bluuebunny/crossref_metadata_2025 huggingface dataset:
Interrelation between Data from Different Physical Tests
Authors: Ninomya Kazuhiko , Furuta Isao
Published: February 2011

Rubber maintains its special mechanical characteristics such as low modulus of elasticity, high elasticity, relatively large shock absorbing power, tensile strength, and others over a wide temperature range. Most products made of rubber are used where those outstanding characteristics are necessary. Thus mechanical properties are generally considered to be some of the most important features in evaluating the quality of rubber products, and consequently are related to the majority of rubber testing standards. Although the present testing standards are fairly well organized, particularly in listing the essential aspects of performance for various rubber products during service, one may conclude after inspection that they are not still satisfactory enough in some respects. There are no general and quantitative rules established for the interrelation between the data from different items in physical tests of the present standards, though everyone knows from experience that they generally depend upon each other to some extent. This may be considerably important in practice when one would try to balance various necessary aspects of performance by changing the compounding and/or curing recipe. For the mechanical behavior of substances, it is a principle that the response consists of two independent factors; namely the excitation and the material factors. The object in the evaluation of the quality is always the response of the product and the judgment is given after comparing the real response with that expected or desired for the purpose. The service and/or the processing conditions provide the details of the excitation factor, whereas the material factor may correspond, in a sense, to fundamental physical properties. Similarly in laboratory physical tests, the testing condition provides the excitation factor and the object in the evaluation is always the response. Then, as can readily be expected, some of the measures defined for separate items in the present standards differ from each other only by their excitation factors. Thus they are interrelated with each other through their mutual material factors. This paper outlines the results obtained so far on this sort of problem by the application of polymer rheology.
Thermodynamic Properties of Natural Rubber and Isoprene
Authors: Warfield R. W. , Petree M. C.
Published: February 2011

Using published specific heat data, the entropy, enthalpy, and Gibbs free energy of natural rubber (NR) have been calculated over the temperature range 0 to 320° K. The thermodynamic function Cp/T as a function of T calculated for NR exhibits a maximum at 50° K and another maximum at 210° K, which is associated with the glass transition. The number of classically vibrating units per repeating unit of NR is 6.61 at 300° K. These functions have also been calculated for isoprene over the temperature range 0 to 300° K. At 298.16° K the entropy of polymerization was found to be 24.00 cal mole−1deg−1 and the free energy of polymerization − 10.7 kcal/mole.
Polymer/Solvent Interaction Parameters
Authors: Sheehan C. J. , Bisio A. L.
Published: February 2011

Solutions in which one of the components is a high polymer and the other component is a small-molecule solvent behave in a markedly different manner than do solutions of low molecular weight components. For example, the latter obey Raoult's law if the heat of mixing is negligible; however, many polymer solutions show pronounced deviation from ideality even at concentrations of one percent or less (Figures 1–7). These deviations are due to enthalpy and entropy effects which arise from large differences in size between solvent and solute molecules. Ability to predict the solubility characteristics of polymer/solvent systems, and to calculate values of the colligative properties of such systems, is important in engineering studies of polymer processes. This paper presents a compilation of data which can be used in conjunction with the Flory-Huggins theory of polymer solutions to predict properties of polymer solutions. A method is given for predicting polymer/solvent interaction parameters (μ) for systems for which experimental data are not available. Also included is a comparison between the proposed method and two other semiempirical methods for predicting μ.
Conformation of Stereoregular Polydienes in the Crystal State
Authors: Corradini Paolo
Published: February 2011

The first synthetic polymer from a diene for which stereoregularity was proved was poly(2-chloro-butadiene). Two stereoregular polymers of isoprene, synthesized by living organisms, were known before: gutta-percha and natural rubber. The crystal structure of all these polymers was established in 1942 by Bunn. After the discovery of Ziegler-Natta catalysts, many stereoregular polymers of dienes were prepared. The first, polybutadiene with 1,1-trans enchainment, was described originally in 1955. Subsequently, between 1955 and 1957, the crystal structures of all the stereoregular isomers of polybutadiene were elucidated. It is now possible to make a sufficiently comprehensive picture of the chain constitution, configuration, and conformation of a great number of stereoregular polymers of dienes.
Progressive Oxidation of Selected Particles of Carbon Black: Further Evidence for a New Microstructural Model
Authors: Heckman F. A. , Harling D. F.
Published: February 2011

A new technique is described for following the effects of successive increments of oxidative attack upon the same particles of carbon black. Oxidation was carried out under controlled conditions outside of the microscope, followed by electron micrography of selected grid areas. Electron micrographs show that normal thermal and furnace blacks generally oxidize from the inside out, forming capsules of unchanged external dimensions. Differences in rate of oxidation of individual particles are observed with thermal blacks; these rates are, however, independent of particle size. In agreement with earlier evidence, graphitized thermal blacks oxidize from the outside in. Strong support is given for a new “concentric crystallite” model of carbon black microstructure. On the basis of this model, slippage of rubber molecules on the surface of carbon black can be readily understood.
Temperature and Rate Effects on Crystalline Transitions in cis-1,4-Polybutadiene as Measured by DTA
Authors: Collins Edward A. , Chandler Lyle A.
Published: February 2011

The crystallization temperature, Tc, and the crystalline melting point, Tm, of cis-polybutadiene are strongly affected by the rate of sample cooling and heating. Cooling at rates of five to several hundred °C/min and subsequent heating at rates less than about 20 °C/min results in two distinct crystalline melting peaks. Outside this range of cooling and heating a single crystalline melting peak is observed. One of the peaks is at —9° C, which is the value generally reported in the literature, while the second peak was found to decrease with increasing cooling rate to a value of —35° C for a cooling rate of about 200 °C/min. When the cooling rates are increased, the crystallization temperature is also observed to decrease. The lowest value of Tc detected was — 61° C, at a cooling rate of 65 °C/min. This is in contrast to the literature value of — 35° C. These data are interpreted in terms of the rate processes of crystallization reported by Wood and Bekkedahl on natural rubber.
A Critical Evaluation of Infrared Methods for Determination of the E/P Ratio of Ethylene Propylene Rubbers
Authors: Corish P. J. , Tunnicliffe M. E.
Published: February 2011

A general method of analyzing ethylene—propylene (EP) copolymers for comonomer content is needed which is applicable to all types of copolymers: random copolymers (I), … EPEEPEPPEPEEE …; alternating copolymers (III), … EPEPEPEP …, block copolymers (II), … PEE … EEPP … PPEE … EEP …; and copolymers containing random (or alternating) segments together with blocks along the chain, i.e., mixed I or III, and II. Random copolymers can contain odd-numbered sequences of CH2 groups if the EP units are head-to-tail; if some head-to-head, tail-to-tail addition occurs, then even-numbered sequences of CH2 groups will also be present (IV; structures I—IV are shown on the next page). Block copolymers sometimes have crystalline polyethylene blocks and may also contain crystalline, isotactic polypropylene blocks. Mixed copolymers are more complex in structure than either random or block copolymers considered individually. In view of the lack of chemical methods for assessment of copolymer type or even for the determination of the propylene content of a copolymer, the most fruitful approach so far has been in the application of infrared spectroscopy. As CH2 groups in the copolymers can appear in many different environments, the method of analysis should be primarily concerned with the assay of CH3 groups. Even if appreciable head-to-head, tail-to-tail addition occurs, these methyl groups are separated by two carbon atoms, and little interaction should occur. Consideration has also been given to the measurement of ethylene content or total thickness in order to complete the basis for the calculation of the E/P ratio.
Application of Pyrolysis and Gas Chromatography to Polymer Characterization
Authors: Groten Barney
Published: February 2011

Pyrolysis and gas chromatography has been applied to several phases of polymer analysis. Qualitative finger-printing conditions have been defined so that a large number (> 150) of polymers can be identified using essentially singular pyrolysis and Chromatograph conditions. Quantitative analytical schemes have been devised for ester types in cellulosics, and for styrene content in SBR vulcanizates. Finally, the technique has been applied to elucidation of polymer microstructure, where it is useful for differentiating blends from true copolymers of ethylene and propylene, and for indicating major differences in stereoregularity in polypropylene.
Mechanical Fatigue Limit for Rubber
Authors: Lake G. J. , Lindley P. B.
Published: February 2011

Investigations of the dynamic cut growth behavior of vulcanized rubbers indicate that there is a minimum tearing energy at which mechanical rupture of chains occurs. The limiting value is characteristic of each vulcanizate, but is in the region of 0.05 kg/cm. The mechanical fatigue limit, below which the number of cycles to failure increases rapidly, is accurately predicted from this critical tearing energy. Characteristics of cut growth at low tearing energies, and effects of polymer, vulcanizing system, oxygen, and fillers on the critical tearing energy and fatigue limit are discussed.
Rheological Analysis of Raw Elastomers with the Multispeed Mooney Shearing Disk Viscometer
Authors: White James L. , Tokita Noboru
Published: February 2011

Mooney's shearing disk viscometer is one of the most important analytical research and process control instruments for elastomers. In this paper a new method is developed for computing the shear stress and shear rate of materials from data obtained on this instrument. In addition, the non-linear viscoelastic behavior of elastomers in the viscometer is analyzed with special emphasis upon normal stress effects. Experimental data for natural rubber, SBR, and polyisobutylene are discussed.
Thermal Degradation and Flammability of Urethan Polymers
Authors: Saunders J. H. , Backus J. K.
Published: February 2011

Polyurethans are well suited to the design of polymers for good ablation and flame-resistance. Best results in flame resistance may be expected when a composite structure is formed from an inorganic component and a self-extinguishing organic binder. The inorganic component should be present in large amounts so that the space between inorganic particles is small. For low overall density the inorganic material preferably should be foamed. The organic binder should be designed to give minimum flame spread, heat of combustion and smoke generation. The authors believe that best practical results will be achieved if the polymer gives a high melt viscosity under decomposition conditions. Those tests which rate a material as self-extinguishing because it melts and flows away from the flame are considered to be of minimum value, and offer a poor guide to the design of really good flame-resistant polymers as far as actual use is concerned. For minimum flame spread a system should be chosen that will have as little combustible gas evolved as possible, and should include a component which will provide a retarder or inhibitor for free radical decomposition mechanisms. The lowest heat of combustion will usually be favored by the incorporation of components having low hydrogen-to-carbon and low (hydrogen + carbon)-to-oxygen ratios (e.g., urethan, aromatic), and which will decompose by reactions which are not highly exothermic. While most decompositions in an oxygen atmosphere are exothermic, the dissociation of urethan groups may be assumed to be endothermic, and to this extent is favorable. The addition of an effective Lewis acid catalyst to promote carbonaceous char and reduce flammable gas formation will reduce the flame spread, and also lower the heat of combustion. Maximum char formation is desirable to serve as an insulating layer, protecting the polymer below. In addition to the Lewis acid catalyst (as may be derived from phosphorus or many of its compounds, antimony oxide, and similar acid or metal compounds) cyclic structures, especially aromatic, are favorable to char formation. These preferably should be polycyclic to minimize their chance for vaporization. Smoke generation is a function of many things, especially of the rate of burning. Hence the ideas discussed above will also be helpful in this respect. Unfortunately, some of the best structures with regard to flame spread and heat of combustion (acetylenic, aromatic) are not good from the standpoint of smoke generation. This may be because of incomplete combustion of the carbon resulting from relatively low heat of combustion. The best approach appears to be to reduce the rate of flame spread, and the heat of combustion, combined with incorporation of inorganic fillers, so that a low rate of smoke generation follows. This was achieved in Einhorn's foam-glass pellet composite of Table V.
Nitroso Rubbers
Authors: Griffis C. B. , Henry M. C.
Published: February 2011

The foundation for the Army's Research and Development Program is based upon the requirements of the tactical and support forces. In meeting hardware requirements and in our attempts to obtain significantly improved weaponry and equipment, we are continually searching for new materials. Many materials needed by the Army must possess special combinations of properties not required in normal commercial use. Military operations are today expected to take place at temperatures down to − 50° F. and much of our equipment is frequently exposed to even lower temperatures. Such low temperatures are found not only in the Arctic, but − 70° F. is a common summer temperature encountered by jets, missiles and their working component parts, only a few miles from the surface of the earth. At the other extreme, ground temperatures of 120° F. are common in various parts of the world and temperatures of 1,000° F. are encountered in many operating components of military equipment. During World War II, in Alaska and the Aleutians, and later in Korea, the hard lesson was learned that commercially available rubbers were not completely satisfactory for use in many military items. Fuel lines and pump diaphragms failed because of embrittlement; rubber covered cables and wires froze and broke on handling or lost electrical insulating properties; chemical warfare protective clothing and gas masks became stiff and unusable; tires developed flat spots; tubes buckled and stiffened; and many gaskets failed to perform their function. Indeed our whole bulk handling system for fuels and petroleum is dependent upon the proper functioning of rubber gaskets in couplings and in rubber fuel lines, containers and liners. In the last ten years, operational requirements for rubber have drastically changed. Nevertheless, rubber is still considered the best fabrication material for containing POL (petroleum, oil and lubricants) chemicals, whether it is a gasket or a 10,000 gallon flexible container. Rubbers are currently needed that, in addition to the already listed requirements, must also be resistant to concentrated acids, propellants and strong oxidizers. Further, it is desirable to have elastomers with high resistance to the effects of flame for use in compounds that may be exposed to short impulses of high intensity heat and radiation. Elastomers with satisfactory properties in one degree normally fail in others. To develop elastomers with the best possible combination of properties has been the goal of our elastomer research program since its inception.
Direct Observations of Polymer Molecules and Determination of their Molecular Weight
Authors: Richardson M. J.
Published: February 2011

An experimental investigation of the conditions necessary for the production of compact, single polymer molecules, in a form suitable for direct observation in the electron microscope, is described. Molecules are isolated by dispersing a dilute solution of the polymer as fine droplets on to a suitable substrate: ideally each droplet should contain either one or no polymer molecules. The solution is a mixture of two solvents, a good one and a poor one. Initially the good solvent predominates so that the probability of polymer aggregation is low. Preferential evaporation of the relatively volatile solvent on the substrate itself gives the poor solvent conditions needed for the formation of well-defined molecular spheres. Factors determining the choice of solvent, precipitant, and the composition of the mixture are discussed. There is little difficulty in obtaining single molecules with glassy amorphous polymers; rubbery polymers collapse and spherical molecules are formed only if the entire preparation is carried out at a temperature below that of the glass transition; crystalline polymers are not amenable to this technique. To obtain sufficient contrast the particles have to be shadowed and it is shown that, although certain dimensions are distorted by the metal coating, the shadow length faithfully represents the true particle diameter. Molecular weights, and their distribution, when of the order of a million and above, can readily be accurately determined. Conventional methods are unreliable in this region of high molecular weight.
Crystallization under Stress and Non-Gaussian Behavior of Macromolecular Networks
Authors: Smith K. J. , Greene A. , Ciferri A.
Published: February 2011

(a) Shape of the isotherm.—The appearance of a “first” upturn in the conventional isotherm is associated with non-gaussian behavior. Crystallization takes place, under usual conditions, in a range of elongation where non-gaussian behavior prevails and tends, initially, to reduce the stress below the value expected for the amorphous non-gaussian network. On further stretching a “second”, steeper up turn may be observed which is associated with a substantial reduction of amorphous content and, therefore, with crystallization. This interpretation, which is coherent with most of the experimental observations (particularly the lack of correspondence between the first upturn and the downturn of the energy component, the swelling behavior and the independence of the first upturn upon the mode of obtaining the isotherm and upon temperature) is satisfactorly fitted in the present picture of behavior of the network under stress. (b) Energy component.—Extensive measurements and theoretical analysis indicate that the ratio fe/f is essentially unaffected by swelling with n-hexadecane and by elongation, even in the elongation range following the gaussian region. The best value, i.e., 0.18, which is affected bya large error (± 0.05) confirms that the unperturbed dimensions of natural rubber molecules increase with temperature, an effect for which molecular description is lacking. Values of fe/f≦0.10, as they may occur for stretched natural rubber networks, are indicative of crystallization. (c) Crystallization under stress.—The following differences between experiments and Flory's approximate theory were noticed: (1) the value of ΔH is about one half the value to be expected on the basis of independent measurements. This indicates that the experimental variation of Tm with α is steeper than predicted; 2) Tm at α=1 appears to be some 30° below the actual isotropic melting temperature; 3) most serious differences between theory and experiments are found in the smooth change of slope of τ vs T curves at constant length in the region immediately following Tm. The part played in these effects by failure to obtain true equilibrium may not be essential judging from the fact that the best attempt made to reach equilibrium conditions did not reveal significant effects. Improved attempts to obtain equilibrium for the present system and using the present experimental technique are precluded by the occurrence of chemical degradation. Further experiments, on different polymer systems focusing attention on the region of incipient crystallization (or, preferably, “final melting”), are suggested.
Elongation at Break as a Measure of Cross-Link Density in Vulcanized Elastomers
Authors: DiGiulio E. , Bellini G. , Giandinoto G. V.
Published: February 2011

After recalling the reaction mechanism suggested for the crosslinking of ethylene propylene copolymers with organic peroxides, the authors consider the relation between concentration of curing agent and crosslink density. It is experimentally found that, as a first approximation, the elongation ratio at break of vulcanizates (unfilled or filled with small quantities of carbon black) is a function of molar concentration of peroxide only: αR=K/P1/2 This relation can be theoretically justified on the basis of the extensibility of polymer chain segments and of the criterion for rupture originally put forward by Taylor and Darin. By applying the above relation to ethylene propylene copolymers it is possible to evaluate the influence of the chain-splitting reaction during cross-linking. The reciprocal of the square of elongation ratio at break (1/αR2) measures the total degree of crosslinking.
Occurrence of Wave Effects in Rubber Antivibration Mountings
Authors: Snowdon J. C.
Published: February 2011

An approximate theory of rod vibration given by Love has been extended to describe the occurrence of wave effects, or wave resonances, in rubber antivibration mountings. Thus, the longitudinal vibration of a mass-loaded rubber mount of significant lateral dimensions and uniform cross section has been determined with the assumption that the elastic modulus and damping factor of the rubber are frequency-dependent quantities. Knowledge of the manner in which the elastic modulus and damping factor of natural rubber, natural rubber filled with carbon black, and a high-damping synthetic rubber depend upon frequency has enabled realistic computations of transmissibility. These computations have been contrasted with results obtained, for the same rubbers, from the simple one-degree-of-freedom theory in which the occurrence of wave effects is disregarded. Effectiveness of the natural-rubber mountings, which have relatively small damping, is overestimated by the simple theory at high frequencies, although transmissibility will normally remain a small quantity. In the case of the high-damping rubber considered, the results of the simple and Love theories are in relatively close agreement.
Filler Reinforcement of Liquid Elastomers
Authors: Rivin D. , True R. G.
Published: February 2011

To realize the potential processing benefits of liquid rubbers, methods must be developed for producing acceptable reinforced compounds which retain the inherent rheological advantages of the uncured polymer. The most promising commercially available liquid rubbers are functionally terminated low molecular weight analogs of common general-purpose elastomers such as poly-(butadiene) or butadiene copolymers. In principle, these low molecular weight polymers can be vulcanized by a combination of chain extension and cross-linking to yield vulcanizates comparable to those from solid elastomers. Both cure reactions can be carried out simultaneously with a chemically specific polyfunctional coupling agent, or alternatively, chain extension with a difunctional reactant can be followed by use of accelerated sulfur or equivalent crosslinking agents. In contrast to certain polar polymers, liquid hydrocarbon rubbers yield relatively weak vulcanizates which are unsuitable for mechanical and tire applications. Physical properties are greatly improved by addition of up to 60 phr of reinforcing fillers such as carbon black or precipitated silica, but at the expense of flow behavior. Important filler-dependent properties of representative liquid rubbers will be described, with emphasis on the rheology of reinforced compounds.
Carbon Black Transfer in Blends of Cis-Poly(Butadiene) with Other Elastomers
Authors: Sircar A. K. , Lamond T. G.
Published: February 2011

The study of carbon black transfer by BR crystallization, elastic modulus, and electrical conductivity provides convincing evidence that carbon black does not transfer from SBR, BR, and NR—all highly unsaturated polymers— when compounds are made by conventional Banbury and mixing procedures. This agrees with the electron micrographic studies of Marsh and coworkers as well as the latest publication of Hess and coworkers. It was shown, however, that a change in the carbon black distribution occurs when a solution BR masterbatch is mixed with fresh BR, providing the former is not premasticated. Black migration also takes place from a low unsaturation polymer (chlorobutyl) toward a high unsaturation polymer (BR) in chlorobutyl—BR blends, irrespective of how the black is added. Electron micrographs reveal that even in this case black does not actually transfer, but migrates to the interface, in agreement with the observation of Marsh and coworkers for NR—CR blend. Black migration in chlorobutyl—BR blends can be reduced by increasing the chlorobutyl—black interaction by heat treating and by using a promoter. The advantages of the above techniques are that these methods are suitable for highly compatible SBR—BR blends as well as for highly loaded systems, which are difficult to examine by micrographical methods. Also, an idea of the degree of compatibility of the different elastomers with BR can be obtained from crystallization studies. The disadvantage of the crystallization method is that it depends on the melting endotherm of BR and is, therefore, unsuitable for combinations that do not include BR. It is evident from the work reported that the sequence of addition of elastomers and carbon black is of paramount importance to the properties of the finished compounds since carbon black migration is the exception rather than the rule: migration takes place only in limited cases and under well-defined conditions.
A Comparison of Methods for Determining Surface Areas of Carbon Black
Authors: Klyne R. A. , Simpson B. D. , Studebaker M. L.
Published: February 2011

1. The various tint tests correlate with each other—it does not make much difference which of the three procedures is used. The discrimination between similar blacks is comparable. Specific surface areas obtained by the three methods are comparable and differences appear to be due to experimental errors. (Compare Figures 5–7). 2. Surface areas larger than some 90 to 100 m2/g cannot be reliably determined from tint strength measurements alone. 3. Structure exerts a pronounced effect on tint strength of furnace blacks, especially above 90 to 100 m2/g. Porosity and/or composition are apparently also variables which affect tinting strength. 4. Densichron reflectance on the dry carbon black can be used to estimate specific surface areas up to about 140 m2/g; but, since theabsoluteerrorincreases as the specific surface area increases, this method loses some of its reliability at values above about 110 m2/g. The relative error in reflectance determinations does not vary greatly over the furnace-black range. Densichron reflectance is influenced by composition, evidently due to composition-related differences in optical properties of the carbons. 5. In CTAB adsorption measurements, titration errors and handling errors tend to be rather constant for blacks of different surface area. Hence, CTAB permits better discrimination among blacks of small particle size. 6. The errors in Densichron reflectance surface area increase with specific surface area. Hence, the deviations between CTAB and reflectance surface area which are due to experimental error increase with the surface area of the sample.
Estimation of Glass Transition Temperatures from Gas Chromatographic Studies on Polymers
Authors: Lavoie A. , Guillet J. E.
Published: February 2011

In a recent communication, Smidsrød and Guillet showed that thermodynamic data on the interactions between poly (isopropylacrylamide) and various gaseous solutes could be obtained by making the polymer the stationary phase in a gas Chromatograph. It was also shown that if a solute was used which was a nonsolvent for the polymer, a plot of the logarithm of the specific retention volume as a function of reciprocal temperature showed a marked inflection at a temperature close to the glass transition temperature for the polymer. We wish to report similar data on several additional polymers which lead us to believe that the phenomenon is a general one and may be used to obtain an estimate of transition temperatures for a variety of polymeric materials.
NMR Study of the Crystallization Kinetics of Cis-Poly(Isoprene)s
Authors: Hirst R. C. , Chen H. Y.
Published: February 2011

The satisfactory agreement between our NMR results and X-ray diffraction results for the crystallinity in stark rubber at room temperature lead us to conclude that the NMR rigid lattice fraction, PRL, may be taken as equal to the fractional crystallinity obtained by other methods. Similarly, the good agreement between the time dependence of PRL at low temperature and the theoretical curve shape strongly suggest that the NMR crystallinity method works well down to at least −25° C for natural rubber and synthetic cis-poly (isoprene). It would be desirable to compare carefully the NMR crystallinity found for rubber crystallized at −25° C with X-ray diffraction results, but we have been unable to find any such X-ray diffraction studies at −25° C. Maximum values of ΔV/V≅0.025 from dilatometric studies appear to imply somewhat smaller crystallinities than those found by NMR, but an accurate comparison is not possible without having X-ray diffraction densities at −25° C. While the present experiments were carried out on unfilled, unstretched, unvulcanized samples, the NMR crystallinity method is equally applicable to samples which are filled, stretched, and vulcanized. Naturally any additive or impurity containing hydrogen is a possible source of interference, but there should be no difficulty in correcting for such interferences.
The Determination of Rubber in Atmospheric Dusts
Authors: Cardina J. A.
Published: February 2011

Samples of airborne dusts were collected near heavily traveled highways and analyzed for rubber by pyrolysis gas chromatography. Dust samples obtained in truck traffic gave pyrolysis chromatograms markedly different from those obtained in passenger car traffic, and which correspond with those derived from known tire tread compounds. The distinction was based on the presence of styrene or dipentene in the pyrolyzates. Quantitative determination of dusts from the Pittsburgh Liberty Tunnel and the Akron Expressway Interchange show the presence of 1.5 to 2.5 per cent rubber, whereas dust from a residential area shows about 0.25 per cent. Methods were developed for sampling atmospheric dusts and preparing small amounts in a form suitable for pyrolysis.
Sequence Length and Crystallinity in Alpha-Olefin Terpolymers
Authors: Davison S. , Taylor G. L.
Published: February 2011

The minimum sequence length for crystallization in a polymer was determined by a novel kinetic approach using sequence analysis of a series of blocky terpolymers. Copolymers and terpolymers of ethylene, propylene, and but-1-ene were prepared with a Ziegler—Natta catalyst system. Compositions of feeds and polymers were analyzed, and kinetic reactivity parameters were calculated using both the Fine—Ross and Alfrey—Goldfinger approaches. The parameters were then applied to determine the sequence length distribution of each component in the terpolymers. Also, deliberate control of sequence lengths enabled synthesis of heptane-soluble, rubbery polymers even using a catalyst system which normally produced blocky materials. Crystalline contents of the terpolymers were determined experimentally by nitric acid digestion. A critical comparison of the measured crystallinities with the calculated sequence length distributions was thereby made possible. From this comparison a minimum sequence length of monomer below which crystallization did not occur was estimated; this length was approximately 20 backbone carbon atoms.
Scorch Control of Carboxylic Elastomers
Authors: Hallenbeck V. L.
Published: February 2011

Carboxylic elastomers can be cured by standard compounding recipes utilizing sulfur and zinc oxide. The zinc oxide, besides aiding the sulfur cure, also gives a secondary cure through an ionic bond with the carboxyl groups. However, because of the affinity of the zinc oxide for the carboxyl group, the stocks tend to have an excessive scorch and a short shelf life. To prevent this excessive scorch the zinc oxide must be isolated from the carboxyl group until the desired cure temperature is reached. Three materials may be used to isolate the zinc oxide : 1) zinc sulfide coated zinc oxide, 2) zinc phosphate coated zinc oxide and 3) metallic alkoxide combined with the zinc oxide. The use of any of these gives scorch control without affecting final physical properties. The amount of zinc sulfide coating, zinc phosphate coating, and metallic alkoxide varies with the type of carboxylic elastomer.
Rubber Microscopy
Authors: Kruse Julius
Published: February 2011

Rubber microscopy was limited in its beginning primarily to the study of the filler materials dispersed in the rubber, to a surveillance of the fineness of these materials, as well as to the investigation of articles made of rubber for the purpose of elucidating technological questions which had to do with structure and preparation or manufacture. In the last few decades considerable improvement in techniques of microscopical investigations have given a new impetus to rubber microscopy so that, in addition to the above named applications, new goals have become possible. Thus today with the aid of electron microscopy, interference microscopy, and also spectrophotometric and polarization optical measurement procedures applied to microscopic objects one can designate rubber microscopy as a valuable aid in the investigation of the microstructure of rubber materials of all kinds. The technology of preparing specimens for electron microscopy has been particularly helpful to produce knowledge concerning the flow phenomena in colloidal situations which take place when carbon black is mixed into the rubber and which lead to the formation of a special network consisting of carbon black and rubber. In addition to this, there was derived from the logical and practical application of the above mentioned investigative procedures an improvement in analytical methods whereby only small amounts of materials are needed for the investigation of mixes or compounds and vulcanizates. Thus today one can name three principal application areas for rubber microscopy: 1. The study of the microstructure of rubber compounds and vulcanizates; 2. The analytical investigation of compounds and vulcanizates; 3. The examination of articles made of rubber in order to clarify their structure as well as to solve technological problems.
Gas—Liquid Chromatography on Polymers. I. Polyisobutylene—Hydrocarbons at 25°C
Authors: Leung Yu-Kwan , Eichinger B. E.
Published: February 2011

The Flory—Huggins mixing parameters χ, obtained by glc agree closely with those derived by extrapolation of results from static vapor sorption and osmometry for the systems PIB—n-pentane and PIB—n-octane. Substantial discrepancies between the two are observed for the systems PIB—benzene and PIB—cyclohexane. It is not clear at this early stage whether this indicates specific interactions between solvent and polymer, including surface adsorption, or if there are large inaccuracies in the sorption data at low concentrations of solvent. As we noted above, and from consideration of the vapor sorption measurements, it does not seem likely that the latter possibility is cause for great concern. Instead, we are inclined to the view that specific interactions, or more general geometrical contraints on cavity formation, are operating in these highly concentrated solutions. Since X12 values from enthalpies of mixing and from glc agree so closely for n-alkanes, we have further evidence for the remarkable accuracy of Flory's solution theory. However, the peculiar discrepancies between the various experimental determinations of χ and between theory and experiment for benzene and cyclohexane suggest possible secondary influences on such systems that have not yet been comprehended. We are hopeful that the temperature coefficient of χ will provide further insight into the nature of such influences that appears to be manifest in the data reported here.
Mechanism of Smoke Inhibition by Hydrated Fillers
Authors: Lawson D. F. , Kay E. L. , Roberts D. T.
Published: February 2011

The smoke inhibitory activity of hydrated fillers in SBR is centered primarily in condensed-phase processes and is analogous to the generally accepted mechanism of flame retardation by the hydrates. Dissipation of heat, which disfavors pyrolysis and favors competing crosslinking reactions is probably involved. These reactions should occur chiefly among polybutadiene segments of the polymers. In addition, the smoke-suppressant efficiency of hydrated fillers should depend upon the crosslinking efficiency of the rubber. Finally, although smoke generation in latex rubber goods presents a challenge, substantial practical reductions in visible smoke can be achieved through the selection of proper hydrated fillers.
Using the SI System of Units
Authors: Conant F. S.
Published: February 2011

SI surpasses previous metric systems in coherence, simplicity, distinction between force and mass, choice of units, and uniformity of usage. Coherence eliminates conversion factors, other than powers of ten, within the system. Through simplification, only seven base units, two supplementary units, fifteen named derived units, and fourteen prefixes are needed to describe the entire system. Introduction of the newton as a unit of force and retention of the kilogram for mass clarifies the difference between the two quantities. Other new units are: pascal for pressure, Siemens for electric conductance and mole for amount of a substance. International agreement minimizes proliferation of specialized units or usage. Adopted conventions include spelling, abbreviations, style, and usage, as well as definitions for the units. Tolerances, rounding of numbers, and elimination of the comma in multidigit numbers assume new significance. Conversion to SI offers a unique opportunity to reduce the number of sizes of many products. Several schemes for metric modularism have been developed for this purpose. In changing from conventional to SI units the key idea is “think metric” rather than use dual dimensioning.
Thermoanalytical Methods in Vulcanizate Analysis I. Differential Scanning Calorimetry and the Heat of Vulcanization
Authors: Brazier D. W. , Nickel G. H.
Published: February 2011

Our objective has been to demonstrate that DSC is a convenient and rapid technique for the study of elastomer vulcanization characteristics. Although we have been concerned only with NR and NR-BR blends, the observation of exothermicity in sulfur vulcanization is quite general. Similar observations on sulfur vulcanization of IIR, SBR, EPDM, CSM, and NBR rubbers have been made in our laboratory. In non-sulfur vulcanization systems, we have found the diurethane cure of natural rubber to be exothermic and amenable to DSC study. As reported by Bruce et al., the magnesium oxide cure of chloroprenes is exothermic, but magnesium oxide-diamine vulcanization of fluoroelastomers is characterized by very low exothermicity. Future studies of the effect of various additives on soft rubber cure could make a significant contribution to our understanding of the complex cure mechanism. Successful kinetic analysis of DSC scans is perhaps the major hurdle to be overcome before the DSC technique can be meaningfully applied to such problems.
Chemical Stress-Relaxation of Filled Vulcanizates under Large Cyclic-Deformation
Authors: Kusano T. , Murakami K.
Published: February 2011

The stress relaxation under cyclic deformation was used to elucidate the fatigue mechanism of carbon-black filled natural-rubber vulcanizates. Below 70°C the rate of stress relaxation of the filled vulcanizates depended on both extension ratio and frequency. Above 70°C it depended on the extension ratio only. The stress relaxation above 70°C is caused by the scission of both the primary bonds of polymer chains and bonds between polymer and carbon black. Below 70°C it is caused by the scission of the bonds between polymer chain and carbon black. However, at very small deformation above 70°C the mechanism of the stress relaxation of the filled system was the same as that of the unfilled system. The failure of the chemical bonds of polymer chains is involved, but not the failure of bonds between polymer and filler. The same relaxation mechanism may be operating in both air and nitrogen under the large deformation, because the amplitude dependence was the same.
Analysis of Fatigue Process of Rubber Vulcanizates
Authors: Hirakawa H. , Urano F. , Kida M.
Published: February 2011

The relationship between energy-input and hysteresis energy-loss during repeated deformation was analyzed, with gum and filled-rubber vuloanizates. It was recognized that the hysteresis energy-loss decreases more quickly with repeated deformation than the energy-input does. After a number of cycles both the energy-input and the energy-loss approach constant values. When these values are plotted against strain, curves similar in shape are obtained, regardless of the type of rubber. This is because the network chain is well relaxed. A group of the linear relationships between log W and log H was found with respect to N and λ. Examining the parameters, g1, g2, f1 and f2 as functions of N and λ, simple expressions, (4) and (5), were obtained for both the first deformation and after many cycles. At the latter state the hysteresis ratio tends to be constant in the wide range of λ. Finally, the relation between W and H at fatigue break is expressed with the same form of equation proposed by Grosch for the tensile break at the first extension.
Effect of Strain-Induced Crystallization on the Elastomeric Properties of Cis-1,4-Polybutadiene Networks
Authors: Su T-K. , Mark J. E.
Published: February 2011

Polymer networks, when studied at very high elongations, frequency show anomalous stress-strain isotherms in that they exhibit values of the modulus or “reduced force” [ƒ*] which increase markedly with increasing elongation. Such isotherms depart appreciably from the form predicted by the molecular theories of rubberlike elasticity and from the Mooney—Rivlin representation adopted from phenomenological arguments as well. For this reason, the interpretation of the increase in [ƒ*] at high elongations has been of great interest for a considerable period of time. For several decades now, this behavior has generally been attributed to the limited extensibility of the network chains. Critical examination of various published results pertinent to this question, in conjunction with more definitive experimental studies reported recently, however, support the alternative suggestion that such atypical isotherms are due to strain-induced crystallization. One experiment particularly relevant to this issue is the study of the stress-strain isotherms of a polymer network as a function of temperature. Such experiments have been carried out on natural rubber, but the relatively poor thermal stability of this polymer and the extent to which its melting point is increased by elongation make it essentially impossible to study the high elongation stress-strain relationships for this polymer at a temperature sufficiently high to ensure complete suppression of strain-induced crystallinity. Similar experiments carried out on networks of a more suitable polymer, polyisobutylene, gave stress-strain isotherms showing the upturn in the reduced force at low temperature, but not at higher temperatures, thus strongly implicating strain-induced crystallization as the origin of this anomalous behavior. These experiments, however, suffered somewhat from the one shortcoming that the increase in temperature required to suppress the upturn in [ƒ*] also decreased the maximum extensibility of the network to below the elongation at which the upturn occurred at the lower temperatures.
Non-Newtonian Flow of Polymer Solutions
Authors: Patat F. , Spott G.
Published: February 2011

Non-Newtonian flow of solutions of polyisobutylene, poly (vinyl acetate), poly (ethylene glycol), and polyisoprene was investigated, as a function of molecular weight, concentration, temperature, and solvent, with a modified rotational viscometer with coaxial cylinders and a newly-developed, high-pressure, capillary viscometer. Analysis of the results of the viscosity experiments was based upon kinematic flow theory, and provided a consistent interpretation of the non-Newtonian flow behavior encountered. Shape of the flow curve is determined by the decreasing degree of association of the polymers with increasing shear stress. Rise in viscosity of the polymer solutions, as compared to that of the solvent, is due chiefly to solvent associated polymer interactions at each stress state involved.
Strain-Dependent Properties of Polymers I
Authors: Warnaka G. E. , Miller H. T.
Published: February 2011

Dynamic elastic moduli of homogeneous, amorphous polymers decrease at moderate to high strains. Under the same strain magnitudes the loss factor goes through a broad maximum. At low strains, dynamic properties are independent of strain amplitude. This paper shows that strain dependence is a basic property of homogeneous, amorphous polymers. Strain dependence is shown to occur in gum, as well as filled, vulcanizates. In addition it is shown that self heating due to flexing at high strains cannot fully explain strain dependent dynamic properties. Testing has been performed on specimens with greatly varying geometries (and, hence, different amounts of self-heating) and at controlled specimen temperatures. These tests have verified the existence of a basic strain-dependency. Strain dependence is here related to time-temperature dependent properties of polymers as described by the well-known work of Williams, Landel, and Ferry. The magnitude of strain dependence and the strain amplitudes at which strain dependence occurs appear to be controlled by the time-temperature dependence of polymers.