Properties of woods

Practical subdivision Botanical subdivisions Description and biological role 

Outer Bark Epidermis Protect underlying tissues from mechanical injuries 

Inner bark Periderm Cortex Periderm cells form when epidermis ruptures due to phloem cells division 

Cambium Cambium Region where the growth in diameter of the tree takes place 

Sapwood Secondary xylem Sapwood that contains prosenchyma cells carries water and dissolved mineral cations from roots to inner cells antd it yields new wood every 

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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. 

Standard Methods of Evaluating the Properties of Wood-Base Fiber and Particle Panel Materials, ASTM D1037-93, American Society for Testing and Materials, Philadelphia, Pa.,... 

Many mechanical properties of wood, such as bending and cmshing strength and hardness, depend upon the density of wood denser woods are generally stronger (6). Wood density is determined largely by the relative thickness of the cell wall and by the proportions of thick-walled and thin-walled cells present. 

At equihbrium with relative humidity below 100%, the moisture ia wood is present primarily ia the cell wads. The moisture content at which the ceU wads would be saturated and the ced cavities empty is caded the fiber saturation poiat. Actuady, such distribution is impossible. Beginning at - 90% relative humidity, some condensation may occur ia smad capidaries. The determination of the fiber saturation poiat is based on the fact that certain properties of wood (eg, strength and volume) change uniformly at first with increasing moisture content and then become iadependent of the moisture content (Fig. 2). The equdibrium moisture content (usuady determined by extrapolation), at which the property becomes constant at 25 to 30% moisture, is represented by the fiber saturation poiat. 

The mechanical properties of wood tend to increase when it is cooled and to decrease when it is heated (6,18). If untreated wood heated in air is not exposed to temperatures of more than - 70° C for more than about 1 year, the decrease in properties with increasing temperature is referred to as immediate or reversible ie, the property would be lower if tested at the higher temperature but would be unchanged if heated and then tested at room temperature. The immediate effect of temperature on strength and modulus of elasticity of clear wood, based on several different loading modes, is illustrated in Figures 4—6 (6). 

Reaction to Heat and Fire. The physical and chemical properties of wood, like those of any organic material, are subject to deterioration. 

The fuel properties of wood can be summarized by ultimate and proximate analyses and deterrnination of heating value. The analytical procedures are the same as those for coal, but with some modifications. Analytical results generally vary about as much within a species as they do between species, except that softwood species generally have a higher carbon content and higher heating values than hardwood species because of the presence of more lignin and resinous materials in softwood species (see Fuels from waste). 

Densities and properties of wood vary considerably allow 20% on the data shown here. All properties vary with moisture content and temperature see text. 

All the properties of wood depend to some extent on the amount of water it contains. Green wood can contain up to 50% water. Seasoning (for 2 to 10 years) or kiln drying (for a few days) reduces this to around 14%. The wood shrinks, and its modulus and... 

The properties of wood are generally inferior to those of metals. But the properties per unit weight are a different matter. Table 26.4 shows that the specific properties of wood are better than mild steel, and as good as many aluminium alloys (that is why, for years, aircraft were made of wood). And, of course, it is much cheaper. 

Discuss, giving specific examples, how the anisotropic properties of wood are exploited in the practical applications of this material. 

Table 4 summarizes the various influences of the molar ratio on various properties of wood-based panels. Table 5 summarizes the molar ratios F/U and F/(NH2)2, respectively, of pure and melamine-fortified UF-resins currently in use in the wood-based panels industry... 

Correlations between the composition of aminoplastic resin and the properties of wood-based panels... 

Influence of the adhesive on the bonding process and the properties of wood products... 

The properties of wood-based panels are determined in principle by three influence parameters (1) wood component (2) adhesive (3) production conditions. Only if all three parameters are appropriately considered, can proper bonding results can achieved. 

The strength of a bond increases with the wood density in the region of approx. 0.7 to 0.8 g/cm Above this density, a decrease of the bond strength occurs. Performance and properties of wood-based panels are strongly influenced by the properties of the used wood. The anisotropy as well as the heterogeneity, the variability of various properties and the hygroscopicity have to be taken into account. Also the orientation of the wood fibers bonding solid wood has to be considered. 

Much wood has been used for the construction of dwellings and public buildings, vehicles and vessels and for functional and decorative objects for everyday life and/or ceremonial rituals. Until the eighteenth century wood was also the main source of fuel for heating and illumination and, since the second half of the nineteenth century, one of the major raw materials for making paper. It is of interest, therefore, to discuss the composition and properties of wood in general as well as the characteristics of wood from different types of trees and shrubs that were used in the past (Hackens et al. 1988). 

Table 7.3 Piloted ignition properties of wood species [ 11 ...

Due to environmental concerns regarding the use of certain classes of preservatives, there has recently been a renewed interest in wood modification. Wood modification represents a process that is used to improve the material properties of wood, but produces a material that be disposed of at the end of a product life cycle without presenting an environmental hazard any greater than that associated with the disposal of unmodified wood. Although wood modification has been the subject of a great deal of study at an academic level for over 50 years, it is only comparatively recently that there has been significant commercial development. 

Since many of the properties of wood are ultimately determined by its chemical constim-ents, wood modification often seeks to make changes at this level, in order to produce a material that has the desired properties. However, there are also wood modifications that do not involve alteration of the chemical composition of the material. 

Many of the physical, chemical and biological properties of wood can be understood by referring to the polymeric chemical constituents. In many cases of wood modification, these polymeric components are modified to some extent. The three structural polymeric components of the wood cell wall are cellulose, hemicellulose and lignin. There are many excellent texts describing the structure and function of these components, and only a brief account is given here. 

Many models have been developed that deal with the sorption properties of wood in the presence of moisture these have been discussed in a number of works (e.g. Skaar, 1972 Siau, 1984). They can be approximately divided into sorption models, such as the Brunauer-Emmett-Teller (BET) model, or solution models (such as the Hailwood-Horrobin, H-H, model). The sigmoidal shapes of sorption or desorption isotherms can be deconvoluted into two components. These are often taken to represent a monomolecular water layer (associated with the primary sorption sites, OH groups), and a multilayer component where the cell wall bound water molecules are less intimately associated with the fixed cell wall OH groups. 

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