Preparation of a flame-retardant waterborne polyurethane with core–shell structure and its application in a fire-resistant microfiber synthetic leather

Abstract

A series of flame-retardant waterborne polyurethane (AWPU-X) compounds with core–shell structures were synthesized by encapsulating hexaphenoxycyclophosphazene (HPCTP) with WPU. AWPU-X, melamine (MA), and AO₁₀D₃-WPU (a flame-retardant WPU self-made in the lab) were synergistically used to prepare flame-retardant microfiber synthetic leather by a two-step method, and the relevant properties of AWPU-X and the microfiber synthetic leather were characterized. The results showed that AWPU-X formed a core–shell structure and had good emulsion stability and film thermal properties. The limiting oxygen index (LOI) value of AWPU-11 reached 27.5% when the HPCTP addition was 11% by mass. The mechanical properties of the flame-retardant microfiber synthetic leather were improved, while the hand-feel of the leather was not affected. When the mass ratio of AWPU-11/MA/AO₁₀D₃-WPU was 60 : 20 : 20, the flame retardancy of the microfiber synthetic leather was the best, with the LOI value of 27.6%, no after-flame, and a damage length of only 0.5 cm in the vertical flame test. At the same time, the peak heat release rate (PHRR) and total heat release (THR) in the cone calorimeter test were reduced by 42% and 30%, respectively. Although the introduction of flame-retardant components decreased the thermal performance of the microfiber synthetic leather, the thermal decomposition residual carbon rate was significantly improved. Based on the results of SEM-EDS, TG-IR, and Raman tests, it was speculated that the flame retardancy of the microfiber synthetic leather was primarily attributed to the joint action of the flame-retardant components in both the gas and condensed phases.