bluuebunny/crossref_metadata_2025 huggingface dataset:
Mastication and Rate of Set-Up. Part II
Authors: Buchan S.
Published: February 2011

In the earlier communication it was shown that the length of time of milling of a mixed rubber exerted a marked effect on the rate at which it commenced to scorch. The longer the time of milling, the slower was found to be its rate of set-up. It is intended in this paper to give a brief account of some experiments which were undertaken with a view to deciding which factor or factors in the process of mastication are responsible for this retardation of the initial stages of vulcanization. During the milling of rubber only a limited number of factors can be considered as having any effect on its subsequent behavior as far as its rate of set-up is concerned. These are, decomposition of the accelerating components due to heat and pressure, softening of the rubber due to mechanical working, disaggregation or other causes, breakdown of the ultimate rubber particles, depolymerization, or, finally progressive oxidation of the rubber throughout the milling and mixing process. The possibility of decomposition of the accelerator during milling was examined by adding the accelerator to one batch at the beginning of the mixing process, adding it to another at the end and comparing the results of the rates of set-up on the two rubbers. Softening of the rubber without resorting to mechanical means was carried out by adding various softeners to the rubber while in solution and dispersing these by gentle stirring. It is of interest to note that the addition of softeners to the mixing without simultaneous mechanical working resulted in only a slight lowering of the plasticity reading (Y value), which seems to indicate that, for the effective development of softening action, mechanical working or the catalytic effects induced during mechanical working are essential.
Comparison of Methods of Examining the Scorching of Rubber Stocks
Authors: Morley J. F. , Scott J. R. , Willott W. H.
Published: February 2011

A comparison has been made between the plasticity and solubility methods of examining the scorching of accelerated rubber stocks; trials with a third method, based on the gelling of a solution of the stock, were unsuccessful. In a comparison using 10 different stocks the plasticity and solubility methods arranged these in practically the same order as regards tendency to scorch, showing that the two methods measure essentially the same property. The plasticity method usually detects an earlier stage of scorching than the solubility method using benzene as the solvent. Attempts to improve the sensitiveness of the latter method by using a less powerful solvent did not give promising results, as petroleum ether and diethyl ether behaved very similarly to benzene, while cyclohexanone did not readily dissolve the unscorched stock. The solubility method is unsuitable for stocks containing considerable percentages of gas black, e.g., tire tread stocks, and presumably also for those containing other strongly reinforcing fillers, because the unscorched stock does not dissolve in benzene. In determining the period for which a stock can be kept at a given temperature, or the temperature at which it can be kept for a given period, without practically serious scorching taking place, the plasticity method is to be preferred on account of its greater sensitiveness. It has the further advantage of giving a quantitative measure of the degree of scorching. However, for purely comparative purposes (but excluding stocks of the type referred to in 4 above) the solubility method is just as reliable, and has the advantage of being much simpler and quicker. By this method, also, it would usually be possible to decide whether any given piece of stock were scorched or not, whereas by the plasticity method this could not be done unless an unscorched piece of the same stock was available for comparison. In using the parallel-plate plastimeter for scorching tests, a relative long period of compression (10 minutes or more) gives the most sensitive indication of the change in plasticity produced by scorching. In the stocks examined the rate of scorching is, on the average, approximately doubled by a temperature rise of 10° C.
Carbon—Silica Dual Phase Filler, a new Generation Reinforcing Agent for Rubber: Part IX. Application to Truck Tire Tread Compound
Authors: Wang Meng-Jiao , Zhang Ping , Mahmud Khaled
Published: February 2011

The application of carbon-silica dual phase fillers (CSDPF) to natural rubber compound was investigated. It was found that these new fillers give significantly better overall performances in comparison with the conventional fillers—carbon black and silica. In a typical truck-tread compound, due to its high polymer—filler interaction and lower filler—filler interaction, the CSDPF E shows a comparable laboratory abrasion resistance and more than 40% reduction in tan δ at 70 °C, a parameter for rolling resistance, compared to compound filled with its carbon black counterpart, N1 10. These properties can, to a certain degree, be further improved by the addition of a small amount of coupling agent, bis(3-triethoxysilylpropyl)tetrasulfane (TESPT). In the case of wet skid resistance measured using the British Portable Skid Tester, the data show that CSDPF gives better performance than the conventional fillers, with and without coupling agent.
Mechanical and Elastic Properties of Sulfur Vulcanized EPDM as a Function of Third Monomer Content
Authors: van Duin Martin
Published: February 2011

A comparison is made of the vulcanization kinetics as studied with rheometry and of the mechanical and elastic properties for 65 ethylene—propylene—diene rubbers (EPDMs) vulcanized with an activated sulfur system according to the ISO 4097 recipe. The selected 50 commercial EPDMs and 15 development grades provide a broad range of chemical and physical structures, including different third monomer (TM) structures and contents ([TM]). At low [TM] (up to 40 mmol TM/100 g EPDM: for example ∼4.5 wt % 5-ethylidene-2-norbornene, ENB) the mechanical and elastic properties of EPDM are strongly affected by [TM], but at higher [TM] they are more or less unaffected. For fully-cured EPDMs this transition at ∼40 mmol TM/100 g is independent of the TM type (ENB, dicyclopentadiene, DCPD, 1,4-hexadiene, HD, etc.). In previous Fourier transform Raman (FT-Raman) spectroscopy and 1H NMR relaxation time studies it was established that for the ISO 4097 vulcanization system the average length of the sulfur crosslinks is ∼3 S-atoms/crosslink. From this it can be calculated that at ∼35 mmol TM/100 g EPDM a stoichiometric point is reached, where all sulfur is used for crosslinking. As a result, the properties of ISO 4097 EPDM vulcanizates level off when [TM] is increased beyond the stoichiometric point. The scatter in data at high [TM] is due to both experimental errors and differences in ethene/propene ratio, molecular weight (distribution) and/or degree of branching. It should be noted that the maximum cure rate (RH), being a kinetic parameter, remains dependent on [TM] over the whole chemical composition range although it also levels off at very high [TM]. In contrast to other studies it was found that RH is first order in both [TM] and [sulfur] at low [TM].
In Situ Filling of Silica onto “Green” Natural Rubber by the Sol—Gel Process
Authors: Kohjiya S. , Murakami K. , Iio S. , Tanahashi T. , Ikeda Y.
Published: February 2011

The sol—gel reaction of tetraethoxysilane produced the fine and well-dispersed in situ silica particles in the “green” natural rubber (NR) matrix before curing. This new method was developed for a NR/silica composite material, and a good reinforcement effect of in situ silica was observed on the NR vulcanizate. The method is expected to be an industrially practical technique. The in situ silica did not much inhibit the accelerated sulfur curing. Thus, it is estimated that the concentration of silanol groups on the in situ silica surface was smaller than those on the conventional silica surface. The silica—silica interaction of in situ silica seems to be weaker to result in better dispersion in the rubber matrix compared with the conventional silica. Atomic force microscopy suggested that the wettability of NR onto in situ silica was higher than that onto conventional silica. The hardness, modulus at 50% elongation and the storage modulus at room temperature of in situ silica-filled NR vulcanizate were smaller than those of conventional silica-filled NR vulcanizate, although the crosslinking density of the former was larger than that of the latter and their silica contents were comparable. These unique characteristics of in situ silica-filled vulcanizate seem to be ascribed to the fine and well-dispersed in situ silica particles in the NR matrix. These observations suggest that NR (a renewable resource)/in situ silica composite has much potential as an ecologically “green” material in the rubber industry.
Self-Crosslinking Rubber/Rubber and Rubber/Thermoplastic Blends: A Review
Authors: Antony Prince , De S. K. , van Duin Martin
Published: February 2011

Blends of two or more polymers having appropriate reactive groups can be crosslinked through condensation or substitution reactions in the absence of crosslinking chemicals when molded at high temperatures for prolonged times. When at least one of the two polymers is a rubber, such blends are called “self-crosslinking rubber blends.” Self-crosslinking rubber/rubber blends included in this review are binary CSM/ENR, ENR/XNBR, CR/ENR, ENR/Zn-SEPDM, CSM/XNBR and CR/XNBR blends, and ternary CR/XNBR/ENR and CSM/XNBR/ENR blends. Self-crosslinking thermoplastic/rubber blends include binary PVC/XNBR, PVC/ENR, PVC/NBR, PVC/HNBR, PAA/CR and PAA/ENR blends, and a ternary PVC/ENR/XNBR blend. The formation of crosslinks in self-crosslinking blends is manifested in the rise of the rheometer torque with time. Solvent swelling studies and dynamic mechanical analysis support the self-crosslinking behavior of the blends. The extent of crosslinking depends on the amount and reactivity of the functional groups of the two blend components, the time and temperature of the reaction. In general, the self-crosslinked rubber/rubber blends behave like conventional rubber vulcanizates with respect to physical properties and can be reinforced by fillers. Infrared spectroscopy has been used to identify the chemical structures formed during self-crosslinking, allowing the elucidation of the mechanism of self-crosslinking.
Modulus Mapping of Rubbers Using Micro- and Nano-Indentation Techniques
Authors: Gillen Kenneth T. , Terrill Edward R. , Winter Robb M.
Published: February 2011

Modulus measurements are among the most useful properties available for monitoring the cure and aging of rubbers. Historically, such measurements were done on macroscopic samples, but over the past 15 years, several penetration techniques have been and are being developed that allow quantitative estimates of modulus to be made with lateral resolutions of 100 μm or better. This review summarizes these developments and the types of unique information that can be generated on rubbery materials. A large part of the review focuses on the types of results available from a modulus profiling apparatus that has been used to study rubbers for the past 15 years. This instrument allows estimates to be made of the inverse tensile compliance (closely related to Young's tensile modulus) with a lateral resolution of around 50 to 100 μm. Several recently developed alternative methods for achieving similar spatial resolution are also described. Finally, a brief review is given of the recent attempts to measure quantitative modulus values for rubbers with even better resolution using instruments historically focused on metals and other hard materials such as nano-indenters, the atomic force microscope and the interfacial force microscope.
Peroxide Vulcanization of Elastomers
Authors: Dluzneski Peter R.
Published: February 2011

This paper discusses the competing chemical reactions involved in the peroxide vulcanization of elastomers. Each of these reactions can have a profound effect on the cure characteristics as well as on the properties of the final vulcanizate. The balance between these reactions is determined by several factors including the type of polymer, type and concentration of peroxide, cure temperature, and the presence of other compound additives such as co-agents and antidegradants. The effects of all of these factors are discussed.
Application of Fracture Mechanics to Crack Growth in Rubber-Cord Laminates
Authors: Lake G. J.
Published: February 2011

The use of a fracture mechanics approach based on the strain energy release rate to assess failure due to the growth of fatigue cracks in rubber—cord laminated structures is discussed. The mechanics of crack propagation is considered for cracking either between the plies or around individual cords, and also for crack initiation and growth near cord ends. Energy release rates can be calculated approximately for each of these cases and enable the laminate results to be related to the independently measured crack growth characteristics of the rubber. Experimental energy release rate determinations, from compliance changes produced by propagating model inter-ply cracks by cutting, provide a check on the accuracy of the calculated energies. The approach identifies material properties relevant to laminate failure and indicates the effects of loading, design and construction parameters on the rate and nature of failure.
On the Mullins Effect in Silica-Filled Polydimethylsiloxane Networks
Authors: Clément F. , Bokobza L. , Monnerie L.
Published: February 2011

Silica-filled polydimethylsiloxane networks are submitted to successive stretching cycles, in order to get the stabilized stretching curve, at variable temperature. This study explains the peculiar temperature dependence of the first stretching curve of filled rubbers, and highlights the molecular origin of the stress-softening phenomenon, known as Mullins effect. Thanks to the comparison between the strain dependence of stress and the molecular orientation, this effect is attributed to the detachment from the filler surface or slippage on the filler surface, of chains having reached their limit of extensibility. Moreover, by taking advantage of Atomic Force Microscopy observations on stretched samples, the Mullins effect is shown to take place mainly in regions of high local concentration of silica. The experimental results are also compared to Bueche's model for the Mullins effect.
Ultrasonic Devulcanization of Unfilled SBR under Static and Continuous Conditions
Authors: Hong Chang Kook , Isayev A. I.
Published: February 2011

A static ultrasonic treatment device was used to investigate the effect of ultrasound on devulcanization of unfilled SBR disks in the absence of shearing effect. Some visible bubbles were observed at the center of the disk sample at low pressure, as well as at the edges at high pressure, as the treatment time increases. Evidently, these bubbles are a proof of the existence of cavitation during the ultrasonic devulcanization. Stronger reduction of crosslink density observed at a higher pressure in the treatment is a direct indication of the significant role of pressure in improving the efficiency of ultrasonic devulcanization. Treatment of the ground sample, having higher concentration of voids, indicated lower crosslink density and gel fraction than those of the sheet sample not having visible voids. The unique correlation between gel fraction and crosslink density of devulcanized rubbers observed earlier in continuous process, was also obtained in the present case. However, this curve is shifted towards higher values of crosslink density. It is concluded that shearing effect has an influence on improving the efficiency of devulcanization.
Finite Element Modeling of Indenter-Sample Contact During Force Imaging of Filled Rubber by Atomic Force Microscopy
Authors: Davis Mark K. , Eby R. K.
Published: February 2011

Finite element analysis (FEA) models were developed to study the interaction between atomic force microscope (AFM) tips and filled rubber compounds during nano-indentation. The filled systems were represented by simple models consisting of one or two discrete hard domains in a rubber matrix in order to study how such a hard domain at or near the location of an indentation measurement affected the force-distance response. Parameters studied included domain size and shape, lateral position and depth from the indentation location, effect of sample thickness, and the ability to measure modulus variation across “rubber-particle” interfaces. The analyses showed the degree to which the underlying and adjacent sample regions influenced the force-distance response at a given location. The results identified several limitations of force imaging as a characterization technique for filled systems and suggested a basis for the development of more complex FEA models.
Cracking Energy Density as a Predictor of Fatigue Life under Multiaxial Conditions
Authors: Mars W. V.
Published: February 2011

Rubber parts in service often experience complex strain histories that can cause mechanical failure. The ability to predict the effects of complex strain histories on fatigue life is therefore a critical need. This paper presents recent results of cyclic, combined tension/torsion fatigue experiments, and compares them with predictions based on a new parameter, the Cracking Energy Density. The Cracking Energy Density is the stored elastic energy density that is available to a crack on a given material plane, and can be calculated for an arbitrarily complex strain history. The ability of Cracking Energy Density to predict the fatigue life and cracking plane is evaluated for both in-phase and out-of-phase histories of combined axial and shear strain.
Elastomer Blends
Authors: Mangaraj Duryodhan
Published: February 2011

Blending of elastomers is often used to enhance he performance characteristics of rubber products. This article reviews the thermodynamic principles underlying polymer-polymer miscibility, with special reference to elastomer blends. It discusses the distribution of fillers, additives and curatives in different phases of the blend and its effect on the properties of the vulcanizate. It describes the different methods used in preparing elastomer blends, with special emphasis on compatibilization. Characterization of blends using optical and electron microscopy, solution properties, thermal and dynamic mechanical methods have been described along with results. The effect of blending on mechanical properties, hysteresis, adhesion and tack, transport properties and electrical conductivity has been discussed. Past attempts for property enhancement by blending elastomers have been reviewed, followed by a discussion of commercial application of elastomer blends.
Crosslinking of Rubbers by Fillers
Authors: Rajeev R. S. , De S. K.
Published: February 2011

Oxygen containing chemical groups on the carbon black surface can react with the carboxyl groups of XNBR, or epoxy groups of ENR, or chlorosulfonated groups of CSM, during high temperature molding of the rubber-filler mixtures. This leads to crosslinking of the rubber phase. The extent of crosslinking increases if the carbon black surface is oxidized, the concentration of the reactive groups of the rubber increases, or a suitable silane coupling agent is incorporated in the rubber-filler mixtures. Similarly, high temperature molding of the XNBR-precipitated silica, ENR-precipitated silica, CSM-precipitated silica, and CR-ferrite mixtures leads to crosslinking of the rubber phases, even in the absence of conventional rubber vulcanizing agents. XNBR-ZnO mixture on high temperature molding also produces crosslinked rubbers consisting of ionic crosslinks. During mixing stage, the reactive fillers interact with the polar rubbers leading to formation of high bound rubber, presumably through hydrogen bond formation. During high temperature molding of the rubber-filler mixtures for a prolonged time, the reactive groups on the filler surface chemically react with the functional groups of the rubber chains leading to crosslinks of the rubber phase. This is evident from the rise in the rheometric torque of the rubber-filler mixture and marked changes in properties of the mixture on high temperature molding. The properties in many instances are similar to that obtained in the case of rubbers crosslinked by conventional vulcanizing agents. Infrared spectroscopy has been used to identify the chemical structures at the filler-rubber interface formed during crosslinking of the rubber by the filler.
Compression of Bonded Rubber Blocks
Authors: Yeoh O. H. , Pinter G. A. , Banks H. T.
Published: February 2011

Many practical rubber component designs involve the compression of rubber blocks bonded to rigid metal plates. The rigorous analysis of such components is very difficult. However, a simple approximate method developed by Gent gives reasonably satisfactory predictions for stiffness and stress distribution provided deformations are kept small. Gent's “pressure” method is briefly reviewed for the classical cases of a long strip and a cylindrical disk. The method is then applied to more complex cases of a rectangular block and an annulus. The usual “incompressibility” assumption is relaxed to “near incompressibility” to yield more accurate solutions. Predictions have been verified using linear finite element analysis.
The Friction and Wear of Rubber Part 2: Micro-Mechanical Description of Intrinsic Wear
Authors: Gerrard David P. , Padovan Joe
Published: February 2011

The concept of a Damage Orientation Distribution Function was introduced in Part 1 of this series to describe the transient affect on wear generated by a dynamically changing slip orientation. In this Part an analytical model of the micro-mechanical processes that occur in a slipping rubber/abrasive interface is offered and serves as the basis for a new relation for the prediction of rubber wear.

The description considers the fatigue fracture processes that occur at the intrinsic nodule level. The assumption is made that each intrinsic nodule undergoes intermittent fractures which are driven by Strain Energy Release Rate levels that range from a minimum at or below the linear region of the material's Fatigue Crack Propagation curve, through the Power Law Region and finally to the catastrophic tear value.

The proposed description is tested against the early data of Schallamach. It is shown that the simple relationships offered in the analytical study can be used to predict rubber wear performance over a wide range of pressures and abrasive asperity sizes.

In light of this analysis, the Damage Orientation Distribution Function of Part 1 is revisited and found to be a useful tool when considering the fundamental processes that occur during unidirectional wear. Changes in slip direction are found to affect the instantaneous wear rate by affecting the Distribution Function in a different manner than changes in pressure or abrasive size. Changes in slip direction are shown to affect the population of intrinsic nodules immediately available for rupture while changes in pressure or abrasive size are shown to influence wear by changing the rate at which nodules move through the Distribution.
Why Do Cracks Turn Sideways?
Authors: Gent A. N. , Razzaghi-Kashani M. , Hamed G. R.
Published: February 2011

Calculations have been made by FEA of strain energy release rates G for a rubber sheet with a small edge crack, subjected to a far-field simple extension. Growth of the crack is considered in both forwards and sideways directions, the latter corresponding to crack splitting or turning. When the imposed extension is large, the value of G at which a small sideways crack will initiate is found to be a substantial fraction, about 60%, of that for further forwards growth. This suggests that crack splitting or turning will occur when the tear strength in the sideways direction is only slightly lower than that for forward growth. However, the value of G for a sideways crack decreases rapidly as the crack grows, indicating that it will stop after a short distance. These conclusions are shown to be in accord with experimental observations of crack splitting in filled rubber compounds and account for the phenomenon of reinforcement by fillers. In particular, they account for the fact that deep edge cracks are less likely to split or turn.
Effect of Third Monomer Type and Content on Peroxide Crosslinking Efficiency of EPDM
Authors: van Duin Martin , Dikland Herman G.
Published: February 2011

Peroxide crosslinking of EPDM is commonly applied in rubber practice. Although the presence of a diene termonomer is not a prerequisite for peroxide crosslinking, it does provide a significant increase of the peroxide crosslinking efficiency. Different explanations for the effect of the type and the amount of the third monomer on the peroxide curing efficiency have been put forward; but, a comprehensive overview and an acceptable explanation of all the effects observed are still lacking. In the present paper, this gap is filled by combining results from low-molecular-weight model studies and rheometer experiments with information from the literature. It is shown that peroxide crosslinking of EPDM proceeds via the combination of two EPDM macro-radicals and the addition of an EPDM macro-radical to the residual EPDM unsaturation. The extent to which the latter radical addition occurs, is governed by the amount of the third monomer and by the steric hindrance of the residual unsaturation of the EPDM, i.e. the lower the number of ipso- and β- alkyl substituents on the unsaturation, the higher the rate of addition. This explains why EPDMs containing termonomers with terminal unsaturations are more reactive than those with internal unsaturations. The same approach was followed to assess the peroxide curing efficiency of polydiene elastomers. It was found that the same steric effects govern peroxide crosslinking of polydiene elastomers, such as NR, IR and BR.
Dynamic Mechanical Properties of Precipitated Silica Filled Rubber: Influence of Morphology and Coupling Agent
Authors: Ladouce-Stelandre Laurence , Bomal Yves , Flandin Lionel , Labarre Dominique
Published: February 2011

Composites that incorporate precipitated silica into a vulcanized rubber were investigated for dynamic mechanical properties. Comparing different types of filler, it was found that the mean distance between particles did not alter Payne effect. On the contrary, the amount and morphology of the fillers played a major role on the macroscopic properties. The nature and amount of coupling or covering agents was also found to be an important parameter. A direct relationship between length and efficiency of interface agents was evidenced: longer silanes were more effective than shorter once independently from a covalent bounding to rubber. The set of studied parameters affecting Payne effect can be reduced to only two independents variables: the total amount of silica-rubber interface (a function of the amount of filler and its BET surface) and the quantity and nature of interface agent. From these data an attempt to relate the rubber to filler cohesion to Payne effect is proposed as well as a molecular mechanism derived from Maier and Göritz model. A mathematical treatment of the proposed mechanisms is currently being investigated that might help giving further insights on novel ways to further reduce Payne effect.
Adhesion Failure in Bonded Rubber Cylinders Part 1: Internal Penny-Shaped Cracks
Authors: Leicht D. C. , Yeoh O. H. , Gent A. N. , Padovan J. , Mullen R. L.
Published: February 2011

Rubber disks bonded between flat parallel metal plates are often used as adhesion test specimens such as ASTMD 429 1999, Method A. However, the mechanics of adhesion failure (debonding) for this geometry have not been fully analyzed previously. Therefore, a study has been conducted of the strain energy release rate (tearing energy) for bonded rubber disks having cracks at the rubber-to-metal bond. In this paper, we consider internal penny-shaped cracks. A future paper will discuss external ring cracks.

Finite element analysis was used to determine the tearing energy as a function of crack length for disks of various dimensions (shape factors). The crack configurations considered were an internal penny shaped crack located at the center of either one or both rubber-to-metal bonds. The rubber was assumed to be linearly elastic and nearly incompressible.

For any bonded disk held in constant tension, the tearing energy was found to be a non-linear function of crack length. For small cracks, the tearing energy was linearly related to the crack length. As the crack grew, the tearing energy increased until it passed through a maximum value. The peak tearing energy was found to depend on the height of the disk. Finally, for large cracks, the tearing energy decreased as the crack grew. Analytical and empirical models were developed and shown to be in good agreement for both small and large cracks in disks of different dimensions.
Novel Dynamically Vulcanized Elastomer-Polypropylene Blends with Improved Elasticity
Authors: Ellul M. D.
Published: February 2011

High elasticity in dynamically vulcanized EPDM-Polypropylene blends, as demonstrated by lower residual deformation upon release of constraint, is a much desired attribute. It has been found that this property can be improved beyond the conventional norms of highly crosslinking the rubber phase. This is achieved through the use of a polypropylene phase with a high degree of long-chain branching. The branching index, g', at molecular weight greater than 1×106 should be less than about 0.6. It is postulated that in the melt and at low frequencies the long-chain branched polypropylene behaves as a network. Therefore in the melt, the dynamically vulcanized alloy behaves as a dual network material: one network being the chemically crosslinked rubber phase, and the other being the physical network arising from the high level of long-chain branching in polypropylene. In the solid state, the co-continuous morphology arising from the choice of long-chain branched polypropylene contributes to the enhanced elasticity of the dynamically vulcanized thermoplastic elastomer.
Correlation of 13C NMR Analysis and Physical Testing Results of Natural Rubber
Authors: Parker Dallas D. , Koenig J. L. , Mori Makio
Published: February 2011

The methods of solid-state 13C NMR and physical testing were used to examine carbon black filled natural rubber samples. The rubber samples were vulcanized under varying parameters of sulfur loading, cure times, and cure temperature. At constant cure time and cure temperature, the two testing methods correlate well over a wide range of sulfur concentrations. Varying cure time and cure temperature produced large changes in the mechanical testing results but small change in the 13C NMR analysis of the sulfur vulcanizates.
Homogeneous Zinc (II) Catalysis in Accelerated Vulcanization: V. The Prevailing Mechanism of Crosslink Formation in Mercaptobenzothiazole Systems
Authors: Damen R. , Nieuwenhuizen P. J. , Haasnoot J. G. , Reedijk J. , Couchman S. M. , Jeffery J. , McCleverty J. A.
Published: February 2011

This paper reports a detailed investigation of the molecular mechanism of crosslink formation in sulfur vulcanization accelerated by mercaptobenzothiazole accelerators, such as bis(mercaptobenzothiazolato)zinc(II) (ZMBT), mercaptobenzothiazole disulfide (MBTS) and N-cyclohexyl-2-benzothiazole sulfenamide (CBS). First, the current state of knowledge regarding the mechanism of crosslink formation in these systems is briefly reviewed.

Subsequently, Reaction-Stage Modeling experiments are reported with the model-crosslink precursor (2,3-dimethyl-2-butene-1-yl)(mercaptobenthiazolato)sulfide (dmb-S2-Bt). These experiments reveal that in the presence of bis(cyclohexylamine)bis(mercapto benzo-thiazolato)zinc(II) (ZMBT·(H2NC6H11)) the precursor dmb-S2-Bt is transformed into a disulfidic crosslink and MBTS via symmetric disproportionation reactions. Also sulfuration and isomerization reactions, leading to a hitherto unknown type of pendent group, namely 2-(2,3-dimethyl-2-buten-1-yl)-1,2-benzisothioazolin-3-thione, were shown to occur. The zinc-amine complex was found to have a pronounced catalytic effect on the crosslink reaction; in its absence, hardly any crosslinks are formed. Reactions performed in the presence of additional MBTS showed an inhibitory effect on crosslink formation, suggesting that the disproportionation reaction is in fact an equilibrium reaction. Indeed, it appeared possible to transform disulfidic model crosslinks into crosslink precursors in the presence of both MBTS and the ZMBT-amine complex. These results have lead to determine the prevailing mechanism by which crosslinks are formed during mercaptobenzothiazole vulcanization, namely through an equilibrated, ZMBT-catalyzed disproportionation reaction of crosslinks precursors. This mechanism not only explains the observations in the present model study, but is also in line with results obtained earlier in real rubber experiments.
Influence of Crosslink Characteristics Induced by Aromatic-Based Antioxidants on the Swelling and Stress-Strain Behavior of Natural Rubber Vulcanizates
Authors: Madkour Tarek M. , Azzam Rasha A.
Published: February 2011

Stress-strain measurements were performed on dry and swollen natural rubber vulcanizates prepared using both sulfur as the crosslinking agent and aromatic-based bound antioxidants acting as a second crosslinking agent. The aromatic-based antioxidants were synthesized and analyzed spectroscopically in order to relate the final behavior of the vulcanizates to the nature of the crosslink characteristics. The anomalous upturn in the modulus values of these networks in response to the imposed stress was shown to persist in the dry as well as the swollen state. Since the swollen elastomeric chains cannot undergo a strain-induced crystallization, the abnormal upturns in the modulus values in an absence of a filler were explained on the basis of the limited extensibility of the short chains of networks prepared using two different crosslinking agents in line with earlier modeling predictions. Remarkably, the swelling experiments revealed the increase in the crosslink density of the networks in the early stages of the thermal oxidative degradation procedure indicating a post-cure of the chemically bound antioxidants to the elastomeric chains, which incidentally corresponds to a maximum in the modulus values of the networks. The rheological and other mechanical properties such as the hardness were shown not to have been affected as a result of the incorporation of the chemically bound antioxidants.
Evaluation of Isobutylene-Based Elastomers in a Model Winter Tire Tread
Authors: Waddell Walter H. , Kuhr Julie H. , Poulter Robert R.
Published: February 2011

The performance of butyl, chlorobutyl, bromobutyl, and brominated isobutylene-co-para-methylstyrene (BIMS) rubbers were evaluated versus a solution-polymerized styrene-butadiene rubber with 20% bound styrene in model winter tire tread formulations containing natural rubber and butadiene rubber. Isobutylene-based elastomer performance was compared in carbon black-filled and silane-coupled silica-filled systems. Based on laboratory dynamic properties predictive of wet and winter traction, and on DIN abrasion index values, BIMS is the elastomer of choice affording increased tangent delta values between 0 °C and −40 °C, and the highest DIN abrasion index values of the isobutylene-based elastomers. Evaluation of BIMS / NR / BR blends in model compounds show its utility as a tread polymer for improving winter performance.
Structure and Properties of Natural Rubber and Modified Montmorillonite Nanocomposites
Authors: Magaraphan Rathanawan , Thaijaroen Woothichai , Lim-ochakun Ratree
Published: February 2011

Montmorillonite clay was organically modified by primary and quaternary ammonium salts (having C12-C18). The modified clay was added to a solution of natural rubber in toluene at various contents. Characterization of the structure of the nanocomposites was performed by using x-ray diffraction and transmission electron microscope. The results showed that the silicate layers of the clay were expanded so that the exfoliated nanocomposites were obtained at clay content below 10 phr; above that the nanocomposites became partially exfoliated. Moreover, long primary amine showed more improved mechanical properties than the quaternary one (at the same carbon numbers). The longer organic modifying agents resulted in better expansion of silicate layer distance indicating more intercalation of natural rubber molecules in between clay galleries. The curing properties were also improved. It was found that a small loading of 7 phr is enough to bring good mechanical properties in comparison to those of high structure silica filled and carbon black filled natural rubber vulcanizates.
Effect of Carbon Black Concentration on Cut Growth in NR Vulcanizates
Authors: Hamed G. R. , Al-Sheneper A. A.
Published: February 2011

Dumbbell specimens containing edge razor-cuts of various depths, c, have been prepared from sulfur-vulcanized natural rubber compositions containing 0–75 phr of N115 black. Normal tensile strengths (c=0) of the gum and all black-filled samples are similar. However, cut growth resistance (CGR) relative to the gum, depends strongly on black content and cut depth. With about 6–15 phr of black, filled specimens are weaker than the gum and fracture occurs by simple forward growth of the original cut tip, i.e., a single crack develops and propagates laterally. At about 18 phr of black, filled specimens become stronger than the gum and cracking becomes complex. Prior to catastrophic rupture, crack splitting occurs near the original cut tip - forming at least two slowly-growing, longitudinal cracks. These reduce the stress concentration caused by the cut, thereby delaying rupture, and marking the onset of “reinforcement”. All pre-cut specimens containing 18–75 phr of black are stronger than the gum and they exhibit crack splitting. Specimens containing 50 phr of black have the highest strength - being about ten times as strong as the gum when cuts are large. The decrease in CGR at low levels of black and increase at high levels is attributed to competing effects upon the addition of carbon black to NR.
Miscibility of EPM-EPDM Blends
Authors: Dikland H. G. , Van Duin M.
Published: February 2011

Blends of elastomers are often used as a basis for compound formulations. For instance, tire tread formulations may contain NR, BR and SBR in order to provide cost-effective products with good mechanical properties, dynamic properties and abrasion resistance. Blends of dissimilar EPDM grades are often used when formulating EPDM compounds. In many cases such EPDM-EPDM blends are used to obtain synergy, i.e. properties of the parent EPDM grades are not averaged, but favorable properties of the blend components are combined or unfavorable properties suppressed. In the present paper the miscibility regime for gum stock EPDM-EPDM blends has been calculated based on elementary thermodynamic considerations. Results of calculations have been validated by experiments, and excellent agreement was found. It was found that the chemical composition of EPDM grades has a major influence on miscibility. It is concluded that, as a rule of thumb, two EPDM grades are thermodynamically miscible if the difference between the combined ethylene and third monomer content is less than 12 % by weight. Based on the results it is possible to understand and to some extent predict the behavior of rubber products based on dissimilar EPDM grades.
Effects of Storage and Service on Tire Performance: Oil Component Content and Swelling Behavior
Authors: Kataoka Takahiro , Zetterlund Per B. , Yamada Bunchiro
Published: February 2011

In order to investigate the effects of storage and service on passenger car tire performance, two separate sets of samples were characterized: (i) tires stored at a temperature of 45–50 °C for different time periods, and (ii) used tires of different mileage. The tires were analyzed with respect to the performance of the tread rubber as manifested in the modulus at 200% elongation, the tensile strength at break, the elongation at break, the hardness, the viscoelasticity of the rubber, swelling, and the oil component content. The change in the properties of the tires as functions of increasing storage time and mileage indicated a marked deterioration in performance. The rate of change in these properties was found to be markedly enhanced by the extra stimuli provided by service, as demonstrated by comparing tires of similar age but different mileage. The results were analyzed and rationalized in terms of the change in the degree of crosslinking and transfer of oil components from the tread rubber to the inner part of the tire or to the surroundings.
Effect of Carbon Black on Crosslinking
Authors: Gent A. N. , Hartwell† J. A. , Lee Ginger
Published: February 2011

For a number of different vulcanization systems, the equilibrium swelling ratios for carbon-black-filled and unfilled samples are shown to be linearly related, as found by Lorenz and Parks, indicating that the degree of crosslinking is not changed by incorporating carbon black. However, filled compounds swell less, and thus the apparent degree of crosslinking is significantly greater. For example, it is about twice as large for compounds containing 50 phr of HAF carbon black. This is confirmed by measurements of the elastic modulus of swollen samples. Relatively strong bonds appear to be formed between rubber molecules and the surface of carbon black particles - bonds that can withstand swelling stresses and temperatures of up to 120 °C. Bonding between rubber and carbon black is also indicated by the limited swelling of filled rubber compounds even before vulcanization, although in this case the apparent degree of crosslinking is smaller. Thus, vulcanization appears to enhance the contribution of rubber-particle bonding to the elastic modulus and restricted swelling of carbon-black-filled vulcanizates. Simple procedures are suggested for estimating the actual degree of crosslinking in filled rubber vulcanizates from measurements of equilibrium swelling or elastic modulus.
Durability Review of Elastomers for Severe Fluid Duties
Authors: Campion Robert P.
Published: February 2011

Durability aspects of elastomers when exposed to fluids under severe conditions for Offshore Oil Production and other applications have been reviewed. Examples are provided of situations where estimations of residual life might be made, and of others where different considerations might be the overriding factors. The approach has been to extend previously-presented overviews focused on the use of elastomers in the hostile conditions of the oil field industry, and made largely from personal experience, to include some work of others with reference to other application areas as well.
Dynamically Vulcanized PP/EPDM Blends: Effects of Different Types of Peroxides on the Properties
Authors: Naskar K. , Noordermeer J. W. M.
Published: February 2011

Thermoplastic vulcanizates (TPVs) or dynamic vulcanizates are thermoplastic elastomers produced by simultaneous mixing and crosslinking of a rubber and a thermoplastic. The effects of different types of peroxides as curing agents on the properties of PP/EPDM TPVs were investigated at a fixed blend ratio. The mechanical properties change significantly with the chemical nature of the peroxides, the extent of crosslinking of EPDM and the extent of degradation of PP. Three main parameters have been identified governing the final mechanical properties of TPVs: the solubility parameter of a peroxide relative to the substrates PP and EPDM, the fragmentation mechanism of the peroxide and the kinetic aspects of the peroxide fragmentation. Dicumyl peroxide gives the best balance of all properties, it complies the best of all with these parameters.
A “Wobble-Plate” Dynamic Test Device
Authors: Gent A. N. , Thompson T. T. , Ramsier R. D.
Published: February 2011

A simple dynamic tester is proposed, in which a disk of rubber is subjected to a rotating tilting deformation. In one arrangement, the rubber disk rests on a horizontal base and a light steel plate rests on its upper surface. A circular groove in the upper surface of the plate is centered on the axis of the rubber disk. An off-center vertical load is then applied to the rubber disk via a steel ball running in the circular groove. As the ball rolls round the groove, driven by friction with a rotating countersurface, the rubber disk undergoes a rotating off-center compression - a tilting deflection - that rotates at the same rate as the ball. If the rubber is perfectly elastic, no torque is required to maintain this motion and the deflection of the rubber will be exactly in phase with the compressive force. The maximum deflection then occurs at the location of the ball. However, if the rubber exhibits delayed elasticity, then the maximum deflection occurs after the ball has passed, at an angular separation δ, where δ is the angle of mechanical loss. Thus, the phase angle δ can be observed and measured directly. Also, if required, the separate components E′ and E″ of the complex dynamic modulus can be calculated from the applied force and deflection, and the torque required to maintain the motion.
Recent Advances in Anionic Synthesis of Chain-End Functionalized Elastomers Using Epoxides and Related Compounds
Authors: Quirk Roderic P. , Gomochak Deanna L.
Published: February 2011

Recent developments are reviewed for the applications of reactions of polymeric organolithium compounds with epoxides and oxetane to obtain the corresponding ω-hydroxy chain-end functionalized polymers. State-of-the-art characterization methods for ω-functionalized polymers are also reviewed. Investigations of the usefulness of functionalization reactions of polymeric organolithium compounds with ethylene oxide, propylene oxide, 1-butene oxide, styrene oxide, oxetane, 3,4-epoxy-1-butene, 3-glycidoxypropyltrimethoxysilane and other epoxides are described. In general, these functionalization reactions are very efficient (> 90% yields of ω-hydroxy-functionalized polymers). The use of substituted epoxides is shown to provide an efficient methodology for attachment of a variety of groups at the polymer chain end.
Atomic Force Microscopy in Analysis of Rubber Materials
Authors: Yerina Natalya , Magonov Sergei
Published: February 2011

Atomic force microscopy (AFM) and electric force microscopy (EFM) have been applied for compositional mapping of a number of elastomers and related multicomponent materials. Several aspects of optimizing AFM experiments on polymers are discussed. AFM images revealed changes of EPDM morphology caused by crosslinking and by loading with fillers [carbon black (CB) and silica particles] and oil. It was shown that the morphology of isotactic polypropylene (iPP)/EPDM vulcanizates, which were studied with AFM and EFM, depends on the ratio of components, degree of cure and processing conditions. Diffusion of oil from the elastomer component to the matrix is evidenced in the AFM images. Selective distribution of CB in the iPP matrix is responsible for the electric conductivity of the thermoplastic vulcanizate.