bluuebunny/crossref_metadata_2025 huggingface dataset:
Purified Rubber for Electrical Insulation
Authors: Kemp A. R.
Published: February 2011

THE water absorption and the dielectric stability of soft rubber insulating compounds under wet conditions is influenced by the kind of crude rubber employed. For most rubber-covered aerial and building wire where moisture conditions are not severe, the better grades of plantation rubber are satisfactory. However, for service involving immersion for long periods in fresh water, a need exists for rubber containing less nonhydrocarbon water-absorbing substances than the plantation product. This is particularly true when the insulating wall is thin and a high degree of electrical stability is required. Only recently has the preparation of such a type of purified rubber been given serious consideration on the plantations in the Far East. In the past, coöperation on such a problem with the plantation has been difficult, and for that and other reasons methods have been developed here for preparing this rubber in the factory. The purpose of this paper is to discuss the nature and role of protein and other substances found in Hevea rubber and to outline various methods for purifying rubber. Data are presented on the composition and properties of the resulting products.
Examination of Rubber Latex and Rubber Latex Compounds. I. Physical Testing Methods
Authors: Jordan H. F. , Brass P. D. , Roe C. P.
Published: February 2011

PRECISE control is essential to the successful operation of any commercial process, particularly of those processes involving the use of rubber latex. Latex is, of course, a complex natural product; it contains a variety of nonrubber constituents, such as proteins, soaps, and others which control or influence its colloidal properties. In order to ensure uniform behavior of latex in process, it is obviously desirable to test its uniformity as a raw product. It is furthermore important that such tests should be, wherever possible, fundamentally sound and free from the personal equation. Unless the results can be expressed in basic fundamental units, which are independent of the apparatus used and of the operator, confusion will result. It is the purpose of this paper to review critically the more important general physical tests and methods of analysis which can be applied to latex, particularly from the standpoint of accuracy and sources of error, and to recommend certain procedures on the basis of commercial experience in the authors' control laboratories. Some of the recommended methods have been developed in these laboratories, while others have been improved over procedures given in earlier works on latex (3, 6, 9). Part I is concerned with physical tests such as pH, surface tension, viscosity, and mechanical stability, while Part II is concerned with analytical methods.
The Preservation of Latex by Acids
Authors: Rhodes Edgar , Sekar K. C.
Published: February 2011

It is shown that by the application to field latex of amounts of formic acid of the order of 9 per cent by weight of the latex or 10 per cent by volume of the 90 per cent commercial acid, a product results which will retain its fluidity for long periods. It is, however, apparently micro-flocculated, and unstable. Because of their instability, it seems unlikely that acid latices of this kind will find technical applications. The findings are in no way contradictory to those of Fullerton, whose experiments on coagulation did not include trials with such large amounts of acid. It is regretted that fuller experimental data cannot be given because most of the relevant records were destroyed recently by fire at the Institute. It is probable that a further study will be made, from which additional experimental data together with a possible explanation of the empirical observations given here may emerge.
Contributions to the Analysis of Rubber. II. The Qualitative Determination of the Serum Components of Raw Rubber and of Vulcanized Rubber
Authors: Dekker P.
Published: February 2011

The use of latex in the rubber industry has been increasing to a considerable extent, and in many cases where formerly solutions of ordinary plantation rubber were used exclusively, e. g., for impregnating fibres, spreading and adhering textiles, and manufacturing dipped goods, latex mixtures are now employed. Then again there is increasing interest in rubber prepared by evaporation or spraying of latex, especially for the production of powdered rubber. Consequently the time has come, as is evident from recent publications, when it may be an important problem whether in the preparation of a rubber mixture it is best to use ordinary plantation rubber, latex, or, perhaps, evaporated latex. Now the peculiarity of a rubber mixture prepared from latex or from evaporated latex is its relatively high precentage of serum substances from the latex. In the first Communication on the present subject, which dealt with the “Determination of the Water-Soluble Components of Rubber,” a method was described for determining the serum substances in vulcanized rubber. In view of the fact that with technical rubber mixtures, and in the presence of zinc, calcium, and magnesium compounds, this method is complicated and tedious, the present experiments were carried out with an aim to developing a procedure for determining qualitatively the serum substances. A method of this kind must naturally be restricted to the identification of some substance which originates in the serum and not in the curvatives or other compounding ingredients. Among the various substances which are present in latex serum, 1-methylinositol is one of the most important, and rubber mixtures prepared from latex or from evaporated latex contain a notable quantity of this substance. Consequently proof of the existence of 1-methylinositol in a mixture should be evidence of the presence of serum substances. The investigation to be described was therefore confined to the development of a characteristic reaction of 1-methylinositol.
Studies in the Vulcanization of Rubber. VII. Unsaturation of Rubber Vulcanized with Nitro Compounds and Benzoyl Peroxide
Authors: Blake John T. , Bruce Phillip L.
Published: February 2011

RUBBER is primarily an unsaturated hydrocarbon. Sulfur adds to its double bonds during vulcanization to form soft and hard vulcanizates. In the formation of soft vulcanized rubber, unsaturation is reduced several per cent by the chemical addition of sulfur. Spence and Scott (10) showed that the proportion of combined sulfur corresponds exactly to the decrease in unsaturation, and therefore that sulfur combination consists entirely of addition to the double bonds of rubber. The studies of one of the authors (1) on the vulcanization of rubber with nitro compounds indicate that these substances or their decomposition products combine with rubber. Van Rossem (8) also showed that vulcanization with benzoyl peroxide is accompanied by a decrease in extractable material, indicating that either the reagent or its decomposition products combine chemically with the rubber. The natural expectation would be that addition to the double bonds occurs and that the unsaturation decreases correspondingly. Van Rossem's proposed mechanism for the vulcanization with benzoyl peroxide would involve no change in unsaturation. Fisher and Gray (2) applied Kemp's method (4) in determining the iodine numbers of a single vulcanizate of each of four compounds. The vulcanizing agents involved were m-dinitrobenzene, trinitrotoluene, and benzoyl peroxide. Their unsaturation values agreed closely with calculated values for the unvulcanized compounds. They concluded from their results that “Ordinary vulcanization is an unknown or undetermined type of change in the hydrocarbon involving no change in the unsaturation and that chemical union of sulfur is a secondary reaction.” If true, this evidence is a serious blow to the chemical theory of vulcanization which postulates that a chemical reaction is essential for the process. The present paper offers evidence that the vulcanization of rubber with these reagents does involve change in its unsaturation.
Natural and Synthetic Rubber. VIII. Products of the Destructive Distillation of Sodium Rubber
Authors: Midgley Thomas , Henne A. L. , Shepard A. F.
Published: February 2011

The pyrolysis products of sodium rubber have been compared with those of natural rubber. They indicate that sodium rubber is isomeric with natural rubber in the positioning of its methyl groups, and that the double bond of sodium rubber differs from the true ethylenic bond of natural rubber. In the latter respect sodium rubber closely resembles overvulcanized rubber.
Crystalline Rubber Hydrocarbon
Authors: Washburn E. W.
Published: February 2011

Substantially all of the chemical and physical evidence concerning the nature of rubber is consistent with the chemical formula (C5H8)x, and this is the generally accepted formula for “rubber hydrocarbon.” An examination of the evidence discloses, however, that the above formula is not the only one which is consistent with this evidence. The difficulty of establishing beyond question the chemical composition of “rubber hydrocarbon” has been due largely to the lack of efficient physical methods for fractionating the “hydrocarbon,” of proving that the final fractions are one-component systems, and of chemically identifying these fractions. If, as seems not improbable, “rubber hydrocarbon” is a mixture of closely related hydrocarbons, not all of which can be represented by the formula (C5H8)x, no single method of fractionation can be relied upon to separate this mixture into its constituents. The only methods heretofore available for this purpose have been those based upon extraction with different liquids and fractional precipitation. One of the most powerful methods for fractionating a mixture of this character is systematic crystallization, and a laboratory technic for applying this method to “rubber hydrocarbon” has recently been developed at this Bureau. The conditions which must be met in order to induce crystallization in such a typically colloidal material as rubber can be predicted. These conditions have been met and are embodied in the following procedure.
Isoprene and Rubber. Part 30. Hydromethylrubber
Authors: Staudinger H. , Brunner M. , Geiger E.
Published: February 2011

When rubber is reduced at 270° under high pressure, a hemi-colloidal hydrorubber is obtained, and it was proved by Geiger and Huber that the product has a higher molecular weight and is less cyclicized if a good catalyst is used in large quantity (for example, active nickel produced by the method of Kelber), while according to the original experiments of Fritschi, who carried out the hydrogenation in the presence of very little platinum, a more degraded and somewhat cyclicized hydrorubber is obtained. The saturated hydrorubber is much more stable than the unsaturated rubber since the loosening action of the double bonds is lacking. A hydrorubber of the average molecular weight of 10,000 is still relatively stable at 270°, while a hemi-colloidal rubber with this molecular weight will he cracked to still smaller fragments at this temperature, and these fragments are then changed by cyclicization. This behavior can be clearly seen in methylrubber. The following reduction proves that it is even more easily decomposed than rubber itself. With nickel as catalyst, Geiger obtained from methylrubber by reduction at 270° and 100 atmospheres a hemi-colloidal hydromethylrubber which had an average molecular weight of 1600 and therefore had a degree of polymerization of about 20. If rubber is reduced under the same conditions a higher molecular product is obtained with an average molecular weight of 3000 to 10,000. Judged by reduction experiments, the chain of butadiene rubber is still more stable, since the hydrobutadiene rubber prepared under the same conditions had the highest average molecular weight. The cleavage of the chains, as in the following formula, is therefore favored by the methyl groups:
Temperature Coefficient of Vulcanization. Determination for Mixes Accelerated with Mercaptobenzothiazole and a Crotonaldehyde-Aniline Condensation Product
Authors: Park C. R. , Maxwell R. B.
Published: February 2011

1. The average temperature coefficient of mercaptobenzothiazole accelerated mixes, based upon physical data, was found to be 1.91 per 10° C. For crotonaldehyde-aniline, the value was 2.32 per 10° C. 2. Based upon combined sulfur data, the value was 2.30 (average) per 10° C., and for crotonaldehyde-aniline 2.67 per 10° C. 3. The values obtained from physical data are to be preferred for all practical purposes.
Measurement of Average Particle Size of Fine Pigments
Authors: Gehman S. D. , Morris T. C.
Published: February 2011

A method of obtaining excellently dispersed suspensions of rubber pigments of accurate concentration is described in which the pigment is milled into rubber and the stock then dissolved in a solvent. The average particle sizes of carbon blacks measured by the Zsigmondy count method were found to range from 0.061μ for rubber gas black to 2.22μ for the coarsest one measured. The zinc oxide pigments had average particle sizes from 0.076μ to 0.57μ.. Measurements on several other pigments of interest are included. Because of the high visibility in the ultra-microscope, this method gives smaller values for average particle size than the photomicrographic methods. The results have been used to calibrate a microturbidimeter of the extinction type for use in measuring average particle size. Curves are included showing how the turbidities of suspensions of zinc oxide and carbon black vary with the average particle size, concentration, and wave length of light used.
Vulcanization with Benzoyl Peroxide. I. Contribution to the Knowledge of the Vulcanization Process
Authors: van Rossem A. , Dekker P. , Prawirodipoero R. S.
Published: February 2011

Three-quarters of a century have passed since the discovery of the vulcanization process by Charles Goodyear, Thomas Hancock, and Alexander Parks without the discovery of an essentially new process of vulcanization. In 1915 Ostromislenski reported the discovery of two new methods of vulcanization, namely, vulcanization with nitrocompounds and vulcanization with peroxides and peracids like benzoyl peroxide. Ostromislenski was of the opinion that vulcanization is a process which can be divided into two distinct phases, “Thus we arrive at the conclusion that the vulcanization of caoutchouc is divided sharply into two fundamental phases: 1, a chemical reaction affecting only an insignificant part of the caoutchouc and, 2, adsorption or swelling of the unchanged caoutchouc into the product of this chemical reaction.” a concept which was developed by van Iterson, Jr., in somewhat different form as a working hypothesis for the vulcanization process. It is noteworthy that only in 1929 did Ostromislenski publish a second communication on vulcanization with benzoyl peroxide, even then without offering any new theoretical points.
The Cause of Variability in the Plasticity of Plantation Rubber after Storage
Authors: Martin G. , Elliott L. E.
Published: February 2011

There are two reasons why a study of the plasticity of rubber is of importance to the planter, viz.: (1) the variable plasticity of plantation rubber leads to many difficulties in manufacturing operations; and (2) first-grade plantation rubber is so hard that it is frequently mixed with inferior grades and other materials to enable it to pass more easily through the different processes. The results of the investigations recorded in this report suggest a definite reason for the hardness and variability of first-grade rubber. Tests carried out by De Vries in Java showed: (1) that freshly prepared plantation rubber is uniform in plasticity, but that many samples gradually become hard or soft on keeping and so develop differences; and (2) that rubber containing more serum substances than usual becomes hard, and that containing less than usual becomes soft. On the other hand, tests carried out by the Scheme on a large number of samples for over three years show that in most cases rubber becomes harder on keeping for six months at 15° C. The hardening of the rubber at European temperatures has been confirmed by Griffiths of the Dunlop Rubber Co., Ltd., who stated that large-scale experiments on rubber from different estates showed that in all cases, after storage for three years, it was necessary to increase the time of milling by about 30 per cent in order to obtain the required plasticity.
The State of Rubber in Solutions, Based on the Surface Properties of the Solutions
Authors: Dogadkin B. , Pantschenkow G.
Published: February 2011

The problem of the constitution of rubber and especially of its state in solutions has recently again become the subject of active discussion. Based on a series of investigations, Staudinger reached the conclusion that dilute solutions contain free colloidal rubber molecules which are composed of closed chains of an unusually large number of isoprene residues. Pummerer considers the molecular weight of rubber to be much less than does Staudinger. (According to Staudinger the molecular weight of rubber is 50,000 to 170,000; according to Pummerer it is 1200 to 1600.) Meyer and Mark assume for the primary valence chain of rubber a molecular weight of about 5000. These latter investigators are of the opinion that there are secondary aggregates of rubber molecules in a rubber solution and that the high values which were found by a number of investigators (Caspari, Kroepelin, and others) do not represent the molecular weight but the average micellar weight of rubber. In deciding the question of the state of rubber in solution the majority of investigators make use of the classic cryoscopic and osmotic methods of investigation. Staudinger has used viscosimetric measurements in an original way in his experiments. In the present work we have turned to a study of the surface properties of rubber solutions, assuming that data along this line might explain some peculiarities in the structure of these solutions.
Rubber Solutions
Authors: Stamberger Paul
Published: February 2011

In my earlier publications the hypothesis was suggested that rubber is a homogeneous substance and not a mixture of homologous polymers. This hypothesis has been criticized from many sides. My conclusions were based on the fact that the diminution of the vapor pressure and of the osmotic pressure of rubber solutions is independent of the origin of the rubber and of the treatment it receives. With regard to the discussion of the objections which have been made, I have obtained evidence that this hypothesis is also supported by other quantitative measurements of the state of equilibrium, e. g., the specific heat. In the course of this discussion, Bary questioned the basic theory by which I arrived at this conclusion when the incompatibility of the Raoult law has been established. Kroepelin calls attention to the fact that, in concentrated swollen substances, molecular groups and not molecules are united with the solvent. In the case of rubber these have double bonds. I do not know any reason that can justify this conclusion of Kroepelin. The investigations which I have undertaken on more dilute solutions do not support such a theory. A little later I shall go into more detail about Bary's comment.
The Reënforcement of Rubber
Authors: Antonoff G.
Published: February 2011

It is a well-known fact that, when mixed in rubber, certain powders reënforce the latter to a considerable extent, whereas others have no effect or only a relatively slight one. Since the nature of the phenomena which take place under these conditions in rubber is far from well established in the present state of knowledge, I have carried out certain experiments of a very simple kind which will by analogy throw some light on the subject. I have found that very important information can be obtained from the study of some physical properties of mixtures of different powders in organic liquids. For a beginning, ordinary paints were tested, but the presence of drying oils complicated matters and it was found advantageous to replace the linseed oil with a non-oxidizing oil, as for example, peanut oil. In this way, pastes of different concentrations were prepared, and the resistance to rupture of the films of these pastes was measured by a method often used to determine the surface tension of liquids. A convenient method of operation is as follows: two thin rods are wet with the paste and are made to adhere to one another. The upper rod A is fastened permanently in a way not shown in Fig. 1. From rod B hangs a pan for small weights which, added in convenient quantity, will finally bring about rupture of the film and separation of the two rods.
Experiments on the Autoöxidation of Rubber and the Catalytic Phenomena Which Are Associated with It
Authors: Dufraisse Charles , Drisch Nicolas
Published: February 2011

This first series of experiments was aimed to establish the value of the method of study which is described, and to indicate its applications. Furthermore, we were less interested in going deeply into the various problems considered than to show by the various examples the convenience and the precision of our method. There still remains the problem of determining the relation between autcöxidation observed in this way and true aging by ordinary methods. This will be a task for the future. However, as far as we have gone in this work, a satisfactory parallelism has often been found between our data and that already obtained by the usual methods. Although we have not made a detailed study of some of the results, we have been led to a certain number of concrete conclusions in the course of the study. Two of them are worthy of being mentioned. One concerns the variation of the action of every catalyst of autoöxidation, the other the future of methods of protection. Moureu and Dufraisse have already emphasized the sensitivity of autoöxidation catalysts to the slightest influences, and this is again confirmed in the case of rubber. Consequently, a catalyst, whatever may be its properties, should not be classified as a good antioxygen in general. It should receive this qualification only for precise conditions where its efficacy has been effectively controlled, because its influence is subject to variations which may extend as far as a change in the sign, oxidation then being accelerated instead of retarded. In regard to the future of the protection of rubber, it is easy to predict from what has been found for other oxidizable substances. Remarkable progress has already been made in the industrial use of antioxygens. Instead of continuing to evaluate them by certain units, the coefficient of protection should be calculated by powers of 10, as with so many other substances. In that case, rubber, at last really stabilized, would find vast markets opened up in which it cannot be used at present on account of its instability.
The Determination of Free Sulfur in Soft Vulcanized Rubber by a Volumetric Method
Authors: Guppy W. D.
Published: February 2011

The methods so far proposed for the determination of the free sulfur in vulcanized rubber depend upon the removal of the sulfur by extraction of the rubber with hot acetone, and subsequent oxidation to sulfuric acid of the sulfur in the extract. The extract is liable however to contain, in addition to sulfur in the elementary state, organic compounds containing sulfur derived from the rubber resins, accelerator, or antioxidant. In the subsequent oxidation this sulfur will be oxidized to sulfuric acid to an extent which depends on the method of oxidation used. In the present work, a method of analysis has been developed which is more rapid than the existing methods, and in which it is considered that the determination of the sulfur present in the elementary state is less likely to be affected by organic compounds containing sulfur. It has been found that when vulcanized rubber placed in contact with a metal, such as tin or aluminum, is boiled in hydrochloric acid, hydrogen sulfide is generated by the action of the nascent hydrogen produced. This reaction occurred with rubber which had been previously treated with acid alone to decompose metallic sulfides, but no hydrogen sulfide was obtained from rubber which had been previously extracted with acetone and was free from metallic sulfides. As these results showed that the reactions were not due to the presence of mineral sulfides, or of sulfur combined with the rubber, it was concluded that the hydrogen sulfide was formed by the reduction of the free sulfur.
Natural and Synthetic Rubber. X. Constituents of the Rubber Hydrocarbon
Authors: Midgley Thomas , Henne Albert L. , Renoll Mary W.
Published: February 2011

1. Fractional precipitation has been used to determine and isolate the constituents of the rubber hydrocarbon. 2. A “standard precipitation point” has been devised and its use advanced as a physical constant of rubber. 3. The presence of a single component, amounting to more than 50% and characterized by a standard precipitation point of 35°, has been demonstrated. 4. The presence of highly soluble portions, of indeterminate s. p. p., has been shown.
Studies of Polymers and Polymerization. IV. Observations on the Polymerization of Isoprene and 2,3-Dimethylbutadiene-1,3
Authors: Whitby George Stafford , Crozier Robert Nelson
Published: February 2011

The polymerization of isoprene and dimethylbutadiene at temperatures ranging from 10° to 145° C. has been studied with reference to the nature of the dimeric products and the influence of the temperature and period of heating on the extent of polymerization, the ratio of oil to rubber and the molecular weight of the rubber and viscosity of its sols. There was no evidence of the formation from either diene of an open-chain dimer, polymerizable to rubber, such as the “β-myrcene” of Ostromislenski. The ratio of oil: rubber from a given diene is approximately constant in different periods of polymerization at a given temperature. The ratio increases with rise of temperature. Isoprene gives far more oily by-product than does dimethylbutadiene. As polymerization progresses, the molecular weight of the rubber and the viscosity of its sols rises. The higher the temperature of polymerization, the lower is the molecular weight ultimately attained. The polymerization is catalyzed by air. The viscosity of the sols of the synthetic rubbers is low and falls on keeping, owing to oxidation.
Isoprene and Rubber. Part 37. Homologous Polypranes
Authors: Staudinger H. , Leupold E. O.
Published: February 2011

According to investigations by Staudinger and Fritschi the hydrorubber obtained by the catalytic reduction of rubber at 270° is a high molecular paraffin hydrocarbon. Concurrently with this work, Pummerer and Burkard were occupied with the reduction of rubber. They describe hydrorubber as an autoöxidizable substance, an observation which has been shown to be incorrect. According to Pummerer and Koch, hydrorubber can be distilled in high vacuo without decomposition, and is a highly viscous oil having the composition (C5H10)10. The hydrorubber obtained in this way is, however, according to experiments by Staudinger and Schaal highly decomposed by cracking. Our concept of the constitution of hydrorubber and the products obtained from it by cracking is again confirmed by the preparation by Karrer, Stoll, and Stevens of two high molecular hydrocarbons with numerous methyl side chains. Like octomethyldotriacontane (G40H82) recently prepared by Karrer, hexahydrosqualene (C30H62)9 and tetramethylhexadecane (C20H42) prepared by Fischer, these new hydrocarbons are to be regarded as lower members of the series of paraffins with branched chains, whose end members are hydrorubbers. Accordingly, in this series of hydrocarbons (the polypranes), representatives from the lowest member, isopentane C5H12, to the highest member, a hydrobalata having the composition ((C5H10)700 and a molecular weight of about 50,000 are known.
The Vulcanization of Rubber in Concentrated Solution in the Presence of Ultra-Accelerators
Authors: Bourbon A.
Published: February 2011

The appearance of an article by Thiollet on the formation of jellies in rubber solutions containing rapid accelerators (Revue Générale du Caoutchouc, Vol. 9, No. 79, 5–9 (1932); Rubber Chemistry & Technology, 5, 296–300 (1932)) has suggested the publication of the present paper, which deals with experiments in the same field. In 1927 the author was occupied in studying the vulcanization of thick solutions of rubber containing ultra-accelerators. On account of lack of time this investigation was never carried as far as was desired, therefore the results may appear to be incomplete and the conclusions may seem a little bold because of a certain lack of precision. The object was to study the rate of vulcanization of these solutions as a function of their concentration. For this reason the effect of a series of solvents under the same conditions was studied, and in this respect the work resembles that of Thiollet. A similar investigation had been made earlier by Boiry (Caoutchouc & gutta-percha, 21, 12257–62, 12293–37, 12335–41, 12386–89, 12454–60 (1924); 22, 12507–509 (1925); India Rubber J., 68, 651–54, 687–89, 727–31, 771–73, 807–808 (1924)), but his work was concerned only with dilute solutions, containing at the most 5 grams of rubber for 100 cubic centimeters of toluene. The present work was under different conditions.
Effect of Overmilling on Compounded Rubber
Authors: Wiegand W. B.
Published: February 2011

The conviction seems more and more prevalent that the full reinforcing capabilities of fine pigments such as carbon black have not as yet been fully developed. A great deal of thought is therefore being devoted to the study of improved means of dispersion of such ingredients in rubber. The various conditions of grinding and the effect of dispersing agents are examples of the lines along which the modern study of this problem is progressing. This naturally leads to the question of what is happening to the rubber phase during the dispersion process. In other words, what damage, if any, will over-mastication do to the rubber quality? What influence do these conditions exert on aging behavior? What is the effect of mill opening during such mastication?
An Investigation of the Visco-elastic Properties of Rubber
Authors: Eccles J. C. , Thompson J. H. C.
Published: February 2011

An account is given of an investigation of the visco-elastic properties of rubber by means of observations on the damping of forced longitudinal vibrations. An attempt is made to determine the visco-elastic limits for rubber, as well as the normal visco-elastic constant τ and the coefficient of normal viscosity E′. The analysis of the experiment predicts the form of the photographic record of the damped vibrations, and gives an expression for τ in terms of the period of vibration and the logarithmic decrement of the amplitude per vibration. Two series of experiments are described in detail. In the first series, where catapult elastic was used, the experimental results are susceptible of detailed analysis. They agree with those predicted by the theory of visco-elasticity when the rate of strain does not exceed 0.1 per second. This is the upper visco-elastic limit. The lower visco-elastic limit for the rate of strain was not reached, so it must be less than 0.017 per second. The value obtained for τ is 28.7×10−4 seconds, and the corresponding value of E′ is 3.42×104 in c.g.s. units. In the second series of experiments pure black rubber was used, and a wider range of frequency of vibration and rate of strain was obtained. Also experiments were carried out at different mean tensions. The experimental results show signs of some unknown disturbance and are difficult to analyze. They suggest 6×10−4 seconds as a probable value Ä , and 0.78×104, for pure black rubber, with a rate of strain 0.1 per second as a probable upper visco-elastic limit (at a mean tension of 150 grams weight). The value of Ä at 300 grams mean tension does not differ significantly from that at 150 grams.
Photoelastic Properties of Soft, Vulcanized Rubber
Authors: Thibodeau Wilfred E. , McPherson Archibald T.
Published: February 2011

This paper describes an exploratory study of the photoelastic properties of transparent, soft, vulcanized rubber. The work was originally undertaken to obtain data on rubber samples that were used in an investigation of stresses in models by the photoelastic method, and was extended to provide general information on the relation of the photoelastic properties to the composition of rubber. Measurements of the photoelastic behavior of rubber have been made by several previous investigators, whose work points to a functional relation between double-refraction and stress. Bjerken made measurements on rubber of unspecified composition at stresses from 5 to 69 bars, which corresponded to elongations from 66 to 434 per cent. Rossi observed the behavior of three types of rubber compositions, (1) crude rubber, (2) the same mixed with oil and wax, and (3) rubber vulcanized with 15 per cent of sulfur and subsequently extracted with benzene. Rossi's measurements extended only to stresses of 5 to 7 bars, which corresponded to elongations of 50 to 100 per cent. The measurements of the coefficient of relative retardation by both Bjerken and Rossi, when plotted as functions of stress, give smooth curves which are either linear or nearly so. Van Geel and Eymers, however, working with sheets of rubber made by the evaporation of latex, obtained a discontinuous relation between relative retardation and stress. Other investigators have studied the double-refraction of rubber in relation to the structure. This latter work is summarized in a recent paper by Rowland.
Ether-Insoluble or Gel Rubber Hydrocarbon, Its Solution, Crystallization, and Properties
Authors: Smith W. Harold , Saylor Charles Proffer
Published: February 2011

A method of purifying and crystallizing ether-soluble rubber hydrocarbon was described in an earlier paper in this journal. The same procedure for purifying the hydrocarbon and separating it into two fractions was followed in the preparation of the insoluble or gel fraction, the properties of which are the subject of this paper. The method of purification was not merely another procedure for removing the impurities from rubber hydrocarbon, but, as stated in the earlier paper, it also “sought to maintain unchanged the structure of rubber hydrocarbon and to permit a sharp separation of the ether-soluble and insoluble fractions.” The latex which has been used was, in part, obtained from H. L. Fisher of the United States Rubber Co. Through the courtesy of the U. S. Department of Agriculture, latex has also been obtained direct from the plantation on the north shore of Haiti. Before the trees were tapped, the area surrounding the intended incision was carefully cleaned. After tapping commenced, the trees were tapped once each day, the latex from the first two tappings was rejected, and that obtained on the third day was put into clean glass bottles, which were filled completely after the addition of a little ammonia as stabilizer. The latex was immediately shipped to this Bureau and stored at a temperature maintained between 0° and 2° C.
The Restraining of Vulcanization in Rubber Manufacture
Authors: Twiss D. F. , Jones F. A.
Published: February 2011

Delayed-Action Accelerators During the past few years, considerable advance has been made in the ordinary method of compounding technic with respect to scorching. The advances fall essentially into two well-marked divisions, viz., the development of “delayed-action accelerators” and the addition of “vulcanization restrainers,” “inhibitors of prevulcanization,” or “antiscorch agents.” With a true delayed-action accelerator vulcanization should not occur until a certain period of time has elapsed, after which rapid vulcanization takes place. The existence of this “time lag” can be explained on the basis that the reputed accelerators are inactive, but on heating are decomposed into other substances which constitute the real accelerators. Some organic accelerators give a temperature lag, and though comparatively safe from prevulcanization in processing, they vulcanize only above a certain critical temperature. Hence, when the rubber mixture is heated, vulcanization does not take place until this temperature is attained. Such accelerators are not delayed-action accelerators in the narrower sense. In all organic accelerators the activity can be associated with a particular grouping, and in the simplest form of accelerator generally with a particular hydrogen atom. Most if not all delayed-action accelerators can be regarded as chemical derivatives of known powerful accelerators in which the place of the active hydrogen atom is occupied by a more or less easily displaceable organic grouping; the delayed-action accelerator is consequently often a compound, e. g., of the thio-ester or thio-ether (or even “thio-anhydride”) type, which itself strictly is not a vulcanization accelerator, but is capable of undergoing decomposition (e. g., “hydrolysis” or fission) with formation of one.
The Tensile Properties of Latex Products
Authors: Barron Harry
Published: February 2011

The rubber manufacturer of today is brought up in the tradition of facts and figures. The one without the other is useless. There can be no doubt that much of the present prosperity of the rubber industry is due to widespread benefits conferred by the publication of research work on rubber, and the standardization of production. The major discoveries in the recent history of rubber, such as the discovery of accelerators, the discovery of reinforcing action, and more recently the rediscovery of latex, have invariably followed a similar trend. The first activities in each case have been purely of a qualitative nature. After the frenzied rush to patent discoveries has subsided, everybody has settled down to find out the quantitative effects of the respective products when incorporated into rubber, subjected to the various rigorous processes normally employed. Careful research work has brought its reward, in so far as the scope of the respective products has widened, quality has improved, and costs have been very much reduced. In every case progress has been made on all sides, physical, chemical, and technical. In this respect latex is lopsided. It is a remarkable fact that at the present time, when latex appears to be more and more widely employed, manufacturers are not at all enthusiastic about it. They certainly are not falling over themselves to apply it. This is a matter that warrants investigation.
A Water Bath Having Submerged Individual Sample-Containers for the Accelerated Aging of Rubber in Air
Authors: Holt William L. , McPherson Archibald T.
Published: February 2011

Improved equipment for conducting the familiar Geer aging test on rubber has recently been installed at the National Bureau of Standards. This equipment consists of thermostatically controlled water baths in which small air ovens are submerged. Each oven serves for the accelerated aging of samples of a single composition, and thus avoids the possibility of contamination, which may be an important factor when samples of different compositions are aged in the same oven. The apparatus differs from that described recently by Milligan and Shaw in that individual sample containers are employed and air circulation is obtained by convection.
Manganese Salts in Plantation Rubber
Authors: Sackett G. A.
Published: February 2011

1. Abnormal amounts of manganese in crude rubber compounded in a gum type stock using mercaptobenzothiazole or diphenylguanidine result in lowered modulus and poorer age resistance. 2. The effects of abnormal amounts of manganese are not as evident in a rubber-sulfur stock as in stocks using an organic accelerator. 3. High-manganese rubber in a mercaptobenzothiazole tread stock gives lower modulus and the age resistance is poorer, but the effect is not as marked as in a gum stock. 4. Phenyl-β-naphthylamine in a gum or tread stock greatly improves the age resistance of a high-manganese rubber stock. 5. Rubber containing abnormally high percentages of manganese cannot always be detected by appearance; in order to avoid the bad effects of manganese in the vulcanized stocks, analysis of the crude rubber is necessary. 6. Because there is apparently no benefit to the crude rubber manufacturer through the use of manganese in any form, and because of the very bad effects on vulcanized stocks, every care should be exercised by the rubber producer to see that manganese salts are not introduced at any step in the process. 7. Rubber containing abnormally high percentages of manganese should not be used in high-quality stocks; when used, they should be blended with large proportions of normal rubber and used in a highly loaded stock containing an antioxidant.
The Elasticity of Rubber
Authors: Meyer Kurt H. , Ferri Cesare
Published: February 2011

In order to explain the elasticity of rubber, several authors assume that long chain molecules have a tendency to form spirals, and that when an external force displaces them from this state of equilibrium, they tend to return to it. These concepts lead in turn to two different points of view. 1. It may be assumed that there are forces of attraction between the different parts of a single molecule, for example, between the double bonds. Upon stretching, these forces of attraction are overcome. The free energy of the stretched thread thus consists of the potential energy of the molecular parts which have been separated from one another. 2. On the other hand, the molecule may be said to have a certain rigidity which, in its final analysis, depends upon the rigidity of the tetrahedric valences of carbon. In this case it is to be assumed that stretching brings about a deformation of the angles between these vectors. The first hypothesis has been developed by several authors. Recently Mack has assumed that there are forces of attraction between the hydrogen atoms in the rubber chains. He attributes the phenomena of elasticity to a mechanism of “evaporation and condensation of hydrogen.” None of these hypotheses explains the elastic properties which are found in substances such as elastic ligaments, and especially in elastic sulfur, which have a wholly different structure from that of rubber. Moreover these two hypotheses, which involve a change in the total potential energy, are incompatible with the fact that the tension of substances such as rubber, which are stretched and held at a constant length, increases with the temperature. Now a rise of temperature ought to diminish the work necessary to overcome on the one hand the forces of attraction and on the other hand the forces which keep the atoms in a position of established equilibrium. The result would be that the tension of a stretched rubber thread would diminish with an increase in temperature.
The Oxidation of Rubber by Hydrogen Peroxide
Authors: Kagan B. , Sukhareva N.
Published: February 2011

It was noticed long ago that rubber changes during storage, and that it loses its valuable qualities. Many authors have tried to explain this phenomenon as a union of oxygen with rubber molecules. The most interesting work on this subject was the early work of Herbst (Ber., 39, 523 (1906)). Herbst blew air for 140 hours through benzene solutions of rubber and obtained two products, C10H16O3, as a main product, and C10H16O, as a very small admixture. Later Peachey and Leon (J. Soc. Chem. Ind., 31, 1103 (1912); 37, 55 (1918)) subjected rubber films to the action of oxygen and found that for each group of C10H16, four atoms of oxygen were added and one atom of carbon was liberated. These workers succeeded in separating several compounds with different degrees of oxidation, viz., C10H16O; C10H16O 4; C6H9O 2. Herbst thought that he had obtained an addition product of oxygen and rubber hydrocarbon, but Peachey considered that the compounds were the result of a splitting and depolymerization of the rubber molecules. Boswell (India-Rubber J., 54, 981, 987 (1922)) and his students investigated the phenomenon of oxidation of rubber and obtained different oxidation products for each oxidizing agent. A solution of rubber in carbon tetrachloride oxidized by means of potassium permanganate in the absence of air (in carbon dioxide) gave a product of the formula, C25H40O, which in turn was readily oxidized in air to C30H48O2. Using 3% hydrogen peroxide as an oxidizing agent, Boswell obtained a product with the formula, C30H48O, which in turn was easily oxidized to C25H40O2.
The Mastication of Rubber
Authors: Behre J.
Published: February 2011

Probably from the beginning of the rubber industry no process has changed so little as that for softening raw rubber, its socalled mastication. Although Hancock's machine, the masticator (1826), consisted of an internal rotating roll and a stationary shell, and modern machines have two rotating rolls, the same principle has always held true, viz., a compression and consequent stretching of the rubber by means of great friction. Even enclosed mixers are essentially only a development of the Hancock principle, the value of which naturally will not be discussed here. In spite of such long experience, the process of mastication is not clearly understood, and it is remarkable that there has apparently been little interest in this problem until recently. Only within the last few years has it received somewhat more attention, and attention should be called to the work of Cotton, in which there is a compilation of the literature. As a result of this lack of knowledge, the conditions under which the most rational processes of mastication can be carried out have not been established, and even today the manufacturers of machines produce for the most part mills which have the most widely varying constants, without any satisfactory reasons for the particular constructions. The following discussion aims therefore to contribute toward the establishment of these conditions, and at the same time to view critically the various theories of the process of mastication. In this discussion plasticity values obtained by the method of Marzetti have been used as a measure of the degree of mastication since, as I have been able to show earlier and has recently been confirmed by others, these plasticity values approach most nearly to practical conditions.
Specific Volume, Compressibility, and Volume Thermal Expansivity of Rubber-Sulfur Compounds
Authors: Scott Arnold H.
Published: February 2011

The specific volume, compressibility, and volume thermal expansivity of rubber-sulfur compounds containing from 3 to 31 per cent of sulfur have been measured at pressures from 1 to 800 bars and at temperatures from 10° to 85° C. The results are expressed in tables, curves, and equations, so that within the indicated limits the value of any of the above properties can be readily determined for a compound of specified composition under specified conditions of temperature and pressure. Specific volume, which is the reciprocal of the density, has been used throughout this paper, because this term is the one which is used directly in the definitions of compressibility and volume thermal expansivity. The work of Kimura and Namikawa indicated that the specific volume of rubber-sulfur compounds at atmospheric pressure was a linear function of the temperature. The use of the specific volume thus leads to equations which are simpler than if the density is used.