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

Abstract

Methylolated nitroparaffins, and in particular the simpler and least expensive exponent of their class, namely tris(hydroxymethyl)nitromethane (TN), function well as hardeners of a variety of tannin-based adhesives while affording considerable side advantages to the adhesive and to the bonded wood joint. In panel products, such as particleboard, medium density fiberboard and plywood, the joint performance which is obtained is of the exterior/ marine 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 bonded wood panel to reduce emission exclusively to the formaldehyde emitted by just heating the wood (and slightly less, thus functioning as a mild depressant of emission from the wood itself). Furthermore, TN can be mixed in any proportion with traditional formaldehyde-based hardeners for tannin adhesives, its proportional substitution of such hardeners inducing a proportionally marked decrease in the formaldehyde emission of the wood panel without affecting the exterior/marine grade performance of the panel. Medium density fibreboard (MDF) industrial plant trials confirmed all the properties reported above, and the trial conditions and results are reported. In the case of cold-setting adhesives for finger-jointing and glulam, tris(hydroxymethyl)nitromethane (TN) can be used to good effect only in radiofrequency curing of such joints, hence also by heat activation, its performance instead not coming up to the requirements of relevant standards in the case of ambient temperature curing due to higher temperature activation characteristics of this hardener.