bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Different Viscometers for Measuring the Viscosity of Latex
Authors: Boucher M. 
Published: February 2011

Abstract
The viscosity values of different samples of latex diluted to different degrees were measured by means of three viscometers of different types, viz., the Brookfield viscometer, the Epprecht viscometer, and the French Rubber Institute viscometer. The results obtained are dependent on the type of apparatus, although within certain limits, the Epprecht and French Rubber Institute viscometers give approximately the same results. The values obtained with the Brookfield viscometer are distinctly different from those with other two viscometers. In spite of these differences, however, each of the viscometers has a field of use, which is indicated and discussed.
Carbon Blacks for Highly Conductive Rubber
Authors: Polley M. H. , Boonstra B. B. S. T. 
Published: February 2011

Abstract
The mechanism of the conductance of the electric current through a carbon black dispersion is still a problem which has not been completely solved. Rubber is an insulator and forms a homogeneous liquid phase, while carbon black is a semi-conductor and forms a dispersible solid phase. Mixtures of these two show electrical properties ranging from a near insulator to a near semiconductor. The picture which has been generally accepted for the mechanism of conductivity in rubber-carbon black compounds is one based on through-going paths of carbon black particles. These through-going paths are formed by carbon black particles either touching or situated so close to adjoining carbon black particles that the electrons have a reasonable chance to jump across the gap. This concept implies that each carbon particle must practically touch its neighbor or else the continuous chain will be broken. The definition of “touching” is not given in this concept. The number of conducting or through-going paths will be a function of loading and the particle size of the carbon black. In addition to the number of the paths, the intrinsic conductivity of the carbon blacks themselves, which is mainly a contact resistance, is of paramount importance. This picture is useful only if it is consistent with the various characteristics of electrically conductive rubber-carbon black compounds.
Stability of Ammoniated Latex and Soap-Stabilized Emulsions in the Presence of Complex Zinc Salts
Authors: McRoberts T. S. 
Published: February 2011

Abstract
The solubility of zinc oxide in solutions of ammonia and different ammonium salts has been determined. The interaction between ammonium laurate and zinc ammine (or ethylene diammine) salts has been studied in aqueous solution, in latex, and in oil emulsions. The results indicate that destabilization of ammoniated latex or soap-stabilized emulsions by dissolved zinc oxide is due to the presence of zinc diammine ions, which form insoluble dilaurates. It is suggested that the increased rate of destabilization at elevated temperatures is most probably due to a decrease in hydration of the zinc diammine dilaurate formed at the surface of the rubber or oil particles.
Crosslinking and Radiation Effects in Some Natural and Synthetic Rubbers
Authors: Charlesby A. , Groves D. 
Published: February 2011

Abstract
When subjected to atomic energy radiation certain polymers crosslink, a process which is equivalent to vulcanization, but occurs without the admixture of extraneous chemical agents. Other polymers degrade by main chain fracture, a process which occurs at random throughout the molecule, and is different from thermal or ultraviolet degradation. Methods available for detecting crosslinking in irradiated polymers, include those based on solubility and swelling which have been used to study the effect of high energy radiation on a number of natural and synthetic rubbers. The polymers investigated include natural rubber, polychloroprene, polyisobutylene, polybutadiene, and thioplasts, as well as some copolymers. The results show the degree of crosslinking to be proportional to radiation dose, and to be reduced by the presence of styrene or acrylonitrile units in copolymers. Possible applications of this physical technique of linking molecules are discussed briefly.
Rubbery Copolymers from Unsaturated Ketones
Authors: Cooper W. , Bird T. B. , Catterall E. 
Published: February 2011

Abstract
The preparation and properties of copolymers from unsaturated ketones with acrylate esters and with butadiene are described. Details of the polymerization reactions and the structure of the copolymers are given. The preparation and properties of compounded vulcanized polymers are described and, in the case of the ketone-acrylate copolymers, the mechanism of sulfur vulcanization is discussed.
The Stress Relaxation of Sulfur Vulcanizates of Natural Rubber
Authors: Berry J. P. 
Published: February 2011

Abstract
An experimental study is reported of the stress relaxation behavior of sulfur vulcanizates of natural rubber maintained at constant extension. Of particular interest is the effect of oxygen pressure on the shape of the force-time curves, and the relaxation proceeding in absence of oxygen. The results are interpreted according to a two-stage process: (1) oxidation at the crosslinks and (2) scission of oxidized crosslinks.
The Vulcanization of Elastomers. VII. The Vulcanization of Natural Rubber with Thiuram Disulfides. Part IV
Authors: Scheele Walter , Stange Peter 
Published: February 2011

Abstract
The present paper deals with the kinetics of the thiuram vulcanization at varying thiuram disulfide concentrations as well as with the influence of the zinc oxide content upon vulcanization at constant temperature (120° C). It was found : 1. The limiting value of dithiocarbamate formation of 66 mole per cent relative to the amount of thiuram disulfide used is—within wide limits—independent of the initial thiuram disulfide concentration. 2. At constant thiuram disulfide concentration the limiting value of dithiocarbamate formation is unchanged when the zinc oxide content is successively increased. 3. Changing the zinc oxide content while the thiuram disulfide concentration is kept constant exerts an influence on the kinetics of the decrease of thiuram as well as on the increase of dithiocarbamate. The rate constants of both reactions increase. 4. It is concluded from these results that in all probability vulcanization is initiated on the surface of the zinc oxide crystals. 5. Even in stocks containing as much as 40 g. zinc oxide per hundred g. of compounds, the limiting value of dithiocarbamate formation remains unchanged. This was verified by the analysis of vulcanizates after extremely long cure times. The average limiting value of two experiments after 24 hours of cure was 65 mole per cent which corresponds to a two-thirds reaction within the experimental error.
Studies of the Vulcanization of Elastomers. VIII. The Vulcanization of Synthetic Rubbers with Thiuram Disulfides (1)
Authors: Scheele Walter , Toussaint Horst-Eckart 
Published: February 2011

Abstract
The vulcanization of Buna S-3 by tetraethylthiuram disulfide is reported. A quantitative study of the transformation reactions led to the following results. (1) Using tetraethylthiuram disulfide as representative of the class, it was found that two thirds of it undergoes transformation to zinc dithiocarbamate during the vulcanization of Buna S-3, independent of the temperature. (2) Both the decrease of thiuram disulfide and increase of dithiocarbamate are first-order reactions within a wide range of the transformation. (3) The rate constants of the decrease of thiuram and of the increase of dithiocarbamate are a little less than a tenth power greater than for the vulcanization of natural rubber. This is possibly explainable by the different structure of the allyl units in Buna S-3. (4) The activation energies of the decrease of thiuram as well as the increase of dithiocarbamate are nearly the same and are greater than for the vulcanization of natural rubber.
The Reaction Mechanism of Thiuram Disulfide Vulcanization of Poly-1,5-Dienes, Particularly of Natural Rubber
Authors: Blelstein G. , Scheele W. 
Published: February 2011

Abstract
In previous publications on thiuram vulcanization we confined ourselves to the presentation and discussion of our extensive experimental work. We had investigated quantitatively the conversion of thiuram disulfides and were in a position to describe the kinetics of thiuram vulcanization. Such investigations are, of course, of particular value to technology for information about the rate and temperature dependence of vulcanization reactions. Our experiments were therefore not primarily designed to determine the details of reaction mechanism, which we had hitherto treated with restraint, and experience shows that the study of reaction kinetics does not always provide the key to a complete solution. All the same, it now seems reasonable to pick out some of the results we have obtained, and so consider the question of a reaction mechanism for thiuram vulcanization. We should, however, like to state, that although the present treatment concerns matters which may include some pertinent points, it does not necessarily represent a final interpretation. It is to be stressed, that any postulated reaction mechanism must explain what we regard as a stoichiometrical, i.e., concentration and temperature independent conversion of thiuram disulfide to zinc dithiocarbamate. The following experimental results thus formed the basis of our considerations:
Stress Relaxation Studies of the Viscoelastic Properties of Polymers
Authors: Tobolsky Arthur V. 
Published: February 2011

Abstract
Extensive studies of the viscoelastic properties of polymers undertaken in the author's laboratory by means of the method of stress relaxation are here reviewed. The discussion is divided into four parts: chemical stress relaxation, stress relaxation in amorphous polymers, stress relaxation in crystalline polymers, and stress relaxation in certain natural polymers and polyelectrolytes. Mathematical description of the phenomena are presented in simple form. The relation between structure and viscoelastic properties of polymers are discussed and a rather complete over-all picture of these phenomena seems to be emerging.
The Investigation of Molecular-Weight Distribution in Rubberlike Polymers
Authors: Bresler S. E. , Poddubnyĭ I. Y. , Frenkel S. Y. 
Published: February 2011

Abstract
In an investigation of three different synthetic rubbers, methods of fractionation were examined and measurements were made of the molecular-weight distribution by analysis of fractions. The following conclusions may be drawn. (1) The method of equivalent Gaussian distributions correctly reproduces the distribution within each fraction and makes it possible to distinguish the broadening of the sedimentation curve attributable to diffusion and that attributable to polydispersion. (2) The method of accounting for the final concentration of the solution under investigation introduced by us result in correct values of molecular weights of fractions and correct values of standard deviations. (3) Comparison of a series (about 10) of fractions of a given polymer makes it possible to transpose the sedimentation constant distributions into the distribution of molecular weights in a simple and natural way. An investigation of the three rubbers demonstrates two facts. (1) Fractionation of rubbers by precipitation from solutions gives true fractions, i.e., mode values of molecular weights and sedimentation constants do not overlap but form continuous series. By this means fractionation of K-1 and K-3 resulted in very homogeneous fractions of Gaussian shape having dispersion coefficients smaller than 0.33. Fractionation of K-2 resulted in less homogeneous fractions of somewhat asymmetric shape; however, in this case, the broadness and asymmetry of fractions, as it is easy to show, does not exceed the limits predicted by the theory of fractionation. (2) The method of determination of molecular-weight distributions by tracing the steplike curve of precipitation, with subsequent smoothing by graphic differentiation, gives a correct picture of the distribution function of polymers for molecular weights; however, the finer details of distribution can be distorted and lost in tracing the steplike curve. The molecular-weight distributions of synthetic rubbers by the ultracentrifuge method must be closely related to the process of genesis of a polymer, i.e., with the mechanism of the polymerization reaction. Thus, with proper experimental technique our method can be applied to the investigation of various mechanisms of polymerization and polycondensation.
Effect of Elongation on the Proton Magnetic Resonance of Natural Rubber
Authors: Oshima Keichi , Kusumoto Hazime 
Published: February 2011

Abstract
Several authors have already reported their studies on natural rubber by the method of proton magnetic resonance. However, since there has been little work on the effect of elongation on proton magnetic resonance absorption, we present our investigation on the proton magnetic resonance absorption of stretched samples of vulcanized natural rubber. For this experiment a large permanent magnet shown in Figure 1 was constructed. The magnetic field strength was 6090 gauss at the center of the gap at 18° C. The magnet had a field inhomogeneity of about 0.01 gauss in a 0.2 cc. sample. The derivatives of the resonance line were recorded at fixed frequency, changing the magnetic field linearly in time with an automatic electronic bias control. Control of the temperature from liquid nitrogen to room temperature was performed by a cryostat similar to that described by Gutowsky.
Rupture of Rubber. IV. Tear Properties of Vulcanizates Containing Carbon Black
Authors: Greensmith H. W. 
Published: February 2011

Abstract
A method of studying tear behavior has been described in a previous paper (Part III, subsequently referred to as III), and was illustrated by results obtained with natural rubber and GR-S gum vulcanizates, i.e., vulcanizates containing no added ingredients apart from those necessary for vulcanization. In the present paper the method is applied to vulcanizates containing different types of carbon black. Vulcanizates of this type are of considerable interest, since the carbon black can appreciably modify physical properties such as stiffness and tensile strength and can induce pronounced anisotropy in tearing, referred to by Buist as knotty tearing.
Nature of Chemisorptive Mechanisms in Rubber Reinforcement
Authors: Garten V. A. , Sutherland G. K. 
Published: February 2011

Abstract
The present state of research in the field of reinforcing rubber fillers is reviewed and it is pointed out that although a strong school of thought still maintains that the strength of bonding depends on particle size, there are many observations indicating the presence of reactive sites and suggesting the possibility of strong bonds of a chemical nature between filler and rubber matrix. The phenomenon of carbon-gel formation as foremost among these, is discussed as lending fresh support to the idea of chemical bond formation. This effect, known to be most pronounced in the presence of an unsaturated matrix is correlated with the mechanism of vulcanization as proceeding via free radical intermediates. It is suggested that the formation of chemical bonds between pigment and rubber constitutes an integral part of the chemical crosslink formation commenced on the rubber mill and completed by vulcanization. This hypothesis is corroborated by results obtained during studies on the reactivity of pigment surfaces towards simple inorganic and organic free radicals. It is shown that active pigments react with free radicals with the formation of nonionic bonds. Hydrophilic blacks have been prepared by treatment with persulfate. Similarly, electrochemically produced stearate free radicals have been reacted with the surface to form hydrophobic carbons. The “benzidine ”blue free radical, being the monooxidation product of benzidine, reacted easily with less active pigments and thus provided a useful measure of activity. From the experiments with free radicals, the number of active sites for various fillers has been calculated and shown to cover a range of 0.01–3.1 per 100 sq. A˚. Multifunctional polystyrene radicals, obtained in the presence of excess oxygen, yielded crosslinked networks with carbon blacks which resisted solvent extraction. These are considered to be complete analogues to carbon gel. The statistical mechanics of the rubber network has been developed to include crosslink formation as caused by rubber-filler interaction. It is shown that the mechanical properties of a rubber compound that are controlled solely by the network structure are directly proportional to σ/r, the ratio between the number of active sites per unit area and the particle radius. Abrasion does not appear to be only a mechanical phenomenon.
Rubber Reinforcement by Resins Formed in Latex
Authors: van Alphen J. 
Published: February 2011

Abstract
Many attempts have been made to combine synthetic resins with rubber. In most cases the resins were incorporated in the dry rubber on the mill and some success has been obtained with thermoplastics, such as high-styrene resins. Phenolic resins are compatible with nitrile rubbers, but not with GR-S or natural rubber. Therefore, attempts have been made to incorporate the resin in an unhardened state and to harden it afterwards in the rubber. In this way rubber can be vulcanized. Such incorporation causes difficulties; an alternative is to mix emulsions of resins with latex and to coprecipitate the resin and the rubber, or to dissolve the partly condensed and still soluble phenolic resin in a caustic soda solution and to mix this solution with latex so as to precipitate the resin and rubber at the same time by the addition of acid. The products obtained after vulcanization were, however, far from satisfactory. Somewhat better results were obtained when the latex was not coagulated but evaporated, and thus the resin partly formed in situ. This method, the formation of the resin in situ, has been followed by some investigators9and most success has been obtained by Le Bras and Piccini, using an alkaline solution of a partially condensed resorcinol-formaldehyde resin, which is mixed with trypsinated, heat-sensitized latex and vulcanizing ingredients. Products with remarkable properties, especially with a high tensile strength and a very high tear resistance were obtained, when the latex was gelatinized, dried, and vulcanized. Their method is a method of latex-reinforcement and the reinforcement disappears completely when the dried but not yet vulcanized product is brought on the mill. For the sake of completeness it may be mentioned that trials have also been made to introduce resins into rubber by polymerizing suitable vinyl derivatives in latex.
Natural Rubber Compounds for Intermittent Low Temperature Service
Authors: Fletcher W. P. , Gent A. N. , Wood R. I. 
Published: February 2011

Abstract
The changes in physical properties of rubber vulcanizates on approaching the so-called second order transition temperature are discussed and distinction is drawn between these phenomena and those associated with crystallization. A simple apparatus of the torsional pendulum type is used to determine the dynamic stiffness and hysteresis loss factor at a frequency of about 0.5 c.p.s. of vulcanizates in the temperature range 20 to −120° C. A large number of liquids are examined as potential plasticizers for lowering the rubber to glass transition temperature and a number are shown to have a high order of efficiency in this respect. Of these materials some also conform to the overriding requirements of low volatility and adequate compatibility with rubber. The loss in physical properties consequent on increase of plasticizer content is not markedly different for most of the plasticizers. Di-iso-octyl adipate is representative of the liquids which give useful low temperature plasticization and a number of commercial type compounds are developed using this plasticizer with carbon black or silica reinforcement, some of these have transition temperatures approaching those of the silicone rubbers but with a better level of general physical properties. A tentative theoretical treatment for the low temperature plasticization of nonpolar rubbers is discussed and this leads to a law which has been found to predict fairly well the transition temperature of a plasticized natural rubber compound in terms of the index of variation with temperature of the plasticizer viscosity.
The Reaction of Molecular Oxygen with Rubber
Authors: Bevilacqua E. M. 
Published: February 2011

Abstract
It is nearly a century since Hofmann and Spiller made the first recorded experimental observations linking oxygen with substantial changes in polyisoprenoid hydrocarbons. In the first sixty-odd years following this work technological progress was slow, but certain characteristic features of the oxidation reaction were observed. It was firmly established that oxygen played an important role in the deterioration of rubber and rubber products with the passage of time, and the accelerating effects of exposure to light or to elevated temperatures were realized. Within a short additional period a very nearly complete solution to the problems of oxygen aging was obtained with the discovery of efficient vulcanization methods and of effective antioxidants. These discoveries made possible the transition of rubber from a relatively expensive, short-lived material of commerce to its present position of a high-volume, low-cost, essential ingredient of our everyday life. Since that period technological progress has consisted in steady refinements of these important discoveries. During these years many observations necessary for understanding the chemistry of the oxidation process were accumulated, but it was necessary to wait for two fundamental developments in order to obtain a complete explanation of the reactions occurring during the reaction of rubber with oxygen. These were, first, a clear realization of the high molecular character of the rubber hydrocarbon and the effect of this on its macroscopic properties, and-second, the work on oxidation of low molecular weight olefins which forms the basis for inferring the nature of steps in the oxidation of rubber inaccessible because of experimental difficulties. Since both of these developments have been made it is quite probable that we shall know in complete detail the reaction sequence in rubber oxidation before the centennial of Hofmann's paper is reached.