Is titania acting as a synergist in intumescent fire retardant coatings designed for improving reaction to fire of wood?

Intumescent coatings based on ammonium polyphosphate (APP), are widely applied as passive fire protection. For flammable materials like wood, a rapid char expansion is needed to limit fuel gas release to the combustion zone and minimize reaction to fire. It is generally accepted that titanium dioxide (TiO) improves the fire performance of coatings and acts as a synergist. This study discusses the role of TiO in intumescent coatings by investigation of real-time measurement of char expansion during heating, rheology, thermal analysis, cone calorimetry, and chemical composition by X-ray diffraction and IR spectroscopy under different TiO loadings. Results show that TiO enhance the rate of char expansion despite increased complex viscosity of the molten coating matrix. Further, thermal decomposition and onset of intumescent reactions remained unchanged by increased TiO loading which results in a lower final char height. Altogether, TiO acts as an incombustible filler reducing char expansion and not fulfilling the definition of a synergist in intumescent coatings for improving reaction to fire of wooden products.