Civil Engineering Reference
In-Depth Information
Wood tar consists mainly of hydrocarbons. Dry distillation from coniferous
trees requires temperatures of 1000°C, and polyaromatic hydrocarbons such as
benzo-a-pyrene are formed. Extraction of beech wood tar takes place at temper-
atures of around 250-500°C. The PAH content of this tar is low - about 0.1 per
cent of the equivalent for carbolineum (chlorinated anthracene oil) which is
extracted from coal. When extracting beech wood tar there is no emission of phe-
nols - something that does occur with other timbers.
Lignin
After cellulose the main constituent of timber is lignin, whose function is to fix
cellulose fibres and protect against mould. In the construction industry, lignin is
sometimes used as a glue in wood fibre boards.
Cholofonium
This is a resin extracted from pine resins used in the paint industry and in the
production of linoleum.
Drying oils
These are extracted from soya beans, linseed and hemp seeds and are used exten-
sively in paint production.
Glycerols
Fatty substances in plants, known as glycerols, can be extracted from fatty acids
by adding lye, and used in the production of soap.
Etheric oils
These are extracted from herbs such as rosemary and lavender and are often used
as aromatic additions to paint products.
Starch
Starch can be extracted from potatoes and wheat and used as a glue or binder in
paint.
Silicates
Siliceous plants contain large quantities of active silicates which react very
strongly with lime, and the ash left over after burning the plant can be used as
pozzolana in cements. Common horsetail ( Equisetum arvense ) is particularly rich
in silica.
Potassium carbonate
Deciduous trees contain a particularly high amount of potassium carbonate, which
is the main constituent of ash after timber has been burnt. Potassium carbonate
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