DISSOLVATION RULES OF LIGNIN AND CARBOHYDRATES DURING RDH KRAFT PULPING OF EUCALYPTUS WOOD

Dissolving rules of lignin and carbohydrates(e.g.glucose,xylose,mannose,arabinose) during rapid displacement heating(RDH) kraft cooking for eucalyptus wood were investigated.Difference of cellulose crystallinity and α-cellulose content of pulps produced by conventional kraft cooking and RDH cooking were also studied.It was (observed) that delignification course during RDH pulping was divided into two phases:bulk phase and residual phase.As compared with conventional kraft pulping,the initial phase of delignification did not obviously occur during RDH pulping,and lignin was rapidly degradated and dissolved in the early period of RDH cooking.The dissolving rates of carbohydrates in the early period of RDH pulping were higher than that of conventional kraft pulping.Glucosidic component was rapidly dissolved in warm black liquor(WBL) stage and hot black liquor(HBL) stage of RDH cooking,but was slightly dissolved after HBL stage.Xylose 44.92%,mannose 33.46% and arabinose 49.09% have been dissolved in WBL and HBL stages of RDH process.After HBL stage,dissolving rates of xylose,arabinose and mannose decreased.As compared with conventional kraft pulps,RDH pulps have relatively high glucose(cellulose) content and relatively low xylose,arabinose and mannose(hemicellulose) content.The α-cellulose content of RDH pulp was a little higher than that of conventional kraft pulp.However,differences of cooking methods and cooking conditions have no significant effect on cellulose crystallinity.