Flexible Biofoams Based on Furanics and Fatty Acids Esterified Tannin

Water repellant, flexible biofoams using tannin esterified with various fatty acid chains, namely lauric, palmitic and oleic acids, by reaction with lauryl chloride, palmitoyl chloride, and oleyl chloride were developed and their characteristics compared with the equivalently esterified rigid biofoams. Glycerol, while initially added to control the reaction temperature, was used as a plasticizer yielding flexible biofoams presenting the same water repellant character that the equivalent rigid foams. Acetaldehyde was used as the cross-linking agent instead of formaldehyde, as it showed a better performance with the esterified tannin. The compression results showed a significant decrease of the Modulus of Elasticity (MOE) of the flexible foams in relation to that of the rigid foams, confirming their flexible character. The lauryland palmitoyl-esterified biofoams presented similar mechanical properties, while the oleyl-esterified biofoam presented different mechanical and morphological result not really showing the expected flexibility. Both the esterified rigid and flexible tannin-based biofoams showed good water resistance and their sessile drop contact angle analysis as a function of time confirmed this characteristic. Scanning Electron Microscope (SEM) analysis showed the flexible foams to present a higher proportion of closed cells than the rigid foams. Conversely, the cells depth of the flexible foams was lower than that of the rigid foam. As regards their thermal resistance, the flexible foams showed a slight loss of mass compared to the rigid ones without glycerol. Both types of foams presented much lower surface friability of non-esterified rigid foams.