Showing papers in "Rubber Chemistry and Technology in 1992"
TL;DR: In this article, carbon black N110 and precipitated silica were used as model fillers to study the effect of filler surface energies on rubber reinfilling performance, and they were selected as fillers with comparable surface area and structure.
Abstract: 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 reinf...
238 citations
TL;DR: In this paper, the utility of fractal and Euclidean geometry in the characterization of carbon-black aggregates has been compared for nineteen different grades of carbon black from a sampling of 1000 aggregates per grade.
Abstract: 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...
92 citations
TL;DR: In this article, the same relation between low-strain modulus and crosslink density is valid independent of the structure of the vulcanizates, and a theoretical approach based on the tube concept was in approximate agreement with the NMR results.
Abstract: 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.
82 citations
TL;DR: The impact energies of different polyethylene-ground rubber tire (GRT) composites were investigated in this article, where the role of functional polymers as toughening agents was identified.
Abstract: 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 s...
80 citations
TL;DR: In this article, a dendrimer carbosilane containing 32 Si-Cl bonds in the perimeter has been prepared and has been used as a coupling agent to prepare 32-arm star polybutadiene.
Abstract: A dendrimer carbosilane containing 32 Si—Cl bonds in the perimeter has been prepared and has been used as a coupling agent to prepare 32-arm star polybutadienes. The dilute-solution properties 〈RG2〉, A2, [η], and D0 have been measured in one good solvent and in one ¸ -solvent. The dimensions of the 32-arm star polymers are compared with those of linear polymers at constant molecular weight. It is shown that the 32-arm star polybutadiene has the characteristic properties of a hard-sphere molecule in dilute solution. The equivalent hard-sphere radii calculated from A2, D0 and [η] are identical and 1.29 times larger than the root mean-square radius of gyration. The Daoud—Cotton scaling model for stars is also tested.
78 citations
TL;DR: In this paper, the authors studied the distribution of silica filler and carbon black in a mixture of natural rubber and epoxidized natural rubber (ENR) and found that carbon black migrated preferentially to the ENR phase.
Abstract: 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.
71 citations
TL;DR: In this article, it was shown that there is no single value of friction coefficient for a particula, and that the coefficient of friction is independent of the diameter of the particula.
Abstract: Vulcanized rubber, as a material, can exhibit extremes in friction level when utilized in all manner of mechanical devices There is no single value of friction coefficient for a particula
59 citations
TL;DR: In this paper, the surface free energies and the energy distribution on the surfaces of precipitated silicas which had been modified with octadecyltrimethoxy silane, 3-thiocyanatopropyltriethoxy (3-THIOCYCLIC) silane and bis(3 trimethoxysilylpropyl)-tetrasulfane, respectively, were investigated by chromatography at infinite dilution and at finite concentration.
Abstract: As shown in previous papers of this series, the main feature of silicas with regard to surface energy, which distinguishes them from carbon blacks, is a low dispersive component, γsd, and a high specific component, γssp, of surface energy. The low γsd, would result in a lack of interaction between filler and hydrocarbon rubbers, while the high γssp would suggest a high degree of agglomeration of the filler particles in the polymer matrix. In this study, the surface free energies and the energy distribution on the surfaces of precipitated silicas which had been modified with octadecyltrimethoxy silane, 3-thiocyanatopropyltriethoxy silane and bis(3-trimethoxysilylpropyl)-tetrasulfane, respectively, were investigated by chromatography at infinite dilution and at finite concentration. A comparison with the initial silica suggests a drastic decrease in surface energy, especially of the specific component, as a result of the modification and a strong dependence of surface energy on the chemical nature ...
57 citations
TL;DR: 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 monotonical....
Abstract: 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 monotonical...
57 citations
TL;DR: In this article, a viscoelaslic model for rubber is presented, which is similar to a Maxwell internal solid model in which all the solids are hyperelastic.
Abstract: 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.
51 citations
TL;DR: For any specific tire use condition, treadwear performance is influenced by three main factor categories: (1), tire construction; (2), tread materials; and (3), environmental and vehicle use conditions.
Abstract: For any specific tire use condition, treadwear performance is influenced by three main factor categories: (1), tire construction; (2), tread materials; and (3), environmental and vehicle use conditions. Tire construction factors are—generic type (bias, belted-bias, radial), tread pattern groove void level, and geometric shape, i.e., aspect ratio. The relative importance of nominal variations in each of these factors for treadwear performance is 100, 46, and 39, respectively. Performance improves for a change from bias to radial; high to low groove void; and high to low aspect ratio. The combined influence of generic type, aspect ratio, and other internal construction features (e.g., belt stiffness) can be described by one parameter, the ratio of the treadband edgewise bending stiffness, KBo and the carcass (spring) stiffness, Kc. Treadlife is a direct linear function of this ratio. Treadwear compound or material performance is a function of the rubber glass-transition temperature (weighted avg. f...
TL;DR: Vulcanizates, to which a curative is added by swelling, can be recured to easily study a variety of aspects of the vulcanization process, such as maturation, reversion, and even how much a...
Abstract: Vulcanizates, to which a curative is added by swelling, can be recured to easily study a variety of aspects of the vulcanization process, such as maturation, reversion, and even how much a...
TL;DR: In this article, a poly(β-hydroxyalkanoate) copolymer containing mostly β-hydroxoctanoate repeating units was produced in a fed batch fermentation process by Pseudomonas oleovorans when grown on sodium octanoate as the sole carbon source.
Abstract: PHO, a poly(β-hydroxyalkanoate) copolymer containing mostly β-hydroxyoctanoate repeating units, was produced in a fed batch fermentation process by Pseudomonas oleovorans when grown on sodium octanoate as the sole carbon source. The polymer from different batches—evaluated with regards to composition, molecular weight distribution, thermal transition temperatures, and decomposition temperature—was found to be highly consistent batch-to-batch. Polymer composition as a function of growth time did not change significantly once the culture reached the stationary growth phase. PHO when crystallized at room temperature from the melt, forms a physically crosslinked network with the crystalline regions acting as the physical crosslinks. The molecular weight between physical crosslinks was determined to be approximately 4000. The stress-strain properties, hardness, and tensile set of PHO were found to be within the range of values defined by a variety of commercially available thermoplastic elastomers wit...
TL;DR: In this article, two common problems and probable solutions in the TG-DTG analysis of unknown elastomer vulcanizates have been discussed, the first problem concerns the difficulty in quantitatively deterministic deterministic analysis.
Abstract: Two common problems and probable solutions in the TG-DTG analysis of unknown elastomer vulcanizates have been discussed. The first problem concerns the difficulty in quantitatively determi...
TL;DR: In this paper, an improved understanding of the carbon-black dispersion process including the understanding of factors which affect the kinetics of dispersion was presented. But the present paper is focused on methodology and is not concerned with the application of carbon black to rubber vulcanization.
Abstract: 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 methodolo...
TL;DR: In this paper, an experimental and analytical investigation of the consequences of removing a high ambient gas pressure environment from a number of elastomers after they had been allowed to equilibrate under high gas pressure is described.
Abstract: This paper describes an experimental and analytical investigation of the consequences of removing a high ambient gas pressure environment from a number of elastomers after they had been allowed to equilibrate under high gas pressure. The elastomers are irreversibly damaged, and the phenomenology of this damage is described. One particular type of damage, the formation of internal symmetrical cracks whose geometry is the same as that of the sample, is examined in detail. The experimental data are interpreted using two models. The first provides a first order, but somewhat artificial, description of the phenomenon observed. A more sophisticated model invokes two separate processes as the origin of the rupture phenomenon. It is argued that ruptures arise as a result of the combined effects of an overall hydrostatic tension and a localized tensile field which is created by the effusion of gas from the polymer. The severity of the latter is shown to be a function of the gas transport properties of the...
TL;DR: Group-transfer polymerization (GTP) as discussed by the authors is a very useful synthetic method for the preparation of acrylic ester polymers and can be used to prepare a wide variety of complex polymer structures.
Abstract: Group-transfer polymerization is a very useful synthetic method for the preparation of acrylic ester polymers. This living polymerization process works well at room temperature and can be used to prepare a wide variety of complex polymer structures. Mechanistic work suggests that GTP is a form of anionic polymerization where propagation occurs via a small concentration of enolate anions which are in equilibrium with dormant silyl ketene acetal chain ends. GTP will find the most use in specialty applications including dispersants, toners, photoresists, and rheology control agents.
TL;DR: In this article, a novel process for the preparation of highly saturated nitrile rubber latex has been developed, which directly converts NBR latex into HNBR latex in one reaction step.
Abstract: A novel process for the preparation of highly saturated nitrile rubber latex has been developed. This process directly converts NBR latex into HNBR latex in one reaction step. The key to the process is the efficient in-situ generation of diimide within the latex by the oxidation of hydrazine hydrate in the presence of a catalyst. At 40–70°C, diimide smoothly and selectively reduces the olefinic bonds while leaving other functionalities unaffected. The process operates at ambient pressures and produces nitrogen and water as by-products. HNBR latex produced by this process has been applied to the manufacture of superior heat-resistant gasketing via the “Beater-Addition” method. This unique new form of HNBR maintains the well known benefits of HNBR (e.g., solvent, heat, and ozone resistance, etc.) while expanding its potential applications into latex-related products.
TL;DR: In this article, it was shown that the abrasion loss has to be expressed as a power function of the dissipated energy and that the relative rating of a compound depends on pressure and on surface roughness.
Abstract: 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 mechani...
TL;DR: In this paper, the mechanism of the sulfur vulcanization of rubber, 2,3-dimethyl-2-butene (C 612 ) was used as a simple, low-molecular-weight model alkene.
Abstract: To study the mechanism of the sulfur vulcanization of rubber, 2,3-dimethyl-2-butene (C 612 ) was used as a simple, low-molecular-weight model alkene. Only equivalent allylic positions are present in this alkene. Treating C 6 H 12 with a mixture of Zn, S 8 , and the accelerator tetramethylthiuramdisulfide at 140°C yields a mixture of addition products (C 6 H 11 -S n -C 6 H 11 ). RP-HPLC in combination with MS and H-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 bonf has occured
TL;DR: In this article, the wear of tank track pads has been studied under different conditions and an HNBR/Zn-methacrylate/peroxide compound gave improved wear rate under all three test conditions.
Abstract: Wear of tank track pads has been studied under different conditions. With T142 pads tested on an M-60 tank, the mode of failure was found to depend on the test conditions. Among eighteen experimental compounds tested, improved wear (vs. the standard compound) under one test condition was generally at the expense of poorer wear under one or both of the other test conditions. However, in agreement with previous results, an HNBR/Zn-methacrylate/peroxide compound gave improved wear rate under all three test conditions. Wear of the T142 pads on a hilly cross-country course and on a combination course was generally by massive chunking. On a paved road course, most compounds wore by pattern abrasion. A few compounds worn on this course formed deep pockets parallel to the surface, resulting in the eventual loss of the large flaps between the pocket and the surface. Pattern abrasion was also found on T156 pads of four different compounds, tested on an M-1 tank on the paved road course. The abrasion patter...
TL;DR: In this article, the fractal dimension of carbon-black particles is determined using adsorption technique using Gases of various surface areas are adsorbed on carbon black samples of particle sizes varying from 20 nm to 100 nm.
Abstract: 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.
TL;DR: In this paper, a series of dynamically vulcanized polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) blends by using chemical blowing agents have been studied.
Abstract: 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...
TL;DR: A wide range of surface modification techniques have been used to modify polymeric surfaces as mentioned in this paper, such as halogenation, addition, etching, and oxidation of polymeric materials.
Abstract: Surface modification as a technology has been employed in various ways for many years, however, the breadth and magnitude of its applications have grown significantly during the last decade. Much of this growth has been facilitated by the development and spread of rapid and reliable surface characterization techniques. And, as would be expected of a maturing field, the bulk of investigations are now turning to applications rather than a pure understanding. Publications in both the scientific literature and patents describe research on a diverse range of polymeric substrates and potential applications using a wide range of modification techniques. Methods include chemical, photochemical, and high-energy physical techniques to modify polymer surfaces. Searches were made of these methods as applied to the surface modification of polymeric materials of particular interest to the rubber industry. Chemical methods include reactions such as halogenation, addition, etching, and oxidation. Photochemical t...
TL;DR: In this paper, a quantitative investigation into the influence of humidity and water content on cure behavior was carried out using a natural-rubber compound with MBS (N-morpholylbenzothiozole-2-sulfenamide) as the principal accelerator.
Abstract: Certain accelerators are susceptible to chemical attack by water. Consequently, the cure behavior of compounds containing these accelerators is likely to be affected by the water content of the compound and the humidity conditions of processing and storage. A quantitative investigation into the influence of humidity and water content on cure behavior was carried out using a natural-rubber compound with MBS (N-morpholylbenzothiozole-2-sulfenamide) as the principal accelerator. Samples of the compound were treated at different humidities, their water contents determined, and their cure curves measured. Scorch time was inversely related to treatment humidity and water content of the compound, whereas cure rate was directly related to humidity and water content. A study of the mechanism by which water affects the cure behavior of the compound revealed that hydrolysis of the accelerator, MBS, would inhibit its scorch-delay action and could produce MBT (2-mercaptobenzothiazole), which would increase th...
TL;DR: In this paper, a realistic mechanical model for the laminated rubber bearing, one of the most important structural members in the base-isolation system, was proposed by means of the finite element method (FEM).
Abstract: 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.
TL;DR: In this paper, the effect of oxidation upon the electrical properties of EPDM rubbers is explained as being due to the presence of polar groups, e.g., carbonyl groups, in between the carbon-black agglomerates which provide shorter distances for the electrons to tunnel through.
Abstract: Oxidative degradation of rubbers, and the development of oxidized layers at the surfaces, results in increased electrical conductivity. This paper shows that for EPDM rubbers heavily oxidized at 200° C, the DC-conductivity increases more than two orders of magnitude, and the percolation threshold for DC conductivity is decreased below 5 phr carbon black. The effect of oxidation upon the electrical properties is explained as being due to the presence of polar groups, e.g., carbonyl groups, in between the carbon-black agglomerates which provide shorter distances for the electrons to tunnel through.
TL;DR: In this article, it has been suggested that 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.
Abstract: 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.
TL;DR: In this article, the isotherms, net heat, and spreading pressures for benzene and cyclohexane adsorption suggest a general trend of increasing surface activity with increases in specific surface area.
Abstract: Carbon blacks ranging from N110 to N990 were characterized by means of inverse gas chromatography at finite concentration. The isotherms, net heat, and spreading pressures for benzene and cyclohexane adsorption suggest a general trend of increasing surface activity with increases in specific surface area. This is in good agreement with surface-energy measurements reported previously. The energy-distribution function of adsorption shows that while the concentrations of low-energy sites are comparable for most of the carbon blacks, differences exist with regard to high-energy sites. These suggest that small-particle-size blacks possess a greater number of high-energy centers. The graphitization of carbon blacks results in a considerable reduction in their adsorption capacity and narrows the energy distribution of their surfaces. One can therefore conclude that high-energy sites play an important role in the determination of the surface energies and reinforcing ability of carbon blacks.