bluuebunny/crossref_metadata_2025 huggingface dataset:
Accelerators and Colors in Sponge Rubber
Authors: Watts John T.
Published: February 2011

The class of products falling under the generic name of sponge rubber may be subdivided into two main sections, depending solely on whether the pores are closed or open. Closed pore structures, in which the gas cells retain their individuality, are characterized by cell size and hardness of the vulcanizate. This latter may vary from the softness of toilet-sponge to the hardness of ebonite. Among the softer grades of closed pore sponge, some of the contributing factors to softness of texture are: (1) the method and degree of plasticizing the raw rubber, (2) the ratio between raw rubber, fillers and softeners, and (3) the type of accelerator used. Open-pore structures include latex sponge and cellular rubber in which the gas cells have been ruptured by mechanical means after curing. For the purpose of this paper the position is simplified by considering latex sponge alone as an open-pore sponge, as the mechanical operation for the production of open-pore from closed-pore sponge follows the rubber manufacturing process. The closed-pore structure in rubber is usually produced by compounding with gas- or vapor-producing materials which, with change in temperature during cure, either liberate gas or change in phase to produce individual cells in the rubber compound. Alternatively, gas (usually nitrogen or carbon dioxide) may be dissolved in the rubber compound under pressure and the stock inflated by either rise in temperature or decrease in pressure, or both.
The Crystal Structure of β-Isoprene Sulfone
Authors: Cox E. G. , Jeffrey G. A.
Published: February 2011

A detailed x-ray analysis has shown that the molecule of β-isoprene sulfone has a heterocyclic structure, in which resonance occurs between the three carbon-carbon bonds of the C4S ring. The bond lengths are C—C (in the ring) 1.41 a., C (ring)—C (methyl) 1.54 a., C—S 1.75 a., and S—O 1.44 a., all ± 0.02 a.; the distribution of the four sulfur bonds is approximately tetrahedal.
Molecular Weights and Intrinsic Viscosities of Polyisobutylenes
Authors: Flory Paul J.
Published: February 2011

Experimental methods for fractionating polyisobutylene and for determining osmotic pressures have been described. The ratio π/c of osmotic pressure to concentration has been found in the case of cyclohexane solutions of polyisobutylene to vary nonlinearly with concentration, contrary to recent theories advanced by Huggins and the writer. The slope of this relationship appears to be independent of molecular weight. Reliable methods for extrapolating π/c to c=0 have been established, enabling the determination of absolute molecular weights with satisfactory precision up to values of about 1,000,000. Molecular weights of polyisobutylenes calculated from Staudinger's equation are too low; the discrepancy is more than ten-fold at high molecular weights. On the basis of data for carefully fractionated samples covering a two-hundred-fold molecular weight range, the intrinsic viscosity is found to be proportional to the 0.64 power of the molecular weight. This decided deviation from Staudinger's “law”cannot in this instance be attributed to nonlinear chain structure, as Staudinger has sought to do in other cases. This dependence of molecular weight on intrinsic viscosity leads to the definition of a “viscosity average”molecular weight which is obtained when the relationship is applied to heterogeneous polymers. The viscosity average is less than the weight average molecular weight, which would be obtained if Staudinger's equation were applicable, and greater than the number average obtained by osmotic or cryoscopic methods.
Properties of Rubber Solutions and Gels
Authors: Huggins Maurice L.
Published: February 2011

Although the data presented suffice to show the general applicability of our theoretical equations to rubber systems large gaps in our knowledge obviously remain. In particular, to would be desirable to have more data on systems having large μ1 values.
Synthetic Rubber. A Spectroscopic Method for Analysis and Control
Authors: Barnes R. Bowling , Liddel Urner , Williams V. Z.
Published: February 2011

Rapid quantitative analysis of compounds of prime interest in the production of synthetic rubber is possible by a relatively simple technique of spectroscopy. An apparatus suitable for such analyses is described, which does not require skilled technicians. It may be easily converted into an automatic control device for the control of production. The spectra of the natural and synthetic rubbers illustrated provide information concerning the structure of rubber molecules and can be used to identify the type of rubber present in unknown samples.
Identification of Carbon Black by Surface-Area Measurements
Authors: Amon F. H. , Smith W. R. , Thornhill F. S.
Published: February 2011

In general then, we may conclude that carbon black can be recovered from rubber stocks with unchanged surface-area. The nitric acid technique is the most effective method of effecting the separation. The digestion temperature must be controlled to between 60° and 70° C, for a total of not more than 3 to, 4 hours. This method of identifying the carbon black in an unknown rubber stock is directly applicable only in the presence of a single type of carbon black. If blends of blacks are employed in the material under investigation, some secondary identification is also required. The nonimpingement-type blacks, for example, are readily identified by microscopic observation. From the known surface-areas of these materials and the total per cent carbon present in the stock, a fairly positive identification of the blend can be made. The fact that carbon black can be recovered quantitatively and with unchanged surface-area from vulcanized rubber stocks appears to lend impetus to a physical concept of carbon black reinforcement. This point of view implies that any chemical combination between the ingredients of the rubber stock and the carbon black would be evidenced by some alteration in the surface of the latter. A few experiments were performed in an attempt to establish to what extent this concept was valid. One hundred grams of Grade-6 carbon black were intimately mixed with 6.6 grams of sulfur. This is about the ratio in which they are present in a standard rubber batch. Samples of this mixture were subjected to the standard curing temperature of 134° C for 30, 60, and 90 minutes. The free sulfur was then extracted for 40 hours with acetone ,and the combined sulfur on the carbon was determined. Values of 0.16, 0.21, and 0.4 per cent combined sulfur were obtained. The original sample of Grade-6 carbon black had a surface-area of 108 square meters per gram. The extracted sample of black containing 0.4 per cent of combined sulfur had a surface-area of 109 square meters per gram. These values are identical within experimental error. While unaltered surface-area need not necessarily be interpreted as evidence of complete lack of surface reactions, it is the authors' opinion that the extent of chemical combination at the carbon black surface is very small. This interpretation is in accord with the views expressed in a previous publication3, where it was suggested that the chief role of carbon black in rubber reinforcement may rest on its ability to orient the chains of rubber molecules and thus alter the extent and type of rubber-sulfur bonds normally formed in non-reinforced rubber stocks.
Electrical Properties of Neoprene
Authors: Yerzley Felix L.
Published: February 2011

This review is based on data selected from tests conducted over a period of years. Under the circumstances it does not happen that identical Neoprene was used throughout. Several types are referred to in the compounds. Each group of tests is consistent within itself, but direct comparison from group to group is not justified. Neither do exact values within a group have individual merit, but the trends of electrical quantities with controlled changes of the variable under study are of primary importance. In general, numerical values reported are the average of results obtained on two samples, but all conclusions have been confirmed by numerous parallel and related tests. Unless otherwise specified, tests were made at 82° F, after the samples had been dried in a desiccator for at least 16 hours. Conventional methods were used. For all tests except those on dielectric strength, tinfoil electrodes 0.001 inch thick, adhered to the test slab by a thin film of petrolatum, were utilized. The test-specimens were usually 6 × 6 × 0.075 inch, except for occasional samples which were approximately 0.020 inch thick. In the case, of the direct-current resistivity test, the upper electrode was a 3-inch-diameter disk of tinfoil surrounded by a guard ring. The lower electrode was a 6-inch square of tinfoil. The Leeds & Northrup test set consisted of a sensitive galvanometer and an Ayrton shunt. An alternating-current bridge was used for measurements of conducting stocks. For the tests of power factor and dielectric constant, the upper electrode was a 3-inch-diameter disk of tinfoil, without a guard ring. The lower electrode was a 6-inch square of tinfoil. General radio equipment was utilized, consisting of a type-716A capacitance bridge, complete with the necessary auxiliaries. A telephone headset was used for detection of null points. All tests reported here were conducted at frequencies of 1000 cycles per second. For the determination of dielectric strength, an American Transformer Public Utility test set, type-TS, having a secondary voltage range from 100 to 50,000 volts was used. The electrodes were of the standard A.S.T.M. type. Ordinarily the test-specimens were about 0.020 inch thick and 6 inches square. The voltage across the electrodes was gradually increased until breakdown occurred. The gauge was then measured adjacent to the punctured spot, and the voltage and dielectric strength were calculated by dividing the value of the voltage by this gauge.
The Elasticity of a Network of Long-Chain Molecules. I
Authors: Treloar L. R. G.
Published: February 2011

The treatment of the elasticity of a molecular network by the method of Wall is discussed and is compared with the earlier treatment of Kuhn. It is shown that a more accurate application of Kuhn's method leads to formulas for elongation and shear in agreement with those of Wall.
The Course of Autoöxidation Reactions in Polyisoprenes and Allied Compounds. Part. VI. The Peroxidation of Rubber
Authors: Farmer Ernest Harold , Sundralingam Alvapillai
Published: February 2011

Peroxides have repeatedly been shown to appear during the slow oxidation (perishing) of rubber in air, and during both its milling in air and the passage of air or oxygen through its solutions: yet in none of the recorded experiments has the production of any very substantial proportion of peroxide been demonstrated. This arises largely because, under many conditions of autoöxidation, no very considerable proportion of peroxide is present in the oxidation product at any stage, but in part because no convenient and reasonably accurate method of determining the peroxide content in so insoluble a substance as rubber has been available. It must inevitably happen in a long-chain molecule of polymer-homologous type containing on the average about 5,000 autoxidisable olefinic units that the progressive entrance of a heterogeneous element will yield a large variety of closely similar products if attack is fairly evenly distributed over the chain, but when, as in the case of oxygen, the heterogeneous element enters the hydrocarbon as a diatomic molecule, the atoms in which can ultimately separate and become attached to the carbon chain in a variety of ways, and causes, as the result of its progressive incorporation, scission of the chain at an ever-increasing number of the olefinic units, then the potential range of diversity of the products becomes enormously increased.
Interaction between Rubber and Liquids. IV. Factors Governing the Absorption of Oil by Rubber
Authors: Gee G.
Published: February 2011

A piece of vulcanized rubber, dropped into benzene, swells to several times its size but retains its shape. With raw rubber, a further stage ensues, in which the rubber flows and ultimately disperses. Inevitably, one tends to form a picture of the rubber attracting and holding the liquid with some strong force. It is the purpose of this paper to explain why this picture is believed to be entirely false, and to give an alternative explanation of the phenomena of swelling and solution. It will be necessary first to consider briefly the way in which simpler materials mix with one another. The simplest possible system is that of two gases which do not react with each other. In a gas the molecules spend most of their time a long way from one another, and the total energy of the system is therefore made up largely of the kinetic energy of thermal motion. As a consequence of this kinetic energy the gas molecules tend, on the average, to distribute themselves uniformly, so that any pair of gases mix completely. A quantitative interpretation can be given to this mixing tendency, in terms of the concept of entropy. Of the various ways in which entropy may be regarded, the most useful for the present purpose is in terms of probability. Qualitatively it is evident that gas molecules in violent thermal agitation are extremely unlikely to arrange themselves so all molecules of one type are confined to one part of the vessel. This is expressed in thermodynamic language by saying that the entropy of such an arrangement would be small. The second law of thermodynamics states that if, as in a gas, there is no change of energy, a system tends to take up the state of maximum entropy, or maximum randomness. A quantitative expression to the relationship between the entropy S and probability W, takes the form:
How Sulfur is Combined in Vulcanized Rubber
Authors: Van Amerongen G. J. , Houwink R.
Published: February 2011

Little is known with any degree of certainty about the way in which sulfur combines with rubber during vulcanization. It is the aim of the present work to examine, with the aid of Stuart molecular models, the various chemical reactions which have been suggested to explain the mechanism of vulcanization, and to decide which of these reactions may actually take place. THE MECHANISM OF THE REACTION BETWEEN RUBBER AND SULFUR Fundamentally, two general types of combination of rubber with sulfur are possible: (1) the formation of intermolecular sulfur bridges between chains of rubber molecules, with resulting formation of a network structure. (2) an intramolecular combination of sulfur with the individual chain molecules of rubber.
Effect of Petroleum Products on Buna-S Vulcanizates
Authors: Morris Ross E. , Mitton Philip , Montermoso Juan C. , Werkenthin Theodore A.
Published: February 2011

The authors believe that the tear resistance data presented in this paper should be kept in mind by anyone contemplating the use of Buna-S in applications where occasional contact with petroleum products may occur. The coincidence of the following three conditions on the surface of a Buna-S vulcanizate will amost certainly lead to a serious tear: 1. Cracking (weather cracks, cuts, gouges, snags). 2. Wetting with petroleum products, particularly the lighter variety. 3. Flexing, static or dynamic. The tear will probably continue through the object until the flexing stress is relieved or until a fabric insert is reached. Thus, a tire tread would be torn through to the breaker fabric.
Nitroparaffins in the Rubber Industry
Authors: Campbell A. W. , Burns J. W.
Published: February 2011

A recent development in the field of industrial chemicals which has met with widespread interest is the first commercial production of nitroparaffins in 1940. The announcement of nitroparaffins to industry was followed by extensive investigations in industrial and research laboratories of the suitability of these compounds in a wide variety of applications, including many in the field of rubber technology. It is the purpose of this paper to summarize the more promising applications of the nitroparaffins in the rubber industry which have so far been reported.
S. K.—The Russian Synthetic Rubber from Alcohol. A Survey of the Chemistry and Technology of the Lebedev Process for Producing Sodium-Butadiene Polymers
Authors: Talalay Anselm , Talalay Leon
Published: February 2011

The question of producing synthetic rubber industrially was raised in Russia as early as 1918, and was fostered principally by the quest of the U.S.S.R. for economic independence. Having recognized that 1,3-butadiene is one of the simplest organic compounds capable of being polymerized to a rubberlike substance, the Russian Government provided funds for research in two directions: (1) To investigate the possibility of obtaining butadiene from a mixture of ethyl alcohol and acetaldehyde, according to the method suggested by Ostromislensky in 1915, for which purpose a pilot plant was erected in Moscow at the Bogatyr Rubber Company. (2) To continue work started in 1915 by B. V. Buizov in the laboratory of the Leningrad Treugolnik Rubber Plant, using petroleum products as a source of butadiene. By 1922 the Moscow plant had proved that Ostromislensky's process had no industrial future, for it yielded only 5 to 6 per cent of butadiene instead of the 15 to 18 per cent originally expected. The experimental station operated by Buizov had likewise met with little success by 1925. Early in 1926, therefore, the Superior Economic Council of the U.S.S.R. announced an open competition for the best industrial method of producing synthetic rubber, setting January 1, 1928 as the deadline. The qualifying conditions were rather exacting. They specified that the synthetic rubber should be neither inferior in quality to, nor substantially different in price from, natural rubber. Aside from a detailed description of the process and a two-kilogram sample of the synthetic product, the competition called for plans of a complete factory layout for its manufacture.
The Interaction between Rubber and Liquids. II. The Thermodynamical Basis of the Swelling and Solution of Rubber
Authors: Gee G.
Published: February 2011

It has been the purpose of this paper to show that the general phenomena of solubility and swelling of rubber could be understood on the basis of the detailed results found experimentally for the rubber-benzene system. Using no arbitrary constants which cannot be related to experiment, temperature coefficients of solubility of the right order of magnitude are calculated. It is clear that the qualitative agreement of this treatment with the meagre experimental data at present available must not be taken as evidence of the accuracy in detail of the equations employed for the heat and entropy of solution. This paper is based on work carried out under the programme of fundamental research on rubber undertaken by the Board of the British Rubber Producers' Research Association.
Swelling of Synthetic Rubbers in Mineral Oils. Swelling in Mineral Oils Containing Polyolefins and in Mixtures of Nujol and Biphenyl
Authors: Powers P. O. , Robinson H. A.
Published: February 2011

The true cloud temperature of a 50–50 weight mixture of aniline and mineral oil is a reliable index of the amount of swelling a synthetic rubber undergoes when immersed in mineral oil. This result is also true of mineral oils which contain polyolefins. Since the presence of both haze and cloud points is characteristic of such oils when mixed with aniline, a method has been worked out for distinguishing between them. Conversely, the presence of both haze and cloud points is believed to be indicative of the fact that polyolefins have been added to the mineral oils. The addition of polyolefins to mineral oils reduces the tendency of those oils to swell synthetic rubbers. The logarithm of the percentage swelling varies inversely with the aniline point. Although mixtures of Nujol and biphenyl can be duplicated fairly well, they offer no advantage over mineral oils for testing the tendency of synthetic rubber compositions to swell. Although the logarithm of swelling decreases as the 50 per cent aniline of the mixture increases, the relationship is not the same as that found for mineral oils. for evaluating behavior under service conditions, immersion tests in oils having the same aniline point as oils which may be encountered in service are believed to be more reliable and more significant.
Solubility of Polybutene in Pure Solvents
Authors: Evans H. C. , Young D. W.
Published: February 2011

During the past few years interest in the preparation and properties of long-chain polymers has been intensified because of their importance in the manufacture of improved petroleum products, plastics, and chemical-resistant paints. Materials such as polybutene and rubber form solutions, the viscosities of which increase rapidly with concentration. Typical viscosity-concentration data on dilute solutions of polybutene have been published. A number of workers have determined the viscosities of several polymers in dilute solutions, and from these investigations equations have been proposed for expressing viscosity as a function of molecular constitution. One of the most important considerations has been the question whether very high polymeric substances exist in solution as long macromolecules, completely dispersed, or as aggregations of much shorter molecules associated in the micellar state. Staudinger, one of the chief proponents of the former view, carried out a large amount of work on the viscosity of solutions of such linear polymers. His conclusions regarding chain length were based almost entirely on such measurements interpreted on the basis of the viscosity relation:
Molecular Structure and Rubberlike Elasticity. III. Molecular Movements in Rubberlike Polymers
Authors: Bunn C. W.
Published: February 2011

In Part I of this work, the crystal structures of β-gutta-percha, rubber and polychloroprene (deduced from x-ray diffraction photographs) were described. In pursuance of the idea that rubberlike properties are due to molecular flexibility which result from the swivelling of the chain units around single chain bonds, it is necessary to consider which chain-bond positions are the most stable and what hindrances there are to rotation away from these positions. The question of the most stable bond positions was considered in Part II. I now consider the evidence for the occurrence of rotation in rubberlike substances, the hindrances to rotation in different molecules, their effect on the crystallization or melting temperature, and the explanation of the mechanical properties of these substances in terms of structure and molecular movement, both above and below the crystallization temperature. Rubber is noncrystalline and elastic at room temperature; but on cooling below 0° C it crystallizes, and in that condition has the mechanical properties of gutta-percha; i.e., a frozen specimen no longer has enormous elasticity, but it can be drawn or rolled out irreversibly, whereby the crystals become oriented. Conversely, if gutta-percha is wanned to 70° C, it becomes amorphous (transparent, optically isotropic and noncrystalline), and its mechanical properties are then like those of rubber—it is soft and elastic. The difference between the two substances thus appears to be essentially a difference of crystallization temperature. These crystallization temperatures are remarkably low; e.g., polyethylene, (—CH2—CH2—)n, of comparable molecular length, crystallizes at 115–125° C. In attempting to understand rubberlike elasticity in terms of molecular behavior, the first question is why are the crystallization points of such enormous molecules so low, and why is the crystallization point of the cis-form of polyisoprene (rubber) lower than that of the trans-form (gutta-percha).
Constitution of Three-Dimensional Polymers and the Theory of Gelation
Authors: Flory Paul J.
Published: February 2011

In three-dimensional polymerizations, gelation is due to the formation of network structures of indefinite extent. These giant structures make their appearance when the degree of branching or cross-linking of the polymer chains exceeds a critical value. Gelation may be considered analogous to explosion in gas-phase reactions propagated by chains which undergo branching. After gelation has occurred, the sharp distinction between gel and sol is analogous to the demarcation between a liquid and its saturated vapor. Observed average molecular weights of three-dimensional polymers must be interpreted with extreme caution, owing to the peculiarity of the distribution of species in the vicinity of the gel point. Applications of the theory to raw rubber, protein gels, and inorganic gels have been discussed.
Rubber Analysis of Plants in South Carolina
Authors: Mitchell J. H. , Rice M. A. , Roderick D. B.
Published: February 2011

In 1930 and 1931 some plants growing in the vicinity of Clemson, South Carolina, were collected and analyzed for the presence of rubber. The plants were collected and identified by M. A. Rice, the chemical tests being made by the other two authors. The results are presented below. The figures given at the right show the percentage of rubber in each case. All determinations were made on a basis of air-dry weight.
A Low-Temperature Stiffness Test for Elastomers
Authors: Morris Ross E. , James Robert R. , Evans Edward R.
Published: February 2011

Most synthetic vulcanizates stiffen more than natural vulcanizates at low temperatures. This behavior has aroused considerable interest in the development of suitable tests for the cold resistance of synthetic vulcanizates. Inasmuch as all rubbers gradually stiffen and finally become brittle as the temperature is lowered, two general types of cold resistance tests have been developed, viz., stiffness tests and brittleness tests. The stiffness tests involve a quantitative measurement of the resistance to deformation of the specimens; the brittleness tests consist in determining the temperature at which the specimens will fracture when rapidly bent. We are concerned here only with stiffness testing.
Effect of Temperature on the Vibration Characteristics of Natural and Synthetic Rubbers
Authors: Morron J. D. , Knapp R. C. , Linhorst E. F. , Viohl P.
Published: February 2011

The results of this work have been to show, that the effect of temperature on the functions of vibration insulators is much greater than would be supposed from the type of tests which have become more or less common in the industry for determining the effect of low temperatures on various elastomers. It has shown also that natural rubber is the outstanding material for vibration insulation at subnormal temperatures. The substitution of any of the synthetics for natural rubber is a problem which requires not only a thorough study of compounding, but also of the practical conditions under which the particular mounting or insulator is supposed to function. An improvement in vibration insulation over a wide range of temperatures may be obtained by means of increased initial deflection. A critical point, called the “barrier point”, which depends not only on the compound but on the design and application of the mounting, is defined. New laboratory methods have been devised to obtain information which design engineers can apply to practical problems. This equipment actually shows the percentage of transmission of vibration. New equipment for the determination of stress-strain curves and tensile tests at all temperatures are likewise described and their uses explained. We hope that the simple, yet accurate instruments which have been devised from commonly available materials will be of some encouragement to others who wish to investigate the properties of different elastomers over a range of temperatures, but are hampered by the limitations of priorities, expense, and the fact that there is a lack of suitable equipment on the market for such investigations.
Surface Film Thicknesses of Polymeric Substances in Relation to Molecular Structure
Authors: Wall Frederick T. , Zelikoff Murray
Published: February 2011

It is well known that certain compounds, such as long chain fatty acids, can form monomolecular films on water and that the areas of such films can be related to the dimensions of the molecules. Certain polymeric substances, including cellulose derivatives, proteins and the polymer of ω-hydroxydecanoic acid likewise form stable films whose areas can be conveniently measured. At this time we wish to report that we have prepared films of some rubberlike polymers as well, and that the results appear to give useful information about their molecular structures, particularly in relation to branching.
Effects of Molecular Structure on Physical Properties of Butyl Rubber
Authors: Flory Paul J.
Published: February 2011

The investigation was undertaken in an attempt to establish the fundamental connections between the physical properties of a typical vulcanized rubberlike polymer and its chemical structure. The structural variables to be considered are the molecular weight of the “primary molecules” entering the vulcanizate, their molecular-weight distribution, and the concentration (or frequency) of cross-linkages introduced during vulcanization. The molecular weights of Butyl rubbers were determined by previously established procedures ; the effects of molecular-weight heterogeneity were suppressed by careful fractionation from very dilute solution. An indirect method, based on the theory of gelation and on the observation of critical molecular weight for incipient gelation (partial insolubility) in “vulcanisates” formed when the cross-linking capacity is fixed, was employed to determine the frequency of occurrence of cross-linked units—a quantity not hitherto evaluated in a vulcanized rubber. In representative pure-gum vulcanizates of Butyl the molecular weight per cross-linked unit ranges from about 35,000 to 20,000, depending (inversely) on the diolefin content of the raw rubber. Micro compounding and testing procedures have been devised for evaluating the necessarily small samples ob- tained in fractionation. Complete evaluation of tensile strength, stress-strain characteristics, swelling in solvents, and creep rate can be obtained with as little as 3 grams of rubber. Results are no less reproducible than those obtained with conventional procedures requiring 50 grams or more. A number of rela- tionships between vulcanizate structure and physical properties have been established. The feasibility of a rational approach to the interpretation of properties of rubber vulcanizates in terms of molecular structure has been demonstrated.
Electrically Conductive Rubber
Authors: Bulgin D.
Published: February 2011

Carbon particles in rubber are at first distributed as individual particles by the shearing action of milling, but the individual particles are in a state of Brownian movement due to the kinetic energy of the system. This causes the particles to drift about at a rate determined by the size of the particles, or particle aggregates, and the effective viscosity of the segments of the rubber molecules which is less than one hundredth of that of bulk rubber. The particles thus soon come into contact with each other, and since they are of a disordered crystalline structure and possess relatively high free surface forces, they cohere. The mobility of the aggregates of the particles is much less than that of the individual particles, due to their large size and size relative to that of the rubber molecules, so finally they are relatively immobilized into a scaffoldlike structure of carbon particles. This structure can be broken by external forces, and the broken structural units reform in vulcanized rubber to a structural state at a rate, and to an extent determined by the kinetic energy of the system. The idea of increasing structure formation with rise in temperature is apparently contrary to the kinetic theory, but the persistance of a stable conductivity value in passage from a high to a lower temperature rules out particle motion as the prime cause of conductivity. Furthermore the attainment of a discrete value for the conductivity (Figure 19) at any temperature rather than an alteration of the rate of change towards some maximum value, suggests that temperature activated energy barriers exist—possibly between the carbon and the rubber—which have to be broken before the carbon particles are free to move. Such a system explains the conductive properties of carbon-rubber mixes containing carbon particles of 250 to 300 A.U. diameter, but the properties of systems containing carbons of greatly different particle size may be considerably different. There is some evidence that the cohesion of carbon particles into structural units is sufficiently high to withstand the shearing forces involved during milling and processing treatments of unvulcanized rubber, and so carbon, structure formation from individual particles is of an irreversible nature. As the structural units grow in size under the influence of the kinetic energy of the system they become increasingly less mobile. This gives rise to permanent reduction in conductivity if the structure built up is violently disturbed; for example, if unvulcanized rubber is remilled after appreciable structural formation has taken place.
The Course of Autoöxidation Reactions in Polyisoprenes and Allied Compounds. XI. Double-Bond Movement during the Autoöxidation of a Monoölefin
Authors: Farmer E. Harold , Sutton Donald A.
Published: February 2011

In an earlier part of this investigation it was shown that the autoöxidation of Δ1,4-diene8 and Δ1,4,7-, etc., polyene compounds produces peroxido derivatives containing conjugated units, and to explain the formation of the latter a reaction-mechanism was proposed which postulated the detachment of hydrogen atoms from the reactive methylene groups under the action of molecular oxygen, and subsequent rearrangement of the resonating radical residues before oxygen and, finally, hydrogen combine therewith to give hydroperoxides: (see PDF for diagram) It was recognized that, if this mechanism is valid for methylene-interrupted diene or polyene systems, it might reasonably be expected to apply also to the formation of hydroperoxides by the action of oxygen either on simple olefins or on polyolefins containing two or more methylene groups between the double bonds. To demonstrate successfully that even the simplest olefin system capable of hydroperoxidation can give both of the oxygenated forms (A) and (B):
Elastic Deformation and Molecular Weight in Polyisobutylene
Authors: Rehner John
Published: February 2011

Although various properties of high polymers are known to depend on molecular weight, there appear to be no published data which show explicitly how the molecular weight of a rubber-like substance influences the modulus of high elasticity, even though a psychological perception of some such relationship has long existed. Also, the various expressions that have been derived by statistical methods contain molecular weight as a factor ranging from an inverse first power up to inverse higher fractional powers. Some time ago a need arose in this laboratory for estimating the average molecular weights of samples of polyisobutylene by a rapid procedure. Because of the slowness of polymer dissolution, methods based on measurements of the polymer in the dissolved state had to be ruled out and an investigation was, therefore, made of the rate of compression of a variety of samples in a Williams parallel-plate plastometer. It was found possible to render negligible the viscous component of deformation by using a sufficiently high compressive load and by limiting readings to an interval of about one minute. When the observed deformation values were plotted against the logarithm of time, straight lines were obtained. The slopes of the lines could be correlated, at least approximately, linearly with the reciprocal average molecular weights of the samples.
Applications of Ultraviolet Spectrography. A Study of Some Accelerators
Authors: Dufraisse Charles , Houpillart Jean
Published: February 2011

Not only is the problem of determining the compounding ingredients originally present in a rubber mixture by an analysis of the vulcanized product of interest from a technical point of view, but it also is of importance from the theoretical point of view to know what becomes of these ingredients as a result of the thermal effects of vulcanization. This is particularly true of that class of ingredients which function as accelerators of vulcanization. Chemical methods which are applicable to this problem are in all cases very complicated and are inconvenient in various ways. For some ingredients there are no methods at all avaifable. Accordingly it was thought that a study of ultraviolet spectra, the general principles of which have already been described and which have already been utilized by Jarrijon for the determination of anti-oxygenic substances, might offer a more rapid and more reliable means of attaining the desired end. The aim of the experiments to be described was simply to show what is to be expected of the method in this particular practical application. The study was devoted to three accelerators: diphenylguanidine, benzothiazyl disulfide, and mercaptobenzothiazole.
Applications of Ultraviolet Spectrography. A Study of the Transformations Which Tetramethylthiuram Disulfide Undergoes during the Vulcanization Process
Authors: Jarrijon André
Published: February 2011

Various experiments make it clear that the method of spectrographic determination can be applied to a complicated case where the product to be determined does not remain intact in a mixture but is transformed into some other compound. Furthermore the results obtained, which were confirmed by chemical tests, are definite and precise enough to make it possible to determine the type of transformation which takes place in rubber when tetramethylthiuram disulfide is used as a vulcanizing agent. The liberation of sulfur is only an accessory reaction, in fact there is probably not even any such reaction. More probably there is a dehydrogenation of the rubber, without liberation of hydrogen sulfide, a dehydrogenation which involves perhaps certain restricted parts of the molecule, e.g., the extremities of the chains, as has been suggested by Boggs and Blake. It is possible to conceive various schemes whereby this dehydrogenation may take place and which would make it possible to explain at the same time the formation of zinc dimethyldithiocarbamate, the decrease in unsaturation found by Hauser and Brown, and the fixation of a certain amount of sulfur on the rubber.
The Terminology of Intrinsic Viscosity and Related Functions
Authors: Cragg L. H.
Published: February 2011

The confusion existing in the use of symbols and names for Kraemer's “intrinsic viscosity” and other functions related to it is illustrated and deplored. The reasonable plea is made that one name be adopted for each function and that it be used with no other meaning. To stimulate discussion and ultimate action, the following names are proposed: “specific viscosity” for ηsp; “reduced viscosity” for ηsp/c, “inherent viscosity” for (ln ηr)/c; and “intrinsic viscosity” for [η], whether determined as “limiting reduced viscosity” limc→0 (ηsp/c), or as “limiting inherent viscosity” limc→0 (ηr/c), or as “limiting viscosity concentration coefficient” limc→0 (dηr/dc). Often, especially in routine practice, it is the relative kinematic viscosity νr, that is determined ; unless this is shown to be numerically equal to the relative viscosity ηr, the symbols and names of the derived functions should be modified accordingly: thus, (ln νr)/c inherent kinematic viscosity, [ν] intrinsic kinematic viscosity. Frequently, also, kinetic energy corrections are neglected; under these circumstances the suggested usage is tr, relative flow time, tsp/c reduced flow time, [t] intrinsic flow time, etc.
The Theory of Permanent Set at Elevated Temperatures in Natural and Synthetic Rubber Vulcanizates
Authors: Andrews R. D. , Tobolsky A. V. , Hanson E. E.
Published: February 2011

Certain materials, including natural and synthetic rubbers, after being deformed for finite periods of time and then released, do not return completely to their original dimensions. This phenomenon is called “permanent set”. There are many different types of measurements, made under a great variety of conditions, all of which are described as measurements of permanent set. The molecular causes of permanent set are not the same under all of these conditions. For this reason we shall restrict ourselves in the present article to a discussion of the permanent set taking place in thin rubber samples which are maintained at constant extension at elevated temperatures. We shall show that the permanent set which occurs under these conditions is due to chemical changes which affect the structure of the rubber network, and that a quantitative molecular description of permanent set can be accomplished by the use of concepts already developed concerning the nature of these deteriorative chemical processes.
Tackiness of GR-S and Other Elastomers
Authors: Busse W. F. , Lambert J. M. , Verdery R. B.
Published: February 2011

The analysis of tackiness shows that it is a complex property which depends on a balance between a large number of different factors, including the geometry of the sample as well as the surface forces and the visco-elastic properties of the material itself. The quantitative measurements of the effect of the rate of removal on the apparent tackiness of pressure-sensitive adhesive tapes show that significant differences are found at very slow removal rates (105 seconds per cm.) which do not show up at much higher removal rates (10 seconds per cm.). These differences may affect the performance of the tapes in service. A simple quantitative test is described which can be used to study the effects of various processing treatments and various softeners, tackifiers and other compounding ingredients on the tackiness of GR-S and other rubbers. Koresin was the most effective tackifier found for GR-S. The authors wish to acknowledge the continued interest of W. E. Hanford, Director of the Laboratory, and the helpful discussions of tackiness measurements with C. E. Schildknecht. Miss Ruth Sellers and Miss J. L. Nuver helped in taking much of the data. The first Koresin samples were prepared in the laboratory by C. E. Schildknecht and A. O. Zoss before the commercial material was available.
Evaluation of the Physical Properties of Rubber Vulcanizates at Low Temperatures
Authors: Mullins L.
Published: February 2011

The technical importance of rubber vulcanizates in fields where they are likely to be subjected to temperatures lower than normal requires no emphasis, and has resulted in considerable activity being directed to the evaluation of the physical properties of rubber vulcanizates at such temperatures. The purpose of these investigations has been to compare the low temperature serviceability of various rubbers, and to study of the behavior of the materials at these temperatures in order that the data obtained may be used to assist design. Such extension of knowledge is of great importance since rubber vulcanizates exhibit considerably increased stiffness and become brittle at low temperatures. Several good summaries of the work exist in the literature; these show that there is a considerable lack of uniformity in the methods of testing and representation. As a result of this wide diversity of test methods, there is no generally accepted index of low-temperature serviceability. Many of the tests which have been used involve the extension of the usual technical tests to lower temperatures, whereas others involve a study of the performance of rubber components in conditions of service. The results of such tests generally have been quoted as a temperature below which a particular property fails to fulfil a given requirement. The endeavor to obtain one temperature or one parameter which characterizes the resistance to low temperatures has been only partially successful, since the interdependence of stress, strain, time and temperature make it impossible to formulate relations of a simple character which describe the behavior of rubber vulcanizates over even a limited range of conditions. First, there is the need for an accepted standard test (or tests) ; secondly there is the need for a convenient method of expressing the resistance to low temperatures, and lastly, there is the need for the development of the ideas of the processes leading to the changes in physical properties at low temperatures. In this paper it is intended to review the various methods which have been suggested for low-temperature testing, to indicate the sources of the inadequacy of the individual tests, and to describe the initial results of an investigation, as yet incomplete, into a convenient means of testing and representing the mechanical properties at low temperatures.
A Study of the Rubber-Metal Bond
Authors: Buchan S. , Shanks J. R.
Published: February 2011

Although the practice of bonding rubber to metal has been in use for many years, no theories appear to have been advanced which explain adequately the mechanism of bonding. It has been stated that the brass bond between rubber and metal functions through chemical linkages, but this can only be regarded as tentative and has yet to be proved. No attempt has been made to find out how ebonite functions as a bonding medium or the more recently discovered derivatives of rubber, such as sulfonated rubber, chlorinated rubber, and rubber hydrohalides. Until it is properly elucidated just how bonding agents do act, further logical development of improved bonding media cannot be pursued. It is intended in this paper to show how the rubber-metal bond behaves at subnormal temperatures and how a low temperature technique may be used for studying the mechanism of bonding. The effect of low temperatures on the tensile strength and associated properties of vulcanized rubber, such as hardness, permanent set, flexibility, resilience and flexing, has been dealt with fairly comprehensively in the literature. Progressive reduction in temperature leads to only a moderate increase, for example, in tensile strength, until the point is reached at which the rubber stiffens and freezes, when a marked increase occurs. Examination of a brass-bonded unit at low temperatures revealed that the graph obtained for bond strength was very similar in slope and character to that for tensile strength. The similarity is illustrated by the data in Table 1 and in Figure 1.
The Sensitive Detection of Organically Combined Bromine
Authors: Kirchhof F.
Published: February 2011

When a few drops of concentrated copper sulfate solution are added to a concentrated solution of potassium bromide, this solution turns yellow or brownish. When it is warmed, the color darkens, and on cooling or by dilution it becomes light again; finally at a definite concentration the color becomes yellow-green. If a drop of the concentrated solution is placed on chemically pure filter paper and is allowed to dry, a bright or dark purple-red color is obtained, the shade depending on the method of drying. This color appears even when drying is at room temperature; it becomes paler when one breathes on the sample, and disappears completely when the colored spot is moistened with water, but on drying reappears as a pale rose color, the intensity of which depends on the concentration. The same purple color, but more brilliant, appears when a few drops of concentrated sulfuric acid are added to potassium bromide—copper bromide solution. In this case the color is extraordinarily intense, and it is visible even when only 0.5 mg. of bromine per liter is present.