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Rubber nanocomposites based on commercially available carbon allotropes and poly (1,4-cis-isoprene) (IR) were investigated. The carbon allotropes used were exfoliated graphene nanoplatelets (xGnPs) of type xg C750, carbon nanotubes (CNT-NC7000) and carbon black (CB-Printex xe2). The master batch based on CB-CNT was first prepared by mixing IR with CB and CNT. Final nanocomposites were obtained by adding xg C750 (from 2 to 15 phr). Role of increasing xg C750 loading in rubber matrix on dynamic-mechanical, thermal and electrical properties is reported. A stability of filler networking was evidenced as demonstrated through multi-hysteresis tests.

e propose a moving-boundary scenario to model the penetration of diffusants into dense and foamed rubbers. The presented modelling approach recovers experimental findings related to the diffusion of cyclohexane and the resulting swelling in a piece of material made of ethylene propylene diene monomer rubber (EPDM). The main challenge is to find out relatively simple model components which can mimic the mechanical behavior of the rubber. Such special structure is identified here so that the computed penetration depths of the diffusant concentration are within the range of experimental measurements. We investigate two cases: a dense rubber and a rubber foam, both made of the same matrix material.After a brief discussion of scaling arguments, we present a finite element approximation of the moving boundary problem. To overcome numerical difficulties due to the \textit{a priori} unknown motion of the diffusants penetration front, we transform the governing model equations from the physical domain with moving unknown boundary to a fixed fictitious domain. We then solve the transformed equations by the finite element method and explore the robustness of our approximations with respect to relevant model parameters. Finally, we discuss numerical estimations of the expected large-time behavior of the material., https://arxiv.org/abs/2012.07591

To model the penetration of diffusants into dense and foamed rubbers a moving -boundary scenario is proposed. After a brief discussion of scaling arguments, we present a finite element approximation of the moving boundary problem. To overcome numerical difficulties due to the a priori unknown motion of the diffusants penetration front, we transform the governing model equations from the physical domain with moving unknown boundary to a fixed fictitious domain. We then solve the transformed equations by the finite element method and explore the robustness of our approximations with respect to relevant model parameters. Finally, we discuss numerical estimations of the expected large -time behavior of the material.

For improvement of elastomer properties, it is a common practice to combine the properties of different rubbers in a blend system. The effect is depending on the morphology of the blend and on the miscibility of the selected polymers. So, it can be expected, that the behaviour of such blends in thermal oxidative ageing or in stabilizing effects by one of the blend partners is influenced by the used polymers itself, the blend ratio and the morphology. Furthermore, fillers should have an influence because of limiting the diffusion of oxygen and they can be a carrier for oxygen beside catalytic effect. To improve material properties and to predict the material behaviour especially under dynamic load, a detailed knowledge about the kinetics and the spatial evolution of the ageing process in dependency on temperature, time and sample composition is necessary. Concerning the spatial evolution of material changes, the DLO effect and stability against cracks are important factors. So, the investigations are focused on the kinetics and the DLO-effect in a two-phase system on the base of EPDM and NBR and on a miscible system consisting of SBR and BR. It is clearly observed that a stabilizing effect of a more stable polymer in the blend needs high miscibility, in ideal case a one phase system. In two phase systems the more sensitive polymer is limiting the properties, but the aging is depending extremely on the blend ratio., For improvement of elastomer properties, it is a common practice to combine the properties of different rubbers in a blend system. The effect is depending on the morphology of the blend and on the miscibility of the selected polymers. So, it can be expected, that the behaviour of such blends in thermal oxidative ageing or in stabilizing effects by one of the blend partners is influenced by the used polymers itself, the blend ratio and the morphology. Furthermore, fillers should have an influence because of limiting the diffusion of oxygen and they can be a carrier for oxygen beside catalytic effect. To improve material properties and to predict the material behaviour especially under dynamic load, a detailed knowledge about the kinetics and the spatial evolution of the ageing process in dependency on temperature, time and sample composition is necessary. Concerning the spatial evolution of material changes, the DLO effect and stability against cracks are important factors. So, the investigations are focused on the kinetics and the DLO-effect in a two-phase system on the base of EPDM and NBR and on a miscible system consisting of SBR and BR. It is clearly observed that a stabilizing effect of a more stable polymer in the blend needs high miscibility, in ideal case a one phase system. In two phase systems the more sensitive polymer is limiting the properties, but the aging is depending extremely on the blend ratio.

Ageing processes determining the service life of elastomer components. Over the course of time mechanical-dynamic (fatigue), oxidation processes, temperature, exposition to UV light (photo oxidation) and aggressive media lead to irreversible changes in the physical and chemical properties of an elastomer material, often resulting in premature functional failure of the component concerned. Especially in presence of high temperatures and mineral oils NBR and HNBR are used high performance polymers. The knowledge about chemical ageing mechanisms, kinetics and about the weak parts in the polymer chain and in the chemical network are fundamental for lifetime prediction and measures in stabilizing the polymer matrix. Already in the mixing and vulcanization process during manufacture as well as in a subsequent tempering operation (postcuring), the material undergoes thermo-oxidative stress, resulting in a certain prior deterioration. The oxidation reactions, responsible for the irreversible changes of properties, begin at the surface and are reduced in direction of the bulk of the material. So, the ageing process is a function of time and space. A gradient in hardness and stiffness from the surface into the bulk of the material is the consequence. This effect is described by the DLO-effect (Diffusion Limited Oxidation). Alongside the selection of polymers, the ageing process is determined mainly by the use of anti-ageing agents. The influence of crosslinking and of fillers on thermal-oxidative ageing has scarcely been investigated. Overall, for the prediction of life time of elastomers and for the application of simulation models an high interest is existing in a complete knowledge about the chemical mechanisms and especially in quantifying the ageing processes by means of kinetic data., Ageing processes determining the service life of elastomer components. Over the course of time mechanical-dynamic (fatigue), oxidation processes, temperature, exposition to UV light (photo oxidation) and aggressive media lead to irreversible changes in the physical and chemical properties of an elastomer material, often resulting in premature functional failure of the component concerned. Especially in presence of high temperatures and mineral oils NBR and HNBR are used high performance polymers. The knowledge about chemical ageing mechanisms, kinetics and about the weak parts in the polymer chain and in the chemical network are fundamental for lifetime prediction and measures in stabilizing the polymer matrix. Already in the mixing and vulcanization process during manufacture as well as in a subsequent tempering operation (postcuring), the material undergoes thermo-oxidative stress, resulting in a certain prior deterioration. The oxidation reactions, responsible for the irreversible changes of properties, begin at the surface and are reduced in direction of the bulk of the material. So, the ageing process is a function of time and space. A gradient in hardness and stiffness from the surface into the bulk of the material is the consequence. This effect is described by the DLO-effect (Diffusion Limited Oxidation). Alongside the selection of polymers, the ageing process is determined mainly by the use of anti-ageing agents. The influence of crosslinking and of fillers on thermal-oxidative ageing has scarcely been investigated. Overall, for the prediction of life time of elastomers and for the application of simulation models an high interest is existing in a complete knowledge about the chemical mechanisms and especially in quantifying the ageing processes by means of kinetic data.

The life time prediction is always at the forefront of materials researchers. The end of the life of seals is defined when a leakage happened. Until a leak happens, materials gradually degrade due to several factors such as mechanical fatigues, oxidation, temperature, media, and pressure. These factors lead irreversible changes in the physical and chemical property of materials. Especially the deformation conditions to which rubber are subjected have a considerable effect and, in many cases, the decisive effect on their service life. Therefore, in practical, it is important to consider thermal oxidation under stress. However, it is difficult to analyze the rubber oxidation even without stress. The available information on the oxidation of materials under stress is very scarce and mostly qualitative in the previous studies.This paper focuses on the oxidative reaction rate and activation energy under deformation., The life time prediction is always at the forefront of materials researchers. The end of the life of seals is defined when a leakage happened. Until a leak happens, materials gradually degrade due to several factors such as mechanical fatigues, oxidation, temperature, media, and pressure. These factors lead irreversible changes in the physical and chemical property of materials. Especially the deformation conditions to which rubber are subjected have a considerable effect and, in many cases, the decisive effect on their service life. Therefore, in practical, it is important to consider thermal oxidation under stress. However, it is difficult to analyze the rubber oxidation even without stress. The available information on the oxidation of materials under stress is very scarce and mostly qualitative in the previous studies.This paper focuses on the oxidative reaction rate and activation energy under deformation.

Concerning mobility elastomers are subject to increasingly high requirements in media, temperature and oxidation stability, to be accompanied at the same time by a high level of mechanical value. These requirements are achieved by elastomers based on rubber types having a saturated main chain like FKM and EPDM, which are crosslinked by peroxides. To further optimize the properties of peroxide cure systems a combination of peroxide and suitable coagents like triallylisocyanurate (TAIC), triallylcyanurate (TAC) and trimethylmethacrylate (TMPTMA) have been evaluated with respect to crosslinking efficiency, product properties and emission of curing fumes. Crosslinking efficiency, kinetic data and physical properties are investigated by means of rheometry, swelling and tensile strain test. The results show that the crosslinking of FKM is mainly depending on coagent concentration. The consequence of this behaviour is a minimal peroxide concentration required in combination with different types of coagents to achieve an adequate crosslinking density with appropriate physical properties. Furthermore, the influence of coagent type on the kinetics of FKM crosslinking is shown., Concerning mobility elastomers are subject to increasingly high requirements in media, temperature and oxidation stability, to be accompanied at the same time by a high level of mechanical value. These requirements are achieved by elastomers based on rubber types having a saturated main chain like FKM and EPDM, which are crosslinked by peroxides. To further optimize the properties of peroxide cure systems a combination of peroxide and suitable coagents like triallylisocyanurate (TAIC), triallylcyanurate (TAC) and trimethylmethacrylate (TMPTMA) have been evaluated with respect to crosslinking efficiency, product properties and emission of curing fumes. Crosslinking efficiency, kinetic data and physical properties are investigated by means of rheometry, swelling and tensile strain test. The results show that the crosslinking of FKM is mainly depending on coagent concentration. The consequence of this behaviour is a minimal peroxide concentration required in combination with different types of coagents to achieve an adequate crosslinking density with appropriate physical properties. Furthermore, the influence of coagent type on the kinetics of FKM crosslinking is shown.

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There is a need to improve the knwledge of the hazardous substances in rubber fumes, in a context of increasing exposure issue on emissions of volatile chemicals to the workplace. This study carried out a fume crossover trial on various formulations, investigating ingredients and processes such as temperature, curing time, moisture, to find fume volatile substances. These identified fume substances were further analysed to find the contamination process between ingredients and reaction products. A database of substances and ingredients was shared which is hoped will become a tool for rubber (re)formation and process substitution., There is a need to improve the knwledge of the hazardous substances in rubber fumes, in a context of increasing exposure issue on emissions of volatile chemicals to the workplace. This study carried out a fume crossover trial on various formulations, investigating ingredients and processes such as temperature, curing time, moisture, to find fume volatile substances. These identified fume substances were further analysed to find the contamination process between ingredients and reaction products. A database of substances and ingredients was shared which is hoped will become a tool for rubber (re)formation and process substitution.

This paper focuses on a study of temperature deficiency and kinetic aspects of thermal-oxidative aging, the infuence of polymer structure on S-SBR's types, the influence of crosslinking density and consumption and mechanistic aspects of antioxidants (p-phenylenediamines)., This paper focuses on a study of temperature deficiency and kinetic aspects of thermal-oxidative aging, the infuence of polymer structure on S-SBR's types, the influence of crosslinking density and consumption and mechanistic aspects of antioxidants (p-phenylenediamines).

The glucose-sensing enzyme glucokinase (GK) plays a key role in glucose metabolism. We report here the effects of a novel glucokinase activator, LY2121260. The activator enhanced GK activity via binding to the allosteric site located in the hinge region of the enzyme. LY2121260 stimulated insulin secretion in a glucose-dependent manner in pancreatic beta-cells and increased glucose use in rat hepatocytes. In addition, incubation of beta-cells with the GK activator resulted in increased GK protein levels, suggesting that enhanced insulin secretion on chronic treatment with a GK activator may be due to not only changed enzyme kinetics but also elevated enzyme levels. Animals treated with LY2121260 showed an improved glucose tolerance after oral glucose challenge. These results support the concept that GK activators represent a new class of compounds that increase both insulin secretion and hepatic glucose use and in doing so may prove to be effective agents for the control of blood glucose levels in patients with type 2 diabetes.