bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Associated Salts on the Polymerization of Butadiene by Organosodium Reagents
Authors: Morton Avery A. , Bolton Frank H. , Collins Frances W. , Cluff Edward F. 
Published: February 2011

Abstract
The alfin catalyst is a combination of sodium salts which causes butadiene to polymerize at extreme rapidity in such a fashion that a greater difference exists between sodium and alfin polymerization than between sodium and emulsion polymerization. Hitherto the combination has been assumed to be binary—allylsodium and sodium isopropoxide—but a new method of preparation has revealed that a halide or pseudohalide salt is essential. Chloride, bromide, and iodide salts of sodium and potassium can be used as the halide component, but fluoride and lithium salts, as a rule, cannot be so employed unless the small size of each ion is compensated by a large cation or anion, respectively, as found in cesium fluoride or lithium iodide. The sodium cation is required for the catalyst. The potassium ion can be tolerated in the alkoxide or halide, but not simultaneousely in both. The lithium ion is in general unsuitable. Alfin polybutadiene is differentiated from sodium-polymerized butadiene by a high proportion of 1,4-structure and by an abnormally high intrinsic viscosity. Iodine chloride causes the polymer to precipitate from solution. All results indicate that polymerization by sodium reagents is in considerable degree controlled by the association of other salts with the sodium reagent.
Effect of Oxygen Concentration on Aging of Rubber Vulcanizates. II. Effect of Partial Pressure of Oxygen on Changes in Physical Properties Accompanying Oxidation
Authors: Shelton J. Reid , Cox William L. 
Published: February 2011

Abstract
The over-all rate of deterioration of physical properties increases with the oxygen concentration, as would be expected from the increased rate of oxygen absorption: The nature of the deterioration resulting from a given amount of oxygen absorbed is influenced also by changes in the partial pressure of oxygen in the aging atmosphere. It appears that chain scission is favored at higher oxygen concentrations, while cross-linking becomes of greater relative importance at lower oxygen concentrations. These data suggest that R⋅ radicals are more effective than RO2⋅ radicals in reacting with double bonds to form crosslinks. Heat aging in the absence of oxygen, as observed by heating a vulcanizate in lamp-grade nitrogen, results in considerable stiffening, particularly in the case of a GR-S black stock. This effect is observed primarily in the first few hours of heating, and may account for some of the erratic behavior observed in the early stages of aging when changes in physical properties are compared on the basis of amount of oxygen absorbed. Higher oxygen concentration brings about a more rapid oxidation, and also results in a higher proportion of chain scission compared to cross-linking for a given amount of oxygen absorbed. As tensile decay is the most evident sign of deterioration of Hevea stocks, it follows that the aging behavior of natural rubber in air at normal storage temperatures will be better than that predicted by high temperature testing in oxygen. In the case of GR-S stocks, on the other hand, oxidative hardening is the most serious result of aging, and consequently, the aging behavior of GR-S stocks in air at normal storage temperatures is poorer than would be expected on the basis of comparative tests in oxygen at higher temperatures.
Technically Classified Rubber—The Non-Rubber Content and the Measurement of Cure Rate
Authors: Veith A. G. 
Published: February 2011

Abstract
The nonrubber content of typical samples of all grades of technically classified rubber has been determined. It is found that the nonrubber content increases in the order: red, yellow, and blue. The chemical analyses performed to determine the nonrubber content were as follows: per cent ash, per cent nitrogen, per cent acetone extract, and per cent fatty acid. The pH of both a slurry of the ash and the aqueous digest indicates that blue rubber is more basic in these respects than are red and yellow rubbers. The measurement of the cure rate of these samples of technically classified rubber has been carried out by means of (1) conventional stress-strain testing, (2) the present ASTM method utilizing the Mooney viscometer, (3) the National Bureau of Standards strain test, (4) a new and more quantitative approach developed by Gee and coworkers, and (5) a utilization of the Mooney viscometer to determine two of the parameters of Gee's equation which gives the time dependence of modulus. All of these methods place the rubbers in the same relative order. The use of the viscometer to determine two of the parameters of Gee's equation was prompted by the degree of correlation between the rate parameter obtained with the present ASTM method and the rate constant k calculated by Gee's methods. As a result of a preliminary investigation as to the causes of viscosity increases at curing temperatures, it was found that, within limits of experimental error, all of the viscosity increase is due to the formation of a cross-linked network, with a linear relationship existing between viscosity increase ΔVc and modulus (at 100 per cent elongation) f. The results of a comparison of the rate constants obtained by the viscometer and by Gee's method indicate that for MBT mixes at 260° F there is good agreement between the methods. Statistical analysis shows that the samples employed for this study are significantly different in their rate of cure. The variance, range, and mean of some of the parameters obtained with the viscometer over a 10-week period are also given. It is suggested that the Mooney viscometer be employed to classify natural rubber according to its cure rate. If this is done, it will be necessary to define the degree of accuracy desired. To determine accurately the cure rate, it is necessary that the viscometer be used in conjunction with a press cure for the estimation of the parameter f∞. If it is not feasible to carry out press cures, an average value for f∞ can be assumed, and then only a short time test with the viscometer is required.
Evaluation of Ozone Protective Agents for Elastomers. Apparatus for the Evaluation under Dynamic Conditions
Authors: Creed K. E. , Hill R. B. , Breed J. W. 
Published: February 2011

Abstract
The widespread acceptance of synthetic elastomers for use in rubber products has greatly magnified the problem of obtaining satisfactory protection against weathering in general and ozone attack in particular. Because the tentative ASTM method of evaluation is not entirely satisfactory, a dynamic apparatus has been developed which provides an effective means for accelerated evaluation of ozone protective agents, using a new mechanical arrangement for flexing the rubber, a new specimen shape, rigid control of the ozone concentration, and a new rating system. The apparatus consists of a series of rotating pulleys within a circular chamber. The test-specimens, circular molded belts, are rotated around two pulleys, which gives them approximately 75 flexes per minute with an elongation of 0 to 20 per cent. The flexing provides a mobile surface, so that rigid waxy films cannot be formed, and the molded specimen eliminates the possibility of freak cracking and anomalies due to minute nicks or imperfections during dieing out. The larger surface available for examination facilitates interpretation of results. Air at a rate of 1 cubic meter per hour passes through the chamber with a controlled ozone concentration of 25 ± 5 parts per 100,000,000 at 30° C. Uniformity is ensured by use of a fan in the chamber. The concentration of ozone is determined by potassium iodide method. By a simplified rating system a non-technical person can rate a large number of specimens rapidly and without elaborate equipment.
Aids in Vulcanization of Lignin-Natural Rubber Coprecipitates. Lead, Copper, and Bismuth Oxides
Authors: Griffith T. R. , MacGregor D. W. 
Published: February 2011

Abstract
No difficulty is experienced in the vulcanization of natural rubber containing lignin added as a dry powder, but this method of addition results in relatively low tensile strengths. When lignin solution was added to latex, however, the masterbatch obtained by coprecipitation was difficult to vulcanize. For example, if conventional acceleration was used, i.e., mercaptobenzothiazole with zinc oxide, the test slabs were soft, tacky, and logy, and could be removed from the mold only with difficulty. Although hydrogen sulfide might be a necessary intermediate in the vulcanization reaction, published experimental evidence shows that an excessive concentration of hydrogen sulfide retards vulcanization, even in the presence of powerful organic accelerators. In order to test the possibility that the retardation of cure with lignin master batches might be due to excessive hydrogen sulfide developed during vulcanization, owing to reaction of sulfur with lignin, various metallic oxides were tried which might react with hydrogen sulfide to form insoluble sulfide, and so reduce the hydrogen sulfide concentration. Lead oxides, copper oxide, and bismuth oxide were successful with lignin masterbatches, particularly when used with a dithiocarbamate accelerator. A lignin compound containing litharge, curing in 20 minutes at 282° F, had a tensile strength about 800 pounds per square inch above that obtainable with MPC carbon black. The Bashore resilience figure for the lignin compound was about double that for MPC carbon black. The aging qualities of vulcanizates containing lead oxide and lignin appear to be good, and even copper oxide, which is normally considered to be detrimental, ages satisfactorily, provided an antioxidant is included. A lignin compound containing 7 parts of copper oxide on 100 parts of rubber and 2 parts of antioxidant showed a drop of less than 20 per cent of its tensile strength after 2 days in an air oven at 90° C.
Cross-Linking in Natural-Rubber Vulcanizates
Authors: Adams H. E. , Johnson B. L. 
Published: February 2011

Abstract
Recently, a method for measuring the average number of cross-links per chain of vulcanized polymer has been developed. It is possible to calculate the degree of cross-linking of the vulcanizate from its amount of swelling in a solvent such as benzene. This method was used by Flory to study the effect of primary molecular weight on the cross-linking of Butyl vulcanizates. An evaluation of the general validity of the method was ascertained by using quantitative cross-linking agents (diazodicarboxylates) to prepare vulcanizates of natural rubber and GR-S. Bardwell and Winkler have also used this technique to study the relationship between the degree of cross-linking and the force of retraction at 300 per cent elongation of GR-S latex vulcanized with potassium persulfate. The formation of cross-linking during the vulcanization by sulfur of several polymers has also been investigated. Gee has compared the formation of cross-linking in natural rubber vulcanizates with the amount of combined sulfur. Carbon-to-carbon cross-links were believed to be formed in a nonsulfur tetramethylthiuram disulfide (TMTD) cure. A similar study of Butyl rubber vulcanizates, cured with sulfur-TMTD, indicates that disulfide cross-links are formed. Scott and Magat have estimated that eight sulfur atoms are associated with each cross-link in Russian SK (sodium polybutadiene). This investigation was undertaken to extend Gee's study on the correlation of the cross-linking of natural-rubber vulcanizates with the amount of combined sulfur.
The Viscometric Detection of Branching in Polymers. I. Branching in GR-S as a Function of Conversion
Authors: Cragg L. H. , Brown A. T. 
Published: February 2011

Abstract
Samples of GR-S were taken from a continuous emulsion-polymerization system at conversions 32.0, 45.1, 61.2, and 73.4 per cent, respectively, and each, after careful drying, was carefully fractionated to give five or six top fractions. For each of these fractions, values of intrinsic viscosity [η] and of the viscosity slope constants, β and k′, were determined. As with normal and cross-linked polystyrene, β and k′ appear to be constant for all linear species, but to have higher values for branched species, the increase being a measure of the extent or degree of branching. From the data obtained it is concluded that in GR-S there is little or no branching at low conversions, that the degree of branching increases markedly with increasing conversion, and that branching occurs to the greatest degree in the species of highest molecular weight. There seemed to be, for this polymer at least, a molecular weight below which branching could not be detected, regardless of conversion, but above which branching increased with increasing molecular weight.
Structural Changes in Rubber Caused by the Action of Molecular Oxygen. V. Destructive Solution of Vulcanized Synthetic Rubbers
Authors: Tarasova Z. , Dogadkin B. 
Published: February 2011

Abstract
1. Vulcanized synthetic rubbers, when heated in a hydrocarbon medium containing molecular oxygen, dissolve completely. The kinetics of destructive solution of vulcanized synthetic rubbers follows the pattern established for the destructive solution of vulcanized natural rubber. 2. The rate of destructive solution of a vulcanizate depends on the molecular structure of the rubber. Rubbers are classified in the following order according to the increase of rate of solution of their vulcanizates : Butyl rubber &lt; sodium-butadiene rubber &lt; butadiene-styrene rubber &lt; polychloroprene &lt; natural rubber. The apparent energy of activation of natural rubber is 19 kcal. per mole, for sodium-butadiene rubber 31.2 kcal. per mole, and for butadiene-styrene rubber 27.1 kcal. per mole. 3. The rate of destructive solution of vulcanized butadiene rubbers depends linearly on the extent of 1,4-structure in the rubber molecule. 4. The mechanical properties of vulcanizates do not appreciably influence the rate of their destructive solution. The type of accelerator used, however, is of essential importance; in fact, its influence corresponds to its influence on the rate of absorption of oxygen. 5. The presence of water slows down the dissolution of vulcanizates of natural and sodium-butadiene rubbers, since it retards their absorption of oxygen. 6. The rate of destructive solution of a vulcanizate in various solvents depends linearly on the coefficient of absorption of oxygen in the solvents. 7. The viscosity of a solution of decomposed vulcanized sodium-butadiene rubber depends linearly on the concentration up to 50 per cent. 8. The mean specific molecular weight, measured cryoscopically, of sodium-butadiene rubber was 2400– 3600, and the osmotic weight, 16,000. The axial ratio of the particles was 1:15. 9. The hypothesis is advanced that solutions of decomposed vulcanizates constitute a special type of colloid solution.
Degradation of Natural Rubber in Solution in Vacuo
Authors: Watson W. F. 
Published: February 2011

Abstract
Rubber in solution degrades in the absence of oxygen. This nonoxidative degradation is the main cause of the decrease of viscosity of rubber solutions on storage. The rate of degradation is proportional to the rubber concentration and is independent of the purity and molecular weight of the rubber initially. The energy of activation for degradation in chlorobenzene is 15.9 ± 0.5 kcal. The rate of reaction is not influenced by different nonpolar solvents for rubber, but is accelerated by acids. These results suggest that rubber polymer possesses one anomalous bond per 1.3×104 monomer units. Evidence is advanced for this phenomenon being associated with the gelling of solid rubber on storage.
Structure and Properties of Loaded Rubber Mixtures. X. Alteration of Carbon Black Structures by Heat Treatment
Authors: Dogadkin B. A. , Pechkovskaya K. , Mil'man Ts 
Published: February 2011

Abstract
1. Raising the temperature of vulcanizates containing carbon black causes changes in the carbon structures, which can be estimated by the value of specific electric resistivity ρ and the index n in the equation: I=cVn, relating the strength of the current I with the voltage V. 2. These changes are nearly independent of the type of rubber and are governed chiefly by the type of carbon black. 3. The change of electric resistivity of vulcanizates with temperature follows an exponential law, and can be expressed by the equation : ρt=ρ0 eαt. 4. The sign of the coefficient α is negative for vulcanizates containing channel carbon black, and positive for those containing nozzle black or lamp black. 5. Heating of vulcanizates (up to 100°) for 30 minutes causes destruction of the nozzle black and lamp black particles, but causes little apparent destruction of channel black structures. 6. Prolonged heating (10 hours or more) at temperatures above 60° C causes destruction of the particles of all the carbon blacks studied. This detruction is more extensive in the case of nozzle and lamp blacks than in the case of channel black. 7. During heat treatment of mixtures containing channel black, it is chiefly the carbon-rubber bonds that are destroyed (the index n decreases); whereas in mixtures containing nozzle, furnace and lamp blacks, it is chiefly the carbon-carbon bonds that are destroyed (the index n increases). 8. The higher the temperature during deformation and relaxation, the greater is the degree of restoration of the carbon structures which are destroyed during deformation. 9. The degree of restoration of the carbon structures under identical conditions of deformation and relaxation of vulcanizates containing nozzle black is greater than that of corresponding vulcanizates containing channel black.
Acrylic Elastomers Preparation and Properties of Vulcanizable Acrylic Ester-Acrylonitrile Copolymers
Authors: Filachione E. M. , Fitzpatrick T. J. , Rehberg C. E. , Woodward C. F. , Palm W. E. , Hansen J. E. 
Published: February 2011

Abstract
Copolymers of various acrylic esters, from ethyl to octyl, with 5 to 15 per rent acrylonitrile or methacrylonitrile, were prepared by refluxing emulsion polymerization and in two instances by redox polymerization. These copolymers were easily vulcanized with sulfur and triethylene tetramine recipes. Heat-resistant vulcanizates were obtained from the copolymers of acrylonitrile with ethyl, butyl, amyl, and hexyl acrylates and also from the copolymer of methacrylonitrile with butyl acrylate. The octyl acrylate-acrylonitrile copolymers and the octyl acrylate, ethyl acrylate, and acrylonitrile terpolymerse did not show similar heat resistance. Terpolymers obtained from ethyl acrylate, butyl acrylate, and acrylonitrile, however, produced heat-resistant vulcanizates. The vulcanizates of lowest brittle points were obtained from copolymers of the higher acrylic esters, but regardless of the acrylic ester used, the brittle point was considerably increased with increasing acrylonitrile content of the copolymer. The copolymers from 95 per cent amyl acrylate—5 per cent acrylonitrile and the copolymer of 91 per cent hexyl acrylate—9 per cent acrylonitrile showed brittle points of −45° and −49° F, respectively. In general, the brittle point of heat-resistant stocks did not change by more than approximately 10° F on heat-aging for 72 hours at 350° F. The butyl acrylate-methacrylonitrile copolymer appeared to have somewhat better heat-aging properties than did the butyl acrylate-acrylonitrile copolymer.
Influence of Carbon Black on the Oxidation of Natural Rubber
Authors: van Amerongen G. J. 
Published: February 2011

Abstract
In this investigation an attempt was made to determine to what extent the solubility of oxygen in natural rubber and the aging resistance are influenced by the incorporation of carbon blacks of various particle sizes in the rubber. The influence of the particle size of carbon black on the oxidizability of GR-S loaded with carbon black had already been proved by Winn, Shelton, and Turnbull. In their explanation of this effect, carbon black was considered to be a catalyst for the oxidation reaction of rubber, although nothing was known about the nature of this catalytic action. Moreover, measurements with natural rubber were lacking.
The Microbiological Deterioration of Rubber Insulation
Authors: Blake John T. , Kitchin Donald W. , Pratt Orison S. 
Published: February 2011

Abstract
Experiments on natural rubber and GR-S insulation in various forms have shown them to be inherently vulnerable to fungus attack unless made sufficiently fungitoxic. Stable fungitoxic GR-S compounds have been developed in this work which have invariably maintained normal high insulation resistance during four years in active soil. Thin Neoprene jackets may be permeable to fungi so that underlying insulation should be fungitoxic or inherently stable. A humid atmosphere as in a wet duct may be a dangerous environment. It has been shown that inoculated wire can fail in moist air due to fungus penetration. Parallel electrical tests on wire and culture tests on agar-filled tubes demonstrated that the electrical failures in soil were caused by fungus penetration. It was possible to detect and identify fungus in transit in thick walls of GR-S insulation. Three types of fungi which can pass through rubber insulation and thin Neoprene jackets have been identified, at least by genus. The most prevalent has been Spicaria violacea Abbott. The presence of fungus in insulation lowers the dielectric strength before the filaments have passed completely through the wall. Impending failure can be detected by voltage breakdown tests. Rubber insulation in buried cables must be sufficiently fungitoxic. Great care is required in formulating stable compounds to insure that other required properties are not harmed.
Ultrasonic Wave Study of Swollen Buna-N Rubber
Authors: Nolle A. W. , Mifsud J. F. 
Published: February 2011

Abstract
The velocity and attenuation of ultrasonic waves are measured as a function of temperature in specimens of a Buna-N vulcanizate swollen to various degrees with methylethyl ketone. The frequencies are 2, 5, and 10 megacycles. The experimental method consists of determining the insertion loss and the time delay due to insertion of a flat sample in the liquid acoustic medium of a pulse-reflection apparatus; an improved technique of observation, in which phase delay as well as envelope delay is examined, leads to more precise time data than previous applications of the method. As solvent content of the specimen increases, the position of the maximum of attenuation with respect to temperature moves to lower temperatures, and the height of the attenuation peak is reduced. It is shown that the height of the attenuation peak, when corrections are made for temperature effects according to the mechanisms of rubberlike elasticity, is proportional to the mass of polymer per unit volume in the swollen specimen; moreover, the temperature of maximum attenuation is a linear function of the ratio, for the swollen specimen, of mass of solvent to mass of polymer. The latter finding indicates, if the concept of energy of activation is applicable, that the reduction of activation energy is proportional to the number of solvent molecules associated with each polymeric chain segment. The paper contains auxiliary data on dimensional and volumetric aspects of swelling and swelling rate.
Accelerator Compounding. Heat History and Compounding
Authors: Garvey B. S. , Yochum D. W. , Morschauser C. A. 
Published: February 2011

Abstract
To summarize, the following hold true for natural rubber: (1) Each compound has a characteristic maximum scorch time, vulcanization time, and cure time, which depend chiefly on the accelerator. (2) For any given batch of compound, both scorch time and cure time are shortened by an amount equivalent to the processing heat history of the batch. (3) The vulcanization time remains constant. (4) These relations help to explain variations in factory cures and indicate the advantages of close control of heat history in factory processing.