Fouling control in a submerged membrane‐bioreactor by the membrane surface modification

To improve the antifouling characteristics, polypropylene microporous membranes (PPHFMMs) were surface‐modified by the sequential photoinduced graft polymerization of acrylic acid and acrylamide. The grafting density and the grafting chain length, which played important roles in the antifouling characteristics, were controlled in the first and the second step, respectively. The ATR/FTIR results clearly indicated the successful modification on the membrane surface. The static water contact angle of the modified membrane reduced obviously with the increase of the grafting chain length. The contact angle of the acrylic acid modified membranes was lower than that of the acrylamide modified membrane with similar grafting chain length. The grafting chain length increased with the increase of UV irradiation time and monomer concentration. The grafting chain length of poly(acrylic acid) (PAAc) was lower than that of the polyacrylamide (PAAm) under the same polymerization conditions. Pure water flux for the modified membranes increased with the increase of grafting chain length, and had maximums. The antifouling characteristics of the modified membranes in a submerged membrane‐bioreactor (SMBR) were evaluated. The modified membranes showed better filtration performances in the SMBR than the unmodified membrane, and the acrylic acid grafted membrane presented better antifouling characteristics than acrylamide modified membranes. The results demonstrated that the surface carboxyl‐containing membranes were better than the surface amido‐containing membranes. The results of Pearson correlations demonstrated that the PAAc modified membranes with longer grafting chain length had higher flux recoveries, while the PAAm modified membranes with longer grafting chain length had lower flux recoveries. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Surface modification of acrylonitrile copolymer membranes by grafting acrylamide. I. Initiation by ceric ions

Surface modification of membranes of an acrylonitrile copolymer (PAN) containing 5.5% methyl methacrylate (MMA) and 4.0% sodium methylpropylenesulfonate by grafting acrylamide (AAm) with cetric ammonium nitrate as initiator in the aqueous medium has been studied. Results showed that the extent of grafting was varied with some parameters, such as dimethyl formamide and Tween-20 amount in the reaction solution, concentration of AAm, and reaction time. The grafted copolymer was verified by infrared spectra and X-ray photoelectron spectroscopy. Both of these methods also showed that the ester group of MMA unit on the surface of PAN membranes may be partially hydrolyzed into carboxyl group in the copolymerization condition. Surface and pore structures of PAN membranes after grafting were viewed under a scanning electron microscope (SEM). From SEM photos we know that AAm homopolymer branches were grafted onto the surface of the membrane and the morphology of membrane did not change. Results of contact angle of isooctane on the membrane under water showed that the wettability of the modified membrane was improved. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1521–1529, 1997     

Al2O3和SiC微滤膜的疏水改性及其油固分离性能研究

以正辛基三乙氧基硅烷和乙醇分别作为改性剂和溶剂,采用接枝聚合法对平均孔径为500 nm的Al₂O₃膜和SiC膜进行疏水改性,考察了改性剂浓度、改性液温度和改性时间对膜表面疏水效果的影响,并对比了疏水改性前后两种陶瓷膜的表面性质及疏水改性后的油固分离性能,进行了反冲实验和稳定性测试。结果表明,两种陶瓷膜材料在改性剂浓度为0.2 mol·L^-1,改性液温度为40℃,改性时间为12 h时,疏水改性效果最好,得到的疏水Al₂O₃膜和SiC膜的水接触角分别为134°±1°和140°±1°,经改性后的SiC膜的疏水效果优于Al₂O₃膜。在油固分离实验中,疏水Al₂O₃膜和SiC膜均对固体炭黑有良好的截留性能,但疏水改性对SiC膜的油品通量提升更为显著,两种膜的稳态通量分别为1134 L·m^-2·h^-1和1408 L·m^-2·h^-1。反冲操作对疏水SiC膜的通量恢复更有利。     

Hydrophilic modification of polypropylene microporous membranes by grafting TiO2 nanoparticles with acrylic acid groups on the surface

Hydrophilic microporous membranes were prepared based on polypropylene (PP) cast films blended with a commercial acrylic acid grafted polypropylene (PP-g-AA) via melt extrusion followed by grafting titanium dioxide (TiO₂) nanoparticles on its surface, annealing and stretching. ATR-FTIR, XPS and EDS analyses showed that the hydrophilic segments of an amphiphilic modifier (PP-g-AA) acted as surface functional groups on the film surface. The results indicated that the presence of the modifier was very important for grafting TiO₂ nanoparticles on the film surface. Compared to PP and PP/PP-g-AA blend films, the water contact angle decreased by a factor of 2.5 after grafting TiO₂ on the surface of the films, meanwhile the water vapor permeability of the microporous membranes prepared from those films increased by a factor of 1.5. All these results indicated that the hydrophilicity of the modified PP membranes was improved.     

Preparation of chlorinated poly(vinyl chloride)‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membranes and their water permeation properties

Chlorinated poly(vinyl chloride) (CPVC) membranes for microfiltration processes were prepared with the combined process of a solvent evaporation technique and the water‐vapor induced‐phase‐inversion method. CPVC membranes with a mean pore size of 0.7 μm were very hydrophobic. These membranes were subjected to surface modification by ultraviolet (UV)‐assisted graft polymerization with N‐vinyl‐2‐pyrrolidinone (NVP) to increase their surface wettability and decrease their adsorptive fouling. The grafting yields of the modified membranes were controlled by alteration of UV irradiation time and NVP monomer concentration. The changes in chemical structure between the CPVC membrane and the CPVC‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membrane and the variation of the topologies of the modified PVC membranes were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, and field emission scanning electron microscopy. According to the results, the graft yield of the modified CPVC membrane reached a maximum at 5 min of UV exposure time and 20 vol % NVP concentration. The filtration behavior of these membranes was investigated with deionized water by a crossflow filtration measurement. The surface hydrophilicity and roughness were easily changed by the grafting of NVP on the surface of the CPVC membrane through a simultaneous irradiation grafting method by UV irradiation. To confirm the effect of grafting for filtration, we compared the unmodified and modified CPVC membranes with respect to their deionized water permeation by using crossflow filtration methods. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3188–3195, 2003     

In situ modification of microporous membranes

Under proper conditions, in situ polymerizations of acrylic acid monomer solutions were performed within the microporous structures of a hydrophobic membrane, Celgard ® 2500. poly(acrylic acid) modified pores have been characterized to be permanently wettable by aqueous solutions, to be capable of gelling water to withstand increased transmembrane pressure gradients, and also to possess a higher transmembrane electrical resistance. In cases of less concentrated acrylic acid monomer solutions, a cross-linker was employed to facilitate polymer permanency within the infrastructure of the hydrophobic membranes. © 1993 John Wiley & Sons, Inc.     

Improving the hydrophilicity of polyethersulfone membrane by the combination of grafting technology and reverse thermally induced phase separation method

In this work, surface grafting modification technology was combined with reverse thermally induced phase separation (RTIPS) method in order to improve the structure and permanent hydrophilicity of polyethersulfone (PES) membranes. Acrylic solution with different concentrations was grafted on the surface of PES membranes while grafting temperature and grafting time were also varied. The modified PES membranes were characterized in all aspects. Attenuated total reflectance Fourier transform-infrared confirmed successful modification of the PES membrane by grafting acrylic acid. Scanning electron microscopy revealed that homogeneous porous top surface as well as spongy-like cross-section structure appeared in the membrane by RTIPS procedure. Moreover, porosity was affected by changes of acrylic acid concentration, grafting temperature, and grafting time. Atomic force microscopy showed that grafting acrylic acid gave a reduction in roughness of PES membrane. Combined with the decreased values of contact angle, the hydrophilicity and antifouling performance of the PES membrane were improved. The pure water flux and BSA rejection rate of the grafted PES membranes were remarkably improved for pure PES membrane and attained a maximum, which was 1,646.24 L/(m²h) and 94.5%, respectively. The long-term test demonstrated that grafting membranes exhibited outstanding elevated water flux recovery ratio (>85%).     

Fabrication and characterization of PFSI/ePTFE composite proton exchange membranes of polymer electrolyte fuel cells

PFSI/ePTFE composite proton exchange membranes were fabricated by impregnating perfluorosulfonic acid resin (PFSI resin, Nafion) into chemically modified expanded PTFE (ePTFE) matrix. Chemical modification of sodium-naphthalene treatment and N-methylol acrylamide (NMA) grafting decreased the contact angle of the as-received ePTFE from 125 ± 0.5° to 67 ± 0.5°, effectively converting the as-received hydrophobic ePTFE to a hydrophilic ePTFE matrix. The composite membrane fabricated with the hydrophilic ePTFE have higher impregnated PFSI loading, much lower porosity and better PTFE/PFSI interface contact, as compared to the composite membranes with the as-received ePTFE. This leads to much lower gas permeability and significantly improves the durability under an accelerated dry/wet cycle test. The fuel cell made from the PFSI/ePTFE composite membranes with hydrophilic ePTFE showed superior performance as compared to that with the composite membrane made from the as-received ePTFE and Nafion 211 membrane.     

Electric double layer capacitors with polymer hydrogel electrolyte based on poly(acrylamide) and modified electrode and separator materials

Activated carbon fiber cloths (AC) and hydrophobic microporous polypropylene (PP) membrane, both modified by acetone aldol condensation products, and filled with polymer hydrogel were used as electrodes, separator and electrolyte in electric double layer capacitors (EDLCs). Polymer hydrogel used was based on poly(acrylamide) (PAAM), KOH and water. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy, compared with a case of the capacitor with only a KOH aqueous solution used as an electrolyte. As a result, the capacitor with polymer hydrogel was found to exhibit higher capacitance than that with the KOH aqueous solution and an excellent high-rate dischargeability. The above results provide valuable information to explore novel composition of EDLCs.     

Characterization of acrylic acid‐grafted PP membranes prepared by plasma‐induced graft polymerization

Acrylic acid (AA)‐g‐polypropylene (PP) membranes were prepared by grafting AA on to a microporous PP membrane via plasma‐induced graft polymerization. The grafting of AA to the PP membrane was investigated using Fourier transform infrared spectroscopy (FTIR). Pore‐filling of the membranes was confirmed by field emission‐scanning electron microscopy (FESEM) and energy dispersing X‐ray (EDX). Ion exchange capacity (IEC), membrane electric resistance, transport number and water content were measured and analyzed as a function of grafting reaction time. The prepared AA‐g‐PP membranes showed moderate electrochemical properties as a cation‐exchange membrane. In particular, membranes with a degree of grafting of 155% showed good electrical properties, with an IEC of 2.77 mmol/g dry membrane, an electric resistance of 0.4 Ω cm² and a transport number of 0.96. Chronopotentiometric measurements indicated that AA‐g‐PP membranes, with a high IEC had a sufficient conducting region in the membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of including a hydrophobic comonomer on the rheology of an acrylamide-acrylic acid based copolymer

Synthesis and design of polymer systems based on acrylamide for enhanced oil recovery (EOR) is essential for reservoirs with high salinity and high temperature conditions. The use of associative monomers or the modification of the polymers with hydrophobic functional groups represents a promising alternative that extends the use of chemical EOR. In this study, terpolymers based on acrylamide, acrylic acid and butyl methacrylate were synthesized and the rheological properties of aqueous solutions of the obtained polymers at different pH values, and salt concentrations were evaluated. The results show that at alkaline conditions the viscosity of aqueous solutions of a polymer synthesized with 68.6 wt% of acrylamide, 22.9 wt% of acrylic acid and 8.6 wt% of butyl methacrylate increases by a factor of more than 1,000 at a 3 wt% concentration. Also, all polymers with the hydrophobic modification showed higher viscosity in saline solutions compared to their acrylamide-acrylic acid analogue.     

Surface Modification of Acrylonitrile Copolymer Membranes by Grafting Acrylamide. II. Initiation by Fe2+/H2O2

Surface modification of membranes of an acrylonitrile copolymer (PAN) containing 5.5% methyl methacrylate and 4.0% sodium methylpropylenesulfonate by grafting acrylamide (AAm) with ferrous ammonium sulfate/H₂O₂ as an initiator in aqueous medium was studied. The grafted copolymer was verified by infrared spectra, X-ray photoelectron spectroscopy, and a scanning electron microscope (SEM). From the SEM photos, we know that the AAm homopolymer branches were grafted onto the surface of the membrane and the morphology of the PAN membrane did not change. The results showed that the extent of grafting was varied with some parameters, such as the pH value of the medium, reaction time and temperature, and concentration of AAm and H₂O₂. The results of the water-absorption percent of the membrane showed that the wettability of the modified PAN membrane was improved. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1907–1915, 1998     

The effect of polymer surface modification via interfacial polymerization on polymer–protein interaction

Membrane separation is an important processing technology used for separating food ingredients and fractionating value‐added components from food processing byproducts. Long‐term performance of polymeric membranes in food protein processing is impeded by the formation of fouled layers on the membrane surface as a result of protein adsorption onto the membrane surface. Surface modification of synthetic membranes, i.e., changing surface characteristics to reduce protein adsorption permanently, is one of the innovative ways of reducing the fouling of membrane surfaces. In this study, surface modification of flat‐sheet ultrafiltration membrane, polyethersulfone (PES), was investigated in improving the hydrophilicity of PES surfaces, thereby reducing adsorption of the protein caused by hydrophobic–hydrophobic interaction between the protein and the membrane. Hydrophilic polymer grafting through thin‐film composite using interfacial polymerization was employed to improve the hydrophilicity of the commercial PES membranes. Poly(vinyl alcohol), poly(ethylene glycol), and chitosan were chosen as hydrophilic polymers to graft on PES membrane because of their excellent hydrophilic property. Modified PES membranes were characterized by contact angle, FTIR, XPS, and AFM. Contact angles of modified PES membranes were reduced by 25 to 40% of that of the virgin PES membrane. XPS spectrum supported that the PES membranes were successfully modified by interfacial polymerization. Tapping‐mode AFM was used to examine the changes in surface topography of modified PES membranes. The PES membranes modified by interfacial polymerization showed lower roughness (from 1.2 to 2.0 nm) than that of virgin PES membrane (2.1 nm). The results of these instrumental analyses indicated that the PES membranes were successfully enhanced hydrophilically through interfacial polymerization. The protein adsorption on the modified membranes was reduced by 30 to 35% as a result of surface modification of the PES membranes using interfacial polymerization technique. Published 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Interfacially polymerized thin-film composite membrane on UV-induced surface hydrophilic-modified polypropylene support for nanofiltration

A novel thin-film composite (TFC) nanofiltration membrane was prepared through interfacial polymerization on surface hydrophilic-modified polypropylene (PP) membrane. Firstly, PP membranes were hydrophilized to ensure the formation of separation layer on it by interfacial polymerization. In this work, the UV-induced grafting of acrylic acid (AAc) was applied to modify the surface of PP membranes. Secondly, the TFC membranes were fabricated on PP membranes with different grafting degrees of AAc via interfacial polymerization. Effects of the UV-induced graft polymerization conditions, such as benzophenone concentration, monomer concentration and UV irradiation time, were systematically investigated. The surface-modified PP membranes and the TFC membranes were characterized with water contact angle measurement, attenuated total reflectance infrared and scanning electron microscopy. Furthermore, the permeation experiments were employed to evaluate the membranes’ nanofiltration performance.     

松木纤维表面超支化接枝改性及其对PP复合材料性能的影响

为了改善松木纤维与聚丙烯(PP)之间的界面结合性能,采用接枝改性技术在纤维表面逐步接枝超支化聚酰胺,并用接枝改性后的纤维与PP及相容剂熔融共混制备复合材料。采用傅里叶变换红外光谱及热重分析对改性前后纤维的官能团及热性能进行了分析表征,并对纤维增强PP复合材料的拉伸强度进行了测定。结果表明,经超支化聚酰胺改性后,纤维表面成功引入了大量的氨基基团。经1.0代超支化聚酰胺接枝改性后,纤维的耐热性有所增加,但经2.0及3.0代超支化聚酰胺接枝改性后,纤维的耐热性均有所下降。经超支化聚酰胺接枝改性后,纤维增强PP复合材料的拉伸强度均有所提高,其中2.0代超支化聚酰胺改性的纤维增强PP复合材料拉伸强度最高。对于未改性或KH–550改性的纤维,其目数为20目时的复合材料拉伸强度较目数为40目的高,但超支化聚酰胺接枝改性的纤维增强复合材料拉伸强度随纤维尺寸的变化情况与此相反。     

Superhydrophobic modification of ceramic membranes for vacuum membrane distillation

The hydrophobically modified ceramic membranes have great potential for energy-efficient membrane distillation.In this work,flat-sheet ceramic membranes with a superhydrophobic surface were fabricated by grafting 1H,1H,2H,2H-perfluorooctyltrichlorosilane or 1H,1H,2H,2H-perfluorodecyltriethoxysilane and followed by ultraviolet irradiation.The surface water contact angle was improved from 46° of original ceramic membrane to 159°,which exhibited a stable and excellent superhydrophobic effect.The modified membranes showed a high flux of 27.28 kg· m-2.h-1 and simultaneously maintained an excellent retention rate of 99.99％,when used in vacuum membrane distillation process for treatment ofa 1 wt％ NaCl (75 °℃) aqueous solution.These results suggested that superhydrophobic modification of ceramic surface is a facile and cost-effective way to achieve higher membrane distillation performance.The superhydrophobically-modified ceramic membrane with an excellent desalination capacity would show considerable potential in practical membrane distillation utilizations.     

Grafting of acrylamide to nylon-6 by electron beam preirradiation. IV. Sorption of water in nylon grafted acrylamide membranes

Membranes prepared by extensive grafting of acrylamide onto nylon-6 films exhibit high water sorption capacity. Swelling of the membranes increases after treatment with aqueous solutions of formic acid. Sorption of water into these annealed membranes reaches values of ca. 25 moles of water per mole of grafted acrylamide. The sorption characteristics of the swollen membrane-gels crosslinked with bis-acrylamide were explored. Membranes grafted with acrylamide, crosslinked with bis-acrylamide and annealed with formic acid reach the maximum swelling capacity at low graft yields.     

Two component polymer membranes

We prepared membranes from synthesized grafted polymers consisting of hydrophobic macromolecules and hydrophilic grafts. We studied especially polyacrylic acid (PAA) grafted on polypropylene (PP) and on ethylene-propylenediene rubbers (EPDM). From a technological point of view, the PP grafted membranes can be classified in three groups: membranes obtained from solution, from bioriented films and from not oriented films. EPDM grafted membranes were prepared from solution.The structure of membranes from solution is characterized by spheroidical domains (diameter ? 5.10^-2μm) situated in a rigid or elastomeric matrix. Good salt rejections can be obtained in the case of grafted PP with small fluxes and high thickness. Ultrafiltration of molecules larger than NaCl can be successful when using low thickness rigid membranes, with high fluxes. Elastomeric membranes, which show a low water permeability, do not allow any flux under pressure.Bioriented PP films after grafting show a layer-like structure with detached layers, partially fractured. This structure allows very small fluxes.The original band-like structure of not oriented PP films is heavily modified by grafting: the resulting structure is characterized by a uniform distribution of PAA, which allows the best salt rejection of all our membrane types, but with rather small fluxes.We explain the behaviour of the membranes from solution, using a mechanical model based on a single swelling sphere immersed in a rigid or elastomeric matrix. Internal stresses due to the PAA swelling are calculated and related to water adsorption. Calculated internal stresses justify fracture in the rigid matrix, thus allowing high fluxes, but not in the elastomeric matrix; this explains its very low permeability.Consequence of the existence of microfractures in the rigid matrix is the high dilatation rate of these membranes when immersed in water: the elastomeric membranes show a much lower dilatation rate.A mathematical model is proposed which relates the elongation to the diffusion coefficient of water and of salt both in the rigid and elastomeric membranes. Diffusion water coefficient is of the order of 10^-8 cm² s^-1 and 10^-10 cm² s^-1 respectively in the rigid and elastomeric membranes. Salt diffusion coefficient is of the order of 10^-12 cm² s^-1 in both cases.     

Hydrophilic modification of P(VDF-co-CTFE) porous membranes

This paper describes fabrication of a poly(vinylidene difluoride-co-chlorotrifluoroethylene) (P(VDF-co-CTFE)) porous membrane via non-solvent induced phase inversion and subsequent hydrophilic modification using high efficient surface initiated atom transfer radical polymerization (ATRP). The effect of viscosities of casting solutions on microstructures of the P(VDF-co-CTFE) membrane was investigated. The surface chemistry, thermal stability, morphological structure, and hydrophilicity of the modified membranes were evaluated by Fourier Transform Infrared Attenuated Total Reflection (FTIR-ATR), Differential Scanning Calorimeter (DSC), Scanning Electron Microscope (SEM), and contact angle measurements, respectively. The degree of grafting and the degree of swelling were measured to analyze the effect of polymerization time on the wettability. The mechanical strength of the membranes after modification was also investigated. The permeability and fouling resistance were evaluated according to pure water flux and protein solution filtration measurements. The results demonstrate that the hydrophobic P(VDF-co-CTFE) membrane can be feasibly modified by immobilization of hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) brushes via surface initiated ATRP.     

Plasma graft polymerization of acrylamide onto crosslinked HTPB based PU membrane for pervaporation

Pervaporation of water-ethanol mixtures through plasma graft polymerization of acrylamide onto crosslinked hydroxyl terminated poly-butadiene (HTPB) based PU membranes, plasma graft polymerization of acrylamide onto crosslinked PU membrane (AAm-p-CPU), were investigated. The grafting was dependent on the discharge power and pretreatment period. The effects of crosslinking, plasma treatment conditions, feed compositions, and feed temperature on the performance of these membranes were studied. The physical properties of crosslinked membrane were better than those of the uncrosslinked membrane. In addition, compared with crosslinked PU membranes (CPU), the plasma modified crosslinked PU membranes effectively improve the pervaporation separation performances.