Solvent-Free Preparation of Reactive Flame-Retardant Polyurethane Resin for Synthetic Leather Applications

In order to reduce the high pollution and flammability of polyurethane in high-performance automotive synthetic leather, the development of a solvent-free flame-retardant reactive polyurethane (RPU) coating material has become a research focus. However, solvent-free environments not only place higher requirements on the fluidity and processability of materials but also present significant technical challenges in achieving a balance between strength and flame retardancy. In this paper, inorganic ionic polymer particle ammonium polyphosphate (APP) was used as filler and reactive polyurethane resin as a carrier to prepare a flame-retardant modified polyurethane composite membrane with a foaming structure through a two-step method. The results showed that adding 4% APP could extend the molding time of reactive polyurethane to 550 s—an increase by about 53%—and increase its mechanical strength to 23.01 MPa. Thermal analysis verified that the cross-linking degree of reactive polyurethane resin was increased due to APP, and its thermal stability could be effectively improved. The reactive polyurethane modified with 4% APP had a residual carbon content exceeding 12% after heat treatment, and its limiting oxygen index can reach 23.7%. Additionally, the peak value of heat release rate (PHRR) was reduced by 10.7% and total heat release rate (THR) by 25.1%, enhancing the flame retardant effect. This method was of great significance to the production of polyurethane for automotive leather.