Wood adhesives -hot melts

Related articles include Wood adhesives - hot melts, Wood adhesives - isocyanates/ urethanes, Wood adhesives - phenolics and Wood composites - adhesives. 

Chem. Descrip. Alkylated petrol, hydrocarbon resin Uses Adhesives (hot-melt pressure-sensitive, mastic) coatings (aluminum, emulsion, industrial, marine, paper, traffic, wire/cable) inks rubber (cements, mechanical and molded goods, tires) concrete-curing compds. caulking compds. plasticizer, softener, processing aid in rubber compds. food-contact adhesives, rubber articles, wood preservatives... 

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. 

Polyurethane adhesives are known for excellent adhesion, flexibihty, toughness, high cohesive strength, and fast cure rates. Polyurethane adhesives rely on the curing of multifunctional isocyanate-terrninated prepolymers with moisture or on the reaction with the substrate, eg, wood and ceUulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before apphcation. Two-component polyurethane systems are also used as hot-melt adhesives. 

Low viscosity cellulose propionate butyrate esters containing 3—5% butyryl, 40—50% propionyl, and 2—3% hydroxyl groups have excellent compatibihty with oil-modified alkyd resins (qv) and are used in wood furniture coatings (155). Acetate butyrate esters have been used in such varied apphcations as hot-melt adhesive formulations (156), electrostatically spray-coated powders for fusible, non-cratering coatings on metal surfaces (157—159), contact lenses (qv) with improved oxygen permeabiUty and excellent wear characteristics (160—162), and as reverse-osmosis membranes for desalination of water (163). 

Simple one-part acrylic compositions containing 9-borabicyclo-[3,3,l]-nonane (often called 9-BBN) cure and give good adhesion to wood [90], It has also been used to cure a reactive acrylic hot-melt [91] (Scheme 11). 

All edge finishing, except the lumber banding, is done after the panel surface has been finished. The wood or vinyl tapes are glued to the edges with PVA or hot melt adhesives. Plastic... 

Phenolic Resins Used for Wood Laminating D 4497 Test Method for Determining the Open Time of Hot Melt Adhesives... 

Kiguchi and Yamamoto [11] prepared hot-melt, self-bonded particleboards from benzylated wood particles. Their internal bonding strengths were about twice those of conventional particleboards. The interparticle bondings of the benzylated particleboards were plane adhesion. 

The thermoplasticization of wood can be subdivided into two categories (Fig. 8) (1) the total thermoplasticization of wood meals to produce products that can be used as wood based adhesives or as moulded substitutes for synthetic plastics [21-23] and (2) partial thermoplasticization of wood. The development of hot-melted and self-bonded wood materials and methods of improving the surface properties of natural wood by partial thermoplasticization of wood are reviewed below. 

Since the bonding strength of benzylated wood surfaces was similar to that achieved using commercial hot-melt adhesives, the development of self-bonded wood materials using surface benzylated particles was possible [32]. Suzuki and Iwakiri [33] reported that self-bonded fiberboard produced from benzylated asplund-processed fibers had high thermoplasticity, dimensional stability, and water resistance. Morita and Sakata also produced hot-melt cyanoethylated fiberboards, but they showed poor water resistance [34]. Both benzylated and cyanoethylated fiberboards lacked many of the inherent good properties of solid wood because they did not retain the cellular construction of wood. 

An emulsion polymer-isocyanate adhesive, a crosslinked polyvinyl acetate adhesive, a resorcinol-formaldehyde adhesive, a phenol-resorcinol-formalde-hyde adhesive, and an acid-catalyzed phenolic-formaldehyde adhesive developed bonds of high shear strength and wood failure at all levels of acetylation in the dry condition. A neoprene contact bond adhesive and a moisture-curing polyurethane hot-melt adhesive performed as well on acetylated wood as untreated wood in tests of dry strength. Only a cold-setting resorcinol-formal-... 

Adhesives wet, flow, and set to a solid during bond formation. The transformation from liquid adhesive to solid bond can be achieved in a number of ways. Where the adhesive is a polymer, the initial starting material is a liquid monomer or prepolymer that, under the conditions of bonding with heat, pressure, and/or catalyst, polymerizes to the solid polymer in the glue line. It is also usual to apply solutions of preformed polymers in suitable solvents to the faces of adherends, and allow bond formation to take place with evaporation of solvent. Alternatively, polymers that can be melted or softened to flow at elevated temperatures can be applied as hot melt adhesives to form the bond on cooling. With porous adherends like wood, penetration of the pores by liquid or molten adhesives is an important factor in bond formation. 

More widely used in wood bonding are hot-melt adhesives based on polyamides. A polyamide is formed when a monomer carrying two amine groups (-NH2) is reacted with another carrying two carboxylic acid groups (-COOH). Each amine group, at either end of the molecule, can condense with a carboxylic acid group of the other monomer to form an amide link (-CONH-) with the elimination of a water molecule ... 

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