Supported Electrospun Ultrafine Fibrous Poly(tetrafluoroethylene)/ZnO Porous Membranes and their Photocatalytic Applications

Supported photocatalytic poly(tetrafluoroethylene) (PTFE)/ZnO porous membranes were prepared by sintering electrospun PTFE/poly(vinylalcohol)/zinc acetate dehydrate composite membranes. Electrospun PTFE membranes were utilized as supports with excellent chemical stability and high specific surface area, while the photocatalyst‐ZnO particles derived from the thermal decomposition of zinc acetate dehydrate were homogeneously immobilized on the surface of ultrafine PTFE fibers. The PTFE/ZnO membranes could be easily recovered and reused after water treatment. PTFE/ZnO membranes are expected to have a wide range of potential applications in photocatalysis and photocatalysis‐membrane reactors, playing the role of a catalyst as well as a selective barrier against contaminants of interest.     

Polycation‐Grafted Poly(vinylidene fluoride) Membrane with Biofouling Resistance

Covalent immobilization of polycations onto a membrane surface has been shown to significantly improve the resistance to biofouling. The poly(vinylidene fluoride)‐graft‐poly(N,N‐dimethylamino‐2‐ethylmethacrylate) (PVDF‐g‐PDMAEMA) copolymer was synthesized via radical grafting copolymerization and fabricated into a flat membrane. The polycation membrane surface was constructed by quaternization of PDMAEMA side chains with 1,5‐dibromopentane and diquaternization of 4,4′‐bipyridine. As revealed by membrane surface morphology, pore size, and porosity measurement, the polycations are distributed on the membrane surface and internal pore channel surface. Water contact angles confirm that the incorporation of polycations remarkably promotes the surface hydrophilicity of a membrane. The polycation membrane surface provides an excellent bactericidal efficiency against Escherichia coli.     

聚四氟乙烯表面等离子体修饰氨基及XPS分析

采用氢气/氮气等离子体对聚四氟乙烯(PTFE)片基表面进行了处理,通过正交实验和接触角的测定优化等离子处理条件;XPS光谱分析了改性后的PTFE的表面官能团的组成。结果表明：PTFE片基经氢气/氮气等离子体处理后,表面的C-F键发生了断裂,形成了大量活性氨基,其表面具有很好的生物活性和亲和性。     

Melting and crystallization behavior of poly(tetrafluoroethylene) by temperature modulated calorimetry

Temperature-modulated differential scanning calorimetry (TMDSC) in the quasi-isothermal mode is applied to investigate melting and crystallization of poly(tetrafluoroethylene) (PTFE) obtained from aqueous dispersion, both melt-crystallized and native (as-polymerized). The differences, shown in the past between the melting behavior of melt-crystallized and native PTFE, have been confirmed and further evidenced through this technique. A large reversing heat capacity is present in the melting and crystallization regions. As proposed by many authors, the presence of the reversing heat capacity can be related to surface melting and crystallization. It can occur on the growth and/or fold surfaces and it has been shown that it is larger for those macromolecules having higher chain mobility that allows rearrangements on the crystal surface. In the present case, the large observed reversing heat capacity can be related to the very high sliding ability of PTFE chains in the pseudohexagonal phase, which is much larger than that of most semicrystalline polymers. Due to the crystal-crystal transition at 30 °C, which can be described as a fusion in the longitudinal direction, melting of PTFE can be considered intermediate between the irreversible melting of macromolecules and the completely reversible isotropization of liquid crystalline polymers.     

Adhesion enhancement of thermally evaporated aluminum to surface graft copolymerized poly(tetrafluoroethylene) film

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film via UV-induced graft copolymerization with glycidyl methacrylate (GMA) and 1-vinylimidazole (VIDz) were carried out to improve the adhesion with evaporated aluminum metal. The surface compositions of the graft copolymerized PTFE films were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the evaporated aluminum to the surface graft copolymerized PTFE film was affected by the type of monomer used for graft copolymerization, the graft concentration, the plasma post-treatment of the graft copolymerized PTFE surface prior to metallization, and the extent of thermal treatment after metallization. The optimum T-peel adhesion strengths of the Al/PTFE laminates were in excess of 10 and 5 N/cm, respectively, for the GMA and VIDz graft copolymerized PTFE films. These adhesion strengths are significantly higher than those obtained between the evaporated aluminum and the pristine or plasma-pretreated PTFE film. The mechanism of adhesion enhancement and the failure of the metal-polymer assembly were also investigated. It was observed that the failure occurred within the PTFE film. The strong adhesion between Al and PTFE arises from the charge-transfer interaction between the Al atom and the epoxide moiety of the grafted GMA polymer, as well as from the fact that the graft chains are covalently tethered on the PTFE film surface as a result of the grafting process.     

Surface Modification of Nanoporous Poly(ϵ-caprolactone) Membrane with Poly(ethylene glycol) to Prevent Biofouling: Part I. Effects of Plasma Power and Treatment Time

Biofouling, a result of protein adsorption and cell adhesion on a surface, is detrimental to membrane performance. The objective of this study is to modify the polycaprolactone (PCL) membrane surface with poly(ethylene glycol) (PEG) to prevent fibroblast adhesion. To achieve this goal, oxygen plasma and PEG(400)-monoacrylate were used to graft the PEG onto the membrane surface through covalent bonding. Various plasma treatment conditions were investigated to optimize the PEG-grafting quality and to achieve minimum fibroblast adhesion. After the treatment, the water contact angle decreased significantly. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) spectra indicated that PEG was successfully grafted onto the PCL membrane with the appearance of the PEG characteristic peaks. X-ray photoelectron spectroscopy (XPS) revealed that different plasma powers and treatment times changed the surface composition of membranes. To evaluate the applicability of this new strategy for the prevention of biofouling, NIH 3T3 fibroblast was used as a model biofoulant. Cell adhesion and morphology studies indicate that either lower plasma power or shorter treatment time is able to improve resistance to the cell adhesion. This simple and efficient method can be applied to inhibit biofouling on the membrane surface.     

Effect of a Drying Pretreatment on Morphology of Porous Poly(Ether-Imide) Membrane Prepared Using Vapor-Induced Phase Separation

Symmetric porous membranes were prepared from concentrated poly(ether-imide) (PEI) solutions using vapor-induced phase separation (VIPS) coupled with a drying pretreatment. Moderately concentrated solutions of PEI in N-methylpyrrolidinone (NMP) (14–16 wt%) were first cast on glass plates and the solvent was then allowed to evaporate under a dry air flow up to the desired concentration (16–38 wt%) before forming the membrane structure by VIPS. The polymer concentration profiles (confocal Raman microscopy) and model predictions were in good agreement to show that the evaporation stage did not induce a polymer gradient concentration with PEI/NMP systems. These results were confirmed by examination of the final membrane morphology (SEM).     

Effect of a Drying Pretreatment on Morphology of Porous Poly(Ether-Imide) Membrane Prepared Using Vapor-Induced Phase Separation

Symmetric porous membranes were prepared from concentrated poly(ether-imide) (PEI) solutions using vapor-induced phase separation (VIPS) coupled with a drying pretreatment. Moderately concentrated solutions of PEI in N-methylpyrrolidinone (NMP) (14-16 wt%) were first cast on glass plates and the solvent was then allowed to evaporate under a dry air flow up to the desired concentration (16-38 wt%) before forming the membrane structure by VIPS. The polymer concentration profiles (confocal Raman microscopy) and model predictions were in good agreement to show that the evaporation stage did not induce a polymer gradient concentration with PEI/NMP systems. These results were confirmed by examination of the final membrane morphology (SEM).     

Surface structures and adhesion enhancement of poly(tetrafluoroethylene) films after modification by graft copolymerization with glycidyl methacrylate

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film were carried out via near-UV light-induced graft copolymerization with glycidyl methacrylate (GMA). The structure and chemical composition of the copolymer surface and interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For PTFE substrate with a substantial amount of grafting, the grafted GMA polymer penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains to form a stratified surface microstructure. The concentration of the surface-grafted GMA polymer increases with the plasma pretreatment time, the near-UV light illumination time, and the monomer concentration. The GMA graft copolymerized PTFE surfaces adhere strongly to one another when brought into direct contact and cured (i) in the presence of a diamine alone or (ii) in the presence of an epoxy adhesive (epoxy resin plus diamine curing agent). In the presence of diamine alone, failure occurs in the interfacial region. For epoxy adhesive-promoted adhesion, the failure mode is cohesive, i.e. it takes place in the bulk of one of the delaminated PTFE films. The lap shear strengths in both cases increase with the amount of surface-grafted epoxide polymer. The development of the adhesion strength depends on the concentration of the surface graft, the microstructure of the graft copolymerized PTFE surface, the interfacial reactions, and the nature of the bonding agent.     

羟基丁酸-戊酸共聚物与聚丙烯酸丁酯的反应性共混

采用反应性共混的方法对羟基丁酸－戊酸共聚物进行改性,使具有生物活性的丙烯酸丁酯在羟基丁酸－戊酸共聚物上接枝聚合,达到提高产物机械性能的同时,保持其生物降解性的目的。系统地研究了反应条件和改性物配比对产物接枝率及共混材料相容性等的影响,发现加料顺序和丙烯酸丁酯用量对产物的接枝率和相容性有很大影响,丙烯酸丁酯含量为２０％～３０％,产物接枝率最高可达２０％以上;在加工时填充４％～６％的滑石粉补强,羟基丁酸－戊酸共聚物／丙烯酸丁酯复合材料的机械性能明显提高。     

Rolltruded Poly(Aryl Ether Ether Ketone) (PEEK) for Membrane Applications

Abstract

An investigation of the transport and separation of several permanent gases (CO₂, N₂, CH₄, and H₂) and vapors (H₂O and ethanol) in unprocessed and rolltruded poly(aryl ether ether ketone) (PEEK) thin films has been conducted to evaluate PEEK for membrane applications requiring thermally and chemically stable materials. Transport coefficients and separation factors have been determined at permeation temperatures ranging from 40 to ca. 180°C. The gas transport coefficients were found to increase by up to 30% depending on the processing conditions. Actual separation factors, determined for a CO₂/N₂ gas mixture (24.6 vol% CO₂), were depressed slightly in comparison to the ideal values obtained from pure component data. In contrast, water and ethanol vapor permeabilities declined between 10 and 15% as a result of processing. For a 39.1 wt% vapor mixture of H₂O in EtOH, ideal and actual separation factors, determined at 130°C, were in good agreement. In contrast, order of magnitude improvements in the actual versus ideal separation factors were found for 11.7 and 7.6 wt% mixtures of H₂O in EtOH in both unprocessed and rolltruded PEEK. A comparison with other membranes considered for high temperature vapor dehydrations suggests that PEEK may be an excellent polymer for these applications.     

Radiation grafting of vinyl monomers onto poly(tetrafluoroethylene) powder produced by γ irradiation and properties of grafted poly(tetrafluoroethylene) filled low density polyethylene

Scrap poly(tetrafluoroethylene) (PTFE) was γ irradiated under an ambient atmosphere in order to produce extensive chain scission and oxidative degradation. After irradiation the PTFE was ground into a fine powder (2°‐PTFE) and grafted with styrene (St), vinyl acetate (VAc), and 4‐vinylpyridine (4‐VP) by using the direct irradiation technique. The grafted PTFE were then blended with low density polyethylene (LDPE). The study covered the characterization of irradiated PTFE and grafted 2°‐PTFE powder with various methods. Mechanical grinding was found to reduce trapped radicals formed during the irradiation process faster than the annealing process. Grafting on 2°‐PTFE was followed by gravimetric analysis, TGA, and the change in the particle size of the samples. Although we reached almost 20% grafting by weight in the St and 4‐VP monomers, VAc grafting was found to be maximum at around 8% by weight at the maximum absorbed dose. The addition of VAc grafted 2°‐PTFE into LDPE produced better final mechanical properties with a fine dispersion. However, as may be expected, the incorporation of the other two 2°‐PTFEs into LDPE showed low film quality and poor mechanical properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 816–826, 2001     

聚对苯硫醚、聚间苯硫醚及其共聚物的合成与表征

用硫磺、对二氯苯和间二氯苯为原料,在极性有机溶剂六甲基磷酰三胺中合成了聚对苯硫醚(p-PPS)、聚间苯硫醚(m-PPS)及其共聚物.用裂解气相色谱、红外光谱、X-射线衍射及热分析对所得聚合物的结构和热性能进行了初步研究.结果表明:p—PPS和m—PPS都是结晶性聚合物,间位结构引入到p-PSS的结构中明显地破坏了p-PPS的高度结晶性,降低了耐热性,但最大失重速率处温度却无多大变化.这一共聚改性途径可望用于改进p—PPS的刚性,提高其韧性.     

Surface Modification of Nanoporous Poly(ϵ-caprolactone) Membrane with Poly(ethylene glycol) to Prevent Biofouling: Part II. Effects of Graft Density and Chain Length

Biofouling is a common problem in wastewater treatments and medical devices. It is important to find a strategy to prevent biofouling and surface modification. This study presents a novel approach to modifying the surface of nanoporous poly(?-caprolactone) membrane with poly(ethylene glycol) (PEG) to prevent biofouling problems. Oxygen plasma and poly(ethylene glycol)-monoacrylates (PEGMAs) were utilized in the surface modification process. Mouse embryonic fibroblast was used as a model biofoulant. The effects of the density and length of PEG chains on surface properties and cell adhesion were investigated. Contact angle measurements and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra illustrated that PEG can be successfully immobilized on the membrane surface. Membranes which were pre-treated with higher PEG concentrations can lead to higher grafting density and greater resistance against cell adhesion. The resistance against cell adhesion cannot be enhanced while the PEG concentration is higher than a certain point, i.e., 0.1 M. For different chain lengths, PEG(400)MA can provide higher resistance to cell adhesion than PEG(200)MA and PEG(1000)MA.     

Adsorption and desorption properties of expanded poly(tetrafluoroethylene) films grafted with DMAEMA and their regeneration

An investigation was undertaken on the adsorption and desorption properties of the expanded poly (tetrafluoroethylene) (ePTFE) films grafted with 2‐(dimethylamino)ethyl methacrylate (DMAEMA) to anionic dye anions with one to three sulfonic groups in response to temperature changes. The amount of adsorbed metanil yellow (MY) anions increased with the grafted amount and most of the dimethylamino groups appended to the grafted PDMAEMA chains worked as an adsorption site to MY anions for the DMAEMA‐grafted ePTFE (ePTFE‐g‐PDMAEMA) films with the grafted amounts of higher than 1.1 mmol/g. When the dye‐anion‐adsorbed ePTFE‐g‐PDMAEMA films were alternately immersed in water at two different temperatures, dye anions were desorbed from the ePTFE‐g‐PDMAEMA films at higher temperatures without any chemical agents. The amount of desorbed dye anions increased with an increase in the temperature of water from 40 to 80°C. Desorption of dye anions is caused by either deprotonation of dimethylamino groups appended to the grafted PDMAEMA chains or thermosensitive contraction of the grafted PDMAEMA chains. These results indicate that the ePTFE‐g‐PDMAEMA films can be applied as a regenerative ion‐exchange membrane for adsorption and desorption processes of anionic compounds in response to the temperature change. The thermally regenerative ion‐exchange properties of the ePTFE‐g‐PDMAEMA films was superior to that of the PE‐g‐PDMAEMA films reported in our previous article in the fact that the total degree of desorption was higher for the ePTFE‐g‐PDMAEMA films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Cellular Response of Limbal Stem Cells on Poly (Hydroxybuthyrate-co-Hydroxyvalerate) Porous Scaffolds for Ocular Surface Bioengineering

The aim of this study was to develop a modified-porous poly (3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) scaffold for limbal stem cell (LSC) expansion that can serve as a potential alternative substrate to replace human amniotic membrane. The human limbal stem cell was used to evaluate the biocompatibility of substrates (porous scaffold, human amniotic membrane and thermoresponsive substrate) based on their viability, proliferation, and attachment ability. Biocompatibility results indicated that the all substrates were highly biocompatible, as LSCs could favorably attach and proliferate on the scaffold surface. Microscopic figures showed that the human limbal stem cell was firmly anchored to the substrates and were able to retain a normal corneal stem cell phenotype. Microscopic analyses illustrated that cells infiltrated the porous scaffold and successfully formed a three-dimensional corneal epithelium, which was viable for two weeks. Gene expression results revealed no change in the expression profile of LECs grown on scaffold when compared to those grown on human amniotic membrane or thermo responsive substrate. In addition, porous PHBV substrate provides not only a milieu supporting LSCs expansion, but also serve as a useful alternative carrier for ocular surface tissue engineering and could be used as an alternative substrate to amniotic membrane.     

Surface grafting polymerization of vinyl monomers on poly(tetrafluoroethylene) films by plasma treatment

Poly(tetrafluoroethylene) films were surface modified by argon plasma treatment followed by graft polymerization. Peroxidе groups were introduced on the surface of poly(tetrafluoroethylene) films after plasma treatment and the consequent contact with air when the films were taken out of the reactor. Grafting polymerization initiated by the surface peroxide (hydroxide) groups was performed on the poly(tetrafluoroethylene) film surface by using acrylic acid, 4-vinylpyridine and 1-vinylimidazole as monomers. Copolymers were obtained with grafting yield from 0.436 to 0.457 mg/cm² for poly(acrylic acid), from 0.299 to 0.390 mg/cm² for poly(4-vinylpyridine) and from 0.212 to 0.256 mg/cm² for poly(1-vinylimidazole), respectively. The free surface energies of the copolymers were determined. The chemical structures and the copolymer surfaces were characterized by IR, XPS and SEM analyses. High energy resolution X-ray photoelectron spectroscopy (XPS) confirmed the grafting of acrylic acid, 4-vinylpyridine and 1-vinylimidazole. The surface hydrophilicities of modified polytetrafluoroethylene films were significantly enhanced after plasma treatment and grafting modification. It is worth emphasizing that in this work acrylic acid, 4-vinylpyridine and 1-vinylimidazole were used as the reactive monomers for grafting on the poly(tetrafluoroethylene) film by plasma treatment. We believe that this vinyl monomers may be employable as functional groups, permitting a potentially wide range of applications: as ionomers, membranes, carriers for immobilization of biomolecules, for complex formation with heavy metals as catalysts.     

Modification of Waste Poly(Ethylene Terephthalate) (PET) by Using Poly(L-Lactic Acid) (PLA) and Hydrolytic Stability

The purpose of this study is the preparation of hydrolytically degradable copolymers of waste poly(ethylene terephthalate) (PET). To achieve this, we modified PET by using biodegradable poly(lactic acid) (PLA). Modification reactions were carried out in o-nitrophenol as solvent at 140 and 170°C for 8, 16, and 24 h in the presence of dibutil tin oxide (DBTO) as catalyst. The amount of the total polymers (PLA and PET) in the reaction mixture was 30% by weight, and the weight ratios of PLA/PET were 10/90, 50/50, and 90/10. These modified products were characterized by Fourier transform infrared spectrometer (FTIR), differential scanning calorimeter (DSC) as well as by hydrolytic degradation determinations. Hydrolytic degradations of the products were determined gravimetrically. Disc-shaped samples were placed in tubes containing phosphate buffer solution of pH 7.2 and kept in a water bath at 60°C for 28 days. The weight loss of the products after hydrolytic degradation ranged from 1.25% to 48.75% after 28 days.     

Ultrasonication‐Induced Modification of Hydroxyapatite Nanoparticles onto a 3D Porous Poly(lactic acid) Scaffold with Improved Mechanical Properties and Biocompatibility

A 3D porous poly(lactic acid) (PLA) scaffold with high porosity and well‐connected pores is fabricated using a vacuum‐assisted solvent casting technique. Its surface is modified with hydroxyapatite (HA) nanoparticles using ultrasonication to prepare an HA‐modified PLA/HA scaffold. For reference, an HA‐blended (b‐PLA‐HA) scaffold is fabricated via the solution blending method. The morphology, porosity, hydrophilicity, swelling ratio, mechanical properties, and cell viability of the PLA, b‐PLA‐HA, and PLA/HA scaffolds are systematically studied. The results show that HA nanoparticles are successfully introduced onto the surface of the PLA/HA scaffold, and strong interactions occur between the HA nanoparticles and the PLA matrix. The PLA/HA scaffold still has a high porosity of more than 85% after ultrasonication. The hydrophilicity and mechanical properties of the PLA/HA scaffold are significantly higher than those of the PLA and b‐PLA‐HA scaffolds. Compared with the PLA and b‐PLA‐HA scaffolds, the attachment and growth of mouse embryonic osteoblasts cells (MC3T3‐E1) cultured on the PLA/HA scaffold significantly improve, due to most HA nanoparticles on the surface, resulting in a good and direct interaction between the cells and the scaffold. Therefore, the PLA/HA scaffold possesses great potential to be used as a tissue engineering scaffold.