bluuebunny/crossref_metadata_2025 huggingface dataset:
The Estimation of Small Percentages of Rubber in Fibrous Materials
Authors: Blow C. M.
Published: February 2011

The estimation of the percentage of rubber in fibrous products treated, for example, with Positex involves several difficulties, and no one method can be adopted on account of the difference in behavior of the various fibers. The fiber may consist of protein such as silk, wool or other animal fiber, and leather, or cellulosic material such as jute, cotton, rayon, paper, kapok, etc. The rubber may be vulcanized or unvulcanized. In addition to fiber and rubber, the presence of other substances such as soap, fats, waxes, oils, dyestuffs, fillers, pigments, etc., must not be overlooked. The problem of analysis appears complex, but may be simplified in some cases by knowing, from the process of manufacture, the definite absence or presence of certain ingredients. The three techniques available are now discussed.
Time and Stress Effects in the Behavior of Rubber at Low Temperature
Authors: Beatty J. R. , Davies J. M.
Published: February 2011

The stiffening of rubberlike materials at low temperature involves several different phenomena, sometimes with their effects superimposed. One of these is crystallization. This is a rate process which is generally very fast at high stresses and very slow at zero stress. In these experiments at temperatures near −25° C and under a shear stress of about 148 lb. per sq. in. the dynamic modulus of the rubber increased at a rate convenient to study. Correlation with x-ray data showed that crystallization was very likely responsible for the increase in stiffness. The rate of change of stiffness increased rapidly with increase in applied stress, and there was no optimum rate at −25° C, as has been found for unstressed rubber. The degree of vulcanization influenced the rate of change, tighter cures giving smaller changes. Neoprene-FR, GR-S, and polybutadiene, which ordinarily show little evidence of crystallization, showed very definite, but small increases in stiffness. Mixing GR-S with natural rubber seems to limit the crystallization of the natural rubber rather effectively, but apparently Neoprene-FR does not mix intimately enough with natural rubber to affect the crystallization of the latter appreciably.
Flow Phenomena in Rubber Samples
Authors: Rössler Fritz
Published: February 2011

A more extended investigation was made of the surprising flow phenomena which were found in an earlier study of rubber at low temperatures. The tensile apparatus was reconstructed so that a dead-weight load could be applied to the rubber test-specimen. Determinations of the dependence of the rate of flow on time of stressing, initial elongation, magnitude of the stress, and temperature showed that a simple law can be derived for expressing the flow phenomena. Yield point, change in color, and deterioration in physical properties, as well as the reversibility of these phenomena were investigated and are discussed. The phenomena of flow at room temperature are expressed by the same constants as at lower temperatures. Only the effective stress increases at low temperatures and only by this change does flow become perceptible. Different types of rubber were compared, and all showed approximately the same value for the flow constant. The essential characteristics of the flow phenomenon can be explained, on a basis of the theory of highly elastic materials, by their microliquid state of aggregation. This applies to the high degree of dependence of the mechanical properties of rubber on the temperature.
Determination of the Molecular Weight of Rubber and Polystyrene by the Methods of Light Scattering and Osmometry
Authors: Dogadkin B. , Soboleva I. , Arkhangel'skaya M.
Published: February 2011

1. Experiments on the determination of the molecular weights of natural rubber and other high-molecular compounds by the methods of light scattering and osmometry are reported. 2. An osmometer of new design, suitable for determining molecular weights, is described. 3. It is shown that the method of light scattering yields values for molecular weights which are in satisfactory agreement with those obtained by the method of osmometry.
Infrared Studies of 1,2- and Trans 1,4-Structure of Polybutadiene and Butadiene-Styrene Copolymers Polymerized at Various Temperatures
Authors: Hart E. J. , Meyer A. W.
Published: February 2011

Infrared methods have been used in determining 1,2- and trans-1,4-addition in polybutadiene polymerized in the temperature range −19° to 97° and butadiene-styrene copolymers prepared at −18°, 5° and 50°. trans-1,4-Addition increases and 1,2-addition decreases with decreasing temperature of polymerization. At −19°, substantially all of the 1,4-addition product is present in the trans-1,4-form. Approximately 20 per cent 1,2-addition occurs at this temperature and is concluded to account for the major part of the non-crystallizable portion of polymers made at low temperatures. The influence of styrene on 1,2- and trans-1,4-addition in butadiene-styrene copolymers is also discussed. Free energy, heat and entropy of activation are calculated for 1,4- vs. 1,2-addition and trans-1,4- vs. cis-1,4-addition in the polymerization process.
Dependence of Elastic Properties of Vulcanized Rubber on the Degree of Cross-Linking
Authors: Flory Paul J. , Rabjohn Norman , Shaffer Marcia C.
Published: February 2011

The results reported above demonstrate a progressive increase in the force of retraction τ at fixed elongation with increase in the fraction p of the structural units which are cross-linked from ρ=0.10×10−2 to 3.0×10−2. Over this range, τ at 100 per cent elongation increases about thirteenfold. Swelling measurements indicate that the increase in τ with ρ continues over an additional tenfold range in ρ. Previous assertions that the modulus of elasticity of soft gum rubber vulcanizates depends largely on chain interaction and entanglements other than those imposed by the cross-linkages, and that the modulus is, therefore, not directly related to the degree of cross-linking, are without foundation. The statistical theory of rubber elasticity expresses the force of retraction as a function of the temperature, vulcanizate structure and elongation; no arbitrary constants are involved. The magnitudes of τ for α=2 are in remarkably close agreement with the predictions of the theory over most of the range in ρ. This fact is of the utmost significance in confirmation of the statistical theory of rubber elasticity and of the analysis of the network structure of vulcanized rubber. On the other hand, τ increases less rapidly with ρ than the direct proportionality prescribed by theory. Forces of retraction are higher than the theory predicts at low degrees of cross-linking, and an opposite deviation is observed for values of ρ greater than about 1×10−2. Previous observations on Butyl rubber, vulcanized to p values from about 0.16×10−2 to 0.28×10−2 indicated forces of retraction (for infinite molecular weight M) which exceed by about threefold those predicted from the theory. This deviation is decidedly larger than has been observed here in the same range for ρ. A substantial part of the discrepancy observed for Butyl rubber may have arisen from failure to secure elastic equilibrium, however. Deviations in the values of τ from theory probably originate largely from oversimplifications in the treatment of the network structure. Entanglements of the sort previously discussed tend to enhance the restraints imposed on the chains when the rubber is elongated. Their percentage effect should be greatest for low degrees of cross-linking, hence the observed τ values are higher than theory at low degrees of cross-linking. “Intramolecular” cross-linkages, yielding short-circuit structures contributing nothing to the elastic reaction of the network, should become increasingly important at higher degrees of cross linking. Such wastage of cross-linkages may account for the low values of τ obtained for higher ρ values.
Giuseppe Bruni 1873–1946
Authors: Schidrowitz Philip
Published: February 2011

Giuseppe Bruni, a pioneer in the development of structural chemistry and the chemistry of solid solutions and isomorphism, and also outstanding for his researches in the chemistry and technology of rubber, was born in Parma, Italy, in 1873, and died in Milan in 1946. The news of Bruni's passing did not, for some unexplained reason, become known to most of his many friends and admirers abroad until the end of 1949. After graduating in Parma in 1896, he joined the renowned Ciamician at Bologna University, where for nearly ten years he worked mainly on the nature and theory of solid solutions and of isomorphism. In 1908, he summed up his researches in this field in a monograph entitled “Solid Solutions and Isomorphism,” published in Germany under the title “Feste Lösungen und Isomorphismus.” He temporarily left Bologna to work with van't Hoff in 1900–1901, and the latter subsequently emphasized the importance of Bruni's researches in the following words: “Ce savant à contribué d'une partie prépondérante à l'adoption des lois sur les solutions solides et les mélanges isomorphes, qui, sans son intervention auraient été troublée par des notions confuses.” [This scholar and master has contributed in a major way to the establishment of the laws of solid solutions and of isomorphic mixtures, for without the part which he played, the formulation of these laws would have been beset by a confusion of ideas.] The year 1907 saw Bruni appointed to the Chair of General and Inorganic Chemistry at Padua, where for a decade he conducted researches on diffusion in the solid state, on the cryoscopic method, etc. In 1917 he was appointed Professor of General and Inorganic Chemistry at the Polytechnic School of Milan—an institution similar in character to the Massachusetts Institute of Technology. He held this post until shortly before his death. In the following, a brief résumé is given of his work in rubber science and technology.
The Degree of Crystallinity in Natural Rubber. III. Correlation between X-Ray and Density Measurements
Authors: Arlman J. J.
Published: February 2011

In 1925 Katz discovered the crystallization of stretched rubber. In the following years several investigators tried to determine the structure of rubber crystallites. The densities of the rubber crystallites calculated from the results of these investigations varied strongly. The results of x-ray and density measurements on crude rubber carried out by the author can be made to correspond only when the latter are based on the unit cell of Bunn. It is shown by experiment that, to measure the correct degree of crystallization, it is necessary to use monochromatic x-rays.
The Degree of Crystallinity in Natural Rubber. IV. The Degree of Crystallization in Frozen Raw Rubber and Stretched Vulcanized Rubber
Authors: Goppel J. M. , Arlman J. J.
Published: February 2011

An improved x-ray technique has been worked out to determine the degree of crystallinity in natural rubber. Inaccuracies which sometimes occur in quantitative x-ray measurements were eliminated, and it has been shown that the amount of crystalline rubber, both in frozen samples of raw rubber and in stretched vulcanized rubber, could be determined fairly accurately. More experiments were carried out and the results are described. These results, which confirm the current views on the problem of crystallization, point to relatively low degress of crystallization, even in highly stretched rubber, and they agree with some other experimental evidence and with a recent theoretical investigation.
The Degree of Crystallinity in Natural Rubber. V. A Discussion of the X-Ray Results on Natural Rubber in Connection with the Work of Flory, Gee and Wildschut
Authors: Arlman J. J. , Goppel J. M.
Published: February 2011

A recent theory, developed by Flory, makes it possible to calculate the degree of crystallization from thermodynamical measurements if certain parameters are properly evaluated. Such evaluation is possible by combining Wildschut's thermodynamical measurements with the x-ray results presented in previous papers. Thus the average length of molecule chains between cross-linkages can be derived; it closely corresponds to the results of swelling measurements carried out by Gee. Other parameters are also evaluated in agreement with their physical meaning.
The Reaction of Sulfur and Sulfur Compounds with Olefinic Substances VI. Factors Influencing Cyclic Sulfide Formation in the Reaction of Sulfur with Polyisoprenes
Authors: Bloomfield George F.
Published: February 2011

Cyclic Sulfides are to a large extent secondary products of the reaction of primarily formed intermolecular polysulfides with polyisoprene hydrocarbon, and undue prolongation of the time of reaction of sulfur with polyisoprenes favors cyclic sulfide formation and so reduces the cross-linking efficiency of the sulfur. Various accelerating substances markedly increase the cross-linking efficiency, either by permitting shorter reaction times to be employed, or by promoting a cross-linking rather than a cyclizing reaction of the sulfur. Thiuram disulfide accelerators in the absence of sulfur bring about cross-linking, the linkages being of C—S—C type rather than C—C.
Tensile Properties of Natural and Synthetic Rubbers at Elevated and Subnormal Temperatures
Authors: Boonstra B. S. T. T.
Published: February 2011

It is necessary to determine the physical properties of rubbers at relatively high temperatures when products made from them are to be used at such temperatures in actual service. The term heat aging is used when the vulcanizate is tested at room temperature, exposed to elevated temperatures for given periods of time, and then tested again at room temperature. The term high-temperature strength is proposed for values obtained when the vulcanizates are tested at the actual higher service temperatures. Effective comparison of natural and synthetic rubbers is best obtained by determining tensile product values, which are the result of the combining of tensile strength and elongation values. In the evaluating of vulcanizates of tire compounds of various rubbers, another factor must be taken into account. Synthetic-rubber tires develop more heat in service than do natural-rubber tires, and the former therefore generally operate at higher temperatures than do the latter. Synthetic-rubber tires therefore require a greater high temperature strength than do natural rubber tires, but, as has been shown, synthetic rubbers actually have a lower high-temperature strength. The part played by carbon black with respect to the tensile properties of some synthetic rubbers is considered that of a substitute for crystallization in natural and other synthetic rubbers, which substitute does not, however, possess the same favorable features. Carbon black even in noncrystallizing rubbers does not increase strength; it merely shifts the optimum strength value to a higher temperature so that this temperature is in the room temperature range. The temperature coefficient of strength for Butyl and Neoprene rubbers is so large at room temperature that a few degrees' difference in temperature causes large changes in strength. The tensile strength and elongation at break of these two rubbers decrease sharply between 20 and 40° C.
Flow Phenomena in Rubber. II. Flow Curves for GR-S Rubber
Authors: Treloar L. R. G.
Published: February 2011

The flow of GR-S at various temperatures was examined by means of the biconical rotor type of Mooney plastometer. Unlike the natural rubber previously studied, the shape of the flow curves was consistent with the Ostwald-de Waele relation. Values of activation energy for flow, determined from the temperature coefficient of flow rate (at constant stress), averaged 10.2 k.cal. per mole.
The Action of Copper and its Derivatives on the Aging of Rubber
Authors: Villain Henri
Published: February 2011

Most copper compounds increase the rate of autoxidation of rubber mixtures, i.e., they are proöxygenic agents and acclerate aging to a dangerous extent. However, copper may occur in a disguised form and have no deleterious action at all. Moreover, the effects vary considerably, even with the same copper compound, according to the composition of the rubber mixture. Thus certain ingredients, notably, tetramethylthiuram disulfide, neutralize the deleterious action of copper, whereas fat acids increase it. Nevertheless, the presence of a fat acid is not indispensable to the process of degradation brought about by copper, as is evident from tests with rubber mixtures in which the natural fat acids were previously removed from the rubber. From the practical viewpoint, protection against copper can be accomplished effectively by means of certain products such as Agerite White, BLE Powder, and disalycylalethylenediamine, all of which are excellent anticopper agents.
Tear Resistance of Vulcanized Rubber
Authors: Nijveld H. A. W.
Published: February 2011

The method now used at the Rubber Research Institute T.N.O. for determining the tear resistance of vulcanized rubber is described in detail. The tearing test has been studied further. The influence of the thickness of the sample on the tear resistance has been investigated, and some experiments carried out to explain this influence are described. Further experiments indicate that, at the moment of tearing, an elongation is reached locally which is practically equal to the elongation at break of a standard tensile test. Comparison of the angle tear test with the above method leads to the conclusion that the Delft method is to be preferred.
Kinetic Study of the Oxidation of Rubber I.—Some Observations in the Case of Raw Rubber
Authors: Le Bras J. , Salvetti A.
Published: February 2011

After a summary of the main works on the mechanism of rubber oxidation and the antioxidant effect, the principle of a method for the direct measurement and automatic recording of oxidation rates under constant pressure is given. The oxygen necessary for the reaction is produced inside the apparatus by the electrolysis of a solution of copper sulfate, and the noncondensable gases formed during the oxidation are absorbed by caustic potash and sulfuric acid-pumice. Some results obtained with this apparatus during a systematic study of the oxidation of purified crepe at 80° C are described. The influence of the oxygen pressure of the concentration of rubber, of the effects resulting from the transformation undergone by purified crepe, and finally of the action of some anti-oxidants, were investigated. Without discussing the theoretical interpretations, various experimental observations can be made. (1) Even when using ordinary methods of conservation in high vacuum, the samples of rubber undergo modifications which alter its characteristics of oxidation; it is, therefore, necessary always to make simultaneous comparative measurements with a blank. (2) The general shape of the rate of oxidation-time curves indicates the existence of a very strong maximum corresponding closely to the same amount of absorbed oxygen. (3) Variations of the oxygen pressure react on the course of the oxidation. (4) Variation of the concentration of rubber (observed on solutions in toluene) shows that the value of the maximum rate of oxidation is inversely proportional to the concentration. (5) Phenyl-μ-naphthylamine has practically no action on the oxidizability of natural crepe, but is a good antioxidant for purified crepe.
Aging of GR-S Vulcanizates. III. Some Effects of Oxygen and Temperature on Aging
Authors: Scott J. R.
Published: February 2011

Experiments at high temperatures (135° to 153° C) show that the fall in tensile strength and elongation and the increase in modulus of GR-S vulcanizates are accelerated by the presence of oxygen. At 70° C an increase of oxygen concentration from 0.2 atm. (air) to 20 atm. likewise promotes both loss of tensile strength and stiffening (increase of modulus), unless the rubber is under-vulcanized, when the increase of oxygen concentration often results in less stiffening. The increase of oxygen concentration also causes the aged rubber to retain more set after stretching. At 80° C, increasing the oxygen concentration from 0.2 to 20 atm. does not promote stiffening even in well vulcanized rubbers, and may even lead to less stiffening. These results indicate the following general conclusions: (1) oxidation, in addition to promoting loss of strength, is one of the causes of the stiffening of GR-S during aging, presumably due to oxygen-bridging between the molecules; (2) oxidation can also cause softening, presumably by chain scission, which further results in a change in the shape of the stress-strain curve and an increased set after deformation; (3) at high temperatures (80° C or above) increase of oxygen concentration, as in the bomb test, favors the softening reaction relative to the stiffening reaction, but at 70° C (and presumably below) this effect is not evident; (4) undervulcanized GR-S is especially susceptible to the softening (chain scission) reaction; (5) the fact that the softening reaction is favored by increase of oxygen concentration at a high temperature casts doubt on the value of a high-temperature oxygen bomb test for simulating the natural aging of GR-S (see Part IV for an analogous conclusion on other accelerated tests). The above conclusions agree with and extend those of Shelton and Winn. Prolonged (60-day) air-aging tests at 100° C confirm a previous suggestion that the tensile strength of GR-S vulcanizates reaches a constant value or even increases eventually; however, they become progressively stiffer and less extensible. Thus, under hot service conditions GR-S is more likely to fail through inability to stretch than through loss of strength.
Aging of GR-S Vulcanizates. IV. Influence of the Vulcanizing Ingredients, Antioxidant, and Softener
Authors: Scott J. R.
Published: February 2011

The results of air aging at temperatures from 25° to 100° C and of oxygen-bomb aging are discussed in relation to the composition of the mix; notes are given also on the relation of composition to the properties before aging. The main conclusions are: (1) a low proportion of sulfur or (still better) vulcanization by tetramethylthiuram disulfide (TMT) improves the maintenance of tensile strength and elongation under all conditions examined; a low-sulfur mix containing selenium gives results intermediate between the normal low-sulfur and TMT-vulcanized mixes; (2) when judged by the stiffening and hardening during aging, the relative merits of these alternative vulcanizing agents are different, age-stiffening being generally least with low sulfur plus selenium and greatest with TMT vulcanization; (3) on the whole, mercapto-benzothiazole (MBT) gave better results than TMT as an accelerator in mixes with the same proportion of sulfur; (4) acetone extraction of raw GR-S did not lead to the bad aging expected from the removal of antioxidant, but this point needs further study in view of contrary conclusions by other workers; (5) a large proportion of softener somewhat improves maintenance of strength but increases age-stiffening; (6) in general the formulation giving the best maintenance of tension strength and elongation does not give the least age-stiffening, and vice-versa; for the former, TMT vulcanization (possibly plus softener) appears best; for the latter an MBT-accelerated low-sulfur mix, possibly plus selenium, and (7) the 100° C air and the oxygen-bomb aging tests may give misleading indications of aging behavior in air at lower temperatures.
Some Observations on the Oxidation of Rubber in Light
Authors: Stafford R. L.
Published: February 2011

An apparatus is described for measuring the oxygen absorption of vulcanized rubber, either in darkness or under illumination from a controlled light source. The light and dark oxidation curves of four vulcanizates at temperatures of 60°, 65°, and 70° C are examined. Three of the four vulcanizates were protected by the incorporation, respectively, of 2 per cent phenyl-β-naphthylamine, 2 per cent mercaptobenzimidazole, and a mixture of 1 per cent each of the above substances. The dark reaction over 60 hours' duration was in all cases similar and could be represented by a standard equation. It is shown that the effects of PBN and MBI on the dark oxidation are clearly different throughout the temperature ranges. From a consideration of the initial reaction, the decay during storage of the initial oxidizability of the vulcanizates is shown. In oxidation under light from a relatively weak source at a given temperature, the total absorption is considered as the sum of the dark thermal oxidation appropriate to the temperature, and a light-activated absorption. The effect of the light is then shown to be similar in all cases, the rate of absorption due to light starting from zero and increasing through a maximum to a constant value. By comparison of these constant light rates, it is shown that PBN and MBI have little effect on the light-activated absorption of the control, but that the mixture (PBN, MBI) effectively reduces this absorption. The persistence or development of an enhanced dark rate after illumination is shown to depend on the period of illumination and the length of dark storage of the vulcanizate.
Interaction between Polymers and Fillers
Authors: Houwink R.
Published: February 2011

In the literature the problem of whether or not filler particles adhere to a polymer is still under discussion. This point is already of interest in the mixing process because here the question resolves itself into whether the particles clog together or each becomes separately surrounded by polymer only. The problem is also of paramount interest with regard to the properties of the final mixture because upon the interaction depends whether or not a filler has a reinforcing action. This is a key problem, especially in the rubber industry. Essentially, the problem of dispersing a filler in a polymer is of the same type as that of dissolving a polymer in a solvent, and for the thermodynamic considerations we know that dispersing occurs if (leaving the entropy factor out of discussion) ΔU(U=internal energy) is negative, that is, heat is liberated. Here the historical measurements of Hock and his coworkers show that, on mixing rubber with carbon black, 11 gcal. per gram of black (which is of the order of 1 gcal. per mole) extrapolated to zero concentration, are developed. This heat is found to decrease with increasing proportion of filler, showing that all particles are no longer in contact with the rubber because of clogging. It has long been a problem to explain the outstanding reinforcing properties of carbon black with the aid of these low values found by Hock. Smith and Schaeffer showed that the initial heat of adsorption between carbon black and C4 hydrocarbons is of the order of magnitude of 15 kcal. per mole, decreasing sharply until about 40 per cent of a monolayer is formed. This indicates that 40 per cent of the carbon black surface is covered with sites of high adsorptive capacity. Between 40 and 100 per cent of this monolayer formation the surface appears to be quite uniform with regard to adsorptive capacity; at the monolayer the values again decrease and approach the heat of liquefaction, EL, of the adsorbate. These results are shown in Figure 1. From the data obtained, it can be derived that the heat of adsorption per CH2 group to carbon black is about 4 kcal./mole.
Mechanism of Reënforcement. IV. Adsorption of GR-S by Carbon Black
Authors: Amborski Leonard E. , Black Carl E. , Goldfinger George
Published: February 2011

Infrared absorption analysis has been carried out to determine whether the adsorption of GR-S (co-polymer of polystyrene and polybutadiene) on carbon black is specific as to the chemical structure of the polymer. The comparison of the relative intensities of the characteristic absorption bands of the original GR-S with the ratios of the intensities of the same bands for the fraction of rubber remaining after certain fractions were specifically removed by carbon black has shown that the adsorption is not specific as to chemical structure within the limits of accuracy of infrared analysis. The particular chemical groups considered were the phenyl structure (infrared absorption at 13.20 and 14.27 microns) of polystyrene and the 1,2 (10.08 and 10.95 microns) and 1,4 (10.37 microns) addition units of butadiene.
Oxygen Absorption of Vulcanizates. A Means of Evaluating Aging Resistance
Authors: Pollack Louis R. , McElwain Robert E. , Wagner Paul T.
Published: February 2011

The rates of oxygen absorption of two natural and six synthetic-rubber stocks have been measured. In addition, the course of aging in the oxygen bomb and air oven was followed by means of changes in tensile strength and in ultimate elongation of the same eight stocks. Correlation between rates of oxygen absorption and deterioration of physical properties is close enough to justify substitution of a rapid oxygen absorption measurement for longer standard procedures in evaluating the aging characteristics of rubber stocks.
The Preparation and Properties of Highly Purified Rubber
Authors: Martin G.
Published: February 2011

A method is described for obtaining highly purified Hevea rubber, 99.9 per cent pure hydrocarbon, by addition of soap to ammonia-preserved latex to displace the protein from the rubber particle surfaces, followed by repeated creaming, solubilization in hexane, centrifuging, precipitation, and extraction with acetone. Prevention or limitation of oxidation of the pure hydrocarbon was obtained by work in darkness, or by treatment of the latex with pyrogallol and extraction with pyrogallol in acetone. Results are given on the vulcanization behavior of highly purified rubber, showing marked improvement in resilience, while there are remarkable differences in the mechanical properties of vulcaniz zates from sol and gel fractions in some mixes.
Kinetic Analysis of Rubber Halides
Authors: Salomon G. , Koningsberger C. , Ultée A. J.
Published: February 2011

A correlation is established between the structure of an organic halide and its rate of reaction with a number of organic bases. Analysis by reaction kinetics, based on this correlation, is applied to the following problems. (1) Estimation of the allylic fraction in the chlorination and bromination of natural rubber. (2) Differentiation between a dichloride and a polychloride from natural rubber. (3) Determination of an equilibrium between natural rubber and hydrochloric acid at 130° C in closed systems. (4) Identification of tertiary chlorides and bromides in natural rubber and allied polymers.
Reaction of Bromine with Rubber in Aqueous Suspension and Its Analytical Use
Authors: Maffei Francisco J. , Outa M.
Published: February 2011

The rubber hydrocarbon is considered to consist of the combination of an indeterminate number of C5H8 or isoprene units. In this unit there is a double bond capable of adding two atoms of bromine. This addition takes place with pairs of C5H8 groups, with formation of the tetrabromide C10Hl6Br4. Under certain conditions the compound C10H15Br5 is formed, in which case bromine replaces one atom of hydrogen and, at the same time, hydrogen bromide is liberated. The direct determination of the hydrocarbon of rubber by its transformation into the tetrabromide has been utilized by various investigators. Rubber dissolved in benzene, chloroform, or carbon tetrachloride is treated with a solution of free bromine and carbon tetrachloride. The tetrabromide which is formed is separated and weighed. The volumetric determination of the rubber hydrocarbon by bromine is generally impaired by the action of the bromine on the solvent and on the impurities which are present in the rubber. We have tried to study in this work the combination of bromine with rubber in aqueous dispersion, particularly in latex, by an indirect method, based on accepted definitions of the dry rubber content and the total dry residue. The bromine is used in the form of a mixture of bromate and bromide in the presence of acid, and the excess is determined volumetrically. In this way, a bromination factor is obtained, which represents the quantity of bromine consumed per unit of rubber.
Adhesion of Rubber and Textiles. I. Preliminary Evaluation of Synthetic Rubbers in Rubber to Fabric Adhesion
Authors: Hammond G. L. , Moakes R. C. W.
Published: February 2011

In the bonding of two fabric layers by means of a polymer film, it seems that there are two factors, (1) the adhesion of the fabric to the polymer film, and (2) the inherent cohesion of the film itself. With polymers in which cohesion is normally poorer than adhesion for nonvulcanizing films, e.g., GR-S, stripping under most conditions is of the cohesive type; the stripping load can be increased, in the case of GR-S only, by certain resins with the stripping remaining of the cohesive type. When such polymers are used in vulcanizing cements, stripping becomes of the adhesive type, due presumably to the improved cohesion of the polymer by cross-linking. Further, adhesion appears to be at a maximum for lightly vulcanized films, and gets progressively poorer with further curing. The importance of control of film thickness in the quantitative evaluation of rubber cements is demonstrated, and a fairly broad picture of the behavior of GR-S in rubber cements is given. It seems that bond strength between two layers of fabric of the same order as with natural rubber can be obtained with GR-S with the addition of suitable resins. The big drawback to its commercial use in cements seems to be the fact that to obtain good bonds it is essential for doubling to be carried out while a fair amount of solvent is still present.
Adhesion of Rubber and Textiles. II. Factors Influencing the Load Required to Strip Rubber from Fabric and Foil Surfaces
Authors: Borroff E. M. , Wake W. C.
Published: February 2011

By means of experiments with chemically treated fabrics in which the mechanical factor is left unchanged and other experiments with foil materials, the part played by specific factors in rubber to fabric adhesion is shown to be relatively unimportant. Specific factors do exist, and their magnitude is connected with the existence of polar groups or groups that can be polarized. The adhesion secured by the use of spun staple fiber effectively outweighs all other factors.
Adhesion of Rubber and Textiles. III. Examination of Test Technique
Authors: Borroff E. M. , Wake W. C.
Published: February 2011

The variation with the rate of stripping of the load required to break rubber-to-fabric bonds is discussed for unvulcanized and vulcanized rubbers, and this is followed by a discussion of the load variation with period of vulcanization. The two features which are evident in stripping tests are separated, and a simple direct tension test is proposed as a more reliable measure of adhesion. An improved stripping test is proposed and this, together with the direct tension test, is discussed in a final section on the relation between the two tests and their application to practical problems.
Adhesion of Rubber and Textiles. IV. Function of Staple Fiber in Rubber to Fabric Adhesion
Authors: Borroff E. M. , Wake W. C.
Published: February 2011

An investigation of the adhesion of rubbers to a series of fabrics woven from spun staple and continuous filament viscose, acetate rayon, and nylon is described. Using the direct tension test, it is shown that adhesion strength is a property of the staple fiber and is directly related to its tensile strength. The number of projecting fibers has been determined and compared with the broken-off ends recovered from a natural rubber cement after stripping from the fabric. The size-distribution histograms of the recovered fiber ends are also given and discussed. Recommendations are made for utilizing the results so far obtained in this investigation for the production of improved rubber-textile articles.
Staining Problems Associated with Rubber Chemicals
Authors: Haworth James , Pryer W. R.
Published: February 2011

This paper describes a program of systematic work carried out on staining phenomena associated with vulcanized rubber. It is realized that information on the subject must inevitably exist within the industry, but it is thought that it consists largely of isolated facts. An attempt has, therefore, been made to gather together the parts so as to present the picture as a whole and at the same time to explore various practical applications where staining is of paramount importance.
Mastication and Compounding of Natural Rubber in an Oxygen-Free Atmosphere
Authors: Blow C. M. , Wood R. I.
Published: February 2011

Confirmation has been obtained that raw rubber when masticated in the absence of oxygen undergoes only a limited amount of breakdown; and it has been shown that two of the better known socalled “peptizers” or chemical plasticizers of rubber, viz., mercaptobenzothiazole and o-o′-dibenzamidodiphenyl disulfide, require oxygen to be effective. A range of pure-gum rubbers has been compounded under nitrogen, and the physical properties after vulcanization compared with corresponding air-compounded rubbers. Some types of acceleration give vulcanizates whose physical properties are very sensitive to changes in the viscosity of the unvulcanized stock, decrease in viscosity giving decreased modulus. Other types of acceleration, notably “boosted” combinations which give high modulus vulcanization, are insensitive to stock viscosity changes over a wide range. This work forms part of a program of research undertaken by the Board of the British Rubber Producers' Research Association.
Investigations in the Field of Rubber Vulcanization. VII. Influence of Organic Accelerators on the Kinetics of Vulcanization and the Properties of Natural-Rubber Vulcanizates
Authors: Dogadkin B. , Karmin B. , Dobromyslova A. , Sapozhkova L.
Published: February 2011

1. Vulcanization accelerators change all parameters of the kinetic strength curve during the vulcanization of natural-rubber mixtures with low sulfur contents. 2. Calculation of the kinetic constants of the fundamental vulcanization equation proposed by Dogadkin, Karmin, and Gol'berg shows that vulcanization accelerators affect both the kinetics of the interaction of rubber with sulfur and the kinetics of the interaction of rubber with oxygen. 3. Direct experiments on the oxidation of rubber have shown that tetramethylthiuram disulfide and diphenylguanidine retard the process of addition of oxygen to rubber, while mercaptobenzothiazole accelerates this process. 4. Data on the rate of plasticization and change in viscosity of rubber solutions during oxidation indicate that tetramethylthiuram disulfide and diphenylguanidine promote the disintegration of molecular chains of rubber during the oxidative destruction of the latter. 5. The activation energy of the process of oxidation of rubber in the presence of mercaptobenzothiazole corresponds to the activation energy calculated from the fundamental vulcanization reaction for the process of oxidative destruction. This provides additional proof of the participation of oxygen in the vulcanization process. 6. It has been established with the aid of the methyl iodide reaction that accelerators increase the bridge-sulfur content of the vulcanizate, which is present in the form of monosulfides, with one sulfur atom connected to an allyl type radical. 7. With increasing temperature, the tensile strength at the vulcanization optimum increases in mixtures containing tetramethylthiuram disulfide, decreases in mixtures containing mercaptobenzothiazole, and remains unchanged in mixtures containing diphenylguanidine. The limiting strength decreases in all cases with increasing temperature. This phenomenon is explained on the basis of the proposed concepts of the character of vulcanization kinetics and of the nature of the vulcanization optimum.
The Tensile Strength of Rubber and Rubber Molecule
Authors: Park Chullchai , Yoshida Usaburo
Published: February 2011

The tensile strengths of crystallized crude rubber and vulcanized rubber are remarkably different from each other at room temperature, but are found to be almost the same at the temperature of liquid air. By assuming that the tensile strength of crystallized rubber at this low temperature is entirely due to its chain molecules, the forced needed to break a chain molecule of rubber at its weakest point is estimated.
The Measurement of Stress Relaxation of Unvulcanized Rubber by Means of the Mooney Shearing-Disc Viscometer
Authors: Blow C. M. , Schofield J. R.
Published: February 2011

The measurement of the tendency of unvulcanized rubber to recover from deformation on the Mooney shearing-disc viscometer has been found to be practicable, and the results correlate fairly well with recovery measurements on the parallel-plate plastometer and shrinkages of rubbers after milling, calendering and extruding. Partial prevulcanization is also indicated.
Some New Compositions Based on Condensation Rubbers
Authors: Harper D. A. , Smith W. F. , White H. G.
Published: February 2011

By the condensation of a dibasic acid and direactive alcohol or amine, linear polymers are produced. Under certain conditions rubbery polymers are obtained, and a number of condensation rubbers with outstanding physical properties have been described. One of these, a diisocyanate-modified polyester amide (Vulcaprene-A) has been found to be compatible with nitrocellulose, polyvinyl formal, cellulose acetate, degraded vegetable tanned leather, gelatin, and glue. These mixtures can be vulcanized by formaldehyde-liberating agents used to cure Vulcaprene, and in most cases the curing reaction appears to take place not only with the Vulcaprene but with other high polymers. Combinations of Vulcaprene and cellulose acetate and of Vulcaprene and degraded leather are of great interest to the leather cloth industry, as they can be spread on to cloth to give coatings with outstanding flex and abrasion resistance. The Vulcaprene-cellulose acetate mixture is of value also as an abrasion-and flex-resisting coating for rubber proofings to give products which, while cheap to produce, are likely to give superior service to prewar leather cloths. This type of coating can be applied also to paper. The diisocyanate modified polyester amide behaves not only as a novel vulcanizable polymeric plasticizer, but, in combination with these high polymers, gives new products of major interest to an important branch of the rubber industry.
Structures in Rubber Reënforced by Carbon Black
Authors: Blanchard A. F. , Parkinson D.
Published: February 2011

The stiffening action of carbon black in rubber is due to structures formed by carbon-rubber bonds and coherent chains of particles. The softening which occurs during prestressing cannot be explained by broken chain structure, and it is thought that substantially the whole of this softening is due to ruptured carbon-rubber bonds. Prestressing does not affect the characteristic chain structure of the black particles; it breaks relatively weak fortuitous chain structures, formed by reversible van der Waals forces between particles, which contribute little to the stiffness except perhaps at small stresses. Heating tends to reform the fortuitous structure, owing to the thermal movement of the rubber molecules, which pulls them from between adjacent particles, so that full contact is established. The majority of carbon-rubber bonds are relatively weak and are readily broken by stressing. In addition to these low-order physical bonds, a comparatively few strong bonds stiffen the rubber considerably at high stresses, and are mainly responsible for increasing the tensile strength and abrasion resistance. Such high energy linkages are possible only at localized areas on the particles.
The Nature and Activity of Carbon Black Surfaces
Authors: Smith W. R. , Schaeffer W. D.
Published: February 2011

While the electron microscope and adsorption isotherm techniques for evaluating the particle size and surface area of carbon blacks have been particularly valuable in interpreting their behavior in rubber, they also emphasize the fact that reinforcement cannot be interpreted solely on this basis. The activity or nature of the surface must also be considered. Heats of adsorption offer a means of evaluating surface activity. The differential heats of adsorption have been measured by precision calorimetry for nitrogen and a series of C4 hydrocarbons on a group of carbon blacks of varying reinforcing ability. Initial sites of high activity were detected. Surface activity decreases with increasing surface coverage. The magnitude of the initial heats parallels the reinforcing properties of the blacks studied. The surface activity and reinforcing ability of an MPC black was found to be greatly reduced by high temperature treatment. These effects were not influenced by the chemical nature of the surface, i.e., the presence of chemisorbed oxygen or volatile substances. In a further phase of this study, the nature of the surface oxide complexes present on carbon blacks has been studied by means of their emission band spectra in a special vacuum discharge tube. Aldehyde and carboxyl radicals were observed in high concentration. Hydroxyl radicals were also present in nearly equal concentration. These data offer a satisfactory interpretation of the pH properties of carbon black and also should prove of value in interpreting other chemical properties.
Theory of Filler Reënforcement. II
Authors: Guth Eugene
Published: February 2011

Modulus-type properties of loaded rubber depend mainly on the shape and the concentration of the filler particles and are almost independent of the size and the surface characteristics of the filler. The author's theory of these properties is patterned after the theory of viscosity of suspensions, and implies nonspecific wetting between rubber and filler particles, making possible considerable mobility of the filler particles in the rubber. Such mobility is in agreement with studies of the electrical conductivity of carbon black loaded stocks and of the adsorption of gases by carbon blacks. Fillers with spherical particle shape like calcium carbonate and P-33 (which do not form chainlike structures) obey the theoretical equations for spherical particles. Fillers like high modulus and channel carbon blacks whose primary spherical particles agglomerate into chainlike secondary particles obey theoretical equations for the secondary particles characterized by a shape factor. The assumed chain formation and the values for the shape factors are in approximate agreement with conclusions from electron micrographs. Experimental arguments are given for the validity of the theoretical equations up to 25 per cent volume concentration, which is the usual technical loading. The agreement between theory and experiment is within the rather large error caused by nonuniformity between and within the test samples, and in some work by the use of commercial testers, and the difficulty of comparable vulcanizations. Refinements of the theory are introduced, including possible solvation, difference between the modulus of rubber in absence (“gum” stock) and in presence of the filler particles, and various degrees of wetting from nonwetting to strong wetting (implying specific chemical bonds between rubber and filler). The above mentioned sources of error in the experimental work prevent safe conclusions about the necessity of introducing such refinements. The experiments include new measurements of stress-strain properties of loaded vulcanized stocks and of the Mooney viscosities of unvulcanized rubber-filler mixes, and a discussion of the pertinent literature. For the dielectric constant of stocks loaded with fillers of spherical primary particle shape, a simple formula is derived.