Thermo- and pH-responsive polypropylene microporous membrane prepared by the photoinduced RAFT-mediated graft copolymerization

Thermo- and pH-responsive polypropylene microporous membrane prepared by photoinduced reversible addition–fragmentation chain transfer (RAFT) graft copolymerization of acrylic acid and N-isopropyl acrylamide by using dibenzyltrithiocarbonate as a RAFT agent. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FT-IR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM) were used to characterize the structural and morphological changes on the membrane surface. Results of ATR/FT-IR and XPS clearly indicated that poly(acrylic acid) (PAAc) and poly(N-isopropyl acrylamide) (PNIPAAm) were successfully grafted onto the membrane surface. The grafting chain length of PAAc on the membrane surface increased with the increase of UV irradiation time, and decreased with the increase of the concentration of chain transfer agent. The PAAc grafted membranes containing macro-chain transfer agents, or the living membrane surfaces were further functionalized via surface-initiated block copolymerization with N-isopropyl acrylamide in the presence of free radical initiator, 2,2′-azobisisobutyronitrile. It was found that PNIPAAm can be grafted onto the PAAc grafted membrane surface. The results demonstrated that polymerization of AAc and NIPAAm by the RAFT method could be accomplished under UV irradiation and the process possessing the living character. The PPMMs with PAAc and PNIPAAm grafting chains exhibited both pH- and temperature-dependent permeability to aqueous media.     

Mitigated membrane fouling in an SMBR by surface modification

Fouling is a major obstacle in membrane processes applied in membrane bioreactor. To improve the antifouling characteristics of polypropylene hollow fiber microporous membranes (PPHFMMs) in a submerged membrane bioreactor (SMBR), the PPHFMMs were surface modified by NH₃, CO₂ plasma treatment, photoinduced graft polymerization of acrylamide and acrylic acid. The structural and morphological changes on the membrane surface were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (FT-IR/ATR) and field emission scanning electron microscopy (FE-SEM). The change of surface wettability was monitored by contact angle measurements. The results of XPS and FT-IR/ATR clearly indicated the successful modification on the membrane surface. The static water contact angle of the modified membrane reduced obviously. The antifouling characteristics of the modified membranes in an SMBR were evaluated. The modified membranes showed better filtration performances in the submerged membrane bioreactor than the unmodified one, and the acrylic acid-grafted membrane presented the best antifouling characteristics. The results demonstrated that (1) the surface carboxyl-containing membranes were better than the surface amido-containing membranes; (2) surface-grafted membranes were better than the plasma-treated membranes.     

Chain-length dependence of the antifouling characteristics of the glycopolymer-modified polypropylene membrane in an SMBR

Membrane-bioreactor processes have increased considerably in recent years. However, the natural disadvantages of common membrane materials, such as hydrophobic surface, cause membrane fouling and cumber further extensive applications. In this work, hydrophilic surface modification of polypropylene microporous membranes was carried out by the sequential photoinduced graft polymerization of d-gluconamidoethyl methacrylate (GAMA) to meet the requirements of wastewater treatment and water reclamation applications. The grafting density and grafting chain length were controlled independently in the first and second step, respectively. Attenuated total reflection–Fourier transform infrared spectroscopy (FT-IR/ATR) and X-ray photoelectron spectroscopy (XPS) were employed to confirm the surface modification on the membranes. Water contact angle was measured by the sessile drop method. Results of FT-IR/ATR and XPS clearly indicated that GAMA was grafted on the membrane surface. It was found that the grafting chain length increased reasonably with the increase of the UV irradiation time. Water contact angle on the modified membrane decreased with the increase of the grafting chain length, and showed a minimum value of 43.2°, approximately 51.8° lower than that of the unmodified membrane. The pure water fluxes for the modified membranes increased systematically with the increase of the grafting chain length. The effect of the grafting chain length on the antifouling characteristics in a submerged membrane-bioreactor for synthetic wastewater treatment was investigated. After continuous operation in the submerged membrane-bioreactor for about 70 h, reduction from pure water flux was 90.7% for the virgin PPHFMM, and ranged from 80.8 to 87.2% for the modified membranes, increasing with increasing chain length. The flux of the virgin PPHFMM membrane after fouling and subsequent washing was 31.5% of the pure water flux through the unfouled membrane; for the modified membranes this ranged from 27.8 to 16.3%, decreasing with increasing chain length. These results demonstrated that the antifouling characteristics for the glucopolymer-modified membranes were improved with an increase in GAMA chain length.     

Surface modification of microporous polypropylene membranes by the grafting of poly(γ-stearyl-l-glutamate)

A polypeptide, poly(γ-stearyl-l-glutamate) (PSLG), was grafted on the surface of hydrophobic polypropylene hollow fiber membranes through the ring opening polymerization of N-carboxyanhydride (NCA) of γ-stearyl-l-glutamate initiated by amino groups which was generated by ammonia plasma. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), together with water contact angle and bovium serum albumin adsorption measurements were used to characterize the modified membrane surface. The XPS and FT-IR spectra demonstrated that polypeptide was actually grafted on the membrane surface despite of the low degree of graft polymerization due to the hydroxyl groups on the membrane surface. To subject the ammonia plasma-treated membrane with γ-(aminopropyl)triethanoxysilane (γ-APS) which can react with hydroxyl groups and leave amino groups, the degree of graft polymerization could be improved. The bovium serum albumin adsorption measurement was conducted to further examine the surface properties of modified and original membranes. Potential applications of the PSLG grafted membranes are expected for enantiomer separation and/or enzyme immobilization.     

INTROMISSION OF WATER-REPELLENT AND HYDROSCOPIC PROPERTIES SIMULTANEOUSLY TO PP BY PLASMA DISCHARGE METHOD

Plasma-induced surface graft copolymerization of acrylic acid on polypropylene non-woven fabric (PP-g-AA) and polypropylene membrane were reported. The extents of grafting were controlled by the plasma and polymerization condition. Hexadecyltrimethyl ammonium bromide was then coupled with the carboxyl group of PP-g-AA to obtain a polyion complex (PIC). At last, CF4 plasma was used to give PICs hydrophobic property. The moisture regain and water-repellency of the processed PICs was investigated. The surfaces were characterized using ATR FT-IR and XPS. The result indicates that the products have very high ability to adsorb moisture, even better than cotton fiber. At the same time, the products show excellent hydrophobic property, which can‘t be wetted by those reagents whose surface tensions were higher than 327mN/m.     

聚丙烯微孔膜基渐变聚合物的制备,结构与性能的研究

以聚丙烯微孔膜为基材，通过扩散控制原位共聚合的方法在人填充了组成沿膜的厚度方向逐渐改变的无规共聚物，Ｘ－光电子能谱（ＸＰＳ）、全反射红外光谱（ＡＴＲ）以及动态粘弹谱的分析结果。说明所制备得到的合膜具有明显的渐变聚合物性质。     

Synthesis of membrane adsorbers via surface initiated ATRP of 2-dimethylaminoethyl methacrylate from microporous PVDF membranes

Surface-initiated atom transfer radical polymerization(SI-ATRP) was used to tether poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) onto microporous PVDF membranes in order to synthesize membrane adsorbers for protein adsorption. The alkaline treatment and bromine addition reaction were used to anchor ATRP initiators on membrane surface. Then PDMAEMA was grafted from the membrane surface via SI-ATRP. Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM) revealed the chemical composition and surface topography of the PVDF-g-PDMAEMA membrane surfaces. These results showed that PDMAEMA was grafted from the membrane surface successfully and a grafting yield as high as 1500 μg/cm2 was achieved. The effects of the grafting time and the density of initiators on the static and dynamic binding capacity of bovine serum albumin(BSA) were systematically investigated. Both the static and dynamic binding capacities increase with the bromination and polymerization time. However, the benefits of the initiator density on binding capacities are limited by the graft density of PDMAEMA chains.     

聚丙烯表面接枝改性络合金的研究

探索了一种通过聚丙烯(PP)改性来络合金金属的新途径.首先在PP膜上经紫外光引发实施丙烯酸的接枝聚合反应,得到表面带—COOH基团的改性PP膜;再用负离子开环聚合的方法在改性后的PP膜上接枝尼龙6.上述处理后的膜表面含有大量O、N的功能基团,故可将此膜用于对溶液中金的络合.利用ATR、SEM、XPS等技术对改性及络合进行了表征.实验结果表明,此方法制备的PP膜对金的络合效果明显.     

铅(Ⅱ)离子印迹复合膜的制备及其性能研究

以聚丙烯微孔膜(MPPM)为支撑,采用共价表面修饰和离子印迹技术,制备了Pb(Ⅱ)离子印迹复合膜.首先通过紫外光引发丙烯酸接枝聚合,在MPPM表面引入羧基;然后基于羧基和氨基的反应,将壳聚糖共价接枝到MPPM表面;再以Pb(Ⅱ)为模板离子、环氧氯丙烷为交联剂,通过配位键作用形成离子印迹位点.制备过程通过ATR-FTIR和XPS分析得到了证实.利用扫描电子显微镜(SEM)-能量色散X射线光谱仪(EDX)对膜表面及截面的形貌及元素分布进行了分析.静态水接触角和纯水通量实验结果显示,印迹复合膜具有良好的表面亲水性和渗透性,在离子印迹聚合物接枝率为174.4μg/cm2时,水通量高达2659±58 L/(m2.h).印迹复合膜对Pb(Ⅱ)离子的吸附亲和性和渗透选择性分别通过平衡结合实验和竞争渗透实验进行评价.与非印迹复合膜相比,印迹复合膜对Pb(Ⅱ)离子展现出更强的吸附亲和性,更快的吸附速率及更好的渗透选择性,以Cu(Ⅱ)和Zn(Ⅱ)作为竞争离子,其渗透选择性因子分别为3.43和3.93.     

Grafting of regenerated cellulose membrane by surface‐initiated atom transfer radical polymerization and its pH‐resposive behavior

Regenerated cellulose (RC) membranes which have pH modulated permeability have been prepared by anchoring the hydroxyl groups on the membrane surface with 2‐bromoisobutyryl bromide, followed by grafting with acrylic acid (AA) using atom transfer radical polymerization (ATRP). The obtained membranes were analyzed by X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared attenuated total reflection spectrometer (ATR‐FTIR), scanning electron microscopy (SEM), TGA and the results showed that AA had been grafted onto the membrane surfaces successfully. Then the pH modulated permeability properties were tested by water flux measurement. All results show that the pH modulated permeability properties of a RC membrane can be obtained by surface‐initiated ATRP. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel photoinduced grafting-chemical reaction sequence for the construction of a glycosylation surface

Carbohydrates play a major role in many recognition events, such as blood coagulation, immune response, fertilization, cell growth, embryogenesis, and cellular signal transfer, which are essential for the survival of living entities. Synthetic carbohydrate-based polymers, so-called glycopolymers, are emerging as important well-defined tools for investigating carbohydrate-based biological processes and for simulating various functions of carbohydrates. In this work, we present a facile strategy for the formation of glycopolymer tethered on polypropylene microporous membrane surface. Acrylamide was grafted onto the polypropylene microporous membrane surface by photoinduced graft polymerization in the presence of benzophenone. The amide groups of grafted poly(acrylamide) were then transformed to primary amine groups by the Hofmann rearrangement reaction. Quantificational evaluation of the rearrangement reaction was carried out by ninhydrin method and mass weighting. Sugar moieties were coupled with the grafted functional layer to form glycopolymer by the reaction between primary amine groups and carbohydrate lactones. The grafting of acrylamide, the conversion of amide groups to amine groups, and the coupling of sugar moieties were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy combined with surface morphology observation by scanning electron microscopy.     

超亲水聚偏氟乙烯中空纤维膜的制备及性能

采用超声辅助接枝聚合技术, 将甲基丙烯酸缩水甘油酯(GMA)接枝到聚偏氟乙烯(PVDF)膜表面, 制备PVDF-g-GMA膜; 再利用氨基诱导环氧基团发生开环反应, 将苏氨酸(Thr)接枝到PVDF-g-GMA膜表面, 制备了具有两性离子结构表面的PVDF-g-GMA-Thr膜. 通过衰减全反射傅里叶变换红外光谱(ATR-FTIR)、 X射线光电子能谱(XPS)、 接触角测试仪、 场发射扫描电子显微镜(FESEM)和牛血清白蛋白(BSA)过滤实验等系统研究了改性前后PVDF膜表面的化学组成、 润湿性能、 表面形貌和抗污染性能. 研究结果表明, 随着PVDF-g-GMA接枝Thr反应时间的增加, PVDF-g-GMA-Thr膜的亲水性能明显提高, 接触角从90°降为0°, 呈现出超亲水性能. 同时PVDF-g-GMA-Thr膜的水通量明显提高, 当Thr诱导开环反应时间为12 h时, PVDF-g-GMA-Thr膜的水通量高达686 L/(m ²·h), 与PVDF原膜相比, 水通量提高了204.5%. 在BSA的过滤测试中, 与PVDF膜相比, PVDF-g-GMA-Thr膜呈现出良好的截留性能和抗污染性能, BSA截留率从42%提高到84%,水通量恢复率从53%提高到87%, 不可逆污染率从47%降到12%, 表明通过接枝Thr构筑两性离子结构表面可以有效减小膜污染.     

Surface glycosylation of polyacrylonitrile ultrafiltration membrane to improve its anti-fouling performance

Surface glycosylation is one of the most promising strategies to fabricate biomimetic surface for membrane. Previous studies confirmed that cyclic sugars provide recognition sites for specific proteins, while ring-opening sugars offer better hydrophilicity and anti-adsorption ability to proteins. To improve the anti-fouling property of polyacrylonitrile (PAN) ultrafiltration membrane, a ring-opening glycomonomer d-gluconamidoethyl methacrylate (GAMA) was grafted onto the surface of the membrane by ultraviolet (UV)-initiated grafting polymerization. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR) and field emission scanning electron microscopy (FESEM) were used to characterize the chemical and morphological changes of the membrane surface. Water contact angle, protein adsorption and protein filtration were employed to evaluate the anti-fouling performance of the membrane. The protein adsorption experiment was carried out with fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA), and the adsorption quantity was measured locally by laser confocal scanning microscope (LCSM). This method supplied a simple and direct manner to evaluate the protein adsorption performance of membrane, and the interference of the support was also avoided. The results revealed that by the surface glycosylation procedure, the hydrophilicity was enhanced and the adsorption of FITC-BSA was inhibited significantly. The flux recovery ratio was also increased after modification, indicating that the anti-fouling performance of PAN membrane was improved by the glycosylation strategy.     

聚丙烯微孔膜表面修饰的葡聚糖固定化研究

糖以各种形式广泛存在于自然界,在人类的许多生理过程中起着不可或缺的重要作用．它具有优良的亲水性和生物特异性．研究表日月,将含糖单体接枝到聚丙烯微孔膜表面或通过共聚引入聚丙烯腈超滤膜,能显著提高常规高分子分离膜的抗污染能力和表面生物相容性,从而扩大其应用范围．     

Surface glycosylation of polysulfone membrane towards a novel complexing membrane for boron removal

In this study, a novel complexing membrane was synthesized for boron removal from aqueous solution. A glycopolymer, poly(2-gluconamidoethyl methacrylate) (PGAMA), was grafted onto the chloromethylated polysulfone (CMPSF) microporous membrane via surface-initiated ATRP (SIATRP). The glycosylated PSF (GlyPSF) membrane was characterized by attenuated total refection-Flourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). It was demonstrated that PGAMA was successfully anchored onto the membrane surface and the grafting yield can be tuned in a wide range up to 5.9 mg/cm(2) by varying the polymerization time. The complexing membrane can adsorb boron rapidly with the equilibrium reached within 2h and has a remarkable high boron adsorption capacity higher than 2.0 mmol/g at optimized conditions. Freundlich, Langmuir, and Dubinin-Radushkevich adsorption isotherms were applied, and the data were best described by Langmuir model. Kinetic data were analyzed, and the data fitted very well to the pseudo-second-order rate expression. The optimal pH for boron uptake is in a wide range of 6-9, and the optimal initial boron concentration is over 300 mg/L. Studies of ionic strength effects indicated the formation of inner-sphere surface complexes. The complexed boron can be leached quantitatively under acid condition.     

Fabrication of glycosylated surface on polymer membrane by UV-induced graft polymerization for lectin recognition

Increasingly, carbohydrate-protein interactions are viewed as important mechanisms for many biological processes such as blood coagulation, immune response, viral infection, inflammation, embryogenesis, and cellular signal transfer. However, the weak affinity of the interactions and the structural complexity of carbohydrates have hindered efforts to develop a comprehensive understanding of carbohydrate functions. Fortunately, synthetic polyvalent glycoligands give us a chance to reveal the nature of these biological processes. In this work a sugar-containing monomer (alpha-D-allyl glucoside (AG)) was grafted onto polypropylene microporous membrane (PPMM) by UV-induced graft polymerization to generate a glycosylated porous surface for the first time. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were employed to confirm the glycosylation. Water contact angle measurement was used to evaluate the hydrophilicity change of the surfaces before and after the graft polymerization of AG. It was found that the grafting density increased reasonably with the increase of AG monomer concentration, and then this increase slowed when the AG concentration exceeded 80 g/L. At the same time a 20-25 min UV irradiation was enough for the grafting polymerization. The photoinitiator concentration also influenced the grafting density obviously, and there was an optimal concentration of the photoinitiator for the grafting process. The water contact angle of the polyAG-tethered membrane surface decreased from 149 degrees to 80 degrees with the increase of grafting density from 0 to 187.76 microg/cm2, which indicated a hydrophilic variation of the membrane surface by the grafting of AG. Results also indicated that the surface-grafted polyAG chains showed weak interaction with Con A when the grafting density was low. However, when the sugar density exceeded 90 microg/cm2, the binding affinity increased dramatically which was the due to the "glycoside cluster effect".     

Amphiphilic PPESK-g-PEG graft copolymers for hydrophilic modification of PPESK microporous membranes

Amphiphilic graft copolymers comprising poly(phthalazinone ether sulfone ketone) (PPESK) backbones and poly(ethylene glycol) (PEG) side chains were synthesized and blended into PPESK casting solutions to prepare hydrophilic and anti-fouling microporous membranes. The graft copolymer was prepared by a modified Williamson etherification method. Sodium alkoxide of methoxyl PEG (PEG-ONa) was used to react with chloromethylated PPESK (CMPPESK). FT-IR spectroscopy, ¹H NMR and solid-state ¹³C CP-MAS NMR analysis confirmed the covalent linking of PEG with PPESK backbones. The incorporation ratio of PEG calculated from ¹H NMR was in agreement with that from TGA tests. The graft products were added into PPESK casting solutions to prepare composite porous membranes using phase inversion method. X-ray photoelectron spectroscopy (XPS) and water contact angle examinations indicated that the grafting copolymers were preferentially excluded to the membrane-coagulant interface during membrane forming, contributing the membranes with improved hydrophilicity and surface wettability. Compared with the neat membrane, the blend membranes exhibited a larger surface pore size and less susceptible to protein fouling.     

Polyethylene Glycol Grafting on Polypropylene Membranes for Anti-fouling Properties

Polyethylene glycol (PEG) chains with different lengths were covalently bonded to polypropylene membranes by means of RF plasma polymerisation of acrylic acid (pp-Aac) followed by mono-amino PEG attachment in liquid phase. Two reactor configurations were tested for the plasma deposition of ppAAc in order to obtain high retention of carboxylic groups in the deposited thin films. A best configuration was assessed evaluating the membrane surface modifications by means of water droplet adsorption time and contact angles measurements, attenuated total reflection (ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis. PEG chains were covalently bonded to the best plasma modified membranes and the resulting anti-fouling properties were evaluated.     

Surface modification of polypropylene membranes by γ-ray induced graft copolymerization and their solute permeation characteristics

Porous hydrophobic polypropylene (PP) membranes were subjected to the surface modification by the γ-ray induced graft copolymerization with hydrophilic 2-hydroxyethyl methacrylate (HEMA). The structural changes and surface morphologies of the modified PP membranes were characterized by a Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA) and field emission scanning electron microscopy (FE-SEM). Peroxides produced from γ-ray irradiation were determined by a 1,1-diphenyl-2-picryl hydrazyl (DPPH) method and the surface hydrophilicities of membranes were measured by a static contact angle measurement. The contact angle of the modified membranes reduced with the degree of grafting (DG) of HEMA onto the membrane surface, and it decreased up to about half of that before modification. The permeation behaviors of all membranes were investigated by a bovine serum albumin (BSA) filtration experiment. As a result, the DG of the modified membrane increased with the reaction time. However, in the case of irradiation dosage it showed the maximum value at 20 kGy. Also, the modified membrane showed a higher solution flux, lower BSA adsorption, and the better flux recovery after cleaning than that of the unmodified membrane. Particularly, 40.6% grafted membrane showed a two-fold increase in a BSA solution flux, 62% reduction in total fouling and three-fold increase in flux recovery after chemical cleaning.     

A FACILE APPROACH FOR THE SURFACE MODIFICATION OF POLY(VINYLIDENE FLUORIDE) MEMBRANE VIA SURFACE-INITIATED ATOM TRANSFER RADICAL POLYMERIZATION

A novel approach for the surface modification of poly(vinylidene fluoride)(PVDF)membrane was successfully realized through alkaline treatment,UV-induced bromine addition,and followed by surface-initiated atom transfer radical polymerization(ATRP)of methyl methacrylate(MMA).Chemical changes on the PVDF membrane before and after modification were analyzed with attenuated total reflectance Fourier transform infrared spectroscopy(ATR/FT-IR)and X-ray photoelectron spectroscopy(XPS).Primary kinetic study revea...