bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Methods for Determination of Bond Strength between Rubbers and between Rubber and Cord
Authors: Tsydzik M. A. , Lukomskaya A. I. , Slonimskiĭ G. L.
Published: February 2011

The standard methods of determination of bond strength between layers of rubber and rubberized fabric and between rubber and other materials (GOST 6768-53, GOST 264-53 and others) are of the static type and do not give a clear assessment of the bond strength of multiply rubber structures which are subject during use to temperature influences and to complex deformations which are repeated many times. This drawback is partially compensated for by carrying out the tests at elevated temperatures. Nevertheless static tests, from their very nature, cannot reproduce the particular character of dynamic conditions. In recent years there have been developed in different countries a large number of dynamic methods of determination of bond strength, which often differ little from each other in principle. In connection with the establishment of production of tires of 100% synthetic rubber, and also the introduction of viscose cord, dynamic methods were established in the Nauchno-Issled. Inst. Shin. Prom. (Tire Research Institute) and at the Moscow and Yaroslavl Tire Works. These methods differ from each other in the nature of the action (repeated compression, repeated shear and the like) and in the shape, structure and dimensions of the specimens being tested, but were fairly similar in the testing routine. If the settling of the specimens in the testing period is negligible, then the testing routine may be regarded as one of constant dynamic deformation, or, more accurately, of constant ampliture of movement of the platens deforming the specimens. In 1954 we established in the mechanical testing laboratory of the Nauchno-Issled. Inst. Shin. Prom. a new method of determination of the bond strength of the rubber with rubber and of the rubber with the cord. The method allows tests to be carried out in repeated compression and in repeated shear in three principal sinusoidal cycles: 1) with constant dynamic loading, 2) with constant dynamic deformation and 3) with constant product of amplitudes of force and movement.
Degradation of Polyisoprene Networks by Oxygen
Authors: Bevilacqua E. M.
Published: February 2011

The insolubility of vulcanized rubber and the relatively low concentration at which oxidation reactions completely degrade the vulcanizate have made it necessary that indirect methods be used to study the reaction of molecular oxygen with rubber. The literature contains many reports of measurements of the absorption of oxygen by vulcanized rubber, which is easy and convenient experimentally. In some of these the rate of oxygen absorption has been the only property measured. This alone gives little information about the mechanism of oxidation, although the fact that the general form of curves of oxygen absorption as a function of time can be predicted by equations based on the known mechanism of oxidation of low molecular weight olefins is indirect support for similar mechanisms of oxidation of polymers. The technologically important reaction accompanying oxidation of natural rubber is scission, not detected by gas absorption measurements. It has been studied principally by determining the decay in stress of a sample at constant strain. The results suggest that scission occurs by a first order process at selected sites in the network. This has been interpreted to mean that crosslinks are the primary locus of oxidation in vulcanized rubber. Estimates of the amount of oxygen required for breaking a bond are available only for samples vulcanized with sulfur. From these it may be calculated that initially 4– 5 moles of oxygen is required per scission, when allowance is made for the effect of entanglements on stress. A marked difference between the relaxation of peroxide-cured and sulfur-cured samples has been reported. Horikx has made an extensive investigation of the solubility and swelling of oxidized vulcanized rubber. His results show that the hydrocarbon chain must be broken during oxidation. The mechanism of scission of unvulcanized rubber has been determined; in this work it was found that low molecular weight products are an important index of scission reactions. The present report describes preliminary work on the scission mechanism in vulcanized natural rubber which has two objectives; to repeat Horikx's experiments with vulcanizates incapable of further cure, and to determine whether low molecular weight products accompany the scission reaction.
Chemical Reactions Induced by Polymer Deformation
Authors: Watson W. F.
Published: February 2011

A review is given of the work establishing the mechanico-chemical mechanism for degradation by the cold mastication of rubber. The relevance of this mechanism to industrial practice, in particular the addition of fillers and vulcanizing agents during mastication, is considered. The degradation by mechanical treatment is shown to apply to a wide range of polymers which are not rubbery at normal temperatures. The mechanism has also predicted the formation of block polymers by the milling together of polymers or a polymer containing a monomer. These predictions have been fulfilled.
The Rotomill—A Continuous Mixing Device
Authors: Juve A. E. , Beatty J. R. , Kline R. H.
Published: February 2011

The Rotomill is a simple device capable of mixing a wide variety of rubber compositions on a continuous basis. We believe that it is the first practical device for achieving this objective. The virtues of continuous operation are better control, greater uniformity, susceptibility to automation and greater economy. While large production units have not yet been built, there appears to be no insuperable obstacles to doing so.
Stress-Strain Isotherm for Polymer Networks
Authors: Ciferri A. , Flory P. J.
Published: February 2011

According to the molecular theory of rubber elasticity, the stress τ is related to the relative length a in simple extension according to τ=kT(ν/V)〈α〉2(α−1/α2), where (ν/V)〈α〉2 is a parameter of the network structure. Improved agreement with experiment has been claimed through use of the relation τ=(2C1+2C2/α)(α−1/α2) which contains the additional parameter C2. In order to explore factors affecting this theoretically inexplicable term, stress-elongation measurements were performed on networks prepared from natural rubber, Butyl rubber, poly-(dimethylsiloxane), poly-(ethyl acrylate), and poly(methyl methacrylate) under a wide range of experimental conditions. Results may be summarized as follows: (1) the C2 term offers improved agreement over the extension phase of an elongation cycle, but not for the subsequent retraction phase; (2) apparent values of C2 (determined on extension) vary widely from one polymer to another, increasing with hysteresis and with proximity to the glass transition temperature; (3) they are insensitive to the degree of crosslinking; (4) C2 is markedly reduced by permanently swelling the network with a diluent, or by swelling and deswelling the sample at each tension ; (5) incorporation of diluent prior to establishing a network by crosslinking with gamma radiation likewise lowers C2, the value characteristic of the unswollen polymer being restored upon removal of the diluent. The results demonstrate that the controversial C2 term arises from the difficulty of attaining elastic equilibrium; under ideal experimental conditions the value of this parameter becomes negligible. An alleged limitation of the theory of rubber elasticity is thus refuted.
Determination of Relative Damping at Various Prestresses
Authors: Kempermann Th , Clamroth R.
Published: February 2011

After a short review of the history of the development of the concept of damping, the definitions—one in words, the other in the form of an equation—given in DIN 53513 are discussed, and their usefulness for measurements at various values of prestress is investigated. It is evident that the mathematical definition given in the Standard applies only in the special case when prestress and alternating stress are equal. For the complete range of prestress, the phase angle δ or some simple function of δ, such as the loss factor, tan δ, should be measured. If it is desired not to relinquish the percentage statement of the energy loss, then a new definition for the relative damping is proposed which is independent of the prestress, just as is tan δ. The dependence upon the prestress of the damping values under discussion is demonstrated in an experimental section, for various types of elastomers.
Reinforcement of Rubber by Fillers Tear Resistance
Authors: Mullins L.
Published: February 2011

The results of experimental studies on 1) the effect of reinforcing fillers on tear strength and on the roughness of the resultant torn surfaces, 2) the relative adhesion of rubber to fillers and 3) the effect of hysteresis on tear strength are critically examined. They show that the maximum reinforcing effect of fillers is only exhibited if sufficient time is allowed for their strengthening role to develop during tearing, and that under these conditions the tip of the growing tear is broader and the torn surface rougher. They also confirm that the surface or immediate environment of filler particles provide a region of relative weakness, and that failure takes place at the interfaces ahead of the advancing tear, the rupture path wandering from one internal flaw to another. In addition they show that the more reinforcing fillers adhere more strongly to the rubber. Further, for gum vulcanizates, it appears that there is a simple relationship between tearing energy and hysteresis and that rubbers with higher hysteresis possess higher tear strength. A synthesis of the results of these three investigations provides a qualitative picture of the role of reinforcing fillers in increasing the strength of rubbers. It appears that a process giving rise to sufficiently rapid relaxation of stress ahead of the tip of a growing tear can in principle result in broadening of the tip of the tear and lead to increased strength. It is considered that this type of process plays an important and sometimes dominant role in the reinforcement of rubbers by fillers or by crystallization, and provides a consistent and coherent mechanism which indicates a source of the roughening of rupture surfaces of filler reinforced rubbers and of their possible branching and knotty tearing.
Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I
Authors: Scheele Walter , Hillmer Karl-Heinz
Published: February 2011

As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.
Investigation of Radical and Polar Mechanisms in Vulcanization Reactions
Authors: Shelton J. Reid , McDonel E. T.
Published: February 2011

The results obtained with free radical traps in a variety of curing systems for SBR rubber give evidence for both polar and free radical mechanisms. There is apparently no one mechanism even for sulfur vulcanization and the relative free radical or polar character of the crosslinking reaction varies over a broad range including situations in which both types occur in the same formulation. This may be due to competing reactions which function independently, or it may be the result of a combination of polar and free radical reactions in a single complex mechanism. For example, certain accelerators may initiate the reaction by dissociation to free radicals which attack the S8 molecule and form polysulfides which then decompose by a polar mechanism to initiate the propagation stage of the reaction. Based on the information obtained in this study and other supporting evidences, it is possible to group the familiar curing systems according to the apparent polar or free radical character of the reaction as observed in SBR. It is interesting to note that the accelerated sulfur curing systems which most closely approximate a polar mechanism either involve an amine (DPG) or a compound which is either present as a zinc salt (dithiocarbamate) or can easily form zinc salts at the curing temperature (thiuram disulfide and mercaptobenzothiazole systems). All curing systems studied which include free sulfur appear to involve a polar mechanism.
Synthesis of Polysulfides Containing Polar Linkages
Authors: Iwakura Y. , Hori T. , Suzuki K. , Wakasugi T. , Kobayashi G.
Published: February 2011

Polysulfide polymers are usually prepared from dihalogen compounds and sodium polysulfide and are used as synthetic rubbers. Also, polyamides or polyurethanes, such as Nylon 66, Perlon U (Igamid U) or Vulcollan, are used because of certain good properties. Therefore, if new polysulfide polymers could be produced when sodium polysulfide reacts with a dihalide having a polar linkage such as an amide group, we might expect excellent properties in the new materials because they might contain urethane, urea or amide linkages. We now show that dichloro compounds, which contain urethane linkages, can be prepared by the reaction between a chlorohydrin (ethylene chlorohydrin or 4-chlorobutanol-l) and polymethylene diisocyanate (where n=3, 4, 6 and 8 in (CH2)n).
Cis-Trans Isomerization in Natural Polyisoprenes
Authors: Cunneen J. I.
Published: February 2011

The cis and trans isomers of many simple olefins and conjugated polyolefins can be interconverted by the action of heat, light, and various catalysts, and in many such systems the changes in geometric configuration can be readily followed and the isomers separated and identified. Previous attempts to isomerize natural rubber and gutta-percha by treatment with ultraviolet light and various chemicals gave no detectable cis-trans isomerization, and in general configurational changes in unconjugated polyolefins have been unknown until recently when Golub converted the cis-1,4 units in polybutadiene into the corresponding trans units. This isomerization was achieved by irradiation of the cis-polymer with ultraviolet light in the presence of various organic bromides and sulfur compounds, but apparently this method did not isomerize natural rubber. In attempts to retard the rate of crystallization of natural rubber at moderately low temperatures—i.e., −10° to −40° C—by the attachment of side groups which would interfere with the molecular packing, it was observed that very small amounts of thiol acids were remarkably effective. This suggested that structural changes other than simply the attachment of side groups were occurring in the polyisoprene molecule. Recently it was found that thiol acids could interconvert the cis and trans forms of a simple trialkyl ethylene—e.g., 3-methylpent-2-ene—and subsequently, the isomerization of natural rubber and gutta-percha by these reagents was also observed. Following this, natural rubber, gutta-percha, squalene and cis and trans forms of 3-methylpent-2-ene have also been isomerized by treatment with sulfur dioxide and allied compounds; this work, including an investigation of the physical properties of the vulcanizates obtained from some of the isomerized polyisoprenes, is described in the present paper.
The Mutual Solubility of Polymers. V. Mechanochemical Blending
Authors: Slonimskiĭ G. L. , Reztsova E. V.
Published: February 2011

1. In the mixing of two polymers with intermixing of molecules, which, depending on the mutual solubility or insolubility, may lead to homogeneous or to mieroheterogeneous systems, there takes place also a mechanochemical mixing consisting of the formation of graft and block copolymers. 2. The proportion of these processes of mixing is determined by the intensity of and duration of the mechanical action in the process of mixing, and also by the concentration of additives capable of inhibiting the free radicals formed in the mixing. Of particular importance are special stabilizers, antioxidants and other such additives to the raw rubbers, and also oxygen. 3. The anomalies previously observed in the dependences of the mechanical properties of the vulcanized rubbers based on a combination of two mutually insoluble raw rubbers may be reduced by increasing the part played by the mechanochemical mixing. This opens up ways of producing high quality mixtures of mutually insoluble polymers.
A Study of Macroradicals in Processes of Polymerization and Degradation. I
Authors: Bresler S. E. , Kazbekov E. N. , Saminskiĭ E. M.
Published: February 2011

The use of a sensitive electronic paramagentic spectrometer permits one to obtain a number of new quantitative and qualitative data regarding the kinetics of polymerization and behavior of macroradicals with large polymerization depths. In particular, it is shown that in the photopolymerization of methyl methacrylate in a block of considerable number of sequestered macroradicals accumulates in the final stages. On the basis of an investigation of the change of the spectra in the heating of the polymer some assumptions are made concerning the secondary reactions of the radicals and concerning the influence of low-molecular impurities on the velocity of these reactions.
The Mechanism of Radiation Damage to Elastomers. I. Chain Scission and Antirad Action
Authors: Bauman Richard G. , Born John W.
Published: February 2011

The effect of antirads on chain scission as measured by stress relaxation is one of inhibition both in the presence of air and to a lesser extent in its absence. This can be explained by assuming a reactivity of the antirads with RO2⋅ radicals yielding stable products, and a somewhat decreased reactivity with R⋅ radicals. A greater tendency of RO2⋅ radicals to lead to chain scission than R⋅ radicals seems to be indicated.
Factors Influencing the Stability of SBR Latex
Authors: Sliemers F. A. , Bennett Bailey , Stickney P. B. , Heiligmann R. G. , deDecker H. K. J.
Published: February 2011

The theory is proposed as a result of this work that under “static” conditions, latex destabilization proceeds through a time-dependent localized polymer-particle dehydration. This dehydration apparently occurs in two stages. In the initial stage more or less reversible aggregates are formed. This creaming is accompanied by a perceptible increase in viscosity. In the second stage the aggregates are further dehydrated and coalescence occurs. This latter process is irreversible. Evidence is presented to support the argument that the prime requirement for the dehydration and, consequently, for the destabilization of high-stability latex is the presence of a static latex surface in contact with an unsaturated gas phase. Three factors involved here are (1) surface area, (2) surface agitation, and (3) the degree of saturation of the gas phase in contact with the surface. In addition, it is shown that particle growth precedes the destabilization and that stability is influenced by a number of other factors, including (1) temperature, (2) polymer concentration, and (3) polymer-particle size, which contribute, either directly or indirectly, to the dehydration process.
Physical Chemical Factors in Bond Strength in Multiply Vulcanized Articles
Authors: Dogadkin B. A.
Published: February 2011

Bond strength between the components of multiply articles in the vulcanized state depends on many factors which make themselves evident in the various stages of manufacture of the articles as well as under service conditions. In the present paper we shall give a description of the main physical chemical factors which were revealed in the course of experimental work in the physics and chemistry divisions of the Tire Research Institute, mainly in 1951 to 1953.
Determination of Static and Dynamic Bond Strength between Vulcanizates
Authors: Reznikowskiĭ M. M.
Published: February 2011

Methods employed for the determination of bond strength between vulcanizates may be classified as static or dynamic. Each of these groups has its own advantages and shortcomings. One undoubted advantage of the majority of static methods is that the tests are carried out under conditions where the stresses and deformations which determine ply separation may be measured directly. It is at the same time easy to determine the temperature since the specimens undergoing ply separation may be thermostatically conditioned. Nevertheless the practical value of the results obtained in static tests is very limited. In the first place, the character of the stresses governing ply separation in no way reproduces the true picture of the service life of multiply vulcanized rubber articles (in particular, tires), and, secondly, the resistance to ply separation for a single loading, for a number of reasons, may not indicate the endurance of the articles under repeated deformation. In dynamic tests we use the endurance under repeated deformations as a criterion of bond strength, presuming that the dynamic pattern of testing in some way reproduces the pattern of service of the material in the article. Unfortunately, the index of service life of any test specimens depends, in a complex manner which we do not in general understand, not only upon the bond strength between the vulcanizates, but also upon the stresses, deformations and also temperatures developed in the boundary layer. These parameters (stress, deformation and temperature) depend in their turn upon the elastic and relaxation properties of the vulcanizates from which the test specimen is made up. If the testing of the specimens is carried out in a dynamic pattern essentially different from that of service, then the results may be quite contrary to the behavior of the materials in an article. The selection of a rational method of dynamic testing applicable to tire compounds is particularly complicated on account of inadequate knowledge of the dynamic pattern of the operation of the component parts of the tire. Summarizing, we see that in investigations and tests of bond strength between vulcanizates we are obliged to use both static and dynamic methods. The static methods, allowing a quantitative interpretation of the results, must be considered more reliable for investigations in the fields of adhesion and covulcanization, particularly in cases where we are studying the effect of factors which essentially alter the properties (above all, the elastic and hysteresis properties) of pliedup vulcanizates.
Determination of Isoprene Unit Structures in Polyisoprene Rubbers
Authors: Kasatkina N. G.
Published: February 2011

Conditions were selected for simple and rapid determination of the percentage of 1,4, 3,4 and 1,2 units in synthetic isoprene rubbers from the curves of the rate of their oxidation by benzoyl hydroperoxide. The content of 1,4, 3,4 and 1,2 units in synthetic isoprene rubbers was determined by comparing the curves of the rate of their oxidation by benzoyl hydroperoxide with the curves of oxidation of model compounds, i.e. limonene and gutta percha.
The Butyllithium-Initiated Polymerization of 1,3-Butadiene
Authors: Kuntz Irving , Gerber Arthur
Published: February 2011

The organolithium polymerization of isoprene (2-methyl-1,3-butadiene) has been studied in some detail. Hsieh and Tobolsky have reported that the polymer prepared in benzene or heptane had more than 90% cis-1,4-structure. Polyisoprenes prepared in ethers showed a change in stereochemistry to 3,4-, 1,2-, and trans-1,4-microstructures. Other research further studied the sensitivity of polymer stereochemistry to solvent and the specific organometallic initiator. Although it was observed long ago that organolithium compounds cause the polymerization of butadiene, the stereochemistry of the polymer has been reported much less completely. The patent literature contains references in this area, and Russian researchers have studied the butyllithium-initiated polymerization of butadiene in the presence of ethers, oxygen, alcohols, and thio ethers. This communication describes the polymerization of butadiene by butyllithium in n-heptane; it discusses the stereochemistry of the polymer obtained and the effect of catalyst and monomer concentration, polymerization temperature, and the presence of ethers on the details of polymer structure. The results obtained are compared with the reported data for the alkyllithium-initiated polymerization of isoprene.
Complex Formation and Chain Structure in the Polymerization of Divinyl with Butyllithium
Authors: Kropachev V. A. , Dolgoplosk B. A. , Nikolaev N. I.
Published: February 2011

It has been established by a number of studies that the chain structure in the catalytic polymerization of monoolefins and dienes is determined to a large degree by the nature of the catalytic complex, participating in the polymerization process. Also it was shown that the initial catalytic complex bears a direct relationship to each elementary act of the chain growth. The isolation of organolithium compounds in the pure state is associated with great experimental difficulties. Together with the formation of the organometal compounds the possibility of a complex mixture of their oxidation products being formed is not excluded. To elucidate the influence of the indicated oxidation products on the chain structure in the polymerization of butadiene it seemed expedient to investigate the influence of oxygen. As the result of the investigation made by us it was established that in the polymerization of 1,3-butadiene with organolithium compounds the introduction of comparatively small amounts of oxygen into the system leads to a substantial increase in the number of 1,2 units in the polybutadiene at the expense of a reduction in the number of 1,4 units. The addition of either alcohol or phenol exerts a similar influence on the structure of the polymeric chain (Table 1).
Molecular Weight Distribution in Polymers. Polymerization of Isoprene and Butadiene with Metal Organic Compounds
Authors: Bresler S. E. , Korotkov A. A. , Mosevitskiĭ M. I. , Poddubnyĭ I. Ya
Published: February 2011

Problems connected with the calculation and analysis of molecular weight distributions of polymers obtained by catalytic polymerization were examined. An approximate method of calculation was proposed which is unique in its simplicity and which gives good approximations in the majority of cases of practical interest. Experimental data from a study of samples of polybutadiene and polyisoprene prepared by polymerization in solution by means of butyllithium were considered. The low degree of polydispersity for these polymers was noted in particular.
The Crystallization of Modified Cis-Polybutadiene
Authors: Trick G. S.
Published: February 2011

From a sample of polybutadiene of high cis-1,4 content, the microstructure is modified by cis-trans isomerization or by crosslinking. Measurements of rates of crystallization and melting point are made on the modified samples. An increase in irons content or crosslink density markedly decreases the rate of crystallization at a fixed temperature. It is found, however, that this retardation in rate may usually be accounted for by the depressed melting point of the modified samples.
Effect of Redox Systems on Thermal Oxidative Plasticizing of Butadiene-Acrylonitrile Rubber
Authors: Devirts E. Ya , Novikov A. S.
Published: February 2011

1. By using a redox system consisting of iron salts plus dimethylphenyl-paracresol, the rate of breakdown was considerably increased and structure-formation suppressed. This enables thermal oxidative plasticization to be used in industry for butadiene-acrylonitrile rubbers. 2. As the number of nitrile groups in the polymer increases, the rate of breakdown during thermal oxidative plasticization decreases and structure- formation occurs more rapidly. Butadiene-acrylonitrile (82:18) rubber has the greatest rate of breakdown, and the (60:40) copolymer the highest rate of structure-formation. 3. Vulcanizates of stocks based on thermally softened experimental butadiene-acrylonitrile rubbers are slightly inferior as regards strength and elasticity to similar vulcanizates of mechanically softened rubber. Their properties are, however, sufficiently high to enable thermal oxidative plasticization to be applied industrially.
Modification of Carbon Black with Ionizing Radiations
Authors: Lezhnev N. N. , Nikitina T. S. , Kuzminskiĭ A. S.
Published: February 2011

It is well-known that the reinforcing properties of carbon blacks used as active fillers for rubber depend to a considerable extent upon the adsorption properties of the surface of the carbon black particles. The presence on this surface of atoms and groups of polar or apolar character chemically bound with it, the surface relief and the presence of atoms with unsatisfied valencies in the hydrocarbon framework of the elementary crystallites determine the specific adsorption properties of carbon black of various types. In the present investigation we demonstrate the possibility of modifying the surface of the carbon blacks by the action of ionizing irradiation and by the radiochemical “sewing-up” of various compounds on their surface. Such modified carbon blacks have a considerable influence upon the physico-chemical properties of the resulting vulcanizates, which may make is possible to create new materials. The investigation was devoted to: (1) Ukhta thermal black—a typical representative of the soft semireinforcing blacks (practically not oxidized) ; (2) channel black from the same works—a hard active black, having a markedly oxidized surface, capable of irreversible interaction with the surface of the rubber and with the compounding ingredients.
Recent Developments in Superior Processing Natural Rubber
Authors: Baker H. C. , Foden R. M.
Published: February 2011

SP rubbers give greater latitude in extrusion and calendering processes by extending the range of operating conditions and giving greater scope for compounding for good physical properties. Compounds based on SP rubbers extrude smoothly with lower die swell at lower temperatures and higher viscosities. Greater productivity is obtained through the faster screw speeds which are possible with SP rubbers in many types of compound. SP rubber compounds calender with greater conformity to gage, greater ease of handling and control of shrinkage of the calendered sheet, at temperatures 10° C lower than normal. The firmer stocks given by SP rubbers and their greater resistance to degradation on milling lead to reduced wastage of unvulcanized compound in the factory, while the stricter control of processing permitted by SP rubbers results in a lower percentage of rejected articles. Evaluation of an experimentally produced SP 90 crepe has indicated the potentialities of a concentrated form of SP rubber as a more efficient processing aid than crosslinked SBR 1009 with NR and SBR.
Polymerization of Vinyl Monomers in Rubber Latexes
Authors: Allen P. W. , Bell C. L. M. , Cockbain E. G.
Published: February 2011

In recent years numerous workers have reported on the polymerization of vinyl monomers, in the presence of polymers, in which graft copolymers and/or homopolymers are formed. Kinetic studies of such reactions have been relatively few, however, particularly for systems involving polymer latexes rather than solutions. In the present paper a kinetic study of the polymerization of styrene, methyl methacrylate, and homologous methacrylic esters in natural rubber latex is reported, and certain abnormal features of the polymerizations are discussed.
Vulcanization of Elastomers. 25. Natural Rubber and Synthetic Elastomers with Sulfur and Sulfenamides. I
Authors: Scheele Walter , Toussaint Horst-Eckart , Chai Yoan-Kun
Published: February 2011

The sulfur vulcanization of Perbunan N 2818 (acrylonitrile-butadiene) was investigated in the presence of N-cyclohexyl-2-benzothiazolylsulfenamide (CZ) at different temperatures and various concentrations of reactants. The following were found : 1. The decreasing sulfur concentration vs. time plot followed the 0.8th order under all experimental conditions and an activation energy of 28.2 kcal/mole was calculated. 2. When using the cyclohexylammonium salt of MBT as accelerator, sulfur decrease proceeds at the same rate as with CZ. 3. It was concluded from 1 and 2 that even in the presence of CZ, the ammonium salt was the actual accelerator, which forms during the scorch or induction period through reaction of CZ with the rubber. 4. In view of the discrepancy found in the relation of reaction order with respect to time and concentration of reactants, the formation of a reactive intermediate is postulated; the analogy between the kinetics of sulfenamide accelerated sulfur vulcanization, and those accelerated with MBT as well as DPG is pointed out. 5. In connection with 3 the dependence of starting rate as well as rate constant of 0.8th order of the decreasing sulfur concentration on the molar ratio of CZ/S8 and on the sulfur starting concentration is discussed.
The Role of Hysteresis in Tire Wear and Laboratory Abrasion
Authors: Schallamach A.
Published: February 2011

The simple theory outlined in this paper accounts for the wear of slipping wheels in their dependence on external parameters. In addition, it draws attention to the importance of the elastic properties and the unsuspected influence of mechanical hysteresis. The experimental evidence brought forward in support of this side of the theory stems mostly from laboratory work. When attempting to apply the theory to road wear, it must be kept in mind that the mechanical properties of tires are only in part determined by the tread, their elastic behavior being largely that of the pneumatic casing. Laboratory experiments carried out with solid wheels give therefore an exaggerated estimate of the influence exercised by the hysteresis of the tread on the rate of wear. Nevertheless, the relation between wear and hysteresis should be as valid for tires as for other slipping wheels, if the resilience pertaining to the tire as a whole is introduced into the calculations. There is another aspect of hysteresis which might usefully be mentioned here. In the foregoing, the rolling resistance of tires has been neglected. While rolling resistance has most probably little effect on the wear mechanism, it does increase with increasing hysteresis of the tire. Thus, lengthening the life of a tire by increasing its hysteresis has to be paid for by an increased fuel bill.
Power and Thrust Force of Mill Rolls during the Mastication of Rubber
Authors: Mikhalev M. F.
Published: February 2011

There is described the dependences of change in plasticity of rubber upon the time of mastication, the peripheral velocity of the rolls, the gap, and the friction ratio. Equations are recommended for practical use which make it possible to determine the magnitude of the power of the machine and of the thrust forces set up in the gap between the rolls during mastication of raw rubber as a function of grade and initial plasticity. In addition, the authors investigated the dependence of these values upon the recovery and softness of the rubbers, a characteristic feature being that the relationships of the alteration in P and N to the recovery and softness remain the same as in the case of plasticity, and differ only in respect of the values of the coefficients and indexes. The equations describing these relationships will be considered by the authors in subsequent articles.
Microhardness Testing, Its Possibilities and Limitations
Authors: Scott J. R. , Soden A. L.
Published: February 2011

The need to test small awkwardly shaped rubber articles, which cannot be tested by normal methods, has led to the development of a scaled-down micro test for hardness. Attention is drawn to the mechanical problems that arise in devising such a micro test, especially those associated with friction in the moving parts and with the measurement of the very small movements of the indentor; the various ways in which these problems have been solved are described. The results of experimental work are presented to show the substantial equivalence in readings between the micro and the normal (macro) test, the good reproducibility of micro test results, the influence of testpiece dimensions, and the advantage of using a foot on the instrument as specified in ISO Recommendation R48 for the normal hardness test. Attention is drawn in particular to the influence of the dimensions of the rubber tested, showing on the one hand that reliable hardness measurements can be made, as expected theoretically, on much thinner and smaller specimens than in the standard test, though on the other hand there are minimum dimensions below which even the micro test cannot be expected to give results agreeing strictly with those of the macro test.
Electron Paramagnetic Resonance Investigation of Vulcanization
Authors: Blokh G. A.
Published: February 2011

New and extensive prospects are being developed with the employment of electron paramagnetic resonance (radiospectroscopy) (EPR) for the investigation of the chemical reactions taking place in the vulcanization of rubber. It is well-known that molecules which are taking part in chemical reactions in the majority of cases pass through the state of forming chemically active free radicals in which there are electrons having unpaired spins, i.e., the radicals have magnetic moments. Observation of the occurrence and disappearance of free radicals in chemical processes may be effected by the investigation of the paramagnetic resonance absorption of these radicals. Measurement of the radio-frequency of any given compound makes it possible to determine the degree of dissociation into free radicals. Consequently it becomes exceptionally valuable to employ EPR to solve the question of the nature of the reactions which take place in vulcanization. If in point of fact vulcanization is a radical reaction, then we ought to be able to observe EPR spectra.
The Lability of Sulfur Atoms in Vulcanization
Authors: Blokh G. A.
Published: February 2011

The application of the isotope method to the investigation of the mechanism of the action of accelerator and vulcanizing agents has made it possible to look at this question in quite a new light. With the help of the isotope S it has been demonstrated that in the process of curing there takes place a continuous exchange of atoms of sulfur in the structure of the accelerators, and of elementary sulfur as a vulcanizing agent, with the formation of unstable intermediate compounds. The sulfur thus liberated undoubtedly has high energy, as a result of which it combines rapidly with the rubber. It must be remembered in this connection that the reacting elementary sulfur is an eight-membered S8 ring, while the sulfur liberated from the sulfur containing compounds has the open chain structure:
Diffusion of Sulfur in Rubber in Relation to Vulcanization
Authors: Ludwig Rudolf
Published: February 2011

The present work is a report concerning the diffusion of sulfur in rubber. Following a suggestion of Prof. W. Seith, it was originally planned to investigate only the diffusion of radioactive, bound sulfur. If such a diffusion took place at all, it would seem to be equivalent to a wandering of the sulfur bridges which crosslink the carbon chains of the polymerized isoprene molecules in the vulcanizate and impart elasticity to the rubber. However, since the sulfur bridges are not exactly defined, and other types of combined sulfur can be present in the rubber, such a conclusion is not quite justified. Before such measurements are undertaken, one should be familiar with the diffusion of free sulfur in the rubber. Furthermore, a possible thermodynamic equilibrium between the free and the bound sulfur might invalidate the measurements. It was thus necessary to first determine the possibility of the occurrence of this equilibrium as well as the rate at which it is established. The diffusion experiments made it mandatory that suitable analytical procedures be found. Because of the multiplicity of the procedures, methods, and results, it appeared to be desirable to subdivide the material to be presented into several sections. First there will be a compilation of literature dealing with the chemistry of vulcanization.
Radiation Crosslinking of Rubber. III. Chain Fracture
Authors: Mullins L. , Turner D. T.
Published: February 2011

Exposure of hydrocarbon polymer molecules to high energy radiation results either in a decrease in their molecular weight or else in an increase with the eventual formation of an insoluble network. The primary faetor determining the behavior is the relative incidence of fracture of the main chain of carbon atoms to crosslink formation. The ratio of fractures to crosslinks β has usually been estimated from studies of the solubility of irradiated polymers. Most of this work has been on polyethylenes, but even under comparable experimental conditions widely differing estimates of β have been reported. The use of stress-relaxation measurements to detect the fracture of network chains during irradiation has also been reported. A recent study of the elastic behavior of crosslinked networks has indicated that comparative estimates of the number-average molecular weights of both (1) the chain segments lying between adjacent crosslinks and (2) the molecular chains crosslinked into the network may be obtained from stress-strain measurements alone. In the present work an attempt has been made to apply all three methods in a study of chain fracture occurring during the irradiation of purified natural rubber in vacuo.
Effects of Type of Rubber, Temperature, and Degree of Crosslinking on the Friction Properties of Elastomers
Authors: Bartenev G. M. , Styran Z. E.
Published: February 2011

1. The data on the influence of temperature and rate of slip on the frictional action of elastomers confirms the results of Schallamach for compounds of natural rubber and indicates that the external friction of highly elastic materials is a molecular-kinetic process of transition of chains, which adhere to the other rubbing surface, over an energy barrier under the action of an external force and thermal motion. 2. The energy barrier, which is dependent on the force of adhesion of the rubbing materials (energy of activation), is changed only slightly by changing the temperature, load and crosslink density for compounds from the same rubber. A greater change in the activation energy occurs by going from one polymer to another (from 18 to 32 kcal/mole). It is higher for polar rubbers (SKN) than for nonpolar rubbers (NR, SKBM, SKS). 3. Independently of the nature of the rubbing pair, the friction of elastomers follows Formula (2) over the range of slip velocities of 0.001–10 mm/min. In spite of the use of extremely small slip velocities, such a limit was not reached which might be attributed to the existence of actual static friction with the highly elastic materials. On the contrary, the drop in the coefficient of friction with decreased rate of slip became sharper the smaller the rate. For all elastomers there is observered a drop in the force of friction up to 60–80°. Above this region is an anomolous portion of the curve, the more sharply expressed, the greater the polarity of the rubber. The anomolous change in the force of friction is connected with the increase in the effective area of contact resulting from the destruction of the secondary bonds in the three dimensional network and a decrease in the static modulus of the compound. 5. High modulus compounds give a linear relationship for the force of friction up to 100–120° while low modulus compounds have a deviation in their linearity which appears, the earlier, the lower the equilibrium modulus. The slope of the linear portion of these compounds is greater than that of the lower modulus compounds which is connected with the increase in the effective area of contact at the transition from a hard to a soft compound. 6. At small normal loads (to 3 kg/cm2) the properties of the law of friction may be described by Coulomb's law. The force of friction is a linear function of the effective area of contact.
The Influence of Polymers with Conjugated Bond Systems on the Stability of Polyvinylchloride
Authors: Berlin A. A. , Popova Z. V. , Yanovskiĭ D. M.
Published: February 2011

We may now consider thermal and light initiated oxidative degradation in halogen-containing carbon-based polymers to occur through a radical-chain mechanism. Obviously the process is initiated by radical products of degradation in macromolecules, particularly by alkoxyl and hydroxyl radicals originating in the breakdown in the polymer of hydroperoxides. The development of the chain process occurs with the splitting out of atoms of hydrogen and halogen, resulting in dehydrochlorination to form double bonds and breaking down of the macromolecule. Although until recently there has been no very well-defined indication of the mechanism of formation, development, and splitting of the chains through thermal and light-oxidative degradation of Polyvinylchloride (PVC) it may be asserted that the most effective inhibition of this process is possible only by using materials which have the ability to accept radicals. Naturally, the radical acceptors employed can only be those which on heating, and exposure to the presence of air will not form hydroperoxides capable of reinitiating the destructive processes. Of major theoretical and practical interest in this connection, there have been described investigations on the effect of thermoxidative degradation in PVC, by a certain type of recently synthesized polyphenylvinylene (PPV) also containing the conjugated bonds of the degradation products of some high polymers, in particular PVC.
Strength and Elastomeric Properties of Rubber Solutions and Their Vulcanizates at High Deformation Rates
Authors: Trapeznikov A. A. , Assonova T. V.
Published: February 2011

Investigations of the strength and elastic properties of rubber solutions and of vulcanizates are of interest in relation to studies of the formation and character of the structures in such solutions. We carried out determinations with the aid of an elastoviscometer for oscillographic recording of P(ε) curves at high values of ˙ε⋅2, and also an elastorelaxometer designed for direct measurements of elastic deformations in flowing systems at high values of ˙ε. P(ε) curves for 6% solution of rubber in decalin are given in Figure 1.