Southern pine wood chips were contacted with pressurized hot water at temperatures of 160, 170, 180 and 190 °C for various times. The time-temperature effect on the extracted yields could be well described by the H-factor approach. A maximum of about 12% of the wood mass was extracted as wood sugars at an H-factor of about 1,500 hours. At an H-factor of about 500 hours, 8% of the wood mass was removed as polymeric sugars, with a minor removal of lignin (0.5% on ODW) and cellulose (0.3% on ODW). The delignification rate constants for kraft cooking of water pre-extracted chips are 40 to 60% higher than corresponding kraft control cooks. Unfortunately the total pulp yield based on the original wood at kappa 30 is 3 and 6% lower than the control at pre-extracting Hfactors of 200 and 500 hours respectively. The pulp viscosity suggests that the strength properties of paper made from the pre-extracted kraft pulps will be similar to that of the control kraft pulps. More research is needed to understand the mechanism underlying the lower kraft pulp yield based on original dry wood after pure water pre-extraction.
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