Fluoropolymer Membrane Research Articles

Investigation on tensional membrane force of the fluoropolymer dust covers in semiconductors

The photomask dust cover used in semiconductor manufacturing comprises a thin fluoropolymer membrane stretched tightly over an aluminum frame. The dust cover plays a vital role in protecting the photomask from dust pollution, thereby ensuring the purity of the exposed patterns and enhancing the wafer yield. However, the membrane is extremely thin and easily damaged during the manufacturing process. Therefore, this research proposes an analytical model for predicting the tensional force induced in the membrane under different distributed loads. The reflective fringe method, combined with a four-step phase-shifting technique, is used to measure the three-dimensional surface topography of the membrane under various distributed loads. A trial-and-error fitting method based on a simulation model of the dust cover is then employed to estimate the tensional force which yields the maximum vertical displacement closest to the experimental observations under different values of the distributed load. The analytical results confirm that a greater distributed load results in a higher membrane tensional force. However, the predicted tensional force reduces as the service life of the membrane increases due to the effects of plastic deformation. Overall, this study presents a simple approach of predicting the tensional force induced in the pellicle membrane under different loads. Thus, by taking the yield strength of the membrane as a threshold value, it serves as a useful tool for assessing the quality of the membrane and excluding its use from the production process if appropriate.

Fluoropolymer Membranes for Membrane Distillation and Membrane Crystallization.

Fluoropolymer membranes are applied in membrane operations such as membrane distillation and membrane crystallization where hydrophobic porous membranes act as a physical barrier separating two phases. Due to their hydrophobic nature, only gaseous molecules are allowed to pass through the membrane and are collected on the permeate side, while the aqueous solution cannot penetrate. However, these two processes suffer problems such as membrane wetting, fouling or scaling. Membrane wetting is a common and undesired phenomenon, which is caused by the loss of hydrophobicity of the porous membrane employed. This greatly affects the mass transfer efficiency and separation efficiency. Simultaneously, membrane fouling occurs, along with membrane wetting and scaling, which greatly reduces the lifespan of the membranes. Therefore, strategies to improve the hydrophobicity of membranes have been widely investigated by researchers. In this direction, hydrophobic fluoropolymer membrane materials are employed more and more for membrane distillation and membrane crystallization thanks to their high chemical and thermal resistance. This paper summarizes different preparation methods of these fluoropolymer membrane, such as non-solvent-induced phase separation (NIPS), thermally-induced phase separation (TIPS), vapor-induced phase separation (VIPS), etc. Hydrophobic modification methods, including surface coating, surface grafting and blending, etc., are also introduced. Moreover, the research advances on the application of less toxic solvents for preparing these membranes are herein reviewed. This review aims to provide guidance to researchers for their future membrane development in membrane distillation and membrane crystallization, using fluoropolymer materials.

Simplified in-situ tailoring of cross-linked self-doped sulfonated polyaniline (S-PANI) membranes for nanofiltration applications

Sulfonated polyaniline (S-PANI) membranes could have wide-ranging applications due to their electrical tunability, antifouling behaviour and chlorine resistance. However, S-PANI membranes below the ultrafiltration (UF) separation range have not been successfully established. This study presents a scalable approach to produce the first in-situ cross-linked S-PANI membranes at nanofiltration (NF) range. S-PANI membranes were produced by non-solvent induced phase separation (NIPS). The presence of sulfonic groups as polymer cross-linking anchors and controlling the coagulation bath's acidic strength resulted in instant stabilisation of the selective layer, which hindered the solvent/non-solvent exchange rate. This enabled the production of a tailored membrane morphology with a dense skin layer, suppressed macro-voids, reduced porosity, enhanced tensile strength, increased hydrophilicity and solvent stability. S-PANI membranes cast in 3 M HCl(aq) with MWCO≈680 g mol−1 (sucrose octa-acetate) showed a rejection of 99 % for PEG 1000 g mol−1 and 91–100 % for dye solution (MW range of 320–1017 g mol−1) compared to 34 % and 74–85 % rejection for a commercial fluoropolymer membrane (nominal MWCO 1000 g mol−1), respectively. The reported approach is simple and can be applied to design new classes of cross-linked solvent stable S-PANI NF membranes.

HCN on Tap: On-Demand Continuous Production of Anhydrous HCN for Organic Synthesis.

A continuous process for the on-demand generation, separation, and reaction of hydrogen cyanide (HCN) using membrane separation technology was developed. The inner tube of the reactor is manufactured from a gas-permeable, hydrophobic fluoropolymer (Teflon AF-2400) membrane. HCN is formed from aqueous reagents within the inner tube and then diffuses through the membrane into an outer tubing containing organic solvent. This technique enabled the safe handling of HCN for three different organic transformations without the need for distillation.

PEM water electrolysis: Innovative approaches towards catalyst separation, recovery and recycling

We report the development of a facile recycling process for catalyst coated membranes (CCMs) used in polymer electrolyte membrane (PEM) water electrolyzers. After performance evaluation in an assembled electrolysis cell, ultrasonication is used to provide high-yield recovery of not only the noble-metal catalyst materials, but also of the fluoropolymer membrane itself, without the release of hazardous gases. Transmission electron microscopy (TEM) and electrochemical characterization are used to confirm the retention of catalyst particle size, and of the performance of the recycled CCMs. Furthermore, our projections indicate that, if this approach is widely employed, existing resources of noble metals will prove sufficient for the gigawatt-scale implementation of PEM water electrolyzers. This has profound implications for the achievement of current targets for reducing the consumption of precious metals for applications in electrolyzers, fuel cells and other energy storage devices.

Amorphous Fluoropolymer Membrane for Gas Separation Applications.

Amorphous fluoropolymers have been studied in the past few decades and received extensive attention due to their unique and useful properties. One of the remarkable properties of amorphous fluoropolymers is high fractional free volume (FFV), and they tend to retain large amounts of solvent inside their polymer chains. In this study, amorphous flouoropolymer membranes were employed to examine the influences of the residual solvent and drying condition on the thermal properties, gas permeation behavior, and structure change by the polymer chains. Thermal properties of the produced membranes were characterized by differential scanning calorimetry (DSC) and a thermogravimetric analysis (TGA) to verify the effects of residual solvent. The residual solvent content and the glass transition temperature (Tg) of amorphous fluoropolymer membranes prepared with both solvents decrease with increasing drying temperature. The effect of the thermal treatment method on the d-spacing between the polymer chains of the prepared membranes was investigated using X-ray diffraction (XRD). The d-spacing decreased with drying below the Tg whereas it drastically increased near the Tg because of chain relaxation. From these phenomena, the helium permeability of the membranes treated at 120 °C radically increased. However, the oxygen and nitrogen permeability decreased with decreasing residual solvent content. The glass transition range shifted to higher temperature, from 75 °C to 133 °C, depending on the reduced amount of residual solvent.

Low-autofluorescence fluoropolymer membrane filters for cell filtration

A fluoropolymer membrane filter with through-holes was fabricated by photolithographic patterning and the dry etching method. 380,000 highly packed through-holes, each with a diameter of 7 µm were able to cover a whole area with a diameter of 13 mm. Ethylene tetrafluoroethylene (ETFE) was used as the membrane, which was suitable for the fluorescence detection of rare cells such as circulating tumor cells (CTCs) in human blood. The device fabrication for the size based capture of rare cells in blood such as CTCs is realized in this study.

Continuous metal scavenging and coupling to one-pot copper-catalyzed azide-alkyne cycloaddition click reaction in flow

Increasing usage of catalytic chemistry calls for efficient removal of metal traces. This paper describes the development and optimization of a scavenger-based extraction in flow to remove metal catalysts. It enables liquid–liquid extraction with slug flow and phase separation with a porous fluoropolymer membrane. The use of this unit for copper scavenging of various copper sources from organic solvent was studied. The effects of scavenger type (EDTA, DTPA, EDDS), concentration and pH were also investigated. Such analysis allowed to achieve extraction performance as high as 99% at pH of the scavenger solution adjusted to 9.4 and molar ratio of scavenger to copper of 10. Process integration is achieved by coupling this unit downstream to a flow reaction using homogeneous metal-based catalysis, i.e. presenting a continuous uninterrupted metal scavenging unit. The copper-catalyzed azide-alkyne cycloaddition click reaction is studied in one-pot eliminating the need to isolate and handle potentially explosive azide. The triazole product is attained in flow with high yield of up to 92% with 30min residence time. The level of purity requirement for pharmaceuticals is met in one stage of extraction.

Comparative study of grafting a polyampholyte in a fluoropolymer membrane by gamma radiation in one or two-steps

Binary graft copolymerization of pH-sensitive monomers (N,N-dimethylaminoethyl methacrylate, (DMAEMA) and acrylic acid (AAc) onto polyvinylidene fluoride (PVDF) membranes with pore sizes of 0.22 and 0.45μm was conducted by one and two-steps grafting using a 60Co gamma radiation source (Gammabeam 651 PT). The DMAEMA and AAc monomers were grafted by an oxidative pre-irradiation method in one-step grafting to obtain PDVF-g-(DMAEMA-co-AAc), and both direct irradiation and an oxidative pre-irradiation method were used to obtain the graft copolymer (PVDF-g-DMAEMA)-g-AAc in two-steps grafting. The optimal conditions, such as reaction time, temperature, solvent, monomer concentration and dose, were studied, the aim of this work was to investigate how these factors affecting the graft percent of DMAEMA and AAc prepared in one and two-steps grafting and their structural differences and also characterize the grafting membrane through analytical techniques.

Microalgae filtration by UF membranes: influence of three membrane materials

To evaluate the impact of membrane material on the ultrafiltration performance of microalgae medium, three types of UF membranes: polysulfone membrane GR40PP (PS, MWCO = 100,000 Da), fluoro polymer membrane FS40PP (PVDF, MWCO = 100,000 Da), regenerated cellulose acetate membrane RC70PP (RCA, MWCO = 10,000 Da) were used in this work. Influence of transmembrane pressure (1.3, 1.8, 2.3 bar) and cross-flow velocity (3.86, 4.83, 5.79, 7.72 m/s) on the permeate flux was studied. It was observed that the permeate flux increased with increasing transmembrane pressure for all membranes. Moreover, permeate flux increased as the cross-flow velocity increased. The fluoro polymer membrane showed the most significant improvement of flux (from 83.27 to 136.32 L/m2h) with increase in cross-flow velocity, which may suggest that the fouling materials attached more weakly on the membrane surface as the cross-flow velocity increased. Hydrophilic RCA membrane had a much lower fouling tendency than hydrophobic PS and PVDF membranes. To maximize flux recovery for the algae-fouled membranes, NaOH, NaOCl, and Ultrasil 10 were applied as cleaning agents. Ultrasil 10 with concentration of 0.5 wt.% was more effective than other agents for membrane cleaning.

The PARACHUTE IV trial design and rationale: Percutaneous ventricular restoration using the parachute device in patients with ischemic heart failure and dilated left ventricles

Left ventricle (LV) remodeling after anterior wall myocardial infarction leads to increased LV volumes, myocardial stress, and, ultimately, heart failure (HF). Patients have high morbidity and mortality risk, and treatment remains limited. Percutaneous ventricular restoration (PVR) therapy using the Parachute device, a fluoropolymer membrane stretched over a nitinol conical frame, is a novel approach to partition off the damaged myocardium. In the European and United States PARACHUTE feasibility trials, the observed rates of death or rehospitalization for HF were <17% at 12 months. These data compare favorably with historical data and support the need of a randomized trial to determine the clinical efficacy of PVR on outcomes for patients with ischemic HF. To determine the safety and efficacy of PVR utilizing a LV partitioning device, Parachute, in a randomized clinical trial compared with optimal medical therapy. This US pivotal trial is approved by the Food and Drug Administration (ClinicalTrials.gov Identifier: NCT01286116) and will randomly assign (1:1) 478 patients with New York Heart Association class III-IV ischemic HF, akinetic or dyskinetic LV wall abnormality, and ejection fraction between 15% and 35% to optimal medical therapy (control) versus Parachute device implantation in approximately 65 hospitals. The primary endpoint is death or rehospitalization for worsening HF. Sample size calculation assumes constant hazards and follow-up ≥12 months using an event-driven trial design. We reported the rational and design of the first multicenter randomized trial to test the efficacy of PVR using the Parachute device to treat patients with ischemic HF and dilated LV.

Recovery and fractionation of different phenolic classes from winery sludge using ultrafiltration

The purpose of the current study is to investigate the possibility of utilizing ultrafiltration (UF) for the fractionation of phenolic compounds recovered from winery sludge (WS) and their separation from other co-extracted components. Thereby, two hydro-ethanolic extracts (a diluted and a concentrated) were prepared, using WS as an initial material, and assayed in a cross-flow apparatus against three membrane types (100kDa- and 20kDa-polysulfone, 1kDa-fluoropolymer). Monitoring of the process was carried out by determining performance parameters and retention coefficients of pectin, sugars, phenolic and anthocyanins classes. Results indicated that solutes retention was affected mainly by severe fouling phenomena due to polar solutes adsorption on membrane surface instead of size exclusion. Indeed, polysulfone membranes were not able to fractionate phenolic classes except for the separation obtained between polymeric and monomeric anthocyanins. Both membranes and especially the one of 20kDa retained high percentages (i.e. >60%) of polar solutes (phenolic compounds and sugars), whereas the one of 100kDa allowed their separation from pectin and hydrolyzed derivatives. As far as polarity is concerned, fluoropolymer membrane separated successfully hydroxycinnamic acid derivatives from anthocyanins and flavonols in the diluted and concentrated extract, respectively, as acids possessed almost 2-fold higher retention coefficients compared to the other assayed classes.

Fast responsive, optical trace level ammonia sensor for environmental monitoring

BackgroundAmmonia is a ubiquitous chemical substance which is created in technical and biological processes and harmful to many different organisms. One specific problem is the toxicity of ammonia in fish at levels of 25 μg/l - a very common issue in today’s aqua culture. In this study we report a development of a fast responsive, optical ammonia sensor for trace concentrations.ResultsDifferent hydrogels have been investigated as host polymers for a pH based sensing mechanism based on fluorescent dyes. A porous hydrophobic fluoropolymer membrane was used as an ion barrier cover layer to achieve a good ammonia permeability. The sensor’s sensitivity towards ammonia as well as crosssensitivity towards pH-value and salinity, and the temperature dependency have been determined. Two different methods to reference fluorescence signals have been employed to eliminate intensity-based measurement drawbacks.ConclusionThe presented sensor features high sensitivity and a fast response even at concentrations near 1 ppb. No cross sensitivity towards pH and salinity could be observed and temperature dependency was determined as compensateable. Both referencing approaches prove themselves to be able to provide a simple use of the sensor for in-field applications.

The Role of Synthetic Membrane Pre-Treatment in Influencing Filtration Performance over Multiple Operational Cycles

Manufacturers of polymeric membrane filters used for treating food streams routinely recommend that they are chemically cleaned prior to first use. In this paper, two pre-treatment methods are compared for the filtration of a spent sulphite liquor [SSL] (17.8 wt.% dry solids) using a 20 kg mol−1 molar mass cut off (MMCO) fluoropolymer membrane. In an extension of previous work that considered the effect of the application of a pre-treatment protocol over a single operational cycle, this paper reports the effect of pre-treatment protocols over four complete fouling and cleaning cycles. The pre-treatment methods evaluated were the conditioning with water at 60°C only [Protocol 1], and the conditioning with water at 60°C followed by cleaning with 0.5 wt.% NaOH [Protocol 2]. Results are presented that demonstrate that for the system examined, the positive effect of the NaOH pre-treatment protocol diminished after three complete operational cycles, and disappeared after four cycles.

Zwitterionic Sulfobetaine-Grafted Poly(vinylidene fluoride) Membrane with Highly Effective Blood Compatibility via Atmospheric Plasma-Induced Surface Copolymerization

Development of nonfouling membranes to prevent nonspecific protein adsorption and platelet adhesion is critical for many biomedical applications. It is always a challenge to control the surface graft copolymerization of a highly polar monomer from the highly hydrophobic surface of a fluoropolymer membrane. In this work, the blood compatibility of poly(vinylidene fluoride) (PVDF) membranes with surface-grafted electrically neutral zwitterionic poly(sulfobetaine methacrylate) (PSBMA), from atmospheric plasma-induced surface copolymerization, was studied. The effect of surface composition and graft morphology, electrical neutrality, hydrophilicity and hydration capability on blood compatibility of the membranes were determined. Blood compatibility of the zwitterionic PVDF membranes was systematically evaluated by plasma protein adsorption, platelet adhesion, plasma-clotting time, and blood cell hemolysis. It was found that the nonfouling nature and hydration capability of grafted PSBMA polymers can be effectively controlled by regulating the grafting coverage and charge balance of the PSBMA layer on the PVDF membrane surface. Even a slight charge bias in the grafted zwitterionic PSBMA layer can induce electrostatic interactions between proteins and the membrane surfaces, leading to surface protein adsorption, platelet activation, plasma clotting and blood cell hemolysis. Thus, the optimized PSBMA surface graft layer in overall charge neutrality has a high hydration capability and the best antifouling, anticoagulant, and antihemolytic activities when comes into contact with human blood.

An experimental investigation into the pre-treatment of synthetic membranes using sodium hydroxide solutions

In this paper the effect of two pre-treatment methods are compared experimentally for the filtration of (i) a spent sulphite liquor (17.8 wt.% dry solids) using a 20 kg mol −1 molar mass cut off (MMCO) fluoropolymer membrane and (ii) a molasses solution (45° Brix) using a polysulphone (Ps f) membrane (1.5 μm pore size). Both feeds are industrially relevant, and subject to severe fouling issues when membranes are used in their subsequent processing. The pre-treatment methods evaluated were: (i) conditioning with water at 60 °C only [Protocol 1], and (ii) conditioning with water at 60 °C followed by cleaning with 0.5 wt.% NaOH [Protocol 2]. Results are presented that confirm the benefits of sodium hydroxide preconditioning upon performance, supporting the suggestion by some membrane manufacturers that this step be included as part of the pre-treatment protocol.

Uniform culture in solid-state fermentation with fungi and its efficient enzyme production

Solid-state fermentation (SSF) has attracted a lot of interest for carrying out high-level protein production in filamentous fungi. However, it has problems such as the fermentation heat generated during the culture in addition to the reduced mobility of substances. These conditions lead to a nonuniform state in the culture substrate and result in low reproducibility. We constructed a non-airflow box (NAB) with a moisture permeable fluoropolymer membrane, thereby making it possible to control and maintain uniform and optimal conditions in the substrate. For the NAB culture in Aspergillus oryzae, temperature and water content on/in the whole substrate were more consistent than for a traditional tray box (TB) culture. Total weight after the culture remained constant and dry conditions could be achieved during the culture. These data demonstrate the possibility of growing a uniform culture of the whole substrate for SSF. The NAB is advantageous because it allows for the control of exact temperature and water content in the substrate during the culture by allowing vapor with latent heat to dissipate out of the box. In addition, several enzymes in the NAB culture exhibited higher production levels than in the TB culture. We believe that culturing in the constructed NAB could become a standard technique for commercial SSF.

Fouling of Ultrafiltration Membranes during Isolation of Hemicelluloses in the Forest Industry

The process streams in the forest industry contain a large amount of hemicelluloses that today ends up in the wastewater. This is an unfortunate loss of a renewable raw material. The hemicelluloses can be isolated from the process stream by using membrane filtration in a process that produces purified water as a by-product, thereby facilitating increased recirculation. However, process streams from the forest industry contain both aromatic compounds and inorganic ions that are known to cause fouling of the membranes. Thus, the most suitable membrane and pretreatment from a cost-efficient point of view must be applied to avoid fouling and life-time shortening of the membranes during operation. In the present investigation, fouling during ultrafiltration of a process stream from the production of Masonite was studied. The fouling of a hydrophilic membrane made of regenerated cellulose was less severe than the fouling of hydrophobic membranes made of polyether sulphone and a composite fluoropolymer. Pretreatment of the wastewater with activated carbon resulted in higher flux and less fouling of both hydrophilic and hydrophobic membranes. Lowering the pH of the wastewater led to less severe fouling of the regenerated cellulose membrane, but lower flux of the composite fluoropolymer membrane.

A Large-Stroke MEMS Deformable Mirror Fabricated by Low-Stress Fluoropolymer Membrane

This letter presents a deformable mirror (DM) which consists of a 25-mm square flexible membrane and an array of 67 hexagonal electrodes that can pull down a membrane by electrostatic force. The membrane is a 2.15-mum-thick fluoropolymer film and is bonded to an electrode substrate with an 80-mum-thick adhesive acrylic spacer. The fabrication process is completed by a microelectromechanical systems batch process. The surface roughness of polymer membrane is approximately 41 nm. The device demonstrated maximum 38-mum center deflection by applying 250 V because of small residual stress (2.2 MPa) and low Young's modulus (15 GPa) of fluoropolymer film. The response time of the DM is experimentally demonstrated around 10 ms in atmosphere. The proposed device is suitable for large stroke and low sampling rate applications.

Isolation of hemicelluloses from barley husks

In this work, arabinoxylan, the primary hemicellulose in barley husks, was isolated from barley husks by steam explosion and ultrafiltration. Ultrafiltration and diafiltration were used to concentrate and to increase the purity of the product which was intended for use as an oxygen barrier film in food packaging. A composite fluoropolymer membrane with a nominal molecular mass cut-off of 10,000 g/mol was used during ultrafiltration and diafiltration. The average flux during ultrafiltration to a volume reduction of 0.85 was 90 L/m 2 h. The flux was approximately constant (50 L/m 2 h) during diafiltration. Polysaccharides constituted about 40% of the solids fraction before ultrafiltration and nearly 70% after diafiltration. Arabinoxylan made up 45% of the polysaccharide fraction after diafiltration.