Chemical pulp
For the production of wood pulp, the pure fibre has to be set free, which means that the lignin has to be removed as well. To achieve this, the wood chips are cooked in a chemical solution.
In case of wood pulp obtained by means of chemical pulping, we differentiate between sulphate and sulphite pulp, depending on the chemicals used. The yield of chemical pulping amounts to approximately 50%. The fibres in the
pulp produced by this process is called woodfree. It is this type of pulp which is used for all Sappi fine papers.
The sulphate process is an alkaline process. It allows for the processing of strongly resinous wood types, but this requires expensive installations and intensive use of chemicals.
The sulphite process utilises a cooking acid consisting of a combination of free sulphur acid and sulphur acid bound as magnesium bi-sulphite (magnesium bi-sulphite process).