Vapor-phase flame retardants

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. 

Vapor-Phase Mechanisms. Phosphoms flame retardants can also exert vapor-phase flame-retardant action. Trimethyl phosphate [512-56-1] C H O P, retards the velocity of a methane—oxygen flame with about the same molar efficiency as antimony trichloride (30,31). Both physical and chemical vapor-phase mechanisms have been proposed for the flame-retardant action of certain phosphoms compounds. Physical (endothermic) modes of action have been shown to be of dominant importance in the flame-retardant action of a wide range of non-phosphoms-containing volatile compounds (32). 

As suggested by such experiments on model flames, it appears possible that vapor phase flame retardants better by one or two orders of magnitude than the best present systems may be found for use in plastics. 

SCHEME 5.1 Elementary steps involved in vapor-phase flame retardation by triphenylphosphine oxide and triphenyl phosphate (M is a third body species). 

Zinc borates are predominately a condensed phase fire retardant. In a halogenated system such as flexible PVC, it is known to markedly increase the amount of char formed during polymer combustion whereas the addition of antimony trioxide, a vapor-phase flame retardant, has little effect on char formation. Analyses of the char show that about 80%-95% of the antimony is volatilized, whereas the majority of the boron and zinc from Firebrake ZB remains in the char (80% and 60%, respectively).48-56 The fact that the majority of the boron remains in the condensed phase is in agreement with the fact that boric oxide is a good afterglow suppressant. The mode of action can be summarized in the following equation (not balanced). 

Flame-retardant styrenic polymers find utility in applications such as building insulation (expanded polystyrene foam) and electronic enclosures (flame-retardant HIPS, ABS and styrenic blends). The most effective flame retardants are halogen-(particularly bromine)-containing compounds these flame retardants act by inhibiting the radical combustion reactions occurring in the vapor phase. Flame-retardant plastics are in a state of flux, due to influences of... 

To provide flame retardancy to the polymer, there are three main mechanisms that a flame retardant can use, and the most effective flame retardants use two or all three mechanisms in concert. The first is by altering the gas phase or combustion chemistry. Additives that work by this mechanism are referred to as vapor phase flame retardants (see Fig. 1) during combustion. Halogenated and some phosphorus flame... 

Highly efficient and versatile for wide range of applications. Requires uses of antimony oxide. Broad range of high-performance products available, as aromatic, cycloaliphatic, and bromine/chlorine paraffins. Vapor-phase flame-retardant mechanism. Flame-retardant elements interrupt chemical reactions of combustion in flame zone. 

The question as to whether a flame retardant operates mainly by a condensed-phase mechanism or mainly by a vapor-phase mechanism is especially comphcated in the case of the haloalkyl phosphoms esters. A number of these compounds can volatilize undecomposed or undergo some thermal degradation to release volatile halogenated hydrocarbons (37). The intact compounds or these halogenated hydrocarbons are plausible flame inhibitors. At the same time, thek phosphoms content may remain at least in part as relatively nonvolatile phosphoms acids which are plausible condensed-phase flame retardants (38). There is no evidence for the occasionally postulated formation of phosphoms haUdes. Some evidence has been presented that the endothermic vaporization and heat capacity of the intact chloroalkyl phosphates may be a main part of thek action (39,40). 

Phosphine Oxides. Development of cyanoethylphosphine oxide flame retardants has been discontinued. Triphenylphosphine oxide [791 -28-6] C gH OP, is disclosed in many patents as a flame retardant, and may find some limited usage as such, in the role of a vapor-phase flame inhibitor. 

Flame retardants currently in use which operate by inhibiting vapor phase flame chemistry may be far from optimum. Those flame retardant systems which evolve hydrogen chloride, and perhaps even those which evolve hydrogen bromide, may be acting by little more than a physical effect (1). Some of our own work on tris(dichloroisopropyl) phosphate in polyurethane foams also suggests a physical mode of action (2). 

The complete absence of cross-linking reactions prevents potential char-forming reactions being favored in the presence of conventional condensed-phase flame retardants, and hence, the most effective flame retardants for polyolefins are usually bromine-based so that flame inhibition in the vapor phase is effected or intumescent-based, where char-promotion arises from the flame retardant itself. 

Flame retardants were not generally effective. The combustion of asphalt occurs in a stable diffusion flame above the material surface. Heat from the flame is transmitted back to the asphalt causing vaporization. Vapors enter the flame, react exothermally, and continue the cycle. Fire retardants must therefore inhibit vapor phase combustion. Retardants tested included ethyl iodide, bromotrichloromethane, methyltri-chlorosilane, all of which increased the flash point appreciably, and chloroform, carbon tetrachloride, and potassium bicarbonate, all of which helped only at higher percent sludge formulations. 

Halogenated flame retardants such as chlorinated paraffins, chlorocycloaliphatics, and chloro- and bromoaromatic additives, which are commonly employed in flame-retarding plastics, are postulated to function primarily by a vapor-phase flame-inhibition mechanism. Flame retardation could be implemented by incorporating fire-retardant additives, impregnating the material with a flame-retardant substance, or using flame-retardant comonomers in the polymerization or grafting. 

Phosphorus promotes char formation to protect substrate, and halogen acts in vapor phase. Good thermal stability. Process with modified PPO up to 550-600°E Flame-retardant mechanism condensed phase. Flame retardant induces reactions in host resin that lead to charring and insulation against further burning. 

Uses Fiame retardant vapor-phase flame... 

The Flamtard grades function as both vapor phase and condensed phase flame retardants and smoke suppressants. This dual phase action acts synergistically in halogenated plastic and rubber formulations. For non-halogenated polymers, the addition of Flamtard with a halogen source will improve fire performance and reduce smoke emission. 

Mechanism. Alumina trihydtate functions as a flame retardant in both the condensed and vapor phases (26). When activated, it decomposes endothermically, eliminating water. 

The mechanism by which tin flame retardants function has not been well defined, but evidence indicates tin functions in both the condensed and vapor phases. In formulations in which there is at least a 4-to-l mole ratio of halogen to tin, reactions similar to those of antimony and halogen are assumed to occur. Volatile stannic tetrahaUde may form and enter the flame to function much in the same manner as does antimony trihaUde. 

Alkyl diphenyl phosphate plasticizers can exert flame-retardant action in vinyl plastics by a condensed-phase mechanism, which is probably some sort of phosphoms acid coating on the char. Triaryl phosphates appear to have a vapor-phase action (29). 

Triphenylphosphine oxide [791-28-6], C gH OP, and triphenyl phosphate [115-86-6], C gH O P, as model phosphoms flame retardants were shown by mass spectroscopy to break down in a flame to give small molecular species such as PO, HPO2, and P2 (33—35). The rate-controlling hydrogen atom concentration in the flame was shown spectroscopically to be reduced when these phosphoms species were present, indicating the existence of a vapor-phase mechanism. 

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). 

Flame Retardants. Flame retardants are added to nylon to eliminate burning drips and to obtain short self-extinguishing times. Halogenated organics, together with catalysts such as antimony trioxide, are commonly used to give free-radical suppression in the vapor phase, thus inhibiting the combustion process. Some common additives are decabromodiphenyl oxide, brominated polystyrene, and chlorinated... 

The mode of action of phosphorus-based flame retardants is believed to take place in either the condensed or the vapor phase (refs. 1,2) depending on the type of phosphorus compound and the chemical composition of the polymer. Phosphorus has been reported to be 3 to 8 times more effective than bromine depending on the polymer type (ref. 3). 

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