bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermographic Study of Elastomers III. Peculiarities of Crystallization of Natural Rubber
Authors: Teitel'baum B. Ya , Anoshina N. P. 
Published: February 2011

Abstract
Thermographic (DTA) study reveals two independent melting regions of natural rubber crystallites and a gap between them which is determined by a sharp difference in the rates of the crystallization process. Crystallites formed at a low temperature (− 25° C) and at room temperatures are distinguished by the degree of development, but pertain to the same crystallographic form. High temperature crystals play the role of seed in low temperature crystallization. During the melting of low temperature crystallites of natural rubber, they recrystallize with a rise in the melting point (without reaching, however, room temperatures). The appearance of this phenomenon on the thermograms is determined by the relation between rates of crystallization and of heating in the course of the experiment. The rate of crystallization of natural rubber and the relative amount of crystallites formed at − 25° C were studied by DTA; the effect of rubber plasticization on these magnitudes was noted.
Effect of Oil and Black on SBR Rheological Properties
Authors: Hopper J. R. 
Published: February 2011

Abstract
Effects of a naphthenic oil and of HAF carbon black on SBR processability were evaluated. Three rheological parameters related to processability are apparent viscosity, extrudate swell and extrudate surface roughness; they were studied with a capillary rheometer over a shear rate range of 10 to 3000 sec−1. This instrument is particularly useful because processability can be evaluated at industrial processing conditions. At constant shear rate an increase in oil level in the compound decreases viscosity, decreases swell, and reduces the shear stress range over which a smooth extrudate can be obtained. An increase in black level increases viscosity, decreases swell, and extends the range over which a smooth extrudate can be obtained. The opposing effects which oil and black have on processability demonstrate that an optimum combination of these two components exist. To best utilize the rubber process oil and carbon black the optimum processable compound must be selected. Such a selection is illustrated by the use of contour graph analysis of the data.
Correlation of Large Longitudinal Deformations with Different Strain Histories
Authors: Zapas L. J. , Craft T. 
Published: February 2011

Abstract
In 1963 Bernstein, Kearsley, and Zapas1 presented a theory of an elastic fluid which gave the correct stress-relaxation response for a large variety of elastomeric materials, including vulcanized rubbers. A principle attractiveness of this theory is its relative simplicity; with a single integral in time, it describes the stress-strain behavior for all types of deformation histories. In the case of simple extension, it predicts the behavior in any uniaxial strain history from the results of single step stress-relaxation experiments which cover the same range of extension and time. We designed a series of experiments to check the validity of this theory and found, as is shown in this paper, excellent agreement with experiment in all cases. We are aware that experiments cannot prove a theory. From our results, however, we feel strongly that a single integral expression with a nonlinear integrand such as the BKZ elastic fluid equation is sufficient to describe the stress-strain behavior of elastomeric materials.
Shear Dependence of Viscosity and Molecular Weight Transitions. A Study of Entanglement Effects
Authors: Chinai Suresh N. , Schneider William C. 
Published: February 2011

Abstract
Flow of concentrated polymer solutions covering molecular weights up to 150,000 was examined at shear rates up to 200,000 sec−1. The viscosity, molecular weight, and shear rate results of previous workers recognizing only single critical molecular weight M*, above which ordinary Bueche entanglements dominated the flow, were compared with our findings in which two distinct critical molecular weights, upper M* and lower M** exist. These results are compared with the theory, and new interpretations are presented.
Molecular Weight Distribution of Network Chains and Swelling Pressure of Vulcanizates
Authors: Gehman S. D. 
Published: February 2011

Abstract
Calculations and experimental results both indicated that effects of a molecular weight distribution of network chains may become evident in swelling pressure curves under favorable circumstances. More precise experiments are required to establish this definitely. The calculations assume that a simple integration such as is used for a continuous medium may be applied to molecular units of structure deduced from the kinetic theory of rubber elasticity. The validity of this can only be determined by further comparisons with experience. Refinement of the theory might take into account interactions of the units.
Ultimate Tensile Properties of Elastomers. III. Dependence of the Failure Envelope on Crosslink Density
Authors: Smith Thor L. 
Published: February 2011

Abstract
Ultimate tensile properties of amorphous unfilled elastomers can be characterized by a failure envelope which results from a plot of log log  σbT0vs.log  (λb− 1) where  σb is the stress at break based on the cross section area of an unstressed specimen,   λb is the corresponding ultimate extension ratio, and T0 and T are, respectively, an arbitrarily selected reference temperature and the test temperature expressed in °K. Values of  σb and   λb are normally obtained from tests made at different extension rates at a series of temperatures. To determine the effect of crosslink density on the failure envelope, a study was made of eight vulcanizates of a hydrofluorocarbon elastomer, Viton A-HV. The number of effective network chains, νe, in these vulcanizates varied from 0.38× 10−4to 9.46× 10−4mole/cm.3 Ultimate tensile properties were determined at temperatures between −5 and 230° C and at seven to ten extension rates at each temperature. The data gave a master failure envelope on a plot of λbσb273/Tvs.log  Ee(λb−1) 273/T, where Ee is the equilibrium tensile modulus. This behavior shows that λbσbT0/T is a function of Ee(λb−1); thus the maximum value of (λb−1) is inversely proportional to νe. Ultimate tensile properties of one vulcanizate were also determined under constant loads at four temperatures and the data were found to yield the same envelope as those from tests made at constant rates of extension.
Structure and Content of Dicyclopentadiene in Ethylene Propylene Dicyclopentadiene Terpolymers
Authors: de Kock R. J. , Veermans A. 
Published: February 2011

Abstract
With the aid of model compounds—derivatives of endo- and exo-dicyclopentadiene—it has been established that a) the 9, 10-double bond (the double bond in the norbornane ring) is involved in the polymerization of dicyclopentadiene with ethylene and propylene, b) dicyclopentadiene, present in the polymerization mixture in the endo-configuration, occurs in the exo-configuration in the polymer chain. The same model compounds enable the dicyclopentadiene content of ethylene propylene dicyclopentadiene terpolymers to be determined by infrared spectroscopic methods. Use is made of the 3045 cm−1 band, which is characteristic of endo-cyclic double bonds in five-membered rings.
Ethylene Propylene Terpolymers
Authors: German R. , Vaughan G. , Hank R. 
Published: February 2011

Abstract
The general technological properties of a polymer are closely related to its molecular structure. It is, therefore, important to know polymerization methods by which to produce reproducible polymers with controlled structures. Use of several monomers in copolymerization significantly increases the difficulty of this problem, but in the end it leads to a much wider spectrum of raw materials. In addition to variations caused by changes in molecular weight and in molecular weight distribution the nature of copolymers may be altered by changing the composition of the monomer mixture and the way monomers are distributed in the polymer chain. Use of Ziegler-Natta catalysts has already given a multiplicity of materials composed of ethylene and propylene: random copolymers are particularly interesting as rubbers. Introduction of a third component to give unsaturation in the terpolymer, so that this may be vulcanized with sulfur and accelerators, has greatly increased the possible areas of application for these polymers. Utility of a diene as the third component to give EPT's which can be used as general purpose rubbers depends on its price, the ease with which it copolymerizes through one double bond, its influence on the velocity or steric course of the ethylene-propylene copolymerization, vulcanization characteristics of the resulting terpolymers, and finally on the technological properties of the vulcanizates. The amount of copolymerized termonomer should be limited to retain the advantageous chemical and physical properties of the original ethylene-propylene copolymers. However very low degrees of unsaturation limit the sulfur and accelerator system, the characteristics of which depend strongly on the structure of the terpolymer as well as on the nature and form of the vulcanization agent. It is therefore essential to have a thorough understanding of this multiple interdependency for optimal application of the materials. We describe here reproducible procedures for production of terpolymers with controlled structures, and the course of vulcanization of the products in relation to terpolymer structure. We shall describe methods, based on these investigations, which may be applied for control of the vulcanization characteristics of the polymers.
Homogeneous Polymerization of Butadiene Catalyzed by Rhodium Salts
Authors: Bawn C. E. H. , Cooper D. G. T. , North A. M. 
Published: February 2011

Abstract
A study has been made of the solution polymerization of butadiene, to predominantly trans 1, 4 polymer, catalysed by rhodium salts. The reaction is accelerated by protonic acids (including water) and by those reducing agents which in aqueous systems would be capable of reducing RhIII to RhI. Ligands such as organic amines, and also bromide and iodide anions, tend to retard or even inhibit the reaction. The overall process appears to be a chain reaction, but is not free radical in character. The mechanism which best fits all the observations is one in which the active species is a π-allylic rhodium hydride, initiation occurring by hydride shift and propagation occurring by a ligand displacement process.
Limitations of the Tobolsky ‘Two Network’ Theory in Interpretation of Stress Relaxation Data in Rubbers
Authors: Thomas D. K. 
Published: February 2011

Abstract
Viton B vulcanized with triethylenetetramine and containing ρ-phenylenediamine relaxes in air at 200° C more slowly than in the absence of the diamine. At 130° C both vulcanizates relax at the same rate, the phenylenediamine reacts to form new crosslinks at 200° C. These results suggest caution in applying the “two network” hypothesis to interpret stress relaxation.
Relation between Stress Strain Behavior and Equilibrium Volume Swelling for Peroxide Vulcanizates of Natural Rubber and cis-1,4-Polyisoprene
Authors: Bristow G. M. 
Published: February 2011

Abstract
Data are reported for the elastic behavior, as described by the parameters C1 and C2, and the equilibrium swelling in n-decane, νr, for cumyl peroxide vulcanizates of natural rubber and cis-1, 4-polyisoprene. For natural rubber vulcanizates the correlation between C1 and νr can be described in terms of the original Flory Rehner equation with χ= 0.41. Tentative evidence is presented which favors this equation rather than the later modified form in which the term in νr1/3 is replaced by one in (νr1/3− νr/2).
Effect of Strain on Thermodynamic Melting Temperature of Polymers
Authors: Krigbaum W. R. , Dawkins J. V. , Via G. H. , Balta Y. I. 
Published: February 2011

Abstract
X-ray diffraction, sonic velocity, and birefringence measurements were used to study the variation of the apparent melting point of strained natural rubber and polychloroprene vulcanizates with elongation ratio and crystallization temperature. The procedure of Hoffman and Weeks was employed to obtain the thermodynamic melting point, tm, for each elongation ratio α. The parameter β relating to the distribution of fold lengths is unusually large for low elongation ratios and decreases into the usual range only at higher elongations. Observed variations of tm with α for these two polymers are compared with the theoretical predictions of Flory and Roe and Krigbaum. Although the predictions of the Flory theory depend somewhat upon the value assigned for the number of repeating units per statistical link, and this parameter is not well known for polychloroprene, we nevertheless conclude that his treatment offers a better representation of the melting point elevation for high elongations. Due to the approximations introduced, the treatment of Flory is not valid for lower elongations. Any attempt to improve this treatment must begin by specifying the free energy of the semicrystalline system, which implies a knowledge of the distribution of crystallite orientations and how this distribution varies with strain and with the crystallization conditions.
Stress Softening in Natural Rubber Vulcanizates. IV. Unfilled Vulcanizates
Authors: Harwood J. A. C. , Payne A. R. 
Published: February 2011

Abstract
Stress softening (Mullins effect) in gum natural rubber vulcanizates is similar in magnitude to that in carbon black filled vulcanizates. The amount of stress softening is slightly greater in vulcanizates cured to produce predominantly polysulfide crosslinks than in those containing monosulfide or carbon to carbon crosslinks. The total recovery of stress softening in the vulcanizates containing monosulfide or carbon to carbon crosslinks suggests that the phenomenon is attributable to a quasiirreversible rearrangement of molecular networks due to localized non-affine deformation resulting from short chains reaching the limit of their extensibility. This nonaffine deformation results in a displacement of the network junctions from their initial random state.
Interpretation of Microstructure of Poly-Isoprene and Polybutadiene Obtained in Anionic Polymerization
Authors: O'Driscoll K. F. , Yonezawa T. , Higashimura T. 
Published: February 2011

Abstract
A mechanism is proposed for the anionic homopolymerization of the diene monomers isoprene and butadiene. This mechanism qualitatively explains how the various polymer microstructures occur. A quantitative model based on this mechanism is treated by LCAO-MO calculations which include the effect of the counterion on the propagating chain. The results of the calculations are then compared with experimental data on microstructure and relative reactivity in hydrocarbon and tetrahydrofuran solvents. In every instance the comparisons give correct, semiquantitative agreement between calculation and experiment.
Investigations of Molecular Weight “Jump” Reactions in Polybutadienes
Authors: Ring W. , Cantow H-J. 
Published: February 2011

Abstract
Stereospecific, solution polymerization of butadiene to cis-1, 4 polybutadiene, using a catalyst system consisting of a cobalt compound and an organoaluminum compound, is a homogeneous reaction. In such a reaction, a diminution in catalyst activity accompanies the chain growth and chain transfer processes. Towards the end of the polymerization, the number of active catalyst centers is very small. The average molecular weight of polybutadiene can be raised in a definitive and reproducible manner, after completion of polymerization, by adding cocatalysts, e.g., alkyl or acyl halides, or certain active hydrogen compounds. Among other things, experiments in which (14C)-tert-butyl chloride was the cocatalyst have substantiated a cationic mechanism for this reaction. Changes in molecular structure are discussed on the basis of molecular weight fractionations with a Baker—Williams column and of results of viscometric and light scattering measurements.
Heterogeneous Polymer Systems. IV. Mechanism of Rubber Particle Formation in Rubber Modified Vinyl Polymers
Authors: Molau Gunther E. , Keskkula Henno 
Published: February 2011

Abstract
Polymerization of a solution of a rubber in a vinyl monomer consists of two stages. In the first stage (0–40 per cent conversion), in which the system is liquid, a polymeric oil-in-oil emulsion is formed, and the size of the rubber particles is established. In the second stage (40–100 per cent) this polymeric oil-in-oil emulsion hardens gradually to a solid dispersion of rubber particles in a matrix of the vinyl polymer, whereby the structure of the emulsion is retained and no significant morphological changes occur. The rubber particles are formed in the phase inversion which occurs in the first stage of polymerization. After the manuscript of this paper had been completed, a publication appeared, in which the dispersion of rubber by a phase inversion was also described. Bender's observations are in agreement with the observations presented in this paper and in the first paper in this series.) At the phase inversion point, the rubber phase is dispersed in the form of droplets in the vinyl polymer. Formation of multiple emulsions can occur at this point. The droplets of the rubber phase harden gradually by polymerization of the monomer and by crosslinking of the rubber and become finally solid rubber particles. The rubber particles contain irregularly shaped, tiny occlusions of vinyl polymer caused by polymerization of the portion of the monomer which was the solvent in the rubber phase. In addition, the rubber particles can contain larger occlusions with round peripheries stemming from multiple emulsions formed at the phase inversion point. Since the high viscosity of rubber solutions has an impeding effect on phase inversion, agitation is necessary in the first phase of the polymerization in order to overcome the inertia of the system and achieve inversion before the emulsions can solidify in the uninverted state.
Light Scattering Study of Carbon Black Structure
Authors: Donnet Jean-Baptiste , Eckhardt Claude , Horn Paul , Premilat Samuel , Voet Andries 
Published: February 2011

Abstract
Light scattering measurements on aqueous dispersions of carbon black confirm the hypothesis that mechanical properties of vulcanizates are closely related to structure of the carbon blacks used. This provides a simple experimental method for predicting the influence of a black on vulcanized rubber.
Effect of Crosslinking on Flatspotting of Nylon 6 Tire Yarn
Authors: Cipriani C. , Papero P. V. , Moore M. S. , Menkart J. 
Published: February 2011

Abstract
Tires containing nylon tire cord exhibit a temporary deformation upon standing under load. The delayed recovery from this deformation, due to the fact that the yield point of nylon is exceeded under normal inflation pressures, results in the phenomenon of “flatspotting.” Previous attempts to improve the viscoelastic characteristics of nylon by crosslinking have been discouraging on account of the general degradation of properties caused by the treatment. It has now been found that short, vapor-phase treatments with diisocyanates, particularly tolylene diisocyanate, produce nylon 6 of greatly improved flatspotting resistance, without undesirable side effects. The development of this procedure, the evaluation methods employed, and the proposed mechanism are discussed.
Typical Damage in Mallory Tubes and Tire Carcasses
Authors: Eccher S. 
Published: February 2011

Abstract
At the end of this survey, several conclusions can be drawn. The relatively small strength losses of the cord in the tire, even after very long road running times, and the corresponding good strength of the individual fibers make it possible to regard as untenable any explanation of fatigue failures by hypotheses relative to molecular structures, molecular forces, or crystallization phenomena. Observations on individual fiber breaks have likewise not contributed much to a better understanding of the causes of the tears. Certain “splitters” (aspects of filament breaks) might perhaps be ascribed to the strongly oriented structure of the fiber itself. Other breaks can very easily be explained by mutual abrasion of fibers; in this manner one can also explain the higher density of broken fibers in the zones of greatest flexing and the concentration of failure in the same zones in separated cords tested on the dynamometer. The fact that cord adhesion shows lower strength in the same zones in the “strip out” tests, requires assuming participation of other causes, e.g., it is necessary to assume the occurrence of separations even of limited extension or widespread tears in the rubber. These kinds of damage occur in tires even when they have sustained markedly different road service. It would doubtless be very interesting to carry out a test with progressively longer road service. In any case, it is quite certain that such damage is present when the mechanical properties of the cord are still very good. It seems therefore, that all observations previously made can be correlated with each other. Fatigue occurs in rubber which, upon cyclic loading, tears between the plies, the cords, and the yarns which form the cord. In addition, it is possible that rubber and adhesive separations set in, since the contact surface is likewise stressed cyclically in a way which can be regarded as chiefly in shear stress. Mutual friction between fibers in the yarns forming the cord is not to be excluded; however, if this should occur independently of other causes, when the adhesion is good and the rubber perfect, then one cannot understand why this process should suddenly lose its intensity, or come to a halt, as is shown by the residual strength in relation to the running time. If this internal process in the cord is excluded, it is possible to point to another mechanism already indicated in the course of the survey. Separations between adhesive and rubber and the tears within the rubber— apart from the fact that they develop heat because of friction—are flaws which continue to grow, and where they contact the fabric, there begins a damaging process due to friction and abrasion because of abnormal movements between yarns and fibers.
Fracture of High Polymers
Authors: Retting W. 
Published: February 2011

Abstract
General considerations of the physics of failure of high polymeric substances were reviewed using the example of one dimensional testing. It is shown that classical failure theory can be applied only with difficulty to viscoelastic substances. Relations between macroscopic failure properties and the parameters of test are reviewed. Several recent investigations have shown a direct relation between relaxation time spectra of high polymers and breaking energy, tensile strength, and elongation at break through their dependence on time and temperature. Finally, the relation between microscopic failure properties and experimental parameters are discussed. The processes occurring at the tip of the failure are determined by relaxation mechanisms just as are the processes which lead to sites of failure in the macroscopic specimen. These are illustrated by recent work in which the specific tearing energy is determined as a function of time and temperature of tearing. From all of the work referred to here, it follows that the very complicated relations at fracture of high polymers are essentially determined by their mechanism of molecular motion in a way analogous to other mechanical properties and are therefore determined by their molecular structure.