bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Structure of Elastomers on Their Permeability to Gases
Authors: Van Amerongen G. J.
Published: February 2011

It is a known fact that rubber membranes are permeable to gases and that the rate of permeation is a specific function of a given gas and rubber. We may picture this permeation of gas through rubber as a process in which gas molecules dissolve on one side of the membrane, then diffuse through the rubber to the other side, and there evaporate out of the membrane. Thus the process of permeation is divided into several independent processes, those of solution and evaporation being governed by Henry's law and that of diffusion by the diffusion equation (Fick's law). The problem to be considered is why a given rubber should possess a given permeability to a given gas. It will at once be evident from what has just been stated that, while studying the problem, the process of solution (or evaporation) and that of diffusion must be dealt with separately. It was shown in earlier investigations on a series of rubber varieties and gases how the chemical structure of the rubber molecules affects the rate at which the gas passes through, and, notably, that the introduction of methyl and polar groups in the polymer molecules and crystallization reduce this rate of diffusion. It was also found that a gas diffuses more slowly as its molecules are larger. The solubility of the gas in the rubber is determined by its tendency to condense and by the interaction between the rubber and the gas molecules. These views will now be put to the test with reference to another series of rubbers and gases. We shall also see that knowledge of the necessary conditions for low permeability may help to evolve new kinds of rubber of low permeability.
Ultra-Speed Tensile of Rubber and Synthetic Elastomers
Authors: Villars D. S.
Published: February 2011

A high speed stress-strain machine has been developed which is capable of recording the stress-strain curve of elastomers at elongation rates up to 270 per cent/msec. Data are reported on two series of gum and tread stocks of Hevea and of the synthetic elastomers, GR-S, Hycar-OR, Butyl, Perbunan, and Neoprene-GN. The second (elastomer) series was also run at 150° C. In general, stress-strain curves fall into two classes. Stocks of elastomers which are known to crystallize on stretching tend to show tensile strengths which decrease with increasing speed up to about 10 per cent/msec, pass through a minimum, and rise more or less drastically to values 100 per cent (or more) greater than the Scott tensile strength. Elastomers which do not crystallize on stretching tend to show a steady rise in tensile strength with increasing speed. Elongation at break curves show a maximum with crystallizing stocks and no maximum with noncrystallizing stocks. The shape of the modulus vs. speed curves is accounted for on the hypothesis of different types of slipping bonds with different characteristic relaxation times. The shift of curves for tread stocks with temperature allows the estimation of a heat of activation of slippage. This comes out to be of the order of 3 kg.-cal.
Stress-Strain Properties of Natural Rubber under Biaxial Strain
Authors: Boonstra B. B. S. T.
Published: February 2011

(1) The stress-strain curves of vulcanized rubber held at definite tangential elongations during stretching differ more from the simple unidirectional-extension-stress curve than the theory predicts. The differences are larger at higher tangential elongations. (2) The relaxation constant determined at 600 per cent elongation is practically unaffected by tangential elongations up to 300 per cent.
Tetramethylthiuram Disulfide Vulcanization of Extracted Rubber. V. Low Molecular Products and the Mechanism of Zinc Oxide Activation
Authors: Craig David , Davidson W. L. , Juve A. E.
Published: February 2011

The essential features of TMTD vulcanization, as revealed by compounding tudies, were discussed in Part I of this series. Thus, TMTM, a product of TMTD vulcanization, and an active accelerator of sulfur vulcanization, was found to be an inhibitor, and ZnDMDC, a main product of TMTD vulcanization, in the presence of ZnO was found to be devoid of activating properties. As a replacement of ZnO, which is a potent activator, ZnDMDC displayed only mild activating effects. Zinc palmitate was even more potent than ZnO. Zinc sulfide was somewhat less active than ZnO. Palmitic acid and DMADC had little or no effect on the cure. The second paper reported that TMTD could be prepared in good yield by the reaction of TMTM with sulfur and also, as a result of radiosulfur techniques, that the four sulfur atoms in the TMTD molecule are chemically identical. Part II also reported that ZnO reacted with TMTD to form sulfur and ZnDMDC in good yield. Other reactions of TMTD were discussed. Part III, in presenting a short-path distillation technique for studying vulcanizates, reported that the nearly complete removal of zinc from the TMTD vulcanizate is not accompanied by devulcanization. Part IV reported on the behavior of rubber as an acid. This behavior results in the liberation of palmitic acid from zinc palmitate. From the comparison of the reaction of TMTD with acids and the reaction of rubber with TMTD, it was inferred that rubber is an OH-containing acid. Acids in the work reported were found to react rather slowly with TMTD to form dimethylamides and sulfur in good yield. The acidic nature of rubber did not seem to be great enough to contribute in any fundamental way to the vulcanization process. The present paper describes further studies of the TMTD vulcanization problem.
Specific Heat of Natural Rubber
Authors: Ichimura Hiroshi
Published: February 2011

The constant volume specific heat of natural rubber is calculated from the constant pressure specific heat, which is measured experimentally, and it is shown that the low temperature part is expressed by a combination of the Debye and Einstein formulas. Some theoretical considerations on the transition phenomena at 200° K are included.
Comment on “Relationship between Gough-Joule Coefficients and Moduli of Vulcanized Rubbers”
Authors: Mooney M.
Published: February 2011

In an article of the title quoted above Conant, Hall, and Thurman were interested in establishing by experiment the theoretical equality between the tangent shearing modulus of a rubber and the ratio of the temperature coefficient of shearing stress to the negative temperature coefficient of shearing strain. Their published data can be used also for calculating the value of an important property, the relative temperature coefficient of relative stress, σ, at constant strain, γ, or T/σ(∂σ/∂T)γ. The value of this coefficient is unity if there is entropy change but no energy change in an isothermal strain, as is postulated in the kinetic theory of elasticity. The values of the coefficient can be calculated from the data given by Conant, Hall, and Thurman for σ/γ, 1/γ(∂σ/∂T)γ, and T, the reference temperature. The calculations yield the results:
Chlorination of Natural Rubber. I. Preparation and Properties of Chlorinated Rubber
Authors: van Amerongen G. J. , Koningsberger C. , Salomon G.
Published: February 2011

The chlorination of rubber has been the subject of extensive investigations, the rubber being commonly treated in solution with gaseous chlorine at a given temperature and pressure. The properties of the products of rubber thus treated vary in close dependence on the chlorine content, which may be as much as 70 per cent. The drawback to a low chlorine content is that, as a rule, the chlorine is loosely bound, with the result that, when exposed to heat or light, it splits off as HC1, with formation of discolored and cyclized products and serious deterioration of the mechanical properties. But the higher the chlorine content, the more stable are these chlorinated rubbers. The stability of chlorinated products of natural rubber containing approximately 65 per cent of chlorine is such that they are used commercially as a component of anticorrosive paint. The instability of chlorinated rubber of low chlorine content is closely connected with its chemical constitution and the mechanism of reaction. The current opinion ten years ago was that chlorine first adds to the double bond of the rubber, and that this primary product, while splitting off HC1, enters into further reaction with chlorine ; but reexamination of this reaction in the laboratory of our affiliated English organization and independently in our own laboratory has led to very different views. It was realized that rubber dichloride (the addition product of chlorine and rubber) is far too stable to act as an unstable intermediate product during the chlorinating reaction. Bloomfield argued that, during the primary reaction, the chlorine is attached by substitution to an α-methylenic carbon atom of the rubber molecule and that there is a considerable amount of cyclization. It was not our sole concern to study the mechanism of reaction; we were also bent on following the chlorination of rubber under the most diverse conditions, starting from dry rubber, rubber in solution, and rubber in latex, and with highly diversified sources of chlorine such as from liquid chlorine, gaseous chlorine, hypochlorites, and sulfuryl chloride. The normal course of reaction, involving the formation of unstable intermediate products, is discussed in Part I of this series; methods of producing comparatively stable rubber chlorides by adding chlorine onto the double bond are considered in Part II.
Determination of Copper in Rubber Latex
Authors: Poulton F. C. J. , Tunnicliffe M. E.
Published: February 2011

Small amounts of copper in rubber latex can be determined by following a dry-ashing procedure for removal of organic matter and concluding with a colorimetric determination of the copper in the ash. Provided the ignition is not undubly prolonged, the ashing temperature can safely rise to 800° C, and recovery of the copper is complete from the ash when a mixture of nitric and hydrochloric acids is used. Results are slightly higher than those obtained by the wet oxidation process. Assay of the copper can be carried out on the solution of the ash, either in aqueous medium or in carbon tetrachloride solution, depending on the extent of interference anticipated from iron and insoluble ingredients, such as clay, and on the degree of accuracy required. Visual color matching in aqueous solution is simpler and quicker, but insoluble material may give rise to considerable personal error. In aqueous solution, the copper equivalent of ferric iron is about 1/100, i.e., the coloration is about 100 times more intense for copper than for iron. for more accurate work, measurement of the color of a carbon tetrachloride solution of the copper diethyldithiocarbamate complex by means of a suitable colorimeter is recommended. The tendency of the complex to fade is overcome by replacing the sodium diethyldithiocarbamate by the zinc salt dissolved in carbon tetrachloride. In such a solution the copper equivalent of ferric iron is about 1/1000, but actual experimental conditions can vary this figure between wide limits. A more satisfactory procedure is, therefore, to measure the total color developed in carbon tetrachloride, and then bleach out the color due to copper with potassium cyanide. The residual (interfering) colors can thus be estimated, and the difference between the readings gives a direct measure of the concentrations of copper in the test solution.
Application of Infrared Absorption Spectra to Studies of the Oxidation of Sodium-Butadiene Rubber
Authors: Dogadkin B. , Kasatochkin B. , Klauzen N. , Smirnova A.
Published: February 2011

The reaction of rubber with molecular oxygen explains well the structural changes which take place in rubber during aging and during a number of important technological processes, such as plasticization and vulcanization. Furthermore, during vulcanization, in addition to its reaction with the vulcanizing agent, rubber also reacts with oxygen contained in the mixture. This may be one of the reasons for an optimum point of vulcanization. However, it is difficult to explain the changes of physical properties of rubber by simple union of oxygen, with formation of oxygen-bearing groups. To account for the changes observed, addition of a large quantity of oxygen would be necessary, whereas actually notable changes are brought about by the absorption of only 2–3 per cent of oxygen. To explain this, it must be assumed that oxygen causes structural changes in rubber and that these changes become evident when the percentage of oxygen in the reaction products is still negligible. In the case of sodium-butadiene rubber, as was shown by one of the authors, this reaction at any particular temperature causes an increase of strength and of elasticity, and a loss of solubility. The object of the present investigation was a qualitative and limited quantitative analysis of those groups which originate during oxidation and also an examination of the structures which determine the changes of the physical and chemical properties in the reaction of rubber with molecular oxygen.
Interaction between Carbon Black and Polymer in Cured Elastomers
Authors: Stearns R. S. , Johnson B. L.
Published: February 2011

This research was initiated to determine whether the interaction at the interface between the surface of finely divided solids, such as carbon black, and cured elastomers is primarily physical or chemical in nature. Further, it was desired to correlate some physical property of the reinforced stock with the surface properties of the solid pigment. Through an examination of the thermodynamic changes accompanying the deformation of loaded stocks it is shown that physical adsorption of the van der Waals type occurring at the interface between pigment and polymer is inadequate to account for the experimental observations. However, if chemical bonding occurs at the interface between polymer and pigment, then the entropy of deformation of the stock may be correlated with the extent of this bonding. By a calorimetric method it was demonstrated that the surface of a carbon black particle contains sites that react with bromine to liberate the same amount of heat as low molecular-weight olefins. It is, therefore, proposed that a carbon black particle be considered as a disordered agglomerate of polymeric benzenoid type molecules which contain around their perimeters various functional groups. The existence of olefinic-type unsaturation on the surface of carbon blacks suggests strongly that, in the case of carbon blacks, the polymer and pigment are combined chemically through pigment-sulfur-polymer bonds into a continuous three-dimensional cross-linked matrix.
Permanganate Oxidation of Polybutadiene Rubbers
Authors: Naples F. J. , D'Ianni J. D.
Published: February 2011

In view of the failure to obtain quantitative yields of the expected carboxylic acids by permanganate oxidation of the several butadiene polymers studied, definite conclusions about their structures cannot be made. The results have a qualitative significance, however, in that the −10° emulsion polymer was found to produce a larger amount of succinic acid than the 50° emulsion polymer and less tricarballylic acid, and thus they correlate with general thinking that lowered temperature of polymerization results in a polymer of more regular structure and less branching. The Alfin polymer, although prepared in a system entirely different from the emulsion system, gave results which indicated a microstructure similar to that of 50° emulsion polybutadiene. Sodium polybutadiene was less completely characterized than the others, but the large amounts of carbon dioxide and β-carboxyadipic acid isolated correlated well with the high percentage of external double bonds known to be present from other methods of analysis.
Direct Reinforcement of Natural Rubber Latex Mixes
Authors: Le Bras Jean , Piccini Ivan
Published: February 2011

The direct utilization of latex has up to the present time been limited to a relatively small number of applications because of lack of knowledge of how to communicate to articles sufficient hardness, modulus, resistance to tearing, and resistance to abrasion. It is possible to obtain such properties by combining the molding of latex (thermosensitized by the action of trypsin) with the addition of partially condensed resins. Numerous types of resins can be utilized, but the best results have been obtained by resorcinol-formaldehyde resins. The mechanical properties of vulcanizates thus prepared are extremely high—for example, the tensile strength may reach 7500 pounds per square inch (with an elongation of 700 per cent), and the resistance to tearing 900 pounds per inch. Operating conditions that must be observed for the formation of the resin are described in detail, as well as the influence on the properties of vulcanizates of different factors: length of condensation of the resin, conditions of vulcanization, proportion of catalyst, molecular ratio of constituents, conditions of drying, etc. A new way is opened for obtaining vulcanizates of natural rubber of outstanding mechanical propoerties.
Retraction Test for Serviceability of Elastomers at Low Temperatures
Authors: Smith O. H. , Hermonat W. A. , Haxo H. E. , Meyer A. W.
Published: February 2011

Elastomer vulcanizates progressively stiffen as the temperature is lowered. Additional stiffening, due to crystallization, may occur as exposure to low temperatures is prolonged. The available methods of testing the low temperature flexibility of rubber and rubberlike materials do not reveal the losses in flexibility caused by crystallization except by using prolonged storage at low temperatures. A retraction test employing large deformations, which greatly increases the rate of crystallization, has been developed. This test rapidly gives a temperature index correlating with the stiffness of elastomer vulcanizates after storage at low temperatures, and can be used to measure the merit for low temperature applications of both crystallizable and noncrystallizable elastomers. This test in conjunction with conventional (room temperature) tests has been used successfully to study the low temperature performance of Hevea, GR-S, Paracril, and polybutadiene vulcanizates along with vulcanizates of many experimental elastomers. Correlation of results with cold compression set and hardness after low temperature storage has been excellent and substantiates the usefulness of the test.
Heats of Solution and Swelling of Some Synthetic High-Molecular Compounds
Authors: Tager A. , Sanatina V.
Published: February 2011

1. The heat of solution of a high polymer depends on the nature of the solvent as well as on the nature of the polymer. 2. The value and sign of the heat of solution of a polymer are related to the structure of the polymer and its mechanical behavior. For polymers which have relatively flexible chains, the heats of solution are negative ; for polymers which have relatively rigid chains, the heats of solution are positive. 3. The value and sign of the heat of solution indicate to a certain degree the change of the barrier potential of the polymer chain in any given solvent.
Relaxation Processes in the Deformation of Unloaded Rubbers and the Influence of the Degree of Vulcanization
Authors: Dogadkin B. A. , Reznikovskii˘ M. M.
Published: February 2011

1. It is shown that the process of stress relaxation at different initial elongations as well as the process of deformation at constant rate for unloaded rubbers at different temperatures (20–70° C) can be represented quantitatively by equations suggested in earlier works. Likewise the possibility of expanding the theories proposed for the kinetics of high-elastic deformation of spatial polymers is substantiated. 2. It is shown that the relaxation properties of soft unloaded vulcanizates of natural rubber and many synthetic rubbers do not undergo essential changes during vulcanization. 3. The conjecture is expressed that the invariability of the relaxation properties during vulcanization continues until the bonds of the spatial network are distributed sufficiently widely not to influence the activity or heat movement of the chain segments between them.
Dynamic Properties of Raw and Vulcanized Polymers
Authors: Enabnit R. S. , Gehman S. D.
Published: February 2011

Theoretical considerations made it probable that the usefulness of measurements of vibrational properties of vulcanizates to evaluate rubberlike qualities and heat generation under flexing might be extended to raw polymers if a suitable technique of measurement could be found. Such a technique was developed and correlations between dynamic properties of raw polymers and vulcanizates were studied. The test conditions, using low amplitude shear vibrations at 60 cycles per second, were such that effects due to plastic flow in raw polymers were suppressed and values of dynamic modulus and resilience were independent of plasticity. The data obtained showed a definite correlation between the dynamic properties of a series of raw polymers and those of vulcanized gum and tread stocks prepared from them. The effect of cure was measured throughout a range from the raw state to overcure for Hevea, polybutadiene, and butadiene- styrene copolymers. The ease of measurement, small quantity of material required, and the nature of the correlations observed indicate the usefulness of dynamic evaluations for raw polymers. Furthermore, it appears possible, with suitable background, to anticipate fairly well from raw polymer measurements the dynamic properties that can be achieved in a vulcanized compound.
Chlorination of Natural and Synthetic Polyisoprenes
Authors: Kraus Gerard , Reynolds W. B.
Published: February 2011

The extent of additive and substitutive chlorination was determined for emulsion polyisoprene, Hevea and gutta-percha chlorinated to different chlorine contents in darkness and in a nitrogen atmosphere. The maximum amount of additive chlorine that can be introduced into the polymer is 1.21 atoms of chlorine per isoprene unit for synthetic emulsion polyisoprene, 1.14 for Hevea. The chlorination involves a cyclization reaction by pairs, leading to isolation of reactive units. The loss in unsaturation due to cyclization has been calculated statistically by the method of Flory and Wall, and has been shown to be consistent with the total amount of additive chlorine in the fully chlorinated product. Cyclization takes place in the early stages of the chlorination simultaneously with the initial substitution. The theoretical limit of cyclization calculated statistically is 86.5 per cent of all isoprene units cyclized for natural rubber and 72 per cent for polyisoprene containing 10 per cent vinyl side chains. Iodine chloride titration gives fair results for samples of low chlorine content, but is not applicable to polymers containing much more than 35 per cent of chlorine. Knowing the degree of cyclization, the unsaturation can, however, be calculated for any polymer from the extent of additive reaction. Substitutive chlorination is catalyzed by oxygen and peroxide, additive chlorination by ultraviolet light. Cyclization is partially prevented by the increase in additive reaction. Under the combined effect of peroxides and ultraviolet radiation, chlorination can be carried to very high degrees.
Volumetric Oxygen-Absorption Test for Rubber Aging
Authors: Shelton J. Reid , Cox William L.
Published: February 2011

A volumetric oxygen-absorption test for aging of rubber has been investigated from the point of view of the effect of cure and the effect of mercapto-benzimidazole on the aging behavior. The test has also been evaluated by comparison with conventional air oven and oxygen bomb aging. A compounded but uncured Hevea black stock is more resistant to oxidation than the vulcanized material, but after a reasonable cure is obtained, further heating produces only a small change in the rate of oxygen absorption. The change in physical properties corresponding to a given amount of oxygen absorbed varies somewhat with time of cure in the initial stages, but after the absorption of 4 or 5 cc. of oxygen per gram of rubber, the changes in most physical properties are a direct function of the amount of oxygen absorbed. Neither time of cure nor the presence or absence of inhibitor has any significant effect on the subsequent rate of change in such properties as tensile strength and ultimate elongation for a given amount of oxygen absorbed. Oven aging data on identical time cures confirm the reported superiority of a combination of mercaptobenzimidazole with a conventional type of anti-oxidant. Oxygen absorption data reveal, however, that mercaptobenzimidazole causes a significant decrease in the rate of oxidation of a Hevea black stock, and thus it clearly functions at least in part as an antioxidant in the usually accepted sense. The deterioration of properties is, in general, proportional to the oxygen absorbed, except in the early stages of oxidation where the mercaptobenzimidazole stocks change somewhat less than the controls for a given amount of oxygen absorbed. When the cures are selected to give comparable initial properties, however, the change in tensile strength of the mercaptobenzimidazole stocks with amount of oxygen absorbed is essentially the same as for the controls, even in the initial stages. These data suggest that the observed protection imparted by mercaptobenzimidazole results from a combination of two factors: (1) the normal antioxidant activity of mercaptobenzimidazole, which reduces the amount of oxygen absorbed; and (2) an effect on the nature of the cure attained when mercaptobenzimidazole is present, such that the absorption of a given amount of oxygen in the early stages is not accompanied by as great a change in properties. Thus, it appears that the deactivating effect may be the result of the effect of this material on the vulcanization process rather than a direct effect on the oxidation process. A comparison of the effect of oxygen absorption, air oven, and oxygen bomb aging methods on changes in physical properties of Hevea black stocks shows that the results obtained by oxygen absorption and air oven methods (both at 100° C) are similar, but that the higher oxygen concentration of the oxygen bomb test (70° C and 300 pounds per square inch) apparently results in a higher proportion of chain scission when compared to cross-linking of the polymer chains.
Contribution to the Physical Chemistry of Hevea Latex. I. Metal Cations in Latex
Authors: Belmas Robert
Published: February 2011

Our knowledge of Hevea latex is still incomplete, and some problems, such, for example, as a study of its natural inorganic ingredients, have not been attacked. Some work of value has been done on the analysis of the ash from latex and on the influence of metals in solution on the colloidal stability of latex, but few facts are available concerning the physico-chemical state of these metals in the natural emulsion and their partition between the serum and rubber particles. The investigation which is described in the present paper is devoted to metal components which are capable of influencing, when in soluble form, the colloidal behavior of latex. These include potassium sodium, calcium, and magnesium and, under some conditions, iron. Copper and manganese were not studied in this work for they have been the object of numerous investigations, and these metals play in effect the part of powerful prooxygenic agents in the oxidation of rubber.
Application of Drop Analysis to the Detection of Compounding Ingredients in Rubber Mlxtures. II
Authors: Kulberg L. M. , Bloch G. A. , Golybkova E. A.
Published: February 2011

1. The method of drop analysis is of wide use in the testing of crude rubber mixtures. 2. Methods of detection of mercaptobenzothiazole, tetramethylthiuram disulfide, diphenylguanidine, sulfur, zinc oxide, and magnesium oxide were developed.
Qualitative Analysis of Rubber Mixtures. II
Authors: Burmistrov S. I.
Published: February 2011

In Part I, reactions by which it is possible to identify Neozone, aldol-α-naphthylamine, tetramethylthiuram disulfide, and diphenylguanidine, when present alone or in the form of simple mixtures with inorganic ingredients, were described. These reactions can serve for the determination of these ingredients in complex mixtures as well, provided that the mixtures are first separated in the pure state. Chromatographic separation on a strip of filter paper is especially suitable for this process. It should be remembered that it is always difficult to determine the various ingredients in finished rubber products when they have undergone chemical changes or decomposition under the influence of high temperatures. In many cases the decomposition products have not been examined, and this naturally has hindered qualitative analysis of the mixtures. For this reason a study of the behavior of various ingredients under actual conditions of vulcanization and from this the development of methods of qualitative analysis became necessary. The author has shown that diphenylguanidine decomposes with formation of aniline under these conditions; it is also well known that diazoaminobenzene forms aniline and aminoazobenzene forms diphenylamine. In certain cases a specific ingredient can be detected by means of its decomposition products. Thus the presence of diphenylguanidine in the original mixture can be established if aniline is detected in the rubber and there are no other ingredients in the mixture which give off aniline during decomposition. In this work methods of detecting Neozone in raw rubber, rubber mixtures, and finished rubber products and also methods of determining mercaptobenzothiazole, diphenylguanidine, diazoaminobenzene, and products of their decomposition are described.
Investigations of the Reversion of Vulcanized Rubber under Heat
Authors: Shankar Uma
Published: February 2011

(1) During reversion of a vulcanizate, the breakdown of cross-linkages, including those of polysulfides, predominates over any simultaneous reformation of cross-linkages. (2) The reverting modulus falls exponentially with time. (3) The calculated molar free energy of activation is 33.3 ± 1.7 kcal., irrespective of the temperature or the atmosphere of cure or the composition of the mix, and is sufficient to rupture an —S—S— bond. (4) The degree of cross-linking, estimated from the equilibrium swelling measurements in benzene, falls during reversion. (5) The exclusion of oxygen during curing does not prevent reversion if the temperature is high enough to supply the energy needed to break up the cross-linkages. (6) During reversion in nitrogen, hydrogen sulfide is freely evolved, and the C/H ratio rises above the value for C5H8. (7) Evidence for the formation and breakdown of polysulfides during reversion is provided by an increase in free sulfur and a decrease in combined sulfur during a given cure, and the methyl iodide reaction of the reverted vulcanizates.
The Action of Unsaturated Compounds on Natural Rubber in Solution. II. The Reaction Induced by Heat Alone
Authors: Delalande André
Published: February 2011

The addition reaction at an elevated temperature (170° C) of maleic N-methylimide with natural rubber in solution was studied. Attempts were made to apply the principles of kinetics to this thermal reaction with a view to understanding the nature of the reaction, but the complexity of the system made impossible any chance of attaining the results hoped for. A comparison of the fixation of acrylonitrile and that of maleic N-methylimide in the temperature range of 160°–200° C showed that the rates of these two reactions are in the ratio of 1 to 25–30. A determination of the unsaturation of the addition products showed that fixation is on the α-methylenic carbon atoms of the rubber hydrocarbon. Finally a mechanism of the reaction is proposed, in which free radicals play a part.
Effects of Antioxidants on Rate of Breakdown of Rubber during Mastication
Authors: Cotton F. H. , Lee K. O.
Published: February 2011

Piper and Scott milled rubber with and without the addition of 2 per cent of hydroquinone on a cold mill. They could not detect any difference between the rates of breakdown. Wren made similar observations, but undefined experimental errors might vitiate his interpretation that phenols do not retard mastication. Phenyl-β-naphthylamine, however, has been reported to retard the breakdown of rubber during mastication in an internal mixer at 160° C. It was, therefore, decided to make an independent investigation.
The Heat Sensitivity of Hevea Latex. I. The Action of Zinc-Ammonium Complexes
Authors: Cassagne Paul
Published: February 2011

Among the different processes for heat-sensitizing latex by the more or less direct action of zinc-ammonium complexes, one has the choice of inorganic and organic complexes. Among the inorganic complexes, zinc-ammonium nitrate seems to be the most effective. Prepared from a 5 N solution of zinc nitrate and 5 N ammonia, it gives good heat sensitization when a volume of 2 per cent, based on the volume of the latex, is used. Among the organic complexes, the formate and acetate are particularly to be recommended because of their great heat-coagulating power. Dicarboxylic amino acids give active compounds, but they are more troublesome. Fat acids containing double bonds, of the type zinc-ammonium undecylenate or the oleate, have the advantage of being applicable to the manufacture of sponge rubber, for the complex, because of its surface-active properties, acts both as a foaming agent and a heat-coagulating agent, and can be added at the moment of use or several hours earlier without difficulty. Thus, the range of heat sensitizing agents of the zinc-ammonium complex type is, in fact, reduced to two or three practical effective agents, namely, the formate and the acetate in the manufacture of solid objects, and the oleate in the manufacture of molded sponge objects. The stearate often used is much less effective.
The Heat Sensitivity of Hevea Latex II. The Process of Heat Sensitization of Degraded Latex
Authors: Cassagne Paul
Published: February 2011

The heat sensitivity of a naturally or biochemically degraded latex is due in large part to the presence of amino diacids liberated by the degradation of proteins. These acids alone are capable of forming zinc ammonium complexes; however, in the case of a highly degraded latex, the monoacids with zinc oxide form soluble salts which are capable of heat coagulating this latex, the chemical stability of which has been much weakened by the desorption of the proteins. The nature of the amino acids governs the solubility of zinc oxide and, consequently, the heat sensitivity of the latex under consideration. In order to complete this work, we would have to determine the behavior of zinc-ammonium complexes in the phenomenon of coagulation, and study their dissociation in the latex. Does coagulation take place by simple neutralization of the negative particles of rubber by the Zn(NH3)4 cation, or rather, as is believed by certain Dutch chemists, does the zinc hydroxide formed by dilution of the complex act in a particular colloidal state? The problem remains unsolved.
Particle Size of Rubber Globules in Hevea Latex
Authors: van den Tempel M.
Published: February 2011

1. The use of visible light in determining the average particle size or the particle-size distribution in Hevea latex renders the results meaningless, as only about 40 per cent of the particles have a diameter of more than 0.2 µ. 2. In considering the size-frequency distribution curve as determined by Lucas, it could be assumed that, actually, the number of particles having a diameter of less than 0.12 µ might be very much larger than has been indicated by him. The agreement with the determination of the number of particles by van Gils, however, may be taken as evidence in favor of the correctness of the curve as given by Lucas. 3. An expression has been given which describes the size-frequency distribution curve, as found by Lucas, with a high degree of accuracy. It is necessary to assume that no particles larger than 5.2 µ are present in the latex. 4. Attention is directed to the considerable difference existing between the various average diameters, caused by the strongly asymmetrical shape of the size-frequency distribution curve. This work forms part of the program of fundamental research on latex problems undertaken by the Research Department of the Rubber-Stichting, Delft, under the management of H. C. J. de Decker.
Quantitative Characterization of Cure. III. Relation between Compound Viscosity and Vulcanizate Stiffness in Pure-Gum Natural-Rubber Vulcanizates
Authors: Blackwell R. F. , Fletcher W. P. , Gee Geoffrey
Published: February 2011

The aim of this investigation was to study the dependence of vulcanizate stiffness on the compound Mooney viscosity, and if possible to derive a method by which account could be taken of variations in viscosity in order to reduce the so-called mixing error in batches of test compound. Investigations covering a range of compounds, raw rubbers, and curing times gave results which for the practical range indicated a relation between modulus at 100 per cent elongation and Mooney viscosity. Using the relationship thus established, a method of adjusting modulus results to correspond to a standard Mooney viscosity was derived. Application of the scheme to batches of ACS1 compound mixed from parts of the same lot of homogeneous raw rubber led to a considerable reduction in the range of modulus values.
Chemical Constitution and Deactivating Effect
Authors: le Foll Jacques
Published: February 2011

The experiments which have been described show that the thiol group is sufficient to develop the deactivating effect. However, its action can be more or less modified by neighboring chemical groups. For the deactivating effect to be pronounced, it is necessary for a thiol group to be associated with certain other chemical groups. The choice of these latter groups is a delicate one, for the final compound must fulfill two conditions which from a practical standpoint are difficult to meet conjointly, viz., (1) the thiol group must not be nullified by any tautometric effect, a phenomenon which is common to many compounds, and (2) the compound must not have too marked an accelerating action, such as that of certain well known very active accelerators containing the thiol group. The present work would indicate, then, that the most effective structure from the viewpoint of the deactivating effect is a cyclic structure, either pentatomic or hexatomic, in which the carbon atom carrying the thiol group is surrounded by two nitrogen atoms or, alternately, by a nitrogen atom and an oxygen atom. This type of structure is notably true of mercaptobenzimidazole, mercaptopyrimidine, and mercaptobenzoxazole.
The Mechanism of Gelation of Latexes
Authors: Panich R. M. , Kalyanova K. A. , Voyutskiĭ S. S.
Published: February 2011

1. The solubility of zinc oxide in ammonia and sodium hydroxide solutions was studied. In this case the presence of an ammonium salt in the system has a strong influence, and increases the solubility of zinc oxide, because the ammonium ion inhibits dissociation of ammonium hydroxide into NH4+ and OH− ions, and thus aids the formation of complex zinc-ammonium ions. We established that, in the 0–60° range, the temperature has little effect on the solubility of zinc oxide in aqueous ammonia. 2. The action of the zinc-ammonium ion on solutions of stabilizers of the soap type is explained, and it is shown that, at sufficiently high alkalinity, zinc-ammonium soaps do not precipitate from solution, but remain in a colloid state, stabilized by the alkaline soap or hydroxyl ion. 3. It is established that, in the absence of the ammonium ion, zinc oxide does not cause gelation of latexes stabilized by soaps. 4. The effect of formaldehyde on the gelation of latexes stabilized with soaps has been studied. 5. The reactions which can take place when zinc oxide is added to ammonia and alkali solutions, to ammonium and alkaline soap solutions, and to ammoniated and non-ammoniated latexes are discussed. A scheme of successive reactions which must take place during the gelation of latexes stabilized with soaps is presented.
Quantitative Determination of Natural Rubber Hydrocarbon by Refractive Index Measurements
Authors: Fanning Rachel J. , Bekkedahl Norman
Published: February 2011

Rubbers from different sources vary considerably in rubber hydrocarbon content, from 70 per cent or less for some of the wild varieties to about 95 per cent for a good grade of plantation rubber. The quality of a rubber is measured to a great extent by the percentage of rubber hydrocarbon. A new procedure for the quantitative determination of this hydrocarbon has been developed, which involves the measurement of refractive index of a solution of a known weight of acetone-extracted rubber in a known weight of 1-bromonaphthalene. From the observed data and from other previously determined or known physical constants, such as the densities and refractive indexes of the rubber hydrocarbon and the solvent, the percentage of hydrocarbon in the original sample can be calculated. This new method gives results as good as, or better than, other existing methods, and is simpler and less time-consuming to perform.
Changes of the Mechanical Properties of Vulcanizates during the Early Stages of Thermal Oxidation
Authors: Kuzminskiĭ A. S. , Lyubchanskaya L. I.
Published: February 2011

1. The structural-mechanical properties of vulcanizates of various rubbers during the time of the induction period and during autocatalytic oxidation were studied. 2. A change of the mechanical properties of vulcanizates in the induction period is a consequence of oxidation (degradation and polymerization) and thermal structure formation, taking place with the participation of the double bonds of the side chains. 3. In complete accord with the theory, at the end of the induction period and in the early stages of autocatalysis, the physical-mechanical properties of vulcanizates change sharply; as a result of this, the vulcanizates lose their technical value. 4. During the heat aging of rubber, the concentration of inhibitor within the range of 0.25–0.5 per cent has no effect on the rate of change of the physical-mechanical properties of vulcanizates, but has a strong influence on the work capacity of the latter.
Determination of Rubber Hydrocarbon by a Modified Bromination Method
Authors: Gowans William J. , Clark Frederick E.
Published: February 2011

Published investigations show that, in the bromination of rubber, addition is accompanied by some substitution. The substitution portion of the bromination reaction is difficult to control and has contributed to low results and occasional poor precision. This work was carried out to investigate the effect of several factors on the bromination reaction and to find a means of inhibiting the substitution reaction. The effect of rubber hydrocarbon concentration on bromination is critical. Iodine accelerates bromination, but is not present in the final product. Temperature and light are important variables. The bromination reaction is insensitive to bromine concentration as long as a considerable excess is present. Trichloroacetic acid in the amounts used to assist in the solution of crude rubber has no effect on the results. Addition of chloroform to the benzene solution of rubber inhibits the substitution reaction with no apparent effect on the addition reaction. A factor of 0.299 for converting rubber bromide to rubber hydrocarbon is obtained for Hevea smoked sheet, which agrees well with the theoretical value. A conversion factor of 0.301 is obtained for guayule rubber, which may or may not indicate that guayule rubber hydrocarbon is slightly more saturated than Hevea. The method should have application for the direct and accurate determination of rubber hydrocarbon in crude rubber.
Mechanism of the Gelling of Hevea Latex by Zinc Compounds
Authors: Kraay G. M. , van den Tempel M.
Published: February 2011

Zinc oxide is known to be soluble to a certain extent in ammoniated Hevea latex. The solubility may be enhanced by several means, such as the addition of ammonium salts, and is due to the formation of zinc-ammonia complexes. The complexes themselves have no coagulating power. When heated, however, zinc ions are produced by dissociation of the complexes, and these ions react chemically with the adsorbed soap on the rubber globules, forming an insoluble zinc soap which links up all the rubber globules into a gel. Evidence in favor of the proposed mechanism was obtained by displacing the adsorbed natural higher fat acids of the rubber particles by a soap which does not form an insoluble zinc soap, such as Igepon-T. A latex treated in this manner does not gel when heated with zinc oxide and ammonium chloride at 70° C. By displacing the Igepon-T with ammonium oleate, the original rapid gelation is restored. Depending on the concentration of zinc ions available at room temperature and the amount and types of higher fat acids on the latex particles, thickening or even gelling may occur at room temperature. The above interpretation of the reaction mechanism may lead to new methods for the evaluation of latex.
Mercaptobenzothiazole Vulcanization Using Sulfur35
Authors: Auerbach Irving
Published: February 2011

A study has been made of the function of raercaptobenzothiazole in the vulcanization process. Radioactive sulfur35 and mercaptobenzothiazole tagged with sulfur35 were used for measuring the sulfur and mercaptobenzothiazole reaction rates. The effects of variations in the zinc oxide, sulfur, and mercaptobenzothiazole concentration on the sulfur combining rates were determined. It was found that a marked induction period exists, during which the zinc mercaptide of mercaptobenzothiazole, the initial product, reacts readily with sulfur. The ratio of combined sulfur to consumed mercaptobenzothiazole is constant during the vulcanization process. A kinetic expression is given which accounts for the data. When polyisobutylene was substituted for GR-S or Hevea, the zinc mercaptide of mercaptobenzothiazole was found to be the initial product. A mechanism is postulated for the accelerating properties of mercaptobenzothiazole. It involves the formation of the zinc mercaptide, which reacts with sulfur and rubber to regenerate mercaptobenzothiazole and form sulfur-rubber compounds.
Ozone Formation in Photochemical Oxidation of Organic Substances
Authors: Haagen-Smit A. J. , Bradley C. E. , Fox M. M.
Published: February 2011

The formation of ozone through photochemical oxidation of alcohols, aldehydes, ketones, acids, and hydrocarbons, such as are present in gasoline, in the presence of small quantities of nitrogen oxides has been demonstrated. Ozone production without the addition of nitrogen oxides has been observed in the photochemical oxidation of biacetyl, bibutyryl, pyruvic acid, and butyl nitrite. The ozone produced in these reactions was identified by chemical and physical methods. The ozone formation is attributed to a peroxide radical chain reaction. The release of large quantities of hydrocarbons to the air and the simultaneous presence of nitrogen oxides from combustion processes explains the relatively high ozone content, and consequent severe rubber cracking, in the Los Angeles area. These findings should be considered in planning rubber storage facilities. In view of the irritating properties of the products formed by this photochemical oxidation, both hydrocarbons and nitrogen oxides should be considered as potential irritants when they occur simultaneously in the air at low concentrations.
The Structure of the System: Filler Rubber. An Electron-Microscopic Study
Authors: Endter Friedrich
Published: February 2011

Electron microscopic investigations of the benzene-extraction residues of filler-natural rubber mixtures which are used for the determination of bound rubber, give a pattern of a three-dimensional network consisting of filler and bound rubber. The unchanged benzene-soluble rubber is present in the interstices of the network in the untreated filler-rubber mixture.