bluuebunny/crossref_metadata_2025_split huggingface dataset:
Particle Size of Rubber Globules in Hevea Latex
Authors: van den Tempel M. 
Published: February 2011

Abstract
1. The use of visible light in determining the average particle size or the particle-size distribution in Hevea latex renders the results meaningless, as only about 40 per cent of the particles have a diameter of more than 0.2 µ. 2. In considering the size-frequency distribution curve as determined by Lucas, it could be assumed that, actually, the number of particles having a diameter of less than 0.12 µ might be very much larger than has been indicated by him. The agreement with the determination of the number of particles by van Gils, however, may be taken as evidence in favor of the correctness of the curve as given by Lucas. 3. An expression has been given which describes the size-frequency distribution curve, as found by Lucas, with a high degree of accuracy. It is necessary to assume that no particles larger than 5.2 µ are present in the latex. 4. Attention is directed to the considerable difference existing between the various average diameters, caused by the strongly asymmetrical shape of the size-frequency distribution curve. This work forms part of the program of fundamental research on latex problems undertaken by the Research Department of the Rubber-Stichting, Delft, under the management of H. C. J. de Decker.
Quantitative Characterization of Cure. III. Relation between Compound Viscosity and Vulcanizate Stiffness in Pure-Gum Natural-Rubber Vulcanizates
Authors: Blackwell R. F. , Fletcher W. P. , Gee Geoffrey 
Published: February 2011

Abstract
The aim of this investigation was to study the dependence of vulcanizate stiffness on the compound Mooney viscosity, and if possible to derive a method by which account could be taken of variations in viscosity in order to reduce the so-called mixing error in batches of test compound. Investigations covering a range of compounds, raw rubbers, and curing times gave results which for the practical range indicated a relation between modulus at 100 per cent elongation and Mooney viscosity. Using the relationship thus established, a method of adjusting modulus results to correspond to a standard Mooney viscosity was derived. Application of the scheme to batches of ACS1 compound mixed from parts of the same lot of homogeneous raw rubber led to a considerable reduction in the range of modulus values.
Chemical Constitution and Deactivating Effect
Authors: le Foll Jacques 
Published: February 2011

Abstract
The experiments which have been described show that the thiol group is sufficient to develop the deactivating effect. However, its action can be more or less modified by neighboring chemical groups. For the deactivating effect to be pronounced, it is necessary for a thiol group to be associated with certain other chemical groups. The choice of these latter groups is a delicate one, for the final compound must fulfill two conditions which from a practical standpoint are difficult to meet conjointly, viz., (1) the thiol group must not be nullified by any tautometric effect, a phenomenon which is common to many compounds, and (2) the compound must not have too marked an accelerating action, such as that of certain well known very active accelerators containing the thiol group. The present work would indicate, then, that the most effective structure from the viewpoint of the deactivating effect is a cyclic structure, either pentatomic or hexatomic, in which the carbon atom carrying the thiol group is surrounded by two nitrogen atoms or, alternately, by a nitrogen atom and an oxygen atom. This type of structure is notably true of mercaptobenzimidazole, mercaptopyrimidine, and mercaptobenzoxazole.
The Mechanism of Gelation of Latexes
Authors: Panich R. M. , Kalyanova K. A. , Voyutskiĭ S. S. 
Published: February 2011

Abstract
1. The solubility of zinc oxide in ammonia and sodium hydroxide solutions was studied. In this case the presence of an ammonium salt in the system has a strong influence, and increases the solubility of zinc oxide, because the ammonium ion inhibits dissociation of ammonium hydroxide into NH4+ and OH− ions, and thus aids the formation of complex zinc-ammonium ions. We established that, in the 0–60° range, the temperature has little effect on the solubility of zinc oxide in aqueous ammonia. 2. The action of the zinc-ammonium ion on solutions of stabilizers of the soap type is explained, and it is shown that, at sufficiently high alkalinity, zinc-ammonium soaps do not precipitate from solution, but remain in a colloid state, stabilized by the alkaline soap or hydroxyl ion. 3. It is established that, in the absence of the ammonium ion, zinc oxide does not cause gelation of latexes stabilized by soaps. 4. The effect of formaldehyde on the gelation of latexes stabilized with soaps has been studied. 5. The reactions which can take place when zinc oxide is added to ammonia and alkali solutions, to ammonium and alkaline soap solutions, and to ammoniated and non-ammoniated latexes are discussed. A scheme of successive reactions which must take place during the gelation of latexes stabilized with soaps is presented.
Quantitative Determination of Natural Rubber Hydrocarbon by Refractive Index Measurements
Authors: Fanning Rachel J. , Bekkedahl Norman 
Published: February 2011

Abstract
Rubbers from different sources vary considerably in rubber hydrocarbon content, from 70 per cent or less for some of the wild varieties to about 95 per cent for a good grade of plantation rubber. The quality of a rubber is measured to a great extent by the percentage of rubber hydrocarbon. A new procedure for the quantitative determination of this hydrocarbon has been developed, which involves the measurement of refractive index of a solution of a known weight of acetone-extracted rubber in a known weight of 1-bromonaphthalene. From the observed data and from other previously determined or known physical constants, such as the densities and refractive indexes of the rubber hydrocarbon and the solvent, the percentage of hydrocarbon in the original sample can be calculated. This new method gives results as good as, or better than, other existing methods, and is simpler and less time-consuming to perform.
Changes of the Mechanical Properties of Vulcanizates during the Early Stages of Thermal Oxidation
Authors: Kuzminskiĭ A. S. , Lyubchanskaya L. I. 
Published: February 2011

Abstract
1. The structural-mechanical properties of vulcanizates of various rubbers during the time of the induction period and during autocatalytic oxidation were studied. 2. A change of the mechanical properties of vulcanizates in the induction period is a consequence of oxidation (degradation and polymerization) and thermal structure formation, taking place with the participation of the double bonds of the side chains. 3. In complete accord with the theory, at the end of the induction period and in the early stages of autocatalysis, the physical-mechanical properties of vulcanizates change sharply; as a result of this, the vulcanizates lose their technical value. 4. During the heat aging of rubber, the concentration of inhibitor within the range of 0.25–0.5 per cent has no effect on the rate of change of the physical-mechanical properties of vulcanizates, but has a strong influence on the work capacity of the latter.
Determination of Rubber Hydrocarbon by a Modified Bromination Method
Authors: Gowans William J. , Clark Frederick E. 
Published: February 2011

Abstract
Published investigations show that, in the bromination of rubber, addition is accompanied by some substitution. The substitution portion of the bromination reaction is difficult to control and has contributed to low results and occasional poor precision. This work was carried out to investigate the effect of several factors on the bromination reaction and to find a means of inhibiting the substitution reaction. The effect of rubber hydrocarbon concentration on bromination is critical. Iodine accelerates bromination, but is not present in the final product. Temperature and light are important variables. The bromination reaction is insensitive to bromine concentration as long as a considerable excess is present. Trichloroacetic acid in the amounts used to assist in the solution of crude rubber has no effect on the results. Addition of chloroform to the benzene solution of rubber inhibits the substitution reaction with no apparent effect on the addition reaction. A factor of 0.299 for converting rubber bromide to rubber hydrocarbon is obtained for Hevea smoked sheet, which agrees well with the theoretical value. A conversion factor of 0.301 is obtained for guayule rubber, which may or may not indicate that guayule rubber hydrocarbon is slightly more saturated than Hevea. The method should have application for the direct and accurate determination of rubber hydrocarbon in crude rubber.
Mechanism of the Gelling of Hevea Latex by Zinc Compounds
Authors: Kraay G. M. , van den Tempel M. 
Published: February 2011

Abstract
Zinc oxide is known to be soluble to a certain extent in ammoniated Hevea latex. The solubility may be enhanced by several means, such as the addition of ammonium salts, and is due to the formation of zinc-ammonia complexes. The complexes themselves have no coagulating power. When heated, however, zinc ions are produced by dissociation of the complexes, and these ions react chemically with the adsorbed soap on the rubber globules, forming an insoluble zinc soap which links up all the rubber globules into a gel. Evidence in favor of the proposed mechanism was obtained by displacing the adsorbed natural higher fat acids of the rubber particles by a soap which does not form an insoluble zinc soap, such as Igepon-T. A latex treated in this manner does not gel when heated with zinc oxide and ammonium chloride at 70° C. By displacing the Igepon-T with ammonium oleate, the original rapid gelation is restored. Depending on the concentration of zinc ions available at room temperature and the amount and types of higher fat acids on the latex particles, thickening or even gelling may occur at room temperature. The above interpretation of the reaction mechanism may lead to new methods for the evaluation of latex.
Mercaptobenzothiazole Vulcanization Using Sulfur35
Authors: Auerbach Irving 
Published: February 2011

Abstract
A study has been made of the function of raercaptobenzothiazole in the vulcanization process. Radioactive sulfur35 and mercaptobenzothiazole tagged with sulfur35 were used for measuring the sulfur and mercaptobenzothiazole reaction rates. The effects of variations in the zinc oxide, sulfur, and mercaptobenzothiazole concentration on the sulfur combining rates were determined. It was found that a marked induction period exists, during which the zinc mercaptide of mercaptobenzothiazole, the initial product, reacts readily with sulfur. The ratio of combined sulfur to consumed mercaptobenzothiazole is constant during the vulcanization process. A kinetic expression is given which accounts for the data. When polyisobutylene was substituted for GR-S or Hevea, the zinc mercaptide of mercaptobenzothiazole was found to be the initial product. A mechanism is postulated for the accelerating properties of mercaptobenzothiazole. It involves the formation of the zinc mercaptide, which reacts with sulfur and rubber to regenerate mercaptobenzothiazole and form sulfur-rubber compounds.
Ozone Formation in Photochemical Oxidation of Organic Substances
Authors: Haagen-Smit A. J. , Bradley C. E. , Fox M. M. 
Published: February 2011

Abstract
The formation of ozone through photochemical oxidation of alcohols, aldehydes, ketones, acids, and hydrocarbons, such as are present in gasoline, in the presence of small quantities of nitrogen oxides has been demonstrated. Ozone production without the addition of nitrogen oxides has been observed in the photochemical oxidation of biacetyl, bibutyryl, pyruvic acid, and butyl nitrite. The ozone produced in these reactions was identified by chemical and physical methods. The ozone formation is attributed to a peroxide radical chain reaction. The release of large quantities of hydrocarbons to the air and the simultaneous presence of nitrogen oxides from combustion processes explains the relatively high ozone content, and consequent severe rubber cracking, in the Los Angeles area. These findings should be considered in planning rubber storage facilities. In view of the irritating properties of the products formed by this photochemical oxidation, both hydrocarbons and nitrogen oxides should be considered as potential irritants when they occur simultaneously in the air at low concentrations.
The Structure of the System: Filler Rubber. An Electron-Microscopic Study
Authors: Endter Friedrich 
Published: February 2011

Abstract
Electron microscopic investigations of the benzene-extraction residues of filler-natural rubber mixtures which are used for the determination of bound rubber, give a pattern of a three-dimensional network consisting of filler and bound rubber. The unchanged benzene-soluble rubber is present in the interstices of the network in the untreated filler-rubber mixture.
Titer Compounding of Neoprene Latex
Authors: Cook G. S. , Fitch J. C. 
Published: February 2011

Abstract
The practical importance of free alkali content on the processing and storage life of Neoprene latexes, both raw and compounded, is demonstrated. It is shown that titer measurements are more sensitive than pH measurements for establishing the alkali level of Neoprene latex, that increasing amounts of alkali increase markedly the life of both raw and compounded latexes, that increasing amounts of alkali decrease the original viscosity of compounds and reduce very much the viscosity increase which takes place during aging but, that, within the ranges checked, the alkali content has little effect on the physical properties of films. A procedure for measuring accurately and adjusting easily the free alkali content of raw latex to a desired level is suggested.
Chemigum SL—An Elastomeric Polyester-Urethane
Authors: Seeger N. V. , Mastin T. G. , Fauser E. E. , Farson F. S. , Finelli A. F. , Sinclair E. A. 
Published: February 2011

Abstract
A great deal of interest has been aroused in recent years in isocyanate chemistry by the announcement of new elastomers based on diisocyanate modification of polyesters. Early du Pont patent literature described diisocyanate modified alkyds, and Vulcaprene A, an elastomeric diisocyanate modified polyesteramide, has been offered to the rubber trade by Imperial Chemical Industries, Ltd., England. Several articles also have been published on Vulcollan by Bayer and associates on work done in the laboratories of Fabenfabriken Bayer Co., Leverkusen, Germany. More recently a new elastomeric polyester-urethane, Chemigum SL, was described by the Goodyear Tire and Rubber Co. These rubbers are first made in the form of processible and storable raw gums, having many of the characteristics of pale crepe natural rubber. They can then be mixed on the mill or in the Banbury with additional curatives, such as diisocyanates and other compounding agents, and cured in standard rubber molds. The cured physical properties of Chemigum SL are very similar to Vulcollan; both exhibit unusual toughness. Tensile strength is very high, as is resistance to cutting and chipping. Since the polyester-urethanes are saturated, cut-growth resistance is excellent. Even when cuts are initiated by sharp objects, there is no tendency to grow, even under stress. In this respect a vast superiority is shown over natural rubber or GR-S.
Surface Condition and Electrical Impedance in Rubber Friction
Authors: Schallamach A. 
Published: February 2011

Abstract
It is shown experimentally, by employing electrically conductive rubber, that, during the frictional gliding of rubber, a thin layer in contact with the track undergoes a deformation which considerably increases the electrical impedance of this layer. In the case of previously abraded rubber, the layer is permanent. If a d.c. potential is applied between sample and track during sliding, electrostatic attraction between sample and track is produced, and this increases the fractional force. The thickness of the layer, estimated from the magnitude of the electrostatic force, is a few thousandths of a centimeter.
Cracking of Stressed Rubber by Free Radicals
Authors: Crabtree J. , Biggs B. S. 
Published: February 2011

Abstract
The characteristic cracking of rubber by ozone has been well known for many years and has been the subject of numerous investigations. While this phenomenon has hitherto been considered unique with ozone, we find it not to be so, and that a cracking of rubber indistinguishable from that produced by ozone follows on exposure of stressed rubber to vapors of volatile peroxides irradiated by ultraviolet light. Moreover, the presence of oxygen is not necessary, the reaction occurring equally well in an atmosphere of nitrogen. Thus, the cracking apparently is due to the free radicals resulting from the photolysis of the peroxides. In the presence of nitrogen peroxide, the reaction is accelerated, as shown by an increase of the rate of rubber cracking and by a peroxide balance sheet, determined by chemical analysis. The photolyzed nitrogen peroxide evidently functions as a catalyst for the breakdown of the peroxide, since no change occurs in the dark. Cracking by such different radicals as tertiary-butoxy, phenyl, benzoyl, acetyl, and hydroxyl has been observed.
The Dissolution of Vulcanized Rubbers and Its Bearing on Problems of Rubber Analysis
Authors: Wake W. C. 
Published: February 2011

Abstract
Dissolution of a sample of vulcanized rubber is a necessary preliminary to several analytical procedures, e.g., the determination of iodine value or total fillers. If an infallible and convenient agent were available for this process, then doubtless other analytical procedures would be possible of development or improvement and examination of infrared transmission spectra of vulcanized samples would prove a feasible means of identification. Although decalin and nitrobenzene have been widely and satisfactorily used for natural rubber (polyisoprene), there have been several references in the literature to difficulties encountered with the most widely used synthetic rubber, GR-S. Devices to overcome these difficulties include comminution on a roller mill, swelling the sample in strong swelling agents before transferring to the solvent to be used for the dissolution, and grinding on a rubber mill with a plasticizer. All these must be regarded as being of the nature of palliatives, knowledge of the nature of the dissolution process being the real need before the best condition for carrying it out can be decided on. It is shown in this paper that the process is essentially oxidative in nature and, provided that the solvent and rubber are miscible at the temperature of the dissolution, temperature and efficient aeration are the most important rate-determining factors. The nature of the solvent is, of course, of importance with respect to the analytic procedure attempted as all solvents are not suitable for iodine value determination.
A New Gravitometer
Authors: Linhorst E. F. 
Published: February 2011

Abstract
Several months ago the Fort Wayne Plant of the United States Rubber Company began to use a new Jolly type of balance for determining the specific gravity of cured rubber. As shown in Figure 1, the apparatus employs two springs whose lower ends are joined to a metal rod that supports a moving scale V. A stationary scale A is placed parallel to the scale V. By using two springs instead of one, it is easier to bring the two scales close together.
Chain-Length Distribution Functions during Polymerization
Authors: Watson W. F. 
Published: February 2011

Abstract
Functions for the distribution of chain lengths of a polymer formed during polymerization have been evaluated in terms of the directly measurable rate and rate of initiation, or the single equivalent measurement of number-average chain length. No details of the reaction mechanism are required, except for the occurrence of termination by combination of polymer radicals. This is in contrast to the usual derivation of distribution functions from the postulated kinetic scheme. The three types of termination are considered, (1) combination absent, (2) combination predominant, and (3) a mixture of combination with other modes of termination. The application to copolymerization is outlined. Relationships between the various average molecular weights are considered.
A Precise Method for the Determination of the Width of a Dumbbell Test Specimen
Authors: Labbe B. G. , Leeper H. M. 
Published: February 2011

Abstract
The inaccuracy of stress-strain data in testing rubber samples is undoubtedly increased by variations of the width of the constricted area of the dumbbell test-specimen. Frequently a die for cutting these test-specimens is purchased and put into service without checking the width of the resulting dumbbell specimen. This situation often develops because of the uncertainty of the methods used for width determinations and the lack of suitable equipment for making the determinations, such as the cathetometer (microscope mounted on rod with cross wires and a scale). The cathetometer provides more accurate results than either the micrometer or the thickness gauge, but is open to the following objections: 1. The edge of the specimen is not always a well-defined line at the magnification necessary, and measurements made on a single strip varies with each observer. 2. Shadows must be completely eliminated because lighting of the sample is critical. 3. If the edges of the strip are not perpendicular to its lateral surfaces, recognition of the upper edge becomes difficult and uncertain. 4. If the sides of the specimen are slightly concave, as is sometimes the case, the cathetometric method yields false results that are high.
Dynamic Damping and Young's Modulus in the Range of Rubberlike Elasticity
Authors: Ecker R. 
Published: February 2011

Abstract
After a brief interpretation of current theoretical concepts of the high elasticity of macromolecular substances, as they have been developed by a number of authors from the laws of thermodynamics, the most important experimental methods of dynamic vibration are pointed out. A newly developed apparatus, which permits the study of the plastic-elastic behavior of high polymers in the rubber-elastic field by means of forced vibrations under tensile stress is described. With a plentiful supply of experimental material, various factors were studied, including the crystallization behavior of polymers, the reinforcing effect of various fillers, polymerization influences, modification of Neoprene-W by accelerators, the elastic behavior of Butyl and Silicone rubber, the influence of certain activators on the reinforcing properties of alumina gel, and the action of softeners in polyvinyl chloride.