bluuebunny/crossref_metadata_2025 huggingface dataset:
Mastication of Rubber
Authors: Fries H. , Pandit R. R.
Published: February 2011

As has been shown, peptizing agents act in the mechanochemical and thermooxidative breakdown of elastomers as radical acceptors at low temperatures and as oxidation catalysts at high temperatures. Modern peptizing agents usually consist of thiophenols or aromatic disulfides combined with metal complexes (chelates) of Fe, Cu, and Co, as catalysts for the oxidative breakdown. The composition must be such as not to affect the mechanical properties, stability, and aging of compounds and vulcanizates. Peptizing agents have practically no influence on the vulcanizate properties. Mastication can be carried out as a separate step or as an integrated part of the mixing process. When mastication is integrated with the mixing process, vulcanizate properties like flex fatigue resistance are improved. The principles discussed enable the compounder to select the most favorable mastication and mixing procedure for any given situation.
The Relationship between Heat Buildup and the Chemistry of Crosslinking Systems
Authors: Kempermann Theo
Published: February 2011

An attempt has been made to describe the mutual correlation of different heat buildup test methods. The results are, for example in the case of the Goodrich flexometer, affected by no fewer than four relevant parameters (E′, tan δ, Δh and h), with their initial values and with their changes in time; so we are concerned with a complex and not easily analyzed system. However the following conclusions can be made: Heat buildup must be regarded as a dynamic cyclic process entailing mechanical work and aging. Much more importance should be attached to the results of long-time tests than to the results of short-time tests. Depending on the duration of the test, completely different results may be obtained. Tests that do not result in permanent deformation of the test specimen are preferable. A method of test in which the specimen of constant dimensions is subjected to a constant and alternating deformation has yet to be developed. Assumptions drawn from the results of laboratory tests may prove completely untrue for tires owing to the phenomenon of sulfur migration from the belt zone into the tread. Laboratory tests clearly favor systems containing little sulfur; tire tests confirm only to a limited extent the desirability of using low-sulfur systems. For laboratory tests, it is therefore preferable to use a constant amount of sulfur, which should not be too small. The results obtained by varying the chemistry of the crosslinking system may be summarized as follows: The heat buildup falls as the amount of sulfur is reduced. Thiazole accelerators give better results than sulfenamides. Sulfenamides give better results than basic accelerators. Some retarders have unfavorable effects. Dithiophosphates have favorable effects in the low-sulfur system.
Some Rheological Aspects of the Peel Strength of Rubbery Adhesives
Authors: Gent A. N. , Hamed G. R.
Published: February 2011

The strength of adhesion between two types of SBS triblock elastomer and polyethylene terephthalate (Mylar) has been measured using a peeling geometry. Three aspects of the measured strength have been studied: its dependence upon thickness of the elastomeric adhesive layer, its dependence upon the speed of peeling, and the occurrence in some circumstances of tearing failure of the elastomer, rather than interfacial separation. The bond with the stiffer SBS elastomer (Kraton 1101) had a peel strength that was independent of thickness over the range studied: 0.1–6 mm. However, the peel strength with the softer SBS material (Kraton 3202) increased linearly with thickness before reaching a constant value at thicknesses greater than about 2 mm. This difference in the dependence of the peel strength upon thickness of the adhesive layer for the two elastomers is attributed to the formation of a relatively thin plastically-yielded layer at the peel front in the former case but not in the latter. The dependence of the peel strength of the Kraton 1101-Mylar bond upon the rate of peeling was strongly influenced by the degree to which equilibrium wetting had been achieved before testing. At low levels of interfacial interaction, the peel strength increased markedly with peeling rate, whereas, when the interaction was relatively strong, the strength did not vary much with changes in the rate of peeling. These features are again attributed to the tensile stress-strain behavior of this elastomeric adhesive, and the occurrence of plastic yielding under high local stresses. The adhesion between Kraton 3202 and Mylar underwent a transition in failure mode from rubber failure to interfacial detachment as the peeling rate was increased. The peeling rate at which the transition occurred was found to be proportional to the thickness of the adhesive layer, in accordance with a characteristic rate of straining. This transition is also attributed to ductile processes within the adhesive.
Filler Choices in the Rubber Industry
Authors: Dannenberg E. M.
Published: February 2011

A wide variety of inorganic fillers are produced for the rubber industry. The most important are the clays, precipitated silicas and silicates, and the ground and precipitated calcium carbonates. The silicas and silicates provide the broadest particle size range falling into the carbon black range from FEF (N550) to finer than SAF (N110). The clays and calcium carbonates are in the larger carbon black particle size range from coarser than thermal black (N990) to FEF (N550). if particle size were the only important parameter determining the usefulness of rubber fillers, these products would meet the requirements presently served by carbon black. Their failure to be interchangeable with the carbon blacks is due to their lower modulus and reinforcement performance. These deficiencies are caused by the nature of their surfaces, which are generally more polar and hydrated than carbon black. This makes them more difficult to adhere to and interact with the rubber phase. In order to improve the surface interaction of inorganic fillers with hydrocarbon rubbers, a number of new polymer-reactive, surface-treated products have been introduced. The addition of silane coupling agents during mixing has also been recommended. Silane treated clays and talc, and polymer-grafted clay and calcium carbonate are commercially available. These products are better than their base materials. For some applications, they have been suggested as alternatives to the lower reinforcing grades of carbon black. For the higher reinforcing carbon blacks, only the precipitated silicas with silane additives can be considered as alternatives. However, in tire tread applications, the performance of these combinations has not been clearly defined, and the high cost of the silanes makes their use with silica prohibitive. A more economic method for coupling may result from recent research on functionalized polymers capable of reacting with the surface silanol groups of silica. This survey also includes two finely divided carbonaceous fillers made from coal and petroleum coke. Blends of these materials with more reinforcing carbon blacks and other fillers have been recommended as alternatives to the carbon blacks in the thermal to SRF range. A number of commercial fillers have been suggested as alternatives to the lower reinforcing grades of carbon black for some applications. There are no satisfactory substitute products for the medium to high reinforcing grades of carbon black.
Current Trends in Fluoroelastomer Development
Authors: Albin L. D.
Published: February 2011

Recent advances in the automotive, petroleum, and energy-related industries have created applications for high-performance elastomers, which often require chemically resistant elastomers with improved high-temperature operating capability. Fluoroelastomers are uniquely capable of withstanding high temperatures in conjunction with aggressive chemicals, fuels, and lubricants. While a number of reviews concerning fluoroelastomers have been published in the last three years, this paper will concentrate on recent developments that have improved fluoroelastomers to meet the requirements of new high-performance applications. Three types of fluorine-containing elastomers—fluorocarbon, fluorosilicone, and fluoroalkoxyphosphazene (phosphonitrilic)—are commercially available. The fluorocarbon elastomers have the highest fluorine content, with general grades having between 53 and 70% fluorine. The high fluorine content of these specialty elastomers imparts exceptional resistance to attack by fuels, oils, and corrosive chemicals. The excellent resistance to high-temperature aging for extended periods of time results in a temperature use range of −46 to 320°C. Fluoro-carbon elastomers are produced in the United States by 3M (“Fluorel” Brand fluoroelastomer) and Du Pont (“Viton” Brand fluoroelastomer) and outside the United States by Montedison (Italy, “Technoflon” Brand fluoroelastomer), Daikin (Japan, “Daiel” Brand fluoroelastomer), and Asahi Glass (Japan, “Aflas” Brand elastomer, a copolymer of tetrafluoroethylene and propylene). Fluorosilicone and fluoroalkoxyphosphazene elastomers contain 30–40% fluorine. Although the fluorine content of these elastomers is less than that of fluorocarbon elastomers, it is high enough to provide moderate chemical resistance to many fluids. The flexible nature of the heteroatoms of the polymer chain backbone in fluorosilicone and fluoroalkoxyphosphazene elastomers results in excellent low-temperature flexibility, giving them a temperature use range of −54 to 230°C. Fluorosilicone elastomers are produced by Dow Corning (“Silastic”) and General Electric (“FSE”), while fluoroalkoxyphosphazene elastomers are produced by Firestone (“PNF”). This paper is a discussion of developments in fluorocarbon elastomer technology that have led to successful use in demanding applications which require high-performance elastomeric parts. Typical properties of fluorocarbon elastomers and improved properties resulting from cure system development and variations in the fluorine content of this type of elastomer will be presented. Applications for fluorocarbon elastomers in the automotive, petroleum, and energy-related industries will be illustrated.
Processing Rubber Compounds with Polymeric Dispersions of Rubber Chemicals by Automated Pellet Feeding Technology
Authors: Topcik Barry
Published: February 2011

This paper describes the cross-fertilization of plastics technology and the processing of rubber compounds in particulated form, employing an extruder as a mixing device. Stress-strain and rheometer test data established that pelletized compounds based on CR, CSM, EPDM, and SBR are successfully extruder-mixed with their respective curative systems predispersed in polymeric binders and pelletized. Since all ingredients in both types of pellets are in dispersed form, only good blending is required, not intensive, high shear mixing. X-ray radiography confirms that intimate mixing of the pellets was obtained by tracing the progress of incorporation of zinc oxide into a CR compound. The need to modify the extruder screw used in this experimental work by insertion of pins to create an improved mixing action is demonstrated. A screen pack at the breaker plate provides the necessary backpressure to further improve the degree of mixing. With other types of mixing screws, not necessarily made with pins, the screen pack may be eliminated. A process is suggested to manufacture extruded items by metering, blending, and extruder-mixing base and curative pellets. The cost of a second pass Banbury mix can be obviated resulting in the virtual elimination of scorched and bin-aged batches while maintaining the cleanliness of the strained base compound.
Finite Element Analysis of Giant Earthmover Tires
Authors: De Eskinazi J. , Ridha R. A.
Published: February 2011

The stress analysis of an off-the-road earthmover tire subjected to inflation pressure was carried out by the finite element technique by using eight-noded isoparametric toroidal elements. A control design, as well as two variations of this design in which cord angles and end counts were varied, have been examined. Deformations and stresses within the tire were predicted. The results show that variations in the cord angles and end counts may lead to significant changes in the deformation and cord load distribution patterns of the tire. Furthermore, it was observed that, because of the relatively large size of the tire, minor variations in the green cord angles (for example, due to production variations) can lead to magnified differences in the values of the cured angles and thereby cured end counts. These, in turn, can significantly affect the deformation and cord load distributions within the tire. The finite element technique used in this study provides an integrated approach for the structural analysis of tires. Detailed responses to various loading conditions and different changes in the design parameters were computed.
Fluoroelastomer Applications for Pollution Control in the Automotive, Petrochemical, and Electric Power Industries
Authors: Campbell R. R. , Stivers D. A. , Kolb R. E.
Published: February 2011

The effects of percent fluorine, filler, and cure systems on the thermal and acid resistance of fluoroelastomers were evaluated over temperature ranges that would be typical of actual flue duct installations and accelerated conditions such as 275°C for thermal resistance and 149°C for concentrated sulfuric acid resistance. FKM 2176, which contains 65% fluorine by weight, became hard and brittle after two weeks of accelerated air aging at 275°C. The balance of physical properties of FKM 2176 were good when aged at 200°C. FKM 4894, which contains 67% fluorine by weight, retained useful properties after six weeks of accelerated air aging at 275°C. This indicates this material has improved properties for flue duct applications compared to FKM 2176. FKM 4894 filled with MT carbon black had improved retention of tensile strength after aging at 232°C relative to the FKM 4894 filled with SRF/HAF black, Austin Black and litharge. FKM 2176 was totally degraded after aging three days at 149°C in concentrated sulfuric acid. Aging of FKM 4894 in concentrated sulfuric acid at 149°C resulted in a loss of approximately 75 percent of the original tensile and an increase in the elongation, and the appearance of the exposed surface did not indicate chemical attack. Although FKM 4894 was superior to FKM 2176 when aged in sulfuric acid at 149°C, there was little difference between FKM 4894 and FKM 2176 when aged at 121 °C for up to four weeks or after eight weeks at 100°C in concentrated sulfuric acid. Austin Black showed the best retention of tensile of the four filler systems evaluated after aging at 100°C in concentrated sulfuric acid. FKM 4826, which contains 69% fluorine and is vulcanized using organic peroxide and triallyl isocyanurate, has indicated a compatibility with fiberglass that is superior to all fluorocarbon elastomer gums that were tested.
A New Gelled Fluoroelastomer
Authors: Tabb D. L. , Finlay J. B.
Published: February 2011

FKM 5737 is a highly gelled fluoroelastomer similar in composition to FKM B. It can be added to other fluoroelastomers to improve their performance in the following areas: 1) improved processing in extrusion and calendering with the greatest advantages in extrusion, 2) atmospheric curability in peroxide-curable blends with FKM GF and 3) ultra high modulus, processable compounds for oil and geothermal applications.
Reinforcement of Rubber by Carbon Black
Authors: Rigbi Zvi
Published: February 2011

The mechanism by which carbon black reinforces elastomers is one of the most interesting problems of modern technology and still a subject of much speculation. The effect itself was discovered by S. C. Mote of the India-Rubber, Gutta-Percha and Telegraph Works Co. of Silvertown, near London, as a result of an effort to improve the properties of rubber even more than was possible by zinc oxide. The (American) Goodrich Company purchased certain manufacturing rights from the Silvertown company in 1912, and by 1915, the inclusion of carbon black in rubber compounds of high quality had become general. The most important effect observed upon introduction of carbon black into rubber was the vast improvement in abrasion resistance. As long as natural rubber was the unique elastomer in general use, other effects of carbon black, although by no means insignificant, were not of the same great importance, with the possible exception of tear resistance. With the outbreak of war in 1939 and the consequent shortage of natural rubber in the industrial West, the introduction of the copolymer of butadiene and styrene, then known as Buna or GR-S, as an almost total replacement for natural rubber, would not have been possible without carbon black. It may be stated, with little likelihood of contradiction, that no other product exists which contributes as much strength and abrasion resistance to noncrystallizing rubbers, while maintaining to a large extent their desirable elastic properties, as does carbon black. In spite of the tremendous consumption of carbon black, mainly in tires, and the steady progress made in improving its quality, the reasons for its unique behavior are still largely a matter of speculation and debate. The subject is enormously complex, as may be gathered from a survey of the literature. Many studies have been published describing one aspect or another of the behavior of carbon black (or carbon blacks, since there are many grades available) and these are still appearing. Some excellent papers and books survey and analyze the available information, such as those by Studebaker, Kraus, Donnet and Voet, and Medalia.
Optimization of Silane-Silica OTR Compounds. Part 1: Variations of Mixing Temperature and Time during the Modification of Silica with Bis-(3-Triethoxisilylpropyl)-Tetrasulfide
Authors: Wolff S.
Published: February 2011

This study of the TESPT modification reaction of silicas gives the compounder new and valuable information about rubber filler-silane interactions. It allows TESPT to be used more practically and economically. It also suggests several areas that would be interesting and worthwhile for further investigation. The conclusions based on this study are: (1) The modification reaction of silica with TESPT in situ cannot be considered as an equilibrium reaction. (2) The degree of modification increases with TESPT reaction time and temperature. Temperature has more effect than time. (3) In natural rubber, the highest and most practical modification reaction temperature is about 160°C. By performing the modification reaction between 150 and 160°C, it produces optimum cure rate and 300% modulus. Above 160°C, the thermal reaction of TESPT with natural rubber starts and reduces the sum of filler/rubber and rubber/rubber crosslinks available in the final cured rubber. (4) Up to 160°C, the number of filler/rubber and rubber/rubber crosslinks remains constant. But increasing temperature and reaction time lead to an increasing ratio of filler/rubber to rubber/rubber bonds. This improves the properties that are the most important for an OTR tread. (5) The higher the yield of filler/rubber bonds achieved by using the optimum reaction temperature and time, the less TESPT is necessary to get the desired properties. This produces better cost/performance. (6) To get the highest modification with TESPT, it should be added with the silica, to make best use of the reaction time dependency. (7) Most of the physical properties are dependent on the ratio of filler/rubber to rubber/rubber bonds and can simply be correlated to the 300% modulus of the compound. (8) The previously published standard mixing procedures' do not have to be changed with regard to the mixing sequence. However, by controlling mixing conditions, it may be possible to lower the level of TESPT and still obtain the desired improvements in compound physical and performance properties.
Short Jute Fiber Reinforced Carboxylated Nitrile Rubber
Authors: Chakraborty S. K. , Setua D. K. , De S. K.
Published: February 2011

Silica is not an essential component in the bonding system in XNBR-jute fiber systems. Mechanical anisotropy is observable only at the higher fiber loadings (40 phr and above) in XNBR-jute fiber composites. In composites containing sufficient amounts of bonding agent and fibers for tensile-strength anisotropy to be observed, tensile failure occurs by both fiber breakage and debonding. Fibers increase the aging resistance of XNBR composites. Mill shrinkage and green strength of XNBR improve, while Mooney viscosity increases and scorch time decreases with the addition of jute fiber to XNBR.
Autohesion of Elastomers
Authors: Bothe Lothar , Rehage Guenther
Published: February 2011

Autohesion is a particular form of adhesion. It occurs when two surfaces of the same elastomer are pressed together. The increase of the autohesive strength, with the increase of contact time, is caused by interdiffusion of mobile macro-molecule chain ends across the boundary face. After a certain time of contact, the contact zone disappears and a homogeneous system is obtained. The autohesive strength is then equal to the bulk strength of uncrosslinked elastomers. The autohesion of polybutadiene, butadiene-acrylonitrile copolymers, ethylene-propylene copolymers and polychloroprene was studied. The influences of microstructure, polar side groups, cristallinity, contact time, test rate, and the influence of solvents on autohesion were investigated in detail.
Thermoplastic-Guayule Rubber Blends—Compositions and Mechanical Properties
Authors: Ramos-DeValle L. F. , Ramírez R. R.
Published: February 2011

An experimental study of the mixing and final mechanical properties of blends of guayule rubber with polyolefins was carried out. It was found that (1) variation in total mixing time during blend preparation produced only minor differences in maximum tensile properties; (2) tensile properties of the blends approach those of the plastic at GR concentrations of 50% and lower, those of the rubber at GR concentrations of 70% and higher; (3) tensile properties of partially crosslinked blends improve if the addition of DCP is effected after partial mixing of the pure homopolymers; (4) the partial cross-linking of the blend exerts a strong beneficial influence on the mechanical properties; (5) the addition of carbon black exerts little influence on the mechanical properties of the blend. It can be suggested that, at 60% GR, both polymers (GR and HDPE) show the same tendency to form the continuous or dominant phase. Above 60%, the rubber tends to be the dominant phase, and below 60% the plastic tends to be the dominant phase. The mechanical properties of partially crosslinked GR-HDPE blends are comparable with those of similar commercially available products. This suggests a further alternative in the commercialization of natural guayule rubber, namely, thermoplastic rubbers.
A Comparative Rheological Investigation of Natural and Synthetic Cis-1,4 Polyisoprenes and Their Carbon Black Compounds
Authors: Montes S. , White J. L.
Published: February 2011

A comparative experimental study of the rheological properties of four cis-1,4 polyisoprenes, two naturally occurring and two synthetic, is reported. The two naturally occurring elastomers are from the hevea tree and guayule bush, and the synthetics are produced by alkyl lithium and Ziegler catalysts. Transient and steady state shear viscosity, stress relaxation and elongational stretching experiments were carried out at 100°C. Shear viscosity was measured using creep and constant shear rate modes in a sandwich viscometer as well as with a capillary rheometer. The hevea based elastomer has the highest viscosity and maximum relaxation time. The likeliest reasons for the higher viscosity and memory of the hevea is the presence of large amounts of gel and higher levels of long chain branching than in the other cis-1,4 polyisoprenes. Rheological measurements are also reported for compounds with 0.1 and 0.2 volume loadings of carbon black. Yield values are observed for the 0.2 loading compounds.
Modification of Asphalt by Block Polymers of Butadiene and Styrene
Authors: Kraus Gerard
Published: February 2011

Elastomeric thermoplastic block polymers of butadiene and styrene are highly effective in converting asphalts into truly rubber-like materials. Additions of 10–14% of these polymers to asphalt result in lower penetration values, greatly reduced flow above room temperature, increases in softening temperature to values in excess of 100°C and superior low temperature flexibility. The blends are characterized by a unique morphology in which the block polymer, swollen with the lower molecular weight constituents of the asphalt, forms a continuous lacework in a bituminous phase enriched with asphaltenes. The polymer-rich phase consists, in turn, of two microphases derived from the block polymer domain structure. At low concentrations, where the swollen polymer forms discrete inclusions in the asphaltic continuum, effects on the physical properties of the asphalt are less pronounced but can still be significant. The multiphase morphology of these composites accounts satisfactorily for the most important features of their mechanical behavior.
Dynamic Mechanical Properties of a Carbon Black-Loaded Butyl Rubber Vulcanizate and a Carbon Black-Loaded Polyisobutylene
Authors: Ferry John D. , Fitzgerald Edwin R.
Published: February 2011

The dynamic mechanical properties of rubbers loaded with carbon black have been the subject of many investigations because of their importance in the performance of products, especially the energy dissipation, skid resistance, and other properties of vehicle tires. However, the important variables of frequency and temperature in oscillating deformations have usually been explored in fragmentary fashion. In particular, the degree to which these variables can be treated with frequency-temperature superposition appears to differ considerably depending on the type of compound investigated. In many cases, data have been insufficient to establish whether the essential criterion for superposition, namely, the same temperature dependence for all relaxation mechanisms, is satisfied. For this purpose, extensive measurements over wide ranges of closely spaced frequencies and temperatures are required. Such data are needed, in any case, to determine the responses of elements of a vehicle tire over the ranges of temperature and time scale to which they are subjected in use and to provide input information for thermo-mechanical modelling of power loss in tires. This paper is intended to be one of a series on dynamic mechanical properties of a variety of carbon black-loaded compounds over wide ranges of frequency and temperature. It describes results for a vulcanized butyl rubber loaded with a medium processing channel black, and the almost chemically identical linear polymer polyisobutylene loaded with a semireinforcing furnace black; these results are compared with previously published data for vulcanized butyl gum and pure polyisobutylene . The shear strain amplitude in these measurements is very small, of the order of 10−5 to 10−7, in a range of linear viscoelasticity as confirmed by sensitive tests, and thus the Mullins effect is avoided. The prominent dependence of viscoelastic properties on strain amplitude, as investigated by Payne and Watson and later workers, appears at considerably higher strains of 10−3 or more. Of course, the behavior in large deformations will be very different from that described here, but it is important to understand first the properties of the structure close to its equilibrium rest state.
The Effect of Petroleum Extender Oil Types on the Properties of a Compounded Radial Styrene Block Thermoplastic
Authors: Recchuite A. D. , Dimeler G. R.
Published: February 2011

This investigation was undertaken to define the relationship between petroleum extender oils and physical characteristics of compounded styrene block elastomer. Styrene block copolymers offer the versatility to be extended with paraffinic, naphthenic, or aromatic type oils. Despite this versatility, highly refined naphthenic oils have found the most use because they offer a better overall balance of YBSR compound properties and color stability. This study verifies the basis for that preference. However, as styrene block copolymers find applications in product areas other than footwear, it is expected that all extender oil types will find wider usage. The compounder can vary oil loading and oil viscosity to achieve the desired properties with the most cost effective formulation.
Flow Criterion for Elastomer Tack
Authors: Hamed G. R. , Shieh C. H.
Published: February 2011

In order to form a tack bond, the first step is to establish molecular contact between the two sample surfaces. This requires viscous flow of material near the surfaces under the contacting pressure. The tack of specimens with model surface roughness has been performed using a T-peel geometry. A simple flow parameter has been found that uniquely correlates with the relative tack of NR samples of varying molecular weights. For various contacting pressures and molecular weights, a single mastercurve was found in which relative tack is a linearly increasing function of the cumulative creep compression strain of the material. For instance, consider two samples of NR, one with a high molecular weight (I) and the other with a lower molecular weight (II). For a given contacting pressure, Sample II will exhibit a greater value of relative tack. However, if a different contacting pressure is selected for each sample such that both exhibit the same extent of flow, (i.e., possess equal cumulative creep compression strains) during tack bond formation, then relative tack is identical for both samples. That is, difference in the tack strength of NR samples of various molecular weights can be completely explained on the basis of differences in viscous flow behavior without consideration of molecular interdiffusion rates.
Processing Parameters of Continuous Microwave Heating of Ethylene-Propylene Terpolymer
Authors: Wang C. S.
Published: February 2011

In continuous microwave heating, the temperature rise of rubber extrudates and the level of unabsorbed or reflected microwave power are strongly dependent upon the microwave power level, residence time, and extrudate configuration. It is therefore essential to control these processing parameters, together with the energy absorption characteristics of rubber materials, to improve the efficiency of microwave heating process.
Effect of Interfacial Bonding on the Self-Adhesion of SBR and Neoprene
Authors: Bhowmick A. K. , Gent A. N.
Published: February 2011

When two elastomer layers are partially crosslinked in contact with each other, the strength of adhesion increases. This effect has now been studied for simple vulcanizates of SBR and for CR vulcanizates crosslinked with sulfur and/or oxide linkages. Under threshold conditions, e.g., at high temperatures and in the swollen state, when both viscous effects and strain-induced crystallization are virtually eliminated, the work of detachment is small and approximately proportional to the inferred degree of interlinking, rising from a few J/m2 when only Van der Waals' attractions are present, up to 40–70 J/m2 in the fully-interlinked state. No significant differences were observed between SBR and CR vulcanizates, or with different types of crosslinking of CR. The principal structural factors governing the adhesive strength under threshold conditions appear to be the number and length of the molecular strands comprising the network and crossing the interface. The threshold fracture energy is directly proportional to the density of such strands and is smaller for shorter strands, in accord with the theory of Lake and Thomas. Under normal conditions, e.g., at room temperature and in the unswollen state, CR vulcanizates were found to adhere much more strongly for a given degree of interlinking, presumably due to strain-induced crystallization. Indeed, some enhancement of strength persisted even at temperatures of 100–150°C, in the unswollen state.
Scale-Up of Internal Mixers
Authors: Manas-Zloczower I. , Tadmor Z.
Published: February 2011

In this paper, a new criterion for scaling Banbury type internal mixers is proposed. The new criterion is a dimensionless number Xt*, representing the product of the fraction of broken agglomerates during one pass through the high shear zone of the internal mixer and the average number of passes through this zone, for a given mixing time. It can be calculated for a given system of polymer-additive from a knowledge of machine geometry and operating conditions. The dimensionless number Xt* is uniquely related to the fraction of undispersed agglomerates, ψ, which is a frequently encountered mixing quality criterion. Experimental results reported in literature, for a broad range of mixer sizes, fit, within practical acceptable error, the theoretical curve ψ versus Xt*, lending support to its validity. Moreover, the dimensionless number Xt* correlates almost linearly with the presently used scaling-up criteria, the unit work input and the total shear strain, which in turn proved to be interrelated to other properties of the compound, such as Mooney viscosity and die-swell. However, while the unit work input and the total shear strain can be used in scaling only as long as proper operating conditions are met, the dimensionless number Xt* provides a reliable scale-up criterion for a broad range of mixer sizes and geometries as well as different operational parameters. Derived from a theoretical model of dispersive mixing in internal mixers based exclusively on fundamental considerations, this new criterion can be used also for mixing cycle optimization and basic machine design.
Small-Strain Modulus of Model Trifunctional Polydimethylsiloxane Networks
Authors: Vallés E. M. , Rost E. J. , Macosko C. W.
Published: February 2011

A number of studies to test quantitatively the molecular basis of the theory of rubber elasticity have been performed during the last few years on elastomeric networks of relatively well-known structure. Many of these studies have been done on end-linked networks, for which the number of chains between junctions, their average length, and the functionalities of the junctions could be calculated. Several studies have been with poly(dimethylsiloxane) (PDMS) networks. One of the major controversial points up to now has been the effect of topological interactions between network chains on mechanical properties. Two groups of researchers have come to quite different conclusions about the role of entanglements with respect to their contribution to the elastic modulus. The first group led by Flory considers that the entanglement contribution to the elastic equilibrium modulus is due to the restrictions that topological interactions impose on junction fluctuations among their mean equilibrium position. The second group follows the hypothesis of Langley and Graessley who argue that these interactions are also present along the chain contour. Their support of this thesis is based on the experimental observation of the rubbery plateau modulus GN0 in linear polymers, which is evidence of topological interactions between chains. These interactions would also be present during network formation, and they will be “trapped”, or prevented from relaxing, by the crosslinking process. Thus, these chain-chain interactions can contribute directly to the modulus. Recently, one of us has reviewed most of the results obtained with PDMS networks. This showed that all the experimental data to date are quite consistent and give support to the second approach. In this work, we add to these data some new experiments obtained by crosslinking trifunctional PDMS networks in different states of dilution. The results give additional evidence of the contribution of chain entanglements to the modulus.
The Formation of Crosslink Precursors in the Sulfur Vulcanization of Natural Rubber
Authors: Morrison N. J.
Published: February 2011

With the accelerator MDB and with MBTS-sulfur, the addition of a relatively small amount of the zinc-accelerator complex (1) caused rapid formation of model crosslinks in 2-methyl-2-pentene under conditions in which neither model crosslink precursors nor model crosslinks were formed appreciably in its absence. In the accelerated sulfur vulcanization of natural rubber, zinc complexes promote both the formation and subsequent reactions of crosslink precursors. At 140°C, the reaction of MBTS-sulfur with 2-methyl-2-pentene gives a disulfidic model crosslink precursor derived by substitution entirely at the methylene site. At 150°C, or in the presence of the zinc-accelerator complex (1) at 130–140°C, precursors are derived by substitution at methylene and methyl sites.
The Natural Higher Fatty Acid Soaps in Natural Rubber Latex and Their Effect on the Mechanical Stability of the Latex
Authors: Chen Seong-Fong , Ng Chiew-Sum
Published: February 2011

The natural HFA soaps present in ammoniated NR latex concentrates are derived from the hydrolysis of the saponifiable lipids on the surfaces of the latex particles. A method based on cold extraction of the soaps has been developed for determining the natural HFA soaps in freshly concentrated latices. This method is better than the hot extraction method, which has been shown to cause some hydrolysis of the lipids. The natural HFA soaps in NR latex increase with time and reach a constant value in 3 to 6 weeks. The rate of increase of the soaps is divided into two linear regions and is more rapid in the first 1 to 2 weeks. More than 92% of the natural HFA soaps are adsorbed on the surfaces of the latex particles. This results in an increase in the negative electrical surface charge density of the particles and causes an increase in the mechanical stability of the latex. In fact, the increase in log MST is linearly proportional to the increase in natural HFA soaps in the latex. After the natural HFA soaps become constant, further increase in MST value is likely to be caused partly by the oxygen from the air.
Model Vulcanization of EPDM Compounds—Part I: Structure Determination of Vulcanization Products from Ethylidene Norbornane
Authors: van den Berg J. H. M. , Beulen J. W. , Duynstee E. F. J. , Nelissen H. L.
Published: February 2011

Vulcanization of ENBH (C9H14), a model for ENB containing EPDM rubber, with a system consisting of zinc oxide, stearic acid, sulfur, TMTD, and MBT at 140°C for 1 h yields slightly more than 30 different crosslinked products C9H13-Sn-C9H13 where n=2,3,4, and 5. In all of the products, the original ENBH structure is maintained (no shift of the double bond) and attachment of the sulfur bridge occurs only at the two allylic positions 3 and 9. Monosulfides (n=1) are probably also formed but no structures could be determined. Only small amounts of the MBT-Sn-C9H13 coupling products and noncrosslinked cyclic sulfides are formed.
Halogenation of Butyl Rubber—A Model Compound Approach
Authors: Vukov R.
Published: February 2011

The study of the halogenation behavior of butyl rubber model compounds has brought about a better understanding of the behavior of these systems. It has been established that the presence of methyl groups, in a position B to the reaction site in the butyl rubber model compound, profoundly influences the course of halogenation. Due to the steric hindrance imposed by these groups, both the products of chlorination and bromination deviate from patterns typical of other trisubstituted alkenes. In the case of chlorination, this deviation is demonstrated by the absence of addition products of chlorine across the double bond. In the case of bromination reactions, the change in product distribution is even more dramatic. Thus, substitution products normally not observed in bromination reactions of other trisubstituted alkenes become predominant products found in yields of between 70–90% depending on the precise reaction conditions. The behavior of the butyl model compound appears to be entirely consistent with the behavior of butyl rubber itself; the model compound approach is therefore a valuable tool for use in the basic study of this type of system.
The Postdispersion Coalescence Phenomenon in Polymer-Polymer Blends
Authors: Jang B. Z. , Uhlmann D. R. , Vander Sande J. B.
Published: February 2011

Three novel experimental techniques have been developed to study the phase separation dynamics and morphology of polymer-polymer blends. Samples prepared from different materials by different methods appear to follow the same phase transformation behavior. The minor phase, dispersed as discrete particles, may change its phase morphology by aggregation and coalescence. The aggregation process involves the change in either particle location (small particles may translate) or particle geometry (to reduce interfacial area). Once the interparticle contact is effected, the flattened interface will break and allow for sintering of particles. The particle size distribution is more or less random and tends to broaden with time. The volume fraction of the second phase has a substantial effect on its growth rate. It has been demonstrated that a combination of hot-staged optical microscopy, transmission electron microscopy, high-speed cinematography, and the three novel sample preparation techniques facilitate a detailed study on the late-stage mechanisms of phase separation of polymeric blends.
Pilot-Scale Guayule Processing Using Countercurrent Solvent Extraction Equipment
Authors: Hamerstrand G. E. , Montgomery R. R.
Published: February 2011

Conventional oilseed processing technology and equipment were successfully utilized to extract rubber from guayule shrubs that had been pretreated to render the rubber accessible to solvent action. When the chopped and ground shrubs are subjected to sufficient shear to rupture cell walls and form agglomerates of material, they can be handled readily in the essentially unmodified percolation, solvent extraction equipment. Although some of the parameters associated with the solvent system have not, as yet, been optimized, rubber recoveries in excess of 80% were achieved with both freshly harvested “lush” shrubs and shrubs that had been field-dried and stored several weeks before processing.
The Deresination of Guayule: A Physical Model. Part I: Effect of Water and Temperature on the Diffusion Coefficients
Authors: Budiman S. , McIntyre D.
Published: February 2011

1. The nature of the static deresination of guayule worms is complicated by the presence of moisture. In analogy with hevea latex coagulum, the moisture occurs in pockets and channels between the rubber agglomerates which contain the solubilized resin, and it enhances desorption of the resin into a solvent. At moisture above a critical level (around 10 wt.%), the pockets are likely to be interconnecting, thus providing easy access for the water-miscible solvent to the interior of the worms through an interchange process with the moisture. 2. Assuming minimal resistance at the surface of the worms, the static deresination is thought to take place in four consecutive steps: (a) the penetration of solvent into the pores of the worms made up of moisture pockets and channels, (b) the absorption (swelling) of the solvent into the rubber phase and subsequent transfer of the solubilized resin from the rubber phase to the solvent, (c) diffusion of the resin as a solute in the solvent through the swollen rubber phase to the internal surface in the pores, and (d) diffusion of the resin solute through the pores to the surface of the worms. 3. The deresination performance of acetone is much better than that of 95% ethanol. 4. The diffusion coefficient of acetone in the rubber phase is shown to be almost one order of magnitude greater than the diffusion coefficient for overall desorption of resin into acetone. This indicates that the rate-limiting step is the diffusion of the resin through the rubber phase to the internal surface of rubber agglomerates inside the pores.
Mechanism and Theories of Rubber Adhesion to Steel Tire Cords—An Overview
Authors: van Ooij W. J.
Published: February 2011

An overview is given of the mechanism and theories of adhesion of brass-plated steel cords to rubber. The literature on this topic in the period 1979–1983 is reviewed. Although the actual type of bond between the interfacially formed copper sulfide film and the cured network still has not been identified conclusively, this aspect of rubber-brass adhesion is becoming rather irrelevant since the literature is unanimous that bond failure seldom occurs adhesively, i.e., between CuxS and rubber, but usually cohesively within the sulfide film or adhesively at the interface sulfide-substrate. A model is described in which most of the recent findings are incorporated. In this model, brass develops a high bond strength to NR as a result of the in situ growth of a thin (≤50 nm) copper sulfide film onto the brass during the early stages of the cure before crosslinking sets in. This sulfide film has good adhesive and cohesive properties but is, on the other hand, so porous that rubber molecules become entangled in this film (interlocking model). ZnS or FeS are considered nonbonding because they lack the microporosity required for interlocking. Synchronization of sulfide growth and rubber cure is not required. The major prerequisite is that sulfide film growth has been completed before cross-linking begins. Previous rubber oxidation theories and the effect of CuxS on crosslink density of rubber adjacent to the cord surface are also discarded for lack of experimental evidence. Ultimate bond strength and bond durability are determined by cord and by compound properties. Optimum cord parameters are predicted by the model as a thin brass coating with a high concentration of diffused iron, a low copper content (60–65%) and a thin but very homogeneous ZnO surface layer which is passivating and which contains copper atoms. Copper oxides are undesirable. The homogeneous ZnO film improves the cords' corrosion resistance, the included Cu atoms are required for rapid initial CuxS formation and prevention of non-bonding ZnS formation. The major compound parameter is the sulfur-to-accelerator ratio. There is evidence that brass is sulfidized by intermediates of the type R-S-Sy-NR where R is an accelerator fragment, rather than by free sulfur. The properties of the CuxS film, such as adhesion, cohesion and stability in corrosive environments depend on the type of CuxS formed. High values of y in the intermediate lead to good CuxS films, low values produce poor films, regardless of the quality of the cord.