bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reaction of Elemental Sulfur and Mercaptobenzothiazole
Authors: Blokh G. A. , Golubkova E. A. , Miklukhin G. P. 
Published: February 2011

Abstract
One of the most important problems in the field of the physics and chemistry of rubber is that of vulcanization. Until now no single theory has been established, which elucidates the complex physico-chemical changes which occur during this process. Still more obscure has been the mechanism of the action of vulcanization accelerators, which, as is well known, not only reduce the time and the temperature of vulcanization, but also influence the physico-mechanical and chemical properties of the rubber. Most investigators have assumed that in the acceleration process a reaction with sulfur converts it to an active form which is capable of bringing about vulcanization at a lower temperature and at a greater rate, than with ordinary elemental sulfur in the absence of an accelerator. This point of view is based on the experimental fact that the vulcanization of rubber by sulfur dioxide and hydrogen sulfide, for example, which form sulfur in the nascent condition, proceeds rapidly even at room temperature. Investigators have also assumed that in the vulcanization process activation of sulfur in the presence of accelerators may occur by different mechanisms. It is possible that the accelerator, reacting with elemental sulfur, forms unstable intermediate compounds, which decompose with liberation of sulfur in an active form. The latter reacts with rubber, and the regenerated accelerator reacts again with elemental sulfur, etc. However, a different process is possible for the activation of elemental sulfur. By this second mechanism the unstable combination of accelerator and sulfur reacts directly with rubber without the formation of active sulfur. Both these mechanisms necessarily assume the formation of intermediate unstable combinations of the accelerator with sulfur. However, direct, experimentally-based demonstrations of such an interaction are lacking in the literature. There exist only theoretical hypotheses concerning the nature of the possible intermediate combination of the accelerator with sulfur. According to Ostromislensky's concepts, further developed by Bedford, such an intermediate compound has the character of a polysulfide. According to Bruni and Romani, this intermediate compound is a disulfide. As is well known, the disulfide theory was placed in doubt by Zaide and Petrov on the basis of data from the vulcanization of rubber in the presence of benzothiazolyl disulfide.
The Structure of Hevea Latex and Its Viscosity. II
Authors: Verhaar G. 
Published: February 2011

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
(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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.