Numerical Study of the Decomposition Mechanism of Intumescent Coating

Abstract

Intumescent coating represents an efficient way to increase the fire resistance of construction materials. During its degradation, intumescent materials expand and form a char layer that acts as an efficient thermal shield between the heat source and the materials.Encouraging predictions of thermal degradation and expansion of intumescent coatings in experimental conditions representative of fires were reported in the last decade by considering models involving conservation equations for mass and energy for the intumescent material coupled to approximate sub-models for describing the swelling mechanism. These degradation models used generally simplified decomposition mechanisms involving one, two or three reactions. In addition, the dehydration process that occurs in the early stage is usually ignored.The objective of this article is to assess the relevance of several multi-step reaction mechanisms to describe the mass loss and the mass loss rate of ICWB, an intumescent coating, in TGA at different heating rates in inert atmosphere. The kinetic parameters of the different reactions were optimized using the Shuffled complex evolution (SCE) technique.Results demonstrate that the drying process, which occurs up to 130°C for ICWB, cannot be neglected since the associated mass loss represents about 5%. In addition, the drying process can be described by a single reaction. The use of a simple mechanism, based on one or two reactions to model the degradation of dry intumescent coating, is insufficient and leads to significant discrepancies on both mass loss and mass loss rate. Considering three reactions improve considerably the predictions but discrepancies are still observed for temperature higher than about 420°C. Model results show that a four-step is required to capture accurately all the details of the degradation of dry intumescent coating under inert atmosphere. Simulations were run under air, showing that an additional reaction for oxidation is required to extend the four-step reaction mechanism for oxidative atmosphere, leading to a five-step reaction mechanism.