bluuebunny/crossref_metadata_2025 huggingface dataset:
Aggregate Structure: Effect on the Agglomerate Morphology and Cohesivity
Authors: Drakopoulou A. , Feke D. L. , Manas-Zloczower I.
Published: February 2011

The relationship between the structure of individual aggregates of carbon black and the packing density and perceived cohesivity of the agglomerates they form is investigated. Five grades of carbon black aggregates have been analyzed for their size and shape characteristics. The aggregates exhibit fractal-like structures and can be distinguished in terms of their perimeter fractal dimension. The cohesivity of agglomerates formed from individual grades of aggregates has been measured using a tensile-test method. These results can be interpreted in terms of Hamaker constants that characterize the cohesive interaction on the length scale of either the aggregate or primary particle. To build a framework in which the morphology and cohesivity of agglomerates can be linked through knowledge of aggregate characteristics, we utilize a three-parameter shape function to describe the configuration of the aggregates. Here, the two-dimensional projections of the aggregates are assumed to be given in polar coordinates by r=α+ε sin (ηθ) where α is related to the aggregate size, η is a measure of the number of projections of the aggregate, and ε gauges the roughness of the aggregate. The shape of the aggregates and the minimum solids loading within a cohesive agglomerate can adequately be represented using this postulated form.
Ultimate Properties of Stereoregular and Stereoirregular 1,4-Polybutadiene Networks and Their Correlation with Theories
Authors: Sharaf M. A.
Published: February 2011

The ultimate properties of stereoregular and stereoirregular 1,4-polybutadiene (PB) networks covering a range in micro-chemical structure (cis-trans-vinyl) have been investigated. The dependence of the ultimate properties, namely the ultimate strength and the maximum extensibility, on sterochemical structure, has been demonstrated at different temperatures. Also, dependence of the ultimate properties on temperature has been apparent. Focusing special attention on the physical processes that culminate in rupture of the network, confirmed and extended the primary role played by strain-induced crystallization. More specifically, strain-induced crystallization enhances attainment of greater values of strength and extensibility. Noncrystallizable elastomers were found to have lower ultimate properties due to the absence of rupture-impeding mechanisms and consequently they become incapable of reaching their maximum extensibility. The frequently observed maximum in plots of the ultimate strength fr vs. the molecular mass Mc has been verified as an intrinsic property of the networks. This property was found to depend on the degree of crosslinking, rather than being time dependent. Values of the ultimate strength fr of both crystallizable and noncrystallizable networks were well reproduced by Bueche's theory of rupture. On the other hand, the Griffith criteria were found to have some success with noncrystallizable networks. Calculated values of the threshold surface free energy G0 were in agreement with those reported in the literature for similar noncrystallizable networks.
The Preparation, Properties and Potential Applications of “Diimide-Hydrogenated” Styrene-Butadiene (HSBR) and Polybutadiene (HBR) Thermoplastic Elastomers
Authors: Parker Dane K. , Roberts Robert F. , Schiessl Henry W.
Published: February 2011

Our unique diimide-based process for preparing HNBR latex from NDR latex without the use of hydrogen, noble metal catalysts or solvents has now been successfully extended to the preparation of hydrogenated thermoplastic elastomers latexes directly from SBR or BR latex precusors. Commercially available SBR latex such as SBR 1502 can be readily reduced to high saturation levels (95+%) via the diimide reduction technique. Latex cast films of the highly reduced elastomer show excellent ozone and oxidation resistance as expected. Unexpectedly however, the hydrogenated polymer films demonstrate high tensile strength and thermoplastic elastomer (TPE) behavior. The TPE properties have been found to be caused by polyethylene crystallites that exist even in the unstretched films under ambient conditions. Latex is an unusual physical form for a TPE material. As a latex, TPE elastomers can be fabricated into sheets or other products by simple dipping or spraying methods—methods not normally available to TPEs in bulk form. In this regard, HSBR or HBR could function as superior replacements for natural rubber (NR) latex in articles such as tubing, gloves, condoms etc., where ozone and oxidation resistance may be required or in applications where good strength properties coupled with the absence of potentially allergenic proteins and/or curatives may be desirable. Alternatively, HSBR or HBR latexes may also be conventionally coagulated and processed using standard rubber/TPE compounding techniques.
Reduced Time Approach to Curing Kinetics, Part II: Master Curve from Nonisothermal Data
Authors: Shyu G. D. , Chan T. W. , Isayev A. I.
Published: February 2011

Nonisothermal curing kinetic data obtained from differential scanning calorimetry (DSC) for a rubber compound are corrected for the effects of temperature lag between the DSC sample and furnace. The method of Eder and Janeschitz-Kriegl, which is based on experimental data alone without reference to any kinetic model, is used for these corrections. A method is presented for shifting the corrected nonisothermal curing kinetic data with respect to an arbitrarily chosen reference temperature to obtain a master curve. The method is based on experimental data alone without assuming any specific form of kinetic model. When the isothermal curing kinetic data for the same material are shifted with respect to the same reference temperature, a master curve is also obtained which basically overlaps the corresponding master curve from nonisothermal data. It follows that nonisothermal DSC measurements provide the same curing kinetic information as isothermal ones, only over a wider range of temperatures. The shift factors obtained from experimental data alone are compared with the corresponding values calculated from a kinetic model with an Arrhenius type of temperature dependence. This serves as a means of model evaluation. It is concluded that the kinetic model is good at describing isothermal curing kinetic data. But it yields reliable curing kinetic information over a narrower range of temperatures than nonisothermal data alone without resort to any model. The Arrhenius extrapolation of the limited isothermal data to a wide range of temperatures is quite good.
Kinetics of the Epoxidation of Butyl Rubber; Development of a High Precision Analytical Method for Unsaturation Measurement
Authors: Puskas Judit E. , Wilds Christopher
Published: February 2011

A precise, simple and inexpensive method was developed for measuring the unsaturation (U) in butyl rubbers. The method, based on the epoxidation of the double bonds using 3-chloroperoxybenzoic acid, was suggested first by Dreyfuss and Kennedy, Their test was refined based on rate measurements. The accuracy and precision of the new, refined version was found to be very good; 44 data points yielded a standard deviation of 0.0128 mol % around the sample mean U=1.78 mol %. The results agreed very well with 500 MHz 1H NMR data, and were shown to be superior to the traditional iodine index test. The epoxidation was shown to be a second order reaction by the kinetic measurements. The rate constant of the epoxidation was found to be k=287 L/mol · s at 25°C. Rate measurements in the 25–40°C temperature range yielded ΔH*=32 kJ/mol (7.66 kcal/mol) for the activation enthalpy of the epoxidation. The reaction was simulated by a fifth order Runge-Kutta numerical integration with adaptive step-size control, using measured rate constants. Measured values under different conditions showed very good agreement with the simulated rate plots. The traditional qualitative analytical approach was shown to require varying reaction times for varying levels of unsaturation due to a minor side reaction. Understanding the kinetics allowed the determination of unsaturation based on ‘kinetic’ approaches, eliminating the problems associated with the traditional approach. One kinetic approach developed uses two rate measurements at t1/t2=2, and does not require the knowledge of the rate constant. Unsaturation values obtained by this method agreed well with 500 MHz NMR data, but its precision was not satisfactory. The other kinetic approach predicts unsaturation from a single rate measurement. Data generated by this method agreed very well with 500 MHz NMR data, and the precision of this method was found to be equal to that of the ‘traditional’ analytical method discussed in this paper.
Mechanical Properties of Blends of Crystallizable Polybutadienes Containing Amorphous Polybutadiene Diblock Copolymers
Authors: Nir Moira Marx , Cohen Robert E.
Published: February 2011

Tensile failure properties of syndiotactic 1,2 polybutadiene/trans 1,4 polybutadiene crystalline blends are improved by addition of 5–10% amorphous 1,2 polybutadiene/1,4 polybutadiene diblock copolymer. The effect of block molecular weight and microphase behavior of the diblock copolymer was investigated. Heterogeneous diblocks enhance blend properties to a greater extent than homogeneous diblocks. In blends with enhanced properties, percent coverage of interfacial surface area by diblock is on the order of 10%.
The Mechanical Behavior of Double Network Elastomers
Authors: Santangelo P. G. , Roland C. M.
Published: February 2011

It was found that at low residual strains, the modulus of double network rubbers can be less than that of an isotropic elastomer of equal crosslink density. At higher residual strains, the equilibrium modulus is higher for the double network. This aspect of the behavior of networks was investigated using two phenomenological descriptions of rubber elasticity, the Mooney-Rivlin (MR) and the Roth, Martin, and Stiehler (RMS) Equations. Calculations using either approach, which make use of the independent network hypothesis, were qualitatively in agreement with the experimental data. The tensile strength of double networks based on natural rubber were found to be independent of the amount of residual strain. This is true even at higher residual strains, wherein the modulus is significantly amplified. This suggests that the conventional compromise between modulus and failure properties can be circumvented using double network rubbers. Their utilization can yield elastomers of better mechanical properties.
“Explosive Decompression Failure” of Rubbers: A Review of the Origins of Pneumatic Stress Induced Rupture in Elastomers
Authors: Briscoe B. J. , Savvas T. , Kelly C. T.
Published: February 2011

The Review first describes the general features of gas induced rupture in elastomers, induced by a reduction in the ambient gas pressure, and introduces the main variables such as the gas-polymer transport and equilibrium properties. The phenomenologieal nature of the failure processes are also described and the characteristics of the failures encountered are summarized. It is proposed that the failure processes, which involve bubble expansion and subsequent tearing of the interior and exterior of the elastomer, arise from the action of at least two stress fields; one is provided by a simple triaxial tension and the other by an evolving gas concentration gradient. Various routes to model this process are described in the Review. In addition, the importance of the main system variables, on these rupture processes, is assessed and means of deducing, and directly measuring the parameters which may influence the rupture process are described. These include various equilibrium and transient properties such as the extent of the gas mass sorption, the associated volume change and the variation of the mechanical and thermal properties of the polymer-gas system at elevated pressures.
The Development of Fracture Mechanics for Elastomers
Authors: Thomas A. G.
Published: February 2011

The energy balance, or fracture mechanics, approach has proved successful in treating a number of fracture phenomena and unifying them in terms of what is believed to be a basic characteristic, the crack growth behavior when expressed in terms of the energy release rate T. It has also enabled some of the underlying physical factors to be identified and incorporated into appropriate theories. There are, however, some important limitations and outstanding problems which remain. For example, we do not at present have any quantitative understanding of what determines the precise form of the crack growth characteristic under repeated stressing. During the development of the approach, numerous checks were made of its validity by comparative experiments on different test piece geometries. This is important, as it is not certain that such comparisons will invariably give equivalent results and that the T vs. rate of tear relation is a true material characteristic. For example, if a test piece, such as the “split” test piece in Figure 2(d), is subjected to large pre-extensions in the direction of tearing, the tear resistance in some cases may apparently be much reduced from its unprestrained value. (Anisotropy is produced which is believed to be important in knotty tear development). Gent and Kim found a similar effect with laterally pre-strained pure shear test pieces. Also, if tear measurements are made with an edge crack test piece of natural rubber and the strains become great enough to produce crystallization in the main bulk of the test piece, the stick-slip behavior is suppressed and the tear strength appears to be increased. Thus it appears that in some cases the assumption that the strains just around the tip at the instant of tearing are independent of the bulk deformation is not true. Fortunately these cases seem to be the exception rather than the rule, but their occurrence demands continuing caution. Some peel tests of rubber-to-metal bonds for example show apparently anomalous force dependencies on peel angle. The current interest in the understanding and prediction of strength and durability of elastomer articles stems from the increasing importance attached to avoiding premature failure in service. The growing availability of finite element programs capable of dealing with large strains has already meant that force-deflection behavior can be at least approximately designed for; but a corresponding failure design procedure based on fracture mechanics is still in the stage of development.
Advances in Natural Rubber Production
Authors: Kadir Abdul Aziz S. A.
Published: February 2011

This paper will attempt to highlight the various advances made to date in the production and processing of natural rubber (NR). The commercially planted rubber tree, Hevea brasiliensis, can yield as high as 3,000 kg of rubber per hectare in contrast to the 500 kg rubber per hectare obtained from the wild Amazonian rubber trees. The high yield of commercial rubber trees is attributed to the successful breeding program, efficient development of agronomic and crop management practices and proper exploitation systems. Today, the Hevea brasiliensis trees not only contribute to the supply of world natural rubber, but also to the ever increasing demand of tropical timber. Latex extracted from the rubber tree is processed to meet the specific requirements of the consumers. In the area of processing, emphasis is on the production of NR as an industrial raw material with improved quality and consistency. Efforts are also placed on processing efficiency, optimum product mix and production of value added modified NR such as epoxidized and deproteinized NR. The processing activities also take into consideration the control of processing effluent with appropriate effluent treatments or conversion of effluent to useful materials.
Compression of Rubber Blocks
Authors: Gent A. N.
Published: February 2011

Many features of the compression of rubber blocks can be deduced by means of a simple analytical treatment which, although approximate, appears to give reasonably satisfactory predictions for stiffness and interfacial stresses. The theory has been redeveloped and refined many times; some principal contributions are noted in References 1–14. While the analysis has been frequently repeated, it is interesting to note that what is probably the first, and in some ways the most comprehensive, theoretical discussion, did not refer specifically to rubber blocks; it dealt with the elastic properties of the periodontal membrane in connection with the tightness of teeth. Apart from an extensive review in connection with the use of rubber compression springs for bridge bearings, general results for small compressions of rubber sheets and blocks have not been collected together previously in one easily-available place, as far as I am aware. A review is therefore given here, with some remarks on its limitations. Attention is drawn to the surprisingly large effect of relatively small departures from absolute incompressibity of rubber, and of the use of frictional restraints instead of perfect bonding at loaded surfaces.
Effect of Crosslink Structures on the Fatigue Crack Growth Behavior of NR Vulcanizates with Various Aging Conditions
Authors: Kim Sang Goo , Lee Suck-Hyun
Published: February 2011

The effect of crosslink structures on the fatigue crack growth (FCG) behavior of unfilled and HAF-filled vulcanizates with conventional (Conv), semi-efficient (Semi-EV) and efficient (EV) cure systems, all with similar levels of total crosslink densities, was investigated before and after aging at 100°C in air and in nitrogen. The unfilled vulcanizates before aging did not show differences in the FCG rate through the whole range of tearing energy applied in this study. However, HAF-filled vulcanizates before aging showed some differences in the FCG rate with an order of EV > Semi-EV > Conv in the range of high tearing energy corresponding to the strain levels from 46 to 85%. Heat aging in air results in a higher FCG rate (compared to before aging) due mainly to the changes of the total crosslink density and the crosslink structures. The Conv cure system in unfilled rubber showed a higher FCG rate than the other cure systems since it had the poorest resistance to heat aging at all the aging periods. Also, heat aging of vulcanizates in air gave higher FCG rates than heat aging in nitrogen because of the dominant effect of oxidative degradation on the mechanical fatigue resistance of the rubber. The various vulcanizates after aging at 100°C in air showed that the FCG rate and slopes (between the FCG rate and the tearing energy) were drastically changed at similar critical tearing energy. The slopes of all samples changed at the critical strain levels of around 40–50% over which the classical statistics theory for rubber elasticity disobeys.
Chemical Interaction between Carbon Black and Elastomers — Crosslinking of Chlorosulfonated Polyethylene by Carbon Black
Authors: Roychoudhury A. , De S. K. , De P. P. , Ayala J. A. , Joyce G. A.
Published: February 2011

Surface oxidation of a carbon black leads to an increased elastomer-filler bonding between the chlorosulfonated polyethylene and the carbon black. The increased interaction appears to be related to the increased concentration and reactivity of the oxygen containing sites in the oxidized carbon black, as deduced from the moisture adsorption and thermometric titration results. The bound rubber content is substantially higher for the oxidized carbon black. The reactive surface sites of the carbon black also promote the crosslinking of the elastomer at elevated temperatures.
Study on Dispersion Morphology of Silica in Rubber
Authors: Li Yingbing , Wang M. J. , Zhang Tao , Zhang Fenhou , Fu Ximei
Published: February 2011

A new model of silica's aggregation in rubber, the Hexagon-linking Model, is proposed and tested in this study, using transmitting, scanning and analytical electron microscopy. When wetted in rubber, silica tends to accumulate, by way of hexagonal rings, differently from carbon black; the “wetted” states can be controlled through mixing procedures. The experimental evidence that aggregation of silica (original size of 20 nm) precedes to a final size of 63.8 nm, as compared to a theoretical value of 60 nm, supports the theoretical model. The wetted filler structure can be controlled by the mixing process, and hence desired composite properties can be achieved.
Fatigue of Cord-Rubber Composites
Authors: Lee B. L. , Liu D. S. , Chawla M. , Ulrich P. C.
Published: February 2011

Fatigue failure mechanisms and their dependence on cyclic loading frequency were assessed in the case of a nylon fiber-reinforced elastomer matrix composite representing the actual carcass of bias aircraft tires. Under uniaxial tension, the angle-plied composite specimens were subjected to a considerably large interply shear strain before failure. The composite specimens exhibited infinite fatigue life when stress amplitude was below a threshold level, i.e., fatigue endurance limit. Under cyclic stresses exceeding the endurance limit, localized damage in the form of fiber-matrix debonding and matrix cracking was formed and developed into the delamination eventually leading to gross failure of the composite. The process of damage accumulation was accompanied by a continuous increase of cyclic strain as well as temperature. Fatigue lifetime and the resistance to damage accumulation of aircraft tire carcass composite were strongly influenced by cyclic frequency. The use of higher frequency resulted in shorter fatigue lifetimes at a given stress amplitude and lower endurance limit. The extent of xdynamic creep at gross failure, which is defined as the increase of cyclic strain beyond initial elastic deformation, was roughly independent of stress amplitude under the frequency of 1 Hz, but decreased with higher stress amplitude when the frequency was raised to 10 Hz. Obviously a critical level of dynamic creep exists for gross failure of the composite and this level appears to be independent of the stress amplitude at low frequency. When the frequency is sufficiently high, heat generation due to hysteretic loss is expected to degrade the materials. In this situation, the critical level of dynamic creep for gross failure seems to be reduced by the loss of matrix flexibility as well as fiber-matrix bonding strength, with the degree of reduction becoming greater under higher stress amplitude.
Precipitation of Silica-Titania Mixed-Oxide Fillers into Poly(Dimethylsiloxane) Networks
Authors: Wen Jianye , Mark James E.
Published: February 2011

Previous studies have demonstrated techniques by which model elastomers prepared by end linking poly(dimethylsiloxane) (PDMS) chains can be reinforced by the in-situ precipitation of silica from a base-catalyzed sol-gel conversion of tetraethoxysilane (TEOS). The present investigation extends this technique to silica-titania mixed oxides through the sol-gel conversion of mixtures of TEOS and titanium n-butoxide. The elastomeric networks reinforced by this novel mixed filler were found to have very good mechanical properties, and swelling equilibrium measurements indicate that there is good adhesion between the SiO2-TiO2 filler and the elastomeric matrix. Compared with networks containing silica alone, the networks containing silica-titania mixed oxides had somewhat better combinations of high modulus and good extensibility. The particle size was typically several hundred A˚ in diameter but was found to be inversely dependent on the crosslink density of the PDMS network. Thus, larger particle sizes can be obtained at lower crosslink densities (which give larger network mesh sizes). The distribution of particle sizes is relatively narrow, and there is very little particle aggregation. The presence of in-situ silica-titania mixed oxides can also increase the onset temperature for degradation of the PDMS host matrix.
Effects of Alkylation of Silica Filler on Rubber Reinforcement
Authors: Ou Yu-Chun , Yu Zhong-Zhen , Vidal A. , Donnet J. B.
Published: February 2011

Rubber reinforcement of silicas with different surface alkylation have been evaluated by studies of NH3-modified swelling, swelling volume fraction, stress-strain tests, and scanning electron microscopy. Effects of silica alkylation on filler dispersion has been explained on the basis of surface energy and acid-base interactions. Bound rubber reductions have been explained according to acid-base interactions and/or physical entanglements. Hysteresis losses have been interpreted based on the reductions of polymer-filler and filler-filler interactions. The results show that the extent of reinforcement in NR and SBR vulcanizates is reduced when the silicas are alkylated, especially in the case of the hexadecyl group. However, in NBR vulcanizates the alkylation seems to have less influence on the reinforcement characteristics of the silica.
Preparation and Characterization of Crystalline 3,4-Polyisoprene
Authors: Hsu W. L. , Halasa A. F.
Published: February 2011

Gel-free, semi-crystalline polyisoprenes containing 70–81% 3,4 units were prepared using an improved iron catalyst. A partially hydrolyzed triisobutylaluminum was used as the reducing agent for the improved catalyst, which allowed the title polymers to be prepared in aliphatic solvents at fast rates.
An Elastomeric Ejection System
Authors: Choi I. S. , Roland C. M. , Bissonnette L. C.
Published: February 2011

The ability of elastomers to store large quantities of energy, which can subsequently be recovered very quickly, makes them attractive materials for propulsion devices. Recently the U.S. Navy has developed a torpedo ejection system based on an elastomeric mechanical capacitor. The criteria governing selection of a material for this application include high elastic energy, sufficient fatigue life, minimal creep, and resistance to deterioration by seawater. This paper describes various approaches to obtaining these material properties.
Large Strain Viscoelastic Constitutive Models for Rubber, Part I: Formulations
Authors: Johnson A. R. , Quigley C. J. , Mead J. L.
Published: February 2011

Constitutive models for large strain isothermal viscoelastic deformations of rubber are reviewed. The models discussed are for materials which have separable long and short term stresses, and for which the short term stresses have separable time and strain effects. They include the history integral model, an internal stress variable model, an internal stretch variable model, and an internal solid model. The internal stretch variable model and the internal solid model were motivated by molecular descriptions of rubber viscoelasticity. The material tests required to determine the constants for these large strain models are discussed. The classical problem of determining a rubber energy density function, used to describe both the long term and short term energy in these models, is reviewed. A method to assure Drucker stability, a commonly overlooked issue, is presented for experimentally determined Rivlin energy density function expansions. Also, an improved method for determining the coefficients of a Prony series, which defines a material's relaxation time spectrum, from experimental relaxation data is presented.
Quantitative Fractography of Rubber by Image Processing Technique
Authors: Ganesan L. , Bhattacharyya Pritimoy , Bhowmick Anil K.
Published: February 2011

In this paper, an image processing technique to quantitatively analyze abraded, torn and fatigue failed surfaces is described. The image surfaces were represented in terms of a closed set of orthogonal polynomials. The significant orthogonal effects were measured and combined to represent the local texture, called pronum. The frequency of occurrence of the pronums is the prospectrum, a global descriptor. Various statistical parameters were calculated from the prospectrum and correlated to the ridge spacings on abraded surfaces. The statistical closeness between various textured surfaces was also quantified. Using the image processing technique, the laborious procedure involved for quantification especially of irregular microfeatures has been shown to be overcome. Author to whom correspondence should be addressed.
Formation of Surface Structure in Vulcanizates and Surface Structure Changes in Air
Authors: Mori Kunio , Kanae Kentaro , Hirahara Hidetoshi , Oishi Yoshiyuki
Published: February 2011

The formation theory of surface structure during vulcanization was developed on the basis of an interfacial concept. The theory showed the chemical compositions of polar and nonpolar components on the vulcanizate surface to be determined as an excess interfacial free energy between rubber compounds and molds decreases. The surface free energies of molds reflected clearly the corresponding surface free energy of vulcanizates prepared from copolymers and polar polymers. Nonpolar polymers were not influenced by the surface free energies of molds. The surface free energies of vulcanizates decreased slightly with the concentration of network chains owing to the entropy of rubber segments. The surface free energies of molds affected the chemical compositions at the topmost surface region to the upper surface region on vulcanizates. NBR vulcanizates with high surface free energy increased the contact angle of water after standing in dry air. In the dry air environment, topmost surface layer nitrile groups were buried in the bulk of NBR vulcanizates and butadiene units subsequently overturn to the topmost, layer. In this case, the vulcanizate surface chemical composition was influenced only at the topmost surface region. ESCA spectra N1s peak intensities on NBR vulcanizates was consistent with these observation.
Effect of Porosity on Mechanical Properties of Rubber
Authors: Kasner A. I. , Meinecke E. A.
Published: February 2011

Cylindrical samples, with different shape factors and levels of porosity, were prepared from a model EPDM compound and tested in compression. The modulus was reduced considerably with the introduction of porosity, especially when the shape factor was high. The stress-strain curves showed nonlinearity which depends on the shape factor and porosity level, and is related to bubble closure. The apparent modulus of bonded blocks was found to consist of two components: homogeneous compression modulus and a hydrostatic contribution. The first was obtained by compression of blocks between lubricated compression plates. It can be predicted from analytical expressions adapted from composite theories for high density foams in tension. The second arises from the pressure buildup inside the bonded blocks and depends on the shape factor and the porosity level. These moduli, after correcting for compressibility, were used to develop approximate relations describing the stress-strain curves of porous bonded blocks. The stress-strain curves of samples with different shape factors and levels of porosity could be predicted from experimental data or FEA estimates.
Novel Ultrasonic Technology for Devulcanization of Waste Rubbers
Authors: Isayev A. I. , Chen J. , Tukachinsky A.
Published: February 2011

A novel patented process and several reactors have been developed for devulcanization of waste rubbers. The technology is based on the use of the high power ultrasonics. The ultrasonic waves of certain levels in the presence of pressure and heat rapidly break up the three-dimensional network in crosslinked rubbers. The devulcanized rubber can be reprocessed, shaped and revulcanized in much the same way as a virgin rubber. The first laboratory reactor has been scaled up to pilot-plant level by the National Feedscrew and Machining, Inc. Various devulcanization experiments were carried out with model styrene-butadiene rubber (SBR) and with ground rubber tire (GRT). Curing behavior, Theological properties, and structural characteristics of rubbers devulcanized at various processing conditions were studied, as well as mechanical properties of revulcanized rubber samples. A possible mechanism of the devulcanization is discussed. The performed measurements indicate that the rubbers are partially devulcanized, and the devulcanization process is accompanied by certain degradation of the macromolecular chains. In spite of these observations, the processing conditions are identified at which the retention of the mechanical properties is found to be good. A further work is in progress to find the optimal conditions of devulcanization and to improve the selectivity of the process towards breaking up the chemical network only.
Molecular Weight Defined in Sol-Gel Analysis and Its Application to Evaluate Branching
Authors: Ahagon Asahiro
Published: February 2011

It is considered that many “linear” polymers are actually branched; however, it is difficult to show this with ordinary methods for an arbitrarily chosen polymer. Branching can be regarded as premature crosslinking below the gel point. Attention is then paid to the well-established Charlesby-Pinner Equation used for sol-gel analysis in crosslinking studies. It contains the number average degree of polymerization before crosslinking as a parameter. The molecular parameter is considered here to be that of the virtual linear polymer which would be obtained by unlinking any branch points contained in the polymer. Evidence is shown to support this. It is then possible to estimate the total number of linear components on an average molecule of a branched polymer by taking the ratio of the number average molecular weight measured by two methods, i.e., sol-gel analysis and an ordinary method like GPC. Further information about the branching structure can be obtained by additional measurements of effective crosslink density for a series of polymers obtained from similar polymerization processes.
Bound Rubber and Elastomer-Filler Interaction
Authors: Meissner B.
Published: February 2011

The statistical theory of bound rubber and the polymer-filler gel formation theory are shown to offer a satisfactory quantitative description of a set of experimental bound-rubber data recently obtained by Wolff, Wang, Tan (Rubber Chem. Technol. 66, 163 (1993)) on SBR compounds filled with 17 furnace blacks covering the whole range of rubber grades. The observed decrease of bound-rubber content per unit of interfacial area with increasing loading and/or specific surface area of carbon black is explained by the theory as being due to the statistical nature of the adsorption process. A correlation was found to exist between specific surface activity of filler D (adjustable parameter of the theory, number of active sites per unit surface area) and filler structure, the latter being characterized by the difference between DBP absorption and crushed DBP absorption. Also, D was found to increase with loading of a high-structure black. The two effects are ascribed to filler aggregates breakdown during mixing, which leads to a new active surface formation for polymer bonding.
Scanning Transmission Imaging of Elastomer Blends Using an Unmodified Conventional Scanning Electron Microscope
Authors: Cudby Paul E. F. , Gilbey Barry A.
Published: February 2011

A novel method for carrying out scanning transmission electron microscopy on a standard scanning electron microscope is described. This method involves the addition of a specially fabricated mount and is accomplished without carrying out any form of modification on the microscope. The method is compared to more conventional microscopy techniques and examples are given showing the advantages of this system.
Hydroxyl-Terminated Polybutadiene Telechelic Polymer (HTPB): Binder for Solid Rocket Propellants
Authors: Ajaz A. G.
Published: February 2011

This paper presents a review of hydroxyl-terminated polybutadiene telechelic polymer (HTPB) with emphasis on its preparation, properties, end group modifications, hydrogenation, role as polyurethane precursors and binders for solid rocket propellants.
Nomenclature of Polymeric Materials
Authors: Fox Robert B.
Published: February 2011

The purpose of this brief review is to aquaint the authors and readers of Rubber Chemistry and Technology with the essentials of polymer nomenclature. To ensure quality communication, it is important that a common language be utilized that is understood, not only by those in the rubber and elastomers field, but by anyone in related areas of polymer science and technology as well. Traditional and trade names of polymeric materials often have time-honored meanings but are obscure or incomplete and frequently fail to convey reasonably accurate information. Many polymer and chemical names are at best ambiguous, but are easily correctable. The methods outlined here have been adopted by the Commission on Macromolecular Nomenclature of the International Union of Pure and Applied Chemistry (IUPAC); their use in Rubber Chemistry and Technology is strongly recommended. Additional details will be found in the appropriate IUPAC publications. Note that for the purposes of this paper italics are generally used to set-off “names” for emphasis. However, when naming polymers for RC&T, Roman characters should generally be used with only the ‘connectives’ or ‘prefixes’ appearing in italics (see Table I). By convention, in manuscripts text that is to be printed in italics should be underlined.
Solid-State C-13 NMR Studies of Vulcanized Elastomers XIII. TBBS Accelerated, Sulfur-Vulcanization of Carbon Black Filled Natural Rubber
Authors: Mori Makio , Koenig Jack L.
Published: February 2011

Solid state C-13 NMR has been used to compare the chemistry of accelerated vulcanization of natural rubber using N-t-butyl-2-benzothiazole sulfenamide in the presence and absence of carbon black. The carbon black filler has an influence on the vulcanization chemistry in addition to its accepted role in reinforcment and stabilization. The basic network structure formation is modified to the extent that crosslink desulfurization from poly to monosulflde structures occurs earlier in the cure in the presence of carbon black. No main chain scission or double bond migration was detected.
Fractal Structures in Carbon Black Reinforced Rubbers
Authors: Klüppel Manfred , Heinrich Gert
Published: February 2011

This paper considers the fractal nature of primary and secondary carbon black aggregates in rubber and the implications for the mechanical and electrical properties of rubber goods. In particular, the effects of dispersion and primary aggregate breakup during mixing are investigated. Founded on recent studies of the disordered growth processes of colloids, a model concerning formation, structure and properties of tenuous secondary carbon black aggregates (clusters) in rubber is formulated. We distinguish between two different mechanisms of cluster growth at carbon black concentrations ϕ below and above the gel point ϕ** of the filler network. For ϕ≤ϕ**, the restricted mobility of the dispersed primary aggregates governs the cluster growth and neighboring clusters are seperated by a rubber-specific minimum distance d0. These gaps between neighboring clusters are joined together in a bond percolation model that determines the conductivity in a transition regime ϕ*≤ϕ≤ϕ** above the electrical percolation threshold ϕ*. The mechanical action of carbon black clusters below the gel point ϕ** is estimated by a hydrodynamical amplification factor that is related to a rigidy condition for the clusters. At sufficient large filler concentration for ϕ≥ϕ**, the restricted mobility of primary aggregates in the rubber matrix is insignificant for the cluster growth and a kinetic cluster by cluster aggregation (CCA) process is applied. The resulting fractal carbon black network corresponds to a spacefilling configuration of CCA-clusters. From this network structure, a scaling invariant power law arises for the small-strain modulus as function of carbon black concentration. The conductivity in the networking regime ϕ≥ϕ** shows a typical power law behavior that is implied by an anomalous diffusion of the charge carriers on the fractal clusters. For the frequency dependence of the conductivity a cross-over to a power law regime at large frequencies results. The predicted properties of carbon black filled rubbers are discussed in the framework of experimental results taken from different authors.
Deformation of Filler Morphology in Strained Carbon Black Loaded Rubbers. A Study by Atomic Force Microscopy
Authors: Maas S. , Gronski W.
Published: February 2011

The changes of the filler morphology of SBR vulcanizates loaded with 10 phr carbon black (N234 and N990) subjected to large strains were studied by Atomic Force Microscopy and image analysis. It was found that the filler particles tend to align in the force field. The average distance of the filler particles at the surface in the direction parallel and perpendicular to the strain direction is much smaller then according to affine deformation. The measurements give evidence of the inhomogeneous deformation of the rubber matrix and demonstrate the onset of failure at large deformation.
The Technological Compatibilization of Natural Rubber/Polystyrene Blends by the Addition of Natural Rubber-graft-Polystyrene
Authors: Asaletha R. , Thomas Sabu , Kumaran M. G.
Published: February 2011

Compatibility of natural rubber (NR)/polystyrene (PS) blend is poor and can be enhanced by the addition of a graft copolymer of natural rubber and polystyrene (NR-graft-PS). The effects of homopolymer molecular weight, copolymer molecular weight, copolymer concentration, processing conditions and mode of addition on the morphology of the dispersed phase have been investigated by means of optical microscopy. The addition of a small percentage of the compatibilizer decreases the domain size of the dispersed phase. The effect levels off at higher concentrations. The leveling off could be an indication of interfacial saturation. The experimental results were compared with the theoretical predictions of Noolandi and Hong. The addition of the graft copolymer improves the mechanical properties of the blend and attempts were made to correlate the mechanical properties with the morphology of the system. Attempts were also made to understand the conformation of the graft copolymer at the interface.
Rheological Studies of Dynamically Vulcanized and Mechanical Blends of Polypropylene and Ethylene-Propylene Rubber
Authors: Han Peter K. , White James L.
Published: February 2011

An experimental study is presented of the rheological properties of (i) polypropylene, (ii) a commercial polypropylene/ethylene-propylene terpolymer a dynamically vulcanized blend (PP/EDPM-TPE) and (iii) a mechanical blend of a polypropylene and an ethylene-propylene copolymer. The polypropylene behaves as a typical flexible chain thermoplastic exhibiting a zero shear viscosity and higher shear rate non-Newtonian viscosity, well defined normal stresses, an elongational viscosity three times the zero shear viscosity, and an equality of the shear viscosity and the complex viscosity (Cox-Merz Rule). The PP/EPM-TPE exhibits an apparent yield value in shear flow, unmeasurable normal stresses and a complex viscosity which is much greater than the shear viscosity. This is behavior similar to that of particle filled compounds, block copolymers and liquid crystalline thermoplastics and suggests a material with a rest state structure. The behavior of the PP/EPM mechanical blend is intermediate.
Sulfur/Olefin Copolymers as Vulcanizing Agents for Rubber
Authors: Colvin Howard , Bull Charles
Published: February 2011

Sulfur/olefin copolymers are known as vulcanizing agents for rubber, but synthetic procedures for these materials are poor and there is little in the literature to relate the structure of the copolymer with the vulcanizate properties of the rubber. This study discusses a new suspension process for the preparation of sulfur/dicyclopentadiene and sulfur/dicyclopentadiene/styrene copolymers. The relationship between the sulfur/olefin copolymer and vulcanizate properties is discussed in terms of the structure of the copolymer and other reaction products.
Direct Analysis of Elastomer Compounds by Soft Ionization, Tandem (MS/MS) and High Resolution (AC-MS) Mass Spectrometry
Authors: Lattimer Robert P.
Published: February 2011

In recent years very effective mass spectrometric methods have been developed for direct polymer compound analysis. The high sensitivity, high specificity, and superb mixture analysis capabilities of modern mass spectrometry make it an invaluable tool in the polymer industry, particularly for qualitative analysis (chemical identification) of organic additives as well as polymeric components. “Survey” mass spectra obtained with soft ionization methods — field ionization (FI-MS) and chemical ionization (CI-MS) — provide diagnostic overviews of chemical composition. The supplemental tandem (MS/MS) and atomic composition (AC-MS) techniques are used to make specific identifications of various organic ingredients. This report describes the direct mass spectrometric analysis of three different elastomer compounds. Organic additives, including curatives, were identified via thermal desorption methods in a commercial EPDM bearing as well as a diene rubber V-belt. The composition of a commercial thermoplastic polyurethane was determined via pyrolysis (Py-CI-MS). These problem-solving examples illustrate the very effective role that mass spectrometry can play in the industrial polymer analysis laboratory.
Correlation between Laboratory and Road Rubber Wear Tests
Authors: Krishnan V. , Ramakrishnan R. , Donovan J. A.
Published: February 2011

The wear resistance ranking of three rubber compounds A, G and K measured in the laboratory at medium to high slip on sharp silicon carbide (SiC) grinding wheels was similar to that determined by road tests at Pecos, Texas. The wear resistance ranking of the three compounds changed on blunt alumina grinding wheels compared to wear resistance rankings on sharp SiC grinding wheels. The change was most probably due to a change of mechanism from mainly cutting on sharp surfaces to predominantly fatigue on blunt surfaces. For these three compounds a change in the ambient temperature from 23 to 75°C during laboratory testing had no effect on the wear resistance ranking. The wear of the rubber compounds on the abrasive grinding wheels and during road tests followed Zapp's relation in which the wear is proportional to the ratio of dynamic modulus to rupture energy.
Influence of Aggregate Structure and Matrix Infiltration on the Dispersion Behavior of Carbon Black Agglomerates
Authors: Li Qi , Feke D. L. , Manas-Zloczower I.
Published: February 2011

The dispersion of carbon black agglomerates in poly(dimethyl siloxane) (PDMS) has been studied experimentally. Both the structure of carbon black aggregates comprising the agglomerate and the presence of the matrix within the agglomerate were found to affect the mode of dispersion, critical stress conditions, and the kinetics of the dispersion process. Agglomerates of high structure carbon black are generally more difficult to disperse than agglomerates of low structure carbon black at the same agglomerate density. Depending on the degree of saturation of the agglomerate by PDMS, the dispersion process may be either enhanced or retarded compared to the dry state.