bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamically Vulcanized Thermoplastic Elastomers
Authors: Abdou-Sabet S. , Puydak R. C. , Rader C. P.
Published: February 2011

Thermoplastic elastomers (TPEs) exhibit the functional properties of conventional thermoset rubber, yet can be processed on thermoplastic fabrication equipment. The great majority of TPEs have hetero-phase morphology, whether the TPE is derived from block copolymers, rubber-plastic compositions or ionomers. Generally speaking, the hard domains (or the ionic clusters) undergo dissociation at elevated temperatures, thus allowing the material to flow. When cooled, the hard domains again solidify and provide tensile strength at normal use temperatures. The soft domains give the material its elastomeric characteristics. In this review article, the focus is on rubber-plastic polymer compositions as a group of TPEs which have achieved significant growth in the marketplace in the last two decades. The growth has been primarily in the nonpolar (olefinic) elastomer/polyolefin thermoplastic materials because of the wide range of products generated, their performance and their significant acceptance by the automotive sector in applications requiring elastic recovery. The field of TPEs based on polyolefin rubber-plastic compositions has grown along two distinctly different product lines or classes: one class consists of a simple blend and classically meets the definition of a thermoplastic elastomeric olefin (TEO), commonly called a thermoplastic polyolefin (TPO) in earlier literature. In the other class, the rubber phase is dynamically vulcanized, giving rise to thermoplastic vulcanizates (TPVs), named elastomeric alloys (EAs) in some previous literature. Both the simple blends and the dynamically vulcanized TPEs have found wide industrial application. It is the dynamically vulcanized TPE that has the performance characteristics required for true thermoset rubber replacement applications. The first TPE introduced to the market based on a crosslinked rubber-plastic composition (1972) was derived from W. K. Fisher's discovery of partially crosslinking the EPDM phase of EPDM/polypropylene (PP). Fisher controlled the degree of vulcanization by limiting the amount of peroxide, to maintain the thermoplastic processability of the blend. Crosslinking was performed while mixing, a process known as dynamic vulcanization. It is worth noting, however, that the dynamic vulcanization process and the first crosslinked EPDM/PP composition were discovered independently by Gessler and Haslett and by Holzer, Taurus and Mehnert in 1958 and 1961, respectively. Significant improvement in the properties of these blends was achieved in 1975 by Coran, Das and Patel by fully vulcanizing the rubber phase under dynamic shear while maintaining the thermoplasticity of the blend. These blends were further improved by Abdou-Sabet and Fath in 1977 by the use of phenolic curatives to improve the rubber-like properties and the flow (processing) characteristics.
Tire Traction vs. Tread Compound Properties—How Pavement Texture and Test Conditions Influence the Relationship
Authors: Veith Alan G.
Published: February 2011

A comprehensive test program conducted on a wide range of compounds with varying Tg and carbon black-oil reinforcement levels, shows that wet traction is influenced by two viscoelastic parameters: tan δ/E′, which represents the hysteresis or deformation friction component, and E″, the adhesion component. Both of these components jointly determine overall traction performance. However the individual component dependence as well as the combined dependence, traction vs. the viscoelastic parameters, changes as pavement texture and test conditions change. These changes may include performance reversals. The mechanisms responsible for most of this behavior are described. The relevance of these relationships to current wet traction evaluation procedures is also discussed.
Studies on a New Antireversion Agent for Sulfur Vulcanization of Diene Rubbers
Authors: Schotman A. H. M. , van Haeren P. J. C. , Weber A. J. M. , van Wijk F. G. H. , Hofstraat J. W. , Talma A. G. , Steenbergen A. , Datta R. N.
Published: February 2011

The mechanism of biscitraconimides (BCI) as antireversion agents for sulfur vulcanized diene rubber was investigated choosing squalene as a model substrate. Curing of squalene with sulfur in the presence of accelerator, activator and BCI at 170°C gave BCI bridged adducts. The products were identified by spectroscopic methods as being results of a Diels-Alder reaction of BCI (dienophile) with conjugated polyenes that are formed as a result of reversion. The rate at which the sulfur network degrades is comparable to the rate in which BCI adduct is formed. As a result of this, a nearly constant crosslink density is obtained after optimum cure time (t90). Based on this concept, the advantage of using 1,3-bis-(citraconimidomethyl) benzene (BCI-MX), a representative of the BCI-class, in NR based compounds is examined.
Selective Interactions in Elastomers, a Base for Compatibility and Polymer-Filler Interactions
Authors: Schuster R. H. , Issel H. M. , Peterseim V.
Published: February 2011

This paper describes the determination of accurate solubility parameters for nonpolar rubbers according to a GLC-method developed by Guillet. The data obtained provide a simple but meaningful thermodynamic characterization of the contribution of microstructure units and comonomers (styrene) in polydienes. On this basis quantitative expressions are derived for δ2-parameters of BR and SBR as a function of the vinyl and the styrene content respectively. The consequences on morphology development and miscibility are presented for blends of NR, SBR, BR and EPDM. Furthermore, it is shown for the first time that the method is able to describe the temperature dependence of the δ2-parameter so that temperature induced phase transitions (UCST and LCST) can be predicted. On this basis morphological predictions are made on average domain size and size distribution as well as on the phase inversion region. The contribution of intermolecular interactions to flow-induced phase morphology is discussed in relation to the influence of rheological factors. An extension to polymer—filler systems is made.
Direct Comparison of the Gent and the Arruda-Boyce Constitutive Models of Rubber Elasticity
Authors: Boyce Mary C.
Published: February 2011

The Arruda and Boyce eight-chain network constitutive model for rubber elastic materials is compared to the new Gent constitutive model for rubber elasticity. The salient features of each of the two models are compared. The ability of both models to predict three dimensional large strain deformation is demonstrated showing the near equivalence of these two model constructions as well as their abilities to predict complex three-dimensional deformation with only two material constants.
Fine Scale Characterization of Crosslinking with the Atomic Force Microscope
Authors: Mareanukroh Methporn , Hamed Gary R. , Eby R. K.
Published: February 2011

Fine-scale variations of the crosslink density of elastomers are important scientifically and technologically. We have shown that the atomic force microscope ( AFM), used in the force/distance mode, is sensitive to the crosslink density. In this mode, the sample is pushed against the tip in a manner similar to that for standard hardness testing. However, the end of the tip of the AFM is only 100 to 500 A˚ in radius. Further, it can be moved in a controlled manner in very fine increments both from point to point over the surface and into the surface of a sample. As a result, it can sample much more finely spaced and smaller volumes of material than either the typical hardness tester or the usual methods of measuring crosslink density. Samples of a styrene-butadiene copolymer were compounded with varying amounts of dicumyl peroxide and cured under compression molding at 160°C. Crosslink density was measured by swelling. The results show a significant variation of force/distance penetrated with crosslink density. A plot of experimental value of force/square of distance penetrated vs crosslink density is comparable to a theoretical one calculated with the crosslink density data and the half angle of the conical probe tip. Measurements at a spacing of 170 nm along straight lines are reported as well as measurements which show the technique to be sensitive to oxidation at short times. The effects of variables such as sample roughness, canting of the tip with respect to the sample surface, tilting of the sample surface, penetration depth, sample oxidation, and other variables are considered.
Abrasion of Rubber by a Blade Abrader: Effect of Blade Sharpness and Test Temperature for Selected Compounds
Authors: Gent A. N. , Nah C.
Published: February 2011

Apparatus has been constructed to abrade the flat surface of a rubber disk by rotating it against a stationary knife-blade scraper at constant frictional torque. The ratio of worn surface area to sample volume is relatively large, giving high sensitivity of measurement. Rates of abrasion were measured for several rubber compounds over a range of frictional torque from 0.05 to 1.2 Nm, corresponding to frictional work input from 150 to 3,600 J/m2 per rotation. For some materials, notably SBR compounds, the rate of abrasion decreased markedly as the experiment continued, due to rapid wear and blunting of the blade. Polybutadiene compounds caused much slower wear. Different blades were worn away at different rates, a zirconia blade showing the least wear. Also different elastomers showed different sensitivities to blade sharpness, the rate of abrasion of a high-styrene (48%) SBR compound being reduced the most with a blunted blade whereas the abrasion rate of polybutadiene (BR) was much less affected. Measurements were carried out with blades of known sharpness for several representative rubber compounds at various fnctional torques and at two temperatures, 25°C and 100°C. The high-styrene SBR compound showed the lowest rate of abrasion Unusually rapid abrasion was observed for SBR and BR compounds when the frictional work input exceeded a critical value, close to the tear ( fracture) energy at the same temperature. Also, periodic fluctuations in rate of abrasion were observed for rapidly-aging compounds at high temperatures. This is attributed to repeated formation and removal of a weakened surface layer.
A Study of the Thermal Degradation Products of Styrene-Butadiene Type Rubber by Pyrolysis/GC/MS
Authors: Ghebremeskel Ghebrehiwet N. , Sekinger J. K. , Hoffpauir J. L. , Hendrix C.
Published: February 2011

Pyrolysis coupled with GC/MS was used to study thermal degradation products of styrene—butadiene rubber (SBR). Introduction of samples, using the pyrolysis carrier gas through the split injection port, followed by sub-ambient focusing of pyrolysis products gave reproducible chromatograms. The styrene content of styrene—butadiene copolymer was determined by plotting the GC areas of styrene and butadiene dimer (4-vinlycyclohexene) vs the percent bound styrene measured by refractive index and infrared spectroscopy. The accuracy and ease of use of the technique in determining the styrene content of styrene—butadiene copolymer is also compared to that of the refractive index and infrared spectroscopy methods. Finally, the effects of carbon black and other fillers on the thermal degradation products of the styrene—butadiene copolymer are also discussed.
Solubility of Antioxidants in Rubber
Authors: Pushpa S. A. , Goonetilleke P. , Billingham N. C.
Published: February 2011

Solubilities of seven phenolic antioxidants in rubber and three antioxidants in low density polyethylene (LDPE) were measured at temperatures ranging trom 40°C–100°C. The antioxidants are more soluble in rubber than in LDPE, which is semicrystalline. The solubility of antioxidants is temperature dependent and both the melting point of the additive and its interactions with the polymer are important in determining solubility. As a general rule, solubility decreases with increasing molecular weight.
Effect of Processing Additives on Carbon Black Dispersion and Grip Property of High-Performance Tire Tread Compound
Authors: Takino H. , Iwama S. , Yamada Y. , Kohjiya S.
Published: February 2011

Rubber and carbon black compounds show complex behaviors in their mixing process due to their complicated microcomposite structure. Therefore, establishing a clear relationship between the mixing state of the rubber compound and the physical properties of its cured rubber has still remained to be solved in spite of formidable efforts by many rubber technologists. This paper investigated the influence of a processing additive on the carbon black incorporation and its dispersion behavior by inspecting Banbury power curves. From this investigation, we considered that good wettability toward the carbon black surface was necessary for processing additives in order to improve carbon black dispersion. The function of the processing additive was thought to enhance the surface lubrication of carbon black for disagglomeration in the early steps of mixing. The dry grip properties of a tire was estimated from the temperature dependence of dynamic viscoelastic properties of rubber compounds, with improved carbon black dispersion due to the processing additive; and it was confirmed by an actual tire running evaluation. Consequently, we found that tread compounds with improved carbon black dispersion had a remarkable effect on tire dry-grip properties at high temperatures.
The Dark Field Cut Surface (DFCS) Test for Estimating the Dispersion of Carbon Black in Rubber Compounds
Authors: Murray G. A. W. , Southwart D. W. , Freakley P. K.
Published: February 2011

A test for estimating the dispersion of carbon black in rubber compounds is described. It works by examining the freshly cut surface of a specimen at low magnification in dark field illumination. Roughness of the surface related to the presence of carbon black causes increased reflection under dark field illumination. The illumination of each field of view is examined as 100 subdivisions and the relative values of these readings give a numerical estimate of the dispersion. Details of how this is done and the corrections applied to the results are described. A second paper reports some initial results obtained with the test. The test works well for certain elastomers, notably NR and SBR. The biggest advantage of the test is its ability to work rapidly and cheaply on small zones at relatively high magnification. This opens up the possibility of detailed studies of macroscopic variations in dispersion, done in reasonable times and at reasonable costs.
Effect of trans-Polyoctenylene on Crosslink Structure of NR and SBR Using Solid State 13C NMR Spectroscopy and RPA 2000
Authors: Chattaraj P. P. , Mukhopadhyay R. , Tripathy D. K.
Published: February 2011

The use of petroleum oil as a processing aid is well established in the rubber industry. However, it has certain demerits when used in a critical rubber compound. To overcome this and to get certain other advantages, new non-conventional processing aids (solid in nature) are preferred. trans-Polyoctenylene (TOR) is one of them which is crosslinkable with sulfur and accelerator. The effect of TOR on natural rubber (NR) and styrene—butadiene rubber (SBR) vulcanizates has shown that the retention (%) of network properties at high temperatures, after aerobic and anaerobic aging, is better with incorporation of TOR in conventional vulcanization (CV) curing systems. This has been attributed to the change of network to a more efficient-like system. The purpose of the present work is to establish the change of network structure/crosslinks and their kind and distribution in NR and SBR, with incorporation of TOR followed by a spectroscopic study of the vulcanizate. The study is extended to different crosslinking systems (CV, efficient vulcanization (EV), and semi-EV (SEV) with respect to NR and SBR) considering the effect of anaerobic aging on the vulcanizates. Crosslink distribution (in CV and EV) and network structural change after aging has been explained by a suitable mechanism. Elucidation of crosslink structure of SBR vulcanizates by NMR and estimation of chemical crosslink density by the Rubber Process Analyzer (RPA 2000) are key points of this study.
Ultrasound Devulcanization of SBR: Molecular Mobility of Gel and Sol
Authors: Johnston S. T. , Massey J. , von Meerwall E. , Kim S. H. , Levin V. Yu , Isayev A. I.
Published: February 2011

In an effort to support the recycling of rubbery polymers and composites, 1H NMR relaxation and pulsedgradient spin echo diffusion measurements have been performed on virgin and unfilled vulcanized strene-butadiene rubber (SBR), and networks after various extents of devulcanization using an ultrasound technique. The NMR methods recognize unentangled light molecules (e.g. sol), but do not distinguish between unattached entangled large molecules and chemical network segments. Devulcanization generates additional sol with a wide mass distribution, thus increasing both sol and gel mobility, but decreasing sol mean diffusivity. The latter effect is accounted for by the increasing mean sol molecular mass but also by the increasing glass transition temperature, which is related to main-chain stiffening seen in our earlier 13C NMR experiments. In addition to improving the molecular-level understanding of devulcanization, this study provides guidance for the optimization of the devulcanization parameters.
Structure and Properties of Reinforcing Fractal Filler Networks in Elastomers
Authors: Klüppel Manfred , Schuster Robert H. , Heinrich Gert
Published: February 2011

The effect of filler networking on mechanical and electrical properties of elastomers is discussed on the basis of percolation theory and a recently developed kinetical cluster-cluster aggregation (CCA) model, respectively. In percolation theory pure geometrical arguments are considered and the physical properties of the filler network are related to the infinite cluster that is formed at percolation threshold. In the CCA-model the particles are allowed to fluctuate around their mean position on length scales that are comparable to the polymer fluctuation length. Upon contact of neighboring particles or clusters they stick together and form larger clusters. At sufficiently large filler concentrations (above the gel point of the filler network), a fractal filler network results that corresponds to a space-filling configuration of CCA-clusters. Structure and properties of the filler network in this model are compared to the fractal characteristics of percolation networks. In particular, the influence of anomalous diffusion of charge carriers on the scaling behavior of the conductivity is demonstrated for both types of fractal networks. For the elastic modulus an universal power law behavior results that is independent of the size of the filler particles and the applied rubber in both cases.
Hydrogenation of Diene Elastomers, Their Properties and Applications: A Critical Review
Authors: Singha N. K. , Bhattacharjee S. , Sivaram S.
Published: February 2011

This chemistry and technology of hydrogenation of diene elastomers have substantially grown during the past decade. New applications of hydrogenated elastomers have emerged. Homogeneous hydrogenation has several advantages over heterogeneous hydrogenation because of its higher selectivity, faster rate and cleaner end products. However, separation of catalysts and recycle/reuse of expensive metals still poses problems. The preferred alternative for the hydrogenation of elastomers in solution is the use of Zeigler type catalyst which are less expensive than the noble metal catalysts like Rh, Pd etc. However, such catalysts are not effective when strongly coordinating groups are present in the elastomer. One approach would be to use transition metals, which have less tendency to coordinate with polar monomers in the elastomer. Research is also warranted in the use of less expensive metals for elastomer hydrogenation (Ni, Co, Ru). Use of large quantities of solvent (to keep the solution viscosity low) is another significant cost center in elastomer hydrogenation. Novel agitator systems/reactor configuration to handle higher concentration of rubber in solution, yet provide adequate heat and mass transfer in gas-liquid hydrogenation reaction, needs to be explored. Hydrogenation of diene elastomers in the latex form using water soluble catalyst appear to be hold great promise at the present time since many diene elastomers (like SBR, CR and NBR etc.) are commercially produced directly in the form of latex. Creative exploitation of biphasic catalysts for hydrogenation is expected to gain momentum since early results look promising. This would require greater fundamental understanding of the aqueous-organic interphase in a latex process and the mechanism of transport of catalytic reagent across this interphase. More studies are needed to achieve homogeneous chemical reaction inside of each individual latex particles.
Thiuram- and Dithiocarbamate-Accelerated Sulfur Vulcanization from the Chemist's Perspective; Methods, Materials and Mechanisms Reviewed
Authors: Nieuwenhuizen P. J. , Reedijk J. , van Duin M. , McGill W. J.
Published: February 2011

This paper describes research methodologies for the investigation of the mechanism of vulcanization and discusses the reactivity of thiuram and dithiocarbamate chemicals. The combined knowledge is subsequently applied to thoroughly review the mechanism and chemistry of both thiuram- and dithiocarbamate-accelerated sulfur vulcanization. Integration of the original mechanistic ideas from the 1960s and the results obtained in the past three decades now have led to a more balanced appraisal of events during vulcanization. Questions have been answered, solutions for old problems are proposed, and remaining fields of endeavor are identified.
Business Information Support for the Rubber Industry
Authors: Long Joan C.
Published: February 2011

This paper is a survey of the organizations which regularly provide business and economic information that concern the rubber and rubber products industry. The publications issued by various organizations are examined with detailed information on availability given in the references. The objective of this review is to provide an awareness of what sources are available rather than the retrieval of the information through the various database services. Among the organizations whose publications are mentioned are the International Rubber Study Group (IRSG), the International Institute of Synthetic Rubber Producers (IISRP) and the Rubber Manufacturers Association (RMA). Publications of commercial organizations such as Crain Communications, Lippincott and Peto, and Rapra Technology Ltd. are also included, as are sources of information from the U.S. Government. Internet sources are briefly reviewed.
The Microstructure of Natural Rubber Latex Films
Authors: Cook S. , Cudby P. E. F. , Davies R. T. , Morris M. D.
Published: February 2011

An electron microscopy technique which has been used to visualize the crosslinked regions in vulcanized blends of dry rubber has now been applied to films made from natural rubber (NR) latex. The method involves swelling the latex film with styrene, polymerizing the styrene, sectioning the sample and then staining with osmium tetroxide to reveal the rubber network when observed by transmission electron microscopy (TEM). The micrographs show the higher ratio of interparticle to intraparticle crosslinks in a sulphur post-vulcanized film as compared with a sulphur prevulcanized film. They also show that, as in dry rubber films, the mesh size of the visible rubber network correlates with the crosslink density of the rubber. The technique also reveals that the crosslink distribution in peroxide prevulcanized latex (PPVL) is significantly different from that in latices prevulcanized using sulphur or radiation.
Effect of Leaching and Humidity on Prevulcanized NR Latex Films
Authors: Amir-Hashim M. Y. , Morris M. D. , O'Brien M. G. , Farid A. S.
Published: February 2011

In an attempt to improve the understanding of the mechanism by which aqueous leaching of prevulcanized natural rubber latex films improves their physical properties, experiments have been carried out on such films after storage under controlled humidity conditions. Under conditions of ambient and high humidity, unleached films were found to absorb much more moisture than their leached counterparts. Results obtained from the equilibrium volume swelling measurements and from the C1 constant of the Mooney-Rivlin plots indicated that crosslink density was not affected by leaching. The effect of leaching on the tensile strength and modulus however was generally significant. Under high humidity conditions an increase in modulus on leaching was observed. These results are explained in terms of the hydrophilic nonrubbers having a stiffening effect under dry conditions and a softening effect when wet. Conditioning humidity also had a direct effect on the tensile strength. As humidity increases, the peak in tensile strength against modulus shifts to lower strength and modulus values. Some of the findings were supported by data from experiments in which a hydrophilic nonrubber component, namely sucrose, was deliberately added to prevulcanized natural rubber latex.
Tire Wear Caused by Mild Tread Slip
Authors: Fujikawa Tatsuo , Yamazaki Shunichi , Uchiyama Yoshitaka
Published: February 2011

The purpose of this study is to examine the relationship between the tread wear of rolling tires and the wear of a sliding rubber pad. In the experiments, frictional parameters, i.e. sliding distances, sliding velocities, and contact pressures, are evaluated at points on the tire-tread surface. Using these experimental results, tread wear rates are estimated from the rubber pad wear tests. The estimated values were found to agree with the actual tread wear rates.
Viscoelastic Properties of Elastomers and Tire Wet Skid Resistance
Authors: Takino H. , Nakayama R. , Yamada Y. , Kohjiya S. , Matsuo T.
Published: February 2011

Many studies concerning tire wet skid resistance have been published in the past, but they have in general involved the use of only a few grades of SBR and BR. We have evaluated the British Portable Skid Tester (BPST) wet skid resistance of eighteen sulfur curable polymers which might be used for automobile tires. These results have been analyzed in relation to the viscoelastic properties of the polymer systems. Analysis of wet skid resistance in terms of the peak value of tan δ over a prescribed temperature range, designated as Tα, and abrasion loss—derived from the theory of rubber friction—was concluded to give a better general relationship for a wide range of polymers.
Frictional Heating of Vulcanized Rubber Surfaces and the Behavior of Race-Tire Treads on Dry Pavement
Authors: Maláč Jiří
Published: February 2011

Frictional heating and rubber “melting” processes have been studied on the basis of laboratory experiments and simple models. A new two-temperature mechanism of rubber “melting” is proposed. Race-tire tread behavior at conditions of competition on dry pavement is discussed. Significance of frictional heating and rubber “melting” processes for behavior of common passenger and truck tires is mentioned.
Tetraisobutylthiuram Monosulfide: How Can It Be Both a Cure Retarder and Accelerator with Benzothiazole Sulfenamides?
Authors: Chasar Dwight W.
Published: February 2011

N, N, N′, N′-Tetraisobutylthiuram monosulfide (TiBTM) performs both as a retarder and kicker when used with 2-benzothiazole sulfenamide accelerators. Model reactions were run and followed by HPLC to identify the intermediates that form between TiBTM (and its various analogs) and the primary accelerators. Some of these intermediates were independently synthesized and evaluated as retarders/kickers. The isobutyl groups are responsible for imparting the scorch delay characteristics to one of these intermediates. One other intermediate is most likely responsible for the kicker effect.
Effect of Crosslink Type on the Ultrasound Devulcanization of SBR Vulcanizates
Authors: Levin V. Yu , Kim S. H. , Isayev A. I.
Published: February 2011

Sulfur-cured non-reinforced SBR with different amounts of poly-, di- and monosulfidic crosslinks is devulcanized by high power ultrasound irradiation in a continuous process under various processing conditions. Total crosslink density, the proportion of polysulfidic crosslinks, gel fraction, and glass transition temperature are measured. The effect of the initial fraction of polysulfidic bonds on the devulcanization process is discussed.
New Technique to Quantitatively Characterize Crosslink Density in IR and Brominated Poly(Isobutylene-CO-Paramethyl Styrene) Blends
Authors: Wang Yu F. , Wang Hsien C.
Published: February 2011

The physical properties and application performance of rubber blends are highly dependent on the curing behavior of blend components, morphology, and network structure. Crosslink density or molecular weight between crosslinks characterizes the network structure. It is desirable to develop correlations between product attributes, such as flex, ozone resistance, and permeability with crosslink density of the individual phase in the blend. This will aid developing high performance rubber blends via curative systems, elastomer components and concentration, bromine composition distribution, and processing condition optimization. One major road block is to quantitatively and unambiguously measure the individual phase crosslink density in the blend.

A method has been developed and verified with solvent freezing point depression technique. The method can quantitatively determine the individual phase crosslink density in polyisoprene (IR)/Brominated Poly-(isobutylene-co-paramethyl styrene) (BIMS) blends. The method is based on the principle that the molecular weight between crosslinks does not change in different solvents. This is coupled with mass balance equations to determine rubber volume fraction of each phase in the swollen blends. The crosslink density of each phase is then calculated by the Flory-Rehner equation.

The method can evaluate the effect of curative distribution, processing conditions, and curative systems on GPR/BIMS blend performance. IR and BIMS blends were cured with zinc oxide and sulfur in this study. It was found that the IR and BIMS phase crosslink density reaches a plateau when the amount of the curing agent is greater or equal to 1.25 phr. The IR phase has a greater crosslinking density than the BIMS phase in the blends. These are valuable information to optimize the curative systems and enhance product attributes.
Strain Induced Crystallization in Stereoregular Poly[Methyl(3,3,3-Trifluoropropyl) Siloxane] Networks
Authors: Kuo Chung-Mien , Battjes Kevin P. , Miller Robert L. , Saam John C.
Published: February 2011

Elastomeric networks based on poly[methyl(3,3,3-trifluoropropyl)siloxane] having a minimum level of stereo-regularity crystallize and self-reinforce when stretched at room temperature. The effect is especially pronounced in networks where the cross-links are uniformly spaced. The polymers are made by modification of a recently described anionic ring opening copolymerization of prescribed mixtures of cis- and trans-1,3,5-trimethyl-1,3,5-tris (3′, 3′, 3′-trifluoropropyl) cyclotrisiloxane. This provides polymers enriched in stereoregularity with nearly monodisperse molecular weight distributions and reactive groups at the chain ends. The end-linked networks show markedly enhanced mechanical properties due to self-reinforcement from strain-induced crystallization. In addition to applied strain, self-reinforcement depends on temperature and the amount of stereoregularity introduced to the polymer. Strained specimens having high levels of stereoregularity and pre-existing crystallinity exhibit plastic flow and, upon release of the applied strain, stress-hardening. Wide angle X-ray scattering (WAXS) on strained specimens establishes that, although the relative degree of crystallinity varies, the basic crystal structure is unaltered by cross-linking, amount of strain, or amount of stereoregularity. Unit cell parameters from WAXS indicate a monoclinic crystal and suggest a 4*11 chain conformation.
Wet Skid Properties of Filled Rubbers and the Rubber—Glass Transition
Authors: Heinrich Gert , Dumler Herbert B.
Published: February 2011

The physical relationships between wet skid resistance of filled rubber compounds and the dynamics of the corresponding bulk polymers in the rubber—glass transition zone are investigated. We show how wet grip data and their ratings correlate with dynamic glass transition temperatures in the N(uclear)M(agnetic)R(esonance) time scale for the spin—spin relaxation time T2 that characterizes the relaxation of transverse magnetization. The corresponding frequency is independent of the Larmor frequency of the NMR experiment. The amount of the frequency is located in the frequency region of the glass—rubber transition and depends on the microstructure of the used polymers. Finally, some molecular aspects of the network dynamics in the transition zone are considered. Damping curves of different rubbers can be predicted using the bead-spring-model of Kloczkowski, Mark and Frisch (KMF), considered as an extented Rouse-model of an entanglement network with tree-like connectivity and a certain number of subchains.
Novel Ether Modifiers for Anionic Polymerization of Isoprene
Authors: Hsu W. L. , Halasa A. F. , Wetli T. T.
Published: February 2011

Because of demands on tire skid resistance, polyisoprenes with high 3,4-content are of particular interest to the tire industry due to their inherently better grip properties. Polar bidentate modifiers such as TMEDA and DIGLYME are widely used in organo-lithium catalyzed isoprene polymerization to increase 3,4-content. However, neither modifier is very effective for making high Tg polyisoprenes due to the fact that a retarded polymerization rate was found for the former while a large excess of modifier was needed for the latter. The new modifiers based on the alkyl ethers of tetrahydrofurfuryl alcohol with alkyl groups from one to six carbon atoms were found to be very effective for producing polyisoprenes with high 3,4-contents. Kinetic studies on both TMEDA and the new ether modified isoprene polymerizations were conducted. The results and the plausible explanation of the rate difference for both systems are discussed.
Longitudinal Cracking in a Carbon Black Filled Natural Rubber Vulcanizate during Chemical Stress Relaxation
Authors: Hamed G. R. , Zhao J.
Published: February 2011

Thin specimens of a black-filled, natural rubber vulcanizate have been held in uniaxial tension at 72°C and 200% elongation in a forced air oven. After substantial oxidative attack (inferred from stress relaxation), small edge cracks formed. Initially, these cracks grew perpendicular to the loading direction, but, upon reaching about 0.1 mm in depth, longitudinal crack growth commenced and fracture progressed by a kind of 0°-peel process with “splitting-off” of successive strands of rubber. This phenomenon is attributed to anisotropy in strength caused both by straining and by oxidative attack.
Simulation of Surface Flaw Propagation Associated with the Mechanical Fatigue Wear of Elastomers
Authors: Razzaghi-Kashani Mehdi , Padovan Joseph
Published: February 2011

Employing a moving template finite element strategy, a simulation scheme was developed to model the surface flaw propagation process associated with the mechanical fatigue wear of elastomer surfaces. Special emphasis was given to (1) experimentally establish the potential existence of precursor flaws on the surface of unworn and worn molded rubber products; (2) determine the trajectory of propagation of surface cracks and their effects on particle removal; (3) establish the influence of size and orientation of initial flaws; and (4) determine the effects of the various phases of the asperity-flaw passing process. These various issues are described in a series of parametric sensitivity studies.
A Simple w′(λ) Function for The Valanis-Landel Form of Stored Energy Function
Authors: Landel Robert F.
Published: February 2011

In the Valanis-Landel formulation of the stored energy function W, stresses depend on the function w′(λ)(=dw/dλ). This function exhibits strong curvature, making it difficult to represent analytically with good accuracy. It is found for both SBR and NR that the function λw′(λ) is not only far less curved, it is essentially linear in λ for the range of about 0.4 < λ < 2.0. The long range of simple proportionality to strain invites examination of molecular theories of rubberlike elasticity. Above the linear range the response can be approximated by kλn. These simplifications should make it easier to convert w′(λ) to the W1 and W2 functions employed in finite element analysis.
Nitrosamine Formation in Rubber: I. Influence of Mixing History
Authors: Willoughby Bryan G. , Scott Keith W.
Published: February 2011

Despite much published research, the influence of fillers on nitrosamine formation in accelerated sulphur vulcanization is not well understood. This paper studies N-nitrosodimethylamine (NDMA) formation in a range of TMTD-accelerated, black-filled rubber formulations encompassing EPDM, SBR, NR, and NBR rubbers. Two levels of TMTD and carbon black were variables in this study as was the type of carbon black used (N330 and N550). The use of statistical experimental design has shown how reliable data on nitrosamine formation in vulcanizates can be obtained by paying strict attention to process history, and has revealed, for the SBR, NR, and NBR rubbers studied, a correlation between the temperatures reached on mixing with the level of nitrosamine generated on subsequent vulcanization. For these rubbers the effect of this process history outweighs that of any ingredient variable. While allowing new insights to be gained on nitrosamine formation in rubber, these findings allow the development of a self-consistent mechanism for nitrosation processes where the reactions in diene rubbers mirror those in air.
Power Transmission Belt Performance and Failure
Authors: Dalgarno Kenneth W.
Published: February 2011

The performance and life of power transmission belts has been investigated by a number of research groups over the past decade or so. Most studies have been directed at a particular problem with or application of belting technology, with synchronous and V-ribbed belts generating the most research activity. This paper reviews contemporary studies on the performance and failure of synchronous and V-ribbed belts to develop an overall picture of how the understanding of belt materials, mechanics, and failure mechanisms has progressed in recent years. The studies which have moved the understanding of belt behavior furthest forward have been those which sought, through an improved understanding of how a belt acts as a composite, to integrate the various strands of materials, mechanics and failure analysis knowledge available to give a clear and coherent picture of how a belt works and fails, although none of the studies seen so far can claim to have accomplished this completely.
Hysteresis Contributions in Carbon Black-Filled Rubbers Containing Conventional and Tin End-Modified Polymers
Authors: Ulmer J. D. , Hergenrother W. L. , Lawson D. F.
Published: February 2011

A methodology was developed to estimate individual hysteresis contributions arising from the carbon black network, polymer free chain ends and effective polymer network chains. The estimation technique was applied to rubber compounds formulated with linear polymers of varied number-average molecular weight (Mn) from each of three different series. The three series corresponded to polymers modified with either zero, one or two tin ends per chain. In general, the relative hysteresis contributions depend on strain amplitude and Mn. For unmodified polymers at strain amplitudes from 0.02 to 0.07, and with Mn in the neighborhood of 150 kg/mole, each of the three hysteresis sources contributes about one-third of the total tan δ. With respect to shear loss modulus (G″), the carbon black network contributes about 60%, while free chain ends and the effective polymer network chains each contribute about 20%. At the same Mn and strain conditions, tin end-modified polymers reduce G″ and tan δ by as much as 60%, in comparison to their unmodified counterparts. The benefit is achieved primarily through reductions of up to 85% in the carbon black network contribution to hysteresis. Since the hysteresis contribution from free chain ends is not reduced so much by tin end-modification, the greatest potential for additional tan δ benefits lies in further free chain end reduction. In addition, it was found that tin end-modification has no measurable effect on the hysteresis contribution from effective network chains. Further, the analysis showed that an ineffective polymer network chain provides approximately ten times the hysteresis and one-half the elasticity of an effective network chain, at the test conditions of the current study. In general, the quantitative results, and some qualitative results as well, will change with compound composition and with temperature. Consequently, the development of a methodology, one that allows estimation of individual hysteresis contributions from different sources, is a major component of the present study.
Distributive Mixing in Variable Intermeshing Clearance Mixers: Simulation and Experiments
Authors: Yao Chih-Hsiang , Manas-Zloczower Ica , Regalia Roberto , Pomini Luigi
Published: February 2011

Distributive mixing performance in Variable Intermeshing Clearance (VIC) mixers was studied numerically and verified experimentally. A fluid dynamics analysis package (FIDAP), based on the finite element method, was employed to simulate the flow patterns in the original lab size mixer (VIC1) and a new design with an enlarged mixing chamber (VIC2). Distributive mixing was studied numerically by means of tracking the evolution of particles originally gathered as clusters. The results of numerical simulations were checked against experimental data to verify the validity of the model. Both the numerical simulations and the experimental data indicate that the VIC2 design, with an enlarged mixing chamber, shows consistently better distributive mixing results in comparison with the traditional VIC1. In both mixers, increasing the inter-rotor clearance improves distributive mixing. However, enlarging the gap size too much in the bridge region, in the VIC2 mixer, becomes detrimental for mixing. The initial position of the clusters is also important in distributive mixing. Clusters located in the middle of the bridge region are better distributed than the ones located on the sides, particularly at small inter-rotor clearances.
Novel Thermoplastic Elastomers: Star-Blocks Consisting of Eight Poly(Styrene-b-Isobutylene) Arms Radiating from a Calix[8]Arene Core
Authors: Jacob Sunny , Majoros Istvan , Kennedy Joseph P.
Published: February 2011

The first synthesis by a core-first strategy of novel star-block copolymers consisting of eight poly(styrene-b-isobutylene) (PSt-b-PIB) arms radiating from a calix[8]arene core is described. An octafunctional methoxy calix[8]arene derivative was used to initiate the living polymerization of isobutylene (IB) to desirable molecular weights, then styrene (St) was added to obtain the sought star-blocks. Molecular weights and PSt contents were determined by triple-detector GPC and 1H NMR spectroscopy. Star-block thermoplastic elastomers containing 17–32% PSt showed high strength and elongation (up to ∼26 MPa and >500%) and relatively low melt viscosities. The mechanical and rheological properties of these star-blocks are superior to those of linear PSt-b-PIB-b-PSt triblocks. PIB-based thermoplastic elastomers may be of use as novel biomaterials.
Experimental Investigations and Numerical Modeling of Incompressible Elastomers during Non-Homogeneous Deformations
Authors: Przybylo P. A. , Arruda E. M.
Published: February 2011

Three hyperelastic constitutive models, the Arruda and Boyce model, the Yeoh model, and the Ogden model, are used to simulate the response of vinyl elastomers in large, non-homogeneous deformation states. A single uniaxial compression test is used to characterize the elastomers to obtain model constants. Drucker stability is enforced by restriction of the coefficients for the Yeoh and Ogden models to produce physically feasible uniaxial results. The ability of the models to predict the global force versus deformation responses and deformed shapes for large deformation shear, tensile deformation of a long bar with fixed grips, and inflation of a thin disk is examined. The experiments used in this study are designed to provide known boundary conditions to eliminate ambiguity in the modeling. We demonstrate for the first time that each of these models may be sufficiently characterized via a simple, homogeneous compression test to allow accurate predictions of large, non-homogeneous deformations involving rotations of the principal stretch directions.
Novel Method for Preparation of Low Molecular Weight Natural Rubber Latex
Authors: Tangpakdee Jitladda , Mizokoshi Megumi , Endo Akiko , Tanaka Yasuyuki
Published: February 2011

Low molecular-weight natural rubber (LNR) and LNR latex was prepared by oxidative degradation of de-proteinized natural rubber (DPNR) latex in the presence of 1 phr of K2S2O8 and 15 phr of propanal, by shaking at 60 °C. The intrinsic viscosity [η] of DPNR with only K2S2O8 decreased from 7.2 to 5.5 after 2 h and then increased to 6.5 after 3 h. By the addition of propanal, DPNR showed a significant decrease in the [η] value of LNR with [η] of about 0.5 after 5 h of the reaction, while rubber from high-ammonia natural rubber (HANR) latex showed a slight decrease in [η]. The concentration of latex and the kind of surfactant used for stabilizing the latex had little effect on the degradation rate of DPNR latex. The LNR latex is stable as the latex form and the dried rubber coagulated from latex is transparent and colorless. The LNR was a telechelic polymer containing aldehyde and ketone groups at both terminals as determined by NMR and molecular weight analyses.
Injection Molding of a Natural Rubber Compound: Simulation and Experimental Studies
Authors: Isayev A. I. , Wan M.
Published: February 2011

Experimental and theoretical results are obtained for the cavity filling of a natural rubber (NR) compound. The shear rate and temperature dependent viscosity function based on the modified Cross model is fitted to experimentally measured viscosity data. A nonisothermal vulcanization model with nonisothermal induction time is fitted to the nonisothermal curing kinetic data obtained by differential scanning calorimetry (DSC). These data are utilized in the simulation of the cavity filling and curing stages. The pressure traces at various locations in the mold during cavity filling are obtained at different inlet and mold temperatures. The predicted results for the pressure traces are in good agreement with those measured in the cavity, but significantly lower than those measured in the nozzle. Evolution of the state of cure in the post-filling stage is predicted and compared with experimental data measured in moldings obtained at various cycle times. The measured states of cure in the moldings are in good agreement with their predicted values. Based on earlier flow studies of SBR compounds, it is shown that the discrepancy between the experimental and predicted pressure traces in the nozzle for the NR compound is due to high local pressure drops arising during the flow in juncture regions of the delivery system and the possibility of flow-induced crystallization. The importance of taking into account the entry pressure losses, viscoelastic effects and flow-induced crystallization in the injection molding process is strongly emphasized. The complexity of the issues related to this subject is discussed.