bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Oriented Platy Filler on the Fracture Mechanism of Elastomers
Authors: Eldred Roger J. 
Published: February 2011

Abstract
Through an investigation of tension fatigue failure modes, oriented platy fillers have been found to provide elastomers with a unique failure mechanism which allows the elastomer to resist destructive crack growth. Samples of chlorosulfonated polyethylene containing talc as a reinforcing agent failed in an interlaminar shear mode, parallel to the applied stress. This fracture pattern resulted from diversion of the classical Griffith-type crack which would normally proceed perpendicularly to the stress. The theoretical criterion for diversion requires the adhesive fracture energy, Gad, in the plane of the diverted crack to be about one-tenth of the cohesive fracture energy, Gco, in the plane of the Griffith crack. Measured values of the fracture energies determined by 180° peel (Gad) tests and trouser tear (Gco) tests showed that the talc-filled elastomer satisfied the criterion. However, the criterion was met, not by the introduction of planes of weakness in the lateral direction (thereby reducing Gad), but by a more than five-fold increase in the cohesive fracture energy over that measured for a control containing carbon black as reinforcing agent. Examination of the fractured surfaces by scanning electron microscopy showed that the increase in Gco was due to the many energy absorbing fracture paths down which the tear was diverted as it advanced through the elastomer. Besides exhibiting high tear energies, the elastomer was found to be highly insensitive to stress risers such as razor cuts. The combination of tear resistance and insensitivity to flaws leads to a prediction that elastomers containing oriented platy fillers will exhibit increased strength and durability. This first practical system affording crack diversion has special application to hoses and topologically similar shapes such as boots and sleeves.
Elastic Behavior of a Rubber Layer Bonded between Two Rigid Spheres
Authors: Gent A. N. , Hwang Y-C. 
Published: February 2011

Abstract
Finite-element methods (FEM) have been employed to calculate the stresses set up in a thin rubber layer, bonded between two rigid spheres, when small tensile or compressive deflections are imposed. Values of stiffness have been calculated for various spacings of the spheres, i.e., for various thicknesses of the rubber layer. They are in good agreement with earlier experimental measurements of compression stiffness and with the predictions of an approximate theoretical treatment. However, they are strongly affected by small departures of the rubber layer from complete incompressibility. The highest dilatant stress (in tension) is found to be set up on the central axis, near the bonded surfaces, where internal failure has been observed to occur in similar bonded layers. For moderately thick layers, the axial tensile stress in the center of the layer is substantially higher than the lateral stresses. This feature suggests that the initiation of failure in this location may not obey the same criterion as for an isotropic stress field, and that a crack, once formed here, will propagate as a tear across the axis of symmetry.
Tandem Mass Spectrometry (MS/MS) for Analysis of Additives in a Rubber Vulcanizate
Authors: Lattimer Robert P. 
Published: February 2011

Abstract
MS/MS appears to have considerable potential as a means for improved direct mass spectral characterization of organic additives in rubber compounds. In this report, we have shown how daughter-ion, parent-ion, and neutral-loss scans can improve the specificity for identification of organic additive components in rubber vulcanizates. The use of MS/MS to reduce the “chemical noise” in the direct analysis of complex mixtures is demonstrated. MS/MS should not be viewed as a technique that will replace other mass spectral methods in rubber applications. For example, desorption ionization methods, GC/MS, LC/MS and high-resolution mass measurements will still have important roles. MS/MS can serve as a supplemental tool for direct mixture analysis that is both rapid and powerful.
Interactions in a Miscible Polymer Blend
Authors: Roland C. M. 
Published: February 2011

Abstract
Characterization of blends of atactic poly(vinylethylene) with cis-1,4-poly-isoprene provides unique insights into the factors governing the properties of polymer mixtures. While studies of polymer blends have heretofore focussed on systems in which chemical reaction between the components enabled miscibility, any properties arising from the blending of PVE with PIP are not a result of greater cohesive energy density or densification. It is also interesting to consider the different crosslinking reactivity of the main-chain unsaturation in PIP versus that of the pendant vinyl group of PVE, which can give rise to interesting network properties. These will be the subject of a subsequent communication. While it is clear that the Flory interaction parameter for these blends must be non-negative, direct determination of its magnitude is best accomplished through measurement of small-angle neutron scattering. Currently deuterated polybutadienes of varying microstructure are being synthesized to enable such experiments to be carried out, and thereby allow the effect of vinyl level on the miscibility and phase behavior to be quantified.
Two-Dimensional Simulation of Injection Molding of Rubber Compounds
Authors: Isayev A. I. , Sobhanie M. , Deng J. S. 
Published: February 2011

Abstract
A general finite-element and finite-difference computer program has been developed for filling a thin cavity during injection molding of rubber compounds. This program employs a finite-element representation of the cavity in the planar dimensions and a finite-difference representation in the gapwise direction and is capable of accommodating any type of rheological equation and vulcanization model and incorporates both viscous heating and heat of vulcanization. A detailed example of an application of this program has been presented for filling a quarter-disk cavity with rubber compounds having a viscosity function obeying a modified Cross model and curing kinetics according to our recently proposed nonisothermal vulcanization model. The pressure, velocity, and temperature fields and melt-front locations have been calculated during the filling stage. The evaluation of state of cure distribution in the rubber moldings has been predicted in the postfilling stage. Comparisons of the prediction of the model with experimental data regarding pressure distribution, melt front position, and distribution of degree of cure in molded parts will be presented in the near future.
On the Role of Bound Rubber in Carbon-Black Reinforcement
Authors: Hamed Gary R. , Hatfield S. 
Published: February 2011

Abstract
A simple model of filler dispersion has been used to approximate particle spacing and the portion of rubber that is restricted as a result of particulate reinforcement. For N330 black, which has an equivalent radius of 20.2 nm, the critical concentration (in SBR of Mw=344 000) for coherent carbon-gel formation upon solvent immersion is 30 phr. At this level of filler, particle-particle spacing is approximately the diameter of the average SBR random coil. In the second part of the study, compositions in which portions of free rubber had been extracted were compared to conventional mixes at the same black concentrations. Conventional and extracted vulcanizates had similar cure behavior and resistance to deformation, however, extracted samples, with excessive bound rubber had reduced strengths, consistent with the presence of inherent flaws. Apparently, the extracted samples, which are torn apart upon mastication are unable to fully reknit together even after compression molding and vulcanization.
Synthesis and Properties of Ring Polybutadienes
Authors: Roovers Jacques 
Published: February 2011

Abstract
Much of polymer science is concerned with the linear joining of monomers and the properties of the new materials that emerge from this process. Of almost equal importance is the formation of tridimensional networks as the result of branching and crosslinking reactions. Ring formation has always been considered an unavoidable consequence of extensive crosslinking and, from the theoretical point, it is often neglected. Nevertheless, rings may contribute to the network properties by means of permanent entanglements. Indeed, rings alone can form special permanent networks without any chemical connectivity between the rings. The interest in flexible ring polymers has grown considerably in recent years with 32, 21, and 34 papers published in 1985, 1986, and 1987 respectively, dealing equally with experimental or theoretical aspects, although the theoretical and experimental papers do not always address the same problems. Most significant has been the work of Semlyen and his coworkers on ring poly(dimethylsiloxane) with molecular weights up to 30 000. This is not very much above the entanglement molecular weight of poly(dimethylsiloxane) (Me=12 000) but the low Tg and chemical inertness of the polymer made it ideally suited for ring-in-network entrapment studies.
Dilutability, a Potential Method to Analyze Polyurethane Elastomers
Authors: Oberth Adolf E. 
Published: February 2011

Abstract
Evidence presented in the foregoing study indicates a strong dependance of dilutability on the fraction of effective chains. There is some dependence on the level of crosslinking and, perhaps, on solvatibility of the polymeric network in question. Thus, it is possible that networks prepared from different prepolymers but with the same FEC might show some difference in dilutability. This is a difficult question to answer, as well-characterized prepolymers that could serve as a standard are not available. Dilutability should be particularly useful in quality-control type applications, where lot to lot differences of essentially the same prepolymer are assessed.
Detection of the Molecular Orientation in Nonvulcanized and Vulcanized Natural Rubber Compounds by the Low-Temperature X-Ray Method
Authors: Udagawa Y. , Ito M. 
Published: February 2011

Abstract
The low-temperature x-ray method can detect the orientation of NR molecules in both vulcanizate samples and nonvulcanizate samples of NR compounds. The presence of carbon black is important for causing the orientation. NR molecules orient in the direction of stretch-relaxation in the case of uniaxially fatigued vulcanizates or in the direction of shear in the case of nonvulcanizates prepared by various processing methods. The orientation of NR molecules in nonvulcanizates usually disappears when vulcanized, but a fairly large extent of molecular orientation remains, even after vulcanization, if there exist crosslinks in the oriented nonvulcanizate and the sample is prevented from shrinkage.
Determination of Crack-Growth Characteristics Using the Angled Testpiece
Authors: Muhr A. H. , Thomas A. G. 
Published: February 2011

Abstract
The anticipated advantages of the angled testpiece have been borne out with some important provisos. For sufficiently thin testpieces and high strain-energy release rates, it is possible to use the angled testpiece geometry and the machine described to determine the cyclic crack-growth characteristics without directly measuring the crack length or carrying out auxiliary elasticity measurements. The modifications to the theory for thicker test pieces (for which the buckling force is significant) should allow the technique to be applied, but one of the main advantages over the other techniques (the avoidance of auxiliary elastic measurements) is then lost. It has also become apparent that working at low strain-energy release rates with a machine of this sort calls for a very stable temperature. For this reason, the machine's capability to do such measurements has not yet been assessed. There is broad agreement between results from the various techniques for both time-dependent crack growth (angled, pure-shear, and trouser testpieces of SBR gum) and cyclic crack growth (angled, pure shear, and tensile testpieces of SBR gum and NR gum). However, although the fracture mechanics approach appears to be generally of considerable value in expressing the crack-growth properties of rubbers, giving results that are essentially independent of testpiece geometry, the latter feature is not invariably found. In the present work, significant discrepancies were found for NR gum at low values of T. Such discrepancies are being investigated further.
The Application of Swollen-State CW-1H NMR Spectroscopy to the Estimation of the Extent of Crosslinking in Vulcanized Polymer Blends
Authors: Loadman M. J. R. , Tinker A. J. 
Published: February 2011

Abstract
It has been shown that the measurement of peak broadening in the 1H NMR spectra of swollen gum vulcanizates can be used as an estimate of the degree of crosslinking in the vulcanizate. A technique for applying this measurement to the individual phases of a vulcanized blend has been developed and validated, first for a physical mixture of gum vulcanizates of NR and NBR and then for a vulcanized, gum blend of these two rubbers.
Mean-Field Calculations of the Dynamic Mechanical Properties of Heterogeneous Elastomer Blends
Authors: Mazich K. A. , Killgoar P. C. , Ingram J. A. 
Published: February 2011

Abstract
A method for calculating the dynamic mechanical properties of elastomer blends with co-continuous structures has been presented. The calculations are based on Kerner's packed-grain model for composite media. Comparisons of theoretical calculations with experimental data show that this model closely approximates the viscoelastic properties of blends with a co-continuous structure, at least in the glass-transition regions of the respective blend components. We have also shown that the storage modulus of co-continuous blends may be well-represented by a discrete-particle model. This result can be misleading, however, if the storage modulus alone is calculated and compared with experimental data. A comparison of viscoelastic data (log E′ and tan δ) with calculation clearly distinguishes the models and indicates that the packed-grain model is the correct representation of the structure of co-continuous blends. The agreement between theory and experiment reported above was principally found in the glass-transition regions of the respective components in the elastomer blend. We extended the comparison well into the rubbery region and found that the agreement between Kerner's mean-field theory and the experimental data was poor, particularly for the loss tangent. Different relaxation mechanisms (relaxations over greater periods of time) are available to the blend in the rubbery region of viscoelastic response, and these mechanisms are apparently not accounted for in the mean-field calculations.
Degradation Behaviors of Natural, Guayule, and Synthetic Isoprene Rubbers
Authors: Lin Sin-Shong 
Published: February 2011

Abstract
The degradation behavior of three isoprene based rubbers, NR, GR, and IR, under accelerated thermal and uv radiative environments have been investigated, and the extents of the degradation are compared. The oxidative degradation introduces oxygen atoms into the elastomer chains to form carbon—oxygen linkages via hydroxyl, ether, carbonyl, and carboxyl functional groups. Some polynuclear aromatic compounds are also found on the severely thermal-degraded surfaces. The secondary atomic constituents of the vulcanizates, such as nitrogen and sulfur, also oxidized during the aging. The formations of sulfate, sulfite, and zinc oxide are observed, but no direct oxidation of nitrogen to nitro or nitroso groups is detected. The atomic surface concentration of carbon decreases significantly (1/2 to 2/3), while that of oxygen increases substantially (2 to 3 times) during the oxidative aging test. The concentrations of minor elements, S and Zn, increase to a few percent more than two fold, but that of N increases only slightly. The surface enrichment of these elements is probably derived from segregation, migration, and oxidation. The element F is present with varying concentrations (less than 10%). The element is derived from remnants of the mold releasing agent containing fluorine. The flex cracking is observed on some severely thermally degraded specimens, but none is observed under the uv radiation. The formation of aromatic cyclic compounds from these linear chain elastomers is positively identified from the π−π* excitation peak in the XPS spectra. The thick, hardened laminated layers are the visual evidences of the formation. In short, NR is found to be slightly more stable than GR and IR in the present aging test. However, the thermal and uv radiation stabilities are strongly influenced by the rubber formulations. The presence of carbon black tends to nullify the differences existing between the degradation behavior of these vulcanizates. The antioxidant in the formulation is believed to be more effective than the characteristics and the origins of the gums in controlling the degradation behavior.
Alkyllithium-Initiated Polymerization of Trans-1,3,5-Hexatriene and Copolymerization with Styrene
Authors: Quirk Roderic P. , Bhatia Rajeev 
Published: February 2011

Abstract
The results reported herein established the complexity of the alkyllithium-initiated anionic homopolymerization, styrene copolymerization and styrene block copolymerization of 1,3,5-hexatriene in comparison to the controlled, predictable behavior observed with dienes. As a result of 1,6- and 1,2-enchainment, conjugated diene units are formed along the polymer backbone which can react with the living carbanionic centers to produce branched polymers as indicated in Equation (1). The general effect of solvent on microstructure, as indicated by infrared spectral analyses, is analogous to that of dienes in that 1,2-addition is increased in polar versus hydrocarbon solvents. The observation of branching reactions suggests that conjugated trienes may be useful as branching agents for copolymerizations or linking reactions analogous to the behavior of divinylbenzenes.
Bonding of Butyl and Nitrile Rubber by in situ Copolymer Formation
Authors: Chung M. H. , Hamed G. R. 
Published: February 2011

Abstract
We summarize and conclude the following: 1. The T-peel adhesion between uncrosslinked layers of IIR and NBR is rate and temperature dependent. Failure is interfacial at low rates; bulk cohesive tearing of the rubber occurs at intermediate rates, while interfacial failure returns at high rates. 2. Adhesion data could be reduced to mastercurves with experimentally determined shift factors which were in reasonable agreement with those calculated from the universal WLF equation with a Tg=−69°C. 3. At the lowest test rates, peel specimens containing in situ-formed copolymer had lower strength than those without the copolymer. This is probably due to the easy slippage of the segments of the low-molecular-weight copolymer in this regime. 4. At intermediate rates, in situ copolymer had no effect on peel strength; specimens failed by bulk cohesive tearing of rubber, whether or not the copolymer was present. 5. At high rates, peel specimens containing the copolymer exhibited improved strengths. The behavior is consistent with previous results on the autohesion of elastomers. Interdiffused chains of relatively low molecular weight are only capable of providing strong adhesion when the test speed is sufficiently rapid.
Long-Term Studies of Rubber Materials by Dynamic Mechanical Stress Relaxation
Authors: Björk Folke , Dickman Ola , Stenberg Bengt 
Published: February 2011

Abstract
The measurement of dynamic stress relaxation can reveal otherwise hidden weaknesses in rubber materials. The stress relaxation of the minimum of the restoring foce has the undesirable characteristic of being greater than the continuous stress relaxation. An increase in the amplitude of the deformation increases the decay in the minimum values of the varying retractive stress, and an increase in the prestrain makes it smaller. The normalized curve for continuous stress relaxation is found to lie somewhere between the normalized curves for the maximum and minimum of the retractive stress. The measurement of network density on specimens aged under continuous and dynamic stress relaxation indicate that the mechanism behind the degradation of the rubber network is the same in both cases. The relations between intermittent, continuous, and dynamic stress relaxation give a reasonable estimate of the dynamic stress relaxation from the other two when proper values of the coefficients are used. This relation says that results both of continuous and intermittent stress relaxation are important for predicting the life time of a dynamic seal. The relations offers an explanation of the differences between maximum and minimum values obtained during the measurement of dynamic stress relaxation and their relation to continuous stress relaxation. From these relations it can be concluded that a rubber intended for dynamic seals should contain neither reversion nor secondary crosslinking. Crosslink density should be high in order to overpower effects on crosslinking of factors in the surroundings.
Light Scattering from Gels
Authors: Patterson G. D. 
Published: February 2011

Abstract
The basic principles necessary to understand light scattering from gels are now well understood. The experimental techniques necessary to measure light scattering from gels are now highly developed. Yet there are many issues that need to be clarified in practice. The spatial correlations that exist in the polymer concentration in a gel need extensive further study. Gel samples with only intrinsic permanent concentration fluctuations need to be prepared. Defects due to dust, microsyneresis or other nonintrinsic inhomogeneities must be eliminated. Then careful measurements of R(q) should yield the necessary information about the microstructure of the gel. The value of the osmotic Poisson ratio is now well understood for gels at rest. Further work needs to be done on samples in partial states of swelling. More work appears promising in the study of critical concentration fluctuations in gels as well.