Effect of Hot-Water Extraction of Woodchips on the Kraft Pulping of Eucalyptus Woodchips

摘要

A study was carried out to investigate the effect of hot-water extraction on the kraft pulping of Eucalyptus woodchips. It was found that the digester yield did not change much after hot-water extraction. Delignification was nearly completed in 90 minutes at 150 deg C for hot-water extracted woodchips and carbohydrate loss during pulping continues throughout the pulping time. The chemical (alkali and sulphide) consumptions were higher, especially during the first 15 minutes of kraft pulping for hot-water extracted woodchips before the temperature even reached the desired 150 deg C. While lower chemical charges were required to render pulps of similar kappa, the residual chemical contents were much lower for pulping hot-water extracted woodchips. The resulting pulp kappa number was lower if mass-removal was higher from extraction, and more pronounced when the alkalinity/sulfidity was lower. Both Scott bond and burst strength decreased with increasing extent of extraction and increasing alkalinity and sulfidity, indicating that the fiber-fiber bonding was more removed due to hot-water extraction and harsher pulping conditions. The most important factor for the hardwood pulp, bulk, was found to be increased due to hot-water extraction.