bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Mechanical Shear on the Structure of Carbon Black in Reinforced Elastomers
Authors: Gessler A. M.
Published: February 2011

The primary aggregate structure in high structure blacks is broken down when the blacks are milled in rubber. The breakdown, it is shown further, involves the disruption initially of more easily disrupted forces, and then subsequently of more difficultly disrupted forces. If the total structure breakdown is segmented accordingly, one finds that carbon blacks differ markedly in the proportion of the breakdown which occurs in each segment. But only the breakage of more difficultly disrupted structure is identified with chemical changes in the black and with concomitantly increased carbon—polymer interaction activity, i.e., with enhanced reinforcement. In studying the breakage of aggregate black structure which occurs when the blacks are milled in rubber, the following factors are considered: (1) Carbon Black Concentration: Breakage increases continuously, though not steadily, with carbon black concentration. This result is used to emphasize the merits of concentrated black masterbatching as the means for producing high quality products from SBR, BR, and EPDM rubbers. (2) Carbon Black Structure: Taking the total structure breakage over a broad range of carbon black concentrations, the extent of the breakage increases with the extent of the primary aggregate structure in the original black. (3) Polymer Viscosity or Molecular Weight: The extent to which breakage occurs on milling increases with the polymer viscosity or molecular weight. Since this result clearly cites the need for high shearing forces during milling, the severe limitations which must attend the use of plasticizing oils is implied. (4) Open Mill vs Banbury Mixing: The extent to which breakage occurs in the Banbury is significantly less than that on the two roll mill. Evidence is presented to show that this, clearly, is a temperature related result and, as in (3) above, that the magnitude of the shearing forces is the critical factor.
Immobilization of Elastomers at the Carbon Black Particle Surface
Authors: Sircar A. K. , Voet A.
Published: February 2011

Determinations have been made of the amount of elastomer unextractable from unvulcanized masticated mixes with carbon black by a given solvent at boil, expressed as immobilized elastomer. Saturated and unsaturated elastomers varying in molecular weights from 2000 to 325,000, were used, while solvents of greatly differing boiling points and solvent power were employed. It could be shown that the bonding between elastomers and carbon black is not a simple adsorption, but involves a higher energy interaction, defined as chemisorption. At successively higher temperatures elastomer is increasingly removed from the carbon black surface. The temperature Tm, obtained by extrapolation of the linear relationship between amounts immobilized and temperature of extraction, represents the temperature theoretically required to eliminate all bonds between carbon black and elastomer and is therefore indicative of the bond strength. Data suggest the existence of a bonding energy spectrum. Upon graphitization, blacks show a considerable decline in high energy bonding ability for elastomers. Saturated elastomers show less bonding than unsaturated elastomers with the same furnace black. “Bound rubber” represents the sum total of physically adsorbed, mechanically entangled, and chemisorbed elastomer. The actual values are greatly dependent upon the procedure used. “Immobilized rubber”, indicating chemisorbed elastomer, is easily determined, is not influenced by the method, and is more significant as an indicator of reinforcement.
Effect of Sulfur and Dicumyl Peroxide on Vulcanization of Natural Rubber with Tetramethylthiuram Disulfide and Zinc Oxide
Authors: Manik S. P. , Banerjee S.
Published: February 2011

The salient features of both non-elemental sulfur vulcanization by TMTD and elemental sulfur vulcanization promoted by TMTD both in presence and absence of ZnO and stearic acid have been studied. TMTD increases the rate of DCP decomposition and lowers the crosslinking maxima due to DCP depending on its concentration. However, with higher amounts of TMTD the initial rate of crosslinking is increased with the increased amount of TMTD, while crosslinking maxima are still lowered due to reversion. ZnO or ZnO-stearic acid, however, seems to alter the entire course of the reaction. Both the crosslink formation and TMTD decomposition are much higher in presence of ZnO or ZnO-stearic acid, but stearic acid seems to have no effect. The reaction mechanisms for TMTD accelerated sulfuration in absence and presence of ZnO have also been studied.
Sulfenamide Accelerated Sulfur Vulcanization of Natural Rubber in Presence and Absence of Dicumyl Peroxide
Authors: Manik S. P. , Banerjee S.
Published: February 2011

Sulfuration by CBS acceleration both in presence and absence of ZnO and stearic acid with or without DCP has been studied in detail. It is observed that CBS increases the rate of DCP decomposition and decreases the crosslinking maxima due to DCP—ultimately leading to zero cross links with high amounts of CBS. In accordance with the observed sulfur decrease, free MBT formation, combined sulfur as MS etc., a predominantly radical mechanism has been presented, presumably not proceeding through intermediate complex formation. In mixes containing DCP together with sulfur, CBS, ZnO, and stearic acid crosslinks are found to be formed nearly additively, further confirmed by methyl iodide treatment of vulcanizates. Attempts have been made to interpret the results in terms of radical and polar mechanisms.
Mechanism of Protection against Ozone by N-Phenyl-N′-Isopropyl-p-Phenylenediamine
Authors: Razumovskii S. D. , Batashova L. S.
Published: February 2011

A number of hypotheses about the mechanism of action of anti-ozonates (AOZ) was verified by experiment. Films and solutions of polybutadiene, and also its mixtures with a model olefin, containing N-phenyl-N′-isopropyl-p-phenylenediamine (PIPP), showed that the ozone reacted first with the PIPP. Kinetic curves of ozone penetration during its reaction with PIPP were plotted at −78° C in solution and the relative reaction rate was determined. PIPP-ozone reaction products were found to contain nitroxide radicals.
The Migration of Extender Oil in Natural and Synthetic Rubber. IV. Effect of Saturates Geometry and Carbon Black Type on Diffusion Rates
Authors: Corman B. G. , Deviney M. L. , Whittington L. E.
Published: February 2011

Migration of oils, curatives, antioxidants, and other compounding materials in a vulcanized rubber matrix is a general phenomenon. A continuing, long range program has been undertaken in these laboratories to understand better this effect, in order that ultimately the compounder can predict, from a knowledge of the molecular nature of the penetrant and the physico-chemical properties of the cured matrix, the distribution of the various components during the service life of the finished rubber product. A sensitive radiotracer approach with earbon—14 is being used to study this system. Earlier work in this program has established the general value of the diffusion coefficient for whole paraffinic oils and for aromatic oils and their fractions. In general, this has shown that moderate variations in the molecular composition of the aromatic portions of the oils have only minor effects on these migration rates. Using similar computer derived diffusion coefficients, the current data indicate that naphthenic molecules migrate at equal to slightly higher rates than aromatic molecules of similar boiling points. Thermal diffusion as a mode of separation of the oil gives fractions showing more selectivity (larger differences in migration rates) than the formerly used silica gel procedures. Variations in carbon black type and loading levels have no detectable effect on migration. The most important factor in diffusion is the polymer matrix, which for the oils studied is in the order : polybutadiene (D≃6.4×10−7 cm2 sec−1 at 100° C), natural rubber (D≃3.5×10−7 cm2 sec−1), ethylene-propylene-diene rubber (D≃2.6×10−7 cm2 sec−1) and styrene—butadiene rubber (D≃1.9×10−7 cm2 sec−1). Activation energies for the diffusion process were PBR, 3.1 ; NR, 7.8; EPDM, 10.3; and SBR, 9.9 (energies in kilocalories per mole).
The Physico-Chemical Characteristics of Commercial Elastomers. I. Molecular Dimensions and Distribution Functions of Polybutadienes
Authors: Curchod J.
Published: February 2011

Without claiming that the comparison of the physico-chemical properties of commercial polybutadienes has been entirely satisfactory, we do think that the method of investigation used, with the essential details given, would be of use for any other type of elastomer. This method allowed a comparison of 14 different samples and the determination for each of the principal molecular parameters ([η] ,Mw) as well as the distribution functions. Even if the results have sometimes been incomplete or imprecise we do hope to have rendered a service to the manufacturers and users of these elastomers, which was after all the essential goal of this study. This article represents only a part of the results obtained. For reasons of volume we have had to defer until a later article the examination of the [η] /M relationship, the comparison of the unperturbed dimensions and their correlation with structure, certain theoretical considerations of the virial coefficients, and the presence of branching.
Molecular Weight Distribution of Polystyrene and of Butadiene-Styrene Copolymers Prepared in Emulsion Systems
Authors: Uraneck C. A. , Burleigh J. E.
Published: February 2011

Polystyrene and butadiene—styrene copolymers (SBR) were parepared in emulsion systems with a homologous series of commercial mercaptan modifiers. The molecular weight distribution (MWD) of the sets of polymers changed in a consistant manner when the regulating index of the mercaptan was relatively low. However the shape of the MWD curves appeared distorted in comparison to theoretical curves when the modifier depleted rapidly and when divinyl-benzene was present in the system. The divergence from the theoretical curve is attributed to a higher degree of branching in the high molecular weight fractions. Differences in MWD of SBR made with n- and tert-dodecyl mercaptans was marked. Notable differences were also found for SBR 1500 samples from the industry at random, but only slight differences were seen in a set of SBR 1503 samples. This study shows how the MWD of polymers prepared in emulsions can be varied simply by use of modifiers with different regulating indexes.
Theoretical and Experimental Values of the Volume Changes Accompanying Rubber Extension
Authors: Christensen R. G. , Hoeve C. A. J.
Published: February 2011

The molecular theory of rubber elasticity assumes the free energy to consist of two parts: a liquidlike free energy that is governed by intermolecular interactions and is independent of strain at constant volume and an intramolecular interaction free energy equal to the sum of the free energies of the chains making up the network. The volume increases of rubber samples as a function of their length were found to be considerably larger than predicted by the molecular theory. Therefore, contrary to common belief, the values of (∂E/∂L)V,T might not be related solely to changes in intramolecular interactions with extension. Also, the usual procedure to obtain values of (∂E/∂L)V,T from measurements of (∂f/∂T)p,L with the aid of the molecular theory is not correct.
An Apparatus to Measure the Dynamic Mechanical Properties of Solid Polymers
Authors: Shroff R. N. , Livingston D. I. , Fielding-Russell G. S.
Published: February 2011

An apparatus designed to measure the tensile storage modulus E′ and tensile loss modulus E″ for rubbers and plastics over a broad temperature range (ca. − 100 to + 150° C) and over two decades of frequency is described. One end of a narrow rectangular strip of the specimen is sinusoidally displaced at small amplitude in the direction of its thickness. The theoretical considerations are given for deriving the dynamic parameters E′ and E″ from the force F measured at the other end of the sample and the phase angle ϕ by which the force leads the driving amplitude Ad. The instrument is distinctive in that the phase angle is measured rapidly and accurately with a rotary variable differential transformer. The use of the instrument is illustrated with results obtained on three polymer vulcanizates : trans 1,4-polypentadiene, an acrylonitrile-butadiene copolymer, and a blend of acrylonitrile—butadiene copolymer with poly (vinyl chloride). The equation of Williams, Landel, and Ferry satisfactorily described the temperature dependence of the shift factors obtained from the plots of E′ and E″ as a function of log frequency.
Methods for the Determination of Internal Energy Contribution to Rubber Elasticity
Authors: Tanaka T. , Yokoyama T. , Yamaguchi Y.
Published: February 2011

In order to determine exactly the contribution of internal energy component to retractive force (fe/f), two methods (one is Single Specimen Method [Successive Contraction Method] and the other Multi Specimen Method), two different reference lengths (one is the initial length of undeformed specimen and the other the final length including permanent set), and two instruments of different type (one is automatic balance type relax-o-meter [ROM] and the other tensile tester) were examined by using natural rubber, cis-1,4-polyisoprene, and polyurethane rubber. The apparent mechanical and thermo-dynamic properties were significantly dependent upon these methods and reference lengths. In spite of the variation of C1 and C2 in Mooney-Rivlin plot, fe/f was almost unaffected and the sign of this value coincided with that expected from the chain conformation as far as ROM-Single or Multi Specimen Method and the final length were adopted. The influences of permanent set, the time used to attain equilibrium, etc. were also discussed.
Crystallization of Cis-Polyisoprenes in a Capillary Rheometer. II. The Effects of Experimental Parameters and Molecular Structure
Authors: Folt V. L.
Published: February 2011

Cis-polyisoprenes are readily crystallized under the pressure and orientation forces existing in a capillary rheometer. The ease at which crystallization can be effected is a complex function of the interrelationships existing among the temperature, the molecular weight, stereoregularity, and the dimensions of the capillary. For a given cis-polyisoprene and capillary, crystallization occurs more readily as the molecular weight is increased. Decreasing the diameter of the capillary and/or increasing the length of the capillary enhances the ease at which a given cis-polyisoprene can be crystallized. Using the optimum conditions presently available, natural rubber has been crystallized at 146° C. The ease at which crystallization is effected decreases drastically as the cis-1,4 content of the polyisoprene is reduced. Trans-1,4 and 3,4 are similarly effective in retarding the crystallization process and their effects are proportional to their concentrations in the molecular chains. However, polyisoprenes which will not crystallize under static conditions at −20° C are readily crystallized in the capillary rheometer at much higher temperatures.
Crystallization of Cis-Polyisoprenes in a Capillary Rheometer. I
Authors: Folt V. L. , Smith R. W. , Wilkes C. E.
Published: February 2011

Natural rubber is readily crystallized under the pressure and orientation forces existing in a capillary rheometer. The crystallization of natural rubber is readily effected over the temperature range covering commercial processing and fabricating temperatures. The crystalline rubber is stable at atmospheric pressure and room temperature. The observed crystalline melting point increases with increasing crystallization temperatures. Wide angle x-ray pictures show the crystals to be highly oriented in the direction of flow. Electron micrographs of fracture surfaces of the crystalline rubber show the existence of a very complex morphology. Where the degree of orientation is highest, a fibrillar structure is observed parallel to the direction of flow. The fibrillar structure changes to a shish-kebab structure about midway down the capillary. Apparently, a regrouping occurs with chain folded lamellae forming at right angles to the oriented fibrillar type crystals. A rotation of the chain-folded lamellae may occur as the exit end of the capillary is approached.
Abrasion Resistance of Pre-Stressed and Stressed Rubber Vulcanizates
Authors: Lambert D. H. , Boonstra B. B.
Published: February 2011

The abrasion resistance of carbon black-reinforced SBR-1500 vulcanizates has been shown to be drastically reduced by the application of tensile strain during the abrasion process. Pre-stressing of similar vulcanizates, however, has no effect upon the abrasion resistance.
Adsorption and Calorimetric Investigations on Carbon Black Surfaces I. Immersional Energetics of Heat Treated Channel and Furnace Blacks
Authors: Wade W. H. , Deviney M. L.
Published: February 2011

Adsorption of gases under reversible conditions on carbon blacks can provide important basic information revealing the highly heterogeneous nature of the surface electronic fields and relating to physical interactions between the black and elastomeric molecules. Precise, immersional, calorimetric measurements likewise document the strongly heterogeneous surface energies and provide a powerful technique for measuring both physical and chemisorptive interactions between the surface and organic adsorbates. In the first phase of this study a broad spectrum of channel and reinforcing furnace blacks has been studied by immersional calorimetry to provide a survey of both integral and, to a lesser extent, differential heats of adsorption using methanol, n-decane, benzene, and water as adsorbates. The blacks studied were thermally treated at appropriate temperatures so that a wide span of surface conditions could be investigated, including the entire range of coverage by oxygenated functional groups and the regions of maximum hydrogen evolution and incipient graphitization. With these heat-treated blacks, marked integral immersional heat differences between channel and furnace blacks were observed with some adsorbates but not with others, and these results are discussed in terms of black surface conditions. Subtle differences between furnace blacks revealed by differential immersional heats are also presented.
Vulcanizate Performance as a Function of Carbon Black Morphology
Authors: Burgess K. A. , Scott C. E. , Hess W. M.
Published: February 2011

A new nomenclature is proposed for carbon black morphology to be based on actual quantitative electron microscopical measurements. Carbon black is now defined in terms of “paracrystalline graphitic units” which are composed of interlocking “domains of rotational graphitic layer orientation”. The measurement of “unit” or “domain” dimensions replaces the earlier imprecise concepts of structure and particle size. Automated measuring procedures have been developed for determining carbon black unit and domain size functions using a Quantimet Image Analyzing Computer. Unit dimensions are expressed in terms of total projected length (L), average width (W), two-dimensional projected area (A), and form factor (L/W). Domain size (d) measurements have been programmed to give comparable results to earlier carbon black “particle” size determinations using a Zeiss Particle Size Analyzer. The new program enables measurement of similar classes of blacks (e.g., tread grades) under identical instrumental conditions, thus greatly reducing the problem of operator subjectivity. Meaningful correlations have been determined for several vulcanizate properties in terms of the above carbon black parameters. Domain size was found to be the most significant variable in the correlations with resilience, showing a positive relationship. Increasing unit form factor, indicated a depressing effect on resilience and was also the most significant single variable in regard to heat build-up and hardness, showing a positive relationship with both of these properties. A significant inverse correlation with heat build-up and hardness was observed for unit or domain size, when the full range of rubber grade carbon blacks were evaluated. Tensile strength showed an inverse relationship with unit or domain size in the SBR and SBR/BR systems that were studied. In natural rubber, however, there was also a significant depressing effect on tensile strength, attributable to increasing unit form factor. Modulus showed a strong positive correlation with unit length or form factor and an inverse relationship with domain or unit size. High unit form factor was also the most significant variable in reducing extrusion swell. High abrasion resistance (treadwear) was favored by high form factor, low unit size, and low domain size in that order of significance.
The Effect of Compositional and Testing Variations on the Dynamic Properties of Compounds Based on Styrene-Butadiene and Polybutadiene Elastomers
Authors: Meyer D. A. , Sommer J. G.
Published: February 2011

Important factors of potential use for manipulating static and dynamic stiffness and the damping characteristics of compounds based on styrene-butadiene and polybutadiene elastomers and their blends have been outlined. Their characteristics have been compared with those of IIR and EPDM compounds. The effects of variations in composition are quantitatively defined to assist the compounder in combining these effects in a manner that will lead to a desired combination of properties. In addition to the expected increase in static spring rate and dynamic spring rate with carbon black level, the following responses to compositional variations were found important: 1. The complex dynamic spring rate is more sharply dependent upon carbon black level than the static spring rate. 2. The complex dynamic spring rate is essentially independent of the level of crosslinking while static spring rate increases. 3. Damping coefficient is directly proportional to the level of carbon black and inversely proportional to the level of crosslinking. 4. Styrene level in a polymer blend and plasticizer composition can be used to adjust loss modulus and storage modulus at a given temperature and also to modify the rate of change of these properties with temperature. 5. The strain dependency of storage modulus was found in one instance to vary with the elastomer composition. The IIR vulcanizate, when formulated to the same static modulus, exhibited a larger strain dependence than the SBR, BR, and EPDM composition.
Carboxy Nitroso Rubber, Chemistry, Properties, and Applications
Authors: Levine N. B.
Published: February 2011

The nitroso copolymer shows excellent promise which has not been realized due to a lack of ability to achieve a suitable cure. The CNR terpolymer, on the other hand, retains the excellent solvent and oxidizer resistance, nonflammability, and wide useful temperature range of the copolymer and can, in addition, be easily fabricated and cured by several techniques into many useful products.
Structure-Property Relationships in Elastomer-Modified Terpolymer Systems
Authors: Hagerman E. M.
Published: February 2011

A number of terpolymers, incorporating as the elastomer phase polybutadiene, polyisoprene, poly-2,3-dimethylbutadiene, poly(butadiene-co-styrene), and poly(butadiene-co-2-methyl-5-vinylpyridine), were studied. Matrices were composed of poly(styrene-co-aerylonitrile) (SAN), poly(α-methylstyrene-eo-acrylonitrile), and poly(styrene-co-acenaphthylene). At constant elastomer content and elastomer molecular weight in systems employing a SAN matrix, Izod impact resistance was found to vary inversely with rising elastomer-glass transition temperature. In systems of various matrix composition, using a polybutadiene elastomer, heat deflection temperatures were found to vary directly and impact resistance inversely with rising matrix-glass transition temperature. In acrylonitrile-butadiene-styrene (ABS), systems of constant matrix composition and elastomer content, varying the elastomer molecular weight from 0.6 to 2.6×105 resulted in increasing the Izod impact resistance from 0.67 to 12.8 ft-1b/in. of notch.
Raman Spectrographic Studies of the Vulcanization of Rubbers. I. Raman Spectra of Vulcanized Rubbers
Authors: Koenig J. L. , Coleman M. M. , Shelton J. R. , Starmer P. H.
Published: February 2011

We have demonstrated that good quality Raman spectra can be obtained from vulcanizates prepared from cis-l,4-polybutadiene. Furthermore, significant differences are seen in the spectra of extracted vulcanizates prepared from various recipes. Tentative assignments have been made for many of the following Raman lines observed in the spectra. 1. The 1633, 1187, 734, and 720 cm−1 lines are thought to be associated with dialkenyl sulfide crosslinks. 2. Lines occurring at 440 and 505 cm−1 are assigned to polysulfidic and disulfidic structures respectively. 3. The 635, 690, and 708 cm−1 lines are thought to be associated with cyclic sulfides. In particular, the 635 cm−1 line with six membered thioalkenes, the 690 cm−1 line with five membered thioalkanes and the 708 cm−1 line with five membered thioalkenes. 4. Pendent side groups derived from TMTD are thought to have lines occurring at 1142 and 577 cm−1. Other lines occurring in the Raman spectra of the vulcanizates examined cannot be assigned with the same degree of confidence. The line occurring at 1606 cm−1 may be associated with conjugation but further work is necessary to verify it. The recipes chosen do not necessarily reflect those used currently in industry but were designed to accentuate certain structural features in the network. Consequently, the weak band at 1587 cm−1, observed only in systems with large amounts of TMTD and associated with vinyl thioether type structures, should not be overemphasized. Lines occurring at 558, 852, and 872 cm−1 are unassigned at present. Although the initial results are encouraging, it must be stated that many problems exist. Due to difficulties associated with fluorescence and degradation, Raman spectra of many important rubber systems will be difficult to obtain. Low levels of fluorescence cause serious problems when weak lines are present and when quantitative measurements of line intensities are made.
The Migration of Extender Oil in Natural and Synthetic Rubber. V. Dependence of Diffusion Rates on Oil Concentration and Elastomer Blend Ratios. The Locus of Oil in a Simulated Tire during Service
Authors: Deviney M. L. , Whittington L. E. , Corman B. G.
Published: February 2011

Using carbon-14 labelled aromatic extender oil as a penetrant species, diffusion rates were measured in practical elastomeric compounds of high oil concentration, and in elastomer compounds based on blended polymers. These results, combined with earlier data, allow the calculation of the locus of oil during the service life of the rubber product. Increasing the concentration of oil increases the rate of diffusion of oil. Butyl rubber was the most sensitive to this effect, albeit the slowest in rate of migration, with a 2-fold increase in migration rate over the range of oil concentration of 2–27%, followed by polybutadiene, 1.53; natural rubber, 1.27; and ethylene-propylene-diene rubber, 1.26, and SBR, 1.00. Polymer blends display no synergism in their effect on diffusion; the diffusivity of oil in the blends was predicted exactly by the weighted average of polymer composition. Further studies of the effect of dynamic flexing indicated that, at constant temperature, static and dynamic conditions gave equal diffusivities. Calculations were made of the locus of the oil in a simulated tire section at 3000, 6000, 9000, and 24,000 miles. These agree very closely with experi mental results on a vulcanized, aged simulated tire segment.
Thin Layer Chromatographic Identification of Rubber Compounding Ingredients
Authors: Kreiner J. G.
Published: February 2011

The many examples related above should provide the rubber analyst with systems well suited to some of his problems and, if not, certainly with direction for the evolution of custom systems for his specific needs. The Rƒ values and colors resulting from the chromatographic conditions employed by the experimenters have generally been well related for the compounds examined. These values and colors are useful as guides to another analyst but cannot be trusted for reliable identifications. Rƒ values are difficult to reproduce from one laboratory to another since the factors influencing Rƒ are not always readily reproduced within the different laboratories. Colors are difficult, if not impossible, to describe accurately or to reproduce faithfully with color photography. In addition, many colors may vary (some quite rapidly) with time after or conditions of indication. An identification is best and most reliably made by comparison to known compounds. An unknown is identified when, after adjusting the sample spot size to match that of the known, it travels the same distance and gives the same color and shape as the known. The use of a chromogenic indicator is advisable, if one suitable is available, since differentiation of samples by both a wide range of colors and Rƒ values makes identification much easier. TLC has been shown to be of great utility for the identification of rubber compounding ingredients by the many examples related above. In addition, TLC has proven a rapid, reliable, relatively simple, and inexpensive technique. Undoubtedly many new papers will appear in the future. Some will enlarge or improve on applications already existent. Hopefully, a quantity will tap areas of rubber analysis yet untouched by TLC.
Micro-Evaluation
Authors: Humpidge R. T. , Maclean A. , Morrell S. H.
Published: February 2011

The work at RAPRA has shown that it is perfectly possible to mix 1 g batches of compound and obtain a variety of physical measurements on the products. This especially of value when only a small amount of the polymer is available as in studies on experimental materials, where the polymer itself is costly, or where it is required to investigate the effect of costly additives. For a number of years, work of this nature has been continued in the authors' laboratories, continually perfecting the apparatus and techniques, and the results quoted above are typical of those obtained on a range of experimental polymers and additives.
Crosslink Density Evaluation of EPDM Vulcanizates
Authors: Zamboni V. , Flisi U. , Giunchi G.
Published: February 2011

Crosslink density of EPDM vulcanizates, both gum and filled, has been evaluated from stress-strain measurements on both dry and swollen samples, by plotting the data according to the Mooney-Rivlin diagram. Values of the C1 constant of swollen specimens were generally found to be much higher than those of the dry ones, and the difference was ascribed to the effect of entanglements, which probably act as stable crosslinks in swollen networks. The Flory-Huggins equation has also been studied and its applicability to EPDM vulcanizates examined ; a large degree of uncertainty was found for the polymer-solvent interaction parameter, μ, that suggests the use of this equation with reservation in the case of EPDM elastomers. Many data of the Mooney-Rivlin C2 constant being available, its dependence on various parameters has been investigated and the hypothesis has been confirmed that it is associated with entanglements and intermolecular structure. The stress-strain curves of samples filled with both mineral and black fillers were analysed using the Mullins and Tobin “strain amplification factor.” This technique, which allows one to describe the behavior of the rubber phase in filled vulcanizates, has given good results that endorse the use of the Mooney-Rivlin plot for the characterization of rubbery networks. The Mooney-Rivlin constants also gave very interesting results for the investigation of the networks obtained from curing elastomer blends.
EPDM Elastomers in Rubber Modified Plastics
Authors: Meredith C. L.
Published: February 2011

The superior resistance of EPDM to thermal and ultraviolet degradation makes the use of this elastomer particularly attractive in rubber modified plastics. Because of difficulty in grafting onto EPDM compared to polybutadiene or SBR, conventional emulsion polymerization processes do not give products with the desired balance of physical properties. In order to obtain the necessary degree of grafting and desired rubber particle size in the plastic matrix, a solution-precipitation polymerization was developed. This process is particularly well adapted for the preparation of EPDM modified styrene-acrylonitrile. Properties are quite dependent upon the EPDM composition used to modify the plastic. The amount and choice of third monomer are the most critical parameters with 5 to 12 C = C/1000 of 5-ethylidene-2-norbornene giving the best balance of properties. Relatively poor plastics result with dicyclopentadiene or 1, 4-hexadiene EPDM. while the physical properties of the EPDM-SAN plastic compare very favorably with commercial ABS, the chief advantage is a much greater resistance to the deleterious effects of aging. This is shown by comparative tests of oxygen uptake, accelerated aging, property retention and discoloration at elevated temperatures and during outside exposure, and rheological stability under severe processing conditions.
Rubber Chemicals from Cyclic Amines. V. Thiocarbamyl Sulfenamide Accelerators Derived from 3-Azabicyclo(3.2.2)Nonane
Authors: D'Amico J. J. , Morita E.
Published: February 2011

Evaluation of thiocarbamyl sulfenamides (I) prepared from 3-azabicyclo-(3.2.2) nonane and other amines indicates that the curing properties of stocks accelerated by (I) are influenced by the amino groups which constitute the thiocarbamyl and sulfenamide moieties, R and R′, respectively, and also vary with the formulation of the rubber stocks. The fastest cures are obtained when R is pyrrolidinyl or dimethyl and slowest cure when R′ is N-tert-butyl or N-morpholino. The lowest maximum crosslink density is obtained with morpholino- or piperidinothiocarbonyl sulfenamide. In a non-extended SBR black stock the crosslinking reaction generally proceeds as a second order reaction. The major part of the crosslinking reaction of the slower curing stocks proceeds by a fast first order rate followed by a slower first order rate.
Ambient Curing of Unsaturated Elastomers with Halomethyl Phenolic Resins
Authors: Petersen K. C.
Published: February 2011

A new vulcanizing agent, CRJ-328, has been developed which is activated at low temperatures by zinc oxide. This material, a phenolic heat reactive which contains bromomethyl groups (28% bromine), vulcanizes unsaturated elastomers of both the functional group containing variety, and those containing unsaturation as the sole reactive moiety. Fillers have their usual effects on the vulcanizates. At the present time, most of the work has been done on liquid elastomers although work is currently progressing on the higher strength solid elastomers. We envision initial application of this new cure system in caulking compounds, sealants, adhesives, coatings, propellant binders, potting, and encapsulating compounds. The advantages of this system are a low temperature vulcanization and formation of light colored stocks. Perhaps the scorchy nature of this cure system can be put to use in applications requiring faster cure times at lower temperatures.
Tread Wear and Wet Skid Resistance of Butadiene-Styrene Elastomers and Blends
Authors: Kienle R. N. , Dizon E. S. , Brett T. J. , Eckert C. F.
Published: February 2011

1. Car, wheel position, driver, inflation pressure, and shoulder drop have a statistically significant effect upon wear loss and need to bo taken into consideration before material factors affecting wear can be studied. 2. Variations in macrostructure of the polymers are not found to have a significant effect on wear as compared to microstructure variations. 3. At least two material factors control wear loss of tire treads. 4. When polymers are tested near their glass transition temperature (within 80° C), wear loss is dominated by viscoelastic properties. Viscoelastic properties can be related to wear loss through Tg or the combined effect of the cis, trans, vinyl, and styrene content. 5. At higher test temperatures (over 100° C above Tg) wear loss is dominated by a material factor that has a positive correlation with temperature. This is particularly noticeable when treads are worn under mild conditions. However, there is evidence that this wear factor is present at the testing nearer to Tg but is masked by the dominant viscoelastic effect. 6. The combined effect upon wear of the different material factors leads to an optimum wear resistance for any polymer in the butadiene—styrene system in the range of 75°–105° C above the Tg for that polymer. 7. For polymers tested at the same ambient temperature, (T), the effect of viscoelastic properties decreases non-linearly as T−Tg increases. 8. In the range of test severity studied, severity has little effect upon the inter-relationship of material factors. 9. In the range of test temperature where Tg dominates wear loss, skid distance on wet asphalt pavement is inversely related to wear rating.
Organic Peroxides for Cure of Ethylene-Propylene Rubbers
Authors: Harpell G. A. , Walrod D. H.
Published: February 2011

The reactivity of crosslinking peroxides decreases in the order 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di-(t-butylperoxide)-3-hexyne. First order decomposition rate constants for these peroxides were inferred from oscillating disk rheometer studies in poly(ethylene). The cure reaction in EPR and EPDM is more complex than in poly(ethylene) and the conventional measure of cure time leaves significant unreacted peroxide in the vulcanizate. Quinoline type antioxidants are preferred because they interfere least with the cure reaction.
Determination of Ethylidenenorbornene in EPDM Terpolymers
Authors: Gardner I. J. , Ver Strate G.
Published: February 2011

Ethylidenenorbornene (ENB) is a diene often employed as the third monomer in the commercial production of ethylene-propylene terpolymers (EPDM). A number of spectroscopic, chemical, and physical property procedures were examined as potential methods for determining ENB content. These included the use of iodine monochloride (ICI) and borane chemistry, nuclear magnetic resonance (NMR), and infrared (IR) analyses, as well as refractive index determinations. To evaluate the accuracy and reproducibility of the various methods, we prepared 24 EPDM terpolymers containing carbon-14 labeled ENB. The labeled diene was prepared via the Wittig synthesis. The ENB content of the EPDM's varied from 1.17 to 17.40 weight per cent. Catalyst systems for terpolymer preparation were employed that were representative of those used commercially in the production of EPDM. The refractive index method was found to combine adequate precision with speed of operation and proved to be the most reliable of the methods studied for determination of ENB content. An iodine number method was equally precise but suffered from the standpoint of speed. Two IR methods employing the 1685 cm−1 and 805 cm−1 absorption bands were not acceptable because of various structural interferences arising from compositional variations within the polymers. Proton NMR requires the use of time averaging and borane. chemistry proves to be a more cumbersome wet method than ICI, although presumably it involves reactions with olefins less complicated by side reactions than with ICI. Interrelationships of the various techniques are examined with regard to information concerning branching reactions. It is concluded that the data are consistent with the idea that commercial EPDM is a highly branched, partially gelled polymer. The basic contribution here is the refractive index technique which we referred to previously.
Mass Spectrometric Identification of 2-Mercaptobenzothiazole Sulfenamide Accelerators in Rubber Vulcanizates
Authors: Hilton A. S. , Altenau A. G.
Published: February 2011

The identification of accelerators in rubber vulcanizates has traditionally been a difficult and tedious task. The mass spectrometric method described in this paper offers a simple and expedient approach to the identification of 2-mercaptobenzothiazole sulfenamides. Neither complicated sample preparation nor solvent extraction of the vulcanizates is required as in the more common methods employed. Only about one-half gram of vulcanizate is needed for the analysis. The sample tube is attached to the mass spectrometer, heated for 15–20 min at 150–200° C and then the mass spectrum of the volatiles is recorded. The characteristic amine fragment ions are utilized for identification of the amine portion while the presence of benzothiazole is indicated by a peak at m/e=135. Spectra obtained from analysis of seven vulcanizates containing different accelerators are presented and the results discussed. The identification of the accelerator in a competitor's tread is also discussed.
Alternating Copolymers by Complexed Copolymerization
Authors: Hirooka M. , Mashita K. , Imai S. , Kato T.
Published: February 2011

There have been few studies on how the nature of copolymers is affected by their sequential structure. This is because, in the past, the sequential structure of most copolymers could not be controlled at will. However, such studies have been realized since it was found that alternating sequential regulation can be attained from many monomer combinations, from which only random copolymers had been obtained previously, provided the copolymerization was carried out in the presence of a Lewis acid, such as an alkylaluminum halide. This kind of reaction is termed complexed copolymerization, as distinguished from the conventional alternating copolymerization. Furukawa and coworkers indicated that alternating butadiene—acrylonitrile copolymer is superior in various properties to the corresponding 1:1 random copolymer. Yabumoto and coworkers noticed that 1:1 styrene—acrylonitrile copolymer obtained in the presence of zinc chloride had a higher glass transition temperature than that of the corresponding 1:1 random copolymer made by radical copolymerization. Moreover, the former was hardly colored due to substantial absence of acrylonitrile—acrylonitrile bonds. Thus, it is very interesting how the properties of eopolymers are affected by sequential structure. The present paper describes various properties of alternating copolymers. The first part of this paper introduces a newly developed alternating copolymer of isobutylene and an acrylic ester and compares it with the corresponding homo-polymers. The latter part deals with comparison of alternating and random copolymers. Equimolar copolymers of styrene and acrylonitrile are compared in physical and mechanical properties. Glass transition temperatures of equimolar alternating and random copolymers of various vinyl compounds are compared. An interesting correlation is shown and discussed on the basis of a thermodynamic treatment.
Multiple Glass Transitions in Butadiene—Acrylonitrile Copolymers. II. Formation of Incompatible Phases during Copolymerization
Authors: Jorgensen A. H. , Chandler L. A. , Collins E. A.
Published: February 2011

Differential Thermal Analysis and Dynamic Mechanical measurements show that the presence of two glass transition temperatures in nitrile rubbers is not unusual. Two glass transition temperatures occur in all commercial non-crosslinked butadiene-acrylonitrile rubbers of less than 35 per cent acrylonitrile even though they have gone previously undetected. We have investigated the changes in composition and glass transition temperatures during the course of the copolymerization. The composition versus conversion results were in agreement with previously published data. Fractionation and polymer-polymer compatibility experiments were used to demonstrate the presence of two incompatible phases of different acrylonitrile content, corresponding to the glass transitions of the original co-polymer. The mechanism for the formation of these two phases is discussed.
An Analog Heat-Flow and Cure Controller Simulator for Rubber
Authors: Claxton W. E. , Holden H. C.
Published: February 2011

This paper has presented in rather general terms the results of experimentation with direct analog methods for simulating heat flow in rubber materials and calculating continuously the attained cure equivalence for interior points. Brief descriptions of both two-dimensional and of one-dimensional prototype instruments are given, along with various applications. Several upward compatible models of the cure simulator-controller are being considered for commercialization.
Accelerated Tire Wear under Controlled Conditions. I. Description of the Test System
Authors: Veith A. G.
Published: February 2011

Tire wear is produced by a series of complex physical and chemical reactions occurring at the rubber-pavement interface. Because of this complexity a rather sophisticated test system is required to study this phenomenon. This paper describes such a system. It consists of an instrumented two wheeled trailer, a towing vehicle with appropriate control and recording instrumentation, and various supplementary measurement devices The conditions or factors that may be directly varied and controlled are tire slip angle and resulting cornering force, camber angle, load, and speed. Factors that may be controlled by suitable choice of test time and location are tire surface temperature and pavement texture. With this system, the three primary external factors that influence tire wear; tire force level, temperature, and pavement texture may be studied independently. This is in marked contrast to ordinary fleet tests where such factors are uncontrolled or mixed into a general matrix of conditions in unknown proportions. This independent factor variation is required for a realistic study of tire wear. The testing is done under accelerated conditions; sufficient losses are obtained in the range 50–500 miles depending upon the levels of the three primary factors. By appropriate choice of the levels of the three primary factors (mainly tire force) the rate of wear may be varied over a range of at least 50 to 1. The effects of tire load and speed on wear are, unlike their effects in ordinary vehicle use, due to the difference in tire force origin. In. trailer tests, the tire force is a sustained dynamic equilibrium force and is thus amenable to precise control. In vehicle use the forces are substantially transient and of an inertial character. The differences between these are pointed out. The system is completely described and operating procedures are outlined. A brief review of the basic factors involved in tire wear is given, including previous literature work on this topic.