Fire-Retardant Treatments for Dry-Formed Hardboard

Building codes are becoming more stringent on the use of wood fiber products in structures because of the flammability of these products. Twenty-one fire-retardant chemical systems known to provide some fire retardancy to solid wood were investigated for their effectiveness in improving fire performance of dry-formed hardboard. An additional step in the board making process was needed to apply the chemicals to the fiber. One hundred percent of the chemical was incorporated into the finished board. Three types of retardants –water-soluble salts, liquid ammonium polyphosphates, and curing-type organic phosphates–were applied at 10 or 20 percent of the fiber weight; this was followed by a phenolic resin treatment. Fire performance in an 8-foot and in a 2-foot tunnel furnace was determined as were strength properties. Results indicated that a moderate reduction in flame spread (to 60 percent) can be obtained at the 10 percent level of treatment with some reduction in modulus of rupture. Increasing the level to 20 percent gave further reductions in flame spread with little additional reduction in bending strength, particularly with a treatment of disodium octaborate tetrahydrate-boric acid, a water-soluble salt.

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