bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and Use of Cyclized Rubber as a Stiffening Resin in Rubber
Authors: Janssen H. J. J. 
Published: February 2011

Abstract
The condition for miscibility of low-molecular liquids is that the cohesion-energy densities should be of the same order of magnitude. The permissible difference decreases sharply as the molecular weight is increased, and a solution of equal amounts of rubber and polystyrene separates into two layers at room temperature when the concentration rises above 2 per cent, whereas low-molecular aliphatic and aromatic hydrocarbons are completely miscible. The undiluted polymers can, however, be mixed to an apparently homogeneous state on the mill if the correct mixing temperature is chosen. Presumably the extreme length of the polymer molecules allows them to be caught and dispersed separately in the stress gradient between the rolls. That the mixture is not stable and tends to separate into the components on extension, even after vulcanization of the rubber, can be deduced from the bending of the stress-strain curve towards the strain axis—generally an indication of irreversible changes in structure for many materials. This tendency to irreversible separation, which is a disadvantage for any application, can be suppressed by the formation of primary bonds between the two polymers. There are at present three methods to produce such bonds : (1) covulcanization (if the added polymer is unsaturated); (2) mastication in an inert atmosphere; (3) graft polymerization. If a sufficient number of such bonds has been formed, the added polymer can no longer be extracted from the vulcanized compound by solvents, and the bend in the stress-strain curve has disappeared.
Oxidative Stress Relaxation of Natural Rubber Vulcanized with Di-Tertiary-Butyl Peroxide
Authors: Ore Svein 
Published: February 2011

Abstract
It has been shown by Farmer and Moore that natural rubber can be vulcanized with di-tert.-butyl peroxide (DTBP), Presumably the free radicals formed by the unimolecular decomposition of the peroxide abstract some of the more labile (e.g., α-methylenic) hydrogen atoms, leading to direct C—C crosslinks between the rubber molecules, with tert.-butanol and acetone as the main reaction products. This preliminary communication presents some of the results of an investigation of the oxidative stress relaxation of the following types of DTBP vulcanizates. (A) First grade pale crepe, DTBP, and carbon black (MPC) mixed on the mill and vulcanized in a press. The carbon black was added to minimize the deleterious effect of impurities. (B) Purified rubber vulcanized: (1) in aqueous heating media; (2) in the press; (3) in DTBP vapor.
Influence of Inhibitors on the Oxidation of Rubber Solutions
Authors: Novikava E. N. 
Published: February 2011

Abstract
1. The nature and distribution of substituent groups (NH2, N(CH3)2, CH3, OCH3, COOH) influences the relative activity of amines as rubber antioxidants. 2. Azo compounds fall in the following order of their inhibiting action on rubber oxidation: p-aminoazobenzene, dimethylaminoazobenzene-o-carboxylic acid, dimethylaminoazobenzene, azobenzene. 3. Phenylsemicarbazide is a more effective antioxidant than Neozone D. 4. Diazoaminobenzene and diphenylthiocarbazone do not inhibit the oxidation of rubber, but initiate it quite rapidly. 5. Sudan I and III inhibit the oxidation of rubber solutions, but less than does 2-naphthol.
The Hardness of Very Soft Rubbers
Authors: Blackwell R. F. 
Published: February 2011

Abstract
Hardness determinations are frequently required on very soft rubbers in the range of 5 to 30 (Shore). It is usual to make such measurements in the shop with a pocket-type tester; however this is not entirely satisfactory for laboratory work where a more precise reading is usually required, calling for a hardness tester of the dead-load type. Such a tester, moreover, is useful to keep a check on the accuracy of pocket testers. The British Standard dead-load hardness tester is not calibrated below 30° BS, but a method of extending the range downwards has been proposed, whereby the standard indentor of this tester is replaced by one of 0.25 inch diam.; unfortunately this method has the disadvantage of involving more than one revolution of the dial gauge needle, and a directly calibrated scale would be out of the question. There is, however, an alternative method in use at BRPRA, which gives hardness readings down to 4° in one revolution; and which replaces the standard added load of 535 grams by one of 70 grams. At present, a calibration curve is provided to convert from scale reading to hardness degrees, but it is intended to add a second scale in due course.
Oxidative and Nonoxidative Thermal Degradation of Rubber
Authors: van Amerongen G. J. 
Published: February 2011

Abstract
The mechanical properties of rubber often undergo a marked change on heating, with deterioration of its elasticity and strength as a result. This behavior is a problem not merely where rubber is used in surroundings of prevailing high temperature; arguments can be advanced to show that thermal deterioration may influence to some extent as seemingly remote a property as wear. The behavior of rubber exposed to heat is strongly influenced by the presence or absence of oxygen. When an ordinary rubber vulcanizate is heated to, say, 100° C in the presence of oxygen or air, it undergoes substantial changes in a comparatively short time. Yet the effects may be similar in the absence of oxygen at temperatures 60° to 100° C higher. The inference is that, although a given rubber heated in air to 100° C, for instance, may be stable owing to its high resistance to oxidation, it may become completely unstable when heated to 180° C on account of thermal decomposition. This paper is published to provide fuller details of the behavior of rubber when heated in the presence and absence of oxygen. The evidence was obtained from experiments with both unvulcanized and vulcanized rubber, differing in composition.
The Limiting Value of Dithiocarbamate Formation during the Vulcanization of Natural Rubber with Thiuram Disulfides
Authors: Scheele Walter , Lorenz Otto 
Published: February 2011

Abstract
This paper disproves an assertion by H. W. Zijp that a fundamental result of our investigations was wrong. The result in question is that the limiting value of dithiocarbamate formation (66 mole-percent of the thiuram disulfide added) is independent of the temperature and, in a certain range, is also independent of the concentration of thiuram disulfide, added. It is shown experimentally that a reaction of thiuram disulfide with rubber which may take place fortuitously during mixing cannot be of any influence on the limiting value of the dithiocarbamate formation.
The Polymerization of Vinyl Monomers in Natural-Rubber Latex
Authors: Bloomfield George F. , Swift P. McL. 
Published: February 2011

Abstract
Practical methods are described for polymerizing methacrylic esters, styrene, and other vinyl monomers in natural-rubber latex. The larger rubber particles require an appreciable time to attain equilibrium with the monomer diffusing into them from a liquid monomer phase dispersed in the serum. Provided that substantial proportions of added surface-active substances are avoided, rubber-soluble monomers can be polymerized almost entirely within the rubber particles, and the modified latex then contains no separately emulsified free polymer. Such conditions favor combination of polymer with rubber. The addition of a sufficiently large amount of dispersing agent favors polymerization of emulsified monomer, with less involvement of the rubber. In this way there can be obtained mixtures of rubber and polymer from monomers whose polymerization is otherwise inhibited by the presence of polyisoprene hydrocarbons.
Crosslinking of Latex Rubber
Authors: Bevilacqua E. M. 
Published: February 2011

Abstract
Most of the properties of rubber are consistent with those expected of a high- molecular-weight linear polymer of isoprene. However, there are some features of its behavior that are inexplicable on this basis. They must be the result of the presence of small amounts of structures other than the regular head-to-tail chain of isoprene units. Bloomfield, in the first fundamental study of the properties of rubber from freshly tapped latex, found that the tree does not continue to build indefinitely a linear polymer, but that branching reactions occur in a rested tree. These reactions eventually convert individual latex particles into substantially single molecules of enormous molecular weight. Bloomfield also observed that small amounts of oxygen are intimately associated with the hydrocarbon, even when it is isolated directly from the tree with careful exclusion of atmospheric oxygen. Craig, Juve, and Davidson have found less certain indications of the presence of carboxyl groups, which, if they are present in the rubber in concentrations even approaching the amount indicated by their results, must be on side chains.
Characterization of Graft Polymers
Authors: Blanchette Joseph A. , Nielsen Lawrence E. 
Published: February 2011

Abstract
Since the earliest recorded attempts to modify rubber by the polymerization of monomers dissolved in rubber considerable work has been directed toward the preparation and characterization of copolymers other than those with random distribution based on the reactivity ratios of the two components. Block polymers consisting of A and B chains coupled to form a linear molecule have been reported by many investigators including Melville and coworkers and Woodward and Smets. Woodward and Smets used the different solubilities in selected solvents and their mixtures to separate block copolymers of styrene-methyl methacrylate and vinyl acetate-styrene from the two homo-polymers with which they occurred. Solution properties of the isolated materials were then investigated. This technique for isolation and characterization has been used with graft polymers in which branches containing all A are attached to a “backbone” of B units. Claesen and Smets prepared and separated vinyl acetate-polymethyl methacrylate and vinyl chloride-polymethyl methacrylate graft polymers from the homopolymer mixture by solubility differences and reported on the osmotic and viscometric behavior of the graft materials. Other investigators have studied conditions and techniques for preparing graft copolymers while attempting partial characterization of the materials produced by using solubility differences for isolation and the usual methods for property studies.
Chain Scissions in a Polymer Network
Authors: Horikx M. M. 
Published: February 2011

Abstract
Relations between degree of crosslinking and gel fraction in a polymer have been derived by several authors. An important parameter in these relations is the crosslinking index γ, the average number of crosslinks to which one original polymer molecule is linked. The relations have been applied to the determination of the degree of crosslinking in linear polymers, but they can be used as well to calculate the soluble fraction of the network in a crosslinked polymer that has been subjected to a degradation process. It will be shown in this paper that a simple relation exists between the soluble fraction of a network that has undergone scission and the effective number of chains in the gel fraction (as determined by swelling measurements). The fraction of soluble material in the degraded network is a measure of the number of scissions. This problem bears upon natural-rubber vulcanizates, which give increasing amounts of extractable material and increasing degrees of swelling on the absorption of oxygen.
Crystallization and the Relaxation of Stress in Stretched Unvulcanized Natural Rubber
Authors: Tobolsky A. V. , Brown G. M. 
Published: February 2011

Abstract
The first observation made in this laboratory in 1946 on the effect of crystallization on stress decay at constant extension was made on a vulcanized Neoprene GN gum stock. It was found that this rubber showed only slight stress decay after 100 hours at 35° C and 50 per cent extension. However, a complete decay of stress to zero stress was observed after only 50 hours at 0° C and 50 per cent extension. Furthermore, the sample after reaching zero stress began to increase in length (spontaneous elongation). This phenomenon was attributed to crystallization. Observations of spontaneous elongation, but no stress decay measurements, were previously reported for vulcanized and unvulcanized natural rubber and for vulcanized and unvulcanized ether polysulfide rubber. It was decided to make a careful study of the effect of temperature and elongation on the stress-decay curves of unvulcanized rubber (cast latex sheet) in the temperature region of crystallization. Some time after these studies were completed, two papers have appeared in which stress decay to zero stress in rubber vulcanizates due to crystallization were reported. In one of these a rather thorough study was made of the decay of stress and change in volume of a natural rubber vulcanizate at −26° C and maintained at four different extension ratios. Our own work on unvulcanized natural rubber was carried out at seven different temperatures in the crystallization region, and were made at five different extension ratios. Quite surprisingly, four of these are the same as were used by Gent. There are interesting differences as well as similarities between our work and the results reported for vulcanized natural rubber.
Dynamic-Mechanical Characteristics of Rubber Compounds
Authors: de Mey S. , van Amerongen G. J. 
Published: February 2011

Abstract
Since rubber articles are often exposed in service to small periodic deformations, great interest attaches to the dynamic-mechanical characteristics of rubber. It has been established that the conditions under which these characteristics are determined have a pronounced influence on the results obtained, so that the measurements must be undertaken under precisely specified conditions. A new test apparatus is described for measuring the dynamic-mechanical characteristics, with which measurements can be performed at any desired stress setting, frequency, temperature, and amplitude on the same samples, both for compression and for shear loading. The incompressibility of filler-free natural-rubber compounds has been demonstrated by measurements made on samples with different shape factors and with varied static initial stress, under compression and with shear loading. The temperature, frequency, and amplitude dependence of the dynamic-mechanical characteristics of different rubber compounds is discussed on the basis of a number of measurements. The maximum value of the loss factor, which occurs in the vicinity of the second-order transition point, appears at a higher temperature in GR-S (cold rubber), Vulkollan, and Butyl rubber than in natural rubber. There is a connection between this fact and the much greater frequency and temperature dependence of Butyl rubber compared to natural rubber in the vicinity of room temperature. A compound based on natural rubber and a styrene-butadiene (85/15) co-polymer shows two maxima in the loss factor. One of these is characteristic of natural rubber, the other of the polymer. The dynamic characteristics of filler-free rubber compounds are not very sensitive to amplitude. It is found that the marked amplitude dependence of reinforced rubber compounds cannot be accounted for by increased temperature or by any nonlinearity of the stress-strain curve. The influence of composition on the dynamic-mechanical characteristics of natural rubber has been tested for a number of compounds. It is established that the carbon black types can have a significant effect on the E′ modulus. At small amplitudes the magnitude is greater for a compound containing SAF or EPC carbon black than for one containing HAF carbon black. Natural rubber reinforced with Aerosil or aniline resin shows a small loss factor, while compounds vulcanized with Thiuram show a large one. The present study is part of a fundamental investigation on rubber carried out by the Research Division of the Rubber-Stichting in Delft under the direction of H. C. J. de Decker.
Oxidative Degradation of Swollen Vulcanizates
Authors: Degteva T. G. , Kuzminskiĭ A. S. 
Published: February 2011

Abstract
1. In the course of a study of the oxidative degradation of vulcanizates with different structures (a thermal vulcanizate, a vulcanizate with Thiuram, one with diphenylguanidine and, one with zinc ethylphenyldithiocarbamate) it was established that the swollen vulcanizate, regardless of the accelerator present, undergoes two simultaneous reactions—destruction and structure formation. 2. It was revealed that the dominance of the destructive process, in the oxidation of swollen vulcanizates, can occur only in the presence of antioxidants; and that only after a considerable consumption of antioxidant does the rate of structure formation equal or exceed the rate of destruction. 3. It was shown that the behavior of antioxidants in swollen vulcanizates is governed not only by the nature of the rubber, but also in large degree by the nature of the solvent.
Chain Scission in the Oxidation of Hevea. III. Effect of Temperature
Authors: Bevilacqua E. M. 
Published: February 2011

Abstract
When molecular oxygen reacts with raw Hevea rubber in latex at 90° C, two molecules of carbon dioxide and two molecules of “volatile acid” (one molecule of acetic acid and one molecule of formic acid) are produced for each apparent scission of the hydrocarbon chain, estimated from changes of solution viscosity. This corresponds to the complete destruction of one isoprene unit, and if the several hydrocarbon end groups are oxidized, requires a minimum of six molecules of oxygen per scission. Estimates of oxygen requirements for scission during the accelerated oxidation of vulcanized Hevea rubber much lower than this have been made. It has been suggested that the apparent high efficiency of scission in vulcanized rubber is the result of the predominance of scission at crosslinks over random cutting of the hydrocarbon chain. To investigate the less likely possibility that the mechanism of the reactions which leads to scission changes sharply with the rate of oxidation, the earlier estimates of yields of scissions and of volatile acids during the oxidation of Hevea latex at 90° C have been supplemented by measurements at 70° C and at 110° C.
Reaction of Natural Rubber with Hydrofluoric Acid
Authors: Tom D. H. E. 
Published: February 2011

Abstract
Within the scope of the research on natural-rubber derivatives carried out in the Rubber-Stichting laboratories, attention was also paid to the reaction of rubber with hydrofluoric acid. Very little work in this field has been achieved by other investigators. The results of their work are mainly to be found in a number of patents. These deal with the preparation of products incompletely described that undoubtedly must be considered as more or less completely cyclized rubbers. The fluorine content of these products is, generally speaking, very low and is often said to be lost on heating or storing. According to Nielsen, it would be possible to obtain products with 30 per cent fluorine when using gaseous hydrofluoric acid. This high percentage is tentatively explained by adopting the incorrect formula H2F2 for hydrofluoric acid. Elsewhere it is stated either that HF cannot be added to rubber or that the addition product is not stable.
Dilaminar Elastomeric Films
Authors: DeFries Myron G. , Schneider Louis , Fram Paul , Leonard Fred 
Published: February 2011

Abstract
While rapid strides have been made in the synthetic organic chemistry of rubberlike materials and in the elucidation of relationships between structure and mechanical properties of elastomers, it is generally not feasible by synthesis alone to construct a rubbery type of polymeric structure which is likely to fulfill all requirements for a given specific application. The tolerances imposed by synthetic methods are very close, and experience indicates that comparatively slight changes in reaction conditions, or monomer, soap, and catalyst concentrations, all may have a profound effect on the balance of properties desired. To aid in the achievement of desired properties, recourse is generally had to compounding. Thus, elastomers are compounded for a variety of reasons. For example, plasticizers are added for improved low-temperature properties, reinforcing agents for improved tensile, tear, and abrasion properties, vulcanizing ingredients for reduced plastic flow and improved elastic recovery, and antioxidants for providing resistance to aging. Furthermore, while optimum combination of synthesis and compounding efforts may achieve adequate bulk properties, the stock may still fail because of surface difficulties, e.g., permanent discoloration on contact with stains, and surface tack development. To overcome these difficulties, in some instances successful use has been made of surface coatings such as talc, waxes, or thin, adherent polymeric films.
Isotope Exchange between Sulfur Atoms in Vulcanization Accelerators in the Presence of Diphenylguanidine and Phenyl-2-Naphthylamine
Authors: Blokh G. A. , Golubkova E. A. , Kurskaya K. V. 
Published: February 2011

Abstract
In previous work it was shown that in the process of vulcanization a continual series of isotope exchange reactions takes place between the sulfur atoms in the various sulfur-containing ingredients of the vulcanizate. It was established that the sulfur atoms which enter into this isotope exchange include not only those which go into the structure of the molecule of accelerator, e.g., mercaptobenzothiazole, benzothiazolyl disulfide, and tetramethylthiuram disulfide, carbamates, and sulfenamides, but also the sulfur atoms which form the polysulfide bonds, R—Sm—R, and, in addition, those present in the form of secondary products formed in the vulcanization process (hydrogen sulfide and zinc sulfide). Evidently the exchange reactions between sulfur atoms in the substances present in an accelerator-type vulcanization, in which sulfur in a reactive form is liberated, and active radicals are formed from the accelerator and take part in structure formation in the rubber, are of prime importance. The formation of a vulcanization network in which the rubber, sulfur, and carbon black are chemically combined, is another result of industrial vulcanization.