Preparation of a three layer, fire retardant particleboard

Claim 1

A method of preparing a composite, flame retardant particleboard from cellulosic furnish comprising the steps of: impregnating a first portion of cellulosic furnish consisting essentially of bark with an aqueous solution of diammonium phosphate whereby said first portion of bark, when dried to oven dry moisture content, contains approximately 14 percent diammonium phosphate by weight; mixing said first portion containing diammonium phosphate with a second portion of cellulosic furnish consisting essentially of bark, said second portion being untreated with a fire retardant substance, the mixed first and second portion comprising approximately 60% by weight untreated bark and 40% by weight treated bark and being combined with about 8 percent by weight urea formaldehyde resin binder; impregnating a third portion of cellulosic furnish consisting essentially of wood chips with an aqueous solution of diammonium phosphate whereby said third portion of chips, when dry to oven dry moisture content, contains from about 20 to about 40 percent by weight diammonium phosphate; mixing said third portion of furnish containing diammonium phosphate with a fourth portion of furnish consisting essentially of wood chips, said fourth portion being untreated with a fire retardant substance, said third and said fourth portions being combined in approximately equal amounts and then mixed with about 8 percent by weight urea formaldehyde resin binder; and then forming the combined wood chips and combined bark into a three layer composite board having a bark core and wood chip surface by pressing and heating whereby a particleboard is formed having improved fire retardancy without substantial degradation of the strength of said board due to the presence of the fire retardant material in a portion of the furnish forming the completed board.

Claim 2

A method of preparing a composite, flame retardant particleboard from cellulosic furnish comprising the steps of: impregnating a first portion of cellulosic furnish consisting essentially of bark with an aqueous solution of diammonium phosphate whereby said first portion of bark, when dried to oven dry moisture content, contains approximately 14 percent diammonium phosphate by weight; mixing said first portion containing diammonium phosphate with a second portion of cellulosic furnish consisting essentially of bark, said second portion being untreated with a fire retardant substance, the mixed first and second portion comprising approximately 60% by weight untreated bark and 40% by weight treated bark and being combined with about 8 percent by weight urea formaldehyde resin binder; impregnating a third portion of cellulosic furnish consisting essentially of wood chips with an aqueous solution of diammonium phosphate whereby said third portion of chips, when dry to oven dry moisture content, contains from about 20 to about 40 percent by weight diammonium phosphate; mixing said third portion of furnish containing diammonium phosphate with a fourth portion of furnish consisting essentially of wood chips, said fourth portion being untreated with a fire retardant substance, said third and said fourth portions being combined in approximately equal amounts and then mixed with about 8 percent by weight urea formaldehyde resin binder; and then forming the combined wood chips and combined bark into a three layer composite board having a bark core and wood chip surface by pressing and heating whereby a particleboard is formed having improved fire retardancy without substantial degradation of the strength of said board due to the presence of the fire retardant material in a portion of the furnish forming the completed board.