bluuebunny/crossref_metadata_2025 huggingface dataset:
Size, Form and Flexibility of the Rubber Molecule
Authors: Schulz G. V. , Mula A.
Published: February 2011

Natural rubber can be brominated in dilute cyclohexane solution, whereby the molecular weight, corresponding to the bromine content, increases. For brominated rubber, increasing bromine content makes cyclohexane an increasingly poorer solvent, which is shown by a contraction of the molecule coils and a decrease in the second virial coefficient. Quantitative results were obtained through viscosity and light scattering measurements. Cyclohexane solutions of brominated rubber containing about 43% bromine have a θ point at room temperature. Here the second virial coefficient is zero and the coil has an ideal Gaussian density distribution. In this state the coil diameter is about 1.6 times bigger than for completely free rotation. A comparison of these data with X-ray low angle scattering could yield a quantitative measure of possible molecular branching. Brominated rubber with about one bromine per isoprene residue is a good starting material for the preparation of electron-microscope samples which can be used for the determination of the molecular weight distribution in rubber. The value of the weight average degree of polymerization determined by an electron microscope is in agreement with that determined through (1) light scattering and (2) ultracentrifuge and diffusion measurements. The molecular inhomogeneity of our sample is of the order of 0.5.
The Strain Dependence of Rubber Viscoelasticity. II. The Influence of Carbon Black
Authors: Mason P.
Published: February 2011

In Part I of this series it was shown how variations in the dynamic Young's modulus with extension could be represented by linear relations for gum rubbers in the region of 0 to 100% extension. The present work uses a similar treatment to examine how the viscoelastic behavior of natural rubber within this extension region is affected by the incorporation of two carbon blacks of widely differing colloidal activity. One of these materials, MT black, consists substantially of spherical particles with a mean diameter of about 0.4 microns: electron microscopy of cut surfaces of the black-rubber compound showed that the individual particles were well-dispersed. The finer material, HAF black, has a mean particle diameter of about 0.04 microns but exists in the rubber compound in a flocculated condition with aggregates up to about 0.3 microns in diameter. The rubber containing the coarse, MT black yielded linear strain relations enabling a direct comparison to be made with the behavior of the gum: the HAF material did not give linear relations for either the dynamic or the equilibrium Young's modulus. To facilitate discussion of this behavior it is desirable to set out more explicitly than in Part I the model underlying the analysis.
Degradation of Polymers
Authors: Wall Leo A. , Flynn Joseph H.
Published: February 2011

Recent literature pertaining to both the theoretical aspects and experimental results of the degradation of polymers by heat and radiation is reviewed and critically evaluated. Theories of random and chain thermal degradation of vinyl polymers and co-polymers are reviewed. The degradation of polymethacrylates, polyacrylates, poly-α-methylstyrene, polyolefins, polystyrene, other vinyl polymers, cellulose, polyesters, polyamides, dienes, natural rubber, and copolymers are discussed in the light of these theories. The thermodynamics and energetics of the degradation of these polymers is also reviewed. Chain scission, crosslinking, and gel formation and the kinetic mechanisms of these processes which take place during degradation of polymers by ionizing radiation and ultraviolet light are included. Degradative, rather than synthetic, effects are emphasized in the discussion.
Some Neglected Problems in the Rheology of High Polymers
Authors: Mooney Melvin
Published: February 2011

In accordance with custom, I have been asked, as a Goodyear Medalist, to address the Division of Rubber Chemistry of the American Chemical Society on the subject of my past work in the science and technology of elastomers. Hoping that I have correctly understood your desires, I shall now give you an informal, anecdotal story of some of this work. Going beyond this story of the past I shall also sketch, as I now see them, certain related unsolved problems, some of which have been rather neglected. While keeping in mind that detailed mathematics and theoretical argument would be inappropriate and even unwelcome on this occasion, I shall endeavor, with very little mathematics, to stimulate some of you to initiate programs of research on some of these problems, if you have not already done so. First let me tell you how, without realizing it, I became a rheologist. When I was employed by the United States Rubber Company in the fall of 1928, my first assignment was to study rubber plasticity, or the flow properties of crude rubbers and raw compounded stocks. When I was told of this problem in a conference with my group leader, Dr. Roscoe H. Gerke, there was a third person present, Dr. Ernest J. Joss, a physical chemist. Dr. Joss had only shortly before been given the same assignment; but with my appearance in the group, he was permitted to drop this work and give his full time to more congenial tasks. At the conference he turned over to me some talced strips of pale crepe which had been cut from a batch on a laboratory mill after various milling times. I knew nothing about rubber at that time; and if I had been asked to guess what these samples were, I could only have replied that they looked like fillets of sole sprinkled with flour and ready for the frying pan. The rheologieal testing devices for raw rubber that were available at that time were of two forms, the compression plastometer and the extrusion plastometer. I quickly decided that neither of these was suitable for the purpose, which, as I conceived it, was to measure the flow behavior of raw rubbers or stocks in their working condition as exhibited on a mill or calender or in a tuber.
Mechanism of Rupture of High Polymers
Authors: Gul V. E.
Published: February 2011

In connection with the wide distribution of high molecular weight compounds and the great successes in the field of synthesis of these materials, the study of the general principles of the processes of irreversible deformation and rupture of high polymer materials may be included among the important tasks of science and technology. In some cases it is desired to increase to the maximum the strength of the high molecular weight material, as for example in preparing articles from synthetic fibers, rubbers, plastics, etc., while on the other hand in others an increase in strength is undesirable. Thus, for example, food products, into whose composition high molecular weight materials are introduced, should naturally not be too strong. The preparation of reclaim from used rubber articles includes grinding. Here it is attempted to find such a combination of grinding conditions that will proceed with the minimum consumption of energy. In order to have the possibility of increasing or decreasing the strength of the high molecular weight substances, it is necessary to clarify the mechanism of ruptures and to know what is the relation between the forces of reaction between the structural elements of the material and tensile strength.
Dynamic Properties of Rubberlike Materials and the Isolation of Mechanical Vibration
Authors: Snowdon J. C.
Published: February 2011

Experiments to determine the dynamic mechanical properties of rubberlike materials frequently employ a sample of material sandwiched between two flat, parallel, and rigid surfaces. The sample is normally bonded to these surfaces or restrained from motion parallel to them by a perpendicularly applied static force. Figure 1 shows diagrammatically a sample attached to parallel rigid plates, which vibrate sinusoidally either in their own plane [Figure l(a)] or in a perpendicular direction [Figure 1 (b)]. In each case the lateral surfaces of the sample are unconstrained. The rubberlike material is commonly said to be stressed in shear in Figure 1 (a) and stressed in compression in Figure 1 (b). Actually, the rubberlike material in Figure 1 (a) will not experience a homogeneous shear deformation unless its thickness is small compared to the sample dimensions in every perpendicular direction. Again, the rubberlike material in Figure 1 (b) will not experience purely homogeneous compression because the lateral surfaces of the sample are not subject to an applied stress, and motion at and parallel to the interfaces between the sample and the plates is not permitted. The mechanical behavior of the rubber will in fact be governed primarily by its bulk modulus only when the lateral dimensions of the sample are large compared with the sample thickness. In this event the resilience normally associated with the rubber will not be apparent because the bulk modulus will be many times greater than the shear modulus of the material.
Determination of the Damping Characteristics of Fabric Reinforced Rubber Strips for Flexural Waves at Audio Frequencies
Authors: Wiener Francis M. , Gogos Creighton M.
Published: February 2011

The damping characteristics of fabric-reinforced rubber structures for flexural vibrations in the audio frequency range are of interest in studying the dynamic behavior of drive belts and automobile tires. To investigate these characteristics experimentally a strip of the material was secured at both ends by clamping the ends of the fabric and excited electromagnetically near the center into bending vibrations. The resulting displacements were observed by an electrostatic pickup arrangement. The quality factor Q was measured for the various resonant modes in the frequency range from near 100 cps to near 1000 cps for different specimens as a function of static loading. The results indicate that beyond about 200 cps the observed damping increases with frequency and appears to be primarily due to energy losses in shear. Although the specimens tested did not structurally duplicate tires or drive belts, it is believed that this study points up ways for the designer to control damping in accordance with the desired dynamic behavior of the finished product.
An Elastorelaxometer for Large Reversible Deformation of Elastomeric Systems and Polymer Solutions
Authors: Trapeznikov A. A.
Published: February 2011

1. A new instrument, the elastorelaxometer (based on the coaxial-cylinder principle) has been developed, for studies of large high-elastic deformations in relaxing colloidal gel systems and polymer solutions. 2. The effects of the following were investigated : a) width of the gap between the cylinders ; b) moment of inertia of the cylinder (with rapidly relaxing colloidal systems, cylinders of the minimum moment of inertia must be used) ; c) nature of the liquid in the bottom of the cylinder ; d) nature of the motion of the inner cylinder at different ultimate deformations. 3. Values of elastic recoil εc for different predetermined deformations ε have been determined in dilute aluminum naphthenate gels in decalin. It is shown that εc passes through a maximum, associated with transition beyond the yield value of the structure, with increase of ε. It is shown that εc can reeah 6000% in 2% gels.
Attrited Carbon Blacks and Their Behavior in Elastomers. III. Effects in SBR and Other Rubbers
Authors: Gessler A. M.
Published: February 2011

The cure of SBR is severely retarded in compounds with attrited blacks. This retardation, not found in butyl, natural, and acrylonitrile-butadiene polymers containing the same blacks, is associated with the sensitivity of SBR to acidity on the part of the black. The cure of SBR-attrited black compounds is sharply activated when glycerol or other aliphatic polyols are added in the compounds. The glycerol activation effect is unique with respect to both the polymer and the black. It is not obtained with SBR containing standard blacks, or with other elastomers, regardless of the black. Cure retardation and glycerol activation effects occur also only in attrited black-SBR systems which are cured with sulfur. They are not observed in peroxide cures. A combined reinforcement-vulcanization reaction is therefore envisioned to include the polymer, the black, sulfur, and glycerol as the reactants. When the compounds are properly cured with glycerol, attrited blacks lead to SBR vulcanizates with improved properties. The results are generally similar to those observed with butyl. Tensile strength and extensibility are increased. The vulcanizates are softer, as is evident from their reduced modulus and shore hardness. The dynamic properties are improved, both the dynamic modulus and the internal viscosity of attrited black-SBR vulcanizates being less than is ordinarily obtained with standard blacks. The increased activity of attrited blacks leads to greater heat treatment responses when glycerol is not present in the compound. The heat treatment of SBR containing both attrited black and glycerol results in a reversal of the normal heat treatment response. The reason for this reversal is not understood. Attrited blacks in natural, acrylonitrile-butadiene, and chloroprene rubbers give results similar to those in butyl. Cure retardation and glycerol activation effects are not encountered with these elastomers.
Ozonation of Butyl Rubber to Estimate Unsaturation
Authors: Ungar I. S. , Lutz G. A.
Published: February 2011

A method has been developed for the estimation of the unsaturation of butyl rubber by ozonation in selected solvents. Under a given set of conditions the ozonation method is reproducible to within 7 per cent and conceivably could be improved by further refinement. The unsaturation of a butyl rubber can be estimated in about 10 minutes when using ozonated oxygen and in about 15 minutes when using ozonated air.
Compounding SBR for Radiation Resistance
Authors: Anderson Herbert R.
Published: February 2011

The radiation resistance of butadiene-styrene cold rubber vulcanizates reinforced with carbon black can be increased materially by increasing the styrene content of the rubber, by extension of rubber with an aromatic oil, by incomplete curing with an accelerated sulfur vulcanization system, and by incorporation of retarders of radiation damage. Incomplete curing produces vulcanization intermediates which are affected by the ratio of sulfur to accelerator and by cure temperature to retard radiation damage. Results of swelling and stress relaxation measurements indicate that extension of the polymeric network with an aromatic oil increases the amount of chain scission during irradiation and decreases the amount of crosslinking to produce a correspondingly more radiation-resistant material. These measurements also show that in the absence of oil the decrease in radiation damage obtained by incomplete curing and with antirads is primarily the result of retardation of crosslinking. However, in the presence of oil, incomplete curing promotes and antirads retard radiation-induced crosslinking and scission about equally. Substitution of air for helium as an irradiation atmosphere accentuates the scission reaction to diminish moderately the changes in stress-strain properties.
X-Ray Diffraction Comparison of Radiation Damage in Rubber
Authors: Shelberg W. E. , Gevantman L. H.
Published: February 2011

This paper describes the use of an x-ray diffraction technique to correlate rubber radiation damage with rubber composition. Correlations between radiation damage and composition are useful as guides for the development of superior radiation resistant elastomers to be used as components of mechanical devices installed in high nuclear radiation fields. Rubber which is stretched and irradiated in an inert atmosphere is readily damaged by chain cleavage, manifested by loss of crystallinity, possible thinning, decreased x-ray diffraction intensities and eventual rupture (Figure 1). Loss of diffraction spot intensity was used to measure radiation damage in stretched rubber, and was tantamount to loss of crystallinity with little specimen thinning until just before rupture. Crystalline longevity was determined fur an irradiated “standard” rubber under standardized conditions and for other rubbers which were similar to the standard except for an added or substituted ingredient. A greater crystalline longevity connoted a greater radiation resistance, and the standard was used as 3 basis for comparing radiation resistance and composition.
Vulcanization of SBR by Gamma Radiation
Authors: Arnold P. M. , Kraus Gebard , Anderson R. H.
Published: February 2011

Experiments on the gamma-radiation vulcanization of butadiene/styrene rubber are described. A systematic investigation of the gamma radiation cure of a tread type compound is presented, which shows the dependence of the physical properties of gamma vulcanizates on the characteristics of the network formed. Swelling and stress relaxation measurements indicate that the crosslinking reaction is not accompanied by an excessive amount of main chain scission. Such measurements show also that the superior retention of stress-strain properties during aging of gamma vulcanizates is due to the elimination of post-vulcanization by chemical curatives. At equivalent crosslinking levels gamma vulcanizates display properties similar to sulfur vulcanizates. Gamma radiation overcomes the inhibition of vulcanization shown by a number of inorganic fillers and appears to enhance their reinforcement potential. The ordinarily high radiation dosage requirement for vulcanization may be reduced by incorporating heavy metal fillers into the rubber matrix. Such promotion depends on the atomic number, loading and state of subdivision of the promoting filler.
The Mechanism of Disulfide Decomposition under Vulcanization Conditions
Authors: Tutorskiĭ I. A. , Ginsburg L. B. , Dogadkin B. A.
Published: February 2011

1. 2,2′-dibenzothiazolyl disulfide (MBTS) labeled in the thiazole ring with the S36 isotope was synthesized. 2. During vulcanization of purified sodium butadiene rubber with MBTS the accelerator is observed to combine with the rubber simultaneously with the sulfur reaction. When all of the sulfur is combined the bonding of the accelerator is sharply retarded in spite of the fact that there is a significant amount of free MBTS left in the reacting mixture. 3. There is a linear relationship between the bound sulfur and the combined accelerator. 4. The rate constant for the combining of MBTS with the rubber increases linearly with the concentration of the accelerator. The limiting quantity of combined MBTS is about 75% of that introduced and does not depend on the concentration of the accelerator. 5. During sulfurless vulcanization with MBTS labeled with S35 in the disulfide bridge the quantity of combined accelerator determined chemically exceeds that determined radiomctrically by more than two times which indicates that there is an unsymmetrical scission of the MBTS. 6. During vulcanization with sulfur in the presence of MBTS labeled in the thiazole ring the ratio between the activity of the extract and the vulcanizate is significantly greater than unity. After all of the sulfur is combined this ratio becomes less than unity. An explanation of this phenomenon is reported.
Apparatus Study of Pore Formation Kinetics in Vulcanization
Authors: Albam M. A. , Pisarenko A. P.
Published: February 2011

The investigation of the processes of formation of microporous vulcanizates is a complex matter, since pore formation depends upon a whole ensemble of simultaneous chemical and physical processes some of which are : the decomposition of the blowing agent with the formation of gaseous products; the solution of these gases in the rubber hydrocarbon; the formation of an independent gaseous phase inside the compounded rubber stock and the foaming of the vulcanizate, which changes its elastic and plastic properties in the course of vulcanization; the escape of the gas. The biggest difficulty is the lack of a satisfactory procedure for investigation. Many specialists have investigated the kinetics of various pure blowing agents, but this differs from the kinetics of the decomposition of a blowing agent in various media, including a compounded rubber stock. In other investigations the force of the blowing action has been assessed from the size of the pressure exerted from the direction of the compounded stock upon a steel diaphragm. Nevertheless this method does not enable us to investigate the kinetics of the process or the influence of external pressure acting upon the compounded stock. All the methods proposed hitherto for investigation of the decomposition of blowing agents enable us merely to judge the relative amount of gas liberated by the various blowing agents, or else the action of whatever blowing agent in the “foaming” of the compounded stock. But with these methods it is impossible to determine the actual amount of gas formed in the compounded stock in the vulcanization period.
Rupture of Rubber. VIII. Comparisons of Tear and Tensile Rupture Measurements
Authors: Greensmith H. W.
Published: February 2011

In previous papers of this series a criterion for tearing of thin sheets of rubber vulcanizates was established on the basis of a characteristic tearing energy, the criterion being applicable either to the initiation of tearing at an incision or to the continuous propagation of a tear. An interpretation of the tearing energy in terms of the strength of a rubber as measured in tensile rupture tests was given, and in the present paper this is used in an attempt to relate tear and tensile rupture measurements, taking into account the observed effects of the speed of the test on such measurements. Data obtained from the tensile rupture measurements given in the preceding paper (Part VII) are first compared with the energy to initiate tearing at an incision with a tip of semicircular form. The data are then compared with the tearing energy for tears propagated at various rates.
The Breeding of Hevea Brasiliensis
Authors: McIndoe K. G.
Published: February 2011

The intrinsic yield of Hevea brasiliensis has been more than tripled over the past thirty-five years largely by the efforts of plant breeders. While it is not to be expected that progress will be as rapid over the next thirty-five years, yet the end is not in sight, and indeed new horizons are opening up. Coupled with the improvements made in other aspects of rubber culture, the industry is now in an excellent position to maintain its competitive status in world markets, and thus to contribute to the prosperity and economic stability of the tropical countries whose fortunes are so closely bound to it.
Biaxial Fatigue Testing Of Vulcanizates
Authors: Gehman S. D. , Rohall P. , Livingston D. I.
Published: February 2011

Extensive fatigue tests of vulcanizates of natural rubber and SBR were carried out using a cycle of alternate stretching in two perpendicular directions. It is shown that the data can be best handled statistically by assuming a lognormal distribution or by the use of extreme probability techniques. Illustrative results are given to compare the fatigue life of different types of SBR ; to show the value of the method for studying the effects of processing variations on fatigue life ; to determine the effect of various loadings of different types of carbon black; and to evaluate the effectiveness of anitoxidants and antiozonants. Exploratory tests using ozone instead of pinholes to initiate the failure eliminated the wide range in fatigue life between natural rubber and SBR, and in this respect gave a result which is more consistent with general service experience. This type of biaxial fatigue testing has many areas of usefulness for developing good endurance qualities in vulcanizates.
The Interaction of Carbon Black with Sulfur, MBT and TMTD in Vulcanization
Authors: Blokh G. A. , Melamed Ch. L.
Published: February 2011

The experimental data collected on the interaction of active centers of carbon black with the rubber on the one hand and of the active centers of carbon black with the sulfur and accelerators, and also with the antioxidants, on the other hand, provide a sound basis for belief that the problem of reinforcement of rubber by active fillers in the process of vulcanization cannot be explained from the physical aspect alone. The facts indicate the considerable importance of the chemical reactions between the active groups of carbon black and the compounding ingredients in the course of vulcanization.
Isotopic Exchange of Free Sulfur with Thiurams, Isothiocyanates and Dithiocarbamates
Authors: Kuzina L. S. , Guryanova E. N.
Published: February 2011

1. Studies were made concerning the exchangeability, with elementary radioactive sulfur, of sulfur atoms in 15 compounds including thiurams, dithiocarbamate and isothiocyanates. The number of exchangeable sulfur atoms in each material was established, as well as the optimal conditions for exchange, and for seven of the compounds the activation energy for the process was determined. The exchange rate of thiurams, with elementary sulfur, increases with the number of sulfur atoms in the polysulfide chain. In tetramethyl-thiuram tetrasulfide the two middle sulfur atoms are more readily exchanged, while the outer four sulfurs, bonded to carbon, are exchanged less rapidly but not sufficiently so to allow carrying out a separate exchange. 2. The velocity of exchange is significantly reduced in the thiuram disulfides when aliphatic radicals are replaced by phenyl radicals. A difference in the influence of amino-group radical variations was noted between the thiurams and the dithiocarbamates. The results of the isotopic exchange of sulfur in these materials have been considered from the viewpoint of their effectiveness as accelerators in the vulcanization of rubber.
The Chemistry of Vulcanization. VIII. Role of Zinc Butyrate in the Reaction of Diphenylmethane, Sulfur and 2-Benzothiazolyl Disulfide
Authors: Fukuda Haruko , Tsurugi Jitsuo
Published: February 2011

Diphenylmethane (DPM) which contains α-methylenic hydrogen has been used as a model of rubber hydrocarbon, and reactions involving DPM, sulfur and thiazole type accelerators in the absence of zinc oxide or soap were reported in previous papers. These papers reported that 2-mercaptobenzothiazole (MBT), 2-benzothiazolyl disulfide (MBTS) and zinc salt of 2-mercaptobenzothiazole (ZMBT) generate the same radical, i.e., 2-benzothiazolesulfenyl which has the accelerating effect. This radical opens the ring of elementary sulfur and thus accelerates vulcanization since the spontaneous splitting of the sulfur ring molecule to a biradical was found to be the rate determining step in the reaction of DPM with sulfur alone. Processes by which accelerators generate this radical differ from each other owing to the types of accelerators, that is, mercaptan, disulfide and zinc mercaptide type. The previous paper reported the reaction involving DPM, sulfur and MBT in the presence of zinc butyrate. According to this, MBT first reacts with zinc butyrate to form butyric acid and ZMBT, the latter then generating the effective benzothiazole-sulfenyl radical. Thus, even in the presence of zinc soap, the essential mechanism of acceleration is the same as in the absence of zinc soap, though the process and rate for forming benzothiazolesulfenyl radical are different in the absence of zinc soap. In the present paper the reaction of DPM, sulfur and MBTS in the presence of zinc butyrate are reported. The reaction mechanism will be deduced from the experimental results obtained here and from conclusions obtained in the previous papers. The rate equation for MBTS consumption and equation for the accelerating efficiency for this accelerator are derived from the mechanism. The theoretical equations were examined by experiments.
First and Second Order Transitions in Neoprene
Authors: Murray R. M. , Detenber J. D.
Published: February 2011

Neoprene vulcanizates crystallize most rapidly at —12° C. The temperature at which a vulcanizate is crystallized determines the minimum temperature at which it will thaw, the thaw point being approximately 15° C higher than the crystallization temperature over the range studied. Brittleness temperature is not changed as a result of crystallization. Crystallization resistance of the general purpose dry neoprene types increases in the following order: W, WB, WX, GN, GRT, WRT. Depending on the neoprene type, crystallization is retarded by a factor of 5 to 10 by vulcanization. Variation of filler type does not change crystallization rate appreciably. Crystallization rate is retarded through the use of sulfur, certain resinous type plasticizers, as well as by increased state of cure. Ester plasticizers which depress brittleness tempterature and reduce stiffening at low temperatures increase crystallization rate considerably and permit crystallization to occur at very low temperatures. Brittleness and 10,000 psi stiffness temperatures are not affected appreciably by neoprene type, state of cure, or amount and type of filler. Glass transition is approximately 12° C lower than the 10,000 psi stiffness temperature and 6° C lower than the brittleness temperature.
Thermal Expansion Measurements and Transition Temperatures. II. An Automatic Recording System
Authors: Dannis Mark L.
Published: February 2011

A differential expansion apparatus useful for studying first- and second-order transitions in polymeric materials was described1 in paper I. This apparatus utilizes a tipping mirror arrangement as part of an optical lever to magnify the expansion of the polymer sample with a change in temperature. Readings of light spot position on a scale and of sample temperature had to be taken almost continuously to obtain useful curves. These readings were very tedious and time-consuming, limiting the usefulness of the technique. Hence, an automatic recording system was developed, greatly expanding the potentialities of this kind of analysis.
Peroxide and Radiation Cured Compounds Filled with Reinforcing Fine Particle Silica
Authors: Sellers J. W. , Wagner M. P. , DeWitt B. J. , Stueber C. C. , Bachmann J. B.
Published: February 2011

The potential of fine particle silica to reinforce elastomers to an extent comparable with the most efficient furnace blacks has been indicated by the extent and nature of bound rubber formation. This potential has been confirmed in peroxide and radiation cures by the increase in crosslink density of the filled over the unfilled natural rubber mixtures. Confirmation in these curing systems stimulates further research designed to realize this high potential not fully attained in present sulfur cures.
Simple Rotary Dynamic Testing Machine
Authors: Gent A. N.
Published: February 2011

A test machine is described for determining the dynamic shear properties of rubberlike materials. It imposes a simple shear deformation, the direction of which is continuously rotated. The observations are easily made, and enable the dynamic shear modulus and damping factor to be determined rapidly; moreover, a relatively wide frequency range seems feasible. The instrument therefore appears suitable for general application. Measurements on a soft butyl rubber vulcanizate are described and compared with observations of free torsional oscillations. Good agreement is obtained. The testpiece is subjected to a rotating shear of constant amplitude, and hence the elastically-stored energy is held constant. The observed energy dissipation therefore confirms a hypothesis of Greenwood and Tabor, that dissipation may occur under such conditions, and indicates the limitations of the “hysteresis” concept that the dissipated energy is a constant fraction of the elastically-stored energy.
Acceleration by Thiourea and Related Compounds of the Tetramethylthiuram Disulfide Vulcanization of Natural Rubber
Authors: Moore C. G. , Saville B. , Watson A. A.
Published: February 2011

It has recently been discovered that thiourea and certain of its N-derivatives and chemically related compounds, accelerate the vulcanization of natural rubber (NR) by tetramethylthiuram disulfide (TMTD)-zinc oxide combinations to such an extent that excellent vulcanizates can be produced at 100° C or lower. A reasonable explanation of this acceleration is now offered, based on a theory of vulcanization by TMTI) and related “sulfurless” curing systems currently being developed here. This theory recognizes the importance of polysulfidic intermediates (I, m>2), formed during the vulcanization process, which subsequently react with the polyisoprene to yield further intermediates (II) which finally react to yield sulfurated crosslinks. The process is broadly schematized as follows:
Standard Materials for Rubber Compounding
Authors: Roth Frank L. , Stiehler Robert D.
Published: February 2011

When the synthetic rubber plants began operation in 1943, the Government took steps to establish a system of quality control that would assure that the rubber produced in 16 plants had essentially the same properties and could be used interchangeably by the manufacturers of rubber products. The most important characteristic for quality control was the curing behavior of the rubber. The measurement of this behavior required mixing the rubber with compounding ingredients, vulcanizing the mixed compound for several periods of time, and measuring the tensile properties of the vulcanizates. Early interlaboratory tests led the Government to an extensive standardization program in order to achieve the necessary quality control of production. In this program, it became obvious that the compounding ingredients as well as the methods of mixing, curing, and testing required standardization. Therefore, in 1944, the Rubber Reserve Co. established standard compounding ingredients for testing synthetic rubbers. The first standards were commercial lots set aside and distributed by their suppliers, and consisted of five materials. By 1946 a total of 14 standards had been established. The Office of Rubber Reserve soon recognized that the establishment of suitable standards was a difficult technical problem and called on the National Bureau of Standards for assistance. Finally, in 1948 this Office requested NBS to assume responsibility for these standards. Shortly thereafter, ASTM Committee D-11 appointed a special subcommittee on standard materials, the forerunner of Subcommittee 29 on Compounding Ingredients. This Subcommittee requested the establishment of about 20 standard compounding materials which included the standards required for the synthetic rubber program. The National Bureau of Standards has now available 17 of these materials, including three standard rubbers.
Volatilization of Phenyl-2-Naphthylamine from Rubber
Authors: Angert L. G. , Zenchenko A. I. , Kuzminskiĭ A. S.
Published: February 2011

1. The rate of volatilization of phenyl-2-naphthylamine from a rubber slab depends on the flow rate of gas over the slab, the slab thickness, and the initial concentration of the ingredient. The activation energy of the volatilization process is 14.0 kcal/mole. 2. The rate of volatilization of phenyl-2-naphthylamine diminishes in the following polymer series: polyethylene > fluoroprene rubber > SKB > SKS-30 > SKN-26 > Nairit. 3. The volatilization rate drops sharply with increase of the density of the vulcanization network, and decreases in presence of fillers. 4. The mechanism postulated for volatilization of ingredients from polymers is confirmed by theoretical calculations.
Oxidative Stress Relaxation Studies of Radiation Cured Vulcanizates, with and without Antioxidant
Authors: Dunn J. R.
Published: February 2011

Turner has shown that irradiation of natural rubber results in the formation of carbon to carbon crosslinks by combination of allylic radicals; the same type of crosslinks are formed by heating rubber in presence of organic peroxides2. Since peroxide vulcanizates may be freed from excess vulcanizing ingredients and by products by extraction while radiation crosslinking may be effected without additive, it is expected that the two types of vulcanizate should age in an analogous manner. The present study was undertaken in order to see whether radiation vulcanizates did show the same aging behavior as peroxide vulcanizates according to measurements of oxidative stress relaxation, and, if so, to ascertain whether the efficiency of antioxidants of the dithiocarbamate type was affected by the irradiation and whether such materials had an adverse effect upon cure. It has been stated that radiation vulcanizates are resistant to aging even in the absence of antioxidant and their stability has been attributed to the presence of purely carbon-carbon crosslinks. However, it has recently been demonstrated that a carbon-carbon crosslink is not a sufficient condition for vulcanizate stability in the absence of antioxidant. Previous studies concerning the aging of radiation cures appear to have been made using materials containing carbon black, which is now known to act as an antioxidant; it is necessary, for work of fundamental significance, to use gum stocks based on very pure rubber.
The Degradation of Main Chains and Crosslinks in the Aging of Vulcanizates
Authors: Lyubchanskaya L. I. , Kuzminskiĭ A. S.
Published: February 2011

In sulfur vulcanizates the energy of the bond between the atoms of sulfur in the crosslinks may differ essentially from the energy of the bonds in the main chains of the polymer since, as is known, the thermal decomposition of the polysulfide bonds may be brought about at considerably lower temperatures than the decomposition of the main chains. It was found by one of the present authors2 that the thermal decomposition of the sulfur bonds brings about an inhibition of the oxidation which develops in the chains of the polymer. Consequently we must not regard the destruction of the chains and the decomposition of crosslinks as independent processes. Nevertheless the difference in the rates of destruction and decomposition is so great that these processes may be separated. There are in the literature different views as to which elements in the structure of the vulcanizates the processes of aging extend to. Tobolsky asserts that the chemical relaxation of stress is caused by oxidative destruction of the polymeric chain of the vulcanizate independently of its structure. On the other hand Watson and coworkers consider that the decomposition of the lattice of the vulcanizate is the result of scission of chemical crosslinks. In the present investigation it was established that, depending upon the composition of the vulcanizate and the conditions of the experiment, the process of aging may involve both the chains of polymer and the crosslinks, forming a three-dimensional lattice of the vulcanizates.
Molecular Ordering in Polymers Precipitated from Solution
Authors: Igonin L. A. , Ermolina A. V. , Ovchinnikov Yu V. , Kargin V. A.
Published: February 2011

1. The variation of the ordering in polyvinyl chloride and polymethylmethacrylate precipitated from solutions in the process of heat treatment was studied. 2. The intensity curves calculated from the electronographic (electron diffraction) data show that the heat treatment leads to the formation of a more ordered arrangement of the chain molecules of these amorphous polymers. 3. The variation of the degree of ordering in these polymers in the heat-treatment process causes a change of the mechanical properties of the polymers and of their capacity for reprocessing. 4. From the data obtained we may conclude that the form of the polymer molecules and their mutual arrangement in the solution differ from those in the condensed state.
Dispersion of Carbon Black in Rubber: Revised Calculation Procedure
Authors: Medalia A. I.
Published: February 2011

Carbon black, the most important reinforcing filler for rubber, must be well dispersed if it is to function effectively. The state of dispersion of the carbon black can be studied effectively by microscopic examination of a thin (2µ) section of the rubber compound, using transmitted light, as described by Tidmus and Parkinson. Under the microscope, agglomerates of undispersed carbon black are visible. These agglomerates, which may range in size up to 100µ or even larger, are sectioned more or less cleanly by the glass knife, and appear as black or dark brown islands in a light brown field. While this method was originally proposed for qualitative estimation of the degree of dispersion, a quantitative calculation was subsequently developed by Leigh-Dugmore, by means of which the percentage of carbon black dispersed below a certain size was calculated. This calculation has been helpful in permitting a quantitative comparison of stocks of widely different visual appearance. As experience has accumulated with the Leigh-Dugmore method, some puzzling observations have been made. Frequently, the modulus level of a stock of a given dispersion was found to be higher than the proportionate modulus of a stock of 100% dispersion. Furthermore, stocks have occasionally been prepared with a measured dispersion rating of less than zero (see below). It thus seemed worthwhile to re-examine the Leigh-Dugmore calculation.
Carbon Black Structure Effects in Synthetic Rubbers
Authors: Bolt T. D. , Dannenberg E. M. , Dobbin R. E. , Rossman R. P.
Published: February 2011

Carbon blacks are composed of spherical particles which are to varying degrees arranged in chainlike structures. This type of particle association, which is readily seen in electron photomicrographs of most carbon blacks, can be termed “primary structure”. The use of the term “structure” to describe interparticle association must not be confused with the basic intraparticle structure of an atomic crystallographic nature. There is strong evidence that primary structure units, and possibly individual particles, can further associate or flocculate in fluid or elastomeric systems. This is a secondary type of structure formation which can be readily disrupted under the influence of mechanical strain. Some investigators have used the term “structure” to describe this strain-sensitive flocculation behavior. It is suggested here that carbon blacks possess both primary structure features and the ability to form secondary structures by flocculation in dispersed systems. The tendency to form secondary structures is probably greater with carbon blacks possessing a high degree of primary structure. Unless otherwise specified, the term “structure” in this paper will be used in the sense of primary structure. The structure of carbon blacks is thought to originate in the flame by the agglomeration of growing carbon nuclei and particles. The appearance of electron micrographs of carbon blacks lends some support to the assumption of simultaneous agglomeration and growth processes. Carbon blacks having a broad particle size distribution are characterized by carbon black chains, where each chain is composed of particles of the same size, rather than a randomized distribution of various sized carbon black particles. Thus, these chainlike structures must result from the continued growth of agglomerates formed from neighboring carbon particles at the same stage of their growth history. This process results in a chemical fusing of these particles as layers of new carbon are deposited on the surfaces of actively growing agglomerates.
The Law of Rubber Friction
Authors: Bartenev G. M. , Lavrentev V. V.
Published: February 2011

The investigation of the law of rubber friction on smooth hard surfaces over a wide range of normal pressures from 1 to 200 kg/cm2 has shown that Coulomb's formula applies in the small load region, and Thirion's formula in the region of larger loads. This conforms with the formula proposed earlier by one of the authors; this formula becomes the Coulomb's formula at small loads and Thirion's formula at large loads. Schallamach's formula has a physical meaning but is not confirmed experimentally.
Rubber Models of Yarns and Cords; the “Doubling” of Single Rods
Authors: Wilson N. , Treloar L. R. G.
Published: February 2011

In any theory of the physical properties of yarns and cords certain basic assumptions must be introduced regarding (a) the geometrical disposition of the filaments or other elements of the structure, (b) the physical properties of the filament material, and (c) the specification of the stresses and strains in the structure. On account of the complexity of the problem, the verification of a theory by experiments on actual textile yarns is not easy, firstly because their geometrical structure is fundamentally irregular and secondly because the elastic properties of typical textile fibers are very imperfect, the stresses not being uniquely determined by the strains. In order to examine the basic elements of the theory of the stresses in twisted filament assemblies, it has been thought desirable to examine certain simpler systems in which these difficulties are eliminated. For this purpose experiments have been carried out with model yarns, employing vulcanized rubber filaments. This material has the advantage of possessing almost perfect elastic properties, which can be simply specified. In addition, its low modulus and high extensibility permit the use of large ‘filaments’ which can more easily be disposed in a geometrically definable manner. The present paper is concerned with the measurement of the stresses in a system comprising two cylindrical rubber rods twisted together, as in the formation of a two-ply cord. Two cases are considered: in the first the two rods are initially free from torsion, while in the second the rods contain initial twist (analogous to singles twist in two-ply cord), before being twisted together. For each of these systems the stresses measured are the tension along the ‘cord’ axis and the couple about this axis, for various values of axial extension and ‘cord’ twist. These are compared with corresponding values calculated theoretically, using the measured values of the parameters defining the geometry of the system and of the elastic constants of the rubber.
Elastomeric Adhesion and Adhesives
Authors: Voyutskiĭ S. S.
Published: February 2011

In a review by Weidner and Crocker, published, under this title, in Rubber Reviews for 1960, there is expressed a series of critical remarks about the development by my collaborators and me of the diffusion theory of specific adhesion of polymers. Unfortunately, the authors of the review made use of only four articles, having ignored a series of recent articles and my special monograph which appeared in 1960. This probably was the cause of the one-sided view of Weidner and Crocker. I will try here very briefly to cite some principles of the diffusion theory of adhesion which the review has disregarded and also I will endeavor to reply to some of the comments of the authors.
Elastomeric Adhesion and Adhesives
Authors: Weidner C. L. , Crocker G. J.
Published: February 2011

We would like to point out first of all that the seven recent publications of Voyutskil were not “ignored” by us but were simply unavailable to us at the time our review was written. We have now had the opportunity of reading all but one of his recent contributions but see no reason to change our original viewpoint. In Voyutskii˘'s cited references, and particularly in his own works, he has emphasized the role of diffusion in adhesion. His viewpoint has been conditioned by his notion that adsorption values are inconsistent with high peeling work, and cannot account for peel adhesion rate dependence, and the strong adhesion of nonpolar polymers. We would fully agree that diffusion often plays a role in adhesion, certainly in autohesion and probably in other cases of polymer bonding as well when the polymers are not too dissimilar. The effect of mutual solubility in promoting strong adhesion has been a long accepted principle. The suggestion of it is inherent in the article on tackiness by Josefowitz and Mark and it had grown in acceptance sufficiently by 1947 to be clearly stated in an encyclopedia article on adhesion by one of us. But to regard this mechanism as dominant in such cases as adhesion of NBR to cellophane seems unjustified.