bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Mechanism of Vulcanization and the Action of Accelerators
Authors: Dogadkin B. A. 
Published: February 2011

Abstract
Vulcanization of rubber is due to the formation of chemical interlinks between molecular chains of rubber. A number of investigators maintain that formation of these bonds is due to reactions of radical character. In the present paper data are presented which were obtained during the study of reactions in which elementary sulfur is liberated at room temperature. As a prototype of such reaction is the interaction of hydrogen sulfide and SO2 which in rubber causes the socalled Peachey vulcanization. The usual views on the mechanism of this process are that the activity of sulfur liberated in statu nascendi is high enough to enable it to react with rubber and to create the spatial structure of the vulcanizate. However, this is an error. We have shown that pure sodium-butadiene rubber, heated to 80° in nitrogen atmosphere, does not vulcanize by the Peachey procedure, e.g., it does not become insoluble and its modulus of elasticity does not reach finite values. Consequently, the reaction causing the vulcanizing effect has a more complex character. To elucidate the mechanism of vulcanization we have studied the reaction of benzothiazolyl disulfide (MBTS) with hydrogen sulfide. In a hydrocarbon medium these compounds react at room temperature forming quantitatively elementary sulfur and mercaptobenzothiazole (MBT). Kinetics of this reaction are shown in Figure 1. If this reaction is carried out in a 10% solution of sodium-butadiene rubber, then the sulfur adds to the rubber, but vulcanization as characterized by formation of a spatial structure does not occur. The rubber solution is not gelatinized. An analogous phenomenon is observed during interaction of benzoyl peroxide with hydrogen sulfide. Sulfur liberated in this reaction also does not cause crosslinking (vulcanization of rubber).
Effect of Mercaptobenzothiazole on Rubber Structure during Oxidation, Heating and Milling
Authors: Dogadkin B. , Dobromyslova A. , Sapozhkova L. , Tutorskiĭ I. 
Published: February 2011

Abstract
1. Mercaptobenzothiazole (MBT) accelerates the oxidation of natural rubber and considerably increases the rate of its oxidative degradation. 2. When benzene solutions of natural rubber are heated in an inert gas atmosphere at 100°, no irreversible changes occur in the rubber whether in presence or in absence of MBT. 3. Plasticization of natural rubber in air at 100–150° is intensified in presence of MBT, which is caused mainly by the accelerating action of the latter on the oxidative degradation of rubber. 4. Mercaptobenzothiazole assists plasticization of rubber at low temperatures in an inert gas atmosphere. MBT is consumed in the process, owing to its interaction with the polymeric radicals formed by mechanical rupture of the rubber molecules. 5. The amount of MBT reacting with the rubber increases with increasing contents of 1, 4 structure in the rubber molecules. 6. It is shown that different fractions of the masticated product contain different amounts of MBT, indicating that MBT reacts preferentially with the end valencies of the radicals formed by cleavage of diallyl bonds. 7. Reaction schemes for the interaction of MBT with rubber in mechanical and oxidative processes are suggested.
Vulcanization of Hard Rubber
Authors: Kuzminskiĭ A. S. , Borkova L. V. 
Published: February 2011

Abstract
1. It has been established that a hard rubber at optimum vulcanization is an unsaturated compound. 2. The decomposition rate of double bonds and the limit of the decrease in unsaturation are independent of the amount of sulfur initially dispersed in the rubber, since the vulcanization proceeds with practically a constant concentration of dissolved sulfur. 3. It has been found that in the process of hard rubber vulcanization a tendency toward the formation and decomposition of sulfur crosslinks appears. The higher the vulcanization temperature the greater the rate of crosslink decomposition. 4. It has been shown that polysulfide links are formed in the early stages of hard rubber vulcanization. In the subsequent vulcanization process their polysulfide chain length decreases through the decomposition of such links, and a hard rubber at optimum vulcanization retains only the monosulfide and disulfide bonds. 5. It has been established that in hard rubbers the forces of intermolecular interaction are increased sharply by the formation of a dense spatial network, which increase is revealed externally by the transition of the material from a viscous-elastic to a glasslike state. (a) This transition in hard rubbers is accompanied by changes in a whole complex of mechanical properties. (b) As the network density of a hard rubber increases its glass transition temperature Tg is shifted to higher temperature regions. 6. It has been shown that hard rubber flows under a load at temperatures of 150– 170° C because of the decomposition of the sulfur links which form its spatial structure. Flow is a specific property of sulfur vulcanizates only. 7. It has been established that in thermal hard rubbers, soft rubber vulcanizates and raw rubbers an intensive spatial structure formation develops at temperatures of 150– 170° C. Structure formation cannot occur in sulfur vulcanizates because of the inhibiting action of the sulfur liberated by the decomposition of the sulfur bonds.
The Kinetics of the Reaction of Organic Sulfides with Methyl Iodide. I
Authors: Scheele Walter , Triebel Wolfgang 
Published: February 2011

Abstract
The reaction of organic sulfides with methyl iodide was subjected to more thorough investigation from a kinetic standpoint. The results were as follows: Both the bimolecular-reacting dialkyl monosulfides and dimethyl disulfide are converted in a methanol solution and in the presence of a great excess of methyl iodide, according to the 1st order to the corresponding sulfonium iodide. The disulfide reacts much more slowly than the monosulfides. Diallyl monosulfide as well as methyl allyl monosulfide react under these conditions with methyl iodide in a wide conversion range, according to the 1st order law. Yet, in the case of diallyl monosulfide at the beginning, and methyl allyl monosulfide at the end of the reaction, deviations from the 1st order law are observed. Activation energies were computed from the temperature functions of the 1st order rate constants. Higher values are obtained with diallyl monosulfide and dimethyl disulfide than with either the dialkyl monosulfides or methyl allyl monosulfide. An accurate method for determining the sulfonium iodide formed was worked out and reported. The results obtained in these investigations are intended to furnish the basis for experiments to be used in the analysis of crosslinking sites in vulcanizates. Our experiments will therefore continue in this direction.
Sound Propagation in Plates and Rods of Elastomeric Materials
Authors: Naake H. J. , Tamm K. 
Published: February 2011

Abstract
The known results for the propagation of sound in plates with Poisson's constant σ=0.5 (liquids) and σ=0.35 (aluminum) are completed by dispersion curves with σ=0.47 (rubber). The dispersion curves are easily understandable because of the large difference between the velocities of transverse and longitudinal waves occurring at this value of σ. Measurements of the propagation of elastic waves in rods of rubber with square cross section in the frequency range 0.1 to 300 kc/s are reported. The amplitude is measured as a function of distance by partly submerging the rod into a waterfilled vessel within which a hydrophone is arranged. The results with respect to phase velocity and attenuation can be explained in terms of the propagation of extensional waves at low frequencies and compressional waves at high frequencies separated by a range with high attenuation.
Oxidation-Reduction Systems for Initiation of Radical Processes. VI. Systems Involving Oxygen for Initiation of Oxidative Degradation of Polymers
Authors: Tinyakova E. I. , Dolgoplosk B. A. , Reĭkh V. N. 
Published: February 2011

Abstract
1. The mechanism of action of various oxidation-reduction systems containing organic reducing agents, iron salts, and oxygen, is investigated, and it is shown that in hydrocarbon media these systems are an effective source of free radicals at low temperatures. 2. The possibility of utilization of these systems for initiation of a chain process of oxidative degradation of unsaturated and some saturated polymers, at low temperatures, is shown.
Ozone Attack on Rubber Vulcanizates
Authors: Buckley D. J. , Robison S. B. 
Published: February 2011

Abstract
The effect of the attack of ozone on rubber vulcanizates is well known in a qualitative way. Only recently have efforts been made to study this problem quantitatively. Because of this the state of knowledge on this subject is not so satisfactory as that obtained for ordinary oxidation. A quantitative study of the rate and extent of the reaction of ozone with rubber vulcanizates and the cracking under strain is discussed herein. The general knowledge on this subject tells us that ozone attack results in the cracking of the surface of vulcanizates. Cracking occurs only when the specimen is under some strain during exposure to ozone. The broad quantitative problem then becomes one of defining the factors controlling the reaction while the specific problem relating to cracking becomes one of measuring such crack generation and crack growth in vulcanizates under strain. The method used in this work may be described as follows. A sample is stretched and allowed to relax until most of the pertinent stress relaxation has taken place. Ozone is then admitted to the stretched and relaxed sample. As cracking occurs the stress in the sample decreases and the length increases. The effect of the ozone produced cracks may be considered as related to change in form of work. The initial work done on the sample by stretching is derived from an equation expressing the network-statistical theory of rubber elasticity. The cracking is considered as a transformation of work to form new surface.
Oxidative Decomposition of the Ozonide of Butadiene Rubber
Authors: Yakubchik A. I. , Kasatkina N. G. , Demidova G. I. , Fedorova G. B. 
Published: February 2011

Abstract
1. Among the products of oxidative decomposition with acetyl hydroperoxide of the ozonide of butadiene rubber (prepared at 5°) are levulinic, formic, succinic, 1,2,4-butanetricarboxylic, 1,2,3-propanetricarboxylic and l,x,y,6-hexanetetracarboxylic acids. Levulinic acid could be formed by isomerization of 1,4-1)2-1,4-chains of the rubber macromolecule and by partial decarboxylation of β-ketoadipic acid, as well as by the peroxy-formate rearrangement in presence of acetyl hydroperoxide. 1,2,3-Propanetricarboxylic acid is more likely to be formed from 1,4-1,4-chains branched at the α -methylene group, or from 1,4-1,2-1,4-chains in which the double bonds had undergone suitable rearrangement, rather than as a result of secondary reactions during oxidative breakdown of the ozonide. 1,2,3-Propanetricarboxylic acid was also detected among the products of ozonolysis obtained under mild conditions of breakdown. 2. Products of oxidative breakdown of the ozonide of the rubber in question with hydrogen peroxide were acetic, formic, succinic, 1,2,4-butanetricarboxylic, 1,2,3-propanetricarboxylic and 1,x,y,6-hexanetetracarboxylic acids. Acetic acid could have been formed from 1,4-1,4-portions of the rubber molecule branched at the α -methylene group, as well as from isomerized 1,4-1,2-1,4-portions.
The Hot Mixing of Rubber. I. Influence of Mixing Conditions on Scorching and on the Physical Properties of the Vulcanizates
Authors: Fromandi G. , Reissinger S. 
Published: February 2011

Abstract
In this work, it is shown that the special characteristics of sulfenamides must be taken into consideration so that the assurance in the processing of rubber compounds in which these reagents are used as accelerators may not be impaired. At higher temperatures the sulfenamides are split into equimolar proportions of 2-mercaptobenzothiazole and amine. This is a combination, which depending on the components and their amounts, makes an especially active accelerator system. The thermal pretreatment of rubber compounds which contains sulfenamides must be so controlled that the decomposition temperature of these accelerators, which depends among other things also on the compounding ingredients, is not prematurely exceeded.
Carboxylic Rubbers. II. Properties of Cured Stocks
Authors: Dolgoplosk B. A. , Reĭkh V. N. , Tinyakova E. I. , Kalaus A. E. , Koryushenko Z. A. , Sladkevich E. G. 
Published: February 2011

Abstract
The experimental evidence shows that the mechanical and elastic properties of the carboxylic rubber compounds far exceed those of the synthetic rubber type compounds. Important qualities of gum and lightly filled carboxylic rubber compounds are: good mechanical and elastic properties, high cut growth resistance and good resistance to heat aging. The disadvantage is the tendency of the carboxylic rubber mixtures to scorch. Carboxylic rubbers are of considerable interest for the preparation of general and special purpose rubber compounds.
Dependence of Tack Strength on Molecular Properties
Authors: Forbes W. G. , McLeod L. A. 
Published: February 2011

Abstract
A method has been developed for the measurement of the tack strength of fresh and reproducibly smooth rubber surfaces. Using this method the tack strength of natural rubber is shown to be independent of polymer purity, and, to a large extent, Mooney viscosity, intrinsic viscosity, gel content and molecular weight distribution. The relative tack strengths of polyisoprenes of different molecular weights prepared in different catalyst systems are measured. The results are discussed in terms of microstructure. A study of the tack strength of oil-extended butadiene-styrene copolymers indicates that relative tack strength is related to the shear viscosity of the bulk polymer. Measurements of relative tack strength on Alfin and free radical butadiene-styrene copolymers, butyl, brominated butyl and butadiene-acrylonitrile copolymers confirm the inportance of shear viscosity in controlling tack strength. Choice of catalyst system and temperature of polymerization cause the largest variation in polymer viscosity. The contact time required for the relative tack strength to become unity is shown to be inversely dependent upon the value of the relative tack strength itself. Shear viscosity measurements are given for six classes of polymer and the values shown to correlate with relative tack strength. It is postulated that molecular weight (and probably also chain entanglement) is the controlling variable. The bond strength between two different uncured polymers is shown to depend upon the difference in cohesive energy densities of the two polymers.
The Reactions of Isocyanates and Isocyanate Derivatives at Elevated Temperatures
Authors: Saunders J. H. 
Published: February 2011

Abstract
Qualitative and quantitative studies with model compounds have shown that a variety of reactions may occur at 100–300° in molecules containing isocyanate, urea and urethane groups. All or most of these reactions are subject to catalysis so that they may be induced to proceed at lower temperatures. These reactions are quite important as they may affect the production and practical use of polyurethanes and polyureas. By the proper selection of reaction components one may design a polyurethane or polyurea molecule which will give both a reasonable rate of cure to the final state and a degree of temperature stability suitable for many rigorous applications. The choice of reactive groups providing approximately the desired rates of reaction and of suitable catalysts may be used to achieve the necessary curing rate. The initial choice of a catalyst which will have a minimum effect on decomposition reactions, or the removal of the catalyst from the cured polymer will favor polymer stability. A selection of reactants which will minimize those decomposition reactions leading to chain rupture, and which will compensate for what rupture may occur, will promote polymer stability. Simple illustrations of such choices would include eliminating tertiary aliphatic hydroxyl groups from the hydroxyl-bearing component and including some degree of branching commensurate with the degree of elasticity or rigidity desired. Branching should be achieved through the more stable groups, e.g., urethane, urea or trimer, rather than through the less stable allophanate and biuret groups. Many thoroughly tested applications of polyurethanes and mixed polyureaurethanes show that it is readily possible to produce such polymers with excellent thermal stability.
Quantitative Measurement of Rate of Ozone Cracking
Authors: Veith A. G. 
Published: February 2011

Abstract
For reliable ozone testing a controlled ozone atmosphere is a necessity. There is a movement under way to correct the deficiencies of the ASTM Method D 1149-55T. These deficiencies are (a) the lack of a sufficient air throughput rate and circulation in the presently specified chamber and (b) difficulties encountered in the analysis of ozone. A new chamber and counter-current ozone absorption column that avoid the above-mentioned shortcomings are described. As part of a program to obtain basic information on the phenomenon of ozone cracking, some preliminary results on the ozone-induced creep of gum vulcanizates are reported. The creep rate has been expressed in terms of the initial rate of cross-sectional area decrease due to ozone cracking. This rate is a measure of the collective growth of ozone cracks. Induction periods during which no creep occurs have been observed. The geometry of the test specimen is an important variable. An “absolute” rate of cross-sectional area decrease can be otained independent of specimen geometry. For practical reasons an approximate “absolute” rate is used where specimen geometry is maintained essentially constant. The rate of cross-sectional area decrease is linearly related to the reciprocal degree of orientation of the network chains (λ0F)−1. The logarithm of the induction period is also linear with (λ0F)−1. Explanations for this particular dependence are offered. The rate of crack growth and the induction period for a series of common polymers were measured. Both parameters placed the polymers in the order that experience would indicate and lend confidence to the creep technique.
Chemical Antiozonants and Factors Affecting Their Utility
Authors: Cox William L. 
Published: February 2011

Abstract
To obtain the maximum effectiveness from antiozonants such as the N,N′-dioctyl-p-phenylenediamines in any given stock, information to date indicates the desirability of: (a) The selection of proper antiozonant-polymer combination. (b) The use of low-oxygen-content reinforcing blacks (thermal or furnace rather than channel). (c) The use of a thiazole-accelerated sulfur cure. (d) The proper design of product to avoid cured-in strain and sharp edges. The choice of antiozonant concentration will depend in part on strain, ozone concentration, and temperature to be encountered in service, as well as the type of service—static or dynamic—and the desired crack-free life of the article. Only through a consideration of all these factors can the maximum results from chemical antiozonants be achieved.
Prevention of Ozone Attack on Rubber by Use of Waxes
Authors: Ferris S. W. , Kurtz S. S. , Sweely J. S. 
Published: February 2011

Abstract
The tendency for stretched rubber, when subjected to outdoor exposure, to form cracks perpendicular to the direction of stress was originally known as suncracking. The work of Newton showed that light was not necessary and identified ozone as the causative agent. That ozone is the principal factor there seems to be no doubt, but we cannot assert that it is the sole factor. Some test specimens, for example, have been found to crack in the shade, but not in the sun, and some investigators suspect that certain atmospheric pollutants may have a modifying effect. It has been known since 1881 that addition of wax to the rubber compound will provide protection against this type cracking. Garvey and Emmett found that oils or oil-like materials would also effect improvement, but by far the major portion of work has been done with petroleum waxes. The two broad classes of petroleum waxes are paraffin and microcrystalline. The value of the literature—and this applies to many fields other than ozone cracking—is sharply limited by the tendency to characterize waxes as either paraffin wax or microcrystalline wax. As a matter of fact, the composition of petroleum waxes is complex, so that there are large differences in composition between different paraffin waxes and different microcrystalline waxes, with resultant differences in their performance when added to rubber.
Stress-Strain Relation in Rubber Blocks under Compression. I
Authors: Schay Géza , Ször Péter 
Published: February 2011

Abstract
For the stress-strain relation of differently shaped rubber blocks submitted to compression, an equation of general applicability is deduced, starting from the idea that compression work must be done also against the tension arising through the increase of the free surface. In this equation the stress is not a function of the compression ratio only, but of the ratio of the fixed to the free surface as well. Besides the shear modulus of the block's substance, this equation involves a single empirical constant which changes only slightly with the shape of the block's cross section. The validity of the equation obtained was tested by measurements performed by the authors on cylinders as well as by data on quadratic prisms published in previous literature. The calculated values are in good agreement with the experimental data within the limits of experimental error.
Measurement of the Isothermal Volume Dilation Accompanying the Unilateral Extension of Rubber
Authors: Hewitt Fred G. , Anthony Robert L. 
Published: February 2011

Abstract
The fractional increase in volume accompanying the isothermal extension of soft gum rubber was measured for four rubber samples at mean extensions of 14, 33, and 51%. The chain molecular weights Mc of the four samples were 5500, 5100, 4400, and 3000, with an estimated uncertainty of about 10% in each value of Mc. The observed fractional increase in volume ranged from 3.2×10−5 to 142×10−5, the latter value being observed for the sample of lowest chain molecular weight and at the extension of 51%. The experimental results for each sample have been represented by theoretical curves based on Gee's expression for the fractional increase in volume as a function of the sample extension. The theoretical curves exhibit good agreement with those of Gee, Stern, and Treloar. The process of fitting the theoretical curves to the experimental points constituted a determination of Young's modulus E for each rubber specimen. As a check on the experimental results, and also on the theory employed, determinations of E were also made by two additional methods, namely, from rough stess-strain curves, and from the relation E=3γρRT/Mc. With one exception, the internal agreement between the three determinations of E for the four different samples was satisfactory. The exception noted can probably be ascribed to the use of too small a value of Mc for the sample of lowest chain molecular weight.