bluuebunny/crossref_metadata_2025 huggingface dataset:
Limitations of the Tobolsky ‘Two Network’ Theory in Interpretation of Stress Relaxation Data in Rubbers
Authors: Thomas D. K.
Published: February 2011

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

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

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

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

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

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

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

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

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

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

General considerations of the physics of failure of high polymeric substances were reviewed using the example of one dimensional testing. It is shown that classical failure theory can be applied only with difficulty to viscoelastic substances. Relations between macroscopic failure properties and the parameters of test are reviewed. Several recent investigations have shown a direct relation between relaxation time spectra of high polymers and breaking energy, tensile strength, and elongation at break through their dependence on time and temperature. Finally, the relation between microscopic failure properties and experimental parameters are discussed. The processes occurring at the tip of the failure are determined by relaxation mechanisms just as are the processes which lead to sites of failure in the macroscopic specimen. These are illustrated by recent work in which the specific tearing energy is determined as a function of time and temperature of tearing. From all of the work referred to here, it follows that the very complicated relations at fracture of high polymers are essentially determined by their mechanism of molecular motion in a way analogous to other mechanical properties and are therefore determined by their molecular structure.
Equilibrium Molecular Weight Distribution of Cyclic and Linear Methylsiloxanes
Authors: Carmichael Jack B. , Heffel James
Published: February 2011

Data are reported for the equilibrium molecular size distributions of cyclic and linear methylsiloxanes in five polymers with number average molecular weights ranging from 459 to 1348. The distributions of linear species agree with the earlier work of Scott and agree reasonably well with the Flory theory of random reorganization. The amounts of cyclic molecules are sharply dependent on molecular weight. However, the equilibrium constants for cyclic formation for cyclic species with four to eight units are shown to be virtually identical with the equilibrium constants for cyclic formation in high molecular weight polymers reported in a previous publication. For octamethylcyclotetrasiloxane, Kav in moles of siloxane units per liter was found to be 0.72 in this study. For high polymers, Kav was previously reported to be 0.74.
Swelling of Rubber in Liquid and Vapor (Schroeder's Paradox)
Authors: Musty J. W. G. , Pattle R. E. , Smith P. J. A.
Published: February 2011

Polymeric substances usually swell less when placed in the vapor of a liquid in a closed vessel than they do in the liquid itself. This is known as “Schroeder's Paradox”, and many attempts have been made to explain it. With lightly vulcanized rubber and carbon tetrachloride the paradoxical behavior is caused by small differences in temperature (of order 0.1° C) which exist under normal conditions between a liquid and its vapor in a closed vessel; the vapor is normally the warmer of the two. Strict temperature control abolishes the paradox.
Solvents for Synthetic Rubbers
Authors: King L. F.
Published: February 2011

The effects of solvent characteristics on viscosities of several synthetic rubber hydrocarbon solutions was determined. Normal and isoparaffins (Ce and C7) yielded lower viscosity solutions than naphthenes and aromatics at 10 weight per cent of solvent and 8 grams of rubber per 100 cm3 of solvent, concentrations of interest to rubber cement and adhesive manufacturers. Solubility varied markedly with elastomer and solvent. Butadiene acrylonitrile copolymer and ethylene propylcnc tcrpolymer were the least soluble; cis-polyisoprene, butyl rubbers, and ethylene propylene copolymer were soluble in all thinners. No general correlation was found on a solvent volume basis between solution viscosity and solvent viscosity or between relative viscosity and hydrocarbon type.
Properties of Random and Block Copolymers of Butadiene and Styrene. III. Three Sequence Styrene-Butadiene-Styrene Block Polymers
Authors: Childers C. W. , Kraus G.
Published: February 2011

In butadiene styrene copolymers containing long block sequences chain segments associate with like segments to form a two phase structure. Properties of such polymers are dependent not only on composition and molecular weight but also on block sequence along the chain. Polymers containing two or more polystyrene blocks per molecule form networks and exhibit elastomeric properties in the uncured state resembling those of filler reinforced vulcanizates. This behavior is shown both by linear styrene-butadiene-styrene elastomers and multichain block copolymers branched in the polybutadiene blocks. A prominent loss tangent peak was observed around —40° C for the multichain polymers. Stress strain following prestretching and stress relaxation measurements indicate some shifting of polystyrene associations during stretching. Tensile strength is reduced by increasing temperature and addition of plasticizers. Reinforcement by polystyrene domains in vulcanized block copolymers is evident from tensile strength, dynamic modulus, and swelling measurements, but decreases with increased crosslinking. The number of styrene sequences in the primary molecules is less important after vulcanization as crosslinking destroys the individuality of the original polymer chains.
NMR Composition Analysis of Copolymers
Authors: Mochel Virgil D.
Published: February 2011

High resolution NMR spectroscopy has been shown to be a most useful tool for elucidation of compositions and structures of polymers. It is a rapid, accurate method of analysis and requires no external calibration. This technique of composition analysis can be applied to any copolymer, terpolymer, or homopolymer with various structural isomers, provided a suitable number of resonance peaks can be unambiguously assigned to at least one proton of each of the structures present. Accuracy depends upon the relative isolation of these selected peaks. The method was applied to butadiene styrene and butadiene isoprene copolymers. Equations developed previously for both systems were extended and modified to give better accuracy. In the former copolymer the NMR analysis for block styrene agreed very well with the chemical oxidative degradation method over the range 0-20 per cent. It is believed that sequence lengths smaller than five styrene units can be observed as block styrene by NMR. It was also shown that there is a sequence distribution effect in the 1,2 addition butadiene olefinic resonance region of the spectrum. This effect is also observed in polybutadienes and in the butadiene isoprene copolymers. Further study of this might be fruitful. Accuracy of the NMR method was demonstrated in the butadiene isoprene case by study of four high conversion, emulsion copolymers and six blends of butadiene and isoprene homopolymers. In all samples except one the total isoprene content found by either the detailed NMR analysis or the much more simplified NMR analysis agreed within 2 per cent of that known to be present. Accuracy is greatest for those copolymers or blends which have relatively low 1,2 addition butadiene contents, such as with butyllithium-catalyzed polymers. Accuracy is poor when the copolymer or blend has an isoprene content less than 10 per cent along with a high 1,2 addition butadiene content. Composition analysis of copolymers by NMR will become increasingly important since it often provides a direct, simple fingerprint of the various structures. However, NMR will probably make its most significant contributions in stereochemical studies of tacticities, sequence distributions, and orientation, such as head-to-head or tail-to-tail linkages. In these problems deuteration techniques, double resonance techniques, and higher field strengths play an indispensable role.
Mechanism of Thermal Degradation of Certain Polyether Polyurethans
Authors: Ingham J. D. , Rapp N. S.
Published: February 2011

Relatively few publications have appeared that describe basic studies of thermal degradative processes that can occur in polyether polyurethans. This article is an account of some studies of the mechanism of degradation of uncrosslinked polyurethan prepared from poly(propylene oxide) (PPO) and 2,4-tolylene diisocyanate (TDI) at temperatures up to 320° C in a vacuum or inert atmosphere. These are referred to as PT polymers.
Application of dn/dc Data for Determination of Partial Specific Volumes of Dissolved Macromolecules
Authors: Heller Wilfried
Published: February 2011

The principles of a method are outlined whereby one can determine the partia specific volume of a solute, V, by means of measurements of dn/dc using a suitable pair of equations and a simple graphical interpolation procedure. The method yields V data which compare well with densitometrically obtained V data if the polarizability of both solvent and solute molecules is unaffected by the solution process. It is tested successfully on solutions of polystyrene in various solvents. The method appears to be particularly attractive for measurements of the change of V with temperature and also for conveniently following the time rate of changes in V such as during the coil → helix transition.
Principle of Strength Reinforcement in Filled Rubbers
Authors: Oberth A. E.
Published: February 2011

Effects of filler on mechanical properties of composites result from stress concentrations developed in the matrix and filler particles. Stress concentrations in filler particles relieve stress in the matrix which, under a given load, deforms less than it would in absence of filler. This accounts for high modulus as well as strength reinforcement in filled materials. Stress concentration in the matrix, decreasing with increasing content of filler, is responsible for internal tearing of composites. Magnitude of this internal tearing, which can be measured by volume increase of a specimen under strain, depends on many factors such as: shape of filler, orientation of filler particles, particle size, particle size distribution, nature of boundary layer between filler and matrix, crosslink density and tear properties of the matrix, as well as environmental pressure in the test. High dilatation results in low tensile strength of the composite and conversely if dilatation is suppressed maximum strength reinforcement is obtained.
Effect of Strain on Rate of Crystallization of Natural Rubber
Authors: Dunning D. J. , Pennells P. J.
Published: February 2011

The crystallization of vulcanized natural rubber under strain gives this polymer a strength which is not present in a noncrystallizing rubber. However, if the rubber is stretched very rapidly the strength falls suggesting that a finite time is necessary for the crystallization to build up. An apparatus was constructed to enable changes in crystallinity to be detected over a time range down to hundredths of a second after the rubber had been stretched. The method consisted in extending the rubber very rapidly by passing a long strip between two sets of rolls, the second of which was rotating at a greater speed than the first. At any chosen point between the rolls there was a sample of rubber which had been stretched for a fixed time. By moving between the sets of rolls one moved along the time scale after stretching. The crystallinity of the rubber was detected by an x-ray technique. The results showed an initial period (which varied from one twentieth sec for an extension ratio of 5 to 20 sec for an extension ratio of 3.6) in which no crystallization was observed. This was followed by a gradual rise in crystallinity. The level of crystallinity was still increasing after periods of a week after stretching.
Nonnewtonian Flow of Poly(Dimethyl Siloxane)
Authors: Ito Yoshio
Published: February 2011

Nonnewtonian flow of poly(dimethyl siloxanes) of various molecular weights has been studied with a short capillary viscosimeter. The experiment covered a wide range of shear rate, from 10−1 to 3×106sec−1. Results were as follows: (1) Flow behavior of the sample changes with the degree of polymerization. For siloxanes with degrees of polymerization less than 1.55×102, flow of the fluid is newtonian throughout the whole range of shear rates; for siloxanes with degrees of polymerization from 3.22×102 to 2.63×103, flow is nonnewtonian at moderate shear rates; it again becomes newtonian at high shear rates. With degrees of polymerization more than 3.31×103, the spiral flow rises to a high shear rate. (2) Plow behavior of the samples is expressed by modifying Shishido's equation proposed for nonnewtonian polymer solutions. (3) When the observed flow curve contains its inflection point, the upper newtonian viscosity can be estimated by a new method proposed here. (4) The relations among the end correction of capillary, the pressure loss, and the shear stress proposed by Shishido for polymer solutions are applicable to poly(dimethy! siloxane) also.
Ordered Structures of Styrene Butadiene Block Copolymers
Authors: Vanzo Ed
Published: February 2011

Anionically prepared block copolymers of butadiene and styrene exhibit solution properties which result from a two dimensional ordering of the polymer molecules. The most notable of these properties is the iridescent colors of toluene solutions which are dependent on concentration and abruptly change on mechanical deformation. Electron micrographs of the surface of cast films indicate that the ordered structure is retained to some degree in the solid state.
Polymer Fractionation at a Lower Critical Solution Temperature Phase Boundary
Authors: Baker C. H. , Clemson C. S. , Allen G.
Published: February 2011

The influence of pressure on a lower critical solution temperature is much more pronounced than on an upper critical solution temperature. Accordingly it is possible to control phase separation at a LCST phase boundary under isothermal conditions by merely adjusting the pressure on the system. An apparatus has been constructed to investigate the isothermal fractionation of polyisobutene in which precipitation is controlled by pressure. Two samples of polyisobutene of Mv=1.76×106 and 9.0×104 have been fractionated in isopentane solution so as to yield up to six and nine fractions respectively. The integral molecular weight distribution curves thus obtained are compared with those obtained from conventional fractionations at an UCST. The sensitivity of the method is poor with regard to the separation of low molecular weight fractions and degradation occurs at the higher temperatures to an appreciable extent.
Recent Advances in Knowledge of Rubber Friction and Tire Wear
Authors: Schallamach A.
Published: February 2011

Progress in the last few years in understanding rubber friction and tire wear justifies a survey of developments since a review of the subject in 1958. Work on fundamental of friction and abrasion has mainly evolved from conceptions formed in the earlier investigations; it had, however, not been realized that wear of tires and, indeed, abrasion on certain laboratory machines brings into play gross properties of the tire or testpiece which affect rate of wear just as much as the actual abrasion resistance of the tread compound. This new field of research has led to rationalization of road testing, and has helped to bridge the gap between laboratory and road. A report on these developments is given. Much of the work is concerned with the viscoelastic nature of rubber friction and abrasion, which has come to light through the experimentally established validity of the rate-temperature equivalence principle for these processes. This principle, which holds good for all viscoelastic processes, is briefly described in the next section in order not to interrupt the subsequent argument.
Role of Computers in Elastomer Research
Authors: Claxton W. E. , Pearson Dale , Clarke R. E. , Conant F. S.
Published: February 2011

Computer usage has spread so rapidly in recent years that these instruments are almost considered to be common tools. Publications may make only casual reference to the computer's role in the investigation or they may omit such reference altogether, if the use was routine in nature. Consequently the literature on elastomer research and technology does not fully represent the growing importance of this extension to human capabilities. Enough references are available, however, to show that computers have penetrated into many areas of rubber science. The aims of this article are, therefore, to review some computer applications that have been made and to indicate potential uses. Perhaps both of these aims can be served by first considering the nature of computers and the type of problem solving for which they are uniquely adapted.
Elasticity Theory for Indentation of a Rubber Plate
Authors: Gehman S. D.
Published: February 2011

Rubber hardness readings with an indenter depend upon thickness of the rubber specimen. This effect has been known and studied since first attempts to develop precision methods to determine hardness. Classical elasticity theory accounted satisfactorily for indentation relations with thick rubber but thickness dependence was treated as an empirical correction.
Effect of a Dispersion of Gelled Polymer Particles on Viscoelastic Properties of a Linear Polymer
Authors: Rigbi Zvi
Published: February 2011

In the rubber industry, it has often been observed that dispersion of a relatively small volume fraction of a crosslinked polymer into a linear high polymer improves processability of the latter markedly. Thus, S. P. rubbers of exceptional processability are produced by coagulation of untreated latex mixed with a minor proportion of prevulcanized latex, the latter remaining in the form of discrete particles during subsequent processing operations. Similar effects are produced in the synthetic rubber industry when SBR crosslinked by means of divinyl benzene (SBR 1009 and similar grades) is mill-mixed with “straight” styrene-butadiene copolymer. In another case, a highly gelled butadiene-acrylonitrile polymer is used to enhance processing properties of oil-resistant rubbers.
Thermoelastic Measurements on Some Elastomers
Authors: Barbie J. A. , Standen J.
Published: February 2011

Length versus temperature curves at a series of constant loads have been obtained for cis-polyisoprene, polydimethylsiloxane and ethylene propylene elastomers in the temperature range 25° to 100° C. Thermoelastic coefficients for these networks are evaluated and compared with values obtained by more direct procedures. The deviation of the stress strain data from the simple gaussian theory is discussed briefly in terms of the C2 constant of the Mooney equation.
Hysteresis in Polymers and its Relation to Strength
Authors: Grosch K. A. , Harwood J. A. C. , Payne A. R.
Published: February 2011

Energy density to break measurements on a number of polymers, either partly swollen or dry, reveal that there is a simple relationship between the energy density to break and the hysteresis obtained in the first stress strain cycle taken very near to break. The hysteresis at break was varied by changing the temperature of test or by swelling the polymer.
Glass Transition in Carbon Black Reinforced Rubber
Authors: Smit P. P. A.
Published: February 2011

It can be stated that the effect of carbon black in a rubber vulcanizate with regard to dynamic properties can be explained by assuming physical adsorption of rubber on the black surface. The effect can be represented by assuming an adsorbed layer having different properties from the bulk rubber taking the layer thickness to be at least 20 A. Adsorption-desorption from this layer causes non-linearity and may contribute to losses observed in the glass transition. This adsorption is analogous to adsorption of simple liquids in microporous systems such as silica gel and activated carbon.
Large Deformation Tensile Properties of Elastomers. I. Temperature Dependence of C1 and C2 in the Mooney-Rivlin Equation
Authors: Smith Thor L.
Published: February 2011

Tensile stress strain data were determined at various extension rates and temperatures on unfilled butyl and silicone vulcanizates and on six hydrofluorocarbon (Viton A-HV) vulcanizates that contain between 0.90 and 12.2×10−5 mole of effective network chains per unit volume of gel rubber. From one min isochronal data, values of C1 and C2 in the Mooney-Rivlin equation were derived. For the butyl and silicone vulcanizates from, respectively, −20 to 150° C and —45 to 200° C, C1 increases with temperature at a rate which is in reasonable agreement with published data from force-temperature measurements. Because C2 is sensibly temperature independent over these extended temperature ranges, it is concluded that C2 is a finite quantity under equilibrium conditions. Time dependent behavior was observed on the Viton A-HV vulcanizates between —5 and 230° C. For each vulcanizate between about 25 and 230° C, C1273/T is temperature independent, but it increases with decreasing temperature below about 25° C. Except at the lowest temperatures, C2273/T decreases with increasing-temperature, the rate of decrease becoming progressively less with an increase in crosslink density. Above 25° C the ratio C2/C1, which ranges from about 90 to 0.6, decreases with an increase in either temperature or crosslink density. The time-dependent behavior of C2273/T appears to arise primarily from molecular processes whose relaxation times are considerably longer than the terminal relaxation time of individual chains.
Reinforcement of Polymers. II. Effect of Vulcanization on Tear Strength of Filler Rubber Mixes and on Elastomer to Filler Adhesion
Authors: Yagnyatinskaya S. M. , Raevskii A. G. , Frumkin L. S. , Voyutskii S. S.
Published: February 2011

It has been shown that an increase in the adhesion of elastomer and filler always led to a corresponding increase in tear strength. It was of interest to clarify whether this applies to vulcanizates. We have now studied the change in adhesion strength of the elastomer to filler bond and of the tear strength of filled systems in vulcanization.
Comparison of Viscoelastic and Dielectric Properties of Natural Rubber and Sulfur Systems
Authors: Havranek A. , Bakule R.
Published: February 2011

This paper presents a comparison of viscoelastic and dielectric retardation time spectra of a rubber-sulfur system with a sulfur concentration ranging from 1.75 to 16.4%. The viscoelastic spectra were obtained from creep measurements which were carried out in the time interval 3×10−2 to 5×10+1 sec and a temperature range from −40° C to +70° C. The dielectric spectra were derived from measurements of the frequency dependence of the real and imaginary part of the complex dielectric constant in the frequency range 3×101 to 3×104 cps or temperatures between − 50° and +35° C. The temperature-time superposition principle was used in the derivation of the spectra. The following conclusions may be deduced from the comparison: (1) The retardation times corresponding to the spectral maxima for mechanical measurements are displaced by several orders toward longer times with respect to those for dielectric measurements. (2) The reference temperatures T8, determined from the WLF equation are higher for viscoelastic measurements than for dielectric measurements, especially for samples with a higher sulfur content. (3) The viscoelastic spectra become narrower, while the dielectric spectra broaden with increasing sulfur content. Further, it was ascertained that the results of dielectric measurements correspond to the presumption that the logarithmic retardation time spectrum has the Gaussian form in logarithmic time scale.
Effect of Temperature on Ozone Cracking of Butyl Rubbers
Authors: Gent A. N. , Hirakawa H.
Published: February 2011

Rates of growth of single ozone cracks have been measured for vulcanizates of two butyl rubbers over the temperature range of 20-160° C. Over most of this range the rates are quantitatively related to the segmental mobility of the polymer and depend upon temperature in accord with the appropriate form of the WLF relation. The rates are also proportional to the concentration of ozone. It is therefore concluded that diffusion of ozone into the polymer before reaction is the rate-controlling step. This is contrasted with the behavior of butadiene styrene copolymers, for which rates of crack growth are also quantitatively related to the segmental mobility, but the rates are somewhat larger at equivalent mobilities and the dependence upon ozone concentration is smaller. The difference is attributed to different penetration distances before reaction in polymers containing low and high densities of reactive sites.
The Chemistry of Sulfur Curing. IV. Effects of Organic Accelerators on the Reaction of Cyclohexene with Sulfur
Authors: Wolfe James R.
Published: February 2011

Cyclohexene reacts with sulfur at 140° in the presence of zinc dimethyldithio-carbamate, tetramethylthiuram monosulfide, or tetramethylthiuram disulfide, to produce 2-cyclohexene-1-thiol as the major product after lithium aluminum hydride reduction of the polysulfide compounds. Secondary products are cis- and trans-1, 2-eyclohexanedithiol and cyclohexanethiol. Zinc dimethyldithiocarbamate is postulated to promote the reaction via an ionic mechanism as it causes more trans than cis-1, 2-cyclohexanedithiol to be formed. Tetramethylthiuram monosulfide and disulfide are postulated to promote the reaction via a free radical mechanism as they cause more cis- than trans-1, 2-cyclohexanedithiol to be formed.
Rheological Properties of Polymer Mixtures
Authors: Natov M. A. , Dzhagarova E. K.
Published: February 2011

It has been established that the flow (and consequently viscosity) of mixtures of polyethylene with polyisobutylene or natural rubber deviates from an additive law.
Functionally Terminated Butadiene Polymers
Authors: French David M.
Published: February 2011

Prepolymer technology is a relatively new science in which polymer structures of any desired type are built from partially polymerized liquid resins containing reactive functional groups. Well over one hundred low molecular weight polymers and crosslinking agents are currently available commercially. The first examples were the liquid phenolic casting resins which appeared in the mid 1930's. Unsaturated polyester-styrene mixtures were available by 1945 followed shortly by the epoxide resins and the liquid polysulfides. Today the chemist or engineer can chose among a wide assortment of liquid polymers: Polymer chain : Polyester, polyether, polyamide, polysulfide, polybutadiene, polyisobutylene Reactive group: Carboxyl, hydroxyl, sulfhydryl, amine, epoxide, isocyanate, olefin These liquid polymers may be separated into two types: those in which the reactive groups are randomly distributed along the backbone chain and those in which the functional groups are located at the ends of the chains. It is the latter with which this discussion is concerned, in particular with the functionally terminated polybutadienes. Uraneck, Hsieh, and Buck have coined the word “telechelic” for polymer molecules having two reactive terminal groups and we will use this term. The word derives from the Greek tele, far off, and chele, claw.
Course of the Terpolymerization of Ethylene, Propylene, and Dicyclopentadiene. II. Two-Step Addition of Dicyclopentadiene
Authors: Cunningham Robert E.
Published: February 2011

Terpolymerizations of ethylene, propylene, and dicyclopentadiene were carried out in which the dicyclopentadiene was added to the reaction system in two equal portions at the beginning and midpoint of each run, while the monoolefins were added continuously. In the resultant elastomers, unsaturation remains much more constant throughout the course of the polymerization than for terpolymers obtained when all dicyclopentadiene is added at the start of the reaction. Yield and molecular weight of the terpolymers produced by either technique are quite comparable, however. With VCl4 catalyst (with Al2Et3Cl3 cocatalyst) in heptane solvent, the two-step addition of the diene gave terpolymers with little gel, in contrast to the high gel in terpolymers formed with the single initial addition of the diene. This system also produced terpolymer with the highest final unsaturation and molecular weight Catalysts of VCl4, VOCl3, or V(C5H7O2)3 (with Al2Et3Cl3) in benzene gave terpolymers of moderate unsaturations and molecular weights.
Some Factors Affecting the Interpretation of the Plasticity Retention Index—P.R.I.
Authors: Smith M. G.
Published: February 2011

The implications of the PRI test are examined, in order to demonstrate how the values may be interpreted by the rubber goods manufacturer. It is shown that consistency of PRI is desirable, to enable product uniformity through control of processing, in particular high temperature mastication. It is demonstrated that PRI cannot be used to assess the quality of natural rubber, in terms of dynamic properties and vulcanizate aging.
The Curing of Polychloroprene Coating Materials with Polyisocyanates
Authors: Hoehne K.
Published: February 2011

Polychloroprene is an unsaturated chlorine-containing polymer and therefore it does not appear at first sight to have reactive positions. Nevertheless it can be proved to react with isocyanates. Although the chemistry of the reaction has not yet been fully explained, it is possible to determine an isocyanate equivalent weight. Recently a polychloroprene modification which was developed specifically for coating purposes, and which has been attracting more and more attention owing to its special properties, became commercially available under the name Plastifix PC®. This polychloroprene modification is crosslinked exclusively with polyisocyanate (e.g., Desmodur L). Used in this way, the product has already been applied to various practical purposes with favorable results. These applications and the properties of the polychloroprene have already been described elsewhere. The contents of that publication can be briefly summarized as follows: The polymer, which is supplied in the form of granules, is dissolved in solvents like any other resin for surface coating materials—preferably in a mixture of aromatics and esters. After the solution has been pigmented with inert carbon black, the composition is ground with normal grinding equipment. In general an antioxidant, usually an aromatic amine, is added as well. The polyisocyanate is added shortly before processing, though, even after it has been incorporated, the composition generally has a potlife of at least three days. Finishes applied with a brush, roller, or spray dry very fast and adhere very well. They are highly extensible and have long-lasting resistance to water, aqueous solutions of inorganic chemicals, and to petroleum, mineral oils, aliphatic hydrocarbons, and alcohol.
EV Systems for NR. II. Further Development of Curing Systems and Vulcanizate Properties
Authors: Russell R. M. , Skinner T. D. , Watson A. A.
Published: February 2011

It was shown in Part I that the use of EV systems in NR provides a simple network in which the crosslinks are mainly monosulfidic. Part II describes in some detail the properties of vulcanizates obtained by the use of EV systems and their relationship to conventional and TMTD-zinc oxide cured vulcanizates. The disadvantages of short scorch time and heavy bloom which accompany the TMTD-zinc oxide system are overcome by the new EV systems. The monosulfidic network obtained by the use of EV systems confers on NR good overall physical properties together with much improved resistance towards thermal and thermal oxidative aging. The thermal stability of this type of network is reflected in the outstanding resistance of the vulcanizates to set and reversion, and their good resistance to heat build-up under dynamic conditions. Vulcanizates derived from EV systems have increased resistance to thermal oxidative aging due to the inherent thermal stability of the networks and good response to antioxidant protection. This increased resistance results in much better retention of tensile properties, tear resistance and fatigue cracking resistance on aging, relative to that of conventionally cured vulcanizates.
Compatibility of Copolymers with Corresponding Homopolymers
Authors: Riess G. , Kohler J. , Tournut C. , Banderet A.
Published: February 2011

Since incompatibility of two homopolymers is the rule, it was of interest to see if mixing a corresponding copolymer (graft, block, or random) with a mixture of two incompatible homopolymers would bring about compatibility. For this study we limited ourselves to two systems of atactic polymers: polystyrene/poly (methyl methacrylate), and polystyrene/cis-l,4-polyisoprene since, in these systems, no crystallization occurs at normal temperatures. Investigation of these systems in the solid state—i.e., as films, prepared from polymer solutions by evaporation, enabled us to establish compatibility limits with considerable accuracy. The most important parameters for compatibility of homopolymer-copolymer mixtures seem to be, among other things: composition, molecular weight, and structure of the copolymers. Ternary diagrams for a mixture of two homopolymers and a copolymer show quite plainly that only block copolymers induce a certain compatibility. This is especially true when the polymer proportion in the block copolymers is approximately 50/50, and molecular weight of the homopolymers is substantially lower than that of the copolymer. Graft and random copolymers have little or no effect at all, upon compatibility. We also examined the relation between compatibility and impact strength for the system: polystyrene/polyisoprene/block copolymer.
Practical Evaluation of the [η]-M Relationship II. Estimation of Kθ Values of Polymer Solutions
Authors: van Krevelen D. W. , Hoftyzer P. J.
Published: February 2011

A method is proposed for the prediction of the intrinsic viscosity of θ-solutions, based on the constitution of the dissolved polymer. The method makes use of additive values for constitutional groups to calculate a quantity that represents the specific chain stiffness per main chain atom.
Temperature Dependence of Orientation Birefringence in Rubber and Semicrystalline Polymers
Authors: Hammack T. J. , Andrews R. D.
Published: February 2011

Results are presented for temperature dependence of orientation birefringence, Δn(T), from −195° to 150° C for the following crosslinked polymers: polydimethyl siloxane, polyethylene, ethylene/propylene copolymers (84/16, 75/25, 48/52 mole ratio) and ethylene/vinyl acetate copolymers (96/4, 82/18). On cooling from the rubbery state under a small constant load, the birefringence magnitude shows an abrupt increase when crystallization takes place, reaching a maximum value (Δnc) when crystallization is complete; Δnc is determined principally by degree of orientation in the rubbery state. In the rigid semicrystalline state, below Tg, magnitude of orientation birefringence decreases with decreasing temperature. The transition temperature for the ethylene/propylene copolymers is lowered by increasing the propylene content; nature of the transition changes progressively from a crystallization in polyethylene to a glass transition in the copolymer having 52 mole % propylene. The observed difference in optical parameters for polyethylene and its copolymers suggests a difference in physical structure which strongly affects the optical properties. We believe that the structure of the copolymers is microcrystalline, contrasting to spherulitic crystallinity of polyethylene (and polydimethyl siloxane).