Environmentally friendly wood adhesives based on chestnut (Castanea sativa) shell tannins

The aim of this work was the formulation of adhesives for particleboards based on tannins extracted from industrial lignocellulosic wastes, namely chestnut shell, chestnut bur and eucalyptus bark. The interest was centred on the possibility of completely removing formaldehyde from adhesive formulations. For this, hardener alternatives to formaldehyde were used: tris(hydroxymethyl)nitromethane (TRIS), glyoxal (GLY) and hexametilentetramine (HEX). The influence of the type and concentration of the hardener and pH on adhesive gel time and pot-life were studied. A comparative structural characterization of the adhesives was performed by 13C-NMR spectroscopy. Thermomechanical analyses (TMA) tests were carried out as an indication of the final strength of the adhesive systems. Particleboards type 2 of interior use (EN 312) were manufactured with adhesives based on chestnut shell tannins alone or mixed with chestnut bur/or eucalyptus bark tannins. Free-formaldehyde was determined, and boards were prepared with TRIS, GLY and HEX tannin adhesives were classified as E0.