Wood products reconstituted

Water-borne adhesives are preferred because of restrictions on the use of solvents. Low viscosity prepolymers are emulsified in water, followed by chain extension with water-soluble glycols or diamines. As cross-linker PMDI can be used, which has a shelf life of 5 to 6 h in water. Water-borne polyurethane coatings are used for vacuum forming of PVC sheeting to ABS shells in automotive interior door panels, for the lamination of ABS/PVC film to treated polypropylene foam for use in automotive instmment panels, as metal primers for steering wheels, in flexible packaging lamination, as shoe sole adhesive, and as tie coats for polyurethane-coated fabrics. PMDI is also used as a binder for reconstituted wood products and as a foundry core binder. 

Wood (qv) is arguably the oldest building material used by humans to constmct their dweUings. It is a natural product obtained from trees, used in both stmctural and decorative appHcations. The chemical composition of wood is largely cellulose (qv) and lignin (qv). Today there are a variety of composite or reconstituted wood products, such as plywood, particle board, wood fiber boards, and laminated stmctural beams, where small pieces of wood or wood fiber are combined with adhesives to make larger sheets or boards (see Laminates). 

Reconstituted Wood Products. This category includes three general varieties wood flake board, particle board, and wood fiberboard. The manufacturiag processes are similar for all these products except for the size of the wood particles that are glued together. 

Uie recycling of wood waste is also increasingly being used, where timber products at the end of life are usually reduced by chipping, or fibre production, and the resultant material is then reused in reconstituted wood products. Strict monitoring and control are required in order to ensure that inappropriately treated waste is not included in the feedstock stream for recycling wood. The use of recycled wood in reconstituted products is rising rapidly for example, in the UK, the panel products industry used 400 000 tonnes of recycled wood in 1999, and this had risen to 932000 tonnes by 2002 (UK Forestry Commission data 2003). 

Phenolics - [BUILDINGMATERIALS-PLASTIC] (Vol 4) -m plywood [BUILDING MATERIALS - SURVEY] (Vol 4) -m reconstituted wood products (BUILDING MATERIALS - SURVEY] (Vol 4) - [COLORANTS FOR PLASTICS] (Vol 6) -electroless plating of [ELECTROLESS PLATING] (Vol 9) -m laminates [LAMINATED MATERIALS, PLASTiq (Vol 14)... 

Property enhancement by acetylation has been frequently reported over the years in other reconstituted wood products such as flakeboards, particleboards, and fiberboards [8,9,11,12,59-64]. Table 16 shows the laboratory decay test of low-density acetylated particleboards made from perishable albizzia wood. They were resistant to attack by Tyromyces palustris (brown rot), Coriolus versicolor (white rot), and Chaetomium globosum (soft rot) above 12% WPG. These acetylated boards with 20% WPG also exhibited an improved resistance to attack by the destructive Formosan termite, Coptotermes formosanus, in the laboratory. However, their performance was unsatisfactory in the wet tropics with a higher hazard of termite attack. High resistance to fungal and bacterial attack in acetylated southern pine and aspen flakeboards was evidenced in laboratory and fungus cellar tests [12]. 

Acetylation and phenolic resin impregnation arc found to be applicable to reconstituted wood products in yielding good biological resistance. Treatments with crosslinking agents and WIC can be applied to these end products but further studies are required to improve production technology. 

Note As this table shows, the largest outlet for amino resins by far is their use as adhesives or binders for reconstituted wood products made from sawdust and wood chips. Urea-formaldehyde resin is most commonly used. Melamine-formaldehyde resin can provide improved water resistance and may be combined with the urea resin to provide an improved product. Molding compounds are about the next most important outlet for amino resins. It is approximately evenly divided between urea and melamine. The primary use for urea moldings is in the electrical field, while the most important area for molded melamine plastic is dinnerware. 

Uses of aqueous-based adhesives Because of the need to remove water, most applications for aqueous adhesives are made with materials that are able to allow transmission of water vapour hence, the major uses are with paper, wood and fabric (see Adhesives in the textile industry), either as binders or laminating adhesives. A list of applications would include the following remoistenable gummed tape, tube winding, box manufacture, plywood manufacture, reconstituted wood products, abrasives and woodworking. 

Reconstituted wood products are produced by the formation of small pieces of wood into large sheets. The finished product can be classified as fiber-board or particleboard depending on the nature of the basic wood component. 

Some reconstituted wood products may be factory-primed with paint and some may even have a factory-applied topcoat. In order to protect wood from fungi and insects, treatment with toxic chemicals provides the necessary protection. A variety of materials may be used but oil and oil-borne... 

Wood has a number of disadvantageous properties as described earlier in this chapter. It is biodegradable, flammable, dimensionally unstable to water, and degradable by ultraviolet light, acids, and bases. There has been a considerable amount of research expended over the years to correct these defective properties for both solid wood and reconstituted wood products. 

The oldest organic construction material was and still is ->wood. Modem reconstituted wood materials are plywood and various kinds of chip boards. Sometimes, RR-based products are used as binders for their production. 

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