bluuebunny/crossref_metadata_2025_split huggingface dataset:
Purified Natural Rubbers. Mechanical Aging, Hygroscopic, and Electrical Properties of the Vulcanizate
Authors: Scott J. R. 
Published: February 2011

Abstract
The fact that the nonrubber components of crude rubber, especially those of a hygroscopic nature, impair the electrical properties of the vulcanizate has long been known, and the preparation of deproteinized or otherwise purified rubbers for use in electrical insulation had reached the commercial stage before the 1939–1945 war. With the rehabilitation of the plantation industry, the question of what special types of natural rubber should be prepared and marketed has become important, and purified rubbers represent one type that merits careful consideration. Published data on the electrical properties of purified rubbers, both before and after vulcanization, relate entirely to types prepared from solid rubber (crepe or sheet) or ammonia-preserved latex in the consuming country, and there is no published record of experiments on rubber purified during its preparation on the plantation. In 1935 the R.A.B.R.M. began investigations on the use of purified rubbers of the latter type in making electrical ebonite; the results will shortly be published. Examination of soft vulcanizates was began in 1937, but war conditions made it necessary to discontinue the work, for which reason the electrical results are less complete and conclusive than could have been wished. Nevertheless, it is hoped that the results obtained will be of value to the rubber manufacturing and plantation industries. Another use of purified rubbers is in the manufacture of transparent articles that come in contact with water or aqueous solutions. Transparent vulcanizates made from ordinary raw rubber quickly become white and opaque owing to absorption of water, but it would be expected that the use of purified rubber would remove or lessen this defect. This point has accordingly been examined. The thanks of this Association are due to the London Advisory Committee for Rubber Research (Ceylon and Malaya) for arranging for the preparation of special purified rubbers, in Ceylon and Malaya, and for examining the water absorption of the unvulcanized rubbers.
X-Ray and Dielectric Investigations of Thermovulcanizates
Authors: Blokh G. A. , Zaĭonchkovskiĭ A. D. 
Published: February 2011

Abstract
Earlier work by the present authors has demonstrated that simple heating of rubber-carbon black systems in the presence of polymerizable vinyl hydrocarbons at moderate temperatures (150–200°) leads to the formation of soft thermovulcanizates possessing the properties of technical vulcanizates. At higher temperatures (260–280°) hard, fully cured thermovulcanizates are formed. These are designated by us as thermoebonites, to distinguish them from sulfur ebonites. Thermoebonites are characterized by superior mechanical, chemical, and electric-insulating properties, and do not have the fundamental shortcomings of sulfur ebonites. These shortcomings, which result from the presence of excess sulfur, are:
Variability of Crude Rubber. Effect of Latex Nonrubber Substances on Vulcanization and Aging Characteristics of Crude Rubber
Authors: McColm E. M. , Haefele J. W. 
Published: February 2011

Abstract
Nine different fractions of nonrubber substances have been isolated from fresh, unpreserved latex, in a condition probably closely resembling the condition in which they existed in latex as it was produced by the tree. A purified rubber, free of nonabsorbed water-solubles and of acetone-extractables, was prepared. The nine fractions were added to this rubber separately and the resulting mixtures compounded in a pure gum recipe containing mercaptobenzothiazole as accelerator and zinc oxide. Of these fractions, only three were found having marked effects on the properties of the vulcanizate. Two additional fractions had small effects. Evidence indicates that very poor cures are obtained if rubber is freed from nearly all the nonrubber components. Addition of at least one substance, which has no effect in the absence of mercaptobenzothiazole, causes a great increase in rate of cure. Crude rubber may possibly be variable for other causes than the amount and character of the nonrubbers present. That portion of the curing variability in a zinc oxide-mercaptobenzothiazole compound due to the nonrubbers is probably due to variation in the following fractions: 1. Lipin 2. Soluble in water, and in ethyl and methyl alcohols 3. Soluble in CCl4-acetone and in acetone Free acid, probably free fat acid, occurs naturally in fresh latex. Quebrachitol (1-methyl inositol) is present in an uncombined form in fresh latex, and has no effect on curing rate or on aging.
Complexity of Fresh Hevea Latex
Authors: Homans L. N. S. , van Dalfsen J. W. , van Gils G. E. 
Published: February 2011

Abstract
Although under difficult conditions, the work at the Netherlands Indies Rubber Research Institute at Buitenzorg (Java) was continued during the Japanese occupation. Since it will be a long time before the accumulated results of the years 1942–45 can be published in detail, some points of general interest are reported here. It is common knowledge that, on addition of small amounts of salts of bior polyvalent cations to fresh latex, partial coagulation follows. The yellow colored coagulum generally contains 10–30 per cent of the rubber and after drying gives a yellow rubber, rich in proteins, and having a high acetone extract. The high acetone extract and the color are produced by the yellow particles, first observed by Frey-Wyssling, which, although generally called “resin particles”, contain mainly lipoids. What, however, is the reason for the high protein content? In 1941 it was observed by one of us (L.N.S.H.) that when fresh latex is centrifuged in tubes, a separation occurs into a heavy yellow fraction, taking up a tenth to a third of the total volume, and a lighter white fraction. The yellow fraction is more viscous and often in itself consists of various layers, bright yellow, gray yellow, orange, or even green. Much information was obtained by studying separately the chemical composition, colloid-chemical and enzymological properties of these fractions.
Natural Antioxidants in Hevea Latex
Authors: Altman R. F. A. 
Published: February 2011

Abstract
An elaborate investigation on the identity and usefulness of the antioxidants naturally occurring in Hevea latex is of value because there is an increasing demand for special types of rubber with low nitrogen and ash contents, less water absorption, better electrical properties, and less odor than common crepe, and because these rubbers are generally unstable in comparison with the usual grades of rubber crepe and sheet. for the purpose of the investigation, fresh latex was separated into main-fractions, the most important of which have been called water-solubles and ether-solubles. These were further separated into various subfractions, which, one by one, have been tested for their antioxidant activity on raw rubber. In the following table only those fractions which show an outstanding antioxidant action are recorded. It is shown further that the amino acids are most remarkable in their antioxidant action : minute quantities exert a strong retarding action on the oxidation of raw rubber. Choline and cephaline are most probably the active components of the second water layer. The active ether-soluble fractions could not be identified due to the small quantities separated.
Latex Strainability Test
Authors: Brass P. D. , Slovin D. G. 
Published: February 2011

Abstract
The presence of fine eoagulum in latex affects some processes very adversely. This coagulum is often wrongly blamed on some complicated chemical or physical action in the compound when the true explanation is that all the larger particles were present in the original latex or dispersions from which the compound was made. The latex strainability test measures the amount of latex that will pass through a filter medium before clogging.
On the Degree of Crystallinity in Natural Rubber. I. An Improved Method to Determine the Degree of Crystallization in Rubber
Authors: Goppel J. M. 
Published: February 2011

Abstract
There are indications that the degree of crystallization in high polymeric substances is of importance in studying mechanical properties. With regard to the crystallization of rubber, few measurements have been made, mainly by Field. The results, however, are in contradiction to estimates of an earlier date, and therefore the necessity was felt to have them checked. An x-ray method, in some respecta differing from that of Field, was developed, the results of which diverged considerably from the figures reported by Field. The present article deals with a description of the method.
On the Degree of Crystallinity in Natural Rubber. II. The Orientation of Rubber Crystallites in Stretched Samples
Authors: Goppel J. M. 
Published: February 2011

Abstract
In the foregoing article a method for determining the proportion of crystalline rubber in stretched samples has been described. A complication due to varying crystallite orientation in different samples appeared to interfere with the application. A simple relation is given between the degree of orientation and an empirical constant which makes possible a rapid determination of the degree of crystallization, regardless of the orientation in the sample under investigation.
Comparative Studies on Photoelasticity of Elastomers and Plastomers
Authors: Heller Wilfried , Oppenheimer Hans 
Published: February 2011

Abstract
Transparent films of elastomers and plastomers were found to differ sufficiently in their photoelastic behavior to make stress double refraction a useful criterion of the prospective mechanical properties of a given material. The stress double refraction in such films is mostly an effect of deformation, of orientation, or of both deformation and orientation of polymer chains. In such polymers, however, which crystallize under stress, a large part of the optical effect may be due to oriented crystallization. In addition to its practical value as a testing method for polymers, the photoelastic method offers, therefore, particularly in combination with simultaneous investigations of mechanical properties, the prospect of correlating mechanical properties of a polymer film with its internal structure, and of correlating changes in both qualities on exposure of the film to different degrees of stress. Although results obtained on such films, by means of x-ray diffraction or x-ray scattering and electron-diffraction, are, in general, easier to interpret, the photoelastic method has the considerable advantage of making possible a quantitative follow-up of rapid changes in film structure, e.g., of relaxations.
The Infrared Spectrum of Vulcanized Rubber and the Chemical Reaction between Rubber and Sulfur
Authors: Sheppard N. , Sutherland G. B. M. 
Published: February 2011

Abstract
In an earlier paper we described an infrared spectroscopic investigation of the vulcanization of rubber, and drew attention to a band at 10.4 µ (960 cm.−1) which appeared in the spectrum of both straight and accelerated vulcanization. We have investigated further this phenomenon, and find that the intensity of this band correlates well with the proportion of sulfur chemically incorporated, but not with the degree of vulcanization as reflected in the physical properties of the finished product. We were unable to explain this band in a convincing manner in terms of C—S linkages, but more recently have found a band in the same position (10.4 µ) and another at 11.2 µ (890 cm.−1) in certain thermally degraded rubbers. Since in this case the two new bands are obviously due, respectively, to the development of new CHR:CHR′ and CRR′:CH2 groups, it seemed probable that the 10.4 µ band might also be caused by new groupings of the former type. An investigation of the spectrum of an ebonite (in which the rubber-sulfur reaction has been carried to an extreme) confirmed this idea. In this spectrum, absorptions in the region of 6 µ showed that a considerable number of bonds remained, but the characteristic absorption at 12.0 µ arising from CRR′: CHR″groups in rubber had largely disappeared. On the other hand, the band at 10.4 µ (although shifted to slightly longer wave lengths) had increased greatly in intensity.
Influence of Structure on Polymer-Liquid Interaction. II. Influence of Nitrile Groups
Authors: Salomon G. 
Published: February 2011

Abstract
Swelling equilibria of a number of copolymers in various organic solvents have already been discussed. The influence of polarity and polarizable groups has been derived from the gradual changes of swelling equilibria. We shall deal with the same problem in the present paper, but, by considering only nitrile groups in the polymer, the resulting picture becomes less complex. The polymers under investigation are the three series of copolymers from acrylonitrile, with butadiene, isoprene, and dimethylbutadiene, respectively. In each series, the mechanical properties change with nitrile concentration, as indicated by a gradual increase in brittleness. The combination of nitrile and methyl groups leads to a further immobilization of the flow units; the copolymers from dimethylbutadiene are, therefore, plastics at room temperature—as has been discussed in another paper.
Preparation and Properties of Rubberlike High Polymers. V. Influence of Nitrile Groups on the Properties of Copolymers
Authors: Salomon G. 
Published: February 2011

Abstract
The introduction of methyl groups in butadiene leads to a decrease in 1,2- and 3,4-addition as well as to a reduction of cross-linking reactions. The same regularity can be observed in a series of copolymers, which will be discussed in the present paper. Apart from these interrelations between diene structure and pattern of the chain molecule, other physical properties such as the second order transition point and the closely related brittle point depend on the presence of methyl groups. Nitrile groups enhance these differences between the three series of diene polymers, as will be seen from the following results. A striking contrast between these widely diverging physical and mechanical properties is the similarity of swelling equilibria, which are obviously determined only by the number of nitrile groups per volume unit of polymer, as will be discussed in another communication.
Measurement of Internal Double Bonds in Polymers by Perbenzoic Acid Addition
Authors: Saffer Alfred , Johnson B. L. 
Published: February 2011

Abstract
Internal double bonds formed by 1,4-polymerization of diene monomers add perbenzoic acid more rapidly than do vinyl double bonds which are the products of the 1,2-type of addition. The extrapolation procedure proposed for determining internal double bond contents of diene polymers is based on this difference in addition rates. Oleic acid mixtures with 10-undeeylenie acid were prepared and analyzed with an accuracy of 1 per cent. However, the method is limited to systems containing 70 per cent or more internal double bonds. Minimum interference of side-chain oxidation by perbenzoic acid was attained by using a low temperature and a small excess of perbenzoic acid. Methyl-substituted emulsion polymers are characterized by high amounts of 1,4-addition. Polymerizations with alkali-metal catalysts result in products of high vinyl double-bond content. A slight preference for the 1,4-type of polymerization is favored in media of low pH. Natural rubbers are formed almost completely by 1,4-polymerization. Heat softening, modifier concentration, and extent of conversion do not influence the degree of 1,4-polymerization.
The Determination of Unsaturation in Butadiene Synthetic Rubber
Authors: Kobeko P. P. , Moskvina E. K. 
Published: February 2011

Abstract
1. It has been found that synthetic rubber does not precipitate from a solution of dichloromethane by the addition of Wijs reagent, whereas natural rubber does precipitate under the same conditions. The reverse relation occurs with carbon disulfide as solvent. 2. A method has been developed for the determination of the unsaturation of butadiene rubber in solution in dichloromethane by the use of Wijs reagent. 3. It has been demonstrated that, by the use of a solution of iodine chloride in carbon tetrachloride, the reaction with rubber is complicated by the hydrolysis of iodine chloride during titration, but not by the substitution of hydrogen by halogen nor by the hydrolysis of the rubber-halogen addition product. 4. The possibility of obtaining accurate values for unsaturation by a calculation of this hydrolysis is demonstrated. 5. Two methods have been developed for the determination of the unsaturation of natural and butadiene rubbers.
Determination of Unsaturation of Synthetic and Natural Rubbers by Means of Iodine Monochloride
Authors: Lee T. S. , Kolthoff I. M. , Mairs Mary Anne 
Published: February 2011

Abstract
The unsaturation of GR-S at various conversions corresponds to the spectrophotometrically determined styrene content. It is concluded that GR-S at various conversions has the theoretical unsaturation. Emulsion polybutadiene was found to have 97 to 98 per cent of the theoretical unsaturation, emulsion polyisoprene 97 per cent. Sodium polybutadiene and polyisoprene had unsaturations which were considerably less than theoretical. The unsaturation of sodium polybutadiene was 92 per cent and that of sodium polyisoprene was 85 per cent. Sodium copolymer of butadiene (75) and styrene (25) also had an unsaturation considerably less than the theoretical value.
Natural Vulcanization Accelerators in Hevea Latex
Authors: Altman R. F. A. 
Published: February 2011

Abstract
As numerous investigators have shown, some of the nonrubber components of Hevea latex have a decided accelerating action on the process of vulcanization. A survey of the literature on this subject points to the validity of certain general facts. 1. Among the nonrubber components of latex which have been investigated, certain nitrogenous bases appear to be most important for accelerating the rate of vulcanization. 2. These nitrogen bases apparently occur partly naturally in fresh latex, and partly as the result of putrefaction, heating, and other decomposition processes. 3. The nitrogen bases naturally present in fresh latex at later stages have been identified by Altman to be trigonelline, stachhydrine, betonicine, choline, methylamine, trimethylamine, and ammonia. These bases are markedly active in vulcanization, as will be seen in the section on experimental results. 4. The nitrogenous substances formed by the decomposition processes have only partly been identified, on the one hand as tetra- and pentamethylene diamine and some amino acids, on the other hand as alkaloids, proline, diamino acids, etc. 5. It has been generally accepted that these nitrogenous substances are derived from the proteins of the latex. 6. Decomposition appears to be connected with the formation of a considerable amount of acids. 7. The production of volatile nitrogen bases as a rule accompanies the decomposition processes. These volatile products have not been identified. 8. The active nitrogen bases, either already formed or derived from complex nitrogenous substances, seem to be soluble in water but only slightly soluble in acetone.
Effect of Prolonged Storage of Unvulcanized Stock on the Properties of the Vulcanizate
Authors: Moakes R. C. W. , Soden A. L. 
Published: February 2011

Abstract
The effects of prolonged storage, in both the unvulcanized and vulcanized states, on the physical properties of four samples of tire tread stock were studied. Storage of unvulcanized stock for four years did not cause any appreciable change in its rate of vulcanization or in the deterioration of any of the important properties of the vulcanizate. Comparison with the results for samples stored in the vulcanized condition shows that the unvulcanized stock was, in fact, more stable than the vulcanizate as far as changes during storage were concerned.
Effect of Storage and Temperature on Flexibility of Natural and Synthetic Rubbers
Authors: Gregory John B. , Pockel Irving , Stiff John F. 
Published: February 2011

Abstract
A new method for measuring the flexibility of rubber has been described. The method consists essentially in determining the stress-strain curve obtained by loading and unloading a loop formed from a one-inch by six-inch strip cut from a test slab. A coefficient of flexibility independent of the thickness of the sample and, in addition, information on per cent resilience were obtained. By the use of the method described, the behavior of various natural and synthetic rubber gas mask facepiece compounds was studied during one month to three months' exposure at various temperatures down to −20° F. Progressive stiffening probably due to crystallization was found for natural rubber, GR-I, and GR-M compounds at low temperatures. No tendency to crystallize was noted for the GR-S compound. Of the crystallizable polymers GR-I was the most resistant, and GR-M the least resistant to stiffening during low temperature storage. It is of course evident that different polymers have inherently different degrees of resistance to low temperatures. Disregarding these inherent differences the work reported indicates that the resistance of elastomer compounds to stiffening during prolonged low temperature storage is favored by the following: 1. Use of interpolymers made from monomer mixtures having a relatively large proportion of each component, thus obtaining mutual intereference with crystallization. 2. Use of a “tight” cure which probably so impedes the movement of the polymer chains as to make crystallization difficult.
Effect of Iron on Aging of GR-S
Authors: Albert H. E. , Smith G. E. P. , Gottschalk G. W. 
Published: February 2011

Abstract
Soluble iron decreases the resistance of the GR-S polymer to aging. The effect of iron is greater than that of copper or manganese. The aging of an aluminum sulfate—coagulated polymer can be improved by the use of low-iron aluminum sulfate instead of the commercial grade of this material. The use of commercial aluminum sulfate as a coagulant gives a polymer somewhat superior in aging to one coagulated with salt and acid. The aging of GR-S vulcanizates is accelerated slightly by polymer-soluble iron. Relatively high iron concentrations are required to produce much effect. The effect of iron on vulcanizate aging is much less than in the case of polymer aging. The presence of iron increases the rate of oxygen absorption of GR-S polymer and vulcanizates, the effect being less in the latter case. The rate of oxygen absorption of aluminum sulfate—coagulated GR-S polymer is decreased by employing low-iron aluminum sulfate instead of the commercial grade. A polymer coagulated by commercial aluminum sulfate absorbs oxygen at a slower rate than one coagulated by salt and acid.