The role of microcrystalline muscovite to enhance thermal stability of boron-modified phenolic resin, structural and elemental studies in boron-modified phenolic resin/microcrystalline muscovite composite

A polymer matrix composite was prepared by incorporating microcrystalline muscovite fillers into a boron-modified phenolic resin. Thermogravimetric analyses indicated that microcrystalline muscovite significantly enhanced the thermal stability of boron-modified phenolic resin under air atmosphere. Then the composite was heated in a furnace. After heated, the homogeneous structure of the composite was converted into a layered structure with a ceramic shell on the surface. The layered structure was investigated by electron probe micro-analysis and energy dispersive spectroscopy. The elemental content and chemical binding state of the layered structure were investigated by X-ray photoelectron spectroscopy. On the surface, the reaction between SiO2 and Al2O3 occurred, thus microcrystalline muscovite fillers were transformed into mullite shell. The mullite shell could protect char from further oxidation at elevated temperatures. Therefore, a amount of reserved char could react with SiO2 to generate Si–C bond in the inner of the composite.