bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rubber Birefringence and Photoelasticity
Authors: Angioletti A. , Eccher S. , Polvara O. , Zerbini V. 
Published: February 2011

Abstract
The phenomenon of birefringence, discovered in 1669 by Erasmus Bartholin and later studied by Christian Huygens, is well known for its appearance in transparent crystalline solids. It is to be traced essentially to internal anisotropy of crystals for light propagation, so that under certain conditions a single wave front may give rise to multiple coherent waves which can cause double refraction or other phenomena such as the appearance of fringes varying in brightness and color due to interference of emerging wave fronts. Birefringence may be expressed as the difference of the velocities of propagation in various directions in the birefringent medium and particularly as the difference between the maximum and the minimum velocity or, alternatively, between the maximum and the minimum refractive index or even as the phase difference between emerging waves, given frequently as a number of wavelengths. While true double refraction phenomena may be observed with ordinary light when the difference n1−n2 between the refractive indexes is very high, the interference phenomena may be obtained only with polarized light, but may be observed even with very small differences between indexes. This is not the place to treat extensively general concepts like polarizer, analyzer, ordinary wave, extraordinary wave, uniaxial crystal, biaxial crystal, etc. which can be found in any good optics treatise. Birefringence is not in any way limited to crystalline media, possessing inherent structural anisotropy. It may also appear in bodies which are normally isotropic, when structural anisotropy is caused by external forces. Then birefringence is quantitatively dependent on force intensities, even if not always in an easily detectable way. This is called “accidental birefringence” or “stress-birefringence”. It was observed by Seebeck in 1813, and later studied in 1816 by Brewster for glass. It is observable in many transparent materials. Stress-birefringence is particularly conspicuous in macromolecular substances, including elastomers, vulcanized or not, where it is determined by the orientation of molecular links. This, of course, may not be ascribed altogether to stress, but sometimes also to partial crystallinity. Other phenomena of accidental birefringence may be observed in liquids or in solutions, especially of elastomers, when they are subjected to a velocity gradient, as when flowing through a capillary tube or, more commonly, when sheared between two coaxial cylinders.
Effect of Oxygen on Natural Rubber Latex
Authors: Bevilacqua E. M. 
Published: February 2011

Abstract
Natural rubber is exposed to oxygen from the time that trees are tapped through its vulcanization and final use. Reaction with oxygen at each stage in its history affects its properties. Extensive studies have been made of the effects in later stages, on raw and vulcanized rubber; much less work has been done on the oxidation of latex. Fresh latex is a dilute aqueous emulsion in which the non-volatile content is approximately 90 per cent rubber hydrocarbon. The rest is a complex mixture of compounds, most of which are normal constituents of plant sera. Rubber exists as high polymer in latex at tapping; in mature trees tapped for the first time, it is of high molecular weight and is extensively crosslinked. In normal commercial practice, when latex is withdrawn as fast as rubber is sythesized by the tree, rubber is essentially all linear high polymer of average molecular weight 105 to 106. As soon as a tree is tapped the latex begins to change. In the short period between tapping and coagulation the changes are small and not usually significant when latex is used for the production of dry rubber. Changes in preserved latex continue over a long time and are significant in its use. Latex of commerce is preserved with ammonia, which serves the dual function of being toxic and controlling pH in a range where latex stability is high. It is sometimes supplemented with another biocide because of the desire to keep ammonia level as low as possible for the convenience of the final user.
Stress-Strain Behavior of Rubber-Reinforced Glassy Polymers
Authors: Newman Seymour , Strella Stephen 
Published: February 2011

Abstract
The main objective of this work has been to develop some rational hypothesis for the toughness of rubber polyblends as defined by the energy to rupture in a tensile measurement. It is shown, both by induction and by direct experimental evidence, that the S/AN rigid phase yields and cold draws. It is thereby established that the toughness of a polyblend is a result of the large energy absorption involved in the cold drawing of the matrix. The presence of inherent flaws or cracks limits the strength and ductility of some glassy polymers, whereas others are known to cold-draw. It is believed, therefore, that the rubber phase in a polyblend acts principally to induce a yielding in the S/AN matrix. There are at least two factors which contribute to this yielding. (a) By limiting the crack growth, the rubber phase effectively strengthens the rigid phase, prevents premature fracture, and permits yielding. In this connection, it is believed that under a tensile strain, the difference in the Poisson's ratio of the rubber and matrix phases results in a triaxial stress field in the environment of the rubber particle. Under such a triaxial stress field, the rubber particle possesses a strength which is greater than in tension and which is sufficient to prevent crack propagation. (b) Secondly, the triaxial field will result in an increase in the free volume of the SAN matrix adjacent to the rubber particle. This, combined with other factors, causes an increase in free volume sufficient to lower the glass transition temperature of S/AN to the point where large-scale molecular motion or cold drawing is further favored.
A Measurement of Carbon Black Pellet Quality and its Significance
Authors: Atkins J. H. , Boonstra B. B. 
Published: February 2011

Abstract
A new instrument for measuring pellet quality is described which records the pellet strength of screened fractions of pellets. Samples large enough to be statistically representative can be measured in a relatively short period of time. The average pellet strength values, for each screened fraction, can be used to predict the incorporation time of the pellets into polymer. The maximum pellet strength values correlate with dispersion and by so doing, effect the stress—strain properties of the compounded elastomer.
Vulcanization Accelerator and Activator Complexes. 2. Chemistry of Amine and Zinc Carboxylate Complexes of Zinc and Cadmium Benzothiazolyl Mercaptides
Authors: Milligan Brian 
Published: February 2011

Abstract
The behavior of zinc benzothiazolyl mercaptide (ZMBT) and its complexes with amines and zinc carboxylates in effecting nucleophilic displacement reactions related to those which occur during accelerated sulfur vulcanization has been studied. Ligands influence the activity of ZMBT in nucleophilic displacement reactions (a) by increasing the solubility of ZMBT in the reaction medium and (b) by increasing the polarity of the Zn—S bond; this increase in polarity only enhances the intrinsic activity of the catalyst if a second zinc species (e.g., a zinc carboxylate) is present. Complexes of zinc carboxylates with ZMBT are very active catalysts for disulfide interchange reactions, but not for sulfur insertion reactions. In the latter, an amine is also necessary to act as a co-catalyst with traces of hydrogen sulfide in order to convert octa-atomic sulfur into a more reactive open-chain polysulfide species. A combination of ZMBT, an amine and a zinc carboxylate provides the best catalyst for effecting sulfur insertion reactions at high temperatures; the active species may be a ternary complex. Amine complexes of ZMBT, either in the absence or presence of a zinc carboxylate, are good accelerators for the vulcanization of cis-1,4-polyisoprene with sulfur.
Elastomers Resistant to Rocket Propellants
Authors: Green Joseph , Levine N. B. , Sheehan W. 
Published: February 2011

Abstract
Resistance of polymers to hydrazine-type fuels, Hybaline A-5, nitrogen tetroxide, and fluorine-containing oxidizers was investigated. Elastomers found suitable for application in hydrazine-type fuels and Hybaline A-5 environments are butyl and ethylene propylene rubbers. Carboxy-nitroso rubber is recommended for long term exposure to nitrogen tetroxide at 165° F while resin-cured butyl rubber is satisfactory for limited application. Fluorocarbon plastics and silicone rubber are most suitable for use with oxygen difluoride, and Teflon, polyethylene, and ethylene propylene rubber with a perchloryl fluoride-tetrafluorohydrazine mixture. Chlorine trifluoride is a very reactive oxidizer and Teflon, Kel-F 81, and uncured nitroso rubber gum are suitable only for limited application.
Elastomeric Seals for the Army's Lance Missile
Authors: McManus S. P. , Pikkn S. 
Published: February 2011

Abstract
The LANCE propulsion system requires dynamic and static seals which must operate under extremely severe conditions for short periods. By analysis and tests it has been found that resin-cured chlorobutyl rubber meets the requirements for low and high temperature operation and retains its properties when exposed to the LANCE propellants for short periods. The chlorobutyl rubber, however, is not a panacea. Its properties become increasingly poorer as exposure time increases. Since the need for high performance, versatile systems should continue indefinitely, it is hoped that research can produce elastomers to meet the growing need for unusual environments such as are described here. For successful accomplishment of this task, the rubber and chemical industry will have to meet the challenge to reach this goal.
Physical Properties of Two O-Ring Compounds after Exposure to Reactor Radiation
Authors: Lewis J. H. 
Published: February 2011

Abstract
Two commercial O-ring compounds, NBR and SBR, specially formulated for radiation resistance were irradiated by means of a nuclear reactor to six gamma-dose levels in the range from 4.9×108 to 15×1011ergs/gm(C). O-rings and compression-set buttons of both materials were irradiated in air at near room temperature; O-rings of NBR were also irradiated in oil. Tensile properties, hardness, and compression set were measured as a function of radiation dose. Fifteen O-rings and five compression buttons were used for each experimental condition to provide statistically valid results. Analytical procedures were used to compute molecular weight between crosslinks and network-chain ratio as a function of dose. The wide dose range provided an accurate assessment of degradation produced by radiation. The highest dose resulted in complete loss of useful mechanical properties. Properties most adversely affected at lower doses were ultimate elongation, hardness, and compression set. While compression set was 50% at a dose of 3×109ergs/gm(C), tensile properties of both materials remained relatively good at a gamma dose of 1.2×1010 ergs/gm(C).
Dynamic Mechanical Testing to Evaluate Radiation Induced Changes in Polymers
Authors: Teaeger R. K. 
Published: February 2011

Abstract
Dynamic mechanical testing is one of the most useful tools for evaluating effects of radiation on polymers. Present property-temperature spectra provide molecular and mechanical information. Property-time spectra are of more fundamental interest but present molecular theories or molecular descriptions of phenomenological theories are too limited to allow interpretations of the spectra. The application of dynamic testing to specimens in a radiation field is a new approach to radiation effects studies and has great potential for further understanding the interaction of radiation with polymers.
Fungus Resistance of Millable Urethans
Authors: Kanavel G. A. , Koons P. A. , Lauer R. E. 
Published: February 2011

Abstract
Sulfur cured polyether and polyester millable urethans inherently possess some fungal inertness. Although they do not support fungal growth, fungicides must be used therewith to provide greater resistance to fungal attack. Only a few of the fungicides tested appear to be practical in the host polyester compositions. Peroxide cured millable polyether and polyester urethans do not inherently possess fungal resistance. Therefore, the need for fungistatic chemicals is even greater.
Stress Softening in Rubber Vulcanizates. Part I. Use of a Strain Amplification Factor to Describe Elastic Behavior of Filler-Reinforced Vulcanized Rubber
Authors: Mullins L. , Tobin N. R. 
Published: February 2011

Abstract
Measurements of Young's modulus of vulcanized rubbers containing thermal carbon black show the predicted dependence on the volume concentration given by relationships derived for a suspension of spherical particles, for example, that due to Guth, Simha, and Gold which gives E=E0 (1+2.5c+14.1c2). A simple interpretation of the results is that the strain in the rubber is increased by the presence of filler so that the ratio of the average strain to the measured overall strain is given by the factor X=1+2.5c+14.1c2. This factor was used to analyze simple extension stress-strain data obtained at larger extensions. For this purpose the Mooney—Rivlin relation was used to describe the behavior of the rubber phase. Values of C1 independent of the volume concentration and in close accord with measurements of the equilibrium volume swelling of the rubbers were obtained. Values of λ* were also consistent with those of #5#. Analysis of stress—strain data obtained on rubbers containing smaller particle-sized carbon blacks is more complex. For these materials the relation due to Guth, viz., E=E0 (1+2.5c+14.1c2), was chosen. By the choice of suitable values of f, good agreement with the Mooney—Rivlin stress—strain relation was achieved at volume concentrations less than about 0.15.
Properties and Structure of Elastomers
Authors: Lal Joginder , Scott Kenneth W. 
Published: February 2011

Abstract
The glass transition temperatures of high molecular weight poly (vinyl n-alkyl ethers) decrease with increasing length of the n-alkyl group. On lengthening the n-alkyl group, 14 per cent of the specific volume increase is free volume. Branching or substitution in the alkyl group of the polymer increases the Tg value. A comparison of poly (vinyl n-alkyl ethers) and polymers of normal α-olefins shows that an ether group and a methylene group in the side chain are equivalent in influencing the glass transition temperature. We have varied systematically the side chain alkyl group in poly (vinyl alkyl ethers) and evaluated at 3 different temperatures the influence of these variations on the dynamic properties of the vulcanizates of these polymers. The relative position of the curves, relating dynamic resilience to dynamic modulus of these polymers, is generally in the order of their glass transition temperatures. The dynamic mechanical property data on poly (vinyl n-pentyl ether) and poly (vinyl 2-ethylhexyl ether), which have the same glass transition temperature, fall on a common curve characteristic of the temperature of measurement. Apparently, the Tg is a major factor in correlating the dynamic mechanical behavior of these elastomers. The size and shape of the alkyl group appear to be reflected primarily in their effect on the Tg. Polysulfidic crosslinks are not essential for the attainment of high tensile strength in natural rubber vulcanizates cured with a sulfur-diphenylguanidine system. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted a curve of tensile strength as a function of 300 per cent modulus for the control samples.
Dynamic Mechanical Properties of Cross-Linked Rubbers. II. Effects of Crosslink Spacing and Initial Molecular Weight in Polybutadiene
Authors: Maekawa Etsuji , Mancke Ralph G. , Ferry John D. 
Published: February 2011

Abstract
The complex shear compliances of eight samples of polybutadiene crosslinked by cumyl peroxide and four samples crosslinked by sulfur have been measured over a frequency range from 0.2 to 2 cps at temperatures from − 6 to 45° C by a torsion pendulum. On four of the samples, measurements were extended by the Fitzgerald transducer from 45 to 600 cps at temperatures from − 71 to 55°. The vulcanizates had been prepared from polymers of two different molecular weights (180,000 and 510,000) with sharp molecular weight distribution; the physical crosslink density ranged from 0.57 to 2.68×10−4 mole/cm3, and the chemical crosslink density calculated following Kraus ranged from 0.22 to 1.49×10−4 mole/cm3. The mechanical data were all reduced to T0=298° K by shift factors calculated from the equation log aT=−3.64(T−T0)/(186.5+T−T0). In the transition zone of frequencies, the viscoelastic functions of the cumyl peroxide vulcanizates were closely similar, except for a shift toward lower frequencies with increasing crosslinking, corresponding to a small but unexpected increase in the monomeric friction coefficient. Cross-linking by sulfur caused a somewhat larger shift toward lower frequencies at a comparable crosslink density. In the rubbery zone, the sample with least cross-linking exhibited a substantial secondary loss mechanism at very low frequencies. The low-frequency losses are evident in all the samples, but their magnitude falls rapidly with increasing crosslink density as previously found for natural rubber. It also falls somewhat with increasing initial molecular weight, indicating a contribution from network strands with loose ends. The possible relation of the low-frequency losses to trapped entanglements is discussed.
Near-Infrared Analysis of Ethylene Propylene Copolymers
Authors: Bly R. M. , Kiener P. E. , Fries B. A. 
Published: February 2011

Abstract
A number of block and random copolymers of ethylene and propylene have been synthesized using C14 labeled ethylene. Using the radio-assay results of these materials, a near-infrared analysis for ethylene content was developed. The 2.275 micron (4396 cm−1) and 2.312 micron (4325 cm−1) near-infrared combination bands are useful for determining monomer ratio concentrations in the 0 to 40% ethylene range regardless of copolymer type. They are superior to the fundamental infrared bands because they are much less sensitive to slight differences in crystallinity. Other advantages include internal thickness calibration by relative peak height measurements on peaks of more nearly equal intensities than the fundamental bands and greater convenience in sample preparation techniques. The fundamental 720 cm−1 band intensity is a good indication of ethylene content in crystalline block copolymers but requires the accurate measurement of sample thickness for an analysis. The 968 cm−1 and 1163 cm−1 bands, ratioed with the the 720 cm−1 band, show definite correlation with monomer concentration but are less precise than the near-infrared data because of sensitivity to randomness and crystallinity.
Radiolytic Stress Relaxation of an Ethylene Propylene Copolymer
Authors: Yu Hyuk , Wall Leo A. 
Published: February 2011

Abstract
The kinetics of network chain scission induced by γ-rays has been studied by stress relaxation at constant elongation under vacuum and in air. The rate of chain scission of a 1:1 ethylene propylene copolymer was found to be independent of initial network chain density, and the initial rates were roughly the same in air and under vacuum. Parameters for crosslinking induced by γ-rays were obtained by sol extraction and by measurement of elastic properties of the resulting networks. Values of G for scission and crosslinking and gel dose, obtained by stress relaxation, by elastic properties, and by sol extraction, were found to agree with each other.
Bonding of Rubber to Carbon Black by Sulfur Vulcanization
Authors: Rivin D. , Aron J. , Medalia A. I. 
Published: February 2011

Abstract
As an approach toward understanding the interaction of rubber with carbon black, we have studied the chemisorption of a model olefin (2-methyl-2-octene) on carbon black. Some olefin becomes chemisorbed on simply heating these two materials together, and can be distinguished from physically adsorbed material by its resistance to removal by solvents at room temperature. The presence of an MBTS accelerated sulfur curing system causes additional chemisorption. The amount of olefin chemisorbed can also be increased by the use of larger amounts of sulfur but is decreased by an increase in MBTS, owing to competitive chemisorption of the MBTS. Sulfur is also chemisorbed, to a somewhat greater extent than the olefin, but is desorbed more readily than the olefin, suggesting that these two components are chemisorbed separately. The chemisorbed olefin is believed to be highly mobile on the carbon black surface, and indeed its stability is ascribed primarily to a loss of translational entropy associated with the rate-determining step in desorption. The curing system decreases the stability of the chemisorbed olefin, apparently due to the formation of localized bonds which decrease the translational entropy of the olefin.
Survey of Treadwear, Groove Cracking, and Carbon Black Properties
Authors: Studebaker Merton L. 
Published: February 2011

Abstract
Resistance to treadwear is dependent upon the particle size, ultimate composition and “structure” of the carbon black used for reinforcement. Under moderate service conditions, reinforcement, as measured by treadwear index, is dominated by particle size. Under severe test conditions, the “structure” of the carbon black makes a very important contribution to the treadwear index. Groove cracking is quite dependent on the nature of the elastomer. Reversals in the effects of the nature of the crosslink, carbon black structure and particle size on groove cracking have been observed when the elastomer is changed from natural rubber to SBR.
Thermal Analysis of Polyurethan Elastomers
Authors: Slade Philip E. , Jenkins Lloyd T. 
Published: February 2011

Abstract
Differential thermal analysis and thermogravimetric analysis were used to evaluate the thermal properties of several types of polyurethan elastomers. The composition of the polymers investigated was changed by varying the substrate, or soft segment, diisocyanate and extender. The data indicated that within the limits of the compositions under study, polyurethans were thermally stable to their melting points, however, above the melt they were susceptible to oxidation unless stabilized by the addition of an antioxidant. On the differential thermograms the absence of a pronounced endothermic peak at the melting point, characteristic of noncrystalline polymers, was observed. The decomposition of polymers made with 4,4′-diphenylmethane diisocyanate (MDI) occurred above 400° C and was at least a two step process, while the decomposition of polymers containing toluene diisocyanate (TDI) occurred below 400° C and appeared to be a one step reaction.