Synergetic improvement of flame retardancy and heat resistance of cationic waterborne polyurethanes by introducing a DOPO-containing flame retardant

The cationic waterborne polyurethanes (CWPU) exhibit excellent affinity towards various materials possessing negative surface charges owing to its positive charge. However, its limited heat resistance and flame retardancy greatly restrict its practical application. In this work, we synthesized a flame retardant , 2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl)-1,4-hydroxyethoxyphenylene (DOPO-HQ-HE), and incorporated it into the skeleton of cationic waterborne polyurethanes to prepare flame-retardant cationic waterborne polyurethanes (CWPU-DHHxs). The obtained CWPU-DHHxs showed excellent flame retardancy, in which the LOI value of CWPU-DHH 12 reached over 26.9 vol% and passed UL-94 V-0 rating. The findings showed that CWPU-DHHxs exhibited remarkable efficacy in both the vapor and condensed phase during combustion. Moreover, the incorporation of DOPO-HQ-HE led to a significant improvement in heat resistance performance by facilitating enhanced microphase separation . Meanwhile, the major comprehensive performance of CWPU-DHHxs, including emulsion storage stability, thermal stability, mechanical performance, and transparency were effectively preserved.