Research on flame-retardant paper prepared by the method of in-pulp addition of ammonium polyphosphate

Abstract

At present, the production of flame-retardant paper usually uses the impregnation method of phos-phorus-nitrogen flame retardants in paper. There are few reports on the application of an in-pulp addition method. In this paper, the solubility of ammonium polyphosphate (APP) and its effect on flame-retardant paper were investigated for use in an in-pulp addition method. It was found that APP particles were square, with an average particle size of 21.88 μm. The particle size decreased significantly after immersion in water at 25°C for 24 h. Furthermore, most of the APPs were dissolved after immersion in water at 90°C for 0.5 h, and the residuals agglomerated and their shape turned into an amorphous form. The APP possessed strong electronegativity and could partially ionize in water. The solubility of APP was 0.18 g/100 mL water at 25°C and increased quickly when the temperature was higher than 30°C. Therefore, APP should be added to the pulp at temperatures below 30°C. The tensile strength of the paper initially increased with the addition of APP, and it reached the maximum value when the APP content was 10% and then gradually decreased. The limiting oxygen index (LOI) value of the paper was 28.7% when the added amount of APP was 30% and cationic polyacrylamide (CPAM) was 0.08%, reaching the flame-retardant level.