Effects Of Ionic Liquid Assisted Ultrasonic Pretreatment On The Separation Of Broad-Leaf Kraft Pulps

Green separation technology for plant fiber components with low energy consumption is an important way to realize the sustainable development of pulp and paper industry.It is also an effective approach to solve the resource shortage and environmental pollution problems faced by the industry.In this work,the application of[BMIM][HSO₄]and[TEA][HSO₄]ionic liquid pretreatment,ultrasonic pretreatment and ionic liquid assisted ultrasonic pretreatment on eucalyptus kraft pulp?KP?during the bleaching process was studied.The effects of pre-hydrolysis and ionic liquid pretreatment on the viscosity,?-cellulose and Fock reactivity of ECF and TCF bleached acacia KP pulps were analysed.The effects of different pretreatment methods on the component separation efficiency and pulp bleachability were investigated.The main results are listed conclusions are as follows:First,the cooking process of eucalyptus sulfate was optimized in this work,where21%alkali,25%vulcanization,90 min heat preservation,170?maximum cooking temperature and 1:5 liquid ratio was used.Under this operating condition,the yield of the pulp was 49.95%and the kappa number was 20.08.For the hand-sheets,its tensile strength was 6.61 N·m·g^-1,the burst index was 5.984 k Pa·m²·g^-1,the tear index was8.044 m N·m²·g^-1,and the folding endurance was 175 times.OAD₀E_OPD₁ bleaching for eucalyptus KP pulp was carried out with ionic liquid and ultrasonic pretreatment.The results showed that both ultrasonic and ionic liquid pretreatment enhanced the component separation efficiency,by promoting the penetration of bleach agents into plant fibers,improving both bleachability and physical strength of the paper.Among them,[TEA][HSO₄]combined with ultrasonic pretreatment presented better performance than that of[BMIM][HSO₄].With The presence of[TEA][HSO₄]assisted ultrasonic pretreatment,the pulp viscosity and brightness increased by 15.0%and 4.1%,the kapper number decreased by 66.2%,the tensile strength increased by 17.0%,the tearing index increased by 19.4%,and the folding endurance increased by 220%.The application of ionic liquid pretreatment for ODP short bleaching sequence was also investigated.The results showed that ionic liquid pretreatment improved the separation efficiency of plant materials and protected pulp fibers from bleaching damages.10 wt%is an optimized usage for ionic liquids pretreatment,at which the pulp showed an improved overall performance.More folds,cracks and holes were observed on the surface of pulp fibers,and the crystallinity of the fiber increased by 28.3%.The[TEA][HSO₄]pretreatment presented better overall performance than that of[BMIM][HSO₄].With[TEA][HSO₄]pretreatment,the cellulose content of the bleached pulp increased by 0.8%,while the hemicellulose and lignin content decreased by 7.8%and 17.8%,respectively.The pulp viscosity and brightness increased by 17.8%and3.0%,and the kappa number decreased by 68.8%.In terms of the hand-sheets,its tensile strength decreased by 14.0%,the bursting index increased by 12.3%,the tearing index increased by 13.6%,and the folding endurance increased by 153%.Ionic liquid pretreatment showed a remarkable effect during the oxygen deligninfication of eucalyptus KP pulp.The results showed that at 10 wt%ionic liquid usage the component separation efficiency of fiber could be improved,where the pulp peroperties were elevated and the physical strength of paper were enhanced.The lignin content in pulp fibers was reduced by 48.0%at most,and the viscosity and polymerization degree of pulp fiber increased by 15.7%and 17.5%,respectively.In terms of the hand-sheets,its tensile strength and tear index increased by 10.6%and15.8%,and folding endurance increased by 110%.The average fiber length,width and kink index were also increased after the pretreatment.Ionic liquid pretreatment selectivily extracted the lignin,hemicellulosed components out from the plant fibers and deconstructed the amorphous regions of cellulose,resulting in the increase of crystallinity by 27.3%.XPS and UV analysis verified that the extracted lignin components concentrated on the fiber surface,where they could be converted into quinone compounds during the oxygen delignification.After the pretreatment,the content of quinones in the pulp increased by 57.3%.These components could be easily removed in the following bleaching sequence.Ionic liquid pretreatment could improve both the component separation efficiency of pre-hydrolyzed raw materials during the cooking process,and the bleaching efficiency of bleaching agents during the subsequent ECF and TCF processes.The results showed that pretreatments with pre-hydrolysis and pre-hydrolysis assisted ionic liquid could reduce the amount of cooking liquid and improve the bleachability of the pulp by loosing the physical structure of fibers.In comparison with the ECF bleached acacia KP pulp without pretreatment,ionic liquid assisted pre-hydrolyzed samples presented better overall performance,where the viscosity of the bleached pulp decreased by 9.9%,the?-cellulose content decreased by 0.5%,and the Fock reactivity improved by 60.9%.while,the viscosity of the bleached pulp decreased by 5.6%,the?-cellulose content decreased by 0.08%,and the Fock reactivity increased by 13.2%.To sum up,this work illiustrated that ionic liquid,ultrasond,and hydrolysis pretreatment mehods could be applied in various pulp and paper-making processes to facilitate the component separation efficiency of broad-leaved woods,elevate the bleachability,and improve the performance of pulp and paper.Therefore,these techanique presented great potential for their applications in pulp and paper industries.