Wood adhesive glue

From antiquity, glues had been made almost entirely from materials of animal or vegetable origin, and were sensitive to moisture, oxidation, and bacterial or fungus attack. Because of these deficiencies, production of durable plywood, for example, was not possible. The modern plywood industry actually owes its growth to the availabiUty of relatively low cost urea adhesives. Plywood and chipboard or wood chip glues are often made at the plywood and chip board mill. 

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... 

The extent to which these new tissue adhesives and hemostats will influence surgical procedures can be seen in the following analogy. An effective carpenter cannot create a masterpiece without a saw to cut wood, nails to ensure local fixation of separate pieces of wood, and glue to cause broad surface apposition between wood surfaces. Similarly, the surgeon presently uses a scalpel to cut and divide tissues as well as a suture to create local fixation of tissues, but until... 

Wood Extractives. Glue bonds can be affected in many ways by extraneous components on or near the surface of wood. Chen (56) showed that extractive removal did improve bond performance and that the extractives, in part, reduce wettability. This effect is reflected also in Figure 2 from Jordan and Wellons (29). Hergt and Christensen (57) also showed that extractives can slow water adsorption from the adhesive into the wood, thus slowing development of cohesion in the adhesive. 

The chemistry of the most important wood components has been studied for hundreds of years and is well reviewed (2). Wood adhesives and glues are also thoroughly studied. However, the chemistry of the presently leading commercial compositions still involves as much art as science (3). The status of the present knowledge of the properties and chemistry of elemental sulfur (4,5) have been reviewed recently, and those of modified sulfur are reviewed in another chapter in this book. 

Casein adhesive glue Adhesive on animal basis, made of acid casein accruing from milk processing. Application as wood adhesive and in the packaging industry (label adhesive). 

The second frontier is a nondestructive technique to monitor the development of an adhesive bond in place. Neither the theoretical approach of surface free energy nor the empirical approach of bond destruction are as desirable as being able to measure adhesive and cohesive strength as they are developing in the glue-line. By constantly observing the science of other materials, we may obtain ideas and techniques that will let us move these and other frontiers in wood adhesion. 

The properties of wood-based panels are determined, in principle, by three parameters wood, adhesive, and processing conditions. Only if all of these three parameters are correct and well balanced in the wood bonding process, can proper bonding results be achieved. The influence of the first parameter, wood, involves several factors. Bonded wood often is described as a chain of several links wood (substance), wood surface, interface between wood and adhesive, surface of the glue line (boundary layer), and glue line itself. As is true for all such chains, the weakest link determines the strength of the chain, and in wood gluing this is in most cases the interface. 

D-0905. Test Method for Strength Properties of Adhesive Bonds in shear by Compression Loading (Fig. 8). A basic compression shear test which is widely used in screening wood glues. It is also used in specifications D-3110 (on nonstructural wood laminating ad hesives), D-2559 and D-3024 (on exterior and interior structural wood laminating adhesives respectively) and D-4317 (on polyvinyl acetate based wood adhesives). 

In D-3024 (see wood adhesive specifications), samples of laminated wood and plywood are tested both before and after water exposure and variously evaluated for shear strength and/or wood failure. These procedures could have applications in other wood glue testing as well. 

Casein is utilized in diverse ways, as an adhesive, as a binder, and as a protective colloid and stabilizer for emulsified adhesive systems. Casein is sold as a raw material, and casein adhesives are sold in both the dry and liquid forms. The useful wood adhesive known as casein glue, which is formulated with lime and sodium salts, will be addressed later. This section will cover other uses of casein, for which the solubilization of the casein is generally accomplished with the use of heat, and at lower pH s than for the lime-containing glues. 

CASEIN AND PROTEIN BLEND GLUES AS WOOD ADHESIVES... 

The wood adhesives discussed here will be the casein-lime-sodium salt glues and similar glues formulated with combinations of casein with soy flour, blood, or both. The pH of these adhesives is 11-12, due to the lime, sodium hydroxide, and sodium salts used for dispersion. 

Canadian Specifications. In Canada, CSA Standard for Wood Adhesives No. 0112.3-M 1977 covers the specifications for casein glue. Glue line requirements for wood doors are covered in CSA Standard 0132.2-M 1977. (Copies may be obtained from Canadian Standards Association, 178 Rexdale Blvd., Rexdale, Ontario, Canada, M9W 1R3. 

An adhesive may be defined as a material which when applied to surfaces of materials can join them together and resist separation. Adhesive is the general term and includes cement, glue, paste, etc. and these terms are all used essentially interchangeably. Various descriptive adjectives are often applied to indicate certain characteristics. For example, to indicate the physical form of the adhesive, e.g. liquid adhesive, liquid two-part adhesive, film adhesive its chemical form, e.g. epoxy adhesive, cyanoacrylate adhesive, polychloroprene adhesive to indicate the type of materials bonded, e.g. metahto-metal adhesive, paper adhesive, wood adhesive or to show the conditions of use, e.g. solvent based adhesive, cold-hardening, or -curing, adhesive, hot-melt adhesive. 

Glue, n Originally, a hard gelatin obtained ftom hides, tendons, cartilage, bones, and so on of animals. Also, an adhesive prepared from this substance by heating with water. Through general use, the term is now synonymous with the term adhesive. However, the term is most commonly used for wood adhesives. 

In the field of wood adhesives we have already seen that the traditional animal glue is capable of making strong joints if correctly made and applied, the bond is actually stronger than the... 

Evostik Wood Adhesive Humbrol Carpenter s Wood Glue Unibond Woodworker Adhesive HMG PVA Adhesive HumbrolCascamite U rea/formaldehyde type, one part, mix with water. 

The 2-imino-4-thiazolines may be used as ultraviolet-light stabilizers of polyolefin compositions (1026). 2-Aminothiazole improves adhesive properties of wood to wood glue (271). Cbmpound 428 exhibits antioxidant properties (Scheme 242) (1027). Ammonium N-(2-thiazolyl)dithio-carbamate (429) is a bactericide and fungicide used in industrial products such as lumber, paint, plastics, and textiles (1037). Compound 430 is reported (1038) to form an excellent volume of foam coating in aluminum pans when ignited with propane. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

In gluing, the adhesive must not saturate veneers or wood chips, but must remain in the glue line on the surface of the chips or between the pHes. The adhesives are generally of high viscosity so that they remain in the glue line. Thickeners and extenders, such as powdered pecan shells and wheat flour, are often used. 

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