Production of paperboard

Pulp is the primary raw material from which corrugated board and base papers are manufactured. Pulp is made from the cellulose fibres from wood. Wood is a fibrous material which is constantly renewed. For making paper, he kinds of wood are used in particular which are obtained from managed woodlands, referred to as waste timber, which otherwise can hardly be put to any use at all. The acceptance of this timber by the paper industry provides the forestry sector with an economic basis to support the management of the woodlands, which is economically vital. The second eminently important raw material is recycling fibre, or secondary fibre material, which is obtained from waste paper and used cardboard.

Raw materials are processed into semi-finished materials. The aim here is to obtain individual fibres from the timber or from the waste paper.

Sulphate pulp is produced by boiling the wood chips with sodium lye, which causes the wood to break down into individual fibres. The paper type which is manufactured from this is called Kraftliner.

Sulphite pulp is obtained when an acid is used in order to release the lignin. If the residual lignin on the fibre is also removed by means of oxygen, white pulp is obtained. In the case of the manufacture of semi-chemical pulp, only a part of the lignin is released from the wood chips by chemical means. In this case the chips are comminuted by mechanical means into their individual fibres. These are retained in the lengths to which they have grown, and the lignin coating which is present causes the individual fibre to be very stiff. The thermoplastic properties of lignin and the high levels of strength referred to make this material very well-suited for the manufacture of the type of paper known as fluting (also called semi-chemical pulp).

The most important raw material for the corrugated board industry in terms of quantity, however, is waste paper. In the pulper the waste paper is again broken down into its individual fibres by using water, which are then fractionated into short and long fibres by means of a screen.

The paper machine makes an endless strip out of the finely-purified finished stuff (1% solids, 99% water), which when rolled up actually only still contains 5-9 % water. Modern paper machines have an operating width of 7.50 metres and a production speed of about 1,000 metres a minute.