bluuebunny/crossref_metadata_2025_split huggingface dataset:
Odd Electrons in Rubber Reinforcing Carbon Blacks
Authors: Kraus Gerard , Collins R. L. 
Published: February 2011

Abstract
The number of unpaired electrons in several rubber-reinforcing blacks has been determined by quantitative electron spin resonance assay. The odd electron concentrations are of the order of 1019 to 1020 spins/gram. These concentrations are consistent with the negative (diamagnetic) net magnetic susceptibility of the blacks. Oxygen and other paramagnetic substances, even in extremely minute quantities, exert a powerful influence on the electron spin resonance observed. Their effect is to broaden the resonance line and this reduces considerably the signal intensity. In extreme cases the intensity may be reduced to the noise level ; in less severe instances the broadening may lead to erroneously low spin assays. Carbon blacks differ in their susceptibility toward line broadening effects. Evidence is presented for a correlation between the odd electron concentration of carbon blacks and the modulus they impart to rubber, suggesting a combination reaction between the carbon black radicals and polymeric free radicals formed during processing or vulcanization. The possibility of such a reaction is supported by electron spin resonance measurements on carbon blacks heated in the presence of rubber, both with and without curatives. On the basis of the results available it is not possible to ascertain the full importance of the odd electrons of carbon black in elastomer reinforcement. It is certain that the unpaired electrons are not necessary for the development of reinforcement effects in general, although they may increase them substantially by providing an additional interaction mechanism for the union of black and rubber.
The Interaction between Carbon Black and Sulfur during Vulcanization
Authors: Blokh G. A. , Yaroshevich A. G. 
Published: February 2011

Abstract
The mechanism of the reinforcement of rubber by carbon black has until recently been interpreted from the physical point of view. According to the researches of P. A. Rebinder and coworkers the extent of the interaction between the filler and the rubber is given by the decrease in the free energy of the system resulting from the wetting of 1 cm2 of the surface of the filler particles by rubber. The rubber is bound to the surface of the carbon black particles through adsorption and forms around these particles an extended film which is characterized by high strength; in this state the rubber is referred to as “bound” or film-like rubber. In systems in which such adsorbed rubber is present there appears on the surface of the filler particles an effect which resembles a kind of “crystallization” of rubber which results in a strengthening of the interaction between individual chains and hence in increased strength of the rubber. According to Kusov, at optimum filling of the rubber with carbon black the mixture constitutes a continuous mass—a molecular space lattice with carbon particles situated in its nodes.
Vulcanization of Elastomers. 12. Perbunan with Thiuram Monosulfide and Sulfur. I
Authors: Scheele Walter , Toussaint Horst-Eckart 
Published: February 2011

Abstract
The vulcanization of Perbunan 2818 by tetramethylthiuram monsulfide plus sulfur (1 mole monosulfide per gram-atom S) was thoroughly studied. The following results were shown: The limiting value for dithiocarbamate formation is 66 mole per cent of the initial thiuram monosulfide, indicating a two-thirds transformation. The limiting value is practically independent of temperature. The formation of dithiocarbamate can be described as a reaction of the first order. The formation of dithiocarbamate is characterized by an induction period which grows longer with lowering of the temperature, and at 100° C it amounts to about 100 minutes. The rate constants for dithiocarbamate formation were calculated, and it was shown that they were practically the same as those for the vulcanization of Perbunan with tetramethylthiuram disulfide. The activation energies as derived from the temperature dependence of the rate constants for dithiocarbamate formation in the vulcanization of Perbunan by thiuram monosulfide plus sulfur on the one hand and with thiuram disulfide on the other, are only very slightly different and are practically the same as the activation energy for dithiocarbamate formation during the vulcanization of natural rubber with thiuram monosulfide plus sulfur. The results were thoroughly discussed in light of the present conceptions of the course of thiuram vulcanizations.
High-Speed Fracture in Rubber
Authors: Mason Peter 
Published: February 2011

Abstract
Cinematographic observations have been made of crack propagation under well-defined boundary conditions in rubbers at speeds up to 30 m/sec. The fracture-markings showed resemblances to those obtained with metals, plastics, and glass, and could be related directly to the corresponding speed of fracture-propagation. In close analogy with Schardin's observations on glass, a non-crystallizing rubber (GR-S) showed a mode of crack propagation in which the fractured surfaces were visually smooth and the speed was about one quarter of the speed of longitudinal elastic waves. A crystallizing rubber (natural rubber) did not show this mode of propagation under the present test conditions. It is suggested that the modes of solid fracture can be usefully classified in three categories: (i) slow propagation, generally with smooth surfaces, obtained by careful control of the boundary conditions; (ii) propagation at intermediate rates with rough surfaces, involving correspondingly greater energy consumption; and (iii) fast propagation with smooth surfaces, the rate of propagation being limited by the speed of elastic waves in the material in accord with Mott's theory.
The Role of Oxidation-Reduction Systems in Vulcanization with Sulfur
Authors: Tinyakova E. I. , Khrennikova E. K. , Dolgoplosk B. A. , Reĭkh V. N. , Zhuravleva T. G. 
Published: February 2011

Abstract
1. The reaction between trichlorothiophenol or dienols and SO2 brings about vulcanization of rubber without separation of elemental sulfur. The mechanism of the Peachey process of rubber vulcanization is examined on the basis of concepts of the role of intermediate products of the reaction—free radicals. 2. Sulfur is found to react with many vulcanization accelerators with formation of considerable amounts of hydrogen sulfide. It is shown that hydroxycarbonyl compounds, which reduce sulfur to hydrogen sulfide, play the part of accelerators of sulfur vulcanization. Thermal breakdown of hydrogen persulfide leads to vulcanization of rubber. 3. The experimental data are applied to the consideration of the mechanism of the action of accelerators of sulfur vulcanization and of the mechanism of formation of mono- and polysulfide bonds.
The Ozonization of Unsaturated Compounds. III. The Addition of Ozone to Internal and External Double Bonds in Butadiene Rubber
Authors: Yakubchik A. I. , Kasatkina N. G. , Pavlovskaya T. E. 
Published: February 2011

Abstract
1. It was established that the curves of ozone absorption by butadiene rubbers do not show breaks. 2. Sodium butadiene rubber was ozonized 25, 50, 75 and 100%. From the quantitative determination of the external double bonds which add ozone it was established that there is no strict selectivity in the ozonization of the double bonds of rubber: the external double bonds are ozonized more rapidly than the internal and their ozonization is completed earlier than the ozonization of the internal double bonds.
Carboxylic Rubbers. I. Synthesis and Structures
Authors: Dolgoplosk B. A. , Tinyakova E. I. , Reĭkh V. N. , Zhuravleva T. G. , Belonovskaya G. P. 
Published: February 2011

Abstract
It is well known that the high strength of unfilled (pure gum) natural rubber and some synthetic rubber compounds can be explained by the homogeneity of the polymer chain which determines its ability to crystallize or to orient on stretching. The character of the vulcanization network as well as the structure of the main chain is of importance. This has been verified by the use of polyethylene polyamines and other chemical compounds as vulcanization accelerators for butadiene-styrene rubber (SKS-30A) to produce high strength (up to 200 kg/cm2) gum rubber compounds. In certain cases, only the structure of the vulcanization network obtained with carboxyl-containing rubber compounds can account for obtaining the same effects as are obtained with natural or other synthetic rubber compounds as a result of homogeneity of polymer chain. The first work done by us on carboxyl-containing (carboxylic) rubbers was done in 1954\2-1955. In this work it was shown that polymers of isoprene and of butadiene, copolymers of butadiene with styrene, butadiene with acrylonitrile, and others, which contain small quantities of methacrylic acid (1\2-2 mole %) in the chain, can be vulcanized with oxides of divalent metals to give pure gum and lightly filled compounds characterized by high strength and elasticity, good resistance to heat aging and good cut growth resistance.
Sorption of Binary Solutions by Vulcanizates of Natural and Synthetic Rubber. I. Isotherms of Effective Sorption
Authors: Starobinets G. L. 
Published: February 2011

Abstract
1. The sorption of binary solutions by vulcanizate of natural and sodium-butadiene rubber was studied over the entire composition range of the following binary systems: benzene-low weight alcohols, benzene-low weight acids, benzene-polar derivatives of benzene, toluene-low weight alcohols, carbon tetrachloride-low weight alcohols, p-dichlorobenzene-low weight alcohols, benzene-acetone, benzene-ethyl acetate, chloroform-acetone, chloroform-methyl ethyl ketone, benzene-ethyl iodide, benzene-propyl bromide, hexane-dioxane. With the help of these data, coefficients of distribution of components between phases and sorption potentials of the components were calculated. Effective sorption isotherms of solvent from all the systems were constructed. 2. There is a close connection between the value of the effective sorption of solvent from systems of the solvent-nonsolvent type and the nature of the binary solution. The effective sorption of solvent is greater the larger the positive quantity of excess free energy of formation of the binary solution. From systems characterized by a negative value of excess free energy the solvent is sorbed to a far smaller degree than from systems with a positive deviation from the laws of ideal solutions. Sorption from binary solutions by rubber produces all four types of effective sorption isotherms that are predicted from thermodynamic considerations. 3. Comparison of effective sorption isotherms from the same solvent-nonsolvent system by vulcanized rubber and by activated carbon shows that the maximum value of effective sorption of solvent is much greater for the rubber than for the carbon. The selective nature of the sorption is also more strongly evident with the rubber : the negative branch of the S-shaped sorption isotherm from binary solutions on carbon is practically missing when the sorption takes place from the same solution on vulcanized rubber. From this it follows that many binary liquid systems as well as mixtures of saturated vapors could be more effectively separated on rubber and its vulcanizates than on activated carbon. This conclusion could have practical value since the effective sorption by rubber changes little with temperature and the desorption process is easier to carry out with rubber than with carbon. 4. It was established that the shape of the equilibrium curve between polymer and binary solutions does not depend on the degree of vulcanization or the composition of the active fillers in the vulcanizate. From this it follows that the efficiency factor of the sorption process is determined only by the nature of the rubber and not by the composition of the vulcanizate. 5. From analysis of the experimental data it follows that sorption of solvent occurs largely as random mixing of its molecules with sections of the polymer chain. Sorption of nonsolvent takes place by more or less strong attachment of its molecules on sorption sites of the polymer.
Mutual Solubility of Polymers and Properties of Mixtures
Authors: Slonimskiĭ G. L. 
Published: February 2011

Abstract
If a homogeneous mixture of two polymers is to be obtained, both components must exhibit fluidity. It is, therefore, necessary first of all to analyze the process of mixing of two amorphous linear polymers capable of developing true irreversible deformation. However, though the mixing of two such polymers, from the thermodynamic point of view, constitutes the mutual solution of two liquid phases, it does not, in fact, take place spontaneously, since the exceptionally high viscosity of polymers1 results in a negligible rate of diffusion of the long-chain molecules, even at elevated temperatures. For this reason, special procedures (mixed milling, evaporation of solvent from mixed solutions, etc.) are used to obtain polymer mixtures which exhibit no heterogeneity, even when examined by means of a good optical microscope. It is, however, quite evident that, should two polymers be mutually insoluble, the spontaneous separation of such artificially prepared mixtures into macroscopically distinct phases must proceed at infinitesimal rates as a result of the enormous viscosity of the system. In such cases, the flexibility of the chain, which permits the relatively rapid translation of individual segments of the chain, is an important factor. This property of chain molecules will result in a process by which the mixture of mutually insoluble polymers becomes resolved in extremely small volume elements, i.e., to the formation of two types of regions whose composition will accord with the thermodynamic conditions of phase separations. Such mixtures of two amorphous polymers structurally closely resemble crystalline polymers, which are also microheterogeneous. In both cases, the dimensions of the regions differing in phase character formed by the segregation of segments are considerably smaller than the length of the chain molecules. For this reason, the macroscopic miscibility of two polymers is by no means equivalent to their microscopic miscibility, i.e., to true mutual solubility of the polymers.
Rupture of Rubber. V. Cut Growth in Natural Rubber Vulcanizates
Authors: Thomas A. G. 
Published: February 2011

Abstract
It has been noted in Part I of this series (referred to hereafter as I), that if a nicked specimen of a natural rubber vulcanizate is slowly stretched, tearing occurs at the tip for quite small applied forces. In the initial stages, this tearing continues only as long as the deformation of the specimen is being increased, and virtually ceases if the deformation is held constant. This tearing is essentially time independent, and is termed “static” cut growth. If, however, the deformation is continued until the cut has grown by a few hundredths of a millimeter the growth becomes time dependent and catastrophic tearing takes place, the cut suddenly increasing in length by perhaps a millimeter or so. If a nicked specimen is alternately stretched and relaxed to the unstrained state, the cut gradually grows even though the applied force is less than that required to produce catastrophic tearing. This phenomenon is termed “dynamic” cut growth. This behavior can be compared to that of gum GR-S vulcanizates described in Part III, where static cut growth of the above type does not occur, a dead load on a test piece producing a more or less steady rate of cut growth. In the present paper, measurements on natural rubber gum vulcanizates only are described, and the numerical results expressed in terms of the theory developed in previous papers (Parts I, II and III). It has been shown in I and II that the tear behavior of differently shaped test pieces cut from thin sheets of thickness t may be correlated by means of the concept of the energy for tearing. This is defined as the value of T[=(1/t)(∂W/∂c)l] at the instant of tear, and is denoted by Tc. In the definition of T, is the total elastic energy stored in the test piece, c the length of the cut, and the subscript l indicates that the differentiation is to be carried out at constant displacement of those parts of the boundary that are not force-free. It was also shown that a convenient and direct method of obtaining Tc is by the use of the “simple extension” tear test piece described in I and shown in Figure 1, and this has been used for most of the experiments. Under most conditions, T for this test piece is nearly independent of the cut length, width of the test piece, and modulus of the rubber; T is very nearly equal to 2F/twhere F is the force applied to the arms. In the cases where the use of the above approximate relation between T and F introduces an appreciable error, the exact theory given in I was used.
Influence of Surface Condition, Duration of Molding, Pressure and Temperature upon Bond Strength between Components of Tire Casings
Authors: Pinegin V. A. , Vasil'eva S. A. , Kepersha L. M. 
Published: February 2011

Abstract
As a result of the above experiments it is shown that the bond strength between components of casings where 100% synthetic rubber is used, may be significantly increased: 1) by maintaining the freshness of the surfaces being plied up by keeping standing to a minimum, by freshening the surfaces by fine (‘velvet’) buffing, and by applying a thin and uniform layer of bonding agent to the previously heated surfaces; 2) by increasing the specific molding pressure during plying up; 3) by increasing the specific pressure upon the constructions during vulcanization; 4) by increasing the duration of action of the specific molding pressure during plying up; 5) by raising the temperature of the components being plied up. The rational exploitation of these points undoubtedly has an important effect and will ensure the improvement of the quality of the finished articles, particularly where 100% synthetic rubber is used.
Enhancement of Bond Strength in Tire Casings by Heat Treatment
Authors: Malkina Kh. E. , Pukhov A. P. 
Published: February 2011

Abstract
Testpieces of carbon black stocks on a 100% synthetic rubber basis which do not adhere to surfaces may be satisfactorily bonded to each other if they are subjected to molding under a given pressure over a prolonged period. In this case the more plastic the stocks the greater the depth of their penetration into each other on molding, and consequently the higher the bond strength between the individual rubberized components. The best and most rapid joint is with components whose plasticity values are close to each other. Carbon black stocks on a 100% synthetic rubber basis are highly thermoplastic. Thus preliminary heating of the blank components with subsequent molding ensures enhancement of the bond strength. As a result of calendering, extruding, building and molding of the various types of component going into a tire casing stresses are set up between these components which tend to separate them and thus reduce the bond strength in the finished product. The removal of such stresses leads to enhancement of bond strength. Since the mechanism of the removal of the stresses is a relaxation mechanism, the lowering of the stresses proceeds more rapidly and fully in heated blanks ; thus the heating and maintenance of the heat of the heated raw casings, particularly before vulcanization, ought to lead to an improvement in their service properties. These things are not usually disputed. Nevertheless until recently the quantitative side of the matter was not clear, i.e., whether it was possible by preliminary heating to increase significantly the serviceability of the casings (in particular on poor roads). Suitable investigations were carried out in the technology division of the Nauchno-Issled. Inst. Shinnoĭ Prom. (Tire Research Inst.) to study this.
The Mechanism of Sulfur Reaction in the Polymerization of Chloroprene and of Thiuram Reaction in the Degradation and Structurization of Polychloroprene
Authors: Klebanskiĭ A. L. , Zukerman N. Ja , Fomina L. P. 
Published: February 2011

Abstract
To elucidate the mechanism of the reaction between chloroprene and sulfur, the following investigations have been carried out: (1) The reaction of a polychloroprene solution with sulfur under conditions of free radical initiation was studied. It was found that sulfur does not react with polychloroprene, whereas under polymerization conditions the addition of sulfur proceeds readily. (2) A study of the polymerization of chloroprene monomer containing various amounts of sulfur (from 0.3 to 10%) showed that the sulfur content of the polymer increased in proportion to the amount of sulfur originally present. Polymers with a high sulfur content (3–5%) were found to be completely soluble at low degrees of polymerization. The latter finding indicates that the sulfur does not effect crosslinking, but that it is bound predominantly in a linear manner in the polymer chain. (3) The predominant form of bonding of the sulfur was found to be in di-and polysulfide linkages. The number of the latter increases with the sulfur content of the polymer. (4) By the action of nascent or catalytically activated hydrogen, the polymer was found to undergo extensive degradation with the loss of 80 to 100% of the bound sulfur and formation of low molecular weight polymer. In the course of the reduction the disulfide links are broken with the formation of polymer mercaptans, which are converted to disulfides by reaction with iodine; this is confirmed by an appropriate increase in the intrinsic viscosity. These findings confirm the copolymerization mechanism of the reaction between chloroprene and sulfur as proposed by Mochel and Nichols. (5) The mechanism of the degradation of polychloroprene sulfide by tetraethylthiuram disulfide (TETD) was studied by means of the following model systems, representing the main types of structures present in such polymers:
A Theoretical Study on the Mechanism of Ziegler-Type Polymerizations
Authors: Uelzmann Heinz 
Published: February 2011

Abstract
Since the discovery of catalysts for the polymerization of ethylene and α-olefins at low temperatures and low pressures by Ziegler and coworkers, extensive experimental work has been done on this subject. Several theories on the mechanism of the catalysis have been discussed in order to illustrate the specific effects of different catalytic systems. In this paper an attempt is being made to consolidate the existing theories into a single basic mechanism and to explain the numerous experimental facts from a different viewpoint. A theory on this subject must explain: (1) An anionic propagation. (2) A “hair-like” growth of polyethylene from one active spot on the catalyst surface. (3) Stereospecific polymerization of α-olefins and an exclusive head-to-tail arrangement according to Natta. (4) Different activities of Ziegler catalysts. (5) Activity and action of modified Ziegler catalysts. Generally these catalysts are prepared by interaction of an aluminum trialkyl and a transition metal in the form of its halogen derivative. Complex formation between both components is believed to occur according to the tendency of transition elements and aluminum to operate with coordination valences. The catalyst has an extremely high activity (low temperature initiation) and, furthermore, imparts strong protection and stabilization to the growing chain end. This is a prerequisite for the formation of very high molecular weight polymers. Besides the initiation, propagation, and termination, an orientation step is involved in the mechanism of catalysis which produce stereospecific polymers. In the following section the initiation of olefin polymerization by different kinds of catalysts is discussed in order to show that only one definite type of initiation seems likely to occur under the conditions of the Ziegler polymerization.