PVDF/TPU相转化法制膜过程中热力学性质和动力学行为

Research on Thermodynamic Properties and Kinetic Behaviors of PVDF/TPU Hollow Fiber Membrane Prepared by Phase Inversion

采用相转化法制备PVDF/TPU共混中空纤维膜。研究浊点数据、铸膜液粘度、凝胶浴的组成和温度、芯液组成对制膜过程中热力学和动力学性质的影响,并探讨了PVDF/TPU成膜机理。结果显示,随着铸膜液和添加剂浓度升高,铸膜液凝胶值下降,体系相容性下降,相分离可能性增大,体现热力学促进作用;同时运动粘度升高,流变阻力抑制铸膜液高分子运动,相分离速度变小,延长相分离发生的时间,又存在动力学的阻碍作用。凝胶浴的温度和组成、芯液的组成主要由动力学扩散作用控制。随着溶剂-非溶剂扩散系数变小,相分离形式从瞬时相分离向延迟相分离转变。结合膜断面的电镜照片,从相态变化的角度分析了膜结构及影响大孔膜形成的机理。

PVDF/TPU blend hollow fiber membranes were prepared by phase inversion. The effects of thermodynamic and kinetic properties were studied by cloud point data, viscosities, composition-temperature coagulation bath and bore liquid component, membranes formation mechanism was discussed. The results showed that with the increasing of casting solution concentration and additive concentration, coagulation values and compatibility decreased, causing the possibility of phase inversion, which was thermodynamic enhancement. While viscosity increased, rheological resistance inhibited macromolecular motion in casting solution, phase separation speed reduced, but phase separation period extended, which was kinetic hindrance. Composition-temperature of coagulation bath and composition of bore liquid were effected by kinetic diffusion. With the decrease of diffusion coefficient between solvent and non-solvent, the forms of phase separation changed from instantaneous demixing to delayed demixing. Membrane structure and macroporous forming were researched with SEM micrographs and phase change analysis.