Wood substrates

Cured amino resins are far too brittle to be used alone as surface coatings for metal or wood substrates, but in combination with other film formers (alkyds, polyesters, acryUcs, epoxies) a wide range of acceptable performance properties can be achieved. These combination binder coating formulations cure rapidly at slightly elevated temperatures, making them well suited for industrial baking appHcations. The amino resin content in the formulation is typically in the range of 10—50% of the total binder soHds. 

By varying molecular weight and functionaUty of the castor polyols and the type of isocyanate, a variety of clear and pigmented urethane coatings can be prepared. Copolymers of vinyl and castor-based urethane have also been reported for use as exterior coatings for plywood and flexible substrates (90) and for appHcation over steel, concrete, and wood substrates (91). 

Once applied, the eure rate will depend heavily on the moisture eontent and/or moisture vapor permeability of the substrates between whieh the adhesive is sandwiehed. For wood substrates, typieally full eure oecurs in a day with the faster systems. Misting of the substrates with water is sometimes conducted prior to adhesive applieation to further speed eure, or when the substrates are substantially moisture impermeable. 

Acid-induced gelling reactions of PF resins can cause severe deterioration of the wood substrate and therefore have lost any importance in the wood adhesives field. Pizzi et al. [85] describe a procedure for the neutralization of acid-hardened PF glue lines by partly using as hardener a mix of p-toluene sulfonic acid with a... 

Chemical modification of wood is defined as the reaction of a chemical reagent with the wood polymeric constituents, resulting in the formation of a covalent bond between the reagent and the wood substrate. 

A wood treatment in which the temperature is sufficient to cure the oil to some extent, but leaves the wood substrate unaltered. 

Wellons, J.D. (1977). Adhesion to wood substrates. In Wood Technology Chemical Aspects, Goldstein, I.S. (Ed.). ACS Symposium Series, 43, pp. 150-168. 

Amino resms are probably the mos important modifiers for alkyd resins. Many industrial baking enamels, such as those for appliances, coil coatings, and automotive finishes (especially refinishing enamels), are based on alkyd-amino resin blends. Some of the so-called catalyzed lacquers for finishing wood substrate require very low bake or no bake at all. 

Balik, C.M. Fornes, R.E. Gilbert, R.D. Williams, R.S. The Micro-Macro Effects of Acid Deposition on Painted Wood Substrates, draft report to U.S. Environmental Protection Agency, 1989. 

Fig. 7.2. The structure of the translocation pathway in mycelial cords. (A) Hyphae fanning out at the distal end of a cord of Phanerochaete velutina (scanning electron microscopy by A. Yarwood) (B) Internal structure of a cord of Serpula lacrymans, showing vessels and cytoplasm-filled hyphae and extracellular matrix material. (C) Diagram of the components of the translocation pathway (adapted from Cairney, 1992) V, vessel hypha f, foraging front a, anastomosis (D) A cord system in beech woodland showing both corded mycelium and diffuse growth in contact with the wood substrate.

Experimental load deflection curves (Fig. 3.) illustrate the large difference in crack propagation observed in each case. A difference in stiffness between both bonded specimens is observed and results from either a difference in the bond line quality or from interfacial conditions. For both specimens, adherends were made from the same sample of wood. Both wood substrates contained no apparent defects and had the same longitudinal Young s modulus (14500 MPa). Both also had the same growth characteristics (oven dry specific density, annual growth rings), and as a consequence very close values of transverse and shear modulus adjacent to the bond line. Thus, any difference in stiffness is likely to be due to... 

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