bluuebunny/crossref_metadata_2025 huggingface dataset:
The Oxidation of Rubber at Atmospheric Temperatures
Authors: Davey W. C.
Published: February 2011

(1) Oxidation at ordinary temperatures in the dark proceeds very slowly for unextracted rubbers, but at quite a reasonable speed for extracted rubber-sulfur mixings. The rate of oxidation of accelerated mixings, even if acetone-extracted, is very slow. (2) The final increases in weight after long aging are higher at ordinary temperatures than at 70° C. and the amount of acetone extract and the (acetone extract)/(increase in weight) ratios are also very much higher. (3) Storage in a moist atmosphere retards the oxidation in comparison with storage in a dry atmosphere, but the relative rates of oxidation in the two media are dependent on the rubbers under consideration. With slowly oxidizing samples, the lower the degree of cure the less the difference in oxidation rates, but with fast oxidizing rubbers the difference in rates of oxidation in the two media is less if the degree of cure is higher. The amount of acetone extract formed is less during storage in a moist atmosphere than in a dry one. (4) The acetone extract curves show definite maxima due to the change of the extract to insoluble matter, but the tendency for this change is small at atmospheric temperatures. (5) The effect of exposure in sunlight is to cause markedly lower acetone extracts to be obtained than when the samples are stored indoors. Exposed in quartz tubes, the extent of the acetone extract change to insoluble matter is of the order of that at 70° in the dark, and the acetone extract curves are of a similar form. Exposed in glass vessels the degree of extract conversion is not so great as at 70° but very much greater than when the samples are stored indoors. Accelerated mixings exposed in sunlight give very high acetone extracts, indicating that the acetone extracts of such mixings have little tendency to pass into an insoluble form.
The Protective Action of Some Antioxidants II. The Metal Halide Compounds of Some Protective Agents against Aging, with Special Reference to Aldol-Alpha-Naphthylamine
Authors: Kirchhof F.
Published: February 2011

The results described in the present paper can be summarized as follows: 1. Certain antioxidants containing nitrogen, like aldol-α-naphthylamine and Stabilite Alba, give in alcoholic solution with higher halides of certain metals, especially those of iron and copper, unstable intense blue-violet as well as stable carmine-red colorations, which may be regarded as more or less stable complex compounds of these antioxidants. A series of other heavy metal halides of which similar behavior would be expected (for example, SnCl4, CoCl3, etc.) give no color reactions of this kind. 2. Both the chemical and the optical behavior of these colored solutions indicate that they contain complexes of ferric chloride and cupric chloride groups attached to tertiary nitrogen, as in the haemin of blood pigment. 3. Of the antioxidants studied here, aldol-α-naphthylamine reacts quickest with the metal halides named above, Agerite the slowest and Stabilite Alba somewhere between the two. The reaction with cupric chloride occurs in every case much more rapidly than that with ferric chloride. It is obvious that this behavior might be utilized to distinguish analytically small quantities of these substances. 4. The complex metal halide compounds show strong oxygen-transporting action, as does the haemin of the blood, which contains iron. This is many times greater with the compounds of antioxidants which contain copper than with those which contain iron compounds, and this agrees with the similar behavior of compounds of these metals with rubber, as has long been known. 5. Since the antioxidants are oxidized in the course of time, as the result of autoöxidation, they protect an autoöxidizable substance like rubber only so long as they are not rendered inactive. Since traces of soluble heavy metal compounds, especially of iron, are invariably present in rubber compounding ingredients, it can be understood why rubber mixtures containing protective agents are more or less strongly and more or less rapidly discolored as a result of the formation of dark-colored metal complex compounds and their oxidation products. 6. Finally it was possible to show that the complex metal halide compounds of the antioxidants studied are remarkably sensitive toward certain catalytic poisons such as hydrocyanic acid, in quite an analogous fashion to known biological oxygen carriers. It is entirely possible that this phenomenon may also be of significance in the use of protective agents in technical rubber mixtures.
Reënforcing Action of Pigment Mixtures on Rubber Compounds
Authors: Beaver D. J. , MacKay J. W.
Published: February 2011

Mixtures of varying ratios of either channel black or a soft carbon black with whiting, lithopone, or clay show additive physical properties. Mixtures of soft carbon with zinc oxide also show additive properties, while mixtures of channel black and zinc oxide show poorer resistance to abrasion, higher modulus, and higher tensile strength than would be shown by purely additive mixtures. The explanation of these results appears to be found in the chemical reaction between the basic zinc oxide and the acidic compounds in the rubber or on the black. These results have been applied to the formulation of a solid-tire stock which will give a better resistance to abrasion and blow-out when using a soft black than when using a channel black.
Determination of pH of Ammonia Latex
Authors: McGavack J. , Rumbold J. S.
Published: February 2011

The pH of latex has been determined at various concentrations of ammonia (1) by the use of indicators, and (2) by the application of the glass electrode. The two curves thus obtained were comparable but not identical. It is shown that the glass electrode gives results reproducible with a high degree of accuracy up to pH 9.5 and a fair degree of accuracy up to pH 11.0. Above pH 11.0 it is necessary to calibrate each electrode. An ordinary galvanometer allowed measurement of the e. m. f. to 1 millivolt. The assymetry of the glass was so small as to be negligible. This paper covers the work done so far in these laboratories on the development of an accurate and rapid method for determining the pH of latex. From a practical viewpoint one of the most troublesome features of the direct use of a hydrogen electrode is the deposition of a film of rubber on the platinum, which by increasing the internal resistance of the cell, so reduces the sensitivity of the null point instrument that after a few determinations the apparatus must become inoperative. A more serious objection to this electrode is the uncertainty attached to measurements made in solutions containing proteins.
Determination of Alkalinity of Reclaimed Rubber
Authors: Palmer Henry F. , Miller George W.
Published: February 2011

A new method is given for determining the relative alkalinity of reclaimed rubber. The extraction of the alkaline material is based on a digestion of the sample in a mixture of ethanol, benzene, and water. The method is compared with the previous method described by the authors in 1928. The experimental figures given show that the new method gives results which are dependable, and approximately four times as accurate as the previous method. The higher degree of accuracy is due to the elimination of much of the personal error, the extraction of a larger percentage of alkaline material, and a more accurate titration end point. The purpose of this paper is to present a method for determining the relative alkalinity of reclaimed rubber which, in the authors??? opinion, has certain advantages over other methods in use at present.
The Effect of Organic Accelerators on the Temperature Coefficient of Vulcanization
Authors: Eliel K. W.
Published: February 2011

(1) The temperature coefficient of vulcanization to a standard modulus is 2.0 in the presence of mercaptobenzothiazole, Ureka, Ureka White, and Vulcafor D. A. (2) The temperature coefficients of vulcanization in the presence of all accelerators tested, including those of delayed action type, are constant over a wide temperature range (110–150° C). None of the accelerators appears to have a critical temperature. (3) Differences between the rates at which modulus develops with accelerators of similar activity may account for the fact that some induce scorching on the compounding mill, whereas others do not. (4) At all temperatures investigated, the period of delay of a delayed action accelerator may represent a constant proportion of the total time required to reach a definite state of cure, as indicated by modulus.
Mechanism of Rubber Vulcanization with Sulfur
Authors: Lewis W. K. , Squires Lombard , Nutting Robert D.
Published: February 2011

THAT vulcanization of rubber with sulfur always involves a chemical reaction consisting in the addition of sulfur to the double bonds of the rubber molecule has been conclusively established (18, 28). The facts indicate that this addition of sulfur to rubber is an irreversible reaction (31). The temperature coefficient of the reaction is high, increasing about 2.65 fold per 10° C. at ordinary curing temperatures (31). Furthermore, the reaction is apparently exothermic (4, 24). It is noteworthy that catalysts are apparently necessary, since synthetic rubbers prepared from pure materials add sulfur slowly, if at all. The proteins and perhaps the resins in natural rubber undoubtedly serve as accelerators. The curves for combined sulfur vs. time of cure for typical mixes are shown in Figures 1 and 2. Figure 1 is taken from the data of Kratz and Flower (16); the composition and temperature of cure for this mix are shown in Cranor's Table I (9). Figure 2, curve 1, is from Table I of Eaton and Day (10), and curve 2 from data obtained in this laboratory (27, Table I). Superficial inspection of these curves shows extraordinary divergence of type. Figure 1 is a typical fadeaway curve, characteristic of most chemical reactions, where the reaction rate decreases with decreasing concentration of the reacting materials. Curve 1, Figure 2, is an entirely different type, where the rate of sulfur addition is constant until nearly 70 per cent of the initial sulfur has reacted. Curve 2, Figure 2, shows even more complex behavior. Again the rate is constant in the initial portions of the cure. However, following this period, the rate increases markedly but later falls off, approaching zero, to give an S-shaped eurve.
Rapid Detection of Accelerators
Authors: Slepushkina E. P.
Published: February 2011

Where doubt exists rubber technologists may at times require a prompt answer as to whether accelerators are present in a rubber compound. It was necessary therefore to develop specific reactions and methods of procedure which make it possible to determine each individual accelerator in the presence of other accelerators. The procedures developed by us for the detection of accelerators in uncured rubber compounds and for mixed accelerators are extremely simple, and require not more than 10–15 minutes for completion of a test. By these methods a technologist can obtain a quick answer, and thus prevent possible spoilage and rejection of finished rubber goods. The additional advantage of these methods is that each individual accelerator can be detected in any combination of accelerators present in the rubber compound. Qualitative identification is performed almost exclusively in aqueous extracts, and is based on the differing solubilities of accelerators in water. The tests, described here in detail, were confirmed by tests of all rubber mixes used at the Yaroslav Rubber and Asbestos Works. These mixes contain the accelerators most commonly used in the rubber industry, such as diphenylguanidine, mercaptobenzothiazole, tetramethylthiuram disulfide, K-1 (a condensation product of aniline 2 mols and acetaldehyde 3 mols), and A-19 (formaldehydeacetaldehydeaniline).
The Falling-Weight Impact Test for Ebonite
Authors: Church H. F. , Daynes H. A.
Published: February 2011

1. With unnotched test-pieces, although impact strength is uninfluenced by variations of width of test-piece, the depth must be fixed. 2. With notched test-pieces, impact strength is independent of the depth of the notch with deep notches, provided the depth of the material above the notch is kept constant. Impact strength is, however, very sensitive to variations of notch radius. 3. Impact strength increases slightly with velocity of the striker, so that this should be kept within reasonably narrow limits for accurate work. 4. The falling weight type of apparatus provides a simple and convenient method of testing the resistance of ebonite and similar materials to damage or fracture by impact. 5. Three variations of the method of use of this apparatus are described which involve the factor of fatigue to different extents. 6. Results with a number of pure ebonites of different compositions and vulcanization times are given to show the influence of those factors on impact strength.
The T-50 Test Applied to Zinc Oxide Compounds
Authors: Haslam George S. , Klaman Clarence A.
Published: February 2011

The T-50 test is an extremely satisfactory tool for the study of the curing rate of zinc oxides. There are small differences in the curing rates of various zinc oxides when used in activation amounts in gum stocks and stocks loaded with inert extenders. In the presence of carbon black, these differences are not detectable. There are marked differences in curing rate between the various zine oxides in stocks containing more than 10 parts of pigment in 100 parts of rubber. The oxides containing sulfur show marked retardation, as do the fine oxides, at high loadings. In the first case, this retardation is caused by the chemical nature of the pigment; in the second case, by the absorption of sulfur and accelerator.
A Study of the Formation of Rubber in the Plant
Authors: Ambros Otto
Published: February 2011

The hypothesis is advanced that the natural polymerization of isoprene in plant cells is induced and accelerated by an oxidation which in turn is brought about through the agency of a system of enzymes. Experiments in a laboratory in the tropics show that the serum of latex has an accelerating action on the polymerization of emulsions of isoprene in water containing hydrogen peroxide, and that this effect is nullified if the action of the enzymes is arrested by an acid or by a poison such as hydrocyanic acid.
Natural and Synthetic Rubber. XVIII. The Protein from Natural Rubber and Its Amino Acid Constituents
Authors: Midgley Thomas , Henne Albert L. , Renoll Mary W.
Published: February 2011

The protein constituent of rubber has been extracted from the natural rubber by removal of the rubber hydrocarbon with solvents followed by electrodialysis of the residue. This material has been analyzed, subjected to hydrolysis, and its amino acid constituents have been separated and identified.
The Kinetics of the Coagulation of Latex of Hevea Brasiliensis and the Separation of the Hydratant Acid
Authors: van Harpen N. H.
Published: February 2011

In the present work, an attempt is made to study the process of coagulation of Hevea brasiliensis latex, so familiar to every rubber expert, from a general colloid-chemical point of view, and to ascertain the physical conditions under which the kenetic phenomena take place. Hevea Brasiliensis Latex as a Physical System In “The Electrometric Determination of the Hydrogen Ion Concentration in the Latex of Hevea brasiliensis and Its Applicability to Technical Problems” the true character of Hevea brasiliensis latex as a physical system and the phenomena which take place during coagulation of this system are discussed in the light of investigations and observations of various rubber experts. Latex is a dispersion composed of polydispersed rubber hydrocarbon, serum components, and water. The rubber component consists of microscopically visible solid or semi-solid particles, in Brownian movement, and judged by the degree of affinity of rubber for water these particles are unquestionably lyophobic. Since the serum components are in a colloidal state, they are present as sols or emulsions, and they impart to the latex its lyophilic properties. It is possible, however, to choose the conditions of coagulation so that, for a given concentration of dispersed substances and at a given temperature, the dispersion will be predominantly lyophobic or lyophilic. This dual standard leads to the conclusion that Hevea brasiliensis latex is a pseudo-lyophilic dispersion. In saying this, it should be noted that, although the dispersion has several lyophilic properties, it is nevertheless essentially a lyophobic system, the properties of which become manifest under the right conditions.
The Concentration of Latex by Creaming
Authors: Baker H. C.
Published: February 2011

Latex consists of a suspension of microscopic particles of rubber, bearing an adsorbed layer of protein, in an aqueous serum containing principally l-methyl inositol, so-called rubber resins, and saline substances. The rubber particles are in continuous oscillatory motion, which may be seen under the microscope. Brownian movement is due to the bombardment of the suspended particles by the molecules of the dispersion medium, and it can be demonstrated that the smaller particles are in more violent oscillatory movement than the larger particles. The rubber particles in latex are sufficiently small to remain in suspension in the aqueous serum for an indefinite period, but if latex is left to stand, a concentration gradient will develop throughout its bulk, leading to the formation of an upper concentrated layer of closely packed rubber globules in a manner analogous to the formation of cream on milk. This behavior is shown by all types of latex, field, preserved, and concentrated, but the effect is stated to be much greater with preserved latex than with field latex (Bishop and Fullerton, Latex Preservation and Shipment Planting Manual, No. 4, Rubber Research Institute of Malaya, July, 1932). The same authors give figures (Table I) which show the magnitude of this effect for freshly ammoniated latices which had remained undisturbed for a period of two months. It will be observed that creaming occurred to a considerable extent in all samples, accompanied by a diminution in the ammonia contents of the surface layers.
Highly Reactive Sulfur or the Reaction of Ammonia and Sulfur Chloride in Rubber Solutions
Authors: Menadue F. B.
Published: February 2011

When sulfur chloride and ammonia gas react in the presence of rubber in a benzine solution, a precipitate is formed which contains, in addition to NH4Cl, sulfur, etc., sulfur combined with the rubber in varying proportions according to the amount of S2Cl2 used and thus the amount of this active form of sulfur produced. A limit is reached, however, beyond which no additional rubber-sulfur product is obtained. The sulfur in the precipitate is classifiable into: (a) uncombined, and soluble in acetone and NaOH solutions. (b) combined with the rubber, not extractable with acetone on extraction for standard periods of time of 8 hours for soft vulcanizates to 60 hours for ebonites, but slowly extractable with 10 per cent NaOH solutions. (c) present in the precipitate as S2Cl2 additive product and as nitride. As much as 39.5 per cent of (b) plus (c) was obtained, the product in such case resembling ordinary ebonite. The nitrogen content in this case was 2.8 per cent, equivalent to 9.2 per cent N4S4, and the S2Cl2 as the additive rubber product was 1.52 per cent. These figures were the highest obtained in any precipitate. Nitrogen was fairly constant between 2.17 and 2.8 per cent for ebonites, and obviously occurred in accordance with some law of equilibrium.
The Isomerization of Rubber
Authors: Ferri Cesare
Published: February 2011

It is already known that rubber and gutta-percha behave as if they were cis and trans isomers. Judged by the roentgenographic observations of Meyer and Mark, of Mark and von Susich, and of Lotmar and Meyer, rubber has the cis form and gutta-percha, the trans form. Numerous attempts have been made to transform rubber into gutta-percha. As is well known, isomerization from the cis to the trans form is often induced by light, and for this reason Meyer and Ferri studied the action of ultra-violet radiation on rubber. They were unable to prove that isomerization took place, but rather found a ‘reticulation’ resulting from polymerization. This latter phenomenon was manifest by the irreversible formation of a gel. Sievers obtained the same result by exposing to visible light, with rigorous exclusion of air, a benzene solution of rubber in the presence of a little iodine. Under these conditions likewise, gelatinization took place, without appreciable polymerization. On the other hand, the technical and patent literature describes a series of reaction products of rubber having physical properties similar to those of gutta-percha; at ordinary temperature they are solids, and at elevated temperatures they become plastic. These substances are formed by treatment of rubber with zinc chloride, toluenesulfonyl chloride, titanium tetrachloride, etc.
An X-ray Study of Stretched Rubber
Authors: Morss Henry A.
Published: February 2011

With the more extensive data from new x-ray films of the diffraction pattern of stretched rubber made in a cylindrical camera, an attempt has been made to find the true unit cell. No really satisfactory solution has been reached. The leading possibilities are described. They are characterized by a change of the angle between the two independent sets of planes which reflect the two strong equatorial spots from 90°, the value which first suggests itself, to 109.5°. The new choice is shown to be consistent with all the evidence. It has the great advantage of resolving fairly well the familiar discrepancy between measured and calculated values of the density of the crystals in stretched rubber. The new value from the unit cell is 1.00. A necessary consequence of the x-ray data is that the carbon atoms of a molecular chain are not co-planar in stretched rubber. The reason appears to be the large repulsive forces which would have to exist in that configuration. In rotations on the single bonds during stretching and retraction the interatomic forces are probably repulsions in the dominating pairs. Repulsions give a plausible explanation of the form of the outer part of the stress-strain curve.
Purification and Concentration of Rubber Latex, with Special Reference to Dialysis
Authors: Stevens H. P. , Dyer J. W. W. , Rowe J. W.
Published: February 2011

Constructional details and methods of operation are described of a pressure dialyzer capable of treating 4 gallons of latex. The removal by dialysis of various substances from latex maintained at constant volume is shown to cause the segregation of a concentrated, pasty layer of latex at the dialyzing membrane. A preliminary investigation of this hitherto unrecorded phenomenon indicates that the degree of paste formation is related to the molecular weight of the diffusing substance. It can be avoided by allowing some dilution of the latex to occur. It is considered that the segregation at the membrane is caused by a bombardment of the colloidal particles of rubber by the diffusing molecules of the solute, and that this effect will be of interest in many cases of diffusion through colloidal dispersions. Concentration of ordinary and dialyzed latex by simple evaporation and by evaporation in a spray dryer is described, and dialyzed latex is shown to have an advantage in giving a concentrate of lower viscosity.
Studies of the System Latex-Colloidal Clay
Authors: van Rossem A. , Plaizier J. A.
Published: February 2011

In the literature of rubber and latex, several references to studies on the use of colloidal clay in latex mixtures are to be found but, surprising as it may seem, the various purposes for which colloidal clay is employed are merely indicated, without any scientific explanation based on quantitative data being offered in a single case. For example, colloidal clay is used for increasing the viscosity of latex, but quantitative data have not been available. for this reason it was considered of importance to undertake a scientific and more nearly quantitative study of the latex-colloidal clay system. Some of the results of this investigation are described in the present communication which deals with experiments on the increase in viscosity brought about by colloidal clay, the diminution in tackiness of a dried latex film, the reinforcement of dried latex rubber by colloidal clay, and the flocculation of the system latex-colloidal clay.
Improved Packing of Rubber
Authors: Jones Fordyce
Published: February 2011

The practice of dusting smoked sheets with a suitable non-sticking powder has now been well tested for over three years, and during that period has proved its value. Large consumers of rubber in many sections of the industry find all that is necessary is to split the bales into suitable-sized pieces ready for compounding in large mills or internal mixers without close examination. It will be appreciated that it is somewhat difficult to make fine surgicals, inflatable or hot-water goods, toys or fancy goods, extruded or proofed goods from rubber without some form of examination. In the writer's section of the industry it is necessary that every sheet of rubber be carefully examined through the light so that it goes to the mill absolutely free from splinters, embedded bark, sand or other foreign matter, and adhered parts of any kind. The necessity of this is appreciated by all who make fine rubber ware successfully. The cost of “pulling” or separating blocks of rubber in this way is a high one; in fact, with gummy rubber, even when warm, the cost of “pulling” with labor at about 1s. 3d. an hour has been as high as ¾ d. per lb. Any way, the cost is always considerable, and as the remedy suggested herewith, and already proved in practice, costs so little and is so satisfactory it is surprising that it has not been adopted more widely.
The Components of Hevea Latex. Part II. Seasonal Variations in the Composition of Typical Seedling Latex
Authors: Roberts K. C.
Published: February 2011

1. Comparative analyses of fresh and ammoniated latices have been made, and the components investigated. 2. The changes effected by ammoniation are profound, and are far advanced in a period of eight weeks. Only the minor components, ammonium salt and ester, are inappreciably affected. 3. The fatty acid and the phosphate complexes of fresh latex undergo extensive hydrolysis within eight weeks of ammoniation, and part of the inorganic matter is firmly retained by the modified hydrocarbon. (See 5 below.) 4. The crude caoutchol of fresh latex is replaced by an increased amount of a viscous fluid which is thought to consist of a disaggregated portion of the hydrocarbon. Caoutchol itself, treated with dilute aqueous ammonia, becomes relatively insoluble, and is presumably retained on analysis by the remainder of the hydrocarbon. 5. The hydrocarbon of fresh latex is replaced by an ash-containing material which has a marked resistance to solvent action. This latter property is due not only to retention of the modified caoutchol (4 above), but also to modification (polymerization?) of the hydrocarbon itself by the action of the ammonia.
Contribution to the History of Latex
Authors: Eck Leo
Published: February 2011

The first move towards the direct use of latex was by Arnold Juliaans in 1780 when he published his “Dissertatio chemica de resina elastica cajennensi.” In this he proposed to use latex for the manufacture of medical instruments such as sounds, catheters, bougies, syringes, milk pumps, etc., either in the form of the original juice from the Hevea tree in America, where it flowed as latex from the trees, or else after transportation of this latex in the liquid state in suitable containers to Europe, where it could be converted into the desired rubber products. It is true that ten years before this Sir Joseph Banks, an English explorer and partner of Cook in his first voyage around the world, had brought back a bottle of latex in good condition, as a narrative by Grossart shows. Unfortunately however, the latex decomposed soon afterward, and Sir Joseph Banks offered in vain 50 gold louis at Lisbon for another bottle of latex. Grossart himself had received, towards the end of the eighteenth century, a half-bottle of milky juice which was sent by d'Arcet from Mauritius. Grossart left it for several winters in an unheated room, and after the very severe winter of 1788–1789 he found it broken. He was thus obliged to give up the experiments which he had in view.
Structure of Stretched Rubber
Authors: Clews C. J. B. , Schossberger F.
Published: February 2011

Investigations of the micellar structure of fiber substances have given rise to two theories. The older theory (Meyer and Mark, 1930; Mark, 1932; Siefriz, 1934; Meyer, 1930; and Nägeli, 1928) considers the micelles as separate crystallites, between which lie the intermicellar spaces. The micelles consist of “Hauptvalenzketten“ bound together along their length by homeopolar bonds and in the transverse direction by van der Waals' forces, the intermicellar binding being also attributed to van der Waals' forces. The original model suggested in work published by Meyer (1930) for cellulose depicts the micelles arranged like bricks in a wall (Fig. 1), and doubtless this is the simplest explanation of the x-ray results. But it is difficult to understand how such an arrangement can give a micellar structure its peculiar mechanical properties, and further how it is possible, when both inter- and intramicellar cohesion are attributed to the same type of force, to cause by swelling experiments an enlargement of the intermicellar spaces, while the “Hauptvalenzketten” remain unaffected.
Studies of Organic Accelerators. XVI. Part 4. Detection and Analysis of Organic Accelerators. Detection of Guanidine Accelerators in Vulcanized Rubber
Authors: Shimada Keichi
Published: February 2011

Rubber vulcanized with a thiuram accelerator such as tetramethylthiuram monosulfide or disulfide was tested with the author's cobalt oleate reagent after extraction with acetone and solution of the residue from the acetone extract in benzene, by testing the benzene extract of such vulcanized rubber. In all cases a characteristic yellowish green coloration of dithiocarbamate was observed. From this it is concluded that thiuram accelerators are transformed into dithiocarbamates during vulcanization. Accordingly, it is difficult to ascertain whether accelerators in vulcanized rubber were originally present as thiuram compounds, except when the rubber is undercured or when an excessive amount of accelerator is used. Here, too, the greater part is detected as dithiocarbamate. An experimental proof of the mechanism of acceleration is offered.
Estimation of the Stability of Rubber Solutions
Authors: Rachner Manfred
Published: February 2011

Various types of rubber products, such as seamless goods and rubberized fabrics, are prepared from rubber solutions and are vulcanized either by the hot or cold process. “Cold vulcanization” is effected either by sulfur chloride vapor or by very dilute solutions of sulfur chloride in solvents such as carbon disulfide, carbon tetrachloride, or benzine. “Hot vulcanization” is carried out by heating with sulfur, organic accelerators, and inorganic substances such as colloidal zinc oxide, to “activate” the accelerators. To safeguard against any unforeseen difficulties, it is necessary not only to ascertain how much tendency mixtures containing powerful accelerators have to vulcanize, but above all to determine for how long a time a solution remains stable, i. e., does not commence to vulcanize during ordinary use. To obtain an insight into the practical utility of a mixture, it is in general necessary merely to heat the mixture at 110° C. in a press. A mixture can be regarded without hesitation as satisfactory for practical use if it shows no indication of vulcanization after one hour at this temperature. On the other hand, products prepared from such a solution should as a rule vulcanize fully in 30 mm. at 125° C. or perhaps in 40–50 mm. at 110° C. In view of this, the practical utility of a mixture is judged by the tendency for incipient vulcanization to take place when the mixture is heated at 70° C. in a press. In the case of solutions of rubber mixtures which contain all ingredients milled into the rubber before the solution is prepared, incipient vulcanization is evident by gelation of the solution, i. e., a change from sol to gel. With mixtures of this kind, incipient vulcanization at 70° C. in a press may be accepted as a reasonable criterion, but in no case should it be regarded as a trustworthy indication of the stability of a solution up to the point of gelation, for the rate of vulcanization of the solution to the point of gel formation, and during gel formation itself, is influenced considerably by the constitution and the concentration of the solvent. The concentration of the solution and the degree of plasticity of the rubber mixture likewise influence gel formation. A test of the dry mixture at 70° C. in a press for incipient vulcanization does not take account of these factors.
The Proteins in Preserved Hevea Latex
Authors: Bondy C. , Freundlich H.
Published: February 2011

1. Two proteins were isolated from preserved Hevea latex. 2. The proteins were distinguished by their electrokinetic behavior and their solubilities in aqueous solutions and in alcohol. Protein A has an isoelectric point at pH 4.55; it is insoluble in distilled water and alcohol. Protein B has an iso-electric point at pH 3.9; it is soluble in pure water and strong (70 per cent) alcohol. 3. A comparison of the electrophoretic mobility of the latex particles as function of the pH with the corresponding curves of the proteins confirms the result of previous investigators that a coating of the rubber particles by proteins is decisive for their behavior. In a range of pH between 5.5 and 8 the curve of the latex particles is practically identical with that of protein A.
Stability of Ficus Elastica Latex
Authors: Daniel F. K. , Freundlich H. , Söllner K.
Published: February 2011

Thanks to the kind endeavors of E. Hoyle (Revertex, Ltd.) of Rengam Estate and to the support given by Mr. Simpson, manager of Rim Estate, we obtained a sample of 2.7 liters of Ficus elastica latex. The latex had been collected at Rim Estate, Malacca, on two successive days from about 10 trees which had not been tapped since 1912. Ammonia was added to the latex in such a quantity that about 700 milliequivalents per liter of free ammonia were present; methyl red was used as the indicator. The dry matter (T. S.) and dry rubber content (D. R. C.) estimations were T. S.=38.8 per cent, D. R. C.=36.5 per cent. Stability of Fresh and Preserved Latex In his report attached to the sample Mr. Hoyle writes: “… we used the ‘Herringbone’ tapping to obtain the latex as quickly as possible. Latex oozed on to the tapping cut freely at first, for a minute or two, but quickly thickened and became apparently half coagulated. Addition of ammonia solution to the tapping cuts did not help the flow appreciably, but addition of ammonia to the latex in the cups during dripping of the trees greatly reduced the viscosity of the latex and minimized the amount of coagulum to be strained off. Hevea brasiliensis trees which have been resting for some months, or which are freshly opened up, also yield only a small quantity of highly viscous latex at first. With the Ficus elastica trees, the cuts made on November 1, 1935, were reopened the next day, but the flow of the latex was then, if anything, worse than on the first day. …“This means that the latex is very unstable at the time it leaves the tree, and that this is so, regardless of the time interval between tappings. We confirmed statements in the literature that this latex when containing ammonia is very stable; when testing our sample seven weeks after tapping we found that it no longer had a tendency to be coagulated, either spontaneously or by the addition of other substances; on the contrary, it was very difficult to coagulate at all, the addition of electrolytes causing only microscopic aggregation and creaming. The cream readily redispersed on shaking.
The Fusion Curves of Rubber and Gutta-Percha
Authors: Meyer Kurt H.
Published: February 2011

It is already known that many rubber-like substances such as elastic sulfur and polyphosphornitryl chloride show crystal interferences when stretched, and that these interferences disappear again when the tension is removed. This shows that the melting point is increased by traction, and von Susich actually determined roentgenographically the relation between the melting point and deformation and thus obtained a “fusion curve.” This phenomenon can be explained by means of the kinetic theory of the elasticity of rubber. According to this theory, the stress set up in rubber when stretched depends on the fact that heat motion tends to restore to the statistically favorable, crooked, and hence shorter form, the primary valence chains which have been extended by traction and thus are in a statistically less probable position and form. For, as a result of free rotation, it is possible to have many curved forms but only one maximum elongated form; the thermodynamic probability β, and on account of the relation: S=R ln β, the entropy S as well, are consequently greater in the unstretched than in the stretched state.
A New Transformation Product of Rubber
Authors: Kratky O. , Philipp H. , Posnansky K. W. , Schossberger F.
Published: February 2011

As investigations carried out long ago have shown, rubber reduces silver nitrate. On the contrary, experiments with specially purified unvulcanized rubber films have shown that the rubber itself is not the reducing agent, but rather impurities in the non-rubber components; in fact, it is even possible to incorporate large quantities (up to about 20 per cent by weight) of silver nitrate in rubber. In the experiments to be described, rubber films were prepared by drying latex which had been electrodecanted repeatedly; these films were swollen in a solution of silver nitrate in a mixture of water and acetone, and were then dried. The films obtained in this way were noteworthy for their high tensile strength compared with the original films, and were studied by means of x-rays. Instead of the diffused ring which appears ordinarily when unstretched rubber is examined, the x-ray diagram of this new product showed a series of sharp rings (see Fig. 1a) which did not correspond to any of those of inorganic silver compounds. When the product was stretched, the diagram changed, without appreciable alteration of the glancing angle, into that shown in Fig. 1b and finally into that shown in Fig. 1c. Figure 1c also shows a fiber diagram different from that of ordinary stretched rubber.
Colloidal Structure of Rubber in Solution. Effect of Precipitants
Authors: Gehman S. D. , Field J. E.
Published: February 2011

RUBBER solutions are somewhat unstable and their colloidal structure, usually characterized by viscosity, can be influenced by a large number of agencies such as light, oxygen, and small amounts of various reagents. The colloidal changes caused by the addition to a rubber solution of typical nonsolvents or precipitants, such as alcohol or acetone, are distinguished by the fact that they are reversible. If the precipitant is removed, the original solution can be recovered. The reversible colloidal changes, which result eventually in precipitation, were studied in the work here reported as a means for acquiring knowledge of the colloidal structure of rubber in solution. As in a former article (8) an effort is made to utilize comparatively recent advances in the general theory of the liquid state (3, 5, 9). Previous publications dealing with the effects of nonsolvents on rubber solutions have been predominantly of technical interest and limited almost exclusively to viscosity measurements. LeBlanc and Kröger (13), Messenger and Porritt (2, 16), Kawamura and Tanaka (11) described the viscosity changes which ensue upon the addition of various nonsolvents to rubber solutions. Whitby (25) classified the reagents which can be used to affect the viscosity of rubber solutions. In a later publication (23) he discussed an interesting experiment during which incipient precipitation was observed with the ultramicroscope. Lens (14) reported the results of a few measurements of the effect of alcohols on the relative intensity of the light transversely scattered by benzene solutions of rubber. Ford (6) and Fabritziev, Buiko, and Pakhomova (4) studied the modification of technical rubber cements by the use of nonsolvents. The colloidal effects of precipitants on solutions of high polymers such as polystyrene have been observed and are of interest in connection with this work (18, 21, 22, 26).
Contributions to the Analysis of Rubber. III. Determination of Copper in Raw Rubber, in Mixtures, and in Fillers
Authors: Dekker P.
Published: February 2011

It is already well known that copper compounds have an extremely harmful effect on rubber articles. Since, however, very small quantities of copper are always present in fillers, in fact, in compounding ingredients in general and even in ordinary plantation rubber itself, it is not possible to manufacture a rubber article which is free of copper. In view of this, one must be content in each case with keeping the copper content within a certain allowable limit. However, it has been found that not only is the quantity of copper of decisive importance, but that still other factors play a part in the harmful effects brought about by the copper. Attention has been called repeatedly in the literature to the fact that copper compounds which are injurious are those which dissolve in the rubber mixture. Nevertheless, it is certain that the harmful effects of copper depend not only on solubility but also on other factors. But since so little is known about this problem, nothing can be done for the time being except to regard any copper which may be found as injurious. In the Netherlands Government Rubber Institute the permissible quantity of copper in rubber articles has been set at 0.001 per cent. Although with this percentage harmlessness is not guaranteed, it may still be expected that, with such small percentages of copper compounds, aging is not affected unfavorably. The present work is concerned chiefly with methods for determining copper.
Analysis of Organic Accelerators
Authors: Robinson J. G.
Published: February 2011

From the viewpoint of the works chemist, a knowledge of the qualitative and quantitative analysis of organic accelerators is desirable as a valuable supplement to a knowledge of their technical applications. Confusion or uncertainty as to the composition of a particular package of material may occur even in the best regulated factories; this may well prove to be an organic accelerator, and the chemist is expected to be able to give a decision in all such cases. Again, many accelerators are still sold under trade names and a knowledge of their chemical composition enables the chemist to use them in a more intelligent way, especially in predicting their vulcanizing characteristics in conjunction with other accelerators, and also in disposing of off-grade compounds by incorporation of a percentage in standard mixings. Although the uniformity of qualtity reached by present-day suppliers of accelerators is of a high order, most works chemists wish as a matter of principle to institute some form of acceptance control. Tests in rubber are obviously desirable, but they take considerable time and require expensive plant; analytical methods, where available, enable some form of control to be exercised in cases where tests in rubber are impracticable owing to shortage of time or other considerations.
Behavior of Antioxidants in Rubber Stocks Containing Copper
Authors: Jones Paul C. , Craig David
Published: February 2011

(1) Deterioration accelerated by copper in a high-grade tread stock, a low-grade tread stock, a high zinc oxide bus-tube stock, and a pure-gum stock has been found to be effectively retarded by the use of suitable antioxidants. (2) Secondary aromatic amines have been found to be much more effective than other antioxidants, in tread stocks, for retarding deterioration due to copper. (3) The degree of protection afforded to rubber compounds containing copper by the use of certain antioxidants, notably secondary aromatic amines, is sufficiently high to make their addition of practical importance.
Early Stages of Oxidation in Rubber. A Quantitative Application of the Pyrrole Test
Authors: Temple J. W. , Cadwell Sidney M. , Mead Morris W.
Published: February 2011

The foregoing will illustrate some of the applications which have been made with the test as developed by the authors. Since the above work was completed, van Rossem and Dekker (5) have published their very significant paper on extraction of rubber with benzene—alcoholic potash mixture. Both methods apply to rubber at the same stage of its life, and it should be interesting to compare results from the same sample. In general it may seem that their method is of somewhat higher accuracy, while the pyrrole test requires less time and labor and is more informative as to the actual processes of oxidation.
Laboratory Evaluation of Flex-Cracking Resistance
Authors: Cooper L. V.
Published: February 2011

A machine has been designed for laboratory evaluation of the flex-cracking resistance of any stock from which a dumb-bell strip may be cut. The conditions under which the stock is tested may be varied at the will of the operator. The results obtained on this machine on tread and sidewall stocks have always evaluated the flex-cracking resistance of stocks in the same order that actual road tests have. MANY factors are involved in the proper compounding of rubber stock. In tread compounding wear resistance is the major consideration, but other factors closely approach it in importance. Among these is the ability to withstand repeated flexing without cracking. Flex cracking produces an unsightly appearance which conveys the idea of inherent weakness in the tire, and also, if the flex cracking becomes very pronounced, the tire may fail from carcass break at that point. A satisfactory tire must not, flex-crack. Flex-cracking resistance is dependent on two things—the stock itself and the stress under which it is working. The design of the tire—that is, size and shape of the buttons, the size and position of the side ribs, and the amount of lettering on the side—regulates the working stress under which the sidewall and tread are operating. This accounts for the fact that two tires made by different companies may be different in flex-cracking resistance although of very similar or even identical compounding.
Phenomena of the Mechanical Deformation of Rubber
Authors: Mark H. , Valko E.
Published: February 2011

It is only during recent years that it has become possible by the use of new technic to detect molecular phenomena produced in the mechanical deformation of substances. As far as metallic substances are concerned, and crystalline substances in particular, the problem has already been solved for the most part. On the other hand, in spite of considerable progress during recent years the study of the deformation of organic substances and of fibers in particular, in which group rubber is included, has not yet been carried on. The mechanical properties of a crystalline system vary according to whether there is a single crystal or an aggregate of crystals. However, in both cases the extensibility of the products originates in a displacement of parallel layers, i. e., a sliding of the parts of the crystal along definite crystalline planes, this phenomenon of sliding being irreversible in these substances. In fact, in these cases the reversible part of the elongation is very weak, and amounts to only a few thousandths of the entire phenomenon. In brief, the phenomena of hardening brought about by deformation (sometimes observable) are due to disturbances of the regular lattice. In particular, the displacement of the atom and the change from its normal position can cause the appearance of irregularities on the surface of sliding.