【作者】 吕睿；

【导师】 杜强国；

【作者基本信息】 复旦大学 ， 高分子化学与物理， 2006， 博士

【摘要】 膜分离技术过程简单，节能，高效，无二次污染，可在常温下连续操作，因为这些优点，膜技术已经广泛应用在各个领域。在水处理方面，膜分离在海水淡化、污水处理、纯净水的生产方面都起着重要作用。目前，用于水处理的膜材料有聚丙烯、聚砜、聚偏氟乙烯等。这些疏水性材料在实际应用中容易被蛋白质吸附而污染，造成膜孔堵塞，从而使分离效率降低，使用寿命减短。而亲水性的聚合物材料如聚乙烯醇、醋酸纤维素等其机械强度和耐溶剂性能又不尽如人意。聚乙烯—乙烯醇(EVOH)是一种半结晶的无规共聚物，该聚合物在所有乙烯组成范围内都能结晶，具有良好的机械强度、耐化学腐蚀性和阻隔性，已经被广泛用于包装材料，如食品、化妆品、化学用品等。由于EVOH具有亲水性的聚乙烯醇链段，该材料的抗污染性要优于聚丙烯、聚偏氟乙烯等。近年来，EVOH作为水处理用膜材料成为一个研究热点。在本文中对热致相分离(TIPS)法制备EVOH微孔膜过程中的物理化学以及膜形态的控制问题进行了研究。在热致相分离法中，相图是重要的信息，它反映了体系的相行为，也是控制膜形态的基础。对体系相图进行预测是一项非常有意义的工作。在本文中计算了EVOH在乙烯摩尔含量为38％和44％(EVOH38，EVOH44)时分别与1，4—丁二醇、1，3—丙二醇和丙三醇体系的相图。为了准确的估算出共聚物与稀释剂之间的相互作用参数，引入了聚合物共混中的二元作用模式。该模式认为体系的相容性不仅与分子间的相互作用有关，也与分子内的相互作用有关。从EVOH38、EVOH44与1，4—丁二醇，1，3—丙二醇和丙三醇的预测结果来看，计算的液固、液液分相线与实验所得的数据及文献数值相符较好。为了说明二元作用模式引入的重要性，用传统的溶度参数理论计算共聚物与稀释剂的相互作用参数，并对EVOH38、EVOH44与1，4—丁二醇和丙三醇体系相图进行了计算。比较两种算法的结果发现，引入二元作用模式的结果与实验数据更加吻合。相图如此的重要，如果能对体系的相图进行控制也很有意义。在本文中使用与EVOH38相容性良好的1，4—丁二醇和相容性较差的聚乙二醇(PEG)400的混合溶剂为稀释剂，研究了不同的溶剂配比对体系相图的影响。结果发现随着PEG400含量的增加，原来不发生液—液相分离的体系渐渐出现了液液相分离区域，而且PEG400的含量越高，液液相线向高温移动，液液分相区域变宽。同时，在同一制膜工艺下，不同溶剂配比的体系得到了不同形态的膜。这也为膜形态的控制提供了一种新的方法。中空纤维由于比平膜具有更大的比表面积而拥有更广泛的用途。以前有人已经对纤维的纺织工艺进行过详细的研究，然而对后处理工艺却涉及较少。在本文中使用丙酮、甲醇和水作为萃取剂处理EVOH微孔中空纤维，研究了不同的萃取剂及不同的干燥工艺对纤维形态及性能的影响。从纤维的干燥体积收缩率可以发现甲醇和水作为萃取剂时，纤维在干燥中体积收缩率较大，接近50％，而使用丙酮时则小得多。通过计算三种萃取剂与EVOH的相互作用参数可以得出，萃取剂与聚合物的相互作用越强，在干燥过程中其体积收缩率越大。为了减小纤维在干燥过程中的尺寸收缩，将中空纤维的两端固定在不锈钢架上进行干燥。结果表明，这种固定干燥法能够有效地降低纤维的体积收缩。通过电镜观察了三种萃取剂处理后纤维的结构形态。从电镜照片可以看到，使用甲醇和水在挥发后造成了中空纤维部分膜孔结构的坍塌。孔结构的坍塌过程是一个需要时间的高分子链蠕动过程，为了减少这一时间将中空纤维处于真空状态下干燥，结果表明，当水作为萃取剂时，真空干燥下纤维体积的收缩率要比自然干燥下的小，而孔结构坍塌的范围也比自然干燥下的小。测量了不同干燥工艺的中空纤维的透气、透水性。从结果可以看出，使用丙酮得到的纤维透气、透水的性能最佳，而用水处理的次之，用甲醇处理得到的是透气性很小且不透水的中空纤维。对比真空干燥和自然干燥的结果可以发现，丙酮和甲醇处理的中空纤维区别不大，而用水处理的纤维，其真空干燥的透气和透水性比自然晾干的要好的多。在本文最后一章中，使用热致相分离(TIPS)的方法制备了EVOH／PVP共混膜。从DSC的结果可以看出EVOH与PVP具有良好的相容性，而从红外分析发现，EVOH与PVP具有氢键作用，两者的相容性可能是分子水平的。PVP的用量也对体系的相行为有着影响，随着体系中PVP含量的增加，浊点向高温方向移动，而结晶温度却变化不大。由于热致相分离制膜工艺的特点，PVP分为包埋于聚合物本体和吸附于膜表面两部分。前者由于PVP与EVOH具有特殊相互作用，不容易被水洗掉，而后者由于只是附着于膜表面，很容易被水洗掉，于是可以通过测量共混膜在水中减少的质量来分析PVP的分布情况。研究表明，膜中PVP的含量越高，本体中的PVP所占的比例越小。通过扫描电镜观察了PVP对膜的形态的影响，从电镜照片中可以看出，膜形态均为蜂窝状，而且膜孔结构随着PVP含量的增加而增大。最后用静态水接触角和BSA吸附试验表征了膜的亲水性和抗污染性，结果表明，PVP的加入改善了膜的亲水性和抗污染性，而且PVP的含量越高，材料的亲水性和抗污染性越好。更多还原

【Abstract】 Membrane separation technology is simple, energy-saving, high-effective, no secondary pollution, operational in room temperature, and has been applied in various fields. In water treatment aspect, membrane separation has been used in salt-water desalination, waster water treatment, and purified water production. In present, the membrane materials used in water treatment are polypropylene (PP), polysulfone (PSF), poly(vinylidene fluoride) (PVF), et.al. Most of these membranes are hydrophobic and thus the separation flux tends to decline during the operations due to solute adsorption and pore blocking. Some hydrophilic materials, such as polyvinyl alcohol (PVA), cellulose acetate (CA), have bad mechanical intensity and solvent resistance.Poly (ethylene-co-vinyl alcohol) (EVOH) is a semi-crystalline random copolymer, can crystallize over whole composition range of ethylene. EVOH has very low gas permeability, excellent chemical resistance and mechanical properties and been widely used as packing material, such as food, cosmetic, chemical product. Because EVOH has hydrophilic vinyl alcohol segment, it has superior properties over other hydrophobic polymers for the prevention of membrane fouling. Recently, EVOH membranes have been the subjects of significant research interest for water treatment applications. In this thesis, EVOH microporous membranes have been prepared via thermally induced phase separation (TIPS), and some research have been done about physical chemical topic and membrane morphology control in preparation process.In TIPS, the phase diagrams provided the critical information about phase behavior of the system and the base to control membrane morphology. Predication of phase diagram is a kind of interesting work. The binary interaction model was applied to estimate the phase diagrams of copolymer and diluent systems. The S-L and L-L phase separation curves of EVOH/ 1,4-butanediol, EVOH/1,3-propanediol, and EVOH/glycerol have been calculated. The fair agreement between the experimental data and the calculated values indicated the feasibility to predict the phase separationbehavior of copolymer-diluent systems on the basis of binary interaction model. In order to confirm the importance of incorporating intra-molecular interaction, calculations with and without the consideration of intra-molecular interaction were performed and compared. And it was found that better results were obtained if intra-molecular interaction was introduced.Phase diagram is important in TIPS, if phase behavior of the system can be controlled, which would be significative. The mixtures of 1,4-butanediol and poly (ethylene glycol)(PEG400) were used as diluents. The phase diagrams of this system were studied. The morphology of microporous membrane was observed by scanning electron microscope (SEM). It was found that the composition of the binary solvents could influence the temperature of L-L phase separation and the morphology of the membrane.A hollow fiber module is more efficient than a flat sheet module because the hollow fiber module has more surface area for separation per unit volume of module than the flat sheet module. For this reason, hollow fibers are more commonly used in industry than flat sheet. EVOH38 hollow fibers were prepared via TIPS process. Water, methanol and acetone were used to extract the diluent in the fibers, respectively. Bigger shrinkage of fibers during extractant evaporation was observed when water or methanol was used. The results of calculation for interactive parameters indicated that the molecules of water and methanol had stronger interaction with EVOH38. Therefore, the affinity of extractant with polymer would be the crucial factor for the shrinkage during extractant evaporation. Besides, the analysis of X-ray diffraction in extraction process indicated that water and methanol could reach the amorphous region of the polymer and destroy the structure of crystal, so that the polymer would be easier to be deformed and shrunk. The smaller pore size and porosity at inner layer of fibers were observed on the SEM images of cross-section of hollow fibers treated with water and methanol. The denser morphology must result from the larger volume shrinkage and the collapse of porous structure caused by the extractants due to the better affinity of the two extractants with the polymer. The measurement results of water and gas permeability are coincident with the SEM images and shrinkage data.In the last chapter of this thesis, Poly (ethylene-co-vinyl alcohol) with ethylene content of 44mol% (EVOH44)/PVP (K30) membranes were prepared via thermally induced phase separation (TIPS). Poly (ethylene glycol) with average number weight of 300 (PEG300) was used as diluent. Differential scanning calorimetry (DSC) andattenuated total reflectance infrared (ATR-FT-IR) spectra were used to investigate the compatibility of EVOH44 and PVP (K30). From disappearance of the melting peak of EVOH, T_g of PVP in DSC, the shift of PVP carbonyl and C-O bonds of EVOH in ATR, it was indicated that they are compatible. The effects of PVP content on phase diagram, PVP distribution and membrane morphology were studied. It was found that the binodal point shifted to higher temperature and proportion of PVP between polymer matrixes to pore surface decreased with PVP content increasing. It was also found that the pore size of the membranes increased as PVP content increased. The hydrophilicity and protein adsorption properties of EVOH/PVP membranes were also measured; the results indicated that they had better hydrophilicity and protein antifouling property compared with pure EVOH membrane.更多还原