【作者】 智锁红；

【导师】 徐志康；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2014， 博士

【摘要】 聚偏氟乙烯(PVDF)具有物化性质稳定、机械强度高等优点,在水处理等领域应用前景广阔,但是聚合物材料本身疏水,在实际应用过程中易产生膜污染,从而引起膜分离效率的下降和操作成本的增加。利用亲水性的无机纳米粒子制备有机-无机复合膜提高膜的亲水性,正成为膜材料领域的研究热点之一。然而,具有高比表面积和表面能的无机纳米粒子容易团聚,造成其在聚合物基体中分布不均匀。同时,有机与无机两相之间相互作用弱,导致无机纳米粒子在膜服役过程中容易流失,起不到持久亲水化改性的效果。本文采用无机纳米粒子表面改性和仿生矿化的方法,构建了亲水化的有机-无机复合膜,并对表面改性、矿化过程以及复合膜的应用性能进行了深入探讨。全文主要内容如下：为提高二氧化硅(Si02)纳米粒子在聚合物基体中的分散性,并增强其与聚合物的相互作用,采用表面引发原子转移自由基聚合在Si02纳米粒子表面分别接枝甲基丙烯酸羟乙酯／甲基丙烯酸甲酯嵌段共聚物,以杂化Si02纳米粒子为亲水性添加剂,分别与PVDF和PAN溶液共混,通过浸没沉淀相转化法制备有机-无机复合膜。考察了杂化SiO2纳米粒子表面接枝聚合物的分子量对成膜过程、复合膜的结构和性能的影响。当Si02纳米粒子表面接枝合适分子量的聚合物时,杂化粒子在成膜过程中向膜表面迁移／富集,其复合膜具有高的表面亲水性、蛋白质截留率和抗蛋白质污染性能。制备了PVDF/聚丙烯酸(PAA)复合膜,进而采用交替浸渍法于膜表面和截面进行矿化。组合表面衰减傅里叶变换红外光谱仪、X射线衍射仪、场发射扫描电子显微镜等分析手段对矿化过程进行了表征,着重考察了矿化条件如溶液浓度、PAA含量、循环次数对矿化膜的形貌和机械性能的影响规律,确定了最优矿化条件。矿化后的膜表面和截面覆盖了由方解石和球文石组成的碳酸钙粒子,呈现高亲水特性,纯水通量提高了3倍,对刚果红的截留率高达90%,且膜性能长期稳定。采用原位矿化法制备了PVDF/PAA/CaCO3复合膜。结合三元相图分析了不同CaCl2含量的铸膜液的分相行为,在CaCl2的存在下,PVDF/PAA在N,N-二甲基乙酰胺/水溶液中的溶解性变差,且出现了“盐出”效应。比较了碳酸钠和碳酸铵为矿化碳酸源对CaCO3粒子的生成和分布以及矿化膜的结构和性能的影响,选择(NH4)2CO3水溶液为碳酸源。通过添加15wt%甘油于(NH4)2CO3水溶液,降低溶剂与非溶剂的交换速度,制备了PVDF/PAA/CaCO3复合膜。该复合膜无大孔结构,膜上表面、皮层和膜截面处的指状孔内均匀负载由方解石和球文石组成的CaCO3粒子,同时具有抗荷正电蛋白质污染的性能。更多还原

【Abstract】 Poly(vinylidene fluoride)(PVDF) is the most extensively used materials for ultrafiltration and micro filtration membranes because of their sufficient chemical stability as well as fine mechanical strength. However, their hydrophobic nature has hindered the use of the membrane in water treatment as they tend to be fouled and hence show rapid reduction in permeability. Much attention has been paid to hydrophilic organic-inorganic composite membranes which are often fabricated through blending polymers with inorganic nanoparticles. But these inorganic nanoparticles are easy to agglomerate, resulting in non-uniform distribution in the membranes because of their high specific surface area and high surface free energy. Furthermore, the inorganic nanoparticles are easy to leach out during long term use, which results from the instability of the interface of inorganic particles and hydrophobic polymers. In this thesis, organic-inorganic composite membranes with high surface hydrophilicity were fabricated by introducing inorganic particles that was grafted with polymers or by biomineralization. The surface modification and biomineralization processes were explored in detail. Our specific studies are concentrated on the following aspects:PVDF ultrafiltration membranes were prepared by immersion precipitation method using poly(hydroxyethyl methacrylate)-block-poly(methyl methacrylate) grafted silica (PHEMA-b-PMMA@SiO2) nanoparticles as hydrophilic additives. The hybrid nanoparticles were synthesized by the surface initiated atom transfer radical polymerization (SI-ATRP). After blending polymer with the hybrid silica nanoparticles, these hybrid nanoparticles influence the structure and performance of the composite membranes obviously. Nanoparticles with appropriate molecular weight of polymer brushes increase the pure water flux, improve the BSA rejection to a high level (>90%), and reduce the membrane fouling at the same time.Organic-inorganic composite membranes were prepared via calcium carbonate (CaCO3) mineralization induced by PVDF/poly(acrylic acid)(PAA) blend membranes. PAA was used as a polyanionic macromolecule in the blend membranes to generate CaCO3particles by an alternate soaking process (ASP). The mineralization condition was optimized based on the concentrations of calcium chloride (CaCl2) and sodium carbonate (Na2CO3) solutions used for ASP, the number of ASP cycles, and the PAA content in the blend membranes. Structures and surface hydrophilicity of the composite membranes were characterized in detail by FTIR-ATR, FESEM, EDX, XRD and water contact angle. Results confirm that CaCO3particles consisting of calcite and vaterite dispersed uniformly in/on the membranes. The membrane hydrophilicity increased dramatically due to the intrinsic wettability of these CaCO3particles. In addition, pure water fluxes of the membranes were improved about three times. Furthermore, the mineralized membranes even showed a high rejection (99.85%) of Congo red with long-term stability, which makes them potential in dye-polluted wastewater treatment.PVDF/PAA/CaCO3composite membranes were prepared by in-situ mineralization method. The mineralization condition was optimized based on CaCl2content in the casting solution and carbonate source selection. Structures and surface hydrophilicity were characterized in detail by FESEM, FT-IR/ATR, EDX, XRD and water contact angle for the prepared composite membranes. Results confirm that CaCO3particles consisting of calcite and vaterite disperse uniformly on the membrane surface and in the membrane cross-section, and the membrane hydrophilicty increases with the increase of CaCl2content in the casting solution. The pure water fluxes of the membranes were improved about ten times. Due to the electrostatic repulsion between the positively charges lysozyme and CaCO3particles, the mineralized membranes possess a high rejection (85.13%) and flux recovery ratio (77.21%), indicating good antifouling property.更多还原