bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Magnetic Resonance Study of Transitions in Polymers
Authors: Holroyd L. V. , Codrington R. S. , Mrowca B. A. , Guth E.
Published: February 2011

Nuclear magnetic resonance absorption line widths have been studied for several high polymers. The proton line widths were studied in a field of 7000 gauss and at a frequency of about 30 mc. Line widths obtained for Hevea rubber and GR-S were very narrow, indicating a large degree of “quasi-free rotation” in these materials. Vulcanization, carbon loading, copolymerization, and crystallization produced a broadening of the lines, as expected from the hindrance to internal motion introduced by these factors. Line width transitions as a function of temperature were observed for several polymers. Linear thermal expansion coefficients and specific heat vs. temperature curves have breaks in the region of line transitions for the polymers studied. Swelling of polymers with benzene produced a narrowing of the absorption line throughout the line transition and lowered the transition temperature. Vulcanization broadened the transition range and shifted it to higher temperatures. Of two closely cut fractions of polystyrene, the larger molecular-weight sample exhibited a line transition range at a higher temperature. The styrene monomer as well as the two fractions exhibited the same low-temperature line width of about 8 gauss. The line-width transitions were also studied for three butadiene-styrene copolymers at temperatures where anomalous behavior was found in dynamic measurements. The theoretical implications of these experimental results, together with a survey of other pertinent work, indicate the possibilities of the nuclear resonance method as applied to the study of high polymers in conjunction with other methods.
Breakage of Carbon-Rubber Networks by Applied Stress
Authors: Blanchard A. F. , Parkinson D.
Published: February 2011

The results of this investigation strongly support previous conclusions by the authors that the softening of reinforced rubber when it is stressed to moderate extensions owes little to breakdown of filler chain structure and is due primarily to rupture of attachments between the filler and the rubber molecules. This means that the stiffness of reinforced rubber is influenced greatly by the mode of attachment of filler to rubber, and the conclusion reached is that such stiffening by finely divided fillers is largely a consequence of linkages between rubber molecules formed through the filler particles by rubber-filler bonds and assisted by the presence of coherent chain structure of the filler particles themselves. The work further suggests that the linkages formed through carbon particles are of two kinds : one a relatively weak type linkage due to physical (van der Waals) attachments, the other a strong type linkage due to chemisorptive attachments which remain unbroken by stressing. The strong linkages are relatively few and have not been found with fillers other than carbon black, but the strength distribution of the weaker type does not depend on the chemical nature or type of filler, although differences are found in the total number of such relatively weak attachments. The weak linkages are substantially all broken in the course of stressing to high elongations and the stiffening at the highest elongations is a consequence of the relatively small number of strong linkages. It is to be expected that among the fully reinforcing carbon blacks, where the particle sizes of the different types are roughly equivalent, those providing the greatest number of strong linkages will have the greatest reinforcing ability, and it may be significant in this connection that HAF black vulcanizates are recognized to have better abrasion resistance than MPC vulcanizates, in keeping with a larger number of strong linkages.
Carbon Black Dispersion and Reinforcement
Authors: Dannenberg E. M.
Published: February 2011

Different mixing conditions were employed to obtain vulcanizates, varying only in degree of carbon black dispersion, with natural and synthetic rubbers, using a single sample of a commercial grade HAF black. Light transmittance measurements on dilute solutions of dissolved unvulcanized stocks prepared by an improved technique were used to evaluate the size of carbon black aggregates in cold GR-S and natural rubber stocks. Electron micrographs of films show the high degree of carbon black aggregation, even after prolonged mixing. A limiting degree of dispersion or a minimum aggregate size is obtained very rapidly as mixing is increased. Black incorporation and dispersion appear to take place simultaneously; a high degree of abrasion reinforcement was noted in most rubbers with mixing (less than 75 seconds) barely sufficient to incorporate the black. Carbon blacks in general respond rapidly to mixing, and the chainlike aggregates characteristic of reinforcing carbon blacks observed under the electron microscope are practically unchanged after mixing with rubber. Dispersion of carbon blacks during mixing depends on the packing and coherence of their agglomerates resulting from such factors as surface oxidation and extent of mechanical bulk densification. There is some evidence that oil-type furnace blacks disperse more easily than channel blacks. A major cause of the disappointing abrasion reinforcement with most noncarbon pigments possessing extreme fineness may be the tendency for excessively strong aggregate binding and resulting large aggregates in rubber. A striking rise in electrical resistivity was observed as the amount of mixing was increased. As the size of the aggregates did not change, the higher electrical resistivity cannot be explained by assuming better dispersion and breakdown of conductive carbon paths. Increased mixing might provide better distribution of the carbon aggregates in in the rubber matrix without change in size of aggregates.
Some Properties of Butyl Rubber-Carbon Black Systems
Authors: Ford F. P. , Gessler A. M.
Published: February 2011

Previous studies have shown that differences in milling conditions cause significant variations in the dispersion of SRF black in Butyl rubber. Recent work has placed such differences on a more quantitative basis. This was achieved by the interrelation of photometric, rheological, and electrical measurements. These observations revealed new phenomena involving changes in the pigment-polymer habit of sueh systems. Analysis of these phenomena has led to the conclusion that they may be interpreted as evidences of pigment-polymer association.
Cracking of Rubber and GR-S in Ozone. Effects of Temperature and Elongation
Authors: Cuthbertson G. R. , Dunnom D. D.
Published: February 2011

Determinations of the effects of elongation on the character of cracking in samples of rubber exposed to ozone have been reported by some of the early workers in the field. Data on some of the effects of temperature on the rate and character of cracking have not clearly shown the effects of the interaction of temperature and elongation on the character of ozone cracking. In the present study, samples of rubber, standard GR-S, and low-temperature GR-S compounds were exposed to a constant concentration of ozone for 4 hours at several elongations and temperatures. Prints were made from the exposed samples by inking the sample surface and taking an impression on paper. The rubber compound cracked at lower temperatures and elongations than either the standard or low-temperature GR-S compounds, and for each temperature there existed an elongation below which no sample cracked; this elongation is termed the cracking threshold for this temperature. The cracking threshold was found to be a function of the temperature, decreasing with increasing temperature. Although this relation is particularly difficult to treat exactly, it is possible to explain this effect on the basis of changes in ozonide film strength and ozonide stability with temperature. Studies of the effects of compounding on the cracking threshold may be of great value in designing compounds to fit the climatic conditions where they are to be used.
Static Exposure Testing of Automotive Compounds
Authors: Winkelmann H. A.
Published: February 2011

Deterioration of rubber products on outdoor exposure is due to the action of sunlight and ozone. Ozone cracking results when rubber is exposed under strain. The type of cracking produced by ozone is not produced by other elements or materials normally present in the atmosphere. Light-energized oxidation produces a crazed condition on the surface of the rubber, which is quite different from the effects produced by ozone. This study was undertaken to determine the factors which influence the resistance of rubber products to ozone. It was found that rubber cured under strain cracks faster than when cured at rest. Manufacturing defects, such as blisters, air traps, foreign matter, and pigment agglomerates, resulted in premature cracking. Certain manganese, copper, and iron salts had an adverse effect on ozone resistance in outdoor and accelerated exposure tests. Some dispersing agents used to make carbon black slurries for GR-S carbon black masterbatches, showed an adverse effect on weather aging. The selection of a polymer, such as natural rubber, GR-S, Neoprene, or Butyl rubber, has a marked influence on the ozone resistance of automotive rubber products. Unless a polymer is handled and compounded properly, good ozone resistance is not obtained. In outdoor exposure the effect of sunlight, ozone, heat, and water varies seasonally in Florida, California, Michigan, and Illinois. Many tests and much good judgment must be exercised in correlating accelerated and outdoor exposure tests.
Detection of Elemental Sulfur in Minute Quantities as in “Blooms”
Authors: Galloway P. D. , Foxton R. N.
Published: February 2011

It appears from the tests performed that the first method given is the more sensitive and is less liable to interference from accelerators.
Effect of Temperature on Rate of Oxidation of Rubber. Nature of Resultant Deterioration
Authors: Shelton J. Reid , Wherley Fred J. , Cox William L.
Published: February 2011

The same reaction appears to be rate-controlling in the oxidation of natural rubber and GR-S stocks at all temperatures in the range studied, 50° to 110° C. This is apparent from the linear relationship established between rate of oxygen absorption and the reciprocal of the absolute temperature. Presumably this would also be true for a reasonable extrapolation to lower or higher temperatures. Thus it is possible to determine the probable rate of oxygen absorption at room temperature on the basis of data obtained in short-term tests at higher temperatures, provided data are available at several temperatures. The effect on properties which accompanies the absorption of a given amount of oxygen varies with the temperature. For example, aging at higher temperatures produces a softer stock with lower modulus and higher elongation than is obtained by the absorption of the same amount of oxygen at a lower temperature. Thus chain scission predominates at higher temperatures, while cross-linking becomes of greater relative importance at lower temperatures. These facts, together with the observation that the same reaction is rate-controlling at all temperatures studied, indicate that the degradation reactions must be secondary reactions which are not rate-controlling. One cannot predict the aging characteristics of a stock by the use of an accelerated test at only one temperature. It is possible, however, to establish a quantitative measure of the rate of change in a given property (per unit amount of oxygen absorbed) as a function of temperature by means of tests at more than one temperature. Thus it is now possible to utilize short-term oxygen-absorption measurements at, say, three temperatures to establish the relationships, and then to extrapolate the data to lower temperatures and predict the time required to absorb a given amount of oxygen and the degradation of properties to be expected under comparable conditions at the lower temperature. If a change from oxygen to air is also involved, the effect of the changes in oxygen concentration must also be taken into account.
Acceleration and Aging
Authors: Haehl Adrien
Published: February 2011

In a study of the protection of vulcanized rubber against aging by combinations of the zinc salt of mercaptobenzimidazole and “true” antioxygenic agents, it has been found that such combinations have a synergetic effect of considerable magnitude in the protection of vulcanizates which are accelerated by mercaptobenzothiazole. On the other hand, in the case of vulcanizates accelerated by diphenylguanidine, the effect is slight or even negligible. On the assumption, therefore, that the nature of the accelerator has a great influence on the effectiveness of the protective agents, the latter were classified with respect to the accelerators used. In this way it was established that bis-(2-hydroxy-3-tert-butyl-5-methylphenyl) methane, when employed alone is by far the best protective agent against the aging of vulcanized rubber accelerated by diphenylguanidine. In addition by combining this “true” antioxygenic agent with the zinc salt of mercaptobenzimidazole it was found that only slightly greater protection can be attained than is possible by the antioxygenic agent alone. Consequently in this case one should not speak of a synergetic effect. The experiments lead quite definitely to the conclusion that the mechanism of protection against aging when a deactivating agent is present depends upon whether the accelerator employed is mercaptobenzothiazole or diphenylguanidine.
Plasticity and Filler Structure in Carbon Black Stocks
Authors: Whorlow R. W.
Published: February 2011

Continuing previous studies on the changes in stiffness of a carbon black masterbatch when stored at normal or elevated temperatures or when subjected to shear deformation, the changes during room temperature storage have been studied in more detail. From the results obtained, a modified hypothesis as to the behavior of carbon black structures in unvulcanized rubber is put forward, which accounts for all the features of the behavior of rubber/black stocks so far observed in this work.
Calculable Properties of Technical Rubber Mixtures
Authors: Schreuer E.
Published: February 2011

As a very enlightening example of nonideal material mixtures, technical rubber compounds show deviations from the additivity of thermodynamic and elastomechanical measured quantities which are to be expected according to the rule of mixed components. The deviations have an intrinsic relationship, and bear a relation to the concentration of the so-called active additives.
Nonlinearity in the Dynamic Properties of Vulcanized Rubber Compounds
Authors: Fletcher W. P. , Gent A. N.
Published: February 2011

Measurements are described of the dynamic properties of rubber, loaded with various amounts and types of filler, when subjected to mechanical vibration in simple shear at amplitudes from 0 to 3 per cent shear in the frequency range 20 to 120 c.p.s. The decrease of dynamic modulus with increasing amplitude is shown, for a wide range of filler types and concentrations, to be determined by the amount of stiffening produced by the filler. This relationship is not influenced by variations in the vulcanizing ingredients, reasonable variations in state of vulcanization, addition of softener, or imposition of static shear strain. Rubber compounds stiffened by mixture with, or chemical combination of, other polymers exhibit a smaller order of nonlinearity than that described above and also exhibit much lower hysteresis values within the amplitude range 0 to 3 per cent shear.
Factors Affecting the Measurement of Strain
Authors: Best L. L.
Published: February 2011

1. Although alteration of the mixing, vulcanizing, and testing cycle for the measurement of strain does affect the physical properties of the final vulcanizate, a high degree of correlation can be obtained between the results of the rapid test and the normal test. The rapid test, which will not consume any more man-hours than the normal test, can be fitted in to the normal daily procedure with little loss of testing capacity, and provides satisfactory data in a period of three hours for thirty-two test-specimens, whereas more than two days are needed by the normal standard procedure. 2. The mixing, curing, and testing error associated with the measurement by the rapid method is less than that obtained with the normal test method. 3. The rapid method can be used for predicting the results which would be obtained by many physical tests carried out by standard procedures and would, therefore, be generally useful for control measurements in industrial concerns. 4. Isothermal conditioning of the compounded stock after mixing does not appear to reduce the error associated with the rapid test, but does alter the relation between the rapid and normal tests. 5. Immersion of test-specimens in cold water after vulcanization does not improve reproducibility or alter the value of the strain measurement. 6. Molded strain specimens are liable to vary in respect of cross-sectional area. Such variations can produce considerable errors in strain measurements, particularly with rubbers of high strain or low modulus characteristics. A simple method for the correction of these errors is advanced which increases the reproducibility of the strain test.
The Velocity and Temperature Dependence of Rubber Friction
Authors: Schallamach A.
Published: February 2011

It is shown experimentally that the velocity of frictional gliding under constant tangential stress of rubber on glass and on silicon carbide cloth is, in the first approximation, an exponential function of the reciprocal absolute temperature and of the tangential stress. It is suggested that frictional gliding of rubber is a rate process.
Plasticization of Rubber in the Form of Latex
Authors: Conté Marc
Published: February 2011

When in the form of latex, rubber can be oxidized by thiols under hot conditions. The reaction apparently proceeds by the same mechanism as that characteristic in the action of peptizing agents on rubber during mastication. The results obtained confirm the hypothesis that the thiol is transformed quantitatively into the corresponding disulfide, with resultant oxidation of the rubbert. This transformation is a function of the pH value, and the best results are obtained when the pH value is around 4 and in the absence of NH4 ions (which have an inhibitory effect). Latex preparations of this type can be utilized for studying the chemical reactions of rubber in emulsion and for the preparation of rubber derivatives which are more soluble than those prepared from rubber latex which has not been degraded. In addition, such latex preparations are excellent adhesives which, in contrast to already known products (latex treated with hydrogen peroxide or other peroxides), give a sticky film by simple drying at room temperature. In this way heating can be avoided in cases where it has harmful effects and where the use of an oven is inconvenient. Finally, this type of latex is more adaptable to certain direct applications, both because of the superior adhesive properties of the rubber and because, with a relatively plastic coagulum, mastication is easier.
Zinc Soap Formation and the Gelling of Latex
Authors: Newnham J. L. M.
Published: February 2011

The gelling effect of zinc oxide on ammoniated latex is known to be due to the formation of zinc soaps. The object of the present work was to investigate the formation of zinc soaps under varying conditions in order to elucidate the gelling mechanism more clearly. The main variables affecting the zinc ammine ion formation in an ammonia solution containing given amounts of ammonium salts and soluble zinc are pH and temperature. Falling pH or rising temperature favor formation of the more chemically reactive lower zinc ammine ions, and give rise to the formation of zinc soaps if soaps are present. It is suggested that zinc soap formation in the serum of ammoniated latex and the consequent gelling of the latex depend on the presence of specific zinc ammine ions.
Fractions from Hevea Brasiliensis Latex Centrifuged at 59,000 g
Authors: Cook A. S. , Sekhar B. C.
Published: February 2011

Homans and van Gils have separated fresh latex, by centrifuging at 2,000 r.p.m. (ca. 1,000 g.) into two fractions, white and yellow, both consisting mainly of rubber particles and serum. They also reported the discovery of another discrete phase in fresh latex, which they called lutoids, and which were found mainly in the yellow fraction. Huret has described the separation of ammoniated latex at 400,000 g. into a white fraction, a yellow layer, and clear serum. We have obtained four distinct fractions on centrifuging fresh latex at 20,000 r.p.m. (59,000 g.), and these have not previously been described, although McColm has reported on the sludge obtained at 40,000 r.p.m. Latex was collected from a field of mixed clonal seedlings at the Rubber Research Institute of Malaya Experiment Station and cooled in an ice-water mixture within an hour of tapping the first tree. Part of the latex was weighed into Lustroid (celluloid) tubes fitted with air tight caps and spun at 59,000 g. in a refrigerated vacuum centrifuge at 5° C for three-quarters of an hour. Another portion of the latex was ammoniated to 0.5 per cent NH3 by weight, using a 20 per cent solution. Part of this latex was centrifuged with the fresh latex and part after 24 hours. Figure 1 represents diagrammatically the separations obtained.
Relaxation Time Spectrum, Elasticity, and Viscosity of Rubber. I
Authors: Kuhn W. , Künzle O. , Preissmann A.
Published: February 2011

By rapid deformation of a medium in which linear molecules are present, various changes are produced simultaneously in the latter. These changes are more or less independent of one another, and can release independently and totally or partially by rearrangement of valence distances and valence angles in the chain molecules. By virtue of such relaxation processes, a portion of the stress originating in the rapid deformation disappears, with a changing time requirement for the various portions. A relaxation time spectrum is thus formed. The relaxation time spectrum consists of a finite number of restoring force mechanisms with proper relaxation times or of a continuous spectrum. Both the creep curves (the dependence of the length of a body on time at constant load), and stress relaxation (decay of the stress observed in test sample kept at constant length after rapid deformation), as well as the total visco-elastic behavior, especially the behavior at constant periodic deformation of the test sample, are determined by the relaxation time spectrum. The appropriate Quantitative relationships were derived.
Hydrogenated Synthetic Elastomers
Authors: Jones R. Vernon , Moberly C. Wayne , Reynolds W. B.
Published: February 2011

Several years ago the Phillips Petroleum Company initiated a study of the properties of hydrogenated synthetic elastomers. The result of this investigation has been the development of a series of thermoplastic hydrogenated polymers, Hydropols, which have certain unusual properties not found in other available plastics. Prior to this investigation, little was known about hydrogenated synthetic elastomers. The hydrogenation of natural rubber had been fairly well investigated since Berthelot heated rubber with concentrated hydriodic acid in a bomb tube and obtained a mixture of high boiling paraffins. Harries stimulated the work of Staudinger and Fritschi and Pummerer and Burkard by his statement, “It would be of great importance to be able to carry out the reduction of rubber, because hydrorubber probably distills unchanged in a high vacuum, and therefore its constitution could be determined for certain.” This hydrogenation of rubber was simultaneously accomplished in 1922 by Staudinger and Fritschi using a platinum catalyst dispersed in purified rubber at 270° C and 93 atmospheres of hydrogen pressure for 10 hours, and by Pummerer and Burkard using dilute solutions of depolymerized rubber in methylcyclohexane with a platinum catalyst at ordinary temperatures and atmospheric pressures.
Copolymerization Reactions of Cinnamic Acid, Its Derivatives, and Some Related Compounds
Authors: Marvel C. S. , McCain G. H. , Passer Moses , Taft W. K. , Labbe B. G.
Published: February 2011

A study of the copolymerization of butadiene with cinnamaldehyde, cinnamic acid, methyl cinnamate, ethyl cinnamate, and trans-cinnamonitrile showed that all these monomers yield rubbery copolymers with butadiene and certain of these have been evaluated and compared to current synthetic rubbers of the GR-S type. In general, these monomers to the extent of 10 to 90 parts of butadiene yield copolymers roughly equivalent to the standard GR-S which contains approximately 25 parts of styrene. The cinnamic acid-butadiene copolymer has excellent tensile strength. The trans-cinnamonitrile copolymer shows no improvement in oil resistance over GR-S. These cinnamic acid derivatives all enter the growing butadiene copolymer chain somewhat more slowly than does butadiene, so that the copolymers contain a lower percentage of the comonomer than does the charging stock used. Some experiments were conducted on the copolymerization of these cinnamic acid derivatives with other monomers than butadiene, the copolymerization of the furan analogs of the cinnamic acid derivatives, and the copolymerization of α-cyano-β-phenylacrylic acid derivatives.
Infrared Examination of Various Polyisoprenes
Authors: Richardson W. S. , Sacher A.
Published: February 2011

It is well known that, in general, the laboratory polymerization of diene monomers leads to materials which are intramolecular mixtures of various types of addition products. Thus, synthetic polyisoprene has been shown to contain chemical groupings arising from 1,2, 3,4, and 1,4 addition of the isoprene units. This is in contrast to the naturally occurring high polymers of isoprene, the rubbers and guttas, which appear to be exclusively cis-1,4 and trans-1,4 adducts, respectively. An exception to this last statement is the polyisoprene derived from chicle, which is a mixture of cis-1,4 and trans-1,4 addition. In this case, however, the mixture is an intermolecular one, and fractionation of the material leads to components which are all cis-1,4 and all trans-1,4. The general problem of diene polymerization is, of course, of great importance, and the synthetic polyisoprenes are of particular interest because of their relationship to natural rubber. The following attempt to obtain a quantitative analysis for the various types of addition occurring in synthetic polyisoprenes may lead to a better understanding of the nature of these materials and may be of help in elucidating the effect of microstructure on rheological properties.
Mechanism of the Crystallization of High Polymers
Authors: Schuur G.
Published: February 2011

The crystallization of higher polymers is a phenomenon which is not yet fully understood, one of the main difficulties being to explain how the spherulites arise. An attempt will be made in this paper to draw a clearer picture of the mechanism of crystallization and thus to account for the origin of spherulites. It will then be seen how several other phenomena involved in the crystallization of natural rubber can be shown to be logically interrelated. The current view is that a crystalline polymer consists of a continuous amorphous phase containing small crystalline regions, the crystallites. The evidence as to the size of these crystallites, however, is at present inconclusive, because only the lower limit of their size can be measured by means of x-ray examination. The reason is that, owing to the absence of reflections of a higher order, the effect of irregularities in the crystallites and of the heat motion of the molecules cannot be measured separately. Another doubtful question is whether the small angle interference maxima are to be interpreted as a measure of mean distances between the crystallites. To do this, Wallner has to resort to the assumption that the crystallites are unstable, whereas it is presumed, on the evidence of the mechanical properties of the high polymers, that a crystallite is stable and permanent. Hoffmann found 82 ± 7 per cent of crystalline material in polychlorotrifluoroethylene and Buckley, Cross, and Ray found as much as 95 per cent in polymethylene. Such high percentages make it doubtful whether the crystalline phase can be discontinuous at all. In this article any volume of material in which the molecules lie parallel is called a crystallite. The direction in which the molecules are oriented is termed the longitudinal direction of the crystallite. It is immaterial to the argument whether a crystallite consists of several crystallites, aligned in parallel separated by a small amount of amorphous material, or of a single crystallite containing large irregularities.
Mechanical Investigations of Elastomers in a Wide Range of Frequencies
Authors: Philippoff Wladimir
Published: February 2011

Many experimental investigations have shown that plastics in general, as well as elastomers and their solutions, do not behave like Newtonian liquids. They both have viscosity and elasticity, the combination of which, according to the Maxwell postulate, causes their properties to be dependent on time, and leads us to call them viscoelastic bodies. This dependence does not exist, either for the Newtonian liquid whose mechanical properties are determined by its viscosity, or for the elastic body whose properties are determined by its elasticity. The time element introduces a peculiar difficulty in measuring the mechanical properties of these substances. Whereas the well-known Maxwell body describes this time dependence in simple mathematical expressions, it does not apply to the experimental results. The properties of viscoelastic bodies are not described by a Maxwellian body, but rather by a distribution of an infinite number of Maxwellian bodies, each having a so-called relaxation time. The existence of this infinite distribution calls imperatively for an investigation of the properties of these viscoelastic bodies in as wide a range of frequencies or times as possible in order to define them. Most investigators have used one method in a range of frequencies no wider than about 1 to 100. This range can be extended by using the observation of Ferry that the properties of viscoelastic bodies investigated at different temperatures, in the case of dynamic investigations with sinusoidal vibrations, seem to be described by shifting one standard curve on the frequency axis. One can superimpose measurements at different temperatures and extend the range of frequencies to about 1 to 1,000,000. But using Ferry's method of reduced variables necessitates some assumptions that, though very probable, have as yet not been proven exactly by experiments. It therefore seemed important to have a method for investigating the mechanical properties of viscoelastic bodies in a frequency range of about 1 to 1,000,000 under isothermal conditions. This paper describes a basic method and the results obtained for several elastomers.
The Vulcanization of Rubber. XI. Influence of the Degree of Vulcanization on the Internal Friction of Unloaded Butadiene-Styrene Vulcanizates
Authors: Reznikovskii˘ M. M. , Yurovskaya V. S. , Dogadkin B. A.
Published: February 2011

1. The relation between the internal friction, which is responsible for heat formation during the dynamic deformation of unloaded vulcanizates of butadiene-styrene rubber, and the content of combined sulfur, which was changed within the limits of 0.5 to 26 per cent in the rubber, was studied. 2. It is shown that internal friction and the related relaxation properties do not depend on the percentage of combined sulfur up to 9.0 per cent. Further increase of the combined sulfur content causes a sharp increase of the internal friction of the rubber. 3. For the same vulcanizates of butadiene-styrene rubber, the equilibrium stress, as well as its energy and entropy components, were measured. It is shown that in vulcanizates which contain combined sulfur in proportions not greater than 8.0 per cent, the nature of the stress is predominantly entropic. Further increase of the combined sulfur content causes an increase of the energy component of the stress. 4. Proceeding from the values of the entropy component of the equilibrium stress, on the basis of the approximate theory of Wall, the values of the molecular weights of a chain segment between the cross-links of the spatial network M* were calculated for vulcanizates containing varying percentages of combined sulfur. 5. It is shown that the value of M* is 7000 for the polymer studied and is critical in the sense that further densening of the network causes a sharp increase of both internal friction and the energy component of the equilibrium stress. The hypothesis is advanced that the value of M*crit. can be regarded as a criterion of the flexibility of the molecular chains of the polymer studied.
Migration Effects in Oven Aging
Authors: Juve A. E. , Shearer R.
Published: February 2011

Aging of materials individually in ovens contaminated from previous usage does not assure freedom from contamination. These contaminants cause an increase in the rate of deterioration. Materials migrating from unlike stocks aged together may have varying effects, adverse, beneficial, or no effect, depending on the compositions being employed. The test-tube method of aging is an excellent method for studying these migration effects as well as for conducting routine aging tests in their complete absence.
Studies of the Heat Deterioration of Specially Prepared Natural Rubber Vulcanizates
Authors: Metz Donald J. , Mesrobian Robert B.
Published: February 2011

In 1949, Flory, Rabjohn, and Shaffer presented an article describing the dependence of the elastic properties of vulcanized rubber on the degree of cross-linking. In order to prepare rubber vulcanizates characterized by known degrees of cross-linkage recently developed, disazodicarboxylate vulcanizing reagents were employed. These reagents react quantitatively with rubber, one cross-linkage being introduced for each molecule of the reagent. Whereas the conventional vulcanization of rubber with sulfur and accelerators is a complex process and it does not appear possible at the present time to specify the exact number of cross-linkages present in sulfur vulcanizates, the use of disazodicarboxylate vulcanizing reagents presents an opportunity to investigate the changes that occur in the physical properties of vulcanized rubber, characterized by known degrees of cross-linkage, on exposure to oxygen at elevated temperatures. Furthermore, the effect of heat deterioration of various chemical agents commonly employed in sulfur vulcanization recipes may be investigated in a unique way by incorporating such chemical agents in the free state into natural rubber previously vulcanized by disazodicarboxylate reagents. Recent studies of the deterioration of rubber vulcanizates at elevated temperatures have been reported by several workers. In this article, the experimental methods employed to study heat deterioration involve measurements of oxygen absorption, stress relaxation, and changes of 100 per cent modulus of natural rubber vulcanized to known extents of cross-linkage by decamethylene-dismethyl azodicarboxylate.
The Flocculation of Dilute Latex by Zinc Sulfate
Authors: Thirion Pierre
Published: February 2011

Within a particular range of temperatures and a particular concentration of rubber, the flocculation of diluted latex by a water-soluble zinc salt is characterized by a critical amount of zinc, termed the salt index, which is necessary and sufficient to destroy abruptly the colloidal equilibrium of the dispersion. In the course of an investigation of a preliminary nature, measurements were made of the changes of the salt index as a function of the concentration and of the initial pH value of different field latexes and of two samples of latex preserved with ammonia. The influence of centrifugation and of buffering agents was likewise investigated. On a theoretical basis, the phenomenon appears to be governed to a major degree by chemical reactions of the zinc with certain substances which are either in solution in the serum or are adsorbed on the rubber particles. From the practical point of view, a systematic investigation is underway to determine whether the salt index as thus defined can be accepted as a new test of the stability of Fresh latex and preserved latex.
Contribution to the Determination of the Abrasion Resistance of Soft Vulcanized Rubber
Authors: Herzog R. , Burton R. H.
Published: February 2011

Of the great number of methods available for the determination of the abrasion resistance of vulcanized rubber, only a few give results which correlate at all well with actual service performance. The part played by the resilience of the rubber, the correct choice of test load, and the manner of application of this load are among the many testing conditions which are of considerable importance. Some of these conditions are considered in the present work, and a new abrasion testing machine is described.
Supplementary Report
Authors: Hommel F.
Published: February 2011

The leading ideas of Giese, Stein and Lauer's work may be expressed by the following statements. 1. In a rolling wheel-and-tire assembly, there are electric fields: (a) Between road and tire surface. (b) Between outside and inside tire surface. (c) Between inside tire surface and tube. (d) Between inside tire surface and rim. 2. Special attention is devoted to the so-called “inner field” between inside tire surface and tube; an attempt is made to measure and control it by suitable means. Regarding these fields it may be remarked that electrical boundary surfaces, and hence charge accumulations due to intimate contact, occur at the following points : 1. Instantaneous contact area between tire and road. 2. Points between casing and tube, especially in the flexure zone, where casing and tube may be displaced somewhat from each other. In the latter case—that of the field between casing and tube, henceforth to be called the “inner field”, the casing and tube section is to be regarded as a capacitance whose magnitude may be estimated as follows: area about 500 sq. cm., plate interval about 10−3 cm., due to elevations and depressions along casing at cords ; hence, capacitance of 5×104μμf. For very intimate contact, the plate interval may be reduced to about 10−6 cm., in which case the capacitance rises to 5×107μμf.
Chromatographic Analysis of Vulcanized Rubbers. Specific Methods for the Detection of Some Dithiocarbamate Accelerators
Authors: Parker C. A. , Berriman Joyce M.
Published: February 2011

Methods are described for the mutual separation and identification of six alkyl-substituted dithiocarbamates by ehromatography of their brown copper complexes on silica gel. These methods have been successfully applied to the detection of dithiocarbamates in vulcanized rubbers, and they form an extension to the scheme for the chromatographic identification of accelerators and antioxidants reported in a previous communication.
An Instrument for Determining the Relaxation and Recovery of Elastomers
Authors: Labbe B. G. , Phillips W. E.
Published: February 2011

Primarily the purpose of this report is to present information obtained with a newly designed instrument to be used for the determination of low-temperature characteristics of elastomers. The versatility of the instrument affords many variations from the testing procedure employed in obtaining the data reported herein.
Electron Microscopy of Hevea Latex Gels
Authors: de Vries A. J. , Dalitz V. Ch
Published: February 2011

The use of preserved concentrated Hevea latex for the production of rubber articles has given birth, during the last decades, to a number of quite new technological methods in rubber manufacture. Starting from an aqueous rubber dispersion of low viscosity as a raw material, instead of the very tough viscoelastic solid rubber, may be advantageous in many respects. Latex technology, however, also presents its particular difficulties and drawbacks, one of which is concerned with the problem of the reinforcement of rubber. Reinforcing fillers like carbon black, which enhance the tear strength and abrasion resistance of masticated rubber, do not exhibit the same beneficial effect on the properties of rubber films cast from latex ; the same is true of all fillers if added in appreciable amounts, with the notable exception of resorcinol-formaldehyde resins formed in situ. Nevertheless, the strength of vulcanized cast films from latex is excellent in comparison with vulcanized sheets of masticated solid rubber. In order to get more insight into the factors which control the rheological and mechanical properties of wet as well as dried and vulcanized latex gels, an extensive study has been undertaken, part of which has been concerned with an elucidation of the structure of these gels by means of electron microscopy. The purpose of this paper is to describe the experimental methods for obtaining electron micrographs and to present some of the results. The rheological and mechanical properties will be discussed in forthcoming publications, one of which has appeared in print already.
Determination of Particle-Size Distribution in GR-S Latexes
Authors: Nisonoff Alfred , Messer W. E. , Howland L. H.
Published: February 2011

A method based on Stokes' law, involving the use of an ordinary laboratory centrifuge, is described for the determination of particle size distribution in GR-S latexes. It is shown to be valid by tests for reproducibility and by comparison with the results of light and electron microscopy. In applying the method, several unusually fluid high-solids latexes made in the pilot plant were found to be characterized by a wide distribution of particle sizes. Data on various latexes in plant production are reported.
Photoelastic Studies Concerned with Fatigue Phenomena in Rubber Articles
Authors: Angioletti Attilio
Published: February 2011

In every case studied, rupture caused by fatigue begins at the stressed surfaces, i.e., conforms to tension isostatics tangent to the external profile, and then extends inward. It is, therefore, necessary to restrict the deformations by surface tensile stresses within the narrowest possible limits. The photoelastic method, even with very simple means, makes it possible to confirm experimentally the existence of local deformations, and facilitates the search for improvements in the fatigue resistance of rubber articles.
Electric Measurements of Rubber-Carbon Black Systems
Authors: Kickstein Gotthold
Published: February 2011

The addition of active carbon black to rubber causes considerable reinforcement and, hence, improves the serviceability of rubber products. On the other hand, electrically conductive carbon black imparts to rubber-carbon black mixtures a strongly polar character which is reflected in the electric constants. The specific direct current-resistance is frequently changed by several decimal powers by the addition of carbon black. With very small concentrations of carbon black, the resistance at first increases somewhat, probably as a result of union of ions by the carbon black. With somewhat greater concentrations (over 10–15 per cent by weight), the resistance decreases slowly, and at 30–35 per cent by weight it reaches a maximum, beyond which it suddenly decreases sharply and, with increasing concentrations (about 70 per cent by weight), approaches a saturation value almost asymptotically. This trend was proved to be true of the system : natural rubber-CK-IV carbon black. Here it must be noted that the exact course of the curve is of only slight significance, since the values obtained are decisively influenced by the nature and duration of the mixing process, the time and temperature of storage, preliminary treatment, temperature of measuring, field strength, and form and quality of electrode, and especially by the duration of the measurements. The direction of the influence of these variables is quite interesting. Mixing on a roll mill gives in most cases higher specific resistance than does mixing in an internal mixer. If samples are taken after so mixing, but before the product is put on a roll mill, no significant difference in the resistance of individual batches is observed, even if they are mixed at different temperatures.
Spontaneous Contraction of Rubber. II. Spontaneous Contraction of Rubber and Its Dependence on the Conditions of Testing, and Some Factors Concerned in Compounding and Technology
Authors: Reznikovskii˘ M. M. , Khromov M. K.
Published: February 2011

1. An apparatus and method for the study of the spontaneous contraction of rubber are described. 2. Data are offered which were obtained in a study of the dependence of spontaneous contraction of unloaded vulcanizates of isoprene, butadiene, and butadiene-styrene elastomers on the experimental conditions (deformation, temperature, and period of deformation), on the type of compound, and on technological factors (time of vulcanization). 3. It is shown that the theory of spontaneous contraction of rubber developed by the authors is in good accord with the experimental results, and makes it possible to use the method of spontaneous contraction for determining experimentally the basic factors characterizing the elastic and relaxation properties of rubber.
Mechanism of the Action of Accelerators of Vulcanization. Vulcanization of Rubber by a Sulfur Radioisotope
Authors: Blokh G. A.
Published: February 2011

The problem of the mechanism of the action of accelerators and vulcanizing agents during the vulcanization of rubber has been studied in earlier works. It was shown that, during the vulcanization of natural and sodium-butadiene rubber, accelerators of the type of mercaptobenzothiazole and tetramethylthiuram disulfide enter into exchange reactions with the vulcanizing agent, sulfur. However, the role of the chemically combined sulfur, that is, the so-called bridge sulfur, in the exchange reactions with the accelerators remained unexplained. As Dogadkin and Tarasova show, in the case of sulfur vulcanizates, the following kinds of bonds between the rubber chains can occur : (1) —C—C—, formed as a result of polymerization or condensation processes (bond energy 62.7 kcal. per mole); (2) —C—S—C—, monosulfide bonds, formed during thiuram vulcanization (bond energy 54.5 kcal. per mole) ; (3) —C—S—S—C—, disulfide bonds; (4) —C—Sn—C—, polysulfides, formed during vulcanization with elemental sulfur in the absence of accelerators containing sulfur (bond energy 27.5 kcal. per mole). These authors established the presence of polysulfide bonds by extracting sulfur from vulcanizates, already extracted with cold acetone, by heating the extracted vulcanizate in a 10 per cent solution of sodium sulfite. Ten to twenty per cent of the total amount of combined sulfur was thus extracted as polysulfide, whereas rubber vulcanized with thiuram contained no sulfur at all which could be extracted by sodium sulfite. In order to study the exchange reactions between accelerators containing sulfur and chemically combined or bridge sulfur, the present investigation was made.