Sustainable bamboo fiber-tannin composite foam: A green substrate for vertical greening systems

Tannin-based biomass foam was prepared through a self-foaming process at room temperature. The material’s density, porosity, microstructure, mechanical properties, thermal stability, limiting oxygen index (LOI), brittleness, as well as water absorption and retention properties, were studied. Adding 2% bamboo fibers in varying forms did not affect the uniformity of the foam cells. The density, porosity, thermal stability, and LOI of the foam material remained largely unchanged. The compressive strength of the unmodified tannin foam was 0.043 MPa, while the addition of 2% bamboo fibers increased the compressive strength by 72%. Even when the effect of density was excluded, the specific compressive strength was enhanced by 60%. Additionally, brittleness, measured as the slagging percentage, was significantly reduced from 16.12% to 4.78%. The modified foam could absorb up to 26.5% of its weight in water, with excellent water retention capabilities of 78.1% after 120 h while retaining its structural integrity under intermittent wetting conditions, making it suitable for vertical greening applications. This demonstrates its suitability for vertical greening applications, where moisture exposure is frequent. In conclusion, the bamboo fiber-reinforced tannin-based foam exhibits excellent mechanical properties and superior water absorption and retention performance.