Tannin-based resins modified to reduce wood adhesive brittleness

In South Africa and Brazil, natural tannins extracted from black wattle (Acacia mearnsii) bark are commercially available as the phenolic adhesive component for bonding wood. This preliminary work deals with the reduction of the brittleness of the tannin-based adhesive joint in such wood materials through the chemical modification of the condensed tannins before reacting with formaldehyde. The brittleness reduction was achieved by the introduction of adipic ester segments between the hydroxyl groups of the compact tannin macromolecules. The exploratory modified tannin-formaldehyde adhesive was tested for plywood mechanical properties under dry, water, and boil test procedures.