Synthetic-resin-free wood panel adhesives from mixed low molecular mass lignin and tannin

Abstract

Mixed interior wood panel tannin adhesive formulations were developed in which lignin is in considerable proportion, 50%, of the wood panel binder and in which no “fortification” with synthetic resins, such as isocyanates and phenol-formaldehyde resins as used in the past, was necessary to obtain results satisfying relevant standards. A low molecular mass lignin obtained industrially by formic acid/acetic acid pulping of wheat straw was used. Environment-friendly, non-toxic polymeric materials of natural origin constitute up to 94% of the total panel binder. The wood panel itself is constituted of 99.5% natural materials, the 0.5% balance being composed of glyoxal, a non-toxic and non-volatile aldehyde, and of hexamine already accepted as a non-formaldehyde-yielding compound when in presence of condensed tannin. Both particleboard and two types of plywood were shown to pass the relevant interior standards with such adhesive formulations. Moreover, the much cheaper non-purified organosolv lignin showed the same level of results as the more expensive purified type.