Pulping
To create the paper a long process is involved to ensure the wood chips that are pulped are clean and suitable for purpose. To start, the trees are cut and lumbered to create tonnes of logs which go through a machine to be debarked and chipped.
These chips are then put through one of two processes – mechanical pulping or chemical pulping. Mechanical pulping involves grinding, to reduce wood to individual cellulose fibres by forcing the debarked logs against a revolving stone to make a pulp.
The stone is sprayed with water to remove fibres from the pulp stone however results in little removal of lignin (a non-fibrous constituent of wood) that binds fibres together and reduces paper quality, however mechanical pulping is low cost and generates a higher throughput.
Chemical pulping involves ‘cooking’ wood chips to reduce the raw material in to individual cellulose fibres. There are two types of chemical cooking, sulphite and sulphate, and both results in better separation and reduction of lignin to produce better quality paper.
The more popular of the two processes is sulphate, which involves using alkaline solutions to digest wood and adding sodium sulphate to increase the strength of the pulp – this is the process where Kraft comes from as it is the Swedish word for ‘strength.’
Out of both of these processes the Kraft is either used there and then and as mentioned before is dark brown in colour, or bleached during the pulping process to produce a white Kraft.