bluuebunny/crossref_metadata_2025 huggingface dataset:
Total Thermal Analysis of NBR Vulcanizates
Authors: Sircar A. K. , Lamond T. G.
Published: February 2011

NBR vulcanizates of different nitrile content can be identified by total thermal analysis. Vulcanizate composition analysis is complicated because of formation of carbon from NBR. The difficulty can be obviated by identifying the specific type of NBR by Tg and making allowances for the known amount of carbon formation for that specific type.
N-(Morpholinothio)Imides as Curing Agents in Semiefficient Vulcanization Systems
Authors: Son P. N. , Krueger R. A.
Published: February 2011

It is well known that both the thermal and oxidative aging characteristics of vulcanizates can be improved by using an efficient vulcanization (EV) or semi-EV system. These desirable aging properties are attributed to the presence of mono- and disulfidic crosslinks in the vulcanizates cured by EV or semi-EV systems. In contrast to a polysulfide crosslink, mono- and disulfide crosslinks are more thermally stable and undergo minimal crosslink modification during aging. One way to achieve such desirable properties is to cure a stock with 2-benzothiazyl 4-morpholino disulfide (BMD) and low levels of sulfur. However, the BMD cure system lacks the scorch protection required for many applications. Moreover, neither N-(cyclohexylthio)phthalimide (CTP) nor N,N′-bis(cyclohexylthio)oxanilide (BCTO) shows an appreciable effect on the scorch time of BMD cure systems. This is true regardless of the level of sulfur used, as shown in Figure 1. The maximum increase in scorch time with 1.00 part CTP was only 35%, and this occurred only when three parts of BMD and no free sulfur was used. When 2.00 parts sulfur was used, scorch time was extended only 18%. Likewise, BCTO did not respond well in BMD cure systems. The poor performance of these retarders in BMD cure systems prompted us to design a cure system in which BMD can be formed during vulcanization.
Effects of Processing Variables on the Mechanical Properties of Carbon Black Filled Rubber
Authors: Wijayarathna B. , Chang W. V. , Salovey R.
Published: February 2011

Vulcanizate properties such as tensile strength, abrasion resistance, and tear resistance, are often enhanced by the introduction of structural heterogeneity. This is usually achieved by incorporating fillers into the polymer matrix. In addition to the type of filler and polymer used, mechanical properties depend on factors such as filler particle size, distribution, filler-polymer interaction, and network homogeneity. These factors are largely governed by the conditions of the mixing. The most widely used filler in rubber is carbon black. Carbon black, produced by the pyrolysis of hydrocarbons, is in the form of fused primary aggregates which flocculate to form large secondary aggregates held together by van der Waal forces. The term structure, as applied to carbon black, commonly refers to both primary and secondary aggregates and is designated as primary or secondary structure. The reinforcement of rubber by carbon black depends considerably on the particle size and structure of the black used. Voet and associates have shown evidence that the primary structure is not broken down by shearing action during mixing. However, Heckman and Medalia and Gessler claim that fracture of the primary structure could result from severe mechanical shear. The general consensus is that breakdown of the primary structure of carbon black is not extensive in the usual mixing process. Boonstra and Medalia, among others, reported that large agglomerates remaining after insufficient mixing have a deleterious effect on the rupture properties of vulcanizates. Hence, an optimal mixing process does not destroy secondary aggregates. The secondary structure plays an important role in the dispersion of carbon black during mixing as rubber is squeezed into both primary and secondary aggregates. Low structure blacks pack much more tightly than high structure ones and are more difficult to disperse.
Differentiation of Natural and Synthetic Polyisoprene by Combined Derivative Thermogravimetry and Gas Chromatography
Authors: Brazier D. W. , Schwartz N. V.
Published: February 2011

A major objective of this study was to develop a general method by which NR and IR can be differentiated and quantitatively determined in unknown vulcanizates. From the above data, it is apparent that none of the thermal analysis methods—DTG, DSC or DTG-GC—can give an unequivocal answer alone, unless the type and loading of carbon black, the sulfur level and the accelerator system of the unknown compounds are known. The general type of carbon black can be determined using a recently published DTG method, and the loading is readily determined by DTG or an ashing experiment. Determination of the exact accelerator system remains a problem. The limitations of each method can be summarized: (1) The DTG thermogram will differentiate NR and IR provided the sample is vulcanized and contains carbon black. (2) The DSC will differentiate NR and IR on the basis of the observed exothermic heat, provided the sample is vulcanized. (3) In DTG—GC, the appearance of dimethylethylbenzene in the distillate is indicative of the presence of IR. For all vulcanized IR compounds, the presence of dimethylethylbenzene is accompanied by a low isoprene/3-methyl-cyclohexene yield. For the analysis of NR:IR blends, calibration curves such as those shown in Figure 7 can be constructed, but the above limitations still apply, i.e. filler loading and type, sulfur level, and accelerator system must be known.
A New Sulfur Modified Polychloroprene
Authors: Schmitt S. W. , Anolick C.
Published: February 2011

Among commercial polychloroprenes, mercaptan modified types cured with thioureas have yielded vulcanizates with the best heat aging and compression set properties. In contrast, sulfur modified polychloroprenes have been inferior in these properties, but superior in hot strength, resilience, and resistance to flexing and tear. In the past the polychloroprene user was forced to choose between the two contradictory sets of properties. A new sulfur modified polychloroprene has been developed which eliminates this compromise. The new product can be cured with metal oxides alone. The vulcanizates have better tear strength than previously obtainable; resilience, flex resistance, and heat aging equal to the best previous; and compression set resistance approaching that of mercaptan modified polychloroprene cured with thioureas. This combination of properties was not available heretofore. Although accelerators are not normally required, the cure cycle of the new polychoroprene product can be modified by conventional techniques.
Vulcanization of a Fluoroelastomer Derived from Tetrafluoroethylene and Propylene
Authors: Kojima G. , Wachi H.
Published: February 2011

An effective vulcanization recipe for tetrafluoroethylene-propylene elastomer was searched for and the following results were obtained: (1) The C2F4-C3H6 copolymer is susceptible only to peroxide and is not crosslinked at all by other reagents. (2) The peroxide vulcanization is greatly accelerated by some coagents, and triallyl isocyanurate was found to be the best cure promoter. (3) The vulcanizate obtained by using a combination of α,α′-bis-(t-butyl-peroxy)-p-diisopropylbenzene with triallyl isocyanurate as curative exhibits good mechanical properties together with excellent heat and chemical resistance. (4) The mechanism of the vulcanization reactions seems to involve a chain reaction which greatly increases the efficiency of the vulcanization reaction by the peroxide.
Thermo-Oxidation of Elastomers by Differential Scanning Calorimetry
Authors: González Virgilio
Published: February 2011

Using the DSC technique it is possible to evaluate the efficiency of antioxidants in rubber, using the increase in Ti of the rubber on adding antioxidant in a known concentration. The creosote bush resin chloroform extract is more efficient in synthetic than natural rubbers. The increase in Ea can be explained by the formation of peroxy-quinolinic intermediates in the slow stage of the reaction and it is possible to calculate the Ea based on this same increase, when the relationships between the reaction and Ti, and between Ea/N calculated by Gorbachev and Ti, are known. These are given for Hr=10°K/min using Equations (7) to (11), which greatly simplifies calculations and reduces experimental tests.
Fluoroelastomer Polymers—Compounding and Testing for Downhole Environments
Authors: West A. C. , Ray T. W.
Published: February 2011

A laboratory screening test simulating sour gas downhole conditions has been developed that provides directional information on the factors that control elastomer seal performance in this harsh environment. The results of this test have been correlated to environmental testing of O-rings in simulated downhole conditions using sour crude oil at 203°C and evaluating the pressure failure over the range of 69 MPa to 138 MPa. The results of this testing program have demonstrated the factors that affect overall seal performance for commercially available fluoroelastomer raw gums in downhole environments in the following order of importance: 1. a vulcanized compound modulus at 50% elongation of greater than 6.9 MPa, 2. cure type order of preference of peroxide > bisphenol > diamine, 3. increases in fluorine level from 65 to 69 weight percent have little effect on seal performance in conditions evaluated, and 4. the compound hardness is not as important a factor in predicting compound failure or success as is molecular weight selected that results in elongation of 70–100% at high filler loadings to achieve high modulus. The laboratory screening/environmental testing sequence reported here has proven successful in predicting fluoroelastomer properties necessary to manufacture seals for actual downhole service.
The Effect of Oxidized Fuel on Polymers
Authors: Trexler Harold E.
Published: February 2011

Some polymers exhibit exceptional resistance to oxidized gasoline as evidenced by minor changes in their tensile and elongation after aging in the oxidized fuel for 1008 hours at 40°C. The polymers with the smallest changes in properties are TFE and polyamide plastics and TPE thermoplastic elastomer followed by PNF, AU-2D, and FKMF elastomers. Other materials which also have good resistance to oxidized gasoline and should be considered for further development in oxidized fuel applications include: FVMQ, FKMV and NBR P-684 elastomers and TPPE thermoplastic. Aging in oxidized diesel fuel generally causes less change in properties of polymers than aging in oxidized gasoline. For this reason, candidate polymers for oxidized gasoline applications will also function well in oxidized diesel fuel.
Vulcanization of Guayule Rubber
Authors: Ramos-De Valle L. F.
Published: February 2011

The vulcanization characteristics of natural guayule rubber (GR) were compared to those of natural hevea rubber (HR). In the case of purified rubbers, vulcanization and tensile properties were shown to be very similar, whereas in the unpurified raw rubbers, HR was faster in vulcanization and attained a higher modulus than GR. These differences between raw rubbers were most pronounced in conventional vulcanization systems using MBT as the sole accelerator. As a result of a variety of different types of measurements on raw and purified rubbers, (relaxed tensile stress [MOD], Monsanto Rheometer curves, degree of crosslinking measurements, and kinetic analysis) it was concluded that the differences between HR and GR were due to the natural occurrence in HR (and absence in GR) of a vulcanization activator of a type similar to a basic secondary accelerator. Finally, in any formulation, the addition of very small quantities of activator or basic secondary accelerator is recommended in GR in order to attain similar properties to those of HR.
Long Chain Branching in Natural Hevea Rubber-Determination by Gel Permeation Chromatography
Authors: Angulo-Sanchez J. L. , Cabaulero-Mata P.
Published: February 2011

The hevea brasiltensis rubber contains, besides the insoluble branched entities, linear and branched molecules in the soluble fraction. The branching characteristics found by analyzing fractions of different molecular weight of rubber coagulated from freshly tapped latex, stabilized with hydroxylamine hydrochloride are: (a) molecules with molecular weights above 6.5×104−1.0×105g/mol (depending on the branch points functionality) are branched and molecules below these limits are linear. (b) The relationship between number of branch points and the logarithm of molecular weight is linear. (c) The branching density is not independent of molecular weight, as has been assumed for several polymers, but it has a maximum. The maximum branching density found in the soluble fraction is between 10.2×10−6 and 31.6×10−6mol/g, which varies little with the molecular weight; it is possible that molecular species with higher values become insoluble. (d) Branching results ˜λ and gel content (36%) of the whole rubber gave a total of 93–98% of branched entities (sol and gel) and 2–7% of linear species.
Significance of Extensional Flow in Processing of Rubbers
Authors: Cotten G. R.
Published: February 2011

Simple shear is the customary mode of deformation for the study of rheology. Simple shear measurements can be done by means of a variety of laboratory instruments such as shearing disks, concentric cylinders, or capillary rheometers. The results so obtained have been successfully used to predict the flow of fluids through tubes and some more complex processes, like extrusion and certain aspects of mixing. However, simple shear experiments do not provide all the information necessary to describe processability of polymers. In particular they are totally unrelated to phenomena of extrusion shrinkage (die swell), extrusion appearance (melt fracture), or crumbling on the mill. A better understanding of these phenomena can be obtained by examining polymers in simple extensional flow.
Rubber-Thermoplastic Compositions. Part III. Predicting Elastic Moduli of Melt Mixed Rubber-Plastic Blends
Authors: Coran A. Y. , Patel R.
Published: February 2011

Blends prepared by mixing rubbers with plastics in the molten state have been known and used for a number of years. The stiffness of such blends vary widely with both the proportions of rubber to plastic and with material selection, even at equivalent rubber to plastic proportions. This report describes correlations between blend stiffness and the properties of the individual blend components. Dynamic shear modulus G′, determined by torsion pendulum measurements, was used to characterize the stiffnesses of the blends. Values of G′ were related to the moduli of the hard and soft (plastic and rubber) phases, G′H and G′S, and the volume fraction of plastic ϕH through a single adjustable parameter by means of a recently proposed relationship. The adjustable parameter was then correlated with other properties of the blend components. In contrast with the work reported in the first two papers of this series, this report is on compositions in which the rubber is not crosslinked.
Polysulfide Sealants
Authors: Ghatge N. D. , Vernekar S. P. , Lonikar S. V.
Published: February 2011

Sealants based on polysulfide liquid polymers are widely used in a number of applications. These sealants are solvent and chemical resistant, having good flexibility and adherence to many substrates such as steel, aluminum, glass, concrete, wood, etc. These are used to line fuel tanks of aircraft and to seal fuel tanks and rivetted joints in aircraft. These sealants, being water resistant, are widely used in ship building to seal decks and planking. Since these sealants have good weather resistance and can withstand stress and strain, they are widely used in the building industry. They are found to be very satisfactory in modern curtain walls and in sealing windshields of motorcars. Their use in airfield and runway constructions is well known. These sealants generally have a two-pot system consisting of (i) a base caulk containing a liquid polysulfide polymer, fillers, plasticizers, adhesive promotors, thickening agents, accelerators or retarders and (ii) a curing agent. Sometimes accelerators and retarders are used as a third pot system to regulate the pot life of caulking compounds.
Rubber Adhesion of Brass-Plated Steel Tire Cords: Fundamental Study of the Effects of Compound Formulation Variations on Adhesive Properties
Authors: van Ooij W. J. , Weening W. E. , Murray P. F.
Published: February 2011

The rubber adhesion of brass-plated steel tire cord has been studied with emphasis on the effects on unaged and aged adhesion of compound formulation variations. A series of 16 test compounds was formulated in which the levels of sulfur, accelerator, stearic acid, zinc oxide and cobalt salt were varied. Adhesion data for two steel cord constructions—4 × 0.25 and 7 × 4 × 0.175 + 0.15—obtained under various unaged and aged conditions are presented. Despite the relatively minor compound differences, a wide variation of adhesion characteristics was observed. Good adhesion following overcure, humidity aging and steam aging was obtained with compounds containing high sulfur levels and high sulfur to accelerator ratios. The adhesion data do not correlate with compound crosslink densities or other physical properties. Rates of brass sulfidization do not correlate with adhesion data either. This was studied in model systems with squalene replacing the natural rubber. Analysis by high-resolution Auger electron spectroscopy revealed differences between the compositions of the sulfide films formed by the good and the poor mixtures of the series. The locus of the adhesion failure of the poor compounds was found to be the interface between copper sulfide and zinc oxide, the two reaction products formed when brass is bonded to rubber. A model was presented which accounted for the effects of compound formulation variations. It is postulated that brass is not sulfidized by the free sulfur in the mixture but by an intermediate containing reactive sulfur. The composition of this intermediate is dependent on the compound formulation. This leads to different types of sulfide films formed by good or poor compounds. This model is based on the chemistry of squalene model system mixtures, which was studied by chromatography. The ranking of crosslink densities observed for the various squalene mixtures was very similar to that determined for the corresponding NR mixtures. Some implications of the findings of this study for tire cord and compounding practice were discussed.
An Approach to the Modeling of Mixing of Elastomers
Authors: Nakajima N.
Published: February 2011

In recent years, the process of mixing elastomers with carbon black has been the subject of various studies. In particular, the process involving the use of the internal mixer has been examined systematically, and Palmgren has published a general review on the state of the art. A method was proposed for the control and scale-up which is based on the energy input for mixing; then, properties were evaluated as a function of the mixing energy. This method was used for evaluating the performance of different types of elastomers and carbon blacks in the internal mixer. Although the method represents significant progress in understanding the mixing process and is of practical importance, it still treats the mixer essentially as a “black box”. In order to elucidate the mechanism of mixing, visualization must be performed. One type is static visualization, in which the machine is stopped at an intermediate stage and the contents are taken out for inspection. Another is dynamic visualization through transparent walls of a mixer. These observations enable us to construct a model for the deformation-flow behavior of materials and a model for the mixing mechanism. These models, in turn, guide us to laboratory measurements of the material behavior which are pertinent to the mixing mechanisms. With respect to mill processability, Tokita and White classified raw material behavior into four regions, which are functions of a given material and dependent on the time scale, temperature, and magnitude of strain. This classification is applicable not only to the millability of the raw elastomer but also to the ease of mixing with carbon black. This interpretation may be extended to the processability of the material in the internal mixer.
A Low Modulus, High Fatigue Life Elastomer Compound for Suspension Applications
Authors: Killgoar Paul C. , Lemieux Marvin A. , Tabar Ronald J.
Published: February 2011

Soft elastomeric suspension bushing compounds have been developed which are based on natural rubber/polybutadiene (NR/BR) blends which have been softened with polyisobutylene (IM). The new compounds have a Shore A hardness of 45 and a fatigue life of 97 kc and 80 kc for the urethane cured and semi-EV cured compounds respectively. This compares with a fatigue life of 62 kc for the current production compound (Shore A 65). It appears that the mechanical behavior, i.e. resistance to crack growth, of natural rubber based compounds is unaffected by the addition of IM. Fatigue life, compression set and retention of physical properties after heat aging of the new compounds are also superior to the production compound. The dynamic mechanical properties of the new compounds were evaluated and found to have a slightly greater temperature sensitivity than the production compounds.
Amine Terminated Reactive Liquid Polymers; Modification of Thermoset Resins
Authors: Riew C. K.
Published: February 2011

Amine terminated reactive liquid polymers (AT-RLP) are synthesized from corresponding carboxyl terminated reactive liquid polymers (CT-RLP) and diamines. The CT-RLPs have a functionality of close to two, the average molecular weight ranging from 2500 to 4000, and Brookfield viscosity ranging from 30 to 600 Pa · s at 27°C. AT-RLPs made from the CT-RLPs have about the same physical properties as the CT-RLPs given above. N-(2-aminoethyl)piperazine (AEP2) is the best diamine among the diamines tried to produce low viscosity and low molecular weight AT-RLPs. Structure of end-groups of AT-RLP is unequivocally identified as a secondary amide and a secondary amine group resulting from the reaction of carboxyl end-groups of CT-RLP and a primary amine group of AEP,. The AT-RLP can be used as a modifier for epoxy resins at room or elevated temperatures to produce castable formulations with properties ranging from plastics to elastomers. The formulations may be useful as a modifier for improvement of crack and/or impact resistance of normally brittle epoxy plastics, as castable elastomers, paints and coatings, sealants, adhesives, especially as solventless adhesives for conveyor belts, hoses, shoes, and as binders for woven or non-woven fibers and cords.
Structural Mechanics of Radial Tires
Authors: Akasaka T.
Published: February 2011

This review has included only theoretical studies of cross-sectional tire shape, structural properties of the belt, and certain topics on structural mechanics of radial tires. Many other papers on these subjects have been omitted because of the space limitation and because of the objective to describe only broad trends and prospects rather than to present an exhaustive review. Many different but interesting problems remain regarding stresses, deformations, and failure of radial tires under various loading conditions, for example: ( 1 ) physico-chemical and mechanical studies of the viscous flow and vulcanization of rubber during tire formation, in order to determine the setting mechanism and residual stresses in the cord-rubber array; (2) theoretical studies of both in-plane and interply loads and deformations in laminates of more than three layers, by developing a three dimensional lamination theory; (3) accurate determinations of spring bed coefficients in equations based on a shell model (e.g. for use in a ring model, which could yield a closed form solution for various tire performance parameters); (4) experimental and analytical studies of elastic properties and strengths of twisted tire cords under various conditions of extension, compression, bending, and torsion; (5) experimental and analytical studies of the distribution of contact pressure between a radial carcass and a belt (which pressure strongly affects the cross-sectional shape of a tire, especially near the belt edges); and (6) theoretical studies of the cross-sectional shape of the inflated radial tire by relating the bending rigidity of the body, particularly near the bead, to the mold shape.
Determination of Sequence Distribution in Styrene-Butadiene Copolymer I. 1H-NMR Study of Styrene Oligomers
Authors: Tanaka Y. , Sato H. , Saito K. , Miyashita K.
Published: February 2011

The 1 H-NMR spectra of styrene oligomers were measured as a model of styrene sequences in SBR. The ortho-phenyl proton, methine proton, and methylene proton signals shift to a higher magnetic field as the degree of polymerization increased. The methine proton signal split into two peaks, reflecting the tacticity. The methylene proton flanked by methylene and methine protons had a higher chemical shift value than the methylene proton flanked by two methine protons. It is demonstrated that the average sequence length of the styrene units in SBR can be determined by the relative intensity ratio of the two methylene proton signals. It is also found that the fraction of styrene sequences longer than 6 units can be estimated from the relative intensity of ortho-phenyl proton signals resonated higher than 6.7 ppm.
Characterization of the Reversion Process in Accelerated Sulfur Curing of Natural Rubber
Authors: Chen C. H. , Koenig J. L. , Shelton J. R. , Collins E. A.
Published: February 2011

From studies of a series of accelerated sulfur vulcanizations of natural rubber, the structural basis of the reversion in macroscopic physical-mechanical properties has been determined. The amount of chemically induced trans-methine butadiene-like structure increases as the reversion process proceeds. When there is no observable reversion, there is no detectable trans-methine butadiene-like structure. The presence of the trans-methine butadiene-like structure is detrimental to the properties of the natural rubber vulcanizate. The vulcanization process involves two competing processes, namely, crosslinking and desulfuration. The latter process produces the trans-methine structure which is responsible for the reversion in properties.
Radial Truck Tire Inflation Analysis: Theory and Experiment
Authors: Kennedy R. H. , Patel H. P. , McMinn M. S.
Published: February 2011

The finite element method is a useful tool in the design process to give deformations, strains and stresses in tires when they are loaded. To show this, a geometrically nonlinear, materially homogeneous, and generally orthotropic finite element model is described and used in the inflation analysis of radial truck tires. The element, a linear strain axisymmetric triangle, has three displacement degrees of freedom at each node in order to correctly model the three-dimensional states of strain and stress present in generally orthotropic structures. Two radial truck tires, a tube-type 10.00R20 and a tubeless 11R22.5, are analyzed both experimentally and analytically for inflation loading. Experimentally, cord forces are measured by cord force transducers, belt edge interply shear strain is measured by a pin rotation technique, sidewall growth is measured by a laser profilometer, and sidewall strains are measured with liquid metal strain gages. These values are compared with those predicted by the finite element model. The model works well for the tube-type 10.00R20 tire and above the mid-sidewall of the tubeless 11R22.5 tire. Further work needs to be done on the lower sidewall and bead area portions of the 11R22.5 tire model. The finite element model and solution procedure for the 11R22.5 radial truck tire is used for trend predictions. Several tire construction features, belt bias angle, belt end count, body ply end count, and bell skim stock modulus are varied, and their effect on inflation growth, strains and cord forces are predicted. The largest effect on inflation behavior was variation of the belt bias angle. The other features had minor effects. These predicted trends are important in giving the design engineer direction in creating new tire types or modifying current designs.
A Curing System for Rubber Bonded to Brass-Plated Tire Cord
Authors: Barker L. R. , Bristow G. M.
Published: February 2011

Devising a suitable vulcanizing system for steel cord carcass mixes presents unusual problems. A relatively high proportion of sulfur needs to be present to react with the brass plating, but this is not generally regarded as good compounding practice, particularly from the point of view of heat-aging resistance. If an attempt is made to improve matters by increasing the ratio of sulfenamide accelerator to sulfur, adhesion suffers. To help resolve these problems, it is suggested that the accelerator N-oxydiethylenebenzothiazole-2-sulfenamide is used in conjunction with dimorpholinyl disulfide. Good adhesion can be obtained with no more than 3.5 parts phr of sulfur and only a moderate amount of vulcanization activator, such as zinc stearate, is needed for maximum state of vulcanization. Insufficient work has been carried out to reach a position where a complete formulation can be recommended, but it is believed that the following vulcanizing system could be used as the basis for achieving a high standard of adhesive bond between a natural rubber tire carcass mix and brass-plated steel tire cord: (see PDF for table)
Softer Conductive Rubber Compounds by Elastomer Blending
Authors: Sircar A. K.
Published: February 2011

Carbon black parameters that impart high conductivity in elastomer compounds, i.e., high surface area, structure, and porosity also increase compound viscosity and thus cause processing problems. In the present study, an attempt has been made to circumvent the problem by modification of the elastomer phase. Many black loaded elastomer pairs show maxima in their electrical conductivity-composition curves; the maxima are several orders of magnitude higher than that exhibited by the component elastomers. Moreover, the curves of viscosity and hardness vs. elastomer composition show either flatter maxima or even minima in some cases. Thus, conductivity with respect to the single elastomers can be increased without corresponding increases in viscosity or hardness values. The above phenomenon can be explained by elastic modulus and electron microscope investigations of black loaded elastomer blends. Elastic modulus data of black loaded blends show increased agglomeration of the carbon network in the case of incompatible elastomer pairs. Electron microscopic examination of these compounds reveals a redistribution of the carbon black. Redistribution occurs from the less reactive or less viscous polymer to the blend interface, even when black is added to the former. Accumulation of black at the interface reduces the gap width by increasing the number of contact points to result in an overall conductivity increase. The conditions for maximum conductivity were determined from the conductivity-composition curves of several elastomer pairs. It was concluded that the redistribution of carbon black, which causes the conductivity increase, can take place if the elastomers in a pair are highly incompatible and differ widely in their black interaction (e.g., NBR-CIIR), or in their viscosity (e.g., NR-CR).
Tear Strength and Tensile Strength of Model Filled Elastomers
Authors: Dreyfuss P. , Gent A. N. , Williams J. R.
Published: February 2011

Measurements have been made of the tear strength, tensile strength, and energy dissipated during stretching for model filled elastomers consisting of polybutadiene with glass beads incorporated. The glass beads were pretreated with various silanes, some of which could, in principle, form covalent bonds with the polybutadiene matrix during free-radical crosslinking of the latter and some of which could not. The tear strength of the elastomer was increased by the addition of glass beads, by about 25% for the largest beads, having a mean diameter of 150 µm. This effect is attributed to increased roughness of the tear path. The breaking elongation in tension was reduced by the addition of glass beads but the breaking stress was only seriously reduced for the least-well-adhering beads. The stored strain energy density at break was reduced in all cases. This is attributed to large glass beads acting as fracture nuclei in tension. Calculated sizes of a Griffith crack, 150–300 µm, are consistent with this hypothesis. Strain energy dissipated due to dewetting was found to be in the range 4–13% of the input energy, depending upon the degree of interfacial adhesion, in addition to about 10% dissipated in the unfilled material. The maximum value observed is in reasonable agreement with theoretical predictions.
Current Perspectives on Silicone Rubber Technology
Authors: Polmanteer K. E.
Published: February 2011

This perspective embraced many factors that are important in understanding silicone elastomer technology and the reasons for the unique properties that they exhibit. The fact that they possess the lowest transition temperatures for any known polymer qualify them as a viscoelastic polymer that can be converted to an elastomer by crosslinking. Important also is the fact that the polymer molecules are predominantly linear prior to vulcanization, which allows high extensibility when the chemical crosslinks are in the desirable range of 100–400 mer units. Siloxane chemistry is uniquely different from hydrocarbon chemistry primarily because silicon is more electropositive than carbon, and the siloxane bonds possess more ionic character. Intermolecular forces for polydimethylsiloxane based elastomers are much lower than hydrocarbon polymer based elastomers. These polymers exhibit unusually high chain flexibility, easy rotation of pendant organic groups attached to silicon, and more free volume at ambient conditions than other polymers. These properties contribute to the lower Tg values and less change in properties (e.g., viscosity of polymers, elastomer modulus and strength) with temperature, compared with organic elastomers. Additional properties that contribute to the unique properties of silicone elastomers are low surface energy, excellent oxidative and thermal resistance formulatibility to provide excellent resistance to hydrolysis and rearrangement of siloxane bonds, easy modification of solubility characteristics by substitution of different organic groups on silicon, and the use of simple chemistry alterations that allow a range of molecular weights for making high and low consistency compositions that can be crosslinked either at elevated or room temperature conditions by a variety of reactions. The unusually high degree of reinforcement obtained with silica fillers compared with nonreinforced silicone polymers is a result of excellent polymer filler bonding which consists of largely physical bonds with some chemical bonds also being present after exposure to elevated temperature curing conditions. The combination of the above mentioned properties contribute to the fact that silicone elastomers have become important engineering materials that find hundreds of difficult-to-satisfy applications. Based on the excellent potential for continued technology advancement for silicone elastomers, it is believed that substantial future growth of this family of elastomers will occur.
Adhesion and Friction of Elastomers
Authors: Roberts A. D.
Published: February 2011

Use of mirror smooth spheres and cylinders of rubber allows the thickness and contour of a liquid film trapped between surfaces to be studied by optical interferometry. Close normal approach reveals the load bearing capacity of electrical double layer forces. In the absence of such forces, a liquid film collapses leading to areas of adhesion over most of the contact region. The adhesion can be interpreted in terms of surface energy. The force required to separate adhered surfaces is found to depend critically upon the rate of separation. Dry contact observations reveal that under nonequilibrium conditions the apparent surface energy may be very much greater than the equilibrium energy. The observations can be used, in certain circumstances, to predict tack, rolling resistance and sliding friction. Such prediction reflects a combination of surface properties and bulk viscoelasticity of the rubber. In particular, the approach has been applied to rolling on rough surfaces and to the friction of rubber on ice.
Morphology of Heat Set Segmented Elastomers
Authors: Van Bogart J. W. C. , Gibson P. E. , Cooper S. L.
Published: February 2011

The technique of small-angle x-ray scattering (SAXS) was used to investigate the morphology of three heat set (200–400% strain at 110–125°C) segmented elastomer samples—two polyester-polyurethanes and one polyether-polyester. The degree of hard-segment ordering in the samples varied from amorphous to slightly crystalline to highly crystalline. The results showed that the hard-segment domains in the semicrystalline materials developed axial ratios of about 2:1 for the axes parallel and perpendicular to the direction of stretch, while the sample with amorphous hard-segment domains showed no similar distortion in hard-segment domain shape and no anisotropy in the thickness of the interface between hard- and soft-segment domains.
Copolymerized Antioxidants in Polyether-Ester Elastomers
Authors: Wolfe J. R.
Published: February 2011

Antioxidants copolymerized into polyether-ester elastomers increase the resistance of the elastomers to degradation by heat aging. Resistance to heat aging increases as antioxidant content increases, with no bloom formation at high antioxidant content. The addition of a small amount of a nonbound amine antioxidant further increases the resistance to heat aging of elastomer protected by copolymerized phenolic antioxidant. The 3,5-di-t-butyl-4-hydroxybenzenepropanamido structure is a more effective antioxidant in these polyether-ester elastomers than the 3,5-di-t-butyl-4-hydroxybenzamido structure.
Thermoplastic Polyurethane Elastomer Melt Polymerization Study
Authors: Schollenberger C. S. , Dinbergs K. , Stewart F. D.
Published: February 2011

It is concluded from the present study that the slightly modified Brabender PlastiCorder torque rheometer is well suited to the study of thermoplastic polyurethane elastomer melt polymerization. The instrument is sensitive and responsive enough over a broad range to sense and record continuously even small changes in polymerizate temperature and viscosity as a function of time. This capability has enabled us to follow the full course of such polymerizations, with the exception of the final polymer maturation process which customarily is effected in the quiescent state. In our study, the effects of several polymerization variables were clearly and quantitatively apparent, including the effects on the course of polymerization and its degree of: macroglycol acidity; antioxidant (stabilizer); temperature; catalyst; polymer composition; presence of shortstop; and reactant balance. The results demonstrate the known acid catalysis of the hydroxyl-isocyanate reaction as well as polyurethane molecular weight modification by polyester glycol acidity. The inclusion of a commercial phenolic antioxidant in the polymerization charge did not have any obvious effect on the course of polymerization but may have limited degree of polymerization somewhat. Increased urethane content greatly speeds the viscosity increase, demonstrating urethane autocatalysis as well as its viscosity contribution, and even low stannous octoate catalyst levels appreciably speeded the inherently rapid polymerization. The shortstopping action of fugitive and persistent primary alcohols is prompt and effective, but excessive amounts produce some irreversible polymer reversion as they readjust the polymer chain molecular weight distribution present in maintaining the urethane equilibrium. This equilbrium also showed clear response to polymerization temperature, reversible urethane dissociation reducing viscosity with increasing temperature. The effect of polymerization reactant imbalance was readily apparent in the appreciably reduced rate and degree of polymerization attending minor isocyanate deficiency. Mastication experiments in the PlastiCorder show dried preformed polyurethane elastomer to drop quickly to viscosity levels much below that reached by the same compositions during polymer formation. The viscosity loss of the former is attributed to polyurethane chain rupture promoted by virtual network restrictions to chain slippage, while the virtual network has not yet developed in the forming polymer.
Morphology-Property Relationships in EPDM-Polybutadiene Blends
Authors: Hamed Gary R.
Published: February 2011

When mixing EPDM and BR in the Brabender a heterogeneous blend results; the dispersed phase is first sheared into fibrous strands and then broken down into micron sized particles. At low doses of irradiation, the morphology of the blend only has a minor effect on the energy to break, whereas at high doses the Eb may increase by a factor of three as the dispersed particle size is reduced from the 100 micron range. The Eb of the blend is the weight-average of the two pure components at low doses (independent of morphology), but is greater than either pure component at higher doses. Interfacial adhesion may play a key role in determining the mechanical properties in rubbery blends.
Degradative Effects of Guayule Resin on Natural Rubber. II. Kinetic Studies
Authors: Keller Robert W. , Stephens Howard L.
Published: February 2011

Qualitative studies reported earlier and the kinetic studies reported here indicate that the unsaturated fatty acids in guayule resin are primarily responsible for the ability of guayule resin to accelerate the oxidative degradation of natural rubber. These unsaturated fatty acids apparently oxidize to form peroxide compounds which function as initiators of rubber oxidation.
Thermal Conductivity of Elastomer Vulcanizates by Differential Scanning Calorimetry
Authors: Sircar Anil K. , Wells John L.
Published: February 2011

A du Pont 990 differential scanning calorimeter was modified to measure thermal conductivity of elastomer vulcanizates. The method is quick and reproducible and is recommended for scouting research of polymeric materials. The thermal conductivity λ values obtained by this method of some known materials compare favorably with those in the literature. Carbon black increases λ values in all elastomers. Particle size and structure of carbon black seem to affect λ values erratically, although the trend is towards higher λ values with larger particle size and higher structure. A linear relationship of λ vs. volume concentration of carbon blacks and other fillers is observed, except at a very high concentration. The extrapolated values of λ for a filler differ in different elastomeric media. Noncompatible elastomer blends increase or decrease λ values according to the nature and proportion of elastomers. The effect of the manner of addition of carbon black does not seem to affect the λ value of compatible blends. Higher temperatures decrease λ values for all the vulcanizates studied.
Rubber-Styrene Block Copolymers in Adhesives
Authors: St. Clair D. J.
Published: February 2011

Rubber-styrene block copolymers are materials such as the A-B-A type block copolymers, where A represents a block of polystyrene and B represents a rubber block, usually polybutadiene, polyisoprene or an olefin rubber. Because polymers of this type form a physically crosslinked network structure, the polymers are thermoplastic as well as being strong and rubbery. Because of their unique structure, block copolymers are well suited for use in a wide variety of adhesives. Block copolymers can be formulated with resins, plasticizers, and fillers to meet performance requirements ranging from those of a soft, tacky pressure-sensitive adhesive to those of a stiff, high strength construction or assembly adhesive. Adhesives based on the block copolymers can be mixed and applied, either in solvent or as hot melts, using standard processing equipment. Research is continuing on block copolymer technology, formulating technology, and processing technology which should further expand the applications of block copolymers in adhesives.
The Use of Elastomers in Regenerative Braking Systems
Authors: Hoppie L. O.
Published: February 2011

Results to date on this project indicate that a regenerative braking system based on elastomeric energy storage is technically feasible, and that improvements in the elastomer further enhance the prospects of such a system. In particular, improvements in energy density are highly desirable, as this would directly reduce the required volume. Reductions in stress-relaxation rates are also desirable because less compensating is needed in the initial design. Finally, improvements in fatigue life are desirable, as this would directly increase the time between replacements of the elastomeric units. Various manufacturers and researchers have been approached to determine if an elastomer more suitable than natural rubber is available or if one is likely to be developed. The general consensus is that natural rubber is now superior to all synthetics, but suitable materials research might lead to significant improvements. No definite plans have yet been made to carry on such materials research.
Effects of Fumed Silica Treated with Functional Disilazanes on Silicone Elastomers Properties
Authors: Maxson M. T. , Lee C. L.
Published: February 2011

The reinforcement obtained with disilazane-treated silica in the platinumcatalyzed silicone elastomer was found to be dependent upon not only the amount of disilazane employed but also the structure of the disilazane and its distribution on the silica surface. Incorporation of a small amount of vinyl-functional disilazane such as (ViMe2Si)2NH along with (Me3Si)2NH (major treating agent) can significantly increase the modulus and hardness of the resulting elastomer. [ViMe2Si(OMe2Si)3]2NH gave higher modulus and hardness than (ViMe2Si)2NH, whereas (HMe2Si)2NH gave lower modulus and hardness values. The random treatment resulted in greater improvement of cured elastomer properties than the heterogeneous treatment at the same treatment level.