Building Chemicals From Plants

Plants are the source of many chemicals used in building. The active ingredients may be extracted using water, alcohols or weak alkaline solutions. They may amount to 5 to 10% of the dry mass of the biomass material. For the most part production takes place in large-scale industrial units. In the late 1980s, however, the concept of smaller 'bio-refineries' was introduced; the concept being to process optimally all the constituents of a given crop in decentralized units near the source of cultivation (Ienica).

Methanol (CH3OH) is the simplest form of alcohol. It is a main constituent of wood vinegar, which deciduous trees - such as beech, poplar and birch - contain in large quantities. Today, methanol is principally produced from natural gas. It is widely used as a solvent, including in paints and cellulose based varnishes.

Methanol forms a base for the production of formaldehyde, used extensively in synthetic glues and some thermosetting plastics. Methanol can also be used to produce ethylene and propylene, the main building blocks for most conventional plastics.

Acetic acid (CH3COOH) can also be manufactured from wood vinegar but is mostly produced from fossil oils today. It has a disinfectant effect on timber that is attacked by mould, and is also important in the production of several bio-plastics.

Terpenes. Turpentine (C10H16) is distilled from wood tar, mostly from coniferous trees. Limonene is extracted from lemons. Both are widely used as solvents, especially in paints.

Fatty acids are produced from plants such as pine, linseed and soya. They are used in alkyd oil paints and varnishes as drying agents. They can themselves also be the binding agents in these products. Some, including butyric acid CH3(CH2)2COOH, are used further in producing bioplastics. Soaps, used for treatment and saturation of wood, are derived by reacting fatty acids with lye (potash) in a process known as saponification.

Starch (C6H10O5)n is a main constituent of potatoes, wheat, rice, maize, etc., and is a major ingredient in many glues used for wallpapers and paper laminates. Starch is also used as binding agent in paints and is a widely used base for bioplastics.

Lignin is a complex chemical compound most commonly derived from wood, where its function is to fix cellulose fibres and protect against mould. The cellulose industry normally produces quite large quantities of lignin as a by-product. Much of this is combusted for energy production. In the construction industry lignin is sometimes used as glue in wood fibre boards, and as additive in gypsum boards and concrete admixtures. It can be used for production of bioplastics, and insulation products of expanded (foamed) lignin are also under development.

Laccases are copper-containing enzymes that are found in many plants, and in fungi and micro-organisms. Laccase is used to activate lignin in plant-based boards and insulation products in order to bind them without the need to add glues.

Silicates. Siliceous plants contain large quantities of active silicates that react very strongly with lime, and the ash left over after burning the plants can be used as pozzolana in cements. Common horsetail (Equisetum arvense) is particularly rich in silica.

Potash. Deciduous trees contain a particularly high amount of potash K2CO3, the main constituent of the ash left over after timber has been burnt. Potash is an important ingredient in the production of glass. These days, however, it is almost exclusively produced industrially from potassium chloride.

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