A process for making an improved gypsum/wood fiber board is described. Products resulting from the process are also described. The process comprises adding a diisocyanate, specifically methylenediphenyldiisocyanate (MDI) to an aqueous slurry of calcium sulfate material and cellulosic fibers, where the MDI is added as an emulsion stable in the conditions in which the slurry is maintained. The process further includes passing the MDI containing slurry onto a flat porous forming surface to form a filter cake; removing a substantial portion of the water from the filter cake through the porous surface; pressing the filter cake to form a board and remove additional water; and drying the board to remove the remaining free water.
Articles, including fiberboard, are made from a pumpable, flowable slurry including alpha-calcined calcium sulfate hemihydrate anchored in pores of host particles, alpha-calcined calcium sulfate hemihydrate, a silicone compound, magnesium oxide, and water. The magnesium oxide catalyzes the reaction of the silicone compound into a silicone resin. In a preferred method of making a water resistant fiberboard calcium sulfate dihydrate is combined with the host particles and water to form a slurry which is heated under pressure to calcine the calcium sulfate dihydrate to form alpha-calcined calcium sulfate hemihydrate. After relieving the pressure, a silicone compound and magnesium oxide are added to the slurry. The slurry is dewatered to form a filter cake, which is then formed into a desired shape and allowed to set.
