Mechanically blown wall-projected tannin-based foams

Condensed flavonoid tannin-based foams from quebracho tannin extract have been developed using a new method of expansion based on fire-fighting or tunneling foams, where a foam concentrate forms a stable liquid foam. This new mechanical method of expansion allows obtaining a solid porous material after curing and hardening at room temperature, through a liquid foam formed by a tannin resin and an aqueous solution of surfactant. The stability of the as-obtained liquid foam and the influence of the amount of catalyst are reported. The use of this new approach for preparing tannin-based rigid foams avoids the problem of shrinkage presented by many other formulations where physical or chemical foaming is employed. Non-ionic surfactants have also been used in the formulation to obtain smaller cells and improve the structure of the new material. Bulk density (0.069-0.080 g/cm3), mechanical (compressive strength of 0.034-0.13 MPa) and thermal (0.045-0.047 W m−1 K−1) properties and morphological appearance of the foams have been characterised and reported.