bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Filler Flocculation in Silica-Filled Rubbers Part I. Quantifying and Tracking the Filler Flocculation and Polymer-Filler Interactions in the Unvulcanized Rubber Compounds
Authors: Lin Chenchy J. , Hergenrother W. L. , Alexanian E. , Böhm G. G. A.
Published: February 2011

Filler flocculation was followed for silica filled compounds containing various alkoxy silanes and non-silane type polar additives. The methodology employed in this paper permitted a quantitative characterization of filler flocculation and polymer-filler interactions after heating the compound under conditions that simulated vulcanization. With the addition of trialkoxy silanes, the reduction of filler flocculation and the degree of polymer-filler interactions were found to depend on the type and the concentration of silane added, and on the mixing drop temperature (Td) used. Greater polymer-filler interactions and flocculation suppression were obtained with a compound containing a tetrasulfane when compared to that containing either a disulfane or a monofunctional-silane. Polar additives such as an amine compound and a sugar alcohol did not reduce the silica flocculation during simulated vulcanization because they were dewetted from the silica surface upon heating. The filler flocculation process was monitored by following the change of dynamic storage moduli using an on-line rheometer. The flocculation process order and process constant were extracted from the non-linear regression analysis of the kinetic data. These kinetic parameters were used to quantify the suppression of filler flocculation by the additives used. Filler flocculation was found not to be affected by the vulcanization process because it occurred prior to the onset of cure.
New Ultra High CIS Polybutadiene Through a Novel Neodymium Catalyst
Authors: Kwag Gwanghoon , Kim Aju , Lee Seunghwon , Jang Youngchan , Kim Pillsung , Baik HunJong , Yoon Dong-Il , Jeong Hoyoung , Lee Jung Goo , Lee Hosull
Published: February 2011

A significant improvement in the catalytic activity of Nd-based catalyst for 1,3-butadiene polymerization has been achieved using a novel neodymium compound, NdH(neodecanoate)4 (Nd( neodecanoate)3 (neodecanoic acid)). The neodymium compound was characterized with a matrix assisted laser desorption ionization (MALDI) mass spectroscopy, with a synchrotron X-ray absorption spectroscopy (XAS), and with computer simulations. A distinguished molecular ion peak (m/z=838.7, [M]) and a pronounced absorption edge are observed in the mass and in the Nd-LIII XANES(X-ray absorption near edge structure) spectra of NdH(neodecanoate)4, respectively, which evidence its monomeric structure. An active-center of the monomeric Nd-catalyst is fully optimized by density functional method (B3LYP/CEP-31G), in which neodymium(III) is coordinated with carboxylate, allylic active end, penultimate double bond, and chloride. The bond distances are Nd-C1 2.586 A˚, Nd-C4 2.741 A˚, Nd-C5 2.738 A˚, Nd-Cl 2.651 A˚, and Nd-O1 2.167 A˚, respectively. The Nd-catalyst shows a high activity (1.6×106 g/Nd md·h) and produces polybutadiene with 99% cis content. The ultra high cis polybutadiene produced by the Nd-catalyst exhibits excellent physical and mechanical properties such as high abrasion resistance, rebound, tensile properties and remarkably low heat build-up, which will greatly improve tire performance.
Strain-Induced Crystallization and Strength of Rubber
Authors: Gent A. N. , Zhang L.-Q.
Published: February 2011

The rate and extent of crystallization in crosslinked samples of natural rubber (NR), cis-1,4-polybutadiene (BR), and butyl rubber (IIR), were studied by observing the relaxation of stress in stretched strips, held at low temperatures. Melting temperatures were measured from the recovery of stress on warming. The melting temperature was raised by stretching, and the rise was significantly greater for NR than for BR, consistent with the lower heat of fusion of NR. In some cases crystallization was also followed by volume changes, or by DSC or x-ray diffraction. The maximum degree of crystallization was estimated to be only about 20% for BR, 28% for NR, and somewhat higher for IIR. On raising the temperature the tensile strength showed a marked drop to only 1–2 MPa when the elastomer failed to crystallize on stretching. At lower temperatures, when strain-induced crystallization occurred, the tensile strength was much higher, but the values were different for the three elastomers: about 10 MPa for BR, 20 MPa for NR, and 30 MPa for IIR, roughly in proportion to the inferred extent of crystallization. We speculate that molecular entanglements (more dense in BR and less dense in IIR than in NR) are severe obstacles to crystallization in high-molecular-weight polymers. Some specific molecular features are inferred that are needed for an elastomer to crystallize on stretching and to exhibit high strength over a wide temperature range.
Simulation of Crosslink and Graft Mechanism of Hydrogenated-NBR/ZINC Di-Methacrylate Composites by Moving Die Rheometer
Authors: Sato Takashi , Fujino Akio , Hayashi Sachio , Oyama Motofumi , Ono Katsumichi
Published: February 2011

This paper studies the crosslink and graft mechanism of hydrogenated-NBR/zinc di-methacrylate (HNBR/ZDMA) composites. The experiments to determine the rate constants of crosslink and graft reaction formulas are from Moving Die Rheometer (MDR) data. Comparison with experimental data and the solution of simultaneous ordinary differential equations for the crosslink and graft reactions are performed. Genetic algorithm optimization of the reaction rate constants allowed for simulation of crosslinking and graft reaction process.

This simulation predicts that the HNBR/peroxide cure system will contain 0.1052-mole/l crosslink between matrix HNBR polymer at 2 phr.-peroxide concentration. The crosslink concentration of 0.1052-mole/l is composed of 0.0308-mole/l-addition reaction and 0.0744-mole/l-termination reaction. Moreover, the HNBR/ZDMA cure system contains 0.0148-mole/l graft of poly-ZDMA to HNBR and 0.0903-mole/l crosslink between matrix HNBR polymer at a 2 phr.-peroxide concentration.
A Novel Method to Recycle Scrap Tires: High-Pressure High-Temperature Sintering
Authors: Morin Jeremy E. , Williams Drew E. , Farris Richard J.
Published: February 2011

High-pressure high-temperature sintering (HPHTS) is a novel recycling technique that makes it possible to recycle vulcanized rubber powders made from waste rubber (namely scrap tires) through only the application of heat and pressure. A brief look into the mechanism of sintering will be presented along with information about the influence of molding variables, such as time, temperature, pressure and rubber particle size on the mechanical properties of the produced parts. One of the most interesting observations is that powders of every crosslinked elastomer attempted sintered together via this technique, including silicone rubber (SI), sulfur cured [natural rubber (NR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR)], peroxide cured butadiene rubber (BR), and fluoroelastomers (FKM). Early work on sintered rubber made from commercially available rubber powder had a modulus of 1 to 2 MPa, strength of 4 to 7 MPa and an elongation at break of 150–250%. Recently, in-house ground samples of SBR have had sintered values over 9.5 MPa strength and 275% elongation, or greater than 60% retention of the original properties. Many of these mechanical properties are comparable with industrially manufactured rubbers, and it is believed that recycled rubbers produced via HPHTS offer the potential to replace virgin rubber in numerous applications.
Monte Carlo Simulation of the Peroxide Curing of Ethylene Elastomers
Authors: Johnston Robert T.
Published: February 2011

Four ethylene octene copolymers covering a range of 0.87–0.91 g/cc density and 0.5–30 melt index were crosslinked using 0.25–8.0 phr dicumyl peroxide and characterized by sol-gel analysis and dynamic viscometry in an RPA 2000 rheometer. Using Monte Carlo simulation, the peroxide initiation efficiency (45–57%) and scission/crosslinking ratio (0.10–0.26) were determined. After using these sol-gel results to calibrate the simulation, the simulation was used to predict and analyze the crosslinked network structure as a function of extent of peroxide reaction. From the simulation output, the RPA 2000 dynamic storage modulus was successfully modeled using a three component model comprised of: (a) an affine modulus contribution related to the number of elastically active chains; (b) a Pearson-Graessley trapped entanglement contribution related to the weight fraction of elastically active network chains and the plateau modulus (which was in turn related to copolymer composition through a polymer backbone weight fraction model); and (c) a relaxation modulus component related empirically to network defects. These results show how misleading curemeter (ODR, MDR, RPA) data can be without application of an appropriate analytical or simulation model for their interpretation, but also how useful, when appropriately analyzed, these data can be for developing a fundamental understanding of polymer structure-network-property relationships.
Characterization of Rubber Micro-Morphology by Atomic Force Microscopy(AFM)
Authors: Jeon I. H. , Kim H. , Kim S. G.
Published: February 2011

Micro-morphology of the rubber compounds, such as polymer compatibility and carbon black distribution, is one of the most important parameters affecting compound performance. Transmission Electron Microscopy (TEM) technique enables us to examine this micro-morphology, but has many difficulties. It requires high skill for sample preparation, high cost and a long time. Atomic Force Microscopy (AFM) technique is a relatively easy way for detecting these images.

Through TM-AFM (Tapping Mode Atomic Force Microscopy) technique, two different polymer domains were distinguished in the unfilled rubber blend (natural rubber/ synthetic rubber blend). In order to verify the images, analogue signal (voltage) histograms for those images were analyzed by Gaussian multi-peak analysis method. Filler morphology was also examined in the filled natural rubber and filled rubber blend compounds.

Silica and carbon black showed different behavior in the rubber blend. Carbon black lies predominantly in the polybutadiene rubber domain whereas silica exists in the natural rubber domain.
Atomic Force Microscopic Studies on Microheterogeneity of Blends of Silicone Rubber and Tetrafluoroethylene/Propylene/Vinylidene Fluoride Terpolymer
Authors: Ghosh Arun , Rajeev R. S. , Bhattacharya A. K. , Bhowmick A. K. , De S. K. , Wolpensinger B. , Bandyopadhyay S.
Published: February 2011

This paper reports the results of Atomic Force Microscopic (AFM) studies on blends of silicone rubber and fluororubber based on tetrafluoroethylene/propylene/vinylidene fluoride terpolymer. The surface morphology of the single component rubbers and their blends and the effect of the blend ratio on the surface morphology were studied using analysis techniques of AFM images including surface plot, section analysis, roughness analysis and power spectral density analysis. The compatibility of the two rubber phases depends on the dimensions of the granules on the surface, measured from the section analysis and the histograms derived from the section analysis. As predicted by the histograms, the surface morphology of the blends is governed primarily by the silicone rubber, even at low concentration of silicone rubber in the blend. The height image, amplitude image, surface plot and section analysis display a distinct surface morphology for the 50/50-silicone rubber/fluororubber blend. The roughness and power spectral density (PSD) analyses show that the 50/50-blend exhibits maximum surface roughness. The results of surface energy measurements of the single component rubbers and their blends in general conform to the findings of AFM studies.
Formation of Rubber Particle Agglomerates During Morphology Development in Dynamically Crosslinked EPDM/PP Thermoplastic Elastomers. Part 1: Effects of Processing and Polymer Structural Parameters
Authors: Goharpey F. , Katbab A. A. , Nazockdast H.
Published: February 2011

Formation of agglomerate structure by the rubber particles through flocculation or networking mechanism during dynamic crosslinking of thermoplastic elastomers based on EPDM rubber and polypropylene has been evidenced. Scanning electron microscopy (SEM) examination performed on the crosslinked blend samples which had been etched by hot xylene suggested that agglomeration occurs mainly through a joint shell mechanism. Reduction of the mixing torque after passing the peak maximum at the dynamic crosslinking stage was concluded to be due to the shear induced breaking down of agglomerates leading to a more defined morphology. Samples removed after the maximum mixing torque showed higher dynamic loss tangent (tan δ) above the PP glass transition. This is attributed to the broadening of the retardation time spectra for the PP matrix in the blend system. Higher mixing torque, higher tensile strength, as well as better extensibility were found for the blend samples based on PP with low MFI value as a result of higher density of aggregates and more extent of their interfacial adhesion with the PP matrix. More defined morphology and higher rate of network breakdown was observed at high mixing shear rate. Mixing torque increased significantly with increasing the rubber content of the blend system from 40% to 60% (W : W) as a consequence of higher interaction of rubber aggregates with the PP matrix. Based on the obtained results, the structure of the rubber aggregates and associated networks as well as extent of interaction between the two phases play an important role in controlling the final morphology, processing behavior and therefore mechanical properties of the dynamically cured blend system.
Modeling Method of Constitutive Law of Rubber Hyperelasticity Based on Finite Element Simulations
Authors: Wang Li-Rong , Lu Zhen-Hua
Published: February 2011

This paper is to present a method and procedure for modeling the constitutive law of anti-vibration rubber hyperelasticity based on finite element simulations. The hyperelasticity of rubber-like material is briefly summarized first. Then a method and procedure for determining an accurate constitutive law of rubber hyperelasticity from uniaxial tension and compression experiment data is presented and implemented. Due to nonlinear elastic properties of rubber and application limitations of various forms of constitutive law, results of finite element simulation to rubber material experiments show that different forms of constitutive law have to be adopted in different ranges of strain. The proposed procedure to obtain an appropriate constitutive law of rubber hyperelasticity of vibration isolator provides engineers with an effective modeling technique for design and analysis of anti-vibration rubber components. Finally, models of three kinds of rubber materials of a hydraulically damped rubber mount (HDM) are determined by tests and finite element simulations and applied to static and dynamic characteristic analysis of the HDM. The predicted elastic characteristics of the HDM and its major rubber components agree well with experimental data, which demonstrates the practicability and effectiveness of the presented modeling technique to modeling engineering rubber materials in dynamic systems.
Utilization of Powdered EPDM Scrap in EPDM Compound
Authors: Jacob Ceni , Bhowmick A. K. , De P. P. , De S. K.
Published: February 2011

Processability, curing characteristics and vulcanizate properties of EPDM compounds containing ground waste EPDM (W-EPDM) have been studied. Ground waste was prepared from factory scraps, using a mechanical grinder with silicon carbide abrasive wheel rotating at 2950 rpm. The particle size shows a range between 2 and 50 μm, with an average size of 10 μm. Particle surface seems to be rough and convoluted and mild oxidation during the abrasion enhances the aggregation of particles. Mooney scorch time and the maximum rheometric torque of the EPDM compound decrease gradually with increasing W-EPDM content. Migration of curatives between the virgin rubber and waste rubber phases is believed to be the reason for the variation in the curing behavior. The processability of the EPDM compound shows improvement on addition of W-EPDM (that is, both die swell and extrudate distortion are less). The vulcanizate properties of the W-EPDM-filled EPDM compounds reveal the reinforcing nature of the ultrafine W-EPDM particles. Comparison of W-EPDM with an inert filler like precipitated CaCO3 in an EPDM compound reveals the potential of W-EPDM as a cheap filler in EPDM compounds. It is also found that W-EPDM can be incorporated into the window seal compound formulation and the drop in properties even at 100 phr of W-EPDM is within acceptable limit, thus providing a scope for on-site recycling of EPDM.
Straining Effects in Silica-Filled Elastomers Investigated by Atomic Force Microscopy: From Macroscopic Stretching to Nanoscale Strainfield
Authors: Lapra A. , Clément F. , Bokobza L. , Monnerie L.
Published: February 2011

Understanding the way fillers can reinforce elastomers requires, among other things, requires a precise description of the behavior of filler aggregates when a macroscopic strain is applied. In this study, Atomic Force Microscopy was used to investigate samples of SBR and PDMS filled with silica. The samples were stretched uniaxially at different strain values (up to 145%) and imaged by Atomic Force Microscopy. The distances between aggregates were followed at the different strains, which allowed calculation of the local strains and comparison of the values obtained with the macroscopic strain value. The main results are (i) that the strain field is highly heterogeneous, depending on the local concentration of filler and (ii) that the strain undergone by elastomer chains can be very high locally, in the regions where distances between aggregates are very short.
Updating a Torsional Dynamic Rheometer for Fourier Transform Rheometry on Rubber Materials
Authors: Leblanc Jean L. , de la Chapelle Christophe
Published: February 2011

A torsional dynamic rheometer has been suitably modified in order to collect actual torque and strain data, in view of studying the non-linear viscoelastic region. Essentially a fast electronic analogic - digital conversion card is used to record and treat torque and strain signals using a purposely written software. A Fast Fourier Transform (FFT) algorithm was first used in order to resolve recorded signals in harmonic peak components. Preliminary investigations were conducted with pure elastomers and filled rubber compounds in order to asses the testing capabilities of the system. As expected, when the non-linear viscoelastic response of a pure, unfilled rubber is produced through increasing strain amplitude, a number of significant odd-harmonic peaks appear in the Fourier Transform Spectrum (FTS). When testing intrinsically non-linear materials such as carbon-black filled rubber compounds, FFT gives also significant odd-harmonics whose relative intensities growth with filler content. Fourier transform rheology has therefore the capability to truly investigate non-linear viscoelasticity but cannot at first sight distinguish between the non-linear behavior appearing upon increasing strain amplitude (extrinsic non-linearity) and the non-linear behavior that reflects the complex heterogeneity of the material (intrinsic non-linearity). Other data analysis techniques were thus investigated; for instance, the detail examination of the actual shape of half-period torque signals. It appears that torque signal distortions are different providing they are obtained either through larger strain amplitude tests on pure polymer or by increasing filler content.
Co-Continuity and Ozone Resistance of Bims Compounds
Authors: Tsou Andy H. , Duvdevani Ilan , McElrath Kenneth O.
Published: February 2011

A co-continuous blend of a high ozone resistant rubber with high diene rubbers, or with a mixture of high diene rubbers, can provide a rubber blend that is both ozone resistant and wear and scuff resistant. High diene rubbers have excellent wear and scuff resistances, but are prone to ozone damage. The high ozone resistant rubbers are rubbers that have saturated backbone after vulcanization, such as BIMS. However, depending on the co-continuous morphology, not all co-continuous blends of an ozone resistant rubber with other rubbers are ozone resistant. In this study, a co-continuity index was proposed to measure the co-continuity morphology of 50/50 BIMS/GPR blends. GPR represents a general-purpose rubber and is a mixture of NR and BR in this study. It was found that BIMS compounds having their co-continuity indices greater than 0.7 are ozone resistant. These ozone-resistant compounds were prepared by first adding GPR followed by adding small N351 CB fillers, as compared with the other large N660 CB used in this work. Thus, smaller CB filler first presence in GPR appears to enhance GPR/BIMS phase compatibility during mixing with later added BIMS leading to strong intermixing between co-continuous phases.
Strains in an Inflated Rubber Sheet
Authors: Mott P. H. , Roland C. M. , Hassan S. E.
Published: February 2011

A technique to measure the strain distribution of an inflated membrane is described, and applied to natural rubber inflated to pole biaxial strains of 12%, 26%, and 33%. The radial strain was found to be nearly constant over the entire surface, while the circumferential strain falls to zero at the edge. Thus, biaxial deformation is limited to a narrow region in the vicinity of the pole. These results are quite different from (the very limited) data published previously. The stress-strain behavior was also measured in uniaxial tension, and the strain distribution of the inflated membrane calculated using finite elements. The experiment results and the modeling were in good agreement.
Experimental Study and Finite Element Simulation of Heat Build-Up in Rubber Compounds with Application to Fracture
Authors: Kerchman Vladamir , Shaw Cheng
Published: February 2011

IR thermography was used to measure surface temperature profiles of cylindrical rubber specimens during cyclic compression. A linearized constitutive approach and finite element analysis were used to evaluate heat generation and associated transient temperature fields. Modeled temperatures compared well with the IR measurements. This led to extended simulation efforts on lab fracture samples. IR thermography was used to measure temperature of filled NR and filled SBR specimens during tensile fatigue cut growth tests. Temperature gradients are expected to relate to kinetics of rubber fracture and identify regions within the sample that are undergoing accelerated damage. The following cut growth issues were addressed: 1) crack propagation direction in a non-uniform stress field; 2) crack propagation direction as a function of the angle of initial cuts; 3) initiation of crack branching; and 4) catastrophic failure. The nonlinear coupled mechanical and thermal FEA was used to evaluate the energy dissipation in the non-homogeneous cyclic deformation of cracked samples. Modeled and measured surface temperatures are in good agreement. Accounting for heat build-up ahead of an advancing crack can improve numerical models that quantify fatigue cut growth behavior in rubber compounds.
Durometer Hardness and the Stress-Strain Behavior of Elastomeric Materials
Authors: Qi H. J. , Joyce K. , Boyce M. C.
Published: February 2011

The Durometer hardness test is one of the most commonly used measurements to qualitatively assess and compare the mechanical behavior of elastomeric and elastomeric-like materials. This paper presents nonlinear finite element simulations of hardness tests which act to provide a mapping of measured Durometer Shore A and D values to the stress-strain behavior of elastomers. In the simulations, the nonlinear stress-strain behavior of the elastomers is first represented using the Gaussian (neo-Hookean) constitutive model. The predictive capability of the simulations is verified by comparison of calculated conversions of Shore A to Shore D values with the guideline conversion chart in ASTM D2240. The simulation results are then used to determine the relationship between the neo-Hookean elastic modulus and Shore A and Shore D values.

The simulation results show the elastomer to undergo locally large deformations during hardness testing. In order to assess the potential role of the limiting extensibility of the elastomer on the hardness measurement, simulations are conducted where the elastomer is represented by the non-Gaussian Arruda-Boyce constitutive model. The limiting extensibility is found to predict a higher hardness value for a material with a given initial modulus. This effect is pronounced as the limiting extensibility decreases to less than 5 and eliminates the one-to-one mapping of hardness to modulus. However, the durometer hardness test still can be used as a reasonable approximation of the initial neo-Hookean modulus unless the limiting extensibility is known to be small as is the case in many materials, such as some elastomers and most soft biological tissues.
A Theoretical Model for the Diffusion-Limited Thermal Oxidation of Elastomers at Medium Temperatures
Authors: Rincon-Rubio L. M. , Colin X. , Audouin L. , Verdu J.
Published: February 2011

A theoretical model is presented to describe the diffusion-limited thermal oxidation of stabilized elastomers, with no assumptions concerning the concentration of oxygen, the kinetic chain length, the ratio of termination rate constants, or the existence of a steady state for oxidation products. Model predictions are found to agree qualitatively with reported main features of elastomer thermal oxidation. The model is used to simulate the thermal ageing of thick natural rubber slabs under ambient air at 80–150 °C. Among others, the effect of stabilizer concentration and thickness of the aged parts on the evolution of the oxidation process is discussed. Conditions are also identified under which the oxidation process may be considered free of oxygen mass transfer limitations.
Fracture Mechanics of Bond Failure in the “Pure Shear” Test Piece
Authors: Yeoh O. H.
Published: February 2011

The “pure shear” test piece consists of a thin, rectangular strip of rubber held by or bonded to rigid grips along its long edges. When the grips are pulled apart, the rubber in the center of the test piece is in a deformed state close to pure shear. This test piece is commonly used for studies of fracture in rubber (rubber tear) because it is amenable to simple fracture mechanics analyses.

The “pure shear” test piece may also be used for study of failure at the rubber-to-metal bond. Its geometry and manner of loading make it especially useful for study of long-term durability of bonds in corrosive environments such as in a salt fog chamber. This paper discusses non-linear finite element analysis results for failure at the bond of the “pure shear” test piece. Results are compared with well-known results for analogous cases in rubber tear. Short and long cracks located in the center and at the free edges are considered.
On the Frequency and Amplitude Dependence of the Payne Effect: Theory and Experiments
Authors: Lion A. , Kardelky C. , Haupt P.
Published: February 2011

In this paper, we develop a physical approach to represent the Payne effect which is observed in filler-reinforced elastomers. The starting point for the constitutive model is the well-known theory of linear viscoelasticity, where the stress is a linear functional of the deformation history. Since the corresponding relations are unable to describe any kind of amplitude dependence, we introduce a nonlinearity into the model. To this end, we replace the physical time, t, by a modified time scale, z, which is a functional of the deformation history. This approach was originally introduced by Valanis in the context of rate-independent plasticity and applied in a modified form; for example, by Haupt and Sedlan to represent process-dependent relaxation properties of rubber. The modified time, z, is a monotonic function of the physical time, t, and can be interpreted as an intrinsic time scale of the material. The rate of this time scale is non-negative and depends on the process history. We propose a constitutive relation for the variable z(t), which is driven by a fractional time derivative of the deformation, calculate analytical expressions for the storage and dissipation moduli and show that such phenomena as the frequency and the amplitude dependence, observed in experiments, are well represented.
The Mechanics and Mechanism of the Carbon Black Reinforcement of Elastomers
Authors: Fukahori Yoshihide
Published: February 2011

The author proposes a new concept, including a model and theory of the carbon black reinforcement of elastomers, based on stress analysis. Two assumptions are introduced: first, that there are very few or no chemical crosslink in the interface layer of carbon particle and matrix elastomer; and, second, that crazing or a craze-like phenomenon takes place within the interface layer. The deformable character of the interface layer depending on the magnitude of extension will realize the dramatic improvement of elastomers over a wide range of extension. At present time, although there is no direct experimental evidence to prove the assumptions, such assumptions just provide a reasonable interpretation of the carbon black reinforcement of elastomers.
Fracture Mechanics and its Application to Failure in Rubber Articles
Authors: Lake G. J.
Published: February 2011

The basis of the fracture mechanics approach that has been developed for elastomers and the range of phenomena, from tearing to cavitation, to which it has been applied are briefly reviewed. The application of the approach to service and related problems is then considered in somewhat more detail, with particular reference to groove cracking in tires and laminate failure studies.
Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model
Authors: Ghosh Prasenjeet , Katare Santhoji , Patkar Priyan , Caruthers James M. , Venkatasubramanian Venkat , Walker Kenneth A.
Published: February 2011

The chemistry of accelerated sulfur vulcanization is reviewed and a fundamental kinetic model for the vulcanization process is developed. The vulcanization of natural rubber by the benzothiazolesulfenamide class of accelerators is studied, where 2-(morpholinothio) benzothiazole (MBS) has been chosen as the representative accelerator. The reaction mechanisms that have been proposed for the different steps in vulcanization chemistry are critically evaluated with the objective of developing a holistic description of the governing chemistry, where the mechanisms are consistent for all reaction steps in the vulcanization process. A fundamental kinetic model has been developed for accelerated sulfur vulcanization, using population balance methods that explicitly acknowledge the polysulfidic nature of the crosslinks and various reactive intermediates. The kinetic model can accurately describe the complete cure response including the scorch delay, curing and the reversion for a wide range of compositions, using a single set of rate constants. In addition, the concentration profiles of all the reaction intermediates as a function of polysulfidic lengths are predicted. This detailed information obtained from the population balance model is used to critically examine various mechanisms that have been proposed to describe accelerated sulfur vulcanization. The population balance model provides a quantitative framework for explicitly incorporating mechanistically reasonable chemistry of the vulcanization process.
Antioxidant Selection for Peroxide Cure Elastomer Applications
Authors: Ferradino Anthony G.
Published: February 2011

For applications demanding the best high temperature aging performance with lowest compression set, polymers are crosslinked with peroxides. The carbon-carbon bonds that are formed are more thermally stable than crosslinks containing sulfur atoms generated by conventional vulcanization by sulfur- and sulfur based cure systems.

However, peroxide crosslinking requires special attention to the selection of compounding ingredients. Materials such as plasticizers, oils, and acidic materials such as silicas and air-floated clays detract from crosslinking efficiency by competing with the polymer for the free radicals produced by peroxides. Antioxidants, as a class, are free-radical scavengers and inhibit peroxide crosslinking.

This paper discusses selecting the best antioxidant systems for peroxide cured elastomers by comparing various classes of antidegradants: peroxy and alkoxy radical traps (amines and hindered phenols), hydroperoxide decomposers, and synergists. Among the most effective include: 1) a quinoline polymerized 1,2-dihydro-2,2,4-trimethylquinoline 2) an amine, p-dicumyl-diphenylamine, 3) a hindered phenol, tetrakis (metylene (3,5-di-t-butyl-4-hydroxy-hydrocinnamate)) methane, and 4) a dithiocarbamate, nickel dimethyl-dithiocarbamate. For optimum performance, these are used in combination with the synergist, zinc-2-mercaptotoluimidazole.

Also presented is an antioxidant system optimization study using a statistically designed experiment.
Adhesion of Rubber to Magnesium Alloys in the Presence of Nickel Branched Alkyl Carboxylates
Authors: Mori K. , Shi X. , Hirahara H. , Oishi Y.
Published: February 2011

The authors investigated the adhesion of rubber compounds containing nickel blanched alkyl carboxylate to surface treated magnesium alloys during curing. Ni i-octylate and Ni i-stearate were used as nickel branched alkyl carboxylate. Rubbers used in the study did not adhere at all to magnesium alloys, such as AZ91, AZ31, AZ 21, and M1 washed with acetone; not even in the presence of Ni i-octylate. Among numerous treating solutions, only sodium hydroxide aqueous solution was effective for adhesion of rubber to magnesium alloys. Adhesion of rubber to magnesium alloy AZ31 treated in 0.5M- sodium hydroxide aqueous solution for 10 min at 80 °C yielded high peel strength and a 100% rubber coverage. Peel strength and a 100% rubber coverage varied with the concentration of additives, such as curing accelerators, sulfur, zinc oxide and Ni-type adhesive accelerators. Ni branched alkyl carboxylates such as Ni i-octylate and Ni i-stearate were effective for accelerating the adhesion of rubber to magnesium alloys treated in sodium hydroxide aqueous solutions during curing. The authors postulate that Ni branched alkyl carboxylate acts to yield interface bonds between magnesium alloys and rubber or Ni-S-rubber linkage.
Distribution of Elastomers and Silica in Polymer Blends Characterized by Raman Microimaging Technique
Authors: Zerda T. W. , Song G. , Waddell W. H.
Published: February 2011

Raman microimaging technique was used to study the distribution of silica filler and elastomer domains in binary and ternary polymer blends containing cis1–4-polybutadiene BR; brominated poly(isobutylenecoparamethylstyrene) BIMS; Natural Rubber, NR; and/or Styrene-Butadiene Rubber, SBR. Contour maps depicting distribution of the elastomer phases and silica within each phase were obtained for 1 μm thick sections of blends having different compositions. All polymers were uniformly distributed throughout the blends. However, on a micrometer scale local fluctuations were clearly observed using Raman microimaging. The BR component is not as compatible with BIMS as are the other polymers based upon the presence of some single-phase BR domains exceeding 5 μm. Addition of the third polymer, either SBR or NR, to the blend improves the BR compatibility with BIMS since the BR domains are not as large. At low concentrations in a ternary blend, the NR phase appears concentrated near the BR domains, but in samples with higher NR concentrations, the natural rubber forms it own network and may also be found near the BIMS domains. The SBR phase was found to be near or within the BR domains. Silica was dispersed throughout the polymers in each blend, but tended to aggregate near the boundaries of the BIMS domains. Sometimes the silica was present within the BIMS domains, but did not locate within a BR domain.
Application of Scanning Transmission X-Ray Microscopy to the Rubber Industry
Authors: Winesett D. A. , Ade H. , Smith A. P. , Urquhart S. G. , Dias A. J. , Stevens P.
Published: February 2011

Materials of commercial significance in the rubber industry are usually multi-component systems composed of several elastomers and various fillers. Elucidating the complex morphology that can arise from blending and understanding how this affects the various properties are essential. A technique advantageous to the study of multi-component elastomeric systems is Scanning Transmission X-ray Microscopy (STXM). STXM utilizes the chemical sensitivity of Near Edge X-ray Absorption Fine Structure (NEXAFS) and combines with relatively high spatial resolution and low beam damage to allow the successful characterization of multi-component materials that may be difficult or impossible with other techniques. An overview of the technique and example applications for the rubber industry is presented.
On the Chemistry of Tetrabenzyl Thiuram Disulfide and Tetramethyl Thiuram Disulfide with Bis (Triethoxysilylpropyl) Tetrasulfide in Silica Compounds
Authors: Datta R. N. , Talma A. G. , Datta S. , Nieuwenhuis P. G. J. , Nijenhuis W. J. , Maslow W.
Published: February 2011

The use of thiurams such as Tetramethyl thiuram disulfide (TMTD) or Tetrabenzyl thiuram disulfide (TBzTD) has been explored to achieve higher cure efficiency. The studies suggest that a clear difference exists between the effect of TMTD versus TBzTD. TMTD reacts with Bis (triethoxysilylpropyl) tetrasulfide (TESPT) and this reaction can take place even at room temperature. On the other hand, the reaction of TBzTD with TESPT is slow and takes place only at higher temperature. High Performance Liquid Chromatography (HPLC) with mass (MS) detection, Nuclear Magnetic Resonance Spectroscopy (NMR) and other analytical tools have been used to understand the differences between the reaction of TMTD and TESPT versus TBzTD and TESPT. The reaction products originating from these reactions are also identified. These studies indicate that unlike TMTD, TBzTD improves the cure efficiency allowing faster cure without significant effect on processing characteristics as well as dynamic properties. The loading of TESPT is reduced in a typical Green tire compound and the negative effect on viscosity is repaired by addition of anhydrides, such as succinic anhydride, maleic anhydride, etc.
A Simple Approach to Characterize Finite Compressibility of Elastomers
Authors: Gurvich Mark R. , Fleischman Thomas S.
Published: February 2011

A hybrid experimental-numerical approach is proposed for accurate dimensionless characterization of rubber finite compressibility. Rubber specimens in the form of bonded rubber disks are considered as elastomeric structures with unknown material properties. These properties are calculated by matching results of FEA with experimental measurements of radial deformations of the axially-loaded disks. The approach may be used for reliable characterization of Poisson's ratio, bulk modulus, or other characteristics of interest. Implementation of the approach is considered for two representative elastomeric compounds with different levels of carbon black. Good experimental verification of the approach is shown at different levels of loading. Moreover, the same parameters of finite compressibility are independently obtained using both compressive and tensile loads. Higher compressibility is observed for a compound with larger content of carbon black as expected.
Devulcanization of Sulfur-Cured Isoprene Rubber in Supercritical Carbon Dioxide
Authors: Kojima M. , Ogawa K. , Mizoshima H. , Tosaka M. , Kohjiya S. , Ikeda Y.
Published: February 2011

A new devulcanization process that utilizes supercritical CO2 (scCO2) along with devulcanizing reagents was studied. Unfilled polyisoprene rubber samples (vulcanizates) with different crosslink distributions were prepared by controlling the cure time and the curatives. Each of the vulcanizates was subjected to the Soxhlet extraction using azeotropic acetone/chloroform to remove residual curatives. The devulcanization was performed at various temperatures (140–200 °C) in the presence of scCO2 for 60 min. The product was fractionated into sol and gel components, and molecular weight of the sol component and the crosslink density of the gel component were determined. Thiol-amine reagent was found to be effective among several devulcanizing reagents; the molecular weight of the resulted sol component was about tens of thousands and the crosslink density of gel component decreased substantially from the initial ones. Yield of the sol component increased with the increase in the CO2 pressure. In the supercritical fluid state of CO2, the vulcanizate was more efficiently devulcanized than in an ordinary gaseous state of CO2. The sol fraction depended considerably on the crosslink distribution in the vulcanizate. These results suggest that the devulcanizing reagents penetrate and diffuse into the vulcanizate in the presence of scCO2.
Influence of the Blend Viscosity and Interface Energies on the Preferential Location of CB and Conductivity of BR/EPDM Blends
Authors: Ibarra-Gómez Rigoberto , Márquez Alfredo , Ramos-de Valle Luis F. , Rodríguez-Fernández Oliverio S.
Published: February 2011

In the present work, the effect of distribution of Carbon Black (CB) and rubber viscosity over the conductivity of rubber blend composites was studied. Preferential location of CB predicted by surface tension measurements and calculation of interfacial energy (wetting coefficient) was corroborated by dynamic analysis (DMA) as well as bound rubber experiments. In this respect, the employment of the DMA technique to infer preferential distribution of CB, through the following of changes in the loss tangent (Tan δ), were proposed and successfully assessed in this study. A double percolation effect was evidenced by the appearance of a maximum in conductivity at relatively low EPDM content and CB concentration; however, when blend viscosity increases due to the addition of EPDM (the most viscous rubber), the double percolation effect is suppressed and the conductivity falls due to the prevailing dispersion effect of CB particles. According to these results, the blend viscosity was found to play a major role in the final conductivity of the studied composites.
Characterizing Gum Elastomers by Fourier Transform Rheometry
Authors: Leblanc Jean L. , de la Chapelle Christophe
Published: February 2011

Fourier transform (FT) rheometry is an emerging new technique that allows the linear and non-linear viscoelastic behavior of polymer materials to be accurately investigated. Basically samples are submitted to torsional harmonic strain at fixed frequency and temperature in order to capture strain and torque signals. A commercial instrument, i.e. the Rubber Process Analyzer RPA 2000® (Alpha Technologies), was suitably modified, essentially in using a fast electronic analogic-digital conversion card to record and treat torque and strain signals using purposely written software. Details of such modifications were previously published and the work presented is a sequel of this development.

The quality of the applied strain is first precisely documented through FT and found excellent, particularly in the high strain range. Three gum EPDM with different macromolecular characteristics (MWD and long chain branching) were analyzed either using standard dynamic testing, i.e. essentially in the linear viscoelastic range, or using the Fourier transform rheometry approach, by considering data gathered in the far non-linear viscoelastic range. Data obtained are considered with respect to know features of the samples.

A series of SBR 1500 samples, collected from various manufacturers, were first analyzed using standard methods; as expected very small differences were seen. Then FT was used to consider torque signals at very high strain (up to 400% at 1 Hz). Using a simple 4-parameter model to treat the variation upon increasing strain of the relative third harmonic component of the torque signal, differences are clearly detected that are discussed with respect to available polymer manufacturing information.
Tailoring Polymer Molecular Structure in the EPDM Slurry Process
Authors: Bhattacharjee Susmita , Bender Harald , Padliya Dilip
Published: February 2011

EPDM is produced by different polymerization processes. Therefore, careful engineering of polymer micro- and macro- structures is necessary to achieve desired performance characteristics. This review highlights the process capability of the EPDM slurry technology to tailor and control the molecular structural design. The catalyst and the polymerization technology produce EPDMs with a wide spectrum of chemical composition and Mooney viscosity. The relatively narrow molecular weight distribution of the polymers has been designed to offer the best combination of processing and physical properties. A unique technology for incorporation of long chain branching in the polymer has been developed. This highly selective catalyst technology controls the degree of branching and molecular weight distribution without any side reaction, while offering the flexibility to vary polymer composition and molecular weight. The EPDMs made with the modified molecular structure have a good balance of processing and performance characteristics.
Effect of Temperature and Pressure on Segmental Relaxation in Polymethylphenylsiloxane
Authors: Pawlus S. , Rzoska S. J. , Ziolo J. , Paluch M. , Roland C. M.
Published: February 2011

Segmental relaxation in a series of polymethylphenylsiloxanes (PMPS) was studied using dielectric spectroscopy. The measurements covered a temperature range of more than 40 deg at pressures from ambient to 115 MPa. The results confirmed that the shape of the loss peak is independent of temperature, pressure and molecular weight. Consequently, the Tg -scaled dependence of the relaxation times was also independent of molecular weight. The pressure dependence of the relaxation times was characterized by means of the activation volume. This quantity changes markedly with pressure at a given temperature. However, the activation volume at the respective glass transition temperatures of the PMPS are essentially invariant to molecular weight. Finally, we measured the dependence of Tg on pressure, with the results well-described by the Andersson equation.