Flame retardants for cellulose

One important thermal degradation mechanism of cellulose fibres (cotton, rayon, linen, etc.) is the formation of the small depolymerisation product levoglucosan (Fig. 8.7). Levoglucosan and its volatile pyrolysis products are extremely flammable materials and are the main contributors to cellulose combustion. Compounds that are able to hinder levoglucosan formation are expected to function as flame retardants for cellulose. The crosslinking and the single type of esterification of 

Chemicals that can yield phosphoric acid during the early stages of fibre pyrolysis form the majority of successful flame retardants for cellulose. However, it is not sufficient to supply just phosphoric acid precursors. The presence of nitrogen has been found to provide a synergistic effect with phosphorous. Minimum levels of added phosphorous and nitrogen for effective flame retardancy have been estimated at 2 % P and 1 % N. However, these minimum levels can vary greatly depending on fabric construction and test requirements. 

Inorganic salts have long been known to provide flame retardancy on cellulosic material that will not be exposed to water, rain or perspiration. The French chemist Gay-Lussac proposed a borax and ammonium sulfate treatment as a flame retardant for cotton in 1820. Today, a mixture of boric acid and borax is still an effective flame retardant for cotton at 10 % solids add-on. Ammonium salts of strong acids, especially phosphoric acid (P/N synergism) are particularly useful as nondurable flame retardants for cellulose. Three commercially important products are diammonium phosphate, ammonium suifamate and ammonium bromide. These salts readily form the corresponding strong acids upon heating (Fig. 8.10). 

Diammonium phosphate and ammonium sulfamate are used at 15 % solids addon and function as condensed phase flame retardants, not only by crosslinking but also by dehydrating cellulose to polymeric char with reduced formation of flammable by-products (Fig. 8.6). The water insoluble ammonium polyphosphate is an effective flame retardant and is added to coatings and binder systems, for example for pigment printing. Ammonium bromide is applied at 10 % solids add-on and is effective in the gas phase. 

Although inorganic salts can provide excellent flame-retardant properties for cellulose, reasonable laundering durability must be incorporated into any finish destined for apparel use. The most successful durable flame retardants for cellulose are based on phosphorous- and nitrogen-containing chemical systems that can react with the fibre or form crosslinked structures on the fibre. The key ingredient of one of these finishes is tetrakis(hydroxymethyl)phosphonium chloride (THPC), made from phosphine, formaldehyde and hydrochloric acid (Fig. 8.11). THPC reacts with urea to form an insoluble structure on cellulose in a pad-dry-cure process (Fig. 8.12). 

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Tin. Tin has been used as a flame retardant for cellulose since the latter 1800s (2). Only since the 1970s has it been used as a synergist for... 

Triphenyl phosphate [115-86-6] C gH O P, is a colorless soHd, mp 48—49°C, usually produced in the form of flakes or shipped in heated vessels as a hquid. An early appHcation was as a flame retardant for cellulose acetate safety film. It is also used in cellulose nitrate, various coatings, triacetate film and sheet, and rigid urethane foam. It has been used as a flame-retardant additive for engineering thermoplastics such as polyphenylene oxide—high impact polystyrene and ABS—polycarbonate blends. 

Early Durable Finishes. Early studies lo produce durable flame retardants for cellulose were based on treatment wilh inorganic compounds containing antimony and titanium. 

Uses Flame retardant for cellulosics including textiles/ paper, particleboard and timber. 

Uses Flame retardant for cellulosic and other textiles, paper, board, and particleboard. 

Water soluble flame retardant for cellulosics and blends with polyester, particularly nonwovens. 

Fyran . [Yorkshire Pat-Chem] Flame retardants for cellulosic fabrics. 

Synonyms Tetrakishydroxymethyl phosphonium chloride polymer with urea Uses Flame retardant for cellulose fabrics and blends... 

Hazardous Decomp. Prods. Heated to decomp., emits very toxic fumes of POx and SOx Uses Biocide for water treatment, sec. oil field recovery flame retardant for cellulosic fabrics and blends... 

Triphenyl phosphate-a solid-ls the most commonly used flame retardant for cellulose acetate. 

Uses Antifoam in paper coatings, aq. adhesives, inks, casein sol ns., textile sizes, and detergent sol ns. plasticizer, solvent for NC, cellulose acetate, chlorinated rubber, and vinyls solvent for natural gums and syn. resins flame retardant for cellulosics, epoxies, PS, PVAc, PVC component in extraction of rare earth metal salts... 

Natural fibers such as cotton (cellulose) are intrinsically flammable and undergo combustion in air, once ignited. Phosphorous-containing compounds like ammonium phosphates have been investigated as flame retardants for cellulosic materials. This role of phosphates as useful flame retardants for cellulose is well known. 

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