Intumescent flame retardants

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. 

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... 

FIGURE 6.6 Phosphorus-nitrogen intumescent flame retardant. (From Gao, F. et al., Polym. Deg. Stab., 91, 1295, 2006.)... 

In this chapter, we have discussed recent developments of intumescent flame-retarded materials in terms of reaction and resistance to fire. Research work in intumescence is very active. New molecules (commercial molecules and new concepts) have appeared. Nanocomposites are a relatively new technology in the held of flame retardancy. This technology gives the best results combined with conventional FRs and leads to synergistic effects with intumescent systems. Very promising developments in the synergy aspects are then expected and efforts should be continued in this way. 

Bourbigot, S., Le Bras, M., and Delobel, R. 1995. Fire degradation of an intumescent flame retardant... 

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. 

Chen, Y.H., Liu, Y., Wang, Q., Yin, H., Nico, A., and Kierkels, R. 2003. Performance of intumescent flame retardant master batch synthesized through twin-screw reactively extruding technology Effect of component ratio. Polym. Deg. Stab. 81 215-224. 

Liu, Y. and Wang, Q. 2008. Reactive extrusion to synthesize intumescent flame retardant with a solid acid as catalyst and the flame retardancy of the products in polypropylene. J. Appl. Polym. Sci. 107 14—20. 

Gao, F., Tong, L., and Fang, Z. 2006. Effect of a novel phosphorous-nitrogen containing intumescent flame retardant on the fire retardancy and the thermal behaviour of poly(butylene terephthalate). Polym. Deg. Stab. 91 1295-1299. 

Wang, D.L., Liu, Y., Wang, D.Y., Zhao, C.X., Mou, Y.R., and Wang, Y.Z. 2007. A novel intumescent flame-retardant system containing metal chelates for polyvinyl alcohol. Polym. Deg. Stab. 92 1555-1564. 

Tang, Y., Hu, Y., Wang, Y.S., Gui, Z., Chen Z., and Fan, W. 2003. Intumescent flame retardant-montmorillonite synergism in polypropylene-layered silicate nanocomposites. Polym. Inter. 52 1396-1400. 

The flammability properties of an intumescent fire retardant PP formulation with added MH has been investigated.65 The results show that the intumescent flame-retardant ammonium polyphosphate-filled PP has superior flammability properties but gives higher CO and smoke evolution. The addition of MH was found to reduce smoke density and CO emissions, in addition to giving superior fire resistance. PP filled with ammonium polyphosphate, pentaerythritol, and melamine has given improved flammability performance, without reducing its mechanical properties. 

In an attempt to provide compatibility between the FR and polymer matrix, Wang et al. reported recently on a novel microencapsulated intumescent system containing 4A zeolite as a potential flame retardant for natural rubber (NR).61 The flame-retardant properties of NR composites loaded with different amounts of intumescent flame retardant (IFR), IFR-4A zeolite, and microencapsulated intumescent flame retardant (MIFR)-4A zeolite agents were studied and compared. The LOI data demonstrate that the NR composite filled with 50phr of MIFR-4A zeolite agent and 50phr of IFR-4A zeolite shows better FR properties as compared to NR and 50phr of IFR-filled systems. 

Wang, J. and Chen, Y., Effect of microencapsulation and 4A zeolite on the properties of intumescent flame-retardant natural rubber composites, J. Fire Sci. 2008, 26, 153. 

More recently, Bourbigot et al. reported the preparation a neutralized intumescent flame retardant (NIFR) by reacting pentaerythritol, phosphoryl trichloride, and melamine.71 The addition of a small amount of the anhydrous zinc borate (2wt.% at the expense of NIFR) in PP leads to a... 

Myers et al. reported that partially dehydrated APB is an effective intumescent flame retardant in thermoplastic polyurethane.77 APB at 5-10 phr loading in TPU can provide 7- to 10-fold improvement in burn-through test. It is believed that in the temperature range of 230°C-450°C, the dehydrated APB and its released boric oxide/boric acid may react with the diol and/or isocyanate, the decomposed fragments from TPU, to produce a highly cross-linked borate ester and possibly boron-nitrogen polymer that can reduce the rate of formation of flammable volatiles and result in intumescent char. 

Myers, R.E., Dicksons, E.D., Licursi, E., and Evans, R. 1985. Ammonium pentaborate An intumescent flame retardant for thermoplastic polyurethanes, J. Fire Sci., November/December, 3(6), 432-449. 

Anna, P., Marosi, Gy., Csontos, I., Bourbigot, S., Le Bras, M., and Delobel, R. 2001. Influence of modified rheology on the efficiency of intumescent flame retardant systems. Polymer Degradation and Stability 74(3) 423M-26. 

H. Ma, L. Tong, Z. Xu, and Z. Fang, Functionalizing carbon nanotubes by grafting on intumescent flame retardant Nano-composite synthesis, morphology, rheology, and flammability, Adv. Funct. Mater., 2008, 18 414 421. 

S. Nie, Y. Hu, L. Song, S. He, and D. Yang, Study on a novel and efficient flame retardant synergist nanoporous nickel phosphate VSB-1 with intumescent flame retardants in polypropylene, Polym. Adv. Technol., 2008, 19 489 195. 

Marosi, G., Bertalan, G., Balogh, I., Tohl, A., Anna, P., and Szentirmay, K. 1996. Silicone containing intumescent flame retardant systems for polyolefins. In Flame Retardants, ed. Grayson, S. London, U.K. Interscience Commun. Ltd. Publ., p. 115. 

Marosi, G., Keszei, S., Matko, S., and Bertalan, G. 2006. Effect of interfaces in metal hydroxide-type and intumescent flame retarded nanocomposites. In Fire and Polymers TV Materials and Concepts for Hazard Prevention, Vol. 922, eds. Wilkie, C. and Nelson, G. Washington, DC ACS, pp. 117-30. 

Lewin, M. and Endo, M. 2003. Catalysis of intumescent flame retardancy of polypropylene by metallic compounds. Polymers for Advanced Technologies 14 3-11. 

Modesti, M. Lorenzetti, A. Simioni, F. Camino G. Expandable graphite as an intumescent flame retardant in polyisocyanurate-polyurethane foams. Polym. Degrad. Stab. 2002, 77, 195-202. 

Wang, B., Wang, X., Shi, Y. et al. 2012. Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer. Radiation Physics and Chemistry 81 308-315. 

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