bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Changes in Rubber Caused by the Action of Molecular Oxygen. V. Destructive Solution of Vulcanized Synthetic Rubbers
Authors: Tarasova Z. , Dogadkin B.
Published: February 2011

1. Vulcanized synthetic rubbers, when heated in a hydrocarbon medium containing molecular oxygen, dissolve completely. The kinetics of destructive solution of vulcanized synthetic rubbers follows the pattern established for the destructive solution of vulcanized natural rubber. 2. The rate of destructive solution of a vulcanizate depends on the molecular structure of the rubber. Rubbers are classified in the following order according to the increase of rate of solution of their vulcanizates : Butyl rubber < sodium-butadiene rubber < butadiene-styrene rubber < polychloroprene < natural rubber. The apparent energy of activation of natural rubber is 19 kcal. per mole, for sodium-butadiene rubber 31.2 kcal. per mole, and for butadiene-styrene rubber 27.1 kcal. per mole. 3. The rate of destructive solution of vulcanized butadiene rubbers depends linearly on the extent of 1,4-structure in the rubber molecule. 4. The mechanical properties of vulcanizates do not appreciably influence the rate of their destructive solution. The type of accelerator used, however, is of essential importance; in fact, its influence corresponds to its influence on the rate of absorption of oxygen. 5. The presence of water slows down the dissolution of vulcanizates of natural and sodium-butadiene rubbers, since it retards their absorption of oxygen. 6. The rate of destructive solution of a vulcanizate in various solvents depends linearly on the coefficient of absorption of oxygen in the solvents. 7. The viscosity of a solution of decomposed vulcanized sodium-butadiene rubber depends linearly on the concentration up to 50 per cent. 8. The mean specific molecular weight, measured cryoscopically, of sodium-butadiene rubber was 2400– 3600, and the osmotic weight, 16,000. The axial ratio of the particles was 1:15. 9. The hypothesis is advanced that solutions of decomposed vulcanizates constitute a special type of colloid solution.
Degradation of Natural Rubber in Solution in Vacuo
Authors: Watson W. F.
Published: February 2011

Rubber in solution degrades in the absence of oxygen. This nonoxidative degradation is the main cause of the decrease of viscosity of rubber solutions on storage. The rate of degradation is proportional to the rubber concentration and is independent of the purity and molecular weight of the rubber initially. The energy of activation for degradation in chlorobenzene is 15.9 ± 0.5 kcal. The rate of reaction is not influenced by different nonpolar solvents for rubber, but is accelerated by acids. These results suggest that rubber polymer possesses one anomalous bond per 1.3×104 monomer units. Evidence is advanced for this phenomenon being associated with the gelling of solid rubber on storage.
Structure and Properties of Loaded Rubber Mixtures. X. Alteration of Carbon Black Structures by Heat Treatment
Authors: Dogadkin B. A. , Pechkovskaya K. , Mil'man Ts
Published: February 2011

1. Raising the temperature of vulcanizates containing carbon black causes changes in the carbon structures, which can be estimated by the value of specific electric resistivity ρ and the index n in the equation: I=cVn, relating the strength of the current I with the voltage V. 2. These changes are nearly independent of the type of rubber and are governed chiefly by the type of carbon black. 3. The change of electric resistivity of vulcanizates with temperature follows an exponential law, and can be expressed by the equation : ρt=ρ0 eαt. 4. The sign of the coefficient α is negative for vulcanizates containing channel carbon black, and positive for those containing nozzle black or lamp black. 5. Heating of vulcanizates (up to 100°) for 30 minutes causes destruction of the nozzle black and lamp black particles, but causes little apparent destruction of channel black structures. 6. Prolonged heating (10 hours or more) at temperatures above 60° C causes destruction of the particles of all the carbon blacks studied. This detruction is more extensive in the case of nozzle and lamp blacks than in the case of channel black. 7. During heat treatment of mixtures containing channel black, it is chiefly the carbon-rubber bonds that are destroyed (the index n decreases); whereas in mixtures containing nozzle, furnace and lamp blacks, it is chiefly the carbon-carbon bonds that are destroyed (the index n increases). 8. The higher the temperature during deformation and relaxation, the greater is the degree of restoration of the carbon structures which are destroyed during deformation. 9. The degree of restoration of the carbon structures under identical conditions of deformation and relaxation of vulcanizates containing nozzle black is greater than that of corresponding vulcanizates containing channel black.
Acrylic Elastomers Preparation and Properties of Vulcanizable Acrylic Ester-Acrylonitrile Copolymers
Authors: Filachione E. M. , Fitzpatrick T. J. , Rehberg C. E. , Woodward C. F. , Palm W. E. , Hansen J. E.
Published: February 2011

Copolymers of various acrylic esters, from ethyl to octyl, with 5 to 15 per rent acrylonitrile or methacrylonitrile, were prepared by refluxing emulsion polymerization and in two instances by redox polymerization. These copolymers were easily vulcanized with sulfur and triethylene tetramine recipes. Heat-resistant vulcanizates were obtained from the copolymers of acrylonitrile with ethyl, butyl, amyl, and hexyl acrylates and also from the copolymer of methacrylonitrile with butyl acrylate. The octyl acrylate-acrylonitrile copolymers and the octyl acrylate, ethyl acrylate, and acrylonitrile terpolymerse did not show similar heat resistance. Terpolymers obtained from ethyl acrylate, butyl acrylate, and acrylonitrile, however, produced heat-resistant vulcanizates. The vulcanizates of lowest brittle points were obtained from copolymers of the higher acrylic esters, but regardless of the acrylic ester used, the brittle point was considerably increased with increasing acrylonitrile content of the copolymer. The copolymers from 95 per cent amyl acrylate—5 per cent acrylonitrile and the copolymer of 91 per cent hexyl acrylate—9 per cent acrylonitrile showed brittle points of −45° and −49° F, respectively. In general, the brittle point of heat-resistant stocks did not change by more than approximately 10° F on heat-aging for 72 hours at 350° F. The butyl acrylate-methacrylonitrile copolymer appeared to have somewhat better heat-aging properties than did the butyl acrylate-acrylonitrile copolymer.
Influence of Carbon Black on the Oxidation of Natural Rubber
Authors: van Amerongen G. J.
Published: February 2011

In this investigation an attempt was made to determine to what extent the solubility of oxygen in natural rubber and the aging resistance are influenced by the incorporation of carbon blacks of various particle sizes in the rubber. The influence of the particle size of carbon black on the oxidizability of GR-S loaded with carbon black had already been proved by Winn, Shelton, and Turnbull. In their explanation of this effect, carbon black was considered to be a catalyst for the oxidation reaction of rubber, although nothing was known about the nature of this catalytic action. Moreover, measurements with natural rubber were lacking.
The Microbiological Deterioration of Rubber Insulation
Authors: Blake John T. , Kitchin Donald W. , Pratt Orison S.
Published: February 2011

Experiments on natural rubber and GR-S insulation in various forms have shown them to be inherently vulnerable to fungus attack unless made sufficiently fungitoxic. Stable fungitoxic GR-S compounds have been developed in this work which have invariably maintained normal high insulation resistance during four years in active soil. Thin Neoprene jackets may be permeable to fungi so that underlying insulation should be fungitoxic or inherently stable. A humid atmosphere as in a wet duct may be a dangerous environment. It has been shown that inoculated wire can fail in moist air due to fungus penetration. Parallel electrical tests on wire and culture tests on agar-filled tubes demonstrated that the electrical failures in soil were caused by fungus penetration. It was possible to detect and identify fungus in transit in thick walls of GR-S insulation. Three types of fungi which can pass through rubber insulation and thin Neoprene jackets have been identified, at least by genus. The most prevalent has been Spicaria violacea Abbott. The presence of fungus in insulation lowers the dielectric strength before the filaments have passed completely through the wall. Impending failure can be detected by voltage breakdown tests. Rubber insulation in buried cables must be sufficiently fungitoxic. Great care is required in formulating stable compounds to insure that other required properties are not harmed.
Ultrasonic Wave Study of Swollen Buna-N Rubber
Authors: Nolle A. W. , Mifsud J. F.
Published: February 2011

The velocity and attenuation of ultrasonic waves are measured as a function of temperature in specimens of a Buna-N vulcanizate swollen to various degrees with methylethyl ketone. The frequencies are 2, 5, and 10 megacycles. The experimental method consists of determining the insertion loss and the time delay due to insertion of a flat sample in the liquid acoustic medium of a pulse-reflection apparatus; an improved technique of observation, in which phase delay as well as envelope delay is examined, leads to more precise time data than previous applications of the method. As solvent content of the specimen increases, the position of the maximum of attenuation with respect to temperature moves to lower temperatures, and the height of the attenuation peak is reduced. It is shown that the height of the attenuation peak, when corrections are made for temperature effects according to the mechanisms of rubberlike elasticity, is proportional to the mass of polymer per unit volume in the swollen specimen; moreover, the temperature of maximum attenuation is a linear function of the ratio, for the swollen specimen, of mass of solvent to mass of polymer. The latter finding indicates, if the concept of energy of activation is applicable, that the reduction of activation energy is proportional to the number of solvent molecules associated with each polymeric chain segment. The paper contains auxiliary data on dimensional and volumetric aspects of swelling and swelling rate.
Accelerator Compounding. Heat History and Compounding
Authors: Garvey B. S. , Yochum D. W. , Morschauser C. A.
Published: February 2011

To summarize, the following hold true for natural rubber: (1) Each compound has a characteristic maximum scorch time, vulcanization time, and cure time, which depend chiefly on the accelerator. (2) For any given batch of compound, both scorch time and cure time are shortened by an amount equivalent to the processing heat history of the batch. (3) The vulcanization time remains constant. (4) These relations help to explain variations in factory cures and indicate the advantages of close control of heat history in factory processing.
Flex-Cracking and Crack Growth Tests Some Important Factors
Authors: Buist J. M.
Published: February 2011

Flex-cracking has been a major cause of failure in rubber articles for many years and since the early 1930's various test methods have been suggested. The whole subject of the mechanism of flex-cracking and flex-cracking tests was reviewed recently, and in 1950 Committee ISO/TC/45 agreed that only the De Mattia machine should be considered for international standardization and that the question of crack growth should be tackled before flex-cracking. Cooperative tests, following the suggested crack-growth procedure, are being carried out in nine laboratories, four laboratories in the United Kingdom, one in Austria, one in France, one in Holland, one in Italy, and one in the United States. Preliminary results show that agreement between laboratories is not good and support the view that the greatest possible care and attention must be given to experimental details if reproducible and comparable results are to be obtained in different laboratories. In the earlier paper referred to above, three important aspects of accuracy of testing are defined as: (a) the accuracy of the measurement of flex-cracking and crack-growth resistance of any one sample; (b) the degree of reproducibility of the test conditions; (c) the degree of reproducibility of the test-specimens.
Self-Closing Grips for Rubber
Authors: Stubbs A. J.
Published: February 2011

The provision of satisfactory grips for holding dumb-bell specimens in tensile testing machines has always presented a number of difficulties. Several styles of self-closing grips are available, but none has been regarded as entirely satisfactory. Thus, the cam type is clumsy and often fails to hold the test-piece at very high extension or when the surface of the rubber is covered with a wax bloom, as sometimes happens. Another type, the bar grip, illustrated in Figure 1, has very much better holding power, but requires the specimen to have undersirably long end tabs.
Colorimetric Determination of 2-Mercapto-Benzothiazole in Compounded Rubber
Authors: Bauminger B. B. , Poulton F. C. J.
Published: February 2011

A method for the determination of 2-mercaptobenzothizaole (MBT) in compounded rubber is based on the formation and evaluation of the red-brown color obtained by reacting the alkaline salt with nickel ion. Application of the method to a variety of compounded rubbers has shown that MBT can be determined with a reasonable degree of certainty in only the simplest rubber mixings. In general, the more complex in composition and the more processing the mixing has undergone, the further will the figure for MBT recovery deviate from the amount originally incorporated. The effect of the other compounding ingredients, notably antioxidants, other accelerators, and softeners, from which considerable interference was anticipated, is in fact negligibly small. Among common accelerators the reagent can be regarded as specific, but the decomposition of those accelerators which yield MBT will naturally be reflected in the final results. High mixing temperatures and longer vulcanizing times favor the transformation of MBT to the disulfide (which, however, can be estimated by reconversion to MBT), and to simpler breakdown products.
Crystal Violet, an Electronic Model Substance for Rubber and Related Olefins
Authors: van Veersen G. J.
Published: February 2011

It is shown that triphenylmethyl dyes like crystal violet can be used as model substances for rubber and related olefins. Arguments are given in support of the assumption that agents which react with rubber and related olefins in a polar manner cause a reversible shift in color from blue to yellow with crystal violet, whereas a fading of the blue color of crystal violet (if alkaline or reducing agents are excluded) points to a radical reaction. Since the electronic structures of donor olefins and crystal violet are considered and not the molecular structure, as usually is done in the choice of a model substance, these dyes have been named electronic model substances. Though crystal violet, as an electronic model substance cannot be used for the study of the overall reactions, information can often be obtained concerning the first step in a reaction of rubber with a certain chemical agent by means of a simple test-tube reaction with crystal violet. It was pointed out that the π-electron availability at the non-methylated carbon atom of the double bond in rubber and at the nitrogen atoms in crystal violet is probably of the same order. As an application of crystal violet as an electronic model substance for rubber, a polar reaction between sulfur and rubber is suggested as the first step in vulcanization.
Partially Chlorinated Derivatives of Rubber
Authors: Woods D. E.
Published: February 2011

Chlorinated rubbers containing from 1 to 17 per cent of chlorine were prepared by direct chlorination, at ordinary temperature, of crepe rubber dissolved in carbon tetrachloride. These products retain, to a greater or lesser degree, rubberlike properties, and are capable of hot or cold vulcanization with or without the addition of vulcanizing agents. The resulting vulcanizates are considerably more resistant to the swelling action of solvents, and also to the action of chlorine, than corresponding products prepared from crepe rubber. The resistance to swelling agents increased with increase in combined chlorine content; tensile strength and elasticity, however, decreased with increasing chlorine content. As expected, hardness increased with increase of chlorine content, and vulcanizates from derivatives containing more than 10 per cent combined chlorine were not sufficiently rubberlike to warrant many experiments. Fully chlorinated rubber was compatible with partially chlorinated rubber, and addition of the former was necessary for vulcanizates to pass the Post Office flame test for cables.
Polar Rubbers and Their Application as Ion Exchangers
Authors: Mastagli Pierre , Austerweil Geza , Zafiriadis Azfiri
Published: February 2011

Most of the ion exchangers in current use are prepared in the form of synthetic resins by the condensation of aldehydes or of ketones with amines or substituted phenols and polymerization these condensation products. However, resins prepared in this way have certain disadvantages, e.g., their solubility, instability, and tendency to swell. As early as 1938, one of the present authors was able to show that it is possible to obtain ion exchangers by avoiding the condensation phase of the process through the introduction of polar groups directly into the macromolecules, which are, and which remain, insoluble even after the introduction of polar groups (wool, aminopolystyrene, azotized rubber, etc.). By eliminating the condensation phase, the —RCH(R′)OH groups and consequently any steric hindrance are avoided; hence, the stability and effectiveness of the products as ion exchangers are enhanced.
Light Stiffening of Rubber
Authors: Newton R. G. , Wake W. C.
Published: February 2011

The form of deterioration which we have designated light stiffening can be detected only when the rubber is in the form of a thin film, as it is, for example, in light-weight single-texture proofings. The implications of this work, however, extend far wider than its immediate application to thin proofings, important though this is, and we have no reason to suppose that the surface crazing seen on articles of rubber exposed to sunlight is not essentially the same thing. It is convenient, for reasons which appear later, to distinguish these two forms of deterioration of rubber, even though chemically and energetically they may have the same fundamental basis. Light stiffening is the noticeable increase in the bending modulus of thin sheets of rubber which occurs with exposure to light and air. This increase is easily observed by handling proofed fabrics so exposed, and in normal speech we refer to a “stiffening” of the article. It is an effect greater at the surface and decreasing with penetration into the bulk rubber, and for this reason is subjectively evident only where the “surface layers” form an appreciable proportion of the total thickness of the rubber. This deterioration becomes essentially a defect confined to thin proofings and other articles, the rubber parts of which form a sheet or layer a few thousandths of an inch in thickness.
Organic Sulfides as Vulcanizing Agents of Rubber
Authors: Sibley R. L.
Published: February 2011

1. It has been demonstrated that a number of organic sulfides possess the property of breaking down under vulcanizing conditions in a rubber compound to produce a cure. 2. Although several scores of sulfur-containing organic compounds other than those discussed in this paper or described in other papers have been tested, as yet there appear possible no generalizations to serve as a guide to further exploratory studies. 3. Organic sulfur compounds which are unstable under temperature conditions higher than normal do not liberate all of their sulfur in all cases. 4. Organic sulfur compounds employed alone as vulcanizing agents usually produce slower-curing rubber stocks than does sulfur, and at the same time lessen greatly the tendency of the stock to scorch. 5. Stocks of satisfactory physical properties, superior aging characteristics, and outstanding freedom from scorchiness are obtained by the use of a fractional part of the normal sulfur requirement together with a sulfur liberator. 6. Morpholine disulfide is a good example of a sulfur liberator, and exhibits its greatest effects in conjunction with a mercaptobenzothiazole type accelerator. 7. Morpholine disulfide gives satisfactory cures when used in place of sulfur in natural rubber, GR-S rubber, and Hycar-OR, but gives slow cures in GR-I rubber.
Alfin Catalysts and the Polymerization of Butadiene
Authors: Morton Avery A.
Published: February 2011

Alfin catalysts are special combinations of sodium salts which cause the rapid catalytic polymerization of butadiene to polymers of unusually high molecular weight. These polymerizations show characteristics which are common to all reactions of organosodium compounds, namely, the tendency to undergo multiple reactions. The reagents are also insoluble aggregates of ions whose behavior is affected by the ions in the aggregate. The history of the discovery is reviewed. The catalytic polymerization shows no property in common with the conventional sodium process for polymerizing butadiene. The present problems center in the elimination of secondary reactions that are known to occur. The theory by which all the reactions occur, including polymerizations induced by organosodium compounds, is discussed. Progress toward the practical use of the alfin polymers is being made.
The Structure of Elastomers and Their Reactivity
Authors: Kuz'minskii A. S. , Lezhnev N. N.
Published: February 2011

It has not yet been ascertained what constituent parts within the structure of various elastomers have the greatest influence on the reactivity of the elastomers. There are indications that the side chains, the presence of methyl groups acting as substitutes, and differences in spatial configurations, etc., all have definite effects. The present authors have investigated the oxidation of several different elastomers at different temperatures. The experiments were carried out both in the presence and in the absence of an inhibitor (phenyl-β-naphthylamine). The elastomers and the inhibitor were first carefully purified. The kinetics of autoxidations were studied volumetrically by means of an apparatus already described by one of the authors. A chainless molecular introduction of oxygen into the double bonds of the elastomer in the presence of the inhibitor was studied with the aid of our own previously described inhibitor methods. The study included the oxidation of butadiene elastomers containing different distributions of double bonds in the main and side chains, divinylstyrene rubber, and the hydrocarbons of natural rubber and gutta-percha. These products are distinguished by their different degrees of unsaturation, the number of side chains, the number of double bonds in both their main and side chains, the length of their molecular chains (the mean molecular weight), and their spatial configurations.
Effect of Fillers on Plasticity of Unvulcanized Rubber
Authors: Mullins L. , Whorlow R. W.
Published: February 2011

An investigation into the effect of fillers on the flow properties of rubber stocks is described. It is shown that rubber stocks containing fillers soften on working and stiffen on standing, and these changes are associated with the breaking down and formation of some internal structure. The amount of this structure which can be broken down or built up in this way depends on the nature of the filler; it is most evident in stocks containing fine reinforcing carbon blacks, but the ability of the filler to form structure can be modified by addition of small quantities of surface-active materials. The measured value of the plasticity of compounded rubber stocks is thus not a definite value characteristic of the stock, but depends on the whole past history of the sample, and a wide range of plasticity values may be obtained, depending on the history and the conditions of test. The practical significance of these results is discussed, and proposals which would assist the revision of ideas on plasticity tests are put forward.
The Mechanical Activation of Rubbers (Oxidation under Mechanical Stress)
Authors: Kuz'minskii˘ A. S. , Maizels M. G. , Lezhnev N. N.
Published: February 2011

In the practical application of rubber products, their fatigue characteristics, i.e., the rate of deterioration under repeated mechanical deformation, are frequently of wide importance. Work by several authors has established the fact that the fatigue effect increases significantly under the influence of oxygen, e.g., the fatigue resistance of rubber in an atmosphere of oxygen is many times lower than in an inert medium. It was found also that in the fatigue process, as in the thermal oxidation of rubber, the inhibitor is consumed. The cause of the more rapid deterioration of rubber with fatigue is the subject of discussion of the present work. Until now the effect of mechanical stresses on the oxidation processes has not been accurately determined. The present authors have investigated the effect of repeated deformations on the rate of oxidation of vulcanized butadiene-styrene rubber in different kinetic periods of the reaction (induction period, autocatalysis). In these experiments, particular attention was devoted to the microkinetics (kinetics of inhibited oxidation) of the inhibition method which was employed. The latter was used in the investigations of the kinetics of the consumption of the inhibitor (phenyl-β-naphthylamine) in the oxidation of rubber. Since in thermal oxidation, this process follows a linear law, the kinetic curve with respect to the time axis gives the rate of reaction. The latter approximates the rate of the initial reaction between the oxygen and the rubber, that is, the rate of initiation of oxidation (Wi) if all the original active centers are eliminated by the inhibitor.
Tetramethylthiuram Disulfide Vulcanization of Extracted Rubber. IV. Behavior of Rubber as an Acid
Authors: Craig David , Juve A. E. , Davidson W. L.
Published: February 2011

The retarding effect of organic acids on vulcanization as well as the activating effect of certain acids on certain accelerators is well recognized. The activating and accelerating effects of bases and metallic oxides is also well recognized. In this connection, the mild activating effect of palmitic acid on vulcanization with TMTD in the presence of zinc oxide was described in the first paper of the present series. With the behavior of acids and bases during vulcanization as a background, the study of rubber itself as an acid has been undertaken. This paper sets forth a description of two reactions investigated during the study. These are the reaction of rubber with zinc palmitate and of TMTD with acids.
Dielectric Relaxation of Natural Rubber Vulcanizates
Authors: Schallamach A.
Published: February 2011

The dielectric loss tangent of different types of vulcanizates of natural rubber has been measured as function of the frequency. Comparisons of the losses in different vulcanizates containing the same amount of combined sulfur show that they decrease with increasing modulus, and it is suggested that the dielectric loss is mostly due to sulfur which has been combined in forms other than cross-links. The dielectric relaxation time is approximately an exponential function of the percentage of combined sulfur. It has been found that moisture increases the audiofrequency losses in rubber more than the radiofrequency losses.
The Role of Intermolecular Forces in the Mechanism of High Elastic Deformation. III. Effect of Swelling on the Mechanical Properties of Vulcanized Rubber
Authors: Dogadkin B. A. , Gul V.
Published: February 2011

1. The construction of an apparatus (elastometer) for the mechanical investigation of high elastic substances is described. This apparatus makes it possible to draw deformation curves and curves of the relaxation of stress atconstant temperature and in different gaseous media, and also to investigate the life at multiple deformations. The sensitivity of the apparatus is: ΔP=0.01 g., Δl=0.01 cm. 2. The molecular weight of the segments of the chains between the bonds of the spatial network of the vulcanizate, calculated by means of Flory's equation, increases with swelling, and approaches a certain maximum value. This is evidence of the rupture of the local intermolecular bonds on swelling. 3. The maximum time of relaxation, calculated according to the equation of Dogadkin, Bartenev, and Reznikovskil, as a consequence of swelling, generally does not change uniformly; it decreases with swelling of natural rubbers in benzene and chloroform in the initial stages, then increases, and finally decreases again in the last stages of swelling. 4. An increase of temperature displaces the minimum times of relaxation to lower degrees of swelling. 5. The increase of the maximum time of relaxation as a result of swelling causes a decrease of the life of the vulcanizate; a decrease of this factor is accompanied, at least within certain limits, by an increase of life. 6. Swelling causes a decrease of tensile strength and of the relative elongation of vulcanizates. 7. The changes recorded above in the equilibrium and kinetic characteristics of high elastic deformation are explained by the presence in the vulcanizate of different intermolecular bonds.
Application of X-Ray Diffraction Methods to the Identification of Natural and Synthetic Rubbers
Authors: Goldspiel S. , Bernstein F.
Published: February 2011

In this paper, x-ray diffraction patterns and data for rubber compounding ingredients are presented and applied to the identification of major crystalline ingredients in several basic rubber stock types. Methods for the identification of natural and synthetic elastomers by low temperature aging and (or) stretching, using film techniques, are described. The extension of such methods to the Geiger counter x-ray spectrometer is presented and discussed.
Plastic Yield of Butadiene-Styrene and Isoprene-Styrene Ebonites
Authors: Scott J. R.
Published: February 2011

In unloaded ebonites made from butadiene-styrene copolymers, the resistance to plastic deformation at elevated temperatures is better the higher the styrene content of the copolymer, at least up to 46 per cent. An isoprene-styrene copolymer ebonite has poorer plastic-yield resistance than a corresponding butadiene-styrene ebonite. All the styrene-containing copolymers, however give ebonites more heat-resistant than natural rubber ebonite, the best giving yield temperatures 30° C above the latter. To attain the best plastic-yield resistance in butadiene-styrene ebonites, the amount of sulfur added should correspond to more than 1 atom (e.g., 1.2 or even 1.4 atoms) per butadiene molecule.
Determination of Unsaturation of Butyl Rubbers and Certain Branched Olefins. Iodine Monochloride Method
Authors: Lee T. S. , Kolthoff I. M. , Johnson Ethel
Published: February 2011

The reaction of iodine monochloride with highly branched olefins and polymers is abnormal in that the addition products formed possess steric strain and tend to decompose. The products of decomposition react further with iodine monochloride, generally leading to high results in the determination of unsaturation. Based upon the fact that the addition of iodine monochloride to the decomposition product is not so rapid as the addition of iodine monochloride to the original olefin or polymer, new procedures have been developed for the determination of unsaturation of highly branched ethylenic substances. The procedures have been shown to give reliable results for olefins such as the diisobutylenes and for copolymers, such as isoprene Butyl rubber and butadiene Butyl rubber.
Chlorination of Natural Rubber. II. Preparation and Properties of Rubber Dichloride
Authors: van Amerongen G. J. , Koningsberger C.
Published: February 2011

As we have seen in Part I, the chlorination of rubber with chlorine under the most varied conditions leads to products in which the chlorine is initially attached fairly loosely to an allylic carbon atom. Consequently, chlorinated rubbers of low chlorine content have rather poor properties. We shall now proceed to describe two methods by means of which, with saturation of the double bond, chlorine is introduced into rubber and the formation of products with allylic chlorine is avoided. In this way chlorinated rubbers of comparatively low chlorine content can be obtained, and these are considerably more stable than the products of the same chlorine content resulting from the direct chlorination of rubber. One of these methods depends on a catalytic additive chlorination of rubber with sulfuryl chloride; the principle of the other is the addition of HC1 onto rubber followed by normal chlorination. The aniline test described in Part I (in which the chlorinated rubber is heated with aniline for 17 hours to 100° C) was again employed to establish the nature of the chlorine bond in chlorinated rubber. Under the conditions of this test, allylic and tertiary combined chlorine reacts quantitatively. Chlorine attached by addition to the double bond of the rubber reacts to the extent of only about 4 per cent. We are therefore in a position to mark off clearly allylic and tertiary chlorine from addition chlorine. This reactive tertiary chlorine is introduced into rubber by the addition of HC1, with the formation of rubber hydrochloride. In the chlorination of rubber we are mainly concerned with allylic and addition chlorine, between which the aniline test distinguishes unmistakably. Moreover, the splitting off of the chlorine from chlorinated rubber with aniline gives us a good idea of its chemical stability.
Kinetic Analysis of Organic Halides. II. Analysis of Macromolecules Built up of Monohalide Units
Authors: Salomon G. , Koningsberger C.
Published: February 2011

A number of hydrochlorides of natural and synthetic rubbers and allied polymers have been prepared and subjected to kinetic analysis with organic bases. The hydrochlorides of natural rubber react at 100° C at a rate identical to that of low-molecular tertiary chlorides. At 50° C the reactivity of the polymer is, however, reduced by physical factors. The hydrochloride of GR-S (a synthetic rubber made from butadiene and styrene) has been prepared for the first time by heating the swollen polymer with HC1 under pressure. Kinetic analysis of this product revealed two fractions: the expected secondary chloride, and a small fraction of a very reactive (tertiary?) chloride. After elimination of experimental difficulties, we succeeded in the preparation and kinetic identification of the pure tertiary hydrobromide of natural rubber. Attempts to prepare the secondary bromide under peroxide conditions failed. Kinetic analysis of two types of Neoprene revealed the presence of a small quantity of allylic groups in the polymer, while 95 per cent of the chlorine in Neoprene has the expected stability of a vinyl chloride. This stability can be used for the identification of Neoprene.
A Rapid Determination of the Average Molecular Weight of Rubber in Hevea Latex
Authors: van Essen W. J.
Published: February 2011

A method is described for determining viscometrically the molecular weight of rubber in freshly tapped latex. For this purpose the latex is dissolved in a toluene-pyridine mixture. From the intrinsic viscosity of this solution the molecular weight of the rubber can be determined by the Staudinger equation and a known viscosity constant. Molecular weights varying between 238,000 and 480,000 have been found, depending on the kind of clone. Rubber in fresh latex does not have a lower molecular weight than in old preserved latex.
Stability of Compounded Latex
Authors: Hayes K. W.
Published: February 2011

Thickening experiments with compounded latex are described showing the maximum thickening effect of zinc oxide when at a concentration of less than 1 per cent on the dry rubber content of a 60 per cent latex compound. Gelation tests with sodium fluorsilicate indicate that the curve relating the pH of gelation to the zinc oxide concentration is closely related to the curve showing the effect on the viscosity of the zinc oxide concentration. A theory is proposed to account for the maximum thickening effect.
Abrasion Resistance and Its Measurement
Authors: Buist J. M.
Published: February 2011

Abrasion resistance is not a specific property of rubber, but depends both on the method of measurement and the machine used. The relation between abrasion resistance and the simpler physical properties, and the use of the regression technique whereby equations relating abrasion resistance, tensile strength, and hardness have been developed, are discussed. Twenty-one existing abrasion machines are reviewed and classified in one of four categories, and, wherever possible, an indication is given of the types of compound where good correlation with service is claimed. Most of the machines have been used for compound development work, but correlation with actual wear trials must be improved before the service life can be forecast accurately. Until the mechanism of abrasion is better understood the I.S.O. decision to adopt a simple method, e.g., du Pont, as a basis for standardization is sound. Work with eight sole and heel compounds and twelve tire treads shows that the order of merit obtained in the normal du Pont test is almost completely the reverse of service. With tire tread compounds, extraction of the test-pieces in ethanol-toluene-azeotrope improved the correlation with service. Further work with compounds of known service wear is required, and the extraction method in its present form does not improve the accuracy of any comparison of two compounds from different polymers, e.g., natural rubber and GR-S. The use of zinc as a standard material for checking the cutting power of the abrasive has been investigated and its use is not recommended for the du Pont type of machine.
Dynamic Shear Properties of Rubberlike Polymers
Authors: Hopkins I. L.
Published: February 2011

A simple apparatus for determining the dynamic properties of elastomers in shear at audio frequencies is appraised. Typical values of shear modulus and viscosity for several elastomers are given, both at room conditions and at 150° F. The frequencies of test range from 100 to 5250 cycles per second, the shear moduli from 0.5×106 to 480×106 dynes per sq. cm. and the viscosities from 20 to 75,000 poises.
Rheometric Tests and Extrusion
Authors: Eccher Silvio
Published: February 2011

A cylindrical rheometer of the Couette type, suitable for the experimental determination of the rheological properties of extruded materials, was designed to provide data which could not be obtained with existing plastometers. The purpose of this study was strictly practical, as the work was performed in connection with a study of extruders. The results obtained on twenty-five different materials—natural and synthetic rubbers and compounds of both with various fillers—are reported; measurements fall within shear rate limits from 1 to 100 seconds−1. In this interval the relationship between logD (rate of shear) and logτ (shear stress) is nearly a straight line. It may, therefore, be analytically interpreted by the power law : D=−(τ/c)n, where n and c are parameters characteristic of the material. As the power law is known to be of limited validity, attempts were made to ascertain the limits of its application in laminar flow through a cylindrical hole. The results of measurements carried out on a 2-inch extruder and employing the same materials as were tested by the rheometer are reported. Measurements of pressure and flow were made, using discharge holes of various diameters and operating the screw at various speeds. Reasonable agreement was found between values of flow and pressure determined with an extruder and those calculated from parameters n and c determined with the cylindrical rheometer.
X-Ray Study of the Crystallization of Vulcanized Rubber during Stretching. II.
Authors: Kasotochkin V. I. , Lukin B. V.
Published: February 2011

1. The relation between the crystal content of stretched vulcanizates to the time of vulcanization for different mixtures of natural rubber was studied by the x-ray method. 2. It was shown that the tensile strength is a function of the crystal content of the stretched vulcanizate and of the total time of vulcanization. 3. The nature of crystal formation depends on the following factors: changes of density of the network of sulfur bridges, their distribution, the degree of oxidative destruction, and the quantity of bound sulfur which has not formed bridges between the molecular chains.
Crystallization in Unstretched Rubber. Microscopic Study in Polarized Light
Authors: Campbell H. N. , Allen M. D.
Published: February 2011

Since many elastomers indicate by their physical properties that crystallization occurs even when such crystallization is not detectable by x-ray diffraction, a direct microscopic study in polarized light was undertaken. This study confirms the presence of such crystallinity not only in rubber but also in polybutadiene and some low-temperature copolymers. Furthermore, the same crystal pattern is reproduced on melting and refreezing provided the intermediate melting temperature is not too high. This indicates that x-ray diffraction is not a very sensitive method for detecting small amounts of crystallinity in high polymers. The reproduction of the crystal pattern on refreezing shows that the molecular segments have limited mobility even at room temperature; this may require revision of current theories of the origin of retractive forces in elastomers.
Vulcanization of Synthetic Rubbers
Authors: Pisarenko A. P. , Rebinder P. A.
Published: February 2011

Although for a century since the discovery of the vulcanization of rubber by sulfur many investigators have worked in this field, the problem of vulcanization can still not be considered to be well understood, either from the theoretical or the practical point of view. The basis of the most widely accepted theory of vulcanization of rubber is the concept of bridges, according to which the vulcanizing agent, sulfur, unites the macromolecules of rubber into spatial chains by primary valences. The concept that such spatial structures are formed during the vulcanization process explains well the decrease in the degree of saturation of the rubber and the changes in its physical properties, e.g., decreases in solubility and plastic flow, and considerable increases in strength, modulus, and resilience. A number of experimentally established facts, however, can never be reconciled with the bridge theory of vulcanization, especially when the vulcanization of synthetic rubbers is investigated. As a consequence of this, a number of investigators in this country have pointed out the shortcomings of the bridge theory and the necessity of finding a better explanation of the physico-chemical and colloidal reactions which take place during the vulcanization of rubber. More recently Dogadkin and his associates have shown that even when an accelerator is added, which leads to an increase of the bridge sulfur content of the vulcanizate, the total amount remains insignificant, e.g., in the case of natural rubber it amounts to only 7–10 per cent and, in the case of synthetic rubber, to 2–6 per cent of the total bound sulfur.
Refractometric Determination of Second-Order Transition Temperatures in Polymers. V. Determination of the Refractive Indexes of Elastomers at Temperatures from 25 to −120° C
Authors: Wiley Richard H. , Brauer G. M. , Bennett A. R.
Published: February 2011

In previous papers a refractometric method was described for determining second-order transition temperatures of polymers whose transitions occur between 75 and −60° C. In the present study, an Abbé refractometer was insulated and used to determine the refractive indexes of polymers down to − 120° C and the transition points of natural rubber and a number of synthetic rubbers.
Study of Bonded Units
Authors: Buist J. M. , Lindsey C. H. , Naunton W. J. S. , Stafford R. L. , Williams G. E.
Published: February 2011

The work was undertaken because no satisfactory and discriminating test is available for evaluating rubber-to-metal bonding agents. In former tests the testing of the bonding agent was confused with the testing of the test unit as a unit. A method was evolved which discriminated between bonding agents which had previously been regarded as equivalent. In the course of the work new facts such as the importance of the volume of the rubber rather than the shape factor (which must, of course be considered from the stability angle) came to light. The significance of the work lies in two directions—better testing of metal-to-rubber bonding agents and a better understanding of the facts underlying the design of rubber-metal spring units. A tentative method for measuring the tear strength of the rubber used in the unit was put forward.
Volume Changes in the Stretching of Vulcanized Natural Rubber
Authors: Gee Geoffrey , Stern Jan , Treloar L. R. G.
Published: February 2011

Measurements are presented of the volume changes accompanying small (≯100%) elongations of vulcanized natural rubber completely free from undissolved particles. The small expansions found agree with those calculated from the known compressibility of rubber and the hydrostatic component of the stretching force. It is pointed out that this volume change mechanism applies generally to any isotropic material, and does not contribute significantly (in rubber) to the tensile stress.
Dynamic Study of Reinforcement
Authors: Waring J. R. S.
Published: February 2011

The measurements were undertaken to obtain a better understanding of the mechanism of the reinforcement of rubber by carbon black. Results are given for the dynamic compression modulus and its temperature and amplitude coefficients, in the temperature range 30° to 70° C and at amplitudes of vibration around 0.0036 cm., for natural rubber, Neoprene Type GN, GR-S, and Perbunan. Data are also given on the effect of vibration and temperature on electrical conductivity. The results are discussed in relation to the general level of reinforcement. Evidence is given for the rupture of more than one type of cohesive bond in repeated cycles of vibration. A tentative system of analysis is proposed. The different effects of temperature and continuous vibration on dynamic modulus are attributed to a thixotropic breakdown in the case of vibration. The significance of such a “structure” dynamically hard at small amplitudes of vibration, is related to abrasion of tires in service.