User:LE BRAS Michel

FIRE PROTECTION OF POLYMERS USING INTUMESCENCE In recent years, concern has been widely expressed about the toxicity of the versatile and highly efficient halogenated flame retardants 1. The modern concept of flame retardancy implies that flame retardants should effectively reduce the probability of fire development and also its consequences, both on humans and on structures 2. Following this concept, halogen-based flame retardants become somewhat unsatisfactory since, on burning, they give rise to dense smoke and to acidic corrosive fumes. In the quest for halogen-free flame retardants much research is being centred on intumescent additives. These systems have provided efficient means for enhancing fire safety performance while presenting an environmentally friendlier approach than the traditional halogen systems. The intumescence process results from a combination of charring and foaming of the surface of the burning polymer, forming a shield that protects the underlying material from the action of the heat flux or flame 3. However, regardless the efficiency of flame-retarded systems, the additional cost of the end products still limits them largely to institutional sales 4. I

ntumescent systems interrupt the self-sustained combustion of a polymer matrix at its earliest stage, that is, the thermal degradation accompanied by the evolution of gaseous fuels 3. On heating, these systems swell to form foamed cellular charred layers on the surface of the burning material. This layer acts as a physical barrier to heat and mass transfer, protecting the underlying material from the heat flux and limiting the diffusion of both the combustible gases generated by pyrolysis that feed the flame and of the oxygen that sustains the burning process 5-8 (Figure 1). Hence, intumescent systems interfere with the action of all the necessary components for the fire triangle, namely heat, oxygen, and fuel. Please help me to introduce (propose the sheme figure, thanks Michel Figure 1.    Schematic action of an intumescent polymeric formulation (from reference 9).

An intumescent formulation generally contains three active components 3, 10: •	an acid source (precursor of acid species), such as ammonium phosphate, ammonium polyphosphate (APP), diammonium diphosphate or diammonium pentaborate. •	a carbonific compound, usually polyhydroxy compounds such as pentaerythritol (PER), xylitol, mannitol, sorbitol and polymers that naturally carbonise under heat or fire (polyamides, polycarbonates and polyurethane). •	a spumific (or blowing) compound that releases large quantities of non-combustible gases such as NH3 and CO2. Salts of phosphoric acid, melamine and guanidine have been used for this purpose.

Intumescent formulations should contain components that fulfil all the three functions. There are compounds that may function in more than one way, viz. ammonium polyphosphate (APP), which acts both as an acid source and as a blowing agent by producing the corresponding acid and by releasing NH3 on heating. The first stage of the accepted mechanism of intumescence involves the decomposition of the acid source to give a mineral acid. The mineral acid then reacts with the carbonific agent to form a carbonaceous layer (char). In the final step, the spumific compound decomposes generating gaseous products, which cause the char to swell, forming a foam-like insulating layer. Continued heating causes the decomposition of the intumescent material and loss of the foamed character 3, 11. The incorporation of active components into an additive system may lead to an additional effect12, an antagonistic effect13 or a synergistic effect 12-15. The use of synergistic agents has deserved increasing attention in flame retardancy. These agents produce more efficient systems while also making it possible to reduce the amount of flame retardants necessary to deliver efficient flame retardancy performance within the stringent regulations imposed 16. Clays and zeolites 13, 14 have been used as synergistic agents in intumescent ammonium polyphosphate (APP) and pentaerythritol (PER) formulations

References 1.	M.S. Cross, P.A Cusack, and P.R. Hornsby, Polym. Degrad. Stab., 2003, 79, 309. 2.	G. Camino in “Fire Retardancy of Polymers: The Use of Intumescence”, ed. M. Le Bras, G. Camino, S. Bourbigot and R. Delobel. The Royal Society of Chemistry, Cambridge, U.K., 1998, pp. v. 3.	M. Le Bras and S. Bourbigot, in “Fire Retardancy of Polymers: The Use of Intumescence”, eds. M. Le Bras, G. Camino, S. Bourbigot and R. Delobel. The Royal Society of Chemistry, Cambridge, U.K., 1998, pp. 64. 4.	M.S. Reisch, Chem. Eng. News, 1997, Feb. 24, 19. 5.	G. Berttelli, G. Camino, E. Marchetti, L. Costa, E. Casorati, and R. Locatelli, Polym. Degrad. Stab., 1989, 25, 277. 6.	S. Bourbigot, M. Le Bras, P. Breant, J.M. Tremillon, and R. Delobel, Fire Mater., 1996, 20, 145. 7.	S.-Y. Lu and I. Hamerton, Prog. Polym. Sci., 2002, 27, 1661. 8.	M. Le Bras, S. Bourbigot, E. Felix, F. Pouille, C. Siat, and M. Traisnel, Polymer, 2000, 41, 5283. 9.	X. Almeras, F. Dabrowski, M. Le Bras, R. Delobel, S. Bourbigot, G. Marosi, and P. Anna, Polym. Degrad. Stab., 2002, 77, 315. 10.	M. Elomaa, L. Sarvaranta, E. Mokkola, R. Kallonen, A. Zitting, C.A.P. Zevenhoven, and M. Hupa, Crit. Rev. Biochem. Molec. Biol., 1997, 27, 137. 11.	D.B. Dahm, Prog. Org. Coatings, 1996, 29, 61. 12.	M. Le Bras, S. Bourbigot, Y. Le Tallec, and J. Laureyns, Polym. Deg. Stab., 1997, 56, 11. 13.	M. Le Bras, and S. Bourbigot, Fire Mater., 1996, 20, 39. 14.	S. Bourbigot, M. Le Bras, R. Delobel, P. Bréant, and J.M. Tremillon, Polym Degrad Stab., 1996, 54, 275. 15.	S. Bourbigot, M. Le Bras, P. Breant, J.M. Tremillon, and R. Delobel, Fire Mater, 1996, 20, 145. 16.	J. Murphy, Reinforced Plastics, 2001, 45, 42.

AUTHORS: Luciana R. DE MOURA ESTEVÃO and Regina Sandra V. NASCIMENTO Instituto de Química – DQO, Universidade Federal do Rio de Janeiro, CT Bloco A, 6o andar, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ, CEP 21941-590, Brazil. Michel LE BRAS PERF, ENSCL, BP 108, F-59652 Villeneuve d’Ascq Cedex, France