bluuebunny/crossref_metadata_2025 huggingface dataset:
The Structure of Hevea Latex and Its Viscosity. II
Authors: Verhaar G.
Published: February 2011

This paper deals with the effect of dilution on the viscosity of sulfite or formaldehyde treated and ammoniated latexes, the relationship between viscosity and DRC for ammoniated field latex and concentrate and the influence of the tapping cycle on the viscosity of whole latex and white fraction latex. An explanation is given of the shape of the viscosity curve of water diluted fresh field latex. It is shown that sulfite in increasing concentrations shifts the maximum viscosity of dilution to regions of higher dilutions and at the same time lowers the viscosity value at the maximum. In formaldehyde treated latexes the maximum viscosity in the dilution curve still occurs at 15–20 per cent dilution, but the maximum viscosity value is considerably lower, especially at higher formaldehyde concentrations. Dilution of ammoniated field latex or concentrate yields a viscosity curve typical for a non-Newtonian liquid. The viscosity-DRC relationship for ammoniated field latexes shows wide discrepancies for individual samples and can not be used as a means for determining the DRC. Individual concentrate samples are in much closer agreement. The influence of the occurrence and removal of viscoids on these phenomena is discussed. A description is given of the influence of the tapping cycle on the viscosity of unpreserved fresh latex and the white fraction prepared therefrom, on the viscoid volume and on the DRC and TS of both whole latex and the white fraction. Finally, the possible role of viscoids in latex formation is discussed in connection with some recent investigations concerning their occurrence in sieve tubes and latex vessels in the Hevea tree.
Determination of Degree of Crosslinking in Natural Rubber Vulcanizates. Part I
Authors: Mullins L.
Published: February 2011

This paper examines the relationship between the stress-strain properties of highly swollen natural rubber vulcanizates and their equilibrium volume swelling. It is shown that the empirical relationship obtained can be described equally well by either the Flory-Huggins equation or the Flory Modification of this equation, and values of the interaction constant µ for natural rubber in decane are determined. Observed differences in the values of µ obtained for sulfur and peroxide vulcanizates are interpreted in terms of the diluent effect of nonrubber constituents in the former. The effect of the initial molecular weight of the unmasticated rubber on these physical properties is examined and an empirical correction making allowance for chain segments terminated by a crosslink at only one end is obtained. The correction is larger than that derived by previous workers and possible sources of the observed differences are discussed. It is considered that internally self-consistent estimates of the degree of crosslinking of natural rubber vulcanizates may be obtained using the methods developed.
Microgel in Latex and Sheet Rubber
Authors: Freeman R.
Published: February 2011

The rubber hydrocarbon in fresh latex can be dispersed in benzene to form a solution that passes easily through a porosity-1 sintered filter. When this solution is treated with a finely divided adsorbent powder, part of the rubber is removed from solution. The powders that have been tried and found effective are calcium sulfate (anhydrous), calcium oxide and hydroxide, kaolin, magnesium oxide, kieselguhr, charcoal, lamp black, furnace black, and channel black. These materials have little in common except a small particle size. The amount of rubber removed varies with the absorbent used. The actual viscosity of the solutions is not affected by the removal of 10–20 per cent of the rubber present. Similar results can be obtained by centrifuging the solution at 144,000 g. These results can be explained by assuming that part of the rubber in normal latex is in the form of microgel, i.e., crosslinked rubber particles of small size. The microgel latexes examined by Bloomfield are shown to be a special type in which most of the rubber is present as microgel. Some microgel is present in every sample of latex examined. The amount of microgel depends on the clone, and varies between 5 per cent and 30 per cent of the total rubber. An average value for bulked latex is 15 per cent. The microgel content of a latex can be increased by treating the latex with a redox system as used to initiate polymerization. The increase of microgel is accompanied by an increase of the Mooney viscosity of the dried rubber. Microgel is not affected by coagulation and smoking of the sheet. In freshly prepared smoked sheet the microgel content is similar to that of the original latex. On storage the microgel is no longer detectable, but a macrogel component appears. The particle size of microgel has been estimated as 0.1 µ. This is smaller than the size of the latex particles from which the microgel was derived.
Chlorinated Rubber and Nitrogenous Plasticizers. I. Viscosity of Mixtures of Chlorinated Rubber and Anhydroformaldehyde Urethan
Authors: Giua Michele , Mancini Corrado
Published: February 2011

The viscosities of solutions of chlorinated rubber in chloroform and in toluene and of mixed solutions of chlorinated rubber and anhydroformaldehyde urethan in toluene were measured. From the data it was possible to determine in an approximate way the mean molecular weight of chlorinated rubber and the mean molecular weights, determined viscometrically, of the mixtures. From the results it was, in turn, possible to derive the α coefficient in the relation of Kuhn. The action of anhydroformaldehyde urethan on chlorinated rubber could then be considered on a quantitative basis.
Preparation and Properties of Condensation Block Copolymers
Authors: Coffey D. H. , Meyrick T. J.
Published: February 2011

By using diisocyanates to link together two different polyesters having terminal hydroxyl or carboxyl groups, copolymers have been obtained in which the two repeating units occur in blocks and not in the random arrangement obtained by normal methods of preparing copolymers. Melting points have been measured by a penetrometer method and the effects of copolymer composition on melting point determined. In a series of crystalline copolymers made by linking various amounts of polyethylene sebacate and polyethylene adipate with hexamethylene diisocyanate, a step-shaped melting point-composition curve is obtained. Copolymers containing up to about 40 per cent of polyethylene adipate have the same melting point as that of polyethylene sebacate. Further increase in the polyethylene adipate content results in a rapid drop in melting point until the melting point of polyethylene adipate is reached. Thereafter increasing amounts of polyethylene adipate do not alter the melting point. Random copolymers of ethylene adipate and ethylene sebacate give a V-shaped melting point-composition curve. The step-shaped curve of block copolymers is almost identical with the melting point-composition curve of melt blends of the two polymers. Stress-strain characteristics and impact strengths of the block copolymers have been measured. In the polyethylene adipate/polyethylene sebacate/ hexamethylene diisocyanate series no great differences are found between random and block copolymers. If, however, the crystalline polyethylene adipate is replaced by the noncrystalline polypropylene adipate, then block copolymers containing 15–30 per cent of polypropylene adipate have outstanding impact strength. Similar high impact strength is obtained by using a compatible rubbery polymer as an external plasticizer with hexamethylene diisocyanate modified polyethylene sebacate. This method of block copolymerization has an advantage over random copolymerization in that a crystalline copolymer can be modified without reduction of its melting point, and by suitable selection of a second component it affords a means of “building in” a plasticizer.
Structure and Solution Properties of High Molecular Weight Butadiene-Styrene Copolymers
Authors: MacFarlane R. B. , McLeod L. A.
Published: February 2011

Production of high molecular weight copolymers of butadiene and styrene for use in oil-extended rubbers has aroused interest in the solution properties of copolymers above the molecular weight range commonly encountered in commercial practice. It has been observed that solubility of such polymers in toluene is a time-dependent phenomenon and the apparent solubility can increase continuously, in the absence of agitation, for as long as 800 hours. Although a standard Harris cage solubility test may show the presence of 50% gel, other properties do not confirm the presence of any appreciable quantities of insoluble material. Mild agitation rapidly promotes almost complete solubility. Dilute solution viscosity measurements are very misleading unless the influence of solution time is recognized and apparent intrinsic viscosities rise progressively with time of contact of the sample with solvent. This time-dependence of solution has been found to occur at conversions higher than 50% and is also a function of the amount of modifier used in the polymerization recipe. It has not been possible to shorten the solution time for viscosity measurements by mild heating or gentle agitation. Mixed solvents cause a change in the amount of increase of the apparent intrinsic viscosity but do not shorten the time to equilibrium. Measurement of the slope constant in the Huggins viscosity equation indicate that these solubility and viscosity effects coincide with the appearance of a marked degree of branching in the polymer molecules. The effect is, therefore, interpreted as being caused by the relatively slow disentanglement of molecules of complex structure.
Cation and Anion Influence in the Alfin Reagent for the Polymerization of Butadiene
Authors: Morton A. A. , Nelidow I. , Schoenberg E.
Published: February 2011

A mixture of allylsodium, sodium isopropoxide and sodium chloride causes a very rapid polymerization of butadiene to a soluble polymer of unusually high molecular weight which has largely a 1,4-structure. The present work is a study of the influence of the sodium cation and of various halide salts, and of the isopropoxide ion as contrasted with the n-propoxide, upon the proportion of 1,4-polymerization. A proper combination of ions will favor greatly the end-to-end polymerization and any given reagent may cause either 1,4 or 1,2-polymerization to take place, depending on the composition of the reagent. An explanation based on adsorption and orientation of diene molecules on the surface of the insoluble aggregate of ions is suggested.
A Technique for Obtaining the Infrared Absorption Spectra of High Gel Rubbers
Authors: Mitzner Bernard M.
Published: February 2011

Several techniques have been previously described for obtaining the infrared absorption spectra of various types of rubbers. The most convenient method is to dissolve the substance under investigation in a suitable solvent and obtain the spectrum as a solution employing a sealed liquid cell. Another technique that is commonly employed is to evaporate a benzene solution of the polymer to dryness on a rock salt plate, thus obtaining a film. A more time consuming procedure consists of floating a polymer solution on a mercury pool which can subsequently be picked up by a steel frame and studied as a film. All the above procedures, although useful when investigating low gel rubbers, cannot be successfully employed with high gel rubbers. Modified polybutadiene crumb rubbers form extremely stable gels, and are almost completely insoluble in all common organic solvents. Because of this great insolubility, one is limited in infrared sample preparation. Attempts to employ the KBr pressed disc technique have met with very little success in our laboratory.
Rapid Determination of Chlorine Content of Rubber Hydrochloride by Means of Density Gradients in Centrifugal Field
Authors: Schuur Gerrit , Klootwijk Arie
Published: February 2011

The density of small particles can be determined by suspending them in a liquid of graduated density and centrifuging. Experimental improvements have been found which make the method suitable for accurate density measurements of rubber hydrochloride from latex. The density of amorphous rubber hydrochloride has been determined in the range from 24 to 33 per cent chlorine. The density measurements provide a means of measuring the chlorine content of rubber hydrochloride in less than 10 minutes, thus enabling one to follow the hydrochlorination of latex closely. Differences as small as 0.1 per cent in chlorine content can be determined. The method is applicable to other polymers as well.
Contribution to the Mechanism of Devulcanization
Authors: Stafford W. E. , Wright R. A. , Sargent D.
Published: February 2011

(1) Three types of natural-rubber vulcanizates have been treated under specific reclaiming conditions. The resultant products have been examined particularly for the manner of sulfur combination and for chloroform extract. The normally accepted, non-reverting tetramethylthiuram disulfide type stock was found to be by far the most amenable to plasticization by thermal agencies. This observation is more or less in line with conclusions of van Amerongen, drawn from a recent study of the oxidative and non-oxidative thermal degradation of rubber. A natural pure-gum type, cured with tetramethylthiuram disulfide only, when heated in the absence of oxygen, at temperatures up to 175° C, was found to revert much more than a similar type cured with 1.0 per cent Santocure and 2 per cent sulfur. Swelling in benzene, after heating 3 days at 150° C, increased considerably with the former, whereas with the latter it remained unchanged. This greater “devulcanizing tendency” is explained on the basis of the tetramethylthiuram disulfide type having comparatively few crosslinks and no free sulfur to form additional ones, hence, “… if any links are broken down, a seemingly unvulcanized rubber results. …” The access of air under the reclaiming conditions used in our work would certainly be limited, and the highly plastic stocks obtained are to be expected in the light of the reference cited. Finally, van Amerongen concludes that in the absence of oxygen, it is inadvisable to use tetramethylthiuram disulfide vulcanizates where thermal stability is important. Mercaptobenzothiazole and rubber/sulfur types did not show any very significant differences in plasticization. (2) Considerable increases in zinc sulfide resulted in all cases, even when free sulfur was virtually removed before reclaiming, and in the latter instance there appears to be a reduction in rubber combined sulfur. In general, the changes are in line with those reported elsewhere in the reversion of natural and Butyl vulcanizates. (3) In all reclaims made, the ratio of sulfur in the chloroform-insoluble rubber to that in the soluble portion is very much lower than that previously published elsewhere. The comparison is not necessarily sound since the products tested are not technical reclaims, and generally the chloroform extracts were of a low order. (4) Under the highly reverting thermal conditions employed in this work, plasticization was generally inferior. This perhaps supports the theory that reclaiming is essentially a depolymerization process associated with traces of oxygen. The line of demarcation between reclaiming and reversion is by no means well defined. Since reclaiming treatments are normally much more severe than those needed to induce the characteristics of reversion, it may well be that reversion is only one factor in the mechanism of reclaiming, but it is a factor which cannot be ignored in any comprehensive consideration of devulcanization.
Apparatus for the Direct Determination of the Dynamic Bulk Modulus
Authors: McKinney J. E. , Edelman S. , Marvin R. S.
Published: February 2011

An apparatus has been developed for the direct measurement of the real and imaginary parts of the dynamic bulk modulus of solid and liquid materials over the frequency range of 50 to 10,000 cps. Piezoelectric crystals serving as driver and detector, together with the sample and a confining liquid, are contained in a cavity small compared with the wavelength of sound at these frequencies. Static pressure is superposed to eliminate the effect of small air bubbles. The complex compliances of the sample, confining liquid, and the cavity, are additive in this region, where the compliance is pure dilatation. The dynamic compliances of several natural rubber-sulfur mixtures were obtained in a preliminary evaluation of the behavior of the apparatus.
Theory of the Non-Newtonian Rheology of Raw Rubbers Consisting of Supermolecular Rheological Units
Authors: Mooney M.
Published: February 2011

A theory of the viscosity of raw rubbers is developed on the postulate that raw rubbers, when subjected to continuous shear in the non-Newtonian region of flow, consist of microscopic rheological units which are semipermanent aggregates of many rubber molecules. The theory treats these units as tacky, elastic solids, whose relative movement and slippage constitute the macroscopic flow of the rubber. The resulting theoretical flow curve differs little from that given by Smallwood, but the interpretation of the parameters is radically different. The new theory leads to expressions for the number of temporary point attachments per unit area between two touching rheological units and for the mean life of these attachments. Agreement with experimental data is slightly better than in Smallwood. Two types of observed deviation from the theory can be interpreted as due to two plausible phenomena not included in the mathematical treatment.
The Absolute, Entirely Viscometric Determination of the Molecular Weight of high Polymers
Authors: Edelmann K.
Published: February 2011

The utility of high polymers in all fields of application depends on the average molecular weight. In general, strength, elasticity and tear resistance under sudden stress increase with the molecular weight. On the contrary, processibility and solubility decrease with increasing molecular weight. The opposing requirements for quality and economy lead to the necessity of possessing as accurate a knowledge of the molecular weight as possible, to make certain that the molecular weight of a product is adequate for the requirements of a definite application. Normally, a simple measurement of viscosity will suffice as a test for the characterization of a definite product. The knowledge of the absolute value of the molecular weight is not required in the case where it is possible to arrange different samples in a correct series. However, in many cases a numerical knowledge of the molecular weight is desirable. In the case of the reactions of cellulose, e.g., it is often necessary to determine at what point decomposition occurs. Normally, this is not possible by means of a simple viscosity determination, since its standardization against absolute methods varies with the degree of substitution and the type of solvent. To this must be added, the causes for the occurrence of structural viscosity in solutions of linear macromolecules, which also make it necessary to determine the molecular weight for the evaluation of these high polymers.
Self-Adhesion (Autohesion) of Polyisobutylene. II
Authors: Voyutskiĭ S. S. , Zamaziĭ V. M.
Published: February 2011

In accordance with our concepts, the autohesion of polymers is caused by diffusion of segments of chain molecules from one layer into another layer of the same polymer brought into contact with the first. This conclusion was drawn by us from generally known facts and modern concepts concerning the nature of high-molecular substances. The present work represents an attempt to confirm experimentally the diffusional theory of autohesion. Polyisobutylene with a molecular weight of 150,000 was used to investigate autohesion. Polyisobutylene was chosen as the material for study because its molecules contain no double bonds. This renders them sufficiently stable in regard to oxidation at ordinary temperature. The strength of autohesion was characterized by the stress necessary to delaminate two laminated fabric strips treated before laminating with the polymer solution. For the preparation of splices subjected to delamination in determining the autohesion of polyisobutylene, use was made of strips of unsized technical cotton fabric with a smooth surface. The working length of the specimen was always 10 cm.; its width was usually 5 cm. The polyisobutylene was applied to the specimens in the form of 6.0–7.5 per cent solution. The polyisobutylene solution was made up in a low-boiling fraction of aviation gasoline, which left no dry residue upon evaporation. The quantity of polyisobutylene, in grams per square centimeter of specimen surface was established from the weight of the absolutely dry initial fabric and of the polymer coated material after drying.
Effect of Molecular Weight, Shape of the Molecule, and Presence of Polar Groups on the Autohesion of High Polymers. III
Authors: Voyutskiĭ S. S. , Shtarkh B. V.
Published: February 2011

1. It is shown for polyisobutylenes of different molecular weight that increase in the size of the chain molecule retards autohesion, but increases the limiting value to which the work of autohesion tends with increasing contact time. 2. Investigation of the temperature dependence of autohesion of polyisobutylenes showed that the activation energy does not depend on the molecular weight of the polyisobutylene. 3. It is shown for polybutadienes with varying contents of 1,4- and 1,2-structures that autohesion decreases with increase in the number of short side groups in the molecule, which apparently hinder diffusion by purely steric causes. 4. Investigation of the temperature dependence of autohesion of butadienenitrile copolymers with different contents of acrylonitrile in the molecule showed that the activation energy of autohesion increases with increase of polar nitrile groups in the polymer. 5. It is shown for the vulcanization of natural rubber that the formation of a spatial structure results in complete disappearance of autohesion in high polymers. It is shown that the kinetics of changes of autohesion during vulcanization can effectively characterize the structural changes which take place in the polymer during the process.
Theoretical Model for the Elastic Behavior of Filler-Reinforced Vulcanized Rubbers
Authors: Mullins L. , Tobin N. R.
Published: February 2011

One of the more important advances in rubber science during the past twenty years has been the development of quantitative theories describing the elastic properties of pure-gum vulcanized rubbers. As a result it is now possible to account for their equilibrium stress-strain behavior with considerable success. There is, however, no adequate theory to describe the elastic properties of filler-reinforced rubber vulcanizates and the work described herein is an attempt to provide a basis for such a theory. When a reinforcing filler is added to rubber it produces a large increase in the stiffness of the vulcanizate. This increase is reduced and may be substantially destroyed by deformation. Numerous attempts have been made to describe the increase of stiffness resulting from the introduction of fillers and relationships describing the dependence of the modulus on the concentration and particle shape of the filler have been developed. However, these do not take into account the softening which results from previous deformation and thus have limited applicability. Recently Blanchard and Parkinson have attempted to develop empirical relationships to describe the elastic properties in simple extension of reinforced rubber vulcanizates after they have been previously deformed. They started with the appropriate stress-strain relationships from the classical kinetic theory and introduced two curve-fitting parameters to describe stress-strain data obtained in conventional tensile tests on a Goodbrand machine. In this way they were able to fit the course of the stress-strain data obtained after previous extension at extensions less than those previously applied and to describe the dependence of the parameters on previous deformation. Unfortunately, the significance of the parameters is obscure.
Changes of Electrical Resistance of Rubbers Loaded with Carbon Black
Authors: Marshall D. G.
Published: February 2011

Many workers have studied the changes in resistivity that occur on deforming rubbers loaded with carbon black. This paper describes three types of experimental investigation that do not seem to have received detailed study previously, and also a theory that explains the results qualitatively in terms of variations of contact resistances between carbon black particles. Firstly, the changes of resistance of vulcanized natural rubber, Butyl rubber, Neoprene, and Thiokol FA loaded with carbon black have been studied during cyclic deformations. Secondly, the initial increase of resistance during stretching testpieces of vulcanized natural rubber containing several loadings of different carbon blacks has been investigated. Finally, the changes of resistance with time that occur after stretching and releasing samples of electrically conducting rubber have been studied. The ingredients and preparation of the compounds used in experiments discussed in this paper are listed in the Appendix. The testpieces used in the following experiments were approximately 0.7 cm. wide, 0.1 cm. thick, and 7.0 cm. long. Electrical contact was established by means of brass strips bonded by molding into the ends of the samples, so that the direction of current flow was along the length of the pieces, and in the same direction as the extensions.
Lignin as a Compounding Ingredient for Natural Rubber
Authors: Sagajllo I.
Published: February 2011

Important claims have been made in recent years regarding the capacity of lignin to reinforce natural and synthetic rubber. In 1949 Dawson reviewed the literature on the use of lignin in rubber and drew particular attention to the work of Keilen and Pollak who had shown that in certain circumstances lignin could be considered to rival EPC black in its ability to yield strong GR-S vulcanizates with high resistance to tear. Raff and his coworkers subsequently showed that the reinforcement of GR-S by lignin is enhanced if the lignin, before coprecipitation with the latex, is subjected to oxidation; other workers studied the application of lignin to the reinforcement of different elastomers, the influence of coprecipitation conditions on the properties of the product, and the problem of overcoming the delaying effect of lignin on vulcanization of lignin-natural rubber coprecipitates. Keilen and Pollak in their experiments incorporated lignin into rubber by coprecipitation at the latex stage, but they indicated that similar results could be obtained if lignin “in the gelled state” was added to rubber by milling. No reinforcement was observed however when lignin was added to rubber as a dry powder. Lignin is potentially an abundant and cheap material which according to the above claims should extend the range of useful compounds available to rubber manufacturers. The present paper describes work undertaken to gain firsthand knowledge of the technique of coprecipitating lignin with natural rubber from preserved latex, to learn something about the properties of natural rubber compounds prepared from lignin coprecipitates, and to study possible ways of incorporating lignin into rubber by means other than coprecipitation. It also records test results for masterbatches prepared by the Rubber Research Institute of Malaya from fresh latex on a pilot plant scale.
Carboxylic Rubbers from Scrap Vulcanized Rubber
Authors: Green Joseph , Sverdrup E. F.
Published: February 2011

Scrap vulcanized rubber has been used principally for the manufacture of reclaimed rubber, which exhibits properties inherent in the original polymers of the scrap. Little has been found in the literature on the utilization of scrap vulcanized rubber as a low-cost starting material for controlled polymer synthesis. In the present investigation scraps containing natural and Type S synthetic rubbers have been modified to produce chemically different polymers possessing properties not usually associated with the initial elastomers. The authors believe that reactions with vulcanized rubber are not usually the same as reactions with the raw polymers and in this work the physical means of accomplishing the reaction are different. In 1938 Bacon and Farmer reported that when masticated raw natural rubber and maleic anhydride were dissolved in a solvent and the solution was heated in the presence of benzoyl peroxide, the ingredients reacted, yielding a variety of tough, fibrous, or resinous products. When vulcanized natural and Type S synthetic rubber scraps were reclaimed in a Reclaimator (a specially designed extruder type plasticator, made by the U. S. Rubber Reclaiming Co., Inc.) in the presence of a critical concentration of certain activated unsaturated compounds, a reaction occurred between the unsaturated compound and the scrap vulcanized rubber. With maleic anhydride, the resulting product was a carboxylated and replasticized rubber. This elastomer exhibited vulcanizing versatility via the carboxyl groups—i.e., curing with bivalent metallic oxides, diamines, glycols, epoxy resins, and diisocyanates. The polarity imparted by the carboxyl groups and the degree of crosslinking of the polymer appear responsible for its oil resistance, a property not normally present in a tire reclaim. The blocking of the double bonds, either by reaction at the double bond or by steric hindrance, added to the good aging properties anticipated with nonsulfur vulcanizates.
Application of Paper Chromatography to the Identification of Accelerators and Antioxidants
Authors: Zijp J. W. H.
Published: February 2011

Various difficulties in the identification of accelerators and antioxidants in rubber compounds are reviewed. A detailed procedure for the detection of four guanidine derivatives by paper chromatography is mentioned. The identification of diphenyl thiourea and diorthotolyl thiourea is also described. A detailed procedure is given for the paper-chromatographic separation and identification of some mercapto-substituted heterocyclic compounds. The detection of these accelerators in rubber mixes and vulcanizates is also described. A detailed procedure is given for paper Chromatographic separation and identification of dithiocarbamates, which are used as ultra-accelerators in the rubber industry. These dithiocarbamates decompose in acid medium into secondary amines. The salts of these amines are better soluble in water than the dithiocarbamates, and are therefore more suitable for a paper-chromatographic separation. A method for the simultaneous detection of dithiocarbamates and thiuram sulfides is also described. The paper-chromatographic separation and identification of various antioxidants is described. Because only few antioxidants can be separated by paper chromatography after coupling with diazotized arylaminosulfonic acids, it is preferable to separate these compounds, which are generally insoluble in water, by means of acetylated filter paper. The identification of antioxidants using acetylated filter paper is described. A detailed procedure is given for the identification of accelerators and antioxidants in rubber mixes and vulcanizates of unknown composition.
Analytical Methods for Calculating Temperatures inside Rubber Articles during Vulcanization
Authors: Fogel V. O.
Published: February 2011

Heating conditions for the vulcanization of rubber articles have been chosen in a purely experimental way up to the present time. Thus, in one tire plant, research on the question of the most efficient heating conditions for tire vulcanization has consisted of making dozens of experiments on the several variables of heat conductors, and then using the experimental temperature curves for further development. However, such experiments under industrial conditions not only require considerable time and material, but yield results which inevitably deviate from the true heating conditions in many cases. These deviations are due to fluctuations in the steam pressure and water temperature in the course of vulcanization, nonhomogeneity of material in the group of rubber articles being tested, etc. All these sources of error confuse the results of comparative experiments to a large extent, often making it impossible to reach any general conclusions. Undoubtedly the most accurate method of determining the ideal heating conditions for vulcanization is a combination of the calculation and experimental methods. In the vulcanization of rubber articles, as in some other branches of industry, heating conditions can be chosen satisfactorily through a preliminary calculation of the temperatures inside the articles, i.e., by a theoretical projection of the heating conditions, followed by a final experimental verification of the calculated results.
Infrared Spectroscopic Analysis of Elastomers
Authors: Davison W. H. T. , Bates G. R.
Published: February 2011

Infrared absorption spectroscopy is the most generally applicable technique available for the analysis of elastomers and other polymers encountered in the rubber industry. The emphasis of this paper is on the general identification and estimation of a wide range of elastomers, rather than the accurate quantitative analysis of particular copolymers and mixtures. The theoretical basis of spectra, particularly of polymers, is described. The additivity of absorbances is the basis of quantitative analyses, for which the procedures are outlined. Although theoretically some interaction between repeating units is to be expected, most repeating units have the same spectra whether in homopolymers or copolymers. Experimental techniques are described for preparing samples for spectroscopic examination from both uncured and cured materials. The latter, particularly when reinforced with carbon black, often give difficulty since they transmit insufficient energy for direct examination. As an alternative to solution or pyrolysis, a reflecting microscope may be used to increase the amount of energy available for measurement of the spectrum. Spectra of a large number of homopolymers, copolymers, and mixtures are reported from 650 to 3600 cm.−1, mostly in simplified line form. Polymers covered include polydienes, polyvinyl and tsopropenyl compounds (including polyketones and acrylates), polyesters, polyurethans, modified polyethylenes, and silicones. A summary of absorptions characteristic of particular polymer structures is given in the form of a correlation chart. The limitations of the technique are discussed, and probable future developments are suggested, i.e., extension of the spectral range below 650 cm.−1, improved techniques of sample preparation, and combinations of spectroscopy with chemical procedures such as pyrolysis.
Shear Dependence of Viscosity of Natural Rubber Solutions
Authors: Golub Morton A.
Published: February 2011

In an earlier paper viscosity measurements on dilute Alfin polyisoprene solutions at quite low shear rates were reported. It was shown that the limiting slope of the intrinsic viscosity vs. rate of shear plot at low shear rates, (Δ[η]/ΔD)D→0, is proportional to the square of the zero shear intrinsic viscosity [η]02. This relationship suggested the possibility of using the slope of the (Δ[η]/ΔD)D→0 vs. [η]02 plot as a molecular weight-independent parameter expressing the magnitude of the shear dependence of intrinsic viscosity, and thus as a possible means for studying polymer microstructure. It was thought that polymers having different structures would give rise to linear plots of the latter type, but with different slopes. To test this view, it was deemed desirable to extend viscosity measurements to another polyisoprene system, namely, natural rubber. This note describes the results obtained from viscosity measurements on Hevea fractions, and shows the comparative shear effects for both the natural as and the predominantly trans Alfin polyisoprenes.
The Role of Diffusion of Polymer Chains in the Mechanism of Adhesion and Autohesion of Rubbers
Authors: Deryagin B. V. , Zherebkov S. K. , Medvedeva A. M.
Published: February 2011

1. The researches so far published on the autohesion of polymers do not make it possible to isolate the influence of the mechanical properties of rubbers, which determine the true area of contact, from the influence of polymer chain diffusion. 2. Studies of the autohesion of thin films of rubber applied by the drain-off method to quartz threads, in relation to the film thickness and contact time, show that for films less than 3.10−5 cm. thick the adhesion force is small and varies very little with contact time. This proves, on the one hand, that in this instance the contact area is small (which is obvious) and does not increase with time, and on the other hand, that diffusion processes play no part in the autohesion of films of this thickness. 3. The effects which depend on mechanical properties and on the specific interaction (per unit area of true contact) between specimens may be separated if the measured values of adhesion between all possible combinations of pairs of rubbers are compared both with their compatibilities, and with their autohesion. 4. The measurements of the adhesional shearing strength of combinations of different pairs of polymers, carried out for this purpose, showed that the results for Butyl rubber may be interpreted on the assumption that diffusion processes do not play any appreciable role and that the adhesion strength is determined both by the true contact area, which depends on the mechanical properties of the corresponding polymer specimens, and also by the influence of forces associated with the electric double layer. 5. For the other rubbers the results may be interpreted only on the assumption that diffusion processes play a significant part. For similar polarities, T12/T11>1 and for dissimilar polarities, T12/T11<1. 6. General conclusion : autohesion and mutual adhesion of rubbers is determined both by mechanical properties, which determine the true contact area, and by diffusional properties. The latter are by no means always decisive. The electric double layer also probably influences the adhesional shearing strength in some instances. It is even more likely to play a role in some cases in measurements of the work of separation of two layers.
The Tensile Strength of Elastomers
Authors: Taylor G. R. , Darin S. R.
Published: February 2011

The theory of strength proposed above appears to describe satisfactorily the effect of crosslinking on the strength of amorphous elastomers, and to apply semiquantitatively to crystallizable elastomers. Further work, involving the effect of primary molecular weight, constitution, swelling, and additives is required to substantiate the general applicability of the theory. The mechanism of rupture, in particular, is poorly understood.
The Mechanism of Accelerator Action
Authors: Krebs Heinz
Published: February 2011

In the year 1839, Goodyear discovered that, on treatment with sulfur at elevated temperatures, natural rubber loses its plasticity and becomes elastic. Around the time of World War I, it was discovered that the reaction of the sulfur with the unsaturated rubber hydrocarbons could be promoted by the action of so-called vulcanization accelerators. The reaction then takes place not only faster and at lower temperatures but, in addition, one also needs less sulfur and the vulcanizates acquire considerably better technical properties. Accordingly a tremendous number of compounds have been examined as accelerators of vulcanization and much effort has been applied to develop accelerators with the most satisfactory properties. Today, accelerators are known which permit vulcanization at room temperature. In the past, the mechanism of accelerator action has been studied mostly with the methods of organic and physical chemistry. In the following, an attempt will be made to consider the problem from the viewpoint of the inorganic chemist. One can attempt to interpret the catalysis from two points of view. Either the reactivity of the unsaturated natural rubber hydrocarbon is enhanced, or the sulfur will be converted into a more reactive form. Twiss concluded from his investigations that the latter possibility is the more likely. Subsequently, this assumption has been supported by further observations. In particular, the discovery of Peachey pointed in this direction, since natural rubber is vulcanizable at room temperature if it is treated successively with hydrogen sulfide and sulfur dioxide gases. The sulfur which is formed by this reaction is in the nascent state and is very reactive.
Evaluating High Polymer Cable Insulations on the Basis of Loss Factor Profile
Authors: Hahne K. H.
Published: February 2011

If we desire to gage the difficulties encountered in judging and testing polymeric insulation, we should remember that, generally speaking, the poorer the electric characteristics of these materials, the better will be their mechanical and thermal qualities. Perhaps this has not been so noticeable in the case of the classic insulating materials, such as rubber and fibers. However, reduction in insulating resistance is the deciding factor with soft PVC where, as is well known, addition of softener will bring about a corresponding ability to withstand cold and bending. It is therefore necessary in this case to select the type and content of softener so that adequate thermal and mechanical characteristics are attained without loss of electric dependability. Also with other polymers, the additives used to improve mechanical and thermal qualities are unfavorable electrically. The test methods used in evaluating cable insulations must make possible the stipulation of optimum compounds. Therefore numerous individual tests must be made, so as to arrive at reliable conclusions in every respect. Table I gives a tabulation of the tests prescribed in Germany for cables with plastic insulation and cover. If special requirements must be met such as, for instance, resistance to chemicals or to ozone, additional tests may be prescribed. Test requirements in other countries are even more comprehensive than in Germany. Such extensive tests render more difficult any evaluation of polymeric cable insulations. They require much time and effort, especially when series of tests are involved in the case of newly developed materials. Inasmuch as each test brings out only a small part of the pertinent characteristics of the material and none can be ignored, it follows that the overall evaluation becomes difficult. It should be in order, therefore, to ask whether it is possible, by means of one single measuring method, to obtain at least a comparative survey of all determining characteristics of such high polymer insulating materials. Potthoff has mentioned, among other things, that too little use is made of the fact that carrying out simple and nondestructive measurements of the frequency and temperature dependent dielectric loss factor permits a deep insight into the characteristics of insulating materials. Actually, this measurement affords the means of grasping the most interesting influences involved with the least effort.
Frictional Temperature Rises on Rubber
Authors: Schallamach A.
Published: February 2011

Frictional temperature rises and frictional forces on rubber at velocities up to about 400 cm/sec and under various normal loads have been determined by employing a thermojunction as slider. In the experimental velocity range, the frictional temperature rises increase approximately proportional to the square root of the sliding velocity. The finite heat conductivity of the slider has been found not at affect the results materially. The temperature rises when plotted against the dissipated frictional energy lie on closely grouped curves. Coefficients of friction as function of load and velocity are given.
The Chemistry of the Active Molecules Formed in the Mechanical Degradation of Polymers
Authors: Berlin A. A.
Published: February 2011

At the present time there is a multitude of data indicating that when polystyrene, natural rubber, polyvinyl acetate, cellulose, starch, proteins and other high molecular weight compounds are mechanically ground up, a degradation of the polymeric chains is observed. The mechanical scission of macromolecules during grinding in a colloid or ball mill, or when they are broken down on mill rolls, proceeds most rapidly at temperatures below the range of the viscous-fluid state, since under these conditions the forces of intermolecular interaction are considerably greater than the strength of the covalent bond. However, the mechanical destruction of macromolecules is also possible through certain mechanical effects acting on solutions of polymers. Thus, for instance, the force of friction generated in the flow of a 0.05% solution of polystyrene (Mcp=6×105) in tetralin through a platinum capillary is due to the scission of macromolecules, which brings about a 30% decrease in the specific viscosity. The significant gradients in the rate and in the forces of friction and cavitation developed in polymer solution through the action of ultrasonic waves with frequencies of the order of 200–300 kilocycles/sec. are due to the mechanical scission of macromolecules of polystyrene, rubber, polyvinyl acetate, cellulose and a number of other high molecular weight compounds.
Quantitative Determination of Antioxidants after Chromatographic Separation on Completely Acetylated Filter Paper. I. Determination of Phenyl-1-Naphthylamine and of Phenyl-2-Naphthylamine
Authors: Zijp J. W. H.
Published: February 2011

In this paper a general method for the quantitative determination of antioxidants is described. After isolation from the rubber compound the antioxidants are separated by partition chromatography, using completely acetylated Whatman paper No. 1. A detailed procedure is given for the quantitative determination of phenyl-1-naphthylamine and of phenyl-2-naphthylamine. These antioxidants are coupled with diazotized sulfanilic acid and determined colorimetrically.
A Spectrophotometric Method for Residual Styrene in SBR Latex
Authors: Hilton C. L.
Published: February 2011

The spectrophotometric method of analysis for residual styrene monomer in SBR latex has several advantages. No standardization of reagents is required. The method is rapid, accurate, and precise. The direct ultraviolet absorption method is applicable only in absence of interferences. The alternate distillation-ultraviolet method is applicable even in the presence of most interferences.
The Reactions of Amines and Sulfur with Olefins. II. The Reaction of Diethlamine and Sulfur with Trialkylethylenes
Authors: Moore C. G. , Saville R. W.
Published: February 2011

The reaction of diethyl and sulfur with trialkylethylenes, R⋅CMe:CHR′, at 140° C yields tert.-alkanethiols and di-tert.-alkyl disulfides as major products, with only minor amounts of the corresponding polysulfides and sulfurated polymers containing three or more olefin units linked by sulfur bridges. The degree of sulfuration is much lower than with the corresponding sym-dialkylethylene, cyclohexene, and monosulfide formation is negligible. Both observations indicate that steric influences govern the nature and the yield of the sulfurated products.
The Reactions of Amines and Sulfur with Olefins. III. The Reaction of Diethylamine and Sulfur with 1,5-Diolefins
Authors: Glazebrook R. W. , Saville R. W.
Published: February 2011

2,6-Dimethylocta-2,6-diene (I) with the sulfur-diethylamine combination at 140° C yields mainly saturated cross-linked sulfides, R⋅Sx⋅R, where R contains thiacyclopentane groups adjacent to the sulfide cross-link (x=1 or 2), together with the cyclic sulfides (II) and (VI), (VII), and (VIII), formed by the intramolecular sulfuration of (I). Infrared spectroscopic evidence suggests the occurrence of similar cyclic structures in squalene polysulfide and in ebonite.