| Morn than 90% of the cigarette filter in the world are currently produced by cellulose diacetate fibers because the cross-setion of the cellulose diacetate tows appears Y-shape owing to acetone solvent evaporation in the spinning column and the filter efficiency of the cigarette tow can reach the maximum value. Meanwhile, not only 55%—60% of the nicotine and tar content can be removed and the harmful ingredients such as phenolics can be selectively absorbed on to the tows, but the nicotine and the taste of cigarettes can be reserved. Therefore, cellulose diacetate fibers are worthy of becoming the first choice of cigarette filter. In 2015, the tows production of cellulose diacetate fibers reached about 850,000 tons, and the production in China was 280,000 tons, accounted for 32.9% of the total world production. However, the demand in China was about 350,000 tons, and the demand in other industry was 50,000 tons, accounted for 70% in our country. Apparently, the production capcity of cellulose diacetate fibers in China can not meet the market demand, and need to pay a large number of foreign exchange to import cellulose diacetate fibers and tows. Consequently, how to improve the production of the cellulose diacetate fibers becomes an impotant subject. Under normal circumstances, increasing the scale of production enterprises is a general way to improve the production of the cellulose diacetate fibers. This study focses on researching the die swell behavior of cellulose diacetate spinning dopes at the exit of the spinneret orifice, ascertaining the reseaonble distance of the adjacent orifices, and increasing the number of spinneret orifices, then achieving the purpose of improving the production of cellulose diacetate fibers. The research contents and conclusions were as follows: 1. Study on the rheological property of cellulose diacetate spinning dopesThe rheological property of spinning dopes has an important influence on die swell behavior. Consequently, the static rheological property and dynamic rheological property of cellulose diacetate as an example were studied.The static rheological properties at shear rate from 101 to 102s-1 and the dynamic rheological properties at angular frequency from 10-1 to 102s-1 of cellulose diacetate spinning dopes with different mass concentrations from 23.5%to 27.5% and various temperatures from 55? to 63? were determined using a Physica MCR101 rheoviscometer. So the effect of mass concentrations and temperatures on the rheological property was obtained.Static rheological properties: The variable curves of the mass concentrations and temperatures to apparent viscosity of cellulose diacetate spinning dopes were drawn. From the curves, it was found that apparent viscosity reduced when shear rate increased, that is, cellulose diacetate spinning dope was a non-newtotian fluid of shearing thinning. Then non-newtotian indexes of the spinning dopes with different mass concentrations and various temperatures were acquired.When dope temperatures were higher, non-newtonian index increased and as the dope mass concentrations increased, non-newtonian index reduced.Dynamic rheological properties: The storage modulus and loss modulus of cellulose diacetate spinning dopes had a great influence on die swell. The relationship between storage modulus and loss modulus of spinning dopes with different mass concentrations and at various temperatures and angular frequency was acquired. The results demonstrated that when dope mass concentration or dope temperature was fixed, the storage modulus and loss modulus appeared incremental trends with increasing the angular frequency. In addition, when angular frequency was kept constant, with increasing of dope mass concentration or decreasing of dope temperature, the storage modulus, loss modulus appeared incremental trends. Such a study provided a basis for verifying the calculated model of die swell ratio. 2.Establish the die swell ratio model of regular triangular spinneret orificeThe pressure drop model of spinning dope through regular triangular spinneret orifice was aquired using second-type surface integrals and rheological knowledge. Then, based on the pressure drop model and the expression researched by D. L. Mclntosh, the calculated model of die swell ratio at the exit of the regular triangular orifice was developed. Not only the calculated model was easy, but it intuitively described the relationship between die swell ratio and every parameter:?1? the relationship between die swell ratio and aparament viscosity and non-newtonian index;?2? the relationship between die swell ratio and storage modulus, loss modulus and angular frequency;?3? the relationship between die swell ratio and flow rate of spinning dopes;?4? the relationship between die swell ratio and the length of the regular triangular side and the length of the spinneret orifice.3.Verify the die swell ratio model of regular triangular spinneret orificeThe pressure drop of spinning dopes with different flow rates, various temperatures and different mass concentrations was determined by differential pressure transducer and the experimental data was compared to the value of the model data. The results showed that the pressure drop was upward when increasing flow rates or mass concentrations. However, it appeared a downward trend with increasing dope temperatures. From the compared results between calculated model data and experimental data, the minmum deviation between them was 0.05% and the maximum deviation was 4.99%. Hypothesis test of single normal population for unknown variance was used to analyzed the maximum deviation, the analyzed results indicated that there was no prominent differences between them, which demonstrated the pressure drop model was reliable.The die swell ratio of spinning dopes with different flow rates, mass concentrations and at various temperatures was determined with a travelling microscope. The results demonstrated the die swell ratio increased with increasing flow rates, mass concentrations or angular frequency. But it descended when rasing dope temperatures. From the compared results between calculated model data and experimental data, the minmum deviation between them was 0.01% and the maximum deviation was 3.52%. Hypothesis test of single normal population for unknown variance was used to analyzed the maximum deviation, the analyzed results indicated that there was no prominent differences between them, which demonstrated the die swell ratio model was reliable. Such a study provided a basis for the design of the adjacent orifices distance. 4. Design the spinneret with the regular trianglur orifice of higer distribution densityAccording to die swell ratio model, the theoretical distance of the adjacent orifices was confirmed as follows: 2 33mD?29?d?28?a B. Meanwhile, the desigh rules of the layers distance and the circumferential disatance were confirmed. Based on the the calculated value of the model, the theoretical distance of the adjacent orifices was 149.955?m when the flow rates were from 0.577 cm3·min-1 to 0.996cm3·min-1, dope temperatures were from 55? to 63? and dope mass concentrations were from 23.5% to 27.5%. The reference of the internal indicators from Nantong cellulose fibers CO.,LTD. was used to describe the relationship between the practical distance and the die swell diameter, i,e,. the practical distance should be 9 times to the die swell diameter? 9A mD 3d.?Therefore, the relationship can be converted into the followings,. The paractical distance should be more than 1.350 mm, which could provide a basis for orifices density distribution.Based on the spinneret with 290 orifices, which had been successfully used in tows production, and on the premise of keeping the spinneret diameter and processing parameter, another three kinds of spinnrets including 325 orifices, 350 orifices and 370 orifices were designed by changing the layers distance, the circumferential disatance and increasing the number of orifices. Then, the tows were produced by the above spinnerets, and the physical properties were tested. Because the physical properties appeared large sample data due to lots of filaments, and it was unable to find the corresponding orifices of evey filament, the mean square deviation was used to analyze the linear density of the filaments, the hypothesis test of single normal population for unknown variance was used to analyze the prominent difference of the mechanical properties and application properties, and the rank sum test was used to analyze the prominent difference of the broken tenacity and sectional area profile form of the filaments produced by the spinnerets. The results that the linear density was complied to the criterion and there was no prominent difference about broken tenacity, ectional area profile form and friction coefficient among the filaments. Meanwhile, the quality of the cellulose diacetate tows produced by the spinneret with 370 orifices met the demand of the application. More importantly, tow productions were increased by 27.6% when spinneret orifices was increased from 290 to 370, which demonstrated that the purpose of this study has achieved. Such the study has been currently used in Nantong Cellulose Fibers Co. Ltd. |
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