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Chemical composition of wood

1. General composition

Wood pellets are made of wood, so there chemical composition is of course the same as dry cord wood. Dry wood is build primarily out the following compounds (in % dry weight):

• cellulose 40-50%
• lignin: 16-25% in hardwood - 23-33% in softwood
• hemi-cellulose: 20-30% in hardwood - 15-20% in hardwood
• other compounds (water, resins,...) 5-30%
• minerals 0,1-3%

The actual structure of wood is formed by the fiberlike structure of cellulose (and hemi-cellulose). Lignin forms the binding agent between these fiberlike structures.

It is in fact the same principle as is used in reinforced concrete.

2. Cellulose

Cellulose is onof the most abundat organic compounds on earth. Not only woody plants like trees are build from it but also all other plants. Cotton fibres are made of cellulose, wood consists for about 50% out of cellulose. One cellulosemolecule is a chain of thousands of glucose molecules. In it's pure form it is a white fibre. Cellulose for paper production is normally harvested from wood but some plants are a good source as well. Cellulose is also used in the chemical industry as a basic material for the production of synthetic products like tissues, coatings, explosives,...
Cellulose is without a doubt one of the most important and versatile products for the economy!

3. Lignine

 

Lignine isan organic polymer, typically found in wood. Softwood contains more lignine as hardwood. It is build from giant, 3-dimensional molecules of a complex composition. It is a dark compound that is a waste product from the paper industry.

4. Hemi-cellulose

Hemi-cellulose is closely related to cellulose. They are both structures build from glucose. But hemi-cellulose contains also other types of sugar molecules in its structures. The fibers are also shorter then those of cellulose, only a few hundreds of sugar molecules. Hard wood contains more hemi-cellulose then softwood.

5. other substances and minerals

There are other organics compounds in wood that don't have constructive properties. But they contribute to color, odor, strength and mass. Oils and fatty molecules, wax, starch,... are some examples.
Besides these organic substances, wood contains also anorganic minerals like calcium, natrium and magnesium in the form of phosphates, silicates, sulphates,...

 

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