PVDF膜的亲水改性及抗污染性能研究

【作者】 张明刚；

【导师】 平郑骅；

【作者基本信息】 复旦大学 ， 高分子化学与物理， 2007， 硕士

【摘要】 聚偏氟乙烯（PVDF）是一种有着极好机械强度、化学稳定性和成膜性的聚合物,是制备超滤或微滤分离膜的优良原料。但是,PVDF的强疏水性使这种膜用于处理水溶液时,存在以下两个问题:一是膜对水的渗透阻力大,因此操作时需较高的工作压力;一是膜在使用过程中,容易受到蛋白质的吸附污染导致渗透通量的急剧下降。对PVDF膜进行亲水改性是解决上述弊端,提高膜的通量,降低膜的污染、延长膜的使用寿命的主要方法,使其更适应于生化、医药、净水等领域的使用。本论文研究了通过表面接枝改性提高PVDF膜亲水性的方法。由于PVDF分子的化学键能高,表面接枝需要很高的能量。为此,我们采用了一种先共混再接枝的方法。首先选用少量光活性聚合物PES与PVDF共混制膜。然后通过表面紫外辐照接枝反应,在PVDF/PES共混膜表面接枝亲水性强的单体。如N-乙烯基-2-吡咯烷酮（NVP）和2-丙烯酰胺基-2甲基丙基磺酸（AMPS）。论文采用DMA、ATR-FTIR、表面接触角测定仪、EDS、SEM等方法系统研究了用上述方法对PVDF膜进行改性的效果,及表面性能和形态的变化。论文通过测定改性前后膜对BSA的静态吸附以及膜对水和BSA溶液的超滤性能系统的研究了接枝反应对膜的抗污性能的影响。研究结果表明,当PES的含量在铸膜液中低于0.5%时,制得的膜的机械性能没有发生变化。通过在PVDF膜中共混少量PES的方法制成的膜容易在能量较低紫外光源辐照下在表面发生接枝反应。亲水性单体的接枝率随着接枝时间的增加而增加,膜的接触角也同步下降,表明改性后膜表面的亲水性有显著改善。膜对BSA静态吸附的结果表明,通过接枝改性后的膜对蛋白质的吸附量明显减小,说明改性膜对蛋白质的抗污染能力有明显提高。超滤的结果表明,接枝改性的PVDF膜的性能相对比较稳定,其纯水通量只需通过简单清洗即能大部恢复。改性膜显示出更强的抗污染能力。例如,用光强为3.44 mW/cm²的紫外光源,在5%NVP溶液中接枝改性7分钟的PVDF/PES膜,其水接触角从74°下降到37°,膜对BSA的吸附量从159±2μg/cm²下降为19±2μg/cm²。与未改性PVDF膜相比,PES/PVDF接枝改性膜在相同的测试条件下,其受蛋白质污染的程度减少了66%,经过化学清洗之后水通量恢复率提高了32%。本论文还研究了通过紫外辐照接枝改性的方法制备荷正电纳滤膜的方法。提出该课题的主要思路是由于荷负电纳滤膜在处理高价阳离子盐溶液时会出现截留率下降的现象。荷正电纳滤膜的制备是通过紫外辐照接枝的方法将一定量的对氯甲基苯乙烯单体接枝到膜表面使形成纳滤膜,然后通过季铵化反应,和盐酸处理使形成荷正电的季铵离子。研究结果表明,用上述方法制成的膜显示荷正电纳滤膜的性能。通过延长接枝时间和增加辐照强度可以使膜的接枝率得到提高。同时随着接枝率的提高和季铵化程度的增加,膜的表面接触角也有了显著的下降。对膜的纳滤性能测试表明,此方法制备的膜在处理高价阳离子时表现出了优异的纳滤性能。例如,当光强度为3.44 mW/cm²时,接枝10min的膜对MgCl₂的截留率达到70%,对NaCl的截留率为39%。更多还原

【Abstract】 Poly (vinylidene fluoride) (PVDF) membranes are widely used in microfiltration (MF) and ultrafiltration (UF) due to their excellent chemical resistance, well-controlled porosity, and good thermal and mechanical properties. However, the higher hydrophobicity of the membrane limited its application in the fields of biotechnology and pharmacy, where the fluid phases to be treated are generally complex and heavily loaded with colloidal matters and hydrophilic membranes with better fouling resistances are required.In this article, a novel method was used to prepare hydrophilic PVDF ultrafiltration membrane. As for PVDF, C-H and C-F bond with high bond energy was difficult to cleave only by UV irradiation. To make graft polymerization easier, we incorporated a small amount of photoactive polymer PES into PVDF in the asymmetric membrane casting, then grafted hydrophilic monomers (N-vinyl-2-pyrrolidinone and 2-acrylamido-2-1-propanesulfonic acid) on the dense layer of the blend membrane under UV irradiation. Firstly, PES/PVDF blend membrane was prepared for photo grafting surface modification. As the content of PES in the blend membrane was low, the modified PVDF was expected to keep well its mechanical properties. The characteristics of the modified membrane were studied by ATR-FTIR, energy dispersive spectrometry (EDS) and contact angle. It was found that the mechanical property of the blend membrane did not change if the PES content in the blend membrane was lower then 0.5% and the contact angle of water on the membrane surface decreased with the grafting time. The modified membrane showed higher fouling resistance. First, the adsorption amount of bovine serum albumin (BSA) on the membranes decreased from 159±2μg/cm~2 to 13±2μg/cm~2 after 10 min of grafting. Secondly, the filtration of a 0.1% BSA solution showed that the modified membrane had lower BSA adsorption and better flux recovery. Compared with the non-modified PVDF membrane, the fouling degree of the blend membrane with 7 min grafting was reduced by 66% and the flux recovery after chemical cleaning increased about 32%.In our investigation of preparation of nanofiltration membrane by UV-graft polymerization on PEK-C ultrafiltration membrane, it was found that negatively charged nanofiltration membrane prepared by grafting acrylic acid (AA) performed lower retention of multi-valent cations. In this article, we firstly developed a method to prepare hydrophilic positively charged nanofiltration membrane by graft polymerization of chloromethylstyrene (CMS) onto surface of PEK-C ultrafiltration membrane and quaternary animation processes. ATR-FTIR spectra detected CMS grafted on the surface of PEK-C, and relative grafting ratio increased with irradiation time, while contact angle of water on the modified membrane surface decreased. The modified membranes showed a good retention of multi-valent cations that is a characteristic of nanofiltration. For example, the retentions to magnesium chloride and sodium chloride of the membrane grafted for 10 min under UV intensity of 3.44 mW/cm~2 was 70% and 39% at 0.4MPa, respectively.更多还原