Kraft pulping and papermaking properties of hot-water pre-extracted loblolly pine in an integrated forest products biorefinery

Our objective in this research was to investigate the effect of hot-water pre-extraction of softwood on the behavior and papermaking properties of kraft pulp. Loblolly pine wood chips were treated with pressurized hot water at an elevated temperature of 170°C until the H-factor reached 200 and 500 hours. Kraft pulping of the extracted wood chips, performed at 15% effective alkali charge and 30% sulfidity, showed significantly improved delignification rates with 40% to 60% higher rate constants than corresponding kraft control cooks. The total pulp yield based on the original wood at a given kappa number was 3% and 6% lower than the control at the pre-extraction H-factors of 200 and 500 hours, respectively. The water pre-extracted kraft pulps showed a reduced refining response to PFI mill refining. The handsheets prepared from bleachable-grade pulps, after kraft pulping of hot-water pre-extracted wood chips for 400 H-factor hours, showed reduced tensile strength because of the lower percentage of hemicelluloses, compared to the control; but comparable pulp viscosity, zero-span wet tensile strength and tear resistance.