bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallization of Vulcanized Rubber
Authors: Bekkedahl Norman , Wood Lawrence A.
Published: February 2011

The formation of crystals at room temperature by stretching rubber, vulcanized or unvulcanized, has been the subject of considerable study. The crystallization of unstretched rubber at low temperatures is also well known, but with a single exception to be discussed later, the effect has commonly been considered to be limited to the unvulcanized material. In the present investigation, however, the crystallization of unstretched specimens of vulcanized rubber of low sulfur content has been accomplished. In commercial vulcanized rubber products, crystallization has not hitherto been recognized as a factor of practical importance. It is probably significant in cold climates, where some rubber products slowly undergo a great increase in rigidity and permanent set. Automobile traffic counters, for example, have been rendered inoperative by the hardening of the rubber tubing used with them. Laboratory tubing and other products made of a number of different commercial rubber compounds have become rigid after storage for some weeks in a refrigerator at about 0° C. Previous work on unvulcanized rubber showed that it can be crystallized at temperatures between + 10° and −40° C, the crystals melting in a range from about 6° to 16° C. Crystallization and fusion are accompanied by changes in volume, heat capacity, light absorption, birefringence, x-ray diffraction, and mechanical properties such as hardness. x-Ray diffraction and birefringence, of course, give the most direct evidence of crystalline structure, but in the present work change of volume, measured in a mercury-filled dilatometer, was chosen as the criterion of crystallization or fusion. Quantitative results are more easily obtained in this manner, and the experimental observations are simple. Furthermore, the method is well adapted to continuous observations over long periods of time, such as were found necessary in the present work.
Effect of Various Sulfur-Accelerator Ratios in Vulcanized Rubber
Authors: Conover F. S.
Published: February 2011

The use of very low sulfur-high accelerator combinations in certain types of rubber products has been highly successful in many cases in which extraordinary resistance to heat aging has been necessary. The tendency toward the use of compounds of this type has increased during the past few years, sometimes apparently with little or no attention to the service characteristics of the final product other than the aging properties already mentioned. The behavior of low-sulfur stocks in respects other than aging has been the subject of some work, notably an investigation by Somerville and Russell. This paper, however, left a number of questions unanswered, and was limited to a discussion of two sulfur-accelerator variations. The work reported in the present article has been designed to broaden the scope of the former investigators, both in compounding variations and in types of test. The program is intended as an aid in answering two specific questions: (1) What advantages, other than aging, are obtained by the use of low sulfur-high accelerator ratios? (2) What disadvantages in test or service are to be expected from low sulfur-high accelerator ratios?
Distillation Products from Waste Rubber
Authors: Pickett F. N.
Published: February 2011

About 1930, during some experiments on new systems of reclaiming waste rubber, it was discovered that certain fractions of the products resulting from the destructive distillation of old tires possessed solvent and softening properties hitherto unsuspected. A complete system of reclaiming based on this discovery was worked out, and many tons of reclaimed rubber were manufactured by utilizing such distillation products. Investigation of the products of distillation was carried out with interesting results. Retort distillation was the method adopted as being the most economical, and experiments were carried out with the aid of the chemists of the Gas, Light & Coke Co., Ltd., at Fulham Research Station. A pilot plant was erected which consisted of seven retorts of the ordinary gas-works type. It had previously been found that a temperature variation of only a few-degrees had considerable effect not only on the percentage yield but also on the components of the distillate. For maximum yield, the most suitable distillation temperature was about 560° C.
Pliolite-Rubber Mixtures
Authors: Thies H. R.
Published: February 2011

Cyclized rubbers have attracted the attention of chemists for a long time. When pure, all of these derivatives of rubber consist of a hydrocarbon or a mixture of hydrocarbons (C5H8)x, and all have less unsaturation than does the parent substance. Their physical properties, however, vary from rubbery to hard shellaclike types, and their formation is attributed to internal cyclic formation, since there is a change in the unsaturation but no change in the composition when compared to the original rubber. Several different methods have been utilized for the preparation of a cyclized rubber. Harries obtained a white inelastic solid by treating a rubber hydrogen halide with an organic base. When rubber is heated under conditions which preclude complete breakdown, a diminution in the number of double bonds is effected, together with increase in density. Cyclization by pyrogenic decomposition was accomplished as early as 1838 by Himly The heat-cyclized rubber obtained by Staudinger and Geiger was a white powder, the solutions of which were of low viscosity. The effect of heat on rubber in solution as investigated by Staudinger and Bondy showed that, up to 150° C, the number of double bonds remained the same, but at higher temperatures cyclization occurred. As early as 1781 Leonhardi referred to a tough elastic product obtained by treating rubber with sulfuric acid. In 1851 Macintosh obtained a patent for a process in which the extruded or moulded articles of gutta-percha were subjected to superficial hardening by immersion in concentrated sulfuric acid. However, the sulfuric- or sulfonic-acid-cyclized rubber of today is based upon the investigations of Fisher and coworkers. These materials, known as Thermoprenes, were shown to be cyclic isomers of rubber hydrocarbon, in agreement with the observations of Kirchhof and Staudinger. Rubber isomers from halides of amphoteric metals, such as stannic and stannous chlorides, aluminum chloride, boron fluoride, and chlorostannic acid, embrace some of the most valuable chemical derivatives of rubber. A comprehensive study of these reactions was made by Bruson, Sebrell, and Calvert. The properties of amphoteric metal halide derivatives of rubber which render them specially valuable as moulding materials were described by Thies and Clifford and by Jones and Winkelmann. Numerous other methods for isomerizing rubber include the silent electric discharge, heating in the presence of surface-active substances, phosphorus oxychloride, and hydrogen fluoride.
Rubber in Compression
Authors: Kimmich E. G.
Published: February 2011

The effects of shape and surface conditions of rubber used in compression have remained somewhat of a mystery because of the apparently conflicting results often obtained. It is to be hoped that the work herein described will: (1) explain some of the difficulties encountered; (2) establish a simple and reasonably accurate procedure for predetermining the compression stress-strain performance of many of the commonly used shapes, and (3) encourage an extension of this work to include more complicated shapes, and to provide further refinement of the results. Compression uses of rubber doubtless far exceed in number the shear and tension uses for industrial applications, and warrant much work in determining the relationships involved, at least to the extent of establishing empirical rules of sufficient scope and accuracy for practical use. The erratic nature of compression-test results has made it difficult to correlate data reported in the technical articles on this subject. It is herein indicated that much of this difficulty may be explained by the condition of the surfaces, the manner of applying the load, discrepancies in hardness measurements, variations in the actual stiffness of the rubber used, and the fact that the stress-strain graph is not a straight line.
Hysteresis Tests on Tire Compounds
Authors: Mackay J. G. , Anderson J. G. , Gardner E. R.
Published: February 2011

(1) The reasons for the selection of the Goodrich flexometer for hysteresis measurements are given. (2) The machine is capable of producing results within ± 1 per cent. (3) For a given cure, the temperature rise of a stock may be increased by increasing the length of stroke, the applied load or the frequency of flexing. (4) For a given set of flexing conditions, there is an optimum cure at which the lowest temperature rise is obtained. Cures shorter and longer than this optimum give increased temperature rise. (5) The differences due to cure may be cut down by reducing the stroke or load, the former having the greater effect. The role of the frequency in this respect is not simple. Reduction of the frequency from 1450 to 830 cycles increases the relative differences due to cure, but a further reduction to 685 has the reverse effect. (6) A set of conditions suitable for testing tread stocks is as follows: load, 150 lbs. per sq. in.; stroke, 0.3 in.; frequency of flexing, 1450 cycles per min. (7) Three examples are given which show that results obtained on the flexometer can be correlated with those obtained on actual tires on the road and on an inside test wheel. (8) Overmilling of a tread stock increases its tendency to heat. (9) Heat-treatment of carbon black-rubber master batches before compounding in tread stocks reduces the tendency of the latter to heat. (10) Tread stocks with low sulfur and high accelerator content give less temperature rise on the flexometer than those with normal sulfur and accelerator. (11) So-called high-resilience accelerators give lower temperature rises than mercaptobenzothiazole in gum stocks, but are no better than mercaptobenzothiazole in tread stocks. (12) Antiflex-cracking antioxidants do not cause a reduction in the tendency to heat compared with normal antioxidants.
The Creep of Natural and Snythetic Rubber Compounds in Shear
Authors: Hahn Stuart H. , Gazdik Ivan
Published: February 2011

Creep tests, extending in some cases as long as 900 days, indicate that both natural and synthetic rubbers such as Neoprene and butadiene copolymer can be compounded to give satisfactory service in shear mountings. At 140° F, creep is from two to nine times greater than at 80° F, depending on the compound. Tests at room temperature do not indicate either the amount of creep or the life to be expected at higher temperatures. Actual creep (measured in inches) increases with stress, but when expressed at percentage of initial deflection, it may be independent of stress. Creep curves are linear over a considerable range of time when plotted on log-log scales. However, extrapolation of such curves to predict results after very long times is not justified, because the curves may not continue to be linear, or failure of the mountings may occur, particularly at high temperatures. Short time tests of any sort are not necessarily indicative of the relative creep or life of compounds in long-time service. The tests reported here are a small portion of a large number which is being continued and augmented. It is hoped that these and other investigations now under way may contribute to clearing the picture of the complex interrelations between the many physical properties of compounds of rubberlike materials. The rubber technologist uses his specialized knowledge to develop a wide variety of compounds, making use of several types of basic rubberlike materials. He chooses whichever fits service requirements best from performance and economic viewpoints. Modern materials and recent developments in processing technique have made possible compounds suitable for a wide range of service conditions.
Permeability of Elastic Polymers to Hydrogen
Authors: Sager Theron P.
Published: February 2011

The permeabilities to hydrogen of natural rubber, Perbunan, Neoprene G, Vistanex, Thiokol DX, and Pliofilm diminished in the order mentioned. The increase in rate of permeation with increasing temperature was exponential in all cases. Values for the activation energies or permeability for hydrogen were found to be 6,800 calories per mole for natural rubber and 8,400 to 9,500 calories per mole for the synthetic materials. The greater magnitude of the energy requirements of the latter indicates that their lower permeability may be attributed to differences in their molecular structure.
Rubber Photogels
Authors: Stevens Henry P.
Published: February 2011

When a rubber sol is exposed to light in an air-tight vessel, it sooner or later gels, provided the concentration of the rubber is not too low and the air space above the surface of the sol is not too large. The first published observation of the gelling of a rubber sol in light was made by Porritt. Finding that the exposure of a rubber sol containing sulfur did not induce vulcanization, he repeated the experiment with the removal of oxygen, providing also a control tube without sulfur. Nothing happened with the tube containing the sulfur, but the control tube “after a few days suddenly set to a gel without any obvious preliminary increase in viscosity.” This gel on exposure (to air) was found to be rapidly transformed to a liquid. From the context it seems that the solvent used was benzene, but no information is given as to the type of rubber, whether raw or milled, concentration or other details, or how the removal of air or oxygen was accomplished. This observation of Porritt's is referred to in two or three subsequent publications by chemists who have noted similar occurrences. Thus, Smith reported the gelling of a sol of ether soluble rubber; and Meyer and Ferri found that, although rubber in solution is readily degraded in light and air, it polymerizes to an elastic jelly when exposed to ultraviolet light. But previous to the publications of Smith and of Meyer and Ferri, the subject had been examined in detail by Pummerer and Kehlen. This paper seems to have been overlooked.
Distribution of Non-Rubber Substances in Preserved Latex
Authors: Baker H. C.
Published: February 2011

The properties of latex depend, not only on its chemical components, but also on the distribution of these components between the rubber and aqueous phases and at the boundary between them. Therefore, to appreciate the function of different components in affecting the behavior of latex, it is necessary not only to know their nature and quantity, but also how they are distributed. For example, a component dispersed in the aqueous phase is not likely to affect coagulation or stability in the same way as the same substance concentrated in the boundary between rubber globules and water. Moreover, a component dissolved in the rubber phase is not likely to have marked effects on the properties of the liquid latex, although it may be of considerable technical importance when the rubber phase has been separated and dried. This paper records experiments made to obtain a satisfactory technique for measuring the distribution of the non-rubber substances in latex; its application in particular to nitrogen, acetone- and alcohol-soluble substances, water-soluble acids and long-chain fat acids; the influence of various factors such as particle size, dilution, pH, the addition of alkalies, enzymes, soaps, storage in the dark; finally, conclusions are drawn relating to the composition of the boundary layer between rubber and serum and of the interior of the rubber globule.
Organic Analysis of Hevea Latex. VI Alkaloids in Whole-Latex Rubber
Authors: Altman R. F. A.
Published: February 2011

The Stas-Otto method makes it possible to separate from whole-latex rubber very small quantities of bitter substances which give the usual alkaloid tests and some color reactions (see table below).
New Development in Rubber Reclaiming
Authors: Essex W. G.
Published: February 2011

The history of rubber reclaiming has been given by Alexander, and it is therefore intended only to make a brief reference to the well-known acid and alkali processes, the latter having proved to be by far the most successful method of reclaiming vulcanized rubber. The alkali process, introduced by Marks in 1899 had the outstanding advantage of simultaneously removing, from the waste, free sulfur, of which from 3 to 5 per cent was present, of destroying the fabric and of plasticizing the waste, this being accomplished by heating in a closed vessel under steam pressure with caustic soda. The acid process destroyed only the fabric, and plasticization by heat was performed in another operation in a separate vessel: by this method little or no free sulfur was removed from the waste. This latter disadvantage has since disappeared, for, with modern rubber compounding, there is little free sulfur left in vulcanized rubber. In recent years there have been widespread changes in the manufacture of rubber goods, particularly in the case of pneumatic motor tires, which are now the main source of raw material for reclaimed rubber. Organic accelerators, anti-oxidants and carbon black have made vulcanized rubber a very tough, resilient article, extremely resistant to aging and to heat, one of the chief agents used in rubber reclaiming. For example, modern motor tire treads, which are heavily reinforced with carbon black, are not so amenable to alkali and heat treatment, and tire treads reclaimed by this process have finally to be plasticized and made homogeneous by a much longer mechanical milling and refining treatment than was formerly necessary; in spite of this the treads still produce a proportion of rough, unrefinable material which has to be separated and rejected from the final reclaim. This increase in milling time, combined with lower finished production due to rejected unrefinable material, has had the effect of greatly increasing the manufacturing cost of the reclaim. Research was therefore started with the object of evolving a process which would successfully offset these difficulties caused by the changes in the properties and characteristics of the initial waste. The result of this work has been the creation of reclaimed rubber from which the disadvantages mentioned have been largely eliminated.
Vulcanization of Rubber by Nitrogen Compounds
Authors: Margaritov V. B. , Guchkova N.
Published: February 2011

The active influence of nitrogen compounds on the structure of the sols of bivinyl polymers, with consequent colloidization of the system, would lead one to assume that films obtained by evaporation of the treated sols would have better mechanical properties and greater elasticity than films of the unmodified polymers. The considerable activity of nitrogen compounds in rubber was first observed by Buizov, who directed attention to the vulcanizing action of diazoaminobenzene. Ostromislensky pointed out that nitrogen compounds are capable of producing phenomena in rubber similar to normal vulcanization with sulfur. Alessandri carried out a reaction of rubber with nitrosobenzene, which was later similarly studied by Bruni and Geiger, and by Pummerer and Gündel. In 1937 Levi observed the transformation of rubber which is brought about by brief heating with diazo compounds and leads to a condition outwardly resembling vulcanized rubber. Levi called particular attention to the fact that the most active agent, diazoaminobenzene, when heated to 150° C, produces free nitrogen amounting to two-thirds of the entire quantity of nitrogen, with the formation of o- and p-aminobiphenyl.
Studies of the Amorphous State. XVII. Dielectric Losses in Swollen Rubbers
Authors: Aleksandrov A. , Dzhian J.
Published: February 2011

1. The maximum of tan δ in rubber and the range of Ε-bending are displaced towards lower temperatures when plasticizers are incorporated. 2. The system: rubber—nonpolar plasticizer possesses the same time-constant, which indicates that the plasticizer affects the whole system and not only a definite part of it. 3. The system: rubber—polar plasticizer possesses the same time-constant, which indicates that one and the same activation energy U is required for orientation of the dipoles, regardless whether they are tied together by chemical bonds or by van der Waals forces.
The Proteins of Hevea Brasiliensis. II. Analysis of a Product Isolated from Crepe Rubber
Authors: Tristram G. R.
Published: February 2011

A protein (2) has been isolated from crepe rubber and analyzed for amidenitrogen, tyrosine, tryptophan and basic amino-acids. The dicarboxylic acids have been shown to be present. The results indicate that preparation 2 is of the same composition as preparation 1. It is now suggested that preparation 1 is a representative fraction of the total protein of latex. Loss of tryptophan has been observed from the protein found in crepe rubber and a reason for this loss has been suggested.
Buna for Hard Rubber Linings
Authors: Gartner E.
Published: February 2011

On the basis of the investigations described in the present paper, certain rules or directions for obtaining the most desirable properties with the various types of artificial rubbers can be laid down. Brinell hardness.—The higher the proportion of vinyl component in a mixed butadiene polymer, the harder is the resulting vulcanizate within the relatively narrow range of percentages of sulfur which were tested. In this respect, acrylonitrile has a greater effect than does styrene. Mechanical properties.—As far as mechanical properties are concerned, Perbunan-Extra is an extraordinarily good material for, in addition to giving high Brinell hardness and tensile strength, it also shows good shock resistance and impact strength. Buna-SS and Perbunan-Extra give, within the range of hardnesses tested, high Martens values. Compared with natural rubber, their resistances to dynamic bending are particularly good.
Investigations of Rubber Fillers. I. Particle Size and Characteristic form of Carbon Blacks and Their Influence on the Properties of Rubber Mixtures, as Judged by Ultra-Microscopic Photographs
Authors: Schoon Th. , Koch H. W.
Published: February 2011

The particle sizes and characteristic shapes of the particles of eighteen blacks used in the rubber industry were determined. The values which were obtained are compared with the physical properties of rubber mixtures prepared from these blacks. The characteristic shape of the particles has the greatest effect on the extensibility and the rigidity at 200 per cent elongation, i.e., on the modulus. When the particle size of a black is over 100 mµ, relatively poor resistance to tearing of vulcanizates containing the black is obtained. In general, the particle size of a black has far less influence on the other physical properties than has been believed in the past. With the aid of electron microscopic photographs, it is possible to estimate the value of a black as a filler in rubber.
Chemical Reactions of Rubber
Authors: Sibley R. L.
Published: February 2011

Most of the literature descriptive of the various known derivatives of rubber is found published as patents rather than as technical papers, thus indicating the commercial possibilities that may be expected from these developments. Fisher, Schidrowitz and, more recently, Jones have summarized and discussed the chemistry of rubber and its commercial derivatives. The decomposition of rubber by heat has been studied by several investigators. Williams showed that isoprene is one of the main products formed by the destructive distillation of either caoutchouc or gutta percha. Later investigators have shown that slow heating in vacuo at 300° C converts somewhat more than one-half of rubber hydrocarbon into a solid, thermoplastic, isomeric product, which has a high molecular weight and less unsaturation than that of the original hydrocarbon. Rapid heating, especially in vacuo, converts almost all the rubber into volatile products. The most complete investigation of the products obtained by the heat decomposition of rubber apparently was carried out by Midgley and Henne. These investigators destructively distilled 200 pounds of pale crepe rubber in 16-pound batches by raising the temperature as rapidly as possible to 700° C at atmospheric pressure in an iron kettle. The condensate was fractionally distilled, and cuts were made every degree between 50 to 176° C. Each cut was then separately examined. Twenty-three different hydrocarbons were identified in the distillate.
Theory of Filler Reinforcement in Rubber
Authors: Weiss Joseph
Published: February 2011

There are many active filler substances capable of improving to a considerable extent the mechanical properties of rubber mixes. The reinforcing effect of fillers is rather a complex problem and is known to depend, not only on the surface area and size of the particles involved, but also the nature and shape of the particles and the nature of the material in which they are situated. The influence of the surface forces between the filler and matrix has been discussed from a theoretical point of view, particularly by Hock and his collaborators. However, a closer perusal of the available experimental material reveals that the surface energy cannot be the only important factor in the reinforcing effect. It is clear that a particle of a foreign substance embedded within the bulk of the rubber will, in general, have a different volume from the actual space in the material available for it. If it is held firmly enough by the surface forces, the particle will either compress or expand the surrounding medium, depending on whether its size is larger or smaller than the hole in the matrix available for it. Consequently, this particle will become the center of a more or less symmetrical stress (compressional or tensional) field. In a discussion of filler reinforcement, the elastic energy generated by the particles must be taken into account. In the following it will be attempted to give a brief discussion of this effect and its relation to the previously treated surface effect of the particles. Although this should not be considered a complete theory, it introduces a new feature into the discussion of this subject, provides a basis for further experiments, and might be helpful in assessing the usefulness of fillers in rubber mixes.
Thermal Decomposition of Natural and Synthetic Rubber Stocks
Authors: Prettyman Irven B.
Published: February 2011

The factors responsible for failure of natural and synthetic rubber stocks in tires in service are primarily thermal in nature. They govern the temperature attained by the stock and the ability of the stock to withstand this temperature. The factors which determine the temperature attained include those dependent upon the stock itself and those dependent upon attendant conditions. In the first group may be mentioned thermal conductivity, internal friction, and elastic modulus. In the second are included the construction and design of the tire, the speed at which it is run, the load to which it is subjected, its inflation pressure, and the temperature of the road and surrounding air. Therefore, assuming a fixed set of conditions for the second group, the problem resolves itself into a determination of the amount of heat generated within the stock, the rate at which the generated heat is conducted away from it, and the temperature it may attain without undergoing chemical degeneration. These characteristics can be investigated independently in the laboratory.
Action of Organic Accelerators in Buna-S
Authors: Vila George R.
Published: February 2011

Buna-S is an unsaturated polymer capable of undergoing vulcanization. This may be effected by the application of heat in the presence of sulfur. The process is accelerated by certain organic substances which are used widely for a similar purpose in natural rubber. Preliminary teats have indicated that most of them are applicable to Buna-S, and appear superior to any other chemicals yet investigated. This is fortunate in view of the present emergency, as plants for their manufacture already exist and the industry is familiar with their use. In spite of superficially similar effects, more careful study has indicated that it is an oversimplification to assume various accelerators will produce ideptical effects in both polymers. A wide range of materials is now available to the industry, and the task of accurately evaluating all of them is complex. In addition, an indefinite number of combinations are theoretically possible. The present investigation was undertaken to determine what effect different chemical types of organic accelerators were likely to have on properties of fundamental importance.
Technical Microscopy in the Rubber Industry
Authors: Allen R. P.
Published: February 2011

For supplying information not obtainable by the usual methods, the microscope is useful and often essential; not only will it disclose details which would otherwise be unseen, but by its unique methods of examination measurements of certain properties of materials can be readily secured which are not otherwise obtainable. When one considers the value of the microscope to the rubber industry specifically, the study of the size of particles is usually the first and frequently the only application which comes to mind, although other uses have been suggested and described. The present paper not only describes the importance of the microscope in determining particle size and shape, but also covers its applications in the solution of other problems which ordinarily are not considered to lie in the field of microscopy. [Chamot describes many interesting applications in different industries which indicate the unusual capabilities of microscopic methods.] In a well-organized industrial laboratory, the microscope is used to supplement and aid other methods for examination of raw materials, control of factory processing, correlation of physical properties with service performance, and solution of factory difficulties. The specific examples cited in this paper represent uses which have originated in connection with the manufacture of rubber goods, but they serve also to illustrate methods applicable to problems of the same type originating in other industries.
The Course of Autoöxidation Reactions in Polyisoprenes and Allied Compounds. II. Hydroperoxidic Structure and Chain Scission in Low-Molecular Polyisoprenes
Authors: Farmer Ernest Harold , Sutton Donald A.
Published: February 2011

One of the most astonishing phenomena connected with the chemistry of rubber is the ease with which it absorbs progressively very small percentages of oxygen, and suffers as a result drastic and progressive reduction of its molecular weight. The natural conclusion to be drawn is that the polyisoprene chains of the rubber are undergoing oxidative scission at one after another of their unsaturated centers, so that the original long hydrocarbon chains become divided into smaller and smaller fragments possessing oxygenated ends. Recent estimates of the molecular weight of rubber by viscosity and osmotic methods range from 240,000 to 360,000 for fractions of decreasing solubility in hydrocarbon solvents. If we accept these figures and assume for the moment that two atoms of oxygen are sufficient to sever the hydrocarbon chains at a double bond, then an absorption of only 0.009–0.013 per cent of oxygen (applied, of course, exclusively to scission reactions) should suffice to reduce the average molecular weight to one-half. If the observed reductions of molecular weight are to be ascribed solely to oxidative scission of the chains, then, provided oxygen-consuming side reactions are few, a fairly exact inverse proportionality may be expected to hold between the uptake of oxygen and the average molecular weight of the degraded rubber. The most striking reductions in the molecular weight per unit of oxygen absorbed must, of course, occur at the very early stages of oxidative fission, while the hydrocarbon chains are still very long, and to be able to follow effectively the quantitative relationship between these important reductions and the oxygen uptake, it is necessary to make experimental provision for the absorption, even distribution, and measurement of very minute quantities of oxygen. Minute though the overall proportion of oxygen necessary to produce a substantial reduction in molecular weight appears in practice to be, however, there is no evidence to indicate that the scission reaction ever follows the course most economical in oxygen, i.e.,
Unsaturation of Synthetic Rubberlike Materials
Authors: Cheyney La Verne E. , Kelley Everett J.
Published: February 2011

The quantitative determination of rubber unsaturation has concerned numerous investigators. The use of iodine chloride as a reagent for this purpose (the well-known Wijs method) has achieved favor in recent years. Under the proper experimental conditions, addition has been shown to be quantitative, and substitution reactions can be kept at a minimum. This procedure has likewise been rather extensively employed as a measure of the residual unsaturation of various rubber derivatives. This reagent does not, however, add quantitatively to all unsaturated compounds, regardless of structure. The presence of a negative substituent on one or more of the unsaturated carbon atoms inhibits the reaction; in fact, it may entirely prevent it, as in the cases of maleic or fumaric acids or dichloroethylene. In other compounds extensive substitution may occur along with addition, as in the case of the unsaturated terpenes. The unsaturation of the polymerized diolefins should be of considerable interest, especially in comparison with natural rubber. It should be of special interest to study the comparative reactions with iodine chloride, which has become practically a standard reagent for rubber. Kemp and Mueller mention that polychloroprene, to which they erroneously refer as polyvinyl chloride, adds iodine chloride to only 30 per cent of theory. This could be due to two causes—the negative influence of the chlorine attached to an unsaturated carbon, and/or possible cross-linkage between chains (cyclization). It is well established that polychloroprene is much less reactive chemically toward other reagents than is natural rubber. It is unfortunate that Kemp and Mueller did not state with more detail the history of the sample studied, as such a result might have shown some interesting correlation with the experiments reported in this paper.
Methylethyl Ketone Extraction of Rubber
Authors: Cheyney La Verne E.
Published: February 2011

The extraction of rubber samples with acetone as an analytical procedure is a classical method; its origin is almost lost in antiquity, at least from the viewpoint of the rubber technologist. It is a valuable procedure, not only for practical evaluation of rubber samples, but from theoretical considerations as well. Acetone is commonly regarded as a polar “nonsolvent” for rubber, although some slight swelling action on rubber samples has been reported. Various investigators have carried out the extraction under differing conditions, and the results have been shown to vary somewhat with the treatment of the sample. The procedure as commonly employed today is well standardized, and great reliance is placed by rubber chemists on the analytical data obtained. The standard procedure, however, suffers from one serious drawback—the length of time necessary to obtain the desired data. With a large number of samples this factor is enormously magnified. When applied to plant control determinations, the disadvantage is too readily apparent. One possible method of reducing this difficulty would be the substitution for acetone of some other solvent, perhaps of higher boiling point, which at the temperature of extraction would have a greater solvent action on the non-rubber components. It should therefore accomplish the desired extraction in a shorter time.
The Permeability of Rubber to Water Vapor
Authors: Van Dalfsen J. W.
Published: February 2011

In connection with a study of various kinds of vulcanized rubber, including rubber films from vulcanized latex and latex films vulcanized in the dry state, it seemed desirable to investigate the packing of the latex particles. To what extent, for example, are these still present or are they coalesced? It is known that the diffusion of water vapor through solid substances may give an indication of the internal structure of matter. With this in mind, a search was made for a simple method to determine the diffusion of water vapor through rubber; high accuracy was not required so much as were simplicity and adaptability to a long series of experiments. Such a procedure was found in the method described by Hoekstra for determining the permeability of varnish films to water vapor. A detailed description of the method is given later in this paper. More accurate methods of determination, applied to rubber, have previously been described by others, but these procedures are less suitable for systematic tests.
Experiments on the Preparation of Transparent Vulcanized Rubbers
Authors: Johnson E. B. , Scott J. R.
Published: February 2011

1. It has been found possible, by the use of combinations of organic accelerators, to prepare accelerated rubbers which contain sufficient zinc oxide for activation but show no trace of pigmentation by the oxide, and are quite as transparent as a mixture containing only rubber and sulfur, and often lighter in color than the latter mixture. These accelerated rubbers have excellent tensile properties. The aging properties vary considerably according to the accelerators used, but in most cases are very good, even if the rubber is over-cured. It is, therefore, possible to make nonblooming rubbers without danger of bad aging. 2. Tests with other activators (zinc carbonate, zinc oleate, and zinc stearate plus magnesium carbonate) showed that these are less effective than zinc oxide, for the vulcanizates obtained had inferior mechanical properties and, in the case of zinc carbonate and oleate, showed a strong tendency to bloom. 3. A combination of accelerators which has been stated to work well without activator was shown to vulcanize very quickly, but to give poor mechanical properties, 4. The tendency of various accelerators to give rubbers, the surfaces of which are easily marked by scratching, presumably owing to efflorescence of accelerator, was noted. 5. The most promising of the mixtures tested for making transparent vulcanized rubbers was one accelerated with diphenylguanidine plus mercapto- benzothiazole, with zinc oxide as activator (mixture F). 6. A mixture is described (mixture K) which gives better aging when vulcanized beyond the optimum tensile properties than when vulcanized short of the optimum cure. 7. Rubbers can be toughened by the use of organic accelerators so as to possess greater resilience and lower permanent set than if toughened by the usual inorganic reinforcing agents. The aging tests described above were all made in the absence of light. For transparent rubber goods which are exposed to light during use, the addition of antioxidants and (or) softeners might be found necessary to give resistance to deterioration by light. In connection with fancy goods, the staining of paper in contact with the rubber may be of importance, and in such cases the choice of accelerators and antioxidants must be made with this in mind. The staining effects of numerous accelerators and antioxidants have already been described. In conclusion, it should be added that the experiments were directed in the first instance towards the production of brown transparent rubbers, for which reason smoked sheet was used. Where a light-colored vulcanizate is required, and especially when it is desired to obtain colored rubbers by adding organic dyes, the use of pale crepe is essential.
Statistical Lengths of Rubberlike Hydrocarbon Molecules
Authors: Wall Frederick T.
Published: February 2011

It has been known for some time that the pure hydrocarbons of balata (or gutta-percha) and natural rubber have the same chemical composition and chemical properties. Both balata and rubber appear to be polymers of isoprene, (C5H8)n, with the same degree of unsaturation. Their physical properties are sufficiently different, however, to make it clear that their structures must differ in some important respect. Since the molecules contain numerous double bonds, it has been suggested that rubber and balata are geometric isomers. Every fourth bond in a rubber or balata molecule is a double bond, so it follows that the possibilities for geometric isomerism are considerable. It was proposed by Meyer and Mark that natural rubber hydrocarbon has a structure for which the molecular chain is cis with respect to all of the double bonds. Balata (or gutta-percha) is then supposed to have a trans-structure throughout, this view having been verified by Fuller and Bunn. It is the purpose of the present paper to consider, from the point of view of recent theories of rubber elasticity, to what extent these structures explain the differences in physical properties. The method to be employed involves calculation of the root mean square lengths of the cis- and trans-structures, which, when compared to their maximum lengths, should give an indication of their extensibilities. In 1932 Eyring treated the problem of the average square length of a hydrocarbon chain. In the present paper a different derivation of Eyring's equation is given (for illustrative purposes), after which this derivation will be extended to the rubberlike molecules with double bonds.
An Electrophoretic Study of the Proteins in Rubber Latex Serum
Authors: Roe Charles P. , Ewart Roswell H.
Published: February 2011

1. The serum from unpreserved rubber (Hevea brasiliensis) latex contains seven electrophoretically distinct protein components. The proteins from whole serum originating in Sumatra and Florida give very similar results in electrophoresis experiments. 2. The relationship between electrophoretic mobility and pH has been determined for five of the seven protein components of unpreserved total latex serum. The results are considerably different from those reported by workers with ammonia-preserved latex, and tend to clarify observed differences in the stability behavior of unpreserved and preserved latex. 3. Ammonia-preservation treatment rapidly alters the electrophoretic behavior of the native protein components of latex serum and reduces the number of resolvable components from seven to two. 4. The preparation of dry latex protein from rubber-free latex serum can be accomplished by the vacuum sublimation of frozen serum. This process does not appear to produce important changes in the electrophoretic properties of the total serum proteins. 5. Minor modifications of the electrodes and of the standard illumination system in the electrophoresis apparatus are described.
USF, A New Crude Rubber
Authors: McGavack John , Linscott Chester E. , Haefele John W.
Published: February 2011

In preparing USF rubber by the preferred method, a field latex is preserved with formaldehyde as soon as possible after tapping. This chemical is effective in quickly and thoroughly stopping bacterial and enzymatic changes in the latex (Table I). Thus one of the most important sources of variability is eliminated at the start. The preserved latex is transported to the USF rubber plant and emptied into a tall settling tank; there it is allowed to stand for 48 hours for sand, dirt, and natural sludge components to separate. At the end of this time the supernatant liquid is withdrawn into a blending tank, and another charge is introduced into the settling tank. This process is repeated until the blending tank is filled. Then a fraction of the well-mixed latex from this tank, equal to a charge added from the settling tank, is removed for processing. The latex to be processed is highly diluted, acid is added, and the whole mass is stirred. Fine floes form on standing and rise to the surface, leaving a clear yellow serum. This is withdrawn, and the flocculates are washed by the further addition of water. The washed flocs are transferred through a pipe to the coagulating tanks normally used for preparing sheet rubber. The flocs have now become sufficiently destabilized, so coalescence to a slab of coagulum may occur by simple standing at air temperature. However, faster coalescence is obtained by brief mild treatment with steam. The coalesced slab is removed and passed through mills for the production of crepe or sheet. The wet rubber is hung up to dry in a conventional dryhouse. Finally the dried rubber is heavily compressed and shipped in rubber-wrapped bales. This process is described in the flow sheet of Figure 1.
Brittle Temperature of Rubber under Variable Stress
Authors: Kemp A. R. , Malm F. S. , Winspear G. G.
Published: February 2011

1. The temperature at which natural and synthetic elastomers fracture on bending depends on the rate of application and the magnitude of the stress applied. The slower the rate of bending and the less the angle of bend, the lower will be the temperature of fracture. 2. A study of the stresses under varying types of service at subzero temperatures must be made in order to select intelligently the laboratory test conditions which will best simulate performance in the field. 3. In the case of synthetic elastomers having high fracture temperatures, the addition of certain types of plasticizers serve to correct this difficulty.
Preventing the Bacterial Oxidation of Rubber
Authors: Dimond Albert E. , Horsfall James G.
Published: February 2011

The recent article by ZoBell and Grant notes the attack of rubber by bacteria under conditions of high moisture. It is suggested that “the life of rubber products which come in contact with moisture may be prolonged if ways can be found to retard or prevent the activity of rubber oxidizing microorganisms”. In the compounding of rubber commercially, native rubber is mixed with a number of chemicals, each of which serves a specific purpose in the properties of the finished product. Among these are accelerators which lower the temperature and shorten the time of vulcanization and lengthen the life of rubber. Two well-known accelerators are mercaptobenzothiazole and tetramethylthiuram disulfide. These compounds have been tested for their ability to inhibit germination of fungi, and gross observations have been made on their ability to inhibit bacterial growth. Mercaptobenzothiazole is a moderately good fungicide, and tetramethylthiuram disulfide is excellent. The latter compound is now being marketed as a seed protectant and for the prevention of turf diseases. Both of these materials have been tested, under field conditions prevailing in Connecticut, by the authors for their efficacy in controlling plant diseases. Mercaptobenzothiazole, although inferior to tetramethylthiuram disulfide, has given partial plant disease control.