Accessory components of wood

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Accessory constituents (from the Latin accedere "to enter") are secondary parts or secondary constituents that occur in wood in addition to the main constituents cellulose , hemicellulose and lignin . The accessory components can be divided into organic and inorganic compounds. The organic components are extract substances that can be extracted from plant tissues using extraction methods. The occurrence of accessory components in wood is limited to a percentage of one to 20 percent. The proportion in the moderate latitudes is predominantly up to five percent. Very large proportions can be found in the tropics (up to 20 percent).

Primary ingredients

Primary ingredients are those substances that are present in every plant metabolism and thus can contribute slightly to a specific determination of wood. Distinctions between types of wood can only be made based on the amount of wood constituents. The primary ingredients in wood include:

carbohydrates

Carbohydrates are an elementary part of the metabolism of plants. A carbohydrate can be represented characteristically with the gross formula C n (H 2 O) m . The polysaccharides are mainly represented in the trees by glucose , fructose and sucrose . These are found in the phloem sap and in the storage tissues of the trees. They are used for cell structure and growth. In the sapwood, the living part of the tree, there is therefore more sugar than in the heartwood . The sugar content in the tree also varies according to the season. This is highest in spring and has its lowest point in October.

The influence of the carbohydrates on the natural durability of the wood depends on the concentration of saccharides in the wood. The assumption is that the resistance to fungi decreases the higher the sugar content in the wood.

Economically, starch has a significant use. The starch, which belongs to the carbohydrates, has cohesive properties and is used, among other things, in the production of corrugated cardboard as a component of glue. In addition, starch is a food product.

amino acids

Amino acids (uncommon aminocarboxylic acids, outdated amido acids) are a class of organic compounds with at least one carboxy group (-COOH) and one amino group (-NH 2 ). They belong to the group of carboxylic acids as well as to that of amines. Their proportion in wood is approx. 0.5% and is free and bound in proteins . The NH2 group is an important food source for wood pests . Accordingly, an increased proportion of amino acids in the wood has a negative effect on the natural durability. Eating damage or fungal attack usually reduce the strength properties of the wood.

Fats

Fats are esters of the trihydric alcohol glycerine (propane-1,2,3-triol) with three, mostly different, mostly even-numbered and unbranched aliphatic monocarboxylic acids , the fatty acids . The natural fats in wood are the primary ingredients and are mainly represented by the glycerol ester compound .

The waxes belonging to the fats are aliphatic polyesters esterified with saturated fatty acids. A substance is called wax if it is kneadable at 20 ° C, solid to brittle, has a coarse to fine crystalline structure, is translucent to opaque in color , but is not glass-like and melts at over 40 ° C without decomposition.

Fats and waxes mainly serve to store carbon and are stored in the parenchymal cells of the wood. Most of the softwoods have fats, whereas hardwoods have fats and waxes. Another function of the waxes is the formation of a cuticular layer on the upper and lower sides of the leaf. This serves to protect against dehydration and to regulate perspiration .

Economically, fats are useful in a variety of ways. Among other things, the oils from seeds or the fats from fruits are used. For example, the Douglas fir wax in the bark is suitable for use as a shoe polish, car wax or lubricant. The carnauba wax has a similar purpose. A well-known product is the oil obtained from the oil palms for the production of bioethanol.

Secondary ingredients

The secondary wood constituents include those substances that are only found in certain types of wood. The amounts and compositions of the ingredients depend on:

  • the type of wood
  • the location (forest type, climate, etc.)
  • the season
  • the age of the tree
  • the type of fabric of the tree

from. The secondary wood constituents include extractable organic ( isoprenoids , aromatic impurities, etc.) as well as non-extractable inorganic accessory components.

Structure of isoprene

Isoprenoids

Many natural substances can be formally derived from isoprene , which are combined to form isoprenoid natural substances. Among other things, two isoprenoid organic secondary wood constituents are known in wood. These include resins, rubber and essential oils. Isoprene has a boiling point of 33 ° C and is one of the volatile organic compounds (VOCs). The isoprene emission is several hundred million tons per year and takes place via needles and leaves.

Resin leakage on a spruce
Resin leakage on a spruce

Resins

Resins act as exudates in wood. Resin is a collective term and describes a variety of chemical compositions in nature. Resins still consist to a not insignificant extent of volatile and aromatic compounds. The field of application of this accessory component is very extensive. Among other things, it will:

  • for the production of adhesives ,
  • for the production of foams ,
  • as impregnation resins (e.g. for electric motors) and
  • for surface finishing and surface sealing

used.

Terpenes

There are mono-, sesqui-, di-, and tri-, tetra-, and polyterpenes. The most common terpenes found in conifers include α-pinene, β-pinene and Δ-carene. Triterpenes are most common in hardwoods. 3-Carene is found in turpentine oils (in Russian turpentine oil, from Pinus sylvestris, as the second most common component), the oil of black pepper and is also found in citrus oils, firs and juniper species. Turpentine oil. In: Römpp Online. Georg Thieme Verlag, accessed on May 25, 2014.

Aromatic accompanying substances

This category includes phenols, tannins, lignans (stilbenes, flavans) and flavonoids in trees. All of these substances are characterized by aromatic characteristics. Aromatic molecules have at least one ring system which, according to Hückel's rule , contains a number of 4n + 2 (n = 0,1,2, ...) delocalized electrons in conjugated double bonds, free electron pairs or unoccupied p-orbitals .

An important representative of the aromatics is the tannin. Due to the chemical structure, the vegetable tanning agents can be divided into the following two groups:

  1. Hydrolyzable tannins, e.g. B. Gallotannins , basic building blocks are tannic acids z. B: Gallic or ellagic acid in connection with glucose
  2. condensed tannins, e.g. B. Pyrocatechins , basic building blocks are aromatic polyhydroxy compounds such. B. catechin

Tanning agents can be used medicinally through the process of tanning. The tissue can be compacted superficially, and a protective membrane is formed, e.g. B. on a mucous membrane.

The best-known representative of the phenols is salicylic acid and is mainly found in the bark of the willow. The acetate of salicylic acid, acetylsalicylic acid , is used as a pain reliever . In plants, salicylic acid from a messenger substance is used for the biosynthesis of antibodies. In general, phenolic ingredients are mainly found in the heartwood of trees and are formed when the parenchymal cells die.

The lignans are dimeric phenylpropanes with a β-β linkage. These are in the heartwood and sores of conifers.

The flavonoids form a large class of natural plant substances. They consist of two aromatic rings linked by a tetrahydropyran ring. The functions of the flavonoids in wood or for humans are:

  • pharmaceutical (taxol from the yew tree for cancer therapy),
  • Messenger substances,
  • Fungicide,
  • Insecticide,
  • Flavor and odor of food (tea, red wine, etc.).

Inorganic components

The inorganic, non-extractable, secondary wood constituents remain when the wood is incinerated (burned). The most common elements are calcium, potassium, magnesium and manganese. A wide variety of inorganic compounds are formed from the macro or micro elements. The low proportion of inorganic elements in wood is very high compared to its influence on wood properties. The proportion of cations or anions is therefore largely responsible for the pH value of the wood. Discoloration of the wood can occur. The fiber properties are influenced, which means that the gluing capabilities and surface treatments change noticeably during the later woodworking.

Analysis methods for determining accessory components

The analytical methods for identifying the wood components and their accessory components are based on various solvents that are added to the wood. The extract substances are released (extracted) through chemical reactions and can be quantified. Examples of extraction agents and what they take from the wood are listed in the following table:

Extractants Extract substance
Pethrolic ethers Free fatty and resin acids in spruce
Acetone with water Free sugars and lignans in spruce
Ethanol with water Beech tannins

The table shows only a very small insight into the extraction methods. The substances that are extracted here are extract substances. Non-extract substances, i.e. some inorganic elements of wood (calcium, potassium, magnesium, manganese, etc.) can be massively analyzed and made visible using SEM images or laser microscopes.

See also

literature

  • Baumann, 1928
  • FW Herrick, HL Hergert: Utilization of chemicals from wood: Retrospect and Prospect , Chapter 11. pp. 443-515. In: FA Loewus, VC Runickles (Ed.): Recent Advances in Phytochemistry . Vol. 11. The Structure, Biosynthesis, and Degradation of Wood . Plenum Press, New York 1977.
  • NI Nikitin: Die Chemie des Holzes , 1955, p. 334
  • In: Römpp Online. Georg Thieme Publishing House
  • Heldt, H.-W. with the collaboration of Fiona Held (1996). Plant biochemistry. Spectrum Akademischer Verlag, Heidelberg, pp.582
  • O. Faix, Fundamentals of Wood Chemistry (2004)
  • Lange / Stevanovic, 1993
  • "The Tree Myth" by Lauert (2000)
  • Hegnauer, R. (1962 to 1994), Chemotaxonomy of Plants. An overview of the distribution and the specific importance of plant substances. Birkhäuser Verlag, Basel
  • Bickel- Sandkötter, S. (2001). Useful plants and their ingredients. Quelle & Meyer Verlag, Wiebelsheim
  • K. Freudenberg
  • Jäckle, S. (2000). Characterization of the distribution of important nutritional elements and soluble carbohydrates in beech and oak wood fresh from the forest. Diploma thesis at the University of Hamburg, Department of Biology
  • Saranpää, P. to N. Nyberg (1987). Seasonal variation of neutral lipids in Pinus sylvestris L. sapwood and heartwood.
  • D. Fengel, G. Wegener: Wood - Chemistry, Ultrastructure, Reactions , Verlag N. Kessel, Reprint 2003, 613 pages, ISBN 3-935638-39-6
  • H. Sixta, Handbook of Pulp, ISBN 3-527-30999-3

Individual evidence

  1. (Baumann, 1928)
  2. ^ FW Herrick, HL Hergert: Utilization of chemicals from wood: Retrospect and Prospect , Chapter 11, pp. 443-515. In: FA Loewus, VC Runickles (Ed.): Recent Advances in Phytochemistry . Vol. 11. The Structure, Biosynthesis, and Degradation of Wood . Plenum Press, New York 1977.
  3. (NI Nikitin: Die Chemie des Holzes , 1955, p. 334)
  4. D. Fengel, G. Wegener: Wood-Chemistry, Ultrastructure, Reactions . Walter de Gruyter, Berlin, New York 1989.
  5. after K. Freudenberg
  6. H.-W. Heldt, Fiona Held: Plant Biochemistry . Spektrum Akademischer Verlag, Heidelberg 1996, p. 582
  7. O. Faix: Fundamentals of wood chemistry