Alkaline Pulping of Portuguese Eucalyptus globulus: Effect on Hexenuronic Acid Content

The effect of alkaline pulping parameters (temperature, effective alkali (EA) and sulphidity) on the hexenuronic acid (HexA) content of Portuguese Eucalyptus globulus pulps was studied. The HexA content was calculated on a pentosan basis. Unlike softwood pulping, the amount of this acid increased during kraft cooking and only started to decrease in the final stage of delignification (kappa number below 12). EA and temperature were shown to be the main factors affecting the amount of HexA in pulps. A good correlation of data with the consumption of EA, regardless of the cooking conditions, was observed. The HexA content was quite high (45–60 mmol/kg pulp) for the kraft pulps obtained in the common range of cooking conditions and it is not advisable to lower this content in the cooking stage to maintain pulp quality.