bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress-Strain Testing of Rubber at High Rates of Elongation
Authors: Dannis Mark L. 
Published: February 2011

Abstract
It is well known that the properties of rubbery materials depend upon the speed or rate at which they are tested or used. A considerable body of work has shown that the dynamic properties of rubber change with the time scale of the test and, in particular, at very short times or at very fast rates, the properties approach those of plastics, i.e., high modulus and low elongation. These dynamic properties are measured by oscillation methods, usually at small strains. In contrast to this class of information, where the material is rarely strained to failure, one can also strain rubbers unidirectionally to failure at strain rates that correspond to the high frequencies of dynamic measurements. In linear extension experiments, as the rate of stretching increases tensile strength rises, elongation drops, apparent modulus increases, and relaxation losses may go up or down depending upon the particular rubber and the time scale of the phenomenon that is being investigated. Extrapolating the change in tensile strength with rate of testing suggests that tensile strength as we know it should change drastically when measured at very high rates of speed. That is, since the viscoelastic properties of rubber are time dependent, and also dependent upon the speed at which they are tested, the tensile properties of rubbers measured at room conditions with the ordinary Scott or Instron machines probably do not have the same values as at the speeds and frequencies that might be encountered in such situations as tire wear. Hence, we should like to measure the properties of rubbers at very high rates of speed, presumably comparable to those encountered in tire tread wear, in order to find out how much properties do change as the speed of test is increased. In order to measure stress-strain properties at rates of elongation comparable to those we believe exist in tire tread usage, we had to develop a small high speed tensile machine. The purpose of this paper is to describe that machine and some results obtained with it.
Liquid Chromatographic Separations Using Rubber as the Stationary Phase
Authors: Brewer P. I. 
Published: February 2011

Abstract
In a previous communication it was reported that certain polymers could be separated from mineral oil by a liquid chromatographic method. n-Heptane was used as the mobile phase and small pieces of thin vulcanized natural latex as the stationary phase. It has now been found that compounds of lower molecular weight can also be separated by this method. The use of rubber for the separation of compounds of low molecular weight was first described by Boldingh; he found it advantageous first to swell the rubber with a different solvent from that used as the mobile phase. The use of a crosslinked dextran (“Sephadex”) for separating compounds in aqueous solution has been described by Gelotte. Vaughan has mentioned the possibility of using crosslinked polystyrene beads for this purpose.
Properties of Resilin, a Rubberlike Protein
Authors: Weis-Fogh Torkel 
Published: February 2011

Abstract
There is much circumstantial evidence in favor of the belief that elastin and some other structural proteins exist in the rubberlike state of matter (see reviews by Wöhlisch, 1939; Astbury, 1940; Meyer, 1950; Kendrew, 1954), but it will be shown that the crucial evidence from thermodynamic experiments is ambiguous. The discovery of a new type of highly elastic structural protein, resilin ( Weis-Fogh, 1960; Bailey and Weis-Fogh, 1961), made it possible to re-investigate the problem by using more suitable samples. Since the thermodynamic experiments reported here gave a clear-cut answer, it was legitimate to interpret in detail the mechanical and optical properties of resilin according to the kinetic theories of rubber elasticity and so to obtain valuable information about the molecular structure of at least one rubberlike protein (Weis-Fogh, in preparation). Resilin is the essential elastic component in certain mechanical springs in the cuticle of arthropods (cf. the Latin resilire, to spring back) and it has a number of properties which make it ideally suited for this type of investigation (Weis-Fogh, 1959; 1960). When swollen with water, it exhibits typical long-range elasticity, it is heat-stable up to 140° C, crosslinked by very stable covalent bonds and insoluble in all solvents that do not break the peptide backbone but it is easily digested by all kinds of proteolytic enzymes. Moreover, it is secreted as thick continuous layers by the epidermis in a pure form unmixed with other proteins, lipids or polysaccharides and spatially separated from chitin, the only other structural component of the rubberlike cuticle (Weis-Fogh, 1960; Bailey and Weis-Fogh, 1961). It is thus possible to obtain native resilin in the form of relatively large, homogeneous samples, 0.1 mm thick and 1 mm long. Such samples are hyaline, devoid of color, and mechanically as well as optically isotropic in all directions and at all degrees of swelling. They are also devoid of structure (light and electron microscopy), and no trace of crystallinity has been found (X-ray diffraction) even in samples that were stretched near to the breaking point and then slowly dried (Elliott, Huxley, and Weis-Fogh, in preparation). The amino acid composition is unique and different from that of elastin, elastoidin, silk fibroin and collagen, and about one third of the side chains carry polar groups (Bailey and Weis-Fogh, 1961). The rubberiness of elastin is generally thought to be intimately connected with the scarcity of polar groups (5%; cf. Lloyd and Garrod, 1946). This paper will deal with experiments that show that the elastic force of resilin is connected with entropy changes caused by deformation, as in true rubbers, rather than with changes in internal energy, as in most solids.
Beta Ray Absorption in Polymers and Determination of First and Second-Order Transition Temperatures
Authors: Zannetti R. , Manaresi P. , Baldi L. 
Published: February 2011

Abstract
It is possible to determine the first- and second-order transition temperatures of polymers, copolymers, and other organic and inorganic substances with good accuracy and reproducibility by measuring their absorption of beta radiation. Variations in the measured absorptions are in essence related to variations in the product of the density and thickness of the sample, so that the method can be employed, in practice, when seeking information concerning variations in density, with the temperature or the time. The technique was used to investigate a number of polymers, e.g., polyethylene terephthalate, polystyrene, polyethylene, 1,4-cis polybutadiene, natural rubber, polyisobutylene, polybutene-1, polypropylene, and certain copolymers of ethylene/propylene and ethylene/butene-1. Finally, data pertaining to phase transitions in organic and inorganic substances are presented. The results are discussed., and compared with those obtained by other methods.
Mechanochemical Phenomena in Polymers. II. The Effects of Initiators and Inhibitors of Chain Processes
Authors: Reztsova E. V. , Kipkina B. T. , Slonimskii G. L. 
Published: February 2011

Abstract
1. The substantial effect of inhibitors and initiators of chain radical processes on the change in the properties of rubbers in milling, as well as on the resistance of vulcanizates to fatigue, has been shown. This indicates a mechanochemical mechanism for processing of polymers and in the fatigue of elastomers. The act of mechanical scission of chemical bonds, with the formation of free radicals which initiate the secondary chain processes, rests on these processes. 2. The possibility has been shown of regulating the properties of polymers during processing, and also of increasing the dynamic fatigue resistance of vulcanizates by incorporating small quantities of additives active in regard to free radicals.
Solution Properties of Polybutadiene and trans-Polyisoprene Fractions
Authors: Cooper W. , Eaves D. E. , Vaughan G. 
Published: February 2011

Abstract
Linear polybutadienes, prepared with butyl lithium as catalyst, and polybutadienes branched by exposure to γ-radiation have been fractionated and the fractions examined by osmometry and light scattering. Turbidimetric second virial coefficients (A2τ) of mixed polymer fractions are virtually the same as those of the higher molecular weight components of the mixtures for most compositions. This is true both for mixtures of linear with linear and linear with branched polymer. The higher the molecular weight of the fraction, the greater the effect; the addition of 1 per cent microgel to a linear polymer reduced A2τ by a factor of three. The presence of microgel or high molecular weight branched polymer has been shown to be responsible for the very high molecular weights previously reported for polybutadienes from light scattering measurements. It is conveniently removed by shaking the solutions with calcium sulfate. Second virial coefficients obtained either by light scattering or osmometry are, within the limits of experimental error, uninfluenced by branching in the polymer. In general those factors which lead to increased branching also result in increased polydispersity, and it is the latter which results in the decrease in A2τ. The fall of the osmotic second virial coefficient (A2τ) with molecular weight is much smaller than would be calculated theoretically, and the fall in A2τ is greater than would be expected, notwithstanding the fact that for some of the fractions Mw/Mn&lt;1.1. This indicates that A2τ is sensitive to the low molecular weight species present in the fractions, whereas the reverse must apply to A2τ. Natural or synthetic trans-polyisoprene showed analogous behavior to polybutadiene, although, owing to experimental difficulties, sharp branched fractions could not be obtained. The following viscosity-molecular weight relationships were obtained in benzene solution: [η]=1.45×10−4M0.76 for butyl lithium-catalyzed polybutadienes, and [η]=4.37×10−4M0.65 for natural and synthetic trans-polyisoprenes.
An Oscillating Blade Microtome for Rubber
Authors: Southern E. , Thomas A. G. 
Published: February 2011

Abstract
In a study of the equilibrium swelling of rubber in thick oils, thin samples, about 0.1 mm thick, were required so that equilibrium could be reached within a reasonable time. Thin sheets can be molded, but they are frequently very anisotropic and therefore undesirable. Although it is possible to microtome very thin samples of rubber at sufficiently low temperatures where it is relatively stiff, only small areas are obtainable, and it is a difficult and inconvenient process if several square centimeters are required. An oscillating blade microtome of simple design was therefore constructed, capable of cutting sufficiently thin slices, about 2 cm square, at room temperature. Because of the sawing action of the blade the cutting force is greatly reduced and deformation of the sample is minimized.
Formation and Decomposition of Hydroperoxides of Atactic Polypropylene
Authors: Manasek Z. , Berek D. , Micko M. , Lazar M. , Pavlinec J. 
Published: February 2011

Abstract
1. The authors study the kinetics of formation and decomposition of peroxides in the oxidation of atactic polypropylene in air in the temperature range from 20° to 120°. 2. The effective energy of activation of accumulation of peroxide (24 to 25 kcal/mole) and of decomposition of peroxides (27 kcal/mole) are determined. 3. It is found that the reduction in the molecular weight is a function of the concentration of peroxides in the polymer.
The Structure of Angular Polycycloisoprene
Authors: Wallenberger F. T. 
Published: February 2011

Abstract
Lewis and Brö nsted acids, heat, silent electric discharge and cathode rays cause progressing isomerization of synthetic and natural cis-1,4-polyisoprene to yield a polymeric product which has the empirical formula, (C5H8)n identical with that of the initial rubber hydrocarbon. The reaction, commonly carried out in benzene with stannic chloride as catalyst, is accompanied by an increase in specific gravity, refractive index and polymer melt temperature and a decrease in unsaturation, intrinsic viscosity and molecular weight of the material. The resulting polymer, readily soluble in a variety of solvents, is known as cyclized rubber, cyclo-caoutchouc, or “Pliolite-NR”, manufactured by the Goodyear Tire and Rubber Company. Staudinger recognized as early as 1926 that the reaction proceeds by isomerization and intramolecular cyclization. D'lanni postulated formation of cyclohexane rings within the polymer chain, while Veersen extended D'lanni's proposal and suggested random protonation of bonds leading to intralinear, mono-, di-, and polycyclic ring polymers. Ideally, complete and stereoselective cyclization would lead to angular polycycloisoprene. Comprehensive reviews concerning the chemistry of the cyclization have been published by Reese and by Bloomfield. This communication provides the first chemical structure proof of the cyclized product. It is based on the cyclization of cis-1,4- and of trans-1,4-polyisoprene. The resulting products were identical and their properties in agreement with literature data. Hence cyclization must have proceeded through a common intermediate.
Mechanics of Foamed Elastic Materials
Authors: Gent A. N. , Thomas A. G. 
Published: February 2011

Abstract
The deformation of a foamed elastic material, both in tension and compression, and its resistance to tearing and to tensile rupture, have recently been derived on the basis of a model consisting of a large number of thin threads joined at their ends to form a three-dimensional network. A general account of this theoretical treatment, and the evidence for it, is presented. The theory is extended to deal with small deformations of closed-cell foams; relations for Young's modulus and Poisson's ratio are derived. The viscous damping of open-cell foams due to air flow through the network of threads is also discussed.
Creep of Pure-Gum Rubber Vulcanizates from Indentation-Time Measurements
Authors: Wood L. A. , Roth F. L. 
Published: February 2011

Abstract
The compliance J (limit of the ratio of strain to stress at zero deformation) has been determined from measurements of the indentation of a flat rubber surface by a rigid sphere, as a function of time t and temperature T. The results are subjected to two successive operations: (1) Jis multiplied by the absolute temperature T and (2) an empirically-determined number is added to the logarithm of the time at each temperature to make the values of JT agree as well as possible. For natural rubber from 25° to −40° C the shift required appears to correspond to a constant “activation energy” of 38kcal/mole; from −40° to − 60° C the shift is in quite good agreement with that predicted by the equation of Williams, Landel, and Ferry. Butyl rubber yields an “activation energy” of 20 kcal/mole while styrene-butadiene rubber gives a value of 22 kcal/mole. The resulting curve of JT against log t shows a sigmoid form with an increase of slope over 2 to 3 decades and a decrease at higher values. There is usually an extended region of nearly constant slope corresponding to the conditions of normal use of rubber products. For natural rubber this slope is 1 to 2% per decade; for the synthetics it is appreciably higher, reaching a value of 15% per decade for nitrile rubber. This behavior differs from that of a classical idealized polymer network, for which the compliance would approach an equilibrium value at long times.
Solution and Diffusion in Silicone Rubber. I. A Comparison with Natural Rubber
Authors: Barrer R. M. , Barrie J. A. , Raman N. K. 
Published: February 2011

Abstract
The diffusion and solubility of n- and isobutane and of n- and neopentane has been studied in the range 30° to 70° C, in polydimethylsiloxane rubbers. The solubilities are very similar to those in natural rubbers and show comparable agreement with the statistical theory of polymer penetrant mixtures. Diffusion coefficients are at least an order of magnitude greater in silicone than in natural rubbers. The very low energy of activation, ED, of about 4 kcal/mole is almost invariant among the hydrocarbons studied and is the same as for self-diffusion and viscous flow in this rubber. The low value of ED means that permeabilities of the hydrocarbons increase as the temperature falls. Because diffusion in silicones is less dependent upon molecular size and shape of penetrant than in natural rubber, the silicones are less selective though much more permeable separation barriers.
Effect of Compression on the Shear Modulus of Rubber
Authors: Payne A. R. 
Published: February 2011

Abstract
When a cylinder of small diameter-height ratio is compressed, it buckles. A theory has been developed by Haringx to describe this, based on the Euler theory of struts. This paper shows how Haringx's theory is applicable to the compression of rubber and to cylinders of moderate shape factor, which do not visibly buckle, and relates the changes in the shear modulus of a rubber which is compressed, to the degree of compression and the shape factor of the cylinder.
Temperature and Frequency Dependence of the Dynamic Deformation and Losses of Elastomers
Authors: Bartenev G. M. , Zelenev Yu V. 
Published: February 2011

Abstract
The results of this investigation of the temperature and frequency dependence of the deformation and mechanical loss of elastomeric network polymers in the temperature range from −90 to +120° C may be understood on the basis of the conceptions of three types of relaxation processes in these materials: orientation of the units of the chain molecules, overcoming of the secondary crosslinks (entanglements) in the movement of the segments, and the process of destruction of the polysulfide bonds, which comprise quite a small part of the total number of the chemical crosslinks. The first process is connected with the glass-transition and leads to the occurrence of a low-temperature maximum of mechanical losses, while the third leads to a high-temperature maximum. The first and third relaxation processes are apparently characterized by narrow spectra of relaxation times, which may be substituted for approximately by the corresponding averaged relaxation times. For the second process the spectrum of relaxation times is probably very wide and it is not possible to make the analogous substitution; this also explains the absence of a third mechanical loss maximum and the occurrence of a well marked frequency dependence of the deformation amplitude in the high-elastic range. The models of a network polymer considered for low and high temperatures give a qualitative description of all the main mechanical properties of these materials.
Use of Lithium Aluminum Hydride in the Study of Surface Chemistry of Carbon Black
Authors: Rivin D. 
Published: February 2011

Abstract
Considerable interest has been focused in recent years on the effects of carbon black surface chemistry on its properties in rubber and other polymer systems. Methods have been developed in our laboratory for the quantitative characterization and description of the surface chemistry of carbon blacks. The total surface acidity as given by the active (acidic) hydrogen is determined by reaction with strongly basic lithium aluminum hydride in diethyl carbitol, or by equilibration with aqueous alkali under nitrogen. Exclusion of oxygen is essential since carbon blacks readily undergo base catalyzed oxidation. Selective neutralization techniques are employed to further differentiate between strong and weak surface acids. For example, using aqueous sodium bicarbonate solution, only those acids stronger than carbonic acid will be neutralized. Strong acids, as determined by bicarbonate neutralization, are shown to be aromatic carboxyl groups, while weak acids determined by difference between total acidity and strong acid content are phenols and hydroquinone derivatives. Neutral quinone and lactone surface groups are quantitatively determined by chemical reduction with lithium aluminum hydride, or alternatively by analysis of their thermal decomposition products (carbon monoxide and dioxide, hydrogen, and water) obtained on vacuum pyrolysis of carbon black. The distribution of neutral and acidic surface groups on representative channel, furnace, and thermal black is discussed in terms of the state of oxidation of the individual carbons.
Internal Field Emission in Carbon Black-Loaded Natural Rubber Vulcanizates
Authors: van Beek L. K. H. , van Pul B. I. C. F. 
Published: February 2011

Abstract
The nonohmic behavior of carbon black-loaded natural rubber vulcanizates was studied. Three samples contained high-abrasion furnace black (HAF) in good, moderate, and poor dispersion. Another sample contained a good dispersion of medium thermal black (MT). The nonohmic behavior of the poor HAF dispersion and that of the MT dispersion could be interpreted as due to internal field emission across insulating gap widths of 2 and 2.5 µ. The existence of such gaps was confirmed by electron micrographs. No clear evidence of internal field emission could be obtained for the good and moderate HAF dispersions where, according to electron micrographs, the gaps are much narrower. There is some indication that the degree of dispersion can be correlated with field emission characteristics.
Reagglomeration as a Cause of Tread Groove Cracking
Authors: Hess W. M. , Burgess K. A. 
Published: February 2011

Abstract
A tendency for zinc and sulfur to reagglomerate, along with wax, has been observed in oil extended SBR and natural rubber tires. In high concentrations these relatively brittle reagglomeration areas are associated with poor resistance to groove cracking. The pigment-polymer environment has a significant effect on the occurrence of non-carbon reagglomeration. An increase in reagglomeration in oil extended SBR treads is favored by: 1. Poor initial dispersion of the non-carbon components. 2. Fine particle size and low structure carbon blacks. 3. Excessive zinc and wax. Conversely, reagglomeration can be reduced or eliminated by good dispersion of all compound ingredients, the use of higher structure or larger particle size carbon blacks, and through blending with polybutadiene.
State of Branching in Regular Polyisoprene
Authors: Poddubnyi I. Ya , Erenburg E. G. 
Published: February 2011

Abstract
Fundamental data about the intrinsic viscosity in an ideal solvent of a fraction of polyisoprene with a cis unit content of approximately 85% comes from branching. Such polyisoprenes were obtained by the action of complex catalysts or by the action of lithium. We have established that the macromolecules of rubber which were obtained with a complex catalyst under the usual conditions appear on the whole to be linear. At the same time, in the samples investigated approximately 10% consists of colloidal strongly to crosslinked polymer. It can be seen that disturbance of the rate of polymerization during preparation of polyisoprene in the presence of complex catalyst brings about the formations of strongly branched polymer. Such polymer contain one branch per approximately 250 monomeric units. Knowledge of the features of the hydrodynamic behavior of macromolecules allows one to express the assumption that the trans units in the polyisoprene macromolecule obtained with a complex catalyst is not disposed in a random manner along the chain but forms a comparatively linear block of trans units. For the polymers investigated an equation for the dependence of the intrinsic viscosity in benzene on the molecular weight was obtained. For polymers which were obtained under action of a complex catalyst this was [η]=1.12×10−4×M0.78 or ln M=5.063+1.28 ln [η] or for isoprene polymers from lithium [η]=1.33×10−4M0.78 ln  or M=4.967+1.28 ln [η].