Lightweight gypsum wallboard
A lightweight gypsum wallboard having a foamed gypsum core reinforced with pre-gelatinized, e.g., pre-gelled, starch and prepared by mixing an aqueous foam into a gypsum slurry comprising a source of calcined gypsum (commonly known as plaster of Paris), pre-gelled starch and a lignosulfonate dispersant; allowing the so-formed gypsum slurry to set, and then drying the set gypsum core.
1. A gypsum slurry suitable for producing a lightweight gypsum board comprising an aqueous mixture of calcined gypsum, a pre-gelatinized starch in an amount of more than 4% by weight of the calcined gypsum, and a lignosulfonate dispersant in an amount of at least 0.3% by weight of the calcined gypsum, wherein no naphthalenesulfonate is present in the gypsum slurry.
2. The gypsum slurry of claim 1 having a sufficient amount of a foam to cause the slurry to harden to a density of no more than 31 pounds per cubic foot.
3. The gypsum slurry of claim 2 wherein the foam comprises an ammonium ether sulfate surfactant.
4. The gypsum slurry of claim 1 having a water to calcined gypsum (water:calcined gypsum) weight ratio in the range of 0.7:1 to 1.3:1.
5. The gypsum slurry of claim 1 wherein the pre-gelatinized starch is in an amount of from 4.5% to 10% by weight of the calcined gypsum.
6. The gypsum slurry of claim 1 wherein the lignosulfonate dispersant is in an amount of from 0.35% to 1.0% by weight of the calcined gypsum.
7. The gypsum slurry of claim 1 wherein no sodium trimetaphosphate is present.
8. A lightweight gypsum wallboard comprising a set gypsum core containing a pre-gelatinized starch and a lignosulfonate dispersant, wherein the set gypsum core, formed by hydration of calcined gypsum supplied in a gypsum slurry, is sandwiched between two facing sheets of a fibrous material and wherein the pre-gelatinized starch is present in an amount of more than 4% by weight of the calcined gypsum, and the lignosulfonate dispersant is present in an amount of at least 0.3% by weight of the calcined gypsum wherein no naphthalenesulfonate is present in the gypsum slurry.
9. The lightweight gypsum wallboard of claim 8 having a sufficient amount of a foam in the gypsum slurry to cause the slurry to harden to a density of no more than 31 pounds per cubic foot.
10. The lightweight gypsum wallboard of claim 9 wherein the foam comprises an ammonium ether sulfate surfactant.
11. The lightweight gypsum wallboard of claim 8 having a water to calcined gypsum (water:calcined gypsum) weight ratio in the range of 0.7:1 to 1.3:1.
12. The lightweight gypsum wallboard of claim 8 wherein the pre-gelatinized starch is in an amount of from 4.5% to 10% by weight of the calcined gypsum.
13. The lightweight gypsum wallboard of claim 8 wherein the lignosulfonate dispersant is in an amount of from 0.35% to 1.0% by weight of the calcined gypsum.
14. The lightweight gypsum wallboard of claim 8 wherein no sodium trimetaphosphate is present.
15. The lightweight gypsum wallboard of claim 8 having a nominal thickness of ½ inch and a weight of from 1000 to 1300 pounds per MSF of board, wherein the two facing sheets are paper and the pre-gelatinized starch is a hydroxyalkylated corn starch.