Adhesives for plywood

Articles made from amino resins are water clear, hard, and strong, but they can crack. They have good electrical properties, and they have better colorability than phenolic resins. Amino resins are used as adhesives for plywood and particleboard but only in interior grades. They have low weather resistance and deteriorate when exposed to sun, heat, cold, and moisture. 

Used in molding applications, appliances, TVs, automotive parts, filler, impregnating paper, varnishes, decorative laminates, electrical parts, countertops, toilet seats, adhesive for plywood, sandpaper, brake linings, abrasive wheels No large industrial applications... 

Paul and Subramaniam, 1997 Roberts et al., 2004), has not been banned and is still being used. It is know that OCPs were imported and used illegally for a few years even after the ban. Furthermore, some OCPs are known to have been used as a non-food additive agent. For example, chlordane was used as an adhesive for plywood and DDTs as an intermediate in the production of dicofol. It was not until the 1990s that regulation of OCPs in South Korea was mandated by the Toxic Chemical Control Act (TCCA). 

The types of adhesives suitable for laminating beams are restricted by the conditions of application and by their end-use requirements. A wider choice of adhesives for plywood depends on whether softwoods or hardwoods are used, whether they are required for internal or external exposures, or whether they are to be used for ornamental or structural purposes. Thus phenol-formaldehyde types would be used for marine or exterior construction uses urea-formaldehyde types would be advantageous for cold pressing, or melamine-urea adhesives might be preferred for hardwood plywood, or lumber-core panels used in furniture production. 

Forss, K., and Fuhrmann, A. (1976). KARATEX—the lignin-based adhesive for plywood, particle board and fibre board. Pap. Puu 58, 817-824. 

The resorcinol-pattern proanthocyanidins are widely used not only for leather tanning, but also for a range of other commercial products, particularly as adhesives for plywood and fiberboard (6,7). Wattle tannin is produced from sustained-yield forests of Acacia mearnsii. largely in southern Africa (6,8). Some of the impetus at least to develop other uses for wattle tannin, apart from... 

Diisocyanates have also generated interest as adhesives for plywood, but they have mainly failed in use because of economics and adhesive application problems (adhesive distribution, penetration into veneer, etc.). Further experiments have shown that mixtures of diisocyanates with the usual fillers and extenders have a very short potlife or give nonhomogeneous glues (5,6). 

The amino-resins are also suited for use on wood-composite products. In some cases the fire retardant can act as the binder for particle board (99, 100), the adhesive for plywood (99, 100), or a... 

Each of these monomers has more than two reactive sites and can react with up to three others to form a cross-linked polymer that is much stronger and more impact-resistant than the linear polymer. The very first synthetic plastic, Bakelite, was made in 1907 from cross-linked phenol and formaldehyde. Modern phenol-formaldehyde polymers are used as adhesives for plywood more than a billion kilograms are produced per year in the United States. 

Synthetic Resin Adhesives for Plywood (Phenolic and Amino plastic), 1945. 

Resi-Mix. [Geoi]gia-Pacific] Ready-to-ase adhesives for plywood. 

The UF adhesives for plywood generally contain less than 2 mole of formaldehyde per mole of urea, and most of them are condensed to a slightly viscous, hydrophilic stage and are quite soluble in water. The degree of polymerization, and hence the viscosity under comparable conditions of UF resins for plywood is generally higher than those of UF resins for particleboard. 

Prior to bonding, all lamellas were planed (removal of wood was less than 1 mm) in order to ensure a smooth and flat surface. Two lamellas were then bonded together with commercial phenol-formaldehyde (PF) adhesive for plywood production, supplied by Fenolit d.d., Borovnica, Slovenia. The adhesive was applied with a roller at an application amount of 180 g/m. The press temperature was 160°C, the pressure was 0.8 MPa, and the press time was 40 min. 

The addition of small percentages of Na+-montmorillomte (NaMMT) nanoclay does not appear to improve much the performance of thermosetting phenol-formaldehyde (PF) and phenol-uiea-formeildehyde (PUF) resins used as adhesives for plywood and for wood particleboard. X-ray diffraction (XRD) studies indicated that NaMMT does not become completely exfoliated when mixed in small proportions to PF resins, contrary to that observed for acid-setting urea-formaldehyde (UF) resins. Differential scaiming calorimetry (DSC) indicated that NaMMT has no accelerating effect on the curing of alkaline PF resins, contrary to that observed for UF resins. 

Amino and phenolic resin adhesives for plywood, fiberglass insulation, laminates, friction products, and abrasive products are reactive oligomers that cure by self-condensation... 

Adhesives of the aminoplastic (see Step polymerization) and phenol formaldehyde (see Phenolic adhesives single-stage resoles and Phenolic adhesives two-stage novolacs) types are most widely used. Although basically similar, an adhesive for plywood manufacture will require a different formulation to one for particle board, or medium-density fibre board (MDF) since methods of application and processing differ. Thus, in plywood, large sheets of veneer must be uniformly coated with adhesive, usually by a roller or curtain coater in particle board, chips or wafers must be coated with very fine adhesive droplets, while small bundles of wet fibres must be sprayed with adhesive in the manufacture of MDF. Hence, formulation and production of resins has become a mixture of art and science, with resin manufacturers able to produce resins tailored for use in a particular board-manufacturing plant, or with a particular species of timber. 

Approaches have been developed that allow some other adhesives to be used with wet wood. The simplest of these approaches uses foamed adhesives. Foaming allows the adhesive to be applied at a higher solid content, often having only 15-20% water, and so higher moisture content in wood can be tolerated, and the composite cures faster since less moisture needs to be removed during cure. A recent investigation reported use of a soy protein-modifled PF as a foamed adhesive for plywood production (38). The soy replaced animal blood in the formulation, which not only improves durability but can alleviate health concerns. 

A by-product of this process is acetone, which is also a commercially important compound. Over two million tons of phenol is produced each year in the United States. Phenol is used as a precursor in the synthesis of a wide variety of pharmaceuticals and other commercially useful compounds, including bakelite (a synthetic polymer made from phenol and formaldehyde), adhesives for plywood, and antioxidant food additives (BHT and BHA, discussed in Chapter 11). 

Herzberg W J 1960 Pinus radiata tannin-formaldehyde resin as an adhesive for plywood. Aust J Appl Sci 11 462-472... 

Phenol/formaldehyde, melamine/formaldehyde, and urea/formal-dehyde prepolymer resins (B-stage) are widely used as thermosetting adhesives for plywood and other wood products. In prior... 

Phenolic resins have found widespread use in numerous areas, in particular, molded and cast plastic articles, adhesives for plywood as laminating resins, and thermal insulation. Because these resins are versatile and inexpensive, numerous reactants have been used to modify the resins in order to improve certain properties, for example, dispersing ability, or to inhibit specific properties that are undesirable for certain uses. 

The main disadvantage associated with these glues was that the working time could be very short. A few degrees drop in temperature could be sufficient to set the adhesive hence their unsuitability as adhesives for plywood applications. Further they were very susceptible to attack by moisture. 

The main outlet for urea formaldehyde resins is in adhesives for plywood and chipboard. The ratio of urea to formaldehyde used will influence the properties of the adhesive. For example, a resin with a high formaldehyde to urea ratio will give an adhesive having the best clarity, water resistance and mechanical properties. The main disadvantage of this type of adhesive is its poor water resistance. Hence, it cannot be used for exterior applications where it is superseded by adhesives based on phenolic resins. 

---