bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoplastic Elastomers—Three Decades of Progress
Authors: Legge N. R. 
Published: February 2011

Abstract
In these three decades of progress, thermoplastic elastomers have risen in 1987 to a position of tenth in the order of commercial thermoplastic sales in the U.S.A., with a growth rate, 1986–1987, of 9.7%. It is very probable that the quantity shown for 1987 sales, 441 million pounds, is low, since it is well known that the largest producer of styrenic TPEs does not report offtake data. Much of the styrenic TPE goes to the adhesive industry, which also is very secretive in regard to materials consumption information. Thus, the 1986–1987 reported growth rate of 9.7% is on the low side. Another indicator of progress in the growth of TPEs has been illustrated by the number of product introductions from January 1986 to June 1987. During that period, TPEs led the major thermoplastics with the introduction of 270 new product types, and the nylons were a close second with 250. A third estimate of the explosive growth in TPEs may be seen in Table V which lists the number of manufacturers of TPEs in 1975, 1985, and 1987, increasing from 10 to 28 to 50. To summarize, the present thermoplastic elastomers, now high-volume commercial products, had roots in the chemistry and technology of polymers in the 1920's. Throughout the history of the “Roots” period one can detect precursor events from which several TPEs could have been foreseen. In each of the three decades of progress, major advances were made in the technology, physical properties, availability, and utilization of TPEs. The numbers of these increased in each succeeding period. Several paradigms appear in this review, for example: 1. The triblock styrene-diene A-B-A copolymers, morphology, and elastomeric character, in the first decade. 2. The copolyesters with (A−B)n morphology and greatly enhanced physical properties in the second decade. 3. The dynamically-vulcanized blends of EPDM and PP, followed in time by the concept of compatibilization to permit practical blends of NBR and PP in the third decade. Throughout these periods, growth was catalyzed by the favorable economics of manufacturing finished elastomeric products via low-cost thermoplastic processing techniques as compared with thermoset rubber processes. The reuse of scrap also provided a major incentive. In addition to these, the concept of component integration is now showing a path toward even more cost reduction incentives. New applicational areas continue to appear. One of these, blending relatively small amounts of TPEs with existing large volume thermoplastics, promises to provide extremely large offtakes of TPEs in the next decade. I am sure that the numbers of papers presented in symposia at meetings of the Rubber Division of the American Chemical Society confirm the continued explosive growth of TPEs we have seen in these past three decades.
Studies on Cure Synergism—Part I: Effect of Bis(Diisopropyl) Thiophosphoryl Disulfide and Thiazole-Based Accelerators in the Vulcanization of NR
Authors: Mandal Swapan Kumar , Datta Rabindra Nath , Basu Dipak Kumar 
Published: February 2011

Abstract
The effect of the synergistic combinations containing diisopropyl thiophosphoryl disulfide (DIPDIS) and a thiazole type of accelerator on the vulcanization of NR has been investigated. MBT, N-oxydiethylene-2-benzothiazole sulfenamide (OBTS), and N-oxydiethylene-2-benzothiazole disulfide (OBDS) represent the thiazole-based accelerators. It has been established from the hplc study that diisopropylthiophosphoryl benzothiazole disulfide (DIBDS) is formed in the synergistic systems along with other rubber additives during the early part of cure. In this exploratory study, it has been observed that DIBDS enhances the torque, modulus, crosslink density, and the tensile strength of the vulcanizates. Chemical characterization of the fine network structure of the NR vulcanizates indicates that synergistic combinations produce about 80% of the monosulfidic linkages. The resultant vulcanizates thus become stable to oxidative aging at 100°C for a considerable length of time. The vulcanizates obtained with DIBDS also produce the same results.
Differential Scanning Calorimetry Study of Natural Rubber and Epoxidized Natural Rubber and Their Binary Blends
Authors: Ng S. C. , Chee K. K. 
Published: February 2011

Abstract
In summary, the ENR exhibits a single Tg, whereas blending two different ENR samples of sufficiently high molecular weights would have no significant effects on their individual phase transition behavior in any event. This important finding implies that the epoxidation of NR basically leads to copolymers of random chemical structure and uniform composition, in line with the theoretical prediction of Scott. Moreover, the specific interactions presumably between the hydrogens of isoprene units and the oxirane oxygens of epoxidized isoprene moieties, are discovered to be strikingly weak, in the sense that the NR and ENR rubbers are positively immisicible.
Photocrosslinking of EPDM Elastomers. Photocrosslinkable Compositions
Authors: Hilborn J. , Rånaby B. 
Published: February 2011

Abstract
EFDM rubbers can be efficiently crosslinked using multifunctional monomers. Several factors must be taken into consideration: 1. Good solubility of the crosslinking agent in the rubber is essential. 2. It is favorable to have a mechanism of crosslinking which gives an alternating addition of rubber and crosslinking agent, as in the case of the stepwise radical thiol-ene system or alternating copolymerization of bis-maleimide with the olefinic rubber. These systems utilize each radical of the photoinitiator to form crosslinks, enhance the rate of crosslinking and prevent homopolymerization of the crosslinking agent. 3. A good match of the UV absorption of the photoinitiator, the UV transmission of the rest of the system, and the UV emission from the lamp is essential. 4. Since disproportionation of photoinitiator radicals in cage is an unwanted side reaction in the rigid rubber system, it is better to choose photoinitiators that mainly recombine to reform a photoactive molecule as before scission.
Effectiveness of New Alkyl-Aryl-p-Phenylenediamines Which Can Be Chemically Bound to Polymers—Model Study
Authors: Engels H-W. , Hammer H. , Brück D. , Redetzky W. 
Published: February 2011

Abstract
The new model compounds described above have all the structural characteristics of the most effective antioxidants, antiozonants, and antiflexcracking agents of the alkyl-aryl-p-phenylenediamine type. Whereas the SCH3 compounds chosen as migratable reference substances have patterns of effectiveness similar to that of 6PPD, attachment to the polymer largely immobilizes the SH compounds. The nonmigratable mercaptans afford less protection from surface degradation processes than the corresponding methylthioethers. The fact that the attached compounds afford almost no protection from ozone underlines the importance of diffusion as a prerequisite of an antiozonant effect. Although the bound molecules have a good antioxidant effect, their loss of effectiveness as a function of aging time is similar to that of the reference compound, which, being migratable, is subject to physical depletion. Under laboratory aging conditions that do not cause extraction, the concept of polymer attachment offers no prospect of proved long-term protection.
Postharvest Degradation of Guayule Rubber
Authors: Kstilai A. , Hamerstrand G. E. 
Published: February 2011

Abstract
Most guayule genotypes lose considerable amounts of rubber after harvest. The time that the harvested shrub stays in storage is an important factor controlling the amount of degradation. This study identifies genotypes which are more stable with respect to postharvest degradation of rubber quality and quantity. Genotypes carrying such an economically valuable trait provide for the development of high-rubber-yielding cultivars that prevent substantial losses between harvest and processing. Further studies are expected to throw light on the mechanisms of postharvest rubber degradation, in general, and on the genetic nature of this variation in particular. More genotypes must be exposed to more storage conditions in order to identify genotypes that may withstand the adverse effects of long storage. The observation that some genotypes continue to synthesize rubber after harvest, at least for a short period of time, is also encouraging. Such genotypes make it possible to handle the shrub between field and processing, within 1 to 2 weeks, with no rubber loss.
The Effect of Specimen Thickness on the Tearing Energy of a Gum Vulcanizate
Authors: Mazich Kenneth A. , Morman K. N. , Oblinger F. G. , Fan T. Y. , Killgoar P. C. 
Published: February 2011

Abstract
We have examined the effect of thickness on the critical tearing energy of a simple gum vulcanizate of SBR in pure shear. Laboratory experiments and finite-element calculations agree that the tearing energy that is measured with a pure-shear specimen increases with the thickness of the specimen. Laboratory measurements indicate that the deformation for crack growth in a pure-shear specimen increases with the thickness of the specimen. Finite-element calculations show that the energy available for release at a given deformation also increases with thickness in the range from t=1.4 mm to t=14 mm. Experiments show that the crtical tearing energy varies linearly with thickness in the range t=0.7 mm to t=2.7 mm. The effect of thickness on the tearing energy was also studied by calculating the J-integral at various points of the crack through the thickness of the pure-shear specimen. In general, the J-integral calculated at the surface of the specimen can be higher than the J-integral calculated at the center of the specimen for specimens that are sufficiently thick. The thickness effect measured in this work suggests that the “critical tearing energy” obtained from standard laboratory specimens may not be a true material property. For this reason, critical tearing energy that is measured on standard specimens may not be generally applied to predict failure in arbitrary elastomeric components.
Network Recovery from Uniaxial Extension: I. Elastic Equilibrium
Authors: Roland C. M. 
Published: February 2011

Abstract
The elastic response of rubber has a direct and controllable dependence on structure. The behavior of the various networks described herein is seen to be consonant with the well-established roles of spatial fluctuations of crosslinks and the inhibition of this Brownian motion by steric and entanglement constraints from neighboring chains. Although elasticity also governs to a large extent the nonequilibrium mechanical response, interpretation of the latter in terms of network structure is obscured by viscoelasticity. The junctions of real networks, having some freedom to reconfigure themselves away from strictly affine displacement, exhibit lower equilibrium stresses than predicted by the statistical model for affine chains. To the extent that this overestimation of the model and the compressive component of the retraction response mimic the effect of departures from equilibrium, some conformance of network behavior during retraction to Equation (1) may be realized. It is such a fortuitous circumstance that likely underlies the various proposals commending such a relationship. A measure of junction density is generally not obtainable from deformation experiments in which dissipative processes are active.
Network Recovery from Uniaxial Extension: II. The Origin of the Mullins Effect
Authors: Roland C. M. 
Published: February 2011

Abstract
The Mullins effect refers to the dissipation in crosslinked rubber of mechanical energy beyond that due to linear relaxation processes or irreversible structural changes. Physically, Mullins softening probably arises from adjustment of local imbalances in segment density and from contraction of the primitive path of network chain ends. The resulting more random chain configuration contributes to the relaxation of the stress, but at a sufficiently rapid rate that it is omitted from the experimentally measured linear relaxation spectrum. This omission is made apparent upon reversal of the applied strain. The mechanism underlying the hysteresis can be modeled empirically by the introduction of irreversibility into the damping function. Although the Mullins effect is a reflection of nonaffine network motion during deformation of rubber, it is independent of the extent to which the junctions of the network are affinely displaced at elastic equilibrium. Randomly crosslinked networks of widely varying structure exhibited comparable degrees of Mullins softening. Corroboration that the network chain ends are a major source of Mullins softening could be obtained by a similar study using end-linked networks. Such experiments on end-linked polytetrahydrofuran rubber are currently in progress.
The Influence of Interstitial Liquids on the Cohesive Strength of Carbon-Black Agglomerates
Authors: Horwatt Steven W. , Rwei Syang-Peng , Manas-Zloczower Ica , Feke Donald L. 
Published: February 2011

Abstract
The influence of interstitial liquids on the cohesive strength of carbon black has been investigated. Calculations of effective Hamaker coefficients for the wet materials predicted order of magnitude decreases from the Hamaker constants for the dry materials. Tensile-strength data showed slight increases over the Hamaker constants for the dry materials. It is clear that further research is needed to elucidate the effects of liquid content and wettability.
Coactivation of Delayed-Action Vulcanization. Part I. Polymeric, Nonmigratory Cure Coactivators for Accelerated Sulfur Vulcanization
Authors: Coran A. Y. , Ignatz-Hoover F. , Davis L. H. 
Published: February 2011

Abstract
Rubbery vinylpyridine-butadiene copolymers, containing 20–65% by weight of vinylpyridine monomer units, are effective coactivators of vulcanization for TBBS-accelerated sulfur-vulcanized SBR. In addition to emulsion SBR, the new co-activator has been evaluated in copositions of solution SBR, BR, NR, and various blends. The co-activator is active in all of the compositions which contain butadiene-derived synthetic rubber. This includes blends such as SBR/BR, solution-SBR/BR, SBR/NR, BR/NR, SBR/BR/NR, etc. There is little or no activity in which NR is the only polymer. The most efficacious copolymers contain between 30 and 60% 2-vinylpyridine. The incorporation of such a copolymer into an unvulcanized butadiene-derived rubber mix can give a substantial increase in the rate of crosslink formation with only a minimum loss of scorch resistance. Since the polymeric coactivators are very high in molecular weight, it can be at least tentatively concluded that they will not migrate from one component stock to another in a built-up multi-stock rubber article, either before or during vulcanization. Since the curing characteristics of a vinylpyridine-copolymer-containing TBBS-accelerated stock can be similar to those of TBBS-accelerated NR, it might be concluded that the new additives will solve some of the problems in balancing the cures of adjacent NR and SBR stocks in a multicomponent cured rubber article.
Effect of Gel and Nonrubber Constituents on the Extrusion Properties of Guayule Rubber
Authors: Montes Sergio A. , Ponce-Vélez M. A. 
Published: February 2011

Abstract
An experimental study on the effect of gel and nonrubber constituents on the extrusion behavior of guayule rubber (GR) has been carried out. At 140°C, gel increases the viscosity at low shear rates. When GR is properly stabilized, no peptizing effect is imparted by the resin. However, the resin acts as a moderate plasticizer as compared to paraffinic oil. At 120°C, the effect of gel is noticeable at high extrusion rates, increasing the viscosity, suggesting an increase in the tendency for the occurrence of flow-induced crystallization.
Rubber-Thermoplastic Compositions. Part VII. Chlorinated Polyethylene Rubber-Nylon Compositions
Authors: Coran A. Y. , Patel R. 
Published: February 2011

Abstract
Nylon resins and CPE rubber can be melt-blended to give compositions which have useful properties. If the rubber is cured by dynamic vulcanization, high strength oil resistant thermoplastic elastomers result. Cold milling of melt-mixed compositions results in nylon-reinforced rubber which can be mixed with curatives and press cured or statically vulcanized to give reinforced rubber compositions which resemble vulcanized rubber-short fiber composites. The reason for the high integrity of either the statically or the dynamically vulcanized composition appears to be that chemical bonds form between the rubber and plastic.
Effect of Crosslink Density on the Critical Flaw Size of a Simple Elastomer
Authors: Hamed G. R. 
Published: February 2011

Abstract
Tensile experiments have been carried out on a gum, amorphous EPDM elastomer. Samples with various crosslink densities and containing precuts of different lengths were tested. The energy, Wb, per unit volume, to fracture a specimen varied inversely with the length of the precut as predicted by simple tearing energy theory. Values of the inherent flaw size, Co, of the samples were determined by extrapolation of Wb to that value obtained when no intentional precut was present. Values of Co decreased with increasing crosslink density. This illustrates the decreasing ability of an elastomer network to blunt the crack tip of a stress-raising flaw as crosslinking is increased. It is suggested that this phenomenon is at least partly responsible for low values of Wb at high crosslink densities.
Stress Analysis of Adhesion Tests
Authors: Ridha R. A. , Crano R. N. 
Published: February 2011

Abstract
The ASTM D 2229-80 test specimen with a circular hole and a pad restriction was analyzed by 3D finite elements. Maximum shear stresses within the specimen are at the cord-rubber interface. Thus, failure is expected to initiate in the vicinity of the cord-rubber interface. This characteristic is similar to that seen in the MICA and TCAT tests; it represents an improvement over other pull-through tests including earlier ASTM tests. The computed tensile stresses normal to the cord indicate that friction forces will not be significant in this test (as they are in the TCAT test) and that debonding will propagate rapidly. In this regard, the D 2229-80 test is similar to the MICA test. Results of photoelastic analysis of the ASTM D 2229-80, MICA, and TCAT tests are in good agreement with the computed results. Maximum shear stress at the cord-rubber interface in the ASTM D 2229-80 test varies with the modulus of elasticity of the rubber. This variation becomes more pronounced with increasing rubber deformations (e.g., at higher loads and with softer rubber compounds). Thus, the cord pullout force will be dependent on the rubber modulus. From the above results we conclude the following: 1. The ASTM D 2229-80 test overcomes one of the serious drawbacks of earlier pull-through tests; failure is expected to initiate in the vicinity of the cord-rubber interface rather than elsewhere in the rubber. The new test's main deficiency is the dependence of the cord pullout force on the rubber modulus; in this regard, the MICA test offers a considerable advantage. 2. The ASTM D2229-80 test may be used in evaluating the adhesion of various steel cords embedded in a control rubber compound. 3. When changes are anticipated in the properties of the rubber compound, the MICA test offers a considerable advantage because the cord pullout force in the MICA test is independent of the rubber modulus.
Processability of Thermoplastic Olefin Elastomers: Vacuum Sheet Forming
Authors: Ho C. C. , Kontos E. G. 
Published: February 2011

Abstract
We have presented a method for evaluating the vacuum forming performance of polymers by comparing their forming window. The window is determined by (a) the sag of the heated sheet and (b) the material's ability to reproduce mold details. We also showed that the vacuum forming window of polypropylene homopolymer can be widened through modification with an olefinic thermoplastic elastomer. Compared to polypropylene homopolymer, TPE-modified polypropylene requires lower tensile stress to extend the sample at temperatures below the polypropylene melting point. In the melt stage. TPE modification enhances the melt viscosity of polypropylene. TPE modification increases significantly the low temperature impact of polypropylene. The flexural modulus becomes lower.
High Temperature Degradation of Silicone Rubber Compounds in a Silicone Oil Environment
Authors: Henry A. W. 
Published: February 2011

Abstract
We have found that silicone rubber compounds undergo a reduction in effective chain concentration when heated in an environment of high temperature silicone oil and that this rate of reduction is dependent upon the effective chain concentration to the 3/2 power. The 3/2 power relationship results from a slower than expected reaction rate due to the dilution influence of further reactions of already ineffective network chains. Based on our experimental findings, we believe that below 204°C, in a silicone oil environment, the predominate degradation of the siloxane network is due to the siloxane rearrangement reaction between silicone oil and the crosslinked network. The resultant bond breaking and reforming have an experimentally determined average activation energy of about 60 kJ/mole. In addition, based on our experiments, we have concluded that above 204°C, the higher activation energy of 105–125 kJ/mole observed for the two compounds containing little or no iron oxide is caused by a depolymerization mechanism which involves breaking of the network and formation of low molecular weight cyclic siloxane materials. With significantly more iron oxide present, as is evidenced in the RTV (Fe2O3 + Al2O3) material, the lower activation energy seen even above 204°C is believed to be caused by the continued catalysis of the siloxane rearrangment reaction by the iron oxide.
Bis(Triethoxysilylethyltolylene)-Polysulfide, a Scorch-Resistant Silane Coupling Agent for Mineral-Filled Elastomers
Authors: Pickwell R. J. 
Published: February 2011

Abstract
Bis(triethoxysilylethyltolylene)polysulfide offers greater scorch safety and reduced odor compared to mercaptosilanes, though its high molecular weight may require up to three times the mercaptosilane loading on a weight basis. This is highly dependent on the rubber formulation. The polysulfidedisilane can be made into stable dispersions on calcium silicate at concentrations up to 70 percent. Order-of-addition recommendations for the polysulfidedisilane are the same as those for mercaptosilanes. Different mix procedures should be checked for each formulation to ensure maximum silane effectiveness.
Structure and Biosynthesis Mechanism of Natural Cis-Polyisoprene from Goldenrod
Authors: Tanaka Yasuyuki , Sato Hisaya , Kageyu Akira 
Published: February 2011

Abstract
The chemical structure of naturally occurring cis-polyisoprene isolated from Solidago altissima was determined by 13C NMR spectroscopy. The alignment of the isoprene units in the polymer was estimated to be in the order: dimethylallyl terminal unit, three trans units, about 1000 to 2200 of internal cis units, and a cis allyl alcohol terminal unit. This demonstrates that the biosynthesis of cis-polyisoprene in this higher plant starts from trans,trans,trans-geranylgeranyl pyrophosphate.