Flame resist finishes

Nearly all successful flame-resistant finishes depend upon the application of compounds contuining phosphorus to the cellulose. Not much is known about the combustion of cellulose, but it has been established that it breaks down into a solid carbonaceous char accompanied by the formation of volatile liquids, gases, and tarry substances. Anything which reduces the formation of volatile products of combustion will retard the rate of propagation... 

Several commercial flame-resistant finishes are based on esterification of the cellulose with phosphoric acid (Perfect, y.S.D.C., 1958, 74, 829) ... 

The first known fire-retardant process found durable to laundering was developed in 1912 (4). A modification of an earlier process (5), this finish was based on the formation of a tin(IV) oxide [18282-10-5] deposit. Although the fabric resulting from treatment was flame resistant, afterglow was reputed to be a serious problem, resulting in the complete combustion of the treated material through smoldering. 

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. 

The Fire Tests for Flame Resistant Textiles and Films, issued by the National Fire Protection Association (NFPA) ia 1989, is the method most used by iadustrial fire-retardant finishers (ca 1993) (50). It has been approved by the American National Standards Institute. 

Phosphonomethylated Ethers. A phosphoms-containing ether of ceUulose can be prepared by the reaction of cotton ceUulose with chioromethylphosphonic acid [2565-58-4] ia the presence of sodium hydroxide [1310-73-2] by the pad-dry-cure technique (62). Phosphoms contents of between 0.2 and 4.0% are obtained. This finish is durable but has high ion-exchange properties and is flame resistant only as the ammonium salt. DurabUity on medium weight fabrics is obtained with chi oromethylph osph onic diamide. This finish has never penetrated the flame retardant market (63). 

The THPOH—NH process was used extensively for children s sleepwear in the early 1970s. However, the advent of the Tris problem on polyester led to a sharp decline in commercial production of chemically finished children s flame-resistant cotton sleepwear. 

As previously noted, the APO system leads to fabrics which combine flame resistance and durable press properties however, the toxicity of the aziridinyl system precludes its use in modem textile finishing. 

Considerable effort is being made (ca 1993) to develop satisfactory flame retardants for blended fabrics. It has been feasible for a number of years to produce flame-resistant blended fabrics provided that they contain about 65% or more ceUulosic fibers. It appears probable that blends of even greater synthetic fiber content can be effectively made flame resistant. An alternative approach may be to first produce flame-resistant thermoplastic fibers by altering the chemical stmcture of the polymers. These flame-resistant fibers could then be blended with cotton or rayon and the blend treated with an appropriate flame retardant for the ceUulose, thereby producing a flame-resistant fabric. Several noteworthy finishes have been reported since the early 1970s. 

THPOH—Ammonia—Tris Finish. By far the most effective finish for polyester—cotton textiles was a system based on the THPOH—NH treatment of the cotton component either foUowed or preceded by the appUcation of Tris finish to the polyester component. This combined treatment appeared to be effective on almost any polyester—cotton blend. A large amount of fabric treated in this way was sold throughout the United States and much of the rest of the world. Shortly after the introduction of Tris finishing, Tris was found to be a carcinogen. Most of the Tris treated production was in children s sleepwear, and this created a situation in which almost aU chemical fire-retardant-treated textiles were unfairly condemned as dangerous. Manufacturers mshed to replace chemically treated textiles with products produced from inherently flame-resistant fibers. Nowhere was the impact more severe than in the children s sleepwear market. New, safer materials have been introduced to replace Tris. Thus far none has been as completely effective. 

Phosphonium Salt—Urea Precondensate. A combination approach for producing flame-retardant cotton-synthetic blends has been developed based on the use of a phosphonium salt—urea precondensate (145). The precondensate is appUed to the blend fabric from aqueous solution. The fabric is dried, cured with ammonia gas, and then oxidized. This forms a flame-resistant polymer on and in the cotton fibers of the component. The synthetic component is then treated with either a cycUc phosphonate ester such as Antiblaze 19/ 19T, or hexabromocyclododecane. The result is a blended textile with good flame resistance. Another patent has appeared in which various modifications of the original process have been claimed (146). Although a few finishers have begun to use this process on blended textiles, it is too early to judge its impact on the industry. 

Miscellaneous. Flame-resistant cross-linked polyethylene can be made with a number of fluoroborates and antimony oxide. This self-extinguishing material may contain the fluoroborates of NH, Na", K", Ca ", Mg ", Sr ", or Ba " in amounts of 4—20% (76). Magnesium fluoroborate cataly2es the epoxy treatment of cotton fabrics for permanent-press finishes (77) (see Textiles). 

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

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). 

Fire Retardants for Ceftnlosics. Phosphorus-containing materials are by far the most important class of compounds used to imparl durable flame resistance lo cellulose. Flume-retardant finishes containing phosphorus compounds usually also contain nitrogen or bromine or sometimes huth. 

In addition to possessing the desired fire and flame resistance, the acoustical fiber-board paints and finishes must possess other requirements of an acceptable paint and finish. 

Many tests have been devised to evaluate the fire and flame resistance of surface-treated acoustical fiberboard. The most widely accepted test, recognized by both the building industry and the building code agencies, is the fire-resistance test specified in federal specification (3). Other tests under consideration, but not universally adopted, are the tunnel test of the Underwriters Laboratories, Inc. (11), and the Factory Mutual room burn out test (2). A small scale test that is being employed for plant control and quick finish evaluation is the Class F fire test (12). 

Viscose In principle all the treatments effective on cotton should be effective on viscose as well. However, the delicate viscose libers cannot withstand the harsh finishing processes, and are rarely treated with a finish. However, Lyocell (Coutaulds) can be treated with Pyrovatex CP (Ciba) to produce FR Lyocell.55 The work at Bolton has shown that this fiber being more reactive than cotton needed only half the normal amount of this FR treatment applied to cotton cellulose to produce an equivalent degree of flame resistance. 

Fibers not having inherent flame resistance often can be given this property by incorporation of a suitable additive. This may be done by copolymerization of the additive into the polymer reaction of the additive with the polymer after polymerization, or by applying a polymeric or monomeric noninflammable finish to the surface as a coating. These additives usually contain bromine, nitrogen, or phosphorus, or a combination of these elements. Great care must be taken in choosing the additive and its level of addition in order to prevent loss of other desirable fiber properties and to avoid any harmful effects to processors or ultimate consumers. 

Numerous end uses for cotton depend on its ability to be treated with chemical agents that confer flame resistance. The chemical FR treatments used to confer flame resistance to untreated cotton depend on many factors [358] is the finish intended to be durable or nondurable is the treatment used is to prevent burning or smoldering what is the... 

The main durable FR finishes used on cotton to meet more severe open-flame resistance requirements are phosphorus based [343,358]. One of the problems with typical phosphorus-based FR treatments on fleece, which only requires a mild treatment to pass the 45° angle test, is that the often-required levels alter the esthetic properties of the fleece, resulting in a fabric that is stiff or matted and often has unpleasant odors. Most common types of dyes used on cotton are affected by pH or oxidation-reduction procedures that are used during the FR treatments. 

Another approach to flame-resistant cotton containing fabrics involves the use of core spun yarns [368 372]. There are two components in these specialized yarns. One component is a central core usually made from a human-made polyester or nylon, or a nonflammable core like fiberglass. The other component is a cotton cover that is wound around the central core to form the core yarn. The core yarn is woven or knitted into an appropriate textile, then treated with a finish to make the flame-resistant cotton cover. When the core yarns are spun to restrict their synthetic content to 40% or less, the FR treatment of the cotton component... 

Most flame-retardant finished textiles are excluded from the Oko-Tex Standard 100 label. In all cases, the durability of the finish is often a problem. It is the responsibility of the fabric finisher to address these issues if commercial flame-retardant fabrics are to be produced. An alternative for the fabric designer without most of the named problems is the use of flame-resistant modified fibres, but... 

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