Cellulose Production

Raw cellulose produced by the kraft process still contains residual lignin, which is responsible for the brown colour of unbleached pulp. Subsequent procedural steps minimise residual lignin to a large extent by oxidation of the chromophorous groups.

Oxygen delignification is the standard procedure in preparation for the subsequent bleaching sequence. In comparison to other chemicals, oxygen shows clear advantages; however, it shows poor reaction selectivity, and causes partial degradation of the cellulose fibres.

Magnesium sulphate has been successfully used as an additive in order to stabilise the cellulose during oxygen delignification. It is also beneficial in alkaline bleaching stages, in which hydrogen peroxide is used.