bluuebunny/crossref_metadata_2025 huggingface dataset:
Equivalent Cures in Specimens of Various Shapes
Authors: Conant F. S. , Svetlik J. F. , Juve A. E.
Published: February 2011

A procedure has been developed for adjusting the curing times and state of cure of rubber products of various shapes and thicknesses to be equivalent to that obtained with a standard tensile sheet at some specified time and temperature. A nomograph has been constructed which permits the calculation of the lag or incubation time involved in curing articles of varying shapes and compositions. If the incubation time is found to be longer than the tensile sheet cure, a correction is applied. This correction is obtained from a curve relating the ratios of tensile sheet cure time and incubation time to product cure time and incubation time. Another nomograph was constructed for transposing cure times at one temperature to those at a different temperature. It was constructed on the basis that in the 280° F range the rate of cure is doubled for an 18° F increase in temperature. This procedure for adjusting the curing times of products to be equivalent to that of the standard tensile sheet is demonstrated. Suggested test methods are given for determining the state of cure in a product as compared with the state of cure in a tensile sheet when given the “best” or most desirable cure. These methods included determination of free sulfur, for materials vulcanized with sulfur; solvent swelling, applicable to articles or specimens which do not contain a high amount of extractables; hardness; modulus at low extension; and set properties.
Hydrogenation of Butadiene Rubber Solutions. II. Influence of the Solvent with Palladium-on-Calcium Carbonate Catalyst
Authors: Yakubchik A. I. , Gromova G. N.
Published: February 2011

Experiments with allyl alcohol demonstrated the influence of the nature of the solvent on the speed and degree of hydrogenation of an unsaturated organic compound on palladium-on-calcium carbonate catalyst. Butadiene rubber was hydrogenated on palladium-on-calcium carbonate in 2,2-dimethyldioxane-1,5 (DMD), and specimens of hydrorubber insoluble in that solvent were obtained. The same relation between degree of hydrogenation and properties was found for hydrorubber obtained with palladium-on-calcium carbonate catalyst in 2,2-dimethyldioxane-1,5 as had been established for hydrorubber obtained in heptane with the same catalyst : fall in relative viscosity of benzene solutions, lowering of refractive index, and fall in the temperature of vitrification of the rubber with increasing degree of hydrogenation. The selectivity of hydrogenation of the outer double bonds of butadiene rubber when hydrogenated in 2,2-dimethyldioxane is more clearly manifested than in the case of hydrogenation in heptane.
Modern Theories of Rubber Reclaiming
Authors: Stafford W. E. , Wright R. A.
Published: February 2011

The general principles of rubber reclaiming have been briefly described. References have been made to some of the more recent work on this subject, and some of the common ground of reversion and reclaiming has been indicated. Some speculation on the possibilities of further basic improvements has been put forward.
Organic Sulfides and Polysulfides. III. Reactions with Amines
Authors: Minoura Yuji
Published: February 2011

1. Mono-, di-, and trimethylamine when treated with benzyl and tolyl mercaptan give disufides ; on the other hand, thioglycolic acid gives the monosulfide. 2. Aniline and diphenylamine do not react with mercaptans or organic sulfides. 3. Mono-, di- and trimethylamine react with organic polysulfides. The tri- and tetrasulfides of the tolyl and benzyl series give disulfides by desulfurization. The glycolic acud sulfides are desulfurized to monosulfide. 4. The relative desulfurization activities of mono-, di- and trimethylamine are (CH3)3N < CH3NH2 < (CH3)2NH. This order is the same as for the basicity of these amines. Aromatic amines, because of their weak basicity, do not react with organic polysulfides. 5. The relative ease of desulfurization is in the order glycolic acid > benzyl > tolyl. The more sulfur a polysulfide contains, the more readily it desulfurizes. The mercaptan to disulfide reaction rate is faster than desulfurization of polysulfides.
Organic Sulfides and Polysulfides. VI. Reactions of Metallic Oxides with Polysulfide Rubbers
Authors: Minoura Yuji
Published: February 2011

1. Both mercaptides and disulfides were obtained by the reactions between benzyl mercaptan or tolyl mercaptan with zinc oxide or lead oxide. Qualitatively, mercaptides were formed from benzyl mercaptan easier than from tolyl mercaptan, and lead oxide reacted with mercaptan easier than zinc oxide with mercaptan. From the fact that no metallic sulfide was present, disulfides were likely formed from the oxidation of mercaptans by air. 2. The mono- or disulfides of the benzyl and tolyl series did not react with zinc oxide or lead oxide. 3. Neither tolyl tri- nor tetrasulfide reacted with zinc oxide, but benzyl tri- and tetrasulfide reacted with zinc oxide to give zinc sulfide. In the case of benzyl trisulfide, hydrogen sulfide, stilbene and benzaldehyde were formed, and in the case of tetrasulfide, we found the formation of hydrogen sulfide, stilbene, benzaldehyde and sulfur. 4. The tri- and tetrasulfide of both the benzyl and tolyl series reacted with lead oxide and they gave lead sulfide and organic disulfide. That is, they were desulfurized by lead oxide. In these reactions the benzyl series was more reactive than the tolyl series and the tetrasulfide was more reactive than trisulfide in the same series. 5. Lead oxide reacted with polysulfide easier than zinc oxide. 6. From the results of reactions between metallic oxide with mercaptan or other sulfide, it was concluded that the vulcanization mechanism of polysulfide rubber by metallic oxide is the reaction represented by Equations (1) to (4), the products being converted to high polymer without formation of a network of polysulfides.
Changes in the Electrical Properties of Natural Rubber/Carbon Black Compounds during Vulcanization
Authors: Desanges H. , Chasset R. , Thirion P.
Published: February 2011

To conclude, let us sum up the advantages of direct current or low frequency measurement of the electrical properties of natural rubber compounds, when operating inside the mold in which vulcanization is occurring. In this way, it is possible to follow the changes in properties during heating or vulcanization more closely and accurately than when operating with samples outside the mold. An orientation of the colloidal structure of compounds above 10% by volume of MPC black is thus easily demonstrated. The dielectric properties of the compounds depend, in this case, on the size of the samples, since this orientation is a function of the dimensions, especially of the thickness of the molded compound. On the other hand, from the behavior of vulcanizable and nonvulcanizable compounds, a distinction may be made between the respective effects of both the vulcanization and the special state of agglomeration of the black colloidal particles in the compounds. This ‘structure’ of the black affects apparently both the losses and the dielectric constant through an electronic polarization phenomenon which can, in principle, be analyzed through the Maxwell-Wagner general theory of heterogeneous dielectrics. The effect of ‘structure’ on low-frequency losses depends essentially upon the nature and ratio of the black and varies like direct current conductivity. This ‘structure’ seems to be influenced also—although to a much smaller extent—by vulcanization, since the level of losses during heating is lower than with a nonvulcanizable compound containing the same ratio of black. When this ratio does not exceed 10% by volume, vulcanization governs the dielectric properties more directly, both by a fixation of polar sulfur to molecular chains, and by an ionic dissociation of vulcanizing ingredients. In the range of this study the only effect of molecular polarization is a rather limited increase of the dielectric constant; the losses are not affected. The sudden decrease of losses noted during the vulcanization of a gum compound is explained by a disappearance of the ions formed by the vulcanization reactions. This ionic polarization of the Maxwell-Wagner type plays no marked part in Compounds containing large amounts of black, no doubt because the ions are adsorbed by the black. By extending this study, as it is hoped, into the field of radio frequencies, it should be possible to improve the theory of the evolution of dielectric properties during vulcanization. From the practical point of view, such work would provide useful experimental data for a rational application of radio-vulcanization.
Filler-Rubber Interaction in Latex
Authors: Dogadkin B. A. , Senatorskaya L. G. , Guseva V. I. , Suslyakov A. V. , Zakharchenko P. I.
Published: February 2011

Conditions for the production of strong vulcanizates by direct addition of channel black to SKS-30 butadiene-styrene latex have been determined. Rubber reinforcement by carbon black in latex mixes occurs on addition of such substances as casein, gelatin, and alginic acid to the mixture. Experimental data are cited to show that the rubber reinforcement effect in the presence of the above substances is due to : a) their destabilizing action and the formation of structures in which the carbon black and rubber particles are in direct contact ; b) conditions in which the latex components are precipitated simultaneously (coprecipitation effect). Electrolytic coagulation of carbon black—latex mixtures results in increased vulcanizate strength. Vulcanization of filled latex compounds proceeds at a lower rate than that of ordinary rubber compounds of the same composition.
Modification of Rubber by Reaction with Maleic Anhydride
Authors: LeBras Jean , Pinazzi Christian , Milbert Gérard
Published: February 2011

The reaction between maleic anhydride and rubber has been studied in solution, by milling and by heating in the solid phase. However, as is most often the case with chemical derivatives of the rubber hydrocarbon, the operating conditions that were employed only yielded products exhibiting considerable impairment to the physical properties characteristic of rubber (especially its high elasticity) as a result of secondary reactions of scission, cyclization and crosslinking. It has subsequently been shown that it is possible, under certain conditions, to minimize these injurious effects, both in the case of the reaction in solution between natural rubber and maleic N-methylimide and in that of the reaction by milling between synthetic olefinic elastomers and maleic anhydride. Inspired by these studies, we have undertaken to re-examine, on more precise chemical bases, the reaction between the rubber hydrocarbon and maleic anhydride.
A Simple Extensometer for Tensile Testing of Polymers
Authors: Eagles A. E. , Payne A. R.
Published: February 2011

The prototype extensometer, which has now been in constant use for over a year, gives satisfactory results which compare favorably with those of the conventional method. The use of this extensometer, which is a simple mechanical device, robust and reliable in operation, removes the last obstacle from autographic recording of tests using dumbbell specimens, thus permitting a considerable increase in speed of tensile testing.
Evaluation of Rubber-Solvent Interaction
Authors: Shvarts A. G.
Published: February 2011

1. The influence of differences in the nature of the intermolecular forces in different solvents on their solvent powers has been examined. 2. A graphical method is proposed for evaluation of the influence of the nature of the intermolecular forces of the solvent on the maximum swelling of vulcanizates. 3. For a given rubber and a given chemical class of solvents, the relationship between δs and (μ−μs)òVs is linear. Lines for different classes of solvents intersect at one point which represents δr, the solubility parameter for the rubber.
Branching in Macromolecules of Different Synthetic Rubbers
Authors: Poddubnyĭ I. Ya , Ehrenburg E. G.
Published: February 2011

Branching in macromolecules of synthetic rubbers is one of their most important structural properties, exerting a pronounced influence on the physical behavior of these materials. The degree of branching evidently depends on the chemical nature of the free radicals or organometallic catalyst initiating the polymerization reaction. It also depends on the conditions of the reactions, particularly on the polymerization temperature, as the latter determines the relative rates of the propagation and branching reactions. The problem of developing a general quantitative method for the determination of branching in the molecules of high polymeric substances cannot yet be considered as solved. This problem appears to be very complicated and only a few experimental data are available. Therefore the development and application of methods with a sound physical background for the qualitative evaluation of branching have not lost their value. Most methods used for the determination of branching are based on the relations existing between the dimensions of molecular coils in solution and the degree of branching. Certain limitations of the methods commonly used for the determination of branching by values of Huggins' constant K′, the thermodynamic parameter μ, or the second virial coefficient arise from the fact that by such methods the above relation cannot be precisely accounted for. Therefore, in the present investigation, the degree of branching has been studied by viscosity measurements and also by determining the dynamo-optical properties of a polymer-fraction solution. The parameters found by this method, namely the dynamo-optical constant [Δn], obtained from the magnitude of the flow birefringence, the rotational friction coefficient, W, calculated from the orientation angles, as well as the intrinsic viscosity [η], all are determined by the dimensions of the molecular coils. By these methods, the investigation of the influence of the polymerization temperature on the branching for a number of synthetic rubbers obtained in the presence of different catalysts was carried out. Moreover, the intrinsic viscosity determinations made it possible, by the use of modern theories of polymer solutions, to estimate quantitatively branching in molecules of some synthetic rubbers.
Adhesion of High Polymers. 3. Effects of the Size, Shape, and Polarity on Adhesion to Cellophane
Authors: Voyutskiĭ S. S. , Shapovalova A. I. , Pisarenko A. P.
Published: February 2011

1. The method developed by the authors has been used to study the influence of size, form, and polarity of macromolecules on the adhesion of high polymers to cellophane. 2. Adhesion of high polymers to cellophane increases with decreasing molecular weight. However, for maximum bond strength, the cohesive properties of the polymer must also be taken into account. 3. Increase of the number of short side chains in the polymer molecule lowers its adhesion. 4. The adhesion of a polymer to cellophane decreases with increasing contents of polar groups in its macromolecules. 5. The results are explained on the basis of the diffusion theory of high polymer adhesion developed by the authors.
Radiation Crosslinking of Rubber—Effect of Additives
Authors: Turner D. T.
Published: February 2011

Rubber is one of the linear polymers which may be crosslinked by high energy radiation. In this paper the effect of a range of additives on the cross-linking of rubber by pile and gamma radiation is reported. Many were found to retard crosslinking and this is of interest mechanistically and as an example of protection against high energy radiation. A major problem in radiation chemistry is the relative importance of ions, excited molecules, and free radicals. An ionic mechanism has been suggested for the crosslinking of polyethylene and both excitation transfer and free radical hypotheses of protection have been suggested in the radiolysis of polymethyl methacrylate. The adequacy of a free radical mechanism may be assessed by comparison of protective power and radical acceptance and in this work most of the additives were chosen because of their known, or reasonably inferred, reactivity towards free radicals and, in particular, of polyisoprenyl radicals.
The Mechanism of 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 one of the most widely used vulcanization accelerators, 2-mercaptobenzothiazole (MBT), has not been sufficiently investigated. It was demonstrated by Wistinghausen, and also Dogadkin and Pevzner (1951) that MBT is consumed during vulcanization, but the quantitative relationships involved in this reaction could not be established due to the lack of a method for determining the disappearance of the MBT. For the present study we made use of MBT labeled with the radioisotope S35 in the thiazole ring. The synthesis of MBT was carried out in the following manner. First, MBT labeled in both sulfur atoms, was prepared from phenly isothiocyanate and elementary S35. The MBT thus obtained was then heated in sealed ampules with excess ordinary sulfur at 140° for 6 hours. Under these conditions, the interchange reaction between the elementary sulfur and the sulfhydryl sulfur leads to an equilibrium. There was a twofold drop in the activity of the synthesized MBT. That is the way in which the labeling of the benzothiazole radical alone was accomplished, so that the radioisotope S35 introduced into the MBT molecule was not exchanged with elementary sulfur under the vulcanization conditions that obtained. This now made possible simultaneous measurements of the rate of sulfur addition and the rate with which the accelerator is added to the rubber.
The Chemistry of Vulcanization. II. Kinetics of Hydrgen Sulfide Evolution during the Reaction of Diphenylmethane and Sulfur
Authors: Tsurugi Jitsuo
Published: February 2011

In Part I, the products and mechanism of reaction between diphenylmethane and sulfur were reported. The reaction products at 180° C were hydrogen sulfide, benzhydryl polysulfide (PS) and thiobenzophenone (TBP). On the basis of this mechanism the theoretical rate equation is now derived and compared with experimental results.
Reaction between Diphenylmethane and 2,2′-Dibenzothiazolyl Disulfide
Authors: Tsurugi Jitsuo , Fukuda Haruko
Published: February 2011

At a lower temperature where no decomposition of the primary product occurred, the reaction mechanism is a radical chain reaction indicated by Equations (1) to (4). At 160° C one of the primary products, MSCHPh2, was decomposed to various secondary products by the radicals which were present in the reaction system. The decomposition mechanism is indicated by Equations (7) and (7′) and from (8) to (11).
The Separation and Characterization of Graft Copolymers from Natural Rubber
Authors: Merret F. M.
Published: February 2011

The solubility of graft copolymers prepared from rubber and vinyl monomers follows a general pattern whereby one of the constituents can be insolubilized while the other remains soluble, the compound forming a stable sol which is largely unaffected by heat or ionic materials at suitable ratios of solvent to precipitant. The onset and flocculation of the sol are such that the graft copolymer can be completely separated from either free constituent homopolymer. This insolubilization of the rubber trunk chain by addition of methanol to a benzene solution of the coploymer has been followed by the changes in the intrinsic viscosity and turbidity, which show that the collapse of the rubber chain continues to a point beyond where the molecularly equivalent free rubber would be precipitated. This period also marks the major increase in turbidity. Osmotic data show that μ-values for the grafted copolymers of rubber are the same as for rubber itself, thus supporting similar assumptions made in the application of the theory of the equilibirium swelling of crosslinked rubber.
The Mechanism of Protection by the Deactivating Effect
Authors: le Bras Jean , Danjard Jean-Claude , Boucher Madeleine
Published: February 2011

In order to better understand the complex phenomena related to aging, the two following propositions should be considered : (a) Each type of vulcanizate has a particular type of network structure, with characteristics dependent on the number and nature of the crosslinks between the macromolecules. Thermo-oxidative degradation may have varying effects according to the network points which are preferentially attacked. (b) The protection at present employed against the consequences of this degradation is based upon two different mechanisms, i.e., through the antioxidant effect, which retards the scission reaction, or through the deactivating effect, which helps to maintain the network by forming additional crosslinks. If we also take into account the fact that each accelerator is able, as is the deactivator, to create specific new bonds by after-cure, we may suggest an explanation for some unexplained aspects of the related phenomena. From our results and the derived deductions ideas emerge, from which it should be possible to establish, by logic (instead of empirically) and by adaptation to each type of vulcanizate, some rules for the best protection with the present-known protective agents. It should be noted that all preceding observations refer exclusively to the most widely used industrial practice, sulfur curing. However, the knowledge we now have of the deactivating effect mechanism has led us to think that it should also be possible, for vulcanizates produced with other vulcanizing agents, to find substances which will play the same part as our present deactivators, although of a totally different chemical composition. As a matter of fact, the so-called deactivators are but slow-acting crosslinking agents, the new crosslinks resulting from either a mobilization of the unused vulcanizing agent in the vulcanizate or from a direct intervention of the deactivator. We therefore doubt whether their name, derived from the first, and inexact, explanation given for their action, is still justified. However, to change it we should have to evoke an after-crosslinking, a source of confusion with other current terms ; moreover, a number of other wrong terms have been confirmed by use, for instance, the English “antioxidant”. As these deactivators make degradation less active, their original name is perhaps not so inappropriate after all.
The Protection of Rubber against Atmospheric Ozone—Cracking
Authors: Biggs B. S.
Published: February 2011

The cracking of rubber by atmospheric ozone is now a well-known phenomenon and for a number of years rubber scientists and technologists have devoted considerable effort to combating it. While the differences of opinion and the confusion of data in this work are sometimes more conspicuous than the successes, nevertheless, there has been considerable success. In spite of the existence of large areas of uncertainty, much progress has been made. A new word, “antiozonant”, has been added to the vocabulary of the rubber man. The substances so designated, together with waxes already well known, enable the compounder to protect natural and synthetic rubbers against both static and dynamic exposure to a fair degree, and this in spite of the fact, now recognized, that certain urban atmospheres may contain much higher concentrations of ozone than were formerly considered normal. In addition, the synthetic polymer chemist has made available a number of commercial rubbers which, because they are saturated, are not at all vulnerable to ozone attack, and serve in many special applications in which extreme resistance to ozone is necessary. The purpose of this paper is to review the present status of the antiozone work.
The Determination of Free Sulfur in Accelerators
Authors: Hively R. A. , Wadelin C. W.
Published: February 2011

Since the amount of sulfur and accelerator added to a rubber stock affects the properties of the vulcanized stock, it is obviously desirable to know the amount of free sulfur in the accelerator. An isotopic dilution method by Ikeda and Kambara seems to be the only reference to work on this problem. The essential steps in their procedure are as follows: A known amount of radioactive sulfur of specific activity must be added to a weighed sample. Then a sufficient amount of free sulfur must be separated from the mixture in a very pure state so that it can be weighed and its activity measured. The method requires radio chemical equipment that might not be available. The modification of the polarographic procedure of Proske by Poulton and Tarrant is both sensitive and accurate for the determination of sulfur. Unfortunately, some of the sulfenamide accelerators interfere in the procedure. Other methods for the determination of sulfur include the reaction with sodium hydroxide, sodium sulfite mercury, potassium cyanide, silver, and triphenylphosphine. Schöberl et al., have shown that alkali hydroxides, sulfites and cyanides react with disulfide linkages. Triphenylphosphine disrupts some disulfide and sulfenamide linkages. Hydrogen sulfide and mercaptans combine with the metals. Adsorption chromatography of a benzene solution on alumina separates free sulfur (weakly adsorbed) from accelerators (more strongly retained). The polarograph offers a sensitive means for determination with some additional specificity of the separated components.
Vulcanization of Elastomers. 19. The Function of Oxides in Thiuram Vulcanization
Authors: Scheele Walter , Grasemann Horst , Mau Günter , Stange Peter
Published: February 2011

This article is a continuation of our discussion of the role of oxides in thiuram vulcanization. The following additional results were obtained: The reaction of TETD and ZnO gives off gaseous products and is pressure dependent. By taking this into account, both the conductometric and the spectrophotometric methods of analysis furnish identical results for the DEDC yields as a function of reaction times. The reaction of TETD with Bi2O3 produces in the presence or absence of NR (independent of the temperature) approximately 82 mole per cent BiDEDC based on the initial amount of TETD. However, no vulcanization takes place. The reaction between TETD and TeO2 produces in the presence or absenee of NR (independent of the temperature) a maximum yield of Te-II-DEDC of 60 to 70 mole per cent based on the initial amount of TETD. Such a yield of DEDC is also observed during a TETD vulcanization with ZnO. Nevertheless, no normal thiuram vulcanization takes place when TETD, TeO2 and NR are heated together. When Te-IV-DEDC is dissolved in various organic solvents, it undergoes disproportionation and equimolar amounts of Te-II-DEDC and TETD are formed. The limiting value of the Te-II-DEDC formation of 60 to 70 mole per cent during the reaction of TETD with TeO5 in the presence or absence of NR can be explained by a primary formation of Te-IV-DEDC in a maximum yield of 80 mole per cent followed by a disproportionation of the Te-IV-DEDC (the same as with a corresponding reaction in the presence of Bi2O3). Of course, it is assumed that the metal oxides during their reaction with TETD give maximum yields of 80 to 90 mole per cent DEDC based on the initial amount of TETD. Furthermore, the experiments showed that thiuram vulcanization obviously is due to the reaction of TETD with ZnO in which NR participates with formation of crosslinks. This concept is supported by the identical activation energies of the TETD decrease and DEDC increase during the reaction of ZnO with TETD in the presence and absence of NR.
Metal Oxides as Vulcanization Activators for Sodium Butadiene Rubber
Authors: Feldshteĭn M. , Orlovsky P. , Dogadkin B.
Published: February 2011

1. Differences have been found in the action of metallic oxides as vulcanization activators for sodium butadiene rubbers polymerized by the rod and rodless methods. 2. It was found that unloaded mixes based on rodless sodium butadiene rubber, containing accelerators of the thiazole and sulfenamide types, do not require the addition of metallic oxides as vulcanization activators. 3. It was shown that addition of zinc oxide to mixes based on rodless rubber with high alkali contents retards the vulcanization process.
The Mechanism of Vulcanization and the Action of Accelerators
Authors: Dogadkin B. A.
Published: February 2011

Vulcanization of rubber is due to the formation of chemical interlinks between molecular chains of rubber. A number of investigators maintain that formation of these bonds is due to reactions of radical character. In the present paper data are presented which were obtained during the study of reactions in which elementary sulfur is liberated at room temperature. As a prototype of such reaction is the interaction of hydrogen sulfide and SO2 which in rubber causes the socalled Peachey vulcanization. The usual views on the mechanism of this process are that the activity of sulfur liberated in statu nascendi is high enough to enable it to react with rubber and to create the spatial structure of the vulcanizate. However, this is an error. We have shown that pure sodium-butadiene rubber, heated to 80° in nitrogen atmosphere, does not vulcanize by the Peachey procedure, e.g., it does not become insoluble and its modulus of elasticity does not reach finite values. Consequently, the reaction causing the vulcanizing effect has a more complex character. To elucidate the mechanism of vulcanization we have studied the reaction of benzothiazolyl disulfide (MBTS) with hydrogen sulfide. In a hydrocarbon medium these compounds react at room temperature forming quantitatively elementary sulfur and mercaptobenzothiazole (MBT). Kinetics of this reaction are shown in Figure 1. If this reaction is carried out in a 10% solution of sodium-butadiene rubber, then the sulfur adds to the rubber, but vulcanization as characterized by formation of a spatial structure does not occur. The rubber solution is not gelatinized. An analogous phenomenon is observed during interaction of benzoyl peroxide with hydrogen sulfide. Sulfur liberated in this reaction also does not cause crosslinking (vulcanization of rubber).
Effect of Mercaptobenzothiazole on Rubber Structure during Oxidation, Heating and Milling
Authors: Dogadkin B. , Dobromyslova A. , Sapozhkova L. , Tutorskiĭ I.
Published: February 2011

1. Mercaptobenzothiazole (MBT) accelerates the oxidation of natural rubber and considerably increases the rate of its oxidative degradation. 2. When benzene solutions of natural rubber are heated in an inert gas atmosphere at 100°, no irreversible changes occur in the rubber whether in presence or in absence of MBT. 3. Plasticization of natural rubber in air at 100–150° is intensified in presence of MBT, which is caused mainly by the accelerating action of the latter on the oxidative degradation of rubber. 4. Mercaptobenzothiazole assists plasticization of rubber at low temperatures in an inert gas atmosphere. MBT is consumed in the process, owing to its interaction with the polymeric radicals formed by mechanical rupture of the rubber molecules. 5. The amount of MBT reacting with the rubber increases with increasing contents of 1, 4 structure in the rubber molecules. 6. It is shown that different fractions of the masticated product contain different amounts of MBT, indicating that MBT reacts preferentially with the end valencies of the radicals formed by cleavage of diallyl bonds. 7. Reaction schemes for the interaction of MBT with rubber in mechanical and oxidative processes are suggested.
Vulcanization of Hard Rubber
Authors: Kuzminskiĭ A. S. , Borkova L. V.
Published: February 2011

1. It has been established that a hard rubber at optimum vulcanization is an unsaturated compound. 2. The decomposition rate of double bonds and the limit of the decrease in unsaturation are independent of the amount of sulfur initially dispersed in the rubber, since the vulcanization proceeds with practically a constant concentration of dissolved sulfur. 3. It has been found that in the process of hard rubber vulcanization a tendency toward the formation and decomposition of sulfur crosslinks appears. The higher the vulcanization temperature the greater the rate of crosslink decomposition. 4. It has been shown that polysulfide links are formed in the early stages of hard rubber vulcanization. In the subsequent vulcanization process their polysulfide chain length decreases through the decomposition of such links, and a hard rubber at optimum vulcanization retains only the monosulfide and disulfide bonds. 5. It has been established that in hard rubbers the forces of intermolecular interaction are increased sharply by the formation of a dense spatial network, which increase is revealed externally by the transition of the material from a viscous-elastic to a glasslike state. (a) This transition in hard rubbers is accompanied by changes in a whole complex of mechanical properties. (b) As the network density of a hard rubber increases its glass transition temperature Tg is shifted to higher temperature regions. 6. It has been shown that hard rubber flows under a load at temperatures of 150– 170° C because of the decomposition of the sulfur links which form its spatial structure. Flow is a specific property of sulfur vulcanizates only. 7. It has been established that in thermal hard rubbers, soft rubber vulcanizates and raw rubbers an intensive spatial structure formation develops at temperatures of 150– 170° C. Structure formation cannot occur in sulfur vulcanizates because of the inhibiting action of the sulfur liberated by the decomposition of the sulfur bonds.
The Kinetics of the Reaction of Organic Sulfides with Methyl Iodide. I
Authors: Scheele Walter , Triebel Wolfgang
Published: February 2011

The reaction of organic sulfides with methyl iodide was subjected to more thorough investigation from a kinetic standpoint. The results were as follows: Both the bimolecular-reacting dialkyl monosulfides and dimethyl disulfide are converted in a methanol solution and in the presence of a great excess of methyl iodide, according to the 1st order to the corresponding sulfonium iodide. The disulfide reacts much more slowly than the monosulfides. Diallyl monosulfide as well as methyl allyl monosulfide react under these conditions with methyl iodide in a wide conversion range, according to the 1st order law. Yet, in the case of diallyl monosulfide at the beginning, and methyl allyl monosulfide at the end of the reaction, deviations from the 1st order law are observed. Activation energies were computed from the temperature functions of the 1st order rate constants. Higher values are obtained with diallyl monosulfide and dimethyl disulfide than with either the dialkyl monosulfides or methyl allyl monosulfide. An accurate method for determining the sulfonium iodide formed was worked out and reported. The results obtained in these investigations are intended to furnish the basis for experiments to be used in the analysis of crosslinking sites in vulcanizates. Our experiments will therefore continue in this direction.
Sound Propagation in Plates and Rods of Elastomeric Materials
Authors: Naake H. J. , Tamm K.
Published: February 2011

The known results for the propagation of sound in plates with Poisson's constant σ=0.5 (liquids) and σ=0.35 (aluminum) are completed by dispersion curves with σ=0.47 (rubber). The dispersion curves are easily understandable because of the large difference between the velocities of transverse and longitudinal waves occurring at this value of σ. Measurements of the propagation of elastic waves in rods of rubber with square cross section in the frequency range 0.1 to 300 kc/s are reported. The amplitude is measured as a function of distance by partly submerging the rod into a waterfilled vessel within which a hydrophone is arranged. The results with respect to phase velocity and attenuation can be explained in terms of the propagation of extensional waves at low frequencies and compressional waves at high frequencies separated by a range with high attenuation.
Oxidation-Reduction Systems for Initiation of Radical Processes. VI. Systems Involving Oxygen for Initiation of Oxidative Degradation of Polymers
Authors: Tinyakova E. I. , Dolgoplosk B. A. , Reĭkh V. N.
Published: February 2011

1. The mechanism of action of various oxidation-reduction systems containing organic reducing agents, iron salts, and oxygen, is investigated, and it is shown that in hydrocarbon media these systems are an effective source of free radicals at low temperatures. 2. The possibility of utilization of these systems for initiation of a chain process of oxidative degradation of unsaturated and some saturated polymers, at low temperatures, is shown.
Ozone Attack on Rubber Vulcanizates
Authors: Buckley D. J. , Robison S. B.
Published: February 2011

The effect of the attack of ozone on rubber vulcanizates is well known in a qualitative way. Only recently have efforts been made to study this problem quantitatively. Because of this the state of knowledge on this subject is not so satisfactory as that obtained for ordinary oxidation. A quantitative study of the rate and extent of the reaction of ozone with rubber vulcanizates and the cracking under strain is discussed herein. The general knowledge on this subject tells us that ozone attack results in the cracking of the surface of vulcanizates. Cracking occurs only when the specimen is under some strain during exposure to ozone. The broad quantitative problem then becomes one of defining the factors controlling the reaction while the specific problem relating to cracking becomes one of measuring such crack generation and crack growth in vulcanizates under strain. The method used in this work may be described as follows. A sample is stretched and allowed to relax until most of the pertinent stress relaxation has taken place. Ozone is then admitted to the stretched and relaxed sample. As cracking occurs the stress in the sample decreases and the length increases. The effect of the ozone produced cracks may be considered as related to change in form of work. The initial work done on the sample by stretching is derived from an equation expressing the network-statistical theory of rubber elasticity. The cracking is considered as a transformation of work to form new surface.
Oxidative Decomposition of the Ozonide of Butadiene Rubber
Authors: Yakubchik A. I. , Kasatkina N. G. , Demidova G. I. , Fedorova G. B.
Published: February 2011

1. Among the products of oxidative decomposition with acetyl hydroperoxide of the ozonide of butadiene rubber (prepared at 5°) are levulinic, formic, succinic, 1,2,4-butanetricarboxylic, 1,2,3-propanetricarboxylic and l,x,y,6-hexanetetracarboxylic acids. Levulinic acid could be formed by isomerization of 1,4-1)2-1,4-chains of the rubber macromolecule and by partial decarboxylation of β-ketoadipic acid, as well as by the peroxy-formate rearrangement in presence of acetyl hydroperoxide. 1,2,3-Propanetricarboxylic acid is more likely to be formed from 1,4-1,4-chains branched at the α -methylene group, or from 1,4-1,2-1,4-chains in which the double bonds had undergone suitable rearrangement, rather than as a result of secondary reactions during oxidative breakdown of the ozonide. 1,2,3-Propanetricarboxylic acid was also detected among the products of ozonolysis obtained under mild conditions of breakdown. 2. Products of oxidative breakdown of the ozonide of the rubber in question with hydrogen peroxide were acetic, formic, succinic, 1,2,4-butanetricarboxylic, 1,2,3-propanetricarboxylic and 1,x,y,6-hexanetetracarboxylic acids. Acetic acid could have been formed from 1,4-1,4-portions of the rubber molecule branched at the α -methylene group, as well as from isomerized 1,4-1,2-1,4-portions.
The Hot Mixing of Rubber. I. Influence of Mixing Conditions on Scorching and on the Physical Properties of the Vulcanizates
Authors: Fromandi G. , Reissinger S.
Published: February 2011

In this work, it is shown that the special characteristics of sulfenamides must be taken into consideration so that the assurance in the processing of rubber compounds in which these reagents are used as accelerators may not be impaired. At higher temperatures the sulfenamides are split into equimolar proportions of 2-mercaptobenzothiazole and amine. This is a combination, which depending on the components and their amounts, makes an especially active accelerator system. The thermal pretreatment of rubber compounds which contains sulfenamides must be so controlled that the decomposition temperature of these accelerators, which depends among other things also on the compounding ingredients, is not prematurely exceeded.
Carboxylic Rubbers. II. Properties of Cured Stocks
Authors: Dolgoplosk B. A. , Reĭkh V. N. , Tinyakova E. I. , Kalaus A. E. , Koryushenko Z. A. , Sladkevich E. G.
Published: February 2011

The experimental evidence shows that the mechanical and elastic properties of the carboxylic rubber compounds far exceed those of the synthetic rubber type compounds. Important qualities of gum and lightly filled carboxylic rubber compounds are: good mechanical and elastic properties, high cut growth resistance and good resistance to heat aging. The disadvantage is the tendency of the carboxylic rubber mixtures to scorch. Carboxylic rubbers are of considerable interest for the preparation of general and special purpose rubber compounds.
Dependence of Tack Strength on Molecular Properties
Authors: Forbes W. G. , McLeod L. A.
Published: February 2011

A method has been developed for the measurement of the tack strength of fresh and reproducibly smooth rubber surfaces. Using this method the tack strength of natural rubber is shown to be independent of polymer purity, and, to a large extent, Mooney viscosity, intrinsic viscosity, gel content and molecular weight distribution. The relative tack strengths of polyisoprenes of different molecular weights prepared in different catalyst systems are measured. The results are discussed in terms of microstructure. A study of the tack strength of oil-extended butadiene-styrene copolymers indicates that relative tack strength is related to the shear viscosity of the bulk polymer. Measurements of relative tack strength on Alfin and free radical butadiene-styrene copolymers, butyl, brominated butyl and butadiene-acrylonitrile copolymers confirm the inportance of shear viscosity in controlling tack strength. Choice of catalyst system and temperature of polymerization cause the largest variation in polymer viscosity. The contact time required for the relative tack strength to become unity is shown to be inversely dependent upon the value of the relative tack strength itself. Shear viscosity measurements are given for six classes of polymer and the values shown to correlate with relative tack strength. It is postulated that molecular weight (and probably also chain entanglement) is the controlling variable. The bond strength between two different uncured polymers is shown to depend upon the difference in cohesive energy densities of the two polymers.
The Reactions of Isocyanates and Isocyanate Derivatives at Elevated Temperatures
Authors: Saunders J. H.
Published: February 2011

Qualitative and quantitative studies with model compounds have shown that a variety of reactions may occur at 100–300° in molecules containing isocyanate, urea and urethane groups. All or most of these reactions are subject to catalysis so that they may be induced to proceed at lower temperatures. These reactions are quite important as they may affect the production and practical use of polyurethanes and polyureas. By the proper selection of reaction components one may design a polyurethane or polyurea molecule which will give both a reasonable rate of cure to the final state and a degree of temperature stability suitable for many rigorous applications. The choice of reactive groups providing approximately the desired rates of reaction and of suitable catalysts may be used to achieve the necessary curing rate. The initial choice of a catalyst which will have a minimum effect on decomposition reactions, or the removal of the catalyst from the cured polymer will favor polymer stability. A selection of reactants which will minimize those decomposition reactions leading to chain rupture, and which will compensate for what rupture may occur, will promote polymer stability. Simple illustrations of such choices would include eliminating tertiary aliphatic hydroxyl groups from the hydroxyl-bearing component and including some degree of branching commensurate with the degree of elasticity or rigidity desired. Branching should be achieved through the more stable groups, e.g., urethane, urea or trimer, rather than through the less stable allophanate and biuret groups. Many thoroughly tested applications of polyurethanes and mixed polyureaurethanes show that it is readily possible to produce such polymers with excellent thermal stability.
Quantitative Measurement of Rate of Ozone Cracking
Authors: Veith A. G.
Published: February 2011

For reliable ozone testing a controlled ozone atmosphere is a necessity. There is a movement under way to correct the deficiencies of the ASTM Method D 1149-55T. These deficiencies are (a) the lack of a sufficient air throughput rate and circulation in the presently specified chamber and (b) difficulties encountered in the analysis of ozone. A new chamber and counter-current ozone absorption column that avoid the above-mentioned shortcomings are described. As part of a program to obtain basic information on the phenomenon of ozone cracking, some preliminary results on the ozone-induced creep of gum vulcanizates are reported. The creep rate has been expressed in terms of the initial rate of cross-sectional area decrease due to ozone cracking. This rate is a measure of the collective growth of ozone cracks. Induction periods during which no creep occurs have been observed. The geometry of the test specimen is an important variable. An “absolute” rate of cross-sectional area decrease can be otained independent of specimen geometry. For practical reasons an approximate “absolute” rate is used where specimen geometry is maintained essentially constant. The rate of cross-sectional area decrease is linearly related to the reciprocal degree of orientation of the network chains (λ0F)−1. The logarithm of the induction period is also linear with (λ0F)−1. Explanations for this particular dependence are offered. The rate of crack growth and the induction period for a series of common polymers were measured. Both parameters placed the polymers in the order that experience would indicate and lend confidence to the creep technique.
Chemical Antiozonants and Factors Affecting Their Utility
Authors: Cox William L.
Published: February 2011

To obtain the maximum effectiveness from antiozonants such as the N,N′-dioctyl-p-phenylenediamines in any given stock, information to date indicates the desirability of: (a) The selection of proper antiozonant-polymer combination. (b) The use of low-oxygen-content reinforcing blacks (thermal or furnace rather than channel). (c) The use of a thiazole-accelerated sulfur cure. (d) The proper design of product to avoid cured-in strain and sharp edges. The choice of antiozonant concentration will depend in part on strain, ozone concentration, and temperature to be encountered in service, as well as the type of service—static or dynamic—and the desired crack-free life of the article. Only through a consideration of all these factors can the maximum results from chemical antiozonants be achieved.