Flame-retardant and thermally-insulating tannin and soybean protein isolate (SPI) based foams for potential applications in building materials

Owing to foreseable extensive shortages in petrochemical resources, energy consumption, and fire safety concerns, recent scientific research in the construction field has been aimed to develop biomass flame-retardants and thermally-insulating materials. Herein, flame-retardant tannin-furanic-SPI bio-foams with outstanding thermal insulation and smoke suppression performance were developed by exploiting the synergistic effect of additives (boric acid, phosphoric acid, and montmorillonite). Their physical and mechanical properties showed that these tannin-based foams are lightweight (82–122 kg/m3), with an acceptable compression strength (0.2–0.35 MPa), and a low pulverization ratio (5.97–12.06%). Moreover, the morphology, thermal stability, thermal conductivity, and flammability were evaluated by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), thermal conductivity tests, limiting oxygen index (LOI), and cone calorimetry, respectively. These foams exhibited closed cell structures, good thermal stability, and low thermal conductivity. Their flammability results showed that higher LOI values were obtained in the range of 37.33–49.05% and that they had a relatively low peak-heat-release rate (PHRR) and total-smoke-produced (TSP). A possible flame retardancy mechanism was suggested. By comparing them to other commercial construction materials, the modified tannin-furanic-SPI foams with integrated properties, such as flame retardancy, thermal insulation, light-weight, environmental-friendliness, and acceptable mechanical properties, show potential applications as thermal insulation for buildings.