Chemical modification of tannin/furanic rigid foams by isocyanates and polyurethanes
Keywords:tannin/furanic rigid foams, isocyanate modification, polyurethane modificaton, microstructure, mechanical properties
Tannin/furanic rigid foams were modifi ed by either polymeric 4,4’ diphenylmethane diisocyanate (pMDI) or a one-component polyurethane still presenting reactive isocyanate groups (PUR). Several diff erent 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 diff erent 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. Th e 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. Th e cell size of pMDI modifi ed foams was largest when the weight fraction of pMDI was 5% and kept decreasing as the pMDI percentage became higher. Th e density of the foams increased with the increase of the weight fraction of pMDI. Th e 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.