Study On Properties Of Lignocellulose Fiber Based On High Concentration Gelation Of Low Temperature Alkaline

The NaOH-thiourea-urea aqueous solution was often used as a cellulose solvent to prepare the cellulose-based functional products at low temperature or fiber concentration, however, to my best knowledge, there have been no reports on the properties of cellulose or lingo-cellulose fiber at medium or high fiber concentration. For these reasons, the solution was used to explore the effects in this paper. It was found that cellulose fiber could be jellified and lingo-cellulose fiber could be swelled and softened effectively under the conditions mentioned above, the fiber properties would be modified, and the treated fibers were more suitable for the preparation of cellulose-based functional materials or the production of pulping and paper-making. The main goal of the present work was to determine the properties of cellulose or lingo-cellulose fiber treated in the solution, find out whether such a treatment could be used in the preparation of cellulose-based functional materials or in the field of pulping and paper-making, and extend the application field of the solution. The main results were shown as follows:（1） The NaOH-thiourea-urea aqueous solution was used to dissolve bleached kraft pulp of wood to determine the cellulose dissolubility in the solution（freezing temperature or dissolving temperature of-10℃, the same below）, finding that the highest dissolving concentration was 12%, which was a medium fiber concentration and higher than that of other alkali-urea system. And, pulp of hardwood could be dissolved more easily than that of softwood, and the cellulose dissolubility would be modified with the increase of beating degree.（2） Cellulose fiber could transform to cellulose sol under the conditions of high alkali concentration and high fiber concentration in the solution. Accoring to this analysis, the solution was used to treat bleached kraft pulp of softwood and prepare the regenerated cellulose. Compared with those of untreated cellulose fiber, there was no significant variations on the degree of polymerization, the crystal, the thermostability, and the structure of functional group, amorphous region, crystalline region or carbon skeleton of the regenerated cellulose fiber. However, the variation on the fiber morphology of the regenerated cellulose fiber was much more obvious, for some treated fibers were kinked, curled, interplaced or twined, which was similar to that of mercerized pulp. The bulk and softness of the regenerated cellulose fiberwas higher than that of untreated cellulose fiber, however, the paper strength was lower.（3） Cellulose fiber could transform to cellulose gel under the conditions of low alkali dosage and medium fiber concentration in the solution. Accoring to this analysis, bleached kraft pulp of hardwood was treated in the solution to prepare the paper with high bulk and strength. The optimal condition was alkali dosage of 9%, fiber concentration of 15%, and freezing time of 75 min. Compared with those of untreated cellulose fiber, the bulk of regenerated cellulose fiber could be increased by 21% with silimar paper strength.（4） Cellulose fiber could transform to cellulose sol under the conditions of high alkali concentration and medium or high fiber concentration in the solution. Accoring to this analysis, quantitative filter paper was treated in NaOH-thiourea-urea aqueous solution to prepare the paper with high dry and wet strength. The optimal condition was alkali concentration of 8%, freezing time of 15 min and washing time of 10min（room temperature）. Then, the aminoalkyl silicone fluid emulsion was used for plastification at room temperature. The wet tensile index of the treated paper could be 400% of that of the body paper, and the wet burst index could be 2400%. Also, compared with those of the body paper, the dry tensile index, dry burst index and the ratio of wet strength and dry strength of the treated paper were increased significantly.（5） Lingo-cellulose fiber could not be jellified under the conditions mentioned above in the solution, however, it could be swelled and softened effectively. Accoring to this analysis, bleached TMP of softwood was treated in the solution to increase the paper strength. The optimal condition was alkali dosage of 8%, fiber concentration of 15% and freezing time of 60 min. Compared with those of untreated TMP, the tensile and burst index of treated TMP could be increased by 100%, and the bulk was decreased by 9%, however, there was almost no variation on the folding strength.（6） Lingo-cellulose fiber could be softened under the conditions of low alkali dosage and medium or high fiber concentration in NaOH-thiourea-urea aqueous solution. Accoring to this analysis, poplar chips were treated in this solution to increase the refining properties. The optimal condition was alkali dosage of 8% and freezing time of 105 min. The order of the effect on refining properties was alkali dosage>freezing time>soaking time. Compared with those of APMP, the refining energy consumption of the chemi-mechanical pulp could be reduced by 40% as other pulping properties were similar.（7） The whiteness of the chemi-mechanical pulp could be increased to 80% in the bleaching process of H₂O₂. The optimal condition for 1st bleaching process was H₂O₂ dosage of 3% and bleaching time of 30min（fiber concentration of 20%, bleaching temperature of 75℃, alkali ratio of 0.75, MgSO4 0.5%, Na₂SiO₃ 2%, DTPA 0.3%）, and H₂O₂ dosage of 4% and bleaching time of 60min（fiber concentration of 20%, bleaching temperature of 75℃, alkali dosage of 0.25, MgSO4 0.5%, Na₂SiO₃ 3%, DTPA 0.3%） was chosen as the optimal condition for 2nd bleaching process. The order of the effect on bleaching properties was H₂O₂ dosage>fiber concentration>bleaching time. Compared with those of APMP, the whiteness and paper strength of the bleached chemi-mechanical pulp were higher and the bulk was lower.（8） In the bleaching process of bagasse RMP, the optimal condition for H₂O₂ bleaching process was H₂O₂ dosage of 3% and bleaching time of 60min（fiber concentration of 20%, bleaching temperature of 75℃, alkali ratio of 0.25, MgSO4 0.5%, Na₂SiO₃ 3%, DTPA 0.3%）, and Na₂S₂O₄ dosage of 1% and bleaching time of 45min（fiber concentration of 10%, bleaching temperature of 55℃, DTPA 0.5%） was chosen as the optimal condition in Na₂S₂O₄ bleaching process. Fiber could be swelled, softened, or jellified in the solution, and the reaction activity might be modified under the conditions mentioned above. According to this analysis, RMP of bagasse was treated in the solution to modify bleaching properties. The optimal condition was alkali dosage of 6% and freezing time of 45min（fiber concentration of 20%）. Compared with that of untreated RMP, the whiteness of treated fiber could be increased by 21%.