bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of Elastomers in Tire Sections by Total Thermal Analysis. IV. Innerliner
Authors: Sircar A. K. , Lamond T. G.
Published: February 2011

Butyl and halogenated butyls are clearly indicated by both DSC and DTG in nitrogen. Binary NR/CIIR blends are also easily characterized by combined DSC and DTG techniques. In ternary SBR/CIIR/NR blends, only CIIR and NR show up in DTG curves when SBR occurs as a minor component. Minor indication of SBR is obtained from DSC curves. Thermal methods fail to distinguish between BUR and CIIR. In elastomer blends, DTG peak temperatures may vary over a wide range depending on the type of the second elastomer. The NR peak temperature (365°C), for example, is lowered by blending with SBR, BR (345–350°C) or CR (325–348°C). These latter elastomers degrade by exothermic reaction. An increase in peak temperature was observed in association with the polymers which degrade by endothermic reaction (EPDM, 369–374°C; CIIR, 373–377°C). This may be caused by abstraction of heat by the second elastomer in the overall decomposition process. Another important conclusion drawn from the blends studies in this series is that thermal stability of the polymers is not materially affected by the presence of another polymer, thus giving rise to the weight-loss peaks at well-defined temperatures, characteristic of each polymer. Thermooxidative stability, however, is very much dependent on the type and composition of the polymers present. The effect of secondary reactions on the degradation curves is also considerably greater in the oxidizing atmosphere. Thermooxidative degradation is very much dependent on sample size, characteristic of a diffusion-controlled reaction. However, it provides auxiliary evidence for idsntification. Except for SBR/BR blends, which show a single Tg changing with composition, all other elastomer blends show transitions at the respective temperatures, indicating the inherent incompatibility of elastomers. However, a second or third transition is not observed when (a) the proportion of the polymer is too small and (b) Tg'a are too close to each other. Thus, obtaining a single glass transition temperature in a polymer blend is not always a proof of its compatibility, as has been claimed so often.
Thermoanalytical Methods in Vulcanizate Analysis II. Derivative Thermogravimetric Analysis
Authors: Brazier D. W. , Nickel G. H.
Published: February 2011

We have shown in this and the preceding paper that fully compounded stocks can be analyzed for all main constituents by use of a combination of DSC, TG, and DTG. Further, this can be achieved on a time scale consistent with routine quality control. DSC gives information on cure characteristics, sulfur, and accelerator levels in approximately five minutes. Elastomer, elastomer ratio, carbon black, oil/plasticizer, and inorganic pigments are determined in about 35 minutes by TG/DTG, at a scan rate of 10°C/min. This time can be reduced by increasing the scan rate, but interference from highly exothermic reactions can be a limiting factor. Each compound must be treated individually to determine the maximum scan rate that can be used without impairing reproducibility. Clearly limitations exist for identification of unknown blends by DTG. The main problem is that many commercial elastomers have very similar thermal stabilities, which results in DTG peaks in the same temperature range. Further work is being undertaken with the DTG—gas chromatography interface to identify not only the pyrolysis products, but the temperature range over which they are evolved. In this manner, the DTG acts essentially as a thermal fraetionation unit and GC analysis of products from a given component in a blend can be achieved.
Thermal Degradation of Copolymers of Butadiene and Acrylonitrile
Authors: Grassie N. , Heaney A.
Published: February 2011

Copolymers and polymer and copolymer blends incorporating two or all three of the monomers, acrylonitrile, butadiene, and styrene, have become important commercial materials. It is therefore important to have information about their stability toward the various degradative agencies. A description of the thermal degradation of copolymers of styrene and acrylonitrile has been given; this paper extends this work to the butadiene—acrylonitrile copolymer system.
Advances in Catalysts Based on Aluminum Hydride Derivatives for the Synthesis of High-Cis Polyisoprene
Authors: Balducci A. , Bruzzone M. , Cucinella S. , Mazzei A.
Published: February 2011

The stereospecific polymerization of isoprene with simple alanes and poly (N-alkyliminoalanes) (PIA) and TiCl4 is critically reviewed and related to the more recent finding on the “cage” structure and composition of PIA's. In particular, the polymer yield was found strictly dependent on the structure of the PIA, which in turn depends on the nature of the alkyl groups bonded to nitrogen. The effects of the chemical composition of the PIA and of the halogen level in its halogenated derivatives on the activity of the catalyst and on the possibility of side reactions is discussed with reference to conventional aluminum alkyl catalysts. The identification of new structures within this class of cocatalysts is discussed
Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Polymers. Part IV. Peak Assignment for Styrene-Butadiene Copolymers
Authors: Katritzky A. R. , Weiss D. E.
Published: February 2011

The low-field region of styrene-butadiene copolymer spectra provides little information because of overlap of peaks and broad representation of diads. The high-field region gives much useful information. From our data and our assignments, we are now proceeding to interpret the microstructure of styrene-butadiene copolymer in terms of diad composition and average run lengths for block styrene and block butadiene Our 13C nmr studies of copolymers show the broad application of this technique for revealing detailed structural information in both vinyl and non-vinyl continuous polymer chains. Previously, tacticity (configuration) and unit sequence both have been indicated in triad (3 unit) resolution for a copolymer of two repeating units and now nearly complete diad resolution is obtained for a copolymer with 4 individual repeating structural units.
The Reaction of t-Butyllithium with Styrene and Isoprene. A Comparison of Chain Initiation with the Isomers of Butyllithium
Authors: Roovers J. E. L. , Bywater S.
Published: February 2011

The use of lithium alkyls as polymerization initiators provides an important method for the production of monodisperse polymers. Surprisingly large differences in initiation rates are observed between straight and branched chain lithium alkyls. s-Butyllithium, for example, initiates several powers of ten more rapidly than n-butyllithium in benzene. Less work has been carried out on t-butyllithium. Hsieh has reported that in cyclohexane the order of efficiency (defined as more complete initiation at lower monomer consumption) is s- > t- > n-butyllithium for the dienes and s > n- > n-butyllithium for styrene. These experiments were carried out using commercial products, and it seemed of interest to repeat these experiments on purified materials as the reactions of lithium alkyls are known to be sensitive to impurities. In addition the exchange reactions of t-butyllithium with other alkyls are known to be slow whereas those of n- and s-butyllitbium are considerably faster. If, as suggested, the slow exchange rate is determined by the rate of dissociation of the predominantly tetrameric t-butyllithium, then it seemed likely that, at least in benzene, some differences in initiation behavior might be expected. In this solvent the initiation mechanism has been suggested to involve a prior dissociation of the aggregates. The rate of addition of t-butyllithium to 1,1-diphenylethylene has already been studied in benzene. At very low monomer concentration, the reaction order in initiator was found to be 0.25, which suggests the dissociative mechanism holds under these conditions. We have, therefore, studied the reaction of t-butyllithium with isoprene in benzene and hexane and with styrene in benzene and cyclohexane. The use of aliphatic hydrocarbon solvents produces quite different initiation behavior to that in aromatic solvents.
Particulate Reinforcement of Polyacrylate Elastomers. II. Mechanical Properties
Authors: Blackley D. C. , Sheikh M. W.
Published: February 2011

This paper presents and discusses the mechanical properties of crosslinked poly (ethyl acrylates) containing various amounts of microscopic glass beads. The adhesion between the glass beads and the elastomer matrix was varied by subjecting the beads to different surface treatments. That the adhesion is affected by surface treatment has been demonstrated in two ways: (1) Unfilled elastomer sheets have been cast in contact with glass surfaces which had been treated with the same reagents as the beads. The force required to peel the elastomer from the glass was then measured and found to depend strongly upon the surface treatment. (2) Scanning electron micrographs of the ruptured surfaces of used tensile test pieces cut from filled elastomer sheets confirm that surface treatment has a profound effect upon the adhesion between bead and matrix. Results are presented for the hardness and tensile stress-strain properties of elastomers containing various amounts of beads. In all cases, the stiffening effect of the beads increases as the adhesion between beads and matrix is improved. Beads which had been treated in such a way as to minimize the adhesion to the matrix were found to cause an apparent softening of the material as revealed by the tensile stress-strain curve. It has been shown that this effect can be satisfactorily explained if it is assumed that in this case the beads merely serve to increase the void content of the material.
Particulate Reinforcement of Polyacrylate Elastomers. III. Swelling Measurements
Authors: Blackley D. C. , Sheikh M. W.
Published: February 2011

This paper presents and discusses results which have been obtained for the swelling in chlorobenzene of crosslinked poly (ethyl acrylates) containing various amounts of microscopic glass beads. The adhesion between the glass beads and the elastomer matrix was varied by subjecting the beads to different surface treatments. The swelling behavior has been found to correlate very closely with the extent of adhesion as judged by peel force measurements and tensile stress-strain properties reported previously. In the case of beads showing pronounced adhesion to the matrix, restrictions on swelling have been interpreted in terms of an apparent enhancement of crosslink density by the reactive beads.
Radiation-Induced Crosslinking of Chlorobutyl and Polydiene Elastomers. Promotion by Polythiols
Authors: Zapp R. L. , Oswald A. A.
Published: February 2011

The response of Chlorobutyl (CIIR), an elastomer with 1,1-disubstituted carbon atoms along the polymer chain, to ionizing radiation has been directed toward a predominantly crosslinking reaction by addition of 1–4 phr of thioetherpolythiols (TEPT) prepared by reaction of trivinylcyclohexane or cyclododecatriene with H2S or low-molecular-weight dithiols. From a fundamental viewpoint, the unique feature of the CIIR-TEPT system is the reversal of expected behavior for a polymer molecule containing 1,1-disubstituted carbon atoms when exposed to high energy radiation: instead of chain scission, cross-linking is the predominant physical change to an extent comparable to that obtained from thermal curing processes. The TEPT becomes part of the radiation-cured network, for, as the radiation dose is increased, there is progressive addition of thiol sulfur to the crosslinked network. Concomitantly, there is a progressive reduction in the chlorine content as radiation-induced vulcanization proceeds. These polythiols are also powerful accelerators of radiation-induced cross-linking of polydiene elastomers, especially those with appreciable amounts of pendent vinyl unsaturation, such as conventional SBR. Evidence exists that a blend of CIIR and SBR can be covulcanized by radiation-induced curing in the presence of TEPT. Experiments were conducted with gamma radiation from a 60Co source and with a 1.4 MeV electron beam at dose rates of 20–120 kJ/kg (2–12 megarads). Physical properties of fully compounded polythiol-promoted CIIR systems crosslinked by radiation are lower than comparable thermally cured compounds, but the strengths would be adequate for many applications. Compounding ingredients, especially common accelerators of sulfur vulcanization, provide a wide range of inhibitory action toward radiation precure. However, with selected types, especially organometallic derivatives which are less soluble in the compound, radiation cure can proceed with a minimum of inhibition.
Factors Influencing the Strength of Rubbers
Authors: Thomas A. G.
Published: February 2011

The strength behavior of rubbers is discussed in terms of fracture mechanics which treats fatigue and tensile failure as crack growth processes from small flaws. Crack growth can be influenced by the presence of oxygen or ozone. The nature of the vulcanizing system affects strength : crosslinks probably rupture and reform under stress. A new approach to the problem of abrasion is presented using fracture mechanics. Schallamach has shown that rubber often develops a pattern of ridges perpendicular to the direction of abrasion. In the simplest case abrasion is produced by a line contact (e.g., a razor blade) which pulls a tongue of rubber from the ridge producing crack growth at the base of the tongue. Provided the surface configuration is in a steady state, the quantity of rubber abraded can be related quantitatively to the frictional force and the crack growth characteristic of the rubber on some reasonable assumptions. Good agreement with experiment is found for noncrystallizing rubbers but the behavior of strain crystallizing natural rubber suggests that crystallization cannot occur under the conditions used so that the rubber is not strengthened by this means.
Viscoelastic Properties of Rubber Networks
Authors: Thirion P.
Published: February 2011

The molecular theory of Rouse, Zimm, and Bueche correctly accounts for the viscoelastic properties of polymers in very dilute solution and, to a large extent, for those of polymers in bulk or in concentrated solution, as long as their mean molecular weight is below about 20 000. Above this MW limit, relaxation times appear which are longer than those provided for in this theory. The “viscoelastic plateau”, which then appears in the long relaxation time region of the dynamic spectrum, is ascribed to entanglements of molecular chains which behave like temporary crosslinks. An analogous phenomenon occurs in the same way in permanent polymer networks, such as rubber vulcanizates. In this case one finds abnormally slow relaxation or creep rates during the approach to equilibrium, as well as increased low-frequency mechanical energy losses under forced sinusoidal vibration. The presence of colloidal fillers, such as carbon blacks used to reinforce rubbers, also seems to increase this hysteresis within the polymer matrix, independent of thixotropic effects which result from the reversible rupture of filler particle aggregates under large-amplitude cyclic deformations. We propose to analyze here the results (obtained jointly at the Institut Français du Caoutchouc and at the laboratory of Professor J. D. Ferry, University of Wisconsin) of measurements over the entire rubbery spectrum of the dynamic properties and of stress relaxation on vulcanizates of natural rubber, cis-polybutadiene, and styrene-butadiene copolymer (SBR) in the absence of secondary crystallization or aging phenomena. Then we examine the interpretation of the behavior of these materials, both at low frequency and during the approach to equilibrium, by analogy with the theories of the “viscoelastic plateau” of linear polymers.
Structural Characterization of Vulcanizates. I. Crosslinking Efficiency of Sulfur in Unaccelerated Natural Rubber-Sulfur Systems
Authors: Moore C. G. , Mullins L. , Swift P. McL.
Published: February 2011

This paper deals with the determination of crosslinking efficiencies of sulfur in a series of unaccelerated XR-sulfur vulcanizates produced at 140° C. The method used is that described under (1) above, values of the degree of chemical crosslinking being derived from stress-strain measurements on the unextracted vulcanizates.
New Vulcanizing Systems for Ethylene-Propylene Elastomers
Authors: Wei Peter E. , Rehner John
Published: February 2011

The absence of chemical functionality in ethylene-propylene elastomers precludes crosslinking with conventional rubber vulcanizing agents. It is known that such elastomers can be vulcanized with combinations of sulfur and certain organic peroxides, but the resulting vulcanizates leave something to be desired from the standpoint of tear strength, odor, and peroxide cost. A chemical study of the reaction between isoparaffins, sulfur, and organic peroxides gave results showing that some important alterations must be made of previous views that have been advanced for the vulcanization of saturated hydrocarbon elastomers by peroxides alone. A new reaction scheme is briefly reviewed. In the course of this study, three new classes of substances have been discovered to be effective vulcanizing agents for ethylene-propylene elastomers, and for other rubbers also. The outstanding characteristics which these new agents produce in ethylene-propylene elastomer vulcanizates are excellent tear strength and no objectionable odor. Data are presented on some properties of vulcanizates prepared with these agents.
Vulcanization of Rubber in the Presence of Organic Accelerators
Authors: Dogadkin B. A. , Shershnev V. A.
Published: February 2011

Rubber Reviews for 1957 included an extensive survey by Craig devoted to the vulcanization of rubber with sulfur. In that survey, however, neither the thinking of Soviets nor of Germans were mentioned; likewise Japanese studies, of which a considerable number had been published in the preceding decade, were omitted. The purpose of the present survey is to supply, in some degree, the deficiency of the Craig review, particularly that part which deals with the problem of the chemistry of vulcanization of rubber by means of sulfur in the presence of accelerators. In recent years the attention of investigators, engaged in the study of vulcanization, has been focused chiefly on the clarification of elementary chemical reactions of the process, on the mechanism of the action of accelerators and on the establishment of the nature of vulcanization structures and their influence on physicomechanical properties of the vulcanizates. For the resolution of these questions, along with chemical analysis methods, attention is drawn to the physical methods of optical and electron microscopy, of isotope interchange, and of analyses of kinetics by means of radioactive sulfur. Important results were obtained through the study of sulfur in model low molecular weight compounds. Furthermore, it has been demonstrated that there are two tendencies toward interpretation of the general nature of chemical reactions of sulfur with rubber. In some studies, radical processes are assigned an important role in the explanation of structural changes in rubber during vulcanization; in others, elementary reactions are considered as proceeding in accordance with a polar (ionic) mechanism. It occurs to us that the differences in points of view, regarding the mechanism of vulcanization, are not so much a matter of approach to the interpretation of experimental factors, as this fact—that for such a complicated phenomenon as vulcanization, it is impossible to support a single mechanism. The mechanism of a reaction may vary, depending on thermodynamic considerations with regard to the reaction, the type of rubber used, and especially on the types of accelerators and activators employed. Such a conclusion was reached also by Shelton and McDonel. For this reason, in this survey we shall present material representing a number of individual viewpoints regarding vulcanization along with a discussion of some general features.
An Electron Microscope Reinforcement Criterion for Carbon Black Masterbatches
Authors: Prestridge Eddie B.
Published: February 2011

With the advent of wet masterbatching methods, which provide a preliminary dispersion of carbon black in latex, techniques for the microscopic evaluation of the quality of this incorporation proved inadequate. Three reinforcement criteria were developed for such evaluations: dispersion, grinding, and bonding. Using these criteria the performance characteristics of a tread stock made with such masterbatches can be predicted with good reliability. The correlation of reinforcement criteria and the raw Mooney of the masterbatch reveals the striking effect of improved carbon black incorporation on this property. Using this correlation it should be possible to evaluate masterbatch production on a continuous basis.
Swelling and Network (Crosslink) Density of Carbon Black-Filled Natural Rubber Vulcanizates
Authors: Westlinning H. , Butenuth G.
Published: February 2011

The method cited by W. Kuhn and coworkers for the determination of network densities on the basis of a thermal analysis of swollen samples has been applied to unfilled and carbon black-filled natural rubber vulcanizates. The results with unfilled rubber on the basis of the new method are in the expected correlation with the measurements of the degree of swelling and the modulus of elasticity. From the results with carbon black-filled samples it is probable that an inhomogeneously crosslinked system is formed under the influence of the filler. It is concluded that there are regions of high network density adjacent to regions of low density. Consequently, the degree of swelling, referred solely to the rubber portion, is to be considered a mean value in the case of filled vulcanizates from which the network density cannot be deduced without additional measurement.
Estimation of Wear Resistance of Tread Vulcanizates
Authors: Gelinas L. P. , Harris I. W. E. , Storey E. B.
Published: February 2011

A simple procedure has been described to provide an estimate of the wear characteristics of a vulcanized polymer by means of a towing device. The present paper describes modifications that have been adopted to increase the efficiency of this procedure and reports the effect of various test conditions that have been explored by statistical methods. Estimates of the wear resistance of various types of rubber in suitable tread recipes are given together with an observed order of rating based upon their response to the severity of the imposed conditions.
Rubber Structure and Coefficient of Friction
Authors: Bartenev G. M.
Published: February 2011

1. As a result of analysis of the formulas of friction of rubber and of a comparison with experimental data for steady-state friction on smooth solid surfaces it is demonstrated that the friction of vulcanized rubber is determined by three constants of the material, depending upon the type of rubber polymer and the structure of the vulcanizate. 2. The constant α characterizes the constant of the formation of the area of actual contact Sa under loading. This constant does not depend upon the rate of slip and the nature of the solid surface, but it does depend upon the stiffness of the vulcanizate, which is directly proportional to the crosslink density. 3. The tangential stress on the actual area of contact α=F/Sa depends upon the temperature, the rate of slip and the two constants of the material Sk and U. The first of these is the effective area of contact of a chain with the solid surface, depending upon the number of chains in the network of the vulcanizate, the second is the activation energy, depending upon the nature of the frictioning surfaces, in particular upon the structure of the polymer chain of rubber. 4. A method is proposed for calculating the area of actual contact of a vulcanizate from the number of chains per unit volume and from the number of chains which are in contact with the solid surface.
Measurement of Friction between Rubber-Like Polymers and Steel
Authors: James D. I.
Published: February 2011

A machine for measuring the coefficient of friction between a flat sheet of polymeric material and a ground steel plate is described in detail. An inverted lathe cross slide forms the basis of the drive mechanism. Frictional force is balanced against the tension developed in a spring (proof ring), the extension of which measured with a commercial displacement pickup, gives a direct reading of coefficient of friction. A few results are given for a PVC sample plasticized with 40% dioctyl phthalate. A circuit for automatic operation and recording is also described.
Calculation of the Behavior of Rubber-Covered Pressure Rollers
Authors: Parish G. J.
Published: February 2011

Data are given which enable the properties of nips between metal and rubber-covered pressure rollers to be calculated from the parameters of the system. The properties with which the calculation is primarily concerned are the nip width and the mean pressure in the nip, but the principle can be extended to include the peak pressure and the distribution of pressure through the nip. The calculation is based on the well-known Hertzian formula and on empirical relations, which express the important effects of the rubber-cover thickness. The data refer not only to roller systems in which the loading is uniform, but also to non-uniform nips, in particular to those which show what is probably the commonest cause of non-uniformity, roller deflection. Although the calculations refer primarily to nips between one hard roller and one relatively soft, covered, roller, they are directly applicable to nips between two identical covered rollers and may be applied, within limits, to systems in which the rollers are dissimilar in properties.
Some Factors Influencing the Ozone Resistance of Rubbers and Methods of Evaluation
Authors: Buswell A. G. , Watts J. T.
Published: February 2011

A selection of some of the factors which can affect the static and dynamic ozone resistance of a rubber is described. The development of suitable methods of evaluating ozone resistance is briefly described.
Radiochromatographic Separation of Mixtures of Sulfur and Accelerators
Authors: Khodzhaeva I. V. , Kissin Yu V.
Published: February 2011

Co, Ni, Fe, Cu, Cd, Pb, Hg-diethyldithiocarbamates and radioactive tetraethyl-thiuramdisulfide (TETD*) were synthesized and the exchange between S35 and TMTD, S35 and MeDEDC, MeDEDC and TETD* was studied. The mixtures were separated by means of paper radiochromatography: S35 + TMTD by ethyl and methyl alcohol; TETD*+MeDEDC by ethyl alcohol. From the radio-chromatographic data the degrees of exchange were calculated.
Reactions of Polymers in Bulk. I. Influence of Fillers on the Degree of Crosslinking of Natural Rubber
Authors: Janacek J.
Published: February 2011

The relation between the degree of crosslinking determined by means of swelling and the theoretical total contact surface of rubber to carbon black was investigated with vulcanizates of two elastomers which were cured by various vulcanization methods and using various concentrations—even extremely high ones—of carbon blacks with different specific surface, degrees of chain structure and chemical activities. A constant, α, the magnitude of which generally depends upon the degree of agglomeration of the carbon blacks and on the chemical nature of their surface as well as on the polymers used and the vulcanization method, but which is practically unrelated to the filler concentration, has been proposed to express the relative crosslinking activity of carbon blacks.
Reactions of Polymers in Bulk. II. Influence of Crosslink Density on the Mechanical Deformation Properties of Filled Vulcanizates
Authors: Janacek J.
Published: February 2011

The mechanical deformation properties as characterized by the modulus at different deformation, hardness and rebound elasticity, were observed in elastomers filled with different carbon-black concentrations referred to the concentration of the effective chains of the rubber network as determined by swelling. The extent of the physical effect of carbon blacks in the elastomers was expressed by the difference between the mechanical deformation values of the filled and unfilled vulcanizates determined at a constant crosslink density.
Dependence of Bound Rubber on Concentration of Filler and on Temperature. II
Authors: Dessewffy Oliver
Published: February 2011

The dependence of the quantity of gel rubber on the extraction temperature was studied, for black-filled natural rubber compounds. Results show that the logarithm of the specific rubber gel quantity increases linearly with the reciprocal of the absolute temperature within a range of 25 to 80° C. The adsorption energies were calculated on the basis of the temperature dependence. The low energy values determined in this fashion supported the assumption that the bondings of the gel structure are largely “weak” bonds of a physical character. The author seeks to explain the observed adsorption phenomena by certain hypotheses.
The Diffusion of Sulfur 35 in Rubber. Effect of Carbon Black Loading on Sulfur Migration from the Breakers in Large Tires
Authors: Auler H. , Bostrom S.
Published: February 2011

This work had two principal objectives; in the first place, to make a contribution to clarifying the dependence of the diffusion characteristics of sulfur in rubber upon the carbon black concentration in the compound and secondly, we attempted to study the process of diffusion in vulcanized large pneumatic tires, using two different procedures with special experimental conditions. It may be assumed that the physical processes which lead to the diffusion of one material in another are basically well known. Work by Fick and by Langmuir and Dushman, among others, is especially valuable in explaining the diffusion process. while the first studies of diffusion of sulfur in rubber used optical methods, the application of sulfur 35 has been stressed for this purpose in the last few years. Auerbach and Gehman were first to use such a procedure. They, as well as Bresler, Prjadilowa and Chainman, followed the migration of sulfur into rubber during the diffusion process. The latter authors worked at technically interesting temperatures, from 130° to 150° C. Diffusion coefficients calculated from the experimental data were in the range 1.9×10−7 to 1.6×10−6 cm2/s. Studies by Mozisek and also by Ludwig represent more recent work in the field of sulfur diffusion. Ludwig used a different method than the preceding authors. After the test specimens were vulcanized, they were cut into thin slices with the microtome and the radioactivity which was present in the slices was determined. The excellent and detailed books by Jost, may be consulted by anyone with either a general or special interest in securing information in the field of diffusion.
The Reaction of Sulfur and Sulfur Compounds with Olefinic Substances. Part XII. Effects of Vulcanizing Additives on the Reaction of Sulfur with 2,6-Dimethylocta-2,6-Diene, and Their Bearing on the Mechanism of Sulfur Vulcanization of Natural Rubber
Authors: Bateman L. , Glazebrook R. W. , Moore C. G.
Published: February 2011

To summarize, we conclude that the course of the interaction of sulfur with an olefin alone is determined principally by the electrophilic reactivity of labile polysulfides and by the reactions of cationic-type intermediates, and that the essential function of zinc salts is to stimulate the reactivity of complementary nucleophilic species. Accelerators of the thiazole-type specifically promote the latter reactivity, as almost certainly do other common vulcanization accelerators, e.g., certain amines, metal dithiocarbamates and xanthates, and thiuram sulfides. It may be noted, for example, that reaction of 2,6-dimethylocta-2,6-diene with sulfur, zinc dibutyldithiocarbamate, and zinc oxide at room temperature, i.e., under conditions where direct sulfur-olefin reaction does not occur, yields a dialkenyl polysulfide and negligible cyclic sulfide (a result also found with tetramethylthiuram disulfide and zinc oxide plus zinc propionate at 140° C), indicative of sulfuration by the nucleophilic mechanism becoming almost fully dominant under especially favorable reaction conditions.
Accelerator Action of Certain Heterocyclic N-Thiocarbamylsulfendialkylamides
Authors: Éitingon I. I. , Feldshtein M. S. , Pevzner D. M.
Published: February 2011

1. The accelerator activities of heterocyclic N-thiocarbamylsulfendialkylamides based on piperidine, morpholine, and piperazine were investigated; it was found that compounds of this type are highly active accelerators of the vulcanization of natural and styrene butadiene rubber stocks, inducing rapid crosslinking and giving rubbers of higher modulus than the usual vulcanization accelerators. 2. The vulcanization kinetics in presence of these heterocyclic N-thiocarbamylsulfendialkylamides depends to a considerable extent on the nature and number of hetero atoms in the accelerator molecule. Morpholine and piperazine derivatives have a slower effect at the initial stage of vulcanization than the corresponding piperidine derivatives, and confer greater resistance to premature vulcanization of the rubber stocks.
Accelerator Activity of 2-Benzothizole Sulfenamide Derivatives and the Exchange of Benzthiazyl Thiyl Radicals with Radioactive 2-Benzthiazyl Disulfide
Authors: Feldshtei˘n M. S. , Chernomorskaya I. G. , Guryanova E. N. , Éitingon I. I.
Published: February 2011

The authors obtained data characterizing the accelerating activity of sulfonamide derivatives of MBT. The reactions of isotope exchange between such derivatives and MBTS labeled with S35 in the disulfide bridge were investigated, using chromatography to separate the components of the reaction mixture. It is shown that between these compounds there takes place an exchange of benzthiazyl radicals. A direct dependence is established between the accelerator activity of the sulfenamide compounds and their capacity for exchange of benzthiazylthio groups. The easier this takes place, the higher the activity of the compounds in the initial stage of vulcanization. The observed reactions of exchange of benzthiazylthio radicals may be used for the synthesis of sulfenamide derivatives of MBT labelled with radioactive S35.
Reaction of Tetraethylthiuramdisulfide with Alkali and Its Bearing on Vulcanization Reactions
Authors: Gessner Teresa
Published: February 2011

Klebanski and Fomina have reported on the action of alkali on tetraethylthiuram disulfide (TETD). They suggested the following equation for the reaction: (see PDF for diagram) This equation is based in part on a premise that TETM is one of the reaction products; we feel this premise is incorrect. As partial evidence for their proposed reaction scheme, Klebanski and Fomina claim the isolation of tetraethylthiurammonosulfide (TETM) from the reaction products. They give both the analysis figures and the melting point of the isolated substance. The melting point quoted by them is 64–65°. The melting point of TETM is, however, 28–33°. We have attempted the isolation of the substance reported by Klebanski and Fomina, and have repeated their experiment according to the published instructions. The only water-insoluble material which we were able to isolate, after 8 hours reaction with 2% aqueous sodium hydroxide, was unreacted TETD (73% of the starting material). The material isolated had a melting point of 68.5–70°, mixed melting point with TETD was 68.5–70°, the nitrogen and sulfur content was: %N 9.38, %S 42.82. Recrystallized from ether the substance melted at 70°, and analyzed as: %N 9.48, %S 43.05, mol. wt. 297; TETD requires; %N 9.53, %S 42.93, mol. wt. 296, m. pt. 70°.
Determination of Thiazole Type of Rubber Accelerators by Amperometric Titration
Authors: Chatterjee Pronoy K. , Banerjee D. , Sircar Anil K.
Published: February 2011

The method of amperometric titration has been applied for the quantitative determination of mercaptobenzothiazole, zinc benzothiazolylmercaptide and dibenzothiazolyl disulfide, the latter two being known to constitute the decomposition products of the first during vulcanization reaction. It has been found that mercaptobenzothiazole as it is, or formed by a suitable reaction from the other two accelerators mentioned above, can be quantitatively estimated amperometrically. The total amount of mercaptobenzothiazole present in a mixture of two or all three of the above-mentioned accelerators and also the total amount of mercaptobenzothiazole liberated in a mixture of two or three of them can be quantitatively estimated.
Determination of Amine Type Antidegradants by High-Temperature Gas Chromatography
Authors: Wise R. W. , Sullivan A. B.
Published: February 2011

High-temperature gas chromatography has been used successfully to quantitatively determine the amounts of high boiling amine antidegradants in vulcanized and unvulcanized rubber samples. The antidegradant content was determined by first extracting from the rubber sample the antidegradant and subsequently analyzing the extract by gas chromatography. The method is rendered quantitative by the use of an internal standard. Typical analyses of several rubber samples containing antidegradants are presented. The method is also applicable to the assay of commercial materials.
Nitrile Rubber-Polyvinylchloride Blends
Authors: Sharp T. J. , Ross J. A.
Published: February 2011

Vulcanizable blends of nitrile rubber and Polyvinylchloride combine excellent weather resistance with the low swelling in petroleum solvents of the nitrile rubbers. The Polyvinylchloride functions as a reinforcing agent and increases the hardness, modulus and tensile strength of the material. The principal disadvantages of the addition of the Polyvinylchloride are the reduction of low temperature flexibility and the poor compression set. By the use of suitable plasticizers in the former case and modification of the vulcanization system in the latter case, these disadvantages can be largely overcome. Mixing can be performed on a mill or in an internal mixer, but it is essential to flux the Polyvinylchloride at some stage or the improvement in weather resistance and physical properties is not obtained. By the use of rubbers of low Mooney viscosity, blends can be produced with good processing characteristics. Variations in the type of Polyvinylchloride can affect the final properties of the blends; general purpose suspension polymers are not recommended for use in masterbatches. Providing that a nitrile rubber containing a nonstaining antioxidant and a nonsulfur staining stabilizer for the Polyvinylchloride are employed, white or brightly colored vulcanizates can be obtained. Applications for these blends which are of interest include hose tubes and covers, belting, particularly food belting, cables and shoe soles.
Polyurethan VC, a Virtually Crosslinked Elastomer
Authors: Schollenberger C. S. , Scptt H. , Moore G. R.
Published: February 2011

Many of the outstanding physical properties that characterize elastomeric Polyurethans have been realized in a soluble, thermoplastic variety, Polyurethan VC, which displays the superficial properties of a rubbery vulcanizate at room temperature and so is considered to be virtually crosslinked. High tensile strength as well as good tear, abrasion, solvent, oil, and ozone resistance characterizes this polymer. Since these properties are realized in the unvulcanized state, many useful applications of the readily processable polymer can be made, avoiding the complications which attend the use of conventional (vulcanizing) urethan elastomers. Outdoor exposure and indoor accelerated weathering studies demonstrated a deficiency in the weather resistance of the raw polymer. Weather-induced changes, believed to be due to ultraviolet-initiated autoxidation, have been estimated by noting changes in the stress-strain properties as well as the ultraviolet and infrared absorption spectra of the polymer on exposure to natural and artificial weather conditions. The beneficial effects of certain carbon blacks, conventional antioxidants, and ultraviolet absorbers on the weather resistance of the polymer have been described.
Adhesion of Synthetic Rubbers to Various High Molecular Substrates
Authors: Voyutskiĭ S. S. , Vakula V. L.
Published: February 2011

In previous work the adhesion of certain synthetic rubbers to cellophane was investigated. In the present paper we present the results of determination of the adhesion of a considerably larger number of rubbers of varying nature to varying substrates, both polar and nonpolar—cellophane, polyamide and polyethylene films—and also two elastomers—the polar rubber SKN-40 and the nonpolar polyisobutylene. The resulting data allow us to draw certain conclusions as to the influence of the molecular structure of adherend and substrate. The adhesion of rubbers to substrates is defined by the film stripping resistance P, in g/cm. The joints were made by plying up a film of substrate (of cellophane washed free of glycerin, of polyamide, or of polyethylene) or of fabric covered with a substrate (SKN-40, polyisobutylene) with fabric strips to which the polymer under investigation had previously been applied from a solution. Not less than 0.025 g/sq. cm of the polymer was applied to the fabric strips, this being sufficient to give reproducibility of results. The plying up was effected by rolling the assembled halves of the joint with a rubber roller, which gave higher pressures than those required to achieve full contact of the surfaces of the elastomeric adherend and the substrate. Such a method of producing joints has definite advantages from the point of view of procedure over the method employed previously, because it makes possible elimination of the influence of prolonged and varying time of interaction of the adherend with the substrate in the drying out which is inevitable in joining an adherend by a solution.
New Vulcanizing Agents for Ethylene-Propylene Elastomers. II
Authors: Wei Peter E. , Rehner John
Published: February 2011

In searching for new vulcanizing systems for ethylene-propylene elastomers, we have found several more classes of active agents, heretofore undisclosed. They are: (a) perhaloalkanes and some polyhaloalkanes; (b) polyhalocycloalkenes; and (c) poly-N-halobenzoguanamines. Specific examples are: hexachloroethane, octachloropropane, octachlorocyclopentene, perchlorofulvalene, and N,N,N′,N′-tetrachlorobenzoguanamine. These agents are all effective in ethylene-propylene rubber, and some are capable of vulcanizing polyethylene, polypropylene, polyisobutylene, butyl, and highly unsaturated rubbers and their blends. The agents are most effective in the presence of sulfur. All are active in carbon black stocks, and at least some are active in mineral-filled and oil-extended stocks. Some of the vulcanizing agents can be accelerated by certain oxides and salts of metals widely distributed over the periodic system. Among the most active accelerators are iron compounds, such as iron tallate, stearate, naphthenate, octoate, and oxalate, and corresponding combinations of iron oxide and the free acids. These accelerators are antagonized by the presence of zinc oxide. The chemical diversity of these classes of vulcanizing agents and the complex behavior of the accelerators mentioned preclude an explanation of the vulcanization chemistry at this time.
Determinants in Research
Authors: Wiegand W. B.
Published: February 2011

We have now outlined some of the precursors of research, which we have called determinants. As to the Teammates, the record shows that the writer has been fortunate beyond his due. Flexibility in working theories, together with resourcefulness in techniques—prerequisites in any mayor research project—turned up when most needed. Trend lines, followed by extrapolation, we found essential, but tricky. Inversion, although great fun, is more a heady wine than a steady diet. The relatively high incidence of Hunches and Contacts, as decisive factors in research, emerges as perhaps the highlights of this modest study. These are determinants which seem to be independent of formal training; they are not to be found in college curricula. Even application forms do not ask “What is your record in successful hunches?” They are qualities which belong to other than the cognitive side of man. The same might be said about Action, which, as Dr. Sparks has reminded us, is an indispensable adjunct to any list of prerequisites for research. But how are these nonintellectual determinants fostered? How do certain individuals acquire the spark which seems to kindle their creativity—their Hunches, their flair for extracting honey from their Contacts, their drive, their motivation? Well, motivation seems to tie up with feeling. The Greeks thought that feeling centered in the diaphragm. With us it is the “heart.” In neither case is it the head. How does one go about acquiring this? In classical Greece kings and potentates sent their sons to one of two schools, not to learn certain skills, but to be exposed to two men—Plato and Isocrates. They counted on contact with these great teachers to inspire their sons and they rated this inspiration above instruction. Are we, perhaps, inclined to over-rate curricula and underrate the importance of personal exposure to teachers who possess, and can communicate, the imagination, the sweep and the scope, which we associate with greatness?
Inhibition of Hardening in Natural Rubber
Authors: Sekhar B. C.
Published: February 2011

It is well known that the polyisoprene of hevea latex undergoes considerable changes after its emergence from the tree. These changes take the form of chain scission or crosslinking depending on the conditions obtaining (see all References). In the solid state the predominant reaction that takes place on storage of rubber is one of crosslinking as indicated by the increase in Mooney viscosity, Williams plasticity and gel content. The plasticity of solid rubber changes continuously from the time it is prepared to the time it is used by the consuming industry. Considerable work has been carried out in the past to study this reaction with a view to controlling or inhibiting it. Wood suggested that peroxide or other free radical forming groups in the rubber may be responsible for the gelation of rubber on storage but gave no indication whether these groups were present in rubber as it leaves the tree or were formed subsequently. In a recent paper, it was shown by the writer that reactive groups are present in the rubber molecule as it leaves the tree. These reactive groups have the characteristic property of carbonyl groups or more specifically aldehyde groups. Condensation of these groups with other groups on the rubber hydrocarbon molecule, e.g., α-methyl or methylene groups, may be responsible for crosslinking of the polymer molecules. In support of this hypothesis, it was shown that reactive monofunctional amines or other carbonyl reagents are capable of inhibiting this crosslinking effectively, and that bifunctional amines can bring about crosslinking. The present investigation is an extension of this work and includes an examination of the effect of excess bifunctional amines, observations on the influence of formaldehyde in de-activating the naturally occurring amines in latex and a study of the reaction between hydroxylamine and a number of rubbers from different clones.
Mastication of Elastomers I. Natural Rubber in Nitrogen
Authors: Bristow G. M.
Published: February 2011

In accordance with theoretical expectation, the mastication of acetone extracted natural rubber in the absence of radical acceptors leads to gel formation. Unextracted rubbers undergo no gelation. The extent of gelation is determined almost entirely by the initial molecular weight of the rubber: under the conditions studied here rubbers of initial molecular weight less than ca. 3×105 do not gel on mastication. Only very small quantities of radical acceptors are required to repress gelation suggesting that acetone extracted rubber still contains appreciable quantities of such materials.