Wood, properties required

Table 1.3 shows a rough breakdown of material prices. Materials for large-scale structural use - wood, cement and concrete, and structural steel - cost between UK 50 and UK 500 (US 75 and US 750) per tonne. There are many materials which have all the other properties required of a structural material - nickel or titanium, for example - but their use in this application is eliminated by their price. 

This has been made possible by the development of suitable adhesive systems that are able to bond the partieles together. The synthetie adhesives offer a consistency of performance that is diffieult to aehieve with natural produets sueh as tannins, and at a cost that has enabled rapid growth to be aehieved. At the same time the adhesive systems have shown a toleranee to a range of wood properties that has enabled most wood residues sources to be used. The environmental effects of formaldehyde emissions from panels made using UF adhesives have been successfully addressed. Initially these required higher resin addition rates to offset a loss in physieal property levels, but further development has reclaimed much of this additional cost. 

Different forms/profiles of plastic/wood are used. Extruded profiles can contain at least 70 wt%, some up to 90%, wood content and produce wood-like appearance. Proper drying of the wood is required since it is hygroscopic otherwise burning can occur and properties are reduced. These products compete in different markets particularly the building and construction market and where water is located like a boating dock. It is entering the 8 billion USA residential siding market that is now at least half vinyl. 

Solution Properties. Lignin in wood behaves as an insoluble, three-dimensional network. Isolated lignins (milled wood, kraft, or organosolv lignins) exhibit maximum solubiUty in solvents having a Hildebrand s solubiUty parameter, 5, of 20.5 — 22.5(J/cm ) (10 — ll(cal/cm ) > and A// in excess of 0.14 micrometer where A]1 is the infrared shift in the O—D bond when the solvents are mixed with CH OD. Solvents meeting these requirements include dioxane, acetone, methyl ceUosolve, pyridine, and dimethyl sulfoxide. 

Nonwood fibers are used in relatively small volumes. Examples of nonwood pulps and products include cotton Enters for writing paper and filters, bagasse for cormgated media, esparto for filter paper, or Manila hemp for tea bags. Synthetic pulps which are based on such materials as glass (qv) and polyolefins also are used (see Olefin polymers). These pulps are relatively expensive and usually are used in blends with wood pulps where they contribute a property such as tear resistance, stiffness, or wet strength which is needed to meet a specific product requirement. 

The anatomical stmcture of wood affects strength properties, appearance, resistance to penetration by water and chemicals, resistance to decay, pulp quabty, and the chemical reactivity of wood (5). To use wood most effectively requires a knowledge of not only the amounts of various substances that make up wood, but also how those substances are distributed ia the cell walls. 

Wood preservatives ate appHed either from an oil system, such as creosote, petroleum solutions of pentachlorophenol, or copper naphthanate, or a water system. Oil treatments ate relatively inert with wood material, and thus, have Htde effect on mechanical properties. However, most oil treatments require simultaneous thermal treatments, which ate specifically limited in treating standards to preclude strength losses (24). 

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