Behavior of xylans from Eucalyptus species. Part 1. The influence of structural features of eucalyptus xylans on their retention in kraft pulp

4-O-methylglucuronoxylans were isolated from the wood and pulp of different Eucalyptus species (E. dunni, E. grandis, E. nitens, E. urograndis and E. urophylla) and characterized by H-1 NMR spectroscopy and size-exclusion chromatography (SEC). The content of 4-O-methylglucuronic acid (MeGlcA) varied between the eucalyptus species from 1.90 to 2.80 expressed as MeGlcA/10 xyloses, whereas in the pulp, the total uronic acid content was approximately 1.02, from which the half was hexenuronic acid (HexA). From the MeGlcA linked to the xylan chain 9-26% are substituted in position O-2 by hexose units. The M-w of the xylans extracted from wood ranged between 26.1 and 28.4 kDa. The retention of 4-O-methylglucuronoxylans (51.3-58.7%) during kraft pulping was high, and the retention is related to the content of MeGlcA group, the content of MeGlcA group substituted at O-2, and the average molecular weight of the xylans. The parameters observed affect the overall pulp yield and pulp properties.