Tannin-based resins modified to reduce wood adhesive brittleness

In South Africa and Brazil, natural tannins extracted from black wattle (Ac acia mearnsii) bark are commercially available as the phenolic adhesive com ponent for bonding wood. This preliminary work deals with the reduction of the brittleness of the tannin-based adhesive joint in such wood materials t hrough the chemical modification of the condensed tannins before reacting w ith formaldehyde. The brittleness reduction was achieved by the introductio n of adipic ester segments between the hydroxyl groups of the compact tanni n macromolecules. The exploratory modified tannin-formaldehyde adhesive was tested for plywood mechanical properties under dry, water, and boil test p rocedures.