Chemistry, Morphology, Microtomography and Activation of Natural and Carbonized Tannin Foams for Different Applications

Abstract Tannin based rigid foams are natural network structures obtained by polycondensations of polyflavonoid tannins and furfuryl alcohol. These foams have a wide range of characteristics. Physical tests such as water absorption, compression resistance, direct flame behaviour and measure of foam cell dimensions were carried out for each foam sample. Tannin‐based rigid foams, prepared from 95% natural material, are suggested for replacing synthetic phenol‐formaldehyde foams in various applications. For that purpose, a few physical properties were measured: resistance to fire and chemicals, absorption of various liquids, permeability, thermal conductivity and mechanical (compressive and tensile) strength. The materials were also found to present good resistance to strong acid and bases, and to solvents. Finally, slightly anisotropic mechanical properties were measured. The materials present a brittle behaviour, whether tested in compression or traction; nevertheless, their strengths, as well as their thermal conductivities, are fully comparable with those of their phenolic counterparts. Carbonisation of polyflavonoid tannin‐formaldehyde‐furfuryl alcohol rigid foams was found by MALDI‐TOF to yield a tridimensional network in which polynuclear aromatic hydrocarbon chains of high molecular weight are covalently linked to some furan resin structures surviving carbonisation. Structure conservation on carbonisation extends to furanic structures derived by the self condensation of furfuryl alcohol which are integral part of the total network. Some complex, tridimensional structures derived by the rearrangement to polyaromatic hydrocarbons of polyflavonoid tannins, constituting of aromatic benzene and furane rings and some formaldehyde‐derived methylene bridges appear to be formed.