bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Rubber/Metal Bond Failures by Surface-Analysis Techniques
Authors: Madura A. R.
Published: February 2011

Surface-analysis techniques including ISS, SIMS, XPS, and SEM are highly complementary and are essential for detailed investigations of rubber/metal bond failures. Multitechnique investigations offer the most effective means of solving problems in bonding applications. EDS, a near-surface analysis technique usually associated with SEM, is a versatile supporting technique for comprehensive studies. Contamination of materials used in bonding applications, especially by silicones, is a commonly encountered factor in bond failures. However, the extent and role of the contamination is often difficult to assess. Prepared test coupons exposed to silicone spray mist considered significant in this study exhibit isolated regions of silicone contamination that did not severely influence peel-test failure modes or maximum peel-load values. The techniques used in this study can be used independently or together to identify surface-treatment effects, determine failure locus, verify the presence of conversion coatings, primers, and adhesives, and identify contaminants in rubber/metal bonding studies. Failure characteristics of bonded assemblies vary and are often complex. Failure investigations of a high-performance mount that exhibits regions of apparent interfacial failure show silicone contamination is present in the failure regions. Intact regions of the same mount failed by fracturing in liquid nitrogen do not contain silicone and show a different failure locus. This suggests that only limited areas of the part were initially contaminated to the extent that bonding was affected; or the regions disbonded in service were exposed to silicone contamination after the failure was initiated.
Combining Cobalt and Resorcinolic Bonding Agents in Brass-Rubber Adhesion
Authors: Hamed Gary R. , Huang J.
Published: February 2011

The bonding of several black-filled natural rubber vulcanizates to brass-plated steel cord was investigated using the TCAT pullout geometry. Compositions using either cobalt naphthenate or an HR bonding system (hexamethoxymethyl melamine plus RFR) had higher pullout forces than a control without these agents. However, the highest pullout forces, both initially and especially after aging, were obtained when the cobalt and HR additives were used together. Results from ATR spectra show that the RFR migrates to the brass surface, and it is proposed that this provides a barrier to attack by moisture of the brass-rubber interfacial region. In support of this idea, moisture uptake is reduced for compositions containing the HR bonding system. Moreover, in the presence of cobalt naphthenate, sulfidation of brass gives a surface topography of substantially higher surface area than seen if this agent is absent. This is expected to promote interlocking between the rubber and the outwardly growing sulfide layer. Finally, the HR resin is able to remove both zinc and cobalt from squalene solution. It is hypothesized that cobalt and the HR resin each have beneficial effects as noted previously, but the subsequent removal of cobalt from the rubber phase by complexing with the HR resin may prevent cobalt, a well-known oxidation catalyst, from promoting degradation of the rubber during aging.
Heat Generation in Elastomer Compounds: Causes and Effects
Authors: Medalia Avrom I.
Published: February 2011

In many important applications, an elastomer is subjected to repeated deformations of sufficient magnitude and frequency to lead to generation of considerable heat and (depending on the rate of heat removal) of a significant rise in temperature. The purpose of this review is to examine the mechanisms of heat generation and to indicate some important effects arising in service. More detailed discussion of various aspects of heat generation, dynamic properties, and viscoelasticity of rubber compounds may be found elsewhere.
Low-Temperature Properties of Hydrogenated Nitrile Rubber (HNBR)
Authors: Hayashi S. , Sakakida H. , Oyama M. , Nakagawa T.
Published: February 2011

HNBR, hydrogenated nitrile rubber, is a heat-, oil-, and fuel-resistant elastomer produced by the selective hydrogenation of NBR. As shown in Table I, HNBR is a highly saturated nitrile elastomer consisting of units of acrylonitrile, ethylene, unsaturated butadiene, and hydrogenated vinyl butadiene. The acrylonitrile gives excellent oil resistance, fuel resistance, and high tensile strength to NBR. The ethylene provides not only excellent rubber elasticity, heat resistance, chemical resistance, and ozone resistance, but also good low-temperature flexibility. The presence of a small unsaturated portion in the butadiene unit makes possible the easy vulcanization of HNBR with either sulfur or peroxide. The vinyl butadiene segments (6–8%) are preferentially hydrogenated at the beginning of the reaction and assist in maintaining the amorphous nature of the elastomer. The low-temperature flexibility of ordinary NBR varies in inverse proportion to its acrylonitrile content. Therefore, low-acrylonitrile NBR has better low-temperature flexibility than high-acrylonitrile NBR. The low-temperature properties of HNBR are different than those of NBR. This paper will show the relation between the acrylonitrile content and degree of hydrogenation and the glass-transition temperature (Tg) and low-temperature flexibility of HNBR. The Tg and low-temperature flexibility as measured by the TR-test and Gehman Torsional Stiffness test of HNBR showed the different behaviors for the various degrees of hydrogenation and acrylonitrile contents. Conversely, the brittle temperature of HNBR becomes lower with an increase in degree of hydrogenation. This paper also describes the effects of polymer composition and of various plasticizers on the low-temperature flexibility of HNBR.
Durability and Life Prediction of Adhesive Bonds in Severe Environments
Authors: Stevenson A. , Priest A. M.
Published: February 2011

1. Life Prediction methods may be used to characterize the durability of adhesive bonds of elastomers to rigid substrates. The primary rate determining mechanism of bond failure is considered to be electrochemical in nature, and its rate may be characterized on an Arrhenius basis. 2. Assumption of a single mechanism (and single activation energy) cannot be made across a wide temperature range. Two different regimes were discovered within the temperature range 20 to 90°C for both sea water and oil environments. 3. Durable bonds between elastomers and structural polymer/composites can be formed using normal rubber technology for rubber/metal bonding. In the case of bond durability in iso-octane/toluene at 90°C bonds of HNBR to E-glass composite surpassed those of HNBR to stainless steel. 4. These methods provide a scientific basis for quantitative determination of the life of engineering components in service. Further research is required at present for each new application, but wider use of these techniques in the future is anticipated, especially for critical applications where component replacement is costly or hazardous. This knowledge can provide confidence for engineers to make more extensive use of those adhesive systems in more demanding applications.
Filler-Elastomer Interactions. Part I: Silica Surface Energies and Interactions with Model Compounds
Authors: Wang Meng-Jiao , Wolff Siegfried , Donnet Jean-Baptiste
Published: February 2011

Inverse gas-solid chromatography, operated at infinite dilution, has been used to assess the surface energies of silicas, both fumed and precipitated. The dispersive components of the surface free energies of the silicas were calculated from the free energies of adsorption, corresponding to the —CH2— group, obtained from n-alkane adsorption. The specific components of the surface energies were evaluated separately by comparison of the free energies of adsorption of polar probes with those of n-alkanes, based on the surface areas covered by the probe molecules. The results indicate that while the dispersive components of silica surface energies is somewhat higher for the fumed silicas, the specific components are much higher for precipitated silicas, probably resulting from the higher silanol concentration on their surfaces. Moreover, the interaction able to take place between rubber matrix and the silicas are also estimated chromatographically from the adsorptions of low-molecular-weight analogs of elastomers. The free energies and enthalpies indicate that the interactions of functional groups with the fillers decrease in the order of nitrile, phenyl ring, double bond. The saturated rubber analogs show lower interactions with silicas. The lowest interactions of iso-alkanes imply poor interactions between butyl rubber and the fillers. As expected, the experimental data reflect an attenuation of polymer-silica interactions with decreasing content of functional groups and degree of unsaturation in NR, BR, SBR, and NBR.
The Examination of Diffusing Materials on Rubber Surfaces by Photoacoustic Infrared Spectroscopy
Authors: Peck M. C. Paputa , Samus M. A. , Killgoar P. C. , Carter R. O.
Published: February 2011

Minor amounts of diffusing materials can be beneficial or detrimental to the performance of elastomeric components. Methods to study these materials have been nonexistent or extremely time-consuming and insensitive for routine use. This report shows that photoacoustic detection Fourier-transform infrared spectroscopy (PAS-FTIR) is a simple method for in situ characterization of diffusing materials in elastomers. In this study, PAS-FTIR was used to monitor the appearance and diffusion of two vulcanization by-products to the surface of a carbon-black-filled natural rubber matrix. The compounds were identified from the PAS-FTIR spectra as a salt of stearic acid (most likely zinc stearate) and dimorpholinyl thione. Three rubber formulations, differing only in the particle size and surface activity of the carbon blacks used, were monitored by PAS-FTIR for a 135-day period to investigate the effect of carbon black on the diffusion of the compounds cited above. Diffusion of the dimorpholinyl thione was not affected by the carbon-black properties presented in this study. Larger carbon-black particle size delayed the appearance of zinc stearate on the vulcanizate surface.
NMR Imaging Studies of Vulcanized Butyl Rubber
Authors: Krejsa M. R. , Koenig J. L.
Published: February 2011

NMR imaging is a useful technique for studying the physical and spatial microstructure of cured elastomers. Different swelling agents can be used as chemical probes to detect varying amounts of microstructural differences. Imaging can be used to detect highly cured regions due to aging, poor mixing, and thermal gradients. NMRI is thus useful to study spatial distribution of crosslinks and is sensitive to changes in this distribution of crosslinks due to thermal gradients and the effects of aging and reversion processes. It can also be used to observed entrapped air in air-aged samples. Spin-lattice T1, relaxation times for solvent in cured elastomers have been shown to be shorter than the bulk solvent T1 values, providing a new method for determining the crosslink density. NMRI results have suggested that cure reversion and postcuring processes produce similar spatial results.
A Model for Tire Wear
Authors: Koutny F.
Published: February 2011

Tire abrasion arises due to slip in the contact of the tread with the road, and so it is closely related to the conditions of the road surface and weather. An attempt at phenomenological modeling of the treadwear process has been presented. A simple differential equation is set up to capture the dependence of the groove depth on the sum of tangential slips. It is shown that stochastic components of the usual meteorological quantities (temperature and humidity) may be approximated with a Markov series. A random process is suggested to simulate these environmental effects. Analytical solution of the model equation gives the average course of the groove depth and its confidence limits due to environmental effects. A nonlinear parameter estimation problem is formulated and several methods for its solution indicated. Some recommendations for circumventing possible difficulties are given. The capability ofthe model has been demonstrated by modeling experimental data. Finally, some aspects of linearization and the consequent simplification are mentioned. Beyond the choice of adequate parameters to represent environmental effects, in particular, geographical regions, other questions remain. For example, structure of the model parameters a, b or their relationship to each other requires further effort. On the other hand, the scope of the present ideas may extend beyond the problem of tire treadwear, perhaps having application in the modeling of weathering problems.
Characterization of Vulcanized EPDM Rubbers by High-Resolution Pyrolysis Gas Chromatography
Authors: Yamada T. , Okumoto T. , Ohtani H. , Tsuge S.
Published: February 2011

Pyrolysis gas chromatography (PyGC) is a powerful tool to give unique information of high polymers. Especially, PyGC is favorable for the practical analysis of insoluble polymeric materials such as vulcanized rubbers. In the previous paper, the structures of commercially available unvulcanized ethylene-propylene-ethylidenenorbornene rubbers (ENB-EPDMs) were investigated by high-resolution PyGC. The observed high-resolution pyrograms of the unvulcanized EPDMs were correlated to the ENB content. In addition, several peaks of the characteristic degradation products were interpreted in terms of the sequence distribution and the ethylene-propylene composition. In this work, vulcanized ENB-EPDMs (V-EPDMs) cured with two types of vulcanizing agents were studied using high-resolution PyGC. Characteristic pyrolysis products formed at 650°C were separated by the high-resolution capillary column, and the resulting pyrograms were interpreted in terms of ENB content in the vulcanized rubber samples. In addition, thermal degradation behavior of the ENB units in V-EPDMs was investigated.
Filler—Elastomer Interactions. Part III. Carbon-Black-Surface Energies and Interactions with Elastomer Analogs
Authors: Wang Meng-Jiao , Wolff Siegfried , Donnet Jean-Baptiste
Published: February 2011

The surface energies, both the dispersive component, γsd, and the specific component, γssp, of dry- and wet-pelletized carbon blacks, ranging from N110 to N990, were evaluated by inverse gas-solid chromatography at infinite dilution. The results indicate that the dispersive components of the surface energy of carbon blacks increase with increasing surface area. This dependence may essentially reflect an effect of microstructure on the surface energies, which can be confirmed by the relationship between the crystallographic parameters of crystallites and the graphitization of the carbon blacks. It was found that smaller crystallites characterized by a lower value of Lc lead to higher surface energy, whereas graphitization of the carbon black points toward lower surface energy, perhaps resulting from the growth of the quasi-graphite structure. Surface area dependence of the specific component of the surface energy characterized by the specific energy of adsorption of a polar probe follows the same pattern as was observed for the dispersive component, i.e., γsd increases with surface area. This is believed to be related to the crystallographic structure and the surface chemistry. Studies on adsorption energies of the low-molecular-weight analogs of elastomers generally show that the interactions between carbon blacks and rubbers depend not only on filler surface energies but also on the structure of the elastomers. Due to their polar functional groups, NBR and SBR show a stronger interaction with blacks than unsaturated rubbers. Among the rubbers simulated, IIR would have the lowest interaction with the filler. A comparison of the surface energies of carbon blacks and silicas points toward a very high γsd, for blacks which may show strong interaction with nonpolar- or low-polar polymers, while the very high Sf value of the silicas, especially precipitated silicas, a measure of the relative polarity of their surface, is considered to be representative of strong particle-particle interaction, leading to the formation of a filler network.
On the Anomalous Freezing and Melting of Solvent Crystals in Swollen Gels of Natural Rubber
Authors: Jackson Catheryn L. , McKenna Gregory B.
Published: February 2011

The anomalously large solvent freezing point depression, ΔTf, observed in crosslinked rubbers swollen in solvent has been a subject of study for over thirty years without clear resolution. While a sizeable ΔTf is accounted for by the lowering of the thermodynamic potential of solvent molecules in a polymer solution derived from the Flory theory, the additional ΔTf observed for crosslinked rubbers has been attributed to various physical effects such as restriction of solvent crystals to small size by the network mesh or difficulty in nucleation of the solvent crystals. In this paper, we identify two points of misunderstanding in the literature on this problem, and attempt to clarify the analysis of ΔTf for solvent swollen rubbers. The first point relates to the application of the Flory calculation to solvent freezing, where nucleation is a concern, rather than for solvent melting, for which it was intended. We present new calorimetric data on both the freezing and melting of solvent crystals in crosslinked and uncrosslinked NR swollen in benzene to illustrate this point. The second point relates to a reconsideration of the hypothesis of Kuhn et al., that the anomalous ΔTf-can be accounted for by small crystallite size. Although Boonstra and coworkers argued against Kuhn's hypothesis based on the results of x-ray line-broadening studies of solvent crystallite size, d, in the frozen gel, we have shown that their interpretation is suspect due to the use of an incorrect value for the solid-liquid surface energy of the solvent in the calculation of the melting- or freezing-point depressions.
Electrical Conductivity in Rubber Double Networks
Authors: Roland C. M. , Peng K. L.
Published: February 2011

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Filler-Elastomer Interactions. Part V. Investigation of the Surface Energies of Silane-Modified Silicas
Authors: Wang Meng-Jiao , Wolff Siegfried
Published: February 2011

As shown in previous papers of this series, the main feature of silicas with regard to surface energy, which distinguishes them from carbon blacks, is a low dispersive component, γsd, and a high specific component, γssp, of surface energy. The low γsd, would result in a lack of interaction between filler and hydrocarbon rubbers, while the high γssp would suggest a high degree of agglomeration of the filler particles in the polymer matrix. In this study, the surface free energies and the energy distribution on the surfaces of precipitated silicas which had been modified with octadecyltrimethoxy silane, 3-thiocyanatopropyltriethoxy silane and bis(3-trimethoxysilylpropyl)-tetrasulfane, respectively, were investigated by chromatography at infinite dilution and at finite concentration. A comparison with the initial silica suggests a drastic decrease in surface energy, especially of the specific component, as a result of the modification and a strong dependence of surface energy on the chemical nature of the grafts and the ratio of these grafts. The energy distribution function shows that, while the surface of the ungrafted silica is heterogeneous, the heterogeneity of the fully modified surface is drastically reduced, particularly when the product was modified with octadecyltrimethoxy silane.
Optimizing Mixing in the Banbury Mixer with Synchronous Technology (ST) Rotors
Authors: Donoian G. S. , Canedo E. L. , Valsamis L. N.
Published: February 2011

This presentation is concerned with the mixing performance of the new ST™ rotor design in Banbury® mixers operating at even speed. Rotor orientation was used to optimize machine performance in mixing a standard one-step rubber formulation, in terms of productivity, energy consumption, and product quality. Experimental data is presented on mixer discharge temperature, Mooney viscosity, and maximum rheometer torque, and their standard deviation. The effect of rotor orientation on these parameters is discussed, and optimal rotor configurations are identified.
Recuring Vulcanizates. II. Effect of Added Accelerators
Authors: Layer Robert W.
Published: February 2011

Vulcanizates, to which more accelerator has been added by swelling, were recured to study the interaction between the accelerator and the sulfur crosslinks. The addition of benzothiazole, or dithiocarbamyl sulfenamides, to SBR, SBR/ BR, or NR vulcanizates caused more crosslinks to form on recuring. A typical induction period was also noted. The results were essentially the same in all rubbers. Crosslink formation, as measured by modulus development or rheometer torque, increased with increasing loadings of accelerator. Similarly, at a given accelerator loading, crosslink formation increased with increasing length of the polysulfide crosslink. These results indicate that an equilibrium exists between the zinc salt of the accelerator and the polysulfide crosslinks.
Direct Characterization of Tire Materials by Photoacoustical Infrared and Proton Induced X-Ray Emission Spectroscopy
Authors: Waddell Walter H. , Parker James R.
Published: February 2011

In an effort to find out if compound composition could help explain the observed differences in “chip/chunk tearing” on worn off-the-road tires from two manufacturers, direct characterizations were made on tread lugs from the two tires. Two nondestructive direct analytical methods were used. They are photoacoustical Fourier transform infrared spectroscopy (PA-FTIR) and proton induced x-ray emission spectroscopy (PIXE). These techniques were also used to examine a variety of rubber compounding ingredients, such as polymers and fillers, and model tire compounds containing different levels of these ingredients. PA-FTIR requires essentially no sample preparation. It was successfully used to determine the polymer structure and to suggest the nonblack filler type in highly loaded carbon-black filled, sulfur-cured compounds and in tire sections. The characterization was based upon structural information derived from vibrational band frequencies. Elemental information was obtained by using direct PIXE spectral analysis of polymers, fillers, and two worn off-the-road tire tread lugs. Again, no sample preparation was needed and quantitative information was obtained on the elements present. Results show that the tire that did not display a tear problem was manufactured with a cushion (tread base) and a tread (cap), both containing silica at the 12–15 phr levels. The tire that had a visible chip/chunk problem was constructed with two layers of a very similar stock, but neither layer contains silica.
Filler-Elastomer Interactions. Part VI. Characterization of Carbon Blacks by Inverse Gas Chromatography at Finite Concentration
Authors: Wang Meng-Jiao , Wolff Siegfried
Published: February 2011

Carbon blacks ranging from N110 to N990 were characterized by means of inverse gas chromatography at finite concentration. The isotherms, net heat, and spreading pressures for benzene and cyclohexane adsorption suggest a general trend of increasing surface activity with increases in specific surface area. This is in good agreement with surface-energy measurements reported previously. The energy-distribution function of adsorption shows that while the concentrations of low-energy sites are comparable for most of the carbon blacks, differences exist with regard to high-energy sites. These suggest that small-particle-size blacks possess a greater number of high-energy centers. The graphitization of carbon blacks results in a considerable reduction in their adsorption capacity and narrows the energy distribution of their surfaces. One can therefore conclude that high-energy sites play an important role in the determination of the surface energies and reinforcing ability of carbon blacks.
Nonlinear Load-Deflection Relations of Bonded Elastomeric Circular Disks and Strips
Authors: Ling Yun , Engel Peter A. , Brodsky William L.
Published: February 2011

The nonlinear load-deflection relations of bonded circular disks and infinitely long strips are studied. Finite element analysis is used to evaluate the empirical formula proposed by Payne, which justifies the need for a better formula to predict the load-deflection relation for blocks with large shape factors under a relatively large deformation. General expressions for the load-deflection relations of blocks under axisymmetrical and plane-strain deformations are presented based on a variational approach, i.e. the Raleigh-Ritz method, in which no specific form of strain energy functions is required. Nonlinear load-deflection relations of circular discs and infinitely long strips made of a Mooney-Rivlin material are explicitly given in a power series form. It is found that these solutions agree well with the finite element results and are much more accurate than the empirical formula. It is shown that the solutions obtained by the Raleigh-Ritz method are not sensitive to deformations assumed.