A char stratification approach to characterization and quantitative thermal insulation performance of hydrocarbon intumescent coatings

To protect structural steel in the event of a hydrocarbon fire, epoxy-based intumescent coatings, which expand to form a multicellular char layer, are increasingly used. Consequently, to improve formulations and understand the performance of such coatings, it is of great industrial and scientific interest to establish relationships between the char properties and the critical heating times of coated steel plates. In this work, a so-called Stratification Parameter (SP) that combines the relative expansions and insulation efficiencies of individual char layers (termed the sponge-like, the macroporous, and the compact phase, respectively), is introduced to characterize the properties of the multilayered intumescent coating char. An approximate linear relationship was revealed between the SP of the char and the fire-resistance performance (i.e., critical times to 400 and 550 degrees C) of the intumescent coating. Furthermore, owing to the mapped-out exponential relationship between the dynamic viscosity minimum and the char appearance, it was discovered that the SP of the char can be effectively used to point out the required dynamic viscosity change of an intumescent coating to form a given char. Finally, results of thermogravimetric analyses suggest that constraining the coating mass loss during char degradation (to less than 28 wt% for the coatings of the present work) may prevent the formation of the less efficient sponge-like phase. The stratification methodology developed can be used to estimate expected thermal insulation properties of non-uniform hydrocarbon intumescent coating chars.