bluuebunny/crossref_metadata_2025 huggingface dataset:
Research for a Uniform Quality Grading System for Tires. IV. Tread Wear
Authors: Brenner F. C. , Kondo A.
Published: February 2011

This research had as its objective the development of a test procedure for rating tires for tread wear. The results of preliminary experiments on roads of different composition and severity are discussed. The authors conclude that the course on which tires are to be rated should include several different pavements and a variety of maneuvers of unequal severity. Two courses, one near Bryan, Texas, and the other near San Antonio, Texas were designed on this principle. Eighteen brands of tires including bias, radial, and G78 belted bias tires were run on each course. The tires ranked in order of decreasing projected mileage on each course were highly correlated, although the mileages were not equal.
High Temperature Relaxation Transitions in Elastomers
Authors: Sidorovich E. A. , Marei A. I. , Gashtol'd N. S.
Published: February 2011

1. For binary mixtures of polybutadienes with differing molecular weights, a high temperature (or low frequency) transition was discovered, with the temperature-frequency position of the transition showing up as a function of the molecular weight of the low molecular weight constituents, and yet the transition does not depend on the concentration of these constituents. The value of the maximum for the mechanical loss tangent is determined by the concentration of low molecular weight components. 2. With regard to the viscoelastic behavior of the mixes at reduced temperatures, the transition reflects mainly the presence of the low molecular weight components, but at high temperatures the transition is indicative of the presence of the high molecular weight constituents. 3. The observed transition is associated with the manifestation of mobility of the molecules of the low molecular weight components, as a whole.
Relaxation of Stress and Electrical Resistivity in Carbon-Filled Vulcanizates at Minute Shear Strains
Authors: Voet A. , Cook F. R. , Sircar A. K.
Published: February 2011

Measurements have been made of the relaxation of stress and electrical resistivity of carbon black-loaded vulcanizates subjected to shear deformation varying between 0.5 and 20%. Samples were initially brought into an equilibrium state by the application of a sinusoidal shear strain for a period of time long enough to ensure equilibrium condition, established by constancy in the dynamic stress- and resistivity-time cycles at each selected strain amplitude. It could be shown that at the small strains employed all phenomena were completely reversible, indicating the absence of rupture of elastomer chains or crosslinks and of strong bonds between carbon and elastomer, as well as of chemical aging. The shear stress relaxation rates show a small initial decrease with deformation and are fairly constant over the rest of the deformation range. Carbon black loading increases the rate—the more, the smaller the particles and the higher, the higher the loading—but the rate is independent of the carbon structure. Actual initial stress values follow the expected stress-strain relations. Resistivity relaxation rates, on the other hand, show a very rapid increase with shear deformation, more pronounced at higher structures and for smaller particles. Initial resistivity values are in complete accord with the dynamic behavior of vulcanizates. An explanation of the shear stress relaxation rates of the loaded vulcanizates has been made on the basis of reestablishment of previously disrupted weak bonds between particles and elastomer chains. Resistivity relaxation rates could be explained by assuming rebuilding of disrupted transient structures, while the unusual behavior of Graphon, with a zero relaxation rate, appears to be caused by its lack of bonding to elastomer chains. Finally, there are indications that the equilibrium resistivity behavior of a carbon-loaded vulcanizate subjected to shear strain at increasing amplitudes under reversible conditions is closely parallel to the reinforcement characteristics of the carbon black filler. Measurement at higher temperature permits calculation of an activation energy which appears to correspond to physical interaction.
Relaxation of Stress and Electrical Resistivity in Carbon-Filled Vulcanizates at Moderate and High Extensions
Authors: Sircar A. K. , Voet A. , Cook F. R.
Published: February 2011

Measurements have been made of the relaxation of stress and electrical resistivity of stretched carbon black-loaded vulcanizates throughout the elongation range up to break. Data were obtained for vulcanizates with a number of carbon blacks, varying in particle size and in structure. The influence of the degree of loading as well as of the type of elastomer was investigated. In a gum vulcanizate there is initially a decline in rate of stress relaxation at increasing elongation as a result of the limited extensibility of the elastomer chains, followed by a constant rate at higher extensions. The level for a carbon-loaded vulcanizate is always higher than for the gum. At lower elongations this is due to an additional relaxation mechanism, the reformation of broken weak bonds between elastomer and filler particles upon standing. At medium and higher elongations, the stress relaxation rate for the carbon-filled vuleanizates increases sharply with increasing extension, due to persistent carbon chain alignment and, at still higher elongation, to rupture of carbon-elastomer bonds, both phenomena leading to additional modes of stress relaxation. Resistivity relaxation rates reflect changes in carbon black distribution. An initial increase at small extensions is due to rebuilding of destroyed transient structures. A decrease in relaxation rates for medium extension ranges is caused by persistent carbon chain alignment, less pronounced at increasing elongation. At the higher elongations carbon-elastomer bonds arc broken, leading to randomization of chains, resulting in negative relaxation rates with higher structure blacks at the highest elongations. All such effects depend to a large extent on the carbon structures. The influence of loading level, of particle size and of elastomer type is discussed.
Formulation for Continuous Vulcanization in Microwave Heating Systems
Authors: Ippen J.
Published: February 2011

For a number of years the rubber industry has been trying to make its processes as continuous as possible. Techniques which dispense with interruptions are particularly desirable in the production of strip and hose, for extrusion is a continuous process whose interruption for the purpose of enabling the goods to be cured is both illogical and unsatisfactory. Several continuous vulcanization methods, such as the use of hot air and the liquid curing method, are receiving attention. A new development in this field is the use of microwave for vulcanization. Microwave curing is a valuable supplement to other continuous vulcanization methods, in comparison with which it offers advantages in some respects.
Hydrolytic Stability of a New Urethane Elastomer
Authors: O'Shaughnessy F. , Hoeschele G. K.
Published: February 2011

A new polyether based liquid casting urethane elastomer having excellent abrasion resistance, improved electrical properties, and superior hydrolytic stability has been described. A good balance of working life, physical properties, and overall handling ease are provided when MDA is used as the curing agent. These elastomers may be safely used as the contact surface of articles intended for use in handling bulk quantities of dry food. This unique combination of properties indicates many practicable applications.
Recent Developments in Acrylic Elastomers
Authors: Vial T. M.
Published: February 2011

The literature on acrylic elastomers between 1962 and the present has been reviewed under four topics: New Crosslinking Sites, Property Improvements, Compounding, and Fundamental Studies.
Elastomers for Implantation in the Human Body
Authors: Braley Silas A.
Published: February 2011

In the continuing effort to heal the ills of their patients, the medical profession has endeavored to make use of many materials, not only as medicines, but also for mechanical devices which could be used to repair damage to the body. At first these devices were simple ones such as tree limbs for crutches, and for splints to hold broken bones in place. As technology developed, it became possible to make less utilitarian devices. Tycho Brahe, the famous astronomer, wore a gold nose to replace his own that was bitten off in a tavern brawl. As medicine became more sophisticated, attempts were made to replace subdermal tissues. These were mostly failures because of the lack of knowledge of sterility and because the body would reject most of the materials used. Some early successes were made, however, notably the use of silver plates to replace missing pieces of skull. It is only in the past 50 years that special alloys have been developed which allow the repair of many bone problems with a good degree of surety. Of recent date, tantalum, Vitalium, and 316L stainless steel have been used to make a wide variety of devices for permanent subdermal implants: hip joints, skull plates, wires, pegs, pins, screws, and plates. However, these are hard, and are, therefore, only useful for the repair of bones. Most of the body is made up of soft tissues, and soft materials must be used to replace or repair them. For instance, one cannot make a satisfactory esophagus from stainless steel, since any motion of the neck or even such small actions as pulsating blood vessels would cause cutting of the soft tissues next to the hard metal. Many soft materials were tried, but all, when placed in the tissues caused intense reactions, and they inevitably had to be removed. This paper will concern itself with the search for and the applications of elastomeric materials for permanent subdermal soft tissue replacement.
Low Strain Dynamic Properties of Filled Rubbers
Authors: Payne A. R. , Whittaker R. E.
Published: February 2011

Carbon black does not exist as single spherical particles but forms itself into a rodlike primary structure. These rodlike structures then form into an aggregated secondary network. This secondary network is believed to be held together by Van der Waals-London attraction forces. The decrease in shear modulus of filled rubber vulcanizates with strain is due almost certainly to these secondary forces. Special mixing techniques such as attrition of the carbon black, increased time of mixing, or the addition of chemical promoters which aim at dispersing the carbon black within the mix better are shown to decrease the value of G′0−G′∞. The absence of any modulus change with strain for unfilled vulcanizates and secondly the little change observed in values of G′0−G′∞ with increasing vulcanization of the rubber when containing the same amount of carbon black confirms that the decrease in modulus with strain amplitude is in no way associated with the gum phase of the filled vulcanizate. The similarity in behavior of carbon black filled rubbers with clay/water and clay/rubber systems indicates that the decrease in modulus with amplitude is due to the breakdown of the three dimensional filler aggregates. A number of rheological studies on clay systems has confirmed that clay particles form into rigid three dimensional structures when dispersed in a medium. Evidence for the aggregated filler structure to be held together by Van der Waals-London attraction forces comes from the reasonable agreement between the experimental values for the forces required to breakdown the carbon black aggregates in paraffin oil and the forces calculated from Van den Tempel's model for flocculated solid particles in a liquid. The successful application of a domain model to the hysteretical behavior exhibited by carbon black filled vulcanizates at low strains indicates that the carbon black structure breaks down under stress but reforms to the original state when the stress is removed. This conclusion is also supported by the similarity in behavior between filled rubbers and a dendritic crystal structure of PBNA in rubber. Under the optical microscope the PBNA is seen to break down and reform under a stress-strain cycle. The breakdown and reformation of this secondary aggregated carbon black structure increases the hysteresis in filled rubber vulcanizates. Other sources of hysteresis include viscoelasticity of the polymer, crystallization, stress-softening, and changes in network structure (e.g., breakage of weak crosslinks). These mechanisms have been discussed in depth in previous publications. Recent work has shown, however, that the strength of a rubber is dependent on the combined effect of the different hysteretical mechanisms. The breakdown and reformation of the carbon black structure at low strains in filler reinforced rubbers therefore not only affects the heat build up, transmissibility, and fatigue behavior but also influences the failure properties of the filled vulcanizate.
Environmental Health Control for the Rubber Industry
Authors: McCormick W. E.
Published: February 2011

To present a review of the health problems and their control for the Rubber Industry requires the making of certain choices relative to the breadth of the discussion. It is well known that the Rubber Industry has many facets. These involve not only the conversion of the natural and synthetic polymers into usable articles, but the manufacture of chemicals, plastics, and numerous other materials. For this reason, this review is restricted to the manufacture of the commonly used synthetic polymers and to the operations incident to the conversion of these polymers and the natural polymer into marketable products. Why should there be a concern with respect to the health problems of the Rubber Industry? (1) It is well known that many different chemicals are used, not only in the manufacture of polymers but in the conversion process. The industry is a huge consumer of chemicals, and these run the gamut of highly hazardous to inocuous. Proper environmental controls must be applied in order to handle them safely. (2) An increased emphasis by governmental agencies for a safe working environment has also been an important factor. (3) And, finally, our society as a whole shows an increasing concern with respect to all environmental factors affecting life and property. Industrial hygienists use a basic guiding principle for all environmental health hazard control: all materials are toxic to some degree, including such common essentials as water and oxygen. The problem is to determine the level or quantity at which a specific material is harmful or produces an adverse effect. The question is always, therefore, not whether a material is toxic; rather, is it hazardous (too much). It would be impossible for most industrial operations to occur if we had to have zero exposure of personnel to materials. The definition of the hazardous amount is frequently very difficult and time consuming, and involves skills of several disciplines, including those of toxicology and medicine. It requires the study of animals under controlled insult conditions and the ongoing observations of humans during their working lifetime.
The Mechanochemistry of High Polymers
Authors: Casale Antonio , Porter Roger S. , Johnson Julian F.
Published: February 2011

Several different schools of workers have dominated research in the field of polymer mechanochemistry. These include the Russian school with Baramboim, Berlin, Butyagin; Watson, Ceresa and others of the Natural Rubber Producers' Research Association; and a host of other European workers. Also active are the Japanese and Rumanian groups. In the U. S. the activity has centered at the National Bureau of Standards and in a number of labs including our own. The tables for the review summarize mechanochemical studies on individual polymers, multicomponent polymer systems, and on polymer solutions. For a field so important, it is surprising so few summaries have been prepared. An early review (1960), emphasizing the mechanical degradation of rubber, was prepared by Watson. The classic book on Mechanochemistry of Polymers by Baraboim was published in English in 1964. In the same year Watson also published an excellent book chapter on mechanochemical reactions. Other general volumes and reviews on polymer degradation and synthesis have been published. This review on mechanochemistry cites the majority of recent publications. The extensive patent literature authored particularly by workers at the NRPRA has not been considered. The review is not intended to constitute an exhaustive report but rather a survey of polymer reactions induced by mechanical means. Studies directed to thermal, oxidative, sonic wave, and additional degradation methods may be cited only incidently as they relate to predominantly mechanochemical reactions. The books by Jellinek and by Grassie remain an excellent source for information on all modes of polymer degradation. The mechanical degradation of polymers has emerged as a fundamental problem of major industrial importance. The effects are important in the processing and use properties of polymers. Mechanochemical reactions of polymers in solution is also an important commercial problem such as in the prediction of stability of polymers in multigrade automobile lubricating oils. Industrial necessities have required scientists to study mechanical reactions by the use of suitable laboratory equipment for the purpose of overcoming this problem. These studies have provided numerous, fundamental and interesting publications involving the chemistry, physics, and mechanics of mechanochemistry. As a prime example, the discovery of the softening of natural rubber by mechanical treatment was reported as early as 1857. This process is still used today in the rubber industry. In other major industrial processes such as extrusion and injection molding, mechanical reactions manifest themselves in the more severe cases as polymer discoloration, embrittlement, and stress cracking. The industrial necessity of grinding plastic wastes for recovery and reuse and the necessity of transferring and spreading polymer solutions are also modes for polymer mechanical degradation.
Halogenation of Ethylene Propylene Diene Rubbers
Authors: Morrissey R. T.
Published: February 2011

The ethylene propylene diene rubbers (EPDM) have been modified by halogenation. The reaction has been considered as one mainly of addition to the double bonds of the diene portion of the rubber. Dehydrohalogenation may occur to varying degrees, depending on the conditions of the reaction and the diene present in the rubber. Part of the halogen is believed to be in the allylic position. The halogenated EPDM may be vulcanized by sulfur as well as many of the curing agents used for other halogen-containing polymers. Both types of curing systems can function in the same compound. Therefore, the halogenated EPDM rubbers can be covulcanized with the highly unsaturated elastomers such as natural rubber, cis polybutadiene, and the SBR rubbers. The excellent properties, resistance to ozone, and flexing, of the halogenated EPDM can be imparted to these elastomers using standard curing systems. Also, the uncured tack of halogenated EPDM can be improved by increasing amounts of natural rubber. In addition, other advantages are adhesion of these blends to other rubber compounds and metal. It has been shown that the cure compatibility properties of the halogenated EPDM can be varied as the halogen is increased in the rubber. Evidence has been presented which shows there is an optimum amount of halogen necessary for the best properties in mixtures with other elastomers.
Stress Relaxation Behavior of Ethylene Propylene-Hexadiene Terpolymers
Authors: Shih C. K.
Published: February 2011

1. The stress relaxation behavior of E/P/hexadiene polymer over wide temperature [Tg to (Tg+140°C)] and composition (molar E/P = 1.7 to 4.4) ranges is described. 2. Although Tg of the polymers is essentially constant (− 60° C), the onset temperature for rubbery flow characterized by an abrupt change in the rate of stress relaxation is highly dependent upon composition. It increases to a higher temperature as the ethylene content is increased. It is also affected by the catalysts used for polymer synthesis. 3. The time-temperature shift factor for one sample was found to follow the WLF equation over the temperature range from − 50° C to 0° C.
Thermoelasticity and Stress Induced Crystallization of EPDM Elastomers
Authors: Flisi U. , Valvassori A. , Novajra G.
Published: February 2011

The thermoelastic behavior of various EPDM rubbers has been investigated by performing stress-temperature measurements at different stretching ratios in order to determine their thermodynamic properties and the occurrence of stress induced crystallization. A broad range of terpolymer compositions was investigated and the regularity of monomer sequence distribution was also taken into account. It has been found that statistical terpolymers, like the commercial ones, are generally amorphous and hardly crystallize under stretching for propylene contents higher than 40% by weight. Below this level it is possible to obtain, in a narrow composition range, amorphous polymers that can crystallize under stretching, provided that their monomer sequence distribution is regular enough. The influence of this microstructural parameter has been studied by testing a 3/1 ethylene/propylene model copolymer, obtained by hydrogenation of a sample of poly-3-methyloctenamer. Studying the influence of stretching ratio on crystallization temperature of standard EPDM rubbers, it has been noticed that crystallization occurs at low elongation, which might be related to the presence of “nuclei” in the undeformed state.
Charge Transfer Complexing Mechanism of Antioxidants. Fate of Aromatic Amines during Thermal Oxidation of Natural Rubber Vulcanizates
Authors: Tsurugi Jitsuo , Murakami Shinji , Goda Kiyoshi
Published: February 2011

Thin vulcanizates containing various amines were oxidized at 100° C under 760 mm Hg oxygen pressure. Oxygen absorption and consumption of the amine were plotted as a function of oxidation time. The fate of amine was traced by extracting the oxidized vulcanizates with acetone and then with dilute hydrochloric acid-ethanol mixture, and by determining free amine or Kjeldahl nitrogen of each of the extracts and of the extracted vulcanizates. We observed that the amine combined with the rubber peroxy radical as an intermediate I, from which nitrogen-containing entity was not extracted with acetone but was extracted with the hydrochloric acid-ethanol mixture. The hydrochloric acid-extracts exhibited absorption spectra of Würster cations of the corresponding amines. Therefore, intermediate I is considered charge transfer complex between the amine and the rubber peroxy radical. We further confirmed that the amine was transformed via the intermediate I into acetone-soluble products II and/or amine-rubber compounds III, from the latter of which the nitrogen-containing entity could not be extracted with hydrochloric acid-ethanol mixture. Antioxidant efficiencies of secondary di- and monoamines and tertiary amine were determined and compared with each other. Furthermore, the efficiencies of I, II, and III (see Results for definitions) from these amines were qualitatively estimated separately by determining oxygen absorptions of specifically prepared vulcanizates. The validity of secondary diamine as antioxidants is interpreted by the results that the complex from secondary diamine reacts further with a second peroxy radical to give two of hydroperoxide and a quinonediimine, while the complex from secondary monoamine and tertiary amine cannot take such a route.
Raman Spectroscopic Studies of the Vulcanization of Rubbers. II. Raman Spectroscopic Studies as a Function of Cure Time
Authors: Shelton J. R. , Koenig J. L. , Coleman M. M.
Published: February 2011

It has been demonstrated that Raman spectroscopy can be used to follow changes that occur in the network of vulcanizates as a function of cure time. In the system studied we have found that dialkenyl sulfides, cyclic sulfides and conjugated triene structures parallel the cure. In other words, the Raman lines due to these structures display an asymptotic trend as a function of cure time with the plateau occurring in the region of the optimum cure time. On the other hand those Raman lines assigned to the trans isomer and conjugated dienes do not exhibit the same asymptotic dependence as a function of cure time but show an increase in intensity as the cure time is prolonged up to at least 2 hours at 150° C. This would appear to indicate that these Raman lines are not solely associated with the vulcanization process but that thermal and allied processes may contribute. The Raman line occurring at 440 cm−1 does not show any definitive trend and is unlikely to be associated directly with the network. It is most probably due to unextracted extra-network ZnO present.
Peroxide-Cocatalyst Curing Systems for Saturated Polypropylene Ether Urethane Elastomers
Authors: Elmer O. C. , Duncan J. S.
Published: February 2011

1. Saturated polypropylene ether urethanes can be cured with peroxide/ sulfur systems. Dicumyl peroxide was used as the free radical generator and sulfur as major co-curing agent. 2. Moduli and tensile strengths of cured compounds were proportional to the Mooney viscosities of the uncured gum rubbers when compared at equal cure time. 3. Aromatic polyglycidyl ethers, diisocyanates and polycarbodiimides show promise as heat and hydrolytic stabilizers for the cured elastomers. 4. Curves of tensile strength versus filler exhibit maxima for both HAF carbon black and fumed silica (Cab-O-Sil M-5). Silica gave higher tensile strength values than HAF carbon black.
Fatigue Performance of Tire Belt Cords
Authors: Lockwood P. A. , Edmunds W. M. , Grimm G. W.
Published: February 2011

At the Fall Meeting of the Division in Chicago, the results of a program to develop a new method for evaluating tire belt cords and belt fabric in dynamic axial fatigue were presented. This paper describes the correlation of that test with tires built and tested in wheel and track tests designed, as was the dynamic fatigue test, to fail cords at an accelerated rate. We are encouraged by the correlation which we have observed between the ranking of cords in the laboratory evaluation and the performance rating of tires built with these cords as the belt reinforcement.
Measurement of Wet cornering Traction of Tires
Authors: Veith A. G.
Published: February 2011

We have shown that the cornering wet traction performance of tires, as measured with a special cornering trailer, is influenced by a number of factors and their interaction with each other. Unlike conventional low speed “spin-out” wet cornering traction testing, we have evaluated tire traction over the range 30–60 mph. Over this range there is a marked speed dependence in the rating of various tread rubbers and tread patterns. In general, tread rubbers show a wide range of performance ratings at the lower speeds (30–35 mph) and a narrower range at high speeds (55–60 mph). Various tread patterns on the contrary show similar behavior at low speeds but a wide divergence in traction level at high speeds. Higher durometer tread compounds show improved high speed traction for any given rubber. Tread hardness cannot be used as an omnibus indicator of wet traction performance, however, as each rubber has its own separate correlation line. Low coefficient pavement can have either low or high degrees of macrotexture, but the lack of microtexture or harshness (asperities in the fraction of a millimeter range) produces this type of pavement. Tires must perform safely on such pavement sections of public highways and the testing reported here was done on such test surfaces. Evaluations of four types of tread rubber show that they rank from high to low traction level in the order: SBR, Butyl, NR and BR (solution type) on smooth, low microtexture surfaces. Although BR gives low traction when used alone it is not so used in commercial tread compounds. When properly blended with SBR or NR, tread compounds containing BR give satisfactory traction performance and improved wear performance. The overall behavior of tires can be explained in terms of the concepts of hydrodynamic and boundary layer lubrication. At low speeds boundary layer lubrication predominates on all but the smoothest pavements. This accounts for the marked influence of tread rubber at low speeds. At high speeds both thick and thin film elastohydrodynamic lubrication predominate. In this speed range tread materials play a lesser role and tread pattern or geometry plays a larger role. The relative softness and deformability of tread compound, compared to pavement aggregate, accounts for the importance of elastohydrodynamic lubrication. Drawing on the work of many previous investigators and the data of this work it is postulated that the fraction of the tire contact area of a cornering tire that is in the elastohydrodynamic mode of lubrication is a linear function of speed. This accounts for the good linearity of the plots of traction as a function of speed. Test variability is discussed and steps taken to measure and control such relevant factors as water depth are outlined. The use of statistically designed testing programs with their inherent averaging character are advocated for those doing this work. In addition to their power at averaging test results, such designs uncover the strong interaction between tire and test variables that underlie all wet traction testing.
The Formulation of Nonburning Elastomer Compounds
Authors: Trexler H. E.
Published: February 2011

In this investigation the flammability of 34 polymers was evaluated in 68 compounds; 28 flame retardants were tested in 275 compounds. Only two of 34 polymers evaluated as black-filled compositions were nonburning in the initial screening, five were self-extinguishing, and the rest were completely combustible. Twenty-three of the 32 combustible and self-extinguishing polymers were reformulated into nonburning polymers by the addition of two flame retardants—antimony oxide and either Chlorowax 70 or Dechlorane 515 (Table XIII). Frequently a plasticizer was required. If Chlorowax is compatible with the polymer, it often acts as a plasticizer. Fyrol FR—2 was the only other plasticizer found to be compatible with most polymers and permitting them to retain their nonburning classification.
Magic-Angle Carbon-13 Nuclear Magnetic Resonance Spectra of Filled Rubber
Authors: Schaefer J. , Chin S. H. , Weissman S. I.
Published: February 2011

Line narrowing by a factor of 3-4 has been achieved in the CNMR spectra of a black-filled, vulcanized cis-poly(isoprenc) by 1 kHz sample rotation at the magic angle. The narrowing permits the resolution of a new methylene carbon line not present in the spectrum of an unfilled, nonvulcanized, otherwise comparable cis-poly (isoprene).
Nature of the Cohesional Strength of Synthetic Cis-Polyisoprene SKI-3 and Carbon Black Compounds Based on It
Authors: Grechanovskii V. A. , Ivanova L. S. , Poddubnyi I. Ya
Published: February 2011

SKI-3 gum rubbers containing tight gel have high cohesional strength (up to 12 kg/cm2) at the same time that sol fractions of these rubbers and also of NR have low cohesional strength (˜2 kg/cm2). The loss by black compounds based on SKI-3 of cohesional strength is explained by the breakdown during milling of networks of physical entanglements existing in these rubbers. For the production of carbon black compounds based on crystallizing elastomers with high cohesional strength, the presence of sufficiently stable networks able to insure the initial chain segment orientation during extension and a high molecular weight of the macromolecule are necessary.
Synthesis and Elastomeric Properties of Copolymers of Butadiene and 1,3-Pentadiene
Authors: Carbonaro A. , Zamboni V. , Novajra G. , Dall'Asta G.
Published: February 2011

Random copolymers of all trans structure have been prepared from butadiene and 1,3-pentadiene, in the presence of vanadium compounds and alkyl aluminum halides composed catalyst systems. Copolymers of butadiene and pentadiene, in the composition range of 30-45 weight per cent of pentadiene, are amorphous at room temperature at rest but crystallize upon stretching. Cured tread stocks show improved technological properties with respect to other synthetic diene-based elastomers. Very good processing and extrusion behavior, high tack, tear strength, and abrasion resistance are outstanding properties of the BP copolymers in the field of general purpose rubbers.
Heterogeneity of Vulcanization Networks in Rubbers
Authors: Dontsov A. A. , Anfimov B. N. , Dogadkin B. A.
Published: February 2011

We suppose that origination of network heterogeneity in the process of crosslinking takes place not only in the investigated cases, but with other methods of vulcanization (among them, sulfur) as a result of the polar character of the curing agents. Network heterogeneity of this type may be examined as a combination of weak and strong crosslinks, which in accord with the literature, appears as a necessary condition of the attainment of optimal physical mechanical characteristics of the vulcanizates.
A Compression Relaxometer for Rubber Materials
Authors: Stenberg B. , Jansson J. F.
Published: February 2011

A relaxometer which permits measurements of stress relaxation for compressed rubber samples is presented. Measurements in the temperature range 316.5 to 412.7° K show the good function of the relaxometer. The relaxometer has also been used in a study of deviations from linear viscoelastic behavior.
Long-Time Creep in a Pure-Gum Rubber Vulcanizate: Influence of Humidity and Atmospheric Oxygen
Authors: Wood L. A. , Bullman G. W. , Roth F. L.
Published: February 2011

The long-time creep of natural rubber cured with a conventional sulfur-accelerator recipe containing no filler can be conveniently shown near room temperature by a plot of ΔE/E1 with a double-abscissa scale, one marked in units of log t and the other in units of t. When experimental data from the present work and from previous studies reported in the literature are plotted in this manner it is noted that invariably the first scale yields a linear relation at short times and the second a linear relation at long times. The limiting linear relations just mentioned suggest the two-constant Equation (2), already proposed as a general creep equation for many materials. In the case of rubber the range of values of t investigated is from about 10 ms as studied by previous investigators to about 70 days in our work and other studies. Any significant deviations from the equation can be noted by inspection of the double-abscissa plot. We found that the equation furnished an excellent representation of almost all our experimental data up to the longest times. In one instance in our work and in a few other cases there was a prerupture increase of ΔE/E1 above the values given by the equation. This behavior can reduce somewhat the upper limit of validity of the general equation. The constants A and B can be evaluated from experimental observations of ΔE/E1 by solving two simultaneous equations obtained from the values at the longest time, at one minute, and at an intermediate time. In the present work, the constant A was essentially the same (about 2.4%/ (unit log t)) when the atmosphere surrounding the specimen was a vacuum, dry nitrogen, or dry air. The value was raised when the atmosphere was room air at 35% relative humidity and became about 4%/ (unit long t) when the air was saturated with water. The constant B was raised tenfold when the atmosphere was dry air instead of dry nitrogen. It was further increased by a factor of about 2, when the air was saturated. The value of B for the specimen in an atmosphere of stagnant room air was still greater than this by another factor of more than 2. It is possible that this atmosphere contained autocatalytic degradation products or other constituents which were removed when the air was bubbled through water or passed over CaCl2. The approximate boundaries of three different regions of time are determinable from the ratios A/B. In the first region, where t is less than 0.1(A/B), ΔE/E1 is approximately linear with log t. In the second region, where t is between 0.1(A/B) and 4.343 (A/B), ΔE/E1 is not linear with either log t or t. In the third region, where t is greater than 4.343 (A/B), ΔE/E1 is approximately linear with t. A fourth region of anomalous increase preceding rupture is sometimes found, especially when B is large.
Network Formation and Reinforcement Studies with Terminally Brominated Polybutadiene
Authors: Edwards D. C.
Published: February 2011

1. It is possible to form essentially complete elastomeric network structures by the reaction of terminally functional polymers with multifunctional curative agents. The process occurs in two distinct rate steps: rapid reaction up to the region of the gel point, followed by much slower reaction of the remaining sites. 2. Reinforcement of such systems with carbon black, to provide strength properties similar to analogous conventional elastomers, is possible. Such reinforcement occurs in the absence of heat and of free-radical processes normally associated with the mastication and vulcanization of rubber. 3. Chemically inert particles (esterified silica) produce reinforcement effects similar to carbon black. When chemical interaction with the elastomer network is deliberately introduced, modulus increases and tensile strength declines. A slight degree of chemical interaction is not disadvantageous, but high levels of interaction result in severe loss of extensibility and strength.
Ground Rice-Hull Ash as a Filler for Rubber
Authors: Haxo H. E. , Mehta P. K.
Published: February 2011

A ground rice hull ash prepared by a new burning process has been found to be a moderately reinforcing filler for rubber. This filler, 85-90% amorphous silica and 10-15% carbon, is made by a controlled incineration process in which the bulk of the organic components of the rice hulls is removed, leaving the skeletal silica structure of the hull intact and in the amorphous state. The resultant ash is easily ground to produce fine particles, generally in the range of 0.1-2.0 μm. This filler does not adversely affect either the vulcanization characteristics or the aging of SBR, natural rubber, nitrile rubber, butyl rubber, neoprene, EPDM, and propylene oxide rubber compounds. As it is predominantly silica, it responds effectively to silane coupling agents in improving properties of the rubber compounds. It is concluded that RHA filler is a satisfactory substitute for MT black and that, in blends with blacks, it can be effectively used as a partial replacement for finer and more reinforcing blacks.
Thin-Layer Chromatographic Separations of Butadiene-Styrene Copolymers on the Basis of Composition and Molecular Weight
Authors: Kotaka T. , White J. L.
Published: February 2011

Experimental methods have been developed for thin-layer Chromatographic separation of butadiene-styrene copolymers according to (i) composition and (ii) molecular weight. The technique of separation according to composition is based upon exploiting the adsorption of polymers from their solutions with less polar solvents through the greater adsorptivity of the relatively polar styrene units. The specific method involved is an elution gradient procedure based upon addition of a good, relatively polar solvent for both polymers (CHCls) to the nonpolar solvent CCl4. Adsorption onto silica gel during the development increases with styrene content so that high Rf values are associated with low styrene contents. The separation method for determining molecular weight distributions is based upon using solvents of marginal solubility and involves adding a highly polar nonsolvent to an initial polar solvent which precipitates the polymer during the development. Specifically, CH3OH is used as the nonsolvent, and a CH3OH-tetrahydrofuran mixture is the initial solvent. Methods of quantitatively interpreting the tlc smears to obtain compositional heterogeneity and molecular weight distribution are described. Detailed calculations for several copolymers are included.
Quantitative Measurement of Isomer Composition in Polypentenamer Using Carbon-13 Nuclear Magnetic Resonance
Authors: Carman C. J. , Wilkes C. E.
Published: February 2011

Polypentenamer ((−CH2CH2CH=CHCH2−)n, is produced by the ring-opening polymerization of cyclopentene. In the past, the determination of the relative concentrations of cis and trans structure was based upon an infrared method developed for analyzing polybutadiene. However, inexact absorption coefficients and problems with band overlap left the resultant analyses open to question. Carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) seemed ideally suited for determining the isomer composition in polypentenamers. We have used 13C NMR as the primary analytical method to precisely determine the isomer composition of a series of eight polypentenamers. These results and samples will provide standards to determine infrared absorption coefficients, and thus provide a new infrared analysis. Two recently published books clearly show that the flurry of research over the past few years has firmly established 13C NMR as a valuable spectroscopic tool for the organic chemist. Its potential for establishing polymer molecular structure has equally been exciting and encouraging. The advantage of carbon-13 over proton NMR has been the dispersion of chemical shifts over a much wider range. This has meant that unique, separate NMR peaks have been obtained which describe molecules with subtle differences in molecular structure. The analytical use of 13C NMR has been suggested and used to a limited extent to quantitatively measure stereoconfiguration and monomer sequence distribution. However, no detailed investigation has been reported on precision or accuracy if 13C NMR is used as the primary analytical method for measuring polymer microstructure. As with proton NMR, measurements of peak areas are necessary to obtain quantitative analyses. Allerhand has predicted that 13C integrated intensity should be valid as a carbon count in spectra of complex molecules. Schaefer subsequently has shown that within a polymer system the carbons undergo equal nuclear Overhauser enhancement (NOE), even though the total NOE of different polymers may not be equal or maximum. Hence one can compare relative areas within a 13C NMR spectrum without fear of inadequately accounting for all of the area of a given structural feature.
Anionic Polymerization of Vinyl Monomers
Authors: Morton Maurice , Fetters Lewis J.
Published: February 2011

Addition polymerizations involving soluble organometallic species have received intensive attention in recent years with special reference to the type of counterion and solvent. An anionic mechanism is proposed for those systems where there is good reason to assume that the metal is strongly electropositive relative to the carbon (or other) atom at the tip of the growing chain. Hence, the metal, e.g. lithium, becomes a cation either in the free state or coupled with the growing carbanion. Under the appropriate experimental conditions, spontaneous termination is avoidable in many of those systems when one of the metals of Group I is used as the counterion. The alkali metals sodium and potassium were revealed to be polymerization initiators of isoprene in the disclosures of Matthews and Strange in 1910 and Harries in 1911. The first unambiguous report of the use of lithium in reactions with diolefins appears to be that of Ziegler and coworkers in 1934. Their work consisted of an investigation of the reaction between the alkali metals (lithium, sodium) or alkyllithium species and butadiene, isoprene, 2,3-dimethylbutadiene, or piperylene.
The Effects of Surface Chemical Interactions on the Properties of Filler-Reinforced Rubbers
Authors: Dannenberg E. M.
Published: February 2011

1. Heat treatment of carbon black-rubber mixtures is a method of “in process” polymer grafting which gives a definite improvement in the dynamic properties of vulcanizates. 2. The heat treatment process can be more effective if chemical promoters are used. These chemical promoters function as coupling agents between filler surface and rubber. 3. With very unreactive butyl rubber an effective interaction is produced both by the addition of chemical promoters and by the use of specially active surface-modified carbon black. 4. In normal unsaturated rubbers, surface modifications of carbon black with a wide variety of groups has shown only minimal effects on rubber-reinforcing ability. Halogenated blacks have a pronounced effect on vulcanization kinetics, giving cured vulcanizates of high crosslink density. 5. Carbon black surfaces can be deactivated by calcining at high temperatures. The loss of surface-bound hydrogen may not account for this loss in surface activity. 6. Grafting of polymers to the surface of carbon black is a new method for surface deactivation. 7. Activation of carbon black surfaces by polymer grafting or other types of surface modification has not as yet been demonstrated for normal hydrocarbon rubbers.
The Constants 2C1 and 2C2 in Phenomeno-Logical Elasticity Theory and Their Dependence on Experimental Variables
Authors: Mark J. E.
Published: February 2011

There has been a very large number of experimental studies of the elastic properties of amorphous polymer networks in uniaxial deformation, particularly elongation, over the past few decades. In spite of these efforts, and related theoretical investigations, major questions remain unanswered with regard to stress-strain isotherms over the range of moderate deformations. The major question in this area is the molecular basis or interpretation of the phenomenological constants 2C1 and 2C2 used to represent the experimentally observed isotherms. It is hoped that the present survey of the results of the most important of these experimental studies, particularly in regard to the effect of experimental variables on 2C1 and 2C2 will encourage additional work, leading to an unambiguous solution to this important unsolved problem in the area of rubberlike elasticity.