Flame retardant concentration

Phosphorus/bromine combinations are perhaps the most effective flame retardant combination (ref. 3) and claims have been made for synergy. The formation of phosphorus trichloride or oxychloride has been postulated by analogy to that of the formation of antimony trichloride and oxychloride but there is no evidence for this mechanism. Some reports of synergy appear to be a result of a nonlinear response to the flame retardant concentration. 

Some of the commercial flame-retardant concentrates are listed in Table 5.15. 

These may present some problems in incorporation into compounds while maintaining the desired physical properties, but a zero-halogen magnesium hydroxide flame-retardant concentrate on a polyolefin base (by Uvtec under the name Safe FR 5000) can easily be dispersed into polyolefin products. It is predispersed to run on existing PVC production equipment and is non-corrosive and non-abrasive to processing equipment. It is halogen free, with low smoke and no acid combustion gas. There is no leaching of the flame-retardant component and it is recyclable and environmentally safe, available in UV-stabilized formulations. 

TABLE 11.4 Flame Retardant Concentrations Required to Achieve Defined LOI Values in Polyamide-6,6 Films... 

FIGURE 11.6 Percentage reduction of each flame retardant concentration required to produce an LOI value of 24 when present with an unspecified commercial clay the specified clays Cloisite Na+ and 30B. (From Ref. 26, with permission from the Textile Institute.)... 

BurnEx 2000 polypropylene flame retardant concentrates are made from nano-dispersible antimony pentoxide and an organic bromine compound. Polypropylene resins of different Melt Flow Index (MFI) are used for different applications. Nyacol Nano Technologies, Inc. can design other concentrates or work with your compounder to formulate a custom product for you. They have a fully equipped compounding laboratory at their Ashland, MA facility. 

Brominated Flame Retardant Concentrations in House Dust... 

An example of a commercial semibatch polymerization process is the early Union Carbide process for Dynel, one of the first flame-retardant modacryhc fibers (23,24). Dynel, a staple fiber that was wet spun from acetone, was introduced in 1951. The polymer is made up of 40% acrylonitrile and 60% vinyl chloride. The reactivity ratios for this monomer pair are 3.7 and 0.074 for acrylonitrile and vinyl chloride in solution at 60°C. Thus acrylonitrile is much more reactive than vinyl chloride in this copolymerization. In addition, vinyl chloride is a strong chain-transfer agent. To make the Dynel composition of 60% vinyl chloride, the monomer composition must be maintained at 82% vinyl chloride. Since acrylonitrile is consumed much more rapidly than vinyl chloride, if no control is exercised over the monomer composition, the acrylonitrile content of the monomer decreases to approximately 1% after only 25% conversion. The low acrylonitrile content of the monomer required for this process introduces yet another problem. That is, with an acrylonitrile weight fraction of only 0.18 in the unreacted monomer mixture, the low concentration of acrylonitrile becomes a rate-limiting reaction step. Therefore, the overall rate of chain growth is low and under normal conditions, with chain transfer and radical recombination, the molecular weight of the polymer is very low. 

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. 

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. 

Inert Gas Dilution. Inert gas dilution involves the use of additives that produce large volumes of noncombustible gases when the polymer is decomposed. These gases dilute the oxygen supply to the flame or dilute the fuel concentration below the flammability limit. Metal hydroxides, metal carbonates, and some nitrogen-producing compounds function in this way as flame retardants (see Flame retardants, antimony and other inorganic compounds). 

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. 

Several appHcations have been found for bis(2-chloroethyl) vinylphosphonate as a comonomer imparting flame retardancy for textiles and specialty wood and paper appHcations. Its copolymerization characteristics have been reviewed (76,109). This monomer can be hydrolyzed by concentrated hydrochloric acid to vinylphosphonic acid, polymers of which have photoHthographic plate coating utiHty (see Lithography). It is also an intermediate for the preparation of an oligomeric vinylphosphonate textile finish, Akzo s Fyrol 76 [41222-33-7] (110). 

Laboratory experiments using rodents, or the use of gas analysis, tend to be confused by the dominant variable of fuel—air ratio as well as important effects of burning configuration, heat input, equipment design, and toxicity criteria used, ie, death vs incapacitation, time to death, lethal concentration, etc (154,155). Some comparisons of polyurethane foam combustion toxicity with and without phosphoms flame retardants show no consistent positive or negative effect. Moreover, data from small-scale tests have doubtful relevance to real fine ha2ards. 

It has already been mentioned in Chapter 5 that plasticisers are often replaced in part by extenders, materials which in themselves are not plasticisers but which can be tolerated up to a given concentration in a polymer-plasticiser system. Refinery oils and chlorinated waxes are widely used in PVC for this purpose with the prime aim of reducing cost although the chlorinated waxes may also be of use as flame retardants (q.v.). 

In Figure 3 where the BrPC and TPP are compared, the bromine concentration increases from left to right and the phosphorus concentration increases from right to left. The two curves intersect at 5 % bromine and 0.5 % phosphorus, indicating that phosphorus is ten times more effective as a flame retardant. At the extremes 1 % phosphorus is equivalent to about 9 + % bromine. 

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