bluuebunny/crossref_metadata_2025 huggingface dataset:
Further Electron Microscope Studies on Colloidal Carbon, and the Role of Surface in Rubber Reenforcement
Authors: Wiegand W. B.
Published: February 2011

(1) Based on preliminary electron microscope analysis, rubber carbons are assigned tentative surface values, ranging from one to upward of 12 acres per pound. (2) In all cases particles are of essentially spherical habit. (3) Indications of chain and network structure have appeared in acetylene carbon and lampblack plates (conclusion not final). (4) Physical properties of carbons in rubber are reviewed, and the advantages of “soft” carbons enumerated. (5) Differences in chemical compositions are found not to square with reënforcing differences in rubber. (6) When colloidal properties, tinctorial properties, and rubber properties are plotted against acres per pound, it is found, as anticipated, that surface is, in general, the dominating influence; subject, however, to important and sometimes controlling anomalies. (7) These anomalies appear to be largely resolved on the assumption that three broad types of carbon behavior exist. (I) Carbon-rubber complexes (reënforced rubber) are formed (examples— semireënforcing carbons, Statex and carbon blacks). (II) Carbon-carbon complexes or networks are formed in addition to (I). Examples, acetylene carbon and lampblack. (III) Carbons are inert—neither (I) nor (II) occurs. Examples—thermal carbons. These relations are brought together in Table 1.
Heats of Combustion and Specific Heats of Buna-S Treated in Various Ways
Authors: Roth W. A. , Wirths Gerhilde , Berendt Hildegarde
Published: February 2011

Measurements of the heats of combustion and specific heats (between 20° and 50° C) of crude untreated Buna-S, highly degraded Buna-S, and cyclized Buna-S are reported. The heats of combustion are then discussed. A well defined relation exists between thermal data and changes which take place in Buna-S. In the case of specific heats, the values of which are less precise, the relation is not so clearly defined.
A Simplified Hot Tensile Test for GR-S
Authors: Braendle H. A. , Valden E. , Wiegand W. B.
Published: February 2011

In September, 1942, the hot-iron test developed by E. Valden, of these laboratories, was demonstrated as a simple rapid method of evaluating the heat embrittlement of GR-S. The test-specimen, a T-50 test-piece, may be cut from the remnants of test sheets cured for stress-strain determinations. for GR-S treads a convenient set of conditions is 200 per cent elongation and an iron temperature of 400° F. The iron is fastened to the test-block at a sufficient height to assure positive contact of the specimen with the iron, and the screws in the spacer blocks are set to give a 200 per cent elongation. The iron, a “patch heater”, for spotting or dry-mounting photo prints, has a built-in thermostat. The time in seconds between contact of the specimen with the iron and its failure due to heat is recorded. The relative behavior of various elastomers with 27.8 volumes of carbon is illustrated in Figure 1. The excellence of Hevea at both optimum and prolonged overcure is apparent. The hot-iron test does not serve to pick best cure. It does provide an effective warning against overcure and a means of recognizing compounding changes which benefit heat stability, as, for example, the use of high carbon high softener ratios.
Reactions of Iodine, Iodine Chloride and Thiocyanogen with the Hydrocarbons of Natural Rubber and Synthetic Rubber
Authors: Medvedchuk P. I. , Aldoshin F. D. , Marovich V. P. , Repman A. V.
Published: February 2011

The reactions of iodine, iodine chloride and thiocyanogen with solutions of natural rubber and of synthetic sodium-butadiene rubber were studied. The experimental results show that the chemical properties of these two hydrocarbons are in general similar, although there are also certain differences which can be explained by the peculiarities of their structures. The products of the reactions of iodine chloride and of thiocyanogen with natural rubber and sodium-butadiene rubber were isolated, and their compositions and some of their properties are described.
Structural Features of Buna-S. Relation to Physical Properties
Authors: Kemp A. R. , Straitiff W. G.
Published: February 2011

The low tensile strength of Buna-S gum stocks is generally believed to be due to failure to obtain effective cross-linkage as the result of vulcanization with sulfur and accelerators. Combined with this is the complete absence of crystallization of Buna-S on stretching which, in the case of natural rubber, reinforces and strengthens the vulcanized gel structure. The absence of crystallization in Buna-S can be explained on the basis of nonsymmetry along the polymer chains. Strictly speaking, Buna-S is not a true polymer, for ozonolysis shows that the styrene units are not spaced evenly in the chain but are grouped together in some locations. Ozonolysis also has proved the presence of vinyl groups attached to the chain, resulting from the polymerization of butadiene in the 1,2 instead of the 1,4 position. These vinyl groups must be unevenly spaced along the chain, and mixed trans and cis isomers must be present. Figure 1 illustrates the chemical units present in Buna-S, rubber, and gutta-percha hydrocarbons. In a Buna-S copolymer containing 24.5 per cent of styrene, there are six butadiene to one styrene units. It appears that about one butadiene in five polymerizes in the 1,2 position in the chain. It should be emphasized that, in Buna-S, ozonolysis has shown that no regular order exists in the location of A, B, and C units in the polymer. An entire lack of symmetry in the positioning of these units in the chain would be expected in view of the nature of the polymerization reaction.
A New Approach to the Theory of Rubberlike Elasticity
Authors: Huggins Maurice L.
Published: February 2011

It has been shown that for a simple hypothetical model substance, containing like independent systems, each capable of existing in two alternative orientations, stress-strain curves may be computed which are similar in form to those ordinarily obtained from rubber and rubberlike materials, provided one introduces a certain dependence of the volume shift per rearrangement on the elongation. With this model, the dependence of the initial elastic modulus and that of the shape of the stress-strain curve on various characteristics of the rearranging systems are readily studied. More detailed comparison of these theoretical results with experimental data and with other theoretical treatments will be postponed until a later date.
Qualitative Spot Tests for Rubber Polymers
Authors: Burchfield H. P.
Published: February 2011

To eliminate processing difficulties and ensure the production of standard natural and synthetic rubber reclaims, the scrap used as the raw material must be carefully segregated. When mold markings are lost, or large consignments of miscellaneous scrap are received, methods for distinguishing between the basic polymers are necessary. This paper describes a new color reaction which will serve to characterize natural rubber, GR-S, and Perbunan. Confirmatory tests included in the same operation distinguish between the remaining commercially important types. The procedure is sufficiently rapid to be practical in the testing of representative samples from carload shipments, or for establishing the identity of materials on which indecisive results are obtained by less specific methods. For the routine assortment of scrap, spot tests are proposed, which are carried out by holding impregnated filter paper strips in the smoke emitted when the sample is branded with a metal rod heated to redness. Color changes take place which indicate the nature of the polymer. One test distinguishes between natural rubber and GR-S ; a second is specific for Butyl ; a third differentiates Neoprene-GN, Neoprene-ILS, and Perbunan from one another and from the hydrocarbon rubbers. The spot reactions can be carried out very rapidly, and are particularly useful when large numbers of samples must be examined.
A Comparison of Different Types of Rubber Obtained from the Same Field Latex
Authors: Van Der Bie G. J.
Published: February 2011

Several comparative investigations of various types of raw rubber have been published, but most of these refer to products of different origin, hence it is not known to what extent the results depended on natural variations in the rubber. Moreover, the investigators, who prepared their own material, worked either with old latex in Europe, in the United States or in the tropics, where the work was confined to only a few types of rubber. The present investigation was conducted with the following objects in view : (1) A comparison of various types of commercial rubber, i.e., smoked sheet, crepe and whole-latex rubber. (2) A comparison of these rubbers with those obtained from different types of latex (or cream latex). (3) The influence of storage of latex (cream latex) on the properties of the rubber. (4) The influence of storage on various types of, rubber. (5) A comparison of the accelerated aging tests of Geer and Evans and of Bierer and Davis.
Natural Rubber from Russian Dandelion
Authors: Eskew Roderick K.
Published: February 2011

A great deal has been published during the past three years regarding the various sources of natural rubber which have been called upon to supplement this nation's stockpile and to meet those special needs for which commercial synthetic rubbers are not entirely satisfactory. We have read of wild rubbers being brought in under great difficulty from Central and South America; of the 32,000 acres of guayule grown by the government, largely in California, and now nearly ready for harvest; and of the large experimental plantings of Cryptostegia in Haiti. Almost nothing, however, has appeared regarding a plant which is known to be potentially rich in high-grade rubber and which has been extensively cultivated outside this country. This is the Russian dandelion, or Taraxacum kok-saghyz. In the course of a systematic investigation instituted in Russia in 1929 to determine the possibilities of producing natural rubber in that country, the kok-saghyz was found near Tien Shan, Kazakstan, near the border of China. By 1932 more than 2,000 acres of this plant were under cultivation in Russia, and it is reported that at the time of the German invasion of Russia approximately 200,000 acres of kok-saghyz had been planted for the production of rubber.
Studies on Deproteinized Rubber. V. Effects of Several Proteins
Authors: Ōkita T.
Published: February 2011

It has been reported that rubber cures slowly when the protein in the rubber is removed, and similar results have been obtained in the author's experiments (Reports 1 and 4). As the phenomenon has relation to evolution of hydrogen sulfide during vulcanization, several experiments were carried out concerning these points. Vulcanization Test 7.5 parts of sulfur were mixed with 92.5 parts of washed smoked sheet or deproteinized rubber, and 5 parts of albumin, glutamic acid, hemoglobin, and gelatin, respectively, were added to the latter. These 6 mixes were cured in sheets 1.2 to 1.4 mm. thick in a press at 148° C. Tensile strengths of these samples are shown inFig. 1. The curing velocity of rubber is accelerated by these proteins. The effect is most pronounced in the case of gelatin, followed by hemoglobin and albumin. Glutamic acid has a slight effect on cure. The deproteinized rubber mixed with gelatin cured in almost the same time as the mixture of washed smoked sheet.
Soluble and Insoluble Rubber
Authors: Staudinger H.
Published: February 2011

A particularly striking property of unvulcanized rubber is that benzene-soluble rubber, which is a colloid capable of unlimited swelling, is transformed on standing into insoluble rubber—a colloid of limited swelling capacity. Scarcely any difference in composition can be found analytically between the two kinds of rubber, which differ so widely in solubility. Insoluble rubber can be reconverted into a soluble form by long standing or by mastication. These apparently reversible transformations between soluble and insoluble rubber were formerly ascribed to a micellar structure of rubber; it was assumed that the swelling phenomena, as also the high viscosity of rubber solutions, were connected with the solvation of the micelles. In contrast to such micellar theories it was shown, by the conversion of polymer-homologous rubbers into the polymer-analogous hydrorubbers, that the colloidal particles in dilute solutions are the macromolecules themselves. The high viscosity of rubber solutions is caused by the thread-like form of the macromolecules and not by a micellar structure; rubber thus belongs to the linear molecular colloids.
Heat of Dilution in the System: Rubber-Toluene
Authors: Meyer Kurt H. , Wolff Eberhard , Boissonnas Ch. G.
Published: February 2011

It is already known that the heat of dilution of a system can be derived from the temperature coefficient of the osmotic pressure. This method is an example of the indirect method supplementing direct calorimetric measurements which have been carried to a high degree of perfection by Swietoslawski. The present brief work is dedicated to this master of calorimetric research. It may be in keeping with the present work first of all to review the theoretical principles of the indirect method. The equation relating heat content to the temperature coefficient of free energy can be expressed thus:
A Machine for the Systematic Testing of Rubber Subjected to Repeated Flexings
Authors: Graffe Lucien
Published: February 2011

The machine which is described in this communication was designed, after due consideration from both the theoretical and practical points of view, to flex rubber samples repeatedly without subjecting them to longitudinal traction, i.e., to flex them at constant length. The test-piece, cut in the form of strips from a sheet or from some particular part of an article, is fastened at each end; one end is held immovable, the other is fastened to a movable support which undergoes reciprocal motion. There seems to be no record of the existence of a machine of this type, in fact most specifications call for tests involving repeated traction. At a recent international rubber conference F. Jacobs described a machine with which test-specimens of special shape can be alternately flexed and subjected to impact, which has an influence on the results. Moreover this machine requires moulded test-specimens, so that it is impossible to test samples prepared from articles in the particular forms in which they are designed for service. At first thought it might be assumed that this machine operates in such a way that the samples are not subjected to longitudinal traction during flexing. In reality, since every deformation of a solid body involves a change in the arrangement of the elementary fibers, and since rubber is apparently no exception to this rule, a sequence of tensions and compressions occurs, the frequency of which is the same as that of the reciprocating motion; the amplitude can be changed at will, and the intensity of the stresses depends on the particular conditions, as the brief analysis which follows will attempt to show.
Purified Latex and Rubber
Authors: Noble R. J.
Published: February 2011

Within the past ten years purified rubber has come to be a subject of considerable interest, particularly in the field of electrical insulation. Several papers have been published relating to methods of preparation and the properties of the resulting product. Numerous patents have been granted covering methods of preparation of purified rubber and its use in the manufacture of insulation, all such methods having as their object the removal of nitrogenous and water-soluble substances so that the final product may have a low degree of water absorption and high dielectric stability. Previous investigators in this field have arrived at somewhat divergent conclusions as to the cause of water absorption, the proper requirements of a purified rubber in this respect, and the efficacy of the various methods of purification. Inasmuch as different lots of rubber or latex with different compositions and properties were used in each case, it is difficult to correlate their results. The object of this paper, therefore, is to review the earlier work and to offer new data and conclusions resulting from the application of several different purification methods to one original latex.
Mechanical Properties of “Two-Dimensional” Rubber. The Micellar Structure of Rubber
Authors: Trapeznikov A. A.
Published: February 2011

It has been suggested by a number of authors that the enhancement in the mechanical properties of rubber by loading it with active fillers is connected with the transition of the rubber into a special state on the surface of the filler particles. Rehbinder and Margaretov, studying the mechanism of activation due to fillers, consider this change in the mechanical properties as a transition of the rubber into a two-dimensional film-state of solvate membranes which, similar to thin liquid layers, possess anomalous mechanical properties (elasticity in shear), as well as a peculiar colloidal structure. In the present investigation the mechanical properties of thin films of rubber were studied with the aim of discovering their anomalies, the appearance of which may be expected for sufficiently thin and, most probably, oriented films. The mechanical properties, characterized by deformation curves during stretching, were studied with an apparatus consisting of a paraffined trough containing water, on the surface of which was placed a film of rubber, spring balances (glass needle) to measure the tension, and two barriers to stretch the film. One barrier, in the form of a paraffined strip of paper floating freely, was joined by steel hooks to the lower ends of the balance; the other, a glass one, moved along the ends of the trough.
Frosting of Vulcanized Rubber
Authors: Tuley W. F.
Published: February 2011

Rubber products, like most commodities today, must meet the public demand for attractive appearance. Anything which damages the finish is a problem for the technical man. An appearance problem which seems to have become frequent in recent years is concerned with a dulling or surface dimming of various types of rubber goods after vulcanization. This effect has been aptly called “frosting,” and it sometimes resembles actual frost. Frosting may be easily confused with bloom. It usually appears within a few hours or days after vulcanization. It differs from bloom in that it is not caused by migration to the surface of a component of the rubber composition. Bloom can usually be removed by solution in weak acid or alkali or in an organic solvent. Frosting cannot be removed. The microscopic appearance is also quite different. Frosting may occur on rubber vulcanized in a press or in an open-air or steam cure, such as is used for footwear. It is most noticeable on the bright finish of air-cured rubber goods. Sometimes it appears almost immediately after removal from the vulcanizer as a bluish sheen, which may later become almost gray. Frosting has been observed on a great variety of rubber products, including footwear, raincoats, inner tubes, druggist's sundries and other molded articles. Unfortunately there is no known way in which frosting can be removed after it has once formed. It can be covered with lacquer or other finish but this is seldom satisfactory when applied after vulcanization. A bloom of sulfur and sometimes of other materials can be removed by additional heating at vulcanizing temperatures, but this is not effective with frosting. If the rubber is not frosted within a few weeks after vulcanization, it seems to develop a resistance to frosting and is unlikely to frost later. Frosting was determined to be due to the ozone in the air. So far as the writer knows, the cause was first determined by S. M. Boyd in 1931. He found that the effect could be reproduced by exposing vulcanized rubber without tension in warm, humid, ozonized air.
Tentative Procedures for Testing the Variability of Normal and Concentrated Latex. Crude Rubber Committee, Division of Rubber Chemistry, American Chemical Society
Authors: Gerke R. H.
Published: February 2011

The Committee desires to emphasize that these tentative procedures for testing variability are not to be considered as actual specifications for buying or selling latex, since tolerances or limits are not given. Rather, it is the desire of the Committee to give what are believed to be reliable methods for the determination of the various properties of latex which have been listed. However, it may be necessary to revise some of these procedures from time to time, since the use of latex is in its infancy and improved methods are being rapidly developed. In listing these procedures the Committee does not mean to suggest that it is always necessary to use all of them in testing a sample of latex. In other words, it is up to the users and suppliers to select such methods and tolerances as they see fit which will best suit their purposes. The Committee desires to express deep appreciation to those who have been instrumental in preparing the attached procedures:
Chemical Reactions during Vulcanization
Authors: Hauser E. A. , Brown J. R.
Published: February 2011

Direct addition or bridging of sulfur seems to occur at the double bonds of the rubber in sulfur vulcanization without accelerators (Figure 5, a and b). In accelerated stocks the fact that sulfur combines in excess of one atom of sulfur saturating one double bond of the rubber hydrocarbon suggests that sulfur may also combine in a dehydrogenation reaction (Figure 5, c), and that this type of sulfur linkage is most effective in producing high tensile strengths. The excess loss in unsaturation on overcure indicates that direct polymerization without sulfur (Figure 5, d), as well as reactions of oxygen at the double bonds, may occur after most of the sulfur has combined, but that these chemical changes are not definitely associated with changes in the vulcanized structure as measured by tensile strength. In the vulcanization of a simple rubber-sulfur compound, infrared absorption data indicate that oxygen is combining with the rubber during overcure to produce a degradation in the hydrocarbon structure which is accompanied by a decided loss in tensile strength.
Catalytic Dehydrogenation of Monoölefins to Diolefins. Source Materials for Synthetic Rubber and Resins
Authors: Grosse Aristid V. , Morrell Jacque C. , Mavity Julian M.
Published: February 2011

Aside from the scientific value of the method described here for the catalytic dehydrogenation of monoölefins to diolefins, the present contribution has an important industrial, commercial, and military value, viz., as an economic source of raw material for synthetic rubber. The production of butenes from butanes and pentenes from pentanes has already been described. The present paper, showing the production of butadiene from butenes and isoprene from pentenes, is the connecting link between the billions of cubic feet of butanes present in natural and cracked gases and of butenes present in the latter, and the billions of gallons of pentanes available in natural gasoline and crude oil on the one hand, and the production of synthetic rubber from these raw materials on the other. The basic raw materials for the production of synthetic rubber therefore now include our tremendous resources of hydrocarbon oils, hydrocarbon gases, and coal to produce synthetic hydrocarbons, if and when our petroleum resources become exhausted. The production of synthetic rubber from butadiene and isoprene is well known. Wallach exposed isoprene to light and produced synthetic rubber. Matthews and Harries independently used metallic sodium to polymerize isoprene to rubber. Similar work has also been done bv others.
Mixing and Moulding without Mastication
Authors: Cotton F. H. , Hodson W. F.
Published: February 2011

The preliminary experiments described indicate the remarkable potentialities of the injection method of moulding rubber articles, whether produced from mixes of powdered or masticated rubber. Employing rubber powder made by the Stam process, intimate mixing with vulcanizing ingredients and fillers is essential, and may conveniently be achieved with simple apparatus by ball milling the ingredients. The necessity for heavy rubber machinery of the orthodox type is eliminated. It is desirable to employ an accelerator of relatively low activity, or a delayed action ultra-accelerator. With very fast accelerators, vulcanization begins either during mixing of the powder or while being forced from the injection cylinder to the mould. Such premature vulcanization leads to serious distortion. It is believed that the stresses to which a compressed rubber powder compound is subjected during the process of injection moulding are sufficient to rupture the individual rubber particles, to ensure cohesion, and promote satisfactory dispersion of compounding ingredients. It is confidently asserted that results superior to those instanced herein could be achieved with an injection moulding device designed to facilitate uniform heating of both top and bottom of the mould cavity. It is also felt that a careful study of the effect of changing the injection pressure and the size of the injection orifice might yield valuable information. The success attending these early experiments warrants extending the investigation to new types of rubber powder (cf. Rubber Age, 19, 335 (1938)).
The Preservation of Latex by Sterilization in the Presence of a Buffer Solution
Authors: Davey W. S. , Beeley F.
Published: February 2011

A method of preserving latex has recently been suggested by Spence which consists of the sterilization of latex by autoclaving in the presence of a buffer reagent. In view of the improved properties claimed for the material, together with the lower cost of production, both of which are of interest to producers of latex, the method has been investigated. It is concluded that the process is not of value as a practical method for the commercial preservation of fresh Hevea latex.
Studies of Hard Rubber Reactions VIII. The Corrected Coefficient of Vulcanization, and Its Upper Limit in the Accelerated Raw Rubber Compound
Authors: Numaziri Seiiti
Published: February 2011

In a previous paper (J. Soc. Chem. Ind. Japan 40, 111B (1939)) it was shown that compounds containing up to 60 per cent of sulfur give coefficients of vulcanization higher than the theoretical maximum value of 47. Strictly speaking, however, the sulfur present in these cases can be divided into the following parts : sulfur soluble in acetone; (a) true elementary sulfur; (b) sulfur combined with organic matter; sulfur insoluble in acetone; (c) sulfur combined with rubber; (d) sulfur combined with resins and proteins; (e) metallic sulfide. In the present experiments, these five kinds of sulfur were separated as far as possible to determine the true or corrected coefficient of vulcanization, and its upper limit.
Test Formulas for Reclaimed Rubber
Authors: Palmer Henry F. , Crossley Robert H.
Published: February 2011

The maximum variation from test to test obtained when testing a sample of reclaimed rubber in compounded test formulas is approximately half that experienced when the reclaim-sulfur test is used. When tested with sulfur alone, reclaimed rubber may show a widely varying tensile strength and elongation from lot to lot, whereas much less variation in results is observed if the reclaimed rubber is tested in a compounded formula. For this reason, and also because the results obtained are more indicative of final performance, test formulas of a general nature are preferable to the reclaim-sulfur test. When test formulas are used in preference to the reclaim-sulfur mix, there is no increase in the work of testing. A combination of dibenzothiazyldimethylthiolurea and diphenylguanidine gives very satisfactory results for most types of reclaim.
Apparatus for Measuring Slow Rates of Consumption, or Evolution, of Gas in a Closed System
Authors: Barr Guy
Published: February 2011

In aging tests of rubber, the temperature and sometimes the oxygen pressure are raised much higher than in normal use; this has been necessary because the criteria of change usually chosen have been insensitive. The uptake of oxygen may be measured with considerable precision and, hence, the aging temperature may be reduced. An apparatus is described in which the absorption of oxygen by rubber is observable after an hour at 50° C; among the samples examined the hourly absorptions varied from 0.6 to 3.4 mg. per 100 grams of rubber. A manometer indicates differences in pressure between two similar bulbs placed side by side, one containing rubber and oxygen and the other containing air only. A formula is given to convert differences in the readings of the manometer to masses of oxygen absorbed.
Analytical Methods in Rubber Chemistry. (IV) The Determination of Peroxidic Oxygen
Authors: Bolland J. L. , Sundralingam A. , Sutton D. A. , Tristram G. R.
Published: February 2011

In the previous publication, of Farmer, Tristram and Bolland, it was stated that methods were required to estimate the various forms in which oxygen occurs united to the rubber molecule, and a method for the estimation of hydroxyl oxygen was discussed. The determination of peroxidic oxygen in oxidized rubber presents two distinct problems. It is necessary to employ a method which, first, is satisfactory in the presence of unsaturation and, secondly, ensures effective contact between the long rubber chains and the analytical reagent. These requirements are both satisfied by the modification described below of the colorimetric method of Young, Vogt and Nieuwland. Before describing the modified technique, some mention must be made of the earlier methods and of the errors which arise when they are applied to the determination of peroxidic oxygen in unsaturated compounds. All the earlier methods for the determination of peroxidic oxygen depend on the oxidation of potassium iodide and titration of the liberated iodine. This method is open to the objection that the liberated iodine immediately attacks the double bonds remaining in the oxidized material. This difficulty was recognized by Stephens, who, using a method in which the peroxidic oxygen was reduced with stannous chloride, succeeded in estimating about 80 per cent of the total peroxide present in cyclohexene peroxide. Yule and Wilson estimated the peroxide in cracked gasoline by shaking with an acid solution of ferrous thiocyanate and back-titrating the resulting ferric salt with titanous chloride. The results were later contested by Young, Vogt and Nieuwland, who described the colorimetric method which has been adopted, with some modification, in the present work.
Accelerators for Latex. Water-Soluble Vs. Water-Insoluble
Authors: Abernathy H. H.
Published: February 2011

The data presented in this paper support the following conclusions : Little, if any, accelerator is lost when rubber latex compounds containing water-soluble accelerators are applied to porous surfaces. The indirect method of analysis used is sensitive enough to detect any appreciable loss of accelerator, and would have detected any loss large enough to have practical importance. The fact that films from a rubber latex compound, made by casting on a porous plate, have lower moduli and tensile strengths and are less resistant to aging than films made by casting on a glass plate, is apparently due to the physical nature of the porous plate.
Heat Resistance of Neoprene-GN Vulcanizates
Authors: Forman D. B.
Published: February 2011

Control of heat deterioration is a continuous problem for the chemist. In the case of rubber and synthetic elastomers, the rubber chemist has charted the changes in the physical properties of vulcanized elastomers during heat aging. He has developed many methods for retarding the deterioration of rubber compounds by heat; but with the newer synthetic elastomers the development of methods of retarding deterioration by heat is now an active subject of investigation. The degree of deterioration depends on the methods of compounding and curing the different elastomers, as well as on the conditions of aging. In general, continuous exposure to high temperatures softens natural rubber but hardens synthetic elastomers. Inherently Neoprene has greater heat resistance than natural rubber. Many investigators have described the heat resistance of rubber vulcanizates, but only a few have reported on the heat resistance of Neoprene vulcanizates, and these reports have been primarily comparisons of given Neoprene vulcanizates with one or more rubber stocks. The compounding of Neoprene (Type GN) for heat resistance was discussed by Catton, Fraser, and Forman. The oxygen bomb aging of Neoprene (Types E and GN) was compared with that of various rubber compositions by Neal, Bimmerman, and Vincent.
Vulcanization or Other Heat Treatment by Electrical Conduction
Authors: Yerzley Felix L.
Published: February 2011

This communication relates to the heating of plastic materials of. a semiconducting nature by passing electricity through them. In particular, it relates to the vulcanization of rubber and rubberlike materials, including Neoprene, with heat generated by the conduction of an electric current and, similarly, it relates to the heat treatment of thermosetting plastics by conduction of an electric current. It is well known that all electrical conductors are heated to some extent by the passage of an electric current. This heating is a direct consequence of internal resistance. The effect so obtained is proportional to the electrical energy absorbed, and is expressed by the equation: power=I2R, in which I is the current in amperes between two points and R is the corresponding resistance in ohms. The unit of power is the watt. Others have used electrical means of heating unvulcanized rubber, but the disclosures differ fundamentally from this proposal. For example, Neerlye coils a steel ribbon and an uncured rubber belt in a spiral and heats the coil by passing electricity through the steel. Newton claims vulcanization by abeam of electrons from a cathode ray tube. The most significant disclosure is by Dufour. This claims the “process for the vulcanization of rubber characterized by the feature that the rubber to be heat-treated is arranged as a dielectric between the electrodes of an electric condenser to which there is applied a high frequency alternating current of a periodicity of several million cycles per second”. This patent is characterized by utilization of high-frequency fields of the order of several megacycles per second. Further, it is not required in induction curing with high-frequency current that the electrodes be in actual mechanical contact with the rubber. Induction curing is facilitated when the material to be heated has both a high power factor and a high dielectric constant, but high electrical conductivity of appreciable amount is not essential to the application of the method.
Hardness Testing of Vulcanized Rubber. II. Comparisons of Readings of Various Instruments
Authors: Daynes H. A. , Scott J. R.
Published: February 2011

Tests have been made on numerous rubbers with the R.A.B.R.M. hardness gauge, the Strachan piezomicrometer, and the Pusey and Jones plastometer (using in each case ¼-in. and ⅛-in. diameter balls) and with the Shore durometer and Schopper hardness tester, to determine the relationships between the readings given by these instruments. The results are tabulated and represented graphically as correlation curves. A conversion chart is given by which the reading obtained with any one instrument or size of ball can readily be converted into the corresponding reading for any of the other instruments or sizes of ball.
Wild Rubber of Tropical Africa
Authors: Martin Geo
Published: February 2011

By common usage the term rubber has come to denote the product of Hevea brasiliensis, which is outstandingly the most economical producer of rubber hydrocarbon known to mankind, and yields a product which, for general utility, has not yet been surpassed. There are, however, hundreds of other plants which yield rubber and before the advantages of Hevea became firmly established, many of them were the subject of preliminary investigation, but the information available, judged by present standards, is incomplete, out of date, and would not enable a modern manufacturer to convert wild rubber into articles of assured quality. This is not because wild rubber hydrocarbon is necessarily inferior or different from that of Hevea, but because of the well-known fact that the chemical behavior of rubber, including capacity for vulcanization and resistance to oxidation, is modified in considerable detail by small quantities of some nonrubber substances, many of which are natural components of plants. These components are not always the same for plants of the same species, and are known to be different in plants of different species. Rubber-bearing plants are found in most countries, but outside the tropics, few of them yield enough rubber to make their cultivation worth while, even in these difficult times. The most prolific source of wild rubber is tropical and subtropical Africa, where there are known to be hundreds of different species of plants which yield appreciable quantities of moderately pure rubber, in addition to many plants which yield resinous latices, some of which are known to contain rubber and others of which, although previously not known to contain rubber, are now found to contain amounts which under present conditions may be regarded as appreciable.
The Compounding of Hard GR-S
Authors: Morris Ross E. , Mitton Philip , Seegman Irvin P. , Werkenthin Theodore A.
Published: February 2011

A survey has been made of hard GR-S with regard to sulfur requirement and effects of various pigments, softeners, and accelerators on tensile strength, ultimate elongation, hardness, and stiffness. Of particular interest where the observations that hard GR-S had a higher tensile strength than hard Hevea rubber, and that hard GR-S did not undergo much loss in tensile strength when compounded with 60 volumes of channel black or semi-reinforcing black.
Rubber Resins: Some Properties and Possibilities of Use
Authors: Mason Charles F.
Published: February 2011

However, their present uses and possible future uses deserve consideration. Their tendency to thicken in certain solvents has been applied to use in imparting false body (thickening) to certain varnishes. In such cases it is likely that the rubber resin is modified to reduce tackiness before compounding it into quick-drying spirit varnishes. As plasticizers for brittle resins and asphalts they afford a very inexpensive raw material. But, again, experiments must be performed to see if the rubber resin is compatible with the natural or synthetic one, as there is little information as to whether plasticizers form solid solutions or only mechanical mixtures with the resins after heating and mixing. In one case a large shoe manufacturer purchased many tons of gutta-percha resin for impregnation of threads used in sewing on soles; the object was to prevent the entrance of moisture into the shoe and to supply a flexible adhesive. Electric friction tape, which must have an eversoft tacky surface, is coated with a compound of a bitumen, regenerated rubber, and a gutta resin, and is similar in composition to readily appliable insulation pastes, which are used on underground electric cables. The use in ever-soft adhesives and in flypaper are only two of the minor ones. The application of these resins to textiles in the form of emulsions shows large possibilities, as they can be emulsified with ammonium oleate or linoleate and, on drying, leave behind films of rubber resin and the fat acid of the emulsifier. A hardened balata resin has been used in linoleum cement. The soft resin or even the oily one can be hardened by heating for four hours at 80° C, after adding 1 per cent of manganese resinate or 0.5 per cent of calcium carbonate. Treatment of the same resin with sulfur chloride results in a viscous resin which, when warm, can be pulled out into ropes like taffy candy and, when cold, is still viscous. In closing, the writer wishes to state that, even if a reader may fail to find here the exact information he desires about a certain rubber resin, let it be hoped that what information he does find will save many hours of fruitless toil.
Thermal Expansion and Second-Order Transition Effects in High Polymers. I. Experimental Results
Authors: Boyer R. F. , Spencer R. S.
Published: February 2011

The results presented here on second-order transitions are in general accord with what has been known for other high polymeric systems. The value of the volume-temperature technique for investigating the nature of polymeric mixtures and the homogeneity of copolymers has been emphasized. In Part II a theoretical treatment of second-order transition effects, including the related brittle point determination, will be given. Finally, Part III will permit a more expanded treatment of the behavior of Saran and other crystalline polymers.
The Stress-Strain Relation of Natural and Synthetic Rubbers
Authors: Wildschut A. J.
Published: February 2011

It is shown that Hatschek's formula for the stress-elongation curve of rubber—better known as Ariano's formula—does not hold for normally vulcanized rubber. The observation has been made that the stress-elongation curves of natural and synthetic rubbers follow nonrectangular hyperbolae closely and practically up to the point of rupture. The axes of symmetry of these hyperbolae make angles of about 40° with the stress-axis in the case of pure-gum mixtures and about 30° for carbon black mixtures. A general formula has been derived which holds for all the rubbers investigated.
Properties of Hard Rubber. XI. Experiments on Aging
Authors: Church H. F. , Daynes H. A.
Published: February 2011

Tests have been carried out to find how the mechanical properties of hard rubber change with age. On prolonged exposure of the whole specimen to air at 70° C, the impact strength of notched and unnotched test-pieces may fall by 50 per cent or more. On the other hand, the plastic yield temperature increases appreciably with 200 days' exposure. The conditions affecting the improvement in such an important property are worthy of further serious study. When certain faces of the specimen are protected from the air, the rapid loss of impact strength does not take place, and cross-breaking strength may remain unimpaired for as long as 200 days. The deterioration on aging appears to be confined within a very short distance of the surface, the bulk of the material retaining its full strength for very long periods. The retention of strength when certain faces are protected may have an important bearing on questions of design. Examination of old samples of hard rubber shows that the mechanical properties remain good under ordinary conditions of storage for periods of 20–30 years, but that weakness may be caused at surfaces which are severely exposed to sunlight.
Processing Characteristics of Synthetic Rubbers and Their Use in the Manufacture of Extruded Products
Authors: Juve A. E.
Published: February 2011

The difference in processing behavior between synthetic rubbers and natural rubber becomes evident when production facilities designed for processing natural rubber are used for synthetic rubbers. All the synthetic rubbers in one respect or another are harder to process than natural rubber. Under circumstances other than the present emergency, processing equipment suitable for handling the synthetic rubbers would gradually be evolved. In the present situation, synthetic rubbers must be processed with equipment already available. In this discussion natural rubber and the general purpose synthetic rubbers, GR-S, GR-M and GR-I, will be considered. The processing of dry rubber consists essentially of the incorporation of vulcanizing agents, pigments, oils, and other ingredients by a process of kneading, followed by the forming of the mix by extrusion or calendering into shapes suitable for fabrication preparatory to final cure. The mixing step, which is accomplished on a two-roll mill or in an internal mixer, requires that the rubber be within a plasticity range that will permit satisfactory dispersion of the ingredients. If the plasticity is too low the rubber tends to crumble, and if it is too high dispersion is poor. Crude natural rubber is quite tough, and before breakdown has some of the properties of vulcanized rubber, such as high recovery after moderate distortion. In the crude state it is extremely difficult to obtain satisfactory dispersion of pigments. It is therefore necessary to soften it by mastication or other means so that the pigments are more readily incorporated and power requirements are lowered. In addition, its nerve or tendency to recover after distortion is greatly reduced. Synthetic rubbers, in general, differ from natural rubber in their susceptibility to softening by mastication, and they show different relationships between nerve and plasticity than does natural rubber.
Identification of Natural and Synthetic Rubbers
Authors: Burchfield H. P.
Published: February 2011

A method is described for identification of the types of elastomers most frequently encountered in the rubber industry. The initial test depends on qualitative measurement of the pH and specific gravity of the pyrolysis products. It can be carried out in a field laboratory in 3 to 4 minutes and will provide sufficient information for a classification of the sample.
Identification of Raw and Vulcanized Rubber-Like Polymers. I. “Reaction Time” in a Mixture of Nitric and Sulfuric Acids
Authors: Parker L. F. C.
Published: February 2011

The time taken for the start of disintegration of natural and certain synthetic rubbers in a mixture of nitric and sulfuric acids has been used as a simple and reliable aid in the identification of an unknown rubber. With Perbunan, Buna-S, and Butyl types of rubber, this test seems sufficient to establish identity, but other types, including chloroprenes, thioplasts and natural rubber, require additional data. Indication is also given of ratios of quantities in binary mixtures of known “rubbers”. The test does not require a chemical laboratory or special personnel.
Recent Advances in the Physics and Chemistry of Rubber. IV. Crystallization in Rubbers
Authors: Treloar L. R. G.
Published: February 2011

In dealing with elasticity and with swelling, we have thus far considered rubber to be composed of a loose network of randomly-kinked long-chain molecules. This simple picture does not fully represent the structure of rubber under all conditions, and gives no explanation of many of the remarkable physical properties of raw rubber. For a more adequate representation we are forced to include the effects of crystallization. In this Part we shall examine some of these effects, and see what light they throw on the mechanism of the process of crystallization and on the structure of rubber generally. At the outset we may find some difficulty in accepting the theory that rubber may contain a crystalline phase. This is because we are accustomed to think of a crystal as possessing a precise geometrical shape. We cannot identify such geometrical forms in rubber. But, on consideration, we see that the essential attribute of a crystal is the internal regularity of the spacing of its constituent atoms. The external geometrical regularity, where it exists, is derived from this more fundamental internal structural regularity. It is frequently found, however, that the internal regularity is not accompanied by external regularity. This is true, for example, of the metals, which are invariably crystalline. The absence of external regularity is due to the small size of the individual crystallites. The same considerations apply to rubbers.