| Presently, lignocellulosic raw materials is increasingly becoming a focus for researchers, which was actuated by the fact that lignin is a renewable, low-cost and biomass resources with unique features, especially, cellulose is an environmentally friendly material. However, natural fiber is a kind of three-dimensional stereoscopic structure of amorphous polyphenol polymers which has high polymerization degree. Lignocellulose can’t be dissolved in common solvents on account of this structure that it will lead to industrialization of natural fiber.Therefore, an environmentally friendly and renewable solvent should be explored for promotion new chemical reactions. Ionic liquids have been developed as green solvents in the past few decades in many fields, such as biomass converison and fiber modification. The swelling and dissolution of single and multiple components of cellulose raw materials was studied.Firstly, the swelling of plant fiber in 1-butyl-3-methylimidazolium chloride (BmimCl) and l-ethyl-3-methylimidazolium acetate (EmimAC) were investigated. Changes on crystallinity, functional groups and morphology of fiber were analyzed as well as the enzymatic bleaching performance.The fiber length increased by 3.76% whereas the fines content decreased by 10.94% when treated with ionic liquids.While improving the quality of fiber, drainability of pulp also was improved.The graphics of the SEM showed more fines on the surface of the fibers, which suggested pretreatment with ionic liquid could facilitate fibrillation and mass transfer. XRD results showed ILs had a significant effect on both crystalline rand amorphous region of cellulose. After treatment by BmimCl and EmimAC, theCrl of the plant fibers decreased by 7.30% andl4.58%, respectively. The decreases of CrI indicated that improvement in accessibility of fiber. Compared to the untreated counterpart, the brightness of paper increased by 2.54%ISO and 4.27%ISO, and the opacity increased by 1.44% and 1.99%. After treated byEmimAC, the tensile index,bursting index, ring crush index, tearing index, and folding resistance increased14.08%,29.80%,22.45%,44.82% and,52.50%, respectively.Secondly, cellulose, as an important component of plant fiber materials, the linear glucan molecules of cellulose were bound together by hydrogen bonds that not only affects its solubility, but also restricts the application and development of cellulose.The changes of the cellulose after treatment with ILs were characterized by SEM, FT-IR, XRD, and viscometric assays.The results show that the solubility was in order of EmimAC>EmimCl>BmimCl. There was no derivatization of fiber demonstrated in FT-IR results which indicated that EmimAC was believed to be non-derivative solvent for cellulose dissolution.The solubility of ILs was probably shaped by various factors, including the species of ILs, raw material and melting temperature. Degree of polymerization (DP) can be reduced in some extent during solvation. Clearly, the degradation level of cellulose increased significantly with the increase of temperature.The results showed that DP decreased from 1900 to 1427 when the temperature increased to 120℃. Furthermore, degradation increase with time, but they aren’t far more pronounced than temperature.Compared tothe control group (59.58%), the CrI of the treated group (40.15%) decreased after IL-pretreatment.The X-ray diffraction contours changed after EmimAC pretreatment, suggesting that the crystalhas changed from celluloseⅠto cellulose Ⅱ after treatment. Therefore, the optimum conditions for ILs dissolution wereat 100 ℃ with residence time of 4 h.Various conditions were studied to optimize the dissolution performance of lignin in BmimCl and EmimAC.The results showed that the EmimAC is better. Under treatment at 85 ℃ with 5% ligninmoisture content for 120 min, it had greatability of dissolving lignin which the best solubility was 399 g/L could be achieved in the experiment. It was showed that dissolved lignin could be synthesized using water as precipitant. The regenerated lignin was characterized by SEM, XRD, FT-IR, NMR and DAWN HELEOS. The results found that there were no significant functional changes of the regenerated lignin samples. However, the particles size were more uniform. Additionally, the aliphatic hydroxyl, syringlhydroxyl and total phenolic hydroxyl content of regenerated lignin increased by 27%,20% and 20% respectively, meanwhile both accessibility and water-soluble increased. The finding built a strong foundation for realized high added value utilization of lignin.Based on the good solubility of EmimAC without degradation on the chemical structure of sample, EmimAC was used to dissolve poplar powder. The most effective condition for the solubility was obtained experimentally. That is 160 ℃,16 h,7.5% powder moisture content and 10 min ultrasonic pretreatment. In this condition the dissolution ratio of poplar powder up to 47.40%. First, the hemicelluloses and theamorphous region of cellulose on the surface of fiber were dissolved during dissolving, then the higher lignin content, which creates the total lignin content of undissolve draw material first rise and then drop. The lignin content increased from 26.28% to 29.43%. The dissolving powder was characterized by XRD, FT-IR and SEM. The results showed that in this process EmimAC may result certain destruction to chemical structure of sample and the CrI re from 45.43% to 29.03% when dissolution time was 16 h. EmimAC were proved to be non-derivative solvent for cellulose dissolution and which built a strong foundation for high added value utilization of cellulose raw materials. |
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