Honeymoon system

Resorcinol additions just prior to use provide acceleration, though they are still not the most cost effective nor technically effective use of resorcinol. In-line addition of a PRF resin Just before application of the resin to the adherend achieves better results at less than half the cost of resorcinol chemical, in most cases and it is easier to handle. A variant of this concept is application of the resorcinol and PF resins to the substrate separately but in a way that permits them to come into contact during the curing process. Such methods are sometimes called honeymoon systems. 

If this method proves to be commercially feasible, a renewable and abundant waste product of forest products manufacture could replace expensive petrochemicals. Additionally, use of an inexpensive waste product from processing of forest products could materially reduce adhesive costs and expand opportunities for manufacture of structural materials from low-quality wood. This benefit is particularly important since the difficulty in producing large, strong, structural members from timber resources of declining quality is growing exponentially with time. The cost-benefit ratios of replacing PRF resins with extracts from conifer barks are, therefore, quite favorable in a honeymoon system. 

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. 

Extracts from southern pine bark obtained by extracting finely ground bark with 4.0% sodium sulfite and 0.4% sodium carbonate at 100 °C can be used to replace 50% of the PRF resin in a honeymoon system forbonding exterior quality structural end-joints in lodgepole pine or Douglas-fir. 

Use of southern pine bark extracts as 50% of the reactive phenolics in endjointing adhesives applied in a honeymoon system has good commercial potential. With proper plant layout and design, the installation, operation, and maintenance of radio-frequency units and their resulting high costs can be avoided. 

In the second approach (120), condensed tannins were purified of co-occur-ring carbohydrates and used as resorcinol replacements in a honeymoon system (116) as described previously in use of wattle tannin adhesives. One surface was spread with a commercial phenol-resorcinol-formaldehyde laminating adhesive, to which additional formaldehyde was added. The other surface was spread with pine bark tannin extract in sodium hydroxide solutions. Bonds meeting the requirements of the American Institute of Timber Construction were also obtained using this approach. It was necessary to remove the carbohydrates, however. Addition of the separated carbohydrates at comparatively low levels (about 10%) resulted in bonds with low wood failure. 

Applications for cold-setting, wood-laminating adhesives initially followed the same approach (47) used for laminating resins from western hemlock (38) (i.e., reaction of tannin with phenol-resorcinol-formaldehyde prepolymers). Improvements resulted through the application of Kreibich s Honeymoon technique (48) wherein one side of the material to be bonded is treated with resin and the other with catalyst. One of the preferred systems (49) was phenol-resorcinol-formaldehyde or tannin-resorcinol-formaldehyde at pH 8 with extra paraformaldehyde on the A-side and tannin at 53% solids or tannin-resorcinol-formaldehyde at pH 12 on the B-side. Such resin systems are currently used to laminate eucalyptus or pine in most South African timber-laminating plants. 

Figure 2. Comparison of the rate of tensile strength development in RF/RF and PRF/PRF honeymoon adhesive systems.

Two component acrylic systems which are known as second generation acrylics in the U.S. and as "honeymoon adhesives" in Europe are discussed in Chapter 10. Acrylic resins have been... 

An unusual type of two component system has recently been introduced in the adhesive industry (1,). These are called reactive adhesives, second generation acrylics, toughened acrylics, modified acrylics (2) or "honeymoon adhesives" (in Europe). 

Acrylic adhesives first appeared about 1937 the acrylic resins may be considered as belonging to the vinyl family [1, p. 305], Today, acrylic adhesives appear in many forms as both pressure-sensitive and non-pressure sensitive formulations in organic solvent and emulsion forms as monomer and polymer cements as anaerobics as cyanoacrylates as so-called reactive or honeymoon two-part systems and as radiation curing formulations. Commercial production of acrylic polymers began in the late 1920s, but it was not until 1958 that the first aerylie sealant was developed [10, p. 226]. The solvent-based acrylic sealants were first introdueed to the eonstruction industry in about 1960 ... 

A particularly interesting system now used extensively in several southern hemisphere countries is the so-called honeymoon fast-setting, separate-application system [66,67]. In this system one of the surfaces to be mated in the joint is spread with a standard synthetic phenol-resorcinol-formaldehyde adhesive plus paraformaldehyde hardener. The second surface is spread with a 50% tannin solution at pH 12. When the two surfaces are... 

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. 

These liquid resins then work at a resorcinol content of only 9 to 11%, hence considerably lower than that of traditional PRF resins. These resins can also be used with good results for honeymoon fast-setting adhesives in PRF tannin systems, thus further decreasing the total content of resorcinol in the total resin system at a level as... 

Figure 2 Typical strength and wood failure increase as a function of time of a pure PRF honeymoon adhesive system on timber at 12% and 22% moisture content [26-29]. Note that at the unusually high moisture content of 22% the requirements of the standards are passed in less than 24h as the timber starts to dry [26-29]. Test on beech strips according to British Standard BS 1204. 

Figure 9 TensUe strength increase as a function of time of beech joints (BS 1204, Part 1) bonded with MUF-based honeymoon adhesive systems effect of the variation of the initial application pH of the resin (component A). 

Significant reductions in resorcinol content have been achieved from pure resorcinol-formaldehyde resins, to today s PRF resins in which the percentage, by mass, of resorcinol on liquid resins is between 15 and 18%. A step forward has also been the development and commercialization of the honeymoon fast-set system, which in certain countries is used to obtain PRFs of 8 to 9% resorcinol content without loss of performance. 

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). 

Pizzi A, Rossouw D duT, Knuffel W E, Singmin M 1980 Honeymoon phenolic and tannin-based fast-setting adhesive systems for exterior grade fingerjoints. Holzforsch Holzverwert 32 140-150... 

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