bluuebunny/crossref_metadata_2025 huggingface dataset:
Notes on the Use of Plasticity Tests to Assess Scorching of Rubber Stocks
Authors: Whorlow R. W.
Published: February 2011

It is shown that the main factor influencing the efficiency of compression plastometers in detecting scorching of a pure-gum rubber mix is the period of compression; this should be at least five minutes for the Williams plastometer at 70° C. Recovery measurements appear to have an even higher efficiency than long period compression tests. Other variations of test conditions are not of great importance. The next point examined is the method of producing scorching in compression test-pieces. Immersion of test-pieces, contained in a metal mold, in a liquid bath gives the most rapid heating. Finally, it is shown that for pure-gum mixes, compression and rotation plastometers give equivalent data, provided that allowance is made for any delay in the heating of test-pieces used for compression tests.
Study of the Factors Affecting the Friction of Tread Compounds on Ice
Authors: Wilkinson C. S.
Published: February 2011

The friction of tread compounds on ice is affected to a great extent by the methods and conditions of measurement. As velocity of sliding is increased from zero to about two centimeters per second, there is an increase in friction, after which there is a gradual decrease with further increase of velocity. Static friction depends on the length of time the sample is in stationary contact with the ice, and is of little practical significance. Of the test variables studied, temperature has the greatest influence. At the lowest temperatures used, −30 to −40° C, the coefficient was approximately double that usually observed slightly below the freezing point. Friction was also found to vary with pressure. An empirical equation of the form,k=C1−C2 log P, was found to fit results in many cases. Minor differences were noted, resulting from changes in sample shape and surface treatment. When testing conditions were held constant, it was found that several variables in the samples themselves affected the friction. The type of polymer used had a definite effect. Of about equal importance was hardness. In similar compounds the softer samples had higher coefficients of friction. The unusual frictional characteristics of rubber sliding on ice may be explained by taking into account the water layer formed between the sliding surfaces. The melting of ice to form this water layer takes place because of the heat generated by the work done against friction. The friction itself is believed to be caused by alternate welding and breaking of junctions between surface asperities. Although the process is initiated in part by pressure melting, that phenomenon has only minor importance after the motion is in progress.
Diazo-Initiated Polymers. Preparation, Properties, and Evaluation
Authors: Willis J. M. , Alliger Glen , Johnson B. L. , Otto W. M.
Published: February 2011

Throughout the great majority of the many investigations on rubberlike synthetic polymers, the initiators employed have been peroxides, either water-soluble (potassium persulfate being the chief example) or oil-soluble, such as benzoyl peroxide or diisopropylbenzene monohydroperoxide. The most notable departure from these initiators has been the use of the diazothio ethers, 4-methoxybenzenediazomercapto-2-naphthalene (MDN) and 4-methylbenzenediazomercapto-2-naphthalene (TDN). These materials have proved to be suitable initiators and also to have some activity as modifiers. However, their possibilities have been explored principally at a polymerization temperature of 41° F. Thus, the field of initiators has been subject to less widespread investigation than most of the other variables in a typical synthetic rubber recipe. The purpose of the present investigation was to develop different initiators, if possible, of a type which would lead to improvement of polymer structure at 122° F. It was felt from the outset that diazo-type compounds offered the best possibilities for development along these lines. During a preliminary survey of these materials, the object was to find examples which did not have the two disadvantages of the diazothio ethers—high cost and low stability. The use of diazo-type compounds as polymerization initiators has been known for many years. The work of Buizov on the polymerization of butadiene with diazoaminobenzene is an example of this. A number of patents have been issued relating to the use of diazo compounds in general as polymerization initiators or activators. These patents, however, were directed toward improving the rate of polymerization, and did not indicate any outstanding improvement in polymer properties. After detailed study of the properties and reactions of diazo materials in general, stabilized salts of diazotized aromatic amines were selected as the specific type of compound with the greatest chance of success. The program was begun with the laboratory preparation and evaluation of diazo salts.
Study of the Viscoelastic Behavior and Molecular Weight Distribution of Polyisobutylene
Authors: Van Holde Kensal E. , Williams J. W.
Published: February 2011

The viscoelastic behavior of linear high polymers has commanded considerable attention in recent years. The very thorough studies by Fox and Flory of the melt viscosity of polystyrene and polyisobutylene, the stress relaxation experiments of Tobolsky and coworkers, and dynamic-mechanical studies by Ferry have contributed greatly to our knowledge of the mechanical behavior of these interesting substances. However, there are many facets of this subject which have not received thorough experimental investigation. In particular, there has been no detailed study of the effect of molecular weight and polydispersity on the elastic behavior of viscoelastic materials. It was felt, therefore, that a study of the viscoelastic behavior of a series of very carefully characterized samples of a representative linear high polymer would contribute substantially to the understanding of this subject. The polymer chosen was polyisobutylene, which displays both flow and elastic behavior at room temperatures.
Effect of the Concentration and Nature of the Emulsifying Agent on the State of Dispersion of Latexes
Authors: Yurzhenko A. I. , Gusyakov V. P.
Published: February 2011

Yurzhenko and Mintz were the first to show that, in the process of emulsion polymerization, the size of the polymeric particles in the latex increases regularly. This phenomenon is in complete accord with the theory that, in the particular case of 1,3-butadiene, polymerization proceeds to a major extent in the micelles of the emulsifying agent. A systematic study of the state of dispersion of synthetic latexes in its relation to the experimental conditions and the processes taking place during their formation would appear to be of great potential value in the study of the mechanism of emulsion polymerization. The present authors have studied the degree of dispersion of synthetic latexes prepared in the laboratory, with different concentrations and types of emulsifying agents. Work in this field has not been reported in the scientific literature, although, in studies of emulsion polymerization, data on the state of dispersion of latexes under certain conditions have been reported. In the present work, the effects of other factors, such as the nature of the monomer, initiator, and electrolytes, on the size of the latex particles and the characteristics of these particles also were studied.
Rubber Evaluations with Instron Testing Machine
Authors: Gehman S. D. , Clifford R. P.
Published: February 2011

The principles of operation incorporated in the Instron machine give it wide distinctive fields of usefulness in a rubber testing or rubber research laboratory. Its principal limitations for rubber testing are usually associated with unique conditions which occur in rubber testing as contrasted to the testing of other materials. The results available should encourage improvements in the equipment and procedures in general use for rubber stress-strain evaluations.
Studies of the Vulcanization of Rubber. III. Kinetics of Change of Tensile Strength of Natural Rubber during Vulcanization
Authors: Dogadkin B. , Karmin B. , Golberg I.
Published: February 2011

1. It is shown that the tensile strength of vulcanized butadiene-styrene rubber is a linear function of the plasticity of the original material. 2. Proceeding from concepts of the presence during vulcanization of a number of opposing processes of structure formation and destruction, both of which influence the molecular weight of the rubber, a general equation is derived which expresses the kinetics of the change of tensile strength of a vulcanizate. 3. Experimental material is offered which proves the applicability of the proposed equation to the representation of the kinetics of vulcanization of mixtures of natural rubber containing relatively small sulfur contents, i.e., up to 3 per cent.
Oxidation and Antioxidant Action in Rubber Vulcanizates
Authors: Shelton J. Reid , Cox William L.
Published: February 2011

The variation of rate of oxygen absorption in the constant rate stage with oxygen concentration involves both a square-root and a first-power term for most rubber vulcanizates, although the latter term may be negligible in some cases. A mechanism of oxidation and antioxidant action has been postulated which is consistent with the observed behavior, and which indicates that the antioxidant may function in at least four ways, some beneficial and some harmful. Direct oxygen attack on the antioxidant may produce radicals capable of initiating oxidation chains. Initiation by this mechanism appears to be more important with amine antioxidants than with phenols. The antioxidant may participate in the propagation stage by a chain-transfer mechanism. While this effect alone for a typical antioxidant would probably have only a small effect on the over-all rate of oxidation, it might also affect in a favorable way the secondary reactions which determine changes in physical properties. Amines also appear to be more inclined to chain transfer than are phenols. Termination by a chain-stopping mechanism is one way in which antioxidants retard oxidation. Phenols appear to be more efficient than amines in this connection. Destruction of peroxide by antioxidant-induced decomposition to stable products reduces initiation by peroxide decomposition, and is thus another important mechanism of antioxidant action. The amines are more efficient than the phenols in this regard, and the presence of carbon black is essential for the amines to exhibit their maximum effectiveness. Carbon black is known to promote the decomposition of peroxide to free radicals, but in the presence of amine antioxidants it also promotes the decomposition to stable products. This dual effect of carbon black results in a reversal of effectiveness of amines and phenols in gum and black stocks. The phenols (which function best as chain stoppers) are more effective in the gum stocks; the amines (which function best by reducing peroxide initiation by directing the decomposition to stable products) are more effective in the black stocks.
Oxidation of Unvulcanized Rubber. Effect of Carbon Black
Authors: Lyon F. , Burgess K. A. , Sweitzer C. W.
Published: February 2011

The effect of carbon black on the autocatalytic stage of oxidation of unvulcanized rubber is shown to be specific for the type of carbon, the reaction conditions, and the polymer. Carbon black is an effective antioxidant for cold rubber when the rubber is heated in air or oxygen. The effectiveness of carbon in inhibiting oxidation increases as the volatile content of the carbon increases. The special case of low loadings of highly oxidized carbons, which completely repress gelation during Banbury mixing, is of particular interest. The opposite behavior of carbon black during rubber gelation is observed when benzoyl peroxide is used as catalyst. With cold rubber, carbon black promotes gelation, while with natural rubber increased scission results. Alteration of any one of these variables produces profound changes in the course and extent of the oxidation reactions.
Measuring Wet-Gel Strength of Coagulant-Dipped Films. Paper Dip Method
Authors: Medalia A. I. , Townsend H. B. , Grover H. N.
Published: February 2011

A property of latex which is considered of fundamental importance in the latex industry is the so-called wet gel strength. This term connotes the tensile strength of the freshly set film, but hitherto there has been no adequate method of measurement of this property, since the film is so weak that it cannot readily be removed from the surface on which it is deposited. The present method is based on the use of absorbent paper of low wet strength, impregnated with calcium nitrate, as a base for the deposition of a latex film. The strip of paper, which may be of a dumbbell shape, is dipped for 30 seconds and then removed from the latex, together with the adhering coagulant dipped film. This film is rinsed in water and then mounted on a special tensile testing machine designed for high elongation and low tensile strength. Elongation and tensile strength are measured at a standard rate of jaw separation of 20 inches per minute. These properties have been studied, using natural and various synthetic latexes. The effects of prevulcanization, compounding, and dilution of these latexes have been determined. Tensile properties of the film from a given latex have also been measured as a function of the time and conditions of drying of the film after deposition.
Vulcanization Structures and Their Influence on the Heat Resistance and Fatigue of Rubber
Authors: Dogadkin B. A. , Tarasova Z. N.
Published: February 2011

(1) The phenomenon of stress relaxation in vulcanizates, due to thermal decomposition of the vulcanization structures, is discussed. The process follows the equation: σt=σ0⋅e−kt, where k is the kinetic constant of decomposition of the vulcanization structures, and therefore can serve as a measure of the heat resistance of a vulcanizate. (2) The amounts of polysulfide and disulfide bonds in various vulcanizates were determined. (3) It is established that the heat resistance of vulcanizates depends on the total quantity and also on the proportions of bonds of the type : R1—C—C—R2, R1—C—S—C—R2, R1—C—S—S—C—R3, and R1—C—Sn—R2. (4) It is shown that the relative contents of various vulcanization structures depends on the type of rubber and on the nature of the vulcanizing group. Thus, vulcanizates with tetramethylthiuram disulfide do not contain any polysulfide bonds, whereas vulcanizates with elemental sulfur (without accelerator) contain predominantly polysulfide bonds. (5) It is established that recombination of the radicals formed during thermal decomposition of a vulcanizate leads to the formation of both intramolecular bonds and new stable bridge bonds. (6) It is suggested that thermal decomposition of sulfur bridges is one of the causes of the phenomenon of a vulcanization optimum (reversion). (7) A relation is established between the nature of vulcanization structures and the resistance of vulcanizates to repeated deformation.
The Microstructure of Diene Polymers. III. Polyisoprenes and Polybutadienes Prepared with Cationic Catalysts
Authors: Richardson W. S.
Published: February 2011

It is well known that catalysts of the Friedel-Crafts type cause the polymerization of diene monomers and that this reaction is ionic rather than free radical in nature. It is also known that such catalysts cause diene polymers to isomerize (cyclize), and one may expect that the polymerization and isomerization reactions will occur simultaneously during the preparation of polymers with these catalysts. While considerable information is available describing methods of preparation and the general properties of such polymers, there seem to be few or no data concerning their microstructures. It is the purpose of this paper to present the results of such structural studies (obtained from infrared spectra) on seven polyisoprenes and three polybutadienes, prepared at temperatures between 30° and −78° C, with various cationic catalysts.
Properties of Hard Rubber. XVII. Influence of Rubber-Sulfur Ratio and Vulcanization Time on the Properties of Pure Rubber-Sulfur Compositions. (3) Swelling, Water Absorption, Aging, and a General Discussion of Results
Authors: Church H. F. , Daynes H. A.
Published: February 2011

(a) Method of Test.—The materials selected were A, 5 hours, and C, 3.75 hours. It was not possible to include sufficient samples to show the separate effects of varying vulcanization time and rubber-sulfur ratio, but the samples show the effect of a considerable difference in combined sulfur, having vulcanization coefficients of 49.5 and 38.7, respectively. To show the dependence of swelling on the nature of the liquid, tests were carried out in twenty different liquids selected to represent various chemical types. Each piece of hard rubber, measuring 20 × 19 × 5.5 mm., was placed in a stoppered bottle with about 40 cc. of the liquid under examination. The bottle was kept in a thermostat at 34° C and shielded from light. The test-piece was then weighed after various periods of immersion ranging from 4 to 4000 hours. The absorption of liquid after each period was calculated from the increase in weight and expressed by the volume of liquid absorbed as a percentage of the initial volume of the test-piece. (b) Results.—No sign of solution of the rubber-sulfur compound was observed, but in certain cases, where swelling was rapid, cracking occurred. In three cases this took place before the first weighing could be made. Full-time swelling curves were obtained, but as most of the liquids are not likely to come into regular contact with hard rubber in electrical service, figures are given in Table 19 for one long and one short period only. In this table, swelling less than 1 per cent is shown as zero. Closer readings for certain liquids of very low absorption are shown in Table 20.
Properties of Hard Rubber. XVIII. Action of Hydrocarbon Oils at High Temperatures (Part XV of Swelling of Rubber)
Authors: Scott J. R.
Published: February 2011

It has already been shown that liquids consisting essentially of aliphatic hydrocarbons, e.g., petroleum ether, paraffin, and transformer oil, had practically no swelling action at 34° C on two samples of hard rubber composed of rubber and sulfur only. Hard rubber shows a pronounced change in properties at temperatures above a critical value (“yield temperature”) in the neighborhood of 50° –80° C, the most noticeable effect being that it becomes much softer and more susceptible to plastic flow. It seemed likely, therefore, that the swelling action of liquids such as those mentioned above might be much greater at temperatures above this critical value. This view was strengthened by the statement of Dunton and Muir that hard rubber is “badly attacked” by immersion for 7 days in “hot” transormer oil. As no data appear to have been published on the effect of temperature on the swelling of hard rubber, experiments were made to examine this effect. Details of the hard rubber samples used are as follows.
The Vulcanization of Rubber with Phenol-Formaldehyde Derivatives. Inapplicability of the Chromane Theory
Authors: Van Der Meer S.
Published: February 2011

The chemistry of phenol-formaldehyde resins has developed enormously since 1938. Zinke, von Euler and Hultzsch in particular have enlarged our knowledge about the constitution of resols and resites by their investigations in the complicated field of resol hardening. In addition, reactions between hydroxyphenols and unsaturated compounds have been studied. Hultzsch proved the formation of a chromane ring system by heating an unsaturated hydrocarbon with a hydroxyphenol. Later Greth described the reaction between resols and fat oils as an analogous one, also in these cases supposing the formation of chromane derivatives. According to the latter two main reactions lead to the formation of macromolecular compounds: (1) the formation of chromane rings between the resol and the unsaturated compound; (2) the formation of intermolecular oxygen bonds between the methoxy groups of the hydroxyphenols and resols. It seemed reasonable to explain the vulcanization of rubber with resols and dihydroxyphenols by this chromane theory. However, it is necessary first of all to have a clear idea of the various possibilities which may be involved. Only after this will it be possible to decide whether the chromane theory may be applied to vulcanization with phenol-formaldehyde derivatives as well.
Vulcanization of GR-S by the Peachey Process
Authors: McPherson Archibald T.
Published: February 2011

It has been found possible to vulcanize GR-S synthetic rubber by subjecting it alternately to hydrogen sulfide and sulfur dioxide gases. This method for curing, known as the Peachey process, was used for natural rubber as long ago as 1921. A simple apparatus was constructed, in which strips of thinly milled rubber were placed on a screen inside a glass tube. One end of this tube was attached to valves connecting it to tanks of hydrogen sulfide, sulfur dioxide, and air, respectively. The other end of the tube led to a series of traps containing solutions which absorbed or destroyed the gases. For each test performed, natural rubber samples were placed inside the tube along with the GR-S samples for comparison. Each strip was weighed before it was inserted in the apparatus. Hydrogen sulfide was first slowly passed over the samples for a period of five minutes. Then air was blown through for a few seconds—just long enough to free the surroundings from the sulfide gas, but not long enough for the gas to be lost from solution in the rubber. Sulfur dioxide gas was next admitted and allowed to pass over the samples for five minutes. A subsequent short sweep of air through the tube completed one cycle of the curing process.
Plasticizers in Rubbers and Plastics
Authors: Jones H.
Published: February 2011

Up to the advent of synthetic high polymers, plasticizer technology was little understood, Plasticizers had been used mainly with cellulose derivatives, which are not at all good materials for the study of plasticizer action. The chemical processing they undergo, e.g., nitration, acetylation, etc., leads to variations on account of irregular chemical action. In addition, these materials are partly crystalline and partly amorphous. The growing numbers of new materials brought a host of problems in their train, and plasticizing was not the least of them, but a study of their behavior with plasticizers has advanced the knowledge of the plasticizer-polymer system. The principal advances have come from a study of regular and amorphous polymers, such as polyvinyl chloride, polyvinyl acetate, polystyrene, butadiene rubbers, and so on. From knowledge of these materials, one can revert to the consideration of irregular polymers such as cellulose derivatives and those produced from high polymers by additional chemical reaction, with a better likelihood of understanding their behavior with plasticizers. Thus the recent extensive use of plasticizers has led to an improved understanding of their action, and it appeared that a paper dealing with the subject might be acceptable.
Sodium-Catalyzed Copolymerization of 1,3-Butadiene and Styrene
Authors: Marvel C. S. , Bailey W. J. , Inskeep G. E.
Published: February 2011

1. A convenient laboratory procedure for the sodium-catalyzed copolymerization of butadiene and styrene has been described. Earlier attempts to accomplish this probably failed because the monomers were not sufficiently pure. 2. The copolymer of butadiene and styrene which results from sodium polymerization is different from the emulsion copolymer, GR-S, in several important respects. The sodium-catalyzed copolymer has a more nearly constant styrene content at different stages of conversion; it is made up of molecules with a relatively narrow molecular weight spread; it has a higher intrinsic viscosity; it is 100 per cent soluble in benzene (i.e., there is no gel) even at 100 per cent conversion; when treated with standard rubber antioxidant, it ages better; and it has a greater amount of the butadiene joined in the 1,2 manner (i.e., greater vinyl side-chain content). 3. The effects of such variables as temperature of polymerization, method of adding the monomer mixture to the catalyst, size of catalyst particles, and possible butadiene impurities on the polymerization have been studied. 4. The method has been extended to cover copolymerization of butadiene and m-methylstyrene to give a soluble copolymer of low molecular weight. Other styrene-type monomers gave less interesting copolymers.
Effect of Carbon Blacks on the Physical Properties of Natural Rubber and Neoprene-GN
Authors: Buist J. M. , Mottram S.
Published: February 2011

1. All the blacks tested can be incorporated into Neoprene-GN much more easily than into natural rubber, and the limits of loading are higher with Neoprene-GN than with natural rubber. 2. A broader maximum in the tensile strength-volume loading curve is obtained with Neoprene-GN, and it has been found that the two coarse blacks do not reinforce Neoprene-GN. 3. Tables show the grading of each carbon black with each physical property. It has been found that, in general, the results correlate with measurements of particle size and surface area. 4. Even so, if dynamic conditions are met in service, it is necessary to evaluate the degree of reinforcement under dynamic conditions. 5. With natural rubber, each black tends to have its own correlation between dynamic and static hardness tests, whereas with Neoprene-GN one correlation exists for all blacks. 6. Within a given polymer it is sufficient to do only compression plasticity (Williams) measurements, and recovery measurements are required only when comparing different polymers. 7. Measurements of tear resistance with Neoprene-GN have shown that, as the particle size of the blacks decreases, the peakiness of the tear resistance volume loading curve is increased, particularly at higher temperatures. 8. Torsional resilience and impact resilience have a very high correlation in natural rubber. 9. Different carbon blacks in Neoprene-GN produce very small changes in resilience. 10. With increased loadings of black the resilience properties of both rubbers become more sensitive to temperature. 11. On both the du Pont and Dunlop abrasion machines, there is fairly good agreement between abrasion resistance and particle size. 12. With natural rubber, if the hardness is maintained constant and resilience increased, the heat build-up decreases, whereas with Neoprene-GN under the same conditions the heat build-up increases. 13. When comparing compounds of different hardness for heat build-up, a constant deformation test is preferable to a constant load test. 14. There is a good correlation between swelling in benzene and modulus measurements. The correlation is better with Neoprene-GN than with natural rubber.
Styrene-Diene Resins in Rubber Compounding
Authors: Borders A. M. , Juve R. D. , Hess L. D.
Published: February 2011

Early in the investigation of butadiene-styrene copolymers as synthetic rubbers, this laboratory became interested in copolymers containing much more styrene than any of the American or German synthetics. This interest was soon directed to the resinous copolymers obtained when the styrene content is increased beyond the range in which rubberlike properties are observed at room temperature. The exploratory work, therefore, involved preparation and evaluation of butadiene-styrene copolymers containing from 65 to 98 per cent styrene. No description of similar polymers has been found. Konrad and Ludwig claimed the improvement of rubberlike properties of butadiene-styrene copolymers by increasing the styrene content from the normal range to “between about 47.5 and about 70 per cent”. The claims and examples of this patent emphasize the improvement of rubberlike properties, such as tensile, elongation, and rebound, at high temperatures. It is well known in this country, however, that increase in styrene content beyond a certain point, perhaps 50–55 per cent, is accompanied by a loss of overall balance of rubber characteristics. Therefore, the copolymers at the upper end of the range described by Konrad and Ludwig have definite limitations for rubber uses—for example, low rebound, high brittle point, shortness, etc. In the writers' laboratory useful resins have been prepared from dienes and vinyl aryl hydrocarbons in the range 5 to 20 per cent diene and 80 to 95 per cent vinyl aryl hydrocarbon. This paper describes the properties and certain uses of one of these copolymers containing approximately 15 parts of butadiene and 85 parts of styrene. This material possesses a combination of physical and chemical properties which permit its use in several applications where cyclized natural or synthetic rubbers are commonly employed. Cyclized natural rubber has been described by Bruson, Endres, and Thies and Clifford. Cyclized synthetic rubbers were described recently by Endres. One product of this type is made from a special synthetic rubber. The new 15 butadiene—85 styrene copolymer is now identified as Pliolite S-3, since it may be used in many Pliolite applications, often with distinct advantages over either the natural or synthetic rubber derivatives.
The Thermoplasticity of Chlorinated Rubber
Authors: Lepetit F.
Published: February 2011

Among the various factors which play a part in the chlorination of rubber, the percentage of combined chlorine, the temperature of chlorination, and the degree of mastication have pronounced effects on the thermoplasticity of the final chlorinated rubber products. By taking advantage of certain operating conditions which are suggested by the work described above, it is possible to obtain a chlorinated rubber with relatively low thermoplasticity. It does not appear to be possible by these means to reduce to any significant degree the thermoplasticity of chlorinated rubber, without perhaps the use of operating conditions which would be difficult to control, e.g., chlorination under pressure or at high temperature.
Abrasion Tests on Rubber
Authors: Lewis T. R. G.
Published: February 2011

Although the abrasion machine to be described has been used in the laboratories of the British Boot, Shoe and Allied Trades Research Association for many years, there has been no publication of a description, nor any account of its performance. The original machine has been modified by the incorporation of an efficient suction device, and redesigned structurally, though still employing the same basic mechanism. Experiments have been carried out on large numbers of war-time substitutes for soling-leather, rubber-soling materials with reduced rubber content, for containing GR-S, and new plastic materials and synthetic rubbers. The machine has been found to give reproducible figures, quickly and under easily controlled conditions, and the results have been of value for comparing various materials. No attempt is made in this paper to judge the significance of these figures or to correlate them with actual wear data.
GR-S Emulsified with Rosin Soap
Authors: Cuthbertson G. R. , Coe W. S. , Brady J. L.
Published: February 2011

One of the most troublesome deficiencies of standard GR-S, in so far as product fabrication is concerned, is the inherent lack of tackiness or the incapability of laminated and spliced surfaces to flow and knit together easily. This was especially bothersome from 1942 to 1944, when the scarcity of natural rubber forced fabricators to use a synthetic polymer before they had developed satisfactory methods and equipment to compensate for its deficiencies. Early in 1942, in anticipation of a later scarcity of fats and oils suitable for making the soap used for emulsification, the several groups working on polymer development problems intensified their efforts to find emulsifying agents which could be made from noncritical domestic materials. Rosin was one of these. Early attempts to use it were unsuccessful, however, because the polymerization reaction was strongly retarded. Later the Hercules Powder Company and The B. F. Goodrich Company, working together, found that the retarding effect could be greatly reduced with the use of disproportionated rosin previously referred to as dehydrogenated rosin. (The treatment given to the rosin results in a molecular disproportionation of the hydrogen, with the elimination of the conjugated double bonds accountable for much of the inhibiting effect on the polymerization reaction.) This work made rosin available for use in the event of an actual scarcity of fats and oils of good quality.
Tear Resistance. More Accurate Results Using I.C.I. Tear Cutter
Authors: Buist J. M. , Kennedy R. L.
Published: February 2011

(1) A new tear cutter has been designed which is capable of easy and rapid operation for routine work. (2) Using the new cutter accurate work is possible, and the error in tear resistance results has been reduced to the same order as that obtained with tensil strength determinations. (3) It is recommended that a tolerance value of ±3 thousand inch be placed on the 0.02-inch depth of nick. (4) It is also recommended that six test-pieces be used, and the median of the results recorded. (5) The observation is made that the angle-tear test is a measure of tear initiation and can, therefore, be considered an addition to the crescent-tear test, which is a measure of tear propagation.
Statistical Evaluation of Variations in Rubber Processes and Correlation in Physical Properties
Authors: Buist J. M. , Davies O. L.
Published: February 2011

The scope for the application of statistics to the field of rubberlike rnaterials is extensive, and various authors have already used statistical methods. Statistical methods derive the maximum amount of information from the results of an investigation, and at the same time supply a means of assessing the reliability and value of the information extracted. The effect of a variety of different blacks at various volume loadings on the properties of natural rubber and Neoprene-GN have been described. In the present paper the data are examined from other points of view, viz., the reproducibility of the results and the relations between the various properties. The main purpose of these investigations was to obtain the technological information already reported. At the same time, however, the program was designed as far as practicable to give information on the testing errors. Further useful information on the relation between the properties could be obtained by the application of the methods of statistical analysis. The program of experimental work with natural rubber covered a period of three months (November 1940–February 1941) and, to obviate as far as possible variations in the raw material, a quantity sufficient for the whole program was master-batched at the outset. The carbon blacks used were from normal supply, but special quantities were kept for this program. In 1942 a similar program was carried out with Neoprene-GN. The details of the mixes used, mixing procedure, and conditions of curing, have been given previously. Each mix was repeated three times on different days, and repeat determinations on the physical properties were carried out.
The Mechanism of Modifier Action in the GR-S Polymerization. I
Authors: Snyder H. R. , Stewart John M. , Allen R. E. , Dearborn R. J.
Published: February 2011

When butadiene and styrene are copolymerized in an aqueous emulsion containing only the monomers, an emulsifying agent, and a peroxidic catalyst, the product obtained is an insoluble substance which is difficult to process and is of little value as a rubber. Useful copolymers are obtained by adding to the polymerization system a substance known as a “modifier”. In the preparation of GR-S, the modifier used is a thiol or a mixture of thiols. The copolymer produced in the presence of such a modifier is soluble in benzene, and it can be milled and processed much like natural rubber. The present work was undertaken in an effort to determine the nature of the chemical action of the modifier. It is now generally believed that vinyl polymerizations induced by peroxidic catalysts proceed by a free radical mechanism in which the essential steps are initiation, propagation, and termination. Peroxide-catalyzed polymerizations of dienes differ from those of simple vinyl monomers in that the steps of initiation and propagation may consist in either 1,4- or 1,2-addition to the diene system, or both 1,4- and 1,2-addition may occur in random fashion. Ozonization studies of polybutadiene indicate that the polymer has a structure of the third type, resulting from both 1,4- and 1,2-addition.
Vulcanization Testing of Reclaim. Relation between Results Obtained in Reclaim-Sulfur and Tire-Tread Mixes
Authors: Moakes R. C. W. , Scott J. R.
Published: February 2011

Literature on the value of the reclaim-sulfur test mix as a criterion of the quality of reclaim is briefly discussed, as a result of which the general conclusion is reached that such a mix is unreliable. This point is further studied by experiments on several reclaims made by the alkali, thermal, neutral, and other processes. The tensile strengths of the reclaim-sulfur mix and of a degraded tire-tread mix (80:40 new rubber/reclaim ratio) definitely tend to run parallel, so that, for instance, a reclaim showing over 1,000 lbs. per sq. in. in the former mix would be unlikely to give a really bad tensile strength in the tread mix, and one showing 300 lbs. per sq. in., or less would be equally unlikely to give a good strength. The reclaim-sulfur mix, however, is only a rough guide, because reclaims shown to be alike by this mix may give very different properties in the tread mix. Other properties of the reclaim-sulfur mix (breaking elongation, modulus, hardness) give no information as to the behavior of the reclaim in a tread mix; neither do the tensile properties of the former give much help in predicting how the tread mix withstands abrasion and flexing. Accelerated aging tests on reclaim-sulfur vulcanizates are of little value, except that a rapid fall in tensile strength would cast suspicion on the reclaim. These results, emphasizing as they do the uninformative nature of reclaimsulfur test results, suggest that, whenever possible, reclaims should be tested in the type of mix in which they are to be used, rather than in an arbitrary standard mix. The dependence of abrasion and flexing of the tread mix on its tensile properties is examined. Abrasion-resistance is not obviously related to these properties, but flex-cracking resistance shows a parallelism with tensile strength and especially with breaking elongation. The data are consistent with the view that the latter is the dominant factor in determining flexing life, and that the substitution of reclaim for new rubber in a tread mix does not affect flexing life except through its influence on breaking elongation; it is not yet demonstrated whether elongation directly determines the flexing life, or whether both are functions of some third property.
The Determination of Copper in Crude Rubber
Authors: Cassagne Paul
Published: February 2011

All types of rubber contain some copper. Although the proportion is in general extremely low, it is well not to disregard it, for this element acts as a catalyst which has a deleterious effect on the aging of rubber. For rubber to age satisfactorily it should contain not more than 1.5 mg. of copper per 100 grams of rubber; hence the interest in any method for determining the copper content of crude rubber. PRESENT METHOD The method used thus far is based on the color reaction which sodium diethyldithiocarbamate gives with a very dilute copper solution. According to the method of the British Standards Institution, the ash is treated with hydrochloric acid, and the metals of the iron group are then precipitated by ammonia. After solution of the precipitate in hydrochloric acid and reprecipitation by ammonia, the filtrate is brought to the boiling point and finally is diluted to a known volume. This solution is then used for a colorimetric determination. As a result of numerous experiments with crude rubbers from different sources in which the method described above was used, it has been found that the reagent called for in this method is not specific enough; in fact it gives a color reaction with metals other than copper, notably with iron, manganese, zinc and heavy metals which cannot be separated reliably by the ammonia method. There would seem to be two solutions to this problem; either to develop another method which employs a reagent having a more specific action, or to improve the currently used method of the British Standards Association in such a way as to eliminate the disturbing ions.
Comparison of Ultraviolet Absorption and Chlorine Analysis Methods for Composition of Butadiene-p-Chlorostyrene Copolymers
Authors: Meehan E. J. , Parks T. D. , Laitinen H. A.
Published: February 2011

The percentage of chlorine in a copolymer containing chlorostyrene can be determined by amperometric titration of the chloride ion present after sodium fusion of the polymer. Since the percentage of chlorine is proportional to the percentage of chlorostyrene, the composition of a butadiene—chlorostyrene copolymer may be determined directly. This absolute method of composition determination affords a means of checking the ultraviolet spectrophotometric method which has been proposed for the determination of the composition of butadiene—styrene copolymers. In the application of the spectrophotometric method it is assumed that the specific extinction coefficient of the copolymer varies linearly with the percentage of styrene between the values of the same wave length for polybutadiene and polystyrene. The spectrophotometric measurements are made at 260.0 mµ or at 269.5 mµ for copolymers of butadiene with styrene or with p-chlorostyrene, respectively.
Comparison of the Bromine and Nitric Acid Methods of Estimating Sulfur in Acetone Extracts
Authors: Morley J. F. , Scott J. R.
Published: February 2011

From the experiments described, it appears that neither the bromine method nor the nitric acid method is perfectly satisfactory, for the following reasons. (1) Neither method gives the true free sulfur in rubbers containing sulfur-bearing accelerators, as these cause positive errors of anything up to 0.2–0.3 per cent. (2) The nitric acid method does not give the true free sulfur in rubbers, without sulfur-bearing accelerators, because the result includes some of the sulfur combined with the rubber “resins” the tests do not show definitely whether this applies also to the bromine method. (3) Neither method gives the total sulfur in the acetone extract, since some of the sulfur combined with the “resins” is not included in the result; the presence of certain sulfur-bearing accelerators increases the error. The statement previously referred to (loc. cit.), that the bromine method approximates more nearly to the elementary sulfur content and the nitric acid method more nearly to the total sulfur content of the extract, appears to be a correct generalization. In most cases, however, the difference between the results obtained by the two methods would be less than 0.1 per cent. In respect of simplicity and rapidity of working, the bromine method has the advantage over the nitric acid method, and therefore in all ordinary circumstances is the one to be recommended.
Effect of Buffing in Preparing Dumb-Bell Tensile Specimens
Authors: Morley J. F. , Scott J. R.
Published: February 2011

1. Experiments are described on the influence of buffing vulcanized rubber, before or after cutting into dumb-bell specimens, on the tensile test results obtained with these specimens. The influence of the following factors is examined: fineness of abrasive used for buffing, thickness of rubber removed per passage over the abrasive wheel, total period of contact between the rubber and the wheel, and rest period between buffing and testing. 2. A machine is described for carrying out buffing under controlled variable conditions; this assures the buffed surface being flat and parallel to the under surface of the rubber, and gives more uniform thickness over the test length than buffing by hand. 3. With very soft (“pure”) rubbers tensile strength may be reduced as much as 15 per cent by using a coarse abrasive, although with stiffer rubber such as tire treads and conveyer belt covers, this effect is much smaller. 4. It appears to be immaterial whether the rubber removed by buffing is taken off in several thin layers or a few thick ones. 5. Varying the total period of time occupied by buffing within reasonable limits (two to eight minutes in the present tests) does not appreciably affect the test results. 6. With increase in the rest period between buffing and testing, the results indicate a distinct fall in tensile strength and a less marked fall in breaking elongation. 7. Tests on a rubber of the tire-tread type show that, if the dumb-bell specimens have been buffed, even with a fine abrasive that leaves a good surface and taking precautions to ensure uniformity of thickness, the tensile strength is some 5 per cent lower than that of dumb-bells cut from sheets with smooth (moulded) surfaces; the breaking elongation also is correspondingly reduced by buffing. On the other hand, the buffed dumb-bells give more closely concordant results, for both tensile strength and breaking elongation, than the smooth ones. 8. The following recommendations relating to the buffing of rubber for the preparation of tensile test specimens are put forward:—(1) A machine, such as that here described, capable of removing a layer of uniform thickness should be used in preference to holding the rubber by hand against an abrasive wheel. (2) A fairly fine abrasive, say 80 grit, should be used, at least for finishing off the surface. (3) The period during which the rubber is in contact with the abrasive wheel should be kept as short as possible. (4) The rubber should be buffed down to the required thickness before the dumb-bell specimens are cut. (5) Tensile tests should be made within definite time limits after buffing, say between twelve and forty-eight hours, and the specimens should be cut just before testing, that is, after any subpermanent deformation in the rubber has been largely eliminated.
The Mechanism of Modifier Action in GR-S Polymerization. II
Authors: Wall F. T. , Banes F. W. , Sands G. D.
Published: February 2011

The chain transfer theory of modifier action has been tested on commercial GR-S by means of molecular weight and sulfur content determination. The number of sulfur atoms per molecule was found to range between 0.7 and 1.1, to be compared to the theoretical value of unity. In view of the experimental difficulties involved, the results are considered to be in good agreement with the theory.
Determination of Hydroperoxides in Rubber and Synthetic Polymers
Authors: Laitinen H. A. , Nelson J. S.
Published: February 2011

Ferrous iron has been used as a reagent for the determination of peroxide by numerous investigators. Yule and Wilson estimated peroxide in cracked gasoline by shaking with an acid solution of ferrous thiocyanate and back-titrating the resulting ferric salt with titanous chloride. The method was criticized by Young, Vogt, and Nieuwland, who used the color of the resulting ferric thiocyanate complex as a basis for a colorimetric determination of peroxide. In this procedure methanol was used as the solvent. Bolland, Sundralingam, Sutton and Tristram modified the method to enable rubber samples to be analyzed by changing the solvent to a mixture of benzene and methanol (73 per cent benzene by volume). For determining peroxide in GR-S (butadiene-styrene copolymer) and other butadiene copolymers it would be desirable to employ a solvent rich in benzene, since these polymers tend towards insolubility upon oxidation. A solvent composed largely of benzene would also improve the sensitivity of the determination, since larger quantities of polymer could be dissolved in a given volume of solvent.