Design of Melamine Formaldehyde Resin Microencapsulated Ammonium Polyphosphate and Its Enhancement to the Flame Retardancy and Hydrophobicity of Cellulose Paper

At present, ammonium polyphosphate (APP) is one of the most popular and eco‐friendly flame retardants. However, the high solubility and electronegativity limit its application in cellulose paper. In this study, APP was microencapsulated with melamine formaldehyde resin (MFR) with varying core‐shell ratios (MFAPP) and incorporated into the pulp to fabricate fire‐resistant cellulosic paper. It was found that APP exhibited a rectangular morphology with a smooth surface. The surface roughness of MFAPP increased gradually as the MFR core‐shell ratio rose, and the electronegativity reduced significantly. When the core‐shell ratio increased from 0 to 10:1, its water contact angle (WCA) increased from 29.28° to 103.88°, and the solubility declined from 1.76 to 0.43 g/100 mL. For paper containing 25% MFAPP10:1 and 0.2% alkylketene dimer, the WCA increased from 108.49° to 115.41°, and the limiting oxygen index (LOI) enhanced from 31.2% to 36.5%. The char residue at 700°C increased from 11% to 17%, which consisted of crosslinked C–O–P/P–O–P, P–N–C/P–N–P, O–P═O/O═P–O–C. Therefore, MFAPP showed a significant enhancement in both the flame resistance and hydrophobic properties of cellulosic paper.