bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Method of Determination of Fillers in Vulcanized Rubber
Authors: Hublin R. A.
Published: February 2011

A new reagent, o-nitroanisol, makes it possible to determine the total filler content of vulcanized rubber much more rapidly and more precisely than heretofore. In addition, the procedure is easier than that of the classic method. It would therefore be desirable if the method of determining fillers by solution of the rubber, which can now be carried out so easily, were to be used in many cases in place of incineration methods, which, in spite of being rapid, are very inaccurate, and also if the new method were to be used in place of the ordinary, relatively inconvenient solution methods.
Buna in the Manufacture of Cables
Authors: Roelig H.
Published: February 2011

The production on an increasingly large industrial scale of the synthetic rubberlike material, Buna, has led to its steadily expanding use in all branches of industry. The cable industry in particular has become interested in the properties of the various types of Buna in a large way in some of its extensive development problems. Buna S and Buna SS (formerly Levulkan), which have excellent aging, heat-resistant and insulating properties, are for example being used for insulating the metallic conductors of the various types of cables and cords for heavy current and low current service. Vulcanized Buna S as well as vulcanized Perbunan (formerly Buna N), the latter having the character of a semiconductor, are being used for the protective jackets of portable cables, ship cables, mine cables and telephone cables. Cable coverings made with Buna are characterized by their high stability over a wide range of temperatures, and by their great resistance to mechanical forces, which is manifest for example in a resistance to abrasion greater than that of natural rubber. In addition, Perbunan has much greater resistance to oils, fats and benzine than does natural rubber. Not only does cable manufacture require a material with high insulating properties and a cable covering of high mechanical quality, but also it is desirable that Buna, if used, have properties which make it process satisfactorily. Most Buna mixtures designed for insulation can be processed in strip-covering machines, Buna mixtures for coverings in ordinary extrusion machines. An extensive experimental program has been necessary to find a way of meeting all these frequently conflicting requirements with a new raw material like Buna. It seems advisable, therefore, to describe in a brief way the electrical and mechanical properties which can be obtained in cable manufacture with Buna as a result of these prolonged experiments.
The Standardization of Durometers
Authors: Larrick Lewis
Published: February 2011

The hardness test is one of the most useful and convenient physical tests which can be made on vulcanized rubber. It is easily made because the equipment can be simple, compact and portable. It is particularly useful in that the test sample may be a production article which can be put into service, undamaged, after the test. Consequently the test appears in the industry in several modifications, and the tester in diverse styles. Several more or less readily portable hardness testers are available commercially. The Shore Instrument and Manufacturing Co. has its line of Durometers, types A, B, C, D, etc.; Schopper, through Testing Machines, Inc., has marketed a tester similar to the Shore type A; the U. S. Gauge Co. has an instrument of the same type using the case of their pressure gage; the Firestone Penetrometer is another well-known tester of the spring-load type, as is the Adams Densimeter. At the present time the Society's Committee D-11 on Rubber Products is studying four portable hardness testers which are based on the specifications of the Standard Method of Test for Hardness of Rubber (D314-39), three of these being spring-operated instruments, the fourth, a dead-load type. In addition to the testers mentioned above, there is the Pusey-Jones Plastometer, which is a dead-weight hardness tester rather than a plastometer.
The Application of Latex to Highway and Floor Surfacing
Authors: Wren W. G.
Published: February 2011

Investigations on the development of latex mixtures for roadways were carried out in Malaya by Hastings during the period 1931 to 1933. Of the different mixtures tried, those containing aluminous cement gave the most promising results. Considerable progress of a practical character in working out the details of a suitable cement-latex mixture was then made, culminating in the laying in 1933 of an experimental section of road 4.5 miles from Kuala Lumpur on the Kuala Lumpur—Port Swettenham Road, where the traffic is fast and fairly heavy. In view of the promising results obtained in these experiments, it was agreed that the subject should be studied further in London, and that particular attention should be given to obtaining a better understanding of the fundamental principles involved in the preparation of latex mixtures for road and floor surfacing. As the economic factors are less exacting for flooring than for highways, it was decided that the application of latex mixtures to flooring should receive prior attention. The main purpose of the investigation has now been fulfilled, and this paper presents a summary of the work carried out and the results obtained. Mixtures of aluminous cement and latex have been in use for some time, both for flooring and other purposes; as early as 1923–4 patents were obtained for mixing cement with specially treated latex. The theory underlying this process is that the cement combines with the water of the latex and becomes hydrated, the latex losing its water and coagulating. How far this occurs in practice was not established at the outset of the work in London, and attempts were made to determine the extent of hydration of the cement and to examine the microstructure of the mixtures. During the course of this work it became apparent that the structure and physical characteristics of the products were largely dependent on the materials used in compounding and especially on the latex stabilizer. A systematic study of the principles underlying the compounding of the mixtures was then undertaken, and the relationship between compounding and physical properties determined. It thus became necessary to develop a series of tests to measure the physical properties, as no suitable methods were available. As a result of these experiments, a number of cement-latex compositions were developed and the most suitable selected for small scale trials. A summary of the work carried out and the conclusions reached are given in the following sections.
Influence of Moisture Content of Carbon Black on Rubber Properties
Authors: Cohan Leonard H. , Johnson C. R.
Published: February 2011

The moisture content of carbon black should be kept approximately constant if maximum accuracy in rubber testing is to be attained. In this laboratory we have found it convenient to equilibrate blacks at about 30 per cent humidity, under which condition most rubber channel blacks adsorb 1.5 to 2.0 per cent water. In the case of most of the properties of tread stocks, this precaution decreases the average deviation from the mean value in any series of experiments. In the case of extrusion tests, the effect of adsorbed moisture is so great that the use of a standard moisture content, or at least the determination of moisture content at the same time as the black is milled for extrusion, is necessary if reproducible results are to be expected.
Hydrodepolymerization of Rubber
Authors: Zelinsky N. D. , Rapoport J. B.
Published: February 2011

In a previous paper, one of the authors showed that the thermal decomposition of both natural and synthetic rubber proceeds easily and rapidly in the presence of aluminum chloride. The product so obtained is a mixture of hydrocarbons particularly rich in cyclic forms. One might, therefore, be led to believe that the polymerization of isoprene or butadiene, both in nature and under synthetic conditions, may be preceded by their dimeric or polymeric cyclization, with subsequent association of these unsaturated cyclic compounds, resulting in the formation of rubber. As a contribution to the knowledge of the chemical nature of highly polymeric substances such as rubber, we present here the results of our investigations on the depolymerization of rubber when subjected to hydrogen under high pressure in the presence of a catalyst. It was found that rubber, in the same way as oil or coal tar, is completely liquefied under such conditions. Experiments showed that, within the relatively short time of 1.5 to 2 hours, at a temperature of 400° C and a hydrogen pressure of 150 atmospheres, and in the presence of molybdenum sulfide or of nickel deposited on aluminum oxide, rubber is completely converted into a mobile liquid consisting of saturated and unsaturated hydrocarbons. The chemical nature of the resultant hydrocarbons casts light on the structure of rubber. It should be noted here that, in the absence of a catalyst, rubber cannot be converted into a mobile liquid when subjected to hydrogen under pressure.
A Manometric Test for Oxygen Absorption by Vulcanized Rubber
Authors: Johnson Robert H.
Published: February 2011

An apparatus can be set up in laboratory glassware that will confirm the results obtained by Dufraisse in his manometric test for oxygen absorption. It has been shown that different rubber compounds possess different tendencies to absorb oxygen. It has also been shown that the differences in the rate at which rubber compounds absorb oxygen are comparable with those differences found in the rate of tensile-strength deterioration of the same compounds aged in the oxygen bomb. This modified Dufraisse manometric method is convenient, efficient, accurate and, above all, a speedy method for measuring the relative aging behavior of vulcanized rubber compounds. Within two hours it is possible to have the results by this method, whereas it is necessary to wait from four days to two weeks for such information by the oxygen bomb method.
Industrial Progress in Synthetic Rubberlike Polymers
Authors: Cramer Howard I.
Published: February 2011

We may survey with some satisfaction the progress made in the development of synthetic rubber in the United States during the last decade. In this period four new types of synthetic elastic polymers have been developed: Neoprene, Thiokol, Koroseal, and Butyl Rubber. Extensive knowledge of the chemistry and engineering involved in the production of a large variety of types has been acquired. The plants in operation and under construction for the manufacture of these varied types are rapidly approaching such capacity as to justify the use of the expression “synthetic rubber industry”. True, it is an infant industry hardly out of the pilot-plant stage and far from ready to relieve the coolie in the Far East of his job; but it is growing rapidly, fed by a more than ample supply of cheap raw materials, and has already taken an important role in the defense program as a producer of vital war materials. Its growth is being stimulated at present by the emergency now facing the country, but it may be expected to continue to expand after the emergency is over because the synthetic rubbers as a group are outstandingly superior to natural rubber under certain severe service conditions.
Brittle Point of Rubber on Freezing
Authors: Selker M. L. , Winspear G. G. , Kemp A. R.
Published: February 2011

The need for a simple method of determining brittle points which would be adaptable to a large number of materials led the writers to develop the apparatus described below. There is presented here, for the first time, brittle point data on certain natural and synthetic rubber compositions. The study of the variation with temperature of the mechanical properties of elastomers is of immediate practical and theoretical interest. Recently Kistler attempted a correlation of temperature-strength data of polymers with their chemical structure. On the other hand, the increasing use of synthetic high polymers at low temperatures for insulation and mechanical purposes requires a more complete knowledge of their behavior under conditions of extreme cold. The determination of the brittle point offers a simple method for investigating the possible use of a new material at low temperatures. In 1928 Kohman and Peek described a method whereby a small strip of material at a known temperature was bent quickly through 90° by a hammer blow. They found that within rather wide limits the brittle temperature was independent of the sample dimensions and bending angle, but that a high rate of deformation was necessary for reproducible results. The brittle point was found to be definite and reproducible within ±2° C for the materials studied. Using this method, Kemp determined the brittle point range of crude and vulcanized rubber, balata, guttapercha, and paragutta.
Determination of Free Sulfur in Vulcanized Rubber
Authors: Mackay J. G. , Avons C. H. J.
Published: February 2011

The following comments pertain to a paper of the above title by Mackay and Avons, published in Transactions of the Institution of the Rubber Industry, Vol. 16, pages 117–122, October 1940, and reprinted in Rubber Chemistry and Technology, Vol. 14, pages 520–524, April 1941. H. P. Stevens draws attention to the penultimate paragraph on p. 522 in which it is pointed out that the bromine method of oxidation is tedious and the reagent unhealthful, whereas perchloric acid may be dangerous. As a result of many years experience he is of the opinion that neither reagent is necessary. After adding nitric acid to the acetone extract in the flask, which should be covered with a watch glass, and when the reaction has subsided, about 0.5 gram of potassium chlorate is added and the mixture kept warm at 50 to 60° C. The top of a water oven is convenient; but the heating must be limited, as the yellow oxides of chlorine are rapidly driven off near 100°, and the liquid changes back from yellow to orange. The flask can be left to itself for an hour or two, but further addition of chlorate may be necessary to complete the oxidation. The contents are evaporated to dryness and taken up twice with concentrated hydrochloric acid preparatory to precipitation with barium chloride. A volumetric method may be preferable when a large number of routine tests have to be made, otherwise the final estimation can be made as barium sulfate.
Improved Semimicrodetermination of Sulfur in Organic Materials. Peroxide-Carbon Fusion Followed by a Titration Using Tetrahydroxyquinone Indicator
Authors: Mahoney John F. , Michell John H.
Published: February 2011

Sulfur combined in a variety of nonvolatile organic compounds was oxidized to inorganic sulfate by a sodium peroxide-carbon fusion, and the sulfate ion was estimated by titration with standard barium chloride solution, using tetrahydroxyquinone as an internal indicator. No special apparatus was required, and 0.5- to 5-mg. quantities of combined sulfur were determined with speed and accuracy. The method should be especially useful for the routine analysis of materials like oil or rubber, with modification, if necessary, to remove interfering ions, and is apparently general for all types of sulfur-containing substances, including sulfonic acid derivatives.
The Compounding of Guayule Rubbers. Effect of Accelerator-Curing Agent Combinations
Authors: Morris Ross E. , James Robert R. , Werkenthin Theodore A.
Published: February 2011

The accelerator-curing agent combinations in most cases have the same effect on the three guayule rubbers as they have on smoked sheet. No accelerator-curing agent combination produces smoked-sheet stocks or guayule stocks excelling in every property; each rubber must be specially compounded for the purpose in mind. The authors conclude from the test data reported above that stocks prepared from domestic deresinated guayule rubber do not show sufficient advantages over similar stocks prepared from domestic resiniferous guayule rubber to justify the extra expense involved in the preparation of the former rubber. On the other hand, stocks prepared from Mexican resiniferous guayule rubber are definitely of poorer quality than similar stocks prepared from the domestic products.
Effect of Petroleum Products on Neoprene Vulcanizates Effect of Gasolines
Authors: Fraser Donald F.
Published: February 2011

The third paper of this series2 showed that the Diesel index may be used as a criterion of the swelling effect of kerosenes and kerosene-benzene blends on Neoprene. It was erroneously stated, however, that “swelling caused by kerosene is not a simple function of the … aniline point”. A recheck of the data, together with additional work, indicates that the aniline point may be used as a criterion of the swelling power of kerosenes, but this correlation is not so precise as with the Diesel index. This is particularly true in the case of kerosene-benzene blends when benzene predominates in the blend. As with kerosenes, the aniline point or Diesel index may be used as an indication of the swelling power of gasolines, and thus these constants may be used to specify standard immersion media of these types.
Influence of Exposing Vulcanized Rubber to Light on Its Subsequent Aging in the Dark
Authors: Scott J. R.
Published: February 2011

The present experiments confirm the observations of Morgan and Naunton by showing that exposure of vulcanized rubber to light may affect the results of oxygen-bomb aging tests made some days, or perhaps even weeks, afterwards. They show also that a few days' exposure to even diffused daylight may noticeably lower the tensile strength of unaged rubber. With normal, i.e., not transparent, rubbers the effect of light on subsequent aging is small, and indeed does not seem to be noticeable at all in relatively slow aging tests, such as that in the Geer oven. Nevertheless, it is clearly advisable, as a precaution, to avoid unnecessary exposure to light of rubbers that are to be subjected to accelerated aging tests.
Brittle Points of Natural and Synthetic Rubber Stocks
Authors: Morris Ross E. , James Robert R. , Werkenthin Theodore A.
Published: February 2011

The slow-bend brittle point test does not have the same practical significance as the Bell Telephone Laboratories brittle point test because most rubber articles which are exposed to low temperatures in service are required to withstand fairly rapid flexing. If the slow-bend brittle point test were used as a criterion of the cold resistance of these rubber articles, it might qualify the rubbers for a lower temperature than they could safely withstand in service. The brittle point test developed by the Bell Telephone Laboratories is simple and sensitive. It is believed that this test may advantageously be used to study all cold resistance problems where damage to the rubber itself and not increase in stiffness is the first consideration.
Sulfur Linkage in Vulcanized Rubbers. I. Reaction of Methyl Iodide with Sulfur Compounds
Authors: Selker M. L. , Kemp A. R.
Published: February 2011

For many years the rubber chemist, in trying to explain the chemical nature of the vulcanization of rubber, was limited by two accepted theories: (1) Sulfur adds at the double bonds of the hydrocarbon, and (2) one atom of sulfur combines for each double bond saturated in the reaction. Therefore it was concluded that only one type of sulfur linkage would occur in vulcanizates. However, it was impossible on this basis to propose a hypothesis to account for all the facts. The few bits of direct evidence available have semed to support the theory of “one sulfur for each double bond saturated”. Since it is difficult to make any direct attack on this problem and since the art of vulcanization has far surpassed the science, it was not until 1938 that grave doubt was thrown on the generality of the “one sulfur atom per double bond saturated” theorem. The work of Brown and Hauser indicated that there were wide variations in the number of sulfur atoms combined for each double bond saturated, depending on the type of acceleration used. Four years later Thornhill and Smith pointed out that, in compounds containing reinforcing channel blacks, no loss of unsaturation could be detected on combination of sulfur during vulcanization. Thus the relation between sulfur combination and changes in unsaturation is at present obscure.
Heats of Vulcanization of Synthetic Rubbers
Authors: Bruce P. L. , Lyle R. , Blake J. T.
Published: February 2011

1. The heats of vulcanization for natural rubber and Buna-S are nearly equal. The data for both materials indicate two different chemical reactions during vulcanization. At low sulfur percentages, the principal reaction forms soft vulcanized rubber and is accompanied by little or no heat evolution. Above the 2 per cent sulfur region, a second reaction predominates, forming hard rubber and producing a relatively large quantity of heat. 2. The presence of an accelerator (Santocure) in Buna-S has little, if any, effect on heat of vulcanization. 3. The addition of carbon black to Buna-S lowers the heat of vulcanization in the region above 4 per cent sulfur. The calories evolved in a 10 per cent sulfur compound decrease linearly with percentage of carbon black. 4. The heats of vulcanization of Buna-N (Hycar OR-15) indicate the presence of two chemical reactions. Unlike natural rubber and Buna-S, the ebonite reaction does not predominate until the sulfur concentration is raised above 10 per cent. 5. The heat of vulcanization of Butyl rubber with sulfur is equal to the heat evolved with natural rubber containing 0.6 per cent sulfur. If one sulfur atom reacts per double bond, the maximum amount combining would be 0.72 per cent sulfur. During the vulcanization of Butyl rubber with p-quinone dioxime and lead peroxide, a large amount of heat is evolved by a side reaction between the vulcanizing agents. The reaction involving the Butyl rubber produces about 6 calories per gram, a considerably higher value than the 1 calorie produced by sulfur vulcanization. 6. The heat of vulcanization of Neoprene-GN without added agents corresponds to a value for smoked sheet rubber containing 4.5 per cent sulfur. The addition of zinc oxide and magnesia decreases the heat of vulcanization.
Effect of Low Temperatures on Young's Modulus of Elastomers
Authors: Liska John W.
Published: February 2011

The data presented should be of value to the rubber technologist who may be called on to produce a compound having a given base polymer capable of performing satisfactorily down to a specified low temperature. Although natural rubber is basically more cold-resistant than some of the other synthetic elastomers, it has been found possible to add larger quantities of softeners and modifiers to the latter (without causing too serious a decrease in mechanical properties) than can be added to natural rubber. Consequently, it is possible to compound synthetic elastomer stocks having better low-temperature properties than natural rubber stocks. In the case of material which does not exhibit crystallization, it should be possible (either from experience or by a simple test at normal temperatures) to set an upper limit for the Young's modulus of the proposed stock consistent with satisfactory operation. A modulus vs. temperature curve of the stock would then indicate definitely whether the observed modulus at the specified low temperature exceeded the limit previously set. If it did not and, in addition, the brittle-point temperature was found to be below the specified operating temperature, successful operation could reasonably be expected. In general, it is not necessary to calculate Young's modulus in all cases. For a given load and sample size, the deflection as measured would serve equally well as an index.
Tread Cracking of Natural and Synthetic Rubber Stocks
Authors: Prettyman Irven B.
Published: February 2011

The development of cracks in the base of the tread grooves of tires has long been recognized as a major factor governing their useful life. A number of laboratory tests have been employed in an effort to evaluate crack initiation and growth. Dumbbell strips, rings, and grooved blocks have been flexed through various tension cycles. Grooved belts and tire treads have been flexed by weaving over pulleys and thereby producing a cycle which involves both tension and compression. Tires themselves have been flexed under load on rotating drums. The strains which produce cracking along the length of a tire groove are complex. They occur on and near the surface in the base of the groove. For the purpose of this discussion, they are defined as the strains at right angles to the groove length and in the plane of the groove base. To devise a flexing machine which reproduces these strains qualitatively, one must consider the forces acting to produce them. The force acting upward on the ribs of the tire tread in the contact region bends the tread to an extent which is determined primarily by the load on the tire, the inflation pressure, the moulded tire shape, and the fabric structure. This bending is concentrated to a large extent in the groove base, with its magnitude substantially independent of the speed of the tire and of the tread stock used; and a compression strain of constant amplitude is produced. This upward force also deforms the ribs and thus contributes a slight additional compression strain of the constant force type. This produces little difference in the compression strain between different stocks, especially since all normal tire treads have moduli in the same general range. Compression strains of the order of 30 per cent have been found in the base of the grooves of passenger tires under static load by means of cement casts of the grooves in which wire brads were embedded as markers.
Emulsion Polymerization of Synthetic Rubber in 10-Gram Systems. An Experimental Technique
Authors: Fryling Charles F.
Published: February 2011

Many manufacturers of monomers, emulsifying agents, initiators, modifiers, and other ingredients going into polymerization reactions find it necessary to have a reliable polymerization procedure for testing the quality of their products. The procedure presented, despite some shortcomings, has many advantages. Minimum amounts of material are required, and large numbers of experiments can be conducted in a relatively short time. A serious effort is made to point out some of the pitfalls which beset investigators of polymerization, regardless of the type of technique employed. The best recommendation for the procedure described is that it has been used to develop certain types of synthetic rubber which are now in commercial production.
Use of the Shore Durometer for Measuring the Hardness of Synthetic and Natural Rubbers
Authors: Taylor Rolla H.
Published: February 2011

The manner in which the readings of the Shore durometer vary with time was studied for 16 different compounds of natural and synthetic rubbers. The data were obtained from motion pictures showing a durometer and a stop watch in the same field of view. To eliminate the personal factor, the durometer was mounted in a frame, and pressure was applied by dead-weight loading. The results indicate both the necessity and the practicability of specifying that measurements be taken at a definite time after the application of the durometer to the specimen. The results also indicate the possibility of using readings taken at two different times as a rough measure of the relative creep of different rubbers.
Artificial Latices
Authors: Madge E. W.
Published: February 2011

An artificial latex is usually understood to mean one prepared by the inversion of the solid plastic, and the main purpose of this paper is to consider latices of this type, although towards the end some attention is given to the synthetic latices. Given the right conditions of dispersion and the correct dispersing agents, satisfactory aqueous dispersions may be prepared from almost any plastic substance. In dispersion processes generally the material to be dispersed may occur as a liquid, as a solid, or as a plastic which is physically intermediate between the two. In all such processes machinery is required capable of inducing a shear at the point of dispersion. It is a relatively simple matter to prepare an aqueous dispersion of a liquid. The technician has at his disposal several types of high-speed colloid mills in which the liquid is subjected to high shearing forces in the presence of suitable colloids. For solids in hard homogeneous massive form, not merely present as aggregates of otherwise fine particles, grinding machinery is necessary. For the intermediate plastics, relatively heavy machinery capable of inducing shearing forces in the material itself is required. Consequently, if the plastic substance can be rendered fluid by solution in a suitable solvent, it can be dispersed by passage through some form of standard colloid mill. On the other hand, if it can be rendered friable by loading with large proportions of powder, it may be dispersed with the aid of some form of grinding machinery. Both methods were practised by the earlier investigators, and in both eases dispersions were obtained in which an undesirable ingredient was present in large quantities. The solvent could, of course, be distilled off, but its use and recovery was an unnecessary expense and the final dispersion was not always controllable as regards stability.
Stress Relaxation of Natural and Synthetic Rubber Stocks
Authors: Tobolsky A. V. , Prettyman I. B. , Dillon J. H.
Published: February 2011

1. The complete decay of stress in the rubbers studied, held at constant elongation, appeared to involve the rupturing of a definite bond, either at some point along the molecular chain or at the cross-linking bond put in by vulcanization. In the case of a Hevea rubber gum stock the data could be fitted very well by ordinary reaction-rate theory, leading to the conclusion that the free energy of activation required for breaking the bond is 30.4 kcal. per mole of bonds. This result was found to be practically independent of the elongation, and of the presence of carbon black in a Hevea rubber tread stock. This is to be compared to a strength of about 90 kcal. per mole for the C—C bond. 2. In the case of other rubbers (Buna-S, Butaprene-N, Neoprene-GN, and Butyl) the activation free energy for breaking the bond did not vary by more than ±2.0 kcal. per mole from that of Hevea rubber. However, these differences were quite definite. For example, the relaxation of stress in GR-S was slower than in Hevea; a small difference in energy corresponding to a 2:1 ratio in the respective times of decay. 3. The effect of temperature on the relaxation of stress appeared to be of the general type characteristic of chemical reactions. By use of the ordinary formula for expressing rate of reaction in terms of energy of activation, one could predict very closely the behavior of the stress-log time curves at different temperatures. 4. Natural rubber and GR-S vulcanized with paraquinone dioxime and lead dioxide showed relaxation curves very similar to those of the sulfur vulcanized stocks. 5. Relaxation experiments in an ordinary air atmosphere and in an atmosphere of commercial nitrogen showed no appreciable differences. 6. Examination of stretched rubber bands in which the stress had decayed nearly completely (at 100° C) gave no evidences of gross oxidation, such as would make the rubber bands sticky or hard, or of surface deterioration. At higher temperatures, however, the rubber could be observed getting sticky, and then brittle. Specimens in which the stress had completely decayed showed very low tensile strength (by hand test). 7. Antioxidant added to a sulfur-stabilized Buna-S stock caused a definite retardation of the rate of relaxation. 8. Comparison of the results of these experiments with previously recorded observations in the literature indicated that the chemical reaction which ruptured the rubber structure and caused the decay of stress in these experiments (and concomitantly a lowering of tensile strength) was an oxidation of the rubber by small amounts of oxygen, the reaction rate being independent of the oxygen pressure in the range between that present in an ordinary air atmosphere and in a commercial nitrogen atmosphere. 9. The tests suggested a convenient and accurate laboratory method of determining the oxidizability of natural and synthetic rubber stock designed for service.
Hysteretic and Elastic Properties of Rubberlike Materials under Dynamic Shear Stresses
Authors: Dillon J. H. , Prettyman I. B. , Hall G. L.
Published: February 2011

The principal problem of the rubber technologist and engineer today is that of applying the various types of synthetic rubber to products which undergo rapid repeated flexure. All commercially available synthetic rubbers possess a greater hysteresis defect than does natural rubber. Hence, the task of designing a product such as a large truck tire, where heat development has been no small problem even with natural rubber, is much more difficult. Consequently, the accompanying problem of evaluating the hysteretic properties of rubberlike materials has assumed new importance.
Unsaturation of Polyisobutylenes and Butyl Rubber. Reactions with Nitrosobenzene, Thiocyanogen, Iodine Monochloride, and Ozone
Authors: Rehner John
Published: February 2011

Table III summarizes unsaturation values obtained for the various polymers. The ranges indicated are, in most cases, extreme values of determinations made with two or more different samples of a given polymer type. Taking into consideration the small amounts of unsaturation involved, the values based on end-group determinations are in reasonably good agreement with one another and with the values based on the viscosity of the degraded polymer. Higher values are observed for the nitrosobenzene determinations, but these are considered to be less reliable because of the ease with which oxidation phenomena can occur with this reagent. The thiocyanogen values are the lowest of all; on the basis of values obtained by the other methods as well as of experimental evidence not included in this paper, these values are believed to result from incomplete reaction. As a class the iodine monochloride methods give considerably higher values than those obtained with the other reagents. This may be attributed to the substitution reaction that readily occurs with that reagent. The effect is perhaps most marked in the data obtained for polyisobutylene sample 2 with 0.1 N Wijs reagent; the upper value (0.4) is far greater than can be explained on the basis of the knowa molecular weight of this polymer and the corresponding terminal double bond contribution. Furthermore, since this polymer sample was fractionated in such a way as to remove all species of viscosity-average molecular weight less than about 50,000, the high value cannot be ascribed to the presence of dimers, trimers, or other small molecules formed during polymerization. In view of the data and the above considerations, it is believed that the unsaturation values based on ozone degradation are correct within the limits of experimental error, and that this reagent makes possible a relatively good estimation of the number of double bonds in polymers such as have been described. A modified procedure more suitable for rapid evaluations is the object of a current investigation.
Solubility and Diffusion of Sulfur in Synthetic Elastomers
Authors: Kemp A. R. , Malm F. S. , Stiratelli B.
Published: February 2011

1. The rate of solution of sulfur in various elastomers during milling depends on the temperature of the elastomer, the solubility and rate of diffusion of sulfur in the elastomer, the particle size and type of sulfur used, and the degree of breakdown of the elastomer. 2. The relative heat build-up on the mill rolls for each elastomer after 30-minute milling increases in the order: natural crepe rubber, Butyl, Buna-S, Neoprene-GN, Perbunan, Hycar OR-15. Conclusions as to extent of cross-linkage, mutual attraction of the chain molecules, and plasticity are indicated from data of this type. 3. The solubility of sulfur in the several elastomers increases with the degree of mastication, as shown in the cases of natural crepe and Buna-S, until a limiting value is obtained. 4. The specific diffusion rate of sulfur through various elastomers was determined. These rates of diffusion decrease in the following order: natural crepe rubber, Buna-S (GR-S), Hycar OR-15, Butyl B-3. 5. In synthetic elastomers the change in sulfur solubility with increase in temperature is greater than in natural rubber, the solubility is less at room temperature, and the rates of diffusion are slower; therefore the possibilities of heterogeneous vulcanization with these elastomers are increased.
Experiments on Synthetic Rubbers of the Butadiene Type. II. Mechanical and Electrical Properties of Buna Ebonites
Authors: Scott J. R.
Published: February 2011

The experiments described here were designed to examine the properties of ebonites made from various kinds of Buna synthetic rubber, including Buna-85, Buna-115, Buna-S and Buna-N. All Bunas are said to form ebonites by vulcanization with the normal amount of sulfur, Buna-85 and Buna-115 giving the best products. The resulting ebonites are stated to have much higher plastic yield temperatures than ordinary ebonite, figures quoted ranging from 100° to 175° C by the Martens test, compared with 70° to 90° C for natural-rubber ebonites. It may be added that Russian butadiene rubber likewise is claimed to give ebonites with much higher yield temperatures, namely, up to 160° C by a Vicat needle test, than ordinary ebonites, which give about 93° C. On the other hand, Buna ebonites are relatively brittle. The electrical properties of these ebonites are said to be good, and in this connection it should be noted that soft vulcanizates made from Buna-85 and Buna-115 have lower power factors than those made from natural rubber. Buna ebonites are more resistant than ordinary ebonite to attack by chemicals and to the swelling action of liquids such as benzene and nitrobenzene. The present report deals with certain properties of Buna ebonites, viz., plastic yield, cross-breaking strength, impact strength, radio-frequency permittivity and power factor.
A New Extrusion Plastometer
Authors: Schultz H. A. , Bryant R. C.
Published: February 2011

Early studies of the processing characteristics of synthetic rubber (GR-S) indicated that it would be desirable to have a laboratory test to determine whether satisfactory tread slabs could be produced from a given batch of tread stock by extrusion through a plate die. In the factory, the material is extruded as a continuous slab, flat on one side and shaped on the other. The extruding material is put under tension and carried away by a moving belt. Since the central portion of the slab, which will eventually become the tire tread, is thicker than the adjoining sidewall portions, it is extruded at a greater rate. Therefore, tensile stresses are set up in the sidewalls after the stock leaves the die. The material either flows to relieve these stresses or it tears. Preliminary work indicated that common methods of measuring plasticity were not adequate to measure or predict the tendency of certain stocks to tear in the sidewalls. Therefore, it was decided to develop a test which should reproduce the essential features of factory extrusion in miniature and under close control. This was accomplished in a new extrusion plastometer by the use of special dies and of a device to apply tension to the extruding sample.
Determination of Brittle Point of Rubber Materials in Cold Air
Authors: Chatten C. K. , Eller S. A. , Werkenthin T. A.
Published: February 2011

The method described herein for determining brittle point is relatively simple, and the results are indicative of the ability of the material to withstand impact combined with bending. It is believed that this combination will more correctly evaluate brittle point than a bent loop test or other moderate flexing tests. If the material is exposed to low ambient air temperatures in service, then tests to determine brittle point should be made in cold air and not in an immersion bath. Appreciable differences in brittle point are obtained by judicious modifications in compounding ingredients of Buna-N and chloroprene synthetic rubbers.
Errors Arising in the Pendulum Test for Resilience of Rubber
Authors: Bulgin D.
Published: February 2011

The resilience of rubber is usually measured by a rebound test, and an accurate instrument for this purpose is the rebound pendulum. This instrument consists of a compound pendulum with a steel ball, fixed at the center of percussion, which strikes a rubber sample held in a suitable holder. The pendulum is released from a known angle, and the rebound angle is measured. The ratio of energy of rebound to energy of fall is the resilience value of the rubber. The distance the ball indents the rubber also can be measured, and under certain defined conditions can be used to determine the hardness of the rubber. An account of the pendulum used by the Dunlop Rubber Co., Ltd., is given by Jones and Pearce, and descriptions of similar instruments derived from the Fort Dunlop pendulum and used by American manufacturers are given in various publications. The instrument is capable of a high degree of accuracy, and angles can be read to 3 minutes of arc or less, giving a maximum error due to this cause on one reading of 1 part in 500. The purpose of this paper is to describe certain refinements in the technique of using the pendulum to improve the precision of the instrument. It is essential that the mechanical construction of the instrument, particularly the rigidity of the pendulum and its supporting column and the location of the striking ball at the center of percussion, shall be precise.
The Statistical Length of Rubber Molecules
Authors: Treloar L. R. G.
Published: February 2011

The paper applies the methods worked out for the determination of the statistical lengths of paraffin chains to the more complex problem of the rubber molecule. Distribution functions covering lengths up to 98 per cent of the fully extended length are given for chains corresponding to molecular weights up to 17,400.
Natural and Synthetic Rubber Fibers. Electron Microscope Studies
Authors: Hall C. E. , Hauser E. A. , leBeau D. S. , Schmitt F. O. , Talalay P.
Published: February 2011

Hevea rubber fibers suitable for observation in the electron microscope were prepared from thin films produced by spreading rubber solutions and dispersions on a water surface. Fibers of guayule, Cryptostegia, Neoprene, and Buna-S were prepared in a similar manner and studied with the electron microscope. Unvulcanized Hevea rubber was separated into sol and gel fractions. Electron micrographs of the sol fraction show fibers bearing many large nodules along their lengths. The spherical shape of many of the nodules is strongly suggestive of fluid properties. The gel fraction shows practically no nodules, but tends to form closely branched networks. The smallest fibers have a characteristically beaded appearance which may be related to the state of aggregation of the isoprene chains. When pale crepe or smoked sheet is worked on the mill, cross-linked networks of the gel fraction disappear, and the milled material takes on the appearance typical of the sol. Vulcanization of milled rubber in solution has the effect of producing cross-linked networks of fine fibers similar to those from the gel fraction. Unvulcanized and vulcanized compounds containing carbon black were examined. From the location and distribution of the carbon in rubber particles, films, and fibers, suggestions are offered concerning the nature of the reënforcement phenomena.
Factors Influencing the Plasticity and Recovery of GR-S
Authors: Neal Arthur M. , Ottenhoff Pieter
Published: February 2011

One of the vital problems connected with the successful conversion from natural rubber to GR-S is the availability of the industry to mill and otherwise process this elastomer. When the polymer was first introduced, reports indicated at least twice as much equipment would be required to handle GR-S as to handle an equal volume of natural rubber. As the production of GR-S has increased, the product has become more uniform and less difficult to handle; it is now estimated that the processing of GR-S will not require more than 10 per cent more equipment than natural rubber. In spite of this improvement the problem of processing GR-S is still important. One of the fundamental difficulties is due to the lack of correlation between laboratory tests and factory processability. Vila showed that there is no relation between the Mooney plasticity and tubing speed, regardless of whether the basis is the plasticity of the compounded stock or of the uncompounded polymer used in the stock. Sturgis and Vincent showed that there is no correlation between the milling characteristics of the raw polymer and plasticity, whether measured by Mooney plastometer, Williams parallel-plate plastometer, or the Williams pendulum plastometer. This apparent lack of correlation between plasticity and processability is difficult to understand. The present work was undertaken to determine whether a study of the changes which take place under various conditions of milling would give information that would explain this anomaly.
Processing Behavior of High Polymers. Correlation with Elastic-Plastic Properties
Authors: Zapp R. L. , Gessler A. M.
Published: February 2011

The difficulties in correlating the processing behavior of synthetic high polymers with results obtained by standard plasticity methods indicate that present methods do not completely evaluate polymer differences. A connecting knowledge between processing qualities and molecular structure would be of increasing value, not only as an aid to process control, but also as a possible guide to polymerization research. Observations on the elastic-plastic properties of high polymers seem to indicate some molecular differences that govern processing behavior. Williams stated that, if one grade of rubber is considered, elastic strain is a function of resistance to flow. When different types of rubber or other materials are considered, the relation between plasticity and elastic strain does not remain constant. The purpose of this paper is to present some of the factors involved in carrying on further study of the plasticity, processing, and molecular structure correlation.
Cellular Rubbers
Authors: Gould Louis P.
Published: February 2011

This paper has presented a report on the progress which has been made in the cellular rubber field during the past several years; now a few words about the future. It is said that Russia has seventeen kinds of Buna-S. At present the United States has only one kind, namely, GR-S. Of course, this country does have several types of Buna-N and several types of Neoprene. Possibly the day will come when there will be available one or more types of both solid and liquid synthetic rubbers made specifically for the manufacture of cellular rubber products. In the past, many production difficulties in this field have been due to variation in the plasticity and in the rate of cure of different lots of natural rubbers, and to variation in the stability and rate of cure of different shipments of natural rubber latices. These difficulties may well be overcome in the synthetic rubbers of tomorrow.