Intumescent fire retardant (IFR) coatings are nowadays considered as the most effective flame retardant (FR) treatment. Nevertheless, the principal compound in an IFR system, ammonium polyphosphate (APP), is highly sensitive to moisture and IFR coating effectiveness decreases quickly. The main objective of this study is to encapsulate APP in a hybrid silica-based membrane by sol-gel process using alkoxysilane tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) precursor. The morphology and structure of APP and microencapsulated ammonium polyphosphate (MAPP) were assessed by scanning electron microscopy and Fourier transforms infrared spectroscopy (FTIR). X-ray photoelectron spectroscopy (XPS) results revealed that APP was well encapsulated inside the polysiloxane shells. The thermal degradation of APP and MAPP was evaluated by thermogravimetric analysis. At 800 °C, the MAPP had higher char residue (70.49 wt%) than APP (3.06 wt%). The hydrophobicity of MAPP increased significantly with the water contact angles up to 98°, in comparison to 20° for APP.
Keywords: Flame retardants; ammonium polyphosphate; hydrophobicity; polysiloxane shell; thermal stability.