bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Structure and Viscosity of Hevea Latex. I.
Authors: Verhaar G. 
Published: February 2011

Abstract
Fresh Hevea latex is characterized by the presence of viscoids of greatly varying size (5–200 microns). When the viscosity of such a latex is determined with a viscometer of the rotary type the values found cover a wide range, having no clear relation to the initial DRC of the latex. Also, with the aid of a rotary viscometer, the structural viscosity of fresh or any other type of latex can be clearly demonstrated. When fresh Hevea latex is treated with ammonia in increasing amounts there is a sharp and regular drop in viscosity up to 0.05 per cent NH3. This runs parallel with a gradual and finally complete disintegration of the viscoids. Treatment with sodium sulfite in increasing concentrations up to 0.30 per cent yields a more slowly decreasing viscosity with end values approximately twice as high as with ammonia. Microscopic investigation shows a slow and only partial breakdown of the viscoids in the same area. Formaldehyde gave irregular results, but, in general, did not decrease or increase the initial viscosity considerably, neither could any influence be established on the size and shape of the viscoids. The viscosity of fresh Hevea latex is profoundly influenced by addition of distilled water giving a considerable increase up to 20 per cent and a sharp drop afterwards. Latex diluted with 20 per cent of water was microscopically found to be in a stage of pre-coagulation, with the immobilized rubber particles embedded in the viscoid complexes. It is concluded that the viscoids play a dominant role in viscosity phenomena of Hevea latex.
Dual Inhibition-Acceleration Role of Carbon Black in Rubber Oxidation
Authors: Lyon F. , Burgess K. A. , Sweitzer C. W. 
Published: February 2011

Abstract
Carbon black can function as an inhibitor or as an accelerator of oxidation and cure of rubber and of other polymers. The inhibiting action of carbon black on the oxidation of unvulcanized cold rubber appears to be related to, if not the cause of, the increased reinforcement of the heat-treated stock. In general, the effect of carbon black on the oxidation of cold rubber and natural rubber is the same. With a more complete understanding of the role of carbon black in polymer oxidation and cure reactions, it should be possible to control the behavior of carbon black so that advantage can be taken of its inhibiting and accelerating properties in prolonging the life and increasing the usefulness of rubber goods.
The Heat Treatment of Butyl-Carbon Black Compounds
Authors: Edwards D. C. , Storey E. B. 
Published: February 2011

Abstract
1. Heat enhancement effects with HAF black-GMF systems do not appear to involve a chemical bonding of the polymer to the carbon surface. The principal reasons for this view are : (a) Very similar physical properties are obtained, in the case of 50-part carbon black masterbatches, whether or not the black is present during the heat treatment. (b) When the carbon black content is increased, it is necessary to increase the quantity of GMF in order to produce a given degree of gelation. 2. With GMF, very satisfactory properties are obtained by heat-treating a highly loaded mixture and diluting this masterbatch with fresh polymer. Such a process is less sensitive to the time and temperature conditions of the heat treatment operation. 3. The application of such a procedure to Butyl-HAF black mixtures results in modulus and hysteresis properties approaching those of a conventionally mixed cold-rubber tread.
Mooney Viscosity of Carbon Black-Rubber Mixtures
Authors: Studebaker M. L. 
Published: February 2011

Abstract
The principal properties of carbon black which must be considered in the study of rubber mixtures containing carbon black are (1) particle size and the related property, (2) surface area, (3) hydrogen content, (4) oxygen content, and finally a property which is more difficult to evaluate but which is related to (5) the tendency to agglomerate. This latter term is referred to in the trade as a “structure” factor, and it is usually determined from oil absorption measurements. Unvulcanized rubber-carbon black mixtures are considered to be analogous to mixtures of carbon black and with other liquid media, for example, mineral oil. It has been demonstrated by Weltmann and Green that the “plastic viscosities” of concentrated suspensions obey a modified “Arrhenius equation”. In this paper it is shown that unvulcanized rubber-carbon black mixtures also obey a similar equation. The rheological properties of concentrated suspensions are profoundly influenced by long-range London-van der Waals forces. Some of the laboratory tests by which these forces are studied by colloid chemists are specific volume of a powdered solid under pressure, sedimentation volume, oil absorption, and plasticity. A correlation is demonstrated between data obtained by these tests and Mooney viscosity. A general equation is presented relating the Mooney viscosity with the concentration of carbon black and oil absorption. This equation applies to all of the data which have been examined in natural rubber. In GR-S another term, the oxygen content of the carbon black, must be included.
Studies on Carbon Black. III. Theory of Bound Rubber
Authors: Villars D. S. 
Published: February 2011

Abstract
Theories of reinforcement may be grouped into two general classes, mechanical and chemical. The mechanical type of theory attempts to explain reinforcement by alteration of direction of tear or by mechanieal entrainment. The chemical type of theory invokes the formation of bonds between the filler and rubber. Because of its implication with respect to the latter, Fielding of Goodyear developed a “bound rubber” test. The amount of rubber bound to carbon black was defined as that unextractable from the raw masterbatch by benzene. Some ten years ago, Baker and Walker reported an insolubilization of GR-S, on mixing with carbon black, over and above the amount of naturally occurring gel. The amount of insolubilized polymer increases with increasing molecular weight of the GR-S, and a selective adsorption of the high molecular weight material was found. Since this phenomenon was obtained also in polymers where they believed chemical gelation to be impossible, the conclusion was drawn by them that it is purely physical—this notwithstanding the fact that they found that extractions at higher temperatures failed to remove the insolubilized polymer. Because the method of analysis for insolubilized polymer used by Baker and Walker was essentially a bound-rubber analysis, interest in the latter was revived and it became desirable to set up a hypothesis to explain the mechanism of bound-rubber formation. (Let us understand the term “rubber” as applying in its more general sense as synonymous with “elastomer”.) The present paper reports a theory developed by the writer about ten years ago to explain various observations on the hypothesis that bound rubber is a gel of carbon black particles, the bonding agent of which consists of the longer polymer molecules. The theory interprets the observed linear dependence of bound rubber on loading in terms of an elemental area associated with the segmental adsorption of elastomer molecules, the molecular weight of these segments, and the functionality of the carbon black particles.
The Identification of Fillers in Vulcanized Rubber
Authors: Endter Friedrich 
Published: February 2011

Abstract
In the analysis of the filler content of any type of vulcanized rubber, it is desirable not only to obtain data on the filler content and its chemical composition, but also to characterize as definitely as possible the individual components. In the case of vulcanizates containing carbon black, this means the identification of the black as a member of one of the known types of blacks, and in the case of vulcanizates containing white fillers, to characterize the individual inorganic fillers as definite physical compounds. These problems cannot be solved by methods of chemical analysis alone.
Secondary Softening Regions of Copolymers, Mixed Polymers, and Graft Polymers
Authors: Ecker R. 
Published: February 2011

Abstract
A polymer is a macromolecular substance which is built up from individual monomeric units by a process of chemical linking into a long chainlike substance. Figure 1 is an attempt to give in schematic form a picture of the general structures of three purported types of copolymers, mixed polymers, and graft polymers.
Nonlinearity in the Dynamic Properties of Rubber
Authors: Payne A. R. 
Published: February 2011

Abstract
The first two sections of this paper deal with the necessity for amending the classical Newtonian equations by assuming a nonlinear stress-strain curve in order to account for the presence of a considerable amount of second harmonic of the test frequency in the restoring forces in a rubber, in both forced-vibration and positive-displacement dynamic testers. The nonlinear stress-strain curve is applied also to a damped free-vibration curve of the Yerzley type, and is shown to account for the asymmetry of the envelope of the vibration curve. The latter part of the paper obtains a relationship between the dynamic modulus of loaded rubbers and amplitude of vibration, leading to equations analogous to those used in rheology to deal with rate of shear effects in non-Newtonian liquids, and to explain the effects of fillers on the static modulus and hardness of vulcanized rubbers. A resonance curve from a resonant vibrator is analyzed and the variation of modulus with amplitude is shown to exhibit the typical thixotropic effect associated with loaded rubbers subjected to vibrations. The last section discusses how the decrease of modulus with increasing amplitude can be attributed to two different mechanisms: (1) thixotropic breakdown of filler structure, (2) in compression, nonlinearity of the stress-strain curve.
Electrochemical Aspects of Rubber Latex, Compounding Ingredients, and Their Mixtures
Authors: Roy Brojeswar 
Published: February 2011

Abstract
The electrophoretic speeds of rubber latex particles as well as of colloidally dispersed compounding agents, e.g., zinc oxide, sulfur, china clay, and mixtures of them as are generally employed in baths for electrodeposition, have been measured in a microcataphoresis cell of the Northrup-Kunitz type. The ζ-potential of latex, calculated from the electrophoretic speeds, is considerably influenced by the presence of the compounding agents. Sulfur sol having the lowest ζ-potential tends to reduce that of latex as well as of others in a mixture, whereas zinc oxide and china clay, which have higher ζ potentials, tend to increase the value for latex. A mixture of zinc oxide and china clay shows the highest (60 mV) ζ-potential compared to latex itself (ζ=28.8mV). The isoelectric point of rubber latex was measured by calculating the ζ-potential from the electrophoretic speed at different pH values, which were maintained by means of Na2CO3⋅NaHCO3 buffers at the higher range and acetate buffers at the lower range. The I.P. was 4.2 and was lowered in the presence of zinc oxide and china clay sols to 3.0 and 3.8, respectively, but increased to 5.1 in the presence of sulfur sol.
Kinetics of Hydrochlorination of Unvulcanized and Vulcanized Latex
Authors: Gordon M. , Taylor J. S. 
Published: February 2011

Abstract
In the van Veersen hydrochlorination of latex, two stages associated with different reaction loci and mechanisms are distinguishable : a surface reaction in an outer shell and a bulk reaction inside the particle. The rate control of the two mechanisms is discussed. The surface reaction stands isolated at low pressures of hydrochloric acid, and is measurable down to about 0.08 atm. of the gas. It affects only about 2 per cent of the rubber in Hevea latex, but up to over 20 per cent of synthetic or selectively creamed Hevea latex with sufficiently fine particles. The saturation of double bonds at the surface locus proceeds in an inward direction from the particle surface, and is limited to about the outer four layers of polymer chains. This restriction is due to the instability of the diffusing reagent in the rubber medium, which also accounts for the enormous nominal reaction order of the surface reaction. This order was found to be about 26 in one run, while the bulk reaction follows zero order kinetics. The kinetics of the isolated surface reaction is shown to be a useful tool in studying the unsaturation of the surface layers in vulcanized latex. By its means it is proved that a surface reaction can also affect latex vulcanization. This is technically important because the film strength of latex decreases critically with increasing vulcanization of the particle surface.
Pyridinium High Polymers—A New Class of Oil-Resistant Synthetic Rubbers
Authors: Reynolds W. B. , Pritchard J. E. , Opheim M. H. , Kraus G. 
Published: February 2011

Abstract
Copolymers of butadiene and 2-methyl-5-vinylpyridine are readily vulcanized by heating in the presence of organic halides. The number of effective crosslinks can be readily calculated from moduli of swollen stocks using the statistical theory of rubber elasticity. Crosslinking depends upon the amount and activity of the quaternizing agent. However, even at low levels of halide concentration, it appears that several quaternary groupings are necessary for each effective crosslink. Zinc oxide greatly increases the moduli of the swollen copolymer-halide systems. However, sulfur and accelerator alone have little effect on the same system and these agents do not further increase the moduli of the swollen ternary system, copoylmer-halide-zinc oxide.
The Rapid Semimicrovolumetric Determination of Sulfur in Natural and Synthetic Rubber Vulcanizates
Authors: Bauminger Bella B. 
Published: February 2011

Abstract
In the first part, a modified form of combustion apparatus for sulfur analyses is described, and the principle of the method and the apparatus itself are illustrated by a schematic diagram. In the determination of sulfur in natural-rubber, Butyl-rubber, and Krylene mixtures which contain no mineral fillers such as barytes and whiting, 50 mg. of finely divided vulcanizate is covered with aluminum oxide, decomposed in a current of oxygen at 1000° C, and the sulfuric acid formed is determined gravimetrically. An analysis requires about 30 minutes. Differences between the analytical values obtained and the calculated values never amount to more than ±1 per cent. In the second part of the work, a newly developed procedure for the determination of total sulfur in rubber mixtures which contain barytes, lithopone, whiting, etc., is described. The sample is covered with a mixture of vanadium pentoxide and zinc oxide and is then decomposed in a current of oxygen at 1000° C Here too the sulfuric acid which is formed is titrated acidimetrically. An analysis requires about one hour. The final part of the work deals with a new method for the determination of sulfur in synthetic-rubber vulcanizates, such as Neoprene, Perbunan, Hypalon, etc. The sulfuric acid formed by their combustion is precipitated by a hydrochloric acid solution of 4-amino-4′-chlorobiphenyl, and titrated with sodium hydroxide. Zinc, chlorides, and nitrates have no disturbing effects on the reaction. The method was tested with vulcanizates of known compositions and was found to give satisfactory results.
Effect of Initial Molecular Weight of a Rubber on the Strength and Fatigue of Its Vulcanizates
Authors: Bartenev G. M. , Novikov A. S. , Galil-Ogly F. A. 
Published: February 2011

Abstract
(1) With decrease of the original molecular weight of rubber, there is a parallel decrease of the durability of its vulcanizates when they contain the same percentage of combined sulfur. On the other hand, this decrease of durability with decrease of the original molecular weight is only slight for vulcanizates having the same equilibrium modulus, i.e., the same density of crosslinks in the three-dimensional network. (2) In dynamic testing which involves repeated stretching, the durability depends on the testing conditions when the vulcanizates contain the same percentage of combined sulfur and at the same time when either the original molecular weight of the rubber is low or the equilibrium modulus is small. On the contrary, when the original molecular weight or the modulus is high, the durability does not depend on the testing conditions. When vulcanizates have the same equilibrium modulus, their durability depends on the original molecular weight. In this latter case the durability increases with increase of the molecular weight, independent of the testing conditions (given maximum load, given maximum deformation, etc.), and reaches a practically constant value at high molecular weights. (3) The fundamental influence of the original molecular weight on the strength and dynamic durability of vulcanizates containing the same percentage of combined sulfur is manifest in the retardation of the formation of a spatial network in low-molecular rubbers when vulcanized. With rubber of low original molecular weight, vulcanization leads to the formation of a thin space network and consequently a large number of molecular chain ends outside the network. For this reason, vulcanizates of low-molecular rubbers when tested are characterized by high permanent set.
Transformation of Sulfur Links in Vulcanizates under the Action of Temperature
Authors: Tikhomirova N. N. , Kuzminskiĭ A. S. 
Published: February 2011

Abstract
1. It was shown that an exchange between free and combined sulfur takes place in vulcanizates. 2. A method for evaluating the relative durability of the sulfur links in vulcanizates was developed with the aid of the radioactive isotope of sulfur and the diffusion rate of sulfur between two vulcanizate films. The value of ilimit characterizes the equilibrium distribution of active sulfur. This method was used for investigation of a series of vulcanizates. 3. The heat treatment of vulcanizates leads to the formation of more durable sulfur links.
Thermal Degradation of Unvulcanized and Vulcanized Rubber in a Vacuum
Authors: Straus Sidney , Madorsky S. L. 
Published: February 2011

Abstract
The history of distillation of rubber under various conditions of temperature, pressure, and atmosphere goes back more than a century. As far back as 1860, Williams distilled rubber in an iron retort at relatively low temperatures and obtained some 5 per cent of crude isoprene. In 1922, Staudinger and Fritschi distilled rubber at 275° to 320° C at 0.1- to 0.3-mm. pressure and obtained 3.1 per cent of isoprene. In 1926 Staudinger and Geiger distilled rubber below 300° C at ordinary pressure in an atmosphere of carbon dioxide and obtained 4.3 per cent of crude isoprene. Distillation of rubber at higher temperatures and under atmospheric pressure yielded as much as 58 per cent of isoprene. In addition to isoprene, dipentene and higher terpene compounds were also identified in the distillation products of natural rubber. More recently, distillations of pure synthetic polyisoprene (a mixture of cis- and trans-polyisoprene), purified natural rubber (cis-polyisoprene), and purified gutta hydrocarbon (trans-polyisoprene) were carried out by the present authors in a vacuum under conditions of molecular distillation. The volatile products were fractionated and analyzed both qualitatively and quantitatively, using the mass spectrometer for the lighter fractions. The volatiles consisted of about 3 to 4 per cent of isoprene and 13 to 20 per cent of dipentene, the rest being large terpene fragments of average molecular weight of about 600. The present paper describes an investigation of the effects of various additions to natural rubber, with or without subsequent vulcanization, on the degradation process during pyrolysis in a vacuum, with the view that such a study might throw some light on the structure of vulcanized rubber. In addition to pyrolysis, a study was also made with unvulcanized and vulcanized rubber of the rates and activation energies of thermal degradation in a vacuum, using techniques and apparatus that were previously developed by the authors in connection with an extensive study of thermal degradation of a number of polymers.
Gamma-Ray Vulcanization of Rubber
Authors: Gehman S. D. , Auerbach I. 
Published: February 2011

Abstract
Vulcanization is the industrial process which transforms rubber from a soft, sticky, readily molded plastic to the highly elastic material familiar to everyone from innumerable uses. It was discovered by Charles Goodyear in 1839 and was one of the series of crucial inventions which started the United States on its industrial revolution in the nineteenth century. The automotive direction of this industrial development has accentuated the importance of rubber in succeeding years. This year the worldwide product volume to which vulcanization will be applied will exceed two and a half million tons. It is readily understood that vulcanization is now a highly developed process, the resultant of many improvements and developments over the course of a century of competitive use. Goodyear's original conception involved simply the heating of rubber with sulfur. The recognition of the chemical nature of the process was followed by the discovery of materials which, when added to the system, accelerated the reaction tremendously, allowed it to be carried out at lower temperatures, and improved profoundly the physical properties, uniformity, and aging resistance of the rubber. Such chemical vulcanizing systems are now applied in great variety. Many ways are known for vulcanizing rubber without using any sulfur, but they are of relatively minor commerical importance. Some of the synthetic rubbers require rather unique systems for vulcanization. There is continuous, intensive chemical research activity to find still better ways of vulcanizing rubber. So with gamma-ray vulcanization, it will be necessary to show some very tangible advantages to find even a few specialized applications. The idea of vulcanizing rubber by exposure to energetic radiation is not new. A patent issued to E. B. Newton in 1933 claimed the vulcanization of rubber by short exposures to 250-kV cathode rays. Effects of pile irradiation on uncured elastomers were studied by Davidson and Geib. Numerous investigations of the effects of radiation on the physical properties of plastics are listed in the bibliography prepared by Sun. Gehman and Hobbs observed the vulcanization of rubber by intense gamma radiation. Jackson and Hale measured the physical properties of rubber-filler mixtures as a function of the radiation dose from a strong Co60 source for a variety of elastomers. Cross-linking of rubber by pile irradiation was studied in a quantitative way by Charlesby. He emphasized the usefulness of radiation crosslinking as a means for studying the average molecular weight, variation of the gel fraction, and the changes in properties of rubber as the degree of crosslinking is varied.
Structural Characteristics of the Sulfur Linkage in Natural Rubber Vulcanizates
Authors: Bateman L. C. , Glazebrook R. W. , Moore C. G. , Saville R. W. 
Published: February 2011

Abstract
Polyisoprenes react with sulfur both intramolecuarly and intermolecularly to yield cyclic sulfides and crosslinked sulfides, respectively. The structures of these have been examined for the reaction of the di-isoprene, 2,6-dimethylocta-2,6-diene, with sulfur at 140°. The cyclic sulfides consist of the two saturated compounds (I) and (II) and the two unsaturated compounds (III) and (IV). The crosslinked sulfide consists of a complex mixture in which unsaturated open chain and saturated and unsaturated cyclic sulfide structures have been identified. The structures of these products suggest a polar reaction mechanism, and also that hydrogen sulfide participates in the reaction. The influence of organic bases, the sulfurizing agent, reaction temperature, and zinc salts on the nature of the sulfur linkage is discussed.