bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of Carbon Black in SBR
Authors: Oono Ryo
Published: February 2011

The interparticle distance between black aggregates in rubber was estimated by Fraunhofer diffraction with the mask of an electron micrograph of filled rubber. Up to 40 phr, the distribution of interpartiele distance has a sharp peak centered at 8000 A˚ with 20 phr and at 7000 A˚ with 40 phr. Above 60 phr, the interparticle distance distributes broadly in the vicinity of 4000 A˚. The size of black aggregates at 20 phr extends from 300 A˚ (one particle) to 3000 A˚, and the average diameter is 1200 A˚. Above 40 phr, black trends to aggregate more than at 20 phr, and the average diameter is about 1500–1600 A˚, the maximum diameter being 5000 A˚. In one black aggregate, there are about 40 spherical particles. The relation between the size and interparticle distance shows that isolated black aggregates are distributed in rubber under 40 phr and that at 40 phr they begin to connect partly with each other. Above 60 phr, a network of chains of black develops everywhere. The contact of black aggregates at 40 phr level corresponds to the abrupt change of physical properties of filled rubber.
Reinforcement of Elastomers by Carbon Black
Authors: Kraus Gerard
Published: February 2011

The reinforcement of elastomers by carbon black is governed by the morphology of the black and its physical and chemical interactions with the polymer. The latter are strongly affected by graphitization and surface oxidation. In modern rubber-grade carbon blacks strong bonding of the polymer to the carbon black surface is effected by several mechanisms, but surface chemical differences between blacks are relatively small, so that the dominant characteristic becomes the morphology. This is determined by the average size and size distribution of the particles which are fused together to form primary aggregates resembling branched random coils, the spatial arrangement of the particles in these aggregates, and the number of particles per aggregate and its distribution. This highly complex morphology can, to a first approximation, be represented by the specific surface area accessible to rubber and some, usually indirect, measure of the volume pervaded by the primary aggregates (“structure”). Important mechanical properties of reinforced rubbers depend to different degrees on these two characteristics, often in rather complex manner. Their effects on viscoelastic and failure properties are described. Additionally, some very recent observations on the effects of carbon black on network structure and the influence of the breadth of the aggregate size distribution on viscoelastic behavior are discussed.
Nonlinear Viscoelastic Behavior of Butadiene—Acrylonitrile Copolymers Filled with Carbon Black
Authors: Nakajima N. , Bowerman H. H. , Collins E. A.
Published: February 2011

Various viscoelastic measurements including dynamic mechanical measurements in tension at 110 Hz from −60–160°C, tensile stress relaxation measurements with 100% elongation at 25, 54, and 98°C, capillary flow measurements at 70, 100, and 125°C, and high-speed tensile stress-strain measurements carried to break at 25, 56, and 98°C were performed on four samples of carbon-black-filled butadiene—acrylonitrile copolymers. All the data were treated with the same equation for time-temperature conversion. The capillary viscosity—shear rate curves were significantly lower than the complex viscosity—angular frequency curves, indicating “strain softening” with extrusion. The viscosity was estimated from the stress-strain relationship at the yield point. The viscosity as a function of the strain rate is significantly higher than the complex viscosity as a function of angular frequency, indicating “strain hardening” with extension. The strain softening and strain hardening are attributable to the structural changes upon deformation of the carbon-black-filled elastomers. With the unfilled elastomers, neither strain softening nor strain hardening were observed in similar measurements.
Adhesion of Elastomers, with Special Reference to Triblock Copolymers
Authors: Gent A. N. , Hamed G. R.
Published: February 2011

Several physical and chemical factors affect the strength of adhesion (as measured by a peeling method) for elastomers adhering to rigid substrates. These factors include: the thickness of the elastomer layer (and of an adhering backing, if present); the rate of detachment and the test temperature; and the presence of chemical bonds between elastomer and the substrate. Adhesion of thermoplastic elastomers, i.e., SBS triblock copolymers, applied as hot melts, is much stronger than for the corresponding random copolymers, crosslinked in situ. These materials also show higher cohesive (tear) strength. Both effects probably arise from the same cause: an energy-dissipation process which operates at large stresses and prevents brittle fracture. This process is thought to be plastic yielding of the polystyrene domains.
The Kinetics of Polymerization Reactions
Authors: Gee G. , Melville H. W.
Published: February 2011

A general treatment of the kinetics of polymerization reactions is given to cover the two extreme conditions in which the lifetime of chain growth is (1) small, and (2) large compared with the half life of the monomer. Case (1) is considered on the basis of the assumption that the velocity coefficients do not depend on molecular size. Case (2) is considered for propagation coefficients which are on the one hand independent, and on the other hand dependent on molecular size. In addition, the distribution of molecular sizes is computed in those cases where the mathematical difficulties are not insurmountable. The application of these results to the analysis of polymerization reactions is discussed. The work described in this paper was completed when war broke out, and was to have been published as part of a book on polymerization processes. In view of the interest and development in these matters, it was felt desirable to give this account of these ideas now.
A New Method for Determining the Resistance of Soft-Rubber Products to Low Temperatures
Authors: Aengeneyndt J. , Kesternich W.
Published: February 2011

A simple method for testing the behavior of vulcanized rubber at low temperatures is described. In this method test-specimens in the form of strips prepared from finished goods, such as packing, hose, etc., are tested by a simple technique, without the necessity of mathematical calculations or the plotting of graphs. It is recommended that the hardening point be used as a criterion of behavior of vulcanized rubber in service at low temperatures, i.e., its resistance to cold. When this method is used, this hardening temperature should be 5° to 15° C below the lowest outside temperature at which the particular product must still operate satisfactorily.
The Evaluation of Tear Resistance in Elastomers
Authors: Graves Floyd L.
Published: February 2011

The fundamental fault in the stress distribution of the crescent tear-specimen has been discussed. A new angle tear specimen has been developed, with improved stress distribution. The specimen provides greater concentration of the pulling force at the point of tearing. The need of razor nicking of the test-pieces has been eliminated, with resulting marked improvement in the uniformity of tear resistance data. Tests carried out on four elastomers indicated that the crescent specimen values are dominated by the modulus and ultimate elongation of the material. Data obtained with the angle tear specimen indicated that tear resistance is a complex function of tensile strength and ultimate elongation. Inasmuch as the two specimens indicate different trends in tear resistance, it is hoped that this work will stimulate further discussion among rubber technologists on the evaluation of resistance to tearing.
Mechanism of Bias Filament Rupture in Fatigue of Nylon
Authors: Patterson Ralph G.
Published: February 2011

Cords in nylon tires fail at points of stress concentration owing to rupture of individual filaments by a characteristic fracture which occurs at an angle to the filament axis. Filaments fail by a crack growth process initiated at the fiber surface at defect sites. Crack formation and growth in single filaments were observed to occur at both natural and artificially induced surface defects. Failure begins at the compression side of the bend in filaments subjected to repeated cyclic bending. Similar findings were indicated for ductile metals. Fatigue failures in nylon filaments were related to the cyclic bending associated with compressive loading on inner ply cords of tires.
Shift in Tg by Elastomer Orientation
Authors: Polmanteer K. E. , Thorne J. A. , Helmer J. D.
Published: February 2011

This study was undertaken to develop a linear expansion method for identifying transition temperatures in elastomers that would be experimentally easier than dilatometry. It was considered desirable to use isotropic elastomer samples. Anisotropic as well as isotropic samples were unavoidably prepared; this led to interesting-results. Filler type, compounding, and molding procedures were each important factors in contributing to anisotropy of elastomers. The elastomers included in this study were natural rubber, butyl rubber, and a series of polysiloxane polymers. Orientation within an elastomer leads to: (a) Greater linear thermal expansion and swelling in the direction perpendicular to orientation, (b) More than one Tg value for some, but not all, elastomers. (c) Increases in ΔTg ranging up to 11° C for the siloxane copolymer elastomers, 15° C for the butyl rubber and 3° C for natural rubber. Isotropic elastomers have equal coefficients of expansion in all directions and one Tg value. An explanation for the shift in Tg is given, assuming a directionally dependent amplitude of vibration concept and that Tg is proportional to inter-molecular binding forces.
Interaction Parameters and Heats of Dilution for Ethylene Propylene Rubber in Various Solvents
Authors: Holly Earl D.
Published: February 2011

Crosslinked ethylene propylene rubber gels were swollen in five solvents at 25–100° C. The solvent polymer interaction parameter μ for each system was determined as a function of temperature and polymer concentration. A thermodynamic criterion of the sign of the heat of dilution, ΔH1, was pointed out. For three of the systems ΔH1 was negative. The entropy contribution to the interaction parameter was found to be smaller than usual for systems having a temperature-dependent heat of dilution. The heats of dilution and the entropy terms may be consistently interpreted in terms of Prigogine's theory of solutions.
Molecular Entanglement Theory of Flow Behavior in Amorphous Polymers
Authors: Graessley William W.
Published: February 2011

An approximate molecular theory of steady flow in amorphous polymers has been developed by considering the properties of a deforming entanglement network. The dynamics of entanglement formation between pairs of molecules and its effect on the density of entanglements during steady deformation were examined. From a simple model for these processes, apparent viscosity was calculated as a function of shear rate. An approximate calculation of the normal-stress differences was also made. Viscosity was found to be dependent on rate of deformation, and at sufficiently high shear rates it approached proportionality with (shear rate)−3/4. Onset of nonNewtonian behavior occurs in the same region of shear rates as that predicted by the coil distortion theory of steady flow. However, unlike the predictions of the latter theory, dynamic-viscosity frequency curves and apparent-viscosity shear-rate curves should not necessarily superimpose, because the dispersion mechanisms are fundamentally different in the two cases. Comparison with experimental results reported in the literature showed generally satisfactory agreement in both the shape of the viscosity master curves and in the order of magnitude of the normal-stress differences.
Hardness, Modulus, and Thickness
Authors: Tangorra G.
Published: February 2011

Series expansions are used to show that a simpler, more practical formula can be adopted to replace previous expressions of correlation between international degrees of hardness and shear moduli. This formula also appears to be nearer to the one deduced from the theory for the Shore durometer. General application is also given to a law relating these factors to the thickness of the test strips, which law has been previously found applicable to indenter hysteresimeters. This formula, which could probably also be used with other instruments with differently shaped indenters, has been particularly carefully checked for the ISO durometer with a ball indenter, and agrees excellently with experimental data. The mathematical relation, which has a single parameter, probably related only to shape and size of the indenter, allows the definition of an exponential parameter which generalizes the use of Scott's formula to smaller thicknesses. Finally, combination of the two new expressions makes it possible to put the dependence of degrees of hardness on thickness into a general form.
Changes in Polysulfide Content during Road Tests of SBR Tires
Authors: Studebaker Merton L.
Published: February 2011

Changes in polysulfide crosslinks can be observed during the service life of SBR passenger tires. Polysulfide content normally decreases. Test conditions which produce a change in polysulfide content of 15 per cent or more also produce groove cracking. For a given change in polysulfide content, HAF-loaded treads crack less than SAF-loaded tire treads and ISAF-loaded treads are intermediate. The addition of high cis-1, 4-polybutadiene reduces groove cracking and cut growth of SBR passenger tires, even though substantial changes in polysulfide content occur during service.
Stress Softening in Carbon Black Reinforced Vulcanizates. Strain Rate and Temperature Effects
Authors: Kraus G. , Childers C. W. , Rollmann K. W.
Published: February 2011

Stress softening of carbon black reinforced butadiene styrene rubber was studied as a function of the rate and temperature of the original tensile deformation. To a good approximation, stress softening depends on the product of the extension rate and a temperature function which is analytically well represented by the familiar Williams-Landel-Ferry relationship. When the elongation of the original deformation is also varied, a good correlation is obtained between stress softening and the maximum stress attained in the original extension, irrespective of the particular combination of strain, strain rate, and temperature used to achieve this stress. Variables which tend to increase the stiffness of the vulcanizate, such as increased degree of crosslinking or carbon black chain structure, also increase stress softening; dilution by plasticizers decreases it. Prestressing at high strain rates and low temperatures affects the stress—strain curve of the softened vulcanizates beyond the elongation of the original extension. Connections are established between stress softening and viscoelastic and failure behavior. The evidence presented favors the contribution of several mechanisms to the general phenomenon of stress softening. These are thixotropy of transient filler structures, network chain rupture, and breakage of “permanent” filler structure. The latter appears to be most important at high strain rates, low temperatures, and with highly reticulated “structure” blacks.
Significance of PRI in Raw and Vulcanized Natural Rubber
Authors: Bateman L. , Sekhar B. C.
Published: February 2011

The Plasticity Retention Index (PRI) has been developed as an objective test for the oxidizability of raw natural rubber and has recently been associated with the Standard Malaysian Rubber Scheme. Oxidizability as measured by PRI significantly affects behavior of rubber in the factory and in service performance and prior information on this property permits adjustments in vulcanizate recipes and in processing conditions to be made so that the most advantageous balance in properties is achieved.
Role of Elastomers in Impact-Resistant Polystyrene
Authors: Angler D. J. , Fettes E. M.
Published: February 2011

Incorporation of elastomers into polystyrene has been used in recent years to overcome its inherent brittleness. Mechanical mixing of rubber with polystyrene has been largely superseded by dissolving the elastomer in the styrene before polymerization. Impact-resistant polystyrene produced by either method is a two-phase system with polystyrene the continuous phase and elastomer the discrete phase. Polymerization of styrene in the presence of an unsaturated elastomer converts the elastomer to a graft copolymer. The graft copolymer is formed by reaction of the polymerization initiator with the rubber to form an active site thereon, which can initiate polymerization of styrene to form a side chain of polystyrene. The graft copolymer is crosslinked in the process. The size of the gel particles must not be too large for a satisfactory product, but can be controlled by shear and by chain transfer agents. The rubber chiefly used with polystyrene has been SBR, but use of polybutadiene is growing because of improved impact resistance at low temperatures. The resistance to impact increases with increasing amounts of elastomer, but surface gloss and hardness decrease. The chief advantage of graft copolymerization over poly-blending is more efficient utilization of the elastomer. The increase in resistance to impact has been attributed to the energy absorbing character of the elastomer. The two-phase system is necessary so as not to lose this basic property of elastomers. The rubber particles may also act to induce many small cracks rather than one large one, thus increasing the energy requirement for total failure. The greater efficiency obtained by a graft copolymer may be due to a more diffuse interface between rubber and polystyrene, leading to more absorption and less reflectance of a stress wave by the particle of rubber.
Structure and Reactivity in Oxidation of Elastomers
Authors: Norling Parry M. , Lee T. C. P. , Tobolsky A. V.
Published: February 2011

Oxidation of hydrocarbons is a much studied and much reviewed subject, yet much remains to be understood about complexities of competing reactions that take place as hydrocarbons react with oxygen. The generally accepted free radical mechanism for low temperature reaction (below 200° C) stems from kinetic studies by Semenov, Hinshelwood, Farmer, Gee, Bolland, and Bateman of hydrocarbon and olefin oxidation in the gas and liquid phase: Such a chain mechanism appears to be straightforward, but studies of autoxidations are complicated by sensitivity to trace metals, which decompose hydroperoxides, and to the nature of reaction products, which may function as inhibitors or accelerators. The character of the reaction may vary considerably with time as these reaction products accumulate. Hydroperoxides may decompose by unimolecular or bimolecular pathways to produce alkoxy, peroxy, or hydroxyl radicals. These are known to have various selectivities and hence will produce different propagating species with differing rates of termination. Alternately hydroperoxides may react with sulfur, nitrogen, aldehydic, basic, or acidic functions producing no radicals at all. Such reactions vary drastically from one system to another. The study of autoxidations thus becomes the challenging problem of trying to separate one reaction from another. One method of avoiding such difficult problems is to work under simplifying conditions. One approach is to study oxidations with an external initiator such as azobisisobutyronitrile or benzoyl peroxide under conditions such that the hydroperoxides formed during oxidation are relatively stable products. This has been most successfully applied to kinetic studies on liquid hydrocarbons containing benzylic or allylic hydrogens. This review is concerned with some recent work on initiated oxidations of hydrocarbon polymers in the solid phase and attempts to show how the results may be related to the more complicated autoxidation process.
Elemental Sulfur as a Plasticizer for Polysulfide Polymers and Other Polymers
Authors: Tobolsky A. V. , Takahashi N.
Published: February 2011

So-called elastic sulfur obtained by quick-quenching molten sulfur from a temperature of 250° C to a temperature of about −10° C is really a mixture of polymeric sulfur and monomeric S8 sulfur, the latter in a metastable condition, Quick-quenched sulfur is elastic because of the plasticizing effect of the liquid S8 sulfur on the polymeric sulfur. In this publication we show that large concentrations of S8 can exist dissolved in a liquid condition in other polymers where it also acts as a plasticizer. In many cases these compositions appear completely stable, i.e., there is no tendency for the dissolved sulfur to crystallize out. The best example is crosslinked polyethylene tetrasulfide polymers. These polymers can retain 40 per cent of dissolved sulfur in the form of liquid S8 over indefinitely long periods of time. We prove that the sulfur is in its elemental form by quantitative extraction with CS2. The specific volume of the dissolved sulfur shows it is in a liquid condition. The mechanical properties of the sulfur plasticized crosslinked polymers are just what would be expected from this type of structure. Preliminary information concerning sulfur in other polymers is presented.
Elastomers in Space and in Other High Vacuum Environments
Authors: Rivera Michael
Published: February 2011

Effects on elastomeric materials of exposure to outer space and to other high vacuum environments are reviewed. Applications and requirements of elastomers for space vehicles and vacuum systems are summarized. Outgassing processes are discussed as functions of permeability and temperature, among other factors. Techniques employed in the measurement of gas and weight loss under vacuum are described and typical results presented. It is observed that gas or weight loss determinations are required for optimum application of available elastomer materials, and that there remains a significant need for elastomer materials suitable for low pressure vacuum systems.
Performance of Elastomeric Silicones in Ablative and Space Environments
Authors: Whipple Clyde L. , Thorne John A.
Published: February 2011

Elastomeric silicones are among the best materials available for many ablative and space applications. In ablative applications, these materials protect launching equipment, safeguard various parts of vehicles and spacecraft during flight, and shield re-entering spacecraft. Generally, elastomeric silicones are used where ablative conditions involve low to moderate heat fluxes and shear forces. Ablative characteristics of materials can vary widely depending on polymer type, fillers, and applications techniques, and no one elastomeric silicone will perform in a wide range of ablative missions. A good knowledge of the ablative characteristics of silicone materials is required to select the best candidates for a given application. In the space environment, silicones are often used for seals, thermal control coatings, potting materials, and other applications because they perform well over wide temperature ranges, and because they are inherently stable to high-vacuum and ultraviolet conditions. Data given in this paper illustrate that silicones show little weight loss or loss of properties on exposure to space environmental extremes. Furthermore, these losses can be made almost negligible by proper conditioning of the finished elastomer.
Effect of High Hydrostatic Pressure on the Permeability of Elastomers to Water
Authors: Lebovits Alexander
Published: February 2011

The permeability of butyl rubber to pressurized water was measured at 10,000 psi hydrostatic pressure using a relatively simple method which consisted of constructing pouches from rubber, filling these with desiccant and exposing them to pressurized water. At this high hydrostatic pressure the permeability was found to be smaller than at atmospheric pressure which suggests the suitability of butyl rubber for the construction of hydrophone boots used at great depths. Similar results found by other investigators for other polymeric materials are cited. A thermodynamic analysis of the process of permeation by activated diffusion was made and a mechanism was discussed which explains the decrease in permeability of butyl rubber to water with increased pressure.
Stability of Urethan Elastomers in Water, Dry Air and Moist Air Environments
Authors: Magnus G. , Dunleavy R. A. , Critchfield F. E.
Published: February 2011

Effects of long-term exposure in moisture-containing environments were examined for corresponding poly (e-caprolactone), polyadipate, and polyether urethan elastomers. Polycaprolactone urethans were more stable than polyadipate. When water-immersed, hydroxyl-cured and amine-cured cast polyether systems were five to ten times more stable than the polycaprolactone. This reduced to about two times when the hydroxyl-cured systems were compared in saturated moist air. A carbodiimide stabilized the polycaprolactone urethan to about the same level as the polyether. Sulfur-cured polycaprolactone urethan millable systems were about twice as stable as similar polyether elastomers. Polyether urethan elastomers degraded more than polycaprolactone systems when exposed to hot, dry air environments. The practical implication of these findings is that, for most applications, polycaprolactone and polyether based urethan elastomers can be formulated to provide continuous service in moisture-containing environments.
Effect of Zinc Oxide and Titanium Dioxide on Heat and Light Stability of Ethylene Propylene Terpolymers
Authors: Baldyga H. , Jones H. C.
Published: February 2011

Oven aging properties at 350° F and 300° F of EPT polymers were substantially improved with additions of zinc oxide up to 10 and 20 phr. Zinc oxide enhanced the elongation retention after aging, and the improvement was significantly greater with French than with American Process zinc oxides. Finer particle size French Process zinc oxides imparted somewhat better aging properties than did the coarser zinc oxides of the same type. The aging advantage for high loadings of zinc oxide was notable both with whiting and clay-filled EPT compounds with low and normal amounts of sulfur. When the pigmentation of the EPT polymer was 50 phr of FEF black, the aging differences between the several American and French Process oxides at loadings of three to 20 phr were less prominent. Replacement of three per cent of EPT with an equal amount of several unsaturated elastomers increased the cure rate of the compound appreciably. Tear resistance was improved and compression set properties lowered. Improvement in heat resistance depends on the polymer added. Several anatase and rutile pigments were essentially equal in heat aging resistance at an equal volume loading in EPT. The reflectance of stocks with zinc oxide alone or in combination with titanium dioxide in an unfilled stock increased during the first three days of Atlas Weather-Ometer exposure. Beyond this point, there was a gradual degradation in reflectance with the loss in reflectance being somewhat greater with a zinc oxide-titanium dioxide blend than straight zinc oxide. These results reflect the observed differences in ultraviolet opacity between zinc oxide and titanium dioxide. In a comparison of anatase and rutile in a whiting loaded stock, anatase was poorer than rutile in reflectance through the initial exposure stages in the Atlas Weather-Ometer; however, after prolonged exposure, there was a reversal in reflectance, due to the chalk layer developed in the anatase sample. EPT stocks pigments with 79.5 phr of whiting with titanium dioxide between 18.5 and 25 phr, and activation amounts of zinc oxide showed no visible sunlight degradation after 70 weeks outdoors.
Stress Softening in Natural Rubber Vulcanizates. Part II. Stress Softening Effects in Pure Gum and Filler Loaded Rubbers
Authors: Harwood J. A. C. , Mullins L. , Payne A. R.
Published: February 2011

Considerable stress softening occurs in both gum and filler-loaded vulcanizates and when compared at the same stress the extent of softening is similar in both gum and filled vulcanizates. It thus appears that the softening process is mainly due to the rubber phase alone. Apparent differences between the stress—strain hysteresis loops of gum and filler-loaded vulcanizates are traced to an increase in the effective strain in the rubber phase resulting from the presence of black. This is discussed in Part I of this series. The mechanism of stress softening in gum vulcanizates is not well understood. Possible sources include (1) breaking and remaking of crosslinks during extension, (2) residual local orientation of network chains persisting after recovery, and (3) breaking of network chains.
Model Interpretation of Thermal Conductivity in High Polymers I. Amorphous High Polymers
Authors: Eiermann K.
Published: February 2011

The following model conception describing heat transfer in amorphous materials, especially in high polymers, is derived. An “elementary” thermal resistance is assigned to each bond between adjacent atoms. The thermal resistance of a macroscopic amorphous specimen is that of a three-dimensional network consisting of elementary thermal resistances with the atoms as the junction points. Elementary thermal resistance decreases with increasing force constant of the bond. Therefore the elementary thermal resistance of a main valence bond is about ten times smaller than that of a van der Waals bond. This simple conception enables us to describe the thermal conductivity of amorphous materials quantitatively, for instance the break in the thermal conductivity curve of amorphous high polymers observed at the second-order transition temperature.
Ethylene Propylene Copolymers: Crystal-Linity, Infrared, and Creep Studies
Authors: Linnig Frederic J. , Parks Edwin J. , Wood Lawrence A.
Published: February 2011

Density, infrared, and creep studies have been made of ethylene propylene copolymers containing up to about 50 mole per cent propylene and their homopolymers. The degree of crystallinity (volume fraction of polyethylene crystals), as measured by density and x-ray studies, decreases with increased propylene content. This change is also reflected in the intensity of the 13.7 μ band in the infrared spectra of the polymers. The measured amount of unsaturation (0.1–0.2 per cent) in the copolymers is too small to account for the presence of several infrared bands which are often attributed to unsaturation. An unsaturation of 0.90 per cent was obtained for a terpolymer where the third component was unsaturated. Indentation-creep studies showed the creep to be nearly proportional to the logarithm of time with a slope of 10 per cent creep per decade for 0.1–10 min. Compliance-temperature graphs were found to be quite similar to those for the styrene butadiene rubber SBR 1500.
Tack in Urethan Elastomers
Authors: Boenig H. V. , Miller C. B. , Shottafer J. E.
Published: February 2011

The phenomenon of tack has been studied in urethan—urea elastomers prepared from polyether or polyester prepolymers and 4,4′-methylenebis(2-chloroaniline). It is shown that tack at zero elongation is attained only in polymers in which the flexible chains, i.e., polyesters or polyethers, contain 50 chain links or more. This coincides with the requirements for the Gaussian vector function in elastomers. The results suggest that, in the absence of flexible chain ends in these polymers, tack is solely contributed by the flexible segments along the polymer chains, while the rigid blocks in the chains do not participate in the formation of tack.
New Nondiscoloring Stabilizer System for SBR and Stereospecific Diene Polymers
Authors: Oberster A. E. , Cook W. S. , Smith G. E. P.
Published: February 2011

This article discloses the discovery and use of a class of imidazolidine-4-thiones as new stabilizers for unsaturated rubbers. Also reported is the preparation of the acid salts of one of these, 7, 14-diazadispiro[5.1.5.2]pentadecane-15-thione (DDPT) and its 7- and 14-nitroso derivatives. Several alkylated derivatives of DDPT were found to be equivalent to DDPT in nondiscoloring stabilization activity. The 7-nitroso derivative was found to be an active stabilizer and was found to counteract some slight cure activation inherent in the imidazolidine-4-thione structure. DDPT was shown to be an efficient polymer stabilizer providing excellent nondiscoloring polymers for use in various tire compounds. This compound was fully equivalent or superior to similar polymers prepared from other commercially available nondiscoloring stabilizers and antioxidants.
Accelerated Oxidations of Polyisoprene. III. Photosensitized Oxidations in Solution
Authors: Mill Theodore , Irwin Katherine C. , Mayo Frank R.
Published: February 2011

Measurements of oxygen absorption at 50° C showed methylene blue to be the most effective of several sensitizers tested. At a concentration of 0.01 mM, it gave a rate of oxidation which was about 12 times that in a control run in the light. About 1600 moles of oxygen were absorbed per mole of methylene blue. To obtain the same rate in the dark, about 100 times as much 2,2′-azobis(2-methyl-propionitrile) (AZBN) would have been required. At least in the initial stages of oxidation, this catalysis by methylene blue was not affected by addition of an oxidation inhibitor. Thus, the photosensitized oxidation is mostly a nonradical reaction.
Influence of Sulfur on Stability and Physical Properties of Peroxide Vulcanized Ethylene Propylene Copolymers
Authors: Dunn J. R.
Published: February 2011

In cumyl peroxide sulfur vulcanizates of ethylene propylene copolymers crosslinked with 4 phr of peroxide, polysulfidic crosslinks are present only at sulfur levels in excess of 0.5 phr in gum vulcanizates and 0.3 phr in black filled vulcanizates. Modulus attains a peak in the presence of 0.5 phr of sulfur in gum vulcanizates and 0.3 phr of sulfur in black filled vulcanizates. Modulus decreases when polysulfides are present. Tensile strength in gum vulcanizates increases continually with increasing sulfur content up to 2.5 phr. The increase in tensile strength is related to a rapid increase in ultimate elongation, promoted by mechanically labile polysulfidic crosslinks. Tensile strength in black filled vulcanizates exhibits peaks at 0.3 and 0.75 phr of sulfur. The first peak represents the technological recipe for this type of vulcanizate and arises from a peak in modulus. The second peak arises from increased breaking elongation promoted by polysulfidic crosslinks. Sulfides present in the vulcanizate act as antioxidants at all sulfur levels. When the sulfides contain one or two sulfur atoms, the antioxidant effect is mild but long lived. The polysulfides yield potent long lived antioxidants. The rapid nonoxidative degradation of the polysulfidic crosslinks is not accelerated by dithiocarbamate and proceeds after the reaction products have been removed by extraction. Dithiocarbamates are potent antioxidants in peroxide vulcanized ethylene propylene rubber both in the presence and in the absence of sulfur.
Fundamentals of Electron Microscopy of Heterogeneous Elastomer Blends. II
Authors: Marsh Peter A. , Voet Andries , Price L. D. , Mullens T. J.
Published: February 2011

Electron and phase microscopy results show that most elastomer blends are heterogeneous, even after extended mixing. Blends of SBR/BR and SBR/EBR, however, are homogeneous. DTA data support these conclusions. Carbon black distribution studies indicate that carbon black does not transfer between elastomers during mixing. Polychloroprene exhibited a strong affinity for carbon black in blends with natural rubber. In this system, with the black predispersed in the natural rubber, the carbon black particles were observed at the polychloroprene interface but had not entered that phase.
Microstructural Variations in Commercial Carbon Blacks
Authors: Hess W. M. , Ban L. L. , Eckert F. J. , Chirico V.
Published: February 2011

Conventional and diffracted beam electron microscopy can be used to resolve the ultimate crystallite units in standard and heat treated carbon blacks. They are very sensitive in the detection of small differences in crystallite size and orientation. Combined with x-ray diffraction methods and conventional vulcanizate testing, high resolution electron microscopy appears to be a useful and practical means to study carbon black surface activity. All commercial blacks appear to conform in part to the Heckman and Harling concentric crystallite model. Surface activity appears to be related to the extent of this alignment; the less the tangential orientation of the graphite layer planes to the surface, the greater the surface activity. Heating carbon blacks in an inert atmosphere for varying times and temperatures (850 to 1400° C) causes a gradual depression of surface activity with increasing treatment severity, defined by increases in the size and concentric orientation of surface crystallites. At no time was the effect of carbon black on vulcanizate properties changed significantly by heat treatment without disrupting the initial orientation of surface crystallites. Carbon blacks differ in the rate of change of crystallite orientation in response to heat treatment. The initial degree of crystallinity, porosity, and surface volatile content all appear to affect the rate of crystallite orientation and growth. Increases in average crystallite height, Lc, are a good measure of effects of heat treatment in excellent agreement with changes in surface crystallite size and orientation observed with the electron microscope. Commercial ISAF carbon blacks of varied structure have relatively minor differences in surface crystallite orientation, indicating small differences in surface activity. The higher modulus and treadwear associated with the use of high structure blacks appear to be predominantly a result of the chain structure itself. Further evidence was obtained showing that black structure and surface activity are independent properties each of which can have a significant influence on vulcanizate properties such as modulus, treadwear, and hysteresis.
Characterization of Ethylene Propylene Block Copolymers by Proton Magnetic Resonance
Authors: Porter Roger S.
Published: February 2011

A high-resolution proton magnetic resonance compositional analysis has been developed for propylene polymers containing 0–40 weight per cent ethylene as either homopolymer or copolymer blocks. The test is independent of tacticity and provides qualitative information on copolymer sequencing and propylene chain structure. The analysis was developed using a series of standard reference polymers synthesized to contain various ratios of C14-tagged ethylene and propylene. The compositional standards were established by radiotracer analysis for C14 and by preparing weighed physical mixtures of homopolymers. Spectra were obtained at 200 ± 10° C by placing externally heated polymer solutions into a conventional probe of a Varian A-60 proton spectrometer. All measurements were made on ≤10 per cent polymer solutions in diphenyl ether. Analyses are accurate to about ±10 per cent at higher ethylene concentrations. The method is sensitive, with less precision, to below 1 per cent for ethylene either as blocks or homopolymer.
Morphological Changes in Latex Films
Authors: Bradford E. B. , Vanderhoff J. W.
Published: February 2011

The mechanism of latex particle coalescence has been considered by a number of investigators. Dillon and coworkers and later Henson and coworkers discussed the role of surface tension forces and the applicability of Frenkel's model for coalescence of spheres by viscous flow. Later Brown postulated that capillary forces derived from the water and air interfacial tension, when the evaporation of the water forms small radii of curvature, provide the major driving force for film formation. Voyutskii stated that the surface tension and capillary forces alone cannot account for the ultimate physical properties observed in cast latex films. He postulated the contribution of autohesion, that is, mutual interdiffusion of the free polymer chain ends across the particle, particle interface in the dried film. According to his hypothesis, this diffusion knits the film into one coherent, continuous mass. It has often been observed that physical properties of latex films improve with aging at room conditions. This improvement occurs after practically all the water has evaporated and the films are transparent. Thus, the empirical observations of such properties as scrub resistance indicate that the dry latex films undergo some change upon aging. The autohesion hypothesis might explain these results. In this study the electron microscope was used to study morphological changes which occur as a latex film ages. The magnification of this instrument allows the observation of individual particles in the film surface and the changes with aging.
Glass Transition of Crosslinked Polyurethan Elastomers and Initial Components
Authors: Lipatov Yu S. , Kerchas Yu Yu , Sinyavskii V. G. , Lipatnikov N. A.
Published: February 2011

Differential thermal and thermomechanical methods were used to investigate glass transitions in many polyurethan elastomers and their initial components—oligoesters and linear prepolymers. Glass transition temperature of oligoesters increases with higher molecular weight to a certain limit, corresponding to a molecular weight of 4000, after which it remains unchanged with increase in molecular weight. This value corresponds to the mechanical segment of the oligomer. Unlike oligoesters, for prepolymers with the same length of oligoester unit, glass transition temperature increases with higher urethan group concentration in unit volume and not with increase of molecular weight. Presence of polar urethan groups and not the three dimensional structure of elastomers has the main effect on increase of glass transition temperature of polyurethan elastomers, as compared with initial oligoesters. Elasticity of polyurethan depends on length of the polyester unit and the chain segment between the units of the network mainly formed by physical bonds.
Reinforcement of Polymers. I. Tear Resistance of Filled Mixes and Adhesion of Elastomer to Filler as a Function of Duration and Temperature of Elastomer and Filler Contact
Authors: Raevskii V. G. , Yagnyatinskaya S. M. , Episeeva S. N. , Voyutskii S. S.
Published: February 2011

In accordance with the concepts being developed by the authors of the present paper, the influence of fillers on the properties of filled systems is determined by adhesion of the polymer to the filler. There are indications of the significance of this factor in many papers dealing with the study of reinforcement. However, they do not advance adhesion as a basic factor which determines reinforcement. This has become possible after the development of a procedure for the evaluation of adhesion of polymers to powdered fillers. This paper lists experimental data on the correlation between the duration and temperature of contact of the elastomer with filler particles on the tear resistance of filled mixes, on one hand, and the time and temperature dependence of the adhesion of the system components to one another, on the other. The selection of tear resistance as a characteristic of the physicomechanical properties of the system is governed by the fact that failure starts, as a rule, from a random local defect. Most frequently this is a small cut or surface crack. For this reason, the assertion of a number of researchers that the operating properties of products are more fully characterized by tear resistance rather than by tensile strength is fully acceptable. Besides, tearing is the most general type of destruction of materials, inasmuch as it takes place during rupture as well as during wear.
Separation of Molecules with Linear and Branched Structures in Natural and Styrene-Butadiene Rubbers
Authors: Dogadkin B. A. , Igumnoya A. V. , Kuleznev V. N.
Published: February 2011

The possibility of separating linear and branched polymer molecules by chromatography on silica gel is demonstrated. Removal of microgel from styrene-butadiene rubber, SKMS-30 increases the mechanical strength of its vulcanizates; removal of microgel from natural rubber, conversely, reduces the strength. The existence of an optimum branched-structure concentration which insures a gain in various mechanical properties is postulated.
Correlations between Structure of Elastomers and the Mechanism of their Degradation by Ozone
Authors: Salomon G. , van Bloois F.
Published: February 2011

Ozone cracking is treated as a special case of stress corrosion. The correlation between delayed fracturing, stress and strain is explained in terms of changing crack geometry. Structural relationships have been studied in the region of minimum, critical stress. Two groups of ozone sensitive polymers can be distinguished: in highly ozone sensitive materials cracks are initiated at very low values of stored elastic energy, while initiation in the more resistant butyl rubbers and EPT rubbers occurs only at much higher values of stored elastic energy. The rate of cracking in neoprene is shown to be much less stress sensitive than the corresponding rate in other polydiene rubbers. It is conjectured that this favorable property of neoprene depends on the rheological behaviour of the ozonized surface layer.
Blends of cis-1,4-Polybutadiene with Natural or Styrene Butadiene Rubber
Authors: Fujimoto K. , Yoshimiya N.
Published: February 2011

Temperature dependence of dielectric loss, mechancial loss, and dynamic modulus were measured to study polymer blending. Results were as follows: Dielectric loss and dynamic modulus of NR—BR blends showed two peaks corresponding to NR and BR, indicating that the blends were microheterogeneous. A single, broad maximum absorption band observed for SBR—BR blends indicated that the blends were microhomogeneous. Mill mixing and solution mixing of NR and BR made very little difference in blended state and physical properties. Nearly homogeneous SBR—BR blends can be obtained with a few minutes mill mixing. In vulcanization of NR—BR blends, BR was overcured rapidly due to migration of sulfur and accelerators from NR.