bluuebunny/crossref_metadata_2025 huggingface dataset:
Isolation from Vibration with a Mounting Utilizing Low- and High-Damping Rubberlike Materials
Authors: Snowden J. C.
Published: February 2011

This paper describes a theoretical investigation of the performance of an antivibration mounting utilizing elements of low- and high-damping rubberlike materials in parallel, arranged such that both materials experience the same strain. Knowledge of the dynamic mechanical properties of natural rubber and a high-damping synthetic rubber has enabled the behavior of the so-called parallel mounting to be estimated realistically. General expressions have been derived from which the response ratio of a parallel mounting employed in one- and two-stage mounting systems may be determined, once the variation with frequency of the mechanical impedance Zω of the foundation of the mounting system is known. The mounting systems have been assumed throughout to possess natural frequencies of 5 cps. To compare the response ratios of the mounting systems, a specific nonrigid foundation has been considered, namely, a simply supported beam possessing damping of the solid type. The beam possesses a “springlike” impedance at frequencies below its fundamental resonance, which is assumed to occur/at 50 cps. The ratio of the mechanical impedance of the beam to the value it takes at low frequencies is plotted in Figure 3 of Reference 1, through the frequency range 1–1000 cps. The mounted item is supposed to behave purely as a lumped mass. “Wave effects” that may occur in the rubberlike mount materials are disregarded. These materials are always assumed to behave in a linear manner.
Mechanical Properties of Rubber at High Rates of Elongation
Authors: Zhurkov C. N. , Sanfirova T. P. , Tamashevskii E. E.
Published: February 2011

1. The mechanical properties of rubbers undergo substantial changes in a range of elongation rates, depending on the nature of the rubber. 2. It is shown that a difference in the nature of the strength dependence on rate for noncrystallizable, crystallizable, and filled rubbers is induced by changes of structure of the material during stretching.
Elastomer Structure and Adhesion. I. Effect of Sulfur Vulcanization on the Adhesion of Rubber to Fiber Forming Compounds
Authors: Raevskii V. G. , Voyutskii S. S. , Livanova I. V. , Shteinberg Z. D.
Published: February 2011

1. A study was made of the effect of sulfur vulcanization of a rubber coating on its adhesion to fiber-forming polymers. 2. It has been established that there is a maximum degree of crosslinking of rubber during vulcanization and after attainment of this there is a sharp drop of the adhesion of the rubber to the fiber-forming polymers. 3. It has been established that for the rubbers investigated and fiber-forming polymers there is a value of the maximum degree of crosslinking (from the magnitude of Mc). It has been shown that this magnitude practically does not depend on the polarity, molecular weight, type of comonomer, and mobility of the segments of the molecules of the investigated elastomers. 4. It has been shown that all the experimental observations of this work are in complete agreement with the diffusion theory of adhesion.
Effect of Hydrogenation on the Properties of Polybutadiene Rubbers
Authors: Yakubchik A. I. , Reikh V. N. , Tikhomirov B. I. , Pavlikova A. V.
Published: February 2011

1. The properties of hydrogenated sodium polybutadienes of various degrees of unsaturation were studied. The tensile strength and relative elongation of the vulcanizates have minimum values when the degree of unsaturation has been decreased by about one half. Elasticity and gas permeability of the vulcanizates decrease and the hardness increases with diminishing unsaturation. The resistance to thermal aging also increases. Order in the polymer chains has a favorable effect on the relative elongation and tensile strength of vulcanizates even if it does not lead to crystallization. The improvement of the freeze resistance of vulcanizates made from hydrogenated sodium polybutadienes is associated with the internal plasticization effect. 2. Studies of the properties of hydrogenated cis-l,4-polybutadienes, which have appreciable crystallinity, showed that vulcanizate elasticity decreases while the hardness increases sharply with decreasing unsaturation. The rise of the glass transition temperature is due to increased rigidity of the polymer chains.
A New Hydrocarbon Elastomer. I. Copolymerization of Olefins and Nonconjugated Dienes
Authors: Gladding E. K. , Fisher B. S. , Collette J. W.
Published: February 2011

The composition of sulfur-curable elastomers derived from olefins and diolefins is described and methods are given for their synthesis using coordination catalysts. Certain factors that influence the laboratory-scale polymer synthesis are discussed and the effects of catalyst type, polymerization temperature, and diene structure on the rate of polymer formation and polymer composition are outlined. Polymer properties are discussed in general terms, with particular emphasis on oxidative stability.
A New Hydrocarbon Elastomer. II. Properties of an Ethylene-Propylene-Nonconjugated Diene Terpolymer
Authors: Verbanc J. J. , Fawcett M. S. , Goldberg E. J.
Published: February 2011

A new hydrocarbon elastomer has been synthesized from petrochemical intermediates using coordination catalysis. This amorphous polymer resembles commercial diene elastomers in general appearance, is completely soluble in hydrocarbon and chlorinated hydrocarbon solvents, and is stable to prolonged storage. It can be vulcanized effectively by the use of accelerated sulfur systems and reinforced by numerous fillers such as carbon blacks, clays, and certain silicas. Reinforced vulcanizates are strong, resilient, and extremely resistant to oxygen, ozone, heat, light, and many chemical agents. Properly compounded vulcanizates exhibit excellent electrical and low temperature properties. Permeability to gases, specifically nitrogen, oxygen, and carbon dioxide, parallels natural rubber. Thermal diffusivity and thermal conductivity are ∼15% greater than polyisoprene. The practical significance of the thermal data remains to be determined.
A New Hydrocarbon Elastomer. III. Compounding with Fillers and Plasticizers
Authors: Schoenbeck M. A.
Published: February 2011

Nordel can be compounded with a wide variety of fillers. Reinforcing carbon blacks and silicas are required for maximum physical properties. Non-reinforcing fillers may be added to the compounds to reduce material costs. As with other elastomers, vulcanizates containing mineral fillers have lower states of cure. One of the outstanding characteristics of Nordel is its extendability. Compounds with large amounts of carbon black and oil are easily processed and have good vulcanizate properties. Hot masterbatching in the presence of promoters significantly improves processing safety, modulus, resilience, compression set, and electrical properties of mineral-filled stocks. Petroleum oils, including aromatic types, are excellent plasticizers for Nordel. Those containing low amounts of nitrogen bases and unsaturates, as indicated by the Rostler method of analysis, are preferred especially in low sulfur recipes designed for maximum heat resistance. The properties of Nordel vulcanizates suggest its use in extruded goods, hose, belts, coated fabrics, molded goods, sponge, heels and soles, wire insulation and jacketing, and tires.
Reactions of Polymers in Bulk. V. Deformation Behavior of Vulcanizates Filled with Inorganic Fillers
Authors: Janacek J.
Published: February 2011

The most marked difference between carbon black and the fillers of inorganic nature is the difference in effect on the interlinking reactions taking place in the rubber. It is shown that the deformation properties of vulcanizates filled with inorganic substances depend upon the same physical characteristics that describe the behavior of carbon black, if the influence of the difference in chemical activity of the fillers is discounted.
Reactions of Polymers in Bulk. VI. Influence of Deformation on the Decrease of Crosslinking Density
Authors: Jánaček J.
Published: February 2011

The influence of deformation on the decrease of the degree of crosslinking as determined by swelling was investigated in vulcanizates which were filled with various concentrations of carbon black and which were crosslinked to different degrees, as well as the stress relaxation of these vulcanizates after deformation to a constant elongation. The decrease of crosslink density depends on the amount of deformation, is directly proportional to the degree of crosslinking of the undeformed rubber, and increases with the specific surface and with the carbon black concentration. Vulcanizates in which the degree of crosslinking has been reduced by deformation, behave like vulcanizates which were crosslinked to a lesser degree by the vulcanization system.
Chemical Compatibility as a Factor in the Dispersion of Fillers in Rubber
Authors: Carlton C. A.
Published: February 2011

Poor dispersion of fillers in rubber compounds has been a troublesome problem since the beginning of the rubber industry. An example of this kind of difficulty is the presence of white pigment lumps in black or dark-colored compounds that are surface buffed, such as some types of shoe soling. Chemical analyses of filler agglomerates removed from a large number of unvulcanized and vulcanized rubber compounds revealed the fact that in practically every instance a substantial amount of zinc oxide was present. This is of major importance since good dispersion of zinc oxide is necessary for the proper vulcanization of a rubber compound. It is quite difficult to identify positively the specific variable or variables in any one given formulation which may cause filler agglomerates. They may be due to the composition of one or more of the ingredients present in the mix, the order in which the ingredients are added, or to the mixing procedure. However, a series of tests indicated one major cause, the addition of acidic materials such as fatty acids, organic acid vulcanization retarders, or acidic accelerators to natural rubber or some synthetic rubbers simultaneously with basic activators such as lime, litharge, magnesia, and zinc oxide, or with some basic fillers such as finely divided calcium and magnesium carbonates. High-temperature mixing (about 325° F) gave better dispersion than low-temperature mixing (about 220° F) when acidic or basic materials were added simultaneously, but in some instances poor dispersion resulted even at temperatures up to 325° F. This was particularly true of litharge and magnesia. It was also found that when zinc oxide and stearic acid were added to synthetic rubber at the same time, dispersion was better in some types of rubber than in others. The stiffer mixes of NBR (nitrile) and cold, unfilled SBR gave better dispersions than those of the softer IIR (butyl) and oil-extended SBR. Regardless of the type of rubber being used, the safest procedure to insure satisfactory dispersion of inorganic oxides is to add any acidic materials separately during the mixing procedure. This approach is particularly necessary if the mix contains resin acids and/or organic acid vulcanization retarders such as benzoic or salicylic acids. If it is not feasible to add the acidic and basic compounding materials separately to the rubber, then the inorganic oxides should be added to the mix in the form of masterbatches.
The Strain Dependence of Rubber Viscoelasticity. III. Natural and Butyl Rubber at High Extensions
Authors: Mason P.
Published: February 2011

In previous papers in this series the linear viscoelastic behavior of gum and filled rubbers has been studied at mean extensions up to 100%. Linearity was assured by allowing each specimen to relax at the required extension to its equilibrium state and then measuring the complex Young's modulus for very small strains superimposed upon this equilibrium extension. Analysis of the data was made either in terms of a Mooney strain-energy function or, more generally, by relation to the experimentally determined equilibrium stress-strain curve of the material. At much higher strains, however, the use of a strain-energy function is invalidated by the hysteretic behavior of the rubber, and the determination of a stress-strain curve at anything resembling equilibrium becomes increasingly difficult. Consequently, in the region of high strain it is preferable to examine the strain dependence of the viscoelasticity without involving a direct comparison with the equilibrium behavior. In principle, the most significant analysis would be obtained from a study of the strain dependence of the relaxation or retardation spectrum. The long-time end of the spectrum could perhaps be measured using a refined creep or stress relaxation technique, although considerable care would be required to separate the effects from the residual behavior resulting from the initial large elongation. In the rubber-glass transition region, with which this work is primarily concerned, the difficulty lies in making measurements over a sufficiently wide frequency range. Normally the Williams—Landel—Ferry (WLF) equation would be used to transform constant-frequency data from a wide temperature range to the equivalent isothermal spectrum over a wide frequency range; however, the validity of this equation has been confirmed only for amorphous polymers, and its application to highly stretched, anisotropic rubber involves several untested assumptions as discussed further below. The main object of the present paper is to describe the observed variations in the viscoelasticity of natural and butyl rubber over a wide range of extension and temperature, although, of necessity, over a limited range of frequency. In addition, a tentative indication of the influence of strain upon the relaxation spectra is given, and the implications of this are examined.
An Interpretation of the Mechanical Properties of Covered-Rubber Yarns
Authors: Treloar L. R. G.
Published: February 2011

The extensibility and other mechanical properties of covered-rubber yarns are considered on the basis of a simple theoretical model in which the covering thread is assumed to be inextensible. It is shown that certain characteristic properties of these yarns are essentially determined by the helix angle during the covering process. The tension in the covering thread and the stresses on the rubber at any state of strain are calculated. The theory is tested by experiments on a series of yarns whose geometrical parameters are systematically varied. The retraction subsequent to the covering process is found to be related to the helix angle of the covering in the manner predicted. The principal features of the force-extension curves are interpreted quantitatively on the same basis. Measurements of the couple about the axis, for singly-covered yarns, provide an indirect check on the theoretical analysis of the tension in the covering thread. It is shown that over a considerable range of extension the coverings are slack, the stress on the yarn being simply the stress on the rubber core. As the breaking point is approached, the fraction of the stress carried by the coverings becomes increasingly important, ultimately reaching a value exceeding 90 per cent of the total tensile force on the yarn in a typical yarn construction. It follows that the rubber core makes no significant contribution to the strength of the yarn, which is determined almost entirely by the strength of the coverings.
Tire Wear at Controlled Slip
Authors: Grosch K. A. , Schallamach A.
Published: February 2011

Tire wear at controlled slip, as realized by setting the wheels of a trailer at a slip angle, obeys the theoretically predicted square law dependence on the slip angle if allowance is made for the effect of temperature and abrasion patterns on the abrasion resistance of the tread compound. The temperature of the tire surface and the intensity of the abrasion patterns increase with increasing slip angle; the severity dependence of the relative wear rating of any two types of tire is largely due to differences in temperature and abrasion pattern coefficients. This applies also to wear on wet roads. The order of magnitude of the absolute wear rates agrees well with the values calculated from the abrasion resistance of tread compounds and the mechanical properties of the tire.
2-Mercaptothiazole and Derivatives as Vulcanization Accelerators
Authors: Trivette C. D. , Morita E. , Young E. J.
Published: February 2011

In this paper the subject of rubber vulcanization accelerated by 2-mercapto-benzothiazole and its derivatives has been reviewed. The technical literature from 1945 through 1960 and patents from 1932 through 1960 have been covered. Topics include: methods of synthesis and manufacture of these accelerators; application and compounding data on their use in rubber processing; and studies of the modes of action and mechanisms for the chemical reactions involved during accelerated vulcanization. Much disagreement exists concerning the mechanism of accelerated vulcanization and the action of thiazole accelerators. However, most of the conflict lies not in the experimental data collected, but in the interpretation of the meaning of the data. It is well documented that MBT and activators (zinc stearate, or zinc oxide and stearic acid) undergo an initial reaction; that these reaction products then react with sulfur and/or rubber hydrocarbon to form intermediate compounds; and that these intermediates then react in some manner to form sulfur crosslinks. Not known, for the most part, are the precise reaction steps involved; the sequence in which these reactions occur; the individual mechanisms, whether ionic, free radical, or neither, by which these reactions proceed; and the side reactions involved, if any (except in natural rubber, in which the non-crosslink forming cyclization reaction is well documented) which might lead to erroneous conclusions from the experimental data, particularly from kinetic studies. These same conclusions apply in general to thiazole sulfenamide accelerated sulfur vulcanization, with the exception that, in contrast to MBT, which has a free thiol group available for immediate reaction, the sulfenamide must first decompose or react in some manner before acceleration occurs. Sulfur and divalent sulfur compounds readily undergo both radical and ionic reactions, depending only on co-reactants and reaction conditions. At present, the reactions of sulfur with hydrocarbons and accelerators are not sufficiently well understood to draw concrete conclusions about the mechanism of acceleration. Further progress on elucidation of the mechanism will come with a better knowledge of the chemistry and mechanisms of sulfur reactions.
Approximate Analysis of the Stressed State of Rubber Specimens, Tear Tested by Various Methods
Authors: Lukomskaya A. I.
Published: February 2011

This paper describes analyses made of the stress and strain changes in the 3 standard ASTM tear specimens and a GOST 270-53 specimen up to the time of tearing. Using the nonlinear theory of elasticity the stresses are calculated and show reasonable agreement with ultimate tensile strength figures. The results refer to natural, sodium-butadiene and styrene-butadiene rubbers.
Dien Rubber: Compounding and Testing
Authors: Smith Ward A. , Willis James M.
Published: February 2011

Over 2,000,000 miles of testing on tires containing Diene rubber in blends with natural rubber or SBR show conclusively the advantages of using these stocks. Important improvements in abrasion and cracking resistance, operating temperature, rolling resistance and gasoline consumption, and traction on snow should be mentioned. At the present time, all of the Diene rubber being manufactured in a pilot plant is being utilized in production of tire stocks. It is certain that this usage will be greatly expanded in the near future when the full scale plant goes on stream.
Structure of the Spongy Polymer of Isoprene
Authors: Spasskova A. I. , Rabinovitch D. I.
Published: February 2011

1. The spongy polymer of isoprene was subjected to ozonolysis and 63.7% of the carbon chain was shown to be linked —1,4—1,4—. 2. Acetic and succinic acids were observed as secondary breakdown products of these —1,4—1,4— chains and they amounted to about 14.5% of the carbon skeleton of the spongy polyisoprene.
Mechanochemical Transformation and Synthesis of Polymers
Authors: Berlin A. A.
Published: February 2011

The mechanical grinding, milling, mixing, homogenization, freezing and other processes of the physico-mechanical processing of high polymers are widely used in the industries of plastics, rubbers, synthetic fibers, food products, silicates and many other branches of technology. Some of these processes have a great significance in biochemistry, medicine and biology. An analysis of the available experimental data permits one to reach the conclusion that in the intensive grinding of natural polymers (cellulose, starch, proteins or synthetics (polystyrene, rubber, polyisobutylene, etc.) a mechanical scission (cracking) of the macromolecules is observed. The possibility of macromoleeular scission under the grinding of high molecular weight substances is due to the high probability of a localization of mechanical energy at different sections of the polymer chain, which under certain conditions causes internal stresses exceeding the strength of covalent or ionic bonds. Mechanical breakdown of macromolecules is possible not only with dry or wet grinding, but also by mechanical action on polymer solutions. Thus, for instance, Staudinger has shown that the high speeds and forces of friction developed in forcing a 0.005 molar tetralin solution of polystyrene, average molecular weight = Mave=6⋅106, through a platinum capillary bring about a scission of the macromolecules which is revealed in a decrease of about 30% in the specific viscosity of the solution. Forcing a solution of polyisobutylene (Mave=3.9×104–23×104) in dichlorobenzene through a capillary with a diameter of 0.2 mm causes a decrease in the intrinsic viscosity and an increase in the constant of the Huggins equation. An increase in the Mave of the polymer structure formation (cross-linking) and a repeated forcing through is conducive to the mechanical breakdown of the macromolecules. It has been established that in mixing together solutions of polymeric substances (starch, gelatine, polyvinyl alcohol, etc.) with high-speed mixers having a rotation speed of over 4000 rpm, a sharp decrease in the intrinsic viscosity [ν] is observed, while the degree of scission increases, with an increase in the rotation speed of the mixer, and also with a decrease in the concentration of the solution.
Determination of Degree of Crosslinking in Natural Rubber Vulcanizates. Part III
Authors: Mullins L.
Published: February 2011

The two previous parts of this series described an attempt to relate the physical properties of natural rubber vulcanizates to their network structure. The first established an empirical relationship between the stress-strain behavior of highly swollen natural rubbers in simple extension, and their equilibrium volume swelling in n-decane. It also examined the effect of changes in initial molecular weight of the unvulcanized masticated rubber on these properties, and an empirical correction making allowance for network flaws due to chain-segments terminated by a crosslink at only one end was obtained. The second part gave measurements of the equilibrium volume swelling and the intrinsic viscosity before vulcanization for each of a range of natural rubber vulcanizates which had been prepared by a method which enabled the number of crosslinks to be determined by chemical analysis. These measurements permitted a comparison to be made between (i) the chemical estimate of the actual number of crosslinks introduced and (ii) the number derived from the data on equilibrium volume swelling, by means of the empirical relations derived in Part I. For this purpose, an assumption was made that the stress-strain behavior of highly swollen rubbers was in accord with the predictions of the statistical theory. Recent studies of both the stress-strain properties of highly swollen rubbers and the method of determining number-averaged molecular weight from intrinsic viscosity measurements have provided an improved basis for the quantitative determination of the degree of crosslinking from measurements of physical properties. The results described in Parts I and II of this series are reinterpreted here to take account of both of these developments ; in addition, the effect of the introduction of a correction for a network defect equivalent to chain entanglements is examined.
Electron Spin Resonance Study of the Interaction of Tetramethylthiuram Disulphide (TMTD) with Rubber and Related Compounds
Authors: Bresler S. E. , Dogadkin B. A. , Kazbekov E. N. , Saminskii˘ E. M. , Shershnev V. A.
Published: February 2011

In the article by Dogadkin and Shershnev electron paramagnetic resonance spectra produced in the laboratory of Prof. S. E. Bresler are put forward to confirm the radical mechanism of the interaction of TMTD with raw rubber in the process of vulcanization. After this paper had been printed we learned of the work of B. R. McGarvey and H. M. McConnel, in which analogous spectra were observed in solutions containing bivalent copper ions. As a result it is suggested that the electron paramagnetic resonance spectra of stocks of natural rubber with TMTD are affected by admixtures of copper compounds. The amount of copper calculated from the magnitude of the resonance spectrum amounts to 0.1% by weight in relation to the TMTD. The same spectrum is observed on heating a benzene solution of copper acetate and TMTD. Its intensity increases sharply and irreversibly on heating the solution to 100°. corresponding to 10% of the copper contained in the solution.
Some Aspects of High Temperature Vulcanization
Authors: Bielstein G.
Published: February 2011

When a thin rubber sample is heated to a high curing temperature, the initial kinetics of cure as derived from Newton's rule can be represented by a well-defined time delay at the final curing temperature. This facilitates quantitative studies for which it is also shown that first order changes in crosslink density can be assessed by modulus measurements. The vulcanization rate constants thus determined in the case of a polychloroprene compound indicate the apparently different action of the vulcanization accelerator at conventional and at high temperatures, which allows a fundamental interpretation to be advanced. Partial reversion at high temperature is shown for both the ACS1 and a thiuram-cured natural rubber compound, and using an appropriate graphical method, vulcanization and reversion can be evaluated as first order processes. Two simple overall reaction schemes are developed to fit the experimental data with only three calculated rate constants. Quinoid and peroxide curing systems are also examined.
Features of the Reinforcing Action of Carbon Blacks Deduced from the Tear Propagation of Filled Vulcanizates
Authors: Lukomskaya A. I.
Published: February 2011

1. The reinforcing action of carbon blacks is most clearly apparent in the knotty tearing of carbon black rubbers. 2. Knotty tearing is characteristic of rubbers filled with carbon black in definite ranges of deformation and temperature, the position of which depends upon the type of rubber and carbon black. 3. With high contents of contact gas black in vulcanizates of sodium butadiene (SKB) and butadiene sytrene (SKS-30) rubbers two ranges of knotty tearing occur. The first is situated at relatively high temperatures and low rates and the second at relatively low temperatures and higher rates. Reduction in the content of black in these vulcanizates leads to the disappearance of the high temperature range of knotty tearing and the displacement of the low-temperature range towards higher temperatures and low rates. This position of the ranges (at medium rates and temperatures) is characteristic also of the said synthetic rubbers containing thermal black. 4. The first range of knotty tearing of filled SKB and SKS-30 vulcanizates with contact black is linked with the presence in them of carbon black chains, while the second range, existing also with vulcanizates with thermal black, is connected with the presence of carbon black particles. 5. Within the ranges ofr ates from 40 to 1000 mm/min and of temperatures from 40 to +100° C filled vulcanizates of natural rubber have one range of knotty tearing situated at lower rates. In the case of the presence in them of contact gas black the range is shifted towards higher rates than in the case of thermal black. 6. Increasing the length of the nick in testpieces being tested for tear propagation leads to a shift in the range of knotty tearing towards higher rates and widens it with respect to temperatures. This same effect is noted on altering the shape of the testpiece, starting with the Delft testpieces and proceeding to types A, B, and C, i.e. increasing the nonuniformity of stress distribution in the deformed testpieces.
The Chemistry of Natural Rubber Production
Authors: Wren W. G.
Published: February 2011

Many advances in the world of science have taken place quietly in field and laboratory, with few to applaud the discoverer or to appreciate his worth. The man we honor today was such a pioneer, whose work received full recognition only many years after its completion. It is, I think you will agree, a very fitting tribute to Ridley to discuss recent advances in the science of natural rubber and to applaud at least some of the contributions made by the many different workers. The field is a large one, and I can hope only to give a brief survey of a few selected items, so I propose paying more attention to research which is concerned with the production of natural rubber rather than with its utilization.
The Structure of Various Natural Rubbers
Authors: Stavely F. W. , Biddison P. H. , Forster M. J. , Dawson H. G. , Binder John L.
Published: February 2011

Although Columbus, on his second journey to America, found the natives playing with balls which bounced and were elastic, it was almost 300 years later before use was made in Europe of the gum used in these balls. Priestley found that it could be used for erasing lead pencil marks. However, when further applications of this material were attempted, it became recognized that rubbers from different parts of the country differed. These differences arose partly from the botanical origin of the plants from which the gum, or rubber, was collected and partly from the methods of collecting and preparing it. With the passage of time, fine Para rubber came to be recognized and used as the best rubber and it held this position until it was supplanted by plantation rubber from Hevea brasiliensis trees. These differences in rubbers from different sources made it necessary for the user to know more about the material. Even the distinguished physicist Faraday became involved in the problem and in 1826 he published an analysis of the latex and also the dry rubber. His results were as follows :
Determination of Latex Particle Size Distributions by Fractional Creaming with Sodium Alginate
Authors: Schmidt E. , Biddison P. H.
Published: February 2011

Knowledge of mass distribution of particle sizes in latex is very important to the latex technologist. Therefore, it is desirable to have available a simple method for the determination of mass distribution of particle sizes. This paper presents a method, based on fractional creaming of latex with sodium alginate, which can be used in any laboratory without special equipment. The method is particularly advantageous for analyzing latexes of very wide particle size distributions. When analyzed with an electron microscope, these latexes require counting a very large number of particles. McGavack found that partial creaming of normal hevea latex with ammonium alginate gives concentrates of larger average particle size than the original latex. He found that the average particle size in the cream approaches that of the original latex as the amount of creaming agent is increased. In a previous paper from this laboratory, Schmidt and Kelsey demonstrated that the phenomenon of fractionation according to particle size with increasing amounts of creaming agent is applicable in a wide variety of anionic latex systems and in colloidal silica. Their results indicated also the existence of a quantitative relationship, independent of the nature of the dispersed particles, between the concentration of creaming agent and size of creamed particles. Maron confirmed fractionation with respect to particle size as a consequence of partial creaming with alginate. He showed that the mass average particle sizes of fractions, determined optically, cumulate to that of the original latex. Although the previous paper by Schmidt and Kelsey implied the basic concept of a method of determining particle size distribution by fractional creaming, it was not exploited at that time. In order to adapt the fractional creaming phenomenon to a quantitative method for particle size determination, we required a more precise knowledge of the relation between creaming agent concentration and size of particles creamed. It was proposed to establish this relationship with the aid of the electron microscope. Various factors influencing the creaming of latex, such as polymer concentration, electrolyte, soap content, and variability of the creaming agent, had to be considered in standardizing the creaming procedure.
A Proposed Method for Estimating Polymer Molecular Weight Distribution without Fractionation
Authors: Rehner John
Published: February 2011

The close agreement which Green has demonstrated between results from the Schulz binomial and the Tung distribution and the applicability of the latter to a variety of fractionation data for different polymers both seem to outweigh possible objection that the present method assumes a particular distribution function. Green's results suggest to us that the apparent exceptions found by Tung for some polyethylenes containing large amounts of low molecular species may possibly be attributed to fractionation inefficiency, rather than to the inadequacy of his function. The internal consistency or smoothness of data does not, of course, constitute proof of precise fractionation. In fact, one can safely say it is no easy matter to find complete fractionation data, of established precision, that can provide a critical test of a distribution function over the entire molecular weight domain. In his study of polyethylenes, Tung suggested that his function tends to exaggerate the low molecular weight end of the distribution, in the sense that the Mn values calculated from his parameters were only about half as large as those obtained by summation of the experimental data for the fractions. His calculated and experimental values of Mw, on the other hand, were in satisfactory agreement. One might be tempted to use this to reconcile the Mn values of the SBR system in Table II with the higher values reported by others. However, this procedure would be indefensible because simply doubling the Mn values would give polydispersity values of less than unity. It would therefore seem incorrect to generalize that the Tung function gives abnormally small Mn values for all polymers, especially when there is some reason to believe that it is better than it seems, even for polyethylenes. Much more likely, the differences between the average molecular weights and the polydispersity of the peroxide-SBR system of Table II, and the corresponding quantities reported by Bueche and Harding for sulfur-SBR and by Booth and Beason for uncompounded SBR, are real and are due to chemical and other factors already mentioned. Although the meager data at hand leave some question as to the accuracy with which the present method can predict absolute values of the various average molecular weights, the key to the matter seems to be the ratio of the true to the physically measured crosslink density for polymers in general, rather than the particular distribution function employed here. Less uncertainty is attached to the polydispersity, since this is a function of only one parameter, b, which is quite insensitive even to large errors in ρ. The method may therefore be useful, even in its present state, for comparative studies in a given system. These might include, for example, the effect of synthesis or processing variables on distribution characteristics and product properties or the effects of stabilizers in aging or other degradative processes.
Mechanical Degradation of High Polymers
Authors: Bueche F.
Published: February 2011

Mastication of rubbers and molten plastics often gives rise to degradation of the polymer molecules. The amount of degradation is severely dependent upon shear rate, melt viscosity, and molecular weight of the polymer, temperature, and the presence of plasticizer. Under certain conditions, usually at low temperatures, one finds that the presence of oxygen is only of minor importance. At high temperatures, at least in certain cases, shear degradation is seriously increased when oxygen is present, even though very little degradation occurs without mastication. In this latter case, oxidative scission does not appear to take place at random along the chain but seems to occur predominantly in the central portion of the chain. The purpose of this paper is to present a molecular theory which unifies these various observations. It will be restricted to the mechanical actions involved during mastication. The effect of oxygen on mechanical degradation will also be considered.
The Mechanochemical Breakdown of Polystyrene by Vibromilling
Authors: Grohn H. , Bischof K.
Published: February 2011

The investigation presented here, including detection of nitrogen, the viscometric investigation, melting point determinations, the ultraviolet and infrared spectra, allow of the qualitative statement that macroradicals are formed in the mechanochemical breakdown of polystyrene by vibromilling. The slight differences between N2 and NO milling may be ascribed in part to a more rapid deactivation of the radicals. On the foundation of the existing knowledge of mechanochemistry there result interesting prospects for science and technology, e.g., the use of macro-radicals as polymerization initiators and as active types of block copolymers and graft polymers by reactions both with monomers and with macroradicals of other polymer materials.
Abrasive Wear Research on Rubber
Authors: Wellinger K. , Uetz H.
Published: February 2011

The abrasion resistance of five different types of rubber were compared with steel (St 37) by various testing methods, such as the abrasive paper method, the abrasion cup method and the sand blasting method. The order of resistance of the various types of rubber against sand blasting is different from the order which is obtained with the sandpaper and abrasion cup methods. However, variations of the testing conditions within one method generally does not change the order. It has been shown, that rubber is more resistant against sand blasting than other materials investigated (basalb, malleable steel, non-alloyed hard castings) if the sand blast is directed essentially perpendicularly against the tested surface.
Non-Linearity in Dynamic Tests. I. Vibration Test Methods
Authors: Gough V. E.
Published: February 2011

In those cases where dynamic tests are to be interpreted in terms of the molecular structure of rubber, there is a definite need for a method of analysis which is wholly free from mathematical assumptions. Such a method of analysis is possible by the use of phase planes of velocity plotted against displacement. This is so because the slope of the trajectory at any point of the motion of any single degree of freedom system can be written solely in terms of physical quantities, namely, driving force, viscoelastic reaction and momentum. The analysis involves no hidden mathematical assumption. Methods of deriving stress strain relationships from phase plane trajectories are described. This phase plane method is discussed in some detail. Examples are given showing the inadequacy of the usual linear analysis in the case of rubberlike materials. Analysis shows that dynamic test machines should either apply a known motion and record a force-deflection curve or apply a force of known wave form and record the resulting motion as a phase plane trajectory. If force and motion are not kept independent of each other in this manner there is an inbuilt mathematical relationship which, more often than not, influences and falsifies the results. An important conclusion is that only when the nature of the non-linearities, or what is the same thing, the character of the functions which correctly describe the actual behavior of a vibrating system have been established by sound analysis of test data, should the phenomena be ascribed to the physical properties of the material. Because of the important consequence of the acceptance of some common mathematical steps in any analysis, certain of these are critically examined and their relevance discussed.
Response of Elastomers to High Temperature Cure
Authors: Smith Frank B.
Published: February 2011

It is well known to production people and to process engineers engaged in manufacturing rubber products that the output of curing operations can be greatly increased by elevating the temperature of vulcanization. For example, work done in the 1920's led to the curing of rubber-covered wire at 400° F using a continuous vulcanization (CV) process. Highly accelerated compounds capable of complete vulcanization in 15 seconds at 400° F are used in the wire industry. More recently the application of high temperature vulcanization methods has been vigorously pressed in the tire industry. While exact curing cycles are closely guarded secrets, it can be stated that passenger tires are vulcanized at temperatures up to 388° F (200 psi steam pressure) using press cycles of the order of 15 to 25 minutes' duration. New automatic presses which shape and then cure the tires at high temperatures—for example, Bagomatic tire curing press, McNeil Machinery & Engineering Co., Akron, Ohio—permit large economies in labor and productivity. Further reductions in curing cycles are anticipated, since the process engineers and rubber technologists continue to develop improved methods of high temperature curing. At this time it appears that the trend to higher temperature vulcanization will not only continue but tend to expand into other lines of rubber products. Considering the economic advantages which a given company may gain by a major advance in high temperature curing of tires or other rubber goods, it is not surprising that there have been only a few disclosures on high temperature curing technology.
Relation of Structure to Properties in Polyurethanes. Effect of Branching
Authors: Cluff E. F. , Gladding E. K. , Rogan J. B.
Published: February 2011

Attaching short N-arylurethane branches to a high molecular weight, linear polyether urethane introduces interchain forces—very likely arising from hydrogen bonding—which increase as the side chains become more polar. These forces are sufficiently strong to increase the bulk viscosity of the raw polymers and, with the more highly polar groups, are strong enough to impart an appreciable elastic memory. At slightly elevated temperatures (80° C) these forces are reduced considerably, which is to be expected if they arise through hydrogen bonding. However they are either not strong enough or are too limited in number to compete with the covalent crosslinks in the elastomer vulcanizates. Thus no significant alteration is observed in the vulcanizate properties which are customarily measured. The marked effect of these short aryl side chains to reduce crystallization tendencies can most likely be attributed to the bulkiness. of the pendant aryl moiety, which prevents—or slows down—the ordering of the polytetramethyleneether chains into a crystal lattice. Long chain branches influence dynamic properties considerably. Present evidence indicates that optimum dynamic properties—as measured by Yerzley resilience—are obtained when “loose ends” are absent.
The Oxidative Aging in Ultraviolet Light of Dicumyl Peroxide Vulcanizates of Natural Rubber in Presence of Various Antioxidants
Authors: Dunn J. R.
Published: February 2011

The oxidative aging of natural rubber vulcanizates at 25° C under irradiation by ultraviolet light of wavelength 365 mµ has been described in a number of communications from this laboratory. At this wavelength naphthylamines were shown to accelerate degradation of peroxide vulcanizates while substituted p-phenylenediamines inhibited it; α-naphthol and a variety of dithiocarbamates were also found to have a protective action. Since some amines and phenolic antioxidants do not absorb light of wavelength 365 mµ but do absorb in the region of 313 mµ, investigations have now been made of the effect of a large number of additives on aging at the shorter wavelength, so that predictions might be made of the most suitable materials to employ in protecting unfilled vulcanizates against crazing in sunlight.
The Chemistry of Carbon Black in Rubber Reinforcement
Authors: Sweitzer C. W. , Burgess K. A. , Lyon F.
Published: February 2011

1. The removal of chemisorbed oxygen from channel black and furnace black, without alteration of the underlying carbon surface, results in only minor effects in reinforcement potential regardless of the curative system employed, whether polar or free radical. 2. When the underlying carbon surface is changed by heat treatment to a state of lower energy, a significant decrease in the reinforcing ability of the carbon black results. 3. Different types of oxygen functional groups added to the carbon surface produce similar effects upon rubber properties. 4. These effects are limited to retardation of cure rate in sulfur curing systems. Only small effects of any kind are produced in the natural rubber-peroxide system. 5. The net conclusion to be drawn is that combined oxygen on the carbon surface plays a relatively minor role in the chemical effect of carbon black upon reinforcement; the nature of the carbon surface itself is of primary importance.
Graft Polymers from PVC and Rubber
Authors: Berlin A. A. , Kronman A. G. , Yanovskii˘ D. M. , Kargin V. A.
Published: February 2011

1. The authors investigate the graft copolymerization of vinyl chloride and butadiene-nitrile rubber by a chain transfer reaction, and also the combined mastication of PVC with various rubbers at elevated temperatures. 2. In physicomechanical properties Viniplasts produced on the basis of the products of graft copolymerization of vinyl chloride with butadiene-nitrile rubber, and also of the modification of PVC by butadiene, isoprene and natural rubbers are not superior to the corresponding characteristics of ordinary Viniplast. 3. In the combined mastication of PVC with Nairit and of PVC with butadiene-nitrile rubber at elevated temperatures compositions are produced which in respect of impact strength are 2 to 4 times superior to Viniplast from PVC. 4. It is suggested that the improvement in the physicomechanical properties in the combination of PVC with SKN-26 is connected with the formation of hydrogen bonds between the molecules of the polymers in question.