Polyphosphate retardants

A series of compounded flame retardants, based on finely divided insoluble ammonium polyphosphate together with char-forming nitrogenous resins, has been developed for thermoplastics (52—58). These compounds are particularly useful as iatumescent flame-retardant additives for polyolefins, ethylene—vinyl acetate, and urethane elastomers (qv). The char-forming resin can be, for example, an ethyleneurea—formaldehyde condensation polymer, a hydroxyethylisocyanurate, or a piperazine—triazine resin. 

Related esters of this alcohol are disclosed by Ak2o as useflil flame retardants for polypropylene, particularly in combination with ammonium polyphosphate (90). 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

While melamine is widely used in flexible foams as a fire-retardant, trichlorphenyl phosphate has been the preferred agent for use in rigid foams. However, the introduction of specifications stipulating halogen-free additives has led to a search for alternatives such as halogen-free phosphorus esters, red phosphorus and ammonium polyphosphate. 

Polyphosphates are also an important class of organophosphorus polymers. In addition to their flame-retardant characteristics, they possess attractive plasticizing properties and can be used as polymeric additives to other polymers [123-128]. In general, polyphosphates can be prepared by interfacial [119,129], melt [130], or solution polycondensation [131,132a,b]. Kricheldorf and Koziel [133] prepared polyphosphates from silylated bisphenols. 

The experimental weight loss in the first and second step (4.0 and 4.5% respectively) is in agreement with that corresponding to condensation to pyrophosphate (4.0%) and polyphosphate (4.2X, n 1). Furthermore, the IR spectra of melamine phosphate and of the residues at 300 and 330 C (Figure 14 spectra A, B and C respectively) show that besides the typical bands of phosphate salts (950-1300 cm-1) which are present in the three spectra, a new absorption due to P-O-P bonds (ca. 890 cm-1) appears in the spectra of the residues. The absorptions due to melamine salt structures (e.g. 780-790 and 1450-1750 cm ) are closely similar in the three spectra of Figure 14. Fire retardants based on melamine pyrophosphate and polyphosphate are reported in the literature 51 as well as methods for preparation of these salts (25-... 

The flame retardant mechanism for phosphorus compounds varies with the phosphorus compound, the polymer and the combustion conditions (5). For example, some phosphorus compounds decompose to phosphoric acids and polyphosphates. A viscous surface glass forms and shields the polymer from the flame. If the phosphoric acid reacts with the polymer, e.g., to form a phosphate ester with subsequent decomposition, a dense surface char may form. These coatings serve as a physical barrier to heat transfer from the flame to the polymer and to diffusion of gases in other words, fuel (the polymer) is isolated from heat and oxygen. 

M. LeBras., Mineral fillers in intumescent fire retardant formulations - Criteria for the choice of a natural clay filler for the ammonium polyphosphate/pentaeythritol/polypropylene system, Fire and Materials, vol. 20, pp. 39-49,1996. 

The aim was to assess the feasibility of substitution with less hazardous flame retardants. They selected red phosphorus, ammonium polyphosphate and aluminium trihydroxide as the least environmentally problematic alternatives. Red phosphorus can technically be used in a variety of polymers to meet even the toughest fire safety standards, although it may network forall applications. ... 

The stabilizer may consist of carboxylic acids and phosphorus-containing organic acid salts such as hexametaphosphates, polyphosphates and phosphonates. The mechanism of action of the stabilizer admixture is thought to be related to the inhibition of CSH and CH nucleation. It is claimed that the nucleation process is controlled more comprehensively than that obtained with conventional retarders [10], Cement hydration is arrested by the admixture acting on all phases of cement hydration including the C3A fraction. The claim is... 

Significant changes in the distribution of the products of pyrolysis were observed with the flame retardants mentioned above. This indicates that the polyphosphoric residue of ammonium polyphosphate modifies the mechanisms of the thermal decomposition of these polymers. 

Many thousands of phosphorus compounds have been described as having flame-retardant utility. The compounds demonstrating commercial utility arc much more limited in number. They include inorganic phosphorus compounds [red phosphorus, ammonium phosphates. insoluble ammonium polyphosphate, phosphoric acid-bascd systems for cellulosics). additive organic phosphorus flstme retardants... 

The crystallization of lactose in frozen concentrated milk has been associated with a denaluration of casein which ultimately appears as a gel structure in the thawed product. Gelation in frozen milk can be retarded by enzymic hydrolysis of pan ol the lactose before freezing or by addilion of a polyphosphate salt. 

The effect of cations on the rate of hydrolysis of cycio-tri- and cvc/o-tetra-phosphates has also been studied.260 Alkali metal cations retarded the hydrolysis of both cyclo-phosphates in acidic solution but accelerated the reaction in basic solution. The catalytic activity followed the sequence Li+ > Na+> K+. Mg11, Ca11 and Ni11 retarded the hydrolysis of the cyclo-phosphates in the pH range 1.0-2.0 or 1.0-2.7, but accelerated the reaction at pH>3. Catalysis by Cu11 is observed above pH 2, while Alni has a marked catalytic effect at pH 1 and 2. A variety of other papers have appeared dealing with metal ion-promoted hydrolysis of polyphosphates.261-264 However, the mechanistic details of these reactions remain unclear and the catalytically active complexes remain undefined. 

Fire-retardant chemicals used by the commercial wood-treating industry are limited almost exclusively to mono- and diammonium phosphate, ammonium sulfate, borax, boric acid, and zinc chloride (4,8). It is believed that some use is also made of the liquid ammonium polyphosphates (9). Some additives such as sodium dichromate as a corrosion inhibitor are also used. Aqueous fire-retardant treatment solutions are usually formulated from two or more of these chemicals to obtain the desired properties and cost advantages For leach-resistant type treatments, the literature shows that some or all of the following are used urea, melamine, dicyandiamide, phosphoric acid, and formaldehyde (10-12) ... 

At the U.S. Forest Products Laboratory, many of the research programs involve fire-retardant-treated wood. This has included extensive basic study of pyrolysis and combustion reactions of wood and its components and the effects of chemical additives on these reactions (15,24-26,28,29,66). A cooperative study (9) with the Division of Chemical Development of the Tennessee Valley Authority, showed the effectiveness of liquid ammonium polyphosphate fertilizers as fire retardants for wood. The commercial use of these products, made from electric furnace superphosphoric acid, has been shown to be economically feasible. Work has been completed by Schaffer (33) on the rate of fire penetration in wood treated with different types of chemicals. Some results of this study are reported elsewhere in this paper. 

J. Zhang, A.R. Horrocks, and M.E. Hall, Flammability of polyacrylonitrile and its copolymers. III. The flame retardant mechanism of ammonium polyphosphate. Fire Mater., 18, 307-312 (1994). 

Ammonium polyphosphates, on the other hand, are relatively water insoluble, nonmelting solids with very high phosphorus contents (up to about 30%). There are several crystalline forms and the commercial products differ in molecular weights, particle sizes, solubilities, and so on. They are also widely used as components of intumescent paints and mastics where they function as the acid catalyst (i.e., by producing phosphoric acid upon decomposition). They are used in paints with pentaerythritol (or with a derivative of pentaerythritol) as the carbonific component and melamine as the spumific compound.22 In addition, the intumescent formulations typically contain resinous binders, pigments, and other fillers. These systems are highly efficient in flame-retarding hydroxy-lated polymers. 

Pentaerythritol phosphate has an excellent char-forming ability owing to the presence of the pentaerythritol structure. The bis-melamine salt of the bis acid phosphate of pentaerythritol is also available commercially. This is a high melting solid that acts as an intumescent flame-retardant additive for polyolefins. Synergistic combinations with ammonium polyphosphates have also been developed primarily for urethane elastomers. Self-condensation of tris(2-chloroethyl) phosphate produces oligomeric 2-chloroethylphosphate. It has a low volatility, and is useful in resin-impregnated air filters, in flexible urethane foams and in other structural foams.11... 

Cyclic oligomeric phosphonates with the varying degrees of structural complexity (Structure 5.4) are also available in the market.25 They are widely used as flame-retardant finishes for polyester fabrics. After the phosphonate is applied from an aqueous solution, the fabric is heated to swell and soften the fibers, thus allowing the phosphonate to be absorbed and strongly held. It is also a useful retardant in polyester resins, polyurethanes, polycarbonates, polyamide-6, and in textile back coatings. A bicyclic pentaerythritol phosphate has been more recently introduced into the market for use in thermosets as well as for polyolefins (preferably, in combination with melamine or ammonium polyphosphate)... 

Melamine polyphosphate Melapur 200 Ciba (Switzerland) PA66/glass fibers, epoxies, synergistic blends with other flame retardants... 

Camino, G., Costa, L., and Trossarelli, L. 1985. Study of the mechanism of intumescence in fire retardant polymers Part V—Mechanism of formation of gaseous products in the thermal degradation of ammonium polyphosphate. Polym. Deg. Stab. 12 203-211. 

Montaudo, G., Scamporrino, E., and Vitalini, D. 1983. Intumescent flame retardants for polymers. II. The polypropylene-ammonium polyphosphate-polyurea system. J. Polym. Sci., Polym. Chem. Ed. 21 3361-3371. 

Wang, Z. Y., Feng, Z.Q., Liu, Y., and Wang, Q. 2007. Flame retarding glass fibers reinforced polyamide 6 by melamine polyphosphate/polyurethane-encapsulated solid acid. J. Appl. Polym. Sci. 105 3317-3322. 

Braun, U., Schartel, B., Fichera, M.A., and Jaeger, C. 2007. Flame retardancy mechanisms of aluminium phosphinate in combination with melamine polyphosphate and zinc borate in glass-fibre reinforced polyamide 6,6. Polym. Deg. Stab. 92 1528-1545. 

Davies, P.J., Horrocks, A.R., and Alderson, A. 2005. The sensitisation of thermal decomposition of ammonium polyphosphate by selected metal ions and their potential for improved cotton fabric flame retardancy. Polym. Deg. Stab. 88 114-122. 

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