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Fluoroelastomers (FKM) are used to manufacture seals and other rubber devices that can withstand harsh operating conditions, including aggressive media and extreme low and high temperatures. Even though nuclear magnetic resonance, Fourier-transform infrared spectroscopy (FTIR), and chromatographic techniques have been extensively used in the characterization of raw FKM molecules, the identification of cured compounds entails a characterization method that is able to overcome the complexity related to this kind of structure. In this sense, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy can outperform other characterization techniques because it does not require solubilization or any special preparation of the sample. In this study, 10 FKM compounds were produced in this study utilizing four commercial types of FKM and the fillers carbon black, barium sulfate, and iron oxide. All unfilled-FKM (as received) and their compounds were analyzed by ATR-FTIR with germanium crystal. Between 15 and 25 analyses were performed for all each FKM type sample and their respective compounds. All spectra were analyzed, and the bands were assigned. Findings regarding the interference of the fillers in the spectra were also reported. From relationships between the height of the spectral zones and the bands at 1397 and 1428 cm−1, it was possible to distinguish all sample compositions of FKM types 1, 2, 3, and 5. This study demonstrates that ATR-FTIR has the potential to be utilized as a technique to detect the type of FKM compounds, an important rubber used in harsh industrial applications. Replacing carbon with BaSO4 reduces the tensile at 50% strain of FKM types 1 and 2 composites. FKM types 3 and 5 composites filled with 30 phr of carbon black have a higher tensile at 50% strain than those of FKM type 1. [ABSTRACT FROM AUTHOR]

Non-linear rheological behaviours of high fluorine content fluoroelastomer (HF-FKM) mixtures with varied carbon black (CB) filling amounts were investigated. Non-linear viscoelastic characteristics of HF-FKM mixture are characterised by large amplitude oscillatory shear (LAOS) tests, correlations between rheological behaviour and CB content were then discussed. Each non-linear viscoelastic parameter of HF-FKM mixture presents a three-stage characteristic with increasing CB content, corresponding to ranges of 0–20 phr, 25–30 phr, and 35–45 phr. Three stages of viscoelasticity characteristics for HF-FKM mixtures were considered to depend on the alteration of CB-elastomer network structure with increasing CB content, corresponding to the states where continuous phase of gum, CB-elastomer mesophase and excessive CB agglomerates predominate in mixture compound, respectively. After vulcanisation, samples with 30 phr CB content show the best resilience performance against thermal ageing, contributing to the existence of CB-elastomer mesophase. Samples with 25 phr CB content possess the second lowest compression sets at 225 and 250 °C ageing conditions but perform no better than those with 35 phr at 275 °C. The reason is presumed to be that the presence of excessive CB agglomerates in HF-FKM vulcanisate reduced irreversible deformation of the CB-elastomer network under compression at elevated temperatures. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) nanoparticles have been used at different concentrations (1–5 wt%) to prepare fluoroelastomer (FKM) nanocomposites. The physico-mechanical features of FKM nanocomposites exhibit an increase in tensile strength, modulus, hardness and elongation at break decrease with increasing concentration of GO nanoparticles. This is due to the good distribution of GO in FKM rubber. The effect of GO concentration on dielectric performances which includes dielectric loss tangent (tan δ), real impedance, imaginary impedance and electrical conductivity were studied as a function of frequency range 10−2 –105 Hz. The intensity of tan δ peak of FKM nanocomposites has a gradual decrease with frequency as well as their peaks also shifts toward lower frequency region. Variation in spectra of real impedance reveal decreasing behavior with frequency and imaginary impedance characterizes the properties like diminished peak intensity for GO/FKM nanocomposites. The Nyquist plots show good semicircles that exhibit polarity with a single relaxation time. The extent of the GO concentration has a significant impact on the dielectric permittivity of the nanocomposites. Using the percolation theory, it has been determined how frequency affects electrical conductivity. The percolation phenomenon has been discussed using electrical conductivity of GO/FKM nanocomposites and found at 4 wt% GO concentration. [ABSTRACT FROM AUTHOR]

Due to their excellent chemical stability, fluoroelastomers have been widely used in various severe circumstances since birth. At present, carbon blacks and inorganic fillers are the two most prominent reinforcing agents in fluoroelastomers. However, despite the rise of silica in the rubber industry, it is still difficult to apply this non‐carbon filler alone as a reinforcing agent in fluoroelastomer. Research on the interaction between silica and fluoroelastomer is even less and not systematical. Based on the above, we analyzed the interaction between silica and fluoroelastomer under different conditions through x‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared spectroscopy, bound rubber (BR) content analysis and rheological properties, and so forth. The interaction between fluoroelastomer and silica can be characterized by the binding energy variation at different temperatures (especially 260°C the new peak at about 685 eV) and wavenumber shift of Si–OH and Si–O–Si in XPS and infrared (IR) analysis, respectively. The BR content varied with loading, temperature, and atmosphere, reflecting the strength of the interaction from a macro perspective. The evolution of the rheological curves of different recipes and test conditions correlate closely with the results of XPS, IR, and BR content analysis, which also shows the sensitive response of polymer‐filler interaction to temperature and load. The observation results of transmission electron microscopy (TEM) directly demonstrate the differences in the dispersion of fillers at different temperatures. The proposed mechanism of fluoroelastomer–silica interaction mode will provide us with novel approaches to the applications of silica in the fluorine industry. Highlights: X‐ray photoelectron spectroscopy analysis indicates new fluorine species on the interfaces.Infrared and bound rubber tests verify the fluoroelastomer–silica interactions.Rheological curves reflect the interaction strength. [ABSTRACT FROM AUTHOR]

The mineralization of fluoroelastomers (FKMs) in superheated water in the presence of potassium hydroxide (KOH) was investigated with the aim of developing a methodology for recycling the fluorine element. Two FKMs—an "uncrosslinked FKM", representing a poly(vinylidene fluoride-co-hexafluoropropylene) (poly(VDF-co-HFP)) copolymer with a VDF/HFP molar ratio of 78/22 and a "crosslinked FKM" consisting of this copolymer (cured by peroxide) and carbon black—were treated. The fluorine content of these FKMs was efficiently transformed into F− ions in the reaction solution using low KOH concentrations (0.10–0.50 M) at 200–250 °C. When the uncrosslinked or crosslinked FKMs reacted with aqueous KOH (0.20 M) at a rather low temperature (200 °C) for 18 h, the fluorine content of these FKMs was completely mineralized (both F− yields were 100%). Although the crosslinked FKM contained carbon black, the fluorine mineralization of the FKM was not inhibited. The addition of Ca(OH)2 to the reaction solutions after the superheated water treatment at 250 °C for 6 h with aqueous KOH (0.50 M) led to the production of pure CaF2, identified using X-ray spectroscopy, with 100% and 93% yields for the uncrosslinked and crosslinked FKMs, respectively. [ABSTRACT FROM AUTHOR]

It has been shown that defect-free Stone–Wales (SW) free few-layer graphene (FLG) can be obtained by carbonizing lignin under conditions of self-propagating high-temperature synthesis (SHS). The obtained few-layer graphene was used as a modifying additive for pyrotechnic compositions. It was found that the addition of 2.5 mass % of few-layer graphene synthesized from lignin to a pyrotechnic complex based on porous silicon and fluoropolymer leads to a significant increase in the combustion intensity of pyrotechnic compositions.

Polymers for implantable devices are desirable for biomedical engineering applications. This study introduces a water-resistant, self-healing fluoroelastomer (SHFE) as an encapsulation material for antennas. The SHFE exhibits a tissue-like modulus (approximately 0.4 MPa), stretchability (at least 450%, even after self-healing in an underwater environment), self-healability, and water resistance (WVTR result: 17.8610 g m−2 day−1). Further, the SHFE is self-healing in underwater environments via dipole–dipole interactions, such that devices can be protected from the penetration of biofluids and withstand external damage. With the combination of the SHFE and antennas designed to operate inside the body, we fabricated implantable, wireless antennas that can transmit information from inside the body to a reader coil that is outside. For antennas designed considering the dielectric constant, the uniformity of the encapsulation layer is crucial. A uniform and homogeneous interface is formed by simply overlapping two films. This study demonstrated the possibility of wireless communication in vivo through experiments on rodents for 4 weeks, maintaining the maximum communication distance (15 mm) without chemical or physical deformation in the SHFE layer. This study illustrates the applicability of fluoroelastomers in vivo and is expected to contribute to realizing the stable operation of high-performance implantable devices. [ABSTRACT FROM AUTHOR]

Fluoroelastomer nanocomposites have been prepared using different concentrations (1-5 wt%) of graphene oxide (GO) nanoparticles through mechanical mixing and compression molding. The surface morphology of prepared fluoroelastomer/GO nanocomposites has been studied by scanning electron microscopy (SEM). The mechanical properties of fluoroelastomer nanocomposites show increase in hardness, tensile strength, modulus, toughness and decrease in elongation at break with the increasing of GO's concentration. This can be attributed towards excellent distribution of GO nanoparticles in the fluoroelastomer matrix. The effect of GO nanoparticle concentration on rheological properties of fluoroelastomer nanocomposites like: loss factor, storage modulus, loss modulus and complex viscosity have been studied as a function of temperature (5-100°C) and at different frequency 1, 10, and 100 Hz. The non-linear relationship between storage and loss moduli have been observed through Cole-Cole plots of fluoroelastomer/GO nanocomposites. The linear relationship of loss factor and storage modulus plots was explained on the basis of fluoroelastomer/GO interactions. The visco-elastic properties show increase in loss modulus, storage modulus, complex viscosity and decrease in loss factor with GO concentration, which can be attributed towards better fluoroelastomer-nanoparticle interactions. [ABSTRACT FROM AUTHOR]

The molecular transport of a series of industrial solvent mixtures into O-rings of Viton fluoropolymers was studied. Sorption, diffusion, and permeation of the individual liquids toluene, cyclohexane, and methanol, and their binary and ternary mixtures, were evaluated from the solvent uptake using a gravimetric method. From the sorption results, the diffusion coefficients were calculated using Fick's equation. A numerical method was employed to calculate the liquid concentration profiles in cylinder-shaped polymers. The desorption mechanism was also evaluated. The composition dependence of sorption, diffusion, and permeation was assessed, and the results were analysed in terms of potential interactions between polymer and penetrant molecules. Observed sorption of methanol and methanol mixtures by the polymer was very high, in some cases higher than for pure liquids. In general, the amount of methanol present in the mixture determined its diffusion coefficient. Methanol showed the smallest solubility coefficient within the polymer, but due to its high mobility and permeability, it was shown to be the liquid that flows faster through Viton fluoropolymers. Flows of toluene and cyclohexane are still considerable, notwithstanding that this fluoropolymer is usually indicated as hydrocarbon resistant. This is an important fact to keep in mind when choosing sealings for applications with a mix of solvent media. [ABSTRACT FROM AUTHOR]

In this study, the effects of heat and radiation on the degradation behaviour of fluoroelastomer under simulated normal operation and a severe accident environment were investigated using sequential testing of gamma irradiation and thermal degradation. Tensile properties and Shore A hardness were measured, and thermogravimetric analysis was used to evaluate the degradation behaviour of fluoroelastomer. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the structural changes of the fluoroelastomer. Heat and radiation generated in nuclear power plant break and deform the chemical bonds, and fluoroelastomer exposed to these environments have decreased CH and functional groups that contain oxygen and double bonds such as CO, C=O and C=C were generated. These functional groups were formed by auto oxidation by reacting free radicals generated from the cleaved bond with oxygen in the atmosphere. In this auto oxidation reaction, crosslinks were generated where bonded to each other, and the mobility of molecules was decreased, and as a result, the fluoroelastomer was hardened. This hardening behaviour occurred more significantly in the severe accident environment than in the normal operation condition, and it was found that thermal stability decreased with the generation of unstable structures by crosslinking.

It has been shown that defect-free Stone–Wales (SW) free few-layer graphene (FLG) can be obtained by carbonizing lignin under conditions of self-propagating high-temperature synthesis (SHS). The obtained few-layer graphene was used as a modifying additive for pyrotechnic compositions. It was found that the addition of 2.5 mass % of few-layer graphene synthesized from lignin to a pyrotechnic complex based on porous silicon and fluoropolymer leads to a significant increase in the combustion intensity of pyrotechnic compositions. [ABSTRACT FROM AUTHOR]

Fluoroelastomer has received increasing attention for energetic materials application due to its high fluorine contents. Different contents (0 wt%–30 wt%) of poly(VDF‐ter‐HFP‐ter‐TFE) terpolymer are added into Al/MnO2 nanothermite. The peak exothermic temperature of thermite reaction for Al/MnO2 system is about 554°C with 1070 Jg−1 heat release. After adding terpolymer, it mainly exists in the gap among Al nanoparticles and MnO2 nanorods, and react with Al and MnO2 at the range of 350 to 540°C before the occurrence of the thermite reaction. 10 wt% terpolymer has relatively little effect on the thermite reaction, but for the samples with higher terpolymer content, more nanothermite components react with terpolymer at an early stage. Ignition and combustion performance show terpolymer can reduce ignition current threshold by up to 9.82% and increase combustion duration time at least several times. The potential reasons for the above results are analyzed. This work can shed light on the application of fluoroelastomer in energetic‐materials. [ABSTRACT FROM AUTHOR]

Abstract Fluoroelastomer has received increasing attention for energetic materials application due to its high fluorine contents. Different contents (0 wt%–30 wt%) of poly(VDF‐ter‐HFP‐ter‐TFE) terpolymer are added into Al/MnO2 nanothermite. The peak exothermic temperature of thermite reaction for Al/MnO2 system is about 554°C with 1070 Jg−1 heat release. After adding terpolymer, it mainly exists in the gap among Al nanoparticles and MnO2 nanorods, and react with Al and MnO2 at the range of 350 to 540°C before the occurrence of the thermite reaction. 10 wt% terpolymer has relatively little effect on the thermite reaction, but for the samples with higher terpolymer content, more nanothermite components react with terpolymer at an early stage. Ignition and combustion performance show terpolymer can reduce ignition current threshold by up to 9.82% and increase combustion duration time at least several times. The potential reasons for the above results are analyzed. This work can shed light on the application of fluoroelastomer in energetic‐materials.

Copyright of China Plastics / Zhongguo Suliao is the property of Journal Office of CHINA PLASTICS and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The melt viscosity of ultra-high molecular weight polyethylene (UHMWPE) is extremely high, rendering its processing exteremely difficult; thus, flow modification is required to improve its flow properties. In this study, calcium stearate (CaSt) and a fluoroelastomer (FP) were used as flow modifiers to improve the flow properties of UHMWPE. The experimental results revealed that both lubricants improved the flowability of UHMWPE: CaSt improved the melt flow index of UHMWPE, while the FP had no significant effect on the melt flow index but significantly reduced the torque. The underlying mechanisms for the above effects were investigated in terms of the structure–property relationships. Rheological and dynamic mechanical analyses revealed that CaSt acted as an internal lubricant, reducing the degree of entanglement among HMWPE molecular chains. Torque rheological measurements revealed that the FP primarily acted as an external lubricant, precipitating to form an external lubricant layer during extrusion, which reduced the torque and die pressure. [ABSTRACT FROM AUTHOR]

The mineralization of fluoroelastomers (FKMs) in superheated water in the presence of potassium hydroxide (KOH) was investigated with the aim of developing a methodology for recycling the fluorine element. Two FKMs—an “uncrosslinked FKM”, representing a poly(vinylidene fluoride-co-hexafluoropropylene) (poly(VDF-co-HFP)) copolymer with a VDF/HFP molar ratio of 78/22 and a “crosslinked FKM” consisting of this copolymer (cured by peroxide) and carbon black—were treated. The fluorine content of these FKMs was efficiently transformed into F− ions in the reaction solution using low KOH concentrations (0.10–0.50 M) at 200–250 °C. When the uncrosslinked or crosslinked FKMs reacted with aqueous KOH (0.20 M) at a rather low temperature (200 °C) for 18 h, the fluorine content of these FKMs was completely mineralized (both F− yields were 100%). Although the crosslinked FKM contained carbon black, the fluorine mineralization of the FKM was not inhibited. The addition of Ca(OH)2 to the reaction solutions after the superheated water treatment at 250 °C for 6 h with aqueous KOH (0.50 M) led to the production of pure CaF2, identified using X-ray spectroscopy, with 100% and 93% yields for the uncrosslinked and crosslinked FKMs, respectively.

Fluoroelastomers are suitable materials for several applications at high temperature. The present paper presents the modifications of material stability of fluoroelastomer Tecnoflon FOR 80 HS under hard operation conditions: thermal and radiation degradation. The sequence of aging stages influences the oxidation state of polymer, which loses its thermal characteristics in the close relation with scission degrees. The chemiluminescence investigation and mechanical testing are the selected procedures for the evaluation of sustained degradation asked for the qualification of O-rings, buffers and gaskets destined to nuclear power plants. The contributions of the two kinds of degrading energies: heat and ionizing radiation are discussed by means of the values of activation energies, which may describe the modification in the oxidation strength. The high temperatures applied in the assessment of material stability (170, 195 and 220 °C) as well as the descendant shape dependencies of the CL intensity vs time indicate the damage tendency with respect to the progress of oxidation in polymer matrix. The large differences between the evolutions of oxidation in the nonisothermal CL spectra of Tecnoflon material depict the existence of different local concentrations of radicals. Their decay takes place over about 100 °C, after which various routes of degradation are followed. [ABSTRACT FROM AUTHOR]

This paper addresses physical and chemical resistance evaluation of tactile sensors. We have developed cantilevertype MEMS tactile sensors embedded in the elastomer. In this work, we used a combination of silicone elastomer with excellent mechanical properties and fluoroelastomer with excellent chemical resistance. As a new embedding method for the sensor, we devised a method of embedding with PDMS with low creep and coating with a fluoroelastomer for surface protection. We further performed three evaluations to demonstrate the physical and chemical resistance of sensors. Consequently, using the devised method, we have demonstrated that the sensor with both physical and chemical resistance are feasible. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The study presents the preparation of acrylamide grafted fluoroelastomer (FKM‐g‐acrylamide) by melt mixing process and its evaluation as a reactive compatibilizer for fluoroelastomer (FKM) and methyl vinyl silicone rubber (MVQ) blend system (at different compositions) in terms of mechanical properties, thermal stability, aging behavior, and morphological aspects. Mechanical properties investigation discloses almost 20% increment in tensile strength after the incorporation of 3 parts per hundred rubber of FKM‐g‐acrylamide into the FKM/MVQ blend. The shifting of the Tgs of both the rubber phases toward each other along with the decrease of the heat capacity value (Cp) attest the effective compatibilization role of the compatibilizer. However, no significant changes in the thermal stability of the blends are observed after incorporation of the prepared compatibilizer. The heat and oil aging behavior shows remarkable percentage retention of the mechanical properties for the compatibilized blend system compared to the uncompatibilized one. The morphological study indicates the abrupt reduction of the FKM domain size (2000–180 nm) in the MVQ matrix for the compatibilized blend. [ABSTRACT FROM AUTHOR]

The preparation of liquid fluoroelastomers that are liquid with excellent mechanical properties remains a challenge. Here, we show a very straightforward method to produce liquid fluoroelastomers by introducing carborane. Carborane-terminated liquid fluoropolymer was synthesized by Steglich reaction of carboxyl-terminated liquid fluoropolymer and 1,7-bis (hydroxy)-carborane. The product is brown, viscous at room temperature and in the semi-solid state. On this basis, HDI Trimer was used as a curing agent to cure liquid fluoroelastomer. Thermogravimetric analysis of the cured products was carried out. The carbon residue rate of the cured product increased from 35% to 58% of the cured product. The results show that the addition of carborane structure can effectively improve the carbon residue rate of liquid fluoroelastomer. The tensile strength, elongation and shore hardness of the cured product were also examined, and the results show that the tensile strength of carborane modified liquid fluorine increased by 463% compared with that before modification, but the elongation at break was reduced by 42%, which was mainly due to the introduction of rigid structure of carborane. At the same time, the solvent resistance test results show that the introduction of carborane structure has little effect on the aviation kerosene resistance and organic solvent resistance of fluororubber, but it can improve its alkali resistance.

The preparation of liquid fluoroelastomers that are liquid with excellent mechanical properties remains a challenge. Here, we show a very straightforward method to produce liquid fluoroelastomers by introducing carborane. Carborane-terminated liquid fluoropolymer was synthesized by Steglich reaction of carboxyl-terminated liquid fluoropolymer and 1,7-bis (hydroxy)-carborane. The product is brown, viscous at room temperature and in the semi-solid state. On this basis, HDI Trimer was used as a curing agent to cure liquid fluoroelastomer. Thermogravimetric analysis of the cured products was carried out. The carbon residue rate of the cured product increased from 35% to 58% of the cured product. The results show that the addition of carborane structure can effectively improve the carbon residue rate of liquid fluoroelastomer. The tensile strength, elongation and shore hardness of the cured product were also examined, and the results show that the tensile strength of carborane modified liquid fluorine increased by 463% compared with that before modification, but the elongation at break was reduced by 42%, which was mainly due to the introduction of rigid structure of carborane. At the same time, the solvent resistance test results show that the introduction of carborane structure has little effect on the aviation kerosene resistance and organic solvent resistance of fluororubber, but it can improve its alkali resistance. [ABSTRACT FROM AUTHOR]

The introduction of new fuels to power internal combustion engines requires testing the compatibility of such fuels with materials commonly used in fuel supply systems. This paper investigates the influence of alternative fuels on the acrylonitrile-butadiene rubber and fluoroelastomer used in the automotive industry. In the study, conventional diesel fuel, its blend with 7% of fatty acid methyl esters and paraffinic diesel fuel produced with the Fisher Tropsch synthesis from natural gas were interacted with the elastomers. The immersion tests were carried out at room temperature (20 °C) for 168 h. The effect was evaluated based on changes in the selected rubber's volume, mass and hardness. It has been confirmed that the synthetic component without aromatic hydrocarbons had a different effect on the tested rubber than did conventional fuel. In follow-up work, the selected rubbers were also subjected to microscopic observation. The most frequently observed effect was the washing out of the seal protective layer. [ABSTRACT FROM AUTHOR]

Previous research into the friction behaviour of elastomers has typically focused on the effects of velocity, contact pressure, counter surface and lubrication on the coefficient of friction. O-ring type elastomer seals are common in many different industries. Friction plays a critical role during the setting and in service of these components. An experimental O-ring friction testing rig has been developed that can measure the effects of sliding speed and hydrostatic pressure on elastomer friction. Finite element analysis (FEA) packages can adopt fixed friction coefficients or ones that are pressure dependent. For the latter case, the dependence of the frictional behaviour is typically obtained from the instantaneous stress response at any given pressure and then related to the normal force response. The friction rig described in this paper uses industry standard dimensions for the O-ring gland, the pre-compression levels, extrusion gap size and pressure rating. The coefficient of friction is derived by dividing the measured friction force by the normal force, which was determined using an FEA modelling approach, as it could not be measured directly. Finally, a relationship between the frictional velocity and surface roughness is obtained in order to provide a frequency dependent Coefficient of Friction (CoF) that is easily translatable between surfaces.

Fluoroelastomers are commonly used as seal, gasket or membrane materials in many industrial applications. The temperature- and environment-dependent material property of rubbers will result in degradation and creep. In this study, the effects of both temperature and concentration of hydrochloric acid solution on mechanical properties and creep behavior of fluoroelastomer are investigated. The tensile test results demonstrate that the mechanical properties of rubber after acid treatment show a continual decrease as temperature or concentration increased. This degradation is attributed to the combination of both the swelling of rubber for the matrix which is penetrated by a number of acid solution molecules and the damage of chain networks where the acid–rubber reactions are generated inside. The tensile creep of the acid-treated rubbers is examined under controlled acidic environmental conditions. The creep rate and creep strain are both increased with increasing temperature or concentration. The creep curves are correctly fitted at long times by standard four-element model to evaluate the contributions from separate creep components. From fitting results, the change of viscoelastic strain component and viscous strain component suggests there are structural rearrangements within rubber chains and deformation of rubber matrix. [ABSTRACT FROM AUTHOR]

The aging behaviors and mechanism of fluoroelastomer (FKM) under lubricating oil (FKM-O) and air (FKM-A, as a comparison) at elevated temperatures were studied from both physical and chemical viewpoints. The obvious changes of mechanical and swelling performances indicate that the coupling effect of lubricating oil and temperature causes more serious deterioration of FKM-O compared to that of FKM-A. Meanwhile, much stronger temperature dependence of both bulk properties and micro-structures for FKM-O is found. Three-stage physical diffusion process is defined in FKM-O due to the competition between oil diffusion and elastic retraction of network. FTIR results reveal that the dehydrofluorination reaction causes the fracture of C-F bonds and produces a large number of C-C bonds in the backbone. The coupling effect of oil medium and high temperature could accelerate the scission of C-C bonds and generate a series of fragments with different molecular sizes. The TGA results, crosslinking density Ve, and glass transition temperature Tg derived from different measurements coherently demonstrate the network destruction in the initial stage and the simultaneous reconstruction occurring at the final stage. The newly formed local network induced by reconstruction cannot compensate the break of the original rubber network and thus only provides lower tensile strength and thermal stability. [ABSTRACT FROM AUTHOR]

Fluoroelastomer (FKM) composite embedded with natural graphite (NG) was prepared and its thermal, mechanical, dielectric, and solvent transport properties were explored as a function of NG loading. The morphology of the composites was done by AFM, SEM, and TEM analysis, and XRD provides the structural analysis. The composite with 20 phr of NG content showed the highest tensile properties and thermal stability and was supported by fracture surface SEM analysis. Enhancement in polymer‐filler interaction in the composite was further confirmed by the increase in Tg value obtained from DSC analysis. The dielectric permittivity value showed tremendous increment by 30 phr of NG addition with decreased dielectric loss. The resistance to solvent uptake with increase in NG loading by the formation of tortuous pathway is also a clear evidence for the exfoliation of the graphite flakes in the FKM matrix. Better inclusion of NG in FKM matrix efficiently enhanced the thermal, mechanical, dielectric and the transport properties of the composites. [ABSTRACT FROM AUTHOR]

Fluoroelastomer and silicone rubber lie in the two different poles of elastomer family in terms of polarity. Hence, combining them in a single material and making it as at least technologically compatible substance is a great challenge. In this article, the compatibilization effect of fluorosilicone rubber (block copolymer) (trifluoropropylpolydimethylsiloxane) with various loading of modified silica filler on the novel advanced polymer architecture based fluoroelastomer (copolymer of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene) and silicone rubber (poly methylvinylsiloxane) blends has been studied in details. The mechanical properties show significant improvement at room temperature (13%) and remarkably more at high temperature (54%) for the compatibilized system. Tan delta peak shifting in DMA study indicates better compatibilization for 2.5 phr loading of fluorosilicone and 15 phr loading of silica at 50/50 blend ratio. The reduction in domain size (from ⁓3 μm to ⁓200 nm) of the fluorocarbon phase by the synergistic effect of silica and fluorosilicone proves the decrease in interfacial tension and better compatibilization. This blend can be judiciously applicable in the sealing system as oil and fuel resistant O-rings and gaskets for a very wide range of temperature. [ABSTRACT FROM AUTHOR]

Nanocomposites with multifunctional properties are of great interest as they meet the needs of the developing industrial and engineering fields. The present study focus on the development of multifunctional elastomeric nanocomposites with exfoliated graphite (EG) as the reinforcing content and the speciality material fluoroelastomer as the polymer matrix. Morphological analysis of the nanocomposites in terms of TEM, AFM and SEM were done to look at the polymer-filler interactions which in turn lead to the property enhancement. The dispersion of the EG in the nanoscale which resulted in the property enhancement is clear from the TEM images. Nanocomposites exhibited improved thermal stability and higher mechanical strength by the addition of 12 phr of EG nanofiller. Moreover the dielectric performance of the nanocomposites was also enhanced by the addition of conductive EG nanofiller and the nanocomposites showed higher dielectric constant value and AC conductivity with lower dielectric loss. In addition to this the solvent transport features of the nanocomposites were also analyzed to reveal the reinforcement effect of the nanofiller and the effective polymer-filler interactions. [ABSTRACT FROM AUTHOR]

Nanocomposites having multifunctional properties with simultaneous improvement in thermal, mechanical and dielectric properties along with improved ferroelectric signature are of considerable interest due to the rapidly growing need in the technological aspect. In the present work, microwave reduced graphene oxide (mRGO)/fluoroelastomer nanocomposites with enhanced dielectric performance and ferroelectric characteristics were developed. mRGO was synthesized from natural graphite via GO and was confirmed by analyzing the chemical changes using X-ray diffraction technique, Fourier transform infrared and Raman spectroscopy studies. The addition of the mRGO improved the mechanical, dielectric and ferroelectric characteristics of the nanocomposites by its better dispersion in the polymer matrix as confirmed by TEM and AFM analysis. The enhanced polymer filler interaction was also confirmed by analyzing the Kraus Plot. Nanocomposite with 0.75 phr of filler loading showed optimum mechanical properties with increased Tg of about −12.25 °C. This is an evidence for the enhancement in properties due to the improved filler-polymer electrostatic interaction. Nanocomposites showed several-fold increase in the dielectric constant value compared to the gum sample. Moreover, the nanocomposites have minimum dielectric loss at 1 MHz frequency. The incorporation of mRGO created a conductive pathway by the microcapacitor effect and the nanocomposites showed enhanced AC conductivity. Ferroelectric studies revealed that the coercive field (Ec) and the remnant polarization (Pr) of the nanocomposites were increased with filler loading that signifies the improvement in ferroelectric signature of the nanocomposites. The samples show excellent dielectric and ferroelectric properties along with better thermal and mechanical stability, and hence, will be promising candidate for ultra-modern storage devices. [ABSTRACT FROM AUTHOR]

The introduction of new fuels to power internal combustion engines requires testing the compatibility of such fuels with materials commonly used in fuel supply systems. This paper investigates the influence of alternative fuels on the acrylonitrile-butadiene rubber and fluoroelastomer used in the automotive industry. In the study, conventional diesel fuel, its blend with 7% of fatty acid methyl esters and paraffinic diesel fuel produced with the Fisher Tropsch synthesis from natural gas were interacted with the elastomers. The immersion tests were carried out at room temperature (20 °C) for 168 h. The effect was evaluated based on changes in the selected rubber’s volume, mass and hardness. It has been confirmed that the synthetic component without aromatic hydrocarbons had a different effect on the tested rubber than did conventional fuel. In follow-up work, the selected rubbers were also subjected to microscopic observation. The most frequently observed effect was the washing out of the seal protective layer.

The present work was focused on studying the effects of different CB loadings on the rheological, thermal, tensile, dynamic mechanical, and electrical properties of polyvinylidene fluoride and FKM composites. To these ends, dynamic mechanical thermal analysis (DMTA) was conducted, and the CB grade and method chosen for compound preparation were CB (N330) by melt mixing with different shear effects were examined, respectively. The composites were melt-blended with CB at 190 °C in an internal mixer, after which the properties of filled and unfilled composites were compared. The DMTA analysis revealed that the area under the loss tangent (tanδ) peak decreased and that the tanδ temperature of the rubber phase increased with CB loading. The presence of CB improved the mechanical properties, such as the Young's modulus and tensile strength, of the composites and increased thermal stability given the high thermal stability of CB and the interaction between the CB particles and the polymer matrices. The increase in the electrical conductivities of the composites under different CB loadings was also examined with different shear effects because of the different dispersion states of CB. The percolation threshold of conductive thermoplastic vulcanizate composite based on conductive CB was observed and the experimental data could be well fitted to the general equation model. [ABSTRACT FROM AUTHOR]

AbstractAcid surface modified carbon nanotube (MCNT)-, Carbon nanotube (CNT)-filled fluoroelastomer (FE) and unfilled-FE were prepared (MCNT/FE, CNT/FE and FE). The compounds were subjected to thermogravimetric analysis (TGA) and heat air aging, and characterized by Energy Dispersive X-Ray (EDX). Results showed that MCNT improved the thermal properties of FE, resulting in a larger amount of FE and char remaining in the temperature range of 400-900 °C relative to unfilled FE and CNT/FE. The MCNT/FE TGA curve shifted towards higher temperatures compared to CNT/FE and FE. The same results also revealed that higher percentages of FE were undegraded or less degraded especially near MCNT in the temperature range of 400-540 °C. Energy Dispersive X-Ray (EDX) results indicated that the percentage of carbon and fluorine in the residue of TGA scans, up to 560 °C, of MCNT/FE were the same as CNT/FE, and were higher than FE. EDX results of TGA residue (run up to 900 °C) showed that most of the undegraded FE, which was not degraded at temperatures below 560 °C, was degraded from 560 °C to 900 °C in both MCNT/FE and CNT/FE, with the char in MCNT/FE being more than that in CNT/FE. EDX analysis of thermal aged specimens under air showed that, with increasing aging time, a greater percentage of C, O and F was lost from the surface of filler/FE and FE. The order of element loss after 24 hour aging time was: MCNT/FE > FE > CNT/FE.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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Organs-on-chips are microfluidic devices typically fabricated from polydimethylsiloxane (PDMS). Since PDMS has many attractive properties including high optical clarity and compliance, PDMS is very useful for cell culture applications; however, PDMS possesses a significant drawback in that small hydrophobic molecules are strongly absorbed. This drawback hinders widespread use of PDMS-based devices for drug discovery and development. Here, we describe a microfluidic cell culture system made of a tetrafluoroethylene-propylene (FEPM) elastomer. We demonstrated that FEPM does not absorb small hydrophobic compounds including rhodamine B and three types of drugs, nifedipine, coumarin, and Bay K8644, whereas PDMS absorbs them strongly. The device consists of two FEPM layers of microchannels separated by a thin collagen vitrigel membrane. Since FEPM is flexible and biocompatible, this microfluidic device can be used to culture cells while applying mechanical strain. When human umbilical vein endothelial cells (HUVECs) were subjected to cyclic strain (~10%) for 4 h in this device, HUVECs reoriented and aligned perpendicularly in response to the cyclic stretch. Moreover, we demonstrated that this device can be used to replicate the epithelial−endothelial interface as well as to provide physiological mechanical strain and fluid flow. This method offers a robust platform to produce organs-on-chips for drug discovery and development.

Acid surface–modified carbon nanotube (ACNT)-, carbon nanotube (CNT)-filled fluoroelastomer (FE), and unfilled-FE compounds were prepared (ACNT/FE, CNT/FE, and FE). The oil-based drilling (OBD) mud aging resistances of these elastomers were assessed by tests of weight gain, swelling, atomic force microscopy (AFM), and optical microscopy. The results show that for ACNT/FE-OBD (OBD mud tested ACNT/FE) and CNT/FE-OBD, there are no blisters, cracks, swellings, and deformed or uneven surfaces; however, for FE-OBD surfaces, these defects exist. ACNT/FE-OBD and CNT/FE-OBD have very low swelling, while for FE-OBD, the swelling is negative which indicates OBD chemical degradation of FE-OBD. All samples under study show low weight gain. AFM results show that roughness and average height of FE-OBD surface decreased considerably compared to that of FE. However, the changes in AFM results of ACNT/FE-OBD and CNT/FE-OBD compared to ACNT/FE and CNT/FE, respectively, are minor. ACNT/FE-OBD has a rougher surface with more average height and height variations compared to CNT/FE-OBD. Optical microscopy images show that the surface of FE-OBD is full of cracks but those of ACNT/FE-OBD and CNT/FE-OBD have no cracks. This study indicates that FE is not resistant to OBD, while ACNT/FE and CNT/FE are resistant to OBD. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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), 1 H nuclear magnetic resonance (NMR), 19 F-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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fluoroelastomer possesses substantial usages in energetic polymer composites owing to its numerous merits. However, fluoroelastomer suffers from inadequate mechanical properties without ability to satisfy practical application requirements. In this study, stretchable, tough, and stiff fluoroelastomer was successfully fabricated by introducing hydrogen bonds with the assistance of tannic acid (TA) self-assembly. The resultant fluoroelastomer/TA composites exhibited evenly distributed TA particles derived from the self-assembly of TA molecules. By adjusting TA contents, diverse morphologies of TA particles were acquired from spherical shape to flake-like shape. Moreover, interfacial hydrogen bonds were found to appear between fluoroelastomer and TA particles. Such interfacial hydrogen bonds acting as sacrificial bonds allowed preferential rupture to dissipate energy. As a consequence, the optimal elongation at break, toughness, and Young's modulus of composites in comparison to pristine fluoroelastomer increased by 171%, 195%, and 114%, respectively. These findings demonstrate that the proposed approach offers a feasible tactic to construct high-performance fluoroelastomer for energetic polymer composites. [Display omitted] • Interfacial hydrogen bonds were introduced into the fluoroelastomer enabled by incorporating tannic acid (TA). • Fluoroelastomer/TA composites exhibited a significant improvement in toughness compared to pristine fluoroelastomer. • The proposed method provides a promising avenue to acquire high-performance fluoroelastomer. [ABSTRACT FROM AUTHOR]