bluuebunny/crossref_metadata_2025 huggingface dataset:
Zinc Oxide Crosslinking Reaction of Polychloroprene Rubber
Authors: Miyata Yoshiaki , Atsumi Masao
Published: February 2011

There was some ambiguity on the reality of the formation of ether crosslinks in the ZnO crosslinking of CR. This report clearly indicates the absence of the ether crosslinks. The main reaction pathway of the ZnO crosslinking of CR is the addition of the carbonium ion formed from the isomerized 1,2 unit to the double bond in the neighboring 1,4 unit, catalyzed by ZnCl2. The isomerized 1,2 unit is formed by the rearrangement of allylic chlorine in the 1,2 unit. The crosslinking reaction takes place between one curing site and one main chain component, not between two curing sites. The intramolecular cyclization predominantly occurs as compared with the intermolecular reaction (crosslinking) in Scheme 2. Therefore, the efficiency of the ZnO crosslinking of CR is quite small as expected from the concentration of the curing sites (1,2 units). Model polymer of low molecular weight and NMR spectroscopy have led to a better understanding of the chemistry of this process.
The Resistance of Rubber Compounds to Brittle Crack Propagation
Authors: Aglan H. , Moet A.
Published: February 2011

1. A theory based on irreversible thermodynamics and minimal entropy production principles is presented. This constitutive model introduces a methodology to describe fatigue-crack propagation behavior in natural rubber vulcanizate over the entire range of the elastic-energy release rate. 2. The utility of this model has been proved and demonstrated in view of the establishment of the damage evolution coefficient μ and the energy barrier μTc−T for one rubber compound. 3. The theory calls for quantitative measurements of the amount of damage associated with crack advance in order to extract the specific enthalpy of damage, γ*. This true material parameter, γ*, which characterizes its resistance to crack propagation (fracture toughness) can be related to the microstructure of the material. Thus a useful microstructure-fracture-toughness relationship based on the present theory can be constructed. Such a relationship can guide the development of rubber compounds with superior fracture toughness.
Fixing between Metals and NBR Vulcanizates and Its Prevention
Authors: Mori Kunio , Watanabe Akira , Saito Minoru
Published: February 2011

When metals and NBR vulcanizates are put into contact an adhesive force is generated between them. The phenomenon is called fixing, and the adhesive force generated is defined as the fixing strength. The fixing strength is divided into an initial fixing at 30 min after loading and an after-fixing which thereafter occurs successively. The former fixing strength is exhibited by the physical adsorption forces of the NBR segments to the metal surfaces. The latter are based on the formation of first-order bonds which are brought about by the chemical reactions between the metals and NBR vulcanizates. These fixing strengths were influenced by the environmental factors such as testing time, temperature, and humidity; by the surface factors such as the surface roughness of the metals and NBR vulcanizates, the hardness of the NBR vulcanizates, and the surface conditions; and by material factors such as the kinds of metals and rubbers, the fillers, and other ingredients in vulcanizates. From the above results, the fixing phenomenon is explained as follows. At first, the segment molecules of the NBR vulcanizates diffuse to the metal surfaces and then the nitrile groups in the NBR vulcanizates are adsorbed on the surfaces of the metals. At this time, secondary-order bond forces are generated between the two materials. Succeedingly, the chemical reactions occur at the contact parts between the two materials and then are combined by first-order bonds. As a result, a high fixing strength, as cohesive failure, is generated. The fixing mechanism leads to the four indicators of fixing prevention: (1) the control of the contact areas, (2) the suppression of molecular motion of the NBR segments, (3) the inhibition of interfacial reactions, and (4) the introduction of inactive crosslinks and side chains. In this paper, the surface curing of the NBR vulcanizates, which leads to the suppression of molecular motion of NBR segments, and the blooming method which leads to the inhibition of interfacial reactions, were investigated. The former method is not always effective for preventing the fixing because it is difficult to produce the NBR vulcanizates with less fixing properties under ordinary industrial conditions. However, stearamide and methylene bis-erucamide are very effective blooming agents to prevent fixing, because they provide barrier films onto the surfaces of NBR vulcanizates.
Dependence of Wet Skid Resistance upon the Entanglement Density and Chain Mobility according to the Rouse Theory of Viscoelasticity
Authors: Rahalkar R. R.
Published: February 2011

Starting with the Rouse theory of viscoelasticity, the Theological behavior can be modeled in the transition zone. The predictions of the model are in qualitative agreement with both the experimentally obtained data in the transition zone and with the wet skid behavior of elastomers. Based upon the linear viscoelastic spectrum for amorphous polymers, the wet skid resistance of elastomers can be related to the chain flexibility. The Rouse mechanism is able to explain the wet skid results qualitatively for most of the commonly used elastomers, including IIR. This study establishes that transition region motions are influential in determining the wet skid behavior of an elastomer, with the glass transition temperature itself perhaps playing a minor role.
Observations Made During Stretching, Tearing, and Failure of NR and SBR Loaded with Various Amounts of Carbon Black
Authors: Goldberg Alfred , Lesuer Donald R. , Patt Jacob
Published: February 2011

Using a 35-mm camera with macro attachments, and focused on the tip of a cut, the stretching, tearing, and failure of notched samples of NR and SBR were documented during continuous testing. The propagation of a cut occurs by the stretching, tearing, and collapsing of fine strands, which we propose consists of bundles of long unwinding molecular chains of the rubber. Two main cut-growth regions are identified: a slow-cut-growth region consisting of irregular-shaped nodules or cells of collapsed rubber strands along short tear paths and a fast-cut-growth region consisting of long intersecting tear or cleavage paths leading to catastrophic failure. Addition of 20.6 phr (15 wt.%) carbon black results in a coarsening of the stretching, tearing, and fracture morphologies relative to those seen with the gum rubbers. Addition of 64 phr (35 wt.%) of carbon black results in all these structures being very fine with the phenomenon of knotty, deviated tearing dominating in the slow-cut-growth region. The knotty tearing is frequently revealed by the presence of chevron-like markings which correspond to the intersection of individual disoriented (deviated) tears. The initiation of tearing occurs at relatively low strains for all three carbon black loadings (0, 15, 35 wt.%); however, the strain to initiate tearing relative to the fracture strain was seen to decrease with an increase in carbon black, especially with the SBR series. Both failure strength and elongation increase significantly with carbon-black additions to SBR up to about 39 phr (25 wt.% of carbon black). With further additions, the elongation falls off, although the engineering strength remains unchanged, while the stiffness and tearing energies increase. With reference to the literature, we discuss the role of carbon black and deviated tearing on strengthening rubbers; suggestions are made for further research in this area.
Nature of Network, Carbon-Black-Rubber Interaction and Heat Aging of Polyethylacrylate Vulcanizates
Authors: Nakajima N. , Miller R. A.
Published: February 2011

Two commercial polyethylacrylate elastomers, having about 50 Mooney Index were selected. They were compounded with 50 parts of N330 carbon black per 100 parts of rubber by weight. One sample having epoxide (EP) crosslinking sites was crosslinked with ammoniumbenzoate. The other having double-bonds by copolymerizing with ethylidene norbornene (ENB) was crosslinked with a sulfur system. The vulcanizates were oven aged at 175°C for 70 h. Tensile stress-strain measurements were performed with the gum rubbers, uncured compounds, unaged vulcanizates, and heat-aged vulcanizates. The data presented as tensile modulus—strain curves revealed the following: at all strain levels, the moduli of ENB gum samples were lower than those of EP gums. After compounding with carbon black, the moduli of two samples became very similar. This indicates that ENB has more affinity with carbon black than EP has. The vulcanizates of two samples has matching moduli at 10% strain but a difference in network structure, since the molecular architecture of the gum rubbers were very different. After heat aging, moduli at small strains increased significantly but not at large strains. The increases were very similar for both samples. The heat-aging characteristics may be very similar for both samples, in spite of the difference in the chemical nature of the crosslinks.
Numerical Simulation of Viscoelastic Flow: A Review
Authors: Crochet Marcel J.
Published: February 2011

It is evident that a major effort has been accomplished over the last ten years toward the development of numerical methods for solving viscoelatic flow. The problem was clearly much harder than expected. Several extensive reviews have been devoted to a detailed account of the difficulties encountered in reaching moderate values of the Weissenberg number. The numerical and analytical work undertaken in parallel by several research groups has led to some important conclusions which paved the way for recent promising development. First, numerical algorithms for solving highly nonlinear advective problems must be used with the greatest carefulness. When spurious solutions or unexpected effects such as limit points arise in numerical simulations, we have learned to question the validity of the numerical method as well as that of the constitutive equation. Typically, successive failures of numerical calculations with the Maxwell model at low values of We have often been attributed to its singular behavior in uniaxial elongational flow but, in the meantime, better adapted algorithms have led to solutions at ever increasing values of We. Secondly, the mathematical analysis of the partial differential equations governing the flow of viscoelastic fluids has revealed the possibility of changes of type of the vorticity equation under some circumstances, i.e., when the velocity of the fluid becomes comparable with the velocity of shear waves. The coexistence of hyperbolic and elliptic regions in a steady flow may be of great importance in explaining a number of experimental observations. Simultaneously, the analysis has led to the identification of artificial changes of type which partly explain some numerical failures, or at least give a pertinent diagnosis of numerical inaccuracy. Thirdly, it has been found that numerical algorithms must take into account the specific features of viscoelastic flow; among these, stress boundary layers, stress singularities, and advective (or memory) terms in the constitutive equations are prominent.
Rubber Mixtures
Authors: Roland C. Michael
Published: February 2011

The thermodynamic and kinetic factors governing the morphology of miscible polymer blends have been much investigated. While conceptually straightforward, modern theories of mixtures are more difficult to implement than the simple lattice theories which consider only molecular volumes. Particularly with regard to rubber mixtures, significant performance advantages associated with miscibility remain to be demonstrated. Phase separated blends are more complex; the factors controlling their structure development are difficult both to elucidate and to control. Nevertheless, extensive applications have been found for such blends. Their utilitization will likely continue to burgeon, particularly as more attention becomes focussed on the details of the spatial distribution of the domains in heterogeneous mixtures.
Design Principles for Vibration Isolation and Damping with Elastomers Including Nonlinearity
Authors: Harris J. A.
Published: February 2011

In this paper, some of the more novel features of the dynamic and static properties of elastomers have been examined in relation to their use in vibration isolation and damping. Exploitation of some of these features in advanced designs could lead to improvements in areas such as the protection of sensitive equipment and could lead to new concepts in systems such as ground-vehicle suspensions for large wheeled or nonwheeled vehicles designed for rough terrain. Elastomers are already used in many critical areas of space technology, however, the problems of temperature extremes and volatility make the space environment a challenging one. New developments in materials technology may yet be required to meet these demands, however, many of the principles discussed will still be applicable. The development of space technology may provide the impetus for new designs in which the potential of elastomeric components may be exploited to the full, with valuable spin-offs to nonspace applications, where cost considerations may currently inhibit the development of advanced devices.
Rheological Determination of Molecular Weight and Molecular-Weight Distribution for Commercial-Type Butyl Elastomers
Authors: Lobos Z. J. , Tang H.
Published: February 2011

1. There exists a linear correlation between rheological parameters (crossover frequency and crossover modulus) and structural parameters (Mw, and MWD) for commercial-type butyl elastomers. 2. There appears to be potential value in utilizing rheological testing for quality control for commercial-type butyl elastomers. 3. Further work is required to resolve testing problems (air entrapment and sample trimming) which affect the precision of the rheological measurements.
Surface Characterization of Rubber by Secondary Ion Mass Spectrometry
Authors: van Ooli W. J. , Nahmias M.
Published: February 2011

It has been demonstrated that static SIMS is potentially a very useful technique for the characterization of rubber surfaces. Its major capability is to provide molecular structural information of the polymer in addition to elemental analysis, which would also be possible with other surface techniques such as XPS or AES. The SIMS spectra are in many cases highly characteristic, and they can be used to identify the type and structure of the hydrocarbon polymer. In addition, structural changes in the rubber surface can be detected, and very useful information on the types and amounts of sulfur crosslinks can be obtained as well, as has been published elsewhere. Therefore, the technique shows great promise as a tool for the study of surface-related rubber phenomena, such as oxidation, wear, tack, antiozonant and antioxidant performance and mechanisms, and also for the study of the adhesion between dissimilar rubbers or between rubbers and other materials, such as metals. Before SIMS can be routinely used in rubber laboratories, a considerable amount of basic and fundamental work will have to be done because the spectra of many materials are not known, and they cannot always be predicted either. Therefore, a rubber-related data base will have to be built up with well-characterized polymers but also using clean films of various rubber additives. Crosslinking studies will have to be confirmed with compounds of known crosslink structures, e.g., by using different polymers, different types of accelerators, and a series of model compounds of organic sulfides.
Anomalous Fatigue Behavior in Polyisoprene
Authors: Roland C. M. , Sobieski J. W.
Published: February 2011

Annealing of a polyisoprene-based elastomer can resuit in significant changes in its failure properties, the nature of which depends on the deformation of the rubber during the annealing. Although a deterioration of properties from low-strain annealing and improved performance from high-strain annealing may be contrary to intuition, the mechanisms which underlie these annealing effects are well known. The behavior described herein simply represents other manifestations of these phenomena. These alterations in performance, moreover, are readily induced at strains within the range of conventional fatigue and crackgrowth experimentation, and thus demonstrate some of the difficulties in relating laboratory characterizations to the performance of materials in other environments.
N-(4-Anilinophenyl)-Methacrylamide, a Polymerizable Amine Antioxidant: Synthesis, Copolymerization, Copolymer Properties, and Performance
Authors: Parker Dane K. , Schulz G. O.
Published: February 2011

In conclusion, we have demonstrated that N(4-anilinophenyl)-methacrylamide (APMA) is a readily polymerizable, nonstaining amine antioxidant molecule that can be incorporated into free-radical emulsion polymerization recipes by a variety of techniques. Furthermore, we have also demonstrated that the polymer-bound APMA's effectiveness can be greatly enhanced in gum or cured rubber when it is used in conjunction with either free or bound sulfur-containing secondary antioxidants (synergists). Superior performance was demonstrated for the polymer-bound antioxidant systems using oxygen absorption, DSC, and aged (extracted) physical property retention techniques.
A Hypothetical Mechanism for Rubber Abrasion
Authors: Gent A. N.
Published: February 2011

A hypothetical mechanism for creating subsurface cracks during frictional sliding has been proposed as part of the process of abrasive wear of rubber. It consists of the unbounded elastic expansion of microscopic precursor voids until they burst open as cracks, under the action of internal pressure or of a triaxial tension in the surrounding rubber. This conjecture accounts for enhanced resistance to abrasion for compounds reinforced with carbon black, in terms of increased stiffness without much loss of extensibility, and for the lack of correlation of abrasion resistance with other measures of strength. It. should be noted that it is specific to soft, extensible materials, and thus it also accounts for marked differences in the nature of the wear process in rubbery materials compared to plastics and metals. Only rubbery materials appear to abrade away by a linking up of microcracks at right angles to the sliding direction to produce characteristic wear ridges known as the Schallamach abrasion pattern. Three mechanisms of generating a sufficiently large inflation pressure or triaxial tension are discussed. The most probable one seems to be thermal decomposition of rubber, generating volatile decomposition products—a microscale blowout process. This would be aggravated by a simultaneous softening of the rubber on heating. Although strictly conjectural, the proposed wear mechanism suggests a number of interesting experiments. For example, it would be helpful to know whether the character of wear changes when abrasion is carried out under a large superimposed hydrostatic pressure. Also, not enough is known about abrasion in vacuo. Is the process altered in kind, as well as in rate? And if thermal decomposition is, indeed, an important mechanism of initating subsurface cracks, what is the effect of changes in thermal conductivity of the abrading material on the rate of wear?
Pull-Out and Push-Out Tests for Rubber-to Metal Adhesion
Authors: Gent A. N. , Kaang S. Y.
Published: February 2011

A study has been carried out of adhesive failure forces for a steel rod embedded in and bonded to a rubber block. Emphasis has been placed on comparing tension (pull-out) and compression (push-out) forces. A fractional contribution to the pull-out force appeared to be significant for rods having a diameter greater than about 0.5 mm in the present experiments. Indeed, it became a large fraction of the total force when the rod diameter was 1 mm or more. On the other hand, it was negligibly small in push-out experiments. They would therefore be preferred on this basis for measuring the strength of adhesion. But experimental difficulties in carrying out compression tests are considerable. Tall blocks become unstable under large compressive loads, and short ones are markedly stiffer than long ones, due to restraints on their lateral expansion, which are difficult to specify and control. Thus, although measurements of push-out force for a wide variety of samples have been shown to be in good accord with a simple theoretical treatment of debonding, ignoring friction, it is recommended that pull-out tests be retained for assessing the strength of adhesive bonds. Caution is necessary to minimize the effect of friction. The theoretical treatment indicates that the product aL of the rod radius a and the embedded length L should be held smaller than the cross-sectional area of the block in which the rod is embedded.
Kinetics of Chain Scission of Natural Rubber
Authors: Sambhi M. S.
Published: February 2011

The first-order and zero-order kinetic models of chain scission, based on random chain scission processes, are critically examined. It is likely that for many practical situations, the first-order chain scission kinetics can be represented by pseudozero-order kinetic types of equations. The kinetic results indicate that chain scission of NR occurs either by a pseudofirst-order or a pseudozero-order process. The pseudozero-order chain scission kinetics of NR are in consonance with the result that chain scission involves the bimolecular reaction of peroxy radicals in the termination step of the oxidation mechanism. However, this does not preclude unambiguously other chain scission reactions. The chain scission activation energy of NR is determined with the use of expressions derived for the oxidative degradation of NR as measured in terms of Wallace plasticities.
Semiempirical Relationships between Properties and Loading in Filled Elastomers
Authors: Pouchelon A. , Vondracek P.
Published: February 2011

The dynamic storage modulus of uncured silica-filled silicone rubber increases sharply when a critical filler loading is reached. A similar behavior has been observed for the conductivity in the same compounds. The experimental data fit a percolation law fairly well, and microscopy confirms the formation of a filler network according to the percolation model. This behavior depends on a polymer-filler interaction level, suggesting a filler network consisting of filler particles bridged together by adsorbed polymer. It has been found that the percolation threshold coincides with the optimum value of elongation at break of the corresponding vulcanizates. The percolation behavior and the relations between properties of filled rubbers described here were observed in various filled rubbers of quite different compositions. This seems to suggest the general validity of the presented relationships in all elastomers reinforced by particulate fillers.
Dynamic Electrical and Electromechanical Properties of Carbon-Black Loaded Rubber
Authors: Burton L. C. , Hwang K. , Zhang T.
Published: February 2011

1. Low-frequency resistance can be dominated by contacts. It was found that silver paint contacts were roughly equivalent to metal contacts bonded during vulcanization. 2. Three electrical regimes are clearly evident, determined by loading: dielectric, percolation, and conducting. 3. Resistance and dielectric constant dispersion for loading above 30 phr agree with Kawamoto's model. 4. Each carbon-black loading results in a distinctive dispersion signature. 5. Dynamic conductivity can be used to delineate persistent and transient carbon-black-structure changes versus composition, DSA, frequency, and potentially other parameters (temperature, stress waveform, etc.). 6. The remaining conductive network during stress is represented by gmin; Δg is determined by network fracture and reformation; gmin−gα is proportional to the amount of remaining transient structure; g0−gα is proportional to the total transient structure; normalized conductivity Z is the remaining-to-total transient-structure ratio. 7. The Δgm=0.525(g0−gα) relation indicates that maximum reformation occurs when approximately half the transient structure is broken down and confirms the correlation between conductivity parameters and transient carbon-black structure.
Solid-State Carbon-13 NMR Studies of Vulcanized Elastomers. VII. Sulfur-Vulcanized Cis-1,4 Polybutadiene at 75.5 Mhz
Authors: Clough R. S. , Koenig J. L.
Published: February 2011

Solid-state C-13 NMR spectroscopy provides a wealth of chemical information concerning sulfur-vulcanized cis-l,4-polybutadiene. New resonances which appear upon curing have chemical shifts which are expected for crosslink and cyclic structures. The DEPT experiment with MAS worked well for the polybutadiene vulcanizate in the solid state. DEPT is very useful as an aid in the assignment of structures to resonances. The new resonances can be assigned to more than one type of structure given only chemical shift and DEPT information. Swelling measurements indicate the majority of the resonances are due to cyclics. Further work involving C-13 NMR characterization of polybutadiene vulcanizates treated with chemical probes and vulcanizates cured with organic accelerators should provide insight into the specific structures responsible for the individual resonances.
Viscoelastic Simulation of Flow of Rubber Compounds
Authors: Sobhanie M. , Isayev A. I.
Published: February 2011

A hybrid scheme has been developed for numerical simulation of a nonisothermal viscoelastic flow in an arbitrary planar geometry of uniform thickness during extrusion and injection molding. This formulation is based on the control-volume finite-element method for solution of the continuity and momentum equations and finite difference method for solution of the energy equation. Application of this numerical technique for simulation of an extrusion and injection molding process was performed in a slit die and a quarter of a circular disk cavity, respectively. Development of pressures, shear and normal stresses, velocities, and temperature fields were calculated during nonisothermal flow of the rubber compound. Furthermore, the relaxation of stresses was calculated after cessation of the flow. The location of the meltfront was predicted during the cavity filling process. The contribution of normal stresses was studied by comparing results following from the viscoelastic and inelastic simulations.
Resistance of Polymers to Permeation by Air Conditioning Refrigerants and Water
Authors: Trexler Harold E.
Published: February 2011

The permeability of several polymers to refrigerants and to water vapor has been determined. The investigation included refrigerant R-12 which is currently used in automotive air conditioning and refrigerants R-22 and R-134A which are considered as future candidates. For the different polymers investigated, the permeability constants for R-22 at 93°C ranged between 0 and cm/11×10−10 cm2 sec cm2  cm Hg for the plastics, 29×10−10 and 124×10−10 for thermoplastic elastomers and 135×10−10 and 276×10−10 for crosslinked elastomers. The permeability decreased with decrease in test temperature and with increase in molecular size of the refrigerants. Hence both R-12 and R-134A exhibited lower permeability constants than R-22 because of their bigger size. Trends in water permeability of the different polymers were mostly opposite to those of the refrigerant permeability. For example, polynorbornene has the lowest water permeability of the polymers tested, but has one of the highest permeability constants for refrigerants. Of the new polymers investigated, the lowest overall permeability to water and refrigerants was exhibited by PET polyester, polypropylene, Hytrel polyester, and plasticized Polyamide 12 (5% plasticizer).
Swelling of Fluoroelastomers in Synthetic Lubricants
Authors: Neppel A. , Kuzenko M. V. , Guttenberger J.
Published: February 2011

Viton A elastomers of variable crosslink density show high swelling in a diester-based lubricant only after heat aging, e.g., at 175°C for three days. Volume increase data in methylethyl ketone and 100% modulus reveal that heat aging induces considerable decrosslinking. Swelling tests in pure diesters and the corresponding Flory-Huggins interaction factors indicate a sharp decrease in the entropy term (of the Hildebrand-Scott equation) of some of the interaction factors upon heat aging. High swelling seems to occur only if the size of the liquid molecules does not exceed a limit since otherwise their diffusion into the elastomer network is hindered. Such a hindrance may be attributed to a large entropy term. Heat aging appears to increase the above limit to molecular size thus diminishing the entropy term and permitting large amounts of swelling even in certain of those liquids whose diffusion into the network was hindered before heat aging.
Elastomer-Gasoline Blends Interactions I. Effects of Methanol-Gasoline Mixtures on Elastomers
Authors: Abu-Isa Ismat A.
Published: February 2011

1. Properties of most fuel resistant elastomers are degraded to a larger extent by mixtures of methanol and gasoline than by the pure components. 2. The data on all elastomers except the fluorocarbon can be explained in terms of the solubility parameter concept. 3. The ultimate tensile strength and ultimate elongation of swelled elastomer networks are quantitatively related to volume swell by simple linear relationships. 4. Ultimate stress and ultimate elongation of swelled elastomer networks obey equilibrium stress-strain relationships.
Elastomer—Gasoline Blends Interactions II. Effects of Ethanol/Gasoline and Methyl-t-Butyl Ether/Gasoline Mixtures on Elastomers
Authors: Abu-Isa Ismat A.
Published: February 2011

The effects of ethanol/gasoline and MTBE/gasoline mixtures on swell and tensile properties of selected automotive elastomers were determined and compared to those of methanol/gasoline mixtures. Two gasolines with aromatic content of 30% and 50% were used in this investigation. Equilibrium swell and tensile measurements were conducted using ASTM standard procedures. Results show that in the case of ethanol/gasoline combinations, the elastomers were more severely affected by the mixtures than by the pure components. The ethanol/gasoline mixtures are less severe than the methanol/gasoline mixtures in their effects on most fuel resistant elastomers. In the case of MTBE, effects of mixtures with gasoline were an average of the effects of the pure components. The presence of a higher aromatic content in the gasoline resulted in increased swell and, hence, increased deterioration of tensile properties of elastomers exposed to the gasoline and its mixtures. Addition of benzene to increase the aromatic content resulted in slightly more detrimental effects on nitrile elastomers than the addition of toluene. The data on all elastomers can be explained in terms of the solubility parameter concept. For most elastomers, the ultimate tensile and elongation values were found to be quantitatively related by simple linear equations to the volume fraction of the rubber swelled in mixtures of gasoline and ethanol or MTBE. They were also found to be related to each other by simple logarithmic relationships.
Tear Strength of Elastomers under Threshold Conditions
Authors: Bhowmick A. K. , Gent A. N. , Pulford C. T. R.
Published: February 2011

Measurements have been made of the tear strength of several elastomeric materials under threshold conditions, e.g., in the swollen state and at high temperatures when dissipative contributions to the work of fracture are minimized. The materials studied were Neoprene WRT, BR, SBR, EPDM, and a castable polysulfide material, LP-32. They were crosslinked to different degrees, using a free-radical source, or sulfur, or a metal oxide as the crosslinking reagent. Values obtained for the threshold tear strength were similar in all cases, lying in the range 50–200 J/m2. They appeared to be approximately proportional to E−1/2, where E is the tensile (Young's) modulus of the elastomer, as predicted by the theoretical treatment of Lake and Thomas. Values for networks with polysulfidic crosslinks were significantly higher than with monosulfide or C—C crosslinks, by about a factor of 2. Values for carbon black-filled materials were higher also, by about the same factor, in comparison with the equivalent unfilled materials. These effects are attributed to rupture of labile crosslinks, or bonds to carbon black, prior to main-chain rupture.
Resistivity and Surface Roughness Analyses for Evaluating Carbon Black Dispersion in Rubber
Authors: Cembrola R. J.
Published: February 2011

A comparison of the three techniques shows that while all can discriminate dispersions, their useful ranges are different. The electrical resistivity method is relatively insensitive at the early stages of mixing but has a high sensitivity at the intermediate and latter stages. This method is directly influenced by the dispersed black. There are limitations, however, to its utilization. The method works only within a narrow range of volume loadings (35–75 phr) and can only be used for small and intermediate particle size carbon blacks. One advantage that the resistivity technique has is that uncured rubber is tested. Elimination of the vulcanization step makes the resistivity technique an attractive quality control test. The Phillips rating and surface roughness are not limited by the volume loading of filler or the nature of the filler. Each technique works quite well at intermediate dispersions and only loses sensitivity at very good dispersions. These methods differ from the resistivity in that they are sensitive to the undispersed filler. The surface analysis is a more objective and quantitative technique than the Phillips rating. The surface analysis technique can have a microcomputer interfaced to store data and calculate results. This reduces the test time to a matter of minutes. The Phillips dispersion rating is made on vulcanized rubber so that there is added sample preparation which leads to a longer analysis time. The surface analysis has been reported for both vulcanized and unvulcanized rubber; however, the unvulcanized samples present special problems in cutting and do not show as strong a correlation with other dispersion ratings.
Stress Relaxation Measurement as a High-Speed Method for Predicting the Long-Term Behavior of Vulcanized Rubber
Authors: Clamroth R. , Ruetz L.
Published: February 2011

Intermittent stress relaxation is well suited for quantifying aging processes in rubber. For NR, the effects of different antioxidants can be measured by the rates at which the modulus falls. In synthetic rubbers (SBR, NBR, and CR), it can be measured through the modulus increases caused by oxygen crosslinking. Equal-value times, e.g., t0.75 for NR and t1.25 for SBR, NBR, and CR, are the times taken by the modulus to decrease or increase to a given percentage of its original level. They are better measures of aging than the modulus change after a given time. For NR, it has been shown that stress relaxation measurements at elevated temperatures and in pure oxygen correlate with the results of conventional aging methods. Thus the testing times can be drastically reduced—from up to 28 days to 1–8 hours. Discontinuous stress relaxation measurements are considerably more accurate and selective than conventional oxygen aging. For the repeatability of a single equal-value time measurement, we obtained a coefficient of variation (s/x) of 5–10% for stress relaxation measurement and about ±20% for oxygen aging. The degree of selectivity for oxygen aging and stress relaxation was found to be 3.6 and 18, respectively. The correlation between the results of stress relaxation measurements and those of the conventional oxygen and hot air aging tests was investigated for a large number of NR compounds and for some SBR, NBR, and CR compounds. The correlation is not very good, but it must be remembered that the equal-value times determined according to the two methods show relatively pronounced variability. With the conventional aging methods, the results also depend on what quantity is measured, e.g., the change in tensile strength or hardness, and on what equal-value time is chosen, e.g., the time taken by the property concerned to decrease to 90 or 75% of its original value. The conclusion of the investigations described above is that intermittent modulus measurement is an interesting high-speed method for the assessment of aging behavior. It will acquire a firm position in the arsenal of rubber testing methods, but will probably supplement, and not completely replace, the aging methods currently used.
Prediction of Hysteresis Properties from Reticulation Studies of Carbon Black Suspensions in Mineral Oil
Authors: Sircar A. K. , Wells J. L.
Published: February 2011

1. A linear log-log relationship was observed both for specific conductivity-time and viscosity-shear rate of carbon black suspensions in liquid vehicles. The slope, n, is related to the rate of recombination of carbon black aggregates, while the intercept (ρ0) is a measure of specific conductivity of carbon blacks after one minute recombination. 2. The reformation rate index, n, varies inversely with the surface area of the blacks. 3. The hysteresis relationship for suspensions (ρ0×1/n), correlates with hysteresis properties in a solid rubber. 4. Thus, hysteresis properties of black loaded elastomers can be predicted from reticulation studies of carbon black suspensions in liquid vehicles.
Innovation in Flame and Heat Resistant EPDM Formulations
Authors: Kato H. , Adachi H. , Fujita H.
Published: February 2011

A series of experiments on the flammability of EPDM formulations which contained a minimum amount (30 phr) of aromatic organic flame retardant (DBDO) revealed that increasing the crosslink density increased the flame resistance. This was especially true when the formulations were cured by a combination of DCP, TAIC, and HVA-2. The best result was obtained in a formulation which was cured by DCP/TAIC/HVA-2 at 2.5/1.0/0.5 phr, respectively. This material had excellent physical properties that would be well suited for use in the wire and cable industry. It was also found that good dispersion of individual ingredients was needed to obtain optimum flame resistance.
Theory of the Elastic Net Applied to Cord-Rubber Composites
Authors: Clark Samuel K.
Published: February 2011

There has been considerable interest over the last twenty years in the subject of the elastic properties of cord-rubber composites. This has been due to the rather intensive study of composite material characteristics, brought about by the increased use of rigid composites in many structural applications. In addition, work on the prediction of cord rubber composite properties has also continued because of the active development of finite element programs for analysis of pneumatic tire properties. These finite element programs require a thorough knowledge of cord-rubber composite elastic characteristics, which in turn are found to be considerably more difficult to calculate than had been originally thought. The present paper introduces a simplified theory for the prediction of such properties with sufficient accuracy for engineering uses.
The Effects of Carbon Black and Other Compounding Variables on Tire Rolling Resistance and Traction
Authors: Hess W. M. , Klamp W. K.
Published: February 2011

The rolling resistance of SBR/BR radial passenger tire treads was varied as a function of carbon black type and loading, as well as other compounding variables, such as oil content, high-viscosity oil and resin addition, and NR substitution. In all instances, the rolling loss variations showed a good correlation with either tan δ or resilience. The tan δ response was valid for a wide range of test temperatures, frequencies, and strain amplitudes. Wet (32 km/h) and dry (64 km/h) traction indicated a high positive correlation with loss compliance (D″). Here, the best correlations were obtained at lower dynamic testing temperatures (0–25°C.) and higher strain amplitudes. High-speed wet traction (97 km/h) appeared to be relatively independent of the tread compounding variables but did show a slight correlation with tan δ measured at ™25°C. The following patterns were observed relative to tread rolling resistance, traction, and wear as a function of compounding variables: 1. Black loading.—Reduced black loading lowers rolling resistance without much effect on traction. About 4% less black in the tread compound lowers rolling resistance by about 5–6% in the formulations which were evaluated. 2. Oil loading.—At a fixed black level, increased oil raises both rolling resistance and traction. About 2% higher rolling resistance was found for a 10 phr increase in oil loading, but the effect on wet traction appeared to be much greater (7–8%). 3. Black type.—Increasing black fineness raises both rolling resistance and traction, the latter effect being considerably less. Increased DBPA has very little effect on rolling resistance but reduces traction. At reduced black loadings, the finer and higher DBPA blacks show the least loss in treadwear resistance. Blacks with broad aggregate size distribution give lower rolling resistance at the same surface area and DBPA. For extreme blends (carcass and tread grades), however, the loss in treadwear resistance is quite severe (∼30%). 4. Curatives.—Increased sulfur and accelerator levels produced a significant reduction in tan δ, with a similar but lesser drop in D″. The same reduction in tan δ with increased accelerator (OBTS) level produced less effect on D″ than the sulfur increase. 5. Natural rubber substitution.—Compounds in which 30 phr of NR were substituted for 25 phr of SBR and 5 phr of BR indicated slightly better performance in terms of both rolling resistance and traction. 6. High-viscosity oil or resin substitution.—Replacing conventional extender oil with high-viscosity oil or resin appears to improve traction but has a greater adverse effect on rolling resistance. 7. Compound optimization.—N299 black gives the best overall balance of performance in terms of rolling resistance, traction, and treadwear at reduced black loadings. N121 confers about 10% better treadwear and equal traction in the same compound, but at about 4% higher rolling resistance.
The Use of a Screening Test for Assessing the Hydrogen Sulfide Resistance of Elastomers
Authors: Pfisterer H. A. , Dunn J. R. , Vukov R.
Published: February 2011

A screening test has been devised which in 24 h exposure at 200°C to a gas mixture containing 32.7 ± 0.7% hydrogen sulfide at 1.725 pressure can distinguish the hydrogen sulfide resistance of a variety of vulcanizates. As expected, fluoroelastomer vulcanizates exhibited the best retention of properties, but carboxylated NBR was also surprisingly stable, especially in modulus retention. The most important variable in regular NBR vulcanizates was the acrylonitrile content. Stability in presence of hydrogen sulfide increased with decreasing acrylonitrile level. The effect of acrylonitrile level has been rationalized by the observation that hydrogen sulfide reacts with nitrile groups to form thioamide, which subsequently enters into crosslinking reactions. The reaction of hydrogen sulfide with double bonds does not result in crosslinking.
Present Status and Future Trends of Specialty Polymers for Automotive Hose in Japan
Authors: Inagami Masaaki , Saito Yoshiomi , Hashimoto Kinro
Published: February 2011

In Japan, official specifications covering automotive devices do not specify the polymer(s) to be used. Accordingly, we have reviewed the market trend of polymer usage for various hoses in these devices, and through a review of published papers, indicated polymer usage reported or suggested in them. As the development of automotive parts requiring higher endurance and reliability has been greatly emphasized in Japan, we, a specialty polymer supplier, have expended our best efforts to comply with such requirements.
Calculation of the Temperature and Extent of Reaction during the Vulcanization of Powdered Rubber
Authors: Accetta A. , Vergnaud J. M.
Published: February 2011

Although vulcanization is a complex series of reactions, the overall result for heat of reaction could be described by an Arrhenius equation and a single activation energy. The activation energy for the vulcanization of powdered rubber recovered from tires was about 106 kJ/mole and the rate of reaction was described by a first-order reaction. With the kinetic parameters determined for the curing reaction by DC, the temperature profiles in rubber sheets were calculated. A numerical method of Dusinberre's generalization was an explicit incremental method applied to one-dimensional conduction and took into account the internal generation of heat due to the cure reaction and the heat transfer through the mold-rubber interface. The last problem was resolved by considering the fact that there was the same heat transfer rate on each part of the interface. This method proved to be as accurate as the implicit Grank Nicholson method, and its great advantage over the latter was that this explicit method needed only a small and inexpensive computer. Experiments pointed out the effect of several parameters on temperature profiles and midplane temperature for rubber sheets. Thus, the sheet thickness, mold temperature, initial rubber temperature, and a single two-step programming of mold temperature were considered. Some importance was given to possible applications. The determination of the time necessary for the midplane temperature to reach particular values such as the mold temperature or its maximum value. It is worth mentioning that our method allowed us to correlate the extent of reaction with the time and, therefore, to predict the time necessary for the extent of the reaction to reach a suitable value with a specified quality of vulcanizate for given operating conditions.
Studies of Vulcanization of Reclaimed Rubber
Authors: Phadke A. A. , Bhattacharya A. K. , Chakraborty S. K. , De S. K.
Published: February 2011

Rubber vulcanizates can be reclaimed by milling them with curing ingredients. Physical properties of the RR vulcanizates are inferior to those of the control vulcanizate. RR compounds exhibit poor processing characteristics. Poor physical properties and processing characteristics can be improved by blending with fresh rubber. However, a higher proportion of RR increases the stiffness and causes brittle failure.
Bulk Polymerization Kinetics by the Adiabatic Reactor Method
Authors: Camargo R. E. , Gonzalez V. M. , Macosko C. W. , Tirrell M.
Published: February 2011

We have shown that the adiabatic reactor method (A.R.M.) is useful to measure bulk polymerization kinetics. The choice of an adequate model is fundamental to represent the kinetics and for use in modeling and processing applications. The definitions of differential and integral errors have been introduced. It has been shown that these definitions lead to different objective functions and minimization problems. With an adequate model, we must be able to find a single set of parameters to minimize both errors simultaneously. We have shown that the n-th order and autocatalytic models are particular cases of a generalized phenomenological model. We continue to study this technique and to develop new forms of estimation. Dynamic models for complex situations which may include heat losses and intermediate species are now under development, and we expect to present them in a forthcoming publication.