bluuebunny/crossref_metadata_2025 huggingface dataset:
The Mechanochemical Modification of High Polymers
Authors: Ceresa R. J.
Published: February 2011

Degradation of natural rubber during mastication has been shown to proceed via two alternative mechanisms, oxidative scission at high temperatures and mechanical scission at lower temperatures. The low temperature process, cold mastication, has received the greater attention. The energy supplied to the extended rubber chains during mechanical deformation is sufficient to cause homolytic scission into polymeric free radicals. The degradation of high polymers by a rupture process via mechanical scission has been shown to occur during the cold mastication of synthetic elastomers and during the mechanical working of high molecular weight vinyl and acrylic polymers in the visco-elastic state. The application of shearing forces to certain polymers in the brittle glass state has provided evidence for both homolytic scission into polymeric free radicals and heterolytic scission into polymeric ions. Polymeric radicals, produced by mechanical chain scission, have been used as initiators of vinyl polymerization to give block copolymers of an essentially linear character. Thus the block copolymerizations of methyl methacrylate, styrene, vinyl acetate, acrylonitrile, and ethyl acrylate have been initiated by mechanically shearing natural rubber, polymethyl methacrylate, polystyrene, polyvinyl acetate, polyethylene, polyvinyl chloride and polyvinyl formal during the process of extrusion of the polymer plasticized to a viscoelastic state with the monomer. Many other polymer-monomer systems have yielded block copolymers by cold mastication. Cold mastication of elastomer blends, such as natural rubber and neoprene, also leads to block copolymer formation by both combinative and hydrogen abstractive processes between the different species of elastomer radicals present. If two polymers are completely compatible so that one continuous phase is present in the blend, and if the polymeric constituents have a common viscoelastic temperature range, then mechanical working during extrusion or internal mixing can lead to block copolymer formation. If the tendency of the polymeric radicals formed by mechanical rupture is to recombine rather than to disproportionate, then the chances of block copolymer formation are increased. The presence of sites for hydrogen or halogen abstraction upon one of the polymer constituents is also an aid to grafted block copolymer formation. Thus polyvinyl chloride-neoprene blends give grafted block copolymers on extrusion or internal mixing and polyethylene-polyvinyl acetate blends block copolymerize when masticated in the absence of oxygen. Block copolymerization is largely controlled by the viscoelastic properties of the systems chosen.
Mechanochemical Phenomena in Polymers. III. Strength of the Bond between Elements of Multiply Polymer Articles
Authors: Slonimskiĭ G. L. , Drugova G. P.
Published: February 2011

1. The basis of the process of ply separation of multiply rubber articles under repeated deformations is fatigue of the material in the region of the joint of the plies, which is a mechanochemical process, as previously studied, consisting of the development of chain chemical processes initiated by free radicals which are formed in the mechanical scission of chemical bonds in the molecules. 2. By the addition of substances inhibiting chain radical processes to the polymer it is possible to raise considerably the strength of the bond between elements of multiply vulcanized rubber articles.
Mechanochemical Phenomena in Polymers. IV. Modification of Raw and Vulcanized Rubbers
Authors: Slonimskiĭ G. L. , Kargin V. A. , Reztsova E. V.
Published: February 2011

1. Mechanical processing of polymers swollen in substances capable of polymerizing leads to the development of processes of radical polymerization initiated by mechanical scission of chain molecules. The new polymeric substances thus formed have a correspondingly altered set of properties. 2. Processes of manufacturing polymers which are closely connected with the development of mechanochemical processes may be used to improve the properties of the processed polymer.
Polymerization of Isoprene by Organomagnesium Compounds
Authors: Fo-shung Wang , Dolgoplosk B. A. , Erusalimskiĭ B. L.
Published: February 2011

1. It was established that ether-free organomagnesium compounds promote the polymerization of isoprene at elevated temperatures. 2. The polyisoprene so-formed is mainly 3,4 linked. The nature of the halogen and radicals in the organomagnesium material has no influence on the microstructure of the polymer chains. 3. The presence of complex-forming agents (ethyl ether and triethylamine) affect an appreciable reduction in the velocity of polymerization and a marked lowering in the content of 3,4 links in the chains.
Absence of 3,4-Structure in Natural Polyisoprenes
Authors: Fraga D. W.
Published: February 2011

The concentration of 3,4 structure in hevea and balata has been the subject of some controversy in the past few years. The controversy concerns the assignment given to an absorption band found at 11.25 µ in the spectra of hevea and balata. It is known from the spectra of simple compounds that the isopropenyl group gives an absorption band at 11.25 µ, and that an absorption occurs at 11.25 µ in the spectra of synthetic 3,4(isopropenyl)-type polyisoprene. Salomon and van der Schee, in 1954, stated that it was tempting to assign the 11.25 µ peak in hevea and balata to the 3,4-type structure; however, they found that the absorption at 11.25 µ survived ozonization of the polymer. This cast some doubt on the validity of the assignment. Binder, in 1957, assigned the absorption at 11.25 µ to 3,4 structure and calculated that hevea and balata contained 2.2 and 1.3 wt-% 3,4 structure, respectively.
Cis-Trans Isomerization of Natural Rubber under the Influence of Hydrogen Chloride or Ethylaluminum Dichloride
Authors: Boldyreva I. I. , Dolgoplosk B. A. , Kropacjeva E. N. , Nel'son K. V.
Published: February 2011

We have established earlier that organo-aluminum compounds, and titanium tetrachloride, bring about the isomerization of the cis-isoprene units in natural rubber into the trans. The isomerization process, as influenced by the above materials, proceeds at appreciable velocity even at room temperature. The present communication reports the results of investigating the cis-trans isomerism of natural rubber as influenced by hydrogen chloride and ethylaluminum dichloride. The isomerizing action of hydrogen chloride upon unsaturated acids and stilbene was dislosed earlier in a series of papers. We investigated the action of dry hydrogen chloride and ethylaluminum dichloride on benzene solutions of natural rubber under the conditions described earlier. Hydrogen chloride was introduced in the form of a saturated benzene solution. In investigating the hydrogen chloride activity, each polymer sample was examined for unsaturation, chlorine content of the polymer chains and microstructure. The latter was characterized with the aid of infrared absorption spectra. As in the previous report, quantitative determination of the cis and trans content was made in the 840 cm−1 region, where the intensity and contour are substantially dissimilar for natural rubber and guttapercha. Furthermore, an additional inspection was made qualitatively in other regions of the IR spectrum (1100–1150 cm−1 and 1300–1330 cm−1), the feasibility of utilizing the 1300–1330 cm−1 region having been reported in a recent publication by Golub, who investigated the isomerization of natural rubber and guttapercha under the influence of selenium at temperatures of 180–220°.
Crystallizability of SKI Vulcanizates by Adiabatic Stretching
Authors: Votinov M. P. , Subbotin S. A. , Samoletova V. V. , Konytovskaya S. P. , Kuvshinskiĭ E. V.
Published: February 2011

Lithium isoprene rubber (SKI) which is very similar to natural rubber (NK) in structure and properties has been synthesized at the S. V. Lebedev VNIISK. During the development of the method of preparation and the investigation of the properties of SKI the necessity of studying the crystallizability of different samples of this new type of rubber became apparent. With this object in view we studied the conversion of work into heat during the adiabatic deformation of rubbers. It was shown that the conditions of preparation and of vulcanization determine whether SKI rubbers will crystallize on stretching or remain amorphous. This paper presents some of our data on the crystallizability of SKI rubber.
Unpaired Electrons in Carbon Blacks
Authors: Collins R. L. , Bell M. D. , Kraus Gerard
Published: February 2011

Two types of unpaired electrons have been observed in a heat treated channel process carbon black. In the original black, and for this material heat treated up to 1400° C, the unpaired electrons are believed to consist of unpaired mobile π electrons stabilized by resonance energy in large condensed ring structures, many of which probably contain oxygen. These disappear with heat treatment above 1400° C and a new species of unpaired spins appear which have been assigned to localized σ electrons at defects in the graphitizing lattice. The unpaired electrons in most commercial carbon blacks are believed to be π electrons, similar in concentration and g value, but varying considerably in line width and oxygen sensitivity. The highly graphitic acetylene black may contain σ electrons also, for its line width is little affected by oxygen. A tentative explanation has been formulated for the origin of unpaired electrons in charred materials and carbon blacks.
The Formation of Urethan Foams
Authors: Saunders J. H.
Published: February 2011

An understanding of the formation of urethan foams involves consideration of the organic chemistry of the reactions leading to gas formation and molecular growth, the colloid chemistry of nucleation phenomena and bubble stability, and the rheology of the polymer system as it cures. Experimental data are not available to permit complete evaluation of all details of the foam formation and cure. Nevertheless enough information has been developed in the urethan and related fields to permit one to develop a fairly reasonable explanation of the process. This summary attempts to present such a picture, and is not concerned with the more familiar areas of foam production and foam properties. A distinction is made between experimentally observed data and reasonable speculation. One may naturally assume that future research will modify and extend the concepts presented here.
The Vulcanization of Elastomers. 13. The Vulcanization of Natural Rubber with Sulfur in the Presence of Mercaptobenzothiazole. II
Authors: Lorenz O. , Echte Elisabeth
Published: February 2011

The vulcanization of natural rubber with sulfur, using mercaptobenzothiazole as accelerator in the presence of zinc stearate, was investigated. The results were as follows: 1) When natural rubber is cured with sulfur in the presence of zinc oxide and mercaptobenzothiazole, as well as zinc stearate, one observes, with the first order diminution of sulfur concentration, an induction period that grows longer as the cure temperature falls. 2) For the disappearance of sulfur there is calculated, from the temperature dependence of the rate constants, an activation energy of 19.5 kcal/mole. This value is considerably smaller than that found for the mercaptobenzothiazole-accelerated sulfur cure when no zinc stearate is present. 3) The percentage loss in mercaptobenzothiazole during vulcanization is, in the presence of zinc stearate, independent of the temperature; there is a reaction, independent of the amount of stearate added of 5 molecules of S8 for each molecule of mercaptobenzothiazole. 4) The diminution in accelerator can also be explained as a first order reaction, and it becomes evident that disappearance of accelerator and sulfur are equivalent-rate processes. 5) The crosslinking, measured by the reciprocal equilibrium swelling, goes according to the first order, yet sulfur disappearance and the crosslinking reaction are not equal rate processes, which was always true in the absence of zinc stearate. In each case the crosslinking rate constants are greater than those for the decrease in sulfur. 6) For the activation energy of network formation, we calculated, from the temperature dependence of the rate constants of the reciprocal equilibrium swelling, 20.5 kcal/mole. 7) When the stearate content is constant, there is a linear relationship between kSI, the rate constant for sulfur diminution, and the given amount of mercaptobenzothiazole, up to an initial molar ratio of mercaptobenzothiazole: stearate = 4:1. Increases in accelerator proportion beyond this initial ratio cause no further rise in the rate constants. 8) The rate constants of the crosslinking reaction also increase with increasing proportion of mercaptobenzothiazole (stearate portion remaining constant), until the initial molar ratio of mercaptobenzothiazole:zinc stearate = 4:1 is reached. Nevertheless, the relationship is not linear. 9) There is a linear relationship between the amount of zinc stearate in the vulcanizate and the maximum sulfur-loss rate constants kSI (max). 10) The maximum rate constants of the network forming reaction kQI (max) are proportional to the square root of the stearate content. 11) The number of crosslinkage points formed is independent of the quantity of mercaptobenzothiazole, when the stearate content is constant. 12) The number of crosslinking points formed increases, however, along with increasing stearate content, and is proportional to the square root of the stearate content. The investigations will be continued.
The Thermal Vulcanization of Synthetic Rubber
Authors: Luttropp H.
Published: February 2011

It is shown that synthetic rubbers, in contrast to natural rubber, can be vulcanized to soft rubber by a simple thermal treatment without any previous admixture of sulfur or accelerators. This process has been designated as “Thermovulcanization” to distinguish it from the regular vulcanization procedure under heat with the addition of sulfur and accelerators. Various synthetic rubbers of Schkopau production have been investigated for their behavior in the process of thermovulcanization. Both butadiene-styrene and butadiene-acrylonitrile copolymers as well as the butadiene block polymerizate lend themselves to vulcanization by this thermal treatment. For the butadiene-styrene copolymer with higher styrene content, thermovulcanization leads to products which are not equivalent to the regular sulfur-accelerator vulcanizates. Natural rubber cannot be vulcanized to soft rubber by thermovulcanization. The investigation of the effect of temperature revealed that a temperature of 195° C, for example, was applicable for all the synthetic rubbers studied. The addition of active carbon was found to accelerate the thermovulcanization process and certain properties of the vulcanizates are improved. The results of some comparative studies are presented, and it is pointed out that thermovulcanizates and normal vulcanizates show agreement in some of their properties and vary in others. The thermovulcanizates, as compared with normal vulcanizates, show somewhat lower tensile strength and somewhat lower fatigue resistance. Also their resistance to swelling is lower. On the other hand they are better in abrasion, have somewhat improved elastic properties, and show improved resistance to aging including surface aging phenomena under static and dynamic stress.
Hydrogenation of Butadiene Rubber
Authors: Yakubchik A. I. , Gromova G. N.
Published: February 2011

1. Solutions of butadiene rubber were hydrogenated at atmospheric pressure and room temperature on the following catalysts: palladium on calcium carbonate; palladium on nickel, platinum black from platinum dioxide, platinized carbon activated with doses of chloroplatinous acid, and Raney nickel. 2. It was established that when butadiene rubber is hydrogenated on these catal sts the activity of the catalyst decreases, evidently owing to its surface being obstructed with products of hydrogenation. It was consequently impossible to study the behavior of the double bonds in butadiene rubber on the basis of the curves of the rate of hydrogenation. 3. Specimens of butadiene rubber were prepared at various degrees of hydrogenation on all these catalysts and the following quantities were measured : total unsaturation, proportion of external and internal double bonds, index of refraction, relative viscosity of 0.08 per cent benzene solutions, and vitrification temperature. 4. It was established that when butadiene rubber is hydrogenated on the catalysts studied the external double bonds of the rubber are hydrogenated more rapidly than are the internal bonds. 5. It was established that an increase in the degree of hydrogenation of butadiene rubber leads to a decrease in the index of refraction, relative viscosity of benzene solutions, and vitrification temperature. 6. The decrease in the index of refraction of rubber during hydrogenation shows the absence of cyclization and can be explained by the disappearance of the double bonds of the rubber molecule. 7. It was shown that the decrease in viscosity of benzene solutions of butadiene rubber with increase in the degree of hydrogenation is due to changes in the shape of the rubber molecule during hydrogenation.
The Wear of Passenger Car Tires
Authors: Geesink H. A. O. W. , Prat P.
Published: February 2011

One can thus say that in the course of tire tests, all of the experimental conditions, whether they affect more particularly the wear by test period or by wheel position, influence the wear results. Notwithstanding the complexity of these influences and of their interactions it has been possible to verify that a relation existed between the tests on special cars and those made on private cars commonly used by everyday users, and to establish a correlation between the normal road tests and accelerated tests on the track. These studies have shown the importance of the severity of the tests for the estimation of the relative value of the mixtures and it has been possible to evaluate the influence of a certain number of factors on this severity which is, in reality, the resultant of the effects of all the experimental conditions on the wear of pneumatic tires. The variations in relative wear of the mixtures as a function of the severity have led to the thought that a correlation might exist between the practical tests on the road or on the track and the experiments made in the laboratory with the aid of abrasion machines. The existence of such a correlation is very important for it will permit an effective selection of the mixtures, destined for the manufacture of treads, in the research investigations. However, one must still look for a suitable adjustment of laboratory tests in order to obtain an estimation which is directly transposable to the complex domain of the pneumatic tire. This simplification, however, will not bring about the disappearance of road tests for it will, after all, be necessary to make a few practical verifications, be it only for studying the road behavior of the experimental mixtures or their resistance to cracking. This study has been made within the framework of the research programs of the Rubber-Stichting and of the French Rubber Institute, the study being in turn a part of the entirety of the investigations pursued under the protection of the International Rubber Research Board.
The Ultimate Properties of Simple Elastomers
Authors: Bueche A. M.
Published: February 2011

The ultimate properties of polymers are very poorly understood. A large mass of practical data is available but at present there seem to be no molecular theories for its correlation or for use as a guide in obtaining new data. In the following pages a theoretical approach to the ultimate properties of simple crosslinked elastomers will be described. The treatment will be limited to the tensile strength and ultimate elongation at temperatures high enough so that crystallinity and the viscous work during extension are negligible. The theory can be extended to cover compressive or shear strength with relatively little effort. The incorporation of the effects of viscosity and crystallinity will require somewhat more work. (After the completion of the major part of this work I learned that Prof. F. Bueche, University of Wyoming, has developed a somewhat similar theory for the tensile strength of viscous elastomers.)
Influence of Molecular Shape on the Tensile Strength of Vulcanizates
Authors: Novikov A. S. , Dorokhina T. V. , Zubov P. I.
Published: February 2011

A study of the mechanism of the formation of albuminous gels has shown that the mechanical strength of films depends on the shape of the chain molecules. Films prepared from globular casein have a lower tensile strength than those prepared from fibrillar casein. It would be natural to assume that the mechanical properties of rubberlike polymers and vulcanizates depend on the shape of the molecular chains. In order to verify this hypothesis, vulcanized films prepared from solutions of butyl rubber in various solvents were examined, assuming that the degree of twisting depends on the nature of the solvent. Benzene and carbon tetrachloride, in which the degree of twisting of the butyl rubber chains is quite different, were chosen as solvents. The tensile strengths given in Table I are the mean statistical data from 25 specimens. Data of the change in relative viscosity of solutions of butyl rubber in benzene and in carbon tetrachloride as functions of the temperature and concentration are shown in Figure 1. It is seen that the relative viscosity of benzene solutions is lower than that of carbon tetrachloride solutions of equal concentration. An increase in the relative viscosity of benzene solutions of butyl rubber is observed with an increase in temperature, while a decrease is observed in carbon tetrachloride solutions. These changes of relative viscosity with an increase in temperature are less pronounced in solutions with concentrations up to 0.3 g per 100 cc, where the polymer forms true molecular solutions, and are more pronounced in concentrated solutions.
The Mutual Solubility of Polymers. I. Physicomechanical Properties of Stocks Prepared from a Mixture of Polymers
Authors: Komskaya N. F. , Slonimskiĭ G. L.
Published: February 2011

1. The mixing of rubbers (or of any amorphous polymers) may be considered as a mutual solution of two liquid phases, conforming to thermodynamic laws. 2. The stocks studied, which were prepared from a base of a combination of different rubbers, fall into two groups as regards the nature of the relation between their mechanical properties and the proportions of the mixed rubbers. The opinion was expressed that the anomalies observed in the properties of combined stocks prepared from a mixture of SKS-30 and SKB are due to the micrononhomogeneous two-phase structure of such stocks. 3. It was shown that the properties of combined stocks are governed primarily by the behavior of the mixed rubbers themselves, and not by the ingredients incorporated into the stocks. 4. The compatibility of two polymers should be considered from two points of view. A macroscopic compatibility can almost always be achieved, provided that the polymer can be converted to the fluid state. However, compatibility in microregions, i.e., the mutual solubility of polymers, is determined by their thermodynamic properties and may not coincide with macrocompatibility. The reason for the discrepancy between macro- and microcompatibility is the chain structure of the polymer molecules, and the resulting large viscosity of polymers which have a high mobility of small segments of the flexible chain molecules.
Mastication. V. Separation and Structural Investigation of Natural Rubber-Polymethyl Methacrylate Interpolymers Formed by Mastication
Authors: Angier D. J. , Watson W. F.
Published: February 2011

Polymerization of methyl methacrylate admixed with natural rubber occurs on rupture of rubber molecules to free radicals by applied shearing forces. The polymeric products after different conditions and extents of reaction have been separated into uncombincd rubber, two interpolymer fractions, and uncombined polymethyl methacrylate by fractional precipitation and extraction methods. The structure of the interpolymers has been investigated by measurement of composition and osmotic molecular weight, ozonolysis to degrade the rubber segments and isolation of the polymethyl methacrylate fragments, autoxidation of the rubber segments, and viscosity measurements on the uncombined rubber. The interpolymer is a linear block polymer containing one polymethyl methacrylate segment and of the order of one or two rubber segments per molecule. The Trommsdorff gel effect has a profound influence on the rate of formation, composition, and structure of the interpolymer.
Mastication of Rubber. VI. Viscosity and Molecular Weight Relationships for Natural Rubber after Cold Mastication
Authors: Angier D. J. , Chambers W. T. , Watson W. F.
Published: February 2011

Values of limiting viscosity number, Huggins' interaction constant, k′, osmostic molecular weight and Flory-Huggins' constant, μ, of masticated and unmasticated rubber have been compared. A calibration of limiting viscosity against molecular weight has been obtained for masticated rubber, but one is not available for unmasticated rubber due to the occurrence of different extents of branching. A mechanism is advanced of rupture during mastication of molecules above a critical molecular weight.
End Groups of Oxidized Rubber
Authors: Bevilacqua E. M.
Published: February 2011

Chain scission during the oxidation of polymeric 1,5-dirnethyl-l,5-dienes occurs nearly quantitatively through the scission of an unusual peroxidic intermediate, followed ultimately by evolution of a group of fragments of low molecular weight at each scission. The composition of this group depends on the reaction conditions. The first known stable intermediates to be formed subsequent to scission are levulinaldehyde and formaldehyde: Bolland's kinetic and analytic studies combined with the requirements of the observed stoichiometry of scission form the basis on which it is possible to write a detailed mechanism for the transformation represented by Equation 1. Nothing is known in detail of the sequence of reactions resulting in Equation 2. It has been suggested that scission is associated with propagation rather than initiation—that is, with decomposition of a peroxy radical rather than of a hydroperoxide as is indicated in this scheme. This is still a moot point. It is now known, for example, that overall scission efficiency is strongly determined by temperature and that benzothiazolethione and o,o′-dibenzamidodiphenyldisulfide both accelerate oxygen consumption as well as scission, in contrast to earlier belief.
Adhesion of High Polymers. 2. A Method for Determination of the Mutual Adhesion of High Polymers
Authors: Shapovalova A. I. , Voyutskiĭ S. S. , Pisarenko A. P.
Published: February 2011

1. A simple and fairly accurate method for determination of adhesion between two high polymers has been developed, based on separation of the joints by a peeling method. 2. It was found, in agreement with data available in the literature, that the manner of separation of the joints changes with variations of the speed of separation. At low speeds, separation of polymer-polymer joints is cohesive in character, at moderate speeds it is mixed, and at high speeds it is purely adhesive. No increase of the work of adhesion with increasing speed of separation was found. 3. It is shown that the width of the joint does not affect the results of the adhesion determinations. 4. It was found that in the limits studied (from 150 to 55µ) the thickness of the polymeric adhesive layer does not affect the value of the specific work of adhesion. 5. It is shown that if the layer of high molecular adhesive on the substrate is formed from solution, the pressure to which the joint is subjected after it is made does not affect the adhesion. 6. It was found that heat treatment of the joints considerably increases adhesion. 7. It is shown that adhesion increases and tends to a definite limit with increasing time of contact between a high molecular adhesive and a high molecular substrate. 8. It is suggested that the increase of adhesion by heat treatment and by increased contact time is caused by diffusion of molecules of the adhesive into the substrate and vice versa, which leads to disappearance of the interphase boundary and to formation of a stronger adhesive joint.
The Mutual Solubility of Polymers. II. The Viscosity of Mixed Rubbers and the Behavior of Solutions of These
Authors: Slonimskiĭ G. L. , Komskaya N. F.
Published: February 2011

1. Mixtures of rubbers and raw rubber stocks prepared from a combination of two rubbers possess anomalous properties in a number of cases, revealed in the appearance of a maximum in the curve of the viscosity of such a system in relation to the proportions of the rubbers. 2. A mixture of solutions of different rubbers equal in concentration in a common solvent separates into two phases in the majority of cases, thus demonstrating the limited mutual solubility of the rubbers. This separation does not take place if the solutions are dilute enough so that the molecules of the two solvents enter into practically no reaction with one another. For a given pair of polymers, the minimum concentration at which the separation still takes place depends on the nature of the solvent. 3. In agreement with present-day theoretical opinion on the solubility of polymers, the results obtained demonstrate the decisive part played by interactions between the chain molecules, i.e., by the heat of mixing; and the insignificant part played by changes of entropy in the process of mutual solution of two polymers possessing chain molecules of equal size and flexibility. 4. The study of mixed polymer solutions is a valuable source of information on the mutual solubility of polymers. The experimentation carried out on rubber solutions confirms the mutual insolubility of a number of pairs of rubbers which was observed earlier in the study of the mechanical properties of vulcanizates prepared from mixed rubbers.
The Mutual Solubility of Polymers. III. Heats of Mixing of Polymers
Authors: Struminskiĭ G. V. , Slonimskiĭ G. L.
Published: February 2011

1. Measurements of the heats of mixing as between different polymers, which we have carried out, have confirmed the correctness of the assumption that the heat effect plays a decisive part in the process of mutual mixing of polymers. 2. The anomalous behavior of mixtures of SKS-30 with SKB and polystyrene with SKB has been revealed. 3. Experimental data on the heats of mixing of polymers, which has substantial value for theoretical and practical research in the field of polymer mixtures and for the evaluation of possible practical applications of these, has been collected.
The Mutual Solubility of Polymers. IV. The Effect of the Packing Density of Polymer Molecules on Their Mutual Solubility
Authors: Slonimskiĭ G. L. , Struminskiĭ G. V.
Published: February 2011

1. It is pointed out that the decrease in volume plays an important part in the mixing of polybutadiene rubber (SKB) with butadiene-styrene rubber (SKS-30) and of polybutadiene rubber with polystyrene. In this connection it is emphasized that the assumption of volumes being additive in the mixing of polymers is limited in application. 2. It was shown that the heat effects of the mixing of polymers does not depend on the degree of polymerization, provided that no contraction takes place in mixing, and that the sign of the heat effects can even be changed if the packing of the molecule becomes more loose as the degree of polymerization increases. 3. From a theoretical analysis of experimental data found in the literature the opinion was advanced that the critical mixing temperatures for the systems polybutadiene rubber-butadiene-styrene rubber and of polybutadiene rubber-polystyrene are low, being somewhat above the vitrification temperature of polystyrene. The existence of lower critical mixing temperatures here is caused by a decreased packing density in the molecules of polystyrene and of butadiene-styrene rubber at temperatures below the vitrification temperature of polystyrene.
The Heat Aging of Natural Rubber Vulcanized with Tetramethylthiuram Disulfide
Authors: Fletcher W. P. , Fogg S. G.
Published: February 2011

Acetone extraction of the TMTD stock, which is known to remove the ZnDMDC formed during vulcanization, also leads to a reduction in heat aging resistance. Addition to the extracted vulcanizate of the appropriate quantity of ZnDMDC from a solution improves the aging behavior although not to the level of the untreated vulcanizate. This failure to restore in full the aging resistance of the initial stock by swelling in the appropriate quantity of ZnDMDC is hardly surprising since it is likely that the ZnDMDC will be present in the original and in the dosed vulcanizate in somewhat different physical forms and distributions. The results demonstrate that the dithiocarbamate formed in situ during TMTD vulcanization plays a major part in conferring heat resistance to such vulcanizates.
The Mechanism of Accelerator Action. Reaction of Mercaptobenzothiazole with Sulfur
Authors: Dogadkin B. , Tutorskiĭ I.
Published: February 2011

The investigation of the reaction of sulfur with mercaptobenzothiazole (MBT) is of great interest from the point of view of clarifying the mechanism of the action of the latter as a vulcanization accelerator. We studied the reaction of MBT with elemental sulfur in the melt and in solvent media—vaseline oil and xylene. The course of the reaction was followed by means of the H2S liberated, which was removed from the reaction medium by a continuous stream of nitrogen and was absorbed in a solution of CdCl2. In Figure 1 are presented the kinetics of the liberation of H2S on heating the mixture in a medium of vaseline oil, the concentration of MBT and sulfur comprising, respectively, 0.06 mole/liter and 0.655 g-atom/liter. This ratio and concentration of reactants corresponds to those in the vulcanization of rubber. As can be seen, the splitting out of H2S under the stated conditions proceeds at a constant rate, which can be explained by the very insignificant change in concentrations of reactants over the entire time (only 1.5% of the MBT introduced reacted in 10 hours at 140°). The kinetics of the liberation of H2S from a melt of MBT and sulfur at 140° practically coincide with the kinetics of the reaction in solution (see Figure 1). The temperature dependence of the rate constants leads to the expression K=3.54⋅1010e33500/RT.
Role of Hydrogen Disulfide in Vulcanization
Authors: Tinyakova E. I. , Khrennikova E. K. , Dolgoplosk B. A.
Published: February 2011

It was shown that the breakdown of hydrogen disulfide in α-olefins results in the exclusive formation of addition products (mono-, di-, and tetrasulfides) without formation of hydrogen sulfide and free sulfur. Similar results were obtained when sulfur reacted with monoethanolamine (vulcanization accelerator) in α-olefin solution.
The Theory of Rubber Reinforcement: Interaction of Carbon Black with Sulfur and Rubber
Authors: Dogadkin B. , Lukin B. , Tarasova Z. , Skorodumova Z. , Tutorskiĭ I.
Published: February 2011

Active channel black combines chemically with sulfur when heated with sulfur solutions. The amount of sulfur combined increases after hydrogenation of the carbon black. The dimensions of the carbon black aggregates increase as the result of the reaction with sulfur. Hydrogenation of channel black increases the content of insoluble rubber in the carbon-rubber gel formed during milling of a rubber-carbon black mixture. Hydrogenation of channel black increases the content of bound sulfur, the modulus, and tensile strength, in comparison with vulcanizates containing the original unhydrogenated channel black. These facts suggest that active carbon black enters the composition of the vulcanizate structure, and this is a factor in rubber reinforcement.
Bound Rubber and Mechanical Properties of Diene Polymers
Authors: Palinchak S. T. , McSweeney E. E. , Mueller W. J. , Stickney P. B.
Published: February 2011

1. Tensile strength is apparently a function of the particle size of the pigment and how well it is dispersed in a polymer. 2. Modulus and abrasion resistance are apparently functions of the interaction of the pigment and the polymer. This cannot be attributed entirely to bound-rubber formation, since bound rubber may occur without reinforcement, as shown by the results with silica pigment. 3. Results of processing studies show that Philblack O has a stabilizing effect on the polymer during processing and more consistent and better properties are obtained if processing is performed with carbon black present at temperatures below those for gel formation. This effect is more pronounced for less stable polymers such as polybutadiene. 4. Philblack O slows down gel formation. 5. It is possible that silica may have a destabilizing effect on polybutadiene unless it is buffered with agents such as resins, stearic acids, and diethylene glycol.
Correlation between Laboratory Abrasion and Road Testing
Authors: Prat C.
Published: February 2011

In a preceding article, we expressed the hypothesis that probably no discontinuity exists between abrasion testing on the road and that on laboratory machines. The latter showed the peculiarity of being characterized by its very high severity. Let us recall briefly that the severity is expressed by the absolute wear of a reference mixture during the test considered. We were able to verify the existence of a relationship independent of the type of testing carried out, but a function of the severity of the tests, between the wear of an experimental mixture and a reference mixture. This relation manifests itself in different types of mixtures in the form of regressing lines. These are shown in Figure 1 where we have used logarithmic coordinates. The correlation coefficients calculated for different regressions are in the neighborhood of 0.93 to 0.95 and consequently very highly significant. The interpretation and use of the curves shown on the graph necessitates, however, a few remarks of importance: Firstly, it must be noted that each of the lines corresponds to a particular standard of comparison. Each of them is independent of the others. for example, for that labelled “Rubber-Resin A”, the comparison rests on the wear of this type of combination rubber-resin as a function of the wear of the mixture (natural rubber containing 28 volumes of HAF black) having served as a reference for the tests, while for the line labelled “Rubber + SAF black”, the reference mixture is a natural rubber containing 28 volumes of MPC black. It will not be necessary then, in any case to compare the curve for “Rubber-SAF Black” to that for “Rubber-Resin A”.
Load-Deflection Relations and Surface Strain Distributions for Flat Rubber Pads
Authors: Gent A. N.
Published: February 2011

Rubber components comprising flat pads of vulcanized rubber secured between rigid flat surfaces are widely used as mountings and couplings. They are subjected to compression or shear, or a combination of both deformations, often of relatively large magnitude. The shear deformation is produced by the displacement of one rigid bounding surface in its own plane with respect to the other. It differs from a homogeneous shear deformation if the pad thickness is comparable with the dimensions of the cross-section, when an appreciable bending component enters into the total deflection. The corresponding load-deflection relations have been examined by Rivlin and Saunders. The compression deformation differs from a state of pure homogeneous compression in that the rubber adheres or is bonded to the rigid compressing faces and sliding at the interface is precluded. The rubber therefore bulges laterally as the deflection is imposed. The loaded surfaces are subjected to a uniform displacement, while the free surface of the pad is subjected to known stresses (zero). The resulting mixed boundary value problem has not proved tractable even for classically small displacements—its solution for large elastic displacements does not appear imminent. This problem has therefore been treated experimentally. Since the preparation of the paper, an approximate theoretical treatment has been developed. It is described in the APPENDIX. for any rubber component the presence in use of excessive local surface strains is undesirable and a longer service life may be anticipated if the geometrical design of the surface is such that high concentrations of strain do not arise. In principle it should be possible to derive the state of strain at the surface by mathematical analysis, but in practice the problem is difficult and conclusions can only be drawn in some restricted cases. Simple measuring techniques are described whereby the distribution of strain over the surface of a rubber component may be examined experimentally. These methods have been used to determine the regime of strain over the free surfaces of some bonded rubber cylinders subjected to overall compression and extension.
The Structure of Cyclized Polybutadiene
Authors: Shelton J. Reid , Lee Lieng-huang
Published: February 2011

Polybutadiene was cyclized with sulfuric acid under rather drastic conditions. The cyclization was confirmed by the decrease of unsaturation and the change of physical properties. The low degree of unsaturation of cyclized polybutadiene, as determined by the iodine-bromide method, suggested the formation of polycyclic structures. Oxidation of cyclized polybutadiene with acidic permanganate gave a dibasic acid, C16H22O4, which corresponds to a tricyclic ring system. Consequently, the structure of cyclized polybutadiene may be considered to include polycyclic structures joined by uncyclized segments of the molecular chain together with isolated six-membered rings. Further study will be necessary to fully establish the structure of cyclized polybutadiene.
Aeration of Natural Rubber Latex. II. Graft Polymerization of Vinyl Monomers with Aerated Latex Rubber
Authors: Sekhar B. C.
Published: February 2011

The peroxidic groups produced on the rubber hydrocarbon when oxygen is absorbed by ammonia-preserved latex are capable of initiating the graft polymerization of methyl methacrylate and other vinyl monomers, in the presence of suitable reducing agents. The products so formed contain only small proportions of unbound homopolymer. In the latex state, the products have a much higher wet gel strength and better film forming properties than materials of the same total vinyl polymer content prepared by other methods.
Melting and Glass Transitions in Polyisobutylene
Authors: Kell R. M. , Bennett Bailey , Stickney P. B.
Published: February 2011

The purpose of this work was to investigate the crystallization behavior of uncompounded, unstressed polyisobutylene and butyl rubber. Glass transition data obtained during the work are also reported. The data were determined dilatometrically. The work was prompted by a literature survey which collected transition data on elastomers. It was found that crystallization information for polyisobutylene and butyl rubber was based largely on x-ray studies of these polymers under high elongation. In fact, it has been assumed generally that these polymers would crystallize only when highly oriented, as by stretching. Because of the resistance of polyisobutylene to ordering when in the unstressed state, no measurements of optimum crystallization temperature or melting temperature, Tm, have previously been reported. Information of this type is important because of its bearing on the mechanical behavior of a polymer. Many types of elastomers will crystallize readily if oriented by a large stress. However, only those having relatively simple structures crystallize readily under zero stress. Such behavior is, of course, a limiting factor in low-temperature serviceability. Polyisobutylene might seem at first to have the required simplicity of structure; however, steric hindrance of the side methyl group forces the chain to crystallize in a helical configuration having a molecular repeat distance of 18.6 A, as shown by Fuller, Frosch, and Pape. This is the greatest repeat distance of any of the elastomers, suggesting that a lengthy exposure period would be required if ordering were to occur at all. A clue to ordering in an isobutylene copolymer was furnished by Gehman, Woodford, and Wilkinson, who reported that a butyl tread stock showed a greatly increased torsional stiffness after storage for about 40 days at −30° C. The aged butyl sample exhibited an x-ray diffraction pattern suggestive of crystallization. These results may be the first showing crystallization in a butyl polymer essentially free of stress. In other work, Radi and Britt, using equilibrium temperature-retraction techniques with samples elongated 300 per cent initially, found that two types of butyl polymers showed optimum crystallization rates at −30° and −41° C. The aggregate of these results suggests that crystallization might occur in unstressed polyisobutylene if sufficient time were allowed, and indicates an optimum rate in the range of −30° to −40° C. This is reasonable by comparison with natural rubber, which has a glass transition temperature very close to that of butyl rubber, and an optimum crystallization rate at about −25°C.
Carbon-Black Loaded Rubber Vulcanizates: Volume Changes in Stretching
Authors: Mullins L. , Tobin N. R.
Published: February 2011

The changes in volume which occur during the stretching of carbon black reinforced vulcanizates have been measured, and the results used to examine crystallization which accompanies the extension of natural rubber. The effect of previous extension on these changes is interpreted in terms of a simple model previously advanced by the authors to describe the stress-strain properties of reinforced vulcanizates.
Efficiency of TMTD Vulcanization
Authors: Bevilacqua E. M.
Published: February 2011

Tetramethylthiuram disulfide (TMTD), together with a sufficient amount of zinc oxide, is the simplest and most efficient vulcanizing agent known for introduction of sulfur crosslinks into rubber. No other combination approaches it in efficiency over a wide range of temperatures, although under limited conditions sulfur cures can be obtained with approximately as high a crosslink density per mole of vulcanizing agent. The stoichiometry of vulcanization with this curative has been explored in some detail in recent work of Scheele and coworkers. They have confirmed the observation by Jarrijon that during vulcanization dithiocarbamate is formed equivalent to close to two-thirds of the TMTD taken. The generality of this result was established in an exhaustive series of experiments, covering a range of structures of thiuram disulfide and of polyolefin, of temperature, and of concentration of reactants.