bluuebunny/crossref_metadata_2025 huggingface dataset:
Organic Analysis of Hevea Latex. IX. Some Details of the Main Fractions
Authors: Altman R. F. A.
Published: February 2011

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Vulcanization of Rubber
Authors: Nemirovskii˘ N. L.
Published: February 2011

The phenomenon of the vulcanization of soft rubber can be regarded as an intramolecular reaction.
Evaluation of the Vulcanization Characteristics of Crude Rubber
Authors: Thirion Pierre
Published: February 2011

Any vulcanization test of crude rubber which is based on a measurement of the strain modulus for only one time of vulcanization is insufficient as a source of information to the investigator of the rate of vulcanization and at the same time of the order of magnitude of the maximum modulus. It is proposed to complete this test by a second vulcanization for a different length of time and to correlate the complete vulcanization curves with the exponential functions of time. In this way it seems possible to derive two experimental values of the modulus: (1) A limiting modulus which characterizes the ultimate stiffness of the vulcanizate. (2) A vulcanization time constant which serves as an index of the rate of vulcanization of a rubber mixture. The more rapid the rate of vulcanization, the smaller is this constant. Application of this method to nine different lots of crude rubber proved that by this means it is possible to show well defined differences between various individual lots of crude rubber. Much more extensive studies will be necessary before it is known whether the method is applicable to the great majority of crude rubbers and whether it is adaptable in its present form to the formulation of a general specification for testing crude rubber. There is reason to believe that the use of the modulus value at 100 per cent elongation, already proposed by Gee, and his coworkers instead of 600 per cent elongation, would from this viewpoint offer numerous advantages.
Douglas Frank Twiss 1883–1951
Authors: Murphy E. A.
Published: February 2011

Among the celebrated names of those who have contributed so much in the last thirty years to rubber technology is that of Douglas Frank Twiss. Born in Birmingham, England, in 1883, he graduated at Birmingham University and received the Doctor of Science degree in 1910. Among other academic qualifications, he was a Bachelor of Science of London University and became a Fellow of the Royal Institute of Chemistry in 1908, on whose Council he served for nine years. He was also one of the pioneer members of the Institution of the Rubber Industry at its inception in 1921, and in 1934 he received the highest honor the Institution awards—the Colwyn Gold Medal—for his outstanding scientific work in rubber technology. During the long and active part he played in the British rubber industry, he served on various committees of the Research Association of British Rubber Manufacturers and the Institution of the Rubber Industry. Dr. Twiss's first appointment was as a lecturer in chemistry at the Birmingham College of Technology until 1914, when he joined the Dunlop Rubber Company to form a Chemical Research Department. Within a year he was appointed Chief Chemist, a position he held until his retirement in 1946. Some idea of his wide and varied interests can be obtained from over seventy scientific publications and two hundred patent specifications bearing his name and sometimes those of his fellow workers. He was also part author of a text book on practical organic chemistry and two volumes on inorganic chemistry dealing with oxygen and sulfur, and he served for many years as Special Editor in rubber and elastomers for British Abstracts.
Studies of the Mechanism of Mastication of Rubber. III. The Mutual Effects of Organic Bases and Softeners on the Viscosity Lowering of Rubber Solutions
Authors: Imoto Minoru
Published: February 2011

1. A large decrease in viscosity of a rubber solution was observed with the addition of furfurylamine in a quantity ten times as much as the softener used, such as furfuranthiol, thiophenol, β-naphthalenethiol, or benzoyl peroxide, but a small change with the addition of a large quantity of an amine, until finally reaching to a point where the decrease was less than that when only a softener was added. 2. For this reason, the following hypothesis is presented. Hyperconjugaation of the group (see PDF for diagram) in the hydrocarbon molecule of rubber increases with the addition of a small amount of an amine, promoting the rearrangement of the electron pairs of the double linkage, but with the addition of a large quantity of the amine, dissociation of the softener into its ionic form takes place and, as a result, the softener merely adds on to the double bond, the rubber molecule being unbroken.
Estimation of the Technological Properties of Rubber Mixtures by Their Fluidity
Authors: Galperina F. I.
Published: February 2011

In our laboratory practice, plastometers of different constructions and operating on different principles are used for determining the plasticity of rubber and of rubber mixtures. With all these instruments, the plasticity is measured at 70° ± 2° C, and this makes impossible any estimation of the properties of rubber mixtures during the initial period of vulcanization, when they are heated to temperatures much exceeding 70° (up to 130° C and higher). Furthermore, the plasticity factor (according to Karrer) is the product of the softness and elasticity, which also are measured at 70° C. For this reason, plasticity gives no indication of the behavior of mixtures at vulcanization temperatures, particularly since there is no simple relation between the softness and elasticity of synthetic rubbers. In the production of shoes by hot vulcanization, it is essential to know the behavior of the rubber mixture in the initial period of vulcanization, i.e., during the period of fluidity, at temperatures from 130° to 140° C and higher, when molding.
Identification of Accelerators and Antioxidants in Vulcanizates by Infrared Spectroscopy
Authors: Mann J.
Published: February 2011

Reliable methods for the chemical analysis of vulcanizates have been available for many years, and standard methods have been published in a British Standard which has recently been revised, but these methods do not cover the identification of accelerators and antioxidants and no comprehensive scheme for this type of analysis has been published. The identification of accelerators and antioxidants in vulcanizates presents a difficult problem because of the small concentrations employed, the close chemical similarity of many of them, and the wide variety of substances used. Many chemical tests have been developed for their identification, but difficulties arise when they are applied to vulcanizates. On the whole these chemical tests are unsatisfactory, and it seems unlikely that a comprehensive chemical scheme can be devised for the identification of accelerators and antioxidants in vulcanizates. There are, however, several physico-chemical methods which can be used for such analyses. The work of Proske has shown that accelerators in vulcanizates can be detected and estimated by the polarograph. The method is applicable to thiazoles, thiuram disulfides, and dithiocarbamates, but cannot be used with such accelerators as guanidines. Chromatography has recently been applied to the problem with considerable success. It has been shown that several accelerators give a characteristic chromatogram when the acetone extract of their vulcanizate is chromatographed on alumina, either alone or in the presence of cobalt oleate. In addition, antioxidants can be separated by chromatography from the rest of the acetone extract and can then be identified by color reactions. Although this method has been found in the R.A.B.R.M. laboratories to be very useful, there are serious difficulties in the way of developing a comprehensive scheme of analysis on this basis. For example, distinction between the various dithiocarbamate accelerators is difficult, and the method sometimes gives ambiguous results when applied to complex mixtures. Ultraviolet spectroscopy has been applied to the detection of accelerators and their decomposition products in vulcanizates, to the estimation of accelerators in masterbatches, and to the quantitative estimation of antioxidants. These applications suggest that ultraviolet spectroscopy should be a useful method for the identification of accelerators and antioxidants in vulcanizates.
Effect of Speed of Stripping on the Measured Adhesion between Conveyor-Belting Plies
Authors: Borroff E. M. , Elliott R. , Wake W. C.
Published: February 2011

No work seems to have been published on the effect of stripping speeds on the load required to separate belting plies. This report is a preliminary study to indicate the order of any effects. Two series of tests were carried out, with stripping rates of 1 inch per minute up to 74 inches per minute. Statistical examination of the results shows that the measured ply adhesion depends on the rate of stripping, and can be regarded as a linear function of the logarithm of the rate. The experimental error in determining ply adhesion is, however, relatively large, and in the second series of experiments the standard deviation was just under 1 pound per inch of width. It follows from this that for a specification rate of stripping of 1 inch per minute no significant difference would, in fact, be found if the rate dropped as low as 0.2 inch per minute or rose to 5 inches per minute. The report should be of interest to those engaged in fixing limits for specification tests.
Modulus and Relaxation of Elastomers in Torsion at Low Temperatures
Authors: Mooney Melvin , Wolstenholme W. E.
Published: February 2011

Second-order transition temperatures, Ts, indicated by volume or specific heat data, have been reported for many high polymer elastomers. Studies of the modulus-temperature relationship in the vicinity of Ts have revealed that the modulus below Ts is always enormously higher than above Ts. In the transition region, roughly from Ts+10°C to Ts, the modulus values, as usually measured, show a progressive rise with decreasing temperature. However, these modulus values, usually measured less than 1 minute after loading, are strictly transient modulus values, since at 1 minute the deformation under constant load is far from being constant. The present investigation was undertaken to determine how the equilibrium modulus, if any exists, varies with temperature in the transition region above the Ts, temperature. The method employed was, in principle, to impose a fixed deformation and to measure the stress after a lapse of time sufficient for the stress to become constant. Cylindrical samples, of 0.25-inch diameter, were twisted one turn per inch in a cold bath, and the torque at constant twist was measured as a function of time. The measurements were continued in many cases for months, but in no case did the torque show any indication of approaching a limiting value other than zero. These tests therefore failed in their initial purpose, which was to establish and measure the equilibrium modulus. However, the torque-relaxation tests did yield some interesting data, which indicated that all the elastomers tested develop crystallinity or a similar-ordered state when subjected to prolonged strain at reduced temperature. Moreover, the equipment used was well suited to low temperature thermo-stress measurements—that is, measurements of stress in a cycle of temperature variation at constant deformation. Two thermo-stress curves on Hevea gum stocks extending to low temperatures have previously been reported, one by Greene and Loughborough and another by Gehman, Woodford, and Wilkinson. In the present work thermo-stress measurements were made on a few elastomers at temperatures extending down as close to Ts, as was experimentally feasible.
Quantitative Characterization of Cure. IV. Definition and Measurement of Rate of Cure for Pure-Gum Natural-Rubber Compounds
Authors: Gee Geoffrey , Morrell S. H.
Published: February 2011

The purpose of this paper is to develop a simple practical method of assessing rate of cure, based on sound theoretical principles, and using only measurements which are normally available or easily made. Mathematical and experimental studies of modulus-time curves are presented, and it is shown that several types of gum compound give curves of a simple mathematical form, equivalent to that of a first-order chemical reaction. It is concluded that in such cases rate of cure can be defined and measured by the value of a first-order velocity constant, having dimensions time−1, the reciprocal of which determines the vulcanization period needed to produce a given percentage cure. Application to a substantial number of rubbers has shown that the method is capable of yielding reproducible results for the rate of cure of a single compound, and of distinguishing with high significance between different compounds. A connection is predicted between rate of cure, as thus measured, and scorch; preliminary data are consistent with expectation.
Transmission of Mechanical Vibrations through Rubbers
Authors: Morris Ross E. , James Robert R. , Snyder Harold L.
Published: February 2011

The purpose of this investigation was to determine how simple compression mountings for machinery compare with regard to transmission of mechanical vibrations when the mountings are made from different rubbers. The only difference between the mountings was the rubber contained; all mountings had the same physical dimensions, the same static modulus, and essentially the same hardness. Natural rubber was found to transmit less vibrational force than any of the other rubbers in the range of frequencies from 25 to 2000 cycles per second; moreover, its transmissibility was practically constant over this range of frequencies. Neoprene Type FR transmitted a little more force than natural rubber. Its transmissibility also remained practically constant over the frequency range except for a rise at low frequencies. The transmissibilities of all other synthetic rubbers tested were higher and increased with rising frequency over the entire range. The information obtained is of considerable value in the design of rubber mountings for isolation of machinery vibrations in the range of audible frequencies.
A Test for Crystallization Effects in Rubbers
Authors: Beatty J. R.
Published: February 2011

A test has been developed for measuring the stiffening of rubberlike materials at low temperature due to crystallization. These measurements are easily performed in existing cold boxes and use any simple tensile specimen. Typical measurements and results of four polymers are shown.
Elastoviscous Properties of Amorphous Polymers in the Transition Region. I.
Authors: Bischoff J. , Catsiff E. , Tobolsky A. V.
Published: February 2011

Experimental data on the stress-relaxation modulus Er,T(t) of a GR-S gum vulcanizate at a series of temperatures in the transition region are presented, and a “master curve” of log Q(t/K) vs. log (t/K) is thereby constructed. The characteristic relaxation time, K, for each temperature is defined and tabulated. A distinctive temperature, Td, is observed at which the activation energy for K is a maximum. Analytical expressions are given which describe the GR-S master-curve with great accuracy. The same analytical procedure can be successfully applied to data previously obtained for polymethyl methacrylate. A reduced equation is proposed which describes the time and temperature dependence of Q(t/K) in the transition region for both polymers.
The Diamagnetic Anisotropy of Natural and Synthetic Rubbers
Authors: Toor Elizabeth Weir , Selwood P. W.
Published: February 2011

The change in anisotropy with elongation has been found for natural rubber and for several synthetic rubbers. Unsaturated rubbers have a large principal susceptibility perpendicular to the direction of stretching, because of the presence of olefinic double bonds. The differences between natural rubber and polybutadiene are attributed to the presence of unsaturated side-groups caused by 1,2-addition in polybutadiene. Probably the magnetic anisotropy of these rubbers depends, not on the actual degree of crystallinity of the rubbers, but on the ability of the long-chain molecules to align themselves parallel to the direction of stretching. Therefore the changes in anisotropy with stretching are large when there is no cross-linking, and small when cross-linking occurs to any large extent. Saturated rubbers have an anisotropy opposite in sign to that of unsaturated rubbers. This must be caused by the broadening of electronic orbits perpendicular to the direction of stretching. Apparently methyl side-groups cause such a broadening of electronic orbits in polyisobutylenes, an effect much greater than the similar effect in polyethylene.
Statistical Kinetics of Hevea Rubber Cyclization
Authors: Gordon M.
Published: February 2011

Rubber cyclization provides a useful illustration of statistical effects intervening in the reactions of long-chain polymers. Analogously to the known cyclizations of simple diisoprenic terpenes, each individual cyclization act links two adjacent isoprene units in the rubber chain into a six-membered ring. However, some of the units remain stranded between neighboring rings and escape cyclization for want of a partner. Thus the final polymer has a copolymer structure of 86.5 per cent of diisoprenic rings and 13.5 per cent of uncyclized monisoprenic units. This result is derived from a statistical theory of Flory, and has previously found accurate experimental verification. The bearing of this statistical effect on the reaction kinetics has now been studied for the first time. Dilatometric experiments on rubber emulsions in sulfuric acid have shown that the cyclization reaction conforms in the main with a statistical cyclization law much better than with a first-order equation uncorrected for the survival of stranded units. High accuracy was required for this experimental distinction, whose importance lies in the implicit proof that the polymer units participate in the rate-determining transition complex, in accordance with the accepted proton transfer mechanism. A kinetic proof has incidentally been furnished for the fact that the rubber polymer contains long chains of identical units. When handled by an emulsion technique, this polymer can provide a useful “model compound” for its simpler terpene analogs. Certain rate abnormalities have been observed, including an induction period of reduced rate, probably connected with diffusion effects. A small volume change subsequent to the cyclization reaction may reflect a prototropic double-bond shift. The activation energy and entropy are found to be lower than in previous work, an effect traced in part to a curvature of the Arrhenius plot. The known dependence of cyclization rate on Hammett's acidity function H0 is quantitatively confirmed.
Action of Light on Sodium-Butadiene Rubber
Authors: Postovskaya A. F. , Kuzminskiĭ A. S.
Published: February 2011

An apparatus was devised and experimental methods of investigating the action of light on polymers in a high vacuum (10™6 mm. of mercury) were developed. The limits of accuracy of the methods for measuring gas formation and decrease of unsaturation are 1–2 per cent. The effect of ultraviolet radiation on sodium-butadiene rubber in a high vacuum is the formation of gaseous byproducts. The latter appear as two fractions: one which condenses at 180° C, and one which does not condense under the same conditions. The noncondensing part comprised 84 per cent of the total, and consisted of 64 per cent hydrogen and 32 per cent methane; this indicates rupture of the —C—C— and —C—H bonds. The action of light on rubber is accompanied by a loss of unsaturation. The change of unsaturation is primarily in the main chains and only to a small degree in the side chains (we know that the reverse is true with respect to the effect of heat). Measurements were made of the light energy absorbed by rubber, and the quantum yield of gaseous products was calculated. The small quantum yield (2×10−3) indicates the incatenate nature of the process. The decrease of solubility of an irradiated polymer is a consequence of a reaction between free radicals forming after rupture of the —C—H bond, and also after rupture of the carbon chain.
Ozone Resistance of Neoprene Vulcanizates. Effect of Compounding Ingredients
Authors: Thompson D. C. , Baker R. H. , Brownlow R. W.
Published: February 2011

The resistance of Neoprene vulcanizates to attack by ozone as measured by accelerated tests has been studied. The known superiority of Neoprene in this property was found to be affected more by compounding ingredients than previously recognized. It was found that neither the presence of accelerators nor their influence on the modulus of fully cured Neoprene vulcanizates affected ozone resistance. The addition of fillers impaired ozone resistance in proportion to the amount used. The coarse particle size fillers were particularly harmful. Petroleum base plasticizers had a negligible adverse effect, but certain of the ester and similar types were significantly deleterious. Unsaturated vegetable oils and their derivatives, as well as wood resin, are beneficial to ozone resistance. Certain softeners and extenders frequently used to promote ozone resistance so function only by virtue of the stress relaxation they induce in vulcanizates. A number of antioxidants, especially those which reduce flex cracking are powerful ozone-resisting agents, particularly when used in large quantities. Certain of the nondiscoloring type of antioxidants are harmful to ozone resistance.
Ozone in Los Angeles and Surrounding Areas
Authors: Bartel A. W. , Temple J. W.
Published: February 2011

It has become rather generally accepted among rubber technologists that ozone stands alone as the cause of exposure check-cracking of rubber. Newton, Crabtree and Kemp, and Fielding are apparently supporters of this view, and the present authors have concurred. The viewpoint, however, need not be considered as fixed. The experiment with nitrogen dioxide, cited by Haagen-Smit, raises interesting speculation of a possible exception, unless indeed the explanation lies in an intermediate formation of ozone in the system nitrogen dioxide-oxygen-sunlight. (This likelihood was suggested by Haagen-Smit in a private communication to one of the authors.) Interesting as some of these variant possibilities might be, however, the present authors record their belief in the simple rather than the complex explanation of rubber checking in Southern California, namely, that of ozone. The general similarity of pattern between the city and noncity stations argues against any dominant effect due to special components of the city atmosphere. The general prevalence of checking in the whole area, relative to that of the country at large, is generally consistent with the high level of ozone indicated by the measurements given here. Under present information, it seems unlikely to us that effects of alternately proposed chemical agents will bulk importantly in the total effect. The further development of information on these questions may be awaited with much interest.
Analysis of Vulcanized Rubbers. Influence of Accelerators on the Determination of Free Sulfur by the Copper Spiral Method
Authors: Mann J.
Published: February 2011

The copper spiral method is being inserted in a revised edition of the “British Standard Methods of Testing Vulcanized Rubber”, and this raises the question of what sulfur compounds react as “free” sulfur. In this method, “free” sulfur is considered to be that part of the sulfur which is present in the acetone extract and which reacts with a copper spiral, placed in the acetone during the extraction, with the production of copper sulfide, the amount of which can be estimated after its removal from the acetone. Since most accelerators contain sulfur, it is obvious that the presence of accelerators or accelerator fragments is a potential source of error. Fourteen accelerators of various types were therefore examined, and it was found that some react with copper, producing compounds which evolve hydrogen sulfide on treatment with hydrochloric acid.
GR-S Latexes in Foam Rubber
Authors: Talalay Leon , Talalay Anselm
Published: February 2011

The superiority of cold GR-S high-solids latex over latex polymerized at 120° F has been demonstrated in foam rubber in terms of greater tensile strength, better elongation at break, higher modulus, improved rebound elasticity, and enhanced low temperature properties. The magnitude of the effect observed is far greater than the corresponding improvement reported in tire tread stocks. A number of polymer modifications in low-temperature polymerized latex were investigated. It was shown that, by the proper choice of styrene content (approximately 10 per cent bound), GR-S foam rubber superior to Hevea foam in subzero properties can be made. The modulus of foam rubber improved significantly with rising Mooney viscosity of the contained polymer, while the elongation at break was affected adversely. The degree of conversion was found to have little bearing on the properties of the resultant foam rubber.
Film from Mixtures of Natural and Synthetic Rubber Latex. Physical Properties
Authors: Pierson R. M. , Coleman R. J. , Rogers T. H. , Peabody D. W. , D'Ianni J. D.
Published: February 2011

When tested in a single standardized procedure for cast latex films, the type of synthetic-rubber latex employed in latex blends containing 70 per cent or more natural-rubber latex had little effect on the stress-strain properties of the mixture. Cold-rubber latexes imparted higher stress-strain values to blends with natural rubber than did the corresponding hot-rubber latexes. The improvement was particularly noted on comparison of tensile product values. Low-conversion synthetic polymers produced higher stress-strain properties than high-conversion polymers in blends with natural rubber, even though their tensile strengths in 100 per cent synthetic stocks were approximately equal. Optimum physical properties were obtained by use of blends with synthetic polymers of medium Mooney viscosity. It is believed that the appearance of an optimum Mooney viscosity is tied in with the necessity of having quite high molecular weight on the one hand, and, on the other, the ability of the particles to knit well, the latter in turn requiring a comparative freedom from tight gel. Tensile product values increased with increasing styrene content in the synthetic polymer, but, correspondingly, the low-temperature stiffening increased. The physical properties of a natural rubber stock are far superior to those of any of the synthetic-rubber latexes tested to date. Cold-rubber latexes now in production are an improvement over high-temperature latexes, for example, in wet gel strength but do not approach natural rubber latex in stress-strain properties.