Eco-friendly and efficient flame retardant rigid polyurethane foam reinforced with lignin and silica aerogel.

With the continuous improvement of living standards, the development of eco-friendly rigid polyurethane foam (RPUF) materials with excellent flame retardancy, thermal insulation, and outstanding mechanical strength has become an urgent challenge. This study presented an innovative strategy using lignin as a mechanical reinforcement and flame-retardant synergist, combined with DMMP and EG as highly efficient flame retardants. Furthermore, the incorporation of a silica aerogel coating via surface post-treatment significantly enhanced the flame retardancy of the composite. Compared to neat RPUF, the Ct-RPUF/L/FR composites exhibited an increased LOI of 25.3 %, a delayed ignition time of 6.0 s, and reductions in total heat release (THR) and total smoke production (TSP) to 8.6 MJ/m and 2.11 m, respectively, while achieving the UL-94 V-0 rating, thereby minimizing fire hazards. Additionally, the compressive strength of the composite improved from 132.4 kPa for neat RPUF to 178.3 kPa, with a thermal conductivity of only 30.11 mW/(m·K), maintaining comparable thermal insulation performance to neat RPUF. Moreover, the evidence provided by the Life Cycle Assessment (LCA) indicated that the fire-retardant strategy used in this study resulted in lower environmental impact (EI) compared to traditional fire-retardant methods. This study highlighted the synergistic effects of lignin, flame retardants, and silica aerogel, providing new opportunities for the development of advanced RPUF materials with enhanced fire safety and durability, suitable for practical applications.