bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Progressive Changes in Elastomer Properties during Vulcanization
Authors: Claxton W. E. , Conant F. S. , Liska J. W.
Published: February 2011

An apparatus and method are described for evaluating state of cure, optimum cure time, rate of cure, induction time for cure, scorch time, induction time for reversion, reversion rate and degree of reversion of elastomeric compounds. Coincident with these determinations vulcanizate specimens are prepared on which more conventional physical test data may be obtained; e.g., compression modulus, compression set, hardness, specific gravity, tensile modulus and elongation. In essence, the method described provides a progressive measure of modulus change during cure or reversion through the change in deformation of a periodically loaded plunger, one end of which is embedded into the specimen. Typical results are given which show application of the apparatus to screening tests, millroom control, reversion studies and to compounds which are too stiff for conventional test methods. Demonstrated advantages for the apparatus include time saving, stock saving and better cure information on a wider range of polymeric compounds than is obtainable from tensile test methods. In a laboratory where a large selection of test instruments is not feasible, the versatility of the apparatus described should prove very advantageous.
The Influence of High-Activity Silica upon the Thermal Aging of Latex Vulcanizates Cured by Thiuram Compounds
Authors: Andresen A.
Published: February 2011

Once it had been shown that high-activity silica, even in comparatively small additions, improves the aging resistance of latex vulcanizates by many times, and that also an effect similar to that of a coactivator is set up by the interaction of high-activity silica with age resistors, ultra-accelerators and atmospheric oxygen in latex mixtures, a like effect was to be expected in sulfur-free latex vulcanizates crosslinked by thiuram compounds. In order to get comparable data it was necessary in the first place to get sulfur-free latex mixtures giving vulcanizates with starting properties in the same order of value as those of latex vulcanizates with the classical sulfur recipe. In addition it was necessary also to develop stocks from which threads could be extruded by the well-known two-stage method, since the investigations mentioned at the beginning were carried out exclusively on vulcanized threads, which lend themselves particularly well to determinations of tensile strength, elongation at break and tensile stress. Above all an attempt was made to manage with vulcanization temperatures below 100° C. To make this possible a thiuram compound active at relatively low temperatures had to be used. Here we had the opportunity of using DPTT (dipentamethylenethiuram tetrasulfide, Tetrone A), which the manufacturers (Du Pont) designate, alone among their thiuram accelerators, as “very active”, and which J. Willums referred to in a German journal as far back as 1944.
Stabilization of Neoprene. I. Protection of Latex Film against Discoloration by Light
Authors: Becker R. O. , Seligman K. L.
Published: February 2011

The tendency for light-colored neoprene vulcanizates made from latex to discolor when exposed to light was inhibited markedly by compounding with triglycerides of long chain fatty acids in combination with non-discoloring (see PDF for table) antioxidants. Effectiveness increased with the degree of unsaturation of the fatty acid up to two double bonds (safflower oil). Resistance to discolorations increased with increasing amounts of oil up to 15 parts. Both the ester linkage and the degree of unsaturation in vegetable oil appeared to influence stability in light. Organo tin compounds were found which functioned synergistically with safflower oil. Discoloration of safflower oil stabilized neoprene latex compounds was not affected appreciably by commonly used acceleration systems, nor by varying the curing conditions up to 120° C. Safflower oil reduced discoloration in all neoprene latex types. Neoprene latex compounds containing safflower oil discolored in sunlight no more than those of SBR or NBR latex. Safflower oil did not affect the discoloration of natural rubber, SBR or NBR latex compounds in sunlight. Other effects of safflower oil on the cured properties of neoprene latex films were reduced modulus and tensile strength but without change in elongation, enhanced heat and ozone resistance and lower brittle temperature.
Time and Temperature Dependence of the Ultimate Properties of an SBR Rubber at Constant Elongations
Authors: Smith Thor L. , Stedry Paul J.
Published: February 2011

A study was made previously of the temperature and strain rate dependence of the stress at break (tensile strength) and the ultimate elongation of an unfilled SBR rubber. In that study, stress-strain curves to the point of rupture were measured with an Instron tensile tester on ring type specimens at 14 temperatures between −67.8° and 93.3° C, and at 11 strain rates between 0.158×10−3 and 0.158 sec−1 at most temperatures. The tensile strength was found to increase with both increasing strain rate and decreasing temperature. At all temperatures above −34.4° C, the ultimate elongation was likewise found to increase with increasing strain rate and decreasing temperature but at lower temperatures the opposite dependence on rate was observed; at −34.4° C, the ultimate elongation passed through a maximum with increasing rate.
The Indentation and Puncture Properties of Rubber Vulcanizates
Authors: Yeh G. S. , Livingston D. I.
Published: February 2011

A detailed study has been made of the indentation and puncture properties of a number of rubber vulcanizates by a puncture method. It is shown that the characteristic relation between the force and depth of penetration, i.e., the two regions of linearity observed in a former study on a log-log plot, can be represented by two equations. The first region, in which the indenter penetrates into the rubber to a depth approximately equal to twice its diameter, can be generally described by Timoshenko's classical relation, FI=2.67 Erd In the second region, an empirically derived equation FII=1.34 Er0.5d1.5 holds. For a given rubber compound, Young's modulus calculated from the second equation is in satisfactory agreement with the modulus obtained from the first. The puncture strength and the puncture depth are both shown to be dependent upon the compounding variations and they provide useful information about the vulcanizates such as stiffness and cure. Valuable information relating to rubber abrasion and road wear may also result from studies of these two puncture properties.
The Mechanism Which Restricts Chain Growth in Polymerization with Alkylaluminum-Titanium Tetrachloride Complex Catalysts
Authors: Bresler S. E. , Mosevitskiĭ M. I. , Poddubnyĭ I. Ya , Guan-I Shi
Published: February 2011

In the production of polymers having a highly regular structure of the molecular chains, catalyst complexes of the Ziegler type are currently in wide use. The development of mechanisms for the separate steps in the catalytic process is of primary significance. This report outlines some results on a study of the mechanisms involved in isoprene polymerization with complexes formed through the interaction of Al (iso-C4H9)3 and TiCl4; the data were obtained from the sedimentation of the polymers in the ultracentrifuge, in combination with data on the kinetics of polymerization. We have indicated previously1 that in isoprene polymerization using the specified catalysts, the growth of the macromolecules proceeds quite rapidly, the time interval between the first appearance of active chains and the termination of reaction being only a few minutes; subsequently there follows an immediate stationary condition. However, with use of the ultracentrifuge we have obtained molecular weight distributions of polymers which are substantially different from the equilibrium distribution expected from present-day kinetic theories of polymerization. They were characterized by relatively low dispersion and, in the main, strongly distorted by high-molecular bands; in most cases, there was practically a complete absence of molecules with a molecular weight less than 200–300 thousand.
Synthesis of Isoprene Tagged with C14
Authors: Korotkov A. A. , Rakova G. V.
Published: February 2011

For a study of the mechanism of catalysis of polymerization of diene hydrocarbons and also for investigation of the process of catalysis of copolymerization the following hydrocarbons tagged with C14 were synthesized: benzene, toluene and isoprene. The simplest ordinary methods possible were used for these syntheses to obtain pure active preparations in good yields from starting materials containing radioactive carbon.
Dynamic Vitrification and the Activation Energy of Rubbery Polymers
Authors: Bartenev G. M. , Zaĭtseva V. D.
Published: February 2011

1. The resistance to brittleness of a wide variety of rubbers was studied by the method of periodic deformation. 2. Dynamic glassing, during which transition from the highly elastic into the brittle state is observed, always occurs in the liquid state of aggregation of a polymer, where the activation energy of molecular rearrangement changes with temperature according to an exponential law. 3. In a small temperature interval the change of the activation energy can be approximated by a linear law; consequently, Equations (1) and (4) expressing the dependence of the temperature of transition of the rubber into the brittle state on the frequency of deformations are satisfied approximately. The constants entering into these equations and their relationship to the activation energy are determined. 4. The activation energy of dynamic glassing is directly proportional to the glass temperature of the polymer and is greater than the activation energy of static glassing by approximately 5–10%, consequently the rate of establishment of the equilibrium structure is greater than the rate of stress relaxation or the rate of development of elastomeric deformation. 5. The relatively high activation energy of dynamic in comparison with static glassing is caused, apparently, by the larger size of the segments of the polymer chain during mechanical action compared to the size during free thermal motion.
Ozone Air Velocity Factor in Ozone Cracking
Authors: Cheetham I. C. , Gurney W. A.
Published: February 2011

Investigations based on the stress relaxation of natural rubber in ozonized atmospheres have produced relationships between cracking, ozone concentration and ozone air velocity. It is shown that at low ozone air velocities the rate of cracking is critically dependent upon the air speed value. The occurrence of discrepancies arising between results from testing chambers operating under identical conditions of concentration, temperature and light intensity is demonstrated at the end of the paper. A brief mention of similar work has been published but it is felt that more detail may help in the standardization of ozone testing procedure.
The Biosynthesis of Rubber
Authors: Fournier P. , Tuong-Chi-Cuong
Published: February 2011

The goal seems now well defined, but the means necessary for its attainment have yet to be chosen. Undoubtedly, isotopic methods will be the appropriate approach to gather the required information. They will be used less for investigation of individual transformations than for establishing the balance of transformation of the precursors. Finally, it is very fortunate that latex can be broadly compared to a homogenate of laticiferous cells. Therefore, it is reasonable to believe that, used with precaution, the latex must reflect the ability of the tree to form rubber and that the study of the points that are mentioned will be possible by using this medium. No matter how successfully the mechanisms limiting or controlling the rubber production will be located, it will remain a problem to modify them in the desired way, because the tree (hevea brasiliensis) forms a system in equilibrium. In this system, all reactions are interdependent and a reaction requiring manganese or calcium will interfere with those which are poisoned by these metals. … In short, it is impossible to modify entirely the plant life. Consequently, the action of the researcher will always be limited because drastic modifications of the state of equilibrium would cause undesirable effects. But just as medicine can modify certain metabolisms of a patient if it proceeds without brutality, it may be possible to act in a limited way upon the basic metabolisms of hevea. This does not mean that the productivity of the tree will not be changed considerably, but in any case the methods employed will have to be very mild. Before reaching this goal, many important problems will have to be solved. As in medicine, identification of the basic metabolism will not suggest the therapeutic method for their acceleration. Without this background information, no treatment can be conceived, but no miracle drug results from diagnosis alone. The dual aspect of any studies in this field is striking: the immense possibilities anticipated are tempered by the problems involved in plant life. In view of the scientific progress of the last five years, such a restrictive statement seems to be out of order. The evolution of our knowledge is so fast, that such preconceived ideas may rapidly become obsolete and so obscure our view for new progress. We believe it necessary to conclude this review with such a warning, making the reader aware of the hopes as well as the limitations of the studies on the biosynthesis of cis-polyisoprene.
Oil-Extended Rubbers
Authors: Storey E. B.
Published: February 2011

One hesitates to close this review by adding a paragraph of conclusions. The term “oil-extension principle” introduced a new concept to the manufacturer of synthetic rubbers. The principle (if it may be identified by such a word) and the application of the products it generated do not involve any novel or unfamiliar approaches to the art of rubber compounding. Indeed, it would be rendering a disservice to the progress of their adoption by industry to suggest that it required a revision in the viewpoint of the rubber compounder. The use of softeners in compounding was almost coincidental with the discovery of rubberlike substances by the explorers of the 16th century. The development of carbon blacks having more useful characteristics in rubber came after the compounder had become familiar with the application of innumerable inorganic fillers in rubber and, indeed, soots and lampblacks. The tailor-made synthetic rubbers were developed by the chemical industry in the second-quarter of the 20th century and it is scarcely likely that higher molecular weight types would not be produced nor that any inherent processing problems would not be solved when there existed an economic and raw material incentive to do so. These are the contributions of the polymerization chemists and the synthetic rubber industry. Where it is more economically-attractive and technically-desirable to add softener and filler to the synthetic rubber in the manufacturing process, oil-extended rubbers and filler masterbatches will be provided as raw materials for the rubber industry. If on the other hand, these ingredients may be added quite readily during factory mixing operations, without any detrimental effects on the polymer quality, the synthetic rubber producer would be quite unwise to attempt to usurp the functions of the rubber manufacturer. The income of the rubber manufacturer, depends upon the skill and economy that he applies to the operation of mixing rubber with liquid and solid materials and this is the prime occupation of a rubber compounder. It would avail the synthetic rubber producer nothing to try and convince the compounder that he is doing something novel and unusual by preparing softener-filler masterbatches. However, the compounder will be receptive to a pre-blended product that enables him to produce rubber mixes of better or different quality at an equal, or lower, cost. This is the aim and accomplishment of oil-extended rubbers.
Instrumental Methods for the Analysis of Polymeric Materials
Authors: Mitchell J. , Lord S. S.
Published: February 2011

Advances in our knowledge of the chemical and physical structure of polymeric substances have been due in large measure to new and improved instrumental methods of analysis. From the standpoint of chemical structure all polymers have at least one functional group, often in low concentration, e.g., an end group. Principal progress has been made, first, in identification of these groups, and, more recently, in their quantitative determination and location within the molecule. In some cases conventional chemical methods have been greatly improved to provide the high sensitivity required for these analyses, particularly for groups such as acid, amine, ester and carbonyl. However, most chemical methods depend on reaction in solution. Often the choice of solvent is limiting, since it must be inert toward both the sample and the reagents as well as be capable of dissolving a significant amount of the material to be analyzed. In many cases a suitable solvent is not available. Many of these restrictions do not apply to instrumental techniques. Infrared spectrophotometric methods, for example, may be (a) nondestructive and the sample can be recovered for other studies, (b) rapid, often being completed within several minutes, (c) direct in which films or dispersions can be handled and, therefore, limited solubility is not a problem, (d) capable of providing information on physical as well as chemical structure, and (e) capable of supplying other useful information during the course of an analysis. Examples of techniques used in analyses for chemical and physical structure are: (see PDF for table) This paper reviews primarily recent advances in instrumental techniques which have been shown to be capable of quantitative analysis for chemical structure. Also, reference is made to the use of infrared spectroscopy, nuclear magnetic resonance spectroscopy, and differential thermal analysis in studies of physical structure. Applications to characterizations of elastomers are emphasized, although for illustrative purposes investigations of other polymers often are discussed.
Nuclear Magnetic Resonance Studies of Elastomers
Authors: Slichter W. P.
Published: February 2011

The remarkable property that we associate with rubberlike elasticity, the high degree of elastic deformability, has long been known to arise from molecular motion. In fact, Joule recognized a century ago that the retractive force in stretched rubber stems from thermal motions of molecules rather than from attractive forces between molecules, a conclusion which was all the more remarkable because Joule had no idea of the polymeric nature of rubber. This review tells of the newest technique for studying molecular motion, nuclear magnetic resonance spectroscopy (NMR), and of its application to studies of rubberlike substances. Appropriately, the most important measurements of rubberlike elasticity have been mechanical—creep, stress relaxation, dynamic response. The visco-elastic properties have been studied theoretically and have been measured profusely. They have told us much about the spectra of relaxation processes, which range over many decades of frequency. However, the mechanical experiments occur at the macroscopic level. Conclusions as to behavior at the molecular level depend upon the soundness of models. Plainly it is also valuable to examine motion directly at the molecular level. There are several techniques that accomplish this end. Infrared spectroscopy and dielectric relaxation studies are two kinds of measurement that directly indicate the motion of atoms and molecules. To these techniques is added nuclear magnetic resonance spectroscopy. This method responds to molecular behavior quite differently from other kinds of measurement, and avoids some of the restrictions encountered in these other techniques. For example, the requirement of a permanent electric dipole moment effectively excludes dielectric measurements for the study of pure natural rubber and other hydrocarbons, yet motion in such substances is readily seen by NMR. On the other hand, there are distinct limitations to the use of nuclear resonance, as we shall note. In this paper, we shall review the phenomenon of nuclear magnetic resonance, with emphasis on its use in studies of molecular motion in elastomers. It would be wrong to say that NMR has achieved the importance of the principal physical techniques used to study elastomers. Indeed, the information on elastomers yielded by NMR consists largely of isolated examples. Still, we shall seek to show that the method is powerful and has great potentialities. For a more detailed review of the fundamental physics than is given here, the reader is referred to the excellent paper by Pake. A comprehensive survey of NMR studies of polymers is given by Powles.
Preformed Aluminum Triisobutyl-Titanium Tetrachloride Catalysts for Isoprene Polymerization
Authors: Schoenberg E. , Chalfant D. L. , Mayor R. H.
Published: February 2011

Variables in the preparation of mixed aluminum triisobutyl-titanium tetra-chloride catalysts for isoprene polymerization were studied. All the preformed catalysts were tested unaged in solution polymerizations at 50° C using various catalyst levels. The yields of solid rubber and low-molecular-weight oily material in the polymerization products were determined. The solid rubber was analyzed for cis 1,4 content, inherent viscosity, and per cent gel. The most active catalysts for the synthesis of cis 1,4-polyisoprene were those prepared at low temperatures, below 20° C. Superior catalytic performance and improved polymer properties were obtained with catalysts preformed by either gradually adding the aluminum alkyl to titanium tetrachloride or by mixing the two cocatalysts at a constant Al/Ti ratio in the range of 0.9 to 1.0. By comparison, the gradual addition of titanium halide to the alkyl resulted in catalysts of lower activity and inferior polymer properties; it also required higher Al/Ti ratios for the preparation of all cis 1,4 rubber. An increase in catalyst preparation temperature led to gradually lower activity to where species preformed at 125° C showed little or no activity. High preparation temperatures, further, caused a shift in the Al/Ti ratio—optimum for cis 1,4 synthesis—to lower values when the aluminum to titanium order of addition was employed, and to higher ratios for the reversed type of addition. Al/Ti ratios above and below the optimum produced a cis 1,4 rubber which was increasingly contaminated with by-products of oily and leathery type polymeric material, respectively. Maximum yields of oily polymers were obtained with low temperature catalysts of Al/Ti ratios within 1.5 and 2.0. Catalysts preformed by the aluminum to titanium order of addition at 90° C produced cis 1,4-polyisoprene at Al/Ti ratios of 0.5 to 0.6. Preformed catalysts are preferred over those prepared in situ in the presence of isoprene because they show higher activity, more reproducible polymerizations and improved polymer products.
Structure Effects and Related Polymer Properties in Polybutadiene. I. Preparation and Characterization
Authors: Berger M. , Buckley D. J.
Published: February 2011

Stereoregular polybutadienes, of both high trans and high cis contents, were isomerized to provide polymers of varying cis-trans content. These isomerizates were used to study structural effects on physical properties. The isomerizations were carried out under photosensitized conditions in benzene solution at 25° C. The reaction was controlled to deliver polymers over the range 0–95 per cent trans content. This range was selected to provide crystalline and semicrystalline polymers whose structures could be examined in terms of sequencing or blocking by established x-ray techniques. Isomer contents were measured accurately by infrared traces. Isomerizations reached an equilibrium of 77 per cent trans regardless of whether the reaction started with high trans or high cis polybutadienes. Intrinsic viscosity was found to increase regularly with trans content in conformity with the larger size of the trans unit. ηsp/c versus c relations were observed to give a complicated form and this subject was deferred for further study. Crystallinity decreased regularly with reduced trans content as the equilibrium of 77 per cent trans was approached. Continued isomerization at the point of equilibrium produced a completely amorphous polymer. The melting temperatures of the crystalline polymers were studied in detail by x-ray camera and counting techniques. These polymers exhibited two crystal forms. One form was stable up to 60° C and invariant with cis-trans content in the range 80–95 per cent trans. Below 80 per cent trans the melting point of this form decreased with further reduction in trans content. The melting temperature of the other crystal form was dependent on trans content and decreased with decreased trans content until it coincided with the melting temperature of the other form. The distributions of trans and cis units and sequences of them were calculated through construction of matrices of transition probabilities. Copolymer theory was invoked to calculate pseudo reactivity ratios for the trans and cis forms. The melting temperatures of the two crystals were found to follow the predicted curves for random copolymers, although not simultaneously. This behavior is discussed. The crystallinity of the isomerizates of high trans content was found to be similar to block copolymers in spite of the fact that the method of their preparation would require that they be characterized as random. The importance of a crystal transition in this case is stressed along with the general effects due to the amount and type of the noncrystallizable unit.
Volatility of Antioxidants and Antiozonants. 1. Pure Compounds in Absence of Rubber
Authors: Spacht R. B. , Hollingshead W. S. , Bullard H. L. , Wills D. C.
Published: February 2011

Comparable volatility data are presented for three phenolic and five aromatic amine compounds. Vapor pressure curves for the materials are given along with the vapor pressure equations derived from these curves. The equations are used to calculate temperatures at which the eight compounds would have equal vapor pressure. Vapor pressures of each material are calculated at specified temperatures. Data are given for several methods of determining actual losses of antioxidants at several different temperatures and at several different airflows. Surface effects are also studied. In general, all methods give the same relative rating of the eight materials, but quantitative data vary considerably with the method used.
Solvent Resistance of Silicone Elastomers: Solvent-Polymer Interactions
Authors: Yerrick K. B. , Beck H. N.
Published: February 2011

The solubility parameters, δp, of a number of polymers have been determined by swelling in a series of solvents with various solubility parameter values, δ0. The δp values were obtained for (see PDF for diagram) During the course of this work it was concluded that solvent nature (polarity and association) play an important role in the swelling power of a solvent. These interactions create considerable ambiguity of the data in cases where dipole interaction or association takes place between polymer-solvent pairs or solvent-solvent pairs. For this reason a series of “select” solvents were chosen that did not display these interactions. Included in these “select” solvents were the aliphatic and aromatic hydrocarbons (δ0=6.0–9.2). In addition the aliphatic alcohols which are strongly hydrogen bonded were included to cover the upper range of δ0 values (δ0=10.8–14.2). This study has revealed that the swelling curves of siloxane copolymers yield only the individual δp values of the homopolymers. From these results it appears as though this type of measurement is not sensitive to copolymer structure, i.e., random or block copolymer structure.
Proton Magnetic Resonance in Natural Rubber: Comparison with Dielectric Measurements
Authors: Kusumoto Hazime , Gutowsky H. S.
Published: February 2011

Proton magnetic resonance studies have been made of cured natural rubber containing up to 31 per cent combined sulfur. Line shapes and spin-lattice relaxation times were observed at temperatures between −190° and 180° C. In the line shape studies, the main effect of the combined sulfur was upon the temperature at which the line width is narrowed by the molecular segmental motions. The temperature at the onset of the major line width narrowing increases from −50° C for raw rubber to about 10° C for 31 per cent combined sulfur. A relation was found between the dependence upon sulfur content of the line width changes and the second-order transition temperature. The proton spin-lattice relaxation time T1 was measured for three cured samples in the temperature range above the motional narrowing region. The T1 vs. temperature curves agree qualitatively with the theory of Kubo and Tomita. The general features of the T1 curves are consistent with a distribution of correlation times which broadens with increasing sulfur content. Energies of activation were computed from these results and they are compared with the dielectric relaxation data obtained previously. The effect of a distribution of correlation time is discussed.
Characteristic Viscoelastic Parameters for Amorphous Polymers
Authors: Tobolsky A. V. , Takahashi M.
Published: February 2011

By use of a reference value of modulus equal to 109 dynes/cm2 and a reference value of time equal to 10 sec, characteristic viscoelastic parameters are defined from stress relaxation master curves and from modulus-temperature curves. Values of these parameters are tabulated for several linear amorphous polymers and slightly crosslinked amorphous polymers.
The Mechanism of Abrasion of Vulcanized Rubber
Authors: Rudakov A. P. , Kuvshinskii˘ E. V.
Published: February 2011

The authors investigated the abrasion of a number of vulcanized rubbers with the sliding of a smooth steel indenter. Abrasion was achieved by repeated action of an indenter, moving reciprocally along one and the same portion of the surface of the rubber. In the surface layer being destroyed the rubber became tacky; the removal of rubber in abrasion took place by the rolling up into “rolls” of the altered (sticky) surface layer. The character of destruction of the rubber in abrasion is affected by the type of the original rubber, and, in some cases, by the presence of oxygen in the atmosphere. The process of abrasion of vulcanizates of natural rubber and SKI is accompanied by perceptible oxidative degradation. Evidently the wear of rubber is linked essentially with the development of mechanochemical degradative processes.
Analysis of Elastomers by Gas Chromatography
Authors: Hulot H. , Lebel P.
Published: February 2011

This study is the last stage in the design of a new analysis method for either pure or mixed elastomers. Such elastomers are polymers which, when brought to high temperatures, are dissociated into their basic constituent monomers (isoprene for natural rubber, isobutylene for butyl rubber, and so on) and other more or less volatile products. The principle of the study consists in analyzing such different fractions with a chromatographic unit which exhibit peaks used to differentiate various polymers according to their relative positions. The main novelty of the method is the elimination of less volatile fractions which are trapped in ice at 0° C, so that only lighter fractions are fed to the chromatograph. In order that the latter may be fully available or ready for analysis, pyrolysis is carried out directly in the carrier gas circuit, in a furnace set-up, instead of in the gas sample feeding system of the chromatographic unit. Pyrolysis made directly in the unit offers several advantages: Very accurate analysis, since all the pyrolyzate is fed to the unit; Very small samples (1–4 mg); Reduced handling.
Heat Resistance of Neoprene Vulcanizates
Authors: Becker R. O.
Published: February 2011

The resistance of neoprene vulcanizates to degradation when exposed to heat is increased markedly by compounding with selected calcium salts in place of magnesium oxide. The preferred material is a product containing 36% calcium oxide prepared by calcining reagent grade calcium carbonate in a laboratory muffle furnace at 1600° F for 30 minutes. Calcium salts of fatty acids containing 18 carbon atoms in the fatty acid portion of the molecule also are effective. The calcium salt of a more highly unsaturated fatty acid is an effective antiozonant. The stress-strain properties and resistance to compression set and swelling in oil are similar for compounds employing calcium salts compared with magnesium oxide. Calcium salts reduce the processing safety of the compounds, and the resistance of the vulcanizates to swelling in water.
Injection Molding of Rubber
Authors: Masson Pierre-Yves
Published: February 2011

We have seen that injection molding of rubber mixtures has now passed beyond the stage of laboratory practice. This forward stride is due to the appearance of new synthetic polymers. Now this technique should become a part of the rubber industry and allow it to be competitive and recover some of the manufactured products which the thermoplastic materials had displaced because of their possibilities for injection. The objective of this conference was to bring the rubber manufacturers up to date on developments and to supply the technical bases for guiding them toward perfecting the manufacturing processes. There still remain many studies to be made, in particular in the field of working out recipes to give the best results, and we believe that many specific problems remain yet to be solved. We hope that the preceding discussion relative to experiments, and the principles we have just described, will provide the necessary orientation for our future work.
Swelling Studies of Filled and Unfilled Vulcanizates
Authors: Butenuth G.
Published: February 2011

Every crosslinked and nonerosslinked polymer shows elastic rubbery properties within some temperature range specific for the material. Within this range it approaches more or less the conditions of ideal rubber elasticity, e.g., the state of unrestricted, coiled molecules without energetic interactions. Noncrosslinked materials flow under the influence of an external force. The centers of gravity of the coils change their relative positions to each other. These materials, therefore, have to be stabilized by introduction of chemical bonds—crosslinking points. At the same time the crosslinking points constitute the end points of the smaller coils between them. The average molecular weight of these coils decreases with increasing crosslinking density. The entropy of the system changes as the average molecular weight between the crosslinking points changes; thus, all properties correlated with the entropy change considerably. for systems fulfilling the theoretical requirements, the correlations between crosslinking density and macroscopic properties like modulus and swelling are well known. The crosslink density can be calculated from macroscopic data. Various deviations from the theoretical correlations will occur in any real system like, for example, sulfur-cured natural rubber. The first purpose of this paper is the discussion of these deviations for nonfilled vulcanizates. Additionally, an attempt will be made to explain the deviations in filled systems.
Failure Criteria for Some Polyurethane Propellants
Authors: Milloway Warren T. , Wiegand James H.
Published: February 2011

Experimental and theoretical studies were made on failure criteria applicable to simple case-bonded hollow cylindrical grains. The minimum strain at break at −75° F for uniaxial tensile test was found to be at least twice the hoop strain at −75° F of a thermally cycled, case-bonded hollow cylinder of propellant when no failures were observed, whereas, when the minimum strain at break was equal to or less than the hoop strain of the cycled cylinder, the grain always cracked. For uniaxial tension, where the rate of elongation and temperature are controlled variables, the failure elongation varies from specimen to specimen and from batch to batch. A study of batch variability of the uniaxial test showed that a test at any test temperature from −40° to 180° F could be used to characterize batch quality. The correlation of breaking strain at different rates and temperatures with the use of the WLF technique on one batch was found to be improved if an additional vertical shift factor was added to account for the lowering of the maximum failure elongation for temperatures below 0° F. However, by using a diagonal shift with rate, a graph of failure elongation versus temperature shows lower variability than does the WLF analysis.
Relation of Mechanical Properties to Solid Rocket Motor Failure
Authors: Bills Kenneth W. , Wiegand James H.
Published: February 2011

Experimental studies of propellant specimen and motor behavior during failure provide insight into the probable mechanisms of failure in a composite propellant system. At low rates and high temperatures, failure results from at least two successive processes: first, a dewetting or breaking of the binder to oxidizer bonds, and second, a tearing in the binder structure initiated at points of stress concentration such as regions of binder-oxidizer dewetting. Stress-strain analysis of a motor shows the potential failure points, and a failure analysis indicates the required mechanical properties to withstand failure. Laboratory testing has given a method of classifying propellant behavior, an estimate of material failure variability, and a method of correlating the uniaxial with biaxial tensile properties and with rate and temperature of test. Uniaxial tensile properties are obtained more conveniently by laboratory measurements, but biaxial properties appear to be related more directly to inner bore grain cracking. Good correlations were demonstrated between motor failures in thermal cycling and the failure properties of the propellant from laboratory tests.
Recent Advances in Mechanical Properties Evaluation of Solid Propellants
Authors: Wiegand James H.
Published: February 2011

Methods of mechanical properties measurement have become more sophisticated as the necessities of nonlinear stress analysis have been appreciated. The linear cases, typical of low temperature failure, have been successfully handled by elastic analysis, but the nonlinear complexities of the higher temperature regimes require analytical correlation of real properties and analytical methods of using such correlations. The wide variability of mechanical properties observed in solid propellants requires that predictions of failure be based on estimates of upper and lower expected limits rather than viewing failure as a point value, as is often done in stress analysis of metallic structures.
Studies on the Kinetics of Vulcanization of Rubber
Authors: Taneja H. L. , Banerjee S.
Published: February 2011

The dependence of the rate of accelerated vulcanization of natural rubber (smoked sheet) on the concentration of mercaptobenzothiazole accelerator has been reported on in this paper. The rate of decrease of free sulfur at the steady state has been found to be proportional to the square root of the initiator concentration expressed as grams/100 grams of rubber. The rate has also been found to be enhanced by the addition of 1% of zinc oxide. Higher amounts of zinc oxide does not lead to a further appreciable increase in the rate.
Estimation, from Swelling, of the Structural Contribution of Chemical Reactions to the Vulcanization of Natural Rubber. Part II. Estimation of Equilibrium Degree of Swelling
Authors: Ellis Bryan , Welding G. N.
Published: February 2011

An investigation has been made of the measurement of degree of swelling of vulcanizates and the estimation of υτ, the volume fraction of polymer in a vulcanizate swollen to equilibrium. Methods have been established for dealing with a volatile swelling liquid, allowing for small percentages of nonpolymer in the vulcanizates, testing for diffusion equilibrium and correcting for swelling increment. The resulting values of υτ are suitable for use as described in the preceding Part I.
Studies of Ozone Attack of Vulcanizates in a Closed System
Authors: McCool John C.
Published: February 2011

1. A new procedure for studying the attack of vulcanizates by ozone in a closed system has been devised which permits measuremont of ozone consumption as a function of strain, environments, and compounding aspects. 2. Extent of attack is best determined by cut growth measurements and by photographic records of the samples after test. 3. The accelerated attack by ozone observed at reduced total pressure reported now as a new observation appears to reflect the probability of ozone collisions with olefinic bonds which are part of uncoiled or “strained” polymer segments. Retraction of the chain ends formed by cleavage due to elastic forces present determines the rate at which sub-surface networks become accessible to ozone. 4. Ozone consumption per se does not predict the resistance of a vulcanizate to ozone attack, nor does it correlate with the presence of antioxidants or antiozonants. 5. Environmental conditioning of vulcanizates has a definite effect on their ozone resistance, indicative of the role which surface films have on protection. 6. The effects of antiozonants appear to represent a protective principle involving their reaction with the ozone cleavage products of olefinic bonds. 7. No evidence has been found to indicate that ozone attack of vulcanizates proceeds through a chain reaction involving oxygen.
Thermodynamics of Elasticity of Natural Rubber
Authors: Allen Geoffrey , Bianchi Umberto , Price Colin
Published: February 2011

The thermoelasticity of a natural rubber strip held in simple elongation at constant volume has been studied experimentally. From the direct measurement of (∂f/∂T)L,V the energetic and entropic contributions to the total elastic force have been evaluated. The results agree with indirect estimates based on data obtained at constant pressure, the energetic contribution to the elastic force being some 20%. The dilation coefficient for natural rubber has also been obtained in a subsidiary experiment.
Vulcanization. Part II. Fate of Curing System during Sulfur Curing of Nr Accelerated by MBT Derivatives and Activated by Zinc Stearate
Authors: Campbell R. H. , Wise R. W.
Published: February 2011

As discussed in Part I it was generally believed that during the sulfur vulcanization of rubber, important vulcanization intermediates are formed as a result of reactions between components of the various curing systems, e.g., sulfur, accelerator, zinc oxide and elastomer. A variety of reaction products have been postulated, however, actual supporting evidence for most of these postulations is limited. This is not surprising considering that the complexity of the system makes the identification and quantitative determination of these intermediates by conventional analytical techniques difficult. Part I of this paper described some analytical methods and the application of procedures for determining the fate of the curing system throughout the vulcanization of natural rubber in the presence of sulfur and various benzothiazole type accelerators. This study confirmed that important vulcanization intermediates are formed during the vulcanization process and that they play decisive roles in delay action acceleration. However, in most practical cases zinc oxide and stearate are also required to obtain satisfactory vulcanization and curing characteristics. It was therefore desirable to extend the studies to curing systems which include zinc and stearate ion.
Ultraviolet Absorption Spectroscopy in the Study of Vulcanization
Authors: Huke D. W. , Kendall C. E.
Published: February 2011

Practically all UV absorption spectroscopy is done in solution, and examples of its use in examination of neat (one component) solid materials are relatively few. In the IR on the other hand, the examination of thin films and microtomed sections of elastomers and plastics is a normal procedure. The reasons for this are fairly obvious: scatter by optically imperfect films is much more serious in the UV, many polymers give no specific UV absorption, and those that do absorb often give such intense absorption that impracticably thin films would be required. The main value of UV is in examination of trace amounts of UV-absorbing materials in those polymers which are more or less transparent, the best example being the study of crosslinking of elastomers. This work cannot be done in solution because the cross-linked polymers are insoluble in all solvents. A great deal of the work on the chemistry of vulcanization has therefore been done on model compounds of low molecular weight, most notably at the Natural Rubber Producers' Research Association. Although the use of model olefins has yielded valuable information, investigations on polymers are required because the different conditions, particularly in steric factors, may appreciably alter the balance of reactions.
Age Resisters for Rubber. A General Study
Authors: Kempermann T.
Published: February 2011

Many scientific and technical problems arise from the phenomenon of aging in elastomers. Aging is not a simple problem, since, in the first place, different elastomers give rise to different degradation effects, and secondly, one and the same elastomer may age in a variety of ways. These may include processes—such as autoxidation and fatigue—which entail complete disintegration of rubber articles under prolonged stress; other processes, however, may certainly impair properties, but under permanent environmental stress a stationary state is reached in which only slight destruction exists. “Frosting” and “crazing” are examples of these effects. Certain aging processes occur exclusively on the surface of an elastomer which is unaffected internally, e.g., ozone cracking. Others, however, arise preferentially within the article concerned, e.g., attrition effects. Finally, there are degradation effects, such as autoxidation which progress uniformly and are not localized. Following these preliminary remarks we shall now proceed to briefly examine the principal aging effects. This paper deals with measures to combat such effects by means of anti-agers or, in North America, simply “age resisters”.
Cement Mortars Modified by SB Latexes with Variable Bound Styrene
Authors: Ōhama Y. , Ibe H. , Mine H. , Kato K.
Published: February 2011

Recently, the practical research and development of SB latex for a cement modifier have taken place and the cement mortars so modified are used in the field of building or civil engineering. The physical and chemical properties of SB latex-modified mortars have already been reported, but the effects of various polymerization conditions for latex synthesis on properties of SB latex-modified mortars have hardly been noticed. The authors discuss the effects of polymerization conditions, in particular, styrene/butadiene monomer ratio on physical properties of SB latex-modified mortar and conclude that the physical properties such as strength, drying shrinkage, adhesion, abrasion and shock resistance, etc., of SB latex-modified mortars are affected more intensely by the variation of bound styrene contents than by the rubber-cement ratios.