bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of Vulcanization of Polysulfide Rubbers
Authors: Fettes E. M. , Jorczak J. S. , Panek J. R.
Published: February 2011

This investigation was carried out to discover the terminal group present in polysulfide rubbers of the kind represented by Thiokol Type FA and the chemical reactions involved in the standard vulcanization recipe. Hydroxyl groups were found to be present as terminals on these polysulfide rubbers. The effects on vulcanization of omitting the compounding ingredients normally used, of varying the amounts of zinc oxide, substituting other metallic atoms for zinc, and of using diisocyanates were studied, and the mechanism was deduced. Knowledge of the end groups present in the polymer chain is helpful in planning supplementary experiments to try to discover the chemical reaction involved in the cure with zinc oxide. It also makes it possible to look intelligently for improved vulcanizing agents for these polysulfide polymers.
Vulcanization of Rubber by Organic Peroxides
Authors: Braden M. , Fletcher W. P. , McSweeney G. P.
Published: February 2011

Comparatively few organic peroxides meet the rather exacting requirements of the ideal peroxidic curing agent for rubber. Only di-tertiary butyl peroxide has yet been found to give satisfactory vulcanization in black stocks. Pure gum vulcanizates of a high degree of transparency and good color have been obtained with two commercially-available non-hazardous peroxides which have also been used successfully with some non-black fillers. The incorporation of resorcinol overcomes a tendency to surface tackiness in peroxide cures and has a beneficial influence on tensile strength.
Infrared Analysis of Some Chlorinated Natural Rubbers
Authors: Salomon G. , van der Schee A. Chr
Published: February 2011

In an earlier paper spectra of polyisoprenes were discussed. In this communication effects due to the introduction of 1 to 4 chlorine atoms per C5H8 unit are reported. Since an unlimited number of polymers with such empirical compositions derived from isomeric monomer units is conceivable, it seems convenient first to compare some prototypes, then to report in more detail our experience, which is a continuation of earlier work in this field.
Behavior of Reclaiming Agents in Sulfur and Nonsulfur GR-S Vulcanizates
Authors: Amberlang J. C. , Smith G. E. P.
Published: February 2011

1. Di-tert-butyl-m-cresol sulfide was found to be less active in reclaiming p-benzoquinone dioxime-cured GR-S than in reclaiming sulfur-cured GR-S. It appeared to have no effect on p-benzoquione dioxime cures activated with red lead, though the presence of litharge or red lead in sulfur cures did not seem to retard reclaiming by the same agent. 2. N,N-di-n-butyl-m-toluidine sulfide had no reclaiming action under alkaline conditions on p-benzoquinone dioxime cured GR-S. Under these conditions the same sulfide reclaiming agent actively catalyzed the reclaiming of sulfur cures either in the presence or absence of litharge activation. 3. Di-tert-butyl-m-cresol sulfide did not affect the reclaiming of GR-S cured with dinitrobenzene and litharge. 4. Di-tert-butyl-m-cresol sulfide had a strong reclaiming action on a non-elemental sulfur cure (diisopropylxanthic disulfide) activated with litharge. 5. n-Octadecylamine was a reclaiming agent for sulfur-cured and benzoquinone dioxime-cured GR-S but less active than 4,6-di-tert-butyl-m-cresol sulfide. For benzoquinone dioxime-red lead and for dinitrobenzene-litharge cures it was an active reclaiming agent; it had no reclaiming effect on a diisopropylxanthic disulfide cure. 6. Oxygen absorption measurements failed to show any simple relation between the rate of oxygen absorption of vulcanizates and their behavior in the reclaiming process. 7. Direct oxygen determinations on vulcanizates before and after reclaiming showed that 4,6-di-tert-butyl-m-cresol sulfide is an oxidation catalyst for GR-S cured with sulfur, unactivated benzoquinone dioxime or diisopropylxanthic disulfide, the same vulcanizates for which it was a reclaiming agent. Octadecylamine appeared not to be an oxidation catalyst for the GR-S vulcanizates under the reclaiming conditions studied. 8. Zinc sulfide determinations on the vulcanizates before and after reclaiming showed an increase as a result of the experimental conditions, but no correlation with reclaiming effects. 9. Low-temperature GR-S (X-611) polymer, softened by the addition of furfural phenylhydrazone or o,o′-dibenzoylaminodiphenyl disulfide, showed slightly lower oxygen content than the control.
The Reactions of Amines and Sulfur with Olefins. I. The Reaction of Diethylamine and Sulfur with Cyclohexene
Authors: Moore C. G. , Saville R. W.
Published: February 2011

The reaction of diethylamine and sulfur with cyclohexene at 140° yields dicyclohexyl monosulfide and disulfide and also saturated polymeric products, C6H11⋅Sx⋅(C6H10)⋅Sx⋅C6H11, containing cyclohexane units linked by sulfur, where x is 1 or 2. N-Ethylthioacetamide (IV) is formed as a major product; minor products include N,N-diethylthioacetamide (V) and diethylammonium hydrogen sulfide (VI), IV, V, and VI are formed also by the reaction of diethylamine with sulfur at 140°. The mechanisms of the olefin-sulfuration processes are discussed.
Test of the Applicability of Dielectric Loss Measurements to the Study of the Aging of Pure-Gum Rubber Mixtures
Authors: Henri-Robert P.
Published: February 2011

The measurement of the dielectric properties at radioelectric frequencies requires a technique and apparatus which are too delicate to serve at the present time as a practical test of the aging of vulcanized rubber. On the other hand, from the viewpoint of research, the dielectric method should furnish valuable data on the way in which oxygen tends to combine with rubber according to the particular conditions of aging. Thus, it has been found in aging tests of three different types of vulcanizates containing no protective agent that there is an increase of polarity, which is in some cases great, an increase of the dielectric viscosity, and a broad distribution of polar groups, formed by oxidation, between the different types of structures. The dielectric absorption leads in particular to the same classification of vulcanizates as do the classic methods of measuring oxidizability and decrease of tensile strength. Finally, in addition, measurement of the dielectric absorption makes possible the estimation at a high level of sensitivity of the degree of polarity of oxidation products.
Mechanical Activation of the Initiation of Oxidation of Elastomers
Authors: Kuzminskii˘ A. S. , Maizels M. G. , Lezhnev N. N.
Published: February 2011

1. This is the first study of the relation of uninhibited oxidation to the conditions of mechanical stress of vulcanized and unvulcanized rubber. Inhibited oxidation is confined to the initiation process. 2. At the end of the inhibition period and in the earliest stages of autocatalysis, the physical-mechanical properties of vulcanizates change sharply, and lose much of their technical value. In practice, one is nearly always concerned with inhibited oxidation, and, consequently, the study of this process is very important. 3. The rate of initiation of fatigued vulcanizates and plasticized rubber is determined by studying the kinetics of consumption of the inhibitor, which in the present work was phenyl-2-naphthylamine. 4. The uniform concentration of initial active centers is directly proportional to the rate of initiation (wi) and inversely proportional to the concentration of inhibitor dissolved in the rubber. The probability of chemical rupture of the hydrocarbon chains increases with increase of wi. 5. An increase of the rate of initiation or decrease of the concentration of inhibitor leads to an increase of the probability of oxidative rupture of the hydrocarbon chains. There is an increase of wi when the temperature is increased, when oxidation catalysts are added, or when the hydrocarbon chain is subjected to mechanical stresses. 6. Repeated stretching or plasticization leads to a decrease of the activation barrier of the initiation reaction, since the mechanical forces conteract the forces of chemical combination. Owing to the relaxation character of deformation, an increase of severity of the conditions of stressing causes an increase of wi. 7. Both the mechanically activated chemical reaction and the direct action of mechanical stresses can lead to rupture of test-specimens. In the case of fatigue, the probability of purely mechanical ruptures is small; during plasticization it is much larger. 8. With an increase of intensity of the mechanical reactions, and a large decrease of the activating energy of initiation, there is a simultaneous abrupt decrease of the pre-exponential factor. The decrease of Ea is functionally related to the decrease of ln A. 9. The decrease of the pre-exponential factor when mechanical stresses are applied is evidently due to a decrease of mobility of the stressed chains. The total number of contacts decreases, while the proportion of effective contacts increases.
Crystallization in Natural Rubber. III. Filled Compounds
Authors: Gent A. N.
Published: February 2011

Measurements are described of the changes of volume accompanying crystallization in filled vulcanized natural rubber, and of the corresponding relaxation of stress in extended test-pieces. The observed changes in the rate of crystallization and relaxation of stress are attributed to the reduction in mobility of the rubber molecules in the neighborhood of foreign particles and to the effective higher orientation of some elements of the rubber matrix when the filled vulcanizate is subjected to simple extension.
The Rheological Unit in Raw Elastomers
Authors: Mooney M. , Wolstenholme W. E.
Published: February 2011

Reasons are adduced for suspecting that, in a raw elastomer subjected to continuous shear, there exist groups of molecules which are held together by entanglement or by thixotropic attachments and move and rotate essentially as elastic solid bodies. Such coherent molecular groups are called rheological units. If an elastomer in continuous shear consists essentially of closely-packed rheological units, such units, rolling on each other, will transfer a rubber-soluble dye across the shear planes as the ink rollers transfer ink in a printing press. This predicted phenomenon has been observed with a Mooney viscometer fitted with a smooth rotor, the face of which is covered with a thin film of dried cement containing a dye in high concentration. From the velocity of the color front, a rough value can be computed for the mean diameter of the rheological units. The diameters for a series of different elastomers lie in the range from 1 to 35 microns.
Effect of Molecular Interaction on the Light Scattering of Rubber Solutions
Authors: Gul V. E. , Klitenik G. S.
Published: February 2011

1. The molecular light scattering of rubber solutions which differ in the polarity of the dissolved high polymer and the polarity of the solvent was investigated. 2. The relation of the angular coefficient of the concentration curves of light scattering to molecular interaction and other factors is discussed theoretically. 3. A relation is proposed which may simplify the procedure of experimentally characterizing polymers by means of the numerical mean and average molecular weights. 4. A method of determining the specific cohesion energy of high polymers according to the data of molecular light scattering in their solutions is offered.
Breakage of Rubber-Filler Linkages and Energy Dissipation in Stressed Rubber
Authors: Blanchard A. F.
Published: February 2011

The marked softening of reinforced rubber by applied stress can be interpreted in terms of a range of strengths of secondary linkages formed by rubber-filler attachments, and this can be described by one common distribution parameter K for several grades and types of filler in natural rubber, and also for at least one type of carbon black in Krylene (GR-S) synthetic rubber. Linkages of this type are of little significance in reinforcement, judged by tensile strength or abrasion resistance. The fact that the filler particle diameter had no influence in these experiments on the energy dissipated in breaking secondary linkages, or their number as reflected by their stiffening action, may be considered a serious objection to the presumption that specific surface or interfacial area determines linkage formation in rubber and, hence (supposedly), the reinforcement. There is evidence of primary (strong) linkages introduced by carbon blacks, and these are likely to have a more important role in determin- ing the breaking, tearing, and abrasion of rubber.
Vulcanizing Variability of Natural Rubber in Pure-Gum and Carbon Black Compounds
Authors: Baker H. C.
Published: February 2011

The history of the ACS 1 compound and its use by natural-rubber producers to assess the variability of plantation sheet and crepe is described. Using modulus at a fixed cure as a criterion of vulcanizing properties, the large variation found in the ACS 1 compound is greatly reduced by the addition of carbon black, but there is good correlation between moduli in the presence and in the absence of black. Detailed results of tests for a range of properties are presented for Red, Yellow, and Blue technically classified rubber in compounds loaded with MPC, HAF, and SRF blacks, and with different accelerators. Some of these properties show a wider range of variation than modulus, and they also indicate that technical classification based on modulus in the ACS 1 compound is justified by the behavior of the black-loaded compounds, both in regard to the level of vulcanizate properties, curing times, and scorch characteristics.
Free-Radical Activity of Reinforcing Rubber Fillers
Authors: Garten V. A.
Published: February 2011

In our studies of the mechanism of rubber reinforcement, we were led to assume that primary valency bonds are likely to form between an “active” filler and the rubber-matrix via free-radical intermediates. The hypothesis was based on the following considerations. (1) Although a strong school of thought still maintains that the strength of bonding depends mainly on van der Waals forces, and therefore on particle size, a number of individual observations suggest the presence of “reactive sites” and formation of strong bonds of a chemical nature between filler and rubber. Foremost among these is the phenomenon that the incorporation of active pigments such as carbon blacks, silicas and the like into rubber results in the insolubilization of a part of the rubber. This part is conveniently called “bound rubber” or “carbon-gel”. (2) Farmer and his school have shown that the vulcanization process is based on a free-radical mechanism, wherein a number of the rubber double-bonds and α-methylene groups, sulfur and accelerator are involved, resulting in the formation of three-dimensional giant networks. The mechanism of mastication is also known to consist of the production of free radicals in the presence of suitable ‘radical acceptors’, such as oxygen. (3) There are some common features in both reinforcement and vulcanization, such as crystallization effects. (4) Little or no reinforcing action of otherwise active pigments is observed with saturated polymers, for example, polyisobutylene.
A Simple Objective Method for Estimating Low Concentrations of Ozone in Air
Authors: Beatty J. R. , Juve A. E.
Published: February 2011

A simple, accurate, and objective method for the estimation of ozone concentrations in air has been developed. It is based on the well known reaction of ozone on rubber subjected to strain, namely, the formation of cracks. The differential creep of a natural rubber thread, one-half of which is subjected to the ozone-containing atmosphere, the other half protected from ozone, is a sensitive measure of the severity of ozone attack or cracking. This differential creep or deflection is essentially linear with time at a given ozone concentration, and the rate of deflection is directly proportional to the ozone concentration. The variables of specimen, machine, temperature, thread elongation, humidity, and sunlight were investigated. The instrument, the B. F. Goodrich Ozonometer, is a small, self-contained unit, which may be operated in the horizontal or vertical position. Two areas of usefulness for this method and machine exist. 1. Tests for ozone concentration in locations inaccessible to ordinary chemical methods by virtue of the equipment and services required. 2. Comparisons of the resistance of rubber compounds to ozone attack under conditions of controlled ozone concentration.
Electron Microscopic Study of the Locus of Latex Reaction
Authors: Crampsey Edward , Gordon Manfred , Sharpe John W.
Published: February 2011

The outstanding example of the study of reaction loci in an emulsion system is Harkins's work in the field of emulsion polymerization. A simpler case presents itself for study when chemical reactions are carried out with preformed polymer emulsions (latexes), as in the hydrochlorination of polyisoprene latex. Here the reaction consists in the progressive conversion of the individual unsaturated isoprene units to their hydrochlorinated form: (see PDF for diagram) the polymer particles preserving their identity throughout the reaction. The hydrochloric acid arrives at the site of reaction by a series of diffusion processes from the vapor phase and through the continuous aqueous phase. In principle there are still two loci at which the isoprene units may react with this reagent: in the bulk of the particle and at (or near) the interphase between the aqueous acid and the polymer particle. We were led by kinetic experiments to conclude that the two loci do react at different rates and by different mechanisms, and it is the purpose of this report to provide quantitative evidence for this conclusion. At the same time we wish to put on record some observations connected with the electron microscopic technique used in the investigation.
Water-Soluble Acids of the Latex of Hevea Brasiliensis
Authors: Bevilacqua E. M.
Published: February 2011

Malic, citric, and succinic acids have been identified as components of the serum of Hevea brasiliensis latex preserved with ammonia. It has been confirmed that the plant acids are present in low concentrations in fresh latex but form a large fraction of the water-soluble serum solids.
The Role of Oxygen in the Vulcanization of Natural Rubber
Authors: Kuzminskii˘ A. S. , Cheetkova V. F.
Published: February 2011

A three-dimensional structure is formed during the vulcanization of rubber. The complex processes of formation, rupture, and regrouping of bonds during vulcanization lead finally to union of the long chain molecules into a compact network. The density of the network formed during vulcanization and the distribution and degree of sulfide formation by the bonds govern to a large degree the work-capacity of vulcanizates. Structure formation in vulcanizates is manifest by the change of their tensile strength, elasticity, swelling, and solubility. During the vulcanization of natural rubber, an optimum is observed in the change of tensile strength and other technically important properties of the material. The decrease of tensile strength of vulcanizates by overvulcanization is usually ascribed to the oxidative destruction of the molecular chains of the rubber. The strong influence which has been observed of oxygen on the tensile strength of natural rubber and its vulcanizates is the basic argument in favor of oxidative destruction. This influence, however, only appears when the rubber is in direct contact with oxygen or air. When, in the rubber industry, vulcanization is carried out in presses, the surface of the rubber mixture is isolated from atmospheric oxygen, and, consequently, destruction in this case can be caused only by the oxygen dissolved in the rubber mixture.
Vulcanization of Crepe Rubber by Sulfur Monochloride. II. The Dilatometric Method
Authors: Glazer J.
Published: February 2011

The vulcanization of rubber by sulfur monochloride is believed to consist of the cross-linking of adjacent isoprene units by thio-ether bonds. Such a reaction, involving polymer aggregation, should be accompanied by an increase of the density of the rubber, and, by choosing a suitably delicate technique, it should be possible to measure the rate of vulcanization by observing density changes. A dilatometric method seemed most suitable, and it was found that the reaction could indeed be followed by observing the rate of decrease of volume of the system rubber-sulfur monochloride when dissolved in a suitable solvent. Initial experiments showed that, during cold vulcanization, the system underwent a volume contraction which was of the order of 10 per cent with respect to the rubber. This comparatively large contraction allowed one to work with extremely dilute solutions (<0.3% w/w) of rubber. It thereby became possible to study the systems under more ideal kinetic conditions of high dilution than has been hitherto possible. In the present investigation, it has not been possible to do more than establish the broad outlines of the kinetic behavior of the system, and, on this basis, to propose feasible mechanisms for the cold vulcanization process.
The Curing of Silicone Rubber with Benzoyl Peroxide
Authors: Bueche A. M.
Published: February 2011

Little has been reported about the action of benzoyl peroxide as a vulcanizing agent for silicone rubber. Knowledge of this action seems to be of consider- able importance, since benzoyl peroxide is the most widely used vulcanizing agent at the present time. Apparently no studies of the kinetics of peroxide decomposition in silicones have been undertaken. It is not known quantitatively whether or not the silicones influence the decomposition rate in the way some of the solvents studied by Cass and by Nozaki and Bartlett do. In this paper we report the results of work undertaken to determine the number of cross-links introduced into polydimethylsiloxane by benzoyl peroxide during the normal vulcanizing process. The apparent efficiency of cross-link production has been determined as a function of the concentration of peroxide, the method of vulcanization, and of the filler content of the sample.
Structure and Dielectric Properties of Rubber Mlxtures Containing Carbon Black
Authors: Dogadkin B. , Lukomskaya A.
Published: February 2011

One of the fundamental steps in solving the problem of the reinforcement of rubber is that of explaining the nature of the reaction between rubber and fillers. The measurement of heat effects during swelling, in addition to presenting experimental difficulties, does not provide a direct evaluation of the intensity of the rubber-filler bond in rubbers used in industry. In order to measure this bond, the present authors studied the frequency and temperature relations of the dielectric constant ε′ and the tangent of the angle of dielectric losses, tan δ, of unvulcanized natural rubber and sodium-butadiene rubber, rubber-carbon black mixtures, and vulcanized rubber containing different loadings of channel and furnace blacks. The measurements were made in the frequency range of 50 to 2.5×107 cycles per second at 20° C and also in the frequency range of 103 to 4×104 cycles per second at temperatures from −75° to 152° C. As the experiments show (see Figure 1), the coefficient of dielectric loss, ε″=ε′⋅ tan δ, of a raw rubber has no maximum within the frequency range and temperature range studied. At the same time, the rubber-carbon black mixtures are characterized by a maximum ε″ at frequencies of (2−2.5)×103 cycles per second, which depends to a slight extent on the temperature. Vulcanizates containing no carbon black have a maximum ε″ at (2−3.5)×106 cycles per second at 20° C, which is displaced to the temperature range −24° to −27° when the frequency is decreased to 103 cycles per second. Both maxima are observed on the ε″ curves with loaded vulcanizates, the first caused by the heterogeneity of the rubber-carbon black mixture, and the second due to the formation of sulfur dipoles during vulcanization. Consequently, the ε′ curves have two regions of change.
Promoters for the Reaction of Rubber with Carbon Black
Authors: Doak Kenneth W. , Ganzhorn George H. , Barton Bernard C.
Published: February 2011

Heating unvulcanized mixtures of rubber and carbon black gives increased electrical resistivity, reduced hysteresis and hardness, higher modulus, and increased abrasion resistance to the vulcanizate. This is believed to result from improved dispersion of carbon black, accompanying a chemical reaction between rubber and carbon black. Butyl rubber, with low unsaturation, reacts more slowly than Hevea rubber or butadiene-styrene copolymers (GR-S). Chemical promoters decrease the time and temperature required for the reaction. Certain quinones and aromatic nitroso compounds are effective in both Hevea and Butyl rubber. t-Butyl perbenzoate and cumene hydroperoxide are particularly effective in Hevea rubber and GR-S containing channel black, and when used in optimum amounts, do not adversely affect tensile strength. Hexachlorocyclopentadiene and hexachlorophenol are effective in both Hevea and Butyl rubber, l,3-Dichloro-5,5-dimethylhydantoin and hexachlorocyclopentadiene are effective in Butyl containing channel or furnace blacks. Chemical promoters are believed to initiate allylic or alkyl radicals on rubber chains, which react with active centers on carbon black, forming primary valence bonds.
Structure and Rheological Properties of Hevea Latex Gels
Authors: De Vries A. J. , Van den Tempel M.
Published: February 2011

Some rheological properties of hydrogels made from Hevea latex have been determined by shear measurements, using a hollow cylindrical test piece. The shear modulus and the viscosity depend on the volume concentration of solids in the gel, the composition of the interfacial layer surrounding the rubber globules, and the particle-size distribution of the rubber globules. An interpretation of the experimental results is given, based on the assumption that no coalescence of the rubber particles occurs. The rheological properties of the gel should then be functions of the number of points of contact between the particles and of the strength of the bonds between the particles in the gel.
Abrasion and Slippage
Authors: Ebert G. , Weidner V.
Published: February 2011

The types of apparatus used technically for testing the abrasion resistance of rubber compounds, in particular tread compounds, have been equipped to operate with 100 per cent slippage. The results obtained under such conditions seldom agree with the results of road tests, because the abrasion of tires under ordinary conditions takes place with relatively little slippage. No method for determining abrasion which takes this fact into account has yet come to the attention of the authors. Although the present work is already rather old, its publication still seems justified, since it focusses attention on some still unpublished results which are essential to any estimation of the practical behavior of tread compounds when subjected to abrasion.
A Study of Some Heat-Sensitizing Agents for Hevea Latex
Authors: Pariente Claude
Published: February 2011

Latex mixtures containing different heat-sensitizing agents were studied from five points of view: conditions of gelation, changes of viscosity, changes of mechanical stability, heat sensitization (with and without zinc oxide), and the physical properties of the vulcanizates. It would seem that conventional heat-sensitizing agents can be replaced to advantage by agents such as triacetin or nitroparaffins, which more nearly approach the ideal agent as defined at the beginning of this work. In addition, triacetin gives latex mixtures which are particularly easy to process. As for the nitroparaffins, they are noteworthy for giving vulcanizates with excellent mechanical properties.
The Accelerated Coagulation of Latex
Authors: Van Gils G. E. , Resing W. L.
Published: February 2011

The object of the study described in this paper has been a very practical one. However, the results from a practical point of view are rather disappointing, mainly because of economic reasons, but we think them interesting enough to have them published, because some light may be thrown on our basic knowledge of the coagulation phenomena of Hevea latex.
Zinc Oxide Testing of Latex
Authors: Madge E. W. , Collier H. M. , Newnham J. L. M.
Published: February 2011

Viscosity changes in concentrated natural rubber latex under different experimental conditions were investigated with the object of determining the mechanism of zinc oxide thickening and to find reasons for inconsistencies in correlating results of the zinc oxide thickening or ZOT test with other latex tests. It has been found that small variations of the amount of naturally occurring soap are of great importance in the thickening of latex containing zinc oxide, especially at the low ammonia content used for the ZOT test. The effect of added soap on the ZOT test was found to vary from latex to latex and to be different for different soaps. Less than about 0.3 per cent of various soaps added to latex prior to the zinc oxide reduced the degree and rate of thickening. With more than this amount of soap, the thickening depended on the soap used. A similar investigation in which the mechanical stability of latexes containing varying amounts of added soap and a standard amount of zinc oxide was measured, showed that the latexes varied anomalously with the amount and the type of soap added. The results of the work presented in this paper show that new tests for the zinc sensitivity of latexes must take into account a number of hitherto unsuspected factors, particularly when such tests are required to have a bearing on processing behavior.
Butyl-Type Polymers Containing Bromine
Authors: Morrissey R. T.
Published: February 2011

Butyl rubber has been modified by attaching bromine to the polymer chain. The reaction has been considered as mainly one of addition to the double bonds, thereby lowering the unsaturation. Both sulfur and metal oxide can serve as vulcanizing agents for brominated Butyl, and both may function in the same compound, thus producing a faster rate of cure compared to Butyl. Brominated Butyl can also be covulcanized with natural rubber and GR-S, and therefore it is now possible to impart to these rubbers the excellent properties of Butyl, such as low air diffusion and resistance to ozone and flex-cracking. Still other advantages compared to Butyl rubber are higher modulus and good adhesion to other elastomers and metals. Data have been presented to show that the properties of these new Butyl-type polymers can be varied by the amount of bromine which they contain. It has also been shown that there is an optimum range of the halogen concentration required for obtaining the best properties both in mixtures with natural rubber and in brominated Butyl polymers used as adhesives. This optimum range of bromine also depends on the original unsaturation of the polymer.
Study of the Reaction Kinetics of Aging of Natural Rubber by Infrared Spectrography IV. Influence of Wave Length of Light and Temperature on Light Aging
Authors: Tkáč A. , Kellö V. , Hrivíková J.
Published: February 2011

The influence of the wave length of radiation on the process of photocatalytic aging of rubber, as well as the relations between the intensity of radiation and the temperature, were studied by infrared spectroscopy. The upper limit of effectiveness of light lies in the range of 4360 A˚. While an increase of temperature greatly accelerates oxidation, an increase of radiation intensity retards it. Numerous analyses reveal an exponential relation between the length of the induction period and the intensity of radiation at constant temperature, and a linear relation between the height of the experimental curves and the temperature at constant intensity. Oxidation destruction and side-chain formation (vulcanization) take place simultaneously during the aging of natural ruber. The relation between these reactions depends on the experimental conditions ; the temperature accelerates oxidation, while the intensity of radiation aids vulcanization.
Viscoelastic Properties of Linear Polymers in the High-Elastic State
Authors: Vinogradov G. V. , Dzyura E. A. , Malkin A. Ya , Grechanovskii V. A.
Published: February 2011

The relation between molecular weight, chain rigidity, and the length of the high-elasticity plateau is determined from frequency and temperature dependences of the storage modulus for polybutadienes and polystyrenes with Mw/Mn≤1.1. Use is made of the concept of equivalence of high-elastic states characterized by equal lengths of high-elastic plateaus for linear polymers. The high-elastic states of the linear polymers studied are equivalent if the polymer chains have equal numbers of dynamic segments and if the reference temperature is T0=1.22Tg, where Tg is the glass transition temperature. The viscoelastic properties of the polymers in the high-elastic state are determined unambiguously by Tg and the molecular weight of the dynamic segment. The quantitative relation between thermomechanical characteristics obtained by measuring deformation versus temperature under a constant time regime and dependence of storage modulus versus frequency under isothermal conditions is discussed.
Influence of Hysteresis on Tensile and Fatigue Failure in Rubbers
Authors: Payne A. R. , Whittaker R. E.
Published: February 2011

The failure criterion developed by Harwood et al. between energy input to break and hysteresis at break for amorphous rubbers has been related to the fatigue and cut growth properties of the rubber which are based on the tearing energy theory. It is found that the constant K in the hysteresis failure criterion is a function of the cut growth constant G and the inherent flaw size C0. The effect of adding fine particulate fillers to amorphous rubbers on the hysteresis and fatigue properties is considered and shown to be in agreement with the theory.
The Actual Contact Area and Friction Properties of Elastomers under Frictional Contact with Solid Surfaces
Authors: Bartenev G. M. , Lavrentjev V. V. , Konstantinova N. A.
Published: February 2011

Using a specially designed apparatus simultaneous measurements were carried out of the area of contact and the friction between elastomers and solid surfaces. For a wide range of load, the friction force is proportional to the actual contact area and the friction constant depends only on the nature of the rubbing solids. In the range of low sliding velocities the actual contact area remains almost constant. At high sliding velocities increase of the friction force is associated with the process of the mechanical glass-transition of the surface layer of the crosslinked rubber which causes the actual contact area to decrease.
Modulus of Plasticized Ionic Rubbers
Authors: Eisenberg A. , King M.
Published: February 2011

The rubbery modulus of a crosslinked ionizable rubber is explored in the absence of the crosslinking effect of ions, that is, only through the effect of ions on conformation. The crosslinking effect is eliminated by plasticizing the rubber with a liquid of high dielectric constant. Experimentally, a rubber is prepared by mixing poly (acrylic acid) and poly (vinyl alcohol) and cross-linking thermally. The relationship between the rubbery moduli of the unionized and the ionized forms of the plasticized material is studied. A theory for the modulus of such a two-component rubber is derived and the predictions are compared with experiment. It is shown that the predicted ratio of the moduli in the acidic and ionic forms is in the same direction as determined experimentally, but that the calculation underestimates the magnitude of the effect. Several reasons for this discrepancy are given.
Heat Schedules in the Vulcanization of Thick-Walled Articles
Authors: Sverdel M. I. , Aronovich F. D.
Published: February 2011

The analytical relationships obtained make it possible to determine the equivalent time and duration of vulcanization of thick-walled rubber articles with constant temperatures on the heating surface without complete calculation of the temperature field. The method is suitable for a preliminary selection and assessment of schedules of vulcanization of covers in shaper-vulcanizers.
The Growth of One-Dimensional Shock Waves in Elastic Nonconductors
Authors: Chen Peter J. , Gurtin Morton E.
Published: February 2011

In this paper we study the propagation of shock waves in elastic materials that do not conduct heat. We derive a differential equation relating the strain and strain gradient behind the wave when the region ahead is unstrained and at constant entropy. Using this equation we are able to give conditions under which the wave will grow or decay at a given time. Generally, the results are qualitatively the same as in the purely mechanical theory.
Hysteretic Losses in Rolling Tires
Authors: Willett P. R.
Published: February 2011

A relationship between the observed energy losses for a tire that has reached a state of thermal equilibrium when operating at a constant speed, and the viscoelastic properties of the tire components has been formulated. The analysis was carried out by systematically varying tire components and operating parameters, using the Vibron Viscoelastometer and tire test wheel dynamometer. The investigation was carried out for 6.95–14 cross ply passenger tires. From the derived dependence of the tire energy losses on viscoelastic properties, the effect of changes in tire tread compound, ply rubber and tire cord on the tire energy losses can be predicted. This enables the design of a tire with the properties to meet desired service characteristics.
The Determination of Network Chain Density and the Chemical Stress Relaxation of Crosslinked Polymers
Authors: Tamura Saburo , Murakami Kenkichi
Published: February 2011

Both initial network chain densities nM(0) and nS(0) of dicumyl peroxide- cured natural rubbers were determined from the tensile stress and swelling method, respectively. The difference between nM(0) and nS(0) was usually constant, independent of the magnitude of network chain density. That is, it was found that the number of entanglement network chains in the crosslinked natural rubber was usually constant, independent of network chain density. The entanglement network chain density nII(0) was 0.7×10−4 mole/cc. This led to the supposition that the molecular weight between entanglement points Me would be about 9000. Although this value is far from exact, it does not differ too greatly from the value found for noncrosslinked natural rubber. Next, in order to calculate the number of main-chain scissions of crosslinked polymers from their chemical stress relaxation, we proposed our modification of Tobolsky's equation. Using our equation, it was found that the scission of dicumyl peroxide-cured natural rubber occurred in the main chain only. Furthermore, this value agreed with the one obtained from the oxidation of toluene solution of noncrosslinked rubber under the same conditions.
Prevulcanization Inhibitor of Sulfur-Free Thiuram Vulcanization
Authors: Ducháček Vratislav
Published: February 2011

On the basis of Mooney scorch measurements at 120° C and of continuous measurements of vulcanization in a Vuremo curemeter at 145° C, sulfenamides which function as inhibitors of the sulfur-free thiuram vulcanization have been investigated. It was found that the actual prevulcanization inhibitor is 2-mercaptobenzothiazole. Its formation from sulfenamides is activated by zinc dimethyldithiocarbamate since the vulcanization of rubber by thiuram disulfides in the presence of zinc oxide is always accompanied by the formation of zinc dithiocarbamate. It seems probable that the inhibition effect of 2-mercaptobenzothiazole is attributable to the formation of a complex with zinc dimethyldithiocarbamate which decreases the reaction rate in the initial steps of the sulfur-free thiuram vulcanization and thus causes the scorch delay.
Effect of the Degree of Dispersion of the Curing System on the Properties of Rubber Compounds and Vulcanizates
Authors: Fedyukin D. L. , Vinogradova T. I. , Danchenko L. A. , Ermilova N. V.
Published: February 2011

The viscosity of a rubber compound and its curing rate are determined by the number of initial aggregates of rubber mobilized around the ingredients of the curing system and by the distances between them. The lower the degree of dispersion of the ingredients of the curing system, the later is the cure stage in which a continuous vulcanization network is formed.
Mechanical Behavior of O-Rings
Authors: Curro J. G. , Salazar E. A.
Published: February 2011

O-ring deformation is approximated as a plane strain contact problem. An integral equation is written for the contact stress which is solved for small deflections. The contact area agrees with the results of the conventional Hertz theory. The displacements of the deformed o-ring are found by requiring zero displacement at the center of the circular cross section. Experimental results on silicone rubber cylinders and o-rings agree with the theory up to approximately 15 per cent strain. A linear viscoelastic solution is constructed from the elastic solution for an o-ring held at fixed deflection for t > 0. For this case the contact area remains constant and the average load is proportional to the relaxation modulus.
Viscoelastic Properties of Truck Tire Compounds and the Related Heat Build-Up
Authors: Kainradl P. , Kaufmann G.
Published: February 2011

Rubber compounds used in the manufacture of tread-cap, tread-base, and for the rubber-coating of the rayon cord for 12.00–20 tires have been varied in composition and, in consequence, their viscoelastic properties have been altered. Operating temperatures, in test-wheel runs, have been measured in the shoulder region of the tire close to the casing, using a needle-thermocouple. Multiple-regression has been used to investigate which combinations of viscoelastic properties of the rubber vulcanizates would give a linear, significant correlation to the heat build-up in the tire with a minimum residual. From the nature of the variables in the regression functions, conclusions have been drawn on the type of load occurring in the different components of the tire. It was found that the tread cap contributed to the heat build-up according to its loss compliance E″/|E*|2 and the carcass according to its loss-factor, E″/E′. Thus, the statistics show that the greater contribution to the heat build-up comes from the tread-base, according to its loss-factor also. The values of temperatures, calculated by the multiple-regression, show deviations of only a few degrees centigrade compared to the average temperatures of tires of the same construction. Therefore the operating temperatures of tires to be expected as a result of the compound variations can be estimated in advance. On individual tires greater deviations, up to 10°C, have been measured. These are due to inevitable inaccuracies in tire building and errors in temperature measurements.
Effect of Casting Solvent on the Mechanical Properties of a Styrene-Butadiene-Styrene Block Copolymer
Authors: Fielding-Russell G. S.
Published: February 2011

The tensile mechanical properties of a number of well characterized solution-cast styrene—butadiene-styrene block copolymer systems are reported within the strain range of 0<ε≤5.0. It was found from the results of repeated stretching experiments (up to 100%) at room temperature that polymers cast from solvents for polystyrene or from solvents for both polystyrene and polybutadiene showed lower stresses on each cycle whereas the stress levels for the polybutadiene solvent-cast sample remained essentially constant. The polystyrene solvent-cast and polystyrene/polybutadiene solvent-cast samples exhibited a yield at ε≈0.3. No “yield” was apparent with the polybutadiene solvent-cast sample. The explanation for these behaviors lies in the material of the continuous phase. When the continuous phase is polystyrene there will be long-time recovery after the yield and consequently the system will be left under residual stress so that lower strains are observed on subsequent straining. When polybutadiene is the continuous phase (a phase inversion) no such yielding is apparent, the form of the stress-strain curve is that of an elastomeric material, and hence the repeated stress-strain curves are practically superposable. It was concluded that the low strain region is governed by the material of the continuous phase. From the viscoelastic measurements it was found that at 1.0≤ε≤6.0 the values of the modulus-temperature dependencies were comparable to that given by polystyrene and that the linearity and the slopes of plots of the logaT as a function of temperature were indicative of a glassy and, moreover, a polystyrene response. It was concluded that the strain region 2.0≤ε≤5.0 is governed by the polystyrene content, whether it be in the continuous phase or not. These results, together with certain proposed model structure, are discussed with the available literature.
An HF-Nickel-R3Al Catalyst System for Producing High Cis-1,4-Polybutadiene
Authors: Throckmorton M. C. , Farson F. S.
Published: February 2011

A relatively new, high cis-1,4-polybutadiene and a novel trialkylaluminumnickel-HF catalyst system have been described. This polybutadiene is unique in that it possesses high tack and has exceptionally good processing qualities; the carbon black-loaded and cured rubber possesses good static and dynamic properties. The catalyst system is very effective for producing high molecular weight rubber, suitable for oil extension, and the molecular weight can be controlled by adjusting 1) HF to R3Al ratio, 2) total catalyst concentration and/or 3) polymerization temperature.
An Improved Wire Adhesion Test Method
Authors: Hicks A. E. , Chirico V. E. , Ulmer J. D.
Published: February 2011

A new type of wire adhesion test method has been developed and has been compared to the conventional ASTM (D-2229) method on the basis of both accuracy and precision. The extent to which the ASTM slot type method can bias adhesion measurements by concentrating stresses at the leading edge of the wire-rubber interface has been demonstrated and is in agreement with the findings of other investigators. No such limitation was found with the CSRC method. In terms of precision, the ASTM and CSRC methods were found to be comparable, but the CSRC method was found to be more sensitive to differences in adhesion. The new method was used to show that carbon blacks with higher levels of EM surface area, unit form factor, porosity, and volatile content increased wire adhesion in a NR-sulfur compound, unaged and tested at room temperature. The effects of EM surface area and unit form factor became more important when the compounds were aged severely and tested at 212° F. Increased porosity and volatile content improved adhesion unaged at room temperature, but when adhesion was tested hot and aged, the quality of the rubber deteriorated and adhesion was lowered as the levels of these variables increased. Carbon black loading and type are important in a natural rubber recipe in developing good levels of wire adhesion at various test conditions: first, by altering the rate of vulcanization in a direction that favorably affects the competing reactions of the rubber and brass for sulfur and second, by increasing the reinforcement of the rubber, particularly at high temperatures.