bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrical Conductivity in Rubber Double Networks
Authors: Roland C. M. , Peng K. L. 
Published: February 2011

Abstract
The consequences on electrical conductivity of the various processing steps used to form a double-network rubber are summarized in Table IV. Although the objective was not achieved herein, the potential for using double-network rubbers to attain enhanced conductivity remains. Alternate procedures enabling residual extensions exceeding 100% are suggested for future work. Specific conclusions drawn from this study are as follows: 1. The time dependence of the electrical resistivity after imposition of a tensile strain depends on the magnitude of the strain. The observed behavior is consistent with breakup of carbon-black floc at low strains (with concomitant reduction in conductivity) and with promotion of interparticle contacting at higher strains. The latter engenders enhanced longitudinal conductivity. The enhancement may be due to orientation of the filler phase, but this remains speculative. The effect of deformation on the transverse resistivity could not be reproducibly characterized. 2. The rate dependence of the electrical resistivity was also dependent on the magnitude of the rubber deformation. At the low strains associated with disruption of the filler phase, higher rates (stresses) increase the maximum in the resistivity. At higher elongations for which the resistivity declines, the effect of deformation velocity is less apparent. 3. Subjecting a filled rubber to heating after mixing reduces the electrical resistivity. The irreversible portion of this reduction is attributed to an acceleration in the recovery of an equilibrium level of filler-particle contacts. The resistivity acquires an invariance to temperature after the initial heating that persists for at least several hours. 4. The fact that extension followed by retraction of a carbon-black-reinforced elastomer results in a permanent increase in electrical resistivity negated in this work the possibility of achieving enhanced electrical conductivity via a double-network structure. 5. Consistent with the strain optical properties, orientational crystallization behavior, and stress-strain response previously found for unfilled rubbers containing a double-network structure, carbon-black-reinforced double-network rubbers exhibit electrical resistivities more sensitive to strain than conventionally cured elastomers.
Solid-State Carbon-13 NMR Studies of Vulcanized Elastomers. IX. TMTD-Vulcanized cis-1,4-Polybutadiene at 75.5 MHz
Authors: Smith S. R. , Koenig J. L. 
Published: February 2011

Abstract
The results of the present study indicate that, for the most part, the variety of C-S bonded structures formed in TMTD-vulcanized cis-BR qualitatively parallel those found in sulfur-cured vulcanizates of the material. Key exceptions include the demonstrated existence of stable rubber-bound accelerator fragments, and the possible elimination of select intramolecular cyclic species. Cis-to-trans isomerization has again been shown to be the predominant feature of the vulcanization reaction sequence and seems to obey first-order kinetics with respect to the concentration of accelerator. While the kinetic rate of conversion among all intermediate species was too rapid to permit a full account of the process, the spectral data demonstrate further that, subsequent to the formation of rubber-bound accelerator residues, sulfur becomes quickly redistributed to form crosslink structures of low average sulfur rank. In contrast to results obtained from elemental sulfur-cured BR vulcanizates, relatively high concentrations of monosulfidic crosslink structures were found in the TMTD vulcanizates at even the shortest reaction times. Similar to the results of the sulfur study, on the other hand, comparison between chemical and physical crosslink densities of the samples indicate the reaction sequence to have been highly localized, producing spatially inhomogeneous networks of elastically inefficient, clustered crosslinks. This latter result can be taken to imply that network morphology in TMTD-vulcanized BR is critically influenced by the solubility of the active accelerator complex in the rubber matrix. The effect was exaggerated in the present study by the omission of a compatible chelating agent for the zinc ions. From the standpoint of efforts aimed at optimization and control of the performance properties of vulcanized rubber articles, systematic investigation of the dependence of this effect on a wider range of formulation variables is warranted.
Kinetic Study of Oxidative Scission in Natural Rubber by Wallace Plasticity Measurements
Authors: Gan L. H. , Ng S. C. , Chee K. K. 
Published: February 2011

Abstract
The kinetics of thermal oxidative degradation of natural rubber (NR) have been studied by Wallace plasticity measurements. On the basis of the Kotliar's model of random chain scission, an expression was derived to interpret the kinetic data collected over a range of temperatures from 80 to 160°C. It has been shown that the kinetic parameter resulting from the present analysis, indeed refers to a diffusion-controlled reaction with an overall activation energy estimated to be 135 ± 6 kJ · mol−1. In addition, the implications of plasticity retention index, which measures the oxidizability of NR, are discussed.
Contact of Rubber Wedges with a Flat Rigid Surface
Authors: Cummings D. , Gent A. N. , Kim W. , Padovan J. 
Published: February 2011

Abstract
Contact widths have been measured for long rubber wedges, with wedge angles ranging from 60° to 115°, pressed against a smooth, flat, rigid surface. The contact width grew rapidly at first to about 50 µm, and then more slowly, in proportion to the applied load. Thus, the mean contact pressure in the early stages of contact was small, about 5 to 10% of Young's modulus, E. It then became substantially constant at about 65% of E for a wide range of applied loads, up to about 300 N/m. Approximately the same results were obtained from FEM calculations for incompressible linearly elastic wedges with slightly rounded tips. The contact width at a given load increased slightly when the wedge was held at an angle to the vertical, up to a tilt angle of about 20°. Above this tilt angle, only one side of the wedge came into contact, and the contact width increased significantly; the mean contact pressure falling to about 0.2 E at a tilt angle of 30°.
A New Process for the Preparation of Highly Saturated Nitrile Rubber in Latex Form
Authors: Parker Dane K. , Roberts Robert F. , Schiessl Henry W. 
Published: February 2011

Abstract
A novel process for the preparation of highly saturated nitrile rubber latex has been developed. This process directly converts NBR latex into HNBR latex in one reaction step. The key to the process is the efficient in-situ generation of diimide within the latex by the oxidation of hydrazine hydrate in the presence of a catalyst. At 40–70°C, diimide smoothly and selectively reduces the olefinic bonds while leaving other functionalities unaffected. The process operates at ambient pressures and produces nitrogen and water as by-products. HNBR latex produced by this process has been applied to the manufacture of superior heat-resistant gasketing via the “Beater-Addition” method. This unique new form of HNBR maintains the well known benefits of HNBR (e.g., solvent, heat, and ozone resistance, etc.) while expanding its potential applications into latex-related products.
Wear of Tank Track Pad Rubber Vulcanizates by Various Rocks
Authors: Thavamani P. , Bhowmick Anil K. 
Published: February 2011

Abstract
Wear of tank track pad compounds against various rocks at different normal loads and frictional work has been investigated. The track pads have been based on natural rubber (NR) and hydrogenated nitrile rubber (HNBR). The rocks have various hardness and chemical compositions. Wear, V, increases with normal load, N, and frictional work, F, and is related by V=KFn, where k and n are constants. The value of n is lower for filled compounds and abrasion against soft rock. At any normal load, the rate of wear of HNBR is much lower than that of NR, though the temperature developed is higher for HNBR compounds. All the results could be explained with the help of dynamic coefficient of friction, frictional work, and structural changes during abrasion. Ridges are found on the abraded surface of NR, and the surface is tarry. A dry and particulate wear is observed in HNBR compounds, and the size of debris increases with frictional work.
Synthesis and Properties of Regular Star Polybutadienes with 32 Arms
Authors: Zhou L-L. , Hadjichristidis N. , Toporowski P. M. , Roovers J. 
Published: February 2011

Abstract
A dendrimer carbosilane containing 32 Si—Cl bonds in the perimeter has been prepared and has been used as a coupling agent to prepare 32-arm star polybutadienes. The dilute-solution properties 〈RG2〉, A2, [η], and D0 have been measured in one good solvent and in one ¸ -solvent. The dimensions of the 32-arm star polymers are compared with those of linear polymers at constant molecular weight. It is shown that the 32-arm star polybutadiene has the characteristic properties of a hard-sphere molecule in dilute solution. The equivalent hard-sphere radii calculated from A2, D0 and [η] are identical and 1.29 times larger than the root mean-square radius of gyration. The Daoud—Cotton scaling model for stars is also tested.
Internal Crack Symmetry Phenomena during Gas-Induced Rupture of Elastomers
Authors: Briscoe B. J. , Liatsis D. 
Published: February 2011

Abstract
This paper describes an experimental and analytical investigation of the consequences of removing a high ambient gas pressure environment from a number of elastomers after they had been allowed to equilibrate under high gas pressure. The elastomers are irreversibly damaged, and the phenomenology of this damage is described. One particular type of damage, the formation of internal symmetrical cracks whose geometry is the same as that of the sample, is examined in detail. The experimental data are interpreted using two models. The first provides a first order, but somewhat artificial, description of the phenomenon observed. A more sophisticated model invokes two separate processes as the origin of the rupture phenomenon. It is argued that ruptures arise as a result of the combined effects of an overall hydrostatic tension and a localized tensile field which is created by the effusion of gas from the polymer. The severity of the latter is shown to be a function of the gas transport properties of the elastomer under the conditions which prevail during the gas desorption process.
Effect of Humidity and Water Content on the Cure Behavior of a Natural-Rubber Accelerated Sulfur Compound
Authors: Butler J. , Freakley P. K. 
Published: February 2011

Abstract
Certain accelerators are susceptible to chemical attack by water. Consequently, the cure behavior of compounds containing these accelerators is likely to be affected by the water content of the compound and the humidity conditions of processing and storage. A quantitative investigation into the influence of humidity and water content on cure behavior was carried out using a natural-rubber compound with MBS (N-morpholylbenzothiozole-2-sulfenamide) as the principal accelerator. Samples of the compound were treated at different humidities, their water contents determined, and their cure curves measured. Scorch time was inversely related to treatment humidity and water content of the compound, whereas cure rate was directly related to humidity and water content. A study of the mechanism by which water affects the cure behavior of the compound revealed that hydrolysis of the accelerator, MBS, would inhibit its scorch-delay action and could produce MBT (2-mercaptobenzothiazole), which would increase the cure rate. It is concluded that compounds containing other benzothiazole sulfenamide accelerators are likely to exhibit similar behavior. The adverse effect of moisture on the cure behavior of compounds can be minimized by carrying out storage and processing at as low a humidity and temperature and for as short a time as possible.
Direct Characterization of Rubber-Surface Chemistry Using Laser Desorption Mass Spectrometry
Authors: Waddell Walter H. , Benzing Kimberly A. , Evans Larry R. , McMahon John M. 
Published: February 2011

Abstract
Laser desorption mass spectrometry (LDMS) was used to directly characterize the surfaces of vulcanized natural-rubber compounds with or without an antiozonant (AOz) and an antioxidant mixture. Molecular ions of five intact molecules were observed on the rubber surface using a single laser pulse. The molecular ions represent the AOz, the three components comprising the antioxidant mixture, and a production impurity in the AOz. The surface chemistry of the AOz, N-(1,3-dimethylbutyl)-.N′-phenyl-para-phenylenediamine (HPPD), was explored in order to investigate the mechanism of rubber-surface aging and protection. Two sets of samples were prepared: ozone-aged HPPD films that had been deposited on a glass plate and ozone-aged cured rubber strips containing HPPD. Rubber samples were continually stretched to 25% elongation and relaxed during exposure to ozone. The mechanisms of ozone reaction with HPPD on glass and on stretched rubber are similar, since many reaction products were identical based on the presence of the same LDMS peaks; however, the reaction on rubber was considerably more complicated, since numerous additional high-mass peaks were observed. Based on the present LDMS data and in agreement with the conclusions of Lattimer, Rhee and coworkers, the mechanism of antiozonant protection of rubber is consistent with both scavenger and protective barrier models being operative. Sections from a truck tire that displayed premature sidewall cracking and a passenger tire that displayed sidewall discoloration were analyzed using LDMS. The specific modes of sidewall failure were determined.
Tire Rolling Resistance from Whole-Tire Hysteresis Ratio
Authors: Pillai P. S. , Fielding-Russell G. S. 
Published: February 2011

Abstract
A simple equation for tire rolling resistance in terms of whole-tire hysteresis ratio, tire load, and footprint dimensions has been developed from energetic considerations. The rolling resistances of a number of radial passenger and truck tires have been calculated using the equation, and the calculated values were successfully compared with the measured results. The general applicability of the equation was illustrated by predicting the rolling resistances of a wide range of tires—from an experimental HR78-8 minitire to a full size 11R24.5 truck tire.
The Effect of Gel on the Deformational Behavior of Polyvinylchloride (PVC) and Nitrile Rubber (NBR) Blends
Authors: Nakajima N. , Liu J. L. 
Published: February 2011

Abstract
Deformational behavior of four different types of PVC and NBR blends were tested by dynamic shear measurements at small deformation and tensile stress—strain measurements at large deformation. Among these samples, three of them were partially compatible blends having the same acrylonitrile content (33%) but different gel contents and gel types (microgel and macrogel) in the NBRs. The last blend was a completely incompatible blend having a lower acrylonitrile content (21%) in the NBR. From the dynamic measurements, a temperature-independent log G′−log G′ curve was obtained for the partially compatible blends. The curve moved to the right as gel content increased, indicating that the sample having higher gel content behaved more elastic. No temperature-independent curve was obtained for the completely incompatible blend. The tensile properties of the completely incompatible blend were much worse than those of the partially compatible blends. The latter showed strain hardening during the course of the deformation. The highest degree of strain hardening was observed with the macrogel-containing sample followed by the microgel-containing sample and the gel-free sample.
Green Strength of Carbon-Black-Filled Styrene—Butadiene Rubber
Authors: Cho P. L. , Hamed G. R. 
Published: February 2011

Abstract
The green strengths of a gum SBR and two black-filled samples, at twenty-three volume percent filler, have been determined at various strain rates and temperatures. At higher temperatures, all samples exhibit yielding, followed by strain-softening. The gum exhibits this type of behavior down to −20°C, whereas, filled specimens undergo strain hardening at this temperature. Yield strength increases with decreasing temperature or increasing rate, indicating that it is largely controlled by chain mobility. Yield strengths at various temperatures may be shifted along the rate axis to form mastercurves. The dependence of yield stress on reduced rate is similar for the gum and the composition filled with the large-sized thermal black (N990). Stiffening is reasonably well accounted for by strain and strain-rate amplification, using the well-known Guth—Gold amplification factor. At low reduced rates, the extent of stiffening is substantially greater for samples filled with the much finer furnace black, N110. Unlike with the N990, SBR filled with N110 forms a coherent bound-rubber gel. This provides a strong resistance to deformation (beyond simple strain or strain-rate amplification) and results in high yield strength. At low temperatures, perhaps when the magnitude of chain—chain and chain—filler internal friction is comparable, the effect of filler size is greatly diminished.
Analysis of Elastomer Vulcanizate Composition by TG-DTG Techniques
Authors: Sircar Anil K. 
Published: February 2011

Abstract
Two common problems and probable solutions in the TG-DTG analysis of unknown elastomer vulcanizates have been discussed. The first problem concerns the difficulty in quantitatively determining the oil and elastomer in compounds where their volatilization temperature ranges overlap. After a review of the published works in this area, isothermal TG (with or without vacuum) is recommended. The “High Resolution” TG also shows promise and should be explored further. The second problem concerns separate determination of the elastomer-carbon residue and added carbon black in the compound, since both often oxidize together. Subtraction of the predetermined elastomer-carbon residue from the total weight loss in oxygen, was suggested in the literature. However, the quantity of char found depends on the type of the elastomer, its concentration, and the curative composition, as well as the TG temperature profile. The problem is not, therefore, fully resolved. Experiments using a slow feed of lean oxygen gas and isothermal conditions were also suggested in the literature. Under this condition, oxidation of carbon black and char may occur at slightly different temperatures and overlapping is minimized. However, this could be achieved only for large- and mediumparticle-size blacks (soft blacks) which oxidize at higher temperatures and not for the smaller particle size blacks used mostly in tire treads. Further work using the slow feed of lean oxygen with a superimposed isothermal program and/or vacuum conditions is recommended.
Rubber Processability Index Using Electrical Resistivity
Authors: Shiga S. 
Published: February 2011

Abstract
It may not be realistic to expect a single processability index to be useful for every feature of rubber mixing due to the complexity of its mechanisms. Many processability indices have been proposed. One can find properties available to define the indices in Table I. The indices can be conceptually classified into two categories. One is founded on the singularity of some properties at the minimum mixing time. The compound mixed over this time is Theologically homogeneous in contrast to that mixed insufficiently. Therefore, this time is a phase-transition point. Not all, but most of the properties indicate the sudden change in the time-derivatives characteristic to singular points. After the time, the change becomes smaller. The other is founded on the properties of final compounds, which could be assumed as existing in a pseudoequilibrium state. Electrical volume resisitivity (resisitivity, hereafter) is chosen for this purpose. It looks simple and suitable for practice, i.e., in rubber factories. Actually, as reported by Boonstra, the measurement requires skill in addition to special equipment and is not a popular method. Nevertheless, we have used it to express the processability and, more generally, to clarify the mixing mechanism. There are three reasons for this methodology: first, we find that EPR, the object of our study, apparently shows constant minimum mixing time; second, the pseudoequilibrium-like resistivity is parallel to other processability indices, namely, the larger the resistivity, the worse the processability as described in Reference 1; third, the resistivity directly corresponds to the percolation theory. Of course, other processability indices have their own theoretical origins. However, properties other than resistivity can not be quantitatively supported by theory because of the complexity of mixing. The exceptions are microscopic methods as exemplified by the counting of large agglomerates and their size distribution, but these are more tedious and require more skill.
A Guide to Estimating the Friction of Rubber
Authors: Roberts A. D. 
Published: February 2011

Abstract
Vulcanized rubber, as a material, can exhibit extremes in friction level when utilized in all manner of mechanical devices. There is no single value of friction coefficient for a particular vulcanizate. Guidelines for estimating the friction of a rubber component can be based on the idea that the friction force will depend upon the real area of contact that the component makes with its counter-surface. That depends upon such factors as vulcanizate hardness, viscoelastic response, shape, and surface finish. The latter can influence hysteresis losses, as can asperities on the counter-surface. The friction will also depend upon the interfacial shear strength. This is related to the nature of the contact materials and is reduced in the presence of any lubricants or contaminants.
Distributive Mixing Characteristics of Batch Internal Mixers
Authors: Freakley Philip K. 
Published: February 2011

Abstract
The distributive mixing characteristics of three internal mixers are examined: a Parrel BR Banbury (1.6 L), a Farrel F40 Banbury (40 L), and a Francis Shaw K1 Intermix (5.5 L). The former two machines have two-wing tangential rotors while the latter has intermeshing rotors. The distribution of sulfur in mixed batches of an EPDM compound and an SBR compound, as measured by curemeter tests on samples taken from random locations within each batch, is used to quantify distributive mixing. The dominant influence on sulfur distribution is total rotor revolutions and a maximum of 20 rotor revolutions is adequate for distribution of powder sulfur in each mixer. The effects on distribution of rotor speed, rubber compound rheology, and mixer size are insignificant.