bluuebunny/crossref_metadata_2025 huggingface dataset:
The Ozonization of Unsaturated Compounds. III. The Addition of Ozone to Internal and External Double Bonds in Butadiene Rubber
Authors: Yakubchik A. I. , Kasatkina N. G. , Pavlovskaya T. E.
Published: February 2011

1. It was established that the curves of ozone absorption by butadiene rubbers do not show breaks. 2. Sodium butadiene rubber was ozonized 25, 50, 75 and 100%. From the quantitative determination of the external double bonds which add ozone it was established that there is no strict selectivity in the ozonization of the double bonds of rubber: the external double bonds are ozonized more rapidly than the internal and their ozonization is completed earlier than the ozonization of the internal double bonds.
Carboxylic Rubbers. I. Synthesis and Structures
Authors: Dolgoplosk B. A. , Tinyakova E. I. , Reĭkh V. N. , Zhuravleva T. G. , Belonovskaya G. P.
Published: February 2011

It is well known that the high strength of unfilled (pure gum) natural rubber and some synthetic rubber compounds can be explained by the homogeneity of the polymer chain which determines its ability to crystallize or to orient on stretching. The character of the vulcanization network as well as the structure of the main chain is of importance. This has been verified by the use of polyethylene polyamines and other chemical compounds as vulcanization accelerators for butadiene-styrene rubber (SKS-30A) to produce high strength (up to 200 kg/cm2) gum rubber compounds. In certain cases, only the structure of the vulcanization network obtained with carboxyl-containing rubber compounds can account for obtaining the same effects as are obtained with natural or other synthetic rubber compounds as a result of homogeneity of polymer chain. The first work done by us on carboxyl-containing (carboxylic) rubbers was done in 1954\2-1955. In this work it was shown that polymers of isoprene and of butadiene, copolymers of butadiene with styrene, butadiene with acrylonitrile, and others, which contain small quantities of methacrylic acid (1\2-2 mole %) in the chain, can be vulcanized with oxides of divalent metals to give pure gum and lightly filled compounds characterized by high strength and elasticity, good resistance to heat aging and good cut growth resistance.
Sorption of Binary Solutions by Vulcanizates of Natural and Synthetic Rubber. I. Isotherms of Effective Sorption
Authors: Starobinets G. L.
Published: February 2011

1. The sorption of binary solutions by vulcanizate of natural and sodium-butadiene rubber was studied over the entire composition range of the following binary systems: benzene-low weight alcohols, benzene-low weight acids, benzene-polar derivatives of benzene, toluene-low weight alcohols, carbon tetrachloride-low weight alcohols, p-dichlorobenzene-low weight alcohols, benzene-acetone, benzene-ethyl acetate, chloroform-acetone, chloroform-methyl ethyl ketone, benzene-ethyl iodide, benzene-propyl bromide, hexane-dioxane. With the help of these data, coefficients of distribution of components between phases and sorption potentials of the components were calculated. Effective sorption isotherms of solvent from all the systems were constructed. 2. There is a close connection between the value of the effective sorption of solvent from systems of the solvent-nonsolvent type and the nature of the binary solution. The effective sorption of solvent is greater the larger the positive quantity of excess free energy of formation of the binary solution. From systems characterized by a negative value of excess free energy the solvent is sorbed to a far smaller degree than from systems with a positive deviation from the laws of ideal solutions. Sorption from binary solutions by rubber produces all four types of effective sorption isotherms that are predicted from thermodynamic considerations. 3. Comparison of effective sorption isotherms from the same solvent-nonsolvent system by vulcanized rubber and by activated carbon shows that the maximum value of effective sorption of solvent is much greater for the rubber than for the carbon. The selective nature of the sorption is also more strongly evident with the rubber : the negative branch of the S-shaped sorption isotherm from binary solutions on carbon is practically missing when the sorption takes place from the same solution on vulcanized rubber. From this it follows that many binary liquid systems as well as mixtures of saturated vapors could be more effectively separated on rubber and its vulcanizates than on activated carbon. This conclusion could have practical value since the effective sorption by rubber changes little with temperature and the desorption process is easier to carry out with rubber than with carbon. 4. It was established that the shape of the equilibrium curve between polymer and binary solutions does not depend on the degree of vulcanization or the composition of the active fillers in the vulcanizate. From this it follows that the efficiency factor of the sorption process is determined only by the nature of the rubber and not by the composition of the vulcanizate. 5. From analysis of the experimental data it follows that sorption of solvent occurs largely as random mixing of its molecules with sections of the polymer chain. Sorption of nonsolvent takes place by more or less strong attachment of its molecules on sorption sites of the polymer.
Mutual Solubility of Polymers and Properties of Mixtures
Authors: Slonimskiĭ G. L.
Published: February 2011

If a homogeneous mixture of two polymers is to be obtained, both components must exhibit fluidity. It is, therefore, necessary first of all to analyze the process of mixing of two amorphous linear polymers capable of developing true irreversible deformation. However, though the mixing of two such polymers, from the thermodynamic point of view, constitutes the mutual solution of two liquid phases, it does not, in fact, take place spontaneously, since the exceptionally high viscosity of polymers1 results in a negligible rate of diffusion of the long-chain molecules, even at elevated temperatures. For this reason, special procedures (mixed milling, evaporation of solvent from mixed solutions, etc.) are used to obtain polymer mixtures which exhibit no heterogeneity, even when examined by means of a good optical microscope. It is, however, quite evident that, should two polymers be mutually insoluble, the spontaneous separation of such artificially prepared mixtures into macroscopically distinct phases must proceed at infinitesimal rates as a result of the enormous viscosity of the system. In such cases, the flexibility of the chain, which permits the relatively rapid translation of individual segments of the chain, is an important factor. This property of chain molecules will result in a process by which the mixture of mutually insoluble polymers becomes resolved in extremely small volume elements, i.e., to the formation of two types of regions whose composition will accord with the thermodynamic conditions of phase separations. Such mixtures of two amorphous polymers structurally closely resemble crystalline polymers, which are also microheterogeneous. In both cases, the dimensions of the regions differing in phase character formed by the segregation of segments are considerably smaller than the length of the chain molecules. For this reason, the macroscopic miscibility of two polymers is by no means equivalent to their microscopic miscibility, i.e., to true mutual solubility of the polymers.
Rupture of Rubber. V. Cut Growth in Natural Rubber Vulcanizates
Authors: Thomas A. G.
Published: February 2011

It has been noted in Part I of this series (referred to hereafter as I), that if a nicked specimen of a natural rubber vulcanizate is slowly stretched, tearing occurs at the tip for quite small applied forces. In the initial stages, this tearing continues only as long as the deformation of the specimen is being increased, and virtually ceases if the deformation is held constant. This tearing is essentially time independent, and is termed “static” cut growth. If, however, the deformation is continued until the cut has grown by a few hundredths of a millimeter the growth becomes time dependent and catastrophic tearing takes place, the cut suddenly increasing in length by perhaps a millimeter or so. If a nicked specimen is alternately stretched and relaxed to the unstrained state, the cut gradually grows even though the applied force is less than that required to produce catastrophic tearing. This phenomenon is termed “dynamic” cut growth. This behavior can be compared to that of gum GR-S vulcanizates described in Part III, where static cut growth of the above type does not occur, a dead load on a test piece producing a more or less steady rate of cut growth. In the present paper, measurements on natural rubber gum vulcanizates only are described, and the numerical results expressed in terms of the theory developed in previous papers (Parts I, II and III). It has been shown in I and II that the tear behavior of differently shaped test pieces cut from thin sheets of thickness t may be correlated by means of the concept of the energy for tearing. This is defined as the value of T[=(1/t)(∂W/∂c)l] at the instant of tear, and is denoted by Tc. In the definition of T, is the total elastic energy stored in the test piece, c the length of the cut, and the subscript l indicates that the differentiation is to be carried out at constant displacement of those parts of the boundary that are not force-free. It was also shown that a convenient and direct method of obtaining Tc is by the use of the “simple extension” tear test piece described in I and shown in Figure 1, and this has been used for most of the experiments. Under most conditions, T for this test piece is nearly independent of the cut length, width of the test piece, and modulus of the rubber; T is very nearly equal to 2F/twhere F is the force applied to the arms. In the cases where the use of the above approximate relation between T and F introduces an appreciable error, the exact theory given in I was used.
Influence of Surface Condition, Duration of Molding, Pressure and Temperature upon Bond Strength between Components of Tire Casings
Authors: Pinegin V. A. , Vasil'eva S. A. , Kepersha L. M.
Published: February 2011

As a result of the above experiments it is shown that the bond strength between components of casings where 100% synthetic rubber is used, may be significantly increased: 1) by maintaining the freshness of the surfaces being plied up by keeping standing to a minimum, by freshening the surfaces by fine (‘velvet’) buffing, and by applying a thin and uniform layer of bonding agent to the previously heated surfaces; 2) by increasing the specific molding pressure during plying up; 3) by increasing the specific pressure upon the constructions during vulcanization; 4) by increasing the duration of action of the specific molding pressure during plying up; 5) by raising the temperature of the components being plied up. The rational exploitation of these points undoubtedly has an important effect and will ensure the improvement of the quality of the finished articles, particularly where 100% synthetic rubber is used.
Enhancement of Bond Strength in Tire Casings by Heat Treatment
Authors: Malkina Kh. E. , Pukhov A. P.
Published: February 2011

Testpieces of carbon black stocks on a 100% synthetic rubber basis which do not adhere to surfaces may be satisfactorily bonded to each other if they are subjected to molding under a given pressure over a prolonged period. In this case the more plastic the stocks the greater the depth of their penetration into each other on molding, and consequently the higher the bond strength between the individual rubberized components. The best and most rapid joint is with components whose plasticity values are close to each other. Carbon black stocks on a 100% synthetic rubber basis are highly thermoplastic. Thus preliminary heating of the blank components with subsequent molding ensures enhancement of the bond strength. As a result of calendering, extruding, building and molding of the various types of component going into a tire casing stresses are set up between these components which tend to separate them and thus reduce the bond strength in the finished product. The removal of such stresses leads to enhancement of bond strength. Since the mechanism of the removal of the stresses is a relaxation mechanism, the lowering of the stresses proceeds more rapidly and fully in heated blanks ; thus the heating and maintenance of the heat of the heated raw casings, particularly before vulcanization, ought to lead to an improvement in their service properties. These things are not usually disputed. Nevertheless until recently the quantitative side of the matter was not clear, i.e., whether it was possible by preliminary heating to increase significantly the serviceability of the casings (in particular on poor roads). Suitable investigations were carried out in the technology division of the Nauchno-Issled. Inst. Shinnoĭ Prom. (Tire Research Inst.) to study this.
The Mechanism of Sulfur Reaction in the Polymerization of Chloroprene and of Thiuram Reaction in the Degradation and Structurization of Polychloroprene
Authors: Klebanskiĭ A. L. , Zukerman N. Ja , Fomina L. P.
Published: February 2011

To elucidate the mechanism of the reaction between chloroprene and sulfur, the following investigations have been carried out: (1) The reaction of a polychloroprene solution with sulfur under conditions of free radical initiation was studied. It was found that sulfur does not react with polychloroprene, whereas under polymerization conditions the addition of sulfur proceeds readily. (2) A study of the polymerization of chloroprene monomer containing various amounts of sulfur (from 0.3 to 10%) showed that the sulfur content of the polymer increased in proportion to the amount of sulfur originally present. Polymers with a high sulfur content (3–5%) were found to be completely soluble at low degrees of polymerization. The latter finding indicates that the sulfur does not effect crosslinking, but that it is bound predominantly in a linear manner in the polymer chain. (3) The predominant form of bonding of the sulfur was found to be in di-and polysulfide linkages. The number of the latter increases with the sulfur content of the polymer. (4) By the action of nascent or catalytically activated hydrogen, the polymer was found to undergo extensive degradation with the loss of 80 to 100% of the bound sulfur and formation of low molecular weight polymer. In the course of the reduction the disulfide links are broken with the formation of polymer mercaptans, which are converted to disulfides by reaction with iodine; this is confirmed by an appropriate increase in the intrinsic viscosity. These findings confirm the copolymerization mechanism of the reaction between chloroprene and sulfur as proposed by Mochel and Nichols. (5) The mechanism of the degradation of polychloroprene sulfide by tetraethylthiuram disulfide (TETD) was studied by means of the following model systems, representing the main types of structures present in such polymers:
A Theoretical Study on the Mechanism of Ziegler-Type Polymerizations
Authors: Uelzmann Heinz
Published: February 2011

Since the discovery of catalysts for the polymerization of ethylene and α-olefins at low temperatures and low pressures by Ziegler and coworkers, extensive experimental work has been done on this subject. Several theories on the mechanism of the catalysis have been discussed in order to illustrate the specific effects of different catalytic systems. In this paper an attempt is being made to consolidate the existing theories into a single basic mechanism and to explain the numerous experimental facts from a different viewpoint. A theory on this subject must explain: (1) An anionic propagation. (2) A “hair-like” growth of polyethylene from one active spot on the catalyst surface. (3) Stereospecific polymerization of α-olefins and an exclusive head-to-tail arrangement according to Natta. (4) Different activities of Ziegler catalysts. (5) Activity and action of modified Ziegler catalysts. Generally these catalysts are prepared by interaction of an aluminum trialkyl and a transition metal in the form of its halogen derivative. Complex formation between both components is believed to occur according to the tendency of transition elements and aluminum to operate with coordination valences. The catalyst has an extremely high activity (low temperature initiation) and, furthermore, imparts strong protection and stabilization to the growing chain end. This is a prerequisite for the formation of very high molecular weight polymers. Besides the initiation, propagation, and termination, an orientation step is involved in the mechanism of catalysis which produce stereospecific polymers. In the following section the initiation of olefin polymerization by different kinds of catalysts is discussed in order to show that only one definite type of initiation seems likely to occur under the conditions of the Ziegler polymerization.
Structure and Properties of Filled Stocks XVI. Polybutadiene Filled with Colloidal Silica
Authors: Dogadkin B. , Pechkovskaya K. , Gol'dman E.
Published: February 2011

1. Colloidal silica can be partially or completely removed from filled rubber stocks by boiling in 1% aqueous NaOH. 2. Degree and rate of extracting directly depend on the reinforcing effect of the silica. The higher the filler activity, the more complete its extractability from the rubber. Inactive samples of silica practically cannot be extracted from filled rubber stocks. 3. The active silica forms a thixotropic chain structure in the rubber, but inactive silica is distributed in rubber as isolated particles or aggregates. 4. The rubber portion that remains after extraction of the active silica is insoluble in common rubber solvents. 5. The equilibrium swelling value in binary solvents (butanol-toluene) is lower, the higher the reinforcing action of the silica. 6. The reinforcing effect of silica is proportional to its moisture takeup capacity, which may be determined by a simple method described. 7. Based on the experiments described, the type of linkages involved and the structure of the rubber stock filled with silica are considered.
Tensile Strength of Filled SBR Vulcanizates
Authors: Bueche F.
Published: February 2011

The molecular behavior responsible for the observed tensile strength properties of unfilled rubbers has been studied in a recent paper from this laboratory. In the present paper we intend to extend that work to the case of rubbers which are filled with carbon black. Measurements of the tensile strength of hot and cold SBR as a function of carbon black concentration, degree of vulcanization, and temperature are reported. An attempt is made to interpret the observed behavior in terms of molecular concepts. Some additional measurements with resin and calcium carbonate fillers are shown to lend support to the conclusions reached.
Oil Extended Styrene-Butadiene Rubber SKS-30M
Authors: Shatalov V. P. , Bashkatov T. V. , Kostiukov N. , Popova E. N. , Chuliukova T. A. , Krygina M. K. G.
Published: February 2011

The results indicate that there is a real possibility of obtaining oil extended SKS-30M-15 rubber with satisfactory physical and processing properties from high temperature, modified latex.
Vulcanization with TMTD
Authors: Bevilacqua E. M.
Published: February 2011

The mechanism reviewed in some detail here appears adequate to explain substantially all that is now known about vulcanization with TMTD. It has predicted accurately the stoichiometric relationships between the reagents entering into the vulcanization reaction and the known products formed. It presumes that vulcanization is a primary consequence of the interaction of rubber, TMTD, and zinc oxide and not an incidental result. It is not, however, fully established by the evidence now available. In particular the studies by Scheele and coworkers (as exemplified by Reference 33). on the reaction of zinc oxide with thiuram disulfides suggest the interesting possibility that primary attack during vulcanization is on the oxide rather than the hydrocarbon, as assumed in this discussion. There is at present no experimental basis on which to eliminate either of these two alternatives. The success of the mechanism reviewed here in delimiting stoichiometry of the reaction makes it a convenient framework from which to develop a complete understanding of the reaction.
The Structure and Properties of Rubbers Produced in Radiation Vulcanization
Authors: Dogadkin B. A. , Tarasova Z. N. , Kaplunov M. Ia , Karpov V. L. , Klauzen N. A.
Published: February 2011

1. The structure and properties of irradiation vulcanizates of technical and purified SKB, NR, SKS-30A, SKS-30AM, and SKI rubbers with and without fillers, made by irradiation in a nuclear reactor and in a cobalt source, with integral doses of 107–108 r, have been studied. 2. The density of the network formed in irradiation vulcanization is determined by the quantity of energy absorbed, the type of rubber, the irradiation conditions (medium, temperature), and certain other factors. The yield of crosslinks per 100 ev in air is ∼12 for extracted butadiene-styrene rubber, ∼4 for extracted NR, and 2.5 for technical SKS-30A. The crosslinking effect increases with increase of temperature and decreases in presence of an oxidation inhibitor (phenyl-2-naphthylamine). 3. The thermomechanical stability of irradiation vulcanizates is superior to that of vulcanizates made with thiuram without sulfur, and such vulcanizates undergo the least changes in properties during chemical relaxation. In contrast to sulfur vulcanizates, the relative rate of stress relaxation in irradiation vulcanizates depends on the density of the vulcanization network. This indicates the C—C type bridges are formed in the course of irradiation vulcanization. The thermomechanical stability of irradiation vulcanizates is raised by the introduction of active blacks. 4. The presence of carboxyl, hydroxyl, ether, and ester groups in irradiation vulcanizates of natural, butadiene-styrene, and sodium butadiene rubbers vulcanized in presence of air has been demonstrated by infrared spectroscopy. A dose of 60·106 r causes almost complete disappearance of double bonds from extracted butadiene-styrene rubber. In the technical rubber, containing phenyl-2-naphthylamine inhibitor, this dose reduces the degree of unsaturation by about 30% of the initial value. 5. The tendency to crystallization on stretching was studied in irradiation vulcanizates of natural rubber. The crystallinity of irradiation vulcanizates made by irradiation with relatively small doses, up to 20–30·106 r, is the same as that of sulfur vulcanizates of the same network density. The degree of crystallization decreases with increasing radiation dose. 6. Conditions for the production of massive multilayer specimens by irradiation vulcanization were investigated. It was found that a uniform vulcanization network can be obtained irrespective of the thickness of the specimen (in the range 0.1–40 mm). 7. The physicomechanical and technical properties of irradiation vulcanizates were studied. In comparison with the best sulfur with the same filler contents, irradiation vulcanizates have a higher resistance to aging (4–5 times as high at 130°), low residual deformations, low hysteresis, high endurance to repeated deformation, and high heat resistance. The tensile strength of irradiation vulcanizates, as a function of the radiation dose, passes through a maximum, but does not reach the values found in the best sulfur vulcanizates.
Swelling Behavior of Rubbers Compounded with Reinforcing Pigments
Authors: Boonstra B. B. S. T. , Dannenberg Eli M.
Published: February 2011

Equilibrium swelling data are presented for vulcanizates of natural rubber, SBR 1500, butyl rubber, neoprene, and nitrile rubber containing fumed silica, precipitated silica, precipitated calcium metasilicate, hard clay and carbon black. Swelling media are chloroform, benzene, hexane, and acetone. It is observed that certain fillers, particularly carbon black, cause a reduction in the swelling of the rubber matrix which is commensurate with the volume loading of the filler. This effect is not specific for a particular solvent or elastomer. When a series of loadings of a filler shows this effect of reducing the matrix swelling in one solvent, it is also shown by the swelling data for the other solvents, but not to the same degree. The system SBR-benzene was studied to determine from the bound rubber measurements and the equilibrium swelling data for the corresponding vulcanizates the number of crosslinks per cubic centimeter in the unvulcanized and vulcanized states. It appears that the number of crosslinks estimated in the bound rubber gel is much too small to account for the increase in crosslink density in the rubber matrix that is caused by the presence of carbon black in the vulcanizate.
Colorimetric Determination of Amine Antioxidants
Authors: Hilton C. L.
Published: February 2011

A method is described for the qualitative identification and quantitative estimation of many of the more common amine antioxidants. The method is comparatively simple and requires less than one-half man hour per determination. The method is accurate and precise. Analyses with known stocks showed an average error of less than 2% relative.
Methods for Determination of Rubber to Cord Bond Strength
Authors: Uzina R. V. , Gromova L. S. , Vasil'eva S. A.
Published: February 2011

In selecting methods for determination of rubber to cord bond strength it is necessary to consider the factors which are subject to variation in the system— the type of cord, the composition of the vulcanized rubber, or the composition of the impregnant. The selection (composition) of the methods of assessment of bond strength was carried out in the present study while keeping the type of cord and the rubber compositions constant ; only the composition of the impregnant was varied. Up to the present there has been no single laboratory method for evaluating rubber to cord bond strength for the determination of the service quality of rubber-fabric structures. The bond strength in such a system is assessed in the majority of cases by the use of a series of methods. The existing methods may be systematized according to the nature of the deformation (static or dynamic), the nature of the specimen (with single thread of cord or with cord fabric) and so on. We adopted the following classification of methods: 1). Determination of bond strength of a single thread of cord with the rubber; 2). Determination of bond strength of rubber to fabric model specimens. Determination of bond strength of a single thread of cord with rubber is an exceptionally widely used type of testing in the rubber industry. It is based either on the principle of stripping of a single thread of cord from the rubber under pressure, or on the principle of pull-out of a thread of cord from a rubber specimen.
Thermoelastic Phenomena in SKS-30A and SKB Rubber Compounds in Adiabatic Deformation
Authors: Votinov M. P. , Kuvshinskiĭ E. V.
Published: February 2011

1. The stretching of vulcanizates of SKS-30A and SKB before break accompanied by the generation of heat equivalent to the work of stretching indicates the kinetic nature of the elastic forces in these vulcanizates. 2. Change in the degree of vulcanization of the compound and the addition of fillers leads only to a change in the modulus of elasticity of the rubber compound. The rules of conversion of work into heat do not change. The absence of crystallization processes even at high elongation (λ=6−7.5) is evidently a result of the irregular structure of the hydrocarbon skeleton of the original rubbers, SKS-30A and SKB. 3. For rubbers containing active fillers (channel black and silica gel) and obtained by optimum vulcanization, there is observed a decrease in heat evolution caused by hardening of the material in the region of high elongation just before break.
Cis-Trans Isomerization of Natural Rubber under the Influence of Organo-Aluminum Compounds and Titanium Tetrachloride
Authors: Dolgoplosk B. A. , Kropacheva E. N. , Nelson K. V.
Published: February 2011

Ziegler catalysts have become of prime importance for synthesis of polymers with regular structure, particularly cis-polyisoprene. The disruption of the structure of the chain by the formation of trans units was, until now, connected only with the influence of the physical and chemical properties of the catalyst on the nature of the addition of the diene monomers during the polymerization process. In the present work it is shown that destruction of regularity of structure can be caused by isomerization of cis units in complete polymer chains into trans units under the influence of the compounds used for initiating the polymerization process. Attempts to isomerize natural rubber by means of ultraviolet light and iodine did not give the expected effect. Ferri established for the first time that under the influence of zinc chloride and titanium tetrachloride natural rubber undergoes changes accompanied by disappearence of crystallization on stretching as shown by x-ray structure analysis. On the basis of these results the authors presumed that under the influence of these agents isomerization of cis units to trans units occurs in the natural rubber chain. The isomerization of cis-1,4 units to trans units in polybutadiene by means of ultraviolet light in the presence of organic bromine or sulfur compounds was first accomplished and proved by Golub. The formation of trans units in natural rubber under similar conditions was not observed. The study of the isomerizing effect of TiCl4 and organo-aluminum compounds was conducted by us on solutions of milled natural rubber (NK) in benzene in sealed glass ampoules. The benzene used was dried and distilled over sodium. All work was conducted in an atmosphere of dry argon. Unsaturation and microstructure of the chain was determined on each sample. The study of microstructure of polyisoprenes was carried out by means of infrared spectra, the relative content of the different configurations of the polymer chain being determined by the absorption in the 800–1000 cm−1 region. The method previously developed by one of us was used for this purpose.
Ozone Resistance of Elastomeric Vulcanizates
Authors: Ossefort Z. T.
Published: February 2011

This review has attempted to categorize and describe the degree of ozone resistance available both within and among the various elastomers. Some of the factors affecting ozone resistance and means for obtaining ozone-resistant vulcanizates have been discussed. It has been indicated that by judicious selection of elastomer and compounding ingredients, resistance to very severe ozone conditions may be obtained with the currently available elastomers. The dependence of ozone resistance on proper compounding of the ozone susceptible rubbers has been emphasized. This has led to the conclusion that certain rubbers considered to be ozone resistant behave in the expected manner only if proper attention is given to compounding variables.
Ozone Cracking in the Los Angeles Area
Authors: Haagen-Smit A. J. , Brunelle M. F. , Haagen-Smit J. W.
Published: February 2011

Cracking of rubber, due to the presence of ozone, was determined in the Los Angeles area by measuring the number of cracks and the crack depth after exposure of standardized bent rubber strips to the atmosphere. The cracking shows a daily and seasonal variation due to the difference in ozone concentration as well as difference in temperature. Results over a three year test period are presented, as well as a comparison with oxidant and ozone values measured in the same area. The ozone concentration usually reaches a maximum during the day and is highest during the summer months. Its origin has been traced to the action of sunlight on mixtures of organic material and oxides of nitrogen, common air pollutants in urban areas. A comparison with chemical measurements of the oxidizing power of the air shows a similar trend. The rubber test is useful in the correct interpretation of outdoor exposure tests of rubber goods, since it integrates the variable action of ozone due to large fluctuations in its concentration and the reaction rate due to climatological factors. The application of the test to area surveys in air pollution studies is suggested.
Weather Aging of Elastomers on Military Vehicles
Authors: England W. D. , Krimian J. A. , Heinrich R. H.
Published: February 2011

The results of the Ordnance Corps Pasadena exposure tests may be summarized as follows: 1. The ozone resistance of synthetic elastomers, particularly SBR, can be substantially improved by the addition of suitable antiozonants and waxes to the rubber compound. 2. The one to two years protection at Pasadena appears to be equivalent to 3–5 years protection in other areas where ozone concentrations are low. 3. Butyl and neoprene rubbers which have inherent high ozone resistance become less effective when plasticized to meet the military's low temperature requirements and require the addition of suitable antiozonants and careful compounding in order to regain their ozone resistance. 4. Polyurethane rubbers promise to play an important role in the manufacture of many end items used on military vehicles when it becomes economically available. 5. For storage purposes a surface coating with a 50/50 mixture of dioctyl-p-phenylenediamine and acetone promises to impart good ozone resistance to tires that were not protected against ozone during manufacture.
Carbon Black Structure and the Tear Resistance of Vulcanizates
Authors: Epshtein V. G.
Published: February 2011

1. The increase in tear resistance of vulcanizates, where carbon blacks are added in considerable amounts, is related to the formation of secondary black structures and is manifested especially when certain blacks are used (channel, anthracene and acetylene). 2. The presence of secondary black structures brings about an increase in the tear resistance at elevated temperatures.
γ-Irradiation of Rubber and Styrene. Graft Polymer Formation
Authors: Turner D. T.
Published: February 2011

In a previous investigation, radiation was used to initiate a free radical reaction in a rubber-monomer mixture, the main object being the separation and characterization of the polymeric products. For this, the most suitable monomer was methyl methacrylate. The present investigation extends this work to quantitative aspects of energy absorption, and, for experimental reasons, styrene is a more convenient monomer. The polymerization of styrene on exposure to high energy radiation has been previously studied. Styrene has also been polymerized in the presence of polyisoprenes, including rubber, but not by irradiation.
Polarographic Determination of Accelerators, Antioxidants, and Other Rubber Chemicals. I.
Authors: Mocker F.
Published: February 2011

The present paper shows that the Polarographic method for the determination of rubber additives (rubber chemicals) delivers fully usable results. The following points are discussed : 1. The method is qualified for a rapid quantitative determination of MBT and 2-mercaptobenzimidazole in raw materials control. 2. The zinc salt of MBT can be indirectly determined after its decomposition with acid. 3. MBT and 2-mercaptobenzimidazole can be determined directly in the methanolic extracts of masterbatches. 4. As with the masterbatches, MBT can be determined directly in the extracts of rubber stocks and vulcanizates when zinc oxide is absent. Magnesium oxide or zinc stearate do not interfere. 5. Experimental conditions are given which permit quantitative determinations of MBT in the presence of zinc oxide in uncured and cured rubber compounds. 6. The experiments have shown that the method is applicable to complex recipes containing MBT as the only accelerator. Of course, the limit of error is higher, that is, around −5%. The investigations are being continued and the results will be presented at a later date.
Sulfur Group Analyses in Natural Rubber Vulcanizates
Authors: Studebaker Merton L. , Nabors Lester G.
Published: February 2011

Uncertainty as to the nature of the crosslinks in vulcanized rubber has been a tremendous handicap to chemical studies of vulcanization. A direct result is that physical methods have been the most successful in providing definite information about the nature of vulcanized rubber. However, these physical methods also possess serious limitations. A brief review may be in order on the methods which have provided insight into the chemical nature of the crosslinks. A tremendous amount of information has been obtained on the reactions between sulfur and various olefins at vulcanizing temperatures. Much, but not all, of this work has been carried out in the laboratories of the British Rubber Producers' Research Association. These studies are too extensive to review in detail here. But some of the impressions gained from studying them are: (1) There is no evidence that reaction with sulfur produces any carbon-to-carbon bonds. (2) The linkages produced between different molecules (intermolecular) are monosulfides, disulfides and polysulfides. The dominant linkage and the amount of polysulfide sulfur depends on the nature of the olefin, the reaction conditions and the presence of auxiliary materials such as accelerators, zinc oxide and fatty acids. (3) In the initial stages of the reaction, more polysulfide groups are present than in the later stages. Some of the sulfur in these polysulfide groups appears to react with the rubber to form five- and/or six-membered rings, and is referred to as “cyclic sulfur”. The intermolecular sulfur-containing groups which survive contain less sulfur on the average than those present during the early part of the reaction.
Derivatives of 2-Mercaptobenzothiazole and Dimethyldithiocarbamic Acid as Vulcanization Accelerators
Authors: Fel'dshteĭn M. S. , Eĭtingon I. I. , Pevzner D. M. , Strel'nikova N. P. , Dogadkin B. A.
Published: February 2011

1. We have synthesized and investigated as vulcanization accelerators the derivatives of 2-mercaptobenzothiazole (MBT) in which the thiol hydrogen is replaced by the nonpolar methyl radical, as well as compounds in which methyl hydrogen of the methyl derivative is replaced by various functional groups. 2. It has been shown that methyl-2-thiolbenzothiazole is not an accelerator. The replacement in this compound of one of the methyl hydrogens by a polar hydroxyl group substantially enhances the activity (see, however, editors note in the text). The substitution of hydrogen by a carboxyl group does not increase vulcanizing activity. 3. We have determined that replacement of a methyl hydrogen by an amino radical increases sharply the accelerating activity. The structure obtained as a result of this reaction, benzothiazolyl-2-thiolmethyldiethylamine (BTMA), is of great practical interest as an accelerator. 4. The accelerator BTMA in stocks of natural and SKS rubber gives vulcanizates which are substantially superior in their properties to rubbers cured with MBT, and are practically equal to vulcanizates obtained with sulfenamide accelerators—sulfenamide BT and sulfenamide Z (Santocure). 5. The accelerator BTMA is much cheaper than sulfenamide BT since its production requires much less diethylamine. 6. It has been determined that, just as in the case of 2-mercaptobenzothiazole derivatives, for the derivatives of dimethyldithiocarbamic acid containing analogous functional groups the same results are obtained for the change in activity depending upon the chemical structure of the accelerator.
Dependence of the Ultimate Properties of a SBR Rubber on Strain Rate and Temperature
Authors: Smith Thor L.
Published: February 2011

The tensile strength and ultimate elongation of polymeric materials depend on both the temperature and experimental time scale. The mechanical properties of amorphous polymers at temperatures above their glass transition temperature Tg are more amenable to treatment in terms of molecular theories than are their mechanical properties at temperatures below Tg or the mechanical properties of crystalline polymers. For amorphous polymers at temperatures above Tg the viscoelastic properties in small deformations have been studied rather extensively, and several molecular theories—essentially identical—have been published. In contrast, few systematic studies have been made of the effect of time and temperature on the ultimate properties. Consequently, only a limited amount of data is available which can serve as a basis for developing and verifying molecular theories dealing with ultimate properties. A recent theory by F. Bueche treats the time and temperature dependence of tensile strength. According to his theory, the tensile strength for a given material is a universal function of a reduced time or a reduced strain rate, except at short times or high strain rates where the material approaches glasslike behavior. Also, to superpose data measured at different temperatures, a shift factor is needed which is determined by the temperature dependence of the frictional factor for polymeric segment mobility and thus is the same factor as used to superpose viscoelastic data measured in small deformations. Thus, according to Bueche's theory, the temperature dependence of the tensile strength is given by the equation of Williams, Landel, and Ferry which is applicable in the temperature range Tg<T<(Tg+100). Bueche reported some tensile data for polybutyl methacrylate which has a glass transition temperature of 8° C. These tensile data were measured under various constant loads at temperatures between 30 and 95° C, and reasonable agreement between theory and experiment was found. Although Bueche did not consider the ultimate elongation, it seems reasonable that such data can be superposed by using the same shift factor as required to superpose the tensile strength data. Other workers have not considered explicitly the effect of viscous forces on the ultimate properties but have considered the effect of such variables as molecular weight, degree of crosslinking, and plasticizers.
The Melting of Crystalline Polymers
Authors: Mandelkern Leo
Published: February 2011

Polymer molecules are characterized by the unique structural feature of being composed of a large number of chain units covalently linked together. Despite this complexity of structure macromolecular systems still retain the ability to exist in different states, a property common to all substances. Two of the states of matter observed for monomeric substances, the liquid and crystalline states, are also found in polymeric substances. The liquid or amorphous state is characterized by the fact that, because of the freedom of rotation about the bonds connecting the chain atoms, a single polymer molecule can assume a large number of configurations. In this state, therefore, the chain units of different molecules are arranged in a random, disoriented array uncoordinated with one another. Under appropriate thermodynamic conditions, however, a spontaneous ordering of portions of the chain molecules can occur, and in contrast there results a state of configurational order, the freedom of rotation being lost. This latter state is termed the crystalline state. Major attention in this review is directed to the consideration of the transformation from the crystalline state to the liquid state. Certain closely related subjects as the morphology and organization of the crystalline state and the mechanisms and kinetics of crystallization from the melt have been recently reviewed and hence will not be considered in any great detail. The melting process that occurs in various types of polymeric systems will be considered and conclusions drawn from the presently available evidence. Presentation from a unified point of view, based on certain fundamental considerations, is aimed for. The basic underlying principles which govern the phenomena will be stressed; experimental results which demonstrate these principles or point out the need for new developments will be presented. An effort will be made to consider problems from the point of view of theoretical expectations and experimental findings. On the other hand, no effort is made to include a description of all work in this field, although care has been taken to be as comprehensive as possible in discussing the basic principles.
Growth and Agglomeration of Particles in Low-Temperature GR-S Type of Latex
Authors: Brown R. W. , Howland L. H.
Published: February 2011

It has been shown that it is possible to prepare high-solids latex by polymerizing to an intermediate solids content and particle size, followed by solvent agglomeration and concentration. It has also been shown that a somewhat similar agglomeration normally takes place at intermediate conversions in conventional high-solids latex recipes. The slow rates of polymerization in the latter recipes after agglomeration are primarily due to the greatly reduced number of particles present. The ratio of hydrocarbon to water is very important in determining the extent of agglomeration both during and after polymerization.
Study of the Kinetics of Polymerization of Isoprene in Aqueous Solutions of Emulsifiers and in Emulsions
Authors: Sheinker A. P. , Medvedev S. S.
Published: February 2011

It has been established earlier that polymerization in aqueous solutions of emulsifiers takes place in the water or in the micellae of the emulsifier, depending on the solubility of the monomer and the initiator. The question of the topochemical properties of polymerization in emulsions has not yet been definitively explained. In a number of studies, the hypothesis was advanced that the process of emulsion polymerization takes place in the micellae of the emulsifier, according to the degree of conversion of the micellae into polymer-monomer particles, with the monomer dissolved in the polymer. In order to explain further the mechanism of emulsion polymerization, the kinetics of polymerization of isoprene in water, in solutions of emulsifier and N-cetylpyridinium bromide, and in emulsions in the presence of a water-soluble initiator (hydrogen peroxide) were studied. The dilatometric method was chosen for the kinetic measurements of solutions of emulsifier not saturated with isoprene, and for emulsions. Experiments with solutions of emulsifier saturated with monomer were made during continuous saturation of the emulsifierinitiator solution with isoprene in the gaseous phase. All the experiments were made at 50° C in the absence of oxygen.
Inhibition of Rubber Oxidation by Carbon Black
Authors: Burgess K. A. , Sweitzer C. W.
Published: February 2011

Indirect measurements have shown that small amounts of carbon black inhibit rubber oxidation during Banbury mastication. To provide a more comprehensive picture of this inhibitory action, a study was made of its effects on some physical properties of fully compounded and vulcanized stocks prepared from masticated natural and synthetic polymers. The action of carbon black, with the exception of its behavior in Butyl rubber, was found to be broadly similar to that of standard antioxidants. The largest change in vulcanizate properties occurred in cold rubber after high-temperature mastication. The usual shortening and stiffening resulting from gelation of the polymer at high mastication temperatures was completely inhibited when the mastication was carried out in presence of small loadings of carbon black.