Pyrolysis of Precious Chinese Xuan Paper Containing Ammonium Phytate as a Flame Retardant

Xuan paper with outstanding cultural and artistic values is one of the most precious Chinese handmade papers and is widely used in traditional calligraphy and painting. However, the highly combustible cellulosic raw materials of Xuan paper present potential fire hazards. Ammonium phytate (AP) originating from biosourced phytic acid has been used for the flame-retardant treatment of Chinese Xuan paper by facile spray coating. The limiting oxygen index value of the treated Xuan paper increased to higher than 40%, demonstrating that the flammability of Xuan paper was greatly reduced by this treatment. The excellent flame retardancy afforded by this treatment was confirmed by cone calorimetry. TGA was used to demonstrate that the presence of AP changed the thermal decomposition process to promote char formation during the degradation of Xuan paper. The flame-retardant mode of action of phytate-coated Xuan paper was investigated using TG-FTIR, SEM, and XPS spectra. A P-N cooperative effect was proposed to account for both the condensed phase and gas-phase flame-retardant actions. The phosphorus component promotes char formation in the condensed phase, while the nitrogen component releases inert species to dilute the fuel load in the gas phase. The ink-wetting property of the coated Xuan paper was influenced negligibly by the coating process. The development of fire-resistant Xuan paper using ecofriendly flame retardants through simple and convenient spray coating has been demonstrated.