Flame Retardant Finishes

Flame-retardant finishes provide textiles with an important performance characteristic. Protection of consumers from unsafe apparel is only one area where flame retardancy is needed. Firefighters and emergency personnel require protection from flames as they go about their duties. Floor coverings, upholstery and drapery also need protection, especially when used in public buildings. The military and the airline industry have multiple needs for flame-retardant textiles. 

Flame Retardant Finishes Cellulosic fibers are among the more flammable fibers and are subject to rapid flaming combustion as well as slow 

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Work began in the 1930s on the development of flame-retardant cottons based on chemical systems that either reacted directly with the ceUulosic substrate, or polymerized on or in the cotton fiber. A serious effort in this direction, mounted from the 1950s through the 1970s, resulted in most of the state-of-the-art flame-retardant finishes for cotton available. 

Nondurable Finishes. Flame-retardant finishes that are not durable to launderiag and bleaching are, ia general, relatively iaexpensive and efficient (23). In some cases, a mixture of two or more salts is more effective than either of the components alone. For example, an add-on of 60% borax (sodium tetraborate) is required to prevent fabric from burning, and boric acid is iaeffective as a flame retardant even at levels equal to the weight of the fabric. However, a mixture of seven parts borax and three parts boric acid imparts flame resistance to a fabric with as Utde as 6.5% add-on. 

In this case, the components are mixed, the pH adjusted to about 6.0 with sodium hydroxide, and the solution appHed to the textile via a pad-dry-cure treatment. The combination of urea and formaldehyde given off from the THPC further strengthens the polymer and causes a limited amount of cross-linking to the fabric. The Na2HP04 not only acts as a catalyst, but also as an additional buffer for the system. Other weak bases also have been found to be effective. The presence of urea in any flame-retardant finish tends to reduce the amount of formaldehyde released during finishing. 

THP—Amide Process. THP has also been made directly from phosphine [7803-5-27] and formaldehyde. The THP so generated contains one less mole of formaldehyde than either THPC or THPOH. It can be used in a THP—amide flame-retardant finish. The pad formulation contains THP, TMM, methylol urea, and a mixed acid catalyst (93—95). 

The identification of Tris as a potential carcinogen dealt a resounding blow to the flame-retardant finishing industry. From 1977 to 1984, several principal supphers of flame-retardant chemicals either reduced the size of their operations or abandoned the market completely. However, Albright and Wilson Corp. (UK) continues to produce THPC—urea precondensate and market it worldwide, and Westex Corp. (Chicago) continues to apply precondensate—NH finish to millions of yards of goods for various end uses. American Cyanamid reentered the market with a precondensate-type flame retardant based on THPS. 

Additives. Because of their versatility, imparted via chemical modification, the appHcations of ethyleneimine encompass the entire additive sector. The addition of PEI to PVC plastisols increases the adhesion of the coatings by selective adsorption at the substrate surface (410). PEI derivatives are also used as adhesion promoters in paper coating (411). The adducts formed from fatty alcohol epoxides and PEI are used as dispersants and emulsifiers (412). They are able to control the viscosity of dispersions, and thus faciHtate transport in pipe systems (413). Eatty acid derivatives of PEI are even able to control the viscosity of pigment dispersions (414). The high nitrogen content of PEIs has a flame-retardant effect. This property is used, in combination with phosphoms compounds, for providing wood panels (415), ceUulose (416), or polymer blends (417,418) with a flame-retardant finish. 

Melamine—Formaldehyde Resins. The most versatile textile-finishing resins are the melamine—formaldehyde resins. They provide wash-and-wear properties to ceUulosic fabrics, and enhance the wash durabiHty of flame-retardant finishes. Butylated melamine —formaldehyde resins of the type used in surface coatings may be used in textile printing-ink formulations. A typical textile melamine resin is the dimethyl ether of trimethylolmelamine [1852-22-8] which can be prepared as follows ... 

One concern in conventional processing is the achievement of uniform reagent appUcation and uniform cross-linking (18). An area in which adequate treatment of aU fibers is necessary is in flame-retardant finishing. One means of obtaining thorough treatment has been the use of vacuum impregnation, in which the fabric is first passed over a vacuum slot to remove air from the fabric interstices, foUowed by exposure to the phosphoms flame-retardant solution in the precondensate ammonia system (19). 

A number of flame-retardant finishes have been developed for outdoor cotton fabrics. Various experimental and commercial finishes have been compared (149). Most noteworthy is that THPOH—NH finishes do not perform as well outdoors as the THPOH—NH precondensate finishes. Likewise, antimony oxide—halogen finishes perform exceptionally well on outdoor fabrics. 

Tetrakis(hydroxymethyl)phosphonium salts are used to produce crease-resistant and flame-retardant finishes on textile fabrics, including children s nightwear. No data on occupational exposure levels were available (lARC, 1990). 

J.-P. Guan and G.-Q. Chen, Flame retardancy finish with an organophosphorus retardant on silk fabrics. Fire Mater., 30 (6), 415 124 (2006). 

Cyclic oligomeric phosphonates with the varying degrees of structural complexity (Structure 5.4) are also available in the market.25 They are widely used as flame-retardant finishes for polyester fabrics. After the phosphonate is applied from an aqueous solution, the fabric is heated to swell and soften the fibers, thus allowing the phosphonate to be absorbed and strongly held. It is also a useful retardant in polyester resins, polyurethanes, polycarbonates, polyamide-6, and in textile back coatings. A bicyclic pentaerythritol phosphate has been more recently introduced into the market for use in thermosets as well as for polyolefins (preferably, in combination with melamine or ammonium polyphosphate)... 

Horrocks, A. R., Flame retarding finishing for textiles, Revs. Prog. Colouration, 1986, 16, 62-101. 

Abdel-Mohdy, F. A., Graft copolymerization of nitrogen- and phosphorus-containing monomers onto cellulosics for flame-retardant finishing of cotton textiles, J. Appl. Polym. Sci., 2003, 89, 2573-2578. 

Horrocks, A.R. 2003. Flame-retardant finishes and finishing, chemical testing of textiles, D.H. Heywood (Ed.), pp. 214—250. Bradford, U.K. Society of Dyers and Colourists. 

Horrocks, A.R. 1986. Flame-retardant finishing of textiles. Rev. Prog. Coloration, 16 62-101. 

Achwal, W.B. 1987. Flame retardant finishing of cotton and silk fabrics. Colourage, 6 16-30. 

The second series of reactions using JV,JV -dimethylurea was studied in an effort to understand the mechanism of fabric flame-proofing (81PS207). Under some conditions these reactions can produce polymers that may be used as flame-retardant finishes for cotton. 

Table 8.3 Comparison of two permanent flame-retardant finishes for cellulosics...

Another approach to durable flame retardant finishes for polyester is the use of highly brominated chemicals as topical finishes. One particularly useful material is hexabromocyclododecane (HBCD, Fig. 8.19). To achieve durable flame retardancy, fabric padded with 8 % of a dispersion of this water insoluble material must be heated above 190 °C or 375 °F to form a film of the flame retardant on the fibre surface."... 

There are also serious side effects to fabric physical properties from flame-retardant finishing that must be recognised, often caused by the high application levels of the flame retardants. Harsh hand, loss of tensile suength and colour effects (fabric yellowing and dye shade changes) are common problems with durable flame-retardant finishes for cotton. The combination with other finishes, such as softeners, easy-care and repellent finishes, must be carefully tested. The flame retardancy of the multi-purpose finish is more often reduced than it is acceptable. 

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