bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sulfur Linkage in Vulcanized Rubbers. I. Reaction of Methyl Iodide with Sulfur Compounds
Authors: Selker M. L. , Kemp A. R. 
Published: February 2011

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.