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Sulphur-free cooking for value added cellulose

: Karlström, K.; Sjögren, B.; Vorwerg, W.; Volkert, B.

Cellulose chemistry and technology 48 (2014), No.9-10, pp.781-786
ISSN: 0576-9787
Journal Article
Fraunhofer IAP ()

To study sulphur- and chlorine-free processes to produce pulps for triacetylation and preparation of films for LCD screen application was one of the aims in the EU project AFORE. It was shown possible to produce pulp suitable for triacetylation from Eucalyptus globulus chips with pre-hydrolysis soda cooking and a single oxygen delignification step. Pre-hydrolysis with water at elevated temperatures extracts wood components, mainly hemicelluloses and the wood matrix is opened to facilitate alkaline pulping. After a severe pre-hydrolysis extracting some 25% of the wood raw material, a subsequent soda cook reduces the lignin content to about 1%. The oxygen delignification step produces a pulp with low lignin content, kappa no 1.4, and low hemicelluloses content, < 2 wt% xylose. The resulting cellulose had high molar mass and produced highly transparent triacetate solutions. It was also possible to produce a transparent cellulose triacetate film by solution casting with good physical properties without using plasticizer. The process also results in a sulphur-free black-liquor suitable for lignin separation by the LignoBoost process. The resulting lignin is of high purity with low hemicelluloses content.