Process for flame retarding cellulosics

Claim 1

A process for rendering cellulosic-containing materials durably flame retardant comprising: a. Impregnating a cellulose-containing material with a flame retarding solution comprising from about 10 to about 40 percent by weight poly(hydroxymethyl) phosphonium cation and from about 0.5 to about 20 percent by weight of a basic catalyst, said solution having a pH of from about 2 to about 9; b. Drying the impregnated material at a temperature of less than 125° C., to a moisture content of from about 0 to about 8 percent by weight; c. Aerating the dried material by directing a current of air from about 1,000 to about 3,000 cubic feet per minute through the dried material to eliminate any formaldehyde formed in said drying step; d. Exposing the aerated material in an enclosed chamber for a period of at least about 5 seconds but less than about 60 seconds to an atmosphere containing at least about 50 percent by volume of gaseous ammonia to cure the phosphorus containing resin in and on the material; e. Contacting the material with water to a wet pick-up of from about 10 to about 60 percent by weight to render the material durably flame retardant; and f. Further exposing the water contacted material for a period of from about 1 to about 10 seconds to an atmosphere containing at least about 50 percent by volume of gaseous ammonia.