 5 parts of Synaqua 4804 0.5 parts of EPS 100 parts of gypsum- 30 m 825 3.81 5 parts of Synaqua 4804 1 parts of EPS 100 parts of gypsum- 30 m 629 2.21 5 parts of Synaqua 4804 1.5 parts of EPS 100 parts of gypsum- 30 m 563 2.2 5 parts of Synaqua 4804 2 parts of EPS 100 parts of gypsum- 30 m 1087 3.16 3 parts of Synaqua 4804 0.5 part of EPS 100 parts of gypsum- 30 m 876 2.24 3 parts of Synaqua 4804 1 part of EPS 100 parts of gypsum- 30 m 769 2.34 3 parts of Synaqua 4804 1.5 parts of EPS 100 parts of gypsum- 30 m 680 1.76 2 parts of EPS 100 parts of gypsum- 30 m 562 1.50 3 parts of Synaqua 4804 2.5 parts of EPS 100 parts of gypsum- 30 m 758 1.13 5 parts of Synaqua 4804 Lightened with foam 100 parts of gypsum- 30 m 640 0.87 5 parts of Synaqua 4804 Lightened with foam 100 parts of gypsum- 30 m 580 0.66 5 parts of Synaqua 4804 Lightened with foam

Example 3

(12) Test specimens in the shape of prisms were prepared from gypsum, a protein-based binder (Soyad, developed by the Hercules group), and a filler material. The density and flexural strength were measured and are set out in Table 3.

(13) TABLE-US-00004 TABLE 3 flexural strength composition density (kg/m3) (N/mm.sup.2) 100 parts of gypsum- 30 m 1066 1.19 3 parts of Soyad 0.5 part of EPS 100 parts of gypsum- 30 m 869 0.8 3 parts of Soyad 1. parts of EPS 100 parts of gypsum- 30 m 733 0.61 3 parts of Soyad 1.5 parts of EPS 100 parts of gypsum- 30 m 642 0.51 3 parts of Soyad 2 parts of EPS 100 parts of gypsum- 30 m 962 3.48 10 parts of Soyad 0.5 parts of EPS 100 parts of gypsum- 30 m 748 2.31 10 parts of Soyad 1 parts of EPS 100 parts of gypsum- 30 m 645 1.74 10 parts of Soyad 1.5 parts of EPS 100 parts of gypsum- 30 m 572 1.5 10 parts of Soyad 2 parts of EPS 100 parts of gypsum- 30 m 875 4.1 13 parts of Soyad 0.5 part of EPS 100 parts of gypsum- 30 m 742 3.58 13 parts of Soyad 1 part of EPS 100 parts of gypsum- 30 m 643 2.66 13 parts of Soyad 1.5 parts of EPS 100 parts of gypsum- 30 m 643 2.36 13 parts of Soyad 2 parts of EPS 100 parts of gypsum- 30 m 759 2.25 13 parts of soyad Lightened with foam 100 parts of gypsum- 30 m 838 4.17 13 parts of soyad Lightened with foam 100 parts of gypsum- 30 m 796 3.19 13 parts of soyad Lightened with foam 100 parts of gypsum- 30 m 636 2.05 13 parts of soyad Lightened with foam 100 parts of gypsum- 30 m 694 2.08 13 parts of soyad Lightened with foam 100 parts of gypsum- 30 m 744 2.94 13 parts of soyad Lightened with foam

Example 4

(14) Test specimens in the shape of prisms were prepared from gypsum, a pine-derived binder (terpene phenol emulsion TR602), and a filler material. The density and flexural strength were measured and are set out in Table 4.

(15) TABLE-US-00005 TABLE 4 flexural strength composition density (kg/m3) (N/mm.sup.2) 100 parts of gypsum- 30 m 1075 1.25 3 parts of TR602 0.5 part of EPS 100 parts of gypsum- 30 m 842 1.09 3 parts of TR602 1. parts of EPS 100 parts of gypsum- 30 m 726 1.28 3 parts of TR602 1.5 parts of EPS 100 parts of gypsum- 30 m 631 078 3 parts of TR602 2 parts of EPS 100 parts of gypsum- 30 m 1093 2.05 5 parts of TR602 0.5 parts of EPS 100 parts of gypsum- 30 m 903 1.92 5 parts of TR602 1 parts of EPS 100 parts of gypsum- 30 m 747 1.87 5 parts of TR602 1.5 parts of EPS 100 parts of gypsum- 30 m 656 1.51 5 parts of TR602 2 parts of EPS

(16) Measurement of Flexural Strength

(17) After production, the prisms were dried for 24 hours at 40 C. and subsequently conditioned at 25 C. and 50% humidity for a further 24 hours. The flexural strength of the prisms was measured under three-point bending using a Zwick universal testing machine.

(18) Production of Prisms

(19) The following protocol was used to produce prisms containing a starch binder. An analogous method was used for prisms containing other binders. 1. Blend the powders: gypsum and additives (light weight fillers for example) 2. Mix water with powder starch 3. Pour the gypsum powder blend into the water/starch mixture 4. Mix the powder blend and the water in a mixer (such as Kenwood mixer) until having a homogeneous slurry 5. If the sample comprises foam as a light weight agent, the foam, generated separately according to processes known in the art, is preferably added at this stage 6. Pour the slurry into the moulds 7. Skim the excess of gypsum slurry 8. Put the mould on a tray. The mould might be covered by a metal tray. 9. Cure/dry the samples in the mould for a suitable time and at a suitable temperature, e.g. 1 h30 at 140 C., 24 h at 40 C., or a time between 1 h30 and a temperature between 40 C. and 140 C.

(20) The mechanical performance of the samples was tested at room temperature. The samples were held room temperature (15-25 C.) for at least a day before testing.

(21) This method may be used for making boards having a thickness of 13 mm. In this case the curing step is: 1 h10 at 120 C. Moreover, it is possible to add a paper liner on both sides before and after pouring the gypsum paste as is known in the art.

(22) Scanning Electron Micrographs

(23) FIGS. 3, 4, and 5 show scanning electron micrographs of gypsum plasterboards produced according to a known calcination and re-hydration process. It can be seen that this process results in the formation of needle-like gypsum crystals, having a high aspect ratio. The length of the needles is approximately 20 m.

(24) By contrast, FIGS. 1 and 2 show scanning electron micrographs of gypsum composite according different embodiments of the present invention. FIG. 1 shows a composite having a soy protein binder, while FIG. 2 shows a plasterboard having a starch binder. The gypsum crystals correspond to the pale areas of the micrograph, while the dark areas correspond to the binder and/or the epoxy resin used to mount the samples.

(25) It can be seen that in gypsum plasterboards according to the present invention, the gypsum particles are more block-like than needle-like. Furthermore, the size of the gypsum particles in building products shown in FIGS. 1 and 2 is much greater than that of the gypsum needles present in the comparative example shown in FIGS. 3 to 5.

(26) FIG. 6 shows a typical particle size distribution for gypsum particles in a composite specimen according to an embodiment of the present invention. From this it can be seen that in general gypsum particles in the composite specimen have a particle size between 1 and 100 m. The majority of particles (measured by volume) have a particle size between 20 and 60 m.