bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact Polystyrene: Factors Controlling the Rubber Efficiency
Authors: Wagner E. R. , Robeson L. M.
Published: February 2011

The rubber phase volume (rubber + occluded polystyrene) can be widely varied in impact polystyrene by controlling the rate of agitation during polymerization. The tensile modulus and magnitude of the rubber phase mechanical loss transitions are related to the degree of polystyrene occlusion. It is shown that the occluded polystyrene can substitute for rubber in determining these parameters. Impact strength and ultimate elongation pass through maxima as the rubber phase volume is increased at constant rubber concentration due to the optimization of rubber phase volume with particle size and rubber phase modulus. Over crosslinking of the rubber and a high concentration of a low molecular weight tail of matrix polystyrene have deleterious effects on the impact strength and ultimate elongation. The optimization of these three factors is required in making efficient use of the rubber in impact polystyrene.
Monomer Sequence Distribution in Butadiene Styrene Copolymers
Authors: Mochel V. D. , Johnson B. L.
Published: February 2011

A method is described for determining styrene sequence distribution in butadiene-styrene copolymers. An analog computer is used to resolve overlapped peaks in the styrene aromatic proton NMR spectrum. In n-BuLi copolymers a quite quantitative distinction can be made between “short” sequences, containing two and three styrene units, and “long” sequences, containing more than three units. With this method it is possible to determine experimentally the styrene-centered triad distributions and approximate styrene sequence distributions of butadiene—styrene copolymers. Agreement between calculated and NMR-curve analysis results is good, especially for n-butyllithium-catalyzed butadiene—styrene copolymers.
Prevulcanization Inhibitor the Chemistry of Scorch Delay
Authors: Leib R. I. , Sullivan A. B. , Trivette C. D.
Published: February 2011

Sulfenamide accelerators serve to perform two functions. They provide the necessary time period required to mix, process and shape rubber compounds. This portion of the overall vulcanization process is usually referred to as scorch delay. In addition, sulfenamides function as accelerators, in that once the crosslinking process has begun, they speed up this reaction. The delay period occurs because the sulfenamide must be converted to polythiobenzothiazoles, the precursors to crosslinking, before crosslinking can take place. The overall reaction of sulfenamide with sulfur is an autocatalytic process with MBT the autocatalyst. The role of PVI in this scheme is to remove MBT from this autocatalytic sequence of reactions, thus delaying those reactions which preceed crosslink formation.
Ozone Cracking and Protection of Rubber
Authors: Lake G. J.
Published: February 2011

Studies of the growth of single ozone cracks show that a critical severity of deformation is required for growth to occur. Above this deformation the rate of single crack growth is essentially independent of strain and for a number of rubbers at normal temperatures is proportional to the ozone concentration. The mechanics of cracking in stretched surfaces is more complex, the rate of growth being dependent on strain and on various other factors such as the gas flow conditions and the test piece size. It is shown that these effects are consistent with diffusion control of the rate of attack; this occurs because the rapidity with which ozone is destroyed by stretched rubber leads to a reduced concentration adjacent to a surface. Certain chemical antiozonants can completely prevent cracking, even at very high deformations. Current investigations suggest that this is due to the formation of a protective layer on the surface of the rubber by direct reaction of the antiozonant with ozone; the diffusion of unreacted antiozonant is an important factor influencing layer development. It appears that the amount of antiozonant required for protection may be determined by the rate at which a coherent layer can be formed in relation to the rate at which ozone is attacking the surface.
A Comparative Study of the Processing and Properties of Natural and Synthetic Polyisoprene Rubber Latex
Authors: Gorton A. D. T.
Published: February 2011

A comparison of natural polyisoprene latex with that of synthetic polyisoprene latex included latex properties, raw latex films, compound stability and processing, prevulcanization, vulcanizate properties, foam rubber, dipping, and adhesives. A number of differences were seen between the two latexes. It is obvious that synthetic polyisoprene latex is a very different latex to its natural counterpart. In many properties in the wet and dry state, raw or vulcanized, the synthetic latex shows inferior properties to that of natural latex. The unique combination of the polyisoprene rubber phase and the stabilizing system of protein/fatty acid soap in natural rubber latex concentrate make it superior in processing and properties to the synthetic polyisoprene latex. Many of the published claims for the synthetic material failed to receive experimental support in this study.
Particle Interaction in Carbon Black Loaded Vulcanizates
Authors: Voet A. , Cook F. R. , Hogue R.
Published: February 2011

Mixtures of SBR and a carbon black were swollen in a nonvolatile hydrocarbon and vulcanized thereafter. The swelling agent was removed by extraction with a volatile solvent in successive steps, thus producing a series of isotropically shrunken vulcanizates. Dynamic modulus values at greatly varying amplitudes were determined for vulcanizates with high and medium structure HAF carbon blacks. Results indicate that the transient carbon black structure is an exponential function of the interparticle distance, confirming a previous hypothesis attributing the transient structure to a mutual particle attraction by van der Waals forces.
Physics of the Slipping Wheel. III. Slip under Camber and Other Forces in Pneumatic Tires
Authors: Livingston D. I.
Published: February 2011

An elementary theory is proposed for the origin of the camber force arising when the plane of a traveling wheel is inclined to the vertical and for its interaction with the lateral slip force when the wheel is at an angle to its traveling direction. The theory considers the path of the periphery of the wheel through the ground contact to be deflected from that taken if the wheel were undeformed, and the resulting tangential stress is summed over the contact area. The results are consistent with experiment for small camber angles.
Determination of Butadiene in SBR-Type Copolymers by Thermographic Analysis
Authors: Sircar A. K. , Voet A.
Published: February 2011

Thermograms of SBR-type elastomers obtained by differential scanning calorimetry in an inert atmosphere, permit the evaluation of the butadiene content of the elastomers by means of determination of the area per unit weight under the exothermic part of the curve.
Characterization of Sulfur-Cured Styrene-Butadiene Copolymer Rubbers and Their Polybutadiene Blends
Authors: Clark J. K. , Scott R. A.
Published: February 2011

Dissolution of sulfur-cured, carbon black-loaded copolymers and their blends with cis-1,4-polybutadiene (PBD) are brought about by boiling with o-dichlorobenzene which contains a small amount of 2,2′-dibenzamidodiphenyl disulfide. The resulting slurries are subjected to a sequence of separations which include high-speed centrifugation to remove solids, and solvent precipitation followed by filtration to isolate the precipitates. The precipitates are washed with solvent to remove soluble organic materials followed by carbon disulfide washing to dissolve the polymers. Cast films of the polymers are obtained by evaporating the carbon disulfide washings onto sodium chloride discs. The infrared spectra of the cast films of these preparations are very similar to those of their respective polymers prior to loading and curing. Calculations for relative concentrations of bound styrene and PBD micro-structures permit nominal identification of the kinds of styrene-butadiene rubber and the amounts of cis-1,4-PBD used in a cured rubber formulation. Absorption bands used are near 3.35 μ for cis-1,4-PBD, 6.65 μ for bound styrene, 10.35 μ for trans-1,4-PBD; and 11.0 μ for vinyl-1,2-PBD. Efforts are being made to improve the data by using a grating infrared instrument and also to extend the calibrations to include other rubber blends.
Characterization of Elution Chromatography Fractions from CIS-Polybutadiene by GPC
Authors: Smith W. V. , Thiruvengada S.
Published: February 2011

A preparative fractionation of about 23 g of a commercial cis-polybutadiene rubber is described. The method employed was a solvent elution chromatographic method with very little temperature gradient. The molecular weight distributions of the fractions obtained were determined by an analytical fractionation of 20 mg of polymer. The method was similar to the preparative fractionation and involved solvent elution chromatography. The fractions obtained were assayed for quantity, molecular weight, and molecular weight distribution by GPC. The low molecular weight fractions of the preparative fractionation had molecular weight distributions which could be closely approximated by two log normal distributions, the low molecular weight component having the narrower width. The ratio of weight to number average molecular weight was found to be about 1.1 for these samples. The higher molecular weight fractions could also be approximated by two log normal distributions; however, in these fractions the low molecular weight component had a very broad distribution but constituted only a small portion of the sample. The widths of the GPC curves of the fractions correlate satisfactorily with the molecular weight distributions found by the analytical refractionations. The GPC width is a sensitive criterion of the width of the molecular weight distribution even when only two columns are used. It is felt that the analytical fractionation procedure presented gives more detailed information on the molecular weight distribution than is easily obtainable from an ordinary GPC curve.
Outstanding Practical Problems in Emulsion Polymerization with Particular Reference to Dienic Hydrocarbons
Authors: Duck E. W.
Published: February 2011

The incentives and problems associated with 100% conversions of polymerization are discussed with reference to the heterogeneity produced by emulsion polymerization of styrene-butadiene rubbery copolymers. Stereospecific problems are also considered together with the influence of latex particle size and particle size distribution on viscosity and solids content and film-forming properties.
Multiple Glass Transitions in Butadiene-Acrylonitrile Copolymers
Authors: Chandler L. A. , Collins E. A.
Published: February 2011

The second order transition temperatures (Tg) have been determined for a range of compositions of polybutadiene-acrylonitrile copolymers. It was found that copolymers having more than 36 per cent acrylonitrile had a single Tg while copolymers with less than 36 per cent acrylonitrile had two main Tg's. The analyses were carried out with differential thermal analysis (DTA). The two Tg's are interpreted as the result of incompatible phases which differ in BD and VCN ratio. The presence of two phases is discussed in terms of polymerization conditions and molecular structure.
Mathematical Notes Concerning the Tire Contour Integral
Authors: Mavrigian G.
Published: February 2011

In developing the mathematics which underlies the design of pneumatic tires, Day and Gehman derived the differential equation for the tire contour shape, valid for any tire, in terms of the tire dimensions and the cord path α(p);
Effect and Detection of Loose Chain Ends in Crosslinked Polyurethane Elastomers
Authors: Oberth A. E.
Published: February 2011

The effect of loose chain ends on tensile properties and equilibrium swelling of crosslinked polyurethane rubbers is studied. As in plasticized elastomers, tensile strength and elastic modulus are reduced approximately by a factor (1−νE,P)2, where νE,P is the volume fraction of loose chain ends, plasticizer, or both. This effect is much larger than predicted by present theory. Also the equilibrium volume swelling ratio, V0/V, of rubbers having terminal chains or an equal volume of plasticizer is the same, provided they do not differ in crosslink density. However, the volume fraction of “network rubber” in the equilibrium swollen specimen, ν2, differs owing to the non-extractability of terminal chains. On this basis a method is proposed which allows experimental determination of the volume fraction of loose ends. Elastomers abounding in loose chain ends show markedly less long term stress relaxation. This effect is not clearly understood but is useful to detect the presence of non load-bearing network.
A Carbon Black Structure-Concentration Equivalence Principle. Application to Stress-Strain Relationships of Filled Rubbers
Authors: Kraus Gerard
Published: February 2011

It is shown that various modulus values of carbon black reinforced rubber are functions of the product of the actual black loading and a structure dependent factor. The structure factor appears to be a linear function of the so-called 24M4 value of the dibutylphthalate absorption and is independent of elongation, temperature, and degree of cross-linking over the ranges covered by the data reported. An interpretation of the results is offered based on the idea of polymer occluded in the interstices of primary structure aggregates and thereby shielded from deformation. Structure-concentration equivalence can only be demonstrated with carbon blacks differing in (primary) structure alone. Deviations are observed whenever the carbon blacks compared vary significantly in specific surface area and surface chemical activity.
Crystallization of Cis-Polyisoprenes in a Capillary Rheometer. III. The Effects of Certain Additives
Authors: Folt V. L.
Published: February 2011

Cis-polyisoprenes are readily crystallized under the pressure and orientation forces existing in a capillary rheometer. Oil-extension retards the rheometer crystallization process. However, natural rubber/oil blends containing up to 50 phr of oil are readily crystallized above room temperature. The retardation effect of oil-extension is not nearly as drastic as that produced by slight alterations in the stereoregularity of the polymer chains. ISAF carbon black significantly enhances the ease at which solidification of the melt can be effected in the capillary. Aging the black/rubber mix at room temperature enhances the ease of solidification. Shearing the aged black/rubber mix results in a retardation of the solidification process but subsequent aging of the sheared mix again enhances the ease of solidification in the capillary. Acetone extracted natural rubber crystallizes more easily in the capillary rheometer than the non-extracted material; a behavior in marked contrast to that observed under static conditions at −20° C where removal of the acetone solubles from natural rubber retards the crystallization process. A brief discussion of the crystallization mechanism in terms of supermolecular flow units is presented.
Surface Properties of Carbon
Authors: Rivin Donald
Published: February 2011

Carbon surface chemistry is relatively new as an independent subject of inquiry, and, judging by the volume of publications, is receiving increasing attention throughout the world. Our conception of carbon black and its functional behavior has changed significantly since the pioneering publication by Studebaker in 1957. Within the last few years there have been a number of excellent reviews covering various aspects of carbon chemistry by authors who are presently active in this field. Donnet, Puri, and Boehm discuss reactions of carbon and the characterization of surface functional groups while van der Plas is particularly thorough on the subject of adsorption properties and porosity. Deviney explores the relationship between surface chemistry and carbon-elastomer interactions, as does Studebaker from the point of view of the practical application of carbon black in rubber. Current monographs containing useful background information are collected in “Les Carbones” and in Walker's continuing series, “Chemistry and Physics of Carbon”. This review will describe how information from diverse sources has contributed to our understanding of the surface reactivity and fundamental adsorption behavior of carbon. It will be shown that most properties of carbon blacks are consistent with a surface structure wherein large deformed basal layers conforming to the topography of the surface are composed of several planar aromatic domains with functional groups at edge and defect sites. Examples of strong molecular interactions are given which involve specific reaction with the basal surface, individual functional groups, or a combination of both.
Tire Temperatures
Authors: Conant F. S.
Published: February 2011

Tire operating temperature is of vital concern to tire engineers because it relates to both service life and power loss in a tire. It may also affect performance in areas such as traction and cornering ability. Operating temperature is a limiting factor in the choice of construction material for truck tires, which run at much higher temperatures than do automobile tires. Adhesion failures are generally believed to be caused by excessive heat. Yet White was unable to produce separation by heat alone, even though he held a tire at 300° F for two hours, then tried to pull the components apart. In high speed operations the high temperature developed may weaken the ply bonds in a tire, which can then be separated by a combination of centrifugal force and fatigue. If the temperature reaches 350 to 400° F, however, tire separations will occur before fatigue type failures are evident. In fact, a rough relationship has been established between attained tire temperature and the type of failure in road tests. Failures more directly related to fatigue are also hastened by high temperatures. Natural rubber softens or reverts, while SBR tends to harden and become brittle under the same conditions. With the exception of groove cracking a typical fatigue failure starts from an inhomogeneity as a small internal crack and grows by heat and mechanical action. The torn surfaces usually rub against each other to cause heat degradation. In this case heat is the result rather than the cause of failure. Tread sections lying at the side of superhighways are evidence that the tires from which they came were overworked. Temperature build-up restricts use of thicker treads, of longer wearing high-grip tread compounds, and the speed potential of any tire. Tread wear is sharply reduced by an increase in temperature, whether ambient or work-induced. So many tire properties are adversely affected by high temperature that heat has been called the great enemy of tires. The two principal purposes of this review are to examine some of the causes and results of tire temperature build-up and to discuss some of the methods which have been used to measure or compute temperatures in various tire regions.
Infrared Determination of Composition of Ethylene-Propylene Copolymers
Authors: Gardner I. J. , Cozewith C. , Strate G. Ver
Published: February 2011

Carbon-14 labeled ethylene and propylene were used to synthesize a series of copolymers of known composition to serve as standards for copolymer analyses. Polymers with broad and narrow compositional distributions and differing sequence distributions were produced by varying the catalyst system. Solution and combustion counting techniques were used to determine sample composition and then infrared calibration curves were determined on pressed polymer films utilizing several different infrared peaks. 1. Within the ranges systematically varied neither compositional nor sequence distributions affect the peak ratios studied. 2. No isotope effects exist in the polymerizations. 3. NMR analysis yields the same results as 14C analysis. 4. Use of the 1378 cm−1 methyl band as calibrated with atactic polypropylene yields agreement with the 14C data if the average of polypropylene and copolymer results is used. 5. We amend the results previously published by our laboratory.
Compounding EPDM for Dynamics Applications
Authors: Hazelton D. R. , Puydak R. C.
Published: February 2011

To conclude, the simplest and least costly approach to EPDM compounds for most dynamics mountings is EPDM filled primarily with FEF black and a medium viscosity naphthenic oil, and cured with a conventional sulfur system. The key to a successful compound, however, is the ratio and amount of black and oil used.
New Accelerators for Blends of EPDM
Authors: Mastromatteo R. P. , Mitchell J. M. , Brett T. J.
Published: February 2011

Through the use of accelerators containing higher alkyl substitution, we have been able to attain improved properties of EPDM diene rubber blends. EPDM/NBR blends vulcanized with sulfur cure systems employing these accelerators compete favorably with CR compounds in heat aging; have essentially the same oil resistance level, and exhibit better low temperature properties. These blends are highly ozone resistant, easy processing, and safe. Because of the versatility of meeting a desired combination of properties by variations both in the ratios of NBR to EPDM and in the selection of the particular grade of each elastomer, these blends will fulfill many sophisticated elastomer applications. These accelerators can also be used to provide non-blooming cure systems for EPDM compounds and safer ultrafast cure systems for diene rubber compounds. We feel that this advance in property improvement in diene rubber EPDM blends through the use of these new accelerators is only the beginning of a whole new compounding technique for blending.
Silane Coupling Agent Effects in Ethylene Propylene Diene Terpolymers
Authors: Ranney M. W. , Pagano C. A.
Published: February 2011

The special performance properties noted for silane coupling agents in mineral filled EPDM compounds result from the interfacial effects related to the dual function reaction of the organofunctional silane. When common alkoxy substituted vinyl silanes are used, the nature of the hydrolyzable groups on the silicon atom is generally not a critical factor with adequate silane-filler bonding occurring under a variety of silane application techniques. It has been shown that to obtain optimum performance, the organofunctional group in the silane monomer must be generally reactive with the cure system being used, and have the ability to interact with the elastomer through co-polymerization or addition. It has been further shown that in the case of the copolymerizable vinyl silane (A-172) only a relatively low level of peroxide-induced vinyl silane-rubber bonding is obtained using standard levels of peroxide. Increasing the peroxide level in these vinyl silane-containing formulations results in a considerably higher level of filler-elastomer reinforcement producing dramatic improvements in modulus, tensile, and tear properties when compared with appropriate controls. In general, an enhanced utilization of silane at the elastomer-filler interface is realized. The use of the mercaptosilane (A-189) in sulfur curing mineral filled EPDM compounds improves the normal physical properties while dynamic testing also shows improvements in flex-life, abrasion, heat build-up, and road wear properties.
Rubber Chemicals from Cyclic Amines. IV. Thiocarbamyl Amine Disulfide Curing Agents
Authors: Morita E. , D'Amico J. J.
Published: February 2011

The cure properties of thiocarbamyl amine disulfide (I) as vulcanizing agents are influenced by the ionic and steric nature of both R and R′. The relative effects of various R and R′ are analogous to those of R and R′ in thiuram disulfides and dithioamines, respectively. However, the cure properties of I are dominated by the type of R rather than R′. Among the types of R investigated relatively longer scorch delay, slower cure rate and lower crosslink density are obtained, when R is morpholino or 3-azabicyclo(3.2.2)non-3-yl.
Rubber Chemicals from Cyclic Amines. VI. 2-(4-Morpholinodithio)Benzothiazole and Related Compounds as Curing Agents
Authors: D'Amico J. J. , Morita E.
Published: February 2011

Unlike the case of the thiazolesulfenamides, the electronic effect of substitution in the thiazole moiety on the curing properties of these compounds is not consistent. The unsubstituted 2-(4-morpholinodithio)benzothiazole 1 is superior to the 6-ethoxy, 5-chloro, or 6-nitro substituted derivatives in curing properties. The 5-ethoxycarbonyl-2-(morpholinodithio)-4-methylthiazole is comparable to 1 in scorch delay and curing activities. It is superior to the 5-acetyl and the unsubstituted 4-methyl thiazole derivatives. Both the benzoxazole and benzimidazole derivatives are inferior to the benzothiazole and 4-methyl thiazole analogs.
The Tensile Strength of Glass Yarn in Rubber and the Effects of Moisture. I
Authors: Gregg R. A.
Published: February 2011

The strength of glass tire yarn depends on its environment so that testing in rubber is necessary to determine the strength of the yarn as used. The techniques described for building and testing glass yarn-rubber composites lead to tensile values of good precision. The techniques allow specification of a standard tensile in rubber for a glass yarn. Tensiles which would exist under non-standard conditions experienced in manufacturing or use can also be determined. Tire operating temperature is one use condition covered. The techniques discriminate sufficiently to show the effects of small differences in moisture level on hot tensile strength. The rubber stock used here did not harm the tensile strength of the glass yarn. The observed tensile strength increase of the glass yarn encased in rubber as compared to air can be attributed to the stress transfer ability of the rubber and to the test piece configuration. The strength of a glass yarn-rubber composite is inversely related to the level of moisture in the composite. High moisture levels in the glass yarn and rubber stock at building and cure can hurt tensile since moisture loss from the composite can be slow. Also, high moisture level at cure may degrade the resin-adhesive system of some yarns. For this particular glass yarn under high humidity, storage at advanced temperatures and/or curing into rubber permanently damages the yarn. These observations were made under absolute humidity levels not usually encountered. The question of the extent of the humidity degradation of this type of glass yarn under practical humidities will be examined. Since the tensile loss is probably due to some degradative action on the sizing or resin, it cannot be assumed that all glass yarns will behave similarly. It will be necessary to determine the susceptibility of each glass yarn to moisture.
Research for a Uniform Quality Grading System for Tires V. Effect of Environment on Tread Wear Rate
Authors: Brenner F. C. , Kondo A. , Cohen G. B.
Published: February 2011

In tests with bias ply, belted bias, and radial commercial passenger car tires it was found that the rate of wear does not change as the tires are worn. It was also shown in a test which there were dry and wet periods that the same tires wore at a faster rate in the wet than in the dry. This observation was reinforced when a comparison of two tests run with duplicate sets of tires in January and June on the same course gave greatly different results; the greater rate of wear occurring in January when the course was continuously wet. Finally an explanation for the observation that tires wear faster on wet pavements has been proposed. The tire is more deformed passing through the contact patch on a wet surface than on a dry. In addition, the water, acting as a lubricant, reduces resistance to motion between surfaces of the cut rubber or the surface of the cutting asperity and the rubber.
Research for a Uniform Quality Grading System for Tires VI. Comparison of the Effect of Front and Rear Wheel Drive Vehicles on Projected Tread Wear of a Tire
Authors: Kondo A. , Brenner F. C.
Published: February 2011

The total number of miles that could be expected for a tire was projected and compared from a test involving two vehicles, one with a front axle drive and one with a rear axle drive. On the front axle drive vehicle the tires when changed by forward-X pattern each 1000 miles wore at twice the rate on the front wheels as on the rear; on the other vehicle they wore at about the same rate on both sets of wheels. The projected mileages for the tires on the two vehicles were 22,400 and 22,500 miles which is not appreciably different.
New Thermoplastic Elastomers. Styrene Grafts on Lithiated Polydienes and Their Hydrogenated Counterparts
Authors: Falk J. C. , Schlott R. J. , Hoeg D. F. , Pendleton J. F.
Published: February 2011

Metalation of diene polymers such as poly (butadiene) and poly(isoprene) with sec-butyllithium and tetramethylethylenediamine in cyclohexane at room temperature forms lithiated polydienes. Reaction of the polylithiodienes with styrene or α-methylstyrene forms graft copolymers. The extent of metalation is much greater than previously reported metalations with n-butyllithium and tetramethylethylenediamine. The grafting efficiencies, determined by acetone extraction and gel permeation chromatography, are greater than 95 per cent. Graft copolymers of poly (styrene) on EPDM rubbers may also be prepared using this technique. The physical properties of the graft copolymers are a function of molecular weight, graft site level, and composition. Products at specific compositions and graft levels are thermoplastic elastomers. Their properties are comparable to SBS rubbers, and offer as an advantage high melt flow. Graft copolymers of poly(styrene) on poly(ethylene) and poly(ethylene-co-butene-1) result from the hydrogenation of the butadiene moeities of graft copolymers of poly (styrene) on 1,4-poly(butadiene) and 1,2 and 1,4-butadiene copolymers, respectively. Complete hydrogenation results in graft copolymers of poly(vinylcyclohexane) on poly(ethylene) and on poly(ethylene-co-butene-1). In both of these cases thermoplastic elastomers result if the proper choice of composition and graft level is made.
Preparation and Properties of Polydienes
Authors: Saltman W. M. , Kuzma L. J.
Published: February 2011

In summary there are presented some new data on the initiation step for poly-(butadiene) polymerization with the AlEt3-Ni-BF3 catalyst which describe what appears to be a “settling down” period of newborn chains at the π-bonded nickel catalyst site. This leads to a segment of higher trans content at the end of each high cis-1,4-poly(butadiene) chain. Comparisons between nickel and cobalt catalysts seem to point up their differences rather than their similarities. We have described the role of water in effectively changing the identity of the aluminum alkyl which in turn has a marked effect on the polymerization rate, on the polymer molecular weight and the extent of crosslinking.
Measurement of Creep
Authors: Livingston D. I. , Fielding-Russell G. S.
Published: February 2011

We have described a multistation apparatus which greatly facilitates the measurement of creep and, by extending the range to shorter times, reduces the total time of the measurements. This apparatus is presently being connected to a computer and will then operate on an increasingly automatic basis. All weights will be lowered at once, the stations automatically sampled, and much of the computation performed. We shall also attempt to extend the measurements to even shorter times and thereby to reduce the number of temperatures necessary to construct the master curve. We have illustrated the operation of the apparatus with typical measurements on a crosslinked SBR sample. While the experiments may be confined to the linear region of viscoelasticity by the use of transducers of lower range and greater sensitivity, we chose to operate at extensions which made it necessary to use the Mooney-Rivlin equation to describe the results. Treatment of the data by the Mooney-Rivlin equation and reduction of the constants to a reference temperature gave a value for C1r whieh was independent of time and temperature. Within the experimental error, all the time dependence, except at very low temperature, was contained in C2r. Several other rubbers have shown similar behavior. The separation of behavior into a substantially elastic and a substantially viscoelastic part has thought-provoking implications.
Precision Treadwear Measurements at Increased Mileages by an Improved Radioiodine Method
Authors: Patel A. C. , Deviney M. L.
Published: February 2011

A greatly improved method for using Iodine-125 is described—one which permits precise, rapid, and convenient measurements of treadwear during road tests of considerably greater mileage (up to 1500–2000 miles) than reported by earlier workers. A highly reproducible laboratory calibration procedure has been developed and very close agreement between calibration curves and actual road test data is demonstrated for automobile tires in four specific treadstock cases: SBR, SBR/BR, NR, and NR/BR. Only a small percentage of the tread surface is tagged with I-125, which is employed at very low activity levels. The tagging procedure has been modified for much greater I-125 tread penetration, and has been simplified, shortened, and standardized for use by ordinary tire test personnel. It is also applicable to non-tire rubber products.
Accelerated Tire Wear under Controlled Conditions. II. Some Factors that Influence Tire Wear
Authors: Veith A. G.
Published: February 2011

Using the test system described in (I), we have determined the effect of some of the important factors in tire wear. There are three primary factors: tire force, pavement texture, and tire surface temperature. The major factor of these three is the sustained or instantaneous tire force. Accelerometer measurements show that cornering or lateral forces are chiefly responsible for wear in contrast to longitudinal (driving and braking) forces and the test system is designed to operate on the basis of such cornering forces. The wear rate depends exponentially on tire cornering force. In the low-moderate tire force range (0–500 lbs.) this may vary from approximately 2 to 4. The exponent depends upon pavement texture, tire temperature, and tread composition. Pavement texture is important in two ways: in the actual rate of wear produced and in the influence on mechanism of wear which is reflected by the value of the above mentioned exponent. Harsh aggregate pavements produce a faster rate of wear than smoother, blunt aggregate pavements. Harsh pavements give exponents of 2.0 to 2.5 which indicate a tensile-tear mechanism; blunt pavements give exponents of 3.5 to 4.0 which indicate a fatigue mechanism. The relative rating of tread compounds can change, including outright reversals, depending upon the pavement texture. The effects of such weather factors as rain are outlined. Rain “on the pavement” lowers wear rate but the “after-effect” of rain is different. The abrasiveness of pavements after a rain increases due to chemical surface etching and this promotes increased wear until the polishing action of traffic reduces this increased abrasive character. Tire surface temperature influences absolute wear rate and compound relative rating. Our data confirm the positive temperature coefficients reported by Schalla-mach. For current tread compounds, wear rate increases approximately 2% per degree Celsius. Tread composition is important. Carbon black colloidal properties, such as structure and tint, have a marked effect on tread compound wear resistance. At low tire force these effects are minimal; at high tire force, however, high structure and tint impart significant resistance to wear. This increased resistance can be quantitatively expressed by the “Severity Index Gradient”. The correlation of accelerated test results and fleet tests is, in general, good; but, due to the overall complexity of wear behavior, tire force levels, as well as pavement texture and tire temperature, must be taken into account in correlation calculations. Otherwise, confusing results will be obtained. It is precisely this ability to vary the three primary wear factors independently that makes this particular approach to tire wear important.
Elastic Modulus of Vulcanizates as Related to Carbon Black Structure
Authors: Medalia A. I.
Published: February 2011

The elastic modulus Gf′ of filled SBR vulcanizates has been measured as a function of strain amplitude A. At low loadings of carbon black (20 phr), where Gf′ is practically independent of A, the value of Gf′ (at 25° C, 0.25 Hz) can be predicted within 5 per eent from the gum modulus Gg′ by the Guth—Gold equation with due allowance for occluded volume, as calculated from the dibutyl phthalate absorption. At normal loadings (50 phr) the value of Gf′ can be predicted fairly well from this treatment if the measurements are made at high amplitude. At 25° C, 0.25 Hz, Gf′ is about 10 per cent higher than predicted due to the residual effect of the carbon black network. The dependence of the high-amplitude Gf′ on frequency and temperature is essentially the same for various reinforcing and semi-reinforcing blacks. Consequently, the value of Gf′ for one black can be calculated from the values found for other blacks. The dependence of Gf′ on A is primarily a function of surface area, but in two cases the dependence is unusually steep for different reasons. With graphitized blacks the low-amplitude Gf′ is higher than that of the ungraphitized blacks, but the high-amplitude Gf′ is low, probably due to molecular slippage. “New technology” blacks, including N339 and N351, give a high-amplitude Gf′ comparable to that of conventional blacks of the same dibutyl phthalate absorption, but give a higher Gf′ at low amplitude, indicating a more effective network structure.
Filler Effect on the Heat Stability of Vulcanized Elastomeric Compositions
Authors: Fetterman M. Q.
Published: February 2011

The purpose of this study was to determine filler effects on heat stability of vulcanized elastomeric compositions. Carbon-black reinforced compounds, designed to have good heat resistance, were modified by substituting hydrated silica for all or part of the black. Since a simple replacement of silica for black would result in dissimilar original properties, the substituted compounds were further revised to minimize this dissimilarity. This was accomplished through curative correction and/or addition of an organosilane coupling agent. Silica substitution did not provide permanency of properties at elevated temperatures, but in all cases the serviceable life of the compound was extended. Since silica substitution had minimum effect on other properties and reduced the rate of degradation at elevated temperature, this may be considered a reasonable alternative to completely redesigning a proven rubber compound in order to improve its heat resistance.
Raman and ESR Spectroscopic Studies of Accelerator Systems. I. Raman Spectra of Thiuram Sulfides and Related Compounds
Authors: Coleman M. M. , Shelton J. R. , Koenig J. L.
Published: February 2011

The Raman spectra of similar thiuram type materials are intense and very distinctive. Raman spectroscopy should prove to be an excellent analytical tool for studying complex mixture of thiuram type materials resulting from the chemical reactions that occur at vulcanizing temperatures.
Raman and ESR Spectroscopic Studies of Accelerator Systems. II. Thermal Degradation Vulcanizing Systems and Its Significance to Vulcanization Mechanisms
Authors: Coleman M. M. , Shelton J. R. , Koenig J. L.
Published: February 2011

Raman and ESR spectroscopy has been used to study the thermal decomposition of accelerator systems based on derivatives of dimethyldithiocarbamic acid. The combination of these two spectroscopic techniques has proved to be a very powerful method for detecting intermediate compounds that are important for the elucidation of the mechanism of accelerated sulfur vulcanization.
Influence of Curing Agents on Rubber-to-Textile and Rubber-to-Steel Cord Adhesion
Authors: Albrecht K.-D.
Published: February 2011

The results presented in this paper show that the dosage of sulfur greatly influences rubber-to-textile and rubber-to-steel cord adhesion. As far as rubber-to-textile adhesion is concerned, the pull-out strength is reduced when the sulfur level falls below 2 phr, the extent of the reduction depending on the type of fiber and the bonding process. With steel cord the lower limit for sulfur is as high as 3 phr. This is discouraging because it shows that the use of efficient and semi-efficient vulcanization in the manufacture of goods reinforced with fabrics or steel cord is, to say the least, highly problematical. On the other hand, it is often desirable to reduce the proportion of sulfur in order, for instance, to increase resistance to aging and reversion and to reduce compression set and heat build-up. The choice of accelerators also has an important influence on adhesion. A sufficiently long scorch time is required to allow complete wetting of the reinforcing material by the rubber compound. If curing starts before complete wetting of the textile or steel cord has occurred, adhesion cannot be built up. For example, unsatisfactory or no rubber-to-textile and rubber-to-steel cord adhesion is obtained, when ultra-accelerators are used. As the scorch time increases, adhesion improves. Best results are obtained with sulfenamides, but sulfenamides showing increasing scorch time give no improvement in rubber-to-textile bonding. However, DCBS gave much better results for rubber-to-steel cord adhesion than the other sulfenamides and thus appears particularly suitable. Although the results given by the other sulfenamides can be somewhat improved by the addition of a retarder, pull-out strength values do not reach those given by DCBS. Any decrease of scorch time of a compound deteriorates adhesion whether scorch time is reduced by compounding ingredients or by heat history imposed by processing. MBI, used as an antioxidant, which reduces scorch time drastically, causes complete loss of rubber-to-steel cord adhesion and also impairs rubber-to-textile adhesion. Most of the antioxidants, however, have a beneficial effect on mbber-to-steel cord adhesion. For zinc-plated steel cord antioxidants of the amine type give results inferior to those of the phenolic type. To obtain optimal rubber-to-textile and rubber-to-steel cord adhesion the compounder primarily has to consider the efficacy of the bonding agents but in addition he has to take into account the effects which may be exerted by compounding ingredients and processing conditions.
Characterization of New Technology Carbon Blacks
Authors: Medalia A. I. , Dannenberg E. M. , Heckman F. A. , Cotten G. R.
Published: February 2011

In this paper we have examined a limited number of conventional and new technology blacks, using the “t” method of nitrogen adsorption for comparison of surface area and dibutyl phthalate adsorption (DBPA) for comparison of structure. At a given “t” area the new technology blacks are of lower iodine number; conversely, at a given iodine number, the new technology blacks are of higher “t” area. This is not due to porosity, but rather to differences in carbon black-iodine surface interaction. The DBPA tests gives a fairly consistent measure of carbon black structure in rubber, for both types of blacks. An important difference between the two classes of black is in the higher tinting strength of new technology blacks, at a given “solid sphere” diameter (which depends primarily on the “t” area and to a lesser extent on the DBPA). We have introduced the use of a disk photosedimentometer for studying carbon black aggregate size distributions and have found that at a given “t” area, the distribution curves for the new technology blacks are shifted in the direction of smaller Stokes diameters. This can account, at least qualitatively, for their higher tinting strength. Electron microscopy supports the shift in Stokes diameters, at least qualitatively, and also indicates a more open aggregate morphology for the new technology blacks. The new technology blacks impart a higher level of reinforcement, at the same “t” area, as shown by tensile strength and roadwear. This is accompanied by a higher loss tangent or lower rebound. These properties may be due in part to a higher surface activity, as shown by a higher moisture adsorption and higher bound rubber, and partly to morphological differences, as shown by the smaller Stokes diameters and higher tinting strength. In summary, the higher bound rubber and higher tinting strength of the new technology blacks reflect differences in surface activity and aggregate size, which are responsible for the superior reinforcement shown by these blacks at a given “t” area.
Chemorheology of Irradiation-Cured Natural Rubber. I. Stress Relaxation Mechanisms for Various Curing Systems in Natural Rubber at High Temperature
Authors: Tamura S. , Murakami K.
Published: February 2011

1. There was no difference of stress relaxation, either in air or in nitrogen, between DCP cures (Sample 1) and irradiation cures (Sample 2). This suggests that these vulcanizates have the same physical and chemical structures. In air Samples 1 and 2 underwent random scission of only the main chain. 2. In the case of irradiation-TMTD cures (Samples 4 and 5), the stress decay was also based on oxidative scission of the main chain. The number of moles of main chain scission, qm(t), was independent of the ratio ρ (of Nc(0)) based on the carbon—carbon bonds to Nm(0) based on the mono- and disulfide links). However, qm(t) was larger than that of Sample 2. The oxidative scission of the main chain seemed to be accelerated by mono- and disulfide. It was found from comparison of Samples 4 and 5 that TMTD cures (Sample 3) underwent random scission on the main chain. The stress relaxation in nitrogen for Samples 3, 4, and 5 was due to thermal scission of the crosslink. 3. The stress relaxation, either in air or in nitrogen, of accelerated-sulfur-cures (Sample 6) and irradiation-sulfur cures (Samples 7 and 8) was expressed by the sum of two exponential terms. The stress relaxation in air of Samples 6, 7, and 8 could be explained by the interchange reaction of polysulfide links and the random scission on the main chain. The stress decay in nitrogen of these vulcanizates was based on both interchange of polysulfide links and thermal scission of crosslinks. The rate of the interchange reaction in air was very closely consistent with that in nitrogen. 4. The apparent activation energy of oxidative scission of the main chain was about 21 kcal/mol for Samples 2, 6, 7, and 8 and 27 kcal/mol for Samples 3, 4, and 5.
Entanglement Networks of 1,2-Polybutadiene Crosslinked in States of Strain. I. Crosslinking at 0°
Authors: Kramer O. , Carpenter R. L. , Ty V. , Ferry J. D.
Published: February 2011

Linear 1,2-polybutadiene is crosslinked at 0° (12° above Tg) by γ-irradiation while strained in simple extension, with extension ratios(λ0) from 1.2 to 2.0. After release, the sample retracts to a state of ease (λg) at room temperature. From (λ0), (λg), and Young's modulus in the state of ease Eg, the molar concentrations of network strands terminated by crosslinks (νx) and by trapped entanglements (νN) are calculated by composite network theories of Flory and others. With increasing irradiation time t, (νx) (corrected for free ends) is directly proportional to t and (νN) attains a constant value. With increasing λ0, νx is constant and νN diminishes somewhat. Extrapolated to λ0=1, νN is somewhat smaller (1.2×10−4 mol cm−3) than the concentration of entanglement strands estimated from viscoelastic measurements on uncrosslinked polymer in the plateau zone (νe=2.5×10−4). Young's modulus was also calculated indirectly from equilibrium swelling in n-heptane. The swelling is slightly anisotropic, being larger in the direction of extension.