bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adhesion of High Polymers. VI. The Effect of Molecular Weight of NBR Copolymers of Various Polarities on Adhesion to Polar and Nonpolar Materials
Authors: Vakula V. L. , Yun-tsui He , Gul V. E. , Voyutskiĭ S. S. 
Published: February 2011

Abstract
1. The adhesion of fractions of NBR of varying polarity to a polyamide has been investigated at room and elevated contact temperatures. 2. The adhesion of each copolymer investigated has been shown to fall with the increase of molecular weight of fractions up to a certain limit (300,000– 350,000). Above this weight the magnitude of adhesion remains practically constant. 3. The adhesion of all fractions tested increases with increasing contact temperature, attaining the cohesive strength of the respective fraction. The lower the value of molecular weight, the lower is this temperature limit. 4. It was shown that at room contact temperature adhesion of nitrile co-polymers to polyamide depends only slightly on the polarity of the adhesive. The lower the polarity of the copolymers, the more the heating of the bonded specimens increases the adhesion strength. The lower adhesion of the polar nitrile copolymers to the highly polar polyamide might be explained by a purely kinetic factor, that is, the lack of flexibility of macromolecules of such polymers and the greater number of intermolecular links, which makes diffusion difficult. 5. It has been established that for bonding at room temperature the adhesion of unfractionated commercial nitrile rubbers to polyamide is determined primarily by the polydispersity of the rubber rather than by its polarity. The adhesion of copolymers at elevated temperatures depends to a high degree on their polarity. 6. It was found that the adhesion of fractions of NBR to nonpolar substrates (PIB) is very low and is independent of polarity and molecular weight, and of temperature of thermal treatment. Smaller values of adhesion in this case are determined by noncompatability of polar adhesive with nonpolar substrates. 7. The results of the work were discussed in the light of the diffusion theory of adhesion.
Vulcanization of Elastomers. 30. Kinetics of the Decrease of Sulfur Concentration during Vulcanization
Authors: Scheele Walter , Cherubim Martin 
Published: February 2011

Abstract
The present discussion deals with the explanation and critical analysis of the kinetics of the decrease in concentration of sulfur in accelerated and unaccelerated vulcanizations of natural and synthetic rubber. A marked distinction is made between the time law and the dependence on concentration of the rate of decrease of sulfur, since there is lack of agreement between them, both in accelerated and unaccelerated vulcanizations, which indicates the complex nature of vulcanization. In unaccelerated vulcanization, the sulfur concentration drops, at all temperatures and independent of the concentration, according to a time law with exponent n=0.6. On the other hand, the dependence on concentration of the initial rate of sulfur decrease proceeds according to a first order reaction. These relations make it seem probable that sulfur decrease involves a process which is catalyzed by reaction products. In accelerated vulcanization, the reduction of concentration of sulfur also is expressed by a time law with the exponent n&lt;1, and this too is independent of temperature and concentration of reactants (sulfur and accelerator). However, the concentration dependence of the rate of sulfur decrease cannot be expressed by a power law, so that we find no order of reaction in the usual sense. We attempt to explain the characteristic trend of the initial rate of sulfur decrease with sulfur concentration at constant accelerator content, or with accelerator concentration at constant sulfur content, by assuming that the vulcanization takes place through intermediate compounds. The pertinent theoretical conceptions are disclosed and critically examined and the attempt is made to show the extent to which they may be brought into accord with the experimental data.
Relation of Structure to Properties in Polyurethanes. Crosslinking Studies
Authors: Cluff E. F. , Gladding E. K. 
Published: February 2011

Abstract
The present work was undertaken to assess the effect of crosslink structure on the properties of the elastic network derived from a linear polyetherurethane elastomer. In order to study this effect, a polyetherurethane was synthesized which contained two types of reactive sites suitable for establishing crosslinks— pendant hydroxyl groups for reaction with diisocyanate curatives and pendant double bonds for vulcanization with sulfur. Incorporation of both types of curing sites within the same linear polymer served to hold constant variables which might otherwise influence vulcanizate properties. Thus, the elastic networks formed by both curing systems were produced from the same polymer, and such factors as polymer molecular weight and molecular weight distribution, interchain forces and cure site distribution remained constant. Furthermore, the curing sites have been placed on pendant groups, well removed from the main polymer chain, in order to avoid degradation of the polymer by side reactions which may accompany sulfur vulcanization. It is recognized that common elastomers with internal unsaturation, such as SBR and natural rubber, can be crosslinked by more than one method (e.g., with sulfur, peroxides, or high energy radiation), but the extent and nature of side reactions which may occur is not known with certainty. There are possibilities of polymer degradation reactions with all of these curing systems, and the occurrence of such degradation reactions would cloud any conclusions concerning the relation between crosslink structure and vulcanizate properties.
The Vulcanization of Neoprene with N,N′-Dinitroso-p-Phenylene-Bis(Hydroxylamine) Salts, a New Class of Curing Agents
Authors: Martel Rock F. , Smith David E. 
Published: February 2011

Abstract
The reaction of nitric oxide with p-benzoquinonedioxime in the presence of sodium methoxide to form disodio-N,N′-dinitroso-p-phenylene-bis (hydroxylamine) (I) in 96% yield has recently been reported. When a water solution of I is treated with soluble metallic salts of Zn++, Ca++, Mg++, etc., the corresponding N,N′-dinitroso-p-phenylene-bis(hydroxylamine) salt is obtained. Stable organic salts can be isolated when the bases piperidine or aniline are employed in place of sodium methoxide. Adducts have also been obtained (see PDF for diagram) using piperazine and ethylenethiourea, but the structures of these materials have not been clarified.
Modern Role of the Electron Microscope in Rubber Research
Authors: Ladd W. A. , Ladd M. W. 
Published: February 2011

Abstract
Until recently, the main role of the electron microscope in rubber research was the determination of particle size and shape of reinforcing pigments and fillers. The electron microscope proved its value in its first industrial problem in 1940 when it showed the particle size of Micronex to be 28 mµ. In 1942 it established the correlation between particle size of carbon and rubber properties. The next contribution was the establishment of reticulate chain structure, in 1945, using stereo-photomicrography. The electron microscope led the way to the carbon gel concept when carbons producing different road wear results were shown to have equal particle size and structure. Micrographs of carbon gel were published in 1951. Studies of rubber latexes, various pigments and fillers were also applications of the electron microscope in which the determination of particle size and shape was involved. Today, improvements in resolution, development of new techniques and accessory equipment have greatly expanded the application of the electron microscope. This paper is concerned mainly with describing these new developments ; first, as a help to electron microscopists in the rubber field; second, to illustrate what can be done with the electron microscope, so that research and production men can recognize possible applications of this discerning tool to the solution of their problems. Electron microscopes have come a long way in the short 20-year period. Figure 1 shows the microscope used in our laboratories. This instrument is currently resolving detail as fine as 10 A or 1 mµ in routine daily operation. Its design makes possible the development of special holders and thereby increases its value as a research tool. Another piece of equipment that is as important in microscope research as the electron microscope itself is the evaporating unit shown in Figure 2. This is used for shadowing and forming replication films under vacuum, thus making possible studies of rubber surfaces and surfaces of pigments and other rubber ingredients. In shadowing, detail is made visible by coating the specimen with metal evaporated at an angle from the tungsten basket at A. Carbon can be evaporated by the arc at B, forming a replicating film or mold of the specimen. This will be discussed under “preparation”. Today, the proper preparation of specimens is the most important step in successful microscopy. The various preparations used are as follows.
Mechanochemical Reactions Leading to Reinforcement. II. Natural Rubber and Phenolic Resins
Authors: Ceresa R. J. 
Published: February 2011

Abstract
The reaction of polyfunctional metallic salts with natural rubber during mastication has been extended to gelation by phenolic resins. High gel contents are achieved by mastication with 1 to 2 per cent of resin in the absence of oxygen. By using polyphenols and phenol alcohols it has been shown that an average of at least three functional groups, —OH or —CH2OH, per molecule are required to achieve gelation. The presence of the gel network in the unvulcanized rubber gives an improvement in processing characteristics.
The Cepar (Cure, Extrusion, Plasticity, and Recovery) Apparatus. An Instrument for Measuring Processing Characteristics of Rubber Mixes
Authors: Conant F. S. , Claxton W. E. 
Published: February 2011

Abstract
The principal advantages of the Cepar apparatus over commercially available plastometers for making processability tests include the following: small sample size; rapidity of testing; the wide range of orifice sizes, driving pressures (loads), and temperatures readily available; versatile controls for incremental extrusions at timed intervals (for studying curing effects) and/or for continuous extrusions; and the feasibility of using this apparatus to evaluate flow characteristics of stiff or “boardy” compounds or even of cured compounds normally considered out of range for conventional tests. The apparatus, in its normal application, will yield values for instantaneous orifice deflection (elastic stiffness factor), the continued rate of extrusion, and hot recovery upon load removal. Tests can also be made upon the removed sample for such things as orifice swell, extruded length, etc. In addition to the applications cited in this paper, the apparatus has been used to study the problem of knitting of factory stocks, as a control instrument to select the best temperature for extrusion processes, and as an evaluation instrument for various compounding studies. It has been used also as an instrument to evaluate the degree of heat softening (up to temperatures of 600° F) occurring in high-temperature heat-resistant stocks, in studies correlating factory extruded tread center gage with Cepar swell measurements, and in tests for degree of polymerization in SBR produced by the continuous process.
Antioxidant Efficiency of p-Phenylenediamines in Natural Rubber Vulcanizates
Authors: Lorenz O. , Parks C. R. 
Published: February 2011

Abstract
The consumption of various p-phenylenediamines during the oxidation of natural rubber vulcanizates has been investigated in the temperature range of 80–120° C. Oxygen absorption was used to follow the oxidation. Diaryl-p-phenylenediamines were consumed mainly in a termination reaction during the constant rate region of the oxygen absorption, where five to six molecules of oxygen were absorbed per molecule of diamine consumed. The constant rate stage of the oxygen uptake was found to be about twice as long as the time of the constant rate consumption of the diamine, indicating that the reaction product also possessed antioxidant activity. The effect of the nature of the curing system, carbon black, structure of the diamine, initial concentration of the diamine, and temperature of oxidation were studied. Dialkyl- and alkyl-aryl-p-phenylenediamines were consumed predominantly by a direct, relatively fast reaction with oxygen, the rate being dependent on the structure of the diamine and also on the nature of the curing system. The oxidation products formed exhibited antioxidant activity, those of N-isopropyl-N′-phenyl-p-phenylenediamine being particularly effective.
Influence of Vulcanization on Adhesion to Non-Vulcanizing Polymers
Authors: Raevskiĭ V. G. , Voyutskiĭ S. S. 
Published: February 2011

Abstract
According to contemporary ideas the mechanisms of adhesion and co-vulcanization of rubbers have much in common. The phenomenon of co-vulcanization, like that of adhesion of polymers, includes the diffusion of macromolecules and of segments of them, which is particularly intensive in the initial period of vulcanization, when the crosslinks have not yet formed. The difference between covulcanization and adhesion lies solely in the fact that the process of interpenetration of the molecular chains in the former case is sooner or later broken off by the vulcanization process being superimposed upon it, securing the macromolecules or portions of them by strong chemical bonds. This leads to the formation of an adhesion joint considerably superior in strength to a joint in which the molecules diffusing through are attached only by weak intermolecular bonds. It is important to ascertain what is the influence of the vulcanization of elastomers upon their adhesion to polymers not capable of forming chemical bonds with them. This case is of immense practical importance, since unvulcanized rubbers are very often used in combination with vegetable and synthetic fibers which are not capable of vulcanizing. As adhesives we selected elastomers of varying molecular structure, polarity and degree of molecular mobility: butadiene-acrylonitrile rubber (SKN-26), butadiene-styrene rubber (SKS-30A), butadiene-styrene oil-extended rubber (SKS-30ARM-15) and butyl rubber. Using these rubbers we prepared stocks both containing and not containing vulcanizing groups (in the latter case the components of the vulcanizing groups were replaced by an equal quantity of inert filler—whiting). The amount of vulcanizing group was set at the optimum for each rubber. The substrates used were films containing no plasticizers—cellophane (cellulose hydrate) and Perfol' PK-4 (polycaprolactam). The adhesive was applied to the substrate by coating on a calender at the optimum conditions for each elastomer. The specimens produced in this way were plied up and subjected to vulcanization. Vulcanization was carried out in a Berstorff apparatus for continuous vulcanization at 143° C and a specific pressure ≈ 0.85 kg/sq cm. The time of cure was varied between 0 and 88 min.
Stress as a Reduced Variable: Stress Relaxation of SBR Rubber at Large Strains
Authors: Landel Robert F. , Stedry Paul J. 
Published: February 2011

Abstract
Stress relaxation measurements on SBR were carried out at temperatures from −5 to +60° C and at initial strains of up to 550%. The effects of strain and time were found to be factorable, so that the isochronal stress-strain curve may be written as a modified Hooke's law with a time-dependent modulus: S=E(t)eƒ(α), where ƒ(α) is an appropriate function of the strain. By defining a strain-reduced stress S*=S/∫(α), i.e., a strain-reduced modulus E*(t)=E(t)ƒ(α), it can be shown that Ferry's method of reduced variables may be extended to large deformations. An appropriate strain function was obtained from the empirical Martin-Roth-Stiehler equation as ƒ(α)=α−2 exp A(α−α−1) with A=0.40. Although it cannot yet be certain that A is truly a constant and the same for all elastomers, this equation has the advantage of being valid right out to the breaking strain.
The Protection of Transparent Vulcanizates against Aging in Sunlight
Authors: Dunn J. R. , Fogg S. G. 
Published: February 2011

Abstract
Care has to he taken in choosing antioxidants for use in transparent natural rubber vulcanizates since some amines commonly employed as protective agents against thermal degradation photosensitize aging in ultraviolet (uv) light. Further studies using the technique of stress relaxation, undertaken in order to find the most satisfactory type of antioxidant for protection against sunlight aging, have shown that, with additives introduced into extracted samples of peroxide vulcanizate by swelling from ethyl acetate solution, the best results were obtained using a mixture of a substituted bis-phenol and an absorber of uv light. Hitherto, nickel isopropylxanthate (NPX) has been regarded as the most potent protective agent against light; however, the rate of degradation in the presence of NPX was unchanged by the addition of uv absorber and the mixture of bis-phenol and absorber was markedly more effective. Furthermore, the nickel salt is green, whereas the bis-phenols are relatively nonstaining. The work described here is an evaluation of vulcanizates in which the phenol and absorber have been incorporated before cure. The phenol employed was 2,2′-methylene-bis(4-methyl-6-tert-butyl phenol) (Antioxidant 2246 of the American Cyanamid Co.) and the absorber was Tinuvin P (a product of undisclosed formula marketed by Geigy Ltd.), chosen since it protected better in the absence of antioxidant than two other commercial absorbers. Two types of transparent vulcanizate were examined, one being an accelerated sulfur cure and the other a dicumyl peroxide cure. The recipes were as follows:
Internal Rupture of Bonded Rubber Cylinders in Tension
Authors: Gent A. N. , Lindley P. B. 
Published: February 2011

Abstract
An unusual rupture process is described. It consists of the sudden appearance of internal cracks in bonded rubber cylinders at a well-defined and comparatively small tensile load. The cracks occur in all the vulcanizates examined, and in particularly weak rubbers are found to cause failure. Their appearance may also lead to marked changes in the load-deflection relationship. A theoretical treatment is presented on the basis of a proposed criterion for crack formation. It is assumed that they form when the negative hydrostatic pressure component of the applied stress reaches a critical value. It is shown by means of the theory of large elastic deformations that a critical value of the negative pressure exists at which any cavity in the rubber will burst, and the calculated value is shown to be in satisfactory agreement with experiment. Moreover, the theory successfully predicts the observed dependence of the cracking stress on the Young's modulus of the rubber, its virtual independence of the rubber strength and extensibility, and the general form of the observed variation of cracking stress and crack disposition with the thickness of the testpiece.
Structure of Filled NBR Vulcanizates by the Stretching Method (Mullins Effect)
Authors: Shvetsov V. A. , Novikov A. S. , Pisarenko A. P. 
Published: February 2011

Abstract
1. It is possible to use the equation of Blanchard for butadiene-nitrile rubbers with channel black and aluminum hydroxide. 2. It is shown that vulcanizates of butadiene-nitrile rubbers with aluminum hydroxide are subjected to more marked softening on stretching in comparison with vulcanizates containing channel black. 3. Ideas are put forward relating to the ratio of primary and secondary linkages in vulcanizates on the basis of SKN-26 with channel gas black and aluminum hydroxide.
Swelling Effect of Liquids on NBR (Nitrile Rubber)
Authors: Starmer Philip H. , Lufter Carl H. 
Published: February 2011

Abstract
Immersion tests in various polar and nonpolar solvents have been undertaken with a range of butadiene-acrylonitrile copolymers. For a particular liquid, it would appear that the volume change can be related to the acrylonitrile content of the rubber' by a Gaussian type curve which is described by three constants α, β and γ. The constant a corresponds to the nitrile content of the rubber which has maximum swelling in the liquid and would appear to be related in some way to the dielectric constant of that liquid. The constants β and γ control the value of maximum swelling. Investigation into the nature of the three constants tends to suggest that α and β are governed by molecular attraction due to the “dispersion forces”. On the other hand, γ seems to be connected with the electrostatic forces of attraction and is probably not a constant over the full range of nitrile content, but should be replaced by an expression governed by two other constants. Therefore, to describe the solvent power of a nonpolar solvent, two parameters are needed while four are required for a polar solvent.
Branching in Butadiene Rubber
Authors: Poddubnyi˘ I. Ya , Erenburg E. G. 
Published: February 2011

Abstract
1. By studying the intrinsic viscosities of fractions in an “ideal” solvent, the degree of branching of potassium-butadiene polymers was determined. It was found that a specimen obtained at 0° was already markedly branched; increasing the temperature of polymerization (to 40–60°) led to the synthesis of highly-branched polymers, containing one branching site per several hundred monomer units. 2. On the basis of quantitative data on the branching of the polymers studied, the difference between the activation energies of the chain growth and branching reactions was calculated for the polymerization of butadiene in the presence of potassium. At the same time it was found that the increase in the degree of branching of the macromolecules with the increase in temperature in the gas phase polymerization of butadiene was determined not only by the mentioned difference in the activation energies, but also to a considerable extent by the temperature dependence of the solubility of the monomer in the polymer. 3. It was shown that for the investigated system, fractionation of the branched polymers by means of fractional precipitation from dilute solutions yields fractions which differ in molecular weight but not in the degree of branching. 4. It is shown that the relation between the intrinsic viscosities of polymers of a given molecular weight but of a different degree of branching, remains constant in the switch from a good solvent to an ideal solvent.
Some Correlations in the Second Order Transition of Rubbers
Authors: Bartenev G. M. , Gorbatkina Yu A. 
Published: February 2011

Abstract
1. The thermal shrinkage was measured for three rubbers (SKS-30, SKN-18, SKN-40) in the temperature interval −180 to +50° at rates of cooling of 0.3 to 30°/minute. 2. The dependence of the glass temperature on the rate of cooling approximately obeys Formula (1), for which the constants C1 and C2 were determined, whereupon C2=0.03 C1, regardless of the type of rubber. 3. The activation energy of the glassing process for the rubbers studied, as indeed for other amorphous substances, is proportional to the glass temperature of the substance. 4. The width of the temperature interval of the glass region and the coefficient of expansion beyond the limits of the glass region are practically independent of the rate of cooling. 5. The greater the rate of cooling, the greater the change of length of the sample in the glass region and the higher on the temperature scale the same region is located.