Intumescent additives

Green White 20 No additional intumescent seals need to be... 

A newer self-intumescent phosphoric acid salt has been introduced by Albright WHson as Amgard EDAP, mainly as an additive for polyolefins. It is a finely divided soHd, mp 250°C, having a reported phosphoms content of 63 wt % as H PO. It appears to be the ethylenediamine salt of phosphoric acid (1 1). Unlike ammonium polyphosphate, it does not require a char-forming synergist (62). 

E. Termine and K. G. Taylor, "A New Intumescent Flame Retardant Additive for Thermoplastics and Thermosets," n Additive Approaches to PolymerModification, SPE RETEC Conference Papers, Toronto, Ontario, Canada, Sept. 1989. 

Intumescent additives. React with the polymer substrate to produce a char layer which forms an effective barrier between heat source and oxygen and... 

Carbonaceous char barriers may be formed by the normal mode of polymer burning, and besides representing a reduction in the amount of material burned, the char may act as a fire barrier. The relationship of char yield, structure, and flame resistance was quantified by Van Krevelen (5) some years ago. For polymers with low char-forming tendencies, such as polyolefins, one approach to obtain adequate char is to add a char-forming additive. Such additives generally bear a resemblance to intumescent coating ingredients (6, 7). 

Melamine and its salts are widely used in formulations of fire retardant additives, particularly of the intumescent type (4-71. The role played by melamine structures in these additives is however not yet understood. The thermal behaviour is of paramount importance in studies of the fire retardance mechanism. It is known that melamine undergoes progressive condensation on heating with elimination of ammonia and formation of polymeric products named "melam", "melem", "melon" (8.91. The following schematic reaction is reported in the literature (10-121 ... 

Passive protection can be used to increase the time to structural failure. For example, intumescent mastic coatings of less than 1 inch thickness have been shown to provide up to 4 hours of fire resistance when applied to steel columns. Cementitious materials have been shown to provide 1-4 hours fire resistance for thicknesses of 2.5-6.3 cm (1-2.5 in). For additional information on passive fire protection, see Chapter 7. 

Intumescent fireproofing— A passive material that undergoes a chemical reaction when exposed to high heat or direct flame impingement that protects against the heat from a fire without additional intervention. 

A successful factory-applied intumescent paint has been developed by the Celotex Corp. for application to acoustic board. In addition, a satisfactory package paint, Due-Tex flame-retardant paint, is available for application over old fiberboard installations, wood, etc. This product bears an Underwriters Laboratories label. 

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. 

A series of compounded flame retardants, based on finally divided insoluble ammonium phosphate together with char-forming nitrogenous resins, has been developed for thermoplastics.23 These compounds are particularly useful as intumescent flame-retardant additives for polyolefins, ethylene-vinyl acetate, and urethane elastomers. The char-forming resin can be, for example, an ethyle-neurea-formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine-triazine resin. Commercial leach-resistant flame-retardant treatments for wood have also been developed based on a reaction product of phosphoric acid with urea-formaldehyde and dicyandiamide resins. 

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... 

The use of polyols such as pentaerythritol, mannitol, or sorbitol as classical char formers in intumescent formulations for thermoplastics is associated with migration and water solubility problems. Moreover, these additives are often not compatible with the polymeric matrix and the mechanical properties of the formulations are then very poor. Those problems can be solved (at least partially) by the synthesis of additives that concentrate the three intumescent FR elements in one material, as suggested by the pioneering work of Halpern.29 b-MAP (4) (melamine salt of 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]-undecane-3,9-dioxide) and Melabis (5) (melamine salt of bis(l-oxo-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octan-4-ylmethanol)phosphate) were synthesized from pentaerythritol (2), melamine (3), and phosphoryl trichloride (1) (Figure 6.4). They were found to be more effective to fire retard PP than standard halogen-antimony FR. 

Delobel, R., Le Bras, M., Ouassou, N., and Alistiqsa, F. 1990. Thermal behaviors of ammonium polyphosphate-pentaerythritol and ammonium pyrophosphate-pentaerythritol intumescent additives in polypropylene formulations. J. Fire Sci. 8 85-92. 

Le Bras, M., Bourbigot, S., Delporte, C., Siat C., and Le Tallec, Y. 1996. New intumescent formulations of fire retardant polypropylene Discussion about the free radicals mechanism of the formation of the carbonaceous protective material during the thermo-oxidative treatment of the additives. Fire Mater. 20 191-203. 

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