A no-aldehyde emission hardener for tannin-based wood adhesives for exterior panels

Methylolated nitroparaffins, and in particular the simpler and least expens ive exponent of their class, namely tris(hydroxymethyl)nitromethane (TN), f unction well as hardeners of a variety of tannin-based adhesives while affo rding considerable side advantages to the adhesive and to the bonded wood j oint. In panel products, such as particleboard, medium density fiberboard a nd plywood, the joint performance which is obtained is of the exterior/mari ne grade type, while a very advantageous and very considerable lengthening in glue-mix pot-life is obtained. Furthermore, the use of this hardener is coupled with such a marked reduction in formaldehyde emission from the bond ed wood panel to reduce emission exclusively to the formaldehyde emitted by just heating the wood (and slightly less, thus functioning as a mild depre ssant of emission from the wood itself). Furthermore, TN can be mixed in an y proportion with traditional formaldehyde-based hardeners for tannin adhes ives, its proportional substitution of such hardeners inducing a proportion ally marked decrease in the formaldehyde emission of the wood panel without affecting the exterior/marine grade performance of the panel. Medium densi ty fibreboard (MDF) industrial plant trials confirmed all the properties re ported above, and the trial conditions and results are reported. In the cas e of cold-setting adhesives for finger-jointing and glulam, tris(hydroxymet hyl)nitromethane (TN) can be used to good effect only in radiofrequency cur ing of such joints, hence also by heat activation, its performance instead not coming up to the requirements of relevant standards in the case of ambi ent temperature curing due to higher temperature activation characteristics of this hardener.