bluuebunny/crossref_metadata_2025 huggingface dataset:
Sorption of Water by Rubber
Authors: Taylor R. L. , Kemp A. R.
Published: February 2011

THE presence of water is one of the principal causes of electrical instability in dielectric materials, often resulting in large variations in direct current resistance, dielectric constant, and power factor. A knowledge of the laws governing the sorption of water is therefore of considerable interest to the electrical and communications industries. The various investigators in the field of sorption of water by rubber have not reported their findings in a manner which will permit of consistent interpretation and correlation for engineering uses. Insufficient attention has been given to the effect of such factors as shape of test specimen, temperature control, variations in vapor pressure, chemical changes in the test specimen, etc. Consequently no sorption coefficient suitable for application to practical problems and no measure of the rate of sorption which will permit an adequate comparison of one material with another is now available. The purpose of this article is to describe the relation between rate of sorption and some of these variables, such as thickness of test specimen, temperature, and vapor pressure, and to show how sorption tests can be applied to certain practical problems. It is not the purpose to present a survey of the literature. The word “sorption” is used in conformity with current phraseology to mean the combined effect of adsorption and absorption.
Azo Dyes Derived from Rubber
Authors: Low Rodolfo
Published: February 2011

At one time the greater part of the rubber used in industry was in the form of wild rubber, and although it is true that even under these circumstances rubber possessed the valuable properties which make it one of the most useful of materials for the widest variety of applications and in general indispensable, it nevertheless varied greatly. This latter fault not only made it difficult to manufacture rubber goods satisfactorily but limited the field of applications of rubber. Then again, sufficiently large quantities of the most useful raw material could not be obtained regularly. In contrast to this, the progress which has been made up to the present time in the cultivation of rubber has put industry in possession of a uniform product which is available in quantities sufficient to fulfil all needs. This has made it possible not only to manufacture rubber products in a more satisfactory way, but also to increase to an unforeseen extent the number of applications of rubber. Moreover, when it is realized that crude rubber is a relatively cheap material, it will be evident why chemists are busy utilizing it for the production of derivatives which, because of new and valuable properties, will necessarily find wide fields of application. This is only one instance of the constant attention which the chemist gives to the possibility of transforming materials which nature has bestowed upon us into other materials of still greater benefit to humanity.
The Deposition of Rubber on to Textile Fibers
Authors: Blow C. M.
Published: February 2011

(a) The preliminary results obtained in an investigation of the deposition of rubber from latex on to textile fibers are recorded. Methods of deposition have been considered in order to avoid the rubbery handle associated with evaporated films of latex. (b) The cationic soap compounds recently produced commercially enable satisfactory deposition to be brought about. (c) Data are given of the adsorption by textile fibers of these compounds. (d) The effect of cationic soap compounds on rubber latex and the production of a latex of reversed charge are described. (e) The two alternative processes for deposition of rubber are discussed: the first employs natural latex in conjunction with textile fibers pretreated with cationic soap; the second employs latex treated with cationic soap in conjunction with untreated fibers. (f) A short discussion of the theoretical basis for the results is given.
Compression Tests of Vulcanized Rubber
Authors: Ariano R.
Published: February 2011

Compression tests are used to a small extent in ordinary control testing of rubber mixtures prepared in the laboratory, but it is not possible with such tests to decide from an examination of various finished products which of the products will give satisfactory service under compression. Results obtained by this test have been in many cases contradictory, and it is safe to say that their conversion into analytical expressions has led to as many conclusions as there are authors who have worked on the subject. It appears then that the number of variables involved in a compression test is so great, and at the same time these variables are so little understood, that the test is meaningless at present. Naturally then one is induced to study the subject in detail, with the hope of being able to decide on the ultimate possibilities of the test and on the most favorable conditions under which it will give clearly defined results. With this in mind, it seemed opportune to determine the distribution of the deformations which take place in cubical test-specimens when their surfaces are lubricated and when they are not, and when the specimens are solid and when they contain holes in various locations.
Some Applications of High-Frequency Electric Currents to the Latex Industry
Authors: Leduc Henri
Published: February 2011

The “radiocoagulation” of latex has been developed in the laboratories of L'Office National des Recherches et Inventions by Dufour and Leduc, who conceived the idea of applying the effect of electric fields of high frequency to rubber latex. When latex is exposed to the action of an electric field of high frequency, the entire body of liquid is heated uniformly, provided that the electric field itself is uniform. The causes of this heating effect are difficult to ascertain because various phenomena are involved simultaneously, e. g., a dielectric loss in the rubber and a loss by the Joule effect in the serum. Each of these effects is, according to conditions, the predominant one, e. g., by increasing the conductivity of the serum, electrolytes such as sodium sulfate or ammonium sulfate increase the Joule loss, U2/R, whereas an increase in the concentration of latex tends to increase the dielectric loss. Finally, since rubber particles are not electrically neutral, they are subject to alternating forces of the electric field, which is a specific effect of the high frequency, and these forces impart to the rubber particles movements throughout the liquid. Now latex can be rendered sensitive to mechanical forces, i. e., some mixtures can be coagulated by slight agitation. Accordingly it is conceivable that a high-frequency electric field, by setting the rubber particles in motion throughout the emulsion, is capable of coagulating a mass of latex exposed to the field.
Processing Characteristics of Rubber Compounds- - -. Effect of Pigment Particle Size and Surface
Authors: Nellen A. H. , Barnett C. E.
Published: February 2011

A STUDY of the processing properties imparted by any pigment to a rubber compound is important in determining the most effective and economical type of pigment for a particular purpose. For example, in a truck tire carcass compound where zinc oxide may be the main pigment, in order to obtain the maximum quality this zinc oxide should be of the type which will give a soft uncured stock and free-flowing qualities so that the cords in the carcass may be thoroughly impregnated during the calendering and curing processes. Also, in a tread compound where channel black is the main pigment, that type of black which will allow faster incorporation into the rubber, faster extrusion, and better flowing qualities will result in manufacturing economies. In the case of both the zinc oxides and the carbon blacks it is essential that these desirable processing characteristics be obtained without losses in other properties, such as rate of cure, tensile strength, and abrasion resistance.
Observations on the Viscosity of Rubber Solutions
Authors: Guth Eugene
Published: February 2011

A simple comparison is sufficient to show the great difference between a latex and a solution of rubber of the same concentration. The viscosity of rubber solutions is as a matter of fact very much greater. Furthermore, the viscosities of solutions of artificial rubber are still greater than those of solutions of crepe rubber. This general difference in viscosity may be ascribed to a difference in shape of latex particles and that of particles of natural and artificial rubber in solutions. Latex particles are spherical, whereas the particles in solutions of natural and of artificial rubber appear to be long filaments. Twenty years ago, Einstein in a fundamental work treated mathematically the problem of viscosity of suspensions of spherical particles. He found that the viscosity of a suspension of spherical particles in low concentration can be expressed by the following equation:
Preparation and Testing of Latex Compounds
Authors: MacKay J. W.
Published: February 2011

Films should be prepared in an atmosphere free from air currents at 60 to 75 per cent relative humidity and at a temperature of 21.2° to 29.2° C. (70° to 85° F.) during the first 8 hours of the drying period. These films should be suspended for complete drying for an additional 48 hours at 0 per cent humidity and 10° to 15.5° C. (50° to 60° F.) before curing. The water-cured films should be dried 3 hours in the open room followed by about 20 hours at 0 per cent humidity and 10° to 15.5° C. (50° to 60° F.) before the preparation of test pieces. The air cures are kept in a desiccator for about 24 hours at 0 per cent humidity and 10° to 15.5° C. (50° to 60° F.) before the preparation of test pieces. The die for preparing test pieces must have perfect cutting edges. Test pieces should be conditioned 48 hours at 0 per cent humidity and 21.1° C. (70° F.) before testing to obtain maximum tensile and modulus results. The effect of humidity on physical test will be greater on normal latex, Revertex, and stabilized latex because of their increased water-soluble constituents which increase water adsorption. Good averages are obtained from three of four test strips broken, but for accurate work the average of the best four of six test strips should be taken.
Surface Application of Age Resisters to Cured Rubber vs. Mill Incorporation Prior to Cure
Authors: Semon W. L. , Sloan A. W. , Craig David
Published: February 2011

If the results of bomb aging, oven aging, and sunlight exposure are compared, one is led to the conclusion that the deterioration of rubber is a complex phenomenon. The relative effectiveness of the different deterioration inhibitors varies with the test applied. The rubber technologist is interested, not only in the protection afforded against heat deterioration, continued cure, oxidation of the rubber, deterioration caused by oxidized sulfur, or deterioration induced by sunlight; but also in properties such as the activation of accelerators giving rise to definite desirable types of vulcanizates, plasticizing or stiffening of the uncured stock, improved dispersion of the pigments, decreased scorching tendencies, elimination of surface tackiness caused by dry air cure, and prevention of flexure cracking in the cured product. Surface application may be effective with respect to all of the properties listed in the first group, but only mill incorporation can lend the advantages enumerated in both groups. Moreover, wear will remove a large part of the age resister applied to the surface which cannot have penetrated by diffusion to a concentration beyond its solubility, whereas abrasive action may expose new portions of age resister milled into the stock.
Method for Preparing Micro-Sections of Rubber
Authors: Steele Tracey F.
Published: February 2011

IN THIS laboratory it is frequently necessary to prepare micro-sections of a large variety of rubber compounds, cured and uncured, containing from 2 to 50 volumes of pigment. Smear mounts are quite satisfactory for the identification of pigments, but not for dispersion investigations. There have been some indications that the pressure required to make the rubber thin enough to transmit light causes changes in the dispersion. Furthermore, rather high temperatures are required to cause the highly pigmented stocks to flow under the cover slip. Green's sulfur chloride method (1) of destroying the elasticity is unsatisfactory with uncured stocks, causes certain undesirable changes in the appearance of some stocks, and requires modifications in procedure with different types of compounds. Freezing with liquid air has the inherent advantage that no permanent change is effected in the rubber and that all compounds, both raw and cured, can be treated essentially the same. Any of the usual mounting materials, however, such as paraffin wax, rosin combinations, etc., either crumble away, leaving little support for the rubber, or become so hard that the microtome knife is damaged.
Overflow during Vulcanization. Its Dependence upon Inactive and Active Fillers, and Errors in Previous Calculations of the Specific Gravity of Vulcanizates Resulting from It
Authors: Ditmar Rudolf , Preusse Carl Heinz
Published: February 2011

1. Raw rubber undergoes no change in volume during vulcanization. 2. Whenever it is vulcanized with sulfur there is an increase in volume. 3. Every inactive filler influences the overflow (increase in volume) in a characteristic way during vulcanization. 4. An increase in the proportion of a given inactive filler influences the overflow curve in a manner characteristic of the filler concerned. 5. Different inactive fillers influence the overflow in various ways. 6. Active fillers influence the overflow curve in a different manner from inactive fillers. 7. An increase in the proportion of a given active filler influences the overflow curve in a manner entirely characteristic of the filler concerned. 8. Different active fillers influence the overflow in quite different ways. 9. The specific gravity of a vulcanizate with sulfur is always less than the specific gravity of the corresponding unvulcanized mixture. 10. All calculations of specific gravity heretofore made in the rubber industry and theories related to them are incorrect because they are based on the false assumption that no increase in volume occurs during vulcanization. 11. Specific gravity determinations of mixtures must be based on overflow determinations.
The Dispersion of Gas Black and the Physical Properties of Rubber Mixtures
Authors: Grenquist E. A.
Published: February 2011

Many rubber technologists have already shown the importance of the dispersion of pigments in order to obtain the maxima physical properties of rubber mixtures. In a recent publication on the physical properties of gas black Carson and Sebrell state that they do not know of any article based on tests which deals with the relations between the dispersion of gas black and the properties of corresponding mixtures. Wiegand has already shown, in discussing mixtures highly loaded with gas black, that an incomplete dispersion of the pigments is no longer possible if the consistency of rubber falls below a definite value. He states that the lustre on the surface of a sample such as is used to determine tensile strength is a good method of estimating the degree of dispersion. Hauser upholds the idea that certain pigments attain a maximum dispersion during milling. In two preceding communications I studied the distribution of gas black in vulcanized and unvulcanized mixtures. I showed that changes in dispersion occur during milling as well as during vulcanization, and I discussed the theoretical possibility of obtaining the maximum dispersion and reënforcement. On the contrary, I am not concerned in these articles with the actual physical properties of the mixtures examined. In the present work, I wish to attempt to establish the relations between the dispersion of gas black and certain physical properties of rubber mixtures, whether vulcanized or not. The dispersion was determined by means of the microscope on freshly cut surfaces of mixtures vulcanized and unvulcanized, using a Leitz vertical illuminator and a Zeiss arc lamp as the source of light. Magnified about 300 times, the aggregates of gas black appear like a non-homogeneous black mass, while on the smoother and more homogeneous surface of the rubber the reflection is so increased that the field remains lighted.
Change of Electrical Properties of Rubber and Gutta-Percha during Storage under Water
Authors: Curtis Harvey L. , Scott Arnold H.
Published: February 2011

A number of samples of rubber and gutta-percha were stored under water for about seven years and electrical measurements made on them periodically to determine the effect of aging on the resistivity, dielectric constant, and power factor. The dielectric constant was measured under three different conditions, namely, 60 cycles alternating current, pulsating direct currentusing 0.6 second charge with 0.1 second discharge, and pulsating direct current using the same time of charge with 1 second discharge. In all cases the dielectric constants increased with time unless failure was approached. A sample was considered to have failed when measurement of its capacitance became impracticable. The changes of the resistivity and power factor varied from sample to sample. The approach of failure was first indicated by the resistivity. When a curve was plotted with time the sample had been under observation as abscissa and resistance of the samples as ordinates, the curves of the sample which failed showed a break or marked change in direction several months before actual failure occurred. With similar curves for power factor and direct-current dielectric constant, breaks occurred at a later time. The time interval between the break in the resistivity curve and the breaks in the other curves was a function of the rate of decrease of the resistivity. These facts indicate that the failure of a sample is the result of its decrease in resistivity. This decrease in resistivity has been ascribed to the formation of fine holes through the material. This explanation was confirmed by the microscopic examination of microtome sections of the samples which failed. These sections showed fern-like figures projecting into the rubber. All of the samples that failed were in the form of tubes, with water electrodes both inside and outside the tubes. Some copper salts were inadvertently allowed to form inside the tubes. The catalytic action of these copper salts accelerated the aging, and probably changed its character.
A Study of Gutta-Percha and Balata by Means of X-Ray Spectra
Authors: Hopff H. , Susich G. V.
Published: February 2011

The x-ray study of gutta-percha and balata has already been undertaken by G. L. Clark, E. A. Hauser, and his collaborators as well as by E. Ott. Their results are contradictory, however, in many respects. For example, Clark gives different values for the lattice of gutta-percha and for the lattice of balata, while Hauser has observed a difference for the angle of deviation only with stretched samples, and consequently proves that the position of the point interferences of the fiber diagrams is identical for both substances. Moreover Ott's values for gutta-percha vary greatly from those given by Clark. The roentgenographic observations referred to agree only in two respects: 1. Gutta-percha and balata are already crystalline in the unstretched state. 2. The lattice of gutta-percha and of balata is different from that of rubber. We have studied gutta-percha and balata by means of x-rays with the idea of clearing up the disagreements in previous publications and of determining whether or not there is any difference between gutta-percha and balata.
The Evaluation of Raw Rubber
Authors: Martin G.
Published: February 2011

The purchase of supplies for a rubber factory often involves a decision as to the relative merits of different samples of raw rubber. In view of the variety of needs the method of arriving at a decision must be left to the wisdom of the technical staffs concerned; but when a large portion of the output from the East is involved, affecting producers and manufacturers everywhere, it is desirable to discuss fully the methods employed to ensure that the final decision is as wise as its importance warrants. A problem affecting the whole of the rubber industry has now arisen in the East in connection with the preparation of smoked sheet. Firewood for smoking is becoming more difficult to obtain, and already some estates have been compelled to consider the production of an alternative form of rubber. As the Tropics become more cultivated, the acuteness of the problem will increase, and unless some change in the method of production occurs, sheet will tend to be replaced by crepe. It is presumed that there is a demand for sheet apart from crepe and that each form of rubber serves a purpose which the other cannot fulfil; but there is no clear and authoritative indication from manufacturers as to the differences which make both forms of rubber essential. it is of interest to point out that apart from form, color, odor, and reaction to swelling agents, there is no test which would distinguish between high grade sheet and crepe rubber unless both are prepared from the same latex, in which case sheet has a slightly higher content of mineral matter (Bull. Imp. Inst., 21, 303 (1923)) and a greater tendency to absorb moisture from the atmosphere (de Vries, “Estate Rubber,” 1920, p. 340), and possibly better aging properties (Martin, Trans. Inst. Rubber Industry 2, 354 (1927)). It is not proposed to discuss the relative merits of sheet and crepe although the subject is an illustration of the difficulty of evaluating raw rubber so as to obtain results which are in agreement with the ideas and experience permeating the industry. To the planter there appears to be a demand for sheet as well as for crepe, and he purposes to meet that demand if it is at all possible.
The Surface Tension of Rubber Solutions
Authors: Shacklock G. W.
Published: February 2011

During the past few years much attention has been paid to the constitution of raw rubber. The much improved methods of production of plantation rubber have resulted in a reasonably pure product available for investigation, and chemical analysis undoubtedly shows an empirical formula of C5H8 for the hydrocarbon. From this point onward, knowledge becomes less certain. Osmotic pressure and molecular weight measurements give no confirmation of a simple molecular structure, but show, in benzene solution, a behavior comparable with that of colloids. This is supported by experiments on swelling and viscosity, and by ultramicroscopic examination, all of which lead to the conclusion that rubber is a lyophilic colloid. Hence arose the concept that the rubber particle is a polymer of simple molecules of formula C5H8 (possibly isoprene), such a structure being in agreement with the production of rubber-like substances by the action of sodium upon isoprene and butadiene (Harries, Annalen, 395, 211 (1912)). The decrease in viscosity of a rubber solution with increasing periods of mastication of the rubber is hence regarded as a measure of depolymerization due to mechanical action; the increased ease of solution after mastication is confirmatory evidence.
Effect of Storage on Milled Crude Rubber
Authors: Carson C. M.
Published: February 2011

Smoked sheets which have been milled to different degrees of plasticity and stored in bale form for periods up to 9 months show a decided increase in modulus, plasticity, and recovery values. The increase in recovery value is the most noticeable, the change being 180 per cent of the original, if the rubber is baled at 40–50° C. and stored at 10–20° C. for 9 months. When the aged, milled rubber is mixed in a tube stock and processed on a tubing machine, the stock is rougher and the speed of extrusion is slower than a similar stock containing freshly milled crude rubber. The plasticity of stocks which are subjected to tubing operations is shown best on an extrusion type plastometer in preference to the compression type. Milled crude rubber “freezes” at temperatures below 0° C. and thaws at room temperature of 15–25° C. It may be permanently frozen by being placed under slight pressure for several months, freezing temperature being unnecessary. In either sheet or milled form this type of frozen rubber requires a temperature of about 50° C. to thaw, whereas temporarily frozen rubber will thaw at room temperature.
Rate of Deposition of Latex on Porous Molds
Authors: Greenup H. W.
Published: February 2011

The effects of pressure, rubber concentration of latex, temperature, and hydrogen-ion concentration upon the rate of deposition of latex on porous molds are described. Pressure, rubber concentration, and temperature were found to be negligible factors in comparison with hydrogen-ion concentration. By adjusting the pH of the latex to 6.1 it was found possible to obtain aggregation of the latex particles and a marked increase in rate of deposition. THE manufacture of rubber articles by dipping porous forms in latex was first described by Condamine (5). He reported to the Paris Academy in 1736 that the natives in South America made such articles as shoes and bottles, using clay molds which, after drying of the deposited layer, were shattered and removed. The idea of making articles by a process of this sort, instead of by coagulating the latex, milling, and then shaping the milled rubber, appeals to the imagination. Increased tensile strength and improved aging have been claimed (10) for articles made directly from latex, and their remarkable resistance to tear, obtained under certain conditions, is well known.
Studies of the Heat of Reaction during Vulcanization of Rubber
Authors: Toyabe Yasushi
Published: February 2011

The results of experiments indicate that an addition of accelerators caused the change of molecular arrangement of the rubber hydrocarbon. This discovery is of a great value in explaining the mechanism of acceleration, which is different from physical, chemical, and physico-chemical theories proposed heretofore.
Isoprene and Rubber. Part 26. Hemicolloidal Hydrorubbers
Authors: Staudinger H. , Geiger E. , Huber E. , Schaal W. , Schwalbach A.
Published: February 2011

The reduction of rubber without solvent takes place only at 270°, according to experiments by Fritschi. Below this temperature rubber is reduced only with difficulty and incompletely. In the dissolved eondition, on the contrary, Pummerer and Burkard showed that rubber can be reduced at ordinary temperature. In an earlier communication it was accordingly assumed that on heating a cleavage of secondary colloid particles into primary ones (into macromolecules) takes place, and that heating, therefore, has about the same effect as strong dilution. A distinction was made between primary and secondary particles, and it was assumed that the strong diminution in viscosity which is observed in dilute rubber solutions depends upon a cleavage of the secondary colloid particles, just as do the decreases in viscosity which rubber undergoes upon heating, and which have been generally described as depolymerization. These earlier ideas of ours are, however, incorrect. An extensive cracking of the rubber molecules takes place upon heating, and this was more carefully investigated by Geiger and later by Bondy. In this way reduction is facilitated. With strong dilution, on the other hand, the rubber solution passes from the gel state to the sol state, the rubber passes into normal solution, and therefore reduction can take place more easily in a dilute solution than in a concentrated one. With reduction by heat, therefore, a derivative of unchanged rubber cannot be expected; instead the hydrorubbers obtained, for example, those first prepared by Fritschi, are not reduction products of rubber itself, but are hemicolloidal decomposition products of the latter. Only by careful reduction in cold solution can one succeed in obtaining a hydrorubber in which the rubber molecules remain unchanged.
The Reinforcing Action and Other Properties of Titanium Fillers in Rubber Stocks
Authors: Bodger W. H. , Cotton F. H.
Published: February 2011

(1) The reinforcing properties of a high-grade titanium white, containing 74 per cent barium sulfate in intimate combination with the oxide, are slightly better than those of “White Seal” zinc oxide in mixes vulcanized with diphenylguanidine. (2) Titanium dioxide is generally inferior to titanium white as a reinforcing agent, and at high loadings gave poor tensile properties, especially in compounds accelerated with mercaptobenzothiazole. (3) The titanium fillers are incapable of behaving as activators of organic accelerators, as zinc oxide does, and from 3 to 5 per cent of zinc oxide is required in the majority of titanium stocks containing organic accelerators. (4) The aging properties of compounds reinforced with titanium fillers are generally similar to those conferred by zinc oxide, but are inferior to the latter at low volume loadings. (5) Better pigmentary and water-resisting properties are conferred by titanium dioxide than by titanium white, and both these fillers are superior to zinc oxide in these respects.
Water Absorption by Rubber. Part II. Vulcanized Rubber
Authors: Skinner S. J. , Drakeley T. J.
Published: February 2011

(1) The process of vulcanization decreases the amount of water absorbed by rubber. (2) Rubber containing a high percentage of protein material will not after vulcanization necessarily absorb more moisture than rubber with a lower nitrogen content. (3) Of the accelerators, diphenylguanidine induced the lowest water absorption and zinc diethyldithiocarbamate the highest. Both litharge and the ultra-accelerator showed higher absorptions than the unaccelerated base mix. (4) After a small initial rise there is a general decrease in water absorption with time of cure. A minimum absorption is noted at, or just after, optimum cure; the amount absorbed increases again after optimum and high absorptions occur with overcured rubber. (5) Zinc diethyldithiocarbamate shows the greatest increase in absorption with degree of overcure. Diphenylguanidine gives a vulcanizate, the absorption of which is rather insensitive to time of cure. (6) The incorporation of fillers lowers the absorption of water.
Rubber and Thioglycolic Acid
Authors: Holmberg Bror
Published: February 2011

Based on its behavior toward halogens, hydrogen halides, nitrous acid, ozone and hydrogen, rubber has one double bond for each C 5H 8 group. One would therefore expect that it would be possible to obtain from the addition products of these substances new compounds which would throw considerable light on the constitution of rubber. With the exception of the ozonides, however, this is true only to a very limited extent, a fact which depends in part upon the almost complete lack of water-soluble derivatives suitable for further reactions. It is true that the bromide of rubber can be converted by phenols into alkali-soluble compounds, but the carbon bonds of the compounds appear to be formed not only between the components but also by a closing of the ring within the rubber skeleton. Moreover in the transformation of the bromide by triethyl phosphine cyclicization appears to take place. In view of this, the constitution of these derivatives indicates that further work with them would be to little purpose, and as a matter of fact until now almost nothing of any great interest has appeared.
Some Aspects of Plasticity and Its Determination
Authors: Usherwood G. W.
Published: February 2011

In recent years the importance of plasticity in determining the ease with which a rubber stock can be processed has become increasingly realized, and several methods for its measurement have been devised. Before examining any of the methods employed for its measurement, it is advisable to consider what is meant by plasticity, since much loose and contradictory usage of the term exists in the rubber industry. The common meaning of plasticity refers to those characteristics of matter which have to do with the receiving and holding of form. A body is said to be plastic or possess plasticity when it can be permanently deformed by any force exceeding a definite minimum. The difference between a viscous substance such as pitch and a plastic substance such as clay is that the former slowly changes its shape under the smallest applied load, that is, its own weight, while the latter requires some force above a minimum before it will deform. In practice one must distinguish between two substances which, although soft and yielding with equal ease to any deforming force, differ widely with the fidelity with which they retain the deformation imparted. One may retain its deformed shape accurately and permanently, as, for example, a piece of sculptor's clay, while the other may, after some interval of time which may be long or short, resume to a considerable extent its original form, as, for example, a piece of masticated rubber. In the first case the clay is said to be more plastic than elastic, while in the second the rubber is said to be both plastic and elastic.
The Solvation of Rubber Sols
Authors: Lens J.
Published: February 2011

The purpose of this investigation was to get some idea of the role played by solvation in organo sols. However, we wish to state first that we do not bind ourselves to a special theory. Accordingly we give these systems the name sols simply because we cannot speak of them without giving them a name. It may be that the name “solution” is a better one, but for our purpose it does not make the slightest difference whether the rubber is dispersed in the medium as molecules or as aggregates of molecules. Hence we do not want to discuss the molecular structure of the rubber particles in detail. There are many methods of measuring the degree of solvation, but they almost never give quantitatively the same results, which cannot be expected at any rate. Previous investigators have used the greatest part of these methods with more or less success. The best known are the investigations of Posnjak on the swelling-pressure of rubber in organic solvents. Furthermore, many investigators have measured the viscosity of rubber sols. But while it is likely that the law of Poiseuille does not hold, and that these sols are plastic, it will be very difficult to interpret the values so obtained in the right way. Recently Stamberger measured the vapor pressure of rubber sole and got a good agreement with Posnjak's values. However, Stamberger did not extend his measurements to concentrations between 67 per cent and 100 per cent rubber, probably because he was looking for this agreement only.
Experiments on Oil-Proof Rubber
Authors: Ishiguro Katsumi
Published: February 2011

Tests of rubber mixtures compounded with nine different accelerators indicated that those with relatively great hardness have relatively little absorption and those with less hardness have more. Rubber products which are not required to be particularly soft can be made with fairly good oil-resistant properties by the proper selection of accelerators and by vulcanizing to the optimum point.
The Effect of Particle Size of Zinc Oxide on the Physical Properties of Rubber
Authors: Haslam G. S.
Published: February 2011

The particle size of the pigment may be expressed in terms of several average diameters, depending on the method of measurement. In this work three of these averages were considered; namely, d1, which is the arithmetical mean, d3, which is the average diameter from which specific surface is calculated, and D, which is the average diameter from which the number of particles per gram is calculated. A series of samples was prepared and these three average diameters were determined These samples were then compounded with rubber and several physical properties measured. As a result of these tests it is shown that, in general, the physical properties vary directly as the specific surface and the number of particles per gram. However, if the number of particles per gram is maintained constant and the specific surface is varied, it was found that the physical properties vary directly as the specific surface. No such relationship was found when the specific surface was maintained constant and number of particles per gram varied. It is further pointed out that the only satisfactory means of measuring the d3 diameter, and therefore the specific surface, is by some microscopic method which determines the size-distribution curve for the pigment.
The Abrasion Question. Some Factors in the Deterioration of Rubber When Exposed to Frictional Contacts with Other Materials
Authors: Cosler V. A.
Published: February 2011

If we accept the proposal that the fundamental effect produced by the machines diagrammed in Fig. 1 is that of dragging a series of saw-toothed paddles across the surface of rubber specimens, we must accept as fact the theorem that the results recorded by these types of machines is a summarization of values rather than a fundamental value. If we accept the evidence that relations cannot be varied on any type of present abrasion testers to duplicate the conditions existing in all situations where rubber is exposed to frictional contacts with other materials, we must accept the fact that some fundamental factor is absent, or is over- or under-emphasized as these relations are varied. Whether these missing reactions can be supplied by evaluating other characteristics which will properly modify the results obtained on any given abrasion tester is an open question. It can be safely stated, however, that results obtained from any type of tester discussed can only be considered as evaluating rubber compositions at or near the point of optimum cure under one particular set of wear conditions. With one exception these conditions may safely be considered as approximating the conditions obtaining between a tire tread and the road under normal operating conditions. The Sproul-Evans tester may safely be considered as more closely approximating sand-blast hose conditions than tire-road conditions. It is the thought of the author that the most promising field of future endeavor lies in the direction of studying the possibility of reproducing more fundamental effects, rather than attempting to add more reactions to the already complex set of conditions present in the known types of abrasion testers. The suggestion is also offered that a most promising field of study lies in the direction of studying the modifying effect of distortion upon the fundamental characteristics of rubber, and attempting to establish the extent of distortion present when rubber is exposed to frictional disintegration in actual service conditions.
Structural Viscosity in Some Lyophilic Sols. II. Rubber Sols
Authors: Gallay Wilfred
Published: February 2011

The relative viscosities of sols of natural and purified rubber in benzene were measured at varying pressures, using the overflow viscosimeter. Deviations from Poiseuille's law to varying extents were found in all cases, with regions of structure and turbulence at various pressures. The limiting concentrations above which structure is evident and Poiseuille's law is not obeyed were found to be in agreement with those calculated by Staudinger on the basis of his theory of the relation between the viscosity and molecular weight of polymeric molecules. Exposure to ultra-violet light was found to decrease considerably the viscosity of a sol of purified rubber.
A Multi-form Plastometer
Authors: Lefcaditis G. D.
Published: February 2011

The methods of measuring plasticity are usually divided into two classes, that applying the principle of extrusion, and that based on compression. There is no considerable difference between methods based on extrusion. The compression methods, however, have been subdivided into categories, such as constant volume of tested material and hence decreasing pressure, or constant area and pressure, etc. It is not the object of the present article to enter into a critical discussion of the theories underlying the various methods. Such attempts are numerous in recent publications. (Griffiths, Trans. Inst. Rubber Ind., 1, 308 (1925); Martin, Ibid., 6, 298 (1930); De France, Ind. Eng. Chem., 23, 824 (1931); Scott, Trans. Inst. Rubber Ind., 7, 169 (1931); Behre, Kautschuk, 8, 2 (1932). If reproduction of figures given in the literature is desired, it is necessary to process the particular modified plastometer by which flue figures in question have been obtained. The compression plastometers being probably the most extensively used nowadays, it was thought that an instrument could be designed which would incorporate the various modifications of the compression plastometer, thus obviating the need for several instruments. In this paper such an instrument is described. An additional feature is a revolving disc, which is of convenience in preheating the test samples.
Some Observations on Rubber Testing
Authors: Scott J. R.
Published: February 2011

The subject of rubber testing and its standardization has received so much attention in recent years, that some apology might seem necessary for discussing it further. A few years ago the present writer had occasion to call attention to several respects in which existing test methods showed unnecessary lack of uniformity (Trans. Inst. Rubber Ind., 5, 139 (1929)), and it must be admitted that this lack of uniformity still persists to a great extent, with a corresponding loss in the value of published test results. It is the object of the present note to call attention more particularly to some unsatisfactory features in the selection of the “best” or “optimum” cure of a mix for purposes of comparison with other mixes. It is scarcely necessary to emphasize the fact that in comparing the properties of different mixings, as in examining the effects of fillers, accelerators, antioxidants, softeners, etc., all the mixings must be vulcanized to comparable states of cure. Nevertheless, an examination of published data shows that often insufficient attention is paid to ensuring strict comparability. For instance, it is not uncommon to find the effect of fillers examined by taking an accelerated base stock, adding the fillers to it, and vulcanizing all the resulting mixings for the same time, it being assumed that the fillers do not affect rate of cure. This assumption is not justifiable, even in the case of seemingly inert materials. An obvious case is that of gas black, which, though chemically inert, retards vulcanization in presence of organic accelerators. Moreover, such “inert” materials as barytes, blanc fixe, whiting, and strontium sulfate may markedly alter the rate of cure. Thus, in some experiments made by the writer, a base mix accelerated with dephenylguanidine (0.75% on the rubber) gave optimum mechanical properties after 90 minutes at 141° C., but mixings containing the fillers mentioned had optimum curing times ranging from 65 to 110 minutes. The writer has, indeed, come across a filler consisting of a very inert compound, which nevertheless completely puts out of action the most powerful organic accelerators. It is thus clearly unsafe to assume that any material will be inert as regards its effect on rate of vulcanization, whether in presence of an organic accelerator or not.
Rubber. XVth Communication. The Polymerization of Rubber, Isoprene, and Styrene by Light in the Presence of Sensitizing Agents
Authors: Pummerer Rudolf , Kehlen Hans
Published: February 2011

Although according to Bernstein, exposure of rubber solutions to light in the absence of air diminishes the viscosity of the solutions, it is the conviction of the present authors that this change takes place only when there is air over the solutions. In 1920 Porritt observed that a rubber solution sealed off from contact with air gelatinized on exposure to light. Kirchhof however found this to be true only with small quantities of rubber solutions in quartz tubes exposed to ultra-violet light. This reaction was of particular interest to the present authors because of its possible relation to the vulcanization reaction, which can be regarded as an increase in molecular size, and as the formation of chains of rubber molecules with and without sulfur. Irradiation is perhaps an effect similar to vulcanization, but is brought about by polymerizations. It was also of interest to compare irradiated and gelatinized sol rubber with gel rubber. All the experiments described in the present paper were carried out with water-clear sol rubber, which was prepared in most cases from crepe.
The Chemistry of Soft Rubber Vulcanization. I. Measurement of Vulcanization
Authors: Garvey B. S. , White W. D.
Published: February 2011

For a series of rubber-sulfur compounds and for four commercial, high-gum accelerated compounds the changes during cure have been measured by a series of physical tests. The change in combined sulfur has also been measured for the rubber-sulfur compounds. Experimental conditions have been so controlled that all results are comparable. Based on the experimental results, a set of criteria has been selected with approximate limiting values for unvulcanized and for vulcanized rubber. Conditions are specified under which the criteria can be used to measure the degree of vulcanization. The selection of these criteria is, in effect, a definition in terms of the changes in physical properties which limits the meaning of the term “vulcanization” in a manner useful for the study of the phenomenon. The difference in the rate of change of the several properties is interpreted as evidence that during vulcanization a mechanical structure is built up.
Oil-Resisting Rubber
Authors: Naunton W. J. S. , Jones Maldwyn , Smith W. F.
Published: February 2011

From the mechanical engineer's point of view, rubber has one serious drawback, and that is the behavior toward lubricating oil. By proper compounding and curing, rubber is being used under circumstances which involve contact with oils, but there is still room for improvement. When one considers that oil-resisting rubber is finding and could find still greater application in the engineering, especially the automobile, electrical, petroleum, gas, paint, printing, agricultural, and other industries, it is not astonishing that this problem is one of the most important of the rubber industry. Little work, however, has been published on this subject prior to the present year. The popular belief that glue protects rubber against oil has been shown to be incorrect, and will be dealt with later in the paper. Ishiguro (Rubber Chem. & Tech., 6, 278 (1933)) studied a large number of fillers, soaps, glue, starch, and accelerators, but in view of the fact that the author did not make a preliminary study of the effect of these substances upon cure, the reader of the paper is left with the impression that the results are due as much to the effect of the various substances upon the state of cure as to their intrinsic oil-resisting properties. It is true that a certain amount of correction was made in the case of accelerators. The paper must, however, be welcomed as the first systematic publication based on experimental work on this subject. Karsten (Kautschuk, 9, 73 (1933)) brings out a very important point in his paper to the effect that the best method of obtaining oil-resistance in rubber must depend upon the use to which the finished article will be put: for example, large proportions of reinforcing fillers and glue cannot be used when a flexible rubber is required, and so on.