bluuebunny/crossref_metadata_2025 huggingface dataset:
NBR Vulcanizates Resistant to High Temperature and “Sour” Gasoline
Authors: Dunn J. R. , Pfisterer H. A. , Ridland J. J.
Published: February 2011

NBR compounded in a conventional fuel hose tube formulation is markedly degraded by “sour” gasoline or “sour” ASTM Fuel C within 7 days at 40°C. Furthermore, the conventional NBR compound is not resistant to aging at 125°C. Use of an NBR designed for heat resistant compounding and an appropriate choice of compound greatly improve resistance to fuel which contains hydroperoxides. The preferred system for “sour” gasoline resistance and resistance to long term aging at 125°C is a cadmium oxide activated low sulfur-sulfur donor compound with silica as the principal filler. This vulcanizate is not much more affected after 7 days at 40°C by gasoline of peroxide number 50 than by clean gasoline, and is less affected by gasoline of peroxide number 200 than are other NBR vulcanizates. The balance of high and low temperature properties can be optimized by appropriate choice of plasticizer and acrylonitrile level. Aging resistance is somewhat improved by increase in acrylonitrile content, and fuel permeability is markedly decreased. Permeability to gasoline with 30 aromatic content can be changed appreciably by compounding, but the resistance to Fuel C with 50% aromatic content does not appear to respond to compounding changes. The stability of NBR vulcanizates in “sour” gasoline is reduced by copper salts and, to a lesser extent, by metallic copper. Bound antioxidant NBR does not appear to offer an advantage in “sour” gasoline resistance over heat resistant NBR compounded in a comparable formulation.
Ethylene Propylene Rubber Telephone Drop Wire
Authors: Gabriel A. P.
Published: February 2011

Initially the development of a third distinct variety of telephone drop wire was undertaken to combine the complexities of the reinforced neoprene array with the simplicities of a PVC drop wire construction. In addition, at no time could the excellent properties be sacrificed for manufacturing convenience. In the final analysis, however, the resultant EPDM insulated drop wire, yielded characteristics which placed it above the other constructions in the market. Since its introduction, about 100 million feet have been installed under a myriad of installation and service conditions within the United States.
Fundamental Aspects of Rubber Adhesion to Brass-Plated Steel Tire Cords
Authors: Ooij W. J. Van
Published: February 2011

During the past several years the fundamental knowledge of the processes which lead to rubber-brass bond formation and to bond degradation has increased considerably. As a result of the application of new instrumental techniques to the study of the rubber-brass interface it has been established that the brass surface is chemically attacked under formation of CuxS, ZnS, and ZnO. These products become an integral part of the rubber-to-metal bond. It has unequivocally been demonstrated that excessive or insufficient formation both lead to a low rubber-brass bond strength. The theories put forward by Buchan in the early forties (culminating in the only monograph on the subject thus far) have thus been proven to be largely correct. The rubber-brass bond can be interpreted as an adhesion of sulfur crosslinks to a sulfidized brass surface. These crosslinks are not necessarily bonded to the surface by fully developed “chemical” bonds, but should rather be interpreted as covalent bonds, comparable to those formed by copper oxide or copper sulfide and various organic complexing molecules containing electron-donating nitrogen or sulfur atoms. In spite of the relatively weak bonds between sulfur crosslinks and sulfidized brass surfaces, the adhesion between rubber and brass exceeds the rubber tear strength, since there is a very intimate contact between rubber and sulfide film which actually grows into the polymer. As a result, the contact area of the two phases is significantly enlarged. There is evidence that only certain types of crosslinks, probably the poly-sulfides, give rise to a high bond strength, possibly because of steric reasons. Best results have been obtained if the brass surface consist completely of cuprous sulfide, although there is evidence that a zinc sulfide surface can also be bonded well, provided the growth of the zinc sulfide layer is high enough to provide a sufficient number of points of attachment to the polysulfide crosslinks.
Chemistry and Structure of Natural Rubbers
Authors: Hager T. , MacArthur A. , McIntyre D. , Seeger R.
Published: February 2011

Natural rubbers are synthesized in thousands of species covering most plant families; moreover, rubber has been obtained commercially from over a dozen of them. A later report has suggested that polyisoprene formation is limited to dicotyledonous angiosperms. In recent years there has been renewed interest in developing alternative sources of natural rubber, different from Hevea brasiliensis. In particular there has been considerable development of guayule as a source of natural rubber. As a result there is a considerable body of recent results, using new techniques and extending older work concluded in the 1950's, which give new insight into the production of rubber in plants. This paper will mainly deal with guayule because it can ideally serve as a background for understanding the production of rubbers in other plants, including hevea. First, it is necessary to describe the physical nature of the rubber from guayule and where in the plant it is formed. Figure 1 shows a cross-section of a stem of guayule. The individual cells (parenchyma cells) are the site of rubber manufacture. The rubber can finally be seen as the small latex droplets inside a single cell (Figure 2). Thus the study of the natural rubber in guayule involves the isolation of the latex particles from the cell. It is extremely easy to separate an industrial rubber from other parts of the plant, including resin, by either laboratory or pilot plant methods. However, it is more difficult to get fresh latex in which no additional particle coagulation has occurred. The description of the average latex particle size and the distribution of sizes has been made and is needed to discuss the biosynthesis of rubber. It will not be discussed further. The question addressed in this paper is the chemical structure of the rubber in the plants—the micro-structure of the rubber, the molecular weight distribution, and the branching or gel content. Guayule natural rubber has the remarkable feature of containing no gel when taken directly from a fresh plant and carefully handled in the laboratory. Even the material from the pilot plant extraction process contains only 1–3 per cent gel. This paper describes extensively the chemical structure of natural rubber extracted from fresh guayule plants. Less extensive measurements on chicle, gutta-percha, and castilla elastica are also reported. Finally, all of the data are analyzed to determine if a model of rubber production can be formulated to encompass all of the above plants. Earlier, a model was proposed for guayule only. In this model the polyisoprene chain is polymerized on the polymerase enzyme site by recurring attachment and intermittent polymerization until the rubber droplet (containing a single polymer chain) can no longer be stabilized or further polymerized by the enzyme.
Short Fiber Reinforced Hose—A New Concept in Production and Performance
Authors: Goettler L. A. , Leib R. I. , Lambright A. J.
Published: February 2011

A simple extrusion process has been developed to orient short fibers contained in a rubber stock into a transverse position on the extrudate. The hardware is no more complex or difficult to use in production than conventional hose dies, which always produce a fiber orientation parallel to the flow. This axial orientation is not useful for many products, particularly hose, whereas the system described in this paper provides the proper circumferential orientation to meet the higher hoop stress. The fiber orientation occurs in response to changes in the shape of the channel in the die. In comparison to conventional cord-reinforced hose, the short fiber system offers many advantages. Processing is simplified by the elimination of the braiding or knitting step and the cover extrusion. The short fiber process is well adapted to continuous cure. Manufacturing costs are estimated to be 12% lower than those for the same process route using a conventional hose construction. Moreover, the short fiber hose can meet performance specifications in most low-to-intermediate pressure applications. It is a unique and functional product.
Flammability Properties of Carpets with Polychloroprene Latex Foam Underlayments
Authors: Anolick C. , Cook G. S. , Stewart C. W.
Published: February 2011

The flammability properties of a carpet underlayment system are dependent on all the components of the system. Most important is the choice of carpet fiber and construction. Large differences in results were seen between the various carpets tested. Once the carpet construction is chosen—and this is most often done for reasons of aesthetics, comfort and wear—the fiammability properties are influenced by the the foam pad or underlayment and by the carpet anchor coat. In all cases tested the use of a foam pad decreases the critical radiant flux of the carpet system as measured by the Flooring Radiant Panel Test. The decrease in critical flux is much less severe for foam pads based on polychloroprene latices than for those based on SBR. This is even true where hydrated alumina filler is incorporated in the SBR foam formulation. From this it is concluded that a carpet with a polychloroprene pad is likely to contribute less to the spread of fire than the same carpet with an SBR pad. Other workers have found polyurethane pads to be equivalent to SBR pads. For the optimum flammability properties, foam density and thickness should be held as low as possible. All results are equivalent whether the pad is attached or separate from the carpet. Where a foam pad is to be installed it is important that hydrated alumina filler be incorporated in the latex anchor coat used to lock the pile in place. It is concluded that where a designer requires a certain level of flammability as measured by the Flooring Radiant Panel Test, the broadest range of carpets can be used if hydrated alumina is included in the anchor coat and if the foam pad is based on polychloroprene latex. Foam pads based on this latex also give excellent results in other flammability and smoke tests as well as excellent physical properties.
Studies of Rubber Abrasion
Authors: Southern E. , Thomas A. G.
Published: February 2011

The general model proposed, which assumes that crack growth plays an important part in the abrasion process when abrasion patterns are produced, is supported by evidence from the behavior of noncrystallizing rubbers. In particular, the rate of movement of the pattern across the surface is closely related to the crack growth behavior. Natural rubber behaves under abrasion conditions as if it were prevented from exhibiting its usual crystallization-enhanced strength. An important factor determining the abrasion rate, in addition to the crack growth behavior, is the angle at which the hypothetical cracks at the pattern base grow. What determines this angle is not yet clear, but it appears to be closely related to the geometry of the pattern, and it seems likely, from a study of this geometry, that much of the loss of rubber occurs from the steeply raked face of the pattern. The pattern spacing, as well as depending on the abrading force, also appears to be influenced by the test temperature and the glass transition temperature of the rubber, suggesting that viscoelastic considerations are important.
EDGE Effect Correction for the Mooney Rheometer
Authors: Nakajima N. , Hareell E. R.
Published: February 2011

The Mooney rheometer has been used universally as a tester for quality control of raw elastomers and compounds. White and Tokita showed that the tester modified to operate at a range of speeds could be used to obtain fundamental viscoelastic properties: steady-state shear stress-shear rate relationship, normal stress effect, and elastic recoil. We have also made effective use of this rheometer to obtain steady-state viscosity as a function of shear rate and complex viscosity as a function of deformation rate. In these investigations, the observed torque was converted to shear stress with a theoretical factor derived by taking into account both the parallel plate section and the concentric cylinder section. It was assumed that the edge effect was negligible. The viscosities calculated in this manner were compared to those obtained with other instruments and reasonably good agreement was obtained. Some time ago, Mooney and Treloar expressed the opinion that the viscosity obtained from the Mooney rheometer is somewhat larger than the correct value, attributing the disagreement to neglect of the edge effect. More recently, White and Tokita have restated the problem. In our recent work, the torque measurements were made with both the small and the large rotor. The viscosities calculated without considering the edge effect tended to be somewhat higher for the small rotor than for the large rotor. This observation implies that an edge effect exists, because measurements obtained with the small rotor, which has larger “edge volume”, would tend to be more significantly affected. In this paper a mathematical expression is sought for the edge correction, so that the correction factor may be calculated from the known properties of the material.
Wax Protection
Authors: Dimauro P. J. , Paris H. L. , Fath M. A.
Published: February 2011

Wax migrates from the bulk of a rubber article to its surface to form a physical barrier to ozone attack. The extent of migration depends upon the solubility/mobility characteristics of the specific wax under a given set of environmental conditions. Factors which influence migration include time and temperature of storage after cure, wax concentration, wax composition, and amount and type of filler and extender oil present. This makes it difficult to select a wax which performs effectively over a broad temperature range. Paraffinic waxes generally protect better at low exposure temperatures, while microcrystalline waxes are more effective at elevated temperatures. Wax blends offer a wider temperature range of protection. An optimum migration temperature exists for each wax, and DTA can predict this optimum. Best ozone resistance is also attained at the temperature corresponding to optimum wax migration. Under dynamic ozone conditions, waxes alone can be harmful. Addition of a chemical antidegradant is required to obtain protection under these conditions.
Structure-Property Relationships in One-Step Urea-Urethan Elastomers
Authors: Rausch K. W. , Martel R. F. , Sayigh A. A. R.
Published: February 2011

A series of one-step urea-urethan cast elastomers has been prepared employing various diisocyanates with 3,3′-dichloro-4,4′-diaminodiphenylmethane and 3,3′-dichlorobenzidine. The effects of diisocyanate structure are not as pronounced as those previously reported for prepolymer systems. Significant variation in stress-strain properties may be obtained, however, depending on the molecular weight and the backbone structure of the polyglycol. A complex catalyst situation, arising from differences in reactivity of the diisocyanates, may also affect these properties considerably as a result of improper balance of reactions during chain buildup. The use of a newly available diisocyanate, “mixed isomer” MDI, which affords high strength elastomers while eliminating safety hazards and cumbersome handling techniques, is also described.
Effect of Intracarcass Pressure Buildup on Tubeless Tire Performance
Authors: Banks S. A. , Brzenk F. , Rae J. A. , Hwa C. S.
Published: February 2011

Intracarcass pressure buildup is generally considered to contribute significantly to separation failures in tubeless tires. This study demonstrates the effect of internal pressure in the cord area on the durability of two-ply rayon tubeless tires. A practical mathematical model has been developed to describe the mechanism of intracarcass pressure build-up and to indicate the effect of liner properties (i.e., permeability and thickness) on this pressure. Liner permeability, thickness and heat resistance have all been shown to be dominant factors in the minimization of pressure buildup in the carcass plies of tubeless tires. In addition, the buildup of air pressure in tire cords has been shown by wheel durability tests to exert a significant influence on the service life and nature of failure of these tires.
Determination of the Surface Tension of Latex
Authors: Aupetit André
Published: February 2011

After describing the Dognon-Abribat tensiometer exclusively used for measurements, the authors compare the two methods—plate and ring—used as a rule to determine the surface tension of latex. The plate method is simple and accurate, gives consistent results and allows both dynamic and static measurements. Differences between the two procedures are slight.
Infrared Studies of the Rubber-Filler System. I. Infrared Absorption Spectra of Inorganic Fillers
Authors: Suito E. , Arakawa M.
Published: February 2011

Infrared spectra of 33 kinds of commercial reinforcing fillers were measured by use of the KBr pellet method in connection with studies of the filler effect in rubber-filler systems. Characteristic absorptions of individual fillers are discussed in relation to their method of preparation.
A Study of Stress Relaxation with Finite Strain
Authors: Bernstein B. , Kearsley E. A. , Zapas L. J.
Published: February 2011

Two simple types of constitutive equations appropriate to materials exhibiting viscoelasticity are presented, one of a basic solid nature and one of a basic fluid nature. The predictions of the equations for a stress relaxation experiment are worked out and compared to the data from some experiments on various elastomers. The fluid theory is shown to be most appropriate in a certain sense.
New Techniques for Radiation Vulcanization
Authors: Bennett J. V. , Pearson R. W. , Mills I. G.
Published: February 2011

Vulcanizates with satisfactory physical properties can be obtained using substantially smaller radiation doses than has formerly been thought necessary.
Polyisobutene Degradation in Laminar Flow: Composition and Shear Variables
Authors: Portes Roger S. , Johnson Julian F.
Published: February 2011

Mechanical degradation of polyisobutene solutions in laminar flow under known shear stress conditions was performed in a thin-film, high-shear, rotational viscometer. Polyisobutenes with molecular weights from 40000 to over a million were studied at several temperatures and concentrations in n-hexadecane. Reduced variables, of a form similar to those used in studies of temporary viscosity losses, can be used successfully to correlate permanent viscosity losses due to degradation. The variables which superimpose are stress, temperature, and concentration. The range in which reduced variables apply corresponds to concentrations and molecular weights where degradation is commonly observed and to the region where polymer entanglements exist.
Dilatometric Measurement of a Transition of Cis-1,4-Polybutadiene
Authors: Pedemonte E. , Bianchi U.
Published: February 2011

Results of dilatometric measurements on three polybutadiene samples with various cis-1,4 contents are reported. In every case a transition is observed; the transition temperature increases with cis-1,4 content.
Effect of Extraction and Rubber Purity on Stress Relaxation of Cumyl Peroxide Vulcanizates
Authors: Dunn J. R.
Published: February 2011

Oxidative stress relaxation of peroxide vulcanizates of various grades of natural rubber has been investigated at 100° C. The rubbers were examined both with and without hot acetone extraction before or after cure. Highly purified rubber vulcanizates exhibited autocatalytic relaxation, but those based on crepe or smoked sheet did not, because they retained natural antioxidant even after extraction. Autocatalysis was no longer found in extracted purified rubber vulcanizates if these were prepared from a mix containing phenyl-β-naphthylamine. The antioxidant reduced network scission but had less effect upon the amount of crosslinking taking place during aging.
Study of Carbon Black Structures in Rubber
Authors: Payne A. R.
Published: February 2011

The effect of carbon-black structures in rubber were studied using dynamic testing techniques. The aspects studied were the effects of the degree of vulcanization and the degree of dispersion on dynamic modulus and loss. Relationships were established between electrical conductivity and dynamic modulus, and between the maximum dynamic viscosity and the carbon-black modulus changes on oscillation. Finally, use was made of carbon-black/paraffin-oil mixtures as model materials in order to explain the effect of carbon-black structures on the modulus enhancement of carbon-black-loaded vulcanizates.
Relevance of Elastic and Loss Moduli of Tire Components to Tire Energy Losses
Authors: Collins J. M. , Jackson W. L. , Oubridge P. S.
Published: February 2011

This study of energy losses in tires was undertaken to obtain a better understanding of the contributions of tire components, and to relate them more precisely to laboratory measured dynamic properties. Details are given of a general method of analysing total tire energy losses into components due to the tread, sidewall, textile and carcass rubber. The method entails measuring the losses, as determined by rolling resistance experiments, of tires in which the composition of the components has been varied systematically. The results have been correlated to the dynamic properties of the tire components, and the tire parameters, deflection and inflation pressure. The method has been applied to two extreme sizes of tires, 9.00–20 and 2.25–8. The work described in this paper will enable the tire designer and rubber and textile technologist, to predict with greater certainty the effects on tire energy losses of any changes in tire materials and will also give them more guidance in formulating these changes.
Influence of Regeneration of Reduced Triphosphopyridine Nucleotide (TPN) on Formation of cis-Polyisoprene in Hevea Brasiliensis
Authors: Ribaillier Daniel , Cuong Tuong Chi , Fournier Paul
Published: February 2011

Hevea brasiliensis latex can use glucose-6-phosphate to produce triphospho-pyridine nucleotide and adenosine triphosphate. Conversion of sodium acetate and mevalonic acid depends on the presence of these cofactors.
Behavior of cis-Polybutadiene during Mastication
Authors: Kraus Gerard , Rollmann K. W.
Published: February 2011

Cold mastication of natural rubber in presence of oxygen leads to scission by a shear mechanism with subsequent stabilization of the free radicals by oxygen, while at high temperatures oxidative scission becomes the dominant mechanism. Studies of the behavior of cis-polybutadiene reveal that similar reactions are effective, but occur at much reduced rates. Shear degradation is particularly difficult to achieve in typical cis-polybutadienes. This is related to the molecular weight distribution of these polymers which usually lack the very high molecular species most subject to shear-induced degradation, in agreement with the theory of F. Bueche. It is shown that when such a high molecular weight fraction is supplied, shear breakdown may be realized. All cis-polybutadienes undergo oxidative breakdown at high temperatures, the scission rate becoming appreciable above 140° C. A number of oxidation catalysts have been found which markedly increase the scission rate without leading to a correspondingly large increase in crosslinking. Significant improvements in processing may be realized in this manner.
Nuclear Magnetic Resonance Studies of Molecular Motion in Some Elastomers
Authors: Slichter W. P. , Davis D. D.
Published: February 2011

The nuclear magnetic resonance (NMR) relaxation has been studied in polyisobutylene and polybutadiene at temperatures from −175° to +200° C and at three resonance frequencies: 20, 30, and 50 Mc/sec. In polyisobutylene, the spin-lattice relaxation time (T1) passes through two minima with change in temperature. The low-temperature minimum is ascribed, as in other compounds, to methyl-group rotation, but in polyisobutylene this motion is found to encounter relatively large hindrance, presumably owing to interlocking among the groups. The high-temperature T1-minimum is ascribed to rotational and translational motion of the segments. The extent of motion is qualitatively gauged by calculation from the Bloembergen-Purcell-Pound theory for NMR relaxation in simple liquids. T1 is insensitive to molecular weight (M.W.) over a wide range, but the dependence of T2 upon M.W. changes abruptly when M.W.≅4×104. In polybutadiene, T1 is found to depend markedly on the cis-trans content.
cis-Polychloroprene
Authors: Aufdermarsh C. A. , Pariser R.
Published: February 2011

cis-Polychloroprene was synthesized by chlorinolysis of 1,4-poly-2-(tri-n-butyltin)-l,3- butadiene. The latter was obtained by free radical polymerization of 2-(tri-n-butyltin)-l,3-butadiene. The structure of cis-polychloroprene was established by ozonolysis, and by infrared and NMR spectroscopy.
Vulcanization of Elastomers. 44. Vulcanization of Polybutadiene with Cumyl Peroxide. I.
Authors: Hummel Klaus , Kaiser Günter
Published: February 2011

Cumyl peroxide vucanization of cis-1,4 polybutadiene with 2“3 per cent 1,2 addition was compared with that of natural rubber. The essential findings are: 1) In both rubbers, cumyl peroxide decomposed at exactly the same rate. 2) As shown earlier for natural rubber, the crosslinking reaction was over in polybutadiene when cumyl peroxide decomposition was complete. 3) Final crosslink density in polybutadiene decreased with increasing vulcanization temperatures. 4) Crosslinking yield in polybutadiene can be estimated simply by comparison with the crosslinking yield in natural rubber.
Antioxidant Properties of Carbon Black in Unsaturated Elastomers. Studies with cis-Polybutadiene
Authors: Gruver J. T. , Rollmann K. W.
Published: February 2011

The thermal antioxidant behavior of carbon black was studied in vulcanized cis-polybutadiene and related to the surface chemistry of the black. Continuous and intermittent stress relaxation and oxygen absorption measurements were employed to determine the antioxidant ability of the carbon blacks. The blacks were characterized by the surface concentrations of oxygen-containing functional groups, using methods described in the literature. Antioxidant activity was found to be highest in carbons containing relatively large amounts of bound oxygen. These carbons are also acidic and decompose peroxides by the ionic mechanism. This was demonstrated with cumyl peroxide. However, even though the acidity and ability to decompose cumyl peroxide to phenol and acetone could be destroyed by methylation, this treatment did not seriously impair the antioxidant activity, so that the role of acidic groups appears to be minor. Evidence is presented which suggests strongly that the antioxidant behavior of carbon blacks is due to surface quinones, possibly hydrogen-bonded with adjacent hydroxyl groups. Measurements made on samples vulcanized in peroxide and sulfur curing systems indicate that the antioxidant behavior of carbon black is independent of the method of vulcanization in the absence of other antioxidants. A characteristic feature of the antioxidant action of carbon blacks is their tendency to repress the oxidative crosslinking reactions, the relative amount of compensation of chain scission by crosslinking being smaller than in gum vulcanizates.
Aging of SBR
Authors: Bevilacqua E. M. , Wenisch W. J.
Published: February 2011

Changes in properties of vulcanized SBR during aging at 130° C in air are the result of reactions involving both the hydrocarbon and the crosslinks. Hydrocarbon oxidation is related to the overall rate of oxidation; it leads to both scission and crosslinking. Sulfur crosslinks are broken and new crosslinks formed in reactions which are affected by oxygen but relatively independent of the overall rate of oxidation. The excess of crosslinking over scission decreases progressively with increasing cure.
Phenothiazine as an Antifatigue Agent for Natural Rubber, Synthetic Polyisoprene and SBR
Authors: Tarasova Z. N. , Eitingon I. I. , Senatorskaya L. G. , Fedorova T. V. , Dogadkin B. A.
Published: February 2011

Phenothiazine has no effect on vulcanization of rubber or standard mechanical properties of the vulcanizates. Phenothiazine considerably increases fatigue resistance of vulcanizates of the rubbers studied, under different fatigue conditions. Under the effect of thermal oxidation and repeated deformation phenothiazine or its conversion products combine with the vulcanizate. The phenothiazine does not combine when subjected only to heating. When used with certain inhibitors of oxidation phenothiazine has a synergistic effect.
Effect of Thio-Derivatives of Amines and Phenols on the Behavior toward Thermomechanical Treatment and on Fatigue of Vulcanizates
Authors: Tarasova Z. N. , Eitington I. I. , Senatorskaya L. G. , Fedorova T. V. , Snisarenko A. M. , Andronova G. I. , Dogadkin B. A.
Published: February 2011

1. It has been shown that thio-derivatives of amines (phenothiazine, benzo-α-phenothiazine, and 9-oxybenzo-α-phenothiazine in comparison with corresponding diphenylamine and phenyl-α-naphthylamine) cause a relatively lower rate of oxygen combination with rubbers and vulcanizates, a decrease in the rate of thermal breakdown of hydroperoxides, retardation of chemical stress relaxation and an increase in fatigue resistance. 2. Thio-derivatives of amines and phenols, by comparison with corresponding amines and phenols, contribute considerably to the preservation of the original vulcanization network in the course of “thermomechanical” action and thermal oxidation. 3. Thio-derivatives of amines and phenols, in combination with amines and phenols exhibit more than additive (reinforcing) action. Synergism in these systems is attributed to the effect of thio-derivatives on breakdown of hydroperoxides.
Measurement of Rubber Tack
Authors: Skewis J. D.
Published: February 2011

An instrument for measurement and study of tack of rubber compositions is described. The method involves pressing together two specimens of polymer compound with a chosen force for a predetermined time, and then measuring the time to separate them with a preselected force. Development of tacky adhesion is related to the product of force and a function of time that the specimens are pressed together. The measure of adhesion also involves the product of force and a function of time required for complete separation. Empirical treatment yields an equation to describe tacky behavior of a rubber composition in terms of the ratio of these products of force and time, the ratio being designated as the tack index of that composition. An example is given by comparing tack of SBR with that of natural rubber. SBR exhibits a tack index of about unity over a wide temperature range while natural rubber has a large tack index at 25° C, which decreases with increasing temperature. It is suggested that the excellent tack of natural rubber is due to crystallization with elongation.
Polymer Flow Behavior from Multispeed Viscometry
Authors: Wolstenholme W. E.
Published: February 2011

A practical viscometric technique has been developed for measuring flow of commercial elastomeric and thermoplastic materials at processing temperatures. A standard procedure for testing bulk polymer samples in a modified shearing disk Mooney viscometer with rotor speeds from .05 to 77 rpm is described in detail. Research, development or process control personnel can rapidly convert viscometer torque dial readings at the various rotor speeds to an isothermal flow curve in absolute units of shear stress and rate of shear by either of two methods shown by examples. Total time to test a polymer sample and plot the flow curve is less than one hour. Representative flow curves illustrate how polymers with essentially equivalent ML-4 @ 212° F can have large differences in flow at processing conditions. A set of isothermal flow curves covering a desired temperature range provides an excellent estimate of processing behavior over a range of temperatures. Numerical determination of the thermal dependence of flow is easily evaluated in terms of activation energy at constant shearing stress, constant rate of shear, or constant viscosity. Activation energy is a useful constant for characterization of non-Newtonian polymer flow.
Determination of Molecular Weight Distributions of Diene-Containing Rubbers by Precipitation Chromatography
Authors: Uraneck C. A. , Barker M. G. , Johnson W. D.
Published: February 2011

Ten variables were studied to optimize fractionation of synthetic elastomers by the Baker—Williams column technique. The two most critical factors were the rate of deposition of the polymer onto the beads within the column and stabilization of polydienes against crosslinking and degradation. After optimizing the fractionation technique certain fractionation and molecular weight distribution problems were studied. A problem frequently encountered in column fractionations is reversion, i.e., a drop in viscosity near the end of the fractionation. Reversion is attributable to branching, but polymer degradation and crosslinking can also contribute. The technique described can be used to detect long chain branching in elastomers. An important characteristic of emulsion polymers is the width of the molecular weight distribution. The fractionations showed that the heterogeneity index, Mv/Mn, of SBR increased with the magnitude of the regulating index of the polymerization modifier used. The most efficient modifier on a weight basis did not necessarily give the smallest heterogeneity index, as is predicted by theory. The heterogeneity index of a polymer prepared by incremental addition of mercaptan modifier was smaller than that of the control. The fractionation results were of value in understanding the behavior of modifiers in emulsion systems. In solution polymers an initiator with a large propagation/initiation rate ratio, or the use of branching or coupling agents, broadened the molecular weight distribution. The use of the Baker—Williams column on a routine basis has been valuable in the preparation of several new commercially accepted elastomers.
Development and Performance of the Portable Skid Resistance Tester
Authors: Giles C. G. , Sabey B. E. , Cardew K. H. F.
Published: February 2011

The portable skid-resistance tester can carry out a wide variety of measurements on the road and in the laboratory. This paper outlines the basic principles underlying the design of the tester and describes the laboratory and field trials conducted during the development of the instrument. The factors influencing its performance are emphasized. In its performance, the instrument behaves as a patterned tire skidding at 30 mph. It is particularly well suited for testing rough-textured surfaces, and readings are independent of gradient, camber, or crossfall on the test surface.
Synthesis of Trichain and Tetrachain Radial Polybutadienes
Authors: Zelinski R. P. , Wofford C. F.
Published: February 2011

Tri- and tetrachain radial polybutadienes have been synthesized by coupling very dilute solutions of linear polybutadienyllithium with stoichiometric amounts of methyltrichlorosilane or silicon tetrachloride. These polymers have three or four long chains (100–2000 carbon atoms) attached to a single atom.
Rheological Properties of Multichain Polybutadienes
Authors: Kraus Gerard , Gruver J. T.
Published: February 2011

The introduction of one or two long chain branches into a polybutadiene molecule to form trichain or tetrachain molecules, respectively, leads to profound changes in Theological behavior. At low molecular weights the Newtonian (zero shear) viscosity is decreased relative to a linear polymer of the same molecular weight. At molecular weights exceeding 60,000 (trichain) or 100,000 (tetrachain), the Newtonian viscosity rises rapidly above the corresponding value for a linear polybutadiene. However, non-Newtonian behavior of the branched polymers becomes more pronounced the higher the molecular weights, so that at moderate to high shear rates the viscosity of the branched polymers is uniformly lower than that of linear polymers of identical molecular weight.
Rheological Properties of cis-Polybutadiene
Authors: Kraus Gerard , Gruver J. T.
Published: February 2011

The steady-state viscosity of a number of cis-polybutadienes was determined as a function of shear rate and temperature by use of a capillary rheometer. Polymers investigated differed in molecular weight distribution and long chain branching. None of the polymers exhibited Newtonian behavior, even at the lowest shear rates attainable. Nevertheless, for polymers of similar molecular weight distribution and minimum branching, all the capillary viscometer data could be reduced to a single curve by a reduced variable treatment. The molecular weight shift function was found to be the same as for polymers exhibiting a Newtonian flow range, i.e., a 3.4th power law in weight-average molecular weight. Broadening the molecular weight distribution or increasing the degree of long-chain branching led to increasingly pronounced non-Newtonian behavior. Tensile creep experiments showed nonlinear viscoelastic behavior for all polymers studied, even at small strains. This behavior was most pronounced in the more highly branched polymers. At very low stresses some of these polymers exhibited extremely high viscosities, the strain being almost completely recoverable. Under larger stresses the viscosity of these rubbers dropped several decades and in the capillary extrusion experiments these polymers flowed readily. This is the same behavior observed previously in high molecular weight branched (multichain) narrow distribution polybutadienes. It is tentatively explained by a constraint of the branch points on the slippage of chain entanglements. The fact that all cis-polybutadienes exhibit this behavior, while linear polybutadienes made by organolithium initiation do not, suggests that all cis-polybutadienes may be branched to some extent.
Swelling of Vulcanized Rubbers in Binary Solvent Mixtures
Authors: Scanlan J.
Published: February 2011

The single-liquid approximation has been applied to the data of Bristow on ternary systems containing benzene and cyclohexane with one of the rubbers, natural, SBR, or butyl. Satisfactory fits are obtained with a constant value of the interaction constant between the two solvents χ12 which differs markedly, however, from the value obtained by measurements on the binary solvent mixture.
Mechanism of Tire Flatspotting and Its Relation to Fiber Properties
Authors: Papero P. V. , Wincklhofer R. C. , Oswald H. J.
Published: February 2011

Tire flatspotting has been shown to be related to cord compression in the footprint area. Because of compression, the cords are under less tension than those cords outside this area, and contract. Cord contraction and the depth of a flatspot which develops in a tire depend on: 1. Cord Physical Properties: Modulus dependence on temperature, Tg, crystallinity and orientation; response to applied stresses, and creep. 2. Tire Design Factors: size, number of plies, cord angle, cord construction (linear density and helix angle). In order to exhibit low flatspotting, a tire yarn must meet the following physical property requirements: high immediate elastic region—high modulus, high glass transition temperature—low creep, high yield point, high intermolecular chain friction (H-bonding, crystallinity) and low moisture regain.
Prediction of Creep Behavior from Stress Relaxation Data for Nonlinearly Viscoelastic Materials
Authors: Wu L. M. , Meinecke E. A. , Tsai B. C.
Published: February 2011

The stress relaxation behavior of many polymeric materials can be expressed in a very simple fashion, because the logarithm of nominal stress fi(t) (based upon the undeformed cross-sectional area of the sample) plotted against the logarithm of time, t, is a straight line. Furthermore, these lines are often parallel, and with linearly viscoelastic materials, one obtains a straight line for the stress-relaxation modulus E(t)=fi(t)/εi, independent of the strain level. Thus, the linear stress-relaxation modulus can be expressed as: Ei(t)=Ei0·t−m, with Ei0 the modulus at t=1 s and m the slope of the straight line in the double logarithmic plot. Most polymers are, of course, nonlinearly viscoelastic (except for infinitesimal deformations); that is, the stress-relaxation modulus is a function of both time and strain. These time and strain effects can be factored out, if the log fi(t) versus log t curves are parallel: Ei(t,εi)=Ei0·t−mϕ(ε), where ϕ(ε), the strain function, is a measure of the nonlinearity of the viscoelastic response. It has been shown elsewhere that Ei0/ϕ(ε) is approximately identical to the modulus observed in the stress-strain measurement. With many polymers, creep experiments also yield approximately straight lines of slope n, when the logarithm of strain εi(t) is plotted against the logarithm of time. With nonlinearly viscoelastic materials, one generally does not obtain a set of parallel lines, when the stress fi, is changed. Therefore, it is not possible to separate the influence of time and stress on the creep compliance Di(t)=εi(t)/fi, as was the case for stress relaxation. It has been shown previously that the creep behavior can be predicted from stress-relaxation data with the help of the convolution integral. The numerical method involved is very laborious, however. It has been shown that the rate of creep may be predicted from the slope of stress-relaxation curves and the shape of the stress-strain curve. The purpose of this paper is to present a method by which the creep behavior of nonlinearly viscoelastic materials can be predicted in a simple fashion from stress-relaxation data. The theoretical predictions have been tested with the stress-relaxation and creep data of a block copolymer.
The Use of Rubber for Impact Protection in Automobiles
Authors: Leaver A. D. W.
Published: February 2011

The requirement that cars should be protected from impacts has led to the adoption of new designs of rubber components and new compounds. There is great scope for designers and engineers to use impact-absorbing rubber units, high-modulus vulcanizates, and paintable rubbers in a wide variety of applications in the automobile field and elsewhere.
Characterization of Tire Emissions Using an Indoor Test Facility
Authors: Williams R. L. , Cadle S. H.
Published: February 2011

A tire emission facility has been built in which several tire-wear modes can be simulated while the gaseous, airborne particulate, and sedimentary particulate emissions are collected. The facility was shown to produce tire temperatures and wear rates typical of operating tires. This approach to tire-emission research has many advantages over previous attempts to study tire emissions. The emission rate of gases and airborne particulate matter was nearly independent of wear rate and accounted for only 1–20% of the total emissions. The balance of the emissions were large particles which would be expected to settle on or very close to roadways. Chemical analysis of these large particles showed that approximately 30% of the SBR is unvulcanized, compared to only 1–2% in the tread. The total organic content of the particles was unchanged. This degradation of the rubber leads to enhanced oxygen absorption rates. However, the full significance of the increased rate of oxidation is not known.
Synthesis and Dilute-Solution Behavior of Model Star-Branched Polymers
Authors: Bauer B. J. , Fetters L. J.
Published: February 2011

The occurrence of polymers branched in a random fashion is common. Chain transfer reactions can cause short- and long-chain branching in polymerizations such as the high-pressure polymerization of ethylene. Branching can also be introduced intentionally by the use of a polyfunctional monomer in end-linking polymerizations. Similar branching can be produced in addition polymerizations by the use of a small amount of difunctional monomer, e.g., divinylbenzene. There also has been much interest in graft polymerization by which long chain branches can be introduced onto a backbone, which is often a different polymer from the branches. The properties of branched polymers can be quite different from those of linear polymers of the same molecular weight. For example, bulk viscosities as well as concentrated and dilute solution viscosities can be lower for branched polymers than for a linear material of equivalent molecular weight. As an example, the melt processing behavior of polymers can be manipulated by alterations in the average molecular weight, molecular weight distribution, and the frequency and length of long branches in the molecules. Thus, there is an obvious need to correlate and characterize the type and degree of branching in a polymer with its effect on the physical properties in solution or melt. In all of the above examples of branching, there is a mixture of branched and unbranched material. The unbranched and branched polymers can have a wide molecular weight distribution, as can the branches themselves. Also, the frequency of branches and the segment lengths between branch points can vary. Hence, the physical properties of such materials represent an average of the properties of all the different species present.
Cord—Rubber Tire Composites: Theory and Applications
Authors: Walter Joseph D.
Published: February 2011

The stiffness and strength behavior of the constituent cord and rubber components of the pneumatic tire have been studied in detail by investigators in the industry since the early days of tire production. For example, the effect of twist on the stress-strain properties of cotton tire cord and the reinforcing effect of carbon black on the modulus of natural rubber were well known phenomena many decades ago. Similarly, differences between the elastic and viscoelastic behavior of cord and rubber have been well documented since the 1940's. On the other hand, the material properties (specifically, the elastic constants) of the cord-rubber composite system that comprises the tire are not as well known and have only begun to receive serious attention in the last decade. These tire elastic properties, whether they be referred to as stiffnesses, compliances or moduli, are anisotropic—i.e., they vary with direction. It is the properties of the anisotropic cord-rubber composite that primarily control the overall performance characteristics of pneumatic tires. Yet, much of present day tire design has been dominated by the separate influences of rubber compounding and textile technology. This situation has arisen perhaps because the functions of the individual cord and rubber components of the tire are well known, at least qualitatively; the low modulus, high elongation rubber contains the air and provides abrasion resistance and road grip; the high modulus, low elongation cords provide reinforcement for the rubber and carry most of the loads applied to the tire in service. However, it is shown later in this discussion that, in order to optimize a given tire performance parameter, a knowledge of the combined cord-rubber composite material properties is required. For example, the crown angle for maximizing the tread wear resistance for a steel-belted radial tire is not the same as for a rayon-belted radial of the same size. While this fact could be empirically established by “trial-and-error” tire building and test methods, such a program involving the wide variety of available tire cord and rubber compounds would be time consuming and expensive. Thus, composite material mechanics, even though in its early stages of development as far as cord-rubber systems are concerned, can and should be used to economically investigate the technical merits of potential tire designs.