bluuebunny/crossref_metadata_2025 huggingface dataset:
Tensile Behavior of an SBR Vulcanizate Containing a Single Rubber Particle
Authors: Gibala D. , Hamed G. R. , Zhao J.
Published: February 2011

The effect of a single, embedded rubber particle on the tensile strength of an SBR vulcanizate has been determined. For a given size, a particle taken from an ambient grind resulted in higher strength compared to a sample containing a particle prepared by hand-cutting with a blade. In the former case, fracture initiated within the particle while, in the latter, fracture was interfacial between the particle and matrix. For both types of particles, strength decreased with increased particle size.
The Evolution of Morphology in NR/HDPE Blends. Part I. Microscopy for Unvulcanized Blends
Authors: Laokijcharoen Pasaree , Coran A. Y.
Published: February 2011

Phase morphology is an important factor in the determination of properties of polymer blends. In this work, methods for determining phase morphology of unvulcanized natural rubber (NR)/high-density polyethylene (HDPE) blends were investigated. Small, quick-quenched samples were taken from the internal mixer for examination under scanning electron microscopy (SEM). There was almost no interruption of the mixing because the sampling device was designed for preventing the coalescence of dispersed particles. Three specimen-preparation methods for SEM were considered: (i) OsO4 vapor staining, followed by carbon coating; (ii) toluene etching of NR phase at room temperature, followed by coating of the surface with a platinum alloy; (iii) crosslinking of NR phase by S2Cl2 vapor and then etching of HDPE phase by using boiling xylene. Method (i), OsO4 staining of cryogenic microtomed samples, was selected for the work on the kinetics of dispersion during the mixing process. Vast differences in phase morphology were observed among the types of samples: quick quenched, cold pressed, and compression molded. We considered the quick-quenched samples to have the phase morphology, which was the most similar to that of the blend during its mixing.
The Chain End Distributions and Crosslink Characteristics in Black-Filled Rubbers
Authors: Ahagon Asahiro
Published: February 2011

A black-filled rubber compound consists of two phases: the free polymer phase, where no particle exists, and the carbon black agglomerate phase, where highly concentrated particles are bound by a small amount of the polymer—so called bound rubber. The Charlesby—Pinner virtual linear number-average molecular weight Mn1 of the polymer in each phase is determined for black-filled compounds to obtain information about the chain end distribution in the compounds. The nominal crosslink density of the bound rubber is also measured by means of the swelling measurement of the “carbon gel” to characterize the crosslink variation in the vulcanizates. The results indicate that the chain end density is much higher in the agglomerate phase than in the free polymer phase due to enhanced chain scission during mixing. The enhancement of scission is considered due to the free radical crosslinking which imposes restriction to chain slippage in the flow field. This together with the previous findings suggests the features of the phase construction in the filled vulcanizates: tightly crosslinked free polymer phase with fewer chain ends, and loosely crosslinked agglomerate phase with more chain ends but, with rather suppressed chain mobility due to the dense nano-scale particles. The features match well with the energy dissipating and the toughened nature of the filled vulcanizates.
Carbon—Silica Dual Phase Filler: Part III. ESCA and IR Characterization
Authors: Murphy Lawrence J. , Wang Meng-Jiao , Mahmud Khaled
Published: February 2011

A series of carbon—silica dual phase fillers have been analyzed using electron spectroscopy for chemical analysis (ESCA) and infrared spectroscopy (IR). These techniques reveal that the silicon in these materials is consistent with that in silica, and the predominant carbon in the carbon phase is similar to the predominant carbon in carbon black. ESCA and IR experiments demonstrate that the carbon—silica dual phase fillers are comprised of composite aggregates, each containing carbon and silica phases. In these dual phase aggregates the silica phase is intimately distributed with the carbon phase. Quantitative ESCA reveals that these dual phase fillers have excess oxygen over the expected stoichiometric amount for the silica present. This excess oxygen is likely due to oxygen groups on the carbon phase. Analysis of the ESCA oxygen Auger lines in combination with various chemical treatments substantiate the presence of carbon phase oxygen groups on the dual phase fillers. Quantitative ESCA in combination with IR spectra of a dual phase filler after removal of the silica phase, by HF treatment, suggests that the carbon phase of the dual phase filler contains more oxygen groups than its carbon black counterpart.
Preparation of Soluble TiCl3 Catalysts and Their Use for Copolymerization of Ethylene with Propylene
Authors: Makino Kenya , Tsuda Kazuichi , Takaki Mikio
Published: February 2011

The solubilization of TiCl3 catalysts in organic solvents was carried out to enhance the activity for random copolymerization of ethylene with propylene. β-TiCl3 · 1/3AlCl3 was solubilized in halogenated hydrocarbon solvents by using an appropriate ether as donor. α-TiCl3 free from AlCl3 was found to be soluble in the presence of a VCl4 or VOCl3 ligand and a suitable ether. The solubilized TiCl3 catalysts showed high catalytic activities for the copolymerization using trialkylaluminum compounds as a cocatalyst. The copolymers obtained possessed low crystallinities. Also, the copolymers seem to contain a microblock type of sequences and outstandingly high tensile strength and elongation at break compared to copolymers by conventional VCl4 and VOCl3 catalysts.
Deformation Index—Concept for Hysteretic Energy-Loss Process
Authors: Futamura Shingo
Published: February 2011

The concept of deformation index can be effectively used to determine the relevant dynamic viscoelastic property which best correlates with the performance of the rubbery material. The concept also indicates the type of deformation that may govern a complex energy loss process, although, in this study, the underlying physical process was not experimentally identified.
Thermal Crystallization of Polytetrahydrofuran Networks
Authors: Roland C. Michael , Buckley Gary S.
Published: February 2011

The formation of a network in PTHF inhibits the crystallization of chain units in proximity to the crosslinks. From melting-point-depression measurements, it is estimated that the suppression in crystallizability extends to as much as 8 chain units away from a network junction. This estimate is consistent with the degree of crystallinity measured in various crosslinked PTHF rubbers. The equilibrium melting point for linear PTHF was determined to be 361°K. Although this is significantly higher than previously reported values, the present result is congruent with the melting temperatures measured for crosslinked PTHF, and its use leads to satisfactory predictions of their melting-point depression. The distribution in the lengths of network chains exerted a trivial influence on thermal crystallization behavior. Although this distribution must in principle influence crystallization behavior in so far as it governs crystallizable sequence lengths, differences between uni- and bi-modal network architectures were moderate under the present experimental conditions.
Metathesis Polycondensation Chemistry as a Route to Unsaturated Elastomers
Authors: Wagener K. B. , Nel J. G. , Duttweiler R. P. , Hillmyer M. A. , Boncella J. M. , Konzelman J. , Smith D. W. , Puts R. , Willoughby L.
Published: February 2011

Acyclic diene metathesis (ADMET) polymerization offers a new opportunity to generate a wide variety of elastic structures using room temperature reaction conditions. It also offers the opportunity to modify existing elastomer structures through trans-metathesis copolymerization reactions. ADMET depolymerization could have tremendous significance if, in fact, the reaction can be applied to the recovery of commercial vulcanized elastomers. All of these opportunities are presently being investigated in our laboratory.
Adhesion between Hydrogenated Nitrile Elastomers and Fibers Is Improved Using Hydrogenated Acrylonitrile-Butadiene Latex
Authors: Kubo Yoichiro , Mori O. , Ohura K. , Hisaki H.
Published: February 2011

1. The hydrogenated acrylonitrile-butadiene latex (HNBR latex) was developed as a heat-resistant adhesive agent suitable for use between HNBR and fibers. 2. In the case of the adhesion of HNBR to nylon, both the initial adhesion strength and the adhesion strength after heat aging using HNBR latex is higher than those using NBR latex. 3. In the case of the adhesion of HNBR to polyester, polyester undergoes hydrolysis by the amines which originate from the accelerators in the recommended recipes. Two prevention methods against the degradation of polyester by amines were developed. a. From the balance between the adhesion strength and cured properties of HNBR, the combination system with tetraethyl thiuram disulfide (TETD) and dibenzothiazyl disulfide (MBTS) was selected as the vulcanization system for HNBR. b. As the preventive function against the penetration of amines from elastomer to polyester, the double layer adhesion system was developed in which the first treatment is given with the carboxylated vinylpyridine-butadiene-styrene latex and the second treatment is given with the HNBR latex.
The Possibility of Using Grafted Waste Rubber
Authors: Adam G. , Šebenik A. , Osredkar U. , Ranogajec F. , Veksli Z.
Published: February 2011

With the addition of 20 phr of BR granulate grafted with ethyl acrylate by the redox or gamma irradiation method to polyacrylic rubber compound, the properties of the rubber worsened, but remained within the range of properties characteristic for these types of rubber. The stability of rubber against swelling in hot mineral oil was satisfactory even when 30 phr of grafted granulate was added to polyacrylic rubber. It can be concluded that polybutadiene granulate when grafted with ethyl acrylate, gains some properties characteristic for polyacrylic rubber due to the introduction of polar groups into the polymeric chain of the BR rubber. This might also be the reason why polybutadiene granulate grafted with ethyl acrylate could be in no case added to polybutadiene rubber regardless of the grafting method. No attempt was made so far to evaluate the economical aspects of grafting waste rubber and the real possibility of using grafted granulate on a large scale.
Nonlinear Elastic Analysis of the Hardness Test on Rubber-Like Materials
Authors: Chang W. V. , Sun S. C.
Published: February 2011

Both the Ogden-Tschoegl nonlinear elastic constitutive law and a contact algorithm in the general-purpose finite-element program AFEM have been used to examine the use of IRHD values to relate the elastic properties of elastomers. We are aware that large deformations of rubber specimens and complicated interface conditions are involved in this so-called simple test. However, from the finite-element results, we find that the linearly elastic Hertz contact solution is a reasonably accurate model. This can be attributed to several points. First, the hardness test involves mainly compression and shear deformation and the linearly elastic behavior is more closely followed in rubbers for the above two types of deformation. Second, although nonlinear effects become significant in soft rubbers and higher indentation cases, the ASTM D 1415 standard defines larger indentation depth differences for smaller IRHD values. The definition itself compensates for the nonlinear effects. Third, although the interfacial stress field changed due to different frictional conditions, we calculated the IRHD values only from indentation depth difference and total load applied to the steel ball. Both the indentation depth difference and the total load are obtained from far-field conditions and do not change significantly. We should note that using linear elasticity to correlate the elastic moduli and IRHD values is simply a special case in rubber elasticity. We conveniently get rubber's elastic moduli from IRHD values based on linear elasticity, but the complete rubber-like material behavior has to be obtained from more general experiments and described by a nonlinear constitutive law such as the Ogden-Tschoegl model.
Effects of Field Storage on Guayule Rubber Quantity and Quality
Authors: Dierig D. A. , Thompson A. E. , Ray D. T.
Published: February 2011

Irrigation treatments affected the amount of biomass produced, but not the NR percentage of the plant or the quality or quantity. Different guayule genotypes varied in their rate of rubber degradation over storage time. All lines tested in this experiment decreased in Mw by the end of the storage period, but degradation in some did not occur until the fourth week of storage. An increase in Mw of most lines was seen after the first week of storage, indicating that the enzymatic processes are still functioning beyond the first few hours of harvest, and for some lines, beyond the initial sample taken after one week of field storage. Other lines may follow this same pattern of degradation, but it was not detected by the sampling protocol in this study. Guayule lines 11605, 11619 and interspecific hybrid AZ101, when irrigated between 4 to 7 times per year (50 to 90 cm/year), harvested in early spring, and then stored in the field as whole plants for no more than 2 weeks, would yield optimum rubber quality and quantity (per acre) with little or no deterioration. Other lines in this study, 11604, N565, 593, and 11634, cannot be field stored for longer than 1 week without a loss of rubber quality and quantity based on these results. The variation seen in the different lines indicates two important points. First, the amount of time plants remain in the field following harvest is an important determinant of rubber quality and quantity. Secondly, selection for degradation characters should be possible for crop improvement.
Analysis of the Dynamic Stress Relaxometer Test Geometry and Conversion of Relaxing-Torque Data to Frequency-Dependent Viscoelastic Properties
Authors: Harrell E. Ray , Porter John P. , Nakajima N.
Published: February 2011

The test geometry of the DSR has been mathematically modeled to provide an adequate description of the strain (and stress) distribution within a test specimen. The consideration of three separate deformation regions were required. Two of these regions, not considered in previous models, contribute 27% to 59% (depending upon the user-selectable closure height) of the total measured torque exerted on the DSR rotor. The utility of this model has been demonstrated by the agreement between the stress relaxation data obtained by converting the DSR relaxing torque measurements, using the modeled form factor, and data obtained with a uniform-strain-deformation instrument (RMS with cone and plate fixture) for four elastomer samples. Furthermore, the transformation of the converted DSR stress relaxation data to the frequency domain revealed good agreement with the frequency-dependent shear loss and storage moduli and complex viscosity obtained from RMS oscillatory experiments.
Effect of Carbon-Black Loading and Crosslink Density on the Heat Build-Up in Elastomers
Authors: Meinecke Eberhard
Published: February 2011

It has been shown that it is possible to predict the viscoelastic response of elastomers and elastomeric engineering components under both load- and position-control conditions if one assumes: a) that the modulus of the materials increases with the strain amplification factor as given by the Guth and Gold equation, b) that the occluded rubber is taken into account when using this equation, and c) that the energy loss per cycle and unit volume of material is increasing with the square of the strain-amplification factor. These calculations were applied to an assembly where one unfilled section is in series with a filled one. The overall filler loading was kept constant, and it was found that the equations derived show completely different heat-generation rates for load- and position-control conditions. While the losses are the same in both sections and equal to that of the assembly as a whole under position-control conditions, they are quite different under load-control conditions. They increase with both filler loading and values of α and abnormally high local overheating in the unfilled section occurs. These considerations indicate that a uniform mixing quality is important for compounds which will be used in dynamically deformed engineering components. Under position-control conditions, poor filler dispersion will give rise to a decrease in the dynamic modulus and the energy loss per cycle, i.e., variations in the quality of the mix will cause variability of the dynamic properties. Under load-control conditions, the situation is even worse, since the energy dissipation increases with poor mixing, and local overheating of the sections containing less than the average amount of carbon black takes place. The model is obviously too oversimplified for qualitative predictions. But it still gives good qualitative indications regarding the heat-generation rate in structures made from two elastomers having different filler loadings or for imperfectly mixed compounds.
Injection Molding of Rubber Compounds: Experimentation and Simulation
Authors: Deng J. S. , Isayev A. I.
Published: February 2011

Results of experimental and theoretical studies of injection molding of rubber compounds have been reported. Characterizations on the rheological properties and the vulcanization kinetics of rubber compounds were carried out by means of MPT and DSC, respectively. The models were employed to fit these experimental data. An attempt has been made in extending the proposed empirical kinetic model based on DSC data to similar curing data obtained by means of the MDR technique. The heat-transfer effect due to the large sample size used in MDR measurements has been found to have a small effect on the kinetic data. Due to the different principle of state-of-cure measurements in MDR and DSC, the model parameters of curing kinetics have been found to be different in these measurements. A two-dimensional flow simulation of generalized Newtonian fluids based on both finite-difference and finite-element methods has been performed. The pressure development at various positions along the flow path during the filling stage of the molds was obtained experimentally for various injection speeds. The predicted results on pressure development during cavity filling showed qualitative agreement with the experimental data. Possible reasons for the observed discrepancy in pressure traces are: neglect of local extra pressure losses (in the juncture sections), compressibility of rubber compounds, leakage (back-flow) of material during injection, and voids formation in the injection chamber. The study on the vulcanization behavior of rubber compounds during injection molding process has also been done. The proposed empirical kinetic and induction time models were able to satisfactorily predict the cure levels of molded rubber products. At the same time, the results predicted by employing nth order kinetics were found to be unsatisfactory. The contribution of nonisothermal induction time in calculating cure levels of the molded rubber products was found to be significant. The mechanical properties and anisotropy have been investigated for two rubber compounds. It is suggested that there exists a mold temperature at which the properties and cycle times are optimal, and the filler type shows a significant effect on the tensile modulus. The rubber moldings were found to be highly anisotropic in mechanical behaviors. The anisotropy could be reduced significantly at high injection speed due to the faster stress-relaxation process.
Polyolefin Thermoplastic Elastomer Blends
Authors: Kresge E. N.
Published: February 2011

Thermoplastic elastomers based on blends of polyolefins are an important family of engineering materials. Their importance arises from a combination of rubbery properties along with their thermoplastic nature in contrast to thermoset elastomers. The development of polyolefin thermoplastic elastomer blends follows somewhat that of thermoplastic elastomers based on block copolymers such as styrene-butadiene-styrene triblock copolymer and multisegmented polyurethane thermoplastic elastomers which were instrumental in showing the utility of thermoplastic processing methods. Polyoleflns are based on coordination catalysts that do not easily lend themselves to block or multisegmented copolymer synthesis. However, since polyolefins have many important attributes favorable to useful elastomeric systems, there was considerable incentive to produce thermoplastic elastomers based on simple α-olefins by some means. Low density, chemical stability, weather resistance, and ability to accept compounding ingredients without compromising physical properties are highly desirable. These considerations led to the development of polyolefin thermoplastic elastomer blends, and two types are now widely used: blends of ethylene-propylene rubber (EPM) with polypropylene (PP) and blends of EPDM and PP in which the rubber phase is highly crosslinked. This article reviews the nature of these blends. Both physical and Theological properties are very dependent on the morphology and crosslink density of the blend system. Moreover, the usefulness of practical systems depends extensively on compounding technology based on added plasticizers and fillers.
Analysis of Resistivity in a Rubber Compound
Authors: Fernández D. Roig , Marzocca A. J.
Published: February 2011

In the tire industry, good dispersion of carbon black in the rubber matrix is very important to obtain optimum mechanical properties of the compound. Usually, this dispersion can be classified in macrodispersion (for particles bigger than 10 μm) and microdispersion (for those smaller than 10 μm). It is known that good microdispersion enables better fatigue resistance and wear. If it is desired to control the degree of dispersion of uncured compounds during the different processes in the factory, it would be necessary to have a simple and rapid test to do it. An appropriate method to detect different degrees of dispersion is based on the measurement of the electrical resistivity of the rubber compound with dc or ac. In recent years, different factors that affect the resistivity of the compounds were studied in several research programs. The internal factors include structure, size, and dispersion of carbon-black particles, the presence of other reinforcement (silica), and the polymer class. Other factors studied are external: mixing level, pressure, temperature, aging, and contact resistance. Boonstra showed that resistivity depends on the degree of dispersion of carbon black. In his paper, resistivity data are compared with the dispersion levels according to the Cabot rating with good correlation. Furthermore, there are several electrical conduction mechanisms that are proposed in the literature to explain experimental data. It is the purpose of this paper to present an improvement of the Boonstra device for the measurement of electrical resistivity of uncured compounds. The influence of temperature, pressure, aging, carbon black level, and time on the mill roll over the electrical resistivity were also studied. Finally, the results were analyzed by a probability model.
Effect of Different Surface Modifications on the Adhesion of Vulcanized Styrene-Butadiene Rubber
Authors: Martín-Martínez J. M. , Fernández-García J. C. , Huerta F. , Orgilés-Barceló A. C.
Published: February 2011

From the above results, the following conclusions may be drawn: 1. A water ultrasonic procedure for cleaning SBR surfaces has been proposed. The peel strengths attained with polyurethane adhesives are not great and increase with the amount and especially with the viscosity of the adhesive. 2. Surface roughening improves the adhesion between SBR and PUA. There are no important changes in peel strength with the amount and viscosity of the PUA. Zinc stearate removal could be responsible for the increase in peel strength. 3. Chlorination of SBR surface increases the peel strength with regard to ultrasonic-cleaned rubber, especially when both SBR test strip pieces are halogenated. This increase depends on the solvent and percentage of TIC, as well as the amount and viscosity of the adhesive. However, the type of solvent for TIC does not induce physical differences in the SBR surface, the variations being explained in terms of the extent of the chlorine reaction with double carbon bonds of butadiene; in fact, IR spectra show some bands due to the C-C1 groups and also for carboxylic groups. On the other hand, SBR chlorination creates cracks in the surface which are larger when the amount of TIC increases. Furthermore, peel strength, contact angle, and surface analysis measurements correspond well. 4. There is a degradation of the PUA during the time when chlorine reacts with the SBR surface. This reaction is favored by large TIC amounts when MEK is the solvent, and there are low adhesive viscosities. 5. The variation of the adhesion strength with the percentage of TIC depends more on the kind of solvent employed to disperse the halogen-precursor than on the chemical nature of the polyurethane adhesive, probably due to a chemical reaction between them which leads to different chlorinated products.
Pulsed NMR Study of Motional Heterogeneity in Acrylonitrile-Butadiene/Poly(Vinyl Chloride) Blends
Authors: Fukumori Kenzo , Sato Norio , Kurauchi Toshio
Published: February 2011

Motional heterogeneity in blends of NBR (AN = 38%) and PVC was studied by 1H pulsed NMR. It was estimated from NMR relaxation measurements that the PVC molecules in the NBR phase form phase domains of the order of less than 10 nm, consistent with the microheterogeneous structure observed by TEM. Furthermore, by spin diffusion experiments using the Goldman-Shen pulse sequence, the size of the PVC phase domains was semiquantitatively evaluated to be 4.2 nm in the case of the cylindrical domains and to be 5.1 nm in the case of the spherical domains. It becomes clear that pulsed NMR complements the results of other analytical methods with more detailed information on the state of the molecular mixing in the blends.
Rheology and Microstructure of Polymer/Asphalt Blends
Authors: Bouldin M. G. , Collins J. H. , Berker A.
Published: February 2011

This work demonstrates the effectiveness of polymers in improving, especially, the high temperature properties of asphalt. The appropriate choice of asphalt, asphalt-grade, polymer type, polymer concentration, and the method of mixing determine if a network-like structure is formed. This morphology significantly improves the creep performance of the binder at elevated temperatures, i.e., the binder has the ability to store deformation energy with subsequent recoil. This is contrary to Newtonian fluids which transform the energy into viscous flow (no recoil). Within the context of dynamic mechanical measurements, the presence of a polymeric network is manifested through the appearance of a plateau modulus. In the case of binders containing block copolymers, we have repeatedly observed that such property improvement in the high-temperature range is generally accompanied by a reduction of the glassy modulus at the low-temperature range as well. It should be noted that by modifying low-viscosity asphalts (i.e., low AC-grades) with polymers, binders can be obtained which exhibit significantly lower moduli at low temperatures and higher moduli at elevated temperatures. This suggests that although using a high AC-grade asphalt may yield satisfactory results at a particular temperature (high temperature), one may instead optimize binders over the entire temperature range (high and low) by starting with a low AC-grade and adding polymer. These results indicate that careful Theological measurements can be a powerful tool in the characterization and design of viscoelastic blends.
Recent Advances in Anionic Synthesis of Functionalized Polymers
Authors: Quirk Roderic P. , Yin Jian , Guo Shao-Hua , Hu Xiao-Wei , Summers Gabriel J. , Kim Jungahn , Zhu Lin-Fang , Ma Jing-Jing , Takizawa Toshiki , Lynch Thomas
Published: February 2011

There has been growing interest and research on new synthetic methods for the preparation of well-defined polymers with in-chain and chain-end functional groups. These functional groups in polymers can participate in (a) reversible ionic association; (b) chain extension, branching or crosslinking reactions with polyfunctional reagents; (c) coupling and linking with reactive groups on other oligomer or polymer chains; and (d) initiation of polymerization of other monomers. It is noteworthy that the use of end-functionalized polybutadienes formed by reaction of poly(butadienyl)lithium with 4,4′-bis(diethylamino)-benzophenone has been reported to provide marked improvements in the wear and traction properties of tires. In order to exploit the unique potential of functionalized polymers, it is important to consider the scope and limitations of current functionalization methodology using anionic polymerization. Anionic polymerization approaches the goal of synthesizing polymers with predictable, well-defined structures in certain systems such as diene, styrene, methacrylate, and heterocyclic monomers, which proceed in the absence of chain termination and chain transfer reactions. These living polymerizations generate stable, anionic polymer chain ends when all of the monomer has been consumed. In principle, these anionic chain ends can react with a variety of electrophilic species to generate a diverse array of functional groups. Unfortunately, many of the reported functionalization reactions have not been well characterized. Another limitation of the use of specific electrophilic functionalization reactions is the necessity of developing, optimizing, and characterizing new procedures for each different functional group. Variables such as chain-end structure, solvent, temperature, concentration, stoichiometry, mode of addition of reagents, and polar additives can have dramatic effects on yield and product distributions. This review will first provide a critical overview of some recent developments in the use of specific functionalization reactions to prepare polymers labeled with carboxyl, hydroxyl, amino, and sulfonate end groups via alkyllithium-initiated polymerization methods. In addition, a recently developed methodology will be described which utilizes the addition reactions of organolithium compounds to substituted 1,1-diphenylethylenes as a general, quantitative functionalization reaction, independent of the specific functional group.
Effect of Surface Cracks on Torsional Damping
Authors: Gent A. N. , Mifune N.
Published: February 2011

Small cracks are often present in the surfaces of rubber samples. They would be expected to lead to enhanced mechanical damping from frictional energy losses as the surface is deformed. Model experiments reported here have shown that marked increases in tan δ, by as much as 10×, can arise from small relative sliding motions of cuts in the surface of rubber samples. The effect is strongly dependent on the area of the cut surfaces, the direction of the cuts relative to the imposed motion, and stresses acting to open the cuts or keep them closed. When a viscous oil was applied to the cut surfaces, the effect was generally enhanced. Not always, however—friction of dry rubber was found to give rise to equally large energy losses in SBR.
Analysis of Nonlinear Stress—Strain Relationship of Large Elastic Deformation of Rubber and Studies on Rubber—Rubber Composites
Authors: Sarkar Amalendu , Dutta Debashis , Bhowmick Anil K. , Majumdar Swapan
Published: February 2011

1. A computer program based on the numerical method of finite-element analysis using Rivlin-Saunder's equation has been developed for the calculation of nonlinear stress-strain behavior of rubber. 2. The experimental stress-strain relationship can be predicted from the above theory. 3. The theoretical deformation pattern of a binary joint composite is in qualitative agreement with the experimental findings. 4. The stress-distribution pattern of the binary joints is largely dependent upon the geometry of the composite. The stress distribution of the transverse-type composite follows a linear relationship, while for the radial type composite, it increases gradually and reaches a maximum value at the bondline junction, then it again decreases with further increments in value of the y-axis. 5. The more acute the joint angle is, the higher is the stress concentration at the angle tip. 6. The higher the difference in the modulus value across the interface, the higher is the shear stress at the junction and the lower the tensile strength. 7. For transverse type composites, the stress concentration at the crack tip near to the edge is much higher than that at the crack tip near the bondline. 8. In the case of adhesively bonded joints, the stresses along the bondline decrease with the increase in distance away from the crack front.
Numerical Prediction of the Aramid-Cord Load in the Goodrich Block Fatigue Test
Authors: de Jong M. C. , Winkler E. M.
Published: February 2011

In the Goodrich Block Fatigue test, tire cords are tested for their (compression) fatigue behavior. The test specimen, a rubber block with a cord in its center, is cyclically extended and compressed. After a certain running time the retained cord strength is measured. The local cord load cannot be measured directly. Therefore, a calculation procedure is provided to predict the local stress and strain along the cord due to clamping, elongation and compression of the specimen. To this end, a few—for aramid only four—basic linear finite-element computations are needed. Calculation results show that clamping causes a complex load distribution along the cord. This load is not uniform but varies along the axis, and the center of the cord is already in compression. By subsequently elongating the specimen, this compressive region decreases while compression of the specimen leads to an increase. From the standard aramid test conditions, it is apparent that the cord remains compressed in the center. The cord part beginning at the end always remains under tension. Furthermore, there is a small cord section at some distance from the center which is cyclically stretched and compressed during the dynamic load. Experiments show that a fatigued aramid cord mostly breaks in this area, where the cord is subjected to both tension and compression. By combining calculation results with experimentally determined breaking positions of cords, accurate information can be obtained about the loading conditions which are most severe. These findings lead to a better understanding of the failure mechanism of tire cords in the Goodrich Block Fatigue test.
Anisotropy of Ultimate Properties in Vulcanizates of EPDM/High-Diene-Rubber Blends
Authors: Coran A. Y.
Published: February 2011

It can be concluded from this work that the ultimate mechanical properties of NR/EPDM blends are indeed anisotropic, but that the tendency towards anisotropy (and, thus, the tendency towards weakness in certain directions, e.g., a tendency to tear with the processing-flow direction or grain) is greatly reduced when one uses the dynamic vulcanization technique. This technique improves cut-growth resistance (in the grain direction), peel strength, and interply adhesion. Also, because of the modification of the EPDM to give reactive sites (pendent succinic-anhydride groups) for vulcanization to occur by a means other than sulfur, the cure-rate incompatibility problem is greatly ameliorated. Thus, improvements in permanent set, hysteresis, and rebound are obtained by using the techniques of this report.
Pattern Abrasion and Other Mechanisms of Wear of Tank Track Pads
Authors: Medalia A. I. , Alesi A. L. , Mead J. L.
Published: February 2011

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 patterns of both types of pads had a shingled appearance, with the ridges pitched so as to bite into the road surface. The abrasion patterns were characterized quantitatively by profilometry, using standard parameters calculated for surface roughness of metals and other materials. The ridge height and its ratio to ridge spacing correlated positively with wear rate on the paved road; whereas there was no correlation of ridge spacing with wear rate. The compounds which gave the lowest wear rate on the paved road, including the HNBR compounds, gave shallow ridges with little or no pattern.
Microencapsulated Antidegradants for Extending Rubber Lifetime
Authors: Evans Larry R. , Benko David A. , Gillick James G. , Waddell Walter H.
Published: February 2011

Microcapsules containing rubber antidegradants were formed in a spray-drying process. Studies were carried out to select the proper wall material based on the processing properties, migration rate of the antidegradant through the capsule wall, thickness of the capsule wall, and overall capsule diameter. The resulting capsules were incorporated into a rubber article, providing a reservoir of antidegradant during the exposure lifetime. Testing of the rubber compounds with microcapsules having diameters less than 50 µm containing AN-(l,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine in a matrix of cellulose acetate showed a significant increase in the crack-free lifetime of the rubber when flexed in exposure to ozone.
Recuring Vulcanizates. I. A Novel Way to Study the Mechanism of Vulcanization
Authors: Layer Robert W.
Published: February 2011

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 accelerator remains active as its zinc salt at the end of the cure. In effect, vulcanizates can be viewed as high-molecular-weight model compounds. In this study, we find that recuring SBR/BR vulcanizates, to which sulfur or the sulfur donor, N,N′ -dithiodimorpholine, is added, develops the same state of cure as the same amount of sulfur (or sulfur donor) added for the initial cure. This suggests that exchange reactions occur between crosslinks and the zinc-sulfur-accelerator complex during the cure and that all of the accelerator remains as its zinc salt at the end of the cure. This last result is interesting, since it is not consistent with the current view that most of the accelerator becomes irreversibly bound to the rubber and lost during the vulcanization of polybutadiene rubbers.
Self-Crosslinkable Polymer Blends Based on Chlorinated Rubber and Carboxylated Nitrile Rubber
Authors: Ramesh P. , De S. K.
Published: February 2011

Melt-mixed blends of chlorinated natural rubber and carboxylated nitrile rubber get crosslinked during prolonged molding at elevated temperatures in the absence of any crosslinking agent. Dynamic mechanical measurements show that such blends are compatible. The physical properties depend on the blend composition. The blends exhibit excellent processing safety, good oil resistance, and high abrasion resistance.
Electrical Conductivity of Barium-Ferrite-Vulcanized Polychloroprene Filled with Short Carbon Fiber
Authors: Jana P. B. , De S. K. , Chaudhuri S. , Pal A. K.
Published: February 2011

Short-carbon-fiber-filled polychloroprene composites, prepared by mill-mixing and cement-mixing methods were vulcanized by barium ferrite. The effects of concentration and aspect ratio (L/D) of short carbon fiber on volume resistivity have been studied. Composites prepared by the cement mixing method having high fiber aspect ratio (L/D 100) show higher hardness and modulus accompanied by lower elongation and volume resistivity than the composites prepared by the mill mixing method, which give low fiber aspect ratio (L/D 25). Experimental values of volume resistivity agreed reasonably well with the calculated values from the theory based on probability of formation of conductive network. The temperature dependence of volume resistivity of the composite shows a positive temperature coefficient. The shape of the hysteresis loop, observed during the heating and cooling cycle in the variation of volume resistivity with temperature, depends on the concentration and aspect ratio of short carbon fiber. Hall-effect studies indicate that increase in fiber concentration and aspect ratio in the composites causes increase in carrier concentration and decrease in mobility of the carriers. With increase in temperature, both conductivity and carrier concentration decrease and mobility of the carriers increases.
Studies on a New Binary Accelerator System for the Sulfur Vulcanization of Styrene—Butadiene Rubber
Authors: Mathew George , Pillai P. Viswanathan , Kuriakose A. P.
Published: February 2011

The chemical reactions involved when a binary accelerator system is used in rubber vulcanization varies with the systems used. The exact mechanism of these reactions is not fully understood even now. Accelerators in which sulfur is combined as S—S, C—S—C, or S—N are generally inactive at low vulcanization temperatures because of the high thermal stability of their sulfur bonds. But sulfur-containing nucleophiles such as thiourea or its derivatives enable accelerators like TMTD or CBS to operate at lower vulcanization temperature, indicating a nucleophilic reaction mechanism in these vulcanization reactions. But, no conclusive evidence is given for such a postulate. In the present study, 1-phenyl-2,4-dithiobiuret and 1,5-diphenyl-2,4-dithiobiuret, which are more nucleophilic than thiourea but which vary in their nucleophilic reactivity, were tried as secondary accelerators in binary systems containing TMTD or CBS in sulfur vulcanization of SBR. Both the above dithiobiurets were found to reduce the optimum cure time considerably compared to the reference mixes. 1-phenyl-2,4-dithiobiuret, which is more nucleophilic than 1,5-diphenyl-2,4-dithiobiuret, is found to reduce the optimum cure time more, showing a nucleophilic reaction mechanism in the systems under review. In both cases, the optimum dosage of the secondary accelerator required has been established. The vulcanizates obtained with these new systems showed definite increase in tensile properties and good retention of these properties after aging. In the evaluation of other physical properties, these vulcanizates gave promising results. In order to correlate these physical properties to the type of chemical crosslinks formed, chemical characterization of the vulcanizates was also carried out. Also, to study the effect of these nucleophiles on the temperature of vulcanization, these mixes were cured and evaluated at two different temperatures, viz., 120°C and 150°C. To overcome the lower green strength and gum tensile strength in SBR, incorporation of fine reinforcing fillers and the use of special combinations of accelerators is required. In this context, the study was extended to evaluate the effect of fillers—carbon black, precipitated silica, and china clay—on the cure characteristics and vulcanizate properties.
Electrical Conductivity of Thermo-Oxidatively-Degraded EPDM Rubber
Authors: Mattson Bengt , Stenberg Bengt
Published: February 2011

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.
Rubber Process Oils for Peroxide Curing of Ethylene—Propylene Elastomers
Authors: Chasey Kent L.
Published: February 2011

Ten rubber process oils were evaluated in a peroxide-cured EPDM compound. The effects of the process oil on cure-development characteristics and stress—strain properties are discussed. Certain types of molecular structures in the oil can significantly interfere with free-radical vulcanization, and analytical methods for the detection of these structures are provided. The combined effects of the process oil and the peroxide—coagent concentration are also described.
Solid-State C-13 NMR Studies of Vulcanized Elastomers X. N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75.5 MHz
Authors: Krejsa M. R. , Koenig J. L.
Published: February 2011

Accelerated sulfur vulcanized cis-polyisoprene was analyzed using C-13 solid-state NMR to determine the chemical microstructure of the network. Three formulations were analyzed consisting of varying accelerator/sulfur ratios. All formulations yielded similar network structures, but the amount of sulfurization varied with sulfur concentration. At low percent cure, only polysulfidic A-type cis-structures were found. For longer cure times, the A-type structures shortened to monosulfldic, and B-type polysulfidic structures, both cis and trans, were formed. The amount of trans-sulfurized product was constant with cure once this resonance appeared. No isomerization, chain scission, saturation, or double bond migration was detected. The NMR measurements appeared to show fairly good agreement with equilibrium swelling measurements.
A Review of Group-Transfer Polymerization
Authors: Brittain William J.
Published: February 2011

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.