bluuebunny/crossref_metadata_2025_split huggingface dataset:
X-Ray Diffraction Studies of Crystallization in Elastomers
Authors: Alexander Leroy E. , Ohlberg Stanley , Taylor G. Russell 
Published: February 2011

Abstract
In general, extension of an elastomer results in a degree of preferred orientation of the molecular chains composing the amorphous phase. Therefore the amorphous fraction of a partially crystalline elastomer must be related to the integrated intensity of the amorphous diffraction halo rather than to the intensity at any one azimuth. A noteworthy exception is natural rubber, for which simple meridional measurements suffice. A Geiger-counter apparatus, with beam monitor and temperature-controlling accessories, is described for making accurate measurements of the x-ray intensities scattered at any azimuth and at small or moderate Bragg angles. Measurements of crystallinity in natural rubber are in essential agreement with the findings of previous workers. When polybutadiene is extended at room temperature, molecular orientation occurs, but little if any crystallization. Measurements at lowered temperatures show that the crystalline fraction becomes appreciable at about 0° C and that it increases with further reduction of temperature and with increasing extension ratio. Preferred orientation of the crystalline regions in extended polybutadiene has been measured quantitatively with the object of providing jointly with birefringence measurements a value of the birefringence of a single crystal of polybutadiene.
Sulfur Exchange Reactions in Vulcanized Rubber
Authors: Tarasova Z. , Kaplunov M. , Dogadkin B. A. 
Published: February 2011

Abstract
In one of our previous works we have shown that vulcanization structures contain mono-, di- and polysulfide bonds between the molecular chains of the rubber. The concentration, proportion, and distribution of these various bonds depend on the type of rubber and the conditions of vulcanization, but mainly on the nature of the curatives. Inasmuch as the vulcanization structures determine in large degree the physical, chemical, and mechanical properties of the vulcanizate, the different methods which enable us to determine the types of sulfide bonds in the vulcanizate are very important. Among the chemical methods applied for this purpose are the reactions of sodium sulfite and of methyl iodide with the vulcanizate. Of great interest in research on the nature of sulfur bonds in vulcanizates is the method of exchange reactions with radioactive sulfur; since sulfur, as numerous experiments have shown, diffuses easily in rubber, thus insuring the possibility of carrying out exchange reactions without having to get the vulcanizate into solution.
The Mechanism of Oxidation of Synthetic Rubbers
Authors: Kuzminskiĭ A. S. , Degteva T. G. , Lapteva K. A. 
Published: February 2011

Abstract
1. Adequately reproducible results were obtained, and a complete balance was achieved between substances entering the reaction and the products of oxidation. 2. It is shown that the oxygen which enters into the reaction at all stages of oxidation is retained mainly in the form of peroxides, acids, and ethers. 3. The kinetics of polymer oxidation, and also the accumulation of intermediate reaction products, were studied at various temperatures. 4. It is shown that the cessation of oxidation occurs long before the exhaustion of the polymer's double bonds; the reasons for this phenomenon are revealed. 5. The decrease of unsaturation in the process of oxidation at different temperatures was studied. 6. It is shown that the process of oxidative decomposition is accompanied by polymerization. 7. It is shown that oxidation extends mainly to the double bonds in the principal chains, while polymerization is confined mainly to the double bonds in the side chains. 8. A diagram of the oxidative mechanism is given, including both of the directions of reaction (decomposition and polymerization).
Determination of Sulfur in Rubber Vulcanizates
Authors: Zimmerman E. W. , Hart V. E. , Horowitz Emanuel 
Published: February 2011

Abstract
A combustion method for rubber which determines the sulfur evolved at 480° to 500° C is compared with the fusion and the zinc-nitric acid methods. In the combustion method an interaction occurs between sulfur and fillers present in the rubber. The effect of particular fillers with respect to this interaction is discussed. A value representative of the organically bound sulfur in an extracted specimen can be obtained by the combustion method when no reaction takes place between the sulfur and the fillers during combustion. The fusion method yields results in good agreement with the total sulfur added in compounding the rubber samples. Except in the presence of barium compounds, the zinc-nitric acid method likewise determines total sulfur. When barium compounds are present, barium sulfate is formed during the oxidation, and low values are obtained for the total sulfur.
Absorptiometric Microdetermination of Total Sulfur in Rubber Products
Authors: Kress K. E. 
Published: February 2011

Abstract
The 1.0 to 2.5 per cent of sulfur normally present in rubber products is oxidized with concentrated nitric acid-bromine reagent, followed by perchloric acid in the presence of excess lead nitrate. Sulfur as lead sulfate is precipitated and washed with acetone. The lead sulfate is dissolved in 50 per cent hydrochloric acid, and absorbance of the lead chloride complex is recorded at 270 mµ. Sulfur is calculated on the basis of the measured lead content of the precipitate. The high sensitivity puts the method in the micro-range. An experienced analyst can analyze 40 to 50 samples a day. Precision and accuracy are comparable to those of the conventional barium sulfate gravimetric method at the low sulfur concentrations normally found in rubber products.
Electrical Conductivity Experiments with High-Abrasion Furnace Black-Loaded Natural Rubbers
Authors: Humphreys N. C. H. 
Published: February 2011

Abstract
Considerable differences may exist between volume resistivities of vulcanizates prepared from a single mixing. Large differences between mixing effects can also occur. Contact resistance effects caused by bonded brass electrodes are shown to be negligible over a considerable range of bond strengths. The profound effects of compressive flexing on the resistance of vulcanizates is demonstrated. A formula containing sufficient HAF black to place the vulcanizates nominally in the electrically antistatic range was employed throughout the work.
Pull-Through Adhesion Test
Authors: Wood J. O. 
Published: February 2011

Abstract
A modified form of the pull-through test is described, followed by a series of experiments, the first three of which demonstrate the precision of the method. Further experiments assess the effect of various factors on the pull-through force. It is found that specimen age has little effect. The tension applied to the cord during construction also produces a small but appreciable effect, amounting to a decrease of 1.3 per cent for a two-fold increase of the tension, but a greater effect, amounting to a 7 per cent increase of the pull-through force, is obtained when the rate of loading is doubled. The pull-through force is also shown to depend on the shape of the mounting device. The twist in a rayon cord does not give a significant effect, though the variability exhibited by the conventionally dipped cord is high. Temperature increase during test reduces the pull-through force; linear plots of the logarithm of the pull-through force against the reciprocal of the absolute temperature are obtained. The cord length embedded in the rubber is shown to bear a hyberbolic relationship to the pull-through force, confirming the theoretical relationship obtained analytically. Finally the pull-through test is considered in terms of the product.
Problems Concerned with the Physical Testing of Vulcanizates
Authors: Kainradl Primus 
Published: February 2011

Abstract
A critical consideration shows that the test methods in current use for vulcanizates often fail to make possible a reliable decision about different rubber compounds out of a series of development formulations with respect to their evaluation for subsequent use. The tester by himself is not in a position to bring about an improvement in this unsatisfactory state of affairs, since this cannot be accomplished by the improvement of existing methods alone or by the creation of a new apparatus. A closer cooperation between the fields of testing and application is necessary.
Determination of Sulfur by Wet Combustion with Perchloric Acid
Authors: Bethge Per Olof 
Published: February 2011

Abstract
Difficulties in the determination of sulfur in wood and pulp samples by the conventional method of Grote and Krekeler have been overcome by applying a wet combustion technique, using perchloric and nitric acids. The sulfur is reduced to hydrogen sulfide by boiling with a reduction mixture, and determined iodometrically. The method gives quantitative yields for pure organic compounds, and is suitable for a great variety of samples with sulfur contents from 0.01 to 100 per cent. Sample weights can be varied from 9 mg. to 5 grams.
Ameripol SN—A Cis-1,4-Polisyoprene
Authors: Horne S. E. , Kiehl J. P. , Shipman J. J. , Holt V. L. , Gibbs C. F. , Willson E. A. , Newton E. B. , Reinhart M. A. 
Published: February 2011

Abstract
The important observation made by Katz in 1925, using x-ray diffraction technique, showed that the mere stretching of crude or soft vulcanized Hevea rubber caused at least a portion of the polymer to undergo crystallization. This and the subsequent experiments of Hock emphasized the point that successful attempts to synthesize a polymer resembling Hevea rubber would have to take regularity into account. The situation is complicated in isoprene polymers by the variety of ways the monomer can enter the growing polymer chain. Four isomeric forms of polyisoprene are shown in Figure 1. Since head-to-tail orientations must be considered because of the asymmetry of the isoprene molecule, there are eight possible arrangements of the units that can occur in polymerized isoprene. Sodium, potassium, emulsion, and alfin polyisoprenes have been shown to contain all four forms of the repeating units. All these uncured polymers have poor tack, and their pure-gum vulcanizates show poor physical properties. They do not crystallize when stretched or cooled. It has long been recognized that polymers of conjugated hydrocarbon dienes would have to be very regular in structure before their properties would approach those of Hevea rubber. Looking back over the last fifteen to twenty years, there has been a slow development, almost imperceptible at first, of catalyst systems which produce polymers that in some degree show an oriented structure. This orientation could result if the monomer, during the propagation phase of the polymerization, is held in a definite position with respect to the growing chain, as by cybotactic forces where polymerization is initiated at the melting point of the monomer, or by adsorption of the monomer onto a solid surface—perhaps to the surface of the catalyst itself. The work reported here deals primarily with the properties of a rubber made by directed polymerization.
A Comparison of the Dynamic Properties of Natural Rubber and GR-S
Authors: Papas L. J. , Shufler S. L. , DeWitt T. W. 
Published: February 2011

Abstract
It is well known that high molecular weight, uncross-linked, amorphous polymers show a characteristic behavior with respect to the dependence of the dynamic modulus on frequency and temperature. Generally these materials, at high frequencies and (or) low temperatures, are glasslike, with a modulus of approximately 1010 dynes/cm.2. As the frequency is lowered or the temperature raised, this modulus drops rather quickly to the region of 106 to 107 dynes/cm.2, and remains in this neighborhood for a while to form somewhat of a plateau, the length of which depends on the molecular weight. With a further lowering of frequency or rise of the temperature, the modulus again drops off in a fashion which is strongly dependent on the molecular weight and molecular-weight distribution and the material enters a plastic or liquid-like region. This general behavior seems to be characteristic of long-chain molecules in general, and differences in structure are more likely to be reflected in differences of detail, and in the temperature ranges in which the afore-mentioned regions occur, than in any considerable divergence from the general pattern. A comparison between the dynamic properties of the two important elastomers, GR-S and natural rubber, is here reported. In preliminary work in this laboratory, it has been observed that GR-S shows an appreciably higher level for the plateau region than natural rubber. It was felt that this and other possible differences between the two materials would merit exploration, particularly for any implication that the results might have for the long-standing problem of the origin of the tendency of GR-S to show a greater development of heat under repetitive stressing than natural rubber.
Chemical Relaxation of Stress in Polyurethan Elastomers
Authors: Offenbach J. A. , Tobolsky A. V. 
Published: February 2011

Abstract
The chemical stress-behavior of polyester urethan elastomers and a polyether elastomer have been determined through a temperature range of 90° to 130° C. Since both the polyether and poylester had approximately the same rates of stress decay, it was necessary to exclude ester-ester interchange as a reaction mechanism, and to regard the known thermal lability of the urea and urethan groups as indicative of possible sites of network scission. A likely possibility for the weak link is the trisubstituted urea (biuret) cross-linkage.
The Photoelastic Examination of Rubber Articles
Authors: Angioletti A. 
Published: February 2011

Abstract
After a short introduction to the photoelastic method and its applications to the examination of transparent planar structural models, some methods of examining plane models representing sections of actual rubber articles are indicated. In many cases it is advisable to place the model between parallel glass plates with their inner faces lubricated and at a distance apart equal to the thickness of the model itself. In other cases free models can be examined. In no case, however, is the law governing the birefringence of transparent materials within a range of small deformations, e.g., less than 1 per cent, equally applicable to greater deformations, e.g., up to 100 per cent. But in this range recourse can then be had to a law, based essentially on theoretical considerations and described by Treloar, which is an extension of the general law and which has been verified experimentally. Some special cases are considered where the law is of general application to the quantitative evaluation of the state of deformation at various points in a model under examination.
Accidental Factors Involved in the Fatigue Breakdown of Rubber Articles
Authors: Angioletti A. 
Published: February 2011

Abstract
Poor dispersion of compounding ingredients, and the presence of granules and of impurities which in some way get into vulcanized rubber and thereby disturb the normal distribution of stresses in an article and thus cause local stress concentration, are regarded as accidental factors in the fatigue breakdown of vulcanized rubber. This problem was studied by developing, by means of the photoelastic method, an adaptable schematic representation of the phenomena. Although only a qualitative evaluation of the local disturbance of the system of stresses caused by these factors is possible, in the particular case of granules, it has been found that the closer a granule is to the outside surface of the rubber article, the greater is the disturbance of the system of forces. Furthermore, the local stress concentration is greatest when there is no adhesion between the granules and the surrounding vulcanized rubber. Finally the stress concentration caused by a small cut or incision made at various locations on a rubber test-strip under tension is considered. This case has been included because fatigue cracks first become manifest in this form.
Mechanical Activation of the Oxidation of Vulcanizates by Static and Dynamic Deformation
Authors: Kuzminskiĭ A. S. , Lyubchanskaya L. I. 
Published: February 2011

Abstract
The deformation conditions to which rubber parts are subjected have a considerable effect, and in many cases the decisive effect, on their service life. One of us made a qualitative study which established the direct influence which the mechanical stresses created in a vulcanizate by dynamic deformation have on the rate of oxidative reactions. In the present work, a comparison was made between the effects of static and of dynamic deformation on the oxidation and breakdown of vulcanizates with differing structures. Dogadkin and Tarasova established that vulcanizates with tetramethylthiuram disulfide form mainly monosulfide bonds. In vulcanizates containing diphenylguanidine, the presence of a large number of polysulfide bonds was noted. In a thermal vulcanizate, a spatial network with —C—C— bonds was formed. All of the above vulcanizates were found to have approximately the same network densities, as determined from their equilibrium moduli. In order to remove the free ingredients remaining after vulcanization (free sulfur, accelerators, and phenyl-2-naphthylamine), all the vulcanizates before testing were extracted with acetone for 50 hours, in a stream of nitrogen, and were then dried in a vacuum. In experiments involving an antioxidant, the latter was introduced into the purified vulcanizate in a benzene solution. The thickness of the vulcanizate samples studied ranged from 0.2 to 0.25 mm. The work on dynamic deformation was carried out in a specially constructed apparatus, with a compensating mechanism for regulating the permanent set created under fatigue. It should be noted that in all the vulcanizates this accumulation of permanent set through fatigue was observed even in the first few cycles of the testing. The total amount of accumulated permanent set in a vulcanizate, from the time the testing began until the break, did not exceed 20–25 per cent of the original length of the sample. For the determination of the fatigue lives of vulcanizates, parallel tests were made on twenty-five samples. A detailed investigation was made of the influence that the type of cross-links in the vulcanizates has on the fatigue lives of the latter.
The Viscosity and Structure Viscosity of Rubber Solutions and Emulsions
Authors: Schurz J. 
Published: February 2011

Abstract
It is well known that the increase of viscosity of a colloidal solution over that of the pure solvent is produced by the frictional resistance to flow of the dispersed particles. The amount of this viscosity increase depends to a great extent on the shape of the particles. If these are spheres, only the ratio of the volume of the solute to the solvent is involved (Einstein's law), while in the other extreme case, namely with fiber molecules, the particle size plays such an important role, as is known, that one can calculate the particle weight of the dispersed phase from the viscosity (Staudinger's law, Mark-Houwink equation). But not only is the viscosity of a colloidal solution influenced by the particle form, but also its structural viscosity depends on it to a great degree. It is easy to understand this. For if the structure viscosity and, consequently, the decrease of viscosity with increasing velocity gradient, result from the fact that the hydrodynamic forces in the flowing solution, on the one hand, orient and distort the dispersed particles in the moving stream, and, on the other hand, oppose an eventual intermolecular mutual effect or aggregate formation of the particles, it is easily seen that the flow forces will be able to manifest these effects all the more readily and markedly the more extended and the stiffer the dispersed particles are. Thus it can be expected that, in general, in spherical particle suspensions no structural viscosity will appear, but that this will manifest itself the more strongly the more asymmetric the particles. With rubber it is easily possible to realize two extremely different dispersion forms. Rubber emulsions, as they exist in the various latexes, are typical definite spherical suspensions, with rather large particles of very uniform size. In rubber solutions, on the other hand, say in toluene or benzene, there is a macromolecular distribution. The dispersed particles are the individual kinky fiber molecules of the rubber, which are known to have a more or less elongated form. In fact these two types of rubber dispersions behave so differently that each of them can be called a typical representative of its class.
Slipping of Molecules during the Deformation of Reinforced Rubber
Authors: Houwink R. 
Published: February 2011

Abstract
It is proposed that, during the deformation of reinforced rubber, the molecules slide along the surface of the filling material, accompanied by breaking of bonds. However, new bonds of similar type are soon formed (reversible breaking of bonds). It is assumed that, in the quiescent state following deformation, the original bonds are eventually restored (disappearance of the Mullins effect); the increase of the entropy is supposed to be the effective source of energy. A model of reinforced rubber is shown in Figure 5.
Mechanism of Formation of Zinc Dimethyldithiocarbamate (ZnDMDC) in Tetramethylthiuram Disulfide (TMTD) Vulcanization
Authors: Craig David 
Published: February 2011

Abstract
Scheele and Bielstein recently have commented at length on the copolymerization (CP) theory of vulcanization which we proposed. They find the theory untenable with respect to TMTD vulcanization as well as with that using equivalent amounts of tetramethylthiuram monosulfide (TMTM) and sulfur. They feel that our presentation lacked in clarity and, therefore, that they did not understand it fully. Scheele and coworkers report that 66 per cent of the TMTD, or of the mixture of equivalent amounts of TMTM and sulfur, reacts to form ZnDMDC according to the first-order rate law during vulcanization in the presence of excess zinc oxide. This finding is a notable contribution. In particular, it suggests the possibility of sulfur-oxygen interchange as a feature of the overall reaction, which we may write: