bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Effective Crosslink Density in Silicone Rubber
Authors: Seeley Robert D. , Dyckes George W. 
Published: February 2011

Abstract
As a result of the investigations reported here, a simple and precise method was evised to measure the compression-deflection of solvent-swollen silicone rubber. The method was found to be reliable, and the resultant data were used to calculate effective crosslink densities of solid and cellular silicone rubber compounds. Empirical equations were derived relating compression and deflection to effective crosslinking of solid and cellular silicone rubber swollen in toluene. The weak swelling action of MEK precludes the derivation of empirical relationships between compression, deflection, and effective cross-linking of the rubber. The investigation further showed that toluene is a better and more useful swelling agent than methyl ethyl ketone (MEK). The volume swelling ratios for toluene and MEK were determined. Toluene was found to be about 1.4 times more effective as a swelling agent than MEK. Limited laboratory physical test data show a reasonable correlation to νe/Vr data. (More testing will be required to establish definite relationships.) This investigation also showed that the method employed here for crosslinking determinations is suitable for cellular rubber, since the data obtained from toluene-swollen specimens agrees quite well with theoretical calculations. Finally, the Flory-Huggins interaction parameters for toluene and MEK were determined.
Viscosity and Molecular Weight of Masticated Styrene-Butadiene Rubber
Authors: Bhatnagar S. K. , Banerjee S. 
Published: February 2011

Abstract
Changes in the value of [η], [ηm], K′, (M) and μ of SBR masticated in the cold at 25.0 ± 5.0° C in presence of oxygen with the times of mastication are reported. An empirical relation has been developed between the intrinsic viscosity [η] and Mooney viscosity [ηm] which permits molecular weight of the rubber to be determined directly from Mooney viscosity. The value of g which appears in the Flory equation connecting true crosslink density with the physically determined one has been calculated for unfilled SBR.
Compounding an Ethylene Propylene Terpolmer Elastomer for Dynamic Applications
Authors: Baseden G. A. 
Published: February 2011

Abstract
Dynamic properties of vibration isolators made with EPT vulcanizates may be controlled, within limits, by choice of compounding ingredients in the vulcanizate. The choice of compounding ingredients will also affect efficiency of the isolator in preventing transmission of vibrations at low temperatures. Efficiency of vibration isolation may be calculated by measuring dynamic spring rates at the temperatures of operation.
Polymerization of Chloroprene in the Presence of Organometallic Compounds: The System Chloroprene-Butyllithium
Authors: Erusalimskii B. L. , Krasnoselskaya I. G. , Mazurek V. V. 
Published: February 2011

Abstract
In the polymerization of chloroprene in the presence of butyl lithium, a substantial role is ascribed to reactions of deactivation of growing chains, which prevents the possibility of attaining a high degree of conversion. Kinetic data indicate the anionic mechanism of the process.
Injection Molding of Rubber: Structure, Processing and Properties
Authors: Tsai Boh C. 
Published: February 2011

Abstract
The anisotropic behavior of an injection molded part from a disk mold is reported. It is concluded that orientation rather than state of cure is responsible for the anisotropic behavior. The slow strain recovery process of elongational deformation of the uncured rubber is the major factor in introducing orientation. This example is used to illustrate the viewpoint that the total injection molding process should be investigated from an integral approach which takes into account the interactions of parameters in various areas. Engineering concepts such as the unit operations approach have been gradually gaining acceptance in injection molding of rubber, and compound development continues to progress satisfactorily. However, the success of injection molding will largely depend on the skillful manipulation of material characteristics, design parameters, and operating variables under some unfavorable constraints to meet the cost and performance requirements.
Tear Strength of Stretched Rubber
Authors: Gent A. N. , Kim H. J. 
Published: February 2011

Abstract
Highly stretched rubber sheets can be split apart quite easily, indicating that the originally isotropic material becomes “fibrous” in character—i.e., much weaker for a tear running in the direction of extension than for one running at right angles to it. This anisotropy of strength is shown most clearly by elastomers which crystallize on stretching, for example, natural rubber compounds; it is not so evident in rubber compounds which do not undergo strain-induced crystallization. Also, it is apparently more pronounced for compounds containing reinforcing fillers, notably carbon black, which stiffen and strengthen elastomers. Indeed, carbon-black-filled natural rubber compounds show anisotropy of strength even after the extension is removed. The test sheet then regains its original dimensions more or less completely, but it remains softer for subsequent deformations in the direction of pre-stretching, and weaker for a tear running in this direction. Although unfilled natural rubber compounds and filled and unfilled noncrystallizing elastomers are also softened to varying degrees by prestretching, they do not appear to show anisotropy of strength to any significant degree when the prior extension is removed. This phenomenon is apparently unique to filled, strain-crystallizing, elastomer compounds. Differences in strength in different directions, induced either by a previous deformation or by a present one, are of considerable practical interest. They are probably responsible for the phenomenon of “knotty” tearing, when a running tear spontaneously deviates from the expected path, at right angles to the principal tensile stress, and turns instead into the stress direction. As a result, stress concentrations at the tear tip are greatly reduced, and the tear stops altogether until the applied stress becomes high enough for a new tear to break ahead. This stick-slip pattern of tearing is characteristic of filler-reinforced elastomers; indeed, it appears to be the principal mechanism of reinforcement because their tear strengths are not much greater than those of unfilled elastomers when knotty tearing is prevented. Thus, reinforcement by fillers is closely associated with, and may depend upon, anisotropy of tear strength in the deformed state.
The Ultimate Properties of Unswollen Polydimethylsiloxane Networks and Their Dependence on Crosslink Density and Dilution during Crosslinking
Authors: Rahalkar R. R. , Yu C. U. , Mark J. E. 
Published: February 2011

Abstract
Polydimethylsiloxane networks were prepared by means of γ-irradiation of the polymer, both in the undiluted state and in cyclohexane solutions. Seven polymer concentrations were employed, and radiation doses were varied at each concentration, thereby giving a series of networks varying in both the amount of diluent present during crosslinking and the degree of crosslinking. A total of 72 networks thus prepared were characterized, unswollen, with regard to their ultimate properties in uniaxial extension at 30°C. For networks prepared at constant polymer concentration, an increase in degree of crosslinking was found to give an approximately linear increase in ultimate strength, as measured by either the nominal stress or reduced stress at rupture. The accompanying decrease in the average length of the network chains caused a corresponding decrease in the maximum extensibility. At a constant crosslink density, decrease in the polymer concentration, in the system which had been used to form the network, generally decreased the ultimate strength. This decrease is possibly due to a change in the network chain length distribution arising from the presence of diluent during crosslinking.
Mechanism of Rubber-To-Brass Adhesion : Effect of Rubber Composition on the Adhesion
Authors: van Ooij W. J. 
Published: February 2011

Abstract
A new adhesion model for the bonding of sulfur-vulcanizable rubber compounds to brass has been presented and discussed. The adhesion is explained on the basis of an autocatalytic effect of a thin film of cuprous sulfide formed on the brass surface by the combined action of sulfur and vulcanization accelerator. This film transfers sulfur atoms to rubber molecules, which results in a high rubber surface polarity. This surface bonds to brass by physical interaction. Although minute amounts of cuprous sulfide are a prerequisite, an excess of this compound is detrimental to the adhesion, as thick films are brittle and nonadherent to the brass substrate. Consequently, all parameters which affect the reactivity of a brass surface for cuprous sulfide formation, have an effect on the adhesion. These parameters are brass copper content, brass surface composition, and rubber compound formulation. The action of the various individual rubber ingredients on the reactions at the interface can be simulated by measuring the rate of sulfidation of a standard type of brass in a paraffin solution containing a simple rubber curing system. In spite of the differences between the conditions during actual rubber vulcanization and sulfidation in paraffin, the latter approach yields information which can be used to explain, on a qualitative basis and within the limits of the adhesion model, certain well-known but hitherto unexplained effects, such as the action of cobalt complexes on the adhesion. The method can also be regarded as a simple test for the effect of rubber compounding ingredients on steel cord adhesion.
Advances in Nitrile Rubber Technology
Authors: Dunn J. R. , Coulthard D. C. , Pfisterer H. A. 
Published: February 2011

Abstract
Considerable advances have been made in NBR technology and still more are possible. The heat resistance of NBR has been raised so that it will with-stand 150°C in air for short periods, instead of 120°C. There is potential in the polymer backbone for still greater stability. It has been demonstrated that the ozone resistance of NBR can be improved by blending with EPDM, but the optimum blend has not yet been developed. The use of PVC to improve the ozone resistance of NBR is now much better understood. Crosslinked NBR has been developed as a non-migratory plasticizer which improves embossing characteristics of PVC and PVC-ABS blends. This, in turn, led to the production of NBR powders which may be used to speed up compounding on conventional equipment and permit rubber to be compounded in equipment generally used for fabricating plastics. Powder black masterbatches of NBR are now being evaluated in industry. Another new product form is liquid NBR, generally with reactive end groups. This is already established as an impact modifier for resins and may be a route to castable reinforced elastomers. Polymer structure modifications such as alternating 50:50 copolymers are interesting but do not appear to have found a market. Carboxylated NBR uses are growing in the wake of improvements in scorch resistance. Reprocessible vulcanizates based on amine-modified NBR have been announced, but a true thermoplastic NBR is still awaited.
Effect of Carbon Black on Dynamic Properties of Rubber Vulcanizates
Authors: Medalia A. I. 
Published: February 2011

Abstract
The term dynamic properties as applied to elastomers refers to the response to periodic or transient forces which do not cause failure or appreciable fatigue (permanent change of properties) during the investigation. Generally this is limited to vulcanizates subjected to deformations not exceeding about 25%; and generally the dynamic properties are measured after several cycles or (in a transient experiment such as resilience) after several preconditioning transients, so that the Mullins effect or difference between first and second strain cycles is not of consequence. Thus, dynamic properties represent the viscoelastic properties of vulcanizates at deformations below about 25%, after reaching a pseudo-equilibrium state. The dynamic properties of rubber are altered tremendously by the addition of a filler. The scope of this article is restricted to the dynamic properties of rubber vulcanizates with carbon black as a filler. The effect covered in this article are important in designing rubber compounds to be used under dynamic conditions, such as tires, power transmission belts, vibration isolation mountings, etc. However, the engineering application of dynamic properties, which has been treated in detail elsewhere, is outside the scope of this review. A certain amount of background material is needed. We will first define the terms used in describing dynamic properties. The methods and instruments used for measuring these properties will be described briefly, and the nature of carbon black will be reviewed. Finally, some historical material is given, together with the dynamic behavior of typical compounds, as a preface to the review of more recent work in this field.
Scrap Tire Disposal Procedures
Authors: Crane G. , Elefritz R. A. , Kay E. L. , Laman J. R. 
Published: February 2011

Abstract
Many procedures and processes for the disposal of scrap tires are available. Because of the complexity of the whole disposal problem—e.g., collection logistics, availability and location of markets for products generated from scrap tires, as well as economics—no one procedure or process is believed to be sufficiently outstanding that all scrap tires would be so processed. Several procedures or processes must be used to solve this industry problem. The procedure or process selected for disposing of scrap tires will be dictated primarily by economics and geographic location. Certainly, all procedures must be proven environmentally acceptable.
13C NMR Characterization of Polychloroprene Microstructure II. Relaxation, NOE, and Quantitative Measurements
Authors: Coleman M. M. , Brame E. G. 
Published: February 2011

Abstract
Spin relaxation, NOE, and quantitative measurements have been performed on chloroprene polymers prepared by free radical techniques in the range −150 to +90°C. 13C NMR has proved to be an excellent method for the characterization of polychloroprene microstructure. From our quantitative results it would appear that the concentration of cis-1,4 structural irregularities has been considerably overestimated in previous infrared studies. In addition, the relative amount of trans-1,4 inversions (HT) appears to be somewhat higher than previously reported.
Unsolved Problems in Polymer Degradation
Authors: Dunn J. R. 
Published: February 2011

Abstract
This review has highlighted some of the major problems in polymer degradation. It will be apparent that the degradation of commercial rubbers and plastics is exceedingly complex, since processing and small quantities of impurities or additives can interact and totally change the behavior of the substrate. It is not sufficient to examine the degradation of pure materials. The pure polymer may be studied as a base line but in order to obtain the full story it must also be studied in presence of known impurities or additives added singly and also in combination. This systematic approach is laborious and seldom used. The need for more realistic tests is now being recognized. Outdoor exposure combines the effects of uv light, heat, rain, ozone, nitrogen dioxide, and sulfur dioxide. A laboratory test should take all such elements into account. If a part is to be exposed to oil and air in the presence of heat, as it may be in an automobile, laboratory tests must examine the combined effects of these. The literature contains a wealth of information on the degradation of model compounds and pure materials, and copious empirical information on the behavior of commercial materials. The explanation of what happens in practice and, especially, the production of commercial polymers which give close to ideal behavior, is much more elusive.
Effect of Elevated Temperature on the Unaccelerated and Accelerated Sulfur Vulcanization of Natural Rubber
Authors: Mukhopadhyay R. , De S. K. 
Published: February 2011

Abstract
High cure temperature up to 180°C seems to have no significant effect on the mechanism of unaccelerated sulfur vulcanization of natural rubber. In the case of accelerated systems, the conventional ones undergo more desulfurization and decomposition of the initially formed polysulfidic crosslinks at higher cure temperature. The EV systems show less dependence on cure temperature, and the main maturing reaction seems to be desulfurization of the polysulfidic crosslinks. The semi-EV system shows behavior intermediate between the conventional system and the EV one. Expectedly, the EV systems show better resistance to reversion at high cure temperature than the conventional and semi-EV systems.
Molding of Rubber
Authors: Sommer J. G. 
Published: February 2011

Abstract
The purpose of this paper is to survey the materials, methods, problems and special treatments associated with molding rubber. Rubbers with quite different rheological behavior are readily molded using various methods such as compression and injection for millable compositions, while the more recent reaction injection molding (RIM) method is used for molding low-viscosity polyurethanes. A comparison of RIM with the more established methods shows advantages for RIM, especially for high modulus compositions. Molding problems such as porosity, shrinkage and mold fouling are briefly reviewed along with means of alleviating these problems. A number of molding variables and their associated ranges are considered. The ranges vary significantly. The weight range of molded parts varies by about ten decades, while the range of thermal diffusivities for different rubbers and compositions is less than one decade. The ratio for in-mold times for different materials and methods is intermediate, varying by three decades. Both pretreatments and posttreatments are associated with molding rubber. For example, preheating off-the-road tires before molding compensates for low thermal diffusivity. Posttreatments permit modifying surface friction, altering and stabilizing dimensions, improving flammability characteristics and other properties.
Influence of Carbon Black on Processability of Rubber Stocks III. Extensional Viscosity
Authors: Cotten G. R. , Thiele J. L. 
Published: February 2011

Abstract
A new instrument for measurement of extensional viscosity was designed and employed in the evaluation of SBR compounds containing carbon black and other non-black fillers. It was shown that carbon black filled rubbers generally do not reach steady-state viscosity ; the stress continues to increase with increasing strain up to the point of rupture, due to rapid orientation of molecular chains during extensional flow. The data was evaluated in terms of the Denn-Marrucci equation, and the effect of carbon black on the two adjustable parameters was found. It was found that higher carbon black loading or structure increases only the viscosity coefficient, i.e., it changes the relative level of the flow curve without changing its shape. On the other hand, an increase in surface area increases both the viscosity coefficient and the relaxation time, i.e., it increases the upward curvature of the flow curve. A very good correlation was observed between Mooney viscosity values and calculated viscosity coefficients. Some agreement was found between calculated relaxation times and the rates of stress relaxation for rubbers containing nonblack fillers, while in carbon black loaded stocks the observed differences in stress relaxation rates were too small to draw definite conclusions. The use of high surface area, low structure carbon black is recommended for applications where stiffening of the SBR compounds during extension is desired.
Measurement of Carbon Black Dispersion in Rubber by Surface Analysis
Authors: Vegvari P. C. , Hess W. M. , Chirico V. E. 
Published: February 2011

Abstract
A stylus-type surface roughness tester has been applied to the study of carbon black dispersion in a number of different rubber systems. The method is based on a freshly cut rubber surface which is tracked by the stylus to provide a roughness trace on a strip chart. Carbon black agglomerates deflect the cut path because of their higher hardness relative to the surrounding matrix. Thus, surface roughness diminishes at increasing levels of dispersion. A quantitative index of dispersion quality may be derived from the frequency and average height of the roughness peaks. The method offers a distinct advantage over previous methods in its ability to provide precise dispersion ratings over a very wide range of rubber processing levels from the masterbatch to the final product. The technique is applicable to the analysis of unvulcanized rubber compounds and could be utilized as a factory quality control procedure. Direct interfacing of the surface analyzer to a programmable calculator would provide quantitative dispersion ratings within five minutes of the receipt of a sample. Studies of varied carbon black dispersions in SBR and SBR/BR passenger tread formulations have confirmed the work of previous authors. Tensile strength, fatigue life, resilience, elongation, and extrusion shrinkage increased at higher dispersion levels, while Mooney viscosity, Shore hardness and heat buildup exhibited a progressive decrease. The properties of a 50/50 NR/BR truck tread formulation showed a more varied response to black dispersion. Tensile strength and resilience showed considerably less dispersion dependence than SBR and SBR/BR. However, the tensile response increases with increasing black fineness and decreasing structure, while resilience showed the opposite trend. Fatigue life and heat buildup showed the same trends observed for SBR and SBR/BR. However, NR/BR treadwear (radial tires) showed considerably less dependence on dispersion above the 70% level, in comparison to those other polymers (bias ply tires). NR/BR with N220 at a dispersion index of 68 gave treadwear resistance that was equivalent to the same compound at a dispersion index of 89. However, dispersion indices of 50 or lower caused severely depressed treadwear resistance for the different blacks that were tested. The milling of NR/BR masterbatches cooled overnight produced significantly higher dispersion levels in comparison to hot batches at the same total mixing energy. This procedure can be employed to optimize treadwear and other properties at lower levels of energy consumption.