bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Polymers by GPC-Lalls. I. Computer Simulation of Fractionation of Branched Polymers by GPC
Authors: Shiga S. , Kato E. 
Published: February 2011

Abstract
Simulation formulae are derived for determining polymer structure in an infinitesimal fraction of GPC elution volume. If a sample is ideally fractionated, the MWD of the momentarily eluted polymer depends chiefly on the DNBP of the injected sample. Statistically branched polymer indicates almost monodisperse MWD at the fraction. Separation is always sharper in the higher molecular weight side of a MWD curve than is in the lower side. Even if the DNBP is broader, the average NBP can be correctly estimated by the method proposed by Kurata et al., as far as the DNBP is nearly Gaussian. When a sample is fractionated by a real GPC with axial dispersion, the MWD of the eluted polymer is mainly controlled by the instrumental spreading function, unless the sample has an extremely wide DNBP or a special MWD. The average NBP by the Kurata et al. equations is expected to be more reliable if a polydisperse linear polymer that yields chromatogram similar to the branched sample is applied as a reference material.
Silane-Grafted / Moisture-Curable Ethylene—Propylene Elastomers for the Cable Industry
Authors: Cartasegna S. 
Published: February 2011

Abstract
The present study has shown the capability of VTMOS grafting and moisture crosslinking of EP Elastomers. These capabilities are very large and have been shown to be dependent on various parameters. In EP copolymers, the crosslinking potential appears to be a function of the ethylene content, molecular weight, and molecular weight distribution. In the case of diene containing terpolymers, the process is shown to be limited by the diene content of the polymer through probable parasitic condensation reactions of grafted alkoxy silane. The good performance of the EP elastomers in silane-grafting/moisture-crosslinking can be also utilized in the modification of LDPE when crosslink rate improvement (elimination of hot-water treatment/hot-water treatment time reduction) or higher flexibility and lower shrinkage are needed. The positive results of this study made possible the development of EP elastomer compounds using silane-grafting and moisture-crosslinking for electrical applications. In Table IX and Table X are reported two EP elastomer compounds respectively for low-voltage and medium-voltage cable insulation applications. The key features of the above mentioned two EP elastomer compounds are the following: • high flexibility (comparable to conventional peroxide cure compound) • good mechanical properties • very fast extrusion (for productivity) • easy/versatile processing • high crosslinking state (set properties) • crosslinkable in ambient conditions.
Stress-Relaxation Measurements on Rubbers in Compression. Equipment and Methodology
Authors: Armah J. C. , Birley A. W. , Fernando K. P. , Hepburn C. , Tahir M. 
Published: February 2011

Abstract
The techniques available for the measurement of stress relaxation in rubbers had been reviewed and the consequent methodology assessed. The conclusion, that none of the equipment was entirely satisfactory, led to the development of new instrumentation which eliminated many of the shortcomings of the current equipment and allowed new and improved methods of test to be adopted which are particularly suited to long-term tests in a variety of environments. The work has drawn attention to the unsatisfactory state of the standards in the field.
Effect of Oxygen on the Tear Strength of Elastomers
Authors: Gent Alan N. , Hindi M. 
Published: February 2011

Abstract
Many measurements have been made of the strength of simple vulcanizates of common elastomers, both under steady and intermittently applied loads. In both cases, the strength is governed by dissipative processes, particularly those arising from internal molecular motions and from stress-induced crystallization. Thus, the intrinsic strength of the molecular network is observable only under nondissipative conditions, at high temperatures and extremely low rates of tearing. Under these circumstances, the strength of rubber networks is in reasonably good agreement with theoretical calculations based on the dissociation energy of main-chain bonds in the molecular strands comprising the network.
Structure and Biosynthesis Mechanism of Rubber from Fungi
Authors: Tanaka Yasuyuki , Mori Makio , Ute Koichi , Hatada Koichi 
Published: February 2011

Abstract
The structure of both terminal units and alignment of the isoprene units give conclusive evidence for the initiation and termination mechanisms of rubber formation in fungi. As shown in Figure 4, the polymerization is estimated to start from trans, trans-farnesyl pyrophosphate and proceeds by successive condensation of IPP to form isoprene units in the cis configuration. The termination is presumed to occur by direct esterification of polyisoprenyl pyrophosphate (PIP-PP) or dephosphorylation of PIP-PP followed by esterification with fatty acids. It is remarkable that the hydroxyl terminal group corresponding to the saponification product from the esterified terminal group was observed in the rubber samples by extraction from sporophores of L. volemus after storage for 2–3 days in a refrigerator without the addition of salt. In these samples, unidentified 13C-NMR signals were also detected. These findings suggest that the direct esterification of PIP-PP is more likely as a termination reaction. It also suggests the occurrence of a chemical or biochemical modification of both terminal groups and the main chain during storage. This is the first information on the termination mechanism of controlling the molecular weight of natural rubber.
Structural Characterization of Ethylene-Propylene-Diene Rubbers by High-Resolution Pyrolysis Gas Chromatography
Authors: Yamada T. , Okumoto T. , Ohtani H. , Tsuge S. 
Published: February 2011

Abstract
Ethylene-propylene-diene rubbers (EPDMs) are now used for various purposes because of their excellent resistance to ozone, weather, and heat. Therefore, many kinds of EPDMs are provided as commercial polymers. Consequently, reliable methods for the structural characterization of EPDM have been needed in the fields of material development, process control, and quality assurance of the cured products. The iodine value method is generally used to determine the diene content in EPDMs. However, it is too time consuming to be a routine method. Until now, spectroscopic methods such as IR and NMR are generally used for the study of the composition and the sequence length distributions in EPDMs. Levine and Haines determined the content of ethylidenenorbornene (ENB) in ethylene-propylene-ethylidenenorbornene rubbers (ENB-EPDMs) by IR. Florence and Loustalot investigated ethylene-propylene-1.4-hexadiene rubbers by NMR. However, these spectroscopic methods often encountered the difficulties in the analysis of vulcanized rubbers since they were insoluble and usually contained many kinds of additives such as curing agents, plasticizers, stabilizers, and fillers. On the other hand, owing to the recent development of excellent pyrolyzers and highly efficient fused-silica capillary columns, pyrolysis-gas chromatography (PyGC) has become a powerful tool to give unique information about structures of high polymers. Furthermore, PyGC is advantageous to the practical analysis of insoluble polymeric materials such as vulcanized rubbers.
Ammonia-Induced Tensile Set and Swelling in Silica-Filled Silicone Rubber
Authors: Vondráček P. , Pouchelon A. 
Published: February 2011

Abstract
A new experimental procedure has been proposed for estimating the level of surface interaction activity of silica fillers in silicone rubber vulcanizates. The method is based on a simultaneous effect of the constant tensile strain and ammonia. The sample of silica-filled silicone rubber vulcanizate is deformed in an ammonia atmosphere for 72 h. The ammonia cleaves the specific silica—PDMS hydrogen attachments. The bonds are formed in new positions in the deformed polysiloxane network between silica surface free silanols and PDMS after evaporation of ammonia. The resulting permanent deformation (tensile set) provides a measure of silica surface reactivity (interaction activity) with respect to a given silicone elastomer. It has been proven that the ammonia-induced tensile set is governed by the same mechanism as the increase of toluene swelling under an ammonia atmosphere. The results indicated that water plays an important catalytic role in the ammonia-induced cleavage of silica-PDMS attachments. It is recommended to use an NH4OH atmosphere to obtain the maximum cleavage when estimating the contribution of polymer-filler bonding (hydrogen or physical) to the total crosslink density in silica-filled silicone rubber.
Finite-Element Calculations on the Stress of an Aramid Cord in a Clamped and Elongated Goodrich Block Fatigue Specimen
Authors: Winkler E. M. , de Jong M. C. 
Published: February 2011

Abstract
In the Goodrich Block Fatigue Test, a rubber block containing a tire cord is cyclically compressed and extended. The retained strength of the cord, obtained after a certain running time, is a measure of the fatigue resistance of the cord. In this test, the compression and extension is applied to the clamps of the block. This induces an indirect loading of the cord through shear forces in the rubber. This cord load varies along its length and depends on variables such as cord modulus and diameter and rubber modulus and cannot be obtained experimentally. A three-dimensional finite-element model together with a calculation procedure is presented. With these, not only the overall force-displacement behavior of the GBF specimen can be predicted, but also the detailed cord stress distribution, both for clamping and elongating the specimen. Only three different linear finite-element computations have to be performed. Results at any arbitrary elongation of the specimen are obtained by superposition of these calculation results. The accuracy can be enhanced by combining them with the measured value for the elongation at which the cord is just fully tensioned. Experimental verification was carried out for an aramid cord with a diameter of 0.6 mm. The presented model produces results that agree well with the measured values for the force on the specimen (both for clamping and elongating) and for the breaking force of the cord. Clamping of the specimen causes compression of the cord in the center area of the block. For the aramid cord used in this study, this compression area has a length of about 10 mm. At an elongation of approximately 0.4 mm (the corresponding extension setting of the machine is 3%), the cord is just fully tensioned. When elongating the block a certain amount above this setting, the stress in the center of the aramid cord is only 6.3% of the stress of a cord which would be strained the same amount as the block. In this study, no account has been taken of temperature and viscoelastic effects, which may play an important role in the actual fatigue test!
Production, Properties, and Stability of NR Latices
Authors: Pendle T. D. 
Published: February 2011

Abstract
The natural latex concentrates used for the manufacture of dipped goods, such as gloves, are products both of nature and technology. They are made using the “field” latex obtained from the tree species Hevea Brasiliensis of the Euphorbiacaea family. As the name implies, this tree originates from Brazil but is today most intensively cultivated in the far east (Malaysia, Indonesia, etc.) and in parts of Africa. Nature provides the raw material, field latex, which is then modified, preserved, concentrated, and tested by scientifically developed methods to produce the commercial concentrates. At least 500 000 metric tons, dry rubber weight, of natural latex concentrates are produced annually at present, and this quantity is expected to increase steadily in the future. Field latex can be concentrated by creaming, evaporation, and centrifugation, but the latter method predominates, and this paper will be confined to concentrates obtained by this process. This paper reviews the current situation of NR latex production, the typical properties of centrifuged concentrates, and also presents results of recent research relating to the understanding of the colloidal stability of NR latex.
Determination of the Degree of Hydrogenation in Hydrogenated Nitrile-Butadiene Rubber (HNBR)
Authors: Marshall A. J. , Jobe I. R. , Dee T. , Taylor C. 
Published: February 2011

Abstract
A number of analytical techniques are available for the measurement of the residual unsaturation in HNBR polymers. However, to insure that high-quality HNBR products are produced, it is necessary to use a standard procedure throughout the industry which is quick, accurate, and precise. The two infrared methods discussed in this paper show good agreement with one another, as shown by the respective mean values in Table V. Thus, in the absence of a totally independent and universally accepted standard procedure, this crosscheck between two separate and absolute measurements for the degree of hydrogenation is the best possible support for their precision (1H-NMR spectroscopy for IR method #1 and IR spectroscopy for IR method #2). The two iodometric methods each exhibit significantly poorer precision ( 10 to 100 times) than either of the infrared methods. This is not surprising, since these wet chemical techniques are not discriminatory to any type of unsaturation present in the HNBR nor are they inherently precise due to the large number of test variables. This lack of precision, and the fact that these wet chemical methods are time consuming, eliminates them from consideration as quality-oriented testing methods for measuring the degree of hydrogenation in HNBR. Both IR methods exhibit good reproducibility which greatly exceeds that of iodometry. The statistical analysis of these IR techniques does not present any significant differences between them. IR method #1 requires virtually no preparation time, since extraction of the HNBR rubber samples is not required. Furthermore, IR method #1 is less susceptible to impurities and subsequent user interpretation, since the hydrogenated butadiene peaks at 723 cm−1 are not required for the analysis. In conclusion, due to simplicity and speed of the analysis, IR method #1 is much more robust for use by the industry and their customers for the measurement of carbon-carbon double-bond unsaturation in HNBR.
Spectroscopic Studies of the Structures of Butyl and Bromobutyl Rubbers
Authors: Cheng D. M. , Gardner I. J. , Wang H. C. , Frederick C. B. , Dekmezian A. H. , Hous P. 
Published: February 2011

Abstract
The 1H-NMR results show that the majority of the isoprene units of butyl rubber are incorporated in 1,4 addition. Approximately 6% of the isoprene units undergo 1,2 enchainment. Based on our study of blends of polyisoprene with polyisobutylene, 1H-NMR provides an excellent method for determining isoprene unsaturation in butyl rubber. Furthermore, based on 1H-NMR measurement, FTIR procedures have been developed to quantify the isoprene content of butyl polymers and the concentrations of the three major bromobutyl isomers.
Finite-Element Analysis in Design with Rubber
Authors: Nicholson David W. , Nelson Norman W. 
Published: February 2011

Abstract
The application of finite-element analysis in rubber technology has been discussed. The intent has been to combine features of a tutorial, an exposition, and a survey. Attention has been limited to homogeneous cured rubber products. The finite-element method is a prime constituent of computer-aided engineering, and, as such, it is a powerful resource for the design and analysis of rubber components. Owing to rapid progress and greater availability of computer hardware and software and, in particular, computer-aided design systems, finite-element analysis is eminently practical. Difficulties such as incompressibility and large deformation, the subjects of a substantial literature, appear to have been successfully addressed. Finite-element analyses of rubber products such as seals and bearings have been published widely, often along with experimental validation. However, note that the implementation of the hyperelastic element in major codes has occurred recently. And, at the time of this review, in several codes, the elements are still quite limited, for example, to plane strain. Thus, it appears that rubber technology has yet to see the full impact of the finite-element method.
Electrical Resistivity of Carbon-Black-Loaded Rubbers
Authors: Aminabhavi Tejraj M. , Cassidy Patrick E. , Thompson Corley M. 
Published: February 2011

Abstract
Uses are growing for rubbers with varying levels of resistivity. High electrical resistivity is very much essential in wire and cable insulation applications. Low levels of resistivity are needed for electrostatic discharge in phonograph records and many medical, industrial, and military products and for semiconductive cable compounds. The level of resistivity depends upon the number of contacts or near contacts between conductive particles in the rubber matrix. Loading level is obviously a major determinant in addition to physicochemical characteristics of the black. In the latter regard, the highly conductive grades are characterized by small particle size, high structure, high surface porosity, and low volatile content. One would, therefore, seek the reverse of those factors for high-resistivity rubbers. One of the goals of materials research now is to create new materials with physicomechanical properties tailored to a particular application and to understand the physical processes which determine the end properties. In this review, an attempt has been made to discuss the electrical properties of carbon-black-loaded rubber composites, a class of materials which covers the range from insulators to conductors. The carbon-black-loaded rubbers are formed by dispersing carbon black into the rubber. The compounding is done by adding the carbon black to the rubber, mixing at temperatures above Tg and subjecting the mixtures to high shears until a uniform blend is obtained. The carbon-black particles may be as small as 14 nm in diameter or as large as 300 nm, and they may be individually dispersed or agglomerated in micron-sized clusters. Morphology of the rubber has a profound effect on its electrical properties. High electrically resistive rubbers are becoming increasingly important. Their wide array of applications include antistatic products, shielding materials, insulating membranes, resistors, etc. In the vicinity of the crystalline transition region the rubber shows a dramatic resistivity increase which can be utilized for self-regulation processes. Compounds suitable for such various applications differ appreciably in the nature of their components and composition depending on the specific performance required.
Tensile Stress—Strain Measurements for Characterization of Gum Elastomers and Filled Compounds
Authors: Nakajima N. , Chu M. H. , Babrowicz R. 
Published: February 2011

Abstract
For a gum elastomer in its amorphous, isotropic state, shear modulus and tensile modulus are related with a factor of three. This relation is maintained in the range of temperature and time scale defining the rubbery region of the material behavior. When a large deformation is imposed, for example, in tensile stress—strain measurements, the above relation may still be preserved, if the nonlinear behavior can be linearized. The strain—time correspondence principle is the linearization scheme of this work. When a gum elastomer contains various structural constraints, the factor three relation does not apply, even after the application of the above linearization scheme. Example of constraints are excessive amounts of long branches, gel, molecular associations, and reinforcing fillers. These constraints usually make the factor larger than three. This is because the constraints make the large, elongational deformation more difficult to achieve compared to shear deformation. An example of gum elastomer in this work is a polyethylacrylate containing a significant amount of gel. With this polymer, both the presence of gel and the molecular association act as the constraints. However, when 50 phr of carbon blacks are added, the fillers do not act as strong constraints as they do when they are in the diene rubbers. This is because the polyethylacrylate is known to have a weaker affinity to carbon black compared to the diene rubbers. Triblock copolymers, styrene—isoprene—styrene, were examined according to the above treatment; 25% polystyrene copolymer exhibited crosslink-like behavior by the polystyrene domains. However, 14% polystyrene copolymers acted as if they are no crosslinks. When these copolymers are diluted to 44% with an addition of 56% tackifier, the ratio of tensile to shear modulus became less than three. The styrene domains must have effective crosslinks at the small shear deformation, but at large tensile deformations such crosslinks must not be present.
Dynamic Mechanical Analysis of Carbon-Black-Filled Rubber Vulcanizates under Swollen Conditions
Authors: Neogi Chanchal , Bhattacharya A. K. , Bhowmick Anil K. , Basu S. P. 
Published: February 2011

Abstract
1. For unswollen vulcanizates, storage modulus (E′) decreases with the increase in temperature and decrease in loading and surface area of carbon-black filler. On partial swelling, these effects are much reduced, and E′ becomes independent of surface area and loading on equilibrium swelling. 2. Loss modulus (E″) of unswollen vulcanizates also follows the same trend. However, on swelling in xylene, E″ increases to a great extent because of contributions from both the solvent and the rubber matrix. 3. Loss tangent (tan δ) also decreases with increase in temperature and decrease in loading of carbon black. On swelling, it optimizes at 30 phr loading. 4. Tan δ increases with ϕΨ for unswollen samples, but swollen vulcanizates show an optimum in tan δ at ϕΨ=2.5. 5. Limiting value of storage modulus has been determined for all the filled samples.
Characterization of Elastic Properties of Carbon-Black-Filled Rubber Vulcanizates
Authors: Yeoh O. H. 
Published: February 2011

Abstract
A novel strain-energy function which is a simple cubic equation in the invariant (I1−3) is proposed for the characterization of the elastic properties of carbon-black-filled rubber vulcanizates. Conceptually, the proposed function is a material model with a shear modulus which varies with deformation. This contrasts with the neo-Hookean and Mooney-Rivlin models which have a constant shear modulus. The variation of shear modulus with deformation is commonly observed with filled rubbers. Initially, the modulus falls with increasing deformation, leading to a flattening of the shear stress/strain curve. At large deformations, the modulus rises again due to finite extensibility of the network, accentuated by the strain amplication effect of the filler. This characteristic behavior of filled rubbers may be described approximately by the proposed strain-energy function by requiring the coefficient C20 to be negative, while the coefficients C10 and C30 are positive. The use of the proposed strain-energy function has been shown to permit the prediction of stress/strain behavior in different deformation modes from data obtained in one simple deformation mode. This circumvents the need for a rather difficult experiment in general biaxial extension. The simple form of the proposed function also simplifies the regression analysis. This strain-energy function is consistent with the general Rivlin strain-energy function and is easily obtained from the popular third-order deformation approximation. Thus, it is already available in many existing finite-element analysis programs.