Fire Behavior of Intumescent Polyurethane: Synergy, Morphology, and Kinetics
Intumescence is a versatile method for providing reaction to fire to materials. The incorporation of ammonium polyphosphate (APP) in polyurethane (PU) coating gives a highly efficient intumescent system. In this paper, it was shown that the addition of a
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Serge Bourbigot, Maryska Muller, and Sophie Duquesne
Abstract
Intumescence is a versatile method for providing reaction to fire to materials. The incorporation of ammonium polyphosphate (APP) in polyurethane (PU) coating gives a highly efficient intumescent system. In this paper, it was shown that the addition of a small amount of nanoparticles (magnesium oxide or MgO, silica or SiO2, and silsesquioxane) in PU/APP enhances dramatically the fire performance. As MgO leads to the highest performance, the mechanism of action was investigated in detail. The beneficial effect of MgO is due to chemical reactions between MgO- and APP-yielding products (i.e., magnesium phosphate evidenced by solid-state nuclear magnetic resonance (NMR) of 31P) able to reinforce the intumescent structure. This incorporation of MgO gives a high char yield and more stable char. It is shown by X-ray tomography that the char developed with and without MgO during the intumescence process has different properties leading to different char morphologies and char expansions (with MgO smaller cells constituting the intumescent char and higher expansion obtained). MgO provides higher efficiency to the intumescence barrier, and hence, fire performance is strongly improved compared to the intumescent system without nanoparticle. Kinetic analysis of the intumescent systems permits to model their thermal decomposition. The beneficial effect of MgO is shown comparing simulated decomposition curves of PU/APP and PU/APP-MgO in the case of cellulosic fire. Keywords
Intumescence Polyurethane Kinetics Morphology
Nomenclature
Greek Symbols
A E f(α) k t
α
Frequency factor (1/s) Activation energy (kJ/mol) Reaction model Kinetic constant (1/s) Time (s)
Degree of conversion (kg/kg)
62.1 S. Bourbigot (*) M. Muller S. Duquesne R2Fire group/UMET – UMR/CNRS 8207, Ecole Nationale Supe´rieure de Chimie de Lille (ENSCL), Avenue Dimitri Mendeleı¨ev – Baˆt. C7a, CS 90108, 59652 Villeneuve d’Ascq Cedex, France e-mail: [email protected]
Introduction
Polyurethanes (PUs) are unique polymeric materials with a wide range of physical and chemical properties. Their applications are numerous, but many of them require flameretardant properties, and thus PUs must be flame retarded
# Springer Science+Business Media Singapore 2017 K. Harada et al. (eds.), Fire Science and Technology 2015, DOI 10.1007/978-981-10-0376-9_62
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S. Bourbigot et al.
[1]. Intumescence is a versatile method for providing reaction to fire to materials: when heating beyond a critical temperature, the intumescent material begins to swell and then to expand forming an insulative coating limiting heat and mass transfer [2]. We may think intumescence is an old concept since the first comprehensive paper was published in the early 1970s, but a brief review of the literature shows that intumescence is still largely employed to make flame-retardant (FR) polymers and FR paints. Some recent developments are very promising for fire protection [3] and for flame retardancy [4].
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