Oxidative-reductive Modification of Alkaline Pulping of Southern Pine Integrated with Hydrothermal Pre-extraction of Hemicelluloses

摘要

The objective of this study was to investigate the effect of process modification of the kraft pulping integrated with hemicellulose pre-extraction on the properties of pulp produced from softwood chips. Loblolly pine chips were pre-extracted with hot water until the sugar extraction yield reached targeted value of 10% and subjected to conventional and modified kraft pulping. Three process modifications were designed to improve the yield recovery capability of kraft pulping preceded by water extraction. These include: oxidative treatment (process modification 1); oxidative-reductive dual treatment (process modification 2); and, oxidative treatment followed by oxidative-reductive two stage treatment (process modification 3) prior to kraft pulping. In process modification 1, about 5% of the lost pulp yield (total 7%) caused by hemicellulose pre-extraction could be recovered with 15-20% polysulfide treatment prior to pulping. A complete recovery (7%) was achieved with simultaneous pretreatment using 15% polysulfide and 0.5% sodium borohydride with 0.1% anthraquinone in process modification 2. Two-stage treatment in process modification 3 using recycled 15% polysulfide followed by simultaneous treatment of 6% polysulfide and 0.4-0.5% sodium borohydride with 0.1% anthraquinone also achieved 100% yield recovery. Continuous recycling of 15% polysulfide employed in the process modification 3 maintains its yield protection efficiency in repeated recycling cycle. No significant changes in paper strength were found in handsheets prepared from three modified kraft pulping preceded by hydrothermal pre-extraction except for a minor reduction in tear strength.