bluuebunny/crossref_metadata_2025_split huggingface dataset:
Processes Resulting from Thermal Rupture of the Sulfur Bonds in Vulcanizates
Authors: Kuzminskiĭ A. S. , Lyubchanskaya L. I. 
Published: February 2011

Abstract
In earlier works we had studied in detail the rupture of the molecular chains of rubber under the action of oxygen, high temperatures, mechanical stresses, and some other factors. V. A. Kargin and G. L. Slonimskii˘ have directed our attention also to the possibility of a thermal rupture of the polysulfide sulfur bonds which form the structural network of vulcanizates. Dogadkin and Tarasova observed a rupture of the polysulfide bonds in vulcanizates under the action of mechanical stresses at temperatures of 100° and 130° C, and also on dissolving the vulcanizates in Synthol (motor oil) at 180–190°. All the experiments were carried out by the authors in the absence of oxygen. There are no indications to be found in the literature as to the behavior of the free radicals which are formed as a result of the rupture of sulfur bonds. The present work is devoted to an exploration of this important question. The experiments were performed with vulcanizates of three types: (1) monosulfide (mainly intermolecular bonds of the type, —C—S—C) ; (2) polysulfide (mainly intermolecular bonds of the type, —C—Sn—C—) ; (3) heat-vulcanizate (—C—C— bonds). Vulcanizing conditions were chosen such that the several vulcanizates would have approximately the same equilibrium modulus.
The Kinetics and Occurrence of Optimum Vulcanization
Authors: Dogadkin B. A. 
Published: February 2011

Abstract
The fundamental reaction of vulcanization is the combination of a vulcanizing agent with rubber. The kinetics of this reaction is expressed by smooth curves. Simultaneously with the combining of the vulcanizing agent, in fact as a result of it, changes take place in a number of physical and chemical properties of rubber—solubility, modulus, tensile strength, and other indexes. Unlike the kinetics of combination of the vulcanizing agent, the changes in these properties are most often represented by curves having a maximum or minimum which characterizes the phenomenon of optimum vulcanization. The extreme form which curves of changes of physical and chemical properties of rubber assume during vulcanization can be explained, in our opinion, by the fact that, during vulcanization, there is a competition between opposing reactions, of which one set are reactions of structure formation (i.e., increase of the molecular weight and the intensity of intermolecular reaction), and the others are destruction reactions. Thus, during vulcanization under factory conditions, at least two reactions take place: (1) the reaction between rubber and sulfur, and (2) the reaction between rubber and molecular oxygen introduced into the vulcanization mix by milling with the ingredients. The amount of oxvgen present here in moles approaches the molar concentration of sulfur.
Chain Scission in the Oxidation of Hevea. I.
Authors: Bevilacqua E. M. 
Published: February 2011

Abstract
The efficiency of chain scission of raw Hevea by molecular oxygen increases rapidly with increase of temperature to a limiting value of about 6.2 molecules of oxygen per bond broken. This value is close to the theoretical for destruction of one isoprene unit per bond broken, which leads to the inference that the higher efficiencies which have been reported for oxidation of vulcanized rubber may be the result of scission at the points of cross-linking.
Some Features of the Aging of Vulcanized Rubber in Light
Authors: Zuev Yu S. , Kuzminskiĭ A. S. 
Published: February 2011

Abstract
The action of light on rubber articles is almost always accompanied by a rise of their temperature. We may assume also, on the basis of a number of literature data, that there is a still more intimate relationship between the processes of light and the heat aging of vulcanizates. It is known that the rate of purely photochemical reactions depends but little on temperature. Such a dependence is noticeable, however, in such cases as the following: (1) when photoreactions and thermoreactions develop parallel to, and independently of, one another, their rates being found to be additive; (2) when they have a common level of reaction and common intermediate reaction products, and also when there exists a reciprocal activation of photo- and thermoreactions by one another. In this case, a change of temperature (within known limits) should bring about a change of the rate of photochemical reactions which is greater than the additive change. This has been confirmed by experiments on a number of vulcanizates. Thus, for example, there are data to the effect that the light aging of a natural-rubber vulcanizate is sharply accelerated by an increase of temperature from 25° to 75–100° C, and the same is true of Butyl rubber.
Kinetics of the Oxidation of Rubber under the Influence of Light
Authors: Postovskaya A. F. , Kuzminskiĭ A. S. 
Published: February 2011

Abstract
A number of investigators have established that the action of ultraviolet light on rubbers in the absence of oxygen causes considerable changes in their structure. For example, exposure of films of sodium-butadiene and natural rubbers results in a decrease of unsaturation and solubility, and by the evolution of gaseous products (hydrogen and methane), and exposure of rubber solutions by a decrease of viscosity at first, followed by gel formation. It has also been established that the simultaneous action of light and oxygen on rubbers causes even greater changes. However, the studies of the light oxidation of rubbers are fundamentally qualitative. Systematic data on the kinetic laws of these processes are lacking. The present study is devoted to the kinetics of the light oxidation of certain rubbers. Sodium-butadiene rubber was the principal object of study. Sheets of purified rubbers were photooxidized. The specimens were exposed to a mercury-quartz lamp PRK-2 at a distance of 25 cm. through a light-filter (pyrex glass), reflecting rays with λ=2960A˚ (these rays are not present in the sunlight which passes through the atmosphere). The kinetics of photooxidation were studied volumetrically in an apparatus described earlier.
The Diffusion and Solubility of Oxygen and Hydrogen in Sodium-Butadiene Rubber at Various Stages of Its Oxidation
Authors: Shanin L. L. 
Published: February 2011

Abstract
We have studied the diffusion and solubility of oxygen and hydrogen in thin strips (about 50µ and thinner) of sodium-butadiene (polybutadiene) rubber at temperatures of 40°, 60°, 80°, and 100° C. The experiments were carried out, not only on the unoxidized rubber, but also on strips which had previously been oxidized to stages of oxidation corresponding to an absorption of 50, 150, 250, 350, and 450 millimoles of O2 by 54 grams (one mole) of the polymer. In cases where the thickness of strips amounted to about 1 mm., all the authors who have studied the diffusion of gases in elastomers have declared Fick's law to be correct:
Identification of Accelerators and Antioxidants in Compounded Rubber Products
Authors: Brock M. J. , Louth George D. 
Published: February 2011

Abstract
A new, simple, and comprehensive approach to the identification of the accelerators and antioxidants used in rubber products is described. This procedure is unusual in that it utilizes the tendency of accelerators to decompose during mixing or vulcanization, or on extraction from compounded stocks. The accelerator fragments are isolated using distillation and liquid-liquid extraction principles. The identification of the fragments is simple, rapid, and unambiguous. The accelerators used are then determined from a knowledge of the decomposition behavior of known compounds. The antioxidants are recovered unchanged and can be identified by their ultraviolet absorption characteristics and color tests. This method is applicable to all types of rubber products, including cements, and is particularly valuable in the identification of accelerators which decompose on mixing, vulcanization, or extraction. Most of the commonly used accelerators and amine antioxidants can be classified or identified by the analytical scheme described. The procedure will be useful in identifying many accelerators and antioxdiants which may be developed in the future.
Volatile Acids and the Quality of Concentrated Natural Latex
Authors: Cook A. S. , Sekar K. C. 
Published: February 2011

Abstract
A simplified procedure for determining volatile fat acids in ammoniated latex is presented. Specific conductivity can be used to indicate an approximate value of the VFA number. Volatile acids can be formed in field latex before and after ammoniating, the extent depending on a number of factors, including time of ammoniation, amount of ammonia added, and period of storage. A small amount of formaldehyde added before ammoniation delays the development of volatile acids. The VFA no. of a 60 per cent d.r.c. concentrate lies between one-third and one-half of the VFA no of the field latex from which it is prepared, and it is shown that the presence of moderate and high concentrations of volatile acids in the concentrate is associated with inhibition of the normal increase of mechanical stability on storage. Low grade concentrate can be purified by recentrifuging and its mechanical stability increased.
Determination of Magnesium, Total Phosphorus, and Free Phosphate in Rubber Latex
Authors: Tunnicliffe M. E. 
Published: February 2011

Abstract
A critical evaluation of the molybdenum-blue method for the determination of orthophosphate and magnesium has been made and the conditions have been established for their quantitative determination in rubber latex. The precipitation of magnesium ammonium phosphate has been shown to be complete under the conditions of the test. For the conversion of phosphate to molybdenum blue, a comparison of several recommended reducing agents has shown that ferrous sulfate gives a stable and reproducible color which varies with the phosphate concentration according to Beer's Law. For the determination of total phosphorus, dry ashing of the sample with magnesium nitrate is proposed, followed by hydrolysis and a determination of the phosphate in the ash as molybdenum blue, as for magnesium. Free phosphate in latex serum is determined directly after coagulation and removal of interfering substances from the serum by cationic exchange.
The Proteins of Hevea Brasiliensis Latex. I. Protein Components of Fresh Latex Serum
Authors: Archer B. L. , Sekhar B. C. 
Published: February 2011

Abstract
1. The aqueous serum phase of unpreserved rubber latex (Hevea brasiliensis) has been separated in two ways: (a) by high-speed centrifuging, and (b) by prolonged freezing at —25°. The protein contents of the serum solids are approximately 18 and 13 per cent, respectively; the difference is attributed to coagulation of protein during prolonged freezing of the latex. 2. There is evidence that organic phosphorus compounds (probably phospholipids) are partially hydrolyzed during the freezing process, and that enzymic or bacterial reactions occur, leading to a fall of pH of the serum. 3. In both types of serum, seven-electrophoretically distinct protein components have been detected, one of which is positively charged at pH 8.6. 4. After treatment with dilute ammonia solution for 15 days, only two of the original protein components are readily resolvable electrophoretically. One of these (no. 5) is a major component of the unammoniated serum.
The Proteins of Hevea Brasiliensis Latex. II. Isolation of the α-Globulin of Fresh Latex Serum
Authors: Archer B. L. , Cockbain E. G. 
Published: February 2011

Abstract
1. One of the two major protein components of fresh Hevea-latex serum has been isolated by an isoelectric precipitation method and the optimum conditions for the precipitation have been determined. 2. Attempts to isolate this component by fractional precipitation of the total serum proteins with ammonium sulfate gave markedly heterogeneous products. 3. A preliminary examination has been made of the purified protein. Analytical and solubility data indicate that it is a globulin lacking non-protein prosthetic groups.
Spot Test Reaction for the Detection of Elemental Sulfur
Authors: Feigl Fritz , Stark Cecile 
Published: February 2011

Abstract
Hydrogen sulfide is formed when free sulfur is heated with fused benzoin. This is the basis of a new and sensitive test for free sulfur in mixtures with organic or inorganic substances. The heating is done in a test-tube, whose mouth carries lead acetate paper. The limit of identification is 0.5µ. Selenium does not interfere. Tests of a wide variety of commercial products gave satisfactory results.
Polymer-Modified Natural Rubber
Authors: Merrett F. M. , Wood R. I. 
Published: February 2011

Abstract
Earlier efforts to prepare and examine rubber-synthetic polymer compositions have made virtually no attempt to determine the nature of the products, that is, whether they were simple mixtures or chemical compounds and, if the latter, of what type, and thus to rationalize, if only broadly, their physical and technological properties in terms of their basic structures. The work now described has had this object in mind, and represents a cooperative program of research, including chemical, physical, and technological aspects.
Mechanical Properties of Polymers in the Range of Their Softening. Elongation Diagrams of Raw and Vulcanized Rubber
Authors: Yuzefovich N. A. , Kuvshinskiĭ E. V. 
Published: February 2011

Abstract
A study of the mechanical properties of polymers through the softening range is interesting for two reasons: on the one hand, it throws light on the process of vitrification, and, on the other, a study of reactions at low temperatures can give at least qualitative indications of the behavior of a material at high temperatures and during rapid dynamic processes, i.e., under conditions where direct investigation involves considerable difficulties in the experimental method. The following substances were studied: unloaded butadiene rubber before and after vulcanization, and vulcanized natural rubber. The temperature range studied was ™100° to 20° C. The elongation diagrams were obtained by means of a mechanism constructed in our laboratory. The specimens were stretched in a temperature-controlled chamber. Variations of temperature below 0° C did not exceed 0.5° C, and above 0° C did not exceed 0.2° C. The deforming force F was measured with a spring ring dynamometer. The opening of the clamps was calibrated with respect to the relative elongation λ. A correction was introduced here for deformation of samples in the clamps. The use of a reducing mechanism made it possible to vary the rate of deformation within the limits v=0.0016 and 0.08 cm. per sec., corresponding to rates of deformation from 0.05 to 2.5 per cent per second.
Abrasion and Friction of Rubberlike Materials
Authors: Boonstra B. B. S. T. , Dannenberg E. M. 
Published: February 2011

Abstract
The relationship between abrasion resistance and the coefficient of friction was observed in the early days of development of the modern synthetic rubbers. It has gained new interest in connection with the appearance on the market of polyester-isocyanate rubbers of the Vulcollan type. The abrasion of a rubber object in contact with a solid depends on the forces interacting at the surface of the two materials. These forces are again dependent on the forces pressing the two surfaces together, on the relative surface speed of the one object with respect to the other, and on the nature of the surfaces of the materials. Forces acting on the rubber surface and tending to pull the surface layer away from the bulk of the material deform the bulk rubber and excite counteracting cohesive forces. Abrasion of the rubber depends on the following two factors: 1) Development of frictional forces at the surface. 2) Counteraction of the force caused by the rubbing by cohesive force in the polymer adjacent to the surface layer. The question may be raised if it is possible to improve abrasion resistance by increasing the cohesive forces (1) without affecting the frictional forces and (2) if so, to what degree. With the help of the modified Cabot-Lambourn abrader, a number of experiments have been carried out that give some answers to the correlation of abrasion and friction. Abrasion is measured in terms of abrasion efficiency, i.e., weight loss per unit of energy. Correlations are established between: (a) Coefficient of friction and normal load. (b) Coefficient of friction and percentage loss of weight. (c) Coefficient of friction and carbon black loading. (d) Abrasion efficiency, coefficient of friction, and carbon black loading. (e) Abrasion efficiency and energy spent on abrasion. (f) Percentage of slip and torque obtained.
Principal Considerations on Tire Wear
Authors: Schallamach A. 
Published: February 2011

Abstract
The prerequisite for tire wear is relative motion between the tire and road in their common area of contact. Such relative motion occurs, for example, when a tire is flattened on entering the area of contact and can also take place when the tire exerts a force on the ground, i.e., during propulsion, braking and, particularly, cornering. The mechanism of abrasion when the wheel is not rolling freely becomes complicated by the fact that, because of the elasticity of the tire, its circumferential velocity with respect to the vehicle can differ from the travelling velocity, and that, furthermore, the tire can have a velocity component normal to its plane without skidding. In other words, slip without noticeable abrasion is possible. The only case discussed here will be when the wheel describes a curved path. The elasticity problem involved has been treated, among others, by Fromm, von Schlippe, and Temple; the essential facts are best visualized by means of the model experiment reproduced in Figure 1. In this experiment, a solid rubber wheel rolled around a Perspex disk, and the area of contact was illuminated by internal reflection. The deformation of the equator (marked in black) shows that two regions can be distinguished in the area of contact. In the front part, the equator is distorted into a curve parallel to the path, i.e., into a circle, and one can easily see that no relative motion between wheel and track occurs here, but that the wheel adheres to the track. The tangential stress necessary to deflect the wheel is maintained by friction until the stress becomes so high that the limiting friction is reached. At this point the second or rear part of the area of contact develops, in which the wheel slides back sideways. Abrasion should, therefore, be expected only in the rear part of the area of contact. It will decrease with increasing elasticity of the tire, but nothing will be gained thereby, since the tire has, after all, to take up the forces arising during driving. In the present case, this involves the side force holding the vehicle on the curve, and what matters is the dependence of abrasion on this side force.
Calorific and Thermal Properties of Natural Rubber in the Oriented and Non-Oriented States
Authors: Gengrinovich B. I. 
Published: February 2011

Abstract
The structural characteristics of high polymers and the sharp dependence of their properties on the physical state create a need for a detailed study of these materials in the region where their physical state undergoes a qualitative change. Besides, a study of the phase transitions of high polymers which crystallize is of independent interest. The study of the transition of natural rubber from the oriented crystalline state to the non-oriented amorphous state was the problem of this work. The determination of calorific and thermal properties in the transition region was adopted as the method of investigation. It should be noted that, for rubbers, these properties have been studied to a much lesser extent than have the other thermodynamic properties, particularly the mechanical properties. In order to obtain crystalline rubber, strips of smoked sheet were subjected to repeated rapid stretching at 50°, followed by cooling of the stretched samples to 12–14° C. The stress applied to the rubber during stretching overcomes the deorienting effect of the thermal motion, which impedes the crystallization of non-deformed rubber. At the same time, the heating employed promotes a more complete straightening of the chains since, during heating, intermolecular action diminishes and the chaotically-grouped oriented portions of the macromolecules present in the samples are disrupted. Rapid cooling of the oriented rubber, obtained under such conditions, to temperatures below the melting point of the crystals which formed led to the preservation of the physical state, which was distinguished by an increase of the crystalline phase content, and by a higher degree of orientation, compared with the state of rubber crystallized during the same time by lowering the temperature without stretching. On an average, the extent of stretching amounted to 1400 per cent of the original length.
Crystallization in Natural Rubber. IV. Temperature Dependence
Authors: Gent A. N. 
Published: February 2011

Abstract
Considerable experimental work on the crystallization of unstrained natural rubber, both vulcanized and unvulcanized, has been described previously. The rate of crystallization of raw rubber increases as the temperature at which the crystallization occurs is reduced, until a maximum value is attained at about −26° C. On lowering the temperature further, the rate decreases continuously. A similar temperature dependence is found for vulcanized rubber, although the rate at any given temperature is lower. Small quantities of certain impurities, for example, stearic acid, greatly increase the rate of crystallization of raw rubber. Such impurities are normally present in plantation smoked-sheet rubber, on which many of the reported measurements of rates of crystallization have been made. The measurements now reported have, therefore, been made with a purified rubber (deproteinized pale crepe) containing negligible quantities of the relevant impurities. Peroxide vulcanizates prepared from such a rubber have also been examined. The crystallization process was followed dilatometrically.
Observations on the Relation between Laboratory and Test-Stand Measurements of Tire Treads and Their Behavior on the Road
Authors: Kern W. 
Published: February 2011

Abstract
The only way to get a complete picture of the characteristics of tire treads is to classify the tests according to the influence of the compound, construction, type of vehicle, and type of road. Only by adapting tests in the laboratory, on the test stand, and on the road to the nature and intensity of practical service conditions, can good correlation be expected. Laboratory tests show at most the effect of the compound and possibly that of the nature of the road (roughness) and that of the climate (temperature). It is reserved for test stand and road experiments to bring out those properties that are affected by the tread pattern and the type of vehicle. We see as an essential task of laboratory testing technique not so much the creation of new complicated laboratory testing apparatus, as in better and better analysis, using new measuring methods, of the action on tires on test stands and in service, in order from this to find improvements in the available test apparatus and to base these on definite unfalsified elementary processes. The knowledge of the practical conditions not only has the advantage of improving the correlation, but makes it possible even in advance to strive for a goal-seeking development aimed at bettering the tire characteristics, since then one knows in advance what conditions are involved.