bluuebunny/crossref_metadata_2025 huggingface dataset:
The Action of Finely Divided Solid Substances on Elastomers
Authors: Endter F. , Westlinning H.
Published: February 2011

The most important conclusions drawn from the concepts discussed can be summarized as follows: 1. The interaction between instability points of the electrostatic surface potential of fillers and the electronic structure in rubber or rubberlike substances leads—as a result of Coulomb's attraction between surface field and induced dipole moment—to at least temporary fixation of rubber molecules at the filler surface. 2. Polarization of the double bond is linked to a very slow process of molecular rearrangement. 3. The rubber molecules are constantly maintained in an unstable reactive state under the polarizing influence of the filler surface. 4. In the limiting case, double bond polarization leads to formation of new C—C linkages. The resulting high molecular compounds are closely related to the phenomenon of bound rubber. 5. The partially polarized state of the double bond is a function of the surface properties of the fillers. It has a substantial effect on the start and course of vulcanization. 6. The excitation conditions of the rubber molecules, which vary from filler to filler, appear to be the cause of the filler-specific properties of vulcanizates. To complete the picture of the interaction between filler and rubber, allowances must be made for a number of other factors. Specifically, chemical groupings at the filler surface will play their specific part in addition to the general processes, just as van der Waals' forces must not be disregarded in the adhesion of rubber molecules to the filler particles. However, the broad course of what happens in the interaction of filler and rubber seems to be determined by the processes described.
Chain Scission Efficiency in the Oxidation of Natural Rubber Vulcanizates
Authors: Veith A. G.
Published: February 2011

Natural rubber when it degrades under the action of oxygen does so primarily by a chain scission reaction. A technique has been developed by Tobolsky and coworkers for assessing the magnitude of this chain scission reaction in vulcanizates by means of continuous stress relaxation measurements. Since the result of the oxygen attack on the rubber is a chain scission reaction, the question of the efficiency of the reaction comes to mind. The influence of antioxidants is of importance in this regard as is the type of vulcanizate or network structure. This paper describes some measurements of the chain scission efficiency of a simple benzothiazolyl disulfide (MBTS) vulcanizate and the effect of several antioxidants on this chain scission reaction. Some of the complications inherent in this type of measurement are discussed. The first published report on the efficiency of the chain scission reaction in vulcanizates was given by Tobolsky, Metz, and Mesrobian in 1950. A more recent publication is that of Baxter, Potts, and Vodden in 1955. Tobolsky has interpreted the stress decay of gum vulcanizates at elevated temperatures as a direct consequence of the cutting of polymer chains of the network. The reduced stress is postulated as being equal to the chain density ratio:
The Determination of 2-Mercaptobenzimidazole
Authors: Zijp J. W. H.
Published: February 2011

2-Mercaptobenzimidazole (M.B.) is used in the rubber industry as an antioxygen or a deactivator. The term deactivator was proposed by J. Le Bras who distinguishes antioxygens from deactivators. This compound is prepared by Farbenfabriken Bayer A.G., Leverkusen, with the name of “Alterungsschutzmittel M.B.” The S.A. des Matières Colorantes et des Produits Chimiques de Saint-Denis (Paris) produces the zinc salt of this compound under the name of M.T.B.Z. The T.N.O. Institute for Rubber Research, which has developed methods for the determination of various antioxidants, has extended this work to the analysis of M.B. This compound, in fact, is not only of practical interest to the rubber industry, but it is also interesting in the study of the deactivator effect. The present paper describes the results obtained from this investigation. The method we have selected for the identification of M.B. was partition chromatography on paper. For the quantitative determination of M.B., we made no attempt to develop a procedure based on this technique since a precise colorimetric method of analysis in this field is not yet available.
Microstructures of Polybutadienes and Butadiene-Styrene Copolymers
Authors: Binder John L.
Published: February 2011

Polybutadienes and butadiene-styrene copolymers were prepared to study the effect of recipe variables on the physical properties and to learn whether there are correlations between the microstructures and physical properties. The changes in the microstructure of emulsion polybutadienes and butadiene-styrene copolymers of the types studied, which can be produced by either recipe variables or changes in temperature, are limited. The maximum amount of cis-1,4-addition amounted to 23 per cent (in the butadiene part of butadienestyrene copolymers) at 100° C, the maximum amount of trans-1,4- was about 80 per cent at −35° C, and the maximum amount of 1,2-addition was about 20 per cent. While the amount of cis-1,4-addition increases with increasing temperature, it is unlikely that polymers containing even 50 per cent cis-1,4-addition can be made at practical temperatures in emulsion systems. The structures of polybutadienes may be changed markedly by alkali-metal catalysts. The structure is affected by the kind of catalyst, by the temperature, and by promotors. Emulsion polymerizations are not likely to yield improved polymers for practical uses, but much can be done to tailor polymers for specific uses by using alkali-metal catalysts in bulk or solution systems.
Experimental Study of Low-Frequency Effects on the Dynamic Modulus of a Buna-N Rubber
Authors: Hutton Allen Q. , Nolle A. W.
Published: February 2011

The linear dynamic Young's modulus of a vulcanized Buna-N gum rubber was measured at frequencies of 0.05, 0.10, and 1.00 cps, in the temperature range − 22° C to 30° C, by a method in which a small differential sinusoidal elongation is superimposed on a 5 per cent static elongation. The width of the dispersion range on the temperature scale (the range in which the logarithm of the modulus increases steeply with decreasing temperature) is only about 10° C, contrasted with widths as great as 25° C found in previous measurements on a similar compound at frequencies of several kilocycles. The modulus-temperature plot shifts upward by only about 4° C per decade of frequency increase of the present range, contrasted with about 10° C per decade in the previous measurements at higher frequencies. It is concluded that this elastomer cannot be described properly by means of the “method of reduced variables”, in which the dynamic properties are ascribed to mechanisms having identical temperature dependence, and that the low-temperature behavior is governed by mechanisms distinct from those effective in the audio-frequency range at room temperature.
Softness, Time of Impact, and Internal Damping of Technical Rubber Mlxtures
Authors: Schreuer E.
Published: February 2011

It is shown that the Hertz theory of impact is applicable to the determination, from softness measurements, of the static modulus of elasticity and from impact tests, of the dynamic modulus of elasticity. A simple relation is then derived which connects the difference of these moduli and the internal damping in impact tests. This relation was checked with the rebound resilience values and proved to be valid for all measurements.
Chemistry in Carbon Black Dispersion
Authors: Barton Bernard C. , Smallwood Hugh M. , Ganzhorn George H.
Published: February 2011

The properties of carbon black and their effect on the physical properties of rubber vulcanizates have been extensively reported. The importance of particle size, reticulate structure, and surface characteristics are generally accepted. The beneficial effects of carbon black are believed to be due in large part to strong adsorption of rubber molecules on the carbon black surface. Many investigators have described the physical nature of this adsorption and have related it to the surface properties of the carbon black. Chemical bonding has also been suggested as being an important factor in the surface interaction between carbon black and rubber. The contribution of chemical bonding to the dispersion of carbon black and its effect on the physical properties of vulcanizates is the subject of the present paper. Gerke, Ganzhorn, Howland, and Smallwood and Bradley found almost twenty years ago that, when rubber-carbon black mixtures were heated at temperatures of 275–400° F, vulcanizates prepared from the mixtures had lower electrical conductivity, lower hysteresis, lower durometer hardness, higher modulus at large deformations, and greater resistance to abrasion than did vulcanizates of the corresponding unheated mixtures. These changes were ascribed to changes in the dispersion of the carbon black. Experimental data will be presented in this paper which suggest that these changes in carbon black dispersion are the result of chemical reactions between carbon black and rubber.
Infrared Analysis of Isomerized, Vulcanized, and Oxidized Natural Rubber
Authors: Salomon G. , van der Schee A. Chr
Published: February 2011

This paper is a continuation of our study on the infrared spectra of natural rubber and its derivatives. It was found previously that, in certain reactions of rubber, the original double bond (I) is shifted to the side group (II) and that this leads to significant changes in the chemical and mechanical behavior of the polymer. Others have also reported the occurrence of groups (II) and (III) in rubber and certain rubber derivatives. Group (II) is also found in synthetic polyisoprenes as a result of 3,4-polymerization. We have now measured the intensities of the absorption bands of the rubber spectrum and changes produced by cyclization and isomerization. Certain statements on the formation of (II) and (III) during vulcanization were at variance with our experience, but a detailed investigation cleared up some misconceptions. Modifications brought about by oxidation are chemically related to those produced by sulfuration reactions. A classification of oxidation reactions, based on typical changes in the infrared spectrum, will be proposed in the discussion.
Aging and Weathering of Rubber
Authors: Buist J. M.
Published: February 2011

Terminology in this field is confused and in need of clarification. In 1945, the various types of breakdown of rubber were classified as follows: (see PDF for table) In general, several of the effects cited above occur simultaneously, and may contribute jointly to the final result. General terms, such as aging and weathering, have been used widely, without any clear definition. Schidrowitz differentiates between the two terms as follows: weathering may perhaps be differentiated from aging by assuming that the former describes the effects of attack on rubber by the atmosphere under conditions of external exposure, i.e., to sun, air, rain, and wind, whereas the latter correlates effects produced in the absence of any continuous or excessive external exposure.
Departures of the Elastic Behavior of Rubbers in Simple Extension from the Kinetic Theory
Authors: Gumbrell S. M. , Mullins L. , Rivlin R. S.
Published: February 2011

It is shown that the equilibrium stress-strain behavior of highly swollen rubber vulcanizates in simple extension agrees with the predictions of the kinetic theory. The departures from these predictions which are found in dry or lightly swollen rubbers have been investigated, and it is shown that they can be described in terms of a single parameter C2. The magnitude of this parameter is large in dry rubbers, and decreases to zero at high degrees of swelling ; this decrease occurs linearly with decrease in the volume fraction of rubber. The value of C2 is found to be independent of the nature of the rubber polymer, of the degree of vulcanization, and of the nature of the swelling liquid. The possible significance of this parameter is discussed in light of these observations.
Milling Procedure Its Effect on Physical Properties
Authors: Martin B. J. A. , Parkinson D.
Published: February 2011

The experiments described roughly represent the three main stages in the preparation of a rubber compound before molding, viz., mastication, mixing, and reworking. At each stage, variations in the process affect, in varying degrees, processability at subsequent stages and the ultimate physical properties. In general, the effects in isolation at any one stage are small when considered against the background of economic processing. Whether uncontrolled or deliberately applied, process variations are, in the main, independent at each stage. Consequently, the magnitude and direction of the effects they produce may also be independent. In any considerable period of time, therefore, the properties of a compound may vary between two extremes which represent the adding together of all the effects at the separate stages. On the evidence presented here it is considered that process changes which might in normal practice be applied for expediency or economy, or such as might occur, between different production units of one company could, by this additive effect, produce total variations of practical significance. The properties likely to be affected most are plasticity, scorch, tear resistance, and electrical resistivity.
Vulcanization of Crepe Rubber by Sulfur Monochloride. I. The Gelation Method
Authors: Glazer J. , Schulman J. H.
Published: February 2011

When a dispersion of rubber (4 per cent) in benzene is treated with sulfur monochloride (1 per cent) at room temperature, the solution becomes opaque and gelation occurs in a few minutes. With a more dilute dispersion of rubber (1 per cent), Meyer and Mark obtained a weak gel, which could be broken up by stirring to give, after one hour, a pale yellow precipitate, corresponding to the formula C10H16SCl2. By analogy with the reaction of ethylene and sulfur monochloride, these workers proposed the following reaction process: (see PDF for diagram) The so-called cold-vulcanization process, which is essentially the above reaction, thus appears to correspond to the cross-linking of adjacent isoprene units by means of thioether-bond formation. This result contrasts with the hot sulfur vulcanization process, where the reaction does not involve the sulfurization of any appreciable number of olefinic groups. The mechanism of the cold vulcanization process is unknown. However, it is known that certain commercial sulfur vulcanization accelerators speed up the above gelation process to a remarkable extent. The present work describes an attempt to investigate the kinetics of the reaction between rubber and sulfur monochloride, with the eventual view of establishing the mechanism of the process. In general, two main methods have been developed for assessing reaction velocities. They are the dilatometric method and a more arbitrary time-of-gelation method. While the former method is of importance in studying the more detailed quantitative features of the reaction, the latter method is of help as a powerful auxiliary. Although it is not yet possible to propose a clear-cut mechanism for the vulcanization process, certain kinetic features have been established, and indications of the most fruitful lines of attack are presented.
Load-Carrying Capacity of Latex Foam Rubber
Authors: Talalay Joseph A.
Published: February 2011

Specifications for latex foam rubber usually include a required hardness, which is measured by the force necessary to compress the material to 75 per cent of its original height. While the hardness of a slab of foam rubber depends primarily on its foam density, it also depends on the type of latex, the curing system, compounding materials, and moisture content. It is likewise affected by cell size (larger cells being more favorable) and cell shape (spherical cells being more efficient than flattened cells). for slab material of any given composition and cell structure, the hardness can be related to density by a simple equation. For cored material, hardness and density can be related by integrating deflections of small increments of height over the entire height of the article. This procedure can be reduced to a few simple equations for most shapes of core pins. With these equations, the effect of mold configuration on the weight of a given foam article has been investigated. for any specified hardness, the required weight of a foam rubber article can be reduced by increasing core-pin diameter, decreasing pin spacing, and reducing the thickness of uncored top stock, or in effect increasing the cored-out volume. Intrinsically this is made possible by the fact that hardness of homogeneous (slab) foam material increases approximately with the square of its density. These design variables have been subjected to both theoretical and experimental study. Their effect and their practical limitations are discussed. The experimental data are primarily based on foam rubber produced by the so-called Talalay process. However, the general relationships presented in this paper are believed to apply equally to latex foam made by the Dunlop method.
Representation of the Mechanical Properties of High Polymers by the Model Method
Authors: Bartenev G. M.
Published: February 2011

1. Simple models are described which are based on physical concepts and which represent the mechanical properties of high polymers having a spatial network (class 1) and having no spatial network (class 2). 2. The physical concept of characteristic mechanical properties of high polymers and their relation to the structural properties of the high polymers were studied. 3. The particular models which represent the three physical states of high polymers are discussed, and the corresponding equations of deformation are indicated.
The Interaction of Polymerizing Systems with Rubber and Its Homologs. II. Interaction of Rubber in the Polymerization of Methyl Methacrylate and of Styrene
Authors: Mebrett F. M.
Published: February 2011

In Part I of this investigation, the effect of dihydromyrcene on four vinyl polymerizing systems was studied, and it was found that this compound reduces both the molecular weight of the polymer formed and the rate of polymerization. With rubber, the results are more complicated. A method for separating the simple polymers from the graft (compound) polymers is developed. This method is based on the peculiar colloidal properties of the graft polymers. These separations show that interaction between the natural and synthetic polymers depends on the catalyst used for initiating the polymerization and, therefore, that more than simple transfer is involved. Thus, with benzoyl peroxide, numerous very short side chains are combined with the rubber, while the free vinyl polymer chain grows to approximately the length predicted from known data. With azoisobutyronitrile, on the other hand, there is little or no reaction between the rubber and vinyl component. It is suggested that the formation of these very short grafted chains in place of the expected long ones may be a general feature of rubber-polymer systems of this type.
Structure and Properties of Loaded Rubber Mditures. XII. Dielectric Properties of Natural Rubber-Carbon Black Mditures
Authors: Lukomskaya A. I. , Dogadkin B. A.
Published: February 2011

1. The temperature and frequency curves of dielectric constant ε′ and coefficient of dielectric loss ε″ of unvulcanized natural rubber and simple rubber-carbon black mixtures, and also vulcanizates of natural rubber containing various proportions of thermal black or channel black, were studied in the frequency range from 50 to 2.5×107 cycles per second at 20° C, and in the temperature range from −75° to 152° C at frequencies of 103 to 4×104 cycles per second. 2. As in the case of sodium-butadiene mixtures, the addition of carbon black to the rubber leads to three kinds of dielectric losses, viz., a loss due to the nonuniformity of the dielectric, a loss due to the passage of a direct current (conductivity), and a loss due to structure formation. Vulcanization of rubber leads to the appearance of dipolar dielectric losses, which can be explained by the orientation of the sulfur dipoles in the electric field. Loading of vulcanizates causes a change of the dipolar dielectric properties, which depend both on the content and type of filler and on the type of vulcanized rubber. 3. For all the types of vulcanizates, the dependence of the dielectric properties (a measure of the orientation processes in the rubber phase) on the form factor ( a measure of the structure-forming capacity of the carbon black) corresponds to the dependence of the physical-mechanical properties on the carbon black content.
Inhibited Oxidation of Elastomers
Authors: Kuzminskii˘ A. S. , Lezhnev N. N.
Published: February 2011

1. The oxidation of elastomers in the presence of true inhibitors, of which secondary aromatic amines are an important class, is for practical purposes an initiation reaction and primary oxidation of the chains is possible only to a slight degree. 2. Inhibited oxidation (initiation) is fundamentally distinct from autocatalytic oxidation. 3. The method of study of inhibited oxidation (initiation) consists in the study of the consumption of inhibitor, while the rate of this process is equal to either the proportional rate of initiation or the constancy of the concentration of dissolved oxygen in the entire mass of the rubber film or specimen studied. 4. In the inhibited oxidation of different types of rubber, the rate of initiation is practically constant for each temperature. The activation energy of the reaction is equal to 22.6 kcal. per mole, and is independent of the nature of the polymer in the absence of electrically negative substituents in the polymer. 5. In the case of strongly activated nitration, the diffusion of oxygen in the rubber may have a retarding influence. Then the concentration of dissolved molecular oxygen [O2] differs at different depths below the surface. The relation of the rate of consumption of inhibitor wi to the concentration of oxygen is a straight-line function, i.e., wi=A[O2]n; at 120° C, n=0.5. 6. The reactivity of rubber hydrocarbons with respect to molecular oxygen and certain other chemically active agents is determined principally by the content of double bonds in the main chains of the molecules of the polymers. Marked structural differences, such as degree of polymerization, spatial configuration, presence of aromatic rings, etc., have practically no influence on the rate of inhibited oxidation. 7. The absorption of oxygen by the double bonds of the side chains of butadiene rubbers has a much higher activation barrier (27–28 kcal. per mole); consequently, the double bonds are practically inactive during the inhibited oxidation of elastomers. 8. The oxidation of polyisobutylene in the presence of phenyl-2-naphthylamine is characterized by the presence of a temperature threshold, below which initiation does not take place. The directly related change of molecular weight and consumption of inhibitor indicate that destruction of the polymer continues until a constant molecular weight is reached. 9. The inhibited oxidation of Butyl rubber is characterized by the simultaneous progress of two rates of oxidation. The first is the rate of oxidation of the chains, which do not reach a constant weight; the second is the rate of absorption of oxygen at the double bonds. In both polyisobutylene and Butyl rubber, the ordinary bonds of the long chains are considerably weakened. Since the concentration of ordinary bonds in Butyl rubber is much higher than the concentration of double bonds, the rate of oxidation of the former is greater than the rate of oxidation of the latter.
Smearing of Vulcanized Rubber
Authors: Gehman S. D. , Wilkinson C. S. , Daniels R. D.
Published: February 2011

The surface heating which occurs at the interface of rubber sliding under a load may be part of the mechanism of abrasion, especially under severe conditions. Removal of rubber by thermal degradation and a smearing process occurs if the rubber attains sufficiently high localized temperatures. A procedure, using a melting point bar, was developed for measuring the temperature at which smearing occurred for rubber vulcanizates. Smear points reproducible to about ±2° F were measured. The effect of compounding variables on the smear point was investigated. The most important variable in this category was the vulcanization system, probably inasmuch as it determined the type of cross-linking. The presence of free sulfur within the rubber also tended to increase the smear temperature. Highest smear points were obtained with mercaptobenzothiazole-tetramethylthiuram disulfide mixtures, and for a non-sulfur compound using p-quinone-dioxime as the curing agent. The highest smear point observed for natural rubber was 475° F, obtained with this system. GR-S tread compounds showed no smearing even at 560° F, which was as high as could be obtained with the apparatus used. The resistance to smearing of GR-S may be an important factor in explaining its superiority in road wear under severe conditions. Laboratory abrasion experiments were performed to illustrate the effect of smearing on the relative abrasion loss of GR-S and natural-rubber tread compounds.
Formation of Rubber Films from Solutions and Aqueous Dispersions
Authors: Sandomirskii˘ D. M. , Gagina K.
Published: February 2011

1. The mechanical properties, shrinkage, and swelling in water vapor of rubber films prepared from various latexes and rubber solutions, were studied. 2. It is shown that the behavior of films varies with the method of preparation. 3. An explanation of the difference in properties of rubber films prepared from solutions and from latex mixtures is suggested, based on the presence in films from latex of a network of nonrubber substances.
Low-Temperature Properties of Plasticized Butadiene-Styrene Copolymers
Authors: Henderson D. A. , McLeod L. A.
Published: February 2011

The second-order transition temperatures of plasticized butadiene-styrene copolymers have been measured by dilatometric techniques. In a series of ester plasticizers, the ability of a given plasticizer to depress the second-order transition temperature of the polymer is related to the swelling effect of the plasticizer on the polymer. The special case of a crystallizing plasticizer (dibutyl sebacate) has been discussed. Common petroleum plasticizers do not appear to behave in a similar manner. The change of coefficient of expansion of the ester-plasticized copolymers is related to the measured transition temperature of the blend.
Aging Stability of Neoprene Latex. Relation between Cross-Linking and Hydrolysis of Allylic Chlorine
Authors: Andersen D. E. , Kovacic Peter
Published: February 2011

Neoprene polymer chains are cross-linked between active chlorine sites on the chains. There are two types of active sites of different reactivity. It is necessary to use more vigorous curing conditions to actuate the less reactive chlorine. The polymer develops cross-links while aging as a latex as well as during cure, and the decline of tensile strength with latex age may be inversely correlated with the amount of cross-linking during aging. The decline of tensile strength can be prevented by compounding with bis (diethylthiocarbamyl) disulfide. The calculations of the swelling data are not so complete as might be desired, primarily because of difficulty of measuring and interpreting the molecular weight of high-conversion polymers and to some uncertainty in determining μ. It is felt that the qualitative observations are justified, and that they serve to define both the technically important effect of film structure on tensile strength and the mechanism of cure.
Mechanism of Formation of Cream in GR-S Latex
Authors: Howland L. H. , Nisonoff Alfred
Published: February 2011

The formation of cream, which occurred in many of the early cold, high-solids GR-S latexes, is undesirable because it results in nonuniformity of the latex and is injurious to the properties of latex films. On the other hand, it is dispersible and, hence, much more tolerable than coagulum. The mechanism of its formation is, therefore, of interest. A cold high-solids latex activated by ferrous sulfide was used as the basis for the study. The giant particles constituting cream begin forming between 18 and 35 per cent conversion in latex stabilized only with the soap present initially, and increase in quantity until the end of polymerization. Their formation can be prevented by the timely addition of sufficient stabilizing soap, or by the use of a soap which initiates a small enough number of particles in relation to its stabilizing capacity. The formation of coagulum, rather than large particles, is favored by decreasing the amount of electrolyte or increasing the amount of water charged, and by the presence of cross-linking in the polymer. The effect of increasing the water level or introducing cross-linking is to increase the size rather than the amount of agglomerates. Methods are suggested for controlling the formation of very large particles.
Infrared Study of the Oxidation of Elastomers
Authors: Field J. E. , Woodford D. E. , Gehman S. D.
Published: February 2011

It is a matter of considerable interest that polymers can combine with the large amounts of oxygen shown in these experiments, with so little evidence of this combination in the infrared spectrum. Either the oxygen must be distributed in a wide variety of types of compounds or it occurs in a type of linkage having low infrared absorption. In accordance with a previous discussion, it is reasonable to believe that a large proportion of these are ether linkages. If, as has been postulated, the initial step in the autoxidation of hydrocarbons is the formation of hydroperoxides, it is not detected in the infrared spectrum. In order to conform to current theories on autoxidation, it must be assumed that the hydroperoxides formed in the initial oxidation reactions are decomposed at a rate about equal to their formation, so that their net concentration is always below the sensitivity of infrared observation. This does not appear to be an unreasonable assumption. Therefore, only the structures of the terminal products of the secondary reactions are believed to be observed in the infrared spectrum.
The Protection of Rubbers against Ozone Cracking
Authors: Zuev Y. S.
Published: February 2011

The paper describes a study of the aging of natural rubber and synthetic rubbers by the action of ozone. Ozone promotes the development of cracks under tension. The cracking does not occur under compressive stress, a fact which suggests a means of protection, namely, precompression. Another suggestion is the formation of a resistant surface layer that is insensitive to the action of ozone, such as Neoprene. Experiments based on these recommendations are described. A practical method of obtaining precompression is to distend the surface of the rubber with suitable swelling agents, such as triethanolamine. The effect is analogous to the shot-blasting treatment used for prestressing metals to protect them from fatigue cracking.
A Study of Permeability to Gases. Mixtures of Natural Rubber and Other Elastomers
Authors: Barbier Jean
Published: February 2011

An investigation of the permeability to nitrogen of various mixtures of natural rubber and synthetic elastomers has brought to light one highly important fact. The lower permeability obtained by the addition of a synthetic elastomer does not depend solely on the permeability coefficient itself of the particular synthetic elastomer. Rather, it depends in addition on another factor, which, in all probability, is a function of the internal structure of the mixture of natural rubber and synthetic elastomer. A study of this structure is not a simple problem, and mention is made only of the fact that, after having attempted unsuccessfully to analyze the structure by classic methods of microscopy, very encouraging results have been obtained with mixtures of natural rubber and Paracril-26 by measuring, at radio frequencies, the loss factor. The results indicate that, at least with natural rubber-Paracril-26 mixtures, milling brings about a certain degree of mutual diffusion of the two elastomers on a molecular scale. However, the vulcanizates give indications of a two-phase colloidal structure, one phase relatively rich in Paracril, the other phase relatively rich in natural rubber. Such a structure would be in harmony, at least qualitatively, with the conclusions drawn in the present investigation on the permeability to gases of mixtures of elastomers.
The Effect of Fillers on the Permeability of Rubber to Gases
Authors: Van Amerongen G. J.
Published: February 2011

The purpose of the investigation was to study the effects of fillers, especially various types of carbon black and new light-colored reinforcing fillers. In the discussion of the problem, it is shown that permeability to gases is related to the rate of diffusion, and to the solubility of the gas in rubber, and it is also shown how these properties were measured. The effect of carbon black on the permeability of rubber to gases is relatively small. Independent of the type of carbon black, the permeability is reduced only about 30 per cent by the addition of 50 parts by weight of carbon black per 100 parts of rubber. The permeability of a rubber mixture to a gas is increased considerably, however, by the presence of fine types of carbon blacks, while the rate of diffusion of the gas is decreased. This fact can be explained by assuming that gas is adsorbed by carbon black in rubber and thereby rendered inactive. The high oxygen adsorption of the finer types of carbon blacks in rubber mixtures explains the high rate of oxidation of such mixtures. A whole series of inorganic fillers, among them some light-colored reinforc- ing agents, have no noteworthy effect on permeability. With 20 parts by volume of such fillers per 100 parts of rubber, the permeability is decreased only about 25 per cent, irrespective of the particular filler. A considerable decrease of permeability, i.e., about 75 per cent, is observed, however, with lamellar fillers, such as powdered aluminum and powdered mica. A rubber mixture containing powdered mica shows, at 100° C, the same permeability to hydrogen and nitrogen that Butyl rubber does. The relation of permeability to the temperature of rubber containing fillers is practically the same as that for an unloaded rubber mixture. The decreases of permeability to gases which are observed, are, therefore, not related to energy factors, but are of a purely mechanical nature.
Mooney Viscosity Changes in Freshly Prepared Raw Natural Rubber
Authors: Wood R. I.
Published: February 2011

In the course of investigations carried out in connection with the technical classification of natural rubber, large permanent increases of Mooney viscosity of the order of 30 to 40 units have been observed when freshly prepared raw or masticated rubber is stored under conditions of low relative humidity. The rate of change and the extent of the increase are both affected by the relative humidity of storage, and the effects are most pronounced in the region below about 30 per cent relative humidity. The rate of change in dry air increases with decreasing thickness of the sample and with rise of temperature, although these effects are masked somewhat by oxidative breakdown on prolonged storage at temperatures higher than about 30° C. Mooney values continue to increase long after the rubber has reached constant weight on drying; the removal of acetone-soluble and nitrogeneous nonrubber components and of oxygen does not prevent the changes from taking place. The effects are only partially reversed by subsequent storage at high relative humidity, and there is evidence to suggest that the hardening is associated with the development of a cross-linked benzene-insoluble gel structure throughout the rubber.
Solubility of Zinc Oxide in Preserved Hevea Latex
Authors: Van den Tempel M.
Published: February 2011

The solubility of zinc oxide in Hevea latex, and in model solutions containing an ammonium salt together with free ammonia, has been measured by means of polarography. It is found that the solubility, at a given value of the pH, is proportional to the concentration of ammonia and ammonium salt together. At a constant concentration of ammonium ions plus free ammonia, the solubility shows a maximum at pH 9.4 A relation between the solubility of zinc oxide in Hevea latex and the concentrations of ammonium ions and free ammonia is given. The relation is checked with a number of latex samples of varying origin, and with samples produced therefrom by the addition of silicofluoride, formaldehyde, or trypsin.
Bisalkylation Theory of Neoprene Vulcanization
Authors: Kovacic Peter
Published: February 2011

Among the organic compounds that are recommended for use with magnesia and zinc oxide as vulcanizing agents for Neoprene are ethylenethiourea (2-imidazolidinethione), p,p′-diaminodiphenylmethane and the di-o-tolylguanidine salt of dicatechol borate. In the absence of sulfur, these agents in combination with zinc oxide do not vulcanize natural rubber. This points up a marked difference in the way these elastomers vulcanize. Although a major structural difference is the chlorine atom in Neoprene in place of the side methyl group in natural rubber, the small amount of tertiary allylic chlorine formed by 1,2-polymerization is the important functional difference. The labile chlorine amounts to about 1.5 per cent of the total chlorine in a general-purpose Neoprene made at 40° C, such as Neoprene Type W used in this work. In Neoprene latex, this active chlorine is gradually liberated, and the polymer becomes cross-linked. This paper demonstrates the importance of the labile chlorine in the vulcanization of dry Neoprene, accounts for the difference in the vulcanization of Neoprene and natural rubber, and suggests a bisalkylation theory of Neoprene vulcanization.
Softening of Vulcanized Carbon Black-Loaded Rubber during Extension
Authors: Marshall D. G. , Walker D. L. , Smith J. G.
Published: February 2011

The results of the observations recorded in this paper may be summarized by the following items. 1. A difference between the first and second load-extension curves is to be expected in any viscoelastic material, although the behavior of black-loaded rubber at large extensions differs in some fundamental respects from a simple viscoelastic material. 2. Within the experimental limits of about ±10 per cent, all of the energy used in softening the black-loaded rubbers studied appears as heat. 3. The ratio between the area of the hysteresis cycle obtained on first stretching a specimen of black-loaded rubber and that obtained during the second extension varies only slightly from compound to compound in the range of extensions studied. 4. Although the modulus of a black-loaded rubber decreases with increasing temperature, the ratio between the hysteresis area of the first extension and that of the second extension remains roughly constant over the temperature range studied. 5. There are electrical resistance changes that correspond closely to the mechanical softening effects experienced with black-loaded rubber. Result (2) suggests that if cross-linkage breaking or changes of state of rubber are specified as mechanisms for producing softening, then the potential energy changes required must be small, compared with the mechanical energy available. Result (5) shows that changes in arrangement of the carbon black particles are associated with the softening process, and therefore suggests that the softening is related to internal strains in the rubber. These results do not prove that the softening observed in rubber is similar in principle to the behavior of a simple viscoelastic model during the first and other extensions. However, these observations are consistent with this view, except for the difficulty connected with the relationship between the softening and the permanent set in the simple viscoelastic material, and the difficulty connected with the persistence of softening. A simple linear model is obviously bound to have considerable limitations in describing the properties of a black-loaded rubber at high extensions. The limitations may arise from the nonlinearity of rubber elasticity and the non-Newtonian nature of rubber flow; alternatively, it may be necessary to postulate some entirely different process, such as rubber heterogeneity or mechanical bond breaking.
Determination of Free Sulfur in Hard Rubber
Authors: Wynne-Evans C.
Published: February 2011

The volumetric method for the determination of sulfur by means of aqueous sodium sulfite has been adapted for the determination of free sulfur present in hard-rubber vulcanizates. This work was carried out because there was not a speedy free sulfur method applicable to hard rubbers, and the investigation has shown that, by the use of aqueous sodium sulfite, it is possible to obtain reliable and extremely accurate free sulfur results in a little over three hours, against the usual three to four days by other methods which are discussed.
Carboxylic Elastomers
Authors: Brown Harold P. , Gibbs Carlin F.
Published: February 2011

Carboxyl groups can be introduced into elastomers by adding olefinic acids to suitable emulsion systems prior to polymerization. In general, such carboxyl groups elevate the elasticity temperature range, impart superior filming properties, increase resistance to swelling by hydrocarbon solvents, and render the polymers susceptible to cross-linkage, gelation, and vulcanization by polyvalent reagents. In vulcanization recipes based on sulfur but containing polyvalent metal salts, the presence of as little as 1 per cent of a carboxylic monomer is recognizable through its influence on vulcanizate properties. Carboxylic elastomers can be cross-linked by reactions of the carboxyl groups. Salt formation with zinc oxide, without pigmentation, gives stocks having stress-strain properties equaling or surpassing those of black-pigmented sulfur-cured vulcanizates of analogous noncarboxylic polymers. Several divalent metal oxides and other salts can be used as vulcanizing agents. The metal oxide vulcanizates possess excellent stress-strain properties, but poor compression sets. Certain vulcanizates are improved by the inclusion of small amounts of organic acids. An excess of organic acid causes devulcanization. Carbon blacks function principally as loading rather than reinforcing pigments.
Steady Flow and Dynamic Viscosity of Branched Butadiene-Styrene Block Copolymers
Authors: Kraus G. , Naylor F. E. , Rollmann K. W.
Published: February 2011

Steady flow and dynamic viscosities were determined for symmetrical linear and star-branched block copolymers of butadiene and styrene above their upper (polystyrene) glass transition. Block structures examined were B-S-B, (B-S-)3, S-B-S, (S-B-)3 and (S-B-)4. At constant molecular weight and total styrene content viscosities were greater for polymers terminating in styrene blocks, irrespective of branching. Branching decreased the viscosity of either polybutadiene-terminated or polystyrene-terminated block polymers, compared at equal Mw. However, comparisons at equal block lengths showed that the length of the terminal blocks, not the total molecular weight, governs the viscoelastic behavior of these polymers to a surprisingly good approximation. This unusual result is rationalized in terms of the two-phase domain structure of these polymers, which persists to a significant degree in the melt. Below the glass transition of the polystyrene blocks the effects of branching were masked by differences in the morphology of the domain structure unrelated to branching.
Chemorheological Study of Vulcanized Rubbers under Mechanical Stress
Authors: Kusano T. , Suzuki Y. , Murakami K.
Published: February 2011

Below the glass transition temperature, the cleavage of molecular chains of extended vulcanized rubbers will occur. The crosslink density of vulcanized rubbers, which were placed at room temperature for about 4 h in a nitrogen atmosphere, increased about 17 per cent after extension of 200 per cent at −76° C. This may be due to the recombination of cleft chains, and this can be shown by the Maxwellian type of curves resulting from a plot of crosslink density as a function of forced strain. The decreasing proportion of crosslink density in the presence of radical acceptors in the rubbers and the increasing crosslink density in the absence of radical acceptors, because of recombination of cleft chains, was ascribed to the recombination of unstable chains produced by the added mechanical stimulus.
Processing of Powdered PVC-NBR Polyblend Compounds
Authors: DeMarco R. D. , Woods M. E. , Arnold L. F.
Published: February 2011

The processing of PVC-NBR compounds in powdered form has been discussed. Advantages of powder over conventional processiag were reviewed. The special requirements of NBR for blending with PVC were noted. Thermal stability requirements, in particular, were emphasized. Typical compound formulations for nonvulcanized applications were given. And the effect of compound variations on physical properties indicated. Injection molding of shoe soles was given as an example of end-product production directly from these powdered compounds.
Solution Autoxidation of EPDM and Termonomers
Authors: Schnecko H. , Walker J. S.
Published: February 2011

Oxygen uptake of 3 low molecular weight ethylene-propylene terpolymers (EPDM) and their respective bicyclic diolefin termonomers (dicyclopentadiene, ethylidene norbornene, and methyl endomethylene hexahydronaphthalene) has been measured at ⩽70°. From the kinetic behavior and from the activation energy, it has been concluded that ethylidene norbornene reacts differently from the other two monomers; its autoxidation is much slower. In all cases, conversion is not very high due to formation of an unidentified inhibitor.
Lithium Polymerization Catalysts. Charles Goodyear Medal Address—1972
Authors: Stavely Frederick W.
Published: February 2011

The growth of the Lithium Polymerization Catalysts system has been an interesting and intriguing study. Abraham Lincoln, in one of his addresses, indicated that no one would long remember what was said or done there on that occasion. Thus unwittingly, he may have forecast the insignificance of this paper in its effect on the scientific world. It is presumed that none of you here, unless he may have been a Charles Goodyear medalist, can recall many of the important statements or thoughts expressed on this occasion by prior Charles Goodyear Medalists. Therefore, you need not recall anything that is said here today. When one starts a research project, the first thing that is done is to review the literature to find out what has already been done in that field. Thus, we find that in 1826, Faraday published his first analysis of rubber latex. He found that it contained water, rubber, vegetable matter rich in nitrogen and extractable material. He also established that rubber contained the elements of Carbon and Hydrogen. His was the first significant publication about rubber since that of de la Condamine in 1751 to the Academie of Science in Paris. There were several other publications prior to the end of that century, but they did not seem too significant from a scientific standpoint. A German scientist, Frederich Karl Himly, had been studying in Göttingen for a year and a half, about rubber and its destructive distillation products, and he discussed his findings in his Doctors dissertation in 1835. Himly's thesis was published in a small paper back booklet but it did not get wide distribution, possibly due to the fact that it was written in Latin, as was often the case in those days. A copy of this publication was found in the Research Library of The Firestone Tire & Eubber Company about 1922. Imprinted on the cover was the name of M. J. Sehleiden and written on the outside, the name of M. Prinzhom. Also there was the name of C. C. Goodrich, and H. W. Kugler, who later became the Chief Chemist of The Firestone Tire & Rubber Company.