bluuebunny/crossref_metadata_2025 huggingface dataset:
Chlorobutyl Rubber—Optimum Processing Procedures
Authors: Ziarnik G. J.
Published: February 2011

Chlorinated butyl rubber cures faster, forms more stable crosslinks, and provides wider compounding versatility than conventional butyl rubbers. Because of chlorobutyl's increased reactivity MgO is added to control scorch. Unfortunately, MgO also retards development of stress-strain properties in cured vulcanizates. While these effects can be explained on the basis of an interference with the vulcanization process, data indicate that MgO retards polymer-pigment interaction as well. Heat treating has been shown to reduce the retarding influence of MgO without sacrificing processing safety. Cure systems respond differently to heat treatment, some showing little or unfavorable effects. Heat treating is effective only with vulcanization systems that crosslink through unsaturation rather than through bis-alkylation reactions involving chlorine. A mechanism is proposed which explains these phenomena in terms of a competition for available chlorine between polymer-polymer crosslinking and polymer-carbon black interaction which together contribute to the final crosslinked network. Processing safety is maintained because of a reaction between MgO and a small fraction of tertiary-allylic chlorine which is believed to contribute to scorch. In processing chlorobutyl compounds, therefore, whenever MgO is used to control scorch safety, heat treatment is desirable in order to reduce the retarding influence on vulcanization and reinforcement. Heat treating is effective, however, only in compounds cured with vulcanization systems capable of crosslinking through unsaturation. Since HCl may be a byproduct of thermal reactions, heat treatment should not be carried at temperatures above 330° F unless a suitable acid scavenger such as MgO, PbO, or CaSiO3 is employed. When such materials are present in the compound, temperatures up to 400° F can be tolerated. Optimum processing procedures for chlorobutyl compounds will depend on the requirements of a given application, the cure system required, and the limitations of available processing equipment.
The Chemistry of Vulcanization. IX. Accelerating Mechanism of 2-Aminothiobenzothiazole
Authors: Fukuda Haruko , Tsurugi Jitsuo
Published: February 2011

2-Aminobenzothiazole, i.e., 2-aminobenzothiazolylaulfenamide, MSNH2 was used as a model of the commercial sulfenamide type accelerators. Behavior of MSNH2 was studied in diphenylmethane, DPM, which served as a hydrocarbon containing α-methylenic hydrogen. MSNH2 decomposes in DPM at 140–160° to give MS· and ·NH2 together with a minor amount of free sulfur radical. This suggests homolytic dissociation of the S—N bond as well as the C—S bond of MSNH2, though the latter bond dissociates in minor degree. Dissociation of both bonds makes the reaction sequence complicated. When sulfur was added to the MSNH— DPM system, the radical MS· (or M·) opens the sulfur ring to accelerate the reaction of DPM with sulfur. The presence of sulfur results in the less complicated reaction products. The activating mechanism of zinc butyrate in the reaction involving MSNH2, sulfur and DPM is the same as that involving thiazole type accelerators. However, the zinc salt of MBT which is produced from MSNH2 and zinc butyrate interacts with the radical ·NH2, giving an intermediate 2-amino-benzothiazole, MNH2. The latter reacts with zinc butyrate to give N-(2-benzo-thiazolyl) butyramide, RCONHM. Evolution of ammonia was observed even in the presence of sulfur and zinc butyrate.
The Chemistry of Vulcanization. X. Accelerating Mechanism of Sulfenamide Type Accelerators
Authors: Fukuda Haruko , Tsurugi Jitsuo
Published: February 2011

The mechanism of acceleration of the commercial sulfenamide MSNR2 (NR2 denotes cyclohexylamino or morpholino and M denotes 2-benzothiazolyl) was studied by using diphenylmethane (DPM) as a model of rubber hydrocarbon. Since amine (NHR2) liberated from MSNR2 complicated the reaction, the results obtained here were compared and correlated with those using the simple sulfenamide MSNH2. The preceding paper reported that ammonia evolved from MSNH2 did not disturb the reaction. The reaction mechanism of MSNR2 in DPM both in the presence and absence of sulfur appear to be the same as those of MSNH2 respectively, though difficulties of the identification and determination of the products did not permit a clear-cut conclusion. In the DPM-sulfur-MSNR2-zinc butyrate system, MBT produced from sulfenamide via 2-benzothiazolylsulfenyl radical interacts with zinc butyrate to give zinc salt of MBT (MSZnSM). This compound, on the one hand, suffers induced decomposition by sulfur to give benzothiazolyl-sulfenyl radical again, and on the other hand, interacts with the radical ·NR2 to yield MNR2. The delayed action of MSNR2 was interpreted by induced decomposition only by ⋅Sx⋅ as compared with that of MSZnSM both by S8 and ⋅Sx⋅. The accelerating entity of the sulfenamide is the 2-benzothiazolylsulfenyl radical, which splits the S8 ring molecule, as in the case of other thiazole type accelerators. However, amine librated from the sulfenamide also is considered to accelerate the vulcanization.
Determination of Free Sulfur in Stocks Cured with Sulfur Containing Accelerators
Authors: Khehaskova E. P. , Okhapkina N. A. , Provorov V. N.
Published: February 2011

For the determination of free sulfur in vulcanized rubber the normal method is the sulfite method, consisting of the heating of a sample of rubber with a solution of sodium sulfite. The free sulfur reacts with the sulfite, forming thiosulfate, which is determined by iodometric titration. The unreacted excess of sulfite is removed with formalin. The method gives good results in the analysis of stocks which do not contain sulfur-containing accelerators. In the presence of these accelerators the results are high: in some cases the method is quite inapplicable, as it is impossible to establish the endpoint of titration accurately. This may be explained by the circumstance that the accelerators and the products of their decomposition during vulcanization can pass into the solution of sodium sulfite and react further with the iodine. The method of determination of free sulfur proposed by Hardmann, consisting of the acetone extraction of the rubber in the presence of copper gauze, is protracted and complicated. A certain improvement in the sulfite method of Bolotnikov and Gurova was introduced in the ASTM method (1952). Sodium stearate is added to the sodium sulfite solution for better wetting of the rubber, and a certain amount of paraffin to prevent the formation of foam. After termination of heating the solution the stearic acid is precipitated with strontium nitrate and certain accelerators with cadmium acetate. For the majority of stocks this method gives correct results, but in a number of cases it is difficult to establish the end of titration at all.
The Mechanism of Optimum Vulcanization in Some Synthetic Rubbers
Authors: Gavrishchuk V. Ya , Zubov P. I.
Published: February 2011

1. We investigated the tensile strength and types of sulfur in vulcanizates prepared from butyl rubber and neoprene. 2. It became evident that optimum vulcanization in these vulcanizates is caused by the disintegration of intramolecular polysulfides.
Dependence of Bound Rubber on Concentration of Filler and on Temperature. I
Authors: Dessewffy Oliver
Published: February 2011

The change in quantity of rubber gel with the concentration of carbon black in filled natural rubber compounds was studied. It was established that there is a linear relationship between the amount of rubber gel and the black concentration, within a range of 20 to 80 parts of black to 100 parts by weight of rubber. No clear-cut relation exists between the quantities of rubber gel or the constants for the linear relations and the physicomechanical properties of the vulcanizates. The factors upon which the amount of bound rubber depend, i.e., the degree of degradation of the rubber, the heat treatment of the mixtures and the extraction temperature, do not alter the linear character of the cited relation. The critical concentration of certain types of blacks was determined. Up to this concentration no coherent rubber/black gel system is formed. The critical values for the black concentration are clearly related to some of the elastic properties of the filled vulcanizate.
cis-trans-Isomerization of 1,4-Polybutadiene under the Influence of Nitrogen Dioxide
Authors: Ermakova I. I. , Dolgoplosk B. A. , Kropacheva E. N.
Published: February 2011

It is well known that, under the influence of various catalytic agents of ionic nature, cis-trans isomerization of natural rubber takes place. Sulfur dioxide, organic aluminum compounds, titanium halides, anhydrous hydrogen chloride and other materials show similar action. Also established is the possible isomerization of cis forms of natural rubber at elevated temperatures, under the influence of selenium, thio acids and a number of compounds which are dissociated through a radical mechanism, an example being benzoyl disulfide. For cis-1,4-polybutadiene, the possibility of isomerization by means of ultraviolet rays and also by means of gamma radiation, in the presence of sensitizers has been demonstrated. This is also accomplished by means of thio acids and several organic sulfides. As may be surmised, isomerization takes place under conditions dependent on consecutive reactions involving addition of free radicals to the double bonds and the dissociation of the products thus formed:
Diisocyanate-Linked Polymers. III. Relationships between the Composition and Ultimate Tensile Properties of Some Polyurethane Elastomers
Authors: Smith Thor L. , Magnusson Alan B.
Published: February 2011

The tensile strength and elongation at rupture of elastomers vary markedly with the experimental conditions used in measurement. For example, when measured at a fixed rate of extension, the tensile strength may increase by a factor of 100 or more as the temperature is decreased, and the ultimate elongation may increase concomitantly by a factor of 10 or more and then decrease to a few per cent. The ultimate properties also depend on the chemical nature of the network chains, the degree of crosslinking, and on the regularity of spacing of the crosslinking sites. In addition, those elastomers which crystallize during extension (e.g., vulcanized natural rubber) normally exhibit higher tensile strengths and ultimate elongations than those which do not crystallize (e.g., SBR rubbers). In seeking relationships between the structure and the ultimate properties of elastomers, these various factors which affect ultimate properties must be carefully considered. Previously a study was made of the tensile strength and ultimate elongation of several series of polyether-polyurethan elastomers prepared from polyoxypropylene glycol 2025 (PPG), trimethylolpropane (TMP), and either toluene 2,4-diisocyanate (TDI) or hexamethylene 1,6-diisocyanate (HDI). The structure of these elastomers was characterized by (1) the number of network chains per unit volume ν and (2) the concentration of urethan groups [U]. These parameters could be varied independently over certain ranges by making appropriate changes in the average molecular weight of PPG 2025 through blending it with dipropylene glycol (DPG). The glass temperature Tg of the elastomers increased linearly with [U], the rate of increase being considerably greater for the TDI-linked than for the HDI-linked elastomers. These elastomers apparently did not crystallize upon extension, and their ultimate properties, measured at a fixed extension rate, were found to depend on both [U] and ν. However, when compared in corresponding temperature states, i.e., at equal values of T−Tg, the ultimate properties over a wide temperature range were found to be independent of [U], or approximately so, when [U] was less than about 1.85 moles/kg. Also, the ultimate elongation was observed to be inversely proportional to ν, although the proportionality constant was temperature-dependent. It thus appears that certain elastomers which do not crystallize have ultimate properties which depend not only on ν and Tg but also on the chemical nature of the network chains.
The Temperature Shift of the Second Order Transition of Natural Rubber by Crosslinking
Authors: Heinze H. D. , Schmieder K. , Schnell Gg , Wolf K. A.
Published: February 2011

The present article reports on dynamic mechanical and infrared spectroscopic tests of natural rubber crosslinked by sulfur, peroxide or high energy radiation. The effect of these vulcanization methods upon the rate of crosslinking, the position of the second order transition temperature and the double bond structure is discussed. Whereas the temperature displacement of the transition range from the second order transition phase to the rubber elastic state during crosslinking by high energy radiation or by peroxide arises from the increasing hindrance of chain movement by the crosslinks, the intramolecular addition of sulfur predominantly is responsible for the much greater temperature displacement—related to the same crosslink density—during sulfur vulcanization. The change of the double bonds which proceeds in the sulfur vulcanization at a much faster rate than in the crosslinking by irradiation also can be considered as indication of intramolecular rings being formed along the chain during sulfur vulcanization. Vulcanization by sulfur and crosslinking by irradiation appear, principally, to be based on the same mechanism. The influence of oxidation on the mechanical properties of the vulcanizates is studied in natural rubber irradiated in an oxygen atmosphere. The two damping maxima observed at the dynamic mechanical test can be ascribed, with the aid of infrared spectroscopy, to the influence of crosslinks and oxidation products on the chain mobility.
Kinetic Interpretation of Rheological Behavior of High Polymers
Authors: Furukawa Junji
Published: February 2011

Rheological behavior of high polymers is interpreted in terms of the pseudo crosslinking hypothesis, i.e., polar groups in a polymer form a kind of pseudolink and contribute to the elastic property of the polymer, but such a crossbond as this is not so firm that plastic flow may not occur to some extent. The ratio of real elongation of polymer chain to overall elongation of specimen is demonstrated as the function of slippage of the polymer chain. Creep and stress relaxation are accounted for as the phenomena involving slippage of the chain accompanied by the elongation of the chain and the dissociation of the crossbond. The stress-strain relation in the ease of constant rate drawing is supposed to show the existence of maximum stress according to the hypothesis. Rupture of linear high polymer is also discussed supposing the breakdown of the second crossbond and the breakdown may be concluded when load applied is larger than the maximum value estimated from the equation for the equilibrium crosslinking. The rate of rupture is also discussed and the logarithmic life time in rupture is concluded to be correlated linearly to the load applied.
A Study of Synthetic Rubber Latexes by the Electron Microscope
Authors: Rupar W. , Mitchell J. M.
Published: February 2011

In emulsion polymerization the number and size of the latex particles govern not only the colloidal behavior of the reacting system but also the rate at which conversion of the monomer progresses. Because of the importance of these factors a wide variety of synthetic latexes have been studied with the electron microscope. The changes in the latex particles—from swollen monomer-polymer particles at low conversion to the final latex particles after removal of the unreacted monomer—have been observed for a typical SBR system. The effects of various post polymerization treatments on the size and size distribution of the latex particles have also been observed.
Elastomer Structure and Adhesion. II. Effect of Sidechain Double Bonds
Authors: Raevskii V. G. , Voyutskii S. S. , Livanova I. V.
Published: February 2011

1. A study was made of elastomers of the effect of double bonds in the side groups, which are capable of adding sulfur, on the variation of the strength of adhesion to fiber-forming polymers during vulcanization. 2. It is shown that the presence of such vinyl groups does not measure the general nature of the dependence of the variation of the strength of adhesion on the degree of vulcanization previously found for elastomers which do not contain vinyl side groups. However, an increase in the content of 1–2 units leads to a drop in the maximum degree of crosslinking (increase in the values of Mc, max) and to a drop in the speed of decrease of this strength after the attainment of optimum adhesion. 3. The experimental data were examined from the point of view of the diffusion theory of adhesion and complete agreement with this theory is shown.
Bonding of Polyethylene to Metals and Rubber with Hydrogenated Polybutadiene
Authors: Yakubchik A. I. , Grilikhes S. Ya , Tikhomirov B. I. , Purlova V. S.
Published: February 2011

The adhesive composition based on hydrogenated unbranched 1,4-polybutadiene gives a high bond strength between polyethylene and brass, and brass-plated metal, and rubber.
Hydrogenation of Natural and Synthetic cis-1,4-Polyisoprene
Authors: Yakubchik A. I. , Tichomirov B. I. , Sulimov V. S.
Published: February 2011

1. Hydrogenation of natural and synthetic cis-1,4-polyisoprene has been accomplished. Polymers of lower molecular weights are more easily hydrogenated. 2. Hydrogenation of cis-1,4-polyisoprene at temperatures of 80–140° are not followed by cis-trans isomerization and apparently is not accompanied by cyclization. 3. The polymers have higher glass temperatures as the degree of hydrogenation is increased.
Polymerization of Butadiene with Alkylaluminum and Cobalt Chloride
Authors: Gippin Morris
Published: February 2011

The diethylaluminum chloride combination with cobaltous chloride or cobaltous chloride pyridinates requires water in a certain mole ratio to the diethylaluminum chloride to activate them as catalysts for butadiene polymerization at 5° C to 98% cis-1,4 structure. The cobalt-pyridine complex is the preferred component because of its ability to function in trace amounts. Several organic derivatives of water failed as substitutes. However, aluminum trichloride is effective as a substitute for water on an equimolar basis. The cis-1,4 content in the polymer decreases at higher polymerization temperatures. The higher pyridinates of cobaltous chloride tend to reduce the polymer molecular weight within narrow limits. The preferred solvent is benzene, in which the concentration of the monomer is a factor in both microstructure and polymer molecular weight. Certain mixtures of benzene and hexane provide another means of controlling molecular weight. The rate of polymerization is linear with respect to time in the initial stages, and is a first-order reaction with respect to monomer at a fixed concentration of catalyst.
Ethylene-Propylene Rubber Vulcanization with Aralkyl Peroxide and Coagents
Authors: Robinson A. R. , Marra J. V. , Amberg L. O.
Published: February 2011

Ethylene-propylene rubber (EPR) has been described in terms of its performance characteristics both by Prof. Natta and by the authors, who concur basically on its merits. Before such evaluations were possible, however, a difficult vulcanization problem was faced. The same paraffin inertness which is advantageous in the vulcanized product ruled out most of the conventional vulcanization technology. Work on the vulcanization problem at Hercules indicates that, with few promising alternatives, aralkyl and alkyl peroxides provide the best practical solution. This paper presents some conclusions and interpretations based on the exploratory work at Hercules on the EPR vulcanization process with dicumyl peroxide. The supporting evidence is derived mainly from crosslink density analysis by the solvent swelling method of Kraus. Special use was made of a “per cent gel” factor and of analysis of the sol fraction of incompletely cured vulcanizates. The copolymers described were prepared in Hercules laboratories.
Ethylene-Propylene Copolymers Produced with Soluble Catalysts
Authors: Kelly R. J. , Garner H. K. , Haxo H. E. , Bingham W. R.
Published: February 2011

Soluble catalyst systems derived from alkyl aluminum halides in combination with vanadium oxytrichloride or tetrachloride produce highly random ethylene-propylene copolymers with high catalyst efficiency. By the choice of the alkyl aluminum halide and molar ratio of aluminum to vanadium, variations in polymerization efficiency and molecular weight are possible. The copolymers prepared with these soluble catalysts show advantages in both processing and physical properties over those prepared with heterogeneous catalysts. Vulcanizates of these copolymers show somewhat different accelerated aging properties depending on the additive used along with the peroxide. Low temperature properties of copolymers containing less than 70 weight % propylene show a tendency for crystallization which is not shown by X-ray diffraction. Overall physical properties and tire tests show some preference for the 65 weight % propylene copolymer over the 50% material.
Theory of Random Filler Dispersions in Rubber
Authors: Gehman S. D.
Published: February 2011

Ideal mixing results in random filler distributions in rubber, in which case the number of particles in a field follows the Poisson distribution deduced from probability theory. There should be no advantage in continuing the mixing after a random distribution has been achieved. The closeness of the approach to a Poisson distribution is to be ascertained by counting the number of particles in many small fields. Random configurations of particles may sometimes be deceptive in suggesting the existence of attractive forces between the particles. The frequency distribution for the thickness of the rubber matrix between the particles in a random distribution is derived by use of a suitable model and probability considerations. The frequency of occurrence decreases exponentially with increase in thickness and is a function of the particle diameter and the volume loading. In theory, the same thickness distribution can be obtained for fillers differing in average particle diameter by suitable variations in the loadings. As a practical matter, the thickness distributions with the finer rubber fillers cannot be duplicated with coarse fillers because of the high loadings required. The model is used to estimate the modulus enhancement to be expected from an increased crosslinking density at the surface of a reinforcing particle which decreases exponentially with the distance from the surface. The results indicate the possibilities of this mechanism for explaining the enhanced modulus exhibited by reinforcing as contrasted to inactive fillers.
Reinforcement of Natural Latex Rubber by Carbon Black and Ionizing Radiation
Authors: Lamm A. , Lamm G.
Published: February 2011

The study of the reinforcement of rubber by carbon black has made it possible to establish the radical nature of the interaction, thus explaining why, in the latex phase and in the absence of sources of radicals, the reinforcing effect of carbon black does not exist and why it has been possible up to the present to obtain it only by mastication of the solid rubber in the presence of black. Irradiation, an excellent source of radicals, should in latex systems lead to a reinforcement of rubber by black. The experiments carried out appear to prove this. Irradiation of the latex and the black in aqueous dispersion, followed by a mixture of the two constituents which is then poured out on a plate, dried and subjected to moderate thermal treatment, makes it possible to obtain mechanical properties which are definitely superior to those of films prepared without irradiation and of films vulcanized with sulfur.
A Molecular Theory of Filler Reinforcement Based on the Concept of Internal Deformation
Authors: Sato Yoshiyasu , Furukawa Junji
Published: February 2011

A molecular theory is presented which gives an analytical method to describe filler-reinforced heterogeneous elastomers and the cavitation therein caused by elongation. By using a suitable model and a new concept a proper method of analysis for a heterogeneous system is obtained. By means of this method the overall internal mechanism of filler reinforcement can be understood; especially it is made clear that reinforcement consists of three effects: a volume effect, a surface effect and a cavitation effect. Also, formulas for several main quantities are derived: tension, swelling tension, Young's modulus, local stress distribution, condition for swelling equilibrium, etc.
The Structurization in Hydrocarbon Suspensions of Carbon Black in Relation to the Behavior of Active Rubber Fillers
Authors: Yampolskiĭ B. Ya , Shu-Tsiu U. , Rebinder P. A.
Published: February 2011

In spite of the numerous investigations of the reinforcing properties of active rubber fillers, up until now the role of interacting particles of fillers, both between themselves and with the dispersion medium, for example macromolecules of polymers, has not been clear. No physico-chemical mechanism for the function of active rubber fillers have been clarified. We have studied the processes of structurization in model systems, using carbon black as an important example of rubber filler. The investigations were conducted with concentrated suspensions in nonpolar hydrocarbon media. The influence of filler content, polymer concentration, surface tension, wetting agents and temperature were studied. We employed the method of measurement of electrical conductivity, recording volt-ampere curves, using a wide range of potential gradients. At the same time, studies of the mechanical structure properties (thixotropy) of the suspensions were made. Volt-ampere curves were obtained from data recorded during the introduction of constant current voltages in intervals ranging from 0.01 V to 100 V. The corresponding fluctuation of potential gradient was of the 4th order, from 0.25 to 250 V/cm. The measurements were carried out over a period of three hours immediately after preparation of the experimental suspension. Thus a suspension of Type A lamp black in non-polar mineral oil was prepared by a standard method, assuring good reproducibility in the experiments. In the period of three hours specific conductivity of greatest value, λm was obtained, with practically no change with time, testifying to the completion of the process of coagulation, or gel structure
Relation of Physical Behavior to Molecular Packing in Crosslinked Rubber
Authors: Mason P.
Published: February 2011

The physical consequences of crosslinking a polymer are, first, the establishment of the molecular network on which the equilibrium rubberlike elasticity depends; Flory has shown how the creation of this network leads to an increase in the internal pressure of the system, so that crosslinking will be expected to produce a reduction in volume on this account alone. Secondly, there is another, more localized, change in molecular packing resulting in a reduction in volume, an increase in the glass-transition temperature, and a shift of the mechanical and dielectric dispersion regions towards higher temperatures. Structural interpretation of these effects has hitherto been impeded by three difficulties: (i) the determination of crosslink density; (ii) the presence of the “foreign” atoms constituting the crosslink; and (iii) modifications to the polymer chains occurring during crosslinking. A system is therefore being studied in which these difficulties are largely avoided. Purified natural rubber is heated with dicumyl peroxide for 1 hour at 140° C; the resulting crosslinks are direct covalent bonds between carbon atoms in neighboring chains. No “foreign” atoms are introduced, and there is substantially no modification of the rubber molecules. After extraction and drying, the equilibrium degree of swelling in n-decane is measured and used to obtain the crosslink density by reference to the original chemical determinations of Moore and Watson. Measurements are then made of the specific volume at 20° C, the thermal expansion behavior and the dynamic mechanical behavior, both over a temperature range including the glass-rubber transition.
Dynamic Testing Apparatus for Rubbers and Plastics
Authors: Trivisonno N. M. , Stearns C. A. , Kime J. M.
Published: February 2011

A dynamic testing apparatus for rubbery and plastic materials has been built. Operation is based on the principle of the electromechanical transducer. Dynamic properties are calculated from direct measurements of the force generating current, the velocity produced voltage, and the phase angle between them. Frequency range is 50 to 500 cps, temperature range −25° C to 100° C, and strain range 0.01 to 0.0001. Results are presented for a standard polyisobutylene sample, natural rubber, synthetic cis-polyisoprene, and perdeuterio cis-polyisoprene. No significant differences were found among the latter three.
The Relation between Structure and Physical Properties in Polyurethans
Authors: Tanaka Takehide , Yokoyama Tetsuo
Published: February 2011

The field of polyurethans is rapidly growing in commercial importance, especially in form and elastomer applications. This group of polymers includes a very broad region of chemical structures and chain length. In many cases polyurethans are synthesized from polyester glycols or polyether glycols and diisocyanates so that the urethan groups are even fewer in number than other functional groups. This process of synthesis enables us to deal with a very wide range of polymer properties, adding interest to the studies of relation between structure and properties. Though a considerable number of publications dealing primarily with the properties of urethan polymers have been published, few of them contribute to better understanding of the relation between these properties and the corresponding polymer structure. Within the last few years information of value has become available, and Saunders has established some semi-quantitative relations by the use of such data. He also discusses in his reports general considerations concerning structure-property relationships. Although his considerations and conclusions show a marked progress, they are not theoretically satisfactory yet, especially from a quantitative viewpoint. The authors have investigated structure-property relationships in polyurethans for a few years and written some papers concerning synthesis, reaction kinetics, some physical properties, network structure, and dynamic behavior of polyurethans.
Volume Changes and Dewetting in Glass Bead-Polyvinyl Chloride Elastomeric Composites under Large Deformations
Authors: Smith Thor L.
Published: February 2011

Elastomeric materials loaded with inert filler have Theological properties which, on the one hand, are qualitatively like those of unfilled polymeric materials, but which, on the other hand, are unique to filled systems. Their stress-strain curves usually have several distinct regions which are similar to those for certain unfilled polymeric materials. The curves have an initial region in which the stress increases with strain, and here the modulus depends primarily on the amount of filler and the properties of the binder. In the second region, the stress may be roughly independent of the strain or may increase at a rate markedly less than that in the initial region. The transition between these two regions may be either gradual and hardly perceptible or sharp, with a well-defined yield point. Thus, in these two regions, the stress-strain curves may be like those for typical unfilled rubbers or for plastics, or they may resemble the curves for rubbers at low temperatures, which cold draw or neck. In the third region the stress increases more rapidly with strain than in the second region and continues to increase until the specimen breaks; again, this is similar to what is observed for certain plastics and rubbers. Thus, both filled and unfilled systems can have sigmoidal stress-strain curves which may or may not have distinct yield points. However, filled systems, and especially those in which the binder wets, but does not react chemically with the filler, exhibit the sigmoidal-type stress-strain curve for different reasons than do rubbers and plastics. In filled systems, the binder adheres to the filler initially, which reinforces or strengthens the system. However, in the transition and second regions of the stress-strain curve, adhesive bonds between the filler and binder break, a process called dewetting, and vacuoles form around the filler particles. After the adhesive bonds are essentially all broken, a further increase in strain only stretches the binder further and enlarges the vacuoles.
The Pico Laboratory Abrasion Test
Authors: Newton Edwin B. , Grinter Hershel W. , Sears D. Scott
Published: February 2011

The Pico abrasion tester can be adjusted to simulate wide conditions of severity. It can also be adjusted to approximate the severity of test encountered in ordinary 60 mph road tests to give laboratory data which agree fairly well with road results. It can evaluate tread stocks made with different polymers quite as well as evaluate different carbon blacks in the same polymer.
Studies on the Structure of SKN-26 and SKN-40 Rubbers Using Ozonolysis Methods
Authors: Yakubchik A. I. , Spasskova A. I.
Published: February 2011

It has been established that the macromolecules of SKN-26 and SKN-40 rubbers are constructed from units linked:
The Shape of Specimen and the Measurement of Permanent Set
Authors: Yabuta Shiro
Published: February 2011

Stress distributions in an ASTM or JSI-specimen and a rectangular strip specimen were investigated. It is concluded that the dumbbell type specimen is not suitable for the determination of permanent set, because of the considerable variations of stress concentration due to the influence of the curved parts on the parallel part. The strip specimen, deforming uniformly, is preferable to the dumbbell specimen.
A New Indentor Hysteresimeter
Authors: Tangorra G.
Published: February 2011

Although the apparatus described here is not without limitations, it has some obvious advantages over the previously described dynamic tests. Owing to the simplicity and rapidity of the test as well as to its apparent standardization possibilities, it seems probable that it could prove of practical use in technological and industrial fields.
Effects of Carbon Black Structure on Tire Tread Wear
Authors: Bolt T. D. , Dannenberg E. M.
Published: February 2011

Oil furnace process carbon blacks have been produced which differ widely in the extent of their primary chainlike aggregation. The effect of the carbon black structure on rubber properties and road wear was evaluated in oil-extended SBR passenger tire tread compounds. The decrease in primary particle aggregation increases the tendency to form strong, dense, secondary agglomerates which require mixing techniques designed to insure that they are well dispersed. The behavior in rubber of a series of oil furnace blacks differing primarily in their structure is most apparent in processing, shrinkage, modulus and hardness. There are small effects on rebound and flex cracking resistance but no significant effects on tensile strength and heat buildup. Carbon black structure can be reduced to some extent without encountering significant loss in road wear resistance under normal wearing conditions. Some decrease in road wear performance occurred under very severe road test conditions. The use of higher black loadings of the normal structure blacks gave good wear resistance under both normal and severe service conditions.
Rupture of Rubber. VI. Further Experiments of the Tear Criterion
Authors: Thomas A. G.
Published: February 2011

In previous papers (I to V of this series), a tear criterion for rubbers has been proposed based on an energy balance approach. This equates the energy required to form new surfaces (the tearing energy) with the loss of elastic strain energy in the test piece. The tearing energy T is assumed to be characteristic of the material and so independent of the overall shape of the test piece. It is thus the fundamental property controlling tear behavior. The correctness of this approach was investigated by making tear measurements on test pieces of different shapes but of the same material and examining the constancy of the T values obtained. The results were consistent with the theory but not wholly conclusive, due primarily to the particular tearing behavior of the materials used (natural rubber gum vulcanizates). Another limitation was that accurate T values could be obtained only if they could be calculated directly from the measured tearing forces or elongations, and the required relationships were known for only two types of test piece. Clearly, the more test pieces available for comparison and the more they differ from each other in shape, the more stringent the test of the basic theory. In the present paper a third test piece is described, the necessary theory given, and experimental results presented on the three test pieces. By comparing the results from these test pieces, which are of widely different shapes, a critical test of the theory is possible. The choice of the experimental material is influenced by several factors. Previous measurements have been made on natural rubber gum compounds, which have the advantage of possessing excellent elastic properties but whose rupture characteristics are such that tearing occurs at a critical load. In contrast, a gum GR-S tears more or less steadily at a rate depending on the load, a characteristic which is experimentally advantageous for the particular test pieces described here. It was therefore used in this investigation.
Rupture of Rubber. VII. Effect of Rate of Extension in Tensile Tests
Authors: Greensmith H. W.
Published: February 2011

There are few published measurements on the effect of rate of extension in tensile rupture tests on rubber vulcanizates. The most extensive data on a single vulcanizate are those of Dogadkin and Sandomirskii˘ and of Smith. These measurements were made on GR-S gum vulcanizates and covered a similar range of rates of extension, from about 0.02 to 20%/sec. Ring specimens were used in both cases, and tensile strength and breaking extension were measured over a wide temperature range. Villars has made tensile strength and breaking extension measurements on double dumbbell specimens of several gum and filled vulcanizates extended at various rates in the range 10,000 to 100,000%/sec. Kainradl and Handler have reported tensile strength measurements for several filled vulcanizates, obtained with dumbbell specimens extended at four different rates of extension covering a range from about 1 to 100,000%/sec. All these results indicate that tensile strength and breaking extension can vary appreciably with the rate of extension of the specimen. Complete load-extension curves are not given in any of these papers. In the present paper an autographic method is described for obtaining the load-extension curves of ring specimens extended at various rates from about 0.1 to 2000%/sec. Results showing the effect of the rate of extension on the tensile strength and breaking extension and on the load-extension curve are given for GR-S vulcanizates. The data were obtained primarily for the comparisons of tear and tensile rupture measurements given in a subsequent paper (Part VIII).
Newer Synthetic Rubbers Derived from Olefins and Diolefins
Authors: D'Ianni J. D.
Published: February 2011

Synthetic rubbers are of significant interest to the petroleum industry, since nearly all of the raw materials required in their production are petrochemical in nature. Many of these petrochemicals are produced in large quantities for other chemical end uses as well. Among the most important of these large-tonnage intermediates are butadiene, styrene, acrylonitrile, chloroprene and isobutylene. The newer developments in synthetic rubber, to which this paper will largely be devoted, have focused greater attention on other monomers, such as isoprene, ethylene and propylene. The following figures will give some idea of the present and future consumption of these raw materials, largely based on petroleum, for chemical manufacture:
The Nature of Static Friction in Elastomers
Authors: Bartenev G. M. , Lavrent'ev V. V.
Published: February 2011

1. A method free from the shortcomings of earlier work is proposed for the measurement of the friction of elastomeric materials in the initial moment of shear. 2. From results of measurement of friction of rubber on steel it follows that static friction, determined as the coefficient of friction in the initial moment of slip, is a conventional parameter, since it depends upon the accuracy of measurement of the movement and upon the rate of application of the tangential force. 3. The conventional coefficient of static friction of elastomeric materials is particularly evident at low rates of application of the tangential force, which fact is connected with the nature of dry friction of rubberlike polymers.
Molecular Basis for The Mullins Effect
Authors: Bueche F.
Published: February 2011

The physical phenomena now widely known as the “Mullins effect” was apparently first studied in detail by Holt in about 1930. He showed that if a vulcanized rubber which contains carbon black is stretched to a relative elongation αm=L/L0 and released, it will not follow the same stress-strain curve when it is stretched once again to this same elongation. Instead, the rubber appears much softer on the second stretch for elongations below αm. Holt examined this behavior in some detail and showed that additional pre-stretches to αm softened the rubber further, but to a lesser degree than was observed on the first prestretch. In addition, Holt showed that the rubber regains a portion of its stiffness if allowed to rest in the relaxed state. Although this recovery was very slow at room temperature, up to about 50% recovery was noted after about an hour at 100° C. Similar softening effects were noted in gum stocks at exceedingly high elongations, but the effects were much less marked than in the filled stocks. This same effect was examined in more detail by Mullins after 1940. His results confirmed and greatly extended the earlier results of Holt. In addition, Mullins speculated about the mechanisms involved but came to no definite conclusion in that regard. Later, however, he and Tobin presented a phenomenological theory for the effect wherein they considered the rubber to be composed of hard and soft regions. They showed that their data could be described by assuming that some fraction of the hard regions became soft after a prestretch. No definite molecular basis for this process was proposed by Mullins and Tobin, although they speculated that either the breaking up of filler particle aggregates or the breaking loose of rubber to filler bonds might be involved. Later work by Blanchard and Parkinson confirmed and extended the data of Holt and Mullins. Further, these authors concluded that the softening was due to the breaking of rubber to filler bonds. They incorporated this idea into a semiempirical theory which agreed with their experiments. In addition, they obtained what they believed to be a distribution for the strength of the rubber-filler bonds. It will be seen in that which is to follow that their distribution probably does not represent what they thought it did, even though their basic ideas were correct.
Non-Linearities in Dynamic Tests II. Impact and Rolling Wheel Tests
Authors: Gough V. E.
Published: February 2011

Viscoelastic properties of rubberlike materials are currently studied by a number of methods: vibration methods involving a single degree of freedom system, measurement of the stress-strain curves under cyclic application of deflection, impact tests and tests using rolling wheels. The effect of non-linearities on the motion of a single degree of freedom system is discussed in detail in Reference 1 and it is concluded that the analysis employed must not contain an arbitrarily assumed equation of motion nor an arbitrary stress-strain relationship if the objective of the tests is to determine the true character of the viscoelastic properties and to relate these to the molecular properties of the material. The character of the viscoelastic properties must be derived from experiment by methods free from inbuilt mathematical assumptions and it is shown that phase plane analysis can be adapted for that purpose. It is also noted in Reference 1 that measurement of the stress-strain properties during cyclic application of deflection is free from inbuilt mathematical assumptions. The question which is examined in this related paper is whether the study of impact tests and rolling wheels using energy methods is subject to similar and/or other necessary conditions.
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

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.