bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural Coagulation of Hevea Latex
Authors: Altman R. F. A. 
Published: February 2011

Abstract
Natural coagulation has been of interest during the last forty years. As no satisfactory explanation could be given for this phenomenon, it still continues to attract attention. It is now accepted that the instability of latex is caused by certain changes in the chemical composition of the latex components, but it is still an open question what those chemical changes are, and by what agents they are caused. The explanations of the changes have given rise to two rival theories, the so-called enzyme theory, and the bacteria theory. The first, supported by Whitby, Campbell, Barrowcliff, Stamberger, Stevens, and Paton, imputes the direct cause of the natural coagulation to the activity of an (unidentified) enzyme. They admit that, under the influence of bacteria, acids are formed in the latex during the process of natural coagulation, but they consider these acids to have only an activating influence on the enzyme. Gorter and Swart, Eaton, Denier and Vernet, Spoon, Belgrave, De Vries and Beumée-Nieuwland, Bobilioff, Corbet, Van Dillen and Heubel, and most of the modern investigators support the bacteria theory, postulated by Eaton and Grantham. According to this theory the acids produced by bacterial action are the direct cause of the natural coagulation.
Organic Analysis of Hevea Latex. IX. Some Details of the Main Fractions
Authors: Altman R. F. A. 
Published: February 2011

Abstract
As a result of attempts to isolate and identify various groups of organic compounds which occur naturally in Hevea latex, e.g., proteins, lecithins, amino acids, amines and betaines, alkaloids, and fat acids, resin acids, sterols and wax alcohols, the author developed some years ago a general scheme for the systematic analysis of latex. This paper, in completion, contains further details of the first fractions which are obtained on application of the general scheme, and which therefore have been called main fractions. Since it appeared desirable for several reasons to limit the analytical investigations to latex of one definite Hevea clone, the figures given below apply exclusively to fresh unammoniated latex of clone Tjirandji 1 (Tjir 1) tapped in the Tjiomas experimental garden near Buitenzorg. The recorded percentages are averages of figures obtained from several duplicate estimations.
Inverse Correlation between Rubber Hydrocarbons and Insolubles in Total Solids of Latex from Hevea Brasiliensis
Authors: Stewart W. S. , Hummer R. W. 
Published: February 2011

Abstract
Recent studies of the total solids in latex from the rubber-bearing plant Cryptogtegia grandiflora indicated that a linear inverse correlation existed between the percentages of rubber hydrocarbons and a crystalline substance isolated from the insolubles. This stimulated a similar investigation into the relationship between rubber hydrocarbons and insolubles in the total solids of latex from Hevea brasiliensis. Accordingly, thirty-four samples of latex from Hevea brasiliensis were collected and analyzed for rubber hydrocarbons and insolubles. In these samples a wide distribution of rubber hydrocarbons from low to high percentages was intentionally sought by bleeding petioles and stems of young seedlings as well as trunk-tapping mature trees in production. Except for six collections, the latex was air-dried on a glass sheet immediately on exudation. When it was dry enough to allow handling, it was removed from the sheet and further dried to constant weight at 60° C. The dried latex, called “latex total solids”, formed the basis on which percentage composition was calculated. The six latex samples not dried on a sheet of glass immediately after exudation were “rubber biscuits” formed in commercial latex collecting cups as remnants of dried latex from the previous tapping. All latex samples were collected from April, 1944, to March, 1945, from two widely separated locations in Mexico and from two locations in Costa Rica. Because of the low yields of latex from petioles and seedlings, these samples were composite collections from five to forty individuals. The trunk latex samples from producing trees of seedling origin were analyzed on an individual tree basis. This allowed for more variation between samples than if they had been composited. The considerable diversity represented by the collections is shown (Table I).
Photolysis of Rubber
Authors: Bateman L. 
Published: February 2011

Abstract
Rubber hydrocarbon irradiated in vacuo is decomposed by ultraviolet light of wave length less than 4000 A˚. The rubber very rapidly becomes insoluble, and liberates a gaseous mixture which consists mainly of hydrogen when the irradiation temperature is less than 150° C. The reaction characteristics have been investigated, and point to the occurrence of dissociation processes similar to those deduced for comparable simple olefins. When irradiated above 150° C, small but significant amounts of isoprene appear in the volatile product, thereby providing an experimental means of determining the activation energy for the separation of isoprene from a polyisoprene chain terminated by an allyl radical.
Chain Structure of Vinyl and Diene Polymers in Relation to Polymerization Mechanism
Authors: Flory Paul J. 
Published: February 2011

Abstract
The structural units of vinyl polymers generally occur in a regular head-to-tail sequence ((see PDF for diagram)) such that the substituent occurs on alternate atoms of the chain. Good evidence for this type of structure has been found for polystyrene, polyvinyl acetate (i.e., polyvinyl alcohol resulting from the hydrolysis of polymerized vinyl acetate), the polymer of methylvinyl ketone, the polymer of methylisopropenyl ketone, and polyvinyl chloride. Polymers of disubstituted ethylenes, such as isobutylene and vinylidene chloride, also possess the head-to-tail structure. Marvel and Cowan concluded that α-haloacrylates polymerize to give some, at least, of the head-to-head, tail-to-tail structure, although the evidence in this instance may be open to question. The prevalence of the head-to-tail arrangement is easily explained in terms of the free-radical mechanism of chain growth. The free radical may add in either of two ways to the monomer:
High-Frequency and Low-Frequency Spectra and the Structure of Rubber
Authors: Girard Pierre , Abadie Paul 
Published: February 2011

Abstract
Under the influence of an alternating electric field, the loss angle and dielectric constant of a sheet of rubber vary as a function of the frequency, while the conductivity remains negligible even at low frequencies. The essential difference between this behavior and that of the crystalloid liquids already studied by the authors is that, instead of a single absorption curve and a single dispersion curve extending through a narrow range of frequencies, there is a series of curves extending a considerable distance toward the low frequencies. However, the relations between absorption and dispersion remain the same as with crystalloid liquids, so here too the losses can be explained by the orientation polarization, and the same qualitative scheme of dipolar oscillators which follows, with a certain dephasing, the alternations of the field. However, instead of being a single type and individually identical, these oscillators are in this case polyisoprene chains which differ in length and consequently in their relaxation times. This variety of dipoles is evident in the many successive curves. (To develop the spectrum, the authors used chiefly absorption curves.) These curves differ in their positions on the abscissa as a function of the dimensions of the dipoles, and by their height as a function of their concentration and form. When for a group of dipoles characterized by a mean relaxation time, the lengths of the chains and the relaxation times vary progressively from one dipole to another, then the resultants of the different absorption curves representing the different dipoles unite into a single flat extended curve. On the contrary, a group of homogeneous dipoles which are identical or almost identical is represented by a single bell-shaped curve.
The Depolarization of Light Scattered in Solutions of Rubber Like Polymers
Authors: Tsvetkov V. , Frisman E. 
Published: February 2011

Abstract
Investigation of the depolarization of light, Δ, scattered by colloidal solutions is one of the methods of determining the dimensions, shape and optical properties of the particles suspended in them. A study of the state of polarization of the scattered light is found to be especially helpful in this respect. If the incident beam is directed along the x-axis of a rectangular system of coördinates and observation is carried out along the y-axis, the degree of depolarization of the scattered light is usually determined by the ratio Δ=Ix'Iz, where Ix and Iz are the x- and z-components, respectively, of the scattered light. Here one should discriminate between the quantity Δv (the electrical vector of the incident light parallel to the z-axis) and the quantity Δh (the electrical vector of the incident light parallel to the y-axis). On the basis of theories advanced by Rayleigh, Mie, and Gans one may draw the following general conclusions regarding the relation between Δ and the properties of the dispersed phase.
A Study of the Structure of Butadiene Polymers by Means of Ozonolysis
Authors: Rabjohn Norman , Bryan Carl E. , Inskeep G. Esler , Johnson H. W. , Lawson J. Keith 
Published: February 2011

Abstract
1. Two samples of the GR-S copolymer of butadiene and styrene were degraded by means of ozonolysis. A number of fragments were isolated and identified so that an approximate idea of the structures of the copolymers was obtained. 2. A series of butadiene copolymers was treated with ozone in an attempt to determine the extent to which the butadiene had polymerized by 1,2-addition in contrast to 1,4-addition. Although the analytical procedure employed afforded only relative values, referred to as ozonization numbers, the results indicate that the manner in which the butadiene molecule enters the growing copolymer chain is not greatly influenced by experimental conditions.
The Structure of a Mixed Polymer of Butadiene and Acrylonitrile
Authors: Alekseeva E. N. 
Published: February 2011

Abstract
1. In copolymers of butadiene and acrylonitrile, both components enter into the constitution of the macromolecules. 2. Approximately one-half the polymer is composed of macromolecules, in which the two monomer structures exactly alternate in the macromolecular skeleton. 3. Approximately one third of the polymer is constructed from macromolecular units in which each molecule of butadiene is placed between two or three molecules of acrylonitrile.
Kinetics and Optimum Phenomenon of Vulcanization
Authors: Dogadkin B. , Karmin B. , Golberg I. 
Published: February 2011

Abstract
The fundamental process of vulcanization consists in the combination of rubber with a vulcanizing agent : sulfur, sulfur monochloride, etc. The kinetics of this process may be expressed by monotonous curves. These may be interpreted either as the result of the heterogeneous character of the reaction or as the result of the combination of several homogeneous reactions. At the same time that the rubber combines with the vulcanizing agent, and largely as a consequence of this, a number of its physical-chemical and mechanical properties—solubility, density, tensile strength and other properties—undergo a change. These changes are extremely interesting from the technological point of view. In distinction to the kinetics of the combination of rubber with the vulcanizing agent, the kinetics of these processes can in most cases be represented by curves with a maximum or minimum. Thus, in the vulcanization of crude rubber, the tensile strength and modulus change according to a curve having a maximum; the solubility change follows a curve with a minimum. This character of the change experienced by the principal technical properties of the rubber determines the so-called “vulcanization optimum”. This term refers to that moment in the process of vulcanization when the particular property attains the necessary maximum or minimum, depending on the technical purposes of the vulcanizate.
The Chemistry of Rubber the Interaction of Ethylenic Compounds and Rubber
Authors: Le Bras Jean , Compagnon Patrice 
Published: February 2011

Abstract
It is known that the hydrocarbon of rubber has an ethylenic structure; its chemical reactions, the basic principles of which were brought out in 1902 by Weber, and which were the object, in 1930, of important work by Fisher, show that it has the general properties of ethylene derivatives, including the addition of hydrogen and metalloids of the first group (chlorine and bromine in particular), the addition of hydracids, scission by ozone, autoxidation, and isomerization by means of catalysts which isomerize ethylene derivatives, such as sulfuric acid and chlorides of metalloids. However, aside from these general reactions, rubber hydrocarbon reacts in other ways which likewise depend on the unsaturation of the molecule and on the macromolecular structure, and which in this particular case are of prime importance because it is on these properties that the processing and applications of rubber depend. As a good example, a fundamental change results from the action of sulfur, viz., vulcanization, whereby rubber passes from a predominantly plastic state to a predominantly elastic state, a change which is manifest by the rubber becoming insoluble. Moreover, sulfur is not the only agent which is capable of bringing about vulcanization; in fact, it has been found that many other agents are capable of vulcanizing rubber. Although Goodyear discovered this reaction in 1839, there is still no general agreement as to the mechanism of vulcanization; however, vulcanization is at present regarded as the transformation of an agglomerate of filiform molecules into a three-dimensional network.
II. Combination of the Two Modes of Action
Authors: Le Bras Jean , Viger Françoise 
Published: February 2011

Abstract
The various experiments described in the present paper show that the combined use of an antioxygenic agent and a deactivating agent makes it possible to improve the aging of rubber mixtures to a considerable extent. This is, then, an experimental confirmation of the hypothesis which had previously been advanced as a result of observations on the relation between oxidizability and aging. It should be pointed out here that the present work is concerned only with static aging, with oxygen as the only factor playing any part in the deterioration occurring in ordinary artificial aging tests. In dynamic aging, other factors undoubtedly play a part, but it is true, none the less, that the action of oxygen is still of prime importance, as has been very clearly shown by Neal and Northam. The improved aging which was observed in the present work should, then, play a part in dynamic aging, and this has been confirmed by preliminary tests, the progress of which cannot be reported at this time. From another point of view, the differences in behavior which seemed to depend on the character of the vulcanizing system, confirm the fact that, even when only static aging is concerned, antioxygenic agents cannot always be rated in the same order. It is, therefore, advisable, as is done in choosing the accelerator, to make a judicious choice of protective agent or combination of protective agents for each rubber mixture, taking care to avoid any general rules which have not been previously checked. Finally, the behavior of mercaptobenzimidazole and of litharge should be an inducement to study other compounds which might be deactivating agents, particularly imidazoles, thiazoles, and oxazoles, in an effort to find products having the greatest possible deactivating power. By the use of a manometer it will be possible to choose, among protective agents against oxygen, those which react in accordance with this mechanism. It will then be possible to proceed systematically in combining these protective agents with normal antioxygenic agents. Such a method of investigation of the improvement of aging offers, therefore, a means of avoiding, at least in part, the empiricism which now prevails in this field, and to formulate on a rational basis mixtures of protective agents having a high degree of effectiveness.
Polyprene and Thioglycolic Acid
Authors: Holmberg Bror 
Published: February 2011

Abstract
By the prolonged action of thioglycolic acid on small strips of crude Hevea rubber, the present author many years ago obtained a product of the composition, C5H8.90O0.01(SCH2CO2H)0.95, which was soluble in alkalies, and a similar product from balata, whereas under the same conditions gutta-percha did not react to any significant extent with thioglycolic acid. In benzene solution the addition of thioglycolic acid to rubber proceeds very slowly. It was found that a combination of the two methods, whereby the two reagents were dissolved in benzene, the benzene then allowed to evaporate spontaneously and the residue allowed to stand in the open air for some time, offered an easy means of carrying the reaction to completion, although the rubber was partially oxidized at the same time. In the procedure described in the present paper, the new method was employed as recently applied to the determination of the rubber contents of samples which were prepared in Svalöv in connection with development work on the rubber-bearing dandelion, Taraxacum kok-saghyz Rodin, carried out by the Sveriges Utsädesförening. As a means of comparison, the experiments were repeated in the same way with crude Hevea rubber, which had been obtained nine years before from the Hälsingborg Gummifabrik A.-B., and had been treated similarly at that time.
Carbon and Hydrogen in Rubber Hydrocarbon
Authors: Wing Henry J. 
Published: February 2011

Abstract
Analyses by combustion of rubber hydrocarbon separated from rubber latex and crystallized from ethereal solutions at low temperatures yielded combined percentages of carbon and hydrogen which totaled slightly less than 100. Midgley, Henne, Shepard and Renoll assumed the difference to be due to oxygen, and they have used the results to substantiate their argument that natural rubber is not a true hydrocarbon but contains a small amount of oxygen in chemical combination. Later, Roberts reported that he had isolated the portion of rubber which contained oxygen. This he called caoutchol to distinguish it from the hydrocarbon, which he named caoutchene. He used Midgley's results to confirm his findings, which he attempted to apply in a new way to the familiar two-phase theory of Fessenden as an explanation of the properties of rubber. However, Schidrowitz has indicated that the method used by Roberts to separate the caoutchol is not free from possible criticism. Some steps in the procedure, e.g., milling, promote oxidation.
Molecular Weight of GR-S Fractions. Simple Glass Osmometer for Use in Hydrocarbon Solvents
Authors: French David M. , Ewart Roswell H. 
Published: February 2011

Abstract
Osmotic molecular weight measurements have been made on a sample of unfractionated GR-S and on eight fractions of this material. The molecular weights ranged from 10,000 to approximately 1,000,000, with a number average at 92,000. The relationship between molecular weight and viscosity for GR-S was determined. A simple all-glass osmometer for use in hydrocarbon solvents is described, and information on its use and the membranes employed is given.
Solubilities of Unvulcanized Rubbers
Authors: Sarbach D. V. , Garvey B. S. 
Published: February 2011

Abstract
Solubility studies on unvulcanized rubbers are very useful both to indicate types of materials most likely to be good solvents and softeners and to indicate the effect of various solvents and oils on vulcanized rubbers. Furthermore, such studies are so simple and relatively economical of time and effort that they make possible the accumulation of a broad background of data which would be impractical to obtain by other means. By investigating the effect of a wide variety of solvents on a single rubber it is possible to tell which groups have good solvent action and which do not. This information makes it possible to predict, with considerable accuracy, the solvent power of any material of known composition. The solvent power of a given material, together with chemical stability, boiling point, melting point, and viscosity, indicates quite well its utility as a softener. In many cases the nature of the solution also indicates whether or not the material is an effective tackifier. The usefulness of such solubility data in cement manufacture is obvious. It is generally true that materials which are good solvents for an unvulcanized rubber are strong swelling agents for the same rubber when vulcanized. Here also such properties as melting point and viscosity have an important bearing on the time required to reach equilibrium and on the permanence of the swelling action. In agreement with the above views, solubility studies were carried out during the early evaluation of a number of synthetic rubbers. Solvents were selected so as to show the effect of various functional groups, different types of hydrocarbon radicals, chain length and branching in aliphatic radicals, and molecular weights. Allowances were made for differences in viscosity and molecular weight. These studies were then used both for the selection of cement solvents and softeners and for predicting the utility of the rubbers for various types of solvent resistance. These studies proved so useful that they have recently been brought up to date for publication.
The Determination of Free Sulfur in Vulcanizates by a Polarographic Method
Authors: Poulton F. C. J. , Tarrant L. 
Published: February 2011

Abstract
The polarographic method offers a rapid and accurate means of determining the “true” free sulfur in vulcanizates. In the case of single estimations, the test takes approximately as long as the copper-spiral method, but for multiple or replicate testing it is much quicker. Since the determination is made directly on the acetone extract, it was necessary to examine at some length the possibility of interference from other ingredients of the extract. It is shown that most of the common accelerators and antioxidants are not likely to interfere, and promising methods of determining certain of these substances were revealed. Thus MBT, MBTS, TCA, A11, ONV, ZDC, TMT, TET, Ureka, and some of the Nonox series of antioxidants give regular Polarographic waves readily distinguishable from that of sulfur, and the development of working processes for their determination should not present any great difficulties. Other accelerators and antioxidants, notably ZIX, some Nonox antioxidants and Agerite White, while showing Polarographic activity, give poor curves in the pyridine electrolyte. No doubt in other base solutions the form of curve could be improved, and their quantitative determination would then follow.