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 POLYPROPYLENE MICROPOROUS MEMBRANE BY TETHERING POLYPEPTIDES

Two kinds of polypeptides were tethered onto the surface of polypropylene microporous membrane （PPMM） through a ring opening polymerization of L-glutamate N-carboxyanhydride initiated by amino groups which were introduced by ammonia plasma and y-aminopropyl triethanoxysilane treatments. X-ray photoelectron spectroscopy （XPS）, attenuated total reflectance Fourier transform infrared spectroscopy （FT-IR/ATR）, scanning electron microscopy （SEM）, together with water contact angle measurements were used to characterize the modified membranes. XPS analyses and FT-IR/ATR spectra demonstrated that polypeptides are actually grafted onto the membrane surface. The wettability of the membrane surface increases at first and then decreases with the increase in grafting degrees of polypeptide. Platelet adhesion and murine macrophage attachment experiments reveal an enhanced hemocompatibility for the polypeptide modified PPMMs. All these results give evidence that polypeptide grafting can simultaneously improve the hemocompatibility as well as reserve the hydrophobicity for the membrane, which will provide a potential approach to improve the performance of polypropylene hollow fiber microporous membrane used in artificial oxygenator.     

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.     

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.     

Surface Heparinization of Poly(ether ether ketone)

Photo-grafting of hydrophilic monomer and space arms was used to enhance the hydrophilicity of poly(ether ether ketone)(PEEK) with the aim of extending its application to biological fields. PEEK films were surface modified by UV grafting of acrylic acid(AA) to introduce ―COOH on PEEK surface. Adipic amine was used as a space arm to introduce heparin on PEEK surface based on the condensation reaction between ―NH₂ and ―COOH. The modified PEEK(PEEK-COOH, PEEK-NH₂ and PEEK-Hep) was characterized by energy-disperse spectroscopy (EDS), X-ray photoelectron spectroscopy(XPS) and water contact angle measurements, which show that heparin was grafted on PEEK surface. The contact angles of modified PEEK films were lower than those of original films, demonstrating a significant improvement of surface hydrophilicity.     

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.     

Enhancing the antifouling property of polyethersulfone ultrafiltration membranes through surface adsorption-crosslinking of poly(vinyl alcohol)

An adsorption-crosslinking process of poly(vinyl alcohol) (PVA) was introduced to modify the surface of polyethersulfone (PES) ultrafiltration membranes for enhancement of their antifouling property. XPS and water contact angle measurement confirmed the obvious enhancement of surface hydrophilicity. Ultrafiltration results showed that the spreading of PVA chains over the hydrophobic membrane surface caused substantial but acceptable decrease on membrane flux. The fouling type analysis indicated that PVA adsorption effectively improved the antifouling property of PES membranes. With a PVA concentration of 0.5 wt% and three cycles of alternative adsorption-crosslinking, the total and irreversible fouling ratio of modified membranes were 0.38 and 0.22, respectively, much lower than those of control PES membrane (0.61 and 0.47), and the flux recovery ratio was increased accordingly. The long-term ultrafiltration experiment demonstrated the improvement of recycling property and the reliability of adsorption-crosslinking process.     

紫外接枝聚合聚乙二醇甲基丙烯酸甲酯制备抗污染聚砜超滤膜

以二苯甲酮(BP)为紫外引发剂,将聚乙二醇甲基丙烯酸甲酯(PEGMA)接枝在聚砜超滤膜表面以提高膜的抗污染性能.在二苯甲酮存在的条件下,波长较长(λ300nm)的紫外光(UV)辐射下发生提氢反应,可以有效防止聚砜分子主链的剪切,保持改性膜的分离性能.考察了PEGMA浓度、UV辐射时间和BP浓度对改性超滤膜接枝度、亲水性和抗污染性能的影响.用表面全反射红外光谱(ATR/FTIR)表征改性前后膜表面化学组成的变化.表面改性膜的纯水通量略有降低而牛血清白蛋白(BSA)截留率有所提高.随着接枝度的提高,PEGMA接枝改性膜的抗污染性能增加.     

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.     

Immobilization of Bovine Serum Albumin on Poly(ether ether ketone)for Surface Biocompatibility Improvement

UV-induced graft polymerization of acrylic acid(AA)on poly(ether ether ketone)(PEEK)films was carried out to introduce-COOH for the subsequent immobilization of bovine serum albumin(BSA).BSA was introd...     

Study of plasma-polymerization deposition of C2H2/CO2/H2 onto ethylene-co-propylene rubber membranes

Ethylene-co-propylene rubber (ERP) membranes were modified by use of acetylene/carbon dioxide/hydrogen (C₂H₂/CO₂/H₂) plasma-polymerization deposition. The influence of flow rate of gases, glow discharge power and deposition time on the amount of deposition was investigated. Infrared spectroscopy and scanning electron microscopy were employed to study the structure and surface morphology of the deposited EPR membrane. The water contact angle and the permeation property were examined as well. The results showed that deposition comprises oxygen-containing groups including >C=O and –OH, the hydrophilicity of EPR membrane was therefore improved. It was also found that the permeation coefficient of plasma modified EPR membrane decreased with the increase of the amount of deposition.     

Thermo-responsive and antifouling PVDF nanocomposited membranes based on PNIPAAm modified TiO2 nanoparticles

A novel hydrophilic nanocomposite additive(TiO2-g-PNIPAAm) was synthesized by the surface modification of titanium dioxide(TiO2) with N-isopropylacrylamide(NIPAAm) via "graft-from" technique. And the nanocomposite membrane of poly(vinylidene fluoride)(PVDF)/TiO2-g-PNIPAAm was fabricated by wet phase inversion. The graft degree was obtained by thermo-gravimetric analysis(TGA). Fourier transform infrared attenuated reflection spectroscopy(FTIR-ATR) and X-ray photoelectronic spectroscopy(XPS) characterization results suggested that TiO2-g-PNIPAAm nanoparticles segregated on membrane surface during the phase separation process. Scanning electron microscopy(SEM) was conducted to investigate the surface and cross-section of the modified membranes. The water contact angle measurements confirmed that TiO2-g-PNIPAAm nanoparticles endowed PVDF membranes better hydrophlilicity and thermo-responsive properties compared with those of the pristine PVDF membrane. The water contact angle decreased from 92.8° of the PVDF membrane to 61.2° of the nanocompostie membrane. Bovine serum albumin(BSA) static and dynamic adsorption experiments suggested that excellent antifouling properties of membranes was acquired after adding TiO2-gPNIPAAm. The maximum BSA adsorption at 40 °C was about 3 times than that at 23 °C. The permeation experiments indicated the water flux recover ratio and BSA rejection ratio were improved at different temperatures.     

PREPARATION OF HIGH DENSITY POLYETHYLENE/POLYETHYLENE-ΒLOCK- POLY(ETHYLENE GLYCOL) COPOLYMER BLEND POROUS MEMBRANES VIA THERMALLY INDUCED PHASE SEPARATION PROCESS AND THEIR PROPERTIES

High density polyethylene (HDPE)/polyethylene-Wock-poly(ethylene glycol) (PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation (TIPS) process using diphenyl ether (DPE) as diluent. The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry (DSC). By varying the content of PE-b-PEG, the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis, Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). Water contact angle, static protein adsorption and water flux experiments were used to evaluate the hydrophilicity, antifouling and water permeation properties of the membranes. It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes. In the investigated range of PE-b-PEG content, the PEG blocks could not aggregate into obviously separated domains in membrane matrix. More importantly, PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation, but also enrich at the membrane surface layer. Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity, protein absorption resistance and water permeation properties, which would be substantially beneficial to HDPE membranes for water treatment application.     

Preparation of high density polyethylene/polyethylene-block-poly(ethylene glycol) copolymer blend porous membranes via thermally induced phase separation process and their properties

<正>High density polyethylene(HDPE)/polyethylene-block-poly(ethylene glycol)(PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation(TIPS) process using diphenyl ether(DPE) as diluent.The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry(DSC).By varying the content of PE-b-PEG,the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy(SEM) and wide angle X-ray diffraction(WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis,Fourier transform infrared spectroscopy-attenuated total reflection(FTIR-ATR) and X-ray photoelectron spectroscopy(XPS).Water contact angle,static protein adsorption and water flux experiments were used to evaluate the hydrophilicity,antifouling and water permeation properties of the membranes.It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes.In the investigated range of PE-b-PEG content,the PEG blocks could not aggregate into obviously separated domains in membrane matrix.More importantly,PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation,but also enrich at the membrane surface layer.Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity,protein absorption resistance and water permeation properties,which would be substantially beneficial to HDPE membranes for water treatment application.     

Electrochemical properties of PP membranes with plasma polymer coatings of acrylic acid

Commercial polypropylene (PP) membranes were modified by plasma polymerization coating of acrylic acid, in combination with oxygen flow or oxygen plasma etching. First, conditions for plasma polymerization coating were optimized in terms of the chemical resistance of the coatings and their ion exchange capacity as a function of plasma power, internal pressure and treatment time. Next, the plasma polymerization coating of acrylic acid was combined with oxygen flow or oxygen plasma etching, and their conditions were also optimized by measuring the ion exchange capacity. Finally, the modified membranes were subjected to electrical resistance and transport number measurements and characterized by -step, FT-IR/ATR and SEM. Among the modification methods, oxygen plasma etching followed by the plasma polymerization coating of acrylic acid provided the best electrochemical properties with 1.75 meq/g (IEC) and 112 Ω cm² (ER), 0.88 (TN).     

Alteration of the morphology of polyvinylidene fluoride membrane by incorporating MOF-199 nanomaterials for improving water permeation with antifouling and antibacterial property

MOF-199@PVDF composite membranes are prepared by blending with different amounts of ultrasonic synthesized MOF-199 nanomaterials for improving the pure water flux (PWF) and achieving better antifouling and antibacterial performance. The membrane morphology, elemental composition, and surface properties are analyzed by various means of characterizations, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and water contact angle measurements. The performance of the modified membranes is also determined from the perspective of the PWF, bovine serum albumin rejection, as well as antifouling and antibacterial properties. Due to the variation in the viscosity of dope solution, the composite membranes possess remarkably different morphology, and the M5 membrane, which exhibited a sponge-like structure, the largest surface pore size, and the highest porosity, shows the highest PWF, reaching up to 185.05 L/m²h. Moreover, with the incorporation of MOF-199 nanocrystals, the antifouling property, together with the antibacterial property, toward both gram-negative bacteria and gram-positive bacteria, based on M5 and M7 membranes, increases dramatically compared with the pristine polyvinylidene fluoride membrane. In addition, the long-term permeation performance and copper leakage of the membrane are investigated. As a result, the composite membrane, M5, shows great potential in real water treatment.     

壳聚糖修饰纳米纤维膜表面对氧化还原酶行为的影响

采用静电纺丝法制备了丙烯腈/丙烯酸共聚物(PANCAA)纳米纤维膜, 研究了纺丝液浓度对纤维形态的影响, 以扫描电子显微镜观察纤维形貌, 遴选得到最佳纺丝条件. 以1-乙基-3-(N,N-二甲基氨基丙基)碳二亚胺/N-羟基丁二酰亚胺(EDC/NHS)为偶联剂, 在纤维膜表面引入壳聚糖修饰层, 采用衰减全反射傅里叶变换红外光谱(ATR/FTTIR)、水接触角和称重法考察了修饰前后膜的变化. 通过戊二醛将过氧化氢酶固定到壳聚糖修饰的PANCAA纳米纤维膜上, 研究了壳聚糖及戊二醛浓度对固定化过氧化氢酶的影响, 结果表明, 在壳聚糖浓度为25 mg/mL及戊二醛质量分数为5%条件下, 壳聚糖修饰膜的固定化酶活性比空白膜提高了41.7%, 稳定性也得到了不同程度的提高.     

Improved protein-adsorption resistance of polyethersulfone membranes via surface segregation of ultrahigh molecular weight poly(styrene-alt-maleic anhydride)

A styrene-maleic anhydride (SMA) alternating copolymer with ultrahigh molecular weight (M_w > 10⁶) synthesized in super critical carbon dioxide (SC CO₂) medium was used as hydrophilic polymeric additive in the preparation of polyethersulfone (PES) membranes. The PES/SMA blend membranes were prepared by immersion precipitation process. X-ray photoelectronic spectroscopy (XPS) measurements confirmed that the hydrolyzed SMA preferentially segregated to membrane–coagulant interface during membrane formation. For the PES/SMA blend membranes, no big change was observed in the cross-sectional structure and the mechanical properties were well maintained after SMA addition except that a thicker top layer was formed. The surface morphology analysis by atomic force microscopy (AFM) showed that the membrane surface roughness increased with the added SMA amount. The results of water contact angle, water absorbance measurements and static protein adsorption experiments revealed that the surface enrichment of SMA endowed PES/SMA blend membranes with significantly improved surface hydrophilicity and protein-adsorption resistance.     

Self-cleaning and Oil/Water Separation of 3D Network Super-hydrophobic Bead-like Fluorinated Silica Pellets/Poly(aryl ether ketone) Composite Membrane Fabricated via a Facile One-step Electrospinning

Novel super-hydrophobic fluorinated silica pellets/poly(aryl ether ketone) composite membranes with controllable structure have been prepared through incorporating poly(aryl ether ketone)s with (3-trifluoromethyl)-phenyl side groups and fluorinated silica pellets(F-SiO₂) by a facile one-step electrospinning. Under the condition of adding 50%(mass fraction) F-SiO₂ in the composite membrane, the water contact angle(WCA) reached its maximum (157°±4.3°). The controllable micro/nano-structures grown on the electrospun fibers could be regulated by the F-SiO₂ loading, which was illustrated by scanning electron microscopy(SEM). Moreover, these super-hydrophobic membranes also demonstrated excellent durability, anti-fouling property and oil-water separation ability after 200 h of water flushing. These promising PAEK composite membranes with controllable structure have the potential values in large-scale application of filtration, oil-water separation and antifouling.     

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.