bluuebunny/crossref_metadata_2025 huggingface dataset:
Relation of Peroxide Decomposition to Rubber Degradation
Authors: Kendall C. E.
Published: February 2011

It appeared that an investigation of the reactions between peroxides and deactivators of rubber degradation, such as mercaptobenzimidazole, would help to explain the action of these sulfur compounds. Le Bras, who proposed the use of these compounds, considered that they function by deactivating the peroxides formed by autoxidation. It was found that mercaptobenzimidazole and simpler related compounds such as thiourea reacted with alkyl hydroperoxides with the formation of hydroxyl or alkoxy radicals and this led to attack on the solvent or on other molecules present, in a manner resembling the action of ferrous salt-hydrogen peroxide. This suggested that rubber would also be attacked and probably degraded. It was found that mercaptobenzimidazole with excess of peroxide gave rapid degradation of rubber in solution if access of oxygen was permitted. Thiourea, thioacetamide, some dithiocarbonates, and aromatic thiols were also effective, but aliphatic thiols and ethylmercaptobenzimidazole were ineffective. Softened or “depolymerized” rubber was prepared by addition of the reagents to rubber solutions or to latex. The use of these sulfur compounds in the presence of peroxides provides a means of obtaining a controlled amount of breakdown of rubber, and products ranging from normal plasticized rubber to a viscous liquid can be prepared. Under different conditions, mercaptobenzimidazole may either promote degradation (as shown in this paper) or retard it (as stated by Le Bras), and a possible explanation for this reversal of behavior is suggested.
Rubber Oxidation and Antioxidant Actions
Authors: Baxter S. , Morgan W. Mc G. , Roebuck D. S. P.
Published: February 2011

Many experimental investigations into the oxidation or aging characteristics of rubbers have been carried out during the last 30 years. Some have studied changes in physical properties during artificial aging and have linked these with culcanizate composition and with changes occurring during natural aging. Others have studied the kinetics and mechanisms of the chemical reactions involved. Both approaches have contributed much to the general body of knowledge on this subject. In more recent years, serious attempts have been made to correlate rate and extent of oxygen absorption with changes in physical properties, and conclusions drawn from this work have proved to be of considerable interest. In most of the work reported, however, oxygen absorption experiments were carried out on one sample of rubber, using a laboratory absorption apparatus, and deterioration of the physical properties of different samples were determined after aging for appropriate periods in an aging oven. Alternatively, direct measurement of the oxygen absorption of a tensile specimen during a given period of aging was made, and the properties of different specimens related. To obtain significant results it has proved desirable to carry out a considerable number of repeat experiments and to subject the data to careful statistical analysis. In an attempt to overcome some of the difficulties inherent in such an approach, a method was developed whereby simultaneous measurement of oxygen absorption characteristics and the change in elastic properties of a single specimen of rubber during aging can be made under closely controlled conditions. It is believed that direct correlations of this nature can lead not only to a much deeper insight into the mechanism of aging, but also to more practical use of present knowledge of the chemistry and kinetics of polymer aging. The investigation reported here is part of a larger investigation designed to lead ultimately to new means of improving age resistance of natural and synthetic rubbers.
Butadiene and Its Polymers. V. Formation of Spongy Butadiene Polymer
Authors: Piotrovskii˘ K. I.
Published: February 2011

1. It is shown that the formation of spongy butadiene polymer is accelerated by the addition to the butadiene of most metals and certain crystalline substances. This spongy polymer is not formed on lead or copper. 2. It is shown that the formation of spongy polymer on iron takes place at practically any polymerization temperature. 3. It is proved that in the absence, both in the butadiene and in the apparatus, of oxygen and peroxides, no spongy polymer is formed, and also that peroxides accelerate the formation of spongy polymer. 4. It is proved that the activation of the formation of spongy polymer by iron is of an adsorptive nature, and the formation of spongy polymer on iron can prevent the formation of a unimolecular layer of a polar substance on the surface of the iron. 5. An outline scheme of the process of thermopolymerization of butadiene is given, with experimental data on the formation of its cyclic dimer, of a rubber-like polymer, and of the spongy polymer.
The Sulfonation of Natural Rubber
Authors: van Amerongen G. J.
Published: February 2011

Like many olefins, natural rubber is capable of reacting with sulfur dioxide, with formation of a sulfone. The reaction is a chain reaction which is started by certain catalysts. The structure of the rubber sulfone is: (see PDF for diagram) and the theoretical proportion of sulfur is 24.2 per cent. Table I gives some experimental results obtained in the reaction of rubber with sulfur dioxide.
Kinetics of Cyclization of Hevea Latex
Authors: Gordon Manfred
Published: February 2011

Kinetic measurements on rubber cyclization now are possible by a latex technique; these were undertaken to elucidate the mechanism of the reaction. According to a patented process, dispersions of Hevea latex particles in 70 to 80 per cent sulfuric acid are reproducibly isomerized to a high molecular weight cyclized rubber. A diffusion gradient technique was adopted for measuring the density of the polymer after exposing it to cyclization for varying times. Unimolecular constants, k, spreading over four decades, were obtained and found enormously sensitive to the percentage, c, of sulfuric acid and absolute temperature, T; thus log10k=6+0.17c−7105/T. The constants, k, correlate satisfactorily with Hammett's acidity function, H0. A statistical theory by Flory shows that 13.5 per cent of the isoprene units originally present in rubber are left uncyclized by the reaction. This is in striking agreement with unsaturation measurements made by Fisher in 1927. The kinetic parameters deduced support a nonchain proton transfer mechanism, deprotonation being rate-determining. The proton affinity of rubber is estimated, and a comparison of the cyclization of rubber and other terpenes is presented. The structure proposed for cyclized rubber rings by D'Ianni and co-workers is supported by mechanistic analysis and physical properties. The method of kinetic measurements on stable emulsions in sulfuric acid is of general promise, and the cyclization of rubber polymer presents a useful model reaction for the smaller terpenes.
The Structure of Cyclized Rubber
Authors: van Veersen G. J.
Published: February 2011

The history of cyclized rubber, including a series of structural formulas previously proposed for this polymer, is reviewed briefly. A new formula for cyclized rubber is suggested by applying electronic interpretations of reactions between electrophilic agents and tertiary alkyl olefins and tertiary halides, respectively, to the corresponding reactions with rubber and rubber halides. It is shown that hydrochlorination can be used for the determination of the unsaturation of cyclized rubber. By varying the conditions of hydrochlorination, two types of double bonds can be detected in cyclized rubber, a fact which is in agreement with the structure suggested. By using our method for the determination of the unsaturation, the rate of cyclization at different temperatures and the influence of solvents on the rate of reaction have been determined.
Rubber Oxidation and Aging Studies Safe Limits of Sample Thickness
Authors: Blum George W. , Shelton J. Reid , Winn Hugh
Published: February 2011

Safe limits of sample thickness for rubber oxidation and aging studies, such that the chemical reaction rather than the rate of diffusion will be rate-controlling have been investigated for natural-rubber vulcanizates and for four synthetic-rubber types. For studies involving the entire range of oxidation, including the autocatalytic stage of rapid oxygen absorption, the conventional 0.075-inch thickness is frequently not satisfactory for accelerated aging and oxidation studies if it is desired to avoid limitation by diffusion. Only in the GR-S black stock was this thickness found to be satisfactory up to a temperature of 100° C. The other stocks, including natural rubber, Butaprene-NXM, and Neoprene black and gum stocks all require thinner samples to ensure that the observed rate of oxygen absorption is free of limitation by diffusion. A method of calculating the probable limiting value of sample thickness, above which the rate of oxidation in the autocatalytic stage is limited by diffusion, has been developed on the basis of volumetric oxygen absorption data obtained with GR-S. The method has also been applied to natural-rubber vulcanizates and to other synthetic-rubber types to locate the approximate limiting values at various temperatures for oxidation and aging studies which extend into the autocatalytic stage of rapid reaction. The constant-rate period of oxidation is more important from a practical point of view than the autocatalytic stage, since properties are so seriously degraded as to make the rubber of little value before it reaches the final stage of rapid oxidation. Somewhat thicker samples may be used for studies that are confined to the earlier stages of oxidation. A 0.075-inch sample is free of limitation by diffusion in the constant-rate stage in the following cases: GR-S black and gum stocks at 110° C; Hevea black with added antioxidant at 100° C; and uninhibited Hevea black and gum stocks at 60° C. A 0.040-inch sample is satisfactory in this range for: uninhibited Hevea black at 100° and gum at 80° C; Butaprene-NXM black at 100° and gum at 90° C; and Neoprene black and gum stocks at 100° C.
Abrasion and Wear of Rubber. Analysis of Wear Curves
Authors: Buist J. M.
Published: February 2011

One of the difficulties of assessing wear test data of rubber articles, e.g., tires, soles and heels, etc., is the fact that the wear index is not necessarily constant throughout the wearing trial. In a previous publication it was suggested that before exact correlations could be established between laboratory and service tests some mathematical method of obtaining constant indexes for both tests must be found. In the subsequent discussion of this paper at Birmingham, the author revealed that wear curves obtained on the Martindale abrasion tester and also some actual road wear curves could be expressed satisfactorily by an equation of the type y=axn. Since that time further work has been done, and it is now proved that if wear curves obtained on a wide range of laboratory machines, e.g., Martindale, du Pont, and Dunlop (Lambourn), are plotted, these curves are all of the same family y=axn. Although this equation is purely empirical, it is of considerable interest to the rubber industry in that it has such a broad application in the field of laboratory abrasion testing and also in service wear trials.
The T-R (Temperature-Retraction) Test for Characterizing the Low-Temperature Behavior of Elastomeric Compositions
Authors: Svetlik J. F. , Sperberg L. R.
Published: February 2011

The utility of the T-R test for determining the freezing points of elastomeric compounds and their tendency to crystallize has been demonstrated. The freezing point is not appreciably influenced by elongation, but from an operational standpoint it is preferable to employ 50 per cent extension of the sample. To determine the tendency to crystallize on cold storage a 50 per cent test elongation is optimum. To determine if a stock crystallizes on stretching the determination must be made at a series of elongations, or a minimum of two test elongations such as 50 and 200–300 per cent. Materials which crystallize almost immediately at low temperature are readily recognized. All materials which crystallize exhibit sluggish retraction characteristics, whether the crystallization is spontaneous, induced by cold storage, or by extension. The T-R test is simple to perform, highly reproducible, and very versatile. A complete characterization of the low-temperature properties of an elastomeric compound can be made by means of the T-R test in a shorter time than by any other method or combination of methods.
Deterioration of Rubber under the Influence of Light and Dry and Moist Heat
Authors: Soden A. L. , Wake W. C.
Published: February 2011

A comparison has been made of the aging of rubber compounds under tropical conditions. Two localities were chosen, one of which has a dry climate, the other heavy rainfall and high humidity. The results are compared with those obtained by ordinary Geer oven aging and by aging at the same temperature, but with 100 per cent relative humidity. This artificial moist heat aging is found to be much more severe than the tropical moist aging, but it is not different in kind to aging in a Geer oven and a simple conversion factor can be used to transpose results. Samples aged under dry conditions in the tropics are more influenced by bright sunlight, even though shielded from its direct rays, than by the heat aging. Recommendations are made concerning both the use of materials in the tropics and methods of accelerating aging to assess their behavior in the tropics.
Study of the Mechanism of Surface Deterioration of Ebonite and of Means of Preventing Deterioration
Authors: Whorlow R. W.
Published: February 2011

Following up earlier work on the subject, experiments are reported showing that the deterioration of the surface resistivity of ebonite caused by a particular quantity of light increases with decreasing intensity of illumination, and from the results of exposures to different types of radiation it is concluded that the surface temperature of the ebonite during exposure is the most important variable causing this difference. The observed effects are explained by assuming that sulfurous acid is produced as an intermediate product in the deterioration, and that this may either decompose to sulfur dioxide and water, or oxidize to sulfuric acid. If the former reaction is favored by a rise in temperature, the observed influence of intensity and type of illumination, and also the changes in resistivity after ceasing exposure can be explained. Possible methods of preventing or reducing deterioration are discussed, and it is concluded that application of an opaque surface coating, possibly incorporating a suitable basic material to neutralize any acid formed, is the only method likely to be really effective. This method is not possible in many cases. Incorporation of a suitable antioxidant (sym, di-β-naphthyl-para-phenylenediamine was the best of those tested) reduced the rate of deterioration. Where surface coating is impracticable, the use of an antioxidant might be considered, although improvement of resistance to deterioration by a factor of more than three has not so far been achieved by this means.
Oxidation of Olefins Representing Some Structural Units of GR-S
Authors: Warner W. C. , Shelton J. Reid
Published: February 2011

Three olefins were oxidized in the liquid phase with molecular oxygen to determine the kinetics of the oxidation reactions and the relationship to oxidation of rubber. The instantaneous rate of oxidation was found to be related to the analytically determined olefin and peroxide concentrations by the equation : Rate=k (unreacted olefin)(peroxide), where rate equals moles of oxygen per mole of original olefin per hour and the parentheses represent molarities. Presence of a phenyl group was found to affect k, but only in a minor way, indicating that the same fundamental kinetic mechanism applies in both aromatic and aliphatic olefins. The data are consistent with the general kinetic mechanism of Bolland involving oxygen attack at the alpha-methylenic group. However, it appears probable that initial oxygen attack can also occur at the double bond, resulting in the formation of a peroxide biradical, which may then react with other olefin molecules, initiating the usual chain reaction mechanism.
The Nature of Structural Changes of Butadiene Rubbers Caused by High Temperatures (100–200° C)
Authors: Kuzminskii˘ A. S. , Shokhin I. A. , Belitzkaya R. M.
Published: February 2011

In theories developed by Kuzminskii˘ and his collaborators concerning the mechanism of oxidation of rubbers, the question of a direct thermal effect on their structure was not discussed. Nevertheless, with certain rubbers, structural changes which are caused by high temperatures play a very important part in the total complex of structural changes undergone by these rubbers during processing and, after vulcanization, by their products during service. Dogadkin, Zayonchkovskii˘, Zayonchkovskaya, Pisarenko, and Astafyez, Kuzminskii˘, Shanin, Degteva, Lapteva, and other Soviet investigators have shown that, when butadiene rubbers are heated in the temperature range of 100–200° C, structural changes take place which are characterized by increases of tensile strength and modulus, decrease of extensibility, decrease of unsaturation, etc. The question of the causes of such extensive changes in rubber is the subject of this discussion. Rebinder has proven unsubstantiated the reasoning of several investigators regarding these processes, and has shown the necessity of carrying out direct experiments which would provide an explanation of their nature.
Effect of Storage of Milled Rubber on Its Molecular Weight
Authors: Cotton F. H. , Lee K. O.
Published: February 2011

No significant difference was observed between the viscosities of solutions made from milled rubber stored for varying periods. Some crystallization of the milled rubber had occurred, but this did not affect the solution viscosity. The plasticity measurements on the samples cooled with solid carbon dioxide confirm this hardening, but it is apparently an effect unconnected with change in molecular weight.
GR-S Aging in Solution
Authors: Jones Giffin D. , Friedrich Ralph E.
Published: February 2011

Photoscission of GR-S in ethylbenzene solution has been shown to require the interaction of oxygen. In principle then an antioxidant which is not a photosensitizer should function as a light stabilizer. The cause of the failure of the antioxidants studied to function as light stabilizers of GR-S is shown to be related to the occurrence of a very low rate of oxidation of the GR-S despite the presence of the antioxidant. The cause of the viscosity rise in GR-S solutions on autoxidation appears to be the formation of an intermolecular peroxide bond which is subject to induced scission.
Studies of the Vulcanization of Rubber
Authors: Kambara Shu , Ohkita Kumakazu
Published: February 2011

In this study much information about the method of distinguishing the state in which sulfur is combined in simple organic compounds consisting of carbon, hydrogen, and sulfur was obtained, and a new theory of vulcanization was postulated as a result of its application to vulcanized rubber. When activated sulfur reacts with rubber, it first adds to the double bonds, forming thioketones, which in turn, as a characteristic of these radicals, combine with each other, with the formation of a thioether structure. This transformation of thioketone into thioether takes place, not only during vulcanization, but also gradually after vulcanization. Because of the presence of thioketone, treatment of vulcanized rubber with hydrazine, forms a new network, that is, a ketoazine cross-linkage. Combined sulfur of the thioketone type was determined by an oxidizing agent, and as the difference of this value and total combined sulfur a method of determining bridge type of combined sulfur has been proposed. By this method, it was found that, even in ebonite, about one-third of the combined sulfur is the thioketone type, and that the bridge type is only about two-thirds of the total. The thioketone type of combined sulfur in soft vulcanized rubber is transformed gradually into the thioether type of cross-linkage when allowed to stand at room temperature, and this transformation is accelerated when the temperature is raised. In the case of hard rubber, this phenomenon is also observable, but the rate of this transformation is much slower compared to the former. This tendency is the same in the case of ketoazine cross-linking when rubber vulcanizates are treated with hydrazine. From these facts, it seems that the distribution of the thioketone radicals is not uniform, and the magnitude of the probability for collision of these radicals to form cross-linkages has a great influence on the properties of rubber after vulcanization. That is, the property of the vulcanizate is greatly affected by the fact whether the thioketone radicals in the vulcanizates are comparatively uniformly distributed or whether they exist in sectional groups or in colonies. The authors are the first to advance this postulate concerning the chemical structure of vulcanized rubber and its transformation. We believe that when the study is extended, using this postulation, problems such as aging and the differences in the properties of vulcanized rubber accelerated with various accelerators will become clear. Moreover, we believe that it will be of interest to physicists studying rubber elasticity to suggest this idea of colony of cross-linkages. We are now carrying on researches on these problems, and we shall report on them later.
Diffusion of Oxygen and Oxidation of Rubbers in the Presence of Phenyl-β-Naphthylamine
Authors: Kuzminskii˘ A. S. , Shanin L. L. , Lezhnev N. N.
Published: February 2011

We know now that the oxidation of rubbers takes place in the absence as well as the presence of antioxidants. However, the mechanism and the rate of the free and inhibited processes are altogether different. In the presence of a sufficient quantity of a good antioxidant (“true inhibited oxidation”), oxygen takes part almost exclusively in the immediate process of oxidation of the rubber, while the developing active centers are deactivated by reacting with the antioxidant. During free autocatalytic accelerated oxidation, the oxygen takes part in various processes; it initiates a chain process in which it takes part, and also causes many secondary reactions, including most of those which cause rupture of the reactive chains. In this article we shall discuss only true inhibited oxidation, which is especially important from the practical viewpoint.
X-Ray Analysis of the Molecular Structure of Rubbers. X-Ray Diffraction of Amorphous Rubber
Authors: Kasatochkin V. I. , Lukin B. V.
Published: February 2011

The potentialities of x-ray analysis of the molecular structure of rubbers can be widely extended by measuring the intensities of the amorphous halo and continuous background of scattering in the diffraction patterns of unstretched test-specimens. This method can be applied to the study of the effect of repeated stretching of rubbers. Questions pertaining to the fatigue of rubbers have immense importance now in the performance of rubber products. The methods of determining the crystallization of natural rubber and of measuring the intensity of the amorphous halo for synthetic rubber were employed for investigating the changes of the molecular structure of rubber due to repeated stretching. The crystallization of raw smoked-sheet rubber decreased as a result of fatigue; a similar phenomenon was observed for its vulcanizates. The vulcanizates which were stretched less than 300 per cent lost their crystallization property altogether after fatigue, and, at greater elongations, the content of the crystalline phase greatly decreased (see Figure 1).
Evaluation of Tread Wear
Authors: Stechert Dietrich G. , Bolt Thomas D.
Published: February 2011

The observed existence of a linear log-log relationship between nonskid loss and mileage in a great number of widely different types of tests may be exploited in order to realize substantial savings in the road testing of tires for tread wear. In many evaluations it is common practice for the Gates Rubber Co. to test tires to one half initial nonskid depth or to some arbitrary mileage only. The regression line and mileage to baldness are then determined. Of course, the greater the amount of data, and the more accurately controlled the conditions of testing, the more reliable will be the mileage to baldness. If in tread wear evaluations tests were terminated prior to baldness, about $180 could be saved for each passenger tire tested, and $490 for each truck tire, for every 10,000 miles. One investigation, to determine the effect of three different tire designs on tread wear, was made at a total cost of $2200. If all tires had been tested to baldness, the cost would have been approximately $4600. In comparison with former common practice, the application of the proposed method of analysis of tire wear measurements can result in more reliable tread wear evaluations, more economical utilization of the tire test fleet, and a more rapid turnover of ideas.
Migration of Materials during Accelerated Aging by the Oxygen Pressure Method
Authors: Fackler Marion B. , Rugg John S.
Published: February 2011

It has been definitely established that various materials migrate and that the magnitude of the resulting error is significance Migration takes place whenever unlike stocks are aged together in a bomb. The most reliable test conditions prevail when separate bombs are used for individual stocks. It is recommended that specifications for oxygen-bomb aging be changed. The change should specify the use of individual bombs.
Determination of Free Sulfur in Vulcanized Rubber Mixtures
Authors: Frey Horst
Published: February 2011

Numerous papers on the determination of free sulfur in rubber mixtures have been published. Most of these are in the older literature, and they offer various methods for determining free sulfur. In principle the methods can be divided into two general groups. The procedures described in the first and larger group involve preliminary acetone extraction before the actual determination of the free sulfur, whereas the methods comprising the second group, which include only two different procedures, do not involve acetone extraction. Of these two methods, only that of Oldham, Baker, and Craytor has found widespread acceptance.
Determination of Total Sulfur in Vulcanized Rubber Mixtures
Authors: Frey Horst
Published: February 2011

A method is described, which, by means of a resin ion-exchange agent, makes possible the elimination of the disturbing effects of foreign cations, particularly iron and chromium, in the determination of the total sulfur in vulcanized rubber mixtures. By this procedure, rapid volumetric methods for determining sulfate, even in the analysis of mixtures containing iron oxide or chromium oxide pigments, can be utilized. The procedure involves precipitation of the sulfate by benzidine and determination by titration with aqueous sodium hydroxide. The method is more rapid and more reliable than ordinary gravimetric methods involving precipitation of barium sulfate.
Temperature Rise in the Rubber in Rotation Plastometers
Authors: Whorlow R. W.
Published: February 2011

The temperature rise that occurs on shearing rubber at high rates in the shearing-cone plastometer has been measured and shown to be about double that which is to be expected from simple theoretical considerations. This discrepancy is apparently due to heating of the rotor. The temperature rise in normal Mooney plastometer tests may be great enough to influence significantly the results, particularly during scorch tests, but relative results on stocks of not very different plasticities (as in control tests of a given mix) would not be appreciably affected.
Quantitative Characterization of Cure. I. Relationship between Modulus and Strain of Pure-Gum Natural-Rubber Vulcanizates
Authors: Blackwell R. F.
Published: February 2011

The object of this investigation was to determine whether the relationship between strain (elongation) and modulus is sufficiently close for one to be calculated from the other. Stress-strain data have been recorded for loads of 2–10 kg. per sq. cm. for a series of ACS1 and other pure-gum compounds. It is shown that the strain at a fixed stress (5 kg. per sq. cm.) is uniquely related to the load required to produce an elongation of 100 per cent. A tentative explanation of this observation is given in terms of the Mooney equation for the stress-strain curve. It is shown that the second constant of this equation does not vary greatly from rubber to rubber.
Quantitative Characterization of Cure. II. Use of Modulus as a Measure of the State of Cure of Pure-Gum Natural-Rubber Vulcanizates
Authors: Fletcher W. P. , Gee Geoffrey , Morrell S. H.
Published: February 2011

The purpose of this investigation was to develop methods of measuring state of cure which involved only measurements normally available or very readily made. Swelling measurements, although suitable in theory, suffer the practical disadvantage of being time-consuming, but it is shown that they can be replaced very satisfactorily by modulus at 100 per cent elongation. This is a good practical measure of state of cure for most purposes, and simple corrections are developed which extend its range of usefulness. An easily constructed machine is described for the accurate measure of modulus at small elongations.
Viscoelasticity of Rubber
Authors: Blizard Robert B.
Published: February 2011

A theory has been obtained for the viscoelastic behavior of rubber in the frequency range above that at which creep is important and below that at which it behaves like a hard solid. The rubber chains are treated as springs in a viscous medium, and a general expression is obtained for the contribution to modulus of a single section of chain as a function of its length and terminations. A statistical estimate is made of the number of chain segments having given length and terminations. A modulus function is found for the group of chains with each kind of termination, and these are added in the proper amounts to give the form of the modulus vs. frequency curve for any amount of cross-linking. Measurements of shear modulus were made on one apparatus at frequencies between 0.0125 and 750 cps. Agreement is good if a pure viscosity is added to the theory. However, at low frequencies the imaginary part of modulus does not decrease as much as predicted.
Formation of Bound Rubber of GR-S Type Polymers with Carbon Blacks
Authors: Duke June , Taft W. K. , Kolthoff I. M.
Published: February 2011

The bound rubber-black complex formed by milling various GR-S polymers and carbon blacks at several temperature levels was studied. The amount of bound polymer increased with greater loadings of black, but per unit of carbon black, it decreased at the higher black loadings. The temperature of mixing likewise has a large effect—at lower carbon black loadings, higher temperatures increase the amount of binding; the effect ia minimized as the loading is increased until at high loadings (100 to 125 parts of black per 100 parts of rubber) this effect is eliminated. By fractionation of the sol portion, it has been shown that polymer of progressively lower molecular weight is bound as the black loading is increased. Polymer of high molecular weight does not replace bound polymer of lower molecular weight; the polymer of higher molecular weight is preferentially bound during mill mixing. Although more polymer appears to be bound as the conversion is increased from 50 to 72 per cent at a loading of 50 parts of black, other factors besides conversion may be determinative. No differences in relationship were found for polymers made at 122° or 41° F.
Application of the Measurement of the Dielectric Constant and Loss Angle to the Study of the Structure of Vulcanizates Loaded with Carbon Blacks
Authors: Thirion P. , Chasset R.
Published: February 2011

In the case of vulcanizates containing carbon black the variation curves of dielectric loss angle as a function of temperature enable the Debye type absorption occurring in the rubber matrix to be distinguished from a supplementary absorption little influenced by variations in temperature and frequency which is characteristic of blacks possessing a structure. The experimental results obtained indicate no difference in physical or chemical state between the matrix occupying the space between the particles of black in a loaded mix and the vulcanizate of the corresponding pure rubber mix. The supplementary losses on the other hand seem to be closely related to the effects of structure in loaded mixes imagined by Mullins to explain the mechanical behavior of these mixes: they decrease very rapidly by elongation or swelling and give rise to various phenomena of hysteresis. It would seem that dielectric absorption could advantageously be applied as a nondestructive test revealing the colloidal structure of rubber mixes based on carbon black. Moreover the dielectric constant would enable information to be obtained on the form factor and the orientation of the particles or agglomerates of particles of black in mixes on the basis of a theory assimilating these particles (or agglomerates) to condenser armatures.
Storage Stability of Unvulcanized Natural, Nitrile, and GR-S Rubber Compounds
Authors: Schroeder Charles H.
Published: February 2011

Loss of plasticity due to interaction of polymer and loading pigment and aging can be overcome by remilling, and therefore is not serious in formulating compounds which can be remilled before use. Compounds which are sold in the unvulcanized state and cannot be remilled after aging and before use must be formulated so as to avoid loss of plasticity due to polymer and pigment interaction or from other cause shown in this paper. The factors influencing the storage stability of unvulcanized compounds both with and without curing agents have been discussed, and it has been shown that by proper formulation it is possible to produce stocks with adequate uncured storage stability.
Some Factors Influencing the Road Wear of Tires
Authors: Stiehler R. D. , Steel M. N. , Mandel J.
Published: February 2011

Three road tests of tires for tread wear were statistically designed. The design of test equalized the treatment of tires, and included a study of some of the factors influencing the road wear of tires in addition to the primary object of the test. Among these factors were the effects of vehicle, wheel position, day of test, climatic conditions, and length of storage. A study was made also of two methods of measurement-depth of tread grooves and weight loss. The information on these factors was obtained at no increase in cost of test. It was found that atire loses weight at essentially a constant rate, whereas, the depth of the tread grooves decreases at a declining rate, which results in a bias in the tread wear ratings. The weight method was also found to be more sensitive than the depth method. The study of the effects of vehicle and wheel positions led to the conclusion that differences in the rate of wear on different wheels do not affect the tread wear comparisons, since the rate in slow wearing positions is proportional to that in fast wearing positions, and the coefficient of variation is about the same. These results led to the conclusion that geometric rather than arithmetic averages be used in evaluating tread wear. The study of the effect of day of testing and of climatic conditions indicated that the surface temperature of the road and tire has a pronounced effect on rate of wear. Natural rubber treads containing channel black wore faster as the temperature increased, whereas, synthetic rubber tread containing furnace blacks wore faster as the temperature decreased. Other treads wore at about the same rate as the temperature changed. The effect of temperature on tread wear was greater in many instances than the effect of a lower coefficient of friction on wet roadways. Storage of tires generally increased the rate of wear; however, some treads did not wear faster after one year of storage. The object of one test was to determine the effect of type of rubber and black on tread wear. It was found that the rubber and black are mutually independent in their effects. The behavior of natural and synthetic rubbers or of channel and furnace blacks with a change in temperature made it impossible to compare them without stating the conditions of test.
Measurement of Refractive Index of Elastomers
Authors: Arnold Aurelia , Madorsky Irving , Wood Lawrence A.
Published: February 2011

The measurement of the refractive index of elastomers is discussed, with particular reference to GR-S rubber and the use of an Abbé type of refractometer. Detailed descriptions of the apparatus used and the procedure for GR-S rubber are given. Common sources of error are discussed and methods of minimizing these errors are given. A detailed stady has been made of the precision obtainable with GR-S polymers using the Abbé type of refractometer with an incandescent light source. It was found that the standard deviation corresponding to variability of a single random determination was 0.00007. The method has been used for several years as the basis for the determination of bound styrene in copolymers of butadiene and styrene, and is currently employed for control purposes in the government-owned synthetic rubber plants. It has also been used for determining the percentage of rubber hydrocarbon in natural rubber and for locating second-order transition temperatures.
Atmospheric Ozone—A Simple Approximate Method of Measurement
Authors: Crabtree J. , Erickson R. H.
Published: February 2011

In recent years the rubber industry has awakened to the significance of the minute amounts of ozone in the atmosphere as a destructive agent by virtue of its unique property of splitting stretched rubber and perhaps also of the possibility of its function as an oxidation catalyst for organic materials in general. Progress in the past has been hampered by lack of a satisfactory method of measurement at the extreme dilution encountered (0–10 parts per hundred million). Particularly does this apply because measurements must be made on the spot. The fugitive nature and high dilution of the ozone obviate any possibility of transporting samples for later measurement in the laboratory. Of the methods available, the fundamentally ideal one is by light absorption at one of the ozone absorption bands. Measurements made by European observers in this way have given values of from one to three parts ozone per 108 parts of air. An air path of three to four miles is necessary, however, and this, apart from other experimental difficulties, renders the procedure hopeless for practical application. Numerous colorimetric and fluorescence methods have been described, but none begins to approach the necessary sensitivity. Resort, therefore, has inevitably been to the classical reaction with potassium iodide, with measurement of the iodine liberated. Here the problems lie in the difficulty of presenting efficiently a very large volume of air to a small volume of reagent, and in the possible presence in the atmosphere of other oxidizing agents, e.g., peroxides—nitrogen, hydrogen, or organic. The volume problem has been solved by presenting the air to the reagent in the form of a fine spray, and apparatus has been described to accomplish this action. The hazard of other oxidizing agents is not usually present, but these can usually be frozen out in cooled traps above the boiling point of ozone. It has been claimed possible to separate the ozone by absorption on silica gel cooled in liquid oxygen and to recover it quantitatively on warming. The present authors, however, have never been able to recover more than 50 per cent of the original ozone in this way. A Russian observer could recover none.
An Improved Apparatus for Determining Moisture in Rubber by Distillation with Toluene
Authors: Tryon Max
Published: February 2011

An improved apparatus has been developed for the determination of water in rubber by distillation with toluene. The volume of the water collected is measured in a graduated capillary tube, which allows more precise measurement than the tapered tube formerly used. The interior of the trap and condenser is coated with a water-repellent silicone polymer to prevent water droplets from adhering to the walls and to improve the accuracy. This paper describes the construction of the apparatus and a procedure for coating its interior with the silicone polymer. A method of calibration of the trap is included in a general procedure for use of the equipment.
Water Vapor Permeability and Sorption of Hevea Latex Films
Authors: Bowler William W.
Published: February 2011

A considerable structural difference exists between Hevea latex films vulcanized after drying and those vulcanized in the latex state. Since these two types of films differ considerably in water vapor permeability and sorption, a careful study has been made of these phenomena. The weight of water permeating an uncompounded film was inversely proportional to the thickness of the film over a wide range of thicknesses, and directly proportional to Δp, the vapor pressure difference across the film, except at very high values of Δp. However, films cast from vulcanized latex were much more permeable to water vapor, sorbed considerably less water, and had a greater negative temperature dependence of permeability than uncompounded or dry vulcanized films. These experiments indicate that diffusion takes place in prevulcanized films by an activated diffusion through capillary holes and in dry vulcanized films by an activated diffusion through the polymer itself or the adsorption layer.
Vibration Characteristics of Tread Stocks
Authors: Gui K. E. , Wilkinson C. S. , Gehman S. D.
Published: February 2011

Nonlinear vibration characteristics of tread compounds, as evidenced by a dependence of modulus and internal friction on amplitude, were studied in order to reach an understanding of these unexplained phenomena in terms of plausible structural alterations which may occur in the tread compounds because of vibration. This information is interesting both for a more exact description of the deformation processes in tread compounds, and because of the necessity of dealing with the effects in any dynamic testing procedure. Nonlinear vibration characteristics are readily observed for tread stocks of both Hevea and synthetic rubbers in the mechanical range of frequencies. Experiments were undertaken to study the extent to which these effects depend on temperature, compounding variables, and type of vibration. It may be shown that the nonlinearity is not due to temperature rise from vibration, although precise measurements are complicated by the temperature rise. The effects occur for stocks reinforced with fine silica pigment, Pliolite resin, and higher loadings of pigments generally considered to be nonreinforcing, as well as for those compounded with reinforcing blacks. The pigment loading necessary for the same degree of nonlinearity increases with the pigment size. The effects are observed in unvulcanized tread stocks and occur for vibrations in both shear, compression, and tension. Measurements of the nonlinearity for tread stocks over a range of temperatures suggest that the vibration elicits structural changes in the rubber analogous to those observed in the rheology of rubber solutions and raw rubber. The nature of these changes can be interpreted by the rheological criteria of structure developed for non-Newtonian systems. Such recognized mechanisms for structural viscosity as orientation, deformation, and breaking and reforming of bonds of the flow units are useful in explaining the phenomena observed. The effects appear to be of such magnitude that they should be taken into account in any exact study of the effect of modulus on tread wear and performance.
Temperature Dependence of Dynamic Properties of Elastomers. Relaxation Distributions
Authors: Ferry John D. , Fitzgerald Edwin R. , Grandine Lester D. , Williams Malcolm L.
Published: February 2011

By the use of reduced variables, the temperature dependence and frequency dependence of dynamic mechanical properties of rubberlike materials can be interrelated without any arbitrary assumptions about the functional form of either The definitions of the reduced variables are based on some simple assumptions regarding the nature of relaxation processes. The real part of the reduced dynamic rigidity, plotted against the reduced frequency, gives a single composite curve for data over wide ranges of frequency and temperature; this is true also for the imaginary part of the rigidity or the dynamic viscosity. The real and imaginary parts of the rigidity, although independent measurements, are interrelated through the distribution function of relaxation times, and this relation provides a check on experimental results. First and second approximation methods of calculating the distribution function from dynamic data are given. The use of the distribution function to predict various types of time-dependent mechanical behavior is illustrated.
Correlation of Dynamic and Static Measurements on Rubberlike Materials
Authors: Andrews R. D.
Published: February 2011

Dynamic and static measurements of rubberlike materials can be related in terms of a generalized Maxwell model which is assumed to represent the mechanical behavior of the system, the individual characteristics of the system being expressed by the nature of the relaxation time distribution of the model. Such properties as dynamic modulus and dynamic viscosity measured in experiments involving sinusoidal vibrations and static modulus measured in experiments of relaxation of stress at constant strain can be expressed by integrals involving the distribution of relaxation times. The distribution of relaxation times can, therefore, be calculated from experimental data of this sort by suitable mathematical methods. Because of the complexity of such calculations when carried out rigorously, the use of approximate methods is often desirable. A number of useful approximate relations can be derived by investigation of the mathematical structure of the integrals relating the distribution of relaxation times to the observed properties and by examination of the behavior of certain particular relaxation time distributions. Attempts to correlate dynamic and static data on the basis of this general theory by use of the approximate relations discussed have been reasonably successful.