bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stability of the Vulcanized Cross-Link in Butyl Rubber: Theory and Application
Authors: Zapp R. L. , Ford F. P. 
Published: February 2011

Abstract
When rubberlike polymers are vulcanized with sulfur, the process involves two competing phenomena. The competing reactions are cross-linking and degradative in nature, and the conditions of vulcanization, as well as the extent, govern the rate at which these actions take place. At lower temperatures (110 to 150° C) vulcanizate degradation is held at a minimum, while higher temperatures usually accelerate the reversion process. A recent stoichiometric study of sulfur addition during Butyl rubber vulcanization revealed that the cross-link was composed of two atoms of sulfur. Calculations from analytical data placed the number of atoms at 1.7 to 2.2 per cross-link. This degree of constancy was maintained, regardless of the extent of vulcanization, until the onset of reversion. Reversion is the degradative process opposite to cross-linking. It can be pictured as the breakdown of the sulfur bridges between polymer molecules, and in Butyl it is evident at vulcanization temperature above 350° F. in 20 minutes. The type of rubber plays an important part in the relative way the two competing reactions occur. In addition, the whole process of cross-linking and reversion may be complicated by oxidative phenomena in predominantly diene type polymers. For example, when the vulcanization of natural rubber is prolonged, softening of the structure is followed by a hardening of the network, attributed to oxidation or cyclization. With Buna type rubbers, the softening action is barely evident before continued heating leads to a harder less extensible material As shown by Andrews, Tobolsky, and Hanson, the stress of a GR-S vulcanizate under intermittent strain increased on aging at 130° C. The stress of a Butyl sample remained essentially unchanged under the same conditions for about 10 hours, whereupon noticeable stress relaxation ensued. The use of an elastomer with a chemical unsaturation of 1 to 2 mole per cent of that found in polyisoprene reduces the opportunities for cyclization reactions. Observations on the stability of the sulfur cross-link can be made with less interference.
The Addition of Thio Compounds to Olefins. III. Reactions of Tri- and Hexamethylenedithiols, and of Bisthioladipic and Bisthiolsebacic Acids
Authors: Cuneen J. I. 
Published: February 2011

Abstract
Certain thiols and bisthiol acids react with natural rubber and with some related olefins in a manner analogous to the corresponding monofunctional compounds. The physical characteristics of the vulcanizates obtained from natural rubber and bisthioladipic acid are described.
The Structure of Chlorinated Rubbers
Authors: Allirot René , Orsini Léon 
Published: February 2011

Abstract
Natural rubber chlorinated to the maximum degree is a homogeneous product in chemical composition and likewise in chemical structure. It is a chemically saturated compound, with a chain structure having the cyclohexane group, C10HxCl7, as the base unit. Such a structure is conceivable only if x has a value of 11, which cannot be determined precisely by any of the methods of organic analysis.
Determination of Volatile Fatty Acids in Natural Rubber Latex
Authors: Philpott M. W. , Sekar K. C. 
Published: February 2011

Abstract
The want of a chemical method to determine incipient decomposition in preserved latex has been long felt by producers and consumers of latex. A method often used is to neutralize the ammonia in latex with boric acid or sulfuric acid, and to judge the extent of decomposition from the intensity of putrefactive odors. This method, besides having limitations common to all subjective tests, is insufficiently sensitive to detect the early stages of putrefaction. Another way of assessing deterioration in latex is to determine the total concentration of acidic substances by KOH titration. Though it is widely used in industry, the method has several disadvantages, both as a test for decomposition and as an index of processing behavior. First, acids are estimated which titrate up to pH 11.2, thus failing to discriminate between stabilizing (i.e. soap forming) and destabilizing (e.g. formic, acetic) acids. Second, conjugate acids of bases, basic groups of zwitterions from amino acids, etc., are included. Third, it fails with latexes to which soaps or fixed alkalies have been added. Following observations made in 1941 by the late W. S. Davey at the Rubber Research Institute of Malaya, we have now shown that a substantial proportion of the acids formed in latex as a result of natural degradation processes can be distilled in steam, and that these volatile acids consist mainly of acetic acid, with some formic and propionic acids. It is considered that a test of spoilage based on the estimation of these acids would be free from the disadvantages that are inherent in the KOH titration, and methods of determining quantitatively the volatile fatty acids in latex have accordingly been worked out.
Electron Microscopy of Rubber Globules in Hevea Latex
Authors: van den Tempel M. 
Published: February 2011

Abstract
The particle size distribution of the rubber globules in Hevea latex has been studied by means of electron microscopy. Most of the particles, even in concentrated latex, are less than 0.2 micron in diameter and are, consequently, not visible in the light microscope. These small particles have considerable influence on the specific interface, but they contain only a few per cent of the rubber present.
Chromatograpic Analysis of Vulcanized Rubbers. Some Rapid Methods for the Detection of Certain Accelerators and Antioxidants
Authors: Parker C. A. , Berriman Joyce M. 
Published: February 2011

Abstract
The chromatographic behavior on silica gel/Celite adsorbent, of thirty-two accelerators and antioxidants has been investigated. Adsorption series have been established with four binary solvent mixtures and, based on these results, some simple and rapid methods have been designed for the identification of the compounds. These depend on the application of various streak reagents to the extruded chromatographic column, and with many of the compounds they give an almost unambiguous identification, even when several compounds are present in admixture. The methods are discussed in relation to those previously available for the identification of accelerators and antioxidants. They offer some important advantages. The methods have been successfully applied to a number of rubbers of known composition. Accelerator transformation products have in some cases been detected or identified. No case of accelerator decomposition during chromatography has been observed, but decomposition of certain accelerators during acetone extraction of the rubber has been noted. The results obtained have been compared with previous work on accelerator transformation products.
Variables Controlling the Cross-Linking Reactions in Rubber
Authors: Barton Bernard C. , Hart Edwin J. 
Published: February 2011

Abstract
During vulcanization, sulfur reacts with rubber and compounding ingredients in various ways to give diversified reaction products. Only the sulfur that forms cross-links between rubber molecules contributes to the transformation of rubber from the plastic to the elastic state. Reactions of sulfur which lead to products other than intermolecular cross-links are considered side reactions of secondary importance to vulcanization. This study was initiated to determine in a relatively quantitative manner the effect of time, temperature, and concentration of reactants on the yield of intermolecular cross-links in the 2-mercaptobenzothiazole-accelerated sulfur-vulcanization of Hevea rubber. This investigation was considered a necessary step in a study of the over-all mechanism of the vulcanization reactions. When conditions necessary for the greatest yield of cross-links per unit of combined sulfur are followed, a linear relationship exists between stress at 200 per cent elongation (a measure of the relative number of cross-links) and combined sulfur. Under conditions that lead to a maximum yield of crosslinks, a linear relationship exists between retractive force and zinc sulfide.
Studies of the Vulcanization of Rubber. X. The Vulcanization of Natural Rubber with a Mixture of Sulfur Dioxide and Hydrogen Sulfide
Authors: Dogadkin B. A. , Keifetz F. 
Published: February 2011

Abstract
1. The dynamics of the changes of the properties of rubber during vulcanization by a mixture of sulfur dioxide and hydrogen sulfide, in distinction from conventional vulcanization by sulfur, is expressed by smooth curves. No vulcanization optimum is observed. 2. With multiple cycles of vulcanization, the increase of bound sulfur content above 3 per cent results in a decrease of tensile strength. 3. Changes of tensile strength of the vulcanizate dependent on changes of sulfur content are attributable to the influence of the density of the spatial network on the orientation processes during deformation.
Mechanism of the Action of Inhibitors of the Oxidation of Elastomers
Authors: Kuzminskii˘ A. S. , Angert L. G. 
Published: February 2011

Abstract
A number of works have been published in the recent scientific literature concerning the action of antioxidants in elastomers. Most of these works are of an empirical nature and are of purely practical value. In certain foreign works, unsuccessful attempts were made to relate the effectiveness of action of antioxidants with one of their specific properties, for example, with their oxidation-reduction potential. The mechanism of inhibited and of free oxidation of elastomers was studied in detail by one of the present authors. Based on a theory of chain reactions, Semenov concluded that the oxidation of rubber involves a chain degradation process, and he showed that the inhibitor, phenyl-β-naphthylamine, breaks the oxidation chains, reacting with the peroxidic radicals which are formed in the rubber molecules during oxidation. The inhibitor is consumed by union with the hydrocarbon molecule. Consumption of inhibitor during heat treatment of rubber is observed only in the presence of oxygen. In the light of our theories of the oxidation of rubber, and also on the basis of contemporary theories of the activity of radicals, according to which the more active molecules in the radical reactions form less active radicals, and vice versa, the mechanism of the action of inhibitors can be described as follows. The peroxide radicals of the rubber detach the more active or mobile hydrogen from the inhibitor molecule, and the radical formed as a result of this reacts with the rubber radicals, breaking the oxidation chains.
Vulcanization Characteristics of Natural Rubber
Authors: Stiehler Robert D. , Roth Frank L. 
Published: February 2011

Abstract
The present classification program for natural rubbers has been handicapped by the lack of adequate means to characterize their behavior on vulcanization. Several methods have recently been proposed for this purpose. Roth and Stiehler described the strain test from which three vulcanization parameters can be calculated. Two of these parameters have been combined by Schade. Thirion proposed a method for calculating two parameters from the customary measurements of stress at 600 per cent elongation. Gee and Morrell have recently suggested a procedure for determining two parameters from measurements of Mooney viscosity and stress at 100 per cent elongation. Workers at The B. F. Goodrich Company have proposed the use of the Mooney viscometer for determining two parameters. The present study was initiated to compare these methods for classifying natural rubbers. At the same time, an investigation was made of several conditions of treatment of the compound before vulcanization and of the temperature of vulcanization to determine their relative effects on the parameters and the classification of the rubbers. For this work, four Hevea rubbers that covered a wide range in both rate of cure and ultimate stiffness of the vulcanizate were chosen. The rubbers were smoked sheet, pale crepe, sprayed latex, and Tensorub. The sample of smoked sheet was from a bale of No. 1 grade rubber, taken at random. The same was true for pale crepe. The sample of sprayed latex rubber was prepared by the U. S. Rubber Co. plantation by spray-drying once-creamed formaldehyde-preserved latex. The sample of Tensorub was produced by Socfin Co., Ltd., in Malaya and was selected to represent a high-quality smoked sheet.
The Vulcanization of Thick Sheets of Rubber
Authors: Bott E. C. B. 
Published: February 2011

Abstract
Schmidt's method for the determination of temperatures attained by various thicknesses of solid sheets during heating and cooling is adapted for the calculation of the amounts of vulcanization obtained for flat sheets of soft rubber and of the extra time needed to obtain a full vulcanization in the center of the sheets. The uniformity of vulcanization of the central portion of the sheets is investigated.
Direct Determination of Oxygen in Rubber. Comparison between Isotopic and Schütze-Unterzaucher Methods
Authors: Kirschenbaum A. D. , Streng A. G. 
Published: February 2011

Abstract
The values obtained by the isotope method for the direct determination of oxygen in rubber agree very nicely with the values obtained for the gain in weight on oxidation. The values obtained by the Schütze-Unterzaucher method, reported herein, are all low. This study indicates that the Schütze-Unterzaucher may give low oxygen values for compounds which form non-vaporizable carbon residues, such as rubber.
Viscometric Detection of Branching in Polymers. II. Branching in Poly(Butadiene-Co-Styrene) as a Function of Polymerization Temperature
Authors: Cragg L. H. , Fern G. R. H. 
Published: February 2011

Abstract
Previous experience with polystyrene, normal and cross-linked, and with GR-S, gave strong support to our belief that, in careful viscosity measurement and evaluation of either of the slope constants β and k′, a useful and convenient means is available for the detection and measurement of branching in soluble high polymers. Moreover, since the measurements are made on separate fractions, information can be obtained regarding the relation between the size of polymer molecules and the degree to which they are branched. In the work reported here, this method was applied in a study of the effect of the temperature of polymerization on branching. It is now well known, of course, that, by reducing the temperature of polymerization, desirable changes of the physical behavior of emulsion polymers may be effected. This observation led to the development of “cold rubber” as an improvement over GR-S for use in tire tread stocks. Many efforts have been made to explain this superiority on the basis of changes in molecular structure. Several effects of lowering the temperature of polymerization have been noted : a narrowing of the molecular-weight distribution, a slight decrease of the proportion of the 1,2-isomer, a more marked increase of the proportion of the trans-form of the 1,4-isomer, and a decrease of the extent of chain branching. Of these various effects, the one most difficult to detect and to measure quantitatively is chain branching.
The Effect of Comonomer on the Microstructure of Butadiene Copolymers
Authors: Foster Frederick C. , Binder John L. 
Published: February 2011

Abstract
The microstructure of butadiene-styrene copolymers having a wide range of styrene contents has been determined by infrared absorption. The results demonstrate that the percentage of trans-1,4-addition increases, the 1,2-addition decreases, and the cis-1,4-addition decreases as the styrene content is increased. Similar measurements of five other butadiene copolymer systems indicate that all these vinyl monomers, acrylonitrile, methacrylonitrile, methylvinyl ketone, vinylpyridine, and α-methylstyrene, change the microstructure in the same direction as styrene, differing only in the magnitude of their effect. A theoretical explanation, consistent with the experimental results obtained, is given for the change in microstructure with comonomer content.
Self-Inhibition in the Oxidation of Butadiene-Acrylonitrile Rubbers
Authors: Kuzminskiĭ A. S. , Popova E. B. 
Published: February 2011

Abstract
Because of their valuable technical properties, copolymers of butadiene and acrylonitrile rubbers have found wide use in the rubber industry in the production of oil-resistant and heat-resistant products. Investigations have established that, during the copolymerization of butadiene with acrylonitrile, the latter enters principally at the 1,4-position of the main chain. This is observed most clearly with relatively large concentrations of acrylonitrile. Our own work showed that the double bonds in the main hains of the rubber molecules are the most active points in the chain. It indicated also that butadiene-acrylonitrile rubbers should oxidize at a fast rate. However, in reality they show great chemical stability. The present study is devoted to an explanation of the nature of oxidation of butadiene-acrylonitrile rubbers. Both the free and inhibited oxidation of copolymers containing, respectively, 20, 29.6 and 35 per cent of acrylonitrile (CKH-18, CKH-26, and CKH-40) was studied. Before oxidation, the rubbers were purified by extraction and double precipitation from benzene solutions. The rubber films were prepared and oxidized with molecular oxygen according to methods described previously.
Chlorination of Natural Rubber in Solution with Gaseous Chlorine
Authors: Ramakrishnan C. S. , Raghunath D. , Pande J. B. 
Published: February 2011

Abstract
The chlorination of rubber solutions by gaseous chlorine was followed by isolating the partially chlorinated products and preparing their ozonides. The ozonides were hydrolyzed, and the acids and aldehydes formed on hydrolysis were determined. By a comparison with the amounts of acids and aldehydes obtained from ozonides of unreacted rubber, the amount of residual isoprenic double bonds present was found. The loss of double bonds attending the introduction of chlorine atoms into the molecule of rubber indicates four definite stages in chlorination : (1) initial substitutive attack by chlorine, with concomitant cyclization, resulting in a loss of one double bond between two isoprenic units, (2) substitution, (3) additive reaction, and (4) essentially substitution. Chlorination of aged rubber solutions differs from the above in that the cyclization reaction (stage 1) seems to be absent.
Carbon Black Particle Size
Authors: Leigh-Dugmore C. H. 
Published: February 2011

Abstract
Carbon black particle diameters tend to be distributed log-normally. This discovery has led, first, to simplified methods for the calculation of mean diameter and specific surface from electron microscope measurements; second, to a demonstration that the observed differences between estimates of surface area from electron-microscope measurements and from low-temperature nitrogen adsorption measurements cannot be entirely explained by supposing the finest particles not to be resolved by the electron microscope, thus adding further support to the porosity explanation; and third, to the argument that any two size characteristics, such as mean particle diameter and specific surface, are entirely sufficient to describe particle size and its distribution and, consequently, their influence on vulcanizate properties.
A Study of the Goodrich Flexometer with Synthetic Polymer Compounds
Authors: Labbe B. G. 
Published: February 2011

Abstract
The relation between the testing temperature (100, 158, and 212° F) and the hysteresis-temperature rise of the synthetic polymers at the cures used was found to behave as a linear function. The slopes of the lines seem to indicate that the relative order of efficiency of the vulcanizates varies at different temperatures of test and cure levels. Frequency variations at 212° F ranged from 980 to 1800 flexures per minute. The temperature rise is a linear function of the frequency for all compounds tested. The increase of temperature rise with an increased rate of flexing is approximately uniform for all compounds (about 2° F per 100 f.p.m.) at the cure levels studied. The state of cure is shown to influence the rate of change of the temperature rise with the change in frequency. The relation of the degree of deflection to the temperature rise characteristics of the rubber samples at 100 and 212° F was studied at 10, 17.5 and 25. per cent deflections. An error of deflection of one percentage unit will cause a .3° to 4° F error in the 10-minute temperature rise value. As the state of cure or the temperature decreases, the error in the temperature rise increases. A change of load has less effect on the temperature rise and set values than any of the other conditions investigated. Most of the lack of reproducibility among laboratories is probably due to failure to adjust precisely the throw (deflection of the specimen) of the test apparatus which is being used.
The Mechanism of the Action of Aromatic Thiols on Rubber Solutions
Authors: Kheraskova E. P. , Gamayunova A. P. 
Published: February 2011

Abstract
1. The effect of aromatic thiols on the kinetics of the change in viscosity of natural-rubber solutions on heating was studied. 2. Aromatic thiols accelerate the oxidation of rubber. 3. In the process of heating rubber solutions, thiols are oxidized to the corresponding disulfides. The rate of oxidation of the rubber depends on the rate of oxidation of the thiol. 4. The mechanism of the action of thiols is explained by the presence of an accompanying reaction, whereby oxidation of the thiol induces oxidation of the rubber.
Birefringence of Rubbers
Authors: Saunders D. W. 
Published: February 2011

Abstract
It has been shown, both theoretically and experimentally, that in simple elongation of a sample of pure-gum vulcanizate, an approximately linear relationship between the tensile stress t and the birefringence (n1−n2) obtains, provided the strain is not sufficiently large to produce crystallization. We may write: (n1−n2)=Ct, where C, the constant of proportionality, is termed the stress coefficient, and is theoretically independent of the degree of cross-linking (vulcanization) of the vulcanizate, and should be identical for all pure rubbers.
The Preparation of Cyclized Rubber from Natural-Rubber Latex
Authors: van Veersen G. J. 
Published: February 2011

Abstract
The hydrochlorination of rubber in the form of latex which has been stabilized by surface-active agents, such as Emulphor-O, or by cationic agents such as Fixanol, shows that hydrogen chloride molecules diffuse very easily into the latex globules. Accordingly it was to be expected that, by replacing hydrogen chloride gas by hydrogen fluoride gas, which is a cyclizing agent of rubber, a cyclized rubber would be obtained. This line of reasoning was confirmed experimentally. As a result of an experimental study, it was proved that boron fluoride, BF8 also, brings about cyclization of rubber in latex, and van Amerongen has already shown that sulfuric acid likewise can be used as a catalyst. Since sulfuric acid is much easier to handle than either hydrogen fluoride or boron fluoride, it was used in most of the experiments in the present work.
Determination of Free Carbon in Cured Rubber Stocks
Authors: Kolthoff I. M. , Gutmacher R. G. 
Published: February 2011

Abstract
A method for the determination of free carbon in vulcanized rubber stocks is described. The sample is softened in boiling p-dichlorobenzene before treatment with tert-butyl hydroperoxide in the presence of osmium tetroxide. No difficulties are encountered in the filtration of the carbon black. The carbon black is washed on the filter with dilute nitric acid to remove acid-soluble inorganic fillers. The method has been successfully applied to natural rubber, GR-S, Butyl rubber, and Neoprene. No correction is necessary.