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Delignification of spruce ( Picea abies  [L.] Karst.) during ASA (modified alkaline sulfite/anthraquinone pulping with alkali splitting) and magnesium bisulfite pulping was studied on a cellular level using scanning UV microspectrophotometry. This improved cellular analytical technique enables direct imaging of the topochemistry of lignin removal within the cell wall at different stages of cooking. The cooks were performed in a laboratory digester with forced liquor circulation. At 30 min intervals samples were taken for chemical and UV microscopic analyses. UV microscopy reveals that delignification during ASA pulping starts in the region of the pit canals and proceeds evenly across the entire S2 layer. As a specific feature of bisulfite pulping, a partial delignification of the radial compound middle lamella can be detected after 60 min of cooking. After 120 min, in both processes, the delignified cell walls show low UV absorbance values of both S2 and compound middle lamella. At this stage, approximately 90% of the initial lignin content is removed. At the end of both pulping processes, only parts of the cell corners can be distinguished by the new UV scanning technique.

holzforschung

Topochemical Investigations on Delignification of Picea abies [L.] Karst. during Alkaline Sulfite (ASA) and Bisulfite Pulping by Scanning UV Microspectrophotometry