bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dependence of the Ultimate Properties of a SBR Rubber on Strain Rate and Temperature
Authors: Smith Thor L. 
Published: February 2011

Abstract
The tensile strength and ultimate elongation of polymeric materials depend on both the temperature and experimental time scale. The mechanical properties of amorphous polymers at temperatures above their glass transition temperature Tg are more amenable to treatment in terms of molecular theories than are their mechanical properties at temperatures below Tg or the mechanical properties of crystalline polymers. For amorphous polymers at temperatures above Tg the viscoelastic properties in small deformations have been studied rather extensively, and several molecular theories—essentially identical—have been published. In contrast, few systematic studies have been made of the effect of time and temperature on the ultimate properties. Consequently, only a limited amount of data is available which can serve as a basis for developing and verifying molecular theories dealing with ultimate properties. A recent theory by F. Bueche treats the time and temperature dependence of tensile strength. According to his theory, the tensile strength for a given material is a universal function of a reduced time or a reduced strain rate, except at short times or high strain rates where the material approaches glasslike behavior. Also, to superpose data measured at different temperatures, a shift factor is needed which is determined by the temperature dependence of the frictional factor for polymeric segment mobility and thus is the same factor as used to superpose viscoelastic data measured in small deformations. Thus, according to Bueche's theory, the temperature dependence of the tensile strength is given by the equation of Williams, Landel, and Ferry which is applicable in the temperature range Tg&lt;T&lt;(Tg+100). Bueche reported some tensile data for polybutyl methacrylate which has a glass transition temperature of 8° C. These tensile data were measured under various constant loads at temperatures between 30 and 95° C, and reasonable agreement between theory and experiment was found. Although Bueche did not consider the ultimate elongation, it seems reasonable that such data can be superposed by using the same shift factor as required to superpose the tensile strength data. Other workers have not considered explicitly the effect of viscous forces on the ultimate properties but have considered the effect of such variables as molecular weight, degree of crosslinking, and plasticizers.
The Melting of Crystalline Polymers
Authors: Mandelkern Leo 
Published: February 2011

Abstract
Polymer molecules are characterized by the unique structural feature of being composed of a large number of chain units covalently linked together. Despite this complexity of structure macromolecular systems still retain the ability to exist in different states, a property common to all substances. Two of the states of matter observed for monomeric substances, the liquid and crystalline states, are also found in polymeric substances. The liquid or amorphous state is characterized by the fact that, because of the freedom of rotation about the bonds connecting the chain atoms, a single polymer molecule can assume a large number of configurations. In this state, therefore, the chain units of different molecules are arranged in a random, disoriented array uncoordinated with one another. Under appropriate thermodynamic conditions, however, a spontaneous ordering of portions of the chain molecules can occur, and in contrast there results a state of configurational order, the freedom of rotation being lost. This latter state is termed the crystalline state. Major attention in this review is directed to the consideration of the transformation from the crystalline state to the liquid state. Certain closely related subjects as the morphology and organization of the crystalline state and the mechanisms and kinetics of crystallization from the melt have been recently reviewed and hence will not be considered in any great detail. The melting process that occurs in various types of polymeric systems will be considered and conclusions drawn from the presently available evidence. Presentation from a unified point of view, based on certain fundamental considerations, is aimed for. The basic underlying principles which govern the phenomena will be stressed; experimental results which demonstrate these principles or point out the need for new developments will be presented. An effort will be made to consider problems from the point of view of theoretical expectations and experimental findings. On the other hand, no effort is made to include a description of all work in this field, although care has been taken to be as comprehensive as possible in discussing the basic principles.
Growth and Agglomeration of Particles in Low-Temperature GR-S Type of Latex
Authors: Brown R. W. , Howland L. H. 
Published: February 2011

Abstract
It has been shown that it is possible to prepare high-solids latex by polymerizing to an intermediate solids content and particle size, followed by solvent agglomeration and concentration. It has also been shown that a somewhat similar agglomeration normally takes place at intermediate conversions in conventional high-solids latex recipes. The slow rates of polymerization in the latter recipes after agglomeration are primarily due to the greatly reduced number of particles present. The ratio of hydrocarbon to water is very important in determining the extent of agglomeration both during and after polymerization.
Study of the Kinetics of Polymerization of Isoprene in Aqueous Solutions of Emulsifiers and in Emulsions
Authors: Sheinker A. P. , Medvedev S. S. 
Published: February 2011

Abstract
It has been established earlier that polymerization in aqueous solutions of emulsifiers takes place in the water or in the micellae of the emulsifier, depending on the solubility of the monomer and the initiator. The question of the topochemical properties of polymerization in emulsions has not yet been definitively explained. In a number of studies, the hypothesis was advanced that the process of emulsion polymerization takes place in the micellae of the emulsifier, according to the degree of conversion of the micellae into polymer-monomer particles, with the monomer dissolved in the polymer. In order to explain further the mechanism of emulsion polymerization, the kinetics of polymerization of isoprene in water, in solutions of emulsifier and N-cetylpyridinium bromide, and in emulsions in the presence of a water-soluble initiator (hydrogen peroxide) were studied. The dilatometric method was chosen for the kinetic measurements of solutions of emulsifier not saturated with isoprene, and for emulsions. Experiments with solutions of emulsifier saturated with monomer were made during continuous saturation of the emulsifierinitiator solution with isoprene in the gaseous phase. All the experiments were made at 50° C in the absence of oxygen.
Inhibition of Rubber Oxidation by Carbon Black
Authors: Burgess K. A. , Sweitzer C. W. 
Published: February 2011

Abstract
Indirect measurements have shown that small amounts of carbon black inhibit rubber oxidation during Banbury mastication. To provide a more comprehensive picture of this inhibitory action, a study was made of its effects on some physical properties of fully compounded and vulcanized stocks prepared from masticated natural and synthetic polymers. The action of carbon black, with the exception of its behavior in Butyl rubber, was found to be broadly similar to that of standard antioxidants. The largest change in vulcanizate properties occurred in cold rubber after high-temperature mastication. The usual shortening and stiffening resulting from gelation of the polymer at high mastication temperatures was completely inhibited when the mastication was carried out in presence of small loadings of carbon black.
Studies of the Vulcanization of High Elastic Polymers. I. The Vulcanization of Natural Rubber with Thiuram Disulfides. Part 1
Authors: Scheele Walter , Lorenz Otto , Dummer Wilhelm 
Published: February 2011

Abstract
The present paper, which is concerned with the clarification of the mechanism of thiuram vulcanization, although the studies are still in progress, nevertheless leads us to the following fundamental facts. 1. In the vulcanization of natural rubber by thiuram disulfides in the presence of excess zinc oxide, the zinc dialkyldithiocarbamate at any stage is the principal, and probably even the sole, reaction product that can be extracted with organic solvents. 2. There are no experimental proofs that make probable the presence of thiuram monosulfide in the extracts. 3. The maximum attainable conversion in vulcanization of any particular tetralkylthiuram disulfide to the corresponding zinc dialkyldithiocarbamate amounts to about 66 per cent, and this is independent of the temperature. 4. The maximum conversion of the thiuram disulfide is practically independent of its concentration in the rubber, provided that the differences in the concentrations involved are not excessive. 5. The extracts of thiuram vulcanizates contain free thiuram disulfide in addition to the zinc dithiocarbamate. The concentration of the thiuram disulfide decreases rapidly with the time of vulcanization and approaches zero asymptotically. This is exemplified by the results with tetrapropylthiuram disulfide. 6. It is shown to be probable that the vulcanization continues to proceed slowly during extraction of the vulcanizate with boiling solvents, so that the analytical results of the hot extracts are not such as to throw light on the kinetics of thiuram vulcanization. 7. The decrease of concentration of the free thiuram disulfide in the vulcanizates evidently takes place more rapidly than the formation of the zinc dithiocarbamate. It is, therefore, probable that the vulcanization of rubber by thiuram disulfides can be separated into two partial processes. There is a rapid reaction of the rubber with the thiuram disulfide, which is presumably “vulcanization-inert”, and there is an additional, slower reaction which involves a splitting off of dithiocarbamic acid from a reaction product between rubber and thiuram disulfide and which leads to the vulcanization. 8. All exhaustively extracted vulcanizates contain sulfur. Apparently the sulfur content in vulcanizates of short reaction times is greater than in those of longer periods of vulcanization. 9. The formation of the zinc dithiocarbamate as sole reaction product in the thiuram vulcanization can hardly be explained otherwise than as a dehydrogenation of the rubber, concerning the mechanism of which we still know, to be sure, scarcely anything. It is reasonable to conceive of a reaction of the disulfides with the α-methyl groups, in which chain radicals may be formed which give rise to cross-linking over C—C bonds. The investigations are being continued and a further communication will appear in the near future.
Stress Relaxation in Rubber I. Evaluation of Antioxidants
Authors: Robinson H. W. H. , Vodden H. A. 
Published: February 2011

Abstract
Conventional evaluation techniques for rubber antioxidants are very time consuming. A method of evaluation based on stress relaxation due to oxidation at elevated temperatures, and an apparatus developed for the study of this phenomenon in a large number of natural rubber stocks, are described in this article. Results are compared with those obtained using conventional air- oven and oxygen bomb aging tests. The apparatus is suitable for testing six rubber samples simultaneously, and uses unbonded resistance wire strain gauges for the measurement of stresses in the samples. The stress vs. time curves are recorded automatically on a roll chart recording potentiometer. It has been found that the curves approximate to exponential decay curves, and, as such, can be characterized by a single parameter—the half life. This parameter, used as a measure of antioxidant efficiency, can be correlated with the loss of tensile strength for samples aged in a conventional air oven. The use of the half-life period as a measure of antioxidant efficiency leads to a rapid and easily interpreted method of evaluation for antioxidants in natural rubber. Good reproducibility and discrimination are features of the method.
Stress Relaxation in Rubber II. Simultaneous Oxygen Absorption
Authors: Baxteh S. , Potts P. D. , Vodden H. A. 
Published: February 2011

Abstract
In any serious study of antioxidant action, it is essential that the oxygen absorption rate of a protected rubber be determined and the changes in the network system caused by the oxygen be assessed. This information is normally obtained from separate oxygen absorption and aging studies. A method is described in this article which enables simultaneous measurements of oxygen absorption and stress relaxation to be made on a given rubber sample. A number of antioxidants have been compounded with natural rubber and, from the results, an estimate is made of the molecules of oxygen absorbed per rubber chain cut. This is found to vary with the antioxidant, although some difficulties of interpretation are pointed out. Variations of deactivating effect among the antioxidants shows clearly that any attempt to understand oxidative degradation in terms of oxygen absorption or decay in physical properties alone is not possible. The method provides a new technique that is of value in any basic study of antioxidant action in elastomers.
Gel Structure. VI. Preparation of Gels and Globular Structures from Rubbers by Vulcanization of Solutions
Authors: Zubov P. I. , Zhurkina Z. N. , Kargin V. A. 
Published: February 2011

Abstract
1. The mechanical properties of gels prepared from solutions of natural rubber and synthetic rubber were studied. 2. It was established that gels of synthetic rubber (polybutadiene rubber) have a wide range of relaxation periods. Gels of natural rubber (smoked sheet) behave like ideally elastic substances, following Hooke's law in the change of rate of deformation by 1000 times. 3. The viscosity of solutions of natural rubber and of polybutiadiene rubber in the presence of sulfur monochloride was studied. 4. We observed that sulfur monochloride sharply decreases the viscosity of natural rubber solutions and has almost no influence on the viscosity of synthetic rubber solutions.
Identification of Curing Agents in Rubber Products. Ultraviolet Absorptiometric Analysis of Selective Solvent Extracts
Authors: Kress K. E. , Mees F. G. Stevens 
Published: February 2011

Abstract
A method has been devised for identification of organic compounds that accelerate the vulcanization of rubber products. Identification of these active trace materials aids product improvement and quality control. Identification is made through ultraviolet spectrophotometric absorbance curves over the 220 to 380 mµ region on the aqueous alkali or acid extracts, or on liquid-liquid ethyl ether extracts of the aqueous solutions. Thiazole, thiuram, thiocarbamate, amine, and guanidine classes of commercial accelerators are regularly identified in 2 grams of uncured or cured rubber products, with less than 4 hours' elapsed time. Interference of common softeners and antioxidants is usually negligible. The method is more rapid than chromatographic procedures and more sensitive and specific than spot-test methods. Quantitative results may be obtained if calibration work is undertaken.
Studies of the Vulcanization of High Elastic Polymers. V. Vulcanization of Natural Rubber by Tetramethylthiuram Monosulfide and Sulfur
Authors: Scheele Walter , Bielstein Georg 
Published: February 2011

Abstract
The vulcanization of natural rubber (pale crepe) by tetramethylthiuram monosulfide and sulfur (1 mole monosulfide per gram-atom of sulfur) has been studied in the temperature range from 90° to 150° C. The following results were obtained : 1. During vulcanization, the concentration of the thiuram monosulfide and also of the sulfur decreases. 2. In accordance with a first-order reaction, about 66 mole-per cent of zinc dithiocarbamate is formed (calculated on the amount of thiuram monosulfide added). Thus the same relationships were found as in vulcanization with thiuram disulfides. 3. The vulcanization of rubber with thiuram monosulfide and sulfur is, therefore, nothing else than vulcanization by thiuram disulfide, whose quantitative formation precedes the actual vulcanization reaction. 4. In no stage of vulcanization could thiuram disulfide be detected with certainty in the extracts of the vulcanizates. It must be assumed, therefore, that it reacts with the rubber instantly after it is formed. 5. The velocity constants derived for the dithiocarbamate formation at the various temperatures both from the experimental results and from the graphical presentations have been given, and their temperature dependence has been discussed. At lower temperatures, the influence of the prior interaction of the monosulfide with sulfur makes its influence on the energy relationships felt. 6. It is once more emphasized that in thiuram vulcanization it cannot be a question of a vulcanization with sulfur. In this connection we take a decided stand also with regard to the results of the more recent investigations of Craig and his coworkers.
The Mobility of Sulfur Bonds in Soft Rubber and Ebonite
Authors: Blokh G. A. , Chuprina L. F. 
Published: February 2011

Abstract
Much attention has been devoted to the problem of the sulfur and oxygen bonds in vulcanized rubber in numerous studies of both Soviet and foreign scholars. In the Soviet Union, the works of a large group of investigators, including B. A. Dogadkin, A. D. Zai˘onchovskii˘, P. A. Rebinder, A. P. Pisarenko, A. S. Kuzminskii˘, and others, have dealt with this problem. The nature of the sulfur structures formed in soft vulcanized rubbers depends on a number of factors, including the nature of the accelerators. It was shown in one work that sulfur vulcanization in the absence of sulfur-bearing accelerators leads to the formation of relatively weak polysulfide bonds. We assume that here a group of different polysulfide bonds is formed at the expense of the passage of octatomic ring sulfur structures into open linear sulfur radicals. For vulcanized rubbers which contain sulfur and diphenylguanidine in their recipe, the group of polysulfide bonds evidently constitutes an excellent criterion of their characteristic vulcanization structures. A number of rubber products, including cable and insulation rubbers, which do not contain sulfur as a vulcanizing agent are also known. In this case vulcanization takes place at the expense of the decomposition of tetramethylthiuram disulfide (thiuram vulcanization). Here stronger intermolecular monosulfide sulfur bonds are formed at the expense of the atomic sulfur, which is liberated during the decomposition of thiuram:
Oxidation of Organic Sulfides. III. A Survey of the Autoxidizability of Monosulfides
Authors: Bateman L. , Cunneen J. I. 
Published: February 2011

Abstract
The reactivity of a variety of organic monosulfides towards molecular oxygen has been investigated at temperatures from 45° to 75°. Formally saturated sulfides by themselves are inert, allylic acyclic sulfides react initially much faster than comparable unsaturated hydrocarbons, and allylic and vinylic cyclic sulfides are still more reactive. Oxygen absorption is promoted by light, by the free-radical catalyst αα′-azoisobutyronitrile, and by certain metallic compounds, but not by peroxides. The azo compound is sufficiently active to catalyze the oxidation of saturates sulfides having C—H bonds adjacent to the sulfur atom, while aryl alkyl sulfides also respond to photocatalysis. A notable feature of these autoxidations is the self-inhibition or strong retardation which generally becomes apparent at small oxygen uptakes. Certain mechanistic details which can be deduced from the experimental findings are discussed.
Graft Polymers Derived from Natural Rubber
Authors: Bloomfield G. F. , Merrett F. M. , Popham F. J. , Swift P. Mc L. 
Published: February 2011

Abstract
Graft polymers result when vinyl monomers are polymerized in the presence of natural rubber, either in solution or as latex, and some of the polymeric chains become attached to the rubber molecules. The properties of the natural rubber can be widely modified according to the nature and the amount of the grafted polymer. The polymer-modified natural rubber appears to be produced by direct growth of polymer chains on to rubber molecules rather than by a transfer reaction involving the rubber. Graft polymers of styrene and methyl methacrylate with natural rubber can be compounded and cured to give light-colored articles of good tensile strength, and rubber-methyl methacrylate graft polymers have outstanding flex-cracking and fatigue resistance.
Filler Reinforcement and Tear Resistance in the Light of Thixotropy
Authors: Houwink R. , Janssen H. J. J. 
Published: February 2011

Abstract
Rubber mixes containing reinforcing fillers may be regarded as being thixotropic, with a very long recovery time. The explanation of this is found in the destruction and the reconstruction of filler-rubber linkages and filler-filler linkages, which adhere to each other as a result of a continuous spectrum of energies of attraction. It is assumed that the rubber-filler complex becomes oriented during the stretching of filled mixes. With unfilled mixes, the rubber molecules are able to spring back again, when the stress is released, into the position which is mostly favorable from the point of view of entropy. As a consequence of the introduction of potential energies by the incorporation of reinforcing fillers, the rubber molecules have their mobility adversely affected, as a result of which a definite orientation may be maintained when the stress is released. For instance, after prestretching of these mixes, a significant increase of the resistance to continued tearing at right angles to the direction of elongation and a decrease parallel to this direction are found. This partial increase of the tear resistance, which is not encountered with unfilled mixes, will presumably contribute, as does crystallization, to reinforcement. This increase indicates that the tearing forces in a stretched mix are distributed in one direction over a large surface area. A series of associated phenomena are explained.
Mastication of Rubber. II. Interpolymerization of Natural Rubber and Neoprene on Cold Milling
Authors: Angier D. J. , Watson W. F. 
Published: February 2011

Abstract
The softening of elastomers on cold milling results from scission of the polymer molecules by the applied shearing forces. The ruptured chains are free radicals, which can undergo mutual combination, interaction with oxygen and various additives, and branching (grafting) on to other polymer molecules. A general method of producing graft and block interpolymers between elstomers is therefore indicated, namely, to cold-mill the polymers together in the absence of small molecules which can terminate the polymeric radicals in order that the radicals may cross-terminate or graft onto the polymer molecules of the other type. A survey of several pairs of the commercially important elastomers, natural rubber, butadiene-styrene, Neoprene, and butadiene-acrylonitrile, has shown that cold milling does effect interlinking. Detailed results for the rubber-Neoprene system are reported in this communication. Experimental verification of polymer interlinking was obtained from the solubility properties of the milled elastomers. Cold milling of Neoprene under nitrogen produces gel, whereas of natural rubber does not, but the milling of mixtures gives gels containing natural rubber. Also, the solubilities and precipitation of the milled mixtures cannot be accounted for by these properties of the individual polymers. Finally, Neoprene-natural rubber mixtures, after and not before cold-milling, can be cross-linked by magnesium oxide, with rubber bound into the vulcanizate.