Effect of pulping conditions on the amount of methylglucuronic and hexenuronic acids in kraft pulps of Eucalyptus globulus

The effect of different pulping conditions, active alkali (15% and 20% AA), H-factor (130 to 2360) and cooking temperature (155 degrees C and 165 degrees C) on the methylglucuronic (MeGIcA) and hexenuronic (HexA) acid content of kraft pulps of Chilean Eucalyptus globulus were evaluated. The initial amount of MeGlcA in wood chips was 255 mmol/kg wood and after pulping the residual amount of MeGIcA was approximately 110 mmol/kg pulp (on a wood basis). In cookings with 15% AA, the HexA content increased to 70 mmol/kg pulp with no decrease with increasing H-factor. In cookings with 20% AA, the HexA content in pulps reached values of 60 mmol/kg pulp followed by a constant decrease with increasing of H-factor. For bleachable grade pulps (kappa number 15), values higher than 60 mmol/kg pulp of HexA were found. The calculated contribution of the HexA to the kappa number of E globulus pulps varied from 10% to 50% and was much more significant in pulps with low kappa numbers.