bluuebunny/crossref_metadata_2025 huggingface dataset:
Variation in the Composition and Properties of Fresh Latex. And Subsequent Changes on Ammoniation
Authors: Rhodes Edgar
Published: February 2011

Systematic examination has been made of 163 samples of latex drawn at the approximate rate of three per week over a period of fourteen months from a single tapper's task on old seedling trees, newly opened after several years' rest on the continuous alternate daily system. The latex samples were all examined, both in the fresh condition and after 10 days and 15 days preservation with 0.7% ammonia; during the last eight months certain tests were also made on the latex immediately after ammoniation on the day of collection. The tests included dry rubber content, total solids, acetone extract and acid number of whole-latex rubber films, surface tension, viscosity, stirring stability and ease of creaming. It has been observed that: (1) The difference between percentage total solids and percentage dry rubber content is greater after 10 days' preservation than in the fresh condition. (2) The acetone extract and its acid number from whole-latex film are less in freshly-ammoniated latex than in fresh latex, and very much greater in ammoniated latex stored for 10 days. The acid number after 10 days preservation is usually about twice that of the fresh latex. These findings and their implications are discussed in the text, in which experimental figures are given. High dry rubber content usually connotes low acetone extract and acid value in the fresh latex. (3) Values for surface tension before and after ammoniation are given. The fall in surface tension as a result of ammoniation has not been proven to be governed by the changes in acetone-soluble material, or the acid number thereof. (4) The viscosity of ammoniated latex is shown to be very significantly correlated with its dry rubber content. In the case of fresh latex the degree of correlation is much less; a possible reason for this is advanced. Experimental results are given. (5) The initial stirring stability is shown to be influenced by the initial dry rubber content of the latex. The data do not provide an adequate explanation of the changes in stability which take place on storage. (6) The creaming ease of new latex appears also to be influenced by its initial dry rubber content, but the present data are not adequate fully to explain the variations which are noted.
The Chromatography of Rubber Solutions
Authors: Cajelli Giampietro
Published: February 2011

In the opinion of Pummerer, there is considerable doubt about the homogeneity of the fractions obtained by fractional precipitation of rubber from dilute benzene solutions, both with respect to the size of the molecules and to the state of aggregation. Based on the results of x-ray measurements of fibrous substances, to which type stretched rubber belongs, Meyer and Mark have advanced the hypothesis of the existence of chains of primary valences and of a micellar structure. PURIFICATION OF RUBBER There are four important and at the same time essentially different ways of carrying out the difficult process of purifying rubber. According to Harries, acetone extraction gives a colored product and leads to profound changes in the elastic properties. Staudinger adopted the method described by Wildmann in 1911, which involves the use of a mixture of acetone and chloroform. On the other hand, Pummerer and Koch used the method of fractional precipitation; the rubber after severe mastication was extracted with acetone, was dissolved in benzene, the liquid was allowed to stand for several weeks, the solution was decanted from the insoluble residue and was fractionally precipitated by alcohol and acetone. More recently this same method has been perfected by Pummerer and Meidel, and by this means a fraction of crystallized rubber was isolated from the mother liquors of the fractional precipitation. Finally Pummerer and Koch have purified rubber by treatment with an alkali, combining the precipitation method with the use of a solution of potassium hydroxide in methanol. Later this method was modified by Pummerer and Pahl. The use of latex in place of crude rubber is the most important development in obtaining a satisfactory product. De Vries and Beumée-Nieuwland have described in detail some results obtained with fresh latex. The total-rubber obtained by the methods just described contains, according to the quality and the age of the sample of latex, from 0.1 to 0.4 per cent of nitrogen which cannot be removed by washing, even when this is exhaustive.
The Properties of Polymers in Solution. X. Ultrafiltrations of Rubber Solutions
Authors: Meyer Kurt H. , Jeannerat Jean
Published: February 2011

It is a recognized fact that ultrafiltration is one of the most valuable methods for the study and treatment of colloidal suspensions formed of compact spherical particles. Not only is it possible to separate this type of particle from a solvent by means of a suitable ultrafilter, but it is also possible to determine the size of the particles by means of calibrated ultrafilters. Up to the present time, however, ultrafiltration has been utilized very little in the study of chain molecules, and no accurate data are available on the behavior of colloidal solutions of chain molecules during ultrafiltration. In the following discussion, the results of some experiments on the ultrafiltration of rubber solutions are described. Dilute solutions of rubber in toluene can be separated completely into rubber and solvent by ultrafiltration under pressure through fine ultrafilters with pores as fine as about 50 ḿ (“Fine” Cellafiltres and Membranfiltres). Solutions of crepe and solutions of masticated rubber give the same results.
Behavior of Rubber Hydrocarbon in a Molecular Still
Authors: Smith W. Harold , Wing Henry J.
Published: February 2011

Some investigators believe that rubber consists of associated molecules, and others accept Staudinger's view that long-chain molecules are formed by polymerization. Pummerer, Andriessen and Gündel have obtained a molecular weight as low as 600. Meyer and Mark believe that it is approximately 5,000, although they calculated on the basis of osmotic pressures values as high as 350,000. They, as well as Pummerer, consider that rubber is an associated colloid and that high molecular weights are caused by aggregates, sometimes called micelles. Staudinger, however, considers that the long-chain rubber molecule itself has a molecular weight of 200,000 or even 350,000, and that products with lower values, which may be formed in rubber, result from degradation. if the molecules are small it might be possible to distil them if their vapor pressure could be sufficiently increased, but none would distil without decomposition if the molecules are very large. Because the vapor pressure of rubber below its decomposition temperature is low, it appeared of interest to attempt to distil the material in a molecular still. Paraffin wax and sugar, both substances of relatively high molecular weight, have been successfully distilled in this type of apparatus. Subsequent to the work described in this paper, the molecular weight of sol rubber prepared at this Bureau was determined by Kraemer and Lansing of E. I. du Pont de Nemours & Co., Inc. They used the Svedberg method of sedimentation equilibrium in an ultracentrifuge with ethereal solutions of sol rubber. The temperature of the solutions during determinations was approximately 10° C, and an average value of 460,000 was obtained. There was evidenced of a mixture of molecular species.
A Contribution to the Characterization of the Plastic-Elastic State
Authors: Rohde E.
Published: February 2011

The manner in which vulcanized rubber can be deformed and yet return almost completely to its original dimensions after the stress is released is a unique and characteristic property. Technically the problem in testing rubber is to evaluate this property and to define it in terms of the factors which are concerned. To define completely this property of rubber whereby it is susceptible to deformation, it is necessary to know the stress, the elongation, the energy expended, the energy lost, the time and the temperature. The stress, elongation and energy expended are closely related and are characterized by the stress-strain curve, which in turn depends on the time and temperature. In addition, it must be borne in mind that rubber can be deformed either by tension or by pressure, but this will not be discussed further here. On the other hand a rather puzzling problem will be considered, the solution of which brings out the fact that the three variables involved in any deformation, viz.: (1) The time or frequency. (2) The temperature. (3) The interrelated factors: stress, elongation and energy expended, must be varied considerably in order to characterize the phenomena of deformation and that when this is done, unexpected results are obtained.
Properties of Hard Rubber. VII. Measurement of Plastic Flow as Affected by Temperature
Authors: Church H. F. , Daynes H. A.
Published: February 2011

The merits of the Martens apparatus as an instrument for measuring plastic flow of solid insulating materials at various temperatures are discussed and the features of a new torsion apparatus which is designed to overcome certain objections to the Martens apparatus are explained. Details of the construction of the new apparatus and of its method of operation are given. Deflection-time and deflection-temperature curves determined with the torsion apparatus for a typical hard rubber are given and the form of these curves is discussed. The “yield temperature” is defined from the characteristic shape of the deflection-temperature curve. It is shown that deflection is proportional to stress, and that the magnitude of the stress used and the dimensions of the test-piece have no influence on the general shape of these curves. An empirical formula connecting deflections, stress and test-piece dimensions is given. The influence of degree of vulcanization on the plastic flow of an unloaded (rubber-sulfur) hard rubber at various temperatures is described. “Yield temperature” increases with time of vulcanization up to some limiting value. Recovery of shape of the test-piece after removal of torsional stress is briefly discussed. Comparative tests on several hard rubbers were made with the Martens apparatus and the torsion apparatus, both used at a series of steady temperatures. The same type of deflection-temperature curve was obtained, but the. “yield temperature” as slightly higher with the Martens apparatus than with the torsion apparatus. The torsion apparatus provides more complete data and is more convenient to operate than the Martens apparatus.
History of the Division of Rubber Chemistry of the American Chemical Society
Authors: Osberg E. V.
Published: February 2011

After long years of experience, the rubber industry of today has come to realize the true worth of the chemist and the value of the interchange of scientific knowledge and coöperation in research. Early meetings and discussions held by the Division of Rubber Chemistry of the American Chemical Society and its predecessor, the Rubber Section, were influential in dispelling early ideas as to the value of the chemist and in breaking down the barrier of secrecy in the rubber trade. The chemistry of rubber during the past two decades has undergone a tremendous growth, and the Division through its many activities has played an important role in disseminating knowledge that has been gained from laboratory research. THE EARLY RUBBER CHEMIST Before the turn of the twentieth century, the rubber industry had little or no knowledge of the chemist or what he might accomplish. Funds for research were generally withheld, with no quick profits in sight as a result of these expenditures. Among the comments of rubber manufacturers of that time were: “I have no use for chemists, druggists and apothecaries”; “I would give more for the guess of my old superintendent than all the certainties of the best chemist on earth”; “I had employed chemists but their cost to the company had been greater than any value received from their work.” In 1899 the chemist, Arthur H. Marks, invented the alkali reclaiming process, and in 1906 George Oenslager discovered organic accelerators. Rubber technology was being revolutionized by the chemist, and larger profits were in sight. The tight grip on the purse strings became loosened somewhat, and money was being cautiously expended on research. Practical and immediate results which could be translated into hasty profits were the principal aims. Little encouragement was afforded those who wanted to tackle fundamentals. Competition was keen among manufacturers; the rubber industry was growing rapidly, and no time or money was available for abstract reasoning or for “profitless” research enterprises. Rubber manufacturers were quite willing for their chemists to meet with chemists of other companies provided they did not divulge any of the firm's “secrets”. With most of those attending these early meetings in the role of listeners, little was accomplished in furthering the knowledge of rubber chemistry through the exchange of ideas. Such was the problem during the life of the Rubber Section and through the earlier years of its healthier successor, the Division of Rubber Chemistry.
The Crystallization of Weakly Vulcanized Rubber by Pressure
Authors: Thiessen P. A. , Kirch W.
Published: February 2011

Crystallization can be brought about in weakly vulcanized rubber by the method described by Thiessen and Kirsch for natural rubber. When samples of this type of vulcanized rubber were exposed to x-rays below + 6° C, but not under pressure, then Debye-Scherrer diagrams corresponding to those of a crystallized latex film were obtained. To determine the influence of pressure on these vulcanizates, samples were subjected to pressure on all sides in the chambers of the pressure apparatus described in the earlier work. After having been exposed for 100 days the sample which had been kept at + 6° C under 30 atmospheres' pressure showed a very marked Debye-Scherrer diagram, whereas samples kept at the same temperature but at normal pressure showed only the halo of an amorphous substance. Consequently pressure has an influence on the crystallization of vulcanized rubber as well as of raw rubber. The melting point of the crystalline phase lies between + 11° C. and +13° C. Obviously then an increase in pressure raises the temperature range of supercooling.
Tensile Tests of Plantation Rubber
Authors: Slbiriakoff I.
Published: February 2011

The investigation which has just been described can be summarized as follows: (1) A technique for the commercial testing of plantation rubber has been developed which is simple and precise, and by means of which it is possible to reproduce control tests, a feature which is indispensable if rubber is to be sold on a basis of quality rather than superficial appearance. (2) The tentative specifications for testing rubber drawn up by the Crude Rubber Committee of the Division of Rubber Chemistry of the American Chemical Society have been found acceptable as a basis for this testing procedure. (3) It has been found necessary, however, to revise the specifications of the Crude Rubber Committee in some ways and to amplify them, so that they fulfill the three conditions described above and also conform to the particular working conditions of laboratories in the tropics. The revisions to the Crude Rubber Committee specifications include: (1) The use of an autoclave for vulcanizing in open steam. (2) A mill roll temperature of 65° C instead of 70° C. (3) A definite, fixed weight of batch, containing 200 grams of rubber, plus accessory ingredients. (4) A temperature of 25° to 30° C during testing. (5) The use of ring test-specimens instead of dumb-bell specimens.
The Viscosity of Preserved and Concentrated Latex. Part I. Relationship between Dry Rubber Content and Viscosity
Authors: Rhodes Edgar , Smith H. Fairfield
Published: February 2011

In the October 1939 issue of Rubber Chemistry and Technology, on pages 655–664, is an article of the above title by Edgar Rhodes. Since the time of its original publication in the India-Rubber Journal, in January 1939, the work has been revised and published in the Journal of the Rubber Research Institute of Malaya, Vol. 9, pages 171–188 (Communication no. 241), December 1939. The attention of Rubber Chemistry and Technology has been called by Mr. H. J. Page, Director of The Rubber Research Institute of Malaya, to the importance of certain revisions in Part I of the work. Mr. Page points out, for example, that “the authors have evaluated separate relationships for ammoniated field latex and for centrifugal concentrates, thereby revising the estimates of the average viscosity of latex of varying dry rubber content at 30° C.” These new data are given in Tables I and II. The discussion on pages 657 and 661–663 of the same issue of Rubber Chemistry and Technology has been altered considerably, and therefore is reproduced in full here.
Analysis of Proteins Present in Hevea Latex
Authors: Altman R. F. A.
Published: February 2011

To analyze the proteins present in rubber-free serum obtained by coagulating latex for the preparation of sheet rubber, the method described by Brazier was adopted. Inasmuch as this method is not wholly satisfactory, particularly in the humid atmosphere of the tropics, is was improved in several ways. Besides several amino acids, some interesting byproducts were isolated, among others a yellow-reddish thick oil, and other ether-soluble substances. Scheme G outlines the results attained. The properties of the products isolated will be discussed in a later publication.
Hevea Latex Sludge. Existence of a Sludge Fraction in Fresh Unpreserved Latex
Authors: McColm E. M.
Published: February 2011

Bruce recorded the results of analyses of the ash of certain crude rubbers, among them of evaporated latex. He found the sample investigated to contain 5.8 per cent MgO and 24 per cent P2O5. It is evident that ammoniation of a latex containing such ions would result in the formation of insoluble MgNH4PO4.6H2O. Hauser refers to this phenomenon, stating that the precipitated salt settles to the bottom of the container. This precipitate, sometimes containing occluded rubber, has been known in the plantation industry as latex sludge, and has constituted a fouling problem in storage containers. The presence of a sludge fraction in fresh unammoniated latex, just as it is produced by the tree, has not been generally recognized. Van Harpen concentrated fresh unpreserved latex by centrifuging and, on opening the centrifuge, observed a sludge deposit in the bowl. He records that this sludge darkened rapidly and states that it was rubber-free and friable. As a beginning in a study of latex desludging procedures in this laboratory, a quantity of the sludge was obtained and analyzed. The data obtained are reported here.
Ultraviolet Irradiation of Rubber
Authors: Srinivasan P. S.
Published: February 2011

The absorption of light by rubber when dissolved in polar and non-polar solvents was measured before and after exposing the solutions to ultraviolet light in the absence of air. It was found that irradiation with ultraviolet light makes rubber more transparent when in non-polar solvents and less transparent when in polar solvents. The state of rubber in solution is reviewed in the light of present-day knowledge, and a tentative explanation of the absorption phenomenon is suggested on the assumption that the rubber molecule in a polar solvent is depolymerized by the field of the solvent molecule and that ultraviolet light produces both polymerization and depolymerization of rubber, according as rubber initially is in a low or high state of polymerization. A probable support to this concept from measurements of viscosity is indicated.
Mechanism of Polymerization Reactions
Authors: Melville H. W.
Published: February 2011

The peculiar properties possessed by molecules consisting of long chains of atoms linked together by primary valence forces are as yet imperfectly understood. Both naturally occurring and synthetic substances of this type are now familiar in a large variety of forms, of which rubber and cellulose are well-known examples of the former type. The problem may be attacked from two points of view. On the one hand by an investigation of the properties of large molecules something may be learned about molecular structure; on the other an attempt may be made to build such molecules synthetically to a predetermined pattern so that a correlation between structure and behavior may be established. This article will be solely concerned with the second aspect of the subject. Here the general problem is to carry out the synthesis under rigidly controlled conditions in order that the precise mechanism of molecule building may be determined with absolute certainty.
The Stability of Chlorinated Rubber and Its Fractions
Authors: Hoekstra J.
Published: February 2011

(1) In ultraviolet rays decomposition occurs in the upper surface of a layer of chlorinated rubber. (2) The amount of chlorine split off from a common commercial specimen of chlorinated rubber when heated dry for 30 days at 100° C was about 0.25 per cent. For the greater part, the chlorine was free of hydrogen chloride. (3) The rate of decomposition when dry heating was applied at 100°, 130° and 150° C leads to the conclusion that the speed of reaction diminishes rapidly at degrees below 100° C until there is soon no reaction at all. (4) The amount of chlorine split off when chlorinated rubber was heated in water at 100° C was about five times as large as when dry heating was applied. (5) From the curves indicating the amount of chlorine split off during “wet”and “dry”heating at 100° C, it is possible to calculate quantities which may be regarded as the maximum amounts of chlorine which can be split off from the respective specimens. These amounts are twice as large when the chlorinated rubber is heated wet as when dry heating is applied; with a given normal specimen about 1.5 per cent was obtained in wet heating. Only in one of eight specimens was a greater quantity found, viz., 3 per cent. (6) In a certain specimen 10 per cent of carbon tetrachloride was found. The splitting off of chlorine is not caused by decomposition of this substance.
Applications of the Manometric Method for Measuring the Oxidizability of Rubber. Oxidizability and Aging in the Geer Oven
Authors: Dufraisse Charles , Le Bras Jean
Published: February 2011

In summary, the changes which take place in the mechanical properties of a rubber mixture when it is aged in a Geer oven, and which are evident by dynamometric measurements, are closely related to the proportion of oxygen absorbed by the sample. It is therefore much more practical and convenient to measure its oxidizability after only a few minutes' aging, using a sample of any shape whatsoever, and a weight of approximately one gram. As far as any particular standard industrial mixture is concerned, there is no good reason for not conforming to the customary practice of rubber technologists of expressing aging on the basis of loss in tensile strength. In this case the only thing necessary to do is to calibrate the manometer in kg. per sq. cm. after having established the curve relating oxygen absorbed to loss in tensile strength.
Some Consequences of the Electrical Double Layer in Rubber Technology
Authors: Twiss D. F. , Carpenter A. S. , Amphlett P. H.
Published: February 2011

The effects of the electrical double layer in connection with rubber manufacturing processes have, in recent years, become of rapidly increasing technical importance. In the last two decades remarkable developments have occurred in the application of aqueous dispersions of rubber, or of rubber-producing materials. The characteristics of these dispersions are largely dictated by the electrical double layer and adsorbed material associated with it. These aqueous dispersions may be of several distinct types, viz.: (1) natural dispersions of natural rubber, in particular the latex of Hevea brasiliensis; (2) artificially prepared dispersions of natural rubber; (3) dispersions of artificial or synthetic rubber in which the rubber-like material has been formed from predispersed parent material; (4) artificially prepared dispersions of artificial or synthetic rubber. It is convenient to discuss these in substantially the reverse order to that in which they have just been enumerated. Artificially prepared dispersions of synthetic rubber-like materials are latexlike fluids which can be applied in the same way as natural latex to manufacturing purposes, and not only impart any advantageous features of the dispersed material, but also possess a potential advantage in that dispersing agents can be selected which are resistant to attack by, or to growth of, bacteria or moulds, with consequent enhancement of stability, or which are favorable to the water resistance of the final product.
Hevea Latex. Correlation of Nitrogen and Ash with Total Solids Content
Authors: McGavack J. , Rhines C. E.
Published: February 2011

The purpose of this paper is to report primarily the correlation of nitrogen and ash with the total solids of Hevea latices. In addition it is desired to show that the nitrogen in the rubber, prepared by acid coagulation, depends on the original total solids content of the latex. A further purpose is to show that the residual nitrogen adsorbed, dissolved in, or directly associated with the rubber phase has a constant value, independent of the concentration of nitrogen in the aqueous phase. It is believed that the proper knowledge of such relations will be helpful in the preparation of better crude rubbers. Arisz made a study of the nitrogen content of latex. His work was directed to observing the change in the nitrogen content of latex as influenced by the use of various systems of tapping, both with regard to time and location of the cut. His results indicate that there is a relation between the total solids content and the nitrogen value. Using his data on tree 1 and plotting the nitrogen as a percentage of the total solids against the total solids content of the latex (Figure 1), we find that the nitrogen content of the total solids is roughly inversely proportional to the total solids content of the latex. When Arisz's data were plotted so that the nitrogen content was a percentage of the whole latex, a line parallel to the x-axis seemed to result. Following the leads obtained from the work of Arisz, we decided to determine the nitrogen content of latex, from particular areas on our plantations, obtained by the usual tapping methods. We also decided, while these samples were available, to see how the ash varied with the total solids content of the latex, and to determine how the nitrogen would be apportioned when latices of various total solids content were coagulated.
Separation and Identification of Lecithins from Hevea Latex
Authors: Altman R. F. A. , Kraay G. M.
Published: February 2011

To identify completely the phospholipids, which according to several authors may occur in Hevea latex, we separated in a very simple way a butter-like substance, which really contains phospholipids. The results of qualitative analysis justify the positive conclusion that this substance contains lecithins composed of glycerophosphoric acid, choline and the fat acids: palmitic acid, stearic acid, arachidic acid, oleic acid and linoleic acid. A glycoside also was shown to be present in the raw material. We found the content of phosphorus, nitrogen and fat acids to be 1.58, 0.54 and 84.1 per cent, respectively. In purifying the crude material by means of fractional precipitation with acetone from the ether solution, we obtained a nearly colorless gum which contained 2.35 per cent phosphorus, 1.05 per cent nitrogen and 61.3 per cent fat acids. It is stated that the purification is accompanied by a considerable loss of fat acids, the latter remaining in the acetone-ether solution.
A Contribution to Knowledge of the Creaming Process
Authors: van Gils G. E.
Published: February 2011

Creaming of latex is a process which is extensively employed, partly because good creaming agents have been developed and partly because of the constantly increasing demand for concentrated latex. Knowledge of the mechanism of creaming is not in proportion to the great practical importance of the process. It still happens too frequently that unexpected variables or phenomena, for which the laboratory investigator can offer no explanation, are encountered. In the present paper we present the preliminary results of tests carried out at the West Java Experiment Station. For a general survey of creaming processes, reference should be made to a recent paper by Kraay. The object of the present paper is to enquire more deeply into various phenomena which are discussed briefly in the paper cited above. Unless otherwise stated, the tests to be described were made with konjak flour, abbreviated here to K flour.
Elastic Recovery and Plastic Flow in Raw Rubber
Authors: Treloar L. R. G.
Published: February 2011

In considering existing information on the mechanical properties of raw rubber, it is not generally possible to distinguish between the effects of elastic and of plastic deformation. In the experiments described great care was taken to secure the complete removal of elastic strain, after stretching to various extensions at different temperatures. The plastic flow increased to a maximum with increasing elongation and fell again at higher elongations, an effect attributed to the increase of crystallization with increasing extension. For rubber held extended for one hour at 25° C the flow was never greater than 2% of the original extension, and for extensions greater than 440% or less than 130% it was negligibly small. Curves showing the decay of tension at constant extension, and the recovery of length after stretching, in conjunction with the observations on plastic flow, are interpreted in terms of a theory proposed by Busse, according to which the rubber molecules are held together at certain points by cohesional linkages of low energy, some of which are broken down during stretching.
A Study of Polymers. III. Technique of Mechanical Tests of Vulcanizates of Rubber and Plastics
Authors: Gurevich G. I. , Kobeko P. P.
Published: February 2011

1. From the point of view of mechanical properties, the special attributes of highly polymeric substances, including rubber vulcanizates, are clearly defined by their reversible highly elastic deformation as a function of time. The time required for attaining this deformation within a given interval of time varies practically from zero to infinity. 2. Disregard of the temperature and time relation of deformation of highly polymeric substances leads to erroneous conclusions regarding their industrial working properties, and is the cause of the unsatisfactory results obtained by conventional methods of investigation. 3. The effect of increased degree of vulcanization on the mechanical properties of rubber is manifest in a decrease in complete elastic deformation and shift of the temperature-apparent modulus (inverse to the deformation in a given time) curve toward higher temperatures. 4. Conventional ideas of the plastic (irreversible) and elastic deformation of solid materials, when applied to highly polymeric substances without concern for the laws governing their deformation, lead to erroneous conclusions regarding the existence of specific properties of individual substances, e.g., ebonite and synthetic resins, and mistaken hypotheses regarding structural changes during their deformation. In the present communication, this is illustrated by studies of various investigators. 5. Conventional methods of studying thermal stability and brittleness, as well as other methods of testing, of highly polymeric substances frequently do not make it possible to evaluate the actual technical utility of materials within intervals of temperature encountered in service and they should be critically reëxamined with regard to the relations between deformation and reversibility, time and temperature.
Swelling of Synthetic Rubbers in Mineral Oils. Effect of Variation in Aniline Point of Oils
Authors: Carman F. H. , Powers P. O. , Robinson H. A.
Published: February 2011

1. There is a marked difference in the swelling caused by different mineral oils on compounds made of any synthetic rubber, such as Neoprene, Thiokol, or Perbunan; the arrangement of the oils by swelling effect tends to remain the same for the synthetic compounds tested. 2. The change in volume is rapid on initial immersion and then gradually approaches equilibrium, except in the case of those systems where marked swelling is encountered. 3. The aniline point, determined at a concentration of equal parts of aniline and oil by weight, appears to be a characteristic of mineral oil which will indicate the probable swelling effect on synthetic rubber compounds. The 50 per cent aniline point is more conveniently determined than is the gravity index, and appears to be at least equally reliable. 4. The viscosity rating of a mineral oil is not a satisfactory criterion of its tendency to swell rubberlike compositions, and should not be the sole description of an oil for acceptance specification testing of synthetic rubber products.
Effect of Operating Conditions on the Life of Rubber Belts
Authors: Perin R. J.
Published: February 2011

The variation in life of rubber belting has been a major technical problem of the rubber industry for many years. Although rubber compounds have been greatly improved, both in flexing life and aging properties, the life of belts on certain types of drives has not increased accordingly. To determine the cause of this variation, a survey was made of the performance records of belts on all types of drives. From this survey it was possible to obtain data on those drives wherein the belt life fell below the average expectancy. An analysis of this information divided these premature failures into two groups, which were designated as “external” and “internal”. The former classification includes failures due to excessive slip, high temperatures, misalignment and other detrimental operating conditions. The latter group includes those failures with no signs of external damage, and where failure involves that common condition, internal separation of the plies. A further examination of the reports on internal failures showed that practically all the drives concerned had one or more of the following characteristics: small pulley diameters, high belt tension, or high belt speed. The problem then resolved into a determination of the relative effect of these conditions on belt life.
Application of the Langmuir trough to the Study of Rubber Latex
Authors: Wren W. G.
Published: February 2011

When a drop of ammoniated latex is allowed to touch a cleaned water surface, it spreads rapidly and evenly at the air-water interface, none entering the bulk of the water. Microscopic examination of such a film shows that, given sufficient spreading area, the latex globules are clearly separate one from another, and form a layer one particle thick. On reducing the area occupied by the globules by compressing the film between waxed glass straight edges lying in the surface of the water, the particles are forced together until visible spaces or voids disappear. The film still appears to be one particle thick, and remains in the surface of the water. Further compression results in irregularities of the surface, which can be seen to consist of folds in the film and, on expansion, a proportion of the latex globules is found to have been forced from the surface into the bulk of the water. If a dilute solution of certain substances is used in place of water, the latex particles all remain on the surface, even under conditions of high compression. Dilute acids and solutions of divalent metal salts are found to be effective in keeping the particles in the surface but, on compression to the point where close packing of the particles occurs, the film sometimes forms a continuous coagulum and on release of the pressure, it does not expand. Solutions of a creaming agent, such as 0.1 per cent sodium alginate (Manucol V), are adequate, not only to prevent particles being forced out of the surface, but also to give films which expand readily on release of the pressure. The fact that the latex is instantly swept to one side by a trace of surface active material, such as oleic acid, confirms that the particles have not penetrated into the interior of the water.
Electrical Resistivity of Rubber Compounds
Authors: Robinson J. G.
Published: February 2011

By means of a new technique for the determination of volume resistivity, the effect of compounding variations in a basic mixing containing about 80 per cent volume of rubber was investigated, with the following outstanding results: (1) Above a certain limiting concentration, substitution of zinc oxide for French chalk gave decreased resistivity. (2) Resistivity increased progressively with increase of stearic acid concentration. (3) Of the three antioxidants examined, two had little effect on resistivity, one produced a decrease. (4) The six accelerators examined produced large differences in resistivity; thus, mercaptobenzothiazole gave values of the order of five times that of diphenylguanidine. (5) Increase in accelerator concentration gave decreased resistivity. (6) The variation of resistivity with time of cure depended on the compound under investigation. The usual behavior was an increase with increased curing time, followed in some cases by a decrease. This is the same type of behavior which is shown by tensile strength, but no general connection could be traced between the development of tensile strength and of resistivity.
The Heat Conductivity of Rubber at Low Temperatures
Authors: Schallamach Adolf
Published: February 2011

The experimental evidence points to the fact that a transition of some kind takes place at about 210° K, which, however, in consequence of supercooling, may take effect at a considerably lower temperature. As is mentioned in the Introduction, there is other evidence of such a transition. The thin curve in Figure 2, which is taken from the paper of Bekkedahl and Matheson, gives the specific heat of amorphous rubber. A sudden rise of this quantity occurs just below 200° K, and we feel sure that this near coincidence is more than accidental. The temperature lag between the two may be accounted for by the fact that Bekkedahl and Matheson worked with pure rubber hydrocarbon, whereas the material used for our investigation was vulcanized rubber. Bekkedahl's experiments on the temperature-volume relationship of various kinds of rubber showed that this transition is shifted towards higher temperatures when the rubber has been vulcanized.
Electrically Conducting Neoprene and Rubber
Authors: Habgood B. J. , Waring J. R. S.
Published: February 2011

(1) The scattered references in the literature dealing with conducting rubber have been collected together. (2) A résumé of existing ideas on the mechanism of electrical conduction is given, from which certain lines of development work suggested themselves. (3) Electrically conducting Neoprene or rubber compounds based on acetylene black are anisotropic, an effect which is particularly pronounced after extrusion. (4) By the use of fine channel black, either alone or in addition to acetylene black, the transverse conductivity is improved, thus reducing the anisotropy. (5) A further improvement can be obtained by using highly plasticized Neoprene or rubber which reduces the shear during extrusion operations. In the case of Neoprene, zinc oxide is omitted from the mixings to prevent set-up. (6) Conducting tubes having a transverse volume resistivity of 300 ohms per cu. cm., and a longitudinal resistivity of 60 to 70 ohms per cu. cm. have been obtained, using a potential difference of 6 volts. (7) Provisional methods of testing conducting rubber are suggested.
A Method for the Testing of Adhesive Tape
Authors: Geer William C. , Wescott W. Burton
Published: February 2011

The authors performed several thousand tests upon adhesives of different compositions, manufactured under excellent controlled factory conditions and carried upon backs of a variety of constructions. One conclusion was clear, which is included here even though this particular paper is devoted largely to a description of the test procedure alone. This is that other things being the same (paper or cloth of the same construction, methods of manufacture, and so on) each adhesive, when tested as described, gives a curve which is characteristic of its composition.
Fractionation and Molecular Weight of Rubber and Gutta-Percha
Authors: Kemp A. R. , Peters H.
Published: February 2011

1. Evaporated latex films and Bolivian fine para contain a chloroform-soluble fraction of about 62 per cent, whereas the soluble portion of crepe and smoked sheets is about 86 per cent. The average molecular weight of these sols, which contain the low polymers and “resin”, range from about 130,000 to 180,000, the more soluble type having the lower value. 2. Diffusion and precipitation methods were employed to fractionate R. C. M. A. crepe, and the following data indicate the approximate composition and molecular weight range of the soluble hydrocarbon fractions separated: 3. The chloroform-insoluble portion of crepe contains a nonlinear type of hydrocarbon, judged by x-ray and viscosity studies. These methods show that the chloroform-insoluble portion of ammonia-preserved latex films contain extremely high-molecular rubber hydrocarbon which is easily oriented to give the regular x-ray crystalline pattern for rubber. 4. Freshly tapped latex contains a large proportion of petroleum-ether-soluble fraction, which becomes insoluble in this solvent on standing in the presence of ammonia. Ammonia-preserved latex films are soluble in chloroform or in hexane containing alcohol-acetone or acetic acid; this insolubility is thus an association effect, which is overcome by the addition of a polar solvent. 5. Viscosity studies on fractions of balata and gutta-percha show that their hydrocarbons have an average molecular weight of about 42,000 and cover a narrow polymeric range.
The Molecular Weights of Rubber and Related Materials: I. Experimental Methods
Authors: Gee G.
Published: February 2011

The osmotic molecular weight of crepe has been measured in several solvents. It is shown that the use of a poor solvent, or a mixture of solvent and precipitant, gives solutions which approach ideal osmotic behavior. Benzene containing 150 cc. of methanol per liter is the best solvent examined, 1 per cent solutions of crepe being almost ideal. Viscosity data are employed to calculate absolute weight average molecular weights, the Staudinger constant being determined by comparison with ultracentrifuge data. Constants are listed for a number of solvents, and shown to vary only by a small factor. The osmotic and viscosity molecular weights of a number of rubbers are compared; the two values agree for three rubber fractions, while for unfractionated materials the viscosity average is the higher. Non-uniformity coefficients are calculated from the ratio of the two molecular weights. The molecular weight of sol rubber is higher than that of gel, showing that the sol-gel separation does not arise from molecular weight difference. The Staudinger law is shown to hold for rubber solutions at least over the molecular weight range 350,000–60,000, and probably very much further.
Viscosity-Molecular Weight of Rubber. Cryoscopic Deviation of Rubber Solutions from Raoult's Law
Authors: Kemp A. R. , Peters H.
Published: February 2011

1. The cryoscopic method is not satisfactory for polyprenes with chain lengths much greater than about 20 isoprene units on account of the failure of their solutions to obey Raoult's law. 2. Since Staudinger's viscosity-molecular weight constants were in many cases determined on nonideal solutions, this subject will be further investigated. 3. The present work has led to the selection of a Kcm value of 0.75 × 104, which is 25 per cent lower that the value chosen by Staudinger, who used higher polymers which do not behave ideally in solution. 4. The use of Staudinger's equation, M=ηsp/CKm, leads to large deviations with the variations in viscosity usually employed, and this deviation is largely avoided by employing the equation M=(log ηr/C)Kcm.
Oxidation of Unvulcanized Rubber in Light
Authors: Blake J. T. , Bruce P. L.
Published: February 2011

When unvulcanized rubber is exposed to light in the presence of air, it develops a tackiness which may proceed far enough to cause partial liquefaction of the rubber. The nature and intensity of the light is unimportant, although the rate is affected. The action is oxidation, and is accompanied in many cases by peroxide formation and a Russell effect. This production of tackiness under the influence of light is susceptible to the action of organic catalysts, both positive and negative. Many materials used regularly as antioxidants in vulcanized rubber are active agents in the development of tackiness. A number of other materials effectively retard the development of tackiness. In many cases they suppress completely the positive action of these commercial antioxidants. Antioxidants appear, therefore, capable of playing a dual role—that of assisting rubber oxidation under some circumstances and that of retarding oxidation under others. This paper describes a method and apparatus for the quantitative study of the rate of oxidation of raw rubber. In the previous paper the tackiness of the raw rubber was of necessity judged wholly by appearance and feeling. Although it increased with time of exposure to light, in many cases it decreased again after having reached a maximum. We assumed that this subsequent decrease in tackiness was due to additional oxidation, but there was no proof. There was also no evidence that the development of the same degree of tackiness in rubber containing different materials represented the same degree of oxidation.
The Isolation of Amino Acids from Rubber Latex
Authors: Whitby G. S. , Greenberg H.
Published: February 2011

The following amino acids are shown to occur in the serum of the latex of Hevea brasiliensis, all except the last having been actually isolated from it: tyrosine, l-leucine, d-iso-leucine, d-valine, d-arginine, l-aspartic acid, i-proline, and phenylalanine. A cursory examination of the amino-acid composition of the heat-coagulable protein of latex has been made. A tabular summary is given of the results obtained by various workers to date on the amino-acid composition of latex and latex proteins.
A Central Organization for Fundamental Research on Rubber
Authors: McPherson Archibald T.
Published: February 2011

Far-sighted leaders of the rubber industry have long recognized the need of more research on rubber, particularly research of a broad, fundamental character. Ambitious plans have been proposed from time to time for the sponsoring of such research by the rubber industry. The usual history of these plans is that they have been ably presented, discussed at length, and ultimately allowed to lapse. This paper, reviving the subject, is the outcome of a conversation with the forward-looking editor of India Rubber World, and is here presented at his suggestion in the hope that it may lead to new interest and ultimately to some tangible accomplishment. The present plan, which involves no essentially new or original features, is that a relatively small, but strong, central organization be created to undertake difficult, long-term, fundamental research on rubber and, at the same time, to promote research in universities and in industry by coöperation through the dissemination of information and by other means.