bluuebunny/crossref_metadata_2025 huggingface dataset:
Redox Systems in the Initiation of Radical Processes. Mechanism of Action
Authors: Dolgoplosk B. A. , Tinyakova E. I.
Published: February 2011

The following redox systems capable of initiating radical polymerizations are discussed: (1) Systems of the first type, where the reaction leads to the formation of a single radical: (a) Mechanism of action of reversible systems involving dienols and salts of metals of variable valency. (b) Mechanism of the decomposition of hydroperoxides by the action of salts of metals of variable valency in their higher oxidation states. (2) Systems of the second type, where the reaction leads to the formation of two radicals. Mechanism of action and effectiveness of systems involving hydroperoxides, quinol, and sulfite. (3) Systems of the third type, in which the formation of free radicals is not directly linked to the redox process. Mechanism of action of systems involving diazoamino compounds and “polyamine” systems. (4) Crosslinking of unsaturated polymers at low temperatures by the action of redox systems. Transition from crosslinking to destructive processes in presence of oxygen.
The Reaction of Ozone with Rubber
Authors: Tucker Harold
Published: February 2011

The reaction of ozone with an unsaturated elastomer is very rapid until the double bonds at the surface have reacted. Only then do the double bonds beneath the surface become available for reaction with ozone. In this respect, unstressed rubber is similar to the metals that are protected from oxidation by a film of oxide formed on the surface. When this protective film is broken and fresh surface is exposed, the reaction can continue. This is the situation that exists when the rubber is under strain. Since the entire rubber surface can be considered as under a uniform bombardment by ozone molecules, to consider cracks in stressed rubber as arising from a directed chain scission process seems unrealistic. On the assumption that the double bonds in the rubber surface are equally reactive, and that ozone does not act as a pair of chemical shears snipping double bonds at right angles to the strain, crack development must then arise from the fact that the stress-strain characteristics of the rubber-ozone reaction product are not indentical to those of the original material and that ultimate elongation decreases continuously with increasing reaction with ozone. That such a mechanism would produce the type of cracks produced by ozone reacting with rubber can be shown by modifying the nature of the surface by vulcanization.
Effect of Degree of Elongation on Ozone Cracking of Rubbers
Authors: Zuev Yu S. , Pravednikova S. I.
Published: February 2011

It is known from the literature that there exists a socalled critical elongation at which disruption of the structure of rubbers under the influence of ozone is most severe. However, the available data concerning this problem are fairly contradictory. According to a number of statements the critical elongation is observed in the case of vulcanizates of natural rubber, but its estimation by different authors varies from 5 to 50%. Some authors consider that a critical elongation exists in the case of synthetic rubbers susceptible to attack by ozone, while others consider that no such characteristic exists. It is said that polychloroprene and butyl rubber do not possess this characteristic. However, none of these data can be regarded as reliable since in most cases ozone cracking of the rubbers was characterized by arbitrary methods, as a rule by the “degree of cracking” expressed by the number of marks. We have carried out a detailed investigation of the effect of the degree of elongation on ozone cracking of rubbers, the rate of growth of cracks being determined by an objective method based on the effective depth of the cracks calculated from the decrease of stress in the relaxed rubber sample when exposed to the action of ozone. The following rubbers—NK, SKS, neurite, SKN, and SKB were investigated in standard formulas, at optimum true tensile strength. Gutta-percha (elastic vulcanizate) and butyl rubber compositions in phr were: gutta-percha 100, MBT 0.8, sulfur 5; butyl rubber 100, stearine 3, MBT 0.65, thiuram disulfide 1.3, zinc oxide 5, sulfur 2.
Cis-Polybutadiene-Natural Rubber Blends
Authors: Railsback H. E. , Cooper W. T. , Stumpe N. A.
Published: February 2011

The preparation of 1:1 cis-polybutadiene-natural rubber blends has been shown to be feasible on a laboratory scale. Blends of this type have displayed hysteresis properties equivalent to the natural rubber control and have exhibited satisfactory modulus, tensile and Shore hardness in the recipes developed. Tests on retread passenger tires have confirmed the excellent service performance indicated for blends of this type compared to natural rubber by giving outstanding abrasion resistance and better resistance to cracking. The compatibility and acceptable processing characteristics of cis-polybutadiene-natural rubber blends have been confirmed by factory mixing. Based on the results to date it appears that 1:1 blends of cis-polybutadiene and natural rubber should be significantly better than natural rubber alone for heavy duty truck tire treads. Road testing of 10:00 inch × 20 inch truck tires is now in progress. If the outstanding performace of the blends is confirmed, the utilization of cis-polybutadiene rubber in truck tires could materially lessen the dependence of the rubber industry on natural rubber.
The Work of Rubber Elongation
Authors: Kusov A. B.
Published: February 2011

1. Curves of the relation between work of deformation and elongation in a vulcanizate are characterized by the absence of an inflection point. Regardless of the type of rubber, the compounding of the stock and the conditions of its preparation, they possess the property of being congruent when superimposed on one another. Because of this property the curves may be considered as parts of some composite curve which reflects the general properties of all vulcanizates. 2. Each of the curves of work vs elongation (and the rubber sample corresponding to it) may be characterized by a coefficient indicating the degree of displacement relative to the comparison sample. One may assume that this property of the curves of the work of deformation vs elongation has a certain physical significance. 3. There is a regular relation between the stress corresponding to the inflection point on the curves of stress vs elongation, and the curves of work vs elongation.
Adhesion Effects in Bonding Rubber to Metal by Leukonat Adhesive
Authors: Medvedeva A. M. , Deryagin B. V. , Zherebkov S. K.
Published: February 2011

1. In bonding of rubber to metal by Leukonat adhesive, the type of filler present in the rubber has a very great influence on the rubber-metal bond strength. 2. Active fillers of the gas channel black type in the rubber mixture increase the interaction of the rubber with the adhesive film. 3. Inactive fillers of the thermal black type have little influence on the interaction of the rubber with the adhesive film. 4. The results of the experiments suggest that Leukonat interacts chemically with active fillers present in the rubber during the bonding process. 5. The following empirical rule is formulated: high rubber-metal bond strength is obtained if the interaction of the adhesive film with the rubber is approximately of the same degree as with the metal. This rule is supported by the experimental data. 6. Sandblasting of the metal surface increases the true contact area by a factor of 1.5\2-2, while the bond strength is increased 20 to 100 times; this indicates that qualitative changes occur in the surface on sandblasting and that the nature of the metal-adhesive interaction is greatly changed in the process. It is difficult to explain this other than on the assumption that the charge of the double layer at the metal-adhesive boundary is increased, and in consequence the work of separation of this layer at the boundary is greater.
New Absolute Molecular Weight Method—Linear High Polymers
Authors: Bueche F. , Harding S. W.
Published: February 2011

It has been shown that the shear-rate dependence of the viscosity of concentrated polymer solutions can be explained in terms of known parameters of the solution. If the concentration, temperature, zero shear viscosity, and molecular weight of the polymer are known, the decrease in viscosity with increasing shear rate can be predicted. Conversely, if one measures the shear-rate dependence of the viscosity, the molecular weight may be computed. We believe this provides a convenient method for the absolute determination of molecular weights of linear, coiling, high polymers.
Stress-Strain Equation for Rubber in Tension
Authors: Claxton W. E.
Published: February 2011

A stress-strain equation is derived for a homogeneous, isotropic material with the assumptions that for any given homogeneous simple tensile strain, the components of the stress tensor are to the first approximation linear, homogeneous functions of the components of the strain tensor and that no volume change occurs during the deformation. Utilizing the dependence of Poisson's ratio upon the extension referred to the initial coordinates, one elastic coefficient, C12, is found to be sufficient to roughly characterize the first stretch stress-strain curve. Although experimentally this elastic coefficient is found to be essentially constant for extensions greater than 250% its value increases rapidly as zero extension is approached. This behavior agrees qualitatively with data by Blanchard and Parkinson as to the distribution of secondary bond strengths, wherein they found a large number of relatively low-energy bonds which would be effective only at small extensions in contributing to modulus reinforcement. Various aspects of stress strain and cure behavior are examined with the derived equation as a basis.
Mechanical Behavior of a Polymer at Temperatures through the Glass Transition Temperature
Authors: Stevens J. R. , Ivey D. G.
Published: February 2011

Stress-temperature (constant strain) and length-temperature (constant stress) measurements have been made on Paracril-35 (a butadiene-acrylonitrile copolymer) in the temperature range −80° C to 25° C, which includes the glasslike, transition, and rubberlike states for this material (Tg∼−25°C). Time effects are observed in the transition region, but for temperature gradients used (down to about 1° C in 4 hours) the behavior at low temperatures is unique, indicating the existence of a real transition. This behavior is independent of the strain imposed at room temperature. The shift in transition temperature (in the length-temperature work) with extension is found to give quantitative support to the theory that the transition occurs at a certain minimum volume. In the rubberlike region, behavior is represented by the usual equation of state.
The influence of Intermolecular Action on the Dynamic Fatigue of Rubbers
Authors: Gul V. E. , Fedyukin D. L. , Dogadkin B. A.
Published: February 2011

The determination of the physical effect of softeners by an investigation of their influence on the swelling of vulcanizates is a convenient method for investigating the optimum composition of a compound which will produce given properties in the cured stock. This makes possible the improvement of such important properties of vulcanizates as fatigue resistance, mechanical loss, freeze resistance and others by using softeners with the appropriate functional groups.
Distribution of Side Force and Side Slip in the Contact Area of the Pneumatic Tire
Authors: Cooper D. H.
Published: February 2011

It is well known that, when a pneumatic tire is rolled over dry ground at a slip angle, a sideways force is developed. With the cornering force rig described here we are able to measure the front to rear distribution of the cornering force along the contact spot, the length of the contact area, the trail and the self-aligning torque. At the same time it is possible to derive the shape of the distorted tread and the front to rear distribution of side slip in the contact spot. By making certain assumptions concerning the distribution of the vertical force along the contact spot a relationship has been established between the forces of friction, rate of side slip and speed of rolling.
Effect of High Pressure on Self Adhesion (Autohesion) of High Polymers
Authors: Igonin L. A. , Ovchinnikov Yu V. , Arzhakov S. A.
Published: February 2011

The phenomenon of self adhesion of high polymers is one of the very important but little studied properties of these materials. Self adhesion of rubberlike polymers has been studied, but there is little work reported on the self adhesion of thermoplastics. There is, however, no doubt about the importance of the role of this phenomenon in the process of producing products from powdered and granular thermoplastics. The influence of temperature and pressure on the self adhesion of some thermoplastic powders was studied in the present work. The conditions for the formation of a transparent sample were found by pressing the powdered material in a heated cylindrical press. The samples pressed were 10 mm in diameter and 4–5 mm thick. The temperature and pressure were varied over a wide range. The samples were pressed in the following manner: The polymer sample was placed in the cold press and a given pressure was applied; the temperature was then raised to a given value and the sample was held at this temperature for 15 minutes; after cooling the press to 50–60° the pressure was released, the sample was removed from the press and the density to visible light was evaluated visually. When a transparent sample is obtained by pressing the thermoplastic polymer, partial or complete coalescence of the grains of the material takes place with a disappearance of grain boundaries. Under these conditions the strength of the sample may not reach the cohesive strength of the material as has sometimes been assumed.
The Coagulation Mechanism of Butadiene—Styrene Latex
Authors: Glikman S. A. , Korchagina E. P.
Published: February 2011

1. It is shown that the absolute values of the coagulation thresholds of SKS-30A latexes diluted down to 0.01% correspond to the usual values for lyophobic sols. The values for NaCl are 200 times those for CaCl2, and increase with the latex concentration. The complete coagulation concentration for NaCl is 30 times that for CaCl2, and does not depend on the dilution of the latex. 2. It was shown by a nephelometric method that the volume of the primary particles formed in coagulation of the latex by sodium chloride is about 10 times the volume of the uncoagulated latex globules, irrespective of the latex concentration. 3. Consideration of the experimental data, in conjunction with facts reported in the literature, leads to the concept of two stages in the coagulation of latex by electrolytes: the first is the consequence of a decrease of the zeta potential, leading to the formation of primary particles, and the second leads to coalescence of these particles. The secondary aggregation processes can be prevented or modified by introduction of certain additives (nonelectrolytes) into the latex. 4. In additon to an explanation of the mechanism of latex coagulation by electrolytes, and a demonstration that this process can be controlled, indications are given of means of an approach to development of conditions for the production of a good blanket by coagulation of latex by sodium chloride, with a much decreased consumption of the latter.
The Structure of Gels. X. Globulization of Rubber under the Action of Nonsolvents
Authors: Zubov P. I. , Zhurkina Z. N. , Kargin V. A.
Published: February 2011

1. Addition of nonsolvents to rubber solutions causes globulization of the macromolecules, similar to that occurring on addition of active substances (sulfur monochloride, halogens, etc.) to rubber solutions. 2. The difference between these processes lies in the fact that the coiling of the rubber molecues under the action of methyl alcohol is very rapid. 3. The globular structures in rubbers, produced by addition of nonsolvents to the solutions, in contrast to the stable globules formed in halogenation and vulcanization of rubber solution, are easily broken down and the molecules assume the linear form characteristic of the original rubber.
Vulcanizates from Natural Rubber and Bisazo Compounds. Aging Properties
Authors: Esser Heinz
Published: February 2011

Nonblack as well as black loaded natural rubber compounds were vulcanized by addition of hexamethylene-1,6-bis(phenyl-azomonocarbonamide) (BAA). The accelerating and vulcanizing action of BAA is discussed on the basis of modulus curves. The experiments show that BAA alone is not active as a vulcanizing agent. To achieve good vulcanization, sulfur is also needed; the optimum sulfur level is much lower than in normal compounds. Furthermore, it is shown that BAA compounds need addition of an accelerator. Aging stability of BAA vulcanizates was tested by modern rapid tests (relaxation, creep, and oxygen absorption) as well as by classical methods (hot air and oxygen bomb aging). Vulcanization in which BAA was substituted for part of the sulfur showed excellent aging, comparable only with thiuram vulcanizates in the rapid tests and in hot air aging; aging in the oxygen bomb gave only fair results.
Effect of Vulcanization on the Dynamic Properties of Rubber
Authors: Kuvshinskiĭ E. V. , Sidorovich E. A.
Published: February 2011

It is a known fact that the mechanical properties of rubber depend essentially upon the density (i.e., the crosslink density) of the vulcanization network. The dependence of the “equilibrium” (statistical) modulus of elasticity upon the concentration of crosslinks as well as the dependence of the tensile strength —has been studied in a series of investigations. In contrast to this, analogous investigations of the dynamic mechanical characteristics are practically nonexistent. We have undertaken our present work with the hope of filling this gap. Series of gum compounds were prepared from natural (smoked sheet) and synthetic polyisoprene (SKI), sodium butadiene (SKB), butadiene-styrene (SKS-30A), and butadiene-nitrile (SKN-26) rubbers which varied in their degree of vulcanization. The percentage of sulfur and accelerator were varied as were the temperature and the time of vulcanization. The mechanical-dynamic characteristics of the rubber at a predetermined impact pressure—the rebound elasticity and the dynamic elastic modulus were studied with the pendulum elastometer KS over a temperature range of 20–100° C. The duration of the stress was .03/.05 second. We estimated the concentration of crosslinks in the rubber samples from the magnitude of the equilibrium modulus. In order to determine this characteristic, we compressed specimens which were 20 mm in height and 10 mm in diameter 15% and studied the relaxation of stress. The specimens were also tested on the pendulum elastometer. Heppler's consistometer operating on the lever weight principle, was adapted for our measurements. The experiments were conducted at 60° C, the thermostatic control being effected with the help of Heppler's ultrathermostat.
Intermolecular Interaction in Rubber Solutions
Authors: Gul V. E. , Berestnev V. A.
Published: February 2011

A study has been made of the viscosities of butadiene acrylonitrile rubber solutions and of the equilibrium swelling of vulcanizates of these rubbers with the same degree of crosslinking, in various solvents. It was found that the viscosity and light scattering characteristics of the solutions, and swelling of the vulcanizates of butadiene acrylonitrile rubbers are not steady functions of the degree of intermolecular interaction, represented by the difference of the square roots of the cohesive energy densities of the polymer and the solvent but pass through a maximum with variations in the polarity of the rubber.
Wandering of Crosslinks in Rubber at High Temperature
Authors: Voorn M. J. , Hermans J. J.
Published: February 2011

There are strong reasons to believe that on heating a crosslinked rubber crosslinks are broken and new ones formed. This has been established by the well-known work on stress relaxation of Tobolsky and his school, and others. In the following we will discuss some experiments which give further support to these views, both of a qualitative and quantitative nature. In the first place, we carried out a few preliminary experiments on stress relaxation at elevated temperatures. This stress relaxation may be due to either or both of two effects : (a) a displacement of the crosslinks, (b) a change in the number of crosslinks per unit of volume (crosslinking density p). A measure of ρ can be obtained from the equilibrium degree of swelling at room temperature, and this gives us a means of comparing changes of ρ in a stretched sample with those occurring in the unstretched state. To this end commercial rubber strips were heated in the stretched state in the absence of oxygen at three different temperatures (80, 106, 122° C) for times varying from 2 to 72 hours. The degree of stretch, i.e., the length of the stretched rubber divided by the original length was α=1 (unstretched) in one series, and α=3 in a second series. The initial stress τ0 (for α=3) and the final stress τ at the end of the heating period were read from the stress-strain diagrams, taking into account that for the heat-treated strips there was a permanent set. In other words, τ is the stress needed to give the heat-treated sample at room temperature a length 3 times the length of the original untreated sample; the ratio τ/τ0 is therefore essentially the ratio between the moduli of elasticity. The cross-linking densities ρ0 and ρ before and after heating were derived from swelling experiments (for details see the sections on swelling).
The Degradation of Elastomers. 2. Oxidative Degradation of Natural Rubber Vulcanizates at Different Elongations and Temperatures. II
Authors: Hillmer Karl-Heinz , Scheele Walter
Published: February 2011

The results of measurements of stress relaxation in natural rubber vulcanizates are reported. In the earlier work, the conditions were denned under which the drop in tension of a vulcanizate—after a pre-relaxation in pure nitrogen—follows a zero order law when tested in oxygen. The temperature dependence of the rate of relative tension relaxation was determined for 8 different vulcanizates. With a constant activation energy of about 29 kcal/mole, the vulcanizates differed in their relative relaxation rates at most by two powers of ten. Several general observations on the course of tension relaxation under different conditions were made on the grounds of experimental evidence. Good qualitative agreement was found with relations reported by Berry and Watson.
Diffusion Processes in the Vulcanization of Tire Stocks
Authors: Blokh G. A. , Kormilzeva Z. P. , Boguslavskiĭ D. B. , Bakharev B. I. , Tikhomirov B. P.
Published: February 2011

1. The diffusion of radioactive S35 during vulcanization of rubber compounds used for tire building was investigated. 2. It was shown that during the vulcanization process an intense diffusion of the radiosulfur between plies can take place. 3. It was established that in the boundary layers “cushion-breaker” and “breaker-carcass” the concentration of the vulcanizing groups is increased; this may be the cause for different kinetics of the vulcanization reaction within any ply and at the boundary between plies. The increased concentration of vulcanizing groups should influence the spatial configuration of the boundary regions and the working qualities of polylayer articles.
The Influence of Activators on the Vulcanization Process. I. The Influence of Zinc Oxide on the Rate of Combination of Sulfur with Rubber
Authors: Beniska J. , Dogadkin B.
Published: February 2011

In this work the effect of zinc oxide and stearic acid on the kinetics of sulfur combination with rubber was traced, in stocks containing accelerators as well as in stocks without the latter. It was proved that ZnO does not increase the rate of sulfur combination in sodium catalyzed polybutadiene rubbers (SKB-25). On the contrary, in stocks with mercaptobenzothiazole, zinc oxide decreases the rate of sulfur combination. In vulcanizates ZnS is formed in the presence of ZnO. The largest amount of zinc sulfide is formed in stocks with phenyl-2-naphthylamine and with stearic acid.
The Influence of Activators on the Vulcanization Process. II. The Influence of Zinc Oxide on the Structure of Vulcanizates
Authors: Beniska J. , Dogadkin B.
Published: February 2011

The influence of zinc oxide and stearic acid on the structures of vulcanizates was traced in stocks with mercaptobenzothiazole by means of the kinetics of swelling. It was found that zinc oxide in the presence of stearic acid has a marked influence on the rate and degree of crosslinked network formation in vulcanizates. In the formation of crosslinks (sulfur bridges) a number of reactions participate: the direct combination of rubber molecules with biradicals of sulfur, during which polysulfide bonds are mainly formed; the oxidation of rubber mercaptans (-SH groups), which is followed by the formation of mono-sulfide, disulfide and polysulfide links; and the decomposition of polysulfide links, which is followed by the formation of new crosslinks with a smaller number of sulfur atoms per crosslink. Zinc oxide has a varying influence on the individual reactions : the first two are activated by it, and the last one is retarded by it, because it does not react with the polysulfide sulfur to form zinc sulfide.
Bulk Polymerization in Natural Rubber Swollen by Methyl Methacrylate
Authors: Swift P. Mc L.
Published: February 2011

Methyl methacrylate absorbed into dry natural rubber has been polymerized under conditions of low heat loss, using as initiator AZBN, alone or in combination with an activated peroxide. With AZBN as sole initiator, some deductions are made from the change of temperature with time, as to the change in molecular weight of the polymer formed as the. reaction proceeds. No graft polymer is formed. With the mixed catalyst system polymerization starts at room temperature. The process has been carried to a semitechnical scale, and some of the properties of the products are given. In general the materials resemble the corresponding materials prepared in natural rubber latex, but have markedly better hot-tear resistance. About 25% of the polymethyl methacrylate is present as a graft polymer.
Swelling of Latex Particles
Authors: Morton Maurice , Kaizerman Samuel , Altier Mary W.
Published: February 2011

A theoretical relation has been derived for the equilibrium swelling of latex particles. The equilibrium solubility and rate of solution of solvents were measured on a series of polystyrene latex fractions of varying particle size. The solvents used were styrene, toluene, and chlorocyclohexane. It was found, as predicted by theory, that the equilibrium amount of solvent imbibed by latex particles is a direct function of the particle diameter and an inverse function of the interfacial energy at the surface of the particles. The molecular weight of the polymer has no effect on the equilibrium swelling, within the range from 100,000 to several million molecular weight units. The rate of imbibition of these solvents appears to be extremely rapid, indicating that equilibrium solubility would appear to be maintained in most polymerization reactions. The fact that a particular solvent is a “good” solvent for the polymer does not necessarily result in a greater swelling of the particles, since the solvent may show a higher interfacial energy against the aqueous phase. The soap titration method is best for determining the average particle size of a latex for purposes of predicting equilibrium swelling.
The Infrared Spectroscopic Identification of Rubber before and after Cure to the Soft and Hard Rubber States
Authors: Hummel Dieter
Published: February 2011

The IR-spectroscopic identification of soft rubbers may be made by : 1. Breaking down the vulcanizate on a mill followed by boiling with o-dichlorobenzene and then the spectroscopic examination of the polymer recovered from the solution. 2. Thermal degradation of the vulcanizates followed by spectroscopic examination of the liquid and gaseous products of pyrolysis. The rubber base of hard rubbers is determined by spectroscopic examination of the materials obtained by thermal degradation of mixtures of the hard rubbers with zinc dust or powdered calcium.
Bond Strength at the Cord-Impregnant (Adhesive)-Rubber Boundary Layer
Authors: Uzina R. V. , Dostyan M. S.
Published: February 2011

The casing construction studied here comprises cord layers-adhesive layerrubber (Figure 1). Owing to the action of external forces and internal tensions, while the cover is in service, separation may occur. Separation takes three forms: (1) the adhesion type, i.e., when the adhesion becomes less than the cohesion of the bonded materials ; (2) the cohesion type, when the adhesion is greater than the cohesion of the bonded materials ; and (3) the combined type when the adhesion approaches the cohesion. In order to eliminate adhesion type separation, it is necessary to increase the bond strength of the system. This can be done by three methods: (1) changing the type of cord; (2) using impregnating compositions; and (3) changing the rubber compound. The type of cord has a marked effect on the bond strength. For example cotton cord results in considerably greater bond strength value than artificial or synthetic fibers. The composition of the rubber compound also shows a marked effect on the strength of bonding with cord. The introduction of a series of plasticizers into the mix results in a fall in the strength of the rubber/cord bonds, and the use of active fillers causes the strength to increase. The effect of cord type and the composition of the casing rubber on the bond strength in the construction studied will be the subject of a separate investigation. The present report deals with the effect of the composition of the impregnating layer on the strength of the bond between the impregnated cord and the rubber.
Application of Strain Gages to the Study of (Tire) Cord at High Elongation Rates
Authors: Pavlov N. N. , Yaminskaya E. Ya , Krymov B. M.
Published: February 2011

1. A new simplified method of recording the stress-strain curve of elastic materials using strain gages was developed and tested. 2. It was found that there is a substantial influence of rate of deformation on the character of the stress-strain curves of the samples tested. 3. It was established that the work of breaking the tested samples decreases with increasing speed of stretching.
Rotary Power Loss Machine
Authors: Bulgin D. , Hubbard G. D.
Published: February 2011

Rubberlike polymeric materials, particularly in the technical form when compounded with carbon black, are imperfectly elastic and the associated energy loss is of considerable practical significance. In some applications a high energy loss is of value to provide high damping, but in many cases and particularly in tires, the temperature rise due to the losses may be a limiting operational factor. The losses cause the tire to exhibit rolling resistance which, in the case of solid tires, can be related accurately to the modulus and resilience of the rubber. An analysis of this system has been carried out by Evans, while Tabor has considered the case of rigid cylinders and spheres rolling on flexible rubber surfaces. In the case of pneumatic tires the composite nature of the construction of fabric and rubber and the complex system of strain distribution make the calculation of rolling resistance from polymer properties extremely complicated. In order to approach this problem it is necessary to know the modulus and resilience of the materials used over a very wide range of temperature and a range of amplitude of deformation and of frequency. The required temperature range may be from −60° C to above 200° C, but the frequency range over which appreciable amplitudes are involved does not extend beyond approximately a thousand cycles per second while the amplitude of deformation does not exceed 50 per cent. In order to investigate adequately the many possible combinations of polymers and compounding systems, the values of resilience and modulus are required over the above range of conditions, and various instruments have been described which measure some or all of these properties. The rebound pendulum was one of the earliest instruments and is widely used for the measurement of resilience because of its inherent simplicity of operation and high accuracy, but as normally operated at a fixed temperature does not provide sufficient information for evaluation of materials for use in tires. This type of instrument also is not well suited for determination of modulus owing to its single cycle method of operation. The vibrator type instruments give more complete information but normally demand a high degree of skill in their operation and in the interpretation of results and are more suited to research than routine work.
Dependence of Dielectric Relaxation Spectrum of Rubber on Stretching
Authors: Müller F. H. , Huff K.
Published: February 2011

The loss angle of a weakly vulcanized rubber sample, as a function of temperature and frequency, changes as the sample is extended. Even at slight extension the loss angle maximum is depressed and shifts by several degrees to lower temperatures. The results are discussed in relation to earlier investigations of changes in the dielectric spectrum when various other rigid high polymers are stretched. Such experiments are interesting, since the close connection between dielectric and mechanical spectra permits conclusions to be drawn about modifications in mechanical behavior caused by stretching. A new method is presented for obtaining additional quantitative data regarding mechanical behavior in the nonlinear region.
The Significance of Rheology in Rubber Processing. 2. Studies of Latex
Authors: Edelmann Kurt , Horn Edith
Published: February 2011

After referring to the importance of rheological studies for the ever growing applications of latex in industry, results are reported for the study of the rheological behavior of several Buna latexes, using a Höppler Rheo-viscometer. The flow curves obtained in this way show a different type of non-Newtonian flow from solutions of rubber. The region of η0, viscosity at rest, is absent. With increasing velocity gratient, the viscosity becomes smaller and smaller and finally reaches a constant value at a relatively high velocity gradient. That is, non-Newtonian flow passes gradually over into Newtonian flow. For those latexes whose Newtonian flow lies within the measurable range, a general flow equation is given which includes the Newtonian portion of the shear stress together with a stress correction. This equation of flow can be used to define the rheological behavior of the latexes. The cause of this type of rheological behavior is found in the thixotropic properties of the latex system. If a Höppler Rheo-viscometer is used and measurements are made first at increasing and then at decreasing shear stresses, the plotted data show a hysteresis loop which is evidence of thixotropy. With those latex systems for which the Newtonian flow behavior falls within the limits of the measurements, and whicn can be called fluids, the viscosities measured with decreasing shear stresses lie below those which are measured with increasing shear stresses. On the other hand, highly concentrated latexes which can be considered as having a gel structure throughout, such as the 70% Buna-Latex S3 used in this work, display a different kind of thixotropic behavior. In such cases, the viscosities measured with decreasing stresses are higher than those measured with increasing shear stresses. A different flow equation is needed to define this different type of thixotropy.
Comparison of Accelerated and Natural Tests for Ozone Resistance of Elastomers
Authors: Vacca G. N.
Published: February 2011

While other data are available, it is believed that the data summarized herein are sufficient to give a good average picture of results obtained in static accelerated ozone versus outdoor exposure tests. At The Bell Telephone Laboratories where most of the work has been with black stocks, results indicate that correlation is dependent on the base polymer in the stocks under test. Thus, in polymers which are inherently resistant to ozone, protective systems are very effective and correlation is very good. This has been true of black neoprene stocks and evidence indicates that it may also be true for butyl stocks. With natural, SBR and NBR rubbers, protection is more difficult and results vary more widely. With the introduction of the newer and more effective antiozonants such as the dioctyl-p-phenylene diamines, correlation is much better. It has been argued that absolute correlation should not be expected since in outside tests there are influences affecting cracking behavior which are absent in the indoor tests. These include sunlight, rainfall, arid temperature as well as ozone concentration fluctuations. It has been observed that specimens from some stocks exposed in the late fall of the year will go through the following summer without cracking, while specimens from the same stock exposed in late spring will crack in a few days. This probably results from a combination of factors. Low ozone concentration coupled with low temperature greatly reduces susceptibility to crack formation and may provide time for stress relaxation or, perhaps, for the formation of a protective coating through the effects of sunlight activated changes in the surface. In the accelerated ozone test, temperature and ozone concentration are carefully controlled and other variables are absent. The test will at least isolate the effect of ozone which alone is responsible for cracking. Aside from the effect of location and season of the year, there is also the question of the duration of the outdoor exposure to be used as a criterion. This may vary widely as between tires where a 4 or 5 yr period will suffice and utility or communication wires where periods in the order of 20 yr are involved.
Ozone Resistance of Rubber Insulations
Authors: Couch W. H. , Hunt G. H. , Pratt O. S.
Published: February 2011

The results of experiments on the ozone and corona cutting of rubber high voltage insulation show that the relaxation of mechanical stress in the insulation plays an important role. Studies were made to establish the stress decay characteristics of various formulations based on natural rubber, SBR and butly rubber. A method was developed for correlating the stress decay and ozone resistance characteristics which permits the performance of bent samples of any formulation to be predicted at ozone concentrations up to 0.2%. Comparisons were made between the cutting in an intense corona discharge and that in high concentrations of ozone outside of the discharge. These comparisons show that the results of ozone tests at constant load together with stress relaxation tests may be used to predict the performance of rubber insulation in corona discharge. Tests were carried out in the products of corona discharge at pressures less than atomospheric. These tests lead to the conclusion that at very low pressures (ca. 1 mm Hg) cutting is caused not by ozone but by atomic oxygen. Compounds based on a variety of polymers were exposed to atomic oxygen and it was found that butyl rubber cuts rapidly in atomic oxygen while natural rubber, SBR, neoprene, and Hypalon do not. Antioxidants do not protect butyl rubber against cutting in atomic oxygen, but surface coatings were found to offer protection.
Factors Influencing the Ozone Resistance of Neoprene Vulcanizates under Flexure
Authors: Murray R. M.
Published: February 2011

The need for dynamic testing conditions, such as mild flexing, to study the attack of ozone on elastomeric vulcanizates, has become increasingly apparent. Many rubber goods, such as belts, tire sidewalls, and hose, are subjected to intermittent or continuously fluctuating strains in service and to evaluate their ozone resistance under constant stress or strain conditions is unrealistic and often leads to entirely erroneous conclusions. For example, it is well known that under static strain a vulcanizate's ozone resistance is enhanced by compounding with a wax which migrates to its surface and forms a protective film. However, numerous investigators have reported that when a wax film is continuously ruptured by dynamic testing, the vulcanizate is even more vulnerable to ozone attack than if no wax were present. Other surface films also may act detrimentally under dynamic conditions. One such film may form under static exposure by the migration of antiozonants to the surface of a sample where they or their ozone reaction products provide a shield against ozone. Also, diene elastomers, even when not under stress, react with ozone without cracking and it has been postulated that the thin films formed as a result of this reaction are less extensible and consequently more subject to rupture on flexing than the unreacted rubber beneath them. It may well be found that the resistance of any surface barrier to dynamic stresses is the limiting factor for many products in service. Consequently, techniques for testing under dynamic conditions are needed at least to supplement testing under constant stress or strain in ozone. Ozone exposure under dynamic conditions may prove to have analytical advantages over the static method. First, because dynamic tests accelerate ozone attack over that obtained statically even though no increased strain is impressed. This permits the more ozone resistant elastomers to be tested at lower concentrations of ozone than would be possible statically. By testing in more dilute ozone, the correlation between results obtained under atmospheric exposure and the ozone cabinet should be better. Also, it seems likely that compounding ingredients which improve ozone resistance under dynamic conditions should provide improvement under static conditions as well, even though the converse is not necessarily true.
The Effect of Carbon Black on Thermal Antioxidants for Polyethylene
Authors: Hawkins W. L. , Hansen R. H. , Matreyek W. , Winslow F. H.
Published: February 2011

Carbon black has been shown to function as a mild thermal antioxidant for polyethylene at 140° C. The amount of protection increases with concentration and is dependent on the chemical nature of the carbon surface. This antioxidant effect is shown by a variety of carbon blacks with a considerable range of particle size, but very coarse carbons in comparable weight concentration exhibit no antioxidant effect. Recent studies concerned with the chemical nature of the carbon black surface indicate the presence of various oxygenated groupings which may account for the weak antioxidant activity of some carbon blacks. In all cases examined, conventional amine and phenol antioxidants in polyethylene are adversely affected by carbon black. This effect can be attributed to adsorption followed by chemical decomposition of the antioxidant on the carbon black. The chemical nature of the carbon black apparently influences the adsorption since the loss in activity of amine antioxidants is much more pronounced with acidic than basic carbon blacks. Whereas the effect of carbon black on antioxidant behavior is observed over a wide pH range, the effect decreases and finally disappears as the particle size of the carbon black is increased.
New Thermal Antioxidants for Polyethylene Containing Carbon Black
Authors: Hawkins W. L. , Lanza V. L. , Loeffler B. B. , Matreyek W. , Winslow F. H.
Published: February 2011

Antioxidants which contain a thioether bond are usually more effective than the simple compounds from which they are derived. More significant is the effect of carbon black on these improved antioxidants, generally resulting in even greater protection than in the clear polymer. This is in contrast to the behavior of conventional antioxidants which do not contain a thio-bond. In all cases examined, these conventional antioxidants lose a large proportion of their effectiveness in the presence of carbon black. Recent studies concerned with the chemical nature of the carbon black surface strongly suggest the presence of reactive chemical groupings which may account for the weak antioxidant activity of some carbon blacks. Apparently the carbon black surface interacts with organo-sulfur antioxidants since this unique behavior has not been observed in other materials of comparable particle size, such as alumina, titania, or silica, nor do these materials themselves inhibit polyethylene oxidation. Thioethers and disulfides which contain no amine or phenol groups and hence no active hydrogen constitute another class of antioxidants which are unusual in that they attain a significant degree of activity only in the presence of carbon black. Although the mechanism through which these simple compounds function as antioxidants has not been established, there is considerable evidence that a relationship exists between antioxidant activity and bond dissociation energy. Some thiols may act to a slight extent as conventional antioxidants in clear polyethylene, but when carbon black is present, they appear to function through the same mechanism as do the simple organo-sulfur compounds which contain no active hydrogen. It is significant that within the general class of organo-sulfur antioxidants, alkyl compounds exhibit strong antioxidant activity in the presence of carbon black, and are often comparable with their aromatic counterparts.
Effects of the Types of Rubber and Carbon Black on the Formation of Carbon-Rubber Gel
Authors: Chernykh Z. V. , Epshtein V. G.
Published: February 2011

1. Carbon-rubber gels are formed in mixtures containing all the types of carbon black tested (channel, acetylene, nozzle, furnace, thermal) and not only active carbons. 2. The amount of carbon-rubber gel formed depends on the amount of carbon black added. With carbon blacks which readily form continuous carbon structures (channel, acetylene) the amounts of gel are greater than with nonstructural blacks, for the same amount of black added. 3. The amount of gel is greater in synthetic than in natural rubber mixtures. 4. More intense extraction conditions do not cause disappearance of the gel, but increase the amount of bound rubber and decrease the amount of carbon in the gel. 5. The carbon-rubber gels formed from structural carbons contain larger amounts of bound rubber. 6. It is suggested that bond stability between carbon black particles (characterized by the formation of a carbon black structure) is one of the basic causes of carbon-rubber gel formation.