A new method for preparing tannin-based foams

• A new method for preparing tannin-based phenolic foams is presented.
• The new method is easier, faster and cheaper than the traditional foaming.
• Physical properties of the new foams are the same as those of standard foams.
• The ranges of porosity and cell sizes are broader than before.
• The structure is controlled by the concentration of the monomer.

Phenolic foams derived from natural precursors, condensed tannin extracts from mimosa trees, were prepared for the first time by curing and drying liquid foams obtained by aeration of tannin solutions containing surfactant and crosslinker. The materials derived from the new method were called tannin-based meringues in reference to the lightweight pastry made in a similar way by whipping egg whites. The new foams were compared with more standard cellular solids having very close composition but obtained by physical or chemical foaming. No significant differences were observed in terms of mechanical and thermal properties. The porous structure was also similar, except the cell sizes which were much higher in tannin-based meringues. The new method is not only easy, fast and cost-effective, but allows producing solid foams having a very broad range of bulk densities and cell sizes, which can be controlled by the concentration of tannin in the initial solution, all other things being equal.

Whipping tannin solutions with surfactant and crosslinker produces liquid foams which are next hardened and dried, leading to the first tannin-based meringues. The porosity of such new rigid foams is controlled by the initial concentration of tannin.Figure optionsDownload as PowerPoint slide