bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Morphology of High-Impact-Strength Blends of EPDM and Polypropylene. Knit-Line Behavior
Authors: Thamm R. C.
Published: February 2011

The blend morphologies of injection moldings of high-impact-strength blends of EPDM or mixtures of EPDM and high-density polyethylene (HDPE) in polypropylene have been elucidated by the use of several classical microscopic techniques. It is demonstrated that, when present, HDPE is located within the EPDM phase, where it probably functions predominantly as a viscosity modifier. Within the core, the dispersed phase has an equilibrium globular shape, whose size can be related to impact strength. Elsewhere, the shape of the dispersed phase accurately reflects the shear forces of viscous flow through the mold cavity. In effect, these small domains serve as tracer elements and provide visual evidence and verification for previously postulated flow patterns. Fast, laminar flow through the center of the cavity to the advancing front and then in a curved path to the wall creates shear patterns such that the dispersed phase is in sheetlike or disk-shaped domains at the melt front and in rapidly crystallized regions near the cold mold wall. When knit lines are formed by union of two melt fronts, these flattened domains are oriented perpendicularly to the flow direction, where they prevent adequate matrix union and probably act as stress concentrators which can provide additional loss of knit line strength. Less easily dispersed, higher viscosity EPDM compositions are recommended where knit-line strength is required.
13C NMR Characterization of Polychloroprene Microstructure I. Spectral Assignments
Authors: Coleman M. M. , Tabb D. L. , Brame E. G.
Published: February 2011

13C NMR spectroscopy has proved to be a very powerful tool for the characterization of polychloroprene microstructure. We have identified and assigned the lines associated with diad and triad sequences involving the predominant trans-1,4 placement, together with other lines associated with cis-1,4, 1,2, isomerized 1,2, and 3,4 structural irregularities. Currently, we are performing 13C NMR, relaxation studies on the chloroprene polymers and will be presenting quantitative data in the near future.
Elastomer Blend Properties—Influence of Carbon Black Type and Location
Authors: Hess W. M. , Chirico V. E.
Published: February 2011

Criteria for minimizing hysteresis in carbon-black-filled elastomer blends are: (1) large black unit size, wide distribution, and low structure; (2) higher black loading in the discrete polymer phase (large zones); and (3) polymer of lower hysteresis as the continuous phase (low black loading). Of the different strength properties that were evaluated, tear and fatigue resistance showed the greatest dependence on black location in NR-BR and NR-SBR blends. Both properties were markedly higher for NR-BR, with most of the black in the NR phase. In NR-SBR, tear strength was higher with high loadings of black in the SBR. Fatigue life showed a reverse pattern, but the variations were not as great in this system. Criteria for maximizing tear resistance are: (1) small black unit size, low structure; (2) higher loading of carbon black in the continuous polymer phase ; and (3) the polymer of higher strength as the continuous phase. There may also be optimum levels of polymer zone size and black size distribution which affect tear strength. Optimized performance in a 50:50 NR-BR radial truck tire tread stock was obtained with a wide-distribution N-375 (50:50 N-351-N-110 blend) black with 75% location in the NR phase. This black gave 5–6°C lower heat buildup, equivalent modulus, 35% higher tear strength, and almost double the fatigue life of a conventionally mixed N-220 at essentially equivalent tread wear resistance (−4%). Optimized performance in 50:50 NR-SBR was indicated for a wide-distribution N-231 type (50:50 blend of N-351-N-119) with 75% of the black in the SBR phase. In comparison to conventionally mixed N-234 and N-220, this black gave about 8–10°C lower heat buildup, about 15% lower modulus, and essentially equal tensile, tear, and fatigue properties. Alternatively, a standard N-231 type with 75% location in the NR phase showed about 5–6°C lower heat buildup, about 20% lower modulus, equivalent tensile strength, 60% higher tear resistance, and 75–120% higher fatigue life.
SEM Study of a Cyclized Rubber Surface
Authors: Bascom W. D.
Published: February 2011

It has been shown that cyclization of a nitrile rubber produces a brittle surface layer. Microcracks develop when the rubber is flexed and, when stressed, severely deform the underlying rubber into an open, fibrous network. These microcracks offer easy penetration and interlocking of the adhesive into the rubber. Evidence was also presented for entrapment of electrolyte solution in the cyclized layer.
Fine-Particle Silicas in Tire Treads, Carcass, and Steel-Belt Skim
Authors: Wagner M. P.
Published: February 2011

HS-200 silicas, modified with the coupling agents, performed in tire treads equivalent to N-200 type carbon blacks. Tread wear and traction in contemporary tire tread compounds could be obtained with HS-200 silica equivalent to those with carbon black. In passenger-car treads containing higher than normal butadiene rubber, HS-200 silica could be compounded for excellent mileage and improved wet road traction. These results are encouraging, but considerably more tire testing would be required for absolute certainty that silicas could, in fact, replace contemporary tread fillers. The data indicate that silicas together with silane coupling agents provide extreme flexibility in the design of tread properties. Although tested only to a limited extent in tires, silicas can be used in sidewall, carcass, and radial-belt compounds of tires, as well. The various filler sizes available, and the flexibility of adjusting surface activity, permits a wide range of rubber properties to be obtained. In a limited number of cases, these properties are virtually identical to those obtained with contemporary carcass and sidewall fillers. Tire performance in carcass and belt-skim compounds showed that silicas could provide tire performance equivalent to conventional fillers in these applications. Based on our observations, we confidently believe the technology exists to meet the performance of today's tire components entirely with inorganic fillers. Obviously, to put these components together in a practical tire requires some development work. Satisfactory performance in individual components is encouraging, but the incorporation of all components into a single harmonious product is still necessary. Fine-particle silicas are truly oil-independent fillers that can be used for tires as well as other quality rubber products.
Chain Scission in the Oxidation of Polyisoprene
Authors: Morand J. L.
Published: February 2011

The composition of the mixture of volatile products formed during the oxidation in air of natural rubber or synthetic cis-polyisoprene in the raw state was investigated in order to obtain further information on the mechanism of chain scission. An important observation was made: in order to obtain, by means of gas chromatography, the peaks of all the constituents, a completely anhydrous solution of the trapped mixture must be used. If the water liberated by the oxidized polyisoprene is present, the peaks of some constituents do not appear. By removing this difficulty, four new less volatile compounds which could result from chain scission were detected on heating extracted polyisoprenes which do not contain protective agents. The concentrations of these four compounds are similar to those of levulinaldehyde, methacrolein, or methyl vinyl ketone, and the structures which were identified correspond to a γ-substituted γ-butyrolactone, a primary γ-ketol, and probably a tertiary γ-aldol and a secondary γ-ketol. These components could arise from a chain scission between two isoprene units, due to a β-scission process of an alkoxy radical. Natural rubber or synthetic polyisoprene which contain protective agents give off mainly the lactone and the tertiary γ-aldol, but levulinaldehyde is produced in small amounts, and methacrolein and methyl vinyl ketone are absent.
A New Fluoroelastomer Derived from Tetrafluoroethylene and Propylene
Authors: Kojima G. , Kojima H. , Tabata Y.
Published: February 2011

(1) A process to produce C2F4-C3H6 copolymer of molecular weight over 150 000 was established by exploiting a new catalyst which permits low temperature polymerization. (2) A vulcanization recipe, comprised of peroxide and TAIC, was established to give the copolymer superior vulcanizate properties. (3) Polymer structure and properties were elucidated, and the high potential as a heat-resistant elastomer was shown. (4) The resultant vulcanizate has been proved to be a unique fluoroelastomer with outstanding heat and chemical resistance as well as mechanical properties which are adequate in practice.
The Polymer-Solvent Interaction Parameter X
Authors: Orwoll R. A.
Published: February 2011

The interaction parameter X has been defined as a measure of the chemical potential of the solvent in solutions with a polymeric solute. Consequently a number of equilibrium properties can be expressed as functions of X. Values of X determined from these properties reveal that for most systems this quantity increases with the volume fraction of polymer in the solution. Accordingly, values of the interaction parameter have been tabulated as a function of concentration, as well as of temperature. The values of X obtained either from experiment or theory can be utilized for predicting the colligative properties and determining the solubility characteristics of polymer-solvent systems.
Continuous Emulsion Polymerization
Authors: Poehlein G. W. , Dougherty D. J.
Published: February 2011

The theories presented can be used for prediction of particle size, particle formation, rate of polymerization, and molecular weight for the emulsion polymerization of styrene in continuous stirred-tank reactors. The incorporation of Stockmayer's modification of the Smith-Ewart theory into Gershberg's continuous reactor model has helped to account for the formation of fewer but larger particles when the reactor is operated at long mean residence times. The use of a different particle generation relation by Nomura and coworkers has led to better agreement between theory and experiment for particle number and polymerization rate at low values of mean, residence time. Their model also fits transient data better than Gershberg's. However, the prediction that free-radical movement into particles is independent of particle size is not very satisfactory. Perhaps the better agreement between theory and experiment results because of the introduction of an additional experimentally determined parameter. Data for other monomers do not follow theoretical predictions as closely as styrene. For methyl acrylate the particle number data are in reasonable agreement with theory but the polymerization rate data show completely different trends. An improved, more general, theory will undoubtedly require a more complete understanding of particle formation and particle growth mechanisms. Particle size distribution measurements would be a valuable asset in developing improved competitive particle growth models.
Fun and Frustrations with Synthetic Rubber
Authors: D'Ianni James D.
Published: February 2011

It is a great pleasure and honor to have this opportunity to share with you some of my experiences in synthetic rubber over the past forty years. I am deeply appreciative of my selection as the thirty-fourth recipient of the Charles Goodyear Medal by the Rubber Division of the American Chemical Society and accept it only as a representative of my many associates at Goodyear who have participated with me in significant developments in synthetic rubber during this period. As the title of this talk indicates, we had both successes and disappointments in our endeavors to develop improved synthetic rubbers. These efforts were greatly stimulated by shortages of natural rubber which occurred in times of national emergencies such as World War II and the Korean War. When we successfully met these challenges it was fun, but to the extent that we were not able to achieve all of our objectives, we suffered a number of frustrations.
Use of Azo Foaming Agents to Produce Reinforced Elastomeric Foams
Authors: Harpell G. A. , Gallagher R. B. , Novits M. F.
Published: February 2011

It is highly desirable to produce elastomeric foams directly from liquid components. Flexible urethanes, the only technologically important elastomeric foams that are commercially available, are enjoying rapid growth. An essential feature of a successful foam system is the ability to attain the appropriate balance between gas generation and cure reaction. We report here a completely new system which allows syrups, consisting of polymer dissolved in free-radically polymerizable monomers, to be foamed directly using certain azo compounds. Our preliminary results show that a number of different azo compounds may be utilized to produce elastomeric foams over a wide density range. The variables which can effectively control the foaming and curing reaction are discussed, but there has been no attempt to optimize the physical properties of the flexible foams. Physical property evaluations will be the subject of future publications. We illustrate the versatility of the system and believe that properties may be easily tailored to end-use needs by appropriate selection of formulation components.
Elastomeric Polyether-Ester Block Copolymers. I. Structure-Property Relationships of Tetramethylene Terephthalate/Polyether Terephthalate Copolymers
Authors: Wolfe J. R.
Published: February 2011

The properties of elastomeric tetramethylene terephthalate/polyether terephthalate copolymers have been related to the chemical structure, chain length, and concentration in the copolymers of the PTMEG-, PEG-, and PPG-derived polyether units. Low-temperature properties and tear strength are dependent on all three polyether-related variables. Melting point, hardness, and stress at 100% elongation appear to be independent of polyether structure. Polyether glycols of low MW volatilize during copolymer preparation. High-MW polyethers tend to crystallize when present in the copolymers. Polyether glycols of intermediate MW (∼ 1000) yield copolymers with the best resistance to low-temperature stiffening. Copolymer synthesis is most difficult with PPG as the polyether glycol. Inherent viscosities are low, and phase separation occurs at lower polyether MW than with PTMEG or PEG. The PEG-based copolymers exhibit high water swell, particularly at intermediate and high PEG MW. The PTMEG-based copolymers are easiest to synthesize and exhibit the best overall combination of properties.
The Processing of Filler-Reinforced Rubber
Authors: Dizon E. S. , Papazian L. A.
Published: February 2011

Further insight into the mixing process has allowed a definition of the intermediate objectives of processing, which relate to the different transformations that occur as mixing energy is added to a rubber formulation. These convert the ingredients into a coherent mass with specific flow characteristics and determine the efficiency of the next unit, therefore contributing to overall productivity. The total energy added to the batch is derived from a combination of Banbury, mill, and extruder. These processing units vary in the efficiency with which they achieve the required material transformations. Proper allocation of mixing energy to the most effective equipment, with a knowledge of the total energy required to achieve the desired quality, allows a rational optimization of productivity and product quality. Operating profiles for each unit have been constructed in order to aid in optimizing the process. Using a fixed total energy input, these profiles were used to estimate the productivity of each processing unit. The study shows that in a semicontinuous operation with laboratory-size Banbury, mill, and extruder, the extruder is the primary determinant of overall productivity. The study also shows that maximizing productivity in a single unit will not necessarily lead to the highest productivity along the equipment train. Material properties affect overall productivity in several ways. In this work, carbon black surface area determined the total energy required to attain the desired quality level, the flow rate in the extruder, and the energy required to attain the maximum flow rate. Future studies should focus on the derivation of operating equations for specific equipment and materials. These equations should quantify the interrelationships between the different engineering parameters (such as screw or rotor speeds and Banbury ram pressure), the processing parameters (such as mixing time, fill factor, and temperature), and material variables (such as Mooney viscosity, carbon black morphology, and black and oil loading).
Fundamental Observation on Deformation and Failure Characteristics of SBR 1500
Authors: Nakajima N. , Collins E. A.
Published: February 2011

The processing of raw elastomers involves viscoelastic properties at both small and large deformations. It also involves ultimate properties, because the deformation under processing conditions often exceeds the failure limit. The present work describes these properties in the processing ranges of temperature and deformation rate. Therefore, the results may be used for interpreting processability. Also, relative differences in molecular weight, its distribution, long-chain branching, and gels may be detected by comparing the above data for different samples. The results summarized in master curves and a failure envelope indicate that the essential information is obtainable with limited experiments, for example, with the Rheovibron and the variable-speed Mooney rheometer.
Application of Headspace Gas Chromatography to Analysis of Residual Volatiles in Synthetic Rubbers
Authors: Pausch J. B. , Sockis I.
Published: February 2011

The environmental concern for chemicals covers a broad spectrum in the world of today. There are traces of chemical compounds in the air, water, and soil that must be measured and identified, especially around a chemical or rubber plant. Likewise, the total composition of our industrial rubber products has become a major issue. We want to protect the rubber manufacturing worker, the rubber processing and fabricating people, and finally the consumer from exposure to possible toxic substances, undesirable odors, or any other type of irritant that may result from residual volatiles or decomposition products of our rubber products. For many years the conventional analytical technique for measuring residual monomers, solvents, and other small molecule impurities in rubber has been gas chromatography (GC). The sample was dissolved in a suitable solvent and chromatographed. However, the analytical requirements in the last couple years have dictated lower levels of detection than are possible with the solution method using flame ionization detection. Different approaches to this analytical problem have been widely discussed and will not be reviewed here. Briefly, they include the use of specific GC detectors, such as the electron capture detector for halogenated and other electron deficient compounds; specific detectors for nitrogen, sulfur, and phosphorus compounds; and the photoionization detector, which has become commercial within the last year. A recent paper described a modified solution approach combined with headspace GC. Each of these methods is suitable in certain analyses but does not represent a good general technique for hydrocarbon analysis in solid rubber materials. This paper describes various aspects of headspace gas chromatography as a general method for direct measurement on solid rubber samples for trace levels of residual volatiles. In addition, several other important advantages result from the elimination of the solvent.
Staining Natural Rubber with Silver Nitrate for Electron Microscopy
Authors: Smith R. W. , Folt V. L.
Published: February 2011

Hevea brasiliensis or natural rubber (NR) has been used for over 500 years. Until World War II, it was the basic raw material of the rubber industry. Since that time, the use of synthetic polymers has steadily increased, but the importance of NR has not diminished. In fact, the future for the natural product is very promising since it is the one polymer that is obtainable without depleting fossil fuel raw materials. Natural rubber latex has been extensively studied by a variety of methods, especially the microscope. All of the early work with NR latex was conducted, of course, with the optical microscope. In the late 1940's the electron microscope began to be used, but at that time synthetic rubbers began to demand attention, and work on NR latex diminished. Perhaps investigators felt they knew all there was to know about the microscopical characteristics of this material. Indeed, some very fine work had been done and keen observations made with optical microscopes that could not even resolve all of the particles in a latex material. This paper deals with the electron microscopy of natural rubber latexes with particular attention to the proteinaceous layer on the particle and the fate of particles during varying stages of mastication. The critical technique used was to stain the proteinaceous layer of the latex particle with silver nitrate.
Isothermal and Nonisothermal Creep of Lightly Crosslinked cis-1,4-Polybutadiene
Authors: Caruthers J. M. , Cohen R. E.
Published: February 2011

A nonisothermal creep experiment has been analyzed to ascertain its suitability for determining the temperature dependence of low-activation-energy viscoelastic processes in elastomers far above Tg. The nonisothermal method was employed to determine the activation energy for creep near 35°C in a lightly crosslinkedcis-1,4-polybutadiene elastomer at small strains within the linear viscoelastic region and at various large deformations up to rupture. The observed activation energy was essentially independent of the level of strain, and the value of ΔHa (∼ 11 kcal/mol) determined via the nonisothermal creep method was in good agreement with the result (∼12 kcal/mol) obtained via time-temperature superposition of isothermal linear viscoelastic creep data. The nonisothermal data allowed for an estimate of the volume of the “flow unit” associated with the controlling viscoelastic creep mechanism, attributed here to slippage of entanglements within lightly crosslinked network.
Physical and Chemical Stress Relaxation of Elastomers
Authors: Curro J. G. , Salazar E. A.
Published: February 2011

In this paper we have developed a method whereby physical and chemical relaxation processes can be distinguished, using stress relaxation experiments as a function of temperature. We assumed that there exists some temperature range above the glass transition temperature over which the chemical effects can be neglected for the time scale of the experiments. The data in this low temperature range were then used to determine the WLF constants and other physical relaxation parameters. The physical component of the stress relaxation could then be subtracted from high temperature experiments in order to extract chemical kinetic information. Based on certain reasonable assumptions, an equation was developed for the relaxation modulus of a chemically reacting system. This equation could be used to determine the time dependence of the crosslink density, or conversely could be used to predict the long-term relaxation modulus from an assumed kinetic mechanism. These calculations were demonstrated for ethylene-propylene and butyl elastomers.
Isochronous Stress-Strain Relationship in Compressive Stress Relaxation of Vulcanizates
Authors: Stenberg B. , Jansson J. F.
Published: February 2011

The mechanical and other properties of natural and synthetic rubbers can be regulated by the incorporation of fillers. The mechanical behavior of the resulting complicated heterogeneous systems is often difficult to describe theoretically. These vulcanizates have wide and useful applications under conditions of multiaxial stresses. In many cases, however, the stresses act mainly in compression, for instance, in gaskets, seals, suspension systems for vibration insulation, etc. Thus the stress relaxation properties in compression are of vital importance. In spite of this, very few studies have given attention to the stress-strain relations in compression, and the results reported in the literature concentrate mainly on the mechanical behavior of rubbers in tension. We now report a study of the isochronous stress-strain relation in compression for some rubbers at 295 K, based on stress relaxation measurements. A comparison is made between the behavior of samples which have been greased and of samples which have been glued to the deformation plates.
An Elastomeric Micrometering System for the Controlled Administration of Drugs
Authors: Wright J. C. , Buckles R. G. , Dunn J. T. , Leeper H. M. , Yum S. I.
Published: February 2011

When drugs are infused, it is often necessary to minimize the volume of fluid delivered. Fluid delivery rates of 1 cm3/h or less are frequently desirable; however, the accurate metering of fluids at such low flow rates to the human body has been difficult to accomplish. The metering devices most commonly used to control flow rate from a constant-pressure source have been micrometer valves, clamped tubes, capillaries, and porous plugs. Each of these devices has specific disadvantages : micrometer valves are expensive and bulky, clamped tubes are not stable for long-term infusion and present a hazard of greatly fluctuating flow rates, capillary tubes are subject to particle blockage and are not adjustable, and porous plugs suffer from lack of adjustability. Recently a valve made of extruded silicone rubber rod with axial holes was reported to yield stable flow rates; it was adjusted by placement in a plastic clamp. A new low-infusion-rate metering system has been developed to overcome the above deficiencies. This system consists of axially aligned polyurethane fibers contained within the lumen of a length of silicone rubber tubing. The fibers fill the lumen to the extent that they are subjected to a compressive hoop stress by the tubing. The assembly represents two elastomeric materials in states of strain, exerting equal and opposite stresses on each other. The elastomeric tubular assembly is contained in a rigid, adjustable, U-shaped enclosure that controls the deformation of the assembly. While other elastomeric materials would be suitable for the elastomeric valving system, we report here on our experience with polyurethane fibers and silicone rubber tubing. These materials were selected for their expected compatibility with most aqueous drugs and their availability.
Role of the Elasticity of Rubber in the Controlled Administration of Drugs
Authors: Leeper H. M. , Buckles R. G. , Guittard G. V. , Lorberbaum M. A. , Sevilla E. R. , Yum S. I.
Published: February 2011

The energy stored in an extended elastomeric reservoir can be usefully employed in the controlled delivery of drug solutions at constant rates of flow through a fixed resistance. The absolute level and constancy of pressure presented to the upstream end of the flow restrictor can be related, respectively, to the geometry and composition of the elastomeric reservoir. (The reservoir is to contain, in its distended form, the volume of drug to be delivered to the human venous system.) It has been established that the defining criteria for minimizing static pressure loss in the reservoir and for maintaining constancy of pressure through most of the delivery interval are stress decay and hysteresis, as measured in uniaxial stress-strain testing. The elastomeric composition most successfully meeting these requirements has been found to be non-reinforced isoprene rubber, crosslinked with a peroxide.
Preparation of Radioactively Tagged Ethylene-Propylene Copolymers. Calculation of the Block-Length Distribution from the Kinetic Data
Authors: Exner J. , Seeger M. , Cantow H-J.
Published: February 2011

A series of statistical copolymers is available for our studies of the mechanisms of thermal decomposition of ethylene-propylene copolymers and their sequence distribution. However, the analytical evidence can be improved appreciably by the use of radioactively tagged copolymers and radio-gas chromatography. A loss of information occurs when untagged polymers undergo α-scission. Even if the chain breaks directly at the tertiary carbon atom, the scission product stabilizes itself by forming a terminal double bond. Accordingly, the position of double bonds gives no information about the location of methyl side groups in copolymers. However, if the α-methyl groups are radioactively tagged, as shown in the formula above, radioactive counting of linear fragments can demonstrate their original methyl side groups. Thus, α-scissions of copolymers can be directly determined.
Visualization of Flow during the Processing of Rubber in an Internal Mixer
Authors: Freakley P. K. , Idris W. Y. Wan
Published: February 2011

The flow visualization method of studying internal mixing has been shown to be a powerful tool for determination of the critical factors influencing flow and mixing efficiency. Correlation of visualizations with results obtained for “practical” rubber mixing confirms the validity of the method for the prediction of flow in conventional mixing operations. Fill factor is identified as one of the key variables influencing mixing uniformity. At this stage it is not possible to make general recommendations since only limited studies were carried out. However, from the dependence of mix uniformity on fill factor derived from a B Banbury having two-wing rotors, fill factors of 0.7–0.8 are shown to give the best results. This range of fill factors provides an adequate and continual filling of the region in front of the rotor tip and ensures that the high stresses required for the fracture of particle material aggregates are generated. It also permits the formation of voids behind the rotor tips. Such voids appear to be essential for the disordering of streamline flow patterns and for promoting effective axial tranfer of material.
New Generation Polyacrylate Elastomers
Authors: Demarco R. D.
Published: February 2011

Polyacrylate elastomers have come a long way since the first large-volume commercial product was introduced in 1948. Rapid cure rates with relatively mild cure systems are now possible. Low temperature limits have been extended from −15°C to the −30 to −40°C range, while maintaining good oil resistance. The need to post cure has been removed in some processes and minimized in others. Future trends in ACM research are aimed at improving strength (especially abrasion), complete elimination of post cures, and improved fuel (especially gasoline) resistance.
The Filler—Elastomer Chemical Link and the Reinforcement of Rubber
Authors: Le Bras J. , Papirer E.
Published: February 2011

The results confirm the rationale which guided the experiments. The mechanical properties of the vulcanizate prepared without any milling and containing a carbon black chemically grafted to part of the elastomer are definitely superior to those of the blank, prepared under the same conditions with an ungrafted black. This indeed proves that merely creation of a chemical bond between the carbon black and the rubber brings about reinforcement and that, therefore, the reinforcement mechanism cannot be solely accounted for by physical interactions. Of course, optimum reinforcement as would be observed by classical mixing is not attained, since in this case complementary effects intervene. We believe that, for the first time, we have given absolute proof that the establishment of a chemical link between the carbon black and the elastomer induces reinforcement. New experiments are in progress with SBR; they should accentuate the differences in mechanical properties taking into account the very low values for nonreinforced vulcanizates.
Creep Resistant Elastomer Formulations
Authors: Meier J. F. , Rudd G. E. , Weir D. F.
Published: February 2011

Over 150 elastomer formulations of NR, DPNR, CR, IIR, AU, EU, EO, ECO, SBR, EPM, EPDM and a silicone rubber have been evaluated to identify the most creep resistant materials. Selected data are presented. Three of the best formulations (DPNR compound 15, CR compound 27 and EPDM compound 49) were found to give excellent creep performance extrapolating to less than 28% relative creep for a 15 year service life. As a result of a requirement for 15 year resistance to 25 pphm O3 concentration, EPDM formulation 49 was selected, and pads were molded and compression tested. Because of the O3 resistance of EPDM, there should not be a significant increase in creep rate.
Mechanics of Fracture in Two-Ply Laminates
Authors: Breidenbach R. F. , Lake G. J.
Published: February 2011

This paper describes a study of fracture in two-ply rubber—cord composites subjected to repeated tensile deformations. Under the conditions used, failure occurs predominantly because of the growth of cracks between the plies. A fracture mechanics approach enables the rate of crack growth to be predicted in terms of the elastic properties and dimensions of the laminate, the magnitude of the deformations and the basic crack growth characteristics of the ply rubber. The theory indicates the growth rate to be determined by the strain energy released from the central region of the laminate and to be independent of crack length once this exceeds a small value. The latter feature has been verified experimentally and the magnitudes of the observed crack growth rates are in reasonable agreement with those predicted for various deformation cycles.
Method of Obtaining Viscosity Curves with Mooney Rheometer
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

A mathematical expression is derived for calculating shear stresses from torque values observed with the Mooney rheometer. Examination of this expression indicates that some improvement is possible in the rotor design. The numerical values of the conversion factor are given for both small and large rotors. The application of these factors to the observed data give viscosities in agreement with those obtained with other instruments. Low shear viscosities down to 10−3 and in some cases 10−4s−1 are obtained with the Mooney rheometer operated at 0.05 rpm for several minutes.
Effect of Vulcanization Temperature and Different Fillers on the Properties of Efficiently Vulcanized Natural Rubber
Authors: Mukhopadyay R. , De S. K.
Published: February 2011

The present work deals with effect of vulcanization temperature on the polymer-filler interaction parameter, vulcanizate structure, and the technical properties of efficiently vulcanized natural rubber stocks in the presence of different fillers. We have used carbon blacks of four different particle sizes (ISAF, HAF, SRF, FT), reinforcing silica, and whiting. In the case of black fillers, as the particle size increases, reversion resistance increases. For all fillers, an increase of curing temperature from 150 to 180°C caused a reduction in strength, modulus, hardness, resilience; and an increase in elongation at break, compression set, and heat build-up. However, the flexing properties and abrasion loss showed improvement at higher curing temperature. Kraus' plots indicate that increase of curing temperature caused reduction in polymer-filler attachment. At both curing temperatures, the activity of fillers follow the order, ISAF > HAF > SRF > FT. Silica showed erratic behavior in that Kraus plots indicate nonreinforcement by the filler. Whiting also behaved abnormally with respect to Kraus plots; at lower filler loading, the system is nonadherent, becoming weakly adherent at higher concentrations. The abnormal behavior of silica-filled compounds has been explained on the basis of a reaction on the silica surface between silanol groups and zinc stearate. Westlinning and Wolff's αF values were found to be independent of curing temperature and characteristic of fillers only (the larger the particle size, the lower is the αF value). The increase in apparent crosslinking density in the case of reinforcing fillers is due to increased υr arising out of increased polymer-filler interaction. Therefore, the sulfur inefficiency parameters (E values) and zinc sulfide efficiency parameters (F values) become less significant in filled vulcanizates.
The Entanglement Plateau in the Dynamic Modulus of Rubbery Styrene—Diene Block Copolymers. Significance to Pressure-Sensitive Adhesive Formulations
Authors: Kraus G. , Rollmann K. W.
Published: February 2011

Styrene-diene (butadiene or isoprene) block copolymers of the SDS or (SD−)x type exhibit a plateau in the dynamic storage modulus located between the glass transitions of the polydiene and polystyrene domains. When the polydiene is the continuous phase, the height of this plateau can be estimated with good success from the entanglement spacing molecular weight of the polydiene and the filler effect of the polystyrene domains. The effect of introduction of a center block-compatible diluent can also be calculated, although the simple procedure used here tends to underestimate the plasticizer effect, particularly at high diluent concentration. Nevertheless, the calculation furnishes a useful criterion of compatibility of the polydiene center blocks and low molecular weight resins used commonly as tackifiers in pressure-sensitive adhesives. Center block compatibility is essential for the development of tack in these compositions.
Ultrasonic Measurements with Rubber Compounds during Extrusion
Authors: Caspary R. , Kretschmer P.
Published: February 2011

The dependence of the Index of Elasticity, E, the reciprocal value of sound velocity, on temperature and pressure is related to specific volume and compressibility of rubbers. The sensitivity of E towards changes of temperature and pressure was calculated, indicating a new versatile possibility for the control of rubber extruders. To confirm this, extruder experiments were carried out with an SHR compound, of which a working diagram was established showing the complete behavior of E=f(p,T). The effect of compound composition, especially of plasticizer and carbon black content, was examined. Viscosity in the extruder primarily determines changes in E. The method was shown to be applicable up to a die diameter of at least 200 mm. The method may also be applied to follow degradation of rubber compounds during mastication.
The Structure of Rubber Networks with Multifunctional Junctions
Authors: Pearson D. S. , Graessley W. W.
Published: February 2011

A number of statistical relationships have been derived for calculating the structure of rubber networks with multifunctional junctions. Some of these quantities appear as parameters in the molecular theory of elastic energy in phantom networks. Others relate to Langley's trapping factor for the entanglement contribution to the modulus, to the maximum extensibility, and to the viscoelastic properties of networks.
The Vulcanization of Styrene-Butadiene Rubber with 2-Pentadecyl-Benzoquinone Dioxime
Authors: Ghatge N. D. , Maldar N. N.
Published: February 2011

The authors propose a new active vulcanizing agent 2-pentadecylbenzo-quinone dioxime, derivable from the indigenous raw material, cashewnutshell liquid. This vulcanizing agent, when oxidized by red lead, gives styrene-butadiene vulcanizates of improved tensile strength and elongation at break, compared to vulcanizates cured by p-benzoquinone dioxime, 2-methylbenzo-quinone dioxime or standard sulfur curing systems. The new vulcanizates have much greater resistance to heat aging than the corresponding sulfur vulcanisates.
Effects of Compounding Variations on the Properties of Guayule Rubber
Authors: Porter L. S. , Stephens H. L.
Published: February 2011

The vulcanization characteristics of guayule and NR respond similarly to compound modifications: the major difference being that the addition of N219 carbon black affects GR more than NR; the gum stock scorch time is higher for GR, but the black stock scorch times are similar (Figures 7 and 8). The GR and NR physical properties respond similarly to compound modifications in all cases. The free rubber static and dynamic response of GR and NR is similar with compound modifications. However, the GR response to dynamic excitations is different than the NR response, as seen by the significantly higher dynamic rates of GR when the static compressions are nearly identical (Figures 15 through 18). The bushing assembly data point out the same characteristics noted for the free rubber. The GR bushing fatigue life appears to be as good as NR and is superior to SN.
Ethylene Propylene Rubber and Crosslinked Polyethylene as Insulations for 90°C Rated Medium Voltage Cables
Authors: Blodgett R. B.
Published: February 2011

Amorphous ethylene propylene rubber insulated power cables are expected to be more stable under high temperature conditions than crystalline crosslinked polyethylene insulated cables. The properties of amorphous EP rubbers are little affected by temperature from −30 to 150°C; those of crystalline XLPE fall off as temperature exceeds the melting point (around 100°C) of the crystalline regions. Probably reinforced amorphous EP rubber insulated cables are expected to be more stable in wet locations than unfilled XLPE insulated cables. They do not fail by the formation of water trees as the primary mechanism, since the bonds between filler and polymer are stronger than the forces responsible for water trees forming in XLPE cables in service. The reinforcing effect of fillers in EP rubber makes questionable any extrapolation from high stress treeing studies of unreinforced PE, XLPE, or EP polymers. For the longest possible life in wet locations insulation should be protected by a water impermeable metallic sheath, which must be protected against corrosion, mechanical damage, fatigue cracks, etc. Any insulation will eventually fail on continued exposure to water and electrical stress.
Modifications of Low Functionality Elastomers
Authors: Baldwin F. P.
Published: February 2011

Last year at the Boston meeting, Herman Schroeder in introducing a session stated, “Research is cheap, it is development which is expensive”. I certainly concur and I would add that it is the dream of all industrial researchers to see the results of their research reach the marketplace. There is no secret to the transition from laboratory to commercial development. What is required is: (1) Personal zeal, a thesis, and a cooperative atmosphere in the laboratory stage. This characterized the people in the Elastomers Group at Exxon. (2) Some good engineers who can devise an economical process for the product. (3) At least one knowledgeable and aggressive product champion in the market development stage. (4) Reliable cooperation and feedback from potential users. (5) A current or impending need in the marketplace. (6) The availability of some risk capital and business people who have the courage and confidence to use it as such. (7) A technical service-research organization that can carry the product through the rough spots encountered in its introduction and thereafter. The researcher must accept the fact that not too many ideas are likely to result in commercial success in any particular milieu, because of these many conditions which must be met in orderly and timely fashion. I have mentioned many names in this talk. Without difficulty and with ample justification, I could mention many more and herewith wish to acknowledge all those who at one time or another contributed to making mine an interesting, exciting and satisfying career in industrial research. I appreciate having had this opportunity to talk to you and am genuinely thrilled, as is my family, that you have accorded me this honor. Beyond that, though times are a bit troubled, be assured that the rubber industry is neither dead nor dying. There is much research to be done and many new products and concepts to be developed. Keep at it, don't get discouraged and best of luck to you all. Thank you.
High Temperature Vulcanization of Elastomers
Authors: Bhowmick A. K. , Mukhopadhyay R. , De S. K.
Published: February 2011

Vulcanization is a process which decreases the plastic properties of rubber while maintaining or improving the elastic properties. The term vulcanization has been applied in the past mainly to the reaction of rubber with sulfur, but now is generally used for the process which results in changes in properties, by sulfur or some other agent. There are four principal changes brought about by vulcanization: (1) rubber is changed from essentially a plastic to a non-plastic material; (2) rubber is changed from a material soluble in a number of solvents to one which is insoluble; (3) rubber is changed to a material with greatly improved physical properties; (4) these properties of vulcanized rubber are maintained over a much wider range of temperature than those of unvulcanized rubber. What is meant by high vulcanizing temperature? There is no unique answer. About 160°C can be taken conveniently as the lower limit; this temperature has been suggested as the highest suitable for some normally compounded sulfur curing rubbers. The upper limit may be 220°C, above which the polymer may begin to degrade. The range in practice extends up to about 250°C in fluid beds and salt baths. Practical vulcanization processes apply heat to the outside of the article being cured and rely on the conduction of heat to the inside. Since no drastic change can be made in the thermal conductivity of practical rubber compounds by compounding modifications, higher temperature is a common method of achieving faster vulcanization. Higher curing temperatures are used in the newer curing or molding processes such as injection molding, the liquid curing medium (LCM) process, and microwave curing.
Scale-Up of Short Fiber Composite Mixing
Authors: Shen K. S. , Rains R. K.
Published: February 2011

A dimensionless parameter, NRS, based on the probable number of passes through the shear zone for an ingredient to be dispersed, was developed for scale-up of mixing of short fiber composite in an internal mixer. A single curve was obtained for the dispersion-NRS relationship of three widely different compounds in five internal mixers of various sizes. The parameter is an improvement over previously reported scale-up parameters, because the temperature profile does not have to be matched for different size mixers. The dimensionless dispersion number concept can be extended to dispersion of other ingredients, as long as the shear stress generated at the mixing temperature is higher than the interaggregate cohesive force of the particles. Based on this parameter, NRS, the dispersion of short fibers can be predicted from one size of internal mixer to another size mixer. It is also possible to predict the mixing time required for a given dispersion rating.
Mechanical Chain-Scission in Rubber Vulcanizate at Low Temperatures
Authors: Kusano T. , Kobayashl K. , Murakami K.
Published: February 2011

When vulcanized natural rubbers are forced to extend in the glassy state, free radicals are produced by the scission of the primary chain. The amount of the free radicals increases with the strain. The tensile yield strain decreases with the decrease of the molecular chain length between crosslinks. This behavior is explainable on the basis of the limited chain extensibility. The extended chains are broken with further increases of the strain. The mechanically produced free radicals are quite stable below about −40°C. The crosslink density of the chain-ruptured material increases about 2∼3×10−5 mol/cm3. This fact shows that the free radicals are consumed not only by recombination but by the intermolecular reaction. In both sulfur and DCP vulcanizates, the network chains rather than the crosslinks are broken by stretching. In an air stream, some free radicals react with oxygen and others form crosslinks.