Study on the effects of cellulose acetate butyrate microencapsulated APP and AlPi on the flame retardancy of cellulosic paper.

The high water solubility of Ammonium polyphosphate (APP) limits its application in paper. In this paper, APP coated with cellulose acetate butyrate (CAB) was synthesized, and the intrinsic flame-retardant paper was prepared in cooperation with aluminum diethyl hypophosphite (AlPi). It was found that the original APP was square with smooth surface. Its surface became rough after CAB microencapsulation, and the electronegativity and water solubility were significantly reduced. When the dosage of APP was 20 wt% with in-pulp addition, compared with Kraft/APP, the limiting oxygen index (LOI) value of Kraft/APP/10%AlPi increased from 26.8% to 27.3%, while that of Kraft/10wt%CAB@APP/10%AlPi increased to 31.2%. Meanwhile, the peak heat release rate (pHRR), total heat release (THR) and effective heat of combustion (EHC) of Kraft/APP/10%AlPi decreased by 73.2%, 5.2% and 51.1%, respectively; that of Kraft/CAB@APP/10%AlPi were further reduced by 78.6%, 10.4% and 54.6%, respectively. The ID/IG values of Kraft/APP, Kraft/APP/10%AlPi and Kraft/CAB@APP/10%AlPi were 1.54, 1.41 and 0.97, respectively, meaning that the residual char layer of Kraft/CAB@10%APP/AlPi contained the highest content of graphitic carbon. Therefore, the synergistic effect of APP and AlPi significantly improved the flame retardancy of the cellulosic paper, and the flame-retardant performance was further improved after APP was coated with CAB.