bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Stress Relaxation of Polyacrylate Elastomers
Authors: Singh Ajaib , Weissbein L.
Published: February 2011

The continually widening range of thermal stresses imposed on elastomeric parts used in the automotive and aeronautical fields intensifies both the need for more thermally versatile elastomers and the need for effective laboratory methods for evaluating elastomer performance. Because stress relaxation provides a means of gauging product performance under both high temperature and external stress that approximate conditions of use, this technique gives a good estimation of an elastomer's commercial potential and its adaptability to a particular application. To demonstrate the value of stress relaxation, the thermal stability of a polyacrylate elastomer crosslinked with various curatives and the effect of certain additives on thermal stability were studied. Polyacrylates are of major interest for applications that require a high degree of thermal stability because of their ability to perform well over wide temperature ranges (−25° to 400° F). These elastomers are mainly copolymers of ethyl acrylate and a chlorine containing monomer such as vinyl chloroethyl ether. Some newer types are based on ethyl and butyl acrylates and chlorine free monomers such as epoxides and substituted amines. Generally, polyacrylates are compounded and prepared for curing according to standard techniques and they can be crosslinked with a variety of curative systems. Curing is accomplished at between 300° and 400° F in times ranging from 45 seconds to 45 minutes, depending on the elastomer and curing recipe used. The thermal stability of these elastomers is frequently determined by measuring the percentage changes in physical properties, e.g., tensile strength, elongation, modulus, after oven or oil aging or both at elevated temperatures. However, heat aging is carried out with no external stresses applied to the test specimens and the physical measurements before or after aging are made at room temperature. Although this type of test has some value, the results do not necessarily reflect the behavior of the elastomers in practice, as is the case with stress relaxation.
Tire Durability with Nitrogen Inflation
Authors: Sperberg L. R.
Published: February 2011

All tires fail due to interior oxidative deterioration, structural defects from manufacturing errors, improper tire design, road hazards, and exterior cracking caused by ozone and ordinary oxidation, most important being interior oxidative deterioration. This failure cause, while being most important, is least understood and appreciated. Oxidative deterioration of tires starts within the interior gas chamber, which acts triply for ride cushioning, as the reservoir of heat generated by the running tire, and as the vessel which contains oxygen to effect the tire's destruction. Arrhenius' law and the mass action law of chemical reactions are followed in that oxidative deterioration is governed by heat (temperature) and oxygen concentration. Since hysteresis (running temperature) can only be controlled within limits, lowering the oxygen concentration of the inflating gas is the only remaining way of inhibiting oxidative deterioration of tires, which is a cumulative effect of time, temperature and interior oxygen concentration. Five carefully controlled passenger and truck tire tests were run during the past eighteen months to investigate oxidation phenomena. In each test, one half the test sample was inflated with ordinary air, the other half with an inert gas to reduce the oxygen concentration. Over 2.5 million tire miles were run in these five tests. A sixth test involving over eighty truck tires was run more than 6.5 million tire miles during the past 36 months to observe the oxidative effect of air inflation upon inner tubes and tire body deterioration. All six tests show strikingly that oxygen-free inflation gas has a profound and major beneficial effect upon overall tire endurance and upon tire wear. Actual performance data show tire endurance of passenger tires to be improved an average of 22 per cent when oxygen concentration is reduced to 0.6 per cent and wear improvement of 15 per cent at a point where tires were only 64 per cent worn.
Laboratory Tire Groove Cracking Test
Authors: Vance Roy M. , Burgess Kenneth A.
Published: February 2011

A new laboratory test for evaluating groove cracking of tire treads was developed. The tread section, including the carcass of a tire, is flexed under similar stress and temperature conditions as in actual tire service. Whole or multiple tread sections may be tested. The test is much less expensive than either road or indoor wheel tests. The test gives results that are reproducible and which are in accord with actual tire performance. In SBR/BR passenger tire tread formulations, finer carbon blacks or lower structure carbon blacks produce more groove cracking in this laboratory test; trends also observed in actual service. The inhibiting effect of antioxidants on groove cracking was demonstrated. In NR/BR treads, inversion of the structure effect was observed. Evidence has also been obtained that the test is capable of correctly predicting the effect of a tread design change upon groove cracking.
Discussion
Authors: Horne W. B.
Published: February 2011

Mr. W. B. Horne (NASA, Hampton, Virginia)—Results in the two papers are in agreement with NASA research results. The papers treated the subjects of tread material, tire construction, road surface texture, and tread design very thoroughly. But one essential ingredient to the problem has been left out of the paper discussions, and that is, the effect of water depth. The importance of the water depth effect, and the need to inform both public and government authorities about the importance of removing worn tires from automobiles for the safety of all, is discussed and illustrated very fully by Leland. An example of what happens when the water depth is 0.4 in. is shown in Figure 1. It can be seen that the water penetrates the tire imprint much more rapidly than in shallow water. The effect of road surface texture on braking friction coefficient is illustrated by the data shown in Figure 2. A smooth tread aircraft tire was successfully braked on five different road surfaces ranging in texture from a large aggregate asphalt surface to wet ice. These surfaces are classified as damp in wetness. The surfaces at the time of testing were wet to the touch but did not have any puddles or standing water. Under this condition, damp smooth concrete (smooth as a table top) gave friction values as low as wet ice. This drastic friction loss decreased as the road surface texture increased. It will be noted that the smooth aggregate asphalt data did not fall off in speed as was shown by Maycock in his paper in Figure 15. In Figure 3 the water depth on the smooth concrete and large aggregate asphalt surface was increased from a damp condition to a flooded condition (0.1–0.2 in.). The character of the friction changes of these surfaces due to change in water depth is remarkable. For example, the smooth concrete increased slightly in value. This is an apparent increase, however, because the deeper water produces a fluid drag term which adds to the tire-surface braking force and gives a higher friction coefficient. This is an academic point, however, since the smooth concrete surface is producing viscous hydroplaning even at low speeds. On the other hand, the asphalt surface which alleviated the viscous hydroplaning effect under damp conditions does not prevent dynamic hydroplaning from occurring to the tire when this surface is flooded to a depth of 0.1 to 0.2 in. To summarize, any surface must be evaluated under a range of water depths before its wet friction qualities can be properly evaluated. Smooth tread tires or badly worn patterned tires have demonstrated poor friction capabilities on most wet or flooded surfaces. For this reason, both aircraft and automobile tires should be removed and replaced before wear produces a smooth tread condition.
Lubricated Friction of Rubber. II. Interaction of Rubber and Sliding Surfaces
Authors: Percarpio E. P. , Bevilacqua E. M.
Published: February 2011

Skid resistance of tires on wet pavements in an important component of tire safety; it is important to evaluate it precisely under conditions which are pertinent to actual use. The closest approximations to practical conditions are provided by measures of side force coefficient or by locked wheel sliding, both of which are related to problems of vehicle control. However, both of these require that a test vehicle be provided with four identical tires, that a surface large enough to test on be available, and that all test conditions including the nature of the surface be reproducible. For any rational program of research, costs of comparing materials of tire and of road would mount astronomically unless a controlled laboratory test were available which is well correlated with field experience, so that many variables can be studied conveniently in the laboratory. Such a test is available in the applications of the Portable Skid Resistance Tester. Results with this apparatus have been shown to correlate well with those from tests of vehicles on roads over a range of road properties, correlations apparently being with properties of a patterned tire. The results have been further shown to be well correlated with accident statistics. This report will show that correlations with tests on vehicles are valid over a wide variation in rubber properties as well.
Lubricated Friction of Rubber. V. Influence of Rubber Resilience and Hardness on Friction
Authors: Percarpio E. P. , Bevilacqua E. M.
Published: February 2011

The dominant importance of hysteresis in lubricated friction of rubber was first outlined by Tabor and has been extensively confirmed since. A number of workers have also shown that dry friction is correlated with hysteresis, but the mechanistic connection is still unclear. Rubber hardness has been less definitely correlated with friction. This may result in part from the choice of surface on which to test the rubber compositions studied. We have previously shown the importance of the test surface and recommended use of wavy glass to simulate actual slippery roads in lieu of a representative road surface. Carr reported our finding that the relative influence of rubber hardness depends on the texture of the hard surface on which it slides. Using the wavy glass and a slippery road surface, we have now studied a very wide range of compositions, both gum and filled, derived from commonly used tire rubbers, as well as others included to extend the range of properties studied. These results fully confirm the importance of hysteresis and more clearly define that of hardness. These two properties together almost completely determine wet friction on slippery roads. Most of the variance not accounted for is attributable to measurement error.
Lubricated Friction of Rubber. VII. Notes on a Standard Tire and Procedure for Skid Testing
Authors: Bevilacqua E. M. , Percarpio E. P.
Published: February 2011

In an effort to achieve uniformity in testing and reporting skid resistance as a necessary preliminary to attempts to make improvements in roads on a rational basis, cooperative efforts have been underway over the past several years to standardize apparatus and equipment. One part of this effort has been the designation of a standard tire (ASTM E249-64T) for skid resistance testing. At the time this standard was set up important factors in skid resistance were not fully known and a composition was chosen on the basis that it was representative of actual tread stocks which have been used and had skid resistance shown by experience to be satisfactory. We have recently described evidence that the skid resistance of tires on real roads can be described absolutely in terms of properties of the tread stock which can be measured readily in the laboratory. In the course of this work we have further found evidence that the proposed standard tire is not as sensitive to variation in properties of the road as others which might be used. We have also shown that important properties of the road surface can be measured without a priori knowledge of the character of the road by the use of more than one rubber composition at the same location. Finally, we have observed that speed sensitivity of friction on road surfaces can be determined by low speed measurements. This report is therefore written to suggest that consideration be given to revision of procedures currently in view to take advantage of advances in our present state of knowledge. Since the recommendations constitute a substantial departure, they are not set forth here in specific detail, but their basis presented for consideration.
Lubricated Friction of Rubber Discussion
Authors: Kummer H. W.
Published: February 2011

The authors have presented a comprehensive and timely review of the likely friction mechanisms of rubber, sliding on lubricated surfaces. They have also advanced several new ideas which should stimulate workers in the field and which might affect the, selection of rubber sliders and test tires for routine pavement friction testers. Since their introductory paper summarizes the principal data and thoughts, presented in papers II to VII, the discussion refers, with one exception, to paper I only. I would like to particularly touch upon : (a) The significance of skidding accident data in their various forms of presentation. (b) Minimum required friction levels to prevent skidding during all “normal” vehicle maneuvers. (c) Friction transients of pavement surfaces at the onset of rain. (d) The existence or nonexistence of adhesion and the relative frictional contribution made by abrasion. (e) The relative merits of portable devices and skid trailers, intended for routine operation in the field.
Method of Determining Damping and Elastic Properties of Rubber Used in Tires
Authors: Moore D. F. , Larson D. B.
Published: February 2011

Dynamic penetration of tread rubber by asperities of a roadbed for a rolling tire was simulated by impact of a rubber specimen on different arrangements of small spheres. The penetration history of the draping rubber was then analyzed to determine its damping and elastic properties. The method of analysis essentially varied two parameters in a nonlinear differential equation that described the system, so as to minimize the error between the integrated equation and test data. Least square of minimization was used. The results indicated that the viscoelastic behavior of the rubber can be represented by a simple Voigt model. The importance of jointly considering both draping and traction zones in the contact patch of a rolling tire is discussed.
Origin of Tire Squeal. II. Tire Squeal Calculation from Materials Properties
Authors: Trivisonno N. M. , Beatty J. R. , Miller R. F.
Published: February 2011

In the first paper of this series, the origin of tire squeal was studied with reference to the location of the vibrating elements and the measurement of their motion. This paper approaches the problem of the relationship of materials properties to tire squeal. A simplified picture of tire squeal leads to the equation of motion of a vibrating tread element. The squeal theory, which takes into account hardness and resilience as measured by dynamic modulus and loss tangent of the material at the squeal frequency, and also the frictional properties of the tread compound as a function of sliding velocity, treats tire squeal as a relaxation oscillation of the tread in shear. The theory determines a squeal trajectory under any given conditions by solving the equation of motion for the sliding tread in contact with the road. The squeal trajectory gives the frequency, displacement amplitude, and velocity amplitude of the squeal oscillation. The simplified theory was checked by a comparison of theoretical and experimentally measured squeal frequencies and intensities on fifteen different tread compounds with widely varying physical properties. It was shown that tire squeal intensity depends primarily on hardness of the tread compound, with harder compounds squealing more. Yerzley resilience has a lesser effect, lower resilience compounds tending to squeal less.
Stiffness of Cord and Rubber Constructions
Authors: Gough V. E.
Published: February 2011

When the function performed by pneumatic tires in guiding vehicles by development of cornering force was first studied many years ago, a number of attempts at analysis were based on the concept that cornering force was developed primarily because of cross-bias construction. None of these attempts provided either a satisfactory or fruitful basis of analysis. Later, adequate guiding properties developed by experimental spring wheel designs when rubber was in short supply (1940–45) indicated that the cross-bias construction was not essential for cornering forces. Designs involving flexible but edgewise rigid belts or tracks were very successful in this regard. Analysis of these structures turned attention to the elastic beam on elastic foundation concept of a tire, not only for radial load carrying capacity but also for lateral and cornering properties. However, consideration as to where in the shoulder region the casing was to be taken as part of the beam and where it was to be considered part of the foundation, proved to be a stumbling block when considering a conventional tire. Development of the tire with radial ply casing and a rigid breaker band resolved this point by providing a tire where the ambiguity did not exist. In subsequent investigations the ambiguity for the cross-bias tire was resolved with measurements by the same experimental procedures at corresponding points on the tread band and discussing the tire in terms of effective stiffnesses.
Crosslinking Reaction of Rubber with Aldehydes
Authors: Minoura Y. , Tsukasa M.
Published: February 2011

The reactions of rubber with aldehydes have previously been studied in latex or in solutions and the reaction products formed by cyclization, condensation, or addition, have been reported. In the present study, solid-state reactions of rubber with aldehydes were carried out. It was found that crosslinked rubbers may be obtained by press curing in the presence of aldehydes with acidic catalysts. Poly-chloroprene and Hypalon especially undergo these reactions without a catalyst or with a small amount of catalyst. In the experiments using various aldehydes, some improvements in the properties of the crosslinked rubber were observed when aldehydes such as paraformaldehyde or α-polyoxymethylene were used. Some Lewis acids such as SnCl2·2H2O were found to be more effective catalysts than the above, and it was found that organic acids such as p-toluenesulfonic acid could also be used. The curing seemed to be an ionic reaction. The physical properties of the crosslinked rubber are similar to those of sulfur-cured rubbers.
Structural Characterization of Vulcanizates Part X. Thiol-Disulfide Interchange for Cleaving Disulfide Crosslinks in Natural Rubber Vulcanizates
Authors: Campbell D. S.
Published: February 2011

The thiol-disulfide exchange reaction is shown to be applicable to cleavage of disulfide crosslinks in accelerated sulfur vulcanizates of natural rubber. The reaction, in conjunction with the previously reported selective cleavage of polysulfide crosslinks, is used to determine the distribution of crosslink types for several accelerated sulfur vulcanization systems as a function of cure time. Discrepancies between the results and published results obtained using the reagent sodium di-n-butyl phosphite for disulfide crosslink cleavage are discussed.
Stress Relaxation of Natural Rubber During Irradiation
Authors: Evans D. , Morgan J. T. , Sheldon R. , Stapleton G. B.
Published: February 2011

The site of chain scission and crosslinking in vulcanized natural rubber irradiated with 4 MeV electrons has been determined by analysis of stress relaxation data. Sulfur and peroxide vulcanizates of different crosslink densities were prepared and the crosslink densities determined from stress—strain measurements. Stress relaxation was measured during irradiation using modified commercial relaxometers. The specimens were maintained in an atmosphere of nitrogen to minimize oxidative side effects. Scission is deduced to take place in the vicinity of crosslinks, since the rate of continuous stress relaxation is independent of crosslink density. Scission may be associated both with crosslinks initially present and with those subsequently introduced by irradiation. Crosslinking by radiation is largely a random process. However, there is a crosslinking reaction dependent to a slight extent on crosslink density as well as a small contribution from random scission reactions. G values for the random reactions are given.
Degradation of Highly Elastic Polymers
Authors: Scheele W. , Hillmer K.-H.
Published: February 2011

The inhibited autooxidation of 1,5-polyenes was studied by means of intermittent relaxation in oxygen, using natural rubber crosslinked by C—C links. The frequency and temperature conditions were so chosen that no degradation would have taken place in nitrogen. It has been found that in the presence of amine and phenolic type of agents during vulcanization with peroxides, the crosslink yield has been diminished considerably, and that the inhibitors are completely, or partially used up in this process. It is also noted that acetophenone and phenyl dimethylcarbinol, which are formed in crosslinking with DCP, interfere with the measurements of degradation by oxygen. Dependable measurements of degradation by oxygen in the presence of inhibitors can be carried out only on samples which have been extensively extracted with acetone in order to remove the acetophenone and phenyl dimethylcarbinol, and subsequently treated with a solution of the inhibitor, and carefully dried in nitrogen or in vacuum before measurement. if these conditions are fulfilled, the relaxation curves show an induction period, during which the stress drop is of zero order; the drop is directly proportional to the concentration of the inhibitor and the proportionality constant depends on the specific chemical constitution of the inhibitor. The rate of the stress drop is constant during the induction period and inversely proportional to the concentration of the inhibitor—which is in agreement with the theory of autoxidation.
Raman Spectra of Polyisoprene Rubbers
Authors: Cornell S. W. , Koenig J. L.
Published: February 2011

The Raman spectra of cis-1,4-, trans-1,4-, and 3,4-polyisoprene are presented, and the frequencies are classified by configurational structure type. The stretching frequency of the carbon-carbon double bond vibrations are used to describe structure content. Only Raman bands characteristic of total 1,4 content and total vinyl content can be observed. Tentative values of structure content determined by both peak height and peak area are presented for two mixed structure rubbers.
New Alfin Rubbers
Authors: Newberg R. G. , Greenberg H. , Sato T.
Published: February 2011

Molecular weight control for alfin catalyzed 1,3-diene polymers by 1,4-diene straight chain or cyclic hydrocarbons (and their derivatives) has been demonstrated. The microstructure of these moderated polymers is identical to the polymers obtained without molecular weight control. From the wide series of copolymers preparable with this improved polymerization method four were chosen for their evaluation after laboratory testing for processability, physicals, and economics. Copolymers of butadiene—isoprene (90/10 and 97/3) and butadiene—styrene (85/15 and 95/5) virgin or oil extended have been shown to be economically attractive and to give superior wear, traction, and adequate heat build up.
Radiotracer Studies of Carbon Black Surface Interactions with Organic Systems. II. Use of Sulfur-35 in Initial Studies on the Reactivity of “Bound” Surface Sulfur
Authors: Lewis J. E. , Deviney M. L. , McNabb C. F.
Published: February 2011

A broad investigation has been undertaken, using primarily radiochemical techniques, of the reactivity of the insoluble or “bound” sulfur on the surface of carbon blacks. The carbon black samples used in this study were prepared in small pilot plant reactors from sulfur-free commercial feedstocks to which had been added, in separate experiments, sulfur-35 tagged elemental sulfur, dibenzothiophene-S-35 and dibenzyl disulfide-S-35. After careful extraction-purification of the blacks, “chemical probe” studies were undertaken to gain knowledge of the nature of the surface sulfur complexes or functional groups, using reagents such as LiAlH4, trivalent phosphorus compounds, tetramethylthiuram disulfide, and hydrogen. These experiments demonstrated that bound surface sulfur possesses a considerable amount of chemical reactivity. Experiments were next designed to determine whether or not bound surface sulfur becomes involved in vulcanization reactions by, for example, exchange with added curing sulfur or accelerator. In radiotracer studies with SBR, natural rubber, and cis-polybutadiene vulcanizates, the results demonstrated that bound surface sulfur enters into the rubber phase during vulcanization. Finally, results from preliminary rubber physical testing and practical vulcanization studies involving pilot plant blacks (2% wt. sulfur) indicate that surface sulfur has little effect upon the vulcanization or final physical properties of SBR and NR.
Electron Micrography of Interplanar Spacings in Carbon Blacks
Authors: Marsh P. A. , Voet A. , Mullens T. J. , Price L. D.
Published: February 2011

High resolution electron micrography makes it possible to visualize the micro-structure of carbon black particles. An improved technique, relying on a graphitized carbon black as a calibration specimen, permitted us to establish an accurate distribution pattern of 002d-spacings in carbon blacks. Included were conventional blacks as well as a special thermal black (petroleum coke) untreated, partially and nearly completely graphitized. A technique was developed to microtome single particles. It was found that in untreated blacks, with a low degree of order, a wide, constant distribution of d-spacings exists, independent of the location within the particle. Upon heat treatment, the distribution pattern becomes increasingly narrower and shifts in the direction of smaller d-spacing values, as found in graphitized blacks. Oxidized blacks appear to have greater ordering of carbon planes, due to removal of unorganized fractions; but the d-spacing distribution remains essentially unchanged. Blacks subjected to high energy electrical discharges show a degree of order as in graphitized blacks. It was concluded that the distribution of d-spacings in a carbon black is a reflection of the particle's internal microstructural order.
A New Type of Crosslinking Agent for Elastomers
Authors: Breslow D. S. , Willis W. D. , Amberg L. O.
Published: February 2011

TBAF is a new type of crosslinking agent, which can be used to vulcanize a wide variety of elastomers, both saturated and unsaturated. The reaction involves the first-order decomposition of the azide function to give a nitrene, which in turn reacts with the polymer chain. The vulcanizates are noted for their lack of odor, lack of bloom, excellent physical properties, and excellent heat-aging resistance.
Preparation, Vulcanization, and Characterization of Syndiotactic Trans-1,2-Polypentadiene
Authors: Fielding-Russell G. S. , Smith G. H.
Published: February 2011

The polymerization, vulcanization, and some physical properties of two syndiotactic trans-1,2 polypentadienes (polypiperylenes) are described. Spectroscopic analysis indicated a significant (≈22%) cis-1,4 structure in the polymer prepared with the Et2AlCl/Co (AcAc)3 catalyst system which, although not in agreement with previously published data, is complementary to recently reported data. It is thought that the presence of water in the catalyst solvent or monomer mixture is responsible for the cis-1,4 content. Water appeared not to influence the Et2AlCl/Co(Octoate)2 polymerization in the same way: a greater than 95% trans-1,2 structure was obtained. Physical measurements on the vulcanizates reflected the structural differences. The copolymer vulcanizate, ≈22% cis-1,4 and ≈78% trans-1,2 structure, was more highly crosslinked than the polymer vulcanizate containing no detectable 1,4 structure. The relative levels and temperature location of the rubbery modulus and the Tg's and loss processes, respectively, are related to the 1,4 content: the vulcanizate containing 1,4 structure shows a higher Tg and rubbery modulus than the vulcanizate containing no detectable 1,4 structure. The inference is that the open copolymer presents a less sterically hindered path to the unsaturation for the bulky crosslinking agent and is therefore more susceptible to vulcanization, giving a tougher rubber that may also be reinforced by crystallization of the cis-1,4 units.
Rheo-Optical Studies of High Polymers. XIV. Study of the Deformation Mechanism in Polymer Blends of Polypropylene with Ethylene-Propylene Rubber
Authors: Onogi S. , Asada T. , Tanaka A.
Published: February 2011

To clarify the deformation mechanism in polyblends of polypropylene with ethylene-propylene rubber having different compositions, simultaneous measurements of the infrared dichroism with stress and strain under a constant rate of strain of 1.64%/min have been carried out. The orientation function of the crystallographic c axis of polypropylene in the blends has been obtained as a function of strain ranging from 0 to 20% and of polypropylene content ranging from 0.3 to 1.0. These results have been compared with the temperature dependences of the dynamic Young's modulus and of the loss modulus, as well as stress-strain curves for the same blends. The modulus data analyzed by Kerner's equation reveal the occurrence of phase inversion at polypropylene contents higher than about 0.5, and this is supported by the infrared dichroism data. The strong effect of quenching on crystalline structure and mechanical properties of pure polypropylene has also been elucidated.
A Topologically Interpenetrating Elastomeric Network
Authors: Frisch H. L. , Klempner D. , Frisch K. C.
Published: February 2011

While chemically different monomers can be mixed, the mixing of the corresponding polymers in the solid state usually results in (multiphase) polyblends. Even the mixing of two different polymer solutions generally produces two liquid phases. This difficulty can be overcome, without resorting to grafting, by producing interpenetrating polymer networks (IPN). By crosslinking an initially linear polymer in the presence of a crosslinked network we can produce a polymeric catenane or an IPN held together predominantly by “permanent” entanglements, assuming chain transfer reactions can be suppressed. Several workers have made IPN's from either chemically identical or chemically similar polymers and have studied their properties. In this work, two different elastomers, a crosslinked polyether-based poly(urethane-urea) and a linear poly(butadiene-acrylonitrile), as aqueous emulsions, are mixed, together with crosslinking agents and stabilizers, films cast, and subsequently cured to form the IPN. A partial chemical structure proof is obtained by separating the crosslinked poly(butadiene-acrylonitrile) from the IPN by essentially total hydrolysis of the interpenetrating poly(urethane-urea) network.
Multicomponent Polymerization. II. The Effect of Mixing on Copolymerization in Continuous Stirred Tank Reactors
Authors: O'Driscoll K. F. , Knorr R.
Published: February 2011

Calculations have been carried out to describe the course of three vinyl copolymerizations which typify free radical copolymerizations. Conversion of monomer to polymer and copolymer average composition, as well as copolymer composition distribution (CCD), have been calculated for these three systems in batch reactors (BR) and in continuous stirred tank reactors which have perfect, homogeneous micromixing (HCSTR) or imperfect mixing which leads to segregation on the microscopic scale (SCSTR). The results of the calculations indicate that conversion and average composition behavior are not necessarily strongly dependent on mixing in a CSTR, although they are in some systems. However, the CCD is strongly affected by mixing in all systems where the composition drifts with conversion. The magnitude of the effect of mixing on CCD increases with conversion. In the limit, a SCSTR gives at high conversion the same CCD as a BR. A HCSTR always gives a monodisperse CCD. Limitations and applications of the calculations are discussed.
Torsion Resilience Pendulum
Authors: Zerbini V.
Published: February 2011

A resilience measuring pendulum, where potential energy is stored in elastic form inside a twisted metal wire, rather than in the more customary gravitational form, is described. The device is of very simple construction and use and, applying it to various test piece thicknesses through the use of the mechanical similitude principle, shows a remarkable accuracy.
Morphological Study on Carbon Black Loaded Rubber Vulcanizate under Stretching
Authors: Shinomura T. , Takahashi M.
Published: February 2011

The morphological change of pure and carbon black loaded butyl rubber vulcanizates with elongation was studied by an electron microscopical method. The main noticeable observations were as follows. The number of cavities increases with the increase of elongation. The shape of cavities grows into longer spindle one with the increase of elongation. Carbon black aggregates break down with the increase of elongation. It is concluded that there are two types of cavitations in carbon black loaded rubber vulcanizates.
EPDM Vulcanization and High Temperature Compression Set
Authors: Baldwin F. P.
Published: February 2011

The data presented are suggestive of the following conclusions regarding the vulcanization behavior and high temperature compression set properties of low unsaturation EPDM polymers: 1. The olefinic residue derived from ENB is more reactive in conventional sulfur vulcanization than is the residue from MNB. However, the ENB residue is more prone to reversion reactions. 2. The structure of the olefinic residue present can have important bearing on the exact nature at the crosslinks produced at a given crosslink density. 3. The conversion of high to lower sulfur rank crosslinks appears to occur partly by a thermally induced interconversion process and partly by concerted reactions in which crosslink bond scission does not occur as a discrete step. Both the nature and the concentration of accelerator present should have important bearing on the competitive balance between these two processes as should the presence of free sulfur. 4. Since the presence of free sulfur can procrastinate the sulfur crosslink rank reduction process, the observed low rate (relative to highly unsaturated elastomers) of conversion of polysulfidic to lower rank crosslinks must be associated with the absence of a large “sink” for sulfur. Thus with a given curing system, stable crosslinks should be generated faster the higher the level of unsaturation present and the lower the sulfur concentration. 5. High temperature compression set performance is influenced not only by the formation of new crosslinks during heating under compression but also by the interconversion of polysulfidic linkages present in the initial vulcanizates. Thus two polymers containing different olefin residues can exhibit identical set properties but for different reasons. 6. In practical terms both crosslink density and stability can be maximized by a combination of a short, high temperature forming cure followed by a long heat soak at a lower temperature. This observation should have important bearing on the economics of production of quality mechanical goods from low unsaturation elastomers via injection molding, the heat soaking step being paid for by the reduction in accelerator cost and molding cycle time.
Predicting Tire Tread Performance from Composition. I
Authors: Lane J. H. , McCall C. A. , Gunberg P. F.
Published: February 2011

Wet skid resistance of tread compounds, as measured by the British Portable Tester, and heat buildup, as measured by the Goodrich Flexometer, can be predicted accurately from a knowledge of composition and modulus, while wear resistance, as measured by the Pico Abrader, can be predicted with only fair accuracy. The predicting relations were developed using multiple regression analysis from data obtained in a designed experimental program. Independent variables included four polymers (emulsion SBR's of 0, 23.5, and 40% bound styrene and cis-polybutadiene), extender level, carbon black N−285 loading, and modulus. Field test results are presented for compounds selected to show improved wet skid resistance while maintaining wear and groove cracking resistance at present-day levels. Test conditions influencing tire wet skid testing results, particularly the phenomenon of partial hydroplaning, are discussed.
Vulcanization of Rubber with Aminomercaptotriazines
Authors: Westlinning H.
Published: February 2011

Aminomercaptotriazines are a new class of accelerators for rubber vulcanization. The kinetics of the vulcanization reaction and the yield of crosslinks depend strongly on the molecular structure of the accelerators. The vulcanization is highly resistant to reversion which is demonstrated by a smaller increase in heat generation under dynamic deformation as well as by higher vulcanization temperatures and longer vulcanization times. In natural rubber and synthetic polyisoprenes aminomercaptodisulfides produce high yields of crosslinks combined with high processing safety. Fatigue strength of natural rubber vulcanizates is considerably enhanced by air aging. In blends of NR and SBR with BR, sulfenamides of dimercaptotriazines produce a very stable vulcanizate combined with good processing safety. Rate of cure can be increased by combination with a mercaptan. With polydisulfides SBR can be crosslinked without elemental sulfur at all. The vulcanizates have a high fatigue strength and a high hysteresis.
Occurrence and Prevention of Changes in the Chemical Structure of Natural Rubber Tire Tread Vulcanizates during Service
Authors: Cunneen J. I. , Russell R. M.
Published: February 2011

The chemical structure of the tread vulcanizate of heavy-duty tires has been investigated before and after service on the road, and after testing under conditions designed to induce tread-lift. Significant changes occurred. These included a marked reduction in the concentration of polysulfide crosslinks, and an increase in the amount of monosulfide crosslinks and main chain modification. Experiments with vulcanizates made in the laboratory indicated that the structural alterations in the tires were due to thermal anaerobic reactions caused by heat build-up, and that they resulted in a deterioration in some of the physical properties of the tread vulcanizate. The rate of desulfuration of ‘model’ polysulfides has been found to depend critically upon the nature of the vulcanization recipe. These novel findings point the way to improving the stability of vulcanizates used in the treads of tires and, consequently, tire performance.
Modification of CIS-1,4-Polybutadiene with β-Naphthylamine
Authors: Kirpichev V. P. , Yakubchik A. I. , Maglysh G. N.
Published: February 2011

Modification of epoxidized cis-1 ,4-polybutadiene (ESKD) with β-naphthylamine has been studied. Reaction is carried out in sealed ampules in toluene solution, argon atmosphere and in pressure of phenol as catalyst. Effects of temperature, time, phenol quantity, and ratio β-naphthylamine :ESKD on reaction extent have been examined. Preliminary test shows high efficiency of the reaction product as a high molecular antioxidant for stereoregular rubbers.
Porosity Studies on Some Oil Furnace Blacks
Authors: Smith W. R. , Kasten G. A.
Published: February 2011

It is generally accepted that the internal area arising from pores in an oxidized carbon black does not contribute to performance characteristics in rubber. While such pores are available to nitrogen, commonly used in evaluating surface area, they do not appear to be accessible to an elastomer molecule. Thus in predicting performance from area measurements one should consider the external area. Of course, for a non porous black the external and total (BET) area will be identical. In the past, the electron microscope provided the only independent means of evaluating external area. However, with the development of oil furnace blacks, particularly the more recent grades of high structure, identification and measurement of individual particles becomes more difficult and the electron microscope procedure less reliable. However, in recent years the so called “t curve” procedure has come into prominence and appears to provide a useful comparative method for detecting porosity and, to a degree, its extent. The method is quite empirical and requires the selection of a “non porous” adsorbent to serve as a standard with which other samples may be compared. A number of standards have been proposed but that of de Boer appears to be most widely used. The de Boer standard is based on a calcined alumina. In undertaking porosity studies on carbon blacks it appeared to us from earlier studies on silicas and titanias that a non polarizing carbon would be preferable to an oxide surface. Accordingly, we have selected a fine thermal black as a t curve standard. The present paper presents some of the results of this study. They differ to a degree from those of other investigations in which the de Boer standard was employed.
The Load Dependence of Side Force and Self-Aligning Torque of Pneumatic Tires
Authors: Schallamach A.
Published: February 2011

A conclusion to be drawn from this analysis of the load dependence of side force and self-aligning torque of pneumatic tires is that agreement between experimental and theoretical side force curves does not necessarily prove the soundness of the theory. On the other hand, even an inadequate theory is successful in suggesting a predictable and useful interrelation between load and slip dependence of the side force. Figure 4 demonstrates that quite a primitive transform of experimental data can lead to a unified presentation of its load and slip dependence although the resulting curve deviates quantitatively from theory in this particular case. This work forms part of a program of research undertaken by the Natural Rubber Producers' Research Association.
Heats of Reaction of Natural Rubber with Sulfur
Authors: Bekkedahl N. , Weeks J. J.
Published: February 2011

An adiabatic copper calorimeter was used to determine the heats of vulcanization of pale crepe natural rubber with sulfur for mixtures varying in composition from 0 to 32 per cent added sulfur. The side reaction that produces hydrogen sulfide was avoided by using reaction temperatures near 155° C. Heats of reaction at 25° C and at 155° C are reported. The enthalpy change at 25° C for compounds containing up to about 18 per cent sulfur is given in joules per gram of vulcanizate by the equation, ΔH25=−21.1·S with a standard deviation of 11 J/g. Here S is the percentage of combined sulfur. Above 18 per cent sulfur the heat of reaction at 25° C remains approximately constant at 380 ± 8 J/g. A comparison is made between the heat of vulcanization and the volume change on vulcanization, both as functions of combined sulfur, by making use of data in the literature.
Measurement of Chain Structure in Carbon Blacks
Authors: Voet A. , Aboytes P.
Published: February 2011

The dual structure of dispersed carbon blacks consists of an irreversible structure of particles coalesced in their formative stage, known as persistent structure and a reversible, transient structure created by mutual attractive forces between particles or persistent structural units. The shear dependence of dielectric constant as well as of electrical conductivities of carbon black dispersions can be explained from the dual structure. Direct measurement of the elastic shear modulus and dynamic conductivity of black reinforced vulcanizates, at amplitudes varying over an extremely wide range, permits evaluation of the contributions of persistent and transient carbon structures separately. A new approach measures persistent structures of blacks dispersed in a mineral oil by means of the minimum value of the conductivity-shear curve, while the transient structure is evaluated in terms of the initial conductivity increment with the logarithm of time immediately after cessation of shear. Relative structural numbers have been introduced by comparing the data with those of very low structure blacks of comparable particle size, dry ball-milled to remove all structural remnants.
Creep of Pure-Gum Vulcanizates of Natural Rubber
Authors: Wood L. A.
Published: February 2011

The creep of vulcanizates of natural rubber cured with varying amounts of dicumyl peroxide was compared with that of vulcanizates cured by typical conventional surfur-accelerator systems. The measurements involved indentation of a flat rubber disk as a function of time t and temperature T. The product of shear compliance J and T as a function of log t was represented by a family of curves with T as the parameter. For the vulcanizates cured with the sulfur-accelerator system, previous work has shown that the individual curves could be shifted along the abscissa to yield a single continuous curve with a slope which increased from a negligible value to a maximum and then decreased, continuing through a region of minimum slope which extended over about 7 decades of time before ending in a region of increasing slope. The value of the creep was 1.5–2.0% per decade in the region of minimum slope. When the same procedures were applied to the vulcanizates cured with dicumyl peroxide, the individual curves of JT against log t at each temperature did not yield a single continuous curve when shifted. In a limited region just above the glass transition temperature, the creep was appreciable, but neither a constant-activation-energy shift nor a Williams-Landel-Ferry shift was satisfactory. Above this region it was clearly impossible to obtain a single curve since the compliance-temperature product at a given time increased with increasing temperature while the corresponding creep of the dicumyl peroxide vulcanizates was generally too small (<0.5% per decade) to be measured between 5 and 600 seconds, except when the compound contained less than 2.5 parts of effective dicumyl peroxide. Outside of these regions the shear modulus was found to increase linearly with temperature. The investigation included temperatures as high as 100° C and effective dicumyl peroxide concentrations as high as 25 parts per hundred of rubber. The present results for the modulus and creep of dicumyl peroxide systems show good agreement with the published data of Chasset and Thirion (obtained by stress relaxation at 30° C) and of Plazek (obtained by a torsion pendulum) over the ranges they investigated.
Laboratory Measurement of Abrasion Resistance Using a Free Flowing Abrasive
Authors: Thelin Jack H.
Published: February 2011

A laboratory abrader utilizing a free-flowing abrasive was described and some operational variables discussed. Various techniques and conditions of abrading elastomers of both practical and research interest were considered. In certain cases significant variations of abrasion resistances with depth of wear were indicated and speculatively related to the non-homogeneity of the samples involved. In addition, the mechanico-oxidative nature of abrasion was clearly demonstrated.