Honeymoon gluing

Adhesives. A description of the honeymoon system of wood gluing was first published in 1974 (1). It is, in principle, a system in which two different adhesive compositions are applied to the two surfaces to be mated. Since wood adhesives penetrate the wood surface (and have to do so in order to provide a good bond), it is important that both individual components of the system ultimately cure to form a solid durable polymer. This can be achieved either by designing the components such that each will fully cure by itself or by providing ingredients in the two components that react after mutual diffusion takes place ultimately, all layers of the glueline must reach the fully cured state. 

In order to establish control values for the adhesives formulated using tannins, the initial work was done with phenol-resorcinol-formaldehyde (PRF) or resorcinol-formaldehyde (RF) resins on both surfaces, but modified for the honeymoon principle. The PRF resin chosen for this work was Borden s resin LT-75 with Borden s hardener FM-260. The RF resin used for a comparison was Chembond s RF-900. These resins have been used for wood gluing in the United States for more than two decades, especially for the manufacture of structural laminated timbers. 

In the past decades, significant reductions in resorcinol content have been achieved from pure RF resins, to PRF resins in which phenol and resorcinol were used in equal or comparable amounts, to the modern-day commercial resins for glulam and fingerjointing in which the percentage, by mass, of resorcinol on liquid resins is on the order of 15 to 18%. A step forward has also been the development and commercialization of the honeymoon fast-set system [3], either composed of just synthetic PRF resins or of a PRF resin coupled with the use of tannin extracts, which in certain countries are used to obtain PRFs of 8 to 9% resorcinol content without loss of performance and with some other advantages (such as gluing of high moisture content timber). This was a system improvement, not an advance on the basic formulation of PRF resins. 

MUF honeymoon adhesive systems for bonding of timber of high moisture content (wet gluing) to produce laminated wood (glulam) and finger-jointing are composed of two components (1) a MUF resin at a pH of approximately 10 with no fillers added, and (2) a low pH aqueous solution of carboxymethylcellulose and formic acid lacking resorcinol in the system (82-85). 

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