Resistance to fire of intumescent silicone based coating: The role of organoclay

The fire performance of a curable-silicone based coatings containing expandable graphite (EG) and an organoclay is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. It is shown that the use of organoclay allows achieving better performance. The influence of the clay as additional filler is investigated on the fire performance and on the mechanical properties of the char. It is shown that the clay increases significantly the mechanical properties of the char and hence, the fire performance of the silicone based coating. In a next part, the silicone/clay material was characterized by electron microscopy, wide-angle X-ray scattering and solid state 29Si nuclear magnetic resonance (NMR). It evidences the nanodispersion of the clay into the silicone matrix and two main interactions: (i) intercalation of some silicate layers and (ii) chemical reactions between the hydroxyl groups of the clay and the silicone matrix. Finally, X-ray fluorescence of the residue after fire testing shows the organoclay is present uniformly throughout the thickness of the char, due to the previous interaction, and hence increasing the cohesion of the char.