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We introduce a volumetric analysis technique to characterize the solubility of hydrogen dissolved in polymers and its diffusion coefficient by electrical capacitance measurement electrodes to determine the water level in graduated cylinders. This new and simple technique measures the volume of hydrogen released from rubber inside a graduated cylinder after a sample is exposed to high-pressure hydrogen and subsequent decompression. A diffusion analysis program is utilized to determine the total uptake (C0) and diffusivity (D) of hydrogen, which are used to calculate the solubility (S) and permeability (P). This method is applied to spherical rubber samples of nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM), which are potential sealing materials for H2 energy infrastructures. C0 follows Henry's law for all samples. No sample size and pressure dependence is observed for S, whereas an appreciable size dependence for the three rubbers is detected for D. The uncertainty is evaluated by considering uncertainty factors that affect the measurement. The correlation between D and density of rubber is found. The developed method can be utilized as a standard test for the transport properties versus pressure of various polymer membranes regardless of the sample shapes and size.

Copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) make up the largest volume of fluoroelastomers sales. Within this family, Viton A (VDF/HFP 60/40 wt%, 66% fluorine) is most important commercially. Determination of thermomechanical properties of such fluorinated polymers is still limited to experimentation or empirical models, while computational prediction of their physical properties is still at its infancy. Considerable efforts have been made to develop molecular force fields for the prediction of properties of various crystalline as well as amorphous fluorinated substances. These force fields were parametrized based on small molecules or oligomers, hence their transferability to longer and more complex (i.e. copolymer) chain architectures must be tested. In this work, thermodynamic, structural, and mechanical properties of the Viton A fluoroelastomer are evaluated using atomistic molecular dynamics (MD) simulations for several force fields and compared with available experimental data. Differences in molecular structure of the chains modeled by different force fields are shown to substantially influence thermodynamic and mechanical behavior. OPLS-derived force fields give rise to extended chains that are more mobile and result in softer material that lack in molecular structure. Other force fields rely on strong nonbonded interactions that interfere with chain dynamics and mechanics. PCFF is shown to most satisfactorily predict structural properties and thermal volumetric behavior around Tg, demonstrating relatively successful transferability to long linear polymer chains.

In this paper, a femtosecond laser manufacturing process is effectively employed to produce a pattern of micro dimples on a fluoroelastomer. To quantify the microtexture tribological performance, two configurations are implemented: non-conformal and conformal contacts are tested on a pin-on-disk tribometer. Due to the reduced number of dimples engaged in the contact region, no significant friction enhancement is obtained in the non-conformal configuration. On the contrary, in the case of conformal contacts, outstanding outcomes in terms of friction reduction - up to 60% - can be achieved by a properly designed micro-texture. Such a result is obtained by improving the wear debris entrapment and the cavitation respectively at low and high speed, without increasing significantly the occurrence of flow eddies.

Elastomer seals are essential for zonal isolation in vertical and deviated wells. They are often used either as O-rings (static seals) or as energized seals (packers). For elastomers to perform their functions effectively over an extended period, it is essential that the elastomer withstand the deleterious effects of pressure, prolonged loading effects, severe temperature, corrosive fluids, and acidic gases. As such it is imperative to understand the various elastomer degradation mechanisms and develop methods to reduce the degradation. The objectives of this study are: to investigate if elastomers are “fit for service” for well construction applications and to evaluate elastomer performances under downhole corrosive conditions. To achieve this goal, some dynamic wellbore conditions which close-to-real field conditions are were simulated in a controlled laboratory setup. The following properties were investigated: elastomer hardness, elastomer compression, and elastomer volumetric swelling. In the experimental setup, four frequently used elastomers in the oil and gas industry were studied: Nitrile butadiene rubber (NBR), Ethylene propylene diene monomer (EPDM), Fluoroelastomer (FKM) commonly known as Viton, and Polytetrafluoroethylene (PTFE). The results indicate that NBR exhibited the most significant deterioration. Viton showed the least amount of deterioration but has poor decompression resistance. The aging condition that proved to be the most damaging is CO2. Analysis of Variance (ANOVA) was also performed on the data from the samples as a statistical analysis indicator. Some other observations and conclusions are that the degree of chain growth and chain rupture depends on the temperature and the degree of chemical exposure.

Utilization of Ionic Liquids (IL) as suitable candidate for nanofiller modification is of considerable interest in the current scenario owing to its peculiar properties. In the present study reduced graphene oxide (rGO) is modified with varying amount of IL to improve the dispersability and interaction with fluoroelastomer (FKM) matrix. The surface modification of rGO using IL, its dispersion and incorporation into the FKM matrix was confirmed by FTIR, Raman, XRD, and AFM surface roughness analysis. The prepared nanocomposites achieved better static and dynamic mechanical properties by the addition of 2 phr of IL to rGO. Moreover the nanocomposites showed an increase in glass transition temperature from DSC (−18.82 for FIL 0 to −14 for FIL 2) analysis that supports the enhanced interaction between FKM and modified filler. Dynamic mechanical analysis of the nanocomposites proved the reinforcing ability and the effectiveness of ILrGO to enhance the properties as a whole. The dielectric study of the nanocomposites showed improved AC conductivity, dielectric constant value (60 with 2 phr of IL content) and a decrease in dielectric heating coefficient value with increase in ILrGO content. These property combinations make the nanocomposites a multifunctional material.

Straight vegetable oils (SVO's) are currently used as renewable sources of fuel in diesel engines for electricity production, transport or agricultural mechanization. Despite various environmental benefits, the use of SVO's may result in shortcomings for the engine operation, in particular, degradation of seals and polymeric components. Thus, deterioration of seals into contact with SVO's in engines must be analyzed to make a safe use of these alternative fuels. In this work, the deterioration of silicone rubber (VMQ), fluoroelastomer/Viton® (FKM), ethylene-propylene-diene monomer (EPDM) and neoprene/chloroprene rubber (CR), upon exposure to straight Jatropha oil (SJO), diesel, and a blend 80% diesel-20% SJO (B20), respectively, was analyzed by immersion tests with measurements of changes in mass, volume, tensile and tear strengths, and hardness. Complementary measurements of changes in viscoelasticity, surface morphology, topography, and chemical composition provided further insight into the understanding of deterioration of the elastomers. Overall, the four elastomers exhibited negligible deterioration with SJO while only FKM exhibited minimal deterioration with diesel and B20. VMQ and FKM were the less deteriorated elastomers by SJO and diesel, respectively. These experimental results were found to be in good agreement with predictions of compatibility based on the use of the Hansen solubility theory.

The conservation of historical buildings and outdoor cultural assets is of great value for the humankind. In this context, consolidation treatments represent a fundamental procedure to assure the survival of deteriorated cultural artefacts. For porous materials characterized by a wide distribution of pore sizes, adequate consolidation treatments require a product with a sufficient penetration depth and homogeneous distribution inside the unconsolidated substrate. Since water is one of the main deterioration agents of stone, the wettability of rock should also be minimized. A non-invasive and non-destructive technique, able to localize the consolidation agent and the water uptake, is needed to evaluate the efficiency of the treatments. NMR techniques are good candidates to satisfy this requirement. The present study aims at investigating the efficiency of two commercial consolidants, i.e. ethyl silicate and nano-silica, and a new formulated mixture of a fluoroelastomer and nano-silica by NMR relaxometry and MRI. The tested compounds showed adequate characteristics to be used as consolidating agents for highly porous carbonate rocks like limestone. All the products, in fact, penetrated uniformly and homogeneously into the porous structure, and preserved the connectivity of the stone matrix, as demonstrated by T 2 - T 2 relaxation exchange experiments. Moreover, the hydrophilic behavior of commercial consolidants could be reduced, when the newly formulated agent was used. This study shows how the combination of different NMR techniques, applied in the time domain and with spatial resolution, is a powerful approach for evaluating the consolidation efficiency.

Carboxylic functionalized multi-walled carbon nanotubes (MWCNTs-COOH) were modified by using ethylenediamine (EDA) to prepare amino-functionalized multi-walled carbon nanotubes (MWCNTs-A). MWCNTs-A were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Fluoroelastomer (FKM) was reinforced by incorporation of MWCNTs-COOH and MWCNTs-A, respectively. The thermal, electrical and mechanical properties of the FKM/MWCNT composites were studied. The results indicated that a more homogeneous dispersion of nanotubes and a stronger interfacial interaction in FKM/MWCNTs-A composites were achieved than in FKM/MWCNTs-COOH ones. As a result, the thermal, electrical and mechanical properties of the FKM/MWCNTs-A composites were higher than that of the FKM/MWCNTs-COOH composites due to the participation of MWCNTs-A in the crosslinking process to form dual crosslinking networks in the FKM matrix.

This study evaluates the dehydrofluorination of fluoroelastomer (poly(VDF-co-HFP) copolymer) which was dissolved by organic solvent and reacted with different concentrations of KOH and different amount of phase transfer catalyst (PTC) at 20–60 °C.The structures, sequence types and contents of double bonds of samples were analyzed and investigated by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy(ATR-FTIR), 1H nuclear magnetic resonance (NMR), 19F NMR spectroscopy and chemical titration method. The results revealed that dehydrofluorination of the studied fluoroelastromers could be carried out at room temperature in alkaline environments, wherein the temperature and alkali concentration were the great factors. And the dehydrofluorination of poly(VDF-co-HFP) copolymer conformed mainly to Zaitsev's rule and partially to Hofmann's rule. The double bonds (–C=C–) would generate in five positions of molecular chains and contents could be controlled. With increase of alkali concentration or reaction temperature, there would be dehydrofluorination accompanied with oxidation reaction whereby some –C=C– converted to hydroxyl groups. Finally, the mechanism of reaction was also deduced.

Electron-induced reactive processing (EIReP) is a sustainable and energy effective processing technology to modify polymeric materials in the molten state by its spatial and temporal precise energy input. In the present research, the influence of EIReP on nano-mechanical properties of polyamide 6 (PA6)/fluoroelastomer (FKM) blends (50/50 w/w) was successfully explored using advanced PeakForce quantitative nano-mechanical mapping (PF QNM) atomic force microscopy (AFM) technique. In addition, the influence of EIReP on long period of PA6 lamellae and its crystallinity in the blends was studied using small- and wide-angle X-ray scattering (SAXS and WAXS). The AFM based DMT (Derjaguin-Muller-Toporov) moduli of the matrix phase (PA6) and the dispersed phase (FKM) were found to increase, whereas, adhesion force, dissipation energy and deformation of both phases decreased with increasing dose (12.5–25 kGy). Besides of the different crystallinity of PA6 in blends compared to pure PA6, WAXS experiments have demonstrated that the unit cell dimension c-axis of PA6 was sensitive to the melt blending and EIReP. SAXS provided information about the lamellar morphology of the blend component PA6. Variations in the long period of the PA6 lamellae could be assigned to parameters of melt blending and EIReP (dose) and were correlated with the interaction parameter of the phase components and the crystallinity of the blends. PF QNM AFM and X-ray scattering studies established the relationship between the nanoscale phase structure and properties of EIReP modified rubber-plastic blends.

We report our study of stress relaxation of Viton™ A hexafluoropropylene-vinylidene fluoride co-polymer fluoroelastomer compressed 25% and irradiated at room temperature in air to nominal absorbed doses of 10 – 106 Gy with 1.17 and 1.33 MeV gammas from a cobalt-60 source. Our data show that the true stresses at room temperature in ring samples of Viton™ A fluoroelastomer compressed 25% decline slightly from 1014±93 kPa at zero dose to 996±115 kPa at a dose of 103 Gy, decrease to 967±98 kPa at 104 Gy and then drop sharply to 640±116 kPa at 105 Gy and 157±32 kPa at 106 Gy. We briefly discuss the implications of this data for the integrity of seals in high-radiation environments.

In this research, the novel nano-filled fluoroelastomer (FKM) composites with excellent thermal and mechanical properties were prepared using the Siligraphene (graphene-like SiC), g-C3N4, and Siligraphene/g-C3N4 composites to improve the thermal and mechanical stability of FKM. The nanocomposites were exposed to heat aging test and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), dynamic mechanical analysis (DMA), and tensile test. Results show that Siligraphene, g-C3N4, and Siligraphene/g-C3N4 improved the tensile properties of FKM before and after exposure to the aging test. Si and N dopants in the graphenic structure of Siligraphene and g-C3N4 nanofillers are the effective parameter to reinforce the properties of nanocomposites. In general, these nanofillers provided better adhesion with FKM matrix. It can be justified by a better distribution of filler and higher interaction between filler and FKM which form the cellulation structure that can improve the mechanical properties and prevent the rubber decomposition at high temperatures by resisting molecular mobility.

Vegetable oils are potential alternative lubricants for the twofold purpose of achieving good tribological properties while protecting the environment. However, any intended use of bio-lubricants in machinery requires of a previous study of their compatibility with the involved sealing materials. In particular, Jatropha oil (JO) is inexpensive and easy to obtain, which make it a good candidate to be used as bio-lubricant in machinery. In this work, a compatibility study of four commercial sealing elastomers, namely, fluoroelastomer (FKM), silicone rubber (VMQ), neoprene/chloroprene (CR), and ethylene-propylene-diene monomer (EPDM) with JO, engine mineral oil (EMO) and a blend of EMO and JO (80-20%) (B20), for the purpose of comparison, was conducted. The analyses include the basic measurements comprised in the ASTM-D471 and ASTM-D7216 methods, namely, changes in mass, volume, tensile and tear resistance and hardness. In addition, non-standard measurements of creep compliance, surface morphology and topography, and chemical composition were performed to achieve a deeper evaluation of the interaction of JO with the elastomers. In general, good compatibility was found regarding the standard methods for the four elastomers with JO, VMQ being the most compatible sealing material. However, FKM, CR and EPDM showed changes in the creep compliance modulus and surface morphology when in contact with the three lubricants, which may considerably affect their sealing performance and decrease their useful life. Overall, pure JO generated much less physical changes on the elastomers than EMO and B20, which can be ascribed to the concentrations of free fatty acids contained in JO.

This study evaluates the dehydrofluorination mechanism, structure and thermal stability of pure fluoroelastomer which was dissolved by organic solvent and reacted with different concentrations of KOH at 20 ∼ 60 °C. The sequence types and contents of double bonds and other oxygen-containing groups of samples were analyzed and investigated by Attenuated total reflectance/Fourier transform infrared (ATR-FTIR), 1H nuclear magnetic resonance (NMR), 19F-NMR spectroscopy and chemical titration method; thermal decomposition temperatures of samples were analyzed by thermogravimetric analysis (TGA). The results revealed that dehydrofluorination of fluoroelastomer would accompain with oxidation reaction whereby some double bonds conforming to Hofmann’s rule had been converted to hydroxyl groups, wherein the temperature and alkali concentration were the important factors. The double bonds generated in seven positions of molecular chains, sequence types were mainly conformed to Hofmann’s rule and Zaitsev’s rule supplemented. With the increase of reaction temperature and concentration of KOH, the thermal stability of fluoroelastomer decreased obviously since hydroxyl groups had a greater effect on it. Finally, the mechanism of reaction was also deduced.

OH-functionalized carbon nanotube (BCNT)-, carbon nanotube (CNT)-filled fluoroelastomer (FE) and unfilled-FE compounds were prepared (BCNT/FE, CNT/FE and FE). The oil based drilling mud (OBD mud) aging resistances of these elastomers were assessed by tests of AFM, weight gain, swelling and optical microscopy and EDX elemental analysis (to determine the elements of C, O, F, Si and Ca). The following results were obtained when the above mentioned test results for FE-OBD (OBD mud tested FE) were compared to those of FE: The roughness and average height of surface decreased considerably (approximately −42% and −37%, respectively). Defects appeared on the surface. The swelling was negative and significant (nearly −15.7%). The surface was full of cracks. A considerable amount of fluorine was lost from the surface (Wt%: 32.0%). The following results were obtained when the before mentioned test results for BCNT/FE-OBD and CNT/FE-OBD compared to those of BCNT/FE and CNT/FE respectively: The changes in AFM results were minor. There were no defects on the surfaces. The swelling was low (approximately 5.7% and 4.1%, respectively). There were no cracks on the surfaces. Nanocomposites did not lose fluorine from the surface (Wt%: roughly 10.3% and 7.3%, respectively). Therefore, BCNT/FE and CNT/FE are resistant to OBD mud and can be used as sealing rubbers (for example o-rings) in OBD drilling for oil and gas. In contrast the original FE compound cannot be used.

Graphene is one of the most promising fillers for functional nanocomposites due to its high strength, high conductivity and high specific surface area, etc. However, its poor interfacial compatibility makes it difficult to simultaneously satisfy high strength and low gas permeability of nanocomposites. Herein, we proposed a novel strategy to regulate interfacial adhesion by fluorine-hydrogen (F-H) polar interaction in the FKM composites. The F-H polar interactions effectively induce the graphene oxide (GO) interact with the chain of fluoroelastomer (FKM) in spatial arrangements on molecular-level, promoting the construction of interconnected GO network. Specifically, a 10-fold increase in tensile strength of FKM/GO-5 with the incorporation of 5 phr GO is realized compared with pure FKM, and the oxygen permeability of FKM/GO-5 decreases by 79%. At the same filler contents, FKM/GO-5 composites exhibit higher mechanical property and lower gas permeability compared with FKM/rGO composites. Such enhanced performances make FKM/GO composites with an interconnected network very competitive for potential applications as multi-functional structural materials. The proposed strategy provides a novel effective approach for developing and designing the high-performances fluorine-based polymer nanocomposites.

The mechanical response of fluoroelastomer F2314 under uniaxial extension and its relation with strain-induced structural change are investigated by mechanical analysis, in-situ small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). Yielding of samples followed by strain hardening is found without necking. Meanwhile, the strain range of strain softening is short, which is 0.77 at 25 °C and 0.3 at 60 °C. Microscopically, solution-cast F2314 shows microphase separation and low crystallinity. Results of WAXS and SAXS indicate strain-induced formation of fibrillar crystal during strain hardening. Based on these findings, it is supposed that the fast relay between destruction of microphase separated domains and formation of fibrillar crystal is the origin of the unique mechanical response.

Fluoroelastomer (FKM)/montmorillonite (MMT) nanocomposites were prepared by fast evaporation mixing and melting mixing, respectively. The mechanical properties and curing behaviors of the nanocomposites prepared by the two methods were compared. The nanocomposites were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), rubber processing analysis (RPA), thermal gravity analysis (TGA) and dynamic mechanical analysis (DMA). The results indicate that the nanocomposites that were prepared by fast evaporation mixing show better mechanical properties than those prepared by melting mixing according to the increase of the MMT contents from 0.5 to 2.5 phr. When the MMT content was 2.5 phr, exfoliated MMT platelets were found to disperse uniformly in the FKM matrix and the nanocomposites possessed a higher tanδ max and weaker Payne effect. By contrast, some aggregated MMT appeared in the matrix by melting mixing, which led to a lower tanδ max and stronger Payne effect. Therefore, fast evaporation mixing is an eco-friendly and simple processing technology that can be used to realize a good dispersion of nano-fillers in a rubber matrix.

The energy storage system (ESS) is widely investigated because it can solve various energy-related problems without additional power plants. Among the ESSs, a vanadium redox flow battery (VRFB) is one of the most promising technologies due to its scalability without explosiveness. The bipolar plate is a multifunctional component that provides an electrical path and separates cells. A bipolar plate should simultaneously have low electrical resistance, high mechanical properties and chemical durability. In this study, a nano carbon/fluoroelastomer composite bipolar plate was developed to substitute for the conventional thick graphite bipolar plate. The ‘soft-layer method’ was adopted to expose the carbon fibers on the surface of the composite to increase its electrical conductivity. The solution casting method was applied to fabricate the high fiber volume fraction composite structure with a dispersion of carbon black. The performance of the carbon/fluoroelastomer composite bipolar plate was evaluated by testing the permeability, mechanical properties, and electrical properties. Finally, unit-cell charge/discharge tests were conducted to verify the performance of the composite bipolar plate.

Computer simulation could be a useful technique to scrutinize the properties of individual polymers as well as their blends. However, there is no work on computer simulation of thermoplastic elastomer from rubber-plastic blends. As representative example, binary compatibility of polyamide 6 (PA6) with fluoroelastomer (FKM) for a 40/60 composition of PA6/FKM thermoplastic elastomer was investigated by atomistic simulation and mesoscale dissipative particle dynamics simulation. The specific volume of PA6, FKM and their blend was studied at various temperatures to estimate the glass-rubber transition. The glass transition temperatures of pristine PA6 and FKM were found to be 336 K and 250 K respectively in line with the experimental values. The blend system displayed two distinct glass transition temperatures (348 K and 254 K for PA6 40FKM 60) as discerned from atomistic simulation. These values were also in agreement with the experimental findings. Two T g s described immiscibility in the present composition. The Flory-Huggins interaction parameter χ, as determined from atomistic simulation, was estimated to be 0.25, also consistent with the experimental result. Among different potential energy contributions, van der Waals energy and torsion energy showed distinct inflection points for both the pristine polymers and their blend. These inflection points were near the glass transition temperature of the respective polymers. Polymer chain mobility depicted from the mean square displacement emphasized faster relaxation of PA6 over FKM in the blend. Dissipative particle dynamics (mesoscale) simulation suggested phase separation and dispersion of FKM in the PA6 matrix in line with the experimental results.

Diamond-like carbon (DLC) coatings are deposited by a hybrid process involving plasma-assisted chemical vapor deposition (PACVD) and pulsed direct-current (DC) magnetron sputtering on three different elastomer substrates, namely, nitrile butadiene rubber (NBR), fluoroelastomer (FKM) and thermoplastic polyurethane (TPU), under self-biased conditions. These DLC coatings and the corresponding elastomer substrates are characterized using confocal optical microscopy, scanning electron microscopy, atomic force microscopy and a contact angle goniometer. Tribological tests are performed using ball-on-disc configuration at a fixed load of 1 N under ambient conditions. Friction reduction after deposition of DLC coatings is highly effective in NBR (56.4%), followed by that in FKM (49.8%) and TPU (28.8%) substrates. Best wear resistance was shown by DLC-coated FKM, which was followed by DLC-coated NBR and TPU. Transfer film formation is believed to be the main tribological mechanism favoring better frictional properties of DLC-coated elastomers. This study elucidates the possible reasons for the differing frictional and wear performance of the three different DLC-coated elastomers under consideration.

The stack of a vanadium redox flow battery (VRFB), which is a promising energy storage system (ESS), is composed of flow frames (FFs), carbon felt electrodes, bipolar plates (BPs) and membranes. The components of VRFB are assembled and compacted using flat gaskets or O-rings to seal the highly concentrated vanadium sulfuric electrolyte. The reliable sealing of the stack is a crucial issue because the highly concentrated sulfuric acid will damage the system when it leaks. In this work, a gasket-less FF composed of fluoroelastomer/glass fiber composite was developed to prevent leakage without using gaskets or O-rings. The fluoroelastomer layer, which has high chemical stability under an acidic environment, was formed at the surface of the composite, which worked as a sealant of the FF owing to its resilience. Glass fiber reinforcement into the matrix was employed to provide mechanical properties for use as a flow frame structure under the compaction pressure. The surface treatment and fabrication methods for the fluoroelastomer/glass fiber composite were developed. Based on the measured mechanical properties and sealability test of the composite with respect to the curing conditions, the zero-leakage compaction pressure for the gasket-less FF was investigated.

The chemical aging behavior of gaskets especially the chemical stability is crucial to the overall performance of PEMFC stack. The chemical stability of gaskets not only depends on the polymer but also heavily depends on the other ingredients. In this paper, we have studied the properties of fluoroelastomer with different amount of the cure agent, acid-acceptor and filler in the simulated PEMFC environment. The weight and volume change of samples was monitored. The surface conditions of the virgin and aged samples were observed using optical microscopy. Leachants in the soaking solution were detected using atomic emission spectrometry. ATR-FTIR was employed to determine the chemical change of samples. These results show that FKM cured with bisphenol system has the best comprehensive properties when the amount of bisphenol AF is set as 2.5 phr and the amount of Ca(OH) 2 is 6 phr. The inert filler BaSO 4 is not suitable for FKM because it has inferior effect on the compression resistance and chemical stability of FKM in this system.

The tensile relaxation modulus of Viton A fluoroelastomers is calculated from the stress-strain response for different strain rates and temperatures using non-equilibrium molecular dynamics simulations. The calculated relaxation modulus is superimposed onto a master curve and compared with the experimentally measured relaxation modulus obtained using dynamical mechanical analysis. Comparison is also made with relaxation modulus calculated from equilibrium molecular dynamics simulation via the Green-Kubo relation and with analytical value of the glassy modulus calculated on the basis of a molecular lattice. Excellent correlation with experimental results is observed at times corresponding to the onset of the glass transition. The simulations capture β-relaxation that is compatible with Arrhenius theory at the onset of the glass transition and at the transition to α-relaxation. The proposed method is time efficient and in most cases more accurately reproduces the experimental behavior compared with the Green-Kubo relation.

Single-walled carbon nanotube (SWCNT) has attracted considerable attention as a promising semiconducting material due to its high field-effect mobility, high current-carrying capability, and superior mechanical durability. However, SWCNT-based thin-film transistors (SWCNT-TFTs) generally show insufficient electrical reliability in terms of the drain-current hysteresis and threshold voltage shift under the bias stress. To facilitate the great advantages of SWCNT in commercial electronic devices, strategies are required for enhancing the electrical reliability of SWCNT-TFTs without compromising their mechanical flexibility. In this work, we demonstrate solution-processed, hysteresis-free, and bias-stable SWCNT-TFTs encapsulated with elastomeric poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) using a lamination method. The dipolar nature of e-PVDF-HFP suppresses the charge trapping, resulting in elimination of hysteresis as well as enhancement of field-effect mobility and subthreshold slope. The bias instability under the negative gate bias stress is also alleviated because the hydrophobic encapsulation layer can exclude physisorbed water/oxygen molecules on the hydrophilic surface. Besides, our solvent-free lamination method effectively prevents the potential damages of the active and electrode layers from the use of the solvents. The proposed encapsulation method with laminating the e-PVDF-HFP film can provide a possibility for realization of wearable applications based on highly reliable solution-processed SWCNT-TFT.

In previous works, we have developed cantilever-type MEMS tactile sensors with the PDMS elastomer that are sensitive to force and light and demonstrated that it can detect complex tactile senses including normal and shear forces, proximity, and temperature. However, it is difficult for this sensor to detect correct response in liquid such as water or ethanol because of luck of resistances to these solutions. In this work, we have newly employed the fluoroelastomer as the elastomer material instead of the PDMS. It is demonstrated that fabricated tactile sensor using fluoropolymer can detect force and light successfully in water, ethanol, and NaClO aqueous solution exactly as detection in air. Therefore, this sensor becomes available for uses in various environment or with cleaning and disinfection processes.

Dynamic vulcanization characteristics of fluoroelastomer during simultaneous mixing with a plastic, polyamide 6, for thermoplastic elastomeric compositions were analyzed in terms of induction time, scorch time, optimum cure and dynamic cure rate for the first time to understand their processing behavior. Also, a new derivative torque vs. time plot was proposed to gain insight into dynamic curing behavior of the rubber. Evolution of morphology and properties during different stages of mixing and dynamic vulcanization was captured. Size of the dispersed rubber phase decreased from ∼450 to ∼130 nm with increasing degree of cure and mixing time. Interestingly, it was revealed for the first time the role of injection molding in transforming the morphology and hence properties of such vulcanizates drastically. Nanometer-sized rubber particles (60–80 nm) were generated in thermoplastic vulcanizates (TPVs) after injection molding, which were clearly reflected from field emission scanning electron microscopy and atomic force microscopy and also theoretically predicted from the critical breakup law of viscoelastic droplets in a matrix. Significant improvement of tensile properties was recorded during dynamic vulcanization and also after injection molding of the samples. Tensile strength and Young's modulus of a TPV were 34.5 MPa and 200 MPa respectively as compared to 26.5 MPa and 92 MPa for the specimen before injection molding.

Development of new elastomers with novel functionality has continued since their discovery in order to meet industrial and defense needs in harsh environments. The recent advance of carbon nanomaterials inspired innovative material design strategies and enable more effective production of high-performance elastomers. In this paper, the free radical initiated crosslinking reaction in graphene/fluoroelastomer nanocomposites was studied and the effects of chemical functionalization of graphene nanosheets were analyzed. It indicated that graphene oxide (GO) enhanced fluoroelastomer nanocomposites demonstrated poor high-temperature stability due to the pyrolysis at around 200 °C. In contrast, reduced graphene oxide (RGO) enhanced fluoroelastomer exhibited good thermal stability, but RGO didn't participate in the crosslinking, resulting in very limited improvement in mechanical properties. In this paper, reduced allyl functionalized graphene was studied for the first time to enhance free radical initiated elastomers. The reduced allyl functionalization of graphene was demonstrated to impart superior thermal stability and enhanced mechanical properties to the elastomer matrices. The study of vulcanization kinetics provided insights that the allyl functional groups participated in and accelerated the crosslinking. These results indicated a scalable method to incorporate the advantages of graphene into polymer matrices through free radical reaction. The discovery is very promising to be used in the industry to fabricate gaskets, o-rings, and membranes for high temperature applications.

The surface modification of fluoroelastomer by using direct fluorination with fluorine gas was investigated. The results of X-ray photoelectron spectroscopy (XPS) indicate that a greater number of CF3, CF2 and CF groups are formed on the surface after fluorination and the photographs of both scanning electronic microscopy (SEM) and three-dimensional digital microscope reveal that the surface of fluoroelastomer becomes smoother and cleaner after fluorination. In addition, the surface energy of fluoroelastomer is decreased and more hydrophobic surface is explored after fluorination due to the more fluorine-contained chemical structures. However, the mechanical properties of fluorinated fluoroelastomer have not been changed apparently, while the friction coefficient is sharply decreased.

A new approach for depositing thin energetic films is introduced using doctor blade casting. Magnesium (Mg) and manganese dioxide (MnO 2 ) is mixed with a solvent that includes a binder and is blade cast onto a foil substrate. This study investigated the effect of binder chemistry and concentration on combustion behavior. The Mg–MnO 2 system was studied in the following binder–solvent systems: Polyvinylidene Fluoride (PVDF) – Methyl Pyrrolidone (NMP); Viton® fluoroelastomer (Viton A) – acetone; and, paraffin–xylene. Films were cast onto substrates to approximately 100 μm thickness. Calorific output and flame velocity were measured for varying binder concentration. Calorific output increased with increasing binder concentration, to a maximum of 4.0 kJ/g, suggesting participation of the binder in the exothermic reaction. Flame velocity decreased with increasing binder concentration, with a maximum of 0.14 m/s. Binders are less conductive than metals and metal oxides thereby hindering the energy propagation with increasing binder content. Confined flame propagation tests were also conducted for the NMP/Mg–MnO 2 –PVDF system, with a maximum recorded flame velocity of 3.5 m/s. High velocity imaging shows considerable differences in flame front, which may suggest a transition in propagation mechanism accounting for the observed increase in flame velocity.

Carbon nanotube (CNT) filled fluoroelastomer (FE) nanocomposites, were prepared and and their properties were compared with those of carbon black (CB) filled- or unfilled-FE. Dynamic mechanical analysis (DMA) and Differential Scanning Calorimetry (DSC) showed that the glass transition temperature ( T g ) of CNT/FE increased when compared to CB/FE or FE. For the CNT/FE and in comparison to others (in their glassy and rubbery states), the storage modulus is higher. However tan δ in the glassy state is lower, but higher in the rubbery state. The DSC and DMA results confirmed that the FE and filler/FE is partially crystalline. The results showed that the crystalline part of FE and CB/FE were mostly in the α-form. However, CNT together with shear and high temperature, induced γ-crystallinity in the FE. X-ray diffraction (XRD) results also confirmed the DSC and DMA results and showed that CNT caused an increase in the γ-crystallinity in FE and decreased α-phase crystallinity compared to others. XRD, DSC and DMA results for FE and filler/FE corroborated these observations.

Two-dimensional one-atom thick graphene inspires intensive studies due to its great potentials in enhancing polymer’s mechanical, gas/liquid barrier, and thermal properties. However, its poor dispersion within highly viscous rubber elastomers by conventional mill mixing posed significant technical challenges and hindered its vast applications. In this paper, graphene oxide (GO) enhanced fluoroelastomer (FKM) was solution-processed to enhance the mechanical and liquid barrier properties of FKM for the first time. Due to the chemical bonding, the GO/FKM performed 1.5-fold increment tensile strength compared with pure FKM and 1.2-fold increment tensile strength compared with Reduced Graphene Oxide/FKM at 150 °C. The reduced permeability of GO/FKM to organic solvent (such as methyl ethyl ketone) indicated the improved liquid barrier properties. This research provides a cost-effective solution process to efficiently enhance the thermal mechanical and liquid barrier properties of FKM with the addition of GO sheets through excellent dispersion techniques and strong GO-matrix bonding.

Novel polyamide 6 (PA6)/fluoroelastomer nanostructured thermoplastic elastomeric blends were developed in the present work. The influence of interaction between the components and morphology on physical properties of the blends was analyzed. Scanning electron microscopy and atomic force microscopy studies, solubility and theoretical analysis of complex modulus clearly indicated that PA6 was the continuous matrix in which fluorocarbon elastomer was present in nanoscale. Low torque ratio (0.34) of rubber/plastic, high mixing speed and long mixing time had an important role in developing the nanostructured morphology of the blend. Tensile strength of the thermoplastic elastomer was about 39.0 MPa which was much higher than that reported earlier and showed significant improvement with increasing PA6 content. Large shifting of the glass transition temperature of the rubber and the plastic phases towards the lower temperature compared to those pristine polymers was also observed. The above properties were explained with the help of interaction between the components and morphology.

Authors believe that two aspects of this manuscript will make it interesting to general readers of the journal “Materials & Design”. First, in this manuscript we report for the first time that a new fluorine-contained thermoplastic vulcanizate (TPV) was successfully prepared through dynamic vulcanization. Our results indicated that the dispersion of FKM particles in PVDF matrix and the mechanical properties of TPVs were significantly improved after dynamic vulcanization. The tensile strength of PVDF/FKM (50/50) blends increased from 16.2 to 33.5 MPa, by about 107%; while elongation at break increased from 125.6% to 468.9%, by 2.7 times after dynamic vulcanization. Second, it was found that the solvent resistant properties of the prepared TPVs are better than the traditional compression molded FKM vulcanizates. The approach proposed here provides a viable technological alternative for the cost-effective preparation of fluorine-contained TPVs with superior properties to substitute present FKM vulcanizates which are difficult to recycle.

The incompatibility and immiscibility of natural rubber (NR)/fluoroelastomers (FKM) blends were improved by incorporation of a graft copolymer synthesized from the free radical graft copolymerization of 2,2,2-trifluoroethyl methacrylate (TFEM) onto NR initiated by benzoyl peroxide via a melt-mixing process. The grafting properties were investigated as functions of the initiator and monomer concentrations, reaction temperature and time. At the optimal conditions, the obtained graft NR (GNR) purified by Soxhlet extraction contained a maximum grafting efficiency of 1.34% with 49.1% monomer conversion. The structure of the purified GNR was analyzed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy ( 1 H NMR and 19 F NMR). The gross GNR was then applied as the compatibilizer for NR/FKM vulcanizates (20/80 (w/w)) cured by peroxide vulcanization. The addition of GNR at 15 parts per hundred of rubber (phr) gave a vulcanizate with the highest tensile strength (9.93 MPa), some 5.31-fold higher than that of the incompatibilized one (1.87 MPa). This is likely to be due to the higher degree of homogeneity of the constituent phases in the GNR-compatibilized blends, as observed by scanning electron microscopy (SEM). The GNR-compatibilized NR/FKM vulcanizates were also resistant to gasohol E85 (85% (w/w) of ethanol).

A fluorinated elastomeric material with enhanced hydrophobic properties has been studied as a protective coating on Lecce stone. The polymer has been applied, as a butyl acetate solution, on stone specimens according to two different methodologies, i.e. brushing and capillary absorption. The application performed by brush (amounts equal or greater than 50 g/m 2 ) induces the formation of a superficial film, which prevents condensed water from penetrating but, at the same time, considerably reduces the vapour permeability. On the contrary, when the fluoroelastomer solution is applied by the capillary absorption technique (amounts in the 25–75 g/m 2 range), reduction of vapour permeability is acceptable but a poor protection against water penetration is observed. It can be due to a deeper penetration of the polymeric material, which is more homogeneously dispersed in the stone without forming a hydrophobic coating on the surface.

Stress-elongation behavior of a Viton A-401C based compound established for backup seals of 500 MW(e), Prototype Fast Breeder Reactor is depicted. Stress-softening effects are negligible during room temperature (RT) or 110 °C measurements on unaged samples at strain rates of 50 mm/min and 500 mm/min because of low filler content. Relaxation is observed during RT property determination at lower strain rate. Stiffening of behavior at 50 mm/min and 110 °C is attributed to Joule-Gough effect and absence of relaxation because of increased molecular chain mobility. The two zone stress-elongation behavior (determined by chemical cross-links up to ∼85% strain and by ionic interactions beyond) propounded in the article by combining air-aged specimen data (32 weeks at 140/170/200 °C) provides a behavior map of bisphenol cured, low filler, fluoroelastomers made of vinylidene fluoride and hexafluoropropylene. This could be extended to peroxide cured fluorocarbon rubbers for verifications and providing qualified compounds of better grades for critical nuclear elastomeric sealing applications.

Breakthrough pressure is an important parameter associated with the performance of water-resistant fabrics. Hydrostatic testing has been utilized to experimentally determine the breakthrough pressure of commercial cotton fabrics treated with various combinations of octakis (1H,1H,2H,2H-perfluorodecyl) polyhedral oligomeric silsesquioxane (F-POSS), a compound with the lowest reported solid surface energy, and the commercial fluoroelastomer, Tecnoflon ® . The breakthrough pressure values (amounting to a few inches of water) were found to be similar to predicted values based on the geometry of the samples and the surface energy of the components. The theoretical predictions, however, do not explain all differences observed among samples, such as the fact that a single dip coating with both F-POSS and Tecnoflon ® produced a higher breakthrough pressure than a single dip coating in either F-POSS or Tecnoflon ® , or sequential dip coating (in either order) of the two components. SEM analysis of the coated fabrics indicated that coatings were conformal at the microscale, but did result in sub-micron scale roughness. Although this roughness may help to increase the contact angles with water, the breakthrough pressure appeared to be primarily determined by the geometry of the individual filaments.

Hexa fluoropropylene–vinylidinefluoride dipolymer, fluoroelastomer (FKM) and ethylene propylene diene rubber (EPDM) blends with and without compatibilizer (MA-g-EPDM) were prepared by two-roll mill mixing. The effects of blend ratio and amount of compatibilizer on mechanical properties and thermal stability were investigated. The cure characteristics and mechanical properties of EPDM, FKM and their blends of varying compositions were studied for unaged and aged samples. The 50:50 (w/w) FKM/EPDM showed highest mechanical properties. The tensile properties of all the composites, especially those with higher proportion of FKM increased with aging. Swelling of the blends was reduced after aging. The thermal stability of FKM/EPDM rubber blends was studied using thermogravimetric analysis (TGA). The incorporation of FKM rubber improved the thermal stability of EPDM rubber. The apparent degradation activation energy (E) of EPDM/FKM reactive blends was calculated by the Coats–Redfern method. The results showed that the EPDM/FKM reactive blends had higher thermal stability but lower E than FKM. The thermal degradation process of both EPDM/FKM reactive blends and FKM were determined by nucleation and growth mechanism. The differential scanning calorimetry (DSC) results suggest that glass transition temperature (Tg) peak for EPDM region is shifted to FKM phase, due to improved compatibility on addition of compatibilizer. The morphology of blends was investigated using scanning electron microscopy (SEM).

Design optimization of static, fluoroelastomer backup seals for the 500 MWe, Prototype Fast Breeder Reactor (PFBR) is depicted. 14 geometric variations of a solid trapezoidal cross-section were studied by finite element analysis (FEA) to arrive at a design with hollowness and double o-ring contours on the sealing face. The seal design with squeeze of 5 mm assures failsafe operation for at least 10 years under a differential pressure of 25 kPa and ageing influences of fluid (air), temperature (110 °C) and γ radiation (23 mGy/h) in reactor. Hybrid elements of 1 mm length, regular integration, Mooney–Rivlin material model and Poisson’s ratio of 0.493 were used in axisymmetric analysis scheme. Possible effects of reduced fluoroelastomer strength at 110 °C, ageing, friction, tolerances in reactor scale, testing conditions during FEA data generation and batch-to-batch/production variations in seal material were considered to ensure adequate safety margin at the end of design life. The safety margin and numerical prediction accuracy could be improved further by using properties of specimens extracted from seal. The approach is applicable to other low pressure, moderate temperature elastomeric sealing applications of PFBR, mostly operating under maximum strain of 50%.

A novel kind of fluoroelastomer nanocomposites based on tube-like halloysite clay mineral were successfully prepared using a bis-phenol curing system, which resulted in prominent improvements in mechanical and dynamic mechanical properties and in the elevation as high as 30 K of the thermal decomposition temperature. Wide-angle X-ray scattering and transmission electron microscopy techniques were employed to assess the morphology developed in the nanocomposites, while stress strain diagrams were used to evaluate the mechanical properties. These nanocomposites were further characterized by moving die rheometer, dynamic mechanical properties and thermo-gravimetric analysis. Structure-properties relationship and the improvement of the mechanical, dynamic mechanical and thermal properties of fluoroelastomers are reported in the present study. Increasing amount of the filler reduced the curing efficiency of the bis-phenol curing system, which was evident from the rheometric and physical properties of the resulting composites. A sort of filler–filler interaction was perceived during the strain sweep analysis of the composites. The polymer–filler interaction was reflected in the improved mechanical and thermal properties which were the consequence of proper dispersion of the nanotubes in the polymer matrix; whereas the intercalation of macromolecular chains into the nanotubes was not reflected in the X-ray diffraction analysis.

The feasibility of producing thin-walled fluoroelastomer profiles under continuous, atmospheric-pressure vulcanization conditions in air has been demonstrated by successful manufacture of ∼2 m diameter test inflatable seals for the 500 MWe, Prototype Fast Breeder Reactor (PFBR) using a 50/50 blend formulation of Viton ® GBL-200S/600S based on advanced polymer architecture (APA). A commercial cold feed screw extruder with 90 mm diameter screw was used along with continuous cure by microwave (2.45 GHz) and hot air heating (190 °C) at a line speed of 1 m/min to produce the seals. The blend formulation promises significant improvement in the performance and safety of the seals. This article depicts the relevant characteristics of the original inflatable seal compound that was used as reference to achieve the objectives through synchronized optimization of material and production technologies. The production trials are outlined and the blend formulation used with minor factory modifications to produce the test seals is reported. Progressive refinements of the original, Viton ® A-401C based compound to the blend formulation is presented along with an assessment of potential performance gains. Possible uses of the reported formulation and production technique for other large diameter, high temperature seals of PFBR are indicated along with the envisaged activities en-route the production of perfected reactor inflatable seals.

Membranes were prepared by casting a solution of a polymer and ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][TfO] or 1-ethylimidazolium trifluoromethanesulfonate [EIM][TfO] typical representatives of aprotic and protic ionic liquid and evaporating the solvent. The following polymers were used: Udel-type polysulfone, polybenzimidazole derivative containing benzofuranone moieties (PBI-O-Ph), poly(vinylidene fluoride -co -hexafluoropropene) (fluoroelastomer) and Nafion. Polymer–ionic liquid compatibility was investigated by swelling, scanning electron microscopy and differential scanning calorimetry. Membranes conductivities in anhydrous atmosphere depended on temperature, ionic liquid concentration in the membrane, and on the type of matrix polymer. No conductivity could be detected with polysulfone-based membranes due to the incompatibility of polysulfone and the two ionic liquids, low conductivities were found with PBI-O-Ph based membranes, the conductivities of the fully compatible systems based on fluoroelastomer or Nafion matrixes amounted to 40% of that of neat ionic liquids.

Polymer electrolyte membrane (PEM) fuel cell stack requires gaskets and seals in each cell to keep the hydrogen and air/oxygen within their respective regions. The stability of the gaskets/seals is critical to the operating life as well as the electrochemical performance of the fuel cell. Chemical degradation of five elastomeric gasket materials in a simulated and an aggressive accelerated fuel cell solution at PEM operating temperature for up to 63 weeks was investigated in this work. The five materials are copolymeric resin (CR), liquid silicone rubber (LSR), fluorosilicone rubber (FSR), ethylene propylene diene monomer rubber (EPDM), and fluoroelastomer copolymer (FKM). Using optical microscopy, topographical changes on the sample surface due to the acidic environment were revealed. Weight loss of the test samples was monitored. Atomic absorption spectrometer analysis was performed to study the silicon, calcium, and magnesium leachants from the materials into the soaking solution. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of the materials before and after exposure to the simulated fuel cell environment over time. Among the five materials studied, CR and LSR in the accelerated solution are not as stable as the other three materials. FSR appears to be the most stable.

Linear low density polyethylene (LLDPE) can suffer from melt extrusion defects including sharkskin, cyclic melt fracture, and gross melt fracture during processing. Arborescent polymers are dendritic macromolecules with characteristics, such as a compact structure and a rigid spherical topology, making them potentially useful as polymer processing additives (PPA) to alleviate melt extrusion defects. Arborescent polystyrene- graft- polyisoprene copolymer samples were synthesized from polystyrene substrates of linear and branched architectures functionalized with acetyl groups, and coupled with polyisoprene macroanions. A linear polyisoprene sample was also investigated for comparison. The polymers were hydrosilylated with (tridecafluoro-1,1,2,2-tetrahydrooctyl)dimethylsilane on 17–52% of the isoprene units and blended with LLDPE at 0.1 and 0.5% w/w to evaluate their performance as PPA by extrusion at different shear rates. All the samples led to some degree of improvement in the extrusion of LLDPE, albeit the performance of the branched additives was inferior to a commercial fluoroelastomer PPA. The lower molecular weight and more compact (G0 or comb-branched) PPA generally performed better than those with a high molecular weight. Several PPA samples induced the early onset of cyclic melt fracture but glossy, defect-free surfaces were obtained at higher shear rates. This suggests that a minimum shear rate is required for these additives to coat the extrusion die under the experimental conditions used.

In this paper, the aging behavior of the reactive blends of fluoroelastomer (FPM) with poly-phenol hydroxy ethylene propylene diene monomer rubber (PHEPDM) in hot air was firstly investigated. The aging mechanism was analyzed by the swelling experiment, attenuated total-reflectance Fourier-transform infrared (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results showed that the aging process increased the crosslinking density and the content of double bond. The O/F or O/C ratios increased and then decreased during aging because of the oxidation reaction of molecular chain and the surface migration of fluoro group. Secondly, thermogravimetric analysis (TGA) was used to study the thermal degradation behavior of the reactive blends. The apparent degradation activation energy (E) of FPM/PHEPDM reactive blends was calculated by the Kissinger and Coats–Redfern methods, respectively. The results showed that the FPM/PHEPDM reactive blends had higher thermal degradation temperature but lower E than FPM. Both the thermal degradation process of FPM/PHEPDM reactive blends and FPM were determined by nucleation and growth mechanism (Am). The general mechanism function was [−ln(1 − α)]1/m. The optimum value of m was between 1/3 and 1/2 for FPM/PHEPDM reactive blends, but 1/2 for FPM. From the results above, it was deduced that the special structure of PHEPDM made itself surrounded by fluoroelastomer and protected from hot-air aging and thermal degradation.

Organo-montmorillonite (OMMT)/fluoroelastomer (FKM) nanocomposites were prepared by melt intercalation. The microstructure of these composites was characterized by TEM and XRD. The effect of OMMT on mechanical properties, thermal stability and solvent resistance of the nanocomposites were investigated. TEM and XRD showed that the FKM was intercalated into OMMT. When the OMMT content was lower than 12 wt.%, the nanocomposites showed excellent tensile properties, which was attributed to the nanometer scale dispersion and the higher aspect ratio of the clay mineral layers. The introduction of a small amount of OMMT also improved the thermal stability and solvent resistance, which was attributed to the gas barrier action of the OMMT layers. Compared to pure FKM, the nanocomposites exhibited a higher glass transition temperature and lower tanδ peak value.

The elastomeric materials used as seals/gaskets in Polymer Electrolyte Membrane (PEM) fuel cells are exposed to acidic environment, humid air and hydrogen, and subjected to mechanical compressive load. Both sealing and electrochemical performance of the fuel cell depend heavily on the long-term mechanical and chemical stability of these materials. In this paper, mechanical property degradation of two elastomeric materials, Fluoroelastomer and EPDM, which are being considered as gasket materials for PEM fuel cells, was investigated using microindentation. Test samples were subjected to various compressive loads to simulate the actual loading in addition to soaking in a simulated PEM fuel cell environment. Two temperatures, based on actual fuel cell operation, 80 and 60 °C, were selected in this study. Mechanical properties of the samples before and after exposure to the environment were assessed. Hysteresis loss energy, indentation load, elastic modulus and hardness were obtained from the loading and unloading curves. Indentation deformation was studied using Hertz contact model. It was found that the mechanical properties of the Fluoroelastomer samples changed significantly after exposure to the simulated environment over time. The exposure medium, temperature and applied compressive load contributed to the degradation of the material. On the other hand, the change of mechanical properties for the EPDM samples was not apparent. It is concluded that EPDM is much more stable than Fluoroelastomer for PEM seal applications.

Biodiesel was prepared from palm oil by transesterification with methanol in the presence of 1.5%K loaded–calcined Mg-Al hydrotalcite. Fatty acid methyl esters content of 96.9% and methyl ester yield of 86.6% were achieved using a 30:1 methanol to oil molar ratio at 100 °C for 6 h and 7 wt% catalyst. The biodiesel was characterized and its impact on elastomer properties was evaluated. The compatibility of B10 diesel blend (10% biodiesel) with six types of elastomers commonly found in fuel systems (NBR, HNBR, NBR/PVC, acrylic rubber, co-polymer FKM, and terpolymer FKM) were investigated. The physical properties of elastomers after immersion in tested fuels (for 22, 670, and 1008 h at 100 °C) were measured according to American Society of Testing and Materials (ASTM). These include swelling (mass change and volume change), hardness, tensile and elongation, as well as the dynamic mechanical property. The results showed that properties of NBR, NBR/PVC and acrylic rubber were affected more than other elastomers. This is due to the absorption and dissolving of biodiesel by rubber in these samples. Co-polymer FKM and terpolymer FKM which are fluoroelastomers show little property change.

High temperature degradation of a fluoroelastomer and its nanocomposites was carried out from room temperature to 700 °C using thermogravimetric analysis (TGA) in nitrogen and oxygen atmospheres. The presence of the unmodified nanoclay enhanced the onset of degradation in both the environments, because of polymer–filler interaction, exfoliation, uniform dispersion and high thermal stability of the layered silicates. In the derivative curve, there was a single T max , indicating one-stage degradation for all the samples. The non-isothermal activation energy of degradation was determined using the Kissinger and the Flynn–Wall–Ozawa methods. The nanocomposites showed higher activation energy than the neat elastomer. The activation energy of degradation, as observed by isothermal kinetics, was 165, 168 and 177 kJ mol −1 for the neat elastomer, modified and unmodified clay filled samples, respectively. Intrinsic viscosity, measured after low temperature ageing (125–175 °C) showed that the viscosity values were higher for the nanocomposites. The mechanism of degradation is discussed.