Preparation of Bio-Based Flame-Retardant Kraft Paper by Chelating Self- Assembly and Its Flame-Retardant Mechanism

Improving the flame retardancy of lignocellulose fibers materials and reducing the use of petrochemical nitrogen and phosphorus flame retardants have important research value in expanding wood- based materials and improving the environmental protection performance of modified wood materials. Layer- by- layer chelation selfassembly was prepared on the surface of kraft paper to form a flame-retardant coating, combined with the form of inorganic salt Ca2+ chelation. The flame- retardant and mechanical properties of kraft paper before and after flameretardant treatment show that the treated kraft paper K-7 forms a carbon layer with a length of only 29.5 mm during the vertical burning test. Compared with the Control, the limiting oxygen index(LOI)of K-7 is increased by 17.9% and the total heat release is reduced by 15.4 kJ/g. Besides, the stiffness and tearing performance of kraft paper after flame retardant treatment were improved. The analysis of functional groups and micro morphology show that the flame retardant coating on the surface of K-7 contains -NH2 group. In addition, the strength of the characteristic peaks of P=O and -HPO3 contained in the coating change. At the same time, a flame retardant layer with high graphitization degree having P, N, Ca and other elements was formed after combustion, including P = O, P2O72- and other characteristic functional groups. Phytic acid, chitosan and Ca2+ formed a layered bio-based flame retardant layer on the surface of kraft paper through electrostatic adsorption and chelation. When heated, the flame- retardant layer exerted its flame- retardant effect through the combination of gas- phase and solid- phase flame- retardant, which effectively imparts flame- retardant properties to lignocellulosic materials and avoids dependence on petrochemicalbased flame retardants. © 2022, Editorial Board of Polymer Materials Science & Engineering. All right reserved.