bluuebunny/crossref_metadata_2025 huggingface dataset:
A Rapid Quantitative Method for Measuring Ozone Cracking and Its Use in Outdoor Dynamic Testing
Authors: Veith A. G.
Published: February 2011

A fairly rapid quantitative technique for measuring the cracking damage done to rubber by ozone has been described. The method consists of microscopic measurement of the length and width of selected ozone cracks. The product of the “average” length and width is termed the “severity of ozone cracking” and is abbreviated, SOC. The SOC value for a specimen is approximately 2 times the void area in arbitrary units. The use of the SOC technique in conjunction with an outdoor dynamic ozone test showed how various antiozonants perform in NR, SBR, and OE-SBR both with and without wax. Some effects of the amount and type of extending oil and of wax melting point are illustrated. Weather plays an important role in regard to ozone attack especially for wax containing compounds. During the warmer months higher melting waxes perform better in natural and OE-SBR while higher melting waxes perform slightly poorer in non-oil extended SBR. Good correlation was found between the outdoor flexing tests and service type outdoor tire tests carried out on an outdoor wheel. Some of the ramifications of this type of testing are pointed out.
The Tensile Strength of Glass Yarn in Rubber. II. The Effects of Normal Humidities
Authors: Gregg R. A.
Published: February 2011

The resinous impregnant in glass yarn influences the stability of the yarn. Some glass yarns suffer tensile degradation on storage and/or vulcanization at high humidities. One type of glass yarn was exposed in atmospheres over the range 0–88% relative humidity at 73° F for times up to 400 days. Tensile losses of 30% or more can occur on storage of the glass yarn at the humidities in the upper end of the range. This loss is permanent as even vigorous drying at high temperatures will not restore the tensile. Under dry conditions the yarn has excellent storage stability. Furthermore, after vulcanization even into thin composites, the glass yarn shows only a small permanent loss of tensile under moisture conditions that would seriously degrade the yarn in a package. An increased degree of vulcanization of the rubber slightly increases the tensile strength of the composite. In addition to its permanent degradative action in long-term exposure, water has a phenomenological effect of reducing glass composite tensile by its presence. A tensile sensitivity to moisture index is suggested and used to characterize the glass yarn. This tensile loss is recoverable by drying but some of the water is bound very tightly. Thin composites do not give up all of the water in 150 days over Drierite® as shown by the fact that more vigorous high temperature drying leads to a further increase in tensile strength. Tensile strength at 300° F is about 25% lower than at 73° F at any moisture content. Higher moisture contents lead to lower absolute tensiles. Tensile values are detailed for conditions that might exist during cure or in a product running at a high temperature. The high temperature incurred tensile reductions from a standard tensile are significant and should be considered in designing products. The detailed observations apply only to this particular glass yarn but the principles and methods are applicable in the evaluation or development of any glass yarn.
Rubber—Black Interaction Influence on Cure Level of Vulcanizates
Authors: Brennan J. J. , Lambert D. H.
Published: February 2011

The crosslink density of vulcanizates has been quantitatively investigated using swelling measurements (Vr) of compounds of cis-1,4-polybutadiene reinforced with N242, N326, or N990 (Vulcan 6H, Regal 300, Sterling MT). Crosslink density in both filled and unfilled stocks is shown to be related to the molar concentration of the curatives in the unbound rubber phase of the vulcanizates and not merely to total concentration. The effects of different carbon black loadings and of cure time are demonstrated to be fully describable by the extent of carbon black—rubber interaction, measured by bound rubber; that occurs during mixing and during the induction period of the cure step. Greater rubber-black interaction, whether achieved by higher black level or from higher reinforcing blacks, always yielded vulcanizates of increased crosslink density compared to an identically vulcanized gum control. Calculating curative concentration on the basis of unbound rubber—rather than total rubber—illustrated the expected dependence of crosslink density upon curative concentration and graphically explains the presence of so-called “excess” crosslinks. Implied, also, is one cause for the “scorchy” character of highly reinforcing blacks and the higher modulus obtained with these blacks.
Review of Basic Oxidation Processes in Elastomers
Authors: Shelton J. Reid
Published: February 2011

The early studies of chain scission in the oxidation of rubber by Dr. E. M. Bevilacqua, and his subsequent work on the identification of the various acids, methyl ketones, and other volatile products of the oxidation reaction, have contributed much to our present knowledge of the nature of the processes involved in the oxidation of elastomers. His numerous research publications and review papers represent a significant segment of the world's literature on oxidation and aging of rubber. This introductory paper of the E. M. Bevilacqua Memorial Symposium is a brief review of our present understanding of some of the basic oxidation processes in elastomers. More extensive reviews of various aspects of the subject are available. This review is primarily concerned with the nature of the chemical reactions involved in the oxidation, degradation, and stabilization of elastomers. The mechanism of uninhibited autoxidation (based on model compound studies) will be compared with the more complicated sequence of reactions observed in the retarded autoxidation of elastomers which occurs in the presence of antioxidants. The oxidative degradation of physical properties will be considered in terms of the resultant effect of the two competing processes of chain scission and crosslinking. The role of antioxidants as stabilizers against oxidative degradation will be discussed from the standpoint of the mechanisms by which different types of stabilizers protect elastomers during aging and use.
The Application of Model Reactions to the Oxidation of Polyolefins
Authors: Allara D. L. , Edelson D.
Published: February 2011

Initial attempts have been made using computational techniques to apply model compound reactions quantitatively to the oxidation of ethylenepropylene copolymers by molecular oxygen at 100° C. The oxidations of n-butane, isobutane, and isopentane (the simplest model of a polypropylene repeat unit) were chosen as models and applied to the prediction of rates and products in the low conversion oxidations of squalane and a series of ethylenepropylene copolymers of differing composition at 100°. For simplicity, these initial calculations were done for a low viscosity fluid phase. For externally initiated reactions, where calculated and experimental rates (mostly amorphous, solid phase) could be compared, agreement was usually within a factor of 3–5, with the calculated rates generally too fast. Our results on both self- and externally initiated systems suggest that the effect of phase change, from liquid to amorphous solid, on the overall oxidation rate is not large, except in a few cases where effects such as chemically induced crystallization may be significant in the solid phase. Calculations for externally initiated oxidations predict that the rate of chain scission is proportional to the rate of radical production in excellent agreement with experimental results. Our initial results indicate that small alkane molecule reactions can be applied usefully, at present with limited accuracy, to the oxidation of hydrocarbon polymers.
Oxidation of Photoexcited Elastomers
Authors: Morand Mme J. L.
Published: February 2011

The sensitivity spectrum of elastomers to sunlight (λ≽300 nm), determined by the variation at 30° C of the initial rate of oxidation or chain scissions as a function of the wavelength of incident light, shows several maxima in the near UV. These maxima are approximately equidistant and the space between them differs only slightly (10 to 11.5 nm) according to the polydienes (polyisoprene, polybutadiene, copolymer butadiene-styrene) in the crude or the vulcanized state, whatever may be the curing system. The identified maxima, existing also under vacuum (10−4 Torr), can be due to the presence of some chromophores in the chains. The latter, in absorbing the light during the primary photophysical process, would initiate the degradation. Among different possibilities, an S0→T1 transition of the isolated double bonds, producing free radicals, seems to be the one likely to explain the results. After the initiation, the photoxidation at 30° C and 5 mW/cm2 proceeds like the thermoxidation near 150° C. For a peroxide vulcanized rubber, the kinetics are similar and the rates of oxidation are somewhat faster under the most harmful sunrays than those observed by Bevilacqua at 120° C. Moreover, the chain scissions are a linear function of the oxygen consumed and their ratio is close to the limiting value of about 6 moles of O2 per broken bond, obtained by this author at 140–150° C.
Molecular Theories of Rubberlike Elasticity and Polymer Viscoelasticity
Authors: Shen Mitchel , Hall William F. , Dewames Roger E.
Published: February 2011

The foundation for nearly all the molecular theories of the physical properties of polymers was laid in 1934 when Guth and Mark and Kuhn first recognized the role of configurational entropy of polymer chains. By virtue of ability of their segments to rotate with respect to each other along the chain backbone, macromolecules are capable of assuming a myriad of conformations. It is this long, flexible chain nature of polymer molecules that provides us a link in interpreting the macroscopic physical properties in terms of microscopic molecular dynamics. In this review we shall demonstrate the utilization of conformational statistics in the formulation of molecular theories for two important aspects of the mechanical properties of polymers. The first part deals with the equilibrium elastic response of a crosslinked rubberlike network. A simplified derivation will be given on the basis of the entropic approach. Some of the underlying assumptions will then be examined, and the contribution of internal energy to rubber elasticity scrutinized. The second part describes the transient viscoelastic properties of linear polymers in solution and in bulk. Limitations of the model will be assessed and its applications to experimental data explored. It should be pointed out that a number of reviews are available in the literature both for elasticity and viscoelasticity of polymers. The present work is not an exhaustive review of these fields, but rather concentrates on the more recent developments not previously discussed. The emphasis will be placed upon polymers in the bulk state, although solution properties will be mentioned where appropriate.
Effective Degree of Immobilization of Rubber Occluded within Carbon Black Aggregates
Authors: Medalia A. I.
Published: February 2011

The conclusions of the present work may be summarized as follows. 1. The effective volume of carbon black in rubber, as measured by the low-strain equilibrium modulus, is equal to the true volume of carbon plus about half of the occluded volume of rubber calculated from the DBP absorption of the carbon black. 2. Breakdown of aggregates on incorporation in rubber may diminish the volume of occluded rubber; thus, calculations based on the same modulus data would give a somewhat higher effectiveness factor—perhaps of the order of 0.6, depending on the degree of breakdown assumed. 3. Under non-equilibrium conditions various processes may either raise or lower the measured modulus and (thus) the occluded volume effectiveness factor : (a) At moderate to high strains, strain amplification raises the modulus. (b) At low temperatures, amplification of the rate of strain raises the modulus (relative to that of the gum). (c) In a highly loaded vulcanizate, the secondary network of carbon black raises the modulus measured at low strain and low or moderate temperature. (d) The modulus can be lowered by molecular slippage, especially with thermal blacks, or with graphitized furnace blacks, at elevated temperatures and/or high strains.
Natural Rubber Latex Concentrate Properties and Processibility
Authors: Gorton A. D. T.
Published: February 2011

The concept of latex concentrate processibility and its relation to raw latex properties and proposed chemical stability tests is examined. The KOH number of latex is shown to have only a limited value as a criterion of latex properties. A new test is proposed based on the viscosity behavior on storage of a fully compounded latex. This test is experimentally compared to other proposed tests, raw latex properties, and the influence of various additives. Methods of controlling latex compound viscosity are suggested.
The Impact of Lithium Initiators on the Preparation of Synthetic Rubbers
Authors: Adams H. E. , Bebb R. L. , Forman L. E. , Wakefield L. B.
Published: February 2011

The impact of the lithium initiator system has begun in the rubber synthesis field; it will surely expand into the production of plastics of controlled and desirable structure. Polymers can be designed in both fields with precise structure control for desired processing characteristics and properties. This will become more useful as the concept of domains and heterogeneity is more fully understood and utilized. The system will also lend itself to planned termination by functional groups where the products will have unusual reactivities. Solution polymerization systems should play an increasing role in the production of synthetic rubber. Of course, the emulsion system must be considered in applications where latex itself is desired and in those cases where monomers with functional groups would react with the organometallic initiator. Otherwise, we believe that solution systems will produce rubber with especially desirable properties more cheaply without as much harm to the ecology.
Carbon-13 NMR of Poly(Butadiene)
Authors: Mochel V. D.
Published: February 2011

By using the carbon-13 NMR technique, it is shown that there are no cis-1,4-trans-1,4 linkages in an n-BuLi-catalyzed poly (butadiene). The polymer consists of “blocks” of cis-1,4 units and trans-1,4 units separated by isolated vinyl units. Preliminary evidence suggests this might also be true for other types of 1,3-diene polymerization. Some of the implications of this finding on the mechanism of polymerization are discussed. Tacticity triad distributions are readily determined in poly(butadiene)s with high 1,2 addition contents.
The Synergistic Effect of Natural Rubber on the Crystallization of Lithium Poly(Isoprene)S (Coral Rubber)
Authors: Brock M. J. , Hackathorn Marjorie J.
Published: February 2011

The influence of silver nitrate on the crystallization of poly(isoprene)s has been demonstrated as well as the synergistic effect of natural rubber on the crystallization of lithium catalyzed poly(isoprene). This synergism does not appear to be a “seeding” effect in the strictly definitive sense, since no seed crystals are actually added. In this case a better description of this effect might be cocrystallization where nucleation is promoted by the addition of a quantity of a highly regular similar species. Actually there is a good probability that the nucleating crystals themselves contain segments of the synthetic poly(isoprene). This conclusion is supported by the data shown in Figure 6 for a 50/50 mixture of natural rubber and a noncrystallizable Alfin polymer. The dilato meter curve for this mixture indicates that the 50 per cent non-crystallizable polymer has a slight retarding effect on the induction period for the crystallization of the natural rubber but the crystallization rate of the natural rubber in the 50/50 mixture is quite rapid up to the total volume change expected for natural rubber portion of the mixture. However, in the presence of 50 per cent of a crystallizable lithium poly(isoprene) (also shown in Figure 6), the crystallization rate of this mixture is much slower due to co crystallization. The proposed change from head-tail cis-1,4 addition to tail-head cis-4,1 addition whenever a 3,4 unit is introduced into the polymer chain seems to explain the experimental crystallinity data obtained in these studies. In addition, it raises some questions about the polymerization mechanisms involved and resulting from the orientation of a 3,4 unit being added to the growing end of a polydienyl chain.
Diene Termonomer Type and EPDM Properties
Authors: Baranwal K. C. , Lindsay G. A.
Published: February 2011

The objective of this work was to study the effects of the type of diene termonomer on properties, especially thermal stability and aging, of EPDM polymers. Five different EPDM polymers using ethylidene norbornene (ENB), butadiene (BD), dicyclopentadiene (DCPD), methyltetrahydroindene (MTHI), and 1,4-hexadiene (HD) as termonomers were made at equimolar unsaturation. The same sulfur/accelerator system was used for curing these polymers. In both gum and filled vulcanizates ENB-EPDM is the fastest curing. In gum stocks HD-EPDM is the slowest curing, but is faster than DCPD-EPDM in filled stocks. These polymers, except for BD-EPDM, have about the same initial crosslink densities. Crosslink density and crosslink type analyses indicate that butadiene units in BD-EPDM chains are blocked. For HD-EPDM, both in gum and filled vulcanizates, 50 per cent of original crosslinks are monosulfidic. The other four EPDM vulcanizates have a lower proportion of monosulfidic crosslinks. At 350° F aging temperature, both ENB and HD polymers have ∼65 per cent monosulfidic crosslinks and about the same energy-to-break values (Eb). However, the higher original monosulfidic crosslink content of HD-EPDM does not seem to offer any better aging than for other polymers. DCPD-EPDM at 350° F aging temperature has the same monosulfidic content but increases further at 550° F aging temperature. At 550° F aging temperature almost all the crosslinks are monosulfidic for these EPDM polymers but the total crosslink densities and Eb are very low presumably due to oxidative degradation. Thermogravimetric analysis in N2 shows that these vulcanizates decompose in 800-935° F temperature range. In air, this range is 750-935° F.
The Influence of Accelerators on EPDM Vulcanizate Structure
Authors: Baldwin F. P.
Published: February 2011

This study of vulcanization has revealed that in low unsaturation EPDM elastomers prepared with ethylidenenorbornene— 1. Stearic acid can be a useful additive for vulcanization. Increasing concentration in the range 0-4 phr leads to faster curing and reduced polysulfidic crosslink concentration at a given crosslink density. 2. Low sulfur and low sulfur/accelerator ratio and/or prolonged curing times are required to generate vulcanizates containing low percentages of polysulfidic crosslinks. 3. At identical crosslink densities, high temperature cures display a lower level of polysulfidic crosslinks than low temperature cures. However, olefin utilization in crosslinking is generally better with low temperature curing. 4. At high sulfur levels, variations in crosslink type distribution resulting from accelerator changes tend to disappear. 5. Mixed acceleration—a dialkylthiocarbamic acid derivative and an accelerator having the benzothiazolylthio radical—appear best suited for the combination of maximizing cure rate and producing stable (lower sulfur rank) crosslinks. Taken together with other information, the results of this study lead to the suggestion that: 6. The stability of the basic accelerator nucleus is influential both on cure rate and on the ability to generate stable crosslinks. 7. The exact structure and concentration of the olefinic moieties present in the polymer have at least as much bearing on the detailed outcome of the vulcanization process as do changes in accelerator. 8. A useful accelerator for these rubbers resulting in the production of vulcanizates containing a high concentration of low rank sulfur crosslink might derive from a MBT type synthesis based on a properly ringalkylated aniline. 9. Some effort devoted to the study of chemicals which may not accelerate crosslinking but could participate in the crosslink shortening process would appear worthwhile.
The Effects of Modulus and Sulfur Concentrations on the Properties of SBR Vulcanizates
Authors: Cox W. L.
Published: February 2011

While it has long been recognized that the original and aged properties of a vulcanizate depend to a very large extent on the number and type of the chemical crosslinks present, the exact nature of this dependence is seldom reported. The present study was undertaken to investigate systematically within a set of sulfenamide-accelerated sulfur vulcanizates of SBR the relative importance of crosslink frequency and character. Since the moduli of rubber compounds differing only in curative concentrations furnish a convenient measure of the relative numbers of crosslinks present, this property was taken as one variable of an experimental design, with sulfur concentration as the other. Obviously, to achieve different moduli values at a given sulfur level, alterations in the accelerator concentration must be made, and any interpretation of data must take this fact into account.
Modulus of Natural Rubber Crosslinked by Dicumyl Peroxide. I. Experimental Observations
Authors: Wood L. A. , Bullman G. W. , Decker G. E.
Published: February 2011

Natural rubber mixed with varying amounts of dicumyl peroxide are crosslinked by heating 120 min at 149° C. The quantitative measure of cross- linking was taken as the amount fp of decomposed dicumyl peroxide, the product of p, the number of parts added per hundred of rubber and f the fraction decomposed during the time of cure. The shear creep modulus G was calculated from measurements of the indentation of a flat rubber sheet by a rigid sphere. The glass transition temperature Tg, was raised about 1.2° C for each part of decomposed dicumyl peroxide. Above (Tg+12) the modulustemperature relations were linear with a slope that increased with increasing crosslinking. The creep rate was negligible except near the glass transition and at low values of fp. Values of G, read from these plots at seven temperatures, were plotted as a function of fp. The linearity of the two plots permits the derivation of the general relation: G=S(fp+B)T+H(fp+B)+A where A, B, H, and S are constants. The lines representing G as a function of fp at each temperature all intersected near the point, fp=0.45 phr, G=2.70 Mdyn cm−2(0.270 MN  m−2). . The constants were evaluated as A=2.70 Mdyn cm−2,B=−0.45 phr, S=5.925×10−3 Mdyn cm−2(phr)−1 K−1 and H=0.0684(Mdyn cm−2) (phr)−1. This equation represented satisfactorily all the data obtained at temperatures from —50 to +100° C for values of fp from about 1 to 24 phr.
Basic Fundamentals of Extrusion and Mixing Theory
Authors: Boguslawski J. J.
Published: February 2011

The first mechanically driven extruders for rubber and rubber-like materials were developed by Francis Shaw in 1879 in England and John Royle in 1880 in the U. S. A. For nearly 60 years the design of extruder screws remained as an art. With rapidly expanding plastic markets and rapidly rising labor and processing machinery costs, the extruder users and builders realized that only close co-ordination and cooperation among scientists, engineers, and process workers could develop an extruder which would be the most universal and economical tool in polymer processing. Between 1946 and 1953 most of the modern extrusion theory was developed. It has been proven that extrusion theory, when combined with test data and practical experience, is an extremely useful tool. Due to an abundance of empirical data and fundamental theory, extrusion technology has now grown far beyond the level of a mechanical art. At least part of the process can be described by mathematical relationships through the application of rheology, thermodynamics, and fluid dynamics theory. Important advances have been made in process control as well as in increasing output. It is significant that the technology of the rubber extruder, the parent of the plastic extruder, can even now benefit directly from these developments. The transition from hot feeding to use of cold rubber particles can be mentioned as an example.
Modern Extrusion Equipment
Authors: Smith D. H. , Christy R. L.
Published: February 2011

Rubber extruders have been developed and refined to a degree where it is not always obvious which is best for a given application. This paper will cover the latest refinements in the hot feed, cold feed, and vented cold feed type single screw extruders and compare their performance, limitations, and capabilities. Shaping the compound into a more useable form has traditionally been the primary extruder function. However, today cold feed extruders are being used in various environments where shaping is secondary to their ability to plasticate efficiently and uniformly on a continuous basis. An example of this is warm-up for calendar and injection molding equipment.
Recent Advances in the Chemistry of Polyurethanes
Authors: Frisch K. C.
Published: February 2011

Major emphasis in recent years has been placed upon efforts to develop aliphatic isocyanates to impart light stability and improved stability toward hydrolysis. Another major area of research activity were new methods for the generation of isocyanates. Aliphatic isocyanates. The first commercial aliphatic diisocyanate used was 1,6—hexamethylene diisocyanate (HDI), OCN (CH2)6NCO, a colorless liquid, boiling at 127° C at 10 mm Hg; it is less reactive than either tolylene diisocyanate (TDI) or 4,4′-diisocyanatodiphenylmethane (MDI). However, in the presence of certain metal catalysts, such as tin, lead, bismuth, zinc, iron, cobalt, etc., the activity of the aliphatic isocyanate groups is equal to or greater than that of the isocyanate groups in TDI. The use of hexamethylene diisocyanate (HDI) leads to urethane polymers having better resistance to discoloration, hydrolysis, and heat degradation as compared to TDI. Due to its high vapor pressure and toxicity, a higher molecular weight modification of HDI is often employed which is made by reaction of 3 moles of HDI with 1 mole of water:
Steel Cord Skim Compounds: The Achievement and Maintenance of Maximum Adhesion
Authors: Ayerst R. C. , Rodger E. R.
Published: February 2011

The adhesion of rubber to brassed steel cord has been assessed by a static pull out test which avoids many of the problems associated with current H tests. The test is simple in operation and with a uniform stress distribution gives results which are independent of modulus, with a high degree of reproducibility. The effect of a range of compounding variables on adhesion has been examined. Curing systems and polymer type were identified as having the greatest influence. High unaged adhesion was achieved with a curing system based on 2-(Morpholinothio)benzothiazole in 100 NR or NR/BR blends.Factory processing can reduce adhesion in the final vulcanizate and the addition of N-cyclohexylthiophthalimide will prevent this. Overcure and oxidative aging also reduce adhesion. Systems based on low sulfur levels with 2(Morpholinothio)benzothiazole and N,N-dithiodimorpholine confer high resistance in NR and NR/BR blends. The antidegradant combination of N(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymerized 2,2,4-trimethyl-l-2-dihydroquinoline gave further improvements in oxidative aging resistance without reducing unaged adhesion.
Transition from Linear to Nonlinear Viscoelastic Behavior. III. Linearity below and above TG
Authors: Yannas I. V.
Published: February 2011

This work correlates diverse data from the literature in an effort to mark the stress and strain limits of linear viscoelasticity theory below and above Tg for amorphous polymers. The data on limits of linear behavior are based on deviation of 3 per cent from theory and extend from Tg−150° C to Tg+150° C. It is shown that, whereas the stress limit of linear behavior drops as Tg is crossed from below, the strain limit increases from ca. 1 to ca. 100 per cent over the same temperature region.
Compression Behavior of Natural Rubber Vulcanized in the Swollen State
Authors: de Candia F.
Published: February 2011

The Gaussian theory for rubberlike network elasticity gives the following expression for the stress
Application of Gas-Liquid Chromatography to the Thermodynamics of Polymer Solutions
Authors: Patterson D. , Tewari Y. B. , Schreiber H. P. , Guillet J. E.
Published: February 2011

It has been well established that gas—liquid chromatography (glc) can give accurate thermodynamic data on binary solutions where the components differ considerably in volatility or molecular weight. The substance of lower molecular weight (component 1) is injected into the moving gas phase and dissolves at effectively infinite dilution in the stationary liquid phase. This is formed by the higher molecular weight material, for example, squalane, biphenyl, dinonyl phthalate, glycerol, or the higher n-alkanes such as C16, C24, C36, etc. The convenience of the technique is such that activity coefficient data have already been obtained for hundreds of systems. In contrast, activity data are available for far fewer high polymer systems, in part certainly because of the need to use the laborious vapor sorption technique. While that technique gives activity data as a function of concentration, it would still be desirable to have data at infinite dilution for a variety of systems in order to test contemporary theories of polymer solution thermodynamics. Recently Guillet and coworkers have applied the glc technique to systems in which the stationary phase is a high polymer. (J. E. Guillet and coworkers refer to the gas-phase component as the molecular “probe”. This avoids the glc teminology in which that component is the solute and the stationary-phase polymer would be the solvent. This terminology is confusing to polymer chemists used to solutions where the polymer is the solute, being present at low, rather than high, concentrations.) Their primary interest has been to demonstrate the versatility of the technique in determining first- and second-order phase transitions, degrees of crystallinity, and other physical characteristics of the polymer, while the present communication considers the determination of thermodynamic quantities. It has been prompted by comments from several workers who have noted the difficulty of applying the usual thermodynamic equations of glc which yield γ1∞, the activity coefficient of component 1 at infinite dilution [Equations (5) and (6)]. The equations require an exact value of the molecular weight of component 2, making difficult their use for polymer systems. Our main objective is to resolve this problem. However, we also wish to stress the utility of the technique in providing data with which to test contemporary theories of polymer solution thermodynamics. We therefore comment on equations which directly relate experimental glc data to the interaction parameter, χ, of polymer solution thermodynamics.
Creativity in Rubber Industry Research. Charles Goodyear Medal Address—1971
Authors: Osterhof H. Judson
Published: February 2011

Over the span of 36 years in rubber research and development, I was involved in a wide range of problems, some of which ended in frustration, others fortunately in success. Overall, during this entire period, I've had a whale of a good time. During these years nothing has provided me more satisfaction than working with creative people. And since this phenomenon of creativity is so important and yet so little understood, I thought I'd see whether from my own experience I could throw a little light on it today. My main qualification is that I have for years been interested in creativity, what it is, how it manifests itself, the type of people who exhibit it, and how they may be encouraged toward greater efficiency. Successful creativity, in general, involves conceiving new ideas and following them through to where they become potentially useful. It does not only mean the synthesis of a new chemical, but more broadly, the achieving of any new, not previously recognized, result. This might involve merely bringing together two well-known mechanical devices never before associated. For example, the electric blanket invented by Kearsley of General Electric: blankets and electric heating wire were well known, separately, but it took Kearsley's imagination to bring them together into a brand-new useful product. Many instances of creativity sart with Observation, the creative person being alert for new combinations and phenomena, being led on by his scientific Curiosity, aroused by his Imagination and Enthusiasm, and drawing upon his Memory, since creative thinking is frequenly no more than bringing together factors not hitherto associated. Among the requisite personal characteristics for creativity arc a prepared mind, a large range of skills and technical know-how, a certain mechanical ingenuity, and a favorable environment. The creative mind must, of course, have imagination, as well as enthusiam. Its results may range from discovering a whole new world of knowledge to merely inventing an easier way of doing an old job. To enhance the creativity of research personnel, management cannot impose a rigid application of job specialization and supervisory control, but must create a climate with such necessary freedom and flexibiliy as to be conducive to invention. Technological innovations can result from following various creativity routes which, for convenience here, I have divided into seven categories. For a clearer picture of how creativity manifests itself, let us examine some appropriate examples, based on projects with which I had direct personal contact. Of these examples, some are important, others relatively minor, the basis of selection being primarily suitability for illustrating various facets of creativity. These might be considered case histories, as it were, of creativity.
Thermal Stability of the Carbon-Carbon Crosslink in Polymer Networks
Authors: Shaw Montgomery T. , Tobolsky Arthur V.
Published: February 2011

The thermal stability of carbon-carbon crosslinkages in elastomeric systems was studied by comparing the vacuum chemical stress relaxation of samples with different concentrations of these crosslinkages. The systems studied included silicone rubber, crosslinked polyethylenes, and Dexsil-201 rubber. Arrhenius activation energies of about 55 kcal/mol were found for the scission of these crosslinkages in the temperature range 300—350°. Crosslinkages added to a sample by additional curing were found to be, in general, more stable than those first formed. A more detailed analysis of the cleavage reaction was performed on peroxide-cured Dexsil-201 elastomer—made possible because the main chains of this material are stable at the temperatures used. Two species of crosslinks were distinguishable: one having the same stability as the carbon-carbon crosslinkage in silicone rubber, another being ten times as stable and probably devoid of normal carbon-carbon bonds.
Radiation-Convertible Polymers from Norbornenyl Derivatives. Crosslinking with Ionizing Radiation
Authors: Colomb H. O. , Trecker D. J. , Osterholtz F. D.
Published: February 2011

Vinyl polymers with pendant norbornenyl (bicyclo [2.2.1]heptenyl) groups crosslink rapidly on exposure to ionizing radiation. Analysis (according to Charlesby-Pinner theory) of extraction data from an ethylene—vinyl acetate copolymer and the corresponding ethylene—vinyl norbornenecarboxylate copolymer shows that the unsaturated polymer crosslinks by a chain reaction. At low doses, the kinetic chain length is about 4. Pendant norbornenyl groups accelerate crosslinking of a vinyl alcohol—vinyl acetate—vinyl chloride copolymer and convert poly(vinyl alcohols) and cellulose acetate from degrading to crosslinking polymers. A novel application of the Charlesby-Pinner plot strongly suggests linear dependence on the extent of crosslinking on the norbornenyl group concentration in a series of modified poly(vinyl alcohols). The greater effectiveness of pendant norbornenyl groups, compared to cyclohexenyl groups demonstrates the importance of the reactivity of the double bond.
Ethylene Propylene Vinylcyclohexene Terpolymers
Authors: Caywood S. W.
Published: February 2011

4-Vinylcyclohexene reacts via the vinyl group with ethylene and propylene in a Ziegler-type polymerization to form an elastomeric terpolymer. The reactivity of vinylcyclohexene in this polymerization is lower than that of 1,4-hexadiene and norbornene by a factor of about 7 and 70, respectively. Ethylene propylene vinylcyclohexene terpolymers respond poorly to typical EPDM sulfur vulcanization systems but react well with a catalyzed resin system or a peroxide recipe.
Vulcanizate Properties from a New Perfluoroelastomer
Authors: Barney A. L. , Kalb G. H. , Khan A. A.
Published: February 2011

Vulcanizate properties of a new high performance elastomer, a terpolymer of tetrafluoroethylene, perfluoro (methyl vinyl ether) and a small amount of a third perfluoromonomer containing an active cure site, are described. The material may be compounded with various reinforcing agents (black exhibits the greatest reinforcing power) or as a gum stock. Perfluorinated oils such as Krytox § may be added as plasticizers. The vulcanizates show outstanding chemical resistance to many alkalies, acids, oxidizing agents and reducing agents; outstanding resistance to air oxidation at temperatures in the 400 ° – 550 ° F range; low volume swell in many organic fluids such as ketones, esters, nitriles, hydrocarbons and halogenated solvents, including the proprietary hydraulic fluids and jet fuels; and good high temperature (to 550 ° F) compression set.
Stress-Strain Behavior of Natural Rubber Vulcanized in the Swollen State
Authors: Price Colin , Allen G. , de Candia F. , Kirkham M. C. , Subramaniam A.
Published: February 2011

Samples of natural rubber were vulcanized in the presence of n-decane, decalin and o-chlorobenzene. The diluents were then removed, and the force-extension characteristics of the samples studied over the range 1.1<α<2.0. The elastic behavior of the solution-vulcanized elastomers appear to be in much closer agreement with the statistical theory of elasticity than is the case for vulcanizates prepared in the dry state.
Liquid Rubbers—General Rubber Products Technology
Authors: Pyne J. R.
Published: February 2011

Mixing and processing methods used in the rubber industry have been designed to use the only form of raw rubber hitherto available—that of a high molecular weight solid. But rubber in high molecular weight form is essential only in the finished product; in principle, similar final properties could be obtained from a low molecular weight raw material provided this could be chain extended before or during the final shaping and vulcanizing operation. This approach has been employed for some time in the rather specialized field of castable polyurethane rubber manufacture. Its exploitation for more general rubber manufacture has become more than just a theoretical possibility with the recent availability of “liquid rubbers” whose molecules have reactive end groups. Those available at present may well prove not fully acceptable, either economically or technically, but it is most unlikely that they represent the best that can be achieved. Material developments will be encouraged if means have been worked out for exploiting liquid rubbers' potential advantages (such as the ability to be processed on lighter and less powerful equipment), and the shortcomings of existing examples have been identified. These considerations led RAPRA to start a processing and compounding study—a decision which seems further justified by the very recent American announcements of development work on a tire manufacturing process using liquid rubber, and of full commerical scale production of several hydroxyl terminated liquid butadiene polymers. This report summarizes the study to date.
Structural Characterization of Vulcanizates. XI. Network-Bound Accelerator Residues
Authors: Campbell D. S.
Published: February 2011

Radiotracer techniques have been used to determine amounts of accelerator which become bound to the vulcanizate networks during the vulcanization of NR with sulfur and CBS, Three different vulcanization systems have been studied, having different proportions of accelerator to sulfur. The vulcanizates have also been characterized in terms of the numbers and types of chemical crosslinks present and the results of the bound accelerator analyses have been considered in relation to the crosslink levels and distribution.
The Effect of Road Surface Texture on Tire Wear
Authors: Lowne R. W.
Published: February 2011

(1) This experimental work has shown that there is a large variation in the degree of tire wear on different surfaces, the wear on the rough, harsh surface being approximately three times as severe as that on the rough polished surface. (2) Measurement of weight loss by the method described provides a sensitive measurement of tire wear. (3) Qualitative analysis has shown that it is the harshness of the surface which is of major importance in tire wear, with surface roughness as a slightly modifying factor. (4) Quantitative analysis of various parameters indicating surface characteristics has shown that the shape of the asperity tips and the low-speed, wet coefficient of friction are major factors. These can be used to predict wear to a high degree of significance within the range of values covered by these measurements, although a large sample of surfaces would be desirable to check this relationship further. (5) A decrease in the severity of wear of six times involving a drop in speed from 50 km/h to 25 km/h has not altered the relative wear ratings of the three surfaces which have been compared and it seems reasonable to assume that the relative wear rates, although not the absolute values, would be the same in normal conditions of use. Consequently, the increased use of rough road surfaces is not expected materially to affect tire wear. (6) Significant increase in tire life from a wear standpoint can be expected from the use of radial ply tires instead of cross ply tires.
The Effects of Varying the Polymer Composition of the Cut Growth Characteristics of E/P/1,4 HD Tire Treads
Authors: Stewart Charles W. , Verbanc John J.
Published: February 2011

Experimental ethylene-propylene—1, 4-hexadiene polymers covering a range of compositions which possess satisfactory processing characteristics and economics have been evaluated in passenger car tires with emphasis on groove cracking. The tearing energy criterion was used in a laboratory test to correctly predict the groove cracking behavior of the tires made from these polymers. Road tests indicate that ethylene-propylene-1,4-hexadiene tripolymers containing 36%–42% propylene and 1.8%–2.2% diene exhibit resistance to cut growth and abrasion which is superior to standard SBR-BR in bias tires. Polymers containing more than 42% propylene or 2.2% diene were inferior in wear and resistance to groove cracking, but sufficient data are not available to pinpoint the reason.
Crosslinking, Filler, or Transition Constraint of Polymer Networks. II
Authors: Blanchard A. F.
Published: February 2011

The theory of Part I is developed by application to filler reinforcement of NR and SBR. For unswollen but prestretched networks it quantifies entire stress-strain curves and applies new concepts of extensibility and strain hardening. Constraint of swelling is expressed by a constant Ø, termed linkage reinforcement, and by an effective hard fraction Cm per cm2 of compound. For rubber-filler swelling vc the modified Flory functions F(νc) in Part I need 3% correction.
Intrinsic Linkage Reinforcement ϕ0 from Swelling Measurements of Effective Values ϕ
Authors: Blanchard A. F.
Published: February 2011

The writer has introduced for rubber with particulate reinforcement the concept of linkage reinforcement ϕ derived from the volume fraction v of rubber or νc of rubber-filled compound at equilibrium swelling in a solvent. Basic elastomer theory was modified to allow for the filler volume fraction C by an effective hard fraction Cm per cm3 of compound, the Flory or Flory-Rehner function F(νr) being replaced by F(νc), and the measure νc of swelling being a compound index replacing the usual νr. On this development of the basic theory, and defining linkage reinforcement ϕ as the ratio of the effective crosslinking of reinforced networks to the 1/Fo(νr) fix points of corresponding gum vulcanizates :
Radiotracer Measurements of Sulfur Diffusion in Rubbers
Authors: Mozisek M.
Published: February 2011

The object of measurement was the diffusion of elemental sulfur labeled with the radioisotope S in representative types of rubber. The highest values of diffusion coefficient were found in cis-1,4 polybutadiene. The lowest measured value was found for butyl rubber. The activation energy, expressing the temperature dependence of the diffusion coefficients, ranges from 4 to 10 kcal mol-1. For some rubbers studied, the activation energy is to a certain degree dependent upon temperature. The values of the diffusion coefficients and the characteristic constants for their temperature dependence are related to the mobility of the macromolecular segments.
The Influence of Precure Dilation on the Stress-Strain Properties of Ethylene-Propylene Terpolymer Networks
Authors: Kirkham M. C.
Published: February 2011

A study has been made of the influence of a dilating liquid, present during vulcanization, on the stress-strain behavior of EPDM vulcanizates. Stress-strain measurements performed on the vulcanizates after extraction of the dilating liquid, taken over a range of strain rates, indicate the effective absence of time-dependent behavior and suggest that a close approach to equilibrium has been achieved. From the experimental data, values of the C1 and C2 constants of the empirical Mooney-Rivlin equation were derived. It was found that both C1 and C2 decreased with increased precure dilation, C2 decreasing more rapidly than C1. The observed decrease in C2 is less than would be predicted by simple analogy with the Gaussian modulus; it is suggested that this difference might be explained by changes in network configuration and topology associated with the precure dilation.
Fluorosilicones as High Temperature Elastomers
Authors: Pierce Ogden R. , Kim Yung K.
Published: February 2011

Two types of fluorosilicone polymers are described, the poly(fluoroalkyl)-siloxanes and the hybrid fluorocarbon silicones. The first type, represented by the structure (CF3CH2CH2SiMeO)n exhibits good solvent resistance, thermal and oxidative stability and is commercially available in the form or rubber, sealants and fluids. The second type, is in the research stage and has demonstrated much improved stability especially under confined heating conditions.
Nucleation and Growth of Bubbles in Elastomers
Authors: Stewart Charles W.
Published: February 2011

The theory of homogeneous nucleation of bubbles is combined with an expression, for their rate of growth in elastomers to obtain approximate expressions for calculating the number of bubbles formed under a high degree of supersaturation. Experimental results are given for several elastomers with argon as the dissolved gas under a variety of foaming conditions. The theory adequately describes the manner in which the number of bubbles formed depends on the temperature, surface tension of the polymer, and permeability of the dissolved gas.