Wood Adhesives from Wattle Bark Extract

Condensed flavonoid tannins from the bark extract of black wattle (Acacia mearnsii De Wild.) were used to prepare thermosetting adhesive resins for the production of exterior grade plywood, block-board and particleboard and a cold-setting adhesive formulation for finger jointing and lamination of timber. An unfortified tannin-formaldehyde resin was used in the manufacture of semi-exterior grade plywood. The panels passed the British Specification 1455 (1963) for BR bonding after 24 hr. soak in cold water, or a 3 hr. boil, and subsequent knife testing. Marine grade plywood was produced with a tannin-formaldehyde formulation containing a phenol-resorcinol-formaldehyde fortifier. The panels passed the requirements of B.S. 1455 (1963) for WBP bonding after 24 hr. soak in cold water or 72 hr. boil. In the construction of blockboard or shutteringboard an adhesive formulation containing a phenol-formaldehyde fortifying resin was used. The boards were subjected to five cycles of alternate soaking (16 hr. in cold water) and drying (8 hr. at 60?C.), before being knife tested according to B.S. 1455 (1963). A maximum of 1.5 percent edge delamination was observed. The main benefits derived from these glues were neutral glue lines and faster press cycles. Unfortified wattle extract solutions, catalysed with formaldehyde, were used to produce adhesive resins for the manufacture of weather resistant particleboard. After conditioning, the density, modulus of rupture, tensile strength perpendicular to the face after soaking in water at 20?C and at 100?C and percentage thickness swelling after soaking in cold water for 2 hr. and 24 hr. periods were determined for each panel. All the requirements of the German Standard DIN 68761(3) (1967) were met, except in the case of the tensile strength after soaking at 100?C and 24 hr. swelling in cold water. Exterior grade particleboard was produced by the use of 12-14 percent of resin based on the mass of the wood chips instead of the initial 10 percent used. A chemically modified tannin based laminating adhesive resin was produced by copolymerizing wattle extract, resorcinol and formaldehyde in stages under controlled pH conditions.

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