bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray Study of Reactions Involving Accelerators. Orientation of Crystalline Phases on Stretching of Rubber Stocks
Authors: Clark G. L. , LeTourneau R. L. , Ball J. M.
Published: February 2011

About a year ago, in the course of a systematic survey of the x-ray diffraction patterns of a number of routine rubber samples with different accelerators present, certain similarities were noted in the diffraction effects from the accelerators in these stocks. Close examination of these effects showed that they were identical. The stocks contained the accelerators tetramethylthiuram disulfide, tetramethylthiuram monosulfide and zinc dimethyldithiocarbamate, which are chemically similar (Table I); the first is the disulfide, the second, the monosulfide, and the third, the zinc salt. Thus, the diffraction patterns indicate that, on curing, the disulfide and the monosulfide in the presence of sulfur react with zinc oxide to form the zinc salt. This is not a new concept. The zinc salts have been extracted with solvents from stocks similar to the above, and it has been supposed that such reactions occur. However, the extraction method leaves some doubt as to whether the salt was originally present in the rubber matrix or whether it was formed in the solvent on extraction. Every crystalline material has its own characteristic x-ray diffraction pattern, which is different from that of every other crystalline material, just as the fingerprints of each person are different from those of every other person. Thus, with x-ray “fingerprint”patterns it is possible to identify positively the presence of these salts in the rubber matrix and show that they must have been formed in the rubber mix on curing. Further, it was noted that this crystalline salt is strongly oriented in the rubber matrix on stretching. It seemed advisable, then, to investigate other similar reactions by the x-ray method and to investigate the significance of the strong orientation of these reaction products in the rubber matrix.
A Direct Determination of Rubber Hydrocarbon. Chromic Acid Oxidation Method
Authors: Burger V. L. , Donaldson W. E. , Baty J. A.
Published: February 2011

A method for the direct determination of rubber is reported. This method utilizes the property of rubber hydrocarbon when oxidized by chromic acid to form definite and reproducible amounts of acetic acid. This determination has been reduced to a comparatively simple laboratory procedure, whose accuracy (in the absence of interferences) is 1 to 2 per cent.
Digest of Cooperative Test Program on Accelerated Light Aging of Rubber
Authors: Ingmanson J. H.
Published: February 2011

The Eveready unit without filters and the Atlas Twin-arc Weatherometer effect a more rapid deterioration of vulcanized rubber on exposure than does ourdoor exposure in summer. The degree of acceleration varies with the particular compound tested. In these tests it was found that from 0.6 to 3.0 hours' exposure in the machines, depending on the compound, was equivalent to 1 day of outdoor summer exposure. The procedure followed in making Eveready tests is not sufficiently standardized to obtain satisfactorily comparable results in several laboratories, with a wide variety of compounds. The Atlas single-arc equipment shows little acceleration in aging rate compared with the Atlas twin-arc and Eveready equipment used in these tests. No broad conclusions can be drawn from the results of tests in the Atlas twin-arc equipment, since results were reported for only one of these machines. It is suggested that measurements of the total radiation may be of greater significance than measurements in the ultraviolet region alone. Further' standardization in connection with ventilation and maintenance of a constant uniform temperature around the exposed specimens appears desirable. Further work is required to determine the effect of the thickness of the exposed sample on the rate of deterioration. If exposure periods are to be for time periods such as were used in these tests, it may be desirable to use thicker specimens.
Evaluation of Small Amounts of Synthetic Rubber
Authors: Garvey B. S.
Published: February 2011

In research on rubber synthesis, as in any broad program of chemical research, it is a distinct advantage to be able to do all work on a normal laboratory or test-tube scale. With rubber, however, the standard laboratory testing methods require from 200 to 500 grams of rubber for each batch. Hence it was obvious that, if the advantages of small-scale work in the preparational stages were to be realized, a new technique of rubber testing would have to be developed. The use of entirely new and unrelated procedures has two definite objections. In the first place the new procedures must be thoroughly tested and compared with the older methods of testing or with the processing and use requirements of the new rubbers. In the second place the significance of the results of such new tests can be conveyed, even to experienced rubber technologists, only after considerable interpretation of the methods. It seemed best, therefore, to modify standard rubber-testing methods so that they could be applied to very small amounts of synthetic rubber. More recently, the shortage of natural rubber has made necessary a reduction in the amount of rubber used for testing. For this purpose the same small-scale procedures are highly advantageous. While some idea of the quality of a sample of natural or synthetic rubber can be obtained from examination of the crude rubber itself, it is much better to know the physical properties of the vulcanized product. This means that one or more balanced compounds must be mixed and tested. The purpose of this paper is to describe a technique which has been developed in the Goodrich laboratories whereby, with as little as 5 grams of rubber, the stress-strain characteristics may be determined, and with 9 grams of rubber a fairly comprehensive evaluation can be made. This method has been used to evaluate polymers made on the 10-gram scale by Fryling.
The Second Mile
Authors: Sebrell L. B.
Published: February 2011

The title “The Second Mile” was inspired by an address given by W. E. Wickenden, of the Case School of Applied Science, on an entirely different subject. Since this title seemed to suit the synthetic rubber situation as it now exists, Wickenden's permission was secured to use the title in connection with this lecture. In its broader aspects, the paper purports to cover the present status of the synthetic rubber situation. Natural rubber will be compared with the copolymers made from butadiene and styrene, butadiene and acrylonitrile, and the copolymers generally known as Butyl rubber. These three materials were chosen for the comparative study because they are the materials which the Government proposes to use in the largest quantities to alleviate the present shortage of rubber. It is hoped that the data will give a fairly accurate picture of the comparative or relative values of these synthetic rubbers and natural rubber. There will be no discussion of the methods of manufacture, which are still more or less secret. It is proposed also to go into the probable structure of these polymers and to indicate some trends of research which might profitably be followed to improve them.
The Structure and Reactions of Rubber. A General Discussion
Authors: Whitby G. S. , Evans A. B. A. , Pasternack D. S. , Gee G.
Published: February 2011

Rubber Chemistby and Technology published, in its July and October 1942 issues, a series of papers comprising a symposium on “The Structure and Reactions of Rubber”, held by the Faraday Society, London, May 29, 1942. The papers were followed by critical discussions, which are assembled in the following pages, with references to the corresponding original papers.
The Plasticization of Buna
Authors: Hagen Harro
Published: February 2011

Recently oxidative thermal softening of Buna has come to the fore, a process which has been called “degradation”, a not too happily chosen term which suggests technical deterioration in quality. Properly speaking, there is loss in quality, just as there is considerable deterioration in quality when natural rubber latex is converted to dry rubber, a deterioration which is made still more extensive by mastication. Thus, while it is possible under laboratory conditions to make tread compounds having tensile strengths of 300–350 kg. per sq. cm. from natural rubber and latex compounds having tensile strengths of 450–500 kg. per sq. cm., the values obtainable with milled natural rubber are considerably lower. Despite this, one would not wish, except in the rarest instances, to dispense with the milling of natural rubber, since its processibility depends on the plasticization which is obtained by mastication. Thermal softening of Buna-S corresponds to the mastication of natural rubber. It has been possible to produce treads of unsoftened Buna-S with tensile strengths of 300 to 320 kg. per sq. cm. from compounds prepared in the laboratory, but these results cannot be obtained on factory mills because of the poor dispersion of fillers. With thermal softening, the tensile strengths of tread compounds made on laboratory mills would, to be sure, be somewhat lower, viz., 280–290 kg. per sq. cm. In mechanical compounds, the improved dispersion of fillers, compared with unsoftened Buna-S, would cause an increase in tensile strength. Oxidative softening is justified, not only from a processing and technical point of view, but above all because of the improvement in the finished product—provided, of course, that the degree of softening is suited to the intended application and that the optimum formula has been worked out. It would, therefore, be better to replace the derogatory word “degradation” by “oxidation” or “thermal softening”.
Cut Growth of Buna-S Compounds. A Method to Determine the Rate of Cut Growth of Buna-S Compounds
Authors: Carlton C. A. , Reinbold E. B.
Published: February 2011

1. A satisfactory laboratory method has been developed for measuring the rate of cut growth of Buna-S compounds. 2. Buna-S compounds are inferior to both natural rubber and Neoprene with respect to rate of cut growth. 3. Cut growth measurements made at elevated temperatures give entirely different results from those made at room temperature. 4. State of cure has a radical effect on the rate of cut growth of Buna-S compounds; the undercures are superior to normal cures or overcures.
Conductivity of Rubber Tread Stocks. Effect of Properties of Carbon Black
Authors: Cohan Leonard H. , Mackey James F.
Published: February 2011

The conductivity of a rubber tread stock compounded with 50 parts of carbon black increases exponentially as the particle size of the black decreases. As the crystal structure of the carbon approaches a more graphitic form, the conductivity increases sharply. Noncarbon surface components, either of the hydrocarbon or carbon oxide type, decrease the conductivity. This effect is less important than particle size or crystal structure. However, increases in conductivity or more than tenfold can be brought about by removal of surface components.
Brass-Plating
Authors: Gurney W. A.
Published: February 2011

Although brass-plating is the best known method of attaching rubber to iron or steel, it is still regarded in many quarters as something of an art or mystery, with a considerable element of uncertainty entering into the process. The brass-plating bath consists essentially of copper and zinc cyanides dissolved in sodium or potassium cyanide, with a total metal content of about 3 ounces per gallon. The composition of the alloy deposited varies with the ratio of copper to zinc in the bath, the pH, the temperature, the current density, and the amount of certain other substances, such as ammonia. Most writers on the subject have endeavored to eliminate the uncertainty by a rigorous specification of the formula of the plating bath, and the conditions under which it is to be used. In his experience, however, the composition of a plating bath can vary widely, and still give plating satisfactory for adhesion. The composition of plate deposited depends on a balance of several factors, and in most published formulas, one or more of these factors is omitted. For example, the pH is often not specified and yet it is possible to deposit a range of brasses from pure copper to pure zinc merely by the change in pH, in any particular bath.
IV. The Micellar Theory of the Structure of Rubber
Authors: Gee G.
Published: February 2011

The molecular weight data reported in Part II depend on the assumption that the values obtained by extrapolating osmotic pressure measurements to infinite dilution represent true molecular weights. This point of view has been strongly criticized, particularly by Pummerer and his coworkers, according to whom rubber normally exists in solution in the form of micelles comprising more or less well-defined aggregates containing a considerable number of chemical molecules. The- osmotic “molecular weight” is then regarded as the weight of an average micelle. If they exist, these micelles may be important in determining both the chemical and physical behavior of rubber, for we should clearly expect the bonds by which the chemical molecules are bound into micelles to be weaker than those within the molecules. It may be noted that it has been shown elsewhere that the physical properties of a series of rubber fractions are closely related to their osmotic and viscosity molecular weights. Since, according to the micellar theory, these fractions can differ only in micelle size, their mechanical behavior must, from this viewpoint, be determined by the size of the micelles, which must therefore remain intact during mechanical deformation of the rubber. It is the object of the present paper to examine in more detail the basis of the micellar theory, and especially to offer an interpretation of the results of the East method, on which Pummerer's arguments are mainly based.
Phase Transition and Elastic Behavior of High Polymers
Authors: Mark H.
Published: February 2011

Present experimental knowledge indicates that linear or moderately branched and cross-linked high polymers are capable of undergoing two types of phase transitions. (1) A first-order transition, characterized by a sudden change of quantities such as specific volume, energy, and entropy, which may be briefly called a “crystallization” (or fusion). The crystallized areas formed in the course of this process are mostly elongated cylindrical or flat bundles of parallelized chainlike molecules, or segments of them, with an average length between 500 and 5000 A.U. and an average diameter of 50–200 A.U. They do not have plane and sharp boundaries, but they represent only regions of higher geometrical order and presumably go over gradually into the mesomorphous and amorphous parts, which approach the structure of a liquid. It seems that one and the same chain can extend through such a crystallite, enter an amorphous area, extend over into another crystallite, etc. Figure 1 is an idealized sketch of this situation. (2) A second-order transition, characterized by a sudden change of quantities such as heat capacity and thermal expansion, takes place at lower temperatures than fusion, and presumably indicates that below this transition point the individual segments of the chain molecules do not carry out rotational and vibrational movements as a whole, but do carry out such internal Brownian movements above this point. Hence, according to the ideas of Eyring, Kuhn and Meyer, they act as independent kinetic units of the system investigated. Figure 2 is an interpretation of this concept.
A Statistical Treatment of Crystallization Phenomena in High Polymers
Authors: Alfrey T. , Mark H.
Published: February 2011

An attempt has been made to explain the anomalous crystallization behavior of high polymeric materials on the basis of entropy changes in the amorphous material. The free energy of the amorphous phase depends not only on the temperature and pressure, but also on the degree of extension and the fraction of crystalline material in the sample. A crude model embodying these characteristics was proposed. On the basis of this model, it is possible to explain the unsharp melting point of rubber, the dependence of crystallization on the degree of extension, and the phenomenon of spontaneous extension.
Evaluation of the Buffer Capacity of Crude Rubbers
Authors: Newton E. B. , Willson E. A.
Published: February 2011

The hypothesis was advanced in the preceding paper that an important factor in determining the rate of cure of rubber is the acid-base equilibrium developed during vulcanization and that such an equilibrium is determined to a large extent by the nature and quantity of the latex serum substances remaining in the crude rubber mass. In effect, this serum material was regarded as a buffer substance. If this were true, it follows that differences in the buffer capacities of various crude rubbers should be demonstrable and, in the following discussion, two sets of experiments designed with this object in view are described.
Polysulfide Theory of Accelerator Action during Vulcanization. Evidence for the Theory
Authors: Morris Ross E.
Published: February 2011

On the basis of indirect experimental evidence, Scott and Bedford proposed about twenty years ago a mechanism of the accelerator action of metallic dithio-carbamates, known as the polysulfide theory. According to these authors, a metallic dithiocarbamate reacts with sulfur during vulcanization to form a polysulfide, which subsequently decomposes and liberates active sulfur for reaction with the rubber hydrocarbon. This theory gained support by the observation of Jones and Depew that the solubility of zinc dimethyldithiocarbamate in rubber is increased when sulfur is added to the mix, since such behavior may result from the formation of a soluble polysulfide. More recently, Scott and Sebrell questioned Scott and Bedford's polysulfide theory, on the basis that no polysulfides of metallic dithiocarbamates have been isolated. The author does not intend to enter into the controversial subject of the mode of action of vulcanization accelerators, but rather to present experimental data which confirms the original supposition of Scott and Bedford that sulfur forms unstable addition compounds, or polysulfides, with metallic dithiocarbamates. The metallic dithiocarbamates investigated were zinc diethyldithiocarbamate and zinc dibutyldithiocarbamate.
Effects of Low Temperatures on Neoprene Vulcanizates
Authors: Yerzley Felix L. , Fraser Donald F.
Published: February 2011

Realizing the need for general agreement throughout the rubber industry on the evaluation of the freeze-resistance of various elastomers, we have outlined several procedures and reported typical test results. Although the procedures described are inadequate as standard tests for complete evaluation, it is hoped that they may stimulate development of procedures which will be generally acceptable.
The Effect of Temperature on the Sunlight Deterioration of a Rubber Compound
Authors: Ball J. M. , Bradley C. E.
Published: February 2011

The subject of this article might be the question: “Does temperature have an effect on the deterioration of rubber in sunlight and, if so, approximately how much effect?” We are interested in any effect of temperature because rubber goods in service are frequently subjected to sunlight over a fairly wide temperature range. There are apparently very few references or comments in the literature on this subject; but we wish to look briefly at some significant experiments of the past which have to do with sunlight without regard for temperature, and then discuss a new experiment.
Colloidal Carbon as Revealed by the Electron Microscope
Authors: Wiegand William B. , Ladd William A.
Published: February 2011

The electron microscope of today may be said to rest on the pioneer work of three outstanding physicists. J. J. Thompson, in 1897, discovered electrons under the name of negative corpuscles. De Broglie, about 1922, established the wave characteristics of electrons. In 1926 Busch established the electron lens. In 1935, E. F. Burton, following a visit to Germany, envisaged the enormous potentialities of the electron microscope and began a program at Toronto designed to eliminate the serious defects of early German instruments. In 1938, this program culminated in the construction of a new and superior instrument by two of his graduate students, A. Prebus and J. Hillier. The publication of their results early in 1939 aroused the immediate interest of the Columbian Carbon Company which later established a Fellowship at Toronto under Professor Burton's direction. In 1940, A. Prebus, assisted by W. A. Ladd, working in Toronto, secured for Columbian the first perfect pictures of Micronex, from which accurate data as to mean surface area and as to particle shape were obtained. Public release followed in June, 1940. Prebus is now Professor at Ohio State University and is pursuing the theoretical side. Hillier is at R. C. A., where instruments, of essentially Toronto design, are being developed commercially, and Ladd has joined the Columbian Carbon Research Laboratories, for the two-fold purpose of further improving the microscope and of applying it to the problems of natural and synthetic rubber reënforcement. This work of Professor Burton and his pupils is of importance under present critical conditions since the replacement of natural by synthetic rubber necessitates a new approach to the theory and practice of rubber reënforcement. With the aid of the electron microscope, it is now for the first time possible to evaluate the role played by surface area in carbon-rubber reënforcement.
The Estimation of Small Percentages of Rubber in Fibrous Materials
Authors: Blow C. M.
Published: February 2011

Rubber is being used in increasing quantity in fibrous materials of all types as a binder or to impart particular and special properties. The percentage of rubber employed varies from 3 to 15 or 20 per cent, and it is becoming of interest and importance to, have analytical methods to estimate with some degree of accuracy the percentage present. This estimation has several difficulties, and no one method can be adopted on account of the difference in behavior of various fibres. The fibre may consist of protein, such as silk, wool and other animal fibre, leather, or cellulose, such as jute, cotton, rayon, paper, kapok, etc. The rubber may be vulcanized or unvulcanized, and partly or completely in the oxidized state. In addition, there may be organic material, such as protein, soap (added as stabilizer for the latex), fats, oils, waxes, dyestuffs and inorganic substances from the fibre, fillers and pigments, coagulants, and so forth—to name only a few possible compositions. The problem appears complex, but may be simplified in some cases by knowing, from the process of manufacture, the definite absence or presence of certain of these likely ingredients.
Static Electric Problems in Tires
Authors: Liska J. W. , Hanson E. E.
Published: February 2011

Since its advent about thirty years ago, the pneumatic tire has been remarkably improved to meet increasingly severe requirements. Improvements in motor vehicles, increased speed of travel and, in general, a more and more critical attitude on the part of the consumer, have introduced difficult problems for the rubber technologist. One of the more recent and unusual of these problems, introduced in part by the popularization of the automobile radio, has been the accumulation of static electrical charges on a moving car. At first difficulty was experienced mainly with radios in passenger cars. In some cases when the auto was stationary and the motor running, the program reception was clear and uninterrupted but, when the car was set in motion and driven for some distance, reception was seriously impaired by loud, intermittent static noises. Later, reports began to circulate of toll-bridge collectors receiving severe electrical shocks on touching any part of a car which had just pulled to a stop after a sustained drive. Similar phenomena reportedly took place when motorcycle police touched cars they had pursued and stopped. Recently, passengers on commercial busses, especially on those operating in hot, dry regions, have experienced electrical shocks on entering or leaving. The object of this paper is to describe some of the methods employed in measuring, and some of the means developed for controlling, the observed effects.
Structure of the Butadiene-Styrene Copolymer
Authors: Alekseeva E. N. , Belitzkaya R. M.
Published: February 2011

The experimental data indicate that joint polymerization of styrene and butadiene results in copolymers of varied structure. Of the styrene, 31.2 per cent forms, with the butadiene, macromolecules in which the two components alternate regularly, whereby the butadiene combines in its 1,4-position. Forty per cent of the styrene forms macromolecules, in which two units of styrene interlink adjacently. Such “styrene pairs” are separated by one or more molecules of butadiene polymerizing in their 1,4-position. The remaining 29 per cent of styrene evidently enters into the composition of branched macromolecules, formed as the result of butadiene linking both in the 1,2- and in the 1,4-positions. Taking into consideration the fact that formic acid must have been formed from macromolecules, with butadiene linked in the 1,2-position, we can conclude that 23.3 per cent of the butadiene polymerized in its 1,2-position, and the rest in the 1,4-configuration.
The Long Spacing in Rubber
Authors: Schallamach Adolf
Published: February 2011

The x-ray diagrams of some rubbers give a long spacing, which was first reported by Clark and collaborators. According to them, it is found only in gel rubber, where it has the value of 54 a.u., but it is absent in sol rubber. This spacing is oriented in stretched rubber, the x-ray reflections contracting into two spots in the equatorial plane. This means that the long spacings lie in planes at right angles to the fibre axis. As we found it difficult to account for this result and, furthermore, had indications that this long spacing might depend on the nature of the rubber, we examined a number of specimens of different origin and preparation. We used a camera of about 10-inch radius, reducing the air scattering by inserting an evacuated length of wide tube with thin cellophane windows at both ends. The x-ray source in these experiments was the 50 kw. x-ray generator of this laboratory, working with an input of 30 to 40 kw.
An Elastic Theory for Rubber
Authors: Latshaw Elmer
Published: February 2011

The elastic properties of vulcanized rubber present a difficult problem to generalize, mainly because of the large number of compounds in common use. There are good reasons for many kinds and grades, and a characteristic common to all is large elastic strain. Even in the best grades of rubber these strains are not perfectly elastic, but this is also true of almost all other materials, including spring steels. An elastic strain theory will be derived for a specific group of rubber compounds, namely, spring stocks. These are dense, strong rubbers, highly elastic within the working stress range, and capable of supporting loads under continuous vibration and shocks. To be of real value, the strain law should closely predict strain for the range of working stress, or more generally for the elastic range, and should indicate the trend at very high stresses where inelasticity becomes more prominent. Figure 1 shows a cylindrical element of rubber having an area A0 and length h when unstressed. If a uniform stress is imposed perpendicular to the end area, the length changes to H and the area to A. These symbols apply whether the stress is tension or compression. The usual definition of strain, i.e., change in length due to stress divided by the unstressed length, is comprehensive and descriptive for the large strains in rubber.
The Plastic-Elastic behavior of Ebonite
Authors: Scott J. R.
Published: February 2011

A hypothesis is put forward to explain the plastic-elastic behavior of ebonite and its dependence on temperature. This is based on the previously described mechanical conception of ebonite as a system comprising a heat-stable elastic phase and a viscous temperature-sensitive phase, but the difficulty of reconciling this two-phase concept with the probable structure of ebonite is avoided by replacing the elastic and viscous phases respectively by primary and secondary (cohesional) bonds, the relaxation of the latter, due to their relatively low temperature-stability, being responsible for all time effects in the deformation of ebonite. The hypothesis explains the main facts relating to so-called plastic yield and to the residual strain after recovery from deformation, and thus appears to form a useful basis for further research on ebonite.
Rubber Photogels
Authors: Naunton W. J. S.
Published: February 2011

1. The conditions of photogel formation and reversion in rubber solutions have been studied. The larger the rubber molecule the more readily is gel formation effected. 2. Photogels exhibit all the properties associated with cross-linked molecules. 3. Photogels made with most synthetic rubbers are not influenced to the same extent by the presence of oxygen, and do not revert on further exposure in the presence of oxygen. 4. The suggestion is made that gel formation is due to oxygen-bridging of already oxygenated centers. This bridging is not possible in the presence of oxygen, since further oxidation results, with cleavage of the molecule. In the case of active solvents, bridging may be due primarily to condensation with solvent. Bridging is also probably accompanied by a limited degree of cyclization.
Dielectric Constant, Power Factor, and Conductivity of the System Rubber-Calcium Carbonate
Authors: Scott Arnold H. , McPherson Archibald T.
Published: February 2011

The results obtained in this investigation indicate that either the formula developed by Wiener (Formula 7) or the exponent formula (Formula 9) may be used for the computation of the dielectric constants of mixtures of calcium carbonate and rubber. Formula 7 may be preferred, since it gives some indication of the shape of the particles and state of dispersion of the powder. There was little difference between values of the dielectric constant and loss tangent at 1 kilocycle per second and at 100 kilocycles per second. The change of the loss tangent with the content of calcium carbonate was not large, but a direct relationship between loss tangent and percentage of calcium carbonate was indicated. The 1-minute-conductivity values increased continuously with increasing content of calcium carbonate when Vistanex was used as the base, but passed through a minimum when natural rubber was used.
Application of Rubber Latex to Woolen Hosiery
Authors: Piper G. H.
Published: February 2011

The application of rubber to textiles has made great progress within the last ten years, and the introduction of rubber latex with its high resistance to aging, which is of great importance where textile apparel is worn next to the skin, has virtually opened up a new field. The sock has not altered greatly, and its greatest defect, the formation of holes at the toe and heel areas still remains. It was with the object of reinforcing these areas by impregnation with rubber latex that this research was commenced, resulting in the present process. Briefly, the process is the application to the knitted sock, at the areas to be reinforced, of a rubber latex containing specified amounts of wetting and stabilizing agents so that the latex coagulates after penetration into the wool to a limited extent. The process is essentially an impregnation process, and the meshes between the threads remain open and free from rubber. The resulting hosiery is comfortable, and shows great resistance to the formation of holes. In the development of the process, which occupied several years, numerous difficulties were encountered, not the least being the severe conditions to which the rubber is exposed. The warmth of the body, perspiration, laundry treatment and other factors necessitated a latex compounded to give high resistance to aging.
Dunlop Fatigue Test for Rubber Compounds
Authors: Gough V. E. , Parkinson D.
Published: February 2011

This paper considers the effects produced inside a block of rubber subjected to repeated cycles of stress. Other types of fatigue, such as flex cracking or the phenomenon recently referred to by Cadwell, Merrill, Sloman and Yost as static fatigue, are not discussed. The fatigue test which will be described in the following pages has been used for a number of years in the Dunlop Rubber Company's laboratories. The test machine, like others which have been described by Martens, Vogt, Abbott, Depew and Snyder, Cooper, Havenhill and Macbride, Havenhill, Lessig, and Roelig, can be used for assessing heat development, the failure produced in the test-piece being then of the “blow-out” type, or it can be used to produce breakdown in specimens which have been stressed for prolonged periods at a moderately high, although steady temperature. The failure may then be considered to be one of fatigue and not one of thermal decomposition, although, as will be shown, the heating effect is one of the most important factors operating to produce failure. Among the test machines referred to above, the one described by Depew and Snyder is similar to the Dunlop machine, an early form of which was already in use for the purpose of evaluating heat generation in solid tire compounds when Depew and Snyder's paper was published in 1929. The present improved machine and technique are the result of several years of subsequent development work. The stressing conditions of the machine, which produce direct compression, are as simple as possible and give results which vary less and are more easily interpreted than those obtained when they are more complex, as, for example, when they introduce shear in addition to compression.
Vulcanization of Buna-S (GR-S) with Organic Sulfur Compounds. II.
Authors: Throdahl M. C. , Beaver D. J.
Published: February 2011

Buna-S (GR-S) was vulcanized with acid, thiocyanic, amine, thiuram and phenolic sulfides. Heat embrittlement and resistance to cut-growth of the vulcanizates obtained with most of these compounds were better than those exhibited by normal stocks containing free sulfur, but heat generation was higher.
Effect of Accelerators on the Heat Embrittlement of GR-S Vulcanizates
Authors: Hunter J. S.
Published: February 2011

Two of the most serious shortcomings of GR-S type synthetic rubber are its poor resilience, leading to excessive heat build-up under severe stress cycles, and its property of hardening during exposure to heat in service. Heat embrittlement aggravates heat build-up and vice-versa, so a vicious circle develops which eventually leads to failure. The problem of minimizing heat embrittlement has received considerable attention, and much work on the subject has been published. Some of this published work is reviewed briefly below, and an account is given of certain experiments carried out in this laboratory. The results of these experiments enable some preliminary conclusions to be drawn on one aspect of the problem, namely, the effect of accelerators on the heat embrittlement of GR-S.
Effect of Milling on Properties of Hevea and Buna Rubbers
Authors: Wiegand W. B. , Braendle H. A.
Published: February 2011

1. The superior cut-growth resistance of Hevea tread stock is partly ascribed to its pronounced relaxation or lengthening when subjected to repeated severe cyclic extensions. Under such conditions the breaking elongation increases from 700 to 900%. GR-S under similar treatment fails to develop any lengthening. 2. As a consequence of this failure to lengthen under repeated severe strains, such as those antecedent to cut-growth failure, GR-S exhibits higher modulus, i.e., at 500 or 600 per cent elongation, or higher retractive forces than does Hevea. This also promotes cut growth. 3. In Hevea, progressive milling (at normal temperature) of tread stocks tends to develop a tensile maximum. At this point of optimum milling, d.c. resistivity reaches a minimum. Overmilling, characterized by a decrease in tensile, shows a sharp rise in log R. 4. With Perbunan, highest tensiles and elongations are realized only after several remillings, at which point modulus and Shore hardness have already shown marked decline. 5. With Buna-S (GR-S), tensile and elongation reach their maxima at about one remilling (at normal temperatures). Milling beyond this point is reflected in sharp degradation of elongation. Log R provides no indication of optimum conditions, since it is rising at this point. 6. In Butyl B, tensile and modulus reach a simultaneous maximum between two and three remillings. Log R in this region is declining and reflects retardation due to the softness of Butyl stocks. 7. Hot milling of GR-S shortens and reduces heat and flex properties. Cold refining lengthens GR-S and improves these properties, but does not protect against subsequent damage from heat. GR-S shortened by heat cannot be restored by subsequent cold refining. The benefits of cold refining apply also to the completely formulated tread. 8. Extreme development of the cold-refining technique produces the following results (based on treatment of complete tread mixing) : Modulus declines continuously to less than 50 per cent of control. Elongation increases continuously to 125 per cent of control. Tensile strength increases to 110 per cent at 20 passes and then remains steady. Hot-iron life (thermal shortening) improves continuously to 310 per cent at 80 passes. Cut-growth resistance improves progressively to 370 per cent of control at 160 passes, and is still rising. 9. The fact that such striking all-round quality takes place at about fifty cold refinings with rolls at 80° F (stock at about 120° F) suggests the importance, in the fabrication of GR-S tires and other products subject to dynamic usage, of (a) avoidance of elevated temperatures at all stages, and (b) further study of the remedial effects of strenuous mastication of refining of GR-S tread type, carbon-reinforced stocks under low-temperature conditions. 10. Attempts to improve GR-S should be oriented in two opposite senses: to decrease its hysteresis at low extensions (under 100 per cent) but to increase its hysteresis, or capacity to relax, at the higher extensions antecedent to cut growth.
Low-Temperature Flexibility of Synthetic Elastomers Effect of Aviation Gasolines
Authors: Wilson G. J. , Chollar R. G. , Green B. K.
Published: February 2011

A tensiometer can be used to measure the stiffness of rubber stocks; accurate data are secured which lend themselves to a quantitative interpretation of the effect of low temperatures on any compound. Where changes in the sensitivity to flexing of thin rubber sections are important, such data, represented by curves of temperature vs. flexibility, seem more important than durometer changes and bend-brittle points. The compounding practice of high plasticizer does not in itself provide low-temperature flexibility where fuel immersion and ensuing plasticizer extraction are conditions of service. Tests designed to evaluate low-temperature flexibility and freeze resistance which utilize organic liquids as temperature conditioners must be double-checked to ensure that the cooling medium is not exerting its own specific effect on the stocks. Graphs indicate the influence of aviation fuels on low-temperature resistance; it has been experimentally proved by the same method that acetone has a similar effect. It is established that some synthetics are more resistant than others to prolonged low temperature. Service requirements and field conditions should be carefully considered in all cases where laboratory evaluation does not include every variable factor. The need for a thorough application analysis of functional stocks cannot be overemphasized.
The Molecular Weights of Rubber and Related Materials. V. The Interpretation of Molecular Weight Measurements on High Polymers
Authors: Gee Geoffrey
Published: February 2011

Unless an ultracentrifuge is available, absolute molecular weight determinations must be based ultimately on osmotic data. Viscosity measurements furnish a convenient method of interpolation, and give reliable results for homogeneous linear polymers. The viscosity molecular-weight of a typical unfractionated polymer would not be very seriously in error unless the polymer were extensively branched. No reliable conclusions about molecular-weight distribution can be drawn from molecular-weight data alone without carrying out a fractionation, although a useful guide to the homogeneity of a polymer known to be of linear structure is furnished by the ratio of the viscosity and osmotic molecular weights.
Staining Rubber in Ground or Milled Plant Tissues
Authors: Haasis Ferdinand W.
Published: February 2011

Accessory to a comprehensive study of guayule production now under way by the United States Department of Agriculture is an analysis of the rubber content of plants of various strains and ages grown under diverse environmental conditions. This analysis is currently made by chemical extraction of the rubber from finely ground tissues by a method based on that described by Spence and Caldwell. This method consists of a number of distinct steps, and it is part of the program to test possible variants of these steps. As a check on the effectiveness of such tentative modifications, the ground samples are examined microscopically, especially the spent charges remaining after extraction.
The X-Ray Diagram of a Buna-S Vulcanizate
Authors: Morris Ross E. , Jordan Charles B.
Published: February 2011

Sebrell and Dinsmore (India Rubber World 103, 37 (1944); Rubber Chem. Tech. 16, 857 (1943)) found that the x-ray diffraction pattern of Buna-S consists of a broad halo similar to that obtained with liquids. This type of pattern was obtained whether the Buna-S was unstretched or stretched. Unstretched natural rubber gives a similar pattern, but stretched natural rubber gives a characteristic fiber pattern. This fiber pattern demonstrates the existence of three-dimensional crystallites. Buna-S would not be expected to yield a fiber diagram while stretched because the molecules of this synthetic rubber are probably not constructed in a regular fashion. The styrene residues are presumably distributed at random along the length of the molecule, and there may be side-chains which branch off the main chain. However, when considerably stretched, a Buna-S vulcanizate would be expected to exhibit some indication in its x-ray diagram that alignment of the molecules has occurred.
Two Modes of Action of Antioxidants in Rubber
Authors: Le Bras Jean
Published: February 2011

It is a commonly accepted belief that antioxidants protect oxidizable products from the harmful effects of oxygen by retarding the rate at which these oxidizable products combine with oxygen. Consequently, if the oxidizability of a rubber mixture containing no antioxidant and the oxidizability of the same mixture to which such an agent has been added are measured under the same conditions, the absorption of oxygen would be expected to be distinctly less rapid in the second case. This has, in fact, been proved to be true in general, not only for rubber, but also for other substances which are protected by antioxidants. In a systematic study of a series of antioxidants of differing chemical compositions, various observations were made which gave indications that these products react in two different ways. In these experiments a rubber mixture of chosen composition was prepared as a blank or control, and was compared with other mixtures of the same base composition to which various antioxidants selected for study had been added in the same proportion in all cases.
Damping, Heat Development and the Length of Life of Vulcanizates
Authors: Springer A.
Published: February 2011

Although it is still not possible to calculate or to predict the behavior and length of life of different types of rubber products under service conditions, it is nevertheless of value to make clear the relations involved, and to trace back the many already known phenomena to their physico-chemical causes. The present work deals with the following aspects of the subject. A relation between damping, shape of test-specimen, heat conductivity, frequency and heat development is derived, with the aid of which both the rise in temperature and the maximum temperature, and in precise measurements the temperature factor as well, can be calculated. With certain assumptions for the sake of simplicity, the energy loss can be calculated from the stress and elastic constant. It appears that the behavior of vulcanized rubber mixtures when they are tested under constant stress is different from that when they are tested at constant deformation. The destructive action brought about by prolonged repeated stressing is ascribed to chemical reactions, and on the basis of this assumption it is shown that the length of life depends on the temperature. Attention is called to the possibility of evaluating Wöhler curves on a mathematical basis. The equations which are formulated are verified by a large amount of experimental data, and a few characteristic diagrams are given by way of illustration.
Stiffening Effect of Pigments in Rubber
Authors: Gehman S. D.
Published: February 2011

The use of reinforcing pigments in rubber, especially in synthetic rubber, is important in securing desirable physical properties. The earlier literature on the subject has been reviewed by Shepard, Street, and Park. Several theories were advanced to explain the effectiveness of reinforcing pigments in rubber. Some of these emphasized the importance of particle size and shape: others, the chemical composition and surface activity. The electron microscope has now furnished more reliable information on the particle size and shape of pigments, especially of carbon blacks, than was available in the earlier work2. The carbon blacks used in rubber compounding are essentially spherical; the mean diameter varies from 28 to 274 mµ for different types. Systematic studies have been carried out to show the influence of particle size and surface area on various physical testing indices used to evaluate rubber compounds. The x-ray structure of rubber stocks containing carbon black has been investigated. Several articles dealing with the theory of pigment reinforcement have appeared. This additional work has not clarified the original concepts advanced to explain filler reinforcement, but the research of Wiegand shows beyond doubt that particle size is the predominating factor in explaining differences in the properties of rubber compounded with various blacks. The present paper will attempt to explain some of the effects of pigment reinforcement of rubber, particularly increased stiffness, by simple mechanical considerations which may be regarded as extensions or extrapolations of the results of measurements on rubber in compression.