Synthesis and Characterization of Sodium Lignosulfonate-Based Phosphorus-Containing Intermediates and Its Composite Si–P–C Silicone-Acrylic Emulsion Coating for Flame-Retardant Plywood

Abstract

Through the substitution reaction between 9,10dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and sodium lignosulfonate (LS), a novel phosphorus-containing sodium lignosulfonate (DAL) was successfully synthesized via the solvothermal method and used as a multifunctional flame retardant to prepare a novel silicone-acrylic emulsion (SAE) composite Si− P−C coating. The structure of DAL was determined by X-ray diffraction (XRD), attenuated total reflection infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (solid-state 13 C NMR and 31 P NMR). The results demonstrated that incorporating an appropriate dosage of DAL (0.9 g, 1.5 wt %) into SAE-based composite coatings enhances flame retardancy and reduces heat release and smoke production during burning. The peak heat release rate (p-HRR) decreases from 236.7 to 120.3 kW•m −2 , total smoke production (TSP) decreases by 71.1%, and the flame-retardant index increases from 1.00 to 4.58. Meanwhile, the coating is transformed into a dense and nonflammable vitreous polyphosphate barrier layer during the firing process to prevent heat or mass transfer. Furthermore, the pyrolysis kinetics identify that the 3D Z−L−T model governs the coatings' pyrolysis, and the appropriate DAL makes the pyrolysis E α climb from 300.98 to 331.30 kJ•mol −1 at 358−439 °C. Hence, this study presents a new synthesis method of multifunctional flame retardant DAL, studies the excellent properties and cross-linking mechanism of DAL-doped SAEcomposite Si−P−C coatings, and explores a halogen-free, low-carbon, and clean eco-technology strategy.