超临界流体诱导相分离制备结晶型含氟聚合物微孔膜的机理研究及其微结构控制

Different from the common method of preparing porous polymeric membranes, we intend to fabricate fluorite polymer hollow fiber membranes with inter-connected co-continuous pores by super critical fluid induced phase separation method. Semi-crystal fluorite polymer was spinned into hollow fiber membranes through twin-screw extruder. The transition effect between solvent/non-solvent of super critical CO2 as an inducer is utilized to induce the micro-phase separation of fluorite polymer system, and realize the construction of membrane co-continuous micro-/nano- pores. The second compatible component and assistant inducer could both control the crystallization rate of fluorite polymers, and reduce the activation free energy of nucleation. The kinetics curve of phase separation will be determined by an on-line monitor through viscosity, cloud point, and near-infrared measurement. Both homogeneous and heterogeneous nucleation rate will be calculated. The evolution behavior of micro-pores nucleation, growth, coalescence, and solidification will be simulated by OpenFOAM. The effect of key processing variables e.g. polymer components, shearing rate, SCCO2 concentration and pressure, spinneret temperature difference and pressure drop etc. on hollow fiber membranes structures and morphologies will be investigated in detail. The permeation flux, selectivity, blood compatibility and blood filtration and hemodialysis performances will be also studied. The research will offer reliable theory instruction for the preparation of semi-crystal polymer membranes with controlled structures and performances by super critical fluid induced phase separation.

不同于通常的聚合物微孔膜制备方法，本课题采用超临界流体诱导相分离机理，以结晶型含氟聚合物为研究对象，通过双螺杆连续挤出成膜方式，制备具有互穿网络双连续微孔结构的含氟聚合物中空纤维膜。其特点是利用诱导剂超临界二氧化碳的溶剂/非溶剂转变效应，引发结晶型含氟聚合物体系的微相分离，实现微孔膜双连续微纳孔的构建。通过相容性第二组分及辅助诱导剂控制含氟聚合物体系的结晶速率，降低微孔成核自由能，提高微孔成核速率。在线测定含氟聚合物体系的相分离动力学曲线。计算均相/异相成核速率，采用OpenFOAM仿真模拟微孔成核、增长、聚集、固化演变行为。研究聚合物组成、剪切速率、超临界二氧化碳的浓度和压力、喷丝头的温度差和压力降等关键变量对中空纤维膜微孔结构形态的系统影响规律。考察中空纤维膜的渗透通量、选择性、相容性及血液过滤、透析性能。为超临界流体诱导相分离制备结构与性能可控的结晶型聚合物微孔膜提供可靠理论指导。

系统研究了超临界诱导相分离的热力学及动力学因素对含氟聚合物微孔膜微结构及性能的影响规律，实现了超临界CO2辅助双螺杆连续挤塑加工含氟聚合物，系统研究了双螺杆连续加工过程中工艺参数对含氟聚合物材料微结构的系统作用规律。具体采用ScCO2诱导相分离制膜法制备PVDF微孔膜，并研究了ScCO2操作条件（温度、压力）、铸膜液浓度及添加剂对微孔膜形貌、亲水性和晶型的影响，通过ScCO2诱导相分离制膜法可以制备形貌可调控的PVDF微孔膜，该调控是由液-液分相过程和成核结晶过程相互竞争引起的。采用SCCO2间歇法制备PVDF/PVP发泡材料，通过分析发泡后的泡孔大小、泡孔密度、泡体密度及体积膨胀率，研究了各种工艺参数（温度、压力、时间）对含氟聚合物微孔膜成型过程的影响。通过引入高分子量的PEO和稀释剂DOP，可制备出较为均匀的FEP微孔滤膜，膜丝强度高。通过引入超临界CO2，使含氟聚合物的加工温度至少降低20℃，拓宽含氟聚合物的加工区间，提高难加工含氟聚合物的可加工性能。利用超临界CO2所制备的膜丝，微孔尺寸比较大（50~100微米），通过添加一些加工助剂（PEO、无机纳米粒子等）可有效减小微孔尺寸。系统研究了非溶剂辅助热致相分离方法调控聚偏氟乙烯微孔膜的互穿网络孔结构，继而通过原位聚合及原位交联的方式赋予微孔膜亲水性及永久稳定性，在此基础上结合聚合物软模板剥离的方法，制备的微孔膜同时具备空气中超亲水和超亲油特性，且水下超疏油和油下超疏水特性的智能转换特性，可以用来分离水包油微乳液和油包水微乳液。研究了抗菌型聚偏氟乙烯中空纤维膜的制备及结构调控，制备了载银分子筛掺杂的聚偏氟乙烯中空纤维膜，可以有效提高抗菌效率。