Preparation of ethyl cellulose microencapsulated ammonium polyphosphate and its application in flame retardant cellulose paper

Ammonium polyphosphate (APP) was microencapsulated with ethyl cellulose (EC) and mixed with cellulose fibers in water to form the flame-retardant paper. It was found that the original APP was quadrate with smooth surface. In contrast, its surface became rough after the EC microencapsulation, and its electronegativity and solubility were significantly decreased. Specifically, its water contact angle increased from 26.54° to 101.52°. Compared with the Kraft/APP, the limiting oxygen index (LOI) value of the Kraft/APP@EC increased from 28.7% to 31.2% at the dosage of the flame retardant of 30%, and the tensile index changed from 56.43 N·m/g to 51.98 N·m/g. Meanwhile, the thermal decomposition process changed from two stages to three stages, during which apparent decreases were observed in the peak heat release rate, the effective heat of combustion and total heat release. Moreover, the residual char weight after the paper combustion increased from 22.09% to 31.81%, the ID/IG decreased from 2.01 to 1.74, and more cross-linking bonds of OP-O-C, P-O-C, and P-O-P generated in the char residue, which proved that a denser char layer was formed. Therefore, APP@EC apparently improved the fire retardancy of the cellulose paper while the tensile strength was basically maintained.