bluuebunny/crossref_metadata_2025 huggingface dataset:
Poly(Dimethylsiloxane) Elastomers from Aqueous Emulsions: II. Mechanical Properties
Authors: Mark J. E. , McCarthy D. W.
Published: February 2011

Stress—strain measurements in simple uniaxial extension were used to characterize the mechanical properties of the elastomers prepared from poly(dimethylsilxoxane) emulsions as described in the preceding paper. The studies were carried out on the materials in the unswollen state, after they had received different treatments, specifically no aging, aging in the dry state, or aging in the wet (emulsion) state. Increase in silane crosslinker concentration was found to increase nominal stresses and moduli but to decrease extensibility, two changes that parallel the observed decreases in soluble polymer fractions and extents of equilibrium swelling reported earlier. The energy for rupture (“toughness”) frequently stays roughly constant because the decreased extensibility at least partially offsets the increased stresses. The changes in mechanical properties are due both to increased crosslinking and to reinforcing effects from silica generated from the silane, with the latter effect generally being the more important. The mechanical properties are much more affected by aging in the wet state, as opposed to aging in the dry state. For example, wet-aged elastomers generally had values of the nominal stress and modulus that were consistently lower than those for the unaged elastomers. Wet aging appears to be the result of the continual breaking and reforming of siloxane bonds in the aqueous environment of the emulsion, as probably accelerated by the presence of the tin catalyst.
Carbon-Black-Elastomer Interaction
Authors: Ayala J. A. , Hess W. M. , Kistler F. D. , Joyce G. A.
Published: February 2011

A number of different techniques were applied to measure carbon-black-surface reactivity and the level of black-polymer interaction in four different elastomer systems (SBR, IIR, NR, and NBR) representing differences in unsaturation, crystallinity and polarity. Known within-grade surface activity variations were based on partial graphitization of an N121-type carbon black. The surface activity of different black grades was studied as a function of variations in both surface area and DBPA. Direct measurements of carbon-black-surface reactivity were based on hydrogen analysis, SIMS, IGC, and moisture adsorption. In-rubber measurements included bound rubber, SIMS of cut surfaces, and an interaction parameter, σ/η, which is derived from the slope (σ) of the stress-strain curve at low elongations, and (η), the ratio of dynamic modulus (E′) at 1% and 25% DSA. The following trends were observed: 1. The σ/η values provided a good measure of black-polymer interaction in all four polymer systems for either the within-grade or across-grade comparisons. 2. Higher σ/η values were indicated for SBR and NBR, followed by NR and IIR in that order. 3. SBR indicated the greatest sensitivity for bound-rubber measurements in terms of distinguishing within-grade variations in black-polymer interaction, followed by IIR, NR, and NBR in that order. 4. Positive SIMS on dry carbon black indicates the presence of complex hydrocarbon structures suitable for chemical reactivity at the carbon-black surface. 5. SIMS analyses on the dry carbon blacks exhibited intensity variations in the negative hydrocarbon fragments which were in line with the within-grade variations in hydrogen content. 6. SIMS analyses on the cut-rubber compound surfaces showed overall variations in intensity which were proportional to the range and level of the bound-rubber measurements. The most meaningful variations were recorded for SBR and IIR. 7. Heats of adsorption derived from IGC measurements with different adsorbates showed an excellent correlation with black-polymer interaction for the within-grade studies. Measurements across grades did not correlate as well with the in-rubber measurements, but the best results were obtained using styrene as the adsorbate. 8. The within-grade moisture adsorption measurements showed excellent agreement with IGC and the other techniques for the N121 series of heat-treated carbon blacks.
Role of Phenolic Tackifiers in Polyisoprene Rubber
Authors: Magnus F. L. , Hamed G. R.
Published: February 2011

The effect of p-tert-octyl phenolic (PTOP) resin on the tack of an IR/N660 compound has been studied before and after aging. The phenolic resin has little effect on unaged tack. Upon aging at 23°C and 45% RH, autohesion of the IR/N660 significantly decreases. However, when the PTOP resin is added, tack is maintained during aging. FT-IR attenuated total reflectance analyses indicate that, upon aging, oxidation leads to cis → trans isomerization. The PTOP resin becomes enriched in the surface region and protects the IR from further oxidation and the accompanying cis → trans isomerization. Additionally, solubilized resin may behave as a plasticizer to enhance tack bond formation. A compound with phenolic monomer (PTOP resin precursor) forms a rapid bloom with aging and experiences rapid tack loss.
Methacrylate Star Synthesis by GTP
Authors: Simms J. A.
Published: February 2011

All process conditions were picked to minimize the back-biting termination reaction so the maximum level of living arm could be carried into the core-forming step. Major contributors to control of termination were: 1. Using 0.2% (mole basis) of catalyst on initiator instead of higher concentrations. Within the constraints defined below, this produces a robust process that is insensitive to minor changes in materials, temperatures, and rates of addition. 2. Minimizing the time between arm formation and core formation. Polymerization of arm monomethacrylate to about 96 to 98% before core formation was the aim because conversion to >99% would have allowed too much time for termination to proceed. 3. Adding core-forming monomer (ethylene glycol dimethacrylate) in about 5 min to keep monomer concentration high in this step. Faster add times may not be desirable because of mixing difficulties in this extremely fast polymerization. 4. Reaction solvent mixture containing 50% tetrahydrofuran. This allowed the reflux temperature to be about 85°C. 5. Keeping monomer concentration high in the arm-forming step by starting the polymerization with half of the monomer in the reactor. This forced the polymerization past the trimer stage, where termination is fastest. 6. Starting the reaction at room temperature so the exotherm could be dissipated by the heat capacity of the system. Two lots of trimethylsiloxyethyl methacrylate used to introduce hydroxyl groups into the product (after unblocking) gave different rates of polymerization, with one lot reaching the core-forming step in about half the time of the other. The monomer lot with the higher reactivity also led to higher levels of free arm. Stars made at high (2.0%) catalyst levels were quite unstable to molecular weight and viscosity increase. Mechanistic studies show that the increase is probably because of star/ star free-radical methacrylate polymerization involving pendant residual methacrylate unsaturation from the core-forming step. Stars made under the recommended conditions using 0.2% catalyst and the above process steps are probably stable enough for commercial use.
A Method to Resolve the Properties of Individual Phases in Carbon-Black-Loaded Elastomer Blends
Authors: Bauer R. F. , Crossland A. H.
Published: February 2011

Properties of the individual phases in a 70/30 carbon-black-loaded BR/NR blend could be successfully resolved using large deformation stress-strain modelling. Since the dispersed NR phase of the example had a lower modulus than the continuous BR phase, the interaction between the blend phases could be modelled by a simple parallel coupling arrangement. The stress behavior of each individual carbon-black-loaded polymer phase was then determined with respect to strain using a specially derived stress-strain relationship. The blend components also have to be characterized with respect to state-of-cure by empirically establishing how the parameters in the stress-strain relationship vary with respect to cure. The properties of the phases in the blend are then determined by finding the combination of component parameters which precisely reproduce the stress-strain behavior of the blend. In the demonstration example of this paper, there was evidence of a significant amount of curative migration between phases during the vulcanization process.
Recent Advances in Thermoplastic Elastomer Synthesis
Authors: Quirk Roderic P. , Kim Jungahn
Published: February 2011

A variety of living polymerization systems are now available for the controlled synthesis of block copolymers. Although living anionic polymerization remains as the method of choice for the most precise structural control, living polymerizations proceeding via other mechanistic types provide extremely useful extensions of this methodology to a wider variety of monomers.
Reflections on the Past and Future of Polyether Elastomers and on Redox Emulsion Polymerization
Authors: Vandenberg E. J.
Published: February 2011

I am greatly honored to have been selected to receive the prestigious Charles Goodyear Medal of the Rubber Division of the American Chemical Society. My work in the rubber field falls into two general areas: (1) early discoveries on the redox emulsion polymerization of styrene-butadiene rubber (SBR) and (2) polyether elastomers. I am perhaps best known for my work on polyether elastomers since I discovered, patented, and helped develop several families of polyether elastomers which were commercialized and are still important speciality elastomers. Most of my talk will be in that area. However, my SBR studies included my first important polymer-science discovery and preceded those who independently discovered the same systems and who were able to develop them commercially to the considerable advantage of our largest volume synthetic rubber, SBR. After briefly reviewing these past areas, I will give you my reflections on what important future developments for the rubber field could arise in the polyether area.
Synthesis of a Model Triblock for Novel Thermoplastic Elastomers
Authors: Verma A. , Nielsen A. , Mcgrath J. E. , Riffle J. S.
Published: February 2011

Thus far, we have been successful in preparing novel diblock and triblock copolymers comprised of poly(methyl methacrylate) and poly(butyl vinyl ether). Future work will focus on studying the morphology of both the diblock and triblock copolymers. Moreover, we are also interested in synthesizing triblocks with long poly(butyl vinyl ether) segments and short PMMA segments, since these polymers have the potential for exhibiting good elastomeric properties.
Laser Mass Spectral Investigations of Rubber Compound Surface Species
Authors: Waddell Walter H. , Benzing Kimberly A. , Evans Larry R. , Mowdood Syed K. , Weil David A. , McMahon John M. , Cody Robert H. , Kinsinger James A.
Published: February 2011

Laser desorption mass spectrometry has proven a uniquely useful technique for the direct characterization of rubber-compound surface species. Mass spectra were obtained for intact molecular ions (M+) of organic chemical rubber additives such as the aromatic processing oil, and the aromatic antiozonant and antioxidants incorporated to protect the rubber. Molecular-weight information from the molecular ions and structural information from the fragmentation ions could be obtained without interference from the fragmentation peaks of the rubber backbone. Rubber compounding ingredients were also characterized by LDMS techniques. Differences in the structure of two carbon blacks were apparent, based upon the relative intensities of the various peaks present such as the significantly higher m/z 26 peak thought to be due to CN− compared to the m/z 24 peak thought to be due to C2−, and the peaks resulting from the presence of hydrogen atom(s) on the carbon clusters for the high NSA and DBPA black. Laser and thermal desorption mass spectral techniques provided complementary structural information, and when coupled with current analytical methods to characterize rubber compounds, can provide the necessary information to positively identify various organic species present on the surfaces of vulcanized rubber.
Effect of Aspect Ratio on Tire Rolling Resistance
Authors: Pillai P. S. , Fielding-Russell G. S.
Published: February 2011

A simple equation has been developed for predicting changes in tire rolling resistance of similarly constructed tires when tire aspect ratio is varied. The equation is expressed in terms of tire parameters listed on the tire sidewall. The usefulness of the equation has been demonstrated by comparing predicted rolling resistance changes with actual changes using available data from a number of radial passenger tires.
Shear and Biaxial Extension Measurements of Reinforcement from in-situ Precipitated Silica
Authors: Wang Shuhong , Xu Ping , Mark James E.
Published: February 2011

Elastomeric networks were prepared by tetrafunctionally end-linking hydroxyl-terminated polydimethylsiloxane (PDMS) chains and were then filled by the in-situ precipitation of silica. The resulting networks were investigated in shear and biaxial extension. The method employed to produce large shears was to stretch a short, wide strip between two clamps. The deformation produced in this way is pure shear; simple shear was calculated directly from the pure-shear data. Biaxial extension measurements were carried out by inflation of circular sheets of the networks. Compared to the unfilled networks, the silica-filled samples showed large reinforcing effects. Specifically, their values of the modulus, ultimate strength, and rupture energy increase significantly. The results thus indicate that the PDMS networks filled by the in-situ precipitation of silica have good mechanical properties, not only in uniaxial elongation, but in shear and biaxial extension as well.
Morphology of Elastomeric Alloys
Authors: Abdou-Sabet Sabet , Patel Raman P.
Published: February 2011

The field of thermoplastic elastomers has shown an explosive growth with the successful commercialization of elastomeric alloys (EAs) in 1981, based on the original work of Coran, Das, and Patel on dynamic vulcanization and the discovery of preferred cure system by Abdou-Sabet and Fath. These discoveries have led to the development of commercial products having true elastomeric properties while maintaining excellent thermoplastic processing. The success of EAs in the marketplace has led to the introduction of new products by Monsanto and others at a rate of 60 products per year in the last half of the eighties. Elastomeric alloys have been characterized as compositions containing rubber particulate domains approximately 1–2 µm in diameter in a matrix of thermoplastic resin. Such dispersed phase morphology has not been widely accepted, especially when it came to explaining the true elastomeric properties of the soft elastomeric products, i.e. 64 and 55 Shore A hardness products. Interaction among the rubber particles leading to a network of vulcanized elastomer phase that gave the appearance of two continuous networks has been proposed. In this paper, the morphology of EPDM/polypropylene elastomeric alloys is examined with some detail, and evidence leading to dispersed phase morphology is provided. There are several variables to such an investigation which can be grouped under the following headings: 1. Molecular weight of EPDM and polypropylene (PP). 2. Ratio of EPDM to PP. 3. Crosslinked or uncrosslinked blend. 4. Degree of crosslinking. 5. Type of crosslinks. 6. Typical and commercial products. It is not the subject of this paper to review the morphology of different binary polymer blends, which have been extensively covered in the literature. It can be concluded that a variety of morphologies can be obtained, however, depending on the mixing conditions, polymer ratios, relative surface energies of the polymer pair, and viscosities and molecular weights of the two polymers. In this study, the mixing conditions were kept similar as much as possible to eliminate the possibility of morphological changes as a function of the applied mixing intensity as influenced by shear rate, mixing time, and temperature.
The Ozonation of N,N′-Di-n-Octyl-p-Phenylenediamine and N,N′-Di-(1,1-Dimethylethyl)-p-Phenylenediamine
Authors: Lattimer R. P. , Layer R. W. , Hooser E. R. , Rhee C. K.
Published: February 2011

Ozone attack on rubber compounds causes characteristic cracking perpendicular to the direction of applied stress. This degradation is caused by reaction of ozone with the double bonds in the rubber molecules. This causes chain scission and the formation of various decomposition products. The general subject of protection of rubber against ozone attack has been reviewed by a number of authors. In order to control the effects of rubber ozonation, either paraffin waxes or chemical antiozonants are added to unsaturated rubbers. The most effective antiozonants are N,N′-disubstituted-p-phenylenediamines (PPDAs), in which at least one of the side groups is alkyl (preferably sec-alkyl). Several theories have appeared in the literature regarding the mechanism of antiozonant protection. The “scavenger” model states that the antiozonant blooms to the surface and preferentially reacts with ozone so that the rubber is not attacked until the antiozonant is exhausted. The “protective film” theory is similar, except that the ozone-antiozonant reaction products form a film on the rubber surface that prevents (physically and perhaps chemically as well) ozone attack on the rubber. A third “relinking” theory states that the antiozonant prevents scission of the ozonized rubber or else recombines severed double bonds. A final theory states that the antiozonant reacts with the ozonized rubber or Criegee zwitterion (carbonyl oxide) to give a low-molecular-weight, inert, “self-healing” film on the rubber surface. Currently, the most accepted mechanism of antiozonant action is a combination of the scavenger and protective film theories.
Bulging of Rubber through Apertures
Authors: Gent A. N. , Kim W.
Published: February 2011

1. When rubber bulges through an aperture, the bulge height varies linearly with applied pressure. It also varies linearly with radius or width of the aperture when the dimensions of the rubber block are much larger than the aperture, in good agreement with linear elasticity theory. When the block is not much larger than the radius or width of the aperture, a simple empirical factor provides a satisfactory correction. 2. FEM results were in good agreement with experiment in all cases and confirmed the empirical correction for relatively large apertures. 3. Bulge profiles were calculated to be elliptical in all cases. 4. Results for an elastic solid are wholly consistent with Roscoe's results for a viscous liquid. 5. Changing slip conditions at the interface had a surprisingly small effect. The exact theory, Equations (5) and (7), is based upon a nonslip condition. When a fully lubricated condition was employed instead, so that free sliding was allowed at the interface, the maximum bulge heights predicted by FEM were only about 5% higher than before for a circular aperture and about 12% higher for a slit. Experimental observations of bulge heights with dry and lubricated interfaces were in good agreement with these predictions. 6. Bulge heights through small apertures provide a simple means of measuring pressure at contact surfaces.
Morphology of Carbon-Black Aggregates: Fractal Versus Euclidean Geometry
Authors: Herd Charles R. , McDonald Gerard C. , Hess William M.
Published: February 2011

A study has been made comparing the utility of fractal and Euclidean geometry in the characterization of carbon-black aggregates. The fractal models used were the perimeter-area relationship, P∼ADp/2, and the mass fractal, M∼RDm. Values of the perimeter fractal, Dp, and the mass fractal, Dm, were determined for nineteen different grades of carbon black from a sampling of 1000 aggregates per grade. The perimeter (P), area (A), mass (M), and size (R) of the aggregates were all measured by on-line transmission-electron-microscopy/automated-image-analysis (TEM/AIA) which enabled rapid sampling. Values of Dp and Dm ranged from 1.05 to 1.23 and 2.85 to 2.47 respectively and were shown to correlate with carbon-black colloidal properties such as dibutyl-phthalate absorption (DBPA) and Euclidean size and shape parameters from TEM/AIA. These parameters were also used to classify aggregates into different shape categories using discrimination analysis techniques. Both perimeter and mass fractals were nearly constant within each shape category. Four carbon blacks of similar particle size and varied DBPA range were also used to show the effects on Dp and Dm upon high-shear mixing of the carbon-black aggregates into rubber and CAB composites.
Fractal Dimension of Carbon-Black Particles
Authors: Zerda T. Waldek , Yang Henry , Gerspacher Michel
Published: February 2011

Fractal dimension of carbon-black particles is determined using adsorption technique. Gases of various surface areas are adsorbed on carbon-black samples of particle sizes varying from 20 nm to 100 nm, and it is shown that surface fractal dimension of the particles is about 2,2 and does not depend on the grade of carbon black.
A Viscohyperelastic Maxwell Model for Rubber Viscoelasticity
Authors: Johnson A. R. , Quigley C. J.
Published: February 2011

A new viscoelaslic model for rubber is presented. It is similar in a Maxwell internal solid model in which all the solids are hyperelastic. A key feature of this model is its ability to accurately predict step-strain relaxation test data for very large strains. A method to obtain the constitutive models for the solids is presented for the three legged version and is used with existing data in the literature to compute variable-rate uniaxial pull tests. The finite-element implementation of this theory is given. Computations are made for a uniaxial constant-strain-rate test using a nearly incompressible axisymmetric version of the finite-element method.
New Elastomers by Reactive Processing. Part II. Dynamic Vulcanization of Blends by Trans-Esterification
Authors: Coran A. Y. , Lee S.
Published: February 2011

The dynamic vulcanization of a rubbery acrylate copolymer (ACR) (the dispersed phase) during its mixing with NBR (the continuous phase) can produce a millable specialty elastomer alloy. The ACR polymer can be crosslinked even without having special molecular sites for vulcanization such as those of the conventional acrylate rubbers (ACM). This is possible because, under the conditions for dynamic vulcanization, the acrylate-derived ester groups themselves can be made to act as sites for vulcanization by using tin-catalyzed ester-interchange chemistry. The millable dynamic vulcanizate containing the crosslinked dispersed phase can be later mixed with curatives for the continuous phase, fillers, antidegradants, etc. and then be vulcanized (e.g., in a heated mold). Since the ACR can be completely vulcanized during the dynamic vulcanization stage of the mixing process, the usual postcuring associated with acrylate rubber (ACM) technology is not necessary. Excellent performance characteristics can be produced by using this technology.
Finite-Element Analysis of Laminated Rubber Bearing Used in Base-Isolation System
Authors: Takayama Mineo , Tada Hideyuki , Tanaka Ryuichi
Published: February 2011

A realistic mechanical model was proposed for the laminated rubber bearing, one of the most important structural members in the base-isolation system. The model was analyzed by means of the finite-element method (FEM), up to the range of large deformation under high compressive load. The physical characteristics of the rubber material was modeled using a strain-energy-density function based on the biaxial elongation tests. The load-deformation relationship calculated by FEM using such strain-energy-density function agreed well with experimental results. Based on the simulated stress and strain distributions in the laminated rubber bearing, a mechanism of supporting the vertical load during horizontal deformation was proposed.
Structure and Density of Crosslinks in Natural-Rubber Vulcanizates. A Combined Analysis by NMR Spectroscopy, Mechanical Measurements, and Rubber-Elastic Theory
Authors: Gronski Wolfram , Hoffmann Uwe , Simon Gerald , Wutzler Andre , Straube Ekkehard
Published: February 2011

13C-NMR MAS solid-state spectroscopy and 1H-NMR relaxation measurements have been applied for quantitative determination of crosslink density in sulfur-accelerated NR vulcanizates. It is shown that the 13C-NMR method is able to distinguish between monosulfidic crosslinks and polysulfldic structures; therefore a quantitative determination of chemical crosslinks was possible. An analysis of 13-NMR transversal relaxation measurements provided the network densities which were in good agreement with the results of the 13C-NMR measurements. Comparing stress-strain data with the spectroscopically determined crosslink density of the NR vulcanizates and calculated crosslink densities of peroxide-cured vulcanizates, it is shown that the same relation between low-strain modulus and crosslink density is valid independent of the structure of the vulcanizates. The chemical crosslink density determined by a theoretical approach based on the tube concept was in approximate agreement with the NMR results.
Abrasion of Rubber and Its Relation to Tire Wear
Authors: Grosch K. A.
Published: February 2011

Sliding abrasion experiments reveal that the abrasion loss has to be expressed as a power function of the dissipated energy. Both the abrasion loss per unit energy dissipation and the power index depend on the compound and on the type of surface on which the experiment is being carried out. Hence the relative rating of a compound depends on pressure and on surface roughness. This nonlinear dependence on energy dissipation leads also to a rating dependence of slip of the wear of slipping wheels or the wear of tires. If the abrasion energy function for different compounds can be determined, then the wear ranking for different tires should be predictable using the slipping wheel theory. Experiments with tires running under controlled slip conditions show that this is not the case. Predictions differ even in ranking of compounds. Dissipation processes generate heat, so that temperature conditions in the contact area and their influence on the abrasion loss have to be considered in addition to mechanical rupture and fatigue. Laboratory experiments using slipping model wheels are being discussed which use testing conditions designed to generate different temperatures in the contact area. Compound rankings and ranking reversals are obtained which are in agreement with tire wear experiments under controlled slip conditions.
Quantitative Estimation of Filler Distribution in Immiscible Rubber Blends by Mechanical Damping Studies
Authors: Maiti Sudarsan , De S. K. , Bhowmick Anil K.
Published: February 2011

The peak value of tan δ at the glass-transition temperature (Tg) in the plot of tan δ versus temperature is lowered on addition of filler to a rubber. This relative lowering of tan δ at Tg can be used to estimate the filler distribution in an immiscible rubber blend. In the present investigation, distribution of silica filler and carbon black was studied in blends of natural rubber (NR) and epoxidized natural rubber (ENR). It was observed that silica migrated preferentially to the ENR phase. The magnitude of the distribution depends on filler loading and the epoxy content of ENR. The amount of carbon black migrated to the NR phase is higher than that of silica at a similar loading in blends of NR and ENR.
Filler—Elastomer Interactions. Part IV. The Effect of the Surface Energies of Fillers on Elastomer Reinforcement
Authors: Wolff Siegfried , Wang Meng-Jiao
Published: February 2011

Carbon black N110 and a precipitated silica, which have comparable surface area and structure, were selected as model fillers to study the effect of filler surface energies on rubber reinforcement. In comparison with carbon black, the surface energies of silica are characterized by a lower dispersive component, γsd, and higher specific component, γssp. It was found that the high γssp of silica leads to strong interaggregate interaction, resulting in higher viscosity of the compounds, higher αƒ, and higher moduli of the vulcanizates at small strain. The higher γsd of carbon black, in contrast, causes strong filler—polymer interaction, which is reflected in a higher bound-rubber content of the compounds and higher moduli of the vulcanizates at high elongation.
Sulfur Vulcanization of Simple Model Olefins, Part I: Characterization of Vulcanization Products of 2,3-Dimethyl-2-Butene
Authors: Versloot P. , Haasnoot J. G. , Reedijk J. , van Duin M. , Duynstee E. F. J. , Put J.
Published: February 2011

To study the mechanism of the sulfur vulcanization of rubber, 2,3-dimethyl-2-butene (C6H12) was used as a simple, low-molecular-weight model alkene. Only equivalent allylic positions are present in this alkene. Treating C6H12 with a mixture of ZnO, S8, and the accelerator tetramethylthiuramdisulfide at 140°C yields a mixture of addition products (C6H11—Sn—C6H11). RP-HPLC in combination with MS and 1H-NMR shows that the products differ only in the length of the sulfur bridge. Small quantities of isomerized products have been found, in which a 1,3-shift of the double bond has occurred.
The Effect of Pressure on the Ultimate Properties of Elastomers
Authors: Pai P. C-H. , Meier D. J.
Published: February 2011

Many studies have been made on the effect of pressure on the mechanical properties of elastomers, but these studies have invariably been limited to small-strain behavior because of equipment limitations. This small-strain limitation has now been removed with the construction of a novel high-pressure chamber which allows large tensile deformations to be applied to samples at pressure up to 300 MPa and temperatures from 0°C to 200°C. The effect of pressure on the ultimate tensile properties of nitrile, butyl, EPDM, Viton®, silicone, and polyisoprene elastomers has been determined. The tensile strengths and moduli all increase with pressure, but not in a monotonic fashion. In several cases, the tensile strengths increase rapidly with increase in pressure up to about 60 MPa, but then they remain almost constant with further increases in pressure. The ultimate extensions show a more complex behavior. Although the ultimate extensions typically increase with pressure, several samples, e.g., nitrile, EPDM, butyl and Viton, show maxima in ultimate extensions vs. pressure. Other than butyl, these samples also show yielding behavior at large extensions. This is attributed to glass-transition effects for nitrile and Viton, and to pressure-induced crystallization effects for EPDM.
Vulcanization Chemistry. Sulfur, Nt-Butyl-2-Benzothiazole Sulfenamide Formulations Studied by High Performance Liquid Chromatography
Authors: Sullivan A. B. , Hann Cynthia J. , Kuhls George H.
Published: February 2011

The paper reports on the sulfur vulcanization chemistry of cis-polyisoprene formulations accelerated with N-t-butyl-2-benzothiazole sulfenamide. High Performance Liquid Chromatography (HPLC) is utilized to examine the kinetics of accelerator—sulfur disappearance and the formation—disappearance profiles of extra-network cure intermediates across the vulcanization process. Cure profile measurements are reported on three formulations covering a wide range of sulfur—accelerator ratios. Also unique aspects of the analytical methodology are highlighted. The observed cure-intermediate concentration profiles reinforce earlier theories about the chemical details of sulfurization and subsequent crosslinking. On all formulations, benzothiazole polysulfides (S1−S4) reach a maximum concentration at the scorch midpoint coincident with slope changes in reactant and product profiles. Although pendant-accelerator crosslink precursors are not measured directly, their presence is implied from material balance calculations. Also, the formation of a small amount of benzothiazole early in the scorch period is a new observation in sulfenamide acceleration. It suggests that accelerator hydrolysis is a competitive side reaction early in the vulcanization process.
The Elasticity of Rubber
Authors: Rivlin R. S.
Published: February 2011

The experiments of Rivlin and Saunders and Gent and Rivlin are consistent with W having the form (33) in which C is a constant and f is a function of I2−3 only, which decreases monotonically as I2−3 increases. With this interpretation of the experiments, the term f (I2−3) represents the departure from the predictions of the kinetic theory. This conclusion is reinforced by the finding of Gent and Rivlin that W1 exhibits no hysteresis, while all of the hysteresis (i.e., departure from ideal reversibility) exhibited by the rubber resides in W2 (i.e., in the term f (I2−3)). This suggests that the model for a vulcanizate adopted in the kinetic theory must be modified by the introduction in the undeformed rubber network of crosslinks which are broken when the rubber is deformed and are re-formed, nearly reversibly, when the rubber returns to its undeformed configuration. However, so far no satisfactory mathematical development of this idea has been carried out; the construction of a convincing theory which accounts for the departure of W from the neo-Hookean form remains an unresolved problem.
Development of Internal-Mixer Technology for the Rubber Industry
Authors: White James L.
Published: February 2011

The early rubber industry was largely based on mixing with two-roll mills. The coming of the pneumatic-tire industry associated with the rise in popularity of the automobile brought increasing production and large quantities of fine particles and poisonous vulcanization accelerators. This made necessary the introduction of internal mixers into the rubber industry by the second decade of the 20th century. This paper treats the development of internal mixer technology from its origins in the 19th century to the late 1980's, largely through critically following the patent literature. There seems to be no other critical review of the development of internal mixer technology, and this manuscript is unique. Briefly, the technology development we will describe is as follows: There were two conflicting design approaches, one based upon a single-rotor masticator devised by Thomas Hancock in the early 19th century and a second based upon two nonintermeshing counterrotating rotors which were championed by Paul Pfleiderer later in that century and manufactured by his firm, Werner and Pfleiderer. As late as the mid 1920's, machines based on both the single rotor and two nonintermeshing rotor designs competed with each other for the internal-mixer market. The insight, perseverance, intensity, and dedication of Fernley H. Banbury and the Birmingham Iron Foundry (later merged into Farrel-Birmingham) brought about the design which proved to be the paradigm of the industry. Innovation, however, continued in internal-mixer technology. The most striking new development of the post-Banbury period was the invention and application of intermeshing counter-rotating rotor mixers in 1934 by Rupert Cooke of Francis Shaw and Company. Werner and Pfleiderer developed and worked with many internal-mixer designs and in time began to manufacture both nonintermeshing- and intermeshing-rotor machines. In the 1950's and 1960's, Kobe Steel and Pomini began to manufacture internal mixers as Farrel-Birmingham licensees. This period also saw developments of nonintermeshing-rotor internal mixers. The basic Banbury design maintained its position and its manufacturer, Farrel-Birmingham (later Farrel), devised improvements of it. Innovations in the design were also made from the late 1970's by Kobe Steel, now operating independently. Pomini also began operating independently, manufacturing not only nonintermeshing machines but a unique intermeshing-rotor machine with variable clearance between the rotors. In recent years, we have seen the development of increasingly improved control systems for the internal mixer.
Structural Analysis of Conveyor Belts. Part I. Analytical Approach
Authors: Harandi J. N. , Kavousian A. , Parvini M. , Soufian M.
Published: February 2011

Closed form equations for calculating forces in plies and shear stresses in interplies of conveyor belts are derived. Eigenvalues for 2 to 6 ply belts are calculated. A three-ply conveyor belt is completely analyzed and it is found that at a rubber interply thickness equal to that of the fabric, the interply shear stress would be minimum.
Foaming of Vulcanized PP/EPDM Blends Using Chemical Blowing Agents
Authors: Dutta A. , Cakmak M.
Published: February 2011

Using two different chemical blowing agents, foaming behavior of partially vulcanized PP/EPDM blends with high EPDM ratio has been studied. The objective was to induce foaming within the EPDM phase prior to complete curing. The results suggest that with proper choice of blowing agent and by optimum balance of curative loading, foams with densities as low as 0.55 g/cm3 could be obtained. This corresponds to nearly 90 percent density reduction which is significantly greater than the 15 to 20% afforded by similar fully-vulcanized dynamically cured blends reported previously. The degree of cure in the rubber phase was determined to play a key role in determining the overall foamability. In particular, the foamability of the blend was found to decrease linearly with increase in the gel content. In addition, the compounding technique also plays a major role in controlling foamability of these blends. Attempts at extrusion foaming of these blends, however, were successful only for blends with a rather low degree of cure.
Different Curing Systems for Ethylene-Propylene Elastomers
Authors: Hernández Luis González , Díaz Andrés Rodríguez , de Benito González Juan Luis
Published: February 2011

The scope of this paper is to review peroxide curing of ethylene-propylene elastomers, where apart from crosslinking, other reactions occur, such as chain scission, which account for the drop in physical properties. The results are compared with an alternative crosslinking system which is being assessed in our laboratory. With the new curing agent the chain-scission reaction is not present and the physical properties of the vulcanizates are improved. The effects of the different crosslinking systems on the reaction transitions are studied with the aid of dynamic mechanical analysis.
The Role of Functional Polymers in Ground Rubber Tire-Polyethylene Composite
Authors: Rajalingam P. , Baker W. E.
Published: February 2011

The impact energies of different polyethylene-ground rubber tire (GRT) composites were investigated. All the thermoplastic composites were prepared on a Haake Buchler batch mixer and injection molded test specimens were tested on Rheometrics drop weight instrumented impact tester. Addition of small amounts of functional polymers increases the impact energy of the polyethylene-GRT composite as much as 60%. The percent improvement in the impact energy for linear low density polyethylene (LLDPE) and the composites prepared from them is greater than for the corresponding high density polyethylene (HDPE) composites. Precoating of GRT particles with ethylene-acrylic acid (EAA) copolymers improves the impact energy of the composite, whereas precoating with the other functional polymers does not. An attempt has been made to identify the role of the functional polymers as to whether they act as toughening agents for the polyethylene matrix or coupling agent at the polyethylene-GRT interface. The results show the increase in impact energy resulting from the addition of styrene block copolymers is due to toughening of the polyethylene matrix while the reactive ethylene copolymers increase the impact energy by a coupling action with GRT.
Influence of Composition and Processing History on the Cellular Morphology of the Foamed Olefinic Thermoplastic Elastomers
Authors: Dutta A. , Cakmak M.
Published: February 2011

Foam extrusion of a series of dynamically vulcanized polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) blends (commercially available Santoprene) by using chemical blowing agents have been studied. Results suggest that foaming occurs only within the thermoplastic phase and for each composition there exists a limiting density which controls the maximum volume expansion. This limiting density is controlled only by the composition and is independent of the blowing agent concentration, extrusion conditions, and the geometry. For the softest and the hardest blends, maximum volume expansion was found to be about 20 and 100%, respectively. Considerable differences in cell structure were also observed with change in the blend composition. As the rubber content increases, bubbles change their shapes from spherical to highly elongated channels where long axes are primarily along the extrusion direction. When the shapes of the bubbles are viewed by cutting the specimen, the bubbles were found to become highly irregular as the rubber content was increased. The fractal dimension of the perimeter profiles revealed that increases in rubber content give increases in the characteristic fractal dimension. Additionally, wide angle x-ray pole figure analysis, which gives an average orientation behavior of the material, indicates that low levels of preferential crystalline chain orientation develop in the extradates. This preferential orientation was found to vary from skin to core.
Chain Ends and the Mullins Effect in Rubber
Authors: Santangelo P. G. , Roland C. M.
Published: February 2011

It has been suggested that “Mullins softening”, which is the anomalously low stress found in crosslinked rubbers that have been subjected to a reversing deformation history, might be caused by retraction of the chain ends along their primitive paths. Using natural rubber networks made from precursors of varying molecular weight, and an end-linked polytetrahydrofuran rubber, the fraction of chain ends was varied. From stress-strain relationships measured on these rubbers, it is concluded that Mullins softening is unrelated to the presence of chain ends, or to polydispersity in the lengths of network strands.
The Dispersion of Carbon Black in Rubber Part I. Rapid Method for Assessing Quality of Dispersion
Authors: Coran A. Y. , Donnet J-B.
Published: February 2011

Carbon black is the most important reinforcing filler for rubbers. The incorporation of carbon black into rubber vulcanizates generally gives improved strength, extensibility, fatigue resistance, abrasion resistance, etc. In order to exert its beneficial influence on the properties of rubber vulcanizates, the carbon black must be sufficiently dispersed therein. Indeed, poor dispersion can, in itself, give rise to detrimental effects (e.g. reduced product life, poor performance in service, poor product appearance, poor processing characteristics, poor product uniformity, raw-material waste, high finished-product rejection rates, and excessive energy usage). These inadequacies are generally the result of the presence of rather large, undispersed agglomerates. The present work was initiated in order to develop an improved understanding of the carbon-black dispersion process including the understanding of factors which affect the kinetics of dispersion. The work described here is focused on methodology for reproducibly mixing carbon black with rubber in the laboratory, and reproducibility, but rapidly and easily estimating the degree of dispersion of the carbon black into the rubber as a function of mixing time. Procedures were developed for introducing rubber, filler, and other ingredients into a small, laboratory internal mixer and for mixing the batches for various periods of time. Also, an improved, simple-to-use, reproducible method for determining the degree of carbon black dispersion in rubber has been adapted. The extent of dispersion was correlated with various measures of tensile strength and with other performance-related properties.
Studies of in-situ Compatibilized Blend of Silicone and EPDM Rubbers
Authors: Kole Swapan , Santra Rabin , Bhowmick Anil K.
Published: February 2011

The effect of three different compatibilizers — ethylene methylacrylate copolymer (EMA), ethylene vinyl acetate copolymer (EVA), and silane grafted polyethylene (VMX) — on the physical properties, ageing behavior, thermal stability, morphology, and dynamic mechanical properties of a 50/50 blend of silicone/EPDM has been studied. Improvement in physical properties is in line with the level of technological compatibilization. Strength of adhesion for silicone-EPDM joints is significantly enhanced by the compatibilizers due to the increase in surface energy of silicone and reaction of the rubbers with the compatibilizers. Morphology study shows smaller domain size for the compatibilized blend. Dynamic mechanical analysis also reflects strong interaction of the compatibilizer with the blend components. Ageing properties are improved with the addition of the compatibilizers. Thermogravimetric analysis indicates an increase in activation energy of degradation and hence marked improvement in the thermal stability of the blends containing compatibilizer.
Morphological Investigations on Carbon-Black Particles by Atomic Force Microscopy
Authors: Niedermeier W. , Stierstorfer J. , Kreitmeier S. , Metz O. , Göritz D.
Published: February 2011

The atomic force microscope (AFM) can profile surfaces similar to the scanning tunneling microscope (STM) at resolutions down to the atomic level. To investigate carbon-black particles and subsequently styrene-butadiene-rubber, filled with carbon black, a STM was modified to run as an AFM. An optical detection system is used to measure the deflection of the cantilever. Atomic resolution was achieved by forces in the order of 5·10−8 N on mica with the AFM. Structural investigations of carbon-black particles of different dimensions with the AFM agree with the data of the manufacturer. The model of the microstructure of such particles, built up of 1–3 nm large, tilted domains of graphite structures, could be confirmed. This surface roughness is probably an important parameter for the strengthening mechanism of carbon black in elastomers.