bluuebunny/crossref_metadata_2025 huggingface dataset:
Absence of Free Radical Cracking of Stressed Rubber
Authors: Layer Robert W.
Published: February 2011

Crabtree has reported that free radicals formed on ultraviolet irradiation of certain organic compounds caused cracking of stressed rubber in the same manner as ozone. Although the types of free radicals used were mentioned, no comment was made concerning the amount of material used, the time of irradiation, the light source, nor the type of rubber used. In fact, experimental details were in general missing. Since this work is now generally being quoted, work was undertaken to determine if the reported free radical cracking of rubber actually occurred in the strict absence of oxygen, and if so, if it occurred under conditions mild enough to be considered important in the degradation of rubber materials. Initially diacetyl, which is well known to give acetyl radicals on ultraviolet irradiation, was used as a radical source. Samples of diacetyl weighing from 0.001 to 0.15 g were sealed in nitrogen-filled bulbed capillary tubes. The bulb and a bent loop vulcanized black natural rubber sample (NR 100, ZnO 5, stearic acid 2, HAP black 50, MBT 1, and S 3 parts vulcanized at 284° F for 60 minutes), 1 cm by 3 cm and 2 mm thick were placed in a 2-liter Pyrex flask. The flask was evacuated to 0.5 mm and filled with lamp grade nitrogen. This process was repeated four more times. The bulb was now broken by shaking the flask, and the flask was irradiated with a Hanovia SC ultraviolet lamp—type 16200—at a distance of 20 cm for 16 hours. The samples were examined under 27 power magnification and found to contain no cracks. Neoprene and SBR black vulcanizates, when exposed to similar treatment, showed no cracks. When compressed air was used instead of the nitrogen, ozone cracking was found to take place. As would be expected, air and diacetyl gave cracks much sooner than air alone. Other possible radical sources were tried but none caused cracking of the rubber sample on ultraviolet irradiation. These materials were di-tert-butyl peroxide, di-n-butyl disulfide, and butyl nitrite.
The Status of the Theory of Bond Strength in Multiply Articles
Authors: Slonimskiĭ G. L.
Published: February 2011

1. Ply separation of multiply specimens and articles, operating under conditions of repeated deformation, is a result of fatigue of the boundary layer. 2. The development of the process of fatigue is determined by the structure and composition of the fatigued material, and also by the pattern of action. 3. The difference of fatigue of the boundary layer from the fatigue of uniform masses of material is governed by their difference in composition and structure, and also by the difference in the patterns of deformations of the boundary layer and of the uniform materials. 4. The formulation, technological and physical chemical factors, which influence each other mutually, determine the structure and compositions of the boundary layer which is eventually formed in the process of contacting the surfaces and vulcanization. 5. The pattern of action of the mechanical forces upon the boundary layer is determined by the applied external forces or deformations, by the construction of the multiply specimen or article and by the ratio of the elastic characteristics of the material (Young's modulus and Poisson's coefficient). 6. The formation of principles of a theory of bond strength between the elements of multiply articles is possible only by ascertaining the mechanism of fatigue of the boundary layer. For this we require the investigation of the viscoelastic properties of the raw stocks, of the phenomena which take place at surfaces of uniform raw stocks and of pliedup raw stocks, and of the process of vulcanization in the boundary layer. All these questions must be investigated as a complex, i.e., with consideration of the internal bonds existing between the formulation, technological and physical chemical factors. In addition it is necessary to analyze the influence of the construction and the elastic properties of the materials upon the character of the stresses, which arise in the joint zone. 7. A further major task in the theory of bond strength is the theoretical consideration of the nature of the tackiness of raw stocks and of the mechanism of the action of bonding agents.
Derivatives of 2-Mercaptobenzothiazole as Accelerators
Authors: Feldshteĭn M. S. , Eĭtingon I. I. , Dogadkin B. A.
Published: February 2011

The wide use in industry of new types of synthetic rubbers calls for the creation of a variety of vulcanization systems of specific action. The quest for such vulcanization systems and, in particular, for vulcanization accelerators with given properties is of course made more difficult by the fact that up to the present time no one has cleared up the question of the influence of the chemical structure of the accelerators upon their vulcanizing activity. As a result of this the provision of experimental data revealing the connection between the chemical structure and the action of vulcanization accelerators is of immediate theoretical and practical value.
The Interaction of Tetramethylthiuram Disulfide with Rubber and with Compounds Containing a Labile Hydrogen Atom
Authors: Dogadkin B. A. , Shershnev V. A.
Published: February 2011

In the interaction of TMTD with rubber, sulfur and nitrogen from the TMTD add to the rubber, a maximum being exhibited on the rate curve for sulfur addition. At the same time dimethyldithiocarbamic acid is formed which, in mixtures containing zinc oxide, becomes bound in the form of Zn-DDC but which decomposes to carbon disulfide and dimethylamine in mixtures containing magnesium and calcium oxides and in the absence of metallic oxides. In the absence of oxides or in the presence of CaO or MgO a less dense three dimensional network is formed and reversion takes place which is accelerated by carbon disulfide and dimethylamine. The degree of crosslinking increases with increase in content of 1,4 structural units while the amount of combined sulfur and the rate of accumulation of zinc dithiocarbamate diminish. Dithiocarbamic acid also forms in the interaction of TMTD with geraniol and isopropylbenzene. The thermal decomposition of TMTD to thiuram monosulfide, sulfur, tetramethylthiourea and carbon disulfide takes place in the absence of compounds with a labile hydrogen atom. The reaction proceeds through the stage of rupture of the S—S and C—;S bonds of TMTD to form free radicals. The radical mechanism of the reaction is confirmed by electronic paramagnetic resonance specta.
Stress Relaxation during the Thermal Oxidation of Vulcanized Natural Rubber
Authors: Dunn J. R. , Scanlan J. , Watson W. F.
Published: February 2011

The photoinitiated oxidative aging of peroxide vulcanized natural rubber (which contains only carbon-carbon cross-links) was found by stress relaxation measurements to be autocatalytic and to be sensitive to the presence of free radical retarders and catalysts. Similar behavior would be expected in thermal aging. However, earlier work in these laboratories indicated that the thermal aging of peroxide vulcanizates was not autocatalytic. Because of this discrepancy the stress relaxation of peroxide vulcanizates at elevated temperatures has now been reinvestigated and the study has been extended to include also the aging of the other types of networks which are produced on vulcanization by tetramethylthiuram disulfide in the absence of sulfur, by sulfenamide-sulfur, and by sulfur alone.
Influence of Accelerator Residues on Age Resistance of Vulcanizates
Authors: Ossefort Z. T.
Published: February 2011

It has been shown that the age resistance of elastomeric vulcanizates is influenced to a very marked degree by residues formed in situ in the vulcanizate during the curing process. By a dual process of removal of these residues and incorporation of selected ingredients subsequent to vulcanization, it has been shown that age resistance (as measured by accelerated oven-aging tests at 212° F) in rubbers cured by sulfur and/or sulfur bearing accelerators, is a prime function of these residues and nearly independent of the stability of the network structure. An extremely active inhibitor is formed in situ during vulcanization of SBR and natural rubber using thiuram accelerators. This inhibitor can be used to “reinhibit” acetone-extracted accelerator-cured rubber. When added to sulfur/accelerator, peroxide, or radiation-cured vulcanizates, it improves their age resistance, but only in the case of the sulfur/accelerator cured rubber is this improvement better than with conventional inhibitors. This leads to the conclusion that the efficiency with which an inhibitor protects a vulcanizate varies widely, and conversely it appears that certain types of network structures are more readily protected or that certain inhibitors can function more efficiently in the protection of certain structures than others. In the case of natural rubber cured with TMTD (zinc oxide present), the bulk of the accelerator residue is ZnDMDC, and this residue has been shown to function as a very efficient antioxidant when incorporated into acetone-extracted, accelerator-cured vulcanizate. It is no more effective than conventional inhibitors, however, when incorporated into an acetone-extracted, sulfur/accelerator-cured vulcanizate. Finally, it has been shown that acetone extraction of the various vulcanizates may lead to improvement or worsening of their age resistance, depending upon the nature of the residues resulting from the curing process.
Important Stability Factors for Styrene-Butadiene Rubber
Authors: Hunter B. A. , Nawakowski A. C. , Barnhart R. R. , Campbell E. M. , Hansen E. B.
Published: February 2011

(1) Styrene-butadiene rubber (SBR) is very susceptible to oxidative degradation unless an effective stabilizing agent is incorporated in the polymer during manufacture. (2) Degradation of SBR appears as discoloration or resinification during drying of the polymer or during storage. Changes in the polymer may appear as variation in Mooney viscosity or as an increase in gel content. (3) Deterioration of inadequately stabilized SBR may also show up during processing operations when the polymer is subjected to heat—as in the Banbury or on a hot mill. (4) Deterioration of SBR polymer will appear as degraded physical properties in the cured vulcanizate. (5) The rubber goods manufacturer will benefit from the use of a really effective SBR stabilizer incorporated in the polymer during manufacture or by adding additional stabilizer to provide more protection against heat degradation in his operations. (6) Tris(nonylated aryl) phosphite exhibits unusual effectiveness as a stabilizer for SBR. (7) The presently widely used method of salt-acid coagulation of SBR polymer leaves room for improvement as far as polymer stability is concerned. (8) The more effective SBR stabilizers exhibit benefits in the aging of SBR vulcanizates.
The Sorption of Antioxidant from Solution
Authors: Novikova E. N.
Published: February 2011

The sorption of amines, hydroxy amines, and naphthols from water and ethyl alcohol by synthetic rubbers was studied with the help of an interferometer and a SF-4 spectrophotometer. It was shown that: 1. SBR (SKS-30) sorbs a large amount of 1-naphthylamine, less of the 1- and 2-naphthols and m-toluidine and m-hydroxydiphenylamine to an insignificant degree. 2. The degree of sorption of 1- and 2-naphthols from water is inversely proportional to their dipole moments and correlates with their activity as antioxidants. 3. The polar rubber (SKN-40) absorbs from ethyl alcohol the amines the best, the hydroxy amines poorly, and an insignificant amount of 2-naphthol. 4. The amines in a decreasing magnitude of sorption on SKN-40 from alcohol fall in a series (phenyl-2-naphtholamine > 2-naphthylamine > diphenylamine) which correlates with their activity as antioxidants. 5. The electronegative OH group, sticking out of the body of the molecule, exerts an influence on the degree of sorption of m-hydroxyphenyl-2-naphthylamine, m-hydroxydiphenylamine and naphthol from polar solvents.
Factors Affecting Bond Strength between the Elements of Tires
Authors: Buĭko G. N. , Arenzon N. M. , Tumanova A. I. , Zinchenko N. P. , Pruzhanskaya N. A. , Pakomova E. A. , Kolomytseva A. I. , Bugrova E. G.
Published: February 2011

1. Ply separation of tires is one of the essential factors reducing their mileage, particularly under difficult service conditions. Enhancement of the dynamic bond strength between elements of the tires is a most important line of study for increasing the mileage of tires based on synthetic rubber. 2. An analysis of defects in tires failing as a result of separation shows that for a given level of technical proficiency in handling synthetic rubber the adhesion type of separation between pliedup compounds or between rubber and cord (of viscose filament) is predominant. This form of failure is particularly characteristic of tires with vulcanizates based on butadiene/styrene rubber in all the main parts. 3. In investigations concerning separation phenomena in tires, decisive importance attaches to methods of determination of bond strength under conditions of dynamic loading of pliedup vulcanizates and rubber cord systems. We still do not have methods which could be regarded as fully satisfying the requirements proposed. However a series of methods have been provided which make it possible to assess, with an accuracy suitable for practical purposes, the effect of this or that factor upon the bond strength and to show the advantages and inadequacies of pliedup systems from the point of view of the operation of tires under actual service conditions. 4. The experimental results obtained show that the dynamic bond strength in pliedup systems, as also the endurance of the tires in relation to separation resistance, is determined by a complex body of physico-chemical and technological factors, by the construction of the articles, and also by the pattern of loading under repeated deformations. The general theoretical ideas developed in articles by some investigators, that the highest bond strength is to be achieved where full adhesion of the raw pliedup stocks takes place, as shown by the disappearance of boundaries between them, and that in all cases the factors which enhance the flowability of the stock enhance also the bond strength between them, were not confirmed experimentally.
The Catalytic Polymerization of Isoprene with Butyllithium
Authors: Korotkov A. S. , Chesnokova N. N. , Truchmanova L. B.
Published: February 2011

1. The kinetics for the polymerization of isoprene with butyllithium in a solution of saturated hydrocarbons were determined. 2. The reaction has the mechanism of a chain catalytic reaction, in which active centers appear that are involved complexes formed from metallorganic compounds and monomer-polymer molecules. 3. Deactivation of growing chains takes place as a result of the reaction of active centers with each other or with metallorganic compounds. With this there are formed new metallorganic compounds of high molecular weight capable of becoming new polymerization centers. 4. The polymer possesses a narrow range of molecular fractions, closely approximating the Gaussion distribution, but the value of the average molecular weight of the polymer after completion of polymerization is inversely proportional to the catalyst concentration. 5. The polymerization temperature, and also the concentrations of the monomer and catalyst, do not affect the microstructure of the polymer (content of 1,2 and 3,4 isoprene units).
The Copolymerization of Isoprene and 1,3-Butadiene by Butyllithium
Authors: Rakova G. V. , Korotkov A. A.
Published: February 2011

Up to now catalytic copolymerization with alkali catalysts has hardly been studied. Only a few papers have been published which give quantitative data. Judging by the values of the copolymerization constants, monomers differ very considerably in their reactivities. Monomers in which the double bond of the vinyl group is conjugated with the multiple bond of a nitrile or a carboxyl group have the greatest activity. The copolymerization of diene hydrocarbons under the action of basic catalysts has not been investigated as yet. It is known that in free radical (emulsion) polymerization these hydrocarbons have relatively similar activities. It seemed interesting to establish the relative reactivity of the diene hydrocarbons, isoprene and 1,3-butadiene, which differ by only a methyl group, in alkali-catalyzed copolymerization. Labeled atoms were used for determining the composition of the copolymers. For this we synthesized isoprene containing radioactive carbon, C14 (from acetylene-C14, prepared from BaC14O3) by a modification of Favorskii˘'s method. Copolymerization and separate polymerizations of isoprene and 1,3-butadiene were carried out in hexane solution with butyllithium at 50°, with a total monomer concentration of 2 moles/liter and a catalyst concentration of 0.0025 mole/liter. Butyllithium was synthesized by the known method. The butyllithium solution was analyzed by the usual method with a double titration. Thoroughly purified and dried monomers and solvent were used for the polymerization. All operations of measuring out the products into the reaction ampules were carried out in a current of dry nitrogen and in a vacuum apparatus having a distributing comb (manifold). The reaction ampules consisted of two sections, separated by a wall and connected with a graduate tube. The solvent and monomers were placed in one section and the catalyst, a solution of butyllithium in hexane, in the other.
Isoprene Polymerization by Organometallic Compounds. II
Authors: Tobolsky Arthur V. , Rogers Charles E.
Published: February 2011

From the above results it would certainly appear that the ionic character of the growing ion pair (polymer−M+) is a very important factor in governing the structure of isoprene homopolymers. Another factor which may be sufficient or necessary for the formation of the unique cis-1,4-eonfiguration is the presence of an orienting surface or complex. It is well known that organolithium compounds are associated in hydrocarbon media, whereas they are probably monomolecularly dispersed in ethers and amines. It is apparent, then, that in hydrocarbon solutions the carbon-lithium chain end may be associated with other carbon-lithium pairs from unreacted initiator molecules or even with other chain ends or, in some cases, it may be associated with the lithium atoms on the surface of lithium particles. The fact that greater than 90 per cent cis-1,4-structure is obtained in hydrocarbons by use of either an apparently clear solution of filtered n-butyllithium or a heterogeneous system of lithium dispersion suggests that the massive surface of the lithium particle is not a necessary factor for the stereospecificity of the reaction. Whether we should consider the butyllithium or the lithium-initiated polymerizations as homogeneous solution reactions or heterogeneous surface reactions depends on the definition of a surface, since an associated complex or micelle may also conceivably serve as an orienting specie in the same way as a surface does. We emphasize this since so many stereospecific polymerizations such as the Ziegler system and the Phillips system appear to occur under heterogeneous conditions, presumably on an orienting surface of rather gross dimensions.
The Mechanism of Isoprene Polymerization Initiated with Ticl4-Trialkylaluminum. Molecular Weight Distribution of the Polymer
Authors: Bresler S. E. , Mosevitskiĭ M. I. , Poddubnyĭ I. Ya , Chesnokova N. N.
Published: February 2011

The molecular weight distribution of polyisoprene obtained by polymerization under the influence of complexes of titanium tetrachloride with tri-isobutylaluminum has been found within broad limits to be independent of the degree of conversion. On the basis of this finding an hypothesis is offered to explain the limitation of polymer chain length according to which chain scission is assumed to increase with the size of the chain.
Kinetics of Isoprenepolymerization Initiated with TiCl4—Trialkyl Aluminum
Authors: Bresler S. E. , Mosevitskiĭ M. I.
Published: February 2011

For the study of the mechanism of polymerization by means of complexes of aluminum organic compounds with titanium chlorides, data on the kinetics of polymerization is of great interest. Up to the present time, the rate of polymerization of propylene has been studied but the interpretation of the kinetic data is difficult because the polymer, which is practically insoluble in the reaction medium, entraps the catalyst resulting in a rate of reaction which is dependent on the diffusion of monomer through the polymer to the active sites. In this work the polymerization of isoprene, which yields polymers soluble in the monomer, in saturated hydrocarbons and in benzene, was studied. The rate of the polymerization reaction was measured by the thermal effect in a calorimeter consisting of a 3.5 1. Dewar flask, with a lid, immersed in a thermostated air bath maintained at approximately the temperature of the reaction. Low viscosity spindle oil, heated to the temperature of the reaction (about 32°), served as the calorimeter fluid. The ampoule holder extended outside of the calorimeter and was connected to a shaking apparatus. The ampoule was divided by a thin partition into two sections each holding 45–50 cc. Into one section previously purified monomers and solvent were distilled. The other section was filled with catalyst components from a Shlenk container. The change in temperature of the calorimeter was determined with a Beckman thermometer with an accuracy of 0.01 °. When the temperature of the calorimeter containing the ampoule remained constant to within 0.01–0.02° for 30–40 minutes, the shaking apparatus was connected and the partition was broken with a striker. Intensive shaking was continued during the entire experiment resulting in mixing of the reaction mixture and of the calorimeter fluid. The rate of reaction was determined by the rate of heat evolution ; in other words, by the temperature rise in the calorimeter. For a rise of 0.1–0.5° the reaction conditions remained practically isothermal. This rise permits the kinetics of the reaction to be observed with sufficient accuracy. Adiabaticity of the calorimeter and the effect of mechanical heat were controlled in separate experiments.
The Diffusion Theory of Adhesion
Authors: Voyutskiĭ S. S.
Published: February 2011

A theory of adhesion of polymers to each other is suggested ; according to it adhesion of dissimilar polymers as well as auto-adhesion is explained by the diffusion of chainlike molecules segmentally or otherwise. Starting with this theory, the effects of various factors on the adhesion of polymers to each other are discussed. The factors considered are: duration of contact between adhesive and substrate, temperature, molecular weight of adhesive, molecular shape and polarity.
A Theory of the Thermodynamic Behavior of Nonelectrolyte Solutions. II. Application to the System Rubber-Benzene
Authors: Maron Samuel H. , Nakajima Nobuyuki
Published: February 2011

The theories of polymer solutions proposed by Flory, Huggins, Miller, and Guggenheim employ the concept of a coiling polymer molecule which may become entangled with other such molecules in solution, and utilize statistical-mechanical considerations to obtain the thermodynamic relations attending the solution or mixing process. The theories of Flory and Huggins are essentially identical, as are those of Miller and Guggenheim. Further, all theories reduce to practically the same result when the molecular weight of the polymer is high. The present status of these theories may be summarized as follows. Except for dilute solutions, the free energies of mixing predicted by theory agree generally quite well with those measured experimentally; however, the heats and entropies of mixing do not. To correct the situation in the dilute region, Flory and Krigbaum developed a special theory which preserves the original model used by Flory, but attempts to take into account the lesser tangling of polymer chains as the solution is diluted. The latter theory appears to work quite well in very dilute solutions, but it suffers from two shortcomings. First, the theory does not apply to concentrations high enough to overlap the original theories, and hence there is a concentration gap for which no theory is available. Second, the Flory-Krigbaum theory employs parameters which are different in significance from those used at the higher concentrations, and, thus far, no relation has been established between them. The result is that polymer solution behavior at low concentrations is expressed in terms of one set of parameters, that at higher concentrations in another, and no means are available to connect these or to cover the concentration gap to which neither theory applies. Recently Maron7 developed a theory of the thermodynamic behavior of nonelectrolyte solutions which is nonstatistical in character, and which expresses the behavior of solutions in terms of parameters whose significance remains unaltered over the full concentration range of the solution. The purpose of the present paper is to show the application of this theory to the system rubber-benzene, for which Gee and Treloar have determined at 25° C the free energies, heats, and entropies of mixing over the entire range of concentration from pure benzene to pure rubber. Subsequent papers in the series will give applications of the theory to osmotic pressure and light scattering behavior of polymer solutions, as well as to the thermodynamic behavior of solutions of low molecular weight substances.
The Determination of Zinc Oxide in Rubber Vulcanizates by X-Ray Diffraction
Authors: Laning Stephen H. , Wagner Melvin P. , Sellers John W.
Published: February 2011

Zinc oxide is a necessary component in most accelerator-sulfur vulcanization systems. While it is not an accelerator, its presence leads to increased modulus, i.e., tighter cures. The manner in which it can effect this better cure is not completely clear. Some insight into the role of zinc oxide has been gained through the analysis of the vulcanizate for reaction products of zinc, such as zinc stearate, the zinc salts of the accelerators, and zinc sulfide. However, these products may not account for all of the zinc oxide which has reacted. An analytical method for the direct determination of unreacted zinc oxide in vulcanizates was therefore needed. The determination of zinc oxide in rubber vulcanizates has received scant attention. Wet-chemical techniques for analysis of the sample after ashing provide only the total amount of zinc from which the amount of unreacted zinc oxide cannot be determined. Endter has reported the use of the Debye-Scherrer x-ray technique for the identification of zinc oxide in rubber samples. While similar to the method developed in this laboratory, Endter employed photographic film for recording the diffraction pattern, and special sample preparation was required to accommodate the photographic technique. This method was satisfactory for qualitative identification of zinc oxide, but was difficult to use for quantitative analysis. Subsequent to this investigation Hagino et al. described the use of x-ray diffractometry for the determination of the mixing ratio of ingredients compounded in rubber. This method was also suggested for the quantitative analysis of zinc oxide, but no studies were reported. During a study in this laboratory to determine the role of zinc oxide in the vulcanization of rubber, a new analytical method, based on x-ray diffractometry, was developed. The method was rapid, nondestructive, and simple. The data were reliable and accurate.
Migration and Distribution of Radioactive Sulfur in Compounded Rubber
Authors: Blokh G. A. , Demidionova V. Ya , Miklukhin G. P. , Kukhtenko I. I. , Rekasheva A. F. , Nikulina R. V. , Przhebylskiĭ M. I.
Published: February 2011

In the production of vulcanized rubber articles it is necessary to take into account the possibility of migration of sulfur from one ply into another. It is well-known that alterations in the concentration of sulfur and accelerators in a stock, taking place as a result of diffusion processes, may lead to alteration in the quality of the rubber. In particular, if in formulating mixes for multiply rubber-fabric articles we take into account the migration processes of the accelerating and vulcanizing agents, it becomes possible to prevent the occurrence of various defects through nonuniform vulcanization. Once again, if the unvulcanized stock is stored in piles, migration means that alterations in the concentration of sulfur and accelerators cannot be ruled out. Another factor closely connected with the quality of the resulting articles is the uniformity of distribution of the sulfur when added to a compounded stock. Thus the study of migration processes takes on considerable practical importance. One promising method of investigation of diffusion processes in vulcanized rubber may be the use of tagged atoms. With it we can effectively and rapidly investigate migration processes at different stages of manufacture. The significance of this method for the investigation of the mechanism of the action of accelerator and vulcanization agents has already been pointed out in the literature. We used the tagged atom method in the investigation described below … a joint investigation by the rubber department of the Kiev Technological Institute of Light Industry, the Institute of Physical Chemistry of the Academy of Sciences of the Ukrainian SSR, and the “Krasnyi Rezinshchik” and “Ukrkabel” works.
The Vulcanization of Rubber under High Pressure
Authors: Okhrimenko I. S.
Published: February 2011

1. The influence of high pressures (up to 10,000 kg/cm2) on the cure of gum and compounded rubbers and also on the properties of the resulting products was studied. 2. It was demonstrated that high pressure accelerates vulcanization and effects the specific formation of stable carbon-carbon crosslinks. Thus, crosslinked polymers may be prepared without any vulcanizing agents, yet the resulting vulcanizates have excellent properties. New methods were designated for obtaining crosslinked block polymers having stable crosslinks. 3. It was determined that cure depends on the reactivity of the rubber, the type of unsaturation and, most important, the amount of spatially more accessible external double bonds. 4. It was shown that during the cure of rubber compounds under high pressure the participation of sulfur in the formation of the vulcanizate is substantially decreased. In a mixture of SKB rubber and sulfur the dominating reaction is the interaction of molecules of rubber. Functional fillers and softeners do not undergo substantial change. The use of initiators of radical polymerization contributes by leading to ultrarapid vulcanization of rubber. 5. An assumption is stated concerning the mechanism of vulcanizing rubber under high pressure as well as certain questions about the use of high pressure as a new method of producing molded rubber articles.
Reversion during TMTD Vulcanization
Authors: Dogadkin B. A. , Shershnev V. A. , Dobromislova A. V.
Published: February 2011

1) Reduction of crosslink density of vulcanizates (reversion of vulcanization) is observed during vulcanization of a mixture prepared in air of NR and SKI with TMTD without metal oxides and with magnesium and calcium oxides. In these cases the dimethyldithiocarbamic acid formed during vulcanization decomposes into carbon disulfide and dimethylamine. 2) During mixing and curing of these mixtures in an argon atmosphere reversion is absent although evolution of carbon disulfide and dimethylamine is observed. 3) During vulcanization of the mixtures containing zinc oxide no reversion occurs as a result of preparation of the mixtures either in air or in argon. Dimethyldithiocarbamic acid in this case is bound in the form of the stable zinc dimethyldithiocarbamate. 4) Reversion of rubber by TMTD is explained by oxidative destructive processes which are intensified by the products of decomposition of dimethyldithiocarbamic acid, i.e., by carbon disulfide and dimethylamine, and are suppressed by reaction of it to form zinc dimethyldithiocarbamate which serves as an inhibitor of the oxidative destruction of the vulcanizate.
Diisocyanate-Linked Polymers. II. Mechanical and Swelling Properties of Some Polyurethane Elastomers
Authors: Smith Thor L. , Magnusson Alan B.
Published: February 2011

In recent years, as a result of pioneering work in Germany and England, diisocyanate-linked polymers have assumed increasing industrial importance. Special interest is being shown in elastomers and foams, although studies of fibers and plastics are continuing. These several classes of diisocyanate-linked polymers, with their markedly different mechanical properties, are possible because substances having two or more groups containing active hydrogen can potentially be linked by diisocyanates to yield a polymer. Since a great number of such substances exist, data which show relationships between polymer structure and mechanical properties have practical importance as well as theoretical interest. The first paper of this series on diisocyanate-linked polymers discussed the dilute solution properties of linear polymers prepared from toluene-2,4-diisocyanate and polyoxypropylene glycol 2025 (PPG). This paper discusses the properties of one class of diisocyanate-linked elastomers prepared by a one-step cast technique, i.e., all reactants are mixed together initially and then allowed to cure. Although these polyurethane elastomers have relatively poor mechanical properties as compared with certain other types of polyurethane elastomers, they are useful in applications where high tensile strength, tear resistance, and ultimate elongation are not required. They also constitute a class of polyurethane polymers convenient for use in studying relationships between chemical structure and mechanical properties.
Rheological Testing of Elastomers at Low Temperatures. Part II
Authors: Boor L. , Hanok M. , Conant F. S. , Scoville W. E.
Published: February 2011

Results are given from a cooperative study to determine the extent to which certain superposition principles are applicable to analysis of different typos of deformation of elastomeric materials. Briefly, these principles are : (1) recovery rate from an equilibrium deformation after removal of a given load is equivalent to the creep rate from zero deformation upon application of that load and, (2) creep, recovery, or stress relaxation curves obtained at different temperatures can be pieced together into a continuous curve of time versus deformation or stress. Both principles are predicated on the use of an essentially equilibrium deformation or stress as a base from which the percentage change with time is calculated. The first of the above principles was demonstrated for both torsional and shear deformations, but not for tensile deformations, possibly because of some inaccuracy in the test method. The second principle was demonstrated for shear creep, shear recovery, torsional creep, torsional recovery, and tensile stress relaxation. Applications of this method of analysis are given to show how the rheological behavior of an elastomer at a given temperature may be predicted for very short or for very long periods of creep, recovery, or stress relaxation from measurements made at a series of temperatures.
Determination of Copolymer Composition by Combustion Analysis for Carbon and Hydrogen
Authors: Wood Lawrence A. , Madorsky Irving , Paulson Rolf A.
Published: February 2011

The procedure described attains its accuracy and precision by the refinement and improvement of conventional simple operations over a periods of years. The trend in analysis recently is, of course, toward the use of rapid physical methods. In a great many instances these involve relative measurements requiring the initial establishment of reference materials with compositions determined by methods such as the one here described, which bases the numbers derived solely on readings of an analytical balance. In fact, as already mentioned, one of the principal applications of the present method has been in the establishment of the relation between refractive index and styrene content for SBR polymers so that refractive index measurements can be used in routine determinations of bound styrene content.
The Attack of Ozone on Stretched Rubber Vulcanizates. II. Conditions for Cut Growth
Authors: Braden M. , Gent A. N.
Published: February 2011

In Part I an experimental study was reported of the factors determining the rate of propagation of a cut through a stretched rubber sheet under the action of an atmosphere containing ozone. It was remarked that no growth took place from a small razor cut made in one edge of the test pieces unless a critical value of the applied tensile stress was exceeded. The value was quite small, of the order of 100 g/cm2 for a soft natural rubber vulcanizate. In the present part an examination is reported of the conditions necessary for a crack to form or, being present, to grow.
The Nature of an Adhesion Bond between Two High-Molecular Weight Compounds
Authors: Morozova L. P. , Krotova N. A.
Published: February 2011

1. The nature of the adhesion bonds in different cases can be determined by investigations of the mechanical characteristics of adhesion, of electrical effects observed on destruction of the bond, and microscopical investigation of the separation boundaries in various systems consisting of polymer pairs, and polymer-metal and polymer-glass systems held together by forces of adhesion. 2. The adhesion bonds between polymer and metal and polymer and glass are electrical in character, as shown by the form of the adhesiogram, the occurrence of electron emission on separation, and the existence of electric charges on the separated surfaces. 3. After separation, the polymer film continues to emit electrons and carries a negative residual charge. The substrate (glass, metal) does not emit electrons and has a positive charge. 4. The breakdown of the adhesion bond between two polar polymers of different structure, or a polar and nonpolar polymer, is accompanied by the same characteristic effects as the separation of a polymer from glass or metal. A sharp boundary is observed in microscopic specimens. 5. Determinations of the velocities of electrons emitted during separation show that breakdown of a firm adhesion bond is accompanied by emission of electrons with higher velocities than those emitted in the breakdown of a weak bond. These results arc in good agreement with the electrical theory of adhesion. 6. The reaction of the substrate (glass) has a strong influence on the adhesion of a polymer (chlorinated polyvinyl chloride) to it. The maximum adhesion is found in the neutral region. The detached polymer film shows a reversal of residual charge in the strongly acid and strongly alkaline regions, accompanied by a sharp decrease of the work of adhesion; this can only be attributed to a decrease of the surface electrification density of the layers of the electric double layer in the charge reversal region. 7. Mechanical treatment of the metal surface increases the adhesion of polymers to it and intensifies electron emission from the regions of the polymer film which were attached to the treated regions of the metal surface. 8. The formation of an adhesion bond between two nonpolar polymers of similar structure is caused by diffusion processes in the contact zone. In such cases no electrical effects are observed during separation, the boundary in microscopic specimens is diffuse, and the work of separation depends relatively little on the rate of separation. 9. The systems studied can be subdivided into two groups: the adhesion bond in systems of the first group is the result of formation of an electric double layer at the boundary; in systems of the second group the adhesion bond is produced by diffusion processes at the boundary.
Role of Pressure and Amount of Blowing Agent in Molding Microporous Footwear Parts
Authors: Al'bam M. A. , Pisarenko A. P.
Published: February 2011

In the All-Union Film-forming Materials and Artificial Leather Research Institute (VNIIPIK) investigations have been in progress for several years with a view to developing a rational method of production of microporous footwear parts, and to eliminating completely expansion of the parts on removal from the press. It had already been demonstrated that to produce microporous molded parts strictly to the set shape they must be vulcanized with an external pressure not exceeding a certain critical value for each stock formula depending upon the amount of blowing agent, the flowability of the stock and the temperature. However the cause of this marked dependence of the process of molding of microporous parts upon the external pressure was not explained. It was merely suggested that a big part was played by the escape of gas from the cells of the molded rubber. In order to work out a theoretical basis for the production of molded parts and for the control of the process of pore formation, it was necessary to study the essential nature of the process. For this purpose we studied the kinetics of the process of pore formation and of the escape of gas from a stock in the process of vulcanization. The method worked out for investigation of the process of pore formation made it possible to study this process under conditions fully corresponding to the actual production conditions of press vulcanization, and to follow simultaneously in one experiment the change in volume of the vulcanization stock and the escape of gas from it. On the basis of these data we plotted the kinetic curves for the processes.
Mechanochemical Phenomena in Polymers. II. The Effects of Initiators and Inhibitors of Radical Processes
Authors: Reztsova E. V. , Lipkina B. G. , Slonimskiĭ G. L.
Published: February 2011

1. The substantial effect of inhibitors and initiators of chain radical processes on the change in the properties of rubbers in milling, as well as on the resistance of vulcanizates to fatigue, has been shown. This indicates a mechanochemical mechanism of the processes occurring in processing polymers and of the fatigue of highly elastic materials (e.g., rubber vulcanizates). The act of mechanical scission of chemical bonds, with the formation of free radicals which initiate the secondary chain processes, rests on these processes. 2. The possibility has been shown of regulating the properties of polymers in the course of their industrial processing, and also of increasing the dynamic fatigue resistance of vulcanizates by incorporating small quantities of additives active in regard to free radicals.
The Effect of Electric Charges Formed during Repeated Deformations on the Fatigue Resistance of Vulcanizates
Authors: Dogadkin B. A. , Gul V. E. , Morozova N. A.
Published: February 2011

Electroelastic and triboelastic effects result in the formation of electric charges on articles made from polymers undergoing deformation. It was of interest to determine the effect of the charges formed during deformation on the fatigue resistance of vulcanizates. No convincing experiments clearly demonstrating the role of electric charges arising during friction or deformation had been carried out previously. Vulcanizates containing different amounts of acetylene black were tested in a machine in which cylindrical specimens with thickened ends were subjected to repeated bending at 1300 cycles/minute. The stocks had the following composition (in parts by weight) : SKS-30A 100, sulfur 2, technical stearin 2, Rubrax 5, black oil 4, MBTS 0.6, diphenylguanidine 0.8, zinc oxide 5, oleic acid 1. Increasing amounts of acetylene black were added to this composition: 6, 12, 18, 20, 22, 30, 40 and 75 wt. parts per 100 wt. parts of rubber.
Analysis of Cis and Trans 1,4 Contents of Polyisoprenes by Near Infrared Spectroscopy
Authors: Corish P. J.
Published: February 2011

A new method for the determination of cis and trans-1,4 units in synthetic polyisoprenes and gutta-rubber mixtures has been developed. The method uses the near infrared region of the spectrum and gives better, more reproducible results than the one using the normal infrared region.
Statistical Treatments of Rubber Structure
Authors: Scanlan J. , Watson W. F.
Published: February 2011

Chemical reactions are random in nature and can therefore be subjected to mathematical analyses based on probability theory. This is a particularly necessary approach to polymer structure in which the effect of chance inherent in the reactions is preserved in physical form and therefore much attention has been given to deductions from such treatments. It is the purpose of this paper to review the results of those investigations which have particular application to rubbery high polymers. Some emphasis will be given to the authors' view that experimental testing of the derived expressions is still far from being satisfactory and that the subject in spite of the effort expended is still only at its beginning. Consideration of details of polymer structure is not merely an academic exercise. The properties of raw rubbers are highly dependent on polymer chain length and for many important ones such as viscosity, either in solution or in the melt, the dependence is not simply linear. Unless linear dependence on the number of molecules and their size does apply, an average value of molecular weight is insufficient to characterize a rubber sample in respect of the property considered and further knowledge of the distribution of molecular weights among the rubber molecules is required. The properties of rubbers are also markedly influenced by the occurrence of branching in the polymer chains; the insolubility and elasticity conferred by vulcanization are the results of the formation of complex branched structures which have been the subjects for statistical treatments.
The Relations between Polymer Structure and Properties in Urethans
Authors: Saunders J. H.
Published: February 2011

Sufficient data are available from studies of urethan foams and elastomers to draw semiquantitative conclusions regarding the effect of any gross structural change on most polymer properties. These relationships apply to other areas of application as well, e.g., coatings, adhesives and sealants. Future research may be expected to provide more reliable control of the many reactions involved in preparing urethans, thus better control over structure. Similarly a more quantitative and extensive knowledge of polymer properties may be expected. The result of these combined efforts will be a more precise knowledge of structure-property relationships and an improved ability to produce polymers having the properties desired for a wide range of applications.
A New Method for Determining the Vulcanization Characteristics of Rubber Compounds
Authors: Peter J. , Heidemann W.
Published: February 2011

The complete course of the vulcanization curve is obtained by measuring the values of the dynamic shear modulus during a period while the test sample is held at the vulcanization temperature. The measurements are made about the position of zero distortion. The curves are in good agreement with those obtained by a step-cure method, and scorch data agree well with those obtained with the Mooney apparatus. The method has the following advantages and disadvantages. A. Advantages 1) The course of the vulcanization curve is established on a single sample without curing in stages. 2) Minimum material is required. 3) The test is quickly performed. 4) Good reproducibility is observed. 5) The unit lends itself readily to automatic recording so that one man can easily operate several instruments. B. Disadvantages 1) The apparatus should be operated by trained workers. 2) The cost of the apparatus is rather high.