bluuebunny/crossref_metadata_2025 huggingface dataset:
Fractionation of Rubber
Authors: Bloomfield George F. , Farmer Ernest Harold
Published: February 2011

Latex rubber which has been purified to the point at which it contains an insignificant amount of nitrogen can be separated by fractional dissolution in a mixture of petroleum and acetone into a series of hydrocarbon fractions of decreasing solubility and increasing molecular magnitude. All these fractions except the highest are soluble in petroleum and in benzene. Crepe rubber, on the other hand, appears invariably to contain a small, most-soluble fraction of oxygenated rubber, and a small similar quite insoluble fraction of material of high molecular weight. Between these extremes the rubber can be divided into fractions of increasing molecular weight, although, up to the present, about 70 per cent of the total rubber has appeared in a single fraction. It may be possible later, by judicious choice of another pair of solvents, to resolve this major fraction into a series of subfractions. Kemp and Peters refer to the effect of polar nonsolvents in reducing the viscosity of rubber solutions and also in assisting to bring gel rubber into solution, phenomena to which the polar molecules conceivably contribute by countering the forces of association between the rubber molecules. The present series of fractionations was conducted throughout in the presence of a polar nonsolvent (acetone), and hence may be considered to approach towards a separation of true rubber molecules as distinct from molecular aggregates. It is found, however, that, whereas the more soluble fractions of acetone-extracted crepe rubber contain small proportions of nitrogen, the least soluble fractions contain substantial proportions. Any effect which the nitrogenous material may have in assisting to link together hydrocarbon molecules to which it is attached, i. e., in contributing to the high-molecular condition of a portion of natural rubber, remains at present uncertain in character. The fractions of rubber, and especially the higher ones, show a strong tendency to become insoluble when they have once been freed from the last traces of solvent. It seems doubtful whether the decreased solubility is due to oxygen as it would require to be effective at exceedingly low concentrations.
Rubber Solvents Which Are Economically Self-Sufficing
Authors: Paselli Piero
Published: February 2011

Mixtures of dichloroethylene and trichloroethylene are not only suitable for preparing rubber solutions, but are superior in solvent power to gasoline now used in practice. If small percentages of alcohol are used in conjunction with these solvents, rubber solutions of lower viscosities are obtained, and in general these mixed solvents have high solvent power and are of value industrially. Mixtures of dichloroethylene and trichloroethylene are also of utility in preparing solutions of artificial rubber, such as Buna. These solutions are to be the subject of a special study. In the recovery of such mixtures of solvents, carried out with saturated steam, the alcohol is lost, evidently because it is miscible with the condensed water, but the other two components are recovered without any decomposition and under the same conditions as gasoline and benzene. In view of all this, chlorinated solvents, which are economically selfsufficing, ought soon to be used, if not in all cases, at least to a great extent, in place of gasoline and benzene, which are much more necessary for other uses than for the impregnation of fabrics. The use of chlorinated solvents has, in addition to this, notable technical advantages, as well as safety. Accordingly it seems likely that chlorinated solvents and their mixtures are destined to assume in the near future a dominant position in the rubber industry in general, and in the Italian rubber industry in particular.
Reclaimed Rubber. Application of the T-50 Test
Authors: Palmer Henry F. , Crossley Robert H.
Published: February 2011

1. If reclaimed rubber is introduced into a rubber compound, the T-50 values for the early part of the cure are lowered. This lowering is due in part to the faster rate of cure of the compound containing reclaim, and probably in part to the influence of the combined sulfur present in the reclaim itself. This lowering of T-50 value manifests itself chiefly during the early cures, diminishes as the cure progresses, and finally disappears. 2. The T-50 test should not be used to compare the relative states of cure of compounds containing different or unknown amounts of reclaimed rubber. 3. The T-50 test can be used to determine the effect of reclaimed rubber on the rate of cure of a compound by comparing the slopes and positions of the T-50 curves at various curing times; conclusions reached in this way can be substantiated by free sulfur data. The T-50 test appears to be somewhat more sensitive for this purpose than tensile and modulus tests. 4. T-50 tests on the reclaim-sulfur mix are more uniform than tensile strength tests, and indicate that variations in tensile strength are caused by factors other than variations in chemical state of cure. The T-50 test will, to a limited extent, distinguish differences in the rates of cure of reclaims in this mix. In general, however, the reclaim-sulfur mix is not so informative in the evaluation of reclaimed rubber as a test of the reclaim in a compound typical of the one in which it will be used. 5. As a means of interpreting the rate of cure of rubber and reclaimed rubber compounds, the T-50 test possesses advantages of speed, simplicity, and accuracy, and is a valuable addition to the standard testing methods now in use.
Vistanex Polybutene—Rubber Blends
Authors: Longman S.
Published: February 2011

From the foregoing data on blends of Vistanex Polybutene and rubber, it is evident that these two materials complement one another. Each has properties which the other lacks, and blends of the two can be made to emphasize the more desirable properties of either one. Extreme flexibility in compounding these blends is possible, since they are perfectly compatible in milled compounds. Therefore, great latitude is given in compounding of these blends to secure any range or degree of properties possible with either of the components. Vistanex Polybutenes should not be considered as synthetic rubber, because they will not vulcanize, and they lack certain characteristics of vulcanized natural rubber. More properly Vistanex Polybutenes should be considered as modifying agents for partial substitution of natural rubber. In many cases, this substitution of a part of the natural rubber in a compound by Vistanex Polybutene confers definite advantages and improves qualities of such compounds for special uses. Therefore, Polybutenes, even in normal times, have a very definite field of usefulness and, in the event that imports of natural rubber become restricted, the availability of the Vistanex Polybutenes in quantity will be of increasing importance to the rubber industry. Since the raw materials for the manufacture of Vistanex Polybutene are petroleum products, the availability of raw materials is a source of no difficulty in this country. Likewise, the manufacturing equipment is not excessively expensive, and, with expanded production, lowered prices may confidently be expected.
Electrical Tests and the Problem of Cure
Authors: Waring J. R. S.
Published: February 2011

Considerable changes in electrical conductivity, as well as in other electrical properties, of rubber mixes occur during the process of vulcanization. The practical man will want to know the answer to such questions as: Are the tests reproducible? To what type of use could the test be put? The answer to the first question is that electrical tests are readily reproducible. There are, however, two main sources of trouble, first the electrode system and, secondly, the lack of uniformity in material submitted for test, due to different previous history. The first difficulty can be overcome either by moulding in the electrodes, as in the oven experiments described, or by using a test in which no electrodes are required, as in the eddy current test. The second difficulty involves checking the processing previous to vulcanization. The following uses are suggested as an answer to the second question: checking processing by following cure on samples supposed to be the same; checking uniformity in rubber articles by tests on the finished products, e.g., a tire tread, without destroying the articles concerned, and checking cure by making tests on small samples in the laboratory. These examples are given by way of illustration. No doubt others could be suggested. Finally, it must be said that, particularly on the processing side, further work needs to be done, and the results will be communicated at a later date.
Determination of Free Sulfur in Vulcanized Rubber
Authors: Mackay J. G. , Avons C. H. J.
Published: February 2011

In a rubber laboratory controlling uniformity of factory production by physical and chemical testing, free sulfur is perhaps the most important determination. In this investigation recently described methods for determining free sulfur have been compared. A previous examination by one of the present authors of various methods of estimating free sulfur led to the adoption of a procedure comprising oxidation of the dried acetone extract by a mixture of nitric acid, perchloric acid and bromine, followed by evaporation with sodium chloride and hydrochloric acid before precipitation of sulfate in the usual manner with barium chloride. In the Avon laboratories considerable use has also been made of the method recommended by the Rubber Division of the American Chemical Society, in which bromine alone is used to oxidize the acetone extract, and the sulfate so produced is estimated gravimetrically as the barium salt. Both methods are accurate, but they are not sufficiently quick for effective factory control. Meantime there had been published several new methods of determining free sulfur which were claimed to be quicker than the older procedures. With the aim, therefore, of finding a rapid method more suited to the requirements of a control laboratory, the following methods have been compared. Methods 1 and 2 below were included as controls. As test-samples, 22 different general rubber products selected from factory production were used. Each product contained at least one sulfur-bearing ingredient in addition to the sulfur added to effect vulcanization.
Phase Transitions in Rubber and Their Connection with the Stress-Strain Curve
Authors: Alfrey T. , Mark H.
Published: February 2011

This paper reviews recent experimental work on phase transitions in rubber—particularly the change from the amorphous to the crystalline form. Several possible explanations are considered to account for the vagueness of the melting point of rubber. Molecular inhomogeneity does not completely explain the phenomenon, and a more satisfactory approach involves a size-distribution of effective kinetic units. It is suggested that the reason for such a variation in size of the kinetic units lies in the mutual interference of growing crystallites. Crystallization of rubber by stretching is discussed, and it is shown that the crystallization process, which takes place mainly in the middle part of the extension, accounts in a reasonable way for the S-shaped nature of the stress-strain curve.
Fractionation of Rubber
Authors: Bloomfield G. F. , Farmer E. H.
Published: February 2011

H. P. Stevens wrote that he had read with interest the above paper and desired to contribute the following observations. The authors refrained from drawing conclusions from the varying nature and proportions of the fractions in the three typical rubbers of which they gave the distribution in three tables. The impression was obtained that those differences resulted from differences in the nature of the three types, either partly chemical or physical (molecular weight variations), or both. It was suggested by the writer that the main differences were of a different nature, and resulted from differences in the coarser structure of the specimens. It would be noted that “crepe rubber” (Table I) was rubber prepared by milling wet or semidry coagulum. “Latex rubber” (Table II) was acetone-coagulated after purification, and “dried-fresh-latex film” (Table III) was neither milled nor purified nor coagulated. The three specimens therefore corresponded to three dissimilar types of raw rubber. They would consequently possess different types of macrostructure. Rubber, however prepared, was not merely a mass of hydrocarbon with nitrogen and other accessory substances homogeneously distributed therein. The distribution was of a structural character.
Analytical Methods in Rubber Chemistry, Part I. General Analytical Considerations
Authors: Farmer E. H.
Published: February 2011

One of the consequences of the high-molecular character of rubber is the smallness of the effect on ultimate quantitative analysis of the presence of one or even several heteroatoms or groups in the long hydrocarbon chains. With rubber molecules possessing an average chain-length of about 4,500 isoprene units, the association of, say, ten nitrogen atoms wtih each chain would provide a nitrogen content of only about 0.0007 per cent, and the incorporation of about 0.005 per cent of ethereal oxygen in pure rubber hydrocarbon would be theoretically capable of providing sufficient linking material for an infinite degree of hetero-polymerization, or, if the oxygen were applied instead to produce the maximum possible degree of degradation, it would be capable of severing from one-quarter to one-third of the rubber chains. In view of these dimensions, and the fact that natural rubber normally contains difficultly removable hetero components, and is ready to take up additional amounts of oxygen, little progress can be made in the fundamental investigation of the complex molecules without a suitably accurate technique of chemical analysis, and this applies particularly to the determination of total oxygen and total nitrogen, and also to the determination of the six types of combined oxygen likely to be present in rubber, viz., hydroxylic, oxido-, ethereal, peroxidic, carbonyl and carboxylic. Unfortunately, great precision in estimation cannot be achieved without increasing greatly the rigour of the analytical technique, and perhaps it is not surprising that Midgley, Henne and Renoll's well-known high-precision method for determining carbon, hydrogen and, by difference, oxygen, still remains after five years the sole such chemical analytical method reported in the literature.
Positively Charged Latex
Authors: Coplan B. V. , Rogers S. S. , Hansen L. A.
Published: February 2011

Latex, like many other colloidal systems, owes its stability to a large extent to the electrical charge carried by each particle in suspension. One possible explanation of how the particles become charged is that the protein adsorbed on the rubber hydrocarbon is capable of ionizing to a slight extent, both as an acid and as a base, much in the same manner as do amino acids. In a highly basic solution the rubber particle acquires a negative charge; whereas in an acid solution the charge is positive. At some stage between strongly acid and strongly basic solutions, the ionization of the adsorbed protein layer would be as much acidic as basic, and the particle would have no net charge. This is known as the isoelectric point, and has been found to be at a pH of 4.2. At or near the isoelectric point, the latex is very unstable, and coagulates rapidly. The charge carried by the particle may, of course, be due also to adsorption of ions from solution. The latex particles are normally negatively charged, but the sign of the charge can be reversed by the addition of acid, by the presence of polyvalent cations, and more recently it has been shown that cationic soaps may reverse the charge. In a cationic soap the positive ion is a long chain, and the negative ion is a halide, sulfate, etc. The hydrophilic group attached to the long chain of carbon atoms is a quaternary ammonium, sulfonium, or phosphonium group. The authors felt that, because positively charged latex seems to have some commercial possibilities, it would be of interest to attempt to prepare latex suspensions of reversed charge of higher concentrations than those used by Blow, which were apparently around 5 per cent.
Organic Analysis of Hevea Latex. V. Ammonia, Amines and Betaines
Authors: Altman R. F. A.
Published: February 2011

This paper describes a method for isolating and identifying nitrogen bases, e.g., ammonia, amines and betaines, present in fresh unammoniated latex. The outline above summarizes the results. The method does not claim perfection. The author wishes to emphasize that the percentages recorded in the outline are not exact, and are given only to indicate the proportions of the respective fractions.
An Immersion Test for Rubber Compounds
Authors: Garvey B. S.
Published: February 2011

The immersion procedure described here is much faster than the present A. S. T. M. method, and gives results of comparable accuracy. It requires less space and less solvent. The most serious objection to it is the occurrence of anisotropic swelling due to grain in the rubber. However, there is usually more grain in manufactured articles, such as hose, than in tensile sheets. Both methods are useful chiefly for the preliminary evaluation of compounds. The final test frequently is made on the finished article under special conditions. The sensitivity of this test to grain effects suggests that its use with a good swelling agent will be a useful tool for measuring the extent of such grain in various compounds.
Rubber and Artificial Resins as “Liquids with Fixed Structures”
Authors: Ueberreiter Kurt
Published: February 2011

Numerous investigations, particularly in recent years, have served to throw much light on the relation between the inner structure and mechanical properties of artificial substances. The rapidly developing, industrial production of artificial materials has given considerable impetus to these investigations, since, as has often been pointed out, the solid state of organic materials represents the practical and usable form of artificial products. Basing his opinion on the fundamental researches of Tammann, Jenckel has classified many artificial substances as glasses; Houwink and others have seen in colloidal structures certain fundamentally important principles; and Kuhn, starting from purely theoretical reasoning, has explained rubberlike elasticity on a basis of molecular kinetics. In renewing the study of the freezing of liquids, an idea was developed which proved to be very helpful in guiding further research, and represented a step toward a better understanding of earlier theories. This new point of view will be discussed in the following pages.
Study of Elastic Relaxation by a Resonance Method
Authors: Mikhailov G. , Kirilina V.
Published: February 2011

The present work gives the results of measurements of the modulus of elasticity and the losses in ebonite by a resonance method. These magnitudes are determined as functions of the temperature for two specimens. At t=19°C, the resonance frequency of one of the specimens was 2784 Hz, of the other 1145 Hz. At these frequencies and higher temperatures ebonite is highly elastic. It is shown that the transition to this state at sound frequencies takes place at a temperature 47° C higher than by the static method.
The Tear Resistance of Rubber Compounds
Authors: Patrikeev G. A. , Melnikov A. I.
Published: February 2011

1. An improved method of measuring tear resistance was developed. The samples which were examined were cut in the direction of stretching. 2. The relation between tear resistance and time of vulcanization was investigated. 3. The tear resistances of synthetic and natural rubbers were compared. 4. It is shown that the tear resistance of samples of natural and synthetic rubber depends on the depth of the initial cut. With short cuts, natural rubber has a higher tear resistance than synthetic rubber, but this difference decreases as the cut is made longer. 5. It is established that the tear resistance of thin rubber specimens is smaller than that of thicker specimens. 6. The mechanism of tear resistance is discussed. Factors such as deformation are considered.
Some Physico-Chemical Properties of Carbon Blacks
Authors: Patryn T. , Pilat S.
Published: February 2011

A study was made of the adsorption of carbon tetrachloride vapor by various types of blacks, and data were obtained on the heats of wetting of blacks by carbon tetrachloride. A study was made of the fat coefficients and the points of spontaneous combustion of various types of blacks. It was found that active blacks can be distinguished from inactive blacks by their powers of adsorption of carbon tetrachloride and also by their heats of wetting. There is no way of telling by its fat coefficient whether a black is of value in rubber. The point of spontaneous combustion gives an approximate idea of the origin and formation of a black. Data on electrical conductivity have thus far not provided any basis for classifying different types of blacks.
Solvation in Dispersed Systems. XII. Influence of Surface-Active Substances on the Structure of Rubber Fractions
Authors: Margaritov V. , Serebryannikova L.
Published: February 2011

We have previously shown that the addition of nitrogen-containing compounds to sols of butadiene polymers results in the development of colloidal structures. To explain the mechanism of this action, the effect of adding similar compounds to fractions of crude rubber of varying degrees of aggregation was studied. These active substances, when dissolved either in low molecular weight fractions of the polymer or in a mutual dispersing medium, become adsorbed on the rubber micelles, change the equilibrium between the fractions, and modify the properties of the colloid. The molecular nature of the dispersing medium has a marked effect on the interaction between the polymer and the active substances. The data obtained by us are shown in Table I.
Intermolecular Forces and Mechanical Behavior of High Polymers
Authors: Mark H.
Published: February 2011

In order to connect the mechanical properties of high polymers with their fundamental architecture, several structural characteristics must be considered. There is, first, the average molecular weight or the average polymerization degree of the substance, which varies between 20,000 and 1,000,000 or between 100 and 5000, respectively. There is the chain-length distribution curve, which describes the heterogeneity of the material, and is comparatively narrow in some cases and fairly wide in others. There is the chemical nature of the monomer, which can be a hydrocarbon, an alcohol, ester, ether, amine, acid, nitrile, etc., so that the polymer can have very different chemical characteristics. There are, finally, the intermolecular forces between the chain molecules, which are a consequence of the chemical nature of the monomer, and which, together with the flexibility of the chains, have a preponderant influence on mechanical performance.
Theory of Rubber Elasticity for Development of Synthetic Rubbers
Authors: James Hubert M. , Guth Eugene
Published: February 2011

Two cardinal problems exist in connection with the production of synthetic rubbers: (1) choice of the type of synthetics, necessary raw materials, and methods of production, and (2) evaluation of the products obtained. The most important and characteristic property of synthetics (and of natural rubbers) is their long-range reversible elasticity.
Equations of State for Natural and Synthetic Rubber-Like Materials. I Unaccelerated Natural Soft Rubber
Authors: Anthony R. L. , Caston R. H. , Guth Eugene
Published: February 2011

Summarizing, the following important conclusions may be drawn from these experiments on a typical unaccelerated soft gum compound. 1. The existence of the inversion point in the stress-temperature curves is shown to be due solely to ordinary volume thermal expansion, and may be eliminated by correcting for this thermal expansion. 2. The curves given in Figure 8a show that, for compounds of this type, the change of entropy with elongation accounts for more than 90 per cent of the total stress at room temperature, while the internal-energy contribution is less than 10 per cent and, to a first approximation, may be neglected. In other words, the retractive force is due almost entirely to the tendency of the extended rubber molecules to return to a less ordered curled-up state. This is in direct contrast to the elasticity exhibited by ordinary bodies, in which case elasticity is due to intermolecular forces. 3. The contribution of the entropy force to the total force is well represented by the theoretical expression of James and Guth. This agreement constitutes our main reason for interpreting the entropy force as being due to the kinetic motion of the rubber molecules.
Specific Heat of the Synthetic Rubber Hycar-OR from 15° to 340° K
Authors: Bekkedahl Norman , Scott Russell B.
Published: February 2011

Measurements of specific heat were made on a sample of Hycar-OR synthetic rubber from 15° to 340° K by means of an adiabatic vacuum-type calorimeter. The experimental values of the specific heat between 15° and 22° K were well represented by the Debye specific-heat equation, using a βν value of 80 and, accordingly, the values below 15° K were calculated with this equation. At about 250° K the material has a transition of the second order, the specific heat increasing by about 40 per cent to a value of 1.84 Int. joules · gram−1 · degree−1 just above the transition. From 250° to 340° K the specific heat-temperature curve is nearly linear, and the values can be calculated to within 0.2 per cent from the formula Cp=0.00283T+1.126, in Int. joules · gram−1 · degree−1. At 298.16° K (25° C) the specific heat is 1.971 Int. joules · gram−1 · degree−1 (0.4712 calories · gram−1 · degree−1). The increase in entropy resulting from heating from 0° to 298.16° K was calculated to be 1.743 ± 0.002 Int. joules · gram−1 · degree−1 (0.4167 ± 0.0005 calories · gram−1 · degree−1).
Vibration Properties of Rubberlike Materials Dependence on Temperature
Authors: Stambaugh R. B.
Published: February 2011

1. The vibration modulus and resilience are independent of the frequency of vibration if the temperature is constant. 2. The internal friction is approximately inversely proportional to the frequency. 3. The modulus decreases as temperature increases. Curves for synthetic stocks at high temperatures are not very different from those of rubber at low temperatures. 4. Resilience rises linearly with temperature. Rubber shows a transition from one slope to another at about 25° C. 5. The dependence of the internal friction of rubber and similar materials on temperature follows the same exponential law as the viscosity of liquids. At certain critical temperatures sudden changes occur in the cohesive forces, which cause a transition from one curve to another. For the natural rubber sample this occurs at about 17° C. 6. The amplitude of vibration has a large inverse effect on the modulus and friction, which cannot be explained by the temperature rise of the sample due to heat generated in it. The effect may be due to nonlinearity of the stress-strain curves. 7. Modulus and friction are affected by temperature in the same way, indicating the dependence of both on some fundamental characteristic of the molecular structure. Natural rubber requires two straight lines for representation on the modulus-friction plot, the junction occurring at about 25° C.
Sponge Rubber
Authors: Cooper A.
Published: February 2011

It is the object of this paper to deal with some of the less known facts concerning sponge rubber, and not with latex sponge, frothed sponge or sponges made by specialized processes, such as the Goodrich and Lindemann methods already described by Brazier, or sponges produced from rubber solutions and spraying processes, or other specialized methods recently developed. In the manufacture of sponge rubber the greatest problem is the plasticity and uniformity of the raw rubber, and more attention has been given to this than to any other aspect of the manufacture of sponge; yet there is still ample room for development and improvement in this connection. Blending and batching of raw rubber and plasticity control are constantly advocated, and the importance of such standardization cannot be overemphasized. Cold breakdown and mastication, chemical plasticizing and the addition of various softeners, factices and reclaims all have their applications, and can be varied according to requirements. The degree of breakdown of the crude rubber, the use of softeners in the compounded mix and the balance between the type of blowing agent, rates of blowing and curing are the all-important inseparable factors of sponge work.
Production of Industrial Sponge Rubber
Authors: May E. J.
Published: February 2011

The production of sponge rubber for industrial use not only involves the blowing of a mass of plastic rubber compound to a given shape of predetermined density, with concurrent vulcanization, but also the production of a sponge product which will withstand the same severe conditions as will solid rubber produced by modern compounding. Until recent years, the aging and heat-resisting properties of sponge rubber left much to be desired, mainly because of the large surface area susceptible to oxidation, and the large amounts of oils and softeners used to plasticize the rubber. The oils themselves, far from beneficial to aging properties, necessitated in many cases high sulfur ratios to restore the nerve to the vulcanized sponge. It is, however, necessary to plasticize the raw rubber to obtain satisfactory blowing. Within limits, the pore size and density of a sponge from a given stock are governed to a greater extent by the plasticity of the mixed compound than by the amount of blowing agent contained in the stock. To obtain maximum physical properties, the method of plasticizing which has the least deleterious effects on the vulcanized product has to be chosen. This may be one, or a combination of, the following: (1) breakdown of the crude rubber on cool mixing rolls; (2) hot breakdown of the crude rubber at temperatures above 120° C on open rolls or in an enclosed mixer; (3) use of chemical plasticizers; (4) use of plantation softened rubber, such as that produced by the Socfin Co. of Malaya, or by the Schidrowitz-Ungar process, and (5) addition of large quantities of softening oils during mixing.
Resilient Energy
Authors: Bott E. C. B.
Published: February 2011

1. The tensile strength of vulcanized rubber may be expressed in terms of its elongation by means of the calculus of finite differences. 2. This expression for tensile strength, based on the theoretical cross-sectional area, gives an expression for the tensile strength based on the original cross-sectional area when the former quantity is divided by the factor (E + 1), E being the elongation. 3. The expression for tensile strength based on the original cross-sectional area is integrated with respect to the elongation to give the resilient energy. 4. The trapezoidal rule has proved itself to be superior to the calculus of finite differences as a practical method of obtaining the resilient energy. 5. The total resilient energies are plotted on graphs against the percentage by volume of reinforcing agent or filler. Tangents drawn at any desired point corresponding to a certain percentage of filler give values for the partial resilient energies of base mix and of filler by the method of tangent intercepts. 6. The expressions for tensile strength are composed of one, two or three functions ; the number of functions is, in general, inversely proportional to the percentage of the filler in the vulcanizate. 7. The expressions for tensile strength and for resilient energies have no significance regarding the structure of vulcanized rubber; they have been evolved from the point of view of usefulness for evaluating compounds. 8. The values of the partial resilient energies of base mix and of filler obtained by the method of tangent intercepts have no physical meaning; they are a means of calculating the total resilient energy of a sample of vulcanized rubber.
Determination of Total Sulfur in Rubber and Rubberlike Materials
Authors: Cheyney La Verne E.
Published: February 2011

The determination of total or combined sulfur in vulcanized rubber and materials of similar type involves numerous difficulties. This fact is attested by the very large number of methods which have been proposed. All the most important methods involve oxidation of the sulfur, in whatever form it may be present, to sulfate and weighing the latter as barium sulfate. The only essential differences lie in the methods of oxidation employed. The methods which seem to be the most popular at the present time are (1) oxidation of the sample in a Parr bomb with sodium peroxide, potassium chlorate, and sugar; (2) oxidation with perchloric acid and nitric acid, sometimes with the additional use of bromine; (3) oxidation with nitric acid and bromine, followed by sodium carbonate-potassium nitrate fusion; and (4) oxidation with nitric acid-zinc oxide mixture, bromine, and potassium chlorate. Serious explosions have been known to occur with perchloric acid oxidations; hence this method is not so popular at present as the other three. The fusion methods are reliable, but they are time-consuming and therefore not convenient when large numbers of samples must be handled.
A Broad Nomenclature for Carbon Blacks
Authors: Cranor Donald F.
Published: February 2011

The introduction of new carbons for use in rubber and the application of established grades to new uses has led to a confusing terminology. Perhaps it should be said that lack of terminology has led to confusion. Since entry of the United States into the War, reclaimed rubber has been used more generously in tires, including tread stocks, to extend the natural rubber stockpile. This has brought about a considerable use of black of the impingement channel type, which is slightly coarser and somewhat less reenforcing than that previously employed in tire treads. The grade in question has long been available for specialized uses, and has been referred to within the carbon industry as “soft channel black”. However, it is unfortunate that rubber compounders have more recently come quite frequently to refer to this type simply as “soft black”. Intermediate carbons not made by the channel process are now receiving wide attention. These, and a large group of already established grades, are distinctly coarser than the softest channel black, so it is a matter of some importance to exercise care in the nomenclature.
Rubber Photogels. II.
Authors: Stevens Henry P.
Published: February 2011

In a previous communication the writer has shown that the formation of gels from rubber sols on irradiation is often accompanied by an increase in weight so that the solvent and (or) sensitizer apparently reacts photochemically with the solute. The increase in weight of the rubber after removal of the solvent was found to be greater the more rapid the gelation of the sol. It was suggested that this increase in weight might result from products formed by reaction between the solvent and sensitizers independently of the rubber; the product in that case might be rubber physically associated with such photochemical products. This seemed unlikely, as prolonged extraction of the moist or dried photogels with acetone and alcoholic potash removed only a part of the increase. As a further check, a mixture of solvents and sensitizers without rubber was irradiated in sealed tubes and the products were examined. These experiments have been repeated by exposure to sunlight in a window with southern aspect for a whole year. In some cases small quantities of nonvolatile substances were obtained, but these were readily soluble in acetone and, therefore, did not account for the increase in weight, or at least for only a small part of it, and that part was acetone-soluble. It appears, therefore, that any reaction which takes place on insolation between the solvents, with or without additional sensitizers, cannot account for the observed increase in weight of dried photogels. The conclusion is reached that a photosynthesis has taken place, and that the gels consist of a rubber reaction product, at least where an increase in weight takes place.
The Vapor-Pressure Equations of Solutions and the Osmotic Pressure of Rubber
Authors: Miller A. R.
Published: February 2011

1. The laws which are obeyed by ideally dilute and by perfect solutions have been obtained by Guggenheim, and he has extended his analysis to obtain the properties of a class of solutions to which the name regular has been given. It is assumed that the solution consists of molecules of two types, α and β, of approximately the same size, and that each molecule, whether of type α or of type β, is surrounded by the same number z of other molecules, and the potential energy is regarded as the sum of contributions from each pair of molecules in direct contact. That is, the molecules are regarded as occupying sites on a regular lattice, and the potential energy arises from the interactions between molecules which occupy closest neighbor sites. Rushbrooke has examined the properties of such a solution, using the Bethe method to set up the partition function for the assembly. The properties of solutions in which the molecules of one type are of such a size and shape that they have to be regarded as occupying two lattice sites have been investigated by Fowler and Rushbrooke, who determined the limiting form of the vapor-pressure equations for extremely dilute and for extremely concentrated solutions. Chang has determined, for a two-dimensional lattice, the value of the combinatory factor, which can be written as g2,1(Nα,Nβ) for the case in which each molecule of type a occupies two closest neighbor sites and each molecule of type β occupies one site. Chang's determination of g2,1(Nα,Nβ) for a two-dimensional lattice is based on an analysis of the corresponding adsorption problem, in which he superimposes some arbitrary assumptions on the Bethe method. It has, however, been shown that the value which Chang obtained for g2,1(Nα,Nβ) is applicable to two- and to three-dimensional lattices in which no two closest neighbors of a given site are also closest neighbors of one another. Fowler and Guggenheim have shown how, once the combinatory factor has been evaluated, it can be used to determine the configurational entropy of mixing and thence the vapor-pressure equations when the energy of mixing is zero. Using Chang's value for g2,1(Nα,Nβ), they obtained for the vapor-pressure equations, when each solute molecule occupies two closest neighbor sites on the lattice and each solvent molecule occupies only one lattice site, the following equations:
The Change in the Raman Spectra of Chloroprene and Isoprene in the Polymerization Process
Authors: Gantmacher A. , Medvedev S.
Published: February 2011

1. When chloroprene and isoprene polymerize, besides the frequency characterizing the conjugate double bond in the monomer, there appears a higher frequency corresponding to the isolated double bond in the polymer. In the polymerization process, the intensity of the frequency of the conjugate double bond decreases and the intensity of the frequency of the isolated double bond increases. Because of the increase in the number of single bonds in the polymer, the intensity of the frequency of the single bond 1005 in the polymer is considerably greater than in the monomer. 2. Even in the case of the samples with high polymer contents (greater than 50 per cent), the intensity of the frequency of the conjugate double bond is considerably greater than the intensity of the frequency of the isolated double bond. This is attributable to the fact that part of double bonds disappear during polymerization. 3. The Raman spectra of the chloroprene and isoprene polymers differ essentially from those of the monomers. To characterize the frequencies of vibration in the polymer molecule, it is essential to investigate its Raman spectrum in a medium free of the monomer. 4. The formation of highly polymeric molecules on polymerization does not result in an increase in the intensity of the continuous background in spectrograms.
The Solubility of Sulfur in Butadiene-Styrene Copolymer
Authors: Williams Ira
Published: February 2011

The solubility of sulfur in rubber has been studied sufficiently for the various phenomena connected with solubility to be well known. Among the important factors are the available concentration of sulfur at any temperature, the diffusion of sulfur in the rubber, blooming of both vulcanized and unvulcanized rubber, and the effect of supersaturation on the formation of bloom. Similar studies have not been reported on synthetic rubbers which are vulcanized with sulfur. The present paper deals with the solubility of sulfur in a butadiene-styrene copolymer. This work was conducted with a copolymer prepared from 75 parts of butadiene and 25 parts of styrene. The polymer contained about 6 per cent of acetone-extractable material, consisting largely of phenylnaphthylamines and soap-forming acids, particularly stearic acid. It was the general type proposed for large-scale production, and was characterized by lack of tack, nerviness, and short break, especially when hot. The general method employed was one already described, and later employed in a modified form. In general, it consists in the observation, with a low-power microscope, of known amounts of finely divided sulfur dispersed in rubber when very slowly heated and cooled in a hot stage. The solubility temperature is taken as the temperature at which all the sulfur disappears, and the limit of supersaturation is determined by the temperature at which the sulfur reappears when the rubber is lowly cooled.
Effect of Temperature on Resilience of Natural and Synthetic Rubber
Authors: Jones H. C. , Snyder E. G.
Published: February 2011

The necessity of the substitution of synthetic elastomers for natural rubber has been forced on the rubber compounder by the exigencies of war. His background of a hundred years of research and compounding is his principal weapon for making this conversion in the shortest possible time. Too often he finds that this background fails and that practices invaluable in the development of natural rubber stocks are worthless in the case of synthetic rubber, or at least are subject to a different interpretation.
A Method of Testing the Elasticity of Synthetic Rubbers at Low Temperatures
Authors: Kish George D.
Published: February 2011

With the appearance of many new synthetic rubber compounds, the need has arisen for quick and practical testing to determine their comparative applicability to uses formerly filled by natural rubber compounds. One of the most important points is the elastic behavior of synthetic rubbers at low temperatures, and such information is imperative when synthetics are to be introduced into the design of a new product. To obtain accurate data, an instrument termed an Elastensometer was devised.
Aging of Rubber in the Oxygen Bomb at Room Temperature
Authors: Scott J. R.
Published: February 2011

The work described below was carried out as a first step in determining whether an oxygen-bomb test at room temperature could be used as an accelerated aging test for unvulcanized rubber compositions, e.g., as used on surgical and adhesive plasters and for combining shoe fabrics, because a high-temperature test is unsatisfactory in such cases, owing to the melting of the compositions. The only infallible way of assessing the value of an accelerated test for such compositions is by comparison with natural aging, but as this is a very lengthy process and as the deterioration is difficult to measure quantitatively, it was decided to make preliminary tests on the effect of high oxygen concentration at room temperature by using vulcanized rubber. Although the results proved to be negative so far as the original purpose of the work was concerned, it is considered of interest to place them on record in view of the prominence given in some papers on aging to the relationship between oxygen concentration and rate of oxidation and deterioration of rubber. A mix composed of rubber 100, sulfur 3, zinc oxide 5, stearic acid 1, and diphenylguanidine 0.75, was vulcanized for 30 minutes at 153° C. Tensile tests, using standard ring-specimens and the Schopper machine, were made on unaged specimens and on specimens that had been aged (1) in an oxygen bomb at 300 lb. per sq. in. oxygen pressure and at room temperature (about 10° C), (2) in a Geer oven at 70° C. Four rings were used for each test, the tensile strength and breaking elongation figures quoted being the average for the two rings giving the highest tensile strength, and the figures for the elongations at constant loads the average of all four rings.
Characteristics of Wild Rubbers
Authors: Tristram G. R. , Gee G. , Treloar L. R. G. , Jeffrey G. A.
Published: February 2011

The work leads to the conclusion, which can be stated with considerable confidence, that the rubbers examined are without exception polyisoprene rubbers, identical in their chemical constitution, and, when purified, similar in physical characteristics, to ordinary Hevea rubber.
The Kinetics of High Elasticity in Synthetic Polymers
Authors: Tuckett R. F.
Published: February 2011

The simple Mark-Kuhn theory of high elasticity of rubber has been extended, on the basis of the work of Alexandrov and Lazurkin, to cover the elastic properties of other polymers. The chief principle invoked is that high elasticity is developed only when rotation of the main C—C chain in the polymer is comparatively free. The effect of molecular structure, plasticizer and cross-links on elastic properties has been indicated, and also a connection with other observed physical properties, such as volume expansion, dielectric dispersion and specific heat.
The Kinetics of Rubberlike Elasticity
Authors: Eley D. D.
Published: February 2011

1. The treatments of relaxation phenomena in polymer systems, due to Kuhn, and Alexandrov and Lazurkin, are outlined and discussed. 2. Eyring's rate equation is used to analyze the rates of orientation of long-chain molecules in a stressed specimen of lightly vulcanized rubber. The data are compared with similar data on viscous flow in raw rubber, and it is suggested that the segment size for movement is the same in both cases. In viscous flow, the segmental movement occurs without appreciable internal rotation within the segment. In elastic orientation, however, it appears that a high degree of internal rotation within the segment accompanies the formation of the activated state. 3. The activation energy for the orientation of long chains is separated into two terms: (1) the energy required to free a segment from its neighbors, (2) the energy of activation for rotation around C—C bonds. It is suggested that the main effect of vulcanization and plasticizers is on term (3); vulcanization tends to increase this term, plasticizers to decrease it. 4. Data on the dielectric dispersion of polyvinyl chloride suggests the need for internal rotational activation in this case, as in orientation elasticity. This is in agreement with what we should qualitatively expect. Possible complications due to crystallinity in rubber at high extensions or low temperatures are briefly discussed.