Abstract
The article presents the results of a so far most extensive study on the effect of tree age on variation of the chemical structure of silver birch wood carried out in Poland. Field studies took place in 12 forestry districts distributed throughout the country. In each district, study sites were selected with stands aged approximately 30, 50, and 70 years in fresh broadleaved forest habitats, as well as in five districts in fresh mixed broadleaved forest habitats. Analyses were made of the contents of substances soluble in cold and hot water, ethanol and 1% NaOH, as well as the contents of cellulose, lignin, pentosans and ash, and the pH, of wood from 306 silver birch trees. Tree age was shown to have a significant effect on the contents of cellulose, pentosans, ash, and substances soluble in 1% NaOH. In the case of the other characteristics, age was found to have no significant effect. The cellulose content was lowest in 30-year-old stands and increased with tree age. Similar observations were made regarding ash content. Contents of pentosans and substances soluble in 1% NaOH were highest in the wood of the youngest trees. Since birch wood is used by the pulp and paper, board and energy industries, the knowledge of its chemical composition, depending on the age of the trees, can be of potential practical importance for its further application.
Highlights
Wood is one of the main sources of feedstock for the production of pulp and paper, boards and furniture, as well as increasingly popular biorefinery products
Samples were taken from birch trees aged approximately 30, 50, and 70 years, growing in habitat types classified as fresh broadleaved forest (FBF) and fresh mixed broadleaved forest (FMBF)
The content of substances soluble in hot water ranged from 0.86% in sample 3 (30 years) to 2.76% in sample 7 (50 years) (Table 1)
Summary
Wood is one of the main sources of feedstock for the production of pulp and paper, boards and furniture, as well as increasingly popular biorefinery products (biochemicals, biomaterials, biofuels, and others). The structural compounds of wood are natural biopolymers such as cellulose, hemicellulose (carbohydrates), and lignin, which together account for 90–95% of the mass of absolutely dry wood. The remaining 5–10% consists of nonstructural components such as mineral substances, substances soluble in organic solvent (extractives) and water (Prosiński 1984). Cellulose is a linear carbohydrate with a crystal structure. Hemicelluloses are noncellulosic carbohydrates that differ from cellulose in their composition and structure. Lignin is an amorphous polymer with a complex structure, mainly consisting of three phenylpropane monomers: p-hydroxyphenyl, guaiacyl and syringyl. The composition and amount of extractives depend on the solvent used (e.g. ethanol–benzene mixture, ethanol, acetone, dichloromethane, and ethyl ether). The ethanol–benzene mixture gives the highest level of wood extractives, but because of the high toxicity of benzene, other solvents like acetone and ethanol are commonly used. Substances soluble in cold and hot water include mineral salts, sugars, tannins, dyes, pectins, free acids, and others (Fengel and Wegener 1989; Han and Rowell 1997; Prosiński 1984)
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