Influence of hydroxyl-terminated phosphoramidates on the flame retardancy of microfiber synthetic leather

As the ideal substitute for natural leather, microfiber synthetic leather (MSL) possesses excellent mechanical/chemical properties and have been commonly applied in our daily life. However, the flammability strictly limits its application in the field with high fire-safety requirement. Herein, three classical phosphorus-containing compounds with terminated hydroxyl groups, named as DTP-OH (dimethyl phosphate derivative), DPPC-OH (cyclic phosphate derivative) and DOPO-OH (DOPO derivative), were synthesized and served as the flame-retardant coating on microfiber synthetic leather. The influence of different phosphoramidates on the flame-retardant performance of microfiber synthetic leather was investigated by vertical flammability test (VFT) and limited oxygen index (LOI). Among them, DPPC-OH and DOPO-OH had better flame retardant efficiency with the comparable loadings. The LOI value increased from 18.1% to 25.7% and 26.1% respectively after coating with DPPC-OH and DOPO-OH, and they successfully passed the vertical burning test. Meanwhile, the thermal degradation and combustion behavior were also analyzed to further confirm the flame-retardant mechanism. It was found that these hydroxyl-terminated phosphoramidates can efficiently improve the char-forming ability of microfiber synthetic leather and the peak heat release rate (PHRR) reduced by 37% for the DPPC-OH modified microfiber synthetic leather. This work indicates that cyclic phosphate and DOPO derivatives has a good application prospect in the preparation of fire-safety microfiber synthetic leather.