Preparation of Flame-Retardant Cellulose Paper via Spray Coating with Lignin, Phytic Acid, and Sodium Silicate

Abstract

A flame-retardant treatment for cellulosic paper was applied by spraying the paper with combinations of lignin, phytic acid, and sodium silicate. Lignin enhanced the flame retardancy in the condensed phase, while phytic acid provided dual-phase flame resistance. Sodium silicate further improved thermal stability by forming silica gel through its reaction with phytic acid. The limiting oxygen index increased from 16.8% to 22.0%, and in vertical flame tests, treated paper self-extinguished within 1.5 s, whereas untreated paper burned completely in 12.0 s. Thermogravimetric analysis revealed enhanced thermal stability, with treated paper retaining 36.5% residual char at 900 °C compared to 0% in untreated paper. Despite the relatively low coating coverage from the spray deposition method, the synergistic interaction of phytic acid, lignin, and silica gel effectively compensated by promoting dense char formation and thermal insulation. Fire retardancy was attributed to phytic acid-catalyzed lignin and silica composite formation in the char layer, enhancing structural stability and shielding efficiency. Raman spectroscopy confirmed improved graphitization (I_D/I_G = 1.20), while scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FT-IR) verified phosphorus and silica retention. This treatment showed potential for high-performance flame-retardant cellulose materials in packaging, construction, and other industries.