Study On The Pulping Technology Of Dissolving Pulp Of Fast-growing Poplar

The fast-growing poplar was chosen as experimental materials in this paper.Theexperiment was conducted by squeezing, prehydrolysis, steam-explosion, cooking,bleaching and enzymatic treatment. The yield of hemicellulose removal in prehydrolysisprocess and effect of prehudrolysisonon nitric acid-ethanol cellulose,benzene-ethanolextract and ash wasstudied. The optimalconditions of hudrolysis and steam-blastingwere defined. thedosages of chemicals in the kraft cooking process were optimized.Bleaching properties of kraft pulpand effect of enzymatic treatment on pulp propertieswere studied. The Pulping properties of fast-growing poplar to produce dissolving pulpwere evaluated.Prehydrolysis of the squeezed and unsqueezed fast-growing poplarwas firstlyexperimented.The effect of temperature, acid charge and liquor ratio on chemicalconstituents of poplar chips was studied. The experimental results showed that theoptimal prehydrolysis conditions were0.75%of acid dosage, temperature165℃and3.5of liquid ration, in this conditions better prehudrolysis results were obtained. Theyield of pentosan removal from poplar chips was98.38%, cellulose content wasincreased to57.57%, and benzene-ethanol extract and ash were slightly changed.Thebetter properties of pulp were obtained when pressure was3Mpa and residence timewas300s in steam explosion treatment process.The cooking conditions of fast-growing poplar were secondly experimented. Forthe prehydrolyzedpolplar chips, the cooking conditions were24%of alkalicharge,26%of sulfidity,5of liquid ratio,168℃of temperature and120min of time. Forthe prehydrolyzedand blasted polplar chips, the cooking conditions were24%of alkalicharge,26%of sulfidity,5of liquid ratio,150℃of temperature and90min of time. Theresults showed that the fiber length, width, and proportion of fine fibers of chips withprehydroltsistogether with steam explosion pretreatment were better than that of chipswith prehydroltsis.Kraft pulp were bleached with ODEOPDfour stages bleaching sequence.In Ostage,the conditions were0.6MPaof oxygen pressure,10%of pulpconcentration,4%ofNaOH,0.5%of MgSO₄,95℃of temperature and90min of time. In D1stage, theconditions were2.5%ofClO2,80℃oftemperature and90min of time. In EOP stage, the conditions were2.5%of NaOH,0.5%of H₂O₂,0.2MPa of oxygen pressure and90minof time. In D2stage, the conditions were1.5%of ClO2,80℃of temperature and90minof time.88%ISO of the pulpbrightnesswas obtained in ODEOPDbieaching sequence.Xylanase treatment can improve the content ofα-cellulose and the reactivityproperties of pulp.The reactivity,α-cellulosecontent, crystallinityand degree ofpolymerization of the enzymatic treated pulp were respectively28.9,89.9%48.15%andrange of200to500.The properties of pulp can meet the quality demand of commercialdissolving pulp. Thereforefast-growing poplar can be used for producing dissolvingpulp.