Polytetrafluoroethylene Fibers Research Articles

High-strength, impact-resistant PP/PTFE composite foam with enhanced surface appearance achieved through mold-opening microcellular injection molding

Poor surface appearance and decreased mechanical performance are critical factors limiting the broad application of Microcellular injection molding (MIM) in foamed polymer products. Herein, in-situ polytetrafluoroethylene (PTFE) nanofibrils reinforced polypropylene (PP) foams with high strength, impact resistance, and enhanced surface quality were prepared by mold opening microcellular injection molding (MOMIM). PTFE nanofibers with different diameters were introduced into the PP matrix via twin screw extrusion and significantly enhanced the crystallinity and viscoelasticity of the PP matrix with the enhancement being more pronounced for the finer PTFE fibers. High-density oriented cellular structures were formed in the MOMIM PP/PTFE foams owing to the heterogeneous nucleation of PTFE and the stretching effect of the mold opening process. The optimum MOMIM PP/PTFE foam fabricated possesses a high cell orientation angle close to 90° and a large cell aspect ratio of 5.3, which reached a 34.37 % increase in tensile strength and a 73.08 % increase in impact strength owing to the synergetic effects of the PTFE network and the highly oriented fine cell structure, which effectively dissipated the tensile stress and impact stress by cell wall twisting and folding deformation. Furthermore, the MOMIM PP/PTFE foam showed a significantly enhanced surface quality compared to the MIM foam due to the reduced dragging flow in MOMIM, which greatly hindered cell rupture on the foam surface. Therefore, this work provides insights into the MOMIM of polymer composites containing fibrous fillers and the enhancement of tensile properties, impact resistance, and surface quality of foam products.

Monomer diffusion tendencies in complex-shaped materials by vapor deposition polymerization

Conformal coatings are crucial for various applications. In this study, we investigate polyurea coatings on complex-shape polytetrafluoroethylene (PTFE) membranes using vapor deposition polymerization. The diffusion mechanism involves monomer adsorption and desorption on PTFE fibers, enhanced by an increased substrate temperature, facilitating monomer diffusion. A system pressure of 100 Pa promoted monomer collisions, forming oligomers with lower desorption rates, aiding polymer thin-film formation. The combination of high substrate temperature for diffusion and gas-phase oligomer formation resulted in uniform polyurea coatings across the PTFE membrane. A non-exhaustion method provided an extensive monomer diffusion, achieving a thorough polyurea deposition throughout the membrane structure.

Influence of the PET-PTFE Separator Pore Structure on the Performance of Lithium Metal Batteries.

The separator is a crucial component in lithium batteries, as it physically separates the cathode and the anode while allowing ion transfer through the internal channel. The pore structure of the separator significantly influences the performance of lithium batteries, particularly lithium metal batteries. In this study, we investigate the use of a Janus separator composed of poly(ethylene terephthalate) (PET)-polytetrafluoroethylene (PTFE) fibers in lithium metal batteries. This paper presents a comprehensive analysis of the impact of this asymmetric material on the cycling performance of the battery alongside an investigation into the influence of two different substrates on lithium-ion deposition behavior. The research findings indicate that when the rigid PET side faces the lithium metal anode and the soft PTFE side faces the cathode, it significantly extends the cycling lifespan of lithium metal batteries, with an impressive 82.6% capacity retention over 2000 cycles. Furthermore, this study demonstrates the versatility of this separator type in lithium metal batteries by assembling the lithium metal electrode with high cathode-loading capacities (4 mA h/cm2). In conclusion, the results suggest that the design of asymmetric separators can serve as an effective engineering strategy with substantial potential for enhancing the lifespan of lithium metal batteries.

The investigation of the energy harvesting performance using electrospun PTFE/PVDF based on a triboelectric assembly

This work presents an investigation into the energy harvesting performance of a combination of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) materials prepared using a one-step electrospinning technique. Before electrospinning, different percentages of the 1 micron PTFE powder were added to a PVDF precursor. The surface morphology of the electrospun PTFE/PVDF fibre was investigated using a scanning electron microscope and tunnelling electron microscope. The structure was investigated using Fourier-transform infrared spectroscopy and x-ray diffraction analysis (XRD). A highly porous structure was observed with a mix of the α- and β-phase PVDF. The amount of β-phase was found to reduce when increasing the percentage of PTFE. The maximum amount of PTFE that could be added and still be successfully electrospun was 20%. This percentage showed the highest energy harvesting performance of the different PTFE/PVDF combinations. Electrospun fibres with different percentages of PTFE were deployed in a triboelectric energy harvester operating in the contact separation mode and the open circuit voltage and short circuit current were obtained at frequencies of 4–9 Hz. The 20% PTFE fibre showed 4 (51–202 V) and 7 times (1.3–9.04 µA) the voltage and current output respectively when compared with the 100% PVDF fibre. The V oc and I sc were measured for different load resistances from 1 kΩ to 6 GΩ and achieved a maximum power density of 348.5 mW m−2 with a 10 MΩ resistance. The energy stored in capacitors 0.1, 0.47, 1, and 10 µF from a book shaped PTFE/PVDF energy harvester were 1.0, 16.7, 41.2 and 136.8 µJ, respectively. The electrospun fibre is compatible with wearable and e-textile applications as it is breathable and flexible. The electrospun PTFE/PVDF was assembled into shoe insoles to demonstrate energy harvesting performance in a practical application.

Dry-processed technology for flexible and high-performance FeS2-based all-solid-state lithium batteries at low stack pressure

All-solid-state lithium batteries (ASSLBs) are considered promising energy storage systems due to their high energy density and inherent safety. However, scalable fabrication of ASSLBs based on transition metal sulfide cathodes through the conventional powder cold-pressing method with ultrahigh stacking pressure remains challenging. This article elucidates a dry process methodology for preparing flexible and high-performance FeS2-based ASSLBs under low stack pressure by utilizing polytetrafluoroethylene (PTFE) binder. In this design, fibrous PTFE interweaves Li6PS5Cl particles and FeS2 cathode components, forming flexible electrolyte and composite cathode membranes. Beneficial to the robust adhesion, the composite cathode and Li6PS5Cl membranes are tightly compacted under a low stacking pressure of 100 MPa which is a fifth of the conventional pressure. Moreover, the electrode/electrolyte interface can sustain adequate contact throughout electrochemical cycling. As expected, the FeS2-based ASSLBs exhibit outstanding rate performance and cyclic stability, contributing a reversible discharged capacity of 370.7 mAh g−1 at 0.3C after 200 cycles. More importantly, the meticulous dQ/dV analysis reveals that the three-dimensional PTFE binder effectively binds the discharge products with sluggish kinetics (Li2S and Fe) to the ion–electron conductive network in the composite cathode, thereby preventing the electrochemical inactivation of products and enhancing electrochemical performance. Furthermore, FeS2-based pouch-type cells are fabricated, demonstrating the potential of PTFE-based dry-process technology to scale up ASSLBs from laboratory-scale mold cells to factory-scale pouch cells. This feasible dry-processed technology provides valuable insights to advance the practical applications of ASSLBs.

Surface modification of polytetrafluoroethylene (PTFE) fibers through methyl methacrylate (MMA) polymerization for self-lubricating composites

PTFE fibers exhibit strong inertia and possess restricted interfacial compatibility with resin, thereby constraining the application of PTFE self-lubricating composites. To address this issue, PTFE-g-MMA fibers were synthesized by grafting MMA onto the surface of PTFE fibers using high-energy irradiation and chemical grafting techniques, resulting in the enhancement of the tribological properties (the friction coefficient has been reduced by approximately 42.2% and the wear rate has been reduced by about 87.9%) and mechanical properties (the interlaminar shear strength (ILSS) experienced a substantial increase of approximately 45.8%) of the composites. The influence of grafting modification on the formation of PTFE transfer films and the effect of modification time on the tribological properties of composites were investigated systematically. The results indicated that graft modification disrupted the C–F bond of PTFE and promoted the formation of metal-chelated carboxylates, facilitating the formation of PTFE transfer films on the counter surface. This research could provide a general and feasible strategy for large-scale modification of PTFE fibers with exceptional comprehensive properties.

Binary fiber membranes with dual transport channels and interfacial demulsification for continuous emulsion separation

Membrane fouling occurred during subsequent filtration weakens the application advantages of membrane separation technology in treating oil–water emulsions. Herein, a functionalized binary fiber membrane with dual transport channels and enhanced interfacial demulsification was fabricated to facilitate continuous emulsion separation. The interpenetrated cellulose acetate (CA) and polytetrafluoroethylene (PVDF) fibers offer independent channels for transferring water and oil in the binary fiber membrane, which enables the timely removal of continuous oil contamination to mitigate membrane fouling. Moreover, a Span 80 functional layer assembled on the binary fiber membrane by a solvent-induced grafting approach promotes dynamic interfacial demulsification and antifouling of membrane materials. Owing to the advantages of the dual oil–water transport channel and Span 80 functional demulsification layer, the binary fiber membrane can separate continuously emulsifier-stabilized oil-in-water emulsions. Consequently, the binary fiber membrane can handle emulsions with high oil content (>5 vol%), and a single-stage separation time can last up to 5 h with a separation efficiency of over 98% because of its dynamic antifouling properties. Significantly, the membrane exhibits desirable cycling performance, and the Span 80 functional layer can be easily assembled to reset the separation performance, which encourages continuous emulsion separation and an extended membrane service life. Overall, this work opens a new avenue to fabricate binary fiber membranes with dual transport channels for sustainable antifouling and continuous emulsion separation, with high potential in practical applications relating to oily wastewater treatment and fuel purification.

Icephobic Coating Based on Novel SLIPS Made of Infused PTFE Fibers for Aerospace Application.

The development of slippery surfaces has been widely investigated due to their excellent icephobic properties. A distinct kind of an ice-repellent structure known as a slippery liquid-infused porous surface (SLIPS) has recently drawn attention due to its simplicity and efficacy as a passive ice-protection method. These surfaces are well known for exhibiting very low ice adhesion values (τice < 20 kPa). In this study, pure Polytetrafluoroethylene (PTFE) fibers were fabricated using the electrospinning process to produce superhydrophobic (SHS) porous coatings on samples of the aeronautical alloy AA6061-T6. Due to the high fluorine-carbon bond strength, PTFE shows high resistance and chemical inertness to almost all corrosive reagents as well as extreme hydrophobicity and high thermal stability. However, these unique properties make PTFE difficult to process. For this reason, to develop PTFE fibers, the electrospinning technique has been used by an PTFE nanoparticles (nP PTFE) dispersion with addition of a very small amount of polyethylene oxide (PEO) followed with a sintering process (380 °C for 10 min) to melt the nP PTFE together and form uniform fibers. Once the porous matrix of PTFE fibers is attached, lubricating oil is added into the micro/nanoscale structure in the SHS in place of air to create a SLIPS. The experimental results show a high-water contact angle (WCA) ≈ 150° and low roll-off angle (αroll-off) ≈ 22° for SHS porous coating and a decrease in the WCA ≈ 100° and a very low αroll-off ≈ 15° for SLIPS coating. On one hand, ice adhesion centrifuge tests were conducted for two types of icing conditions (glaze and rime) accreted in an ice wind tunnel (IWT), as well as static ice at different ice adhesion centrifuge test facilities in order to compare the results for SHS, SLIPs and reference materials. This is considered a preliminary step in standardization efforts where similar performance are obtained. On the other hand, the ice adhesion results show 65 kPa in the case of SHS and 4.2 kPa of SLIPS for static ice and <10 kPa for rime and glace ice. These results imply a significant improvement in this type of coatings due to the combined effect of fibers PTFE and silicon oil lubricant.

Triple-Phase Photocatalytic H2O2 Production on a Janus Fiber Membrane with Asymmetric Hydrophobicity.

Photocatalytic O2 reduction is an intriguing approach to producing H2O2, but its efficiency is often hindered by the limited solubility and mass transfer of O2 in the aqueous phase. Here, we design and fabricate a two-layered (2L) Janus fiber membrane photocatalyst with asymmetric hydrophobicity for efficient photocatalytic H2O2 production. The top layer of the membrane consists of superhydrophobic polytetrafluoroethylene (PTFE) fibers with a dispersed modified carbon nitride (mCN) photocatalyst. Amphiphilic Nafion (Naf) ionomer is sprayed onto this layer to modulate the microenvironment and achieve moderate hydrophobicity. In contrast, the bottom layer consists of bare PTFE fibers with high hydrophobicity. The elaborate structural configuration and asymmetric hydrophobicity feature of the optimized membrane photocatalyst (designated as 2L-mCN/F-Naf; F, PTFE) allow most mCN to be exposed with gas-liquid-solid triple-phase interfaces and enable rapid mass transfer of gaseous O2 within the hierarchical membrane, thus increasing the local O2 concentration near the mCN photocatalyst. As a result, the optimized 2L-mCN/F-Naf membrane photocatalyst shows remarkable photocatalytic H2O2 production activity, achieving a rate of 5.38 mmol g-1 h-1 under visible light irradiation.

Synergistic effect of thermoplastic polyester elastomer and polytetrafluoroethylene in situ fibrillation on the resilience and compression strength of long‐chain branched polypropylene foam

AbstractExcellent resilience and compression resistance are the key characteristics of cushioning and water–oil separation materials. Although polypropylene (PP) offers excellent performance and affordability of PP, it exhibits poor resilience. To address this shortcoming, polymer blends with long‐chain branched PP (LCBPP), thermoplastic polyester elastomer (TPEE), and polytetrafluoroethylene (PTFE) were prepared via melt blending, and their mechanical properties were tested. The LCBPP/TPEE/PTFE composites were subjected to physical foaming using supercritical CO2 (scCO2) as the blowing agent. The synergistic toughening mechanism of the elastomer/nanofiber and the effect of the structure and crystallization of the dispersed phase on the foam resilience and foam compression strength were investigated. The results revealed that fibrous PTFE and spherical TPEE formed a composite dispersed phase in LCBPP. The impact and tensile strengths of the unfoamed LCBPP were found to have been simultaneously optimized owing to the synergistic effect of the elastomeric toughening of TPEE and the reinforcement of the PTFE fiber–induced fibrous crystal structure. Compared with pure LCBPP, the impact strength of the LCBPP/TPEE/PTFE composite increased by 216%, whereas its tensile strength decreased by only 6%. In particular, the synergistic effect of TPEE/PTFE improved the resilience and compression strength of the LCBPP foam. Compared with the pure LCBPP foam, the permanent strain of the LCBPP/TPEE/PTFE foam was reduced by 13.8% after five cycles of compression and its compression strength increased by 27.3%. The experimental results of our study could be used to prepare LCBPP foams with exceptional resilience, high compression strength, and good application prospects.

Synergistic effects of carbon fiber and polytetrafluoroethylene on the friction and wear behavior of polyarylene ether nitrile under dry lubrication condition

AbstractThe synergistic effects of carbon fiber (CF) and polytetrafluoroethylene (PTFE) on the friction and wear behavior of polyarylene ether nitrile (PEN) under dry lubrication condition were studied. According to the scanning electron microscopy (SEM) on the composites' surface after wear, the wear mechanism of the composites under dry sliding condition was analyzed. The research results show that the addition of solid lubricants PTFE and carbon fibers to PEN helps to enhance the properties of friction and wear. The specific wear rate is decreased to 5.7 × 10−7 mm3/N m at a PTFE composition of 5 wt%, which is optimized by 33.4% more than PEN/CF composites. In addition, wear mechanisms are mainly abrasive wear, accompanied by adhesive wear and plowing of the friction ring.

Modeling of CO2 absorption in a membrane contactor containing 3-diethylaminopropylamine (DEAPA) solvent

Among the pollutants known as greenhouse gasses, carbon dioxide (CO2), although it is less toxic than the others, has by far the most significant amount of pollution in the earth's atmosphere. Also, it is one of the typical components of natural gas, which is removed due to the increase in fuel value and the adjustment of pipeline standards to prevent acid corrosion. There are various techniques for CO2 removal, among which membrane processes are a new and applied technology with many advantages in industrial separation. 3-diethylaminopropylamine (DEAPA) is a new amine absorbent with good interaction with CO2 molecules and increased absorption capacity, which shows good potential for CO2 separation. This study aims to investigate the performance potential of CO2 absorption by an aqueous solution of DEAPA as an absorbent in a hollow fiber membrane contactor (HFMC) with hydrophobic porous polytetrafluoroethylene (PTFE) fibers. A two-dimensional mathematical model was presented and solved based on the finite element method (FEM) to evaluate the CO2 removal efficiency. The effect of different parameters such as amine concentration, liquid and gas flow rate, liquid temperature, CO2 partial pressure, membrane tortuosity, number of hollow fibers, and packing density on CO2 absorption performance was investigated. The model results showed that increasing the gas flow rate and membrane tortuosity has a negative effect on CO2 removal. Also, increasing the amine concentration, packing density, the number of hollow fibers, DEAPA concentration, liquid temperature, and CO2 partial pressure improve the CO2 separation efficiency.

Enhanced filtration characteristics of a PTFE foam-coated filter using PTFE nanofibers

Polytetrafluoroethylene (PTFE) is a bag filter material with limited options for fiber production methods because of its high melt viscosity. In this study, a new method for fabricating a PTFE composite filter with high filtration performance was proposed. PTFE nanofibers produced by electrospinning, were coated on the surface of the PTFE foam-coated filter, and heat-treated, resulting in the fabrication of PTFE composite filter. The optimal conditions for preparing PTFE nanofibers with a uniform fiber distribution were determined using a systematic approach. A uniform fiber morphology of the electrospun fibers was prepared by controlling the PTFE-Polyvinyl alcohol (PVA) mixing ratio and the electric field strength, and pure PTFE fibers were obtained by heat-treatment at an optimal temperature based on TGA, DSC, and FT-IR analyses. The filter quality factor of the resultant PTFE composite filter, which represents the filtration performance, was approximately twice that of the PTFE foam-coated filter for all particle sizes. Furthermore, the cleaning cycle and cleaning efficiency of the PTFE composite filter improved by 9% and 3.9–5.4%, respectively, compared to those of the PTFE foam-coated filter, which was closely related to high contact angles of water and oil.

Hollow fiber polytetrafluoroethylene membrane heat exchanger with anti-corrosion properties

Thin hollow polytetrafluoroethylene (PTFE) fibers (thickness: 200 μm; outer diameter: 1.3 mm; inner diameter: 0.9 mm) were produced by a specially designed die via stretching and sintering, and assembled into a shell-and-tube membrane heat exchanger. The effects of the flow velocities on the heat transfer performance and thermal resistance were studied in a water-water system. The maximum overall heat transfer coefficient (OHTC) was up to 391 W/(m2‧K) (flow velocities: 0.24 m/s for hot water; 0.11 m/s for cold water). The OHTC became larger (increased from 229 to 391 W/(m2‧K)) at a higher cold water flow velocity (increased from 0.02 to 0.11 m/s) on the shell side when maintaining the hot water flows on the tube side. The OHTC increased from 119 to 391 W/(m2‧K) first and then decreased to 298 W/(m2‧K) with the increase of the hot water flow velocities (from 0.08 to 0.40 m/s) on the tube side, while maintaining the cold water flow velocity on the shell side. The thermal resistance results showed that the increased flow velocity (0.11 m/s) on the shell side significantly reduced the thermal resistance to 2.56 × 10−3 K m2/W on the shell side. Furthermore, the flow turbulence on the tube side is favorable for the heat transfer, and the optimum flow velocity on the tube side was 0.24 m/s. The hollow PTFE fibers were extremely stable and durable in corrosive solutions, with less than 1% changes in bursting strength, tensile strength at break, and elongation at break. This work opens new opportunities for the fabrication and application of hollow fiber PTFE membrane heat exchangers to reuse waste heat in high temperature corrosive environments.

A Research on the Air Permeability of High Polymer Materials Used to Produce Sports Clothing Fabrics

Composite fabrics based on Polytetrafluoroethylene (PTFE) polymer displays several notable properties. They are waterproof, windproof, permeable to moisture and thermally insulating at the same time. In the present study, PTFE fibers are used as raw material to make fiber membranes. The film is formed by crisscrossing interconnected fiber filaments and the related air permeability: tensile creep characteristics and other properties are tested. The results show that the pore size, thickness, and porosity of the film itself can affect the moisture permeability of the film. The water pressure resistance of the selected fabric is 8.5 kPa, and the moisture permeability is 7038 g/(m2·24 h).

Высокопрочные фторопластовые композиты с повышенной сопротивляемостью к деформациям под нагрузкой

This paper presents the results of research on the development of technology for plastic deformation of polymer blanks based on polytetrafluoroethylene (PTFE) and carbon fibers of the UVIS-AK-P brand in order to increase their strength and creep resistance. The dependence of the physico-mechanical and tribotechnical characteristics of the obtained composites is investigated and compared with a composite of the same composition, but obtained using a previously developed technology. It is established that the use of plastic deformation technology for the properties of PCM based on PTFE and carbon fibers of the brand UVIS-AK-P is an effective solution for obtaining high-strength, wear-resistant composites, characterized by increased resistance to tensile loads. The developed composites obtained using plastic deformation are characterized by 3 times increased tensile strength and 22 – 29 times reduced creep compared to the original PTFE obtained by standard technology. Structural studies of the technology of plastic deformation of polymer blanks have shown that this technology leads to the orientation of the carbon fiber (CF) in the direction of the flow of the material and a change in the spiral conformation of macromolecules with a transition to a more stable conformation, which favorably affects its operational properties. The use of this method will make it possible to obtain high-strength polymer materials with increased resistance to deformation, promising for use for loading schemes with high tensile loads.

An in situ self-charging triboelectric air filter with high removal efficiency, ultra-low pressure drop, superior filtration stability, and robust service life

Applying air filters is a practical approach to protecting people from particulate matter (PM) pollution. However, high pressure drop or removal efficiency decay remains a considerable challenge for existing air filters while maintaining desirable removal efficiency. Generating charges by TENG technology is one of the significant advances for high-efficiency air filters. While TENG-based air filters usually require an additional TENG to achieve high removal efficiency that is only effective during TENG operation, resulting in increased redundancy and complexity of filters for practical applications. Using nonwoven carding and through-air bonding techniques, here we report an in situ Self-charging Triboelectric Air Filter (S-TAF) consisting of silica nanoparticles modified polytetrafluoroethylene (PTFE) fibers and polypropylene/polyethylene (PP/PE) core-shell fibers. The S-TAF can be bipolarly charged in situ due to the triboelectrification effect between fibers during the carding process, thus dramatically enhancing the PM removal efficiency by electrostatic attraction. The unique core-shell structure of PP/PE fibers and the application of the through-air bonding process endowed the filter with a fluffy structure, high porosity, and large pore size, enabling the S-TAF with ultra-low pressure drop and robust service stability. Notably, the removal efficiency and quality factor (QF) of the S-TAF reached 99.28% and 0.19 Pa−1, and the pressure drop was only 26.46 Pa. Besides, the S-TAF also exhibited superior charge and filtration stability. Our unique design of the S-TAF may provide a new direction for fabricating high-performance air filters with integrated properties of high removal efficiency, ultra-low pressure drop, superior QF and filtration stability, and robust service life.

Reanalysis of historic elemental speciation filters to investigate the presence of fibrous mineral particles using microscopy techniques.

A case is presented for the value of archiving air quality filters to allow for retrospective analysis of emerging contaminants, that is filter constituents not considered to be harmful (and thus not identified or quantified specifically) at the time of collection but subsequently considered to be of interest. As an example, filters from a 20-year historical archive consisting of 16,000 filters from three sites across Auckland are re-examined for the presence of elongated mineral fibres known to be present in rock across the city. Originally collected for the purpose of the source apportionment of particulate matter, 10 filters from each of the three sites were chosen for reanalysis based on their high silica and aluminium content, and thus considered more likely to contain fibre-like particles (FLP). These filters were analysed using various microscopic methods, including phase contrast microscopy (PCM), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). The results show that although the commonly used fibrous polytetrafluoroethylene (PTFE) material of the filters may hamper the visual identification of any fibre-like particles under a certain length, their key components are able to be identified using a combination of PCM and SEM when they are of a suitable dimension and have settled in a certain orientation on the filter. In this case, the use of EDS confirmed the silicon content of the fibres and also revealed elemental spectra. Although the exact identification of the mineral fibre is uncertain, the EDS scan is consistent with hazardous zeolites such as erionite, known to be present in the rock found in Auckland. This study highlights the value in maintaining filter archives for the purpose of investigating the historical evolution of emerging atmospheric pollutants.

Nitrogen Recovery from Landfill Leachate Using Lab- and Pilot-Scale Membrane Contactors: Research into Fouling Development and Membrane Characterization Effects.

Membrane contactor technology affords great opportunities for nitrogen recovery from waste streams. This study presents a performance comparison between lab- and pilot-scale membrane contactors using landfill leachate samples. Polypropylene (PP) and polytetrafluoroethylene (PTFE) fibers in different dimensions were compared in terms of ammonia (NH3) recovery on a lab scale using a synthetic ammonium solution. The effect of pre-treating the leachate with tannin coagulation on nitrogen recovery was also evaluated. An ammonia transfer on the lab and pilot scale was scrutinized using landfill leachate as a feed solution. It was found that PTFE fibers performed better than PP fibers. Among PTFE fibers, the most porous one (denoted as M1) had the highest NH3 flux of 19.2 g/m2.h. Tannin pre-treatment reduced fouling and increased NH3, which in turn improved nitrogen recovery. The mass transfer coefficient of the lab-scale reactor was more than double that of the pilot reactor (1.80 × 10−7 m/s vs. 4.45 × 10−7 m/s). This was likely attributed to the difference in reactor design. An analysis of the membrane surface showed that the landfill leachate caused a combination of inorganic and organic fouling. Cleaning with UV and 0.01 M H2O2 was capable of removing the fouling completely and restoring the membrane characteristics.

Polytetrafluoroethylene fiber fabrication from the continuous melt-spinning process and its properties

Polytetrafluoroethylene (PTFE) has high thermal stability and chemical resistance, and hence is gaining great attention in the industrial field of high-performance filters, membranes, and medical applications. However, since PTFE possesses a narrow gap between melting (330°C) and decomposition temperatures (350°C), the melt-spinning process that is required to satisfy industrial needs for mass production has been limited. Here, perfluoro(propyl vinyl ether) (PPVE) was introduced to decrease the melting point of PTFE then fiber fabrication was performed with the melt-spinning process using a single-screw extruder, enabling the PTFE fiber to fabricate continuously. We selected an optimal melt-spinning condition and obtained PTFE fiber from the melt-processable PTFE/PPVE copolymer. The as-spun PTFE fiber showed low mechanical strength (0.90 g/denier or 89.1 MPa of tenacity). A post-thermal drawing process was performed to increase the mechanical strength of the PTFE as-spun. It demonstrated that the thermally drawn PTFE fiber showed higher mechanical strength (1.84 g/denier or 220.0 MPa of tenacity) due to the increased degree of crystallinity. Also, the other trial, thermal stabilization under N2, suggested as a future modification method to increase mechanical strength further, preventing thermal constriction of the PTFE fiber. The melt-spun and thermally drawn PTFE fibers were knitted and it was confirmed that the fiber has high chemical resistance and similar surface chemistry to conventional PTFE fibers. This study developed a method to enable a melt-processable PTFE fiber fabrication and opens up opportunities for mass production that is crucial in the industrial aspect.