bluuebunny/crossref_metadata_2025 huggingface dataset:
A Fatigue Cracking Test for Tire Tread Compounds. Some of the Laws of Fatigue
Authors: Rainier E. T. , Gerke R. H.
Published: February 2011

AN IMPORTANT factor in the service rendered by a tire tread is its ability to resist cracking. Cracking of tire treads in service may be classified into two kinds or phases—the initiation or start of cracks, and the growth of cracks or cuts once started—and the two phases must be differentiated. Nearly all tires in service soon develop small cracks or “checking” due to the action of ozone in the atmosphere (9), and may suffer cuts due to sharp objects on the road. In many cases such cuts and ozone cracks may be harmless, but if the cracks grow too rapidly they will extend to the carcass before the tire is worn out (4). We define the growth of cracks under the influence of mechanical action as fatigue cracking. The quality of rubber in respect to its resistance to fatigue cracking can be improved by addition of antioxidants (3, 7), and by such factors as the proper choice of accelerators (4), the proper balance of fillers (1, 3), and the proper cure. The quantitative evaluation of such chemicals and compounding ingredients in the laboratory depends upon the validity and precision of a test. It is the purpose of this paper to describe a laboratory test which has been found to correlate with shoulder cracking in tires, and to present data from which certain laws of fatigue cracking have been deduced.
Plasticity and Elasticity, with Special Reference to Unvulcanized Rubber
Authors: Hoekstra J.
Published: February 2011

When working in the field of elastic and plastic properties of plastic materials such as unvulcanized rubber, one is confronted with the fact that there is very little reliable knowledge in that field. Some time ago Prof. J. M. Burgers, in an address before the Foundation of Biophysics, gave a fundamental and extended explanation of the theory of plasticity and its relation to elasticity. Previous to experimental investigations of plasticity, elastic-plastic behavior was assumed to be so simple that it could be reproduced by means of a system of steel springs and pistons of constant friction. It was thus clearly a problem of hydrodynamics and mechanics. Up to the present time, the mechanical properties of highly polymerized substances have remained a mystery to research workers. In an investigation of polymers of high molecular weight, Meyer, Susich, and Valko proposed that the elasticity of these substances depends on the transverse motion of the long molecules, and is thus closely analogous to the elasticity of gases. Their strong argument in favor of this is the fact that the elasticity of rubber, for example, has a positive temperature coefficient, which is in agreement thermodynamically with their suppositions. It is now known from the great difference between the mechanism of the elasticity of rubber and of metals, and also from the stress-strain diagram of rubber (the well-known S-curve), that it is very improbable that the properties expressed by means of pistons and springs can be correctly applied to a substance like rubber. The same holds true for other highly polymerized substances. In spite of the foregoing, it is not surprising that the measurements of Scott, of Peek, and of Houwink showed close agreement with the theory, at least in a great number of fields of flow which were investigated. The agreement always holds true for relatively large shearing forces, viz., when the shearing forces are great compared with the intramolecular or thermodynamic forces. When the latter forces cease to operate, there appears a flow which is generally known as viscous flow. For smaller shearing forces, however, the change in shape and the plastic flow are not measurable by the methods applied by the above-named authors.
Rationalization of the Hardness Testing of Rubber
Authors: Scott J. R.
Published: February 2011

The object of this paper is to draw attention to the present unsatisfactory state of the hardness testing of vulcanized rubber and the need for standardization of this test, and also to present some results of an investigation into the theoretical basis of hardness testing and the practical significance of hardness measurements. In this paper the word “hardness” will be used in the sense generally accepted in the rubber industry, that is, to denote resistance to indentation. The most commonly used types of hardness tester measure hardness in terms of the depth of the indentation made by a rigid ball or blunt pin pressed into the rubber by either a dead weight or a spring. The reading given by such an instrument, usually termed the hardness number, must depend on several variable factors, namely (1) the dimensions of the ball or pin; (2) the weight used to press it into the rubber, or the compression characteristics of the spring in the case of spring-loaded instruments; (3) the direction of the scale of the instrument, i. e., whether the reading increases with the depth of indentation, as in the Pusey-Jones Plastometer, or in the reverse direction, as in the Durometer; (4) the units in which the indentation is measured, i. e., whether in 100ths of a millimeter, 1000ths of an inch, or arbitrary units. In addition to these factors relating to the instrument, the reading must also depend on the dimensions of the rubber test-piece, especially its thickness, the nature of the rubber surface, and the period for which the ball or plunger is pressed on to the rubber before the reading is taken.
Porosity in Vulcanized Rubber
Authors: Bodger Walter H.
Published: February 2011

A systematic investigation has been made of the factors likely to promote porosity in vulcanized rubber. Of the methods developed for assessing the degree of porosity, measurement of the percentage decrease in specific gravity is shown to be the most satisfactory. The permeability of the sheet to moisture, the acetone extraction of aged samples, and visual examination also give some indication of the degree of porosity. Severe over-mastication, particularly on cold rolls, plasticizes rubber and increases the entrapment of gases during mixing. If the pressure applied during vulcanization is low, the volume decrease, which occurs as the rubber vulcanizes, causes further lowering of pressure; some of the entrapped gases are liberated, and as the rubber is partially set up free escape is prevented and pores are developed. The effect of over-mastication can also be produced by heat or oxidation treatment of the raw rubber. Mechanical treatment of the mix, such as sheeting from the mill at friction speed, calendering to a thick gage, or extrusion of thick articles may increase the tendency for porosity under the appropriate conditions. Softeners added to the mix produce the same effect as over-mastication in increasing porosity, whereas stiffening fillers oppose its production. When no mechanical pressure is applied during vulcanization, porosity is likely to develop, but a slight pressure may cause even worse porosity through preventing the free escape of gases during the soft stage before vulcanization commences. The degree of porosity depends on the conditions prevailing during the initial stages of vulcanization and is, in fact, a useful indication of setting up when scorching tests are being carried out. It is not influenced by the action of heat, in the later stages of vulcanization on the rubber-sulfur or oxygenated rubber complexes. Moisture, derived from the ingredients of the mix, the processing or the methods of vulcanization, increases the porosity under appropriate conditions. The use of ultra-accelerators or high-curing temperatures, tends to increase porosity of mixes liable to this defect, as the escaping gases are more completely entrapped by a rapid setting up of the rubber. Some applications of the results to methods of overcoming porosity under works conditions are given.
Thermal Plasticization of Rubber. I. Structural Changes in Thermally Plasticized Rubber
Authors: Farberov M. I. , Margolina Yu
Published: February 2011

1. The results of the experiments give a more or less complete picture of the relative changes in rubber brought about by mechanical and thermal plasticization, and show that there is an analogy between the two effects. 2. The fundamental factor in thermal plasticization is oxygen (for a given set of thermal conditions), whereby a definite numerical relation exists between the plasticization effect and the oxygen concentration. In the experiments described, the quantity of oxygen absorbed by rubber did not exceed 0.55 per cent at the maximum temperature and time of treatment (170° C. for 120 minutes). Thermal plasticization in a medium devoid of oxygen (in carbon dioxide, nitrogen, and ammonia) proceeds very feebly. 3. In treatment at reduced pressure (in vacuo), and consequently with a diminished oxygen content, the higher the vacuum, i. e., the lower the concentration of oxygen, the less was the plasticization obtained. 4. The effect of temperature in thermal plasticization was evident in the acceleration of the reaction between rubber and oxygen. The most effective temperature was in the interval of 150° and 170° C. 5. For an equal plasticity, the internal structure of rubber was preserved to a greater degree after thermal treatment than after mechanical plasticization, judged by the structural viscosity, n, and the magnitude, Q. 6. It was observed that rubber treated at high temperature (170° C.) in carbon dioxide, nitrogen, and ammonia lost to a considerable degree its ability to dissolve in common rubber solvents.
Thermal Plasticization of Rubber. II. Technical Characteristics of Softened Rubber
Authors: Farberov M. I. , Susliakov A. V.
Published: February 2011

1. The method of thermal plasticization makes it possible to prepare rubbers of widely varying but regulated degrees of plasticity. 2. The use of thermally plasticized rubber gives a considerable saving of power in the production of stock. In our experiments the saving of power amounted to 15–50 per cent, depending upon the proportion of rubber in the stock and on the required plasticity. The greater the proportion of rubber, and the more plastic the rubber required for the stock in question, the greater will be the saving in changing from ordinary masticated rubber to thermoplasticized rubber. Based on equal plasticities, the saving is due essentially to the elimination of the process of mechanical mastication. 3. Mechanical properties of vulcanizates made from thermoplasticized rubber, both before and after aging, are in no way inferior to those of vulcanizates made from ordinary masticated rubber, if the plasticities of the rubbers are equal. 4. Thermoplasticized rubber has a smaller calender-grain effect than standard masticated rubber. 5. Thermoplasticized rubber is distinguished by a considerably smaller water absorbing capacity (about one-half) than ordinary masticated rubber.
Investigations of Dispersing Agents and Stabilizing Agents for Latex Mixtures, and the Behavior of Latex Mixtures When Stored
Authors: Bächle Otto
Published: February 2011

The great sensitivity to mechanical as well as to chemical influences which is possessed by latex, in common with all hydrophobic colloids, leads to immediate difficulties in the preparation of its mixtures. The ingredients, which in most cases are insoluble in water, must first be finely ground and then dispersed in water before being added to the latex mixture. Good dispersion is effected only by the use of high efficiency mechanical dispersion apparatus (ball mill, pigment grinding mill, etc.) and at the same time by the use of a suitable dispersing agent. Moreover, since latex mixtures may have to be stored for a long time, and since premature coagulation may take place during the preparation of such mixtures by the ingredients added or by mechanical influences, and later by incipient vulcanization, it is necessary to stabilize these latex mixtures in practice so that they can be handled safely. Much work has already been done on the stabilization of latex and latex mixtures, as a result of which a great number of products are recommended and used today. A certain stabilizing action is obtained by the addition of water, a greater stabilizing action by aqueous solutions of alkalies. Furthermore, soaps and soap-like compounds are used, e. g., casein is in general a good medium. A few special products are offered today by the chemical industry.
Raman Spectrum of Rubber and Some Related Hydrocarbons
Authors: Gehman S. D. , Osterhof H. J.
Published: February 2011

A Raman line spectrum has been secured for rubber and balata by using clear gels of the purified hydrocarbons. It was not found possible to eliminate the background entirely. The most intense frequency for both rubber and balata is the same, 1670 cm.−1, ascribed to the double bond. Comparison of the frequencies for rubber and balata with those of trimethylethylene, myrcene, isoprene, and limonene shows that the primary linkages in rubber are very similar to those in trimethylethylene, thus supporting the view that the rubber molecule consists of a long chain of isopentene units. Differences in the spectra require an explanation, however. The spectrum of balata shows differences from that of rubber such as might be expected from a cis-trans relationship. The spectrum of myrcene is largely a superposition of the isoprene and trimethylethylene spectra.
Fundamental Studies on the Attributes of Organic Accelerators. XI. Peculiarity of Some Accelerators toward Rubber Sols
Authors: Shimada Keichi
Published: February 2011

Experiments lead to a revision of former views regarding the action of heat and of Group C accelerators on rubber solutions. The changes in the viscosities of dilute rubber solutions by heating or by the addition of Group C accelerators are attributed to a destruction of the remaining micelles, i. e., a disaggregation and subsequent depolymerization of the rubber molecules thus formed and those already present.
Reinforcement and Stearic Acid
Authors: Barron Harry
Published: February 2011

(1) Addition of stearic acid does not increase reinforcement of carbon black mixes to an appreciable extent; however, the work of retraction is considerably augmented, and the hysteresis loss is reduced. (2) The action is two-fold; free stearic acid lubricates, thereby reducing internal friction, while dissolved stearic acid reduces interfacial tension, thereby increasing wetting or true reinforcement. (3) Addition of more than 2 per cent of stearic acid lowers reinforcement, since the lubrication effect decreases that portion of reinforcement due to internal friction. (4) “Blooming” of stearic acid occurs because it decreases surface tension of rubber, and consequently concentrates in the surface. (5) Removal of stearic acid causes complete disappearance of reinforcement, as measured by work of extention to rupture.
Studies on the Acetone Extraction of Raw Rubber. VII. The Time of Acetone Extraction of Raw Rubber and the Saponification Value of the Acetone Extract and Residue
Authors: Endô Hidemaro
Published: February 2011

During acetone extraction of pale crepe, the free acids and saponifiable matter were extracted almost completely in 1 or 2 hours. The saponification value (A) had a tendency to decrease rapidly and to reach a minimum after 12 hours (in non-continuous extraction) or after 16 hours (in continuous extraction). The cause of the decrease of the saponification value (A) from the commencement of extraction up to the time mentioned is thought to be due to a gradual increase in the amount of extracted non-acidic compounds and unsaponifiable matter with increasing time of extraction, and to the neutralization of acids by other compounds, as by esterification. After reaching the minimum point, the saponification value (A) had a tendency to increase gradually. This increase is thought to be due to (1) a gradual increase of ester extracted, (2) the formation of acids by oxidation, and (3) the formation of free acids by decompositions of esters, though the last factor does not increase materially the saponification value. The change of saponification value of the acetone extract with increasing time of extraction is not due to any change in the type of compounds gradually extracted, but to a change in the acetone extract in the acetone solution during extraction. This is in agreement with the acid value. It was observed in a previous paper (III) that almost all of the free acids contained in pale crepe were extracted by acetone in 1 hour. But by extraction for 1 or 2 hours, a small portion of the saponifiable matter still remain unextracted. This remaining part could not be extracted even by prolonged extraction. It is believed, therefore, that the free fatty acids are dissolved in the saponifiable matter, and that the latter are dissolved in the rubber hydrocarbon. As the acetone extract is very labile, so far as the change of acetone extract is concerned, the acetone extract, whether it be dried or left in solution, should not be stored for too long a time. The results obtained by such long extraction by acetone as multiples of ten hours, as used by Whitby and Winn (J. Soc. Chem. Ind., 41, 336T (1923)), are thought to be quite unreliable.
Determination of Free Sulfur by Titration
Authors: Faĭnberg B.
Published: February 2011

In a recent article on the “Iodometric Method of Determination of Free Sulfur” by Bolotnikov and Gurova (J. Rubber Ind. U. S. S. R., 10, 61 (1933); Rubber Chem. and Technology, 8, 87 (1935)), the authors described a rapid method for determining free sulfur in rubber without a preliminary extraction.
Effect of Oxygen Absorbers in Rubber
Authors: Somerville A. A.
Published: February 2011

In this discussion of flex-cracking, its causes, and a means of controlling it, the theory that oxidation of the rubber is the main factor involved has been used as a foundation. No attempt has been made to prove chemically that oxidation of the rubber actually takes place. This would be difficult, since flex-cracked rubber does not necessarily show the ordinary signs of deterioration, but the work of Neal and Northam (4) has indicated that oxygen plays a part. The facts that oxygen absorbers definitely retard flex-cracking and also that the more strongly they are able to absorb oxygen, the greater is their retarding effect, would be difficult to explain on any other basis. The mechanism of the reaction, however, is obscure and is further complicated by the fact that the oxygen absorbers develop their full effect only in the presence of a catalytic antioxidant. As a working hypothesis it may be assumed that the oxygen absorber removes dissolved or absorbed oxygen within the rubber before and during vulcanization, while the antioxidant protects the rubber surface against atmospheric oxygen during service. It is realized that this hypothesis does not explain every fact connected with the use of oxygen absorbers to complete satisfaction and will doubtless be subject to change or modification as practical experience with these agents accumulates. In the meantime it is believed that a practical commercial means of greatly retarding the flex-cracking tendency of rubber goods has been developed.
Hydrazines as Rubber Softeners
Authors: Williams I. , Smith C. C.
Published: February 2011

THE process of softening rubber has received much less study than its importance deserves. Since the method of softening rubber by mastication was devised by Hancock, the greatest advances have been in the introduction of machines of greater mechanical efficiency and greater capacity. Prior to 1920 the effect of such variables as temperature was little understood. Long and inefficient periods of milling at high temperatures were common. In case milling did not produce the required plasticity, recourse was had to the addition of oils, resins, and other soft materials sometimes in considerable amounts. Such conditions have not yet entirely disappeared. Various methods have recently been proposed for plasticizing rubber in a more uniform manner and with less power consumption. Worthington and Hyde (24) softened rubber by heating it in a nonoxidizing atmosphere. Bradley and Ferrettie (1) concluded that the rubber should be water-soaked before it is heated and should be kept wet during the process. Tuley (21) patented the process of softening rubber by the addition of lead dioxide during the period of mastication, and Gerke (7) used a mixture of lead dioxide with an organic acid anhydride. Cruikshank (4) proposed the use of solvents containing alcohols of high molecular weight or sulfonated petroleum products as mastication assistants. According to Martin (10) the addition of nitrites to the latex before coagulation produces rubber of superior plasticity. Rubber softened by heating in an oxidizing atmosphere according to the method of Unger and Schidrowitz (22) has recently become a commercial product.
Hard Rubber. Its Carbon and Hydrogen Content
Authors: Fisher Harry L. , Schubert Y.
Published: February 2011

IN THE course of a study of vulcanization it became necessary to compare the ratios of carbon, hydrogen, and sulfur in hard rubber. A search of the literature revealed no analyses for carbon and hydrogen, although many analyses for sulfur in hard rubber have been recorded. Combustion analyses were therefore made on several samples of hard rubber, and the data are recorded here. The saturation of the double bonds in the rubber hydrocarbon with sulfur should give a compound, (C 5H8S)x, which contains 32.02 per cent of combined sulfur, and some of the recorded results agree with this figure. Since it is also possible to obtain products having greater amounts of combined sulfur than that called for by the theory of addition alone, some of the sulfur must consist of sulfur of substitution (7). It is theoretically possible that substitution and addition of sulfur can go on simultaneously; as the result of these two reactions, it may happen that the total sulfur in combination will equal the theoretical amount required by addition alone. In such a case there would be some free double bonds, but attempts to determine free double bonds in several samples by the Kemp-Wijs method (5) were unsuccessful.
X-Ray Spectrography of Polymers and in Particular Those Having a Rubber-like Extensibility
Authors: Katz J. R.
Published: February 2011

For many years Staudinger defended the theory that polymers have—in the simplest ease—a long chain form of molecules, in which a certain small unit repeats itself regularly along the chain, the units being united by primary valencies. His arguments were not, however, at the beginning of 1927, sufficiently convincing. The decisive argument was forthcoming shortly afterwards by the application of x-ray spectrography. I would like to begin this article by bringing a few personal memories about this development. At the meeting of the Naturforscherversammlung in Innsbruck in September, 1924, I first heard him defend this theory, especially for the ease of polyoxymethylenes, but also for some other cases. Neither I myself nor some others to whom I spoke were convinced by his very interesting exposition. His conception seemed possible, but, many of us thought, not proved. And the whole subject did not yet look attractive to many of us. At the meeting of the Naturforscherversammlung in Düsseldorf in September, 1926, where a symposium on high molecular weight substances was held, he again defended this theory. In 1926, the interest in the subject had already increased a good deal, as is clearly shown by the fact that a symposium on the subject had been arranged. Yet, Staudinger's conceptions did not seem to many of us really convincing, nor was the decisive value which x-ray spectrography could have for the subject yet understood at this meeting. Under these circumstances there can be little doubt that the priority of the idea of the long chain molecules for polymers is chiefly due to Staudinger.
Chloroprene Synthetic Rubber (Sovprene)
Authors: Klebanskiĭ A. L. , Tzyurikh L. G. , Dolgopol'ski I. M.
Published: February 2011

1. A method is described for the continuous polymerization of acetylene at low temperatures in a dilute aqueous solution of the catalyst, CuCl.NH4Cl. Monovinylacetylene is obtained as the chief product of the reaction, with a 75–80 per cent yield, based on the acetylene entering into the reaction, and 25–30 per cent of trimers and higher polymers of acetylene as by-products. The conversion of acetylene by a single passage of the gas is 40 per cent. The yield, based on the acetylene, is nearly 100 per cent. 2. Data on the optimum amount of the catalyst are compiled, and the principal factors which affect the process of polymerization of acetylene with the formation of monovinylacetylene as the chief product are shown. 3. The problem of the mechanism of the polymerization of acetylene is discussed. 4. A method of separation and collection of the reaction products by absorption in solvents is described. 5. A method for the discontinuous synthesis of chloroprene without excess pressure is described. 6. A procedure for the continuous production of chloroprene from pure monovinylacetylene and its mixture with acetylene is described. 7. The conditions of the polymerization of chloroprene to α-polymer are described, with particular reference to the conditions which inhibit the formation of rapidly aging and hardening polymers. The latter are considered as balata-like products. 8. A process of polymerization in solvents, with formation only of the α-polymer is described.
The Internal Heating of Ebonite during Vulcanization
Authors: Daynes H. A.
Published: February 2011

It is known that the reaction between rubber and sulfur to form ebonite is strongly exothermic, and under certain conditions may cause a marked internal rise of temperature during vulcanization. This heating is sufficient in many cases to accelerate the rate of vulcanization of the center of the mass to an important extent, so that the degree of vulcanization of the center differs from that of the surface, the product thus being non-uniform in physical properties. In more severe cases the temperature may rise sufficiently to cause decomposition, evolution of gas and porosity, or even violent explosion. This internal heating is favored by a high temperature of vulcanization, by great thickness of the mass to be vulcanized, by the addition of accelerators of vulcanization, and by the omission from the mixing of inert compounding ingredients, which act as diluents. It is, perhaps, not so commonly known that the heating is greater in an open steam cure, owing to the lower rate of dissipation of heat from the surface, though this factor may have been one of those leading to the common adoption of the water immersion method of cure. In technical practice the inconvenience of this phenomenon is avoided as far as possible by a control of the factors mentioned, including such devices as the inclusion of semi-vulcanized ebonite dust or crumb, building-up from semi-vulcanized sheets, “stepped” or rising cures, or, where possible, by designing the object so as to facilitate conduction of heat from the center by means of recesses or metal inserts.
Internal Protective Coatings for Latex Containers. Investigations of Internal Protective Coatings for Latex Containers and Their Value in Minimizing Discoloration in Preserved Latex
Authors: Rhodes Edgar , Sekar K. C.
Published: February 2011

In a previous publication (cf. J. Rubber Res. Inst. Malaya, 5, 176 (1934); Rubber Chem. and Tech., 7, 433(1934) the present authors have discussed fully the causes of discoloration in preserved latex and have shown that the iron drum which is in common use as a latex-shipment vessel is in itself a predisposing factor in the discoloration of latex. Users do not however look with favor on the substitution of a non-metallic container for the steel drum, and since suitable alternative metallic containers are prohibitive in cost, there remains little alternative but to endeavor, by the internal application of some protective medium, to reduce to a minimum the objectionable effects of the iron drum on its contents. Since discoloration is due to the formation of dark-colored colloidal and amorphous sulfides of iron, a satisfactory drum-coating medium should prevent contact of the latex with the iron of the drum, and also if possible react with any sulfur compounds which may be liberated in the latex, to form sulfides which are either white in color or so nearly white that when present in latex they are not detectable by the eye. It is essential that the coating should not be so brittle as to crack or flake away from the metal when drums are roughly handled in transit. If flaking occurs, serious contamination of the latex may result. The requirement is a tough, elastic film which will adhere well to the metal and which will not be appreciably affected by long contact with ammoniated latex, except in so far as it may combine with sulfur compounds to produce a white product.
A Simplified Extrusion Plastometer for Unvulcanized Rubber
Authors: Dillon J. H.
Published: February 2011

An extrusion plastometer operating at rates of shear comparable with those existing in rubber tubing machines has been described previously. This plastometer was not designed to be a routine testing instrument, but rather was intended for use in the determination of the value of a high speed extrusion test for the factory control of rubber stocks. The plastometer served satisfactorily in the capacity of a research instrument, and has for some time been in constant use as a physical testing instrument where great rapidity of operation is not essential. The results obtained with this plastometer were found to correlate with tubing machine behavior. It was also found that the extrusion plastometer results agreed better with factory experience with various types of masticated rubber than did the Williams plastometer results. It was learned by experience with the extrusion plastometer, when used as a physical testing instrument, that its results agreed closely with calender behavior. In many cases, it was found that the extrusion plastometer results did not correlate with the Williams plastometer results and that, in general, the extrusion plastometer appeared to be much more sensitive than the Williams plastometer. The next step after establishing the value of the high speed extrusion test was to design an extrusion plastometer suitable for routine control testing. Such an instrument must be rugged in construction, rapid and simple in operation, and must yield precise results. The extrusion plastometer, which is described in this paper, was designed to fulfill these requirements and at the same time to give the same type of test results as those given by the original experimental plastometer.
An Impact Cutting Test for Tire Tread Stocks
Authors: Dillon J. H.
Published: February 2011

The impact cutting device described in this paper is recommended for testing the cutting resistance of tread stocks because of its simplicity and the accuracy with which its results agree with road test results. The fact that the device was designed on semi-quantitative theoretical grounds gives some additional confidence in its results. It is possible that other cutting devices, designed with no regard to theory whatsoever, might operate as well as the impact device. However, it is felt that, since most laboratory tests on rubber stocks are necessarily largely empirical, it is well to attempt to design a testing machine which will operate in the ranges of the variables found in service.
A New Plastic Material—AXF
Authors: Shinkle S. D. , Brooks A. E. , Cady G. H.
Published: February 2011

RUBBER technologists are familiar with the increasing number of uses to which rubber has been put in recent years through modifications and adaptations effected by skilful compounding. At the same time, however, active research has been carried out, stimulated by the desire for new materials to meet still more exacting requirements—for example, greater resistance to oils and solvents and to oxidation. In general these investigations have taken one of two directions; they have been directed to a search for new synthetic rubber-like materials or to a study of new derivatives of rubber. In both of these fields of research, achievements of outstanding importance have been disclosed. Whitby and Katz (9) reviewed and summarized the development work on synthetic rubber from its early beginnings. The announcement of poly-chloroprene or DuPrene by Carothers (2) and his associates was soon followed by recognition that this product is a synthetic rubber-like material with physical properties not only rivaling those of rubber but superior in many particulars in which rubber is most deficient. Various olefinpolysulfide reaction products have been described by Patrick (6) and, under the trade name of Thiokols, have been presented to the industry. Other synthetic products which have attracted the attention of rubber compounders include the glyptal resins (10), flexible phenol resinoids, and the recently announced Koroseal (1). A paper by Thies and Clifford (8) has summarized the reactions of the rubber hydrocarbon, apart from oxidation and vulcanization reactions.
The State of Rubber in Solutions. Part II. The Effect of the Temperature on the Viscosity of Solutions of Various Concentrations
Authors: Dogadkin B. , Lawrenenko M.
Published: February 2011

1. The relative viscosity of a rubber solution, the concentration of which does not exceed 0.3 per cent, does not change with change in temperature. 2. The viscosity of rubber solutions at concentrations from 0.3 to 10 per cent diminishes in direct proportion to an increase in the temperature. 3. Based on the results mentioned above and on the measurements of Abernethy the state of rubber in solutions is characterized by the fact that at concentrations up to 0.3 per cent the solutions are molecular. At concentrations from 0.3 to 10 per cent the solutions contain micelles. In solutions of still higher concentrations the rubber forms a continuous phase of the system.
Diphase Rubber. The Diphase-forming Tendency of Rubber as Shown by the Action of Pigments
Authors: Menadue F. B.
Published: February 2011

In recent years increasing attention has been paid to a fact emphasized by Weber, viz., that when rubber is carefully treated with solvent two layers separate out, the one drying out to a rubber considerably tougher than the other. The former is the well-known “insoluble” portion, though with exclusion of the protein component it is merely insoluble to a greater degree than the other portion. Its toughness is also to an extent due to the protein it contains. It has been suggested that rubber is a diphase substance, and also that the harder portion occupies the shell or the skin of the particle. Other very interesting suggestions have been that elasticity is due to the association of the two phases, while recently Whitby has stressed the striking theory that rubber is composed of an unbroken series of polymers. By the following series of experiments the author has sought to investigate further the suggested diphase property of rubber by an investigation into the separation into “phases” exhibited by the action of pigments. The investigations also produce matter of interest in relation to vulcanization and the behavior of rubber in general.
The Stress-Strain Relationships of Vulcanized India-Rubber. Part I. The Inflection Point
Authors: Shacklock Cecil Wilson
Published: February 2011

Definition.—The relation between applied load and the resulting extension of vulcanized or unvulcanized rubber may be represented graphically as a curve which is “s” shaped, and there is a point of inflection in the curve. If a load W grams be applied to the rubber, and the resulting length be L, the point of inflection is defined as the point on the curve where the second differential becomes zero and changes sign. More simply, the point of inflection is where the tangent to the curve crosses the curve. It is well known that the point of inflection exists, but there appears to be no reference in the literature to any attempts to determine precisely its position. It is also apparent from the many stress-strain curves of rubber which have been published that the point of inflection varies with both the period of cure and the compounding of the rubber. What follows is an account of some experiments made to investigate the position of the point of inflection in the stress-strain curve of vulcanized rubber.
Studies on the Nature of the Action of Organic Accelerators for Vulcanization. VI. Detection and Analysis of Organic Accelerators. 3. The Analysis of Water-Soluble Ultra-Accelerators and a New Colorimetric Method for the Micro-Analysis of Copper and Manganese
Authors: Shimada Keiichi
Published: February 2011

(1) A reliable method has been described for the quantitative analysis of the so-called water-soluble dithiocarbamate accelerators, such as piperidine pentamethylenedithiocarbamate, diethylamine diethyldithiocarbamate, dimethylamine dimethyldithiocarbamate, sodium diethyldithiocarbamate and sodium dimethyldithiocarbamate. It depends upon the fact that these ultra-accelerators readily react with soluble nickel salts in solution, forming very sparingly soluble precipitates which can be estimated quantitatively by gravimetric analysis, the weight of the insoluble nickel derivatives obtained being a direct measure of the dithiocarbamate present. Copper, cobalt and zinc react similarly with the accelerators and form sparingly soluble precipitates, respectively, but the solubilities of these metallic derivatives, determined from the results of the conductivity measurements, are about three times as large as that of the nickel derivatives; hence the precipitation of the accelerators with these metals does not give a means of evaluation by practically quantitative yields with the accelerators met with commercially.
The Volumetric Determination of Free Sulfur in Rubber
Authors: Robertson J. A. , Young J.
Published: February 2011

The determination of free sulfur is probably the analytical process most frequently carried out in the chemical laboratory of a rubber factory, and it would be even more often used, could it be more quickly performed. For the oxidation of the sulfur contained in the acetone extract from rubber, Mackay (J. Soc. Chem. Ind., 49, 401-3T (1930)) has described a rapid method which has been used in these laboratories for several years with complete success, but the sulfate produced has to be determined gravimetrically and the process is still too slow for use in factory control work. The acetone extraction of the rubber samples can usually be carried out at night on a bath with automatic time control, and if a rapid method for the determination of sulfur in the extract were available, the results of the analysis could be ready early next day. From a review of the literature the volumetric determination of sulfate by rhodizonate (Strebinger and von Zombory, Z. anal. Chem., 79, 1 (1929)) appeared to be promising, and on trial has given satisfactory results.
The Influence of Time on the Elongation of Soft Rubber under Constant Load
Authors: Everts W. W. C.
Published: February 2011

According to specifications for the testing of rubber prepared by Committee Thirteen of the Deutscher Verband für die Materialprüfung der Technik, there are at the present day two common and at the same time distinct methods for studying the mechanical properties of soft rubber, viz., tensile tests, and, secondly, determinations of elasticity. As carried out in practice, the tensile test is based fundamentally on the tensile testing of metals. With its great elastic properties, however, soft rubber exhibits to a very high degree changes in its elongation with time, and earlier testing methods give relatively unsatisfactory information about the effect of time during the stretching of rubber. Of course the determination of elasticity in the specifications mentioned above, where the so-called permanent elongation is measured, gives a certain insight into this influence of time. Nevertheless this earlier method is not suitable for obtaining comparable results in all cases.
Studies of the Conditions Affecting the Vulcanization of Rubber. V. The Effect of Accelerators on the Heat of Vulcanization
Authors: Toyabe Y.
Published: February 2011

The heat of vulcanization of rubber compounds containing various quantities of sulfur and several organic vulcanization accelerators were traced by means of a differential thermocouple during the vulcanization. The profiles of the heating curves were similar to those obtained in the case of unaccelerated compounds, but the temperature maxima appeared sooner with accelerated than with unaccelerated compounds. The vulcanizates corresponding to the temperature-maxima were analyzed chemically by ordinary methods and the ratios of the free to total sulfur were calculated. They vary a little from 50 per cent, and show that the extent of sulfur combination is not much different from that with unaccelerated compounds. The accelerators tested were hexamethylenetetramine, aldehyde-ammonia diphenylguanidine, di-o-tolylguanidine, p-nitrosodimethylaniline, thiocarbanilide, “Vulkacit P”, “Vulkacit PX”, “Vulkacit M”, and tetramethylthiuramdisulfide The results of the experiments show that these accelerators promote the disaggregation of the micellar structure of rubber (as shown in reports II and III 0. this work) before chemical combination of rubber and sulfur occurs. By thus making the single micelle of rubber smaller, they increase the number of chemical units of rubber coming into reaction with sulfur; i. e., the probability of combination of rubber and sulfur becomes greater. The times for the temperature maxima to appear in the experiments above, which are shortened by accelerators, show that this theory holds good, when it is considered that the temperature maxima correspond to the disaggregation maxima of the rubber hydrocarbon under consideration.
Isoprene and Rubber. Part 22. Isorubber Nitrone
Authors: Staudinger H. , Joseph H.
Published: February 2011

Rubber Micelles or Macromolecules The idea of Pummerer that the parent molecule of rubber is [C5C8]8 is based upon molecular weight determinations carried out by him and his colleagues upon rubber in menthol and above all upon isorubber nitrone. This latter product, which has been prepared by Alessandri and again by Bruni and Geiger by the action of nitrosobenzene on rubber has, according to Pummerer and Gündel, the constitution [C5H6,C6H5NO]8. On this subject the authors say that: We made cryoscopic molecular weight determinations of isorubber nitrone iii benzene and nitrobenzene. Even in these generally used solvents the nitrone gives depressions which indicate a molecular weight lying between 1200 and 1400. For a parent rubber molecule of 8 isoprenes which reacts with 8 molecules of nitrosobenzene with a splitting off of 16 atoms of water, a weight of 1384 is calculated, agreeing very well with the above. As is the case with determinations of rubber in menthol, here the final measurements can be undertaken only when the constant is obtained (in this case after 1-2 hours) and not immediately after the solid substance disappears, for otherwise the value will be about 1000 or 2000 higher, which probably results from a still incomplete solution of the micelles. The study of isorubber nitrone, therefore, supports our opinion on the size of the parent rubber molecule which was expressed earlier. These opinions apparently do not conform to the view expressed by one of us some time ago, according to which rubber has a very high molecular weight, and the primary colloid particles, therefore, the particles in dilute solution, form macromolecules. These have a molecular weight of about 68,000, so that approximately 1000 isoprene residues are united in a chain . This concept was based on a study of models, especially on experiments on polysterol and further by conversion of rubber into colloid-soluble rubber-phosphonium salts, by the preparation of homologous polymeric series of polyprenes, by the decomposition of rubber, and finally by relations between viscosity and molecular weight in this series.
The Fusion Curve of Natural Rubber
Authors: Susich G. v.
Published: February 2011

Katz has shown that the melting point of frozen raw rubber is 35°–38° C. when determined by the disappearance of the crystal interferences upon warming. The discontinuous changes in the specific gravity, in the hardness, and in the light absorption, as well as the γ-anomaly of the specific heat, lie within this temperature range.
Micromanipulations of Latex in the Dark Field
Authors: Hauser E. A.
Published: February 2011

It can be conclusively proved that the individual particle in latex of Hevea brasiliensis after the evaporation of the dispersing agent is surrounded by an adsorbed layer, probably of protein and resin. In the dispersed condition, the particle shows a difficulty penetrable and not deformable surface. After puncture a highly viscous mass flows out from the interior, and at the moment it comes in contact with the dispersing agent it stiffens to a plastic jelly, while the remaining shell exhibits remarkably elastic properties. After the evaporation of the dispersing agent, there occurs a progressive gelation and transformation into an elastic substance. The same result is obtained when the rubber phase is coagulated by acids or electrolytes. The establishment of this fact is important in connection with the usual preparation of raw rubber. It was proved that the consistency of the particles and the thickness of the elastic shell are dependent on the age of the trees. We are dealing not with a definite membrane, but with a variable enveloping shell whose strength seems dependent on the degree of polymerization of the hydrocarbon. In general the results of the present work prove the latest concepts of the structure of rubber, i. e., the existence of various degrees of polymerization, which can be traced back to the structure of the latex particles.
Hard Spots in Vulcanized Rubber Compounds
Authors: Howey J. H.
Published: February 2011

Although positive evidence is lacking, it is believed that the correlation between localized internal flow and the accompanying hardness of the “flowed” regions must be due either to the production of a local grain effect by the flow or to an alteration of the dispersion in that region, or possibly to both. The correlation cannot be attributed to non-uniformity in the mixture, elastic strains, or orientation of the original grain. This explanation is a matter of theoretical interest in connection with the divergent views now held as to the mechanism of reënforcement by pigmentation. However, the results of this investigation may be applied to increase the precision of testing the hardness of carbon-black stocks whether we understand the underlying phenomena or not.