Dry wood

Table 2. Additives Used in Production of Particleboard as a Percentage of Dry Wood Weight...

Operation Energy consumed per dry wood produced, MT/t Total consumption, %... 

Larch Gum. Larch gum [37320-79-9] (larch arabinogalactan) is obtained by water extraction of the western larch tree, iLarix occidentalism the heartwood of which contains 5—35% on a dry wood basis. In the early 1960s, a countercurrent hot water extraction system was developed, and the gum was produced commercially by the St. Regis Paper Co. under the trade name Stractan. The potential production capacity of this gum is 10,000 t/yr based on the wood residues from the lumber industry. However, the product could not compete with gum arabic, and commercial production is now limited to small batches for a specific medical appHcation. 

The word lignin is derived from the Latin word lignum meaning wood. It is a main component of vascular plants. Indeed, lignin is second only to polysaccharides in natural abundance, contributing 24—33% and 19—28%, respectively, to dry wood weights of normal softwoods and temperate-2one hardwoods. 

The cells that make up the stmctural elements of wood are of various si2es and shapes and are firmly bonded together. Dry wood cells may be empty or pardy filled with deposits such as gums, resias, or other extraneous substances. Long and poiated cells, known as fibers or tracheids, vary gready ia length within a tree and from species to species. Hardwood fibers are - 1 mm long, and softwood fibers are - 3 to 8 mm. 

Carbohydrates. Carbohydrates are the principal components of the cell wall, comprising 65—75% by weight of the dry wood. Total hydrolysis yields simple sugars, primarily glucose and xylose in hardwoods and glucose and mannose in softwoods. Minor amounts of galactose, arabinose, and rhamnose are present. 

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

The values expressed are for percent oven-dry wood and extractive-free wood. Australian-grown wood. Percent oven-dry wood. 

Fig. 1. Relationship between the moisture content of wood (% of dry wood) and relative humidity at different temperatures.

At low relative humidities, adsorption is due to interaction of water with accessible hydroxyl groups. These are present on the lignin and on the carbohydrates ia the noncrystalline or poorly crystalline regions. The high differential heat of adsorption by dry wood, - 1.09 kJ/g (469 Btu/lb) water. 

For extended, noncyclic exposures, it can be assumed that the entire piece teaches the temperature of the heating medium and is, therefore, subject to permanent strength losses throughout the piece, regardless of size and mode of stress application. Because dry wood is a good insulator, it often does not teach the daily extremes in temperature of the air around it in ordinary constmction thus, estimates of long-term effects should be based on the actual wood temperatures experienced by critical stmctural parts. 

Capacitive interference of pipelines is of minor importance. It arises in the immediate vicinity of overhead power lines or railway power lines in the construction of pipelines where the pipe is laid on a foundation that is well insulated from soil (e.g., on dry wood). The pipeline picks up a voltage with respect to the soil. The value of this voltage depends on the voltage of the interfering conductor at the time as well as the capacities between the conductors and the pipeline. 

Oriented strandboard (OSB) resins are quite similar to plywood resins, though they tend to be lower in alkalinity and higher in solids. Sinee OSB resins are sprayed onto dry wood in small discrete droplets rather than applied in glue lines, the problems associated with holding the glue on the wood surfaee are not usually issues of coneem. Adhesive dry-out and loss of flow displace over-penetration as major difficulties. 

Because the porous growth patterns of wood vary, the densities of various dry woods also vary (200-1200 kg/m- ). The porosity of wood, of course, greatly influences the wood s utility as a substrate. The wood porosity affects also the type and form of the adhesive as it affects the ability of the substrate to absorb water and other solvents from the adhesive, as well as allowing some of the adhesive to be absorbed over larger surface areas. 

Medium-density fiberboard (MDF) a flat pressed wood composite panel composed of randomly oriented wood fibers obtained by thermomechanical wood pulping and bonded by hot-pre.ssing by using thermosetting adhesive resins. The panel has generally a density of approximately 850 kg/m- and the average amount of resin solids in the board core section is between 11 % and 14% on dry wood. 

Obviously, the closer the particles are to each other, the more likely it is that they will stick together and form larger clumps, which usually means that the flow is not uniform. This view combined with Eq. (14.18) is a greatly simplified explanation of why the mass flow ratio q, for dry wood chips can rise to five or even higher and still the flow of the mixture of air and large chip particles can be handled as a uniform suspension, a uniform dilute-phase flow, although it is not actually dilute. The mass flow ratio for fine coal powder, however, has to be much less than five in order for the flow to be handled as a uniform dilute flow. 

Wood has very useful thermal properties. Dry wood has a low thermal conductivity and a high heat capacity, and is resistant to thermal decomposition at temperatures up to 250°C for short periods of time. 

Acetylated polysaccharides form part of the structure of wood, the acetyl radical constituting some 2-5Vo by weight of the dry wood. Hydrolysis to free acetic acid occurs in the presence of moisture at a rate varying from one species to another a wood of lower acetyl content can liberate acetic acid much faster under given conditions than another wood of higher content Small quantities of formic, propionic and butyric acids are also formed but their effects can be neglected in comparison with those of acetic acid. There is a broad, but only a broad, correlation between the corrosivity of a wood and its acidity. The chemistry of acetyl linkage in wood and of its hydrolysis has been examined in some detail. ... 

Since much of the wood in common use today for joinery, including external window frames and roof trusses, is redwood, such as Pinus sylvestris, preservative treatment is very necessary. However, whilst it is known that little corrosion of fasteners can take place in dry wood (<15 Vo moisture... 

Heat Treatment Temperature (°C) Weight Loss (X of Dry Wood) Initial Rate of Oxygen Chemisorption x lO3 (mmole g min" ) Oxygen Chemisorption (mmole g )... 

Species Total resin acids (kg/tonne of dry wood) References... 

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