bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the Fine Structure of Rubber Vulcanizates Fatigued by Repeated Force
Authors: Udagawa Y.
Published: February 2011

A novel method to detect the orientation of SBR molecules in SBR vulcanizates has been developed. It has been found that the swelling agent, benzene, crystallizes in SBR vulcanizates (oriented crystallization), reflecting the orientation of SBR molecules. This method is named the “Benzene Crystallization Method”.
Determination of Sequence Distribution of Styrene Units in Cured SBR
Authors: Tanaka Yasuyuki , Nunogaki Kazuki , Adachi Junichi
Published: February 2011

The sequence distribution of styrene units in cured SBR was analyzed by high-resolution GPC measurement on the ozonolysis products obtained by ozonization of finely powdered samples suspended in methylene chloride followed by reductive degradation with lithium aluminum hydride. The conversion of the ozonolysis products, which were soluble in the organic layer, approximated that of an uncured sample when 100% of the calculated amount of the ozone required to react with the double bonds in the butadiene units was used. The conversion decreased slightly as the amount of ozone was increased to 220%. The fraction of monad, diad, and triad styrene sequences which were flanked by 1,4-butadiene units, and styrene long sequences—observed at the GPC exclusion limit of 3×103—leveled off at about 100 to 150% of the required ozone. In the GPC fraction corresponding to long styrene sequences, the residual butadiene units, as measured by 1H-NMR, decreased from 77 to 47% as the ozone increased from 3.7 to 80% of the required amount. Ozonization was believed to proceed rapidly on the surface of the swollen rubber particles in the initial stage, and then it progressed gradually into the inner part upon introducing excess ozone. Cured SBR samples, with and without carbon filler, showed sequence distributions of the styrene units which were similar to the uncured sample when 130% of ozone was used.
From Vulcanization Model to Process Control
Authors: Veltman B. , Van Hastenberg C.
Published: February 2011

A simulation model has been presented, which is able to predict, quantitatively, the degree of cure, if temperatures in the product rise above a start temperature of the vulcanization reaction and if a correct initial temperature is used as input. The importance of controlled injection temperature and monitored cavity pressure for process reproducibility have been elucidated. The Cure Command was tested and was found to be useful within limits. A superior process control has been suggested, which could be realized nowadays using microcomputer technology.
Sulfur Vulcanization with Two Plateaus—Formation of an Inhibitor during Vulcanization?
Authors: Loo C. T. , Porter M. , Tidd B. K.
Published: February 2011

Efficient sulfur vulcanizing systems based on thiazolesulfenamide accelerators derived from secondary amines show unusual and complex vulcanization kinetics in NR. This feature does not appear to have been reported previously. Depending on the nature and purity of the accelerator, the ratio of accelerator to sulfur, the cure temperature, the type of rubber being used, and the presence of other additives, two distinct periods of crosslinking may be evident, separated by a more or less well-defined plateau. This plateau is longer and more distinct if the accelerator is pure, its ratio to sulfur is high, the cure temperature is low, and there are no other additives present. Sulfenamide accelerators derived from both primary and secondary amines may give rise to this behavior in rubbers other than NR. The observed behavior has been shown to be due to the formation, during the first cure period, of an extractable crosslinking inhibitor. The structure of this inhibitor is still in doubt, but the present balance of evidence favors it being an aminodithiobenzothiazole [Structure (1)] or a dithiobisdialkylamine [Structure (2)] or a polythio variant of those structures.
Blends of Dissimilar Rubbers—Cure-Rate Incompatibility
Authors: Coran A. Y.
Published: February 2011

The mechanical properties of a vulcanizate of a blend which comprises both a high-diene rubber such as NR and an ozone-resisting concentration (at least 30 to 40 wt.% of the polymers) of EPDM can be greatly improved if the EPDM is chemically modified by the action of maleic anhydride. The effect of the EPDM modification of the vulcanizate properties is to give increased tensile strength, improved fatigue resistance, and reduced hysteresis and set. The excellent ozone resistance which results from the presence of about 30 to 40% unmodified EPDM is also obtained when the modified EPDM is used. Good results are obtained when only 1 to 2% (as a wt.% of EPDM) of maleic anhydride is used in the modification of the EPDM. Good results are obtained when only part of the EPDM is modified by the action of maleic anhydride. However, best results are obtained when all of the EPDM is treated with maleic anhydride. The ozone-resisting effect provided by the incorporation of a para-phenylenediamine antidegradant into a 60/40 NR/EPDM blend vulcanizate is overwhelmed and made obscure by the very large beneficial effect due to the presence of the EPDM. However, the use of an antidegradant such as 6PPD is still necessary because of its ability to impart a great improvement in fatigue life.
A Rheo-Optical Study of the Influence of Additives on Crystallization Rates in Cis-1,4 Polyisoprene
Authors: Chen Yun-Jin , White James L. , Min Kyonsuku , Nakajima Nobuyuki , Weissert Frederick C.
Published: February 2011

A rheo-optical study of the influence of additives on crystallization rates in synthetic cis-1,4 polyisoprene (IR2200) at room temperature is presented. Nine different additives at a 1% concentration were examined. This study has found many additives which seem to be effective in enhancing the rate of stress-induced crystallization in IR2200. We have found that there is a good relation between enhancement of green strength and fraction of stress-induced crystallinity, ϕc, in IR2200 caused by additives.
Statistical Methods in Rubber Research and Development
Authors: Derringer George C.
Published: February 2011

As this article has demonstrated, statistical methods have considerable utility in rubber research and development. Such methods are cost effective and perhaps, more important, help the user to formulate questions in such a way as to make research programs more productive. The use of statistical methods in formulation development have been particularly fruitful. For example, without statistical methods, the compounders common task of simultaneously achieving a specific balance of cost, property levels, and processing behavior would be an expensive undertaking at best and hopeless at worst. Statistical methods help the practitioner make sound decisions in the light of often extreme variability in the data. This is especially the case when the data is fatigue, tensile strength, or some other fracture property of rubber. In the light of such broad distributions, hit or miss and one variable at a time strategies are seriously flawed. It is not hard to find a sequential study in which decisions about each trial were driven simply by changes due to random variability which were erroneously attributed to the intentional changes in variable level(s) from the previous trial. Such research studies are very similar to random walks. Many excellent and innovative studies are reported above. However, given the wide utility of statistical methods, these methods appear to be underutilized judging from the unexpectedly small number of papers which were found. Similarly, it is not difficult to find published rubber research which would not have benefitted by the use of statistical experimental design and/or data analysis. Fortunately, however, this appears to be changing. The increasing availability of good affordable software for personal computers makes it possible for good statistics to be done with less dependence on trained statisticians which are not available in many organizations. As this trend continues, the number of studies employing statistical methods will surely grow.
Silicone Rubber, Its Development and Technological Progress
Authors: Polmanteer Keith E.
Published: February 2011

This paper has described silicone rubber, its first commercial development in 1944, and its technological progress since then. Pioneering research on silicon opened the door to the development of silicone polymers and silicone rubber. The substitution of two methyl groups on silicon was present in the first examples of silicone rubber and still is the predominant organic group in commercial silicone rubber today. Silicone rubbers have filled a need in the marketplace because of their combination of unusual properties not found in other rubbers. The alternating inorganic main-chain atoms of silicon and oxygen, and the two pendant organic groups, primarily methyl, provide strong chain bonds, backbone flexibility, ease of side-group rotation, and low “inter” and “intra” molecular forces. This molecular makeup and properties thereof are primarily responsible for the observed performance of silicone rubbers. Many significant advances in silicone rubber have been discussed in chronological sequence to trace its history from 1944 to 1987.
Application of Finite-Element Analysis in the Design of Automotive Elastomeric Components
Authors: Morman Kenneth N. , Pan Tsung Y.
Published: February 2011

FEA provides more detailed information for design than can be possibly measured on an actual component part or computed using classical closed-form solutions. Based on this observation, FEA is an ideal means for developing concept designs. No parts are needed for FEA, while conceptual design evaluation using “cut and try” procedures of the past requires that component parts be molded for testing. Once a rough concept has been developed, FEA can be used more effectively to evaluate design modifications in less than the time required by “cut-and-try” iterations. The major benefit that is realizable from FEA is in time savings. Computer costs can be justified by factors such as efficiency and better component reliability and performance.
The Resolution of Binary Elastomer Blend Properties by Stress-Strain Modelling
Authors: Bauer R. F. , Crossland A. H.
Published: February 2011

For elastomer/elastomer blends in which the dispersed phase has a lower modulus than the matrix, it was shown that the phases are mechanically coupled in a simple parallel manner. Once the stress behavior of each blend component, cured separately, is known as a function of both strain and state of cure, the properties of the blend phases can be resolved unequivocally. This modelling technique, as applied to a 70/30 blend of NR/CIIR, showed that in this blend, curative migration increases the modulus of the NR phase by a factor of three.
Load, Speed, and Pressure Effects on Passenger Car Tire Rolling-Loss Distribution
Authors: Schuring D. J. , Clark J. D.
Published: February 2011

The procedure explained in this paper permits calculation of individual tire region contributions to rolling loss without altering the tire. Many different tire-build configurations can be considered using this technique. Different belt, bead, and subtread materials' contributions to rolling-loss distribution can be studied; different tire shapes and thicknesses can be considered. Only a single tire of each configuration need be built, and it can be retested if necessary. Results obtained here show that the tread region of the tire tested behaves differently than the other regions. Changes in tire pressure, load, and speed lead to changes in the remaining individual tire regions' contributions that are in the same direction as the overall tire loss. A tire design that is altered to accommodate new specifications may lead to an increase in rolling loss that is greater than some designated value. An analysis of the type presented here may show which region of the new tire design should be changed to bring the loss within desired limits. The heat-transfer coefficient of the tire in this model is a linear function of velocity, independent of tire load and pressure. We have confidence in this relation as the model results are derived from both loss measurements and tire surface temperature measurements made in the laboratory. The model output is based on fundamental heat-transfer precepts and treated mathematically by established analysis techniques.
Cure Modification Effected by Cycloalkylthioamines in the Vulcanization of NR Accelerated by Thiocarbamyl Sulfenamides and Dibenzothiazyl Disulfide
Authors: Das Prasanta Kumar , Datta Rabindra Nath , Basu Dipak Kumar
Published: February 2011

The role of the thioamines as retardera in the vulcanization of NR accelerated by the binary system comprising thiocarbamyl sulfenamide and MBTS has been investigated. Several thioamines, namely, cyclohexyl thiomorpholine (CM), cyclohexyl thiopiperidine (CP), cyclohexyl thiodibutylamine (CDBA), cyclohexyl thiodiphenylamine (CDPA), cyclohexyl thiodiisopropyl amine (CDIPA), dicyclohexyl dithiopiperazine (DCDPz), cyclohexyl thiodiethylamine (CDEA), and cyclohexyl thiodibenzopyrrole (CDBP) had been selected for the study. It has been observed that these thioamines provide better cure retardation than CTP and almost in all the cases, cure rates and torque values of the resulting vulcanizates are increased. It is further noticed that the vulcanizates obtained from the stocks containing CDEA, CDBP, and CDPA exhibit notably more heat and age resistance than those obtained from CTP. Some hplc studies were made to understand cure activation. MBT and N-oxydiethylenethiocarbamyl benzothiazole disulfide (OTBD) seem to activate cure, especially in the presence of thioamines. Antioxidants like di-β-napthyl-p-phenylenediamine (DNPD) and N-phenyl-N-sopropyl-p-phenylenediamine (PIPPD), when present in the respective stocks, further enhance both heat and age resistance properties of the resulting vulcanizates.
Prediction of Zero-Shear Viscosity of Linear Polybutadienes from the Crossover Point Using Doi-Edwards Theory
Authors: Rahalkar Ramesh R. , Tang Henry
Published: February 2011

Based upon the Doi-Edwards theory, a simple expression has been obtained for zero-shear viscosity in terms of the plateau modulus and the crossover frequency. There are no adjustable parameters in the expression. The model is in very good agreement with the zero-shear viscosity values for linear polybutadienes, the typical discrepancy being ∼5–10%. If the model can be validated for other linear amorphous polymers, it may become possible to estimate the zero-shear viscosity by measuring a single Theological parameter (the crossover frequency).
Resistivity of Rubber as a function of Mold Pressure
Authors: Thompson Corley M. , Besuden T. W. , Beumel L. L.
Published: February 2011

For this N550 carbon black, loaded over a narrow but typically used range, high molding pressure caused a decrease in electrical resistivity of several orders of magnitude. The earlier in the cure cycle the high pressure was applied, the greater was the decrease in resistivity. A suggested mechanism for the effect is the formation of covalent bonds between carbon-black particles that are pushed into closer proximity by the high mold pressure. This postulate is supported by the limited kinetic data available. Clearly, pressure applied to a rubber sample during molding must be given as careful consideration as the loading of carbon black when materials requiring high resistivities are prepared. Although it has not been pursued in this work, the effect of pressure on the electrical resistivity of conductive rubber formulations may be significant. Further work underway is addressing the effect of mold pressure on the electrical resistivity of other rubber compounds as well as loadings of some other types of carbon black.
Dynamic Testing and Reinforcement of Rubber
Authors: Funt J. M.
Published: February 2011

A series of experiments have been run to determine which mechanisms dominate carbon black reinforcement of rubber. A broad range of compounds using oil-extended and non-oil-extended rubbers and carbon blacks covering the spectrum of tread blacks have been tested. The results for measurements made in an all-SBR formulation are reported here. The primary experiment consisted of measurement of the dynamic modulus and hysteresis of the cured and uncured compounds over a broad range of frequencies, temperatures, and strains. Ternperatures ranged from −70°C to +90°C; frequencies varied from 0.01 to 10 Hz; double strain amplitudes varied from 0.5% to 35%. From a discussion of the literature and evaluation of the experimental results, two mechanisms have been found to control the primary effects of carbon black on rubber reinforcement, where reinforcement refers to a general enhancement of properties, such as modulus, as well as the tensile strength of the compound. Hydrodynamic interaction, which is the increase in properties caused by the modification of strain fields in the region of an aggregate, dominates the large-strain dynamic and tensile properties of the compound. The primary carbon black variable in this mechanism is the effective aggregate size, such as measured by tint, which controls the effective volume loading of the carbon black at a given weight loading of carbon black. At low strains, the modulus is even higher than that predicted from the hydrodynamic-interaction/effective-volume model. This additional reinforcement is caused by the entanglement network formed between the tightly absorbed bound rubber on the carbon black surface and the bulk rubber far removed from the surface. The main carbon black variables in this mechanism are surface area and surface chemistry. The strain dependence of modulus is caused by the breaking and reforming of effective crosslinks in the rubber forming a transition zone between the bound rubber and the bulk rubber. To a large extent, this mechanism is dominated by the rubber properties, such as molecular weight and molecular-weight distribution. However, the dynamics of the entanglement network may be modified by altering specific interactions between carbon black and rubber.
Development of Material Constants for Nonlinear Finite-Element Analysis
Authors: Finney Robert H. , Kumar Alok
Published: February 2011

The determination of the material coefficients for Ogden, Mooney-Rivlin, Peng, and Peng-Landel material models using simple ASTM D 412 tensile data is shown to be a manageable task. The application of the various material models are shown to be subject to the type and level of deformation expected, with Ogden showing the best correlation with experimental data over a large strain range for the three types of strain investigated. At low strains, all of the models showed reasonable correlation.
The Mechanism of Phenolic Resin Vulcanization of Unsaturated Elastomers
Authors: Lattimer Robert P. , Kinsey Robert A. , Layer Robert W. , Rhee C. K.
Published: February 2011

It is well known that during the sulfur curing of unsaturated rubbers, two competing reactions occur: (a) crosslinking or vulcanization, and (b) reversion or devulcanization. In the case of butyl rubber, these two competing reactions have been summarized in earlier reports. Tire curing bag (bladder) compounds are usually made of butyl rubber (IIR), a copolymer of isobutene and isoprene, with typically 1–5% of the diene monomer. Curing bags were originally manufactured using sulfur cures. The high temperatures (140–180°C) employed in tire curing caused reversion, however, and these bladders had very short service lives. The deterioration of the IIR bladders was evidenced by a gradual softening of the surface. A major technical advancement for increasing the service life of curing bladders was the development of phenol/formaldehyde (resole) resins for vulcanizing IIR. These resins can give IIR cures with very thermally stable crosslinks. The vulcanizates are essentially immune to reversion, even at the high use temperatures of tire curing operations. The basic curing resins used are generally 2,6-dihydroxymethyl-4-alkylphenols 1 or their condensation polymers 2 (Scheme 1). These materials are produced via the base-catalyzed reaction of the p-substituted phenol with formaldehyde. R is typically methyl, t-butyl, or t-octyl in commercial resins. The use of a blocking substituent in the para position maximizes the formation of o-hydroxymethyl groups. R′ is either methylene (—CH2—) or dibenzylether (—CH2—O—CH2—), depending on the conditions of the resin synthesis or the cure.
Diels-Alder Reaction Curing of Chlorobutyl Rubber by bis-Maleimides
Authors: Ho K. , Steevensz R.
Published: February 2011

Different bis-maleimides are found to have different efficiencies and reactivities in the crosslinking of CIIR in the presence of zinc oxide. Although the degrees of crosslinking of CIIR by bis-maleimides cannot be defined absolutely, some trends concerning the efficiencies of the crosslinking are evident. In general, the aromatic bis-maleimides gave higher degrees of crosslinking than the aliphatic analogs. The reactivity and crosslinking efficiency of an individual bis-maleimide is very much affected by its end-to-end chain length and its electronic distribution, resulting from the interaction between the maleimide groups, and from the interaction between the maleimide groups and other functional groups present in the same molecule. The longer the bis-maleimide molecule and the more electron deficient the maleimido double bond, the greater its effectiveness as a crosslinking agent. Other curing mechanisms, possibly including polymerization of the maleimido groups, appear to be operative when using aromatic bis-maleimides as curing agents for CIIR.
Nonseparable Behavior in Rubber Viscoelasticity
Authors: Sullivan J. L. , Mazich K. A.
Published: February 2011

New large-strain rubber viscoelasticity results for a filled and an unfilled IIR vulcanizate and previously published results for two NR gum vulcanizates have been discussed. The data show that the “mixed” response functions of large-strain stress relaxation, and the incremental storage and relaxation moduli do not demonstrate factorizability of time and strain effects. This is a consequence of the elastic and relaxation contributions in each of the mixed functions being different. The incremental dynamic data also show that the loss modulus for the filled IIR and unfilled NR vulcanizates (unavailable for the unfilled IIR) are separable functions of time and strain. This directly shows that the relaxation spectra for the filled IIR and unfilled NR vulcanizates are independent of strain for the deformations studied. In fact, it is argued that a necessary and sufficient condition for the relaxation spectrum to be independent of strain is that the loss modulus is a factorizable function of time and strain effects. The quantitative success of the Generalized Solid-Liquid (GSL) model in representing the viscoelastic behavior of the gum NR vulcanizate has been reviewed. Although the GSL model applies only to unfilled vulcanizates, it has also been successfully used to qualitatively interpret the results for the filled IIR compounds. Both successes are attributed to the physical assumptions intrinsic to the GSL model; more specifically, 1) the relaxation spectrum is independent of the state of strain, and 2) the deformational dependences of elastic and relaxation contributions to the overall response of the system need not be the same. Physical arguments justifying these assumptions have been covered. It has also been shown with the aid of the GSL model, that a material might exist which demonstrates factorizability in stress relaxation and incremental loss modulus behaviors but nonfactorizability in the incremental storage and relaxation moduli.
Solid-State Carbon-13 NMR Studies of Vulcanized Elastomers. VI. Relaxation in Sulfur-Vulcanized Natural Rubber
Authors: Andreis Mladen , Liu Juwhan , Koenig Jack L.
Published: February 2011

Molecular motions in sulfur-vulcanized NR are investigated by solid state 13C NMR relaxation techniques. Since the high-resolution spectra of crosslinked samples exhibit overlapping in the aliphatic region, a combined application of variable temperature spin-lattice relaxation measurements and the computer simulation of the overlapped spectral region is used in order to detect resonance signals. Motional restrictions introduced by crosslinks are investigated from the temperature dependence of nT1 relaxation times for individual carbons. The V-curves for all polyisoprene signals and for the detectable signals arising from the network units exhibit a similar general trend with increased curing time: curve broadening, shift of the minima to higher temperatures, and increase of the T1 min values. All the backbone carbons show quantitatively similar effects of vulcanization on the spin-lattice relaxation. At shorter curing times, motional restrictions for the methyl side group are more pronounced compared to the main-chain carbons. The experimental data suggest that the isotropic motion is strongly affected by the crosslinking. Librational motion is less affected, while the change in rotational motion has no significant influence on the relaxation curve. Although experimental data cover a relatively narrow temperature range, not sufficiently wide for a more accurate quantitative analysis, the results indicate that concepts of plural correlation times and a distribution of correlation times are applicable.
Fracture Morphologies of Carbon-Black-Loaded SBR Subjected to Low-Cycle, High-Stress Fatigue
Authors: Goldberg Alfred , Lesuer Donald R. , Patt Jacob
Published: February 2011

In the absence of a mechanical defect at the surface, failure is almost always initiated in the bulk of a sample at a material flaw. A variety of flaw morphologies are observed; however, the extent of cyclic damage could not be related to either flaw size or flaw type. Energy dispersive spectographic analysis did not reveal any differences in chemistry between a flaw site and regions remote from a flaw. The size and definition of a flaw increase with an increase in carbon-black loading. Initiation flaw sites are enveloped by fan-shaped or penny-shaped regions which develop during cycling. With the highly loaded carbon-black samples, these regions consist of concentric bands which increase in number and become more prominent with an increase in test temperature. This is attributed to the presence of knotty tearing. With low carbon-black loadings, the absence of any significant disorientations in the tearing paths during either a cycle or a series of cyclic events results in the absence of individual resolvable bands within the fatigue-tear regions. The size and morphology of a fatigue-tear region appears to be independent of the fatigue load or the extent of the damage (strength loss). By contrast, either an increase in cycling load or an increase in damage at constant load increases the definition of the fatigue-region morphology for all formulations of carbon black. The morphologies in regions leading to failure during the final cycle are identical to the morphologies of fractured surfaces obtained in conventional tensile tests—tear steps or ridges at low magnifications and slow crack-growth with coarse tear paths and fast crack-growth with fine tear paths at high magnifications. Morphologies typical of slow crack-growth are also seen within the banded (fatigue) regions. On the finest scale, the morphology can be described in terms of tearing of individual groups of rubber strands, collapsing to form a cell-like structure.
Network Formation by Association of Polar Groups in Elastomers
Authors: Nakajima N. , Huang C. D. , Scobbo J. J. , Shieh W. J. , Harrell E. R.
Published: February 2011

If an elastomer containing polar groups forms interchain associations, can we observe them independently from the effect of chain entanglement? Polyethylacrylate and polyepichlorohydrin are polar elastomers. Our previous deformational study indicated that these elastomers contain interchain associations, which are stronger than the physical entanglements. The conclusion was based on the results of large, unidirectional extension and small simple shear measurements. On the other hand, butadiene—acrylonitrile copolymer (NBR) containing 33% acrylonitrile did not indicate a presence of such a strong interchain association. In this work, we examined NBRs containing 40% acrylonitrile. The polar association, though weak, was detected with these elastomers. This indicates that the effective association involves a number of polar groups closely placed along the polymer chain. Also, in this work, nonpolar elastomers, SBRs, were chemically crosslinked and used as models. The polar association turned out to be not as strong as the chemical crosslinks. This indicates that the polar association disengage and reengage during the deformation.
Analysis of Components in Rubber Compounds Using Mass Spectrometry
Authors: Lattimer Robert P. , Harris Robert E.
Published: February 2011

A large number of very successful mass-spectrometric methods have been developed for rubber-compound analysis. The high sensitivity, high specificity, and superb mixture analysis capabilities of modern mass spectrometry make it an invaluable tool in the polymer industry, particularly for qualitative identification of organic additives. In many cases, mass spectrometry can provide unique information that is not available by use of any other technique.
The Radial Tire, a Peaceful Revolution
Authors: Massoubre Jean-Marie
Published: February 2011

Now, summing up in terms of everyday life, the consequences of the turning the tire industry took 40 years ago, we can refer to a peaceful revolution. It resulted in: 1. Precise steering and cornering. 2. Higher speeds, together with safer and more stable conditions. 3. Less wear and longer use (at least twice as many kilometers, high re-treadability for heavy trucks). 4. Materials and energy savings. 5. Much lower cost per mile. 6. Much safer and quieter drive. 7. Transportation of persons and goods never a problem. Can we imagine today our industry turning out 2 or 3 times more tires than it does, manufacturing 3 or 4 times more rubber, our vehicles burning 15–20% more fuel, to say nothing of the extra energy needed for production. What about the mountains of scrap tires, 2 or 3 times higher? Just like any radical change, we cannot imagine bypassing it. The only dark side can be found in the forgetfulness or contempt of a valiant and inexpensive servant, which ends in bad maintenance and dangerous neglect.
Pulsed NMR for Molecular Structure Analysis of EPDM
Authors: Tomlinson Richard W. , Sheridan Daniel F.
Published: February 2011

The use of pulsed NMR analysis under proper operating conditions has proven to be useful for controlling various polymer compositions in the manufacture of EPDM. It can be used in determining the amount of oil incorporated into oil-extended EPDMs. At higher oil contents, the differences in EPDM properties will affect this test method, which will require a separate calibration curve for each type of polymer. It can be used to measure the propylene content of EPDM. Comparison data have shown that this technique is more accurate in predicting crystallinity or propylene content than the standard IR method within the propylene range of 22 to 41%. Pulsed NMR can also be used to predict uncured EPDM compound tensile strength and EPDM/PP compression-molded tensile strength. Since these properties are affected by the crystallinity of EPDM, of which percent ethylene is the major contributor, then tensile strength can be determined indirectly. Based on the tensile and SER correlation, it seems obvious that this technique is measuring the spin-spin relaxation times of the crystalline phase, whereas the ir method is only measuring propylene content.
Crack Initiation and Propagation in Model Cord-Rubber Composites
Authors: Huang Y. S. , Yeoh O. H.
Published: February 2011

The present study suggests that the development of penny-shaped cracks at cord ends is the first stage of fatigue failure of cord-rubber composites. An approximate theory for calculating the strain-energy release rate (tearing energy) for the propagation of penny-shaped cracks and predicting the life of model composites has been outlined. The basic premise of this theory is that the rate of propagation of these penny-shaped cracks is governed by the usual crack-growth characteristics of rubber vulcanizates customarily determined using simple test pieces such as the pure-shear test piece. Fatigue studies on two model composites show experiment and theory to be in semiquantitative agreement. Breidenbach and Lake have already established the relationship between the crack-growth characteristics of the rubber material to interply crack propagation, a later stage in the fatigue failure of cord-rubber composites. Therefore, it is clear that the crack-growth characteristics are an important screening criterion for compound development aimed at improving the life of cord-rubber composites.
Application of Elasticity Models with Constraints on Chains and Junctions to Characterization of Randomly Crosslinked Networks
Authors: Queslel J. P.
Published: February 2011

Characterization of randomly crosslinked networks requires a topological description of imperfect network structure and a molecular-elasticity theory, preferably with a minimum number of adjustable parameters, relating macroscopic stress and strain or swelling ratios to molecular deformation. It is shown that simple relationships exist between the molecular weight between consecutive junctions, the molecular weight of linear precursor chains, the cycle rank, and the number of junctions for networks having no defects other than chain ends. The idealized affine deformation model (in which the constraints on junction fluctuations are infinite) and the idealized phantom-chain model (in which the constraints are absent) are inadequate for network characterization. The more realistic Flory-Erman constrained junction model is applied to the description of cis-polyisoprene cured with dicumyl peroxide. Swelling equilibrium experiments are in agreement with stress-strain measurements. Analysis of these stress-strain data with the constrained-junction and constrained-chain models gives similar results. This validates the Flory hypothesis that it is generally sufficient to concentrate the effects of the constraints on the junctions. Nevertheless, the constrained chain model proposed by Erman and Monnerie has the advantage of depending on one parameter, KG, instead of two, κ and ζ, for the constrained junction model.
Flexible Rubber-Steel Sandwich Springs
Authors: Muhr A. H. , Thomas A. G.
Published: February 2011

This novel form of spring has been developed to the point where the force-deflection behavior can be predicted with confidence from the known modulus of the rubber and the bending stiffness of the metal layers. Different geometries have been studied including three-point bend and cantilever configurations, with satisfactory agreement between theoretically predicted and experimentally measured stiffnesses. Dynamic behavior can be controlled by selection of the rubber compound. Depending on the geometry, the proportion of the deformation energy stored in the rubber itself, compared with the metal, can be varied, and this also influences, in a predictable manner, the overall damping characteristics of the spring. Epoxidized natural rubber, for instance, may be a candidate for the applications requiring higher damping. As the deflection of the spring is increased, a point is reached at which waves form in the metal layer that is under compression. This leads to a buckling of this layer and clearly limits the deformation which the spring can undergo. This important failure process has been studied experimentally and theoretically, and it is possible now to predict with some confidence the conditions under which it will occur. Fatigue failure under repeated stress has also been studied for a cantilever configuration. Lifetimes of over a million cycles were obtained with a range of samples, even when the deflection was close to that required to produce catastrophic buckling. However, for certain metal thicknesses, there is some indication that fatigue failure of the metal itself due to bending may become the dominant failure process. No failures either in the rubber or at the bond were observed.
Miscible Elastomer Mixtures
Authors: Roland C. M. , Trask C. A.
Published: February 2011

The degree of miscibility of the various IR/BR mixtures is not obvious from inspection of the chemical structures. IR and 1,2-BR, despite their distinct differences in chemical structure, form blends that are always homogenous. On the other hand, the liquid structural differences between IR and 1,4-BR overwhelm their chemical similarities, and it is the former that governs the phase behavior. As the 1,4 content of BR increases, the thermodynamic behavior of BR/IR blends ranges from nearly ideal mixing to the occurrence of an LCST due to negative excess mixing volumes. While the observation of lower critical solution temperatures in polymer mixtures in which no specific interactions exist is unusual, the same mismatch in liquid structure gives rise to the LCST commonly observed in polymer solutions. The interaction parameter for 1,2-BR in blends with IR is circa 2×10−4, which is remarkably low given the absence of specific chemical interactions. These mixtures most closely approximate ideal mixing behavior of any known pair of chemically distinct polymers. Even mixtures of BR isotopes are more nonathermal than blends of 1,2-BR with IR; moreover, the thermodynamic behavior of these isotope mixtures are not in conformance with simple Flory-Huggins lattice theory.
Heat Aging Performance of Ethylene Propylene Elastomers in Electrical Insulation Compounds
Authors: Spenadel L.
Published: February 2011

It is possible to develop an EPDM insulation compound with outstanding heat stability in the 160–180°C temperature range. Several key compounding ingredients are necessary in order to achieve the desired heat aging performance. They include the use of EPDM with high ethylene, low unsaturation, polychloroprene at the 5–10 phr level, zinc oxide at the 10–15 phr level, TMPT at the 2–4 phr level, hydrated alumina as the major mineral filler, reaction product of acetone and diphenylamine at 1 phr level, zinc salt of methylmercapto benzoimidazole at the 2–3 phr level, and dicumyl peroxide at the 5–6 phr level.
Compaction as a Part of the Mechanism in Incorporating Carbon Black into an Elastomer
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

The first stage of mixing elastomer with carbon black is the incorporation, where the free carbon black becomes incorporated inside the elastomer matrix. During this process, elastomer and carbon black are compacted to become a solid mass. The compaction requires, first, deformation of elastomer domains to conform with the topology of the carbon black and next, relaxation of the elastomer in the deformed state. A model experiment has been conducted to characterize both deformation and relaxation behavior during the compaction. A preblended powdered rubber and carbon black were loaded into a Rheometrics Mechanical Spectrometer and compressed in the space confined by a molding ring and the parallel plates. The deformation was characterized as a change in the apparent volume with compressive force being held constant. From this result, a degree of compaction was evaluated as the extent of penetration by elastomer into the void volume of carbon black. The relaxation behavior was represented by the relaxation of compressive force. The temperature dependence of relaxation was well represented by the temperature-time shift of the elastomer component. The energy required for compaction estimated from the compression data was about 6% of the energy spent for the incorporation process.
Ammonium Salt Catalyzed Crosslinking Mechanism of Acrylic Rubbers
Authors: Giannetti E. , Mazzocchi R. , Fiore L. , Crespi E.
Published: February 2011

Crosslinking mechanisms of acrylic rubber containing both carboxylic and epoxy curing active sites were studied on low molecular weight polymers using different recipes. High cure rates were obtained with quaternary ammonium salts and/or triaryl nucleophiles of Group Va elements. A reaction mechanism based on carboxylate onium salt activity was suggested. Very high reaction rates were obtained with catalysts having low basicity and high steric hindrance, whereas polyamines like o-tolylbiguanidine were less effective. A very simple method for scorch time regulation was devised.
A One-Dimensional Numerical Model of Heat Transfer in the Process of Tire Vulcanization
Authors: Schlanger H. P.
Published: February 2011

A one-dimensional heat flow model based on the Crank-Nicolson system of nodes is described. Conventional cooling theory has been incorporated into the model which may then be entirely represented in matrix form as a generalized theory. A considerable amount of investigation of the tire shoulder region has shown that by simulation, one-dimensional heat transfer theory is applicable to the molding process of tire vulcanization. The problem is one in which a unique set of thermal constants may specify the basic process. In heating, these constants are the apparent thermal diffusivity and equivalent tire shoulder thickness and, in cooling, the so-called surface heat transfer coefficients are used to define the material. The tire curvature and groove geometries may be considered to perturb the linear model but are accounted for by adjustments of the equivalent tire thickness which is determined empirically. Generally, agreement between theory and experiment is very good, and hence, such a model paves the way for on-line computer control of the production press.
Studies on the Reaction between Thiocarbamylsulfenamides and Diebenzothiazyl Disulfide
Authors: Adhikari Basudam , Pal Dhananjay , Basu Dipak Kumar , Chaudhuri Ajit Kumar
Published: February 2011

The use of binary systems as accelerators in the vulcanization of rubber has received considerable attention, since many of them in suitable combinations, have been shown to provide efficient vulcanization systems. Dogadkin and co-workers and Skinner and Watson reported mutual activation with a number of popular accelerator combinations. It was suggested that the mutual activation occurs by the interaction of the accelerators to form intermediate complexes which decompose to produce free radicals responsible for initiating the various reactions involved in the vulcanization process. Recently Krymowski and Taylor studied the reaction between N-oxydiethylenethiocarbamyl-N′-oxydiethylenesulfenamide (OTOS) and N-oxydiethylene-2-benzothiazylsulfenamide (OBTS), a synergistic accelerator system, in tetrachloroethane at 142°C, and identified the various products formed. Many of these reaction products themselves are familiar as vulcanization accelerators and thus may contribute to the synergistic activity observed with the OTOS-OBTS system. In the present investigation, we have studied the reaction between thiocarbamylsulfenamides and dibenzothiazyl disulfide (MBTS) in the solid phase in order to get an insight into the mutual activity provided by this system in filled and gum vulcanizates of NR.
The Thermal Stability of Monosulfidic Crosslinks in Natural Rubber
Authors: McSwkeeney G. P. , Morrison N. J.
Published: February 2011

(1) Networks containing mainly monosuifidic crosslinks at methylene sites in the polyisoprene chains of natural rubber are expected to be more thermally stable than existing efficiently vulcanized networks. (2) Certain zinc-accelerator species promote the decomposition of crosslinks at high temperatures, but may be deactivated by complexation with zinc stearate (which is formed from stearic acid during vulcanization).
Effect of Accelerator Type on Brass-Rubber Adhesion
Authors: Hamed G. R. , Donatelli T.
Published: February 2011

A natural rubber compound accelerated with tetramethylthiuram disulfide (TMTD) was studied and compared to an N-oxydiethylene-2-benzothiazolesulfenamide (MBS) accelerated compound in order to determine the factors resulting in the poor adhesion to brass of the former. Adhesion to brass-plated steel cord was measured by using the TCAT pull-out test. Vulcanization time and temperature were varied. Also, both compounds were analyzed for crosslink density and type at different states of cure by selective cleavage of the crosslinks with thiol reagents. The poor adhesion to brass of the TMTD compound was not accounted for by cure rate or crosslink density or crosslink type. Synchronization of the rubber cure rate with the sulfidation rate of the brass surface appeared to be unimportant in determining the brass adhesion characteristics of that compound. This was investigated by testing the adhesion of the TMTD compound to brass plated steel cords of different reactivities. Cords were analyzed for copper sulfide formation by an energy dispersive x-ray (EDX) technique after pull-out and also after immersion in squalene solutions containing each accelerator with and without added free sulfur. This analysis showed that there is significant sulfidation of brass in the presence of TMTD accelerator. Atomic absorption analyses of the squalene solutions, after the cord immersions, showed relatively large amounts of copper and zinc present in the TMTD solutions as compared to the MBS solutions. This indicates that TMTD corrodes brass to a much greater extent than the MBS accelerator. From the data presented, the following conclusions can be drawn: (1) The poor adhesion to brass of TMTD accelerated compounds is not related to: (a) their rapid cure rates, (b) a lack of synchronization between cure rate and sulfidation rate, or (c) crosslink density or type. This implies that a deficiency of physical entanglements of rubber crosslinks within the copper sulfide layer is not a reason for the poor adhesion to brass of these compounds. (2) Considerable sulfidation of brass occurs in squalene solutions with TMTD indicating that lack of sulfur availability for brass sulfidation is not a valid explanation for the poor brass adhesion of TMTD compounds. Contrarily, in fact, the data suggest that excessive sulfidation of brass occurs in the presence of TMTD. (3) The corrosive nature of TMTD toward brass has been documented for cords dipped in TMTD/squalene solutions. This characteristic of TMTD likely results in a copper sulfide layer on the brass which is porous and mechanically weak. It is proposed that this direct interaction of TMTD with brass provides an explanation for the poor adhesion to brass of TMTD accelerated compounds. The mechanism by which the TMTD causes the very rapid removal of the brass into solution is not known at this time. Perhaps the TMTD or its decomposition fragments form relatively stable complexes with copper and zinc such that their removal is favored.
The Role of Filler Properties in the Creep Deformation of Filled Elastomers
Authors: Thiele J. L. , Cohen R. E.
Published: February 2011

The use of the creep T-jump experiment as a sensitive tool for elucidating the mechanistic behavior during the deformation of a complex material such as the carbon black filled elastomer has been illustrated. The activation energy for creep was determined as a function of stress for various vulcanizates. The effects of the choice of elastomer, and of variations in surface chemistry, structure, and loading of the filler, were studied. The T-jump results combined with electrical conductivity measurements confirmed the presence of a carbon black network which is considerably involved in the creep deformation process at low strain but not at high strain. In NR vulcanizates, there is a high-strain mechanism not observed in SBR vulcanizates; presumably strain-induced crystallization is responsible for the NR behavior. Oxidation of filler surfaces had essentially no effect on the creep deformation mechanisms, suggesting that, during creep, slippage of elastomers along the surface does not occur to any great extent for conventional or oxidized surfaces.