Flame retardants general

Although much work has been carried out on the mode of action of flame retardants generally, the mechanisms associated with tin additives are only partially understood. It is clear that tin-based fire retardants can exert their action in both the condensed and vapor phases, and that the precise action in any particular system depends on a number of factors, including incorporation level, the amount and chemical nature of other additives present, and the nature of the polymer itself. 

WHO/ICPS. Environmental Health Criteria 192 Flame Retardants — General Introduction, World Health Organization, Geneva, 1997. 

Blend into the formulation inorganic compounds of known flame retardancy, generally inorganic salts or hydrates of inorganic compounds. 

A filled flame retardant, general purpose isophthalic offering resistance to some chemicals and solvents. Approved by Lloyd s Registry for marine application. 

Phosphorus is the most flame retardant element known typically 5% P in polyolefins gives good flame retardance. Generally organic phosphorus is... 

Acryhc and modacryhc fibers are sold mainly as staple and tow products with small amounts of continuous filament fiber sold in Europe and Japan. Staple lengths may vary from 25 to 150 mm, depending on the end use. Eiber deniers may vary from 1.3 to 17 dtex (1.2 to 15 den) 3.2 dtex (3.0 den) is the standard form. The appearance of acryhcs under microscopical examination may differ from that of modacryhcs in two respects. Eirst, the cross sections (Eig. 1) of acryhcs are generally round, bean-shaped, or dogbone-shaped. The modacryhcs, on the other hand, vary from irregularly round to ribbon-like. The modacryhcs may also contain pigment-like particles of antimony oxide to enhance their flame-retardant properties. 

Useful materials incorporating fire-retardant additives are not always straightforward to produce. Loadings of 10% are common, and far higher levels of flame retardants are used in some formulations. These concentrations can have a negative effect on the properties and functions for which the materials were originally intended. Product-specific trade-offs are generally necessary between functionaUty, processibiUty, fire resistance, and cost. 

Ammonium fluoroborate is both a condensed and vapor-phase flame retardant. It is available from M T Hatshaw, General Chemical Cotp., and Spectmm Chemical Cotp. 

Alumina Trihydrate. Alumina trihydrate is usually used as a secondary flame retardant in flexible PVC because of the high concentration needed to be effective. As a general rule the oxygen index of flexible poly(vinyl chloride) increases 1% for every 10% of alumina trihydrate added. The effect of alumina trihydrate on a flexible poly(vinyl chloride) formulation containing antimony oxide is shown in Figure 5. 

Chlorinated Additive Flame Retardants. Table 7 is a general listing of chlotinated compounds used as additive flame retardants. 

In general, the acute toxicity of halogenated flame retardants is quite low. Tables 11—14 contain acute toxicity information from various manufacturers material safety data sheets (MSDS) for some of the flame retardants and intermediates Hsted in the previous tables. The latest MSDS should always be requested from the suppHer in order to be assured of having up-to-date information about the toxicity of the products as well as recommendations regarding safe handling. 

Physical or chemical vapor-phase mechanisms may be reasonably hypothesized in cases where a phosphoms flame retardant is found to be effective in a noncharring polymer, and especially where the flame retardant or phosphoms-containing breakdown products are capable of being vaporized at the temperature of the pyrolyzing surface. In the engineering of thermoplastic Noryl (General Electric), which consists of a blend of a charrable poly(phenylene oxide) and a poorly charrable polystyrene, experimental evidence indicates that effective flame retardants such as triphenyl phosphate act in the vapor phase to suppress the flammabiUty of the polystyrene pyrolysis products (36). 

TrioctylPhosphate. Trioctyl phosphate [1806-54-8/, C24H 04P, has been employed as a specialty flame-retardant plasticizer for vinyl compositions where low temperature flexibHity is critical, eg, in military tarpaulins. It can be included in blends along with general-purpose plasticizers (qv) such as phthalate esters to improve low temperature flexibHity. 

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. 

Ammonia—Gas-Cured Flame Retardants. The first flame-retardant process based on curing with ammonia gas, ie, THPC—amide—NH, consisted of padding cotton with a solution containing THPC, TMM, and urea. The fabric was dried and then cured with either gaseous ammonia or ammonium hydroxide (96). There was Httle or no reaction with cellulose. A very stable polymer was deposited in situ in the cellulose matrix. Because the fire-retardant finish did not actually react with the cellulose matrix, there was generally Httle loss in fabric strength. However, the finish was very effective and quite durable to laundering. 

Flame retardants designated for nylon include halogenated organic compounds, phosphorous derivatives, and melamine cyanurate (160—163). Generally, flame retardants are difficult to spin in nylon because of the high loading required for effectiveness and their adverse effects on melt viscosity and fiber physical properties. 

Whilst the development of flame retarders has in the past been largely based on a systematic trial-and-error basis, future developments will depend more and more on a fuller understanding of the processes of polymer combustion. This is a complex process but a number of stages are now generally recognised and were discussed in Chapter 5. 

Fillers. Fillers are not commonly added to CR adhesives. Calcium carbonate or clay can be primarily added to reduce cost in high-solids CR mastics. Maximum bond strength is obtained using fillers with low particle size (lower than 5 [jim) and intermediate oil absorption (30 g/100 g filler). In general, fillers reduce the specific adhesion and cohesion strength of adhesive films. Although polychloroprene is inherently flame retardant, aluminium trihydrate, zinc borate, antimony trioxide or... 

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