Resistance to fire of curable silicone/expandable graphite based coating: Effect of the catalyst

The fire performance of two curable-silicone based coatings containing 25% expandable graphite (EG) are evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. In this paper, the influence of the catalyst on the fire performance are investigated. Two organometallic titanium based- and tin based catalyst are used to make the curable silicone crosslink. When titanium based catalyst is used, the fire performance are higher and the mechanical properties of the char is better than that when tin is used as catalyst. To explain this surprising different fire behavior, the two residues after the furnace test were analyzed by X-ray photospectroscopy. It has been demonstrated that in the case of titanium based catalyst, the char is composed of graphite embedded by crosslinked silicone structure compare to linear silicone structure in the case of tin based catalyst. The two silicone resins were characterized by Fourier Transform Infrared spectroscopy, 29Si NMR, thermogravimetric analyses, EPMA (electron probe microanalyses). It was highlighted that the tin migrates into the surface during the crosslinking of the matrix leading to a low thermal stability and, thus, low fire performances. Whereas, when titanium based catalyst is used, it participates to the silicone network with the formation of Si–O–Ti bounds increasing the thermal stability of the matrix and so enhancing the fire performance of the silicone/EG based coating.