bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Balance and Heat Transfer in Mixing of Elastomer Compounds with the Internal Mixer
Authors: Nakajima N. , Harrell E. R. , Seil D. A.
Published: February 2011

An energy balance was obtained for mixing of an elastomer compound in the internal mixer. The mixing operation was done reproducibly, and pertinent data were collected with relatively simple instrumentation. Out of the total mechanical energy input into the compound, 41–46% went to raise the temperature of the compound, and 40–45% was removed by the cooling water. The heat loss from the mixer wall to the room was very small and negligible. This energy balance is based on the average temperature profile, which assumes uniform temperature of the stock. The actual temperature measurement of the stocks gave temperature differences of as much as ±13.5°C, indicating temperature nonuniformity within the stock. This is very plausible because rubber is a poor conductor, the shear field within the mixing chamber is exceedingly nonuniform, and thus, the viscous heating of the material is very nonuniform. Heat transfer coefficients were evaluated for the overall heat transfer from the stock to the cooling water and for the heat transfer from the stock to the chamber wall. The data indicate that the compound was not uniform in the beginning of the mixing, in spite of the fact that a premixed powdered rubber was used. The nonuniformity must be in the degree of incorporation of carbon black rather than in the composition. There is also nonuniformity in the temperature. The heat transfer coefficient has a high value when the carbon black is on the surface of rubber but decreases to a constant value with the incorporation of carbon black into the rubber. Although it is not the objective of this paper to evaluate the effectiveness of mixing, the compound after curing gave mechanical properties which indicated thorough mixing.
Electron Microscopical Examination of Worn Tire Treads and Tread Debris
Authors: Smith R. W. , Veith A. G.
Published: February 2011

Tire wear is an important phenomenon, and the industry needs to know as much as possible about the mechanism of rubber abrasion that results in wear. A wealth of information can be obtained by studying tread surfaces and debris particles using the scanning electron microscope, energy dispersive x-ray analysis, and transmission electron microscopy of ultrathin sections. Such an examination was conducted on the worn tread surface of an SBR compound containing 75 phr N285 carbon black and 45 phr oil. A liquid-like layer composed of an intimate mixture of degraded rubber and road silt could be seen on the worn tread surfaces. The thickness of this layer is variable but generally in the micron and submicron region, except where it had been rolled up and was about to be thrown off as a debris particle. A general examination of NR and BR tread compounds revealed a similar appearance. Several collections of rubber debris particles were also examined and found to have the same composition of degraded rubber and road silt that was observed on the tread surface. These observations are in agreement with the results of Boonstra, Heckman, and Kabaya with respect to the analysis of road silt materials on tread surfaces. Since the silt is within the thin layer of degraded rubber, it cannot be washed off the tread surface with soap and water. It can be removed with benzene swabbing. In addition, this report provides visual documentation of tire wear that serves to support previous speculations. These results emphasize the importance of considering the abrasion of tire treads as a three-bodied system: the tread compound, the road surface and the layer between the two, which is composed of an intimate mixture of degraded rubber and road silt. Previous references to the presence of road silt particles on worn tread surfaces implied their incidental nature. This study shows that road silt penetrates into and becomes a part of the substructure of worn tread surfaces. Furthermore, the internal morphology of this substructure is identical to the morphology of the tread debris thrown off from the tread surface.
Configuration of the Brass on Brass-Plated Steel Wires in Tire Cords
Authors: Giuffria Ruth , Marcelli Angela
Published: February 2011

Study of the brass configuration on wires from a number of cords from different sources shows that the brass on all of the wires is highly nonuniform in its distribution. It is not a “layer” as the word is generally understood. In some areas, the steel is almost bare; in some areas, brass coverage may be 0.1–0.2 µm thick; in still other areas there are “intrusions” of brass extending into the steel much more than a micrometer. It is believed that this brass configuration is typical of all steel wires which have been drawn after brass plating; hence, it is probably typical of all wires currently used in brass-plated steel tire cord. Consideration should be given to this erratic brass configuration in studies of adhesion of tire rubber to brass-plated steel tire cord. Perhaps the current model(s) should be modified to include the possible effect of the reservoirs of brass in the “intrusions” which exist in the steel.
The Role of Chemical Bonding in the Adhesion of Elastomers
Authors: Gent A. N.
Published: February 2011

A review is given of several studies of the effect of interfacial bonding upon the mechanical strength of an adhesive joint. In the first, polybutadiene layers were crosslinked by a free radical process while in contact with silane-treated glass. A direct proportionality was found between the minimum peel strength of the joint, at high temperatures and low rates of peeling, and the vinyl content of the silane treatment liquid. Covalent bonding between the diene polymer and vinyl groups on the treated glass was inferred. When radioactively tagged silanes were employed, extensive combination with the glass substrates was demonstrated. Again, the greater the amount of vinyl silane found on the treated glass surface, the greater the mechanical strength of adhesion between the treated glass and a polybutadiene overlayer. In another series of experiments, two partially crosslinked sheets of polybutadiene were pressed together before the crosslinking was taken to completion. The additional crosslinking was determined from measurements of the elastic properties and of the degree of equilibrium swelling by a compatible liquid. Again, the mechanical strength of adhesion between the two sheets under threshold conditions was found to be directly proportional to the inferred degree of interfacial interlinking. Thus, at least at high temperatures and low rates of peel, there is substantial evidence for a direct correlation between the mechanical strength of a joint and the degree of interfacial chemical bonding. Moreover, the relationships established in these studies allow other bonding systems to be diagnosed as chemical or physical in nature. For example, a dramatic increase in the strength of adhesion between two crosslinked polybutadiene layers was observed if they were exposed to air or oxygen for periods of an hour or two before being pressed into contact. It is inferred that interfacial chemical bonds are formed as a consequence of rapid surface oxidation reactions.
Characterization of the Structures of Diene Polymers by NMR
Authors: Harwood H. James
Published: February 2011

Nuclear magnetic resonance spectroscopy (NMR) has become a very powerful tool for characterizing the structures of elastomers, providing information about their compositions and the arrangements of their constituents along their chains. Elastomers derived from diene monomers by homopolymerization or copolymerization can be very difficult to characterize because of the large number of structural features that may be present. Dienes can be incorporated as 1,2, 3,4, cis-1,4, or trans-1,4 units, and also as cis-4,1 or trans-4,1 units in some cases, for example. This leads to the possibility of head-head and tail-tail linkages as well as head-tail linkages and to the possibility of several stereochemical arrangements existing between pairs of 1,2-units. In spite of this difficulty, quantitative information about the structural characteristics of polymers derived from dienes can be obtained from their NMR spectra, and this information has been very useful in studies on polymerization mechanisms and elastomer properties. In some cases, it is possible to study the structures of growing chain ends by NMR spectroscopy. This, of course, provides valuable information about the polymerization mechanism. Nuclear magnetic resonance can be used to monitor chemical changes occurring in elastomers, such as oxidation or vulcanization. It can also provide information about the dynamic characteristics of elastomeric chains. Reviews on the characterization of elastomer structure by nuclear magnetic resonance are available, but developments in the characterization of polymers derived from dienes have occurred so rapidly that it is appropriate to review this specific topic at this time.
Recent Advances in the Chemical Modification of Unsaturated Polymers
Authors: Schulz D. N. , Turner S. R. , Golub M. A.
Published: February 2011

This article surveys recent advances in the chemical modification of unsaturated polymers, with emphasis on the literature since 1974. Among the topics covered are hydrogenation, halogenation, cyclization, isomerization, epoxidation, cycloaddition, sulfonation, carbenation, and silylation. The olefin functionality is a useful target for modification because of its varied reactivity, and recent work in unsaturated polymer reaction chemistry has yielded significant discoveries and valuable new information. For example, modern synthetic reagents and catalysts (e.g., as phase-transfer catalysts) have been advantageously employed to improve process and/or product quality. Synthetic techniques have been refined to allow the selective modification of specific polymer microstructures or blocks. Moreover, new structural and mechanistic insights have been derived from the judicious use of model compounds and/or specialized characterization methods. The relationship between chemically modified polymer structure and properties is being more clearly defined, and sequence effects are beginning to be appreciated. Finally, important new applications (e.g., elastomers, plastics, motor oil additives) have been discovered for chemically modified diene polymers.
Applications of Computerized Nuclear Magnetic Resonance and Infrared Spectroscopic Techniques to Rubber Analyses
Authors: Hirst Robert C.
Published: February 2011

Fourier transform spectroscopy is without doubt one of the most important developments in spectroscopy in the last few years. Although the basic principle had been known for many years, its applications in spectroscopy became practical only because of advances in small computer technology. In the case of nuclear magnetic resonance and infrared spectroscopy, the digital computer has had a special effect, in that it has caused, or at least made possible, the total redesign of NMR and IR instrumentation based on the Fourier transform (FT) concept. Because of its advantages over conventional methods, the FT method has caused great changes in NMR and IR spectroscopy, and FT instruments have made possible the solutions to many problems which previously were technically too difficult. NMR spectroscopy was reviewed in this Journal in 1976 and infrared spectroscopy was reviewed in 1972. Developments since those reviews will be emphasized here. In a short, selective review of this type, it is necessary to omit references to many excellent contributions in the literature. For very comprehensive listings of literature references, the reader may wish to consult the biennial reviews in “Analytical Chemistry” on NMR spectroscopy, infrared spectroscopy, rubber, analysis of high polymers, and coatings.
Energy Measures of Efficient Mixing
Authors: Nakajima N.
Published: February 2011

Several significant developments have taken place recently in the understanding of elastomer behavior in the internal mixer. An elastomer must be treated as a viscoelastic solid rather than a viscous fluid. The material behavior is recognized as transient instead of steady state. Elongational deformation plays an important role and the rate of such deformation is fast. Relevant fundamental properties are the viscoelastic properties at large deformations and ultimate properties. Views on the mechanisms of mixing have also changed recently. Instead of the laminar flow model, which accepts steady state shear flow, a comminution and lamination model has been proposed to represent large deformation, rupture, and recovery of the elastomer during mixing. With the comminution model and the fundamental measurements of rupture energy, a theoretical minimum mixing energy was estimated. The difference between the actual energy spent for mixing and the theoretical energy required is substantial. This suggests that there is room for saving energy through process improvements. Two examples of energy saving have been reported recently; one is the use of warm water cooling with an efficient heat transfer and another is a new configuration for four-wing rotors. The optimum processing temperature can be estimated from fundamental measurement of the ultimate properties of the elastomer. This points towards the use of warm water cooling. The new rotor design avoids impinging streams, which result in wasting energy for mixing viscoelastic material, although it mixes low viscosity fluids efficiently.
Curing of Fluoroelastomers by Peroxides
Authors: Apotheker D. , Finlay J. B. , Krusic P. J. , Logothetis A. L.
Published: February 2011

Peroxide-curable fluoroelastomers offer advantages in acid and steam resistance over their conventional counterparts. The peroxide-curability is provided by incorporating a bromine-based cure site in the vinylidene fluoride copolymers or terpolymers. The peroxide cure system comprises an aliphatic peroxide, an appropriate coagent, and an acid acceptor. The preferred coagent is triallylisocyanurate but other compounds having two or three olefinic groups attached to hetero atoms such as N, Si, or O are also effective. The concentration of the curesite monomer affects the rate, state, and stability of the cure. A cure mechanism is proposed in which the initiation step involves radical formation from peroxide decomposition and addition of the radicals to the coagent. Propagation involves the abstraction of bromine atoms from polymer molecules by coagent radicals to give fluorocarbon polymer radicals, which, in turn, add to coagent molecules to generate new radicals. This type of mechanism is supported by the cure characteristics, by the nature of the coagents, by analysis of the volatile by-products emitted during the cure, and by ESR data on model compounds.
Rubber-Thermoplastic Compositions. Part VI. The Swelling of Vulcanized Rubber-Plastic Compositions in Fluids
Authors: Coran A. Y. , Patel R. , Williams D.
Published: February 2011

The swelling of thermoplastic vulcanizates in immersion fluids is constrained. The amount of swelling is less than the average swelling of the rubber and plastic. The constraint in swelling increases with the difference between the swelling of vulcanized rubber and that of the plastic, per se. However, the swelling constraint decreases with increases in the amount of fluid imbibed by the plastic or hard phase material. The thermoplastic vulcanizates prepared by dynamic vulcanization swell less than do the thermosetting (less thermoplastic) compositions prepared by static vulcanization. Swelling is anisotropic, especially for the compositions containing major proportions of rubber.
Interply Behavior Exhibited in Compliant Filamentary Composite Laminates
Authors: Turner J. L. , Ford J. L.
Published: February 2011

Cord-rubber composite systems allow a visualization of interply shear strain effects because of the compliant nature of the matrix material. A technique termed the pin test was developed to aid this visualization of interply shear strain. The pin test performed on both flat pads and radial tires shows that interlaminar shear strain behavior in both types of specimens is similar, most of the shear strain being confined to a region approximately 10 interly rubber thicknesses from the edge. The observed shear strain is approximately an order of magnitude greater than the applied extensional strain. A simplified mathematical model, called the Kelsey strip, for describing such behavior for a two-ply (±θ) cord-rubber strip has been formulated and demonstrated to be qualitatively correct. Furthermore, this model is capable of predicting trends in both compliant and rigid matrix composites and allows for simplified idealizations. A finite-element code for dealing with such interply effects in a simple but efficient manner predicts qualitatively correct results.
Rubber Elasticity
Authors: Mark J. E.
Published: February 2011

Rubber elasticity may be operationally defined as very large deformability with essentially complete recoverability. In order for a material to exhibit this type of elasticity, three molecular conditions must be met: (1) the material must consist of polymeric chains, (2) the chains must be joined into a network structure, and (3) the chains must have a high degree of flexibility. The first requirement arises from the fact that the molecules in a rubber or elastomeric material must be able to alter their arrangements and extensions in space dramatically in response to an imposed stress, and only a long-chain molecule has the required very large number of spatial arrangements of very different extensions. This versatility is illustrated in Figure 1, which depicts a random spatial arrangement of a relatively short polymer chain. In this random arrangement, the chain extension (as measured by the end-to-end separation) is quite small. For even such a short chain, the extension could be increased approximately fourfold by simple rotations about skeletal bonds, without any need for distortions of bond angles or bond lengths. The second characteristic cited is required in order to obtain the elastomeric recoverability. It is obtained by joining together or “crosslinking” pairs of segments, approximately one out of a hundred, thereby preventing the extended polymer chains from irreversibly sliding by one another. The resulting network structure is illustrated in Figure 2, in which the crosslinks are represented by dots. These crosslinks may be either chemical bonds [as would occur in sulfur-vulcanized natural rubber' or physical aggregates (for example the small crystallites in a partially crystalline polymer or the glassy domains in a multiphase block copolymer). The last characteristic specifies that the different spatial arrangements be accessible, i.e., changes in these arrangements should not be hindered by constraints as might result from inherent rigidity of the chains, extensive chain crystallization, or the very high viscosity characteristic of the glassy state.
Development of Synergistic Curing Systems for Polychloroprene
Authors: Kato H. , Fujita H.
Published: February 2011

Of the dihydric phenols, catechol exhibited a significant synergistic accelerating effect on joint use with TMTD. Aging characteristics of catechol/TMTD accelerated CR vulcanizates were improved when the aromatic nucleus of the catechol was bonded to sulfur. Dicatechol sulfides (XX-125) derived from catechol and S2Cl2 gave improved thermal stability of the vulcanizates. Curing properties of XX-125 seemed enhanced by use with TMTD. A variety of practical CR accelerators has been developed by blending XX-125 with TMTD at the weight ratio to obtain the desired cure rates and physical properties. The essential nature of synergism in these curing systems has yet to be resolved. On detailed practical evaluation of CR vulcanizates cured by these accelerators, XX-125S, -R, -T and -U are suitable substitutes for NA-22 in curing CR.
Rubber Recycling—Upgrading of Scrap Rubber Powder by Vulcanization. II
Authors: Accetta A. , Vergnaud J. M.
Published: February 2011

Vulcanizates from scrap tires have interesting mechanical properties that widen the range of their uses. These properties and dynamic characteristics (compression modulus, damping coefficient) undergo great changes as sulfur percentage is varied. This fact is particularly important in regard to the design of damping devices for the vibration absorption of industrial machines. The size of the machine as well as the vibration frequency must be taken into account to optimize the transmissibility factor of the damped system. The favorable results obtained for our materials in the damping of impact noises and their small compressibility foreshadow an efficient application in resilient coverings in buildings. Rubber slabs when stuck directly on the floor can be covered with a thin coating consisting, for instance, of thin tiles. The resilient covering can also be stuck on the floor and covered with lean mortar, a traditional way of laying tile.
Silica- and Clay-Reinforced Carboxylated Nitrile Rubber Vulcanized by a Mixed Crosslinking System
Authors: Chakraborty S. K. , De S. K.
Published: February 2011

The polymer-filler interaction of silica- and clay-filled XNBR vulcanizates has been analyzed. The presence of carboxyl groups in the polymer chain gives better polymer-filler interaction, and no coupling agent is essential. Properties of silica-filled XNBR vulcanizates containing different carboxyl contents in the polymer chain have also been studied. SEM studies of fracture surfaces have been made to understand the failure behavior of gum and filled vulcanizates.
Dispersive Mixing in Internal Mixers—A Theoretical Model Based on Agglomerate Rupture
Authors: Manas-Zloczower I. , Nir A. , Tadmor Z.
Published: February 2011

The mixing of solid additives into a matrix of rubber or plastics is an energy intensive process. Such a mixing operation generally involves rupture of agglomerates formed by the solid phase, separation of closely packed particles after rupture, and distribution of the separated particles throughout the polymeric matrix. Dispersive or intensive mixing refers primarily to the first two steps, whereas, the third step is by and large an extensive mixing process. Depending upon the polymer-additive system and mixer machine design, each of these steps may be rate determining. The most important and most investigated system is the carbon black-elastomer system. Mixing of such a system is generally carried out in batch Banbury type internal mixers (Figure 1). The dispersive mixing process in internal mixers is quite complex with many subtle features. A detailed review of the subject is outside the scope of this paper. However, careful reading of reviews and publications in the field, indicate that a great deal is known about the mixing process in internal mixers, the scale-up procedures using various criteria, the effect of the mixing process and mixer geometry on processability and ultimate properties, and the flow patterns and fluid dynamics in the various regions of mixers. However, there seems to be no published attempt to a priori predict the mixing process from fundamental considerations.
The Rheology and Processing of Olefin-Based Thermoplastic Vulcanizates
Authors: Goettlier L. A. , Richwine J. R. , Wille F. J.
Published: February 2011

Olefinic thermoplastic vulcanizates (OTV's) comprise rubber in the form of discrete, completely crosslinked particles uniformly dispersed in an olefinic thermoplastic matrix. By their nature, they flow like filled polymer melts: die swell is low, and shows evidence of a particle association at low shear rate and high temperature; viscosity obeys a power law relationship with shear rate over a wide range. In place of a Newtonian plateau at low shear rate, the viscosity of OTV's begins to rise precipitiously in building toward a yield stress. As with other olefinic thermoplastic elastomers, their viscosity is more highly sensitive to shear rate than to temperature. Both shear viscosity and die swell were measured for evidence of morphological character and definition of fabricability. Due to their high shear sensitivity, these OTV's can be easily processed by injection molding and extrusion. Processing temperatures are not critical, but lower ranges are preferred to optimize appearance and promote melt stability. The thixotropic nature of the melt minimizes drooling and allows easy cooldown without distortion of the formed part. Melt viscosity is little affected by moisture or repeated processing. Although melt extensibility is only moderate, it is sufficient to qualify these materials for most extrusion and blow molding applications. Low shear processing, such as the compression molding of prototype parts or calendering, is equally feasible. Thus, olefinic thermoplastic vulcanizates can be fabricated under a wide range of conditions by using conventional plastics processing tooling and methodology. They represent a versatile class of new elastomers that can be economically processed for across-the-board applications in industrial rubber products.
Chain Extension Studies Relevant to the Completeness of End-Linking in Elastomeric Polyurethane Networks
Authors: Mark J. E. , Sung P. H.
Published: February 2011

Polyurethane elastomers may be prepared by end-linking hydroxyl-terminated (atactic) poly(propylene oxide) chains with an aromatic triisocyanate. As is invariably the case, networks thus formed are insoluble and very difficult to analyze with regard to the completeness of the end-linking reaction. Relevant information can, however, be obtained by studying the products of the analogous reaction, between a structurally similar diisocyanate and the same polymer chains, under identical conditions. Since both reactants now have functionalities less than three, the reaction gives chain extension rather than crosslinking (gelation), and it is now possible to measure molecular weights before and after the reaction. Such experiments were carried out using diphenylmethane-4,4′-diisocyanate with poly(propylene oxide) chains which had viscosity-average molecular weights ranging from 10−3Mv=1.15−4.50 g mol−1. Values of Mv were found to increase by factors of 20–30, which indicates high extents of reaction. These results are relevant with regard to the probable efficiency of polyurethane curing techniques, and also for the characterization of “model” networks used in the quantitative evaluation of the molecular theories of rubberlike elasticity.
Improved Adhesion of EPDM Sulfur Vulcanizates to RFL-Treated Fabrics
Authors: Tomlinson Richard W.
Published: February 2011

EPDM stocks containing 5-norbornene-2,3-dicarboxylic anhydride and cobalt naphthenate, when sulfur vulcanized onto RFL-treated fabrics, show a significant increase in peel adhesion properties. EPDM's containing ENB, as the termonomer, have been found to give the best results. The accelerator is an important part of the total adhesion system. Only the slower curing types are applicable, such as sulfenamides and thiazoles. Both soluble and insoluble sulfur yield equivalent adhesion properties, but the insoluble form has the advantage of producing a higher modulus stock. This adhesion system is applicable to only RFL-treated fabrics in which the latex is a styrene-butadiene-vinyl pyridine type. Reduction of compounded stock cost is possible by increased filler loadings or by the use of a skim coat technique, while still providing improved adhesion properties. Variations in both carbon black and oil levels produce corresponding changes in modulus development and curing time. These properties can be used to predict adhesion results.
Factors Influencing the Mechanical Behavior of Raw Unfilled Natural Rubber
Authors: Campbell D. S. , Fuller K. N. G.
Published: February 2011

The influence of gel and soluble nonrubbers on the relaxation behavior of raw, bale NR has been studied by testing fractionated and solvent-extracted rubber. The fractionation was carried out by progressive dissolution, each fraction being recovered by evaporation of the solvent. The tests were performed in tension for extensions up to 70%. Removal of the soluble nonrubbers from the bale was found to decrease the rate of stress relaxation quite markedly, especially at longer times. The fractions fell broadly into three categories: sol rubber, “sol + microgel”, and undissolved macrogel. The last, in the case of the more complete dissolution, was an extremely stiff, almost nonrelaxing material. Despite this, the relaxation behavior of the whole bale rubber was closely reproduced by the “sol / microgel” fraction. Comparison of this fraction with the sol rubber showed that the microgel had predominantly a stiffening effect, though it did also significantly reduce the rate of relaxation.
Contributions of Elastomer Behavior to Mechanisms of Carbon Black Dispersion
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

In order to achieve good mixing of elastomer and carbon black, the elastomer domains must be reduced in size, that is, the elastomer must be broken into smaller pieces. If this is the only requirement, Region I of the Tokita-White scheme may be most preferred, because the elastomer easily breaks up at this state. However, it is too stiff for compaction of the compound; that is, the elastomer is too stiff to conform to the complex topology of carbon black. If the compaction is the only requirement. Region IV is most preferred, because the material is in the melt-flow state. In reality, Region II, the rubbery, highly stretchable state gives the best result. It appears that the use of Region II is a compromise. However, there is a more important reason for the preference of Region II, that is, the effectiveness of this region for the breakdown of carbon black agglomerates. The breakdown mechanism involves elastomer as a medium for the transfer of force. The effectiveness of the elastomer medium depends on its ability to stretch with the development and maintenance of a high stress. The former may be characterized by the failure envelop and the latter by the stress relaxation experiments. In roll mill as well as internal mixer processing, the folding of compound and the subsequent stretching of it, e.g., lamination mechanism, are the effective means for carbon black dispersion. It is postulated that the lamination mechanism generates localized high shear fields, which force carbon black agglomerates to rotate in the high modulus medium; this results in peeling of the aggregates from the outer shells of the agglomerates.
A Parametric Study on Interlaminar Shear Strains in Cord-Rubber Composites
Authors: DeEskinazi J. , Cembrola R. J.
Published: February 2011

The effect of different design variables used in the construction of tire belts on the interply shear phenomenon was studied using a simple, belted cylinder structure. Only balanced belt constructions were considered. The finite element method was used in the analysis of the belted structure. Predicted results were verified by performing experiments with selected combinations of the design parameters studied. Predicted and experimental results indicate the presence of interply shear strains in the cross-sectional plane of the belts; however, due to difficulties involved in measuring these strains experimentally, they have not been treated in this study. Results for shear strains in the circumferential planes only have been presented. Results for the interply shear strains at the belt edge indicate that the belt cord angle has a very strong influence on the interply shear phenomenon. It was shown that the shape of the curve depicting the relationship between cord angle and interply shear strains is influenced by other design variables of the belt as well as properties of adjacent plies, such as the bladder used to simulate a radial tire carcass ply. Interply shear strains decrease with increasing thickness between the plies and modulus of the interply rubber. In the case of a stiffer rubber, the reduction in shear strain is entirely due to a reduction in the relative motion between the belts. However, in the case of an increased interply thickness, which is accompanied by an increase in relative motion between the belts, the reduction in shear is the result of the relative motion being distributed over a larger thickness. Increasing the belt cord modulus results in an increase in interply shear strains for relatively low values of the modulus. However, beyond a certain value, approximately the modulus of fiberglass cords, increasing the cord modulus does not significantly affect interply shear strains. The shear strain-belt width relationship is strongly influenced by the cord angle used in the belts. Depending on the value of the latter, the shear strain can be a decreasing function of belt width or remain relatively constant as belt width is varied. The degree of localization of the interply shear phenomenon at the belt edge was also studied. All of the variables considered in this study, with the exception of the cord modulus, seem to affect the distribution of the shear strain along the width of the belt to varying extents. The belt width seems to have a strong influence, with wider belts resulting in significant shear strains confined to the vicinity of the belt edge.
Structure-Property Relationships of Perfectly Alternating Polycarbonate-Polydimethylsiloxane Block Copolymers, Part II
Authors: Tang S. H. , Meinecke E. A. , Riffle J. S. , McGrath J. E.
Published: February 2011

The relationships between the properties and microstructures of two series of perfectly alternating bisphenol A-polycarbonate-polydimethylsiloxane block copolymers were studied. In the first series, the polycarbonate (PC) block length was kept constant while the block length of polydimethylsiloxane (PDMS) was varied. The tensile properties of these block copolymers were found to be a function of composition. Dynamic mechanical properties measured as a function of temperature revealed the two-phase nature of these materials. Transmission electron micrographs showed that all samples had a sponge-like morphology independent of composition. The rheological maximum viscosity for the sample containing PC and PDMS blocks of equal molecular weight and extrudate swells increased with PC content. Takayamagi's mechanical coupling model was used to predict the maximum loss tangent at the glass transition temperature of PDMS using the known properties of pure components. The predictions agreed fairly well with the experimental results. In a second series of block copolymers, the block molecular weights of both PC and PDMS were varied to keep the composition constant. The tensile strength of these samples was found to increase with block molecular weights, except for the sample having the highest block molecular weights. The lower tensile strength of this material was attributed to its lamellar type morphology. Cold crystallization of PDMS blocks was found for samples having high PDMS block molecular weight (greater than 8000 g/mole). The Tg of PC blocks followed the Fox-Flory equation with a higher K value than expected. The PDMS content in PC domains was calculated to range from 11% for material of low block molecular weights to about 1.3% for high block molecular weight material.
Cryoground Rubber-Natural Rubber Blends
Authors: Phadke A. A. , Chakraborty S. K. , De S. K.
Published: February 2011

Addition of cryoground rubber (CGR) causes changes in curing characteristics (decrease in Mooney scorch time, optimum cure time, and reversion time) and shows a detrimental effect on most of the vulcanizate properties (tensile, resilience, flex, hysteresis, set, and abrasion). Tear strength, however, is not adversely affected by CGR. Higher doses of curatives (sulfur 3.5 phr and acelerator 1.4 phr) and addition of reinforcing carbon black make up the losses in physical properties. Scanning electron microscope fractographs show that there is little adhesion between natural rubber and CGR. But addition of carbon black overshadows the effect of CGR, and the fractographs show the characteristics of black-filled vulcanizates.
Tack and Related Properties of Isopropyl Azodicarboxylate Modified Polybutadiene
Authors: Hamed G. R. , Shieh C-H.
Published: February 2011

Polybutadiene has been modified by reaction with isopropyl azodicarboxylate (IAD). The reaction is quite efficient, resulting in a structure in which there are pendant hydrazoester groups dangling from the BR backbone. The Tg's of the modified polymers increase with IAD content. Eventually, at high levels of modification, two Tg's are observed, indicating the presence of two phases. Infrared analysis indicates the presence of H-bonding within the modified polymers. The green strength of these polymers increases with IAD content, whereas, tack passes through a maximum with increasing IAD level. At low IAD levels, the increase in green strength is attributed to increased polar interactions between chains, whereas, at higher IAD levels, there appears to be an additional contribution from strain-induced phase separation (see Reference 1). This type of behavior is favorable for high tack. The initial increase in tack as IAD is incorporated is due, in part, to the enhanced green strength. A more important feature is that the green strength is enhanced without great loss of the molecular mobility needed to form a tack bond. This occurs because of 1) the slow rise in Tg and 2) a lowering of the entanglement density with modification. Blocky additions of the IAD contributes to the former effect as does the presence of the alkyl group (isopropyl) in the polar IAD moiety. Additionally, it is inferred that the IAD-BR molecules do not have to interdiffuse as far across the interface to develop a strong tack bond as do purely hydrocarbon BR chains. Evidence for this is the rapid initial increase in relative tack for the IAD modified elastomers. Finally, the loss of tack at high IAD levels is due to a severe decrease in chain mobility, thereby prohibiting the formation of an extensive tack bond.
Advances in SEM of Polymers
Authors: White J. R. , Thomas E. L.
Published: February 2011

We hope that this review contains convincing evidence of the value of scanning electron microscopy in polymer studies. Much information has been provided by this technique which could not be obtained by any other means. We hope, too, that we have indicated the kinds of problems that are confronted when dealing with this class of materials. Charging can be a problem, but this can normally be countered by applying a conductive coating. More serious is radiation damage, which may cause image deterioration and artifact production. Sometimes this will obscure the features about which information is sought and could lead to false interpretation. Proper controls should be applied and observations made at several magnifications and several beam potentials and currents to establish the best conditions. Although we have emphasized the difficulties that may be encountered when studying polymers in the SEM, many polymers provide very easy subjects, especially if high resolution (∼ 10 nm) is not sought, and standard SEM procedures are very straightforward. We hope that the value of the technique indicated by the many successful applications to which we have referred will act as sufficient incentive to outweigh any deterrent message that might be derived from our more cautionary passages relating to the difficulties.
Dispersive Mixing in Rubber and Plastics
Authors: Manas-Zloczower I. , Nir A. , Tadmor Z.
Published: February 2011

Most useful plastics and rubber products are mixtures of pure polymers or copolymers with a variety of additives such as pigments, stabilizers, antioxidants, flame retardants, crosslinking agents, fillers, reinforcing agents, plasticizers, foaming agents, etc. Moreover, much attention is being placed recently on the preparation of blends of polymers, leading to products of unique properties. The distribution of additives into the polymeric matrix and the detailed topological structure of the blends depend on the nature of the mixing mechanisms, hence they are intimately related to the mixing equipment configuration and mixing operating conditions. It is convenient to distinguish between two mixing mechanisms extensive and intensive or dispersive. The former, in the very viscous polymeric systems, is achieved by and large by convection. It may either be distributive or laminar. Distributive mixing may involve an ordered or random rearrangement process. Laminar mixing is achieved by imposing on the material permanent deformation in various laminar flow patterns (e.g., shearing, squeezing, or elongational flows). The objective of extensive mixing is to bring about composition uniformity throughout the mixture. For extensive mixing, large strains have to be imposed upon the liquid. This requirement, however, must be complemented by the equally important requirement of distribution of interfacial elements (or solid additives) throughout the system. Initial orientation and spatial location may be critical in laminar mixing. Dispersive mixing generally involves rupture of agglomerates formed by a solid phase and separation of closely packed particles after rupture. This is followed by the distribution of the separated particles throughout the polymeric matrix, which of course, is an extensive mixing step. The most investigated dispersive mixing operation is that of carbon black into rubber. The mechanical properties of the rubber are directly affected by carbon black dispersion. In this review, dispersive mixing mechanism and equipment are reviewed. Although the emphasis is on rubber-carbon black systems, the discussion is relevant to dispersive mixing operations of other solid fillers in rubber and plastics as well as to dispersion of one liquid polymeric phase in another (homogenization) as in blending of polymers. First, mixing equipment and its hydrodynamic analysis are reviewed. Next, the chemical and physical characteristics of some of the solid additives, specifically carbon black, are discussed. The dispersion of the solid particles takes place in various deformation fields. Hence, the behavior of single particles in flow field, of doublets and swarms of particles is relevant, as well as the interaction between particle and matrix. Finally, various postulated dispersive mixing mechanisms, consequent scaleup techniques, and the quantitative characterization of the mixture are discussed in some detail.
Polymer-Bound Antioxidants
Authors: Kuczkowski J. A. , Gillick J. G.
Published: February 2011

The service demands placed on finished rubber products continue to increase year after year. Tires, hose, automotive belts, and components are expected to perform without failure for periods which are now two to three times those expected just ten years ago. Many of these increased demands are the result of radical and innovative changes in the design and construction of rubber products. One obvious change has been the change from bias ply to radial passenger tire construction. This has increased the expected service mileage from approximately 20 000 miles (32 Mm) to over 40 000 miles (64 Mm). Other changes have resulted in response to environmental legislation. The switch to nonleaded gasoline has increased the aromatic content of our fuel. It has also resulted in the use of additional and different fuel additives such as methanol, ethanol, and t-butylmethyl ether. These aggressive solvent changes obviously affect the extractability of stabilizers from hose products. Additional legislation has changed mileage and pollution requirements for engines. This has, in general, increased the operating temperature under the hood, resulting in more severe aging conditions for belts, cables, and hoses. At the same time, it has increased the demands placed on seals and gaskets which are in contact with hot lubricating oils. Similar situations also apply in areas outside the automotive area. Rubber products used in the garment and carpet industries are also exposed to extraction conditions during detergent washing and dry cleaning processes.
The Effect of Variations in Chain Connectivity on Strain-Induced Crystallization in Unvulcanized EPDM Elastomers
Authors: Scholtens B. J. R.
Published: February 2011

The introduction of a small amount of chemical or physical crosslinks has an enhancing effect on SIC in EPDM. This situation results from a decrease in stress relaxation or creep, so that the individual chains are deformed more affinely. At the same time, there is no deleterious effect of crosslinks on the crystallization of nonstretched EPDM because of its copolymeric nature. Therefore, the higher connected chains have a smaller melting entropy upon stretching, which promotes the crystallization process. In both EPDM green rubbers and black compounds, the amount of crystallinity and the end-melting temperature increase considerably with strain, in contrast to literature reports. These are desirable qualities for rubber tack. In spite of the positive effect of a higher chain connectivity on SIC, chain connectivity has a detrimental influence on tack. This effect is the result of a drastic reduction in bond formation caused by diminished material flowability and chain interdiffusion. Hence, we conclude that a tack-grade EPDM should, preferably, contain no branched or lightly crosslinked structures.
Model Vulcanization of EPDM Compounds—Part II: Influence of Temperature and Time on the Vulcanization Products from Ethylidene Norbornane
Authors: van den Berg J. H. M. , Beulen J. W. , Hacking J. M. H. , Duynstee E. F. J.
Published: February 2011

Influence of vulcanization temperature and time on the sulfur crosslinks in vulcanized EPDM (third monomer ENB) was studied using the low-moleular model compound ENBH (C9H14). For each vulcanization condition (60 min at 180°, 160°, 140°, and 120° and 60, 30, 15, and 5 min at 140°), the nature of the crosslinks is represented by the composition of the C9H13−Sn−C9H13 vulcanization mixture as indicated by its HPLC chromatogram. In this way it is shown that increase in temperature favors formation of disulfidic crosslinks at the expense of the higher-sulfide crosslinks. Under the mildest vulcanization conditions (60 min at 120° or 5 min at 140°), disulfidic crosslinks are nearly absent and penta-sulfidic crosslinks are the most important.
Mechanisms of Antioxidant Action: Aromatic Nitroxyl Radicals and Their Derived Hydroxylamines as Antifatigue Agents for Natural Rubber
Authors: Dweik H. S. , Scott G.
Published: February 2011

Diarylnitroxyl radicals and their reduction products, the diaryl hydroxylamines are effective anti-fatigue agents for rubber, confirming the previously proposed mechanism of action of the diaryamincs. The nitroxyls are reduced by sulfur species formed during the vulcanization reaction to a mixture of hydroxylamines and parent amines, and these species act as reservoirs for the nitroxyl radical during fatiguing. Removal of the reservoir of reduced species by solvent extraction removes the antifatigue activity.