Effects of titanium dioxide on the flammability and char formation of water-based coatings containing intumescent flame retardants

Rutile-type TiO2 (r-TiO2) or anatase-type TiO2 (a-TiO2) in association with a conventional intumescent flame retardant system which contains ammonium polyphosphate/pentaerythritol/melamine (APP-PER-MEL) was introduced to silicone-acrylate coatings to improve the fire resistance. The effect of TiO2 on the fire-resistance and thermal properties of APP-PER-MEL coating has been investigated by using big panel method and thermogravimetry (TG). The limit of fire-resistance of the sample containing 30 phr rutile-type TiO2 (73 min) is much longer than that of the sample containing 30 phr anatase-type TiO2 (34 min). The morphology and structure of charring layers were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The relationship between charring process and melt flow rate (MFR) of silicone-acrylate was also discussed. It is suggested that MFR value can significantly affect the formation of char, and a moderate silicone-acrylate MFR is required to form good quality char.