Spruce lignin mild hydrolysis

Isolation and characterization of lignin structures Hydrolysis and separation. Mild hydrolysis has previously been used for the structural analysis of both softwood and hardwood lignins (10 -14). About 20% of the lignin was liberated from spruce wood and 40% of the lignin from beech wood by percolation of finely ground wood meal with water at 100 °C for several weeks (72). Such a mild hydrolytic treatment can be expected to lead to the rupture of only... 

Biphenyl structures and a-carbonyl-p-aryl ether structures, which are both assumed to be present in native lignin with a higher abundance than coniferyl alcohol structures (22,23) and both considered to be important leucochromophores, were not observed among die products, presumably because they are not present in spruce lignin as end groups. Both these types of structures are very stable and unlikely to be structurally changed during mild acid hydrolysis (24). 

Mild hydrolysis. Nimz 318,319] subjected wood to water percolation at 100 C for several weeks. Approximately 20% and 40% of the lignin from spruce and beech wood, respectively, became soluble. Sakakibara [320] obtained similar results using a 50% aqueous dioxane at 180°C. These soluble products were assumed to come mainly from the cleavages of a-aryl ether units. 

The natural content of stilbenes is considered to be very low in spruce wood lignin and this was confirmed in the present work (Figure 5). Analysis of the aqueous extracts after mild acidic hydrolysis revealed, however, that from wood to unbleached pulps and further to bleached pulps a stepwise conversion of diarylpropane to diguaiacyl stilbene structures takes place (Figure 5). The content of diarylpropane structures was found to be 25% less in the unbleached pulp samples than in the wood with a simultaneous increase in the content of stilbene structures. After hydrogen peroxide bleaching, the content of diarylpropane structures further decreased and the... 

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