Non-durable and semi-durable flame retardants based mostly on phosphate or phosphonate salts continue to be used on infrequently washed or disposable goods, and recent improvements have been made to impart better `hand' or some limited wash resistance. Backcoating with insoluble ammonium polyphosphate, usually with additives and binders to provide intumescence, has been found effective on charrable fabrics. However, the leading backcoating effective on a wider range of fabrics, including synthetics and blends, is decabromodiphenyl ether plus antimony oxide. Newer candidates in development for textile coating are polymers and copolymers of pentabromobenzyl acrylate.
The leading durable finish for cellulosic fibers, in use for about 50 years, continues to be based on tetrakis(hydroxymethyl)phosphonium salts reacted with urea and cured with gaseous ammonia. Softer versions have been recently developed using chemical or process modifications, or using selected fiber blends. Somewhat less durable phosphonic ester methylolamide finishes, not requiring gaseous curing, are used on cellulosic fabrics, especially overseas. Other competitive wash-durable phosphorus-based finishes for cellulosics and blends are in development.
Polyesters continue to be flame retarded using a phosphonate or hexabromocyclododecane in a `thermosol' process. Polyesters with built-in phosphinate structures are available as specialty fabrics. A dialkylphosphinate salt has been recently introduced as a melt spinning additive in polyester. A tribromoneopentyl phosphate melt spinning additive has been developed for polypropylene fiber.
A number of inherently flame retardant synthetic fibers recently achieving increased usage include melamine-based fiber, viscose rayon containing silicic acid, aramides, oxidized polyacrylonitrile, and polyphenylene sulfide fibers. Some of these are used in protective clothing.
The recent California and Federal mattress open-flame test standards have brought barrier fabrics into prominence. Some of these barriers use boric acid on cotton batting, others are proprietary composites and blends, both woven and nonwoven, comprising inherently flame retarded fibers combined with lower cost non-flame-retardant fibers. Upholstered furniture open-flame standards are pending.