bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Processes during Deformation of Rubberlike Elastic Bodies
Authors: Meter Kurt H. , Van Der Wyk A. J. A.
Published: February 2011

It has been demonstrated that the elastic force of a moderately vulcanized rubber kept at a constant stress is proportional to the absolute temperature, T, in the region of medium elongations. In this respect, rubber behaves somewhat like an ideal gas, the pressure of which at constant volume is also proportional to T. By applying the first and second laws of thermodynamics, it can be shown that the internal energy of isothermally stretched rubber changes as little as that of an ideal gas if its volume is increased or decreased isothermally. In both cases, however, the entropy of the system changes. Meyer, Susich, and Valkó, Karrer, and Busse explain this behavior in the following way. All rubberlike substances consist of long, flexible, chain molecules whose links are thermally mobile. In the undeformed amorphous rubber, the molecules represent randomly coiled chains ; as a result of the deformation their shape is changed, e.g., partly stretched by elongation. Thus a thermo-dynamically less probable shape is forced on them ; the thermal agitation tends to eliminate it ; because of the reciprocal felting and intertwining of the molecules, a return to the thermodynamically more probable state is possible only if the deformation can be reversed. The thermally mobile chain links are referred to as kinetic units or chain segments. In the present paper, we shall discuss the molecular processes taking place in the course of deformation, in particular such questions as: “How is the deforming force transferred to an individual chain molecule and its segment?” “How does the molecule react to this force?” After having discussed these questions, we shall examine how far the requirements are complied with for a quantitative theory such as the derivation of an equation to calculate the modulus of elasticity from structural data. We shall also discuss the attempts known to have been made in this direction so far.
A Study of the Various Molecular Fractions of Rubber and Their Behavior during Vulcanization
Authors: Hauser E. A. , Le Beau D. S. , Shen Yen
Published: February 2011

Hevea prime ribbed smoked sheets were subjected to diffusion fractionation. The rubber recovered from the separate fractions was compounded and vulcanized. The physical and chemical properties of the vulcanizates showed pronounced differences. A tentative explanation for these results is offered on the basis of the molecular and colloidal structure of the rubber hydrocarbon.
The Mechanism of Reinforcement. II
Authors: Goldfinger George
Published: February 2011

Further experimental evidence is given which indicates that, when a dilute solution of GR-S is mixed with carbon black, certain fractions of the rubber are preferentially adsorbed by the black. After removal of the carbon black and the adsorbed fractions by centrifuging, the “treated” GR-S is obtained by precipitation from the solution. Samples compounded as GR-S gum stock show increasing modulus with increasing amounts of carbon black used for adsorption treatment. However, when the GR-S thus treated is compounded with carbon black, then the effect is reversed. The more black used in the treatment and the higher the modulus of the gum stock, the lower the modulus of loaded stock.
Specific Heats of Hevea, GR-S, and GR-I Stocks
Authors: Hamill W. H. , Mrowca B. A. , Anthony R. L.
Published: February 2011

1. A calorimeter, suitable for determining the specific heats of various rubber compounds (with a precision of 1 per cent or better), is described. Although the results reported are for room temperature (actually 26–27° C), the calorimeter could be operated with minor changes at other temperatures. 2. Employing values of the specific heat at room temperature as given by the National Bureau of Standards for various raw rubbers, it is shown by direct measurement on various gum and loaded stocks that the specific heats of these materials can be calculated from a knowledge of the specific heats of the ingredients. 3. A 5 per cent deviation from linearity in the stress-temperature curves at constant length can cause a total variation in cL of only about 0.00014 calorie per cc. per 1° C over an elongation range of 0 to 200 per cent. This result holds, provided an equation of state exists and provided the region of temperature and elongation considered is one in which phase changes do not occur. Subject to these restrictions, we may neglect variations in cL with elongation and may interpret cL (in calories per gram per ° C) as being identical with cp (in calories per gram per ° C) at the same temperature. 4. Accurate knowledge of cL is needed for the correlation of the reversible heat developed when rubber is stretched rapidly with the entropy component of the stress-strain curve. It is also needed to correlate calculated energy losses with rise in temperature in flexometer experiments.
The Photogelation of Rubber Sols in the Absence of Accelerators
Authors: Buckingham R. , Planer G. V.
Published: February 2011

Irradiation of rubber sols with ultraviolet light in the absence of oxygen results in gelation under certain conditions. From a study of the reaction curves the mechanism of this reaction was shown by the authors in a previous paper to consist mainly of a three-dimensional polymerization. The curves were derived by following the reaction by means of viscosity measurements, in the presence of an accelerator, benzophenone, with carbon tetrachloride as solvent. It was deemed of interest to compare these curves with those obtained without the use of benzophenone, and the experimental work described in the following deals with the study of the reaction in the absence of accelerators. The products obtained on removing the solvent from photogels differ markedly for various solvents, but are in all cases insoluble and show elastic properties similar to those of lightly vulcanized rubber. The solvents used are of two types, active and inactive. In the case of the active ones, such as carbon tetrachloride, the solvent molecules condense with the rubber, and on removal of the solvent from the resulting photogels, the products are often considerably heavier than the original rubber samples. When carbon tetrachloride is used, the reaction product has been shown to contain appreciable amounts of combined chlorine. With inactive solvents like benzene, ligroin, etc., no increases in weight are observed and gels are generally formed less readily.
Nonsulfur Vulcanization. II. An Experimental Study
Authors: Alfrey Turner , Hendricks J. G. , Hershey Robert M. , Mark Hermann
Published: February 2011

In Part I the literature on nonsulfur vulcanization was reviewed, with particular emphasis on the reaction mechanisms involved. The present paper reports a series of experiments conducted in this laboratory. The first part deals with a chemical investigation of dinitrobenzene vulcanization ; the second part deals with the physical properties of nonsulfur vulcanizates, and includes some results reported in the literature as well as those experimentally established here.
Oxidation of GR-S Vulcanizates
Authors: Shelton J. Reid , Winn Hugh
Published: February 2011

Oxygen absorption studies on a tread type GR-S vulcanizate show: 1. There are three stages involved in the oxidation: (1) an initial rapid absorption, of apparent first order at constant pressure, which is of short duration and appears to involve a limited number of especially reactive centers in the vulcanizate ; (2) a constant-rate reaction, of apparent zero order at constant oxygen pressure, which would extend over most of the useful life of the vulcanizate in service ; (3) an autocatalytic reaction, beginning after a given stock has absorbed a definite amount of oxygen that is independent of the temperature at which the absorption takes place. 2. The rate of oxygen absorption increases with temperature. The temperature coefficient for the constant rate reaction is 2.6 for a 10° C change in temperature over the range 80° to 120° C. 3. Diffusion is not rate controlling, provided the specimen thickness does not exceed 0.080 inch at 100° C or 0.040 inch at 120° C. 4. The effect of cure on the rate of oxygen absorption by GR-S vulcanizates is slight, and consequently, the technique is particularly useful for studying the effect of changes in compounding upon aging resistance. 5. Oxygen absorption data can be satisfactorily correlated with changes in physical properties during aging. While the fundamental nature of the mechanism of the oxidation of GR-S is still unknown, considerable information has been obtained with respect to some of the factors involved, and the general nature of the reaction has been established. This information, together with the work still in progress, should be of value in pointing the way toward possible methods of improving the resistance of GR-S to aging.
Recent Advances in Rubber Analysis
Authors: Wake W. C.
Published: February 2011

There is considerable overlap between the various methods reviewed above, some of which are completely self-contained, whereas others have to be grouped together to provide a complete analytical scheme. There are, consequently, several ways of building up a comprehensive system, and which way is preferred in practice depends on the amount of information already in the possession of the analyst, and his purpose in carrying out the analysis. In the case of an unknown vulcanized sample requiring full investigation, the following order of procedure will be found helpful. (1) Sufficient of the rubber for the tests required is acetone-extracted and dried. (2) Preparations for determining swelling ratios should be made. Unless the modified micro-method is used this result will not be available for a week. However, it is definitely worth starting as the preparations take only the time required for weighing and although the rest of the analysis will be completed, confirmation of such work arriving after a few days will be valuable as in independant check and an insurance against error or accident. (3) The systematic scheme for qualitative analysis given in U.9 should be used, starting with the sodium fusion for elements. Even if elements characteristic of certain types are present, it must be assumed that hydrocarbon polymer is present also and that part of the scheme given for cases where characteristic elements are absent should be used. It may, however, be abbreviated by limiting it to the use of color tests for natural rubber and GR-S, although there is danger of missing the presence of alkali reclaimed natural rubber if this is done. (4) From the qualitative composition such rubbers, as are indicated present, are determined quantitatively. (5) It is useful to make certain that the results obtained are in agreement with any physical properties that can readily be noted, e.g., freeze resistance and specific gravity.
Rubber Plastometer with Uniform Rate of Shear—Shearing-Cone Plastometer
Authors: Piper G. H. , Scott J. R.
Published: February 2011

A new shearing-cone plastometer, suitable for investigating the plastic-flow relations of highly viscous materials over a wide range of stress, is described. A mushroom-shaped rotor, having upper and lower surfaces of conical type, is rotated in the plastic material contained in a cylindrical mould. With this type of shearing surface the rate of shear is uniform throughout the material, except for a small edge zone, thus overcoming some disadvantages of previous plastometers. The mechanical design is based on the Mooney shearing-disk plastometer except that provision is made for a wide range of speeds of rotation.
An Improved Brittle Point Apparatus
Authors: Graves F. L.
Published: February 2011

In the paper “Evaluating Low Temperature Stiffness and Brittle Point in Elastomers” several methods for determining the brittle points of rubber and rubberlike compounds were reviewed, and the apparatus developed in these laboratories in 1942 for this test was described in detail.
The Statistical Length of Long-Chain Molecules
Authors: Treloar L. R. G.
Published: February 2011

A formula is derived for the complete function representing the probability of a given distance between the ends of a chain of universally jointed equal links. The formula is computed for chains of 25 and 100 links. The distribution functions derived from this formula are compared with those previously worked out by an independent method for polyisoprene and paraffin chains. It is shown that the polyisoprene chain is statistically equivalent to a randomly-jointed chain of length corresponding to 1.42 links per isoprene unit. This work forms part of a program of fundamental research on rubber undertaken by the Board of the British Rubber Producers' Research Association.
Preparation and Properties of Rubberlike High Polymers. I. Polymerization of Dienes and Vinyl Compounds in Bulk
Authors: Koningsberger C. , Salomon G.
Published: February 2011

The polymerization of dienes under the influence of heat, of diazoaminobenzene, and of benzoyl peroxide has been studied. Diazoaminobenzene probably acts as a slow but continuous source of free radicals, giving quantitative yields of methyl rubber of good quality from dimethylbutadiene after a few days to a few weeks at 100–125° C. The effect of diazoaminobenzene on butadiene is the same, but the rate of the uncatalyzed dimerization of butadiene at 100° C is as fast as that of dimethylbutadiene at 150° C and, therefore, dimerization interferes much more strongly with the polymerization of butadiene. Only 60 per cent of polybutadiene has been obtained. A few experiments with isoprene showed its position between the two other dienes. The effect of benzoyl peroxide on the polymerization of the dienes appeared to be much smaller than was expected from its known catalytic action on the polymerization of vinyl compounds, e.g., styrene, for in this case its activity is about 100–1000 times greater than that of diazoaminobenzene. It is assumed that a larger number of radicals, produced by the fast decomposition of benzoyl peroxide, causes this difference. Diazoaminobenzene has about the same effect on the polymerization of styrene and acrylonitrile as on that of dienes. The catalytic effect of benzoyl peroxide on the polymerization of dienes is, on the contrary, 10,000–100,000 times smaller than on that of vinyl compounds. This difference can be understood by the assumption that the catalyst is quickly used up by oxidizing the dienes and their polymers. Whereas methyl rubber and the polyisoprene resemble raw natural rubber, polybutadiene, prepared under comparable conditions, is hard, swells moderately, and has a tendency to become brittle as a result of oxidation (aging).
Spectrophotometric Determination of the Styrene Content of Butadiene-Styrene Copolymers
Authors: Meehan E. J.
Published: February 2011

The ultraviolet absorption of polystyrene, with maximum absorption at 262 mµ, is due to the presence of phenyl residues in the polymer. The specific extinction coefficient is constant, i.e., independent of the molecular weight of the polymer. This shows that the extinction of the phenyl residues is additive. On the basis of this fact, it is shown that the styrene content of a butadiene-styrene copolymer (such as GR-S rubber) can be determined by ultraviolet spectrophotometry. The relative precision of the determination is about 1 per cent, the probable relative accuracy is about 3 per cent.
An X-Ray Study of Some Synthetic Elastomers. Polychloroprenes
Authors: Fournier Henri , Trillat Jean Jacques
Published: February 2011

Synthetic rubbers prepared from isoprene and other unsaturated hydrocarbons have been studied by means of x-rays by various investigators, including Carothers, Katz, Meyer, and Sebrell and Dinsmore. In general, these synthetic products differ markedly from natural rubber in that when they are stretched, they do not give any fibre diagrams. On the contrary, μ-polychloroprene (Neoprene), H2C:CC·CH:CH2, when stretched to about 500 per cent, gives a somewhat diffused fibre diagram with an identity period of 4.8 A˚.U., corresponding to the length of a chloroprene unit in the trans form. We have verified this fact, and have found, in addition, that preliminary heating of the polychloroprene facilitates this orientation process which takes place upon stretching. The investigation was continued by a study of a product which had not previously been studied, viz., chloroisoprene:
The Structure of Some Synthetic Elastomers. Ethylene Polysulfide
Authors: Trillat Jean Jacques , Tertian Robert
Published: February 2011

As a result of x-ray studies of different synthetic elastomers a number of works have been published which show that, in general, these products behave somewhat differently from natural rubber. When stretched, some elastomers, e.g., Buna-S and Buna-N, show no evidence at all of crystallization; others, e.g., Neoprene and Vistanex, show much less well defined indications of crystallization than does natural rubber. These differences in behavior leave the field open to hypotheses regarding the origin of elasticity. As is well known, the condensation product of dichloroethane and sodium poly8ulfide gives rise to an ethylene tetrasulfide, which polymerizes in linear chains, ((CH2CH2S4)n. When mixed with suitable compounding ingredients and vulcanized, this polymer gives a substitute for rubber (Thiogomme and Thiokol), which can replace the latter in certain applications. Katz and Fuller have shown that stretched Thiogomme is capable of giving crystalline interferences, and a model of the elementary cell has been proposed by these investigators. The present authors have examined pure polymerized ethylene tetrasulfide and commercial Thiogomme, both when at rest and when stretched, utilizing for this purpose the Kα radiation of copper (λ=1.54 A˚.U.) The results which were obtained may be summarized as follows.
Vulcanization Reactions in Butyl Rubber. Action of Dinitroso, Dioxime, and Related Compounds
Authors: Rehner John , Flory Paul J.
Published: February 2011

Experiments have been carried out to determine the chemical reactions that occur when Butyl rubber is vulcanized by quinone dioxime or related compounds. Observations have been made of the reactions of these substances with simple olefins, and of the effect of oxidizing agents on the dioxime-type of vulcanization of Butyl in solution. The theory is proposed that, in the vulcanization of Butyl by quinone dioxime or its esters, in presence of oxidizing agents, the active agent is p-dinitrosobenzene formed by oxidation of the dioxime. Chemical reactions are suggested for the subsequent cross-linking or vulcanizing steps, and the results of confirmatory experiments are presented. p-Dinitrosobenzene and other polynitroso compounds are active vulcanizing agents for Butyl, natural rubber, Buna-S, Buna-N, and Neoprene, and do not require the addition of an oxidizing agent. It is suggested that vulcanization of natural rubber by polynitro compounds involves their reduction to corresponding nitroso compounds as the first step, and that the nitroso group adds to rubber to produce cross-linkages.
The Mobility of Foreign Molecules Dissolved in Rubber
Authors: Haegel Jean
Published: February 2011

Current theories of the elasticity of rubber view this property as originating in thermal agitation of the rubber molecules themselves. In any consideration of this problem, a major point to be considered is the degree of freedom of this agitation, first, because only segments of these very long molecules are concerned, and secondly because large brownian movements which might otherwise profoundly alter the structure are impossible. These phenomena should hold true also of rubber containing no solvent to swell it. A convenient means of studying thermal agitation of this character is to investigate the mobility of foreign molecules or segments of these molecules when they are dissolved in rubber. This can be done in a practical way by adding a colored substance to the rubber. Investigations already carried out in the laboratory have not completely settled this problem, but at least have led to rather unexpected results; it therefore seemed advisable to continue the study.
Crystallization of Rubber by Pressure
Authors: Thiessen P. A. , Kirsch W.
Published: February 2011

The knowledge which has been acquired as the result of studies by means of polarized light and x-rays of the behavior of rubber when stretched has led to the conclusion that rubber is a polyphase system, in which crystals and the liquid phase are in a state of equilibrium which depends not only on the temperature but to a considerable extent on the pressure. This concept is founded on the observation that there is an increase in the crystalline phase after rubber which has been stretched is allowed to rest, and that the anisotropy shows a reversible effect at definite temperatures and degrees of elongation. Experimental proof of this dependence on pressure has, however, been lacking heretofore, because investigations have been confined to unidirectional stretching, and consequently to pressure in one definite direction. If the conclusion stated above were correct, it would be expected that pressure from all directions would lead to crystallization under conditions whereby it would not otherwise occur. An experiment of this kind was planned at the time of the earlier work, has been in progress since then, and has recently been completed. The results are described in the present paper.
The Statistical Theory of the Elasticity of Rubber
Authors: Dostal H.
Published: February 2011

The theoretical investigations of various authors, with the aid of which the physical properties of rubber-like substances have become understood on a basis of intermolecular statistics, have not, at least from a quantitative point of view, kept pace with investigations relating to kinetic theories of gases. However, only the facts of rubber elasticity have become understood, and to point out one case, the coefficient of elasticity cannot be derived, and much less the tension zone, beyond proportionality. The reason for this is that, although statistics of a single chain molecule of finite size can be compiled, the bond of the chain molecule and, as a further instance, the behavior of a molecule of infinite size formed by interlacing have not been clearly understood up to the present time. Consequently, it has been possible to gain an insight into the statistical behavior of individual chain molecules much more easily than into that of a piece of rubber, and therefore to deduce with less difficulty theories of the viscosity of high molecular solutions and similar systems. In the case of rubber, progress has been more difficult in explaining the effects which take place.
Properties and Uses of Chlorinated Rubber
Authors: Baxter J. P. , Moore J. G.
Published: February 2011

Although rubber was first chlorinated in 1846 to improve its aging properties (Parks, British patent 11,147), it was not until 1888 that a product containing 65.18 per cent of chlorine was isolated and the formula C10H13Cl7 given by Gladstone and Hibbert. Nearly thirty years later the United Alkali Company marketed a solution of chlorinated rubber, Duroprene, made under the Peachey patents, and for ten years this remained the only chlorinated rubber on the market. During the past ten years interest in this material has rapidly developed, as shown by the numerous brands at present available, namely: Alloprene (I. C. I.) ; Tornesit (New York Hamburger Gummiwaaren Compagnie, later Chemische Fabrik Buckau); Tegofan (Tegofan Gesellschaft, later Chemische Fabrik Buckau); Pergut (I. G. Farbenindustrie) ; Detel (Detel Products) ; Aizen (Hadogaya Soda K. K., Japan); Nippon (Nippon Soda K. K., Japan) ; Protex (Soc. Ellettrica ed Elettrochimica del Caffaro, Italy); and Dartex (Metallgesellschaft A.-G.). The patent literature indicates that interest in chlorinated rubber is also taken by Russia, France, Austria, and Jugoslavia.
Rubber Elasticity and Gas Elasticity
Authors: Mark H.
Published: February 2011

All substances which are composed of long mobile chains show one peculiar property, highly reversible elasticity. Even though the range of temperature of this property may be notably variable (in the case of polyvinyl alcohol and rubber at about room temperature, in the case of polystyrene, sulfur, or Thiokol only at a higher temperature) still it is to be noted that for rubber-like elasticity the presence of long flexible chains is an indispensable factor. Thus, typical rubber elasticity occurs in polyvinyl alcohol (Vinarol), polybutadiene (Buna), polymethyl-butadiene (methyl rubber), polyacrylic ester and also in its mixed polymerisate with vinyl chloride. This type of elasticity occurs also in sinew fibrin and muscle fibrin, in polychlorobutadiene (Neoprene, Sovprene), in polyethylene sulfide (Thiokol, Baerite), polyphosphornitrile chloride and finally in vulcanized oils (factice) and also in elastic sulfur. In the cases so far examined (natural rubber, Buna, methyl rubber), it has been found that the coefficient of elasticity increases proportionally to the absolute temperature, and that during the stretching heat is evolved. This behavior is contrary to that of normal elastic materials, steel, quartz, glass, etc. It is striking that the substances which have this property of highly reversible (rubber-like) stretching are widely different chemically. This tempts one to ascribe that property to the similarity of their construction. For example, all the substances mentioned consist of long chain-molecules, which display a high degree of internal mobility. The number of members in these chains varies from 102 to 104 and their mobility is due to the kind of linkage between the members, mostly simple C—C bonds.
Values of the Physical Constants of Rubber
Authors: Wood L. A.
Published: February 2011

A critical survey has been made of the values of 16 basic physical constants of rubber in the fields of mechanics, heat, optics and electricity. The value for each constant which seems most reliable has been indicated and, when necessary, has been corrected to the standard conditions of normal atmospheric pressure and a temperature of 25° C. The values have been given for rubber in four different forms: purified hydrocarbon, commercial raw rubber, soft vulcanized rubber containing 2% combined sulfur and hard rubber containing 32% sulfur. The survey indicates that there are significant gaps in present knowledge of the fundamental properties of rubber. In some cases data are lacking, while in many others the best values available are not of the accuracy required for present-day scientific and industrial work. This paper may therefore serve not only as a summary of selected values of the different constants, but also as a basis for the planning of future investigations.
The Distribution of Combined Sulfur in Vulcanized Rubber and Its Bearing on the Sulfide Linkage Theory of Vulcanization
Authors: Williams I.
Published: February 2011

No direct evidence exists to support the sulfide linkage theory of vulcanization, which assumes that cross-linking of the molecules with sulfur would retain the elasticity and decrease the plasticity of the rubber. The following facts do not favor the sulfide linkage theory of vulcanization : (1) Vulcanized rubber can be peptized under conditions which do not appear to rupture a sulfide linkage. (2) No direct relation exists between the physical properties of vulcanized rubber and the amount of combined sulfur. (3) No direct relation exists between the ease of peptization and the physical properties of the vulcanizate. (4) Combined sulfur appears to assist the solvation of rubber. Rubber vulcanized with thiuram disulfides in the absence of free sulfur has poor physical properties but peptizes with difficulty. An increase in combined sulfur without a corresponding improvement in physical properties assists solvation. (5) Rubber having the best physical properties is also the most heterogeneous with respect to sulfur. The sulfide linkage theory would suggest that an even distribution of sulfur would produce the best physical properties. (6) Fractions of peptized vulcanizates, on evaporation of their solutions, leave insoluble vulcanized films, which shows that linkage by means of primary forces is unnecessary for producing the vulcanized condition.
The Interaction of Maleic Anhydride with Rubber
Authors: Bacon R. G. R. , Farmer E. H.
Published: February 2011

(1) Maleic anhydride is known to react (a) with conjugated compounds, e.g., butadiene, usually producing simple cyclic systems, and (b) with unsaturated olefinic substances like styrene and vinyl acetate, producing long-chain heteropolymers. It is now demonstrated that maleic anhydride, under the influence of a little benzoyl peroxide, will react in solution with rubber on heating, yielding a variety of tough, fibrous or resinous products. (2) It is shown that these derivatives are not produced by the action of maleic anhydride alone or of benzoyl peroxide alone, nor are they mixtures of rubber and maleic anhydride polymer. (3) As a result of the reaction, rubber has been found to undergo an increase in weight ranging from a few per cent up to about 120%, according to experimental conditions. The corresponding derivatives differ greatly from rubber in mechanical properties, and range from products which are tough, rubbery and non-tacky, to hard and brittle resins. (4) The effect of varying the quantity of benzoyl peroxide between 1% and 10%, and of using greater excess, is demonstrated. (5) The effect of varying the maleic anhydride/C5H8 ratio between 0.05 and 5 is demonstrated. (6) It is is shown that the nature of the solvent greatly influences the extent of reaction. The use of benzene, toluene, xylene, carbon terachloride, chloroform, decalin, and cyclohexane is discussed. (7) The influence of concentration and the occurrence of gelling have been investigated. (8) The derivatives are very different from rubber in their solubility characteristics.
An Accelerated Aging Test at Room Temperature
Authors: Marzetti B.
Published: February 2011

Accelerated aging in an oven, heated to a more or less elevated temperature, is one of the most valuable tests at the disposal of the rubber technologist for examining the behavior of different compounds in practical use. Geer in 1916 described a now well-established oven test at 160° F., he and Evans giving more details in 1921. In this latter paper they stated in particular that with proper use of their test, one day in the oven could be taken as equal to six months of natural life. Other attempts to foretell more exactly the natural life of rubber from accelerated aging data have proved useless. The figures obtained for life at different temperatures are not always in the same ratio, so that calculation of the corresponding times at room temperature depends on the temperature used in the heat test. This has been shown in experimental work of many authors, particularly Williams and Neal, Milligan and Shaw, Bierer and Davis, and Somerville and Russell. The matter has been thoroughly discussed in a “Symposium on Aging” presented before the New York Rubber Group of the American Chemical Society in 1929.
Rubber-Vulcanizing Properties of Colloidal Carbons
Authors: Wiegand W. B. , Snyder J. W.
Published: February 2011

1. Experiments with rubber-sulfur mixings showed that colloidal carbons accelerated vulcanization instead, as generally stated in the literature, of retarding. The fact that this acceleration was found to be independent of the pH value of the carbon suggests that the carbon rubber reinforcement “reaction” and (physical) vulcanization may be related phenomena. 2. When colloidal carbon is used, as in tire treads, in conjunction with other accelerators, disturbances occur due to the selective adsorption properties of the carbon colloid. These disturbances, which are greatest with basic organic accelerators, less with acidic organic accelerators, and least with inorganic accelerators such as litharge, have led to the description of colloidal carbons as quick-or-slow-vulcanizing. 3. The best guide to this “rate of vulcanization” characteristic of rubber carbons is their pH value. 4. Adsorption data are given for cobalt, manganese, lead and zinc soaps, and vary widely for different colloidal carbons. This variation as to the zinc requirements was confirmed by a rubber compounding series. Thus each carbon, depending on its pH and particle size, presents an individual problem in adsorptive requirements, involving fat acid, zinc oxide and accelerator, which should be adjusted in this order. 5. For use with basic accelerators, e.g., D.P.G., colloidal carbons of maximum surface (which involves high fat acid additions with resultant interference with the accelerator) or carbons with low pH (which requires high soluble zinc and therefore high fat acid) are not recommended. Low pH carbons tend to disturb the alkalinity essential to best results, and to adsorb the accelerator. 6. With acid accelerators, e.g., mercaptobenzthiazole, the finer colloidal carbons of moderate to low pH may safely be used. The higher fat acid dosage (soluble zinc) which these carbons require can be freely supplied, since it does not deactivate the accelerator.
The Behavior of Rubber at Low Temperatures
Authors: Sagajłło M. , BobiŃska J. , Saganowski H.
Published: February 2011

(1) Raw rubber, smoked sheet as well as crepe, freezes to a high degree at low temperatures. The difference between the freezing at −10° and −60° C. is comparatively small at initial elongations of 300 and 400%. With smaller initial elongations there is a greater difference in degree of freezing at temperatures of − 10° and −60° C. A complete loss of the elastic properties of the rubber takes place at −70° C. (2) Previous heating of raw rubber, even at a temperature of 140° C, has no effect on its freezing-resistance. (3) The susceptibility of rubber to freezing increases with increase of the elongation, this effect being strongly marked above an elongation of 200%. (4) An increase in the vulcanization temperature, and therefore a shortening of the vulcanizing time, has only an insignificant effect on the freezing-resistance of rubber compounds. (5) The freezing effect increases as the temperature is lowered. (6) An entire loss of the elastic properties of vulcanized rubber takes place for the lower initial elongations at a temperature of —70° C; for higher elongations; however, they are still retanied at this temperature in a very small degree. (7) “Pure” rubber compounds have a much greater resistance to freezing than loaded ones. (8) The minimum susceptibility to freezing for loaded compounds is obtained with those that are slightly overvulcanized. At the higher elongations this minimum is distinctly shifted into the region of overvulcanization. (9) Softeners have in general no effect in reducing susceptibility to freezing. (10) The use of phenyl-β-naphthylamine has no effect on the susceptibility to freezing. (11) The aging of rubber, even when producing 40% of loss of tensile product, has no effect in lowering its resistance to freezing either at −10° or −60° C. and at initial elongations of from 100 to 400%. On the other hand, the resistance to freezing of aged samples is less at temperatures of −40° and −50° C. with initial elongations of 100 to 200% ; at an initial elongation of 300% they show almost no change in relation to unaged samples, while at an elongation of 400% they show a distinct increase in resistance to freezing. (12) Airplane and balloon shock-absorbers of “pure” rubber compounds possess, within the limits of their elongation during use, even at a temperature of — 40° C, quite insignificant susceptibility to freezing. An entire loss of their elastic properties occurs at −70° C. (13) Keeping airplanes in improvised sheds in winter time even at −20° C. has practically no effect on the usefulness of rubber shock-absorbers.
The Composition and Characteristics of the Rubber in Hevea Latex
Authors: Twiss D. F. , Carpenter A. S.
Published: February 2011

IMPORTANCE OF THE SERUM SUBSTANCES The importance of the non-rubber components of latex, and particularly the protein components, in deciding the behavior towards coagulating agents was recognized at a relatively early date. Indeed, some investigators regarded the coagulating effect as being exerted only by way of the protein, the addition of the coagulants leading initially to its precipitation from solution in the serum, and thereby to the aggregation of the rubber globules. To-day the stability of latex as an aqueous dispersion of rubber globules is still regarded as being dependent on the non-rubber components of the latex. The material actually responsible for its stability, however, is now known to be adsorbed on the surface of the globules, and the physical behavior of the latex globules towards extraneous influences depends on the adsorbed film rather than on the rubber. This is remarkable, as the adsorbed layer, based on the approximation that one gram of protein covers a surface area of 107 cm.2, probably constitutes only 0.6% of the weight of the rubber globules, or thereabouts. The protective layer is not immovably attached, although in fresh latex it is possibly more firmly held than in preserved latex. It should be noted that the adsorbed coating normally represents only a small fraction of the total hydrophilic surface-active substances in the latex, and the stability of latex is less influenced by decrease in the proportion of the non-rubber components than might at first be expected. Latex purified by triply centrifuging shows little, if any, increased tendency to coagulation.
The Chemistry of Natural Rubber. III. The Effect of Ammoniation on the Latex of Hevea Brasiliensis
Authors: Roberts Kenneth C.
Published: February 2011

The bulk of the liquid latex of commerce is protected against putrefaction by addition of 0.7–1.5% of ammonia. It is widely recognized that latex is profoundly affected by this procedure, but little insight has hitherto been obtained into the chemistry of the changes. The problem has now been approached by applying to latex before and after preservation with ammonia the method of analysis described in Part I (Rubber Chem. Tech. 10, 1(1937)). Ammoniated latex which has been kept under representative conditions of storage for periods of 8 weeks to 18 months differs in general in composition from fresh latex in the manner shown in the table. The quantitative findings for ammoniated latex, however, vary appreciably with the time of storage and with the ammonia content. The analysis recorded was made on latex containing 0.7% of ammonia after 18 weeks' storage.
X-Ray Diffraction Patterns of Crystalline Sol Rubber Prepared from Ethereal Solution
Authors: Clark George L. , Gross Siegfried T. , Smith W. Harold
Published: February 2011

In a previous publication there was reproduced an x-ray diffraction pattern of crystals obtained from a solution, cooled to temperatures between −40° and −50° C, of an ether-gel fraction of rubber from Hevea brasiliensis. Measurements of three strong interferences indicated that the crystals were similar to those of stretched gel rubber and of frozen sol, gel and total rubber. Although many attempts were made at that time, unsatisfactory diffraction patterns were obtained with crystalline ether-sol rubber. The interferences were faint and not suitable for accurate measurement and analysis. Since the crystalline material is bulky and some specimens are more compact than others, it seemed possible that the average number of cell diameters was too small to permit sharp definition, and that more material was required for the examination by x-rays. However, it is not certain that lack of definition was caused by insufficient crystalline rubber. The possibility that parts of the long-chain molecules become crystalline and that parts remain amorphous is not excluded, and might be its cause. Additional work with crystalline sol rubber, using a slightly different experimental procedure and more material than in earlier experiments, finally resulted in a satisfactory pattern.
External Influence and the Internal State of Rubber
Authors: Wittstadt W.
Published: February 2011

With continued progress in technology, highly elastic products have come to be of great importance at the present time. Whereas in earlier years rubber was the only product which could be classed in this category, in the last few years many new products with properties resembling those of rubber have been added to the list. This is to a great extent due to the fact that chemical research has given a better insight into the parent substance of rubber and the structural nature of rubber itself. According to these researches, rubber is representative of a group of highly polymeric, organic natural substances, whose long molecules are composed of small structural units in uninterrupted repetition. By reproducing artificially the relations existing in the structure of the rubber molecule, it has been possible by chemical synthesis to prepare highly elastic substances from allied substances or from substances which polymerize in an analogous way. But in spite of this success, chemical investigations have not yet reached a point where it is possible to explain the mechanism of elasticity, for actually elastic phenomena do not depend on chemical changes ; an explanation is rather to be sought in changes which take place in the relative positions and forms of the rubber molecules.
Inhibition of Crystallization of Rubber by High Pressure
Authors: Dow R. B.
Published: February 2011

Bekkedahl has shown that crude rubber at atmospheric pressure freezes in the temperature range from −40° to + 10°C. and melts in the temperature range from 6° to 16° C. The transition is from amorphous rubber to crystalline rubber which is the stable modification between −72° and 6° C. His measurements of the freezing at 0° C. showed that about 280 hours were necessary for completion of the transition, the volume decreasing by 2.2 per cent in such a manner that the volume-time curve was S-shaped. This communication reports the inhibition of crystallization at high pressure. Crude smoked sheets were packed tightly in a pressure chamber and isopropyl alcohol was used to transmit the pressure. The chamber was kept at 0° C. in a well-circulated ice bath. A pressure of 8000 kg. per sq. cm. was applied, and its constancy observed over a period of 14 days. The sensitivity of the manganin gauge used for pressure measurement was such that changes of 5 kg. per sq. cm. were detectable. Outside of slight erratic pressure changes caused by change of temperature around part of the press that was not kept at 0°, “no change of pressure due to crystallization was detected during the 14 days.” Examination of the rubber immediately after pressure was released showed that it was still in the amorphous state.
The Dependence of the Stress on the Temperature of Rubber Elongated to a Constant Degree
Authors: Hauk V. , Neumann W.
Published: February 2011

An instrument for measuring stresses was constructed, whereby changes in tension brought about by changes in temperature in rubber maintained at constant elongation were measured. These measurements were carried out with three types of vulcanizates. After measures were taken in the case of weakly vulcanized samples to eliminate the disturbing factors arising from crystallization, the fact was established that stress is directly proportional to the absolute temperature for all types of vulcanized rubber, as required by theory. It is shown that under some conditions the stress-temperature coefficient depends on the degree of vulcanization, the coefficient decreasing with increase in the degree of vulcanization. The experimental results are discussed, and an explanation is offered to account for the dependence of the stress-temperature coefficient on the degree of vulcanization.
Preparation and Properties of Halogen Derivatives of Rubber from Latex
Authors: Baker H. C.
Published: February 2011

The paper deals with the preparation and properties of chlorine and bromine derivatives of rubber from latex, obtained by the generation of nascent chlorine in situ and by the addition of bromine water. Attention was given to compounds containing small amounts of halogen, which still showed marked elasticity, in addition to the powders containing large proportions of halogen. When stabilized preserved latex was treated with an excess of hydrochloric acid and a suitable amount of oxidizing agent, an exothermic reaction occurred which, if uncontrolled, led to the formation of white powders containing about 50% chlorine which swelled in organic solvents without dissolving. If, however, the temperature was not allowed to rise substantially above atmospheric, at least in the early stages of the reaction, products of similar appearance and chlorine content were obtained, which nevertheless were readily soluble in a wide range of solvents, including vegetable oils, to give thin solutions which formed brittle films adhering strongly to glass and metal. Analysis of a chlorinated rubber containing 55.8% chlorine corresponded approximately to the formula C20H26Cl11O2.
Improvements in Methods for the Rapid Analysis of Rubber
Authors: Marty A.
Published: February 2011

In the course of experiments carried out by the research laboratory of the Compagnie du Gaz of Paris on rubber gaskets for gas lines, we were led to search for a more precise method for the determination of ingredients in vulcanized rubber which would be more rapid than the method involving mild incineration in a crucible. When it is desired to make a rapid determination of the inorganic and organic substances in rubber, it is customary to incinerate the rubber in a closed crucible under moderate conditions. Although this method is rapid, it is not possible to separate with any degree of certainty the rubber from carbon black and mineral substances, for the rubber may carbonize in the crucible and leave a deposit of black, which adds itself to the black originally in the rubber and thus vitiates the results. It was felt that incineration in an inert medium would give results which would approach more closely to the true values. Since in this case a crucible could not be utilized satisfactorily, recourse was had to a Pyrex tube containing a platinum boat. The apparatus finally adopted is described in the following pages.
Color Measurement and Its Application in the Rubber Industry
Authors: Willott W. H.
Published: February 2011

The object of this paper is to bring to the notice of rubber technologists the recent advances which have been made in the science of color measurement and its applications. As the demand for colored articles increases, it becomes necessary to use a more specific way of recording color than to say that an article is “rose pink” or “olive green.” The use of standard samples is cumbersome in regard to storage, and may be misleading in the case of rubber products, as they are liable to color changes. The increasing use of raw rubber in the form of latex has raised the question of the measurement of its “whiteness” as a guide to its quality. It has been suggested also that the transparency of thin dried latex films could be used for this purpose. Both these methods entail the measurement of the color of almost white objects. MacAdam has shown that it is difficult to judge the whiteness of articles by direct vision. He asked 30 observers, half of whom were women, to arrange white objects in order of increasing whiteness. The arrangements showed great divergence, and the observers were unable to repeat their observations. When these samples were classified by means of a suitable colorimeter, consistent and reproducible results were obtained by different observers. Visual observations are subject to the effect of many variables, and are therefore so misleading that it at once becomes apparent that such determinations can only be successfully carried out with a colorimeter used under carefully standardized conditions. Besides the measurement of the whiteness of latex such problems arise as the covering power of pigments, especially of white pigments, the use of dyestuffs in brightly colored articles, the transparency of rubber lacquers and varnishes, all of which require a measurement of color in some form or another.