Polytetrafluoroethylene Polymer Research Articles

Mechanical and wear behaviour of PEEK, PTFE and PU: review and experimental study

Abstract Soft polymers such as polyether ether ketone (PEEK), polyurethane (PU) and polytetrafluoroethylene (PTFE) have gained significant research interest in the last few decades owing to their excellent material properties which can be harnessed to meet the demands of various applications such as biomedical implants and accessories, insulation panels to cooking utensils, inner coating material for non-stick cookware etc. In the present study, we provide a comprehensive review on the mechanical and tribological behaviour of PEEK, PU and PTFE polymers. Samples of these materials were also fabricated and the experimentally obtained tensile strength, flexural strength, wear rate and coefficient of frictions were ascertained with values reported in literature. It is highlighted that coefficient of friction of polymers were highly dependent on the surface texture of the polymer’s surface; where an uneven surface exhibited higher coefficient of friction. Perspectives for future progress are also highlighted in this paper.

Potentio-tunable FET sensor having a redox-polarizable single electrode for the implementation of a wearable, continuous multi-analyte monitoring device

The emerging field of wearable devices for monitoring bioanalytes calls for the miniaturization of biochemical sensors. The only commercially available electrochemical wearable monitoring medical devices for bioanalytes are the amperometric continuous glucose monitoring (CGM) systems. The use of such amperometric methods to monitor glucose levels requires a relatively large electrode surface area for sufficient redox species collection, allowing accurate measurements to be made. Consequently, miniaturization of such sensors bearing large electrodes is challenging. Furthermore, it is difficult to introduce and deploy more than one electrode–based sensor per device, thereby limiting the number of analytes that can be monitored in parallel. To address these limitations, we have employed a non-referenced, single polarizable electrode coupled to a fin-shaped field-effect transistor (Fin-FET). We have discovered that by passivating the FET area by a relatively thick oxide and/or polytetrafluoroethylene (PTFE) polymer, leaving only the polarizable working electrode (WE) exposed, we can monitor redox analytes at the micromolar to millimolar concentration range. We attribute this effect to the WE polarization by the solution redox species. We have exploited the superior sensitivity of the adjacent silicon-based Fin-FET to detect changes in sensor electrode potentials induced by the redox species. Furthermore, we demonstrated the correlation between a specific analyte and the biasing WE potential on the accumulation/depletion of the coupled Fin-FET channel as manifested by the transistor source-drain current. Moreover, we utilized the analyte-electrode potential interaction, which is analyte-specific, to tune the specificity of the sensor towards an analyte of choice. In addition, we demonstrated the use of a single-electrode potentiometric sweep to assist in identifying the accumulation/depletion as a result of analyte-WE state. Collectively, the tiny potentio-tunable electrochemical sensor (PTEchem sensor) area is ~50 × 50 µm, and dedicated wireless transducer facilitates the use of this sensor for wearable continuous, multi-metabolite monitoring.Graphical abstract

Modeling Fracture Formation, Behavior and Mechanics of Polymeric Materials: A Biomedical Implant Perspective

In industrial applications where contact behavior of materials is characterized, fretting-associated fatigue plays a vital role as a failure agitator. While considering connection, it encounters friction. Biomaterials like polytetrafluoroethylene (PTFE) and ultra-high-molecular-weight polyethylene (UHMWPE) are renowned for their low coefficient of friction and are utilized in sophisticated functions like the hip joint cup and other biomedical implants. In addition to the axial stresses, some degree of dynamic bending stress is also developed occasionally in those fretting contacts. This research investigated the fracture behavior of a polymer PTFE under bending fretting fatigue. Finite element analysis justified the experimental results. A mathematical model is proposed by developing an empirical equation for fracture characterization in polymers like PTFE. It was found that the bending stiffness exists below the loading point ratio (LPR) 3.0, near the collar section of the specimen. Along with fretting, the bending load forces the specimen to crack in a brittle-ductile mode near the sharp-edged collar where the maximum strain rate, as well as stress, builds up. For a loading point ratio of above 3, a fracture takes place near the fretting pads in a tensile-brittle mode. Strain proportionality factor, k was found as a life optimization parameter under conditional loading. The microscopic analysis revealed that the fracture striation initiates perpendicularly to the fretting load. The fretting fatigue damage characteristic of PTFE may have a new era for the biomedical application of polymer-based composite materials.

O2 and H2O Barrier-Based High Reliability and Stability Using Polytetrafluoroethylene Passivation Layer for Solution Processed Indium Oxide Thin Film Transistors

The excellent chemical stability and hydrophobicity of Polytetrafluoroethylene (PTFE) polymer lead to its applicability in high-performance flexible electronic appliances. Though the detailed investigation for PTFE passivated metal oxide thin-film transistors (TFTs) is still lacking. Here, we report the highly stable oxygen barrier based on the PTFE passivation layer (PVL) spin-coated upon the lowtemperature solution-processed indium oxide (In₂O₃) TFTs. Particularly, by using the solution-process method, fabrication cost and multiple time-consuming steps are eliminated in the counterpart of the radio frequency magnetron sputtering. The PTFE PVL can significantly suppress the adsorption of surrounding moisture and oxygen from environments owing to its most chemically robust carbon-fluorine bond. In addition, the comprehensive electrical performance in terms of the saturation mobility, on-off current ratio, threshold voltage, subthreshold swing, and interface trap density of the In₂O₃ TFTs passivated with different weight ratios of PTFE are compared. The results show that 1 wt.% PTFE passivated In2O3 TFT demonstrates a drastically reduced threshold voltage and highest stability under constant bias. Consequently, oxygen barrier-based PTFE is a promising PVL material for various emerging electronic devices.

Creep and thermal ratcheting characterization of polytetrafluoroethylene-based gasket materials

Characterization of Teflon polymer based gaskets under expedited aging is the objective of this work. Teflon gaskets are exploited frequently as a replacement to asbestos fiber gaskets because of their excellent leak tightness and nonhazardous physical degradation properties. The research focuses profoundly on the adverse influence of temperature and thermal cycles on the creep and cumulative damage phenomenon under compressive load. Virgin and expanded PolyTetraFluoroEthylene (PTFE) are tested under 28 and 41 MPa of gasket stress at different temperatures. Intricate analysis of creep under coalesces of thermal ratcheting and principal stress is achieved through Universal Gasket Rig (UGR). The instigated cumulative damage is distinguishable into upper and lower bound temperature region indicating the escalation and decrease of thickness change during cycling which saturates after 12 thermal cycles for expanded PTFE while no saturation is reached for virgin PTFE in even after 20 thermal cycles. Percentage of thickness reduction at different applied stress is nearly the same for virgin PTFE whereas expanded PTFE shows largest reduction under lower stress. Compressive creep bespeaks the impact of temperature and load, thereby dictating the magnitude of ratcheting damage and contrariwise. Finally, the creep and thermal ratcheting has a proliferating effect on value of the coefficient of thermal expansion for all chosen gaskets. Copyright © 2017 VBRI Press.

Cyanide removal from aqueous environment by resting cells and PTFE immobilized cells of Sphingobacterium spp.

Microbial detoxification of cyanide offered an inexpensive, safe, and viable alternative to physiochemical processes for the treatment of cyanide in industrial effluents or contaminated sites. This study involved isolation of novel strain with high resistance against cyanide toxicity and able to degrade the cyanide radical. The strain was isolated from rocky area and identified as Sphingobacterium multivorium using 16S ribosomal RNA. Resting pregrown cells were used in simple reaction mixture to avoid the complication associated with the media. One-gram fresh weight of this bacteria was able to remove 98.5% from 1.5 g/L cyanide which is a unique result. Factor affecting the biochemical process such as pH, temperature, agitation, glucose concentration was examined. The optimum conditions were, pH 6-7, 30-40°C, and 100-150 rpm shaking speed and 0.25% glucose. Furthermore, the cells were used after immobilization in polytetrafluoroethylene (PTFE) polymer. The PTFE is very safe carrier and the cells withstand the entrapment process and were able to remove 92% (1 g/L cyanide). The immobilized cells were used for six successive cycles with about 50% removal efficiency. The storage life extended to 14 days. No previous work studied the cyanide removal by Sphingobacterium spp. The strain showed good applicable characters.

Clinical Outcomes following Large Vessel Coronary Artery Perforation Treated with Covered Stent Implantation: Comparison between Polytetrafluoroethylene- and Polyurethane-Covered Stents (CRACK-II Registry).

Data on the clinical outcomes comparing synthetic fluorocarbon polymer polytetrafluoroethylene- (PTFE, GraftMaster) and polyurethane- (Papyrus) covered stents (CSs) to seal coronary artery perforations (CAPs) are limited. We aimed to evaluate 30-day and 1-year clinical outcomes after PCI complicated by CAP and treated with CS. We assessed 106 consecutive patients with successful CAP sealing (122 CSs): GraftMaster (51 patients, 57 CSs) or Papyrus CS (55 patients, 65 CSs). The primary endpoint was the occurrence of major adverse cardiac events (MACE), defined as the composite of cardiac death, target lesion revascularisation (TLR), and myocardial infarction (MI). The mean age of subjects was 69 ± 9.6 years (53.8% males). No significant differences were identified between the GraftMaster and Papyrus groups at the 30-day follow-up for MACE, cardiac death, MI and stent thrombosis (ST), while significantly lower rate of TLR and TVR (p = 0.02) were confirmed in the Papyrus group. At one year, differences remained similar between stents for MACE, a trend towards a lower rate of TLR (p = 0.07), MI (p = 0.08), and ST (p = 0.08), and higher for cardiac death (p = 0.07) was observed in the Papyrus group. This real-life registry of CAP illustrated that the use of Papyrus CS is associated with lower rates of TLR and TVR at 30-day follow-up in comparison to the GraftMaster CSs and no significant differences between both assessed CS at one year of follow-up.

Degradation Mechanisms Occurring in PTFE-Based Coatings Employed in Food-Processing Applications

The application of polytetrafluoroethylene (PTFE) coatings to metal surfaces is a well-known procedure carried out to avoid fouling phenomena on food-processing surfaces. Fluorine-based polymers are generally chemically and thermally stable, thus allowing them to be the preferred choice when designing anti-stick coatings in the food service industry. Their lifespan, however, depends on the environmental conditions. It is well known that thermal ageing can affect the properties of PTFE polymers and reduce their mechanical, thermal, and chemical properties causing failures and contaminating food. The main goal of the study is to identify the different failure mechanisms occurring in PTFE-based coatings, using both SEM/EDXS and ATR FT-IR data to reveal the starting point of degradation phenomena in food processing applications. The results from this research reveal that the preferential points for failures are mainly the polymer/substrate interfaces, the polymer/filler interfaces, or the polymer matrix itself.

Recent, Bioelectricity-Related Articles Selected by Ann M. Rajnicek, Media Editor of Bioelectricity.

Recent, Bioelectricity-Related Articles Selected by Ann M. Rajnicek, Media Editor of Bioelectricity.

Investigation on fracture toughness of polytetrafluoroethylene with impact essential work of fracture method

Polytetrafluoroethylene (PTFE) polymer has a wide range of applications in various industries. Therefore, for designers it is essential to know the strength properties of the material under dynamic loads. In this study, pure-PTFE, bronze and carbon filled-PTFE are tested under dynamic load. In addition, pure and carbon filled specimens were used to determine the temperature effect of PTFE. All tests were carried out in the Charpy impact device according to impact essential work of fracture method. At 23°C, pure-PTFE showed the highest impact strengths, bronze filled-PTFE and carbon filled-PTFE showed lower respectively and it has been found that the carbon filler increases the fracture toughness approximately two times at high temperature (150°C). On fracture surfaces phase transitions effects of PTFE and behavior of fillers used were investigated with Scanning Electron Microscope.

PTFE-Carbon Nanotubes and Lipase B from Candida antarctica—Long-Lasting Marriage for Ultra-Fast and Fully Selective Synthesis of Levulinate Esters

An effective method for levulinic acid esters synthesis by the enzymatic Fischer esterification of levulinic acid using a lipase B from Candida antarctica (CALB) immobilized on the advanced material consisting of multi-wall carbon nanotubes (MWCNTs) and a hydrophobic polymer—polytetrafluoroethylene (Teflon, PTFE)—as a heterogeneous biocatalyst, was developed. An active phase of the biocatalyst was obtained by immobilization via interfacial activation on the surface of the hybrid material MWCNTs/PTFE (immobilization yield: 6%, activity of CALB: 5000 U∙L∙kg−1, enzyme loading: 22.5 wt.%). The catalytic activity of the obtained biocatalyst and the effects of the selected reaction parameters, including the agitation speed, the amount of PTFE in the CALB/MWCNT-PTFE biocatalyst, the amount of CALB/MWCNT-PTFE, the type of organic solvent, n-butanol excess, were tested in the esterification of levulinic acid by n-butanol. The results showed that the use of a two-fold excess of levulinic acid to n-butanol, 22.5 wt.% of CALB on MWCNT-PTFE (0.10 wt.%) and cyclohexane as a solvent at 20 °C allowed one to obtain n-butyl levulinate with a high yield (99%) and selectivity (>99%) after 45 min. The catalyst retained its activity and stability after three cycles, and then started to lose activity until dropping to a 69% yield of ester in the sixth reaction run. The presented method has opened the new possibilities for environmentally friendly synthesis of levulinate esters.

AF2400/polyketone composite organic solvent reverse osmosis membrane for organic liquid separation

Organic liquid separation is frequently encountered in chemically relevant industries. Herein, an organic solvent reverse osmosis (OSRO) membrane fabricated by spin coating a Teflon polymer, AF2400, onto a solvent-resistant polyketone support is proposed for organic liquid separation. Nonpolar AF2400 promotes the permeation of nonpolar liquids while inhibiting the transportation of polar liquids, resulting in the efficient separation of polar and nonpolar liquids. A mixture of ethanol and 1-hexane was used as a model, and the effects of feed composition, applied pressure, and filtration time on separation performance were investigated. The optimized membrane demonstrated an impressively high separation factor of 9.5 for 1-hexane over ethanol and an acceptable flux of 1.6 kg m−2 h−1 under 4 MPa (a permeance of 0.04 kg m−2 h−1 bar−1), outperforming the reported membranes in selectivity. The separation performances in alcohol/1-hexane, ethanol/alkane, and ethanol/toluene mixtures were also investigated and the results demonstrated that the molecular size and polarity of the liquids affected the selectivity. The developed membrane contributes to the development of energy-efficient approaches for separating organic liquids.

Flexible graphite bipolar plates for vanadium redox flow batteries

The effects of polytetrafluoroethylene (PTFE) additives on expanded graphite bipolar plates (BPs) for vanadium redox flow batteries (VRFB) are investigated. Pure expanded graphite plates have immense potential for use in low-cost, rapid, and continuous fabrication of high performance VRFBs. However, pure expanded graphite BPs suffer from severe swelling in vanadium electrolytes over short periods of time, exhibiting decreased efficiency of 2.3% within 35 charge/discharge cycles. In contrast, expanded graphite BPs containing 6 and 10 wt% PTFE do not experience swelling or efficiency loss during cycle tests. The prevention of swelling is a key factor contributing to the use of expanded graphite plates for VRFB stacks. Microstructural analysis reveals that our fabrication method provides uniform PTFE distribution. PTFE polymers suppress swelling by providing coverage of surface cracks, repelling aqueous solutions due to their hydrophobicity, and more importantly, providing binding forces between expanded graphite layers. PTFE additives increase electrical resistivity, but improve flexibility, allowing for the fabrication of very thin plates. Thin flexible BPs exhibit low areal electrical resistance and thus the ohmic voltage loss of the BPs with 6 wt% PTFE is less than 1.2 mV (<0.1% of the VRFB nominal voltage of 1.25 V) even at a high current density of 0.2 A cm−2, which is negligible compared with other factors.

Unexpected Frictional Behavior of Laser-Textured Hydrophobic Surfaces

Hydrophobic surfaces can allow a liquid to slip over the surface and can thus reduce friction in lubricated contact working in a full film regime. Theory supports that the amount of slip can be increased if super-hydrophobic surfaces that are composed of a textured low surface energy material are used. In this work, polytetrafluoroethylene (PTFE) polymer samples were textured with a femto second laser to create super-hydrophobic surfaces by machining a hexagonal network of small circular holes with 10 and 20 μm lattice sides. The frictional behavior of these surfaces was compared to the smooth PTFE samples. Surprisingly, the textured surfaces revealed higher friction coefficients than the smooth surfaces. This higher friction can be explained by a change of wetting regime due to high pressure in fluid and a possible generation of vortices in the cavities.

Influence of Current Spreading on Polymer Surface on Determination of Total Surface Energy

Total surface energy of a polytetrafluoroethylene polymer film modified in a nonequilibrium plasma of a low-current atmospheric-pressure surface discharge has been determined. It has been shown that the total surface energy and its dispersive and polar components are inhomogeneous and substantially depend on the current spreading over the film surface.

Synthesis and Characterisation of Polytetrafluoroethylene Composite for Electrical Insulation and Dielectrics

This work provides an experimental study to measure the electrical properties of Polytetrafluoroethylene polymer and how it improves through the process of mixing with different volume rates of Poly (methyl methacrylate) PMMA. The relationship of the actual dielectric constant with frequency for pure and dopped models with different concentrations of PMMA (5%, 7%, 10%) and for a range of frequencies ranging between 1-1000 KHz, at the room temperature was investigated. The results show an increase in the dielectric constant of the composites compared to the pure models for all concentrations, which indicates that the polymers interaction gives support to the polytetrafluoroethylene infrastructure. The mixing process, also, leads to an increase in the values the imaginary part of the dielectric constant compared to the pure model, and this is due the significant increase in the number of dipoles resulting from the addition process which in turn led to increase the amount of energy lost due to rotation or friction of the dipoles with each other. This increase, in turn, led to a corresponding rise in the values of the loss tangent tanδ and the AC conductivity of the models. The experimental results show a 90 % increase in the dielectric constant of the composite at 500 KHz compared to the pure Polytetrafluoroethylene, which provide a good electrical insulation material for electronic circuits.

A Highly Efficient and Durable Kirigami Triboelectric Nanogenerator for Rotational Energy Harvesting

While sliding-mode triboelectric nanogenerators (S-TENGs) have been considered as one of the most promising devices for rotational energy harvesting, their inherently poor durability has been a serious bottleneck for applications. Herein, we report a three-dimensional kirigami TENG as a highly efficient and durable rotational energy harvesting device. The kirigami TENG consisted of cube-shaped paper, aluminum (Al) foil electrode and polytetrafluoroethylene (PTFE) polymer film, and converted rotational motion into multiple folding-unfolding vibrations. The rotation-folding (R-F) kirigami TENG generated an open-circuit voltage of 31 V, a short-circuit current of 0.67 μA and an instantaneous power (power density) of 1.2 μW (0.13 μW/cm2) at 200 rpm, which was sufficient to turn on 25 light-emitting diodes and a thermo-hygrometer. The triboelectric outputs of the R-F kirigami TENG were only slightly decreased even after 288,000 continuous rotations, i.e., the output remained at 86% of its initial value. This work demonstrates that an R-F kirigami TENG could be a plausible candidate to efficiently harvest various forms of rotational energy with a long-term durability.

Data-driven approach to optimize composition and process parameters of hydrophobic coating formulation

Coating formulation design often demands numerous experiments, expertise, and prior knowledge. The formulation is a multi-component system; each component should be present in precise quantity so that it will provide appropriate significance – a functionality. Often, these functionalities have counter effects; one functionality is compromised while achieving another functionality. To achieve juxtaposing benefits, the optimum formulation should be designed. In the present study, a hydrophobic silica-alumina hybrid coating formulation is designed by data-driven approach with minimum number of experiments. We have determined the effect of concentration of nanoparticles, polytetrafluoroethylene (PTFE) polymer percentage and speed of spin coating (rpm) on different characteristics of the coating. These different characteristics include contact angle, roll off angle, scratch hardness, adhesion, and thickness. Three by three full factorial design of experiment was performed. Correlation between each parameter with every coating characteristics was determined by Spearman's rank correlation. Statistical analysis concluded that, nanoparticles majorly contributed for hydrophobicity elevating the contact angle and reducing the roll off angle. Whereas, PTFE and rpm contributed for the adhesion and thickness. Finally, a coating formulation was determined for higher contact angle, lower roll of angle and improved mechanical properties.

Two-dimensional clay nanosheet-reinforced polytetrafluoroethylene composites and their mechanical/tribological studies

Polytetrafluoroethylene (PTFE) polymer is used extensively in industry as a solid lubricant because of its lack of reactivity with most industrial materials. However, PTFE has a low abrasive resistance, limiting its application. In this study, the mechanical and tribological characteristics of PTFE-based composites with the addition of clay nano-sheets (CNSs) were investigated. Clay nano-sheet-PTFE composites (CNSTCs) containing 1, 3, and 5 wt. % of CNSs were prepared by employing a compression moulding method. To investigate the tribological characteristics and wear mechanism of CNSTCs, a pin-on-ring test, scanning electron microscopy (SEM), and optical microscopy (OM) were employed. The results indicate that adding CNSs decreased the friction coefficient substantially. Additionally, the wear rates decreased from 1.09 × 10−3 mm3/(Nm) in the pure PTFE sample to 0.32 × 10-5 mm3/(Nm) for the 5 wt. % CNSs filled composite. This shows that the wear rate of the PTFE-based composite is reduced by up to 340 times with the addition of 5 wt. % CNSs. SEM and OM observations revealed that CNSs could inhibit the growth of microcracks in CNSTCs and change the wear mechanism from adhesive to abrasive. Furthermore, adding CNSs resulted in a more uniform and thinner transition film formation, with reduced secondary wear and friction. The effects of the size, percentage, and type of embedded fillers were compared with previous studies. The analysis revealed that in addition to competitive cost and high availability, CNSs have superior characteristics and can be employed to enhance the tribological properties of PTFE nanocomposites.

Fabrication, structural investigation and comparative optical characterization of copper polymer nanocomposites

In this work, a homemade ion beam deposition technique is used to fabricate nanocomposites films consisting of copper nanoparticles (CuNPs) embedded in a polyethylene terephthalate (PET) and in polytetrafluoroethylene (PTFE) polymers. Then study the comprehensive effect of the deposited CuNPs on the optical and structural properties of PET and PTFE polymers. The structural investigation of the PET and PTFE polymers as well as the Cu/PET and Cu/PTFE composites is carried out using X-ray diffraction (XRD). The XRD data showed CuNPs are deposited successfully on PET and PTFE films. The optical characterization of the prepared films is studied using UV–Vis spectroscopy techniques, to confirms the changes in the optical band gap Eg and carbon cluster number N. The UV–Vis optical absorption demonstrate a slight shift in the absorption edge towards visible region by increasing Cu deposition time on both PET and PTFE polymers. Increasing Cu deposition time is leads to slight decrease in optical energy band gap Eg and an increase in the numbers of carbon cluster N. The Eg is decreased from 3.8 to 2.2 eV for Cu/PET and from 3.1 to 2.3 eV for Cu/PTFE while N is increased from 82 to 244 for Cu/PET and from 113 to 224 for Cu/PTFE by increasing the Cu deposition time from 25 to 75 min. The obtained results of Cu/PET and Cu/PTFE polymer nanocomposites are opening new fields for applicable optoelectronic devices.