bluuebunny/crossref_metadata_2025 huggingface dataset:
The Vulcanization of Rubber by Diazoamino Compounds
Authors: Levi T. G.
Published: February 2011

Vulcanizing agents for rubber can be classified in the following six types: (1) Sulfur, including α-sulfur, β-sulfur, γ-sulfur, precipitated sulfur, and nascent δ-sulfur. (2) compounds containing sulfur, e. g., sulfur chloride, sulfur iodide, sulfur dioxide, phosphorous sulfides, hydrogen persulfides, nitrogen sulfide, and alkaline polysulfides. (3) elements of the sulfur group and their compounds, e. g., selenium, tellurium, selenium sulfur chloride, and selenium diethyldithiocarbamate. (4) halogens and halogenated compounds, e. g., chlorine, bromine, iodine, hypochlorous acid, hypochlorites, and benzoquinone dichloride. (5) oxygenated compounds capable of liberating nascent oxygen at vulcanizing temperatures, e. g., persulfates (such as ammonium persulfate), peracids (such as perbenzoic acid), nitro compounds (such as 1,3,5-trinitrobenzene, tetranitronaphthalene, and nitrocyclohexane in the presence of metallic oxides), and organic peroxides (such as benzoyl peroxide). (6) derivatives of rubber, e. g., rubber ozonide, chlorinated rubber, brominated rubber, and rubber hydrochloride.
Tests on Crepe Soling. III. Water Absorption
Authors: Messenger T. H. , Scott J. R.
Published: February 2011

The main results obtained are summarized below: (1) The following observations made by previous workers are confirmed. The absorption by crepe immersed in pure water continues for a very long time, if not indefinitely; the initial rate of absorption and the amount absorbed after long immersion increase rapidly with rise of temperature. The influence of temperature is probably due largely to its effect on the mechanical properties of the rubber, the softening induced by heat facilitating the distension of the rubber. (2) Soling crepes vary enormously in rate of water absorption; this result is ascribable to a variety of causes, as there is direct evidence that water absorption is influenced by the number of plies and the ease of penetration of water between the plies, while the porosity (permeability) of the rubber and its content of water-soluble matter must also come into play; the rigidity of the rubber would be expected to have some influence, although this is not evident in the present experiments. (3) Water absorption does not differentiate sharply between estate and factory-prepared soling crepes, though there are indications that on the average factory crepes absorb water somewhat less rapidly. (4) Among the soling crepes examined, water absorption bears no obvious relationship to mechanical properties or solution viscosity. (5) Addition of solutes to the water in which rubber is immersed reduces the water absorption, and this occurs quantitatively in accordance with the osmotic theory of water absorption. These results indicate that water-absorption tests do not in general yield any information as to the mechanical or physical properties of crepe soling or its mode of manufacture, and are therefore of value only in relation to the water-absorbing properties of the material. Absorption at atmospheric temperatures is so slow that under normal conditions of use it probably does not affect more than a thin surface layer. This layer, however, is responsible for the grip of the soling on the pavement, and if absorption of water influences this gripping power, the control of water-absorbing capacity becomes important. The wide variation at present found between different crepes suggests that an investigation of the factors governing water absorption would enable this property to be closely controlled over a wide range. Penetration of water between the plies, which will occur especially when the soling is somewhat worn, may be more serious than absorption at the outer surface, since water cannot readily dry out from between the plies, and the absorption may therefore become cumulative and lead to weakening of the ply-adhesion.
Studies on Vibration Tests of Rubber
Authors: Saito Shohei , Ishiguro Katsumi
Published: February 2011

Experiments were carried out to determine the resistance of rubber products to vibration. There were no essential changes in mechanical properties as a result of vibration for 50 to 100 hours. There were on the other hand considerable changes in electrical properties, e. g., the insulation resistance decreased with increase in time of vibration. Further experiments in connection with this problem will be carried out to obtain data on the effects of vibration for prolonged periods. The authors wish to thank Messrs. Endo, Taguma, Hamono, and Wada for their aid in the experimentation.
Rubber-Lined Equipment. Fundamental Principles of Design
Authors: Hoover J. R. , Klein H. C.
Published: February 2011

IN 1924 a process known as Vulca-lock, discovered by chemists of The B. F. Goodrich Company, made possible the first successful steel tank car for hydrochloric acid service. The tank was lined with acid-resisting vulcanized rubber bonded to the steel shell with adhesion exceeding 500 pounds per square inch. A new material of chemical construction was thus made available in practical form. The resulting widespread and rapidly increasing use of rubber-lined equipment in the processing industries is well known. Basically, the value of such construction lies in properly combining the unique corrosion- and abrasion-resistant properties of rubber with the rigidity, strength, and adaptability of steel or other structural materials. It is essential, therefore, that chemical engineers be familiar with certain principles of design, upon which the successful use of rubber-lined equipment depends. No attempt will be made in this paper to define the broad field of usefulness or the limitations of rubber linings. The fact must be emphasized, however, that an extremely wide range of chemical and physical properties is available in commercial rubber compounds and that these compounds, like metals and alloys, are designed for specific uses.
Natural and Synthetic Rubber. XVII. The Separation of Sol Rubber and Gel Rubber
Authors: Midgley Thomas , Henne Albert L.
Published: February 2011

Sol rubber prepared by a single diffusion in ether can be separated into two components by fractional precipitation, whereas sol rubber prepared by a single fractional precipitation completely diffuses in ether, thus indicating the superiority of the fractional precipitation method as a means of preparing sol rubber.
The Viscosity of Latex and of Latex Mixtures
Authors: Bächle O.
Published: February 2011

For the rubber technologist, a change in the plasticity of rubber mixtures is one of the most important indications that fundamental changes are taking place within the mixture. For example, a decrease in plasticity would lead to the conclusion that incipient vulcanization had taken place, and an increase in plasticity would indicate degradation resulting from unfavorable conditions of storage, from the action of deleterious substances in the rubber, etc. Corresponding to these increases and decreases in plasticity in the case of dry rubber mixtures, increases or decreases in the viscosity of rubber solutions are found. These changes in viscosity and plasticity unquestionably conform to the facts which are now known about rubber and its behavior on degradation and on vulcanization. Further, latex, which is becoming of increasing importance, and mixtures prepared from it, undergo changes in viscosity on standing as well as during the processes of manufacture. There are many of these changes in the viscosity of latex, and accordingly it is much more difficult to ascertain them individually than it is in the case of solutions in organic solvents. It might be of importance to know more about the factors which influence the viscosity of latex. Then again in studying the viscosity of latex a great number of phenomena and problems are encountered which require explanation, so that a report of all the observations made during our investigation may be found of general interest.
The Viscosity of Raw Rubber
Authors: Smallwood Hugh M.
Published: February 2011

1. Eyring's equation for the viscosity of a non-Newtonian fluid describes Mooney's data satisfactorily for all except the lowest shearing stress. 2. From the standpoint of the present theory, the behavior at low shearing stresses may most readily be explained by any of the following assumptions: (1) the moving particle is larger at low than at high shearing stresses; (2) the rubber as a whole is less oriented by the lower shearing stress; (3) the distance “jumped” at the low shearing stress may be less than that at high stresses. 3. According to the present interpretation, the moving particle (corresponding to the molecule of a simple liquid) is larger than the rubber molecule. It does not seem profitable to interpret this finding as evidence for the existence of a rubber micelle. 4. Both the activation energy of viscous flow for this particular sample of rubber, and the factor determined by the spatial requirements which must be fulfilled by the moving particle, are much larger than the analogous quantities for low molecular hydrocarbons.
The Effects of Elastic Stretch on the Infrared Spectrum of Rubber
Authors: Williams Dudley , Taschek Richard
Published: February 2011

Previous studies of the infrared absorption of rubber have been made by Stair and Coblentz and by Williams. Stair and Coblentz observed a small band at 6µ and an intense band near 12µ, in addition to the usual hydrocarbon bands at 3.4µ, 7.0µ, and 7.3µ. An interesting study of the effects of aging (oxidation) was carried out by these authors, and it was found that marked increases in absorption occurred at 2.8µ, at 6.0µ, and in the region between 7µ and 12µ. Williams obtained transmission data for several types of latex rubber and compared the spectra of these materials with those of related hydrocarbons, such as isoprene and styrene. It was found that the small absorption band observed at 6µ by Stair and Coblentz was actually a complex band having several maxima. The results obtained were in fair agreement with the Raman data obtained by Gehman and Osterhof in their studies of solutions of rubber compounds, although the Raman studies revealed the presence of a number of minor frequencies which did not appear in the infrared work. It has been suggested by a number of writers that the mechanism of elastic stretch is intimately connected with the structure of the rubber molecule, and a theory has been developed by Mack which accounts for stretch and retraction in terms of a rotation about single bonds in the isoprene polymer. That profound changes take place in the structure of rubber when stretched has been revealed by x-ray studies, which show that the diffraction patterns of unstretched rubber consist of the diffuse bands characteristic of liquids, while the patterns of stretched rubber are well defined as in the case of crystalline substances. Other evidences of radical changes in structure accompanying stretch are the variations in optical properties which occur. It was suggested that further infrared studies might be of value in obtaining additional information concerning the mechanism of stretch. Hence it was decided to obtain transmission curves for rubber under different conditions of stretch in an effort to detect any changes that might occur.
High-Speed Vulcanization of Rubber
Authors: Kemp A. R. , Ingmanson J. H.
Published: February 2011

PRIOR to about 1906 when organic accelerators were first employed in the tire industry, vulcanization practice for soft rubber generally involved the use of larger amounts of sulfur than is now customary. Acceleration of vulcanization was obtained by the use of liberal amounts of one or more of the oxides of zinc, calcium, magnesium, or lead. As the new and faster organic accelerators have been employed, the amount of sulfur used has been gradually decreased until it now ranges from about 0.5 to 5 per cent of the rubber; the general tendency is towards the use of the smaller quantity. In the rubber-insulated-wire industry in this country, it is becoming general practice to employ the Western Electric Company's continuous vulcanizing process (1) whereby highly accelerated soft-rubber insulating compositions are completely vulcanized at 198° C. in a few seconds on the wire as it passes continuously at high speed from the insulating machine through a long pipe filled with steam under about 200 pounds per square inch (14.1 kg. per sq. cm.) pressure. This process is rapidly displacing the older one of coiling the insulated wires on drums or in pans filled with soapstone powder and vulcanizing in large autoclaves for periods of 1 to 5 hours under 20 to 40 pounds steam pressure (126° to 142° C.). The continuous process eliminates the objectionable soapstone dust and produces more uniformly vulcanized wire which is free from crossover defects and flattening of the insulation. The process also provides attractive economies in manufacture.
A Vulcanization of Rubber Latex by Potassium Ferricyanide
Authors: Spence D. , Ferry J. D.
Published: February 2011

(1) Vulcanization of rubber is produced by heating latex, from which the diffusible serum components have been removed, with potassium ferricyanide in the absence of air. (2) In the course of the treatment, the ferricyanide is reduced to ferrocyanide. (3) A similar effect may be produced by certain other metallic oxidizing agents in the absence of air.
Rubber in Compression
Authors: Morrison J.
Published: February 2011

Rubber is hardly ever used under simple stresses or strains. A tire tread or conveyor cover is subjected to compression, shear, tension, cutting, and tearing in such a variable and complicated manner that an exact analysis of working conditions is obviously impracticable. Therefore physical tests on samples of rubber will probably never assume the same degree of importance from the point of view of design as in the case of metals, and their primary function will remain that of providing standards for relative comparison of different qualities. Moreover, the comparative value of physical tests is severely handicapped by the variable nature of rubber and by its great deformability, which prevent its being subjected to completely and accurately known stress or strain. Reece (Trans. Inst. Rubber Ind., 11, 312 (1935)) has pointed out the non-uniform distribution of stress which occurs in tensile testing with dumb-bell test-pieces owing to the necessity for enlarged ends and having to grip the ends and apply the tensile loading initially as a shear through the surface of the test-piece. In compression testing, the difficulties of securing uniform behavior are much more pronounced. The obvious way to compress rubber is to use a cylindrical test-piece which must be short enough in relation to its diameter to avoid lateral buckling and compress it endwise between parallel plates. Although this does not involve actually gripping the test-piece, the frictional resistance to lateral sliding of the end surfaces on the plates is so great that the rubber deforms to a barrel shape, and the stresses and strains vary in an unknown manner and to such an extent that test-pieces of different sizes behave quite differently.
Extrusion Qualities of Rubber. Effect of Temperature and Mill Roll Opening
Authors: Nellen Arthur H.
Published: February 2011

EVERYDAY milling practice shows that rubber becomes softer when milled on a cold mill than when milled for the same length of time on a hot mill, and also that a tight mill will produce softer rubber than an open mill, using the same number of passes. Although this may seem obvious to one who is experienced in rubber milling, the published work on variations in the softness of rubber resulting from differences in roll temperatures and mill roll setting is meager; additional data on this subject would not be unwelcome in rubber literature. Also, a series of tests to determine the effects of these factors on the working qualities of rubber provides a satisfactory means for describing a method for operating a tubing machine plastometer which has proved to be of considerable value in this laboratory.
A New Revised Rebound Resiliometer
Authors: Bashore H. H.
Published: February 2011

The following points seem to cover the field of utility for this instrument: for measuring resilience, a property differing from hardness, modulus, elongation, plasticity, etc. For greater speed and accuracy in duplicating rubber compounds. For simplified method for control of factory mixing. For measuring plasticity, since rubber becomes less resilient and more plastic on prolonged mixing. For controlling and comparing the quality of finished products. For measuring the resilience and softness of sponge rubber.
X-Ray Study of Rubber Structure
Authors: Acken Marshall F. , Singer William E. , Davey Wheeler P.
Published: February 2011

IT IS SHOWN by x-ray diffraction methods that a time interval is required to build up a fiber structure in stretched rubber. Four rather obvious types of explanation for this effect are pointed out, and serious objections to three of these are mentioned. The most probable explanation seems to be that time is required either to squeeze out unfavorably oriented molecules to the interfaces of fibers made up of favorably oriented molecules; or to pull out, in the direction of fiber-orientation, tangled portions of molecules. Such a picture would cause the easily stretched, favorably oriented molecules to assume the role usually played by the more solid phase of a gel, and would cause the less favorably oriented molecules (or portions of molecules) to play the part ordinarily played by the liquid phase of a gel.
Reactions during Vulcanization. I—Influence of Zinc and Lead on Rate of Cure of Stocks Accelerated with Tetra-methylthiuram Monosulfide
Authors: Jones H. C. , Depew Harlan A.
Published: February 2011

The acceleration of the vulcanization of rubber by thiurams at low temperatures is reduced by the addition of free lead oxide and water-soluble lead salts, but not by insoluble lead salts. The retardation is due to the inactivation of part of the accelerator by the lead through the formation of an insoluble compound, and the amount inactivated is related to the amount of lead present. An equilibrium apparently exists between the amounts of zinc oxide and lead oxide and the accelerator, which is ordinarily on the side of a very large amount of the lead compound. When an excess of the thiuram is present, a white product can be obtained even when litharge is present in the stock, which indicates further that the lead combines with the accelerator to form an insoluble material inactive at low temperatures. The increasing activity of the lead compound with increasing temperatures can be explained by increasing solubility in rubber. The insolubility of the lead compound is further indicated by the fact that if the thiuram is added to a stock containing soluble lead, it is less effective than if it had been added after the lead so that the particles of accelerator would have had time to disperse in the rubber, rather than be coated by the insoluble lead compound.
Oxidation Studies of Rubber, Gutta-Percha, and Balata Hydrocarbons
Authors: Kemp A. R. , Bishop W. S. , Lasselle P. A.
Published: February 2011

The oxidation mechanism of rubber and gutta-percha hydrocarbons has been studied. Rubber hydrocarbon in sheet form oxidizes more slowly and less completely than precipitated gutta-percha, which is believed to be due to the smaller surface exposure of the former material. Gutta-percha hydrocarbon in finely divided form oxidizes to a fairly definite degree in oxygen at room temperature, corresponding to a weight increase of about 38 per cent. The length of the autocatalytic induction periods for rubber and gutta-percha varies over a wide range and is shortened by heating the hydrocarbon in high vacuum before oxidation and by exposure to light. The rate of oxidation of gutta-percha in air, as compared with oxygen, is reduced in proportion to the oxygen concentration, and the induction period is correspondingly increased. Carbon dioxide, water, formic acid, and formaldehyde are identified in the volatile oxidation products, and their relative amounts determined. Six to eight per cent of the hydrocarbons are converted to volatile oxidation products. The percentage unsaturation of both rubber and gutta-percha hydrocarbons is reduced in proportion to oxygen absorbed. The ratio of hydrogen to carbon decreases as a result of oxidation. The solid oxidized products are of such a nature that they cannot be resolved into crystalline materials. They are amorphous acid substances, free from aldehyde and ketone groups. They contain a small amount of peroxides; and the acidity, saponification value, and other properties indicate that most of the oxygen is combined in the form of hydroxyl, carboxyl, and lactonic groups. The mechanism of oxidation of rubber and gutta-percha appears to be the same, and the possibility of a chain mechanism to explain the facts is discussed.
New Condensation Products of Rubber Hydrocarbons by the Aid of Benzyl Chloride
Authors: Kirchhof F.
Published: February 2011

The application of the long-known Friedel-Crafts reaction to rubber hydrocarbons led to a new type of condensation products which may be called provisionally aral cyclorubbers (“benzylidene rubbers”), since their benzylidene groups are probably condensed with the polyprene skeleton to cyclic systems. It would not have been foreseen without further work that rubber would form this type of condensation product with aral halides in the presence of aluminum chloride, since on the one hand benzyl chloride is known to form, by the action of aluminum chloride in the Friedel-Crafts reaction, an amorphous, apparently high molecular hydrocarbon of the empirical composition (C7H6)x, and on the other hand rubber in solution is transformed by the metal chlorides, especially aluminum chloride, into amorphous polycyclorubbers. Under definite conditions of condensation with aluminum chloride aral groups are combined with the skeleton of the rubber hydrocarbon with the formation of white to yellowish amorphous bodies which contain, in addition to a small proportion of organically combined chlorine, only carbon and hydrogen, and are therefore to be regarded as hydrocarbons. In their physical and chemical properties these substances resemble the already known amorphous substance of the empirical formula (C7H6)x, which doubtless is polybenzylidene, probably hexabenzylidene.
The Nature of Vulcanization. Part IV (Continued)
Authors: Stevens H. P. , Stevens W. H.
Published: February 2011

In a previous communication the authors have discussed the limiting figure for combined sulfur in vulcanized rubber, and shown that under suitable circumstances the coefficient of vulcanization can exceed the figure of 47, which is that required by the formula C5H3S. It was thought that the combined sulfur in excess of this amount resulted from the substitution of sulfur for hydrogen. (Further information on this point will be found in the second part of this paper.) In the course of these experiments use was made of the ether-hydrochloric acid extraction method for the removal of mineral sulfides in soft vulcanized rubber. It was thought that this extraction method might not be suitable for use with vulcanites, since the amount of swelling produced by the ether was relatively inappreciable, and consequently the metallic sulfides were not necessarily decomposed. It was also thought that the acid mixture might react with a part of the rubber sulfide and result in a lower coefficient, which would depend on the time of extraction. It is known that vulcanite can be decomposed by the action of alcoholic potash, and the combined sulfur has been reduced in some cases to 26 per cent. It is reasonable to suppose that decomposition takes place in the presence of concentrated hydrochloric acid. In order to determine the extent to which the sulfide is decomposed by the action of the acid a series of extractions was made.
Micellar and Molecular Solutions of Rubber
Authors: Bary Paul
Published: February 2011

The chief interest in studying the degradation of rubber lies in the fact that it makes possible an investigation of the manner in which substances first swell in a liquid before they disperse. There are two opinions current about the state of rubber in its solutions; one, for several years the most popular, is that rubber consists of micelles in the liquid; the other is that rubber is a molecular dispersion with the molecules in the form of chains which may be very long. This latter hypothesis has been taken up comparatively recently by Staudinger, and is supported by a large number of experiments. In the investigation being carried out by the author and E. Fleurent on the degradation of rubber, of which the preliminary results have already been published, the object has been first of all to determine the law according to which the degradation progresses with time under different conditions of solvent, concentration and temperature. When one operates with dilute solutions (0.4 to 2%), the law of degradation is easily proved to be proportional to the time, but these solutions have no appreciable rigidity until they are homogeneous, and all the viscosity measurements of the solutions can be made with a single viscosimeter, without waiting for too long a period of flow.
Isoprene and Rubber. Part 29. High Molecular Hydrorubbers
Authors: Staudinger H. , Feisst W.
Published: February 2011

The molecular concept in organic chemistry is based upon the fact that the molecules, whose existence is proved by vapor density determinations, enter into chemical reactions as the smallest particles. If now it is assumed that organic molecular colloids like rubber are dissolved in dilute solution in molecular form then it must be proved that in the chemical transposition of macromolecules as well no change in the size of the macromolecules occurs. In the case of hemicolloids, therefore for molecular colloids with an average molecular weight of 1000 to 10,000, this has been proved by the reduction of polyindenes, especially of polysterenes, to hydroproducts with the same average molecular weight, and also by the fact that cyclorubbers do not change their molecular weight upon autoöxidation. The molecular weights of hemi-colloidal hydrocarbons are therefore invariable. This is much more difficult to prove in the case of rubber, although there are many more ways in which unsaturated rubber can be transposed than the stable polysterenes, polyindenes, and poly cyclorubbers. In most of the reactions with rubber, as in its action with nitrosobenzene, oxidizing agents, hydrogen halides, and halogens, an extensive decomposition takes place as a result of the instability of the molecule, which is referred to in another work. Therefore derivatives of rubber are not formed, but derivatives of hemi-colloidal decomposition products. The catalytic reduction of rubber in the cold appears to be the most suitable process of making it react without changing its molecular size in order to prove that in a chemical transposition its molecular weight remains the same.
Mastication. A Preliminary Study
Authors: Cotton F. H.
Published: February 2011

1. The oxygen present during mastication of raw rubber is responsible for the increase in plasticity which normally occurs. 2. Rubber does not soften appreciably when masticated in nitrogen. There are indications that rubber free from adsorbed oxygen would undergo no change on mechanical working in pure nitrogen. 3. The value of the so-called constant n in the plasticity equation K=XYn changes from one sample of masticated rubber to another. It varies from 0.07 in the case of a tough raw rubber full of nerve, to 0.28 in the case of the same rubber masticated in air or oxygen until thoroughly “killed.” 4. Small quantities of ozone are formed by the static electrical charges produced on rubber during mastication. 5. Rubber does not masticate more rapidly in ozonized air or ozonized oxygen than in air and oxygen, respectively. 6. The volatile products of the action of ozone on. vulcanized rubber have a retarding action on the mastication of rubber, particularly during the initial stages. 7. Dry rubber gains steadily in weight during mastication in air. The rate of absorption of oxygen decreases slightly until the rubber has gained 0.22 per cent in weight. Thereafter, the rubber becomes tacky and the rate of absorption increases. 8. During mastication of rubber in air or oxygen, volatile products are evolved having an acrid odor resembling that of the aldehydic products of the reaction between ozone and vulcanized rubber. 9. A suggested mechanism of mastication has been put forward to explain the above findings.
Impure Iron Oxide as a Rubber Pigment. I. Effect of Ferric Sulfate on Cure and Aging of Rubber
Authors: Ayers Joseph W.
Published: February 2011

1. Traces of ferric sulfate in oxide of iron will accelerate aging of rubber. 2. Traces of ferric sulfate in oxide of iron will cut down the rate of cure of rubber. 3. The Bierer-Davis bomb aging tests and the Geer oven tests lead to the same conclusions, although the stocks perform differently in each case. 4. By changing the ferric sulfate to ferrous carbonate with sodium carbonate in solution and washing out the residual sodium sulfate, the ferric sulfate is neutralized to an inactive salt. 5. Iron oxide aggregated by ferric sulfate will not break down on milling in rubber. 6. Increased aggregation reduces the specific surface and the coloring or tinting value of the pigment.
The Determination of Sulfur in Rubber by Means of the Calorimetric Bomb
Authors: Saladini B.
Published: February 2011

For determining the total sulfur content of rubber, industrial laboratories ordinarily use some method which is based on the destruction of the organic substances, and oxidation of the sulfur to sulfur dioxide in an open vessel, e. g., by sodium peroxide, perchloric acid, or a potassium carbonate-potassium nitrate mixture. Particular attention should be called to the method of Butironi which is based on the fusion of the substance with dry potassium hydroxide in a silver crucible, and subsequent oxidation of the sulfur to sulfuric acid by potassium nitrate. This method can be used for hard rubber. There is also an interesting method of Losana, which involves heating the substance with powdered iron and sodium bicarbonate, treatment of the iron sulfide with hydrochloric acid, passage of the hydrogen sulfide into zinc acetate solution, addition of a known excess of iodine solution, and titration of the excess iodine. All these methods are tedious and delicate, and leave much to be desired from the point of view of precision because of losses through spattering or incomplete oxidation. Because of this, and because of the great simplicity and rapidity of execution with many organic substances other than rubber, the possibility of utilizing the calorimetric bomb for the determination of sulfur in rubber was investigated. Many tests on mineral oils and organic substances containing sulfur have proved the simplicity of the method and the certainty of perfect combustion and complete oxidation of the sulfur when the procedure is carried out with proper skill.
The Absorption of Water by Rubber and Its Relation to the Protein Content
Authors: Skinner S. J. , Drakeley T. J.
Published: February 2011

1. The absorption of water by rubber is dependent upon the degree of division, and comparable results are obtained in a reasonable time only by using shredded samples of rubber. 2. The moisture in rubber appears to be present in two forms, (a) that removed after, say, three days, over sulfuric acid, and (b) what has been termed the residual moisture, which is more difficult to extract from the rubber, but which is evolved by heating the sample for an hour or so at 100° C. In general, the higher the protein content the lower the percentage of residual moisture. 3. Solutions of sulfuric acid provide suitable means of adjusting the humidity of the air. 4. The temperature must be kept constant to avoid deposition of dew upon the rubber. 5. The rate of absorption of moisture decreases rapidly after the first 24 hours of exposure to the prescribed atmosphere. The absorption after 5 days is very slow, and equilibrium was attained in approximately one week. 6. In general the rate of absorption is higher with rubbers containing a large percentage of protein matter. The rate of absorption in an atmosphere of humidity of less than 80 per cent is slow, and for experimental purposes a humidity of approximately 95 per cent is shown to be suitable. 7. It has been found that the ratio of the water absorbed at a constant humidity to the residual moisture is in all cases related to the protein content. 8. In general, the total weight of water absorbed per 100 parts of rubber rises with rising protein content provided the humidity of the air in contact with the rubber is 85 per cent or higher. 9. The proportion of moisture absorbed in atmospheres of less than 70 per cent humidity is small, but increases rapidly with increasing humidity.
Experiments on the Electrodeposition of Rubber from Latex
Authors: Mackay J. G.
Published: February 2011

Freshly tapped latex contains on the average from 27 to 35 per cent of rubber and from 1.2 to 1.7 per cent of acetone-soluble matter, such as resin and water-soluble sugars, from 1.5 to 2.0 per cent of protein and 0.25 to 0.20 per cent of mineral matter. The last consists mainly of the phosphates of calcium, magnesium, and potassium, with organic salts of these metals and a small amount of sulfate. Doubts have been expressed as to the existence of rubber as such in latex, since the physical properties of the dispersion bring it within the category of emulsions, i. e., of dispersions whose dispersed phase is liquid. Thus it has been suggested that the dispersed particles must consist of some simpler hydrocarbon which is polymerized to rubber during coagulation. From results obtained with the micro-manipulator, Freundlich and Hauser (Kolloid-Z., 36, 75 (1925)) concluded that the particles in latex consist of an elastic (solid) outer skin containing a viscous liquid, and assumed that the inner liquid hydrocarbon and the outer solid represent different stages of polymerization of the basic hydrocarbon isoprene C5H3. It is, of course, quite probable that the ejection of liquid which these investigators observed when a latex particle is punctured resulted from the rupture by the needle of the field of force at the surface of a liquid particle, and it is perhaps advisable to adhere to the more conservative conclusion of Stamberger (“The Colloid Chemistry of Rubber” (1929)) that in all raw rubber dispersions we are mainly concerned with liquid disperse phases. Latex is a relatively coarse dispersion with an average particle size of 0.5μ, and the particles vary in size from 2.0 to 0.1μ, i. e., from microscopic to ultra-microscopic particles (von Weimarn, Kolloid-Z., 46, 217 (1928)).
Isoprene and Rubber. Part 33. End Groups in Rubber
Authors: Staudinger H.
Published: February 2011

In a recent work, Pummerer, Ebermeyer, and Gerlach attempted to identify end members in the rubber molecule by ozone decomposition, and in this way to determine the molecular weight of rubber by chemical means. In this connection they say: The basis for the validity of the conclusions derived from the cleavage fragments on the average length of the rubber chain is that this hydrocarbon contains no structurally foreign impurities, but is built up of homogeneous molecules, though of perhaps different lengths. Pummerer abandons his earlier view, according to which rubber is composed of a uniform base molecule, in favor of concepts held by me for years on the constitution of rubber and other high polymeric substances. As was first proved for synthetic products and as shown for balata and rubber, these substances consist of a mixture of similarly constituted molecules of various lengths and therefore of a mixture of homologous polymers. Pummerer has now adopted this concept, but on the other hand he does not agree on the question of the molecular weight.
Isoprene and Rubber. Part 34. Molecules or Micelles in a Rubber Solution
Authors: Staudinger H. , Bondy H. F.
Published: February 2011

Measurements of the Viscosity of Rubber Solutions In the literature may be found numerous measurements of the viscosity of rubber solutions, the object of which was to throw light on the nature of colloidal solutions and changes in these solutions by various operations. These investigations give no insight into the structure of colloid particles and the reason for changes in rubber solutions because they are based on false assumptions, particularly the assumption that rubber has a micellar structure. Often highly viscous solutions were studied, and though these appeared to be of special interest to the colloid chemist, they were unsuited for such investigations, for they are gel solutions in which the structure of the colloid particles is much more difficult to explain than is that in dilute solutions (sol solutions), where the molecules have freedom of movement and do not disturb one another. The earlier works also contain references to the sensitivity of rubber to oxygen, though no special precautions were ever taken in the measurements to exclude oxygen; in fact this was unnecessary as a rule, for crude rubber solutions are much more stable, because of anticatalysts present, than solutions of pure rubber in which these have been removed. Pure rubber was prepared by the method of Pummerer and Pahl and, as described in the following work, was separated by fractional extraction into portions of different average molecular weights. Viscosity measurements of the individual fractions were then carried out under various conditions. The study of the rubber solution, like that of the balata solution, must be carried out with complete exclusion of air, and the solvent (tetralin or benzene) must be distilled in an atmosphere of pure nitrogen and be freed of oxygen. The filtration of the rubber solution, the filling of the viscosimeter, as well as the measurements themselves, are likewise made in an atmosphere of pure nitrogen. Measurements were taken in the Ubbelohde viscosimeter at different pressures, as a rule at 10.30 and 60 cm. mercury pressure. Very dilute solutions were also measured in the Ostwald viscosimeter, since the deviations from the Hagen-Poiseuille law are of no great importance at low concentration. Finally, it should be mentioned that these special precautions during the viscosity measurements, above all the careful exclusion of air, are necessary only in the case of rubber, not with the saturated hydrocarbons, polystyrene, and hydrorubber.
The Minimum of Sulfur Required for Vulcanization. A Résumé
Authors: Bruni G.
Published: February 2011

The problem of the minimum proportion of sulfur necessary to effect vulcanization is fundamental to an interpretation of the very nature of vulcanization itself. Since the introduction of ultra-accelerators, it has been recognized that very small quantities of sulfur are sufficient to bring about vulcanization. In experiments carried out in 1918 in collaboration with G. Menghi in the Laboratory of Chemical and Physical-Chemical Research of the Pirelli Company of Milan, the author found that by the aid of zinc dimethyldithiocarbamate or of similar substances there is an appreciable vulcanization with 0.2 per cent of sulfur. This fact was made public in patents applied for by the author the next year. On the other hand, it is generally recognized today that all vulcanization originates in a chemical reaction, though a fundamental difficulty lies in the fact that it has never been possible to give an exact definition of what is meant by vulcanization. When is a rubber considered vulcanized? From a technical point of view this question may be answered, but there has not been a satisfactory explanation up to this time.
Applications to Rubber of the Concept of Antioxygens and Proöxygens. The Case of Litharge
Authors: Dufraisse Charles , Drisch Nicolas
Published: February 2011

It is known that the oxidation of autoöxidizable substances can be retarded or accelerated by the addition of a small proportion of certain compounds. To these latter Moureu and Dufraisse have given the name antioxygens and prooxygens, have shown that they act catalytically, and have proposed a theory to explain their action. Like other autoöxidizable substances, rubber is sensitive to pro- or antioxygenic catalysis, and this fact is of particular interest, since autoöxidation is one of the principal causes of its spontaneous deterioration or aging. It seemed worth while therefore to undertake a systematic study of this oxidation, with the hope of drawing practical conclusions in connection with industrial processes and the preservation of rubber. The change brought about by autooxidation is a complex phenomenon, and only when each of the factors is studied separately can exact conclusions be reached. In our case we have tried to, distinguish each of the influences which may play a part. In our study we used the experimental method of Moureu and Dufraisse, which in principle involves measuring the rate of oxidation by the manometric method in the cold and at 80°. Since earlier observations and our own preliminary experiments showed that oxygen in the proportion of 1 to 100 was sufficient to make the rubber useless, all our experiments are concerned only with the beginning of oxidation.
A Simplification and Improvement in the Determination of Copper in Fabrics and Rubberized Materials
Authors: Kirchhof F.
Published: February 2011

The determination of small quantities of copper in fabrics and in rubberized materials can be simplified by destruction with concentrated nitric acid, which accelerates the ignition to the final ash. At the same time, this method avoids the usual danger of volatilization of copper as chloride as a result of the presence of chlorine from white factice or from cold vulcanization. Likewise, precipitation of the copper as sulfide can be avoided by repeating the precipitation of the extract from the ash, which contains predominantly aluminum and iron, with ammonia. In this second precipitation, only around 1 to 2 per cent of the total quantity of copper is retained in the precipitate and filter, and this quantity may in most cases be neglected. The ordinary colorimetric method used in the past for the detection of copper as complex cuprammonium ion can be made about ten times as sensitive by making use of the reaction: Cu+ + + 2I− → CuI + I. This is, however, applicable only in the complete absence of the ferric ion and of nitric acid in the test solution. The sensitivity can be increased still more by the addition of starch. Another advantage of the determination of copper by measurement of the equivalent quantity of iodine lies in the fact that, if necessary, only one-tenth as much sample need be used, but in this case as in all such determinations, the copper must be distributed uniformly throughout the material to be analyzed.
Lipin from Latex
Authors: Cotton F. Harriss
Published: February 2011

Recent papers by Rhodes and Bishop and by Eaton, Rhodes, and Bishop have described work carried out at the Rubber Research Institute of Malaya on the isolation of lipin from the serum of latex, and its effect on vulcanization. Aside from its accelerating power, it was found that when it was added to rubber during mastication on hot rolls, the plastic mass became opaque and had a great tendency to crumble. The receipt of about four ounces of lipin extracted from Hevea latex gave the opportunity to verify this peculiar effect of lipin on rubber during mastication and to find some industrial application of this property. Approximately two hundred grams of pale crepe rubber were masticated on a small experimental mill until the rubber ran around the front roll in a smooth sheet. Two grams of the waxy lipin were then added. This did not adhere to the rubber, but rolled around in a lump on the bank of rubber at the nip. As the surface of the masticating rubber became smeared with the lipin, the sheet coming around the front roll began to break up, as if it were scorching, and in a few moments the rubber began to crumble like vulcanized scrap being shredded. After a time, the lipin worked into the rubber, which then reunited in the form of a sheet.
Reactions during Vulcanization. II Reaction between Zinc Soaps and Mercaptobenzothiazole
Authors: Depew Harlan A.
Published: February 2011

Fatty acids react rapidly with zinc oxide to form zinc soaps during milling, and accordingly the action of fatty acid in the presence of zinc oxide is the same as that of an equivalent amount of the corresponding zinc soap. In accelerated stocks, the zinc soaps in the mix react with the accelerator to form the active zinc accelerator compound. The dynamic equilibrium between the accelerator and zinc soaps results in the formation of a smaller amount of the zinc accelerator compound in the case of mercaptobenzothiazole than for many accelerators, and accordingly relatively large amounts of zinc soaps are required with it. Since the zinc reacts with mercapto benzothiazole as the zinc soap, and since there is sufficient time for the reaction between zinc oxide and the fatty acid to proceed to practical completion, irrespective of the particle size of the zinc oxide, it follows that particle size of the zinc oxide is not a factor in the activation of mercaptobenzothiazole.
Effect of Cadmium Compounds on Typical Organic Accelerators during Vulcanization
Authors: Easley M. K. , Eide A. C.
Published: February 2011

Cadmium may occur in zinc oxide in the form of oxide, hydroxide, sulfate, sulfide, chloride, and carbonate in quantities up to 0.5 per cent or slightly more. Using 10 parts of zinc oxide which contains 0.5 per cent of cadmium, the latter would not exceed 0.05 part on the rubber. Owing to testing inaccuracies and the masking effect of impurities, small amounts of cadmium may be difficult to detect. To eliminate such complications, a base formula was selected using chemically pure zinc oxide to which were added various amounts of cadmium compounds. With few exceptions, these compounds retard tetramethylthiouram monosulfide but slightly advance the rate of cure of butyraldehyde aniline, diorthotolylguanidine, and mercaptobenzothiazole.
Experiences with a Direct Accelerator-Adsorption Test
Authors: Amon F. H. , Estelow R. K.
Published: February 2011

A method for determining the accelerator adsorption properties of carbon blacks is described. This method is novel in that an extremely dilute solution of diphenylguanidine in benzene is employed. Application of the test to a large number of carbon blacks has revealed its practical value as a measure of those variations in adsorption properties which are of teal significance to the rubber manufacturer. The method has been employed in several separate control laboratories and it has been found to be of distinct value in indicating quality of production. Since the results can be interpreted without knowledge of source or history of the particular carbon black being tested, the test can be employed for control purposes by the rubber manufacturer as well as by the carbon black manufacturer.
Variations in Plantation Sheet Rubber
Authors: Bishop R. O. , Fullerton R. G.
Published: February 2011

An examination of the samples of sheet rubber collected at a recent Exhibition discloses a high degree of variation in the vulcanization properties of the rubber. Similar variations in the normal produce of first class estates are recorded. Other properties of rubber, such as plasticity, may be expected to show similar variability. Figures are given to indicate the extent of the irregularities and how they would be reflected in technical mixes. The bearing of this on the industrial uses of raw rubber is discussed.