Rigid foams flame retardancy

PHZ Blends PHZ or its copolymer with a siloxane polymer, and/or elastomer bisazoformamide (foaming agent) gave semi-rigid, highly flame retardant foams Dieck and Quinn, 1977... 

Diester/Ether Diol of Tetrabromophthalic Anhydride. This material [77098-07-8] is prepared from TBPA in a two-step reaction. First TBPA reacts with diethylene glycol to produce an acid ester. The acid ester and propylene oxide then react to give a diester. The final product, a triol having two primary and one secondary hydroxyl group, is used exclusively as a flame retardant for rigid polyurethane foam (53,54). 

The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

Triphenyl phosphate [115-86-6] C gH O P, is a colorless soHd, mp 48—49°C, usually produced in the form of flakes or shipped in heated vessels as a hquid. An early appHcation was as a flame retardant for cellulose acetate safety film. It is also used in cellulose nitrate, various coatings, triacetate film and sheet, and rigid urethane foam. It has been used as a flame-retardant additive for engineering thermoplastics such as polyphenylene oxide—high impact polystyrene and ABS—polycarbonate blends. 

Phosphorus-Containing Diols and Polyols. The commercial development of several phosphoms-contaiuing diols occurred in response to the need to flame retard rigid urethane foam insulation used in transportation and constmction. There are a large number of references to phosphoms polyols (111) but only a few of these have been used commercially. 

One noteworthy neurotoxic response was demonstrated in laboratory pyrolysis studies using various types of phosphoms flame retardants in rigid urethane foam, but the response was traced to a highly specific interaction of trimethylolpropane polyols, producing a toxic bicycHc trimethylolpropane phosphate [1005-93-2] (152). Formulations with the same phosphoms flame retardants but other polyols avoided this neurotoxic effect completely. 

This reaction is catalyzed by hydrogen chloride and yields can be essentially quantitative when using either free phosphonic acid or its diesters. The flame retardant, Eyrol 6, produced by Akzo Chemicals, Inc. and used for rigid urethane foams, is synthesized as follows (24). 

In the 1990s novel polyols included polyether-esters, which provided good prerequisites for flame retardancy in rigid foams and polyether carbonates with improved hydrolysis stability. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

Tris(2-chloroethyl) phosphate is used as a flame retardant in plastics, especially in flexible foams used in automobiles and furniture, and in rigid foams used for building insulation. No data on occupational exposure levels were available. Tris(2-chloroethyl) phosphate has been detected in drinking-water, river water, sea water and sediments in various parts of the world (IARC, 1990). 

The newer open-cell foams, based on polyimides (qv), polybenzimidazoles, polypyrones, polyureas, polyphenylquinoxalines, and phenolic resins (qv), produce less smoke, are more fire resistant and can be used at higher temperatures. These materials are more expensive and used only for special applications including aircraft and marine vessels. Rigid poly (vinyl chloride) (PVC) foams are available in small quantities mainly for use in composite panels and piping applications (see Flame retardants Hrat-rrststantpot.ymf.rs). 

Witte, A. and Krieger, W., (Clariant GmbH), Halogen-free, pentane-blown, flame-retardant rigid polyurethane foam and a process for its production, U.S. Patent, 2001 6 593 385. 

With regard to reactive flame-retardants, two routes can be followed to improve thermal stability and fire behavior of PU foams use of brominated or phosphorus-containing polyol or, for rigid foams, the introduction inside polymer backbone of more thermally stable structure than urethane, mainly isocyanurate, but also uretidione rings or carbodiimide.19... 

Also phosphorus- and nitrogen-containing polyols are shown to be effective in flame retardancy of PU foams24 such as polyols based on phosphonic acid ester or obtained by partial or full substitution of methylol groups of tetrakis(hydroxymethyl)phosphonium chloride with amine several examples of such polyols were reported by Levchik and Weil.15 Rigid PU foam modified with these polyols showed improved oxygen index values moreover better results were achieved with higher functionality polyols. 

Sivriev, C. Zabski, L. Flame retarded rigid polyurethane foams by chemical modification with phosphorus-and nitrogen-containing polyols. Fur. Polym. J. 1994, 30, 509-514. 

Shi, L Li, ZM Xie, BH. et al. Flame retardancy of different-sized expandable graphite particles for high-density rigid polyurethane foams. Polym. Int. 2006, 8, 862-871. 

Bian, XC Tang, JH Li, ZM. et al. Dependence of flame-retardant properties on density of expandable graphite filled rigid polyurethane foam. J. Appl. Polym. Sci. 2007, 104, 3347-3355. 

Bonsignore, P.V. Levendusky, T.L. Alumina trihydrate as a flame retardant and smoke suppressive filler in rigid high density polyurethane foams. J. Fire Flammability 1977, 8, 95-114. 

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