AbstractsChemistry

The colouring matter is the name applied to a coloured material believed to be present in chemical wood pulps and regarded, by workers in the field, to be of considerable importance in the bleaching of these pulps. In the production of a good quality white pulp from wood, two main steps are involved, namely the "cooking" of the wood, and the bleaching of the raw pulp obtained. [...] Of the two main types of chemical pulps used commercially, namely, (a) acid or sulphite pulps, (prepared by heating under pressure with acid bisulphite solutions), and (b) alkaline pulps (prepared by heating under pressure with aqueous alkalies), the latter present by far the greater problem from the point of view of bleaching. Kraft pulps are especially difficult to bleach to a permanent white colour. The final colour is almost always slightly yellowish despite the fact that the "chlorine consumption" of these pulps is much larger than with sulphite and soda pulps. At this point it may be advisable to define the terms kraft and sulphate, since the careless use of these terms often leads to confusion. Sulphate pulp is produced by any alkaline "cooking" process in which the alkali lost is replaced by the addition of sodium sulphate in the regeneration of the "spent-liquor". Kraft is a type of sulphate pulp which has been intentionally undercooked to obtain a pulp of high strength. [...]