bluuebunny/crossref_metadata_2025 huggingface dataset:
The Optical Properties of Rubber
Authors: Wood Lawrence A.
Published: February 2011

The general survey which has been presented here shows that, while a number of the optical properties of rubber have been investigated, the measurements of most of them have been more or less preliminary or exploratory in nature and often directed towards some immediately practical application. There appears to be ample opportunity for extended, systematic research on the optical properties for their own sake. The results to be expected from such study may lead in two directions, each of them illustrated in a very preliminary fashion, by examples given in the present paper. The one direction is that of more fundamental knowledge of the constitution of rubber, especially when optical methods are used in conjunction with other types of measurement. An illustration already mentioned is the use of molecular refractivity to confirm the existence of a C5H8 unit containing one double bond as the unit group in rubber. Such work might well be extended as assistance in elucidating the constitution of vulcanized rubber. Another illustration is the use of infrared spectra or Raman spectra to determine the types of chemical bonds present in rubber. The other direction in which a study of the optical properties of rubber may lead is toward the direct solution of practical problems without regard for the theoretical significance of the measurements. Problems of control or analysis might be approached in this manner, since optical methods usually require only small amounts of material, and are often easily adaptable to rapid and precise measurements. Such applications have already been illustrated in preliminary form by the use of refractive index to determine amounts of combined or dissolved sulfur. The solution of practical problems by optical methods is also illustrated by the use of the photoelastic method for the analysis of stresses in rubber. Optical measurements in the past have been restricted in most cases to samples having fairly high light transmission. On this account the work has included only unvulcanized rubber and vulcanized compounds of the “pure gum” type. By the use of very thin sections or by employing methods which are based on the reflection of light rather than its transmission, it should be possible to extend the measurements to many practical rubber compounds which appear to be opaque, but which in reality are dispersions of filler particles in a matrix of transparent rubber.
Effect of Reinforcing Pigments on Rubber Hydrocarbon
Authors: Thornhill F. S. , Smith W. R.
Published: February 2011

Several investigators have established that sulfur vulcanization of rubber involves chemical combination of sulfur and rubber hydrocarbon. A definite decrease in unsaturation of the rubber hydrocarbon as vulcanization progresses has been generally noted. While it has often been concluded that a double bond is saturated for each atomic equivalent of combined sulfur, recent work by Brown and Hauserdemonstrates that this conclusion cannot be applied in all cases. In certain compounds they found the loss in unsaturation with extent of vulcanization to be considerably less than anticipated on the basis above. Their results indicate that stocks reaching optimum cure with the least loss of unsaturation possess the greatest tensile strength. Although a considerable amount of work has been done on this problem, we have not found a published account of similar investigations performed on stocks containing significant loadings of reinforcing fillers. Since, as pointed out below, the nature of the bonding between such fillers and the rubber molecules has not been clearly defined, one is not justified in applying previous results obtained on stocks containing no reinforcing fillers to those bearing appreciable loadings of such substances. Accordingly one portion of the present investigation was concerned with determining the effect of various fillers on the course of sulfur vulcanization, as judged from combined sulfur and unsaturation values. As pointed out by Gehman and Field it is undoubtedly true that the black particle in a carbon-black-reinforced rubber stock is firmly attached to the rubber molecule. The nature of the bonding between the black and rubber has not been clearly defined. Some investigators maintain that the association is physical and involves definite forces of adhesion or adsorption; others have suggested the formation of primary valence linkages with rubber hydrocarbon. The opinion of the present authors is that if such linkages are formed, the ethylenic bonds of the rubber molecule would probably be involved. If this latter view is correct, then a specific loss in unsaturation of rubber hydrocarbon, due to the reinforcing filler, should occur. Thus the second objective of the present study was to determine whether it was possible by chemical means to detect such a linkage. If measurable, this effect, together with the surface area determinations reported previously, would be particularly valuable in estimating the reinforcing value of various fillers.
Discoloration of Dried Latex Films
Authors: Blow C. M.
Published: February 2011

In the course of work on the application of latex to textiles, a staining effect was encountered which is the subject of this short note. Briefly stated, an uncompounded concentrated latex was applied to a cotton fabric; some months after manufacture, pink-brown stains developed. The appearance of the stain suggested iron, and both the circumstances and further facts indicated that light was a likely contributory factor. It was established that oxalic acid would not remove the stain, although this fact did not entirely rule out iron, since the rubber possibly prevented access of the oxalic acid. Furthermore, the stain was not removed by acetone, nor was it affected by a soap and soda scour, whereas if the fabric was treated with cobalt linoleate solution so as to oxidize the rubber, the stain was removed with the rubber in the course of subsequent scour. This suggested that the stain was associated with the rubber. An investigation was therefore commenced on the effect of light on the color of dried films of latex in the absence, and in the presence, of iron. The results obtained appear of some interest, and have revealed a phenomenon not previously recorded as far as the author is aware.
Note on the Product of a Reaction between Aqua Regia and Latex
Authors: Wentworth V. H.
Published: February 2011

Arising from experiments to repeat on fresh latex the halogenation experiments made by Baker on ammoniated latex, the sodium chlorate and hydrochloric acid reagents were replaced by aqua regia. After numerous unsuccessful trials with different stabilizers and combinations of mixed acids, a method was evolved which produces a product in the form of a fine free-flowing powder. Sibley stated in a recent lecture that a wide variety of products could be obtained from rubber by reaction with increasing proportions of aqua regia, and this note gives the details of a method of producing an interesting product by the action of aqua regia on rubber in the form of fresh latex.
Equipment for Accelerated Light-Aging of Rubber, and Methods of Evaluation of Ultraviolet Light and Sunlight
Authors: Werkenthin T. A. , Richardson David , Thornley R. F. , Morris R. E.
Published: February 2011

In connection with the development of a suitable light-aging test for evaluating the light-aging properties of rubber, plastics, dyed fabrics, and paints, a considerable amount of research work and literature search was undertaken. The purpose of this article is to make readily available these data to facilitate additional work in the evaluation of the weathering and light-aging of the above-mentioned materials. It is intended to present these data in a somewhat informal style, and to set forth not only the successful experiment, but also those tests which have been disproved as being either impracticable or not applicable to the particular material under investigation. Most of the work has been done in connection with rubber compounds and synthetic rubber-like materials, with the primary purpose of differentiating between satisfactory and unsatisfactory materials from the standpoint of light-aging and weathering resistance. However, there is a secondary purpose which, at present writing, is far more important and outweighs the mere procurement of material, that is, its use in improving rubberlike compounds themselves.
Simple Vulcanizates of Buna-S and Sulfur. Physical and Chemical Properties
Authors: Cheyney La Verne E. , Robinson Arthur L.
Published: February 2011

The earliest vulcanizates of rubber consisted of only two ingredients, rubber and sulfur. Actually, at least one other ingredient, fat acid, was probably present in the so-called acetone extract of the rubber. However, it was not long before the use of other compounding ingredients, especially inorganic accelerators, was developed. After the introduction of organic accelerators, most rubber goods were compounded with them, together with various activators. Simple products containing only rubber and sulfur were practically forgotten. Those in the ebonite range, however, were found to possess interesting properties and were studied in more detail. The only studies of the simple rubber-sulfur system over the entire range from soft to hard rubber have been those concerned chiefly with the mechanism of vulcanization. Houwink presents graphically the variation of stress-strain properties with sulfur content. Blake and Jessup and Cummings present data for such a series, although their samples were vulcanized to the absence of significant sulfur in the free state.
Studies in Compounding Guayule Rubber I
Authors: Hauser E. A. , Le Beau D. S.
Published: February 2011

It has been shown that different solvents used in the extraction of the resin from crude guayule exhibit different time-temperature relations. Of all the solvents tested, 2-furaldehyde was found to be the most efficient solvent for its speed and for the amount of resin extracted. It does not affect adversely the properties of the hydrocarbon.
Macromolecular Compounds. CCCXII. Halogen Derivatives of Rubber Hydrocarbons
Authors: Staudinger Hermann , Staudinger Hansjürgen
Published: February 2011

It has been assumed by Kuhn and by numerous other investigators that the threadlike molecules of rubber are kinked or tangled, both in the solid state or in solution, like the molecules of other high polymers, because of free rotation of their carbon bonds. This characteristic configuration is represented schematically in Figures 1a and 1b. According to this view, the elasticity exhibited by rubber can be explained by assuming that the fibre molecules are straightened out when the rubber is stretched, and return to their original state when the rubber retracts on release of the stress. When they are straightened out in this way, the fibre molecules may arrange themselves in the form of a lattice. On this basis it is easy to account for the well-known fact that rubber crystallizes when stretched. Kuhn has pointed out also that the viscosity law for fibre molecules is in accordance with this kinking or entanglement of such fibre molecules.
The Compounding of Guayule Rubbers. Effect of Various Factors on Physical Properties
Authors: Morris Ross E. , James Robert R. , Caldwell Ernest B. , Werkenthin Theodore A.
Published: February 2011

The authors conclude, from the work reported herein, that commercially available deresinated guayule rubber may best be compounded in the same manner as Hevea rubber, with an expectation of obtaining approximately 75 per cent of the tensile strength of a similar Hevea stock. It is concluded further that deresinated guayule rubber may generally be processed and cured in the same manner as Hevea rubber without sacrificing quality to a greater extent than is done with Hevea rubber.
Bonding of Rubber to Metals
Authors: Buchan S.
Published: February 2011

Rubber has been used for many years as a medium for minimizing and absorbing mechanical vibrations. Until comparatively recently, however, its employment for this purpose has been limited by the practical difficulties encountered in uniting it successfully with other more rigid materials, such as metals. At this stage, technical development in the rubber industry fell short of engineering design and manufacturing requirements. Earlier methods for uniting rubber to metal consisted either of attaching the rubber by mechanical means or by using a layer of ebonite between the soft rubber and the metal. These methods, however, were open to criticism, either on mechanical or chemical grounds, and the bond strengths were obtained at the expense of some of the flexibility of the units. Later, derivatives were produced by the action of sulfuric acid on rubber which gave excellent bonding properties, although they were thermoplastic and tended to weaken at temperatures over 60° C. Recently, cements based on rubber hydrochlorides have been put on the market which are superior in all respects to previous types. These are the “Ty-plys”.
Deterioration of Vulcanized Rubber by Copper and Manganese Compounds
Authors: Bott E. C. B. , Gill L. D.
Published: February 2011

The deterioration of vulcanized rubber containing increasing percentages of copper and manganese compounds and the extent of the protection given to the stocks by a secondary naphthylamine have been investigated. Jones and Craig showed that the addition of copper stearate made no difference to the type of aging of stocks containing various percentages of antioxidant when measured by decrease in tensile strength, and the results of Taylor and Jones indicate that the decrease is proportional to the time of aging in the Geer oven. Preliminary work.—Experiments were made on the base mix to determine its suitability and its optimum cure. The optimum cures of the base mix plus copper or manganese compounds after storage for six weeks in the dark at normal room temperature and of the base mix plus sym. di-β-naphthyl-p-phenylenediamine also were obtained. The following compounds A, B, C and D were mixed on a laboratory mill having 12 × 6 in. rolls.
Unsaturation of Butadiene and Related Polymers. As Determined by Iodine Chloride Addition
Authors: Kemp A. R. , Peters Henry
Published: February 2011

The procedures outlined in this paper make it possible to determine accurately the unsaturation of a wide range of synthetic rubberlike substances prepared by the polymerization of monoölefins and diolefins.
Physical Methods of Analysis of Synthetic and Natural Rubber
Authors: Barnes R. Bowling , Williams Van Zandt , Davis A. R. , Giesecke Paul
Published: February 2011

In a compounded rubber stock, the ratio of natural to synthetic rubber can be estimated approximately from a knowledge of the phosphorus content of the rubber hydrocarbon. A considerably more exact analysis can be carried out by infrared spectroscopic methods, which permit a determination of the type as well as the amount of rubber present. Complete details and comparative results of these two methods of analysis are given, as well as a simple procedure for separating the rubber hydrocarbon of a rubber stock from carbon black and other compounding ingredients.
The Elasticity of a Network of Long-Chain Molecules. II
Authors: Treloar L. R. G.
Published: February 2011

Wall's treatment of the elasticity of a molecular network is extended to cover the general homogeneous type of deformation of rubber. An equation is derived for the work of deformation in terms of the three principal strains, from which certain general stress-strain relations are deduced. These relations involve only one physical constant of the material. The use of the formulas is illustrated by their application to a number of simple cases. It is shown that the effective rigidity in respect of a shear in a plane at right angles to a previous elongation is inversely proportional to the elongation.
Macromolecular Compounds. CCXCII Polyisobutylene
Authors: Staudinger H. , Bebger G. , Fischer Kl.
Published: February 2011

An explanation of the chemical constitution of macromolecular substances has to a great extent been made possible by the preparation and study of various homologous series of polymers. In these investigations, the relations between the average degrees of polymerization and the physical properties of the particular substances concerned were studied. As a result of these studies, it was found that the unusual physical properties of macromolecular substances, such as toughness, elasticity, swelling in liquids, and above all, the colloidal nature of their solutions, are dependent on the size and form of their macromolecules, and not on a special micellar structure, as had been so widely assumed previously. It has been found possible to prepare a complete series of homologous polymers, starting with the low members, and passing through the hemicolloids and mesocolloids, to the highest molecular members, the eucolloids, by polymerization of vinyl derivatives under various conditions. It has not been found possible, however, to prepare a complete series of homologous polymers from all vinyl derivatives. At present, for example, there are still no known eucolloid members of polyindenes and of polyanetholes. On the other hand, in the polymerization of styrene, vinyl chloride, acrylic esters and vinyl acetate, it has been found possible to prepare, by the proper choice of conditions during polymerization, members extending from hemicolloids to eucolloids. An analogous complete series of homologous polymers can be prepared from polyisobutylenes. In this case it is possible, by the choice of various catalysts, to obtain polymerized products extending from the lowest to the highest degrees of polymerization. The hemicolloid members of this series are used technically as lubricating oils; the mesocolloid and eucolloid products are of importance in other ways because of their rubberlike properties.
Macromolecular Compounds. CCCII. Polymerization of Acrylonitrile. Polyacrylonitrile
Authors: Kern Werner , Fernow Helmut
Published: February 2011

Products obtained by the polymerization of vinyl compounds and acryl compounds are among the most important of synthetic organic materials. Each of these unsaturated compounds imparts special properties to the simple polymers and mixed polymers prepared from them, and it is because of these special properties that the polymers have found such wide application. Acrylonitrile, for example, is used technically on a large scale, particularly as a component in mixed polymerizations, and it imparts characteristic properties to the mixed polymers, e.g., resistance to organic solvents. In contrast to most other polyvinyl and polyacryl compounds, polyacrylonitrile is insoluble in organic solvents, and because of the unusual behavior of this polymer, it seemed of interest to study the polymerization of acrylonitrile and some of the products of its polymerization. In the polymerization of vinyl compounds, either soluble or insoluble polymers are obtained, depending on the type of monomer and the choice of operating conditions. Styrene, vinyl acetate, methacrylonitrile, and acrylic and methacrylic esters of monohydroxy alcohols yield soluble polymers. On the contrary, when divinylbenzene and likewise acrylonitrile are polymerized, insoluble polymers are obtained. Vinylmethyl ketone, butadiene and other compounds yield either soluble or insoluble products, depending on the experimental conditions.
Statistical Thermodynamics of Rubber. III
Authors: Wall Frederick T.
Published: February 2011

The kinetic theories of rubber elasticity which have been developed within recent years have grown out of one fundamental idea, namely that the elastic forces involved are due to the thermal motions of the molecules rather than to deformations of valence bonds and angles. In deriving theoretical equations of state for rubber, the usual procedure has been to connect entropy concepts with the probability functions for molecular shapes, assuming that molecules can have different shapes as a result of rotation about some of the valence bonds. Although the various authors started with substantially the same idea, their theories differed as to the way in which entropy changes were calculated. Recently, however, Treloar has shown that by eliminating certain approximations from Kuhn's treatment, then Kuhn's theory gives precisely the same result as does the theory of the present author. A basic postulate of the author's theory and of Kuhn's theory as amended by Treloar is that, when a piece of rubber is deformed, the components of the lengths of the molecules change in the same ratio as the corresponding dimensions of the rubber. To illustrate this specifically, let us consider a one-dimensional problem. If x is the component of the length of a molecule in the direction under consideration, then for a piece of unstrained rubber the probability of finding a molecule with a value of x in the range x to x+dx will be given by:
Stability of Butadiene
Authors: Robey Richard F. , Wiese Herbert K. , Morrell Charles E.
Published: February 2011

1. The most prominent polymerization of pure butadiene in the absence of peroxides is dimerization. This reaction is thermally activated, and does not appear to be catalyzed by peroxides or by steel surfaces. 2. Butadiene is also capable of independent polymerization to high-molecular-weight polymer, but in the absence of peroxides this reaction is insignificant compared to dimerization. The effect of temperature on the rates of each of these reactions has been determined. 3. In the presence of appreciable amounts of peroxides, polymerization to high-molecular-weight polymer becomes prominent, and is superimposed additively on the thermal dimerization reaction. 4. The addition of suitable antioxidant inhibits the formation of high-molecular-weight polymer, but has no appreciable effect on the rate of dimer formation. 5. The rate of high-molecular-weight polymerization is directly proportional to the square root of the concentration of peroxides (active oxygen). 6. Butadiene is readily peroxidized by air, but this peroxidation may be inhibited for a time by the presence of antioxidants. 7. The peroxides are not readily volatile, and tend to accumulate in the residue if the diene is evaporated or distilled away. Concentration beyond a certain point yields an unstable residue which may decompose with violence when heated. Precautions for distillation of such peroxidized material are given.
Froth Flotation of Rubber and Resin Components of Milkweed and Other Plants That Contain Resins, Rubber, Balata, or Related Gummy Substances
Authors: Turrall Wm T. , Klassen J. , Smedley H.
Published: February 2011

Some of the more important features of froth flotation in the separation of rubber-resin from milkweed and other plants are summarized as follows. 1. It removes the bulk of the waste material at an early stage of the operation. 2. In the flotation of the rubber-resin component from milkweed, no additional flotation reagents are needed to cause a separation, but they have been found necessary in the flotation treatment of some other plants. 3. The grade and the recovery of the rubber-resin fractions appear to depend on the size of the agglomerates. 4. Agglomeration of the rubber-resin fraction takes place during ball-milling only when certain conditions are favorable, e.g., density and alkalinity. If conditions are not favorable, the rubber-resin remains fine and well dispersed. Flotation on such a product results in the separation of a rubber-resin fraction. 5. It is not necessary to take the specific gravity of the rubber-resin components into consideration. 6. The flotation method is applicable to the concentration of the rubber-resin components from such plants as milkweed, dogbane, goat's-beard, sow thistle, wild lettuce, and possibly many other plants, with or without the use of chemicals. 7. It presents the possibility of a continuous process of rubber-resin extraction from plants.
Drift and Relaxation of Rubber
Authors: Mooney M. , Wolstenholme W. E. , Villars D. S.
Published: February 2011

Numerous studies have been published on the relaxation and drift, or creep, of soft vulcanized rubber. In the present work, tests of this kind have been extended considerably beyond previously published work, both as to duration of the test and range of the initial stress or elongation. Some compression drift tests have now been in progress for eight years. A new method of measuring stress relaxation at fixed elongation has been developed, particularly with the purpose of conserving space. This method has made it possible and practical to carry out a large number of tests, many of them lasting for many months. An additional advantage of the test is that the samples can be kept in a controlled atmosphere as well as at a controlled temperature. Some of the more extensive relaxation data have been used to test the Tobolsky-Eyring theory of relaxation. Good agreement is obtained by assuming two relaxation mechanisms. An alternative or modified theory of relaxation is presented.
Rubber, Polyisoprenes, and Allied Compounds. VI. The Mechanism of Halogen-Substitution Reactions, and the Additive Halogenation of Rubber and of Dihydromyrcene
Authors: Bloomfield George F.
Published: February 2011

The chlorination of cyclohexene by chlorine or by sulfuryl chloride (in the absence of a peroxide catalyst) yields substituted as well as additive chlorination products, and the former retain in full the original olefinic unsaturation, as indicated by iodine-value determination ; but whereas sulfuryl chloride forms only the additive dichloride and a monochloroölefin which is substituted exclusively in the 3-position, chlorine yields a mixture of saturated trichloro derivative (chloro-substituted addition product) and isomeric monochloroolefins (3- and 4-substituted), with some additive dichloride. No evidence of substitution at the ethylenic methine carbon atom has been obtained in the chlorination of cyclohexene, dihydromyrcene, and rubber by chlorine. The diminished unsaturation of the chloro-substitution products of the last two hydrocarbons is attributed to cyclization—a process which is complete in the case of rubber, but affects only a minor proportion of the molecules of dihydromyrcene. The same cyclizing tendency appears in the substitutive bromination of rubber by N-bromosuccinimide, but not to any appreciable extent in the similar bromination of dihydromyrcene. Additive chlorination products are formed when rubber is brought into reaction with chlorine liberated by the thermal dissociation of phenyliododichloride, or of sulfuryl chloride in the presence of a peroxide. The mode of reaction of bromine with rubber, about which many contradictory statements have been made, is found to be entirely additive if the solvent contains a trace of alcohol and the temperature is 0°. A method based on bromine addition may be used for estimating rubber hydrocarbon. Additive bromo and chloroderivatives of rubber are comparatively stable, and give no indication of the spontaneous elimination of halogen acid, either through cyclization reactions or the reformation of double bonds at temperatures up to 80°. The provision of chlorine in free-radical form appears to be an essential condition for obtaining the wholly additive chlorination of rubber and allied olefins. The reaction of molecular chlorine or bromine, on the other hand, follows a course which can be adequately explained by the initial formation of an activated dihalide, the fate of which is determined by the nature of the olefinic system and the experimental conditions.
Chemistry of Sulfur-Olefin Reactions. Application to Vulcanization
Authors: Armstrong Robert T. , Little Julian R. , Doak Kenneth W.
Published: February 2011

During recent years there has been general acceptance of the theory that the marked alteration in physical properties of rubber, termed “vulcanization”, is a consequence of progressive cross-linking through primary valence bonds. Attempts have been made to place this theory on a quantitative basis in the kinetic theory of elasticity. Accompanying phenomena such as isomerization, cyclization, and degradation reactions (reversion) may occur, and account for the differences observed under various conditions of vulcanization in the early stages or soft rubber range. These secondary reactions probably become very important in the ebonite stage. The vulcanization of saturated hydrocarbon polymers, such as polyisobutylene, has been notably unsuccessful in contrast with polyenes, such as natural rubber, drying oils (to produce factice), and butadiene polymers and copolymers. The vulcanization of polychloroprene (or its conversion from δ-polymer to μ-polymer in Carothers' terminology) can proceed without the addition of other reactants and is, therefore, distinct in type from the others mentioned. The difficulties inherent in a direct study of the chemistry of sulfur vulcanization, when rubber itself is used, follow from the fact that, in the commercial range of soft rubber vulcanizates, only from one to six sulfur atoms are combined for each hundred double bonds; also, the product becomes insoluble even before the lower amount has been combined. In this paper it is proposed, as a working hypothesis, that the chemical reactions which proceed during the vulcanization of natural rubber or diene polymers can be duplicated by the reaction of simple olefins of analogous structure (2-methyl-2-butene or 2-butene). with the vulcanizing agents, and that the pure reaction products have their counterpart in the vulcanizate.
Vulcanization of Buna-S (GR-S) with Organic Sulfur Compounds
Authors: Beaver D. J. , Throdahl M. C.
Published: February 2011

1. Buna-S has been vulcanized by a number of organic sulfur compounds, most interesting of which are alkylxanthogen disulfides. 2. The optimum results were obtained with a stock containing 4.00 per of ethylxanthogen disulfide, with either 2.00 per cent of N-cyclohexylbenzothiazyl-2-sulfenamide or 0.50 per cent of tetramethylthiuram disulfide. 3. The effect of small additions of t-butyl-, xylyl-, and p-methylphenylthiols was a pronounced improvement in the flex-cracking resistance of a vulcanizate containing ethylxanthogen disulfide. These observations suggest the industrial application of ethylxanthogen disulfide to alleviate some of the serious deficiencies so characteristic of Buna-S vulcanizates.
Changes in Physical Properties of Hard Rubber Shortly after Vulcanization
Authors: Daynes H. A.
Published: February 2011

Preparatory to a full investigation of the properties of various specimens of hard rubber, it was considered necessary to decide on a minimum time interval between vulcanization and testing. This was desirable to allow specimens to attain a stable condition, and thus to avoid anomalies which might result from testing during a transition period, soon after vulcanization, when the physical properties are changing relatively rapidly. It was necessary to approach the problem from the standpoint of the following properties which it was desired to investigate.
Strains in an Inflated Rubber Sheet, and the Mechanism of Bursting
Authors: Treloar L. R. G.
Published: February 2011

The two principal strains in a circular sheet of rubber clamped round its circumference and inflated are measured at all points on the surface of the spheroidal balloon thus formed. The principal strains may show relatively-large variations over an area in which the form is nearly spherical and the thickness is approximately constant. The reasons for this, and for certain other effects brought out in the experiments, are discussed. In experiments on the bursting of sheets of various rubbers (natural and synthetic), there appeared to be a general relation between the hardness at the instant of breaking and the number and regularity of the radial tears. From the strain measurements it is concluded that these radial tears are not caused by the relatively slight radial orientation of the molecules in the sheet. A detailed mechanism of bursting is suggested, in which the radial tears are compared with the radial cracks associated with glass fractures.
The Variation with Temperature of the Dynamic Properties of Rubber and Synthetic Rubberlike Materials. II. Compounded Rubbers
Authors: Blow C. M. , Fletcher W. P. , Schofield J. R.
Published: February 2011

The whole of the dynamic modulus results may be summarized as follows. (1) A general sensitivity to temperature over the range studied is shown by all rubbers, natural and synthetic. (2) Natural rubber is least sensitive, followed by Neoprene-GN and GR-S. Next in order come Neoprene-YD and butadiene-acrylonitrile copolymers with low acrylonitrile contents. In general, the higher the acrylonitrile content, the more sensitive to temperature is the polymer. Neoprene-Z is only slightly less sensitive than Hycar OR-15 (45–55). (3) Broadly speaking, the effect of compounding with P-33 black and gas black is to increase the sensitivity to temperature. Notable exceptions are Neoprene-GN and GR-S containing extender, which appear almost unchanged, and Neoprene-YD, which shows a decreased sensitivity with loading. (4) It is evident from the results that any specification for dynamic modulus should be accompanied by a specified temperature of test; in design, account must be taken of the variations which it has been shown can be quite considerable for synthetic rubbers now coming into commercial use, even under normal seasonal variation of temperature. (5) Static methods of determining freeze points, e.g., torsion and bending tests, in general place materials in a similar order with respect to their low-temperature behavior as the present dynamic experiments, although no appreciable temperature effects are noted in the temperature range of the experiments discussed here. The results of resilience measurement are not easy to summarize. Suffice it to say that, over the limited range of temperatures investigated, very great differences in resilience are observed between different polymers. The superiority of natural rubber is again evident, although it is somewhat less marked in loaded stocks. In the case of Thiokol-RD and Hycar OR-15, minima in the resilience curves are indicated at 23° C and about 10° C, respectively. This has been reported by previous workers. In all polymers the resilience-temperature curve is in two parts, with a more or less sharply defined transition point, the temperature of which seems to depend largely on the chemical structure of the polymer. Again this is confirmed to some extent by reference to the literature.
Mechanism of Exposure-Cracking of Rubbers. With a Review of the Influence of Ozone
Authors: Newton R. G.
Published: February 2011

“Exposure-cracking” is the fissuring which occurs when stretched rubber is placed in an atmosphere containing ozone, and is frequently wrongly described as “sun-cracking”. These cracks form in the rubber at right angles to the applied stress and must be distinguished from crazing, the fissures of which occur in an oxidized surface layer and may run in any direction. It is shown that there is a “critical elongation” at which cracking is maximal, but that the relation between the severity of cracking and the surface strain can be greatly modified by changes in the compounding ingredients. Butadiene type of rubbers do not differ greatly in resistance to exposure-cracking, whereas the Neoprene types and Thiokol-FA possess marked resistance. The only factors essential for the production of exposure-cracking are ozone and strain in the sample, and sufficient ozone must be present in the atmosphere to produce the deterioration observed. Light is not only unnecessary, but actually has a retarding effect on the production of cracks. Three different phenomena must be carefully distinguished (1) the rate of ozone attack ; (2) the rate of formation of cracks ; and (3) the rate of growth of cracks. The rate of formation of cracks increases with increase of strain until a maximum is reached at about 75 per cent elongation, but the mean rate of growth of cracks is most rapid at 20 per cent elongation because the surface strain is most persistent at this elongation. The actual growth of cracks has been studied microscopically, and it is shown that large cracks are formed by the coalescence of small cracks, and the collapse of neighboring ones. The rate of ozone absorption is considered, and speculations are advanced to explain the formation of cracks and their greater incidence at high strains. The course of ozone attack indicates that there is little likelihood of producing improvement in resistance by altering compounding ingredients such as fillers and antioxidants, and confirms that the most efficient methods will be based on some type of surface protection.
Retraction and Stress Propagation in Natural and Synthetic Gum and Tread Stocks
Authors: Mrowca B. A. , Dart S. L. , Guth Eugene
Published: February 2011

Natural and synthetic rubbers (elastomers) are characterized by their long-range reversible elasticity. More particularly, the existence of a retractive force distinguishes rubbers from materials like beeswax, which may be extended but do not snap back. Whereas all rubbers show a snapback, the good rubbers show a fast snapback. Thus the speed of snapback is an outstanding index to the quality of the rubber. For instance, both Hevea and Butyl show snapback, but Butyl snaps back much more slowly than Hevea. This is the reason for the poor rebound in Butyl. Incidentally, the speed of snapback may be, and actually is, used as a simple “hand test” for progress of cure. One bends a cured sheet and observes how fast it straightens out again. In this example the speed of recovery after bending is observed. The speed of snapback may be studied, of course, for any deformation : bending, torsion, shear, compression, extension, etc. Since stress-strain data are used so extensively in rubber technology, snapback after extension was studied first. Snapback will be used in this restricted sense in the following text. Besides characterizing the quality of a polymer, the speed of snapback is of great direct importance for tire construction. Sluggish snapback may lead to increased flexing, i.e., increased heat generation. In addition, slow snapback means less grip of the tire on the road, assuming equal wetting conditions.
Some Physical Properties of Elastomers at Low Temperature
Authors: Greene H. E. , Loughborough D. L.
Published: February 2011

The design of a laboratory test to duplicate the service performance of a product is always difficult. When carried out carefully, it becomes as involved as a direct use test. To circumvent these difficulties in low temperature measurements, we have chosen to measure well defined constants over a range of independent variables. From an interpretation of these data, one can predict performance in a way not possible by service-simulating tests. The analysis does, however, demand an understanding of the physical nature of stress-strain properties, including at least a qualitative understanding of the mechanism involved. Below the second-order transition temperature an elastomer is hard and brittle. This glassy state is characterized by an elastic modulus in the neighborhood of 107 lbs. per sq. in. As the temperature increases, the modulus decreases rapidly along a sigmoidal curve until the modulus has reached a value of approximately 102 lbs. per sq. in. With further increase in temperature the modulus increases linearly with absolute temperature in a manner successfully explained by the kinetic thermodynamic approach. The modulus-temperature curve consists, then, of three parts: (1) a glassy region; (2) a transition; (3) an elastic region.
The Proöxygenic Effect. Changes Which Take Place in Vulcanized Rubber
Authors: Chovin Paul
Published: February 2011

The autoöxidation of rubber is sensitive to the action of catalysis; anti-oxygenic compounds are antagonistic to the process and retard its progress; proöxygenic compounds on the contrary promote autoöxidation, and in their presence the effects of autoöxidation are evident sooner. In the present paper, experiments are described, the object of which was to study the action of a few typical proöxygenic compounds on rubber hydrocarbon. Among the substances which accelerate the action of oxygen, certain salts of copper, iron, cobalt, and manganese are known to be very active. Various organic derivatives of these metals were studied in the present work, including (1) copper acetylacetonate, oleate, linoleate, sulforicinoleate, elaidate, stearate, enanthate, pelargonate, hendecenate, erucate, and diethylthioneethiolcarbamate; (2) iron acetylacetonate, oleate, linoleate, sulforicinoleate, and pelargonate, and the dibenzoylmethane derivative of iron; (3) cobaltous oleate, linoleate and sulforicinoleate, and cobaltic acetylacetonate; (4) manganous oleate, linoleate, sulforicinoleate and pelargonate, and manganic acetylacetonate. A study was also made of certain more complex metal derivatives, including salts of the dithizone of cupferron, of mercaptobenzothiazole, of α-nitrose-β-naphthol, of benzyldioxime, etc. The method followed involved two steps: (1) incorporation of a predetermined percentage of a proöxygenic metal compound into samples of vulcanized rubber, (2) estimation of the acceleration of autoöxidation induced by the particular proöxygenic compound. In the first step, the rubber sample was cut into small cubical pieces 2–3 mm. on a side, and these were placed in a chloroform solution of the particular salt under investigation. The average content of proöxygenic compound which was absorbed was about 0.1 per cent. The swelling of the rubber in the solution was the determinant factor in the total amount of proöxygenic compound and solvent which were absorbed.
Plasticity Measurements in the Rubber Industry. IV
Authors: Behre J.
Published: February 2011

In the present work, the volume of rubber which flows in unit time from an extrusion plastometer as a function of the pressure and temperature was determined, and the socalled yield value was calculated. This latter value represents the critical shearing stress which must be overcome for true plastic flow to take place. It is shown also that the yield value depends greatly on the temperature and preliminary treatment undergone by the sample.
High-Temperature Oven Aging of Oil-Resisting Synthetic Rubber Compounds
Authors: McCarthy G. D. , Juve A. E. , Boxser H. , Sanger M. , Doner S. R. , Cunningham E. N. , McWhorter J. F. , Crossley R. H.
Published: February 2011

An investigation of the effect of varying conditions of high-temperature exposure has shown that, at a constant temperature, the supply of oxygen is the principal factor which causes stiffening of the vulcanizates. The loss of volatile plasticizers, when present, also contributes to the stiffening. The test-tube technique, developed in the course of this investigation, in which dumbbell samples are suspended in stoppered test-tubes (38 by 300-mm.) heated by immersion in an oil bath, appears to give results which are considerably more duplicable than those obtained by the usual aging in circulating air ovens. The test-tube technique also gives somewhat better differentiation between good-heat aging and poor-heat aging compounds. The rate of deterioration as measured by elongation change is doubled for an 18° F increase in the exposure temperature. As measured by hardness change the rate is doubled by an increase of 42° F. Tests run at 250° F by this method are no more reproducible than those run at 300° F.
Physical-Chemical Investigations of Goldenrod Rubber. IV. Increase in Viscosity and Formation of Photogels by Irradiation of Goldenrod Rubber in the Absence of Oxygen
Authors: Graff Morris M. , Skau Evald L.
Published: February 2011

The viscosity of goldenrod rubber can be increased until gelation takes place by irradiation of its benzene solution in the presence of catalysts and in the absence of oxygen. Benzophenone, benzaldehyde and carbon tetrachloride seem to be the best of the activators tested.
“Rubber Acid” Damage in Fire Hoses
Authors: Thaysen A. C. , Bunker H. J. , Adams M. E.
Published: February 2011

The conclusions to be drawn from the experiments which have been carried out would appear to be that : The production of rubber acid in hose is due to the activity of sulfur-oxidizing bacteria of the Thiobacterium thioöxidans group. Such acid will invariable be formed in rubber-lined hose which is stored with the linings wet, when the responsible bacteria are present, and when the free sulfur content of the hoses exceeds 0.1 per cent. If acid production is to be prevented, it is necessary to ensure, either that the rubber-lined hose is stored dry, or that its content of free sulfur is less than 0.1 per cent. The alternative of preventing the introduction of the causal bacteria does not appear practicable, since the water used in fire-fighting is a frequent habitat of these bacteria. In a series of additional experiments it was established that various organic sulfur compounds, commonly used in the vulcanization of rubber, failed to give rise to acid production, even in the presence of sulfur-oxidizing bacteria.
Composition of Rubber from Different Botanical Sources
Authors: Bennett H.
Published: February 2011

Natural rubber from botanical sources other than Hevea brasiliensis now forms an appreciable proportion of the total rubber available to manufacturers in Allied countries. The principal source of this wild rubber is the African continent, the home of Landolphia, Funtumia and other rubber-producing vines and trees. RUBBER HYDROCARBON CONTENT The information given in Table 1 summarizes the general chemical characteristics of natural rubber from different botanical sources and, in particular, shows the amount of rubber hydrocarbon normally present in each type. Column 9 shows the values obtained by difference and column 10 those obtained by direct estimation, using the chromic acid oxidation method (ASTM Bull. No. 120, Jan. 1943, p. 23; Rubbee Chem. Tech. 16, 660 (1943)). The difference method assumes that the nitrogen is present as protein with a factor of 6.25; and, in calculating the results, allowance is made for the nitrogen and ash in the material insoluble in boiling nitrobenzene (See Table II). The direct estimation calls for no special comment except that the samples required very thorough blending to obtain concordant results, and varied considerably in the time required for digestion with oxidizing mixture.