bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionic Crosslinking of Chlorosulfonated Polyethylenes
Authors: Maynard John T. , Johnson Paul R.
Published: February 2011

A new and simple technique for curing chlorosulfonated polyethylene elastomers has been found that offers an economical means of making white and light-colored vulcanizates that do not contain sulfur compounds. This kind of stock can therefore be used directly in contact with bare copper, as in wire coverings, or with lead, as in lead press cures of hose and cables. In applications where the presence of litharge is acceptable, excellent water resistance can be developed. Aging characteristics of vulcanizates are generally comparable to those employing other curing systems, although extensive data are not now available. Because crosslinking is achieved entirely through electrostatic bonding of ion pairs, compression set values of these compounds are high, and this should be recognized in considering the applicability of this technique.
Poly(1-Butene) Chain Flexibility from Sorption Data
Authors: Pavlyuchenko G. M. , Gatovskaya T. V. , Kargin V. A.
Published: February 2011

A previous investigation of the sorption properties of polyethylene over a wide range of temperatures, above and below the melting point, showed that this polymer, the simplest member of the polyolefin series, has chains of quite high flexibility, a factor which also governs its extent of crystallization. The present work is devoted to the study of the sorption properties of crystalline polybutene to obtain data on chain flexibility. This polymer is of considerable interest, since it exhibits elastomeric properties as well as crystalline structure. A polybutene sample with an intrinsic viscosity of 1.14 (determined in decalin at 90°) was used in the study. Observation in a polarization microscope showed that the sample melted in the temperature range 94.3° to 104.8°. Isotherms for sorption of n-octane by polybutene at 50°–115° (Figure 1) were obtained by means of a spring balance placed in a high temperature air thermostat. As Figure 1 shows, sorption increases regularly with temperature up to a relative adsorbate vapor pressure of 0.45, with the exception of the isotherm obtained at 50°, which lies above the isotherm at 60°. This somewhat unexpected result is possibly associated with the less dense packing of the chains at 50°, a factor which also results in higher sorption. At higher relative vapor pressures, when chain flexibility increases as a result of the plasticizing effect of the solvent, the density of molecular packing increases, and sorption becomes lower than at 60°.
Cyclization of Diene Polymers
Authors: Tutorskii I. A. , Markov V. V. , Fomina L. P. , Belyanin V. B. , Dogadkin B. A.
Published: February 2011

1. During the cyclization of natural rubber (unmasticized pale crepe) in phenol solution containing P2O5 as a catalyst, there is a drop in viscosity of the solutions—sharply at the beginning of the process and insignificantly after 5 hours cyclization time. 2. The speed of solution of rubber in phenol containing P2O5 is considerably greater than in pure phenol. This indicates that cyclization is started in the gel state and proceeds to full solution, and accelerates the breakdown of the gel fraction of the rubber. 3. Release of acetic acid, during oxidation of rubber for various periods of cyclization with chromic acid, diminishes in the course of the first four hours of the process, and then remains constant, whereas the viscosity continues to lessen. This serves to show that the process of breakdown goes forward even after the cyclization process is completed. 4. Unsaturation of cyclorubber, determined by the reaction with perbenzoic acid, amounts to approximately 25% of the original known unsaturation of rubber. 5. The presence in the ultraviolet spectrograph of cyclorubber of absorption bands at 275–280 mµ and in the infrared spectrograph of a series of absorption bands at 690 and 740−1, and again at 1500 to 1600 cm−1, indicates bound phenol in cyclorubber.
The Gel Phase in Natural Rubber
Authors: Allen P. W. , Bristow G. M.
Published: February 2011

Evidence is presented which suggests that the true gel phase in natural rubber is composed of small crosslinked latex particles (microgel), whose presence is revealed by light scattering and by electron microscopy. These are combined into a matrix with soluble rubber molecules, forming the apparent gel phase. The rate of solution (and hence the apparent gel content) of this phase varies with solvent and is governed by the diffusion rate of solvent into rubber. Prolonged extraction removes the soluble component. Since the redissolution of the soluble component is very rapid, it is inferred that it is initially bound to the microgel particles by specific forces which have to be overcome by the diffusing solvent. Mastication of crepe breaks up the matrix, leaving microgel particles whose presence can be detected in solution.
Radiochemical Investigation of Polymer Unsaturation. Reaction of Butyl Rubber with Radiochlorine
Authors: McNeill I. C.
Published: February 2011

The reaction between chlorine and butyl rubber is of interest for two reasons: because of the industrial importance of the reaction the mechanism of which has not been fully understood, and because of the possibility of using it as a method for the determination of unsaturation. By the use of (36Cl)-chlorine, it has been possible to study the reaction on a conveniently small scale, the radiochlorine being manipulated quantitatively by a vacuum line technique. It has been shown that the reaction with chlorine is freer from side effects than the iodine chloride reaction. Two atoms of chlorine are incorporated in the polymer for each double bond originally present. These are incorporated not by addition but by a substitution process which is probably not free-radical in nature. A mechanism is proposed for the reaction. Radiochlorine is demonstrated to be potentially a useful reagent for investigating very low unsaturations in polymers.
Mold Release Agents in the Rubber Industry
Authors: Bertram Hans-Herwig
Published: February 2011

The efficient production of high quality molded products in the rubber industry depends substantially on the use of suitable mold release agents and mold lubricants. Their function is to release even odd shaped articles from the molds. Since the mechanical strength of the stock at curing temperature is only a fraction of the room temperature value mold release agents play an important role in this operation. Effective mold release agents decrease the percentage of rejects and shorten the time between release and injection. A number of additional qualities are required of an “ideal” mold release agent. No decomposition residues should build up on the mold surface, since this would affect the product surface and would require cleaning of the mold after each use. The mold surface should be protected against corrosion, thus a mold release agent should be thermally stable and chemically inert. Furthermore, a mold release agent should produce a good appearance and a convenient finish while avoiding undesired side-effects detrimental to the color, the adhesive properties or the lacquer acceptance of the rubber. The mold release agent should affect neither the aging properties nor the odor and taste of the product and must be nontoxic. In addition, a virtually unlimited shelf life is expected. In view of the multitude of technical requirements it is not surprising that no single compound will combine all these qualities. Practically, a compromise is made and a few shortcomings have to be accepted. The following is an attempt to characterize the most important groups of mold release agents with respect to their technological properties.
The Chemistry of Thiazoles and Dithiocarbamates as Antioxidants
Authors: Brooks L. A.
Published: February 2011

Using a strictly qualitative approach, the present work suggests a possible explanation for the observed antioxidant action of dithiocarbamates. It has been shown that dithiocarbamates react with hydroperoxides to form a new oxidized intermediate which in most cases is stable. These have been identified as semisulfinates: (see PDF for diagram) With continued oxidation, a normal sulfinate is formed, the structure of which is probably best represented as follows where M is a divalent metal and R is, e.g., a simple alkyl group: (see PDF for diagram) The stability of the above compound will depend upon the metal M and the nature or size of the alkyl group. These compounds further decompose into a thiuram monosulfide and the corresponding metal sulfate. Particularly active or sensitive dithiocarbamates are oxidized directly to the metal sulfate and thiuram monosulfide. In these cases, the ephemeral formation of the semi-sulfinate and normal sulfinate as intermediates is probable. In the presence of excess hydroperoxide, the thiuram monosulfide undergoes further oxidation to form a carbamyl thiocarbamyl disulfide: (see PDF for diagram) Compounds of this structure are moisture sensitive and readily undergo hydrolysis. In the presence of zinc oxide and water such as would be found on the surface of a conventional rubber stock, it is suggested that a further reaction occurs to form a zinc dithiocarbamate which will then undergo the sequence of reactions described above until the dithiocarbamate is completely consumed. It is suggested that these reactions account for the antioxidant behavior of dithiocarbamates in a hydrocarbon system such as rubbers and petroleum products where the oxidizing agent is a hydroperoxide or some peroxygen compound which, if not destroyed, would in turn degrade the product to one of no utility.
Sulfur Vulcanizable Ethylene-Propylene Rubbers
Authors: Natta Giulio , Mazzanti Giorgio , Crespi Giovanni , Valvassori Alberto , Sartori Guido
Published: February 2011

Our research directed to obtaining new rubbers based on the copolymerization of ethylene with propylene started some years ago. We soon succeeded in establishing that it was possible to prepare copolymers of these two monomers showing interesting elastomeric properties. From the beginning, the problem arose of how to vulcanize these copolymers: while certain interesting methods for direct vulcanization were investigated and identified, we also investigated the possibility of terpolymers containing unsaturation and therefore vulcanizable with the ingredients normally employed in the rubber industry, particularly for the low unsaturated rubbers. The problem involved some difficulties, due to the following three reasons. (1) In order to maintain the peculiar characteristics of resistance to aging and chemicals, typical of ethylene-propylene copolymers, it was necessary to obtain terpolymers in which the unsaturation was present in a very small amount. (2) To obtain valuable properties in the vulcanizates, the unsaturation had to be well distributed in all the macromolecules. (3) In order to avoid branching or crosslinks, the residual double bond of the diene entering the polymer chain must not be able to react further during polymerization. Our research led to a number of monomers which may copolymerize with ethylene and propylene and which, under suitable conditions, gave terpolymers having a sufficiently homogeneous composition. Investigation of the behavior, in anionic coordinated polymerization of hydrocarbons containing internal double bonds led to an interesting solution to the problem of producing terpolymers.
Microscopy of Pigment-Elastomer Systems
Authors: Hess W. M. , Ford F. P.
Published: February 2011

Rubber technologists have always been fascinated by the remarkable effects produced in rubber by carbon black. Many people have contributed to an understanding of these phenomena. We have referred to some, but by no means all of such individuals' efforts in this review. In retrospect, it may not be inappropriate to recall some observations made 40 years ago by Ellwood Spear. In a remarkably perceptive paper on carbon black reinforcement, published in 1923, he said: “It is believed that the rubber is adsorbed on the surface of the carbon particles and that adsorption … is the real cause of the effect of carbon black in rubber”. And further: “The distinction between mere fillers … and those substances which reinforce rubber to an appreciable degree, lies in the hypothesis that the latter adsorb rubber strongly, whereas the former form a very weak union with it”. There are perhaps few chemists, physicists, rubber compounders, or microscopists who will disagree with these observations. But the measure of their success in unravelling the mysteries of carbon reinforcement of rubber will be the real facts they are able to find in support of such speculations. We hope that the present review will be helpful to others in their search for such facts. If we have succeeded in answering a few questions as well as in evoking some new ones, then perhaps our efforts will have been worthwhile.
Electrical Properties of Elastomers and Related Polymers
Authors: McPherson Archibald T.
Published: February 2011

Interest in the electrical behavior of elastomers stems from several widely different sources. From the theoretical standpoint electrical measurements provide a valuable tool for the study of the molecular structure of elastomers and other polymers and the relation of structure to properties. From a practical point of view an understanding of the electrical behavior enables the manufacturer of wire and cable to produce insulation that will better withstand the severe conditions of space flight, or that will meet price competition and show a profit. The present day applications of elastomers are so many and varied that nearly any type of compound is likely to be employed for some practical purpose. A cable for x-ray equipment, for example, may be made wholly from elastomers with conductor, insulation, and jacket each from a different compound. At one time when almost the only electrical use of rubber was to provide the highest practical degree of electrical insulation it was correct to speak of “good” and “poor” electrical properties. Now, however, an elastomer that is a poor insulator may be excellent in an antistatic application. Communication cables require an insulation of the lowest practical dielectric constant, but for power cables a layer of insulation of high dielectric constant next to the conductor may be essential to prevent excessive electrical stresses. Modern technology not only calls for a wide diversity of electrical properties but it often requires further that elastomers having these properties be available in a wide range of mechanical properties. For example, the insulation on a cable for use in an airplane must be as thin and light as possible to save weight while an unarmored cable for laying in shallow water must have insulation that is thick and tough for mechanical protection and of high specific gravity to prevent the cable's being moved by waves or tide. Thus, the diversity of present and possible future applications is such that no one in the industry is likely to escape for long some contact with an application involving an electrical property. Accordingly, this review has been prepared to acquaint the rubber chemist and technologist with current information in the field. In the 25 years that have elapsed since an earlier review was prepared by the same author a great deal of work has been done on the relation between the properties of polymers and their molecular composition and structure. It is now possible to predict the properties of some polymers from their structural formulas, and a beginning has been made in relating the properties of simple elastomeric compounds to the properties of the different ingredients. However, knowledge in the field is still far from the state at which it would be possible to compile a table of functions such that the electrical properties of a multi-ingredient insulating compound could be computed from the properties of the individual ingredients.
Some Stereoregular Polymerizations of Conjugated Dienes
Authors: Lehr Marvin H.
Published: February 2011

After nearly a decade since man discovered how to carry out stereoregular polymerizations of dienes, his understanding of the reactions is disappointing in spite of the many studies that have been made. Part of the difficulty lies with patent disclosures as discussed by Natta in his forward to Gaylord and Mark's book. But most of the difficulty in this reviewer's opinion lies in the reporting of experimental work in the published literature. Too little attention is paid to those details needed for critical evaluation, and too much space is devoted to interpretation and speculation. In view of the many variables in preparing Ziegler catalysts, it would seem obvious to include, for example, such information as the order of addition and purity of reagents. Likewise, in view of the uncertainties, it would seem prudent to consider more carefully the merits of alternate interpretations. The author believes that progress in a field is often achieved by following an interpretation to its logical end. However, in preparing this review he found himself frequently frustrated because of insufficient experimental details. If the reporting continues as it has been, he feels that our knowledge will continue to remain in a rudimentary state in comparison to the effort expended.
Practical Parameters for Mixing
Authors: Van Buskirk P. R. , Turetzky S. B. , Gunberg P. F.
Published: February 2011

(1) Compounds mixed under high-shear conditions in a laboratory Brabender Plastograph or in larger Banbury mixers can be quantitatively compared on the basis of work input per unit volume. This quantity, unit work Wu, is proposed as a useful parameter for characterizing the effects of polymer, filler, and other ingredient on mixing performance. (2) This work supports the principle that, independent of the size and speed of a mixer, there is a unique relationship between unit work and such in-process properties of the compound as Mooney viscosity, die swell, etc. It has been shown that this relationship extends to other high-shear mixers, such as the Shaw Intermix and a cam-head type Brabender Plasticorder. (3) Practical unit work ranges for passenger tire-tread mixing found typical of factory operations are: first stage, 300–800 MJ/m3; second stage, 150–400 MJ/m3; final mix, 2000–4500 MJ/m3. Mixing to these unit-work levels in the laboratory achieved mixing quality that closely duplicated large-scale high-shear mixing. (4) Process profiles (the changes of certain in-process properties such as Mooney viscosity and die swell as functions of unit work) yield additional behavior indices that are characteristic of each individual rubber—filler mixture: The viscosity-work index (VWI), for instance, reflects the rate of change in the compound viscosity with increasing unit work, while the position of the maximum in the die swell vs. unit work curve is a good indicator of the minimum unit work required to obtain low levels of undispersed carbon black. (5) A second scaling parameter, based on an expanded concept of the total shear-strain performance for Banbury-type mixers, is proposed. It offers an alternative approach to scaled mixing when the actual measurement of unit work is not convenient. The total shear-strain parameter, as derived, is a dimensionless number Γ defined as Γ = [(shear rate) (time) (volumetric throughput ratio) (land-length ratio)]. Its use implies ideal viscous flow during mixing plus an accurate knowledge of mixer rotor and chamber dimensions.
Application of an Equivalent Strain at Equal Stress Principle to the Dynamic Hysteresis of Carbon-Black-Loaded and Oil-Extended SBR
Authors: Ulmer J. D. , Chirico V. E. , Dizon E. S.
Published: February 2011

A principle of equivalent strain at equal stress has been applied to dynamic measurements of hysteresis. At 24°C and 25% ptp dynamic strain, the relation of hysteresis to strain amplitude and the equivalence principle lead to an expression which describes the measured hysteresis of SBR-1712 filled with a wide variety of carbon black types and loadings to within about ±25%. At 105°C and 25% strain, the experimental results are much larger than the theory predicts, but are better described by the theory if an empirically determined exponent n is introduced in the equivalence principle. At strain amplitudes below 10%, the experimentally determined hysteresis is much lower than the theory predicts, but this deviation is described by the change in elastic modulus with strain amplitude at both 24° and 105°C. The deviations of the results from the theoretical predictions which are not described by the rate of change of elastic modulus with strain amplitude appear to be a function of carbon black surface area, structure, and loading.
Identification of Elastomers in Tire Sections by Total Thermal Analysis. III. White Sidewall Compounds of Neoprene Rubber Blends
Authors: Sircar A. K. , Lamond T. G.
Published: February 2011

DSC curves of sulfur-cured CR differ from peroxide-cured vulcanizates in the shape of the exotherm and the peak temperatures. The exothermic reaction, attributed to dehydrochlorination and subsequent crosslinking, is accelerated by sulfur. TG and DTG curves support this contention. In blends with NR, BR, or SBR, the second polymer intervenes in the crosslinking reaction, resulting in a lower residual weight for the CR network. White sidewall compounds of NR/CR or NR/CR/CSM can be identified by their DSC peaks in nitrogen, glass transition temperature, and DTG peaks. DSC and thermogravimetric curves supplement each other in the identification of these elastomers.
Molecular Structure of Elastomers Determined with Carbon-13 NMR
Authors: Carman C. J. , Baranwal K. C.
Published: February 2011

Characterization and identification of elastomers are important analytical needs for those involved in rubber technology. High resolution pulsed Fourier transform 13C NMR has been shown to be a powerful tool which can supply much detail as to sequence distribution, chain configuration, steric purity, or identification of polymer mixtures. One can also use 13C to distinguish polymer blends from copolymers of similar composition. This information about elastomers commonly used in the rubber industry provides not only a new tool for analytical problem solving, but also provides analytical information to guide the chemist as he makes elastomeric materials with structural features which impart specific physical properties.
Dilute Solution Properties of Trans-Polypentenamer: [η]—M Relations and Molecular Conformation
Authors: Gianotti G. , Bonicelli U. , Borghi D.
Published: February 2011

The values of the mean-square unperturbed dimensions of trans-polypentenamer, expressed by (r02/M)1/2, agree well with literature data for polymers with similar structure. In particular, the low value of the structure factor, r02/r0f2 is quite interesting. It tends to prove that the short-range interactions exert a negligible effect for the trans double bond structure. However, the value of this ratio is certainly influenced also by the not completely trans structure of the polymer, which certainly affects the experimental value of (r02/M)1/2. On the basis of the relations proposed, reproducible values of KΘ have been obtained by viscosimetric measurements, when at least one of the solvents is rather poor. On the other hand it is well known that the various relations allow less reliable extrapolations on increasing α. The relation proposed by Berry gives a linear extrapolation in the case under examination, which coincides with that in a pseudoideal solvent. However, this does not mean that it is of general validity and that it must always be preferred to the other analogous relationships reported.
Electron-Impact-Induced Fragmentation of N-(Substitutedthio)Phthalimides. A Rationalization for their Pre-Vulcanization Inhibition
Authors: D'Amico J. J. , Potts K. T. , Kane J. , McKeough D. , Moschner K. F.
Published: February 2011

The pre-vulcanization inhibitor activity of a series of N-(substitutedthio)-phthalimides is attributed to thermal cleavage of the N—S bond with formation of phthalimide and the corresponding thiol radical, which subsequently acts as a scavenger for 2-mercaptobenzothiazole giving the unsymmetrical 2-benzothiazolyl disulfide.
The Energetic Contribution to Rubber Elasticity in the Range of Small Uniaxial Compression and Moderate Elongation
Authors: Wolf F. P. , Allen G.
Published: February 2011

The relative energetic contribution to the retractive force of a deformed rubber sample, fe/f, has been evaluated from thermoelastic measurements at constant pressure. Extension ratios λ have been studied in the range 0.88⩽λ⩽1.79 at 20° and 40°C. The results are given for a reference temperature, 30°C. Since data in the transition region from uniaxial elongation to compression were to be evaluated, a new set of equations was derived on the basis of the Gaussian force law, because the usual equation for measurements at constant pressure tends towards infinity when approaching the undeformed state λ=1. Considerable difference between the results obtained by different, though apparently equivalent, equations have their origins in the deviation of the experimental data from ideal Gaussian behavior. The influence of this inaccuracy on the terms of the equations is discussed and the most reliable functions for small deformations 0.88⩽λ⩽1.15 and for moderate elongation λ>1.10 have been identified. With these precautions the Gaussian force law is a satisfactory approximation for the determination of reliable values of fe/f. The evaluation of data at small deformations is extremely sensitive to experimental error. Even smoothed polynomials L(f) were not sufficient to eliminate an apparent maximum in the fe/f vs. λ curve. Therefore the linear thermal expansion coefficient, βlin(λ), which is a major term in all the fe/f equations at small deformations, had to be scrutinized critically. Although experimental data in this range showed that βlin(λ) is a slightly S-shaped function, a linear approximation is adequate at moderate elongations. Using one of the new equations together with the linear approximation for βlin(λ) in the region of small deformations, and two equivalent equations at moderate elongation, the energetic contribution to the total stress was found to be fe/f=0.18±0.02 for lightly crosslinked natural rubber. Little variation in fe/f was observed over the full range of measurements: 0.88⩽λ⩽1.70.
Crosslinking of Polyolefins in the Presence of New s-Triazines
Authors: Ahne H. , Wiedenmann R. , Kleeberg W.
Published: February 2011

In the crosslinking of polyolefins (such as polyethylene, ethylene-propylene copolymers, and ethylene-(vinyl acetate) copolymers), multiply unsaturated s-triazines (such as triallylcyanurate (TAC), 2-alkylamino-4,6-diallyloxy-s-triazines, and the bridged 2-alkylenamino-4,6-diallyloxy-s-triazines) make it possible to decrease the concentration of the peroxide curing agent, or the radiation dosage, necessary to achieve adequate degrees of crosslinking. The multiply unsaturated alkyl(ene)-amino-s-triazines, most of which are novel compounds obtained by aminolysis of TAC, though similar to TAC in their effectiveness, provide better compatibility with the polymers and, accordingly, improved compound shelf life and processability. The 2-alkyl(ene)amino-4,6-diallyloxy-s-triazines or the bridged alkylamino-s-triazines present special advantages in peroxide crosslinking of filler-containing polyolefins. Especially when acidic fillers, such as calcined kaolin, are used in polyolefins, the addition of small amounts of alkylamino-s-triazine can induce an extraordinarily high degree of crosslinking in the polymers. Complete polymerization of the allyl groups under crosslinking conditions is desirable for optimum aging resistance of the crosslinked polyolefins. In the case of a polyethylene stabilized, for example, with an oligomerized trimethyldihydroquinoline, peroxide crosslinking in the presence of 2-alkyl(ene)amino-4,6-diallyloxy-s-triazines will bring about a further significant improvement in the stability to thermal oxidative degradation.
Fracture Energy of Elastomers in Mode I (Cleavage) and Mode III (Lateral Shear)
Authors: Ahagon A. , Gent A. N. , Kim H. J. , Kumagai Y.
Published: February 2011

Attention has been drawn here to three different reasons why measurements of fracture energy by different methods may not agree: (1) When the test involves propagation of a tear by stored strain energy, as in the method shown in Figure 1, the energy available to cause rupture will be less than that supplied, because of dissipation within the elastomer. Calculation of the fracture energy on the basis of input energy would then lead to an overestimate, by about 100 per cent or more for typical filled elastomers. (2) As shown in Figures 4a and 5, the tear path is sometimes wider than the thickness of the test sheet. In consequence, fracture energy calculated from the sheet thickness would be too large, by about 40 per cent in the cases considered here. (3) Even when allowance is made for the true width of the tear path, measurements of fracture energy in shear (Mode III) are about 50 per cent larger than in cleavage (Mode I). This is attributed to frictional work expended in sliding the rough torn surfaces past each other.
Structural Characterization of Vulcanizates. II. Use of Triphenylphosphine to Determine the Structures of Sulfur Linkages in Unaccelerated Natural Rubber-Sulfur Vulcanizates
Authors: Moore C. G. , Trego B. R.
Published: February 2011

In Part I of this series it was shown that reaction of about 40 to 55 sulfur atoms are required to produce one chemical crosslink in networks obtained from unaccelerated natural rubber-sulfur systems at 140°C. The low crosslinking efficiency of sulfur in these systems is ascribed on the basis of the products derived from model olefin sulfurations at 140° C. to the sulfur being wastefully combined in: (a), polysulfidic crosslinks, rubber—Sx—rubber, where x>1; (b), cyclic monosulfides situated along the polyisoprene chains at sites distant from the crosslinks; and (c), nonrandom crosslinks as in structures (I) and (II) where sulfur attachments are on vicinal carbon atoms of the polyisoprene chain. The crosslinking efficiency data given in Part I necessarily
Reactions of Isoparaffins with Sulfur and DI-t-Butyl Peroxide
Authors: Wanless G. G. , Wei Peter E. , Rehner John
Published: February 2011

The role which sulfur plays in the peroxide vulcanization of polyisoparaffins has been investigated. The problem was studied by using a system in which 2,4dimethylpentane is a model for the polyisoparaffin chain. Two alternative reaction mechanisms are proposed. Work with the model system shows that polysulfides formed from the isoparaffin are the dominant products. By analogy it is inferred that polysulfide linkages join the polyisoparaffin chains, preferably at what were formerly tertiary hydrogen sites. Nearly all of the high boiling products are disulfides and, or, polysulfides, and these total at least a 28 mole per cent yield based on peroxide charged. Thus, it is indicated that sulfur plays a major role, and does not simply prevent minor side reactions. Study of the gaseous reaction products indicates that sulfur does not alter the course of the initiation step. A reaction mechanism is proposed which is consistent with literature and with our experimental work.
The Blooming of Sulfur and Other Ingredients from Compounded Stocks
Authors: Kuzminskiĭ A. S. , Feldshteĭn L. S. , Reĭtlinger S. A.
Published: February 2011

“Blooming” is the name given to the crystallization of compounding ingredients usually on the surface of a stock, cured or uncured, accompanied by the migration of the substance from the bulk to the surface. Almost all ingredients which are soluble in rubber possess the capacity to bloom: sulfur, selenium, many accelerators, antioxidants, organic pigments, fatty acids and so on. Blooming reduces the tackiness of the stock, which causes difficulties in forming multi-ply articles (tires, belts, etc.). To restore tackiness the bloomed substances are washed off with a solvent, and in cases of particularly intense blooming the surface is wet with rubber solvents. The need for these operations reduces labor productivity and hinders automation. In the production of molded articles blooming of ingredients causes nonuniform stresses to be set up. Blooming is a cause of rejection in production (stains on overcoat fabric, on the surface of colored rubbers and so on) and greatly harms production. However, in some case blooming proves useful; films formed as a result of blooming protect rubber from the action of light and air. Thus for instance Graffe notes that vulcanized rubber which is coated with bloomed sulfur proved more resistant to aging under service conditions than rubber without this coating. At the present time wide use is made of the capacity of antioxidants and waxes for giving coatings by blooming which protect vulcanized rubber from ozone aging. All this shows how important are the recognition and correct understanding of the causes of blooming.
Theoretical Strength and Critical Rupture Strength of Solids
Authors: Bartenev G. M. , Razumovskaya I. V.
Published: February 2011

We shall distinguish between two recognized properties: theoretical strength and critical stress. The theoretical strength, calculated for rock salt by Born and Zwicky, is the maximum of the quasi-elastic force to rupture an ideal defect-free lattice under conditions of homogeneous (equal) deformation (in Born's treatment this is uniform dilation, in that of Zwicky it is uniaxial strain). The critical stress is the maximum of the quasi-elastic force under the special conditions in the tip of a crack. The first value is a constant of the material, while the second changes not only from crack to crack, but also for any one crack in the process of its growth. The processes considered by Born and Zwicky are dissociative—volumetric in the first case and along planes perpendicular to the strain in the second. Since in an ideal material there are no defects, neither in any one direction nor along any one surface, and no free surface is formed. The potential energy of each particle, increasing smoothly, approximates asymptotically to a certain limit (different in the first and second treatments) as is characteristic of the potential curve of Coulombican interaction between two particles. The quasi-elastic force passes through a maximum (Figure 1, Fm is the theoretical strength calculated for a single linkage).
Stress Relaxation and Creep of Several Vulcanized Elastomers
Authors: Watanabe Kenzo
Published: February 2011

It is well known that polymeric materials in general creep with increasing time under a given constant stress and that stress relaxes with increasing time under a given constant strain. Recently, theoretical studies en these phenomena have been made in detail for polyisobutylene, vulcanized natural rubber and polymethylmethacrylate. Both properties for any vulcanized elastomer depend on the molecular structure of the network, the temperature and the amount of original stress or deformation, but it can be deduced from the Tobolsky and Eyring theory of viscoelasticity for polymers that both properties are linearly related to log time. In fact, however, the polymers begin to deviate rapidly from such a linear relationship if they are placed in air at high temperature for a long time, because thermal degradation by oxidation occurs. For elastomers used in electrical machinery and for other industrial uses, for example rubber packaging, diaphragms, or vibration and shock absorbers, it is required that we understand thoroughly the behavior of both properties at each temperature and each time for individual materials in order to make a proper choice of material suitable in behavior for each purpose. The author has studied these properties experimentally for natural rubber as well as for several synthetic elastomers and then investigated the relation between thermal life and the temperature employed. This paper describes a few results obtained up to the present.
Crack Propagation in a Strain-Crystallizing Elastomer
Authors: Andrews E. H.
Published: February 2011

The dependence of small-scale crack propagation in a strain-crystallizing elastomer (natural rubber) upon the applied strain has been studied under conditions of cyclic deformation over a range of frequencies. During each cycle the crack propagates along a well-defined path, different from the axis of symmetry, which is identified as the locus of maximum stress in a stationary stress distribution (i.e., one which does not move with small advances of the crack). The stationary stress hypothesis also accounts for the quantitative dependence of crack growth upon the external constraint. It is shown that a stationary stress distribution could arise as a result of the severe mechanical hysteresis displayed by strain-crystallizing rubbers.
Rolling Radius of Rubber-Covered Cylinders
Authors: Borchardt H. A.
Published: February 2011

Although the data were not comprehensive, definite trends can be established. They are: 1. A solid-rubber covered cylinder driven by an all-metal roller of the same outside diameter has a lower average surface speed than the driving metal cylinder. 2. A solid-rubber covered cylinder driving an all-metal cylinder of the same outside diameter has a lower average surface speed than the driven metal cylinder. 3. Per cent of speed difference as a function of deformation of rubber surface approximates a straight-line relationship for higher values of deformation. 4. The slope of the straight line approaches zero for increased radial rubber thickness and infinity for decreased thickness. Slope approaches a finite limit for increased axial rubber length and zero for decreased length. Slope remains nearly constant for different rubber hardnesses.
The Analysis of Pigment Dispersion in Rubber by Means of Light Microscopy, Microradiography, and Electron Microscopy
Authors: Hess William M.
Published: February 2011

The significance of these dispersion studies can be summarized as follows: 1) A simple but highly versatile liquid nitrogen freeze technique makes it possible to microtome pigment loaded rubber stocks into thin (0.05–0.1 microns, e.g.) cross sections for examination by means of light microscopy, microradiography or electron microscopy. All of the common elastomers including polybutadiene and silicone rubber have been successfully sectioned for each of these techniques. Thus the state of dispersion can readily be traced from coarse pigment agglomerates, a few hundred microns in size, down to the ultimate particles which can be below 20 millimicrons. 2) Through the use of one of the techniques described or by the coordinated use of all of them (“dispersion in depth”), most dispersion problems can be resolved. A very complete analysis of this type is often necessary to explain pigment effects upon reinforcement. 3) The effects of varied dispersion quality can now be studied directly using special x-ray and electron microscope tensile specimen holders with which small rubber specimens can be examined under strain. Actually these procedures have a greater scope than simply measuring dispersion. The reinforcing capabilities of different pigments in a variety of polymers may be compared by the use of these techniques.
The Applications of Infrared Spectroscopy to Polymers, Particularly 1,3 Diene Polymers
Authors: Binder John L.
Published: February 2011

As a result of the discovery of methods for making stereospecific polymers, the whole field of polymer chemistry has broadened considerably from its state in the early post-war years. Infrared spectroscopy has played an important role in the study and development of such polymers and has been applied to the study of polymer features which were not considered before the advent of stereospecific polymers. The present review is concerned with some of these applications, particularly to 1,3 diene polymers, such as microstructure determinations, polymer spectra and structures, isomerization, degree of crystallinity, vulcanization, and rubber derivatives. The survey covers the literature to the end of 1960. Some of these applications are discussed in a book edited by Clark and applications of infrared spectroscopy to other types of polymers are also discussed there. Krimm has published an excellent paper on the theoretical analyses of some polymer spectra which leads to assignments of many of the bands in the spectra of the polymers. Diene polymers were not discussed by him but the method he developed should be applicable to such polymers.
Mullins Effect and Rubber-Filler Interaction
Authors: Bueche F.
Published: February 2011

A previously-reported theory for the Mullins softening effect has been used to interpret various new data for the behavior of filled SBR, rubber under tensile load. The strength of the filler-rubber bond, the filler surface area per polymer molecule attachment, and the average filler surface separation have been determined for two fillers, HAF black and Hi Sil-233 (a silica). A styrene-butadiene type filler (Pliolite S-6) has also been investigated. The temperature dependence of the filler-rubber bond has been measured; results lead to the conclusion that the bonds to carbon black and silica are high energy bonds, probably chemical in nature. It is shown that the recovery of hardness in prestretched, filled SBR is a rate process having an activation energy of about 22 kcal ./mole. It is inferred from this and from permanent set data that the recovery is the result of the chemical breaking and reforming of the rubber chain network at the higher temperatures where recovery occurs. Silica-filled rubbers are shown to possess a pseudo-yield stress which gives rise to an anomalous shape for the stress-strain curve of this material when it is stretched for the first time. A prestretched, silica-filled rubber recovers its hardness when left at 115° C for 20 hr, but the anomalous portion of the curve is replaced by more normal behavior. Possible interpretations of the observed results are given.
The Swelling of Unfilled and Highly Filled Polymers
Authors: Bills K. W. , Salcedo F. S.
Published: February 2011

The swelling of elastomers in solvents is a useful method for determining the effective crosslinking of the polymeric structure. However, it is now shown that this method may be applied satisfactorily to highly filled polymers. A unique method has been devised for the accurate measurement of the swelling ratio of the gel phase of the filled polymers. The method is based on the observation that the binder-filler bond, for most filler particles, releases on swelling. The binder around the particle swells, leaving a hollow pocket which becomes filled with solvent. Corrections for this “waste” solvent lead to the equations from which the swelling of the polymer can be calculated. Experimental verification is given for several filled systems.
An Electron Microscope Study of Filler-Rubber Mixtures
Authors: Shvetsov V. A. , Pisarenko A. P. , Shtarkh B. V. , Novikov A. S.
Published: February 2011

1. Observations of solutions of reinforced rubbers in the electron microscope revealed the presence of rubber sol and gel fractions and secondary filler structures. 2. Most important factors in rubber reinforcement are high dispersity and low aggregation tendency of the fillers and the ability of aluminate and silicate fillers to form network and chain structures.
Influence of Concentration of Ozone upon Cracking of Vulcanized Rubber
Authors: Zuev Yu S. , Pravednikova S. I.
Published: February 2011

1. The character of the dependence of the time to first cracking (τ0), of the rate of crack growth in the steady-rate portion (v) and of the time to rupture (τ1) upon deformation does not alter on altering the ozone concentration from 0.15 to 0.0002%. 2. The value of the critical deformation does not alter with alteration in the ozone concentration. 3. The process of destruction of deformed rubber in ozone proceeds kinetically, i.e., it does not depend upon the rate of supply of ozone to the surface of the specimen. The character of the dependences τ0 and τ1 and of the rate of crack growth (vgrowth) upon the ozone concentration is determined by equations of the type of the Freundlich adsorption equation. 4. In the determination of the relative resistance of various vulcanized rubbers to ozone cracking it is desirable to select as an index the value of the ozone concentration at which we get a time to rupture equal for all vulcanized rubbers. 5. The relative resistance of the different vulcanized rubbers to ozone cracking (in assessment by the time to rupture) depends upon the ozone concentration at which it is determined. It is advisable to determine the resistance to cracking at the critical deformation of the vulcanized rubber. 6. The order of resistance to ozone of specimens of one rubber deformed by differing amounts does not depend upon their concentration in the range of concentrations under investigation and usually employed. However, if in the range of high concentrations of ozone the times to rupture of the specimens have values close to each other, then in the range of low concentrations of ozone these values may differ markedly.
Influence of the Temperature upon the Durability of Rubber in Corrosion Cracking
Authors: Zuev Yu S. , Borshchevskaya A. Z. , Pravednikova S. I. , Yue-Jin U.
Published: February 2011

1. The rate of reaction of an undeformed rubber stock with a reactive medium is determined by the diffusion, while the rate of destruction of a deformed stock is determined by its chemical interaction with the medium. 2. The magnitude of the apparent activation energy (u) of the rupture of a stock in the presence of a reactive medium does not undergo perceptible alteration in the range of deformations 30 to 80%, while on transition to deformations of 500 to 700% the values of the apparent activation energy increase. 3. The temperature coefficient of rupture depends upon the nature of the bonds being destroyed and upon the capacity of the reactive medium for adsorption on the stock. On rupture in the gaseous phase the apparent activation energy has a lower value than on rupture in a solution of the same agent. 4. In a wide range of deformations the time to rupture of stocks obeys a complex system of laws, passing through a minimum value in the region of the critical deformation, εcrit. The position of εcrit depends upon the temperature, type of ‘aggressor’ (i.e. reactive agent) and physical state of the medium (gas, solution). 5. As a result of the shift of εcrit with alteration in temperature there is possible the phenomenon of anomalous dependences for certain deformations, i.e., the time to rupture at low temperatures are less than for higher temperatures with identical deformations and concentrations of the medium.
Metal Halides in Vinylpyridine Rubber (PBR)
Authors: Brucksch W. F.
Published: February 2011

It has been found that PBR is made stronger by the addition of certain metal halides. A kind of cross-linking results, probably by coordination of pyridine nitrogens. This crosslinking can be used as a supplement to that produced by curing with sulfur. The result is improved physical properties in vulcanized products. Gum stocks show higher tensile strength. Filled stocks show higher tensile strength and elongation at 100° C and greater resistance to abrasion and to cut-growth. The system also has the capacity to develop high modulus. Because of this, lesser amounts of filler may be used. The result is a compound which has hysteresis properties like a carcass stock and abrasion resistance like a tread stock. This is an interesting combination of properties, which should fine useful applications.