Construction of Waterborne Polyurethane Composites via Phytate-Chitosan-Modied Boron Nitride and DOPO Derivative Synergy for Flame Retardancy

Hexagonal boron nitride (h-BN) is inherently hydrophobic and lacks active functional groups on its surface. In this study, we modified h-BN with phytic acid and chitosan to create BN@PA-CS particles. These particles integrated into an aqueous polyurethane (WPU) matrix, along with the DIDOPO flame retardant, to form the WPU/BN@PA-CS/DIDOPO nanocomposite. We investigated the composite’s flame retardancy, thermal stability, rheological properties, and mechanical properties. The results demonstrated that BN@PA-CS and DIDOPO exhibit a significant synergistic effect in both gas and condensed phases for flame retardancy. When the mass fractions of BN@PA-CS and DIDOPO were 2 wt% and 7 wt% relative to WPU matrix, the optimal formulation WPU/BN@PA-CS2/DIDOPO7 achieved a UL-94 V-0 rating and increased the limiting oxygen index (LOI) to 24.2%. Additionally, the peak heat release rate (pHRR) and total heat release (THR) decreased by 49.3% and 66.1%, respectively, compared to pure WPU. Rheological and mechanical measurements indicated that the formulation WPU/BN@PA-CS2/DIDOPO7 exhibited a compatible combination of tensile stiffness, ductile toughness, and melt flow behaviour relative to other composite groups.Therefore, the DIDOPO/BN@PA-CS composite strategy provides experimental observations and mechanistic speculation for developing high-performance flame-retardant polyurethane composites, optimizing synergistic effects at specific ratios to enhance flame retardancy and mechanical properties. Graphical