聚偏氟乙烯中空纤维膜表面改性研究

【作者】 韩珣；

【导师】 吕晓龙；

【作者基本信息】 天津工业大学 ， 材料学， 2004， 硕士

【摘要】 聚偏氟乙烯（PVDF）作为膜材料由于其疏水性而限制了其在水相分离体系中的应用。本文采用化学接枝改性的方法对PVDF中空纤维膜进行亲水改性，研究了预处理条件对接枝反应的影响，以及改性后膜性能的变化。 首先，以强碱和强氧化剂处理体系对PVDF中空纤维膜进行预处理。采用傅立叶红外光谱（FTIR）和X光电子能谱（XPS）对预处理前后PVDF中空纤维膜表面化学结构进行分析。实验结果表明，预处理后PVDF中空纤维膜表面有羟基等极性基团生成。考察预处理条件对PVDF中空纤维膜力学性能及接枝反应的影响，确定预处理条件为：[KOH]=2.3mol／L、KMnO₄％=3wt％、T=50℃和t=10min。然后，选用硝酸铈铵作为引发剂，2-丙烯酰胺-2-甲基丙磺酸（AMPS）为接枝单体，在水溶液体系中进行接枝共聚反应制备PVDF—g—AMPS中空纤维膜，并利用傅立叶红外光谱（FTIR）、X光电子能谱（XPS）、扫描电子显微镜（SEM）及原子力显微镜（AFM）等检测手段证实了接枝共聚物的存在。 实验表明，在PVDF中空纤维膜表面接枝AMPS可有效提高PVDF中空纤维膜的亲水性。改性PVDF中空纤维膜对带有相同负电荷的小分子染料达旦黄具有明显的截留效果。聚丙烯酰胺基甲基丙磺酸为高分子电解质，接枝在膜表面后高分子链与溶质分子相互作用，可使接枝链构象发生变化，从而改变膜孔径的大小，使膜具有环境响应。考察了溶液pH值和离子强度对改性膜通量的影响，实验发现，当pH值较高或离子强度较低时，改性中空纤维膜通量相对较低；相反，当pH值较低或离子强度较高时，改性中空纤维膜通量相对较高。更多还原

【Abstract】 Due to the hydrophobicity of poly(vinylidene fluoride) (PVDF), the application of PVDF membrane was limited. In this paper, we adopt a simple chemical modification method for the surface functionalization and grafting of polar monomers onto PVDF membranes, which provides excellent hydrophilicity to the polymeric surfaces.Firstly, the porous membranes of hydrophobic polyvinylidene fluoride were pretreated by a strong alkali solution containing an oxidizing agent to introduce a polar group on the membrane surface. The surface compositions of the pretreated PVDF membrane were determined by Fourier transform adsorption spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS). From the FTIR and XPS results it was evident that HO-C groups were formed. Optimum conditions for pretreatment were ..found to be [KOH] = 2.3mol/L, KMnO4% =3wt%, T=50 C and t =10min. Secondly, the grafted membranes were prepared by grafting 2-Acrylamido-2-methyl propane sulfonic acid (AMPS) on pretreated membranes using cetric ammonium nitrate (CAN) as an initiator in the aqueous medium. The surface compositions of the grafted membranes were determined by Fourier transform adsorption spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS). And the morphology of the grafted membranes was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM).Water content test revealed that grafting AMPS on PVDF membrane was an effective method to improve the hydrophilicity of PVDF membrane. It was found that the flux of water decreased with increasing surface concentration of the grafted AMPS polymer, while the pore size remained almost unchanged. The grafted membranes were capable of rejecting an anionic dyestuff.In common with other polyelectrolytes, the conformation of grafted AMPSA polymeric chains is sensitive to environmental factors such as pH and ionic strength (I). For the conformation of AMPSA polymeric chains, fluxes through the grafted membranes were very sensitive to the solution ionic strength and also to the solution pH. At higher pH or lower /, the flux through the grafted membranes was lower; conversely, the flux through the grafted membranes increased as pH decreased or I increased.更多还原