Effects of delignification on residual lignin-carbohydrate complexes in normal pine wood and pine wood enriched in compression wood. 1. Kraft pulping

Delignifcation in the cooking stage to low kappa numbers is restricted by l oss of yield and deterioration in fiber properties, both of which may be at tributed to the wood raw material and the cooking conditions. Effects of wo od raw material from normal wood and wood enriched in compression wood on t he properties of unbleached pulps cooked under identical kraft pulping cond itions were investigated. The isolated residual lignin-carbohydrate complex es (RLCC) were characterized in order to follow the changes in the structur es of the lignin and carbohydrate part of the RLCC as a function of the woo d raw material and molecular size. After an identical kraft cook the compression wood pulp had a slightly high er kappa number and coarser fibers than the pulp fibers from the normal woo d. The RLCC contained a high molar mass and galactan-rich fraction, which w as suggested to originate from the outer layers of the fiber wall. The lowe r molar mass fraction containing monosaccharides from hemicelluloses and ce llulose was suggested to originate mainly from the secondary wall. The high molar mass fractions were slightly more condensed than the low molar mass fractions and they were present in greater amounts in pulps containing comp ression wood fibers.