干喷湿纺制备中空纤维膜的喷丝头结构优化模拟

Simulation on structural optimization of spinneret for hollow fiber membrane fabricated by dry-jet wet spinning

在干喷湿纺法制备中空纤维膜的过程中,喷丝头作为关键的纺丝组件之一,其尺寸及内部几何形状对于聚合物分子链的取向和最终的膜形态有着重要影响,通过优化喷丝头结构有助于提高膜丝可纺性和产品质量。采用数值模拟的方法,建立三维喷丝头溶液流道模型,探讨了环隙直管长度、环隙间距、锥形流动角等流道结构参数对溶液在喷丝头内的剪切流动、出口挤出胀大以及气隙中拉伸流动的影响。模拟结果表明:纺丝液流经喷丝成型孔入口处的压力及压力降随着直管长度增加而增大,随环隙间距、锥形流动角的增大而减小,且环管流道越长,越有助于溶液流动充分发展;相比于直管长度,环隙间距和锥形流动角对溶液的挤出胀大行为影响更显著,随着环隙间距和锥形流动角的增大,挤出胀大现象减弱。直管长度和锥形流动角对气隙中的初生纤维外径分布影响不明显。增大直管长度和环隙间距、采用锥形环管,有利于增加膜丝取向度和强度、提高纺程中的流动稳定性。模拟优化得到的喷丝头结构为直管长度1.1 mm,环隙间距0.11 mm(即长隙比为10左右),锥形流动角大于30°。

In the process of fabricating hollow fiber membranes by dry jet wet spinning,spinneret as one of the key components,its dimension and internal geometry have an important effect on the orientation of polymer molecular chains and the final membrane morphology.Optimizing the spinneret structure is helpful to improve the spinnability of membrane filaments and product quality.A three-dimensional spinneret flow channel model was established and the effects of flow channel structure parameters such as the length of straight channel,annulus-gap dimension and flow angle of conical channel on the shear flow in the spinneret,die swell at the outlet of spinneret and the elongational flow in the air gap were investigated by numerical simulation.The simulation results show that the pressure and pressure drop of the dope solution flowing through the inlet of the spinneret forming hole increase with the increase of the length of straight channel,and decrease with the increase of the annulus-gap dimension and flow angle of conical channel,and the longer the straight channel,the more conducive to the full development of the solution flow.Compared with the length of straight channel,the annulus-gap dimension and the flow angle of conical channel have a more significant effect on die swelling behavior of the solution.With the increase of annulus-gap dimension and flow angle,the die swelling phenomenon decreases.The length of straight channel and flow angle of conical channel have no obvious effect on the outer diameter profile of the primary fiber in the air gap.The orientation and strength of the membrane filament can be increased,and the flow stability in the spinning process can be improved when the length of straight channel and annulus-gap dimension are increased and the conical channel spinneret is used.The optimized structure of the spinneret is as follows:the length of straight channel is 1.1 mm,the annulus-gap dimension is 0.11 mm(that is,the ratio of length to gap is about 10),and the conical flow angle is greater than 30°.