bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastomeric Adhesion and Adhesives
Authors: Weidner C. L. , Crocker G. J.
Published: February 2011

An increasing number of papers in the field of adhesion have been appearing in Rubber Chemistry & Technology. In the period 1941–1950 twenty-two papers appeared in this Journal covering various aspects of adhesion, whereas in the year 1959 alone eleven papers appear. The Rubber Division Library at the University of Akron has compiled bibliographies as follows: Bibliography # 10, “Use of Synthetic Resins in Natural and Synthetic Rubbers”, covering the period 1930–1952; Bibliography # 18, “Rubber to Metal Bonding”, in two parts, one covering the period 1937–1954 and a supplement covering 1955–1958; and Bibliography #20, “Reclaim Rubber Cements”, covering the period 1927–1954. In addition, special bibliographies were prepared covering the period 1949–1958 on the subjects “Rubber to Wood Adhesives”, “Rubber to Fabric Adhesives”, “Bonding of Polyurethanes”, “Metal to Metal Adhesives”, and “Chemistry of Rubber Adhesives”. The most comprehensive text in the field is “Adhesion and Adhesives” edited by N. A. DeBruyne and R. Houwink. More limited in scope are “Adhesive Bonding of Metals” by Epstein, “Adhesives for Wood” by Knight, “Adhesive Bonding of Reinforced Plastics” by Perry. Also “Rubber to Metal Bonding” by Buchan, which stresses the brass plating technic. Skeist has recently edited a “Handbook of Adhesives”. The Encyclopedia of Chemical Technology contains articles on “Adhesives” in Volume I and the First Supplement Volume. Various symposia have been sources of worthwhile papers on adhesion. The Division of Paint, Plastics, and Printing Ink Chemistry, ACS, published such papers in their preprint booklets, volume XV, No. 1 (1955) and volume XX, No. 1 (1960). Papers given at this division's “Recent Advances in Adhesives” symposium in 1957 are also published. Publication of papers at two symposia held in 1952 (Society of The Chemical Industry, London; Case Institute of Technology, Cleveland) form a valuable collection. Papers from The Second International Congress of Surface Activity in London in 1957 are also published. Papers from a Symposium on Adhesion held by the Society of Rheology in 1959 are published in volume IV of the Society's Transactions. General review articles on adhesion with extensive bibliographies were published as follows : Rinker-Kline “Survey of Adhesives and Adhesion; Kline-Reinhart “Fundamentals of Adhesion”; Brantley-Charnell “Investigation of the Nature of Forces of Adhesion”; Reinhart-Callomon “Survey of Adhesion and Adhesives” and Rutzler “Types of Bonds Involved in Adhesion”. The Reinhart-Callomon survey is quite extensive in its bibliography.
Ionizing Radiation and Elastomers
Authors: Gehman S. D. , Gregson T. C.
Published: February 2011

The phenomena which are observed in investigations concerned with high energy ionizing radiation and elastomers follow generally from the principles of related fields such as the interactions of radiation with matter; radiation, polymer, and polymerization chemistry ; and the molecular structure of elastomers in relation to their physical properties. The way in which the knowledge from these various fields is integrated to account for the results with elastomers gives a specialized aspect to the interpretations, which however is very much the same for elastomers as for polymers in general. As usual, the modifying circumstance is the generally greater sensitivity of the physical properties of elastomers to changes in structure than is the case for ordinary polymers. In sketching the relatively short history of work with intense, high energy radiation and elastomers, it is not possible to ignore the unusual circumstances under which it has progressed. The Atomic Energy Act of 1946 transferred control of atomic energy from military to civilian agencies. But it retained such a tight government monopoly in the field that there was little incentive for independent research looking toward peaceful applications from the military developments. However, the Oak Ridge National Laboratory did begin the distribution of isotopes under a licensing system in 1947 which provided opportunities for a broader acquaintance with the characteristics of isotopic sources of radiation and techniques for handling them although the levels were, as a rule, quite low. The Atomic Energy Act of 1954 encouraged a much more liberal participation of private enterprise in the atomic energy program. After the passage of this Act many segments of industry became actively interested in exploring the significance of the new knowledge and technologies for their operations.
Ski Rubber, a New Polyisoprene
Authors: Subbotin S. A. , Samoletova V. V. , Znamenskaya A. K.
Published: February 2011

It is known that the industrial synthesis of general purpose rubbers has been accomplished and has been developing on the basis of the use of divinyl as the starting monomer, taken either in the pure state (sodium-divinyl rubber) or in mixture with another monomer—styrene (divinylstyrene rubber). However, synthetic polymers of isoprene have, to this day, found no practical application despite the fact that natural rubber (NR) is a polyisoprene and the first samples of synthetic rubber were obtained from isoprene. This is explained by the circumstance that, up to the present time, it was not possible to synthesize an isoprene or a copolymer-isoprene rubber which would have substantially improved properties over a similar rubber obtained on the base of divinyl; in addition isoprene is a less plentiful raw material than divinyl. Divinyl rubbers differ from natural rubber not only in their microstructure but also in the chemical nature of the link of the polymer chain; and still, with time, they successfully replaced natural rubber in the production of a large number of rubber goods. At the same time, due to various new properties possessed by the divinyl rubbers, their application led to the improvement in the quality of certain goods and, in many cases, to a simplification and reduction in cost of production of the latter. Nevertheless even the most modern general purpose commercial rubbers, which are obtained from divinyl, possess various substantial shortcomings in comparison with natural rubber. The most significant shortcoming of the divinyl rubbers is their reduced elasticity. This shortcoming is especially significant all the more, since rubber mixes with these rubbers as a base must, because of their low strength, be prepared with a large content of carbon black. For this reason such rubbers cannot serve as an equivalent substitute for natural rubber in carcass and breaker rubbers for tires, especially truck tires, and in the manufacture of various technical and also household, highly elastic goods.
Crosslinking of Oriented Rubber
Authors: Charlesby A. , von Arnim E.
Published: February 2011

Smoked sheet rubber, previously oriented in the calendering process, was crosslinked by exposure to 2 Mev high energy electrons in the absence of vulcanizing agents. Even after annealing, the resultant rubber showed anisotropic elastic properties, having a high elastic modulus and a low elongation at break in the direction of orientation. It is suggested that radiation in addition to crosslinking causes main chain fracture and stress relaxation in stressed molecular chains. The G value for crosslinking (1.05) by electron irradiation agrees well with that (1.1) previously found by elastic measurements of pile irradiated rubber.
Adduct Rubbers: A Versatile New Family of Elastomers
Authors: Pierson R. M. , Gibbs W. E. , Meyer G. E. , Naples F. J. , Saltman W. M. , Schrock R. W. , Tewksbury L. B. , Trick G. S.
Published: February 2011

A versatile family of elastomers has been prepared by free radical addition of aliphatic mercaptans to the double bonds of diene polymers. High saturation levels were readily achieved without degradation of the basic polymer chain. The technology is similar to ordinary emulsion polymerization. By varying the nature of the base polymer, the mercaptan used, and the extent of saturation, a wide range of compositions and of physical properties were attained in the adducts. In general, resistance to aging, ozone attack, heat, solvent swelling, and to permeation by gases increased with increasing extent of saturation. Outstanding performance in these qualities was achieved by adducts of polymers whose double bonds had been over 90 per cent saturated. A highly saturated methyl mercaptan adduct of polybutadiene showed (1) stress-strain and air aging properties at 400° and 500° F better than commercially available ethylacrylate copolymers and various semicommercial heat resistant elastomers; (2) permeability resistance equivalent to butyl; (3) solvent swell intermediate between neoprene and medium nitrile content butadiene-acrylonitrile rubbers, with a Tg below −30° C; (4) ozone resistance comparable to the better commercially available saturated rubbers. Increased solvent resistance was obtained by preparing adducts of the appropriate butadiene-acrylonitrile copolymers. Adducts with saturation levels up to about 85 per cent could be cured by the same procedures used for the base polymers. Activated or butyl-type curing systems were required for higher saturation levels. The relative rates at which aliphatic mercaptans add to the several types of double bonds present in emulsion diene polymers have been examined in a preliminary way.
The Oxidative Softening of Synthetic Rubber Latex
Authors: Herte P.
Published: February 2011

A method is described for plasticizing Buna S3 when still as a latex. A plasticization of Buna S3 to the Buna S4 stage is carried out in the presence of metal sols or alkyl phenols, and through use of air or oxygen-enriched air. Softening takes place under low gage pressure, at temperatures around 100° C, and at rates that are technically feasible. In contrast to Buna S4 that has been produced soft by means of polymerization control, the Buna S4 obtained through this softening process has certain advantages, e.g., higher elasticity values in heavily-loaded compounds. So-called recovery can be retarded by careful dosing with phenyl-2-napththylamine. The introduction of this process into the synthetic rubber industry, using continuous latex breakdown in a countercurrent reaction tube, is discussed.
Reactions of Free Radicals in Solution. V. Destruction of Polymeric Molecules by Free Radicals
Authors: Bresler S. E. , Dolgoplosk B. A. , Krol V. A. , Frenkel S. Ya
Published: February 2011

1. It was established that free radicals produce degradation of polymer chains. 2. Ideas were put forward on the possible mechanism of the reaction leading to the breaking of a carbon-carbon bond in polymer molecules.
The Vulcanization of Elastomers. 16. The Vulcanization of Natural Rubber with Sulfur in the Presence of Dithiocarbamates (I)
Authors: Scheele Walter , Birghan Klaus
Published: February 2011

The kinetics of vulcanization of natural rubber with sulfur (initial concentration: 1 mole S8 in 10 kilograms of mixture) was investigated in the presence of varying amounts of zinc diethyldithiocarbamate (ZnDEDC). The following results were obtained. 1. At all temperatures and, depending upon the dithiocarbamate content of the mixture, over practically the entire, or at least the greater, extent of vulcanization, sulfur decrease is a zero order process. 2. The rate of sulfur decrease is, as long as it proceeds according to zero order, independent of the molar ratio S8:ZnDEDC. From the slope of the log rate versus 1/T plot is derived an activation energy of 29.2 kcal. 3. During vulcanization the dithiocarbamate content declines as long as the sulfur decrease follows the zero order. With decreasing starting content of dithiocarbamate, the stock finally uses up all the zinc dithiocarbamate during vulcanization. In other cases, a constant limiting value of dithiocarbamate decrease appears. 4. When zinc dithiocarbamate and zinc oxide are both present, sulfur decrease again takes place according to zero order. Under these conditions the process will use up less dithiocarbamate and shortly after the onset of vulcanization a constant final value of dithiocarbamate appears. 5. After the initial lag, crosslinking, measured by reciprocal equilibrium swell in benzene, proceeds according to zero order over the major extent of vulcanization. The temperature function of relative rates of crosslinking furnishes an activation energy similar to that for the rate of sulfur decrease. 6. Reciprocal equilibrium swell deviates from zero order time dependence as soon as the dithiocarbamate decrease reaches its final value, and the sulfur decrease also experiences a considerable lag. 7. It is shown that the limiting value of equilibrium swell increases as the starting content of dithiocarbamate decreases and also that reversion sets in at higher temperatures. When the molar ratio of mixing S8:ZnDEDC amounts to 1 or to 0.5, the limiting value of the swelling index is reached independent of temperature, i.e., the degrees of crosslinking are the same for these two ratios. The investigations will be continued.
The Vulcanization of Elastomers. 17. The Role of the Oxide in Vulcanization with Thiuram Compounds. II
Authors: Scheele Walter , Grasemann Horst , Mau Günter
Published: February 2011

The reaction of tetraethylthiuram disulfide with zinc oxide, in which significant amounts of zinc dithiocarbamate are formed, was investigated quantitatively. The decrease in thiuram disulfide and increase in dithiocarbamate were followed by conductometric titration with HCl (dithiocarbamate) and with CuSO4 in the presence of hydroquinone (thiuram disulfide) as well as by a spectrophotometric method. Both methods gave as the limiting value for the dithiocarbamate formation, 90 mole %, calculated on the initial thiuram disulfide. This value is independent of the reaction temperature. Judging from this evidence on dithiocarbamate formation, it seems clear that some condition holds here other than that which holds in the case of a thiuram vulcanization. In the latter case, the limiting value for dithiocarbamate formed, also independent of temperature, is 66 mole % based on the initial thiuram disulfide. In incompletely reacted mixtures of ZnO and thiuram disulfide, the spectrophotometric method indicates higher dithiocarbamate content than does the conductometric method of analysis. This shows that spectrophotometry shows at least one (unknown) compound which conductometry does not detect. The spectrophotometric analyses of thiuram vulcanizates are in agreement with the results of conductometric titrations of the vulcanizate extracts; both methods indicate 66 mole % as being the limiting value for dithiocarbamate formation; likewise, the same kinetic relations are found by the two methods. The use of the spectrophotometric method was carefully checked with control tests.
The Radioactive Tracing of the Diffusion of Sulfur in Cable Rubbers
Authors: Blokh G. A. , Korniltseva Z. P. , Olshanskaya L. A. , Kolobenin V. N.
Published: February 2011

The use of radioactive isotopes is a progressive and promising innovation in the study of the manufacture of cable rubber. Thus, in an earlier article the authors demonstrated the possibility of using the radioactive isotope of sulfur, S35, in the study of diffusion processes in cable rubbers during vulcanization. The use of labelled sulfur as the vulcanizing agent in core rubber mixtures has shown: (1) an intensive diffusion of sulfur from the core rubber mixture into the insulating rubber during vulcanization; (2) the presence of a high concentration of accelerators in a thin (0.1 mm) surface layer of the insulating rubber ; this is a fundamental cause of the overcure of the insulating rubber, which leads to the appearance of cracks, accelerated aging, and other defects; (3) an intensive exchange of sulfur atoms among the accelerators and between them and the bound polysulfide sulfur. Thus, as a result of the diffusion of sulfur from the core mixture to the insulating rubber, the nature of the sulfur bonds is changed, and a number of polysulfide structures are formed. It has been shown that the polysulfide-bound sulfur is mobile, that is, it takes part not only in the isotopic exchange of sulfur atoms, but also in the diffusion process. According to Bresler, the coefficients of diffusion of free polysulfide sulfur can be calculated from measurements of the radioactivity.
Tension Flaws in Bonded Cylinders of Soft Rubber
Authors: Gent A. N. , Lindley P. B.
Published: February 2011

It is not uncommon to subject rubber-to-metal bonded components to tensile loads lower than that required to break a well-bonded unit as a routine check of the bonding efficacy. We have observed that internal fractures occur in soft vulcanized natural rubber cylinders bonded to metal endpieces when subjected to comparatively low tensile loads. Such internal flaws may well pass undetected, but their presence might be expected to impair the strength, service behavior and life. No previous account of their occurrence is known to us. The rubber mixes used contained little or no carbon black, and gave vulcanizates having hardnesses in the range 30–45° British Standard. The test-pieces, in the form of cylinders 2 cm in diameter and 0.07–0.50 cm in height, were prepared by a molding process and bonded by means of cements (‘Ty Ply’ UP and RC) to metal endpieces during vulcanization. Load-deflection relations in tension were determined using a Hounsfield tensometer, the deflection being imposed at a speed of 0.16 cm/min.
The Nature of the Particle Surface in Hevea Latex and Pastes of Rubber Hydrochloride and Polyvinyl Chloride
Authors: Schuur G.
Published: February 2011

The colloid-chemical properties of natural rubber latex are influenced by many factors, such as the pH, the concentration of surface-active agents and the presence of ions of different kinds. Many of these factors have been studied intensively. However, it has usually been assumed that the surface of the rubber particles consists of plain hydrocarbon. Up to now it has been impossible to investigate the properties of the surface free from adsorbed soaps and proteins, for the removal of these surface-active agents results in coagulation of the latex. But the latex particles can be obtained in a hard and nontacky form by hydrochlorination and crystallization according to the methods of van Veersen and the author. The various surface-active agents can then be removed by filtering, washing, and extraction with organic solvents, without the loss of the surface by coagulation of the particles. The reactions of most organic chemical groups with hydrochloric acid are fairly well known and, though the original properties of the surface may be modified to some extent by the hydrochlorination, an investigation of the surface of rubber hydrochloride may give useful information regarding the properties of the original surface of the rubber particles. A suitable method for studying the nature of the surfaces of various rubber hydrochlorides would be to investigate the rheological properties of concentrated dispersions in organic media. Dispersions in plasticizers were selected, in the first place, because the experimental work is then not complicated by the volatility of the solvents, and secondly, because these dispersions in plasticizers are of some technical interest, since they can be used for the preparation of monofilaments from rubber hydrochloride.
Some Properties of Polymer Networks Formed from Oriented Chains of Natural Rubber
Authors: Roberts D. E. , Mandelkern L.
Published: February 2011

Highly oriented natural rubber samples prepared by a modification of the racking process described by Feuchter were crosslinked by means of γ-radiation. Some of the physical properties of the networks prepared in this manner were studied and compared with networks formed from chains which were randomly arranged prior to the introduction of the crosslinks. In accord with the theoretical considerations of Flory it was found that the swelling behavior, isotropic length, and isotropic melting temperature of the networks depend not only on the fraction of units crosslinked but also very markedly on the arrangement of the chains prior to network formation. It also was observed that the crystalline oriented racked rubber was crosslinked twice as effectively by γ-radiation as was the amorphous rubber.
Crystallization in Natural Rubber. V. Chemically Modified Rubber
Authors: Gent A. N.
Published: February 2011

Small amounts of crosslinking have been shown to reduce the rate of crystallization of natural rubber by large factors. It has also been inferred from measurements on peroxide and sulfur vulcanizates of various kinds that sulfur combined in forms other than crosslinks may retard the crystallization process efficiently. A simple banned volume mechanism has been proposed to account for the influence of crosslinking and sidegroup combination on the rate and final extent of crystallization, and has been shown to predict the form of the observed dependences for crosslinked rubber, and approximately the relative magnitudes, but good quantitative agreement was not obtained. Measurements are described below of the rate and final extent of crystallization in natural rubber which has been modified by the chemical combination of sidegroups to the rubber molecule. It has not proved possible to account quantitatively for the observed rates of crystallization, but it is thought that a description of the extremely large effects found to accompany slight chemical modifications will be of general interest. The preparation of the modified rubbers is described elsewhere. The substances added were six thiol acids; namely, monochlorothiolacetic, trichlorothiolacetic, thiolbenzoic, 1-thiolnaphthoic, thiolsalicylic, and thiol-stearic acids. The reactions were carried out in the solid phase by addition of the thiol acid to purified rubber on an open mill, in solution by addition of the thiol acid to a solution of purified rubber in benzene, and in the latex phase.
Vulcanization of Elastomers. 18. Vulcanization of Natural Rubber with Sulfur in the Presence of Mercaptobenzothiazole. III
Authors: Lorenz Otto , Echte Elisabeth
Published: February 2011

The present work is concerned with the influence of the concentration of sulfur and the zinc oxide content on the kinetics of the vulcanization of natural rubber with sulfur in the presence of mercaptobenzothiazole, zinc stearate and zinc oxide. The following results were obtained. 1. The velocity constant of the sulfur decrease, kSI, is inversely proportional to the initial concentration of sulfur. 2. The velocity constant of the change with time of the reciprocal equilibrium swelling, kQI, is inversely proportional to the square root of the initial concentration of sulfur. 3. The limiting value of the reciprocal equilibrium swelling, 1/Q∞ (degree of crosslinking), at constant stearate content, is proportional to the square root of the initial concentration of sulfur. 4. The amount of accelerator consumed during vulcanization increases with increase in the initial amount of sulfur. The decrease in the accelerator is a first order reaction having approximately the same rate as the decrease of sulfur. 5. The velocity constants of the sulfur decrease and the change with time of the reciprocal equilibrium swelling are practically independent of the amount of zinc oxide. Other situations exist, of course, for compounds without zinc oxide. 6. Empirical equations were derived to express the dependence of the constants kSI, kQI and 1/Q∞ on the composition of the mixture.
The Influence of Structure on the Chemical Activity and Vulcanizability of Butadiene Polymers
Authors: Dogadkin B. A. , Dobromyslova A. V. , Tolstukhina F. S. , Samsonova N. G.
Published: February 2011

1. Differences between the chemical reactivities of 1,4- and 1,2-structures of butadiene are found in the reactions with perbenzoic acid, iodine chloride, and sulfur. 2. The interaction of perbenzoic acid with solutions of butadiene polymers is represented by kinetic curves with an initial region of a high rate, mainly corresponding to the reaction of the double bonds of 1,4-structure, and a final linear region of a low rate, characterizing the reaction of the double bonds in the vinyl side chains of 1,2-structure. By extrapolation of the linear region to the ordinate axis it is possible to determine the relative contents of the 1,4- (and hence of the 1,2-) structure in the polymer. 3. The kinetic curves for the interaction of the polymer solutions with iodine chloride are of analogous form. The initial region of the kinetic curve represents addition at the double bonds, while the linear region corresponds to the substitution reaction. By extrapolation of the linear region to the ordinate axis it is possible to determine the actual double bond content of the polymer. 4. The kinetic curves for iodine liberation are also of similar form ; here the linear region corresponds to the substitution reaction, and the initial region corresponds to the cyclization reaction. The amount of iodine liberated in this reaction is a linear function of the content of the 1,2-structure in the polymer. 5. Mainly the double bonds of the 1,4-structure react when sulfur interacts with the polymer solutions. The total rate of sulfur addition is a linear function of the content of the 1,4-structure. 6. The activation energy for sulfur addition increases with increasing relative content of the 1,2-structure in the polymer. 7. Formation of sulfur crosslinks in vulcanizates occurs mainly as the result of reactions in the 1,4 polymer structure. In consequence, the degree of crosslinking ΔE/ΔS is a linear function of the relative content of 1,4-structure in the polymer.
Two Stages in the Process of Network Formation in Polymers
Authors: Bartenev G. M.
Published: February 2011

1. The two-stage nature of network formation in polymers is discussed, and a formula is derived connecting the number of chains in the network with the initial molecular weight of the polymer and the number of crosslinks. It is shown that below a certain critical number of crosslinks a network is not formed. 2. The application of the derived relationships in determination of the number of sulfur atoms in the crosslinks, the critical molecular weight, and the degree of globulization of the rubber, has been studied in the case of rubber vulcanization. 3. The first vulcanization stage is shown to be of considerable practical importance, as it determines the correct technological conditions for the vulcanization of rubber in molding presses, multilayer articles, etc. For this reason, determinations of the vulcanization optimum in rubber technology must be augmented by studies of the initial stage of the process. A method for determining the duration of the first stage of vulcanization is described.
Organic Sulfides and Polysulfides. I. Desulfurization Reactions
Authors: Minoura Yuji
Published: February 2011

Mercury, copper, potassium cyanide and sodium sulfite were found to desulfurize organic polysulfides. In the p,p′-ditolyl and in the dibenzyl series, the di-, tri- and tetrasulfides gave disulfide by desulfurization. On the other hand, in the case of diglycolic acids, di-, tri- and tetrasulfides gave monosulfides. The sulfide, which has high polarity in its radical, is easily desulfurized. The relative ease of desulfurization is—diglycolic acid > dibenzyl > p,p′-tolyl. In the same series, the higher the sulfur content, the more unstable it seems to be. Mercury is more reactive with sulfides than is copper.
Organic Sulfides and Polysulfides. V. Reactions with Methyl Iodide
Authors: Minoura Yuji
Published: February 2011

Mercaptan and polysulfides of the benzyl and p-tolyl series were heated with methyl iodide in sealed tubes for two hours at 100° C with the results: 1. Benzyl mercaptan and benzyl mono-, di-, tri- and tetrasulfide gave tri-methylsulfonium iodide. 2. Tolyl mercaptan and tolyl mono-, di-, tri- and tetrasulfides did not react with methyl iodide, contrary to previous thinking for the action of mono and disulfides. 3. Free sulfur did not react with methyl iodide.
A Uni-Rotor Mixer for Rubbers and Plastics
Authors: Watson W. F. , Wilson D.
Published: February 2011

The most pertinent advantages of this one-rotor machine as compared with two-rotor laboratory mixers may be summarized briefly as follows : (1) Simplicity and cheapness of construction and robustness. Energy available of up to 1-hp per g material. Even torque characteristics. No contact of masticating materials with seals or glands. (2) Ease of operation and economy of batch size. No ram required nor feed for additives. (3) A five-fold variability of charge without impairing mixing efficiency. Insignificant charge losses or batch-to-batch retention. (4) Rigid control over temperature and gases present.
Rheological Measurements for the Characterization of High Polymers
Authors: Edelmann Kurt , Horn Edith
Published: February 2011

Since the Umstätter structural viscometer represents the only viscometer that operates on the capillary principle, the most accurate measuring principle in viscometry, with a shear stress range above 104, this paper describes the necessary steps, from the long term experience of the authors with this apparatus, which permit a rapid and true determination of a complete flow curve. Also the necessary calculations are given and explained in an example. From this method, the critical velocity gradient G^, the inflection point of the flow curve, was obtained as a characteristic material constant, dependent only on the molecular weight of the high polymer and its absolute value for inhomogeneity. It is the hope of the authors that scientific practice for characterizing high polymers will increasingly refer to the flow behavior of (their) solutions by determining the flow curve.
The Chemistry of Vulcanization. I. Diphenylmethane as a Model of Rubber Hydrocarbon for Its Reaction with Sulfur
Authors: Tsurugi Jitsuo
Published: February 2011

Following the discovery of vulcanization of rubber by Goodyear, a vast number of experiments and speculations have been carried out, but the final clarification of the mechanism of vulcanization and acceleration has remained unsettled. Overemphasis of physical and technological criteria in the investigation of vulcanization may have contributed to the failure to attach importance to the purely chemical investigation. In fact rubber vulcanizates defy chemical investigation because they are insoluble and infusible. However, in 1947 Farmer and collaborators, using olefinic substances such as cyclohexene, dihydromyrcene and squalene as model compounds, proposed a new theory on the vulcanization of rubber by sulfur. According to them α-methylenic hydrogen adjacent to olefinic double bonds is attacked by sulfur, and a hydrocarbon radical is formed. Then this radical couples with the diradical ⋅Sx⋅ and this leads to polysulfides as primary reaction products. Farmer's theory laid the ground work for the chemical investigation of vulcanization but the reaction of olefins with sulfur is too complex to indicate the reaction mechanism. Diphenylmethane (DPM) contains α-methylenic hydrogen (to a benzene ring) and may be expected to react with relative readiness. Moreover the reaction of DPM with molecular oxygen is already reported to produce water, diphenylmethyl hydroperoxide, tetraphenylethane and benzophenone. It is expected then that when DPM reacts with sulfur, it should give the thio analogs of these compounds. Since the reaction and reaction products of sulfur with DPM are considerably less complex than those with olefinic substances, the reaction mechanism should be elucidated by using the simpler hydrocarbon as a model compound. Comparative studies of the reaction with and without accelerator will present the key to the mechanism and theory of acceleration. As fundamental studies of rubber vulcanization as well as acceleration the following are the two objects of this paper. The first is the reaction mechanism of DPM with sulfur at 180° C and the second is the pyrolysis of the primary product (dibenzhydryl polysulfide) to the secondary product (thiobenzophenone) at the same temperature. Investigations on the reaction of DPM with sulfur in the presence of accelerators will be reported in other papers of this series.
The Chemistry of Vulcanization. V. Action of 2,2′-Benzothiazolyl Disulfide on the Reaction of Diphenylmethane and Sulfur
Authors: Tsurugi Jitsuo , Fukuda Haruko
Published: February 2011

The reaction involving diphenylmethane, sulfur and 2,2′-benzothiazoIyl disulfide is summarized as follows. A. The reaction products and material balance among them are indicated. B. A reaction mechanism was decided upon. C. The rate equation for MBTS consumption was derived from the above mechanism and the results interpreted satisfactorily. The activation energy for thermal dissociation of 2,2′-benzothiazolyl disulfide was found to be 32.7 kcal/mole. D. The accelerating efficiency of this accelerator was defined, discussed and evaluated. These studies are being continued and further communications on the studies of accelerators in the presence of zinc oxide or zinc soap will appear in the near future.
The Structure and Molecular Refraction of Organic Polysulfides
Authors: Minoura Yuji
Published: February 2011

The molecular refraction of benzyl and tolyl polysulfide have been measured. The molecular refraction of benzyl and tolyl polysulfides increases with an increasing number of sulfur atoms by 9–10 units per sulfur atom. From the fact of constancy of increase of molecular refraction per sulfur, the structure of polysulfides is considered to be linear.
Graft Polymers with Preset Molecular Configurations
Authors: Merrett F. M.
Published: February 2011

The concept of “tailor-made” macromolecules when applied to graft polymers implies an effective correlation between the chemical and physical properties of the component parts and the technological properties of the resultant whole. Earlier experiments have indicated that, for a given graft macromolecule of natural rubber and polymethyl methacrylate, one extreme physical configuration could readily be effected in solution, viz., with the rubber trunk chains collapsed and the methyl methacrylate side chains extended. The complementary configuration—rubber chains extended and the methyl methacrylate chains collapsed—seemed equally easy of achievement. If these configurations could be carried through to the solid state then comparison of the properties of the dry rubbers would provide one such correlation between established physical configurations and resultant technological properties. The evidence for these definite configurations is briefly described below followed by preparative methods for bulk quantities of the dry rubbers and the evaluation of their technological properties.
On the Relation between Indentation Hardness and Young's Modulus
Authors: Gent A. N.
Published: February 2011

A relation between British Standard and International rubber hardness and Young's modulus is derived from classical elasticity theory, and compared with the empirical relation given in B.S.903:1950. An experimental examination of the load-indentation relationship for a rigid sphere pressed into a flat rubber pad is described ; it indicates that the theoretical relation is more appropriate than the empirical one for small indentations, corresponding to hardnesses exceeding about 60° B.S. & I.R.H., and equally valid for hardnesses between about 40° and 60°. Moreover, the numerical constants are not subject to experimental uncertainty. If reduced major loads are stipulated for determining the hardness of rubbers of less than 35° to 40° B.S. & I.R.H., the theoretical relation should apply over the entire useful range. An approximate relation between Shore hardness and Young's modulus is derived similarly. The approximate equivalence of the British Standard and International rubber hardness and Shore hardness scales over the major part of the hardness range is confirmed.
The Reaction of Sulfur and Sulfur Compounds with Olefinic Substances. Part VIII. The Reaction of Sulfur with Mono-Olefins
Authors: Bateman L. , Glazebrook R. W. , Moore C. G. , Porter M. , Ross G. W. , Saville R. W.
Published: February 2011

Earlier Parts of this series reported the partial separation and identification of the complex products of certain sulfur-olefin and related reactions chosen as models for examining the mechanism of vulcanization of natural and synthetic rubbers by sulfur. The main conclusion was that sulfur-olefin interaction proceeds by free-radical chain processes, and this has been quoted elsewhere and widely accepted. Results are now presented which extend and correct the earlier findings and lead to the different mechanistic conclusion that the reactions are polar in type, involving heterolysis of S—S and C—H bonds. This paper and Part XI deal with the products of the reactions of sulfur with mono-olefins and a 1,5-diolefin, respectively, and Part X presents a complementary kinetic investigation, the first for such reactions. All the experimental evidence is collated in Part XI in a general theory of sulfur-olefin interaction.
The Reaction of Sulfur and Sulfur Compounds with Olefinic Substances. Part IX. The Reaction of Sulfur with 2,6-Dimethylocta-2,6-Diene
Authors: Bateman L. , Glazebrook R. W. , Moore C. G.
Published: February 2011

Farmer and Shipley showed that reaction of sulfur with 2,6-dimethylocta-2,6-diene (I) at 140° yields a cyclic monosulfide and a crosslinked polysulfide. No detailed investigation of the structures of these cyclic monosulfide or polysulfide products was undertaken, but it was deduced that the former contained 6-ethyl-2,2,6-trimethylthiaeyclohex-3-ene (VIII) and a compound having vinylidene unsaturation, CH2:CRR′, as apparently revealed by the infrared spectrum, and this has formed part of the evidence on which broad mechanistic conclusions have been based. This reaction has now been re-examined in greater detail; the compositions of the cyclic sulfide and crosslinked polysulfide fractions and their variation with time of reaction have been determined. Results and conclusions differing in important respects from those advanced by the earlier workers have been reached, as reported preliminarily elsewhere.
Stability of High Polymer Latexes and Their Electrokinetic Potentials
Authors: Voyutskiĭ S. S. , Panich R. M.
Published: February 2011

The stability of colloid systems is a central problem of colloid chemistry. Therefore, many papers have been devoted to studies of coagulation and to the development of criteria of stability for colloid systems. For a long time a prevalent opinion was that the stability of colloidal particles could be explained by the fact that like charge on the particles prevents agglomeration of particles which collide due to Brownian motion. This opinion was first expressed by Hardy and later developed by Powis, Ellis and a number of other scientists. According to this point of view, electrokinetic potential (ζ potential) is the measure of stability. However, after detailed investigation of coagulation phenomena and accumulation of experimental data the correctness of this point of view became less obvious, and the statement that the electrokinetic potential is a criterion of stability of colloidal systems underwent vigorous criticism. The reasons for the measured values of electrokinetic potentials not always corresponding to the stability of certain systems are as follows: firstly, the exact determination of electrokinetic potential is work of great experimental difficulty which seems to some investigators insuperable. Some of these difficulties are (1) the necessity of performing the mocroelectrophoresis in a medium which has the same characteristics as the colloidal system under investigation, (2) the influence on electrophoresis of the simultaneously occurring electrolysis (3) the wash out of the boundary line between the solution and the colloidal system, and a number of others. In the case of microelectrophoresis, these difficulties are replaced by others, which are not less difficult to overcome.
Foam Stability. A Fundamental Investigation of the Factors Controlling the Stability of Foams
Authors: DeVries A. J.
Published: February 2011

Although the production of foam rubber on an industrial scale has been for a considerable time a rather well-controlled process, all factors involved are still insufficiently known. The most critical phase of the manufacturing process is undoubtedly the gelation of the foam produced. This consists of a clotting of the dispersed rubber particles while a simultaneous destabilisation of the dispersed gas bubbles has, however, to be prevented. In order to gain a better insight into the present and similar processes, a fundamental knowledge of foams in general and of their stability conditions in particular is indispensable. The author studied the technology of foam rubber manufacture in the laboratories of the Rubber-Stichting at Delft and carried out the research described in this review in order to get at the “fundamentals”. Since he comes from the University of Utrecht, the school of thought inherent to the laboratories of physical chemistry there has been the basis of his reasoning. He is indebted to Professor J. Th. G. Overbeek for many helpful suggestions.
Odd Electrons in Rubber Reinforcing Carbon Blacks
Authors: Kraus Gerard , Collins R. L.
Published: February 2011

The number of unpaired electrons in several rubber-reinforcing blacks has been determined by quantitative electron spin resonance assay. The odd electron concentrations are of the order of 1019 to 1020 spins/gram. These concentrations are consistent with the negative (diamagnetic) net magnetic susceptibility of the blacks. Oxygen and other paramagnetic substances, even in extremely minute quantities, exert a powerful influence on the electron spin resonance observed. Their effect is to broaden the resonance line and this reduces considerably the signal intensity. In extreme cases the intensity may be reduced to the noise level ; in less severe instances the broadening may lead to erroneously low spin assays. Carbon blacks differ in their susceptibility toward line broadening effects. Evidence is presented for a correlation between the odd electron concentration of carbon blacks and the modulus they impart to rubber, suggesting a combination reaction between the carbon black radicals and polymeric free radicals formed during processing or vulcanization. The possibility of such a reaction is supported by electron spin resonance measurements on carbon blacks heated in the presence of rubber, both with and without curatives. On the basis of the results available it is not possible to ascertain the full importance of the odd electrons of carbon black in elastomer reinforcement. It is certain that the unpaired electrons are not necessary for the development of reinforcement effects in general, although they may increase them substantially by providing an additional interaction mechanism for the union of black and rubber.
The Interaction between Carbon Black and Sulfur during Vulcanization
Authors: Blokh G. A. , Yaroshevich A. G.
Published: February 2011

The mechanism of the reinforcement of rubber by carbon black has until recently been interpreted from the physical point of view. According to the researches of P. A. Rebinder and coworkers the extent of the interaction between the filler and the rubber is given by the decrease in the free energy of the system resulting from the wetting of 1 cm2 of the surface of the filler particles by rubber. The rubber is bound to the surface of the carbon black particles through adsorption and forms around these particles an extended film which is characterized by high strength; in this state the rubber is referred to as “bound” or film-like rubber. In systems in which such adsorbed rubber is present there appears on the surface of the filler particles an effect which resembles a kind of “crystallization” of rubber which results in a strengthening of the interaction between individual chains and hence in increased strength of the rubber. According to Kusov, at optimum filling of the rubber with carbon black the mixture constitutes a continuous mass—a molecular space lattice with carbon particles situated in its nodes.
Vulcanization of Elastomers. 12. Perbunan with Thiuram Monosulfide and Sulfur. I
Authors: Scheele Walter , Toussaint Horst-Eckart
Published: February 2011

The vulcanization of Perbunan 2818 by tetramethylthiuram monsulfide plus sulfur (1 mole monosulfide per gram-atom S) was thoroughly studied. The following results were shown: The limiting value for dithiocarbamate formation is 66 mole per cent of the initial thiuram monosulfide, indicating a two-thirds transformation. The limiting value is practically independent of temperature. The formation of dithiocarbamate can be described as a reaction of the first order. The formation of dithiocarbamate is characterized by an induction period which grows longer with lowering of the temperature, and at 100° C it amounts to about 100 minutes. The rate constants for dithiocarbamate formation were calculated, and it was shown that they were practically the same as those for the vulcanization of Perbunan with tetramethylthiuram disulfide. The activation energies as derived from the temperature dependence of the rate constants for dithiocarbamate formation in the vulcanization of Perbunan by thiuram monosulfide plus sulfur on the one hand and with thiuram disulfide on the other, are only very slightly different and are practically the same as the activation energy for dithiocarbamate formation during the vulcanization of natural rubber with thiuram monosulfide plus sulfur. The results were thoroughly discussed in light of the present conceptions of the course of thiuram vulcanizations.
High-Speed Fracture in Rubber
Authors: Mason Peter
Published: February 2011

Cinematographic observations have been made of crack propagation under well-defined boundary conditions in rubbers at speeds up to 30 m/sec. The fracture-markings showed resemblances to those obtained with metals, plastics, and glass, and could be related directly to the corresponding speed of fracture-propagation. In close analogy with Schardin's observations on glass, a non-crystallizing rubber (GR-S) showed a mode of crack propagation in which the fractured surfaces were visually smooth and the speed was about one quarter of the speed of longitudinal elastic waves. A crystallizing rubber (natural rubber) did not show this mode of propagation under the present test conditions. It is suggested that the modes of solid fracture can be usefully classified in three categories: (i) slow propagation, generally with smooth surfaces, obtained by careful control of the boundary conditions; (ii) propagation at intermediate rates with rough surfaces, involving correspondingly greater energy consumption; and (iii) fast propagation with smooth surfaces, the rate of propagation being limited by the speed of elastic waves in the material in accord with Mott's theory.
The Role of Oxidation-Reduction Systems in Vulcanization with Sulfur
Authors: Tinyakova E. I. , Khrennikova E. K. , Dolgoplosk B. A. , Reĭkh V. N. , Zhuravleva T. G.
Published: February 2011

1. The reaction between trichlorothiophenol or dienols and SO2 brings about vulcanization of rubber without separation of elemental sulfur. The mechanism of the Peachey process of rubber vulcanization is examined on the basis of concepts of the role of intermediate products of the reaction—free radicals. 2. Sulfur is found to react with many vulcanization accelerators with formation of considerable amounts of hydrogen sulfide. It is shown that hydroxycarbonyl compounds, which reduce sulfur to hydrogen sulfide, play the part of accelerators of sulfur vulcanization. Thermal breakdown of hydrogen persulfide leads to vulcanization of rubber. 3. The experimental data are applied to the consideration of the mechanism of the action of accelerators of sulfur vulcanization and of the mechanism of formation of mono- and polysulfide bonds.