bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations in the Field of Rubber Vulcanization. VII. Influence of Organic Accelerators on the Kinetics of Vulcanization and the Properties of Natural-Rubber Vulcanizates
Authors: Dogadkin B. , Karmin B. , Dobromyslova A. , Sapozhkova L. 
Published: February 2011

Abstract
1. Vulcanization accelerators change all parameters of the kinetic strength curve during the vulcanization of natural-rubber mixtures with low sulfur contents. 2. Calculation of the kinetic constants of the fundamental vulcanization equation proposed by Dogadkin, Karmin, and Gol'berg shows that vulcanization accelerators affect both the kinetics of the interaction of rubber with sulfur and the kinetics of the interaction of rubber with oxygen. 3. Direct experiments on the oxidation of rubber have shown that tetramethylthiuram disulfide and diphenylguanidine retard the process of addition of oxygen to rubber, while mercaptobenzothiazole accelerates this process. 4. Data on the rate of plasticization and change in viscosity of rubber solutions during oxidation indicate that tetramethylthiuram disulfide and diphenylguanidine promote the disintegration of molecular chains of rubber during the oxidative destruction of the latter. 5. The activation energy of the process of oxidation of rubber in the presence of mercaptobenzothiazole corresponds to the activation energy calculated from the fundamental vulcanization reaction for the process of oxidative destruction. This provides additional proof of the participation of oxygen in the vulcanization process. 6. It has been established with the aid of the methyl iodide reaction that accelerators increase the bridge-sulfur content of the vulcanizate, which is present in the form of monosulfides, with one sulfur atom connected to an allyl type radical. 7. With increasing temperature, the tensile strength at the vulcanization optimum increases in mixtures containing tetramethylthiuram disulfide, decreases in mixtures containing mercaptobenzothiazole, and remains unchanged in mixtures containing diphenylguanidine. The limiting strength decreases in all cases with increasing temperature. This phenomenon is explained on the basis of the proposed concepts of the character of vulcanization kinetics and of the nature of the vulcanization optimum.
The Tensile Strength of Rubber and Rubber Molecule
Authors: Park Chullchai , Yoshida Usaburo 
Published: February 2011

Abstract
The tensile strengths of crystallized crude rubber and vulcanized rubber are remarkably different from each other at room temperature, but are found to be almost the same at the temperature of liquid air. By assuming that the tensile strength of crystallized rubber at this low temperature is entirely due to its chain molecules, the forced needed to break a chain molecule of rubber at its weakest point is estimated.
The Measurement of Stress Relaxation of Unvulcanized Rubber by Means of the Mooney Shearing-Disc Viscometer
Authors: Blow C. M. , Schofield J. R. 
Published: February 2011

Abstract
The measurement of the tendency of unvulcanized rubber to recover from deformation on the Mooney shearing-disc viscometer has been found to be practicable, and the results correlate fairly well with recovery measurements on the parallel-plate plastometer and shrinkages of rubbers after milling, calendering and extruding. Partial prevulcanization is also indicated.
Some New Compositions Based on Condensation Rubbers
Authors: Harper D. A. , Smith W. F. , White H. G. 
Published: February 2011

Abstract
By the condensation of a dibasic acid and direactive alcohol or amine, linear polymers are produced. Under certain conditions rubbery polymers are obtained, and a number of condensation rubbers with outstanding physical properties have been described. One of these, a diisocyanate-modified polyester amide (Vulcaprene-A) has been found to be compatible with nitrocellulose, polyvinyl formal, cellulose acetate, degraded vegetable tanned leather, gelatin, and glue. These mixtures can be vulcanized by formaldehyde-liberating agents used to cure Vulcaprene, and in most cases the curing reaction appears to take place not only with the Vulcaprene but with other high polymers. Combinations of Vulcaprene and cellulose acetate and of Vulcaprene and degraded leather are of great interest to the leather cloth industry, as they can be spread on to cloth to give coatings with outstanding flex and abrasion resistance. The Vulcaprene-cellulose acetate mixture is of value also as an abrasion-and flex-resisting coating for rubber proofings to give products which, while cheap to produce, are likely to give superior service to prewar leather cloths. This type of coating can be applied also to paper. The diisocyanate modified polyester amide behaves not only as a novel vulcanizable polymeric plasticizer, but, in combination with these high polymers, gives new products of major interest to an important branch of the rubber industry.
Structures in Rubber Reënforced by Carbon Black
Authors: Blanchard A. F. , Parkinson D. 
Published: February 2011

Abstract
The stiffening action of carbon black in rubber is due to structures formed by carbon-rubber bonds and coherent chains of particles. The softening which occurs during prestressing cannot be explained by broken chain structure, and it is thought that substantially the whole of this softening is due to ruptured carbon-rubber bonds. Prestressing does not affect the characteristic chain structure of the black particles; it breaks relatively weak fortuitous chain structures, formed by reversible van der Waals forces between particles, which contribute little to the stiffness except perhaps at small stresses. Heating tends to reform the fortuitous structure, owing to the thermal movement of the rubber molecules, which pulls them from between adjacent particles, so that full contact is established. The majority of carbon-rubber bonds are relatively weak and are readily broken by stressing. In addition to these low-order physical bonds, a comparatively few strong bonds stiffen the rubber considerably at high stresses, and are mainly responsible for increasing the tensile strength and abrasion resistance. Such high energy linkages are possible only at localized areas on the particles.
The Nature and Activity of Carbon Black Surfaces
Authors: Smith W. R. , Schaeffer W. D. 
Published: February 2011

Abstract
While the electron microscope and adsorption isotherm techniques for evaluating the particle size and surface area of carbon blacks have been particularly valuable in interpreting their behavior in rubber, they also emphasize the fact that reinforcement cannot be interpreted solely on this basis. The activity or nature of the surface must also be considered. Heats of adsorption offer a means of evaluating surface activity. The differential heats of adsorption have been measured by precision calorimetry for nitrogen and a series of C4 hydrocarbons on a group of carbon blacks of varying reinforcing ability. Initial sites of high activity were detected. Surface activity decreases with increasing surface coverage. The magnitude of the initial heats parallels the reinforcing properties of the blacks studied. The surface activity and reinforcing ability of an MPC black was found to be greatly reduced by high temperature treatment. These effects were not influenced by the chemical nature of the surface, i.e., the presence of chemisorbed oxygen or volatile substances. In a further phase of this study, the nature of the surface oxide complexes present on carbon blacks has been studied by means of their emission band spectra in a special vacuum discharge tube. Aldehyde and carboxyl radicals were observed in high concentration. Hydroxyl radicals were also present in nearly equal concentration. These data offer a satisfactory interpretation of the pH properties of carbon black and also should prove of value in interpreting other chemical properties.
Theory of Filler Reënforcement. II
Authors: Guth Eugene 
Published: February 2011

Abstract
Modulus-type properties of loaded rubber depend mainly on the shape and the concentration of the filler particles and are almost independent of the size and the surface characteristics of the filler. The author's theory of these properties is patterned after the theory of viscosity of suspensions, and implies nonspecific wetting between rubber and filler particles, making possible considerable mobility of the filler particles in the rubber. Such mobility is in agreement with studies of the electrical conductivity of carbon black loaded stocks and of the adsorption of gases by carbon blacks. Fillers with spherical particle shape like calcium carbonate and P-33 (which do not form chainlike structures) obey the theoretical equations for spherical particles. Fillers like high modulus and channel carbon blacks whose primary spherical particles agglomerate into chainlike secondary particles obey theoretical equations for the secondary particles characterized by a shape factor. The assumed chain formation and the values for the shape factors are in approximate agreement with conclusions from electron micrographs. Experimental arguments are given for the validity of the theoretical equations up to 25 per cent volume concentration, which is the usual technical loading. The agreement between theory and experiment is within the rather large error caused by nonuniformity between and within the test samples, and in some work by the use of commercial testers, and the difficulty of comparable vulcanizations. Refinements of the theory are introduced, including possible solvation, difference between the modulus of rubber in absence (“gum” stock) and in presence of the filler particles, and various degrees of wetting from nonwetting to strong wetting (implying specific chemical bonds between rubber and filler). The above mentioned sources of error in the experimental work prevent safe conclusions about the necessity of introducing such refinements. The experiments include new measurements of stress-strain properties of loaded vulcanized stocks and of the Mooney viscosities of unvulcanized rubber-filler mixes, and a discussion of the pertinent literature. For the dielectric constant of stocks loaded with fillers of spherical primary particle shape, a simple formula is derived.
Fresh Hevea Latex. A Complex Colloidal System
Authors: Homans L. N. S. , Van Gils G. E. 
Published: February 2011

Abstract
Fresh Hevea latex is a complex system, containing two dispersed phases : (1) rubber globules; (2) lutoids, i.e., small irregularly shaped, viscous colloidal bodies. The lutoids dissolve in ammonia and other alkalies, coagulate when the latex is diluted with water but retain their form if the latex is diluted with salt solutions of certain concentrations. By centrifuging, the lutoids are collected at the bottom of the tube as a separate layer with a sharp boundary. After separation, the fractions (now called the yellow and the white fractions) may be examined separately. Their properties are reviewed. The importance of the lutoids for the general properties of the latex is discussed.
Alteration of Neoprene by Polymerization Temperature
Authors: Walker H. W. , Mochel W. E. 
Published: February 2011

Abstract
Changes of the temperature at which 2-chloro-1,3-butadiene (chloroprene) is polymerized, with other variables held constant, gives Neoprenes with marked differences in the rate of crystallization and dispersion in solvents of the raw polymer and in the physical properties of the vulcanizates. For example, plastic polychloroprene formed at 10° C crystallizes quickly, forms homogeneous solutions, and exhibits high tensile strength; whereas polymer produced at 100° C fails to crystallize, only swells in solvents, and has low tensile strength. These changes in properties appear to be caused by alterations of the structure of the polymer, notably the side-branching, cross-linking, spacing of the chlorine atoms, and possibly cis-trans-isomerism. The structural differences are small in magnitude and difficult to detect. Ozonolysis reveals that a soluble form of polychloroprene, as well as highly insoluble “popcorn” polymer, is at least 93 to 95 per cent 1,4-addition product and x-ray diffraction shows the polymer chains to have essentially a transconfiguration. Infrared spectroscopy indicates the absence of side vinyl groups. Branching and cross-linking explain the decreased rate of crystallization and other properties of the less soluble polymers, and it is considered that varying minor portions of 4,1-1,4 or 1,4-4,1 addition or of intramolecular cis-isomers are a factor in the crystallization of the soluble polymers. Technical advantages of the variations in Neoprene effected by polymerization temperature are outlined.
Refractive Index of Natural Rubber for Different Wave Lengths
Authors: Wood L. A. , Tilton L. W. 
Published: February 2011

Abstract
The refractive index of natural rubber and its variation with temperature and wave length are those which would be predicted for a similar hydrocarbon of low molecular weight. A two-constant equation of the Cauchy or Sellmeier type is inadequate to express the relation between refractive index and wave length for rubber. For convenient reference the best values resulting from the present investigation are recapitulated in Table VI.
The Control of Undesirable Viscosity Increases in Latex Compounds
Authors: Flint C. F. 
Published: February 2011

Abstract
A latex stabilizer of the nonionogenic class, consisting of a fatty alcoholethylene oxide condensate, similar in chemical type and technological properties to Emulphor-O (I.G.), is shown to be effective in controlling zinc oxide effect thickening and similar undesirable increases in the viscosity of compounded latex mixes, e.g., in the presence of active accelerators under conditions where an older and better known stabilizer of the anionic synthetic detergent class is not adequately effective. The proposed stabilizer may be effective in as low an amount as ¼ per cent on the rubber, and the material actually used in the experimental work was Vulcastab-LW.
Latex-Reclaim-Casein Mixtures for Rubber-Cord Fabric Adhesion
Authors: Gardner E. R. , Williams P. L. 
Published: February 2011

Abstract
A good bond, resistant to flexing, is afforded between rubber and rayon cord by the interposition of a mixed casein-rubber film. In a series of solutions in which the proportion of rubber solids was kept constant and the quantity of casein varied progressively, it was found that there was an optimum amount of casein for maximum adhesion. Taking into consideration also the handling of the solution and the stiffening of the cord, it would appear that for an adhesive with the usual total solids content of 15 to 20 per cent, the ratio of casein to rubber hydrocarbon should be approximately 1:6. When the rubber hydrocarbon is supplied by dispersed reclaim, the adhesion is a little higher than when latex is used. The most satisfactory solution from all points of view, however, contains approximately equal quantities of rubber hydrocarbon derived from the two sources. Wetting agents may be employed to improve the uniformity of application of the adhesive. The amount used must be very small, otherwise the adhesion is impaired. By dipping cord successively in casein and latex solutions and vice versa in the adhesive film, casein acts as a specific adhesive for rayon, whereas the rubber in the film gives the necessary affinity for the casing rubber which surrounds it. Treating a cord successively in a casein-rich mixture and then in a rubber-rich mixture appears to give a slightly better bond than the conventional treatment. The subsequent application of a rubber cement to a cord dipped in latex-reclaim-casein solution results in an improvement in the bond.
A Combustion Method for the Estimation of Carbon Black in Compounded Rubber
Authors: Bauminger B. B. , Poulton F. C. J. 
Published: February 2011

Abstract
The method described in this paper is based on the removal of volatile organic ingredients of the compound by heating in a current of purified nitrogen and, on the subsequent combustion of the carbon black to carbon dioxide, which is collected and weighed. The effect of the adsorptive nature of the carbon black has been studied, and the volatile components of many of the standard grades of carbon black used in the industry have been determined under the experimental conditions used.
A Tackmeter for Rubber Testing
Authors: Beaven E. W. J. , Croft-White P. G. , Garner P. J. , Rooney G. 
Published: February 2011

Abstract
In the hand test for tackiness commonly used, two surfaces of the compound are pressed together for a short time and are then separated, the force required for separation giving a measure of the tackiness of the compound. The magnitude of the separating force depends largely on such factors as the load applied to the contacting surfaces, the duration of application ef the load, and the surface area in contact, but none of these factors can be controlled within reasonable limits of reproducibility. Moreover, the results of this test can be recorded only in rather general terms such as “fair”, “good”, so recorded results may vary from one operator to another and they depend very largely on the experience of the individual operator. It thus becomes evident that in any investigation which calls for the evaluation of the tack properties of a fair number of different compounds, some method of test is required in which the personal element is entirely eliminated. In the course of an investigation into the tackiness of GR-S compounds, Busse, Lambert, and Verdery (J. Applied Physics 17, 376 (1946)) designed an apparatus which enabled the measurement of tack values to be put on a quantitative basis, and the principles of the apparatus reported by them have been embodied in the tackmeter described below.
The Direct Determination of Oxygen in Rubbers. Application of the Unterzaucher Method
Authors: Chambers W. T. 
Published: February 2011

Abstract
The direct determination of oxygen in organic compounds by reduction with carbon on a microscale by the Unterzaucher method is described, together with criteria of purity for the carbon and iodine pentoxide reagents employed. The method has been applied to rubbers and a relative precision of 2 per cent has been obtained i.e. : ±0.01 in the range 0 to 0.5% oxygen, ±0.02 in the range 0.5 to 1.0% oxygen, ±0.04 in the range 1.0 to 2.0% oxygen. For compounds containing larger percentages of oxygen, the method gives an absolute accuracy of ±0.2 or better. The method is speedier and yields more accurate results than when oxygen is determined by difference or by hydrogenation. A single determination requires but 30 minutes.
Thixotropic Behavior of Carbon Black in Rubber
Authors: Mullins L. 
Published: February 2011

Abstract
The addition of carbon black may cause considerable changes in the physical properties of rubber. Often rubbers compounded with carbon black or other fillers show evidence of thixotropic behavior—their properties depend on the past history of the rubber and may be changed on the one hand by continuous standing and on the other hand by working. This paper describes investigations into the behavior of both unvulcanized and vulcanized rubbers, and discusses the thixotropic build-up and breakdown of colloidal carbon black structures which are shown to exist in rubber. The importance of this build-up and breakdown of structure has not been adequately appreciated in many measurements on compounded rubbers; for example, the terms viscosity, plasticity, and stiffness (modulus) can only be defined when complications due to thixotropy are carefully controlled before and during the actual measurement. A knowledge and understanding of this behavior enables the significance of the results of various tests on these materials to be more correctly assessed and accounts for behavior which has previously appeared to be anomalous. The deficiencies of earlier theories of the reënforcement of rubber produced by carbon black are indicated, and modifications which make allowance for thixotropic filler structure are proposed.
Elongation Hysteresis of Hevea and Synthetic Elastomers
Authors: Mooney M. , Black S. A. 
Published: February 2011

Abstract
A hysteresis test has been developed which measures directly the energy loss per cycle of elongation. Six samples are stretched, like the spokes of a wheel, between a small disk and a large disk. The large disk is motor driven, and the small disk, mounted on a ball-bearing, is displaced eccentrically with respect to the larger disk. In the elongation cycle which each sample undergoes with each revolution, the hysteresis causes an average force on the small disk, which is normal to the eccentric displacement and is proportional to the energy loss per cycle. A lever and balance system makes it possible to measure this force continuously while the machine is running. Measurements were made on gum stocks of Hevea and five commercial synthetic elastomers. Testing conditions included temperatures, T, of 0°, 35°, 70°, and 105° C; frequencies, f, of 5 and 50 c.p.s.; mean elongations, e, of 50, 100, and 200 per cent and elongation amplitude, A, 25 per cent. Absolute hysteresis, H (loss/cycle-(amplitude)), at first decreases with increasing e and then flattens or goes through a minimum. Hysteresis decreases with increasing T. The temperature coefficient between 0° and 35° C is very large for Hycar. Hysteresis usually increases with f, but only slightly in most cases; and Hevea at e=400 per cent shows a reversal of frequency effect, which is presumably associated with crystallization effects. Under the same conditions, the hysteresis of the synthetics is 10 to 20 times that of Hevea. When the hysteresis data for all synthetic stocks at various temperatures are plotted against T−Ts, Ts being the second-order transition temperature of the respective elastomer, the data lie within a rather narrow band. From this it is concluded that the hysteresis of synthetic elastomers arises from the same molecular forces which cause hardening and embrittlement at and below Ts.
Low-Temperature Behavior of Butadiene-Styrene Copolymers. Effect of Compounding Variables
Authors: Juve R. D. , Marsh J. W. 
Published: February 2011

Abstract
Synthetic rubbers and natural rubber increase in stiffness at low temperatures and tend to lose their elastic characteristics. This stiffening and hardening phenomenon occurs in varying degrees with various elastomers. Natural rubber and certain synthetic rubbers crystallize during extended exposure at low temperature, whereas other synthetic rubbers such as GR-S remain amorphous. In a general review of the low temperature properties of synthetic rubber, Liska has shown that decreased styrene in butadiene-styrene copolymers improves the flexibility at low temperature. The low temperature flexibility of vulcanized articles made from any particular rubber or synthetic rubber is influenced by the compounding ingredients admixed with the elastomer. This paper shows the results of some studies of the effect of these compounding ingredients on the low temperature serviceability of butadiene-styrene copolymers. Somewhat similar work on the effect of a large number of plasticizers in GR-S has been conducted at the Rubber Laboratory, Mare Island Naval Shipyard, with particular emphasis on compression set at low temperature.