bluuebunny/crossref_metadata_2025_split huggingface dataset:
Degradation of a Vinylidene Fluoride-Hexafluoropropylene Copolymer in Neutral and Alkaline Aqueous Solutions
Authors: Bryan C. J. 
Published: February 2011

Abstract
During the preparation for the launch of Skylab I, it was noted that the poly(vinylidene fluoride co hexarluoropropylene) (Viton A®, FKM), bladder in the Apollo telescope mount coolant storage tank was perforated, and coolant water, buffered to a pH of 9.2 for corrosion control, was found in the gas pressurization side of the storage tank. Careful examination of the bladder and storage tank before disassembly revealed that the position of the hole in the bladder did not coincide with any protrusion or irregularity in the tank. After disassembly of the system, the bladder was found to have several cracks in the surface exposed to the coolant water in addition to the previously mentioned hole. Samples of the failed bladder were tested on an Instron, and the tensile strength and elongation were found to have decreased to 48% and 42.5%, respectively, of the values determined by the fabricator at the time of manufacture. In order to better understand the degradation of FKM in neutral and alkaline aqueous solutions, the rate and extent of change in the tensile strength, elongation, and per cent swell of FKM were studied as a function of temperature (50°, 70°, and 90°C), pH (7.0, 9.0, and 11.0), and time of exposure to the test solutions.
13C NMR Characterization of Copolymers Of 2-Chlorobutadiene-1,3 and 2,3-Dichlorobutadiene-1,3
Authors: Brame E. G. , Khan A. A. 
Published: February 2011

Abstract
Due to the facile free-radical polymerization of 2-chlorobutadiene-1,3 (chloroprene, CB), most experimental studies and commercial polymer preparations involve free-radical-initiated emulsion systems. From the reactivity ratios published in the literature and the calculated propagation rate of CB at 40°C, its rate is about 10 times faster than that of butadiene. Uniquely, among all the vinyl and diene monomers known, 2,3-dichlorobutadiene-1,3 (DCB) is more reactive than CB. Modification of the properties of polyCB through copolymerization is often relatively difficult. The comonomer most frequently used with CB is DCB, even though many other dienes and vinyl monomers have been tested. Copolymerization of DCB with CB modifies the polymer properties, as judged by evidence from increased crystallization resistance and the retention of building tack. The effect of DCB on the properties of the copolymer of CB and DCB is markedly influenced by the amount of comonomer present. Since no detailed studies have been reported on this monomer pair, we report here microstructure analyses by both 1H and 13C NMR on CB-DCB copolymers. However, it was the 18C NMR analyses which provided the major characterization of these copolymers, while the 1H NMR was only used for the analysis of their composition.
Crystallization Behavior as a Tool for Assessing the Degree of Dispersion of Elastomer Blends
Authors: Ghijsels A. 
Published: February 2011

Abstract
The present study has demonstrated the suitability of the DSC technique for studying the blending characteristics of unvulcanized unloaded BR-SBR blends. It has been shown that, especially during the initial stages of the blending process, BR-SBR blends can be conveniently characterized in terms of the index M, which can be derived from composition (heat of fusion) measurements on a number of spot samples taken at random from the blend. During the later stages of the blending process, moreover, additional information about the degree of blending can be obtained from the degree of interference of SBR with the crystallization of BR. Furthermore, it has been found that the BR-SBR systems investigated follow an exponential rate law of blending during the early stages of blending, which allows blending processes to be described quantitatively by a single parameter, the rate constant. The approach adopted appears to be useful for a suitable characterization of BR-SBR blends in terms of the degree of blending and also for assessing the influence of blending conditions and the performance of blending equipment. An additional advantage of this method is that it can easily be extended to the characterization of unvulcanized (probably also vulcanized) black-loaded compounds which are difficult to examine by other methods. Finally, it should be noted that this approach is not necessarily restricted to BR-SBR blend systems, but can also be applied to other elastomer systems, (e.g. butadiene rubber and natural rubber, natural rubber and isoprene rubber), blends of thermoplastic materials (e.g. polyethylene and polystyrene), or blends of elastomers and thermoplastics. The only limitation, however, is that one of the components of the blend must be able to crystallize under conditions where the other component, is not.
Analysis of Morphology Formation in Elastomer Blends
Authors: Tokita N. 
Published: February 2011

Abstract
Based on the assumption that an equilibrium particle size of dispersed phase will be reached when the breaking-down rate and the coalescence rate are balanced, a theoretical expression was obtained. The theory showed qualitatively that the equilibrium particle size becomes smaller when (1) the stress field is increased, (2) the interfacial tension between matrix and dispersed phase becomes smaller, and (3) the concentration of dispersed phase decreases. Qualitative verification of the theory was obtained by experimental examination of the NR-EPM blend system. In practice, in order to obtain a small particle size in a short time at above 20% volume fraction, the matching of rheological properties of the matrix and the dispersed phase is desirable. On changing from internal mixer to mill, the temperature became one of the most influential factors that control the particle size. Future work, such as the quantitative value of interfacial tension as a function of temperature, and macroscopic breaking energy measurement, etc., is necessary to confirm the theory quantitatively.
Effect of Adsorption on Reinforcement of Filled Polyurethane
Authors: Seto J. 
Published: February 2011

Abstract
The effective network chains, ns formed at the polyurethane-particle interface are brought about by physical adsorption of the polymer from solution. The relation between ns and adsorption, Γs, is given as Equation (3). The coefficient K is evaluated as 10. This value supports multicontact adsorption and agrees with random coil dimensions. The pretreating of powder by a surfactant (oleate) brings about neither adsorption nor network chain formation. The glass transition temperature increases with increasing amount of adsorption.
Reinforcement of Elastomers by Silica
Authors: Voet A. , Morawski J. C. , Donnet J. B. 
Published: February 2011

Abstract
The physical characteristics of silica pigments covering a wide range of properties were determined and related by regression analysis to the static and dynamic mechanical properties of SBR vulcanizates reinforced with these silicas. Three morphological parameters were found to determine the vulcanizates' characteristics: the external surface area by CTAB adsorption, the structural index, and the DBP absorption number. The adherence between silica and elastomer was studied by means of swelling in solvents, by determination of the volume increase on deformation, and by scanning and transmission electron micrography. It was found that dewetting, the formation of vacuoles on deformation, is a most important factor, limiting reinforcement by silica at loadings above 40 phr. Equally, at such loadings the pH of the silica has an important influence : the higher the acidity, the less the adherence between pigment particle and elastomer. Silane coupling agents not only increase adherence, but also improve the degree of dispersion of the silica, which is frequently characterized by the presence of large, partly unwetted particle clumps under conventional conditions of incorporation, thus severely limiting the strength properties of the vulcanizates. The curing system employed and the accelerators used are also of paramount significance for adherence.
Diisocyanate Vulcanization of 1-Chlorobutadiene-Butadiene Rubber
Authors: Yamashita S. , Tamuba M. , Terada J. , Kohjiya S. 
Published: February 2011

Abstract
TDI-d was found to react quantitatively with hydroxyl group in CB-BR under relatively mild curing conditions to give CB-BR vulcanizates, while AEP afforded vulcanizates having a certain amount of pendent AEP. The latter could be used to increase the network-chain density by postcuring with TDI. This crosslink formation was found to proceed almost quantitatively through the reaction of pendent AEP and hydroxyl groups with equimolar amounts of TDI in CB-BR under suitable curing conditions.
Creep of Rubber under Repeated Stressing
Authors: Derham C. J. , Thomas A. G. 
Published: February 2011

Abstract
Under conditions of high stresses and/or strains it is not possible to predict cyclic creep behavior by combining a knowledge of Boltzmann's superposition principle with a knowledge of the static creep. Although experiments here have been restricted to tensile measurements, the effect is likely to occur also in other modes of deformation. It may be of significance in applications where alternating stresses are applied to rubber components and indicates a further reason for keeping working stresses low and designing to avoid fully relaxed conditions.
Flammability of Elastomeric Materials
Authors: Fabris H. J. , Sommer J. G. 
Published: February 2011

Abstract
The use of synthetic polymeric materials in numerous consumer-oriented applications has increased rapidly over the past few decades. This trend has caused considerable concern regarding the responses of these materials to fire, and this concern has resulted in a flurry of activities by numerous agencies (private and government) directed toward better characterization of the flammability of manmade polymers as well as toward regulations to reduce any potential hazard these materials may present. As a consequence, the number of end uses for polymers requiring some degree of flame retardancy has risen sharply over the last several years. Much of the original action was in the field of plastics, and relatively little attention was paid to the flammability of elastomeric products. Even though the ignition and burning characteristics of rubbers were a matter of some concern in a few specific applications, the total volume of rubber used in these applications was rather small and, consequently, research on this subject lagged considerably behind the corresponding efforts spent in the field of plastics. The rapid increase in the use of elastomers in many consumer-oriented, nontire applications has, however, more recently caused greater emphasis to be placed on the flammability behavior of these polymer classes. The awakening interest in flammability characteristics of elastomer products is reflected in the sharp increase of published information on the subject over the last decades.
Incorporation of Antioxidant Groups into Polydienes. I. Via Chain Transfer Reactions of Symmetrical Dithiodiphenols
Authors: Weinstein A. H. 
Published: February 2011

Abstract
A number of substituted symmetrical dithiodiphenols and related monothio-and trithiodiphenols were prepared and characterized. Some of these dithiodiphenols showed chain transfer activity either in bulk styrene or in emulsion diene polymerizations. The fact that phenolic sulfide units were incorporated into polyisoprene and polybutadiene by use of one of these compounds, 2,2′-dithiobis(6-t-butyl-p-cresol), as chain transfer agent was confirmed by ultraviolet analysis. It was demonstrated that selfresistance to oxidation was incorporated into various diene homo- or copolymers, to varying degree, by use of some of these dithiodiphenols as chain transfer agents, on the basis of oxygen absorption tests on preextracted polymers.
Shear Degradation of Polyisobutene
Authors: Abbås K. B. , Porter R. S. 
Published: February 2011

Abstract
A polyisobutene of Mw 1.98×106, Mw/Mn 1.8, was extruded in an Instron capillary rheometer. Shear degradation occurred at high shear stresses, approaching melt fracture, and was more prominent at lower extrusion temperatures for tests at 60–140°C. The capillary was 51 mm long with a length/diameter ratio of 66.7 and a 90° entrance angle. Repetitive extrusions at constant shear rate caused a decrease in a molecular weight and a simultaneous narrowing of the molecular weight distribution. Extrudate expansion was measured after each successive capillary pass for tests at 80°C. Extrudate swelling correlated well with (Mz+1)Mz/Mw, except for the two first passes, where melt fracture was pronounced. The correlation with equilibrium extrudate expansion was almost as good for (Mz/Mw)3.7 (Mill's correlation) and for Mz+1 alone. The efficiency of bond rupture is low, with the energy required to rupture 1 mol of bonds being about 840 MJ at 80°C.
The Role of Morphology and Structure of Carbon Blacks in the Electrical Conductance of Vulcanizates
Authors: Verhelst W. F. , Wolthuis K. G. , Voet A. , Ehrburger P. , Donnet J. B. 
Published: February 2011

Abstract
The low electrical resistance of vulcanizates loaded with conductive carbon blacks in a given particle size range is cause by the low density of the particles, high structure, or both. In addition, the smaller the particle size of the black, the lower the resistivity. The same factors also cause high modulus and, in liquid dispersions, high viscosity. It is shown that acetylene black owes its lower resistivity in vulcanizates to its high structure. Vulcan XC 72 owes its even lower resistivity to both high structure and low particle density, while EC Black owes its lowest resisitivity to an extremely low particle density caused by the presence of a large number of hollow-shell particles, as indicated by electron micrography. It was shown that the resistivity of vulcanizates loaded with EC Black is practically unaffected by deformation up to 150%, in contrast to other conductive blacks at comparable resistivities. It has been observed that increasing the degree of loading leads to a lower limit of resistivity, about equal for all of the blacks. The various phenomena could be explained by the concept that the resistivity of carbon black loaded vulcanizates resides in the gaps between particles or aggregates and is determined by a process of electron tunneling.
Elasticity of Rubbery Networks in the Region of Zero Strain
Authors: Faṣina A. B. 
Published: February 2011

Abstract
1. Contrary to the widely held view of linearity through the origin of the Gaussian stress-strain plot (σ versus (Λ − Λ−2)), there does exist a curvature in the plot around the region of zero strain though the plot is continuous to the origin. 2. The inability of the Mooney-Rivlin expression to describe accurately the behavior of rubbery networks in the region of zero strain is not indicative of non-Gaussian character of the network, nor can it be ascribed to entanglements, or supramolecular organization in the network.
Carbon Black Morphology in Rubber
Authors: McDonald G. C. , Hess W. M. 
Published: February 2011

Abstract
Electron microscope image analysis of carbon blacks in specific rubber compounds has greatly expanded the range of useful applications for studies of this type. This dispersed carbon-gel procedure has improved the sampling and test precision at operating speeds that are now reasonably comparable to the simple colloidal procedures for characterizing carbon black. Improved models have been developed for deriving black surface area and intraunit occlusion capacity. The EM image analysis approach has been useful in applying certain principles of reinforcement theory, as well as in explaining rubber property differences that are attributable to carbon black variables. Studies on hysteresis at constant strain (E″) have indicated that the important black variables, in diminishing order of significance, are loading, structure (intraunit occlusion and anisometry), unit size, unit size distribution, and surface activity. For hysteresis at constant energy (resilience), the most important black variables appear to be black loading, unit size, unit size distribution, surface activity, and structure. In terms of tread wear resistance (moderate wear rates with SBR-BR), a somewhat different pattern of carbon black variables is apparent. At constant loading, the most important black properties appear to be specific surface area, surface activity, structure, and unit size distribution. At any given tread wear-surface area level, hysteresis can be lowered by broadening the unit size distribution and increasing the surface activity of the black.
Studies of Viscoelastic Relaxation of Some Nitrile Rubbers under Compressive Stress
Authors: Stenberg B. , Jansson J. F. 
Published: February 2011

Abstract
Stress relaxation in rubbers is usually supposed to be due to chemical aging phenomena of a mainly elastic material. Considerable physical viscoelastic processes can, however, be observed in the rubbery region, depending upon the type of rubber, crosslink density, type of crosslink, filler, and so on. Thus, in chemical stress relaxation experiments chemical and physical mechanisms are superimposed and can seldom be distinguished. Stress relaxation curves registered at different temperatures contain contributions from both types of mechanism. From a practical, as well as a theoretical, point of view it is therefore essential to find methods of distinguishing between the two relaxation processes. This would be possible if the relaxation curves were obtained during periods of time so short that the chemical relaxation can be neglected. The long-term physical relaxation is then obtained by shifting the curves by, for instance, the method of reduced variables. This technique has been utilized by Curro and Salazar. We now present an alternative procedure by which the physical viscoelastic stress relaxation behavior is determined from dynamic data. The physical relaxation curves are calculated from values of E′(ω) and E″(ω) obtained at different frequencies and temperatures. In this method of determining the physical relaxation, no change of sample is needed, nor is it necessary to allow the sample to relax between measurements. The stress relaxation behavior under compression of three nitrile rubbers has been studied, and it is shown that physical mechanisms dominate just above room temperature, while chemical mechanisms dominate at higher temperatures.
Mechanical Behavior of Lightly Crosslinked Polyurethanes
Authors: Dzierża S. , Janáček J. 
Published: February 2011

Abstract
Polyurethane elastomers are a numerous group of polymeric materials of wide practical application. They are usually formed by polyaddition of diisocyanates with hydroxyl-terminated polyesters or polyethers in the presence of low molecular weight diols or diamines as chain extenders. One may consider urethane elastomers to be block copolymers, consisting of moderately flexible long linear polyester or polyether segments and relatively stiff segments of aromatic and urethane groups. The length and structure of each block can be easily controlled. Crosslinking by an excess of diisocyanate can occur only at the stiff segments, and the number of branch points can also be controlled. The properties of these elastomers can be widely changed using components of different structures and varying their quantitative ratios. They are the results of a combination of segment flexibility, crosslinking, chain entanglement, orientation of segments, hydrogen bonding and other van der Waals forces, as well as rigidity of aromatic units. In the urethane systems, hydrogen bonding and other van der Waals forces, play a much more pronounced role than in familiar olefin-derived elastomers. Although polyurethane elastomers have very good mechanical properties at room temperature, their application is strongly limited by rapid deterioration of properties which takes place at elevated temperatures. The decay of mechanical properties of polyurethane is caused by the breaking of hydrogen and other secondary bonds, as well as by the presence of relatively weak crosslinks that make up their network. The properties of polyurethanes at elevated temperatures may, perhaps, be improved by forming additional crosslinks, besides the typical ones. Some efforts concerning this problem have been published. The aim of our study was to obtain and check the properties of polyurethane elastomers having unsaturated bonds, on which some additional crosslinks were expected to be formed in the presence of a suitable crosslinking agent.
Short-Fiber-Reinforced Elastomer Composites
Authors: O'Connor J. E. 
Published: February 2011

Abstract
The reinforcement of elastomers with short fibers results in composites with a wide variety of properties. The performance and properties are a function of fiber type, fiber content, fiber aspect ratio, fiber orientation, fiber dispersion, fiber-matrix adhesion, processing methods, and properties of the elastomer matrix. A composite with almost any desired property can be obtained by manipulation of these parameters. Of the five fibers studied in this work, glass and carbon are the poorest for increasing mechanical properties. The cellulose, aramid, and nylon fibers all reinforce elastomers to give composites of approximately the same magnitude in properties. Alignment of reinforcing fibers by milling creates a significant anisotropy in the composite properties. The degree of fiber alignment is best for glass, carbon, and cellulose fibers. The uniformity of fiber dispersion is again best for glass, carbon, and cellulose fibers. Aramid and nylon fibers tend to clump together and do not disperse easily. Fiber-to-matrix adhesion is a problem. No evidence of consistently good fiber-matrix adhesion is observed except for the precoated cellulose fibers. The interaction between fiber and elastomer can only improve with a coating or sizing that is compatible with both the fiber and its matrix. Adhesion-promoting bonding agents also improve fiber-matrix adhesion. However, each fiber and/or elastomer may be influenced differently by a bonding agent. Adhesion promoters specific to the type of composite being prepared must be sought in order to obtain optimum properties.
Theory of Elasticity of Polymer Networks. The Effect of Local Constraints on Junctions
Authors: Flory P. J. 
Published: February 2011

Abstract
The effects of restrictions on the fluctuations of network junctions imposed by neighboring chains are treated by resort to a model in which these restrictions are represented by domains of constraint. Whereas in a phantom network devoid of such constraints the displacements of junctions from their mean positions are invariant with strain, involvements with neighbors in a real network render them dependent on the strain. The observed stress consequently is increased above predictions for the equivalent phantom network. On the plausible assumption that the dimensions of the domains are transformed linearly (affinely) by the macroscopic strain, the constraints become less restrictive in the direction of a principal extension λt with increase in λt. Hence, the relative enhancement of the stress diminishes with the strain. The characteristic departures of the observed tension (ƒ)-extension (α) curve for elongation from the expression ƒ α kT(α−α−2) of previous molecular theories are qualitatively reproduced by the present theory, which also accounts for the approximate constancy of ƒ/(α−α−2) observed in compression and the decrease of this ratio with dilution.