bluuebunny/crossref_metadata_2025 huggingface dataset:
The Shear and Elongational Flow of Polymer Melts Containing Anisometric Filler Particles; Part I
Authors: Utracki L. A.
Published: February 2011

There is a dichotomy in the information on flow of anisometric particles. Most of the fundamental studies only consider dilute suspensions in Newtonian liquids, although some authors venture into a semiconcentrated (two-body collision) region and others into pseudoplastic liquids. These publications provide a solid base for understanding the behavior of the high-concentration systems of industrial importance, but without the desirable quantification. The description of these systems is experimental or, at best, qualitative, via simplified constitutive models. At high concentration of anisometric particles, one must consider: yield stress, plug flow, shear segregation, and a change of relaxation spectrum. There is no simple method to correlate the steady-state and dynamic test data. The magnitude of the stress overshoot in transient tests increases with concentration and deformation rate. While the normal stress increases with concentration, the die swell decreases. The yield stress in elongation is larger than that in shear, and the maximum strain at break initially increases with addition of filler, goes through a maximum, and falls to very low values at high loading. The orientation of anisometric particles can be accomplished in converging and diverging, i.e., extensional flow. In a simple shear field, the effect depends on the rate, concentration, and matrix viscosity—in general, shearing causes disorientation of aligned particles. All these effects influence melt processing. For extrusion, the plug flow narrows the range of processing variables, increases the solid-conveying zone, and may lead to flow instability. In injection molding, gating, pattern of orientation (modulated by solidification), and the transient effects depend on the specificity of the rheological behavior of the filled pseudoplastic liquids.
Polymer Self-Diffusion in Entangled Systems
Authors: Tirrell Matthew
Published: February 2011

This article has focused on work in the last several years, a period during which theoretical insights and experimental techniques pertaining to polymer self-diffusion in entangled systems have advanced enormously. The point has been to lay out for the reader the means by which this information has been developed and to lay out the available information itself. The objective has been to facilitate comparisons regarding use and applicability of techniques, quality, and interpretations of data and the trends present in the various data. Presentation of the information in this style leads to a few definite conclusions and a larger number of problems which come more sharply than before into focus as ripe for continued study. Specific conclusions which seem reasonable at this point are: The molecular weight dependence of Ds is, in entangled systems, an inverse square law, consistent with the prediction of the reptation model. The self-diffusion coefficient becomes quite insensitive to the matrix molecular weight Mm at sufficiently high Mm. The variation of Ds with concentration in entangled solution is very strong, considerably higher than the c−3 law suggested by scaling arguments with the reptation model. Free volume effects on the monomeric friction coefficient are at the root of this. Outstanding problems include the following areas and questions: It is necessary to ascertain why there is, in melt Ds data, a reproducible discrepancy between NMR data and those data obtained via other methods. Is NMR sensing the slowest translational mode of motion? Is the marking which is necessary for all the other techniques affecting the measurements? In solution data, the origin of the QELS “slow mode” and the marked disparity between these data and those from other methods must be determined. Critical conditions for the onset of entangled or reptation behavior (in terms of M and c) in Ds must be studied and defined more clearly both experimentally and theoretically. Is the observation that Ds∼M−2 down to unexpectedly low molecular weight an indication that diffusion proceeds via a reptation-like mechanism even for molecular weights which show no other manifestation of entanglement, OI is there another set of conditions which produce Ds∼M−2 scaling? Incisively designed experiments to study matrix and molecular architecture effects seem likely to be most fruitful. Stars, combs, rings, and polydisperse samples hold new information on diffusion mechanisms. A comprehensive experimental and theoretical picture of polymer self-diffusion will advance the state of practice of a wide range of technological applications. The current status of available diffusion information is good enough that the time scales of many practical processes can be predicted approximately. More precise predictions of, for example, diffusion-controlled reaction rates, await the availability of more extensive data and of the resolution of some of the remaining questions and discrepancies highlighted here.
Recent Advances in Controlled Grafting of Elastomers
Authors: Quirk Roderic P.
Published: February 2011

This review describes recent results for preparing graft copolymers with controlled structures. In general, the macromonomer approach appears to be the most promising method for preparation of graft polymers with well defined structures. Not only can macromonomers be prepared using radical, cationic, or anionic polymerization procedures, but the resultant macromonomers can be polymerized using these same methods. Obviously, the macromonomer functionality must be high and well defined. In addition, the average chain length and chain length distribution should be well characterized. In principle, the macromonomer approach can provide comb-type graft copolymers with a random distribution of well characterized graft branches. However, the actual copolymerization of the macromonomers with a variety of comonomers requires careful examination under a variety of reaction conditions before that expectation can be realized. These macromonomers provide an excellent opportunity to examine the effects of chain length on the problem of heterogeneity (i.e., phase-separation) which is expected and found in many grafting systems. “Grafting-from” reactions also should provide graft polymers whose structures are more amenable to prediction and analysis. Like the macromonomer method, it should be possible to eliminate the presence of unwanted homopolymer using this method. However, much more research is required before the generality and value of this method can be evaluated. In conclusion, this era appears to be an exciting time for graft polymerization research. The potential exists for the preparation of model graft polymers with precise structural definition using the methods described herein. This development will, at last, provide graft polymers which can be used to define the relationships between the structure, morphology, and properties of these materials.
Elastomeric Ionomers
Authors: MacKnight W. J. , Lundberg R. D.
Published: February 2011

Ionomers are a class of materials which are emerging as important commercial polymers but yet have many intriguing scientific characteristics. Typically, ionomers consist of a low level of inorganic salt groups pendent to a polymer chain. For this article, we will consider ionomers to possess a maximum level of about 10 mol% ionic groups pendent to a hydrocarbon polymer chain. While this definition is somewhat arbitrary, it is one generally accepted in the polymer field. Unlike homogeneous polymer systems, the pendent ionic groups can interact to form ion-rich aggregates contained in the nonpolar polymer matrix. The resulting ionic interactions can have a major influence on polymer properties and applications which have made this area an extremely fertile one for research and development.
Improvement of Sour Gasoline Resistance for Epichlorohydrin Rubber
Authors: Mori Kunio , Nakamura Yoshiro
Published: February 2011

The resistance to sour gasoline of epichlorohydrin-ethylene oxide terpolymers with allyl groups was studied for various curing systems, antioxidants, and allyl contents. A rubber with 5% of allyl content, cured by a triazine trithiol-MgO-CaCO3 system, showed the best resistance, probably due to the presence of thiol groups in the crosslinks.
The Effect of the Structure of Sulfur—Containing Silane Coupling Agents on Their Activity in Silica-Filled SBR
Authors: Vondráček Petr , Hradec Miroslav , Chvalovský Václav , Khanh Hua Dang
Published: February 2011

A comparative study of α- and γ-functiona1 sulfur-containing silane coupling agents in the silica-filled SBR cured by the conventional sulfur system showed that the influence of the silanes on the vulcanization kinetics and their coupling effectiveness depends on the structure and positioning of the rubber-reactive groups. All the tested silanes containing mercapto or sulfide functional groups led to an improvement in tensile properties and affected the cure kinetics of the system employed.
A Novel Class of Rubber to Steel Tire Cord Adhesion Promoters
Authors: van Ooij W. J. , Biemond M. E. F.
Published: February 2011

A series of eight novel rubber-brass adhesion promoter systems are introduced and discussed. They can be divided in four categories, viz., homogeneous inorganic polyborosilicates of cobalt or nickel; inorganic cobalt or nickel ions adsorbed on an inert substrate, e.g., silica or alumina; metal-organic cobalt or nickel salts deposited on a similar substrate; and inorganic ion exchangers loaded with cobalt or nickel. The organic systems have the major advantage that they are much more active than if they were used without support. Because of this effect, they can replace the currently used metal-organic cobalt salts but at reduced levels. The inorganic systems all show an improvement of initial and of aged adhesion which is comparable to that of currently used commercial systems. However, they can be used at much higher levels than metal-organic salts since for the first time, promoters are offered which show virtually no negative effect on physical compound properties. Such promoters are insoluble in rubber and act solely as corrosion inhibitors. At high levels, therefore, the performance of the inorganic promoters is far superior to that of the metal-organic systems. A consequence of such promoters being corrosion inhibitors is that nickel salts generally perform as well as the cobalt-containing materials. Another advantage is that such promoters can also reduce the rate of iron corrosion. This was demonstrated for the polyborosilicates. It is expected that the rate of rust formation in the tire will be reduced because of this propensity and also because the inorganic systems have a long-range action due to a slow-release effect. In the development of these unusual promoter systems, extensive use has been made of liquid low molecular weight model systems. A good correlation is reported between crosslinking of NR and of squalene if the levels of sulfur, DCBS accelerator, or ZnO are varied. If levels of cobalt or antioxidant are varied, squalene does not react as NR. For such studies, dodecene-1 is shown to be a better model molecule. This system further has the advantage that it is amenable to gas chromatography analysis which allows the crosslink distribution to be determined quantitatively.
Mechanisms of Rubber Abrasion in Unsteady State
Authors: Zhang S. W.
Published: February 2011

Abrasion of rubber under the action of mechanical stress appears to involve two basic processes: micromolecular fracture and macrodelamination. The formation of ridges mainly results from the effect of tearing and tensile rupture, but the production of small particles is mainly due to the effect of microcutting. Ridge and small particle formation are basic characteristics of rubber abrasion. The physical processes during dry wear are gradual tearing leading to crack growth and also rupture of the tongue tip. A new concept of rupture length per revolution has been introduced, which is itself a function of the number of revolutions that have occurred during the unsteady state. Based on this, a quasi-theoretical relation for the rate of wear has been proposed. It reflects the influence of several factors on the rate of wear in a comprehensive way, and, it was verified by the experimental results. In the unsteady state of abrasion, the rate of wear and the spacing of the abrasion pattern not only depend upon the frictional force but also upon the number of revolutions. The relationship between the spacing and the frictional force is exponential. The influence of the rotational speed on the wear rate could be neglected when the speed did not exceed 18 rev/min. Oily wear was found at relatively small frictional forces (kN/F=0.24−0.41 m). The action of microcutting and the decomposition of the rubber are both prerequisites and sufficient conditions for oily wear to be produced. The same rubber shows two different modes of wear under different frictional forces. But a quantitative condition for the change from dry wear to oily wear is not yet clear.
A Mass Spectrometric/Fourier Transform Infrared Study of the Vulcanization of Chlorosulfonated Polyethylene
Authors: Devlin Edward F. , Folk Theodore L.
Published: February 2011

This work has confirmed that the thermal decomposition found to occur in a model alkanesulfonylchloride also occurs in an elastomeric CSM at the cure temperature. Therefore, less emphasis should be placed on the existence of ionic sulfonate salt bridges as the mode of crosslinking in cured chlorosulfonated polyethylenes. Though we have not presented any evidence to show that carbon-sulfur crosslinks arc involved in the cure, the need to incorporate sulfur-bearing accelerators in the formulation for practical cures suggests that activated sites adjacent to unsaturated double-bonds may be involved.
Some Factors Influencing the Traction of Radial Ply Tires
Authors: Grosch K.
Published: February 2011

The radial ply construction is inherently more suited to provide better traction and cornering capability than the older bias construction. Since it also provides a better wear resistance, some of this advantage is traded off to obtain still higher wet traction through a more open tread design. Compounds for high traction require high hysteresis, which in principle means a high rolling resistance. Since, however, the frequency range operative in adhesion friction is much higher than the one responsible for rolling resistance, compounding both for high adhesional friction and low rolling resistance is possible at least in principle, not by changes in glass transition temperature, but by changes in portions of the relaxation spectrum. A cap and base construction is a compromise which is used successfully today. Modern tread pattern design assists traction by sophisticated block and block/rib design combinations. This, in turn, allows more flexibility in compound formulation. By carefully balancing traction, wear, noise, and rolling resistance, modern tire design, both for passenger and commercial tires, has advanced substantially in all these criteria.
Plasticization by in Situ Grafted Acrylates II—Effect of Graft Structure
Authors: Eldred Roger J.
Published: February 2011

Grafting of acrylate monomers, such as 2-ethylhexyl acrylate, onto nitrile rubber during the cure cycle leads to improved low temperature flexibility. The effect of graft structure on the improvement was determined by utilizing chain transfer agents to reduce the molecular weight and increase the number of grafts. In every instance, incorporation of a chain transfer agent led to a compound with greater low-temperature flexibility than a control. The amount of improvement was correlated with the effectiveness of each additive in chain transfer reactions. Since there was no evidence of either degradative chain transfer or changes in cure state, it was concluded that the increased low-temperature flexibility was a direct result of alterations in the graft structure. The plasticization achieved with chain transfer agents and 2-ethylhexyl acrylate monomer was better than previously obtained using more effective acrylic monomers without the additives. This means that the structure of the graft is the major factor in determining the effectiveness of in situ grafted acrylate monomers as plasticizers.
Buckling of Viscoelastic Columns. Part I: Constant Load Buckling
Authors: Wang Shau-Chew , Meinecke Eberhard A.
Published: February 2011

The constant load buckling of viscoelastic columns has been studied extensively in the past and equations have been derived to predict the buckling time from the geometry of the columns and the constitutive equation of the material. These theories restrict themselves to columns loaded with an axial load only. A variety of linear as well as nonlinear creep laws have been utilized. In this study, existing creep-buckling equations have been modified to include the effect of lateral loads on the time to buckle. The constitutive equation used is the power law which applies quite well for well-vulcanized elastomers. Furthermore, the viscoelastic response of the material was assumed to be linear, which can be justified by the extremely small compressive strains found before buckling occurs. The validity of the equations has been compared to experimental data obtained on well-vulcanized elastomeric columns of different slenderness ratios under a variety of loading conditions. An attempt has been made to explain some discrepancies between theory and experimental findings.
Experimental Measurement of Dynamic Bulk Modulus Using Holography
Authors: Holownia B. P.
Published: February 2011

The results show that the dynamic bulk modulus for NBR at room temperature is about 50% higher than the static bulk modulus in the frequency range of 1–200 Hz. The limiting factor was the servo-valve used which does not give enough dynamic pressure fluctuations above 200 Hz to obtain accurate results of the dynamic bulk modulus. The holographic method discussed here offers a number of advantages over other methods used in measuring dynamic bulk modulus. (i) The samples are of realistic size and any soft spots in the sample which would distort the results can be immediately identified. (ii) Dynamic bulk modulus can be measured accurately in the frequency range of 1 Hz–1000 Hz or higher, provided the hydraulic servo-valve used can respond in the frequency range. Work is already in hand which extends this frequency range to 1200 Hz. (iii) The change of volume of the sample is a direct measurement unlike other indirect methods, therefore, there is more confidence in the results.
Characterization of Ban Copolymers
Authors: Gupta H. K. , Salovey R.
Published: February 2011

Molar mass and compositional distributions in copolymers of butadiene and acrylonitrile have been analyzed by gel permeation chromatography with multiple detection. In some cases, a third component could not be separated by size-exclusion chromatography and was presumed to be an antioxidant attached to the copolymer chains. The amount of this antioxidant was measured by ultraviolet detection at 280 nm of chromatographic effluents and found to increase in amount with decreasing molar volume. Molar mass and compositional distributions were derived from corrected ultraviolet responses at 254 nm coupled with refractive index detection of BAN solutions separated by GPC. The variation of composition with molecular size depends on the composition of the monomer feed and, presumably, the conversion. For copolymers close the azeotropic composition (36% ACN), the composition was fairly uniform over the entire molecular weight distribution and showed a single Tg by differential scanning calorimetry. Some of the materials showed gel or insoluble fractions which had to be separated from the soluble moieties prior to GPC. Copolymers of composition slightly above azeotropic showed a single Tg but could be separated into sol and gel fractions which differed in composition. Infrared and calorimetric analysis showed that, in these cases, the gel was enriched in acrylonitrile. A sample containing 20% acrylonitrile showed marked deviations from compositional uniformity, and the high molecular weight components were enriched in butadiene. Infrared and calorimetric analysis of the sol and gel fractions showed that they were enriched in acrylonitrile and butadiene, respectively. In fact, the elastomer evidenced two glass transition temperatures. We suggest that gel permeation chromatography with multiple detection, specifically refractive index and ultraviolet absorption at 254 and at 280 nm, permits a fairly complete characterization of BAN elastomers. With computer analysis, a sophisticated raw material quality control is feasible and simple. We plan to reexamine our assumptions using laboratory synthesized BAN copolymers. Moreover, we hope to relate the physical properties of elastomers and rubber compounds with the molecular characterization of BAN copolymers. As an alternative to ultraviolet detection in GPC, it may be possible to get a more complete functional group analysis by infrared spectroscopy.
Interaction of Tire Material and Design
Authors: Clark S. K. , Dodge R. N.
Published: February 2011

An analytical study based on the Halpin-Tsai equations in their complex form has been conducted over a reasonably practical range of variables typical of a composite construction involving steel-cord reinforcement in a rubber matrix. Curves are presented which show the influence of several material properties on the composite characteristics of bias-angle constructions. From these curves, it is possible to deduce the influence of these constituent material properties on the overall composite response. The most significant deductions from these results are: (1). The elastic extension modulus of the composite, E′, is highly dependent on the bias angle and moderately dependent on the volume fraction of cord. On the other hand, E′ is essentially independent of the loss modulus of the matrix E″r. (2). The elastic shear modulus of the composite, G′, is also dependent on the bias angle and volume fraction of cord, but independent of the loss modulus of rubber. Also G′ is symmetric about a 45 degree bias angle. (3). The loss modulus in tension of the composite, E″, is highly dependent on the bias angle and moderately dependent on the volume fraction of cord and loss modulus of the matrix. (4). The loss modulus in shear of the composite, G″, is dependent on the bias angle and volume fraction of cord and nearly independent of the loss modulus of the matrix except at bias angles near zero and 90 degrees. (5). The loss tangent in tension of the composite, tan ΔE′ is highly dependent on the bias angle from 0 to 20 degrees and is approximately a constant for all other bias angles. The magnitude of the constant value is the same as tan δr of the matrix. (6). The loss tangent in shear of the composite, tan ΔG′ is nearly a constant except for very small or very large bias angles. The magnitude of this constant is approximately the small value of the loss modulus of the cord. Also tan ΔG is symmetric about 45 degrees. (7). For most bias angles, the loss tangent of the composite in shear is much less than the loss tangent of the composite in tension.
Mechanism of Degradation of Fluorocarbon Elastomers in Engine Oil
Authors: Abu-Isa Ismat A. , Trexler Harold E.
Published: February 2011

The loss in properties of fluorocarbon elastomers observed after aging of the polymer in engine oil is the result of interactions of some of the oil additives with elastomer. The degradation in mechanical properties of the elastomer is not due to any extensive dehydrofluorination reaction, but instead it is the result of increased crosslinking and hardening of the surface caused by these additives.
An Improved Adhesive System for Textile-Reinforced Rubber Products
Authors: Lattimer M. B. , Weber C. D. , Hardt Z. R.
Published: February 2011

Resorcinol Formaldehyde Latex (RFL) adhesive systems have been used for over forty years to bond synthetic fibers to rubber compounds. The original RFL formulation was developed by Charch and Maney. The adhesive was applied primarily to rayon fibers and later extended to nylon and glass fibers. At the same time, the formulation evolved with the introduction of synthetic latexes and preformed resorcinol formaldehyde resin solutions. The RFL treated fibers are used to reinforce rubber products (e.g., tires, conveyor belts, hoses, V-belts). With the commercialization of polyester fibers, it was found that the RFL system did not satisfactorily adhere polyester to rubber compounds. The difficulty in bonding to polyester fibers has been attributed to the lack of reactive sites in the polymer structure, as well as its hydrophobic nature. New adhesive systems were developed which consisted of free isocyanates in solvent solutions. These systems were undesirable due to the associated health and fire risks. As a result, the use of aqueous dispersions of blocked isocyanates was investigated. Blocked isocyanates consist of isocyanate molecules which are chemically reacted with a blocking agent to prevent reactions with other materials at room temperature conditions. At higher temperatures, the blocking materials dissociate to free the reactive isocyanate groups. The blocked isocyanates are generally available in solid form and are chemically stable in water. Common blocking materials include phenols, oximes, and lactams. Shoaf developed a two-step, water based, adhesive system that effectively bonded polyester to rubber. This system consists of a first-step dip application which contains a polyepoxide and blocked aromatic polyisocyanate. In the second step, the treated fiber is overcoated with an RFL mixture. The reaction product of the polyepoxide and polyisocyanate has been identified as a polyurethane structure which physically adheres to polyester. Iyengar attributed this physical interaction to the similarity between the cohesive energy density values for the polyester and polyurethane structures.
Nondestructive Evaluation of Tires
Authors: Trivisonno N. M.
Published: February 2011

The application of nondestructive evaluation (NDE) methods to tires is a growing field. Increasingly more stringent demands have been placed on tire performance as vehicles have become more refined, roads have become better, fuel economy has become an important consideration, and the customer has become more critical. In addition, radial tires have become increasingly dominant, and the performance of radial tires is much more sensitive to the placement of components than is true for bias-ply or belted-bias tires. Therefore, it has become necessary to develop several different types of NDE equipment for tires. Quality-control instruments are needed to monitor production to keep tires within specifications. Inspection equipment is needed for retread candidate tires to cull out tires with unacceptable anomalies. Research and development equipment is needed to measure the effects of material, construction, and production variations on tire performance. NDE methods are being used to improve the efficiency of tire testing by separating out tires with pretest anomalies and by monitoring tires during testing. Increasing efforts are being made to use NDE methods to identify anomalies and material and construction factors which can be related to tire durability and other performance factors. At this time, x ray, holography, ultrasonics, and infrared are the most important NDE methods for tires. As NDE technology continues to evolve, more techniques will be developed, instrumentation will become more reliable and more automated, and more knowledge will be developed to relate tire performance to the features which NDE methods can detect.
Systems for Tire Cord-Rubber Adhesion
Authors: Solomon T. S.
Published: February 2011

The last comprehensive review of tire-cord adhesion to rubber was reported by T. Takeyama and J. Matsui in Rubber Reviews for 1969. They covered this subject in depth from its scientific beginnings and dealt mostly with rayon, nylon, and polyester tire-cord adhesion. The objective of this present review will be to up-date the 1969 review. The resorcinol-formaldehyde-latex (RFL) adhesive system developed as a fiber adhesive in the early 1940's is still in use throughout the rubber industry at the present time. No other resin has replaced the resorcinol-formaldehyde resin and no other latex has replaced 2-vinylpyridine-butadiene-styrene latex as components in adhesive dip recipes. This will probably be true into the foreseeable future. There was really no need to improve the adhesion of rayon and nylon to rubber, so very little development work was done with the adhesion of these two fibers. However, a considerable amount of work was done with polyester adhesion and this coincided with the expanded use of poly(ethylene terephthalate) fibers in passenger tires. Much of this effort was concerned with single-step adhesive dips where the adhesion activating ingredients were added to a standard RFL mixture.
Applications of Mass Spectrometry to Synthetic Polymers
Authors: Lattimer Robert P. , Schulten Hans-Rolf
Published: February 2011

Mass spectrometry has earned its rightful place as one of the three principal spectroscopic methods (along with magnetic resonance and infrared) for the analysis of polymeric materials. It is clear that a large and efficient arsenal of mass spectrometric techniques has been developed to examine these complex and intractable materials. Improved pyrolysis methods, soft ionization modes, higher mass analyzers/detectors, and sophisticated chemometric treatment of the spectral data appear to be the main lines of future development.
Elastomer Modification of Structural Adhesives
Authors: Pocius Alphonsus V.
Published: February 2011

An attempt has been made to review the highlights of the chemistry and physical properties of the rubber modification of structural thermosetting polymers that are used as adhesives. The elastomers are added in order to improve the characteristics of these structural thermosets such that they would be more useful as structural adhesives. The addition of an elastomer acts to increase the resistance of the structural thermoset to crack propogation. The resistance to crack propogation is obtained either by plasticization to increase the ductility of the thermoset or by generation of a two-phase system where the structural polymer forms a matrix in which the phase-separated elastomeric particles are imbedded. In the case of flexibilization by plasticization, the increase in peel strength (fracture toughness) is accompanied by a decrease in shear strength (modulus) at high temperatures. In the case of the two phase system, the matrix properties are unaffected for the most part, and increases in peel strength are not accompanied by significant decreases in high-temperature shear strength. In the case of flexibilization, the increase in fracture toughness is accomplished by increasing the ductility of the resin while in the case of the two-phase system, the rubber particles act as stress concentrators to cause conditions of exceeding the yield stress of the matrix near the particles. Exceeding the yield stress increases the amount of plastic deformation of the matrix. We have briefly reviewed the chemistry and physical properties of phenolic, epoxy, acrylic, and polyimide structural adhesives and their modification with vinyl, nitrile, acrylic, siloxane, and other types of elastomers.
Molding of Rubber for High Performance Applications
Authors: Sommer J. G.
Published: February 2011

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

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>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

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

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

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

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

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

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

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

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

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.