NALT Full

Kraft pulping involves cooking (digesting) wood chips in an alkaline solution (sodium hydroxide, hydrosulfide, and sodium sulfide) for several hours during which time the chemicals attack the lignin in the wood. The dissolved lignin is later removed leaving behind the cellulose fibres. Unbleached kraft pulp is dark brown in colour, so before it can be used in many papermaking applications it must undergo a series of bleaching processes.