Alkaline Tannin Rigid Foams

Abstract

Condensed fl avonoid tannin foams were obtained under alkaline conditions. This entailed the elimination of furfuryl alcohol from these formulations, as under alkaline conditions, foam preparation could not rely on the heat generated by the self-condensation of furfuryl alcohol, which occurs only under strongly acidic conditions. The approach used to formulate the alkaline foam was: (i) the total elimination of furfuryl alcohol from the formulation, (ii) coupled with the use of an aldehyde hardener different from formaldehyde (for environmental reasons) and (iii) the application of moderate heat to allow foaming. These were not tannin/ furanic foams as their acid-curing counterparts, but tannin only foams. The open cell foams were evaluated for bulk density, compressive strength, thermal conductivity and fi re resistance. Their characteristics were similar to the acid-curing tannin/furanic foams.