bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamic Aspects of the Glass-Rubber Transition
Authors: Staverman A. J. 
Published: February 2011

Abstract
In 1933 Ehrenfest defined transitions in which not only the thermodynamic potential but also the specific volume and entropy of the two states are equal. For these transitions he derived three relations, between the differences of the coefficients of dilatation and of compressibility and the specific heat on one hand and the slope of the transition curve in p-T-space on the other hand. Although it is beyond any doubt that the glass-rubber transition in polymers is not a second order transition as defined by Ehrenfest, yet the term “second order transition” is often applied to it. The confusion arising from this abuse of a physically well defined concept is enhanced by the fact that some of Ehrenfest's relations are under certain circumstances valid for the glass-rubber transition, although in those cases the physical background of these relations is quite different from that of a second order transition in Ehrenfest's sense. In fact, the essence of the glass transition was formulated clearly and correctly by Simon in 1931 and consists in the assumption that in a glass one or more internal parameters are not in equilibrium but are frozen in. Conditions required for the validity of each of Ehrenfest's relations are inspected. The equality of two functions of the dilatation and the compressibility coefficients and the specific heats of the two states depends on the condition that there is only one frozen parameter in the glass state. If there is more than one frozen parmeter, then the equality turns into an inequality and the physical meaning of the difference between the two sides is derived. Similar relations as those derived between the quantities mentioned, can be derived between specific heat, modulus of elasticity and temperature coefficient of that modulus. These new relations are more interesting for practical purposes and less subject to experimental errors than the older ones. Finally expressions for the slope of the transition curve are investigated. Validity of any one of the expressions depends on the physical condition required for a material to become a glass. Inversely from the validity of any of the possible expressions insight in the glass transformation can be derived. The scarce available data give the impression that a material turns into a glass whenever its excess entropy decreases below a critical value.
Applicability of Free Volume Concept to Relaxation Phenomena in the Glass Transition Range
Authors: Kovacs A. J. 
Published: February 2011

Abstract
Except for discrepancies mentioned with respect to pressure investigations, which need future clarification, we can conclude in a general way, as follows. As far as only average parameters of macroscopic specimens are considered (complex moduli, or dielectric constants, volume or heat content etc...), the free volume concept can relate variations of molecular mobility to changes of an average free volume in a semiquantitative way. This average free volume can no longer fully characterize the wide variety of molecular motions involved in the kinetics of redistribution of holes in the liquid during recovery experiments. These kinetic processes involve a wide distribution of retardation times, which may be associated with local distribution of holes, or with that of cooperating groups of molecules, or molecular segments. On the other hand, free volume is not necessarily the fundamental molecular parameter which controls rate of configurational changes, characterized by variation of entropy of the liquid. Even if this is the case, most of the above discussion may be applied to any other average excess parameter, as far as the Doolittle equation is formally adopted, in which f/b is expressed in terms of the new parameter, rather than that of free volume. However, since relaxational free volume, as determined from the WLF equation, and independently measured volume changes are often in close agreement, this means that variations of excess entropy, or those of configurational free energy, and changes in volume are closely related. This conclusion is in agreement with that of Eisenberg and Saito, who found that the Gibbs—Dimarzio theory, based on configurational entropy, is practically equivalent with the free-volume approach. Thus, the free volume concept remains still a valuable tool for unifying different kinds of rate processes from both a theoretical and an experimental point of view, especially in the glass transition range.
Thermoelasticity and the Temperature Coefficient of Unperturbed Polymer Dimensions
Authors: Puett D. 
Published: February 2011

Abstract
The strain dependence of fe/f (ratio of the internal energy component of the force to the total retractive force) for a crosslinked, amorphous network is analyzed in terms of the C2 factor which appears in the semiempirical relation for rubber elasticity. Appropriate equations are derived and applied to literature data for several polymers and copolymers. The temperature coefficients of the mean square end to end distances thus obtained are often quite different from the values determined by averaging ƒe/ƒT at several extensions.
Thermodynamic Examination of the Polymorphic Transition of Trans-1,4-Polybutadiene. I. Theoretical Premises
Authors: Natta G. , Pegoraro M. , Sziálgyi L. 
Published: February 2011

Abstract
It is known that oriented fibers of trans-1,4-polybutadiene shrink when heated, in correspondence with the solid-solid state transition. In ideal fibers this occurs at a temperature which is solely a function of applied stress. The possibility of converting thermal energy into mechanical work by a cyclic process is examined, for an ideal fiber, on the basis of the contraction taking place under a predetermined axial stress at the corresponding temperature, and a subsequent elongation occurring at lower temperatures, under an axial stress which is either zero or lower than the previous one. A theoretical study is made of a possible thermodynamic cycle, and the resulting efficiency is calculated.
Thermodynamic Examination of the Polymorphic Transition of Trans-1,4-Polybutadiene. II. Experimental
Authors: Natta G. , Pegoraro M. , Szilágyi L. 
Published: February 2011

Abstract
Using actual fibers of trans-1,4-polybutadiene of high steric purity, it is possible to realize a thermodynamic cycle of the type described in Part I, and to measure the mechanical work obtainable. Reasons are indicated for the principal differences between cycles conducted with actual fibers and cycles calculated for ideal fibers. The lower efficiency of real cycles is also explained. A simple laboratory apparatus is illustrated which demonstrates the practical possibility of transforming thermal energy into mechanical work in this manner.
Infrared Spectra of Reaction Products of Natural Rubber with Alkylphenol Formaldehyde Resins
Authors: Nikitin Yu N. , Epshtein V. G. , Polyak M. A. 
Published: February 2011

Abstract
Infrared spectroscopic studies were carried out with reaction products of natural rubber with 101K tertiary butylphenol-formaldehyde resin without activators and in the presence of stannous chloride dihydrate and zinc oxide. No reduction was observed in unsaturated rubber content during reaction with resin. Reaction of resin with rubber probably takes place at the α-carbon atom and not at the double bonds. A reduction in the proportion of resin phenol hydroxyl is basically due to its participation in recombination reactions of radicals formed during breakdown of ether bridges of resin. At 150° C activators accelerate decomposition of resin ether bridges, but increase the stability of phenol hydroxyl. In the case of zinc oxide, phenol hydroxyl is sufficiently resistant even at 180° C.
Thin-Layer Chromatographic Method to Distinguish Natural Rubber and Synthetic Polyisoprene
Authors: Davies J. R. 
Published: February 2011

Abstract
With advent of increasing production of synthetic polyisoprene and subsequent use in commercial vulcanizates, there was an obvious need for a simple, reliable method to distinguish between natural rubber and synthetic polyisoprene, to be used in a research program of the Association. Present analytical methods, e.g., the Weber test, infra red spectroscopy etc., will only identify the polymers as cis-polyisoprene and will not differentiate between natural rubber and synthetic polyisoprene. Several methods have been published which depend on identification of a minor constituent of natural rubber not found in synthetic polyisoprene. Disadvantages of these methods are that they are time-consuming and present some uncertainty when dealing with rubber of unknown origin. Natural rubber contains about 1% w/w of extractable lipid materials consisting of phospholipids, sterols, tocopherols, tocotrienols, carotenes, squalene etc., whereas synthetic polyisoprene will contain only ingredients added during manufacture. A new approach to this problem is based on examination of a solvent extract of the rubber by thin-layer chromatography, in order to characterize and distinguish between the lipid components in natural rubber and additives in synthetic polyisoprene.
Considerations on Structure of Natural Rubber Vulcanizates
Authors: Westlinning H. , Wolff S. 
Published: February 2011

Abstract
Deep insight into the chemistry of vulcanization, its kinetics, and network structures have been provided by the elucidation of reactions of mono and diolefins with sulfur and accelerators, primarily at NRPRA, and the kinetic measurements of transformation of vulcanizing agents with 1,5-polyenes by Scheele and co-workers at the Kautschuk Institute der Technischen Hochschule, Hannover. It is now established that both accelerated and unaccelerated vulcanization of 1,5-polyenes with sulfur begins with formation of polysulfide crosslinks. As sulfur disappearance and formation of polysulfide proceed, secondary reactions participate increasingly. These involve a series of transformations of the crosslinks originally formed. This leads to a continual change in chain length of crosslinks, in their chemical constitution, and in structural features of the polymer. Figure 1 shows schematically the results of sulfur vulcanization. Crosslinks consist of mono, di, or polysulfide structures, depending on vulcanization time and temperature. As polysulfide bonds disappear, the polymer is modified by the appearance of monosulfidic ring structures and conjugated double bonds in the chain. Secondary reactions may change the crosslink density of the vulcanizate. There are three possibilities: shortening of the crosslink chain length can proceed (a) without change in, (b) with decreasing, or (c) with increasing, crosslink density. Which occurs must be determined for each system. For each polymer the density of crosslinking, its chemical structure, and the extent of polymer modification determine physical, chemical, and technological properties of the vulcanizate.
Effect of Temperature on Decay of Radicals Formed during Radiolysis of Solid Rubbers
Authors: Kozlov V. T. 
Published: February 2011

Abstract
Temperature-time curves for radical decay, when radicals formed in rubbers by low-temperature radiolysis (−196° C) are heated, have been studied by the EPR method. Analysis of results shows that radical decay processes begin much below Tg, with simple increase in the amplitude of thermal vibrations. Extent of decay is greater the lower the steric hindrance in the monomer unit, the order of this effect being SKD &gt; SKS &gt; KHK &gt; SKI, NR, SKEP. On the other hand, contribution of the sudden change in the region of Tg in the processes of unfreezing of motion and decay of radicals is greater in rubbers with side chains. Results obtained permit determination of a number of important energy characteristics of the polymers, in particular molecular energy barriers, UT, activation energies for radical decay, ET and energies of thermal motion at which radical decay begins. These results show that the radical decay process at low temperatures begins before movement of macromolecules relative to one another and is dependent on a migration mechanism with very low energy of activation. This process consists in migration of “secondary” ions formed by capture of charges by free radicals. Schemes of radical decay processes involving a combination of reactions between radicals and “secondary” ions of radical origin are suggested.
Abrasion Resistance of Stereoregular Butadiene Rubber Treads as a Function of Tire Operating Conditions
Authors: Evstratov V. F. , Buiko G. N. , Sakhuovskii N. L. , Arenzon N. M. , Karmanova A. I. 
Published: February 2011

Abstract
In operating tires on Group A roads, the abrasion resistance of SKD/SBR and SKD/NR blends is substantially higher than that of SKS-30 ARKM-15. The abrasion index of butadiene rubbers increases with the severity of the test conditions, as in operating on mountain roads, with partial braking and acceleration. In operating tires on Group B and V roads (for example, in quarries), the abrasion index of SKD rubbers, particularly those with high SKD content, decreases considerably as a result of increased chipping and cutting of the tread pattern. In summer, the superiority of BR rubbers over SKS-30 ARKM-15 in abrasion resistance is less apparent than in winter. This is particularly characteristic for SKD/NR blends. For automobile tires of different types and sizes, the selection of composition and properties of treads in which SKD is used should be carried out in such a way as to take into account operating conditions.
Rubber Chemicals from Cyclic Amines. I. Preparation of Dithioamines, Derivatives of Dithiocarbamates and Thiazolethiols, and Related Compounds
Authors: D'Amico John J. , Morita Eiichi , Young Evan J. 
Published: February 2011

Abstract
The synthesis of dithioamines, derivatives of dithiocarbamates and thiazolethiols and related compounds derived from cyclic amines is reported. Novel or alternate methods for the preparation of 2-benzothiazolyl disubstituted dithiocarbamates and 2-(iminodithio)-benzothiazoles along with their possible mechanisms are discussed.
Rubber Chemicals from Cyclic Amines. III. Iminocarbodithioates as Accelerators and Curing Agents
Authors: Mortia Eiichi , D'Amico John J. , Young Evan J. 
Published: February 2011

Abstract
Evaluations of cyclic iminocarbodithioates as accelerators and vulcanizing agents are described. The starting amines include morpholine and 3-azabicyclo-[3.2.2]nonane and vary in ring size from tetra- to octamethylenimine. The chemical structure of these compounds is correlated with their cure characteristics and the kinetics of vulcanization. Basicity and ring size of the amine moiety govern the activity of the iminocarbodithioates.
Rubber Abrasion Test with Paper Tape
Authors: Bassi A. C. 
Published: February 2011

Abstract
The hypothesis of oxidative and fatigue abrasion phenomena as the major cause of tire tread wear in normal operation has led to development of a laboratory test machine for which low severity, obtained by using paper tape as abrading material, and full temperature control are outstanding characteristics. Good uniformity and reproducibility of abrasion are obtained if proper care is taken. Proof of the basic theory and of its applicability to such a machine has been obtained through a survey of the effects of antioxidants in compounds and of test temperature variation. Application of this test method to tire tread compounds has given fair results here it has been possible to establish testing conditions sufficiently related to those in road tests. When these latter include a large range of severities, comparisons are less favorable and further study is being made to try to accommodate such cases.
High Speed Tensile Testing of Tire Textiles
Authors: O'Neil K. B. , Dague M. F. , Kimmel J. E. 
Published: February 2011

Abstract
Techniques for testing tire-reinforcing materials in the laboratory under simulated operating conditions of high speed and high temperature are presented. The effects of these conditions on breaking strength and breaking energy of rayon, nylon, polyester, and fiber glass are compared. The tests include an individual cord impact test, and three dynamic tire tests using a pendulum, a ballistic plunger, and a resiliometer bruise. The value of each test is weighed against test results obtained from conventional testing methods and tire field performance based on vehicle fleet testing. A comparison is shown between the conventional slow speed tests, high speed tests and vehicle tests and shows that the high speed laboratory tests give a better correlation with tire bruise failures.
Impact Resistance of Automobile Tires
Authors: Lothrop E. W. 
Published: February 2011

Abstract
The construction and operation of a high speed plunger test machine to determine the impact energy required to produce failure of automobile tires are described. The equipment has been designed to operate over an energy range of 1500 to 15,000 in. lb at preselected velocities between 40 and 100 mph and at preselected temperatures between 75 and 300° F. These ranges are adequate to permit the testing of passenger tires over a range of conditions simulating those encountered in high speed driving. The test machine consists of a pneumatic gun for propelling the plunger at an inflated tire, mounted in a temperature controlled cabinet, and photoelectric devices for measuring plunger velocity. In a test the kinetic energy of the plunger is increased in increments, until failure occurs. The minimum kinetic energy required to cause failure of the tire fabric is taken as a measure of the carcass breaking energy. Data on rayon and nylon cord tires indicate that the breaking energy of a tire is dependent on both speed and temperature and that the relationship between energy, speed, and temperature depends on the cord-reinforcing material in the tire. As a result it is impossible to predict the relative impact resistance of tires under use conditions on the basis of laboratory test results obtained with the standard static plunger test, in which the plunger penetrates the tire at 2 in./min at room temperature.
Tire to Wet Road Friction at High Speeds
Authors: Allbert B. J. , Walker J. C. 
Published: February 2011

Abstract
The general problem of loss of tire grip on wet road surfaces is discussed. The initial section of the paper covers a description of testing techniques employed for the investigations reported. These include both road and indoor rig techniques developed to study limiting tire braking and cornering properties under a wide range of operating conditions. The level of friction between a tire and a wet road is primarily related to the ability to remove a water film from the ground contact area. The contact area is considered to be separated into three effective zones. Initially the ‘bulk’ of the film is displaced leaving a thin residual film to be penetrated at, or absorbed from, the interface before substantially dry contact can be established. The size of this dry area, at the rear of the contact zone, has an overriding control on the level of available friction and depends on the time occupied in displacing the water film in the frontal zones. An increase in the peripheral speed of the tire reduces the time available for water displacement and effectively shortens the area of actual ground contact. In the limiting condition the vertical load on the tire becomes entirely supported on the water film and the condition of aquaplaning exists. The requirements for this condition to occur are briefly discussed. Tread pattern and road surface design are shown to exert a considerable influence on the rate of water displacement from the contact area and hence on the relative sizes of the water supported zones. The forces developed in the dry zone at the rear of the ground contact depend on the frictional characteristics of the tread material. A section of the paper considers the wide scale effects of tread pattern, tread material, and road surface characteristics and discusses the nature of the interactions between these three variables. Some results of recent studies related to different types of tread pattern, specific pattern design features, and the effect of tire casing construction are included and future potential development of the tire contribution is reviewed.
Lubricated Friction of Rubber. I. Introduction
Authors: Bevilacqua E. M. , Percarpio E. P. 
Published: February 2011

Abstract
This review introduces a series of reports on a quantitative study of friction of rubber on wet surfaces. It was derived from concern over safety aspects of skidding on wet roads; this first paper deals with the relation between safety and traction. Subsequent papers deal with: A quantitative approach to characterization of road surfaces, identification of the surface features of importance, and estimation of their relative contributions to lubricated friction. Quantitative estimates of effects of properties of rubber materials on lubricated friction and an analysis of their relative importance in interaction with the significant features of the road surface. A quantitative basis for evaluation of wet skid resistance of roads, the choice of the rubber to be used in this evaluation, and methods of testing. An improved technique to measure the property of tread rubber important for wet skid resistance of tires. Identification and interpretation of the nature of friction on ice at low temperatures.
Lubricated Friction of Rubber. III. Components of Friction in Mating Surfaces
Authors: Percarpio E. P. , Bevilacqua E. M. 
Published: February 2011

Abstract
Friction is usually discussed in terms of contributions from two processes: deformation and adhesion. This terminology has been retained in discussions of lubricated friction of rubber although there is not apparent any clear mechanism by which adhesion might occur. Our study of wet friction leads us to suggest that the components making up frictional resistance to sliding might more appropriately be referred to as deformation and abrasive components. On this basis, there is an obvious mechanism for both processes, and some of the disagreements about interpretation of certain experimental results may be resolved. The basis for our interpretation is implicit in the literature but was originally expressed somewhat tentatively and has not been restated in recent discussions. Greenwood and Tabor pointed out that hysteretic losses make an important contribution to friction of rubber sliding on a lubricated surface and that this contribution is independent of asperity size or distribution so long as only the asperities support the load and the radius of curvature at the asperity tip is above a critical limit which is remarkably low. Further, the experiments of Sabey showed that it was difficult to obtain coefficients higher than 0.4 with spherical sliders. Mean average local pressures high enough to give high friction coefficients could be obtained only with sharp asperities. In the laboratory experiment these were cones. Greenwood and Tabor found that with these damage to the rubber becomes visible at just the semiangle at which the coefficient began to rise abruptly (Figure 1). It is entirely reasonable to call the process causing this damage abrasive friction.