| Apart from being used to printing, packaging, paper writing and household paper, paper which is a type of functional material, has been increasingly used in food, industrial, construction, scientific research and other fields. As a filterable fluid medium with the separate function to remove fine particles of fluid, filter paper is of treat development prospect in medical and industrial. Moreover, as a specialty paper possessing extremely high permeability and high porosity, filter paper is produced with plant fiber, which is appropriately curly and highly swollen. Generally, beating is still difficult to meet the requirements of high permeability filter paper. In the conventional filter paper industry, the performance requirements of filter paper are often met via mercerization. Pulp fiber modification is of important meaning to prepare high permeability filter paper.Based on a large number of experiments reported in the literature and the preliminary exploration experiments showed that the research chosen the aqueous NaOH/urea/thiourea solution as the modification agent and softwood kraft pulp as the raw material. Pulp fiber was treated in NaOH/urea/thiourea system with cooperation of ultrasonic. The process conditions, such as modification temperature, modification time, the ration of liquid on the effect of modification were studied. Permeability of filter paper, bulk, maximum pore size, average pore size, zero-span tensile strength and modification pulp yield were determined to evaluate the effect of modification and deduce mechanism of modification. According to the result analysis comparison, the best technological condition was determined. When the treatment was conducted at -2 ℃ for 30 min and the ration of liquid was 8:4:8, the permeability increased to 1229.5 L/(m2·s), maximum pore size reached 51.3μm, average pore size was up to 46.2μm, bulk increased to 5.654 cm3/g and the treatment resulted in only a slight reduction in the zero-span tensile strength to 146.8N. The study found that modified fibers exhibited marked curl and swelling. The fibers curled noticeably increased (from 22.3% to 27.1% in curl index), kink index raised by 42.3% (from 2.175 to 3.094) and obviously swelled (increased from 160.8 to 179.1 μg/m in coarseness) with treatment.In addition, the effect of ultrasonic on pulp fiber modification by NaOH/urea/thiourea solution was also studied. Experiments showed that ultrasonic treatment resulted in unmodified filter paper a slight reduction in permeability (150.1 L/(m2·s) to 130.2 L/(m2·s)) and decrease from 1013.1 L/(m2·s) to 956.4 L/(m2·s) for modified filter paper. After twice solution and ultrasonic cyclic treatment was completed, the permeability of filter paper raised to 1089.6 L/(m2·s) and pore size decreased. Moreover, there was little difference for more than once cyclic treatment between maximum pore size and average pore size (the difference for once cyclic treatment was 6.2μm, but the difference for twice cyclic treatment was 1.1 μm and three times cyclic treatment was 0.9μm). Ultrasonic treatment could improve the filtering accuracy of filter paper and give great uniformity to inside aperture structure.In this study, waste liquid of modification was recycled and reused. Pulp fiber modified in NaOH/urea/thiourea solution was a hydrogen bond damaged process without chemical reaction. By testing and analyzing waste liquid ingredients, regenerate solution was prepared by adding moderate urea and thiourea. Then, pulp fiber was modified in regenerate solution. When 12g/300ml of urea and 12g/300ml thiourea were added to regenerate solution, the permeability reached 931.6 L/(m-s) and closed to the permeability (956.4 L/(m-s)) of filter paper whose fiber was modified in original solution. |
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