A Novel Strategy Inspired by Steaming Chinese Steamed Bread for Preparation of Tannin-Furanic Rigid Bio-Foam

Tannin-furanic rigid foam material has been receiving extensive attention due to its renewable, easy-preparation, lightweight, thermal insulation, and flame retardancy, that been considering a potential flame-retardants and thermally-insulating materials in construction field. The most fashionable approaches for tannin-furanic foam manufacturing, currently, are the self-blowing expansion with the aid of blowing agent with/without extra heating, and foaming via mechanical stirring in presence of non-environmentally friendly crosslinker. Herein, a novel and green strategy was proposed for tannin-furanic rigid foam preparation without blowing agent and additional crosslinker by steam-driven foaming. The performance of steam-driven tannin-furanic based foam (SDTF) was evaluated systematically and a possible foaming mechanism was suggested. The results indicated that a totally different surface but similar microstructure morphology of SDTF was developed, which displayed a larger cell size and thicker cell wall than standard tannin-furanic-formaldehyde foam (STF). A much lower pulverization ratio (approximately 4.6%) was reached for SDTF with respect to STF even though its compression strength was only less than half. An excellent thermal insulation performance was verified by the thermal conductivity of SDTF, only approximately 0.0286 W/m center dot K, which is considered ultra-low value that the STF cannot reach or seldom reach after STF modification or/and special structure design. The flame retardancy of SDTF was investigated by LOI and ignition experiment, which demonstrated a strong flame resistance and self-extinguishing nature, rendering it superior to STF. This preparation strategy provides a promising sustainable and environmentally friendly method for fabrication of green tannin-furanic foam for industry applications.