Hardwood chemical composition

The chemical compositions of selected North American hardwoods and softwoods are given in Table 1 (10). 

Timber is derived from a great number of botanical species, and has a wide range of properties. Variability also occurs within a single species and in order to achieve acceptable levels of uniformity, selection by grading is necessary. The timber trade differentiates between softwoods and hardwoods, and the latter are again separated into temperate and tropical types. Hardwoods are derived from broad-leaved and mainly deciduous trees, which are anatomically more complex and differ in chemical composition... 

Similar studies were conducted by Kudzin and Nord (64) on the hardwoods oak, birch and maple. The fungus employed to bring about the decay of these wood samples was Daedalea quercina. The results of the periodic analyses of the decayed wood and the chemical compositions of the alcohol extractable lignins are outlined in Tables 6 and 7 respectively. 

The chemical composition of paper will depend greatly upon the chemical treatment which the wood has been subjected to during its conversion to pulp. When the pulp has received little or no chemical treatment, as in the case of pulp for newsprint, the chemical composition is very similar to that of the native wood. However, in those papers which have been chemically delignified, the composition may be very different. The natural compositions of native wood (softwoods and hardwoods) and the chemical pulps derived from them are shown in Table 2.2. 

Wood contains a small proportion (usually less than 5%) of components which are extractable by organic solvents such as ethanol or dichloromethane. The proportion of these extractives varies in hardwoods and softwoods and also between species. Although many of these substances are removed during the chemical pulping process, some may still be retained in the final sheet of paper. Their chemical composition is very varied, and they include alkanes, fatty alcohols and acids (both saturated and unsaturated), glycerol esters, waxes, resin acids, terpene and phenolic components. The proportion which remains in pulp and paper depends upon the pulping process used. In general, acidic components such as the resin and fatty acids are relatively easily removed by alkali by conversion to their soluble... 

Table 28.1 compares the chemical composition of extractive-free hardwoods and softwoods. As cellulose and the hemicelluloses are both polysaccharides, it is obvious that the polysaccharide of wood is by far the dominant component, making up approximately 70 percent of both hardwoods and softwoods. 

The fuel characteristics are provided in Table 2. There are significant variations in ash content and net calorific value due to the fuel nature and moisture content. Fuel chemical compositions are in the typical ranges for softwood Pinus radiata) and hardwood ( . nitens) (12). 

Table V. Supplementary Chemical Composition Data for South and Central American Hardwoods...

Table XIV. Chemical Composition of Selected Hardwoods from the Southeastern United States (Percent Oven-Dry Wood) T3 m g...

Wood extractives vary in nature and amount within and between species, and within trees there is generally a decrease in extractive content with tree height. With both softwoods and hardwoods, extractives are more abundant in heartwood and generally these differ in chemical composition from those in sapwood, although in Pinus sp. some extractives are common to both (Hillis, 1962). Wood extractives... 

In Fig. 15, it is seen that the sheet made of cotton linters is more conductive than the other sheets. The sheet made with "Seagull W" hardwood pulp is the least conductive while the three other pulps have intermediate conductivity values. This behaviour seems to be related to the size of the different types of fibers used to make the sheets. As mentioned previously, hardwood fibers are shorter than softwood fibers, and consequently, there are more interfiber contacts in the sheets made of hardwood fiber. The surface area of a contact is very important to the conductivity. There may be a constrictive effect due to smaller surface at these contacts which results in a restricted flow of ions through the paper, and therefore a lower conductivity. Cotton linters are chemically different and longer than wood fibers and the sheet made of these fibers is more conductive. The difference between the three softwood pulps is probably related to a different chemical composition of its fibers. 

TABLE 3.2 A typical chemical composition of hardwoods, softwoods, and rice hulls... 

Even if, in the first instance, it might seem that this material does not vary a lot, the different amounts and differing chemical composition of the polyoses (see Section 9.4.2.3) and the lignins (see Section 9.4.2.4) in hardwood and softwood strongly affect the manufacturing processes. This applies for the extractives too, which due to their large chemical diversity influence some of the properties of wood and behave respectively different with regard to the chemical utilization of the wood. 

The application of heat to wood results in chemical changes in the material. The properties of the modified products depend on the one hand on the specific chemical composition of the different wood species, but, most notably between hardwoods and softwoods, on the other hand on the process conditions. Maximum temperatures, atmosphere and the duration of the thermal load are among the main parameters. Further influencing factors are the sample dimensions and whether the system is open or closed. 

Table 3A.7 Chemical composition of hardwood- and softwood-derived hydrolysates (%ofinitial wood dry matter) ...

Wood structure within a given tree species is not uniform but varies depending on the conditions under which the tree is growing. For example, trees compensate for exposure to wind or other types of bending pressure by the production of reaction wood. In softwood, the formation of reaction wood is induced on the compressed side of a bending trunk (compression wood), whereas in hardwood, reaction wood is formed on the elongated side of the trunk (tension wood). Reaction wood cells are morphologically similar to normal wood cells but differ in their cell wall structure and chemical composition. 

Wood is a naturally formed organic material composed of cells arranged in a parallel manner. The chemical composition of the woody cell walls is approximately 40-50% cellulose, 15-30% lignin, less than 1% mineral, 25-35% hemicellulose, and the remainder extractable matter of various kinds. Softwoods and hardwoods both contain approximately the same cellulose content. 

Besides cellulose, wood has several other constituents, the most important of which are hemi-celluloses and lignin. The chemical composition of wood varies widely according to source but a typical hardwood analysis might be as follows ... 

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