bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Seal with Elastomeric Rotating Element. Part 1: Theory of Operation
Authors: Kholodenko Arnold , Rivkin Michael
Published: February 2011

This paper presents the results of fundamental research on flexible faced mechanical shaft seals. The effect of stretch and preload on the contact stress were investigated using a nonlinear finite element modeling package. The characteristics of the rubber materials including the stress-strain curves to elongation at break were required to complete the analysis. Pressure forces resulting from the static pressure in the pump stuffing box as well as the friction effects on all contacting surfaces were considered in the model. Stress distribution across the contact surface established the basis for the formation of multiple distinct lips: at least one on the outside or fluid side of the seal and the other on the inside or air side of the seal. This phenomenon is explained by the step change in magnitude of axial stress while traversing the contact in the radial direction allowing the formation of exterior lips and the development of an annular region trapping debris products and process fluid. Photomicrographic images of the wear track taken with a Scanning Probe Microscope show distinct wear tracks and the topology of each. Although the chemical composition of the debris in the annular spaces has not been determined quantitatively, increased levels of fluorine were present, suggesting fragments of the monomers in the elastomeric rotary or migration of Teflon fillers. Axial variations in the stretched rotary dimensions (waviness) affects seal performance. Statistics for a typical batch of rotary elements are presented and a method of factoring these variations into the seal design is presented. The formation of axial waves on the contact vertex affects the seal performance and is considered in the final design of the seal pair configuration. The results of this work were incorporated into a suite of mechanical face seals covering shaft sizes from 1.125 to 5.000 inches using seven pairs of seals, each pair consisting of a stretched rotary sliding against an unlapped silicon carbide annular ring. Each of these seal pairs were tested on an experimental test device to determine the heat generation and friction coefficients for a wide range of temperature, pressure, speed, and sealing fluid. Results of the experimental work are reported in a companion paper.
Sulfur Vulcanization of Simple Model Olefins Part III: Vulcanization of 2,3-Dimethyl-2-Butene in the Presence of Different Metal Complexes
Authors: Versloot P. , Haasnoot J. G. , Reedijk J. , van Duin M. , Put J.
Published: February 2011

The mechanism of the sulfur vulcanization of rubber was studied by using 2,3-dimethyl-2-butene (C6H12) as a simple, low-molecular model alkene. Only equivalent allylic positions are present in this alkene. Treating C6H12 with a mixture of ZnO, S8 and the accelerator tetramethylthiuramdisulfide at 140°C yields a mixture of addition products (C6H11—Sn—C6H11). Similar reactions in the presence of various metal oxides instead of zinc oxide show poor vulcanization results. Experiments with various metal dithiocarbamate complexes show a reactivity towards vulcanization in the following sequence: Zn(detc)2>Cd(detc)2>Cu(detc)2>Pb(detc)2>Zn(dmtc)2>Ni(detc)2>Cu(dmtc)2.
3D Morphological Characterization of Carbon-Black Aggregates Using Transmission Electron Microscopy
Authors: Gruber Tyler C. , Zerda T. W. , Gerspacher Michel
Published: February 2011

A three-dimensional modeling technique is used to characterize the structure of carbon-black aggregates. The relative positions of individual particles in aggregates are determined using transmission electron microscopy (TEM). Data are acquired from two-dimensional projections taken with the aggregates at two different orientations with respect to the electron beam. Computerized aggregate models are generated using data from TEM projections in our reconstruction algorithm. Inspection of these models shows that their projections very closely replicate the TEM micrographs. Quantitative analysis of the aggregate models reveals that aggregates generally exhibit anisotropy, in the form of a reduction of aggregate breadth, or “flatness,” in one direction. The flat sides tend to align preferentially, along the plane of the TEM sample grid. The dimensions for each aggregate with respect to its best-fitting plane of flatness are determined, and are related through a “flatness index.”
Analysis of the Mechanism of N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene
Authors: Krejsa M. R. , Koenig J. L. , Sullivan A. B.
Published: February 2011

Results of previously published work involving network analysis and accelerator intermediate analysis of cis-polyisoprene were compared to help correlate and rationalize network/chemistry relationships. Both classical chemical probe network analysis and further NMR measurements (DEPT analysis) were used as necessary to verify NMR peak assignments. Furthermore, samples of the conventional formulation were vulcanized in the absence of zinc oxide and stearic acid to help elucidate the role of zinc in the vulcanization process. Polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic substituted cis-polysulfides both with and without double bond migration, while zinc polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic cis and trans polysulfides substituted structures with no double bond migration. Polysulfidic substitution on the isoprene methyl carbon was shown to result from exchange reactions during network maturation. The network-chemistry relationships were compared with earlier mechanistic studies and several points of agreement were noted.
The Application of Small Angle Neutron Scattering to Elastomers
Authors: Lohse David J.
Published: February 2011

The last twenty years have seen a dramatic increase in the application of small angle neutron scattering to polymer science. In this review the use of SANS to study elastomers and elastomeric systems has been summarized. This has focused on those applications most significant to the understanding of rubber. These have included the dimensions of polymer chains in the bulk melt state, the miscibility of polymer blends, the structure of block copolymers, and the nature of crosslinked networks. The information that has been obtained so far has cleared up many of the outstanding questions about elastomers, and one can only expect that this use will increase in the future and will yield a wealth of useful information.
Elastomers for Biomedical Applications
Authors: McMillin Carl R.
Published: February 2011

Over 11 percent of the gross national product of the U.S.A. is currently being spent in areas related to health care. Medical applications of polymers account for about six percent of the dollar sales of processed polymer products, or over three billion dollars annually. Medical devices, consumables, and their packaging are estimated to have used 2.3 billion pounds of polymers in 1992. This paper describes research and development within the biomedical elastomer and rubber segments of this market. Elastomers used in biomedical applications can be roughly divided into three groups; the commodity elastomers that happen to be used in the biomedical field, medical grades of elastomers that are certified for food contact or for short-term physiological contact, and a small group of elastomers that are suitable for longer-term physiological contact or implantation. Although significant from a national perspective, the many uses of commodity elastomers in the medical field will not be discussed in this paper. Some of the additional material requirements that occur when elastomers are employed in contact with biological systems include: more stringent quality control, higher purity, more controlled and cleaner manufacturing facilities, and much more additional paperwork—including information so that traceability is maintained. In most cases, the elastomers must have a degree of biocompatibility. Other specific features may also be needed, such as the ability to be sterilized by gamma irradiation or steam autoclave. Materials that are manufactured with these ends in mind are often called “medical grade.” The number of candidate materials for the high profile, implantable speciality elastomers market is considerably smaller. These elastomers must survive much more rigorous biocompatibility testing and are sometimes optimized for specific properties such as blood compatibility, extraordinary fatigue strength, or controlled biodegradability. Because there are relatively few rubbers or elastomers that are suitable for use in vivo, it is particularly significant that several of the most important of these have been withdrawn from the market because of perceived product liability issues.
Penetration of Silicone Polymers into Silica Agglomerates and Its Influence on Dispersion Mechanism
Authors: Bohin F. , Manas-Zloczower I. , Feke D. L.
Published: February 2011

The dispersion of silica agglomerates suspended in silicone fluids undergoing simple shear flows has been studied. Two different breakup mechanisms, denoted “rupture” and “erosion” have been observed. These two breakup modes produce significantly different fragment size distributions. Penetration of the suspending fluid into the silica agglomerate was found to affect the mode and the conditions necessary for dispersion of the agglomerate. Silica agglomerates totally penetrated by silicone fluids resist dispersion much better than unpenetrated agglomerates. The kinetics of matrix penetration was modeled on the basis of capillary forces driving the penetration and viscous effects resisting it. Agreement of this model with experimental observations is excellent.
Viscoelastic Effects in Cutting and Tearing Rubber
Authors: Gent A. N. , Lai S-M. , Nah C. , Wang Chi
Published: February 2011

Measurements of cutting resistance have been made for a crosslinked styrene—butadiene copolymer over a wide range of cutting speeds and temperatures. A characteristic fracture energy was determined using the procedure of Lake and Yeoh. A lower limit, about 150 J/m2, was obtained at low cutting speeds. This value is significantly higher than the threshold tear strength, about 30 J/m2, due to roughness of the blade tip. The tear resistance increased dramatically as the test temperature was lowered, by a factor of over 1000X, whereas the cutting resistance remained largely unchanged over a considerable temperature range. Much of the enhanced tear resistance at low temperatures is therefore attributed to increasing roughness of the tear tip, the intrinsic strength remaining approximately constant. As the tear strength followed a WLF temperature dependence closely, roughening of the tear tip is associated with viscoelastic effects. Higher cutting resistance was shown by a sulfur vulcanizate, but carbon black had no additional effect. Variations in tensile strength with rate of elongation and temperature are discussed in terms of tearing from an initial edge flaw.
Reactive Compounds for Effective Utilization of Silica
Authors: Mandal Swapan Kumar , Basu Dipak Kumar
Published: February 2011

Bis(diisopropyl)thiophosphoryl disulfide (DIPDIS), diisopropyl thiophosphoryl-N-oxydiethylene sulfenamide (DIPTOS), diisopropyl thiophosphory)-N-oxydiethylene disulfide (DIPTOD), diisopropyl thiophosphoryl-2-benzothiazole monosulfide (DIBMS), diisopropyl thiophosphoryl-2-benzothiazole disulfide (DIBDS) and bis(diisopropyl)thiophosphoryl monosulfide (DIPMS) react with silica and generate isopropyl alcohol as a result of rubber-DIPDIS-silica interactions. Increasing the amount of DIPDIS in the system brings about a corresponding increase in silica-rubber coupling, resulting in enhancement of ΔTf−ΔTg modulus and tensile strength. The vulcanizates containing 14 mmol DIPDIS and 35 phr of silica exhibit highest torque and tensile strength. This is commensurate with the optimum loading derived from Lee's method. The synergistic system containing DIPDIS and N-oxydiethylene-2-benzothiazole sulfenamide (OBTS) provides a very useful combination of accelerators. The vulcanizates obtained from this system exhibit highest torque and tensile value even at a lower concentration of accelerator (DIPDIS : OBTS = 7: 3.5) for the same loading of silica (35 phr).
The Correlation among Vulcanizate Properties Using Computer Aided Design
Authors: Zhengji Jin , Jianming Gu , Weidong Liu , Shiqi Zhang
Published: February 2011

The concepts of optimizability and correlative matrix are proposed and evaluated as a means of correlating the mechanical properties of rubber compounds — elongation at break, tensile strength, set, elastic resilience, tear strength, abrasion loss, aging coefficient, fatigue life, crack initiation, and aged stress — with the rubber formulation variables —NR/SBR/BR composition, accelerator level, sulfur level, antioxidant level, antiozonant level, silica level, and extender oil level.
Oxidation of Elastomers in Aqueous Environments
Authors: Riaya Ascencion , Shaw Montgomery T. , Garton Andrew
Published: February 2011

Crosslinked 1,4-poly butadiene (BR) and styrene-butadiene rubber (SBR) were oxidized in various ionic environments (water, neutral salt solutions, acidic and basic buffers). The acceleration of oxidation when the elastomer was immersed in neutral and basic aqueous solutions, compared to dry air, is consistent with nucleophilic attack by peroxy anions on polymer hydroperoxides to give free radicals capable of initiating further oxidation. Acidic solutions retarded oxidation, compared to air, presumably because of decomposition of hydroperoxides to nonradical products. This phenomenon is in addition to the well-known effects of extraction of antioxidants by liquid media, and the accelerating effect of transition metal ions. The accelerating effect of basic solutions was greatest at the polymer surface, providing an inexpensive route to surface modification of elastomers. As an example, scrap rubber crumb was treated with aqueous alkaline hydrogen peroxide solution or sodium hypochlorite solution and evaluated as an impact modifier for brittle polymers.
Method for Estimating the Chemical Crosslink Densities of Cured Natural Rubber and Styrene-Butadiene Rubber
Authors: Lee Shirley , Pawlowski Henry , Coran A. Y.
Published: February 2011

Chemical crosslink densities of gum and carbon black-filled natural rubber (NR) and styrene-butadiene rubber (SBR) were estimated by using a newly developed rheometer. The rheometer is the Rubber Process Analyzer (RPA 2000) which is designed specifically to measure dynamic properties such as shear storage modulus G′ and shear loss modulus G″ in cured and uncured rubber. It was found that the differences between the G′ values of dicumyl peroxide-cured NR and those of uncured samples yielded estimates of the crosslink densities which were nearly the same as the values inferred by chemical analysis. For TMTD-cured SBR, the same procedure yielded estimates of chemical crosslinks very close to those estimated by a tensile stress-strain method and by NMR. In addition, accelerated sulfur-cured natural rubber was also investigated. The agreement between the crosslink densities of these stocks determined from G′ values and from a solvent-swelling method was very good.
Failure Properties of Natural Rubber Double Networks
Authors: Santangelo P. G. , Roland C. M.
Published: February 2011

When measured parallel to the curing deformation, double networks of natural rubber have a higher modulus than single networks of equal crosslink density. The difference is greater at higher strains. Despite the higher modulus, the mechanical fatigue lifetimes of double networks were found to be as much as a factor of ten higher than for conventionally crosslinked NR. The double network's tensile strength, on the other hand, was slightly lower. In contrast to these results, the modulus and tensile strength in the direction transverse to the curing strain are minimally affected by the presence of a composite network.
Phase Separation Dynamics of Blends of Telechelic Epoxy Terminated Polybutadiene and Maltene
Authors: Yamamoto Tsunehiro , Kyu Thein
Published: February 2011

Thermally induced phase separation in a mixture of telechelic epoxy terminated polybutadiene (ETPB) and maltene has been studied by means of time-resolved light scattering and optical microscopy. Maltene, consisting of various hydrocarbon derivatives, was extracted from asphalt with n-heptane and isolated by centrifugation. The cloud point studies of the ETPB/maltene mixture showed an upper critical solution temperature (UCST) which is thermally reversible. Several deep temperature quench experiments were conducted at an off-critical composition (27/73 ETPB/maltene) from a single phase (80°C) to a two-phase region (27, 29, 31 and 33 °C). The time-evolution of the structure factor for the late stage of spinodal decomposition (SD) was analyzed in the framework of nonlinear and dynamical scaling laws. The reverse quench experiments were also undertaken to elucidate the phase dissolution process.
Nonlinear Elastic Analysis of the Adhesive Strength between Rubber-Like Materials and Rigid Surfaces
Authors: Sun Shochang M. , Chang W. Victor
Published: February 2011

A nonlinear elastic finite element analysis of the adhesive strength between rubber-like materials and rigid surfaces has been conducted based on fracture mechanics principles. The finite element model is an elastomer half sphere adhering to a rigid flat surface. An analytical solution for the system was first developed by Johnson, Kendall and Roberts (JKR) in 1971, which agrees well with experimental data for small contact area. The objective of this paper is to elucidate the relationship between the adhesive fracture energy, tensile loads and debonding process of the system when the contact area is large. A general analysis procedure for nonconforming adhesion-contact problem has been established in this study, which allows us to determine the adhesive fracture energy from measurements of the final pull-off force Pc or the zero-load contact radius α0. Our results agree well with JKR's prediction when the zero-load contact radius is less than 25% of the radius of the sphere. However, as the contact radius increases, the debonding process deviates from JKR's prediction.
Physical Adsorption of Polymers on Disordered Filler Surfaces
Authors: Heinrich Gert , Vilgis Thomas A.
Published: February 2011

The problem of polymer adsorption on carbon black surfaces is considered within the concept of disorder-induced localization of polymer chains on disordered or fractal surfaces. The model describes how physical adsorption properties are enhanced compared to the adsorption on a flat surface. The difference is based on the configurational entropy which is less restricted in the disordered case than in the flat case. In fact, the surface of the carbon black particles is disordered over certain length scales and several experimental techniques have shown that the particle surface is fractal. This fractal nature can be quantified by the surface spectral density and the noninteger fractal surface dimension. As a main consequence, the coupling between filler and polymer is caused by entanglements formed between tightly adsorbed bound rubber on the filler surface and the bulk rubber far removed from the surface. The corresponding density of couples is estimated for several filled polymer networks using tensile test results. The stress-strain relations used are based on a new rigorous molecular-statistical model of filled polymer networks with quenched topology that includes the entanglements within the mobile rubber phase (configurational tube-model).
Effect of Precipitated Silica Physical Properties on Silicone Rubber Performance
Authors: Okel Timothy A. , Waddell Walter H.
Published: February 2011

Nitrogen BET surface area is a highly accurate predictor of the physical performance of silica-filled and silica and carbon black-filled, cured organic rubber compounds. The effectiveness of predicting performance of a high-temperature-vulcanized, high-consistency silicone rubber, based on precipitated silica physical properties, is presented. Correlation and regression analyses were performed for twenty-five silica physical properties and fourteen silicone rubber performance characteristics. Silica properties studied included measurements of surface area, structure, impurities, particle size, pH and adsorbed moisture. Silicone rubber performance included measures of processing, curing, reinforcement, resiliency, stress whitening, color and clarity. The present study confirms that no single silica physical property can predict silicone rubber performance. A combination of surface area, oil absorption, particle size, pH, adsorbed moisture, residual sodium and/or residual salt can qualitatively predict the physical performance of high-temperature-vulcanized, high consistency, precipitated silica-filled silicone rubber.
Large Strain Viscoelastic Constitutive Models for Rubber, Part II: Determination of Material Constants
Authors: Quigley Claudia J. , Mead Joey , Johnson Arthur R.
Published: February 2011

A method for determining material constants in large strain viscoelastic materials was demonstrated for a highly saturated nitrile rubber. Material constant selection was based on viscoelastic stress relaxation data at small and large strains, under both tension and compression, and was constrained to assure Drucker stability. Assuming that the viscoelastic strain energy function was both time and strain separable, a Prony series was constructed for the time dependent material constants. For comparison, four different Prony series were developed from collocation methods and a nonlinear regression analysis, each separately based on either large or small tensile strain relaxation data. In addition, a final Prony series was constructed from dynamic data. These Prony series were included in this comparison to judge their ability to predict both large and small strain material behavior. Finite element analyses of large and small step-strain relaxation tests and a single cycle hysteresis loop at large deformations were performed for each set of Prony series. The results were then compared to experimental behavior. The Prony series based on the constrained method accurately predicted step-strain relaxation behavior at all strain levels, for both tension and compression. The finite element results for the other Prony series show that large strain material behavior was best predicted by those Prony series based on large strain material behavior. Similar findings were found for small strain material behavior. The constrained Prony series and the two large strain based Prony series best modeled the experimental hysteresis loop.
Dynamic-Mechanical Properties of Tin-Coupled SBRs
Authors: Sierra C. A. , Galán C. , Gómez Fatou J. M. , Quiteria V. Ruíz Santa
Published: February 2011

The interaction between rubber and carbon black in compounds for road tire treads has been analyzed by using mechanical and dynamical measurements in three cured compounds based on SBRs. The rubbers were prepared in solution by anionic polymerization, and coupled with tin compounds in which the carbon-tin bond at the end of the chain may correspond to styryl or butadienyl terminations. The interaction parameter, defined by the ratio of mechanical and dynamic terms, has been used for the first time for the evaluation of the compounds. The SBRs with tin-butadienyl bonds exhibit an improved interaction with the filler, with increasing tin content.
A New Method to Hydrogenate Nitrile Rubber in the Latex Form
Authors: Singha Nikhil K. , Sivaram S. , Talwar S. S.
Published: February 2011

A water soluble analog of Wilkinson catalyst — chloro-tris-(sodium diphenylphosphino-benzene-m-sulfonate) rhodium(I), CAS 67178-14-7, i.e. RhCl(DPM)3— has been found to hydrogenate NBR latex. More than 60 mol% hydrogenation can be achieved at 75°C and 1 atmosphere hydrogen pressure. Hydrogenation was accompanied by an increase in gel content of the latex.
Mechanism of Carbon-Black Reinforcement of Rubber Vulcanizate
Authors: Kawabata Sueo , Yamashita Yoshihiro , Ooyama Hajime , Yoshida Shuichi
Published: February 2011

The mechanism of reinforcing rubber with carbon black particles is investigated by comparing the strain energy density functions of pure and reinforced rubbers. Finite deformation biaxial extension experiments are used to measure the strain energy density. The functional form of the reinforced system, which has been proposed by Kawabata, is examined and its validity was confirmed over a temperature range of −20°C to 80°C. The functional form is: W(I1,I2)=CT(I1−3)+β(I1,I2)+γ(I1), where I1 and I2 are the invariants of the deformation tensor. Parameter C is a constant and T is the temperature. The reinforcement effect on W appears as the γ function which is not affected by temperature. The results are analyzed with respect to a network mechanical model consisting of molecule bundles connecting carbon-black aggregates. The function W is calculated and it is shown that the functional form of Wis very similar to that of the reinforced rubber.
Fractal Analysis of Commercial and Pyrolytic Carbon Blacks Using Nitrogen Adsorption Data
Authors: Darmstadt H. , Roy C. , Kaliaguine S. , Sahouli B. , Blacher S. , Pirard R. , Brouers F.
Published: February 2011

The surface fractal dimension of commercial rubber-grade carbon blacks and of pyrolytic carbon blacks (CBp) was determined using nitrogen sorption data. The CBp were produced by vacuum pyrolysis of used tires at different temperatures and pressures. Commercial carbon blacks and CBp obtained at low pyrolysis pressures have a similar fractal dimension of the surface (Ds) or roughness. CBp produced at higher pyrolysis pressures have a smaller fractal dimension than commercial grades, suggesting a smoother surface. Complementary SIMS and ESCA investigations showed that the decreasing fractal dimension with increasing pyrolysis pressure is due to the formation of carbonaceous deposits on the CBp from the pyrolyzed organic material.
Fatigue and Fracture of Elastomers
Authors: Lake G. J.
Published: February 2011

The use of an energetics approach to treat various aspects of fatigue and fracture in elastomers is reviewed. Topics covered include tearing, crack growth and fatigue, tensile failure, oxidative effects, environmental cracking, cutting by sharp objects, abrasion, adhesion, friction (under circumstances where it is determined mainly by the making and breaking of contact), and cavitation. Application of the approach to service problems is also considered. Finally, physical and chemical factors affecting the crack growth characteristics—the material property linking various types of cohesive failure—are discussed.
Nitrile Rubber—Past, Present and Future
Authors: Hertz D. L. , Bussem Hermann , Ray T. W.
Published: February 2011

Nitrile rubber (NBR) has been the work-horse elastomer in oil and gas production for the past fifty years. Random seal and packer failures have been encountered in the more agressive fields. The higher temperatures and increasing percentages of hydrogen sulfide (H2S), naturally occuring or through well stimulation directly or indirectly, initiate the failure mechanism(s). Future applications of nitrile rubber in higher temperature production should only be considered after reviewing the range of potential chemical attacks that are possible by of the aqueous environment (well fluids, completion fluids and stimulation fluids). This paper briefly outlines the scope of chemical attacks that can and will be encountered.
Sulfur Vulcanization of Simple Model Olefins, Part IV: Vulcanizations of 2,3-Dimethyl-2-Butene with TMTD and Activated Zinc Dithiocarbamate/Xanthate Accelerators at Different Temperatures
Authors: Versloot P. , Haasnoot J. G. , Reedijk J. , van Duin M. , Put J.
Published: February 2011

The mechanism of the accelerated sulfur vulcanization of rubber was studied by the use of 2,3-dimethyl-2-butene (C6H12, TME) as a simple, low-molecular model alkene. Treatment of TME with a mixture of ZnO, S8 and the classical accelerator TMTD at temperatures above 100°C yields a mixture of addition products ((C6H11—Sn—C6H11) ). In the temperature range of 50 up to 100 °C only intermediate products, C6H11—Sn—S(S)CN(CH3)2 are obtained. Room temperature vulcanization is feasible using highly reactive accelerators, such as xanthate derivatives. These derivatives result in formation of the crosslink precursors which are converted to the actual crosslink in the presence of zinc dithiocarbamates. The addition of (secondary) amines enhances the solubility of the dithiocarbamates, and therefore the reactivity of the xanthate/zinc dithiocarbamate combination.
Crosslink Densities and Phase Morpholgies in Dynamically Vulcanized TPEs
Authors: Ellul Maria D. , Patel Jaymini , Tinker Andrew J.
Published: February 2011

Recent developments in characterization techniques have permitted estimation of the crosslink density attained in dynamically vulcanized thermoplastic elastomers. The range of techniques available for investigation of the phase morphology of this type of TPE has also increased. The characterization of experimental TPEs based on natural rubber/polypropylene and EPDM/polypropylene is reported here. A combination of several optical and electron microscopy techniques were employed. Crosslink densities estimated by swollen-state NMR spectroscopy are presented and are corroborated by estimates from a network visualization technique for TPEs.
Rubber Cylinders under Hydrostatic Pressure with Variable Poisson's Ratio
Authors: Holownia B. P.
Published: February 2011

Elastomers are increasingly used in specialized engineering applications where their complex shape often requires a detailed stress analysis. Specialized programmes have to be used for incompressible materials such as elastomers, since the standard computer finite element packages are unable to give accurate solutions for rubbers with Poisson's ratio close to 0.5. The present paper uses an established finite difference method to examine the deflected shape of rubbers under hydrostatic pressure. A particular case of a rubber cylinder subjected to hydrostatic pressure is examined, where a natural tendency is to assume that the rubber cylinder will reduce slightly in volume, evenly all the way round. However, by performing a detailed finite difference analysis, it was found that the final shape, under pressure, was dependent on the value of Poisson's ratio, and height to diameter ratio of the rubber cylinder. An interesting result is that the end of the cylinder, and the circumferential surface will change shape from a concave to a convex surface by changing the value of ν for certain cylindrical shapes of rubber.
Evaluation of the External Surface Area of Carbon Black by Nitrogen Adsorption
Authors: Magee R. W.
Published: February 2011

Specific surface area is an important property for carbon black grade classification, production control, and prediction of rubber reinforcement characteristics. Total surface area alone is insufficient for estimating the reinforcing properties of a microporous carbon black because the internal area of the micropores is inaccessible to rubber molecules. The CTAB surface area test, based on adsorption of a molecule too large to enter the micropore, measures the surface area available to rubber. Although widely used, the CTAB method has failed to gain wide popularity due to its labor-intensive nature and poor testing precision. In the present paper, the extent of microporosity on the surface of carbon blacks is investigated. The external surface area derived from the nitrogen adsorption characteristics is compared to CTAB surface area for a number of standard rubber carbon blacks. This study reports the optimum testing conditions to achieve precise external surface area measurements and the ability of this method to overcome the disadvantages of the CTAB method. Other advantages of this technique are discussed.
A Triboelastic Model for the Cyclic Mechanical Behavior of Filled Vulcanizates
Authors: Coveney V. A. , Johnson D. E. , Turner D. M.
Published: February 2011

Aspects of the mechanical behavior of filled vulcanizates are reviewed with reference to existing mathematical models. The basic equations of the triboelastic theory, previously described by Turner, are derived. A standard triboelastic solid (STS) three parameter model, analogous to the standard linear solid, is described and a computationally efficient approximation developed. Comparisons are made between the predictions of the STS model and the behavior of testpieces of heavily filled natural rubber vulcanizates when subjected to simple and to complex deformation histories at various frequencies; the model is found to give a satisfactory representation of material behavior. Limitations of the STS model are also discussed.
Solubility of Sulfur and Dithiocarbamates in Natural Rubber
Authors: Morris M. D. , Thomas A. G.
Published: February 2011

Knowledge of equilibrium solubilities of sulfur and accelerators in rubbers at various temperatures allows prediction of whether blooming is possible in particular compounds or products. Reliable data of this nature for natural rubber appeared not to exist in the literature. Immersion of 1 mm thick sheets of peroxide-vulcanized natural rubber in both liquid and, more surprisingly, powdered solid curatives was found to be an adequate method for measuring solubilities. The same experimental method also enabled some diffusion data to be obtained. Solubilities of sulfur, zinc diethyldithiocarbamate (ZDEC) and zinc di-n-butyl dithiocarbamate (ZDBC) were determined at various temperatures between 23° and 135°C. The experimental results did not agree well with the theory which had previously been found to describe the solubility of waxes in natural rubber. This theory, which is a combination of the Flory-Huggins Equation with an expression for the latent heat of fusion, was modified to take into account the dependence of the interaction parameter on temperature and on degree of swelling. The new expression gave much better agreement with the experimental results for all three substances.
Effect of Bromination on the Properties of Ethylene-Propylene-Diene Rubber in the Presence of Divinylbenzene
Authors: Yoon J. R. , Ikeda Y. , Hashim A. S. , Kohjiya S.
Published: February 2011

The curing behavior and vulcanizate properties of EPDM and brominated EPDM (BEPDM) were compared using a dicumyl peroxide curing system. The BEPDM displayed lower torque and crosslink density, but better tensile properties than the EPDM. In the presence of divinylbenzene (DVB) coagent, all vulcanizates, i.e., EPDM, BEPDM, and their blends with natural rubber, had improved tensile properties. At low DVB concentration, the filler effect of DVB on the modulus enhancement was noticed. At high and comparable DVB concentration, both the BEPDM and NR/BEPDM blend showed significantly higher modulus (M100) and tensile strength than their EPDM counterparts. The BEPDM was also found to have higher crosslink density and storage modulus (E′) than the EPDM. This observation could be attributed to the better dispersion of DVB in the BEPDM and NR/BEPDM vulcanizates, as supported by TEM measurements. The TEM data is also consistent with the properties observed on the uncured mixes, in which the NK/BEPDM + DVB mix has favorable viscosity and die swell properties due to the more homogeneous DVB dispersion in the rubber phases. Thus, the bromination of EPDM has resulted in better processing and vulcanizate properties of the rubber and its blend with natural rubber.
Encapsulation in Ternary Elastomer Blends
Authors: Koseki Yasuaki , Lee Moo Sung , Macosko C. W.
Published: February 2011

Ternary elastomer blends of acrylonitrile-butadiene rubber (NBR), chlorinated polyethylene (CM), and ethylene-propylene rubber (EP) have been investigated using transmission electron microscopy (TEM). Especially the effect of comonomer content, chlorine in CM and acrylonitrile in NBR, on blend morphology is studied. The blend ratio of NBR/CM/EP is fixed at 10/20/70 by weight: EP acts as matrix and NBR and CM comprise dispersed phases. TEM observation is possible without staining due to a natural contrast between NBR and CM. From TEM micrographs it is clear that NBR/CM/EP blends show encapsulated structures. Which component will be the encapsulating layer depends on comonomer contents. For blends containing high acrylonitrile content (NBR46), CM forms the encapsulating layer; whereas, for blends with low acrylonitrile (NBR16), NBR16 encapsulates CM. The encapsulation behavior of NBR/CM/EP blends is interpreted in terms of a spreading coefficient concept combined with solubility parameter and melt viscosity differences between NBR and CM. Our calculation based on simple thermodynamic considerations explains the morphology observed in this study except for the NBR16/CM29/EP blend.
Thermal Properties and Crystallization Behavior of Highly Deproteinized Natural Rubber
Authors: Kawahara Seiichi , Kakubo Takashi , Suzuki Michio , Tanaka Yasuyuki
Published: February 2011

Natural rubber was deproteinized with a proteolytic enzyme and surfactant to reduce nitrogen content less than 0.02%. The deproteinized rubber was further purified by acetone-extraction followed by transesterification with sodium methoxide. The density of rubber decreased and the thermal expansion coefficient increased by deproteinization and transesterification. The glass transition temperature, Tg, was slightly reduced after deproteinization and transesterification. These were explained in relation to the decrease in gel content of the rubber. The equilibrium melting temperature, Tm0, was practically unchanged by these treatments. The low-temperature crystallization between −30 and −10 °C was significantly influenced by free fatty acids present as a mixture and fatty acid groups linked to the rubber chain. The crystallization behavior was independent of Tg and Tm0 values.
Deformation of Laminated Elastomer Composites
Authors: Luo Shen-Yi , Taban Faruk
Published: February 2011

Flexible elastomer composites subjected to finite deformation are usually associated with significant fiber re-orientation and configuration change which cannot be described by classical composite lamination theory. Utilizing the Lagrangian description and a strain-energy density approach, this work presents a set of 2-D constitutive equations in terms of the overall deformation of laminated composites. This model includes both geometric and material nonlinearities of the laminate. Interlaminar shear deformation is addressed but not studied in this analysis. Theoretical predictions have been compared with the available experimental data about symmetric laminates with various fiber orientations in the finite deformation range. Also, a parametric study has been performed under various ratios of biaxial deformation.
2-t-Butylbenzothiazole Sulfenamide Accelerated Sulfur Vulcanization of Polyisoprene
Authors: Gradwell M. H. S. , van der Merwe M. J.
Published: February 2011

The mechanism of 2-t-butylbenzothiazole sulfenamide (TBBS) accelerated sulfur vulcanization of polyisoprene was investigated. Samples of compounded rubber were heated in a differential scanning calorimeter to preselected temperatures or degrees of vulcanization, the reaction stopped, and the products analyzed. TBBS polysulfides, formed from the reaction of TBBS with sulfur, react with the rubber chain to form benzothiazole pendent groups and free t-butylamine. The delayed action of TBBS accelerated sulfur vulcanization was shown to be due to an exchange reaction involving benzothiazole terminated pendent groups and TBBS. Crosslinking occurred very rapidly once the TBBS was depleted. Special reference was made to the role of the amine. Reaction mechanisms were proposed to account for the formation of products.
The Mechanical Behavior of a Slightly Compressible Rubber-Like Material: Correlation of Simulations and Experiments
Authors: Moreau C. , Thuillier S. , Rio G. , Grolleau V.
Published: February 2011

The purpose of this paper is to present a different approach for modeling the mechanical behavior of a compressible rubber-like material. In this approach, the motion of the body is described in the current configuration in convected material frames and the Cauchy stress tensor and Almansi strain tensor are used. The hyperelastic constitutive law, corresponding to this approach, is also presented. Non-homogeneous experiments on compact chloroprene specimens were carried out, in order to show the possibilities of the model. The material parameters are identified using an inverse problem approach, based on the minimization of the gap between the experimental load-displacement curve and the simulated one and on a numerical calculation of the cost function gradient. Results show that over a set of three different non-homogeneous and multiaxial tests, there is a good correlation between experiments and simulation.
Characterization of Hevea Brasiliensis Rubber from Virgin Trees: A Possible Role of Cis-Polyisoprene in Unexploited Tree
Authors: Sakdapipanich Jitladda , Tanaka Yasuyuki , Jacob Jean Louis , d'Auzac Jean
Published: February 2011

The role of rubber in Hevea brasiliensis was analyzed based on the structural analysis of rubber in rubber trees as latex. The rubber obtained from a mature-tree which has never tapped before, so-called “virgin mature-tree” (Vir-NR), contained the gel fraction higher than 80%, while that from a regularly tapped mature-tree (Reg-NR) was less than 3%. The gel showed almost the same structure as a crosslinked rubber prepared from fresh latex in the presence of peroxide, with the molecular weight between crosslinks (Mc) of 3×103. This value is extremely low comparing with that of 7×105 observed for the soft-gel in rubber from high-ammonia latex and Pale crepe. The sol fraction from Vir-NR was an oxidative degraded product containing aldehyde and epoxide groups. Aging properties of Vir-NR are much worse than those of Reg-NR. This indicates that rubber accepts free-radicals to form C-C crosslinking and partly oxidative scission of main-chains during storage in laticiferous tubes of Hevea trees. This suggests that a possible role of rubber is a scavenger of free-radicals in latex, due to lack of the naturally occurring antioxidants. The consecutive tappings of latex from the first opening mature-tree resulted in the formation of rubber similar to that obtained from Reg-NR, after six days. This modification indicates that the new regulation mechanisms in latex biosynthesis, which is induced by exploitation, can avoid the rubber chain crosslinkings and increase their elongations.
Effect of Water Soluble Polymers on Radiation Vulcanized Natural Rubber Latex Films
Authors: Varghese Siby , Katsumura Yosuke , Makuuchi Keizo , Yoshi Fumio
Published: February 2011

Technological properties of radiation vulcanized latex after mixing with water soluble polymers (WSP) such as poly(vinyl alcohol), poly(ethylene oxide) etc. have been studied in detail. The properties of water soluble polymer incorporated vulcanizates depend mainly on the type of the polymer blended into the latex. Most of the polymers showed a drastic increase in tear strength with polymer content and a reduction in tackiness of the vulcanized films. Radiation processing increases the water soluble protein content in the serum phase whereas that in the rubber phase decreases. Addition of water soluble polymer causes the fast leaching of soluble proteins from the dried films, which reduces the prolonged leaching commonly adopted for rubber vulcanizates. Aging properties of radiation vulcanized films incorporated with water soluble polymers are excellent. The thermal degradation behavior of radiation vulcanized films and that of water soluble polymer incorporated films is almost the same. Transparency of the rubber films can be increased by the addition of suitable water soluble polymers.
Studies of Peroxide Curing of cis-1,4-Polyisoprene/Diallyl Phthalate Blends by Spectroscopic Techniques
Authors: Oh Sung Joon , Koenig Jack L.
Published: February 2011

Peroxide curing of cis-1,4-polyisoprene/diallyl phthalate blends was studied by the analytical techniques of equilibrium swelling, differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), and solid-state nuclear magnetic resonance (NMR). Although the overall curing kinetics are controlled by the peroxide decomposition rate, the addition of a coagent into the rubber matrix catalyzes the curing reactions. The increase in peroxide and coagent concentrations in the blend results in a decrease in T2 relaxation times, which is caused by restricted segmental mobility due to the increase in crosslink density. It is suggested that phase separated coagent domains are chemically bound with the rubber matrix, providing the decrease in segmental mobility.
Effect of Surface Oxidation of Carbon Black on Its Bonding with Epoxidized Natural Rubber in the Presence of Silane Coupling Agent
Authors: Manna Ajay K. , De P. P. , Tripathy D. K. , De S. K. , Chatterjee M. K.
Published: February 2011

Results of bound rubber determination, Monsanto rheometry, solvent swelling studies and measurement of physical properties reveal that high temperature molding of epoxidized natural rubber (ENR) filled with intermediate super abrasion furnace (ISAF) carbon black and surface oxidized ISAF carbon black, in the presence of silane coupling agent, namely, N-(4-vinylbenzyl)-N′-[3-(trimethoxysilyl)propyl]ethane-1,2-diamine monoHCl salt, results in crosslinking of the rubber phase, even in the absence of the vulcanizing agents. Infrared spectroscopic studies show formation of silyl ether, in the case of ISAF carbon black, whereas the oxidized grade forms both silyl ether as well as silyl ester and amide linkage. Oxidation of ISAF carbon black causes an increase in the extent of coupling bond formation.
An Extended Tube-Model for Rubber Elasticity: Statistical-Mechanical Theory and Finite Element Implementation
Authors: Kaliske M. , Heinrich G.
Published: February 2011

A novel model of rubber elasticity—the extended tube-model—is introduced. The model considers the topological constraints as well as the limited chain extensibility of network chains in filled rubbers. It is supplied by a formulation suitable for an implementation into a finite element code. Homogeneous states of deformation are evaluated analytically to yield expressions required e.g., for parameter identification algorithms. Finally, large scale finite element computations compare the extended tube-model with experimental investigations and with the phenomenological strain energy function of the Yeoh-model. The extended tube-model can be considered as an interesting approach introducing physical considerations on the molecular scale into the formulation of the strain energy function which is on the other hand the starting point for the numerical realization on the structural level. Thus, the gap between physics and numerics is bridged. Nevertheless, this study reveals the importance of a proper parameter identification and adapted experiments.