bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations on the Relation between Laboratory and Test-Stand Measurements of Tire Treads and Their Behavior on the Road
Authors: Kern W.
Published: February 2011

The only way to get a complete picture of the characteristics of tire treads is to classify the tests according to the influence of the compound, construction, type of vehicle, and type of road. Only by adapting tests in the laboratory, on the test stand, and on the road to the nature and intensity of practical service conditions, can good correlation be expected. Laboratory tests show at most the effect of the compound and possibly that of the nature of the road (roughness) and that of the climate (temperature). It is reserved for test stand and road experiments to bring out those properties that are affected by the tread pattern and the type of vehicle. We see as an essential task of laboratory testing technique not so much the creation of new complicated laboratory testing apparatus, as in better and better analysis, using new measuring methods, of the action on tires on test stands and in service, in order from this to find improvements in the available test apparatus and to base these on definite unfalsified elementary processes. The knowledge of the practical conditions not only has the advantage of improving the correlation, but makes it possible even in advance to strive for a goal-seeking development aimed at bettering the tire characteristics, since then one knows in advance what conditions are involved.
Apparatus for the Continuous Measurement of Stress Relaxation in Vulcanized Rubber
Authors: Danjard J. C.
Published: February 2011

The measurement of stress relaxation in vulcanized rubber is based on the principle that, when kept at constant elongation, a stretched sample of rubber shows a progressive decrease of stress with time and that this decrease depends both on the nature of the compound and on the temperature of testing. The resultant curve is a decreasing potential, which is expressed approximately by the equation: σt=σ0⋅e−kt, where σt is the instantaneous stress at time t, σ0 is the initial stress, and k is a reaction rate constant which depends on the free activation energy of the rubber chain molecules. Tobolsky was the first to apply the relaxation theory to the study of the oxidation behavior of compounds and to the approximate determination of the nature of vulcanization structures. Certain types of apparatus are available for the discontinuous measurement of this stress relaxation, but we have designed, with the aid of the French Rubber Institute technical service, a relaxometer for the continuous recording of this phenomenon.
A New Method for Determining the Dynamic Mechanical Properties of Rubber
Authors: Morris R. E. , James R. R. , Guyton C. W.
Published: February 2011

In submarines, machinery with reciprocating rotating parts is placed on rubber mountings to isolate noise and vibration from the hull of the vessel. Otherwise the hull would radiate the noise to the sea and facilitate detection of the submarine by the enemy. The dynamic mechanical properties of the rubber in the mountings determine to a large extent their effectiveness in isolating noise and vibration. Only within the last ten years has reliable information become available on the dynamic mechanical properties of rubber at high frequencies of vibration. Most of this advance has been due to Nolle. Other workers in this field have been Witte, Mrowca and Guth, Hillier, Cramer and Silver, and Morris, James and Snyder. Nolle gave an excellent description and analysis of techniques for measuring the dynamic mechanical properties of rubber in the frequency range of 0.1 to 120,000 cycles per second (cps). The methods which he described were identified as rocking-beam oscillator, vibrating reed, strip transmission, strip resonance, and magnetostriction. Guth and associates, Hillier, and Cramer and Silver used the strip transmission method in their respective investigations. Morris, James, and Snyder used a bar transmission method which had not been previously described. This paper deals with a modification of the bar transmission method, whereby the resonant frequency and dispersion of the vibrational energy above and below the resonant frequency are measured. From this information the velocity of sound, Young's modulus, and loss factor of the rubber are calculated.
Studies of the Vulcanization of Elastic High Polymers. VI. The Vulcanization of Natural Rubber with Benzoyl Peroxide. Part 1
Authors: Lorenz Otto , Scheele Walter
Published: February 2011

The vulcanization of natural rubber by benzoyl peroxide between 110° and 50° C has been investigated. The analysis of the kinetics has led to the following results: 1. The benzoyl peroxide concentration decreases at all temperatures according to a reaction of the first order. The velocity constants have been given. 2. Benzoic acid is formed in a slower reaction, but also according to a first order rate. The limiting value of benzoic acid formation depends on the temperature. It decreases with increasing temperature. The velocity constants for benzoic acid formation have been calculated. 3. With larger additions of peroxide to the rubber, both reactions are of the zero order as long as the solubility limit of the peroxide is exceeded. 4. The temperature dependence of the velocity constants of both reactions has been discussed, and it has been shown that at lower temperatures the formation of benzoic acid and the decrease of peroxide become equally rapid. 5. The analogy between thiuram vulcanization and peroxide vulcanization with respect to their kinetics has been pointed out. 6. It has been made apparent that, in both peroxide vulcanization and thiuram vulcanization, one is obliged to assume the formation of an intermediate compound. But, at the same time, it is not possible to make this consistent with the reaction mechanism which Farmer has developed for peroxide vulcanization, nor to apply to peroxide vulcanization the relationships found by Bartlett for the polymerization of allyl acetate by benzoyl peroxide.
The Vulcanization of Butadiene-Styrene Rubber in the Presence of Sulfenamide Accelerators
Authors: Dogadkin B. , Fel'dshteĭn M. , Pevzner D.
Published: February 2011

1. It is established that N,N-diethyl-2-benzothiazolesulfenamide has a structure-forming effect in stocks of butadiene-styrene rubber when these are heated at vulcanization temperatures, even in the absence of the usual vulcanizing agent, sulfur. These stocks, after extraction with acetone, still contain chemically combined sulfur and nitrogen, and the contents of these increase with a longer heating period. 2. The change of the modulus of the above stocks is a linear function of the amount of N,N-diethyl-2-benzothiazolesulfenamide which has reacted. 3. The structure-forming action of N,N-diethyl-2-benzothiazolesulfenamide can be regarded as a polymerization reaction, brought about by the free radicals formed in the thermal decomposition of this compound. 4. It is possible to vulcanize ordinary sulfur-containing butadiene-styrene rubber stocks in the presence of sulfenamide accelerators without the use of the accelerator activator, zinc oxide. 5. The kinetic curves of combination of sulfur and of the change of the equilibrium modulus, for ordinary sulfur stocks containing the sulfenamide accelerators (N,N-diethyl-2-benzothiazolesulfenamide and N-cyclohexyl-2-benzothiazolesulfenamide), is S-shaped, and shows an initial “induction” period in the vulcanization. This latter is especially distinct in stocks containing N,N-diethyl-2-benzothiazolesulfenamide. 6. Multilayer rubber articles made from plied stocks containing sulfenamide accelerators have stronger adhesive bonds. There are two reasons for this increased bond strength : (1) the retardation of the vulcanization kinetics in the initial stage of the vulcanization process, which is characteristic of the accelerators in question, and which has the effect of prolonging the length of time that the plied stocks remain in a semiviscous condition; and (2) the formation of the stronger —C—C— bonds as a result of polymerization reactions, which are stimulated by sulfenamide accelerators. 7. Vulcanizates prepared with sulfenamide accelerators are different from those with a combination of benzothiazolyl disulfide and diphenylguanidine in that the former have a lower heat build-up and a somewhat greater dynamic deformation resistance.
A Study, by Means of Radioactive Sulfur, of the Mechanism of Vulcanization of Rubber. I
Authors: Bresler S. E. , Pryadilova V. I. , Khainman V. Ya
Published: February 2011

1. In the present work a method was developed for the measurement of the diffusion and the solubility of sulfur in rubber. Values of the diffusion coefficient and the solubility were obtained for a broad range of temperatures. It is shown that the free sulfur in rubber dissolves and diffuses in the form of S8 molecules. 2. The kinetics of sulfur combination with rubber in the presence of an accelerator was investigated. It is shown that at low sulfur concentrations the kinetics is of the first order. The rate constants of sulfur combination were determined, as well as the activation energy (U=23,000 cal./mole) of the process. 3. A study was made of the kinetics of the isotope exchange reaction between elemental sulfur and tetramethylthiuram disulfide in an inert solvent. The experiment showed that the rate constant of the isotope exchange and the rate constant of the combination of sulfur with rubber are equal to one another at all the temperatures investigated (120°–150° C). 4. The conclusion is drawn that the first stage of vulcanization, which governs the overall rate, and likewise the first stage of the isotope exchange reaction, consist in the decomposition of thiuram into radicals, with the diatomic biradical S2 being split off. 5. It is shown that, with an increase in the sulfur concentration, the kinetics of the sulfur combination with rubber ceases to conform to a linear equation. A secondary sulfur combination reaction, taking place at the point where the primary bonding of sulfur to rubber occurred, was discovered. A hypothesis is put forward as to the radical character of the primary sulfur combination, and regarding the union of polysulfide chains with the radicals in polymer chains, radicals which were formed by means of the primary action of sulfur upon the hydrocarbon.
Mastication. Part III. Chemical Verification of the Mechanical Degradation Mechanism of Cold Mastication
Authors: Ayhey G. , Moore C. G. , Watson W. F.
Published: February 2011

The plasticization of natural and synthetic rubbers by cold mastication results from the degradation of the macromolecules. In Part I experimental evidence was presented that such degradation is caused by mechanical rupture of primary carbon-carbon bonds in the polymer (R—R) to give polymer radicals (R · ) which are stabilized by oxygen to give degraded polymer molecules. Such a mechanism, invoking mechanical shear, had been advocated previously, e.g., by Staudinger, most explicitly by Kauzmann and Eyring, but required systematic mastications under nitrogen with a large variety of compounds (radical acceptors) to demonstrate more critically its consistency with experimental observations. However, Part I provided no direct chemical evidence supporting the mechanism by demonstrating reaction between the rubber radical and radical-acceptor molecule. Considering that only of the order of 0.1 per cent of radical acceptor is required for radical termination to give marked degradation, especially favorable reactions and sensitive analytical techniques are required for detecting the basic chemical reactions. The incorporation of radical acceptors into two types of elastomer on mastication has been demonstrated by the use of two radical-acceptor molecules and two distinct analytical techniques: (1) the incorporation of 1,1-diphenyl-2- picryl hydrazyl into natural rubber, using a spectrometric method, and (2) the incorporation of 1,1′-dinaphthyl [S35]-disulfide into GR-S, using a radiochemical method. The incorporation of the radical acceptors should be correlated with extent of degradation measured by decrease in molecular weight. Quantitative correlations have been obtained for both the above radical acceptors.
Adiabatic Stretching as a Method of Investigation of the Elastic Properties of Rubberlike Materials
Authors: Votinov M. P. , Kuvshinskiĭ E. V.
Published: February 2011

1. A direct method has been proposed for the study of the elastic characteristics of rubber stocks under nonequilibrium deformation conditions. 2. This method has been successfully applied in the study of the elastic characteristics of “crystallizing” and “noncrystallizing” unloaded rubber compounds.
Transformation by the Action of Heat and Oxygen of the Sulfur Bonds Which Compose a Vulcanization Network
Authors: Degteva T. G. , Kuzminskiĭ A. S.
Published: February 2011

1. A study of the effect of combined sulfur on the oxidation of swollen and unswollen polybutadiene vulcanizates shows that stocks vulcanized with different types of accelerators (tetramethylthiuram disulfide, diphenylguanidine, and zinc ethylphenyldithiocarbamate) form sulfur bonds which differ in their content of long polysulfide groups. 2. It is shown that sulfur liberated by the polysulfide bonds in vulcanizates reduces the speed of the oxidation reaction and the equilibrium concentration of stable peroxides. The sulfur content also governs the structure-forming process which develops when a raw polymer containing sulfur is oxidized at 90° C. The decomposition products of the polysulfide groups likewise lower the speed of oxidation in swollen vulcanizates at 150°. 3. When swollen vulcanizates are heated in the absence of oxygen at 150°, only the polysulfide bonds decompose. Heating unswollen vulcanizates under the same conditions, however, brings about the reverse effect, viz., structure formation. 4. Sodium sulfite and alcoholic alkali do not remove completely the polysulfide sulfur from vulcanizates. 5. In the process of vulcanization a rearrangement of the sulfur bonds takes place, and this is accompanied by a reduction of the polysulfide content.
Role of Particle Diameter and Linkage Formation in Rubber Reinforcement
Authors: Blanchard A. F.
Published: February 2011

Fillers with little effect on abrasion resistance differ further from carbon blacks in having little or no tendency to introduce some form of strong-type linkage which could sitffen and strengthen the rubber at high extensions. Such linkages are here termed primary to distinguish them from secondary (weak-type) linkages, which have a range of lower strengths as revealed by breakage with applied stress, and contribute little to reinforcement. The abrasion resistance for a given filler concentration is much improved even by remarkably small numbers of primary linkages if the particles are sufficiently small; and it is comparatively insensitive to the number of primary linkages in the quantities normally obtained with carbon blacks. For instance, a considerable degree of reinforcement is obtained with the partially graphitized black known as Graphon, although this black shows drastically reduced capacity to form linkages and little change in particle diameter. The large differences in the wear resistance of vulcanizates containing different grades of carbon black must therefore be attributed mainly to the particle diameter itself rather than to the linkages formed. Moreover, primary linkages as reflected by stress-strain measurements could not explain the effect of particle diameter on reinforcement because they are unrelated to particle diameter. For good wear resistance the particles probably need to have macro-molecular dimensions, though small. To regard the effect of particle diameter in terms of the interfacial area for linkage formation is inconsistent with the above conclusions. For a given dispersion and concentration of filler it is suggested that reinforcement is most likely to find proper expression in terms of the number of linkages per particle and the number of particles. This is expressed mathematically in a tentative, empirical form of equation designed to fit general conceptions, and to correlate roughly the abrasion resistance with filler particle diameter and with primary linkages as reflected by stress-strain measurements. The equation implies that reinforcement increases with diminishing particle diameter until an optimum is reached, and thereafter decreases to become negligible for particles of molecular dimensions.
The Sorption of Water by Rubber
Authors: Tester D. A.
Published: February 2011

In the absence of air the absorption of water by a vulcanized crepe rubber tends to an equilibrium value in accordance with an osmotic mechanism of absorption. An equation for absorption as a function of time, derived by consideration of such a mechanism, represents the experimental data adequately. A relationship may be derived from the basic rate equation, correlating equilibrium absorption with ambient vapor pressure. This equation also gives good agreement with the experimental data. The divergence from the theoretical relationship found for absorption in the presence of air may be attributed to oxidative aging of the rubber. This effect is most marked at elevated temperatures, where the results of absorption under nitrogen are very much lower than those for absorption in the presence of air.
The Quantitative Analysis of Rubber Chemicals. I.
Authors: Scheele Walter , Gensch Christa
Published: February 2011

Studies of the reactions occurring during mastication and vulcanization of rubber must be regarded as still far from completed despite the many valuable experimental contributions. Although many theories have been developed on the mechanism of the processes to be discussed here, either based on the results of direct studies of the chemical processes or on the results of indirect physico-technological methods, one still has the impression that a thorough interpretation of all the relationships is not possible at present. Mastication and vulcanization are undoubtedly very difficult problems which are chosen by the experimenter mainly because of their importance. It is convenient to distinguish between those studies that deal with the elucidation of the reactions of the molecular chains of rubber during mastication, cyclization, and vulcanization, and those that deal with the performance of all the compounds which influence the course of these processes. At present we are interested in the second of these studies. In order to undertake the experimental work, it seemed to be desirable to have analytical methods by which we would be able to determine quantitatively the smallest amounts of accelerators, age resistors and, as well, the decomposition products of various of the rubber chemicals in question. We feel that the development of these methods is absolutely necessary for scientific studies of the kind mentioned and also desirable for the industrial laboratory. Many procedures for the analysis of rubber compounding ingredients, especially of vulcanization accelerators and age resistors, have been published; most of these, however, are for qualitative identification only. Besides precipitation and color reactions, physico-chemical methods are of considerable importance. Spectroscopic investigations of all kinds, and especially the characterization of substances by their ultrared, ultraviolet, and infrared spectra have been widely applied. Work on the application of polarography has become known. Chromatographic analysis has been put to use with marked success to separate compounds of interest and then to identify them by characteristic reactions.
Urethan Rubber from a Polyether Glycol. Properties of Raw Polymer and Vulcanizates
Authors: Hill F. B. , Young C. A. , Nelson J. A. , Arnold R. G.
Published: February 2011

In recent years, the synthesis of polymers by reacting organic diisocyanates with compounds containing two or more active hydrogens has been studied extensively. Much of the pioneering work on the chemistry of organic polyisocyanates and their reaction products was carried out by Du Pont chemists. The products were fibers, elastomers, and plastomeric solids. In Great Britain, research of the Imperial Chemical Industries, Ltd., was directed toward the reaction of polyesteramides with organic diisocyanates to produce vulcanizable polymeric plasticizers, designated Vulcaprenes. In Germany, Bayer and co-workers developed the elastomer known as Vulcollan through their study of the reaction of polyester glycols with organic diisocyanates. Recently, interest in isocyanate-based addition polymers has been stimulated by the commercial availability of a number of polyisocyanates. An elastomer, Chemigum-SL polyester-urethan, was announced by the Goodyear Tire & Rubber Company in 1953. Both Vulcollan and Chemigum-SL are addition polymers of polyester glycols and organic diisocyanates, and both exhibit outstanding toughness and abrasion resistance relative to GR-S or natural rubber. Adiprene-B urethan rubber is a new addition polymer. It differs from other diisocyanate elastomers in that its polymeric segments are aliphatic polyethers rather than polyesters. Adiprene-B is a distinctive elastomer which combines in a single product high strength, abrasion resistance, solvent and ozone resistance, and excellent low-temperature properties.
Studies on Abrasion and Wear of Rubber. I. The Chemistry of Carbon Black and Its Effect on Abrasion as Determined by the National Bureau of Standards Method
Authors: Garten V. A. , Eppinger K. , Weiss D. E.
Published: February 2011

A series of carbon blacks of approximately constant surface area were prepared by heating a strongly acidic carbon black in N2 in the range of 200–1000° C. Their adsorption capacity for alkali and acid, catalytic behavior in H2O2 decomposition, and magnetic susceptibility have been studied and related to their effect on abrasion resistance when incorporated into a standard tire tread stock in the absence of antioxidants. It is suggested that there are, at least, two distinct chemical mechanisms by which carbon blacks can produce reinforcement, that is, by their (irreversible) action as polyphenol type antioxidants (acidic = low-temperature blacks), or in a catalytic (reversible) fashion through temporary stabilization of broken rubber chains on their surface (neutral = medium-temperature blacks).
The Structure of Crystalline 1,2-Polybutadiene and of Other Syndyotactic Polymers
Authors: Natta G. , Corradini P.
Published: February 2011

Systematic x-ray and electron diffraction studies of polymers of 1,3-butadiene prepared by different anionic catalysts have made it possible for us to identify two types of highly crystalline materials. One of us (G. N.) has already reported that our synthesis was carried out with the aid of different highly selective catalysts. The description of the preparation of these catalysts, which have made it possible for the first time to prepare these new polymers, will be separately published by one of us (G. N.) with L. Porri. Infrared analysis carried out by E. Mantica and D. Morero in our Institute has established that one type of these crystalline polymers obtained with heterogeneous catalysts represents a continuous l,4-trans arrangement of the monomer units. X-ray diffraction has shown that this material is dimorphous, having one crystalline modification that is stable at room temperature and another stable above 60° C. The x-ray melting point of a polymer having a molecular weight of the order of 100,000 is around 130° C. The low-temperature modification has an identity period of 4.9 A along the chain axis and a hexagonal packing with a period of a=4.54 A perpendicular thereto, but the symmetry of the crystals, as a whole, is lower. The high temperature modification seems to have the chains in helicoid form. The other crystalline polymer consists essentially of 1,2-monomer units; infrared studies have shown that more than 90 per cent of its double bonds are of the vinyl type and the residual 10 per cent represents a mixture of cis and trans. The higher the proportion of 1,2-units, the more crystalline is the material. Figure 1 shows the infrared absorption curves of two different typical samples of the product. In this article, we limit ourselves to describing the structure of the latter polymer, which, in our opinion, is the more interesting material and which we shall simply call 1,2-polybutadiene. We shall report on the structure of the two modifications of the l,4-trans-polybutadiene in another paper together with the study of the structure of other crystalline polydienes.
The Structure and Viscosity of Hevea Latex. I.
Authors: Verhaar G.
Published: February 2011

Fresh Hevea latex is characterized by the presence of viscoids of greatly varying size (5–200 microns). When the viscosity of such a latex is determined with a viscometer of the rotary type the values found cover a wide range, having no clear relation to the initial DRC of the latex. Also, with the aid of a rotary viscometer, the structural viscosity of fresh or any other type of latex can be clearly demonstrated. When fresh Hevea latex is treated with ammonia in increasing amounts there is a sharp and regular drop in viscosity up to 0.05 per cent NH3. This runs parallel with a gradual and finally complete disintegration of the viscoids. Treatment with sodium sulfite in increasing concentrations up to 0.30 per cent yields a more slowly decreasing viscosity with end values approximately twice as high as with ammonia. Microscopic investigation shows a slow and only partial breakdown of the viscoids in the same area. Formaldehyde gave irregular results, but, in general, did not decrease or increase the initial viscosity considerably, neither could any influence be established on the size and shape of the viscoids. The viscosity of fresh Hevea latex is profoundly influenced by addition of distilled water giving a considerable increase up to 20 per cent and a sharp drop afterwards. Latex diluted with 20 per cent of water was microscopically found to be in a stage of pre-coagulation, with the immobilized rubber particles embedded in the viscoid complexes. It is concluded that the viscoids play a dominant role in viscosity phenomena of Hevea latex.
Dual Inhibition-Acceleration Role of Carbon Black in Rubber Oxidation
Authors: Lyon F. , Burgess K. A. , Sweitzer C. W.
Published: February 2011

Carbon black can function as an inhibitor or as an accelerator of oxidation and cure of rubber and of other polymers. The inhibiting action of carbon black on the oxidation of unvulcanized cold rubber appears to be related to, if not the cause of, the increased reinforcement of the heat-treated stock. In general, the effect of carbon black on the oxidation of cold rubber and natural rubber is the same. With a more complete understanding of the role of carbon black in polymer oxidation and cure reactions, it should be possible to control the behavior of carbon black so that advantage can be taken of its inhibiting and accelerating properties in prolonging the life and increasing the usefulness of rubber goods.
The Heat Treatment of Butyl-Carbon Black Compounds
Authors: Edwards D. C. , Storey E. B.
Published: February 2011

1. Heat enhancement effects with HAF black-GMF systems do not appear to involve a chemical bonding of the polymer to the carbon surface. The principal reasons for this view are : (a) Very similar physical properties are obtained, in the case of 50-part carbon black masterbatches, whether or not the black is present during the heat treatment. (b) When the carbon black content is increased, it is necessary to increase the quantity of GMF in order to produce a given degree of gelation. 2. With GMF, very satisfactory properties are obtained by heat-treating a highly loaded mixture and diluting this masterbatch with fresh polymer. Such a process is less sensitive to the time and temperature conditions of the heat treatment operation. 3. The application of such a procedure to Butyl-HAF black mixtures results in modulus and hysteresis properties approaching those of a conventionally mixed cold-rubber tread.
Mooney Viscosity of Carbon Black-Rubber Mixtures
Authors: Studebaker M. L.
Published: February 2011

The principal properties of carbon black which must be considered in the study of rubber mixtures containing carbon black are (1) particle size and the related property, (2) surface area, (3) hydrogen content, (4) oxygen content, and finally a property which is more difficult to evaluate but which is related to (5) the tendency to agglomerate. This latter term is referred to in the trade as a “structure” factor, and it is usually determined from oil absorption measurements. Unvulcanized rubber-carbon black mixtures are considered to be analogous to mixtures of carbon black and with other liquid media, for example, mineral oil. It has been demonstrated by Weltmann and Green that the “plastic viscosities” of concentrated suspensions obey a modified “Arrhenius equation”. In this paper it is shown that unvulcanized rubber-carbon black mixtures also obey a similar equation. The rheological properties of concentrated suspensions are profoundly influenced by long-range London-van der Waals forces. Some of the laboratory tests by which these forces are studied by colloid chemists are specific volume of a powdered solid under pressure, sedimentation volume, oil absorption, and plasticity. A correlation is demonstrated between data obtained by these tests and Mooney viscosity. A general equation is presented relating the Mooney viscosity with the concentration of carbon black and oil absorption. This equation applies to all of the data which have been examined in natural rubber. In GR-S another term, the oxygen content of the carbon black, must be included.
Studies on Carbon Black. III. Theory of Bound Rubber
Authors: Villars D. S.
Published: February 2011

Theories of reinforcement may be grouped into two general classes, mechanical and chemical. The mechanical type of theory attempts to explain reinforcement by alteration of direction of tear or by mechanieal entrainment. The chemical type of theory invokes the formation of bonds between the filler and rubber. Because of its implication with respect to the latter, Fielding of Goodyear developed a “bound rubber” test. The amount of rubber bound to carbon black was defined as that unextractable from the raw masterbatch by benzene. Some ten years ago, Baker and Walker reported an insolubilization of GR-S, on mixing with carbon black, over and above the amount of naturally occurring gel. The amount of insolubilized polymer increases with increasing molecular weight of the GR-S, and a selective adsorption of the high molecular weight material was found. Since this phenomenon was obtained also in polymers where they believed chemical gelation to be impossible, the conclusion was drawn by them that it is purely physical—this notwithstanding the fact that they found that extractions at higher temperatures failed to remove the insolubilized polymer. Because the method of analysis for insolubilized polymer used by Baker and Walker was essentially a bound-rubber analysis, interest in the latter was revived and it became desirable to set up a hypothesis to explain the mechanism of bound-rubber formation. (Let us understand the term “rubber” as applying in its more general sense as synonymous with “elastomer”.) The present paper reports a theory developed by the writer about ten years ago to explain various observations on the hypothesis that bound rubber is a gel of carbon black particles, the bonding agent of which consists of the longer polymer molecules. The theory interprets the observed linear dependence of bound rubber on loading in terms of an elemental area associated with the segmental adsorption of elastomer molecules, the molecular weight of these segments, and the functionality of the carbon black particles.
The Identification of Fillers in Vulcanized Rubber
Authors: Endter Friedrich
Published: February 2011

In the analysis of the filler content of any type of vulcanized rubber, it is desirable not only to obtain data on the filler content and its chemical composition, but also to characterize as definitely as possible the individual components. In the case of vulcanizates containing carbon black, this means the identification of the black as a member of one of the known types of blacks, and in the case of vulcanizates containing white fillers, to characterize the individual inorganic fillers as definite physical compounds. These problems cannot be solved by methods of chemical analysis alone.
Secondary Softening Regions of Copolymers, Mixed Polymers, and Graft Polymers
Authors: Ecker R.
Published: February 2011

A polymer is a macromolecular substance which is built up from individual monomeric units by a process of chemical linking into a long chainlike substance. Figure 1 is an attempt to give in schematic form a picture of the general structures of three purported types of copolymers, mixed polymers, and graft polymers.
Nonlinearity in the Dynamic Properties of Rubber
Authors: Payne A. R.
Published: February 2011

The first two sections of this paper deal with the necessity for amending the classical Newtonian equations by assuming a nonlinear stress-strain curve in order to account for the presence of a considerable amount of second harmonic of the test frequency in the restoring forces in a rubber, in both forced-vibration and positive-displacement dynamic testers. The nonlinear stress-strain curve is applied also to a damped free-vibration curve of the Yerzley type, and is shown to account for the asymmetry of the envelope of the vibration curve. The latter part of the paper obtains a relationship between the dynamic modulus of loaded rubbers and amplitude of vibration, leading to equations analogous to those used in rheology to deal with rate of shear effects in non-Newtonian liquids, and to explain the effects of fillers on the static modulus and hardness of vulcanized rubbers. A resonance curve from a resonant vibrator is analyzed and the variation of modulus with amplitude is shown to exhibit the typical thixotropic effect associated with loaded rubbers subjected to vibrations. The last section discusses how the decrease of modulus with increasing amplitude can be attributed to two different mechanisms: (1) thixotropic breakdown of filler structure, (2) in compression, nonlinearity of the stress-strain curve.
Electrochemical Aspects of Rubber Latex, Compounding Ingredients, and Their Mixtures
Authors: Roy Brojeswar
Published: February 2011

The electrophoretic speeds of rubber latex particles as well as of colloidally dispersed compounding agents, e.g., zinc oxide, sulfur, china clay, and mixtures of them as are generally employed in baths for electrodeposition, have been measured in a microcataphoresis cell of the Northrup-Kunitz type. The ζ-potential of latex, calculated from the electrophoretic speeds, is considerably influenced by the presence of the compounding agents. Sulfur sol having the lowest ζ-potential tends to reduce that of latex as well as of others in a mixture, whereas zinc oxide and china clay, which have higher ζ potentials, tend to increase the value for latex. A mixture of zinc oxide and china clay shows the highest (60 mV) ζ-potential compared to latex itself (ζ=28.8mV). The isoelectric point of rubber latex was measured by calculating the ζ-potential from the electrophoretic speed at different pH values, which were maintained by means of Na2CO3⋅NaHCO3 buffers at the higher range and acetate buffers at the lower range. The I.P. was 4.2 and was lowered in the presence of zinc oxide and china clay sols to 3.0 and 3.8, respectively, but increased to 5.1 in the presence of sulfur sol.
Kinetics of Hydrochlorination of Unvulcanized and Vulcanized Latex
Authors: Gordon M. , Taylor J. S.
Published: February 2011

In the van Veersen hydrochlorination of latex, two stages associated with different reaction loci and mechanisms are distinguishable : a surface reaction in an outer shell and a bulk reaction inside the particle. The rate control of the two mechanisms is discussed. The surface reaction stands isolated at low pressures of hydrochloric acid, and is measurable down to about 0.08 atm. of the gas. It affects only about 2 per cent of the rubber in Hevea latex, but up to over 20 per cent of synthetic or selectively creamed Hevea latex with sufficiently fine particles. The saturation of double bonds at the surface locus proceeds in an inward direction from the particle surface, and is limited to about the outer four layers of polymer chains. This restriction is due to the instability of the diffusing reagent in the rubber medium, which also accounts for the enormous nominal reaction order of the surface reaction. This order was found to be about 26 in one run, while the bulk reaction follows zero order kinetics. The kinetics of the isolated surface reaction is shown to be a useful tool in studying the unsaturation of the surface layers in vulcanized latex. By its means it is proved that a surface reaction can also affect latex vulcanization. This is technically important because the film strength of latex decreases critically with increasing vulcanization of the particle surface.
Pyridinium High Polymers—A New Class of Oil-Resistant Synthetic Rubbers
Authors: Reynolds W. B. , Pritchard J. E. , Opheim M. H. , Kraus G.
Published: February 2011

Copolymers of butadiene and 2-methyl-5-vinylpyridine are readily vulcanized by heating in the presence of organic halides. The number of effective crosslinks can be readily calculated from moduli of swollen stocks using the statistical theory of rubber elasticity. Crosslinking depends upon the amount and activity of the quaternizing agent. However, even at low levels of halide concentration, it appears that several quaternary groupings are necessary for each effective crosslink. Zinc oxide greatly increases the moduli of the swollen copolymer-halide systems. However, sulfur and accelerator alone have little effect on the same system and these agents do not further increase the moduli of the swollen ternary system, copoylmer-halide-zinc oxide.
The Rapid Semimicrovolumetric Determination of Sulfur in Natural and Synthetic Rubber Vulcanizates
Authors: Bauminger Bella B.
Published: February 2011

In the first part, a modified form of combustion apparatus for sulfur analyses is described, and the principle of the method and the apparatus itself are illustrated by a schematic diagram. In the determination of sulfur in natural-rubber, Butyl-rubber, and Krylene mixtures which contain no mineral fillers such as barytes and whiting, 50 mg. of finely divided vulcanizate is covered with aluminum oxide, decomposed in a current of oxygen at 1000° C, and the sulfuric acid formed is determined gravimetrically. An analysis requires about 30 minutes. Differences between the analytical values obtained and the calculated values never amount to more than ±1 per cent. In the second part of the work, a newly developed procedure for the determination of total sulfur in rubber mixtures which contain barytes, lithopone, whiting, etc., is described. The sample is covered with a mixture of vanadium pentoxide and zinc oxide and is then decomposed in a current of oxygen at 1000° C Here too the sulfuric acid which is formed is titrated acidimetrically. An analysis requires about one hour. The final part of the work deals with a new method for the determination of sulfur in synthetic-rubber vulcanizates, such as Neoprene, Perbunan, Hypalon, etc. The sulfuric acid formed by their combustion is precipitated by a hydrochloric acid solution of 4-amino-4′-chlorobiphenyl, and titrated with sodium hydroxide. Zinc, chlorides, and nitrates have no disturbing effects on the reaction. The method was tested with vulcanizates of known compositions and was found to give satisfactory results.
Effect of Initial Molecular Weight of a Rubber on the Strength and Fatigue of Its Vulcanizates
Authors: Bartenev G. M. , Novikov A. S. , Galil-Ogly F. A.
Published: February 2011

(1) With decrease of the original molecular weight of rubber, there is a parallel decrease of the durability of its vulcanizates when they contain the same percentage of combined sulfur. On the other hand, this decrease of durability with decrease of the original molecular weight is only slight for vulcanizates having the same equilibrium modulus, i.e., the same density of crosslinks in the three-dimensional network. (2) In dynamic testing which involves repeated stretching, the durability depends on the testing conditions when the vulcanizates contain the same percentage of combined sulfur and at the same time when either the original molecular weight of the rubber is low or the equilibrium modulus is small. On the contrary, when the original molecular weight or the modulus is high, the durability does not depend on the testing conditions. When vulcanizates have the same equilibrium modulus, their durability depends on the original molecular weight. In this latter case the durability increases with increase of the molecular weight, independent of the testing conditions (given maximum load, given maximum deformation, etc.), and reaches a practically constant value at high molecular weights. (3) The fundamental influence of the original molecular weight on the strength and dynamic durability of vulcanizates containing the same percentage of combined sulfur is manifest in the retardation of the formation of a spatial network in low-molecular rubbers when vulcanized. With rubber of low original molecular weight, vulcanization leads to the formation of a thin space network and consequently a large number of molecular chain ends outside the network. For this reason, vulcanizates of low-molecular rubbers when tested are characterized by high permanent set.
Transformation of Sulfur Links in Vulcanizates under the Action of Temperature
Authors: Tikhomirova N. N. , Kuzminskiĭ A. S.
Published: February 2011

1. It was shown that an exchange between free and combined sulfur takes place in vulcanizates. 2. A method for evaluating the relative durability of the sulfur links in vulcanizates was developed with the aid of the radioactive isotope of sulfur and the diffusion rate of sulfur between two vulcanizate films. The value of ilimit characterizes the equilibrium distribution of active sulfur. This method was used for investigation of a series of vulcanizates. 3. The heat treatment of vulcanizates leads to the formation of more durable sulfur links.
Thermal Degradation of Unvulcanized and Vulcanized Rubber in a Vacuum
Authors: Straus Sidney , Madorsky S. L.
Published: February 2011

The history of distillation of rubber under various conditions of temperature, pressure, and atmosphere goes back more than a century. As far back as 1860, Williams distilled rubber in an iron retort at relatively low temperatures and obtained some 5 per cent of crude isoprene. In 1922, Staudinger and Fritschi distilled rubber at 275° to 320° C at 0.1- to 0.3-mm. pressure and obtained 3.1 per cent of isoprene. In 1926 Staudinger and Geiger distilled rubber below 300° C at ordinary pressure in an atmosphere of carbon dioxide and obtained 4.3 per cent of crude isoprene. Distillation of rubber at higher temperatures and under atmospheric pressure yielded as much as 58 per cent of isoprene. In addition to isoprene, dipentene and higher terpene compounds were also identified in the distillation products of natural rubber. More recently, distillations of pure synthetic polyisoprene (a mixture of cis- and trans-polyisoprene), purified natural rubber (cis-polyisoprene), and purified gutta hydrocarbon (trans-polyisoprene) were carried out by the present authors in a vacuum under conditions of molecular distillation. The volatile products were fractionated and analyzed both qualitatively and quantitatively, using the mass spectrometer for the lighter fractions. The volatiles consisted of about 3 to 4 per cent of isoprene and 13 to 20 per cent of dipentene, the rest being large terpene fragments of average molecular weight of about 600. The present paper describes an investigation of the effects of various additions to natural rubber, with or without subsequent vulcanization, on the degradation process during pyrolysis in a vacuum, with the view that such a study might throw some light on the structure of vulcanized rubber. In addition to pyrolysis, a study was also made with unvulcanized and vulcanized rubber of the rates and activation energies of thermal degradation in a vacuum, using techniques and apparatus that were previously developed by the authors in connection with an extensive study of thermal degradation of a number of polymers.
Gamma-Ray Vulcanization of Rubber
Authors: Gehman S. D. , Auerbach I.
Published: February 2011

Vulcanization is the industrial process which transforms rubber from a soft, sticky, readily molded plastic to the highly elastic material familiar to everyone from innumerable uses. It was discovered by Charles Goodyear in 1839 and was one of the series of crucial inventions which started the United States on its industrial revolution in the nineteenth century. The automotive direction of this industrial development has accentuated the importance of rubber in succeeding years. This year the worldwide product volume to which vulcanization will be applied will exceed two and a half million tons. It is readily understood that vulcanization is now a highly developed process, the resultant of many improvements and developments over the course of a century of competitive use. Goodyear's original conception involved simply the heating of rubber with sulfur. The recognition of the chemical nature of the process was followed by the discovery of materials which, when added to the system, accelerated the reaction tremendously, allowed it to be carried out at lower temperatures, and improved profoundly the physical properties, uniformity, and aging resistance of the rubber. Such chemical vulcanizing systems are now applied in great variety. Many ways are known for vulcanizing rubber without using any sulfur, but they are of relatively minor commerical importance. Some of the synthetic rubbers require rather unique systems for vulcanization. There is continuous, intensive chemical research activity to find still better ways of vulcanizing rubber. So with gamma-ray vulcanization, it will be necessary to show some very tangible advantages to find even a few specialized applications. The idea of vulcanizing rubber by exposure to energetic radiation is not new. A patent issued to E. B. Newton in 1933 claimed the vulcanization of rubber by short exposures to 250-kV cathode rays. Effects of pile irradiation on uncured elastomers were studied by Davidson and Geib. Numerous investigations of the effects of radiation on the physical properties of plastics are listed in the bibliography prepared by Sun. Gehman and Hobbs observed the vulcanization of rubber by intense gamma radiation. Jackson and Hale measured the physical properties of rubber-filler mixtures as a function of the radiation dose from a strong Co60 source for a variety of elastomers. Cross-linking of rubber by pile irradiation was studied in a quantitative way by Charlesby. He emphasized the usefulness of radiation crosslinking as a means for studying the average molecular weight, variation of the gel fraction, and the changes in properties of rubber as the degree of crosslinking is varied.
Structural Characteristics of the Sulfur Linkage in Natural Rubber Vulcanizates
Authors: Bateman L. C. , Glazebrook R. W. , Moore C. G. , Saville R. W.
Published: February 2011

Polyisoprenes react with sulfur both intramolecuarly and intermolecularly to yield cyclic sulfides and crosslinked sulfides, respectively. The structures of these have been examined for the reaction of the di-isoprene, 2,6-dimethylocta-2,6-diene, with sulfur at 140°. The cyclic sulfides consist of the two saturated compounds (I) and (II) and the two unsaturated compounds (III) and (IV). The crosslinked sulfide consists of a complex mixture in which unsaturated open chain and saturated and unsaturated cyclic sulfide structures have been identified. The structures of these products suggest a polar reaction mechanism, and also that hydrogen sulfide participates in the reaction. The influence of organic bases, the sulfurizing agent, reaction temperature, and zinc salts on the nature of the sulfur linkage is discussed.