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

ABSTRACT 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.