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From an environmental and economic viewpoint, it is a win-win strategy to use materials obtained from renewable resources for the production of high-performance elastomer composites. Lignin, being a renewable biomass, was employed as a functional filler material to obtain an elastomer composite with a higher degree of mechanical performance. In the presence of a suitable coupling agent, an elevated temperature was preferred for the reactive mixing of lignin with polybutadiene rubber (BR). It is quite fascinating that the mechanical performance of this composite was comparable with carbon black-filled composites. The extraordinary reinforcing behavior of lignin in the BR matrix was understood by an available model of rubber reinforcement. In rubber composite preparation, the interfacial interaction between polybutadiene rubber and lignin in the presence of a coupling agent enabled the efficient dispersion of lignin into the rubber matrix, which is responsible for the excellent mechanical properties of the rubber composites. The rubber composites thus obtained may lead to the development of a sustainable and cost-effective end product with reliable performance. This novel approach could be implemented in other type of elastomeric materials, enabling a genuine pathway toward a sustainable globe. publishedVersion

The major controlling factors that determine the various mechanical properties of an elastomer system are type of chemical crosslinking and crosslink density of the polymer network. In this study, a catalytic amount of acrylonitrile butadiene copolymer (NBR) was used as a co-accelerator for the curing of polybutadiene (BR) elastomer. After the addition of this copolymer along with other conventional sulphur ingredients in polybutadiene compounds, a clear and distinct effect on the curing and other physical characteristics was noticed. The crosslinking density of BR was increased, as evidenced by rheometric properties, solid-state NMR and swelling studies. The vulcanization kinetics study revealed a substantial lowering of the activation energy of the sulphur crosslinking process when acrylonitrile butadiene copolymer was used in the formulation. The compounds were also prepared in the presence of carbon black and silica, and it was found that in the carbon black filled system the catalytic effect of the NBR was eminent. The effect was not only reflected in the mechanical performance but also the low-temperature crystallization behavior of BR systems was altered.Materials science; Materials chemistry; Crosslinking accelerator; Sulphur network; Solid state NMR; Curing kinetics; Activation energy; Acrylonitrile butadiene; Polybutadiene; Low-temperature; Crystallization., This work was partially funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - within the Research Training Group RTG 2430 "Interactive Fiber Elastomer Composites".

The article focuses on comparing the friction, abrasion, and crack growth behavior of two different kinds of silica-filled tire tread compounds loaded with (a) in-situ generated alkoxide silica and (b) commercial precipitated silica-filled compounds. The rubber matrix consists of solution styrene butadiene rubber polymers (SSBR). The in-situ generated particles are entirely different in filler morphology, i.e., in terms of size and physical structure, when compared to the precipitated silica. However, both types of the silicas were identified as amorphous in nature. Influence of filler morphology and surface modification of silica on the end performances of the rubbers like dynamic friction, abrasion index, and fatigue crack propagation were investigated. Compared to precipitated silica composites, in-situ derived silica composites offer better abrasion behavior and improved crack propagation with and without admixture of silane coupling agents. Silane modification, particle morphology, and crosslink density were identified as further vital parameters influencing the investigated rubber properties. publishedVersion

Elastomers are often filled with various reinforcing particles to meet the desired performance measures, namely mechanical properties. These reinforcing filler particles, for example electrically conductive carbon allotropes, are used in quantities above the percolation threshold and thus form clusters or even filler networks that determine the ultimate performance of the final rubber product. Any changes or effects on the state of the filler network will immensely influence the performance of the rubber product. Therefore, lots of pioneer works could be found that study the changes of the filler network with respect to an external force (strain, temperature, etc.) and correlate to changes in mechanical & dynamic-mechanical properties. In our work an attempt is made to characterise changes in the integrity of filler networks inside rubber composites during mechanical loading in-situ by changes in electrical conductivity. Thus the dynamic piezoresistive characteristics were studied in detail on conducting rubber composites and temporal changes in the filler network could be correlated to the mechanical performance during dynamic deformation. The knowledge gained in our investigations will provide a potential tool for development of "self-sensing" rubber materials and future rubber based sensors suitable for dynamic loading conditions.

We report about systematic studies on dynamic piezoresistive characteristics of conductive rubber composites. The temporal changes in electrical resistance of flexible electrically conductive rubber composites were simultaneously monitored during dynamic mechanical loading. Thus, influences of physical parameters such as frequency, temperature, strain amplitude, and matrix stiffness were explored in detail, and the mechanisms behind qualitatively discussed. The filler clusters were found to rearrange in the elastomer matrix during dynamic deformation, witnessed by the decrease in electrical resistance over time. Each test parameter had its own specific effect on the piezoresistance response, and the findings offered an understanding on the filler networking inside the solution styrene butadiene rubber matrix from the perspective of the dynamic piezoresistive characteristics. Higher piezoresistive response was observed near the glass transition temperature. We offer a deeper insight into the behavior and temporal changes in corresponding filler clusters during dynamic deformations of conducting rubber systems.

This is an original study on the rubbing of ruptured bubbles on a hydrophobic solid surfaces. A bubble protruding from a capillary tube attached to the objective of a microscope was pressed gently against a hydrophobic solid surface by gradually increasing the pressure inside of the capillary tube. At a certain special “gap” value the pressure inside of the capillary tube caused the formation of a wetting film, which was observed interferometrically. The film ruptured a short time after its formation, leading to the development of three-phase contact line (TPCL) on the solid surface. The TPCL rubs on the surface as the latter moves tangentially. At a certain critical speed of motion of the solid surface the bubble detaches from the surface. The value of this critical speed depends on the pressure inside the bubble, the level of the hydrophobicity and the visco-elastic modulus of the surface. We call for further investigation of this interesting phenomenon.

The phase specific localization of the reinforcing fillers like carbon black (CB), which has been known to influence the physical and mechanical performance of the rubber blends, can be determined by different characterization techniques, however, only for binary rubber blends. They have been failed so far when applied for more complicated systems like filled ternary rubber blends. In the present work we introduced a new technique using the attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) with germanium crystal for characterization of the specific localization of CB in a ternary blend of solution styrene butadiene rubber (SBR), butadiene rubber (BR) and natural rubber (NR). It is the first time we could follow the change of the amount of CB localized in each phase of this blend along the mixing time. CB firstly is incorporated into the NR phase and then it obviously migrates from the NR phase to the SBR phase as a function of mixing time that corresponds very well with the theoretical prediction based on the Z-model using the surface tension values of the filler and rubber blend components. The interaction between CB and rubber components can be qualitatively proved by the shift of the FTIR peak. Thermogravimetric analysis (TGA) was used to support the results obtained by the FTIR method. The study was further extended to follow the CB distribution in multi-step mixing.

For the development of intelligent vehicle tires, especially for future self-driving cars, suitable strain sensors are mandatory. The design of such a strain sensor must fulfil several criteria, most important of all, it must be easily mounted or implanted into the tire and the elastic nature of the sensors must be synchronized with the deformation behaviour of the tire. To our knowledge, we evaluate for the first time, the piezoresistive characteristics of a composite developed from tire rubber, taking into account the morphology (distribution and dispersion of the fillers), filler network structure, crosslinking density and the stiffness (hardness) of the rubber matrix. We use a commercially available synthetic solution polymerized styrene butadiene rubber (SSBR) which is widely used in modern car tire industries. As the internal structure of the filler particles can rearrange or alter during deformation, it is extremely important to study the piezo-resistive performance with respect to crosslinking density, hardness and modulus of the rubber composites in details. The present paper focusses on the development of strain sensors by exploiting conductive elastomeric composites based on SSBR with conducting carbon fillers like carbon black and carbon nanotubes. The sensors can be stretched to several hundred percent of their original length and a sensitivity could be achieved as much as ∼1000 (gauge factor) in a given strain regime of ∼100%, while maintaining the mechanical robustness. Some of the mechanical properties like tensile strength (∼20 MPa), and modulus at 100% elongation are found to be quite satisfactory indicating the suitability of the materials for real applications.

A sol-gel transformation of liquid silica precursor to solid silica particles was carried out in a one-pot synthesis way, where a solution of styrene butadiene elastomer was present. The composites, thus produced, offered remarkable improvements of mechanical and dynamic mechanical performances compared to precipitated silica. The morphological analysis reveals that the alkoxy-based silica particles resemble a raspberry structure when the synthesis of the silica was carried out in the presence of polymer molecules and represent a much more open silica-network structure. However, in the absence of the polymer, the morphology of the silica particles is found to be different. It is envisaged that the special morphology of the in situ synthesized silica particles contributes to the superior reinforcement effects, which are associated with a strong silica-rubber interaction by rubber chains trapped inside the raspberry-like silica aggregates. Therefore, the interfaces are characterized in detail by low-field solid-state

Rubber composites were prepared by mixing bromobutyl rubber (BIIR) with silica particles in the presence of 1-butylimidazole. In addition to pristine (precipitated) silica, silanized particles with aliphatic or imidazolium functional groups, respectively, were used as filler. The silanization was carried out either separately or in situ during compounding. The silanized particles were characterized by TGA, 1H–29Si cross polarization (CP)/MAS NMR, and Zeta potential measurements. During compounding, the bromine groups of BIIR were converted with 1-butylimidazole to ionic imidazolium groups which formed a dynamic network by ionic association. Based on DMA temperature and strain sweep measurements as well as cyclic tensile tests and stress–strain measurements it could be concluded that interactions between the ionic groups and interactions with the functional groups of the silica particles strongly influence the mechanical and viscoelastic behavior of the composites. A particularly pronounced reinforcing effect was observed for the composite with pristine silica, which was attributed to acid–base interactions between the silanol and imidazolium groups. In composites with alkyl or imidazolium functionalized silica particles, the interactions between the filler and the rubber matrix form dynamic networks with pronounced self-healing behavior and excellent tensile strength values of up to 19 MPa. This new approach in utilizing filler–matrix interactions in the formation of dynamic networks opens up new avenues in designing new kinds of particle-reinforced self-healing elastomeric materials with high technological relevance.

In the present work, self-healable rubber blends consisting of modified bromobutyl rubber (BIIR)/natural rubber (NR) blends filled with silica (Si)/carbon nanotube (CNT) hybrid filler were prepared as model system. It was found that an addition of a low loading of silica as secondary filler for CNTs significantly enhances the tensile strength of the BIIR/NR blends while maintaining the self-healing properties. The synergistic effect of the hybrid filler on the mechanical properties of BIIR/NR blends can be explained by taking into account the selective wetting of the hybrid filler. Thus, a new method based on the wetting concept has been further developed for quantification of the selective wetting of hybrid filler in the BIIR/NR blends. The migration of silica to the BIIR/NR interfacial region and preferential location of the CNTs in NR phase may impart the BIIR/NR blends better mechanical performance and high electrical conductivity. The BIIR/NR blends filled with hybrid filler Si/carbon black (CB) were prepared as reference system. Its similarities and differences with the model system were discussed regarding the selective filler wetting and localization.

The main goal of present work is to study the dynamic viscoelastic properties of reinforced elastomers with a help of a recently developed superposition approach. To investigate the influence of the filler surface characteristics on the viscoelastic properties, a number of rubber compounds, based on a solution-polymerized styrene butadiene rubber and different types of fillers, was chosen. The master curves for the small strain storage E ′ ( ω ) and loss E ″ ( ω ) moduli were constructed at a reference temperature of 0 ∘ C with a help of a self-developed shifting procedure based on the time-temperature superposition principle. To fit the master curves for reinforced elastomers in the whole range of frequencies over many decades, we propose to split the polymer matrix into two fractions. One fraction contains the free network chains far away from the filler particles, while the other fraction is composed from the chains localized near and on the filler surface. Such superposition approach allows to extract the characteristics of a fully localized polymer layer with a changed dynamic-mechanical behaviour. Importantly, based on the scaling behaviour of localized layer we show that the surfaces of studied fillers can impose quite different constraints on the rubber chains.

The solution SBR and silica-based composites are prepared by hydrolysis of tetraethylorthosilicate in the presence of an organic solution of SBR and n-butylamine as catalyst. Further addition of bis[3-(triethoxysilyl)propyl]tetrasulfide, a silane coupling agent, improves the performance and properties of the composites. All the results are compared with commercial precipitated silica at similar loading conditions. The generated silica particles from this alkoxide route resulted in lower Mooney viscosity of the compound and showed less filler flocculation compared with standard commercial precipitated silica in reference compounds. A detailed dynamic mechanical study also indicated that alkoxide silica in model tire compounds could offer a lower rolling resistance and a higher wet skid resistance compared to the reference. Other properties such as heat build-up, rebound resilience, and hysteresis loss were found to be very promising for alkoxide silica composites, too. The silica particles (aggregated) developed by the alkoxide method were relatively large (∼150–200 nm) compared with the primary particles of precipitated commercial silica. The synthesis of sol–gel silica particles in presence of the polymer allowed for the trapping of some polymer molecules inside the filler aggregates and therefore offers exceptional mechanical reinforcement of the rubber.

The paper presents studies of the properties of elastomeric materials based on the solution-polymerized styrene-butadiene rubber (S-SBR) filled with nanoparticles of different geometry – grainy (nanodiamonds), layered (graphene nanoplates) and fibrous (nanotubes). Despite the introduction of a small amount of fillers, the significant strengthening of the matrix is exhibited. Of particular interest is the behavior of the nanodiamond-filled elastomer composite, for which a double increase in rupture stress with an increase in rupture strain is observed at the filler volume fraction approximately equal to 2%. The structure of composites is investigated by optical and atomic force microscopy. In addition to standard mechanical testing, experiments of successive cyclic loading along each of two mutually perpendicular axes of plane elastomeric samples were conducted with use of a Zwick 4-vector test stand (biaxial testing machine). The phenomenon of induced anisotropy in materials is analyzed. A hypothesis to explain its manifestation is suggested.

The performance of elastomeric materials, i.e. in car tires, is substantially determined by the used reinforcing filler system. In particular, the flocculation tendency of filler particles to form clusters and even network-like structures significantly determines the mechanical properties of these elastomer materials and enhances especially their energy dissipation under periodic mechanical deformations. In a simplified thermodynamic model, inspired by a segregation model from game theory, we describe fundamental mechanisms of filler structure formation. As the final goal of this paper we want to demonstrate how similar structures in society, nature or materials like rubbers emerge when supposing obvious cardinal mechanisms of structure formation in complex systems.

The aim of this work was to study the effect of the ionic liquids (ILs) with respect to their anion type and the length of alkyl chain as dispersing and coupling agent in carbon nanotube (CNT) filled styrene butadiene rubber (SBR)/natural rubber (NR) blends. We characterized the ILs by their surface tensions whereupon their different values explain the different compatibilities of ILs with the rubber components and the filler. The wetting concept was further developed in order to experimentally characterize the effect of the rubber-IL and CNT-IL compatibility on the selective wetting of CNTs in rubber blends. It was found that all the used ILs improved the dispersion of CNTs in rubber blends significantly. During the mixing process the IL layer pre-bound to the CNT surface was replaced mainly by the NR phase and, partly, by the SBR phase. Thus, ILs cannot be used as coupling agent in this rubber blend. For the ILs with surface tension similar to that of CNTs the filler was partly wetted by IL that imparts the mixture a high electrical conductivity directly after the mixing process. This high conductivity can be used for triggering the vulcanization of the blend by means of the Joule heating. The preferential localization of ILs in the rubber matrix - but not in rubber-filler interphase - considerably influences the cross-link behavior of the vulcanizates and thus their final mechanical properties significantly.

A new biomimetic stimuli-responsive adaptive elastomeric material, whose mechanical properties are altered by a water treatment is reported in this paper. This material is a calcium sulphate (CaSO4) filled composite with an epoxidized natural rubber (ENR) matrix. By exploiting various phase transformation processes that arise when CaSO4 is hydrated, several different crystal structures of CaSO4·xH2O can be developed in the cross-linked ENR matrix. Significant improvements in the mechanical and thermal properties are then observed in the water-treated composites. When compared with the untreated sample, there is approximately 100% increase in the dynamic modulus. The thermal stability of the composites is also improved by increasing the maximum degradation rate temperature by about 20 °C. This change in behavior results from an in situ development of hydrated crystal structures of the nanosized CaSO4 particles in the ENR matrix, which has been verified using Raman spectroscopy, transmission electron micros...

Specific physical and reactive compatibilization strategies are applied to enhance the interfacial adhesion and mechanical properties of heterogeneous polymer blends. Another pertinent challenge is the need of energy-intensive blending methods to blend high-tech polymers such as the blending of a pre-made hard polyurethane (-urea) with rubbers. We developed and investigated a reactive blending method to prepare the outstanding blends based on polyurethane-urea and rubbers at a low blending temperature and without any interfacial compatibilizing agent. In this study, the polyurethane-urea (PUU) was synthesized via the methylene diphenyl diisocyanate end-capped prepolymer and m-phenylene diamine based precursor route during blending at 100 &deg, C with polar (carboxylated nitrile rubber (XNBR) and chloroprene rubber (CR)) and non-polar (natural rubber (NR), styrene butadiene rubber (sSBR), and ethylene propylene butadiene rubber (EPDM)) rubbers. We found that the in situ PUU reinforces the tensile response at low strain region and the dynamic-mechanical response up to 150 &deg, C in the case of all used rubbers. Scanning electron microscopy reveals a stronger rubber/PUU interface, which promotes an effective stress transfer between the blend phases. Furthermore, energy filtered transmission electron microscopy (EFTEM) based elemental carbon map identifies an interphase region along the interface between the nitrile rubber and in situ PUU phases of this exemplary blend type.

We explore, both experimentally and theoretically, the possibility to use a composite of natural rubber (NR) and multiwall carbon nanotubes (MWCNT) as a piezoresistive tensile sensor. As an essentially new feature relative to the previous work, we have performed a systematic study of the mechanism of the piezoresistance at large deformations in a wide range of MWCNT concentrations and crosslinking degrees of the host rubber material. In qualitative agreement with the previous work, the conductivity of the unstrained NR/MWCNT nanocomposite is shown to be adequately described by the percolation theory with the critical exponent evaluated to ∼2.31. Varying tensile stress-induced strains in the composite has been shown to results in a non-linear electrical response that cannot be described by simple modifications of the percolation theory. In order to explain the observed non-linear dependence of the resistance R of the composite on the strain e, we have developed a scaling theory that relates this resistance to the structural changes in the conducting MWCNT network caused by deforming the host NR. Based on the obtained results, we discuss the ways of using the highly stretchable conductive elastomer composites as an efficient piezoresistive tensile sensor.

The role of the room temperature ionic liquid, 1-decyl 3-methyl imidazolium chloride (DMIC) as dispersing and coupling agent in multi-walled carbon nanotubes (CNTs)/styrene butadiene rubber (SBR) compounds was investigated. The kinetics of the selective wetting and dispersion of CNTs, which were pre-treated by DMIC, in SBR compounds was studied by means of two methods: (i) the online measured electrical conductance and, (ii) the modified wetting concept. It was found that DMIC shows a good compatibility to SBR and improves the CNT dispersion significantly. A DMIC layer, which is physically pre-bound to the CNT surface, is partly or completely replaced by the SBR molecules during mixing as a result of thermodynamic driving forces. The filler network formation of CNTs in SBR and its effect on the electrical and mechanical properties of the compounds were characterized and discussed by taking into consideration the selective wetting of CNT surface.

The selective wetting behavior of silica in emulsion styrene butadiene rubber (ESBR)/solution styrene butadiene rubber (SSBR) blends is characterized by the wetting concept, which is further developed for filled blends based on miscible rubbers. It is found that not only the chemical rubber–filler affinity but also the topology of the filler surface significantly influences the selective filler wetting in rubber blends. The nanopore structure of the silica surface has been recognized as the main reason for the difference in the wetting behavior of the branched ESBR molecules and linear SSBR molecules. However, the effect of nanopore structure becomes more significant in the presence of silane. It is discussed that the adsorption of silane on silica surface constricts the nanopore to some extent that hinders effectively the space filling of the nanopores by the branched ESBR molecules but not by the linear SSBR molecules. As a result, in silanized ESBR/SSBR blends the dominant wetting of silica surface by the tightly bonded layer of SSBR molecules causes a low-energy dissipation in the rubber–filler interphase. That imparts the low rolling resistance to the blends similar to that of a silica-filled SSBR compound, while the ESBR-rich matrix warrants the good tensile behavior, i.e., good abrasion and wear resistance of the blends.

The investigation of the molecular mobility of polymer chains and networks in the presence of active fillers such as carbon black or silica presents a big interest for the physics of reinforced rubbers. A better understanding of the physical characteristics of the filler–rubber interface is necessary to improve the overall macroscopic properties of these elastomers. The main goal of our work is to develop a physically based multi-scale approach for description of the viscoelastic properties of reinforced elastomers. Rubber compounds, based on a solution-polymerized styrene butadiene rubber filled with precipitated silica, were investigated. Dynamic-mechanical experiments were carried out in a wide range of temperatures to construct master curves for the small strain storage E′(ω) and loss E″(ω) moduli for nearly 20 decades of frequencies at a chosen reference temperature. The developed multiscale theoretical approach allows to analyze the master curves across the 20 decades of frequencies and to investigate the effects of the filler particles on the relaxation processes in simple rubber compounds at different time scales.

Incorporation of precipitated silica rubber compounds is now a standard technology in energy efficient green tire manufacturing process. In the present work silica nanoparticles were generated by an in situ sol–gel technique in solution styrene butadiene rubber (SSBR) using tetraethylorthosilicate (TEOS) as silica precursor. A full control over the amount of silica and size of the silica particles is realized while maintaining a good distribution and dispersion level of the nanosilica particles. In the present case the amount of synthesized silica were varied from 10–50 phr (parts per hundred) and the particles size was found to remain in the range of 200–300 nm. The in situ silica based rubber composites offer better processing characteristics as compared with standard commercial precipitated silica at the same loading level. The reinforcing character of in situ silica was further enhanced by the use of a silane coupling agent, i.e. bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT). Various instrumental techniques, such as tensile test, dynamic mechanical analysis and strain sweep analysis, abrasion test, rebound test and Mooney viscometry reveal superior mechanical performance and good processability of the in situ silica composites. Scanning and transmission electron microscopy studies indicate that the particle size distribution remains in the same range irrespective of the concentration of the silica particles.

In this work we describe layered double hydroxide (LDH), known as naturally occurring hydrotalcite, based rubber composites that can serve as outstanding fire retardant elastomeric materials. The preparation and detailed characterization of these composites are presented in this study. The inherent slow sulfur cure nature of EPDM rubber is considerably improved by the addition of LDH as realised by the observation of a shortening of the vulcanization time and an improvement of ultimate rheometric torque. This behavior of LDH signifies not only the filler-like character of itself, but also offers vulcanization active surface properties of layered double hydroxide particles. A good rubber–filler interaction was also realised by observing a positive shift of the glass transition temperature of ethylene propylene diene rubber (EPDM) in dynamic mechanical analysis (DMA). The flame retardant property was studied by the cone calorimeter test. The cone calorimeter investigation with sulfur cured gum rubber compounds found a peak heat release rate (PHRR) value of 654 kW m−2. However, at a higher phr loading of Zn–Al LDH i.e., at 40 phr and 100 phr, the PHRR is diminished to 311 kW m−2 and 161 kW m−2, respectively. Thus, this present work can pave the way to fabricate environmentally friendly fire retardant elastomeric composites for various applications.

A simplified reactive blending method is investigated to blend effectively the nitrile butadiene rubber (NBR) and in-situ synthesized polyurethane–urea (PUU). The in-situ synthesis of PUU via the prepolymer route was realized in presence of NBR in an internal mixer at a reactive blending temperature of 100 °C that was determined from the chemo-rheological analysis of PUU reactive premix of 4,4′-diphenylmethane diisocyanate-terminated prepolymer and 1,3-phenylene diamine. The 1H NMR spectroscopic analysis showed high conversion (∼87 ± 3%) of amino groups of 1,3-phenylene diamine during rapid in-situ addition polymerization with isocyanate groups of prepolymer. The peroxide-cured NBR/PUU blend vulcanizates exhibited remarkable improvements in cure characteristics, mechanical and dynamic-mechanical properties. The dynamic-mechanical analysis of blend vulcanizates demonstrated a concentration-dependent higher storage modulus (E′) and a lower loss factor (tan δ) in a stable rubbery plateau region extending up to 180 °C. The improvement in performance characteristics of blend vulcanizates was attributed to the strong interfacial adhesion developed during the reactive blending process and was verified by SEM and energy filtered TEM measurements.

Small-strain-sensors, based on conductive carbon black (CB) filled conductive rubber composites (CRCs), have been developed. An ionic liquid (IL) was used to improve the way that the piezoresistive response is independent of strain rate at small strains. Cyclic sensing behaviour at small strains was investigated under a sequential alteration of strain rates. At small strains, the CRCs without IL respond inefficiently to slow deformation cycles, giving a strain-rate dependent sensitivity. On the contrary, the presence of IL enhances the response to slow deformations. At elongations up to 3%, the loosely packed conducting parts and the sufficient rubber-filler interaction achieved with the use of an IL/CB ratio of 1.0 make the piezoresistive responses efficiently independent of the strain rates. Also, the sensitivity is at least threefold higher, compared with CRCs without IL. So, the IL enables the construction of strain-rate independent small-strain-sensor.

Conductive polymer composites for use as stretchable strain sensors have recently been developed for use in wearable electronic devices capable of detecting various stimuli such as human body motion. In this work, we report the development of a flexible strain sensor based on conductive thermoplastic vulcanizate (TPV) by the incorporation of conductive carbon black (CCB). By adopting special processing conditions, the percolation threshold of the CCB could be minimized to a value as low as ~4 wt% as compared to a value of 10 wt% for conventional TPV. Under static and cyclic loading, the strain sensing behavior of the conductive TPV depended on the morphology and filler content. The result also revealed that interconnected TPV exhibited superior piezoresistive characteristics with good sensitivity. Therefore, the good strain sensing performance of this conductive TPV can be considered as a promising material for use in wearable human-motion and wearable strain sensors.

A mechanically adaptable elastomer composite is prepared with reversible soft-stiff properties that can be easily controlled. By the exploitation of different morphological structures of calcium sulfate, which acts as the active filler in a soft elastomer matrix, the magnitude of filler reinforcement can be reversibly altered, which will be reflected in changes of the final stiffness of the material. The higher stiffness, in other words, the higher modulus of the composites, is realized by the in situ development of fine nanostructured calcium sulfate dihydrate crystals, which are formed during exposure to water and, further, these highly reinforcing crystals can be transformed to a nonreinforcing hemihydrate mesocrystalline structure by simply heating the system in a controlled way. The Young's modulus of the developed material can be reversibly altered from ∼6 to ∼17 MPa, and the dynamic stiffness (storage modulus at room temperature and 10 Hz frequency) alters its value in the order of 1000%. As the transformation is related to the presence of water molecules in the crystallites, a hydrophilic elastomer matrix was selected, which is a blend of two hydrophilic polymers, namely, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer and a terpolymer of ethylene oxide-propylene oxide-allyl glycidyl ether. For the first time, this method also provides a route to regulate the morphology and structure of calcium sulfate nanocrystals in a confined ambient of cross-linked polymer chains.

In this work, we report about the mechanical relaxation characteristics of an intrinsically self-healable imidazole modified commercial rubber. This kind of self-healing rubber was prepared by melt mixing of 1-butyl imidazole with bromo-butyl rubber (bromine modified isoprene-isobutylene copolymer, BIIR). By this melt mixing process, the reactive allylic bromine of bromo-butyl rubber was converted into imidazole bromide salt. The resulting development of an ionic character to the polymer backbone leads to an ionic association of the groups which ultimately results to the formation of a network structure of the rubber chains. The modified BIIR thus behaves like a robust crosslinked rubber and shows unusual self-healing properties. The non-covalent reversible network has been studied in detail with respect to stress relaxation experiments, scanning electron microscopic and X-ray scattering. publishedVersion

We study the adhesion, friction and leak rate of seals for four different elastomers: Acrylonitrile Butadiene Rubber (NBR), Ethylene Propylene Diene (EPDM), Polyepichlorohydrin (GECO) and Polydimethylsiloxane (PDMS). Adhesion between smooth clean glass balls and all the elastomers is studied both in the dry state and in water. In water, adhesion is observed for the NBR and PDMS elastomers, but not for the EPDM and GECO elastomers, which we attribute to the differences in surface energy and dewetting. The leakage of water is studied with rubber square-ring seals squeezed against sandblasted glass surfaces. Here we observe a strongly non-linear dependence of the leak rate on the water pressure ΔP for the elastomers exhibiting adhesion in water, while the leak rate depends nearly linearly on ΔP for the other elastomers. We attribute the non-linearity to some adhesion-related phenomena, such as dewetting or the (time-dependent) formation of gas bubbles, which blocks fluid flow channels. Finally, rubber friction is studied at low sliding speeds using smooth glass and sandblasted glass as substrates, both in the dry state and in water. The measured friction coefficients are compared to theory, and the origin of the frictional shear stress acting in the area of real contact is discussed. The NBR rubber, which exhibits the strongest adhesion both in the dry state and in water, also shows the highest friction both in the dry state and in water.

In the present work, a strong filler–filler network of conductive carbon black was strategically established in an elastomer matrix, which leads to a unique combination of electrical and mechanical properties. The novelty of our composites was the development of a strong percolated morphology of nanostructured conducting carbon black particles by the incorporation of relatively large nonreinforcing spherical silica particles, inside the soft elastomer matrix. This technique allowed us to fabricate solution styrene butadiene rubber (S-SBR) composites with outstanding electrical conductivity of 40 S/m, tensile strength ∼10 MPa, and extensibility up to 200%. Furthermore, the electrical conductivity was strain-independent up to 50% elongation strain. The electrical conductivity was found to be unaltered after 2000 loading–unloading cycles. This is the first ever report of a robust elastomeric system with such high electrical conductivity where all the basic ingredients used were selected from well-known comme...

The formation and stability of carbon nanotube (CNT) network in natural rubber (NR), deproteinized NR (DPNR) and polyisoprene (IR) compound were investigated by means of the method of the online measured electrical conductance in a whole process from processing and rolling over pressing/cross-linking to post-stretching. The kinetics of CNT flocculation was described and explained by taking into consideration the depletion force considered as driving force and the thickness of the bound rubber layer considered as hindering factor. The presence of linked phospholipids in NR and DPNR improves the rubber-filler interaction of CNTs through the cation-π bonding that hinders the filler flocculation. The absence of the cation-π bonding in CNT/IR compound and the related thin layer of bound rubber are the reason for the strong tendency of flocculation of CNTs in IR even at room temperature. The effect of pressing time, temperature and cross-linking reaction as well as mechanical deformation on the formation and stability of CNT network in NR compounds was also investigated and discussed by taking into consideration the role of the linked phospholipids.

We report about the successful ‘expanded organoclay’ (EMt) assisted dispersion of multiwall carbon nanotubes (MWCNT) and the subsequent synergy of both fillers in non-polar natural rubber (NR) compounds. Higher upward shifting of G band and substantial reduction of I D /I G ratio of MWCNT in the Raman spectroscopy in the presence of EMt was an indication of strong interactions between MWCNT and EMt particles which further improved the dispersion of MWCNT in the NR matrix. Attributed to the strong affinity of MWCNT with EMt we find significantly exfoliated EMt and homogeneously networked in these composites. The EMt driven dispersion of MWCNT, particularly at high content in the NR, was evidenced from transmission electron microscopy (TEM). The fractal dimension ( d f ) of the MWCNT clusters in NR matrix both in the presence and absence of EMt was predicted utilizing the phenomenological Huber–Vilgis model. Interestingly, a lower value of d f of MWCNT clusters was documented in the presence of EMt. Additionally, both the electrical and mechanical percolation threshold of MWCNT was reduced marginally with the addition of EMt.

Layered double hydroxides (LDHs), inorganic clay materials with mixed metals present in the structure along with some interlayer cations, have immense potential for use as a filler in rubbers. We report the preparation and properties of a set of novel nanocomposites consisting of a LDH dispersed in carboxylic–acrylonitrile–butadiene rubber (XNBR). We succeed in obtaining significantly improved physical properties by altering the chemical structure of a LDH with Zn and Al ions (Zn-Al LDH). In particular, we discover a significant reinforcing effect. This occurs despite the size difference between the LDH and traditional reinforcing fillers such as precipitated silica and carbon black. Both the elastic modulus and tensile strength increase. This increase is a function of the LDH concentration and, reaches a maximum value when the LDH concentration is at 100 phr. Experimental evidence suggests that this reinforcing effect is due to direct ion-to-ion interaction between the filler and the matrix. In addition, we report that the presence of the nanofiller positively affects the flame retardence and thermal decomposition of the nanocomposites. We attribute this effect to the presence of a layer formed by the nanofiller.

A detail study concerning the strain (tensile) dependent electrical conductivity of elastomeric composites is reported in this present paper. Multiwall carbon nanotubes (CNT), conducting carbon black (CB), and their combinations were considered as conducting filler in cross-linked natural rubber matrix. The loadings of the fillers were considered from 3 to 11 phr (filler concentration close to their percolation threshold). Without hindering the elastic nature of the composite (reversible stretchability up to several 100%), the change of relative resistance, ΔR/R0 (ΔR is the change in the resistance with respect to strain and R0 is the initial resistance of the sample) of the CB filled composites was found to be as much as ∼1300 at around 120% elongation. This value is much higher than any other reported values obtained from conducting polymeric composites. It was found that CNT offered a strong strain dependent character in the regime 100% to 150% elongation, whereas, the carbon black filled natural rubbe...

Blends of nitrile butadiene rubber (NBR) and in-situ synthesized thermoplastic polyurethane-urea (PUU) are prepared by a reactive blending method. The PUU is synthesized in-situ from the polyaddition of 4,4′-diphenylmethane diisocyanate-terminated prepolymer with Bisaniline-M during blending with NBR in an internal mixer. The 1H NMR spectroscopic analysis shows up to 93% conversion of Bisaniline-M to PUU in NBR/PUU blends. The incorporation of PUU improves the tensile characteristic, tear and abrasion resistance however a temperature dependent softening of amorphous PUU phase diminishes the dynamic-mechanical behavior of blend vulcanizates. Improvement in physical properties of blends is attributed to good interfacial adhesion between dispersed PUU domains and continuous NBR matrix as seen by TEM.

The overall mechanical performance of ionic elastomers, such as carboxylated nitrile rubber (XNBR), is largely governed by ionic clusters formed during the cross-linking of the elastomers with zinc oxide. These ionic aggregates promote microphase separation and show additional high-temperature relaxation behavior in dynamic mechanical analysis. In this study, the nature of these ionic aggregates is explored for the first time. We find that some zinc-containing compounds, such as zinc–aluminum-layered double hydroxide and zinc chloride, do not exhibit any extra high-temperature dynamic mechanical relaxation processes, although ionic cross-linking reactions with XNBR occur with all of these zinc compounds. Detailed analysis by Fourier-transform infrared spectroscopy and dynamic mechanical analysis revealed that this high-temperature relaxation behavior does not originate from ionic cross-linking but is associated with the formation of an additional zinc-enriched polymer phase that arises due to reactions be...