bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molding of Rubber for High Performance Applications
Authors: Sommer J. G. 
Published: February 2011

Abstract
This paper broadly considers rubbers (elastomers), molding methods, and some problems associated with molding for high-performance (HP) applications. Molding procedures are then reviewed for several products used in HP applications. The elastomers mainly discussed are NR, SBR, CR, NBR, chloro-sulfonylpolyethylene rubber, silicone rubber, hydrofluoroelastomer and perfluorelastomer. NR is used in HP applications because it possesses desirable properties such as excellent fatigue resistance and high strength. Other rubbers or elastomers, such as silicone or perfluoroelastomer, are used in HP applications because they resist high temperatures and aggressive fluids. When molding these elastomers by compression, transfer, and injection, special procedures are sometimes necessary. These are discussed along with factors that affect molding behavior and the quality of molded products. These factors include: rheology, rubber shrinkage, inserts in moldings, mold fouling, mold materials, and design factors for molds. A special design is used for a compression mold for O-rings made from perfluoroelastomer. These are used to seal against aggressive fluids like dinitrogen tetroxide. In other HP sealing applications, NBR lip seals are used; molding factors are discussed which significantly affect their sealing capability. Also discussed are laminates, where NR is bonded to metal. These are used as bridge bearings and the steel plates in them cause nonuniform shrinkage. A nozzle bearing for the space shuttle is another HP application for an NR laminate; over 100 thermocouples were used to monitor temperature during molding. This paper concludes with a brief discussion of molding silicone rubber for spark plug boots and electrical connectors.
Study of the Effect of Soft-Segment Length and Concentration on Properties of Polyetherurethanes. I. The Effect on Physical and Morphological Properties
Authors: Petrović Zoran S. , Budinski-Simendić Jaroslava 
Published: February 2011

Abstract
1. Densities of elastomers with crystallizing soft segments were higher than that of the noncrystallizing ones. However, the effect of the soft segment length is not regular and may reflect some specific interactions between two phases as well as instantaneous morphology. 2. Phase inversion as judged by drop of hardness takes place at about ssc=60° or more; a shift to higher ssc gives a greater segment length. 3. Tg of the soft segment in samples with well separated phases is independent of ssc, e.g., the presence of hard phase does not change mobility of the soft phase in samples with ssc=50° or more, in all series. However, Tg is strongly dependent on the soft-segment length. Tg for the soft segment of Mn=650 was −43°C, for Mn=1000 was −62°C, and for Mn=2000, Tg was −75°C. The effect of the presence of the hard phase on mobility of the soft phase seems to vanish for M&gt;2500. 4. Tg of the hard segment at 77°C was clearly observed only in quenched samples with a high hard-segment concentration (80%) and at 93°C in a pure hard segment. 5. Melting of both phases were observed in polymers with long soft segments (Mn=2000). Soft segments of Mn=650 and 1000 do not crystallize. The hard phase crystallizes if its Mn is about 1000 or more or if the degree of polymerization of the hard segment is 3 or above, although exceptions were found in the A series. 6. Spherulitic structures were observed in polymers with low ssc (20% and 40%) polymers and in one with ssc=80°. Thus, both hard and soft phases can form spherulitic structures.
Flow Patterns in Elastomers and Their Carbon Black Compounds during Extrusion through Dies
Authors: Ma Chin-Yuan , White James L. , Weissert Frederick C. , Isayev Avraam I. , Nakajima Nobuyuki , Min Kyonsuku 
Published: February 2011

Abstract
A basic study of flow patterns in elastomers in the entrance region of a die has been carried out for various gum elastomers including emulsion and solution butadiene—styrene copolymers, polybutadiene, and natural rubber. All exhibit streamline flow into the entrance with the exception of a cold mastication degraded natural rubber which gave evidence of vortices in corners. A study of a die with a sharp diverging region showed dead spaces for all the elastomers. Carbon black compounds all exhibited converging streamline flow in a 180° entrance angle die and stagnant regions in the sharply diverging die. Evidence based on marker motions has been presented for slip in elastomer compounds in the entrance region.
Cord/Rubber Material Properties
Authors: Cembrola R. J. , Dudek T. J. 
Published: February 2011

Abstract
Recent developments in nonlinear finite element methods (FEM) and mechanics of composite materials have made it possible to handle complex tire mechanics problems involving large deformations and moderate strains. The development of an accurate material model for cord/rubber composites is a necessary requirement for the application of these powerful finite element programs to practical problems but involves numerous complexities. Difficulties associated with the application of classical lamination theory to cord/rubber composites were reviewed. The complexity of the material characterization of cord/rubber composites by experimental means was also discussed. This complexity arises from the highly anisotropic properties of twisted cords and the nonlinear stress—strain behavior of the laminates. Micromechanics theories, which have been successfully applied to hard composites (i.e., graphite—epoxy) have been shown to be inadequate in predicting some of the properties of the calendered fabric ply material from the properties of the cord and rubber. Finite element models which include an interply rubber layer to account for the interlaminar shear have been shown to give a better representation of cord/rubber laminate behavior in tension and bending. The application of finite element analysis to more refined models of complex structures like tires, however, requires the development of a more realistic material model which would account for the nonlinear stress—strain properties of cord/rubber composites.
Flow Visualization of the Motions of Elastomers and Molten Plastics in an Internal Mixer
Authors: Min Kyonsuku , White James L. 
Published: February 2011

Abstract
A basic study of flow visualization of motions of elastomers in a model internal mixer with Banbury rotors has been presented. The behavior of butadienestyrene copolymers (SBR), cis-polybutadiene (BR), natural rubber (NR), and various molten plastics has been investigated. The SBR's and BR behave similarly, exhibiting tearing when stretched by the moving rotor tip away from the bridge in the mixer. This results in large stagnant regions between the bridge and ram in the mixer. The NR does not tear but stretches out when the rotor tip pulls it around the rotor circumference. At low fill factors, the NR bands about the rotors. Studies of molten plastics including low density, high density polyethylene and polystyrene are also reported. Longitudinal motions of rubber on the rotors have been investigated.
Covulcanization of Polymer Blends
Authors: Inoue T. , Shomura F. , Ougizawa T. , Miyasaka K. 
Published: February 2011

Abstract
A general problem on the covulcanization of polymer blends is one of understanding the nature and physical properties of the polymer blends in which a complex chemical reaction has been superimposed on a complex physical state. Our study was on the former aspect. An attempt was made to elucidate the structural change during the covulcanization of polymer blends via the light-scattering studies on the novel specimens (BR/SBR) with the regularly phase-separated structure having periodic distances ranging from 1 to a few µm. A structural change proposed is the broadening of the polymer-polymer interface. The structural change appears to be from the fact that the phase dissolution in the dissimilar polymer system with UCST type phase diagram is promoted by the curing reaction. Effects of curing temperature, curing agents (various peroxides and sulfur-accelerators), and the periodic distance in the uncured blends on the rate of phase dissolution were also investigated. The results may be interpreted in the framework of the above concept.
Time-Dependent Tearing of Carbon Black-Filled and Strain Crystallizing Vulcanizates
Authors: Stacer R. G. , von Meerwall E. D. , Kelley F. N. 
Published: February 2011

Abstract
1. Unstable tearing can be minimized and tear-tip diameter held reasonably constant for carbon black-filled and strain-crystallizing vulcanizates using a constrained trouser tear testpiece first suggested by Gent and Henry. In the absence of these complicating features, the tear energy has been shown to be thermo-rheologically simple, readily lending itself to time-temperature superposition over a broad range of temperatures and rates. 2. Shift factors used to superpose tear energy data at different temperatures for both filled and unfilled SBR also superposed small deformation stress-relaxation data. This result did not hold for the NR formulations tested, indicating that the temperature dependency of the principal viscoelastic process is different for these properties. Evidence of this was observed in the thermal expansion coefficient, a, derived from the WLF coefficients, which increased by a factor of 10 for tear energy data. It is concluded that even with the tear path constrained, strain-induced crystallization still occurs near the tear tip for the NR formulations. 3. Temperature-reduced tear energy master curves for both filled and unfilled vulcanizates showed the same general tear behavior when referenced to Tg. At high rates or low temperatures, the master curves coincide, approaching a characteristic tear energy of approximately 50 kJ/m2, regardless of formulation. Only at lower rates did the different nature of the rubbers become apparent. All the master curves showed evidence of a tear energy plateau between −15 and −10 decades in rate, with the NR compounds showing the lowest slopes in this region. 4. Addition of filler increases the tear energy by approximately 20–40% over most of the master curves. This supports a previous conclusion of Gent and Henry that the major effect of reinforcing filler is to dissipate energy over a larger volume of material without significantly increasing inherent strength. Addition of filler also tended to mask the plateau in the tear energy master curve and decrease both the free volume at Tg and the thermal expansion coefficient of the material.
Novel Wet-Process Silica Prepared from Alkyl Silicates. Part I: Synthesis
Authors: Lutz Michael A. , Polmanteer Keith E. , Chapman Harry L. 
Published: February 2011

Abstract
A simple procedure for preparing a silica filler possessing both the necessary structure and surface character to be useful as a reinforcing filler for silicone elastomers has been developed. The novel, one-step process involves hydrolysis and condensation of alkyl silicates in the presence of a silica surface treatment agent exemplified as follows: (see PDF for diagram) Only easily recycled by-products are generated during the synthesis of the new WPH silica. Performance of the resultant WPH silica filler in reinforcing silicone elastomers will be discussed in detail in Part II of this series, while their use in silicone elastomers for optical applications will be described in Part III.
Novel Wet-Process Silica Prepared from Alkyl Silicates. Part II: Performance in Reinforcing Silicone Elastomers
Authors: Chapman Harry L. , Lutz Michael A. , Polmanteer Keith E. 
Published: February 2011

Abstract
The wet-process hydrophobic (WPH) silica process provides a technology which allows control of surface area, structure, and surface treatment. These are the primary factors which determine the extent to which a silica can reinforce silicone elastomers. Thus, it is possible to tailor the silica to achieve specific desirable elastomer property profiles. Reinforcing capability of WPH silica is greater than that of pyrogenic silica. The unique method of passivating the silica by introducing the treating agent prior to formation of the silica eliminates the need for separate processing steps to passivate the silica and produces well treated silica, as evidenced by the exceptional shelf stability of silicone bases containing WPH silica. The optical properties of silicone elastomers reinforced with WPH silica is described in Part III of this series of papers.
A Study of Aliphatic Polyurethane Elastomers Prepared from Diisocyanate Isomer Mixtures
Authors: Byrne Catherine A. , Mack Daniel P. , Sloan James M. 
Published: February 2011

Abstract
Linear polyurethane elastomers are block copolymers which are elastomeric because they are phase separated. The soft block is derived from a hydroxy terminated telechelic polymer, frequently a polyether or polyester of a molecular weight less than 3000 and a glass transition temperature well below room temperature. The hard block, having a Tg above room temperature, consists of a diisocyanate and a diol. Most frequently the diisocyanate is aromatic and the diol is 1,4-butanediol. The elastomers produced are frequently opaque and then yellow in storage due to the presence of the aromatic rings. For applications where transparency and nonyellowing are important, aliphatic diisocyanates are the compounds of choice. One such diisocyanate is methylene bis(4-cyclohexyl-isocyanate), which is conveniently called H12MDI. It is prepared from the same diamine as methylene dianiline diisocyanate (MDI), but the aromatic rings are hydrogenated before phosgenation. The hydrogenation leads to a mixture of three aliphatic diamine isomers. Phosgenation leads to a diisocyanate which is a mixture of the three isomers shown in Figure 1. The isomer content is adjusted by the manufacturer, and the product received is a liquid. Another example of a diisocyanate which is marketed as a mixture is toluene diisocyanate, an 80:20 mixture of the 2,4:2,6 isomers being the most common. The aromatic diisocyanates are planar molecules or bent planar molecules like MDI. The H12MDI is also bent, but does not contain planar rings. Even if polymers from one pure diisocyanate isomer are examined, the cycloaliphatic compounds are much less likely to form highly ordered or crystalline regions in the hard-segment phase due to the greater difficulty in packing correctly. A desire to know the isomer composition of the diisocyanate and what effect the isomer composition has on the properties of the elastomers led to this study. Mixtures of the isomers varying from approximately 10% of the trans-trans isomer up to 95% (t-t) have been prepared and the properties of polyurethanes prepared from them have been studied.
New Curing System Components
Authors: Davis L. H. , Sullivan A. B. , Coran A. Y. 
Published: February 2011

Abstract
Asymmetric disulfides derived from dibutyldithiophosphoric acid and from 2-ethylamino-4-diethylamino-6-rnercapto-sym-triazine can be used in NR as nonreverting accelerators. A new accelerator, 2,2′-dithiobispyridine-N-oxide, behaves similarly. By using the appropriate combination of these accelerators with conventional benzothiazole based accelerators or with each other, scorch delay can be controlled and crosslinking rate can be increased. Significantly, reversion resistance can be greatly improved. These effects can now be achieved without any change in vulcanizate mechanical properties.
Sequence Structure of Styrene-Butadiene Copolymer Determined by Ozonolysis-HPLC Method
Authors: Tanaka Yasuyuki , Nakafutami Yasunobu , Kashiwazaki Yasushi , Adachi Junichi , Tadokoro Kaoru 
Published: February 2011

Abstract
The configurational sequence of styrene units and the arrangement of styrene and 1,2-butadiene units in styrene-butadiene copolymers were characterized by 1H- and 13C-NMR analysis of the ozonolysis products which were separated by a combination of GPC and HPLC. The ozonolysis products from diad and triad styrene sequences flanked by 1,4-butadiene units showed two and three peaks in HPLC, respectively, reflecting the diad and triad tacticity. The probability of racemic addition was found to be 0.56 and 0.58 for radical and anionic SBR, respectively. The ozonolysis products from styrene-1,2 sequences were separated into three fractions by HPLC. The first and second fractions were assigned to a 1,4-1,2 styrene-1,4 (VS) structure differed only in cotacticity. The third fraction was considered to be a mixture of the meso and racemic forms of the l,4-styrene-l,2-l,4 (SV) sequence. The GPC fraction corresponding to a sequence consisting of two styrenes and one 1,2 units was separated into four peaks by HPLC. Both large peaks contained SSV + VSS structures, where one peak consisted of meso configurations with respect to the two styrene units, and the second peak contained racemic styrene alignments. The two small peaks were SVS with the separation due to cotacticity. Based on the intensity of HPLC peaks, it was deduced that the addition of a 1,2 unit after the styrene terminal predominated the addition of a styrene unit after the 1,2 terminal.
Melting Temperatures as a Function of the Strain of Oriented Polymer Networks
Authors: Göritz D. , Grassler R. 
Published: February 2011

Abstract
The reduction in conformational entropy on stretching elastomers causes an increase in melting point of the temperature-induced crystallisation. The dependence of the melting point on degree of deformation is relatively weak. The high melting points of the strain-induced crystallites must be caused by regions whose orientation is markedly higher than that which corresponds to the macroscopic strain. Such a bimodal orientation distribution is explained by an inhomogeneous deformation of the rubber. There exist either regions in the specimen which do not participate in the deformation or regions with very low strength. Stretching leads to an affine deformation of a part of the specimen. If one lets this crystallize, temperature-induced crystallites find themselves in surroundings whose orientation is describable with the assumption of a Gaussian network. Correspondingly, the increase in melting point as a function of strain can be calculated with the aid of the statistical theory of entropy elasticity, in the way Roe and Krigbaum did. The other, essentially smaller part of the sample contains the inhomogeneities. They cause locally highly oriented fibrillar-like regions which lie in the deformation direction. The strain-induced crystallites are formed within these regions of exceptionally low entropy. The simultaneous existence of temperature- and strain-induced crystallisation is interpreted as evidence for inhomogeneous deformation in elastomers.
An Empirical Model for the Design of Rubber Shear Bushings
Authors: Petek N. K. , Kicher T. P. 
Published: February 2011

Abstract
The objective here was to formulate guidelines for the design of a particular class of rubber bushings exhibiting nonlinear load/deflection behavior. This was accomplished by the derivation of an empirical model of bushing performance based on data from a designed experiment. The data from a two-level, full factorial experiment with six design variables were reduced to equations for the prediction of ten response variables. The range of applicability of the prediction equations was extended with an effective dimensional analysis, validating similarity relationships of the system's variables. Thus, an empirical model useful for the first approximation of rubber shear bushing design is established. Further details regarding this model are contained in Reference 3. The nonlinear load/deflection characteristics of rubber shear bushings offer a designer several unique features to utilize advantageously. The plateau region near the center of their stroke provide bushings with low stiffness in their operating range. Unlike linear springs, nonlinear bushings can achieve their load carrying requirement for the operating range while maintaining compact package size. Although similar to Belleville washers in that geometric parameters can be varied to tailor the load/deflection behavior, rubber bushings offer an additional design variable by virtue of their material. The stiffness and damping properties of rubber compounds are readily modified to attain a desired bushing performance.
Determination of PVC in Presence of Reactive Fillers
Authors: Walter S. E. 
Published: February 2011

Abstract
PVC content in thermoplastic materials can be determined from the total chlorine or more specifically from organic chlorine content. Organic chlorine content can be determined by ASTM D 1551 using the described modifications. Presence of reactive fillers such as CaCO3 results in large negative errors. When reactive fillers are expected to be present, the quantity of PVC should be determined with methods measuring total chlorine or by TGA. TGA can be used successfully for the analysis of such samples. Plasticizers and PVC stabilizers are extracted before analysis to eliminate interfering or variable mass loss in PVC thermograms. This technique can also be used for the analysis of PVC/NBR mixtures. In unknown compounds, the technique should be used in conjunction with FTIR analysis to facilitate polymer identification and to rule out interference by other halogenated polymers. Excess of unreacted CaCO3 can be observed and the amount determined from thermograms. Remaining CaCO3 can be determined from mass loss due to elimination of CO2. If a cooling step is introduced before the atmosphere is switched from nitrogen to air, a clearer separation of residue oxidation and CO2 elimination are obtained. On reheating, residue oxidation then takes place between 450 and 500°C, well separated from CO2 elimination at about 700°C. Variation of thermograms using PVC obtained by different polymerization procedures needs to be further investigated. Structural differences and thermal stability of PVC samples made by emulsion, suspension, and bulk polymerization have been examined by various techniques, but no thermogravimetric data are given.
Pressure-Sensitive Adhesion of Isopropyl-Azodicarboxylate-Modified Polybutadiene to Glass
Authors: Chen J. C. , Hamed G. R. 
Published: February 2011

Abstract
The pressure-sensitive adhesion (i.e., adhesive tack) of isopropyl azodicarboxylate modified polybutadiene contacted with glass has been studied using a 180°-peel geometry. Fracture energies were studied as a function of IAD content, contact time, and peeling rate. Additionally, the creep compliance J was measured and related to the peeling response. At low levels of modification, J decreases with increasing IAD content; however, J increases at intermediate IAD levels—indicative of softening in the material. This is thought to be due, at least in part, to a reduction in the entanglement density and is a condition that favors wetting. For example, the elastomer with 33% IAD achieves 46% of its equilibrium bond strength to glass after 2 min of contact while, after the same tc, IAD-29 (with its lower compliance) attains only 26% of its ultimate bond strength. In some circumstances, there is an interesting decrease in the fracture energy as contact time is increased. This is accompanied by a change in the locus of failure from Ig to Im. When failure is Im, the adhesive layer remains flat during peeling and hence, no energy is expended to bend this layer; this results in a lowering of the fracture energy.