{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,10]],"date-time":"2026-04-10T20:38:51Z","timestamp":1775853531590,"version":"3.50.1"},"reference-count":47,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2021,5,15]],"date-time":"2021-05-15T00:00:00Z","timestamp":1621036800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["31770628, 31901267"],"award-info":[{"award-number":["31770628, 31901267"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Provincial Key Research and Development Program of Shandong","award":["2019JZZY010326, 2019JZZY010328"],"award-info":[{"award-number":["2019JZZY010326, 2019JZZY010328"]}]},{"name":"Foundation of State Key Laboratory of Biobased Material and Green Papermaking","award":["ZZ20190214"],"award-info":[{"award-number":["ZZ20190214"]}]},{"name":"Pilot Project for Integrating Science, Education and Industry","award":["2020KJC-ZD14"],"award-info":[{"award-number":["2020KJC-ZD14"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Oxygen delignification presents high efficiency but causes damage to cellulose, therefore leading to an undesired loss in pulp strength. The effect of ionic liquid pretreatment of [BMIM][HSO4] and [TEA][HSO4] on oxygen delignification of the eucalyptus kraft pulp was investigated at 10% IL loading and 10% pulp consistency, after which composition analysis, pulp and fiber characterizations, and the mechanism of lignin degradation were carried out. A possible dual effect of enhancing delignification and protecting fibers from oxidation damage occurred simultaneously. The proposed [TEA][HSO4] pretreatment facilitated lignin removal in oxygen delignification and provided fibers with improved DP, fiber length and width, and curl index, resulting in the enhanced physical strength of pulp. Particularly, its folding endurance improved by 110%. An unusual brightness reduction was identified, followed by detailed characterization on the pulps and extracted lignin with FTIR, UV, XPS, and HSQC. It was proposed that [TEA][HSO4] catalyzed the cleavage of \u03b2-O-4 bonds in lignin during the oxygen delignification, with the formation of Hibbert\u2019s ketones and quinonoid compounds. The decomposed lignin dissolved and migrated to the fiber surface, where they facilitated the access of the oxidation agent and protected the fiber framework from oxidation damage. Therefore, it was concluded that ionic liquid pretreatment has a dual effect on oxygen delignification.<\/jats:p>","DOI":"10.3390\/polym13101600","type":"journal-article","created":{"date-parts":[[2021,5,17]],"date-time":"2021-05-17T02:31:34Z","timestamp":1621218694000},"page":"1600","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["The Dual Effect of Ionic Liquid Pretreatment on the Eucalyptus Kraft Pulp during Oxygen Delignification Process"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1509-9985","authenticated-orcid":false,"given":"Letian","family":"Qi","sequence":"first","affiliation":[{"name":"State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jinke","family":"Liu","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jianmin","family":"Peng","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Guihua","family":"Yang","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Fengfeng","family":"Li","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yu","family":"Xue","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jiachuan","family":"Chen","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,5,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"11559","DOI":"10.1021\/acs.chemrev.5b00155","article-title":"Catalytic Transformation of Lignin for the Production of Chemicals and Fuels","volume":"115","author":"Li","year":"2015","journal-title":"Chem. Rev."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1081\/WCT-120018613","article-title":"Oxygen Delignification Chemistry and Its Impact on Pulp Fibers","volume":"23","author":"Yang","year":"2003","journal-title":"J. Wood Chem. Technol."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"13703","DOI":"10.1021\/acsomega.0c00869","article-title":"Evaluating the Potential to Modify Pulp and Paper Properties through Oxygen Delignification","volume":"5","author":"Esteves","year":"2020","journal-title":"ACS Omega"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"3149","DOI":"10.1007\/s10570-021-03713-0","article-title":"Differences and similarities between kraft and oxygen delignification of softwood fibers: Effects on chemical and physical properties","volume":"28","author":"Esteves","year":"2021","journal-title":"Cellulose"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"123984","DOI":"10.1016\/j.jclepro.2020.123984","article-title":"Lignin degradation in cooking with active oxygen and solid Alkali process: A mechanism study","volume":"278","author":"Ding","year":"2021","journal-title":"J. Clean. Prod."},{"key":"ref_6","first-page":"201","article-title":"Factors limiting oxygen delignification of kraft pulp","volume":"79","author":"Akim","year":"2001","journal-title":"Can. J. Chem."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"e3393","DOI":"10.18671\/scifor.v48n127.19","article-title":"A one-pot catalysis combining laccase with Cu(salen) for selective removal of refractory lignin units during oxygen delignification of bamboo kraft pulp","volume":"48","author":"Zhou","year":"2020","journal-title":"Sci. For."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"443","DOI":"10.1007\/s00226-006-0121-6","article-title":"Cellulose microfibril aggregates and their size variation with cell wall type","volume":"41","author":"Donaldson","year":"2007","journal-title":"Wood Sci. Technol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2055","DOI":"10.1007\/s10570-015-0593-3","article-title":"Delignification and cellulose degradation kinetics models for high lignin content softwood Kraft pulp during flow-through oxygen delignification","volume":"22","author":"Jafari","year":"2015","journal-title":"Cellulose"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"7754","DOI":"10.1021\/ie040061w","article-title":"Polyoxometalate-Catalyzed Oxygen Delignification of Kraft Pulp: A Pilot-Plant Experience","volume":"43","author":"Gaspar","year":"2004","journal-title":"Ind. Eng. Chem. Res."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1677","DOI":"10.12841\/wood.1644-3985.208.04","article-title":"Comparison of reinforced oxygen delignification methods for old corrugated board (occ) fibres","volume":"60","author":"Koc","year":"2017","journal-title":"Drewno"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.biortech.2018.02.122","article-title":"Fundamental understanding of distracted oxygen delignification efficiency by dissolved lignin during biorefinery process of eucalyptus","volume":"258","author":"Zhao","year":"2018","journal-title":"Bioresour. Technol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"573","DOI":"10.1007\/s00226-010-0367-x","article-title":"Influence of plum gum and sodium perborate addition on spruce kraft pulp properties during oxygen delignification","volume":"45","author":"Kirci","year":"2011","journal-title":"Wood Sci. Technol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2518","DOI":"10.15376\/biores.10.2.2518-2525","article-title":"Boosting Oxygen Delignification of Poplar Kraft Pulp by Xylanase Pretreatment","volume":"10","author":"Ji","year":"2015","journal-title":"Bioresources"},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Wasserscheid, P., and Welton, T. (2003). Physicochemical Properties of Ionic Liquids. Ionic Liquids in Synthesis, Wiley-VCH Verlag GmbH Co. KGaA.","DOI":"10.1002\/3527600701"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Abushammala, H., and Mao, J. (2020). A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids. Polymers, 12.","DOI":"10.3390\/polym12010195"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"114577","DOI":"10.1016\/j.molliq.2020.114577","article-title":"Evaluation of current and future solvents for selective lignin dissolution\u2014A review","volume":"321","author":"Rashid","year":"2021","journal-title":"J. Mol. Liq."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Hasanov, I., Raud, M., and Kikas, T. (2020). The Role of Ionic Liquids in the Lignin Separation from Lignocellulosic Biomass. Energies, 13.","DOI":"10.3390\/en13184864"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"208","DOI":"10.1016\/j.carbpol.2017.10.064","article-title":"Efficient conversion of lignocellulosic biomass to levulinic acid using acidic ionic liquids","volume":"181","author":"Khan","year":"2018","journal-title":"Carbohydr. Polym."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Lopes, A.M.D.C., Jo\u00e3o, K.G., Morais, A.R.C., Bogel-\u0141ukasik, E., and Bogel-\u0141ukasik, R. (2013). Ionic liquids as a tool for lignocellulosic biomass fractionation. Sustain. Chem. Process., 1.","DOI":"10.1186\/2043-7129-1-3"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"371","DOI":"10.1016\/j.biortech.2016.04.113","article-title":"Synergistic effects of surfactant-assisted ionic liquid pretreatment rice straw","volume":"214","author":"Chang","year":"2016","journal-title":"Bioresour. Technol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"487","DOI":"10.1016\/j.biortech.2016.04.121","article-title":"Powerful peracetic acid\u2013ionic liquid pretreatment process for the efficient chemical hydrolysis of lignocellulosic biomass","volume":"214","author":"Uju","year":"2016","journal-title":"Bioresour. Technol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"406","DOI":"10.1016\/j.biortech.2017.03.081","article-title":"Pretreatment of eucalyptus with recycled ionic liquids for low-cost biorefinery","volume":"234","author":"Xu","year":"2017","journal-title":"Bioresour. Technol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"6565","DOI":"10.15376\/biores.10.4.6565-6575","article-title":"Ionic Liquids as a New Platform for Fiber Brittleness Removal","volume":"10","author":"Zhang","year":"2015","journal-title":"Bioresources"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1483","DOI":"10.1007\/s10570-016-1180-y","article-title":"Ultrasonic-assisted ionic liquid treatment of chemithermomechanical pulp fibers","volume":"24","author":"Chen","year":"2017","journal-title":"Cellulose"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"29897","DOI":"10.1039\/C4RA05284F","article-title":"Highly selective and efficient extraction of lignin in kraft pulp by aqueous ionic liquids for enhanced bleaching properties","volume":"4","author":"Pang","year":"2014","journal-title":"RSC Adv."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"2275","DOI":"10.1351\/pac200072122275","article-title":"Influence of chloride, water, and organic solvents on the physical properties of ionic liquids","volume":"72","author":"Seddon","year":"2000","journal-title":"Pure Appl. Chem."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"3078","DOI":"10.1039\/C7GC00705A","article-title":"An economically viable ionic liquid for the fractionation of lignocellulosic biomass","volume":"19","author":"Gschwend","year":"2017","journal-title":"Green Chem."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"115013","DOI":"10.1016\/j.molliq.2020.115013","article-title":"Pyridinium protic ionic liquids: Effective solvents for delignification of wheat straw","volume":"325","author":"Asim","year":"2021","journal-title":"J. Mol. Liq."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"578","DOI":"10.1016\/j.molliq.2018.06.021","article-title":"A brief overview on lignin dissolution","volume":"265","author":"Melro","year":"2018","journal-title":"J. Mol. Liq."},{"key":"ref_31","first-page":"16","article-title":"Effect of Ultrasonic-assisted Ionic Liquid Pretreatment on the Bleachability and Properties of Eucalyptus Kraft Pulp","volume":"51","author":"Peng","year":"2019","journal-title":"J. Korea Tech. Assoc. Pulp Pap. Ind."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"6299","DOI":"10.15376\/biores.15.3.6299-6308","article-title":"Enhancement of Delignification by Ionic Liquids Pre-treatment and Modification of Hardwood Kraft Pulp in Preparation for Bleaching","volume":"15","author":"Peng","year":"2020","journal-title":"BioResources"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"364","DOI":"10.1007\/BF00776397","article-title":"Combination treatment of kenaf bast fiber for high viscosity pulp","volume":"46","author":"Mazumder","year":"2000","journal-title":"J. Wood Sci."},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Liu, J., Qi, L., Yang, G., Xue, Y., He, M., Lucia, L., and Chen, J. (2020). Enhancement of Lignin Extraction of Poplar by Treatment of Deep Eutectic Solvent with Low Halogen Content. Polymers, 12.","DOI":"10.3390\/polym12071599"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"92","DOI":"10.1016\/S0169-4332(98)00920-9","article-title":"Evaluation of surface lignin on cellulose fibers with XPS","volume":"144\u2013145","author":"Johansson","year":"1999","journal-title":"Appl. Surf. Sci."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"137","DOI":"10.1016\/j.biortech.2013.01.049","article-title":"An advanced understanding of the specific effects of xylan and surface lignin contents on enzymatic hydrolysis of lignocellulosic biomass","volume":"132","author":"Ju","year":"2013","journal-title":"Bioresour. Technol."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"786","DOI":"10.1177\/004051755902901003","article-title":"An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose Using the X-ray Diffractometer","volume":"29","author":"Segal","year":"1959","journal-title":"Text. Res. J."},{"key":"ref_38","unstructured":"Peng, J. (2020). Effects of Ionic Liquid Assisted Ultrasonic Pretreatment on the Separation of Broad-Leaf Kraft Pulps. [Master\u2019s Thesis, Qilu University of Technology]."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"5019","DOI":"10.1039\/C5GC01314C","article-title":"Structural changes in lignins isolated using an acidic ionic liquid water mixture","volume":"17","author":"Brandt","year":"2015","journal-title":"Green Chem."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"4224","DOI":"10.1039\/C8GC00953H","article-title":"An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: A mechanistic study","volume":"20","author":"Li","year":"2018","journal-title":"Green Chem."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"10023","DOI":"10.1039\/C6OB01915C","article-title":"The synthesis and analysis of lignin-bound Hibbert ketone structures in technical lignins","volume":"14","author":"Neal","year":"2016","journal-title":"Org. Biomol. Chem."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"719","DOI":"10.1002\/cssc.200900242","article-title":"Oxidative Depolymerization of Lignin in Ionic Liquids","volume":"3","author":"Taccardi","year":"2010","journal-title":"ChemSusChem"},{"key":"ref_43","first-page":"47","article-title":"Effects of Kneading Treatment on the Properties of Various Pulp Fibers","volume":"47","author":"Kim","year":"2015","journal-title":"J. Korea Tech. Assoc. Pulp Pap. Ind."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"6193","DOI":"10.15376\/biores.9.4.6193-6204","article-title":"Hydrothermal Pretreatment of Hardwood Chips Prior to Alkaline Pulping and D0(EP)D1 Bleaching","volume":"9","author":"Chi","year":"2014","journal-title":"BioResources"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"481","DOI":"10.1080\/02773819308020530","article-title":"Structural and Concentration Effects on the Diffuse Reflectance Ftir Spectra of Cellulose, Lignin and Pulp","volume":"13","author":"Bouchard","year":"1993","journal-title":"J. Wood Chem. Technol."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"325","DOI":"10.1016\/S0144-8617(96)00018-5","article-title":"Fractional and structural characterization of wheat straw hemicelluloses","volume":"29","author":"Sun","year":"1996","journal-title":"Carbohydr. Polym."},{"key":"ref_47","unstructured":"Roberts, J.C. (1996). The Chemistry of Paper, The Royal Society of Chemistry\/Information Services."}],"container-title":["Polymers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4360\/13\/10\/1600\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:02:01Z","timestamp":1760162521000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4360\/13\/10\/1600"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,5,15]]},"references-count":47,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2021,5]]}},"alternative-id":["polym13101600"],"URL":"https:\/\/doi.org\/10.3390\/polym13101600","relation":{},"ISSN":["2073-4360"],"issn-type":[{"value":"2073-4360","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,5,15]]}}}