Wood adhesives derived from alkaline extracts of maritime Pine bark: preparation, physical characteristics and bonding efficacy

An alkaline extract of maritime pine (Pinus pinaster) was investigated for its solubility in water or aqueous NaOH, for its stability when stored in the form of a solution in 5% NaOH, and for the physical properties and bondability of formulations prepared by incorporation of tannins into a PF resin. The extract is poorly soluble even in aqueous NaOH and its reactivity towards formaldehyde increases with time when it is stored in the form of an alkaline solution. The incorporation of a solution of tannins made with 5% NaOH into PF resin did not affect adversely the physical properties of the resin. But also just the extract in 5% NaOH solution, when heated at 175 degreesC, develops strength comparable to the PF resin, as experienced with impregnated paper strips. Furthermore, these formulations develop bonds to wood and even a solution of just tannins presented a 100%-wood failure with the majority of the replicate samples, after bond strength tests.