bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Carbon-Rubber Bond
Authors: Braendle H. A.
Published: February 2011

Dry mixing involves compacting latex into solid rubber and then tearing it down to make a place for the carbon black. Likewise it involves compacting the carbon both before and after it enters the Banbury and then tearing it apart to develop its full surface. Such operations involve the application of enormous compacting and shearing forces that do neither colloid any good. By recognizing the time element the two colloids are brought together when they both are in a dispersed phase and therefore free to act as colloids; and by taking advantage of the time rate of this reaction the process effects the best spatial distribution of black in rubber so far attained. Nothing is added to interfere with the normal affinity of these two colloids. A better distributed and stronger bond results, as is evidenced by substantially enhanced road wear in tires made from such rubber.
Factors Affecting Laboratory Cut-Growth Resistance of Cold SBR Tread Stocks
Authors: Auer E. E. , Doak K. W. , Schaffner I. J.
Published: February 2011

By using an existing cut-growth test in a new way it has been possible not only to increase the reproducibility of the results, but also to show important relations between cut-growth resistance and modulus, or the elongation at break of cold SBR tread stocks. The logarithm of the cut-growth resistance of cold SBR vulcanizates as measured on a modified De Mattia machine, is shown to be a linear function of the 300 per cent modulus, except for certain undercured stocks. The slope of the curve is dependent on the type and the amount of black, but is relatively independent of the type of curing system, amount of antioxidant, and time of Geer aging. An equation has been found which relates cut-growth resistance at 150° F with the elongation at break of the vulcanizate. Except for stocks having black loadings in excess of about 55 phr and having in addition modulus values less than 800 psi, this relation appears to be nearly independent of black loading, type of black, curing system, time or temperature of cure, antioxidant concentration, and extent of Geer aging. The elongation at break of an SBR tread stock thus appears to be a primary factor governing its groove-cracking behavior. The relation between cut-growth resistance and modulus is of secondary significance and evidently depends upon the interrelation between the modulus and breaking elongation of these formulations. The breaking elongation, however, cannot be the sole factor governing the groove-cracking behavior; otherwise there would be no restrictions on the validity of the breaking elongation equation.
Mechanical Properties of Natural and Synthetic Rubbers
Authors: Bueche F.
Published: February 2011

It is felt that the reason for the large heat generation in SBR under flexure is now reasonably well understood. According to the present view, it is the result of the fact that Mn is too low in SBR thereby making it impossible to form a satisfactory network within the polymer. When the molecular weight is increased, as is done with SBR used in oil extended polymers, a more suitable network is formed in the rubber during vulcanization and as a result this rubber shows less heat development. Addition of carbon black to the rubber tends to increase the stability of the vulcanization network. Whether this is a result of the purely mechanical effects of solid particles imbedded in the existing network or whether the black actually enters into the network structure through chemical bonding is still not clear. In any event, it serves the function of retarding the creep of the polymer at long times. The fact that the addition of black increases the generation of heat for the same amplitude of deformation is probably the result of the necessary increase in Fmax needed to attain this deformation as predicted by Equation (1). The black's important function in regard to strength properties was discussed briefly in a previous report from this laboratory and will be investigated more in the future. It should be pointed out that many of the observations and conclusions presented here have previously been presented by others although it is believed that now they will appear more logical and conclusive. Obviously it is impossible to mention all the pertinent work carried out in this field which has led others to conclusions similar to those presented here. Omission of such references was made necessary by the mere fact of their great number.
Contributions to the Mechanism of Devulcanization II
Authors: Stafford W. E. , Allcroft J. B. , Sargent D. T.
Published: February 2011

Certain aspects of the reclamation of natural, butyl, and GR-S rubbers have been considered. While there are specific characteristic changes in all cases, e.g., zinc sulfide formation, etc., at the same time, important differences are recorded. The relation between some physical characteristics of cured reclaims and their parent vulcanizates have been discussed. The wide differences in the quality of reclaims, dependent upon the nature of the vulcanizing system employed in the parent vulcanizate, are interpreted as being substantially in agreement with previously published work, which has demonstrated the importance of curing mechanism upon reclaiming susceptibility.
Ski Rubber, Polyisoprene, Similar to Natural Rubber
Authors: Anikanova K. F. , Betts G. E. , Zhakova V. G. , Komskaya N. F. , Karmin B. K. , Priss L. S. , Reznikovskiy M. M. , Chernikina L. A. , Sheteyn E. B.
Published: February 2011

Years of research at the S. V. Lebedev All-Union Scientific Research Institute for Synthetic Rubber have provided industry with a number of methods for making synthetic rubber from isoprene. Of all the known synthetic rubbers this comes closest to natural rubber in structure and properties; it is the best available substitute of natural rubber, possessing a high degree of elasticity and strength. The present article is a brief summary of the basic work on isoprene rubber done by the Scientific Research Institute of the Tire Industry. On the basis of this work recommendations were made for the development of the production of synthetic isoprene rubber and the substitution of isoprene rubber for natural rubber in the manufacture of heavy duty truck tires. By using different polymerization processes it is possible to produce isoprene rubbers whose chain structures are very similar, but whose molecular weights, and therefore physical and technological properties, are very different. The cis structure of the 1,4 polyisoprene chains is the basic structural element of the new isoprene polymer. Therefore these synthetic isoprene rubbers (SKI) obtained through catalytic polymerization when vulcanized show a crystalline structure when x-rayed in the stretched state. The x-ray photographs also show that the geometric distribution of interference spots in SKI rubbers corresponds to the distribution of interference spots in natural rubber, but that the relative intensities of the crystalline, liquid, and amorphous scatterings in the two rubbers are different (Figure 1).
Ozonolytic Degradation of Interpolymers of Natural Rubber with Methyl Methacrylate and Styrene
Authors: Barnard D.
Published: February 2011

The preparation of graft and block interpolymers of natural rubber and synthetic polymers has made it desirable that the number and size of polymer chains attached to rubber be readily determinate. The degradation of unsaturated polymers with tert-butyl hydroperoxide in the presence of osmium tet oxide has been used for the determination of free polystyrene in SBR and carbon black in several elastomers, and has recently been applied to the present problem. The accurate determination of the rubber content of interpolymers by quantitative ozonolysis essentially according to the method of Boer and Kooyman suggested that this might be made the basis of isolation of the attached polymer, the rubber being degraded into fragments of low molecular weight, from which the polymer could be separated by conventional techniques. The method should be applicable to any interpolymer, or mixture, of a polyunsaturated and a saturated polymer and is illustrated with reference to interpolymers of natural rubber (NR)-polymethyl methacrylate (PMM) and NR-polystyrene (PS).
Vulcanization of Elastomers XV. The Vulcanization of Natural and Synthetic Rubber with Sulfur in Presence of Organic Bases (I)
Authors: Schelle Walter , Cherubim Martin
Published: February 2011

The results obtained from preliminary kinetic studies of the vulcanization of natural rubber (NR) with sulfur in the presence of organic bases may be summarized as follows. 1) The change of concentration of sulfur with time during reaction with NR for an initial sulfur concentration of 2.5 g per 100 g of mixture follows a fractional reaction order, n, of 0.6 at all temperatures. This result and the findings of other authors suggest that the reaction of sulfur with rubber is autocatalytic. From the temperature dependence of the rate constant the activation energy is found to be 35.3 kcal. 2) In the presence of zinc oxide and with a similar initial sulfur concentration, the reaction is first order and the activation energy, namely 35.6 kcal, is practically the same. 3) In the presence of diphenylguanidine (DPG) during cure sulfur decrease is a reaction of fractional order, n=0.75, and the activation energy is 29.8 kcal. 4) For a given initial concentration of sulfur and at constant temperature the rate of sulfur decrease during vulcanization increases with rising DPG content and reaches a limiting value; i.e., the rate constant depends on DPG concentration. Also, for various base (DPG is basic) concentrations sulfur decrease is of various fractional orders, n=0.5…0.7, etc. 5) The influence of base on the rate of sulfur decrease is interpreted broadly as a case of intermediate-catalysis (Zwischenstoff-Katalyse). 6) Vulcanization with sulfur is unaffected by tertiary amines and secondary amines have only a slight effect. 7) Primary amines, depending on basic strength, are strong accelerators of the rate of sulfur decrease. 8) In the presence of organic bases (aromatic amines) other than DPG, sulfur decrease is of fractional order where n varies between 0.5 and 0.7.
Mechanism of Mill Breakdown and Vulcanization in the Presence of 2-Mercaptobenzothiazole
Authors: Dogadkin B. A. , Tutorskiĭ I. A. , Pevzner D. M.
Published: February 2011

The mechanism of the action of 2-mercaptobenzothiazole, MBT, one of the most commonly employed accelerators of vulcanization, remains unclear. L. Wistinghausen and B. A. Dogadkin and D. M. Pevzner (1951, unpublished) showed that MBT is consumed in vulcanization, but these authors, because of the crudity of their methods, did not obtain quantitative relationships. In the present work there has been employed a preparation of the MBT which was tagged in the thiazole ring by the radioisotope S35. The synthesis of this compound was carried out in the following manner. MBT, tagged in both of its sulfur atoms, was first synthesized from phenyl isothiocyanate and elementary S35. The resulting MBT was then heated in a sealed ampule with an excess of inactive elementary sulfur for six hours at a temperature of 140°. Under these conditions the exchange reaction between the elementary sulfur and the sulfur of the mercapto group of the MBT reaches equilibrium. The activity of the resulting MBT fell to one-half of the original value. In this way the benzothiazole radical was tagged, by the introduction into the molecule of MBT of the radio-isotope S35 which does not exchange with elementary sulfur, under the conditions of vulcanization, and it thus became possible to measure simultaneously the velocity of the addition of the sulfur and the velocity of addition of the accelerator to the rubber.
Bound—Rubber Formation in Diene Polymer Stocks
Authors: Stickney P. B. , McSweeney E. E. , Mueller W. J. , Palinchak S. T.
Published: February 2011

The phenomenon of insolubilization of rubber by carbon black has been known for at least twenty-seven years. There have been many attempts during this time to establish a relationship between insolubilization, or bound rubber formation, and reinforcement of rubber by carbon black. It was postulated, as far back as 1925, that there was a parallelism between particle size and insolubilization. This in spite of the fact that the methods available for determining particle size of very fine powders at that time were relatively crude. It was postulated at that time that there was a close relationship between the phenomena of vulcanization and reinforcement. This concept has had recurrent periods of popularity since that time. The insolubilization of rubber by carbon black, or other pigments, has been estimated by various techniques by the early investigators in the field. In more recent work, the trend has been toward a very straightforward experimental approach. Bound rubber in an uncured rubber-filler compound is usually determined by static extraction using the same apparatus and techniques used in determining the gel content of unfilled polymers. It follows that, using this method, polymer insoluble because of crosslinking, or gel, cannot be distinguished from polymer insolubilized by incorporation of fine fillers. In investigating the formation of bound rubber, therefore, the presence of gel in the polymer being used, or formation of polymer gel during processing must be taken into account.
Aeration of Natural Rubber Latex. I. Effect of Polyamines on the Hardness and Aging Characteristics of Aerated Latex Rubber
Authors: Sekhar B. C.
Published: February 2011

Evidence has been presented to support the hypothesis that the absorption of oxygen by ammoniated latex at room temperatures creates reactive groups on the rubber hydrocarbon. These reactive groups impart to the rubber peroxidic properties. Such peroxidic group formation is responsible for the breakdown and build up of rubber under different conditions of storage. Suitable reducing systems, particularly the alkylene polyamines crosslink rubber in latex and enhance the aging properties of rubber.
Monolayer Studies of Some Hydroxylated Polyolefin Rubbers
Authors: Dean W. R. , Perera V. , Glazer J.
Published: February 2011

The study of high polymer monolayers by the Langmuir balance technique has been almost wholly restricted to those polymers which contain polar groups, e.g., cellulose, proteins, polyacrylates, etc. Nonpolar polymers do not spread and so little attention has been paid to the hydrocarbon rubbers. Wall and Zelikoff have reported that natural rubber, gutta-percha, and butadienestyrene copolymers do not form stable monolayers on water, but that when these materials are modified chemically by thiocyanogen they form relatively thin films of varying thickness. Sivaramakrishnan and Rao have recently confirmed that natural rubber does not form a monolayer on water. However, they find that it spreads spontaneously on a subsolution of aqueous acidic potassium permanganate. We have investigated the surface reaction between certain polyolefins and aqueous permanganate ; the kinetic features of these reactions, discussed elsewhere, suggest that definite chemical end-products are formed on the surface. The purpose of this communication is to characterize the end-products obtained from natural rubber (cis-1,4-polyisoprene), gutta-percha (trans-1,4-polyisoprene), polybutadiene, and two butadiene-styrene copolymers of differing styrene content, when these react under controlled conditions at the surface of an acidic aqueous permanganate subsolution.
Thermodynamics of Shrinkage of Fibrous (Racked) Rubber
Authors: Oth J. F. M. , Flory P. J.
Published: February 2011

Highly oriented natural rubber samples of Roberts and Mandelkern, prepared by racking and subsequently crosslinked using γ-radiation, undergo a spontaneous shrinkage upon melting which closely resembles the shrinkage of collagen. If the transformation is arrested by application of a tensile force, a state of equilibrium may be established between two distinct zones, or phases, one being totally amorphous (shrunken) and the other unchanged (i.e., racked). Determination of the stress τeq required for phase equilibrium at various temperatures is described. Extrapolation to τeq=0 gives equilibrium melting temperatures Tmi, which are about 8° below the temperatures Tsi for spontaneous shrinkage. The heat of transformation of racked to amorphous rubber calculated from the dependence of τeq on T is 4.5 cal g−1. Since the degree of crystallinity is only 0.24, the heat of fusion calculated for 1 g of crystalline rubber is ca. 19 cal, which agrees satisfactorily with the value 15.3 cal, deduced by Roberts and Mandelkern through use of the melting point depression method. The shrinkage of racked rubber displays all of the important features associated with the similar contraction of fibrous proteins.
Changes in the Specific Volume of Rubber during Elongation
Authors: Kusov A. B. , Trofimova V. I. , Nilova Yu I.
Published: February 2011

1. It was shown that an increase in volume under strain, which reaches 2% at the maximum elongations, is observed in both loaded and unloaded stocks based on different rubbers. 2. The curves of specific volume versus elongation are characteristically S-shaped in the general case, and the inflection points of these curves correspond to the same elongations as do the inflection points in the curves of stress versus elongation. 3. Natural rubber stocks show a drop in volume, related to the crystallization of the rubber, until a certain elongation is reached ; the higher the state of cure, the higher this elongation.
The Role of Metal Oxides as Activators of Vulcanization
Authors: Feldstein M. , Orlovsky P. , Dogadkin B.
Published: February 2011

1. The activation effect of metal oxides on the process of culvanization of nonpigmented compounds of rod polymerized sodium butadiene rubber differs from the effect in rodless polymerized rubber. In the latter case zinc oxide not only is not an activator but it retards the vulcanization process. 2. The role of activators depends, to a large degree, on the type of vulcanization accelerator and active filler used. 3. Metal oxides increase the amount of structure formation in the vulcanizate. 4. With regard to butadiene styrene rubber (SKS-30A), calcium hydroxide appears to have stronger activating effect on vulcanization than zinc oxide. 5. The special effectiveness of calcium hydroxide in compounds of butadiene styrene rubber is a result of its independent structure forming ability and accelerating influence on the reaction between rubber and sulfur. 6. Magnesium oxide has a positive influence on the technical properties of rubber and on the durability of tires prepared with butadiene styrene and sodium butadiene rubbers.
Vulcanization of Elastomers. 14. Role of the Oxide in Vulcanization with Compounds of the Thiuram Series. I
Authors: Scheele Walter , Toussaint Horst-Eckart , Stange Peter
Published: February 2011

The present paper is concerned with the influence of TETD concentration and of zinc oxide content upon the kinetics of the vulcanization of natural rubber and Perbunan 2818 with TETD. The following results were obtained for vulcanization at 120° C. 1. The velocity constants of TETD decrease and ZnDEDC formation are linear functions of the zinc oxide content at constant TETD concentrations. 2. If TETD and zinc oxide are present in constant molar mixing ratios, then the velocity constant of TETD decrease is independent of the amount of the mixture while that of ZnDEDC formation rises linearly with zinc oxide addition. 3. The velocity constant of TETD decrease diminishes with increasing TETD concentration when the zinc oxide content of the mixture is held constant. Under these conditions the velocity constant of ZnDEDC formation remains unchanged. 4. Everything shows that the velocity constant of ZnDEDC formation depends only on the zinc oxide content of the mixture while that of TETD decrease is dependent on the molar ratio of zinc oxide and TETD. 5. The relationships found are expressed mathematically, and the practical significance of the relationships is pointed out.
The Chemical Structure of the “Popcorn” Polymer of Butadiene
Authors: Yakubchik A. I. , Spasskova A. I.
Published: February 2011

1. The chemical structure of spongy butadiene polymer, obtained at 15–20° was examined by the ozonolysis method. 2. The per cent of chains with external double bonds in the spongy polymer was found to be 22.8%. 3. The spongy polymer of butadiene is composed, like the rubbery polymers, of chains with external and internal double bonds. 4. It was established that parts of the molecule of spongy polymer have the same structure as the rubbery butadiene polymers: -1,4-1,4-; -1,4-1,2-1,4-; -1,4-1,2-1,2-1,4-. 5. A chloroform-soluble rubberlike polymer was separated from the butadiene autopolymer. The degree of unsaturation of the chloroform-soluble polymer was determined (86.7%), also the relative content of internal and external double bonds.
Organic Sulfides and Polysulfides. IV. Reactions with Doctor Solution, Silver Nitrate, Cupric Acetate and Lead Acetate
Authors: Minoura Yuji
Published: February 2011

1. In mixtures of doctor solution and benzyl and p-tolyl sulfides, di-, tri- and tetrasulfide reacted and formed lead sulfide, but monosulfide did not react. 2. In the case of thiodiglycolic acid and dithiodiglycolic acid, dithiodiglycolic acid gave lead sulfide. 3. Sulfur gave lead sulfide by reaction with doctor solution. 4. Mercaptide formed by the reaction between silver nitrate and mercaptan. Mono- and disulfide of the benzyl and tolyl series gave no reaction. Tri- and tetrasulfide showed desulfurization, and gave disulfide. Dithiodiglycolic acid reacted with silver nitrate and gave silver sulfide. 5. Lead acetate and cupric acetate reacted readily with mercaptan. Mono-, di-, tri- and tetrasulfides of the benzyl and tolyl series gave no reaction even on heating. 6. Mercaptan was most reactive in the reactions with doctor solution and with silver nitrate. The more sulfur the organic polysulfide contained, the more reactive it was. The relative order of reactivity in these series were : glycolic acid > benzyl > tolyl.
Tire Abrasion at Different Temperatures
Authors: van Amerongen G. J. , Benders J. F. , de Decker H. C. J.
Published: February 2011

The relative abrasion resistance of tire treads of various types was determined by relatively short but statistically reliable standard tests, with automobiles driven on streets. It has been found earlier that this relative abrasion resistance is a function of the ambient air temperature, and that at medium and lower temperatures, natural rubber treads show better resistance to abrasion than do treads made of SBR. In the present work, it is shown that it is possible to establish the absolute abrasion of a tire and also its dependence on temperature. It appears that the dependence on temperature of the abrasion for SBR is markedly less than for natural rubber. Different carbon blacks show different degrees of dependence on temperature for the abrasion of the compounds. This temperature dependence of abrasion can be reduced for natural rubber by oil extension.
Infrared Study of Some Structural Changes in Natural Rubber during Vulcanization
Authors: Linnig Frederic J. , Stewart James E.
Published: February 2011

A knowledge of the structure of vulcanized rubber is essential to the interpretation of vulcanization and oxidation studies and the physical properties of the material. In the present work an infrared study has been made of structures resulting from a number of different methods of vulcanization. Sulfur vulcanizates show the presence of a shifted double bond, originally observed by Sheppard and Sutherland. The presence of conjugated double bonds is also indicated. Accelerators such as tetramethylthiuram disulfide and zinc dibutyl dithiocarbamate increase the rate of the double-bond shift and reduce the amount of conjugated double bonds. Neither the double-bond shift nor conjugation is observed as a result of vulcanization with tetramethylthiuram disulfide alone, hydrogen sulfide and sulfur dioxide (Peachey process), a peroxide, or gamma rays. These result in a possible decrease in carbonyl structures, and in the case of the last three, possible increased absorption due to OH and ionized carboxyl groups. Apparently, the double-bond shift and conjugation are primarily phenomena related to the use of elemental sulfur. The other vulcanization systems studied evidently involve different mechanisms. An implication of the present work is that there may be a relationship between the reported ease of oxidation of sulfur vulcanizates, accelerated vulcanizates, and sulfurless vulcanizates (tetramethylthiuram disulfide alone), which decreases in the order named, and the probable amount of conjugation in the compound, which decreases in the same order.
Changes in Polysulfide Chain Length in Sulfur Structures of Vulcanizates by Light
Authors: Postovskaya A. F. , Salimov M. A. , Kuzminskiĭ A. S.
Published: February 2011

In previous work we showed that sulfur vulcanizates of polybutadiene rubber (polysulfide and thiuram vulcanizates), which differ in their type of crosslinks, also differ in their stability to light. The best light stability is shown by a polysulfide vulcanizate. The action of ultraviolet light in this case is accompanied by decomposition of sulfur bonds with the formation of a type of free sulfur which, in contrast to elemental sulfur, does not take part in photovulcanization processes, i.e., remains “inactive”. Just what the nature of this inactive sulfur is, and the change in length of the polysulfide chains in the sulfur structures of the above-mentioned vulcanizates under the action of light, had not yet been established. Hence it was impossible to give a well-defined answer to the highly important question of why a polysulfide vulcanizate has greater stability to light than a thiuram vulcanizate. The present work is devoted to a study of this question. Although the study of the types of sulfur bonds in vulcanizates is of considerable importance, no reliable methods for their determination are given in the literature. Ascertaining the nature of the bonds in a vulcanizate by chemical methods involves great difficulties because of the impossibility of separating out the sulfur structures with different polysulfide chain lengths, as well as identical sulfur structures combined with the polymer in varying forms.
The Effect of Swelling on the Strength of Vulcanizates
Authors: Dogadkin B. A. , Fedyukin D. L. , Gul V. E.
Published: February 2011

1. It is shown that, in addition to the previously described steady decrease of tensile strength of vulcanizates during swelling, there are cases in which the strength passes through a maximum at low degrees of swelling. 2. Variations of a similar character during swelling are also found for the relative elongation of vulcanizates. 3. Such variations of tensile strength and relative elongation are found when the increase of chain flexibility and the associated increased orientation effect is greater than the effect of weakened intermolecular bonding in the polymer caused by penetration of the solvent molecules into the polymer. 4. A strength maximum may also be found if the swelling agent (softener) is introduced into the rubber composition on rolls before vulcanization.
The Chemistry of Vulcanization. IV. Action of 2-Mercaptobenzothiazole on the Reaction of Diphenylmethane and Sulfur
Authors: Tsurugi Jitsuo , Nakabayashi Takeshige
Published: February 2011

In Part I of this series, the mechanism of the reaction of diphenylmethane (DPM) and sulfur was discussed, and in Part II, a kinetic investigation was carried out. In this paper, the mechanism and kinetics of the reaction involving DPM, sulfur and 2-mercaptobenzothiazole (MBT) will be reported and compared with those of Parts I and II, respectively. Thus the accelerating effect of MBT has been elucidated clearly. DPM which has no olefinic double bonds but which has α-methylenic hydrogen adjacent to aromatic double bonds has been shown to be an excellent model for studying the mechanism of acceleration by the methods of organic chemistry. The significance of DPM as a model of rubber hydrocarbon in the presence of sulfur alone was discussed in Part I. British investigators using olefins such as dihydromyrcene and squalene as models studied the mechanism of acceleration. However, they could not deduce the mechanism so clearly as we in this paper, only because the reaction of olefins with sulfur seemed to be more complex than that of DPM. Investigations on the reaction of DPM, sulfur and accelerators in the presence of either zinc oxide or zinc soap will be reported in other papers of this series.
CIS-1,4 Polyisoprene Prepared with Alkyl Aluminum and Titanium Tetrachloride
Authors: Adams H. E. , Stearns R. S. , Smith W. A. , Binder J. L.
Published: February 2011

By adjustment of the relative amounts of the two components of the catalyst and the temperature of polymerization, cis-1,4 polyisoprene can be produced free from trans-1,4 configuration. Catalysts containing a mole ratio of alkyl aluminum to titanium tetrachloride of 1.0 produce polymers with this configuration at room temperature. At lower temperature of polymerization, somewhat higher ratios are needed to achieve the same result. Solution polymerization was used to control the reaction and obtain a uniform product. It was necessary to use 3 to 5 phm of total catalyst to obtain 100 per cent yield in 4 hours at room temperature. The inherent viscosity of the polymers made under these conditions is low, usually 2.0 to 2.5. However, higher molecular weight polymers are produced at lower polymerization temperature. Compounding studies indicate that vulcanizates of these polymers possess both normal and hot tensile properties comparable to natural rubber. Hysteretic properties of the carbon black vulcanizates of the polymers studied are inferior to those of natural rubber.
Perdeuterio SN Rubber
Authors: Semon W. L. , Craig David , Fowler R. B. , Regenass F. A. , Tucker Harold , Yanko John A. , Shipman J. J. , Belt R. F.
Published: February 2011

The recently reported stereospecific polymerization of isoprene and the availability of D2O has made possible the preparation of synthetic-natural (SN) rubber in which most of the hydrogen atoms are D atoms. Acetone-d6 was prepared from 99.5 per cent D2O and acetone-h6 in the presence of K2CO3. Nine stages were applied. Each required fractionation of acetone from water, and it is estimated that each replaced approximately half of the light hydrogen remaining from the previous stage. Acetylene-d2 was prepared from D2O and calcium carbide. The procedure of Bergmann for the Favorskii˘ reaction of acetylene and acetone to form 2-methyl-3-butyn-2-ol was followed except that in our work perdeuterio reactants were used. The triple bond of the butynol selectively absorbed D2 over the Lindlar catalyst, and the resulting 2-methyl-3-buten-2-ol dehydrated readily over Al2O3 to give isoprene-d8. Standard fractionation techniques were used for the isoprene and for all the intermediates. The isoprene was finally distilled over sodium to remove acetylenes, acetone, and alcohols. The same methods were applied to the corresponding perprotio derivatives. Table I gives the properties of most of the compounds prepared and used in this study.
Ozone Resistance of Natural Rubber Vulcanizates. Part I. Apparatus for Exposure at Low Ozone Concentration
Authors: van Pul B. I. C. F.
Published: February 2011

An apparatus is described for evaluating the cracking resistance of rubber specimens exposed under static or dynamic conditions to ozone concentrations between 5 and 50×10−8 ml/ml of air. Ozone concentration is kept constant automatically however much is destroyed at the walls of the cabinet or at the surfaces of the rubber testpieces. Temperature can be regulated between 20° and 100° C.
Ozone Resistance of Natural Rubber Vulcanizates. Part II. Influence of Fillers and Waxes
Authors: van Pul B. I. C. F.
Published: February 2011

Commerical waxes whose melting points, refractive indexes and numbers of side chains are within the ranges described seem likely to give good ozone protection under static conditions. All waxes lead to worse cracking under dynamic conditions than if none had been included and it is clearly better to use no wax if the rubber is likely to be submitted to intermittent stretching.
Ozone Resistance of Natural Rubber Vulcanizates. Part III. Influence of Accelerators and Antioxidants
Authors: van Pul B. I. C. F.
Published: February 2011

An investigation of the ozone protection given to natural rubber vulcanizates by different accelerators and antioxidants has shown that, of the accelerators investigated, the thiuram derivatives appear to be the best antioxidants, when they are used as vulcanizing agents; of the large number of antioxidants examined. NN′-di-sec-octyl p-phenylene diamine appears to be the best antiozonant. Vulcanizates containing this material showed no cracks after being exposed for 400 hours to an ozone concentration of 25×10−8 ml/ml under static conditions; it was far superior to all other materials examined.
Speed of Mixing Rubber as a Factor in Processing
Authors: Priklonskaya N. V.
Published: February 2011

1. The work conducted confirms the expediency of using fast mixing methods for synthetic rubbers. 2. It is shown that future improvement may be obtained by using one step loading of all ingredients in the mixer, combined with greater pressure on the mixture and faster rotor speed. 3. We recommend the wide introduction, in production, of the two stage mixing process with increased rotor speed in the first stage. 4. In a factory producing two million tires a year, this decreases the investment by 7.5 million rubles and cuts operating expenses by 2 million rubles per year.
Surface Heating by Friction and Abrasion by Thermal Decomposition
Authors: Viehmann W.
Published: February 2011

In this research, an attempt is made at determining the frictional temperatures which may occur in tires under various driving conditions. This is based on phenomenological theories of heat conduction. Since these temperature pulses are to be traced back to heat current pulses which may last in the neighborhood of 10−2 second, the resulting warming will be localized in boundary layers of the order of 10−2 cm. From the estimated values of the temperatures, it is concluded that the abrasion which occurs under normal driving conditions is purely mechanical. Only under extreme conditions, such as in very rapid acceleration, or in case of locked wheels—particularly at what we call “contact bridges” or surface elevations—may we expect high frictional temperatures, which lie far above the decomposition temperature of rubber.
The Organic Nature of Carbon Black Surfaces
Authors: Hallum Jules V. , Drushel Harry V.
Published: February 2011

Evidence is presented for the existence of quinone groups and aromatic hydroxyl groups on the surface of carbon black particles. This evidence is based largely upon polarographic analyses of slurries of carbon blacks. A mechanism for the chemical interaction of carbon blacks with elastomers is proposed on the basis of these functional groups.
Analysis of Accelerators and Antioxidants
Authors: Parker C. A.
Published: February 2011

For many years the identification of accelerators and antioxidants in vulcanized rubbers was attempted by the application of color reactions directly to the solvent extract of the rubber. Unfortunately very few of the reactions were specific for one compound and they were frequently masked by other colored compounds in the extract. The problem is, of course, complicated by the fact that the compounds appearing in the solvent extract from the vulcanized rubber are not necessarily those which are added to the original mix. The accelerators in particular are liable to undergo considerable decomposition during vulcanization. At first sight the ultraviolet absorption spectrum of the extract might be expected to give the necessary information. The ultraviolet absorption spectra of some of the compounds are reasonably characteristic (Figure 1) but in the extract from the rubber the ultraviolet absorption from the other ingredients (e.g., pine tar) is nearly always sufficient to mask that due to the accelerator or antioxidant. It is usually not possible even to identify the presence of a particular compound, let alone determine its concentration. A selective method of separation of these compounds must be applied before the ultraviolet absorption method can be used. Direct identification is however possible in some cases by other methods. For example recent work has shown that certain constituents of a rubber extract can be identified and quantitatively determined by spectrofluorimetry without separation from the other constituents. This very useful technique is of course only applicable to those constituents which fluoresce.
The Use of Radioactive Sulfur in Vulcanization
Authors: Blokh G. A.
Published: February 2011

One of the newest and most promising physical-chemical methods consists of the use of radioactive tracer atoms, particularly in such varying fields of knowledge as research, industry, agriculture, etc. It should not be surprising therefore that these methods are favored in the study of rubber, especially in connection with the very complex vulcanization process. The use of the isotope method introduces new, realistic prospects to the experimental study of vulcanization. These include the interaction of sulfur-containing chemicals, such as accelerators, in mixtures subjected to vulcanization. A study of the interaction of accelerators with vulcanizing agents, based on isotopic exchange, makes possible a determination of the mobility of sulfur atoms at carbon-sulfur bonds and other bonds of organic substances. By the isotope method it is possible to observe the movements of sulfur tracer atoms and of tagged sulfur compounds in the complex and manifold curing process. The mobility of sulfur in various combinations with carbon is directly related to accelerator structure and activity and, consequently, to the synthesis of new accelerator types. It is very important to clarify the question as to whether the mobility of sulfur atoms and the intensity of the isotope exchange can serve as a criterion for accelerated activity in curing. Tracer atoms can be used extensively to solve many technological problems in the rubber industry. This review deals with scientific studies made in the field of tagged sulfur vulcanization.
The Reaction of Sulfur and Sulfur Compounds with Olefinic Substances. Part X. The Kinetics of the Reaction of Sulfur with Cyclohexene and Other Olefins
Authors: Ross G. W.
Published: February 2011

As stated in Part VIII, the kinetic studies now reported are complementary to product studies described in Parts VIII and IX in a program of work aimed at elucidating the mechanism of sulfur-olefin interaction at about 140°. Attention has been given mainly to the reaction of sulfur with cyclohexene, because the latter is a relatively good solvent for sulfur, but reactions with 1-methylcyclohexene, oct-1-ene, hept-2-ene, 2-methylpent-2-ene, 2,6-dimethyloct-2-ene, and the 1,5-diene, 2,6-dimethylocta-2,6-diene, have also been examined. The rate of reaction increases until about 20% of the sulfur has reacted and then continues at an almost steady value until nearly all the sulfur is consumed. Further reaction between the product and excess of olefin proceeds at a diminishing rate. Kinetic analysis has been confined mainly to the period of accelerating rate (ra), and the information obtained appears to justify this procedure rather than considering the steady maximum rate (rm).
The Reaction of Sulfur and Sulfur Compounds with Olefinic Substances. Part XI. The Mechanism of Interaction of Sulfur with Mono-Olefins and 1,5-Dienes
Authors: Bateman L. , Moore C. G. , Porter M.
Published: February 2011

Believing an alkenyl alkyl polysulfide to be the major product of sulfurmono-olefin interaction at about 140° and the main constituent of the cyclic monosulfide fraction likewise obtained from 2,6-dimethylocta-2,6-diene to bo the thiacyclohex-3-ene (II), Farmer and his coworkers1 advanced the following free-radical chain mechanism for olefinic sulfuration: (see PDF for diagram) In the special case where the sulfurated radical formed in (2) contains one sulfur atom, alternative reactions to (3) and (4) were proposed, viz., capture of a hydrogen atom, followed by polar or radical addition of the alkenethiol to a second double bond, and this was regarded as the main route to the cyclic monosulfides from 1,5-dienes:
The Elasticity of Rubber
Authors: Wood Lawrence A.
Published: February 2011

Rubbers, natural and synthetic, are unique in being highly extensible and in retracting forcibly and quickly to substantially their original dimensions when released. It has been found that the stress-strain curves for extension and compression of most of the simplest vulcanizates of natural rubber and the three most important synthetic rubbers are similar in shape. The relationship is expressed by the equation F/M=(L−1−L−2) exp A(L−L−1) where F is the stress, L the ratio of stretched to unstretched length, and M and A are constants. The constant M depends on the nature of the rubber, the extent of vulcanization, and the time of creep. The constant A has a value of about 0.38. By a study of stress-temperature relations it is found that the most important factor in the retraction of stretched rubber is the tendency of long chain flexible molecules to return to a configuration which is statistically more probable than the one which the stretching has forced them to assume. Calculations of entropy changes arising from stretching can be made from probability considerations, and a strain energy function deduced from the entropy changes. Stresses calculated from the strain energy function agree with those observed in compression but are greater than those observed in extension by almost 50 per cent at L=3. A phenomenological approach shows that the strain energy should be expressible as a function of certain quantities called strain invariants, calculable from the deformations. The simplest behavior is found in the region of compression (L less than 1), where the strain energy is merely the first invariant times a constant calculable from the entropy changes. For values of L between 1.5 and 3 a different constant and an added term involving the second strain invariant are required. The explanation of this behavior in molecular terms is one of the most important current problems of rubber elasticity.
Friction and Abrasion of Rubber
Authors: Schallamach A.
Published: February 2011

Experimental evidence is adduced for the view that rubber friction is similar in character to viscous flow and therefore, in contrast to solid friction, not necessarily accompanied by abrasion. This theory implies that the forces of rubber friction are proportional to the true area of contact. The true area of contact is determined by elastic deformation of the asperities on the rubber surface, with the result that Amontons' law is not obeyed by rubber. The laws of rubber friction are deduced from simple models and satisfactorily confirmed by experiment. Abrasion of rubber is due to mechanical failure under the tractive stresses produced frictionally by the asperities of the track. In this process, certain periodic structures are often created on abraded rubber which have been called “Abrasion Patterns”. Abrasion patterns are found to increase the rate of abrasion; a distinction is therefore made between “Intrinsic Abrasion”, occurring in the absence of patterns, and “Pattern Abrasion”. Both types of abrasion are treated theoretically, and qualitative agreement with the experimental results is obtained. The phenomenon of pattern abrasion has the important consequence that the relative abrasion rating of any two compounds can depend pronouncedly on the conditions of the test.
The Vulcanization of Elastomers. 20. Sulfur Vulcanization Accelerated with Thiuram Compounds. I
Authors: Scheele Walter , Franck Adolf
Published: February 2011

The present paper deals with the results of an orientating, quantitative investigation of sulfur vulcanization accelerated by thiuram disulfide, with tetramethylthiuram disulfide as the representative example. It was found: In the sulfur cure of natural rubber with tetramethylthiuram disulfide at different TMTD:S ratios, the rates of TMTD decrease and dithiocarbamate formation increase with increasing sulfur concentration, the TMTD content being kept constant. The rates practically do not change any further when the compounds contain 6 gram atoms of sulfur per mole of thiuram disulfide. The peak value of dithiocarbamate formation increases with the increase of sulfur concentration and reaches a constant end value of about 90 mole per cent based on the amount of original thiuram disulfide, when the stocks contain 4 gram atoms of sulfur per mole thiuram disulfide. This end value is identical to the end value of dithiocarbamate formation in the reaction of thiuram disulfide with zinc oxide (in the absence of rubber). The crosslinking, as measured by the change of reciprocal equilibrium swelling per time unit is also a reaction whose rate increases with the sulfur concentration to the point where the compounds contain 6 gram atoms of sulfur per mole of thiuram disulfide. The optimum degrees of crosslinking are roughly proportional to the sulfur concentration; at high sulfur levels the vulcanizates tend to revert. As in the pure TMTD vulcanization, the TMTD decrease as well as the dithiocarbamate formation are always first order reactions. The reversion at higher sulfur levels as well as the complicated course of the increase of combined sulfur during vulcanization render all but impossible an accurate determination of the reaction order for the crosslinking at higher sulfur levels. Nevertheless, in vulcanizations with 1 mole TMTD per 1 or 2 gram atoms of sulfur the crosslinking is a first order reaction.
Stress-Strain Relation of Pure-Gum Rubber Vulcanizates in Compression and Tension
Authors: Wood Lawrence A.
Published: February 2011

The empirical function of Martin, Roth, and Stiehler represented by Eq. (1) where A has the value of 0.38 may be regarded as an adequate representation of the available experimental data covering both the compression and tension of pure-gum vulcanizates. The stress and strain are to be measured after a constant time of creep. The approximate validity extends over the range 0.5<L<3.5. The success of the single empirical function in representing data obtained in both compression and tension over a range as great as this is regarded as very significant. In the range of values of L from 0.5 to 1.0 (compression) the empirical function gives results in agreement with the predictions of the statistical theory of rubber elasticity. After representing the stress and strain in a transition region extending from L=1.0 to 1.5, the empirical function gives approximately constant coefficients C1and C2 in the Mooney equation over the range from 1.5 to about 3.5. The behavior of the empirical function in the transition region from L=1.0 to L=1.5 shows that the statistical theory of elasticity fails to represent the experimental data even at the lowest elongations while proving satisfactory in the compression region. The Mooney-Rivlin equation also fails to furnish adequate representation of the experimental data at low elongations. The most satisfactory method of determining Young's modulus from experimental observations of stress and strain in pure-gum vulcanizates involves a plot of log F/(L−1−L−2) against (L−L−1). For observations within the range of L=0.75 to 2.0 the simpler plot of F/(L−1−L−2) against (L - 1) is thoroughly satisfactory. In both cases M is obtained from the intercept, and the constant A in Eq. (1) is determined from the slope.