bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Treatment of Hydrated Silica Pigments for Reinforcement of Rubber Stocks
Authors: Stearns R. S. , Johnson B. L.
Published: February 2011

Many finely divided solids have been added to elastomers to effect reinforcement of the cured stocks. It is generally agreed that the more finely divided the solid and the greater the degree of physical adhesion (wetting) between the surface of the filler and the polymer chains, the greater will be the general overall reinforcing effect. However, recent work on the mechanism of reinforcement has indicated that an important, if not limiting, property of the filler, in at least modulus reinforcement, is the immobilization of polymer segments on the solid surface. The immobilization is effected by the formation of strong chemisorptive bonds, if not covalent bonds, between the polymer and the filler. The application of this concept to carbon blacks has been discussed in detail by the authors, and similar conclusions have been reached by Blanchard and Parkinson and by Barton, Smallwood, and Ganzhorn. Up to the present time carbon blacks are unique as reinforcing agents in Hevea and GR-S type polymers. The numerous inorganic fillers which have been studied are generally inferior to the carbon blacks in one or more respects. The rubber chemist and technologist is chiefly interested in such properties as modulus, tensile strength, abrasion resistance, and resilience of the compounded stock. Tensile strength and resilience as commonly measured are primarily a function of the extent of surface, the particle-size distribution, and the degree of dispersion of the added pigment or filler. The chemical nature of the solid surface appears to be of secondary importance. Abrasion resistance is a difficult quantity to measure, especially in the laboratory. Therefore, in studying the mechanism of reinforcement and the reinforcing effect of different types of fillers, measurements have been confined to an evaluation of the so-called “equilibrium modulus”, from which an apparent work of retraction may be calculated. It has been found that the work of retraction is highly sensitive to changes in the chemical nature of the solid surface and the results may be interpreted in terms of the kinetic theory of elasticity.
Reaction of Ozone with Natural Hevea and Acrylonitrile-Butadiene Rubbers
Authors: Kendall F. H. , Mann J.
Published: February 2011

The cracking of rubber vulcanizates when exposed to the atmosphere in a state of stress is a well-known phenomenon which has been studied extensively. A comprehensive review of the literature on this subject has been published by Newton. Following the lines of earlier work Newton showed conclusively that the cracking is produced by traces of ozone present in the atmosphere. The simultaneous presence of both stress and ozone is required for cracking to occur and the cracks that form are oriented with their lengths perpendicular to the direction of the stress. It has been reported, however, that similar cracking is produced when stretched rubber is exposed to free radicals produced by the thermal breakdown of organic peroxides. Unstretched vulcanizates do not crack when exposed to ozone, nor do they crack when stretched after exposure to ozone. Apart from the frosting effect described by Tuley, which is stated to require the presence of moisture and which may require the presence of small stresses, there seems to be no record in the literature of a visible effect being produced by the action of ozone on unstretched vulcanizates. The effect of ozone on unstretched vulcanizates has been investigated more completely and the results are reported in the present paper. Little is known of the mechanism of the reactions that lead to cracking of vulcanizates and this paper describes experiments designed to throw some light on this. The products of the reaction between ozone and solid rubber have been investigated by means of infrared spectroscopy. Allison and Stanley have previously described the infrared spectra of products formed from solutions of Hevea and various synthetic rubbers and Salomon and van der Schee have recently reported changes which occur in the infrared spectrum of a film of Hevea rubber when exposed to ozonized air.
Urethan Rubber from a Polyether Glycol. Factors Influencing Processability
Authors: Rugg J. S. , Scott G. W.
Published: February 2011

Adiprene-B urethan rubber is a high-viscosity thermoplastic elastomer that can be compounded and otherwise processed on conventional rubber manufacturing equipment. There are fundamental differences between Adiprene-B and the more common elastomers in processing which must be taken into consideration. 1. Processing temperatures should be less than 121° C to ensure smooth plastic flow and reduce the rate of scorching. 2. Processing temperature is proportional to Mooney viscosity, and both can be reduced by the use of plasticizers. 3. Moisture increases the rate of scorch, and it should be held to a minimum through all phases of processing. 4. Since stocks containing Adiprene-B increase in viscosity during storage, close scheduling of operations will ensure the maximum processable life.
2-Methyl-5-Vinylpyridine Elastomers in Oil-Resistant Service
Authors: Svetlik J. F. , Railsback H. E. , Cooper W. T.
Published: February 2011

Butadiene-MVP copolymers and butadiene-acrylonitrile-MVP terpolymers are a new class of rubbers which can be rendered oil-resistant by reaction with organic halogen compounds during vulcanization. The rubbers respond normally to reinforcement by carbon black and are highly reinforced by mineral fillers such as clay. Oil resistance depends on MVP content of copolymers and MVP and acrylonitrile content of terpolymers. The type and quantity of quaternizing agent also regulate the properties and oil resistance of the vulcanizates. Excellent performance of the experimental rubbers was demonstrated after immersion in ketones, amyl alcohol, ethyleneglycol, acid, caustic soda, a 70/30 2,2,4-trimethylpentane-toluene mixture, and ester solvents. The terpolymers offer better resistance to aromatic hydrocarbons. The experimental rubbers are also superior to the butadiene-acrylonitrile control compounds in contact with hot diester lubricants, giving much higher tensile strength after exposure for 72 hours at 300° F or 48 hours at 158° F. The MVP-containing rubbers possess excellent resistance to flex crack growth. They are also considerably better than the controls in resistance to blowout under severe conditions of rapid cyclic deformation under heavy load at elevated temperatures.
Observations on the Physical Aspects of Resistance to Skidding on Dry Roads and Particularly on Wet Roads
Authors: Knauerhase K.
Published: February 2011

To ensure safety from skidding, attention has up to now been devoted to building rough surface roads, to the development of the proper vehicle construction with respect to this feature, and to the factor most directly involved, the tires. Special attention has been directed in connection with this latter phase to a much more open tread patterning and to the effect of decreasing tire inflation, both of which affect the life of the tire adversely. These steps neglected to take advantage of the physical effect of adhesion, which, without lowering the durability, now makes possible an enhanced contribution to the cohesive friction by the profile grooves which are of necessity retained to keep the weight down. The goal is, therefore, to provide the smooth surfaces of the tread pattern that come in contact with the road with the greatest possible physical gripping power, or adhesion. After illustrating the interfacial magnitudes with the help of a vector diagram, we shall survey the laws of boundary surface adhesion. Here the great influence of the liquid involved in wet friction becomes clear and the particularly favorable interfacial tension property of water can be assessed. Since skidding can occur only at the interfaces : rubber-water, or water-road, the requirement is as follows : both the greatest possible wetting power between rubber and water, and also between water and road surface, that is, hydrophilic properties in the rubber and hydrophilic road surfaces, in order to reduce the danger of skidding. Good insurance against skidding requires hydrophilic rubber and a hydrophilic road surface, for a tire that has been developed to be nonskidding holds on a hydrophilic road surface and skids on a hydrophobic road surface. A hydrophobic tire, on the other hand, skids on any wet road. Although considerable advances have been made with respect to safety from skidding since rubber tires were first developed for motor vehicles, with increase of speeds this problem demands our attention to a greater and greater degree. Safety from skidding can result only from the combined efforts of road and car builders, tire makers, and the chemists and physicists of all three groups.
Tire Wear and Fuel Consumption
Authors: de Decker H. C. J. , Van Amerongen G. J. , Benders J. F.
Published: February 2011

In order to survey the economics for a given country of driving with cold GR-S and natural-rubber tires, we proceeded as follows. With the usual average life of a tire as a starting point, the difference in life was calculated for the two types of rubber on the basis of relative wear resistance measurements. Based on the price of the tire this difference at each temperature is expressed in terms of money. There is obtained in this way, therefore, for the country selected, a curve showing price difference vs. temperature. This curve has to be further corrected because of the greater fuel consumption when the driving is done with cold GR-S tires. Even with equal tire life, it is certainly an advantage to save some fuel. Since our observations on fuel consumption showed no dependence on temperature, this correction only produces a parallel displacement of the curve of price difference vs. temperature. As an example, the resulting curve for West Germany is given in Figure 7 (lower diagram). With the aid of this curve every car driver in West Germany can calculate for himself what is the advantage or disadvantage of natural-rubber tires. For this he needs only to know how many kilometers he has gone at the different temperatures. The upper half of Figure 7 gives a view of the distribution of kilometer performance (mileage) of all private cars in West Germany. The percentage of the tire mileage at the different temperatures is given. In deriving these results, use was made of some statistical data on the traffic density in different months of the year. These data were from the Central Bureau voor de Statistiek in the Hague. Also the meteorological mean temperature values for definite hours of the day and months of the year were taken into account. The conclusion for West Germany is that, on the average, there is a distinct advantage in driving with natural-rubber tires. Conclusions for other countries can be drawn in a similar manner. They are given in very brief form in Figure 8. Surprisingly enough Figure 8 shows that GR-S is advantageous only in a very warm, i.e., tropical, climate. In all other countries, natural rubber shows more or less advantage. An estimate by J. C. Gerritsen, to whom we also are indebted for most of the preceding calculations, shows that over 70 per cent of the motor vehicles in the world can run more economically on natural-rubber tires.
The Enzymic Synthesis of Rubber
Authors: Teas Howard J. , Bandurski Robert S.
Published: February 2011

Studies of the mechanism of biosynthesis of rubber in seedlings and cultured tissues of guayule have established that the carbon of the isoprenoid chain can be derived exclusively from acetate, and flax enzyme preparations have indicated that the branched chain acids, β-methyl crotonic acid and β-methyl-β- hydroxyglutaric acid are probably intermediates in the formation of the basic isoprenoid unit. However, the requirement for intact plants or tissue cultures has made detailed studies of the biosynthesis of rubber difficult. We have now observed that incubation of C14-labelled acetate results in the incorporation of radioactivity into rubber.
Possible Methods of Recharging the Surfaces of Particles of Latexes Stabilized with Soaps
Authors: Voyutskii˘ S. S. , Panich R. M. , Kalyanova K. A.
Published: February 2011

1. It is shown that the surfaces of particles of a synthetic latex stabilized with soap can be recharged by acidification or by the addition of an aluminum salt. 2. It is established that a necessary condition for this recharging is a low-solids concentration in the latex, which makes it possible for the particles to be recharged without the formation of any considerable amount of coagulum. 3. The opinion is expressed that recharging by acidification occurs through the adsorption of positively charged hydrogen ions by the particles of the latex; recharging by the addition of aluminum salts is due to the formation of an amphoteric aluminum hydroxide which is adsorbed by the surfaces of the particles.
Effect of Storage Conditions on the Properties of Latex. I.
Authors: Collier H. M.
Published: February 2011

Working with ammonia-preserved natural-rubber latex, concentrated by centrifuging, the author shows that the slight fall in mechanical stability associated with the shipment of bulk supplies of latex can be explained by the fact that, during shipment, latex does not have access to the oxygen of the air. The mechanical stability of samples taken at the time of shipment increased in value when there was an appreciable air-space in the storage bottle, but fell when the bottle was full and air was excluded. These differences were accentuated when air was replaced by oxygen and was then possible to find marked differences not only in mechanical stability time but also in the volatile fat acid content of the latexes. The increase of volatile fat acid content of the samples stored in the absence of air was much greater than in the sample stored in the presence of oxygen. The fall of mechanical stability in the absence of air is ascribed to the formation of increasing quantities of salts, such as ammonium acetate. In the presence of oxygen, the rate of formation of salts of this type is very much less, and at the same time other changes take place which lead to a marked increase of mechanical stability.
Comparison of Different Viscometers for Measuring the Viscosity of Latex
Authors: Boucher M.
Published: February 2011

The viscosity values of different samples of latex diluted to different degrees were measured by means of three viscometers of different types, viz., the Brookfield viscometer, the Epprecht viscometer, and the French Rubber Institute viscometer. The results obtained are dependent on the type of apparatus, although within certain limits, the Epprecht and French Rubber Institute viscometers give approximately the same results. The values obtained with the Brookfield viscometer are distinctly different from those with other two viscometers. In spite of these differences, however, each of the viscometers has a field of use, which is indicated and discussed.
Carbon Blacks for Highly Conductive Rubber
Authors: Polley M. H. , Boonstra B. B. S. T.
Published: February 2011

The mechanism of the conductance of the electric current through a carbon black dispersion is still a problem which has not been completely solved. Rubber is an insulator and forms a homogeneous liquid phase, while carbon black is a semi-conductor and forms a dispersible solid phase. Mixtures of these two show electrical properties ranging from a near insulator to a near semiconductor. The picture which has been generally accepted for the mechanism of conductivity in rubber-carbon black compounds is one based on through-going paths of carbon black particles. These through-going paths are formed by carbon black particles either touching or situated so close to adjoining carbon black particles that the electrons have a reasonable chance to jump across the gap. This concept implies that each carbon particle must practically touch its neighbor or else the continuous chain will be broken. The definition of “touching” is not given in this concept. The number of conducting or through-going paths will be a function of loading and the particle size of the carbon black. In addition to the number of the paths, the intrinsic conductivity of the carbon blacks themselves, which is mainly a contact resistance, is of paramount importance. This picture is useful only if it is consistent with the various characteristics of electrically conductive rubber-carbon black compounds.
Stability of Ammoniated Latex and Soap-Stabilized Emulsions in the Presence of Complex Zinc Salts
Authors: McRoberts T. S.
Published: February 2011

The solubility of zinc oxide in solutions of ammonia and different ammonium salts has been determined. The interaction between ammonium laurate and zinc ammine (or ethylene diammine) salts has been studied in aqueous solution, in latex, and in oil emulsions. The results indicate that destabilization of ammoniated latex or soap-stabilized emulsions by dissolved zinc oxide is due to the presence of zinc diammine ions, which form insoluble dilaurates. It is suggested that the increased rate of destabilization at elevated temperatures is most probably due to a decrease in hydration of the zinc diammine dilaurate formed at the surface of the rubber or oil particles.
Crosslinking and Radiation Effects in Some Natural and Synthetic Rubbers
Authors: Charlesby A. , Groves D.
Published: February 2011

When subjected to atomic energy radiation certain polymers crosslink, a process which is equivalent to vulcanization, but occurs without the admixture of extraneous chemical agents. Other polymers degrade by main chain fracture, a process which occurs at random throughout the molecule, and is different from thermal or ultraviolet degradation. Methods available for detecting crosslinking in irradiated polymers, include those based on solubility and swelling which have been used to study the effect of high energy radiation on a number of natural and synthetic rubbers. The polymers investigated include natural rubber, polychloroprene, polyisobutylene, polybutadiene, and thioplasts, as well as some copolymers. The results show the degree of crosslinking to be proportional to radiation dose, and to be reduced by the presence of styrene or acrylonitrile units in copolymers. Possible applications of this physical technique of linking molecules are discussed briefly.
Rubbery Copolymers from Unsaturated Ketones
Authors: Cooper W. , Bird T. B. , Catterall E.
Published: February 2011

The preparation and properties of copolymers from unsaturated ketones with acrylate esters and with butadiene are described. Details of the polymerization reactions and the structure of the copolymers are given. The preparation and properties of compounded vulcanized polymers are described and, in the case of the ketone-acrylate copolymers, the mechanism of sulfur vulcanization is discussed.
The Stress Relaxation of Sulfur Vulcanizates of Natural Rubber
Authors: Berry J. P.
Published: February 2011

An experimental study is reported of the stress relaxation behavior of sulfur vulcanizates of natural rubber maintained at constant extension. Of particular interest is the effect of oxygen pressure on the shape of the force-time curves, and the relaxation proceeding in absence of oxygen. The results are interpreted according to a two-stage process: (1) oxidation at the crosslinks and (2) scission of oxidized crosslinks.
The Vulcanization of Elastomers. VII. The Vulcanization of Natural Rubber with Thiuram Disulfides. Part IV
Authors: Scheele Walter , Stange Peter
Published: February 2011

The present paper deals with the kinetics of the thiuram vulcanization at varying thiuram disulfide concentrations as well as with the influence of the zinc oxide content upon vulcanization at constant temperature (120° C). It was found : 1. The limiting value of dithiocarbamate formation of 66 mole per cent relative to the amount of thiuram disulfide used is—within wide limits—independent of the initial thiuram disulfide concentration. 2. At constant thiuram disulfide concentration the limiting value of dithiocarbamate formation is unchanged when the zinc oxide content is successively increased. 3. Changing the zinc oxide content while the thiuram disulfide concentration is kept constant exerts an influence on the kinetics of the decrease of thiuram as well as on the increase of dithiocarbamate. The rate constants of both reactions increase. 4. It is concluded from these results that in all probability vulcanization is initiated on the surface of the zinc oxide crystals. 5. Even in stocks containing as much as 40 g. zinc oxide per hundred g. of compounds, the limiting value of dithiocarbamate formation remains unchanged. This was verified by the analysis of vulcanizates after extremely long cure times. The average limiting value of two experiments after 24 hours of cure was 65 mole per cent which corresponds to a two-thirds reaction within the experimental error.
Studies of the Vulcanization of Elastomers. VIII. The Vulcanization of Synthetic Rubbers with Thiuram Disulfides (1)
Authors: Scheele Walter , Toussaint Horst-Eckart
Published: February 2011

The vulcanization of Buna S-3 by tetraethylthiuram disulfide is reported. A quantitative study of the transformation reactions led to the following results. (1) Using tetraethylthiuram disulfide as representative of the class, it was found that two thirds of it undergoes transformation to zinc dithiocarbamate during the vulcanization of Buna S-3, independent of the temperature. (2) Both the decrease of thiuram disulfide and increase of dithiocarbamate are first-order reactions within a wide range of the transformation. (3) The rate constants of the decrease of thiuram and of the increase of dithiocarbamate are a little less than a tenth power greater than for the vulcanization of natural rubber. This is possibly explainable by the different structure of the allyl units in Buna S-3. (4) The activation energies of the decrease of thiuram as well as the increase of dithiocarbamate are nearly the same and are greater than for the vulcanization of natural rubber.
The Reaction Mechanism of Thiuram Disulfide Vulcanization of Poly-1,5-Dienes, Particularly of Natural Rubber
Authors: Blelstein G. , Scheele W.
Published: February 2011

In previous publications on thiuram vulcanization we confined ourselves to the presentation and discussion of our extensive experimental work. We had investigated quantitatively the conversion of thiuram disulfides and were in a position to describe the kinetics of thiuram vulcanization. Such investigations are, of course, of particular value to technology for information about the rate and temperature dependence of vulcanization reactions. Our experiments were therefore not primarily designed to determine the details of reaction mechanism, which we had hitherto treated with restraint, and experience shows that the study of reaction kinetics does not always provide the key to a complete solution. All the same, it now seems reasonable to pick out some of the results we have obtained, and so consider the question of a reaction mechanism for thiuram vulcanization. We should, however, like to state, that although the present treatment concerns matters which may include some pertinent points, it does not necessarily represent a final interpretation. It is to be stressed, that any postulated reaction mechanism must explain what we regard as a stoichiometrical, i.e., concentration and temperature independent conversion of thiuram disulfide to zinc dithiocarbamate. The following experimental results thus formed the basis of our considerations:
Stress Relaxation Studies of the Viscoelastic Properties of Polymers
Authors: Tobolsky Arthur V.
Published: February 2011

Extensive studies of the viscoelastic properties of polymers undertaken in the author's laboratory by means of the method of stress relaxation are here reviewed. The discussion is divided into four parts: chemical stress relaxation, stress relaxation in amorphous polymers, stress relaxation in crystalline polymers, and stress relaxation in certain natural polymers and polyelectrolytes. Mathematical description of the phenomena are presented in simple form. The relation between structure and viscoelastic properties of polymers are discussed and a rather complete over-all picture of these phenomena seems to be emerging.
The Investigation of Molecular-Weight Distribution in Rubberlike Polymers
Authors: Bresler S. E. , Poddubnyĭ I. Y. , Frenkel S. Y.
Published: February 2011

In an investigation of three different synthetic rubbers, methods of fractionation were examined and measurements were made of the molecular-weight distribution by analysis of fractions. The following conclusions may be drawn. (1) The method of equivalent Gaussian distributions correctly reproduces the distribution within each fraction and makes it possible to distinguish the broadening of the sedimentation curve attributable to diffusion and that attributable to polydispersion. (2) The method of accounting for the final concentration of the solution under investigation introduced by us result in correct values of molecular weights of fractions and correct values of standard deviations. (3) Comparison of a series (about 10) of fractions of a given polymer makes it possible to transpose the sedimentation constant distributions into the distribution of molecular weights in a simple and natural way. An investigation of the three rubbers demonstrates two facts. (1) Fractionation of rubbers by precipitation from solutions gives true fractions, i.e., mode values of molecular weights and sedimentation constants do not overlap but form continuous series. By this means fractionation of K-1 and K-3 resulted in very homogeneous fractions of Gaussian shape having dispersion coefficients smaller than 0.33. Fractionation of K-2 resulted in less homogeneous fractions of somewhat asymmetric shape; however, in this case, the broadness and asymmetry of fractions, as it is easy to show, does not exceed the limits predicted by the theory of fractionation. (2) The method of determination of molecular-weight distributions by tracing the steplike curve of precipitation, with subsequent smoothing by graphic differentiation, gives a correct picture of the distribution function of polymers for molecular weights; however, the finer details of distribution can be distorted and lost in tracing the steplike curve. The molecular-weight distributions of synthetic rubbers by the ultracentrifuge method must be closely related to the process of genesis of a polymer, i.e., with the mechanism of the polymerization reaction. Thus, with proper experimental technique our method can be applied to the investigation of various mechanisms of polymerization and polycondensation.
Effect of Elongation on the Proton Magnetic Resonance of Natural Rubber
Authors: Oshima Keichi , Kusumoto Hazime
Published: February 2011

Several authors have already reported their studies on natural rubber by the method of proton magnetic resonance. However, since there has been little work on the effect of elongation on proton magnetic resonance absorption, we present our investigation on the proton magnetic resonance absorption of stretched samples of vulcanized natural rubber. For this experiment a large permanent magnet shown in Figure 1 was constructed. The magnetic field strength was 6090 gauss at the center of the gap at 18° C. The magnet had a field inhomogeneity of about 0.01 gauss in a 0.2 cc. sample. The derivatives of the resonance line were recorded at fixed frequency, changing the magnetic field linearly in time with an automatic electronic bias control. Control of the temperature from liquid nitrogen to room temperature was performed by a cryostat similar to that described by Gutowsky.
Rupture of Rubber. IV. Tear Properties of Vulcanizates Containing Carbon Black
Authors: Greensmith H. W.
Published: February 2011

A method of studying tear behavior has been described in a previous paper (Part III, subsequently referred to as III), and was illustrated by results obtained with natural rubber and GR-S gum vulcanizates, i.e., vulcanizates containing no added ingredients apart from those necessary for vulcanization. In the present paper the method is applied to vulcanizates containing different types of carbon black. Vulcanizates of this type are of considerable interest, since the carbon black can appreciably modify physical properties such as stiffness and tensile strength and can induce pronounced anisotropy in tearing, referred to by Buist as knotty tearing.
Nature of Chemisorptive Mechanisms in Rubber Reinforcement
Authors: Garten V. A. , Sutherland G. K.
Published: February 2011

The present state of research in the field of reinforcing rubber fillers is reviewed and it is pointed out that although a strong school of thought still maintains that the strength of bonding depends on particle size, there are many observations indicating the presence of reactive sites and suggesting the possibility of strong bonds of a chemical nature between filler and rubber matrix. The phenomenon of carbon-gel formation as foremost among these, is discussed as lending fresh support to the idea of chemical bond formation. This effect, known to be most pronounced in the presence of an unsaturated matrix is correlated with the mechanism of vulcanization as proceeding via free radical intermediates. It is suggested that the formation of chemical bonds between pigment and rubber constitutes an integral part of the chemical crosslink formation commenced on the rubber mill and completed by vulcanization. This hypothesis is corroborated by results obtained during studies on the reactivity of pigment surfaces towards simple inorganic and organic free radicals. It is shown that active pigments react with free radicals with the formation of nonionic bonds. Hydrophilic blacks have been prepared by treatment with persulfate. Similarly, electrochemically produced stearate free radicals have been reacted with the surface to form hydrophobic carbons. The “benzidine ”blue free radical, being the monooxidation product of benzidine, reacted easily with less active pigments and thus provided a useful measure of activity. From the experiments with free radicals, the number of active sites for various fillers has been calculated and shown to cover a range of 0.01–3.1 per 100 sq. A˚. Multifunctional polystyrene radicals, obtained in the presence of excess oxygen, yielded crosslinked networks with carbon blacks which resisted solvent extraction. These are considered to be complete analogues to carbon gel. The statistical mechanics of the rubber network has been developed to include crosslink formation as caused by rubber-filler interaction. It is shown that the mechanical properties of a rubber compound that are controlled solely by the network structure are directly proportional to σ/r, the ratio between the number of active sites per unit area and the particle radius. Abrasion does not appear to be only a mechanical phenomenon.
Rubber Reinforcement by Resins Formed in Latex
Authors: van Alphen J.
Published: February 2011

Many attempts have been made to combine synthetic resins with rubber. In most cases the resins were incorporated in the dry rubber on the mill and some success has been obtained with thermoplastics, such as high-styrene resins. Phenolic resins are compatible with nitrile rubbers, but not with GR-S or natural rubber. Therefore, attempts have been made to incorporate the resin in an unhardened state and to harden it afterwards in the rubber. In this way rubber can be vulcanized. Such incorporation causes difficulties; an alternative is to mix emulsions of resins with latex and to coprecipitate the resin and the rubber, or to dissolve the partly condensed and still soluble phenolic resin in a caustic soda solution and to mix this solution with latex so as to precipitate the resin and rubber at the same time by the addition of acid. The products obtained after vulcanization were, however, far from satisfactory. Somewhat better results were obtained when the latex was not coagulated but evaporated, and thus the resin partly formed in situ. This method, the formation of the resin in situ, has been followed by some investigators9and most success has been obtained by Le Bras and Piccini, using an alkaline solution of a partially condensed resorcinol-formaldehyde resin, which is mixed with trypsinated, heat-sensitized latex and vulcanizing ingredients. Products with remarkable properties, especially with a high tensile strength and a very high tear resistance were obtained, when the latex was gelatinized, dried, and vulcanized. Their method is a method of latex-reinforcement and the reinforcement disappears completely when the dried but not yet vulcanized product is brought on the mill. For the sake of completeness it may be mentioned that trials have also been made to introduce resins into rubber by polymerizing suitable vinyl derivatives in latex.
Natural Rubber Compounds for Intermittent Low Temperature Service
Authors: Fletcher W. P. , Gent A. N. , Wood R. I.
Published: February 2011

The changes in physical properties of rubber vulcanizates on approaching the so-called second order transition temperature are discussed and distinction is drawn between these phenomena and those associated with crystallization. A simple apparatus of the torsional pendulum type is used to determine the dynamic stiffness and hysteresis loss factor at a frequency of about 0.5 c.p.s. of vulcanizates in the temperature range 20 to −120° C. A large number of liquids are examined as potential plasticizers for lowering the rubber to glass transition temperature and a number are shown to have a high order of efficiency in this respect. Of these materials some also conform to the overriding requirements of low volatility and adequate compatibility with rubber. The loss in physical properties consequent on increase of plasticizer content is not markedly different for most of the plasticizers. Di-iso-octyl adipate is representative of the liquids which give useful low temperature plasticization and a number of commercial type compounds are developed using this plasticizer with carbon black or silica reinforcement, some of these have transition temperatures approaching those of the silicone rubbers but with a better level of general physical properties. A tentative theoretical treatment for the low temperature plasticization of nonpolar rubbers is discussed and this leads to a law which has been found to predict fairly well the transition temperature of a plasticized natural rubber compound in terms of the index of variation with temperature of the plasticizer viscosity.
The Reaction of Molecular Oxygen with Rubber
Authors: Bevilacqua E. M.
Published: February 2011

It is nearly a century since Hofmann and Spiller made the first recorded experimental observations linking oxygen with substantial changes in polyisoprenoid hydrocarbons. In the first sixty-odd years following this work technological progress was slow, but certain characteristic features of the oxidation reaction were observed. It was firmly established that oxygen played an important role in the deterioration of rubber and rubber products with the passage of time, and the accelerating effects of exposure to light or to elevated temperatures were realized. Within a short additional period a very nearly complete solution to the problems of oxygen aging was obtained with the discovery of efficient vulcanization methods and of effective antioxidants. These discoveries made possible the transition of rubber from a relatively expensive, short-lived material of commerce to its present position of a high-volume, low-cost, essential ingredient of our everyday life. Since that period technological progress has consisted in steady refinements of these important discoveries. During these years many observations necessary for understanding the chemistry of the oxidation process were accumulated, but it was necessary to wait for two fundamental developments in order to obtain a complete explanation of the reactions occurring during the reaction of rubber with oxygen. These were, first, a clear realization of the high molecular character of the rubber hydrocarbon and the effect of this on its macroscopic properties, and-second, the work on oxidation of low molecular weight olefins which forms the basis for inferring the nature of steps in the oxidation of rubber inaccessible because of experimental difficulties. Since both of these developments have been made it is quite probable that we shall know in complete detail the reaction sequence in rubber oxidation before the centennial of Hofmann's paper is reached.
Tire Cord Fatigue and Fatigue Testing
Authors: Goy R. S.
Published: February 2011

Examination of failed tires shows that fatigue failure mostly occurs on the inner plies, i.e., those subjected to compressive bending stress when the sidewall is bent. Continual flexing of the sidewall leads to a reduction of tensile strength of the cords until eventually the sidewall breaks up and the tire fails. This fatigue failure is essentially a function of the complex structure of the tire. When a tire is inflated all the cords are in tension throughout and when it is loaded the sidewall of that part of the tire in contact with the ground is bent so that some of the cords are subjected to relieved tensile stress or, if the deflection is very great, to compressive stress, and the rest of the cords to tensile stress. When the cord goes from tension to compression it tends to collapse but this is complicated by the constraining action of the surrounding rubber. If the tire now rotates the cords will be subjected to alternate tension and quasi-compressional stresses leading to ultimate failure. Fatigue performance is usually assessed by the average mileage to failure of the tire. If the plies of a tire are tested by extracting cords before failure occurs it can be shown that there is a progressive loss of strength of those plies undergoing compression. It has been asserted that this drop is linear with tire life and is greatest on the innermost ply, i.e., at the point of greatest compression. The outer plies undergo a cyclic increase and decrease of tension at constant stress and although there is a small reduction in breaking strength, this does not usually contribute to tire failure.
Aluminum Block Heater for Aging Rubber and Rubber Compounds at High Temperatures
Authors: Bradbury E. J. , Clark R. A.
Published: February 2011

A description is given of the design and construction of an aluminum block heater, drilled with holes to contain test tubes for the aging of rubber or other organic materials at temperatures up to 800° F.
Viscosity of Natural Rubber Solutions at Very Low Rates of Shear
Authors: Golub Morton A.
Published: February 2011

The shear dependence of viscosity of benzene solutions of natural rubber was studied at rates of shear from about 500 down to less than 1 sec.−1. Measurements involved following the change of pressure head with time of the various solutions flowing in a capillary, U-tube viscometer. Curvature in the plots of the logarithm of pressure head versus time indicated non-Newtonian flow. From such curves, reduced viscosity data over the above-mentioned shear range were readily derived. As a check, data over the range 100–500 sec.−1 were also obtained with a five-bulb viscometer of the Krigbaum-Flory type, and these data overlapped those obtained with the U tube. The reduced viscosity increased very sharply with decrease in gradient, making extrapolation to the viscosity axis quite unreliable. However, a theoretical relation proposed by Bueche fitted the composite data rather well. This work furnished a nice technique for determining the zero shear reduced viscosity (ηsp/c)0 without the necessity of performing an uncertain extrapolation: evaluate the parameters of the Bueche formula which best satisfies the experimental data over a fairly wide range of shear rates, and then calculate (ηsp/c)0 directly.
Interaction of Rubber and Carbon Tetrachloride
Authors: Pande J. B. , Raghunath D. , Ramakrishnan C. S.
Published: February 2011

Carbon tetrachloride has been used for studies on the solution properties of natural rubber. It has been tacitly assumed that no chemical reaction between the two takes place; but carbon tetrachloride has been found to show a negative heat of mixing with natural rubber. There is absorption of heat (0.37–1.36 cal./g.) with benzene, dichloroethylene and toluene, while there is evolution of heat (2–3 cal./g.) with carbon tetrachloride and chloroform. There is considerable evolution of heat on mixing cellulose triacetate with tetrachloroethane and the solvent is found to be completely bound with the polymer. It appears therefore that similar combination between rubber and carbon tetrachloride may occur, when these are brought together. An indication of chemical interaction of carbon tetrachloride and rubber has been found in an examination of the spectra of carbon tetrachloride solutions of natural rubber. Chemical analysis of rubber, aged in solution at the laboratory temperature, showed that chlorine was incorporated into the rubber. In the present investigation a progressive detailed study of the system of deproteinized rubber-carbon tetrachloride has been carried out from the instant the two are brought in contact till either a homogeneous solution (in darkness only) or a gel is obtained (visible radiations).
Tack of Pressure-Sensitive Tape
Authors: Chang Franklin S. C.
Published: February 2011

A new method has been found, as a result of this investigation, for measuring the tack of pressure-sensitive tape, which is simple and precise enough for practical purposes. By using this method, tack testing yields reproducible quantitative records in lieu of the ambiguous descriptive results from the empirical finger test. In light of the fact that, of the tapes made with the same adhesive, the one with crepe paper gave lower tack than the one made of flat paper, surface of contact must be one of the factors determining tack. Any pressure applied on the tape after the tape is put on the testing panel would, to a certain extent, increase the contact surface, hence, the force required to peel the tape from the panel. The stiffness of paper, through the depression effect, would have the same effect on the peeling force, in this case, the adhesion strength. Since tack is defined to be free of added pressure and depression effect, this explains the independence of tack and dependence of adhesion strength on stiffness of paper. Fom this point of view, one may consider tack as the limiting value of adhesion strength.
Helical Spring Stress Relaxometer
Authors: Berry J. P.
Published: February 2011

Changes in the tensile properties of rubber are obviously of great practical importance. Consequently, measurements of the change in force required to maintain or produce a given extension under controlled conditions of temperature and atmosphere have frequently been made and have advanced our understanding of the physical process of crystallization and of the chemical reactions responsible for thermal aging to the extent that they may become routine test procedures. The decrease in the force required to maintain a constant extension during the period of aging (stress relaxation) has been the most common measurement, in part because rubber elasticity theory predicts an equality between the fractional decrease in force and the fraction of the network chains originally supporting the stress which have become ineffective. Stress-relaxation behavior may characterize the type of scission reaction occurring; for example, the stress relaxation of most vulcanizates can be interpreted as a first-order scission of crosslinks, and not as a random scission of monomeric units in the chains between crosslinks. Stress-relaxation results, however, do not provide all the necessary information on network changes—the final properties of the rubber depend not only on crosslink or chain scission but to a comparable degree on crosslink formation during aging, which does not affect the force at constant extension. To examine this second effect requires measurements on the intermittent stretching of an unstrained sample to a constant extension. Parallel measurements of force at constant and intermittent extension under identical aging conditions are therefore required. The several designs of apparatus already described have usually been rather complicated and require practice and skill in use. A simple apparatus developed in these laboratories, which can readily be used for routine operations, is described in the following paragraphs. The fractional change in force is read directly from a vernier scale on the instrument, and may be immediately plotted on a force-time graph, preferably as log10 (force/forcet=0) vs. time (cf. Reference 3).
The Vulcanization of Elastomers. X. The Vulcanization of Natural Rubber with Thiuram Disulfides (V)
Authors: Lorenz Otto , Scheele Walter , Redetzky Wolfgang
Published: February 2011

The kinetics of crosslinking natural rubber during vulcanization with tetramethyl and tetraethylthiuram disulfide was investigated. The following results were derived: 1. The increase of crosslinking during vulcanization which was measured by the change of reciprocal swelling is first order over a wide range of reaction time and temperature. 2. During vulcanization, crosslinking and dithiocarbamate formation are reactions which proceed with identical rate. From this we had to conclude that the formation of dithiocarbamate is the immediate cause of the crosslink formation. 3. The concentration of the thiuram disulfide decreases much faster with respect to vulcanization time than crosslinking increases. In other words, the thiuram decrease can only be considered a reaction which precedes crosslinking.
Improved Resilience in Butyl Rubber through Chemical Modification
Authors: Leeper H. M. , Gable C. L. , D'amico J. J. , Tung C. C.
Published: February 2011

A new approach is presented toward obtaining improved properties in Butyl rubber vulcanizates through chemical modification of the Butyl rubber polymer by N-methyl-N,4-dinitrosoaniline. Chemical modification by this additive may be carried out in a Banbury mixer at conventional mixing times and temperatures. The use of modified polymer is advantageous in both black- and non-black-loaded stocks and is advantageous also with respect to variation over the spectrum of vulcanizing systems which are normally used with Butyl rubber. A successful plant demonstration of chemical modification has been carried out.
Chemical Aspects of Reinforcement
Authors: Watson J. W.
Published: February 2011

Hydroxyl free radicals were chemisorbed on to the surface of fully reinforcing carbon blacks by reacting them with an aqueous solution of potassium persulfate or of sodium hypochlorite. Both treatments caused a marked decrease in reinforcing ability, from which it was concluded that free radical interaction between these carbon blacks and rubber is a factor in reinforcement. Bound rubber and swelling index, which were determined for commercial carbon blacks covering the full range of particle size used in rubber compounding, were found to be no better related to reinforcing ability than was specific surface. In addition, after hydroxyl free radical treatment, bound rubber and swelling index remained unaltered though the reinforcing ability had been reduced. It was concluded, therefore, that the free radical interaction between carbon black and rubber which contributes to reinforcement occurs mainly during vulcanization, not during milling.