bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Fatigue Process of Rubber Vulcanizates
Authors: Hirakawa H. , Urano F. , Kida M. 
Published: February 2011

Abstract
The relationship between energy-input and hysteresis energy-loss during repeated deformation was analyzed, with gum and filled-rubber vuloanizates. It was recognized that the hysteresis energy-loss decreases more quickly with repeated deformation than the energy-input does. After a number of cycles both the energy-input and the energy-loss approach constant values. When these values are plotted against strain, curves similar in shape are obtained, regardless of the type of rubber. This is because the network chain is well relaxed. A group of the linear relationships between log W and log H was found with respect to N and λ. Examining the parameters, g1, g2, f1 and f2 as functions of N and λ, simple expressions, (4) and (5), were obtained for both the first deformation and after many cycles. At the latter state the hysteresis ratio tends to be constant in the wide range of λ. Finally, the relation between W and H at fatigue break is expressed with the same form of equation proposed by Grosch for the tensile break at the first extension.
Effect of Strain-Induced Crystallization on the Elastomeric Properties of Cis-1,4-Polybutadiene Networks
Authors: Su T-K. , Mark J. E. 
Published: February 2011

Abstract
Polymer networks, when studied at very high elongations, frequency show anomalous stress-strain isotherms in that they exhibit values of the modulus or “reduced force” [ƒ*] which increase markedly with increasing elongation. Such isotherms depart appreciably from the form predicted by the molecular theories of rubberlike elasticity and from the Mooney—Rivlin representation adopted from phenomenological arguments as well. For this reason, the interpretation of the increase in [ƒ*] at high elongations has been of great interest for a considerable period of time. For several decades now, this behavior has generally been attributed to the limited extensibility of the network chains. Critical examination of various published results pertinent to this question, in conjunction with more definitive experimental studies reported recently, however, support the alternative suggestion that such atypical isotherms are due to strain-induced crystallization. One experiment particularly relevant to this issue is the study of the stress-strain isotherms of a polymer network as a function of temperature. Such experiments have been carried out on natural rubber, but the relatively poor thermal stability of this polymer and the extent to which its melting point is increased by elongation make it essentially impossible to study the high elongation stress-strain relationships for this polymer at a temperature sufficiently high to ensure complete suppression of strain-induced crystallinity. Similar experiments carried out on networks of a more suitable polymer, polyisobutylene, gave stress-strain isotherms showing the upturn in the reduced force at low temperature, but not at higher temperatures, thus strongly implicating strain-induced crystallization as the origin of this anomalous behavior. These experiments, however, suffered somewhat from the one shortcoming that the increase in temperature required to suppress the upturn in [ƒ*] also decreased the maximum extensibility of the network to below the elongation at which the upturn occurred at the lower temperatures.
Non-Newtonian Flow of Polymer Solutions
Authors: Patat F. , Spott G. 
Published: February 2011

Abstract
Non-Newtonian flow of solutions of polyisobutylene, poly (vinyl acetate), poly (ethylene glycol), and polyisoprene was investigated, as a function of molecular weight, concentration, temperature, and solvent, with a modified rotational viscometer with coaxial cylinders and a newly-developed, high-pressure, capillary viscometer. Analysis of the results of the viscosity experiments was based upon kinematic flow theory, and provided a consistent interpretation of the non-Newtonian flow behavior encountered. Shape of the flow curve is determined by the decreasing degree of association of the polymers with increasing shear stress. Rise in viscosity of the polymer solutions, as compared to that of the solvent, is due chiefly to solvent associated polymer interactions at each stress state involved.
Strain-Dependent Properties of Polymers I
Authors: Warnaka G. E. , Miller H. T. 
Published: February 2011

Abstract
Dynamic elastic moduli of homogeneous, amorphous polymers decrease at moderate to high strains. Under the same strain magnitudes the loss factor goes through a broad maximum. At low strains, dynamic properties are independent of strain amplitude. This paper shows that strain dependence is a basic property of homogeneous, amorphous polymers. Strain dependence is shown to occur in gum, as well as filled, vulcanizates. In addition it is shown that self heating due to flexing at high strains cannot fully explain strain dependent dynamic properties. Testing has been performed on specimens with greatly varying geometries (and, hence, different amounts of self-heating) and at controlled specimen temperatures. These tests have verified the existence of a basic strain-dependency. Strain dependence is here related to time-temperature dependent properties of polymers as described by the well-known work of Williams, Landel, and Ferry. The magnitude of strain dependence and the strain amplitudes at which strain dependence occurs appear to be controlled by the time-temperature dependence of polymers.
Strain-Dependent Properties of Polymers II
Authors: Miller H. T. , Warnaka G. E. 
Published: February 2011

Abstract
Work is described to relate strain-dependent properties of polymers to time-temperature dependency. Methods for graphically shifting frequency-strain properties are shown. The paper also shows the development of frequency-strain equations similar to the well-known WLF equation. This type of equation has been written for many types of polymeric materials with excellent correlation with measured values. Correlation with experimental data for a number of polymers is shown. Relationships between temperature and strain have similarly been developed. These relationships are also illustrated and compared with experiment. Finally, the generalized frequency-temperature-strain dependence of the dynamic mechanical properties of homogeneous, amorphous polymers is discussed.
Stress Optical Behavior of Rubber Networks at Large Deformations
Authors: Smith K. J. , Puett D. 
Published: February 2011

Abstract
The birefringence of natural rubber networks at large deformations has been investigated experimentally and compared with the simultaneously determined stress—strain behavior. Our data is analyzed using a statistical theory of flexibly jointed chains, derived herein, which is believed to be more significant for the particular range of deformation used than the theories of Treloar and of Kuhn and Grün. In addition, the experimental data of Saunders is commented on in light of our theoretical development. We find that for network extensions exceeding those of the Gaussian region there is little correlation between the observed and theoretical behavior of the stress and birefringence (based upon the theory of flexibly jointed chains) and this lack of agreement is attributed to the fact that the statistical parameters needed for the description of the optical chain properties differ in magnitude from those required for the mechanical properties. Furthermore, by considering the points of incipient crystallization the strain behavior of the stress-optical coefficient is highly indicative of nonGaussian behavior rather than crystallization, and therefore yields strong support for the position that nonGaussian behavior does exist in rubber networks.
Diffusion in Amorphous Polymers
Authors: Paul D. R. , DiBenedetto A. T. 
Published: February 2011

Abstract
Diffusion and solubility coefficients are presented for He, Ne, Ar, and N2 in three ethylene propylene copolymers, two styrene butadiene copolymers and a cis-polybutadiene at five temperatures in the range 0–50° C. The data were obtained by using a slightly modified Dow Gas Transmission Cell and analyzed by a new modified time lag technique which properly accounts for the increase in pressure on the downstream side of the cell. Activation energies were calculated for the twenty-four diffusion systems and correlated with polymer intermolecular forces and gas molecule sizes by using a cell theory for amorphous polymers which employs a potential energy depth parameter, ε*, a range parameter, ρ*, the number of degrees of freedom per structural unit (center), 3Cm, and the number of centers per unit cell, n. The first three parameters were evaluated from thermodynamic data, while n was evaluated from the diffusion data. It is believed that n is an indication of the number of backbone carbon atoms active in polymer segmental motion. The values obtained here (5–9) agree well with existing values estimated from polymer viscous flow data. A correlation for the solubility data is shown and a linear free energy relationship is discussed.
Characterization of Block and Random Ethylene Propylene Copolymers by Differential Thermal Analysis
Authors: Barrall Edward M. , Porter Roger S. , Johnson Julian F. 
Published: February 2011

Abstract
DTA furnishes a reliable method for the analysis of physical mixtures and for multisegment and bisegment block copolymers of ethylene and propylene in cases where chain randomness is minor. If a secondary method of analysis which is independent of crystallinity is possible, e.g., use of C14-tagged samples, the DTA method can aid in elucidating the chain structure, including degree of copolymer randomness. Block copolymers and physical mixtures have been found to have thermograms with endothermal minima at approximately 138 and 163° C. The ratio of heights of the two minima has been found to be a function of the ethylene and propylene content for mixtures of homopolymers and for block copolymers without randomnness. Cooling thermograms of block copolymers have been demonstrated to have two exotherms in all cases where the block ethylene content exceeded 10 per cent; the propylene limit was not fixed. Mixed homopolymers do not exhibit two freezing exotherms. The total heat of fusion of the polymer has been found to be a usable measure of chain randomness and block nature. Conditions for observation of single and multiple transitions have been extended. The following conclusions can be drawn from Table I. Multisegment block copolymers are characterized by heats of fusion almost equal to or lower than corresponding physical mixtures. Bisegment block copolymers have heats of fusion equivalent to physical mixtures within experimental error. Cooling curves definitely indicate that samples 3–6 and 3–13 are block copolymers according to Ke's criterion of double exotherms. Sample 3–3 may be inferred to have a large amount of randomness between blocks from its low heat of fusion, which is comparable to that of polymers with known randomness. Samples 3–35 and 3–40 are both block copolymers by the double freezing point technique. The block copolymer identification and the high heat of fusion (almost as large as a comparable physical mixture) indicate long block length and only a few blocks. Very little randomness is present (compare data of Figure 2). Low heats of fusion consistent with short block segments in sequential arrangement are noted for samples 3–30 and 3–31. No confirmation of the block nature can be obtained from freezing point data due to low ethylene content. The displacement from curve in Figure 2 indicates noncrystalline segments in the chain. Multisegment block copolymers are identified from heat of fusion data and freezing point thermograms; note samples 3–32, 3–33, and 3–34. The location of the peak height ratios in Figure 2 indicates the presence of random copolymer with some crystallinity between blocks in all cases.
Stress Softening in Natural Rubber Vulcanizates III. Carbon Black Filled Vulcanizates
Authors: Harwood J. A. C. , Payne A. R. 
Published: February 2011

Abstract
This paper has confirmed the conclusions of the previous paper that the stress softening (Mullins effect) of a black-loaded vulcanizate is similar in magnitude to the stress softening of a gum rubber if the two vulcanizates are stretched initially to the same stress. The initial stress used in the present work was 180 kg/cm2, which is very near to the breaking stress of these vulcanizates. The similarity of the normalized stress-strain curves for all the vulcanizates, both gum and loaded with 60 phr of different types of black, suggests that the main difference between the stress-strain characteristics of a filled and a pure gum rubber, after the initial stressing cycle, can be accounted for by the strain amplification factor X. The more reinforcing blacks possess the higher X factors, i.e., they stiffen the rubber more than, for example, a fine thermal black. It is concluded that the black is acting mainly in a stiffening capacity due to the hydrodynamic effects of the degenerate carbon black networks. For sulfur crosslinked pure gum vulcanizates, in which the crosslinks are polysulfidic, the stress softening is partly associated with the breakage of polysulfide linkages. These reform in the extended condition and produce a real permanent set, but the major stress softening is attributed to the incomplete recovery of the crosslinked network to its initial random state due to network junctions or similar associations being displaced in a nonaffine way during extension. For example, junctions at the ends of chains which become fully extended at relatively low extensions will be displaced in this way. Thus when the rubber is subsequently strained, the network is already in a preferred disposition.
Recent Studies in the Aging of Natural Rubber
Authors: Bell C. L. M. , Cain M. E. , Elliott D. J. , Saville B. 
Published: February 2011

Abstract
Natural rubber, when properly compounded, produces articles having an unrivalled combination of properties such as strength, elastic modulus, and resilience. However, in common with the properties of all other polymers, these excellent qualities progressively deteriorate on contact with oxygen, especially at elevated temperatures. The increasing demand for elastomers capable of service at even higher temperatures requires more stringent efforts by research workers for the production of aging-resistant natural rubber, and, in general, two approaches are possible. On the one hand further developments may be sought in the efficiency of the protective systems used. This will necessitate a reasonable understanding of the mechanisms of antioxidant action, and recent reviews have shown the large amount of research effort being applied to this end. On the other hand, modification of the present vulcanization methods to give vulcanizates with inherently greater resistance to aging is a possibility, although progress in this direction requires a detailed knowledge of vulcanization mechanism and vulcanizate structure. The recent work of the Vulcanization Group at NRPRA has shed considerable light on both these aspects of natural rubber chemistry and improved the prospects of success in this direction. In this paper we report results of studies carried out in both the fields described above which have led to the development of technologically acceptable vulcanizates having improved aging resistance.
Thermal Stress Relaxation of Vulcanizates of Various Structures
Authors: Tarasova Z. N. , Dogadkin B. A. 
Published: February 2011

Abstract
Heating stressed vulcanizates in the absence of oxygen results in purely thermal degradation of the three dimensional network accompanied by reduction of the stress; this process is called thermal relaxation. Thermal relaxation of various rubbers (natural, polybutadiene, butadiene styrene, isoprene and carboxylated rubber) vulcanized with various vulcanizing mixtures and methods, including vulcanization by irradiation, is first order. The rate constants of thermal stress relaxation decrease with network density. The product of the rate constant and the initial number of crosslinks (q=N·K) which yields the number of bonds broken per unit time, is independent of the network density if degradation proceeds by rupture of the molecular chains. This product increases with the network density if relaxation is due to rupture of crosslinks. Hence, examination of the relationship between the relaxation rate and the network density is a way to find the points where the network is ruptured. Thermal relaxation of stress in natural rubbers vulcanized by irradiation is mainly due to rupture of the molecular chains. Here, relaxation is accompanied by a decrease of the network density because the polymer radicals formed are localized by reaction with the compounds of low molecular weight, by formation of ring structures and by disproportionation. Thermal stress relaxation in rubbers vulcanized with metal oxides is due to rearrangement of the salt crosslinks by exchange. Here, the molecular chains remain intact, and the number of crosslinks is not altered. Thermal relaxation in rubbers vulcanized with sulfur is due to preferential rupture and rearrangement of the weak polysulfide crosslinks. The new crosslinks contain a smaller number of sulfur atoms. In this case the number of crosslinks may either rise or fall, depending on the secondary reactions of the polymer radicals formed.
Labile Crosslinks in “Saturated” Elastomers as Measured by Stress Relaxation
Authors: Lyons P. F. , Lee T. C. P. , Tobolsky A. V. 
Published: February 2011

Abstract
Stress relaxation measurements have been made on ethylene propylene terpolymer (EPT) vulcanizates. The relative stability of the EPT backbone, compared with highly unsaturated elastomers, makes it possible to isolate the reactivity of the crosslink. The effects of type of cure, cure time and change of atmosphere on the stress relaxation characteristics have been studied.
Oil Extended Natural Rubber for Tire Treads
Authors: Grosch K. A. , Swift P. Mc L. 
Published: February 2011

Abstract
Large amounts of oil can be added along with reinforcing carbon blacks to natural rubber or natural rubber plus polybutadiene in high speed factory mixers. Unmasticated rubber is used, premastication cycles are eliminated, and mixing cycles are less than three minutes long. A new and important principle is established by trials on passenger cars that the wear rating of one tread compound relative to another is unequivocally determined by the tire surface temperature, over wide limits of absolute wear loss of any one compound. In consequence, accelerated wear tests can be combined with conventional car tests to give average annual service ratings of OENR or OENR-BR compounds which can be markedly better than similar compounds based on OESBR. The wet skid rating of one compound relative to another is independent of speed and road surface. On wet road surfaces the skid rating of OENR-based compounds is comparable to that of OESBR-based compounds. On dry ice at sub-zero temperatures the OENR-based compounds are much superior to the OESBR-based compounds. In many thousands of miles of passenger car tire testing groove cracking, tread separation, chipping or cutting has never been a problem.
Improvement of Impact Strength of Polystyrene by Compounding with Styrene-Grafted Ethylene Propylene Elastomeric Copolymers
Authors: Natta G. , Pegoraro M. , Severini F. , Dabhade S. 
Published: February 2011

Abstract
Ethylene propylene copolymers having good elastomeric properties lend themselves very well to improving impact strength of fragile polymeric materials, such as polystyrene. In order to obtain good results, the percentage of copolymer to be added should be chosen in such a way that the strength of the resulting mixture is as high as possible, but compatible, however, with the practically useful values of the hardness and of the modulus of elasticity, which decrease regularly with an increase in the percentage of elastomer. The best results, for an equal percentage of elastomer, are obtained when the polystyrene is mixed with polystyrene grafted on the ethylene propylene copolymer, rather than with the ethylene propylene copolymer alone. This we attribute to the improved dispersion of the elastomer in the polystyrene matrix that is found in case of the use of the graft polymer. Thus, formation of vitreous and elastomeric microphases, rather than of macrophases, occurs, and there is a better adhesion between these. The use of a graft polymer prevents, in practice, the phenomena of migration and sorting of the phases, and guarantees the maintenance over a period of time of a microphasic structure. The use of a saturated elastomer, such as that used by us, permits, additionally, an improvement in the resistance to aging, in comparison with the traditional materials consisting of mixtures of polystyrene and unsaturated elastomers.
Interactions of Elastomers and Reinforcing Fillers
Authors: Kraus Gerard 
Published: February 2011

Abstract
Use of reinforcing fillers in elastomers ranks as one of the two most important processes in rubber technology—only vulcanization can be considered to surpass it in its universal application. From the time of the earliest observations that certain pigments are capable of imparting reinforcement to natural rubber, particularly against wear, people have been concerned with interactions between filler surfaces and rubbers and their role in the mechanism of reinforcement. Progress, initially painfully slow, received a great boost about 30 years ago with the application of the electron microscope to establish the role of particle size. However, it very soon became apparent that particle size, while undoubtedly the single most important variable in rubber reinforcement, cannot account for all the effects of fillers in elastomers and that specific interactions between rubbers and fillers must also play an important part. Today the importance of these interactions is universally recognized, although much remains to be learned about the exact mechanisms by which they give rise to reinforcing effects.