bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lubricated Friction of Rubber. VI. Portable Rebound Tester, with Particular Application to Wet Skid Resistance of Tires
Authors: Percarpio E. P. , Bevilacqua E. M. 
Published: February 2011

Abstract
An important conclusion from Part V of this series is that the wet skid resistance of a tire tread rubber is almost completely determined by its resilience and hardness, resilience being the more important variable. A useful feature of this relation is that both measurements are nondestructive and can be made, in principle, on a finished tire. Hardness is easily measured with commercially available instruments, such as the Shore Durometer, but a comparably useful instrument, one portable and suitable for use to measure resilience of finished and mounted tires, was not available. We have made and used such an instrument and have found additionally that it has features which make it useful for other purposes, notably measurement of resilience of very thin rubber specimens.
Measurement of Rolling and Sliding Friction Coefficients of Tread Compounds
Authors: Clamroth E. , Heidemann W. 
Published: February 2011

Abstract
We have described two methods to measure friction forces arising from sliding and rolling on a wet surface. In rolling friction we showed that energy of deformation of a braked rubber specimen could be estimated and separated from friction energy. Rolling friction shows a characteristic slip dependence for various compounds. The rise at low slip values can be quantitatively explained. Especially with polybutadiene vulcanizates, at higher slips the friction coefficient decreases; this is attributable to thickness of the water layer between specimen and friction surface and depends on ease of wetting with water. Wetting can be altered by addition of a wetting agent like Pril, and measured by the contact angle of a water drop on the rubber surface. In wet friction, the changes in the water layer outweigh the temperature and velocity dependent shifts expected for adhesion and deformation friction components. A sort of mixed friction occurs on wet surfaces. The true contact surface, that is, surface not covered with water, has a strong effect on the magnitude of friction forces. In general only the highest asperities of the friction surface extend above the water and are in direct contact with the rubber surface. It is therefore understandable that surface asperity has a strong effect on friction coefficients. Finally we have compared friction coefficients determined with our apparatus with those obtained using the Portable Skid Resistance Tester and with results of road tests. The Portable Skid Resistance Tester provides a single point method, which has good reproducibility and whose results correlate well with those on the road at a speed of about 48 km/hr. Our apparatus has the advantage that test conditions such as velocity, temperature, and load can be widely varied. In this way, various actual driving conditions can be approximated and one may seek to determine the mechanism of friction from dependence of friction coefficients on these parameters.
Calculated Deflected Contours and Load-Deflection Curves for Tires
Authors: Gehman S. D. 
Published: February 2011

Abstract
The tire contour equation is derived for a flexible tire body with radial cords and a complete circumferential deflection, corresponding to the case of a radial-ply tire or a tire inflated inside a constraining cylinder. Equations are derived to calculate the load on a single cord in the deflected region using parameters of the un-deflected contour. It is then shown how the reasoning and equations can be generalized for a tire body with any cord path having a complete circumferential deflection so that the load-deflection curve for a single cord can be calculated. A new approximation method is described so that the integrals involved in these calculations can be evaluated in terms of incomplete elliptic integrals of the first and second kind with any desired accuracy. Finally, a procedure is given for summing cord loads in the usual spot deflection of a tire so that the load-deflection curve for a flexible tire body can be calculated from contour parameters of the undeflected tire. An illustrative calculation is included. Although the load-deflection curve for a single cord is convex toward the load axis, that for the tire is concave because more cords are involved as deflection progresses. A calculated contour does not exist beyond a limiting deflection, at which, presumably, buckling starts above the bead.
Recent Advances in Glass Transitions in Polymers
Authors: Eisenberg A. , Shen M. 
Published: February 2011

Abstract
Since the publication of our review “Glass Transition in Polymers” in 1966, a number of interesting advances have been made in this field. The present article is intended to be an addendum to this review, reporting the progress that has been made by various workers during the past three years. In addition, a number of topics were not covered in the previous article due to the relatively incomplete understanding at that time. These will now be discussed. This is not because these topics are at present fully understood. Rather, we hope it will serve as a progress report to stimulate further interest in areas where further work is needed. The numbering systems and notations in this paper will follow those in the previous article for the sake of continuity.
Theory of Adhesion, Mechanism of Bond Failure, and Mechanism for Bond Improvement
Authors: DeLollis N. J. 
Published: February 2011

Abstract
The various theories of adhesion are discussed, with mention of some aspects that are inconsistent with recent bonding developments. A mechanism for adhesive failure is proposed on the basis of thermodynamics and experimental phenomena. Surface treatments are described which significantly improve adhesion and which suggest that chemical bonds are necessary to achieve the ultimate in bond durability.
Internal Energy Contribution to the Elasticity of Natural Rubber
Authors: Shen Mitchel 
Published: February 2011

Abstract
It has recently been noted by a number of workers that the relative energy contribution, fe/f, to the elastic stress of rubberlike materials appears to depend on the extension ratio at which thermoelastic measurements were carried out. This apparent strain dependence is in contradiction to the free energy additivity principle of the statistical theory of rubber elasticity. In this paper we resolve this problem by determining fe/f from the temperature coefficient of shear moduli. The shear moduli were not directly determined from measurements of shear, but calculated from tensile elongation data. This method circumvents the difficulty encountered in directly obtaining the relative energy contribution from stress—temperature data. Both constant length and constant stress thermoelastic measurements were used to obtain fe/f. A series of natural rubber samples, crosslinked in the presence of various amounts of n-hexadecane, were investigated. It is found that the relative energy contribution to the elasticity of natural rubber is 0.18. Changes in inter-molecular interactions, brought about by the incorporation of diluents, produce no variation in the value of fe/f. This observation supports the hypothesis that the energetic stress in rubber elasticity is wholly attributable to intrachain energies of the network chains.
Large Elastic Deformations of Some Cord-Reinforcedrubber Shells
Authors: Charrier J. M. 
Published: February 2011

Abstract
A simple theoretical treatment of certain large elastic deformations of a symmetrical network of cords embedded in rubber is explained. The calculations are based on the main assumptions of thin, inextensible and incompressible cords and a rubber behaving like a Neo-Hookean solid. This model, although simple, respects the physical characteristics of certain cord reinforced components which would be designed for large deformations. Calculations for the simple extension of the composite material, the two-dimensional extension and its application to the inflation of tubes, are compared to experiments with reasonable success. Theoretical predictions are made for related problems of the behavior of tubes in contact with plates.
The Raman Spectra of Polybutadiene Rubbers
Authors: Cornell S. W. , Koenig J. L. 
Published: February 2011

Abstract
The Raman spectra of cis-1,4-, trans-1,4-, and 1,2-polybutadiene are presented. Analysis of the spectra of these model compounds, and the normal coordinate results, enable the Raman frequencies to be classified by configurational structure type. The Raman carbon—carbon double bond stretching vibrations can be used to describe uniquely the structure content in polybutadienes.
Studies in the Morphology and Vulcanization of Gum Rubber Blends
Authors: Gardiner J. Brooke 
Published: February 2011

Abstract
The solvent extraction of 1 mil films of cured gum rubber blends is an attractive semi-quantitative method for determining the extent of cure. Material balance and ir analysis give a good picture of which rubber is curing. Indirect evidence from this method indicates that massive curative diffusion is occurring from one zone to another. A theory based on curative diffusion, before or during cure, and different cure rates and curative solubility in the rubbers appears to explain most of the results. The importance of zinc oxide and stearic acid in addition to a sulfur cure for an NR/chlorobutyl blend cure has been established. Different cure packages can give considerably different results in overall cure. Some indication of a phase inversion in an NR/chlorobutyl system has been found.
Chemical Structures in CIS-1, 4-Polybutadiene Vulcanizates. Model Compound Approach
Authors: Gregg E. C. , Katrenick S. E. 
Published: February 2011

Abstract
We studied the vulcanization reaction of one curing recipe for cis-1,4-polybutadiene (CB). The curing recipe was zinc oxide (ZnO), diphenylguanidine (DPG), 2,2′-bis(benzothiazolyl) disulfide (MBTS), and sulfur and it produced only polysulfidic crosslinks. Devulcanization of this CB vulcanizate by phenyllithium solution permitted a comparison of the molecular weight of the CB before and after vulcanization. A small but measurable reduction of the molecular weight of the rubber occurred as a result of the vulcanization reaction. Reaction of the curing recipe in cis, cis-1,5-cyclooctadiene (COD) permitted the study of the fate of the curing chemicals in the vulcanizate because COD is an accurate chemical model for CB. This study showed that: 1. The vulcanization reaction consumes none of the DPG and none of the ZnO. 2. An insoluble coating forms on the ZnO and separates it from the vulcanization reaction during at least part of the reaction. 3. All of the MBTS reacts to form one compound: an S-alkyl derivative of 2-mercaptobenzothiazole attached to the rubber molecule at a point next to a thiacyclohexene ring. 4. All the sulfur reacts to form crosslinks and intramolecular rings. The rings are three-, five-, and six-membered thiacycloalkanes and five- and six-membered thiacycloalkenes. Some of the rings are isolated and some are next to crosslinks. 5. The three-membered rings are episulfide and they are very likely the key intermediate to the formation of the cyclic and crosslink structures. 6. The crosslinks are polysulfidic and occur singly and as clusters of two and four. The more crosslinks in a cluster, the less unsaturation in its vicinity. The four-link cluster has no unsaturation and occurs as two pairs with thiacyclopentane rings between. The sum of the single crosslinks and clusters of crosslinks in the model network agrees with the number of elastically effective chemical crosslinks found in the CB vulcanizate as measured by swelling in benzene. The elastically effective chemical crosslinks in the vulcanizate were calculated by the Flory-Rehner equation and the Moore-Watson calibration curve. This agreement proves that the theory of rubber elasticity in the form of the Flory-Rehner equation and the Moore-Watson calibration curve may be used to count the number of elastically effective chemical crosslinks in a sulfur vulcanizate. Three new chemical compounds and a new method for quantitatively titrating mercaptans are disclosed. The success of this technique recommends it for further study of sulfur vulcanization by other recipes and the study of other vulcanizate changes.
Pendent Accelerator Groups in Rubber Vulcanizates
Authors: Parks C. R. , Parker D. K. , Chapman D. A. , Cox W. L. 
Published: February 2011

Abstract
A rapid build-up of pendent accelerator groups in the initial stages of vulcanization of natural rubber has shown that they are the precursors to the formation of crosslinks. Larger amounts of attached accelerator fragments were found for efficient and so-called sulfurless systems than for conventional accelerator-sulfur systems especially at short cure times. Cleavage of disulfides and polysulfides in the pendent groups by hexanethiol in piperidine showed a build-up of di- and polysulfides in the initial stages corresponding to that of accelerator fragments. Analyses were made by liquid scintillation counting using 14C-labeled accelerators. Due to the necessity of using liquid samples, vulcanizates were degraded in xylene solution with tert butyl hydroperoxide using osmium tetroxide as a catalyst. The use of a dual vulcanization system of dicumyl peroxide followed by the addition of sulfur and labeled accelerator by swelling techniques made possible the determination of accelerator fragments at short cure times when their concentration was the greatest. Polysulfides were found to have a profound and detrimental effect on the hardening of SBR during accelerated aging in air. An increase in attached accelerator fragments was found to take place during aging which may contribute to additional crosslinking and hardening.
Relationships between the Structures of Natural Rubber Vulcanizates and Their Thermal and Oxidative Aging
Authors: Blackman E. J. , McCall E. B. 
Published: February 2011

Abstract
Accelerated sulfur NR vulcanizate networks are known to contain poly-, di- and monosulfidic crosslinks, sulfur-containing main chain modifications including cyclic sulfides and pendent accelerator groups, and extra-network material, primarily vulcanization residues. Both oxidative and non-oxidative aging characteristics of the vulcanizate can be improved by use of an efficient or EV curing system. These systems utilize either a high accelerator to sulfur ratio or an accelerator in conjunction with a sulfur release agent to insert predominantly mono- and disulfidic crosslinks, and produce a minimum of main chain modifications. The resulting vulcanizates have excellent aging properties, but fatigue life is poor in comparison to that of a conventional vulcanizate. With a compromise between the conventional and EV curing systems, namely use of intermediate accelerator to sulfur ratios or mixtures of sulfur and sulfur donor, vulcanizates with good fatigue properties and improved aging characteristics can be obtained. Since the most obvious difference between EV and conventional vulcanizate networks is the per cent of monosulfidic crosslinks, it has been assumed that monosulfide crosslinks are responsible for the poor fatigue resistance of EV systems. Recently, it was found that a zinc dimethyldithiocarbamate (ZDC) EV system gave an NR gum vulcanizate having fatigue resistance equal to that of a conventional sulfenamide accelerated compound. The main features of the network are a high percentage of monosulfide crosslinks and extensive main chain modification. In this paper, the aging and fatigue behavior of black filled substituted phenylenediamine protected NR ZDC accelerated systems is examined. The ZDC EV vulcanizate has imaged fatigue resistance equal to that of a conventional sulfenamide accelerated vulcanizate, but oxidative aging is very poor. By decreasing the ZDC/sulfur ratio, a vulcanizate structure equivalent in every measurable way to that of a conventional sulfenamide accelerated system is obtained. Unaged fatigue properties of the two compounds are similar. However, oxidative aging resistance of the ZDC compound is again very poor, and fatigue life of an air aged specimen is virtually zero. It is concluded that fatigue life is not necessarily a function of the crosslink type distribution. Accelerator residues and possibly main chain modifications play an important role insofar as oxidative and non-oxidative aging characteristics are concerned.
Complex Stress Relaxation in Rubber
Authors: Williams J. G. , Major T. J. 
Published: February 2011

Abstract
Rubber is frequently employed in engineering in states of complex stress where stress relaxation is an important factor. The mathematical analysis of the strain systems involved can be accomplished by numerical methods, and this is illustrated with a thick-walled cylinder problem. Data from simple tension and pure shear tests are used to predict the relaxation behavior of a cylinder in which the internal diameter is increased.
Modified Equations of Rubber Elasticity Applied to the Inflation Mechanics of a Thick-Walled Rubber Cylinder
Authors: Skala D. P. 
Published: February 2011

Abstract
The mechanics of the inflation of a thick-walled, gum rubber cylinder are predicted on the basis of the Neo-Hookean and Mooney theories of rubber elasticity. These predictions are compared to experimental results for two rubber cylinders of different geometries. The Mooney theory predicts pressures that are too high while the Neo-Hookean theory predicts pressures that are too low. Moreover, the Mooney theory fails to predict the observed instability (bulge of the tube). Data from the literature is used to show that gum rubber has different elastic properties in tension than in compression. This difference is allowed for in a modified description of rubber elasticity. The modified theory is then used to predict the mechanics of inflating thick-walled, rubber tubes. Agreement with experimental results is good.
Load-Compression Behavior of Flexible Foams
Authors: Rusch K. C. 
Published: February 2011

Abstract
The load-compression behavior of a foam reflects its geometric structure and the physical properties of the matrix polymer. Quantitative relations between these parameters have been established in the present study. Based on both theoretical analyses and experimental data obtained on a flexible polyurethane foam, it is shown that the compressive stress can be factored into the product of two terms: (1) a dimensionless function of the compressive strain, ψ(ε), calculated from experimental load-compression data and reflecting the buckling of the foam matrix; and (2) a factor, εEƒ, where Eƒ is the apparent Young's modulus of the foam (which is a function primarily of the modulus of the base polymer E0 and of the volume fraction of polymer, φ). Thus the compressive stress behavior of a foamed polymer is determined by E0, φ, and the matrix geometry, the latter described by the function ψ(ε). Using these established relations, it now is possible to delineate precisely the structural features a foam must possess—density, cell shape and size distribution, and modulus of the base polymer—to meet a given load-compression specification.
Thermodynamic Properties of Rubber Vulcanizates Based on Ethylene-Propylene Copolymers
Authors: Flisi U. , Crespi G. , Valvassori A. 
Published: February 2011

Abstract
The study of the stress-temperature curves of ethylene-propylene copolymers having different compositions revealed that ethylene-rich samples crystallize under stretching at room temperature. The results obtained suggest that crystallization is probably the outcome of two phenomena: orientation of the microcrystallites, undetectable by x-ray analysis, and true crystallization under stretching. These phenomena are accompanied by strong negative variations of internal energy; these variations, when occurring at low stretching ratios, cannot be distinguished from the variations of conformational internal energy. Therefore, when calculating the ratio ƒE/ƒ in samples containing equimolecular amounts of the two monomers, and even more in the ethylene-rich ones, at room temperature, the values may be affected by uncertainty due to the occurrence of crystallization. The calculation of ƒE/ƒ at high temperature, where the rubbery network follows Equation (2) perfectly, even in ethylene-rich samples, shows that this ratio is always negative and depends on the stretching ratio α, for any composition.
Degradation of Highly Elastic Polymers. VI. The Intermittent Chemo-Stress Relaxation of Crosslinked 1,5-Polyenes
Authors: Hillmer K.-H. , Scheele W. 
Published: February 2011

Abstract
Measurements of the continuous stress relaxation of thiuram vulcanizates and intermittent stress relaxation of both sulfur and C—C crosslinked vulcanizates of natural rubber were discussed. These measurements were made in the presence of either oxygen or nitrogen at various temperatures both with and without sample pretreatment. The following conclusions were drawn: 1. Determination of the rate of continuous tension loss is not suitable for measuring the oxidative degradation of vulcanizates from 1,5 polyenes according to a stress relaxation method. The reason for this is that rheological processes superimpose themselves on the chemical reactions initiated by oxygen, cause a reduction in tension, and affect both the form of the relaxation curve and also the rate of tension loss. This is particularly noticeable in the case of vulcanizates containing polysulfide bonds. 2. It was possible, using intermittent stress relaxation and by choosing suitable temperatures and frequencies, to eliminate the influence of rheological processes and thus to measure only the rate of tension loss due to oxidative degradation.
A Study on Heat History of Organic Accelerators in Rubber Stock (BR Base)
Authors: Imase I. 
Published: February 2011

Abstract
Rubber with some exceptions must generally undergo such processes as mastication, mixing, warming-up, extrusion, spreading, calendering, etc. prior to vulcanization under heat to obtain cured articles. Consequently the rubber matrix receives a heat history caused by mechanical frictional heat or the heat which cannot be avoided during these processes. On the other hand, when an uncured rubber compound, ready for vulcanization, containing such curing agents as sulfur, such activators as zinc oxide, and organic accelerators is heated during the processes or during storage between individual processes, each incremental effect of heat is accumulated with time. It is a well-known fact that this accumulation of heat can lead to the trouble of scorching, etc. As a cause for the trouble, organic accelerators seem to play the most important role. A few reports have been published on the action of accelerators under heat, but, to my knowledge, no report is available on the behavior of accelerators in rubber stocks, namely, on the change of the properties of uncured rubber compounds and on its influence on the properties of vulcanizates. This paper shall report these problems, though it describes only the results of the tests carried out under specific conditions.
Stress-Induced Birefringence of Swollen Polymer Networks
Authors: Gent A. N. 
Published: February 2011

Abstract
Stress-optical coefficients have been determined for lightly crosslinked samples of cis- and trans-polyisoprene, swollen to a high degree in a variety of nonpolar solvents. A strong dependence on the geometrical asymmetry of the solvent molecule has been observed. Solvents with long, straight molecules gave large values of the stress-optical coefficient whereas those with compact, symmetrical molecules gave minimum values. This effect is attributed to short-range orientational order, due to packing effects in a molecularly anisotropic medium. The large values obtained for unswollen polymers correspond to those in relatively anisotropic solvents, and thus indicate a significant degree of local order in the bulk phase. The minimum values are interpreted, using calculated optical anisotropies of chain repeat units, as measures of the stiffness of isolated chains.