bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the Molecular Weights and the Structures of Rubber, Gutta-Percha and Balata. Communication No. 258 on Macromolecular Compounds. Communication No. 49 on Isoprene and Rubber
Authors: Staudinger H. , Fischer Kl
Published: February 2011

The method used to determine the constitutions of rubber, gutta-percha and balata is essentially the same as that used for organic substances of low molecular weights, i.e., the substance is dissolved in a solvent, and the size and character of the particles in solution are determined. For a long time the nature of colloidal solutions of these hydrocarbons was in dispute. Up to twenty years ago, it was commonly assumed that the molecules of these hydrocarbons are relatively small, and that their colloidal particles are formed by the assemblage of small molecules into micelles through the agency of secondary forces. It seemed to Pummerer, Nielsen and Gündel that in certain solvents, such as camphor and menthol, rubber is dissolved in a low-molecular state. Subsequently, however, this observation was proved to be incorrect. According to the opinion of Meyer and Mark, colloidal particles of rubber are composed of relatively long primary-valence chains, which contain from 75–150 isoprene residues. These chains are, in turn, assembled into micelles by “micellar forces.” The authors explain this in the following way: “The high viscosity of rubber solutions, e.g., in benzene, would lead one to conclude that very large, highly solvated micelles are present in these solvents.” At the time, this hypothesis seemed to explain quite satisfactorily the nature of rubber and its solutions, for the great tendency of these solutions to undergo certain changes on standing, which are manifest by an increase or decrease in viscosity, is readily comprehensible on this basis.
The Constitution of Butadiene Polymers. Communication No. 259 on Macromolecular Compounds. Communication No. 5o on Rubber
Authors: Staudinger H. , Fischer Kl
Published: February 2011

When butadiene is polymerized, the resulting polymers are composed of macro-molecules which have branched structures. The actual linking of butadiene molecules to form polymers may proceed in different ways. Not only can linking take place at the 1,4-position (see Formula 1) or at the 1,2-position (see Formula 2), but an addition reaction can take place at the 1,2- and 1,4-positions (see Formulas 3a and 3b). As a result, extensively branched molecules are formed, for the lateral chains unite by means of their double bonds with more butadiene molecules, either in the 1,2-position or in the 1,4-position. Finally it is not impossible that, to at least a small extent, two butadiene molecules unite directly, in accordance with a diene synthesis, to form vinylcyclohexene, which, after activation of its double bonds, reacts with more butadiene molecules in the 1,2-position or in the 1,4-position. Technically, butadiene was at first polymerized with sodium (Bunas with numerical designations), but today it is polymerized chiefly in the emulsified form5, and this process is used also to prepare mixed polymers (Bunas with letter designations). In the investigation to be described, this latter group of Buna rubbers was not studied, because in most cases they are insoluble, or swell only to a limited extent, and therefore it is impossible to determine either the size or the shape of their macromolecules, as can be done with soluble sodium polymers and emulsion polymers.
Permeability in Relation to Viscosity and Structure of Rubber
Authors: Barrer Richard M.
Published: February 2011

Some properties of flow of solutes in and through rubbers are outlined. These properties indicate that, due to fluctuations of thermal energy, activated zones exist in certain polymers, of which viscous flow and diffusion are a consequence. A simple statistics of activated zones has been given, and from it equations are obtained for ΣN, D, Ds, and η, denoting respectively the total number of activated zones in rubber, the diffusion constant of simple solutes in the polymer, the self-diffusion constant of rubber, and its viscosity. Functional relations are predicted between log Do, log ηo, or ΔS* (the entropy of activation) and the Arrhenius energy of activation for diffusion or viscous flow. The available data clearly demonstrate this relationship. They also indicate no discontinuity between rubbers and liquids as diffusion media.
Chemical Reactions during Vulcanization. III
Authors: Hauser E. A. , Sze M. C.
Published: February 2011

From the preceding discussion the following conclusions may be drawn: A. Vulcanization with Sulfur in General 1. Vulcanization with sulfur is fundamentally a chemical change involving activated sulfur and organic double bonds. 2. Sulfur must decompose from S8 (in the form of an eight-membered ring) to smaller molecular units, perhaps to S2 and S1 before it can be activated and react. 3. The ratio of atoms of sulfur combined to the number of double bonds lost is not restricted to one atom of sulfur for each double bond, but may have other values, which depend on the conditions and the reactions involved. B. Factice Formation 1. The rate of reaction of sulfur with tung and linseed oils is greatly influenced by small proportions of such agents as zinc oxide and mercaptobenzothiazole. 2. Combination of sulfur with the conjugated double bonds of the eleostearic acid in tung oil takes place at the terminal carbon atoms of the conjugated system, giving a typical 1,6-addition. 3. The following possible chemical reactions explain adequately the process of factice formation from tung and lineseed oil. Under different conditions different reactions predominate.
Curing Rate of Rubber. Effect of Phosphate Buffer Mixtures on the Rate of Cure of Crepe Rubber
Authors: Newton E. B.
Published: February 2011

The phenomenon of variability in the rate of vulcanization of crude rubber by sulfur and heat has been studied by rubber technologists for more than forty years. Whether early workers recognized differences in any particular commercial grade is difficult to say, as a result both of the lack of discriminating tests and of the secrecy which was formerly maintained in the industry. However, three developments, all coming near the beginning of this century, combined to make workers more aware of any differences which might exist: (1) Weber's work on the chemistry of rubber, which led to the first theory of cure and to the idea of the sulfur coefficient of vulcanization; (2) the wider availability and use of standardized tensile testing machines, although earlier but limited use of such machines was known; and finally, (3) the rise of the plantation industry in the Middle East. The first two of these developments supplied methods of sufficient accuracy to detect differences other than by the empirical comparisons of hand tests. The third gave rise to many investigations designed to ascertain differences between the newer plantation and the standard Para grades.
Physical Properties of Polystyrene as Influenced by Temperature
Authors: Carswell T. S. , Hayes R. F. , Nason H. K.
Published: February 2011

The physical properties of plastics are markedly influenced by the ambient temperature, but comparatively few quantitative data on polystyrene have been published. The variation of flexural strength and deflection at break for compression-moulded polystyrene and for a number of other compression-moulded plastic materials at temperatures from —70° to +200° C was described by Nitsche and Salewski. Jenckel and Lagally determined the tensile strength of extruded polystyrene filaments at 30° to 60° C. The elongation at 20° to 90° C was reported for extruded and racked polystyrene foil by Müller. Since the mechanical properties of plastic materials are profoundly influenced by the methods used in preparing the test specimens, data on such properties are meaningless unless the details of preparation also are known. This paper describes variations in some of the mechanical properties of injection-moulded polystyrene over the range from —75° to +100° C. This method was chosen because injection moulding is by far the most commonly Used commercial process for the fabrication of polystyrene.
Structure of the Butadiene-Methacrylic Nitrile Copolymer
Authors: Alekseeva E. N.
Published: February 2011

In the joint polymerization of butadiene and methacrylonitrile, the bulk of the polymer consists of macromolecules, in which the two unit components correctly alternate, and the butadiene combines in its 1,4-position. Only much fewer macromolecules are encountered in which several molecules of butadiene consecutively intercombine in 1,4-positions.
Rubber, Polyisoprenes, and Allied Compounds. I. The Synthesis of Low-Molecular Polyisoprenes of the Rubber and the Squalene Type
Authors: Farmer Ernest Harold , Sutton Donald A.
Published: February 2011

A synthesis for dihydrofarnesene, H⋅[CH2⋅CMe:CH⋅CH2]3⋅H, has been devised which appears to be capable of utilization in the formation of other low-molecular dihydropolyisoprenes, H⋅[CH2⋅CMe:CH⋅CH2]n⋅H, in which the individual isoprene units are uniformly arranged in head-to-tail fashion. This synthesis, starting from geraniol, gives a triene hydrocarbon which differs in one of its additive properties from a product described as dihydrofarnesene in the literature. The reason for the difference has been investigated. A new synthesis for squalene has been devised which appears to be capable of utilization in the formation of other symmetrical dihydropolyisoprenes, H⋅[CH2⋅CMe:CH⋅CH2]n⋅[CH2⋅CH:CMe⋅CH2]n⋅H, of the squalene type. This starts from geranylacetone and the Grignard derivative from 1,4-dibromobutane.
Physical-Chemical Investigations of Artificial Rubber
Authors: Springer A.
Published: February 2011

Among the physical methods of which use has been made to explain the structure of organic compounds, thermal measurements, particularly measurements of heats of combustion, have played a particularly important part. With the aid of data on heats of combustion, it is possible to draw conclusions on the energy relations within molecules and on the heat tones of chemical transformations. Such measurements have been carried out on highly polymeric substances. In some cases, the object was to study the reactions of formation. e.g., polymerization; in other cases it was to explain the transformations which high polymers themselves undergo. Studies of polymerization reactions by thermal methods have shown that, in distinction to monomers, a decrease in the heat of combustion with increase in the degree of polymerization is to be expected. The polymerization process is accordingly exothermic, and the difference between the heats of combustion represents the heat of polymerization which is liberated. A direct comparison of heats of polymerization found experimentally by different investigators is, however, not possible because, in most cases, no information on the degree of polymerization, branching of the chain molecules, or other significant properties of the polymers are given.
Rubber in Vibration
Authors: Gehman S. D.
Published: February 2011

In most of the uses to which rubber is put, it is subjected to deformations which are relatively small compared to the ultimate deformation of which the rubber is capable. For many products, such as vehicle tires, motor mountings, and belts, the deformations are periodic. There is, therefore, a great deal of interest attached to the physical properties of rubber when measured under vibratory, as contrasted to static, conditions. The use of rubber in mountings for the absorption or isolation of vibration, with which this paper is principally concerned, has led to a number of systematic investigations of its static properties from the standpoint of the engineer who might be interested in employing it for such purposes. As representative of such contributions may be cited the work of Keys, Smith, Brown, Haushalter, Hirshfeld and Piron, and Kimmich. The principal concern was to determine the rules which govern the deformation of rubber pieces of various sizes, shapes and hardnesses. Related questions of permanent set, creep, and the effect of temperature also came into the discussion. The importance of dynamic measurements was realized, but information on this phase of the subject was beyond the scope of the work.
Analytical Methods in Rubber Chemistry. Part V. Estimation of the Oxygen of Highly Autoöxidized Rubber Contained in Carboxyl, Ester, Carbonyl, Epoxide and Hydroxyl Groups
Authors: Hilton F.
Published: February 2011

In the course of a study of the autoöxidation of natural rubber and of low-molecular olefins of allied structure, it has been necessary to ascertain the nature and relative proportions of the functional groups to which the ingoing oxygen may give rise. Up to the present it has been established that the products of autoöxidation reactions are in general highly complex mixtures, and that even such simple olefins as dihydromyrcene and cyclohexene may give rise to molecules which bear a varied assortment of hydroperoxide, alcoholic hydroxyl, epoxide and carbonyl groups. Available evidence further indicates that the primary products of autoöxidation are hydroperoxides, formed by the reaction of oxygen at methylene groups adjacent to double bonds, and that it is the secondary reactions which these hydroperoxides undergo which are responsible, directly or indirectly, for the formation of the other oxygen-containing groups which have been observed. Molecules of rubber hydrocarbon contain, on an average, several thousand methylene groups adjacent to double bonds. Each such methylene group is at least the potential seat of oxidative attack, and it might be anticipated that if the autoöxidation of rubber proceeds in a manner analogous to that of simpler olefins, the products of reaction would be extremely complex and that they might contain any or all of the following functional groups
Aging of GR-S Vulcanizates in Air, Oxygen, and Nitrogen
Authors: Shelton J. Reid , Winn Hugh
Published: February 2011

The results of aging GR-S vulcanizates in air, oxygen, and nitrogen show: 1. The decrease in tensile strength observed in both bomb and oven aging is caused by the action of oxygen. 2. The modulus increase obtained in the oxygen bomb at 80° C is not caused by oxygen in the aging atmosphere. 3. At 100° C in air, more than half of the hardening, measured by the modulus increase obtained after five days, may be attributed to the action of oxygen. It therefore appears that oxygen acts on GR-S vulcanizates in two distinctly different ways: 1. A reaction leading to tensile breakdown, which no doubt involves chain scission. This reaction takes place at both 80° and 100° C, and is effectively retarded by the antioxidant, phenyl-β-naphthylamine. 2. A reaction producing a stiffening of the GR-S, as shown by the modulus increase. This stiffening suggests the formation of polymeric products—for example, by cross-linkage. This reaction was not observed at 80° C, but was a major factor in the aging at 100°, and was little affected by the antioxidant employed.
Pigment Incorporation in GR-S through Latex
Authors: McMahon W. , Kemp A. R.
Published: February 2011

The physical properties of GR-S gum stock are decidedly inferior to those of natural-rubber gum stock, and they have to be greatly enhanced for practical use of the elastomer. At present these physical properties are augmented to the greatest degree by compounding with reinforcing pigments, especially carbon blacks. Furthermore, experience has shown that, for a given pigment, the reinforcement it affords is proportional to the degree to which it is dispersed in the elastomer. A thorough dispersion of pigment on the mill or in the Banbury mixer is not feasible with schedules which can be applied in the factory, particularly with those pigments which are more difficult to disperse. A study of the relation between the characteristics of pigments used as fillers in GR-S and their reinforcing properties indicated that the particle size of the pigment was the predominant characteristic associated with reinforcing ability. The finer carbon blacks yielded the greatest reinforcement, measured by ultimate tensile strength; also, a fine grade of magnesium oxide yielded compounds with tensile strengths approximately equal to stocks made with blacks of the same particle size. Stocks made from a coarser magnesium oxide were considerably lower in tensile strength, and zinc oxides and calcium carbonates fell roughly in the order of their particle sizes. The calcium carbonates, zinc oxides, and magnesium oxides had to be worked on the mill much more than the carbon blacks to develop maximum reinforcement; and, even though well worked, the finest zinc oxide and calcium carbonate did not yield compounds with properties which their particle size indicated they should have. It was felt that this was due to inability to disperse these materials properly on the mill; thus their effective particle size in the compound was much greater than their ultimate size. Accordingly, a better means was sought to disperse fillers in GR-S than that afforded by milling. It was known that excellent dispersions of pigments could be made in water with the aid of dispersing agents. It was also reported that the polymer particles in GR-S latex were very finely divided, less than one-tenth the diameter of particles in natural rubber latex. If, then, a water suspension of well dispersed pigment was mixed with latex, and the filler and polymer were precipitated or coagulated simultaneously, it was thought that the pigment might be more thoroughly dispersed in polymer than it would be through dry milling; the physical properties of compounds made in this manner should then show improvement over those made on the mill.
Incorporation of Carbon Black into GR-S Latex on a Production Scale
Authors: Rongone Ronald L. , Frost Charles B. , Swart Gilbert H.
Published: February 2011

1. A commercially feasible method for adding carbon black to latex has been developed and tested. The black-latex mixture can be handled in essentially the same way as normal GR-S throughout the various steps of coagulation, washing, drying and baling. 2. By incorporating black into GR-S latex, an increase in milling capacity of about 35 per cent is possible. 3. The total power required for mixing this black-rubber is at least 20 per cent less than for tread stock mixed in the conventional way. 4. Mixing temperatures are lower for latex-black stocks. 5. Physical properties and preliminary tire tests show that carbon black incorporated with the latex produces stock equivalent in physical properties to stocks prepared by mixing carbon black into dry rubber. 6. Considerable savings are made possible by the use of this method. 7. The amount of dirt now present in the millrooms of the rubber manufacturing plants should be greatly reduced.
Effect of Moisture on Curing Rate of GR-S
Authors: Braendle H. A. , Wiegand W. B.
Published: February 2011

1. Moisture content of uncured GR-S compounds must be reckoned with because of its effect on curing rate and the serious consequence of overcure. 2. Excessively dry polymer (below about 0.15 per cent water) will, in general, be slow curing (Figure 2). 3. Mixed stock with less than 0.5 per cent water will, in general, be slow curing and erratic in curing rate (Figure 5). 4. The normal moisture range of carbon black does not affect the curing rate of GR-S (Figure 4). 5. The normal moisture content of carbon black is not available to the polymer for stabilizing its curing rate. 6. Mixed stock which is dry and slow curing may be conditioned to stable curing rate by storage under humid conditions. A moisture content of 0.5 to 1.0 per cent is indicated. This moisture content seems also to iron out differences in curing rate between polymers. 7. Since conditioning of mixed stocks is not always feasible on the factory scale, the stabilization of cure by direct water addition during mixing should be given consideration. 8. Laboratory-scale tests on a GR-S tread compound indicate that an addition of about 2.5 to 5 per cent water (on the polymer) during mixing will result in a mixed-stock moisture content giving minimal cure variation for normal-curing and slow-curing (very dry) polymers for periods of stock layover up to about 3 weeks. 9. Any additions of water as suggested above will, on the factory scale, require adjustment, since moisture retention is a function of the compounding ingredients, mixing cycle and temperature, storage time, and humidity conditions actually obtaining.
Effect of Elastomer Crystallization on Tests for Freeze Resistance
Authors: Forman Don B.
Published: February 2011

At subzero temperatures cured elastomers become stiff and may or may not become brittle. As stiffness increases, elasticity decreases and stress at any given elongation increases. Brittleness occurs when the elastomer reaches an inelastic state. Both time and temperature of exposure are important factors which affect these changes in properties. Under any given testing methods, the degree of stiffness and conditions of brittleness are intrinsic properties of the elastomers and their compounds. Summaries of these factors have been given by Liska and Graves and Davis. Crystallization, which explains some of the results to be described, has been known for a long time to occur in rubber. Factors influencing the crystallization of rubber were investigated by Bekkedahl. He concludes that the crystals formed during the freezing or the stretching of rubber are identical. It is believed that this is true for crystallizable elastomers. Carothers and coworkers and later Sebrell and Dinsmore reported that the x-ray pattern of Neoprene (polychlorobutadiene) crystals obtained on stretching resembles those of rubber. Wood showed that Neoprene, like rubber, crystallizes at low temperatures. The most favorable temperature for Neoprene Type GM appears to be 0° C, and Neoprene Type FR shows no crystallization at low temperatures. Some properties of the latter at low temperatures were reported by Yerzley and Fraser.
Morphology of Latex Particles as Shown by Electron Micrographs
Authors: Hendricks S. B. , Wildman S. G. , McMurdie H. F.
Published: February 2011

Morphological features of particles from latices of sixteen plant species were studied by means of electron micrographs, a number of which are reproduced. The smallest particles have about the volume required to contain a very small number of molecules. Evidence is given for both form-retaining and fluid properties of latex particles. Difficulties with the hypothesis that these particles have fluid interiors covered by a surface film of gel rubber are pointed out. A new hypothesis accounting for the observed properties is advanced. According to it, the latex particles contain rubber molecules entwined as if they were odd lengths of string with other latex components held between the meshes.
Distribution of Oxygen in Oxidized Rubbers
Authors: Naylor Ralph F.
Published: February 2011

It has been fairly well established that the initial products of the auto-oxidation of polyisoprenes are hydroperoxides. The course of subsequent reactions is not, however, so clear. Under normal conditions the peroxides are unstable, and give rise to a large variety of secondary oxidation products. The object of the present work is to study the distribution of oxygen in the various groups which have resulted from these secondary reactions. The course of oxidation.—Oxidative fission of the double bond of an isoprene unit may be expected normally to give rise to a carbonyl and an aldehyde group, and the latter may be further oxidized to carboxyl. The hydroperoxide groups which effect this oxidation are, as experience shows, mainly reduced to alcohol groups. Epoxides may result from transference of the active oxygen from the peroxide groups to the olefinic bonds, and esters and ethers by subsequent reactions of the alcoholic groups. Thus any or all of the following functional groups may be expected to be present in an oxidized rubber:
The Dependence of Damping and Dynamic Modulus on Temperature as a Means of Evaluating the Elastic Behavior of Raw and Vulcanized Rubber. The Dynamic Resistance of Soft Rubber to Cold
Authors: Roelig H.
Published: February 2011

The dependence of the damping and elastic modulus of a vuleanizate on its temperature makes it possible to evaluate its elastic behavior throughout the temperature range which is of technical importance. Measurements were carried out at a constant frequency of 16⅔ Hertz units (1) to determine the damping effect, in which case the freezing temperature of the vulcanizate, the maximum damping above the freezing point, and in many cases the decrease in damping with increase in temperature above 0° C, were determined, and (2) to determine the elastic modulus, in which case the freezing temperature of the vulcanizate, the freezing range, and the dynamic modulus of elasticity were determined.
Structural Changes in Vulcanization of Buna-S
Authors: Keck Max H. , Cheyney La Verne E.
Published: February 2011

In conclusion, the data presented here indicate that two types of chemical reactions take place during the vulcanization of Buna-S stocks of a specific type: (1) a combination with sulfur, which may or may not involve the double bonds in the polymer, and which may be similar in character to the primary vulcanization reaction of natural rubber; (2) a second reaction, presumably polymerization, which accompanies the first and is related to and possibly initiated by it, and which continues on over cure.
Effect of Pressure on the Melting of Crystalline Rubber
Authors: Wood Lawrence A. , Bekkedahl Norman , Gibson Ralph E.
Published: February 2011

The effect of hydrostatic pressure on the melting of crystalline rubber has been the subject of a brief investigation extending to pressures above 1,000 atmospheres. With a particular sample of stark rubber, it was found possible to raise the temperature of meltings as determined by the disappearance of birefringence, from about 36° to 70° C by the application of a pressure of 1,170 bars (1,170×105 dynes per sq. cm.). The results, including observations at intermediate pressures, can be represented adequately by the equation: log10 (p+1,300)=5.9428−(875/T).
Effect of Moisture on GR-S Rate of Cure and Physical Properties
Authors: Rush Ian C.
Published: February 2011

Moisture has been discussed as a factor which may give rise to variable rates of cure of GR-S. This moisture may be present in GR-S itself or in the compounding ingredients used. Accordingly, a program was initiated in the spring of 1944 to establish the influence of moisture, not only on the rate of cure of GR-S, but also on its physical properties. Since that time two papers have been published on this subject by other investigators. The results reported here verify some of the conclusions drawn by these investigators but seem to be at variance with others. In this study various proportions of water were added in the following ways : by premixing with carbon black, by adding directly on the mill rolls at the completion of normal milling, and by soaking GR-S crumb in water. Curing curves were obtained for each batch, and were used to evaluate the rate of cure. To eliminate day-to-day variations in physical properties due to error in testing methods, three batches of different moisture contents were mixed and tested on the same day. This same group was then remixed and tested on successive days until at least three batches had been tested for each moisture content and each method of addition. The averages of the individual results (stress-strain data and percentage moisture retained) on batches to which the same percentage of water was added, were then considered free from day-to-day variations.
Organic Analysis of Hevea Latex VIII. Development of a General Scheme of Analysis
Authors: Altman R. F. A.
Published: February 2011

An attempt is made in this work to show the desirability and the practicability of a complete analysis of Hevea latex. It has been found that fresh, unammoniated latex is the only trustworthy starting material for analysis. Difficulties encountered in the analysis are due principally to (1) the trouble-some property of the rubber hydrocarbon to adsorb, and hold firmly, the other components of latex; (2) probable chemical, enzymic, and bacterial changes, which cause great difficulties in the isolation of those components in the state in which they are originally present in latex, and (3) the lack of proven methods of quantitative separation of the various groups of organic compounds. In his attempt at an ideal method of analysis, the author, due to the above-named difficulties, is faced with the apparent impossibility, as yet, of separating the various components of latex quantitatively and in the original state in which they are present in the latex. As a result of much theoretical considera- tion and practical experience, gained meantime, the author has reached a method, the scheme of which is described in the present work.
Using The Mooney Viscometer
Authors: Buist J. M.
Published: February 2011

The increased use of the Mooney viscometer in America for checking the plasticity of different batches of synthetic rubber has led to a wider appreciation of the care which is necessary for accurate operation of this apparatus. A recent article dealt fairly fully with most of the factors affecting results obtained with the Mooney viscometer. Some results obtained on the instrument at Blackley are extremely interesting and publication may help other users to avoid the trap of using Vistanex for calibration purposes. Vistanex is a stable material chemically, which is essential for a standard material, but other factors overcome this advantage and preclude its use. The mechanical method of calibrating the machine checks the spring at readings 0 and 100 and as long as the spring is not taken beyond its elastic limit there is no point in checking intermediate values. Vistanex gives a reading of 50 when tested at 100° C in the standard manner. It has been assumed that if a reading of 50 is obtained with Vistanex, the instrument must be working correctly. This view is wrong.
The Proportion of Crystalline and Amorphous Components in Stretched Vulcanized Rubber
Authors: Wildschut A. J.
Published: February 2011

Determinations of the tension-temperature relation of stretched vulcanized rubber can provide us with data about the proportion of crystalline and amorphous components. The amount of crystalline material appears to be 30–32 per cent at 600 per cent elongation and at 20° C. An expression is derived relating percentage of crystalline material and temperature. The results are in close agreement with those of x-ray measurements carried out by Goppel, but diverge largely from those obtained by Field. The cause of this difference is not yet clear. Stretched vulcanized rubber consists of a predominating amorphous phase, with crystallites embedded in it. On stretching orientation occurs, and a systematic addition of secondary valency forces is possible. This is the main cause of the existence of a certain tensile strength. Crystallization, though important as an indication on orientation, is more or less an incidental phenomenon. The distance function of the secondary forces may be of equal importance with the orientation.
Stress-Time-Temperature Relations in Polysulfide Rubbers
Authors: Stern M. D. , Tobolsky A. V.
Published: February 2011

Polysulfide rubbers of various internal structures have been investigated by measurements of continuous and intermittent relaxation of stress and by creep under constant load at temperatures between 35° C and 120° C. Continuous stress relaxation measurements indicate that these rubbers obey approximately the simple Maxwellian law of relaxation of stress, which indicates that one definite type of bond in the network structure is responsible for stress decay. The activation energy for the relaxation process in each of the polysulfide rubbers is nearly the same, indicating that the same type of bond is responsible for the relaxation behavior of all the polysulfides investigated. In contrast to hydrocarbon rubbers, oxygen is not the cause of high temperature relaxation in polysulfide rubbers, nor does heating in air at moderate temperatures for times comparable to the relaxation time produce changes in physical properties as determined by modulus or by appearance of the samples. Several possibilities regarding the mechanism of the relaxation process and the type of bond involved are considered in the light of the experimental results.
The Influence of Milling on the Plasticization of Rubber
Authors: Haehl Adrien , Le Bras Jean
Published: February 2011

In the first part of this work, the influence of the temperature of the mill rolls and of their friction ratio on the plasticization of rubber was examined in a systematic way. The experiments described in this second paper had as their object the determination of the influence of the speed of the mill rolls, and comprise a series of measurements at three different temperatures, viz., 20°, 60° and 100° C. The machine and equipment were, as before, a Troester mill, each roll of which was equipped with a temperature control and a speed regulator. In addition a wattmeter made possible the recording of the power consumed by each of the motors. In general the operating conditions of the previous work, which were described in detail in the previous paper, were followed in the present work. (1) Rubber.—First latex crepe (from the same lot as that used in the first part of the work). (2) Mill rolls.—Diameter 20 cm. ; effective length 30 cm. (3) Spacing of the mill rolls.—When loaded, 1 mm. (4) Bank of rubber.—Diameter about 10 mm., which was held constant by decreasing the effective length of the rolls to compensate for successive withdrawing of samples. (5) Plasticity measurements.—Williams apparatus, with test-samples of 1 cc. volume.
Isothermal and Adiabatic Stress-Strain Curves of Vulcanized Rubber
Authors: Hauk V. , Neumann W.
Published: February 2011

The stress-strain diagram of rubber has been the subject of a large number of investigations, including those of Röntgen, Gough, and Joule in the nineteenth century, those on isothermal phenomena by Meyer and Ferri, and Wiegand and Snyder, and most recently those on adiabatic phenomena of Ornstein, Eymers, and Wouda. The investigations of Meyer and Ferri are concerned chiefly with the dependence of the stress-strain phenomena on the temperature, and they confirm experimentally the hypothesis that within a certain range of temperature and with highly vulcanized samples, the stress is proportional to the absolute temperature, i. e., S=aT+b. At lower states of vulcanization this proportionality does not hold true. The work of Ornstein and his collaborators, which is frequently cited in the literature, is concerned with the phenomena which take place when raw rubber and weakly vulcanized rubber are stretched adiabatically; that of Wiegand and Snyder is concerned chiefly with a thermodynamic interpretation of stress-strain curves obtained experimentally. Now in spite of the fact that stress-strain curves of rubber have been determined so frequently, particularly under isothermal conditions, these measurements are for the most part of limited value, since the chemical nature of the types of rubber employed is not described definitely. Then again in most cases little attention was paid to the difference between isothermal and adiabatic stretching. In view of these facts, it seemed desirable to throw further light on the problem by obtaining stress-strain curves of one particular well-defined material. The object of the present work was then: 1. To obtain true isothermal stress-strain curves as a function of the degree of vulcanization and as a function of the temperature, and thus to study stresses as a function of temperature. 2. To obtain data on the same vulcanizates under adiabatic conditions. 3. To compare the stress-strain results under isothermal conditions with those under adiabatic conditions.
Influence of Copper on Rubber. VII. Effects of Metallic Salts on the Evolution of Hydrogen Sulfide
Authors: Ōkita T.
Published: February 2011

It is concluded that maximum tensile strength is reached more quickly than normally when the amount of hydrogen sulfide increases above normal. If considerable acid is formed during cure, the amount of hydrogen sulfide evolved decreases, and curing is retarded. The heat-resisting properties are increased by addition of a salt which depresses the amount of hydrogen sulfide evolved. On the contrary, when much strong acid is formed, the deteriorating effect of the acid on the rubber becomes very great and the contrary result is obtained.
Application of Thermodynamics to the Chemistry of Rubber
Authors: Bekkedahl N.
Published: February 2011

The purpose of this paper is to show how thermodynamic data on rubber and related substances can be employed in studying and predicting their reactions. The method will be illustrated by the results of recent studies on rubber and iso-prene made at the National Bureau of Standards. These results enable us to predict the conditions which favor the polymerization of isoprene to form rubber, and also the conditions which favor the reverse reaction, the thermal decomposition of rubber to give isoprene. Rossini, in his review paper on “Modern Thermodynamics,” makes the following statement : “The ultimate end of chemical thermodynamics may be said to be the evaluation of the free energy of formation, from the appropriate fundamental units of matter, of every substance in all possible states….” Our chief object, then, for rubber is to obtain as accurately as possible the free energies of formation of rubber, sulfur, rubber-sulfur compounds and other forms of vulcanized rubber, isoprene and all other substances with which rubber reacts or from which it may be made.
Tackiness and Consistency of Rubber after Treatment by Alkali
Authors: De Vries O.
Published: February 2011

Our knowledge of the chemistry of tackiness in plantation raw rubber is still incomplete. We know that under different circumstances distinct types of tackiness develop. Traces of copper, for instance, cause rubber to liquefy, with formation of a sticky, transparent mass, which then gradually hardens, first on the surface and afterwards throughout, whereby it is transformed into a hard and brittle resin-like substance, easily soluble in acetone. The viscosity of a 1% benzene solution decreases from the normal figure of 30 to, say, 2. This type of tackiness is independent of light, as it develops quite readily in the dark. It is accompanied by an increase in weight of 7 to 13%. The change is regarded as an oxidation catalyzed by copper, but more knowledge about the course of this oxidation and the intermediate and ultimate products would be welcome. Hydrochloric acid, for instance when used as a coagulant, causes another characteristic form of tackiness, which is very dependent on the action of light, one side of a piece of crepe, for instance, becoming sticky and liquefying, while the other side, turned away from the light, shows no change. During this process also the rubber changes into transparent, yellow oily products, which gradually become hard and brittle; the increase in weight is 9 to 12%.
Influence on Final Product of Fast and Slow Vulcanizing Rubbers
Authors: Heywood M. M.
Published: February 2011

The object of this paper is to endeavor to carry beyond the laboratory stage the tests which have been hitherto published on the variability in vulcanization found in plantation rubber. It is easily appreciated that, when one is handling large quantities of rubber, it is impossible for economic reasons to buy from one estate or even one group of estates, but the whole of the available rubber has to be surveyed before purchases can be made. There are accepted classifications in London which, in many instances, are based on appearance rather than on intrinsic quality of the rubber. Cleanliness or eye value, although desirable, should not be the sole standard for quality of rubber. Each broker, agent, dealer or middle man between producer and user has his own type sample. Each user has his own conception of what he wants and generally has a type sample also. But variation in available rubbers does influence the final product, especially in regard to the manner in which a rubber vulcanizes. For the purpose of experiment, two wellknown rubber types have been chosen, and factory production runs covering a considerable tonnage have been studied.
Rubber Terminology
Authors: Dawson T. R.
Published: February 2011

A definite part of scientific activity consists in applying words to connote materials and ideas. Observed phenomena and the hypotheses derived from them are systematized and generalized by means of such terminology. Progress itself depends on words or equivalent symbols, for we have no other means of exchanging information. The universality of speech and writing tends to obscure the remarkable complexity of these processes, and the editor of Chemical Abstracts, in a recent admirable lecture, had occasion to deplore the numerous and serious deficiencies in chemical terminology. All that he said of chemical words in general applies, with perhaps greater cogency, to the terminology of the rubber industry. The science and technology of rubber are but in their infancy. They have been superadded to an industry developed for a century by practical men in the rough-and-tumble of the works. It is not surprising, therefore, that verbal exactitude has scarcely been considered. The infant rubber science has, however, shown' vigorous development in the last two or three decades, and there are signs that its attention is being awakened to the need for putting its verbal equipment in order. The issue is not only a scientific one. It is complicated by commercial considerations which cannot be ignored. Pithy trade names are undeniably better sellers than cumbrous systematic chemical names. The persistent use by the leather and leather footwear industries of the term “substitute soleing,” for what is, quite simply, rubber soleing, has undoubtedly prejudiced an excellent and serviceable product. The coining of some happy alternative, following the example of the replacement of “artificial silk” by “rayon,” would probably have effects measurable in terms of dividends. It must be realized, therefore, that any attempts to improve rubber terminology will be limited in some directions by trade considerations. That is not a reason why the industry's scientific literature, at least, should not be given all the clarity and precision that can be achieved. In the following discussion several directions are pointed out in which improvement would be welcome. The illustrative examples given are typical only and, unfortunately, are far from exhaustive.
Spontaneous Coagulation of Rubber Latex
Authors: Stamberger Paul
Published: February 2011

As early as 1913, Whitby advanced the view that spontaneous coagulation in rubber latex takes place before decomposition processes begin. Arguments against this view have since been advanced by several investigators, and the opinion generally held at present is that the coagulation of fresh latex is caused by formation of acid from the bacterial decomposition of the serum components. Recent investigations made on latex of Hevea brasiliensis have provided confirmation of the view held by Whitby. Experiments were conducted throughout on latex obtained immediately after collection from the trees, which had been tapped three or four hours previously. The formation of ions from decomposition of latex was followed by conductivity measurements. The conductivity of latex did not change until coagulation was complete. This occurred 6–11 hours after collection of the latex, varying from sample to sample. The resistance of the conductivity cell increased after gel formation, due to contact resistance on the electrodes.
Examination of Thin Rubber Films by Electron Diffraction
Authors: Tanaka Kenzo
Published: February 2011

It was reported in a preceding paper (Mem. Coll. Sei. Kyoto Imp. Univ. [A] 21, 85(1938)) that when a thin film of certain organic long-chain molecules coating a polished metal surface is heated, the regular arrangement of the molecules of the substance becomes haphazard at a temperature which is characteristic of the substance and differs from its melting point. This temperature was called the transition temperature of the molecular arrangement of the substance. In the present experiments the manner of the arrangement of the rubber molecules in a thin film deposited from benzene solution on a polished metal surface was examined in the same manner as before. To obtain rubber films of different thicknesses, a small piece of polished copper which served as the backing of the film was dipped for a moment in a benzene solution of rubber. The range of rubber concentration of the solution was from 2 to 0.005 per cent. By subsequent evaporation of benzene, a uniform coating of rubber was obtained, which was so thin as to show the interference fringe by light in most cases. The typical diffraction patterns obtained by an electron beam which impinged on the rubber film in a direction almost parallel to its surface are such as shown in Fig. 1. But these are rare cases, and generally the rubber films deposited as above stated gave rise at first to diffuse halos of amorphous structure. However, when these amorphous films were heated at about 70° C. for a while and cooled to room temperature, they gave rise to the same diffraction patterns illustrated in Fig. 1. The regular pattern showing the regular arrangement of the rubber molecules is well defined for very thin films, and becomes more diffuse with increasing thickness of the film, as in the case of other substances.
A Few Corrections of Statistical Theories of the High Elasticity of Rubber
Authors: Houwink R.
Published: February 2011

Theories have of late been developed to account for the high elasticity of certain substances, particularly rubber, over a particular range of elongation. These theories are based on the assumption that the molecules have taken a spherical form, which is the one statistically most probable. We wish to prove that, in order to avoid wrong conclusions, certain modifications in these theories are necessary, and we wish especially to make a stand against the following two assertions: (1) That rubber-like high elasticity is always associated with the presence of chain molecules. (2) That when rubber is elongated, no attractive forces are broken down and no valence angles are deformed until an elongation of about 350% is reached.
Cyclized Rubber, Particularly Halide Transformations
Authors: Stevens H. P. , Miller C. J.
Published: February 2011

Boron trifluoride or materials which give rise thereto effect a “cyclization” of rubber in solution: that is, the product is less unsaturated than the original rubber. A particular degree of conversion has been shown to give a tough material, which produces strongly adherent films possessing a high degree of alkali-resistance. When used as a paint medium the material acts as an unsaponifiable “breather” and pigment protector, allowing (unlike “sealers”) the passage of aqueous solutions. For this reason it appears suitable for use on plaster and concrete. Analysis of the purified product indicates appreciable oxidation at some stage and it may be further oxidized by aging at raised temperature or by reagents such as hydrogen peroxide. The oxidation products are not identical. The conversion product yields also a hard vulcanized product resembling hard vulcanized rubber, but less thermoplastic and containing less sulfur than hard rubber produced under the same conditions. This work has been carried out on behalf of the Rubber Producers' Research Association, to whom the authors are indebted for permission to publish.