Waterborne polyurethane composites flame retardancy based on the bi-DOPO derivatives and dangling poly(dimethylsiloxane) chains

The composites phosphorus-silicon flame retardant was simultaneously employed to modify waterborne polyurethane (WPU). The WPU films modified with the composites flame retardant were characterized in detail. The composites flame retardancy, residual carbon morphology, and graphitization of the films were evaluated by cone calorimetry, scanning electron microscopy (SEM), and Raman spectroscopy, respectively. The results showed that the weight loss temperature of the WPU film was 402.45 °C when the weight loss rate was as high as 90 % in the N2 atmosphere, and the PHRR and THR values of the flame-retardant films were as low as 222.3 kW/m2 and 22.9 MJ/m2, respectively. Compared with the neat WPU, the LOI of the film decorated with the composites flame retardant was increased by 39.13 %. The high graphitization degree of the residue char was formed to improve strength and shield properties of the modified WPU film. The flame-retardant mechanism was attributed to the active phosphorus-containing free-radical quenching effect and diluting effect of nonflammable gases in the gas phase, and owing to the catalysis effect the formation of phosphorus/silicon-rich char residue layers in the condensed phase.