Chemical modification of tannin/furanic rigid foams by isocyanates and polyurethanes

Tannin/furanic rigid foams were modified by either polymeric 4,4’ diphenylmethane diisocyanate (pMDI) or a one-component polyurethane still presenting reactive isocyanate groups (PUR). Several different sequences of mixing the isocyanate and polyurethane with the chemicals used to prepare tannin-based foams were tested. Scanning electron microscopy (SEM) showed that addition of either pMDI or PUR yielded a more ordered microstructure of the foam and a larger cell size. Series of two different cell sizes were noticed: those obtained by the evaporation of the blowing agent used for classical tannin-based foams and those caused by the formation of CO2 issued by the reaction of the isocyanate groups with water. The cell size, density, thermal conductivity and mechanical property of tannin/furanic foams were controlled by changing the amount of blowing agent and weight fraction of pMDI. The cell size of pMDI modified foams was largest when the weight fraction of pMDI was 5% and kept decreasing as the pMDI percentage became higher. The density of the foams increased with the increase of the weight fraction of pMDI. The addition of pMDI increased slightly the thermal conductivity of tannin/furanic foam with the foams still presenting good thermal insulation. Moreover, the addition of pMDI in tannin/furanic foams improved markedly the foam's mechanical properties.