bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Elastomers through Control of Network Chain-Length Distributions
Authors: Mark J. E.
Published: February 2011

Methods are described for obtaining elastomers of controlled network chain-length distributions by restricting the reactivity of the polymer chains to their ends, and then end linking these chains with a multi-functional reactant. The networks of this type that have proved to be of greatest interest consist of short chains end linked with long chains to yield a bimodal distribution of network chain lengths. These bimodal elastomers have unusually high extensibility for their values of the modulus and ultimate strength, and thus considerable toughness, even in the unfilled state. Most such elastomers have been prepared from chains of poly(dimethylsiloxane), by carrying out either a condensation reaction between hydroxyl-terminated chains and tetraethoxysilane, or an addition reaction between vinyl-terminated chains and a poly(methylhydrogen siloxane) oligomer. The material presented in this review discusses the preparation of such elastomers, the characterization of some of their properties, and the interpretation of some of these properties in terms of the molecular theories of rubber-like elasticity.
Synthesis and Characterization of Novel Multiarm-Star Polyisobutylene-Polystyrene Thermoplastic Elastomers
Authors: Puskas Judit E. , Pattern Wayne , Wetmore Paula M. , Krukonis Val
Published: February 2011

New multiarm-star block copolymers of polyisobutylene (PIB) and polystyrene (PS) were synthesized by living carbocationic polymerization using a novel hexafunctional initiator in conjunction with TiCl4. The new initiator, hexaepoxy squalane (HES) was prepared by a simple epoxidation (RT, 5 min) of commercial squalene. The homopolymerization of isobutylene (IB) initiated by HES is living, demonstrated by linear ln([M]o/[M]t) vs time and Mn vs conversion plots and relatively narrow molecular weight distributions (MWD=1.2). The branched nature of the PIBs was proven directly by diphenyl ethylene end capping, and indirectly by kinetic analysis and size exclusion chromatography (SEC). Subsequent blocking of PIB with PS was demonstrated by triple detection SEC: refractive index (RI), multiangle laser light scatering (MALLS) and ultraviolet (UV). A new multiarm-star and a conventionally prepared linear triblock copolymer sample were subjected to supercritical fluid (SCF) fractionation and the fractions were analyzed by SEC and 1H NMR. Analysis of the fractions indicated living conditions for the PS blocking in the star-block. Interestingly, the linear triblock showed bimodal distribution in terms of PS content and molecular weight.
Miscibility of Blends of Saturated Hydrocarbon Elastomers
Authors: Lohse David J. , Garner Richard T. , Graessley William W. , Krishnamoorti Ramanan
Published: February 2011

Over the last several years, a great deal of progress has been made in understanding the basic miscibility between saturated hydrocarbon polymers. This has mainly been accomplished through the use of neutron scattering, but has also benefited by the results from light scattering, pressure-volume-temperature (PVT) measurements, and other techniques. This paper concentrates on the results that apply to elastomers such as polyisobutylene (PIB) and ethylene-propylene-diene rubber (EPDM).
Phase Behavior and Properties of Polyurethane-PVC Blends and Fibers
Authors: Petrović Zoran S. , Javni Ivan , Shull Jonathan , Waddon Alan
Published: February 2011

A polyester urethane elastomer is blended with rigid poly(vinyl chloride) (PVC) and the miscibility of the components studied over the entire range of compositions. The polyurethane elastomer was a block copolymer with a low degree of crystallinity, while PVC was practically amorphous. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) methods showed that polyester urethanes were partially miscible with PVC since two distinct glass transitions, which changed with the change of concentration of components, were observed. Although the PVC content was varied from 0–100%, the aim of the work was to examine if PVC at low concentrations would form fibrils in the urethane matrix and act as a reinforcing agent for the polyurethane elastomer. The morphology of the blends was studied by scanning electron microscopy and x-ray scattering. The blends were then spun into fibers to force the dispersed phase to elongate and form fibrils (draw ratio was about 100). A high degree of miscibility is obtained at low concentration of either of the components. The PVC phase in fibers spun from the blends have higher glass-transition temperature (Tg) than in isotropic blends, presumably due to increased orientation. No fibrillation of the rigid phase in the elastomeric matrix could be observed. The fibers displayed higher strengths but lower elongation at break than the isotropic blends of the same composition. Intermeshing morphology (at about 50/50 concentration) gave the lowest strengths.
Mechanical Behavior of Particle Filled Elastomers
Authors: Bergström Jörgen S. , Boyce Mary C.
Published: February 2011

The strong influence of relatively small amounts of filler particles, such as carbon black, on the mechanical properties of elastomers has been well known for decades and has significantly contributed to increased use of elastomeric materials in many commercial applications. Even though the use of fillers is ubiquitous, satisfactory understanding and modeling of the micromechanisms by which fillers alter the mechanical behavior of elastomers has still not been realized. In this work the influence of filler particles on the equilibrium stress-strain response has been investigated. First, an experimental investigation probing the behavior of a chloroprene rubber with varied filler content has been performed. The experimental data allowed for a direct evaluation of both a newly developed constitutive model based on the amplification of the first strain invariant, and a number of other models proposed in the literature. A direct comparison with experimental data suggest that the new model generates superior predictions, particularly for large strain deformations. Then, in an effort to examine some of the assumptions that are common in the constitutive modeling and also to try to determine which of the input parameters are most important, a detailed series of micromechanical models were constructed using two- and three-dimensional finite element simulations. The results indicate that the effect of filler particles on the equilibrium behavior of elastomers can be accurately predicted using stochastic three-dimensional simulations suggesting that successful modeling mainly requires a rigorous treatment of the composite nature of the microstructure and not molecular level concepts such as alteration of mobility or effective crosslinking density in the elastomeric phase of the material.
Tread Groove Void and Developed Tread Width (Aspect Ratio): Their Joint Influence on Wet Traction
Authors: Veith Alan G.
Published: February 2011

Other than treadwear testing, tires are normally evaluated for important performance features in the virgin or new state. One performance feature that changes, as the tire wears in service, is wet traction. For any given tread compound the wet traction performance is jointly influenced by the groove void level (it changes with wear) and a factor that is a function of the aspect ratio, the “developed tread width,” i.e., the actual width that contacts the road surface. Based on a comprehensive testing program, a wet traction performance parameter called the “specific discharge capacity” has been developed. This accounts for the interactive or joint influence of both of these factors and how this influence changes across a range of operating conditions (speed, pavement texture). The specific discharge capacity is especially important at high levels of “criticality”, i.e., deep water, slippery pavement, high speed.
A Model for Rubber Degradation under Ultrasonic Treatment: Part I. Acoustic Cavitation in Viscoelastic Solid
Authors: Yashin V. V. , Isayev A. I.
Published: February 2011

The physics of rupture of a rubber network under the action of powerful ultrasound is considered. It is assumed that rubber degradation occurs mainly around pulsating microcavities (bubbles) usually present in rubbers. The maximal level of strain is attained in the vicinity of these cavities. A Lodge-like model of finite viscoelasticity is utilized to describe the strain profile around the vibrating cavity at a given ultrasonic pressure. Network degradation rate is taken to be proportional to the number of overstressed network chains. Detailed analysis is given for the case of a thin layer of cured rubber placed between an ultrasonic horn and a die and subjected to static pressure. Ultrasonic pressure in the layer is shown to depend on the thickness of the layer with its value found to be higher than that in the bulk. The static pressure is found to increase the ultrasonic power consumption and to enhance the degradation process. This is due to a decrease in compressibility of the bubbly media leading to a reduction in the ultrasonic attenuation. Calculations are carried out using styrene-butadiene rubber as an example.
Effect of Gasoline Contamination on the Permeation of Organic Liquids through Rubber Membranes
Authors: Xiao S. , De Kee D. , Bovenkamp J.
Published: February 2011

The effect of gasoline and oil contamination on the barrier properties of natural rubber, nitrile rubber and bromobutyl rubber have been experimentally studied for the following organic environmental contaminants: dichloromethane, acetone and toluene. Oil contamination has little effect on the subsequent transport of these organic penetrants. However, gasoline contamination alters the subsequent transport behavior of these organic penetrants, depending on the nature of the rubber and the contamination conditions. Nitrile rubber experiences minor effects, while natural rubber is severely affected. Penetrant breakthrough times as well as limiting diffusion coefficients increase with increasing temperature and/or contamination time.
Orientation Texture and Gas Transport in Semicrystalline Block Copolymer Blends
Authors: Kofinas Peter , Drzal Peter L. , Halasa Adel F.
Published: February 2011

The shear-induced morphologies produced by plane strain compression, using a channel die, were investigated in semicrystalline ethylene/ethylene-propylene (E/EP/E and E/EP) block copolymers blended with semicrystalline low density polyethylene and amorphous polyisoprene homopolymers. Two dimensional small-angle x-ray scattering (SAXS) was used to determine the lamellar orientation relative to the specimen boundaries. Using a cooling rate of 0.27 °C/s and a load of 9.2 MPa, a normal to the plane of shear microstructure orientation texture was produced in the blends. The E homopolymer chains co-crystallize within the confinement of the oriented microphase separated E block copolymer domains. The long period spacing of the oriented microphase separated E/EP block microstructure remained unchanged, while the spacing associated with the crystallization of the E chains increased with increasing weight percent of E homopolymer in the blend. Gas permeability coefficients for He and CO2 were measured for isotropic and oriented blends. The separation properties of these polymer systems was altered by changing the mechanism of gas transport. A selective solvent was used to develop a uniform porous structure in the oriented blend morphologies. The semicrystalline block copolymer blend structure oriented perpendicular to the direction and normal to the plane of shear presents the opportunity to create a high flux porous structure, while keeping the pores of nanometer dimensions, thus providing some selectivity and retaining mechanical strength.
Quantification of Tire-Tread Particles Using Extractable Organic Zinc as Tracer
Authors: Fauser Patrik , Tjell Jens Christian , Mosbaek Hans , Pilegaard Kim
Published: February 2011

A method for identifying and quantifying tire-tread particles in the environment has been developed. It is based on the measurement of extractable organic zinc. The high sensitivity of atomic absorption spectrometry (AAS) with a heated graphite atomizer (HGA) permits assessment of submilligram amounts of tire debris in environmental samples. The analysis is performed on aerosol and soil samples. This new method is more accurate and faster than the previously reported IR method.
Structural Characterization of Sulfur-Vulcanized Rubber Networks
Authors: Saville B. , Watson A. A.
Published: February 2011

Studies of the chemistry of vulcanization today occupy a central position in current efforts to achieve better product performance from available natural and synthetic rubbers. They provide technologists with increasingly realistic pictures of the molecular make-up of vulcanizates from which relations between physical properties and chemical structure may be deduced. In addition these studies are aimed at an understanding of vulcanization, sufficiently advanced in chemical mechanistic terms, to permit the effect of changes in curing system on vulcanizate structure to be rationally predicted. Perhaps the most important and fascinating aspect of current activities in vulcanization chemistry is the problem of determining the structure of rubber vulcanizates. Part of this problem forms the subject of this Review. In order to keep this article within reasonable proportions two limits have been observed. First, attention in Section IV has been restricted to “sulfur-vulcanized” rubbers, i.e., where vulcanization is effected using recipes containing elemental sulfur or sulfur donor (e.g., thiuram disulfides or dithiobis-amines). Secondly, we shall distinguish between the in toto vulcanizate and the corresponding network (as defined by Moore) restricting our attention to the latter. Thus, we are concerned with the crosslinked assembly of rubber chains (the network) apart from filler particles, residual curatives and simple molecular products of the vulcanization reactions. These latter constituents are extra to the network and may be examined as a separate analytical exercise. The physical and chemical analyses of rubber networks cannot be undertaken entirely by classical means, and some unique problems are encountered which have required, and still require, imaginative techniques for their solution. An attempt has been made to deal with the important progress which has been made to date, emphasis being given to the most practicable and reliable methods which have been adopted and practiced. It will become evident that there are wide gaps in our knowledge, some of which must be filled even before structural characterization of certain networks can be tackled. It is therefore part of the intention of this review to point out the important outstanding problems and to stimulate activity in these areas while defining as clearly as possible the numerous pitfalls which exist in this demanding type of investigation.
Mechanics of the Pneumatic Tire
Authors: Frank F. , Hofferberth W.
Published: February 2011

We have attempted to describe the mechanical problems of tires, from the point of view of elasticity theory, and have, in this connection, regarded research on the stresses and deformations in the casing as the primary problem of tire mechanics. Less attention was paid to factors which have to do with the behavior of tires with respect to the vehicle, because we believe that the effects of the choice of any design or structural parameters or materials, upon the behavior of tires, are not explainable in a sufficiently general manner, as long as the above problem, designated as the chief one, cannot be handled, at least numerically. How far we still have to go, in spite of many efforts, can be seen from Section III. The striking thing here is that belted tires have scarcely been investigated up to now. This may be due, in part, to the fact that the prerequisites for a theoretical investigation, reported in Section I, have been provided only imperfectly for this type of tire, up to now. Our own contribution, in this respect, was an outline of a generalized theory of the tire cross section, found useful for the belted tire. Measured against the state of knowledge in related fields, the present survey of the literature available to us shows that tire mechanics still represents a rather poorly developed field of research which might arouse the interest of scientists working at academic centers, for example. Section II of this work can also be thought of as stimulating interest in further development, as it mostly presents methods which can be taken over from other fields.
Vacuole Formation and the Mullins Effect in SBR Blends with Polybutadiene
Authors: Smith Ronald W.
Published: February 2011

Electron microscopic examination of stretched thin films of black loaded vulcanizates of SBR and polybutadiene blends shows that vacuole formation is prevalent when the polybutadiene content drops below one-third. The vacuoles that formed on stretching these stocks did so at small coherent carbon black agglomerates rather than at individual carbon black particles. It is felt that the mixing characteristics were such that stocks with more polybutadiene experienced more grinding action, which resulted in destroying the small agglomerates that caused vacuoles in stocks with less polybutadiene. Hysteresis data on the same series indicated that for the vacuole forming stocks the ratio of the areas of the first to the second hysteresis loop reflects the fact that vacuoles are being formed. The overall Mullins' effects displayed by all members of the series was similar, and a mechanism was proposed that slightly modifies the hysteresis criteria of Harwood, Mullins, and Payne. It is suggested that this mechanism can also be used to explain the effects that various particle size carbon blacks have on extensions following the initial one. The effect of vacuole formation on the overall Mullins stress softening was minor and equivalent to disrupture of filler structure.
Elucidation of Polymer Microstructure by High Resolution NMR Spectroscopy
Authors: Ferguson Raymond C.
Published: February 2011

High resolution NMR spectroscopy is proving to be a useful experimental technique for determining the microstructures of high polymers. Its major utility, aside from identifying structural features often not detectable by other methods, lies in quantitative applications. Some examples are the determination of monomer ratios in copolymers, polymer tacticity, sequence isomerism of monomer units, and other types of structural isomerism. The applicability of the method is being enhanced by continuing development of high-field spectrometers, special accessories, and new experimental techniques, and by application of computers to the analysis of spectral data.
Sequence Distribution in Copolymers Chemical Studies
Authors: Harwood H. James
Published: February 2011

Various chemical procedures are available for studying the sequence distribution in copolymers, but none can be applied routinely. The run-number approach permits the results of such studies to be treated with ease; all results obtained to date are consistent with classical copolymerization theory.
Viscoelastic Properties of Multiple Network Polymers. IV. Copolymers of Styrene and Divinylbenzene
Authors: Shibayama Kyoichi , Suzuki Yasukira
Published: February 2011

Copolymerization of vinyl and divinyl monomer is a typical method for preparing a network polymer. A multiple network structure, in which one network entangles with another, is supposed to be produced when a network polymer is swollen in the monomer mixture and then polymerization of absorbed monomer is carried out so as to superpose the second network on the first. Viscoelastic properties and degree of swelling in solvents were investigated for composite polymers prepared from styrene and divinylbenzene. Results were consistent with presumed characteristics of multiple network structures.
Effect of Molecular Weight on Dynamic Mechanical Properties of SKD cis-1,4-Butadiene Rubber
Authors: Marei A. I. , Sidorovich E. A.
Published: February 2011

In the high-elastic temperature range the molecular weight has a considerable effect on the dynamic mechanical properties of linear (uncrosslinked) SKD cis-1, 4-butadiene rubber. In this temperature range an unequivocal correlation exists between the rebound resilience at a given temperature and the viscosity average molecular weight, and the determination of the resilience can therefore be recommended as a rapid method of finding the molecular weight of SKD. A similarity is found in the dynamic mechanical behavior of rubbers of different molecular weights in the high-elastic temperature range. In the low-temperature range an increase in the molecular weight of crystalline polymers of SKD is accompanied by an impairment of their elastic properties.
Resistance to Ozone Cracking in Elastomer Blends
Authors: Andrews E. H.
Published: February 2011

The phenomenon of ozone cracking has been investigated for elastomer blends containing an ozone reactive phase (natural rubber) and an ozone inert phase (ethylene propylene rubber). Electron microscopical studies reveal phase separation in the blend and the locus of ozone attack. Ozone cracks traverse the reactive phase and occasionally jump across inert particles without severing them. This mechanism provides the basis of a theory which correctly predicts the dependence of both the critical stored energy for ozone cracking and the crack density upon the blend composition.
Elastic Properties of Networks Formed from Oriented Chain Molecules II. Composite Network
Authors: Greene A. , Smith K. J. , Ciferri A.
Published: February 2011

Elasticity measurements were carried out for several natural rubber and poly (ethyl acrylate) networks crosslinked in two stages (first in the isotropic state and then in the stretched state). These composite networks were shown to be similar in behavior to networks formed by crosslinking in the fibrous state and differed significantly from the usual network formed by crosslinking in the isotropic state. The anisotropic elasticity exhibited by these composite networks cannot be fully accounted for by finite chain extensibility. It appears that the deviation of the behavior of these networks from theoretical expectation is associated with the same kind of effects responsible for deviations from rubber elasticity theory in conventional networks.
Crystallization of Natural Rubber
Authors: Bekkedahl Norman
Published: February 2011

It is, indeed, a very great honor to have been chosen as the Charles Goodyear Medalist for 1967, and I very much appreciate the opportunity of coming here to tell you about some of the research work in the field of rubber with which I have been associated for a number of years. The bylaws of the Division of Rubber Chemistry, A.C.S., require that the recipient of this award deliver a lecture before the Division on a subject that is related to the elastomer field and presented in accordance with the contribution for which the medal is awarded. It should, therefore, be quite appropriate for me to discuss one of my favorite subjects, the crystallization of natural rubber. My first thought was to talk on a broader subject, transitions in rubber, which would have included the glass transition, but such a paper was found to be much too long. Even the subject of the crystallization and melting transition is so broad that only a very condensed version can be given here today. In fact, the references for a proper review would run into the hundreds, so therefore I decided to restrict the paper to cover only the research work that has taken place in our own laboratories of the National Bureau of Standards. I should like to consider this award as one given not to me alone but rather to the group of us at the National Bureau of Standards who have been conducting scientific research on rubber during the past few decades. The names of most of these investigators who have made contributions in the area of rubber crystallization will appear in the bibliography of the published paper, but I should like at this time to name a few of the senior scientists whose work we shall discuss here.
Stereochemistry of Rubber Biosynthesis
Authors: Archer B. L. , Barnard D. , Cockbain E. G. , Cornforth J. W. , Cornforth Rita H. , Popják G.
Published: February 2011

The stereochemistry of the formation of natural rubber and trans-trans-farnesyl pyrophosphate in latex has been studied in vitro using [2−14C−(4R)−3H1] and [2−14C−(4S)−4−3H1]mevalonates as substrates. The proton eliminated from C-2 of isopentenyl pyrophosphate during the formation of farnesyl pyrophosphate in latex has the same steric position as that released in the liver system, and is epimeric with that eliminated during the biosynthesis of rubber. Complete stereospecificity is exhibited by the enzymes in the two cases. In rubber biosynthesis isoprene residues are incorporated directly in all-cis configuration without the intervention of trans structures.
Road Surface Characteristics and Skidding Resistance
Authors: Sabey Barbara E.
Published: February 2011

When roads are wet their skidding resistance is reduced by the lubricating action of the film of water on the road. Under some circumstances this reduction may be substantial and the extent of it is largely dependent on the characteristics of the road surface. The first requirement for a good skidding resistance on wet roads is to facilitate break through of the water film in order to establish areas of dry contact between the road and the tire. Drainage channels, provided by the large scale texture of the road or by a pattern on the tire, assist in getting rid of the main bulk of water and are of increasing importance the higher the speed. The penetration of the remaining water film can be achieved only if there are sufficient fine scale sharp edges in the road on which high pressures (about 1000 lb/in2) are built up. The existence of such fine scale sharpness gives the surfaces a harsh feel. When vehicles are travelling at speeds of about 30 mph the fine scale texture of the road is the dominant factor determining skidding resistance. However, as they travel faster, it becomes increasingly difficult to penetrate the water film in the time available, however harsh the surface. At high speeds the requirements for a good skidding resistance are therefore different. The resistance to skidding arises to a larger extent from energy losses in the rubber of the tire as the surface of the tread is deformed by projections in the road surface and, although the physical properties of the tread rubber are important in this respect, it is essential to have sufficiently large and angular projections in the road surface to deform the tread, even though a water film may still be present on the surface. At higher speeds the coarseness of texture becomes as important as its harshness.
Elastic Properties and Network Structure in Silicone Gum Vulcanizates
Authors: Bobear W. J.
Published: February 2011

A model of a rubber network formed from finite, linear polymer chains is treated, using expressions from accepted elastic theory as well as relations that have been less generally used or only implied. The resultant empirical mathematical expressions conform very closely to the predictions of the simple kinetic theory of rubber elasticity and are mathematically consistent, in that the major properties and measurements are interrelated, and apparent inconsistencies in the literature are reconciled. As a consequence, an empirical equation is developed for the relationship between elastic properties and network structure in silicone gum vulcanizates. This equation is then applied to the estimation of peroxide crosslinking efficiencies.
Steady State Melt Viscosity of Plasticized Hydrocarbon Elastomers
Authors: Kraus G. , Gruver J. T.
Published: February 2011

The steady state melt viscosity of several plasticized hydrocarbon elastomers is described by a reduced variable treatment which allows superposition of the viscosity and shear rate curve for any polymer containing a diluent on the viscosity curve of the pure polymer. The shift factors which accomplish this superposition may in turn be broken up into two factors: (1) a function of the volume concentration of the diluent alone, which represents the loosening of the entanglement network, and (2) a factor representing the effect of the diluent on segmental friction and chain configuration. The latter is shown to be related to the temperature of measurement and the glass transition temperatures of both polymer and diluent. The relationships developed permit predictions of plasticizer efficacy for any diluent and polymer combination from glass transition and density data alone.
Entropy Elasticity in High Polymers
Authors: Linhardt Friedrich
Published: February 2011

Vulcanized rubber has an unusual property, known early in the 19th century, but not understood until 1935: it increases in stiffness with rise in operating temperature. A strip of rubber loaded with a weight and heated does not stretch; on the contrary, it contracts to some extent. Theoretical interpretations of this effect showed deformation of rubber, as well as its softness and high extensibility, to be determined by entropy, among other things. “Entropy elasticity” was looked upon as a peculiarity of rubber. It was thus only logical, when materials were classified as “rubbers” that they should be distinguished from all other materials by using the expression “entropy elastic behavior”. To be sure, one is inclined today to consider entropy elasticity a characteristic of all high polymers, including those not crosslinked. The present article reports an experimental approach to this problem.
Simple Theory of Stress Strain Properties of Filled Polymers
Authors: Nielsen Lawrence E.
Published: February 2011

By the use of simple models of filled plastics, approximate equations are derived for elongation to break in the case of perfect adhesion between the phases and for the tensile strength in the case of no adhesion between the polymer and filler phases. By combining these equations with equations for the modulus (assuming Hookean behavior) all the stress strain properties can be derived, including rough estimates of the impact strength, as a function of filler concentration. The theory predicts a very rapid decrease in elongation to break as filler concentration increases, especially with good adhesion; it is also predicted that the tensile strength of a filled polymer can be greater than that of an unfilled polymer.
Forms of Combination of Sulfur in Vulcanization of Rubber
Authors: Scheele Walter
Published: February 2011

A certain portion of the sulfur used appears as polysulfide sulfur in all vulcanization processes. The polysulfide concentration passes through a maximum with time, so that it must be considered to be an intermediate product which disappears to form final products. It is shown that the dependence of polysulfide sulfur concentration on time may be described by an empirical equation with three constants, of which one is related to the system, the other two depending in a characteristic way on concentration or temperature. The application of this equation permits recognition of a close relation between the kinetics of sulfur decrease and that of polysulfide formation. This leads to a kinetic theory of formation and decrease of polysulfide sulfur which is developed in detail. Applying the experimentally determined first order velocity constants of sulfur decrease and conditions obtaining for polysulfide maximum, velocity constants for polysulfide decrease can be calculated. With these, equations for the functional relation between polysulfide sulfur and time as well as for the increase of final products may be set up. Good correspondence between theory and experiment is found for the dependence of polysulfide sulfur in the vulcanizate on time. Comparisons were examined which indicate the validity and applicability of the kinetics developed.
Reactions of Carbenes with Unsaturated Polymers
Authors: Lishanskii M. S. , Tsitokhtsev V. A. , Vinogradova N. D.
Published: February 2011

The literature has a limited amount of data on chain reactions of unsaturated polymers, in particular diene polymers. The appearance of a paper dealing with addition of dichlorocarbene to polyisoprene and to polybutadiene has impelled us to publish results of studies we made on reactions of unsaturated polymers with carbenes, which have made it possible for the first time to obtain polymers containing in the main chain, or in the side chains, cyclopropane groups with polar substituents. Addition of carbenes to cis-1, 4-polyisoprene, trans-1, 4-polyisoprene, 1, 4-polybutadiene, and 1, 2-polybutadiene was accomplished through decomposition reactions of diazoacetic esters catalyzed by copper salts (for carbethoxycarbene and carbomethoxycarbene) and the reaction of the ethyl ester of trichloroacetic acid with sodium methylate (for dichlorocarbene).
Determination of Double Bonds in Ethylene Propylene Terpolymer Rubbers
Authors: Hank R.
Published: February 2011

Developments in the field of sulfur vulcanized unsaturated ethylene propylene terpolymer rubbers, also known as EPT rubbers, have progressed rapidly in recent years. Considerable success has been achieved in producing EPT rubbers from ethylene, propylene, and various dienes. Initial difficulties, involving introduction of double bonds into already known ethylene propylene copolymers, were soon overcome when it became clear that it was not the then commonly conjugated dienes such as butadiene and isoprene, but rather nonconjugated dienes, which were required for successful terpolymerization with ethylene and propylene, according to the Ziegler process. As with butyl rubber, it is sufficient, for vulcanization purposes, to incorporate one or two mole per cent of such dienes into the terpolymer. It is especially important, not only for polymerization, but also for rubber processing, to know the type and amount of unsaturation. In this article we wish first of all to report on double bond determinations in general and then, in particular, on qualitative and quantitative dicyclopentadiene determinations in ethylene propylene terpolymers. It is especially important, not only for polymerization, but also for rubber processing, to know the type and amount of unsaturation. In this article we wish first of all to report on double bond determinations in general and then, in particular, on qualitative and quantitative dicyclopentadiene determinations in ethylene propylene terpolymers.
Fracture of Amorphous Polymers
Authors: Landel R. F. , Fedors R. F.
Published: February 2011

At sufficiently high temperatures compared to the glass temperature, both experimental evidence (Figure 7) and Equation (10) predict that failure envelopes obtained from samples differing in νe will superpose to a common response curve f(ε) independent of chemical structure of the polymer when σb is normalized to unit νeT. At lower temperatures, experiment and Equation (8) indicate that in such a normalized plot, individual failure envelopes will diverge from the common response curve, f(ε), due primarily to the effect of the chain flexibility parameter n. As the temperature is lowered still further, Equation (6) shows that the shapes of individual envelopes may vary if the time dependences of E and g differ. This effect is presumably the factor which produces the difference in shapes between the Viton elastomers and the others shown in Figure 7. In addition, Equation (4) relates the maximum value which λb can attain to other readily measured parameters, notably νe. Thus knowledge of these two parameters, νe and n, is sufficient to predict to a good approximation the shape and location of the failure envelope up to the region of (λb)max.
Crystallization in Stretched Polymer Networks. I. trans-Polychloroprene
Authors: Gent A. N.
Published: February 2011

Changes in tensile stress afford a simple means of studying the rates of crystallization and the melting temperatures in crosslinked polymers subjected to simple extension. The form and magnitude of the stress changes in networks of trans-polychloroprene are closely similar to those observed for cis-1:4-polyisoprene and cis-l:4-polybutadiene networks. They are in accord with the formation of oriented crystallites and incompatible with folded chain crystallization at extensions as low as 15 per cent. It seems likely that the present networks do not crystallize by chain folding even in the unstretched state. The large increases in rate of crystallization with extension are approximately accounted for by corresponding increases in the equilibrium melting temperature. Direct measurements of the melting temperature show similar rises with extension. The rise in melting temperature is in good agreement with Flory's theoretical treatment of oriented crystallization at extension ratios of three and higher (when the crystallite orientation is complete) for three networks having different degrees of crosslinking. When referred to a constant segmental mobility, namely, that obtaining at Tg+50° C, the rates of crystallization at various extensions obey a common dependence upon the degree of supercooling. This relation is in fair accord with theories of nucleation kinetics, except at the lowest temperatures where there is some indication of the appearance of a new crystal form.
Preparation and Properties of Polymer Mixtures
Authors: Pazonyi T. , Dimitrov M.
Published: February 2011

A useful and generally accepted method of increasing the available selection of plastics is the manufacture, by blending existing polymers, of mixed materials with new properties. Properties of the blend can be expected to correspond to the additive properties of the plastics making up the mixture, in accordance with their proportions. This is very often the sole purpose of the process, e.g., when plasticizing a brittle polymer with a more plastic one. It can however also be expected that some properties of the blend may be better than what would be given by pure additivity, as is observed with some mixed solvents or alloys. Polymers are mixed industrially on processing machinery similar to that used for processing plastics, or mixing in additives, i.e., on mills, in internal mixers, mixing extruders, Ko-Kneaders, etc. Adequate mixing is often only possible at the processing temperature of the material which requires the highest temperature. Experience has shown that in the usual processing conditions only certain polymers are miscible. Nonmiscible polymers separate in the course of or at the end of the mixing process. Such material disintegrates into thin layers or fibers on cooling. The practical compatibility of polymers is not easy to explain theoretically. We shall see that in some systems the mixtures are mutual solutions of their components, while in others the possibility of forming a true mixture must be excluded, yet blends with valuable properties are easily obtained in practice.
Vapor Pressure of a Swollen Crosslinked Elastomer
Authors: Gee G. , Herbert J. B. M. , Roberts R. C.
Published: February 2011

This investigation was undertaken with the aim of using vapor pressure measurements to study the configurational free energy changes involved in the isotropic dilation of a network. The main conclusion is that the assumptions implicit in this approach require further study. These same assumptions are involved in conventional determinations of crosslinking from swelling. There is reason to suspect that such measurements overestimate crosslinking.
Radiation Induced cis and trans Isomerization of Polyisoprenes and Temperature Dependence of the Equilibria
Authors: Tsurugi Jitsuo , Fukumoto Tsugio , Yamagami Masayuki , Itatani Hiroshi
Published: February 2011

The cis and trans interconversion of polyisoprenes in solutions induced by γ-radiation in the presence of a sensitizer, which is any one of organic bromides or n-butyl mercaptan, was studied by using hevea and gutta percha as starting substances. The percentage cis remaining or converted after irradiation was determined by the infrared absorption. The equilibrium constants for the interconversion at 22, 60, and 100° C were found to be 3.00, 5.25, and 7.33, respectively. The firstorder rate constants for as cis → trans and trans → cis isomerizations at 22° C were calculated to be 9.05 and 2.91, respectively. The results were interpreted by the mechanism proposed by Golub, according to which the double bonds from π complexes with radiolytic fragments from sensitizers give a radical transition state capable of interconversion. However, our results showing that heating shifts the equilibrium toward trans isomer are not in accord with the mechanisms of the radiation-induced isomerization of polybutadiene of Golub and those for photoisom-erization of aromatic azo compounds.
Kinetics of Urethan Cleavage in Crosslinked Polyurethans
Authors: Singh Ajaib , Weissbein Leonard
Published: February 2011

A series of clean, well defined polyurethan networks was synthesized from polyester glycols, 2, 4-tolylene diisocyanate, and 1, 1′, 1″-trimethylolpropane by means that afforded precise control over the content of urethan groups per network chain. The thermal cleavage of these networks was studied using the technique of stress relaxation. Analysis of the stress relaxation data on each network structure revealed two exponential decay processes differing in rate by about an order of magnitude. The rate of the slower process, which dominates the overall stress decay, was shown to be directly dependent on the content of urethan groups per network chain. Positive identification of this process with urethan cleavage was thereby established. The kinetic and thermodynamic constants associated with urethan cleavage were then calculated from data on this process at different temperatures. The more transient stress decay process was not uniquely definable, but probably originated from the cleavage of one or more types of weak linkages found in small but variable proportions in the different polyurethan networks. The nature and origin of these weak linkages was discussed.
Application of the Hydrodynamic-Structural Theory of Non-Newtonian Flow to Suspensions which Exhibit Moderate Shear Thickening with Particular Reference to “Dilatant” Vinyl Plastisols
Authors: Gillespie T.
Published: February 2011

A general equation, derived in previous work, fits flow data for moderately shear thickening dispersions of poly (vinyl chloride) particles in an oil. The theory on which the equation is based predicts that the number of structural links in a disperse system can increase with increasing shear rate without shear thickening, provided n∞/n0<2, where n∞ and n0 are the number of links per cubic centimeter at infinite shear rate and zero shear rate, respectively. This could account for the unexplained occurrence of “volume dilatancy” without “rheological dilatancy” previously reported in the literature. When n∞/n0<2, viscosity increases with increasing shear rate to a maximum value and then the viscosity decreases with further increase in shear rate. This effect is explained as a competition between increase in the number of links with increasing shear rate and decrease in link lifetime with increasing shear rate. Aging of vinyl plastisols is examined and found to involve changes in both hydrodynamic and structural viscosity which can be explained by absorption of oil into the porous poly (vinyl chloride) particles.
Rapid Treadwear Ratings with Radioactive Isotopes
Authors: Gehman S. D. , Reilly P. J. , Larsen G. M.
Published: February 2011

Incorporation of radioactive isotopes in small surface areas of tire treads permits wear measurements by counting before and after wear. The isotope is limited to a depth of about ten mils so that the fraction of activity worn off is appreciable in a hundred miles or so. Such experiments were made with S35, Zn65O, and I125. The first two were applied to uncured tires in thin sheets chemically identical to the tread compounds. Zn65 was counted with a shielded Geiger—Müller tube. For S35, miniature specimens were cored from the tire treads, dissolved in hot xylene, and counted in an automatic, liquid scintillation counter. Filter paper was laminated to aluminum foil and dipped in a solution of iodine and Iodine-125 in toluene. Small disks or strips were applied to tire treads, usually after a break-in run of several hundred miles. The iodine diffuses rapidly into the rubber, combining stably in some compounds and otherwise being fixed by subsequent application of a solution of silver perchlorate in toluene. Counting was preferable with a scintillation probe about ninety times more sensitive than a Geiger-Müller tube. Wear calibration curves were secured by controlled grinding and counting of a similarly tagged specimen of each tread compound. Physical properties were not affected appreciably by these iodine concentrations. Radioactivity in a tire tagged by strips across the tread at five places was about two microcuries. Results correlated well with conventional techniques. Road contamination from such tests is insignificant. The I125 method has advantages in versatility, acceleration of tire wear tests, fast recognition of localized wear and wear patterns, better “control” of weather, road, and vehicle conditions by shortening the tests, and should reduce compound interaction for test tires made with sectors of different tread compounds.
Coefficient of Wet Friction of Tire Treads
Authors: Kern W. F.
Published: February 2011

The schematic presentation in Figure 1 is an attempt to demonstrate the importance of friction coefficient in matters of driving safety and abrasion resistance, which are of interest to both tire manufacturers and users. References 1 to 3 present the viewpoint of road engineers, designers of motor vehicles, tire producers, rubber compounding experts, and various suppliers of different raw products. The numerous factors involved in producing skid resistant tires are summarized in Figure 2. From among such factors, we take up, here, only the tire element within the contact surface of the tire. The coefficient of friction for this element was investigated with test specimens, preferably under wet conditions, as a function of speed, temperature, and load, and against friction bases that exhibited a variety of grip characteristics. This coefficient of friction is affected by a number of other variables, Tables I and Ia, some of which will be discussed in this article.
Carbon Black Surface Areas by the Harkins and Jura Absolute Method
Authors: Kraus G. , Rollmann K. W.
Published: February 2011

The Harkins and Jura (HJ) absolute method of surface area determination (Harkins and Jura, J. Am. Chem. Soc. 66, 919, 1944) has been applied to a large number of carbon blacks. Surface area is calculated from the heat of immersion of the solid powder covered by a preadsorbed multilayer of the immersion liquid. For non-porous carbon blacks good agreement with nitrogen adsorption surface areas is obtained, but with porous blacks the HJ method gives smaller values since micropores are filled and bridged over by the pre-adsorbed film. Thus the HJ areas are more nearly representative of particle size and may be used to calibrate indirect methods of particle size determination. An example of this is shown using light reflectance values on dry carbon black and possible complications due to particle size distribution in the use of the reflectance test are discussed.
Effect of Carbon Black Densification on Structure Measurements
Authors: Dollinger R. E. , Kallenberger R. H. , Studebaker M. L.
Published: February 2011

A simple method of pretreating carbon black has been developed which permits measurements to be made on the dry carbon black which reflect on the basic property called “structure.” Correlation between these measurements and extrusion shrinkage of raw stocks is demonstrated. With a small surface area adjustment, this correlation is believed to be as reliable as extrusion shrinkage values.