热致相分离法制备聚丙烯腈中空纤维膜及膜孔结构与成形机理研究

Polyacrylonitrile (PAN) hollow fiber is low price, corrosion-resistant, and ageing-resistant. It also has good biocompatibility and hydrophilicity. However, the conventional approach for producing PAN-based fiber is solution-spininning. The membrane structure is not easy to be controlled and has a poor mechanical property. Furthermore, solution spinning is complex, high power consumption and polluting the environment. In this study, the melt processable acrylonitrile-methylacrylate copolymer (AN-MA) was used as a precursor, the AN-MA hollow fibers were formed by thermally induced phase separation method (TIPS) and stretching. This project will be identified mainly in the following three aspects: 1) the interactions between thinner mixture and AN-MA copolymer, effects of the interactions on the phase separation behaviors and phase diagrams; 2) the changing law and forming mechanism of pore structure under non-isothermal and stress conditions, completing non-isothermal kinetics of droplet growth, establishing growth kinetics model of membrane pore under stress condition; 3) influences of spinning technology on the crystallization and orientation of PAN hollow membrane, effects of supercritical extraction on structures and properties of hollow fiber. We aimed at establishing a basic theory of preparing PAN hollow membrane by TIPS. Based on the theory and experiment results, the structures of membrane pores and fiber could be controllable. Project achievements agree with current requirements of energy-saving and emission-reduction, rich the basic theory of TIPS, and promot the rapid growth and stable development of PAN hollow fiber membrane.

聚丙烯腈(PAN)中空纤维膜具有成本低廉、耐腐蚀、抗老化、亲水性较好等特点，但国内外一直只能采用溶液纺丝法制备，膜结构不易控制、力学性能差，工艺复杂、能耗高且污染环境。本课题以自制的可熔融丙烯腈-丙烯酸甲酯共聚物(AN-MA)为基体，采用热致相分离法(TIPS)结合拉伸工艺制备PAN中空纤维膜。主要在以下三方面展开研究：1)混合稀释剂与AN-MA的相互作用对相图及相分离过程的影响；2)非等温及应力作用下膜孔结构的变化规律及成形机理，完善非等温液滴生长动力学，建立应力下膜孔生长动力学模型，实现膜孔结构的可控；3)纺丝工艺对PAN中空纤维膜结晶和取向的影响规律；超临界流体萃取对膜结构及性能的影响。总体目标：建立TIPS法制备PAN中空纤维膜的基础理论，在理论和实验的支持下，实现膜孔和纤维结构的可控。项目成果符合绿色低碳的要求，进一步丰富TIPS的基础理论，促进PAN中空纤维膜的快速、稳定发展。

聚丙烯腈(PAN)中空纤维膜具有成本低廉、耐腐蚀、抗老化等特点，但国内外一直采用溶液纺丝法制备，膜结构不易控制、力学性能差，工艺复杂且污染环境。本课题以自制的可熔融丙烯腈-丙烯酸甲酯共聚物(AN-MA)为基体，采用热致相分离法(TIPS)制备PAN基微孔膜。主要完成了以下研究工作：1) γ-丁内酯(γ-BA)/三乙酸甘油酯(GTA)混合稀释剂、碳酸乙烯酯(EC)/柠檬酸三乙酯(TEC)混合稀释剂及不同配比对AN-MA共聚物基微孔膜相分离机理、微孔膜表面、断面及膜孔形貌的影响；2)研究了共聚物/不同混合稀释剂体系在降温过程中膜孔结构的变化规律及成形机理、对上、下表面及断面膜孔结构影响；3) 研究了不同冷却介质（水、空气、乙醇）、不同第二单体含量对微孔膜相分离过程、膜孔结构与性能的影响。结果发现：.1).高γ-BA/GTA配比、低AN-MA浓度及快的冷却速率均使得微孔膜的形成过程中易发生旋节线分相导致树枝状结构；反之，其分离是成核-生长机制，膜断面结构表现为未封闭/半封闭的胞腔状孔和完全封闭的胞腔状孔； .2).以投料摩尔比为85/15的AN-MA共聚物为基体，较慢冷却速率有利于TIPS过程，但膜皮层较厚；而快的冷却速率体系同时发生TIPS和NIPS过程，微孔膜除具有TIPS的微孔结构外，断面还有指状孔结构，有效地改善微孔膜的致密皮层。复配稀释剂中EC含量为65 wt.%，聚合物浓度为15 wt.%时，AN-MA微孔膜的水通量最高可达18.2 L/(m2h)；.3).改变MA的投料量，制备了80/20AN-MA和75/25AN-MA共聚物，以0 oC冰水浴为凝固浴，采用TIPS法制备AN-MA微孔膜。降低复配稀释剂中EC含量和AN-MA浓度有利于旋节线分相，膜孔结构为连通的树枝状结构；反之，其相分离机理为成核-生长，膜孔结构为开放/封闭式的胞腔状孔结构；.4).采用摩尔比为80/20的AN-MA共聚物为基体，以EC和TEC为复配稀释剂，浓度为9 wt.%，EC为60 wt.%，水通量约为66.0 L/(m2h)，断裂强度和伸长率分别为4.6 MPa和43.8 %；以己内酰胺和聚乙二醇单甲醚为混合稀释剂时，浓度为18wt.%，混合稀释剂中良溶剂为87.5wt.%，微孔膜的纯水通量可达313 L/m2.h；对平均粒径为166 nm浓度为0.3 g/L的墨汁截留率达93.1%