bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Latex as a Colloidal System
Authors: Verhaar G.
Published: February 2011

Natural rubber latex as a raw material for industry is relatively young. Although solid rubber has been known ever since the days Christopher Columbus and his men marvelled at the natives of Haiti playing with a ball made from the gum of a tree—which was in 1496—latex received little attention until the third decade of the twentieth century. By that time the rubber plantation industry had developed to such an extent that it appeared feasible to collect, preserve and transport latex on a large scale. Malaya was the first to export latex in commercial quantities in 1922, followed by Indonesia in 1926 and by Liberia in 1935. At the outbreak of World War II annual world production of latex had reached 44,000 tons but it was not until 1948 that production was back at the same level again. The last ten years have shown a rapid increase with world production reaching 168,000 tons in 1957. This would not have been possible without the application to manufacturing of scientific methods which in turn were based on an ever increasing amount of fundamental knowledge of its properties. It is well known that natural latex, as a liquid of biotic origin, may at times show considerable variations in composition and colloidal structure as the result of biotic, geotic, cilmatic and other influences. It is these differences which account for the variability in the properties of latex and rubber, a variability which is sometimes the cause of difficulties in processing these materials to a product of well defined and uniform properties. Great strides have been made over the last twenty years and it is the purpose of this review to outline the principal facts regarding natural latex as a colloidal system and to indicate the progress made in this field of research.
Diffusion of Antioxidants in Rubber
Authors: Kuzminskiĭ A. S. , Reitlinger S. A. , Shemastina E. V.
Published: February 2011

The study of the diffusion of polymers in order to determine the size and shape of the macromolecules in solutions has been the subject of numerous recent works. Considerably fewer studies have been devoted to the problem of the diffusion of low-molecular substances dissolved in polymers, and the existing works in this field refer principally to gas-polymer systems. It is also known that the rate of diffusion in polymers of solid and liquid low-molecular compounds governs in a number of cases the kinetics of processes of great practical importance. In particular, the kinetics of a process as important to the rubber industry as the oxidation of rubber is, to a large degree, related to the rate of diffusion of antioxidants and other soluble ingredients in the rubber. Rubber as a diffusion medium is distinguished from liquids and solid crystalline substances by certain properties which are governed by the characteristic heat movement of the macromolecules. Thus, Brün showed that Einstein's equation cannot be applied in the case of diffusion in rubber, and Barrer developed a theory of diffusion of gases in rubber, according to which the presence of an activation zone is necessary for the initial process of diffusion. The present study concerns the diffusion of certain solid antioxidants dissolved in rubber (phenyl-2-naphthylamine, dinaphthylamine, and dinaphthyl-phenylenediamine).
Adsorption of Elastomers on Carbon Black
Authors: Kraus Gerard , Dugone Joseph
Published: February 2011

During the past three years considerable progress has been made in the study of adsorption of high polymers on the surfaces of solids from solution. A number of experimental investigations have established that linear polymers are adsorbed at a number of segments along the molecular chain and that an apparent saturation value of the adsorption is reached with increasing concentration, leading to isotherms that exhibit considerable similarity with the classical Langmuir isotherm. Kolthoff and others have shown that poor solvents favor adsorption and that fractions of high molecular weight are adsorbed preferentially. Polymer of low molecular weight is adsorbed more rapidly, but is eventually replaced by fractions of higher molecular weight. Kolthoff and Gutmacher also observed some evidence of adsorption hysteresis in rubber-carbon black systems. Preferential adsorption effects have also been described by Goldfinger and others, who, in addition, furnished an estimate of the thickness of the adsorbed layer. Theoretical explanation for many of these effects has recently come from a detailed statistical mechanical treatment of polymer adsorption by Frisch, Simha, and Eirich.
Studies of the Vulcanization of High Elastic Polymers. II. Vulcanization of Natural Rubber with Thiuram Disulfides. Part 2
Authors: Scheele Walter , Lorenz Otto , Dummer Wilhelm
Published: February 2011

This paper gives some insight into the kinetics of thiuram vulcanization. The following results were obtained. 1. The decrease of concentration of thiuram disulfides during vulcanization is a first-order reaction in the range of short vulcanization times. At longer reaction times, departures occur. The process then takes place more slowly. 2. The departures from the course of a first-order reaction are displaced with decreasing temperature toward the range of longer vulcanization times. 3. At 87° C, the reaction of tetramethylthiuram disulfide is of the first order over the whole range of vulcanization temperatures chosen, and at this temperature no deviations whatever are observed. 4. The same relationships are found in the kinetic study of dithiocarbamate formation. 5. From the combined results, it is concluded that, besides the two reactions occurring independently of each other during vulcanization, the diffusion of the reaction partners also has some influence on the kinetics. 6. The limiting value of dithiocarbamate formation is correlated with the macromolecular structure of the polyisoprene, and it is shown to be probable that this limit is not determined fundamentally by the chemistry of the vulcanization reaction.
Constant Power Principle in Abrasion Testing
Authors: Powell E. F. , Gough S. W.
Published: February 2011

This paper has been mainly concerned with presenting the case for power control in abrasion testing, and the implications of the better understanding of the mechanism of abrading. It is not claimed that the test machines described are perfect in their ability to assess resistance to wear action. There is still much to be done to remove anomalies that can still occur in results. One underlying principle, that of constant rate of energy dissipation at the abrading surface, is proposed as a criterion for comparison of the validity of test design for the many different types of laboratory test in regular use for assessment of wear resistance. Modification of the Lambourn constant-slip machine to make it conform with the constant-power principle is described, and the degree of correlation with service data on tires given. The effects of several major variables on the abrasion loss of rubber tread compounds, when tested with the modified Lambourn machine, are reported, including work on combating stickiness. Experiments with the Du Pont and U. S. Bureau of Standards abraders, modified to conform to constant-power principles, are also reported in this paper. The relations between work done in mechanically grinding rubber and the energy associated with the bonds ruptured in the grinding action are considered. It is suggested that a correlation may exist between abrasion and high-temperature flexibility properties of rubber.
Cut Growth and Flex Testing of Natural Rubbers and Synthetic Elastomers
Authors: Kaiser Rudolf
Published: February 2011

In the last decades, numerous studies have appeared concerning the behavior of tears in natural rubber and synthetic elastomers. In the United States' and England there are even standardized test methods. It can be seen from all the investigations and test instructions that the results are very poorly reproducible and only rarely agree with practical experience. In investigations on the behavior of tears, the two stages—the beginning of the tear and the growth of the tear (tear propagation)—must be differentiated. The following factors must be given primary consideration in starting the tear: external damage, the action of ozone and oxygen, frequently changing tensile or compression stresses. Here oxygen plays a role similar to that in the corrosion of metals. Fatiguing mechanical stress undoubtedly leads to the appearance of tears. But it can be assumed that the beginning of a tear observed in the area of maximum stress takes place at a preferred point on the surface. Such preferred points are always present. As is well known, the surface of a material— even on a high polymer—must not be regarded as completely “smooth”. In place of this supposed smoothness, there appears under microscopic or electron-microscopic observation a kind of “mountain system”. Observed under sufficient magnification, the “valleys” or cuts in the mountains are comparable to tears. Under mechanical stress, such cuts will then continue to grow particularly rapidly (nick effect). Now it is largely dependent on the kind of observation and the observer as to whether a small irregularity in the surface is called a tear. The beginning of the tear cannot, therefore, be defined clearly. The case is quite different with tear growth. The initial conditions—the tear present at the beginning of measurement—are given and only the growth of the tear has to be followed by measurement. The growth of the tear therefore seems to us to be well suited for detailed investigation.
Experimental Examination of the Statistical Theory of Rubber Elasticity. Low Extension Studies
Authors: Baldwin F. P. , Ivory J. E. , Anthony R. L.
Published: February 2011

The results of this study may be summarized as follows : (1) The agreement observed between theory and experiment is remarkably good in this region of low extensions—almost to within the estimated experimental errors. (2) The predicted nonlinear dependence of stress on temperature is confirmed by the experimental data. (3) In agreement with the Guth-James theory, the thermoelastic inversion extension is found to be a function of temperature, and is observed to increase with increasing temperature. (4) Small deviations from the predicted dependence of the stress on temperature are observed. These appear to increase in magnitude with decreasing temperature, and are strongest for the Paracril rubber at low extensions and temperatures. It seems probable that these deviations are the result of intermolecular forces not specifically included in the theory. That the deviations should be stronger for the Paracril-35 rubber is not at all surprising in view of the highly polar nature of the nitrile groups. At the higher temperatures employed in the experiment, such forces may be neglected to a first approximation, because of the greater average distances between molecular groups and the greater thermal kinetic energies. At lower temperatures, however, these forces are no longer negligible, and the molecules exhibit an increasing tendency to “lock-up” as the glassy region is approached. (5) Finally, an inspection of Figures 6 and 7 reveals a tendency for the theoretical stress-strain curve to lie above the experimental curve at the higher extensions. Recent studies indicate that this is a real deviation, and that it increases rapidly with increasing extension. Similar deviations at somewhat higher extensions have been noted by Treloar and by Gumbrell, Mullins, and Rivlin.
A Comparison of the Flow of High Polymers in the Cavity of a Mooney Plastometer
Authors: Fensom D. S.
Published: February 2011

From idealized Mooney plasticity-time curves for Butyl and GR-S synthetic rubber, the distinctive features of the various parts of the shearing curve are pointed out. Actual experimental curves are given for Butyl, GR-S, “cold rubber”, polyisobutylene, polybutadiene, polystyrene, and some natural-rubber gum stocks. For polymers which were produced in emulsion, the degree of branching as indicated by the Huggins k′ value seemed to be loosely correlated with the time to reach the primary peak in the Mooney flow curve. Cross-linking and entanglement in structure as indicated by high gel content seemed to be correlated with secondary rise in shearing force shown during a long test. An hypothesis of flow in the cavity of the Mooney machine is advanced to explain these phenomena, supported by drawings of cross-sections of samples run in the machine. According to this hypothesis, some high polymers shear in a streamline fashion, others shear along certain slip planes and may even exhibit a mixing of parts which seems to be similar to turbulence in fluids.
Chlorination of Rubber and Some Products of Its Partial Chlorination
Authors: Troussier Maurice
Published: February 2011

A study of the chlorination of rubber, and of products of its partial chlorination, by physical and chemical methods has made it possible to suggest a mechanism of chlorination. This mechanism, which is in good accord with the analytical results of Bloomfield, involves cyclization reactions, and thus confirms the cyclized structure of chlorinated rubber which has been attributed by some authors to completely chlorinated rubbers.
Abrasion of Butyl Rubber
Authors: Zapp R. L.
Published: February 2011

By using the Lambourn abrader, a concept of abrasion has been proposed that fits the performance of a wide variety of compounds. The ability of this type of machine to give varying degrees of slip and braking forces has aided in the selection of the proper conditions for abrasion studies. By using a small tread pattern on the sample wheel, laboratory results are brought into closer agreement with actual road wear tests. The work of Schallamach and the analysis of abrasion by a needle abrader have been extended to an abrasive surface. To the considerations of compound strength and surface friction or traction has been added the consideration of dynamic hardness. The abrasion of rubber has then been related to a ratio of dynamic modulus over rupture energy. Thus if a compound is made dynamically softer or more conformable without a sacrifice of its resistance to rupture, a superior abrading tread will result. In simple terms, what is needed for best abrasion resistance is the softest toughest material. Butyl owes its comparable or superior abrasion resistance (compared to other rubbers) to the fact that its vulcanizates are dynamically softer. The heat treatment of Butyl carbon black mixtures produces vulcanizates that are still softer in relation to their rupture energy. This is the sole advantage of such a mixing procedure. Other polymer and compounding variables that tend to decrease the ratio of dynamic hardness to rupture energy improve abrasion resistance. These changes include increasing the molecular weight of the polymer and reducing somewhat the unsaturation. A certain quantity of plasticizer to increase softness and a reduction of the state of cure have been shown to be beneficial. The latter change produced by a reduction of the amount of sulfur in the compound, which limits the extent of cross-linking, has resulted in distinctly superior tire treads.
Power Transmission—Slippage-Abrasion. An Investigation of the Abrasion of Tread Compounds
Authors: Viehmann Walter
Published: February 2011

The abrasion behavior of vulcanizates of the tire-tread type have been studied by the method of constant energy, with a test apparatus operating on the principle of the Dunlop-Lambourn machine. As a result of this work, the following facts were established. Up to a critical slippage, the value of which is characteristic of every individual vulcanizate, the abrasion, i.e., the amount of rubber worn off per unit of time, increases with the square of the slippage. The slippage increases linearly with the power transmitted. To this quadratic relation between the power transmitted and the slippage corresponds a linear dependence of the abrasion power, i.e., it is possible to assign a specific abrasion energy to every individual vulcanizate. The specific abrasion energy is inversely proportional to the temperature and also inversely proportional to the mean particle size of the abrasive material. A comparison of the measured specific abrasion energy with the corresponding value to be expected by theoretical calculation shows that the experimental value is too high by a factor of 106. From this, one is led to the conclusion that the abrasion power is practically completely consumed as heat in the abrasion boundary layer, an idea which is supported by measurements of the temperature of abrasion and a comparison of this with the calculated values. Above the critical slippage value, the simple linear dependence of the abrasive wear on the abrasion power no longer holds true, and a specific abrasion energy cannot be defined. In addition, the abrasion patterns described by Schallamach then appear, and any correlation between laboratory tests and road wear tests is lost.
Effect of the Temperature of Polymerization on the Structure of Butadiene-Styrene Copolymers
Authors: Sheĭnker A. P. , Medvedev S. S.
Published: February 2011

The addition of monomer molecules to the growing polymer chain during the polymerization of dienes may take place in several ways. In the polymerization of butadiene, the addition takes place in the 1,2- and 1,4-positions. In the latter case polymer chains are obtained with structural variations, e.g., the position of CH2 groups at the double bonds is cis or trans. The resulting polymer chains vary in configuration. It is of interest to determine how the configuration is affected by different conditions of polymerization. Several papers related to the subject are to be found in the literature. In this work, we studied with an infrared spectrometer the compositions of butadiene-styrene copolymers prepared at different temperatures. Also determined was the content of the various configurations of butadiene links in the polymer chains. The samples were prepared by polymerizing emulsions by the dilatometric method in the absence of oxygen. A satisfactory emulsion was obtained with a magnetic stirrer inserted into the dilatometer (Figure 1 ). The rotation of the stirrer (activated by a magnet attached to the axis of a motor under the thermostat) sucked the upper part of the liquid through the upper opening (1) and expelled it through the side opening (2); this assured emulsification.
Some Features of the Kinetics of Catalytic Copolymerization. Copolymerization in the Butadiene-Isoprene and Butadiene-Styrene Systems
Authors: Gantmakher A. R. , Medvedev S. S.
Published: February 2011

In the course of research into carbon-chain polymerization under the influence of the acid-type catalysts, aluminum chloride, boron fluoride, stannic chloride, and others, a series of investigations have established the fundamental mechanisms of these chain processes, indicating that they have an ionic character. On the basis of this research, it was suggested that the active center in carbon-chain polymerization is a compound with a tervalent positive carbon atom at the end. The kinetics of catalytic copolymerization had not been studied until the present. There has been only a little work published in connection with determining the composition of copolymers and calculating the copolymerization constants for the systems in question. We initiated some research into the dependence of the speed of catalytic copolymerization on the composition of the original mixture, in conjunction with a determination of the speeds of separate polymerization of the monomers involved, since a comparison of data on the kinetics of copolymerization with that of separate polymerization gives a more complete representation of the mechanism of the process. A study was made of the speed of copolymerization of the systems : isoprene-butadiene and styrene-butadiene, and also of the kinetics of separate polymerization of these monomers. Polymerization was carried out in ethyl chloride with stannic chloride as the catalyst, at 0° C, by the dilatometric method.
Influence of Crystallization on the Sorption of Hydrocarbons by Natural Rubber and Gutta-Percha
Authors: Kargin V. A. , Gatovskaya T. V.
Published: February 2011

It has been known that the mechanical properties and structure of amorphous and of crystalline polymers differ from one another sharply. However, the influence of the phase state of polymers on their thermodynamic properties has not been made clear. Hence it has been of interest to evaluate the effect of polymer crystallization on the polymer's sorption properties. For this purpose it was essential to compare the sorption properties of a polymer which can exist in either the amorphous or the crystalline state at the very same temperature. The most suitable material is natural rubber, which is capable of crystallizing either during prolonged aging or under stress and, therefore, may be obtained at the same temperature in both the amorphous and the crystalline states. With the aid of a McBain balance in a high vacuum and under isothermal conditions, curves for the sorption of n-hexane by amorphous and crystalline samples of natural rubber at 0° and 25° C were obtained. In the experiment at 0°, the sorbent consisted of strips of natural rubber, some of which had been aged 8 months at 0° (the crystallized sample), and others aged for the same period at room temperature (the amorphous sample).
A Thermochemical Study of High Molecular Weight Compounds
Authors: Khokhlovkin M. A.
Published: February 2011

Among the classical methods which have found application in research on high-molecular compounds, the method of Calorimetry is noteworthy. It is sufficient to mention the investigations into heat capacity, which, along with other measurements, helped to establish the second-order transition points, as well as the influence of crystallization temperature on the liquefaction of high polymers. The determination of the heat capacity of isoprene and of natural rubber, in combination with data on their heats of combustion, permitted a calculation of the change of free energy of formation of natural rubber. According to the data of Hock and Schmidt, the heat of swelling of natural rubber in various solvents ranges from +1.36 to −3.0 cal./gram. These data agree with those obtained from osmotic measurements. Thus the change of free energy when natural rubber goes into solution is approximately determined by the entropy term; i.e., ΔF=−TΔS. Bearing in mind that the heats of solution of rubber are of the same order of magnitude as the heats of mixing for two liquids, and are considerably lower than the heats of solution of solid bodies in liquids, we may conclude that the rubberlike state has more in common with liquid than with solid substances as regards solubility.
The Comparative Determination of the Molecular Weight of Rubber by the Methods of Light-Scattering and Osmometry
Authors: Dogadkin B. , Soboleva I. , Arkhangelskaya M.
Published: February 2011

1. An account is given of experiments to determine the molecular weight of natural rubber and other high molecular-weight compounds by light-scattering and osmometry. 2. A new design of osmometer for determining molecular weight is described. 3. It is shown that the light-scattering method gives molecular weight values which agree satisfactorily with those given by the osmotic method.
Dynamic Fatigue of Rubber and the Mechanism of Failure by Repeated Deformations
Authors: Bartenev G. M. , Galil-Ogly F. A.
Published: February 2011

Dynamic fatigue is thn reduction of the maximum tensile strength of a material by repeated periodic loads or deformations. The dynamic fatigue of vulcanized rubber is basically the result of chemical oxidation processes, destruction during repeated deformations taking place by rupture of the chains throughout the rubber as a result of mechanically activated chemical processes. Physical factors also influence dynamic fatigue. However, the question of the nature and mechanism of dynamic fatigue of vulcanized rubber has not yet been explained ; nor has the relation between fatigue and tensile strength of rubbers been clarified. The results of studies which make it possible to establish the fundamental laws of dynamic fatigue of rubbers and the destruction mechanism during repeated deformations are presented below. Two widely used sinusoidal systems of repeated deformation were studied: (1) constant (maximum) elongations or deformations, ε = const.; (2) constant (maximum) loads or conventional stress, f = const. The number N of cycles before failure and the time before breaking, or the life of a specimen, were determined in these tests. In the first system, the breaking load, fixed by the apparatus, was less than the initial maximum load, owing to the process of “dynamic relaxation“, and in the second system they were equal. The breaking load divided by the initial cross-section and the cross-section at break gives, respectively, the conventional f and the true dynamic tensile strength σ of the specimen.
Application of Radioactive Sulfur to the Study and Control of the Vulcanization Process
Authors: Tarasova Z. N. , Kaplunov M. Ya , Dogadkin B. A.
Published: February 2011

Ordinarily the kinetics of the vulcanization process is controlled by the proportion of combined sulfur, which is determined by the method of oxidation with nitric acid and bromine, the method of fusion with metallic potassium and magnesium, and other methods. A considerable increase of the rapidity and accuracy of the determinations may be achieved if labeled sulfur, containing the isotope S35, is used as the vulcanizing agent. The half-life of this isotope is 87.5 days, and the energy of the β-particles amounts to 0.17 Mev. The combined sulfur content is determined from the intensity of theβ-radiation. The method which we developed can be described as follows. A rubber stock, containing labeled sulfur of known radioactivity, is mixed on a laboratory mill. A sheet of this rubber stock, wrapped in cellophane, is vulcanized in a press at a given temperature and pressure. The thickness of the sheets should not be less than the maximum length of the path of β-particles in the rubber. for a soft rubber, this thickness amounts to 0.3 mm.
Processes Resulting from Thermal Rupture of the Sulfur Bonds in Vulcanizates
Authors: Kuzminskiĭ A. S. , Lyubchanskaya L. I.
Published: February 2011

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.