bluuebunny/crossref_metadata_2025 huggingface dataset:
The Autoöxidizability of the Alkyl Groups in Xylene
Authors: Farmer Ernest Harold , Narracott Eric S.
Published: February 2011

In the course of early experiments on the oxidation of rubber, it was observed that its solutions in commercial xylene, when exposed at 75° to a stream of oxygen, in presence of acetic anhydride (added to accelerate reaction) and a cobalt catalyst, gave m- and p-toluic acid, together with neutral liquids which were clearly not derived from the rubber. For instance, when a solution of 675 g. of rubber in 6075 g. of xylene was mixed with 844 cc. of acetic anhydride and 42 g. of cobalt naphthenate, and the mixture (in 4 batches) was treated at 75° for 2 days with a stream of oxygen, there were obtained, respectively, (1) by extraction of the xylene solution with 10% caustic alkali and (2) by subsequent distillation at approximately 1 mm. pressure of the volatile product from the residual xylene liquor, about 10 g. of crystalline acid and 80 g. of volatile neutral oxidation products. The acid was toluic acid (found: C, 70.6; H, 6.1; equiv., 135; calculated for C8H8O2: C, 70.55; H, 5.95%; equiv. 136), from which samples of both the m- and the p-isomeride (m. p. 110° and 176°, respectively) were isolated by fractional crystallization.
Vulcanization of Latex. Differences in the Behavior of Fresh, Old, and Purified Latex
Authors: Dalfsen J. W. Van
Published: February 2011

Patents granted to Schidrowitz show that when latex is vulcanized and then dried at room temperature, the product has the properties of vulcanized rubber. Films produced in this way show tensile strengths and elasticity which correspond to those of latex films vulcanized in the dry state. It is apparent, however, that when fresh latex is vulcanized under certain definite conditions, the product has fair tensile strength and elasticity only at a relative humidity of zero, but which under ordinary atmospheric conditions is brittle, seems to be overcured, and is practically without tensile strength. This tensile strength, however, is increased by additional dry vulcanization, so there can be no question of overcure. Just as soon as vulcanization has proceeded to a point where brittle films without tensile strength are obtained, the latex, when treated with acid, does not coagulate, but merely flocculates. Nor can such vulcanized fresh latex at this stage be made to coagulate coherently by other means. This form of latex is not sticky. The flocculate referred to can be obtained only by vulcanizing fresh latex in the presence of zinc oxide, and under conditions such that hydrolysis of the nonrubber substances is a minimum. It is, therefore, desirable to have recourse to ultra-accelerators and to be sure that the vulcanization temperature is not too high. By keeping fresh latex alkaline, or by purifying it, it will not flocculate. Latex that has been purified or aged may occasionally, under similar conditions, give a brittle and incoherent coagulum, whereas in other cases a normally coherent but somewhat brittle coagulum results. The nature of the coagulum is governed by the degree of purification and hydrolysis of the nonrubber substances; hence all transition stages between a flocculate and a completely coherent coagulum may occur. By adding serum from fresh latex to purified latex, the behavior of such purified latex changes in the sense that it behaves more like fresh latex. In studying experimentally the difference in behavior of fresh latex and purified latex, the first thing considered was the combination of sulfur. It was found that sulfur first dissolves in the serum, after which it dissolves in the rubber itself. Only then does vulcanization take place. This became evident from the definite acceleration of the combination of sulfur in the latex stage, when before vulcanization, latex was heated with sulfur alone. By this preparatory treatment too, dry vulcanization at room temperature was accelerated, but there was no noticeable effect on dry vulcanization at 80° and 110° C. At 30° C, about 1 per cent of the sulfur dissolved in the rubber particles, in the form of free sulfur. From this it was concluded that it is not possible to remove by mechanical means (as by clarification) excess free sulfur from vulcanized latex. No essential difference could be found between the combined sulfur of fresh latex and that of purified old latex.
Electrodecantation for Concentrating and Purifying Latex
Authors: Murphy E. A.
Published: February 2011

The chief methods employed in the production of concentrated latex have been confined to the controlled evaporation of water from the latex by the application of heat, concentration by centrifuging, and separation of the latex into layers of different concentrations by the action of creaming agents. Recently, another process has been used commercially, which produces concentrates similar to those obtained by the centrifuging and creaming methods in that a substantial part of the serum constituents is removed during the concentration. The new method is based on phenomena observed by Pauli and his co-workers on the behavior of colloidal sols when subjected to electrodialysis. It was noted that in the purification of sols, such as silicic acid and serum albumen, by subjecting them to electrodialysis between vertical semipermeable membranes, separation was frequently obtained into superimposed layers containing different concentrations of the sol. The more concentrated layers were uppermost, or vice-versa, according to the relative densities of the sol and dispersing medium. This stratification is probably the result of the combined influence of the electrical potential and gravitational force under suitably chosen conditions. The colloidal particles migrate to one of the membranes under the influence of the electric field, with consequent concentration at the membrane surface. If the field strength is not too great, the particles become more under the influence of gravitational force than of the electrical force, tending to cause deposition on the membrane. The concentrated layer of particles tends, therefore, to move upwards or downwards along the surface of the membrane in accordance with its relative density with respect to that of the surrounding liquid. Conversely, there is a corresponding reduction in the concentration of the sol at the other membrane surface, which promotes a flow of more dilute dispersion in the opposite direction to that of the stream on the other membrane. If this action is allowed to continue, the dispersions of different concentrations spread out through the cell liquid in the form of horizontal layers which may be decanted.
Low Temperature Flexing Apparatus
Authors: Martin S. M.
Published: February 2011

For the past ten months, Sub-Committee V of SAE-ASTM Technical Committee A on Automotive Rubber has been working on the standardization of synthetic rubber specifications. Insofar as possible, methods of tests have followed ASTM procedures. ASTM has no recommended procedure for measuring the low temperature flexibility of synthetic rubber. This committee, after careful consideration, has recommended the use of a modification of the Thiokol Corporation's freeze test. This method of testing for low temperature flexibility has been incorporated into a number of recent Aeronautical Material Standards Specifications covering synthetic rubber. The modified test uses the same apparatus as that used in the Thiokol Corporation's Laboratory, or slight modifications of this. Because of the interest in this apparatus, a short description of it is here given.
Ionic and Radical Mechanisms in Olefinic Systems, with Special Reference to Processes of Double-Bond Displacement, Vulcanization and Photogelling
Authors: Farmer Ernest Harold
Published: February 2011

The α-methylenic reactions discussed in the preceding two papers recall a series of interesting observations by Baker and Nathan, which indicate that a p-methyl substituent attached to the benzene nucleus can permit electron release to the nucleus in a manner that appears only in lesser degree in higher alkyl groups, and may be absent in some (e.g., Buγ). Thus in p-methylbenzyl bromide, the suggested function of the methyl group (dotted arrows in (I) permits (see PDF for diagram) additional electron release at the C—Br bond, and so facilitates the anionization of the bromine. Baker and Nathan suggest that the electrons of the duplet constituting the C—H bond of the methyl group are less localized than those in a similarly placed C—C bond, and hence that a methyl group attached to the necessary conjugated unsaturated system is capable of electron-release by a mechanism similar to the tautomeric effect:
Statistical Thermodynamics of Rubber. II
Authors: Wall Frederick T.
Published: February 2011

During recent years, considerable progress has been made in connection with theories of rubber elasticity. Two general types of theories have been advanced, one from a macroscopic point of view and the other from a molecular point of view. An example of the former is the theory of Mooney, who arrived at an equation which agrees well with observation. For molecular theories, the reader is referred to the work of Guth and Mark, Kuhn, and Pelzer, who carried through calculations of a statistical nature. More recently, the author extended the statistical theory along lines which avoided some of the earlier difficulties. In the present paper, the calculations will be carried still further, and the molecular theory will be related to the macroscopic theory of Mooney. It will also be shown theoretically that, although rubber does not obey Hooke's law for ordinary elongation, it should obey Hooke's law for shear. It will be supposed that individual rubber molecules are long chain hydrocarbons capable of assuming various lengths and shapes as a result of free rotation about carbon-to-carbon valence bonds. When a piece of rubber is under no stress, the rubber molecules have a certain distribution of shapes. When the rubber is subjected to a stress, however, the molecules assume another distribution of lower probability. The theory here advanced relates this probability to the entropy of strain, thus providing a means of arriving at the mechanical properties of rubber. Two postulates are made. (1) When a macroscopic piece of rubber is strained, the components of the lengths of the individual molecules (along some set of axes) change in the same ratio as does the corresponding dimension of the piece of rubber. (2) When a piece of rubber is elongated, no change in total volume takes place. The first assumption was made in the earlier paper of this series, whereas the second was not. Experimental support for the second postulate has been given by Holt and McPherson. Our first problem is to investigate the effect of this second assumption on the equation of state for rubber.
The Effect of Temperature and Solvent Type on the Intrinsic Viscosity of High-Polymer Solutions
Authors: Alfrey T. , Bartovics A. , Mark H.
Published: February 2011

1. The specific viscosity of a dilute solution of polystyrene or rubber is strongly dependent on the nature of the solvent; the specific viscosity is high in a good solvent, and low in a poor solvent or a solvent-nonsolvent mixture. This has been interpreted as being due to changes in mean molecular shape. The specific viscosities of cellulose acetate solutions are not so sensitive to the nature of the solvent. 2. The extrapolated specific viscosity at the limit of solubility is in the same range for several different solvent-nonsolvent systems. 3. The effect of a temperature increase is to lower the specific viscosity of rubber or polystyrene solutions in a good solvent, but to increase the specific viscosity in a mixture of solvent and nonsolvent. 4. The specific viscosity of a dilute polystyrene solution is more nearly linear with concentration in a toluene-methanol mixture than in pure methanol. The quadratic term b in the equation: (ηsp=ac+bc2), is reduced relatively more than the linear term a by the presence of the nonsolvent.
Further Studies of the Infrared Absorption of Rubber
Authors: Williams Dudley , Dale Brock
Published: February 2011

The transmission spectrum of natural rubber has been studied in the region between 1µ and 15 µ and the effects of linear and radial stretch have been observed. Linear extension greater than 400 per cent of the original length produces an increase in the C—C vibrational frequency. Both linear and radial stretch produce an increase in absorption coefficient and a decrease in reflection coefficient. The changes in absorption and reflection coefficients are greatest at short wave-lengths.
Properties of Hard Rubber. XIV. Influence of Some Ingredients on Surface Deterioration in Sunlight
Authors: Church H. F. , Cooper L. H. N. , Daynes H. A.
Published: February 2011

Experiments have been made to find to what extent ingredients capable of reacting with sulfuric acid to form insoluble sulfates can prevent the loss of insulating properties of hard rubber on exposure to daylight. Hard rubbers containing small and large percentages of calcium and barium carbonates and litharge have been tested, along with a comparable unloaded material and one containing an inert filler, barium sulfate. In no case was there a substantial improvement. Although the basic fillers gave better results than the inert filler, the samples containing them were inferior to the unloaded sample. The partial recovery of insulating properties on removal from light after a low surface resistivity has been reached has been investigated. Appreciable recovery took place in all cases, but this was most marked with the sample containing calcium carbonate. It was anticipated that the basic ingredients examined would to some extent prevent the undesirable effects of acid forma- tion in cases where the exposure to light was not continuous or so severe as bright north daylight. Further experiments on this point are recommended. The value of benzidine as an ingredient which forms an insoluble sulfate was tested by treating the surface of hard rubber with aqueous and benzene solutions of this material. Appreciable improvement was observed in each case. Attempts to prepare vulcanizates containing benzidine or derivatives of it having the same protective effect were unsuccessful.
Factors Affecting Results Obtained with the Mooney Viscometer
Authors: Taylor Rolla H.
Published: February 2011

Experience with the operation of the Mooney viscometer in 18 laboratories indicates the need for better reproducibility of results. A study of the available data from these laboratories along with numerous experiments made at the National Bureau of Standards have shown the factors that must be considered in improving the reproducibility. If uniformity in the values of Mooney viscosity on the same sample with different viscometers and in different laboratories is to be obtained, the methods of adjustment that must be followed and the precautions that must be taken are cleaning, mechanical calibration, dimensions of dies, die holders, and rotors, die closures, and preparation of testpieces. Each of these items and the errors which may result from maladjustments and lack of precautions in the use of this instrument are discussed.
The Hertzian Spectrum of Rubber and Its Micellar Constitution
Authors: Girard Pierre , Abadie Paul
Published: February 2011

The spectra which were studied lie within the region of hertzian frequencies, and can be represented either by dispersion curves showing the dielectric constant of the substance as a function of the frequency (or wave length λ), or by absorption curves showing the loss angle as a function of this frequency. These two types of curves represent the same phenomenon, i.e., orientation of the dipolar molecules in the alternating electric field, in accordance with the theory of Debye. The spectra and their interpretation depend chiefly on whether the molecules are crystalloid with relatively small and similar dimensions, or are colloidal, with large and unequal dimensions. In the first case, the spectra gives evidence chiefly on the form of the molecules and their structural features. Dilution in a nonpolar solvent shows for certain dipolar compounds, e.g., alcohol, considerable deformations, which differ according to the solvent. In the case of colloids, e.g., rubber, which has a permanent moment, the spectra and the meaning of these spectra are far different. In this case the spectra indicate that the absorption and dispersion values in the hertzian region are closely related to the micellar constitution, i.e., to the different types of micelles, to their size, and to the proportion of each type.
Applications of Infrared Methods in the Structural Examination of Synthetic Rubber
Authors: Field J. E. , Woodford D. E. , Gehman S. D.
Published: February 2011

Infrared absorption spectra have been long recognized as a convenient means for studying the structure of organic molecules. The interpretations of the spectra are based on the energy interactions of the molecule and the radiations which arise from the vibration of the constituent atoms and molecular rotations. For simple or highly symmetrical molecules, the determination of the normal modes of vibration and the calculation of the absorbing frequencies are relatively simple and straightforward. For more complicated organic molecules, this becomes increasingly difficult because with each additional atom, the number of degrees of freedom is increased by three and the determination of the normal modes of vibration becomes practically impossible. However, interpretations can be made to a useful extent through empirical comparisons with the absorption spectra of simpler known structures. The data that have been accumulated by investigators in this field have made it possible to assign rather definite absorption frequencies to some of the chemical linkages and functional groups. These correlations which have appeared in numerous places in the literature are partially reproduced in Table I. Organic compounds generally have strong absorption bands below 1300 cm−1, to which few definite assignments can be made with certainty because the vibrations of many of the atoms of the molecule may be involved rather than a specific part of it. It is clear that such empirical relationships must be relied upon in studying the structural variations of the long chain, complex molecules which occur in butadiene and isoprene polymers and copolymers and other synthetic rubbers. This procedure has been applied to determine the effects of oxidation and of variations in monomers and polymerizing conditions on the structure of synthetic rubber. It is practically certain that physical deficiencies of synthetic rubber are due principally to the structure of the long chain molecules rather than to the chemical nature of the monomers used.
Crystallization of Unvulcanized Rubber at Different Temperatures
Authors: Wood Lawrence A. , Bekkedahl Norman
Published: February 2011

Crystals may be formed in natural rubber under varied experimental conditions. Different combinations of stretching and cooling have been used to induce crystallization in unvulcanized and in vulcanized rubber. The appearance and disappearance of crystals have been studied by observations of the volume, heat capacity, light absorption, birefringence, x-ray diffraction, hardness, and other mechanical properties. There has, however, been no comprehensive study of the effect of temperature on the crystallization. The present investigation was undertaken to explore this field. In the work reported here it has been the aim to study crystallization at different temperatures under the simplest possible conditions. The main features of the crystallization of vulcanized rubber have been shown to be similar to those of the crystallization of unvulcanized rubber, vulcanization decreasing the rate of crystallization. Consequently unvulcanized rubber was selected for study. Stretching obviously complicates the experimental conditions, and so was not employed. Of the different methods of measuring crystallization, it seems that change of volume is the simplest and best adapted to yielding quantitative data on the course of the crystallization or fusion. The present work is, therefore, concerned with a general study of the volume changes in unvulcanized rubber at different temperatures.
Optical and Dimensional Changes Which Accompany the Freezing and Melting of Hevea Rubber
Authors: Smith W. Harold , Saylor Charles Proffer
Published: February 2011

At suitable, low temperatures, unvulcanized rubber loses its elasticity and becomes hard and opaque. Similar changes frequently occur in baled rubber which has been tightly compressed before shipment. It is said to be frozen or “boardy.” The phenomenon has been studied by many investigators who have determined changes of volume, softening temperatures, the effects of increasing time of storage at low temperatures, the influence of pressure during freezing, and changes in heat capacity and entropy. These effects have generally been ascribed to a form of crystallization, and x-ray diffraction powder patterns indicate that crystals are present in frozen rubber. When total rubber is stretched, there are changes of volume and of heat content such as attend crystallization. With x-rays a crystal fiber pattern is obtained. It and the powder pattern obtained with frozen, compact rubber have been shown to indicate similar spacings and are assumed to be caused by the same type of crystal, the differences being ascribed to conditions of orientation. Dilute solutions of rubber hydrocarbon in ethyl ether yield small crystals of the hydrocarbon when they are subjected to temperatures between −35° and − 60° C. for several hours. The optical properties and melting points of these crystals and their x-ray diffraction patterns indicate their identity with the crystals in stretched and frozen rubber. Under the best conditions the crystals appear in spherulitic groupings, the individual needles in each spherulite having optical properties that closely approach those of a uniaxial crystal with negative elongation. The crystals of sol rubber which we obtained, melted between 9.5° and 11.0° C. Crystals of gel rubber melted between −2° and 14° C., but the melting ranges within this interval were not the same for all samples. Numerous observations have repeatedly confirmed the data. About 90 per cent of the rubber in solution may be obtained as birefringent material at −65° C. Temperatures between −40° and −50° C. have been preferred, however, because better crystals are obtained in that range.
The Problem of Making Uniform Crude Rubber and Its Standardization
Authors: Bocquet M.
Published: February 2011

The problem of attaining uniformity in crude rubber and of standardizing its properties has become of the greatest concern to planters, and at the present time two facts are evident: 1. In evaluating the product which the planter has furnished him, the rubber broker has based his judgment solely on the superficial appearance of the rubber, which frequently has nothing in common with its intrinsic quality. 2. The manufacturer has found frequent cause of complaint in the variability of different lots of rubber which he has purchased and which it has been impossible for him to distinguish by superficial examination. for these reasons the planters, in agreement with the manufacturers, should welcome the classification of crude rubber into a small number of types based on the physical and chemical properties of the product. However, considering the variability of rubber at the present time, crude rubber must obviously be uniform before any attempt is made to draw up specifications. As is shown by M. Bocquet in the following discussion, the production of uniform rubber should not require any great efforts on the part of the planters, and if the planters prefer not to change their methods at the present time, it is because their methods are adjusted to the output of commercial sheet rubber, the only kind salable on the open market.
An X-Ray Study of Rubber Hydrochloride
Authors: Gehman S. D. , Field J. E. , Dinsmore R. P.
Published: February 2011

The x-ray diagram of rubber hydrochloride is a worthy addition to those of other natural high polymers and derivatives, and its study is a fruitful field for investigating the internal structure of such materials. Various peculiarities have been pointed out which have raised a question as to whether the properties of rubber hydrochloride can be explained on the basis of a chemical structure consisting of long, chlorinated, paraffin chains. These disturbing facts are (1) the effect on the x-ray diagram of the first addition of hydrogen chloride; (2) the failure to secure the theoretical chlorine content; (3) the possibility of vulcanization; (4) the amorphous diagram of balata hydrochloride, and (5) the shortening of the chains compared to normal paraffin chains. A partial departure from the strict formula may, in turn, lead to a colloidal structure which may be essential for such properties as the elasticity shown at higher temperatures and the ability to rack. The interpretation of the x-ray diagram seems to be possible on the basis of such long chains if some deformation from the zig-zag form is permitted to shorten them about 10%.
Mechanism of Oxidation of Rubber and Its Bearing on Accelerated Aging Tests Parts I And II
Authors: Morgan L. B. , Naunton W. J. S.
Published: February 2011

1. An apparatus is described for the measurement of the rate of oxidation of rubber at either constant pressure or constant volume. Provision is made for further additions of oxygen during the oxidation. 2. It was confirmed that the rate of oxidation of rubber is independent of the oxygen pressure. 3. The zero order reaction rate of oxidation varies with temperature according to the Arrhenius equation. 4. The depth of oxygen penetration decreases exponentially with temperature, and is reduced by low oxygen pressure, low oxygen permeability or by a fast rate of oxidation. 5. If the dimensions of the rubber sample are too large, or the temperature is too high, it is probable that only the outside layers of the rubber will undergo oxidation, and the low rate of oxidation observed will depend on the depth of oxygen penetration. 6. On exposure to light the propensity of the rubber for oxidation gradually increases, and the data suggest the slow attainment of a photostationary state between two opposing reactions, involving the formation of peroxide by light and disappearance by a dark reaction. 7. On removing light-activated rubber into the dark, the enhanced oxidation rate persists for a considerable time. 8. All specifications for accelerated aging tests should specify the importance of not exposing the samples to a bright light before submitting them to the aging operation. 9. The peroxide formed by the action of light can be destroyed by the action of heat in vacuo.
High-Speed Apparatus for Determination of Plasticity in Rubber Works and Some Results
Authors: Hoekstra J.
Published: February 2011

Since the day that Hancock invented his wooden masticator, plasticizing has been one of the outstanding features of the rubber industry. Although the application of rubber in the form of latex, thus avoiding the process of mechanical softening, is increasing, this does not imply that the use of heavy machinery for plasticizing coagulated rubber is lessening. It is now commonly accepted that plasticizing or mastication of rubber is a chemical process, occurring under combined mechanical and chemical (oxygen) influences and resulting in a diminishing of the length of the hydrocarbon molecules. This breakdown of rubber is of great technical importance, because the plasticity of rubber stock determines its workability. The degree of plasticizing or breakdown, especially when mastication has been prolonged, has also some effect on mechanical and aging properties after the plasticizing has been counterbalanced by the action of vulcanization. It follows from the foregoing that control of plasticity during fabrication is of great interest from a technological standpoint. From the standpoint of works economy the problem is not less urgent, because energy used by internal mixers and mixing rollers as well as extra costs resulting from wrong plasticity in calendering and moulding are of importance in total production costs.
The T-50 Test for State of Vulcanization. II
Authors: Gibbons W. A. , Gerke R. H. , Cuthbertson G. R.
Published: February 2011

The uses and applications of the T-50 test for state of vulcanization have been listed. New combined sulfur data corrected for sulfur combined as zinc sulfide have been presented. The T-50 values for vulcanizates which contain no zinc oxide, but which are widely different in composition, give identical curves when plotted against the total combined sulfur. The T-50 values for vulcanizates which contain zinc oxide and which are widely different in composition do not give identical curves when plotted against either the total or the corrected combined sulfur.
The Influence of Vulcanization on the Oxidizability of Rubber. Vulcanizing Agents Other Than Sulfur
Authors: Dufraisse Charles , Le Bras Jean
Published: February 2011

In a previous publication the influence of vulcanization by sulfur and sulfur compounds on the oxidizability of rubber was shown. The most important conclusion was that, in principle, the higher the proportion of combined sulfur, the greater is the oxidizability. However, with very high proportions, the activity of the sulfur changes, i.e., above a certain upper limiting range, the oxidizability tends towards a plateau, whereas below a lower limiting range the oxidation curve passes through a minimum. After having obtained these results, it seemed to be of interest to complete the investigation by studying the effects of vulcanization by agents other than sulfur on oxidizability. In the present work we have examined vulcanization by nitro compounds and peroxides, taking as examples m-dinitrobenzene, trinitrobenzene and benzoyl peroxide. This domain of rubber chemistry has been relatively little explored and certain points either have not received final confirmation or have even led to contrary conclusions. Accordingly it seemed useful to review from a purely objective point of view what has been done on this subject.
Chloroform Extract of Reclaimed Rubber
Authors: Palmer Henry F. , Kilbourne F. L.
Published: February 2011

1. For any given reclaim, increased chloroform extract means greater softness and plasticity, but different types of reclaim with equivalent chloroform extracts may have widely different plasticities, or with the same workability may have widely different chloroform extracts. 2. While longer time of heat treatment at a given temperature increases the chloroform extract, increased temperature raises it decidedly. At elevated temperature (263° C) there is a transformation of chloroform-soluble into acetone-soluble material. 3. Within practical operating temperature limits, the milling and straining operations do not affect the chloroform extract. Increased number of passes through a refiner increases the chloroform extract. This fact is of importance in the chloroform determination. Cool refining gives a product with higher chloroform extract than hot refining. 4. The chloroform extract is unaffected by slow or rapid cooling of finished reclaim slabs. The slow-cooled reclaim, however, is somewhat drier and nervier. 5. Reclaimed rubber has a lower chloroform extract after natural aging than when freshly made. The aging process is also accompanied by an increase in the nerve and a decrease in the tackiness of the reclaim. 6. The use of oils as plasticizers in preference to excessive heat plasticization is not detrimental to reclaim quality, but is often desirable in producing many types of reclaimed rubber. 7. The percentage of chloroform extract present in typical commercial reclaims usually lies between 30 and 40 per cent, based on the rubber content. Values below 20 per cent indicate a low degree of devulcanization. Values above 50 per cent are rare but, when they do occur, indicate an excessive devulcanization. The amount of chloroform extract is an insensitive criterion of workability. Since a high chloroform extract does not indicate improved quality, a performance test must be used.
Production of Decorative and Ornamental Rubber Products
Authors: Griffiths J. P. , Pinnell C. R.
Published: February 2011

It is proposed to deal with the production of rubber goods which can lay claim to being decorative and ornamental, not according to their classification in a sales catalog, but according to the machines which produce them. CALENDERING One of the difficulties in a works handling rubber qualities ranging from pure gum stocks to the more heavily compounded variety, such as flooring, is to obtain sheets of the same thickness across the width. The wider the sheet the more difficult this becomes. With perfectly cylindrical rolls, the pressure of the rubber bank at the nip will cause the roll to bend, so that a sheet of rubber coming from between such rolls will be thicker in the middle. This variation is overcome by making the rolls a little thicker in the middle by only a few thousandths. However, the amount of bending depends on the type of stock being calendered, so that one calender cannot produce sheet of even thickness from all types of mixings. The greater thickness of the rolls in the middle compared with the ends is referred to as the camber. When the machine is under load, the camber corrects the bending so that the effect is equivalent to using perfectly cylindrical rolls that do not bend. Unless a firm has more than one calender for different types of stock, there is always one class of mix which cannot be the correct thickness right across the sheet. For many classes of goods this variation is not important, but for sheets of rubber intended for flooring to be cut to tiles and pure gum sheet to be cut to thread, it is obvious how important the question of uniform thickness becomes. One cannot expect mechanical pressure during vulcanization to correct this fault or, if it does, other effects are spoilt. For example, the marble pattern on flooring may be spoilt by a sideways flow of rubber under a powerful press, especially where considerable variation was present in the thickness of the calendered sheet. A recent method of correcting camber is to swing the top bowl of, say, a three-bowl calender, so that the axis of one bowl is at an angle to the one immediately underneath. The rollers are, of course, perfectly cylindrical, and only have to be swung through a few degrees.
Vulcanization of Rubber Compounds
Authors: Booth E. W. , Beaver D. J.
Published: February 2011

1. Rubber dissolves approximately one per cent of hydrogen sulfide when saturated at room temperature. 2. All types of commercial accelerators are retarded in rate of vulcanization as a result of treatment with hydrogen sulfide, and the retardation is directly proportional to the hydrogen sulfide content. 3. The physical properties of mercaptobenzothiazole types of accelerators and diphenylguanidine are not permanently affected by hydrogen sulfide, but dithiocarbamates, thiuram sulfides, aldehydeamines and litharge are permanently affected. 4. Rubber compounds containing mercaptobenzothiazole types of accelerators or diphenylguanidine, which have been treated with hydrogen sulfide and then degassed in a vacuum oven, show normal rate of vulcanization. Compounds containing aldehydeamines, litharge or carbon black show permanent retarding, even after degassing. 5. Increased zinc oxide or sulfur has no appreciable effect on the retardation. 6. Little or no zinc sulfide is formed as a result of treatment with hydrogen sulfide. 7. Hydrogen sulfide treatment of rubber compounds retards the rate of combination of sulfur with rubber. 8. In no case did hydrogen sulfide treatment improve the physical properties of the vulcanizate.
Studies in the Sterol Group. Part XLIII. The Unsaponifiable Portion of the Acetone Extract of Plantation Rubber
Authors: Heilbron I. M. , Jones E. R. H. , Roberts K. C. , Wilkinson P. A.
Published: February 2011

In previous studies of this material, the isolation and identification of a sterol, C27H46O, and octadecyl alcohol have been described. It is now shown that the former is a mixture of isomeric sterols, which include β-sitosterol and probably a 24,28-dehydrostigmastanol, and that the aliphatic alcohol is eicosyl alcohol. No other pure component has yet been isolated in sufficient quantity for investigation, since the remainder of the neutral action undergoes extensive pyrolysis on distillation, even in a high vacuum. Evidence has, however, been obtained that a portion of the unsaponifiable substances becomes increasingly intractable as rubber ages, and it is possible that the present failure to obtain the ketone C15H24O and the socalled liquid sterols, C27H42O3 and C20H30O, reported by Bruson, Sebrell, and Vogt, may be due to this cause.
Rubber, Polyisoprenes, and Allied Compounds. IV. The Relative Tendencies towards Substitutive and Additive Reaction during Chlorination
Authors: Bloomfield George F.
Published: February 2011

Although the established mode of reaction of chlorine with unsaturated systems is primarily additive, it has recently been shown by Groll and his collaborators that, under suitable conditions, substitutive reaction may not only occur but may become the major reaction, to the exclusion of addition. According to these authors, high temperatures in the range of 300–600° seemed generally to be necessary if substitutive reaction is to predominate, but subsequently it was shown by Rust and Vaughan that a considerable degree of substitutive reaction can be realized at temperatures in the range 130–200°, provided certain catalysts which produce free radicals in contact with the halogen are present. The polyisoprene system has been found to be particularly susceptible to substitutive attack by oxygen, and it has long been known that, judged by the quantity of hydrogen chloride liberated, the chlorination of rubber proceeds largely by substitution in the earlier stages of reaction. The character of the products thus produced and the influence of the experimental conditions on the course of reaction were not, however, studied in any detail by McGavack.
Determination of Total Sulfur in Rubber
Authors: Luke C. L.
Published: February 2011

With the recent increase in research on natural and synthetic rubber, there has arisen a need for a rapid method for the determination of total sulfur in rubber samples where only a semimicrosample can be spared for analysis. The usual methods in which the rubber is oxidized by digestion with acid, followed in some cases by fusion to complete oxidation, and the sulfur is precipitated and weighed as barium sulfate, yield good results on semimicro-samples, but are time-consuming, because quantitative precipitation of the sulfate cannot be attained unless the solution is allowed to stand overnight before filtration. Several volumetric methods, most of which depend on the precipitation of sulfur as barium sulfate, have been described, but none is very satisfactory in the determination of small amounts of sulfur. St. Lorant has proposed a volumetric method for the determination of microsamples of sulfate, in which the sulfate is reduced to sulfide with hydriodic acid, and the hydrogen sulfide is distilled off and determined colorimetrically. The author has recently developed a modification of this method which has proved to be very satisfactory for the analysis of sulfur in small samples of rubber. The procedure consists essentially of oxidation of the rubber in the usual manner, reduction of the sulfate to sulfide, separation of the hydrogen sulfide by distillation, and titration of the latter iodometrically. The new method is very rapid (20 to 25 minutes for the distillation and titration), and is not subject to the errors of adsorption, occlusion, and solubility encountered in the gravimetric barium sulfate method, or to difficulties in detection of the end-point encountered in some volumetric methods. It possesses the distinct advantage over some of the gravimetric methods that it is applicable to the analysis of rubber containing barium, lead, and calcium. The only serious objections to the method from the standpoint of general use are that hydriodic acid is expensive and that the applicability of the method is somewhat limited because of the fact that no more than about 5 mg. of sulfur can be handled conveniently. This means that the sample size must be small when analyzing rubber high in sulfur; and when small samples are used there is always the danger of error due to unequal distribution of sulfur in the sample.
The Mechanism of the Action of Mercapto-Benzothiazole and of Its Derivatives in the Vulcanization Process
Authors: Petrov K. D.
Published: February 2011

In our work we confirmed that, in the process of vulcanization of rubber, the normal zinc salt of mercaptobenzothiazole changes into mercaptobenzo-thiazole. Based on this and on other facts described earlier, a probable mechanism of the action of mercaptobenzothiazole and its derivatives in the vulcanization of rubber is suggested.
The Effects of Milling on the Softness of Rubber. I. Temperature and Friction
Authors: Haehl A. , le Bras Jean
Published: February 2011

Although the process of softening rubber by mastication has been the subject of repeated investigation, the literature contains no references to systematic experiments in this field. It is with a view to making up for this lack of information that the work described in the present paper was undertaken. A survey of the literature shows several papers of interest in connection with the work to be described in the present paper, particularly the papers of Grundy and Schidrowitz, Griffiths, The Goodyear Tire and Rubber Company, Shoaff, Bachmann, Behre and Blankenstein, and Busse and Cunningham. Grundy and Schidrowitz attempted to establish a relation between plasticity and work expended in milling. Griffiths studied the influence of the size of batch, temperature, etc., on plasticity. The Goodyear Tire and Rubber Company Laboratories investigated the influence of the temperature during milling on mastication. Shoaff determined the energy expended in mastication. Bachmann, Behre and Blankenstein made a study of the dependence of the mastication on the spacing of the mill rolls, on the speed of the rolls, and on other factors. Finally Busse and Cunningham investigated the dependence of plasticity on the temperature of mastication and on atmospheric oxygen.
Effect of Temperature on the Mechanical Properties of Rubberlike Materials
Authors: Fletcher W. P.
Published: February 2011

In the course of investigations into the mechanical properties of natural and synthetic rubbers intended for use in antivibration devices, variations of a large order were encountered. As these variations seemed to be largely dependent on temperature, a preliminary detailed examination in the region of 5° to 40° C was made. With the aid of a mechanical vibrator somewhat similar to that employed by Gehman, and working at 20–60 c.p.s., measurements of dynamic elastic compression modulus and associated resilience were made by the well known resonance method. A detailed description of the apparatus, method, and results is to be published later; for the present time, it may be said that the test-pieces were in the form of cylindrical rubber blocks, 0.875 inch in diameter and 0.875 inch high, bonded at each end to steel screws by the conventional brass-plate method.
Recent Advances in the Physics and Chemistry of Rubber. I. The Size and Shape of the Rubber Molecule
Authors: Gee Geoffrey
Published: February 2011

During the last decade, enormous strides have been made in the scientific study of rubber and related polymers. The main factors combining to make this possible have been the realization that the physical behavior of these materials depends on their long chain character, while their chemical properties are essentially those of a low molecular substance of similar structure. Contrary to earlier belief, neither the physics nor the chemistry of rubber involves any mysterious new forces or reactivities unknown among smaller molecules. Since such importance attaches to the size and shape of the rubber molecule, we begin by reviewing briefly the evidence on which our present theories are based. Methods of determining molecular weights may be divided into “counting” methods and “weighing” methods. The former include the determination of any of the “colligative” properties of a solution; the latter depends on the use of an ultracentrifuge.
A Modified Method for the Direct Estimation of the Absorption of Oxygen by Rubber
Authors: Van Amerongen G. J.
Published: February 2011

A modification of Dufraisse's oxygen absorption apparatus is described, with which it is possible to carry out the determination under constant pressure. As a result the oxygen absorption of rubber can be read directly in absolute terms, a secondary advantage being that the determination proceeds roughly four times as quickly as by the manometric method. Some results are given which show clearly, among other things, how considerable is the effect of preliminary exposure of the rubber to light on the oxidation.
Diode Laser Cyclophotocoagulation versus Cyclocryotherapy in the Treatment of Refractory Glaucoma
Authors: Tzamalis Argyhos , Pham Duy-Thoai , Wirbelauer Christopher
Published: February 2011

Purpose

The aim of the present study was to evaluate the efficacy of diode laser cyclophotocoagulation (DCPC) and cyclocryotherapy (CCT) in the treatment of refractory glaucoma and compare the postoperative complications and discomfort rates.

Methods

In a prospective, randomized, controlled clinical study, 40 eyes of 40 patients with refractory glaucoma were randomly assigned in 2 groups of 20 eyes each to receive either DCPC or CCT. Patients underwent follow-up examinations on the first 3 days and then 1 week and 1, 3, 6, and 12 months after initial treatment. Complications and discomfort after treatment using a visual pain analogue scale were recorded.

Results

In the DCPC group, the mean intraocular pressure (IOP) decreased (p<0.05) from 44.3±16.4 mmHg preoperatively to 24.1±7.6 mmHg, 22.8±5.6 mmHg, and 22.5±5.1 mmHg 3, 6, and 12 months posttreatment, respectively. Regarding the CCT group, the mean IOP was reduced (p<0.05) from 46.5±10.4 mmHg to 26.6±12.2 mmHg, 21.2±7.7 mmHg, and 20.6±5 mmHg at the same time intervals. In the DCPC group, the mean IOP reduction was strongly correlated with the number of laser effects (r=0.65; p<0.01), but 35% needed retreatments. The mean postoperative pain was 5.6±2.9 (DCPC) vs 5.7±2.3 (CCT) (p=0.91). No severe complications were observed.

Conclusions

Both DCPC and CCT proved to be safe and effective IOP-lowering methods in patients with refractory glaucoma. Diode laser cyclophotocoagulation should be considered as the primary treatment option in refractory glaucoma using an individual treatment dosage.