bluuebunny/crossref_metadata_2025_split huggingface dataset:
Test for Evaluating Extrusion Resistance for Oil Well Packer Applications
Authors: Shell Robert L. 
Published: February 2011

Abstract
A standard test has been modified such that the extrusion resistance of a cured compound can be determined. A simple visual rating system has been developed which can be used to quantify cured rubber extrusion resistance thus allowing easy comparison of the effect of various compounding materials. Twenty-three compounding ingredients have been investigated at various levels for their effect on extrusion resistance. Test results have been determined for several commercial oil well packer compounds. Thus compounds developed in the laboratory can be compared directly with known workable formulations. Excellent performance combined with improved processability is no longer just a dream but a real possibility. The modified annular orifice extrusion test is currently being used to develop superior compounds for the oilfield industry.
The Solubilization of Sulfur in the Latex Vulcanization Process
Authors: van Gils G. E. 
Published: February 2011

Abstract
Recent work has shown that optimum properties of rubber vulcanizates are obtained when the vulcanizing ingredients are very well dispersed in the rubber, preferably dispersed to the molecular state, in other words, dissolved in the rubber. The process by which the vulcanization of latex is carried out seems to contradict this. Here the vulcanization ingredients are present in the water phase, and vulcanization of the rubber particles can be accomplished by heating the latex. Apparently molecular dispersion in the rubber phase is not necessary. In the case of sulfur, if we assume that the sulfur particles have the same size as the latex particles and that the density of sulfur is 2 and that of rubber is 1, then only one sulfur particle per 100 rubber particles is needed to obtain a sulfur concentration of 2 phr. The question is, how the sulfur is transferred from that one particle to the 100 rubber particles. It can only be through the water phase. However, sulfur is not soluble in water nor in aqueous ammonia. The experiments described below show that sulfur can indeed “dissolve” in the water phase (serum), be it in very small amounts, and subsequently is transferred into the rubber phase at concentrations sufficient for curing.
Resistivity of Unvulcanized Compounds of Rubber and Carbon Black
Authors: Boonstra B. B. 
Published: February 2011

Abstract
1. A coaxial probe has been developed which allows measuring electrical resistivity of uncured carbon black-rubber compounds with good precision (mean coefficient of variation 4%). 2. For a given compound the resistivity correlates well with the standard dispersion rating and thus can be used for rapid monitoring of dispersion at various stages of processing. 3. Resistivity may also serve as a check on the loading and type of black in a rubber compound. 4. The resistivity of uncured compounds is higher by a factor of 2–10 than the corresponding vulcanizate value. 5. The logarithm of the resistivity appears to be a linear function of the reciprocal of the absolute temperature. The apparent activation energy of conductance for SBR compounds is 14.7–29.3 kJ/mol, the higher values being found for the better dispersions. The activation energies of EPDM compounds were found to be approximately 50% higher than those of SBR.
Properties of Polyether-Polyester Thermoplastic Elastomers
Authors: Lilaonitkul A. , Cooper S. L. 
Published: February 2011

Abstract
The viscoelastic properties of polytetramethylene oxide—polytetramethylene terephthalate block polymers are strongly influenced by phase separation of the 4GT hard blocks into crystalline domains. Thermal analysis reveals a single Tg which increases with increasing 4GT content. This suggests that short sequences of hard segments form a compatible interlamellar amorphous phase with the polyether component. The Gordon-Taylor equation was found to model Tg behavior accurately, provided that the crystalline polyester component was not included in the definition of the hard segment. The melting point of the polytetramethylene terephthalate blocks depends on the average block length of crystallizable segment. Incorporating non-crystallizing polytetramethylene 1,4-cyclohexanedicarboxylate into the hard segment reduces the 4GT melting point and degree of crystallinity. The morphological features of the copolymers depend on sample composition and fabrication procedure. The basic structure is spherulitic. Three different types of spherulite were observed: positive and negative spherulites, as well as spherulites which have their optical axis 45° to their radial direction. The different spherulite types are relatively stable; annealing the samples at elevated temperatures does not alter their morphology. Annealing does increase the degree of crystallinity somewhat and produces crystallites in equilibrium at the annealing temperature. Infrared dichroism studies reveal that, at low deformations, the hard segment lamellae orient as a whole in the stretching direction. This is refleeted by the initial negative orientation of the hard segments. At this stage of elongation, the deformation of the crystallites is nearly reversible. At higher strain levels, the lamellae are disrupted and the hard segments orient positively with a high degree of orientational hysteresis. The soft segments, however, orient almost reversibly in the stress direction at all strain levels studied. It is concluded that the extensive stress softening is brought about by plastic deformation of the crystalline hard segments.
A New Method for Measuring Adhesion of Vulcanized Rubber to Steel Cord at Elevated Temperatures
Authors: Dietrick M. I. , Emmert D. E. 
Published: February 2011

Abstract
The analysis of variance of the elevated temperature tests conducted in this study showed that the experimental sample holder gave slightly higher values than tests run in an oven with the standard sample holder. However, this difference was less than 1% of the average adhesion value. Student's t-tests of the individual unit-to-unit comparison rated the test procedures equivalent over a wide range of temperature and aging histories. The advantages of this experimental sample holder are: 1. lower equipment costs; 2. rapid means of testing steel cord adhesion at elevated temperatures; 3. ease and simplicity of operation; 4. adaptability of the experimental holder to various tensile testing equipment.
Effects of Diffusion in the Oxidative Degradation of Vulcanized Rubbers. I. Rate of Chain Scission in the Steady State
Authors: Ono K. , Kaeriyama A. , Murakami K. 
Published: February 2011

Abstract
The effects of diffusion in the oxidation of cis-1,4-polyisoprene vulcanizates were investigated by means of the stress relaxation method. It was assumed that the diffusion of oxygen is coupled with first-order oxygen consumption and that the rate of chain scission is proportional to the rate of oxygen consumption. The diffusion equation of this process was solved under the steady-state condition to give a simple relation between the rate of chain scission and the film thickness. The experimental results were in good agreement with the theoretical treatment. The true activation energy as well as the ratio of the rate of oxidation k to the diffusion constant D could be estimated.
Efficient and Semiefficient Vulcanization Systems Employing 2-(Morpholinodithio)-Benzothiazole Generated in Situ
Authors: Lawrence J. P. 
Published: February 2011

Abstract
The MBTS-N-(morpholinothio)phthalimide vulcanization system has been found to be effective in producing heat resistant semi-EV and EV cures in a variety of representative rubbers. When used as a direct replacement on a molar basis for 2-(morpholinodithio)benzothiazole (MDB), improvements in processing safety were found in all cases studied. In this respect it is most effective in NR, SBR, and NBR. The experimental system also generally gave slower-curing stocks. The heat resistance of the experimental stocks was found to be equal to or better than that of the MDB control stocks. Substantial improvements in heat resistance for both SBR and IIR unexpectedly resulted from the use of the MBTS—imide system. This result suggests that the nature of the crosslinks formed by the two vulcanization systems are to some extent different in these two elastomers. This, in turn, may reflect upon the mechanisms of crosslink formation.
Viscoelastic Characterization of Ethylene-Propylene-Diene Terpolymer Elastomers
Authors: Nakajima N. , Harrell E. R. , Collins E. A. 
Published: February 2011

Abstract
A practical range of frequency with the Rheometric mechanical spectrometer for the determination of G′ and G″ was shown to be from 2.5×10−2 to 2.5×102s−1, but one decade lower frequency may be reached routinely. The values G′ and G″ may be calculated from the steady-state viscosity curve obtained with the variable-speed Mooney rheometer. However, with samples having long-chain branching, the calculated G′ and G″ are somewhat higher, the difference being close in magnitude to the error of the measurements. With the variable-speed Mooney rheometer, the highest available shear rate is 16 s−1, about one decade less than that with the Rheometrics instrument. With high-molecular-weight rubbers, the range is further reduced, because of “slipping” or “fracturing” of the polymer. On the other hand, the Mooney rheometer enables one to extend the low-frequency range to 2×10−3s−1 very conveniently. The degree of long-chain branching may be estimated from the viscoelastic behavior by comparing complex viscosity and steady-state viscosity at the same time scale, both measurements being made with a Mooney rheometer at a slow speed with a single charge of sample.
The Thermal Diffusivity and Conductivity of Natural Rubber Compounds
Authors: Hands D. , Horsfall F. 
Published: February 2011

Abstract
New methods of measuring the conductivity and diffusivity of rubbers from ambient to 250°C have been developed. The method of measuring diffusivity described in this paper is simple to use and very much quicker than previous methods, the whole temperature range being covered in about half an hour. The accuracy is about 5%. Two disk-shaped samples are used, 48 mm diameter and 2 mm thick, but the geometry can be changed to accommodate samples of varying thickness. The method is suitable for anisotropic samples but, because the measurement is made over a small area, they must be homogeneous. Diffusivity and conductivity measurements have been made on a series of carbon-black-loaded natural rubber compounds. Both thermal properties depend on temperature, type of rubber, and the type and quantity of carbon black. Empirical equations have been obtained relating diffusivity and conductivity to temperature and black loading. These fit the data to better than 10%.
Static Friction of Smooth Clean Vulcanized Rubber
Authors: Roberts A. D. , Thomas A. G. 
Published: February 2011

Abstract
This picture of the origin of static friction for smooth rubber indicates that it is governed by the purely elastic consideration of the strain necessary to produce surface instability. The interfacial adhesion energy required to detach the rubber, which will be the true thermodynamic value at zero peel rate, does not appear to be the limiting factor. The rate effects observed, which persist to surprisingly low rates, are due to the viscoelastic behavior of the rubber. Once sliding has begun, the energy is lost in the peeling process, and this is then dominated by interfacial peel adhesion scaled by viscoelastic characteristics. At zero rate the value found here of F8/G=0.09 implies a static friction coefficient of about 0.6. However, if the normal load were reduced to zero, a finite contact area would remain, at least for smooth surfaces, due to surface attraction, and to express static friction as a coefficient would be meaningless in this case. It is believed that this investigation demonstrates the existence of a true static friction for smooth clean rubber and suggests that its magnitude is determined by the elastic deformation and consequent instability of the rubber.
The Thermal Transport Properties of Polymers
Authors: Hands D. 
Published: February 2011

Abstract
Values of thermal diffusivity and thermal conductivity are needed for heat-flow calculations, for the determination of structure-property relationships, and for material selection and comparison. However, all aspects are hampered by a dearth of reliable data and anything more than a superficial glance at the literature is apt to be discouraging for the uninitiated. Hardly any thermal diffusivity data exist, and the reported values of thermal conductivity show very large scatter. The present state of confusion can be seen, for example, in Figures 1 and 2, which show the reported thermal conductivity values for polystyrene and gum natural rubber. Not only do the values differ at some temperatures by more than 100%, and in the case of rubber by almost 300%, but different trends are indicated throughout the temperature range. Discrepancies of this size cannot be due to sample variations, and they give some indication of the experimental difficulties associated with thermal property measurements.
Prevulcanization Inhibitors
Authors: Trivette C. D. , Morita E. , Maender O. W. 
Published: February 2011

Abstract
Conversion of raw rubber to a usable product is basically a three-step process. Crosslinking ingredients, fillers, and other components are added, the compounded green stock is shaped into the desired form, and the form is heated (cured) to introduce crosslinks (covalent bonds) between the rubber polymer chains and produce a three-dimensional network with vastly improved properties. The crosslinked product no longer flows and thus cannot be reprocessed. The curing system is activated by heat, heat is required for and generated by processing, and faster processing is desirable for economic reasons. Thus, a basic conflict exists between the processing and curing stages. The balance is delicate because the compounder, again for best economics, wants the product to cure rapidly after it is processed. Modern curing systems provide a scorch delay time, during which heating produces no crosslinks, followed by a period of rapid crosslink formation. The compounder then adjusts process conditions to provide enough heat history to eliminate most of the scorch delay so that the cure time will be minimized. Since the compounder is balancing processing against cure, subtle and sometimes uncontrollable changes in factory equipment or operating parameters can produce unprocessable (scorched) rubber stocks. Such changes can be compensated for by making adjustments in the curing system or in the processing conditions. However, relationships between curing system and properties are complex, and considerable effort is generally required to develop a new formulation. Thus, the need exists for an additive which increases only the scorch delay time with minimal effects on other cure parameters and vulcanizate properties. Such compounds, called prevulcanization inhibitors, scorch inhibitors, or retarders, are in commercial use. A number of papers and patents describing the chemistry and use of these compounds have been published and are reviewed here.
Incorporation of Antioxidant Groups into Polydienes. II. Via Free-Radical Reactions of Phenol- or Amine-Substituted Sulfur Compounds
Authors: Weinstein A. H. 
Published: February 2011

Abstract
Methods for incorporation of effective antioxidant groups into both emulsion diene homo- or copolymers and stereospecific diene homopolymers via free radical reactions of sulfur-containing compounds were described. They involved either chain transfer reactions of phenol- or amine-substituted mercaptans or disulfides in emulsion diene polymerization systems or free-radical additions of phenol- or amine-substituted alkyl mercaptans to polydienes after polymerization. The latter reactions were applicable both to polydiene latexes and to solutions of stereospecific polydienes. The potential effectiveness of certain phenol- or amine-substituted mercaptans and disulfides to interact with polymer radicals was determined by measurement of chain transfer constants in bulk styrene polymerization. The efficiency of conferment of antioxidant activity upon polydienes by sulfur-containing compounds via chain transfer or addition reactions was determined by oxygen absorption studies of preextracted polymers. In some instances the relationship between the degree of oxidation resistance conferred upon a polymer with its concentration of chemically bound antioxidant function was determined by colorimetric or uv spectrophotometric analysis.
Sulfurless Crosslinking of Diene Rubbers with 2-R-4,6-Dithiol-S-Triazines
Authors: Nakamura Y. , Mori K. , Akaishi F. 
Published: February 2011

Abstract
A novel crosslinking formulation comprising a combination of 2-dibutyl-amino-4,6-dithiol-s-triazine (DB) with a radical agent gave a crosslinked polybutadiene in which 2-dibutylamino-s-triazine-4,6-dithio crosslinks were formed. The recommended radical agents are dibenzothiazyl disulfide, 1-(o-nitrophenylazo)-p-cresol, benzeneazo-α-naphthylamine, dicumyl peroxide, and 2,5-dimethyl-2,5-di-t-butylperoxyhexane. The crosslinking efficiency and aging resistance of the resulting vulcanizates were much improved compared to vulcanizates with a similar formulation without DB. The BR crosslinking formulation using 2-R-4,6-dithiol-s-triazines, where R was an antioxidant substituent, gave vulcanizates with aging resistant properties remaining after solvent extraction. Similar crosslinking effects were also confirmed on diene rubbers to yield vulcanizates with improved aging resistance. Typical formulations and the properties of the resulting vulcanizates are given for SBR, IR, NBR, NR, and EPDM.
Chemical Reactions between Thiocarbamylsulfenamides and Benzothiazylsulfenamides Leading to Cure Synergism
Authors: Krymowski J. F. , Taylor R. D. 
Published: February 2011

Abstract
A combination of N-oxydiethylenethiocarbamyl-N′-oxydiethylenesulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and sulfur was found to be synergistic in acceleration of vulcanization. The combination reacts at 142°C to form a number of new covalent compounds, most of which eventually decompose to ionic species. The types of compounds produced and the kinetics of formation of these intermediate compounds explain the good scorch delay, high cure efficiency, and high thermal stability of the vulcanizates when combinations of these two sulfenamides are used as vulcanization accelerators.
Spectroscopic Study of Photosensitized Oxidation of Polyisoprene
Authors: Golub M. A. , Rosenberg M. L. , Gemmer R. V. 
Published: February 2011

Abstract
The microstructural changes which occur in cis- and trans-1,4-polyisoprenes and in squalene during photosensitized oxidation were investigated with the aid of infrared and proton and carbon-13 NMR spectroscopy. The singlet oxygenation of these isoprenic compounds resulted in allylic hydroperoxides with shifted double bonds, according to the expected “ene”-type process. In contrast to trans-1,4-polyisoprene and squalene, which displayed the three possible double bond shifts, cis-1,4-polyisoprene showed essentially two of the shifts (to di- and trisubstituted double bonds) and very little of the third (to exomethylene groups). A suitable measure of the extent of hydroperoxidation was afforded by the absorbance ratio, A3400/A1440≡A′. Similar correlations of A′ with oxygen uptake were obtained for the three isoprenic compounds, using chlorophyll or methylene blue as sensitizer. The use of rose bengal gave erratic results indicative of some autoxidation accompanying the hydroperoxide formation. The singlet oxygenation followed zero-order kinetics, the relative rates for cis- and trans-1,4-polyisoprenes being approximately 1.0:1.5.
Miscibility Studies on Heterogeneous Polymer Blends by Radioluminescence Spectroscopy and Particle Coarsening Measurements
Authors: Böhm G. G. A. , Lucas K. R. , Mayes W. G. 
Published: February 2011

Abstract
Interest in the subject of polymer miscibility has been stimulated by the investigation and common use by industry of heterogeneous polymer systems. Particularly, in recent years we have seen the development of materials, such as ABS, high-impact polystyrene, block copolymers, thermoplastic elastomer blends (TPR, etc.), and many more, which owe their unique properties to a certain critical degree of immiscibility of the polymeric constituents. This subtle difference in miscibility contributes to the formation of morphological features in the above-mentioned materials. More importantly, it governs the adhesion between the domains of the phase-separated polymeric composite. The latter property provides for stress transfer across the interface and thus is needed for the attainment of physical strength. Thus the questions posed by researchers are not so much concerned with whether two polymers are fully miscible on a molecular scale, a rare event indeed, but rather in the degree of miscibility of the two materials. In spite of recent advances made, the bulk miscibility of polymers cannot be predicted by theory. The lattice theory of Flory leads to unsatisfactory conclusions. It can, however, be used for an after-the-fact representation of experimental findings by use of an empirically determined concentration- and temperature-dependent polymer interaction coefficient. More insight and qualitative postulates on polymer miscibility are provided by the equation-of-state theory. It correctly predicts the marked influence of the degree of polymerization and of the thermal expansion and pressure coefficients and, more importantly, it anticipates the lower critical solution temperature observed in a number of polymer systems. However, the equations are complicated and contain many generally unknown, but experimentally accessible, parameters, and thus this theory too is of little help to the investigator seeking miscibility data for a specific pair of polymers.
Identification of Natural and Synthetic Polyisoprene Vulcanizates by the Carbon-14 Dating Technique
Authors: Chen H. Y. 
Published: February 2011

Abstract
The idea of using the radiocarbon dating technique for the differentiation of natural rubber from synthetic rubber is novel and has never been tested before experimentally. The experiments were designed to demonstrate the feasibility of the approach rather than to perfect the technique. With the limited data gathered here, it was shown that the radiocarbon dating technique furnishes results with accuracy quite satisfactory for the analysis of gum rubbers. For the cured samples, the accuracy is reduced mainly by the errors introduced from steps other than that of the radioactivity measurement. A further reduction of the accuracy results if the age of the natural rubber in the stock is not known. We conclude that the technique is feasible and yields results of an accuracy which is probably the best ever achieved by any known technique.