摘要
作为一种绿色高效的新型分离技术,超滤在生物分离领域具有广阔前景。目前,膜污染依然是制约超滤应用效率的瓶颈。膜材料是影响膜污染的主要因素,开发亲水性膜材料或者提高现有材料的亲水性被认为是降低膜污染的有效途径。本论文以降低高分子超滤膜在生物分离中的污染为出发点,系统研究了膜的制备和膜表面的亲水改性。
采用反相成膜法制备聚乙烯醇缩丁醛(PVB)超滤膜,并通过酸催化水解对其进行化学处理改性。对改性后的PVB膜进行表征,XPS和接触角实验结果表明膜表面的羟基含量增加,亲水性增强,SEM照片显示膜结构未发生明显变化,机械强度和孔隙率实验结果也与未改性膜接近;超滤实验数据表明化学处理改性对膜分离性能有一定影响;通过对膜污染的系统分析发现化学处理改性可以提高PVB超滤膜的抗污染性能,当使用1.0 M盐酸处理4 h时,膜的通量损失率由45.1%下降至38.1%,而通量恢复率则由58.8%上升至78.5%。
通过吸附法改性聚醚砜(PES)超滤膜,将亲水性PVA吸附到疏水性膜表面,并对改性膜进行表征和评价。XPS数据证实了改性膜表面PVA的存在,接触角数据证实了膜表面亲水性的增强,而SEM则显示膜结构并未发生明显变化;超滤实验表明吸附改性会导致膜通量的降低,但可有效提高PES超滤膜的抗污染性能,当PVA溶液浓度为0.5 wt%,吸附次数为3次时,改性膜的总污染和可逆污染指数分别从0.61和0.47降至0.38和0.22,通量恢复率由53.1%上升至78.2%;长期运行实验表明PVA吸附改性膜具有较高的稳定性。
通过共混法使用含有聚乙二醇(PEG)链段的梳状共聚物PS-b-PEG对PES膜进行改性,并对共混膜进行表征和评价。接触角、XPS等表征结果表明共混超滤膜表面亲水性得到显著提高,PEG链段发生了表面富集现象;SEM和机械强度结果表明共混膜结构未发生显著变化,机械性能仍可满足超滤操作要求;蛋白质吸附实验表明共混膜具有良好的抑制蛋白质吸附能力,最低吸附量降至0.5μg/cm2;超滤实验表明共混膜的通量略有提高,其原因主要是梳状共聚物起一定的致孔作用;通过对膜污染的系统分析证实共混改性提高了PES膜抗污染性能,总污染和不可逆污染指数均显著降低。
As a green and energy-efficient separation technology, ultrafiltration exhibits a vast prospect of application in bioseparation, while membrane fouling still constitutes a bottleneck of its development. Membrane materials show great impact on membrane fouling. Major approaches for fouling reduction include exploitation of novel hydrophilic membrane materials and hydrophilic modification of membrane materials applied. In this dissertation, with the aim of reducing membrane fouling during biosepration, preparation and hydrophilc modification of ultrafiltration membranes were investigated.
Poly (vinyl butyral) (PVB) ultrafiltration membranes were prepared via the phase inversion process and modified through an acid catalyzed hydrolysis process. XPS and water contact angle results indicated the increase of hydroxyl groups at membrane surface and the enhancement of surface hydrophilicity, and SEM suggested that modified membranes remained asymmetric structure; meanwhile, the mechanical property and porosity were close to the values of control PVB membranes.
Ultrafiltration results showed that separation performance was affected to some extent by chemical modification. The systematical analysis of membrane fouling confirmed that chemical modification could effectively improve the antifouling property of PVB membranes. When treated with 1.0 M HCl solution for 4 h, the flux loss ratio was decreased from 45.1% to 38.1% while the flux recovery ratio was increased from 58.8% to 78.5%.
Polyethersulfone (PES) ultrafiltration membrane was modified through adsorption to introduce the hydrophilic poly (vinyl alcohol) (PVA) chains to the hydrophobic membrane surface. The modified membranes were characterized and evaluated. XPS results confirmed the presence of PVA at membrane surface, and the value of water contact angle indicated the hydrophilicity enhancement. The membrane structure had no significant changes according to SEM. Ultrafiltration results showed that adsorption would reduce membrane flux, but it had effectively improved the antifouling property of PES membranes. When PVA concentration was 0.5 wt% and adsorption cycle was 3, the total and irreversible fouling ratio of modified membranes were 0.38 and 0.22, respectively, much lower than control PES membrane, of which the value were 0.61 and 0.47. The flux recovery ratio was increased from 53.1% to 78.2%, while the long term ultrafiltration experiment showed an ideal stability of modification.
A comb copolymer PS-b-PEG, which contained hydrophilic poly (ethyl glycol) (PEG) chains, was blended with PES to fabricate ultrafiltration membrane, and the blend membranes were characterized and evaluated. The PEG segments were spontaneously segregated to the membrane surface and the surface hydrophilicity was correspondingly enhanced, which was confirmed by the water contact angle and XPS results. The membrane structure had no significant changes and the mechanical property could still well meet the need of ultrafiltration. The protein adsorption experiments indicated the blend membranes had excellent protein adsorption resistance; the lowest adsorption amount reached 0.5μg/cm2. Ultrafiltration results showed that the blend membranes had a little higher flux, which was due to the pore-forming effect of the copolymer. The fouling investigation confirmed the antifouling property improvement of PES membrane through blending; the total and irreversible fouling were both remarkably reduced.
引文
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