双功能亲水性修饰物的分子设计及其对分离膜亲水改性的研究

Membrane process as a novel and powerful technique has received tremendous attention in wastewater treatment. The adsorption and deposition of pollutant on membrane surfaces and/or pore walls (the so-called membrane fouling), which often cause severe decrease of permeate flux. In practical application, membranes fouling lead to the increase of handling expenses and operating intensity, becoming a bottleneck of further application of membrane technology. It is well known that the membranes with hydrophilicity and charge effect had a superior antifouling property. In order to improve membrane permeability and antifouling property, many efforts have been devoted to membrane modification, polymer blend and surface modification. Surface coating is a convenient method, which had been widely used in surface modification. Meanwhile, the introduction of crosslinking could improve the stability of the modifier on membrane surface. In this study, a concept of bifunctional antifouling modifier is proposed. The bifunctional antifouling modifier has crosslink group with high chemical reaction activity and functional group for antifouling. The main optimized methods of this study are as follows: Antifouling groups are selected though solvation function and charge effect. Crosslinking groups are chosen though crosslinking agent and reaction condition. crosslinking and functional groups are introduced in the antifouling modifier by radical polymerization. Membranes made by poly (vinylidene fluoride) are used to antifouling modification. The flux, separation and antifouling property of the modified membranes are investigated. The surface coating-crosslink method is not only a novel research method, but also could be applied to the modification of commercial membrane. The study had important scientific importance and application prospect.

膜污染是指料液中的污染物在膜表面或膜孔中沉积，导致渗透速率下降的现象。膜污染导致处理费用增加，操作强度变大，已成为制约膜技术进一步应用的瓶颈。表面涂覆交联法操作简便，适用性广，交联过程可提高亲水性修饰物在膜表面的稳定性。本项目根据表面涂覆交联法的特点，提出了双功能基团亲水性修饰物的概念。通过分子设计得到亲水性修饰物，修饰物中同时含有交联基团和亲水基团。通过溶剂化作用和静电作用筛选亲水性基团，根据交联剂和交联反应条件筛选具有较强反应活性的交联基团，通过自由基聚合将二者引入到亲水性修饰物中。以聚偏氟乙烯分离膜为改性对象，测试其渗透分离、耐污染性能及亲水交联层在膜表面的稳定性。探索亲水性修饰物结构，涂覆条件，交联方法和改性膜性能之间的关系。本项目不仅提供了一种新型通用性亲水改性方法，而且可以直接应用于多种膜材料制备的商业化分离膜亲水改性过程，具有重要的科学意义和实际应用前景。

本项目的研究内容包括以下两个方面内容：.在第一方面：利用多巴胺的自聚复合对PTFE中空纤维膜进行亲水改性，考察了改性方法（浸渍涂层、双面涂层和错流过滤涂层法）以及涂层条件对涂层效果的影响。由于聚四氟乙烯超强的不粘性，常规的浸渍涂层法改性效果很不明显。双面涂层的方法使多巴胺的聚合同时发生在PTFE中空纤维膜的内外表面，其亲水性得到一定程度改善。通过多巴胺错流过滤的方法对PTFE中空纤维膜进行亲水改性，以使改性深入膜孔内部，其亲水性得到显著改善。对多巴胺错流过滤改性得到的中空纤维膜进一步分析表征，表面电镜照片、红外光谱图和表面元素分析均表明随改性时间的延长，膜表面聚合的多巴胺增多，最终覆盖整个膜表面。改性后膜润湿性得到极大提高，可干态保存。使用BSA作为污染物对改性前后PTFE膜进行了抗污染实验，结果表明改性后膜具有优异的抗污染性能。.在第二方面包括以下几方面工作：.(a) 通过Friedel–Crafts反应，利用丙烯酸和无水四氯化锡在聚砜膜表面产生羧基，再利用酰胺反应将含有胺基的聚乙二醇单体接枝在膜表面，改性超滤膜亲水性和抗污染性能的影响。与未改性的聚砜超滤膜相比，改性膜的截留率和纯水通量未显著改变，但抗污染性能显著提高。.(b)以硝酸铈铵为引发剂，戊二醛为交联剂，通过化学接枝-交联的方法将两性离子和丙烯酰胺共聚交联到经过硫酸钾氧化后的聚砜膜表面，直接制备两性离子亲水改性膜。两性离子复合膜能够有效抑制BSA的污染，并且随着接枝单体浓度的增加，膜的抗污染能力增强。.(c) 通过多巴胺(PDA)自聚合及表面接枝的方法将PHGH引入到聚砜膜上，制备PSf/PDA-PHGH复合膜。随着PHGH浓度的增加，复合膜通量逐渐降低，对无机盐和染料的截留率升高。经50 h 的大肠杆菌溶液污染后，膜通量恢复率可以达到81%。复合膜在长时间操作过程中性能稳定。