bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Resistivity of Carbon-Black-Loaded Rubbers
Authors: Aminabhavi Tejraj M. , Cassidy Patrick E. , Thompson Corley M.
Published: February 2011

Uses are growing for rubbers with varying levels of resistivity. High electrical resistivity is very much essential in wire and cable insulation applications. Low levels of resistivity are needed for electrostatic discharge in phonograph records and many medical, industrial, and military products and for semiconductive cable compounds. The level of resistivity depends upon the number of contacts or near contacts between conductive particles in the rubber matrix. Loading level is obviously a major determinant in addition to physicochemical characteristics of the black. In the latter regard, the highly conductive grades are characterized by small particle size, high structure, high surface porosity, and low volatile content. One would, therefore, seek the reverse of those factors for high-resistivity rubbers. One of the goals of materials research now is to create new materials with physicomechanical properties tailored to a particular application and to understand the physical processes which determine the end properties. In this review, an attempt has been made to discuss the electrical properties of carbon-black-loaded rubber composites, a class of materials which covers the range from insulators to conductors. The carbon-black-loaded rubbers are formed by dispersing carbon black into the rubber. The compounding is done by adding the carbon black to the rubber, mixing at temperatures above Tg and subjecting the mixtures to high shears until a uniform blend is obtained. The carbon-black particles may be as small as 14 nm in diameter or as large as 300 nm, and they may be individually dispersed or agglomerated in micron-sized clusters. Morphology of the rubber has a profound effect on its electrical properties. High electrically resistive rubbers are becoming increasingly important. Their wide array of applications include antistatic products, shielding materials, insulating membranes, resistors, etc. In the vicinity of the crystalline transition region the rubber shows a dramatic resistivity increase which can be utilized for self-regulation processes. Compounds suitable for such various applications differ appreciably in the nature of their components and composition depending on the specific performance required.
Tensile Stress—Strain Measurements for Characterization of Gum Elastomers and Filled Compounds
Authors: Nakajima N. , Chu M. H. , Babrowicz R.
Published: February 2011

For a gum elastomer in its amorphous, isotropic state, shear modulus and tensile modulus are related with a factor of three. This relation is maintained in the range of temperature and time scale defining the rubbery region of the material behavior. When a large deformation is imposed, for example, in tensile stress—strain measurements, the above relation may still be preserved, if the nonlinear behavior can be linearized. The strain—time correspondence principle is the linearization scheme of this work. When a gum elastomer contains various structural constraints, the factor three relation does not apply, even after the application of the above linearization scheme. Example of constraints are excessive amounts of long branches, gel, molecular associations, and reinforcing fillers. These constraints usually make the factor larger than three. This is because the constraints make the large, elongational deformation more difficult to achieve compared to shear deformation. An example of gum elastomer in this work is a polyethylacrylate containing a significant amount of gel. With this polymer, both the presence of gel and the molecular association act as the constraints. However, when 50 phr of carbon blacks are added, the fillers do not act as strong constraints as they do when they are in the diene rubbers. This is because the polyethylacrylate is known to have a weaker affinity to carbon black compared to the diene rubbers. Triblock copolymers, styrene—isoprene—styrene, were examined according to the above treatment; 25% polystyrene copolymer exhibited crosslink-like behavior by the polystyrene domains. However, 14% polystyrene copolymers acted as if they are no crosslinks. When these copolymers are diluted to 44% with an addition of 56% tackifier, the ratio of tensile to shear modulus became less than three. The styrene domains must have effective crosslinks at the small shear deformation, but at large tensile deformations such crosslinks must not be present.
Dynamic Mechanical Analysis of Carbon-Black-Filled Rubber Vulcanizates under Swollen Conditions
Authors: Neogi Chanchal , Bhattacharya A. K. , Bhowmick Anil K. , Basu S. P.
Published: February 2011

1. For unswollen vulcanizates, storage modulus (E′) decreases with the increase in temperature and decrease in loading and surface area of carbon-black filler. On partial swelling, these effects are much reduced, and E′ becomes independent of surface area and loading on equilibrium swelling. 2. Loss modulus (E″) of unswollen vulcanizates also follows the same trend. However, on swelling in xylene, E″ increases to a great extent because of contributions from both the solvent and the rubber matrix. 3. Loss tangent (tan δ) also decreases with increase in temperature and decrease in loading of carbon black. On swelling, it optimizes at 30 phr loading. 4. Tan δ increases with ϕΨ for unswollen samples, but swollen vulcanizates show an optimum in tan δ at ϕΨ=2.5. 5. Limiting value of storage modulus has been determined for all the filled samples.
Characterization of Elastic Properties of Carbon-Black-Filled Rubber Vulcanizates
Authors: Yeoh O. H.
Published: February 2011

A novel strain-energy function which is a simple cubic equation in the invariant (I1−3) is proposed for the characterization of the elastic properties of carbon-black-filled rubber vulcanizates. Conceptually, the proposed function is a material model with a shear modulus which varies with deformation. This contrasts with the neo-Hookean and Mooney-Rivlin models which have a constant shear modulus. The variation of shear modulus with deformation is commonly observed with filled rubbers. Initially, the modulus falls with increasing deformation, leading to a flattening of the shear stress/strain curve. At large deformations, the modulus rises again due to finite extensibility of the network, accentuated by the strain amplication effect of the filler. This characteristic behavior of filled rubbers may be described approximately by the proposed strain-energy function by requiring the coefficient C20 to be negative, while the coefficients C10 and C30 are positive. The use of the proposed strain-energy function has been shown to permit the prediction of stress/strain behavior in different deformation modes from data obtained in one simple deformation mode. This circumvents the need for a rather difficult experiment in general biaxial extension. The simple form of the proposed function also simplifies the regression analysis. This strain-energy function is consistent with the general Rivlin strain-energy function and is easily obtained from the popular third-order deformation approximation. Thus, it is already available in many existing finite-element analysis programs.
Solid State NMR Characterization of Crosslinked Brominated Poly(Isobutylene-co-4-Methylstyrene)
Authors: Eckman R. R. , Gardner I. J. , Wang H-C.
Published: February 2011

The curing of brominated poly(isobutylene-co-4-methylstyrene) was studied using solid-state magic-angle-spinning NMR, a technique which is uniquely suited to investigate cured or crosslinked polymers. This brominated copolymer contains 4-bromomethylstyryl and 4-methylstyryl functional groups and was compression cured with pure ZnO. It was proposed that a precomplex is formed between zinc and the 4-bromomethylstyryl group, which generates a benzylic carbocationic intermediate. Crosslinking predominantly occurs by alkylation of the phenyl ring of another 4-bromomethylstyryl group by the benzylic intermediate. The ZnO brings the two bromides of these groups into proximity. The dependence of the cure chemistry on the concentration of 4-bromomethylstyryl functional groups was studied. Conversion of some 4-bromomethylstyryl groups to oxygenated species upon curing was also observed.
Basic Studies of Extrusion of Rubber Compounds in a Pin Barrel Extruder
Authors: Shin Kyung-Chul , White James L.
Published: February 2011

An experimental study of the flow, pumping, and mixing characteristics of three different rubber-carbon black compounds in a model pin barrel extruder is presented. These are a model SBR/BR passenger tire compound, a NR truck tire compound, and a NBR mechanical goods compound. Comparisons are made of the initial extruder without pins or slices/grooves in the screw flights, an extruder containing slices or grooves in its flights, and a pin barrel extruder. It is found for each compound that introducing slices in screw flights improves mixing/homogenization and decreases pumping ability. Introduction of pins improves mixing/homogenization and has little effect on pumping. The homogenization is best for the passenger tire tread compound and worst for the NBR mechanical good compound.
Polystyrene-Natural-Rubber Mixtures: Preparation and Properties
Authors: Valić S. , Topić M. , Andreis M. , Ranogajec F. , Veksli Z. , Šincek-Pećanić V.
Published: February 2011

Thermoplastic elastomers were prepared from mixtures of polystyrene and natural-rubber latexes. The mechanical measurements, thermally stimulated depolarization current measurements, and NMR spin-spin relaxation measurements have shown that the properties of prepared thermoplastic elastomers depend on the composition and the interface created by changing the size of the accessible polystyrene surface.
Influence of Some Parameters on the Solution of a Thermal Model of Vulcanization
Authors: Burger Jacques , Burger Nicole , Pogu Marc
Published: February 2011

The thermal behavior of a piece of rubber during a vulcanization process is modelized by a set of two coupled differential equations. The first one is a classical nonlinear heat equation while the second is a reaction equation. The aim of this article is first to solve numerically the two equations using a finite element procedure for the partial differential equation and a Runge-Kutta like scheme for the reaction equation, and then to study the sensitivity of the solution to variations in some parameters.
Solid State Carbon-13 NMR Studies of Elastomers. XL N-t-Butyl Benzothiazole Sulfenimide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75 MHz
Authors: Krejsa M. R. , Koenig J. L.
Published: February 2011

The network structure of TBSI-accelerated vulcanization of cis-polyisoprene was studied using C-13 solid-state NMR. The initial crosslink products consisted of A1c (cis) and A2c (cis) polysulfides. As the percent cure is increased, the A1c and A2c structures reduce in rank to monosulfides, and polysulfidic B1c (cis) and B1t (trans) structures are formed. During the maturation period C1c (cis) polysulfidic structures are also formed. The percent of sulfurization was shown to vary directly with sulfur concentration, while the efficiency of sulfurization (crosslink/cyclic-structure ratio) was shown to vary with accelerator content. TBSI-accelerated vulcanization was found to be more inefficient (lower crosslink/cyclic-structure ratio) than TBBS-accelerated vulcanization during the initial cure region. However, this results in shorter sulfur chains, which decreases the reactivity of TBSI vulcanizates as compared to TBBS vulcanizates during the reversion regime.
Electrophilic Addition of Brominated Poly(Isobutylene-co-4-Methylstyrene) to Olefins Catalyzed by Zinc Salts: A Model Study
Authors: Fréchet J. M. J. , Bielski R. , Wang H-C. , Fusco J. V. , Powers K. W.
Published: February 2011

The chemical reactivity of a new elastomer based on brominated poly(isobutylene-co-4-methylstyrene) in electrophilic additions to olefins has been investigated using model compounds as well as appropriate polymers. The reactions catalyzed by zinc salts are influenced by the solubility as well as the composition of the catalyst. While the reactivity of zinc bromide is limited by its low solubility in nonpolar medium, zinc oxide and zinc stearate can afford excellent results once an induction period has elapsed. The induction period likely corresponds to the formation of more reactive zinc based moieties through interchange reactions with the benzylic bromide groups. The mechanism of the addition process involves initial formation of carbocationic complexes with the zinc salts, followed by addition to the double bonds of the olefins. The products resulting from these additions have been characterized by NMR as well as gas chromatography-mass spectrometry. A comparison of potential crosslinking processes involving olefin addition or electrophilic aromatic substitution reactions shows that the former process is preferred. The findings of this study are directly applicable to the co-curing of elastomers based on brominated poly-(isobutylene-co-4-methylstyrene) with polyolefins.
Filler-Elastomer Interactions. Part VIII. The Role of the Distance between Filler Aggregates in the Dynamic Properties of Filled Vulcanizates
Authors: Wang Meng-Jiao , Wolff Siegfried , Tan Ewe-Hong
Published: February 2011

Based on the concepts of the occlusion of rubber and random packing of spheres whose volume is equivalent to that permeated by individual aggregates, an equation was deduced to estimate the distance between carbon-black aggregates in filled rubber. It was found that when the interaggregate distance reaches a critical point which is approximately identical for all carbon blacks investigated (furnace blacks), the elastic modulus measured at very low strain deviates from the modified Guth-Gold equation. Tan δ and resilience are mainly determined by the distance between aggregates. These phenomena are related to filler networking which is determined by the attractive potential and the distance between individual aggregates. Since the factor Sf, used to characterize the strength of secondary filler networks in hydrocarbon rubbers and measured by means of inverse gas chromatography, is approximately the same for all furnace blacks, the interaggregate distance seems to determine filler networking. A comparison of fillers with different Sf (graphitized vs. nongraphitized carbon blacks, carbon black vs. silica) shows that at the same interaggregate distance, a lower Sf leads to higher tan δ of the filled vulcanizates.
FT-IR Spectroscopy, a Major Tool for the Analysis of Peroxide Vulcanization Processes in the Presence of Coagents. I. Mechanism of EPM Peroxide Vulcanization with Aromatic bis(Allyl)Esters as Coagents
Authors: Dikland H. G. , van der Does L. , Bantjes A.
Published: February 2011

In this paper the results of investigations on the mechanism of EPM peroxide vulcanizations in the presence of various bis(allyl)esters of aromatic diacids—as coagents—are presented. These coagents are commonly used in the rubber industry to increase the crosslinking efficiency, however, until now the mechanism of this process remained unclear. In our studies it is demonstrated that when using FT-IR spectroscopy in combination with equilibrium swelling techniques and atomic force scanning microscopy, the role of the coagents can be elucidated.
Improved Quantitative Determination of Elastomers in Tire Rubber by Kinetic Simulation of DTG Curves
Authors: Yang J. , Kaliaguine S. , Roy C.
Published: February 2011

A method of identifying and quantifying elastomers and processing oil in tire rubber, called DTG curve simulation method, is proposed. This method is based on DTG (derivative thermogravimetry) analysis of the straight elastomers NR, BR and SBR, which produces a series of decomposition rate data and pairs of kinetic constants. DTG curves of binary elastomer systems NR/SBR, NR/BR and BR/SBR are measured. The samples are qualitatively identified following the shape of their DTG curves. Quantitative determination is achieved by DTG curve simulation using a least squares method. When correct elastomers and proper compound ratio are chosen, minimum simulation error is achieved leading to effective identification. Satisfactory results were obtained when applying the method to elastomer mixtures of known composition and to tire rubbers of unknown composition. The study advanced the capability of the TG-DTG technique for quantitative determination of elastomers and blends.
FTIR and NMR Studies on Crosslinking Reaction between Chlorosulfonated Polyethylene and Epoxidized Natural Rubber
Authors: Roychoudhury A. , De P. P. , Dutta N. K. , Roychoudhury N. , Haidar B. , Vidal A.
Published: February 2011

A blend of chlorosulfonated polyethylene and epoxidized natural rubber undergoes a self-crosslinking reaction at elevated temperatures. Sulfonyl chloride groups of chlorosulfonated polyethylene react with epoxy groups of epoxidized natural rubber to give ether crosslinks between the two polymers. In addition to the self-crosslinking reaction, these two polymers undergo a number of side reactions as evidenced by spectroscopic studies.
Comparison of Four-Flighted and Two-Flighted Internal Mixer Rotors Using Cylindrical Coordinate Hydrodynamic Lubrication Theory
Authors: Hu Benfei , White James L.
Published: February 2011

Internal mixers have played a key role in the polymer industry. Internal mixers with four-flighted rotors are attracting more and more attention today. In this paper, we apply a new model based on cylindrical coordinate hydrodynamic lubrication theory for internal mixers to various rotor designs. Numerical techniques were used to carry out the calculations of the pressure field, mean flux field, and various mixing characteristic parameters. Comparisons were made for both four-flighted and two-flighted rotor designs. This was done assuming a fully filled mixing chamber. The simulation effort is important for the understanding of mixing mechanisms in internal mixers and to provide a basis for the rational design of internal mixers.
Blends of Crystallizable Polybutadiene Isomers
Authors: Nir Moira Marx , Cohen Robert E.
Published: February 2011

Precipitated blends of two crystallizable polybutadiene (PBD) isomers were characterized in terms of crystallization and phase behavior, morphology, and tensile mechanical properties. The isomers are syndiotactic 1,2 PBD (Mv=32.5 kg/mol) and trans 1,4 PBD (Mv=425 kg/mol). The blends exhibit heterogeneous behavior over the full range of composition. Using a solvent precipitation method, blends are obtained with heterogeneity on the order of 1 µm. Tensile properties of these semicrystalline blends are generally intermediate between those of the corresponding semicrystalline homopolymers, with some enhancement at approximately 10% 1,2 PBD content. Comparisons are made with previously reported data on amorphous PBD blends.
Analysis of Fatigue Crack Propagation in NR/BR Rubber Blend
Authors: Lee M-P. , Moet A.
Published: February 2011

Fatigue behavior in a blend of natural rubber (NR) and polybutadiene rubber (BR) has been investigated. The energy release rates measured from load-displacement curves recorded during the fatigue test could be used to characterize the fatigue crack propagation (FCP) history of NR/BR blend. Crack propagation kinetics showed an initial low slope “ozone crack regime” with an S-shaped “mechanico-oxidative cut growth regime”. The blend has a mechanical fatigue limit of 2.4 kJ/m2. The crack initiation constituted 25% of the total fatigue life and the low slope stage comprised 40% of the crack propagation life. Examination of the fracture profile and the fracture surface revealed that microcracks and crack tip roughening were two damage mechanisms controlling the resistance to crack propagation in the “mechanico-oxidative cut growth regime”, while the reverse herringbone pattern near the notch corresponded to the “ozone crack regime”.
States of Carbon Black Dispersion and Extensibility of Rubbers
Authors: Ahagon Asahiro
Published: February 2011

Analysis is made for the origin of the mixing-induced tensile property variation of a filled rubber. Attention is paid to the hydrodynamic effect f(ϕe) of the filler, defined here as the factor to adjust the deviation of 100% modulus from the theory of rubber elasticity. For the rubbers mixed under variety of conditions, the f(ϕe)'s are calculated from the observed values of the modulus, at 25°C and 100°C, and the crosslink density. The variation of the f(ϕe) is considered to be governed by the mobility of the polymer confined in agglomerates of the filler. The mobility variation due to mixing seems to be mainly influenced by agglomerate size at 25°C, and by agglomerate size and chemical constraints at 100°C. Therefore, the f(ϕe)'s at the two temperatures are suggested to be useful measures of the state of carbon-black micro-dispersion. The extensibility of the rubbers is closely related f(ϕe). This indicates that the failure property is also governed by the mobility of the confined polymer.
A Review of Sulfur Crosslinking Fundamentals for Accelerated and Unaccelerated Vulcanization
Authors: Krejsa M. R. , Koenig J. L.
Published: February 2011

This work has reviewed and summarized the present understanding of the fundamental science and chemistry of rubber vulcanization. The future of this area holds much potential. Recent studies have begun to fully elucidate the accelerator and accelerator complex chemistry, and definitively answer questions that have been open for debate for many years. Additionally, the understanding of the network structure is rapidly progressing through advances in analytical techniques. The largest area of future research will be the use of multiple experimental techniques to fully elucidate and understand the relationship between accelerator chemistry and the formation of specific network structures. With this knowledge, it will then be possible to molecularly engineer vulcanizates with specific properties.
Reactive Processing of Rubbers
Authors: Burlett Donald J. , Lindt J. Thomas
Published: February 2011

Although alluded to occasionally during the previous discussions of chemistries used for reactive processing, the physical nature of the product probably has a significant effect on its useful properties. At the same time, the chemistries used often are dominant in the preparation of the final product. This is also one of the least well characterized aspects of reactive processing. The type of matrix formed during alloying, blending, modification, graft polymerizing, etc. (dispersion, co-continuous network or interpenetrating network) and the domains (characterized by various sizes and shapes) depend both on the chemistry being utilized and the mixing produced by the equipment used. A fine balance is maintained between the chemistry being used—its time and temperature requirements—and the physical aspects of mixing and dispersion. The design of the mixing operations must consider the interplay of these two aspects to control the physical properties of the products generated. The area of reactive processing of rubbers will continue to grow and many of the factors that control the physical properties of the product will be controlled by variations in the mixing and chemical processes developed.
129Xe NMR in Polymers
Authors: Miller J. B.
Published: February 2011

Through the efforts of many researchers, 129Xe NMR has shown to be a sensitive probe of phase morphology in polymers, providing a unique means of investigating the amorphous phase of bulk polymers. Recently developed models of the 129Xe chemical shift in polymers open the possibility of measuring van der Waals' interaction energies and chain dimensions from xenon spectra. In most cases, the information obtained from 129Xe NMR pertains only to the amorphous phase of the polymer, even in semicrystalline systems. The use of spin-polarized xenon has opened the possibility of probing the surface and near surface regions of polymers.
A Study of Thiocarbamyl Sulfenamide/Zinc Oxide and TMTD/Zinc Oxide Sulfurless Cure Systems
Authors: Layer Robert W.
Published: February 2011

In sulfurless cures of NR, soluble thiocarbamyl sulfenamides are found to produce the same state of cure as thiuram disulfides when compared on an equivalent dithiocarbamyl group basis. The addition of MBTS or benzothiazole sulfenamides to thiocarbamyl sulfenamides, or to thiurams, increases the modulus in proportion to the amount added. Adding sufficient benzothiazole sulfenamide appears to double the amount of sulfur donated by these thiocarbamyl accelerators and simultaneously increases monosulfide crosslink formation. The addition of zinc dibutyldithiocarbamate to thiocarbamyl sulfenamides significantly increases the modulus but has no effect on TMTD. Thiuram disulfides are generally reported to donate one sulfur per mole for crosslink formation. However, critical analysis of the literature and the above data indicates that two moles of TMTD are required to form one crosslink, i.e. donate one sulfur.
Thermally Induced Crosslinking in Blends of Poly(Vinyl Chloride) and Hydrogenated Acrylonitrile—Butadiene Rubber
Authors: Manoj N. R. , De S. K. , De P. P.
Published: February 2011

A blend of Poly(vinyl chloride) (PVC) and hydrogenated acrylonitrile—butadiene rubber (HNBR) undergoes crosslinking at high molding temperatures in the absence of any external curing agents. This is evident from Monsanto rheometric, solvent swelling, and infrared spectroscopic studies. The reaction proceeds through the interaction of allylic and tertiary chlorine in PVC, with amide and acid groups in HNBR formed during molding. The network structure is believed to consist of amide and ester crosslinks. Dynamic mechanical analysis and differential scanning calorimetry show that the blend components are miscible Variation in molding time and temperature has no effect on the miscibility.
Fracture Toughness of PVC/NBR Blends Evaluated by the J-Integral
Authors: Nakajima N. , Liu J. L.
Published: February 2011

The effect of gel on the fracture toughness of four PVC/NBR (50/50) blends was characterized by two different J- integral methods. Three of these blends are compatible blends with 33% acrylonitrile in NBRs, and the fourth with 21% acrylonitrile content, is an incompatible blend. Two types of gel are involved in this study microgels and macrogels. The J-integral methods are (1) conventional method proposed by Bagley and Landes and (2) crack initiation locus method proposed by Kim and Joe. The same load-displacement curves are used in both methods. However, the latter eliminates the energy dissipation away from the crack tip in the determination of Jc, while the former does not. Both methods produced almost the same results indicating that the energy dissipation away from the crack tip is negligible in these samples. The fracture toughness of a macrogel-containing blend is much greater than that of a microgel-containing blend, which, in turn, is only slightly greater than that of a gel-free blend. This implies that the two gel-containing blends have different fracture processes. The incompatible blend has the lowest fracture toughness due to weak interaction at the boundaries of the two phases.
An Experimental Study of Failure in Circumferentially Notched Elastomer Cylinders
Authors: Quigley Claudia J. , Dooley Robert , Parks David M.
Published: February 2011

Cylindrical dumbbell specimens containing deep circumferential cracks were loaded in tension until failure to investigate the fracture process in thick carbon black filled elastomers. Failure occurred at large deformations and was characterized by material tearing and small amounts of slow stable crack extension until rupture. The tearing process itself consisted of two distinct phenomena, delamination and crack extension. Upon load application, parabolic and asymmetric blunting of the crack tip was observed followed by a visible separation of the fabricated crack surfaces into upper and lower crack surfaces connected by an inner core of elastomer material. Localized material failure, identified as delamination, occurred along the outer surface of this inner core between the fabricated crack surfaces. Crack extension in the load direction was found above and below the fabricated crack surfaces. Both qualitative and quantitative aspects of failure were studied. Load and crack mouth opening displacement (CMOD) histories were examined, and the stretch ratio and tearing energy at rupture were measured. Finally, a model describing the tearing process was discussed.
Ground Rubber Tire / Thermoplastic Composites: Effect of Different Ground Rubber Tires
Authors: Rajalingam P. , Sharpe J. , Baker W. E.
Published: February 2011

Thermoplastic composites containing different Ground Rubber Tire (GRT) materials, Linear Low Density Polyethylene (LLDPE) and, in some case, a coupling agent (IB‘E’, an ethylene glycidyl methacrylate copolymer) were prepared by melt blending. The impact energies of all the thermoplastic composites (normally containing 40 wt % GRT) were evaluated using an instrumented impact tester. The effects of the GRT particle-size, particle size distribution and shape, the mode of grinding, and the oxygen surface concentration were analyzed. The wet-ambient-ground GRT based composites show higher surface oxidation and give better impact energy than cryo-ground and normal air-ground GRT based composites. Smaller GRT particle size results in a small increase in the impact property of the composite and a greater influence on the melt processability of the composites. Of the different GRT surface modification techniques studied for improved composite interfacial adhesion and impact properties the composites from electron beam radiation treated GRT yield higher increases in impact energy in comparison to corona and plasma treated GRT based composites.
Carbon-Black-Elastomer Interaction II: Effects of Carbon Black Surface Activity and Loading
Authors: Ayala J. A. , Hess W. M. , Joyce G. A. , Kistler F. D.
Published: February 2011

Carbon black morphology, surface activity and loading have been varied systematically to study the effects on an SBR formulation. The surface activity of five commercial grades of carbon black was varied by heat treating the standard grade samples at 1100°C and 1500°C in an inert atmosphere. Measurements on carbon black-elastomer interaction were based on a parameter I, defined elsewhere. The parameter I exhibited the previously reported correlation with known indicators of the surface activity of carbon blacks. The heats of adsorption by inverse gas chromatography at infinite dilution have been found useful as a measure of the carbon-black surface energy related to rubber interaction. These measurements have been employed in conjunction with carbon-black morphology and loading to develop a surface-area-modified and a surface energy-modified effective volume fraction V′ and ψ, respectively. The parameter V′ was utilized to explain the variation of the dynamic elastic modulus E′ at 1 % double strain amplitude (DSA) for all rubber compounds. The parameter ψ was used to explain the variation of E′ at 25% DSA and the factor σ in the calculation of I. The parameters V′ and ψ provide a model for the estimation of I from fundamental carbon-black morphological properties and surface energy.
Electropolymerization of Aniline on Conductive Vulcanizates and Charge-Discharge Properties
Authors: Mori Kunio , Oishi Yoshiyuki , Hirahara Hidetoshi , Kumagai Naoaki , Tanno Kazuo
Published: February 2011

To obtain electrode materials with good charge-discharge properties, the electrochemical polymerization of aniline on conductive vulcanizates containing Ketjin black was investigated along with the charge-discharge properties of these materials. When EPDM vulcanizates containing Ketjin black greater than 20 phr were used as working electrodes, the polymerization of aniline occurred easily and conductive laminates of vulcanizate and polyaniline were obtained. This required an EPDM vulcanizate conductivity of more than 0.1 S/cm. The selection of elastomers and solvents for the electrochemical reaction is important. A combination of EPDM and water solvent was found to be suitable for the electrochemical polymerization of aniline. Polyaniline products on vulcanizate electrodes had lower film densities than polypyrrole products, and exhibited greater adhesion to the vulcanizates than to Pt electrodes. Li battery cells, using these polyaniline vulcanizate electrodes, possessed remarkably higher charge-discharge capacity and greater cycles life than the polyaniline Pt electrode. The vulcanizate electrode retained good charge-discharge properties even at a current density exceeding 1.0 mA/cm2.
Reduced Time Approach to Curing Kinetics, Part I: Dynamic Rate and Master Curve from Isothermal Data
Authors: Chan T. W. , Shyu G. D. , Isayev A. I.
Published: February 2011

A reduced time approach has been used to predict nonisothermal curing kinetics based on isothermal kinetic data. This approach makes it clear that the conversion in a kinetic process is a function of the reduced time alone and allows for the construction of a master curve from isothermal kinetic data, indicating that the dynamic (or nonisothermal ) rate is equal to the isothermal rate. The approach can be applied to curing, crystallization, and other physico-chemical kinetics. A method is also described for correcting the nonisothermal curing kinetic data obtained from differential scanning calorimetry ( DSC ) for a temperature lag between the sample and the DSC furnace. For two rubber compounds, it has been found that the nonisothermal curing kinetic data corrected for this temperature lag are in better agreement with the predictions based on isothermal kinetics than the uncorrected data.
Cure and Mechanical Behavior of Rubber Compounds Containing Ground Vulcanizates. Part II—Mooney Viscosity
Authors: Gibala D. , Laohapisitpanich K. , Thomas D. , Hamed G. R.
Published: February 2011

Mooney viscosities and thixotropic behavior have been determined for SBR melts containing carbon black and/or ground vulcanizate particles. A composition containing ambiently ground rubber has a higher viscosity than one with cryogenically ground rubber. This is attributed to occlusion of continuum rubber within the sponge-like, ambiently ground rubber; occlusion is not possible with the smooth, cryo-ground particles. Viscosity was independent of particle size. On an equal phr (weight) basis, the addition of N330 carbon black and cryo-ground rubber augment Mooney viscosity to a similar extent. While the Guth-Gold Equation is approximately applicable to black-filled melts, samples containing ground rubber are a much better fit by the simple Einstein Equation. Ground rubber addition has only a minor influence of thixotropy, in contrast to carbon black, which greatly increases thixotropy.
Electron Beam Initiated Grafting and Crosslinking of Ethylene Vinyl Acetate Copolymer. Part-I: Structural Characterization
Authors: Datta Sujit K. , Chaki Tapan K. , Bhowmick Anil K.
Published: February 2011

Electron beam irradiation of Ethylene vinyl acetate, EVA (VA content 12, 28 & 45%) copolymer was carried out in presence of trimethylolpropane trimethacrylate (TMPTMA) and triallyl cyanurate (TAC) and the structure of the modified copolymers was determined with the help of IR spectroscopy and gel content measurements. The IR absorbance peak at 1640 cm−1 disappears at lower radiation dose indicating that the grafting and crosslinking reactions take place through double bonds. Some carbonyl groups are formed during irradiation. The concentration of carbonyl group increases with the radiation dose and the level of multifunctional monomers. The grafting level of TAC onto EVA determined from IR absorbance peak at 1565 cmx−1 remains almost constant with the variation of radiation dose and increases with TAC level. The gel content increases with radiation dose, but changes marginally with TMPTMA and TAC levels. The percent gel content increases linearly with vinyl acetate content in EVA.
Strain Dependence of Dynamic Mechanical Properties of Carbon Black-Filled Rubber Compounds
Authors: Ulmer J. D.
Published: February 2011

The strain dependencies of dynamic mechanical properties of carbon black-filled rubber compounds have been modeled by Kraus. Evaluation of the Kraus model with carbon black loadings up to 110 phr shows that it provides a fairly good overall description of elastic modulus, G′, as a function of strain, γ. The model description of G′ strain dependence improves with decreased carbon black loading, and is very good with carbon black loadings of 50 phr and less. The model description of viscous modulus strain dependence, G″(γ), is less successful than the G′(γ) description. Several empirical modifications of the viscous modulus model are examined. The most improved model is a very good approximation to viscous modulus over a wide experimental strain-range. Its utility, and that of the Kraus G′(γ) model, are illustrated through calculation of simple shear dynamic properties from torsion property measurements on a solid cylinder, where the strain amplitude varies across the specimen radius. The models allow transformation of the apparent moduli, reported as functions of strain amplitude at the cylinder's outer edge, to their true counterparts, G′(γ) and G″(γ), as functions of uniform strain amplitude. Although the G′(γ) and modified G″(γ) models apply to a wide range of experimental strains, some uncertainties associated with each model's accuracy remain, and there are inconsistencies in the relation of one model to the other. Reservations associated with the models might be resolved through refined treatments of the test specimen geometries.
Viscoelastic Behavior of Styrene-Butadiene-Styrene Block Copolymers in Temperature Range of Glass-Rubber Transition of Styrene Block
Authors: Nakajima N.
Published: February 2011

Dynamic mechanical measurements were performed with styrene-butadiene-styrene (SBS) block copolymers, Kraton D-1101 and D-l 102. Isochronal data were obtained from −130 to 85°C in the tensile mode at 1 Hz and from 60 to 160°C in the shear mode at 1 rad/s. The isothermal measurements were also performed at 60, 90, 120, 140, and 160°C in the frequency range of 0.0316 to 100 rad/s. The results suggest that the two polymers have different morphologies although the styrene content and the diblock content are about the same for both polymers. Kraton D-1101, which has 1.5 times higher molecular weight, has 3–5 times higher rubbery modulus, compared to D-1102. The lower molecular weight polymer, D-1102, appears to have a larger amount of the mixed phase at the boundary. This is suggest by the lower temperature of the “domain disruption”, Tdd and the higher magnitude of tan δ at Tdd. This explains the difference in the rubbery moduli of the two polymers.
Chemical Modifications of Rubber Surfaces: XPS Survey of the Reactions of Trichloroisocyanuric Acid at the Surfaces of Vulcanized Elastomers
Authors: Lawson David F. , Kim Kyung J. , Fritz Tammy L.
Published: February 2011

X-ray photoelectron spectroscopy (XPS or ESCA) was used to examine the outermost 100 A˚ of selected elastomer substrates, and to classify the predominant reactions that occur there between the substrates and trichloroisocyanuric acid (TCICA). About four monolayers deep, this surface region represents the locus of interfacial and adhesive processes. From these experiments, we concluded the following: (1) at the outermost surface of NR, substitution reactions of TCICA predominate, but a minor amount of addition is also evident; (2) addition and substitution reactions compete on the surfaces of the butadiene-containing polymers, BR and SBR; (3) no detectable functionalization by TCICA takes place on EPDM or CIIR — polymers which lack sufficient olefinic sites for surface modification; (4) isocyanuric acid or other nitrogenous residues are present on treated surfaces before washing; (5) reconstruction of functionalized surfaces may occur upon swelling for extended periods; (6) surface oxygen levels in these experiments were variable, and could not be relied upon as indicators of the functionalization chemistry.
A New Carbon Black-Rubber Coupling Agent to Improve Wet Grip and Rolling Resistance of Tires
Authors: González L. , Rodríguez A. , de Benito J. L. , Marcos A.
Published: February 2011

The compound p-aminobenzenesulfonyl azide was developed as a new type of carbon black to rubber coupling agent. Its addition to rubber compounds increases resilience and moduli while reducing abrasion loss. The behavior of this coupling agent is confirmed by the dynamic mechanical response of the vulcanizates—the rubber Tg is shifted to higher temperatures. Rubber compositions containing this coupling agent may be used in tire treads to reduce rolling resistance and improve wet skid resistance. These attributes were estimated from dynamic property measurements.
Styrene-Butadiene Rubber Filled with Fluorinated Carbon Black: Part II. Effect of Curative Level
Authors: Ames K. , Gibala D. , Hamed G. R.
Published: February 2011

The cure and tensile properties of sulfur vulcanized styrene-butadiene rubber filled with a conventional furnace black or a fluorinated black have been determined. Compositions with the fluorinated black and normal curative levels exhibit retarded cure compared to corresponding ones with the furnace black. This is due to a reaction between the sulfenamide accelerator and the fluorinated black. Notwithstanding, a fluoro-filled composition with no curatives substantially crosslinks when molded at 150°C. Thus, fluoro-black filled specimens have competing effects toward crosslinking. On the one hand, crosslinking is inhibited by reaction with the accelerator, while, on the other hand, the fluoro-black itself can cause crosslinking.
Injection Molding of Rubber Compound with Rheology Affected by Vulcanization: Part I. Material Characterization
Authors: Isayec A. I. , Wan M.
Published: February 2011

Rheological behavior of rubber is highly sensitive to the thermal history and cure kinetics. Rheological characterization for SBR compound is carried out using a capillary rheometer and modified Mooney viscometer. The viscosity function, which is not only temperature and shear-rate dependent but also cure-level dependent, is constructed. A modification of Cross model is proposed and verified to predict the rheological and chemorheological behaviors of SBR compounds. This rheological characterization is combined with vulcanization kinetic characterization. The parameters of vulcanization are obtained from DSC measurement under several nonisothermal conditions. The significance of correcting for temperature lag in the DSC measurements and the corresponding rate-of-vulcanization lag resulting from the nonisothermal DSC scan is illustrated. The proposed rheological function is further modified to incorporate the temperature- and state-of-cure-dependent yield behavior of rubber compounds at low shear rates. The proposed model is suitable for use in the simulation of processing operations.
Injection Molding of Rubber Compound with Rheology Affected by Vulcanization: Part II. Modeling and Experiment
Authors: Wan M. , Isayev A. I.
Published: February 2011

Experimental and theoretical results are reported on the effect of vulcanization on viscosity and yield stress during cavity filling with an SBR compound. Rheological and vulcanization models were utilized in simulation of the cavity filling process. Numerical schemes was based on the hybrid approach of control volume finite-element and finite-difference techniques. The pressure profiles at various locations along the flow path in the mold during cavity filling were obtained by conducting the experiments at various mold and inlet temperatures and mold injection speeds. It was found that the predicted pressure profiles followed the trend determined in the experiments. Comparing two versions of the modified Cross viscosity models — with and without the effect of cure on viscosity — it appears that use of a viscosity model which accounts for the cure-effect improves the accuracy, and thus the usefulness, of the cavity pressure prediction models. Evolution of the state-of-cure in the postfilling process are predicted and compared with the state-of-cure in moldings. The predicted results on the development of the state-of-cure during the postfilling stage show good agreement with the experimental data. The rubber compound exhibits yield behavior during cavity filling at very low injection speeds. The modified Cross model was further extended to include the yield stress and was implemented in the simulation program. In the case of low injection speed, the results showed a significant improvement in the prediction of cavity pressure, compared with the earlier reported predictions.
Thermoelastic Generalization of Isothermal Elastic Constitutive Models for Rubber-Like Materials
Authors: Zeng Nianning , Haslach Henry W.
Published: February 2011

Existing thermoelastic constitutive models are not able to predict important thermal properties of rubbers. For example, the modified entropic elasticity theory fails to predict that the temperature coefficient of stress, the energetic contribution to the stress, and the specific heat at constant deformation depend on both deformation and temperature. A class of thermoelastic constitutive equations is proposed that generalizes given isothermal models and predicts the temperature and deformation dependence. The Helmholtz free energy is written as the sum of the isothermal energy function, but with temperature-dependent material moduli, and a function of temperature. Conditions on the Helmholtz energy are given to ensure that three inversion effects which characterize rubber are predicted. As an application, an isotropic, homogeneous, mechanically incompressible thermoelastic constitutive equation is generalized from the isothermal Mooney-Rivlin model. The three uniaxial thermal inversion effects are successfully reproduced by this model.
Porosity in Rubber, a Review
Authors: Kasner A. I. , Meinecke E. A.
Published: February 2011

An overview of the causes and effects of porosity in rubber has been presented. The formation of porosity in rubber can be attributed to the heterogeneous nucleation and diffusion controlled bubble growth. The process proceeds simultaneously with vulcanization, so bubble formation in viscous fluids and in crosslinked rubber has been used to elucidate the mechanism. Porosity is caused by the supersaturation of rubber with volatiles and by insufficient external pressure during vulcanization. Some of the sources of these volatiles have been described. The effects of compounding, mixing and processing on porosity have been covered, and various methods of detecting and preventing porosity have been reviewed. Finally, the effects of porosity on the mechanical properties of rubber have been described.
Recent Advances in Anionic Synthesis of Functionalized Elastomers Using Functionalized Alkyllithium Initiators
Authors: Quirk Roderic P. , Jang Sung Hoon , Kim Jungahn
Published: February 2011

The results described herein demonstrate the advantages of functionalized initiators with respect to the efficiency of α-chain-end functionalization and the ability to effect post-polymerization functionalization and linking reactions with the living ω-carbanionic chain ends. Not all functionalized initiators are useful, however, because either: (a) they are not soluble in hydrocarbon solvents; or (b) they are not reactive enough to initiate polymerization at rates which are competitive with propagation to prepare polymers with narrow molecular weight distributions and controlled molecular weights; or (c) they are either too difficult to prepare or too expensive to prepare to be readily available for commercial elastomer production. The advantages of using funcitonalized initiators, however, should encourage further scientific and technological developments in this area.