bluuebunny/crossref_metadata_2025 huggingface dataset:
Note on the Extraction of Raw Rubber with Acetone
Authors: Stevens H. P. , Rowe J. W.
Published: February 2011

We have shown that if raw rubbers are exposed to light during acetone extraction, the extract does not reach a steady value but continues to increase slowly with time of extraction. If extraction is carried out in the dark, constant values for the extract are obtained after about 15 to 20 hours' extraction. In the same time the values obtained in the light are about 10% higher than the true values, obtained in the dark. If, however; in an attempt to obtain constant values, the extraction in light is continued for 70 hours, values are obtained about 25% in excess of the true ones. If, therefore, accurate values for acetone extract of raw rubber are required, extraction must be. carried out in the dark until a constant value is reached. If, for convenience, light is not carefully excluded, it would appear that a comparatively short extraction, e.g., 5 to 6 hours, would give the best results, since over 90% extraction is obtainable in 4 hours (Table II), and oxidation is not likely to be considerable in this period. In any case, shielding from direct sunlight is advisable. In view of the general trend of the curves for acetone extract obtained by Endo, it is probable that oxidation of the rubber occurred, and that his results, particularly for the longer periods of extraction, are complicated by the presence of rubber oxidation products. This work has been carried out on behalf of the Rubber Producers' Research Association, to whom the authors are indebted for permission to publish this paper.
An Investigation of the Performance of Flat and V-Type Transmission Belts
Authors: Brazier S. A. , Holland-Bowyer W. , Mellers C. E.
Published: February 2011

A major problem in engineering is and always will be the efficient and effective transmission and distribution of motive power. In spite of the extensive developments which have taken place in individual direct, gear or chain coupled drives, there still remains an extremely large number of drives installed or being installed for the transmission of power in which belting of one kind or another is preferable. Such drives also vary tremendously in character and type, from small machines requiring a fraction of one horse power, to heavy industrial drives, as those used in rolling mills, where the power transmitted often extends to several hundred horse power. The nature of the load may be smooth and uniform or subject to heavy peak loads such as occur in the case of ore crushers or pumping machinery. The use of belting for the transmission of power actually dates almost from the time that mechanical power began to be used, and in fact the name of Leonardo da Vinci has been mentioned as one of the first to devote attention to the fundamental principles of belt drives as well as being the inventor of the tension or jockey pulley. In spite of this, however, very little development in what may be termed the technology of belting appears to have taken place until the latter part of the nineteenth century and, as may be anticipated, most of the earlier writers gave special attention to the question of leather belting.
The Properties of Rubber Prepared from Dialyzed Latex
Authors: Stevens H. P. , Rowe J. W.
Published: February 2011

Rubber articles are prepared from ammonia-preserved latex by two principal processes, viz., evaporation or coagulation, or by a combination of both. The object of this work was to determine what advantages are to be obtained by the use of a latex purified by dialysis. An 8-gallon batch of normal ammoniapreserved latex (from Hevea brasiliensis) was available and all the rubbers were prepared from this batch unless otherwise stated. The latex was kept for several days and decanted from the sludge which settles out. After straining, it was stored in one-gallon cans until required for use. Some of the latex was dialyzed through membranes of regenerated cellulose in the apparatus previously described by the authors. Some aqueous ammonia was added to the latex daily to preserve stability, and three charges of distilled water were used to complete the purification. A pressure was applied to the latex and adjusted to allow slight dilution so that there was no formation of paste on the membranes. The latex was analyzed, before and after dialysis, for total solids and dry rubber content. The former were determined by evaporating a weighed portion of the latex to constant weight at 70°. The dry rubber content was determined by coagulating the latex with about an equal volume of 1% acetic acid, crepeing the coagulum on a washing machine, and drying the crepe at, 70°
An X-Ray Investigation of Crystallinity in Rubber
Authors: Gehman S. D. , Field J. E.
Published: February 2011

The crystalline structure which rubber exhibits under certain circumstances has come to be regarded as associated with a secondary or micellar structure of long chain molecules. The exact mechanism by which the localized ordered regions appear is a speculative subject in recent developments of the micellar theory of long chain polymeric materials. The views of various workers on this subject have been summarized by other authors. The crystalline structure of rubber displays varying degrees and types of orientation of the crystal units, depending on the conditions under which crystallization occurs. The amorphous x-ray diffraction pattern of unstretched rubber is shown in Figure 1, the unoriented crystalline diagram for frozen rubber in Figure 2. When crystallization is induced by stretching, the crystallites are aligned along the axis of stretching, giving the fiber diagrams of Figures 3 and 4. In this case there is random orientation of the other two axes of the crystallites. “Higher orientation,” in which all three axes of the crystallites are aligned, gives the diagram of Figure 15 and can be secured with suitable dimensions of the stretched piece.
Highly Polymeric Compounds. CLXIV. Unit Cell Diagrams and the Microstructure of “Single Crystals” of Rubber. Determination of the Lattice of Macromolecules of Rubber according to New X-Ray Methods
Authors: Sauter Erwin
Published: February 2011

1. The macromolecular lattice of rubber is rhombic and has the constants: a .......................12.60 ± 0.05 A.U. c ....................... 8.91 ± 0.05 A.U. b ....................... 8.20 ± 0.05 A.U. 2. The number of isoprene residues in the cell is computed to be 7.92, i.e., essentially 8; the density obtained roentgenographically is 0.974, which is in reasonable agreement with the value of 0.965 found experimentally. The discrepancies of earlier measurements are at the same time eliminated. (3) The four chains which pass through the unit cell in the direction of the fiber axis are probably columnar tub-like chains with a cis-arrangement at the double bonds which are assembled after the manner of a lattice face-centered on one side. (4) After being stretched to a considerable extent at ordinary temperature, eucolloidal “fused” rubber crystallizes with formation of microscopic crystalline regions of indefinitely great linear tension.
The Crystal Structures of Cellulose and of Rubber
Authors: Mark H. , Meyer Kurt H.
Published: February 2011

Sauter has made the statement that the interference A2, which was reported by the present authors as a simple point, is the result of the superimposing of two interferences, which he designates as (002) and (300). In addition, he shows photographs of highly oriented rubber. In his diagram on page 725 of this issue of Rubber Chemistry and Technology, it is evident that the strong reflection A2 is quite distinguishable near the inner equatorial point A1 ((200) according to Lotmar and Meyer). However, as can easily be shown, Sauter has fallen into the same error that he did in his work on cellulose, i.e., he has mistaken an incompletely oriented substance for a highly oriented substance. As far back as 1928 Mark and von Susich published diagrams of highly oriented rubber, from which it was quite evident that in no case did the interference (300) show any notable intensity. This experiment was repeated by the present authors. The illustration shows a diagram of highly oriented rubber and also a fiber diagram. The intensity of the interference (200), as well as that of (400), is approximately the same on the two diagrams. Whereas the reflection A2 is very intense on the fiber diagram, only a slight intensity is visible in place of reflection A2 on the photograph of the highly oriented rubber. Even if this intensity originated from the plane (300) it would obviously be much too small to bring about an appreciable displacement of the approximately twenty-times stronger reflection (002) on the fiber diagram. Sauter's displacement of the interference (002) in relation to the position assigned by Mark and von Susich, as well as by Lotmar and Meyer, is therefore without foundation experimentally and consequently his unit cell is invalid.
The Chemistry of Natural Rubber
Authors: Haefele J. W. , McColm E. M.
Published: February 2011

Roberts (J. Chem. Soc., 1938, 215, 219) dissolved air-dried films from fresh latex in acetone-carbon tetrachloride and coagulated the solution by the addition of further acetone; the supernatant liquid contained an ingredient which was soluble in ligroin, contained sulfur, might be elastic, and was termed by Roberts, caoutchol. Roberts stated that removal of this caoutchol ingredient caused marked changes in the properties of the remaining rubber, “characterised by its lack of tensile strength and the remarkably low viscosity of its solutions.” This rubber was dried in air for 24 hours, dissolved in benzene, centrifuged, and emulsified with water and the benzene removed by steam distillation. The rubber remaining was tacky and feebly elastic after drying in a vacuum, and was termed caoutchene. Roberts developed the theory that the elasticity of crude rubber is due to the presence of caoutchol and that, without caoutchol, rubber has very poor elasticity and low viscosity in solution. Insufficient attention has been paid to the role of oxygen in the purifications described. Roberts states: “The process has been carefully examined, particularly with respect to the possibility of oxidative or other changes in the constituents. No evidence of such changes has been obtained.” Yet the coagulated rubber, after removal of the caoutchol but prior to steam distillation, was milled in air, and dried in air for 24 hours, during which time considerable oxidation could have occurred.
On the Crystallization of Crude Rubber. I Experimental Results
Authors: Park Chullchai
Published: February 2011

It has already been ascertained that crystallization of rubber can be induced in various ways, such as stretching, freezing, milling and compressing. if a narrow strip of smoked sheet rubber is stretched extensively, the x-ray diffraction pattern shows a fibrous arrangement of the microcrystals. At an elongation of about 150 per cent, a faint fibre diagram is obtained and at 500 per cent elongation, the diffraction spots become sharp and intense. The amorphous halo peculiar to unstretched rubber remains unchanged in width and position, but its intensity decreases with increase in elongation, in contrast to the increase in intensity of the fibrous spots. It was found by Katz and Bing that crepe rubber is crystalline. This point was confirmed by Tanaka and the writer; the Debye-Scherrer rings obtained by them with crepe rubber is shown in Fig. 1 of Plate I. In preparing a sheet of crepe rubber, coagulated strips are passed between rolls 8 to 12 times, and the coagulated strips are strongly crystalized by such severe milling. In preparing smoked sheet, milling of the coagulated sheets is not so severe as in the case of crepe rubber, and some of the rubber crystals formed during milling melt when heated in the process of smoking.
Specific Heat of Strained Rubber
Authors: Boissonnas Charles G.
Published: February 2011

The specific heat of unstrained rubber as a function of temperature has been the subject of many investigations; but only one set of data has been published on the specific heat of strained rubber. (Ornstein, Wouda and Eymers, Proc. Acad. Sci. Amsterdam, 33, 273 1930). Ornstein and his coworkers heated samples of strained vulcanized rubber to 80° C and dropped them into a calorimeter at room temperature. The results they obtained are presented in Figure 1, where the specific heat of one gram of rubber is plotted against extension: As Figure 1 shows, the specific heat diminishes to about two-thirds of its original value when the extension is increased from 0 to 100 per cent (Δl=1); it increases again on further extension. According to Ornstein et al., “the form of the curve for the specific heat is most interesting, as the strong variation of this quantity with the elongation must be of utmost importance for the understanding of the molecular state of rubber.” In order to check these results by another method, the writer measured the specific heat of rubber at room temperature (19° to 21° C) by a process involving temperature changes of less than 0.1° C. Two samples of rubber were chosen. Sample I was highly vulcanized for 30 minutes under 3 atmospheres' pressure. Its composition was as follows:
Oil-Resisting Rubber. Part XII. Vulcanized Rubbers Containing Organic Accelerators
Authors: Scott J. R.
Published: February 2011

In spite of the vast amount of work which has been devoted to organic accelerators and their influence on the physical properties of the vulcanizate, very little information can be found in the literature concerning their influence on the swelling of the vulcanizate in organic liquids. The present experiments were not intended to form a systematic investigation of the influence of organic accelerators on the swelling properties of the vulcanizate, but rather to obtain a general idea of the swelling of rubbers containing the commoner types of commercial accelerators and to find out to what extent swelling could be correlated with the mechanical properties and combined sulfur content of the vulcanizate.
Fatigue in Rubber. Part III. Fatigue and Reinforcement
Authors: Naunton W. J. S. , Waring J. R. S.
Published: February 2011

Rubber, unvulcanized and vulcanized, is both elastic and plastic and it is generally accepted that the function of vulcanization is to decrease the plasticity rather than to develop elasticity. It is, of course, essential that unvulcanized rubber after mastication should be predominantly plastic to allow all of the usual factory processing of the unvulcanized material. Incidentally it should be mentioned that this is one of the most difficult problems connected with the synthesis of artificial rubbers, namely, to produce a rubber which is essentially plastic before vulcanization and yet predominantly elastic after vulcanization. From the point of view of theoretical conceptions, various theories have been put forward to explain the elasticity of rubber. The old mechanical analogies of elastic bags containing fluid are of historical interest only. The first theory, which was attractive in many respects, was the spiral molecule theory of Meyer and Mark, but it has since been generally recognized that it is not in agreement with many of the known facts, and the theory has been dropped.
Multipore—A Thin Perforate Latex Sheet
Authors: Shriver G. E. , Jordan H. F.
Published: February 2011

Charles Goodyear, who perhaps anticipated more fully the versatility of rubber than anyone since his time, suggested in his treatise on rubber that perforated rubber might be used for “sieves, colanders and strainers” and that it might “also be substituted in a great many cases, if not generally, for woven wire cloth.” With the need for products of this type intensifying in recent years, much research has been done toward improving the processes and products related to this field. Two recently developed porous sheet rubber products are Multipore and microporous hard rubber. Both have extensive application as aids to filtration, and each has other potential uses peculiar to itself. The present article will be devoted to a discussion of Multipore, and microporous hard rubber will be treated in a succeeding article. Multipore is a porous rubber sheet made from latex rubber, and derives its porous characteristics from many minute and uniformly spaced holes that extend perpendicularly through the sheet. The types now produced commercially have 1,100 to 6,400 holes per square inch and poor diameters of 0.012 to 0.004-inch, depending on the type. At present Multipore can be obtained in soft rubber, hard rubber, flexible hard rubber and soft Neoprene.
Nomenclature of Synthetic Rubbers
Authors: Fisher Harry L.
Published: February 2011

Sixty years ago, synthetic indigo, a dream of organic chemists, became a reality. Thirty years ago the increase in the knowledge of the chemistry of rubber made organic chemists dream also of synthesizing that important natural product. However, rubber or more specifically the rubber hydrocarbon has not yet been synthesized, in spite of the tremendous amount of time and effort already expended on this intriguing problem. But in scientific journals, books, newspapers and advertisements there is much that is published about “synthetic rubbers”. Indigo was synthesized, and there is no question about speaking of synthetic indigo. Since rubber has not been synthesized, why do we hear so much about synthetic rubbers? Are there any other names which could be used to describe the various “synthetic rubbers” and other rubberlike products? These are the questions which will be discussed in this paper. Indigo is crystalline and can be purified easily; rubber hydrocarbon can be crystallized only under very special conditions, cannot be distilled, and therefore is not easy to purify. Indigo has a comparatively low molecular weight which can easily be determined; rubber hydrocarbon is an elastic polymer, the molecular weight of which is very high and cannot be determined with precision. A determination of the identity of natural and synthetic samples of indigo can readily be made, but with rubber it is almost impossible with our present methods to show the absolute identity of two specimens, although it is possible for all practical purposes to do so.
The Specific Gravity of Rubber in Hevea Latex
Authors: de Vries O.
Published: February 2011

Since my former communication on this subject several papers have appeared which form valuable contributions to the interesting problem of the actual specific gravity of the rubber particles in (original or preserved) Hevea latex. Rhodes recalculated his data, and came to an average figure of 0.9064 for the specific gravity of rubber in ammoniated latex, preserved during several weeks in the East; the rubber content being determined after coagulation by acetic acid in the usual way. Using the term proposed in my former paper, this may be called the specific gravity of “crepe rubber in preserved latex”, which may differ from that of “crepe rubber in original latex” by the effect of possible changes by the prolonged action of ammonia, by the settling out of the sludge (ammonium magnesium phosphate, mixed with protein-like substances), and other changes that occur in preserved latex. Leaving these unknown factors out of consideration, we have to take into account the fact that the rubber content was determined by acid coagulation, which means that a certain amount of serum substances, principally proteins, was precipitated with the rubber, and may have influenced its specific gravity. In my former communication I have shown that the specific gravity of “crepe rubber in latex” is found lower, the higher the rubber content of the original latex, i.e., the smaller the ratio of serum to rubber, and the smaller, therefore, the amount of acid-precipitated serum proteins in per cent of the rubber. Plotting, in this line of thought, Rhodes' figure in the graph (Figure 1), it will be seen that it corresponds to 45 grams rubber per 100 cc, or about 46.6 in percentage of weight, not abnormal for a preserved latex. Protein, precipitated with the rubber, has a still smaller effect in another figure given by Rhodes, namely, the specific gravity of rubber from a centrifuged cream of 56.7 per cent rubber content (acid coagulation). The corrected figure for the specific gravity of this rubber is given by Rhodes as 0.9011, which in Figure 1 corresponds to 55.5 grams of rubber per 100 cc, or about 58.5 per cent by weight; this is in reasonable agreement with the real figure of 56.7, taking into account the unavoidable errors of an extrapolation, such as in Figure 1.
The Action of Pyridine on Chlorinated Rubber
Authors: Lichtenberger J. , Naftali M.
Published: February 2011

In the various publications on the properties of chlorinated rubber which have appeared, the solubility in pyridine has been mentioned frequently. In 1935 and 1936 the present authors had occasion to occupy themselves with this problem, and the present paper deals with some of the results which were obtained. Chlorinated rubber is extremely soluble in pyridine, even in the cold; in fact from a practical point of view the solubility is unlimited, and chlorinated rubber and pyridine may almost be regarded as miscible in all proportions. Two definite phenomena were observed during the dissolution of chlorinated rubber on pyridine: (1) a gelation of the system, and (2) the formation of a quaternary pyridinium salt. By the correct choice of conditions, the reaction can be made go, at least partially, to either of these two directions.
The Quantitative Determination of Zinc in Transparent Rubber Articles
Authors: Casazza Edmondo
Published: February 2011

The method to be described is particularly suitable for the quantitative determination of zinc, present in the form of zinc oxide or of zinc salts, in transparent rubber articles. Rubber articles of this type contain very small quantities of zinc compared with the quantities present in non-transparent rubber articles, in fact the lower limit is only 0.05 per cent, i.e., only about one-hundredth as much as the normal content. The analytic determination of the zinc content when present in such extremely low percentages as this is extremely difficult by ordinary, methods, and even with higher but nevertheless small percentages of zinc, the use of relatively large quantities of material is necessary and the analytical results are often far from precise. The ordinary method of incineration in a porcelain crucible does not lend itself to the isolation of small quantities of zinc because the latter is easily fixed by the silica of the crucible. On the other hand incineration in a platinum crucible is not suitable because of the tendency of this metal to form a carbide in contact with the carbonaceous substances in the rubber. The novel feature of the method of analysis to be described is the procedure for obtaining a solution of the inorganic substances in the rubber. This involves destruction of the rubber by concentrated sulfuric acid and subsequent oxidation of the organic residue by concentrated nitric acid. This gives a solution of the zinc in the form of sulfate. It is then isolated as zinc sulfide and is redissolved and determined volumetrically by the already known method of precipitation with a standard solution of potassium ferrocyanide. The most suitable concentration, acidity and temperature to give precise results by this procedure for low percentages of zinc in rubber were established.
X-Ray Diffraction Patterns of Hevea, Manihot and Other Rubbers
Authors: Clark George L. , Gross Siegfried T. , Smith W. Harold
Published: February 2011

When rubber from Hevea brasiliensis is stretched quickly and exposed to a beam of x-rays, a crystal fiber diffraction pattern is obtained.” During previous work, done jointly by the National Bureau of Standards and the University of Illinois on sol and gel fractions of this rubber, no pattern was produced by the stretched sol fraction. With the stretched gel fraction, however, the pattern was sharp and intense. Rubber from Manihot glaziovii also may be separated into sol and gel fractions, and in recent work they, too, have been stretched and examined by x-rays. With the stretched Manihot sol, a few interferences were obtained, but many more resulted with the stretched gel. When crystallized by “freezing” at low temperatures for 24 hours, the interferences from the gel again outnumbered those from the sol. The x-ray measurements of Manihot rubber agree with those of Hevea rubber and indicate that the same structure exists in each. Rubbers obtained from latices of Funtumia elastica, Cryptostegia grandiflora and Castilla elastica were also examined. Their structures, too, were like that of Hevea rubber, and the similarity confirms earlier observations made when x-ray technique was less highly developed. In crystallized specimens, the crystals melted within the range of temperatures previously observed with Hevea rubber. In earlier work a large spacing was observed in a specimen of unstretched Hevea gel rubber. This spacing has been observed also in a new specimen of stretched Hevea gel rubber, together with a second spacing approximately twice as large.
The Joule Effect
Authors: Wiegand W. B. , Snyder J. W.
Published: February 2011

With reference to a paper by Gleichentheil and Neumann on “The Gough-Joule Effect in Vulcanizates,” we should like to call attention to the similarity between the results reported in their paper and the earlier work reported by Wiegand and Snyder entitled “The Rubber Pendulum, the Joule Effect and the Dynamic Stress-Strain Curve.” The latter authors analyzed from a thermodynamic point of view the rubber stress-strain curve as affected by temperature. As a result of this analysis the stress-strain curve was divided into three groups, Region A, Region B and Region C. Each region was characterized by different trends as regards the Joule effect and internal energy changes. The following description is taken from the original paper: “Region A, The Steel Spring.—This region, extending to approximately 300 per cent elongation for the conditions in the experiments described, is characterized by the comparative absence of heat transfers . … little or no Joule effect.” “Region B, The Gas (and the Crystal).—In region B the region of the Joule effect . … there is the maximum of heat evolution. It should be noted that Region B extends from approximately 300 per cent elongation to 700 per cent elongation. “Region C, The Friction Member.—This region is characterized by the almost entire absence of reversible effects. The Joule effect has disappeared. There is no evolution of heat….“
Vulcanization of Rubber
Authors: Fisher Harry L.
Published: February 2011

Charles Goodyear, a hundred years ago, saved the rubber industry and made available for human needs and satisfaction a material of unique and useful properties. In the 1830's the industry was in bad straits. People wanted its products, but unfortunately the rubber of which they were made became soft and sticky in summer and stiff and inelastic in winter, and also deteriorated rapidly. Through several years of all kinds of difficulties Goodyear persisted in his idea that he could find a method of preserving the good properties of crude rubber and finally discovered not only how to preserve but also how to enhance them. Sulfur and heat gave him his answer. Sulfur and heat also formed the basis of the name “vulcanization” by which the process has been known. It was given by Brockedon, a friend of Thomas Hancock, who was the famous English pioneer in the rubber industry, a contemporary of Goodyear, and rediscoverer of the method of vulcanization. Goodyear's method was the result of much painstaking effort, although as with all important discoveries it really is quite simple. He knew nothing of and was not required to use organic accelerators, accelerator activators, accelerator retarders, antioxidants, antiflex-cracking agents, reinforcing materials, reclaim, plasticizers, stiffeners, odorants, blowing agents, rubber substitutes, etc. However, he had plenty of headaches in getting his process into action, not only from the technical but also from the business angle. People were disgusted with rubber products and the companies which manufactured them, and he had to overcome much prejudice and antagonism. His process has an unusual record since, even now, a century afterwards, it is still the basis of the rubber industry. This statement does not mean that there have been no advances. The very length of the list of different types of materials given above for use with sulfur in rubber indicates the extent of some of the technical advances which have been made. Also, other important advances have been made in the apparatus used in the factory and in the methods of testing the products. Goodyear tacked his sheets of rubber on the outside of his house or hung his products from the rafters of a barn to find out the effect of cold and heat. Later men used their teeth and trained their bite to gage and compare tensile strengths. But these simple and useful methods have long since been displaced by the accurate methods of the modern testing laboratory, which produce results that can be evaluated by anyone skilled in rubber work.
The Lattice of Rubber
Authors: Misch Lore C. , Van Der Wyk A. J. A.
Published: February 2011

The lattice of rubber has already been the subject of a number of investigations. All the unit cells suggested in these papers give an x-ray density which is far higher than the measured one (8–10 per cent). Furthermore, in all Weissenberg pictures published, it is striking that the equator reflection A2 is much longer than A1 and A3. We believe therefore that A2 is not a single reflection and that the angle between A1 and A2 is not 90° or nearly 90°. While we investigated this question experimentally, Morss published a paper, also assuming that A2 is a double reflection and making the assumption of double orientation. He calculated the unit cell for a number of angles and found an agreement with the observations at the angle of 70.5°. The cell contains 8 chains.
The Action of Ozone in the Phenomenon of the Cracking of Rubber Subjected to Repeated Mechanical Stresses
Authors: Eccher Silvio
Published: February 2011

Various rubber articles are subjected in ordinary service to repeated stretching, compression and cutting and to combinations of such forces. Repeated flexing is frequently encountered also. All these forces cause repeated changes, either positive or negative, in the dimensions of the outside surface of the rubber article. Among the important rubber products which undergo such stresses are tires, belts and shoe soles. The stresses to which the tread of a tire is subjected are certainly complex and variable. In this particular case, there are, in addition to the initial static tension, forces of compression, flexing and torsion. A rubber belt offers a simpler problem, for in this case it is possible to distinguish the following cycle of changes on the outside surface: a constant elongation in the taut section of the belt; a sudden increase in elongation on passing over the driving pulley, during which time a constant flexing stress (which depends on the curvature of the pulley) must be added to the tension on the belt; a decreased elongation along the surface of the belt in contact with the pulley; and finally a rapid return to the minimum value existing in the belt when under no tension. An analogous cycle of changes takes place at the driven pulley. Each element of the surface of a belt undergoes, therefore, during each complete revolution, two periods of tension, between which the element is alternately in the taut and in the slack section of the belt.
Studies of Hard Rubber Reactions. VI. Liberation of So-Called Free Sulfur and Changes in the Acetone Extract of Vulcanized Rubber by Repeated Extraction and Heating
Authors: Numaziri Seiiti
Published: February 2011

1. True Free Sulfur.—In the case of the pure rubber-sulfur compound, as shown in the graph, the quantity of true free sulfur liberated from the thermally active hard rubber product by 120 minutes' cure was generally a little greater than that from the thermally nonactive sample with 300 minutes' cure. During the whole course of the extraction and heating, there occurs a lowest point in the true free sulfur curve, which increases again. In view of this fact, liberation of free sulfur can not be attributed to the insufficiency of the acetone extraction but is probably attributable to depolymerization of the vulcanizate or the like. 2. Acetone Extract.—Although purified rubber was used, the corrected acetone extract due to the formation of resinous substances from the depolymerized or aged hard rubber product showed relatively high values at the beginning of extraction and heating. To some extent, the change in acetone followed a course similar to that of the true free sulfur.
Dispersion of Pigments in Aqueous Medium. I. Mechanism and Evaluation of Dispersing Agents
Authors: Daniel F. K.
Published: February 2011

(1) In Part I the difference in the functions of wetting, dispersing and protecting agents is discussed, and explanations of the different mechanisms by which they act are suggested. (2) The known methods for testing dispersion are cited. (3) In Part II the dispersing qualities of four different types of agents are compared by the method of sedimentation volume. From the results of this test a newly discovered dispersing agent appears to be the most efficient of the four agents tested. (4) It is found that this new agent has the peculiar property of making a number of pigments actively dilatant. Dilatancy was previously known only as an inherent property of certain substances, not as a property which can be induced by means of surface active agents. (5) Dilatancy is linked with dispersion. It is shown that flocculation, thixotropy, passive dilatancy and finally active dilatancy can be regarded as different states of dispersion, with no distinct line of demarcation between them. Active dilatancy is obtained only at a most complete degree of dispersion. (6) The dilatancy test is regarded as a quick and convenient method of evaluating dispersions in all cases where dispersions of a relatively high degree are obtained. (7) An inconsistency in the results between the sedimentation volume and dilatancy tests on the one hand and the consistency test on the other hand is discussed. Systems containing agent C show no dilatancy and have a relatively large sedimentation volume; yet they remain fluid at concentrations even higher than those reached by dilatant systems. This discrepancy cannot be fully explained, but it is not believed to invalidate the above deductions on the relation between dilatancy and small volume of sedimentation on the one hand and dispersion on the other hand. (8) The mechanism of dilatancy is discussed. The ζ potential and hydration are assumed to be the most important factors. With the addition of discharging cations, dilatancy is gradually destroyed and the state of dispersion reversed.
Refractometer Studies on Rubber-Pigment Mixtures
Authors: Jones H. C.
Published: February 2011

Several years ago, McPherson and Cummings published data on the refractive index of rubber and of rubber-pigment mixtures. They found no difference in the refractive index of rubber from various sources. The degree of mastication did not appreciably change the refractive index. Sulfur in combination with rubber altered the refractive index relatively more than free sulfur in rubber. With the exception of zinc oxide, the pigments and fillers they examined did not affect the refractive index. In the case of zinc oxide, there was a significant increase in refractive index and the fine particle size oxide (Kadox) developed a higher value than the coarser oxide (XX Red). They suggested that zinc oxide probably reacts with the nonrubber components to form salts which dissolve and change the refractive index. This laboratory found that, for a series of various particle size zinc oxides in rubber, the increase in refractive index was inversely proportional to the particle size of the oxides; that is, a fine particle size zinc oxide increased the refractive index somewhat more than a coarse oxide. It was also observed that the refractive index of zinc oxide-rubber mixtures increased proportionally with each addition of zinc oxide until the opacity of the zinc oxide-rubber mixture became too great (over 6 per cent) to allow measurement by transmitted light.
Rubber as Antivibration Material
Authors: Kosten C. W.
Published: February 2011

The idea of using rubber as a material for the damping and insulation of mechanical vibrations is not new. That this application of rubber has had no great scope up to now can be ascribed to a combination of circumstances: on the one hand there are unlimited varieties of rubber, concerning which rubber manufacturers publish no technical data, which can be relied on for specific projects; on the other hand there is a lack of knowledge of the behavior of rubber by builders themselves. In these circumstances it seemed desirable that the Rubber Foundation should endeavor to assist builders in this respect, and to this end a basic research into the vibration characteristics of rubber has been carried out. We shall report here on several points resulting from this investigation. Moreover we shall also discuss what can be expected of rubber, how it can be most economically used, and what advantages it shows over other materials. Rubber at the present time is unjustly considered an untechnical material, yet of late the rubber industry has made enormous advances. Types of rubber of different hardnesses can be made which for practical purposes are ideally elastic, since they are in no way plastic, and their durability is so great that a piece a few centimeters thick has almost an unlimited length of life, for example, ten to twenty years, without any appreciable change in properties. The generally feared aging symptoms in rubber for technical applications are now of secondary importance. These are actually not more than a surface oxidation which can injure thin rubber articles of poor quality in a comparatively short time, but has no influence on thicker articles. However, this does not mean that adequate attention should not be given to this question. For such a purpose one must use a superior type of rubber, from the best material, vulcanized by an expert.
A Quantitative Method of Expressing Flex-Cracking Results
Authors: Newton R. G.
Published: February 2011

In addition to providing a means of obtaining accurate quantitative results for individual flex-cracking tests, such as the De Mattia or Du Pont tests, the application of discriminant function analysis suggests a basis for standardizing the entire test method, so that objection to the test for specification purposes is thus concerned only with the reproducibility of the results, a problem which can now be investigated with greater confidence and ease. In connection with the accuracy of the method it may be contended that much depends on the subjective attitude of the tester who grades the samples with the photographs. When half-scores were not employed, the accuracy was limited mainly by the coarseness of the scale. This suggests that the grading is objective and, although no comparison, based upon statistical methods, has been made to determine the discrepancies between operators, no circumstance has occurred to suggest that important divergencies of opinion do exist. In addition, the analysis has been repeated on a further series of fifty samples, and the values found for the scoring constants were not substantially different from those obtained in this investigation. There is thus good reason to believe that this method of assessing the results will form a valuable means of investigating the causes of variation in flex-cracking test results and of recording the conclusions from the tests. The author wishes to thank the Board of Management of the Research Association of British Rubber Manufacturers for permission to publish the results given in this paper.
Hevea Latex: Effect of Proteins and Electrolytes on Colloidal Behavior
Authors: Kemp A. R. , Straitiff W. G.
Published: February 2011

1. Three protein fractions have been isolated from fresh and ammoniated latex serum. The usual color and precipitation reactions have been carried out, and they place these proteins in the classification of conjugated glycoproteins. Proteins from fresh latex differ in composition from, and are less sensitive to, coagulating influences than protein from ammonia-preserved latex. 2. Coagulation tests using latex coagulants were performed on the protein hydrosols. It was found that, as the concentration of electrolytes decreased, coagulation of the proteins was inhibited, whereas coagulation readily took place when salts were present in sufficient concentration. 3. Normal ammoniated latex has been subjected to extensive dialytic treatment in specially constructed apparatus. As the ash content of the total solids from the latex approached a value of 0.1 per cent, the mechanical stability decreased and the chemical stability increased. Addition of excess acid or alkali to dialyzed latex yielded stable latices which were highly resistant to spontaneous coagulation. 4. Quantitative coagulation studies, using methyl alcohol and salts of varying types and made on dialyzed latex adjusted to various pH conditions, show that small amounts of a dissolved salt greatly aid coagulation. Considerable variation in the effectiveness of different salts was found. In acid latex of pH 2.5 the charge on the latex particles was reversed from negative to positive, and the salt effect was shown to be different from that experienced in the case where the pH was on the negative side of the isoelectric point. 5. The amount of alcohol required to coagulate dialyzed latex depends on the pH of the latex. It is shown that the amount of alcohol required for coagulation increases on each side of the isoelectric point, which was determined to be at a pH of 4.15. 6. The protective mechanism of proteins has been discussed on the basis of the electrical charges induced on the surface of the latex particles by the presence of the protein layer. The zwitter-ion effect induced by the presence of free amino and carboxyl groups in the rubber proteins is of fundamental importance in determining the colloidal characteristics of latex.
The Proteins of Hevea Brasiliensis. 1. Analysis of a Product Isolated from Dried Latex
Authors: Tristram G. R.
Published: February 2011

A protein has been isolated from dried Hevea latex and analyzed for amido-nitrogen, tyrosine, tryptophan, cystine, methionine, the basic amino-acids and the dicarboxylic acids. The dicarboxylic acids were estimated in 4.0 grams of protein, experiments on casein having shown that, under such conditions, approximately 90% of the glutamic acid and aspartic acid was recovered as crystalline derivatives. It was also found possible to estimate arginine and lysine in the filtrate from the calcium salts of the dicarboxylic acids. The protein is, in many respects, similar to the proteins found in leaves of other plants (Table IV). Further work is in progress to investigate the relationship of the isolated protein to the total protein of latex.
The Dialysis of Latex and the Properties of Dialyzed Latex
Authors: Van Gils G. E.
Published: February 2011

Since the dialysis of latex is becoming more and more important, a brief sketch will be given here of the principle on which the process is based, together with some information on the properties of dialyzed latex. Whereas, in the beginning, dialysis was carried out only in the laboratory, the process has slowly acquired more significance in practice. Moreover, as applied to latex, dialysis has proved useful not only for physicochemical investigation of the product but also, among other uses, as an important aid in preparing special latexes.
Diffusion of Sulfur in Rubber. Relation to Vulcanization
Authors: Kemp A. R. , Malm F. S. , Winspear G. G. , Stiratelli B.
Published: February 2011

A survey of the literature failed to disclose any previous attempt to determine the. rate of diffusion of sulfur through rubber. The present paper is intended to fill this gap and to show the importance of diffusion and solubility of sulfur in rubber on control of the vulcanization reaction. The vulcanization of rubber cannot be considered as a homogeneous chemical reaction since the reactants, i. e., sulfur, accelerators and activators, are seldom completely in solution or uniformly dispersed. The limited solubility of sulfur, many accelerators, and zinc soaps in rubber leads to the presence of these substances partly in solution and partly in the dispersed state during vulcanization. Local high concentrations of these substances occur in solution around the dispersed phase, owing to their increased solubility which results from the temperature rise during vulcanization, coupled with their slow rate of diffusion through rubber. This paper presents the results of a detailed study of the effects of solubility, diffusion, and crystallization of sulfur on heterogeneity of vulcanization. Results showing the effect of various methods of mixing and handling on the physical properties of certain rubber compounds are presented. The diffusion of sulfur into rubber to form a solution during vulcanization, followed by the separation of globular sulfur on cooling, and its transition into dendritic and finally into rhombic sulfur on standing, was observed under the microscope by Loewen and Endres. Several factors which influence the migration and crystallization of sulfur internally and as a surface bloom on rubber were studied by Rimpel, Endres, Twiss, Loewen, and Graffe. The absorption of sulfur by rubber at elevated temperatures was studied by Skellon and by Venable and Green, and the solubility of sulfur at various temperatures was investigated by Venable and Green, Endres, Kelly and Ayers, Loewen, Morris, and Williams.
Synthetic Rubber from Acetylene. III. The Preparation of Butadiene by Catalytic Hydrogenation Of Monovinylacetylene in the Gaseous Phase
Authors: Hurukawa Zyunzi , Nakaguti Kôhei
Published: February 2011

Of the various technical methods for the preparation of butadiene from monovinylacetylene, the present authors chose to make first of all a thorough investigation of the continuous hydrogenation process, utilizing gaseous monovinylacetylene with various catalysts. As a result of this work the following conclusions were reached. The chief fault of this continuous hydrogenation process lies in the fact that, in addition to butadiene, large quantities of butene and oily polymerization products of monovinylacetylene are formed, as a result of which the yield of butadiene is small. This disadvantageous course of the reaction is attributable to the great heat of reaction which is evolved locally on the surface of the catalyst. In the experiments carried out by the present authors, the chief efforts were directed toward overcoming this drawback. As may be seen in Table II, a series of experiments were carried out with palladium as catalyst, which was used with excess carrier having a low heat conductivity, e. g., diatomaceous earth and Japanese acidic earth. This catalyst was expected to have a weakening effect on the activity, for this effect is very pronounced in the hydrogenation of acetylene to ethylene. In the present case, however, the results were unsatisfactory; dilution of the reaction gas with water vapor, a change in the gas current, and a change in the proportion of hydrogen to monovinylacetylene, were all tried. The maximum yield of butadiene at 80° C was 33.7 per cent, based on the monovinylacetylene.