Honeymoon MUF adhesives for exterior grade glulam

Abstract

An exclusively MUF- (melamine-urea-formaldehyde) based honeymoon adhesive for glulam and fingerjoints is presented in which one component is composed of a high performance MUF resin, while the second separate application component is based on just slightly acid water thickened to the same viscosity of the first component by the addition of 1.5% carboxymethyl cellulose (CMC). MUF-based, honeymoon-type, fast-setting, separate application adhesive systems, which do not need any resorcinol, are shown here to be capable of performing as adhesives for structural exterior-grade joints and glulam and to satisfy all the requirements of the relevant adhesive specifications for such an application. The parameters which are shown to be determining are mainly the performance of the MUF resin, if and once an excellent resin formulation is available, both the ratio of melamine to urea and the molar ratio having a lesser effect. The performance only starts to drop lower than the requirements of relevant standards from M:U weight ratios well below 20:80 and of the order of 10:90. Addition of resorcinol at these failing levels while improving slightly the performance do not solve the problem, and resorcinol addition does not allow satisfaction regarding specification requirements. At the higher M:U ratios such as M:U = 47:53, but even lower, addition of resorcinol does not improve at all the results, its addition again revealing itself superfluous. The reasons for such a behaviour are presented and explained. The MUF honeymoons present all the other usual advantages associated with honeymoon adhesives, namely high curing rate, long pot-life, tolerance to higher moisture content of the substrate, and tolerance to even quite severe imbalances in viscosity and proportions between the two components.