bluuebunny/crossref_metadata_2025 huggingface dataset:
The Thermoelastic Properties of Rubber
Authors: Meyer Kurt H. , Van der Wyk A. J. A.
Published: February 2011

In an earlier communication it was shown that, within a certain range of elongations, viz., 100 to 300 per cent, and at constant elongation, the stress in stretched rubber is directly proportional to the absolute temperature. Within this range, therefore, the stress is analogous to the pressure of an ideal gas, which at constant volume is likewise proportional to the temperature. This behavior of rubber and of other rubberlike substances is said to be ideal. However, a sample of rubber the behavior of which is ideal at elongations of 100 per cent and higher deviates from this behavior when its elongation is less than 100 per cent or greater than 500 per cent. One of the reasons for these deviations from ideal behavior at high deformations has already been discussed in a previous publication; as a result of stretching, rubber begins to crystallize. The crystallites do not contribute to the elastic force, but if the temperature is raised, they fuse and thereby increase the stress, which then increases more rapidly than that of an ideal rubber. The deviations from ideal behavior at small deformations have not in any way been studied thoroughly, so the first part of the present work is concerned with these deviations from ideal behavior. First of all it is well to discuss some experimental facts. The thermal coefficient of the force F at constant elongation Δl, (∂F/∂T)Δl, is negative for low elongations (up to about 10 per cent), i.e., the force decreases with rise in temperature, and the coefficient of linear expansion in the direction of traction remains positive, like that of an ordinary material. At elongations of approximately 10 per cent, the stress is independent of the temperature; at this point the coefficient of linear expansion in the direction of stretching is, therefore, equal to zero. At higher deformations, the stress increases with rise in temperature, a phenomenon which indicates a negative coefficient of linear expansion.
Mechanism and Theory of Vulcanization
Authors: Stiehler Robert D. , Wakelin James H.
Published: February 2011

x-Ray and stress-strain data have been obtained which indicate that accelerators and divalent metallic compounds, as well as sulfur, react with rubber molecules during vulcanization and become a part of the rubber vulcanizate. The vulcanization reaction was found to behave like a normal chemical reaction in solution, which is influenced by the temperature, solubilities of the reacting ingredients, relative strengths and concentrations of the acids present, pH, and chemical nature of the vulcanizing agent. On the basis of these results and the known characteristics of vulcanized rubber, the original hypothesis of Goodyear and the more recent conclusions of Midgley, Henne, and Shepard were developed into a theory of vulcanization which postulates that vulcanization is a process by which the intermolecular forces are increased through the introduction of polar groups, generally acidic in nature, into the rubber molecules. This is accomplished by the reaction of certain types of oxidizing agents with the alpha-methylene carbon atoms or double bonds. These intermolecular forces are further increased with soluble divalent metallic compounds by the formation of ionic valences between divalent metallic ions and polar acidic groups of the rubber vulcanizate. These divalent metallic ions may bridge the rubber molecules through ionic valences in the form of a salt. Intermolecular forces established during vulcanization give rigidity to the molecular structure, which retards plastic flow and crystallization of rubber molecules. They also are responsible for other characteristics of vulcanized rubber. The molecules in vulcanized rubber are presumably not joined by primary-valence bonds through sulfur or oxygen bridges, but retain their individual existence.
The Combined Action of Maleic N-Methylimide and p-Bromobenzoyl Peroxide on Natural Rubber
Authors: Delalande André
Published: February 2011

It is already known that natural rubber is capable of combining, under certain conditions, with various unsaturated compounds. Bacon and Farmer, for example, have fixed maleic anhydride on rubber in solution in the presence of benzoyl peroxide. This reaction has been applied likewise to acrylic acid, to acrylonitrile and to methacrylonitrile. Bacon and Farmer carried out the reaction with solutions of rubber which were refluxed for 18 hours, without, however, attempting to avoid the extraneous effect of atmospheric oxygen. The present author was, therefore, prompted to carry out the reaction protected from air in sealed tubes into which the solvent was introduced by distillation in a vacuum according to a technique based on that employed by Moureu and Dufraisse in their studies of autoxidation. In an effort to explain the mechanism of the reactions, maleic N-methylimide was chosen as the unsaturated reagent in the reaction and p-bromobenzoyl peroxide as the catalyst. These two compounds, in virtue of the nitrogen atoms and bromine atom in their respective molecules, made it possible to determine by analysis what became of them as a result of the reaction.
The Photoelastic Properties of Rubber. I. Theory of the Optical Properties of Strained Rubber
Authors: Treloar L. R. G.
Published: February 2011

From the consideration of vulcanized rubber as a network of randomly kinked molecular chains, the optical constants corresponding to the most general type of homogeneous strain are derived. Under such a strain the rubber is shown to acquire the properties of an optically biaxial crystal, characterized by three principal refractive indices in the directions of the principal axes of strain. For directions of light propagation parallel to one of the principal axes, the birefringence is shown to be a simple function of the principal extensions and is, moreover, proportional to the difference between the two corresponding principal stresses. If the rubber is swollen with a liquid having the same refractive index as itself, the birefringence for a given state of strain varies inversely as the cube root of the swelling ratio, as do also the principal stresses.
The Photoelastic Properties of Rubber. II. Double Refraction and Crystallization in Stretched Vulcanized Rubber
Authors: Treloar L. R. G.
Published: February 2011

From an investigation of the variation of birefringence, with elongation in vulcanized rubber extended at temperatures ranging from −50° to +100° C, it is possible to distinguish the effects of crystallization from the true strain-birefringence. The latter agrees closely with theoretical expectations in its dependence on stress and on elongation. The data do not permit of a quantitative estimation of the relative amounts of crystalline material present under various conditions. Experiments with stretched swollen rubber further confirm the theory and yield further evidence on the effects of crystallization.
Equilibrium Properties of High Polymer Solutions and Gels
Authors: Gee Geoffrey
Published: February 2011

The equilibrium between a polymer and a liquid is of fundamental importance in a number of problems of considerable practical as well as theoretical interest. As examples may be mentioned: (1) the choice of a solvent or plasticizer for a given polymer; (2) choice of a suitable polymer for use, e.g., as a gasket in contact with specified liquids; (3) the combined solvent or swelling action of a mixture of liquids; (4) the effect of mechanical deformation, e.g., compression, on the solvent resistance of a polymer; and (5) the separation of a polymer into fractions by the use of solvent-precipitant mixtures. It must be emphasized at the outset that in some of them other factors are involved, but these are not considered in the present paper. The basic assumption is made here that, given enough time, a system comprising polymer and liquid will reach a steady state, and that if two condensed phases are then present, they must be in true thermodynamic equilibrium. The disturbing influence of such time-dependent processes as degradation and plastic flow may, in certain practical cases, prevent the attainment of a steady state, but these possibilities require separate discussion. Within the limited space available, all that can be attempted is a brief outline of the general methods which have been used, illustrated by applying them to the first two of the above problems.
Preparation and Properties of Rubberlike High Polymers. IV. Correlation between Structure and Properties of Elastomers Derived from Dienes
Authors: Salomon G. , Koningsberger C.
Published: February 2011

The correlation between structure and properties of elastomers prepared from dienes, natural rubber, gutta-percha, as well as those of some significant derivatives of natural rubber, are discussed. The similar influence exerted by methyl groups on the brittle point, elastic recovery, and permeability to gases is demonstrated and separated from the effect caused by insertion of —CH2— CHR— groups in straight-chain polybutadiene, which takes place during co-polymerization or 1,2 addition. The preponderant influence of an unbranched-chain structure on tensile strength at elevated temperatures and in the swollen state is illustrated. Complex compounds with silver nitrate provide further evidence for the particular symmetry of the natural rubber chain: They are reinforcing agents for synthetic elastomers. The brittle points of hydrochlorides from natural rubber, gutta-percha, and polyisoprene are compared with those of polyvinyl compounds. Correlation between the structure of molecular units in a polymeric paraffin derivative and its elasticity is pointed out.
Some Structural and Chemical Aspects of Aging and Degradation of Vinyl and Diene Polymers
Authors: Mesrobian Robert B. , Tobolsky Arthur V.
Published: February 2011

The chemical reactivity of vinyl and diene polymers manifested during aging and degradation is similar to the reactivity manifested during polymerization. The activated intermediates are radicals, and the reaction proceeds by a chain mechanism. A discussion of the possible types of aggregative and disaggregative processes involved in aging is presented. On the basis that polymerization and degradation occur by means of the same radical mechanism, experimental evidence is given to indicate that under certain conditions both reactions may occur simultaneously. Viscosity changes of solutions of mono- and polystyrene and methyl methacrylate were studied under varying conditions of heat, oxygen, catalysts, light, and photosensitizers. An analysis of the concurrent aggregative and disaggregative reactions involved in aging may be obtained by isolating one reaction from the other, either by various physical methods, such as intermittent and continuous stress relaxation, or by such classical methods as sol—gel determinations and aging in solution. A comparative study of the rate of oxygen absorption of a large number of polymer types was undertaken to evaluate the factors affecting oxidation. Evidence is presented to show that these factors may be specified by the following: (1) chemical structure of the polymeric material, (2) presence of antioxidants, and (3) compounding and vulcanization. The oxidizability of polymeric materials was also studied in a circulating oxygen absorption apparatus to determine the effect of evolved, gaseous oxidation products. A preliminary study of the effect of light on the aging of Butyl and GR-S, measured by oxygen absorption and stress relaxation, is presented.
Properties of Polychloroprene Molecules in Solution
Authors: Svedberg Ingrid , Kinell Per-Olof
Published: February 2011

Polychloroprenes from emulsion and bulk polymerization were investigated in the ultracentrifuge and by means of diffusion experiments. It was found that the sedimentation constants for B-polymers are independent of the polymerization conditions. This is not to the same degree the case for A-polymers. The diffusion coefficients of both types of polymers are more sensitive to differences in size of the molecules formed. A linear relationship between diffusion coefficient and the inverse value of the molecular weight has been established for B-polymers, and an inverse square root dependence for A-polymers. In the terminology of Kuhn and Kuhn, the molecules of the B-polymers should be completely drained and the molecules of the A-polymers incompletely drained. The shape of the molecules and the polydispersity of the substances are discussed. The difficulties of obtaining true and accurate values of molecular constants for such an inhomogeneous material are pointed out. This investigation is a part of fundamental research work on synthetic rubber carried out at the request of the Government Commission on Industry in Sweden and under the direction of Professor The Svedberg. The authors wish to express their sincere thanks to Professor The Svedberg for his very kind interest and for the main facilities put at their disposal.
Evaluation of Sodium-Catalyzed Copolymers of 1,3-Butadiene and Styrene
Authors: Juve A. E. , Goff M. M. , Schroeder C. H. , Meyer A. W. , Brooks M. C.
Published: February 2011

Sodium-catalyzed butadiene-styrene copolymers (S-BS), of composition 75 weight-per cent butadiene: 25 weight-per cent styrene, have been compounded in tread type recipes. Evaluation tests showed properties significantly different from those of GR-S, the emulsion-phase free radical—catalyzed copolymers of identical monomer composition. 1. The processing characteristics of S-BS are considerably superior to those of GR-S, although one experience with a high temperature internal mix may indicate some limitation. Objective laboratory processing tests show that S-BS resembles high-styrene emulsion copolymers in that it can be satisfactorily fabricated from stocks containing less filler than is required in GR-S stocks for similar uses. 2. Stress-strain properties based on limited compounding studies are similar to those of GR-S. 3. The flex crack growth—hysteresis balance for S-BS vulcanizates is much superior to that of GR-S vulcanizates. Vulcanizates of emulsion polymers of high styrene content also had a flex crack growth—hysteresis balance superior to that of GR-S vulcanizates. 4. The low temperature properties of S-BS vulcanizates are inferior to those of GR-S vulcanizates. Brittle points and low temperature Young's modulus of S-BS vulcanizates are much higher than those of GR-S vulcanizates.
Effects of Cross-Linking and Branching on the Molecular Constitution of Diene Polymers
Authors: Flory Paul J.
Published: February 2011

Reaction mechanisms whereby cross-linked and branched polymer structures may be formed during the polymerization of dienes are discussed. A kinetic treatment of the formation of cross-linkages via the occasional addition of a free radical to the unsaturated carbon of a structural unit of a previously polymerized molecule is presented. It is pointed out that the rate of this addition step relative to monomer addition can be deduced from the average chain length and the conversion at which gelation occurs. Cross-linkages introduced by the mechanism under consideration are not distributed at random, but the deviations from a random distribution are unimportant except at high conversions. Conditions are examined under which the cross-linking reaction decreases the total number of molecules more rapidly than they are formed. Physical properties of polymers (with particular emphasis on vulcanized rubbers) are most conveniently interpreted in terms of (1) the primary molecular weight (i.e., molecular weight in the absence of cross-linkages) and its distribution, and (2) the concentration of cross-linkages. The actual molecular-weight distribution, which may be severely distorted by the presence of cross-linkages, is inappropriate for direct correlation with the more important physical properties. The modifiers or regulators commonly employed in diene polymerizations suppress gel formation by reducing the primary molecular weight; they do not actually reduce cross-linking. This reduction in molecular weight is not without other undesired consequences, however.
The Addition of Thio Compounds to Olefins. II. Reactions of Thiolacetic and Mono-, Di-, and Trichlorothiolacetic Acids
Authors: Cunneen J. I.
Published: February 2011

Cyclohexene, 1-methylcyclohexene, dihydromyrcene, squalene, and rubber combine additively with the above named thio acids, the reactions proceeding similarly to, but more easily than, those reported earlier for thiols. The parallelism noted previously between the ease of thiol addition and the facility of proton removal from the S—H bond, as measured by acidity, not only extends to thiol acids generally, but also accords with the fact that among the latter themselves the more acid chloro-substituted compounds are the more active addenda. A reactivity order, cyclohexenes > dihydromyrcene > squalene > rubber, is again evident, but whereas this serves to make the last olefin inert towards thiols, yet thio acid adducts are readily prepared, and these are of considerable technological interest as oil- and gasoline-resistant rubbers.
Crack Growth in GR-S Tread Stocks. Relation to State of Cure and Composition
Authors: Juve A. E.
Published: February 2011

A quantitative relation has been established between rate of crack growth and temperature rise, as determined in the Goodrich flexometer test, for GR-S tread stocks compounded with normal quantities of EPC or MPC blacks. This is shown in Equation 1. The relation is valid for all variations which affect the state of cure—that is, time of cure, sulfur or accelerator variation, retarding or activating softeners, etc. For other variations in the tread composition, such as an increase or decrease in the loading of the EPC or MPC black, Equation 2 holds. This relation is valid for all other known recipe modifications which do not involve carbon blacks other than EPC or MPC. Improvements in the balance between flex-cracking and rise in temperature, obtained by compounding or by an improvement in the polymers, may be expressed as the ratio of the observed flexing life to the calculated flexing life using the equation appropriate to the case. This ratio is termed the quality index. Coarser blacks substituted for the EPC or MPC blacks give an improvement in the balance between temperature rise and crack growth. The slope of the curve relating crack growth to heat rise is the same for a variety of flexing machines and for various testing temperatures. Knowledge of this relation has made it possible to evaluate, with some confidence, compounding changes intended to improve the resistance to crack growth without a sacrifice in temperature build-up, and also to evaluate small quantities of experimental polymers without the necessity for precise adjustments in either the proportions of curing agents or curing time.
Measurement of the Scorch and Cure Rate of Vulcanizable Mixtures, Using the Mooney Plastometer
Authors: Shearer R. , Juve A. E. , Musch J. H.
Published: February 2011

The Mooney plastometer may be used to measure the scorching rate and the curing rate of vulcanizable mixtures through a range of temperatures, including the usual processing and curing temperatures. From the data obtained the temperature coefficients of the two processes can be readily calculated. The values for the latter, for the particular mixtures tested, were as follows: The combined cure-rate coefficients should correspond to those determined from stress-strain data. These were found to be: This agreement confirms the accuracy of the corrections applied to the Mooney data as well as the Mooney method for these measurements. When the scorch and cure-rate coefficients are known, both rates may be measured at one temperature, and the results obtained extrapolated with some confidence to higher or lower temperatures.
The Coefficients of Adhesion of Rubber
Authors: Thirion Pierre
Published: February 2011

What conclusions can be drawn from all these experiments? Attempts to find a possible relation between the adhesion characteristics and other mechanical properties of rubber have been unsuccessful. Nevertheless, from a purely qualitative point of view alone, the coefficients of adhesion become progressively less sensitive to pressure as the rubber approaches more and more to the solid state. This seems to be a general rule to which there is no exception. The theoretical interpretation of this peculiar property of rubber cannot be discussed within the scope of the present paper; in fact it offers a complicated problem, for scientific data on the behavior of rigid solids in contact are extremely scarce. Theories advanced to explain the external friction of solids are numerous, but none gives a truly complete explanation of the phenomenon. However, it seems probable at least that the peculiar behavior is attributable to the characteristic state of materials with rubberlike properties, i.e., a state intermediate between that of liquids and of solids. There are numerous applications where advantage is taken of the high resistance to sliding of rubber on the surfaces of dry solid bodies. There would be no point in calculating a priori their coefficients of adhesion under service conditions from the results obtained in the present work, for conditions in service are generally of a very complex nature and, also are extremely variable. Pneumatic tires on automobiles are a very good example of such conditions. On the other hand, in applications such as transmission belts and autorail pneumatic tires, which operate under much more uniform conditions, there is reason for believing that systematic tests of this kind might be of some use.
Precision of Tests for Tear Resistance
Authors: Morris Ross E. , Bonnar Robert U.
Published: February 2011

The Winkelmann tear test with the crescent specimen has been widely used in the rubber industry. The American Society for Testing Materials has adopted this test, using two forms of the crescent specimen, with a single nick in each as recommended by Poules. Recently Buist demonstrated that the result obtained with the A.S.T.M. type B crescent specimen is very sensitive to the depth of the nick. He found that the same blade-setting did not make the same depth of nick in all stocks. To overcome this difficulty he developed a cutting machine in which the blade setting could be changed to secure, by cut and try, a nick depth of exactly 0.02 inch, as specified by the American Society for Testing Materials. Just previous to the publication of Buist's work, a paper by Graves described tests on an angle-tear specimen, and gave data and observations to show that this specimen had the following advantages over the crescent specimen: 1. No nick is required. 2. Test results are more reproducible. 3. Pulling stress is more concentrated at the point of rupture.
Correlation of Laboratory and Service Abrasion Tests of Rubber Tire Treads
Authors: Juve A. E. , Fielding J. H. , Graves F. L.
Published: February 2011

There appears to have been no substantial improvement in the degree of correlation between laboratory abrasion tests and service tests on rubber tires since the 1931 Symposium on Abrasion Testing of Rubber. The limitations with respect to compounding variations are essentially the same today as then. The data on rubber products other than tires are too few to permit any conclusion to be drawn. The reasons for the failure of laboratory tests to correlate with road results are many and varied. Some of these are listed in this report. They represent not only weaknesses in the laboratory procedures but also difficulties in standardizing service tests. A better laboratory test method should incorporate the following features: 1. Cushion the test-specimen to minimize the modulus effect. 2. Provide means to prevent gumming of the abrasive. 3. Provide means to conduct the test over a range of temperatures. 4. Slow the rate of wear, partly by abrading intermittently and partly by use of less load and duller abrasive. 5. Use a test-specimen of a size which can be cut from a tire tread if desirable.
The Brabender Plastograph in the Rubber Laboratory
Authors: Juve A. E. , Hay D. C.
Published: February 2011

With suitable modifications the Brabender plastograph can be used to advantage in studying, on a small scale, the factors which influence the changes in consistency of rubbers during their mastication. Typical results reported herein show that the temperature coefficient of the rate of breakdown for natural rubber is 1.47 and for GR-S, 1.36. The rate of softening of butadiene-styrene copolymers is shown to depend, among other factors, on the original consistency of the rubber and the type of modifier used in polymerization. The influence of commercial peptizing agents on the rate of softening of natural rubber, GR-S, and GR-I at 150° C is shown. The reproducibility of the mastication test was found to be good.
Spontaneous Coagulation of Hevea Latex
Authors: Van Gils G. E.
Published: February 2011

Fresh Hevea latex can only be kept fluid for a few hours. After tapping in the morning, one observes a thickening of the latex in the afternoon, and in the evening the whole mass is coagulated. This coagulation may begin sooner or later, depending on circumstances. Contamination with rain water running along the bark of the tree may cause the latex to spoil during collection. Several investigators have tackled the problem, but no theory has been able to account fully for the facts observed. The most obvious explanation that coagulation occurs as a result of acidification cannot hold, as the acidity does not drop below pH 6.0–6.3, an observation which has been made by several authors. Even if the pH is held constantly at 7.0 by adding continuously small amounts of sodium hydroxide, spontaneous coagulation is not prevented or retarded. It is obvious that in the hours after tapping several changes take place in the latex. Spoon showed that the potential acidity, i.e., the amount of alkali needed to neutralize the latex, increases. Ultee and van Dillen proved the formation of carbon dioxide. Schrieke made extensive experiments on this subject, and reached the conclusion that carbon dioxide leads to an increase of the potential acidity but that the spontaneous coagulation is not affected by it.
The Reaction of Sulfur and Sulfur Compounds with Olefinic Substances. V. Rubber Vulcanization
Authors: Bloomfield G. F.
Published: February 2011

Data presented for a range of vulcanized rubbers prepared under different conditions show that, while olefinic unsaturation becomes reduced by vulcanization in the proportion of one double bond for each sulfur atom combined with a C5H8 unit, the original H/C ratio of 8/5 is not altered. The loss of unsaturation is somewhat modified when zinc oxide or certain accelerators also are present. Oxygen has a slight inhibiting effect on vulcanization; hydrogen sulfide and thiols markedly catalyse the vulcanization reaction without, apparently, affecting the efficiency of the sulfur cross-linking reaction. In confirmation of the results of Hull, Olsen, and France, a small proportion of zinc oxide or a soluble zinc soap promotes a reaction between sulfur and mercapto groups whereby di- and polysulfides are formed with liberation of hydrogen sulfide. The same type of activity is shown by some of the nitrogenous accelerators commonly used in rubber vulcanization. Substantial conversion of mercapto groups into polysulfide linkages is, therefore, to be expected when vulcanization is conducted in the presence of these auxiliary substances.
Sulfur Bond in Vulcanizates. Vulcanization by Dithiols
Authors: Hull C. M. , Weinland Louis A. , Olsen S. R. , France Wesley G.
Published: February 2011

The expected vulcanizing activity of dithiols has been demonstrated. It seems likely that mill scorching results from peroxide-catalyzed thiol addition; milling at higher temperatures would tend to inhibit reaction by destroying peroxides. The development of considerable tensile strength in stocks containing dithiols and the gelling of cements by dithiols give strong support to the thiol addition reaction as a feasible step in sulfur vulcanization, as proposed in the first two papers of this series.
Some Thermodynamic Properties of High Polymers, and Their Molecular Interpretation
Authors: Gee Geoffrey
Published: February 2011

The past decade has witnessed a rapid growth in the understanding of the thermodynamic properties of polymers and their solutions. This has been achieved largely by the development of statistical theories of rubberlike elasticity and of the free energy of mixing of polymers with liquids. A number of reviews are available dealing with portions of this field of work, but for the most part they are addressed to specialist workers. The object of this review is to survey in broad outline a number of related topics, without entering into detailed discussion of statistical theories. The emphasis is, therefore, laid on the experimental thermodynamic data which form the basis for these theories, and on their physical significance. An attempt is made to develop the argument as far as possible in physical terms, although it must be realized that this is essentially a field in which we are concerned with quantitative measurements and their mathematical interrelations. One fundamental experimental difficulty which is common to nearly all the problems to be discussed below is that of ensuring that the system under investigation has reached a state of equilibrium. The significance of the concept of equilibrium in measurements on polymers has recently been very clearly discussed by Ubbelohde. The difficulty arises from the fact that many processes in a polymer take place so slowly that they may to a good approximation be said not to occur at all during the time involved in an experiment. When this is the case, it is clear that the system cannot be assumed to reach a state of equilibrium with respect to this particular process. It is, indeed, common to find that certain properties of a polymer depend greatly on the previous history of the specimen; examples will be given later. Even when this is the case, the system may still be in equilibrium with respect to other possible changes, and it is, therefore, permissible to apply the thermodynamic criteria of equilibrium. Care is needed in relating the experimental results to theories to make sure that the theory is not based on the assumption of equilibrium with respect to changes which are so slow as to be virtually negligible. The usefulness of considering partial equilibria in this way depends on the possibility of choosing a time scale for the experimental work long enough for the rapid processes to be complete, and at the same time short enough to exclude other slower processes.
Structure of Chloroprene Polymers as Determined by Ozonolysis. XI
Authors: Klebanskiĭ A. , Chevychalova K.
Published: February 2011

1. Chloroprene polymers obtained by various methods of polymerization (with a regulator, in emulsion, thermally at 80° C) and a liquid chloroprene polymer were subjected to ozonolysis. 2. Succinic acid was formed in all the experiments, as the main decomposition product of the ozonide, in quantities from 82 to 96 per cent of the carbon skeleton, 3. Decomposition of the ozonides was effected with absolute alcohol containing hydrogen chloride gas, with and without the addition of orthoformic ester, with the aim of establishing the relative arrangement of the units. The diethyl ester and the acetal of succinic acid, as well as the ethyl ester of the dimer or a mixture of the monomer and the trimer of β-formylpropionic acid, were obtained. The structure of this product requires further investigation. 4. In spite of the many different methods used, the presence of succinaldehyde could not be detected either in the α-polymer obtained with the aid of a regulator or in the other polymers. 5. Control of the ozonolysis was accomplished by quantitative change of the bromine numbers during ozonolvsis : the consumption of bromine appeared to be constant up to a critical point corresponding to the end of the ozonolysis; at this point the bromine numbers fell off sharply. 6. It was found that the consumption of bromine occurred chiefly at the expense of the substitution reaction, which was indicated by the evolution of hydrogen bromide. 7. Based on the data, it is believed that the chloroprene polymers obtained by different methods possess a substantially normal structure of a macro-molecule with units arranged in the 1,4-1,4 position. 8. The low yield of succinic acid (85 per cent from chloroprene polymerized in emulsion) and the incomplete balance (89.3 per cent instead of 97.78 and 99.58 per cent) when polymerized in a mass were caused by the insufficient purification of the insoluble μ-polymer from the emulsifier and other admixtures constituting the ingredients of the emulsion. 9. In a similar way, the low yield of succinic acid (82.16 per cent) and the incomplete balance of the experiment (87.66 per cent) when the liquid batch of the polymer obtained in the presence of a regulator was ozonized depend, probably on the presence of the reaction products of the polymers with the regulator which were not accounted for or investigated in detail. The latter polymers will be investigated at a later date.
X-Ray Investigation of the Crystallization of Vulcanized Rubber on Stretching
Authors: Lukin B. V. , Kasatochkin V. I.
Published: February 2011

1. x-Ray methods have been used to investigate the amount of crystalline phase in stretched samples as a function of the vulcanization time. 2. Curves relating the percentage of crystalline phase to the vulcanization time have sharply defined maxima. 3. A comparison of the curves relating tensile strength to vulcanization time with the curves of crystal formation shows their analogous character, the position of the maxima approximately corresponding to one and the same vulcanization time. 4. The position of the maxima on the curves of crystal formation is not related to the degree of stretching. 5. The effect of accelerators is to shift the maximum on the curve of crystal formation to the region of short vulcanization times and to increase the percentage of crystalline phase. 6. The curves of crystal formation and of tensile strength, and thus the behavior of the stress-strain curves for various vulcanization times, is interpreted from the point of view of the existence of two processes—the process of forming a network of cross-links by the interaction of rubber with sulfur, and the process of oxidative degradation of the rubber.
X-Ray Diffraction Study of Some Synthetic Rubbers at Low Temperatures
Authors: Hanson E. E. , Halverson G.
Published: February 2011

A certain amount of ordering has been found in “noncrystalline” synthetic rubbers, which were studied by the use of the technique of cooling the raw polymer before it is elongated and freezing it immediately after stretching to prevent relaxation. Polybutadiene and polydimethylbutadiene, whose monomer units were structurally symmetrical, displayed the greatest degree of ordering. The presence of a high percentage of 1,2-units in sodium-polymerized butadiene destroyed almost all of the ordering observed in the emulsion polymer. GR-S and emulsion polybutadiene showed the presence of small amounts of crystallites, presumably of 1,4-addition polybutadiene, probably the trans-form. Polydimethylbutadiene showed the presence of crystallites presumably of 1,4-addition in the cis-form. The intermolecular distance between the extended chains increased with increasing amounts of side groups. The departure of the Bragg angle spacing of the amorphous halo from the corresponding quantity for the liquid monomer increased with increasing amounts of side groups.
The Quantum Yield of Oxidation of Hevea Rubber and GR-S
Authors: Hart E. J. , Matheson M. S.
Published: February 2011

The initial quantum yields of photoöxidation for purified Hevea rubber have been measured for various mercury arc lines in the wave length region 2537– 17,400 A˚. All experiments were carried out at room temperature and at an oxygen pressure of one atmosphere. At the outset of irradiation all quantum yields of combined oxygen are less than unity, although the quantum efficiency rises above 1.0 at 2537 and 3130 A˚. as photoöxidation proceeds. The low quantum yield suggests that in its initial stages (less than 0.1 per cent oxygen combined on the rubber) photoöxidation is not a chain reaction. It is postulated as the first step in rubber photoöxidation that the light activated rubber group reacts with oxygen to give a relatively stable intermediate which does not immediately dissociate to give a free radical reaction chain. The quantum yields of photoöxidation of purified GR-S were also measured under the same conditions as used for rubber. At each wave length the quantum yield was lower than for rubber, indicating formation of a stable intermediate in the initial reaction also.
The Mechanism of Reënforcement of Elastomers by Pigments
Authors: Cohan Leonard H.
Published: February 2011

Modulus appears to be independent of average particle diameter. With respect to the dependence of modulus on loading, calcium carbonate pigments which are symmetrical follow the equation derived by Guth and Gold for the relation between modulus and volume concentration of symmetrical inelastic particles. Up to about 80 parts by weight loading, HMF black follows a similar equation derived for rod-shaped particles, assuming a value of six for the ratio of the length to the diameter of the particles. The agreement with these theoretical equations is surprisingly good, and holds out the eventual possibility of calculating modulus over a wide loading range from tests at a single loading. Hardness and plasticity increase with loading in qualitative agreement with the equations. The behavior of modulus as a function of loading and average particle diameter of pigments indicates that vulcanized natural or synthetic rubber is not adsorbed in appreciable quantities or with sufficient force to be rendered inelastic at the surface of either calcium carbonate or carbon black pigments. Qualitative predictions based on the hypothesis that tensile strength is a measure of the force required to separate rubber chains from each other rather than to break rubber chains, and that pigment particles act as cross-linking agents holding the chains together, are in agreement with the behavior of calcium carbonate and carbon black pigments of widely different surface area over a considerable loading range.
Chromatographic Fractionation of Some Synthetic Elastomers
Authors: Landler Ivan
Published: February 2011

Mark and Saito were the first to fractionate a high polymer (cellulose acetate) by chromatographic adsorption on blood carbon. They found that molecules of low molecular weight were adsorbed first, and that the mean molecular weight of the product which remained unadsorbed was higher than the original molecular weight. Levi and Giera confirmed this result, but did not succeed in fractionating Buna-S or polyisoprene, for these polymers were eluted by the solvent during the washing operation in the column. The present authors have carried out further experiments in this field with a study of three commercial synthetic elastomers, viz., GR-S (butadienestyrene copolymer), Perbunan-N (butadiene-acrylonitrile copolymer), and Visitanex (polyisobutylene). The polymer was adsorbed by starting with a poor solvent composed of a mixture of toluene and methanol ; the quantity of alcohol added was just below the threshold of precipitation. The adsorbent used was a mixture of 75 per cent of lamp black (80 square meters per gram) and 25 per cent of coarse active carbon. The latter served to prevent agglomeration of the lamp black. The adsorbent was divided into three layers, of 10 grams each. At the end of the tube was a filter of fritted glass. Filtration was carried out under pressure, the rate of flow thereby being maintained constant, The polymers were characterized by their intrinsic viscosities. The molecular weights which were estimated by means of the relation, found experimentally between the molecular weight and viscosity, are only approximate, for this relation holds true only for narrow fractions.
Vulcanization of Synthetic Rubbers by the Peachey Process
Authors: Bekkedahl Norman , Quinn Fred A. , Zimmerman Elmer W.
Published: February 2011

The Peachey process, which vulcanizes natural rubber by subjecting it alternately to sulfur dioxide and hydrogen sulfide gases, has been found to vulcanize the more common synthetic rubbers. The polymer studies were natural rubber, GR-S; GR-M, GR-I, GR-A, Hycar OR-15, Hycar OR-25, Hycar OS-10, Hycar OS-20, and Hycar OS-30. Good cures were obtained with all of the polymers except GR-M. None of the synthetic rubbers cured any faster than natural rubber. The nitrile and the styrene copolymers of butadiene cured at about the same rate or somewhat slower. GR-I required roughly 50 times as long as natural rubber for an equivalent cure, and GR-M required even longer.
Purified Natural Rubbers. Mechanical Aging, Hygroscopic, and Electrical Properties of the Vulcanizate
Authors: Scott J. R.
Published: February 2011

The fact that the nonrubber components of crude rubber, especially those of a hygroscopic nature, impair the electrical properties of the vulcanizate has long been known, and the preparation of deproteinized or otherwise purified rubbers for use in electrical insulation had reached the commercial stage before the 1939–1945 war. With the rehabilitation of the plantation industry, the question of what special types of natural rubber should be prepared and marketed has become important, and purified rubbers represent one type that merits careful consideration. Published data on the electrical properties of purified rubbers, both before and after vulcanization, relate entirely to types prepared from solid rubber (crepe or sheet) or ammonia-preserved latex in the consuming country, and there is no published record of experiments on rubber purified during its preparation on the plantation. In 1935 the R.A.B.R.M. began investigations on the use of purified rubbers of the latter type in making electrical ebonite; the results will shortly be published. Examination of soft vulcanizates was began in 1937, but war conditions made it necessary to discontinue the work, for which reason the electrical results are less complete and conclusive than could have been wished. Nevertheless, it is hoped that the results obtained will be of value to the rubber manufacturing and plantation industries. Another use of purified rubbers is in the manufacture of transparent articles that come in contact with water or aqueous solutions. Transparent vulcanizates made from ordinary raw rubber quickly become white and opaque owing to absorption of water, but it would be expected that the use of purified rubber would remove or lessen this defect. This point has accordingly been examined. The thanks of this Association are due to the London Advisory Committee for Rubber Research (Ceylon and Malaya) for arranging for the preparation of special purified rubbers, in Ceylon and Malaya, and for examining the water absorption of the unvulcanized rubbers.
X-Ray and Dielectric Investigations of Thermovulcanizates
Authors: Blokh G. A. , Zaĭonchkovskiĭ A. D.
Published: February 2011

Earlier work by the present authors has demonstrated that simple heating of rubber-carbon black systems in the presence of polymerizable vinyl hydrocarbons at moderate temperatures (150–200°) leads to the formation of soft thermovulcanizates possessing the properties of technical vulcanizates. At higher temperatures (260–280°) hard, fully cured thermovulcanizates are formed. These are designated by us as thermoebonites, to distinguish them from sulfur ebonites. Thermoebonites are characterized by superior mechanical, chemical, and electric-insulating properties, and do not have the fundamental shortcomings of sulfur ebonites. These shortcomings, which result from the presence of excess sulfur, are:
Variability of Crude Rubber. Effect of Latex Nonrubber Substances on Vulcanization and Aging Characteristics of Crude Rubber
Authors: McColm E. M. , Haefele J. W.
Published: February 2011

Nine different fractions of nonrubber substances have been isolated from fresh, unpreserved latex, in a condition probably closely resembling the condition in which they existed in latex as it was produced by the tree. A purified rubber, free of nonabsorbed water-solubles and of acetone-extractables, was prepared. The nine fractions were added to this rubber separately and the resulting mixtures compounded in a pure gum recipe containing mercaptobenzothiazole as accelerator and zinc oxide. Of these fractions, only three were found having marked effects on the properties of the vulcanizate. Two additional fractions had small effects. Evidence indicates that very poor cures are obtained if rubber is freed from nearly all the nonrubber components. Addition of at least one substance, which has no effect in the absence of mercaptobenzothiazole, causes a great increase in rate of cure. Crude rubber may possibly be variable for other causes than the amount and character of the nonrubbers present. That portion of the curing variability in a zinc oxide-mercaptobenzothiazole compound due to the nonrubbers is probably due to variation in the following fractions: 1. Lipin 2. Soluble in water, and in ethyl and methyl alcohols 3. Soluble in CCl4-acetone and in acetone Free acid, probably free fat acid, occurs naturally in fresh latex. Quebrachitol (1-methyl inositol) is present in an uncombined form in fresh latex, and has no effect on curing rate or on aging.
Complexity of Fresh Hevea Latex
Authors: Homans L. N. S. , van Dalfsen J. W. , van Gils G. E.
Published: February 2011

Although under difficult conditions, the work at the Netherlands Indies Rubber Research Institute at Buitenzorg (Java) was continued during the Japanese occupation. Since it will be a long time before the accumulated results of the years 1942–45 can be published in detail, some points of general interest are reported here. It is common knowledge that, on addition of small amounts of salts of bior polyvalent cations to fresh latex, partial coagulation follows. The yellow colored coagulum generally contains 10–30 per cent of the rubber and after drying gives a yellow rubber, rich in proteins, and having a high acetone extract. The high acetone extract and the color are produced by the yellow particles, first observed by Frey-Wyssling, which, although generally called “resin particles”, contain mainly lipoids. What, however, is the reason for the high protein content? In 1941 it was observed by one of us (L.N.S.H.) that when fresh latex is centrifuged in tubes, a separation occurs into a heavy yellow fraction, taking up a tenth to a third of the total volume, and a lighter white fraction. The yellow fraction is more viscous and often in itself consists of various layers, bright yellow, gray yellow, orange, or even green. Much information was obtained by studying separately the chemical composition, colloid-chemical and enzymological properties of these fractions.