环境刺激响应性聚偏氟乙烯/凹凸棒石复合超滤膜制备及抗污染易清洁性能

Owing to good membrane-forming and excellent physicochemical properties, polymer membranes have gained extremely popularities in membrane filtration. Unfortunately, hydrophobic nature of polymers always accumulates adsorptions or depositions between membrane surfaces and organic foulants (NOMs, pathogens, polysacchrides and proteins, etc.) in water, which subsequently decreases membrane permeation flux. Fouling is one of the greatest obstacles in the widespread implementation of membranes for liquid purification. To improve membrane fouling resistance and easy-cleaning, and enhance filtration performance, the nanocomposite poly (vinylidene fluoride) (PVDF) ultrafiltration membrane exhibiting high efficiency of membrane clean in protein separation will be prepared by blending with stimuli-responsive polymer (SRP) grafted nanoattapulgite (NATP). A series of novel stimuli-responsive nanocomposite additive (SRP-g-NATP), coupling of hydrophilic modifier, selfdispersant, and pore-forming agent (porogen), will be synthesized by the surface modification of nanoattapulgite with stimuli-responsive polymer via "grafting from" polymerization. The synthesis process,reaction conditions,and mechanisms will be studied in detail.The nanocomposite membrane of poly(vinylidene fluoride) (PVDF) and SRP-g-NATP will be fabricated by wet phase inversion method. The effects of the SRP-g-NATP and manufacture process on structures, morphologies, surface composition, and chemistry of the nanocomposite membranes will be sysmatically investigated by varieties of spectroscopic and microscopic characterization techniques. Furthermore, the rejection behavior, antifouling performance and easy-cleaning properties of the nanocomposite membrane will be evaluated by filtering protein aqueous solution. The fouling resistance abilities of the membranes will be evaluated by the reduction of flux. The flux recovery ratio will be used to evaluate the hydraulic cleaning efficiency and easy-cleaning properties of the membrane. The relationship between separation performance and the structure characters of the stimuli-responsive polymers structure will be determined. On the meanwhile, we can obtain some new theory and method about the fouling resistance and easy-cleaning membrane, which also provide some experience in the aspect of membrane material design, preparation and application. This work also may afford a new idea for studying and developing polymer separation membranes.

围绕新型高分子分离膜设计制备中的共性问题，以膜材料结构和表面性质协同调控实现膜污染的源头控制为目标，采用环境刺激响应性高分子改性凹凸棒石共混调控聚偏氟乙烯超滤膜结构与性能，同步实现膜表面和膜孔壁的均匀及持久改性，制备集无机纳米纤维改性和刺激响应高分子改性于一体的新型抗污膜。通过接枝聚合反应将刺激响应高分子"锚定"在凹凸棒石表面，设计合成具有刷状链结构形态的共混改性剂，研究接枝聚合条件对接枝链结构的影响规律；采用浸没沉淀相转化法制备复合超滤膜，系统研究无机纳米纤维、敏感性高分子刷状链结构及相转化过程对膜结构和性能的影响规律，探讨敏感性高分子刷状链结构与复合膜抗污染及易清洁性能之间的关系，阐明复合膜的抗污染及易清洁机制，建立新型抗污染易清洁复合超滤膜设计、制备以及结构和性能优化控制的基本方法和理论。这对研制具有高抗污染和易清洁特性的新型高分子超滤膜具有指导意义，为提高膜应用的针对性提供新思路。

膜污染及其控制一直是膜技术研究的重要内容，也是推动膜技术在分离领域应用的关键。不同纳米材料的引入使得纳米复合膜在机械强度、热稳定性、抗污染能力、渗透性和选择性等方面得到了不同程度的提升。纳米凹凸棒石是一种层链状结构的镁铝硅酸盐矿物，其外形呈纤维状或棒状，具有纳米尺度的晶体直径，直径30～70nm，长度约0.5～5μm。项目以膜材料结构和表面性质协同调控实现膜污染的源头控制为目标，采用环境刺激响应性高分子改性凹凸棒石共混调控聚偏氟乙烯超滤膜结构与性能，同步实现膜表面和膜孔壁的均匀及持久改性。在相转化过程中凹凸棒石起到了成核剂的作用，随着加入量的增加，聚偏氟乙烯膜的微晶结构逐渐变小，凹凸棒石的加入使得聚偏氟乙烯超滤膜的纯水水通量显著增加。随改性剂量的增加，PVDF/PGS-g-PNIPAAM膜指状孔变短，热稳定性增强，纯水通量变大，当改性剂添加量为7 wt.%时，20℃下膜纯水通量达到246 L•m-2•h-1，约是纯膜的两倍；改性剂的加入提高了膜的机械强度；凝固浴温度会影响PNIPAAM分子链的迁移，具有表面偏析现象，低温下制备出的膜孔周围及膜表面含有的PNIPAAM含量较多，亲水性与渗透性能更强，温敏性能更优越，膜结构也最为优越。当添加量为7 wt.%时，其通量恢复率高达91%，而纯膜仅为39%。将PGS-g-PDMAEMA与PVDF共混制备了PVDF/PGS-g-PDMAEMA混合基质超滤膜，其机械强度、伸长率、孔隙率均有所提高。PGS-g-PDMAEMA添加量为1 wt.%时，膜表面缺陷孔最少，孔径分布最窄，接触角最小为75.8 °。对膜进行BSA过滤，考察渗透通量随时间变化率，随改性剂量增加，其渗透通量衰减速率逐渐下降，且稳定渗透通量增大。PGS-g-PDMAEMA添加量为1 wt.%时，BSA静态吸附量最少为256.06 μg•cm-2；BSA稳定渗透通量为17.92 L•m-2h-1，截留率为100 %；清洗后通量恢复率最高，达54.17 %，具有优异的抗污染易清洗性能。本研究对研制具有高抗污染和易清洁特性的高分子超滤膜具有一定指导意义，为增加高分子分离膜的品种，扩大高分子分离膜的选择范围，提高应用的针对性提供了新思路。