Surface modification of ammonium polyphosphate-diatomaceous earth composite filler and its application in flame-retardant paper

Ammonium polyphosphate (APP)-diatomaceous earth (DE) composite prepared by in situ polymerization was modified with silane coupling agent (KH550) and was applied as filler to prepare flame-retardant paper. Fourier transfer infrared, X-ray diffraction and thermogravimetry were used to characterize the structure and properties of the fillers, and limiting oxygen index (LOI), cone calorimeter and field-emission scanning electron microscope were used to investigate the flame-retardant properties of the filled paper. Results showed that chemical bonds occurred between APP-10 % DE filler and KH550, and APP-10 % DE filler had lower water solubility and better crystallization and thermostability after it was modified with KH550. Paper filled with modified APP-10 % DE filler had higher LOI value and lower heat release rate and mass loss at the same filler loading, and its charred residue collected after cone calorimeter test was more compact and strong. Surface modification of APP-10 % DE filler with KH550 improves its flame-retardant effect on paper.