异形二醋酯纤维干法纺丝成形过程模拟及其截面分析

Simulation of dry spinning process and cross-section analysis of profiled diacetate fibers

为研究异形二醋酯纤维的干法纺丝成形过程,基于三角形喷丝孔推导了用于描述截面异形度变化的计算方程,并耦合到典型一维干法纺丝模型中,构建出可高效计算的混合动力学模型,模拟计算了异形二醋酯纤维的干法纺丝成形过程。采用工业化纺丝实验装置制备纤维样品,分析了截面形态数据并与模拟计算结果进行对比。结果表明:二醋酯纤维的纺丝过程中溶剂蒸发和温度变化剧烈,恒温蒸发区不明显,在纺程1 cm左右达到卷绕速度,并在喷丝口下方短距离内迅速完成固化,截面积基本恒定;二醋酯纤维异形度受溶剂蒸发和表面张力2个因素共同控制,其中溶剂蒸发是主要控制因素;纤维异形度的实验值为74.4%,模拟计算值为72.8%,二者基本相近,同时纤维截面积实验值为642.0μm^(2),模拟计算值为614.8μm^(2),差异率为4.2%,模型对纤维截面变化趋势有较好的预测性;纤维样品截面呈规则的“Y”形,异形度具有较高的一致性,变异系数为1.12%;纤维样品的截面积变异系数为4.17%,单丝间的截面积差异相对较为明显。

Objective The forming mechanism of profiled fibers of dry spinning involves heat transfer,mass transfer,phase change,deformation,and so on.The cross-sectional shape changing process,in particular,is affected by surface tension,solvent diffusion and evaporation,and it is difficult to develop quantitative research on this process.The previous studies on dry spinning process dynamics were mainly focused on circular cross-section fibers,and research on dry spinning of profiled diacetate fibers is yet to be carried out.The purpose of this research is to establish a dry spinning dynamics model of profiled diacetate fibers,and compare and validate the simulation results of fibers cross-section against the experimental data.Method A profile degree calculation equation was derivated from the triangle spinneret hole to describe the variation of fibers cross-section,and combined with a typical one-dimensional dry spinning model to establish a hybrid dynamic model which has advantage in efficient computing.Based on this model,the variations of filament solvent mass fraction,temperature,velocity,tension and cross-sectional area during the spinning process could be obtained,so could the variation in cross-section profile degree.Profiled fibers were prepared by industrial spinning device.Stereomicroscopy was adopted to observe the cross-section of fibers,and the experimental results were compared with the simulation calculation values.Results Spinning solution quickly evaporated after being extruded from the spinneret since its temperature is higher than the atmospheric boiling point of acetone.Besides,the small diameter of spinneret hole contributed to solvent diffusion and evaporation,and the curing point of filament was only about 50 cm away from spinneret.The glass transition temperature showed an opposite trend to the solvent content,reaching the maximum value after the filament was cured.Filament temperature was rapidly decreased by flash evaporation,with the minimum temperature dropping to-12℃.Because of the high specific surface area and fast heat transfer rate of profiled diacetate fibers,the constant temperature evaporation zone of spinning process was only about 20 cm.As the rapid reduction of solvent content during flash evaporation,the filament tension quickly increased under the and accelerated stretching.After that,the tension increased along with the spinline,and the friction force between filament and air was the main influence factor.The filament instantaneously accelerated to take-up velocity after being extruded from spinneret and keeps a plateau value throughout the spinning process.The variation trend of the cross-sectional area was similar to that of the solvent content.The profile degree of diacetate fibers was controlled by solvent evaporation and surface tension with solvent evaporation was found the main control factor.Length of the major and minor axes of the filament cross-section were affected by flash evaporation and significantly shortened in a few centimeters from the spinneret hole,then slowly decreased along the spinline to a plateau value at z=50 cm.However,the decrease ratio of minor axes was larger than major axes so that the profile degree could be increased.The experimental profile degree was 74.4%,and the simulation value was 72.8%.While the experimental fibers cross-sectional area is 642.0μm^(2),and the simulation value is 614.8μm^(2).Conclusion A dry spinning dynamic model was established to simulate the spinning process of profiled diacetate fiber.The results show that solvent evaporation and temperature changes dramatically,and the constant temperature evaporation section is not obvious.Filament approaches the take-up velocity at z=1 cm and cures rapidly near the spinneret while the cross-sectional area reaches a constant value.The simulation results of the dry spinning model of fibers cross-section are consistent with the experimental values.As shown in the experiment,the cross-section of diacetate fibers exhibits as a regular"Y"shape with a high consistency of profile degree,and while there are a little differences in the cross-sectional area among single fibers.It is found that the coefficient of variation of profile degree(CV=1.12%)is smaller than the cross-sectional area(CV=4.17%).