bluuebunny/crossref_metadata_2025 huggingface dataset:
Short Silk Fiber Reinforced Natural Rubber Composites
Authors: Setua D. K. , De S. K.
Published: February 2011

(1) The resorcinol-hexa-silica bonding system is essential for NR-silk fiber systems. (2) Mechanical anisotropy is observable only at higher fiber loadings (20 phr and above) in NR-silk fiber systems. (3) In composites containing a sufficient amount of bonding agents and fibers for tensile anisotropy to be observed, tensile failure occurs by both fiber breakage and debonding. (4) Addition of silk fiber to NR causes (a) increase in hardness, (b) reduction in resilience and elongation at break, (c) increase in heat buildup and set, and (d) increase in tear resistance. (5) The aging resistance of silk fiber-reinforced NR composites is excellent only beyond a fiber loading of 20 phr. (6) Mill shrinkage and green strength of NR improve, while Mooney viscosity and scorch time increase with the addition of silk fiber to NR.
Study of Cure Synergism of the Thiocarbamylsulfenamide-Dibenzothiazyl Disulfide Accelerator System in the Vulcanization of Natural Rubber
Authors: Pal D. , Adhikari B. , Basu D. K. , Chaudhuri A. K.
Published: February 2011

N-cyclopentamethylenethiocarbamyl-N′-cyclopentamethylenesulfenamide (CPTCS) and dibenzothiazyldisulfide (MBTS), as binary accelerators in a mixture have been found to provide significant mutual enhanced activity with regard to modulus, tensile strength, hardness, and elongation at break in the vulcanization of NR gum stocks. The synergistic activity of the CPTCS-MBTS system is very much dependent upon the accelerator ratios, concentration of sulfur and accelerator, as well as the temperature of vulcanization. Investigations carried out with the Monsanto rheometer also corroborate the above results. It is suggested that the synergism arises out of the interaction between CPTCS and MBTS which produces intermediate accelerators. N,N-Diethylthiocarbamyl-N′-cyclohexylsulfenamide (DETCS) in conjunction with MBTS, produces similar results in the vulcanization of NR. Structural characterization of the vulcanizates obtained at 140 and 160°C reveals that predominantly monosulfidic linkages are obtained with CPTCS or DETCS and MBTS combinations. The intermediate combinations, at near equimolar concentration of the two accelerators, exhibit maximum crosslink density. An attempt has been made to correlate physical properties with crosslink density as well as various types of crosslinks.
Strain-Time Correspondence: Critical Examination of the Principle and Its Application to Classification of Gum Elastomers
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

The first step in elastomer processing is compounding, where the behavior of gum elastomer has a decisive influence. For this reason, characterization of processability of gum elastomers in the compounding step is very important. The elastomer behavior in compounding may be described as large deformation and fracture. These behaviors have been subjects of our fundamental studies. This paper is concerned with the deformation aspect of the processability, but not the fracture. The focal point of the study is how to describe a large deformation in a concise, systematic manner. The discovery and subsequent adoptation of the “strain-time correspondence principle” enables us to achieve this objective, namely, the viscoelastic data obtained with different instruments, employing different modes of deformation, were shown to be transformed to a master curve encompassing wide ranges of time scale. The implication of the achievement, although not fully proven, is two-fold; first, if one type of deformational behavior is observed over a sufficiently wide range of time scale, any other type of deformational behavior may in principle be calculated. Second, the master curve may be used as an indirect expression for processability of a given elastomer, although the master curve itself does not describe the deformations in the processing. In demonstrating the strain-time correspondence, various examples of master curves were shown. In these, the experimental data had rather large errors, although the scattering was random. The primary reason for the scattering of the data lies in the use of high-speed tensile stress-strain measurements, in which the experimental errors were rather large. For this reason, a more accurate demonstration of the strain-time correspondence principle is attempted in this work. A cone-and-plate assembly was used in rotational, oscillatory, and relaxation modes of testing with both small and large deformations.
Rubber-Thermoplastic Compositions. Part VIII. Nitrile Rubber Polyolefin Blends with Technological Compatibilization
Authors: Coran A. Y. , Patel R.
Published: February 2011

The results of this work suggest a practical route to hot-oil-resistant thermoplastic elastomers based on NBR and a polyolefin resin (such as polypropylene). Although these two types of polymer are normally grossly incompatible with each other, a melt-mixed blend thereof is technologically improved by the presence of a small amount of a compatibilizing block copolymer which contains both polar and nonpolar segments. Ideally, the block copolymer should contain molecular segments of the types of polymers to be compatibilized. The compatibilizing block (graft) copolymer can form in situ during melt-mixing. Dynamic vulcanization (during melt-mixing) of a compatibilized NBR-polypropylene blend produces a thermoplastic elastomer with mechanical properties about as good as those of a corresponding composition of EPDM and polypropylene (two polymers which are nearly mutually compatible in a thermodynamic sense). The compatibilizing NBR-polypropylene graft copolymer might act by reducing (molten-state) interfacial tension at the NBR-polypropylene interface and also by increasing the interfacial adhesion in the “solidified-state” composition during its use. The hot-oil resistance of the compatibilized NBR-polypropylene thermoplastic vulcanizates is excellent. Also, the NBR-polypropylene compositions can be blended with thermoplastic vulcanizates based on EPDM and polypropylene to obtain thermoplastic elastomeric compositions which exhibit both good hot oil resistance and low temperature brittleness characteristics.
Reactivity Optimization of Prevulcanization Inhibitors
Authors: Sullivan A. B. , Davis L. H. , Maender O. W.
Published: February 2011

A series of phthalimide-based prevulcanization inhibitors has been used to probe the relationship between MBT reactivity and inhibitor performance efficiency in NR accelerated with TBBS. Based on these results, there appears to be a reactivity window for best performance. For the phthalimide series, it occurs with secondary alkyl mercaptans. Inhibitors with MBT reactivity below the optimum are less effective because they do not compete with the accelerator for the autocatalyst. The activity also falls off at higher reactivities. There are two explanations for this behavior. First, as proposed by others, the very reactive inhibitors may not completely survive mixing and precuring, so that some of the inhibitor is lost to unproductive side reactions. Over and above this effect, the performance declines because the MBT is trapped less securely when the BtSSR is derived from a more reactive mercaptan. Although other leaving groups were not evaluated in this work, it is clear that reactivity optimization can be achieved with any leaving group, L, by proper selection of -SR. For example, in the work of Morita and Sullivan with thioketal type prevulcanization inhibitors, it was demonstrated that primary alkyl and aromatic mercaptans were required to achieve optimum inhibitor activity.
The Effect of Reptating Species on the Tear Strength of Elastomeric Networks
Authors: Hamed G. R. , Ogbimi F.
Published: February 2011

The “snake-like” motion which an unattached polymeric chain undergoes as it diffuses through a molecular network has been termed “reptation”. Several studies of the low-strain dynamic properties of networks containing reptating chains have been carried out. At relatively high temperatures or low rates of deformation, reptating species may contribute greatly to the mechanical loss of elastomeric networks because the reptating chains are sufficiently mobile to adjust their conformations greatly, and this motion causes the dissipation of mechanical energy into heat. On the other hand, at sufficiently low temperatures or high rates of testing, entanglement couplings of the reptating chains with the network (or with themselves) behave essentially as crosslink points. In this case, the dynamic mechanical properties of networks containing reptating chains are virtually the same as those without reptating chains. Although the low-strain viscoelastic properties of networks containing reptating chains have been studied, there has been no systematic investigation of the tear strength of such systems. It is the purpose of this paper to report such a study. Mixtures of butyl rubber (IIR) with polyisobutylene (PIB) were crosslinked with sulfur, leaving the PIB molecules free to reptate in the butyl rubber networks. The trouser tear strengths of these materials were then determined as a function of the molecular weight and concentration of the reptating species, the crosslink density of the host IIR network, and the test temperature. In addition, the tear strengths of networks in which the IIR was mixed with inert low molecular weight diluents (of varying solvent power) before vulcanization were also measured.
Quinoid Curing of Butyl and Natural Rubbers
Authors: Gan L. M. , Chew C. H.
Published: February 2011

The vulcanization of butyl and natural rubbers by p-dinitrosobenzene (DNB), p-quinone dioxime (GMF) and p-quinone dioxime dibenzoate (dibenzo GMF) oxidized by various oxidants was investigated. Good curing efficiency (E=1.2) was achieved for a butyl system containing GMF or dibenzo GMF oxidized by red lead (Pb3O4). It was estimated that about 85% of the combined quinoid agent was in the form of crosslinks and the remaining 15% might be present as pendant groups. In contrast to butyl rubber, NR could also be cured slowly by GMF or dibenzo GMF alone. Simple ZnO or PbO was effective in activating dibenzo GMF to produce quinoid-NR vulcanizates with good scorch safety. But the highest crosslink density was obtained from equimolar dibenzo GMF/Pb3O4. Low crosslinking efficiency (E=3–6) was generally observed in the quinoid-NR systems. Quinoid vulcanization mechanisms are discussed. The crosslinks consist mainly of the anil structure in the butyl system, while azoxy crosslinks might also be present in the NR system.
Emulsion Polymerized Polydimethylsiloxane
Authors: Graivek Daniel , Huebner David J. , Saam John C.
Published: February 2011

The observations are consistent with the formation of grafts of hydrophilic silicates to the silanol chain ends at the surface of the PDMS emulsion particles prior to removal of the water. The silicates may be introduced into the system directly or through the alkaline colloidal silica, which contains appreciable amounts of dissolved silicates. Monomeric, or possibly dimeric, silicate grafted to more than one chain end could migrate to the interior of the PDMS emulsion particle to form further crosslinks. Grafts to higher molecular weight silicates and silicate grafts bearing anionic change would be solvated with water and tend to remain at the oil-water interface. These grafts can provide additional stabilization to the cured particles. The dialkyltin carboxylate is pictured as playing a role in the grafting and crosslinking process. Evaporation of the water would eventually cause collapse of the stabilizing elements surrounding the PDMS particles to allow contact between particles of silica and the silicate grafts coating the particles of PDMS. The ensuing formation of interparticle hydrogen bonds and siloxane bonds, which can occur readily at room temperature under alkaline conditions, completes the formation of the elastomer network. This is represented in Figure 8. The resulting elastomeric network thus consists of the original emulsion particles, now crosslinked, which are surrounded by a hydrophilic hard phase of silicates and silica. In some aspects, this resembles the morphology proposed for films from dried natural latex.
Vulcanization Studies of Elastomers Using Solid-State Carbon-13 NMR
Authors: Patterson Dwight J. , Koenig Jack L. , Shelton J. Reid
Published: February 2011

With the use of solid state carbon-13 NMR, changes in the structure of natural rubber and cis-polybutadiene were observed spectroscopically. Cis-trans conversion has been shown to occur in the naturaal rubber by the rearrangement of the allylic free radical. At least four structurally different methyl groups have been detected in the crosslinking of natural rubber by dicumyl peroxide, which indicates that the simple combination of allyic free radical is an oversimplification of the curing process. Quaternary aliphatic carbons have been detected which results from double bond migration. Polybutadiene showed only methine and methylene carbons present in the crosslinked network with a small amount of methyl end-groups. The increase in the line width of the highly crosslinked elastomers was shown to be dominated by the carbon-hydrogen static dipolar interaction. Fourier-transform infrared analysis observed the formation of a molecular complex between dicumyl peroxide and polybutadiene. The formation of trans double bonds was observed in the infrared spectra of polybutadiene. Weak broad bands around 1320 cm−1 were observed in the difference spectrum of cured rubbers and were assigned to carbon-carbon crosslinks. From the structural interpretation of spectra obtained from solid state carbon-13 NMR and Fourier-transform infrared, models are proposed for the crosslinked networks of natural rubber and polybutadiene, obtained from peroxide vulcaniation.
Effect of Cure Systems and Reinforcing Fillers on Dynamic Mechanical Properties of Chlorobutyl Elastomers for Potential Vibration-Control Applications
Authors: Capps Rodger N.
Published: February 2011

The effects of four different types of cure systems upon the physical and viscoelastic properties of chlorobutyl elastomers have been investigated. Five different types of carbon black fillers have also been evaluated. Effects of carbon black loading were also studied. The basic conclusions that may be drawn from the experimental determination of the viscoelastic properties of these elastomers and the subsequent use of these to evaluate their potential in various vibration-control applications are as follows: (1) Both the red lead-thiourea cure system, and the resin-cure system give vulcanizates with very similar physical and dynamic mechanical properties. Use of a resin cure is preferable to a red lead-thiourea cure due to the much shorter cure time and lower cure temperature. (2) Chlorobutyl elastomers possess suitable viscoelastic properties for vibration-control applications, due to the diffuse nature of the glass-rubber transition in this class of polymer. Use of other types of fillers, such as silane-treated mica, may be useful in further broadening the temperature-frequency damping range of these materials by introducing additional damping mechanisms. (3) Increased loading of a moderately reinforcing carbon black improves the transmissibility and extensional damping characteristics of CIIRs. An intermediate loading of approximately 35 phr appears to work best for the constrained-layer configuration considered here. (4) An experimental determination of the temperature and frequency dependence of the viscoelastic properties of polymeric materials, coupled with the type of modeling described here, provides a convenient means of assessing the relative merits of various types of polymeric materials in the design of vibration-control systems.
Effects of Storage on the Molecular Weight of Rubber Contained in Guayule
Authors: Black L. T. , Swanson C. L. , Hamerstrand G. E.
Published: February 2011

Although this was a limited study based on only two guayule varieties, the trends relating to rubber degradation with storage time and temperature condition are clear. Whole guayule plants, and especially chopped guayule awaiting processing, cannot be stored for long periods at elevated temperatures without at least partial degradation of the molecular weight of the rubber in the plant. These studies are now being expanded to determine if the observed differences in stability are, in fact, attributable to variety or are the result of postharvest treatment or agronomic practices.
A New Look at Measurements of Network Density
Authors: Hayes Robert A.
Published: February 2011

A two-solvent method for determining the polymer-solvent interaction parameters independently of stress-strain data is described. The values obtained are much lower than those reported previously. Network densities calculated from swelling data and these interaction parameters are in good agreement with those calculated from the return portion of a hysteresis loop at high elongations.
On the Origin of Strain-Induced Crystallization
Authors: Göritz D. , Kiss M.
Published: February 2011

DSC measurements on stretched polybutadiene held at fixed length show two melting regions. The first is shifted a small amount to higher temperatures relative to the isotropic endotherms. The occurrence of two melting regions is considered to be evidence for an inhomogeneous deformation of the rubber. The melting point increases on stretching are taken to be due to entropy effects.
Effect of Butyl Rubber Coating on Accelerated Aging of Natural Rubber
Authors: Stenberg Bengt , Peterson Lars-Olof , Flink Per , Björk Folke
Published: February 2011

From these results it is possible to draw the following conclusions: The primary protection against thermo-oxidative degradation comes from the butyl coating. The butyl coating works mainly by stopping diffusion of oxygen from the surrounding air, which is more important than stopping the antioxidant from diffusing out of the rubber, since the antioxidant effect is small.
Compression of Rubber Layers Bonded between Two Parallel Rigid Cylinders or between Two Rigid Spheres
Authors: Gent A. N. , Park Byoungkyeu
Published: February 2011

An approximate theoretical treatment is presented for small compressions of a rubber layer bonded between two opposed curved rigid surfaces, cylindrical or spherical in shape. The deformation is treated in two parts: a simple compression; and shearing deformations necessary to maintain zero slip at the bonded surfaces. Forces and hydrostatic pressures due to the second deformation are found to be the major terms for thin layers. Predicted compression stiffnesses are compared with measured values for various initial separations of the two rigid surfaces (and hence various thicknesses of the rubber layers).
Extensibility of Black Filled Elastomers
Authors: Ahagon Asahiro
Published: February 2011

Unique empirical relations are found to exist between the extension ratio at break λb and the crosslink density ν λb ∝ ν−0.75 in the absence of gross strain induced crystallization, and λb ∝ ν−0.2 in the presence of gross strain-induced crystallization. With black-filled elastomers, the modulus at 100% strain, M100, is proportional to the crosslink density over a wide temperature range. Thus, unique empirical relations exist between λb and M100 of black-filled elastomers; λb ∝ M100−0.75 in the absence of gross strain-induced crystallization, and λb ∝ M100−0.2 in the presence of gross strain-induced crystallization. The proportionality constants can be used as convenient measures of the extensibility in material evaluation on a constant modulus basis.
Fatigue Crack Growth in High Load Capacity Rubber Laminates
Authors: Stevenson A.
Published: February 2011

The main conclusion from the work reported here is that the rate of fatigue crack growth in high load capacity and high shape factor rubber/steel laminates loaded in compression can be predicted from a tearing energy (i.e., fracture mechanics) theory of fracture. This conclusion is not just a point of scientific interest but is potentially of practical value in the design of many rubber engineering components. There is now a growing body of evidence that by adopting suitable simplifying assumptions, the fracture mechanics approach can successfully describe the fracture behaviour of rubber composites even when the detailed stress distributions are complex. A very similar approach has been successful in the study of fracture in 2-ply rubber-cord laminates—a situation that would at first sight seem intractable. These results encourage confidence that fracture mechanics could become much more widely used as a basis for the design of rubber engineering components than it is at present.
Measurement of Dynamic Bulk Modulus and Phase Angle Using ESPI
Authors: Holownia B. P. , Rowland A. C.
Published: February 2011

The measurement of the dynamic bulk modulus of elastomers by the direct method using ESPI has been achieved within the frequency range of 50–1000 Hz. The two types of Nitrile rubbers tested show that the dynamic bulk modulus increases with frequency, but the rate of increase depends on the type of rubber used. A novel method of measuring the phase angle using ESPI was successful in principle, although the resolution error on the oscilloscope prevented definite conclusions being reached regarding its variation with frequency.
Test of Strain-Time Correspondence Principle with Gel-Containing Elastomers
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

With four NBR samples and one EPR, oscillatory measurements and stress-growth measurements were performed, the former being at very small deformation and the latter leading to large deformation. The Rheometrics mechanical spectrometer was used with a cone-plate fixture. The temperature was 100°C. The stress-growth data of NBR's, converted to complex viscosity-frequency data through the application of stress-time correspondence principle, were in good agreement with those observed in the oscillatory measurement. Thus, the stress-growth data including the large deformation were “linearized” to form a master curve. With the EPR sample, such a linearization was not necessary. The stress-growth data were adequately treated with the linear viscoelastic theory up to shear stresses approaching the steady state. The difference in behavior between the NBR's and EPR is caused by differences in type and extent of long branching and gel present in the samples.
Butyl Networks Containing Unattached Polyisobutylene Chains: Part II, Correlation of Tear, Tensile, and Hysteretic Properties
Authors: Hamed G. R. , Ogbimi F.
Published: February 2011

Butyl networks containing either unattached polyisobutylene chains or a low-molecular-weight plasticizer have been made by crosslinking butyl rubber in the presence of one of these diluents. With dodecane as a plasticizer, tear strength is reduced both because of a decrease in the density of load-bearing chains and diminished hysteresis. On the other hand, when the diluent is a high-molecular-weight polyisobutylene, tear strength is enhanced if the test rate is sufficiently high. In this case, the polyisobutylene chains are load bearing (at least initially) before slipping at higher strains to relieve local crack-tip stresses and blunt the propagating tear. This hysteretic mechanism delays the onset of crack propagation, thereby enhancing the fracture energy. However, at low tear rates, in which there is adequate time for the unattached chains to relax such that they bear little load and hysteresis is minimized, tear strength decreases with increasing free-chain content—much the same as occurs with a low-molecular-weight diluent. Finally, under conditions in which the average propagating tearing energy is enhanced for the butyl-polyisobutylene system, the initiation tearing energy is increased only moderately. This suggests that crack-tip blunting during steady-state tearing is at least partially responsible for increases in strength in the presence of free chains.
The Mechanics of Short Fiber-Reinforced Composites: A Review
Authors: Abrate S.
Published: February 2011

Proper constitutive equations and transformation laws to describe short-fiber-reinforced composites have been reviewed. The mechanisms of load transfer between matrix and fibers have been presented. Micromechanics analyses were discussed in order to predict mechanical properties of the composite given those of the constituents. Such approaches have been used successfully for cord-rubber and particulate-filled elastomeric composites. The use of such methods for short-fiber reinforcement has been limited so far. The problem is more complex in this case, but the need for a reliable method is even stronger in order to evaluate the influence of a parameter change on the various mechanical properties. Elastomeric composites pose a greater change due to the large ratio of fiber-to-matrix moduli, and predictions may not always be accurate. However, the interest of micromechanics approaches is that they allow determination of the effect of a perturbation in the parameters about a given level. Areas for future work include the development of micromechanics methods to determine viscoelastic constants and strength under various loading conditions. The development of a multiaxial strength criterion is needed, and basic fatigue failure mechanisms have to be studied.
Bound Rubber and Carbon Black Reinforcement
Authors: Dannenberg E. M.
Published: February 2011

The first description of the bound rubber phenomenon was by Twiss in 1925, who made the observation that the resistance of carbon black-natural rubber mixes to solvents was related to improved mechanical properties. Boiry studied many of the factors influencing the insolubilization of NR by fillers including type and amount of fillers, and mixing and testing variables. In 1937 J. H. Fielding of Goodyear developed a so-called “bound rubber” test because of his interest in the possibility of chemical bond formation between fillers and rubber. During the start of the U.S. synthetic rubber program, Baker and Walker reported in 1945 an insolubilization of SBR when mixed with carbon black significantly greater than the amount of normal gel in the unfilled elastomer. They were also the first to report that the amount of gel increased with increasing molecular weight and that a selective adsorption of high molecular weight material occurred. Since that time, many investigations have confirmed these findings with other elastomers, and theories of “bound rubber” formation have been based on these observations. The early concept that “bound rubber” is a gel of carbon black particles held together in a three-dimensional lattice by longer interparticle polymer molecules is still valid. The nature of the segmental attachments of the polymer molecules to the filler surfaces now appears to be both physical and chemical, depending upon filler surface activity and chemical functionality, and the chemical composition and functionality of the elastomer. Regardless of the type of interaction, the bonding is essentially permanent and can only be disrupted by extraction with good solvents at high temperatures.
Chemical Stress Relaxation of NR Networks Prepared in the Swollen State
Authors: Suh Kyung-Do , Oikawa Hidetoshi , Murakami Kenkichi
Published: February 2011

From the experimental results of the present investigation, it is apparent that two kinds of networks which have a different three-dimensional network structure give quite different behavior of chemical stress relaxation, even if both networks have the same network chain density. The difference in three-dimensional network structure for the two kinds of rubber arises from the degree of entanglement, which changes with the concentration of the polymer chains prior to the crosslinking process. The direct cause of chemical relaxation is due to the scission of network chains by degradation, whereas the total relaxation is caused by the change of geometrical conformation of network chains. This then casts doubt on the basic concept of chemorheology which is represented by Equation 2.
New Extensional Rheometer for Elongational Viscosity and Birefringence Measurements: Experimental Results and Interpretation
Authors: Froelich D. , Muller R. , Zang Y. H.
Published: February 2011

This study shows that by using the recoverable strain, one can represent the elongational viscosity ηe=σe/˙ε as a linear function of the quantity λr2−λr−1, characteristic of a neo-Hookian material. The elongational viscosity is then the sum of two contributions: One is related to the entropic elasticity of the chains through the recoverable deformation of the sample. The other is related to the shear viscosity at a shear rate equivalent to the extensional strain rate. In absence of a simple theoretical justification for such an equation, more experiments are being undertaken with different polymers and rubbers in order to understand how the recoverable strain is related to the chemical structure of the chain and to check the generality of the equation.
Visualization of Textile Reinforcing Materials in Cord-Rubber Composites after Dissolution of the Rubber with Peracids
Authors: van Blokland P. H. G. M.
Published: February 2011

The examples illustrate that the dissolution method is a helpful tool for making damage to cords visible both in laboratory tests and in reinforced rubber goods that have been used in practice. However, from these examples, the conclusion may not be drawn that the damage shown is characteristic of the test or type of reinforcing material. After laboratory testing, a considerable amount of damage can be found, and the examples only serve to show the suitability of peracids for the removal of vulcanized rubber from the cords. To understand the fatigue mechanisms, a lot of work is still required.
Temperature Dependence of Viscoelastic Properties of Carbon-Black-Filled Rubbers in Small Shearing Deformations
Authors: Arai Koichi , Ferry John D.
Published: February 2011

Measurements of dynamic storage and loss shear moduli G′ and G″ (0.12 to 2 Hz) and shear relaxation modulus G(t) (up to 104 s) have been made on six vulcanized and one unvulcanized carbon-black-filled rubber compounds over a temperature range from −22.5° to 63°C. The maximum shear strain in the oscillatory deformations was less than 0.005 and in the stress relaxation measurements, 0.015. The temperature dependence of viscoelastic properties could not be fully described in terms of horizontal shifts (αT) of logarithmic time or frequency scales. It could, however, be largely described by vertical shifts (ST) corresponding to uniform temperature dependence of the magnitudes of contributions to modulus from a spectrum of relaxation mechanisms. There were some departures from this behavior, especially in a blend containing two rubber species and in the unvulcanized compound at long times. The temperature dependence of the ST shift factors followed the van't Hoff equation with values of ΔH from 5.9 to 14.7 kJ/mole, attributable to a heat of dissociation of contacts between particle aggregates. The slow relaxation over many logarithmic decades of time scale in the rubbery zone of viscoelastic behavior is attributed to adjustments of such contacts by Brownian motion, which leave the density of the structure unchanged as shown by constancy of the differential dynamic modulus measured by superposed small oscillating deformations.
The Effect of Cure Variables on Cis/Trans Isomerization in Carbon-Black-Reinforced Cis-1,4-Polybutadiene
Authors: Devlin Edward F.
Published: February 2011

This work confirms the results that Corish has published on gum vulcanizates. While the carbon-black-reinforced stock apparently cures at a faster rate at this temperature than the gum vulcanizates did at 273°F (134°C), the observed trends and the extent of isomerization (7%) are in agreement.
Characterization of Polymers by GPC-Lalls. I. Computer Simulation of Fractionation of Branched Polymers by GPC
Authors: Shiga S. , Kato E.
Published: February 2011

Simulation formulae are derived for determining polymer structure in an infinitesimal fraction of GPC elution volume. If a sample is ideally fractionated, the MWD of the momentarily eluted polymer depends chiefly on the DNBP of the injected sample. Statistically branched polymer indicates almost monodisperse MWD at the fraction. Separation is always sharper in the higher molecular weight side of a MWD curve than is in the lower side. Even if the DNBP is broader, the average NBP can be correctly estimated by the method proposed by Kurata et al., as far as the DNBP is nearly Gaussian. When a sample is fractionated by a real GPC with axial dispersion, the MWD of the eluted polymer is mainly controlled by the instrumental spreading function, unless the sample has an extremely wide DNBP or a special MWD. The average NBP by the Kurata et al. equations is expected to be more reliable if a polydisperse linear polymer that yields chromatogram similar to the branched sample is applied as a reference material.
Silane-Grafted / Moisture-Curable Ethylene—Propylene Elastomers for the Cable Industry
Authors: Cartasegna S.
Published: February 2011

The present study has shown the capability of VTMOS grafting and moisture crosslinking of EP Elastomers. These capabilities are very large and have been shown to be dependent on various parameters. In EP copolymers, the crosslinking potential appears to be a function of the ethylene content, molecular weight, and molecular weight distribution. In the case of diene containing terpolymers, the process is shown to be limited by the diene content of the polymer through probable parasitic condensation reactions of grafted alkoxy silane. The good performance of the EP elastomers in silane-grafting/moisture-crosslinking can be also utilized in the modification of LDPE when crosslink rate improvement (elimination of hot-water treatment/hot-water treatment time reduction) or higher flexibility and lower shrinkage are needed. The positive results of this study made possible the development of EP elastomer compounds using silane-grafting and moisture-crosslinking for electrical applications. In Table IX and Table X are reported two EP elastomer compounds respectively for low-voltage and medium-voltage cable insulation applications. The key features of the above mentioned two EP elastomer compounds are the following: • high flexibility (comparable to conventional peroxide cure compound) • good mechanical properties • very fast extrusion (for productivity) • easy/versatile processing • high crosslinking state (set properties) • crosslinkable in ambient conditions.
Stress-Relaxation Measurements on Rubbers in Compression. Equipment and Methodology
Authors: Armah J. C. , Birley A. W. , Fernando K. P. , Hepburn C. , Tahir M.
Published: February 2011

The techniques available for the measurement of stress relaxation in rubbers had been reviewed and the consequent methodology assessed. The conclusion, that none of the equipment was entirely satisfactory, led to the development of new instrumentation which eliminated many of the shortcomings of the current equipment and allowed new and improved methods of test to be adopted which are particularly suited to long-term tests in a variety of environments. The work has drawn attention to the unsatisfactory state of the standards in the field.
Effect of Oxygen on the Tear Strength of Elastomers
Authors: Gent Alan N. , Hindi M.
Published: February 2011

Many measurements have been made of the strength of simple vulcanizates of common elastomers, both under steady and intermittently applied loads. In both cases, the strength is governed by dissipative processes, particularly those arising from internal molecular motions and from stress-induced crystallization. Thus, the intrinsic strength of the molecular network is observable only under nondissipative conditions, at high temperatures and extremely low rates of tearing. Under these circumstances, the strength of rubber networks is in reasonably good agreement with theoretical calculations based on the dissociation energy of main-chain bonds in the molecular strands comprising the network.
Structure and Biosynthesis Mechanism of Rubber from Fungi
Authors: Tanaka Yasuyuki , Mori Makio , Ute Koichi , Hatada Koichi
Published: February 2011

The structure of both terminal units and alignment of the isoprene units give conclusive evidence for the initiation and termination mechanisms of rubber formation in fungi. As shown in Figure 4, the polymerization is estimated to start from trans, trans-farnesyl pyrophosphate and proceeds by successive condensation of IPP to form isoprene units in the cis configuration. The termination is presumed to occur by direct esterification of polyisoprenyl pyrophosphate (PIP-PP) or dephosphorylation of PIP-PP followed by esterification with fatty acids. It is remarkable that the hydroxyl terminal group corresponding to the saponification product from the esterified terminal group was observed in the rubber samples by extraction from sporophores of L. volemus after storage for 2–3 days in a refrigerator without the addition of salt. In these samples, unidentified 13C-NMR signals were also detected. These findings suggest that the direct esterification of PIP-PP is more likely as a termination reaction. It also suggests the occurrence of a chemical or biochemical modification of both terminal groups and the main chain during storage. This is the first information on the termination mechanism of controlling the molecular weight of natural rubber.
Structural Characterization of Ethylene-Propylene-Diene Rubbers by High-Resolution Pyrolysis Gas Chromatography
Authors: Yamada T. , Okumoto T. , Ohtani H. , Tsuge S.
Published: February 2011

Ethylene-propylene-diene rubbers (EPDMs) are now used for various purposes because of their excellent resistance to ozone, weather, and heat. Therefore, many kinds of EPDMs are provided as commercial polymers. Consequently, reliable methods for the structural characterization of EPDM have been needed in the fields of material development, process control, and quality assurance of the cured products. The iodine value method is generally used to determine the diene content in EPDMs. However, it is too time consuming to be a routine method. Until now, spectroscopic methods such as IR and NMR are generally used for the study of the composition and the sequence length distributions in EPDMs. Levine and Haines determined the content of ethylidenenorbornene (ENB) in ethylene-propylene-ethylidenenorbornene rubbers (ENB-EPDMs) by IR. Florence and Loustalot investigated ethylene-propylene-1.4-hexadiene rubbers by NMR. However, these spectroscopic methods often encountered the difficulties in the analysis of vulcanized rubbers since they were insoluble and usually contained many kinds of additives such as curing agents, plasticizers, stabilizers, and fillers. On the other hand, owing to the recent development of excellent pyrolyzers and highly efficient fused-silica capillary columns, pyrolysis-gas chromatography (PyGC) has become a powerful tool to give unique information about structures of high polymers. Furthermore, PyGC is advantageous to the practical analysis of insoluble polymeric materials such as vulcanized rubbers.
Ammonia-Induced Tensile Set and Swelling in Silica-Filled Silicone Rubber
Authors: Vondráček P. , Pouchelon A.
Published: February 2011

A new experimental procedure has been proposed for estimating the level of surface interaction activity of silica fillers in silicone rubber vulcanizates. The method is based on a simultaneous effect of the constant tensile strain and ammonia. The sample of silica-filled silicone rubber vulcanizate is deformed in an ammonia atmosphere for 72 h. The ammonia cleaves the specific silica—PDMS hydrogen attachments. The bonds are formed in new positions in the deformed polysiloxane network between silica surface free silanols and PDMS after evaporation of ammonia. The resulting permanent deformation (tensile set) provides a measure of silica surface reactivity (interaction activity) with respect to a given silicone elastomer. It has been proven that the ammonia-induced tensile set is governed by the same mechanism as the increase of toluene swelling under an ammonia atmosphere. The results indicated that water plays an important catalytic role in the ammonia-induced cleavage of silica-PDMS attachments. It is recommended to use an NH4OH atmosphere to obtain the maximum cleavage when estimating the contribution of polymer-filler bonding (hydrogen or physical) to the total crosslink density in silica-filled silicone rubber.
Finite-Element Calculations on the Stress of an Aramid Cord in a Clamped and Elongated Goodrich Block Fatigue Specimen
Authors: Winkler E. M. , de Jong M. C.
Published: February 2011

In the Goodrich Block Fatigue Test, a rubber block containing a tire cord is cyclically compressed and extended. The retained strength of the cord, obtained after a certain running time, is a measure of the fatigue resistance of the cord. In this test, the compression and extension is applied to the clamps of the block. This induces an indirect loading of the cord through shear forces in the rubber. This cord load varies along its length and depends on variables such as cord modulus and diameter and rubber modulus and cannot be obtained experimentally. A three-dimensional finite-element model together with a calculation procedure is presented. With these, not only the overall force-displacement behavior of the GBF specimen can be predicted, but also the detailed cord stress distribution, both for clamping and elongating the specimen. Only three different linear finite-element computations have to be performed. Results at any arbitrary elongation of the specimen are obtained by superposition of these calculation results. The accuracy can be enhanced by combining them with the measured value for the elongation at which the cord is just fully tensioned. Experimental verification was carried out for an aramid cord with a diameter of 0.6 mm. The presented model produces results that agree well with the measured values for the force on the specimen (both for clamping and elongating) and for the breaking force of the cord. Clamping of the specimen causes compression of the cord in the center area of the block. For the aramid cord used in this study, this compression area has a length of about 10 mm. At an elongation of approximately 0.4 mm (the corresponding extension setting of the machine is 3%), the cord is just fully tensioned. When elongating the block a certain amount above this setting, the stress in the center of the aramid cord is only 6.3% of the stress of a cord which would be strained the same amount as the block. In this study, no account has been taken of temperature and viscoelastic effects, which may play an important role in the actual fatigue test!
Production, Properties, and Stability of NR Latices
Authors: Pendle T. D.
Published: February 2011

The natural latex concentrates used for the manufacture of dipped goods, such as gloves, are products both of nature and technology. They are made using the “field” latex obtained from the tree species Hevea Brasiliensis of the Euphorbiacaea family. As the name implies, this tree originates from Brazil but is today most intensively cultivated in the far east (Malaysia, Indonesia, etc.) and in parts of Africa. Nature provides the raw material, field latex, which is then modified, preserved, concentrated, and tested by scientifically developed methods to produce the commercial concentrates. At least 500 000 metric tons, dry rubber weight, of natural latex concentrates are produced annually at present, and this quantity is expected to increase steadily in the future. Field latex can be concentrated by creaming, evaporation, and centrifugation, but the latter method predominates, and this paper will be confined to concentrates obtained by this process. This paper reviews the current situation of NR latex production, the typical properties of centrifuged concentrates, and also presents results of recent research relating to the understanding of the colloidal stability of NR latex.
Determination of the Degree of Hydrogenation in Hydrogenated Nitrile-Butadiene Rubber (HNBR)
Authors: Marshall A. J. , Jobe I. R. , Dee T. , Taylor C.
Published: February 2011

A number of analytical techniques are available for the measurement of the residual unsaturation in HNBR polymers. However, to insure that high-quality HNBR products are produced, it is necessary to use a standard procedure throughout the industry which is quick, accurate, and precise. The two infrared methods discussed in this paper show good agreement with one another, as shown by the respective mean values in Table V. Thus, in the absence of a totally independent and universally accepted standard procedure, this crosscheck between two separate and absolute measurements for the degree of hydrogenation is the best possible support for their precision (1H-NMR spectroscopy for IR method #1 and IR spectroscopy for IR method #2). The two iodometric methods each exhibit significantly poorer precision ( 10 to 100 times) than either of the infrared methods. This is not surprising, since these wet chemical techniques are not discriminatory to any type of unsaturation present in the HNBR nor are they inherently precise due to the large number of test variables. This lack of precision, and the fact that these wet chemical methods are time consuming, eliminates them from consideration as quality-oriented testing methods for measuring the degree of hydrogenation in HNBR. Both IR methods exhibit good reproducibility which greatly exceeds that of iodometry. The statistical analysis of these IR techniques does not present any significant differences between them. IR method #1 requires virtually no preparation time, since extraction of the HNBR rubber samples is not required. Furthermore, IR method #1 is less susceptible to impurities and subsequent user interpretation, since the hydrogenated butadiene peaks at 723 cm−1 are not required for the analysis. In conclusion, due to simplicity and speed of the analysis, IR method #1 is much more robust for use by the industry and their customers for the measurement of carbon-carbon double-bond unsaturation in HNBR.
Spectroscopic Studies of the Structures of Butyl and Bromobutyl Rubbers
Authors: Cheng D. M. , Gardner I. J. , Wang H. C. , Frederick C. B. , Dekmezian A. H. , Hous P.
Published: February 2011

The 1H-NMR results show that the majority of the isoprene units of butyl rubber are incorporated in 1,4 addition. Approximately 6% of the isoprene units undergo 1,2 enchainment. Based on our study of blends of polyisoprene with polyisobutylene, 1H-NMR provides an excellent method for determining isoprene unsaturation in butyl rubber. Furthermore, based on 1H-NMR measurement, FTIR procedures have been developed to quantify the isoprene content of butyl polymers and the concentrations of the three major bromobutyl isomers.
Finite-Element Analysis in Design with Rubber
Authors: Nicholson David W. , Nelson Norman W.
Published: February 2011

The application of finite-element analysis in rubber technology has been discussed. The intent has been to combine features of a tutorial, an exposition, and a survey. Attention has been limited to homogeneous cured rubber products. The finite-element method is a prime constituent of computer-aided engineering, and, as such, it is a powerful resource for the design and analysis of rubber components. Owing to rapid progress and greater availability of computer hardware and software and, in particular, computer-aided design systems, finite-element analysis is eminently practical. Difficulties such as incompressibility and large deformation, the subjects of a substantial literature, appear to have been successfully addressed. Finite-element analyses of rubber products such as seals and bearings have been published widely, often along with experimental validation. However, note that the implementation of the hyperelastic element in major codes has occurred recently. And, at the time of this review, in several codes, the elements are still quite limited, for example, to plane strain. Thus, it appears that rubber technology has yet to see the full impact of the finite-element method.