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.     

Controlled pore functionalization of poly(ethylene terephthalate) track-etched membranes via surface-initiated atom transfer radical polymerization

A new method for surface-initiated atom transfer radical polymerization (ATRP) on the technical polymer poly(ethylene terephthalate) (PET) has been developed which allows controlling and estimating the layer thickness of the grafted polymer in the isocylindrical pores of track-etched membranes. After PET surface treatment by oxidative hydrolysis, the bromoalkyl initiator was immobilized on the PET surface in a two-step solid-phase reaction; the isoporous membrane structure was preserved, and the pore diameter was increased from 760 to 790 nm. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted under ATRP conditions from a methanol/water mixture at room temperature. Both monomer concentration and reaction time could be used as parameters to adjust the degree of grafting. Effective grafted layer thickness and its response to temperature were estimated from pure water permeability. All data, especially the high polymer densities (0.37 g/cm3) in the swollen layers at 25 degrees C, indicate that grafted PNIPAAm with a "brush" structure has been achieved. For dry PNIPAAm layer thicknesses on the PET pore walls of up to 80 nm, a temperature-induced swelling/deswelling ratio of approximately 3 had been observed. Reduction of the brush grafting density, via composition of the reaction mixture used in solid-phase synthesis for initiator immobilization, led to an increase of that swelling/deswelling ratio. Further, density and temperature response of the grafted PNIPAAm layers synthesized via ATRP were compared with those obtained in the same membranes by less controlled photografting, leading to lower grafting density and larger gradients in grafted layer density and, consequently, much higher swelling/deswelling ratios (>15).     

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.     

Use of a MDI-functionalized reactive polymer for the manufacture of modified bitumen with enhanced properties for roofing applications

In this study, the suitability of a reactive polymer, synthesized by reaction of 4,4′-diphenylmethane diisocyanate (MDI) with a low molecular weight polyethylene-glycol (PEG), as a modifying agent for the manufacture of bitumen-based waterproof membranes, was evaluated. With that purpose, rheological and thermal analysis tests, and microstructural observations by AFM were carried out on different samples of modified bitumen having a MDI–PEG content ranging from 0 to 10 wt.%, cured at room temperature for a period of time within 0–30 days. The results obtained demonstrate that the addition of the reactive polymer proposed in this work to bitumen is very suitable at high in-service temperatures, because a noticeable increase in the values of viscosity, at 60 °C, of the resulting modified bitumen samples is observed on a time-scale of days. AFM observations, carried out at 50 °C, evidenced that the reactive polymer MDI–PEG leads to a new microstructure, displaying a higher level of stiffness. Therefore, this polymer should be seriously taken into consideration as a modifier of bituminous coatings for the waterproofing industry.     

Development of Poor Cell Adhesive Immersion Precipitation Membranes Based on Supramolecular Bis‐Urea Polymers

A variety of biomedical applications requires tailored membranes; fabrication through a mix‐and‐match approach is simple and desired. Polymers based on supramolecular bis‐urea (BU) moieties are capable of modular integration through directed non‐covalent stacking. Here, it is proposed that non‐cell adhesive properties can be introduced in polycaprolactone‐BU‐based membranes by the addition of poly(ethylene glycol) (PEG)‐BU during immersion precipitation membrane fabrication, while unmodified PEG is not retained in the membrane. PEG‐BU addition results in denser membranes with a similar pore size compared to pristine membranes, while PEG addition induces defect formation. Infrared spectroscopy and surface hydrophobicity measurements indicate that PEG‐BU is retained during membrane processing. Additionally, PEG‐BU incorporation successfully leads to poor cell adhesive surfaces. No evidence is observed to indicate PEG retention. The results obtained indicate that the BU system enables intimate mixing of BU‐modified polymers after processing. Collectively, the results provide the first steps toward BU‐based immersion precipitated supramolecular membranes for biomedical applications.     

Photochemical modification of 10 kDa polyethersulfone ultrafiltration membranes for reduction of biofouling

Poly(ether sulfone) 10 kDa ultrafiltration membranes were modified by photolysis using ultraviolet light and graft polymerization of hydrophilic monomers onto the membrane surface to create more hydrophilic and lower fouling membrane surfaces. The modified membrane surfaces were characterized by FTIR/ATR and captive bubble contact angle measurements to determine chemical and hydrophilicity changes during modification. The modified membranes were compared with an unmodified poly(ether sulfone) (control) membrane as well as a commercial regenerated cellulose and a low protein adsorbing poly(ether sulfone) membrane using a newly developed standardized filtration protocol with 1 wt% bovine serum albumin. The best performing modified membrane was with N-vinyl-2-pyrrolidinone and showed a 25% increase in hydrophilicity, a 49% decrease in bovine serum albumin fouling, and a 4% increase in bovine serum albumin retention compared to the unmodified poly(ether sulfone) membrane. While the regenerated cellulose membrane had the lowest fouling and the low protein adsorbing membrane had the highest flux of all tested membranes, the N-vinyl-2-pyrrolidinone-modified membranes had the best combination of low fouling and high flux.     

Blended chitosan and polyvinyl alcohol membranes for the pervaporation dehydration of isopropanol

Homogeneous membranes were prepared by casting the solution of blended chitosan and polyvinyl alcohol (PVA) on a glass plate. The percent weight of chitosan in the membrane was varied from 0 to 100%. The membrane thickness was in the range of 15–30 μm. The membranes were heat treated at 150 °C for an hour. After that the membranes were crosslinked by glutaraldehyde and sulfuric acid in acetone aqueous solution. The membranes were tested at 30–60 °C for dehydration performance of 50–95% isopropanol aqueous solutions. At around 90% of isopropanol in the feed mixture, permeate flux increased whereas the percent of water in permeate tended to decrease when the feed temperature increased for all membranes, except that the water content in permeate from the membrane containing 75 wt.% chitosan remained constant. The swelling degree in water and the total flux increased with increasing chitosan content in membranes. The effect of temperature on permeate flux followed the Arrhenius relationship. The permeate flux decreased when isopropanol in the feed increased for all membranes. However, water content in permeate and isopropanol concentration in the feed formed complex relationship for different chitosan content membranes. Sorption did not appear to have significant effects on separation. The membrane containing chitosan 75% performed the best. For a feed solution containing 90% isopropanol at 60 °C, the permeate flux was 644 g/m² h with water content of nearly 100% in the permeate. At 55% isopropanol in the feed at 60 °C, the permeate flux was 3812 g/m² h. In the range of 55–95% of isopropanol in the feed, the water content in permeate was more than 99.5%. This membrane showed very excellent performance with good mechanical strength. It is promising to develop this membrane for industrial uses.     

Surface modification of mesoporous membranes by fluoro-silane coupling reagent for CO2 separation

The potential of hybrid organic–inorganic membranes for separating organic molecules from air, based on solubility selective mechanism, was evaluated. Alumina and titana membranes with average pore size near 4 nm were surface modified using trimethoxysilane fluorinated coupling reagent. The permeabilities to helium, nitrogen, methane, ethane, propane, butane and carbon dioxide were evaluated at feed pressures lying between (1.5 × 10⁵ and 3.5 × 10⁵ Pa) 1.5 and 3.5 bar and permeate outlet near 1 × 10⁵ Pa (1 bar). The permeabilities of the grafted membranes generally decreased by about two to three orders of magnitude compared with the untreated membranes. The CO₂/N₂ permselectivity increased significantly in the case of the TiO₂ grafted membrane. The membranes performances were compared and the TiO₂ grafted membrane exhibits higher permselectivity and permeability, so that, it is a good candidate for CO₂ to N₂ separation and CO₂ to hydrocarbon separation.     

Silica gel ethyleneimine and its adsorption capacity for divalent Pb, Cd, and Hg

Activated silica gel was directly modified with a cyclic molecule, ethyleneimine, yielding a surface with various nitrogen basic centers, ≡Sil–O(CH₂CH₂NH)_nCH₂CH₂NH₂. Infrared spectroscopy, ¹³C NMR, thermal, and elemental analyses confirmed the covalent attachment of the organic species onto the silica matrix. The purpose of this paper is to describe the interaction involving the grafted species on silica surface with the divalent heavy cations, Pb(II), Cd(II), and Hg(II), from aqueous solutions at room temperature. The process of metal extraction was followed by the batch method and the order of the maximum extraction capacities found was: 1.27 ± 0.04, 1.02 ± 0.02, and 0.98 ± 0.01 mmol g⁻¹ for Pb(II), Cd(II), and Hg(II) chlorides, respectively. These interactions were followed by calorimetric titration. The enthalpies of these processes are: −3.05 ± 0.02, −1.09 ± 0.01, and −9.88 ± 0.03 kJ mol⁻¹ for Pb(II), Cd(II), and Hg(II), respectively. The standard molar Gibbs free energies are in agreement with the spontaneity of the proposed reactions between cation and basic center.     

Thermal behaviour of lyocell fibres

Fourier-transform infrared (FTIR) spectroscopy has been applied in combination with wide-angle X-ray diffraction and measurements of strength, fluidity, yellowness, birefringence, and moisture regain to detect microstructural changes in lyocell fibres, a regenerated cellulose fibre, subjected to direct heat and annealing treatments. TMA, and SEM were used to show the effect of direct heat and annealing on lyocell fibres. The FTIR spectroscopy results show that a decrease in intermolecular hydrogen bonding occurs at 70 and 80 °C for annealed and directly heated samples, respectively. The results demonstrate increase of the intensity of O–H stretching vibrations, this associated with hydrogen bonds reforming around 130 °C. Lyocell fibres shrink with direct heating in the temperature range 130–160 °C. The crystallinity decreases gradually with increasing temperature. There is no significant change in colour of the samples annealed up to 150 °C. A continuous increase in the fluidity occurs for the annealed samples in the range 150–230 °C. The tenacity and breaking extension of heated samples decrease with increasing temperature. The lower annealing temperatures cause no observable change in the smooth and void-free surface, but in the annealing temperature range 170–230 °C, substantial non-uniformity is apparent on the surface of the fibres.     

聚丙烯表面接枝PNIPAAm膜Ⅰ.光接枝反应和表面形态结构研究

以氧杂蒽酮或二苯甲酮为引发剂 ,通过紫外光引发表面接枝聚合的方法在聚丙烯薄膜表面引入了具有温度敏感特性的聚异丙基丙烯酰胺 (PNIPAAm)接枝聚合物层 .提高紫外光强度和接枝反应温度均有利于接枝率增大 ,而单体浓度对接枝率的影响存在最佳值 ,为 0 1 8mol L .在引发剂预浸渍引发接枝和休眠基引发接枝这两种方式中 ,后者能够实现更高的接枝率 .红外光谱 (FTIR)、X射线光电子能谱化学分析 (ESCA)和扫描电子显微镜 (SEM)等对接枝层组成的表征结果证实了接枝层的存在 .在不同温度下 ,接枝膜的FTIR谱图中酰胺I带和酰胺II带特征吸收峰发生位移 ,表明它具有温度敏感特性 .同时 ,SEM研究发现由于接枝膜的温度敏感特性而导致的球状表面形态结构     

New proton conducting hybrid membranes for HT-PEMFC systems based on polysiloxanes and SO3H-functionalized mesoporous Si-MCM-41 particles

For increased efficiency of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC), new types of membranes have to be developed. This approach has been realized by preparing hybrid membranes containing SO₃H-functionalized mesoporous Si-MCM-41 as hydrophilic inorganic modifier in a polysiloxane matrix exhibiting sulfonic acid groups and basic heterocyclic groups like benzimidazole. The proton conductivity of sulfonated particles was modelled on the atomic scale in order to understand the influence of the density of sulfonic acid groups and of the presence of water molecules. The different hybrid membranes are characterized concerning their thermal stability, water uptake, and proton conductivity. Whereas the proton conductivity of well-established, but expensive and at >120 °C not long-time stable Nafion membranes continuously decreases with increasing temperature, the polysiloxane membranes, which suffer from a low-proton conductivity at around 100 °C, recover at about 120 °C due to intrinsic proton transport. At 180 °C the pure polysiloxane shows a proton conductivity which is only one order of magnitude lower than that of Nafion. Moreover, if the polysiloxane membrane contains additionally 10 wt.% of an SO₃H-modified Si-MCM-41, the proton conductivity of such hybrid membrane at temperatures >180 °C and low relative humidity <10% is higher than that of Nafion membranes by a factor of 10.     

Study on the effect of spinning conditions and surface treatment on the geometry and performance of polymeric hollow-fibre membranes

Hollow-fibre membranes were prepared by the wet-dry spinning technique from polyether sulfone (PES). The effect of spinning conditions such as the flow-rate of the internal coagulant and the flow-rate, composition and temperature of the polymer solution on the geometry and performance of hollow fibres was studied. In particular, five different ratios of pore former/polymer covering the range 0.2–1.0 were investigated while the polymer content was kept constant. Since the viscosity of the spinning dope affects the morphology of the hollow-fibre membrane, hollow fibres were prepared at different temperatures of the spinning dope from 25 to 60°. By scanning electron microscopy (SEM) two layers sandwiching a finger-like cavity structure were observed. Also, the surface on the bore side of the hollow fibre was modified by grafting polyethylene glycol (PEG) with γ-ray irradiation to improve the ultrafiltration performance.     

Surface‐initiated atom transfer radical polymerization from porous poly(tetrafluoroethylene) membranes using the C?F groups as initiators

This work reports the surface‐initiated atom transfer radical polymerization (ATRP) from hydrogen plasma‐treated porous poly(tetrafluoroethylene) (PTFE) membranes using the C? F groups as initiators. Hydrogen plasma treatment on PTFE membrane surfaces changes their chemical environment through defluorination and hydrogenation reactions. With the hydrogen plasma treatment, the C? F groups of the modified PTFE membrane surface become effective initiators of ATRP. Surface‐initiated ATRP of poly(ethylene glycol) methacrylate (PEGMA) is carried out to graft PPEGMA chains to PTFE membrane surfaces. The chain lengths of poly(PEGMA) (PPEGMA) grafted on PTFE surfaces increase with increasing the reaction time of ATRP. Furthermore, the chain ends of PPEGMA grown on PTFE membrane surfaces then serve as macroinitiators for the ATRP of N‐isopropylacrylamide (NIPAAm) to build up the PPEGMA‐b‐PNIPAAm block copolymer chains on the PTFE membrane surfaces. The chemical structures of the modified PTFE membranes are characterized using X‐ray photoelectron spectroscopy. The modification increases the surface hydrophilicity of the PTFE membranes with reductions in their water‐contact angles from 120° to 60°. The modified PTFE membranes also show temperature‐responsive properties and protein repulsion features owing to the presence of PNIPAAM and PPEGMA chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2076–2083, 2010     

Heterogeneous ion-exchange membranes based on sulfonated poly(1,4-phenylene sulfide) and linear polyethylene: preparation, oxidation stability, methanol permeability and electrochemical properties

Poly(1,4-phenylene sulfide) was sulfonated with chlorosulfonic acid in 1,2-dichloroethane. The product (IEC = 2.38 mequiv./g) was ground and sieved (mesh size 63 μm) to obtain small particles. The particles and linear polyethylene were mixed in various ratios and the resulting blends were press-molded at 150 °C to obtain the membranes. Membranes containing up to 66 wt.% of sulfonated particles could be prepared without any problem in mechanical strength. The membranes were characterized by their stability in oxidative environment, ionic conductivity, and diffusive permeability to methanol. The membrane containing 66 wt.% of sulfonated particles was almost as conductive as Nafion 117; it exhibited, however, much lower diffusive permeability to methanol. In a strongly oxidative environment (3% aqueous H₂O₂ at 70 °C), the prepared membranes were less stable than Nafion 117, but much more stable than membranes with sulfonated poly(styrene-co-divinylbenzene) particles. In preliminary laboratory tests with H₂/O₂ and direct methanol fuel cells, the prepared membranes with high concentrations of sulfonated particles performed similarly to Nafion 117.     

Synthesis of industrial scale NaY zeolite membranes and ethanol permeating performance in pervaporation and vapor permeation up to 130 °C and 570 kPa

NaY zeolite tubular membranes in an industrial scale of 80 cm long were synthesized on monolayer and asymmetric porous supports. The quality of synthesized membranes were evaluated by pervaporation (PV) experiments in 80 cm long at 75 °C in a mixture of water (10 wt.%)/ethanol (90 wt.%), resulting in higher permeation fluxes of 5.1 kg m⁻² h⁻¹ in the monolayer type membrane and of 9.1–10.1 kg m⁻² h⁻¹ in the asymmetric-type membranes, respectively. The uniformity with small performance fluctuation in longitudinal direction of the membranes were observed by PV for 10–12 cm long samples at 50 °C in a mixture of methanol (10 wt.%)/MTBE (90 wt.%). The ethanol single component permeation experiments in PV and vapor permeation (VP) up to 130 °C and 570 kPa were performed to determine the relations between the ethanol flux and the ethanol pressure difference across the membrane which is represented by permeance (Π, mol m⁻² s⁻¹ Pa⁻¹) for estimate of potential of ethanol extraction through the present NaY zeolite membranes applying feasible studies. Results indicate that (1) the permeation fluxes are linearly proportional to the driving force of vapor pressure for each sample in VP and PV. The permeances through an asymmetric support type membrane were rather constant of 0.6–1.2 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ in the wide temperature range of 90–130 °C in PV and VP, indicating that the ethanol permeances have weak temperature dependency with the feed at the saturated vapor pressure.

The results of superheating VP experiments showed that ethanol permeation fluxes are increased with increasing of the degree of superheating at a given constant feed vapor pressure. The ethanol permeances are increased with increasing of temperature at a given feed vapor pressure. The superheating VP could be a feasible process in industry.     

Preparation of a pinhole-free Pd–Ag membrane on a porous metal support for pure hydrogen separation

A pinhole-free palladium membrane with a thickness of 3 μm has been prepared on the surface of a porous sintered stainless steel tube coated with a thin silver layer as a diffusion barrier. Filling of aluminum hydroxide gel in the surface pores of the tube is effective in preventing defect formation during electroless plating of the palladium layer, while the volume of the hydroxide beneath the membrane decreases greatly upon thermal treatment up to 500 °C. The hydrogen flux at 400–500 °C is reasonably proportional to the pressure difference between the two sides of the membrane. Addition of a 2 μm Pd_0.8Ag_0.2 alloy layer on the membrane by electroplating does not greatly decrease the hydrogen permeability.     

Closure characteristics of a thermally responsive single ion-track pore determined by size exclusion method

Cross-linked poly(N-isopropylacrylamide) (NIPAAm) gel was grafted on the wall of a single ion-track pore in poly(ethylene terephthalate) (PET). The opening and closing of the pore is controlled by temperature and observed by electric conductivity. In the shrunken state of the gel, ions and molecules can penetrate the membrane through the free volume of the pore. In the swollen state, the gel clogs the pore. Using mixtures of polyethylene glycol (PEG) of various molecular weights and 0.1 N potassium chloride, it was demonstrated that the responsive pore acts as a thermally controllable valve preventing the passage of PEG molecules larger than 2 nm. The mean value of the hydrogel mesh size is estimated to be (1.3±0.05) nm.     

Membrane purification of Cl2 gas: I. Permeabilities as a function of temperature for Cl2, O2, N2, H2 in two types of PDMS membranes

Permeability (P) of Cl₂, O₂, N₂ and H₂ was measured in polydimethylsiloxane (PDMS) composite membranes with two different degrees of cross-linking. The permeability was measured in the low pressure range (1–3 bar absolute) over a fairly large temperature range 35–120°C. The functionalities of the membranes were compared on the basis of permeation rate and ability to separate the gases Cl₂–O₂. These results are part of an extensive survey where perfluorinated and carbon membranes are also included (not reported here). The purpose of the project is to develop an industrial membrane with high permselectivity for either O₂ or Cl₂ (depending on the type of membrane) at temperatures preferably above 70°C. Process conditions are set in an industrial project. The PDMS membranes are good candidates for this separation, having a high permeation rate for Cl₂ and a selectivity of Cl₂/O₂ in the range of 8–25 depending on temperature. Durability of the PDMS membranes in this aggressive environment is found to be very dependent on process conditions and on how the material is polymerized and cured. For documentation of durability, various silicones were tested; these results are to be reported separately.     

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.