Synthesis of condensed lignin model compound and the formation mechanism of LC bonds during kraft pulping (II)

The changes of the synthesized condensed lignin model compound and the formation mechanism of lignin-carbohydrate (LC) bonds during kraft pulping were investigated in this paper. After dehydrodivanillylalcohol was synthesized, it was cooked by kraft method in the existence of xylose. In order to study the LC bonds between lignin and xylose in details, the products from kraft pulping were classified into four fractions by acidification and ethyl acetate extraction. Then the four fractions were determined by FT-IR and C-13-NMR. The results showed that dehydrodivanillylalcohol was very stable although it was cooked by kraft method in the existence of xylose. There were lots of undegraded dehydrodivanillylalcohol and new LC bonds in ethyl acetate extractives. However, most of undegraded xylose existed in the acid-soluble fractions. There were no newly formed LCC in the acid-insoluble fractions and acid-soluble fractions. Furthermore, it was also found that condensed lignin structures could connect with xylose through benzyl ether bonds which were stable in alkali solution.