Showing papers in "Kgk-kautschuk Gummi Kunststoffe in 2007"

Thermoplastic polyurethane filled with carbon nanotubes for electrical dissipative and conductive applications

Abstract: Recently, carbon nanotubes (CNT) have been shown to be attractive fillers for achieving electrical conductivity of polymers at relatively low CNT contents. Amounts lower than 1wt% are reported to be sufficient to get conductive polymers which is much less as compared to carbon black. This efficient behavior of CNT is caused by the excellent electrical properties in combination with the very high aspect ratio, as high as 1000. In addition, mechanical properties may be enhanced due to the fiber like shape of the filler. Thus, it is is also promising to use CNT as additives in polyurethanes for electrically conductive or antistatic applications. The aim of this study is the melt modification of a commercial thermoplastic polyurethane using different multi-walled carbon nanotubes and the study of electrical, mechanical, and thermal properties of the nanocomposites.

Role of Naturally Occuring Lipids and Proteins on Thermal Aging Behaviour of Purified Natural Rubber

Abstract: The effect of naturally occurring lipids and proteins on thermal oxidative degradation was investigated for deproteinized natural rubber (DPNR) and lipids-removed natural rubber (LRNR) obtained from fresh latex of Hevea brasiliensis clone RRIM 600. Chemical and physical changes of heat-aged samples were monitored by Wallace Plasticity, gel permeation chromatography (GPC) and tensile test. The DPNR added with the extracted lipids was the most sensitive for oxidative degradation than that of the neat DPNR but the proteins originally comprised in the NR exhibited as one of the natural antioxidants to hinder the activity of alkylperoxyl radicals under heat accelerated condition.

Characterization of elastomer networks by NMR parameters. Part I sulfur-cured NR networks -

Abstract: 1 H-NMR relaxation measurements are used as a new method for characterizing the network structure of NR vulcanizates. The 1 H-NMR relaxation parameters of NR vulcanizates cured with different amounts of sulfur show different molecular mobility due to differences in crosslink density, hence the differences in the NMR relaxation parameters. The temperature dependence of T 1 , T 2 are also measured. The evolution in the Mc and in the fractions of crosslinked and uncrosslinked parts in the samples cured can be used to caracterize the joining of the long molecular chains to the network during the curing process.

Electrical and mechanical properties of SBR filled with carbon black-silica blends

Abstract: Styrene butadiene rubber (SBR) samples loaded with different concentrations of carbon black -silica blend were investigated with respect to their electrical and mechanical properties. The dielectric properties were described in the frequency range 10 2 to 10 5 Hz as a function of the filler blend concentration. The conductivity has been measured against the filler blend loading, frequency and temperature, to determine the percolation limit. Moreover the change of conductivity during the heating and cooling cycles demonstrates electrical hysteresis. Silane treatment has been carried out for a comparative assessment of its influence on the previous properties and the filler-rubber interaction. The filler dispersion, as revealed by SEM, has been found to be influenced by silane treatment.

Performance enhancement in rubber by modern filler systems

Abstract: This paper identifies potentials to improve rolling resistance of tires using innovative carbon blacks, silicas and a new rubber silane. In particular with the new silane VP Si 363 a significant reduction of the rolling resistance of passenger tires by more than 10% can be achieved. Simultaneously the emission of volatile organic compounds (VOC's) is cut by up to 80%. A new class of silicas with an exceptional morphology provides also a significant drop in hysteresis and simultaneously improves the reinforcement of rubber compounds. The Ecorax family produces an excellent compromise between hysteresis and abrasion resistance and therefore is especially dedicated for the application in truck tire treads. This family was expanded by an extremely low surface area carbon black for the use in tire body compounds to cut hysteresis. Both the understanding of rubber reinforcement by very fine particles and the progressive process technology lay the foundation for the development of these innovative reinforcing filler systems.

On the modelling of rubber ageing and performance changes in rubbery components

Abstract: The long term performance of rubber components was studied using a constitutive model which allows for molecular network degradation and the evolution of a secondary molecular network in a deformed state while subjected to elevated temperature and/or aggressive fluids.

Study on reduction of zinc oxide level in rubber compounds. Part I Influence of zinc oxide specific surface area and the interphase transfer catalyst 18-crown-6

Abstract: The impact of reducing zinc oxide content in IR and E-SBR compounds on vulcanisation kinetics and vulcanisate properties was investigated by using active ZnO(100 nm) and standard ZnO (1μm) and by considering the activation of ZnO by the phase transfer catalyst 18-crown-6. It was found that active ZnO tends to agglomerate in rubber compounds. The difference in activity between active and standard ZnO grades is smaller in IR compounds than in SBRones. It was proven that 18-cown-6 can play an active role in catalyzing the cross-linking reaction, while causing increased reversion in IR compounds. It is shown that the ZnO content can be reduced in carbon black filled IR compounds to 2 phr and in E-SBR compounds even to 1 phr without affecting vulcanisation kinetics and vulcanisate properties.

Properties of the EPDM with modified PTFE nanopowder

Abstract: The use of irradiated PTFE nanopowder in EPDM showed enhanced physical properties as compared to non-irradiated PTFE. Influence of the radiation induced free radicals and structure alterations on the properties of vulcanizate have been investigated. These free radicals generated after irradiation are available for chemical coupling with the unsaturation in EPDM. The improvement in the physical properties is primarily due to the chemical coupling. Further evidence for the existence of chemical coupling is established from the dynamic mechanical analysis and scanning electron microscopy.

The Effect of Oil Swelling on the Fatigue Life of Elastomers Subjected to Cyclic Bubble Inflation

Abstract: This paper describes the behaviour of rubber in multi-axial fatigue, with respect to oil resistance. A series of tests were carried out on EPDM specimens subjected to varying degrees of swelling. The control methodology and the loading mechanism employed in the testing of elastomers using dynamic multi-axial bubble inflation are outlined. Swollen specimens were cycled to failure and the results were analysed. The number of cycles to failure for a given engineering stress amplitude was plotted for both unswollen and swollen specimens. Fracture surfaces for each set of specimens were analysed. The effect of swelling on the stress-strain behaviour and the change in complex modulus for each specimen set is discussed.

Effect of filler-elastomer interaction on tire tread performance Part I Hysteresis of filled vulcanizates

Abstract: It is generally accepted that dynamic hysteresis, wet friction, and abrasion resistance of tread compounds play dominant roles in rolling resistance, wet skid resistance and wear resistance of tires, respectively. For filled vulcanizates, these properties are significantly affected by the filler morphology and its surface characteristics. The first part of this series will briefly review the effects of filler-polymer and filler-filler interactions on dynamic properties. Both theoretical and practical aspects of these effects are discussed. The following parts are dedicated to wet friction, especially micro-elasto-lubrication and abrasion resistance.

Reinforcement of rubber compounds with nano-filler

Abstract: Nano CaCO 3 is one of the many emerging applications of nanotechnology that is already finding successful commercial application. Reinforcing effect of Nano CaCO 3 in different compounds - NR and NR/NBR blend used in Sports Goods (laminated sheet for inflated balls), NR based cycle tube, bromobutyl based pharmaceutical closures and CPE/CSM blend used for coated fabric was studied with one characteristics in mind that is to improve barrier properties as all these products have requirement of one common property-air retention. Rheometric study and physical properties of the vulcanized compounds have been reported.

Thermal oxidation aging of rubbers - : Characterization by chemiluminescence

Abstract: The investigations ofthermal-oxidative aging on polydienes with systematic varied microstructure showed that high concentrations of double bonds in the polymer backbone play the significant role. From the shift of OlT-values it is observed, that styrene units have a relatively more stabilizing effect than vinyl units. Semi-quantitative infrared spectroscopic measurements taken during the course of CL analysis show much higher reactivity for 1,4-butadiene-units in comparison to vinyl. The kinetic evaluation of the CL curves results in rising reaction rate constants with increasing temperature and leads to activation energy values consistent with the reactivity of the polymers. In the investigations on the influence of processing it could be observed, that the raw polymer stabilizer is consumed during milling due to the effect of temperature, shearing and oxygen.

Lightly epoxidized polybutadiene with efficient interaction to precipitated silica

Abstract: Lightly epoxidized cis-polybutadiene (EpBR) was prepared and used to partly substitute cis-BR in passenger tread compounds containing silica. The rubber-filler interaction was characterized by investigating processing characteristics, the filler dispersion, the mechanical and dynamic properties of the vulcanizates. It was evidenced that the reaction between EpBR and silica could be easily monitored and controlled during the mixing process in an internal mixer. It was also observed an increase in the bound rubber content proportional to the amount of EpBR added. Due to the more efficient polymer-filler interactions compounds containing EpBR/cis-BR showed Payne Effect 40 % lower and higher tans at low temperatures than the analogous ones were TESPT was employed as coupling agent.

An approach to the estimation of long-term stress relaxation in elastomers

Abstract: A concept to increase the precision of the prediction of long-term stress relaxation in elastomers from tests conducted over short time frames is discussed. A method to separate physical and chemical relaxation processes has been developed. The basis of the method is to evaluate the continuous relaxation time spectrum for each test temperature in order to separate the relaxation processes. Subsequently a summation of all processes may be used to produce a time and temperature dependent curve fit.

A new rubber silane for future requirements : Lower rolling resistance; Lower VOCs

Abstract: This contribution focuses on a new rubber silane for the tire industry-VP Si 363. It is shown that compared to traditional silanes a reduction of rolling resistance by more than 10% is achievable while additionally the emission of volatile organic compounds (VOCs) is reduced by up to 80%. Beside results of a tire test detailed in-rubber investigations are presented. Synergisms with different compounding ingredients are discussed and mechanistic explanations are given.

Axial stiffness of carbon black filled rubber bushings : Frequency and amplitude dependence

Abstract: A simple engineering model for the axial dynamic stiffness of carbon black filled rubber bushings in the frequency domain including amplitude dependence is presented. The axial stiffness is calcula ...

Modeling and practice of ethanol-devolatilization of silica-silane rubber compounds in an internal mixer

Abstract: During mixing of a silica-silane rubber compound, the mixer is not only used for dispersion, but also for a chemical reaction. A good dispersion is reached by high shearing forces, preferably applied at lower temperatures, whereas the reaction rate of the silanization is increased with increasing temperature, but at the expense of scorch safety. Another limiting factor for the silanization reaction is the ethanol concentration, requiring effective devolatilization of the compound. A model for the devolatilization of a silica compound in an internal mixer is theoretically derived and experimentally verified. The most important factors are identified: the frequency of surface renewal and the surface-to-volume ratio of the compound as well as a low ethanol pressure in the void space of the mixer are the main contributors.

Crosslinking of nitrile rubber by electron beam irradiation at elevated temperatures

Abstract: The influence of different temperatures on electron beam irradiation of nitrile rubber with 18% acrylonitrile content in presence and absence of polyfunctional monomers like trimethylolpropane triacrylate (TMPTA), tripropyleneglycol diacrylate (TPGDA), trimethylolmethane tetraacrylate (TMMT) and m-phenylene bismaleimide were studied. The structural changes with different doses of radiations were investigated with the help of FTIR spectroscopy (in the ATR mode), dynamic mechanical thermal analysis and sol-gel analysis. The ratio of scissioning to crosslinking for nitrile rubber has been determined using the Charlesby-Pinner equation. The mechanical properties have been studied and the tensile strength is found to increase with grafting of polyfunctional monomers on irradiation at high temperature.

Investigation of the elastomer-foam production with single-sided NMR

Abstract: Single-sided NMR Sensors, like the NMR-MOUSE, are in use for non-destructive quality control of arbitrarily sized elastomer parts for some time. In this work we calibrate NMR relaxation times and signal amplitudes with data of cross-link density and density determined by conventional methods for natural rubber foams. A sensor that excites a thin sensitive slice, was used to detect inhomogeneities of foam density and cross-link density spatially resolved across the samples. The results show that single-sided sensors can be used to simultaneously measure profiles of both properties with the ability to detect failures and to provide new insights into the foaming process.

Friction of rubber sliding against ceramics Part I Dry and water lubricated conditions

Abstract: The static friction coefficient between rubber specimens and ceramic surfaces was measured. Rubber test specimens in the form of square cross section with V-grooves were tested at 50,100 and 150 N normal load at dry and water lubricated ceramic surface. Dry sliding of the rubber test specimens displayed the highest value of friction coefficient due to increased adhesion and deformation. The friction coefficient increased as the load applied on the rubber specimens decreased and the height of the V-grooves increased. For water lubricated ceramics, the value of the friction coefficient dropped compared to dry sliding. A further decrease in friction coefficient was observed when the water contains soap.

Processing properties of various grades of thai natural rubber

Abstract: This work was an attempt to investigate variations in processing properties of various grades of Thai natural rubber (NR) before and after compounding, i.e. viscosity, elasticity and plasticity retention index (PRI). It was found that variation in Mooney viscosity, MR 30 and PRI in NR samples of both smoked sheets and standard block rubbers was not affected to the consistency in processing properties. The mixing properties such as black incorporation time (BIT), mixing time and mixing energy, of NR were also investigated. The properties of the obtained rubber compounds were also fairly consistent. The constant-viscosity graded NR (CV-NR) was proved to be the most consistent grade of NR in aspect of the rheological properties and resistance to oxidation (PRI).

The potential of the NMR-method within the rubber industry

Abstract: Nuclear Magnetic Resonance (NMR) is a well established tool in medical diagnostics and chemical analysis. Magnetic relaxation times correlate with chain mobility in polymer compounds. For example the crosslink density or the state of ageing can be determined. Short measurement times, a very easy sample preparation, and the small amount of sample material needed makes the NMR-method attractive for the rubber industry. The principle of the method is briefly reviewed and the use of NMR in material development, process engineering and quality control of rubber products is discussed. Finally an outlook on the future possibilities of NMR in the rubber industry is given.

Friction of Rubber Sliding Against Ceramics Part ll1 Influence of Oil and Oil-Water Lubrication

Abstract: The static friction coefficient caused from sliding of rubber specimens against ceramic surfaces lubricated by oil and oil diluted by water was investigated on test specimens with V-grooves at 50,100 and 150 N normal load. For oil lubricated ceramic, the friction coefficient decreased with increasing height of the grooves. The decrease may be from the well adherence of oil on the rubber surface and a film formation. A mixture of oil and water displayed values of friction much lower than that observed for oil lubricated condition. Friction coefficient decreased as the height of the grooves increased and consequently the capacity of the groove increased to restore lubricant fluid and feed once again into the contact area as load decreases.

Diimide hydrogenation of polydienes

Abstract: The hydrogenation of natural rubber (NR), styrene-butadiene rubber (SBR) and butadiene rubber (BR) with high 1,4-cis content was investigated by using diimide generated in situ from thermal decomposition of p-toluenesulfonylhydrazide (TSH). The degree of hydrogenation increased with the augmentation of reaction time, the molar ratio of the reagents and the temperature. FT-IR and iodometry were employed to determine the changes in the chemical composition. The thermal behavior of the hydrogenated rubbers was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

Strain-induced crystallization of crosslinked natural rubber

Abstract: Characteristics of the strain-induced crystallization (SIC) of crosslinked natural rubber with different network-chain densities (v) was reviewed, which were investigated by a simultaneous tensile and time-resolved synchrotron wide-angle X-ray diffraction measurement. In order to appear the reason for excellent mechanical properties of natural rubber (NR), the SIC behavior ofsulfurcured NR (S-NR) was compared with that of sulfur-cured isoprene rubber (S-IR). The SIC of peroxide-crosslinked NR (P-NR) was also studied using a synchrotron radiation system at SPring-8. The elongation ratio at the onset of strain-induced crystallization (α c ) was found to become smaller with the increase of vfor P-NR, differently with the result of S-NR, where α c, was independent on v. The result of P-NR agreed with the prediction by Flory and was consistent with the classical theory of rubber elasticity. Thus, the network structure of P-NR was suggested to be more homogeneous comparing with that of S-NR.

Equibiaxal test of elastomers

Abstract: The aim of this work is to set up nonlinear viscohyperelastic material parameters of elastomers for numerical finite element simulation (FEM). The study is focused on equibiaxial elongation by using the "bubble inflation" technique. These data together with those from uniaxial tests were used to create a FEM model.

Improving the Prediction of Stress Softening in Rubber Components

Abstract: This research develops a method for assimilating stress softening of elastomers into finite element analysis (FEA) using standard software and phenomenological material models. This required the design and implementation of a user subroutine which can be included in standard code to allow accurate simulation of stress softening effects for elastomeric components or test specimens. Experimental methods corroborated the FEA simulations and hence validated the subroutine allowing its implementation. The method used in conjunction with physical testing was 3D Image Correlation Photogrammetry using the commercially available system ARAMIS. The paper also describes the experimental procedure to conduct measurements of localised deformations and strains using ARAMIS for specimens of different geometries. A comparison of experimental values from ARAMIS and those from FEA was made to validate the FEA simulation of stress softening effects. The results for different rubber specimens are presented.

Magnetorheologische Elastomere : Einfluss der Partikelausrichtung auf die Schaltbarkeit

Abstract: The logical and dynamic mechanical properties of composite materials consisting of magnetically active particles embedded in an elastomeric matrix strongly depend on the orientation of the magnetic particles. This article shows the influence of the parameters temperature, time, and magnetic flux density during the vulcanization process on the orientation of the particles and thus the achievable anisotropy of mechanical properties and magnetorheological effect.

Thermogravimetrischer Analyse an Kautschuk-FUllstoff-Gel : Bestimmung der phasenspezifischen Füllstoffverteilung in Kautschukblends

Abstract: This work presents a new and convenient method for the estimation of the phase selective carbon black distribution in rubber blends by means of thermogravimetry on the rubber-filler gel. The calculated carbon black distribution corresponds very well with the given carbon black distribution in blends on the basis of masterbatches, and with results from online-conductance measurements. At short mixing times, initially the wetting behaviour of the rubber affects the phase specific carbon black distribution. The carbon black localizes firstly in the blend phase with the highest wetting ability (NR). With increasing mixing time, the influence of the rubber-carbon black affinity dominates. A carbon black transfer from the NR to the SBR phase was observed.

From tires to AVS-products : Modern silica systems

Abstract: The modern silica systems are based on 4 points: highly dispersible silicas, a chosen elastomer, an efficient coupling agent and a specific mixing process. Their major properties are a lowering of the Payne effect and an improvement of the fillers dispersion in the matrix. This induced a breakthrough in traditional compromises: the compromise adherence/rolling resistance/wear in the tire industry, and the compromise comfort/handling/endurance in the AVS industry. These "Green" compounds show the potential of research for an innovating company like Michelin and its ability to transfer its discoveries and its knowledge in the whole fields for which the company is implied.