bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shift in Tg by Elastomer Orientation
Authors: Polmanteer K. E. , Thorne J. A. , Helmer J. D. 
Published: February 2011

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.