Wood materials main constituents

Wood is a composite material that is made, up basically of a mixture of three main constituents, cellulose, hemicellulose, and lignin (see Textbox 54), all of them biopolymers synthesized by the plants, which differ from one another in composition and structure (see Textbox 58). The physical properties of any type of wood are determined by the nature of the tree in which the wood grows, as well as on the environmental conditions in which the tree grows. Some of the properties, such as the density of wood from different types of trees, are extremely variable, as can be appreciated from the values listed in Table 71. No distinctions as to the nature of a wood, whether it is a hardwood or a softwood, for example, can be drawn from the value of its specific gravity. 

Interest in renewable resources as raw materials for chemicals and energy has intensified in recent years as a result of anticipated shortages of petroleum and natural gas ( 1, 2, 3). A significant part of this effort has been devoted to the production of alcohols, particularly methanol and ethanol, from wood ( - ) Methanol is the main constituent of "wood alcohol", made for a great many years by the destructive distillation of wood, especially hardwoods W. From a ton of hardwood, one could expect about 60 lb, that is 7.5 gallons of methanol, along with a variety of other chemicals. Wood alcohol is no longer made. The processes discussed in recent reports, are quite different,... 

Ar human civilization. Indeed, archaeol-Y ogists organize early human history in terms of materials—the Stone Age, in which only natural materials such as wood and stone were available the Bronze Age, in which implements were made of copper alloyed with tin and the Iron Age, in which ornaments, weapons, and tools were made of iron. Copper and iron are still of enormous importance. Copper is used to make electrical wiring, and iron is the main constituent of steel. 

Naphthalene is a bicyclic aromatic compound with the formula CioHg and structure 122. It was the main constituent of mothballs for many years, but toxicity led to its replacement with 1,4-dichlorobenzene (characterized as an insecticidal fumigant). Naphthalene is planar, with 10 7t-electrons in a ji-cloud above and below the plane of the 10 carbon atoms like benzene, it is aromatic and particularly stable. Another polycyclic aromatic compound has three rings fused together, as in 123 this aromatic molecule (14 7i-electrons) is called anthracene (formula C14H10). It is an important starting material in the synthesis of dyes such as the red dye alizarin (125) and is used in wood preservatives and insecticides. 

Cellulose is a very widely distributed polymer since it is the main constituent of the ceU-wall of all plants. Within the context of this book, the cellulosic materials which are of technological importance are cotton fibre and wood together with a few other substances of less significance. These various materials are briefly considered below. 

Conventionally, woody trees were broadly classified as softwood or gymnosperm and hardwood or angiosperm. Hardwood comes from angiosperms, such as oak, eucalyptus, and alder, which are dicots (Octave and Thomas, 2009). Softwood usually comes from evergreen conifer trees like pine or spruce. Other classifications of forest-based plants are broad-leaved trees and pine-leaved trees. Almost 46% of biorefinery prefers raw materials from conifer species, mainly spruce, pine, etc., and 31% of broad-leaves such as eucalyptus. Mostly stem wood is preferred as a suitable feedstock for the biorefinery process. Approximately 8% of the known biorefinery processes utilize all parts of the tree (Fitzpatrick et al., 2010). Thus the consensus in the biorefinery industry is that the feedstock selection should be based on the main constituents of the wood (cellulose, hemicellulose, and lignin) and not on specific chemicals (glucose, xylose, etc.) generally considered in conventional fermentation processes. 

Pine Oil. This oil is obtained by extraction and fractionation or by steam distillation of the wood of Pinuspalustris Mill, and other species. Most of the oil is produced ia the southeastern United States. The composition of the oil depends on the fractions chosen, but the chief constituents are terpene alcohols, mainly terpiaeol. Piae oil finds use as a germicide ia disiafectants and soaps as an ingredient ia iasecticides, deodorants, poHshes, sweepiag compounds, and catde sprays and as raw material for the manufacture of perfumery-grade terpiaeol [8000-41 -7], anethole [104-46-1], fenchone (137), and camphor (35). 

Raw materials are isolated from various parts of plants, e.g., blossoms, buds, fruit, peel, seeds, leaves, bark, wood, roots, or from resinous exudates. Different parts of the same plant may yield products with different compositions. For instance, steam distillation of the bark of the cinnamon tree gives cinnamon bark oil, which contains mainly cinnamaldehyde, whereas cinnamon leaf oil obtained from the leaves of the tree contains eugenol as its major constituent. 

The different main polymers in wood appear to have structural roles that are related to this microarchitecture. Cellulose, an intrinsically rigid crystalline material, provides the reinforcing framework of the cell walls. Theoretical treatments of stress-strain relationships in wood under load indicate that the stiflhess of the material is imparted primarily by cellulose fibrils 10). The main function of hemicellulose and lignin is to buttress the fibrils. Degradation of any of these wood constituents results in a decrease in the strength of the material. 

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