The paperboard product
Since the mid-19th century the primary source of cellulose fibre has been wood. The fibre is separated by either chemical or mechanical means from naturally occurring species. In the case of Iggesund these species are mainly spruce, pine and birch from managed forests in Scandinavia and elsewhere in Europe. Such forests are maintained and expanded by the industries that rely on good access to timber. As a result of these efforts the stock of growing trees is increasing every year. In many areas growth now exceeds the amount of timber that is harvested.
This careful forest management ensures that even in the future the forests will form part of the sustainable cycle of nature and be a permanent source of raw materials.
The fibres in a tree trunk run parallel to its length. The fibre length varies according to the tree species. The relationship is indicated by the table below.
Cellulose and the laws of nature
Click to enlarge.
Carbon dioxide and water are converted into simple glucose-based sugars by the action of sunlight on the green chlorophyll-containing cells of the plant kingdom. This process is known as photosynthesis and is accompanied by the emission of oxygen. The natural sugars can be polymerised in plants to produce cellulose.
Cellulose has a high molecular weight and a straight-chain molecular structure. Plants use cellulose to grow by constructing cells – what we call fibres – and other structures which support the life of the plant. Each species has its own characteristic fibrous structure. Many tree species
have been cultivated and developed over time into a renewable source of raw materials for the production of a wide range of paper and paperboard products. Careful forest management and the manufacture of paper products are therefore closely linked.
Different levels of magnification of the wood
fibre, revealing the difference between the
seasonal growth and a close-up of the fibre
showing its hollow interior and the thin layer
of lignin holding the fibres together.
Cellulose makes up around 44 % of the wood fibre. Pure cellulose fibres are soft, flexible and white. The other constituents are hemicelluloses, lignin and extractives. Hemicelluloses are a group of substances related to cellulose but have lower molecular weight and a more complicated chain structure. Lignin is a more complex polymer and very different from cellulose. It is hard and brittle. Both hemicelluloses and lignin occur in the fibre but the main concentration of lignin is between the fibres, giving adhesion and rigidity to the structure of wood.
The process of fibre separation, or pulping, takes advantage of the differences between lignin and cellulose.
More laws of nature
There are natural properties which all wood fibres have to a greater or lesser degree as well as specific properties associated with the fibres of particular tree species. Fibre characteristics are also influenced by the method of pulping which is used.
The general properties
• The ability of fibres to grip each other and bond into a strong, homogeneous structure.
• Flexibility, shape and dimensional properties which enable fibres to form a uniform interlaced network.
• The capacity of the fibres to be favourably modified, mechanically or by using additives, during the production process.