bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reaction of a Thiuram and Sulfur
Authors: Blokh G. A. , Sazonova L. P. 
Published: February 2011

Abstract
In a previous article the occurrence of an intensive interchange between atoms of elemental sulfur when present as vulcanizing agent and the sulfur atoms of the mercapto group of mercaptobenzothiazole as accelerator was shown by the isotopic method, i.e., by the application of tagged atoms of radioactive sulfur. Thus, the existence of a reaction between the accelerator and the vulcanizing agent during the vulcanization of rubber was established. The application of isotopes as tagged atoms is an effective new method of investigating the chemical structure of substances, their reactivities, and the mechanism of chemical reactions in which they take part. This method is being successfully developed in our country, particularly by the work of Brodskii˘ and his pupils. The present study is devoted to the problem of the reaction of tetramethylthiuram disulfide (hereafter called thiuram) and elemental sulfur. Studies in this field are of great scientific and practical interest, since the mechanism of the accelerating action of thiuram is not yet clear. We assume that the chemistry of the reaction is as follows. Thiuram is decomposed during vulcanization, with the formation of a dithiocarbamate and free active sulfur. Because of this, the thiuram can vulcanize rubber without the addition of elemental sulfur to the mixture. Such vulcanizates are particularly widely used in the cable industry.
Studies of the Mechanism of the Mastication of Rubber. VIII. The Reaction of Natural Rubber with 3,5-Dibromobenzoyl Peroxide
Authors: Imoto Minoru , Kiriyama Shigeru 
Published: February 2011

Abstract
The reaction of a natural-rubber solution with 3,5-dibromobenzoyl peroxide was carried out, and the following results were obtained. 1. Lowering of the viscosity of the rubber solution was observed. 2. Bromine contents in the degraded rubber were determined. 3. The molecular weight of the degraded rubber was determined. The reaction of rubber with DBPO is discussed on the basis of these observations.
Importance of the Polar Component of Mixed Fluids in the Swelling of Vulcanizates
Authors: Ermolenko I. N. , Mazel M. I. , Ermolenko N. F. 
Published: February 2011

Abstract
The problem of the relation of the swelling of vulcanizates to the nature of the liquid medium is very important in explaining the nature of vulcanization and determining the nature of the bond between the separate macromolecules in the vulcanizate. The relation of the swelling of vulcanizates to the molecular polarization of mixed liquids has been studied several times; however, the mechanism of the reaction of the polar component of a mixed liquid with the rubber molecules during swelling is still not very clear. According to contemporary theory, the swelling of polymers, particularly rubber, is thermodynamically analogous to the mixing of low-molecular liquids. Swelling is caused by a decrease of the free energy of the system: ΔG=ΔH−T⋅ΔS, which in the case of nonpolar polymers is due principally to an increase of entropy, T⋅ΔS, as a result of the separation of the molecular chains and their increased elasticity. For polar polymers, ΔH is the important factor. In this work rubber is regarded as a polymer in which the molecular chains are bound by nonequivalent bonds with varying amounts of energy, as appears in the swelling process, and not as a union of molecular chains surrounded by a uniformly strong field. It is evident from other studies that the latter assumption is not entirely correct. On the basis of a study of the protective action of antioxidants during the oxidation of rubber by oxygen, one of the authors regarded the mechanism of this action as the result of solvation of the antioxidant in the polar segments of the rubber molecule by the polar molecules.
Thermodynamics of the Swelling of Natural Rubber and Sodium-Butadiene Rubber in Binary Mixtures
Authors: Starobinets G. L. , Aleksandrovich Kh M. 
Published: February 2011

Abstract
1. The swelling of vulcanizates of natural rubber and sodium-butadiene rubber in the saturated vapors of binary systems of benzene and low-molecular alcohols (from methyl to butyl) at 20° and 50° C was studied in the entire range of composition of binary solutions. 2. The general form of the curves of isothermic equilibrium between the swollen polymer and binary solution were found to conform to Konovalov's law. 3. The absorption of a binary solution by both polymers has a very pronounced selective character. The selectivity of absorption of the solution is more pronounced, the greater is the density of energy of cohesion of the alcohol. In natural rubber, the capacity of selective absorption is more pronounced than in sodium-butadiene rubber. This is probably due to the larger concentration of oxidized groups in natural rubber. 4. The changes of the free energy, the heat content, and entropy for the passage of one gram-mole of alcohol from an infinitely dilute solution into the polymer were calculated from the experimental data. These calculations indicate that the reaction of the alcohol molecules with the polar groups of the polymer is dipole-dipole. 5. The passage from pure benzene to a swollen polymer of any particular composition is characterized by a large increase of entropy in comparison with the passage to a binary solution of the same composition. The relation in alcohol is the reverse. The increase of the entropy of benzene can serve as a measure of the elasticity of the polymer chains. A decrease of the entropy of alcohols indicates the content of free polar groups in the polymer phase. 6. The values of the partial heat content of the low-molecular components are positive; consequently, the decrease of free energy during their sorption by the polymer is due exclusively to an increase of entropy.
Performance of Carbon Blacks. Influence of Surface Roughness and Porosity
Authors: Dannenberg E. M. , Boonstra B. B. S. T. 
Published: February 2011

Abstract
Porous blacks of high surface area can be produced without changing particle size either directly, in the normal furnace black process, or indirectly, in the laboratory by the air oxidation of a normal commercial and essentially nonporous HAF black raw material. Blacks of high surface area produced by the direct process are characterized by a retardation of rate of vulcanization, lower rebound resilience, and high electrical conductivity. Laboratory-prepared products of high area show cure retardation, but their electrically conductive and resilience properties show relatively little dependence on the degree of porosity and surface area. Bound rubber measurements, modulus, tensile strength, and abrasion properties of the laboratory-oxidized samples indicate an increase of reinforcement with increasing surface area.
The Abrasion of Rubber
Authors: Schallamach A. 
Published: February 2011

Abstract
Theoretical results on the abrasion of rubber have been deduced from a few simple assumptions concerning the initiation of the surface damage. The abrasion is proportional to the normal load, independent of the particle size of the abrasive if the particles are polyhedral, and proportional to their mean radius of curvature if they can be approximated to hemispheres. The spacing of the abrasion pattern is proportional to the cube root of the normal load, proportional to the two-thirds power of the particle size on an abrasive with polyhedral particles, and directly proportional to the particle size on an abrasive with hemispherical particles. These predictions have been reasonably well confirmed by experiment.
Evidence for a Hydrochlorination Retarder within Natural-Rubber Latex Particles
Authors: Gordon Manfred , Taylor James S. 
Published: February 2011

Abstract
Kinetic evidence is presented for the occurrence in Hevea latex particles of a trace substance that retards the hydrochlorination reaction. No retardation effect is observed with synthetic polyisoprene latex. The chemical nature of the retarder in Hevea latex particles is not known, but it is likely to be a basic substance. Its retardation action reflects its power to deactivate the reactive precursor of the hydrochlorination reaction, which is interpreted as a form of ion pair (H+, Cl−). A constant amount of the precursor is deactivated by the retarder, irrespective of the temperature or the pressure of the hydrochlorination reaction.
Nature of Stark Rubber
Authors: Roberts Donald E. , Mandelkern Leo 
Published: February 2011

Abstract
The melting behavior and x-ray diffraction patterns of four different samples of stark rubber have been investigated. The melting temperatures, 39° to 45.5° C, are substantially higher than that observed for natural rubber crystallized by cooling. The x-ray diffraction patterns indicate that the crystallites in stark rubber are oriented. This observation can explain the higher melting temperatures. Thus, the previous assignment of an equilibrium melting temperature, 28° (±1°) C, to unoriented crystalline natural rubber is shown to be appropriate. Several different methods that have been used successfully in preparing stark rubber under controlled conditions in the laboratory are outlined.
Combination of Rubber and Carbon Black on Cold Milling
Authors: Watson W. F. 
Published: February 2011

Abstract
Although the structure of carbon black is imperfectly known, x-ray analysis has shown it to consist of layers of condensed rings of carbon atoms. Unsaturation and discontinuities in the layers are likely to provide sites for attack of free radicals, and thus make carbon black a radical acceptor of a special polyfunctional type. Assuming combination of rubber radicals and carbon black, a particle could terminate more than one sheared rubber chain. Furthermore, rubber chains attached to a carbon black particle could also undergo scission by shear and be terminated by combination with other particles. The result anticipated from this picture is a network of rubber and carbon black held together by chemical bonds. In rubber solvents, such a network would be insoluble and merely become swollen gel. Insolubilization of rubber on milling with carbon black has been reported on occasion, but the evidence is not sufficiently extensive to draw reliable conclusions as to its cause. This paper reports a systematic investigation of the occurrence of rubber-carbon black gel on cold milling. This gel has been shown to form, and the conditions for its formation and its properties have been interpreted as strong evidence for the above hypothesis of chemical-bond attachment of rubber and carbon black.
Determination of the Fatigue Resistance of Rubber Parts under Cyclic Shear Stress in Relation to Their Shape and Energy
Authors: Roelig Hermann , Fromandi Guido 
Published: February 2011

Abstract
Rubber is used far less frequently in tension than in compression for spring suspensions and vibration isolation. But for particularly soft springs, it is used in shear. For example, the compression modulus (at a deformation of 10 per cent of the height of the specimen) of a rubber cylinder 25 mm. in diameter and 25 mm. high, of 60° Shore hardness, may be 45 kg. per sq. cm., while its shearing modulus is only 7 kg. per sq. cm. Thus one may obtain a 6.5 times softer spring suspension by a shear mounting for the same volume of rubber. The use of rubber shear suspensions is facilitated by rubber-metal bonds, the quality of which today can be safely controlled technically in rubber factories. Thus we find shear suspensions in rubber-cushioned railway cars and automobile and aircraft construction. The exact design of such spring suspensions still is handicapped by lack of precise data on their fatigue strength, which can be obtained from dynamic tests. Such information would also facilitate the study of new elastomers and their comparison with those currently in use.
New Instruments for Measuring Hardness
Authors: Oberto Stefano 
Published: February 2011

Abstract
This report describes the characteristics of an instrument for measuring the hardness of rubber which has been designed in the laboratories of Pirelli S.p.A., and which is characterized by both precision and efficiency. The instrument meets the requirements for measuring hardness in International Rubber Hardness Degrees in accordance with the recommendation developed by the ISO/TC 45, the essential features of which are summarized. The usefulness of a hardness test for determining shear modulus, even when determined statically, and also the means of allowing, at least in part, for the associated after elastic effects are discussed. Finally, a durometer for determining hardness, using the same units, and of service when the thickness of the rubber sample is of the order of one millimeter, is described.
Rubber Hardness Testing
Authors: Scott J. R. 
Published: February 2011

Abstract
Dictionaries give a confusing array of explanations of “hard” and “hardness”. A hard material, according to the Oxford English Dictionary, is one “that does not yield to blows or pressure; not easily penetrated or separated into particles; firm and resisting to the touch …”. “Hardness” implies “difficulty of penetration, inflexibility, rigidity, stiffness …”. Even the earlier scientific workers on rubber were equally vague; thus, Dawson in 1927 regarded hardness as “an ill-defined little understood property” and considered that resistance to penetration—the practical criterion of hardness—“brings into play not merely forces associated with the surface cohesion, but also more deep-seated disturbances connected with elasticity, plastic deformation (or set), internal friction, resilience, and energy absorption”—truly an intractable mixture! The practical man, disregarding theoretical difficulties, has always judged hardness by some form of indentation test, if only with the thumb-nail or a pencil point, and out of such crude beginnings have grown the precise standardized tests of today.
Ozone Resistance of Butyl Vulcanizates
Authors: Edwards D. C. , Storey E. B. 
Published: February 2011

Abstract
A study of the cracking behavior of Butyl-rubber vulcanizates, exposed under static strain in an atmosphere containing 25 parts of ozone per 100 million parts by volume of air, is described. An account is given of sampling and testing procedures, including the development of a means of rating the severity of cracking in triangular strip specimens. The factors studied include polymer unsaturation, black and oil loadings, antioxidants, state of cure, and mixing variations. Cracking increases moderately with increasing raw polymer unsaturation, and is markedly reduced with increasing state of cure. Black loadings in excess of 40 parts per 100 parts of polymer are desirable. Plasticizers are generally detrimental to ozone resistance; the effect is proportaional to plasticizer loading, but varies considerably between plasticizers. The antioxidants tested were all of some benefit, but none offered complete protection at conventional loadings. Variations of laboratory mixing and processing techniques caused no substantial change in cracking behavior. By the careful choice of compounding ingredients and the use of a high state of cure, it is possible to prepare low-cost, highly resistant compounds without reliance on waxes or excessive antioxidant loadings.
Correlation of Room-Temperature Shelf Aging with Accelerated Aging
Authors: Youmans R. A. , Maassen G. C. 
Published: February 2011

Abstract
In 1931, a series of compounds was mixed to obtain data for publication purposes. After the necessary data for use at that time had been obtained, the remaining vulcanized test slabs of each compound were tied together in a bundle and stored in a desk drawer without wrapping. The compounds used for this series of tests contained different percentages of antioxidant. After being stored for 22 years, the several stocks were analyzed to determine whether there had been any migration of antioxidant from stocks containing antioxidant to those containing no antioxidant. A definite migration was found; compounds that had originally contained no antioxidant definitely showed its presence. It was, therefore, decided in this work to use a compound that had originally contained antioxidant, so that the results would not be affected by the gradual acquisition of an antioxidant.
The Shrinkage of Mold Cured Elastomer Compositions
Authors: Juve A. E. , Beatty J. R. 
Published: February 2011

Abstract
The coefficient of expansion of elastomer compositions depends on the kind of polymer employed, the volume per cent of polymer plus all other organic materials, and the kind and the amount of pigment present. The specific effects of pigments in retarding the shrinkage are shown. A procedure is given by which the shrinkage of most soft rubber compositions of the principal rubbers may be calculated from the recipe. The major part of the shrinkage of elastomer compositions is due to the much greater thermal contraction of the composition than of the material from which the mold is made. This portion of the shrinkage depends on the thermal coefficient of expansion of the composition and the mold material and the temperature difference between the curing temperature and room temperature. A minor part of the shrinkage is due to a contraction of volume resulting form vulcanization. For normal soft rubber stocks with sulfur ratios of three parts or less and for normal Neoprene stocks, this factor may be neglected. For stocks having higher sulfur ratios, an allowance needs to be made for this factor.
Temperature Control during Mixing of Rubber Compounds
Authors: Roth Frank L. , Decker George E. , Stiehler Robert D. 
Published: February 2011

Abstract
A study was made of the effect of the surface temperature of the rolls of a 6 × 12-inch laboratory mill on the properties of GR-S compounds and means of controlling this temperature. It was found that the properties of the GR-S compound depend on the surface temperature of the mixing rolls. No practical method of controlling the temperature of conventional rolls was found because of the slow rate of heat transfer. Therefore three types of special rolls, including one designed at the National Bureau of Standards, were investigated. The heat transfer characteristics of the NBS rolls permitted automatic control of their temperatures to within 7° F during mixing of natural rubber and several synthetic elastomers, with only one controller being used. A mill with the special NBS rolls has been in operation for about a year, and has resulted in a marked improvement in the control of mixing of rubber compounds. The automatic temperature control has been much more convenient than manual control, and has saved considerable time, since the rolls do not have to be warmed by milling scrap rubber.
Influence of Salt Coagulants on the Properties and on the Aging of Rubber Products Made by the Dipping Process
Authors: Thorsrud A. 
Published: February 2011

Abstract
The limited time which we had for this work permitted us to give only an outline of the effects of different salts on processing and on the properties, notably aging, of rubber articles prepared by the dipping process. Nevertheless this work justifies the following conclusions. 1. Ammonium salts have a thickening effect on a latex mixture, the extent of which depends on the nature of the anion. 2. Ammonium salts and salts of bivalent cations influence the wetting of the form by the latex mixture and, in addition, they have an effect on the uniformity of the deposit. 3. The rate of vulcanization of rubber containing a salt is greatly retarded and, in general, this retardation increases with the content of the salt. 4. Tensile strength is considerably lowered, especially by salts of bivalent cations; on the other hand it is only slightly influenced by ammonium salts. 5. Cations have a much more pronounced effect on the rate of vulcanization than do anions. 6. In a general way all the salts have a deleterious effect on the aging of vulcanizates, although it is impossible to differentiate with certainty between the effects of the anion and the cation. However, it would seem that chlorides have a more deleterious effect than acetates. Nitrates are definitely less harmful. 7. The hygroscopicity of the salts influences the rate of vulcanization, but it does not play so important a role in the aging of latex products as one might be led to expect a priori. 8. The natural aging of test samples containing barium chloride, calcium chloride and calcium acetate is particularly poor. In addition, the present work confirms the fact that different results are obtained by different methods of aging and seems to make it advisable to replace calcium chloride by calcium nitrate. Nevertheless, the avoidance of inorganic salts of any kind is recommended. Finally it should be pointed out that the structure of rubber in a product which has been washed (microporous) is not the same as that of rubber which has not been washed, as in the present work; consequently one cannot apply these conclusions to latex products which have not been through the washing process.
Effect of Sulfuric Acid Coagulation on Properties of Natural Rubber
Authors: Best L. L. , Morrell S. H. 
Published: February 2011

Abstract
The data indicate that the use of sulfuric acid in normal amounts as a coagulant has no deleterious effect on the properties of the raw rubber or on vulcanizates made from the raw rubber. When four times the normal dosage of sulfuric acid was employed, there was a slight softening of the raw rubber, but all samples examined had properties within the normal range of plasticity associated with natural rubber. The tendency to scorch and the rate of vulcanization of rubbers do not appear to be affected appreciably by the method of coagulation: any differences which may exist are not of such a magnitude as to cause the production of abnormal rubbers. It would seem that the use of excessive quantities of sulfuric acid during the coagulation of latex may cause some deterioration to the rubber. The sole advantage in using excess would appear to be a reduction of the time needed to complete coagulation. It should be noted, however, that the main reason for the use of sulfuric acid is economic, and it does not seem logical that the producer would use more than is necessary and thereby increase his coagulation costs. If the producer were to use four times the normal dosage of sulfuric acid, the material costs would be about twice those for the normal quantity of formic acid.
The Significance of the Yellow Fraction in Spontaneous Coagulation
Authors: Paton F. J. 
Published: February 2011

Abstract
The characteristics of the heavier yellow fraction which is separated on centrifuging fresh latex have been described in the literature. This material is made up of a loose aggregate of particles which have a relatively high specific gravity. It can be dispersed in dilute salt solutions, but tends to coalesce into an irreversible precipitate when diluted with water. It is still not quite clear what happens when water is added to the yellow fraction. After diluting latex with water, the formation of a layer at the bottom of the tube no longer takes place, the flocculated rubber carrying the bulk of the aggregate to the top of the tube. The observed phenomena can be explained on the assumption that the yellow fraction is made up of a number of cells, and some evidence for the existence of membranes has been offered by Ruinen. On such an assumption, they can be accounted for as osmotic phenomena. However, this explanation is not entirely satisfactory, since volume shrinkage does not appear to take place in a hypertonic solution.